HK1036467A - Chemical mechanical polishing slurry useful for copper/tantalum substrates - Google Patents

Description

Chemical mechanical polishing slurry for copper/tantalum substrates

Technical Field

The present invention relates to a chemical mechanical polishing slurry which can polish a substrate including a copper portion and a tantalum portion when used continuously. The present invention includes a first chemical mechanical polishing slurry comprising an abrasive, an oxidizing agent, a complexing agent, and at least one organic amino compound. The invention also includes a second chemical mechanical polishing slurry comprising an abrasive, an oxidizing agent, and a complexing agent, wherein the weight ratio of oxidizing agent to complexing agent is greater than 15. The invention also includes a method of continuously polishing a substrate comprising a copper portion and a tantalum portion with a first and a second chemical mechanical polishing slurry.

Description of the Prior Art

Integrated circuits are made up of millions of active elements formed on or within a silicon substrate. These initially separate active elements are interconnected to form functional circuits and components. These elements are interconnected using well-known multilevel interconnects. The interconnect structure typically has a first level of metallization of the interconnect layer, a second level of metallization, and sometimes a third level and subsequent metallization. Interlayer dielectrics such as doped and undoped silicon dioxide or low- κ dielectric tantalum nitride are used to electrically isolate silicon substrates or wells (wells) of different metallization levels. The electrical connections between the different interconnect layers are made by using metallized vias. US5,741,626 (incorporated herein by reference) describes a method of preparing a dielectric tantalum nitride layer.

In a similar approach, metal contacts are used to form electrical connections between interconnect layers formed in the well and the elements. The metal vias and contacts may be filled with various metals and alloys, including tantalum (Ti), tantalum nitride (TiN), tantalum (Ta), aluminum-copper (Al-Cu), silicon aluminum (Al-Si), copper, tungsten (W), and combinations thereof. These metal vias and contacts typically use a bonding layer such as tantalum nitride (TiN), titanium (Ti), tantalum (Ta), tantalum nitride (TaN), or combinations thereof, to bond the metal layer to the SiO₂And (4) connecting the substrates. At the contact layer, the bonding layer acts as a diffusion barrier to prevent the filled metal from reacting with SiO₂And (4) reacting.

In one semiconductor fabrication process, metal vias or contacts are made by blanket metal deposition followed by Chemical Mechanical Polishing (CMP). In a typical process, via holes are etched through an interlayer dielectric (ILD) to an interconnect line or semiconductor substrate. A thin adhesion layer, such as tantalum nitride and/or tantalum, is then typically formed on the ILD and directly connected to the etched via hole. A metal film is then blanket deposited over the adhesion layer and within the etched via. Deposition is continued until the via hole is filled with blanket deposited metal. Finally, the excess metal is removed by Chemical Mechanical Polishing (CMP) to form metal vias. Methods of fabricating and/or CMP vias are disclosed in US4,671,851, 4,910,155 and 4,944,836.

In a typical chemical mechanical polishing process, a substrate is brought into direct contact with a rotating polishing pad. A load weight is used to apply pressure to the back of the substrate. During polishing, the pad and the platen rotate while maintaining a downward force on the back side of the substrate. An abrasive and a chemically active solution (commonly referred to as a "slurry") are applied to the pad during polishing. The slurry initiates the polishing process by chemically reacting with the film being polished. The polishing process is facilitated by the rotational motion of the pad relative to the substrate under the application of the slurry at the wafer/pad interface. Polishing is continued in this manner until the desired film on the insulator is removed. The slurry composition is an important factor in the CMP step. The slurry can be conditioned according to the choice of oxidizing agent, abrasive, and other suitable additives to provide effective polishing at a desired polishing rate while minimizing surface defects, abrasion, and abrasion. In addition, the polishing slurry can be used to provide controlled polishing selectivity to other thin film materials used in current integration technologies, such as tantalum, tantalum nitride, and the like.

CMP polishing slurries typically contain an abrasive, such as silica or alumina suspended in an aqueous oxidizing medium. For example, US5,244,523 to Yu et al reports a slurry containing alumina, hydrogen peroxide and potassium or ammonium hydroxide that can be used to remove tungsten at a desired rate with little removal of the underlying insulating layer. U.S. Pat. No. 5,209,816 to Yu et al discloses a slurry comprising perchloric acid, hydrogen peroxide and a solid abrasive in an aqueous medium that can be used to polish aluminum. U.S. Pat. No. 5,340,370 to Cadien et al discloses a tungsten polishing slurry comprising about 0.1M potassium ferricyanide, about 5 wt.% silicon dioxide, and potassium acetate. Acetic acid was added to buffer the pH to about 3.5.

U.S. Pat. No. 4,789,648 to Beyer et al discloses slurry dosing with alumina abrasives with sulfuric acid, nitric acid and acetic acid, and deionized water. US5,391,258 and 5,476,606 disclose slurries for polishing metal and silica composites comprising an aqueous medium, abrasive particles, and an anion which controls the rate of silica removal. Other polishing slurries for CMP are described in U.S. Pat. No. 5,527,423 to Neville et al, U.S. Pat. No. 5,354,490 to Yu et al, U.S. Pat. No. 5,157,876 to Medellin et al, U.S. Pat. No. 5,137,544 to Medellin et al, and U.S. Pat. No. 4,956,313 to Cote et al.

Many mechanisms for polishing metal surfaces with slurries are disclosed in the prior art. The metal surface can be polished with a slurry that does not form a surface film when treated by mechanical removal of the metal particles and their dissolved species from the slurry. In this mechanism, the chemical dissolution rate should not be reduced to avoid wet erosion. However, a more preferred mechanism is the continuous formation of a thin abradable layer by reaction of the metal surface and one or more components of the slurry, such as the complexing agent and/or film-forming agent. The wear layer is then removed in a controlled manner by mechanical action. A thin passivation film is left on the surface thereof when the mechanical polishing process is stopped and controls the wet etching process. It is easier to control the chemical mechanical polishing process when polishing with the CMP slurry of this mechanism.

Copper-containing substrates currently being polished chemically and mechanically are also coated with Ta and TaN binders. Ta and TaN are very chemically passivated and mechanically hard, and thus difficult to polish away. The use of a single slurry with high Cu to Ta selectivity requires extended polishing times for Ta, i.e., significant overpolishing times for copper, during which damage resistance and corrosion performance are significantly reduced.

Several related Cu chemistries are discussed in the publications, but each does not provide a method to successfully address all of the key requirements of chemical mechanical polishing slurries for substrates comprising copper and tantalum. As a result, there is a need for one or more CMP slurries that can be successfully used to polish copper and tantalum-containing substrates.

Summary of The Invention

The present invention is directed to a first chemical mechanical polishing slurry capable of selectively polishing the copper portion of a substrate comprising copper and tantalum or tantalum nitride.

The invention also relates to a second chemical mechanical polishing slurry capable of selectively polishing tantalum and/or tantalum nitride portions of a copper-containing and tantalum and/or tantalum nitride substrate.

In addition, the invention relates to a method for continuously polishing a substrate comprising a copper portion and a tantalum and/or tantalum nitride portion with a first and a second chemical mechanical polishing slurry.

Another aspect of the present invention is first and second chemical mechanical polishing slurry precursors that are oxidizer free and are combined with an oxidizer separately prior to use to make a useful CMP slurry.

The present invention is a first chemical mechanical polishing slurry. The first chemical mechanical polishing slurry comprises at least one abrasive, at least one oxidizing agent, at least one complexing agent, and at least one organic amino compound. One preferred embodiment of the first polishing slurry is a composition comprising alumina, at least one oxidizing agent, tartaric acid, benzotriazole, and at least one organic amino compound.

The present invention also includes a second chemical mechanical polishing slurry comprising at least one abrasive, at least one oxidizing agent, and acetic acid, wherein the weight ratio of the oxidizing agent to the acetic acid is greater than about 10. One preferred embodiment of the second chemical mechanical polishing slurry is a composition comprising an aqueous dispersion of alumina, hydrogen peroxide, about 0.01 to about 3.0 wt.% acetic acid, and about 0.01 to about 0.2 wt.% benzotriazole, wherein the weight ratio of oxidizing agent to acetic acid is greater than about 10, and wherein the pH of the slurry is about 4 to about 9.

The invention is also a method of polishing a substrate comprising a copper moiety and a moiety selected from tantalum or tantalum nitride. The method comprises polishing by applying a first aqueous chemical mechanical polishing slurry comprising at least one abrasive, at least one oxidizing agent, at least one complexing agent, and at least one organic amino compound to a substrate. And removing a portion of the copper to yield a partially polished substrate by contacting the pad with the substrate and moving the pad relative to the substrate. A second chemical mechanical polishing slurry is applied to the partially polished substrate. The second chemical mechanical polishing slurry comprises a composition comprising at least one abrasive, at least one oxidizing agent, and acetic acid, wherein the weight ratio of the oxidizing agent to the acetic acid is greater than about 10. At least a portion of the tantalum or tantalum nitride is removed to provide a polished substrate by contacting the pad with the substrate and moving the pad relative to the substrate.

Detailed description of embodiments of the invention

The present invention relates to two chemical mechanical polishing slurries and a method for continuous polishing of substrates containing copper moieties and tantalum or tantalum nitride moieties with acceptable rates and little defectivity using the two slurries. In addition to being used in combination to polish copper and tantalum-containing substrates, a first chemical mechanical polishing slurry can be used to polish copper or copper alloy-containing substrates and a second chemical mechanical polishing slurry can be used to polish tantalum-containing or tantalum nitride-containing substrates.

Before describing in detail various preferred embodiments of the present invention, certain terms used herein are defined. Chemical mechanical polishing slurries ("CMP slurries") are useful products of the present invention and include oxidizing agents, abrasives, complexing agents, organic amino compounds, and other optional ingredients. The CMP slurry is used to polish multiple metallization layers, including but not limited to: semiconductor thin films, integrated circuit thin films, and any other films and surfaces in which CMP methods may be used.

The terms "copper" and "copper-containing alloy" are used interchangeably herein, as those skilled in the art will recognize, and the terms include, but are not limited to, substrates comprising pure copper, copper aluminum alloys, and Ti/TiN/Cu layers, as well as Ta/TaN/Cu multilayer substrates.

The terms "tantalum" and "tantalum-containing alloy" are used interchangeably herein to refer to a layer of tantalum and/or tantalum nitride underlying a conductive layer, such as a conductive copper layer.

The first chemical mechanical polishing slurry is useful for the polishing of metal, particularly copper and copper-containing alloy metal layers, associated with a substrate selected from the group consisting of integrated circuits, thin films, multilayer semiconductor layers, and silicon wafers.

First chemical mechanical polishing slurry

The first CMP slurry can be particularly advantageous for high-speed polishing of substrates including copper portions and tantalum portions. The first chemical mechanical polishing slurry can be used to polish other metal layers besides copper.

The first CMP slurry includes at least one oxidizing agent. The oxidizing agent helps to oxidize the multi-metal layer to its corresponding oxide, hydroxide, or ion. For example, in the first CMP slurry, an oxidizing agent may be used to oxidize the metal layer to the corresponding oxide or hydroxide, such as titanium to titanium oxide, tungsten to tungsten oxide, copper to copper oxide, and aluminum to aluminum oxide. It is advantageous to add the oxidizing agent of the present invention to the first CMP slurry to polish metals and metal-based components, including titanium, titanium nitride, tantalum, copper, tungsten, aluminum and aluminum alloys such as aluminum/copper alloys and various mixtures and compositions thereof, by mechanically polishing the metal to remove the corresponding oxide layer.

The oxidizing agent used in the first CMP slurry of the present invention is one or more of inorganic and organic per-compounds. A per-compound as defined by Hawley's Condensed Chemical Dictionary is a compound containing at least one peroxy group (-O-) or a compound containing an element in its highest oxidation state. Examples of compounds containing at least one peroxy group include, but are not limited to, hydrogen peroxide and its adducts such as urea hydrogen peroxide and percarbonates, organic peroxides such as benzoyl peroxide, peracetic acid and di-t-butyl peroxide, monopersulfates (SO)₅ ⁼) And dipersulfate (S)₂O₈-) and sodium peroxide.

Examples of compounds containing an element in its highest oxidation state include, but are not limited to, periodic acid, periodate salts, perbromic acid, perbromate salts, perchloric acid, perchlorate salts, perboric acid, perborate salts, and permanganates. Examples of non-per-compounds that meet this electrochemical potential requirement include, but are not limited to, bromates, chlorates, chromates, iodates, iodic acid, and cerium (iv) compounds such as cerium ammonium nitrate.

Preferred oxidizing agents are peracetic acid, urea-hydrogen peroxide, monopersulfate, dipersulfate, and salts thereof, and mixtures thereof including mixtures of urea and hydrogen peroxide. The most preferred oxidizing agent is a combination of hydrogen peroxide and urea.

The oxidizing agent may be present in the first chemical mechanical polishing slurry in an amount of about 0.3 to about 30.0 wt.%. Preferably, the oxidizing agent is present in the first chemical mechanical polishing slurry in an amount in the range of about 0.3 to about 17.0 wt.%, and most preferably in an amount in the range of about 1.0 to about 12.0 wt.%.

One optional oxidizing agent is urea hydrogen peroxide. Since urea hydrogen peroxide is 34.5% hydrogen peroxide and 65.5% urea, a large amount of urea hydrogen peroxide must be included in the first CMP slurry to achieve the desired oxidant addition set forth above. For example, 0.5 to 12.0 wt.% oxidizing agent corresponds to three times or 1.5 to 36.0 wt.% of the weight of carbamide hydroperoxide.

The first CMP slurry including urea hydrogen peroxide can also be formulated by mixing urea hydrogen peroxide with water and combining in an aqueous solution in a molar ratio of about 0.75: 1 to about 2: 1 to form a urea hydrogen peroxide oxidizing agent.

The first CMP slurry of the present invention forms a passivation layer on the surface of the substrate. When forming the passivation layer, it is important to interfere with the passivation layer to facilitate removal of the metal oxide from the substrate surface by the abrasive component of the first CMP slurry. One class of compounds included in the first CMP slurry to interfere with the passivation layer are complexing agents. Useful complexing agents include, but are not limited to: acids such as citric, lactic, malonic, tartaric, succinic, acetic, oxalic, and other acids, as well as amino acids and amino sulfuric acids, phosphoric, phosphonic, and salts thereof. The preferred first CMP slurry complexing agent is tartaric acid.

The amount of the complexing agent in the first CMP slurry of the invention is about 0.2 to about 5.0 wt%, preferably about 0.5 to about 3.0 wt%.

The first CMP slurry of the present invention includes at least one organic amino compound. The organic ammonia compound adsorbs on the polished substrate and suppresses the removal rate of the substrate. The organic amino compound used for the first CMP slurry includes alkylamine, alkanolamine, amino acid, urea derivatives, and a mixture thereof. Preferred organic amino compounds are long chain alkylamines and alkylolamines. The term "long chain alkylamines" refers to alkylamines having 7-12 or more carbon atoms, including, for example, nonanamine and dodecylamine. Useful alcohol amines include, but are not limited to, monoethanolamine and triethanolamine. Examples of useful urea derivatives include, but are not limited to, diurea. Preferred organic amino compounds are long chain alkylamines, dodecylamines. The preferred alcohol amine is triethanolamine.

The amount of organic ammonia in the first CMP slurry should be in the range of about 0.005 to about 10.0 wt%. More preferably, the organic amino compound is present in the first CMP slurry in an amount in the range of about 0.01 to about 5.0% by weight.

The first CMP slurry of the present invention may include an optional film-forming agent. The film-forming agent may be any compound or mixture of compounds capable of facilitating the formation of a metal oxide passivation layer and a dissolution-inhibiting layer on the surface of the metal layer. Passivation of the surface layer of the substrate is important to prevent wet etching of the substrate surface. Useful film-forming agents are nitrogen-containing cyclic compounds such as imidazole, benzotriazole, benzimidazole, benzothiazole, and derivatives thereof having hydroxy, amino, imino, carboxy, mercapto, nitro and alkyl substituents, as well as urea, thiourea and the like. A preferred film former is benzotriazole ("BTA").

The amount of optional film former in the first CMP slurry should be about 0.01 to about 1% by weight. Preferably, the film former is present in the first CMP slurry in an amount in the range of about 0.01 to about 0.2 percent by weight.

The BTA or other film former contained in the first CMP slurry destabilizes the uniform dispersion of the abrasive in the slurry. In order to promote stability of the first polishing slurry against sedimentation, flocculation and decomposition, various optional additives such as a surfactant, a stabilizer or a dispersant may be used. If a surfactant is added to the first CMP slurry, the surfactant may be an anionic, cationic, nonionic, or amphoteric surfactant, or a combination of two or more surfactants may be used. In addition, the addition of surfactants can be used to reduce the within-wafer-non-uniformity (WIWNU) of the wafer, thereby improving the surface of the wafer and reducing the surface defects of the wafer.

The amount of additives, such as surfactants, generally useful in the present invention should be sufficient to achieve effective stability of the slurry, and will generally vary depending on the particular surfactant selected and the surface properties of the metal oxide abrasive. For example, if insufficient amounts of surfactant are selected, little or no effect on stability is obtained. On the other hand, too much surfactant in the CMP slurry can lead to undesirable foaming and/or flocculation in the slurry. Stabilizers such as surfactants should generally be present in an amount of about 0.001% to 0.2% by weight. In addition, the additives may be added directly to the slurry or the metal oxide surface may be treated by known techniques. In each case, the amount of additive is adjusted to achieve the desired concentration in the polishing slurry. Preferred surface active agents include sodium lauryl sulfate, ammonium lauryl sulfate and mixtures thereof. Examples of useful surfactants include TRITON  DF-16 manufactured by Unino Carbide and SURFYNOL  manufactured by Air Products and Chemicals.

It is desirable to maintain the pH of the first CMP slurry of the invention at a pH of about 2.0 to about 12.0, preferably about 4.0 to about 8.0, to help control the CMP process. The pH of the CMP slurry of the present invention can be adjusted with any known acid, base, or amine. However, it is preferred to use an acid or base free of metal ions, such as ammonium hydroxide and amines, or nitric acid, phosphoric acid, sulfuric acid, or organic acids, to avoid introducing undesirable metal components into the CMP slurry of the present invention.

Second chemical mechanical polishing slurry

The second CMP slurry is formulated so that it has a low polishing rate for copper, and typically for tantalum or tantalum nitride. Thus, it is preferred that the second CMP slurry have a copper to tantalum polishing rate of less than about 2 to about 1, and most preferably less than about 1 to about 5.

The second CMP slurry includes at least one oxidizing agent. The oxidizing agent helps to oxidize the multi-metal layer to its corresponding oxide, hydroxide, or ion. For example, in a second CMP slurry, an oxidizing agent may be used to oxidize the metal layer to the corresponding oxide or hydroxide, e.g., tantalum to tantalum oxide. It is advantageous to add the oxidizing agent of the present invention to the second CMP slurry to polish metals and metal-based components, including titanium, titanium nitride, tantalum, copper, tungsten, aluminum and aluminum alloys such as aluminum/copper alloys and various mixtures and compositions thereof, by mechanically polishing the metal to remove the corresponding oxide layer.

The oxidizing agent used in the oxidizing agent for the second CMP slurry of the present invention is one or more of inorganic and organic per-compounds. A per-compound as defined by Hawley's Condensed Chemical Dictionary is a compound containing at least one peroxy group (-O-) or a compound containing an element in its highest oxidation state. Of compounds containing at least one peroxy groupExamples include, but are not limited to, hydrogen peroxide and its adducts such as urea hydrogen peroxide and percarbonates, organic peroxides such as benzoyl peroxide, peracetic acid and di-t-butyl peroxide, monopersulfates (SO)₅ ⁼) And dipersulfate (S)₂O₈-) and sodium peroxide.

Examples of compounds containing an element in its highest oxidation state include, but are not limited to, periodic acid, periodate salts, perbromic acid, perbromate salts, perchloric acid, perchlorate salts, perboric acid, perborate salts, and permanganates. Examples of non-per-compounds that meet this electrochemical potential requirement include, but are not limited to, bromates, chlorates, chromates, iodates, iodic acid, and cerium (iv) compounds such as cerium ammonium nitrate.

Non-exclusive examples of preferred oxidizing agents include, but are not limited to: peracetic acid, urea-hydrogen peroxide, monopersulfate, dipersulfate, and salts thereof, and mixtures thereof including mixtures of urea and hydrogen peroxide. A preferred oxidizing agent is hydrogen peroxide.

The oxidizing agent may be present in the second chemical mechanical polishing slurry in an amount of about 0.3 to about 30.0 wt.%. Preferably, the oxidizing agent is present in the second CMP slurry in an amount in the range of about 0.3 to about 17.0 wt.%, most preferably in the range of about 1.0 to about 12.0 wt.%.

One class of compounds included in the second CMP slurry are complexing agents. Useful complexing agents include, but are not limited to: acids such as citric, lactic, tartaric, succinic, acetic, oxalic and other acids, as well as amino acids and sulfamic, phosphoric, phosphonic and salts thereof. A preferred complexing agent is acetic acid. The amount of the complexing agent in the CMP slurry of the invention is about 0.1 to about 5.0 wt%, preferably about 0.1 to about 3.0 wt%.

It is important that the second CMP slurry contains a complexing agent in an amount much less than the weight of the oxidizing agent in the slurry. The second CMP slurry should have a weight ratio of oxidizing agent to complexing agent greater than about 10, and preferably greater than about 25.

The second CMP slurry of the present invention may include an optional film-forming agent. The film-forming agent may be any compound or mixture of compounds capable of facilitating the formation of a metal oxide passivation layer and a dissolution-inhibiting layer on the surface of the metal layer. Passivation of the surface layer of the substrate is important to prevent wet etching of the substrate surface. Useful film-forming agents are nitrogen-containing cyclic compounds such as imidazole, benzotriazole, benzimidazole, benzothiazole, and derivatives thereof having hydroxy, amino, imino, carboxy, mercapto, nitro and alkyl substituents, as well as urea, thiourea and the like. A preferred film former is benzotriazole ("BTA"). The amount of film former in the second CMP slurry should be about 0.01 to about 1% by weight. Preferably, the film former is present in the second CMP slurry in an amount in the range of about 0.01 to about 0.5 percent by weight.

The BTA or other film former contained in the second CMP slurry may destabilize the uniform dispersion of the abrasive in the slurry. To promote stability of the second polishing slurry against sedimentation, flocculation and decomposition, various optional additives such as a surfactant, a stabilizer or a dispersant may be used. If a surfactant is added to the second CMP slurry, the surfactant may be an anionic, cationic, nonionic, or amphoteric surfactant, or a combination of two or more surfactants may be used. In addition, the addition of surfactants can be used to reduce the within-wafer-non-uniformity (WIWNU) of the wafer, thereby improving the surface of the wafer and reducing the surface defects of the wafer.

The amount of additives, such as surfactants, generally useful in the second CMP slurry of the invention should be sufficient to achieve effective stability of the slurry and will generally vary depending on the particular surfactant selected and the surface properties of the metal oxide abrasive. For example, if insufficient amounts of surfactant are selected, little or no effect on stability is obtained. On the other hand, too much surfactant in the CMP slurry can lead to undesirable foaming and/or flocculation in the slurry. Stabilizers such as surfactants should generally be present in an amount of from about 0.001% to about 0.2% by weight. In addition, the additives may be added directly to the slurry or the metal oxide surface may be treated by known techniques. In each case, the amount of additive is adjusted to achieve the desired concentration in the first polishing slurry. Preferred surface active agents include sodium lauryl sulfate, ammonium lauryl sulfate and mixtures thereof. Examples of useful surfactants include TRITON  DF-16 manufactured by Uninocarbide, and SURFYNOL  manufactured by Air Products and Chemicals.

It is desirable to maintain the pH of the second CMP slurry of the invention at a pH of about 2.0 to about 12.0, preferably about 4.0 to about 8.0, to help control the CMP process. The pH of the CMP slurry of the present invention can be adjusted with any known acid, base, or amine. However, it is preferred to use an acid or base free of metal ions, such as ammonium hydroxide and amines, or nitric acid, phosphoric acid, sulfuric acid, or organic acids, to avoid introducing undesirable metal components into the CMP slurry of the present invention. Most preferably, the second CMP slurry has a pH of about 4 to about 7.5.

III abrasive material

Both the first and second CMP slurries of the present invention include an abrasive. The abrasive is typically a metal oxide abrasive. The metal oxide abrasive is selected from the group consisting of alumina, titania, zirconia, germania, silica, ceria and mixtures thereof. The first and second CMP slurries of the present invention preferably each include about 0.5 to about 15.0 wt% or more abrasive. However, more preferably, the first and second CMP slurries of the present invention each include about 1.5 to about 6.0 wt% abrasive.

The metal oxide abrasive can be produced by any process known to those skilled in the art. The metal oxide abrasive may be produced by any high temperature process such as sol-gel, hydrothermal or plasma processes, or by a process that produces fumed or precipitated metal oxides. The metal oxide is preferably a calcined or precipitated abrasive, more preferably a fumed abrasive such as fumed silica or fumed alumina. For example, the production of fumed metal oxides is a well-known process that involves the hydrolysis of a suitable feedstock stream (such as aluminum chloride used to produce alumina abrasives) in a hydrogen and oxygen flame. During the combustion process, approximately spherical molten particles are formed, the diameter of which can be varied by means of process parameters. These molten spheres (generally called primary particles) of alumina or similar oxide are fused to each other at their points of contact by collision to form branched, three-dimensional chain-like aggregates. The force required to break the aggregate is considerable and is generally considered irreversible. During cooling and collection, the aggregates are subjected to further collisions, which can cause some mechanical entanglement, thereby forming agglomerates. These agglomerates are loosely connected by Van der waals forces and reversible (i.e. the agglomerates can be removed by suitable dispersion in a suitable medium).

Precipitated abrasives may be produced by conventional techniques, such as by coagulation of the desired particles from an aqueous medium under the action of a high salt concentration, acid or other coagulating agent. These particles are filtered, washed, dried and separated from the residue of their reaction products by conventional methods known to those skilled in the art.

Preferred metal oxides may have a surface area of about 5m²G to about 430m²A/g, preferably about 30m²G to about 170m²The surface area is calculated by the methods of s.brunauer, p.h.emmet and i.teller, commonly referred to as BET (american chemical society, vo1.60, p309 (1938)). Due to the stringent purity requirements in the IC industry, the preferred metal oxides should be of high purity. By high purity is meant that the total impurity content from sources such as feed impurities and trace process contaminants is generally less than 1%, preferably less than 0.01% (i.e., 100 ppm).

The metal oxide abrasive used in the slurry of the present invention may comprise metal oxide aggregates or individual spherical particles. The term "particle" as used herein refers to both aggregates of more than one primary particle and individual particles.

Preferably, the metal oxide abrasive comprises a composition of metal oxide aggregates having a particle size distribution of less than about 1.0 μm (i.e., less than 1.0 μm diameter for all particles), an average aggregate diameter of less than about 0.4 μm, and a sufficient amount to repel and overcome van der Waals forces between the abrasive aggregates. These metal oxide abrasives have been found to be effective in minimizing or avoiding scratches, micro-spotting, divot and other surface defects during polishing. The aggregate size distribution of the present invention can be determined by known techniques such as Transmission Electron Microscopy (TEM). The aggregate mean diameter refers to the mean isosphere diameter when analyzed with TEM images, i.e., the diameter based on the aggregate cross-section. Force means that the surface potential or hydration force of the metal oxide particles must be sufficient to repel and overcome the van der Waals force between the particles.

In another preferred embodiment, the metal oxide abrasive may be composed of particles having an initial particle diameter of less than 0.4 μm (400nm) and a surface area of about 10m²G to about 250m²(iv) isolated individual metal oxide particles in grams.

The metal oxide abrasive is preferably added to the aqueous medium of the polishing slurry as a concentrated aqueous dispersion of metal oxide, which typically contains about 3% to about 45% solids, preferably 10% to 20% solids. The aqueous metal oxide dispersions can be produced by conventional techniques, such as by slowly adding the metal oxide abrasive to a suitable medium (e.g., deionized water) to form a colloidal dispersion. The dispersion is typically prepared by subjecting it to high shear mixing as known to those skilled in the art. The pH of the slurry can be adjusted away from the isoelectric point to obtain maximum colloidal stability.

IV, optional additives

Other known polishing slurry additives may be added to the first CMP slurry and/or the second CMP slurry. One type of optional additive is an inorganic acid and/or salt thereof that can be added to the first and/or second CMP slurry to further increase or improve the polishing rate of silicon wafer barrier layers, such as titanium and tantalum. Useful inorganic additives include ammonium, potassium, sodium, or other cationic salts of sulfuric, phosphoric, phosphonic, nitric, HF, ammonium chloride, sulfuric, phosphoric, phosphonic, and hydrochloric acids.

Method for preparing and using first and second CMP slurries

The first and second CMP slurries of the present invention can be produced by conventional processes known to those skilled in the art. Typically, the oxidizing agent and other non-abrasive components are mixed into an aqueous medium, such as deionized or distilled water, at a predetermined concentration and under low shear until the components are completely dissolved in the medium. A concentrated dispersion of a metal oxide abrasive, such as fumed alumina, is added to the medium and diluted to the desired amount of abrasive in the final CMP slurry.

The first and second CMP slurries of the present invention can be provided in a packaged system including all slurry additives. However, considering the problem of transporting CMP slurries containing oxidizing agents, particularly hydrogen peroxide, it is preferable that the first and second CMP slurries of the present invention are prepared and packaged as CMP precursors containing each component other than the oxidizing agent, transported to the customer's site, and mixed with hydrogen peroxide or other oxidizing agent at the customer's plant before use. Accordingly, one aspect of the present invention is a first and second CMP composition or and/or slurry precursor comprising one or more components selected from the group consisting of a catalyst, an abrasive, and a stabilizer, in dry or aqueous form, but in the absence of an oxidizing agent. The first and second CMP slurries are each mixed with at least one oxidizing agent prior to use.

It has been determined that the first and second CMP slurries of the invention comprising urea hydrogen peroxide can be formulated by adding hydrogen peroxide to a slurry precursor comprising urea and any other suitable slurry components to obtain a CMP slurry comprising urea hydrogen peroxide.

Preferred slurry precursors of the invention include dry or aqueous mixtures of urea and at least one metal oxide abrasive. Additional components may also be included in the urea-containing slurry precursor for the first and second CMP slurries.

Although the CM slurry of the present invention can be used to polish any metal-like layer, it was found that the first chemical mechanical polishing slurry of the present invention has a high copper polishing rate, low tantalum and tantalum nitride polishing rates. In addition, the second chemical mechanical polishing slurry has a desirably low polishing rate for a copper layer, while having a desirably high polishing rate for a tantalum dielectric insulating layer.

The first and second CMP slurries can be applied to the desired metal layer of the silicon wafer by any standard polishing equipment suitably employed. The first and second CMP slurries of the present invention are most suitable for polishing a substrate comprising a tantalum or tantalum nitride portion and a copper-containing alloy portion on a dielectric layer.

When used to polish a substrate comprising a tantalum or tantalum nitride portion and a copper-containing alloy portion, a first chemical mechanical polishing slurry is applied to the substrate and the substrate is polished by a conventional method using a polishing machine and polishing pad. When polishing of the substrate with the first CMP slurry is complete, the substrate may be rinsed with deionized water or other solvent to remove the first CMP slurry from the partially polished substrate. Next, the second CMP slurry of the invention is applied to a substrate and the substrate is polished by conventional techniques, preferably to polish the tantalum or tantalum nitride portion relative to the copper portion of the partially polished substrate. When the second polishing step is complete, the substrate is washed with deionized water or other solvent and is ready for further processing.

In both polishing steps, the first and/or second polishing slurry can be applied directly to the substrate, the polishing pad, or both, in a controlled manner during the polishing of the substrate. However, it is preferred that the polishing of the substrate be accomplished by applying the first and second CMP slurries to the pad, then positioning the pad relative to the substrate, and then moving the pad relative to the substrate.

The first and second CMP slurries polish copper, titanium nitride, tantalum, and tantalum nitride layers at a good rate in a controlled state. The polishing slurry of the present invention can be used at various stages in the manufacture of semiconductor integrated circuits to provide effective polishing at a desired polishing rate while minimizing surface defects.

Examples

We have found that the first CMP slurry is capable of polishing copper at a high rate, tantalum and tantalum nitride layers at a lower rate, and the second CMP slurry polishes tantalum and tantalum nitride layers at an acceptable rate, polishing copper at a relatively lower rate than the first CMP slurry.

The following examples illustrate preferred embodiments of the present invention and preferred methods of using the CMP slurries of the present invention.

Example I

In the present embodiment, CMP polishing is performed by using two CMP slurries. The first slurry comprised 3.0 wt% fumed alumina abrasive (from SEMI-SPERSE  W-A355 dispersion sold by Microelectronic materials Division of Cabot Corporation, in Aurora, Iilinois), 2.5 wt% hydrogen peroxide, 3.65 wt% urea, 1.25 wt% tartaric acid, and an aqueous dispersion of 50ppm Triton DF-16 surfactant. The second slurry included all the components of the first slurry plus 0.015 wt.% dodecylamine. Both slurries tested were adjusted to ph7.0 with ammonium hydroxide.

The CMP slurry was tested in two ways. The dissolution rates of Cu and Ta were electrochemically tested for each CMP slurry. The apparatus used a rotating disk electrode in a three electrode cell with a 273 potentiostat and coroson Software (supplied by PAR). The rotor and electrode and abrasive pad (5 lb/in) were rotated with the electrode at a preselected 500rpm (or 19.94 m/sec, max.)²Downward force) or upward pad contact to obtain electrochemical data. The foregoing values are considered approximate values of the chemical data in polishing, and the latter values yield the corrosion rate of the metal in the given slurry. Specifically, electrochemical data were recorded as potential-kinetic polarization curves with potential changes from about-0.25V cathode to open circuit potential to some anode potential at a rate of 10 mV/sec. The test results are shown in columns 3-4 of Table 1.

Copper and tantalum polishing rates using the same slurry were evaluated using an IPEC 472 polisher at 5 lbs/inch²Downward force, stage speed 55rpm and spindle speed 60 rpm. The CMP slurry was coated at a rate of 200 ml/min on IC1000/SUBA IV manufactured by Rodel. The polishing results are shown in columns 5-6 of Table 1.

TABLE 1

	Slurry material	Metal dissolution rate w/abrasion angstrom/min	Metal corrosion rate after abrasion	Metal removal rate in polishing	Cu to Ta selectivity ratio
						1	3% alumina, 2.5% H2O23.65% urea, 1.25% tartaric acid, 50ppm Triton DF-16	Cu:240Ta:140	Cu:36Ta:0.4	Cu:2750Ta:415	6.6∶1
2	With 1 and, in addition, 0.015% by weight of dodecylamine	Cu:240Ta:60	Cu:4.8Ta:0.12	Cu:2250Ta:50	45∶1

The addition of a small amount of dodecylamine to the slurry inhibited Ta removal and significantly improved the Cu to Ta selectivity ratio to 45: 1. This makes the slurry containing the organic ammonia compound more suitable for use as a copper polishing slurry, which stops polishing Ta.

The results of table 1 also show that: the electrochemical trend in polishing again indicates that: dodecylamine inhibits the dissolution of Ta during abrasion, which in turn results in a polishing rate that is significantly different from that of copper. Thus, dodecylamine is a dissolution inhibitor for Ta.

Example 2

This example investigated the effect of varying the weight ratio of oxidizing agent to complexing agent in the second CMP slurry of the invention on Cu and tantalum polishing rates. This example used a CMP slurry having the following composition: 1.25 wt% tartaric acid, hydrogen peroxide in the amounts listed in Table 2, 3.0 wt% alumina abrasive (W-A355), 50ppm Triton DF-16 surfactant, and the balance deionized water. The ph of the slurry was adjusted to 7.0 with ammonium hydroxide.

The polishing results for slurries with varying ratios of tartaric acid and hydrogen peroxide oxidizing agents are listed in table 2. In addition to the compounds listed in Table 2, each slurry contained 3.65 wt.% urea. The polishing rate was determined from an IC1000/SUBA IV pad manufactured by Rodel, a blanket silicon wafer placed on an IPEC 472 tool. Using 3 lb/in²The silicon wafer was polished with a downward force, a table speed of 55rpm, a spindle speed of 30rpm, and a slurry flow rate of 200 ml/min. TABLE 2

Number of times #	Tartaric acid%	HPO％	T∶HPO	Cu polishing rate of angstroms per minute	Ta polishing rate of angstroms/minute
						1	1.25	7.5	1∶6	2,622	288
2	1.25	5.0	1∶4	3,265	304
						3	1.25	2.5	1∶2	4,711	274

The polishing results show that: increasing the tartaric acid/peroxide weight ratio increased the Cu removal rate without significantly affecting the Ta rate.

The metal dissolution rates using the same substrate slurry described above but varying the tartaric acid content (T) and varying the hydrogen peroxide content (HPO) were evaluated electrochemically as described in example 1 and the results are listed in table 3. TABLE 3

Number of times #	Tartaric acid%	HPO％	T∶HPO	Cu dissolution rate in Angstrom/min at the time of abrasion	Cu etching rate Angstrom/min after abrasion
						1	0.5	6	1∶12	163	16.3
2	1	6	1∶6	163	19.2
						3	0.5	2	1∶4	240	19.2
4	1	2	1∶2	314	38.4
						5	3	6	1∶2	360	57.6
6	1	1	1∶1	344	50.4
						7	2	2	1∶1	336	62.6
8	3	2	1∶1	336	62.6

The results in tables 2 and 3 show that: the polishing rate of copper corresponds to the activity of copper as measured electrochemically, both of which decrease with increasing weight ratio of oxidizing agent to complexing agent, while the tantalum polishing rate and electrochemical solubility are substantially unaffected by compositional variations.

Example 3

The trends observed in Table 3 of example 2 were used as the basis for formulating a second chemical mechanical polishing slurry for polishing tantalum and tantalum nitride. The polishing rates for copper and tantalum for several second polishing slurries are listed in Table 4 below. The abrasive used in the chemical polishing slurry was SEMI-SPERSE  W-A355 fumed alumina dispersion sold by Cabot Corporation, Aurora, Illinois. TABLE 4

	Slurry material	Copper removal rate of angstroms per minute	Ta removal rate in angstroms/minute	PETEOS removal rate is angstrom/min	Cu to Ta selectivity
						1	2% alumina, 5% H2O20.5% tartaric acid, pH7.0	651	337	64	1.9∶1
2	5% alumina, 5% H2O20.2% tartaric acid, 0.2% acetic acid, 2% urea, 0.08% BTA, 50ppm Criton DF-16, pH6	260	244	8	1∶1
						3	3% alumina, 5% H2O20.2% acetic acid, 0.08% BTA, 50ppm Tinton DF-16, pH5.0	66	135	135	1∶1.45

Increasing the oxidant to complexing agent ratio to a value greater than 10 significantly reduced the copper removal rate, as shown in table 4. In addition, the data of table 4 also indicates that: acetic acid, which is an undesirable complexing agent for copper, significantly suppresses the copper removal rate, while the tantalum removal rate is substantially unaffected.

Claims (52)

1. A chemical mechanical polishing slurry precursor comprising:

at least one abrasive;

acetic acid; and at least one film former.

2. The chemical mechanical polishing slurry precursor of claim 1 wherein the acetic acid is present in an amount of about 0.01 to about 3.0 wt%.

3. The chemical mechanical polishing slurry precursor of claim 1 having a pH of from about 4 to about 9.

4. The chemical mechanical polishing slurry precursor of claim 1 wherein the film-forming agent is benzotriazole.

5. The chemical mechanical polishing slurry precursor of claim 4 comprising about 0.01 to about 0.5 wt.% benzotriazole.

6. The chemical mechanical polishing slurry precursor according to claim 5 wherein the abrasive is at least one oxidizing agent.

7. A chemical mechanical polishing slurry comprising the chemical mechanical polishing slurry precursor of claim 1 and at least one oxidizing agent.

A chemical mechanical polishing slurry comprising:

at least one abrasive;

at least one oxidizing agent; and

acetic acid, wherein the ratio of oxidant to acetic acid is greater than about 10.

9. The chemical mechanical polishing slurry of claim 8 comprising a film-forming agent.

10. The chemical mechanical polishing slurry of claim 9 wherein the film-forming agent is benzotriazole.

11. The chemical mechanical polishing slurry of claim 9 comprising about 0.01 to about 0.5 wt.% benzotriazole.

12. The chemical mechanical polishing slurry of claim 8 wherein the amount of acetic acid is about 0.01 to about 3.0 wt%.

13. The chemical mechanical polishing slurry of claim 8 having a pH of from about 4 to about 9.

14. The chemical mechanical polishing slurry of claim 8 wherein the abrasive is at least one metal oxide.

15. The chemical mechanical polishing slurry of claim 14 wherein the metal oxide abrasive is selected from the group consisting of alumina, ceria, germania, silica, titania, zirconia, and mixtures thereof.

16. The chemical mechanical polishing slurry of claim 8 wherein the abrasive is an aqueous dispersion of a metal oxide.

17. The chemical mechanical polishing slurry of claim 16 wherein the metal oxide abrasive consists of metal oxide aggregates having a size distribution less than about 1.0 μm and an average aggregate diameter less than about 0.4 μm.

18. The chemical mechanical polishing slurry of claim 17 wherein the metal oxide abrasive is composed of particles having a primary particle size of less than 0.400 μm and a surface area of about 10m²G to about 250m²(iv) composition of separated individual metal oxide spheres per gram.

19. The chemical mechanical polishing slurry of claim 8 wherein the metal oxide abrasive is selected from the group consisting of precipitated metal oxide abrasives or fumed metal oxide abrasives.

20. The chemical mechanical polishing slurry of claim 8 wherein the abrasive is an aqueous dispersion of alumina.

21. A chemical mechanical polishing slurry comprising:

at least one abrasive;

at least one oxidizing agent;

acetic acid; and

at least one film forming agent, wherein the weight ratio of oxidizing agent to complexing agent is greater than about 10, and the pH of the slurry is from about 4 to about 9.

22. The chemical mechanical polishing slurry of claim 21 comprising about 0.01 to about 0.2 wt% benzotriazole.

23. The chemical mechanical polishing slurry of claim 21 wherein the abrasive is an aqueous dispersion of a metal oxide.

24. The chemical mechanical polishing slurry of claim 23 wherein the alumina is present in the slurry in an amount of about 0.5 to about 15.0 percent by weight.

25. The chemical mechanical polishing slurry of claim 21 wherein the oxidizing agent is hydrogen peroxide.

26. A chemical mechanical polishing slurry comprising:

an aqueous dispersion of alumina;

hydrogen peroxide;

about 0.01 to about 3.0% by weight of acetic acid;

about 0.01 to about 0.5 weight percent benzotriazole, wherein the slurry comprises about 0.5 to about 15.0 weight percent alumina, wherein the weight ratio of oxidizing agent to acetic acid is greater than about 10, and the pH of the slurry is about 4 to about 9.

27. The chemical mechanical polishing slurry of claim 26 wherein the weight ratio of oxidizing agent to acetic acid is greater than about 25.

28. A method of polishing a substrate comprising a copper portion and a Ta portion, comprising:

applying a first aqueous chemical mechanical polishing slurry comprising at least one abrasive, at least one oxidizing agent, at least one complexing agent, and at least one organic amino compound to a substrate comprising a copper portion and a tantalum portion;

removing a portion of the copper from the substrate by contacting the pad with the substrate and moving the pad relative to the substrate to yield a partially polished substrate comprising a copper portion and a tantalum portion;

applying a second chemical mechanical polishing slurry to the partially polished substrate, the second chemical mechanical polishing slurry comprising at least one abrasive, at least one oxidizing agent, and acetic acid, wherein the weight ratio of oxidizing agent to acetic acid is greater than about 10;

at least a portion of the tantalum portion is removed from the substrate by contacting the pad with the substrate and moving the pad relative to the substrate to provide a polished substrate.

29. The method of claim 28, wherein the first slurry polishes the copper of the substrate at a rate that is at least 10 times faster than the first slurry polishes the tantalum.

30. The method of claim 28, wherein the second slurry polishing portion polishes the tantalum portion of the substrate at a rate that is at least 7 times faster than the second slurry polishing portion polishes the tantalum portion of the substrate.

31. The method of claim 28, wherein the first chemical mechanical polishing slurry is applied to the pad before contacting the pad with the substrate.

32. The method of claim 28, wherein the second polishing slurry is applied to the pad before the pad contacts a portion of the polishing substrate.

33. The method of claim 28, wherein substantially all of the first polishing slurry is removed from the portion of the polished substrate prior to applying the second slurry to the portion of the polished substrate.

34. The method of claim 28, wherein the first slurry and the second slurry each comprise a complexing agent selected from the group consisting of acetic acid, citric acid, lactic acid, tartaric acid, succinic acid, oxalic acid, amino acids, salts thereof, and mixtures thereof.

35. The process of claim 34, wherein the complexing agent used in the first slurry is tartaric acid and the complexing agent used in the second slurry is acetic acid.

36. The method of claim 35, wherein the first slurry comprises tartaric acid in an amount of 0.5% to about 5.0% by weight and the second slurry comprises acetic acid in an amount of about 0.01% to about 3.0% by weight.

37. The method of claim 28, wherein the first slurry organic amino compound has 7 to 15 carbon atoms.

38. The method of claim 28, wherein the first slurry organic amino compound is selected from the group consisting of alkyl amines, alcohol amines, urea, derivatives of urea, and mixtures thereof.

39. The method of claim 28, wherein the first slurry comprises from about 0.005 to about 10.0 weight percent of the at least one organic amino compound.

40. The method of claim 28, wherein the first paste comprises a film former.

41. The method of claim 28, wherein the first and second slurries each comprise an abrasive selected from the group consisting of alumina, ceria, germania, silica, titania, zirconia, and mixtures thereof.

42. The method of claim 28, wherein the first and second slurries each comprise an abrasive that is an aqueous dispersion of a metal oxide.

43. The method of claim 42, wherein the abrasive is selected from the group consisting of precipitated abrasives and calcined abrasives.

44. The method of claim 28, wherein the first and second slurries each comprise an aqueous dispersion of alumina.

45. The method of claim 28, wherein the pH of the second slurry is from about 4.0 to about 9.0.

46. The method of claim 28, wherein the second paste comprises a film former.

47. The method of claim 38, wherein the film forming agent is about 0.01 to about 0.2% by weight benzotriazole.

48. A method of polishing a substrate comprising a copper moiety and a moiety selected from the group consisting of tantalum, tantalum nitride and mixtures thereof, comprising:

applying a first slurry comprising alumina, at least one oxidizing agent, tartaric acid, benzotriazole, and at least one organic amino compound to a substrate;

removing at least a portion of the copper from the substrate by contacting the pad with the substrate and moving the pad relative to the substrate to yield a partially polished substrate;

applying a second chemical mechanical polishing slurry to the partially polished substrate, the second chemical mechanical polishing slurry comprising an alumina dispersion, hydrogen peroxide, about 0.01 to about 3.0 wt.% acetic acid, about 0.01 to about 0.2 wt.% benzotriazole, and wherein the weight ratio of oxidizing agent to acetic acid is greater than about 10, and the slurry has a pH of about 4 to about 9;

at least a portion of the substrate selected from the group consisting of tantalum, tantalum nitride, or a combination thereof is removed from the substrate by contacting the pad with the partially polished substrate and moving the pad relative to the substrate to provide a polished substrate.

49. The method of claim 48, wherein the first slurry polishes the copper of the substrate at a rate that is at least 45 times faster than the first slurry polishes the tantalum or tantalum nitride.

50. The method of claim 48, wherein the first chemical mechanical polishing slurry is applied to the pad before contacting the pad with the substrate.

51. The method of claim 48, wherein the second chemical mechanical polishing slurry is applied to the pad before the pad contacts a portion of the polishing substrate.

52. The method of claim 48, wherein substantially all of the first polishing slurry is removed from the portion of the polished substrate prior to applying the second slurry to the portion of the polished substrate.