Machining method for improving surface shape precision of large-size semiconductor wafer

Abstract

The invention 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. Comprising the following steps: cleaning a GaN single crystal substrate and a base plate, placing the substrate on a spin coater for spin coating of liquid wax, attaching one side of the substrate with wax to the base plate, pressurizing, cooling and fixing, placing the substrate on a polishing head of grinding and polishing equipment, and polishing the surface of the substrate on the polishing head of the grinding and polishing equipment. The surface shape parallel to a GaN single crystal substrate wafer on a polishing head is trimmed on a grinding disc through a turning tool system, finally, grinding and polishing treatment is conducted on the GaN single crystal substrate through the grinding disc with the trimmed surface shape, and wax removal and cleaning are conducted after treatment is completed. According to the method, on one hand, the problems that a wax layer is too thick and difficult to clean in a traditional waxing mode are solved; on one hand, the surface shape parameter of a large-size wafer is reduced by means of trimming the grinding disc, and a foundation is laid for subsequent preparation of small-size and high-power GaN-based devices.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor crystal processing, and relates to a processing method for improving the surface accuracy of a large-size semiconductor wafer. Background Art

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

[0003] The surface parameters (TTV, BOW, Warp) of semiconductor wafers are very important factors that must be considered in chip manufacturing. These three parameters together reflect the flatness and thickness uniformity of semiconductor wafers, and have a direct impact on many key steps in the chip manufacturing process. GaN has high hardness and high brittleness. During slicing and thinning, it is easy to produce quality problems such as warping on the surface and sub-surface of the wafer, which affects the development of the subsequent process. Therefore, the precision control requirements for warping (Warp), bending (BOW), and total thickness deviation (TTV) are very high. Nowadays, the wax sticking method has problems such as easy adsorption and cracking, thick wax layer, uneven application, and difficult wax layer removal, which have an unignorable impact on the surface parameters of the substrate, resulting in poor performance in chip preparation. In addition, the grinding disc used in the existing grinding and polishing process will have severe surface deformation due to uneven pressure and temperature changes after long-term processing of the wafer, which has an adverse effect on the surface accuracy of the substrate. Summary of the invention

[0004] The present invention aims to solve the problems that when processing GaN wafers using the existing wax sticking technology, the wax layer is difficult to clean, the wax layer is uneven, the surface accuracy of the GaN substrate is reduced during processing, and subsequent device preparation is affected. In addition, after long-term processing of the wafer, the grinding disc will have serious surface deformation due to uneven pressure and temperature changes, thereby reducing the surface accuracy of the substrate. A technology combining a spin wax coating method for large-size semiconductor wafers and a grinding disc shape design is invented, and finally a GaN single crystal substrate with high surface accuracy is obtained.

[0005] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions: A processing method for improving the surface accuracy of a large-size semiconductor wafer comprises the following steps: (1) Substrate and baseplate cleaning: The GaN single crystal substrate and baseplate were ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 10-30 min in sequence; (2) Spin coating: Turn on the coater and vacuum pump, vacuum absorb the substrate onto the sample stage, set the parameters to 2000-5000 rpm, time 1-3 min, turn on the spin coating switch, and use a dropper to quickly add 1-5 mL of liquid wax for spin coating; (3) Baking and fixing: The substrate with spin-coated wax is baked on a heating table at 90-120 °C for 1-3 min, and then the substrate is turned over and placed on a preheated substrate, and pressed with an air bag or a pressure head for at least half an hour, and the substrate is cooled and fixed; (4) Substrate processing: Place the GaN single crystal substrate on the polishing head of the grinding and polishing equipment, and use the turning tool system to trim the grinding disc to a surface parallel to the GaN single crystal substrate wafer on the polishing head, such as Figure 1 As shown. Measure the diameter of the polishing head and the number of thousandths of the radius by the "well" method; adjust the position of the turning tool so that the tool head is close to the surface of the large disk, turn on the telescopic switch of the turning tool system, and withdraw the turning tool from the large disk; turn on the large disk speed to 80-100 rpm, the turning tool drops 10-30 μm, the turning tool system moves forward at a speed of 1-5mm / min, and starts to trim the plane to remove the original use marks of the grinding disk until the entire disk surface is trimmed and stopped; adjust the large disk speed to 50-80 rpm, the turning tool drops 10-30 μm, the turning tool system moves backward at a speed of 20-50 mm / min, and starts to trim the surface shape; measure the disk diameter and the number of thousandths of the radius; finally, use the grinding disk after trimming the surface shape to grind and polish the GaN single crystal substrate; the principle is as follows Figure 2 shown.

[0006] (5) Dewaxing: After processing, the GaN single crystal substrate sample is placed on a heating table at 120-150 °C for baking to remove the wax. The processed GaN single crystal substrate is then ultrasonically cleaned with dewaxing water, acetone, anhydrous ethanol, and deionized water in turn.

[0007] Preferably, in step (1), the substrate and baseplate are ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 30 min in sequence to remove surface oil and other impurities.

[0008] Preferably according to the present invention, the size of the substrate in step (1) is 2-6 inches.

[0009] Preferably, in the step (2), the spin coating parameters are 3000 rpm and the time is 2 min. Spin coating speed that is too fast or time that is too short will cause the wax layer to be unevenly spin-coated and unable to be fixed on the substrate.

[0010] 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.

[0011] Preferably, according to the present invention, the liquid wax is dripped in step (2) by a dropper vertically dripping the liquid wax onto the middle of the substrate after the spin coating starts.

[0012] Preferably, according to the present invention, in step (3), the substrate on which the wax is spin-coated is baked on a heating platform at 100° C. for 3 min, in order to expel the air in the liquid wax and solidify it.

[0013] Preferably, according to the present invention, the pressure of the airbag pressure or the pressure head in step (3) is 10 N.

[0014] Preferably, according to the present invention, in step (4), the surface of the grinding disc is parallel to the GaN single crystal substrate wafer at the polishing head, with an error of ≤5 μm.

[0015] Preferably, according to the present invention, in step (4), the angle between the cutter head and the large disk surface is 85° to 95°.

[0016] Preferably, according to the present invention, after the grinding disc is trimmed in step (4), the error is greater than 5 μm, and a correction wheel can be used for local correction.

[0017] Preferably, according to the present invention, when dressing the grinding disc in step (4), the temperature of the large disc is maintained at 20-25°C.

[0018] Preferably, according to the present invention, in step (5), the sample is placed on a heating table at 150° C. to bake and remove the wax.

[0019] The beneficial effects of the present invention are as follows: On the one hand, the method of the present invention solves the problems of the traditional wax coating method, such as the wax layer being too thick and difficult to clean; on the other hand, the means of trimming the grinding disc reduces the surface parameters of large-size wafers, paving the way for the subsequent preparation of small-size, high-power GaN-based devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the turning tool repairing system of the present invention; Figure 2 A schematic diagram of the principle of dressing the grinding disc to reduce the surface parameters of the present invention; Figure 3 The surface parameters of the GaN substrate processed in Example 1 are as follows: thickness distribution diagram (a); warpage distribution diagram (b); Figure 4 The surface parameters of the GaN substrate after processing in Comparative Example 1: thickness distribution diagram (a); warpage distribution diagram (b). DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with embodiments and drawings, but the protection scope of the present invention is not limited thereto.

[0022] Example 1 A processing method for improving the surface accuracy of a large-size semiconductor wafer comprises the following steps: (1) Substrate and baseplate cleaning: The 2-inch GaN single crystal substrate and baseplate were ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 30 min respectively; (2) Spin coating: Turn on the coating machine and vacuum pump, vacuum absorb the GaN single crystal substrate sample on the sample stage, set the parameters to 3000 rpm, time 2 min, turn on the spin coating switch, and use a dropper to quickly drop 2 mL of liquid wax vertically in the middle of the substrate for spin coating; (3) Baking and fixing: The substrate with spin-coated wax is baked on a heating table at 100 °C for 3 min to expel the air in the liquid wax and solidify it. Then the substrate is turned over and placed on a preheated glass substrate or ceramic substrate, and a 10 N air bag press or pressure head is used for at least half an hour, and the substrate is cooled and fixed; (4) Substrate processing: Place the GaN single crystal substrate on the polishing head of the grinding and polishing equipment, and use the turning tool system to trim the grinding disc to a surface parallel to the polishing head, such as Figure 1 As shown. The operating temperature of the test disk is 23°C. The diameter of the polishing head and the thousandth of the radius are measured by the "well" method. The diameter direction is 2, 3, 0, 1, and the radius direction is 2, 1, 1, 1. Adjust the position of the turning tool so that the tool head forms a 92° angle with the disk surface, turn on the telescopic switch of the turning tool system, and withdraw the turning tool from the disk. Turn on the disk speed of 100 rpm, the turning tool drops 20 μm, the turning tool system moves forward at a speed of 5 mm / min, and starts to trim the plane to remove the original traces of use until the entire disk surface is trimmed and stopped. Adjust the disk speed to 60 rpm, the turning tool drops 15 μm, the turning tool system moves backward at a speed of 30 mm / min, and starts to trim the surface. The measured disk diameter directions are -2, -2, 1, 0 and the radius directions are -1, 0, 0, 0. The error is less than 5 μm, and the GaN single crystal substrate can be ground and polished. The principle is as follows Figure 2 As shown, the color depth represents the thickness, the darker the color, the thicker the thickness.

[0023] (5) Dewaxing: After processing, the sample is placed on a heating table at 150 °C to bake and remove the wax. The processed GaN single crystal substrate is then ultrasonically cleaned with dewaxing water, acetone, anhydrous ethanol, and deionized water in sequence.

[0024] The test results of 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.

[0025] Comparative Example 1 A surface processing method for a large-size semiconductor wafer comprises the following steps: Compared with Example 1, the other steps remain unchanged, and the disc surface is not trimmed for special surface shape, and the disc surface is trimmed to be flat. Step (4) Substrate processing: Place the GaN single crystal substrate on the polishing head of the grinding and polishing equipment, and use the turning tool system to trim the grinding disc to a flat surface. The operating temperature of the test disc is 23°C. The diameter of the polishing head and the number of millimeters of radius are measured by the "well" method. The diameter direction is 6, 4, 0, 1, and the radius direction is 4, 1, 0, 0. Adjust the turning tool position so that the tool head and the disc surface are perpendicular to each other at 90°, turn on the turning tool system telescopic switch, and withdraw the turning tool from the disc. Turn on the disc speed of 100 rpm, the turning tool drops 20 μm, the turning tool system advances at a speed of 5 mm / min, and starts to trim the plane to remove the original traces of use, and stops when the entire disc surface is trimmed. Adjust the disc speed to 60 rpm, the turning tool drops 15 μm, the turning tool system retreats at a speed of 30 mm / min, and starts to trim the surface shape. The disk diameter direction is measured as 0, 0, 0, 0 and the radius direction is 0, 1, 0, 0. The error is less than 5 μm, and grinding and polishing are performed.

[0026] In order not to modify the grinding disc to a special surface 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.

[0027] Example 2 A processing method for improving the surface accuracy of a large-size semiconductor wafer comprises the following steps: (1) Substrate and baseplate cleaning: The 2-inch GaN single crystal substrate and baseplate were ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 30 min in sequence; (2) Spin coating: Turn on the coater and vacuum pump, vacuum absorb the sample on the sample stage, set the parameters to 4000 rpm, time 3 min, turn on the spin coating switch, and use a dropper to quickly add 2 ml of liquid wax for spin coating; (3) Baking and fixing: The substrate with spin-coated wax is baked on a heating table at 100 °C for 3 min to expel the air in the liquid wax and solidify it. Then the substrate is turned over and placed on a preheated glass substrate or ceramic substrate, and pressed with an air bag or a pressure head for at least half an hour, and the substrate is cooled and fixed; (4) Substrate processing: Place the GaN single crystal substrate on the polishing head of the grinding and polishing equipment, and use the turning tool system to trim the surface of the grinding disc to be completely parallel to the wafer on the polishing head. The operating temperature of the test disc is 23.5℃. Measure the diameter and radius of the polishing head in thousandths by the "well" method. The diameter direction is 1, 0, 2, 2, and the radius direction is -1, 1, 1, 2. Adjust the turning tool position so that the tool head forms an angle of 87° with the disc surface, turn on the turning tool system telescopic switch, and withdraw the turning tool from the disc. Turn on the disc speed of 90rpm, the turning tool drops 25 μm, the turning tool system advances at a speed of 5 mm / min, and starts to trim the plane to remove the original traces of use. Stop when the entire disc surface is trimmed. Adjust the disc speed to 70 rpm, the turning tool drops 20 μm, the turning tool system retreats at a speed of 30 mm / min, and starts to trim the surface. Measure the disc diameter direction as 2, 2, 1, 0 and the radius direction as 1, 1, 0, 0. The error is less than 5 μm, and the repaired grinding wheel can be used for grinding and polishing of GaN single crystal substrates.

[0028] (5) Dewaxing: After processing, the sample was placed on a heating table at 150 °C for baking and dewaxing, and then the processed GaN single crystal substrate was ultrasonically cleaned with dewaxing water, acetone, anhydrous ethanol, and deionized water in sequence. 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.

[0029] Example 3 A processing method for improving the surface accuracy of a large-size semiconductor wafer comprises the following steps: (1) Substrate and baseplate cleaning: The 2-inch GaN single crystal substrate and baseplate were ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 30 min in sequence; (2) Spin coating: Turn on the coater and vacuum pump, vacuum absorb the sample on the sample stage, set the parameters to 4000 rpm, time 3 min, turn on the spin coating switch, and use a dropper to quickly add 2 ml of liquid wax for spin coating; (3) Baking and fixing: The substrate with spin-coated wax is baked on a heating table at 100 °C for 3 minutes to expel the air in the liquid wax and solidify it. Then the substrate is turned over and placed on a preheated glass substrate or ceramic substrate, and pressed with an air bag or a pressure head for at least half an hour, and then the substrate is cooled and fixed; (4) Substrate processing: Place the GaN single crystal substrate on the polishing head of the grinding and polishing equipment, and use the turning tool system to trim the surface of the grinding disc parallel to the wafer on the polishing head. The operating temperature of the test disc is 23.5℃. Measure the diameter and radius of the polishing head in thousandths by the "well" method. The diameter direction is 0, 0, 2, 2, and the radius direction is -1, -1, 3, 3. Adjust the turning tool position so that the tool head forms an angle of 85° with the disc surface, turn on the turning tool system telescopic switch, and withdraw the turning tool from the disc. Turn on the disc speed of 90 rpm, the turning tool drops 30 μm, the turning tool system advances at a speed of 5 mm / min, and starts to trim the plane to remove the original traces of use. Stop when the entire disc surface is trimmed. Adjust the disc speed to 70 rpm, the turning tool drops 20 μm, and the turning tool system retreats at a speed of 25 mm / min to start trimming the surface. Measure the disc diameter direction as 7, 5, 2, 1 and the radius direction as 6, 2, 2, 0. If the error is greater than 5μm, use the correction wheel to trim for 5 minutes, and the disc diameter direction is 4, 2, 2, 1 and the radius direction is 3, 2, 2, 0. Then perform grinding and polishing.

[0030] (5) Dewaxing: After processing, the sample was placed on a heating table at 150 °C to bake and dewax, and then the processed GaN single crystal substrate was ultrasonically cleaned with dewaxing water, acetone, anhydrous ethanol, and deionized water in sequence. 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 a large-size semiconductor wafer, characterized in that: The following steps are involved: (1) Substrate and baseplate cleaning: The GaN single crystal substrate and baseplate were ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 10-30 min in sequence; (2) Spin coating: Turn on the coating machine and vacuum pump, vacuum absorb the substrate on the sample stage, set the parameters to 2000-5000rpm, time 1-3 min, turn on the spin coating switch, and use a dropper to quickly add 1-5 mL of liquid wax for spin coating; (3) Baking and fixing: The substrate with spin-coated wax is baked on a heating table at 90-120 °C for 1-3 min, and then the substrate is turned over and placed on a preheated substrate, and pressed with an air bag or a pressure head for at least half an hour, and the substrate is cooled and fixed; (4) Substrate processing: Place the GaN single crystal substrate on the polishing head of the grinding and polishing equipment, use the turning tool system to trim the grinding disc to be parallel to the GaN single crystal substrate on the polishing head, and measure the diameter and radius of the polishing head in millimeters by the "well" method; adjust the turning tool position so that the tool head is close to the disc surface, turn on the turning tool system telescopic switch, and withdraw the turning tool from the disc; turn on the disc speed to 80-100 rpm, lower the turning tool by 10-30 μm, and advance the turning tool system at a speed of 1-5 mm / min to start trimming the surface and remove the original use marks of the grinding disc until the entire disc surface is trimmed and stop; adjust the disc speed to 50-80 rpm, lower the turning tool by 10-30 μm, and retreat the turning tool system at a speed of 20-50 mm / min to start trimming the surface; measure the disc diameter and the radius in millimeters; finally, use the grinding disc after trimming the surface to grind and polish the GaN single crystal substrate; (5) Dewaxing: After processing, the GaN single crystal substrate sample is placed on a heating table at 120-150 °C for baking to remove the wax. The processed GaN single crystal substrate is then ultrasonically cleaned with dewaxing water, acetone, anhydrous ethanol, and deionized water in turn.

2. A processing method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: In the step (1), the substrate and the base plate are ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 30 minutes in sequence; preferably, the size of the substrate in the step (1) is 2-6 inches.

3. A processing method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: The spin coating parameters in step (2) are 3000 rpm and the time is 2 min. Preferably, the thickness of the spin-coated wax layer in step (2) is 1-5 μm.

4. A processing method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: The method of dripping the liquid wax in step (2) is that after the spin coating starts, the dropper vertically drips the liquid wax on the center of the substrate for spin coating.

5. The method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: In the step (3), the substrate on which the wax is spin-coated is baked on a heating platform at 100° C. for 3 min.

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

7. The method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: In the step (4), the surface of the grinding disc is parallel to the GaN single crystal substrate wafer at the polishing head, with an error of ≤5 μm.

8. The method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: If the error after the grinding disc dressing in step (4) is greater than 5 μm, a correction wheel can be used for local correction.

9. The method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: When trimming the grinding disc in step (4), the temperature of the disc is maintained at 20-25°C; preferably, in step (4), the angle between the cutter head and the disc surface of the disc is 85° to 95°.

10. The method for improving the surface accuracy of a large-size semiconductor wafer according to claim 1, characterized in that: In step (5), the sample is placed on a heating table at 150° C. to bake and remove the wax.

Images