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CN115609163B - Silicon carbide ingot slicing method, device and application - Google Patents

Silicon carbide ingot slicing method, device and application Download PDF

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Publication number
CN115609163B
CN115609163B CN202111108143.0A CN202111108143A CN115609163B CN 115609163 B CN115609163 B CN 115609163B CN 202111108143 A CN202111108143 A CN 202111108143A CN 115609163 B CN115609163 B CN 115609163B
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laser
energy
absorption layer
sic
femtosecond laser
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CN115609163A (en
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仇旻
石理平
孙潇雨
耿娇
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West Lake Instruments Hangzhou Technology Co ltd
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36Removing material
    • B23K26/38Removing material by boring or cutting

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
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Abstract

The invention discloses a silicon carbide ingot slicing method, which comprises the following steps: firstly, focusing the laser at low energy femto-second inside the SiC crystal to break part of Si-C bonds to form an absorption layer, and then thoroughly breaking the SiC chemical bonds in the absorption layer by using the laser at high energy femto-second to finish slicing; and taking the incidence direction of the laser as the top side, wherein the focal plane of the high-energy femtosecond laser is positioned below the absorption layer. The invention utilizes the carbonized absorption layer to prevent the damage depth of high-energy femtosecond laser wire forming in the SiC from being overlarge, thereby reducing the material waste rate.

Description

Silicon carbide ingot slicing method, device and application
Technical Field
The invention belongs to the field of semiconductor processing, and particularly relates to a silicon carbide crystal ingot slicing method, a silicon carbide crystal ingot slicing device and application.
Background
The first generation and the second generation of semiconductors, especially in the chip field, the whole country is behind for at least twenty years compared with the advanced country of technology, but the development of the third generation of semiconductor materials represented by wide forbidden band materials silicon carbide (SiC) and gallium nitride (GaN) can be precisely up to about 5 years at present. The third generation semiconductor technology leads the development of new energy, intelligent manufacturing, information technology and other fields in recent years. With the commercialization of 5G, the development of artificial intelligence and the demand of green cities, the technology brings more development space for the third-generation semiconductor technology. Compared with the downstream process of catching up with the traditional materials, the Chinese enterprises want to achieve the technical lead in the semiconductor field, and obviously, the development of the third-generation semiconductors is more intelligent. Every time a new material is replaced, the material needs to be re-surrounded, and corresponding subsequent processes and manufacturing procedures are developed.
However, siC is extremely hard, inferior to the hardest diamond material, and therefore is not easily cut. At present, the industry adopts a wire saw cutting mode, but the wire saw cutting mode has higher process requirements and long time consumption, and requires strict control on winding and stretching of the wire saw, so that the cutting quality and the cutting efficiency are lower. Meanwhile, the method adopts the steps of firstly cutting into slices, and then carrying out subsequent grinding and thinning to obtain slices with specific thickness, so that the loss of SiC materials is large, and more than 50% of materials are wasted. Based on the technical problems, the Chinese patent document with publication number of CN109909627A discloses a laser processing method of SiC ingots, which respectively adopts two nanosecond lasers with different types to treat the SiC ingots to be processed, and the method still belongs to laser thermal processing. The thermal processing method has a thermal diffusion effect and still has a damage area, and the technical problems are not basically solved. Accordingly, the industry is eager to study new techniques for cutting SiC wafers. This is critical not only for the development of the semiconductor industry, but also for the development of a new generation of new technology industry based on semiconductors.
Disclosure of Invention
The invention provides a silicon carbide ingot slicing method, which utilizes an absorption layer with broken part of Si-C bonds to prevent the damage depth of high-energy femtosecond laser wire forming in SiC from being too large, thereby reducing the material waste rate and improving the slicing efficiency and slicing quality.
The invention also provides a processing method of the device with different optical functions, which utilizes the combination of high and low energy lasers to realize carbonization of the material with the preset thickness in the SiC, and simultaneously induces the carbonized Si and C to reorder to form a Si layer and a C layer, thereby respectively obtaining a mirror structure with corresponding functions and a black surface structure.
A method of slicing a silicon carbide ingot, comprising: firstly, focusing the laser at low energy femto-second inside the SiC crystal to break part of Si-C bonds to form an absorption layer, and then thoroughly breaking the SiC chemical bonds in the absorption layer by using the laser at high energy femto-second to finish slicing; and taking the incidence direction of the laser as the top side, wherein the focal plane of the high-energy femtosecond laser is positioned below the absorption layer.
A processing method of devices with different optical functional surfaces comprises the following steps: firstly, forming an absorption layer with partial Si-C bond fracture inside SiC in advance by using low-energy femtosecond laser, and then, completely breaking the SiC chemical bonds in the absorption layer by using high-energy femtosecond laser to finish the processing of the device, wherein one side surface close to the incidence direction of the laser is a mirror surface structure (a Si compact layer is formed on the top layer of the fracture layer), and the other side surface is a black surface structure (a C compact layer is formed on the bottom layer of the fracture layer); and taking the incidence direction of the laser as the top side, wherein the focal plane of the high-energy femtosecond laser is positioned below the absorption layer.
When SiC is processed by the method, the position of the absorption layer and the thickness of the absorption layer can be determined by controlling the position of the focal plane of the low-energy femtosecond laser and adjusting the position. An absorbent layer having a thickness of less than 20 microns can be obtained by the method of the present invention. The absorption layer with broken part of Si-C bonds is used for preventing the damage depth caused by the subsequent high-energy femtosecond laser wire forming in the SiC from being too large, so that the material waste rate or the influence on the physicochemical properties of silicon carbide at other parts is reduced; meanwhile, the absorption layer with partial broken Si-C bonds has stronger laser absorption efficiency, so that the subsequent high-energy laser energy is concentrated in the carbonized absorption layer formed by the low-energy laser, the complete breaking of the Si-C bonds is rapidly realized, and the thickness control of the cutting layer is realized.
The SiC may be irradiated with a high-energy minute-second laser alone to break its chemical bonds and form a broken layer, but the broken layer having a deep breaking depth may be formed by laser filament formation. The invention utilizes the low-energy minute-second laser which is easy to control and has little influence on the adjacent area to form an absorption layer with set thickness at a set position in SiC at first; subsequently, the SiC chemical bonds are broken by high-energy minute-second laser irradiation, and the energy absorption is concentrated on a carbonization absorption layer formed by low-energy laser, so that the deep damage depth caused by the wire formation of the high-energy laser in the material is avoided; the preformed absorption layer plays a role in isolation and induction, so that the damage of high-energy minute-second laser to the SiC non-processing area can be effectively prevented; while it serves to guide the position and thickness of the fracture layer.
Preferably, the power density at the low energy femtosecond laser focus is < 5x 10 15W/cm2. The low energy femtosecond laser carbonizes the SiC portion at its focal point, thereby causing it to be opaque, featuring high absorption of light in the visible and near infrared bands of the laser. As a further preferred aspect, the low energy femtosecond laser focus has a power density <5×10 15W/cm2 and 1×10 15W/cm2 or more. As a further preferred aspect, the low-energy femtosecond laser has a power density at the focal point of <4×10 15W/cm2 and 2×10 15W/cm2 or more.
Preferably, the power density at the focal point of the high energy femtosecond laser is >1×10 16W/cm2. Preferably, the power density at the high energy femtosecond laser focus is >1 x 10 16W/cm2, but less than 50 x 10 16W/cm2. As a still further preferred aspect, the power density at the focal point of the high-energy femtosecond laser is 1×10 16W/cm2~5×1016W/cm2. The high-energy femtosecond laser can be used for rapidly realizing the fracture of Si-C bonds and cutting, and simultaneously, the carbonized absorption layer is used for preventing the damage depth caused by the wire formation of the high-energy femtosecond laser in the SiC from being too large, so that the material waste rate is reduced.
Preferably, the thickness of the absorption layer is 15-25 μm. The Si-C bond part of the SiC material is broken by utilizing low-energy minute-second laser, during processing, siC can be placed on a two-dimensional scanning translation table of a two-dimensional movement mechanism, the focal position is kept unchanged, and the SiC forms an absorption layer in the whole plane by changing the position of a sample; of course, the position of the silicon carbide sample can be kept unchanged, and the laser spot position is moved to finish the processing of the absorption layer in the whole plane.
Preferably, the laser pulse width of the low-energy femtosecond laser is less than 1 picosecond; the laser energy before focusing is 5-20 mu J; the diameter of a light spot at the focus is about 0.8-1.5 mu m; the scanning speed is 3-10 mm/s.
Preferably, the spot diameter of the high-energy femtosecond laser is 5-30 microns, the laser energy before focusing is 40-60 mu J, and the scanning speed is 3-10 mm/s.
Preferably, the focal plane of the high-energy laser is located at a position 10-30 μm below the bottom layer of the absorption layer.
An apparatus for carrying out the method of any one of the preceding claims, comprising:
A laser emitter capable of providing high and low energy femtosecond laser;
The light intensity adjusting element is used for adjusting the energy of the femtosecond laser to obtain the high-energy and low-energy femtosecond laser (such as an attenuation sheet can be adopted);
a focusing element (such as a microscope objective lens) for focusing the high and low energy femtosecond laser at a set position inside the silicon carbide material;
And the three-dimensional movement mechanism adjusts the relative position of the object to be processed and the laser focal plane, and completes the processing of the absorption layer and the complete breaking of the SiC chemical bonds.
The present invention relates to slicing of SiC wafers using a femtosecond laser. Because SiC is transparent to laser in a near infrared band, siC molecular bonds at a laser focal plane are broken by utilizing a multi-photon excitation mechanism, and accurate slicing processing of the SiC is realized through point-by-point scanning. However, a single Shu Fei second laser creates a light filament within the transparent SiC material, extending the longitudinal depth of destruction of the laser within the material. In order to solve this problem, the present invention proposes a method of using two scans.
The invention focuses a beam of low-energy femtosecond laser in the SiC material to break the SiC chemical bond part of the material at the focal plane. The peak power of the low-energy femtosecond laser is lower than the filamentation threshold of the SiC material, so that the longitudinal absorption layer thickness is not prolonged due to the filamentation effect. By means of laser direct writing, siC sample is set on one three-dimensional motion mechanism and scanned point by point in two-dimensional plane to form one SiC modifying layer inside SiC. The depth of the low energy femtosecond laser focus inside the SiC material is precisely positioned by the z-direction of the three-dimensional translation stage.
The carbonized SiC modified layer has stronger absorption to laser. Subsequently, the laser energy is increased to focus the modified layer again, and the chemical bond of SiC is completely broken by the high-energy laser. Due to the strong absorption of the modified layer to light, the modified layer can prevent the high-energy femtosecond laser from forming wires inside the SiC crystal, thereby reducing the longitudinal damage depth in the sample scanning process and reducing the waste rate of materials.
Drawings
Fig. 1 is a schematic view of forming an absorption layer on a focal plane by two-dimensional scanning using femtosecond laser focusing inside a SiC crystal.
Fig. 2 is a transmission spectrum of an SiC crystal before irradiation with 10 μj femtosecond laser and after scanning with the femtosecond laser to form an absorption layer.
Fig. 3 is a cross-sectional view of an absorption layer formed inside a SiC crystal by a 10 μj femtosecond laser.
Fig. 4 is a plan view of an absorption layer formed inside a SiC crystal by a 10 μj femtosecond laser.
Fig. 5 shows that the high-energy laser directly irradiates SiC, and the depth of damage is deep due to the formation of filaments.
Fig. 6 shows that the sample is scanned again with a high energy femtosecond laser with its geometrical focal position below the absorption layer to prevent the laser from filamentation in the SiC crystal.
Fig. 7 is a mirror image of a 10 μj femtosecond laser after one and two scanning layers of a SiC crystal, respectively: the solid line frame is a cross-sectional view of the low-energy laser after single scanning, and the broken line frame is a cross-sectional view of the low-energy laser after two scans of the high-energy laser.
Detailed Description
The invention is further described below with reference to the accompanying drawings:
as shown in fig. 1, a schematic diagram of slicing silicon carbide wafers using a femtosecond laser to reduce material waste during slicing is provided. In this example, the high and low energy femtosecond lasers may be provided by a laser transmitter. After the femto-second laser beam 2 is emitted, the femto-second laser beam 2 is focused in the silicon carbide 3 material by using the 50-time micro objective lens 1, so that the Si-C bond part of the SiC material at the laser focal plane 4 is broken, the silicon carbide sample is moved by an x-y motion unit of the three-dimensional motion mechanism 5, the sample is scanned in a two-dimensional plane perpendicular to the incidence direction of the laser, and the SiC chemical bond part on the focal plane is broken, so that the partially carbonized absorption layer 6 is formed. Wherein the depth position of the absorption layer is precisely positioned by scanning the three-dimensional movement mechanism along the laser transmission direction (i.e. the movement unit in the z direction).
In this example, a 50-fold microobjective was used, the numerical aperture was 0.55, the spot diameter at the focal point was about 1.2 μm, the rayleigh length was about 1.1 μm, the low-energy femtosecond laser repetition rate was 85 kHz, the scanning speed was 5 mm/s, the scanning was performed twice in the z direction (i.e., perpendicular to the focal plane direction) (see fig. 7), the longitudinal distance between the two scans (z-axis) was 20 μm, the laser energy before focusing was 10 μj, the femtosecond laser was gaussian spot, the center wavelength was 1030 nm, the pulse width was 260fs, the pulse energy, the repetition rate, and the power density at the focal point was 2.5x10 15W/cm2.
Fig. 2 shows the transmission spectra of the 4H-SiC crystal before and after the femtosecond laser action. Before the femtosecond laser is used, the transmittance of the 4H-SiC in the visible near infrared band is about 60 percent. When the femtosecond laser of 10 mu J irradiates on the focal plane inside the SiC crystal, the light transmittance is reduced to be within 10 percent. Meanwhile, the absorption layer formed at the side of the sample at the focus of the clearly visible laser has a length of about 18 μm in the laser transmission direction as shown in fig. 3, i.e., the thickness of the absorption layer can be controlled within 20 μm under the irradiation of the low-energy femtosecond laser as marked by the broken line in fig. 3. Fig. 4 shows an optical microscope photograph (top view) after formation of the absorber layer.
After the absorption layer is formed in the SiC by the first step of 10 mu J femtosecond laser, the energy of the incident femtosecond laser beam 2 is increased by rotating the attenuation sheet 7, and the sample is scanned again in the x-y plane by using the high-energy femtosecond laser to thoroughly break the SiC chemical bonds in the modified layer, so that the upper layer and the lower layer of SiC are stripped. In this example, the pulse energy of the high-energy femtosecond laser is 50 μj (the power density at the focal point is 1.2x10 16W/cm2). As shown in fig. 6, in order to prevent the high-energy femtosecond laser from forming filaments in the crystal, the geometric focus of the laser needs to be adjusted to below the absorption layer. In the example, the geometrical focus of a 50 μj femtosecond laser (spot diameter 20 microns, repetition rate 85kHz, scan speed 5 mm/s, center wavelength 1030 nm, pulse width 260 fs) was 20 microns just below the absorber layer, after scanning the SiC fracture layer.
Meanwhile, the SiC crystal ingot obtained by the method is observed from the top side and the bottom side respectively, and a mirror structure is formed when the side close to the incidence direction of laser is observed (the top side), and the Si layer is formed on the top surface of the fracture layer after the high-energy femtosecond laser acts; the fracture layer underlayer forms a C layer, as seen from the underside, exhibiting a black-sided structure. The method can be used for processing devices with different optical functions.
In contrast, when the silicon carbide ingot at the same position is directly irradiated with a 50 μj high-energy femtosecond laser according to the same process, a cut layer can be formed at the focal plane, but the depth of damage due to the wire formation of the high-energy femtosecond laser inside SiC is excessively large (about 100 μm in this embodiment). As shown in fig. 5.

Claims (5)

1. A method of slicing a silicon carbide ingot, comprising: firstly, focusing the laser at low energy femto-second inside the SiC crystal to break part of Si-C bonds to form an absorption layer, and then thoroughly breaking the SiC chemical bonds in the absorption layer by using the laser at high energy femto-second to finish slicing; taking the incidence direction of laser as the top side, wherein the focal plane of the high-energy femtosecond laser is positioned below the absorption layer;
The power density at the low energy femtosecond laser focus is <5 x 10 15W/cm2; the power density at the high energy femtosecond laser focus is >1 x 10 16W/cm2;
The laser pulse width of the low-energy femtosecond laser is less than 1 picosecond; the laser energy before focusing is 5-20 mu J; the diameter of a light spot at the focus is about 0.8-1.5 mu m;
the focal plane of the high-energy laser is located at the position 10-30 mu m below the bottom layer of the absorption layer.
2. A method of processing a device having different optical functional surfaces, comprising: firstly, forming an absorption layer with partial Si-C bond fracture inside SiC in advance by using low-energy femtosecond laser, and then completely breaking SiC chemical bonds in the absorption layer by using high-energy femtosecond laser to finish the processing of the device, wherein one side surface close to the incidence direction of the laser is of a mirror surface structure, and the other side surface is of a black surface structure; taking the incidence direction of laser as the top side, wherein the focal plane of the high-energy femtosecond laser is positioned below the absorption layer;
The power density at the low energy femtosecond laser focus is <5 x 10 15W/cm2; the power density at the high energy femtosecond laser focus is >1 x 10 16W/cm2;
The laser pulse width of the low-energy femtosecond laser is less than 1 picosecond; the laser energy before focusing is 5-20 mu J; the diameter of a light spot at the focus is about 0.8-1.5 mu m;
the focal plane of the high-energy laser is located at the position 10-30 mu m below the bottom layer of the absorption layer.
3. The method according to any one of claims 1-2, wherein the thickness of the absorbing layer is 15-25 microns.
4. The method according to any one of claims 1 to 2, wherein the scanning speed is 3 to 10mm/s.
5. The method according to any one of claims 1-2, wherein when the absorption layer is processed, scanning is performed on an upper layer and a lower layer, respectively, where the absorption layer is located.
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CN116179838A (en) * 2023-02-06 2023-05-30 西南交通大学 A Composite Strengthening Method of Femtosecond Laser Superimposing Uncoated Laser Shock Strengthening
CN117672875B (en) * 2024-01-30 2024-05-17 天津中科晶禾电子科技有限责任公司 PMMA and Si bonding method

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CN106346148A (en) * 2015-07-13 2017-01-25 株式会社迪思科 POLYCRYSTALLINE SiC WAFER PRODUCING METHOD
CN107262945A (en) * 2016-04-06 2017-10-20 株式会社迪思科 The generation method of chip
CN110549016A (en) * 2019-09-23 2019-12-10 北京工业大学 Femtosecond laser cutting method for silicon carbide

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JP5836998B2 (en) * 2013-04-23 2015-12-24 株式会社豊田中央研究所 Crack generation method, laser cutting method and crack generation apparatus
JP2016030292A (en) * 2014-07-29 2016-03-07 株式会社プロダクトサポート Method for scribing interior of transparent material, and laser dicing device

Patent Citations (3)

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Publication number Priority date Publication date Assignee Title
CN106346148A (en) * 2015-07-13 2017-01-25 株式会社迪思科 POLYCRYSTALLINE SiC WAFER PRODUCING METHOD
CN107262945A (en) * 2016-04-06 2017-10-20 株式会社迪思科 The generation method of chip
CN110549016A (en) * 2019-09-23 2019-12-10 北京工业大学 Femtosecond laser cutting method for silicon carbide

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