US20250326085A1

US20250326085A1 - Method and System for Conditioning a Polishing Pad

Info

Publication number: US20250326085A1
Application number: US18/643,511
Authority: US
Inventors: Dinusha Priyadarshani Karunaratne; Jong Hyup Lee
Original assignee: Wolfspeed Inc
Current assignee: Wolfspeed Inc
Priority date: 2024-04-23
Filing date: 2024-04-23
Publication date: 2025-10-23
Also published as: WO2025226793A1

Abstract

A method for conditioning a polishing pad of a polishing system is provided. The method comprises performing an in-situ pad conditioning process and an ex-situ pad conditioning process outside of a polishing operation. The in-situ pad conditioning process comprises causing a pad conditioner to contact the polishing pad during the polishing operation. The ex-situ pad conditioning process comprises causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad.

Description

FIELD

The present disclosure relates generally to semiconductor workpieces and fabrication processes for semiconductor workpieces, such as semiconductor wafers used in semiconductor device fabrication.

BACKGROUND

Power semiconductor devices are used to carry large currents and support high voltages. A wide variety of power semiconductor devices are known in the art including, for example, transistors, diodes, thyristors, power modules, discrete power semiconductor packages, and other devices. For instance, example semiconductor devices may be transistor devices such as Metal Oxide Semiconductor Field Effect Transistors (“MOSFET”), bipolar junction transistors (“BJTs”), Insulated Gate Bipolar Transistors (“IGBT”), Gate Turn-Off Transistors (“GTO”), junction field effect transistors (“JFET”), high electron mobility transistors (“HEMT”) and other devices. Example semiconductor devices may be diodes, such as Schottky diodes or other devices.
Power semiconductor devices may be packaged into various semiconductor device packages, such as discrete semiconductor device packages and power modules. Power modules may include one or more power devices and other circuit components and can be used, for instance, to dynamically switch large amounts of power through various components, such as motors, inverters, generators, and the like.
Semiconductor devices may be fabricated from wide bandgap semiconductor materials, such as silicon carbide and/or Group III nitride-based semiconductor materials. The fabrication process for power semiconductor devices may require processing of wide bandgap semiconductor wafers, such as silicon carbide semiconductor wafers.

SUMMARY

Aspects and advantages of embodiments of the present disclosure will be set forth in part in the following description, or can be learned from the description, or can be learned through practice of the embodiments.
One example aspect of the present disclosure is directed to a method for conditioning a polishing pad of a polishing system. The method includes performing an in-situ pad conditioning process and an ex-situ pad conditioning process. The in-situ pad conditioning process includes causing a pad conditioner to contact the polishing pad during a polishing operation. The ex-situ pad conditioning process is performed outside of the polishing operation and includes causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad.
Another example aspect of the present disclosure is directed to a method for conditioning a polishing pad of a polishing system. The method includes performing an in-situ pad conditioning process, measuring a process condition, and changing the in-situ pad conditioning process based at least in part on the process condition. The in-situ pad conditioning process includes causing a pad conditioner to contact the polishing pad during a polishing operation.
Another example aspect of the present disclosure is directed to a system for polishing a semiconductor wafer. The system includes a platen operable to rotate about an axis, a polishing pad coupled to the platen, a workpiece carrier operable to bring a semiconductor workpiece into contact with the polishing pad, a pad conditioner, a sensor configured to measure a process condition, and a controller comprising one or more control devices operable to bring the pad conditioner into or out of contact with the polishing pad based at least in part on the process condition.
These and other features, aspects and advantages of various embodiments will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the related principles.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed discussion of embodiments directed to one of ordinary skill in the art are set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 depicts an example polishing system for a semiconductor workpiece during in-situ pad conditioning according to example embodiments of the present disclosure;

FIG. 2 depicts an example polishing system for a semiconductor workpiece according to example embodiments of the present disclosure;

FIG. 3 depicts an example polishing system for a semiconductor workpiece during ex-situ pad conditioning according to example embodiments of the present disclosure;

FIG. 4 depicts a flow chart of an example method according to example embodiments of the present disclosure; and

FIG. 5 depicts a flow chart of an example method according to example embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the embodiments, not limitation of the present disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments without departing from the scope or spirit of the present disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that aspects of the present disclosure cover such modifications and variations.
Power semiconductor devices are often fabricated from wide bandgap semiconductor materials, such as silicon carbide or Group III-nitride based semiconductor materials (e.g., gallium nitride). Herein, a wide bandgap semiconductor material refers to a semiconductor material having a bandgap greater than 1.40 eV. Aspects of the present disclosure are discussed with reference to silicon carbide-based semiconductor structures as wide bandgap semiconductor structures. Those of ordinary skill in the art, using the disclosures provided herein, will understand that example embodiments of the present disclosure may be used with any semiconductor material, such as other wide bandgap semiconductor materials, without deviating from the scope of the present disclosure. Example wide bandgap semiconductor materials include silicon carbide and the Group III-nitrides.
Power semiconductor devices may be fabricated using epitaxial layers formed on a semiconductor workpiece, such as a silicon carbide semiconductor wafer. Power semiconductor device fabrication processes may include surface processing operations that are performed on the silicon carbide semiconductor wafer to prepare one or more surfaces of the silicon carbide semiconductor wafer for later processing steps, such as surface implantation, formation of epitaxial layers, metallization, etc. Example surface processing operations may include grinding operations, lapping operations, and polishing operations.
Aspects of the present disclosure are discussed with reference to a semiconductor workpiece that is a semiconductor wafer that includes silicon carbide (“silicon carbide semiconductor wafer”) for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that aspects of the present disclosure can be used with other semiconductor workpieces. Other semiconductor workpieces may include carrier substrates, ingots, boules, polycrystalline substrates, monocrystalline substrates, bulk materials having a thickness of greater than 1 mm, such as greater than about 5 mm, such as greater than about 10 mm, such as greater than about 20 mm, such as greater than about 50 mm, such as greater than about 100 mm to 200 mm, etc.
Grinding is a material removal process that is used to remove material from the semiconductor wafer. Grinding may be used to reduce a thickness of a semiconductor wafer. Grinding typically involves exposing the semiconductor wafer to an abrasive containing surface, such as grind teeth on a grind wheel. Grinding may remove material of the semiconductor wafer through engagement with the abrasive surface.
Lapping is a precision finishing process that uses a loose abrasive in slurry form. The slurry typically includes coarser particles (e.g., largest dimension of the particles being greater than about 100 microns) to remove material from the semiconductor wafer. Lapping typically does not include engaging the semiconductor wafer with an abrasive-containing surface on the lapping tool (e.g., a wheel or disc having an abrasive-containing surface). Instead, the semiconductor wafer typically comes into contact with a lapping plate or a tile usually made of metal. Lapping typically provides better planarization of the semiconductor wafer relative to grinding.
Polishing is a process to remove imperfections and create a very smooth surface with a low surface roughness. Polishing may be performed using a slurry and a polishing pad. The slurry typically includes finer particles relative to lapping, but coarser particles relative to chemical mechanical planarization (CMP). Polishing typically provides better planarization of the semiconductor wafer relative to grinding.
CMP is a type of fine or ultrafine polishing, typically used to produce a smoother surface ready, for instance, for epitaxial growth of layers on the semiconductor wafer. CMP may be performed chemically and/or mechanically to remove imperfections and to create a very smooth and flat surface with low surface roughness. CMP typically involves changing the material of the semiconductor through a chemical process (e.g., oxidation) and removing the new material from the semiconductor wafer through abrasive contact with a slurry and/or other abrasive surface or polishing pad (e.g., oxide removal). In CMP, the abrasive elements in the slurry typically remove the product of the chemical process and do not remove the bulk material of the semiconductor wafer, often leaving very low subsurface damage.
Polishing tools (e.g., such as chemical mechanical polishing (CMP) tools) may be used after grinding operations to polish and/or smooth a semiconductor wafer surface. Polishing tools, such as CMP tools, may use a combination of chemical and mechanical forces to remove excess materials from a wafer surface, ensuring desired flatness and smoothness. Polishing tools, such as CMP tools, may include a rotating platen, polishing pad, and a slurry containing abrasive particles and chemical agents. As the wafer is pressed against the polishing pad and rotated, the slurry chemically reacts with and/or mechanically removes material, resulting in a highly planar and smooth surface.
Grinding and polishing silicon carbide semiconductor wafers may pose several challenges due to the inherent properties of the material. Silicon carbide is an extremely hard and brittle compound with a high level of abrasiveness, making the polishing process more demanding. One challenge is the potential for excessive tool wear and heat generation during grinding or polishing, which can affect the quality of the finished product. The hardness of silicon carbide may also lead to the formation of cracks or fractures if not properly managed, impacting the structural integrity of the material. Additionally, achieving precise dimensions and surface finishes can be challenging due to the resistance of silicon carbide to abrasion. Controlling parameters such as polishing pad selection, rotational speed, slurry composition, and/or cooling mechanisms may be important to overcoming these challenges and ensuring the successful fabrication of silicon carbide components with the desired properties and performance.
Pad conditioning is an important part of the polishing (e.g., CMP) process. Pad conditioning is the process of dressing the pad using a conditioning disk or dresser (e.g., a diamond pad conditioner) to remove the polish biproducts and particles adsorbed/absorbed on the pad material to avoid pad glazing and to regenerate a fresh pad surface asperity to maintain a uniform surface profile. The right choice of pad conditioning for silicon carbide polishing helps maintain high and consistent material removal rates and acceptable pad temperatures by reducing pad glazing.
Due to the very high chemical resistance and mechanical hardness, CMP of silicon carbide wafers is a challenging process. For silicon carbide workpiece processing in particular, CMP may be the most expensive fabrication step due to lengthy processing times. Additionally, there are benefits to using single wafer CMP processes, which offer wafer level process optimization and can achieve the desired material removal rate and surface finish in a more controlled and efficient manner. However, throughput is reduced when employing single wafer CMP processes if the cycle times and process parameters are not optimized. As such, it would be desirable to use more time efficient processes for polishing silicon carbide workpieces to increase throughput.
In some instances, for silicon carbide wafer polishing, the polishing pad is conditioned only ex-situ, or only between polishing of different wafers. However, according to examples of the present disclosure, the process can be improved by the use of in-situ pad conditioning, or pad conditioning during the polishing of a wafer. For example, in-situ conditioning can change the process temperature profile and material removal rate during polishing compared to using ex-situ conditioning alone. Additionally, ex-situ pad conditioning may be used in combination with in-situ pad conditioning due to the nature of the slurries (e.g., permanganate-based slurries) typically used for silicon carbide polishing. For instance, in some examples, a cleaning agent (e.g., reducing agent) may be used to clean the pad after polishing and regenerate the polishing pad for the next polishing cycle. However, cleaning agents containing reducing agents and/or organic compounds can cause redox type degradation reactions between the slurry and the cleaning agent, which can form particle agglomerates (e.g., manganese dioxide), leading to excessive scratches. Therefore, the use of such cleaning agents may be avoided during in-situ pad conditioning and employed only during ex-situ pad conditioning.
The in-situ pad conditioning can be performed at the beginning of polishing, at the end of polishing, intermittently during polishing (e.g., at regular or irregular intervals), or continuously throughout the entire polishing process. However, in some instances, continuous conditioning can cause rapid degradation of the pad and thus shortened pad conditioner life. Continuous pad conditioning can also affect the pad surface temperature and the roughness profile. Therefore, according to examples of the present disclosure, intermittent or segmented in-situ pad conditioning may be performed, and in-situ pad conditioning can be started and stopped based on a preset schedule or based on various process conditions.
In this regard, example aspects of the present disclosure are directed to methods for conditioning a polishing pad of a polishing system. In some embodiments, the method includes performing an in-situ pad conditioning process and an ex-situ pad conditioning process outside of the polishing operation. The in-situ pad conditioning process includes causing a pad conditioner to contact the polishing pad during a polishing operation. The ex-situ pad conditioning process includes causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad.
In some embodiments, the method includes performing the in-situ pad conditioning process, measuring a process condition, and changing the in-situ pad conditioning process based at least in part on the process condition.
A system for polishing a semiconductor workpiece is also provided. The system includes a platen operable to rotate about an axis, a polishing pad coupled to the platen, a workpiece carrier operable to bring a semiconductor workpiece into contact with the polishing pad, a pad conditioner, a sensor configured to measure a process condition, and a controller comprising one or more control devices operable to bring the pad conditioner into or out of contact with the polishing pad based at least in part on the process condition.
Aspects of the present disclosure provide technical effects and benefits, For instance, the use of such processes and systems according to examples of the present disclosure can improve throughput by reducing the frequency and/or duration of ex-situ conditioning required. Additionally, aspects of the present disclosure may increase material removal rates during polishing, which can further improve throughput while also reducing slurry consumption rates.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
It will be understood that when an element such as a layer, structure, region, or substrate is referred to as being “on” or extending “onto” another element, it may be directly on or extend directly onto the other element or intervening elements may also be present and may be only partially on the other element. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present, and may be partially directly on the other element. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
As used herein, a first structure “at least partially overlaps” or is “overlapping” a second structure if an axis that is perpendicular to a major surface of the first structure passes through both the first structure and the second structure. A “peripheral portion” of a structure includes regions of a structure that are closer to a perimeter of a surface of the structure relative to a geometric center of the surface of the structure. A “center portion” of the structure includes regions of the structure that are closer to a geometric center of the surface of the structure relative to a perimeter of the surface. “Generally perpendicular” means within 15 degrees of perpendicular. “Generally parallel” means within 15 degrees of parallel.
Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “lateral” or “vertical” may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.
Embodiments of the disclosure are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. The thickness of layers and regions in the drawings may be exaggerated for clarity. Additionally, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Similarly, it will be understood that variations in the dimensions are to be expected based on standard deviations in manufacturing procedures. As used herein, “approximately” or “about” includes values within 10% of the nominal value.
Like numbers refer to like elements throughout. Thus, the same or similar numbers may be described with reference to other drawings even if they are neither mentioned nor described in the corresponding drawing. Also, elements that are not denoted by reference numbers may be described with reference to other drawings.
Some embodiments of the invention are described with reference to semiconductor layers and/or regions which are characterized as having a conductivity type such as n type or p type, which refers to the majority carrier concentration in the layer and/or region. Thus, N type material has a majority equilibrium concentration of negatively charged electrons, while P type material has a majority equilibrium concentration of positively charged holes. Some material may be designated with a “+” or “−” (as in N+, N−, P+, P−, N++, N−−, P++, P−−, or the like), to indicate a relatively larger (“+”) or smaller (“−”) concentration of majority carriers compared to another layer or region. However, such notation does not imply the existence of a particular concentration of majority or minority carriers in a layer or region.
In the drawings and specification, there have been disclosed typical embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation of the scope set forth in the following claims.
FIG. 1 depicts an example polishing system 100 for a semiconductor workpiece (e.g., silicon carbide wafer) 105 according to example embodiments of the present disclosure. The polishing system 100 is a CMP system operable to perform one or more polishing operations for a silicon carbide wafer 105. The silicon carbide wafer 105 may include 4H silicon carbide, 6H silicon carbide, or another crystal structure. The silicon carbide wafer 105 may be an on-axis workpiece (e.g., end face parallel to the (0001) plane) or an off-axis workpiece (e.g., end face non-parallel to the (0001) plane). The polishing operation may be performed on a carbon face or a silicon face of the silicon carbide wafer 105. The silicon carbide wafer 105 may be doped or undoped. In some embodiments, the silicon carbide wafer has a diameter from about 100 mm to about 300 mm, such as about 100 mm, such as about 150 mm, such as about 200 mm. In some examples, the polishing system 100 includes a platen 110 with a polishing pad 120, a workpiece carrier 130, a delivery system 140, a pad conditioner 150, and a controller 160.
More specifically, the polishing system 100 includes the platen 110. The platen 110 may be operable to rotate about an axis 104. The platen 110 may be operable to rotate about the axis 104 in either a clockwise or counterclockwise direction. In some examples, the platen 110 may rotate, for instance, at a rotational speed in a range of about 10 rpm to about 10000 rpm, such as about 10 rpm to about 7500 rpm, such as about 10 rpm to about 2000 rpm, such as about 10 rpm to about 1000 rpm, such as about 10 rpm to about 500 rpm, such as about 10 rpm to about 120 rpm.
The platen 110 may include a receptacle 112. The receptacle 112 may be configured to hold a polishing pad 120 for a CMP process. The receptacle 112 may be a surface configured to support or receive the polishing pad 120. In some examples, the receptacle 112 may be a planar surface that supports the polishing pad 120.
The polishing pad 120 may provide a surface for polishing the silicon carbide semiconductor wafer 105. The polishing pad 120 may include durable and chemically resistant materials such as polyurethane and/or polyether ether ketone (PEEK) material. The polishing pad 120 may have a surface with a specified roughness and porosity to facilitate polishing a silicon carbide semiconductor wafer 105. The polishing pad 120 may include grooves or dimples to increase slurry distribution and reduce edge effects during the CMP process. The polishing pad 120 may include a cushioning layer (e.g., foam or rubber), in some examples, to facilitate adaptation of the polishing pad 120 to the topography of the semiconductor wafer 105, providing improved planarity of the semiconductor wafer 105.
The polishing pad 120 may have a diameter. The diameter may be greater than a size of the silicon carbide semiconductor wafer 105. The polishing pad 120 may have a diameter in a range of, for instance, about 150 mm to about 820 mm, such as in a range of about 150 mm to about 400 mm, such as in a range of about 150 mm to about 300 mm. In some examples, the diameter of the polishing pad 120 may be smaller or nearly the same size as the diameter of the platen 110 (FIG. 1 ). However, the diameter of the polishing pad 120 may be larger than the diameter of the platen 110 without deviating from the scope of the present disclosure. In some examples, the polishing pad 120 may have a thickness in a range of about 2 mm to about 40 mm, such as in a range 5 mm to about 40 mm, such as in a range of about 10 mm to about 40 mm.
In some examples, the polishing system 100 includes a delivery system 140. The delivery system 140 may be used to deliver a slurry to the polishing pad 120 on the platen 110 during a CMP process, for instance, from a slurry delivery outlet 142. In some embodiments, the slurry delivery outlet 142 may include a nozzle for delivering the slurry. In some examples, the slurry may include an oxidizing agent. For example, the oxidizing agent may include, potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, or potassium persulfate. In some example embodiments, the oxidizing agent may include sodium permanganate and/or potassium permanganate and optionally one or more other oxidizing agents, such as those listed above. Other suitable slurries with one or more abrasive elements (e.g., abrasive particles) may be used without deviating from the scope of the present disclosure.
The delivery system 140 may further include fluid delivery outlet 144. The fluid delivery outlet 144 may be configured to provide a cleaning agent. In some embodiments, the fluid delivery outlet 144 may include a nozzle for delivering the cleaning agent. The cleaning agent may include a reducing agent. In some embodiments, for example, the reducing agent may include hydrogen peroxide, urea peroxide, carboxylic acids (e.g., citric acid, oxalic acid, and the like), hydrazine, hydrophosphorous acid, phosphorous acid, sulfurous acid, sodium metabisulfite, ammonium metabisulfite, potassium metabisulfite, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, hydroxylamine, hydroxylamine salts, dimethylhydroxylamine, diethylhydroxylamine, reducing sugars chosen from galactose, xylose, glucose, fructose, lactose and maltose, hydroquinone, catechol, tetrahydrofulvalene, N,N-dimethylanilinebenzylamine, or a mixture thereof. The delivery system 140 may further include one or more additional fluid delivery outlets (not shown), which can dispense one or more additional fluids (e.g., coolant, additive, lubricant, etc.) to the polishing pad 120 during a polishing process. In some examples, the delivery system 140 may include an additive delivery system 145 configured to deliver one or more additives (e.g., oxidizing material, oxide removal material) either with the slurry through the slurry delivery outlet 142 or separate from the slurry through an additional fluid delivery outlet.
Aspects of the present disclosure are discussed with reference to providing a slurry and/or a cleaning agent to the polishing pad 120 through fluid delivery outlets 142 and 144 for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that the delivery system 140 may deliver materials (e.g., slurry, oxidizing materials, oxide removal materials, cleaning agent) to the polishing pad 120 in various ways without deviating from the scope of the present disclosure, such as from a plurality of fluid delivery outlets, from apertures in the platen and/or the polishing pad, or from other fluid delivery techniques.
In some examples, the polishing system 100 includes a workpiece carrier 130. The workpiece carrier 130 is operable to bring one or more silicon carbide semiconductor wafers 105 into contact with the polishing pad 120 to implement a polishing process. In some examples, the workpiece carrier 130 may be operable to hold a single silicon carbide semiconductor wafer 105 for single wafer processing. In some examples, the workpiece carrier 130 may be operable to hold a plurality of silicon carbide semiconductor wafers 105 for batch processing. As explained above, the methods described herein, in some instances, are particularly useful for single wafer processing due to the need for improved efficiency to increase throughput. However, the methods are similarly useful for batch processing.
The workpiece carrier 130 may be operable to rotate the silicon carbide semiconductor wafer 105 about an axis 132. The axis 132 is not aligned with the axis 104 associated with the platen 110. The workpiece carrier 130 may be operable to rotate the silicon carbide semiconductor wafer 105 about the axis 132 in either a clockwise or counterclockwise direction. In some examples, the workpiece carrier 130 may rotate, for instance, at a rotational speed in range of about 10 rpm to about 10000 rpm, such as about 10 rpm to about 7500 rpm, such as about 10 rpm to about 2000 rpm, such as about 10 rpm to about 1000 rpm, such as about 10 rpm to about 500 rpm, such as about 10 rpm to about 120 rpm. The workpiece carrier 130 may rotate in the same direction as the platen 110 or in a different direction relative to the platen 110.
The workpiece carrier 130 may be able to provide a downforce 134 of the silicon carbide semiconductor wafer 105 against the polishing pad 120. The downforce 134 of the workpiece carrier 130 may be controlled to adjust the polishing rate of the polishing process of the silicon carbide semiconductor wafer 105.
The workpiece carrier 130 may also oscillate in a lateral direction along the surface of the polishing pad 120. This will allow exposure of the semiconductor wafer 105 to different portions of the polishing pad 120 (e.g., at different radii of the polishing pad 120) during a polishing operation.
The polishing system 100 may include a pad conditioner 150. The pad conditioner 150 may rotate about an axis 152, such that the pad conditioner 150 rotates along the surface of the polishing pad 120 (e.g., in either a clockwise or counterclockwise direction). In some examples, the pad conditioner 150 may be on a swing arm 154 that may swing about an axis 156 to move the pad conditioner 150 to different locations on the polishing pad 120. The pad conditioner 150 may include an abrasive-containing material having one or more abrasive elements (e.g., diamond) that are used to condition or dress the polishing pad 120 as the polishing pad 120 is subject to glazing during a polishing process. In some embodiments, the abrasive elements may include one or more of: (i) diamond; (ii) ceramic; (iii) metal carbide; (iv) metalloid nitride (e.g., silicon nitride); (v) metalloid oxide; (vi) metalloid carbide (e.g., silicon carbide); (vii) carbon group nitride; (viii) carbon group oxide; (ix) carbon group carbide, (x) boron nitride (e.g., c-BN or w-BN), or any other suitable abrasive materials having a similar hardness.
The system 100 includes one or more control devices, such as a controller 160. The controller 160 may include one or more processors 162 and one or more memory devices 164. The one or more memory devices 164 may store computer-readable instructions that when executed by the one or more processors 162 cause the one or more processors 162 to perform one or more control functions, such as any of the functions described herein. The controller 160 may be in communication with various other aspects of the system 100 through one or more wired and/or wireless control links. For instance, the controller 160 may control the platen 110, the workpiece carrier 130, the delivery system 140, and/or the pad conditioner 150 to implement polishing processes according to examples of the present disclosure.
For instance, in some examples, the controller 160 may control the delivery system 140 to deliver one or more materials to the polishing pad 120. For instance, the controller 160 may control the delivery system 140 to provide an oxidizing material to the polishing pad 120 (e.g., through slurry delivery outlet 142) and to provide a cleaning agent for ex-situ conditioning to the polishing pad 120 (e.g., through fluid delivery outlet 144).
The controller 160 may control the pad conditioning process. For example, the controller can control whether or not the pad conditioner 150 contacts the polishing pad 120. To enact in-situ pad conditioning, the controller can control the pad conditioner 150 to contact the polishing pad 120 while the silicon carbide workpiece 105 is in contact with the polishing pad 120 and a polishing process is being conducted on the workpiece 105 (e.g., the workpiece and polishing pad are being rotated relative to one another while a slurry is on the polishing pad). Additionally, during in-situ pad conditioning, the controller may control the delivery system 140 to provide a slurry to the polishing pad 120 (e.g., via the slurry delivery outlet 142) and control the platen 110, the workpiece carrier 130, and the pad conditioner 150 to rotate. The controller may also control the pad conditioner 150 to move along the platen 110 such that the pad conditioner 150 contacts the polishing pad 120 at different locations along its radius.
FIG. 1 shows an example of the system during in-situ pad conditioning. For instance, it can be seen that the pad conditioner 150 is in contact with the polishing pad 120 while the silicon carbide workpiece 105 is in contact with the polishing pad 120. Additionally, the delivery system 140 is providing a slurry to the polishing pad 120 through slurry delivery outlet 142. No cleaning agent is being provided through fluid delivery outlet 144.
To stop in-situ pad conditioning, the controller 160 can control the pad conditioner 150 to move away from polishing pad 120 (e.g., via swing arm 154) such that the pad conditioner 150 no longer contacts the polishing pad 120. FIG. 2 shows an example of the system after stopping in-situ pad conditioning. In this regard FIG. 2 shows an example of the system during a polishing operation while neither in-situ nor ex-situ pad conditioning is being performed (i.e., no pad conditioning is occurring). For instance, it can be seen that the pad conditioner 150 is lifted off of the polishing pad 120 while the silicon carbide workpiece 105 is in contact with the polishing pad 120 and the delivery system 140 is providing a slurry to the polishing pad 120 through slurry delivery outlet 142. No cleaning agent is being provided through fluid delivery outlet 144.
To enact ex-situ pad conditioning, the controller 160 may control the pad conditioner 150 to contact the polishing pad 120 outside of the polishing operation. For example, the silicon carbide workpiece 105 can be removed from the carrier 130 manually or the controller can control the workpiece carrier 130 to remove the workpiece 105 from the polishing pad 120 (e.g., by lifting it vertically or by swinging it out from the polishing pad 120). It should be understood that the method for removing the silicon carbide workpiece 105 from the polishing pad 120 is not limited and any suitable method can be employed. During ex-situ pad conditioning, the controller 160 can also control the delivery system 140 to provide the cleaning agent to the polishing pad 120 (e.g., via the fluid delivery outlet 144) and control the platen 110 and/or the pad conditioner 150 to rotate. The controller may also control the pad conditioner 150 to move along the platen 110 such that the pad conditioner 150 contacts the polishing pad 120 at different locations along its radius.
FIG. 3 shows an example of the system during ex-situ pad conditioning. For instance, it can be seen that the pad conditioner 150 is in contact with the polishing pad 120 while the silicon carbide workpiece 105 has been removed from the polishing pad 120. Additionally, the delivery system 140 is providing a cleaning agent to the polishing pad 120 through fluid delivery outlet 144. No slurry is being provided through slurry delivery outlet 142. In some examples, a rinsing operation may be conducted to remove slurry from the polishing pad 120 prior to providing the cleaning agent to the polishing pad 120.
To stop ex-situ pad conditioning, the controller 160 can control the pad conditioner 150 to move away from polishing pad 120 (e.g., via swing arm 154) such that the pad conditioner 150 no longer contacts the polishing pad 120.
During either in-situ or ex-situ pad conditioning, it should be understood that the fluid delivery system 140 does not need to continuously provide either the slurry or the cleaning agent to the polishing pad 120 during the entire process. For example, in some embodiments, the fluid delivery system 140 can provide the slurry or the cleaning agent to the polishing pad 120 prior to rotating the platen 110 and/or pad conditioner 150. In other embodiments, the fluid delivery system 140 provides the slurry or the cleaning agent to the polishing pad 120 while the platen 110 and/or pad conditioner 150 are rotating but stops dispensing the slurry or fluid before the pad conditioning process is complete. In other embodiments, the fluid delivery system 140 provides the slurry or the cleaning agent to the polishing pad 120 continuously throughout the process.
As shown in FIG. 1 , in some examples, the system 100 may include a sensor 170. The sensor 170 is configured to measure a process condition. For example, the process condition may be a temperature of the polishing pad 120, a roughness of the silicon carbide workpiece 105, a roughness of the polishing pad 120, a wear condition of the polishing pad 120, or other parameter. When the process condition is the temperature of the polishing pad 120, the sensor 170 may be a temperature sensor, such as a non-contact infrared thermometer. When the process condition is surface roughness of the silicon carbide workpiece 105 or the polishing pad 120, the sensor 170 may be an optical sensor configured to measure the surface roughness.
The controller 160 may be configured to receive information about the process condition from the sensor 170 and determine whether to change the in-situ pad conditioning process. In some embodiments, for example, the change may include stopping the in-situ pad conditioning process in response to the process condition. In such embodiments, the controller 160 may be configured to start in-situ pad conditioning at the start of a polishing operation or after a certain time has elapsed since the start of the polishing operation. For example, the controller 160 may be configured to start in-situ pad conditioning from about 50 seconds to about 100 seconds, in some embodiments from about 50 seconds to about 75 seconds, in some embodiments from about 75 seconds to about 100 seconds, and in some embodiments, from about 65 to about 85 seconds after starting the polishing operation. The controller 160 may then be configured to stop in-situ pad conditioning in response to the process condition measured by the sensor 170.
In some embodiments, for instance, the controller 160 may be configured to stop in-situ pad conditioning when the temperature of the polishing pad 120 reaches a set threshold temperature. The threshold temperature may be correlated to the degradation temperature of the various components contained in the slurry. In some embodiments, the threshold temperature can be from about 40° C. to about 55° C., in some embodiments from about 40° C. to about 50° C., in some embodiments from about 40° C. to about 45° C., in some embodiments from about 45° C. to about 55° C., and in some embodiments, from about 50° C. to about 55° C.
In other embodiments, the change may include starting the in-situ pad conditioning process in response to the process condition measured by the sensor 170. For example, the controller 160 may be configured to start in-situ pad conditioning when the temperature of the polishing pad 120 reaches a first threshold value. In some embodiments, the controller 160 is also configured to then to stop in-situ pad conditioning when the temperature of the polishing pad 120 reaches a second threshold value. The first threshold temperature can be from about 40° C. to about 55° C., in some embodiments from about 40° C. to about 50° C., in some embodiments from about 40° C. to about 45° C., in some embodiments from about 45° C. to about 55° C., and in some embodiments, from about 50° C. to about 55° C. The second threshold temperature may be as described above.
In other embodiments, the controller 160 may be configured to start in-situ pad conditioning at the start of the polishing operation or after a set period of time since starting the polishing operation as described above and then to stop in-situ pad conditioning when the surface roughness of the silicon carbide workpiece 105 reaches a set threshold roughness. In some embodiments, the threshold roughness can be from about 0.2 nm to about 0.4 nm, in some embodiments from about 0.3 nm to about 0.4 nm, in some embodiments from about 0.35 nm to about 0.4 nm, in some embodiments from about 0.2 nm to about 0.3 nm, and in some embodiments, from about 0.2 nm to about 0.25 nm. In this regard, in-situ pad conditioning is employed while the roughness of the workpiece is highest and in-situ pad conditioning is stopped as the workpiece nears the desired roughness.
In another embodiment, the controller 160 may be configured to start in-situ pad conditioning when the surface roughness of the workpiece 105 reaches a first threshold value. In some embodiments, the controller 160 may be configured to then stop in-situ pad conditioning when the surface roughness of the workpiece 105 reaches a second threshold value. The first threshold roughness can be from about 0.2 nm to about 0.4 nm, in some embodiments from about 0.3 nm to about 0.4 nm, in some embodiments from about 0.35 nm to about 0.4 nm, in some embodiments from about 0.2 nm to about 0.3 nm, and in some embodiments, from about 0.2 nm to about 0.25 nm. The second threshold surface roughness may be as described above.
In some embodiments, the controller may be configured to start the in-situ pad conditioning process in response to a process condition, as described above, and then to continue in-situ pad conditioning for a set period of time or until the polishing operation is complete.
In some embodiments, the system 100 may include multiple sensors 170, such as a temperature sensor and an optical sensor. In such embodiments, the controller 160 may be configured to change the in-situ pad conditioning process in response to more than one process condition or in response to one of multiple process conditions reaching a threshold value. For example, the controller 160 may be configured to stop in-situ pad conditioning when the temperature of the polishing pad 120 reaches a threshold temperature or when the surface roughness of either the polishing pad 120 or the silicon carbide workpiece 105 reaches a threshold value, whichever occurs first. Alternatively, the controller may be configured to start in-situ pad conditioning when the surface roughness of the polishing pad 120 reaches a threshold value and to stop in-situ pad conditioning when the temperature of the polishing pad 120 reaches a threshold temperature. In this regard, in-situ pad conditioning can be started when glazing is indicated but stopped before the temperature becomes too high.
In some embodiments, the controller 160 may be configured to start in-situ pad conditioning at the start of the polishing operation or after a set period of time since starting the polishing operation as described above and then to stop in-situ pad conditioning after a predetermined elapsed time period. For example, the controller 160 may be configured to stop in-situ pad conditioning after a time period from about 50 seconds to about 100 seconds, in some embodiments from about 50 seconds to about 75 seconds, in some embodiments from about 75 seconds to about 100 seconds, and in some embodiments, from about 65 to about 85 seconds after starting in-situ pad conditioning or after starting the polishing operation. The duration of in-situ pad conditioning may be optimized for maximum throughput, polishing pad temperature, and/or material removal rate based on data collected from previous in-situ pad conditioning processes. For example, in some embodiments, the controller 160 may be configured to determine the elapsed time period based on the material removal rate during a polishing operation performed on a least one preceding semiconductor workpiece.
It should be understood that the controller 160 can be configured to start in-situ pad conditioning in any manner described herein and can be configured to stop in-situ pad conditioning in any manner described herein. These methods can be mixed with each other without deviating from the scope of the present disclosure.
The controller 160 may be configured to perform ex-situ pad conditioning after polishing each workpiece. For example, when polishing a plurality of silicon carbide workpieces in series, ex-situ conditioning can be performed between polishing of each workpiece. In this regard, the controller 160 can be configured to stop the polishing operation of one workpiece, start ex-situ pad conditioning, stop ex-situ pad conditioning, and then start a polishing operation of a subsequent workpiece.
In other embodiments, the controller 160 may be configured to perform ex-situ pad conditioning after a set number of workpieces have been polished within a series of workpiece polishing operations. For example, the controller 160 may be configured to perform ex-situ pad conditioning after polishing every 2 workpieces, such as after polishing every 3 workpieces, such as after polishing every 4 workpieces, such as after polishing every 5 workpieces, such as after polishing every 6 workpieces, such as after polishing every 7 workpieces, such as after polishing every 8 workpieces, such as after polishing every 9 workpieces, such as after polishing every 10 workpieces.
In other embodiments, the controller 160 may be configured to perform ex-situ pad conditioning based on a process condition. For example, ex-situ pad conditioning may be performed when the material removal rate during polishing of a workpiece drops below a threshold value. For example, the controller can be configured to perform ex-situ pad conditioning if the material removal rate during polishing of the immediately preceding semiconductor workpiece meets a threshold material removal rate, for example if the material removal rate drops about 10% or more, in some embodiments about 20% or more, and in some embodiments about 30% or more from the material removal rate during polishing of the previous workpiece or the average material removal rate during polishing of the previous 2 to 5 workpieces. Similarly, the controller 160 may be configured to determine the number of workpieces to polish between each ex-situ pad conditioning process based on the material removal rates during polishing of previous workpieces. For example, the controller may be configured to optimize or nearly optimize the number of workpieces to polish between ex-situ pad conditioning processes to maximize throughput.
FIG. 4 depicts a flow chart of an example method 200 according to example embodiments of the present disclosure. The method 200 may be implemented, for instance, using the polishing system 100 of FIG. 1 . The method 200 depicts operations performed in a particular order for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that the operations of any of the methods described herein may be adapted, expanded, performed simultaneously, omitted, rearranged, include steps not illustrated, and/or modified in various ways without deviating from the scope of the present disclosure.
At 202, the method 200 may include performing an in-situ pad conditioning process. For instance, the in-situ pad conditioning process may include causing a pad conditioner to contact a polishing pad during a polishing operation. The pad conditioner may be brought into contact with the polishing pad via a pad conditioner carrier on a swing arm. In some embodiments, the polishing pad may include polyurethane. The polishing operation may be a chemical mechanical planarization (CMP) operation. For example, the polishing operation may include providing a slurry to the polishing pad while the polishing pad is rotating and in contact with a semiconductor workpiece (e.g., a silicon carbide wafer). In some embodiments, the workpiece is also rotated (e.g., by a workpiece carrier) in the same or a different direction as the polishing pad. The polishing pad may be rotated by a platen to which the polishing pad is attached.
The slurry used in the polishing operation may include an oxidizing agent. For example, suitable oxidizing agents include hydrogen peroxide, urea peroxide, potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, or potassium persulfate. In some embodiments, particularly when the semiconductor workpiece is a silicon carbide workpiece, the oxidizing agent contains permanganate ions. The slurry may be provided via a nozzle within a fluid delivery system.
In some embodiments, the in-situ pad conditioning process may be started at the same time the polishing operation is started. In other embodiments, the in-situ pad conditioning process may be started after the polishing operation is started. For example, in some embodiments, the in-situ pad conditioning process may be started after a predetermined length of time after the polishing operation is started. For example, in-situ pad conditioning may be started after a time period from about 50 seconds to about 100 seconds, in some embodiments from about 50 seconds to about 75 seconds, in some embodiments from about 75 seconds to about 100 seconds, and in some embodiments, from about 65 to about 85 seconds after starting the polishing operation.
In other embodiments, the in-situ pad conditioning process may be started based on a process condition. For example, the process condition may be the temperature of the polishing pad, and in-situ pad conditioning may be started when the temperature reaches a predetermined temperature in a range from about 40° C. to about 55° C., in some embodiments from about 40° C. to about 50° C., in some embodiments from about 40° C. to about 45° C., in some embodiments from about 45° C. to about 55° C., and in some embodiments, from about 50° C. to about 55° C. In other embodiments, the process condition may be the surface roughness of the semiconductor workpiece, and in-situ pad conditioning may be started when the surface roughness of the workpiece reaches a first threshold value, such as a value in the range from about 0.2 nm to about 0.4 nm, in some embodiments from about 0.3 nm to about 0.4 nm, in some embodiments from about 0.35 nm to about 0.4 nm, in some embodiments from about 0.2 nm to about 0.3 nm, and in some embodiments, from about 0.2 nm to about 0.25 nm. The various process conditions may be measured through one or more sensors within the polishing system.
At 204, the method 200 may include stopping the in-situ pad conditioning process during the polishing operation based at least in part on a process condition. In some embodiments, for instance, the process condition is the temperature of the polishing pad, and in-situ pad conditioning may be stopped when the temperature of the polishing pad reaches a set threshold temperature. The threshold temperature may be correlated to the degradation temperature of the various components contained in the slurry. In some embodiments, the threshold temperature can be from about 40° C. to about 55° C., in some embodiments from about 40° C. to about 50° C., in some embodiments from about 40° C. to about 45° C., in some embodiments from about 45° C. to about 55° C., and in some embodiments, from about 50° C. to about 55° C. In other embodiments the process condition is the surface roughness of the semiconductor workpiece, and in-situ pad conditioning may be stopped when the surface roughness of the semiconductor workpiece reaches a set threshold roughness. In some embodiments, the threshold roughness can be from about 0.2 nm to about 0.4 nm, in some embodiments from about 0.3 nm to about 0.4 nm, in some embodiments from about 0.35 nm to about 0.4 nm, in some embodiments from about 0.2 nm to about 0.3 nm, and in some embodiments, from about 0.2 nm to about 0.25 nm. In other embodiments, the process condition is the surface roughness of the polishing pad, and in-situ pad conditioning may be stopped when the surface roughness of the polishing pad reaches a set threshold roughness.
In other embodiments, the process condition is time since starting either the polishing operation or the in-situ pad conditioning process, and in-situ pad conditioning is stopped after a predetermined elapsed time period. For example, in-situ pad conditioning may be stopped after a time period from about 50 seconds to about 100 seconds, in some embodiments from about 50 seconds to about 75 seconds, in some embodiments from about 75 seconds to about 100 seconds, and in some embodiments, from about 65 to about 85 seconds after starting in-situ pad conditioning. The duration of in-situ pad conditioning may be optimized for maximum throughput, polishing pad temperature, and/or material removal rate based on data collected from previous in-situ pad conditioning processes. For example, in some embodiments, the time period may be based on the material removal rate during a polishing operation performed on a least one preceding semiconductor workpiece.
It should be understood that stopping the in-situ pad conditioning process during the polishing operation is an optional step within method 200. For example, in other embodiments, in-situ pad conditioning may be performed throughout the remainder of the polishing operation.
At 206, the method 200 may include stopping the polishing operation. For example, stopping the polishing operation may include removing the semiconductor workpiece from the polishing pad and stopping the providing of the slurry to the polishing pad. Removing the workpiece from the polishing pad can be done in any suitable manner, such as removing the workpiece from a workpiece carrier or causing the workpiece carrier to lift the workpiece upward or outward from the polishing pad.
At 208, the method 200 may include performing an ex-situ pad conditioning process outside of the polishing operation. For example, the ex-situ pad conditioning operation may include causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad. The pad conditioner may be brought into contact with the polishing pad via a pad conditioner carrier on a swing arm. The polishing pad may be rotated during ex-situ pad conditioning, for example, by rotating a platen to which the polishing pad is attached.
The cleaning agent may be applied via a nozzle within a fluid delivery system. For example, the fluid delivery system may include multiple nozzles including one for delivering the slurry and one for delivering the cleaning agent to the polishing pad. The cleaning agent may include a reducing agent. For example, suitable reducing agents include hydrazine, hydrophosphorous acid, phosphorous acid, sulfurous acid, sodium metabisulfite, ammonium metabisulfite, potassium metabisulfite, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, hydroxylamine, hydroxylamine salts, dimethylhydroxylamine, diethylhydroxylamine, reducing sugars chosen from galactose, xylose, glucose, fructose, lactose and maltose, hydroquinone, catechol, tetrahydrofulvalene, N,N-dimethylanilinebenzylamine, or a mixture thereof.
In some embodiments, the method 200 is performed for polishing a plurality of semiconductor workpieces in series. In such embodiments, ex-situ pad conditioning may be performed after polishing each workpiece within the series. In other embodiments, ex-situ pad conditioning may be performed periodically. For example, ex-situ pad conditioning may be performed after polishing every 2 workpieces, such as after polishing every 3 workpieces, such as after polishing every 4 workpieces, such as after polishing every 5 workpieces, such as after polishing every 6 workpieces, such as after polishing every 7 workpieces, such as after polishing every 8 workpieces, such as after polishing every 9 workpieces, such as after polishing every 10 workpieces.
In some embodiments, ex-situ pad conditioning is performed based at least in part on a process condition. For example, after completing a polishing operation on each workpiece within a series, a process condition can be evaluated to determine whether or not to perform ex-situ pad conditioning. For instance, in some embodiments, ex-situ pad conditioning may be performed when the material removal rate during polishing of a workpiece drops below a threshold value. For example, ex-situ pad conditioning can be performed if the material removal rate during polishing of the immediately preceding semiconductor workpiece meets a threshold material removal rate, for example if the material removal rate drops about 10% or more, in some embodiments about 20% or more, and in some embodiments, about 30% or more from the material removal rate during polishing of the previous workpiece or the average material removal rate during polishing of the previous 2 to 5 workpieces.
Similarly, in embodiments wherein ex-situ pad conditioning is performed periodically after a set number of workpieces have been polished, the number of workpieces to polish between each ex-situ pad conditioning process can be determined based on the material removal rates during polishing of previous workpieces. For example, the number of workpieces to polish between ex-situ pad conditioning processes can be optimized to maximize throughput.
In some embodiments, the steps of method 200 can be carried out at least in part by a controller within a polishing system as described above with respect to FIG. 1 . However, such processes do not need to be automated by a controller and can be carried out by any suitable method.
FIG. 5 depicts a flow chart of an example method 300 according to example embodiments of the present disclosure. The method 300 may be implemented, for instance, using the polishing system 100 of FIG. 1 . The method 300 depicts operations performed in a particular order for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that the operations of any of the methods described herein may be adapted, expanded, performed simultaneously, omitted, rearranged, include steps not illustrated, and/or modified in various ways without deviating from the scope of the present disclosure.
At 302, the method 300 may include performing an in-situ pad conditioning process. The in-situ pad conditioning process may be performed as described above with respect to FIG. 4 .
At 304, the method 300 may include measuring a process condition. For example, the process condition may be a temperature of the polishing pad, a roughness of the silicon carbide workpiece, a roughness of the polishing pad, or a time elapsed since starting the polishing operation or since starting the in-situ pad conditioning process. In some embodiments, the process condition may be measured by a sensor within the polishing system. For instance, when the process condition is the temperature of the polishing pad, the sensor may be a temperature sensor, such as a non-contact infrared thermometer. When the process condition is surface roughness of the silicon carbide workpiece or polishing pad, the sensor may be an optical sensor configured to measure the surface roughness.
At 306, the method 300 may include changing the in-situ pad conditioning process based at least in part on the process condition. The change may include starting in-situ pad conditioning, stopping in-situ pad conditioning, or altering a parameter of the in-situ pad conditioning process, such as the rotational speed of the pad conditioning head or the force applied by the pad conditioner to the polishing pad.
In some embodiments, for example, in-situ pad conditioning may be stopped in response to the process condition. For instance, in-situ pad conditioning may be stopped when the temperature of the polishing pad reaches a set threshold temperature. The threshold temperature may be correlated to the degradation temperature of the various components contained in the slurry. In some embodiments, the threshold temperature can be from about 40° C. to about 55° C., in some embodiments from about 40° C. to about 50° C., in some embodiments from about 40° C. to about 45° C., in some embodiments from about 45° C. to about 55° C., and in some embodiments, from about 50° C. to about 55° C.
In other embodiments, in-situ pad conditioning may be stopped when the surface roughness of the semiconductor workpiece reaches a set threshold roughness. In some embodiments, the threshold roughness can be from about 0.2 nm to about 0.4 nm, in some embodiments from about 0.3 nm to about 0.4 nm, in some embodiments from about 0.35 nm to about 0.4 nm, in some embodiments from about 0.2 nm to about 0.3 nm, and in some embodiments, from about 0.2 nm to about 0.25 nm. In this regard, in-situ pad conditioning is employed while the roughness of the workpiece is highest, and conditioning is stopped as the workpiece nears the desired roughness.
In other embodiments, in-situ pad conditioning may be stopped after a predetermined time period has elapsed. For example, in-situ pad conditioning may be stopped after a time period from about 50 seconds to about 100 seconds, in some embodiments from about 50 seconds to about 75 seconds, in some embodiments from about 75 seconds to about 100 seconds, and in some embodiments, from about 65 to about 85 seconds after starting in-situ pad conditioning. The duration of in-situ pad conditioning may be optimized for maximum throughput, polishing pad temperature, and/or material removal rate based on data collected from previous in-situ pad conditioning processes. For example, in some embodiments, the time period may be determined based on the material removal rate during a polishing operation performed on a least one preceding semiconductor workpiece.
In some embodiments, the in-situ pad conditioning process may be started based on the process condition. For example, in some embodiments, in-situ pad conditioning may be started when the temperature of the polishing pad reaches a first threshold value, which may be from about 40° C. to about 55° C., in some embodiments from about 40° C. to about 50° C., in some embodiments from about 40° C. to about 45° C., in some embodiments from about 45° C. to about 55° C., and in some embodiments, from about 50° C. to about 55° C.
In other embodiments, in-situ pad conditioning may be started after a certain time has elapsed since the start of the polishing operation. For example, in-situ pad conditioning may be started after a time period from 50 seconds to about 100 seconds, in some embodiments from about 50 seconds to about 75 seconds, in some embodiments from about 75 seconds to about 100 seconds, and in some embodiments, from about 65 to about 85 seconds after starting the polishing operation.
In other embodiments, in-situ pad conditioning may be started when the surface roughness of the workpiece reaches a first threshold value, which may be from about 0.2 nm to about 0.4 nm, in some embodiments from about 0.3 nm to about 0.4 nm, in some embodiments from about 0.35 nm to about 0.4 nm, in some embodiments from about 0.2 nm to about 0.3 nm, and in some embodiments, from about 0.2 nm to about 0.25 nm.
In some embodiments, the in-situ pad conditioning process may be changed in response to more than one process condition or in response to one of multiple process conditions reaching a threshold value. For example, in-situ pad conditioning may be stopped when the temperature of the polishing pad reaches a threshold temperature, when the surface roughness of either the polishing pad or the silicon carbide workpiece reaches a threshold value, or when the time elapsed reaches a set length, whichever occurs first. Alternatively, in-situ pad conditioning may be started when the surface roughness of the polishing pad reaches a threshold value and stopped when the temperature of the polishing pad reaches a threshold temperature. In this regard, in-situ pad conditioning can be started when glazing is indicated but stopped before the temperature becomes too high.
In some embodiments, in-situ pad conditioning may be started at the start of the polishing operation or after a set period of time since starting the polishing operation and then stopped after a predetermined elapsed time period. For example, in-situ pad conditioning may be stopped after a time period from about 50 seconds to about 100 seconds, in some embodiments from about 50 seconds to about 75 seconds, in some embodiments from about 75 seconds to about 100 seconds, and in some embodiments, from about 65 to about 85 seconds after starting in-situ pad conditioning. The duration of in-situ pad conditioning may be optimized for maximum throughput, polishing pad temperature, and/or material removal rate based on data collected from previous in-situ pad conditioning processes.
At 308, the method 300 may include continuing the polishing operation. For example, after changing the in-situ pad conditioning process (e.g., starting or stopping it), the polishing operation may be continued by, for example, applying the slurry to the polishing pad and rotating the polishing pad and/or the workpiece carrier while the workpiece is in contact with the polishing pad, as described above. In some embodiments, in-situ pad conditioning may be performed multiple times within one polishing operation. In other embodiments, the in-situ pad conditioning process is only performed once during the polishing operation.
At 310, the method 300 may include stopping the polishing operation and performing an ex-situ pad conditioning process after stopping the polishing operation. For example, stopping the polishing operation may include removing the semiconductor workpiece from the polishing pad and stopping the providing of the slurry to the polishing pad. Removing the workpiece from the polishing pad can be done in any suitable manner, such as removing the workpiece from a workpiece carrier or causing the workpiece carrier to lift the workpiece upward or outward from the polishing pad.
The ex-situ pad conditioning process may include causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad. The pad conditioner may be brought into contact with the polishing pad via a pad conditioner carrier on a swing arm. The polishing pad may be rotated during ex-situ pad conditioning, for example, by rotating a platen to which the polishing pad is attached. The cleaning agent may be applied via a nozzle within a fluid delivery system. For example, the fluid delivery system may include multiple nozzles including one for delivering the slurry and one for delivering the cleaning agent to the polishing pad. The cleaning agent may include a reducing agent, such as those described above.
In some embodiments, method 300 is performed for polishing a plurality of semiconductor workpieces in series. In such embodiments, ex-situ pad conditioning may be performed after polishing each workpiece within the series. In other embodiments, ex-situ pad conditioning may be performed periodically. For example, ex-situ pad conditioning may be performed after polishing every 2 workpieces, such as after polishing every 3 workpieces, such as after polishing every 4 workpieces, such as after polishing every 5 workpieces, such as after polishing every 6 workpieces, such as after polishing every 7 workpieces, such as after polishing every 8 workpieces, such as after polishing every 9 workpieces, such as after polishing every 10 workpieces.
In some embodiments, ex-situ pad conditioning is performed based at least in part on a process condition. For example, after completing a polishing operation on each workpiece within a series, a process condition can be evaluated to determine whether or not to perform ex-situ pad conditioning. For instance, in some embodiments ex-situ pad conditioning may be performed when the material removal rate during polishing of a workpiece drops below a threshold value. For example, ex-situ pad conditioning can be performed if the material removal rate during polishing of the immediately preceding semiconductor workpiece meets a threshold material removal rate, for example if the material removal rate drops about 10% or more, in some embodiments about 20% or more, and in some embodiments, about 30% or more from the material removal rate during polishing of the previous workpiece or the average material removal rate during polishing of the previous 2 to 5 workpieces.
Similarly, in embodiments wherein ex-situ pad conditioning is performed periodically after a set number of workpieces have been polished, the number of workpieces to polish between each ex-situ pad conditioning process can be determined based on the material removal rates during polishing of previous workpieces. For example, the number of workpieces to polish between ex-situ pad conditioning processes can be optimized to maximize throughput.
In some embodiments, the steps of method 300 can be carried out at least in part by a controller within a polishing system as described above with respect to FIG. 1 . However, such processes do not need to be automated by a controller and can be carried out by any suitable method.
Example aspects of the present disclosure are set forth below. Any of the below features or examples may be used in combination with any of the embodiments or features provided in the present disclosure.
One example aspect of the present disclosure is directed to a method for conditioning a polishing pad of a polishing system. The method includes performing an in-situ pad conditioning process and an ex-situ pad conditioning process. The in-situ pad conditioning process includes causing a pad conditioner to contact the polishing pad during a polishing operation. The ex-situ pad conditioning process is performed outside of the polishing operation and includes causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad.
In some examples, the polishing pad comprises polyurethane.
In some examples, the cleaning agent is applied to the polishing pad while the polishing pad is rotating.
In some examples, the cleaning agent comprises a reducing agent.
In some examples, the reducing agent comprises hydrogen peroxide, urea peroxide, a carboxylic acid, hydrazine, hydrophosphorous acid, phosphorous acid, sulfurous acid, sodium metabisulfite, ammonium metabisulfite, potassium metabisulfite, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, hydroxylamine, hydroxylamine salts, dimethylhydroxylamine, diethylhydroxylamine, reducing sugars chosen from galactose, xylose, glucose, fructose, lactose and maltose, hydroquinone, catechol, tetrahydrofulvalene, N,N-dimethylanilinebenzylamine, or a mixture thereof.
In some examples, the polishing operation comprises providing a slurry to the polishing pad while the polishing pad is rotating and in contact with a semiconductor workpiece.
In some examples, the slurry comprises an oxidizing agent.
In some examples, the oxidizing agent comprises potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, or potassium persulfate.
In some examples, stopping the polishing operation comprises removing the semiconductor workpiece from contact with the polishing pad and stopping the providing of the slurry to the polishing pad.
In some examples, the in-situ pad conditioning process is performed continuously throughout the polishing operation.
In some examples, the in-situ pad conditioning process is performed intermittently throughout the polishing operation.
In some examples, the method further comprises stopping the in-situ pad conditioning process during the polishing operation based at least in part on a process condition.
In some examples, the process condition is an elapsed time period since starting the in-situ pad conditioning process.
In some examples, the elapsed time period is determined based on a rate of material removal during a polishing operation performed on at least one preceding semiconductor workpiece.
In some examples, the process condition is a temperature of the polishing pad.
In some examples, the process condition is a surface roughness of a semiconductor workpiece.
In some examples, the method is performed for polishing a plurality of semiconductor workpieces.
In some examples, the method comprises performing the ex-situ pad conditioning process after polishing each semiconductor workpiece of the plurality of semiconductor workpieces.
In some examples, the method comprises performing the ex-situ pad conditioning process after every X workpieces of the plurality of semiconductor workpieces, wherein X is an integer from 2 to 10.
In some examples, the method comprises performing the ex-situ pad conditioning process based at least in part on a process condition after completing polishing of each semiconductor workpiece of the plurality of semiconductor workpieces.
In some examples, the process condition is a material removal rate during polishing of an immediately preceding semiconductor workpiece meeting a threshold material removal rate.
In some examples, the polishing operation is a chemical mechanical planarization (CMP) operation.
In some examples, the polishing operation is performed on a semiconductor workpiece comprising silicon carbide.
Another example aspect of the present disclosure is directed to a method for conditioning a polishing pad of a polishing system. The method includes performing an in-situ pad conditioning process, measuring a process condition, and changing the in-situ pad conditioning process based at least in part on the process condition. The in-situ pad conditioning process includes causing a pad conditioner to contact the polishing pad during a polishing operation.
In some examples, the polishing pad comprises polyurethane.
In some examples, the polishing operation comprises providing a slurry to the polishing pad while the polishing pad is rotating and in contact with a semiconductor workpiece.
In some examples, the slurry comprises an oxidizing agent.
In some examples, the oxidizing agent comprises potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, or potassium persulfate.
In some examples, the process condition is an elapsed time period since starting the in-situ pad conditioning process.
In some examples, the method is performed for polishing a plurality of semiconductor workpieces and the in-situ pad conditioning process is stopped when the elapsed time period reaches a length determined based on a rate of material removal during a polishing operation performed on at least one preceding semiconductor workpiece of the plurality of semiconductor workpieces.
In some examples, the process condition is a temperature of the polishing pad.
In some examples, the process condition is a surface roughness of a semiconductor workpiece.
In some examples, the method further comprises stopping the polishing operation and performing an ex-situ pad conditioning process after stopping the polishing operation, wherein the ex-situ pad conditioning process comprises causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad.
In some examples, the cleaning agent is applied to the polishing pad while the polishing pad is rotating.
In some examples, the cleaning agent comprises a reducing agent.
In some examples, the reducing agent comprises hydrogen peroxide, urea peroxide, a carboxylic acid, hydrazine, hydrophosphorous acid, phosphorous acid, sulfurous acid, sodium metabisulfite, ammonium metabisulfite, potassium metabisulfite, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, hydroxylamine, hydroxylamine salts, dimethylhydroxylamine, diethylhydroxylamine, reducing sugars chosen from galactose, xylose, glucose, fructose, lactose and maltose, hydroquinone, catechol, tetrahydrofulvalene, N,N-dimethylanilinebenzylamine, or a mixture thereof.
In some examples, stopping the polishing operation comprises removing the semiconductor workpiece from contact with the polishing pad and stopping the providing of the slurry to the polishing pad.
In some examples, the method is performed for polishing a plurality of semiconductor workpieces.
In some examples, the method comprises performing the ex-situ pad conditioning process after polishing of each semiconductor workpiece of the plurality of semiconductor workpieces.
In some examples, the method comprises performing the ex-situ pad conditioning process after every X workpieces of the plurality of semiconductor workpieces, wherein X is an integer from 2 to 10.
In some examples, the method comprises performing the ex-situ pad conditioning process based on a process condition after completing polishing of each semiconductor workpiece of the plurality of semiconductor workpieces.
In some examples, the process condition is a surface roughness of the semiconductor workpiece.
In some examples, the process condition is a material removal rate during polishing of an immediately preceding semiconductor workpiece meeting a threshold material removal rate.
In some examples, the method further comprises continuing the polishing operation.
Another example aspect of the present disclosure is directed to a system for polishing a semiconductor wafer. The system includes a platen operable to rotate about an axis, a polishing pad coupled to the platen, a workpiece carrier operable to bring a semiconductor workpiece into contact with the polishing pad, a pad conditioner, a sensor configured to measure a process condition, and a controller comprising one or more control devices operable to bring the pad conditioner into or out of contact with the polishing pad based at least in part on the process condition.
In some examples, the polishing pad comprises polyurethane.
In some examples, the system further comprises a cleaning agent.
In some examples, the system further comprises a nozzle configured to dispense the cleaning agent.
In some examples, the cleaning agent comprises a reducing agent.
In some examples, the reducing agent comprises hydrogen peroxide, urea peroxide, a carboxylic acid, hydrazine, hydrophosphorous acid, phosphorous acid, sulfurous acid, sodium metabisulfite, ammonium metabisulfite, potassium metabisulfite, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, hydroxylamine, hydroxylamine salts, dimethylhydroxylamine, diethylhydroxylamine, reducing sugars chosen from galactose, xylose, glucose, fructose, lactose and maltose, hydroquinone, catechol, tetrahydrofulvalene, N,N-dimethylanilinebenzylamine, or a mixture thereof.
In some examples, the system further comprises a slurry.
In some examples, the system further comprises a nozzle configured for dispensing the slurry.
In some examples, the slurry comprises an oxidizing agent.
In some examples, the oxidizing agent comprises potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, or potassium persulfate.
In some examples, the sensor comprises a temperature sensor.
In some examples, the temperature sensor comprises an infrared thermometer.
In some examples, the infrared thermometer is configured to measure the temperature of the polishing pad.
In some examples, the sensor comprises an optical sensor.
In some examples, the optical sensor is configured to measure a roughness of a surface of the semiconductor workpiece.
In some examples, the pad conditioner is on a swing arm.
In some examples, the semiconductor workpiece comprises a silicon carbide semiconductor wafer.
In some examples, the silicon carbide semiconductor wafer has a diameter from about 100 mm to about 300 mm.
In some examples, a diameter of the silicon carbide semiconductor wafer is about 200 mm.
While the present subject matter has been described in detail with respect to specific example embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing can readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.

Claims

1. A method for conditioning a polishing pad of a polishing system, the method comprising:

performing an in-situ pad conditioning process, wherein the in-situ pad conditioning process comprises providing a slurry to the polishing pad and causing a pad conditioner to contact the polishing pad during a polishing operation, wherein the slurry comprises one or more of potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, and potassium persulfate, wherein the polishing operation comprises providing the slurry to the polishing pad while the polishing pad is rotating and in contact with a semiconductor workpiece surface comprising silicon carbide; and

performing an ex-situ pad conditioning process outside of the polishing operation, wherein the ex-situ pad conditioning process comprises causing the pad conditioner to contact the polishing pad while a cleaning agent is applied to the polishing pad.

2. The method of claim 1, wherein the cleaning agent is applied to the polishing pad while the polishing pad is rotating.

3. The method of claim 1, wherein the cleaning agent comprises a reducing agent.

4. (canceled)

5. The method of claim 1, wherein the slurry comprises sodium permanganate or potassium permanganate.

6. The method of claim 1, further comprising stopping the polishing process, wherein stopping the polishing operation comprises removing the semiconductor workpiece from contact with the polishing pad and stopping the providing of the slurry to the polishing pad.

7. The method of claim 1, wherein the in-situ pad conditioning process is performed continuously throughout the polishing operation.

8. The method of claim 1, wherein the in-situ pad conditioning process is performed intermittently throughout the polishing operation.

9. The method of claim 1, further comprising stopping the in-situ pad conditioning process during the polishing operation based at least in part on a process condition.

10. The method of claim 9, wherein the process condition is an elapsed time period since starting the in-situ pad conditioning process.

11. The method of claim 10, wherein the elapsed time period is determined based on a rate of material removal during a polishing operation performed on at least one preceding semiconductor workpiece.

12. The method of claim 9, wherein the process condition is a temperature of the polishing pad.

13. The method of claim 1, wherein the method is performed for polishing a plurality of semiconductor workpieces.

14. The method of claim 13, wherein the method comprises performing the ex-situ pad conditioning process after polishing each semiconductor workpiece of the plurality of semiconductor workpieces.

15. The method of claim 13, wherein the method comprises performing the ex-situ pad conditioning process after every X workpieces of the plurality of semiconductor workpieces, wherein X is an integer from 2 to 10.

16. The method of claim 13, wherein the method comprises performing the ex-situ pad conditioning process based at least in part on a process condition after completing polishing of each semiconductor workpiece of the plurality of semiconductor workpieces.

17. The method of claim 16, wherein the process condition is a material removal rate during polishing of an immediately preceding semiconductor workpiece meeting a threshold material removal rate.

18. (canceled)

19. A method for conditioning a polishing pad of a polishing system, the method comprising:

performing an in-situ pad conditioning process, wherein the in-situ pad conditioning process comprises providing a slurry to the polishing pad and causing a pad conditioner to contact the polishing pad during a polishing operation, wherein the slurry comprises one or more of potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, and potassium persulfate, wherein the polishing operation comprises providing the slurry to the polishing pad while the polishing pad is rotating and in contact with a semiconductor workpiece surface comprising silicon carbide;

measuring a process condition; and

changing the in-situ pad conditioning process based at least in part on the process condition.

20. A system for polishing a semiconductor wafer, the system comprising:

a platen operable to rotate about an axis;

a polishing pad coupled to the platen;

a workpiece carrier operable to bring a semiconductor workpiece surface comprising silicon carbide into contact with the polishing pad;

a pad conditioner;

a delivery system configured to deliver a slurry to the polishing pad, wherein the slurry comprises one or more of potassium hypochlorite, sodium hypochlorite, ammonium persulfate, potassium peroxymonosulfate, sodium permanganate, potassium permanganate, potassium periodate, and potassium persulfate;

a sensor configured to measure a process condition; and

a controller comprising one or more control devices operable to bring the pad conditioner into or out of contact with the polishing pad based at least in part on the process condition.

21. The method of claim 1, wherein the slurry comprises sodium permanganate.