Silicon wafer cleaning process for reducing Fe content of silicon wafer

Abstract

The invention relates to a silicon wafer cleaning process for reducing the Fe content of a silicon wafer. The silicon wafer cleaning process comprises the steps that S1, the silicon wafer is treated for 20-30 min at the high temperature of 600-680 DEG C; s2, the cooled silicon wafer is put into an HF aqueous solution with the mass concentration of 9-12% to be soaked for 240-360 seconds, after the silicon wafer is taken out, the silicon wafer is put into a first cleaning solution flowing circularly to be soaked and cleaned for 360-420 seconds, and the first cleaning solution contains ammonia water and hydrogen peroxide; next, the silicon wafer is placed in a second cleaning solution flowing circularly to be soaked and cleaned for 180-240 s, the temperature is raised to 40-60 DEG C, the second cleaning solution contains suspended microbeads, the particle size is 2-4 mm, and the surfaces of the suspended microbeads are modified with organic phosphonic acid groups; and S3, taking out the silicon wafer, drying, detecting the Fe content, and if the Fe content does not reach the standard, continuously processing according to the method of S1-S2 until the Fe content of the silicon wafer is reduced to the qualified standard. The method can efficiently reduce the content of Fe contained in the silicon wafer.

Description

Technical Field

[0001] The invention relates to the field of silicon wafer production technology, and in particular to a silicon wafer cleaning process for reducing the Fe content of the silicon wafer. Background Art

[0002] With the development of the semiconductor industry, higher and higher requirements are placed on the quality of silicon materials, among which the minority carrier (minority carrier) diffusion length and minority carrier lifetime are important physical parameters that characterize material performance. Since metal impurities can diffuse from the surface of silicon wafers into the interior through thermal processes and become interstitial metals, forming very effective recombination centers, they will greatly promote the recombination of carriers, thereby reducing the minority carrier lifetime of silicon wafers, and further affecting the performance and reliability of devices. Therefore, metal contamination is one of the main factors affecting the minority carrier diffusion length and minority carrier lifetime.

[0003] However, in the process of silicon wafer manufacturing, since silicon wafers inevitably come into contact with metal equipment or metal fixtures, it is very easy to form Fe metal contamination on the product. When making devices, silicon wafers contaminated by Fe metal will seriously affect the reliability and yield of the devices. At the same time, if there is Fe metal contamination on the surface of silicon wafers, it will cause contamination of subsequent silicon wafer processing equipment, and the corresponding silicon wafers entering the subsequent equipment will also be contaminated by the equipment, causing cross contamination between silicon wafers and equipment, and then causing the failure of the entire batch of devices. Therefore, in the process of silicon wafer production, it is very critical and necessary to control Fe contamination on the surface and superficial surface of silicon wafers. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a silicon wafer cleaning process for reducing the Fe content of silicon wafers, which can effectively reduce the contamination of Fe on silicon wafers and production equipment during the silicon wafer manufacturing process, which is beneficial to improving the silicon wafer qualification rate and thus ensuring the quality of silicon wafer electronic devices.

[0006] (II) Technical solution

[0007] The present invention provides a silicon wafer cleaning process for reducing the Fe content of the silicon wafer, comprising the following steps:

[0008] S1. Treat the silicon wafer at a high temperature of 600-680°C for 20-30 minutes to allow the Fe ions inside the silicon wafer to precipitate onto the surface of the silicon wafer;

[0009] S2, soaking the cooled silicon wafer in a HF aqueous solution with a mass concentration of 9-12% for 240-360 seconds, taking it out, and then soaking the silicon wafer in a circulating first cleaning solution for 360-420 seconds, wherein the first cleaning solution contains ammonia water and hydrogen peroxide; then, soaking the silicon wafer in a circulating second cleaning solution for 180-240 seconds, and raising the temperature to 40-60° C., wherein the second cleaning solution contains suspended microbeads with a particle size of 2-4 mm, and the surface of the suspended microbeads is modified with organic phosphonic acid groups;

[0010] S3. Take out the silicon wafer, dry it, and test the Fe content. If it does not meet the standard, continue to process according to S1-S2 until the Fe content of the silicon wafer is reduced to the qualified standard.

[0011] According to a preferred embodiment of the present invention, in S1, the silicon wafer is treated at a high temperature of 650° C. for 20 minutes.

[0012] According to a preferred embodiment of the present invention, in S2, the mass concentration of the HF aqueous solution is 10%.

[0013] According to a preferred embodiment of the present invention, in S2, the first cleaning liquid is composed of ammonia water, hydrogen peroxide and ultrapure water in a volume ratio of 8-12:18-22:80-100, wherein the mass concentration of the ammonia raw water is 25-30%, and the mass concentration of the hydrogen peroxide raw water is 30-50%.

[0014] According to a preferred embodiment of the present invention, in S2, the first cleaning liquid is contained in the first cleaning tank, and a conical guide baffle is provided in the first cleaning tank, and a through hole is provided in the middle of the conical guide baffle, and the through hole connects the upper and lower parts of the conical guide baffle; a horizontally arranged partition net is provided above the conical guide baffle, and the silicon wafer to be cleaned is placed on the partition net; the circulation speed of the first cleaning liquid is 0.5-0.8m / s, and it rotates and circulates in a clockwise or counterclockwise direction.

[0015] According to a preferred embodiment of the present invention, in S2, the first cleaning tank is connected to the auxiliary tank, so that the first cleaning liquid in the first cleaning tank is transported from the bottom of the auxiliary tank to the auxiliary tank, and a group of inclined corrugated plates are provided in the auxiliary tank, and the horizontal spacing between adjacent corrugated plates is 1-5mm, and a liquid outlet is provided above the corrugated plates, and the liquid outlet is connected to the first cleaning tank.

[0016] According to a preferred embodiment of the present invention, in S2, a filter is provided between the liquid outlet of the auxiliary tank and the first cleaning tank.

[0017] According to a preferred embodiment of the present invention, in S3, the suspended microbeads in the second cleaning solution are PS microbeads or PMMA microbeads; the relative density of the suspended microbeads is 1.05-1.2.

[0018] According to a preferred embodiment of the present invention, in S3, the method for grafting organic phosphonic acid groups on the surface of the suspended microbeads is: pretreating the surface of the suspended microbeads with an amino-containing silane coupling agent, and then reacting with the organic phosphonic acid to fix the organic phosphonic acid to the surface of the suspended microbeads.

[0019] According to a preferred embodiment of the present invention, the method for preparing suspended microbeads is: first, the suspended microbeads are subjected to ultrasonic and heat treatment using anhydrous ethanol to remove surface impurities and increase surface active sites; then, the suspended microbeads are soaked in an ethanol solution of a silane coupling agent (such as APTES) for 12-24 hours, the suspended microbeads are taken out, placed in an aqueous solution of a compound containing a phosphonic acid group, 5-10% nitric acid is added to promote the reaction, and the suspension is soaked for 12-24 hours. The suspended microbeads are taken out, washed with deionized water 1-3 times, and dried.

[0020] Preferably, the compound containing a phosphonic acid group is diethylenetriamine penta(methylenephosphonic acid) DTPMPA, hydroxyethylidene diphosphonic acid HEDP or diethylenetriamine pentaacetic acid DTPA; the silane coupling agent is at least one of 3-aminopropyltriethoxysilane APTES, 3-aminopropyltrimethoxysilane APTMS, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane AEAPS and N-(2-aminoethyl)-3-aminopropyltriethoxysilane AEAPES.

[0021] According to a preferred embodiment of the present invention, the second cleaning liquid is contained in the second cleaning tank, and the filling volume ratio of the suspended microbeads in the second cleaning tank is 30-50% of the volume of the second cleaning liquid; the suspended microbeads are removed by filtration or centrifugation every 4-6 hours, and fresh suspended microbeads are added; the removed suspended microbeads are regenerated and washed with water using an acidic pH regulator to obtain fresh suspended microbeads for recycling.

[0022] According to a preferred embodiment of the present invention, the circulation speed of the second cleaning liquid is 0.2-0.4 m / s, and the rotation direction of the second cleaning liquid in the second cleaning tank is not limited.

[0023] In the present application, the first cleaning tank, the auxiliary tank, the second cleaning tank, the filter, the connecting pipes, the driving pump, etc. are made of resin materials, and metal materials are avoided as much as possible from directly contacting the first cleaning liquid, the second cleaning liquid, etc.

[0024] (III) Beneficial effects

[0025] The present invention firstly adopts high temperature heat treatment to make Fe ions inside the silicon wafer precipitate to the surface of the silicon wafer and form oxides, so that the subsequent cleaning process can more efficiently remove Fe in the silicon wafer, and then HF is used to slightly corrode the surface of the silicon wafer, so that the surface of the silicon wafer becomes flat on the one hand, and more iron oxides are exposed on the other hand, and iron ions are generated by HF and enter the solution, and then the first cleaning solution containing ammonia water and hydrogen peroxide raw water is used for cleaning, so that the iron ions and the hydroxide and hydrogen peroxide therein generate iron hydroxide, and the Fe on the surface of the silicon wafer is further removed; then, the residual iron ions contaminated on the surface of the silicon wafer are gently washed by suspended microbeads with surface modified organic phosphonic acid groups, so that the iron ions are complexed by the organic phosphate groups on the surface of the suspended microbeads and adsorbed and fixed, and the suspended microbeads fix the Fe ions in a solid form, so that the Fe ions are prevented from continuing to remain in the second cleaning solution in a free state, and the probability of Fe ions contaminating the silicon wafer again is reduced. The suspended microalgae used for a period of time are fished out by filtering or centrifugation, and reused after regeneration. After the Fe content of the silicon wafer is reduced to the qualified standard, it is rinsed with ultrapure water overflow and cleaned with pure water ultrasonically, and then dried by infrared irradiation. The present invention has a very significant effect of removing Fe contained in the silicon wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of a first cleaning tank in a silicon wafer cleaning process in one embodiment.

[0027] Figure 2 Schematic diagram of the structure of the first cleaning tank in the silicon wafer cleaning process in another embodiment. DETAILED DESCRIPTION

[0028] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0029] The present invention provides a silicon wafer cleaning process for reducing the Fe content of the silicon wafer, comprising the following steps:

[0030] (1) The silicon wafer is treated at a high temperature of 600-680° C. for 20-30 min, preferably at a high temperature of 650° C. for 20 min, so that the Fe ions inside the silicon wafer are precipitated onto the surface of the silicon wafer.

[0031] (2) Soak the cooled silicon wafer in an HF aqueous solution with a mass concentration of 9-12%, preferably 10%, for 240-360 seconds and then take it out. During this period, the chemical reaction that occurs is as follows:

[0032] Si+6HF→H2SiF6+4H++4e-(1)

[0033] 2H++2e-→H2(2)

[0034] Fe 2+ +2e-→FeO

[0035] (3) Soak the silicon wafer in the circulating first cleaning solution for 360-420 seconds. The first cleaning solution is composed of ammonia water, hydrogen peroxide, and ultrapure water in a volume ratio of 8-12:18-22:80-100. The mass concentration of ammonia water is 25-30%, and the mass concentration of hydrogen peroxide water is 30-50%. The first cleaning solution is contained in the first cleaning tank. In the first cleaning tank, the chemical reaction that occurs is as follows:

[0036] NH3·H2O=reversible=NH4 + +OH -

[0037] Fe 3+ +3OH - =Fe(OH)3

[0038] 2Fe+3H2O2=2Fe(OH)3

[0039] like Figure 1 As shown, it is a schematic diagram of the structure of the first cleaning tank 1 in one embodiment of the present invention. The first cleaning tank 1 includes two parts, the upper part is a cylindrical tank body 11, and the lower part is a conical body 12. The height of the conical body 12 is 2-4 times, preferably 3 times, of the height of the cylindrical tank body 11. The upper part and the lower part are connected to form a structure similar to a cyclone separator. A horizontal partition 13 is provided at the position where the upper part and the lower part are connected. The silicon wafer to be cleaned is placed on the partition 13. The liquid level of the first cleaning liquid exceeds the partition 13 by a certain depth, and the exceeded depth is preferably sufficient to immerse the silicon wafer to be cleaned. A cleaning liquid outlet is provided at the bottom of the conical body 12, and the cleaning liquid (containing iron hydroxide precipitation) discharged from the cleaning liquid outlet enters the auxiliary tank 2. A group of inclined corrugated plates 21 are provided near the liquid surface in the auxiliary tank 2, and the horizontal spacing between adjacent corrugated plates 21 is 1-5 mm. A liquid outlet 22 of the auxiliary tank is provided above the corrugated plates 21, and the liquid outlet 22 is connected to the first cleaning tank 1, and a filter 23 is provided on the connecting pipeline. The bottom of the auxiliary tank 2 is set as a conical tank, and the bottom of the conical tank has a slag discharge port. The first cleaning liquid is stirred in the first cleaning tank 1 by a stirring device or by using a driving pump 24 between the auxiliary tank 2 and the first cleaning tank 1. The driving pump 24 provides a certain initial velocity of the first cleaning liquid for the return, so that the first cleaning liquid is circulated in the first cleaning tank 1 at a speed of 0.5-0.8 m / s, and the rotation direction can be clockwise or counterclockwise.

[0040] like Figure 2As shown, it is a schematic diagram of the structure of the first cleaning tank 1 in another embodiment of the present invention. A conical guide baffle 14 is provided in the first cleaning tank 1. The conical guide baffle 14 extends obliquely downward from the inner wall of the first cleaning tank. A through hole 141 is provided in the middle of the conical guide baffle (the lowest position of the conical guide baffle). The area of ​​the through hole 141 only occupies 1 / 36-1 / 100 of the cross-section of the first cleaning tank 1. Preferably, the first cleaning tank 1 is a cylindrical tank body as a whole. The through hole 141 penetrates the upper and lower parts of the conical guide baffle 14. The conical guide baffle 14 is arranged in the middle section of the first cleaning tank 1, that is, the connection part between the conical guide baffle 14 and the first cleaning tank 1 can divide the cylindrical tank body into a height ratio close to 1:1 from top to bottom. In order to facilitate more stable placement of silicon wafers, a horizontally arranged partition 15 is provided above the conical guide baffle 14, and the silicon wafers to be cleaned are placed on the partition 15. The liquid level of the first cleaning liquid exceeds the partition 15 by a certain depth, and the exceeding depth is suitable for immersing the silicon wafers to be cleaned. The first cleaning liquid is circulated in the first cleaning tank 1 at a speed of 0.5-0.8m / s by a stirring device or by using a driving pump 24 between the auxiliary tank 2 and the first cleaning tank 1, and the rotation direction can be clockwise or counterclockwise. Further, if Figure 2 As shown, the first cleaning tank 1 is connected to the auxiliary tank 2, and a cleaning liquid outlet is provided at the bottom of the first cleaning tank 1. The cleaning liquid (containing iron hydroxide precipitation) led out of the cleaning liquid outlet enters the auxiliary tank 2. A group of inclined corrugated plates 21 are provided near the liquid surface in the auxiliary tank 2. The horizontal spacing between adjacent corrugated plates 21 is 1-5 mm. A liquid outlet 22 of the auxiliary tank is provided above the corrugated plates 21. The liquid outlet 22 is connected to the first cleaning tank 1, and a filter 23 is provided on the connecting pipeline. The bottom of the auxiliary tank 2 is set as a conical tank, and the bottom of the conical tank has a slag discharge port.

[0041] The inner diameter of the conical guide baffle 14 is continuously reduced in the downward direction, so that the iron oxide particles are continuously aggregated into large particles and sink from the through hole 141 to the bottom of the conical guide baffle 14. The iron oxide particles that enter the bottom of the conical guide baffle 14 are difficult to float to the top again, thereby greatly reducing the probability of the iron oxide contacting the silicon wafer again and improving the cleaning effect. Iron oxide itself is a flocculant that can adsorb a variety of impurity ions in the cleaning solution, including but not limited to iron ions. In addition, due to the setting of the conical guide baffle 14, the height of the entire first cleaning tank 1 can be relatively shortened, so Figure 2 The structure of the first cleaning tank 1 is better than that of embodiment 1.

[0042] (4) Continue to soak and clean the silicon wafer in the circulating second cleaning solution for 180-240 seconds, and raise the temperature to 40-60°C. The second cleaning solution contains suspended microbeads with a particle size of 2-4 mm, and the surface of the suspended microbeads is modified with organic phosphonic acid groups. In order to make the suspended microbeads suspend better, the material used is PS or PMMA, and the relative density of the material is 1.05-1.2, so that it can circulate with the second cleaning solution and achieve a gentle flushing effect on the surface of the silicon wafer. The particle size of the suspended microbeads is 2-4 mm, which can flow well to any corner of the silicon wafer and every gap between two silicon wafers. The use of 2-4 mm suspended microbeads is not easy to cause new pollution sources due to electrostatic adsorption on the surface of the silicon wafer. The second cleaning solution is heated to a temperature of 40-60°C, which can promote the adsorption and fixation of iron ions by organic phosphonic acid groups, reduce the electrostatic adsorption effect, and avoid the suspended microbeads from causing new pollution sources due to electrostatic adsorption on the surface of the silicon wafer. In the second cleaning tank, the complexation reaction between the iron ions and the organic phosphate groups on the surface of the suspended microbeads mainly occurs, and the iron ions are fixed by the solid suspended microbeads.

[0043] The filling volume ratio of the suspended microbeads in the second cleaning tank is 30-50% of the volume of the second cleaning liquid, and the suspended microbeads are removed by filtration or centrifugation every 4-6 hours, and fresh suspended microbeads are added; the removed suspended microbeads are regenerated and washed with water using an acidic pH regulator to obtain fresh suspended microbeads for recycling. The circulation speed of the second cleaning liquid (through the stirring device) is 0.2-0.4 m / s, and the rotation direction of the second cleaning liquid in the second cleaning tank is not limited.

[0044] When modifying the surface of the suspended microbeads with organic phosphoric acid groups, ultraviolet light or other forms of light can be used to initiate graft polymerization of monomers containing phosphonic acid groups on the PMMA surface, or bifunctional molecules (such as DCC / HOBT) can be used to graft organic phosphonic acid groups through reactions between amino groups and phosphonic acid groups. A blending or copolymerization method can also be used to copolymerize monomers containing phosphonic acid groups with other monomers when preparing PMMA / PS materials, so that the phosphonic acid groups are evenly distributed throughout the suspended microbeads.

[0045] In the present invention, the organic phosphonic acid groups are grafted onto the surface of the suspended microbeads by an amino-containing silane coupling agent. Specifically, the preparation method can refer to the following method:

[0046] First, the suspended microbeads are ultrasonically treated and heated to 50-80°C for about 30 minutes with anhydrous ethanol to remove surface impurities and increase surface active sites; then, the suspended microbeads are soaked in an ethanol solution of APTES with a mass concentration of 5% for 12 hours, the suspended microbeads are taken out, placed in an aqueous solution containing DTPA, nitric acid (the concentration after the addition of nitric acid is 5wt%) is added to promote the reaction, soaked for 12 hours, the suspended microbeads are taken out, washed with deionized water 3 times, and dried. Among them, DTPA can be replaced with DTPMPA or HEDP, and the silane coupling agent can be replaced with one of APTES, APTMS, AEAPS, and AEAPES.

[0047] (5) After the above cleaning, the silicon wafer is taken out and dried, and the Fe content is tested. If it does not meet the standard, continue to process according to steps (1) to (4) until the Fe content of the silicon wafer is reduced to the qualified standard. After the Fe content of the silicon wafer is reduced to the qualified standard, it is rinsed with ultrapure water overflow and ultrasonically cleaned with pure water, and then dried by infrared irradiation.

[0048] In the present application, the first cleaning tank, the auxiliary tank, the second cleaning tank, the filter, the connecting pipes, the driving pump, etc. are made of resin materials, and metal materials are avoided as much as possible from directly contacting the first cleaning liquid, the second cleaning liquid, etc.

[0049] The scheme and effects of the present invention are described below in conjunction with the embodiments of the present invention.

[0050] Example 1

[0051] This embodiment provides a silicon wafer cleaning process for reducing the Fe content of the silicon wafer, comprising the following steps:

[0052] (1) Treat the silicon wafer at 650℃ for 20 minutes.

[0053] (2) The cooled silicon wafer was immersed in a 10 wt % HF aqueous solution for 300 seconds and then taken out.

[0054] (3) Immerse the silicon wafer in a circulating first cleaning solution for 400 seconds. The first cleaning solution is composed of ammonia water, hydrogen peroxide, and ultrapure water in a volume ratio of 10:20:90, with a mass concentration of ammonia water being 30% and a mass concentration of hydrogen peroxide being 35%.

[0055] The first cleaning liquid is contained in the first cleaning tank. The structure of the first cleaning tank 1 is as follows: Figure 1As shown. The first cleaning tank 1 includes two parts, the upper part is a cylindrical tank body 11, the height of which is 30cm, and the lower part is a conical body 12, the height of which is 60cm. The horizontal spacing between adjacent corrugated plates of the inclined corrugated plates in the auxiliary tank 2 is 2-3mm. A filter and a pump are provided between the liquid outlet of the auxiliary tank 2 and the first cleaning tank 1. The filtered first cleaning liquid is input into the first cleaning tank 1 through the pump, and the output power of the pump is used to make the first cleaning liquid rotate and circulate in the first cleaning tank 1 at a speed of 0.6m / s.

[0056] (4) Continue to place the silicon wafer in the circulating second cleaning solution and soak for 200 seconds, the temperature is raised to 55°C, and the filling volume ratio of the suspended microbeads in the second cleaning solution is 40%. The suspended microbeads are PMMA microbeads with a particle size of 2-4 mm and a specific gravity of 1.17. A large amount of DTPA is grafted on the surface of the microbeads. The preparation method is as described above. The circulation speed of the second cleaning solution is 0.3 m / s.

[0057] (5) After the above cleaning, the wafer is rinsed with ultrapure water overflow and then enters the drying channel for infrared drying. After each cleaning, the Fe on the surface of the silicon wafer is tested. The experimental results are as follows:

[0058] atoms / cm 2 (Number of particles per square meter)

[0059] Before cleaning Clean once Cleaning twice Wash three times 0.331 0.124 0.003 0.000

[0060] Example 2

[0061] This embodiment provides a silicon wafer cleaning process for reducing the Fe content of the silicon wafer, comprising the following steps:

[0062] (1) Treat the silicon wafer at 650℃ for 20 minutes.

[0063] (2) The cooled silicon wafer was immersed in a 10 wt % HF aqueous solution for 300 seconds and then taken out.

[0064] (3) Immerse the silicon wafer in a circulating first cleaning solution for 400 seconds. The first cleaning solution is a mixture of ammonia water, hydrogen peroxide, and ultrapure water in a volume ratio of 10:20:100. The mass concentration of the ammonia raw water is 30%, and the mass concentration of the hydrogen peroxide raw water is 40%.

[0065] The first cleaning liquid is contained in the first cleaning tank. The structure of the first cleaning tank 1 is as follows: Figure 2As shown. The area of ​​the through hole 141 of the conical guide baffle 14 only occupies 1 / 64 of the cross section of the first cleaning tank 1. The first cleaning tank 1 is a cylindrical tank body as a whole. The connection part between the conical guide baffle 14 and the first cleaning tank 1 can divide the cylindrical tank body into a 1:1 height ratio, and the upper and lower heights are 40cm respectively. The horizontal spacing between adjacent corrugated plates of the inclined corrugated plates in the auxiliary tank 2 is 2-3mm. A filter and a pump are provided between the liquid outlet of the auxiliary tank 2 and the first cleaning tank 1. The filtered first cleaning liquid is input into the first cleaning tank 1 through the pump, and the output power of the pump is used to make the first cleaning liquid rotate and circulate in the first cleaning tank 1 at a speed of 0.6m / s.

[0066] (4) Continue to place the silicon wafer in the circulating second cleaning solution and soak for 200 seconds, the temperature is raised to 60°C, and the filling volume ratio of the suspended microbeads in the second cleaning solution is 40%. The suspended microbeads are PMMA microbeads with a particle size of 2-4 mm and a specific gravity of 1.17. A large amount of DTPA is grafted on the surface of the microbeads. The preparation method is as described above. The circulation speed of the second cleaning solution is 0.3 m / s.

[0067] (5) After the above cleaning, the wafer is rinsed with ultrapure water overflow and then enters the drying channel for infrared drying. After each cleaning, the Fe on the surface of the silicon wafer is tested. The experimental results are as follows:

[0068] atoms / cm 2 (Number of particles per square meter)

[0069] Before cleaning Clean once Cleaning twice Wash three times 0.317 0.011 0.001 0.000

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements, or the technical features in the above embodiments may be combined in the manner described in the embodiments if they do not conflict with each other, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon wafer cleaning process for reducing Fe content in silicon wafers, characterized in that: The steps include: S1. Treat the silicon wafer at a high temperature of 600-680°C for 20-30 minutes to allow the Fe ions inside the silicon wafer to precipitate onto the surface of the silicon wafer; S2, soaking the cooled silicon wafer in a HF aqueous solution with a mass concentration of 9-12% for 240-360 seconds, taking it out, and then soaking the silicon wafer in a circulating first cleaning solution for 360-420 seconds, wherein the first cleaning solution contains ammonia water and hydrogen peroxide; then, soaking the silicon wafer in a circulating second cleaning solution for 180-240 seconds, and raising the temperature to 40-60° C., wherein the second cleaning solution contains suspended microbeads with a particle size of 2-4 mm, and the surface of the suspended microbeads is modified with organic phosphonic acid groups; S3. Take out the silicon wafer, dry it, and test the Fe content. If it does not meet the standard, continue to process according to S1-S2 until the Fe content of the silicon wafer is reduced to the qualified standard.

2. The silicon wafer cleaning process according to claim 1, characterized in that: In S1, the silicon wafer is treated at a high temperature of 650° C. for 20 minutes; in S2, the mass concentration of the HF aqueous solution is 10%.

3. The silicon wafer cleaning process according to claim 1, characterized in that: In S2, the first cleaning solution is composed of ammonia water, hydrogen peroxide and ultrapure water in a volume ratio of 8-12:18-22:80-100, the mass concentration of the ammonia raw water is 25-30%, and the mass concentration of the hydrogen peroxide raw water is 30-50%.

4. The silicon wafer cleaning process according to claim 1, characterized in that: In S2, the first cleaning liquid is contained in the first cleaning tank, which is provided with a conical guide baffle, and a through hole is provided in the middle of the conical guide baffle, and the through hole connects the upper and lower parts of the conical guide baffle; a horizontally arranged partition net is provided above the conical guide baffle, and the silicon wafer to be cleaned is placed on the partition net; the circulation speed of the first cleaning liquid is 0.5-0.8m / s, and it rotates and circulates in a clockwise or counterclockwise direction.

5. The silicon wafer cleaning process according to claim 1, characterized in that: In S2, the first cleaning tank is connected to the auxiliary tank, so that the first cleaning liquid in the first cleaning tank is transported from the bottom of the auxiliary tank to the auxiliary tank. A group of inclined corrugated plates are provided in the auxiliary tank, and the horizontal spacing between adjacent corrugated plates is 1-5mm. A liquid outlet is provided above the corrugated plates, and the liquid outlet is connected to the first cleaning tank.

6. The silicon wafer cleaning process according to claim 5, characterized in that: In S2, a filter is provided between the liquid outlet of the auxiliary tank and the first cleaning tank.

7. The silicon wafer cleaning process according to claim 1, characterized in that: In S3, the suspended microbeads in the second cleaning solution are PS microbeads or PMMA microbeads; the relative density of the suspended microbeads is 1.05-1.

2.

8. The silicon wafer cleaning process according to claim 1 or 7, characterized in that: The method for grafting organic phosphonic acid groups on the surface of the suspended microbeads is: pre-treating the surface of the suspended microbeads with an amino-containing silane coupling agent, and then reacting with the organic phosphonic acid to fix the organic phosphonic acid on the surface of the suspended microbeads.

9. The silicon wafer cleaning process according to claim 8, characterized in that: The method for preparing suspended microbeads is as follows: firstly, using anhydrous ethanol to perform ultrasonic and heat treatment on the suspended microbeads to remove surface impurities and increase surface active sites; then, using an ethanol solution of a silane coupling agent to soak the suspended microbeads for 12-24 hours, taking out the suspended microbeads, placing them in an aqueous solution of a compound containing a phosphonic acid group, adding 5-10wt% nitric acid to promote the reaction, soaking for 12-24 hours, taking out the suspended microbeads, washing them with deionized water for 1-3 times, and drying them.

10. The silicon wafer cleaning process according to claim 1, characterized in that: The second cleaning liquid is contained in the second cleaning tank, and the filling volume ratio of the suspended microbeads in the second cleaning tank is 30-50% of the volume of the second cleaning liquid; the suspended microbeads are fished out by filtering or centrifuging every 4-6 hours, and fresh suspended microbeads are added; the fished out suspended microbeads are regenerated and washed with water using an acidic pH regulator to obtain fresh suspended microbeads for recycling; the circulation speed of the second cleaning liquid is 0.2-0.4m / s.

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