A method for removing silicon mesa of MOEMS device

Abstract

The application provides a method for removing MOEMS device silicon grass, which comprises the following steps: S1, selecting an SOI wafer and etching to form a step; S2, cleaning the SOI wafer; S3, etching the top layer silicon and the step to form a comb structure and silicon grass; S4, arranging a thick passivation layer on the comb structure and the silicon grass; S5, removing the passivation layer on the horizontal plane by etching gas; S6, drilling the root of the step and the silicon grass by etching gas; S7, removing the passivation layer on the surface of the silicon grass by etching gas; S8, etching the silicon grass on the step by etching gas; and S9, cleaning the residual passivation layer and the silicon grass. The application is convenient to operate, the silicon grass is removed completely, the use reliability of the device is effectively improved, and the working life is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of MOMES device manufacturing technology field, specifically a kind of method for removing MOEMS device silicon grass of step. BACKGROUND

[0002] In the manufacture of a kind of MOMES device, often first form step, then carry out comb tooth structure etching, at this time there will be grass-like burr (silicon grass) at step, because these burrs are very like small grass under electron microscope, so we call it "silicon grass", these silicon grass are generally fragile, but under larger electrostatic force, easy to cause short circuit and damage comb tooth structure, thereby reduce the working reliability of device, shorten working life. And remove step silicon grass, the method commonly used is, after comb tooth structure etching, SF6 (sulfur hexafluoride) gas is inhaled for a certain time to etch silicon grass.

[0003] The problem of this removal mode is that when etching silicon grass, the side of comb tooth structure is exposed to etching gas and is also etched, thereby causing damage. At the same time, in order to reduce the damage of comb tooth structure, the flow, power and time of SF6 gas need to be strictly controlled, which leads to the difficulty in completely removing the step silicon grass. SUMMARY

[0004] The present application is to overcome the deficiencies in the prior art, and provides a method for removing MOEMS device step silicon grass.

[0005] The present application provides the following technical solutions:

[0006] A method for removing MOEMS device step silicon grass, comprising the following steps: selecting an SOI wafer and etching to form a groove body; S2, cleaning the SOI wafer; S3, etching the top layer of silicon to form a second groove body, forming a comb tooth structure and silicon grass, characterized in that: S4, using C4F8 gas to form a passivation layer on the comb tooth structure and silicon grass and the second groove body; S5, using SF6 gas to remove the passivation layer horizontally distributed on the second groove body, comb tooth structure and silicon grass; S6, SF6 gas performs horizontal etching on the bottom of the comb tooth structure and silicon grass, so that the silicon grass collapses; S7, using SF6 gas to remove the passivation layer on the upper surface of the collapsed silicon grass; S8, using SF6 gas to etch away the silicon grass; S9, cleaning the wafer to clean the residual passivation layer on the lower surface of the silicon grass and the remaining small amount of silicon grass debris.

[0007] On the basis of the above technical solutions, the following further technical solutions can also be provided:

[0008] In the step of S4, C4F8 gas becomes plasma under the action of radio frequency power, the time of C4F8 gas is 8s-12s, the flow rate is 300sccm-350sccm, the source power is 2500W-3000W, and the pressure is 30mtorr-40mtorr.

[0009] In the step of S5, SF6 gas becomes plasma under the action of radio frequency power, and positive particles SF5 + , the SF6 gas is bombarded under the action of lower electrode platen pull power, the time of SF6 gas is 3s-4s, the flow rate is 300sccm-350sccm, the source power is 2500W-3000W, the platen power is 300W-400W, and the pressure is 20mtorr-30mtorr.

[0010] In the step of S6, SF6 gas becomes plasma under the action of radio frequency power, and F* free radicals are generated, the time of SF6 gas is 10s-20s, the flow rate is 300sccm-350sccm, the source power is 2500W-3000W, the platen power is 30W-40W, and the pressure is 20mtorr-30mtorr.

[0011] In the step of S7, SF6 gas becomes plasma under the action of radio frequency power, and positive particles SF5 + , the SF6 gas is bombarded under the action of lower electrode platen pull power, the time of SF6 gas is 3s-4s, the flow rate is 300sccm-350sccm, the source power is 2500W-3000W, the platen power is 300W-400W, and the pressure is 20mtorr-30mtorr.

[0012] In the step of S8, SF6 gas becomes plasma under the action of radio frequency power, and F* free radicals are generated, the time of SF6 gas is 5s-10s, the flow rate is 300sccm-500sccm, the source power is 2500W-3000W, the platen power is 30W-40W, and the pressure is 20mtorr-30mtorr.

[0013] In the step of S9, the wafer is cleaned using EKC solution, and the cleaning time is greater than 30min, and the temperature is 75℃-85℃.

[0014] Advantages of the application:

[0015] The beneficial effect of the present application is that after forming the step and comb structure, the thick passivation layer is first used to protect the side of the comb structure, then the positively charged particles SF5 + bombard to remove the horizontal passivation layer, and then etch the step silicon grass root. Because the etching can be performed for a long time, the widest silicon grass root can also be completely etched. After the silicon grass is poured on the step, the side of the silicon grass has a passivation layer, and the positively charged particles SF5 + bombard to remove the horizontal passivation layer, and then etch the silicon grass, which can completely etch the silicon grass at the step. Finally, using an organic solvent to clean the surface of the step and the comb structure can effectively completely remove the passivation layer and the silicon grass. Thus, the reliability of the device is significantly improved, and the service life is increased. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structure schematic diagram after step S1 is completed;

[0017] Figure 2 is a structure schematic diagram after step S3 is completed;

[0018] Figure 3 is a structure schematic diagram after step S4 is completed;

[0019] Figure 4 is a structure schematic diagram after step S5 is completed;

[0020] Figure 5 is a structure schematic diagram after step S6 is completed;

[0021] Figure 6 is a structure schematic diagram after step S7 is completed;

[0022] Figure 7 is a structure schematic diagram after the silicon grass is etched in step S8;

[0023] Figure 8 is a structure schematic diagram after step S8 is completed;

[0024] Figure 9 is a structure schematic diagram after step S9 is completed. DETAILED DESCRIPTION

[0025] Example 1

[0026] As Figures 1-9 shown, a method for removing MOEMS device step silicon grass includes the following steps: selecting an SOI wafer, the wafer including a substrate 1, a buried oxygen layer 2, a top layer of silicon 3, a patterned oxide layer 4 and a bottom reaching buried oxygen layer 2 groove 31 formed on the top layer of silicon 3 surface. The height of the groove 31 is 25 μm, and the height of the groove 31 is defined as the height difference between the top layer of silicon 3 surface and the buried oxygen layer 2 surface.

[0027] S2, cleaning the SOI wafer with the EKC solution for more than 30 minutes at 76°C. This step can clean the passivation layer left over from the etching process.

[0028] S3, etching the second groove 34 on the top silicon layer 3 by Bosch process to form the comb structure 33 and the silicon grass 32. The depth of the comb structure 33 is usually 20 μm, and the width is usually 5 μm. The width of the silicon grass 32 is less than 1 μm, so the width of the comb structure 33 is much larger than that of the silicon grass 32.

[0029] S4, introducing C4F8 gas into the etching chamber, and the C4F8 gas becomes plasma under the action of the radio frequency power, thereby forming a passivation layer 5 with a thickness of more than 100 nm on the bottom surface of the second groove 34, the horizontal surface of the comb structure 33, the side surface of the comb structure 33, and the horizontal surface and side surface of the silicon grass 32. The C4F8 gas is introduced for 9 s at a flow rate of 310 sccm, the source power is 2700 W, and the pressure is 32 mtorr.

[0030] S5, introducing SF6 gas into the etching chamber, and the SF6 gas becomes plasma under the action of the radio frequency power, thereby generating positively charged particles SF5 + under the platen power, and the passivation layer 5 on the bottom surface of the second groove 34, the horizontal surface of the comb structure 33, and the horizontal surface of the silicon grass 32 is removed. However, the passivation layer 5 on the side surface of the comb structure 33 and the silicon grass 32 is retained, and the passivation layer 5 on the side surface of the comb structure 33 can block the etching gas SF6, thereby protecting the side surface of the comb structure 33. The SF6 gas is introduced for 3 s at a flow rate of 310 sccm, the source power is 2600 W, the platen power is 3200 W, and the pressure is 22 mtorr.

[0031] S6, the SF6 gas is introduced into the etching chamber again, and the SF6 gas becomes plasma under the action of the radio frequency power, thereby generating F* free radicals to perform lateral etching 35 on the bottom of the comb structure 33 and the silicon grass 32 and the contact with the bottom surface of the second groove 34. At this time, the passivation layer 5 on the side surface of the comb structure 33 and the silicon grass 32 blocks the F* free radicals, thereby protecting the side surface of the comb structure 33 and the silicon grass 32, and only the groove at the root of the comb structure 33 and the silicon grass 32 is etched. Since the width of the silicon grass 32 is much smaller than that of the comb structure 33, the comb structure 33 is still vertical when the root of the silicon grass 32 is completely etched and collapses. The SF6 gas is introduced for 12 s at a flow rate of 350 sccm, the source power is 3000 W, the platen power is 30 W, and the pressure is 20 mtorr.

[0032] S7, SF6 gas is introduced into the etching reaction chamber again, and the SF6 gas becomes plasma under the action of radio frequency power to generate positively charged particles SF5 + The passivation layer 5 on the surface of the silicon grass 32 is removed by bombarding the passivation layer 5 on the surface of the silicon grass 32 under the lower electrode platen under the pull power. The SF6 gas is introduced for 3 s at a flow rate of 300 sccm, the source power is 2500 W, the platen power is 40 W, and the pressure is 30 mtorr.

[0033] S8, SF6 gas is introduced into the etching reaction chamber again, and the SF6 gas becomes plasma under the action of radio frequency power to generate F* free radicals, and the silicon grass 32 is etched away, and a small amount of silicon grass 32 debris may remain. The SF6 gas is introduced for 5 s at a flow rate of 500 sccm, the source power is 2500 W, the platen power is 30 W, and the pressure is 20 mtorr.

[0034] S9, the wafer is cleaned with the EKC solution to clean all the passivation layer 5 remaining on the other side of the silicon grass 32. The cleaning time is greater than 30 min, and the temperature is 75°C. In the cleaning process, the remaining small amount of silicon grass 32 debris is also completely cleaned.

[0035] Example 2:

[0036] As shown in Figures 1-9 A method for removing MOEMS device step silicon grass, comprising the following steps: selecting an SOI wafer, the wafer comprising a substrate 1, a buried oxygen layer 2, a top layer of silicon 3, a patterned oxide layer 4 and a bottom groove 31 reaching the buried oxygen layer 2 formed on the surface of the top layer of silicon 3 by etching. The height of the groove 31 is 78 μm, and the height of the groove 31 is defined as the height difference between the surface of the top layer of silicon 3 and the surface of the buried oxygen layer 2.

[0037] S2, the SOI wafer is cleaned with the EKC solution for more than 30 min at a temperature of 84°C. This step can clean the passivation layer remaining during the etching of the step.

[0038] S3, a Bosch process is used to etch a second groove 34 on the top layer of silicon 3 to form a comb tooth and a silicon grass 32. The comb tooth structure 33 has a depth of 48 μm and a width of 7.5 μm, and the silicon grass 32 has a width of less than 1 μm, so that the width of the comb tooth structure 33 is much greater than the width of the silicon grass 32.

[0039] S4, C4F8 gas is introduced into the etching reaction chamber, and the C4F8 gas becomes plasma under the action of radio frequency power, thereby forming a passivation layer 5 with a thickness greater than 100 nm covering the groove bottom surface of the second groove body 34, the horizontal surface and side surface of the comb teeth, and the horizontal surface and side surface of the silicon grass 32. The C4F8 gas is introduced for 11 s at a flow rate of 350 sccm, the source power is 2900 W, and the pressure is 38 mtorr.

[0040] S5, SF6 gas is introduced into the etching reaction chamber, and the SF6 gas becomes plasma under the action of radio frequency power, thereby generating positively charged particles SF5 + The passivation layer 5 distributed on the groove bottom surface of the second groove body 34, the horizontal surface of the comb teeth, and the horizontal surface of the silicon grass 32 is removed completely under the bombardment of the SF6 gas under the pull power of the lower electrode platen. However, the passivation layer 5 on the side surface of the comb teeth and the silicon grass 32 is retained, and the passivation layer 5 on the side surface of the comb teeth can block the etching gas SF6 and play a role in protecting the side surface of the comb teeth. The SF6 gas is introduced for 4 s at a flow rate of 350 sccm, the source power is 2900 W, the platen power is 3200 W, and the pressure is 29 mtorr.

[0041] S6, SF6 gas is introduced into the etching reaction chamber again, and the SF6 gas becomes plasma under the action of radio frequency power, thereby generating F* free radicals to perform lateral etching 35 on the bottom of the comb teeth and the silicon grass 32 and the contact position with the groove bottom surface of the second groove body 34. At this time, the passivation layer 5 on the side surface of the comb tooth structure 33 and the silicon grass 32 blocks the F* free radicals and protects the side surface of the comb tooth structure 33 and the silicon grass 32, and only the groove at the etching position of the root of the comb tooth structure 33 and the silicon grass 32 is etched. Since the width of the silicon grass 32 is much smaller than the width of the comb tooth structure 33, the comb tooth structure 33 is still vertical when the root of the silicon grass 32 is completely etched and collapses. The SF6 gas is introduced for 19 s at a flow rate of 300 sccm, the source power is 2500 W, the platen power is 40 W, and the pressure is 30 mtorr.

[0042] S7, SF6 gas is introduced into the etching reaction chamber again, and the SF6 gas becomes plasma under the action of radio frequency power, thereby generating positively charged particles SF5 + The passivation layer 5 on the surface of the silicon grass 32 is removed completely under the bombardment of the SF6 gas under the pull power of the lower electrode platen. The SF6 gas is introduced for 4 s at a flow rate of 500 sccm, the source power is 3000 W, the platen power is 30 W, and the pressure is 20 mtorr.

[0043] S8, SF6 gas is introduced into the etching chamber again, and becomes plasma under the action of radio frequency power, to generate F* free radicals to etch away the silicon grass 32, and possibly a small amount of silicon grass 32 debris remains. The SF6 gas is introduced for 10 s, with a flow rate of 300 sccm, a source power of 2900 W, a platen power of 39 W, and a pressure of 30 mtorr.

[0044] S9, the wafer is cleaned with EKC solution to clean the passivation layer 5 remaining on the other side of the silicon grass 32. The cleaning time is greater than 30 min, and the temperature is 84℃. In the cleaning process, the remaining small amount of silicon grass 32 debris is also completely cleaned.

Claims

1. A method for removing silicon precipitates from MOEMS devices, comprising the following steps: S1. Select an SOI wafer and etch it to form a groove (31); S2. Clean the SOI wafer; S3. Etch the top silicon layer to form a second groove (34), forming a comb structure (33) and a silicon grass (32). The features are: S4. Use C4F8 gas to form a passivation layer (5) on the comb structure (33), the silicon grass (32) and the second groove (34); S5. Use SF6 gas to remove the passivation layer (5) horizontally distributed on the second groove (34), the comb structure (33) and the silicon grass (32), with a platen power of 300W-400W; S6. Use SF6 gas to perform lateral drilling (35) on the bottom of the comb structure (33) and the silicon grass (32), causing the silicon grass (32) to collapse, with a platen power of 30W-40W; S7. Use SF6 gas to remove the passivation layer (5) on the upper surface of the collapsed silicon grass (32). S8. Use SF6 gas to etch away the silica fume (32), with a platen power of 30W-40W. S9. Clean the wafer to remove the residual passivation layer (5) on the lower surface of the silica fume (32) and all remaining silica fume (32) debris.

2. The method for removing silicon deposits from MOEMS devices according to claim 1, characterized in that: In step S4, C4F8 gas is converted into plasma under the action of radio frequency power. The C4F8 gas usage time is 8s-12s, the flow rate is 300sccm-350sccm, the source power is 2500W-3000W, and the pressure is 30mtorr-40mtorr.

3. The method for removing silicon deposits from MOEMS devices according to claim 1, characterized in that: In step S5, SF6 gas is transformed into plasma under the action of radio frequency power, generating positively charged SF5 particles. + The SF6 gas is bombarded on the second groove (34), the comb structure (33) and the passivation layer (5) on the upper surface of the silica grass (32) under the pull-down power of the lower electrode platen. The time of the SF6 gas is 3s-4s, the flow rate is 300sccm-350sccm, the source power is 2500W-3000W, and the pressure is 20mtorr-30mtorr.

4. The method for removing silicon deposits from MOEMS devices according to claim 1, characterized in that: In step S6, SF6 gas is transformed into plasma under the action of radio frequency power, generating F* free radicals. The time for SF6 gas is 10s-20s, the flow rate is 300sccm-350sccm, the source power is 2500W-3000W, and the pressure is 20mtorr-30mtorr.

5. The method for removing silicon deposits from MOEMS devices according to claim 1, characterized in that: In step S7, SF6 gas is transformed into plasma under the action of radio frequency power, generating positively charged SF5 particles. + The passivation layer (5) is bombarded with SF6 gas for 3s-4s, with a flow rate of 300sccm-350sccm, a source power of 2500W-3000W, and a pressure of 20mtorr-30mtorr.

6. The method for removing silicon deposits from MOEMS devices according to claim 1, characterized in that: In step S8, SF6 gas is transformed into plasma under the action of radio frequency power, generating F* free radicals. The time for SF6 gas is 5s-10s, the flow rate is 300sccm-500sccm, the source power is 2500W-3000W, and the pressure is 20mtorr-30mtorr.

7. The method for removing silicon deposits from MOEMS devices according to claim 1, characterized in that: In step S9, the wafer is cleaned using EKC solution for a time of more than 30 minutes at a temperature of 75°C-85°C.

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