Method for improving poor particle pollution of silicon substrate with polycrystalline silicon growing on back surface

Abstract

The invention provides a method for improving poor particle pollution of a silicon substrate with polycrystalline silicon growing on the back surface, which mainly comprises the following steps of: cleaning a completed silicon wafer by using an RCA cleaning machine; and the cleaned silicon wafer is subjected to the following technological processes of wafer combination, furnace loading, polycrystalline silicon deposition, cooling and wafer separation. After the flow is completed, the obtained silicon wafer can be used for a subsequent polishing process and the like. According to the method, the problem that the pollution of the silicon substrate particles with the polycrystalline silicon growing on the back surface is poor due to the defects in the prior art can be solved, so that the problem that the pollution of the silicon substrate particles with the polycrystalline silicon growing on the back surface is poor in the technological process is solved, and the yield of the silicon wafer is improved.

Description

Technical Field

[0001] The invention provides a method for improving the particle contamination of a silicon substrate on which polysilicon is grown on the back, and is used to solve the problem of particle contamination and polishing defects of the silicon substrate on which polysilicon is grown on the back in a process flow. Background Art

[0002] In order to reduce the impact of micro defects on the surface quality of silicon wafers or prevent the self-doping effect of "heavily doped" silicon wafers during the silicon epitaxial process, the back surface of the silicon wafer needs to be treated with "back surface" according to IC process requirements.

[0003] According to IC process requirements, for "heavily doped" silicon wafers, a silicon dioxide film is generally required to be grown on the back of the silicon wafer. For "lightly doped" silicon wafers, a polysilicon film is required to be grown on the back of the silicon wafer to play the role of external impurity gettering. This process is called "LPCVD" (polycrystalline silicon deposition).

[0004] The general LPCVD (polysilicon deposition) process can perform enhanced gettering technology on the back surface of the silicon substrate to grow polysilicon, which can make the quality of the polysilicon film and silicon dioxide film grown on the back surface of the silicon wafer meet the requirements of the IC process, and the uniformity of the film thickness is relatively ideal. However, during the growth, some particles will adhere to the surface of the silicon wafer, and then the particles will leave marks on the back of the silicon wafer, forming particle pollution. It will appear in the subsequent polishing process, resulting in the problem of flatness defects in the silicon wafer. Summary of the invention

[0005] In order to improve the above situation, the purpose of the present invention is to provide a method for improving the poor contamination of silicon substrate particles with polysilicon grown on the back side, to improve the problem of poor contamination of silicon substrate particles with polysilicon grown on the back side which cannot be solved due to the shortcomings of the prior art, thereby solving the problem of poor contamination of silicon substrate particles with polysilicon grown on the back side in the process flow and improving the yield of silicon wafers.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] In one embodiment of the present invention, the method places the silicon wafer in a corresponding wafer basket for cleaning, and the cleaning process is: SC-1→DQR→SC-1→QDR→SC-2→QDR→O / F→Spin Dryer.

[0008] In one embodiment of the present invention, the method uses SC-1 cleaning, the cleaning temperature is 60-70° C., and the cleaning time is 240-360 seconds.

[0009] In one embodiment of the present invention, the method uses SC-2 cleaning, the cleaning temperature is 50-60° C., and the cleaning time is 240 to 360 seconds.

[0010] In one embodiment of the present invention, the silicon wafer of the present method needs to enter the polysilicon deposition furnace within 1 hour. If a timeout occurs, the cleaning process is rearranged to improve particle contamination on the wafer surface.

[0011] In one embodiment of the present invention, in the wafer joining process, the wafer basket is placed on a special fixture, and the H surface of the wafer basket corresponds to the U surface of another wafer basket. The wafer on the H surface should not contact the U surface of any wafer. If it does, a re-cleaning process is arranged. When joining, keep the H surface facing up and slide the wafer smoothly into the wafer basket. After completion, hold the sides of the wafer boat and the wafer basket, flip 180° in the vertical direction, and transfer the wafer into the quartz wafer boat.

[0012] In one embodiment of the present invention, during the furnace loading process of the method, the quartz crystal boat with the wafers arranged is placed into the furnace tube from the left side; 1-5 formal quartz crystal boats are placed each time. Two crystal boats filled with baffles are placed in front and behind the silicon wafers, and the five quartz crystal boats in the middle are silicon wafers. When there are less than 5 formal crystal boats, baffles are placed to replace them. Position reference Figure 1

[0013] In one embodiment of the present invention, in the polysilicon deposition process of the present method, before the reaction gas (SiH4) is introduced, the pipeline must be purged with N2 to ensure that the wafers in the furnace tube are not contaminated by particles.

[0014] In one embodiment of the present invention, the method includes N2 purging, the purge flow rate is 20-40 LPM, and the purge time is 5-10 min.

[0015] In one embodiment of the present invention, during the cooling process of the method, the wafer boat needs to be moved to the workbench more than 10 minutes after the arm completely stops, and then cooled for more than 30 minutes before arranging the wafers. Do not collide with the wafer boat when moving it.

[0016] In one embodiment of the present invention, during the slicing process of the method, a suction pen is used to separate the wafers on the wafer boat and transfer them to a wafer basket.

[0017] In one embodiment of the present invention, the polysilicon deposited silicon substrate obtained by the method has significantly improved particle contamination in appearance, and its flatness after polishing is better than that of a process not using the method.

[0018] Based on the above, the advantages and characteristics of the present invention are that the polysilicon deposited silicon substrate obtained by the method has significantly improved appearance particle contamination, and the flatness performance after polishing is better than the process without using the method. Therefore, the problem of particle contamination and polishing defects of the silicon substrate with polysilicon growing on the back side due to the shortcomings of the prior art is improved, thereby solving the problem of particle contamination and polishing defects of the silicon substrate with polysilicon growing on the back side in the process flow and improving the yield of silicon wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is how the crystal boat is placed during the furnace loading process.

[0020] Description of Figure Numbers

[0021] 1 Wafer boat for placing real chips

[0022] 2. Crystal boat with baffle

[0023] 3 Furnace tail

[0024] 4 Furnace mouth DETAILED DESCRIPTION

[0025] The following is a detailed description of a specific implementation of a method provided by the present invention for improving particle contamination of a silicon substrate having polysilicon grown on the back side.

[0026] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are described.

[0027] Step 1: Use RCA cleaning machine to clean the finished silicon wafer for step 2;

[0028] Step 2: The cleaned silicon wafers are processed according to the following process flow: wafer assembly, furnace loading, polysilicon deposition, cooling, and wafer separation. After completing the above process, the obtained silicon wafers can be used for subsequent polishing processes, etc. After the silicon wafers are cleaned, they need to be placed in the polysilicon deposition furnace within 1 hour. If a timeout occurs, the cleaning process should be rearranged to improve the particle contamination on the surface of the silicon wafer. In the wafer assembly process, the wafer basket is placed on a special fixture, and the H surface of the wafer basket corresponds to the U surface of another wafer basket. The wafer on the H surface should not touch the U surface of any wafer. If it touches, the cleaning process should be re-arranged. When assembling, keep the H surface facing up and slide the wafer into the wafer basket smoothly. After completion, hold the side of the wafer boat and the wafer basket, flip 180° vertically, and transfer the wafer into the quartz wafer boat. During the furnace loading process, the quartz crystal boat with arranged wafers is placed into the furnace tube from the left side; 1-5 formal quartz crystal boats are placed each time. Two crystal boats filled with baffles are placed in front and behind the silicon wafers, and the 5 quartz crystal boats in the middle are silicon wafers. When there are less than 5 formal crystal boats, baffles are placed instead. Among them, N2 purge, the purge flow rate is 20-40LPM, and the purge time is 5-10min. In the polysilicon deposition process, N2 must be used to purge the pipeline before the reaction gas (SiH4) is introduced. In the cooling process, it is necessary to wait for more than 10 minutes after the arm stops completely, move the crystal boat to the workbench, and then cool it for more than 30 minutes before arranging the wafers. Do not collide when moving the crystal boat. In the slicing process, use a suction pen to separate the wafers on the crystal boat and transfer them to the wafer basket.

[0029] The silicon wafer obtained by this method and the polysilicon deposited silicon substrate obtained have significantly improved appearance particle contamination, and the flatness after polishing is better than the process without this method. The effect is compared with the figure below, which can greatly reduce the problems of polysilicon deposited silicon particle contamination and polishing defects.

[0030] It should be understood that the specific embodiments described herein are only used to understand the present invention and are not used to limit the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A method for improving the particle contamination of a silicon substrate with polysilicon grown on the back, which is used to solve the problem of particle contamination and polishing defects of a silicon substrate with polysilicon grown on the back in the process flow. The method is: using an RCA cleaning machine to clean the silicon wafer; and following the following process flow to clean the silicon wafer: wafer assembly, furnace loading, polysilicon deposition, cooling, and wafer slicing.

2. A method for improving particle contamination of a silicon substrate on which polysilicon is grown on the back side as claimed in claim 1, characterized in that: The silicon wafer needs to enter the polysilicon deposition furnace within 1 hour. If a timeout occurs, the cleaning process will be rearranged.

3. A method for improving particle contamination of a silicon substrate on which polysilicon is grown on the back side as claimed in claim 1, characterized in that: In the wafer joining process, the wafer basket is placed on a special fixture, and the H surface of the wafer basket corresponds to the U surface of another wafer basket. The wafer on the H surface must not touch the U surface of any wafer. If it touches, a re-cleaning process is arranged. When joining, keep the H surface facing up and slide the wafer smoothly into the wafer basket. After completion, hold the sides of the wafer boat and the wafer basket, turn them 180 degrees in the vertical direction, and transfer the wafer into the quartz wafer boat.

4. A method for improving particle contamination of a silicon substrate on which polysilicon is grown on the back side as claimed in claim 1, characterized in that: In the furnace loading process, the quartz crystal boat with arranged wafers is placed into the furnace tube from the left side; 1-5 formal quartz crystal boats are placed each time; 2 crystal boats filled with baffles are placed in front and behind the silicon wafers, and the middle 5 quartz crystal boats are silicon wafers. When there are less than 5 formal crystal boats, baffles are placed instead.

5. A method for improving particle contamination of a silicon substrate on which polysilicon is grown on the back side as claimed in claim 1, characterized in that: In the polysilicon deposition process, before the reaction gas (SiH4) is introduced, the pipeline must be purged with N2; wherein the N2 purge has a purge flow rate of 20-40 LPM and a purge time of 5-10 min.

6. A method for improving particle contamination of a silicon substrate on which polysilicon is grown on the back side as claimed in claim 1, characterized in that: During the cooling process, the arm must be completely stopped for more than 10 minutes before the wafer boat is moved to the workbench, and then cooled for more than 30 minutes before arranging the wafers. Do not collide with the wafer boat when moving it.

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