阅读说明：本技术 高性能mems惯性传感器的晶圆制作工艺流程 (Wafer manufacturing process flow of high-performance MEMS inertial sensor ) 是由 郭述文 何凯旋 刘磊 王鹏 郭群英 于 2020-04-13 设计创作，主要内容包括：本发明公开了一种MEMS惯性传感器的晶圆制作工艺流程,包括以下步骤：提供具有顶部平面和底部平面的第一基板,所述底部平面下方设置有一氧化物层；提供具有上平坦表面的第二基板；将第二基板的一部分从上平坦表面蚀刻,以形成多个凸起和浅腔,每个凸起具有上平坦表面；将第一基板的顶部平面结合到凸起的上部平坦表面以形成锚固部分；刻蚀掉第一基板的一定位置的氧化物层；从底部表面和/或顶部表面蚀刻第一基板的一部分至第一基板的总厚度,以形成具有一定结构可自由旋转的敏感结构。在硅硅键合时不需要进行图标对准,使得键合工艺简单,形成的梁的厚度与质量块相等,不会产生误差,具有更好的结构对称性。(The invention discloses a wafer manufacturing process flow of an MEMS (micro-electromechanical system) inertial sensor, which comprises the following steps of: providing a first substrate having a top plane and a bottom plane, an oxide layer disposed below the bottom plane; providing a second substrate having an upper planar surface; etching a portion of the second substrate from the upper planar surface to form a plurality of protrusions and shallow cavities, each protrusion having an upper planar surface; bonding a top planar surface of the first substrate to the upper planar surface of the protrusion to form an anchor portion; etching off the oxide layer at a certain position of the first substrate; a portion of the first substrate is etched from the bottom surface and/or the top surface to a total thickness of the first substrate to form a sensitive structure having a structure that is free to rotate. The method has the advantages that icon alignment is not needed during silicon-silicon bonding, so that the bonding process is simple, the thickness of the formed beam is equal to that of the mass block, no error is generated, and the method has better structural symmetry.)

1. A method of manufacturing a MEMS inertial sensor, comprising the steps of:

s01: providing a first substrate having a top plane and a bottom plane with an oxide layer disposed below the bottom plane, the bottom plane being substantially parallel to the top plane;

s02: providing a second substrate having an upper planar surface;

s03: etching a portion of the second substrate from the upper planar surface to a first predetermined depth to form a plurality of protrusions and shallow cavities, each protrusion having an upper planar surface;

s04: bonding a top planar surface of the first substrate to the upper planar surface of the protrusion to form an anchor portion;

s05: etching off the oxide layer at a certain position of the first substrate;

s06: etching a portion of the first substrate from the bottom surface and/or the top surface to a second predetermined depth at least equal to the total thickness of the first substrate to form a sensitive structure on the first substrate having a structure that is freely rotatable, the sensitive structure including a structured mass around the anchor portion.

2. The manufacturing method according to claim 1, wherein the total thickness of the first substrate is 50 to 150 μm.

3. The manufacturing method according to claim 2, wherein the first predetermined depth is 3 to 10 μm.

4. The manufacturing method according to claim 1, further comprising, after the step S03:

forming fixed electrodes in the shallow cavities at the two sides of the middle bulge;

and depositing an oxide layer on the surface of the fixed electrode.

5. The manufacturing method according to claim 1, further comprising, after the step S08, the steps of:

providing a cover wafer; and

etching a portion of the cap wafer to form a top recess; and

the capping wafer is bonded to the second substrate such that the freely rotatable sensitive structure is enclosed within the recess of the capping wafer.

6. The method of manufacturing according to claim 5, further comprising depositing a thin film on a portion of the surface of the recess by getter sputtering.

7. The method of manufacturing of claim 5, further comprising printing a glass paste on the contact surface of the cap wafer with glass frit printing;

and completing vacuum bonding of the cover wafer and the second substrate under high vacuum condition.

8. A method of manufacturing according to claim 1, wherein portions of the surface are etched away on both sides of the anchoring portion of the first substrate to form beam structures for connecting the proof mass.

9. A method of manufacturing according to any of claims 1-8, wherein the sensitive structure is a hollow structure, a comb-tooth structure or a ring structure.

Technical Field

The invention relates to a manufacturing process of an inertial sensor, in particular to a wafer manufacturing method of an MEMS inertial sensor.

Background

High performance accelerometers and gyroscopes with near microgravity resolution, high sensitivity, high linearity and low bias drift are needed for a wide variety of applications, particularly aerospace applications such as inertial navigation systems, guidance systems and airborne data measurement systems. The thermo-mechanical brownian noise of the sensor limits the resolution of high performance accelerometers and gyroscopes, which is determined by the damping coefficient and mass of the structure and the reading electronics.

Fabrication techniques play a crucial role in ensuring that simultaneously large masses, large capacitances and small damping are obtained, as well as achieving microgravity resolution. Previously, many high performance silicon accelerometers and gyroscopes have been reported. These devices incorporate capacitive, resonant or tunneling current sensing schemes that can achieve high sensitivity with greater detection quality. Of all these, silicon capacitive accelerometers have many advantages that make them very attractive in a number of applications ranging from low cost, large volume automotive accelerometers to high precision inertial grade microgravity devices. The silicon capacitance type accelerometer has high sensitivity, good direct current response and noise performance, low drift, low temperature sensitivity and low power consumption.

Capacitive accelerometers are generally vertical and lateral structures. Some designs use a teeter-totter structure with a proof mass such as a flat plate suspended by a torsion beam. The structure is typically asymmetrically shaped so that one side has a greater mass than the other, resulting in the centre of mass being offset from the axis of the torsion bar. When the acceleration forces generate a moment about the torsion bar axis, the plate rotates freely, constrained only by the spring constant of the torsion bar.

The sensitivity of these types of accelerometers is defined as the ratio of deflection to acceleration. The mass of the plate, the distance from the center of mass to the torsion bar axis and the stiffness of the torsion bar determine the sensitivity. To increase the offset of the center of mass, the plate structure is designed to have an asymmetric shape. For example, the width of one side of the plate may be greater than the width of the other side of the plate, or the length of one side of the plate may be greater than the length of the other side. However, increasing the center mass shift by the asymmetric shaping method described above may result in an increase in the total mass of the plate, which results in a decrease in the resonant frequency and a decrease in sensitivity. Increasing the center mass offset by asymmetric shaping also results in sacrificing some of the dynamic g-range, which is determined by the spacing between the fixed sensing element and the pendulum acceleration sensor plate. Another method of increasing center mass offset involves lengthening a portion of the pendulum sensor plate. The center mass offset is proportional to the length of the plate extension. However, one side of the extension plate may cause unbalanced gas damping, resulting in performance degradation. The gas damping can be balanced by perforating the expansion plate. However, such perforations also reduce center mass shift and therefore sensitivity. In addition, extending one side of the board may result in an increase in the overall chip size. It is defined by the distance between the fixed sensing element and the pendulum acceleration sensitive structure. Another method of increasing center mass offset involves lengthening a portion of the pendulum sensor plate. The center mass offset is proportional to the length of the plate extension. However, one side of the extension plate may cause unbalanced gas damping, resulting in performance degradation. The gas damping can be balanced by perforating the expansion plate. However, such perforations also reduce center mass shift and therefore sensitivity. In addition, extending one side of the board may result in an increase in the overall chip size. It is defined by the distance between the fixed sensing element and the pendulum acceleration sensitive structure. Another method of increasing center mass offset involves lengthening a portion of the pendulum sensor plate. The center mass offset is proportional to the length of the plate extension. However, one side of the extension plate may cause unbalanced gas damping, resulting in performance degradation. The gas damping can be balanced by perforating the expansion plate. However, such perforations also reduce center mass shift and therefore sensitivity. In addition, extending one side of the board may result in an increase in the overall chip size. Another method of increasing center mass offset involves lengthening a portion of the pendulum sensor plate. The center mass offset is proportional to the length of the plate extension. However, one side of the extension plate may cause unbalanced gas damping, resulting in performance degradation. The gas damping can be balanced by perforating the expansion plate. However, such perforations also reduce center mass shift and therefore sensitivity. In addition, extending one side of the board may result in an increase in the overall chip size. Another method of increasing center mass offset involves lengthening a portion of the pendulum sensor plate. The center mass offset is proportional to the length of the plate extension. However, one side of the extension plate may cause unbalanced gas damping, resulting in performance degradation. The gas damping can be balanced by perforating the expansion plate. However, such perforations also reduce center mass shift and therefore sensitivity. In addition, extending one side of the board may result in an increase in the overall chip size. This can lead to performance degradation. The gas damping can be balanced by perforating the expansion plate. However, such perforations also reduce center mass shift and therefore sensitivity. In addition, extending one side of the board may result in an increase in the overall chip size. This can lead to performance degradation. The gas damping can be balanced by perforating the expansion plate. However, such perforations also reduce center mass shift and therefore sensitivity. In addition, extending one side of the board may result in an increase in the overall chip size.

Other conventional structures utilize a deeper gap below the extended plate portion to increase the maximum angle of rotation while maintaining balanced gas damping. This structure can increase the dynamic g range to some extent. However, the extended portion of the plate increases the size of the overall chip size, resulting in unbalanced gas damping and lowering the resonant frequency of the rotating structure, which again results in reduced performance of the accelerometer.

US patent application No. US7736931B1 discloses a method for manufacturing a pendulum accelerometer, wherein a first substrate is provided by first etching a recess with a depth from the top plane (lower surface of the mass), then performing direct pattern-aligned silicon bonding with a second substrate, and then etching a mass with a certain cavity depth from the upper surface of the mass, the sum of the etching depth of the lower surface and the etching depth of the upper surface is just the thickness of the mass, that is, the etching depth of the upper surface is just enough to etch through the entire mass, and the entire structure is released. And the thickness of the beam connecting the central anchor point and the mass blocks on the two sides is equal to the thickness of the mass block minus the etching depth of the lower surface. However, the above process requires the first substrate to etch a groove with a certain depth, and then performs pattern alignment bonding, which makes the bonding process complicated; and the thickness of the beam is smaller than that of the mass block, and the gravity center of the structure is inclined upwards, so that certain error is generated in the output symmetry of +/-1G of the accelerometer sensor.

Disclosure of Invention

In view of the above technical problems, the present invention aims to: the wafer manufacturing process flow of the high-performance MEMS inertial sensor is provided, icon alignment is not needed during silicon-silicon bonding, the bonding process is simple, the thickness of the formed beam is equal to that of the mass block, no error is generated, and the wafer manufacturing process flow has better structural symmetry.

The technical scheme of the invention is as follows:

a method of manufacturing a MEMS inertial sensor, comprising the steps of:

s01: providing a first substrate having a top plane and a bottom plane with an oxide layer disposed below the bottom plane, the bottom plane being substantially parallel to the top plane;

s02: providing a second substrate having an upper planar surface;

s03: etching a portion of the second substrate from the upper planar surface to a first predetermined depth to form a plurality of protrusions and shallow cavities, each protrusion having an upper planar surface;

s04: bonding a top planar surface of the first substrate to the upper planar surface of the protrusion to form an anchor portion;

s05: etching off the oxide layer at a certain position of the first substrate;

s06: etching a portion of the first substrate from the bottom surface and/or the top surface to a second predetermined depth at least equal to the total thickness of the first substrate to form a sensitive structure on the first substrate having a structure that is freely rotatable, the sensitive structure including a structured mass around the anchor portion.

In a preferred technical scheme, the total thickness of the first substrate is 50-150 μm.

In a preferred embodiment, the first predetermined depth is 3 to 10 μm.

In a preferred embodiment, after step S03, the method further includes:

forming fixed electrodes in the shallow cavities at the two sides of the middle bulge;

and depositing an oxide layer on the surface of the fixed electrode.

In a preferred embodiment, after step S08, the method further includes the following steps:

providing a cover wafer; and

etching a portion of the cap wafer to form a top recess; and

the capping wafer is bonded to the second substrate such that the freely rotatable sensitive structure is enclosed within the recess of the capping wafer.

In a preferred technical scheme, the method further comprises the step of depositing a thin film on a part of the surface of the groove through getter sputtering.

In the preferred technical scheme, the method further comprises the steps of printing glass slurry on the contact surface of the cover wafer by using glass frit printing;

and completing vacuum bonding of the cover wafer and the second substrate under high vacuum condition.

In a preferred embodiment, two sides of the anchoring portion of the first substrate are etched to form a beam structure for connecting the proof mass.

In a preferred technical scheme, the sensitive structure is a hollow structure, a comb tooth structure or an annular structure.

Compared with the prior art, the invention has the advantages that:

the top plane (lower surface of the mass block) of the first substrate is not pre-etched, but a light plate without patterns is directly bonded with the second substrate through silicon and silicon, then a structural pattern is etched from the upper surface of the mass block by adopting a double-sided photoetching technology, a part needing to be etched with grooves is covered with silicon dioxide with a certain thickness, and because the silicon dioxide is much slower than the etching rate of silicon, in the process of etching the next structure release deep silicon, when the whole mass block is ready to be etched through (namely the structure is released), the area covered by the silicon dioxide is not etched through, and a mass block with grooves is formed. The method has the advantages that:

1. the silicon bonding does not need to carry out icon alignment, so that the bonding process is simple;

2. the alignment precision of the double-sided photoetching is higher than that of silicon-silicon bonding alignment, so that the structural symmetry is better;

3. the thickness of the formed beam is equal to that of the mass block, so that certain error cannot be generated in the output symmetry of the positive and negative 1G of the accelerometer sensor.

Drawings

The invention is further described with reference to the following figures and examples:

FIG. 1 is a flow chart of a wafer fabrication process for a high performance MEMS inertial sensor of the present invention;

FIG. 2 is a cross-sectional view of an accelerometer structure made by the method of manufacture of the invention;

FIG. 3 is a schematic view of a first substrate according to the present invention;

FIG. 4 is a schematic structural diagram of a second substrate according to the present invention;

FIG. 5 is a schematic structural diagram of a second substrate after shallow trench etching in accordance with the present invention;

FIG. 6 is a schematic structural diagram of a second substrate after etching of the fixed electrode according to the present invention;

FIG. 7 is a schematic diagram of the structure of the invention after silicon-silicon bonding;

FIG. 8 is a schematic view of the structure of the present invention after removal of the substrate;

FIG. 9 is a schematic diagram of the structure of the present invention after etching of the oxide layer;

FIG. 10 is a schematic diagram of a structure of the present invention after etching of the structural layer;

FIG. 11 is a schematic diagram of the packaged structure of the present invention;

FIG. 12 is a cross-sectional view of an accelerometer of the symmetrical comb configuration of the present invention;

FIG. 13 is a schematic diagram of the sensitive structure of the ring gyroscope of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.