A sensor shape control method and its application

Abstract

The present invention relates to the field of semiconductor technology, and specifically to a sensor morphology control method and its application. The method comprises: performing shallow groove etching and deep groove etching on a first silicon wafer, forming a cavity structure with an opening on the top and A pillars and B pillars inside on the first silicon wafer; the height of the A pillar is less than that of the B pillar; bonding the first silicon wafer to the second silicon wafer through an oxide layer, and thinning the second silicon wafer; deep silicon etching the second silicon wafer to form movable teeth and gas introduction openings, the gap of 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; the etching gas is introduced through the gap of 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. The method can avoid damage to the side wall of the movable structure, and can also overcome the problem of residual oxide layer of the bonded 3D structure, ensuring the reliable performance of the device; improving the impact resistance of the device and improving reliability.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a sensor morphology control method and application thereof. Background Art

[0002] The structural manufacturing process of the inertial sensor with a comb-tooth structure is well compatible with the conventional integrated circuit manufacturing process, and thus has attracted widespread attention. Common inertial sensors with a comb-tooth structure include comb-tooth structure capacitive acceleration sensors.

[0003] The structure of the inertial sensor with a comb-tooth structure is usually made by bonding a silicon wafer to another silicon wafer with a cavity structure through direct wafer bonding, and then etching the upper silicon wafer through the cavity structure to form a comb-tooth structure through deep silicon etching. Figure 1 As shown in the figure, the comb teeth 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 ​​of the design. Figure 2 As shown, the idealized comb-tooth structure has a vertical and flat morphology, and the morphology of the comb-tooth structure plays a crucial role in the performance of the inertial sensor.

[0004] During the process of etching the upper silicon wafer step by step through the deep silicon etching process, the movable teeth's movable space is gradually released. Due to the etching rate characteristics of the wafer-level etching process, there needs to be an over-etching time to ensure the etching effect of the entire wafer. After the movable space is released, the etching process still needs to continue for a period of time. Figure 3 As shown, during the 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.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] One aspect of the present invention relates to a method for controlling the morphology of a sensor, comprising the following steps:

[0007] (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;

[0008] (b) forming an oxide layer on the upper surface of the first silicon wafer;

[0009] (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;

[0010] (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;

[0011] (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.

[0012] The sensor morphology control method can overcome the problem of residual oxide layer of the bonded 3D structure while avoiding damage to the side wall of the movable structure. It has a large redundancy for the etching process of the oxide layer, ensuring the reliable performance of the device. After adding the buffer stop pile, the impact resistance of the device is improved, and the reliability is further improved.

[0013] Another aspect of the present invention also relates to a method for preparing an inertial sensor, including the above-mentioned method for controlling the morphology of the sensor.

[0014] 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.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) 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. 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 further improved.

[0017] (2) The inertial sensor prepared by the method for preparing the inertial sensor provided by the present invention has reliable performance, good comb-tooth structure morphology, high sensitivity and high impact resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1A schematic top view of a comb-tooth structure of an existing comb-tooth capacitive acceleration sensor;

[0020] Figure 2 is a schematic diagram of an idealized comb structure;

[0021] Figure 3 Schematic diagram of the damaged comb structure;

[0022] Figure 4 It is a schematic diagram of shallow groove etching of the present invention;

[0023] Figure 5 A schematic diagram of the etching position of deep trench etching of the present invention;

[0024] Figure 6 A schematic top view of the etching position of deep trench etching of the present invention;

[0025] Figure 7 A schematic diagram of etching to form deep grooves according to the present invention;

[0026] Figure 8 A schematic diagram of the growth of an oxide layer according to the present invention;

[0027] Fig. 9 A schematic diagram of bonding the first silicon wafer and the second silicon wafer of the present invention;

[0028] Fig.10 It is a schematic diagram of etching a second silicon wafer according to the present invention;

[0029] Fig.11 A schematic diagram of the gas flow when removing the oxide layer according to the present invention;

[0030] Fig.12 This is a schematic diagram of the present invention after the oxide layer is removed.

[0031] Reference numerals:

[0032] 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

[0033] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, 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 invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0034] One aspect of the present invention relates to a method for controlling the morphology of a sensor, comprising the following steps:

[0035] (a) providing a first silicon wafer 4, and performing shallow trench etching (such as Figure 4 as shown) and deep trench etching (as Figure 5 , Figure 6 and Figure 7 As shown, the etched portion of the deep groove etching is shown as the shaded portion in the figure), the deep groove etching area partially covers the shallow groove etching area, so that a cavity structure with an opening on the top and an A column 6 and a B column 7 inside is formed on the first silicon wafer 4, and the height of the A column 6 is less than the height of the B column 7;

[0036] (b) forming an oxide layer 8 (such as Figure 8 shown);

[0037] (c) providing a second silicon wafer 9, bonding the first silicon wafer 4 to the second silicon wafer 9 through the oxide layer 8, and thinning the second silicon wafer 9 to a preset thickness (e.g. Fig. 9 shown);

[0038] (d) Deep silicon etching the second silicon wafer 9 to form a movable tooth 1 and a gas introduction opening 5, wherein the gap of the movable tooth 1 exposes the oxide layer 8 located on the upper surface of the B column 7, and the gas introduction opening 5 is located on the side of the A column 6 away from the B column 7 (such as Fig.10 shown);

[0039] (d) introducing etching gas 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 column 7 to release the movable tooth 1 (such as Fig.12 shown).

[0040] Based on the morphology control method of the above-mentioned sensor, 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 column 7 is also anchored through the oxide layer 8 and the corresponding area of ​​the second silicon wafer 9, that is, the B column 7 plays the role of a fixed anchor, which is used to prevent the movable tooth 1 from tilting during the deep silicon etching process, 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 column 7, and there is a risk of adhesion between the residual oxide layer 8 and the movable tooth 1. By setting a gas introduction opening 5 on the side of the A column 6 away from the B column 7, sufficient etching gas can be introduced, and the gap between the A column 6 and the second silicon wafer 9 helps to guide the etching gas to flow to the B column 7, thereby solving the problem of residual oxide layer 8 and ensuring that the movable tooth 1 is released.

[0041] The following is a more detailed description of the morphology control method of the above-mentioned sensor.

[0042] like Figure 4 As shown in FIG. 1 , a shallow groove 3 is formed by shallow groove etching, and the depth of the shallow groove 3 is D. Figure 5-Figure 7 As shown, deep groove etching is further performed on the basis of shallow groove etching, and the area of ​​deep groove etching partially covers the area of ​​shallow groove etching. In this way, A pillar 6 and B pillar 7 of different heights are formed by sequentially performing shallow groove etching and deep groove etching, and the height of A pillar 6 is less than the height of B pillar 7. Specifically, the distance from the upper surface of A pillar 6 to the upper surface of the first silicon wafer 4 is equal to the depth of shallow groove 3, and the upper surface of B pillar 7 is flush with the upper surface of the first silicon wafer 4, that is, the height difference between A pillar 6 and B pillar 7 is the depth of shallow groove 3.

[0043] The B column 7, through the oxide layer 8 on its upper surface, acts as a fixing anchor for the movable tooth 1 during the process of deep silicon etching to form the movable tooth 1, preventing the movable tooth 1 from tilting due to its own gravity or internal electrostatic force, thereby avoiding damage to the side of the movable tooth 1.

[0044] Since the height of the A pillar 6 is less than that of the B pillar 7, there is a gap between the A pillar 6 and the second silicon wafer 9. The etching gas entering through the gas introduction opening 5 can flow to the B pillar 7 under the guidance of the gap, and fully etch the oxide layer 8 on the upper surface of the B pillar 7, thereby releasing the movable tooth 1. In addition to guiding the etching gas in cooperation with the second silicon wafer 9, the A pillar 6 itself also plays a role of blocking and buffering. Specifically, as Figure 1As shown, in a normal state, when the movable tooth 1 senses the corresponding external movement, it moves in the left and right directions in the plane. However, the movable tooth 1 may produce out-of-plane movement under the action of unexpected external force or its own inertia. At this time, the A column 6 can play a role of blocking and buffering to prevent the movable tooth 1 from being damaged due to a large amplitude. The depth of the shallow groove 3 determines the gap between the A column 6 and the movable structure where the movable tooth 1 is located in the vertical direction. If the gap is too large, it will not play the role of blocking and buffering. If the gap is too small, the activity space of the movable structure is restricted. Based on this, the depth of the shallow groove 3 is comprehensively designed. Preferably, the depth of the shallow groove 3 is 0.5-5μm (for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm).

[0045] The height difference between the A pillar 6 and the B pillar 7 is the depth of the shallow groove 3. Therefore, preferably, the height difference between the A pillar 6 and the B pillar 7 is 0.5 to 5 μm (for example, 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).

[0046] Combination Figure 1 and Fig.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. Under the action of unexpected external force or its own inertia, the movable tooth 1 generates a smaller vibration amplitude at the end connected to the gear pivot 2, and a larger vibration amplitude at the free end of the movable tooth 1. 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 from the gear pivot 2, so as to ensure that the A column 6 and the B column 7 will not affect the normal movement of the movable tooth 1, and the A column 6 can timely block and buffer the movable tooth 1 when the movable tooth 1 vibrates.

[0047] Preferably, the shallow trench etching is performed using a deep silicon etching process.

[0048] Preferably, deep trench etching is performed using a deep silicon etching process.

[0049] 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.

[0050] Combination Figure 10-12, a gas introduction opening 5 and a gap between the A column 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 a space for the etching gas to enter. The gap between the A column 6 and the second silicon wafer 9 is conducive to guiding the etching gas to the oxide layer 8 on the B column 7, so as to be conducive to etching the oxide layer 8 on the B column 7 cleanly, thereby releasing the movable teeth 1. There is only a gap between the movable teeth 1 above the B column 7, and the gap is small, making it difficult for the etching gas to enter. The direction of the gas when removing the oxide layer 8 is as follows Fig.11 As shown, the arrow in the figure indicates the direction of the etching gas.

[0051] 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.

[0052] Preferably, the thickness of the oxide layer 8 is 0.9-1.1 μm (eg, 0.9 μm, 1.0 μm or 1.1 μm), which can ensure the bonding strength and facilitate etching and removing the oxide layer 8 on the B column 7 .

[0053] Preferably, the oxide layer 8 comprises a silicon dioxide layer.

[0054] Preferably, 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 impact on the bonding area, and a certain etching buffer area is required in the bonding area.

[0055] Preferably, 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.

[0056] Another aspect of the present invention relates to a method for preparing an inertial sensor, including the above-mentioned method for controlling the morphology of the sensor.

[0057] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. 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 thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

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 method for controlling the morphology of a sensor according to claim 1, 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 claim 1, 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 claim 1, characterized in that: Using deep silicon etching process to perform shallow trench etching; And / or, deep trench etching is performed using a deep silicon etching process.

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

7. The method for controlling the morphology of a sensor according to claim 1, characterized in that: The oxide layer includes a silicon dioxide layer.

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

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

10. 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 9.

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