Photoelectric auxiliary chemical mechanical polishing device

Abstract

The invention provides a photoelectric auxiliary chemical mechanical polishing device which comprises a polishing disc, a grinding pad, a polishing head and a chemical liquid spray head, the polishing disc is electrically connected with a cathode of a power supply, the polishing head is electrically connected with an anode of the power supply and is used for adsorbing a wafer, and a lamp tube is embedded in the top surface of the polishing disc. The grinding pad is arranged above the polishing disc, abrasive particles and vertically-through liquid passing holes are formed in the grinding pad, and the chemical liquid spray head is arranged above the grinding pad and used for spraying chemical liquid to the grinding pad. According to the photoelectric auxiliary chemical mechanical polishing device provided by the invention, the surface of silicon carbide is subjected to electrochemical reaction under the action of an electric field, so that the oxidation efficiency of the surface of a wafer is improved, and the silicon carbide is removed through mechanical polishing; under the action of the light field, the light with the energy higher than the absorption threshold value of the silicon carbide material is irradiated to the to-be-polished surface of the wafer, the to-be-polished surface of the wafer is oxidized through a series of chemical reactions to form an oxide layer, the polishing efficiency of the wafer is improved, and the polishing quality of the wafer is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical mechanical polishing, and more specifically, relates to a photoelectric assisted chemical mechanical polishing device. Background Art

[0002] Silicon carbide (SiC), as a third-generation semiconductor material, has the advantages of wide energy band gap, excellent thermal conductivity, high breakdown electric field and good chemical stability. It is a popular wafer material and is widely used in the manufacturing process of semiconductor products.

[0003] The traditional polishing method is to use abrasive liquid containing abrasives to polish on an ordinary polishing pad. For hard and brittle materials such as silicon carbide, only polishing liquid containing hard abrasives can be used, but its use cost is high and the removal efficiency is low.

[0004] In the prior art, silicon carbide is mainly polished by chemical mechanical polishing (CMP), which mainly uses chemical raw materials (polishing liquid) to chemically modify the surface to be polished, and then mechanically removes the modified layer. In the prior art, the oxidation rate of the SiC wafer surface can be effectively accelerated under the action of an electric field, which can increase the polishing efficiency of CMP to a certain extent, but the removal difficulty is still relatively large, and the ability to improve the polishing efficiency is limited. Summary of the invention

[0005] The object of the present invention is to provide a photoelectric assisted chemical mechanical polishing device, which eliminates the effect of grinding liquid by arranging abrasive particles on the grinding pad, and at the same time adopts a photoelectric assisted method to improve the surface polishing efficiency of silicon carbide.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: to provide a photoelectric assisted chemical mechanical polishing device, including a polishing disk, a grinding pad, a polishing head and a chemical liquid nozzle, the polishing disk is electrically connected to the cathode of the power supply, the polishing head is electrically connected to the anode of the power supply and is used to adsorb the wafer, a lamp tube is embedded on the top surface of the polishing disk, the grinding pad is arranged above the polishing disk, and the grinding pad is provided with abrasive grains and liquid holes running through the top and bottom, and the chemical liquid nozzle is arranged above the grinding pad and is used to spray chemical liquid onto the grinding pad.

[0007] In a possible implementation, the lamp tube includes a first lamp tube and a second lamp tube, a plurality of the first lamp tubes are arranged in parallel, and the second lamp tube is arranged perpendicular to the first lamp tube.

[0008] In some embodiments, the polishing plate is provided with a first groove for installing the first lamp tube and a second groove for installing the second lamp tube, and the depth of the second groove is greater than the depth of the first groove.

[0009] In a possible implementation, the lamp tube is used to emit auxiliary light, and the auxiliary light is one of light of a single wavelength, composite light of two wavelengths, and composite light of more than two wavelengths.

[0010] In some embodiments, the auxiliary light has an irradiation intensity of 0.2W / cm²-3W / cm², and the wavelength of the auxiliary light emitted by the lamp tube is less than 384nm.

[0011] In a possible implementation, the polishing disk is made of stainless steel or platinum alloy, and the grinding pad is made of polyurethane.

[0012] In some embodiments, the abrasive particles are one or more of diamond, iron powder, SiO2, CeO2, Al2O3, TiO2, MnO2, and Fe2O3, and the particle size of the abrasive particles is 2um-80um.

[0013] In a possible implementation, the liquid passage hole is circular, rectangular, triangular or polygonal, and the area of ​​the liquid passage hole is greater than or equal to 25 square millimeters.

[0014] In some embodiments, a plurality of the liquid passage holes are provided at intervals on the polishing pad, and the plurality of the liquid passage holes are arranged in a matrix on the polishing pad, and a distance between two adjacent liquid passage holes is smaller than a hole diameter of the liquid passage hole.

[0015] In a possible implementation, the chemical liquid nozzle is used to spray chemical liquid, the chemical liquid is an electrolyte, the mass percentage content of the solute in the electrolyte is 1wt%-10wt%, the 2 of the electrolyte is less than pH 13, and the transmittance of the electrolyte is >95%.

[0016] The scheme shown in the embodiment of the present application is compared with the prior art. The photoelectric-assisted chemical mechanical polishing device provided in the embodiment of the present application polishes silicon carbide with photoelectric assistance. Under the action of the electric field, an electrochemical reaction occurs on the surface of the silicon carbide, which accelerates the oxidation efficiency of the wafer surface and generates an oxide layer that is softer and easier to remove, so that the silicon carbide can be removed by mechanical polishing. Under the action of the light field, light with energy higher than the absorption threshold of the silicon carbide material is irradiated onto the surface to be polished of the wafer, thereby generating electrons and holes on the surface of the wafer. In addition, due to the action of the external electric field, the electrons generated by photocatalysis move in a certain direction, and the surface to be polished of the wafer is oxidized through a series of chemical reactions to form an oxide layer, thereby improving the polishing efficiency of the wafer and ensuring the polishing quality of the wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 A schematic diagram of a partial cross-sectional structure of a photoelectric assisted chemical mechanical polishing device provided in an embodiment of the present invention; Figure 2 For the embodiment of the present invention Figure 1 A schematic diagram of the top view of the polishing plate and the lamp tube; Figure 3 For the embodiment of the present invention Figure 2 A schematic diagram of the top view of the structure of the middle polishing disc; Figure 4 A schematic diagram of a top view of another embodiment of a polishing disc and a lamp tube provided in an embodiment of the present invention; Figure 5 For the embodiment of the present invention Figure 1 Schematic diagram of the top view of the grinding pad.

[0019] Among them, the reference numerals in the figure are: 1. Polishing disc; 11. First groove; 12. Second groove; 13. Second conductor; 2. Grinding pad; 21. Liquid hole; 3. Polishing head; 31. First conductor; 4. Chemical liquid nozzle; 5. Lamp; 51. First lamp; 52. Second lamp; 6. Polishing table; 7. Wafer. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or indirectly on the other element. It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "back", "top", "bottom", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. The terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "several" is two or more, unless otherwise clearly and specifically defined.

[0022] Please also read Figures 1 to 5 , the photoelectric assisted chemical mechanical polishing device provided by the present invention is now described. The photoelectric assisted chemical mechanical polishing device comprises a polishing disc 1, a grinding pad 2, a polishing head 3 and a chemical liquid spray head 4. The polishing disc 1 is electrically connected to the cathode of the power supply, the polishing head 3 is electrically connected to the anode of the power supply and is used to adsorb the wafer 7. A lamp tube 5 is embedded on the top surface of the polishing disc 1. The grinding pad 2 is arranged above the polishing disc 1, and the grinding pad 2 is provided with abrasive grains and a liquid through hole 21 extending from top to bottom. The chemical liquid spray head 4 is arranged above the grinding pad 2 and is used to spray chemical liquid onto the grinding pad 2.

[0023] Compared with the prior art, the photoelectric-assisted chemical mechanical polishing device provided in this embodiment polishes silicon carbide with the assistance of photoelectrics. Under the action of the electric field, an electrochemical reaction occurs on the surface of silicon carbide, which accelerates the oxidation efficiency of the surface of wafer 7 and generates an oxide layer that is softer and easier to remove, so that silicon carbide can be removed by mechanical polishing. Under the action of the light field, light with energy higher than the absorption threshold of the silicon carbide material is irradiated onto the surface to be polished of wafer 7, thereby generating electrons and holes on the surface of wafer 7. In addition, due to the action of the external electric field, the electrons generated by photocatalysis move in a certain direction, and the surface to be polished of wafer 7 is oxidized through a series of chemical reactions to form an oxide layer, which is removed, thereby improving the polishing efficiency of wafer 7 and ensuring the polishing quality of wafer 7.

[0024] In this embodiment, the polishing head 3 is located above the polishing disc 1, and the polishing disc 1 is mounted on a rotatable polishing table 6. The polishing head 3 is connected to the anode of the power supply through a first wire 31 arranged through the axis of the polishing head 3, and the polishing disc 1 is connected to the cathode of the power supply through a second wire 13 arranged through the axis of the polishing bar. It can be lifted and moved to drive the wafer 7 to move down and contact the grinding pad 2. The polishing head 3 can rotate around its own central axis, and can also swing horizontally relative to the polishing disc 1. The polishing head 3 and the polishing disc 1 both rotate in the counterclockwise direction, and the rotation speed of the polishing head 3 is less than the rotation speed of the polishing disc 1.

[0025] Specifically, by embedding abrasives on the grinding pad 2, the use of grinding liquid can be eliminated when polishing the wafer 7. Only chemical liquid is sprayed through the chemical liquid nozzle 4. The grinding pad 2 embedded with abrasives has a longer service life than the grinding liquid containing the same abrasives, thereby achieving the effect of cost saving.

[0026] Among them, the chemical liquid should be a neutral or acidic and alkaline electrolyte, and the grinding liquid containing abrasive dispersion should not be used to avoid the doped ions in the grinding liquid agglomerating under the influence of power during the electrochemical mechanical polishing process, thereby affecting the polishing effect. At the same time, since the above electrolyte has no abrasive dispersion, its light transmittance is very good, which is conducive to the auxiliary light directly irradiating the surface of the wafer 7, significantly improving the electronic transition performance of the surface of the wafer 7, and greatly improving the oxidation rate.

[0027] After power is turned on, the first wire 31, the polishing head 3, the wafer 7, the chemical liquid in the liquid hole 21, the polishing plate 1, the polishing table 6 and the second wire 13 form a power circuit. At this time, an electrochemical reaction occurs on the surface of the wafer 7 to form a silicon dioxide oxide layer. Then, the light tube 5 that can emit light is powered on, and the emitted light passes upward through the chemical liquid in the liquid hole 21 and irradiates the surface of the wafer 7 to be polished, reducing the activation energy of the surface of the wafer 7, which is conducive to the formation of the oxide layer. During irradiation, the electrons in the valence band of the surface of the wafer 7 are excited by the light energy and transition to the conduction band, generating a large number of electron-hole pairs. The electron-hole pairs are separated under the action of the electric field, and the electrons move to the cathode along the external circuit, while the holes move to the surface of the wafer 7. The holes have strong oxidizing properties and can oxidize the surface of the wafer 7 into an oxide layer through chemical reactions. The above-mentioned photoelectrically assisted oxide layer is removed by mechanical grinding through the relative movement of the polishing head 3 and the grinding pad 2 to expose the new surface of the wafer 7, which continues to be oxidized by power and light. By repeating the above-mentioned oxidation and grinding process, the polishing efficiency of the wafer 7 is greatly improved.

[0028] The valence band refers to the highest energy band in a solid material that can be occupied by electrons at absolute zero. The electrons in the valence band are basically continuous, and these electrons cannot move freely in the solid. However, when the electrons in the valence band are excited by sufficient energy, such as light or thermal excitation, they can transition to an energy band with higher energy, which is called the conduction band. The above-mentioned light energy can cause the electrons to transition to the conduction band by light energy excitation.

[0029] Specifically, in semiconductors, the valence band is the lowest energy full band, while the conduction band is the higher energy empty band. When the electrons in the valence band absorb enough energy to transition to the conduction band, the valence band becomes partially filled and the conduction band becomes full. This transition usually requires light or thermal excitation.

[0030] In one possible implementation, please also refer to Figure 2 and Figure 4 The lamp tube 5 includes a first lamp tube 51 and a second lamp tube 52. A plurality of first lamp tubes 51 are arranged in parallel, and the second lamp tube 52 is arranged perpendicular to the first lamp tube 51. By arranging a plurality of mutually parallel first lamp tubes 51 and a second lamp tube 52 perpendicular to the first lamp tube 51, auxiliary light can be effectively irradiated to different areas of the wafer 7, thereby satisfying the photoelectric auxiliary effect during the polishing process of the wafer 7.

[0031] For some examples, see Figure 3 The polishing plate 1 is provided with a first groove 11 for mounting the first lamp tube 51 and a second groove 12 for mounting the second lamp tube 52 . The depth of the second groove 12 is greater than the depth of the first groove 11 .

[0032] In this embodiment, the surface of the polishing disc 1 is grooved to obtain a first groove 11 and a second groove 12. A plurality of first grooves 11 are arranged in parallel, and a second groove 12 is arranged perpendicular to the first groove 11. The first groove 11 can be set to have a width of 3 mm and a depth of 3 mm, and is used to install the first lamp 51 in the first groove 11, so that the first lamp 51 forms an effect of being embedded in the top surface of the polishing disc 1.

[0033] The second groove 12 can be set to have a width of 3 mm and a depth of 6 mm, and is used to install the second lamp tube 52 in the second groove 12, so that the second lamp tube 52 is embedded in the top surface of the polishing plate 1 and is located below the first lamp tube 51. The first lamp tube 51 and the second lamp tube 52 are used to synchronously irradiate the upper wafer 7 with auxiliary light.

[0034] It should be noted that the arrangement of the lamp tubes 5 and the form of the grooves on the surface of the polishing disc 1 include but are not limited to the above methods. Various different methods such as concentric rings or cross grids can also be used, and the groove depth and groove width can also be adaptively changed.

[0035] In a possible implementation, the lamp tube 5 is used to emit auxiliary light, and the auxiliary light is one of a single wavelength light, a composite light of two wavelengths, and a composite light of two or more wavelengths. The auxiliary light can be a single wavelength light or a composite light of two or more wavelengths, and the above multiple methods can all achieve the irradiation effect of the auxiliary light on the wafer 7.

[0036] In some embodiments, the auxiliary light irradiation intensity is 0.2W / cm²-3W / cm², and the wavelength of the auxiliary light emitted by the lamp tube 5 is less than 384nm.

[0037] In this embodiment, if the wavelength is greater than 384nm, the electrons on the surface of the wafer 7 cannot be caused to transition, and the light-assisted effect cannot be achieved. Therefore, the wavelength of the lamp 5 can be selected to be any wavelength less than 384nm, which can meet the irradiation effect of the auxiliary light. At the same time, the irradiation light intensity should meet the range of 0.2W / cm²-3W / cm², which can not only ensure the irradiation effect, but also reduce the energy consumption during the polishing process.

[0038] In a possible implementation, the polishing disc 1 is made of stainless steel or platinum alloy, and the grinding pad 2 is made of polyurethane. The polishing disc 1 is made of stainless steel or platinum alloy, and has excellent conductivity and corrosion resistance. The grinding pad 2, as one of the main consumables, is made of polyurethane, which is simple and convenient to manufacture, low in cost, and effectively reduces the polishing cost of the wafer 7.

[0039] In some embodiments, the abrasive particles are one or more of diamond, iron powder, SiO2, CeO2, Al2O3, TiO2, MnO2, and Fe2O3, and the particle size of the abrasive particles is 2um-80um.

[0040] In this embodiment, the grinding pad 2 is embedded with abrasives, which can save the use of grinding liquid when polishing the wafer 7. The chemical liquid is only sprayed by the chemical liquid nozzle 4. The grinding pad 2 embedded with abrasives has a longer service life than the grinding liquid containing the same abrasives, thereby achieving the effect of cost saving. Abrasives can be selected from a variety of different materials, including one or more of diamond, iron powder, SiO2, CeO2, Al2O3, TiO2, MnO2, and Fe2O3. The selection of abrasives includes but is not limited to the above, and all can achieve effective grinding effects.

[0041] Specifically, the particle size of the abrasive is greater than or equal to 2um and less than or equal to 80um. If you want to quickly remove the oxide layer, you can use a grinding pad 2 with a large particle size, but the surface roughness of the wafer 7 will be poor; if you use a grinding pad 2 with a small particle size, the polishing efficiency will be low, but the surface roughness of the wafer 7 will be better and smoother. Therefore, you can choose an abrasive particle size that can ensure the grinding efficiency and meet the roughness requirements within the above parameter range.

[0042] In one possible implementation, see Figure 5 , the liquid hole 21 is circular, rectangular, triangular or polygonal, and the area of ​​the liquid hole 21 is greater than or equal to 25 square millimeters. The liquid hole 21 can be selected from a variety of different shapes, all of which can achieve effective circulation of the chemical liquid. The single area of ​​the liquid hole 21 is greater than 25 square millimeters, and the more liquid holes 21 are set, the better, so as to meet the illumination intensity of the auxiliary light on the surface of the wafer 7 and improve the polishing efficiency. Because if the area is less than 25 square millimeters, the electrochemical reaction rate and the illumination intensity of the auxiliary light on the surface of the wafer 7 will be greatly slowed down, slowing down the polishing efficiency.

[0043] For some examples, see Figure 5 A plurality of liquid passage holes 21 are provided on the polishing pad 2 at intervals. The plurality of liquid passage holes 21 are arranged in a matrix on the polishing pad 2 , and a distance between two adjacent liquid passage holes 21 is smaller than the aperture of the liquid passage hole 21 .

[0044] In this embodiment, the liquid passage holes 21 are distributed on the entire polishing pad 2 in a matrix array, and the distance between two adjacent liquid passage holes 21 meets certain requirements, that is, the distance between two adjacent liquid passage holes 21 is smaller than the aperture of the liquid passage hole 21, that is, it is difficult to set another liquid passage hole 21 between two adjacent liquid passage holes 21, and another liquid passage hole 21 with the same aperture cannot be placed).

[0045] In a possible implementation, the chemical liquid nozzle 4 is used to spray chemical liquid, the chemical liquid is an electrolyte, the mass percentage content of the solute in the electrolyte is 1wt%-10wt%, the electrolyte has a pH of 2<pH<13, and the transmittance of the electrolyte is >95%.

[0046] In this embodiment, the chemical liquid is a neutral or acidic or alkaline electrolyte having excellent conductivity and light transmittance, and the electrolyte flows through the liquid hole 21 of the polishing pad 2 and flows onto the polishing disc 1. The solute content and acidity and alkalinity of the electrolyte meet the requirements of the above parameter range, and H2SO4 or KOH can be used as a regulator when adjusting the pH, which is convenient to adjust and low in cost.

[0047] The selection of the above electrolyte, combined with the abrasive grains embedded in the polishing pad 2, not only reduces the amount of abrasive grains used, but also avoids the influence of the abrasive grains on the auxiliary light irradiation, ensures the rapid formation of the oxide layer on the surface of the wafer 7, and improves the oxidation efficiency of the wafer 7.

[0048] During the photoelectrically assisted chemical mechanical polishing of wafer 7, a grinding pad 2 embedded with abrasives is used instead of grinding liquid, which saves the consumption of abrasive particles and saves costs. In addition, the use of chemical liquid with conductive properties can prevent the abrasive particles in the grinding liquid from agglomerating due to the influence of electricity, which helps to improve the polishing efficiency of wafer 7.

[0049] At the same time, the chemical liquid without abrasive particles has good light transmittance, which is conducive to the auxiliary light directly irradiating the wafer 7, and the auxiliary light forms an oxidation effect on the wafer 7, thereby improving the polishing efficiency of the wafer 7. Experiments have shown that this polishing method has a polishing efficiency that is more than doubled compared to traditional chemical mechanical polishing.

[0050] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Photoelectrically assisted chemical mechanical polishing device, characterized in that: The invention comprises a polishing disc (1), a grinding pad (2), a polishing head (3) and a chemical liquid spray head (4); the polishing disc (1) is electrically connected to the cathode of a power supply; the polishing head (3) is electrically connected to the anode of a power supply and is used to adsorb a wafer (7); a lamp tube (5) is embedded on the top surface of the polishing disc (1); the grinding pad (2) is arranged above the polishing disc (1); and the grinding pad (2) is provided with abrasive grains and a liquid through hole (21) extending from top to bottom; the chemical liquid spray head (4) is arranged above the grinding pad (2) and is used to spray chemical liquid onto the grinding pad (2).

2. The photoelectrically assisted chemical mechanical polishing device according to claim 1, characterized in that: The lamp tube (5) comprises a first lamp tube (51) and a second lamp tube (52); a plurality of the first lamp tubes (51) are arranged in parallel, and the second lamp tube (52) is arranged perpendicular to the first lamp tube (51).

3. The photoelectrically assisted chemical mechanical polishing device according to claim 2, characterized in that: The polishing disc (1) is provided with a first groove (11) for installing the first lamp tube (51) and a second groove (12) for installing the second lamp tube (52); the depth of the second groove (12) is greater than the depth of the first groove.

4. The photoelectrically assisted chemical mechanical polishing device according to claim 1, characterized in that: The lamp tube (5) is used for emitting auxiliary light, and the auxiliary light is one of light of a single wavelength, composite light of two wavelengths, and composite light of more than two wavelengths.

5. The photoelectrically assisted chemical mechanical polishing device according to claim 4, characterized in that: The auxiliary light irradiation intensity is 0.2W / cm²-3W / cm², and the wavelength of the auxiliary light emitted by the lamp tube (5) is less than 384nm.

6. The photoelectrically assisted chemical mechanical polishing device according to claim 1, characterized in that: The polishing disc (1) is a component made of stainless steel or platinum alloy, and the grinding pad (2) is a component made of polyurethane.

7. The photoelectrically assisted chemical mechanical polishing device according to claim 6, characterized in that: The abrasive particles are one or more of diamond, iron powder, SiO2, CeO2, Al2O3, TiO2, MnO2, and Fe2O3, and the particle size of the abrasive particles is 2um-80um.

8. The photoelectrically assisted chemical mechanical polishing device according to any one of claims 1 to 7, characterized in that: The liquid passage hole (21) is circular, rectangular, triangular or polygonal, and the area of ​​the liquid passage hole (21) is greater than or equal to 25 square millimeters.

9. The photoelectrically assisted chemical mechanical polishing device according to claim 8, characterized in that: A plurality of the liquid passage holes (21) are arranged at intervals on the polishing pad (2); the plurality of the liquid passage holes (21) are arranged in a matrix on the polishing pad (2); and the spacing between two adjacent liquid passage holes (21) is smaller than the aperture of the liquid passage hole (21).

10. The photoelectrically assisted chemical mechanical polishing device according to any one of claims 1 to 7, characterized in that: The chemical liquid spray head (4) is used for spraying chemical liquid, the chemical liquid is an electrolyte, the mass percentage content of the solute in the electrolyte is 1wt%-10wt%, the 2 of the electrolyte is less than pH<13, and the light transmittance of the electrolyte is greater than 95%.

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