Method for effectively cleaning and removing boron element residues on surface of silicon carbide wafer

Abstract

The invention discloses a method for effectively cleaning and removing boron element residues on the surface of a silicon carbide wafer, which comprises the following steps of: transferring the silicon carbide wafer to a PFA (Polyfluoroalkoxy) clamping plug, and feeding; the silicon carbide wafer is soaked in SPM liquid medicine; transferring the silicon carbide wafer into a pure water tank; the silicon carbide wafer is soaked in APM liquid medicine; transferring the silicon carbide wafer into a pure water tank; repeating the steps S2 to S5 at least once; transferring the silicon carbide wafer into a pure water tank; the method comprises the following steps: soaking a silicon carbide wafer in a DHF liquid medicine, transferring the silicon carbide wafer into a pure water tank, transferring the silicon carbide wafer into a spin dryer, and rapidly spin-drying the silicon carbide wafer; the spin-dried silicon carbide wafer is transferred into a cleaned PP clamping plug, and discharging is completed; according to the cleaning agent, pollutants, organic matters and metal ions on the surface of the carbonized wafer can be cleaned, and meanwhile, boron element residues on the surface of the silicon carbide wafer can be effectively cleaned and removed.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide wafer surface cleaning, and in particular to a method for effectively cleaning and removing boron element residues on the surface of a silicon carbide wafer. Background Art

[0002] Wet cleaning technology effectively uses chemical solutions or gases to remove dust, metal ions, non-metallic, and organic impurities remaining on silicon carbide wafers without damaging the wafer's surface and electrical properties. Wet cleaning uses liquid chemical solvents and DIW water to oxidize, etch, and dissolve contaminants, organic matter, metal ions, and non-metallic contamination on the silicon carbide wafer surface.

[0003] Existing cleaning methods can effectively control the residual concentration of metal ions to ≤5E10 atoms / cm2. The metal elements include: Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Au, Ag, V, Hg, W, Mg, Ca, and Na; and the residual concentration of boron to ≤5E12 atoms / cm2.

[0004] During the silicon carbide wafer cleaning process, including but not limited to the processing environment, equipment operation, wafer transfer, and contact fixtures, silicon carbide wafers can become contaminated with surface contaminants, organic matter, metal ions, and non-metallic contamination. Existing cleaning methods can effectively remove dust, organic matter, and metallic impurities, as well as some non-metallic elements, from silicon carbide wafers. However, as market demand escalates, existing cleaning methods are unable to meet this demand, and their inability to remove residual boron has become a significant constraint.

[0005] As market demand increases, requirements for residual boron concentration on silicon carbide wafers are becoming increasingly stringent. For example, for a 6-inch wafer, the standard for residual boron concentration on the surface is ≤1E11 atoms / cm². Current cleaning technology is able to control boron (B) residues to ≤5E12 atoms / cm². 2 , it is difficult to meet the standard requirements. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and provide a method for effectively cleaning and removing boron residues on the surface of silicon carbide wafers. In addition to ensuring that pollutants, organic matter and metal ions on the surface of the silicon carbide wafers can be cleaned, the boron residues on the surface of the silicon carbide wafers can also be effectively cleaned.

[0007] To achieve the above object, the present invention provides a method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer, comprising the following steps:

[0008] Step S1: Transfer the silicon carbide wafer to the PFA plug for loading;

[0009] Step S2: Soaking the silicon carbide wafer in SPM solution, wherein the soaking temperature of the SPM solution is controlled within a range of 120-130° C. and the treatment time is controlled within a range of 20-25 minutes;

[0010] Step S3: Transfer the silicon carbide wafer to a pure water tank and perform water ultrasonic cleaning for 10 to 15 minutes;

[0011] Step S4: Soaking the silicon carbide wafer in APM solution, wherein the soaking temperature of the APM solution is controlled within a range of 45-55° C., and the treatment time is controlled within a range of 20-25 minutes;

[0012] Step S5: transferring the silicon carbide wafer to a pure water tank and performing water ultrasonic cleaning for 10 to 15 minutes;

[0013] Step S6: Repeat steps S2 to S5 at least once;

[0014] Step S7: Transfer the silicon carbide wafer to a pure water tank and let it stand for 40 to 50 minutes;

[0015] Step S8: Soaking the silicon carbide wafer in DHF solution, wherein the soaking temperature of the DHF solution is controlled within a range of 20 to 30° C., and the treatment time is controlled within a range of 20 to 25 minutes;

[0016] Step S9: transferring the silicon carbide wafer to a pure water tank and performing water ultrasonic cleaning for 10 to 15 minutes;

[0017] Step S10: transferring the silicon carbide wafer to a spin dryer to quickly dry the silicon carbide wafer;

[0018] Step S11: Transfer the dried silicon carbide wafer into the cleaned PP plug to complete the unloading.

[0019] Preferably, in step S10, high-purity nitrogen is introduced during the drying process for protection, and the drying time is 10 to 15 minutes; the silicon carbide wafer is dried at a speed of 900 rpm.

[0020] Preferably, in step S11, a wafer reversal device is used to transfer the wafer from the PFA plug to the PP plug in one go.

[0021] Preferably, in step S2, the ratio of the SPM solution is: 98% concentrated sulfuric acid: 30%-32% hydrogen peroxide = 3:1; the 98% concentrated sulfuric acid and 30%-32% hydrogen peroxide are electronic grade chemicals, and the metal ion content needs to be less than 1ppb.

[0022] Preferably, in step S4, the ratio of APM solution is: 28% to 30% ammonia solution: 30% to 32% hydrogen peroxide: deionized water DIW = 1:1:5; the 28% to 30% ammonia solution and 30% to 32% hydrogen peroxide are electronic grade chemicals, and the metal ion content needs to be less than 1ppb.

[0023] Preferably, in step S8, the ratio of DHF solution: 49% hydrofluoric acid solution: deionized water DIW = 1:50, the hydrofluoric acid grade is electronic grade chemical, and the metal ion content needs to be less than 0.1ppb.

[0024] Preferably, the water ultrasonic cleaning uses deionized water DIW, the temperature is controlled in the range of 20-30°C, the ultrasonic cleaning frequency adopts 80-120KHz frequency conversion mode, and the ultrasonic transmission mode is longitudinal liquid transmission; the water ultrasonic cleaning process includes water inlet, overflow, ultrasound and drainage.

[0025] Preferably, the ionized water DIW is added with a boron removal filter to filter the existing water quality, so that the boron concentration is ≤100ppt and the metal ion concentration is ≤50ppt.

[0026] Preferably, in step S11, the PP plug is cleaned for 10 minutes using water ultrasound, and the PP plug is quickly dried in a spin dryer.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In the present invention, sulfuric acid in the SPM solution chemically reacts with boron at 120-130°C, thereby enhancing the ability to remove boron. Under the action of the APM solution, oxidation and corrosion are repeated, so particles, metals, and boron elements attached to the surface of the silicon carbide wafer also fall into the cleaning solution along with the corrosion layer. Steps S2 to S5 are repeated to continue promoting the reaction and dissolution of the boron element. Deionized water ultrasonic cleaning further dilutes and removes the residual boron elements on the surface of the silicon carbide wafer. DHF solution cleans and removes the natural oxide film on the surface, so that the metals and boron elements attached to the natural oxide film are once again dissolved in the cleaning solution. In addition to being used to remove pollutants, organic matter, and metal ions on the surface of the silicon carbide wafer, the wet cleaning technology of the present invention can effectively remove the boron element on its surface and control the residual boron element concentration to ≤1E11 atoms / cm2. 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0030] Figure 1 Schematic diagram of a method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer provided by the present invention;

[0031] Figure 2 is the residual concentration of boron after cleaning using the cleaning method of the prior art;

[0032] Figure 3 is the residual concentration of boron element after cleaning using the cleaning method provided by the present invention;

[0033] Figure 4 It is a box diagram of the boron element B content in the prior art and the cleaning method (new technology) provided by the present invention. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solution in this embodiment of the present invention in conjunction with the drawings in this embodiment of the present invention. Obviously, the embodiment described is only one embodiment of the present invention, not all embodiments of the present invention. Based on this embodiment of the present invention, all other embodiments of the present invention obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] Please refer to Figures 1 to 4 The present invention provides a method for effectively cleaning and removing boron element residues on the surface of silicon carbide wafers.

[0036] This embodiment provides a cleaning method for removing boron residue from a 6-inch silicon carbide wafer, comprising the following steps:

[0037] Step S1: Place a 6-inch silicon carbide wafer into a PFA plug and place it on a loading platform for cleaning.

[0038] Step S2: Select the SPM solution immersion program, transfer the PFA plug loaded with the 6-inch silicon carbide wafer into the SPM immersion tank, and start the immersion program.

[0039] The ratio of the SPM solution is: 98% concentrated sulfuric acid: 30%-32% hydrogen peroxide = 3:1; the 98% concentrated sulfuric acid and 30%-32% hydrogen peroxide are electronic grade chemicals, and the metal ion content needs to be less than 1ppb.

[0040] The SPM solution immersion treatment time is controlled at 20-25 minutes. The SPM solution has strong oxidizing properties and can effectively remove organic matter, inorganic compounds, metal ions, etc. on the surface of the silicon carbide wafer. By increasing the temperature of the SPM solution, the oxidizing property of the SPM solution can be increased, thereby improving the cleaning effect of the silicon carbide wafer. Therefore, the SPM solution immersion temperature of this embodiment is controlled at 120-130°C to enhance the removal ability of the boron element B. The reaction equation of hot sulfuric acid and boron element B is:

[0041]

[0042] After the SPM solution immersion is completed, it is necessary to control the lifting speed of the PFA plug out of the tank and the residence time after lifting. In this embodiment, the SPM solution immersion lifting speed is controlled at 0.08~0.1m / s; the residence time is controlled at 2~3s; by controlling the lifting speed and residence time, the problems caused by the long-term retention and drying of the solution can be avoided.

[0043] Step S3: Transfer the PFA plug loaded with the 6-inch silicon carbide wafer into a water ultrasonic tank for water ultrasonic cleaning;

[0044] In this embodiment, the water ultrasonic bath uses deionized water (DIW) at a temperature controlled within a range of 20-30°C. The ultrasonic cleaning frequency utilizes a variable frequency method of 80-120 kHz, and the ultrasonic transmission method is longitudinal liquid transmission. The water ultrasonic frequency is controlled by an electric current, which is controlled at 1.4-1.6A. The water ultrasonic process includes water inlet, overflow, ultrasonic flow, and rapid drainage, with a three-cycle cycle lasting 10-15 minutes. This water ultrasonic process quickly removes residual chemical solutions and microparticle impurities from the surface of the silicon carbide wafer, leaving the silicon carbide wafer surface clean and preventing contamination of the APM solution used in the subsequent immersion process.

[0045] The ionized water DIW is added with a boron removal filter to filter the existing water quality, so that the boron concentration is ≤100ppt and the metal ion concentration is ≤50ppt (including at least 18 metal elements: Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Au, Ag, V, Hg, W, Mg, Ca, Na).

[0046] Step S4: Immerse the PFA plug loaded with the 6-inch silicon carbide wafer in APM solution. The immersion temperature of the APM solution is controlled within the range of 45-55°C, and the treatment time is controlled within the range of 20-25 minutes. The APM solution ratio is: 28%-30% ammonia solution: 30%-32% hydrogen peroxide: deionized water (DIW) = 1:1:5. The 28%-30% ammonia solution and 30%-32% hydrogen peroxide are electronic-grade chemicals, and the metal ion content needs to be less than 1 ppb.

[0047] During the APM soaking process, hydrogen peroxide oxidizes and easily forms an oxide film on the surface of the 6-inch silicon carbide wafer. This oxide film is then corroded by the ammonia solution, and immediately oxidized again. This oxidation and corrosion cycle repeats, causing particles, metals, and boron B attached to the silicon wafer surface to fall into the cleaning solution along with the corroded layer. After the APM soaking process is completed, the lifting speed and residence time of the PFA out of the tank must be controlled. In this embodiment, the lifting speed of the APM soaking process is controlled at 0.08-0.1 m / s, and the residence time is controlled at 2-3 seconds. This control of the lifting speed and residence time prevents the problem of the solution drying out due to prolonged retention.

[0048] Step S5: The PFA plug containing the 6-inch silicon carbide wafer is transferred to a water ultrasonic bath for water ultrasonic cleaning. In this embodiment, deionized water (DIW) is used for water ultrasonic cleaning. The water ultrasonic frequency is controlled by current, and the water ultrasonic current is controlled at 1.4 to 1.6 A. The water ultrasonic process includes water inlet, overflow, ultrasonic cleaning, and rapid drainage, and is repeated three times for a duration of 10 to 15 minutes. Water ultrasonic cleaning can quickly remove residual chemical solutions and microparticle impurities on the surface of the silicon carbide wafer, leaving the silicon carbide wafer surface clean.

[0049] Step S6: Repeat steps S2 to S5 at least once to continue promoting the reaction and dissolution of the boron element B.

[0050] Step S7: Transfer the PFA plug loaded with the 6-inch silicon carbide wafer to a deionized water (DIW) tank and soak it at room temperature for 40 to 50 minutes to further dilute and remove the residual boron ions B on the surface of the silicon carbide wafer.

[0051] Step S8: Transfer the PFA plug loaded with the 6-inch silicon carbide wafer to a DHF solution for immersion. The immersion temperature of the DHF solution is controlled within the range of 20-30°C, and the treatment time is controlled within the range of 20-25 minutes. The DHF solution ratio is: 49% hydrofluoric acid solution: deionized water (DIW) = 1:50. The hydrofluoric acid grade is electronic grade chemical, and the metal ion content is required to be less than 0.1 ppb.

[0052] During the DHF solution immersion process, the natural oxide film on the surface of the silicon carbide wafer is removed due to HF cleaning, so the metal and boron element B attached to the natural oxide film are dissolved into the cleaning solution again. At the same time, DHF cleaning can inhibit the formation of natural oxide film, inhibit the adhesion of metal and boron element B in the cleaning solution, and improve surface cleanliness.

[0053] Step S9: The PFA plug loaded with the 6-inch silicon carbide wafer is transferred to a water ultrasonic tank for water ultrasonic cleaning. In this embodiment, deionized water DIW is used for water ultrasonic cleaning. The water ultrasonic frequency is controlled by current, and the water ultrasonic current is controlled at 1.4 to 1.6 A. The water ultrasonic process includes water inlet, overflow, ultrasonic cleaning, and rapid drainage, and is repeated three times for a time of 10 to 15 minutes.

[0054] Water ultrasound can quickly remove residual chemical liquid and micro-particle impurities on the surface of the silicon carbide wafer, making the surface of the silicon carbide wafer clean.

[0055] Step S10: Transfer the PFA plug loaded with 6-inch silicon carbide wafers to a rotary dryer, and dry the wafer surface through centrifugal force. To prevent water splashing back and contaminating the wafer during the drying process, the speed and time of the dryer need to be controlled. In this embodiment, the speed of the dryer is controlled to 900 rpm, and the time is 10 to 15 minutes. After the drying is completed, the surface of the wafer is dry and there is no water stain left. Anti-static control is required during the drying process to prevent the occurrence of electrostatic adsorption, and high-purity nitrogen is introduced for protection. It is worth noting that the inner wall of the dryer needs to be cleaned before drying. In this embodiment, dust-free cloth and ultrapure water are used for cleaning. After cleaning, a strong light is used to visually check the cleanliness to ensure that there is no dirt.

[0056] Step S11: The dried silicon carbide wafers are transferred from the PFA block to the PP block using a clean wafer reversing device, completing the unloading process. The use of tools such as suction pens and edge trimmers is eliminated during the wafer transfer process to reduce contamination sources.

[0057] In the step S11, the PP plug is cleaned for 10 minutes using water ultrasound, and the PP plug is quickly dried in a spin dryer.

[0058] like Figure 2 As shown, the residual concentration of boron ions after cleaning using the existing technology is between 91.97 and 320.48; the average level is between 150 and 200; the fluctuation is large, and the stability of the cleaning effect is poor.

[0059] like Figure 3 As shown, the residual concentration of boron ions after cleaning using the cleaning method provided by the present invention is between 5.83 and 7.93, with an average level between 6 and 7; the fluctuation is small, and the cleaning effect is more stable; it is significantly better than the cleaning method of the prior art.

[0060] like Figure 4 As shown, it is a box diagram of the boron element B content of the prior art and the cleaning method provided by the present invention (new technology); it can be clearly seen from the figure that the cleaning method provided by the present invention is significantly better than the cleaning method of the prior art; the concentration range of the prior art is larger at 179.35; the concentration range of the present invention is smaller at 6.68.

[0061] 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 considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for effectively cleaning and removing boron residue from the surface of a silicon carbide wafer, characterized in that: The following steps are involved: Step S1: Transfer the silicon carbide wafer to the PFA plug for loading; Step S2: Soaking the silicon carbide wafer in SPM solution, wherein the soaking temperature of the SPM solution is controlled within a range of 120-130° C. and the treatment time is controlled within a range of 20-25 minutes; Step S3: Transfer the silicon carbide wafer to a pure water tank and perform water ultrasonic cleaning for 10 to 15 minutes; Step S4: Soaking the silicon carbide wafer in APM solution, wherein the soaking temperature of the APM solution is controlled within a range of 45-55° C., and the treatment time is controlled within a range of 20-25 minutes; Step S5: transferring the silicon carbide wafer to a pure water tank and performing water ultrasonic cleaning for 10 to 15 minutes; Step S6: Repeat steps S2 to S5 at least once; Step S7: Transfer the silicon carbide wafer to a pure water tank and let it stand for 40 to 50 minutes; Step S8: Soaking the silicon carbide wafer in DHF solution, wherein the soaking temperature of the DHF solution is controlled within a range of 20 to 30° C., and the treatment time is controlled within a range of 20 to 25 minutes; Step S9: transferring the silicon carbide wafer to a pure water tank and performing water ultrasonic cleaning for 10 to 15 minutes; Step S10: transferring the silicon carbide wafer to a spin dryer to quickly dry the silicon carbide wafer; Step S11: Transfer the dried silicon carbide wafer into the cleaned PP plug to complete the unloading.

2. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 1, characterized in that: In the step S10, high-purity nitrogen is introduced for protection during the drying process, and the drying time is 10 to 15 minutes; the silicon carbide wafer is dried at a speed of 900 rpm.

3. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 1, characterized in that: In step S11, a wafer reversal device is used to transfer the wafer from the PFA plug to the PP plug at one time.

4. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 1, characterized in that: In step S2, the ratio of the SPM solution is: 98% concentrated sulfuric acid: 30%-32% hydrogen peroxide = 3:1; the 98% concentrated sulfuric acid and 30%-32% hydrogen peroxide are electronic grade chemicals, and the metal ion content needs to be less than 1 ppb.

5. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 1, characterized in that: In step S4, the ratio of the APM solution is: 28% to 30% ammonia solution: 30% to 32% hydrogen peroxide: deionized water (DIW) = 1:1:5; the 28% to 30% ammonia solution and 30% to 32% hydrogen peroxide are electronic grade chemicals, and the metal ion content needs to be less than 1 ppb.

6. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 1, characterized in that: In step S8, the ratio of DHF solution: 49% hydrofluoric acid solution: deionized water (DIW) is 1:50, and the hydrofluoric acid grade is electronic grade chemical, and the metal ion content needs to be less than 0.1 ppb.

7. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 1, characterized in that: The water ultrasonic cleaning uses deionized water DIW, the temperature is controlled in the range of 20-30°C, the ultrasonic cleaning frequency adopts 80-120KHz frequency conversion mode, and the ultrasonic transmission mode is longitudinal liquid transmission; the water ultrasonic cleaning process includes water inlet, overflow, ultrasonic and drainage.

8. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 1, characterized in that: The ionized water DIW is added with a boron removal filter element to filter the existing water quality, so that the boron concentration is ≤100ppt and the metal ion concentration is ≤50ppt.

9. The method for effectively cleaning and removing boron residue on the surface of a silicon carbide wafer according to claim 3, characterized in that: In the step S11, the PP plug is cleaned for 10 minutes using water ultrasound, and the PP plug is quickly dried in a spin dryer.

Images