A processing method for improving the surface shape precision of a large-size semiconductor wafer

Abstract

The application belongs to the technical field of semiconductor crystal processing, and relates to a processing method for improving the surface shape precision of a large-size semiconductor wafer. The method comprises the following steps: after cleaning a GaN single crystal substrate and a substrate, the substrate is placed on a glue uniformizing machine to perform liquid wax spin coating; then, the substrate is pressed and cooled to be fixed after the wax-coated side of the substrate is attached to the substrate; then, the substrate is placed on a polishing head of a grinding and polishing device; a lathe tool system is used to grind the grinding disc to be parallel to the surface shape of the GaN single crystal substrate wafer on the polishing head; finally, the GaN single crystal substrate is ground and polished by using the grinding disc after the surface shape is modified; and after the processing is completed, the wax is removed and the substrate is cleaned. The method solves the problems of the traditional wax coating method, such as the over-thick wax layer and the difficulty in cleaning; and the method for modifying the grinding disc reduces the surface shape parameters of the large-size wafer, and lays a foundation for the preparation of subsequent small-size and high-power GaN-based devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor crystal processing technology and relates to a processing method for improving the surface accuracy of large-size semiconductor wafers. Background Technology

[0002] After more than half a century of rapid development, semiconductor power devices have become core components of various power electronic systems. With the continuous development of emerging technologies such as artificial intelligence, 5G communication, and new energy vehicles, the performance requirements for semiconductor power devices are becoming increasingly stringent. Gallium nitride (GaN) possesses advantages such as a large bandgap (3.4 eV), high thermal conductivity, high breakdown field strength, high saturation drift velocity, good chemical stability, and strong radiation resistance, making it an ideal material for fabricating high-performance semiconductor power devices. However, GaN is classified as a difficult-to-process material due to its extremely high hardness and strong chemical stability, making wafer fabrication very challenging.

[0003] Semiconductor wafer surface shape parameters (TTV, BOW, and Warp) are crucial factors that must be considered in chip manufacturing. These three parameters collectively reflect the flatness and thickness uniformity of the semiconductor wafer, directly impacting many critical steps in the chip manufacturing process. GaN, with its high hardness and brittleness, is prone to quality issues such as warping on the wafer surface and subsurface during slicing and thinning, affecting subsequent processes. Therefore, high precision control is required for warp, BOW, and total thickness deviation (TTV). Current wax bonding methods suffer from problems such as easy wafer cracking, thick wax layers, uneven application, and difficulty in wax removal, significantly impacting the substrate surface shape parameters and resulting in poor chip fabrication performance. Furthermore, the polishing pads used in existing grinding and polishing processes can experience severe surface deformation due to uneven pressure and temperature changes after prolonged wafer processing, adversely affecting the substrate surface shape accuracy. Summary of the Invention

[0004] This invention addresses the problems of existing wax coating techniques for processing GaN wafers, such as difficulty in cleaning the wax layer, uneven wax layer leading to reduced surface accuracy of GaN substrates, affecting subsequent device fabrication, and severe surface deformation of the polishing pad due to uneven pressure and temperature changes after prolonged wafer processing, resulting in deterioration of substrate surface accuracy. The invention proposes a spin-coating wax method for large-size semiconductor wafers combined with a polishing pad design, ultimately obtaining GaN single-crystal substrates with high surface accuracy.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A processing method for improving the surface accuracy of large-size semiconductor wafers includes the following steps:

[0007] (1) Cleaning of substrate and substrate: The GaN single crystal substrate and substrate are ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 10-30 min in sequence.

[0008] (2) Spin coating: Turn on the spin coater and vacuum pump, vacuum the substrate onto the sample stage, set the parameters to 2000-5000 rpm, time 1-3 min, turn on the spin coating switch, and quickly add 1-5 mL of liquid wax with a dropper for spin coating;

[0009] (3) Baking and fixing: The wax-coated substrate is baked on a heating table at 90-120 ℃ for 1-3 min, and then the substrate is flipped and placed on the preheated substrate. It is pressed with an airbag or pressure head for at least half an hour until the substrate cools and is fixed.

[0010] (4) Substrate processing: The GaN single crystal substrate is placed on the polishing head of the grinding and polishing equipment. The lathe tool system is used to shape the grinding disc into a surface parallel to the GaN single crystal substrate wafer on the polishing head, such as... Figure 1 As shown. The diameter and radius of the polishing head are measured using a micrometer reading via the "well" method; the tool position is adjusted so that the tool tip is close to the surface of the large grinding disc, and the tool extension switch is activated to retract the tool beyond the large disc; the large disc rotation speed is set to 80-100 rpm, the tool descends 10-30 μm, and the tool system advances at a speed of 1-5 mm / min to begin trimming the surface, removing any previous wear marks on the grinding disc, until the entire disc surface is trimmed; the large disc rotation speed is adjusted to 50-80 rpm, the tool descends 10-30 μm, and the tool system retreats at a speed of 20-50 mm / min to begin trimming the surface shape; the diameter and radius of the disc are measured using a micrometer reading; finally, the trimmed grinding disc is used to polish the GaN single crystal substrate; the principle is as follows. Figure 2 As shown.

[0011] (5) Dewaxing: After processing, the GaN single crystal substrate sample is placed on a heating stage at 120-150 ℃ to bake and dewax. Then, the processed GaN single crystal substrate is ultrasonically cleaned with dewaxing water, acetone, anhydrous ethanol and deionized water in sequence.

[0012] According to a preferred embodiment of the present invention, in step (1), the substrate and the substrate are ultrasonically cleaned sequentially with acetone, anhydrous ethanol and deionized water for 30 min to remove surface oil and other impurities.

[0013] According to a preferred embodiment of the present invention, the size of the substrate in step (1) is 2-6 inches.

[0014] According to a preferred embodiment of the present invention, the spin coating parameters in step (2) are 3000 rpm and 2 min. Spin coating speed that is too fast or time that is too short will cause uneven spin coating of wax layer, which cannot be fixed on the substrate.

[0015] According to a further preferred embodiment of the present invention, the thickness of the spin-coated wax layer in step (2) is 1-5 μm.

[0016] According to a preferred embodiment of the present invention, the liquid wax is added in step (2) by vertically adding it to the center of the substrate after spin coating begins.

[0017] According to a preferred embodiment of the present invention, in step (3), the substrate coated with spin wax is baked on a heating table at 100 °C for 3 min, the purpose of which is to remove the air from the liquid wax and solidify it.

[0018] According to a preferred embodiment of the present invention, the pressure of the airbag or the pressure head in step (3) is 10 N.

[0019] According to a preferred embodiment of the present invention, in step (4), the surface shape of the grinding disk is parallel to the GaN single crystal substrate wafer at the polishing head, with an error ≤ 5 μm.

[0020] According to a preferred embodiment of the present invention, the angle between the cutter head and the large disc surface in step (4) is 85° to 95°.

[0021] According to a preferred embodiment of the present invention, if the error is greater than 5 μm after the grinding disc is finished in step (4), a correction wheel can be used for local correction.

[0022] According to a preferred embodiment of the present invention, the temperature of the grinding disc is maintained at 20-25°C during the grinding disc preparation in step (4).

[0023] According to a preferred embodiment of the present invention, in step (5), the sample is placed on a heating table at 150 °C to bake and remove wax.

[0024] The beneficial effects of this invention are as follows:

[0025] The method described in this invention solves the problems of excessively thick wax layers and difficulty in cleaning in traditional wax coating methods. On the other hand, the method of trimming the polishing pad reduces the surface parameters of large-size wafers, paving the way for the subsequent fabrication of small-size, high-power GaN-based devices. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the cutting tool dressing system of the present invention;

[0027] Figure 2 This is a schematic diagram illustrating the principle of the present invention for adjusting the grinding disc to reduce surface parameters;

[0028] Figure 3 The surface shape parameters of the GaN substrate processed in Example 1 are shown in: thickness distribution diagram (a); warpage distribution diagram (b).

[0029] Figure 4The surface parameters of the GaN substrate after processing in Comparative Example 1 are shown in the following diagrams: thickness distribution (a) and warpage distribution (b). Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto.

[0031] Example 1

[0032] A processing method for improving the surface accuracy of large-size semiconductor wafers includes the following steps:

[0033] (1) Cleaning of substrate and substrate: The 2-inch GaN single crystal substrate and substrate were ultrasonically cleaned for 30 min each with acetone, anhydrous ethanol and deionized water respectively.

[0034] (2) Spin coating: Turn on the spin coater and vacuum pump, vacuum absorb the GaN single crystal substrate sample on the sample stage, set the parameters to 3000 rpm and 2 min, turn on the spin coating switch, and use a dropper to vertically and quickly drop 2 mL of liquid wax into the middle of the substrate for spin coating.

[0035] (3) Baking and fixing: The substrate coated with spin wax is baked on a heating table at 100 ℃ for 3 min to remove the air in the liquid wax and solidify it. Then the substrate is flipped over and placed on a preheated glass or ceramic substrate, and pressed with an airbag or pressure head at a pressure of 10 N for at least half an hour, and the substrate is allowed to cool and solidify.

[0036] (4) Substrate processing: The GaN single crystal substrate is placed on the polishing head of the grinding and polishing equipment. The grinding disc is shaped to be parallel to the polishing head using a cutting tool system, such as... Figure 1 As shown. The test disk operates at 23℃. The diameter and radius of the polishing head are measured using a micrometer reading via the "well" method. The diameter direction is 2, 3, 0, 1, and the radius direction is 2, 1, 1, 1. The tool position is adjusted so that the tool tip forms a 92° angle with the disk surface. The tool system extension switch is activated, and the tool is withdrawn from the disk. The disk speed is set to 100 rpm, the tool descends 20 μm, and the tool system advances at 5 mm / min. The surface is then trimmed to remove previous wear marks until the entire disk surface is trimmed. The disk speed is adjusted to 60 rpm, the tool descends 15 μm, and the tool system retreats at 30 mm / min. The surface shape is then trimmed. The disk diameter direction is measured as -2, -2, 1, 0, and the radius direction as -1, 0, 0, 0. An error of <5 μm indicates that GaN single-crystal substrate grinding and polishing is possible. The principle is as follows. Figure 2 As shown, the depth of color represents the thickness; the darker the color, the thicker the thickness.

[0037] (5) Dewaxing: After processing, the sample is placed on a heating table at 150 ℃ to bake and dewax. Then, the processed GaN single crystal substrate is ultrasonically cleaned in sequence with dewaxing water, acetone, anhydrous ethanol and deionized water.

[0038] The test results for this method are as follows: Figure 3 As shown, the TTV value is 14.17 μm, the Bow value is -16.77 μm, and the Warp value is 40.63 μm.

[0039] Comparative Example 1

[0040] A surface processing method for large-size semiconductor wafers includes the following steps:

[0041] Compared with Example 1, other steps remain unchanged, except that no special surface shaping is applied to the disk surface, which is then shaped into a flat surface. Step (4) Substrate processing: The GaN single crystal substrate is placed on the polishing head of the grinding and polishing equipment, and the grinding disk is shaped into a flat surface using the cutting tool system. The operating temperature of the large disk is tested at 23℃. The diameter and radius of the polishing head are measured using the "well" method. The diameter direction is 6, 4, 0, 1, and the radius direction is 4, 1, 0, 0. The cutting tool position is adjusted so that the tool head is perpendicular to the disk surface at a 90° angle. The cutting tool system extension switch is turned on, and the cutting tool is pulled out of the disk. The disk speed is turned on to 100 rpm, the cutting tool descends by 20 μm, and the cutting tool system advances at a speed of 5 mm / min. The flat surface is then shaped to remove the original wear marks until the entire disk surface is shaped. The disk speed is adjusted to 60 rpm, the cutting tool descends by 15 μm, and the cutting tool system retreats at a speed of 30 mm / min. The surface shape is then shaped. The diameter of the disc is measured at 0, 0, 0, 0, and the radius is measured at 0, 1, 0, 0. If the error is less than 5 μm, it is then subjected to grinding and polishing.

[0042] To avoid modifying the grinding disc to a special shape, the test results are as follows: Figure 4 As shown, the TTV value is 31.432 μm, the Bow value is -42.869 μm, and the Warp value is 56.3 μm.

[0043] Example 2

[0044] A processing method for improving the surface accuracy of large-size semiconductor wafers includes the following steps:

[0045] (1) Cleaning of substrate and substrate: The 2-inch GaN single crystal substrate and substrate were ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 30 min in sequence.

[0046] (2) Spin coating: Turn on the spin coater and vacuum pump, vacuum the sample onto the sample stage, set the parameters to 4000 rpm and 3 min, turn on the spin coating switch, and quickly add 2 ml of liquid wax with a dropper for spin coating;

[0047] (3) Baking and fixing: The substrate coated with spin wax is baked on a heating table at 100 ℃ for 3 min to remove the air in the liquid wax and solidify it. Then the substrate is flipped over and placed on a preheated glass or ceramic substrate, and pressed with an airbag or pressure head for at least half an hour until the substrate cools and is fixed.

[0048] (4) Substrate processing: The GaN single crystal substrate is placed on the polishing head of the grinding and polishing equipment. The lathe tool system is used to shape the grinding disk into a surface that is completely parallel to the wafer on the polishing head. The operating temperature of the large disk is tested at 23.5℃. The diameter and radius of the polishing head are measured using the "well" method. The diameter direction is 1, 0, 2, 2, and the radius direction is -1, 1, 1, 2. The lathe tool position is adjusted so that the tool head forms an 87° angle with the disk surface. The lathe tool system extension switch is turned on to retract the lathe tool out of the disk. The disk speed is turned on to 90 rpm, the lathe tool descends 25 μm, and the lathe tool system advances at a speed of 5 mm / min. The surface is then trimmed to remove the original wear marks until the entire disk surface is trimmed. The disk speed is adjusted to 70 rpm, the lathe tool descends 20 μm, and the lathe tool system retreats at a speed of 30 mm / min. The surface shape is then trimmed. The disk diameter direction is measured as 2, 2, 1, 0, and the radius direction is measured as 1, 1, 0, 0. With an error of <5 μm, the GaN single crystal substrate can be ground and polished using the trimmed grinding disc.

[0049] (5) Dewaxing: After processing, the sample was baked on a heating stage at 150 ℃ to remove the wax. Then, the processed GaN single crystal substrate was ultrasonically cleaned sequentially with dewaxing water, acetone, anhydrous ethanol, and deionized water. The TTV value of the processed substrate was 15.35 μm, the Bow value was 8.99 μm, and the Warp value was 38.26 μm.

[0050] Example 3

[0051] A processing method for improving the surface accuracy of large-size semiconductor wafers includes the following steps:

[0052] (1) Cleaning of substrate and substrate: The 2-inch GaN single crystal substrate and substrate were ultrasonically cleaned for 30 min in sequence with acetone, anhydrous ethanol and deionized water.

[0053] (2) Spin coating: Turn on the spin coater and vacuum pump, vacuum the sample onto the sample stage, set the parameters to 4000 rpm and 3 min, turn on the spin coating switch, and quickly add 2 ml of liquid wax with a dropper for spin coating;

[0054] (3) Baking and fixing: The substrate coated with spin wax is baked on a heating table at 100 ℃ for 3 min to remove the air in the liquid wax and solidify it. Then the substrate is flipped and placed on a preheated glass or ceramic substrate, and pressed with an airbag or pressure head for at least half an hour until the substrate cools and is fixed.

[0055] (4) Substrate processing: The GaN single crystal substrate is placed on the polishing head of the grinding and polishing equipment. The lathe tool system is used to shape the surface of the grinding disk parallel to the wafer on the polishing head. The operating temperature of the large disk is tested at 23.5℃. The diameter and radius of the polishing head are measured using the "well" method. The diameter direction is 0, 0, 2, 2, and the radius direction is -1, -1, 3, 3. The lathe tool position is adjusted so that the tool head forms an 85° angle with the disk surface. The lathe tool system extension switch is turned on to retract the lathe tool out of the disk. The disk speed is turned on to 90 rpm, the lathe tool descends by 30 μm, and the lathe tool system advances at a speed of 5 mm / min. The surface is then trimmed to remove the original wear marks until the entire disk surface is trimmed. The disk speed is adjusted to 70 rpm, the lathe tool descends by 20 μm, and the lathe tool system retreats at a speed of 25 mm / min. The surface shape is then trimmed. The disk diameter direction is measured as 7, 5, 2, 1, and the radius direction is measured as 6, 2, 2, 0. If the error is >5μm, use a correction wheel to adjust for 5 minutes, with the diameter direction of the disc being 4, 2, 2, 1 and the radius direction being 3, 2, 2, 0. Then perform grinding and polishing.

[0056] (5) Dewaxing: After processing, the sample was baked on a heating stage at 150 ℃ to remove the wax. Then, the processed GaN single crystal substrate was ultrasonically cleaned sequentially with dewaxing water, acetone, anhydrous ethanol, and deionized water. The TTV value of the processed substrate was 18.34 μm, the Bow value was 20.31 μm, and the Warp value was 30.24 μm.

Claims

1. A processing method for improving the surface accuracy of large-size semiconductor wafers, characterized in that, Includes the following steps: (1) Cleaning of substrate and substrate: The GaN single crystal substrate and substrate are ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 10-30 min in sequence. (2) Spin coating: Turn on the spin coater and vacuum pump, vacuum the substrate onto the sample stage, set the parameters to 2000-5000 rpm, time 1-3 min, turn on the spin coating switch, and quickly add 1-5 mL of liquid wax with a dropper for spin coating; (3) Baking and fixing: The wax-coated substrate is baked on a heating table at 90-120 ℃ for 1-3 min, and then the substrate is flipped and placed on the preheated substrate. It is pressed with an airbag or pressure head for at least half an hour until the substrate cools and is fixed. (4) Substrate processing: Place the GaN single crystal substrate on the polishing head of the grinding and polishing equipment. Use the cutting tool system to shape the grinding disk into a surface parallel to the GaN single crystal substrate on the polishing head. Measure the diameter and radius of the polishing head using the "well" method. Adjust the cutting tool position so that the tool tip is close to the surface of the large disk. Turn on the extension switch of the cutting tool system and pull the cutting tool out of the large disk. Turn on the large disk speed to 80-100 rpm, lower the cutting tool by 10-30 μm, and advance the cutting tool system at a speed of 1-5 mm / min to begin trimming the surface and remove the original wear marks on the grinding disk. Stop when the entire disk surface is trimmed. Adjust the large disk speed to 50-80 rpm, lower the cutting tool by 10-30 μm, and retreat the cutting tool system at a speed of 20-50 mm / min to begin trimming the surface. Measure the diameter and radius of the disk in the direction of the cutting tool. Finally, use the trimmed grinding disk to grind and polish the GaN single crystal substrate. (5) Dewaxing: After processing, the GaN single crystal substrate sample is placed on a heating stage at 120-150 ℃ to bake and dewax. Then, the processed GaN single crystal substrate is ultrasonically cleaned with dewaxing water, acetone, anhydrous ethanol and deionized water in sequence.

2. The processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (1), the substrate and the base plate are ultrasonically cleaned in sequence with acetone, anhydrous ethanol and deionized water for 30 min.

3. The processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, The substrate size in step (1) is 2-6 inches.

4. A processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (2), the spin coating parameters are 3000 rpm and the time is 2 min.

5. The processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, The thickness of the spin-coated wax layer in step (2) is 1-5 μm.

6. The processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (2), the liquid wax is added by dropping the dropper vertically onto the center of the substrate after spin coating begins.

7. A processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (3), the substrate coated with wax by spin is baked on a heating table at 100 °C for 3 min.

8. A processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (3), the pressure of the airbag or the pressure head is 10 N.

9. A processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (4), the surface shape of the grinding disk is parallel to the GaN single crystal substrate wafer at the polishing head, with an error ≤ 5 μm.

10. A processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (4), after the grinding disc is finished, if the error is greater than 5 μm, a correction wheel can be used for local correction.

11. The processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (4), the temperature of the grinding disc is kept at 20-25℃ when it is being repaired.

12. The processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (4), the angle between the cutter head and the large disc surface is 85° to 95°.

13. A processing method for improving the surface accuracy of large-size semiconductor wafers according to claim 1, characterized in that, In step (5), the sample is placed on a heating table at 150 ℃ to bake and remove wax.

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