Sensor morphology control method and use

Abstract

The present invention relates to the technical field of semiconductors, and in particular to a sensor morphology control method and a use. The method comprises: performing shallow trench etching and deep trench etching on a first silicon wafer, to form on the first silicon wafer a cavity structure having an opening on the top and a stand column A and a stand column B in the interior, the height of the stand column A being smaller than that of the stand column B; bonding the first silicon wafer and a second silicon wafer by means of an oxide layer, and thinning the second silicon wafer; performing deep silicon etching on the second silicon wafer to form movable teeth and a gas introducing opening, gaps between the movable teeth exposing the oxide layer located on the upper surface of the stand column B, and the gas introducing opening being located on the side of the stand column A distant from the stand column B; and introducing etching gas by means of the gaps between the movable teeth and the gas introducing opening to etch the oxide layer located on the upper surface of the stand column B so as to release the movable teeth. The method can prevent the side wall of a movable structure from being damaged, can further solve the problem of a residual oxide layer for bonding 3D structures, and ensures that the performance of a device is reliable, improving the impact resistance of the device, and improving the reliability.

Description

A sensor shape control method and its application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 2023111107660, filed with the Chinese Patent Office on August 30, 2023, entitled “A method for morphology control of a sensor and its application,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present disclosure relates to the field of semiconductor technology, and in particular to a sensor morphology control method and application thereof. Background Art

[0004] The structural manufacturing process of inertial sensors with a comb-tooth structure is well compatible with conventional integrated circuit manufacturing processes, and therefore has attracted widespread attention. Common inertial sensors with a comb-tooth structure include comb-tooth structure capacitive acceleration sensors.

[0005] The structure of an inertial sensor with a comb-tooth structure is usually made by directly bonding a silicon wafer to another silicon wafer with a cavity structure, and then deep silicon etching is used to etch through the upper silicon wafer above the cavity structure to form the comb-tooth structure.

[0006] Research by the authors found that as the upper silicon wafer is gradually etched through the deep silicon etching process, the movable teeth's free space is gradually freed up. Even after this free space is freed up, the etching process must continue for a period of time. During this over-etching period, the movable teeth tilt due to their own gravity and internal electrostatic forces, exposing their sides to the plasma bombardment and causing structural damage.

[0007] Summary of the Invention

[0008] The objectives of the present disclosure include, for example, providing a sensor morphology control method and its application, which can overcome the problem of residual oxide layer of bonded 3D structure while avoiding damage to the side wall of the movable structure, and has a large redundancy in the etching process of the oxide layer to ensure the reliable performance of the device; after adding a buffer stop pile, the impact resistance of the device is improved and the reliability is enhanced.

[0009] In a first aspect, the present disclosure provides a method for controlling the morphology of a sensor, comprising the following steps:

[0010] (a) providing a first silicon wafer, and sequentially performing shallow trench etching and deep trench etching at predetermined locations on the first silicon wafer, wherein the deep trench etching area partially covers the shallow trench etching area, thereby forming a cavity structure on the first silicon wafer having an opening at the top and having pillars A and B therein; wherein the height of the pillars A is less than the height of the pillars B;

[0011] (b) forming an oxide layer on the upper surface of the first silicon wafer;

[0012] (c) providing a second silicon wafer, bonding the first silicon wafer and the second silicon wafer via the oxide layer, and thinning the second silicon wafer to a predetermined thickness;

[0013] (d) deep silicon etching the second silicon wafer to form movable teeth and a gas introduction opening, wherein the gap between the movable teeth exposes the oxide layer on the upper surface of the B pillar, and the gas introduction opening is located on the side of the A pillar away from the B pillar;

[0014] (e) introducing an etching gas through the gap between the movable teeth and the gas introduction opening to etch the oxide layer on the upper surface of the B pillar to release the movable teeth.

[0015] The described sensor morphology control method can overcome the problem of residual oxide layer in the bonded 3D structure while avoiding damage to the side walls of the movable structure. It has a large redundancy in the etching process of the oxide layer, ensuring the reliable performance of the device. After adding a buffer stop pile, the impact resistance of the device is improved, and the reliability is optionally improved.

[0016] Optionally, the shallow trench etching has a depth of 0.5 to 5 μm.

[0017] Optionally, the height difference between the A pillar and the B pillar is 0.5 to 5 μm.

[0018] Optionally, when the deep silicon etching is performed on the second silicon wafer to form the movable tooth, the portion of the second silicon wafer connected to the movable tooth constitutes a gear pivot, the B column is close to the gear pivot of the movable tooth, and the A column is close to an end of the movable tooth relatively away from the gear pivot.

[0019] Optionally, a deep silicon etching process is used to perform shallow trench etching.

[0020] Optionally, a deep silicon etching process is used to perform deep trench etching.

[0021] Optionally, the oxide layer has a thickness of 0.9 to 1.1 μm.

[0022] Optionally, the oxide layer includes a silicon dioxide layer.

[0023] Optionally, VHF is used to etch the oxide layer.

[0024] Optionally, the oxide layer is formed by a low pressure chemical vapor deposition method.

[0025] Optionally, the distance between the upper surface of the A pillar and the upper surface of the first silicon wafer is equal to the depth of the shallow groove, and the upper surface of the B pillar is flush with the upper surface of the first silicon wafer;

[0026] The height difference between the A column and the B column is the depth of the shallow groove.

[0027] Optionally, the size of the bonding area between the first silicon wafer and the second silicon wafer is larger than an actually required bonding size, and the excess portion serves as an etching buffer zone.

[0028] Optionally, the gas introduction opening is communicated with the cavity structure of the first silicon wafer.

[0029] In a second aspect, the present disclosure provides a method for preparing an inertial sensor, including the aforementioned method for controlling the morphology of the sensor.

[0030] The inertial sensor prepared by the preparation method of the inertial sensor has reliable performance, good comb-tooth structure morphology, high sensitivity and high impact resistance.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The morphology control method of the sensor provided by the present invention can overcome the problem of residual oxide layer of the bonded 3D structure while avoiding damage to the side wall of the movable structure, and has a large redundancy in the etching process of the oxide layer, thereby ensuring the reliable performance of the device; after adding a buffer stop pile, the impact resistance of the device is improved, and the reliability is optionally improved.

[0033] (2) The inertial sensor prepared by the method provided in the present disclosure has reliable performance, good comb-tooth structure morphology, high sensitivity, and high impact resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] FIG1 is a schematic top view of a comb structure of a conventional comb-tooth capacitive acceleration sensor;

[0036] FIG2 is a schematic diagram of an idealized comb structure;

[0037] FIG3 is a schematic diagram of a damaged comb structure;

[0038] FIG4 is a schematic diagram of shallow trench etching according to the present disclosure;

[0039] FIG5 is a schematic diagram of etching positions for deep trench etching according to the present disclosure;

[0040] FIG6 is a schematic top view of the etching position of the deep trench etching disclosed in the present invention;

[0041] FIG7 is a schematic diagram of etching to form deep trenches according to the present disclosure;

[0042] FIG8 is a schematic diagram of growing an oxide layer according to the present disclosure;

[0043] FIG9 is a schematic diagram of bonding a first silicon wafer and a second silicon wafer according to the present disclosure;

[0044] FIG10 is a schematic diagram of etching a second silicon wafer according to the present disclosure;

[0045] FIG11 is a schematic diagram of the gas flow during the removal of the oxide layer according to the present disclosure;

[0046] FIG12 is a schematic diagram of the present disclosure after the oxide layer is removed.

[0047] Reference numerals: 1- movable tooth, 2- tooth pivot, 3- shallow groove, 4- first silicon wafer, 5- gas introduction opening, 6- A column, 7- B column, 8- oxide layer, 9- second silicon wafer. DETAILED DESCRIPTION

[0048] The technical solutions of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but those skilled in the art will understand that the embodiments described below are part of the embodiments of the present disclosure, rather than all of the embodiments, and are only used to illustrate the present disclosure, and should not be considered as limiting the scope of the present disclosure. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present disclosure. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0049] As shown in Figure 1, the comb structure is divided into movable teeth and fixed teeth. The width of the comb teeth and the distance between the comb teeth are fixed values ​​by design.

[0050] As shown in FIG2 , the idealized comb-tooth structure has a vertical and flat morphology. The morphology of the comb-tooth structure plays a crucial role in the performance of the inertial sensor.

[0051] As the upper silicon wafer is gradually etched through the deep silicon etching process, the movable teeth gradually free up space. Due to the etch rate characteristics of the wafer-level etching process, an over-etching period is required to ensure the etching effect of the entire wafer. After the freeing space is released, the etching process still needs to continue for a period of time.

[0052] As shown in FIG3 , during the over-etching time, the movable tooth will tilt due to its own gravity and internal electrostatic force, thereby exposing the side of the movable tooth to the bombardment range of the etching plasma and causing structural damage.

[0053] Therefore, the present disclosure proposes a method for controlling the morphology of a sensor, comprising the following steps:

[0054] (a) Providing a first silicon wafer 4, and sequentially performing shallow trench etching (as shown in FIG. 4 ) and deep trench etching (as shown in FIG. 5 , FIG. 6 , and FIG. 7 , with the etched portions of the deep trench etching indicated by the shaded portions in the figures) at predetermined locations on the first silicon wafer 4 , wherein the deep trench etching area partially covers the shallow trench etching area, thereby forming a cavity structure on the first silicon wafer 4 having an opening at the top and having A pillars 6 and B pillars 7 therein, wherein the height of the A pillars 6 is less than the height of the B pillars 7 ;

[0055] (b) forming an oxide layer 8 on the upper surface of the first silicon wafer 4 (as shown in FIG8 );

[0056] (c) providing a second silicon wafer 9, bonding the first silicon wafer 4 and the second silicon wafer 9 via the oxide layer 8, and thinning the second silicon wafer 9 to a predetermined thickness (as shown in FIG. 9 );

[0057] (d) Deep silicon etching is performed on the second silicon wafer 9 to form movable teeth 1 and gas introduction openings 5. The gaps between the movable teeth 1 expose the oxide layer 8 on the upper surface of the B pillar 7. The gas introduction openings 5 ​​are located on the side of the A pillar 6 away from the B pillar 7 (as shown in FIG. 10 ).

[0058] (d) An etching gas is introduced through the gap of the movable tooth 1 and the gas introduction opening 5 to etch the oxide layer 8 on the upper surface of the B pillar 7 to release the movable tooth 1 (as shown in FIG. 12 ).

[0059] Based on the above-mentioned sensor morphology control method, while the first silicon wafer 4 and the second silicon wafer 9 are bonded through the oxide layer 8, the upper surface of the B pillar 7 is also anchored to the corresponding area of ​​the second silicon wafer 9 through the oxide layer 8. It can be understood that the B pillar 7 acts as a fixed anchor and is configured to prevent the movable tooth 1 from tilting during deep silicon etching, thereby improving the morphology of the movable tooth 1. In addition, the etching gas introduction space formed by the gap of the movable tooth 1 is small, and it is difficult to introduce sufficient etching gas only through the gap of the movable tooth 1, so there is a risk of incomplete etching of the oxide layer 8 on the upper surface of the B pillar 7, and there is a risk of adhesion between the residual oxide layer 8 and the movable tooth 1. By providing a gas introduction opening 5 on the side of the A pillar 6 away from the B pillar 7, sufficient etching gas can be introduced, and the gap between the A pillar 6 and the second silicon wafer 9 helps to guide the etching gas to flow to the B pillar 7, thereby solving the problem of residual oxide layer 8 and ensuring that the movable tooth 1 is released.

[0060] The following is a more detailed description of the above-mentioned sensor morphology control method.

[0061] As shown in Figure 4 , shallow trenches 3 are formed by shallow trench etching, with a depth of D. As shown in Figures 5-7 , deep trench etching is further performed on top of the shallow trench etching, with the deep trench etching partially covering the shallow trench etching. Thus, by sequentially performing shallow trench etching and deep trench etching, pillars A 6 and B 7 of different heights are formed, with pillar A 6 being shorter than pillar B 7.

[0062] Specifically, the distance from the upper surface of column A 6 to the upper surface of the first silicon wafer 4 is equal to the depth of the shallow groove 3 , and the upper surface of column B 7 is flush with the upper surface of the first silicon wafer 4 , that is, the height difference between column A 6 and column B 7 is the depth of the shallow groove 3 .

[0063] The B column 7 acts as a fixing anchor for the movable tooth 1 through the oxide layer 8 on its upper surface during the process of deep silicon etching to form the movable tooth 1, preventing the movable tooth 1 from tilting under the action of its own gravity or internal electrostatic force, thereby avoiding damage to the side of the movable tooth 1.

[0064] Because the height of pillar A 6 is less than that of pillar B 7 , a gap exists between pillar A 6 and the second silicon wafer 9 . Etching gas entering through gas introduction opening 5 can be guided by this gap toward pillar B 7 , fully etching the oxide layer 8 on the upper surface of pillar B 7 , thereby releasing the movable tooth 1 . In addition to guiding the etching gas in conjunction with the second silicon wafer 9 , pillar A 6 itself also acts as a barrier and buffer. Specifically, as shown in Figure 1 , under normal conditions, when the movable tooth 1 senses corresponding external motion, it moves in a plane in a left-right direction. However, the movable tooth 1 may experience out-of-plane motion due to unexpected external forces or its own inertia. In this case, pillar A 6 acts as a barrier and buffer, preventing damage to the movable tooth 1 due to large amplitude vibrations. The depth of the shallow groove 3 determines the vertical gap between pillar A 6 and the movable structure where the movable tooth 1 resides. A gap that is too large will not function as a barrier and buffer, while a gap that is too small will restrict the movable structure's range of motion.

[0065] Based on this, the depth of the shallow groove 3 is comprehensively designed. Optionally, the depth of the shallow groove 3 is 0.5-5 μm. For example, the depth of the shallow groove 3 in the present disclosure can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0066] The height difference between pillars A 6 and B 7 is equal to the depth of the shallow groove 3. Therefore, the height difference between pillars A 6 and B 7 is optionally 0.5 to 5 μm. For example, in the present disclosure, the height difference between pillars A 6 and B 7 can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm.

[0067] In conjunction with Figures 1 and 12, when the second silicon wafer 9 is deep silicon etched to form the movable tooth 1, the portion of the second silicon wafer 9 connected to the movable tooth 1 constitutes the gear pivot 2. That is, one end of the movable tooth 1 is connected to the gear pivot 2, and the other end is a free end. When the movable tooth 1 is subjected to an unexpected external force or its own inertia, the vibration amplitude generated by the end of the movable tooth 1 connected to the gear pivot 2 is smaller, and the vibration amplitude generated by the free end of the movable tooth 1 is larger. Based on this, the B column 7 is close to the gear pivot 2 of the movable tooth 1, and the A column 6 is close to the end of the movable tooth 1 relatively far away from the gear pivot 2, to ensure that the A column 6 and the B column 7 do not affect the normal movement of the movable tooth 1. At the same time, the A column 6 can timely block and buffer the movable tooth 1 when the movable tooth 1 vibrates.

[0068] Optionally, a deep silicon etching process is used to perform shallow trench etching.

[0069] Optionally, a deep silicon etching process is used to perform deep trench etching.

[0070] It is understandable that both shallow trench etching and deep trench etching can adopt deep silicon etching process and can use the same type of equipment, which can help reduce the investment in equipment types and reduce production costs.

[0071] In conjunction with Figures 10-12, a gas introduction opening 5 and a gap between the A pillar 6 and the second silicon wafer 9 are provided. The gas introduction opening 5 is connected to the cavity structure of the first silicon wafer 4, providing space for the etching gas to enter. The gap between the A pillar 6 and the second silicon wafer 9 facilitates the guidance of the etching gas to the oxide layer 8 on the B pillar 7, thereby facilitating the etching of the oxide layer 8 on the B pillar 7, thereby releasing the movable teeth 1. However, above the B pillar 7, there is only a gap between the movable teeth 1, which is relatively small and difficult for the etching gas to enter. The flow of gas when removing the oxide layer 8 is shown in Figure 11, where the arrows indicate the flow of the etching gas.

[0072] In order to prevent the etching gas from etching the oxide layer 8 and affecting the bonding strength, the size of the bonding area between the first silicon wafer 4 and the second silicon wafer 9 is larger than the actual required bonding size, and the excess part serves as an etching buffer, thereby ensuring that the bonding strength between the first silicon wafer 4 and the second silicon wafer 9 meets the requirements.

[0073] Optionally, the thickness of the oxide layer 8 is 0.9 to 1.1 μm. For example, in the present disclosure, the thickness of the oxide layer 8 can be 0.9 μm, 1.0 μm, or 1.1 μm. This configuration ensures bonding strength while also facilitating etching and removing the oxide layer 8 on the B-pillar 7.

[0074] Optionally, the oxide layer 8 includes a silicon dioxide layer.

[0075] Optionally, VHF (gaseous hydrofluoric acid) is used to etch the oxide layer 8. Using VHF as etching gas can etch the oxide layer 8 in the desired area while having little effect on the bonding area, and a certain etching buffer area is required in the bonding area.

[0076] Optionally, the oxide layer 8 is formed by a low-pressure chemical vapor deposition process. The oxide layer 8 grown by this method has good step coverage, good uniformity, dense material, and high bonding quality.

[0077] Another aspect of the present disclosure relates to a method for preparing an inertial sensor, including the aforementioned method for controlling the morphology of the sensor.

[0078] Although the present disclosure has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features therein may be replaced by equivalents, without departing from the spirit and scope of the present disclosure. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present disclosure. Therefore, this means that all such replacements and modifications within the scope of the present disclosure are included in the appended claims. Industrial Applicability

[0079] The sensor morphology control method provided by the present invention can overcome the problem of residual oxide layer of the bonded 3D structure while avoiding damage to the side wall of the movable structure, and has a large redundancy in the etching process of the oxide layer, thereby ensuring the reliable performance of the device; after adding a buffer stop pile, the impact resistance of the device is improved, and the reliability is optionally improved.

Claims

1. A method for controlling the morphology of a sensor, characterized in that: The following steps are involved: (a) providing a first silicon wafer, and sequentially performing shallow trench etching and deep trench etching at a set position on the first silicon wafer, wherein the deep trench etching area partially covers the shallow trench etching area, so that a cavity structure having an opening at the top and having A columns and B columns inside is formed on the first silicon wafer; the height of the A column is less than the height of the B column; (b) forming an oxide layer on the upper surface of the first silicon wafer; (c) providing a second silicon wafer, bonding the first silicon wafer and the second silicon wafer through the oxide layer, and thinning the second silicon wafer to a preset thickness; (d) deep silicon etching the second silicon wafer to form movable teeth and a gas introduction opening, wherein the gap between the movable teeth exposes the oxide layer on the upper surface of the B pillar, and the gas introduction opening is located on a side of the A pillar away from the B pillar; (e) introducing an etching gas through the gap of the movable tooth and the gas introduction opening to etch the oxide layer on the upper surface of the B pillar to release the movable tooth.

2. The method for controlling the morphology of a sensor according to claim 1, characterized in that: The shallow groove etching has a depth of 0.5 to 5 μm.

3. The sensor morphology control method according to claim 1 or 2, characterized in that: The height difference between the A column and the B column is 0.5-5 μm.

4. The method for controlling the morphology of a sensor according to any one of claims 1 to 3, characterized in that: When the second silicon wafer is deeply silicon-etched to form the movable tooth, the portion of the second silicon wafer connected to the movable tooth constitutes a tooth pivot, the B column is close to the tooth pivot of the movable tooth, and the A column is close to an end of the movable tooth relatively far from the tooth pivot.

5. The method for controlling the morphology of a sensor according to any one of claims 1 to 4, characterized in that: The shallow trench is etched using a deep silicon etching process.

6. The method for controlling the morphology of a sensor according to any one of claims 1 to 5, characterized in that: The deep trench etching is performed using a deep silicon etching process.

7. The method for controlling the morphology of a sensor according to any one of claims 1 to 6, characterized in that: The thickness of the oxide layer is 0.9-1.1 μm.

8. The method for controlling the morphology of a sensor according to any one of claims 1 to 6, characterized in that: The oxide layer includes a silicon dioxide layer.

9. The method for controlling the morphology of a sensor according to any one of claims 1 to 8, characterized in that: The oxide layer is etched using VHF.

10. The method for controlling the morphology of a sensor according to any one of claims 1 to 9, characterized in that: The oxide layer is formed by a low pressure chemical vapor deposition method.

11. The method for controlling the morphology of a sensor according to any one of claims 1 to 10, characterized in that: The distance between the upper surface of the A column and the upper surface of the first silicon wafer is equal to the depth of the shallow groove, and the upper surface of the B column is flush with the upper surface of the first silicon wafer; The height difference between the A column and the B column is equal to the depth of the shallow groove.

12. The method for controlling the morphology of a sensor according to any one of claims 1 to 11, characterized in that: The size of the bonding area between the first silicon wafer and the second silicon wafer is larger than the actually required bonding size, and the excess portion is used as an etching buffer zone.

13. The method for controlling the morphology of a sensor according to any one of claims 1 to 12, characterized in that: The gas introduction opening is communicated with the cavity structure of the first silicon wafer.

14. A method for preparing an inertial sensor, characterized in that: A method for controlling the morphology of a sensor comprising the steps of any one of claims 1 to 13.

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