Method for improving surface quality of gallium arsenide wafer

Abstract

The invention belongs to the field of semiconductors, and particularly discloses a method for improving the surface quality of a gallium arsenide wafer. According to the method, the specific polishing solution is adopted for chemically and mechanically polishing the gallium arsenide, chemical and mechanical actions in the polishing process are matched with each other, the wafer falling rate in the gallium arsenide polishing process is increased, the wafer surface roughness is reduced, and the polishing quality is improved. And the surface of the polished gallium arsenide wafer is free of obvious corrosion pits, obvious lines, polishing solution residues, scratches and other defects, and the purpose of improving the overall quality of the surface of the gallium arsenide wafer is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of semiconductors, and particularly relates to a method for improving the surface quality of a gallium arsenide wafer. BACKGROUND

[0002] Gallium arsenide (GaAs) semiconductor compounds are important semiconductor materials next only to silicon. A gallium arsenide wafer is made of a gallium arsenide single crystal material synthesized and grown from pure arsenic and gallium, and is made after slicing, grinding, polishing and cleaning processes. The polishing process polishes and removes a damage layer of the gallium arsenide wafer surface remaining from previous processes, so that the wafer surface is flat, and it is desired to control the surface roughness as appropriate as possible, so that it is easier to adhere and deposit a target object as a substrate, and is a key process to achieve the requirements of an epitaxial process. The polishing process mainly relies on chemical action in a polishing liquid and mechanical action of mechanical polishing to achieve the precision requirements of the wafer surface. There are many factors in the polishing process that affect the precision of the wafer surface. At present, the polishing rate is usually about 0.5 μm / min, the dropping speed is slow, and the processing cycle is long; and the roughness of the wafer is more than 0.25 nm, and the roughness needs to be further reduced to meet the more uniform growth of the gallium arsenide downstream epitaxial layer growth. When polishing the gallium arsenide wafer, it is difficult to control the wafer surface roughness within a suitable range, and the wafer surface dropping rate is low. To polish and remove the damage layer on the surface of the previous process to make it flat, the overall polishing time is long. If the polishing rate is directly increased, the roughness is increased, and the polishing time is shortened, it will easily cause corrosion pits on the wafer surface or surface residues of the polishing liquid and obvious lines or even scratches, resulting in low surface quality. Therefore, it is still necessary to develop a new polishing process to achieve the purpose of obtaining better gallium arsenide wafer surface quality at a higher polishing rate. SUMMARY

[0003] In view of the above problems of the prior art related to poor gallium arsenide wafer surface polishing quality, the present application provides a method for improving the surface quality of a gallium arsenide wafer.

[0004] To achieve the above-mentioned purpose, the specific technical solutions include the following:

[0005] In a first aspect, the present application provides a polishing liquid for a gallium arsenide wafer, which comprises the following components with the mass concentrations: sodium thiosulfate 5-15 g / L, H2O2 0.001-0.01 g / L, sodium dichloroisocyanurate 5-10 g / L, acid sodium carbonate 1-6 g / L, sodium sulfate 5-15 g / L, and sodium polyphosphate 5-10 g / L, with the balance being water.

[0006] The polishing liquid for gallium arsenide wafer can provide an oxidation environment by H2O2, oxidize the surface of the gallium arsenide into metal oxide, form a soft oxide layer which is easy to be removed mechanically, and improve the removal rate; sodium thiosulfate can dissolve the oxide on the surface of the gallium arsenide synchronously, avoid the surface of the gallium arsenide from being excessively oxidized to form a dense oxide film; sodium dichloroisocyanurate can ensure the oxidation reaction on the surface of the gallium arsenide to proceed continuously and uniformly, and its strong oxidizing property can decompose residual organic matters, further improve the removal rate of the surface of the gallium arsenide and reduce the roughness; sodium polyphosphate can adjust the pH and avoid the precipitation of insoluble hydroxide, improve the removal rate and reduce the roughness; acid sodium carbonate can increase the ionic strength of the solution, reduce the adsorption of impurity particles on the surface of the gallium arsenide wafer due to the electrostatic effect, and avoid the damage and roughness increase of the surface of the gallium arsenide caused by residual particles; sodium sulfate can prevent the surface of the gallium arsenide from being excessively etched due to the too fast dissolution of the surface of the gallium arsenide. Therefore, the components in the polishing liquid of the present application can cooperate with each other, on the basis of improving the removal rate of the wafer, reduce the roughness of the surface of the wafer, avoid the surface of the wafer from appearing obvious corrosion pits, lines, scratches, residual polishing liquid and surface whitening defects, and improve the overall quality of the surface of the gallium arsenide wafer.

[0007] In addition, the use amount of each component in the polishing liquid also has a significant influence on the polishing quality. For example, if H2O2 is excessive, the oxidation layer is thickened but not dissolved enough, and the polishing rate is limited by the mechanical removal efficiency; if sodium thiosulfate is excessive, the surface of the gallium arsenide is directly dissolved to cause corrosion, and H2O2 and sodium thiosulfate can realize the matching of the oxidation and dissolution rates within the above-mentioned use amount range, maximize the polishing efficiency, and take into account the polishing surface quality.

[0008] Preferably, the polishing liquid for gallium arsenide wafer comprises the following components with the following mass concentrations: sodium thiosulfate 10-14 g / L, H2O2 0.004-0.005 g / L, sodium dichloroisocyanurate 6-8 g / L, acid sodium carbonate 3-5 g / L, sodium sulfate 8-10 g / L, and sodium polyphosphate 7-8 g / L, and the balance is water.

[0009] Preferably, the polishing liquid for gallium arsenide wafer comprises the following components with the following mass concentrations: sodium thiosulfate 10-14 g / L, H2O2 0.004-0.005 g / L, sodium dichloroisocyanurate 3-4 g / L, acid sodium carbonate 3-5 g / L, sodium sulfate 8-10 g / L, and sodium polyphosphate 7-8 g / L, and the balance is water.

[0010] Preferably, in the polishing liquid for gallium arsenide wafer, the mass fraction of H2O2 in sodium thiosulfate is 0.01%-0.05%, specifically, it can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, or a range formed by any two of these values.

[0011] Preferably, in the polishing liquid for gallium arsenide wafer, the sodium dichloroisocyanurate accounts for 25%-55% of the mass of the sodium thiosulfate, specifically, it can be 25%, 30%, 40%, 45%, 50%, 55%, or a range formed by any two of these values.

[0012] Preferably, in the polishing liquid for gallium arsenide wafer, the sodium dichloroisocyanurate accounts for 25%-55% of the mass of the sodium thiosulfate, specifically, it can be 25%, 30%, 40%, 45%, 50%, 55%, or a range formed by any two of these values.

[0013] In a second aspect, the present application provides a method for improving the surface quality of a gallium arsenide wafer, comprising the following steps:

[0014] S1, mechanically polishing a gallium arsenide wafer to be polished to obtain a pretreated gallium arsenide wafer;

[0015] S2, using the polishing liquid for gallium arsenide wafer as a polishing liquid to chemically mechanically polish the pretreated gallium arsenide wafer, and then cleaning to obtain a gallium arsenide wafer after polishing.

[0016] In the method of the present application, the gallium arsenide wafer to be polished is sequentially subjected to mechanical polishing and chemical mechanical polishing. The wafer surface is pretreated by the mechanical action of mechanical polishing, and then the gallium arsenide wafer is subjected to chemical and mechanical action by using the polishing liquid with a specific formula in chemical mechanical polishing, so that the wafer is uniformly and stably polished. On the basis of high drop rate, the wafer surface is flattened and the roughness is appropriately reduced, the wafer surface quality is improved, and the subsequent requirements of the gallium arsenide wafer as an epitaxial growth substrate are met. The chemical action and mechanical action of the specific polishing liquid are matched to improve the wafer drop rate, wafer surface roughness and quality during polishing, shorten the construction period, and the method of the present application is stable. In addition to processing pure gallium arsenide wafers, it can also process doped gallium arsenide wafers, has a wide range of applications, and has a relatively low cost.

[0017] Preferably, in step S1, the rotation speed in the mechanical polishing is 20-80 rad / min, preferably 40-60 rad / min, more specifically, it can be 20 rad / min, 30 rad / min, 40 rad / min, 50 rad / min, 60 rad / min, 70 rad / min, 80 rad / min, or a range formed by any two of these values.

[0018] Preferably, in step S1, the vacuum disc pressure in the mechanical polishing is 500-1500 N, specifically, it can be 500 N, 700 N, 900 N, 1100 N, 1300 N, 1500 N, or a range formed by any two of these values.

[0019] Preferably, in step S2, the flow rate of the polishing solution is 800-1200 mL / min, specifically, it can be 800 mL / min, 850 mL / min, 900 mL / min, 950 mL / min, 1000 mL / min, 1050 mL / min, 1100 mL / min, 1150 mL / min, 1200 mL / min, or a range formed by any two of these values.

[0020] Preferably, in step S2, the temperature of the polishing solution is 10-20℃, specifically, it can be 10℃, 11℃, 12℃, 13℃, 14℃, 15℃, 16℃, 17℃, 18℃, 19℃, 20℃, or a range formed by any two of these values.

[0021] Preferably, in step S2, the rotation speed in the chemical mechanical polishing is 20-80 rad / min, specifically, it can be 20 rad / min, 30 rad / min, 40 rad / min, 50 rad / min, 60 rad / min, 70 rad / min, 80 rad / min, or a range formed by any two of these values.

[0022] Preferably, in step S2, the vacuum disc pressure in the chemical mechanical polishing is 500-1500 N, specifically, it can be 500 N, 700 N, 900 N, 1100 N, 1300 N, 1500 N, or a range formed by any two of these values.

[0023] During the chemical mechanical polishing process, the components and their amounts of the polishing solution, the temperature of the polishing solution, the polishing rotation speed, and the polishing pressure cooperate with each other, which can significantly improve the quality of the surface of the gallium arsenide wafer.

[0024] In a third aspect, the present application provides a gallium arsenide wafer, which is prepared by the method for improving the surface quality of the gallium arsenide wafer, and the average roughness of the surface of the gallium arsenide wafer is 0.1-0.25 nm, specifically, it can be 0.1 nm, 0.12 nm, 0.14 nm, 0.16 nm, 0.18 nm, 0.2 nm, 0.22 nm, 0.24 nm, 0.25 nm, or a range formed by any two of these values.

[0025] By the method of the present application, the roughness of the surface of the gallium arsenide wafer can be significantly reduced while having a high drop rate during the polishing process, and the wafer surface has no obvious defects such as corrosion pits, lines, no polishing solution residue, and scratches, and the overall quality of the wafer surface is good.

[0026] Compared with the prior art, the present application has the following beneficial effects: the present application uses a specific polishing liquid to polish gallium arsenide by chemical mechanical polishing, the chemical and mechanical actions are coordinated with each other in the polishing process, the wafer drop rate in the gallium arsenide polishing is improved, the wafer surface roughness is reduced, and the polished gallium arsenide wafer surface has no obvious defects such as corrosion pits, obvious lines, polishing liquid residues and scratches, and the purpose of improving the overall quality of the gallium arsenide wafer surface is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The flowchart of the method for improving the surface quality of the gallium arsenide wafer of the present application.

[0028] Figure 2 The surface picture of the polished gallium arsenide wafer of Example 1 is obtained.

[0029] Figure 3 The surface picture of the polished gallium arsenide wafer of Comparative Example 6 is obtained.

[0030] Figure 4 The surface picture of the polished gallium arsenide wafer of Example 2 is obtained.

[0031] Figure 5 The surface picture of the polished gallium arsenide wafer of Example 3 is obtained.

[0032] Figure 6 The surface picture of the polished gallium arsenide wafer of Example 4 is obtained.

[0033] Figure 7 The surface picture of the polished gallium arsenide wafer of Example 5 is obtained.

[0034] Figure 8 The surface picture of the polished gallium arsenide wafer of Example 6 is obtained. DETAILED DESCRIPTION

[0035] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available unless otherwise specified.

[0036] The gallium arsenide wafers to be polished used in the following examples and comparative examples have a diameter of 4 inches, a surface roughness of 0.6-0.8 nm, a flatness of (≤20 μm), and a thickness of 300-650 μm.

[0037] Example 1

[0038] A method for improving the surface quality of a gallium arsenide wafer, the flowchart is as shown in Figure 1 The specific steps include the following steps:

[0039] S1, a polishing solution is prepared according to the following components with the following mass concentrations: sodium thiosulfate 13.9 g / L, H2O2 0.0045 g / L, sodium dichloroisocyanurate 7 g / L, sodium acid carbonate 4 g / L, sodium sulfate 9 g / L, and sodium polyphosphate 7.5 g / L, wherein the solvent is 1 L of deionized water, and the raw material of H2O2 is hydrogen peroxide with a mass fraction of 28-32%, to obtain the polishing solution;

[0040] S2, a gallium arsenide wafer to be polished is prepared;

[0041] S3, the gallium arsenide wafer to be polished is fixed in the wafer clamping part of the polishing machine, mechanical polishing is performed on the workbench of the polishing machine without adding the polishing solution, the wafer is pre-processed and polished, the rotation speed of polishing is 40 rad / min, the time is 5 min, and the wafer is subjected to pressure by a vacuum disc, wherein the pressure of the wafer by the vacuum disc is 900 N, to obtain a pre-processed gallium arsenide wafer;

[0042] S4, the polishing machine is continuously operated at a rotation speed of 40 rad / min and a vacuum disc pressure of 900 N, the polishing solution prepared in step S1 is slowly and uniformly injected onto the polishing workbench during the operation of the polishing machine, and the pre-processed gallium arsenide wafer is subjected to chemical mechanical polishing at the same time, so that a mirror surface is formed on the wafer surface, the processing time is 5 min, the flow rate of the polishing solution is 1000 mL / min, the temperature of the injected polishing solution is 15°C, and after the chemical mechanical polishing, the gallium arsenide wafer is cleaned to obtain a polished gallium arsenide wafer;

[0043] S5, atomic force microscopy (AFM) is used to detect the surface of the polished gallium arsenide wafer, the time of the polishing process is recorded, and the thickness change of the gallium arsenide wafer before and after polishing is measured to calculate the drop rate, the drop rate (μm / min) = drop (thickness change value before and after polishing, unit: μm) / total polishing time (min).

[0044] Examples 2-6

[0045] The process of examples 2-6 is referred to example 1, the difference is the amount of components in the polishing solution, the polishing solution temperature, the polishing rotation speed and the vacuum disc pressure, see table 1 in detail.

[0046] Comparative examples 1-6

[0047] The process of comparative examples 1-6 is referred to example 1, the difference is the components and the amount of the polishing solution, see table 1 in detail.

[0048] The surface of the polished GaAs wafer is tested by AFM to observe the surface roughness, whether there are lines, scratches, polishing liquid residues, whitening and other defects, and to test the average roughness of the surface, and then the wafer quality is evaluated as a whole, and the specific results are shown in Table 2. The surface effect of the GaAs wafer after polishing obtained by AFM testing of some embodiments and comparative examples of the present application is shown in Figures 2-8 .

[0049] Table 1

[0050]

[0051] Table 2

[0052]

[0053]

[0054] From the above examples and comparative examples, it can be seen that the specific polishing liquid is used in combination with appropriate polishing speed and pressure to improve the polishing quality of the surface of the GaAs wafer and improve the surface roughness.

[0055] From Examples 1-6, it can be seen that changing the component amount, temperature, polishing speed and polishing vacuum chuck pressure of the polishing liquid has a certain influence on the quality of the GaAs wafer surface. Through mutual cooperation of the above influencing factors, a suitable wafer surface roughness and high-quality wafer surface can be obtained.

[0056] From Examples 6 and Comparative Examples 1-6, it can be seen that the sodium thiosulfate, H2O2, sodium dichloroisocyanurate, sodium polyphosphate and other components in the polishing liquid cooperate with each other to obtain a high-quality GaAs wafer; the sodium polyphosphate can improve the wafer drop rate and thus improve the surface quality of the wafer.

[0057] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A polishing slurry for gallium arsenide wafers, characterized in that, The components include the following mass concentrations: sodium thiosulfate 5-15 g / L, H2O2 0.001-0.01 g / L, sodium dichloroisocyanurate 5-10 g / L, sodium carbonate 1-6 g / L, sodium sulfate 5-15 g / L, sodium polyphosphate 5-10 g / L, and the balance being water.

2. The polishing slurry for gallium arsenide wafers as described in claim 1, characterized in that, The components include the following mass concentrations: sodium thiosulfate 10-14 g / L, H2O2 0.004-0.005 g / L, sodium dichloroisocyanurate 6-8 g / L, sodium carbonate 3-5 g / L, sodium sulfate 8-10 g / L, sodium polyphosphate 7-8 g / L, and the balance being water.

3. The polishing slurry for gallium arsenide wafers as described in claim 1, characterized in that, The composition includes the following components in the indicated mass concentrations: sodium thiosulfate 10-14 g / L, H2O2 0.004-0.005 g / L, sodium dichloroisocyanurate 3-4 g / L, sodium acid carbonate 3-5 g / L, sodium sulfate 8-10 g / L, sodium polyphosphate 7-8 g / L, with the balance being water.

4. The polishing slurry for gallium arsenide wafers as described in claim 1, characterized in that, In the polishing solution for gallium arsenide wafers, the H2O2 accounts for 0.01%-0.05% of the mass of sodium thiosulfate.

5. A method for improving the surface quality of gallium arsenide wafers, characterized in that, Includes the following steps: S1. The gallium arsenide wafer to be polished is mechanically polished to obtain a pretreated gallium arsenide wafer; S2. Using the gallium arsenide wafer polishing slurry according to any one of claims 1-4 as the polishing slurry, the pretreated gallium arsenide wafer is subjected to chemical mechanical polishing and cleaning to obtain the polished gallium arsenide wafer.

6. The method for improving the surface quality of gallium arsenide wafers as described in claim 5, characterized in that, In step S1, the rotational speed during mechanical polishing is 20-80 rad / min, and the vacuum disk pressure during mechanical polishing is 500-1500 N.

7. The method for improving the surface quality of gallium arsenide wafers as described in claim 5, characterized in that, In step S2, the flow rate of the polishing fluid is 800-1200 mL / min.

8. The method for improving the surface quality of gallium arsenide wafers as described in claim 5, characterized in that, In step S2, the temperature of the polishing fluid is 10-20℃.

9. The method for improving the surface quality of gallium arsenide wafers as described in claim 5, characterized in that, In step S2, the rotational speed in the chemical mechanical polishing is 20-80 rad / min, and the vacuum disk pressure in the chemical mechanical polishing is 500-1500 N.

10. A gallium arsenide wafer, characterized in that, The method for improving the surface quality of gallium arsenide wafers according to any one of claims 5-9 is used to prepare the wafers, wherein the average surface roughness of the gallium arsenide wafers is 0.1-0.25 nm.

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