A method for reducing the concentration of silicon impurities on the surface of indium phosphide wafers
By using a SiO2-free fine polishing slurry and a mixed weak acid solution, the problem of high silicon impurity concentration on the surface of indium phosphide wafers was solved, resulting in a significant reduction in silicon impurity concentration and an improvement in surface quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHUHAI DINGTAI XINYUAN CRYSTAL CO LTD
- Filing Date
- 2022-09-07
- Publication Date
- 2026-05-15
AI Technical Summary
In the existing technology, the silicon impurity concentration is high during the surface treatment of indium phosphide wafers, which affects the wafer quality. In addition, the SiO2 in the traditional polishing solution causes silicon impurity residue, which is difficult to effectively reduce.
The process involves using a SiO2-free fine polishing solution and a mixed weak acid solution. The fine polishing solution contains tripolyphosphate, thiosulfate, bicarbonate, and citric acid, while the mixed weak acid solution contains HF acid, NH4F, and H2O2. Through chemical reactions and corrosion, the concentration of silicon impurities is reduced.
It effectively reduces the silicon impurity concentration on the surface of indium phosphide wafers from 10¹⁵ atom/cm² to 10¹² atom/cm², improving surface flatness and uniformity.
Smart Images
Figure CN116230518B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor materials technology, and specifically relates to a method for reducing the concentration of silicon impurities on the surface of indium phosphide wafers. Background Technology
[0002] Indium phosphide (InP) material has high electron mobility, a wide bandgap range, and a lattice constant that matches that of ternary materials such as InGaAs or InAlAs. It is widely used in high-speed optical communication, millimeter-wave imaging, high-speed, high-frequency electronic devices, and other fields. Indium phosphide wafers are semiconductor materials composed of compounds of group III element In and group V element P. The performance of all InP devices depends on the quality of the InP substrate material and surface. Using molecular beam epitaxy (MBE) and metal-organic vapor deposition (MOCVD) techniques to grow epitaxial layers on InP substrates, the polishing quality and cleanliness of the surface of the indium phosphide wafer are crucial. Chemical wet cleaning processes are widely used as pretreatment before wafer epitaxy. The purpose of these wet chemical treatments is to create a surface free of metal impurities, a particle-free surface, and a very thin oxide layer. In order to achieve high-quality indium phosphide wafers ready to use out of the box, the surface of the indium phosphide wafer must meet the following three conditions: (1) the surface is free of metal impurities and particles; (2) the surface oxide layer must be completely removed after thermal cleaning; and (3) the surface must be flat.
[0003] Indium phosphide (InP) wafers are semiconductor materials composed of a compound of group III element In and group V element P. The chemical properties of group III and group V elements are inherently unstable, and thermal stress during material growth can easily cause deviations in the chemical stoichiometry of group III In and group V P. Furthermore, the different chemical properties of group III and group V P elements can lead to the adsorption of more impurities on the wafer surface. Total internal reflection X-ray fluorescence (TXRF) uses extremely low-angle X-rays to excite the polished wafer surface to obtain the concentration of surface metallic contaminants. The concentration of residual silicon on InP wafer surfaces is generally high. TXRF technology detected non-metallic impurities Si, S, and Cl; and metal ions K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zn, with impurity concentrations reaching 10¹⁵ atom / cm³. 2 The demand for indium phosphide (IP) wafers is quite high. Due to the continuous development of optoelectronic and microelectronic devices, the international demand for IPP wafers is also increasing, but it is mainly concentrated in sulfur-doped N-type and iron-doped semi-insulating wafers. Fe, as a dopant, is widely used to compensate for the remaining charge carriers (shallow donors) in IPP wafers to achieve semi-insulating properties. The segregation coefficient of Fe in IPP wafers is very small (0.001), making it easy to form non-radiative recombination centers. This also leads to the easier adsorption of high-concentration impurities on the surface of the Fe-doped semi-insulating InP substrate, resulting in a significant impact on the background concentration of the epitaxial layer, especially the Si impurity concentration.
[0004] In traditional surface treatment processes, polishing of indium phosphide wafers mostly uses polishing slurries containing SiO2. The silicon dioxide in the polishing slurry mainly plays the role of removing excess silicon and reducing surface roughness. However, using polishing slurries containing SiO2 will result in a large amount of Si impurities remaining on the surface of the indium phosphide wafer, thus affecting the final quality of the indium phosphide wafer.
[0005] Therefore, it is essential to strictly control silicon contamination and its sources during the processing and cleaning of indium phosphide wafers, reduce the impurity concentration on the surface of indium phosphide wafers, and improve the surface flatness and uniformity. Summary of the Invention
[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for reducing the silicon impurity concentration on the surface of indium phosphide wafers, which can not only reduce the impurity concentration on the surface of indium phosphide wafers, but also improve the surface flatness and uniformity.
[0007] This invention provides a method for reducing the concentration of silicon impurities on the surface of indium phosphide wafers.
[0008] Specifically, a method for reducing the concentration of silicon impurities on the surface of an indium phosphide wafer includes the following steps:
[0009] The indium phosphide wafers are first rough polished, then fine polished with a fine polishing solution; after fine polishing, the indium phosphide wafers are cleaned and dried, and then treated with a mixed weak acid.
[0010] The fine polishing solution contains tripolyphosphate, thiosulfate, bicarbonate and citric acid;
[0011] The mixed weak acid comprises HF acid, NH4F and H2O2.
[0012] Preferably, in the fine polishing solution, the mass concentration of the tripolyphosphate is 0.5%-5%, the mass concentration of the thiosulfate is 3%-10%, the mass concentration of the bicarbonate is 1%-6%, and the mass concentration of the citric acid is 0.1-2.0%. More preferably, in the fine polishing solution, the mass concentration of the tripolyphosphate is 1%-3%, the mass concentration of the thiosulfate is 3%-8%, the mass concentration of the bicarbonate is 1%-5%, and the mass concentration of the citric acid is 0.5-1.5%.
[0013] Preferably, the pH value of the fine polishing solution is 5-6.
[0014] Preferably, the fine polishing solution is composed of tripolyphosphate, thiosulfate, bicarbonate, citric acid and water.
[0015] Preferably, the preparation method of the fine polishing slurry includes the following steps:
[0016] Sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate, and citric acid are added sequentially to deionized water, dissolved, and the pH value is controlled between 5 and 6 to obtain the fine polishing solution.
[0017] Preferably, during fine polishing, the fine polishing liquid is diluted with water at a volume ratio of 1:(5-20) before use; more preferably, during fine polishing, the fine polishing liquid is diluted with water at a volume ratio of 1:(8-15) before use.
[0018] Preferably, during fine polishing, the flow rate of the fine polishing liquid is 300-500 mL / min; more preferably, during fine polishing, the flow rate of the fine polishing liquid is 350-450 mL / min.
[0019] Preferably, the polishing pressure is 1-3 psi and the polishing time is 5-15 minutes. More preferably, the polishing pressure is 1-3 psi and the polishing time is 8-12 minutes.
[0020] Preferably, in the mixed weak acid, the volume fraction of the HF acid is 0.5%-2%, the mass concentration of the NH4F is 3.5-6.0 g / L, and the volume fraction of the H2O2 is 1.0%-10.0%; more preferably, the volume fraction of the HF acid is 0.5%-1.5%, the mass concentration of the NH4F is 3.5-6.0 g / L, and the volume fraction of the H2O2 is 1.0%-5.0%.
[0021] Preferably, the treatment time of the indium phosphide wafer with the mixed weak acid is 60-120s, and the treatment temperature of the indium phosphide wafer with the mixed weak acid is 10-25℃; more preferably, the treatment time of the indium phosphide wafer with the mixed weak acid is 80-100s, and the treatment temperature of the indium phosphide wafer with the mixed weak acid is 10-20℃.
[0022] Preferably, after treating the indium phosphide wafer with a mixed weak acid, the process further includes rinsing the indium phosphide wafer with water.
[0023] More specifically, a method for reducing the concentration of silicon impurities on the surface of an indium phosphide wafer includes the following steps:
[0024] (1) A liquid wax coating machine is used to coat and fix the ground indium phosphide wafers: Liquid wax is introduced onto the indium phosphide wafers via an inlet method. The indium phosphide wafers are adsorbed onto the tray and can rotate at high speed. At a set time, liquid wax is dripped onto the back of the high-speed rotating indium phosphide wafers. After the liquid wax coating is completed, the robot arm leaves the tray and the indium phosphide wafers are flipped and attached to the ceramic disk on which the indium phosphide wafers are fixed. The air bladder above the wax coating machine presses down on the indium phosphide wafers coated with liquid wax and fixed to the ceramic disk, pressing the indium phosphide wafers firmly onto the ceramic disk. After the indium phosphide wafers are pressed firmly on the ceramic disk, there will be liquid wax squeezed out around them. This is wiped away with an organic solvent to ensure that there is no liquid wax residue around the indium phosphide wafers and on the ceramic disk.
[0025] (2) Rough polishing of indium phosphide wafers: The ceramic disk holding the indium phosphide wafers is installed in a single-sided polishing machine. Under polishing pressure of 4-8 psi and polishing fluid flow rate of 1200-1800 mL / min, rough polishing is performed for 40-45 minutes. The rough polishing fluid is prepared as follows: sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate, and silica sol are added to deionized water, and the pH is controlled between 3 and 4. The mass concentration of the tripolyphosphate is 7-9%, the mass concentration of the thiosulfate is 3-10%, the mass concentration of the bicarbonate is 8-10%, and the mass concentration of the silica is 3-5%. After rough polishing, the indium phosphide wafers are rinsed with deionized water and dried.
[0026] (3) Fine polishing of indium phosphide wafers: Polishing is performed for 5-15 minutes at a polishing pressure of 1-3 psi and a polishing solution flow rate of 300-500 mL / min. The fine polishing solution is prepared as follows: sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate, and citric acid are added sequentially to deionized water, and the pH value is controlled between 5 and 6. The mass concentration of the tripolyphosphate is 0.5%-5%, the mass concentration of the thiosulfate is 3%-10%, the mass concentration of the bicarbonate is 1%-6%, and the mass concentration of the citric acid is 0.1-2.0%. After fine polishing, the indium phosphide wafers are rinsed with deionized water and dried.
[0027] The rough polishing process can remove the surface damage layer remaining from the previous processing steps and basically achieve geometric dimensional accuracy; the fine polishing process further removes fine scratches and polishing haze and other defects from the surface of the indium phosphide wafer, achieving an atomic-level surface, reducing the roughness of the wafer surface, and improving surface flatness and uniformity.
[0028] (4) Remove the wax from the indium phosphide wafer; rinse with deionized water and dry;
[0029] (5) Treatment of indium phosphide wafers with mixed weak acid: The indium phosphide wafers are placed in a mixed weak acid solution for etching for 60-120s at a temperature of 10-20℃. The mixed weak acid solution contains HF acid, NH4F and H2O2, wherein the volume fraction of HF acid is 0.5%-2%, the mass concentration of NH4F is 3.5-6.0g / L, and the volume fraction of H2O2 is 1.0%-10.0%. Finally, the indium phosphide wafers treated with the mixed weak acid are rinsed with deionized water and dried.
[0030] Traditional cleaning processes typically use a single acid or a single alkali, which can remove silicon to some extent, but the effect is poor. This invention proposes using a mixed weak acid solution to treat indium phosphide wafers. This mixed weak acid solution contains HF acid, NH4F, and H2O2. The fluoride ions in HF can react chemically with Si ions to generate SiF4, which can be removed by water. The addition of hydrogen peroxide causes any remaining Si ions to undergo an oxidation reaction. A small amount of hydrogen peroxide oxidizes the surface Si ions to SiO2, which then readily reacts with the mixture of HF and NH4F to generate water-soluble SiF4. Simultaneously, the K and Ca ions on the surface of the indium phosphide wafer are also oxidized by a small amount of hydrogen peroxide to generate water-soluble KOH and Ca(OH)2. HF acid, NH4F, and H2O2 have a synergistic effect and are all indispensable.
[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0032] (1) The method provided by the present invention uses a SiO2-free fine polishing slurry. By adding citric acid to the fine polishing slurry, the chemical reaction between the indium phosphide wafer and the polishing slurry is enhanced. In the subsequent cleaning process, the corrosive effect of the mixed weak acid is combined, which not only reduces the adsorption of Si impurities during fine polishing, but also further reduces the residue of Si impurities on the surface of the indium phosphide wafer and other impurities in the environment during the subsequent cleaning process, so that the Si impurity content is reduced from 10% in the traditional process. 15 atom / cm 2 Reduced to 10 12 atom / cm 2 .
[0033] (2) The method provided by the present invention uses a polishing liquid without SiO2 for fine polishing, and combined with the corrosion effect of mixed weak acid, which can effectively reduce the micro-roughness of indium phosphide wafers and improve their surface flatness and uniformity. Attached Figure Description
[0034] Figure 1 An atomic force microscope image of the indium phosphide wafer obtained in Example 1;
[0035] Figure 2 An atomic force microscope image of the indium phosphide wafer obtained in Comparative Example 1. Detailed Implementation
[0036] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.
[0037] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.
[0038] Example 1
[0039] A method for reducing the concentration of silicon impurities on the surface of an indium phosphide wafer includes the following steps:
[0040] (1) A liquid wax coating machine is used to coat and fix the ground indium phosphide wafers: Liquid wax is introduced onto the indium phosphide wafers via an inlet method. The indium phosphide wafers are adsorbed onto the tray and can rotate at high speed. At a set time, liquid wax is dripped onto the back of the high-speed rotating indium phosphide wafers. After the liquid wax coating is completed, the robot arm leaves the tray, and the indium phosphide wafers are flipped and attached to the ceramic disk on which the indium phosphide wafers are fixed. The air bladder above the wax coating machine presses down on the indium phosphide wafers coated with liquid wax and fixed to the ceramic disk, pressing the indium phosphide wafers firmly onto the ceramic disk. After the indium phosphide wafers are pressed onto the ceramic disk, there will be liquid wax squeezed out around them. This is wiped away with an organic solvent to ensure that there is no liquid wax residue around the indium phosphide wafers and on the ceramic disk.
[0041] (2) Rough polishing of indium phosphide wafers: The ceramic disk holding the indium phosphide wafers was installed in a single-sided polishing machine. Polishing was performed for 40 minutes at a polishing pressure of 6 psi and a polishing fluid flow rate of 1500 mL / min using a rough polishing solution. The rough polishing solution was prepared as follows: sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate, and silica sol were added to deionized water, and the pH was controlled to approximately 3.5. The mass concentrations of tripolyphosphate, thiosulfate, bicarbonate, and silica were 8%, 5%, 9%, and 4%, respectively. After rough polishing, the indium phosphide wafers were rinsed with deionized water and dried.
[0042] (3) Fine polishing of indium phosphide wafers: Rhom & Hass polishing pads were used. Polishing was performed for 10 minutes at a polishing pressure of 2 psi and a polishing fluid flow rate of 400 mL / min. The fine polishing fluid was prepared as follows: 5000 g of deionized water was taken, and 100 g of sodium tripolyphosphate, 300 g of sodium thiosulfate, 150 g of sodium bicarbonate, and 45 g of citric acid monohydrate were added sequentially to control the pH value at 5.5. The fine polishing fluid was stirred evenly and then diluted with water at a volume ratio of 1:10 for fine polishing. After fine polishing, the indium phosphide wafers were rinsed with deionized water for 90 s and dried in a high-speed rotating spin dryer at a speed of 1000 rad / min.
[0043] (4) The indium phosphide wafer obtained in step (3) is placed in a packaging box and then rinsed in isopropanol for 60 seconds to remove wax. Then it is rinsed with deionized water at a temperature of 55°C for 60 seconds.
[0044] (5) Treatment of indium phosphide wafers with a mixed weak acid: The indium phosphide wafers obtained in step (4) were placed in a mixed weak acid solution for etching for 100 seconds at a temperature of 15°C. The mixed weak acid solution was prepared as follows: 2000 mL of deionized water was taken, 20 mL of HF acid (industrial grade) was added, 20 mL of NH4F solution with a mass concentration of 500 g / L was added, and 250 mL of H2O was added. Finally, the indium phosphide wafers treated with the mixed weak acid were rinsed with deionized water and dried.
[0045] Example 2
[0046] A method for reducing the concentration of silicon impurities on the surface of an indium phosphide wafer includes the following steps:
[0047] (1) A liquid wax coating machine is used to coat and fix the ground indium phosphide wafers: Liquid wax is introduced onto the indium phosphide wafers via an inlet method. The indium phosphide wafers are adsorbed onto the tray and can rotate at high speed. At a set time, liquid wax is dripped onto the back of the high-speed rotating indium phosphide wafers. After the liquid wax coating is completed, the robot arm leaves the tray, and the indium phosphide wafers are flipped and attached to the ceramic disk on which the indium phosphide wafers are fixed. The air bladder above the wax coating machine presses down on the indium phosphide wafers coated with liquid wax and fixed to the ceramic disk, pressing the indium phosphide wafers firmly onto the ceramic disk. After the indium phosphide wafers are pressed onto the ceramic disk, there will be liquid wax squeezed out around them. This is wiped away with an organic solvent to ensure that there is no liquid wax residue around the indium phosphide wafers and on the ceramic disk.
[0048] (2) Rough polishing of indium phosphide wafers: The ceramic disk holding the indium phosphide wafers was installed in a single-sided polishing machine. Polishing was performed for 40 minutes at a polishing pressure of 6 psi and a polishing fluid flow rate of 1500 mL / min using a rough polishing solution. The rough polishing solution was prepared as follows: sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate, and silica sol were added to deionized water, and the pH was controlled to approximately 3.5. The mass concentrations of tripolyphosphate, thiosulfate, bicarbonate, and silica were 8%, 5%, 9%, and 4%, respectively. After rough polishing, the indium phosphide wafers were rinsed with deionized water and dried.
[0049] (3) Fine polishing of indium phosphide wafers: Rhom & Hass polishing pads were used. Polishing was performed for 10 minutes at a polishing pressure of 3 psi and a polishing fluid flow rate of 450 mL / min. The fine polishing fluid was prepared as follows: 5000 g of deionized water was taken, and 150 g of sodium tripolyphosphate, 250 g of sodium thiosulfate, 120 g of sodium bicarbonate, and 40 g of citric acid monohydrate were added sequentially to control the pH value at 5.5. The fine polishing fluid was stirred evenly and then diluted with water at a volume ratio of 1:10 for fine polishing. After fine polishing, the indium phosphide wafers were rinsed with deionized water for 90 s and dried in a high-speed rotating spin dryer at a speed of 1000 rad / min.
[0050] (4) The indium phosphide wafer obtained in step (3) is placed in a packaging box and then rinsed in isopropanol for 60 seconds to remove wax. Then it is rinsed with deionized water at a temperature of 55°C for 60 seconds.
[0051] (5) Treatment of indium phosphide wafers with a mixed weak acid: The indium phosphide wafers obtained in step (4) were placed in a mixed weak acid solution for etching for 100 seconds at a temperature of 15°C. The mixed weak acid solution was prepared as follows: 2000 mL of deionized water was taken, 20 mL of HF acid (industrial grade) was added, 20 mL of NH4F solution with a mass concentration of 500 g / L was added, and 250 mL of H2O was added. Finally, the indium phosphide wafers treated with the mixed weak acid were rinsed with deionized water and dried.
[0052] Example 3
[0053] A method for reducing the concentration of silicon impurities on the surface of an indium phosphide wafer includes the following steps:
[0054] (1) A liquid wax coating machine is used to coat and fix the ground indium phosphide wafers: Liquid wax is introduced onto the indium phosphide wafers via an inlet method. The indium phosphide wafers are adsorbed onto the tray and can rotate at high speed. At a set time, liquid wax is dripped onto the back of the high-speed rotating indium phosphide wafers. After the liquid wax coating is completed, the robot arm leaves the tray, and the indium phosphide wafers are flipped and attached to the ceramic disk on which the indium phosphide wafers are fixed. The air bladder above the wax coating machine presses down on the indium phosphide wafers coated with liquid wax and fixed to the ceramic disk, pressing the indium phosphide wafers firmly onto the ceramic disk. After the indium phosphide wafers are pressed onto the ceramic disk, there will be liquid wax squeezed out around them. This is wiped away with an organic solvent to ensure that there is no liquid wax residue around the indium phosphide wafers and on the ceramic disk.
[0055] (2) Rough polishing of indium phosphide wafers: The ceramic disk holding the indium phosphide wafers was installed in a single-sided polishing machine. Polishing was performed for 40 minutes at a polishing pressure of 6 psi and a polishing fluid flow rate of 1500 mL / min using a rough polishing solution. The rough polishing solution was prepared as follows: sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate, and silica sol were added to deionized water, and the pH was controlled to approximately 3.5. The mass concentrations of tripolyphosphate, thiosulfate, bicarbonate, and silica were 8%, 5%, 9%, and 4%, respectively. After rough polishing, the indium phosphide wafers were rinsed with deionized water and dried.
[0056] (3) Fine polishing of indium phosphide wafers: Rhom & Hass polishing pads were used. Polishing was performed for 10 minutes at a polishing pressure of 1 psi and a polishing fluid flow rate of 350 mL / min. The fine polishing fluid was prepared as follows: 5000 g of deionized water was taken, and 80 g of sodium tripolyphosphate, 320 g of sodium thiosulfate, 160 g of sodium bicarbonate, and 50 g of citric acid monohydrate were added sequentially to control the pH value at 5.0. The fine polishing fluid was stirred evenly and then diluted with water at a volume ratio of 1:10 for fine polishing. After fine polishing, the indium phosphide wafers were rinsed with deionized water for 90 s and dried in a high-speed rotating spin dryer at a speed of 1000 rad / min.
[0057] (4) The indium phosphide wafer obtained in step (3) is placed in a packaging box and then rinsed in isopropanol for 60 seconds to remove wax. Then it is rinsed with deionized water at a temperature of 55°C for 60 seconds.
[0058] (5) Treatment of indium phosphide wafers with a mixed weak acid: The indium phosphide wafers obtained in step (4) were placed in a mixed weak acid solution for etching for 100 seconds at a temperature of 15°C. The mixed weak acid solution was prepared as follows: 2000 mL of deionized water was taken, 20 mL of HF acid (industrial grade) was added, 20 mL of NH4F solution with a mass concentration of 500 g / L was added, and 250 mL of H2O was added. Finally, the indium phosphide wafers treated with the mixed weak acid were rinsed with deionized water and dried.
[0059] Comparative Example 1
[0060] The main difference between Comparative Example 1 and Example 1 is that a traditional SiO2-containing fine polishing slurry was used, as detailed below:
[0061] A method for reducing the concentration of silicon impurities on the surface of an indium phosphide wafer includes the following steps:
[0062] (1) A liquid wax coating machine is used to coat and fix the ground indium phosphide wafers: Liquid wax is introduced onto the indium phosphide wafers via an inlet method. The indium phosphide wafers are adsorbed onto the tray and can rotate at high speed. At a set time, liquid wax is dripped onto the back of the high-speed rotating indium phosphide wafers. After the liquid wax coating is completed, the robot arm leaves the tray, and the indium phosphide wafers are flipped and attached to the ceramic disk on which the indium phosphide wafers are fixed. The air bladder above the wax coating machine presses down on the indium phosphide wafers coated with liquid wax and fixed to the ceramic disk, pressing the indium phosphide wafers firmly onto the ceramic disk. After the indium phosphide wafers are pressed onto the ceramic disk, there will be liquid wax squeezed out around them. This is wiped away with an organic solvent to ensure that there is no liquid wax residue around the indium phosphide wafers and on the ceramic disk.
[0063] (2) Rough polishing of indium phosphide wafers: The ceramic disk holding the indium phosphide wafers was installed in a single-sided polishing machine. Polishing was performed for 40 minutes at a polishing pressure of 6 psi and a polishing fluid flow rate of 1500 mL / min using a rough polishing solution. The rough polishing solution was prepared as follows: sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate, and silica sol were added to deionized water, and the pH was controlled to approximately 3.5. The mass concentrations of tripolyphosphate, thiosulfate, bicarbonate, and silica were 8%, 5%, 9%, and 4%, respectively. After rough polishing, the indium phosphide wafers were rinsed with deionized water and dried.
[0064] (3) Fine polishing of indium phosphide wafers: Rhom & Hass polishing pads were used. Polishing was performed for 10 minutes at a polishing pressure of 2 psi and a polishing fluid flow rate of 400 mL / min. The fine polishing fluid was prepared as follows: 5000 g of deionized water was added sequentially with 100 g of sodium tripolyphosphate, 300 g of sodium thiosulfate, 150 g of sodium bicarbonate, and 500 g of SiO2 sol. The SiO2 particles in the SiO2 sol were controlled to have a particle size of 10-30 nm and a concentration of 20%. Alkaline KOH was added as a pH adjuster to control the pH value at 10.0. The mixture was stirred evenly to obtain the fine polishing fluid, which was then diluted with water at a volume ratio of 1:10 for fine polishing. After fine polishing, the indium phosphide wafers were rinsed with deionized water for 90 s and dried in a high-speed rotating spin dryer at a speed of 1000 rad / min.
[0065] (4) The indium phosphide wafer obtained in step (3) is placed in a packaging box and then rinsed in isopropanol for 60 seconds to remove wax. Then it is rinsed with deionized water at a temperature of 55°C for 60 seconds.
[0066] (5) Treatment of indium phosphide wafers with a mixed weak acid: The indium phosphide wafers obtained in step (4) were placed in a mixed weak acid solution for etching for 100 seconds at a temperature of 15°C. The mixed weak acid solution was prepared as follows: 2000 mL of deionized water was taken, 20 mL of HF acid (industrial grade) was added, 20 mL of NH4F solution with a mass concentration of 500 g / L was added, and 250 mL of H2O was added. Finally, the indium phosphide wafers treated with the mixed weak acid were rinsed with deionized water and dried.
[0067] Comparative Example 2
[0068] The difference between Comparative Example 2 and Example 1 is that H2O2 is not added to the mixed weak acid solution of Comparative Example 2, while the other components and treatment methods are the same as those in Example 1.
[0069] Comparative Example 3
[0070] The difference between Comparative Example 3 and Example 1 is that in the preparation of the fine polishing solution in Comparative Example 3, citric acid monohydrate is replaced with an equal amount of hypochlorous acid, while the remaining components and treatment methods are the same as in Example 1.
[0071] Product effectiveness test
[0072] (1) The surface roughness of the indium phosphide wafers treated in Example 1 and Comparative Example 1 was tested using atomic force microscopy (AFM). The AFM image of Example 1 is shown below. Figure 1 As shown, the atomic force microscope image of Comparative Example 1 is as follows: Figure 2 As shown. Figure 1After processing with image processing software, the Rq value is 0.160nm and the Ra value is 0.117nm. Figure 2 After processing with image processing software, the Rq value is 0.162 nm and the Ra value is 0.124 nm. Figure 1 and Figure 2 It can be seen that the surface of the indium phosphide wafer treated by the method provided in Example 1 is smoother and more uniform.
[0073] (2) The residual metal ion content of indium phosphide wafers treated in Examples 1-3 and Comparative Examples 1-3 was tested using total reflectance fluorescence spectroscopy (TXRF), with units of 10⁻⁶. 10 atom / cm 2 The test results are shown in Table 1.
[0074] Table 1
[0075]
[0076] As shown in Table 1, the residual metal ions on the surface of indium phosphide wafers treated by the method provided in the examples are lower, especially the Si content, which is significantly lower than that of indium phosphide wafers treated by conventional methods (Comparative Example 1). Analysis of Comparative Examples 2-3 shows that even after changing the composition of the fine polishing solution and the mixed weak acid, it is still not possible to achieve a good effect in reducing the concentration of impurities on the surface of indium phosphide materials.
Claims
1. A method for reducing the silicon impurity concentration on the surface of an indium phosphide wafer, characterized in that, Includes the following steps: The indium phosphide wafers are first rough polished, then fine polished with a fine polishing solution; after fine polishing, the indium phosphide wafers are cleaned and dried, and then treated with a mixed weak acid. The rough polishing solution is prepared as follows: add sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate and silica sol to deionized water, and control the pH between 3 and 4. The fine polishing solution is composed of tripolyphosphate, thiosulfate, bicarbonate, citric acid, and water; in the fine polishing solution, the mass concentration of tripolyphosphate is 0.5%-5%, the mass concentration of thiosulfate is 3%-10%, the mass concentration of bicarbonate is 1%-6%, and the mass concentration of citric acid is 0.1-2.0%. The mixed weak acid consists of HF acid, NH4F and H2O2.
2. The method according to claim 1, characterized in that, The pH value of the fine polishing solution is 5-6.
3. The method according to any one of claims 1-2, characterized in that, The preparation method of the fine polishing solution includes the following steps: adding sodium tripolyphosphate, sodium thiosulfate, sodium bicarbonate and citric acid to water in sequence, dissolving them, and controlling the pH value between 5 and 6 to obtain the fine polishing solution.
4. The method according to claim 3, characterized in that, During fine polishing, the flow rate of the fine polishing fluid is 300-500 mL / min.
5. The method according to claim 1, characterized in that, The polishing pressure is 1-3 psi, and the polishing time is 5-15 minutes.
6. The method according to claim 1, characterized in that, In the mixed weak acid, the volume fraction of the HF acid is 0.5%-2%, the mass concentration of the NH4F is 3.5-6.0 g / L, and the volume fraction of the H2O2 is 1.0%-10.0%.
7. The method according to claim 6, characterized in that, The volume fraction of the HF acid is 0.5%-1.5%, the volume fraction of the NH4F is 0.5%-1.5%, and the volume fraction of the H2O2 is 1.0%-5.0%.
8. The method according to claim 7, characterized in that, The treatment time for indium phosphide wafers with mixed weak acid is 60-120 seconds, and the treatment temperature for indium phosphide wafers with mixed weak acid is 10-25℃.
9. The method according to claim 7, characterized in that, After treating the indium phosphide wafer with a mixed weak acid, the process also includes rinsing the indium phosphide wafer with water.