Gallium nitride wafer polishing process

Abstract

The application discloses a gallium nitride wafer grinding process. The process is to add diamond grinding liquid and alkaline grinding liquid simultaneously in the gallium nitride wafer grinding process, wherein the abrasive particle size D50 of the alkaline grinding liquid is less than the diamond particle size D50 of the diamond grinding liquid. Compared with the existing grinding process using the diamond grinding liquid, the wafer processing grinding efficiency of the method can be improved from 25-30 μm / h to 35-40 μm / h, and the yield can be improved from 95% to more than 98%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of semiconductor wafer processing, and particularly relates to a gallium nitride wafer grinding process. BACKGROUND

[0002] Nowadays, gallium nitride single crystal material is difficult to grow and expensive, so it is urgent to improve the yield and efficiency of each process. At present, domestic production of gallium nitride wafer generally needs to go through coarse grinding (double-sided grinding) - fine grinding (single-sided grinding) - polishing (mirrorization). The existing technology generally uses neutral diamond liquid for fine grinding after coarse grinding. Due to the characteristics of gallium nitride itself, the efficiency and yield of the fine grinding process are low. SUMMARY

[0003] In order to overcome the above-mentioned problems in the prior art that diamond liquid is used for fine grinding of gallium nitride wafer, the present application provides an improved gallium nitride wafer grinding process, which accelerates the grinding efficiency while improving the wafer yield.

[0004] The technical scheme adopted by the present application to achieve the above-mentioned purposes is as follows:

[0005] A gallium nitride wafer grinding process, characterized in that: during the gallium nitride wafer grinding process, diamond grinding liquid and alkaline grinding liquid are added at the same time, wherein the abrasive particle size D50 of the alkaline grinding liquid is smaller than the diamond particle size D50 of the diamond grinding liquid.

[0006] Preferably, the ratio of the abrasive particle size D50 of the alkaline grinding liquid to the diamond particle size D50 of the diamond grinding liquid is 0.2-0.6:1.

[0007] Preferably, the pH value of the diamond grinding liquid is 6-8, and the diamond particle size D50 is 3-10 μm.

[0008] More preferably, the diamond particle size D50 of the diamond grinding liquid is 5 μm.

[0009] Preferably, the alkaline grinding liquid is an alumina grinding liquid with a pH value of 9-13.

[0010] More preferably, the alkaline grinding liquid is an alumina grinding liquid with a pH value of 11.

[0011] Preferably, the diamond content of the diamond grinding liquid is 40-80 carats per liter, the abrasive content of the alkaline grinding liquid is 3-7 wt%, and the flow ratio of the diamond grinding liquid to the alkaline grinding liquid is 1:1-2.

[0012] Preferably, resin copper disc is used to grind the gallium nitride wafer.

[0013] Preferably, the pressure is 450-600 g / cm 2The ratio of the up and down disk speed is 0.8-0.9, and the flow of the diamond liquid is 3-10 g / min. The pressure is the pressure per square centimeter of the wafer.

[0014] Preferably, the diamond polishing liquid and the alkaline polishing liquid are subjected to ultrasonic treatment before being added.

[0015] Compared with the prior art, the present application has the following technical effects:

[0016] 1) The polishing efficiency of the method of the present application can be improved from 25-30 μm / h before improvement to 35-40 μm / h, and the roughness Ra (50*50 μm) value can be reduced from about 500 nm to about 300 nm.

[0017] 2) The problem of scratches on the wafer surface is avoided, and the yield of wafer processing is improved from 95% to more than 98%. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The figure is a structural schematic diagram of the polishing liquid dripping system of the present application.

[0019] Figure 2 The figure is a flow schematic diagram of the single-side polishing of the gallium nitride wafer of the present application.

[0020] In the figure, 1 is a single-side polishing machine, 2 is a resin copper disc, 3 is a first polishing liquid dripping tube, 4 is a second polishing liquid dripping tube, and 5 is an ultrasonic cleaning device. DETAILED DESCRIPTION

[0021] The technical solutions of the present application are further described below in combination with examples.

[0022] The neutral diamond polishing liquid is used as the first polishing liquid, and the alkaline alumina polishing liquid is used as the second polishing liquid in each embodiment of the present application, which are dripped to the disc surface through the polishing liquid dripping systems as shown in the figures, respectively. Figure 1 When the ultrasonic treatment is performed, the ultrasonic frequency is 40-80 kHz.

[0023] The polishing system uses the polishing liquid in combination with the resin copper disc, and the thickness of the resin copper disc is 3 cm.

[0024] The diamond particles in the neutral diamond liquid can have different morphologies, such as single crystal, polycrystal or polycrystal-like.

[0025] The alumina particles in the alkaline alumina polishing liquid can be spherical or rhombic.

[0026] The neutral diamond polishing liquid (hereinafter referred to as diamond liquid) and the alkaline alumina polishing liquid (hereinafter referred to as alumina liquid) are commercially available products.

[0027] Example 1

[0028] The flow of the single-side polishing of the gallium nitride wafer is as shown in the figure.Figure 2 The procedure is as follows:

[0029] S1, the 2-inch gallium nitride wafer after rough grinding is cleaned, and is grouped according to thickness, with a thickness error of less than 2 μm in the same group. Each group has 64 wafers, each group has 4 trays, and each tray has 16 wafers.

[0030] S2, the thickness of the center point of all the gallium nitride wafers from the starting wafer is measured, and the serial number and thickness data are recorded.

[0031] S3, the gallium nitride wafers prepared in S1 and S2 are pasted on 385 mm ceramic trays by an automatic waxing machine, 16 wafers per tray, 4 trays per group, and placed in order on a 13B single-side polishing machine. The polishing equipment has 4 pressure heads, and each pressure head processes 16 pcs of 2-inch gallium nitride wafers.

[0032] S4, the wafer processing conditions are as follows: the pressure of the pressure head is 160 kg (the corresponding pressure on the wafer is 509 g / cm 2 ); the rotation speed of the lower tray is 50 rpm, and the rotation speed of the upper tray is 45 rpm; the pH value of the diamond liquid is 7, the flow rate is 5 g / min, the diamond particle size D50 is 5 μm; the pH value of the alumina liquid is 9, the flow rate is 10 g / min, and the alumina particle size D50 is 3 μm.

[0033] S5, the thickness and surface quality of the polished wafers are measured, including measuring the center point thickness of each wafer from the starting wafer by using a gauge, and measuring the surface quality of the wafer by using a roughness meter and an electron microscope. The results are shown in Table 1.

[0034] Example Two

[0035] S1, the 2-inch gallium nitride wafer after rough grinding is cleaned, and is grouped according to thickness, with a thickness error of less than 2 μm in the same group. Each group has 64 wafers, each group has 4 trays, and each tray has 16 wafers.

[0036] S2, the thickness of the center point of all the gallium nitride wafers from the starting wafer is measured, and the serial number and thickness data are recorded.

[0037] S3, the gallium nitride wafers prepared in S1 and S2 are pasted on 385 mm ceramic trays by an automatic waxing machine, 16 wafers per tray, 4 trays per group, and placed in order on a 13B single-side polishing machine. The polishing equipment has 4 pressure heads, and each pressure head processes 16 pcs of 2-inch gallium nitride wafers.

[0038] S4, the wafer processing conditions are as follows: the pressure of the pressure head is 160 kg; the rotation speed of the lower tray is 50 rpm, and the rotation speed of the upper tray is 45 rpm; the pH value of the diamond liquid is 7, the flow rate is 5 g / min, the diamond particle size D50 is 5 μm; the pH value of the alumina liquid is 11, the flow rate is 10 g / min, and the alumina particle size D50 is 3 μm.

[0039] S5, measure the thickness and surface quality of the wafers after polishing, including measuring the center point thickness of each wafer from the starting wafer using a gauge, and measuring the surface quality of the wafer using a roughness meter and an electron microscope. The results are shown in Table 1.

[0040] Example Three

[0041] S1, clean the 2-inch gallium nitride wafers after rough polishing, group them by thickness, with a thickness error of within 2 μm in the same group. Each group has 64 wafers, each group has 4 trays, and each tray has 16 wafers.

[0042] S2, measure the center point thickness of all the gallium nitride wafers from the starting wafer, and record the serial number and thickness data.

[0043] S3, use an automatic waxing machine to paste the gallium nitride wafers prepared in S1 and S2 on 385 mm ceramic trays, 16 wafers per tray, 4 trays per group, and place them in order on a 13B single-side polishing machine. The polishing equipment has a total of 4 pressure heads, and each pressure head processes 16 pcs of 2-inch gallium nitride wafers.

[0044] S4, wafer processing conditions: pressure of the pressure head is 160 kgf / cm 2 ; the lower tray rotation speed is 50 rpm, and the upper tray rotation speed is 45 rpm; the pH value of the diamond liquid is 7, the flow rate is 5 g / min, the diamond particle size D50 is 5 μm; the pH value of the alumina liquid is 13, the flow rate is 10 g / min, and the alumina particle size D50 is 3 μm.

[0045] S5, measure the thickness and surface quality of the wafers after polishing, including measuring the center point thickness of each wafer from the starting wafer using a gauge, and measuring the surface quality of the wafer using a roughness meter and an electron microscope. The results are shown in Table 1.

[0046] Example Four

[0047] S1, clean the 2-inch gallium nitride wafers after rough polishing, group them by thickness, with a thickness error of within 2 μm in the same group. Each group has 64 wafers, each group has 4 trays, and each tray has 16 wafers.

[0048] S2, measure the center point thickness of all the gallium nitride wafers from the starting wafer, and record the serial number and thickness data.

[0049] S3, use an automatic waxing machine to paste the gallium nitride wafers prepared in S1 and S2 on 385 mm ceramic trays, 16 wafers per tray, 4 trays per group, and place them in order on a 13B single-side polishing machine. The polishing equipment has a total of 4 pressure heads, and each pressure head processes 16 pcs of 2-inch gallium nitride wafers.

[0050] S4, wafer processing conditions: pressure head pressure 160 kg; lower plate speed 50 rpm, upper plate speed 45 rpm; diamond liquid pH 7, flow rate 5 g / min, diamond particle size D50 5 μm; alumina liquid pH 9, flow rate 10 g / min, alumina particle size D50 1 μm.

[0051] S5, measure the thickness and surface quality of the polished wafer, including measuring the center point thickness of each wafer from the starting wafer using a scale, and measuring the surface quality of the wafer using a roughness meter and an electron microscope. The results are shown in Table 1.

[0052] Example Five

[0053] S1, clean the coarsely ground 2-inch gallium nitride wafers, group them by thickness, and the thickness error of the same group is within 2 μm. Each group has 64 wafers, each group has 4 trays, and each tray has 16 wafers.

[0054] S2, measure the center point thickness of all the gallium nitride wafers from the starting wafer, and record the serial number and thickness data.

[0055] S3, the gallium nitride wafers prepared in S1 and S2 are pasted on 385 mm ceramic trays using an automatic waxing machine, 16 wafers per tray, 4 trays per group, and placed in order on a 13B single-sided polishing machine. The polishing equipment has 4 pressure heads, and each pressure head processes 16 pcs of 2-inch gallium nitride wafers.

[0056] S4, wafer processing conditions: pressure head pressure 160 kg; lower plate speed 50 rpm, upper plate speed 45 rpm; diamond liquid pH 7, flow rate 5 g / min, diamond particle size D50 5 μm; alumina liquid pH 11, flow rate 10 g / min, alumina particle size D50 1 μm.

[0057] S5, measure the thickness and surface quality of the polished wafer, including measuring the center point thickness of each wafer from the starting wafer using a scale, and measuring the surface quality of the wafer using a roughness meter and an electron microscope. The results are shown in Table 1.

[0058] Example Six

[0059] S1, clean the coarsely ground 2-inch gallium nitride wafers, group them by thickness, and the thickness error of the same group is within 2 μm. Each group has 64 wafers, each group has 4 trays, and each tray has 16 wafers.

[0060] S2, measure the center point thickness of all the gallium nitride wafers from the starting wafer, and record the serial number and thickness data.

[0061] S3, the gallium nitride wafer prepared in S1, S2 is pasted on the 385mm ceramic disc by automatic waxing machine, 16 pieces per disc, 4 discs per group, and placed on the 13B single side polishing machine in order. The polishing equipment has 4 pressure heads, and 16pcs 2-inch gallium nitride wafers are processed per pressure head.

[0062] S4, wafer processing conditions: pressure of the pressure head is 160kg; the rotation speed of the lower disc is 50rpm, and the rotation speed of the upper disc is 45rpm; the pH value of the diamond liquid is 7, the flow rate is 5g / min, and the diamond particle size D50 is 5μm; the pH value of the alumina liquid is 13, the flow rate is 10g / min, and the alumina particle size D50 is 1μm.

[0063] S5, the thickness and surface quality of the polished wafer are measured, including measuring the center point thickness of each wafer from the starting piece by using the scale, and measuring the surface quality of the wafer by using the roughness meter and electron microscope. The results are shown in Table 1.

[0064] Comparative Example

[0065] Process before improvement:

[0066] S1, the 2-inch gallium nitride wafer after rough grinding is cleaned, and grouped according to thickness, and the thickness error of the same group is within 2μm. 64 pieces per group, 4 discs per group, and 16 pieces per disc.

[0067] S2, the center point thickness of all the gallium nitride wafers from the starting piece is measured, and the serial number and thickness data are recorded.

[0068] S3, the gallium nitride wafer prepared in S1, S2 is pasted on the 385mm ceramic disc by automatic waxing machine, 16 pieces per disc, 4 discs per group, and placed on the 13B single side polishing machine in order. The polishing equipment has 4 pressure heads, and 16pcs 2-inch gallium nitride wafers are processed per pressure head.

[0069] S4, wafer processing conditions: pressure of the pressure head is 160kg; the rotation speed of the lower disc is 50rpm, and the rotation speed of the upper disc is 45rpm; the pH value of the diamond liquid is 7, the flow rate is 5g / min, and the diamond particle size D50 is 3μm.

[0070] S5, the thickness and surface quality of the polished wafer are measured, including measuring the center point thickness of each wafer from the starting piece by using the scale, and measuring the surface quality of the wafer by using the roughness meter and electron microscope. The results are shown in Table 1.

[0071] Table 1: Comparison of gallium nitride wafer performance before and after polishing process improvement

[0072]

[0073] Note: the diamond content of each example diamond liquid is 60 carat / liter, the alumina content of each example alumina liquid is 5 wt%, and no recycle liquid is used.

[0074] Finally, it should be noted that the above only for the preferred embodiments of the present application, and is not intended to limit the present application, although the foregoing embodiments of the present application has been described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement of the technical solutions described in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included within the scope of the present application.

Claims

1. A gallium nitride wafer polishing process, characterized in that: During the grinding process of gallium nitride wafers, diamond polishing slurry and alkaline polishing slurry are added simultaneously. The abrasive particle size D50 of the alkaline polishing slurry is smaller than the diamond particle size D50 of the diamond polishing slurry. The ratio of the abrasive particle size D50 of the alkaline polishing slurry to the diamond particle size D50 of the diamond polishing slurry is 0.2~0.6:1; The pH value of the diamond polishing slurry is 6~8, and the diamond particle size D50 is 3~10μm; The diamond grinding slurry has a diamond particle size D50 of 5 μm; The alkaline polishing slurry is an alumina polishing slurry with a pH value of 9-13; the diamond polishing slurry has a diamond content of 40-80 carats / liter, the alkaline polishing slurry has an abrasive content of 3-7 wt%, and the flow rate ratio of the diamond polishing slurry to the alkaline polishing slurry is 1:1-2.

2. The gallium nitride wafer polishing process according to claim 1, characterized in that: The alkaline grinding fluid is an alumina grinding fluid with a pH value of 11.

3. The gallium nitride wafer polishing process according to claim 1, characterized in that: Gallium nitride wafers are ground using a resin-copper disk.

4. The gallium nitride wafer polishing process according to claim 3, characterized in that: Pressure 450-600g / cm 2 The speed ratio of the upper and lower plates is 0.8-0.9, and the flow rate of the diamond grinding fluid is 3-10 g / min.

5. The gallium nitride wafer polishing process according to claim 1, characterized in that: The diamond polishing fluid and alkaline polishing fluid are ultrasonically treated before being added.

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