Machining method for edge chamfer of gallium nitride single crystal

Abstract

The invention belongs to the technical field of semiconductor processing, and particularly relates to a method for processing an edge chamfer of a gallium nitride single crystal. According to the method, edge damage generated by cutting in the previous procedure is removed through rough chamfering of the chamfering machine, then certain grinding machining is carried out to guarantee the good edge quality, then secondary finish machining is carried out to enable the chamfer contour to reach the initial chamfer design value, stress is further released, and therefore the optimal surface quality is achieved; and obtaining the gallium nitride chamfered wafer of which the edge has no micro-crack and edge breakage defects and the chamfered surface width meets the epitaxial requirement. The feeding amount and the number of cutters in the chamfering process are optimized, the grinding process is matched, damage to the edge of the gallium nitride wafer is reduced, the wafer chamfering edge face with good quality is obtained, and the requirement of a gallium nitride epitaxial device is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor processing, and particularly relates to a processing method for edge chamfering of a gallium nitride single crystal. BACKGROUND

[0002] As a core material of the third generation of semiconductors, gallium nitride (GaN) has become a global research hotspot due to its unique physical and chemical properties. Its band gap is 3.4 electron volts, which is 3 times that of silicon, the breakdown field strength is 10 times that of silicon, the thermal conductivity is 2 times that of silicon, the electron migration rate is 1.5 times that of silicon, and the saturated electron drift speed is 3 times that of silicon. Therefore, compared with silicon-based chips, gallium nitride-based chips can reduce energy loss by more than 50%, and the volume is reduced by more than 75%, which shows significant advantages in 5G communication, new energy, high-power optoelectronic fields and fast charging scenarios. In addition, gallium nitride has high chemical stability, is stable to water and dilute acid (such as hydrochloric acid and sulfuric acid) at room temperature, but can be corroded by hot concentrated acid (such as phosphoric acid and sulfuric acid) or strong alkali (such as molten potassium hydroxide), and has a high melting point of 1700 DEG C, high hardness and radiation resistance, and is suitable for harsh environments such as high temperature, high pressure and strong radiation.

[0003] However, due to the high stability and high hardness of the gallium nitride single crystal, its processing is difficult. Especially when using the HVPE method to prepare a gallium nitride single crystal substrate, as the size gradually increases, the stress generated also increases, which may cause the gallium nitride single crystal to produce microcracks, edge collapse or lattice damage at the edge during subsequent processing, which will expand in subsequent processes (such as polishing and ion implantation), leading to the rupture of the wafer or the introduction of impurity diffusion paths, which greatly limits the preparation and use of gallium nitride devices. SUMMARY

[0004] In view of the above problems, the application provides a processing method for edge chamfering of a gallium nitride single crystal. This technology can further reduce mechanical damage to the edge of the gallium nitride, and maximize the maximum value of the chamfer surface while releasing the edge processing stress.

[0005] The application provides the following technical solutions: A processing method for edge chamfering of a gallium nitride single crystal, comprising the following steps: S1. Determine the size and thickness of the wafer after cutting, and edit the chamfering program; S2. Fix the wafer on the stage by using a limiting mold, and use a vacuum pump for adsorption at the same time, replace the tool bit with a centering rod, and use a three-point centering method to determine the center of the wafer; S3. Remove the centering rod, install a rough chamfering tool bit, zero compensate the tool bit contact position according to the wafer thickness, determine the starting point of the processing height, and ensure that the tool bit can completely process the entire edge region of the wafer; S4. Using the mechanical hand to control the platform and the chamfering tool to approach each other, rough chamfering is carried out, the tool head has 1000 meshes, the tool head diameter is 8mm, there is no specific groove design, the tool head feed rate is 30-50 μm / r, the spindle speed is 36000rpm, and the total removal amount is 0.6-0.8mm; S5. The wafer after rough chamfering is taken out, fixed on a quartz plate using paraffin after water and alcohol washing, double-side grinding is carried out on a grinding machine using 100nm diamond abrasive grains, the removal thickness is 200-300 μm, and the wafer diameter and thickness are measured again after grinding; S6. The wafer after double-side grinding is subjected to fine chamfering, an I-shaped chamfering tool with a specific groove design is replaced, the tool has 3000 meshes, the diameter is 8.82mm, the first groove depth is 0.4mm, and the distance from the first groove center line to the tool bottom is 1.4mm, the chamfering program is modified according to the wafer diameter measured in S5 and the tool diameter used in fine machining, and the program is set according to the wafer thickness measured in S5 and the tool groove spacing, and the lower tool position depth in the program is set as = wafer thickness / 2+ distance from groove center to tool bottom; S7. The wafer after double-side grinding is also fixed by using the limiting mold and the vacuum pump, and three-point centering is carried out again, the tool Z-direction position is zero-compensated according to the chamfering tool size and the wafer thickness, so that the I-shaped tool bottom is at the same horizontal plane as the wafer upper surface, and the I-shaped tool is used for fine chamfering; the I-shaped tool feed rate is 5 μm / r, the spindle speed is 36000rpm, and the total removal amount is 0.1-0.2mm; S8. The wafer after fine chamfering is subjected to water and alcohol washing and drying, the wafer diameter and edge quality are measured, and finally the gallium nitride chamfering wafer with no micro-cracks, no edge collapse defects and a chamfering surface width meeting the epitaxial requirements is obtained. The beneficial effects of the present application are as follows: The present application provides a gallium nitride edge chamfering method, the feed amount and tool mesh number in the chamfering process are optimized in combination with the rough chamfering and fine chamfering, the grinding process is used, the damage of the gallium nitride wafer at the edge is reduced, the wafer chamfering edge surface with good quality is obtained, and the requirements of the gallium nitride epitaxial device are met. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 The process flow chart of the gallium nitride wafer edge chamfering method is shown in the figure; Figure 2 The limiting mold structure for fixing the wafer is shown in the figure; Figure 3 The I-shaped tool structure is shown in the figure; Figure 4 The appearance of the gallium nitride wafer edge processed by the method of the present application is shown in the figure. Figure 5 Figure 2 is a topographic map of the edge of a gallium nitride wafer after processing according to the method of Example 2 of the present application; Figure 6 Figure 3 is a topographic map of the edge of a gallium nitride wafer after processing according to the method of Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0007] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application will be further described in conjunction with specific examples. It should be noted that the embodiments of the present application and the features in the examples can be combined with each other without conflict.

[0008] Example 1 A processing method for chamfering the edge of a gallium nitride single crystal, the process flow chart of the processing method is as shown in Figure 1 Figure 1: A non-intentionally doped self-stripping GaN wafer grown by HVPE method is used as the gallium nitride wafer to be chamfered in this embodiment, and the wafer size is ≥55 mm.

[0009] (1) The diameter of the gallium nitride after laser cutting is determined to be 51.8 mm, the thickness of the wafer is determined to be 1080 μm, the chamfering program is written, the tool diameter is determined to be 8 mm, the tool lifting speed is determined to be 100 mm / min, the tool lowering speed is determined to be 100 mm / min, and the spindle speed is determined to be 36000 rpm.

[0010] (2) The wafer is limited on the stage using a limiting mold, the structure diagram is as shown in Figure 2 Figure 2, and the wafer is adsorbed by opening the vacuum pump. The tool bit is replaced with a centering rod, and the center position is determined using a three-point centering method.

[0011] (3) The centering rod is removed, a rough chamfering tool bit is installed, the tool is zero compensated according to the thickness of the wafer, and the processing height starting point is determined to ensure that the entire wafer edge can be processed by the tool.

[0012] (4) The program is run, the stage and the chamfering tool are slowly approached using a mechanical hand, and the rough chamfering processing is started according to the set parameters. The tool bit diameter is 8 mm, the mesh number is 1000, the tool feed amount is 40 μm / r, and the total removal amount is 0.8 mm.

[0013] (5) After the rough chamfering is completed, the wafer is removed, the wafer is washed with water and alcohol, the wafer is fixed on a quartz plate using paraffin, the wafer is ground on both sides using a diamond abrasive grain with a diameter of 100 nm, the thickness of the wafer is removed by 200 μm, and after the grinding, the wafer is removed and the diameter and thickness are measured again. The diameter is 51 mm, and the thickness is 880 μm.

[0014] (6) Replace the I-shaped chamfering tool with a mesh number of 3000, a diameter of 8.82 mm, a first groove depth of 0.4 mm, and a pitch of 1.4 mm (the specific shape and size are shown in FIG. 6, purchased from Shenzhen Changxing Technology Co., Ltd.), modify the program according to the measured wafer diameter, change the I-shaped chamfering tool diameter to 8.82 mm, keep the tool lifting speed, tool lowering speed, and spindle speed unchanged, use the first groove of the I-shaped grinding wheel during chamfering, and set the feed lowering position depth in the program to a compensation value = wafer thickness / 2 + distance between groove center and tool bottom = 1.84 mm according to the wafer thickness of 880 μm and the groove pitch of 1.4 mm. Figure 3

[0015] (7) Similarly, use the limiting mold and vacuum pump to adsorb and fix the wafer, and re-perform three-point centering. Compensate the Z-axis zero point so that the bottom surface of the I-shaped tool head is at the same level as the upper surface of the wafer. Run the program to perform fine chamfering processing, set the feed rate of the tool to 5 μm / r, the total removal amount to 0.2 mm, and the final target diameter to 50.8±0.05 mm.

[0016] (8) After chamfering, take out the wafer to wash with water and alcohol and dry it, measure the wafer diameter to be 50.81 mm, which meets the size requirement, the edge collapse is ≤8 μm, and no micro-cracks are observed. Finally, a gallium nitride chamfered wafer with no micro-cracks, edge collapse defects, and a chamfered surface width that meets the epitaxial requirements is obtained.

[0017] The morphology of the edge of the gallium nitride wafer after processing is shown in FIG. 6B, which can be seen to have good edge quality, effectively overcoming the technical bottleneck of easy damage to the edge of the gallium nitride wafer, thereby limiting the subsequent use of the wafer, and improving the edge quality of the gallium nitride wafer. Figure 4

[0018] Example 2 A method for processing a gallium nitride single crystal edge chamfering: Steps (1)-(4) are consistent with Example 1, and the gallium nitride wafer diameter is measured to be 50.98 mm and the thickness is 850 μm after step (5).

[0019] Step (6) is different from Example 1 in that the feed lowering position depth is set to a compensation value = wafer thickness / 2 + distance between groove center and tool bottom = 1.825 mm according to the wafer thickness of 850 μm and the groove pitch of 1.4 mm.

[0020] Step (7) is different from Example 1 in that the total removal amount is 0.18 mm.

[0021] Step (8) is different from Example 1 in that the final wafer diameter is measured to be 50.79 mm.

[0022] ​​The morphology of the edge of the processed gallium nitride wafer is shown in Figure 5 It can be seen that the edge quality is good, the edge collapse is ≤8 μm, and no micro-cracks are observed. It can also meet the subsequent use requirements.

[0023] Comparative Example 1 A gallium nitride wafer chamfering method (1) The unintentionally doped self-stripping GaN wafer grown by HVPE method is used as the gallium nitride wafer to be chamfered in the embodiment, and the wafer size is ≥55 mm.

[0024] (2) The gallium nitride wafer is laser cut, and the size is 51.8 mm.

[0025] (3) The program is written according to the wafer size, the tool diameter is 8 mm, the tool lifting speed is 100 mm / min, the tool lowering speed is 100 mm / min, and the spindle speed is 36000 rpm.

[0026] (4) The wafer is limited on the stage by using the limiting mold, and the wafer is adsorbed by opening the vacuum pump. The tool bit is replaced with a centering rod, and the three-point centering method is used to determine the center position and chamfer position. (5) The centering rod is removed, the chamfering tool is installed, the tool bit diameter is 8 mm, the mesh number is 1500, the tool is zero corrected according to the wafer thickness, and it is ensured that the entire wafer edge can be machined by the tool.

[0027] (6) Run the program, slowly approach the stage and the tool, start chamfering according to the set parameters, the tool feed amount is 25 μm / r, and the total removal amount is 1 mm.

[0028] (7) After chamfering, the wafer is taken out and washed with water and alcohol in the cleaning place, the wafer size is measured as 50.77 mm, which meets the size requirement.

[0029] The morphology of the edge of the processed gallium nitride wafer is shown in Figure 6 As can be seen from the figure, the gallium nitride wafer chamfered by using the traditional chamfering process has damage at the edge, the edge collapse is ≥10 μm, and it cannot meet the subsequent gallium nitride device epitaxy requirements.

Claims

1. A method for processing edge chamfering of a gallium nitride single crystal, characterized in that: The processing method comprises the following steps: S1. Determine the wafer size and thickness after cutting and edit the chamfering program; S2. Secure the wafer to the stage using a stopper mold while applying suction using a vacuum pump. Replace the cutting head with a centering rod and determine the wafer center using the three-point centering method. S3. Remove the centering rod and install the rough chamfering tool head. Perform zero point compensation on the tool contact position according to the wafer thickness to determine the starting point of the processing height. S4. A manipulator was used to move the stage and chamfering tool closer together for rough chamfering. The tool head had a grit of 1000, a diameter of 8 mm, no specific groove design, a feed rate of 30-50 μm / r, and a spindle speed of 36,000 rpm. The total removal volume was 0.6-0.8 mm. S5. Remove the roughly chamfered wafer, rinse it with water and alcohol, then mount it on a quartz plate. Grind both sides of the wafer using diamond abrasives on a grinder to remove 200-300 μm of material. After grinding, measure the wafer diameter and thickness again. S6. Perform fine chamfering on the double-sided ground wafer, replace the I-type chamfering tool, modify the chamfering program based on the wafer diameter measured in S5 and the tool diameter used for fine processing, and set the tool position in the program based on the wafer thickness and tool groove spacing measured in S5; S7. Similarly, the double-sided ground wafer is fixed using a limit mold and vacuum pump, and the three-point centering is re-performed. The Z-position of the tool is zero-compensated based on the chamfering tool size and wafer thickness, so that the bottom surface of the I-shaped tool is at the same level as the top surface of the wafer. The first groove of the I-shaped tool is then used for fine chamfering. S8. Wash the wafer after fine chamfering with water and alcohol and blow dry it to obtain a gallium nitride chamfered wafer with no microcracks or edge collapse defects on the edge and a chamfer width that meets the requirements of epitaxy.

2. The processing method according to claim 1, characterized in that: The step S3 determines the starting point of the processing height to ensure that the tool can completely process the entire wafer edge area.

3. The processing method according to claim 1, wherein The feed rate of the tool head in step S4 is 40 μm / r.

4. The processing method according to claim 1, characterized in that: In step S5, paraffin wax is used to fix the wafer on the quartz plate.

5. The processing method according to claim 1, characterized in that: The diameter of the diamond abrasive grains in step S5 is 100 nm.

6. The processing method according to claim 1, characterized in that: In step S6, the mesh number of the I-type chamfering tool is 3000, the diameter is 8.82 mm, the depth of the first groove is 0.4 mm, and the distance from the center line of the first groove to the bottom surface of the prop is 1.4 mm.

7. The processing method according to claim 1, characterized in that: The cutting depth in step S6 = wafer thickness / 2 + distance between the groove center and the bottom of the cutting tool.

8. The processing method according to claim 1, wherein During the fine chamfering process in step S7, the feed rate of the I-type tool is 5 μm / r, the spindle speed is 36000 rpm, and the total removal amount is 0.1-0.2 mm.

9. The processing method according to claim 1, characterized in that: In step S8, after drying, the wafer diameter and edge quality are measured to see whether they meet the requirements. If not, reprocessing is required.

10. A gallium nitride chamfered wafer obtained by the processing method according to any one of claims 1 to 9, having no microcracks or edge collapse defects at the edge and a chamfer width meeting epitaxial requirements.

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