A MEMS chip structure and etching method

Abstract

The present invention relates to the field of semiconductor MEMS chip process technology, and more particularly to a MEMS chip structure and etching method. The chip structure comprises quartz, with metallic chromium formed on the quartz surface, and an inorganic compound formed on the metallic chromium surface, with the inorganic compound forming a mask on the metallic chromium. The etching method comprises the following steps: after growing the inorganic compound on the metallic chromium, first photoetching a portion of the inorganic compound to form an etching groove, then dry-etching the metallic chromium using the remaining inorganic compound, and finally wet-etching the remaining silicon. The MEMS chip structure and etching method of the present invention form a layer of inorganic compound on the metallic chromium as a mask. During dry etching of the metallic chromium, chlorine and oxygen do not react with the inorganic compound, thereby eliminating the positive angle generated by the metal layer and ensuring that the angle is as vertical as possible, thereby facilitating the production of a high-precision MEMS chip.

Description

Technical Field

[0001] The present invention relates to the technical field of MEMS chip etching processes, and in particular to a MEMS chip structure and an etching method. Background Art

[0002] Ultrasonic sensors based on MEMS chips convert ultrasonic signals into other energy signals (usually electrical signals). Ultrasonic waves are mechanical waves with a vibration frequency exceeding 20kHz. They have high frequency, short wavelength, minimal diffraction, and, most notably, excellent directionality, capable of propagating in a directional manner as rays. Ultrasonic waves have a strong ability to penetrate liquids and solids, especially solids that are opaque to sunlight. When ultrasonic waves strike impurities or interfaces, they produce significant reflections, forming echoes. When they strike moving objects, they can also produce a Doppler effect. Ultrasonic sensors are widely used in industry, defense, and biomedicine.

[0003] In the prior art, when metal Cr is etched with photoresist, a positive corner will appear, such as Figure 1 As shown, this affects the performance and accuracy of MEMS chip-based ultrasonic sensors. Furthermore, during the photoresist etching process for metallic Cr, the selectivity ratio is 5:1 (meaning that etching 1mm of Cr requires 5mm of photoresist), which is costly. In contrast, using inorganic compounds, the selectivity ratios of SiO to Cr are 1:5, and the selectivity of silicon to Cr is 1:40, which can reduce process costs.

[0004] The invention application with application number 202011529954.3 discloses a closed vibration membrane piezoelectric MEMS speaker and its preparation method. It can be seen from its preparation method that the etching process used for the metal electrode layer will produce positive corners, which will affect the finished product quality of the MEMS chip. Summary of the Invention

[0005] In view of the above problems, the present invention aims to provide a MEMS chip structure and etching method. When dry etching is used for metal Cr, the cost is high and the problem of positive corners may occur.

[0006] The purpose of the present invention can be achieved through the following technical solution: a MEMS chip structure includes quartz, a metal layer is grown on the surface of the quartz, an inorganic compound is grown on the surface of the metal layer; the inorganic compound forms a mask on the metal layer.

[0007] As a further embodiment of the present invention, the inorganic compound material is silicon oxide and / or silicon.

[0008] As a further embodiment of the present invention, the inorganic compound has a double-layer structure, wherein the bottom layer is silicon and the top layer is silicon oxide.

[0009] As a further solution of the present invention, the thickness of the silicon oxide is 40-70 nm, the thickness of the silicon is 10-20 nm, and the thickness of the metal layer is 200-300 nm.

[0010] An etching method based on the above chip structure comprises the following steps:

[0011] S1, growing an inorganic compound on the metal layer;

[0012] S2, dry etching part of the inorganic compound by photolithography to form an etching groove;

[0013] S3, dry etching the metal layer using the remaining inorganic compound to form a mask;

[0014] S4, a wet process is used to remove the residual silicon of the inorganic compound.

[0015] As a further solution of the present invention, the dry etching of the metal layer in S3 includes the steps of:

[0016] S31, dry etching the upper portion of the metal layer to consume silicon oxide;

[0017] S32. Dry-etching the lower portion of the metal layer to consume silicon.

[0018] As a further solution of the present invention, the gases used in the dry etching are chlorine and oxygen.

[0019] Beneficial effects of the present invention:

[0020] 1. The MEMS chip structure and etching method of the present invention generate a layer of inorganic compound on the metal Cr as a mask. When the metal Cr is dry-etched, chlorine and oxygen do not react with the inorganic compound, which can eliminate the positive angle generated by the metal layer and ensure that the angle is vertical as much as possible. In fact, the angle θ can be guaranteed to be greater than 88°, which is conducive to obtaining a high-precision MEMS chip.

[0021] 2. The inorganic compound bottom layer of the present invention uses silicon. When etching the upper part of Cr, the top silicon oxide will be consumed. When etching the lower part of Cr, part of the silicon will also be consumed. The remaining silicon can be easily removed by soaking it with a wet method, which simplifies the process flow and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of a positive corner caused by an existing etching method;

[0023] Figure 2 This is a schematic diagram of the MEMS chip structure of the present invention;

[0024] Figure 3 This is a schematic diagram of the MEMS chip etching process flow of the present invention.

[0025] 100, quartz;

[0026] 200, metal layer;

[0027] 300. Inorganic compounds; 310. Silicon oxide; 320. Silicon. DETAILED DESCRIPTION

[0028] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar symbols throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0029] Example 1:

[0030] like Figure 2 As shown, the present invention discloses a MEMS chip structure, comprising quartz 100, a metal layer 200 and an inorganic compound 300 stacked in sequence. Optionally, the metal layer 200 is composed of metal or metal compound; specifically, the metal layer 200 is metal Cr.

[0031] Metal Cr 200 is grown on the surface of the quartz 100 , and an inorganic compound 300 is grown on the surface of the metal Cr 200 .

[0032] The inorganic compound 300 is made of silicon oxide 320 and / or silicon 310 , etc. The inorganic compound 300 forms a mask on the metal Cr 200 .

[0033] When the existing process uses photoresist as a mask to dry-etch metal Cr200, a positive corner will appear, such as Figure 1 As shown, the accuracy of the MEMS chip is affected.

[0034] In the present invention, after the inorganic compound 300 is formed on the metal Cr200, the inorganic compound 300 is made of silicon oxide 320 and silicon 310, and the inorganic compound 300 forms a mask on the metal Cr200. Chlorine and oxygen are used as dry etching gases. When the metal Cr200 is dry-etched by chlorine and oxygen, the chlorine and oxygen do not react with the inorganic compound, so the positive corners can be effectively eliminated. Figure 1 As shown, the angle θ can actually be guaranteed to be greater than 88°, meeting the use requirements and improving the processing accuracy of the MEMS chip.

[0035] Furthermore, the inorganic compound 300 has a double-layer structure, in which the bottom layer is silicon 310 and the top layer is silicon oxide 320. The thickness of silicon oxide 320 is controlled to be 40-70nm, the thickness of silicon 310 is controlled to be 10-20nm, and the thickness of metal Cr200 is controlled to be 200-300nm. When etching metal Cr200, the selectivity ratio of SiO to Cr in the inorganic compound is 1:5, and the selectivity ratio of silicon to Cr can be 1:40. Appropriate thickness control not only saves costs but also improves etching accuracy.

[0036] Example 2:

[0037] Based on the MEMS chip structure described in Example 1, the present invention further discloses an etching method, comprising the following steps:

[0038] S1, growing inorganic compound 300 on metal Cr200;

[0039] S2, dry-etching part of the inorganic compound 300 by a photolithography process to form an etching groove; the etching groove is a small line width etching groove with a width of 200-400 nm.

[0040] S3, using the inorganic compound 300 forming the etching groove as a mask to dry-etch the metal Cr200;

[0041] S4, using a wet process to remove the inorganic compound residual silicon 320.

[0042] like Figure 3 As shown in A, an inorganic compound 300 is used to form a mask on the metal Cr200. When etching the inorganic compound 300, a photolithography process is first used to form an etching groove with a certain line width in the inorganic compound 300, and then the metal Cr200 is etched by a dry process using oxygen and chlorine as the medium.

[0043] Furthermore, when the metal Cr200 is dry-etched using the remaining inorganic compound 300, Figure 3 As shown in B, including:

[0044] S31, dry etching the upper portion of the metal Cr200, consuming silicon oxide 320;

[0045] S32 , dry-etching the lower portion of the metal Cr200 to consume silicon 310 .

[0046] When etching metal Cr200, dry etching uses chlorine and oxygen. Chlorine and oxygen will not react with inorganic compounds, and can effectively eliminate the positive corners of metal Cr200.

[0047] The inorganic compound adopts a double-layer structure, with the bottom layer being silicon 310 and the top layer being silicon oxide 320. The advantage of using silicon 310 for the bottom layer is that it is easy to remove and can be removed by wet soaking. When etching the upper part of the metal Cr200, the silicon oxide 320 will be consumed. When etching the lower part of the metal Cr200, part of the silicon 310 will also be consumed. Finally, the silicon 310 can be removed by wet method. The wet liquid does not react with silicon oxide 320, which reduces the process steps and reduces the process cost.

[0048] Compared with the traditional process, the etching process proposed in this embodiment first generates a layer of inorganic compound 300 on the metal Cr200. The inorganic compound 300 is made of silicon oxide 320 or silicon 310 to form a mask. The inorganic compound 300 is first photoetched to form an etching groove with a certain line width in the inorganic compound 300. Then, the metal Cr200 is dry-etched by gas. In this way, when etching the metal Cr200, the inorganic compound 300 on the metal Cr200 serves as a mask. Since chlorine and oxygen do not react with the inorganic compound, the positive angle generated by the metal Cr200 can be eliminated. The angle θ can actually ensure that the angle is greater than 88°, which is conducive to obtaining a high-precision MEMS chip.

[0049] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

[0050] It should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the present invention.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0052] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0053] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

Claims

1. A method for etching a MEMS chip structure, the MEMS chip structure comprising quartz (100), a metal layer (200) grown on the surface of the quartz (100), an inorganic compound (300) grown on the surface of the metal layer (200); the inorganic compound (300) forming a mask on the metal layer (200); The inorganic compound (300) has a double-layer structure, wherein the bottom layer is silicon (310) and the top layer is silicon oxide (320); It is characterized in that The etching method of the MEMS chip structure comprises the following steps: S1, growing an inorganic compound (300) on the metal layer (200); S2, dry etching a portion of the inorganic compound (300) using a photolithography process to form an etching groove; S3, using the remaining inorganic compound (300) to form a mask to dry-etch the metal layer (200); S31, dry etching the upper portion of the metal layer (200) to consume silicon oxide (320); S32, dry etching the lower portion of the metal layer (200), consuming silicon (310); S4, removing the residual silicon (310) of the inorganic compound (300) by a wet process; Wherein, the gases used in the dry etching are chlorine and oxygen.

2. The etching method of the MEMS chip structure according to claim 1, characterized in that: The thickness of the silicon oxide (320) is 40-70 nm, the thickness of the silicon (310) is 10-20 nm, and the thickness of the metal layer (200) is 200-300 nm.

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