Method for controlling silicon thickness of MEMS cavity structure based on ion beam trimming technology

Abstract

The invention discloses a method for controlling the silicon thickness of an MEMS cavity structure based on an ion beam trimming technology, and the method comprises the following steps: S1, depositing a dielectric layer on a silicon substrate, and forming a patterned wet etching mask layer; s2, on the basis of the position of the mask opening, etching the silicon through alkali etching liquid to form a preliminary MEMS cavity, and controlling the thickness of the residual silicon to be greater than the target thickness by H2 reservation at most; and S3, measuring the silicon thickness at the cavity after the step S2, calculating the difference H2 between the actual thickness and the target thickness, and removing the H2 thickness at the bottom of the silicon substrate through a TRIM (ion beam trimming) technology. According to the method, a small amount of time is shortened in the process of wet etching of the silicon substrate, the thickness of residual silicon in the cavity is increased to a redundant target value, and then the redundant thickness is transferred to be removed by TRIM (ion beam trimming) to form the cavity and reach the target value, so that the influence of wet etching on thickness uniformity and micro-size can be eliminated.

Description

Technical Field

[0001] The invention relates to the technical field of MEMS pressure sensor processing, and in particular to a method for controlling the silicon thickness of a MEMS cavity structure based on ion beam trimming technology. Background Art

[0002] MEMS pressure sensors are widely used in the automotive industry / medical equipment / Internet of Things and other fields. The current MEMS pressure sensors need to prepare a certain cavity structure. The existing method of controlling the silicon thickness of the cavity structure is relatively simple, that is, through wet etching, in which the choice of etching liquid includes KOH (potassium hydroxide) and TMAH (tetramethylammonium hydroxide). However, both of these etching liquids have inevitable shortcomings, which affect the final remaining silicon thickness. The main reason is: during the etching process, the product cavity requires a thickness of up to several hundred microns, and then a long time of etching is required. The concentration control of the etching machine may fluctuate, so the etching rate may have a certain deviation, and the final thickness may fluctuate compared to the cavity target value, and it cannot be completely and accurately controlled at the target value. Finally, when testing matching, the thickness difference affects the stress difference, which leads to electrical failure during matching and low device qualification rate. Therefore, how to accurately control the silicon thickness at the cavity silicon stress film is a technical problem that needs to be solved urgently. Summary of the invention

[0003] In order to solve the technical problems existing in the background technology, the present invention proposes a method for controlling the silicon thickness of a MEMS cavity structure based on ion beam trimming technology.

[0004] The present invention proposes a method for controlling the silicon thickness of a MEMS cavity structure based on ion beam trimming technology, comprising the following steps:

[0005] S1. Depositing a dielectric layer on a silicon substrate to form a patterned wet etching mask layer;

[0006] S2. Based on the mask opening position, the silicon is etched by alkaline etching solution to form a preliminary MEMS cavity, and the remaining silicon thickness is controlled to be at most H thicker than the target thickness. 2预留 , H 2预留 Not more than 3μm;

[0007] S3. Measure the silicon thickness at the cavity after step S2, calculate the difference H2 between the actual thickness and the target thickness, and remove the bottom H2 thickness on the silicon substrate through TRIM (ion beam trimming) technology.

[0008] Specifically, in step S1, a patterned mask layer is formed by photolithography and etching.

[0009] Specifically, the dielectric layer in step S1 may be silicon dioxide or silicon nitride.

[0010] As a further optimized solution of the present invention, the alkaline etching solution in step S2 is KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide).

[0011] As a further optimization scheme of the present invention, the thickness to be removed by TRIM (ion beam trimming) technology is divided into at least two TRIM (ion beam trimming) technologies, and the thickness removed by the previous TRIM (ion beam trimming) technology is greater than the thickness removed by the next TRIM (ion beam trimming) technology.

[0012] As a further optimized solution of the present invention, specifically S3 includes:

[0013] S31. Perform the first TRIM (ion beam trimming) technology to remove the H 21 Thickness;

[0014] S32. Measure the remaining silicon thickness after the first TRIM (ion beam trimming) technology, and perform the second TRIM (ion beam trimming) technology to remove the value H 22 Thickness;

[0015] S33. Measure the remaining silicon thickness after the second TRIM (ion beam trimming) technology, and perform the third TRIM (ion beam trimming) technology to remove the value H 23 Thickness;

[0016] H 21 >H 22 ≥H 23 , H 21 +H 22 +H 23 =H2.

[0017] As a further optimized solution of the present invention, H 21 =Silicon thickness at the cavity after the measurement step S2 - target thickness - 1 μm.

[0018] H 21 = silicon thickness at the cavity after step S2 measurement - target thickness - 1 μm;

[0019] As a further optimization scheme of the present invention, the remaining silicon thickness after the first TRIM (ion beam trimming) technology is measured, and the thickness of the second TRIM (ion beam trimming) is calculated: H 22 = silicon thickness at the cavity after the measurement step S31 - target thickness - 0.5 μm;

[0020] Measure the remaining silicon thickness after the second TRIM (ion beam trimming) technology and calculate the thickness of the third TRIM (ion beam trimming): H 23 To measure the difference between the remaining silicon thickness and the target thickness after the second TRIM (ion beam trimming) technology.

[0021] At present, the silicon thickness of the MEMS cavity structure is controlled by KOH or TMAH wet etching. During the etching process, the product cavity requires a thickness of up to several hundred microns, which requires a long time to etch. The concentration control of the etching machine may fluctuate, so the etching rate may have a certain deviation, and the final thickness may fluctuate compared to the cavity target value, and it cannot be completely and accurately controlled within the target value range. Among them, the TRIM (ion beam trimming) technology has a lower etching rate and a longer etching time, and it is more difficult to accurately control the silicon thickness. The present invention reduces a small amount of wet etching time, and then transfers part of the thickness to TRIM (ion beam trimming) for removal, so that the remaining silicon thickness fluctuates within the target range, eliminates the deviation caused by wet etching, and improves the device qualification rate.

[0022] In the present invention, the proposed method for controlling the silicon thickness of the MEMS cavity structure based on ion beam trimming technology reduces a small amount of time during the wet etching of the silicon substrate, so that the remaining silicon thickness in the cavity exceeds the target value, and then the excess thickness is transferred to TRIM (ion beam trimming) for removal, forming a cavity and reaching the target value, thereby eliminating the influence of wet etching on thickness uniformity and micro size. Furthermore, the silicon thickness is precisely controlled by adding multiple TRIM (ion beam trimming) technologies, and the existing equipment on the process line is used to expand the existing process capabilities and ensure that the wafer yield rate becomes higher.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a silicon with a thickness of H1 first etched by wet etching according to an embodiment of the present invention;

[0025] Figure 2 Schematic diagram of the structure of ion beam trimming (step S3) in this embodiment of the present invention;

[0026] Figure 3 For the present invention Figure 2 A partial enlarged view of area A in the middle. DETAILED DESCRIPTION

[0027] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar symbols throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0028] like Figure 1A method for controlling the silicon thickness of a MEMS cavity structure based on ion beam trimming technology is shown, comprising the following steps:

[0029] S1. Depositing a dielectric layer on a silicon substrate to form a patterned wet etching mask layer. Specifically, the patterned mask layer can be formed by photolithography and etching. Specifically, the dielectric layer can be silicon dioxide or silicon nitride;

[0030] S2. Based on the mask opening position, the silicon is etched by alkaline etching solution to form a preliminary MEMS cavity, such as Figure 1 The silicon thickness of the wet etching is H1; specifically, the remaining silicon thickness is controlled to be 2 μm more than the target thickness. It should be noted that the alkaline etching solution can be KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide);

[0031] S3. Measure the silicon thickness at the cavity after step S2, and calculate the difference H2 between the actual thickness and the target thickness. The thickness H2 at the bottom of the silicon substrate needs to be removed by TRIM (ion beam trimming) technology. Here, H2 is 3 μm.

[0032] Preferably, the thickness to be removed by the TRIM (ion beam trimming) technology is divided into at least two TRIM (ion beam trimming) technologies, and the thickness removed by the previous TRIM (ion beam trimming) technology is greater than the thickness removed by the next TRIM (ion beam trimming) technology; specifically, S3 includes:

[0033] S31. Perform the first TRIM (ion beam trimming) technology to remove a thickness of 1.5 μm;

[0034] S32. Perform a second TRIM (ion beam trimming) technique to remove a thickness of 1 μm;

[0035] S33. Perform a third TRIM (ion beam trimming) technique to remove a thickness of 0.5 μm;

[0036] H 21 >H 22 ≥H 23 , H 21 +H 22 +H 23 =H2.

[0037] By performing TRIM (ion beam trimming) three times, the thickness uniformity can be precisely controlled to avoid thickness deviation caused by fluctuations in wet etching rate, and the final film thickness can be measured within the target range.

[0038] Although the TMAH etching rate is low and the etching time is longer, it is more difficult to accurately control the silicon thickness. The present invention reduces a small amount of wet etching time and then transfers part of the thickness to TRIM (ion beam trimming) for removal, so that the remaining silicon thickness fluctuates within the target range, eliminates the deviation caused by wet etching, and improves the device qualification rate. Furthermore, the silicon thickness is accurately controlled by adding multiple TRIM (ion beam trimming) technologies, and the existing equipment on the process line is used to expand the existing process capabilities and ensure that the wafer output rate becomes higher.

[0039] Embodiment 2

[0040] The difference between this embodiment and the above embodiment is that:

[0041] A method for controlling the silicon thickness of a MEMS cavity structure based on ion beam trimming technology comprises the following steps:

[0042] S1. Depositing a dielectric layer on a silicon substrate to form a patterned wet etching mask layer. Specifically, the patterned mask layer can be formed by photolithography and etching. Specifically, the dielectric layer can be silicon dioxide or silicon nitride;

[0043] S2. Based on the mask opening position, the silicon is etched by alkaline etching solution to form a preliminary MEMS cavity, such as Figure 1 The silicon thickness of the wet etching is H1; specifically, the remaining silicon thickness is controlled to be 2 μm more than the target thickness. It should be noted that the alkaline etching solution can be KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide);

[0044] like Figure 2 As shown, S3. Measure the silicon thickness at the cavity after step S2, calculate the difference H2 between the actual thickness and the target thickness, and remove the bottom H2 thickness on the silicon substrate through TRIM (ion beam trimming) technology, where H2 is 2μm;

[0045] Preferably, the thickness to be removed by TRIM (ion beam trimming) technology is divided into at least two TRIM (ion beam trimming) technologies, and the thickness removed by the previous TRIM (ion beam trimming) technology is greater than the thickness removed by the next TRIM (ion beam trimming) technology; Figure 2-3 As shown, specifically S3 includes:

[0046] S31. Perform the first TRIM (ion beam trimming) technology to remove the H 21 Thickness;

[0047] S32. Measure the remaining silicon thickness after the first TRIM (ion beam trimming) technology, and perform the second TRIM (ion beam trimming) technology to remove the value H 22 Thickness;

[0048] S33. Measure the remaining silicon thickness after the second TRIM (ion beam trimming) technology, and perform the third TRIM (ion beam trimming) technology to remove the value H 23 Thickness;

[0049] H 21 >H 22 ≥H 23 , H 21 +H 22 +H 23 =H2.

[0050] Specifically, H 23 To measure the difference between the remaining silicon thickness and the target thickness after the second TRIM (ion beam trimming) technology.

[0051] H 21 = silicon thickness at the cavity after step S2 measurement - target thickness - 1 μm;

[0052] H 22 = silicon thickness at the cavity after measurement step S31 - target thickness - 0.5 μm.

[0053] By performing TRIM (ion beam trimming) three times, the thickness uniformity can be precisely controlled to avoid thickness deviation caused by fluctuations in wet etching rate, and the final film thickness can be measured within the target range.

[0054] The difference between this embodiment and the above-mentioned embodiment is that the remaining silicon thickness is measured before each TRIM technical rest, and the thickness of each TRIM technical rest is obtained by calculation, thereby further increasing the accuracy and ensuring a higher wafer yield.

[0055] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for controlling the silicon thickness of a MEMS cavity structure based on ion beam trimming technology, characterized in that: The following steps are involved: S1. Depositing a dielectric layer on a silicon substrate to form a patterned wet etching mask layer; S2. Based on the mask opening position, the silicon is etched by alkaline etching solution to form a preliminary MEMS cavity, and the remaining silicon thickness is controlled to be at most H thicker than the target thickness. 2预留 , H 2预留 Not more than 3μm; S3. Measure the silicon thickness at the cavity after step S2, calculate the difference H2 between the actual thickness and the target thickness, and remove the bottom H2 thickness on the silicon substrate through TRIM (ion beam trimming) technology.

2. The method for controlling silicon thickness of a MEMS cavity structure based on ion beam trimming technology according to claim 1, characterized in that: In step S1, a patterned mask layer is formed by photolithography and etching.

3. The method for controlling silicon thickness of a MEMS cavity structure based on ion beam trimming technology according to claim 1, characterized in that: In step S1, the dielectric layer is silicon dioxide or silicon nitride.

4. The method for controlling silicon thickness of a MEMS cavity structure based on ion beam trimming technology according to claim 1, characterized in that: The alkaline etching solution in step S2 is a KOH (potassium hydroxide) solution or a TMAH (tetramethylammonium hydroxide) solution.

5. The method for controlling silicon thickness of a MEMS cavity structure based on ion beam trimming technology according to claim 1, characterized in that: In step S3, the thickness to be removed by TRIM (ion beam trimming) technology is divided into at least two TRIM (ion beam trimming) technologies, and the thickness removed by the previous TRIM (ion beam trimming) technology is greater than the thickness removed by the next TRIM (ion beam trimming) technology.

6. The method for controlling silicon thickness of a MEMS cavity structure based on ion beam trimming technology according to claim 5, characterized in that: Specifically, step S3 includes: S31. Perform the first TRIM (ion beam trimming) technology to remove the H 21 Thickness; S32. Perform the second TRIM (ion beam trimming) technology to remove the H 22 Thickness; S33. Measure the remaining silicon thickness after the second TRIM (ion beam trimming) technology, and perform the third TRIM (ion beam trimming) technology to remove the value H 23 Thickness; H 21 >H 22 ≥H 23 ,H 21 +H 22 +H 23 =H2。 7. The method for controlling silicon thickness of a MEMS cavity structure based on ion beam trimming technology according to claim 6, characterized in that: H 21 = silicon thickness at the cavity after step S2 measurement - target thickness - 1 μm; Measure the remaining silicon thickness after the first TRIM (ion beam trimming) technology and calculate the thickness of the second TRIM (ion beam trimming): H 22 = silicon thickness at the cavity after the measurement step S31 - target thickness - 0.5 μm; Measure the remaining silicon thickness after the second TRIM (ion beam trimming) technology and calculate the thickness of the third TRIM (ion beam trimming): H 23 To measure the difference between the remaining silicon thickness and the target thickness after the second TRIM (ion beam trimming) technology.

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