A method for cleaning silicon carbide epitaxial wafer silicon surface after film application

Abstract

The invention discloses a cleaning method for a silicon carbide epitaxial wafer after film pasting on the silicon surface, which relates to the field of semiconductor cleaning technology, and includes wet cleaning and gas phase cleaning. The gas phase cleaning is to use hydrogen etching to remove stubborn organic matter on the wafer surface, wherein the temperature of the hydrogen is controlled at 900-1500°C; the wet cleaning of the technical solution is mainly used to remove polishing liquid adhered to the surface, inorganic pollutants on the surface, some organic pollutants on the surface and other strongly adsorbent substances, and the gas phase cleaning method mainly removes strongly adsorbent organic matter on the epitaxial surface. The technical solution can effectively solve the organic pollution of the epitaxial surface caused by film pasting protection on the surface of the silicon carbide epitaxial wafer, solve the problem of back growth layer or silicide, and ensure the wafer cleaning quality, thereby improving the cleaning efficiency; the invention solves the technical problem in the prior art that stubborn organic matter will remain on the epitaxial surface due to film pasting protection.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor cleaning process, and in particular to a method for cleaning a silicon carbide epitaxial wafer after film bonding on the silicon surface. Background Art

[0002] At present, silicon carbide is an important basic material for the development of the third-generation semiconductor industry. Silicon carbide power devices, with their excellent high-voltage resistance, high-temperature resistance, low-loss performance, etc., can effectively meet the high efficiency, miniaturization and lightweight requirements of power electronic systems. It has obvious advantages in the fields of new energy vehicles, photovoltaic power generation, rail transportation, smart grids, etc.

[0003] In recent years, new energy vehicles have driven the rapid growth of the silicon carbide industry. With the development of new energy vehicles, the demand for power devices has increased, and the requirements for the performance indicators and reliability of silicon carbide power semiconductor devices have also increased. This has led to an increase in the demand for epitaxial materials for making silicon carbide devices, and the requirements for various indicators have become more stringent.

[0004] In the early days, there were no requirements for the back growth layer and silicide of silicon carbide epitaxial materials. In order to solve the impact of the back growth layer or silicide on device manufacturing, conventional cleaning technology is difficult to remove the back growth layer or silicide. Currently, only physical methods can be used to perform CMP on the back, which requires film protection on the epitaxial layer, resulting in stubborn organic matter residue on the epitaxial surface. Please refer to Figure 1 , which is difficult to be effectively removed using existing wet cleaning technology. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and provide a method for cleaning the silicon surface of a silicon carbide epitaxial wafer after film application, which solves the technical problem in the prior art that film protection causes stubborn organic matter residues on the epitaxial surface.

[0006] To achieve the above-mentioned purpose, the present invention provides a method for cleaning the silicon surface of a silicon carbide epitaxial wafer after film bonding, including wet cleaning and vapor phase cleaning, wherein the vapor phase cleaning uses hydrogen etching to remove stubborn organic matter on the surface of the wafer, wherein the temperature of the hydrogen is controlled at 900-1500°C.

[0007] In the above technical solution, the flow rate of the hydrogen is controlled at 25L / min to 40L / min, and the time for the hydrogen to etch the surface of the wafer is controlled at 5 to 15 minutes.

[0008] The above technical solution includes the following steps:

[0009] S1, removing particles from the silicon carbide epitaxial wafer after CMP, and then peeling off the epitaxial silicon surface protective film of the silicon carbide epitaxial wafer;

[0010] S2, soaking and cleaning the silicon carbide epitaxial wafer after the film is removed by an organic solvent, wherein the temperature of the organic solvent is controlled within 30 to 45° C., and the treatment time is controlled within 20 to 40 minutes;

[0011] S4, transferring the silicon carbide epitaxial wafer to a pure water ultrasonic tank, and performing circulating pure water overflow ultrasonic treatment;

[0012] S5, immersing the silicon carbide epitaxial wafer in SPM solution, wherein the immersion temperature of the SPM solution is controlled within a range of 120 to 140° C.;

[0013] S6, transferring the silicon carbide epitaxial wafer to a pure water ultrasonic tank, and performing pure water circulating overflow ultrasonic cleaning;

[0014] S7, soaking the silicon carbide epitaxial wafer in APM solution, wherein the soaking temperature of the APM solution is controlled in the range of 45 to 70° C.;

[0015] S8, transferring the silicon carbide epitaxial wafer to a pure water ultrasonic tank, and performing pure water circulating overflow ultrasonic cleaning;

[0016] S9, spinning the silicon carbide epitaxial wafer at a speed of 1200 rpm;

[0017] S10, performing vapor phase cleaning on the silicon carbide epitaxial wafer.

[0018] In the above technical solution, the concentration of the organic solvent in step S2 is in the range of 60%-99.9%, and the organic solvent is an acetone solution or an isopropanol solution.

[0019] In the above technical solution, in step S2, ultrasonic treatment is added during the temperature-controlled immersion cleaning in an organic solvent, and the time of the ultrasonic treatment is controlled within 5 to 15 minutes.

[0020] In the above technical solution, in the step S5, the ratio of SPM solution: 98% concentrated sulfuric acid: 30%-32% hydrogen peroxide = 3:1 or 5:2, wherein the SPM solution immersion treatment time is controlled at 10 to 30 minutes.

[0021] In the above technical solution, in the step S7, the ratio of APM solution is: 28%-30% ammonia solution: 30%-32% hydrogen peroxide: pure water = 1:1:5 or 1:1:6, and the treatment time is controlled at 10 to 30 minutes.

[0022] In the above technical solution, the cycle of pure water overflow ultrasonic cleaning in S4, S6 and S8 is 2-4 times, and the processing time is controlled at 5-15 minutes.

[0023] In the above technical solution, the ultrasonic cleaning frequency in S4, S6 and S8 adopts a 40-80KHz frequency conversion mode, the ultrasonic power range is 500-800W, and the ultrasonic transmission mode is longitudinal liquid transmission.

[0024] In the above technical solution, the drying process in step S9 is purged with nitrogen, and the drying time is 5 to 8 minutes.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) It can effectively remove strongly adsorbed organic substances, inorganic substances and other organic substances on the epitaxial surface;

[0027] (2) Ensure the surface cleanliness of silicon carbide epitaxial wafers and improve the quality of silicon carbide epitaxial wafers;

[0028] (3) Effectively solve the organic pollution on the epitaxial surface caused by the film protection on the surface of the silicon carbide epitaxial wafer, solve the problem of the back growth layer or silicide, while ensuring the wafer cleaning quality and improving the cleaning efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 This is a photographic image of silicon carbide epitaxial wafer 1# after cleaning using a conventional cleaning method;

[0031] Figure 2 This is a photographic image of silicon carbide epitaxial wafer 6# after cleaning using a conventional cleaning method;

[0032] Figure 3 This is a photographic image of silicon carbide epitaxial wafer 1# after being cleaned using the cleaning method of the technical solution;

[0033] Figure 4 This is an image taken after the silicon carbide epitaxial wafer 6# was cleaned using the cleaning method of the present technical solution. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0036] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0038] The present embodiment provides a cleaning method for the silicon surface of a silicon carbide epitaxial wafer after film bonding, which includes wet cleaning and gas phase cleaning. The gas phase cleaning is to use hydrogen to etch and remove stubborn organic matter on the surface of the silicon carbide epitaxial wafer, wherein the temperature of the hydrogen is controlled at 900-1500°C. The flow rate of hydrogen is controlled at 25L / min-40L / min, and the time for hydrogen to etch the surface of the silicon carbide epitaxial wafer is controlled at 5-15min. Gas phase cleaning mainly uses hydrogen to remove organic substances with strong adsorption on the surface of the silicon carbide epitaxial wafer, which can effectively solve the organic pollution caused by the film protection on the surface of the silicon carbide epitaxial wafer, solve the problem of the back growth layer or silicide, and ensure the wafer cleaning quality and improve the cleaning efficiency.

[0039] Wet cleaning includes SPM cleaning, APM cleaning, pure water cleaning, etc. Preferably, the gas phase cleaning step is performed after the wet cleaning step, mainly to remove the organic matter remaining on the surface of the silicon carbide epitaxial wafer after the wet cleaning. In this embodiment, it is preferred to soak the silicon carbide epitaxial wafer in an organic solvent before wet cleaning, so that the organic matter on the surface of the silicon carbide epitaxial wafer can be dissolved first, which is convenient for stripping the silicon carbide epitaxial wafer and the organic matter on its surface during wet cleaning.

[0040] The cleaning method of the silicon carbide epitaxial wafer after film bonding in this embodiment comprises the following steps:

[0041] S1, removing particles from the silicon carbide epitaxial wafer after CMP, and then peeling off the epitaxial silicon surface protective film of the silicon carbide epitaxial wafer;

[0042] S2. The silicon carbide epitaxial wafer after the film is removed is soaked and cleaned with an organic solvent, wherein the temperature of the organic solvent is controlled within 30 to 45°C, and the processing time is controlled within 20 to 40 minutes; preferably, the organic solvent can be an acetone solution or an isopropanol solution, and other organic solvents can also be used in other embodiments, so it is not limited to this. In addition, the organic solvent concentration range is 60%-99.9%, and a high concentration of organic solvent can effectively dissolve the organic matter on the surface of the silicon carbide epitaxial wafer. The main function of the organic solvent soaking and washing is to dissolve the organic matter on the surface of the silicon carbide epitaxial wafer and provide a prerequisite for the next step of organic stripping. Preferably, ultrasonic treatment is added to the organic solvent temperature control soaking and cleaning, and the time is controlled within 5 to 15 minutes. Ultrasonic treatment can provide power for the organic matter dissolved on the surface of the silicon carbide epitaxial wafer, making it easier for the organic matter to strip off the surface of the silicon carbide epitaxial wafer and dissolve in the organic solvent.

[0043] S4. Transfer the silicon carbide epitaxial wafer to a pure water ultrasonic tank for circulating pure water overflow ultrasonic cleaning, wherein the cycle is about 2-4 times, and the processing time is controlled at 5-15 minutes. During the ultrasonic cleaning process, a frequency of 40-80KHz frequency conversion mode is used, an ultrasonic power of 500-800W, and an ultrasonic transmission mode of longitudinal liquid transmission is used. This step is mainly to remove organic solvents and large-sized particles on the surface of the silicon carbide epitaxial wafer to avoid contamination of the SPM solution for immersion in the next step.

[0044] S5. Soak the silicon carbide epitaxial wafer in SPM solution, wherein the ratio of SPM solution is: 98% concentrated sulfuric acid: 30%-32% hydrogen peroxide = 3:1 or 5:2, and the SPM solution soaking treatment time is controlled at 10 to 30 minutes. SPM solution has strong oxidizing properties and can effectively remove organic matter, inorganic compounds, and heavy metal ions such as Hg and Ge on the surface of the silicon carbide epitaxial wafer. In addition, increasing the temperature of the SPM solution can increase the oxidizing property of the SPM solution, thereby improving the cleaning effect of the silicon carbide epitaxial wafer. Therefore, the SPM solution soaking temperature of this embodiment is preferably controlled at 120 to 140°C.

[0045] S6. Transfer the silicon carbide epitaxial wafer to a pure water ultrasonic tank and perform pure water circulating overflow ultrasonic cleaning; wherein the cycle is about 2-4 times, the processing time is controlled at 5-15 minutes, and during the ultrasonic cleaning process, a frequency of 40-80KHz frequency conversion mode is used, an ultrasonic power of 500-800W, and an ultrasonic transmission mode of longitudinal liquid transmission is used. This step is mainly to remove the SPM solution and particles on the surface of the silicon carbide epitaxial wafer to avoid contamination of the APM solution in the next step of APM solution immersion.

[0046] S7. Soak the silicon carbide epitaxial wafer in APM solution. The soaking temperature of APM solution is controlled in the range of 45-70°C. The ratio of APM solution is: 28%-30% ammonia solution: 30%-32% hydrogen peroxide: pure water = 1:1:5 or 1:1:6. The soaking time is controlled in 10-30 minutes. During the soaking process of APM solution, the surface of the silicon wafer is prone to generate an oxide film due to the oxidation of H2O2. The oxide film is corroded by NH4OH, and oxidation occurs again immediately after corrosion. Oxidation and corrosion are repeated, so particles and metals attached to the surface of the silicon wafer also fall into the cleaning solution along with the corrosion layer. The soaking of APM solution is mainly to strip the cations and particles on the surface of the silicon carbide epitaxial wafer.

[0047] S8. Transfer the silicon carbide epitaxial wafer to a pure water ultrasonic tank and perform pure water circulating overflow ultrasonic cleaning; wherein the cycle is about 2-4 times, and the processing time is controlled at 5-15 minutes. During the ultrasonic cleaning process, a frequency conversion mode of 40-80KHz is used, an ultrasonic power of 500-800W, and an ultrasonic transmission mode of longitudinal liquid transmission is used. This step is mainly to remove the APM solution and particles on the surface of the silicon carbide epitaxial wafer.

[0048] S9, spin-drying the silicon carbide epitaxial wafer at a rotation speed of 1200 rpm. In addition, nitrogen is preferably used for purging during the drying process. The drying time is 5 to 8 minutes.

[0049] S10, performing vapor phase cleaning on the silicon carbide epitaxial wafer, using hydrogen etching to remove organic substances with strong adsorption on the surface of the silicon carbide epitaxial wafer, and further improving the cleaning effect of the surface of the silicon carbide epitaxial wafer.

[0050] See also Figure 1 and Figure 2 It can be clearly seen that the cleaning method of this embodiment greatly improves the cleaning ability compared with the cleaning method of the prior art, thereby improving the cleanliness of the silicon carbide epitaxial wafer. The wet cleaning of this embodiment can remove the polishing liquid adhered to the surface of the silicon carbide epitaxial wafer, the inorganic pollutants on the surface, some organic pollutants on the surface and other strongly adsorbent substances. The gas phase cleaning method mainly removes the organic substances with strong adsorption on the surface of the silicon carbide epitaxial wafer. This cleaning process can effectively solve the organic pollution caused by the film protection on the surface of the silicon carbide epitaxial wafer, solve the problem of the back growth layer or silicide, and ensure the wafer cleaning quality while improving the cleaning efficiency.

[0051] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

[0052] Embodiment 2

[0053] The cleaning method of this embodiment includes soaking in organic solvent, water washing, wet cleaning, and gas phase cleaning. The cleaning method of the prior art is wet cleaning. Among them, wet cleaning includes SPM washing, water washing, APM washing, water washing, and N2 environment centrifugal drying.

[0054] The organic solvent used for soaking in this embodiment is acetone, the soaking time is 30 minutes, the temperature of the solution during soaking is 35°C, and the gas phase cleaning is to use 1000°C hydrogen to etch the silicon carbide epitaxial wafer for 5 minutes. Please refer to the following table. Table 1 is a comparison of experimental data between the cleaning method of this embodiment and the cleaning method of the prior art.

[0055]

[0056] Table 1

[0057] See also Figure 1-Figure 4 As shown in the table above, the cleaning effect of the prior art using wet cleaning is poor, with the maximum total number of particles on the wafer surface being 1963 and the minimum being 174. The range and variance of the particle count data on the wafer surface are large, and the cleaning effect is prone to instability. The maximum total number of particles on the surface of the silicon carbide epitaxial wafer cleaned using this technical solution is 77 and the minimum is 18. The number of particles on the surface of the silicon carbide wafer cleaned by this method is less, and the cleaning is cleaner, and the range and variance of the particle count data on the wafer surface are small, indicating that the cleaning method of this technical solution is relatively stable and has a good cleaning effect.

[0058] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for cleaning the silicon surface of a silicon carbide epitaxial wafer after film application, characterized in that: Including wet cleaning and vapor cleaning, The following steps are involved: S1, removing particles from the silicon carbide epitaxial wafer after CMP, and then peeling off the epitaxial silicon surface protective film of the silicon carbide epitaxial wafer; S2, soaking and cleaning the silicon carbide epitaxial wafer after the film is removed by an organic solvent, wherein the temperature of the organic solvent is controlled within 30-45° C., and the treatment time is controlled within 20 min-40 min; S4, transferring the silicon carbide epitaxial wafer to a pure water ultrasonic tank, and performing circulating pure water overflow ultrasonication; S5, immersing the silicon carbide epitaxial wafer in SPM solution, wherein the immersion temperature of the SPM solution is controlled within a range of 120-140° C.; In the step S5, the ratio of SPM solution: 98% concentrated sulfuric acid: 30%-32% hydrogen peroxide = 3:1 or 5:2, wherein the SPM solution immersion treatment time is controlled within 10-30 minutes; S6, transferring the silicon carbide epitaxial wafer to a pure water ultrasonic tank, and performing pure water circulating overflow ultrasonic cleaning; S7, immersing the silicon carbide epitaxial wafer in APM solution, wherein the immersion temperature of the APM solution is controlled within a range of 45-70° C.; In the step S7, the ratio of APM solution: 28%-30% ammonia solution: 30%-32% hydrogen peroxide: pure water = 1:1:5 or 1:1:6, and the treatment time is controlled within 10-30 minutes; S8, transferring the silicon carbide epitaxial wafer to a pure water ultrasonic tank, and performing pure water circulating overflow ultrasonic cleaning; S9, spinning the silicon carbide epitaxial wafer at a speed of 1200 rpm; S10, performing vapor phase cleaning on the silicon carbide epitaxial wafer; The gas phase cleaning is to use hydrogen etching to remove stubborn organic matter on the surface of the wafer, wherein the temperature of the hydrogen is controlled at 900-1500°C; The flow rate of the hydrogen is controlled at 25 L / min to 40 L / min, and the etching time of the wafer surface by the hydrogen is controlled at 5 to 15 minutes.

2. The method for cleaning the silicon surface of a silicon carbide epitaxial wafer after film application according to claim 1, characterized in that: The organic solvent concentration in step S2 is in the range of 60%-99.9%, and the organic solvent is an acetone solution or an isopropanol solution.

3. The method for cleaning the silicon surface of a silicon carbide epitaxial wafer after film application according to claim 1, characterized in that: In step S2, ultrasonic treatment is added during the temperature-controlled immersion cleaning in an organic solvent, and the time of the ultrasonic treatment is controlled within 5 to 15 minutes.

4. The method for cleaning the silicon surface of a silicon carbide epitaxial wafer after film application according to claim 1, characterized in that: The cycle of the pure water overflow ultrasonic cleaning in S4, S6 and S8 is 2-4 times, and the processing time is controlled within 5-15 minutes.

5. A method for cleaning a silicon carbide epitaxial wafer after film application according to claim 4, characterized in that: The ultrasonic cleaning frequency in S4, S6 and S8 adopts a 40-80KHz frequency conversion mode, the ultrasonic power range is 500-800W, and the ultrasonic transmission mode is longitudinal liquid transmission.

6. The method for cleaning the silicon surface of a silicon carbide epitaxial wafer after film application according to claim 1, characterized in that: The drying process in step S9 is purged with nitrogen, and the drying time is 5 to 8 minutes.

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