CN104569491B - The Z axis structure and its production method of a kind of accelerometer - Google Patents

Abstract

The invention discloses a Z-axis structure of an accelerometer and a production method thereof, comprising a substrate, a fixed electrode, and a mass block, a first anchor point is arranged on the surface of the substrate, and the fixed electrode passes through its end Connected to the first anchor point, the fixed electrode is suspended on the substrate through the first anchor point; an intermediate anchor point is also arranged on the surface of the substrate, and the mass block is suspended on the substrate through the intermediate anchor point Above the fixed electrodes, a plurality of through holes are arranged on the mass block and the fixed electrodes. In the Z-axis structure of the present invention, the fixed electrode is connected to the substrate through the first anchor point, so that there is a certain gap between the fixed electrode and the substrate, which cuts off the deformation transmission channel from the substrate to the fixed electrode, reducing the The contact area between the electrode and the substrate can effectively prevent the deformation of the substrate caused by external stress and temperature changes from being transmitted to the fixed electrode, greatly reducing the zero point drift of the Z-axis structure.

Description

Z-axis structure of accelerometer and production method thereof

technical field

The invention belongs to the field of micro-electro-mechanical (MEMS), more precisely, relates to a micro-electro-mechanical accelerometer, in particular to a Z-axis structure in the accelerometer; the invention also relates to a production method of the Z-axis structure.

Background technique

The previous Z-axis accelerometers are all flat capacitive, and the movement mode of the mass block is a structure similar to a seesaw. Referring to FIG. 1 , on the substrate 1 below the mass 3 , there are two fixed electrodes 2 made of metal, and the fixed electrodes 2 are attached to the surface of the substrate 1 . The proof mass 3 and the two fixed electrodes 2 form two capacitors C1 and C2 respectively. Wherein, the mass block 3 is supported above the substrate through the anchor point 4 .

The Z-axis structure of this structure is relatively sensitive to deformation caused by external stress and temperature changes. The deformation caused by external stress and temperature change first acts on the substrate 1 , and then spreads to the fixed electrode 2 . Since the fixed electrode 2 is attached to the substrate 1 , the deformation of the substrate 1 is directly reflected on the fixed electrode 2 . Under normal circumstances, the deformations produced by the two fixed electrodes 2 cannot be equal. As a result, in the absence of an accelerometer input, the capacitances of the two fixed electrodes 2 to the movable mass 3 are not equal, and an error signal will eventually be output. Reflected on the chip, this is the zero offset of the Z-axis plus speedometer. From the designer's point of view, it is hoped that the smaller the zero offset, the better. However, for accelerometers with this structure, the zero point offset caused by external stress and temperature changes is unavoidable.

Contents of the invention

An object of the present invention is to provide a new technical solution for the Z-axis structure of the accelerometer.

According to a first aspect of the present invention, a Z-axis structure of an accelerometer is provided, including a substrate, a fixed electrode, and a mass block, and a first anchor point is arranged on the surface of the substrate, and the fixed electrode passes through it. The end is connected to the first anchor point, and the fixed electrode is suspended on the substrate through the first anchor point; an intermediate anchor point is also arranged on the surface of the substrate, and the mass block is suspended through the intermediate anchor point Placed above the fixed electrode, a plurality of through holes are arranged on the mass block and the fixed electrode.

Preferably, the fixed electrode is integrally formed with the first anchor point.

Preferably, said first anchor point is adjacent to an intermediate anchor point.

Preferably, the fixed electrode is made of polysilicon material.

Preferably, the thickness of the fixed electrode is more than 5 μm.

Preferably, the lower surface of the fixed electrode is also provided with a reinforcing structure.

Preferably, the reinforcing structure is a mesh structure.

The present invention also provides a production method of a Z-axis structure, comprising the following steps:

a. Depositing a first sacrificial layer on the substrate, and etching the regions of the first anchor point and the first intermediate anchor point on the first sacrificial layer;

b. Depositing a fixed electrode layer on the first sacrificial layer and the regions of the first anchor point and the first intermediate anchor point;

c. Etching a fixed electrode connected to the first anchor point and a pattern of the first intermediate anchor point on the fixed electrode layer, and etching a plurality of through holes on the fixed electrode;

d. Depositing a second sacrificial layer on the fixed electrode and in the area of the first intermediate anchor point;

e. Etching away the second sacrificial layer directly above the first intermediate anchor point;

f. Depositing a mass layer on the second sacrificial layer, and etching patterns of the mass and the second intermediate anchor point on the mass layer, wherein the second intermediate anchor point is located directly above the first intermediate anchor point; and A plurality of through holes are etched on the proof mass;

g. removing the first sacrificial layer and the second sacrificial layer to form a Z-axis structure.

Preferably, a step of flattening the fixed electrode layer to a predetermined thickness is further included between the steps b and c.

Preferably, in the step f, before etching the mass layer to form patterns of the mass and the second intermediate anchor point, a step of planarizing the mass layer to a predetermined thickness is also included.

In the Z-axis structure of the present invention, the fixed electrode is connected to the substrate through the first anchor point, so that there is a certain gap between the fixed electrode and the substrate, which cuts off the deformation transmission channel from the substrate to the fixed electrode, reducing the The contact area between the electrode and the substrate can effectively prevent the deformation of the substrate caused by external stress and temperature changes from being transmitted to the fixed electrode, greatly reducing the zero point drift of the Z-axis structure.

The inventors of the present invention found that in the prior art, the deformation of the substrate caused by external stress and temperature changes will be transmitted to the fixed electrode, thereby causing deformation of the fixed electrode, so that the difference between the two capacitances is not equal. Therefore, the technical tasks to be achieved or the technical problems to be solved by the present invention are never thought of or expected by those skilled in the art, so the present invention is a new technical solution.

Other features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

Figure 1 is a schematic diagram of a traditional Z-axis structure.

Fig. 2 is a schematic diagram of the Z-axis structure of the present invention.

3 to 10 are schematic flowcharts of the production method of the Z-axis structure of the present invention.

detailed description

Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangements of components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

The following description of at least one exemplary embodiment is merely illustrative in nature and in no way taken as limiting the invention, its application or uses.

Techniques, methods and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods and devices should be considered part of the description.

In all examples shown and discussed herein, any specific values should be construed as exemplary only, and not as limitations. Therefore, other instances of the exemplary embodiment may have different values.

It should be noted that like numbers and letters denote similar items in the following figures, therefore, once an item is defined in one figure, it does not require further discussion in subsequent figures.

The accelerometer of traditional structure, its X-axis, Y-axis direction all adopts translation mode, and Z-axis all adopts seesaw deflection mode, with respect to traditional Z-axis accelerometer structure, the present invention provides a kind of Z in accelerometer The axis structure can be used to detect the Z-axis acceleration signal in the vertical direction.

With reference to Fig. 2, the present invention provides a kind of Z-axis structure of accelerometer, and it comprises substrate 1, proof mass 3, also comprises two fixed electrodes 2, is provided with two first on the surface of described substrate 1 The anchor points 20 are respectively used to connect two fixed electrodes 2, and the fixed electrodes 2 are connected to the first anchor point 20 through their ends. L-shaped, the fixed electrode 2 is located in the horizontal direction, and the first anchor point 20 is located in the vertical direction. The fixed electrode 2 is arranged approximately parallel to the substrate 1. Due to the setting of the first anchor point 20, there is a certain gap between the fixed electrode 2 and the surface of the substrate 1, that is, the fixed electrode 2 passes through the first anchor point 20. Suspended on the substrate 1. The fixed electrode 2 can be fixed by a single first anchor point 20, of course, it can also be fixed by using multiple anchor points.

An intermediate anchor point 4 is arranged between the two first anchor points 20, and the intermediate anchor point 4 is fixed on the surface of the substrate 1, and the mass 3 is elastically suspended on the fixed electrode 2 through the intermediate anchor point 4. above. For example, the mass block 3 is connected to the intermediate anchor point 4 through an elastic beam, so that the mass block 3 is elastically supported above the substrate 1 and the fixed electrode 2. Of course, there is a certain gap between the mass block 3 and the fixed electrode 2, so that the mass block 3 3 and the two fixed electrodes 2 can respectively form two detection capacitors, which belongs to the common knowledge of those skilled in the art and will not be repeated here.

Wherein, a plurality of through holes 6 are provided on the mass block 3 and the fixed electrode 2, which can facilitate the structural release of the fixed electrode and the movable mass block.

In the Z-axis structure of the present invention, the fixed electrode 2 is connected to the substrate 1 through the first anchor point 20, so that there is a certain gap between the fixed electrode 2 and the substrate 1, which transmits the deformation from the substrate 1 to the fixed electrode 2 Cutting off the channel reduces the contact area between the fixed electrode 2 and the substrate 1, which can effectively prevent the deformation of the substrate caused by external stress and temperature changes from being transmitted to the fixed electrode, and greatly reduces the zero point drift of the Z-axis structure.

In the Z-axis structure of the present invention, the first anchor point 20 is adjacent to the middle anchor point 4 . The two first anchor points 20 are symmetrically distributed on both sides of the middle anchor point 4. Under the premise of not affecting the acceleration performance, the first anchor point 20 is as close as possible to the middle anchor point 4, so as to greatly reduce the external stress, The difference in capacitance due to temperature changes.

Further, the fixed electrode 2 is made of single crystal silicon material to improve the deformation resistance of the fixed electrode 2 . The thickness of the fixed electrode 2 is preferably more than 5 μm. Of course, if the process capability can be achieved, the fixed electrode 2 can be less than 5 μm. In order to further ensure the strength of the fixed electrode 2 , a reinforcement structure, such as a mesh-like rib structure, may be provided on the lower surface of the fixed electrode 2 .

Referring to Fig. 3 to Fig. 10, the present invention also provides a production method of a Z-axis structure, comprising the following steps:

a. Depositing a first sacrificial layer 7 on the substrate 1 , the first sacrificial layer 7 may be a silicon oxide material. And etch the area of the first anchor point and the first intermediate anchor point on the first sacrificial layer 7; specifically, depending on the shape of the first anchor point and the first intermediate anchor point, for example, two first anchor points The points need to be symmetrically distributed on both sides of the first intermediate anchor point, so corresponding etching regions should also be made on the first sacrificial layer 7 , as shown in FIG. 3 .

b. Depositing a fixed electrode layer a in the area of the first sacrificial layer 7, the first anchor point, and the first intermediate anchor point. Referring to FIG. 4, the fixed electrode layer a includes a fixed electrode directly above the first sacrificial layer 7, and The first anchor point 20 and the first intermediate anchor point 21 located in the area of the first anchor point and the first intermediate anchor point. Since the first sacrificial layer 7 in this area has been etched away, the first anchor point 20 and the first intermediate anchor point 21 are directly deposited on the substrate 1, realizing the first anchor point 20, the first intermediate anchor point 21 connection to the substrate 1. The fixed electrode layer a may be polysilicon material, so as to improve the strength of the fixed electrode layer.

Wherein, in view of the influence of the first anchor point and the first intermediate anchor point region, in order to finally obtain a fixed electrode layer with a predetermined thickness, the deposition thickness of the fixed electrode layer will be greater than the predetermined thickness, and then planarization treatment is performed, that is to say , etch and thin the deposited fixed electrode layer, and then perform step c.

c. Etching patterns of the fixed electrode 2 and the first intermediate anchor point 21 on the fixed electrode layer a, and etching a plurality of through holes 6 on the fixed electrode 2 . That is to say, the fixed electrode 2 is separated from the first intermediate anchor point 21 , and the fixed electrode 2 is connected to the substrate through the first anchor point 20 , referring to FIG. 5 .

d. Deposit the second sacrificial layer 8 above the fixed electrode 2 and the first intermediate anchor point 21, the second sacrificial layer 8 is not only located above the fixed electrode 2 and the first intermediate anchor point 21, but also deposited into the through hole 6 In, and in the gap between the first intermediate anchor point 21 and the fixed electrode 2, refer to FIG. 6 . For the same reason as above, the deposition thickness of the second sacrificial layer 8 will be greater than the predetermined thickness, and then planarization treatment is performed, that is, the second sacrificial layer 8 is etched and thinned, and then step e is performed.

e. Etching away the second sacrificial layer 8 directly above the first intermediate anchor point 21 to form a groove 80, referring to FIG. 7 ;

f. Deposit the mass block layer above the second sacrificial layer 8. At this time, the mass block layer is not only deposited above the second sacrificial layer 8, but also deposited into the groove 80, and connected to the first intermediate anchor point 21 Together. For the same reason as above, in view of the influence of the groove 80, in order to finally obtain a mass block layer with a predetermined thickness, the deposition thickness of the mass block layer will be greater than the predetermined thickness, and then planarization treatment is performed, that is to say, after deposition The quality block layer is etched and thinned, and then the subsequent etching process is performed.

Etch the patterns of the mass block 3 and the second intermediate anchor point 31 on the mass block layer, wherein the second intermediate anchor point 31 is located directly above the first intermediate anchor point 21; and etch a plurality of For the through hole 6, refer to FIG. 8 . That is to say, the mass block 3 and the second intermediate anchor point 31 are etched out on the mass block layer, so that the mass block 3 and the second intermediate anchor point 31 are only connected together by elastic beams, finally. That is to say, the above-mentioned intermediate anchor point 4 of the present invention includes the first intermediate anchor point 21 and the second intermediate anchor point 31 deposited together, wherein the first intermediate anchor point 21 is etched from the fixed electrode layer, and the second intermediate anchor point Two middle anchor points 31 are etched out from the mass layer. The first intermediate anchor point 21 and the second intermediate anchor point 31 deposited together constitute the intermediate anchor point 4 for supporting the proof mass 3 above the substrate 1 and the fixed electrode 2 .

g. Remove the first sacrificial layer 7 and the second sacrificial layer 8 to form the Z-axis structure of the present invention, refer to FIG. 9 . The first sacrificial layer and the second sacrificial layer 8 can be etched away by HF solution or gaseous HF, which belongs to the common knowledge of those skilled in the art and will not be repeated here. Through the through holes provided on the mass block 3 and the fixed electrode 2, the corrosion of the first sacrificial layer 7 and the second sacrificial layer 8 can be accelerated, and the mass block 3 and the fixed electrode 2 can be released quickly.

Of course, the production method of the present invention also includes the step of pressing the casing 5 on the substrate 1, so as to package the components in the casing 5, as shown in FIG. 10 .

The first sacrificial layer 7 in step a and the second sacrificial layer 8 in step d are not limited to silicon oxide materials, and organic materials such as polyimide (PI) can also be used.

In the production method of the present invention, during the deposition process of the fixed electrode layer, the internal stress of the film can be increased by adjusting the process parameters; and during the deposition process of the mass block layer, the internal stress of the film can be reduced by adjusting the process parameters .

Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and not intended to limit the scope of the present invention. Those skilled in the art will appreciate that modifications can be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims (10)

1. A kind of 1. Z axis structure of accelerometer, it is characterised in that：Including substrate (1), fixed electrode (2), mass (3), in institute State and the first anchor point (20) is provided with the surface of substrate (1), the fixed electrode (2) is connected to the first anchor point by its end (20) on, the fixed electrode (2) is suspended on substrate (1) by the first anchor point (20)；On the surface of the substrate (1) also Middle anchor point (4) is provided with, the mass (3) is suspended at the top of fixed electrode (2) by middle anchor point (4), described Multiple through holes (6) are provided with mass (3), fixed electrode (2).
2. 2. Z axis structure according to claim 1, it is characterised in that：The fixed electrode (2) and the first anchor point (20) one Shaping.
3. 3. Z axis structure according to claim 1, it is characterised in that：The neighbouring middle anchor point (4) of first anchor point (20).
4. 4. Z axis structure according to claim 1, it is characterised in that：The fixed electrode (2) uses polycrystalline silicon material system Into.
5. 5. Z axis structure according to claim 1, it is characterised in that：The thickness of the fixed electrode (2) is more than 5 μm.
6. 6. Z axis structure according to claim 1, it is characterised in that：The lower surface of the fixed electrode (2), which is additionally provided with, to be added Strong structure.
7. 7. Z axis structure according to claim 6, it is characterised in that：The reinforcement structure is network structure.
8. 8. a kind of production method of Z axis structure, it is characterised in that comprise the following steps：

   A, the first sacrifice layer (7) is deposited on substrate (1), and is etched on first sacrifice layer (7) in the first anchor point, first Between anchor point region；

   B, on the first sacrifice layer (7) and the first anchor point, the area deposition stationary electrode layer (a) of the first middle anchor point；

   C, the fixed electrode (2) and the first middle anchor point being connected with the first anchor point (20) are etched on stationary electrode layer (a) (21) pattern, and multiple through holes (6) are etched on fixed electrode (2)；

   D, on fixed electrode (2) and the first middle anchor point (21) the sacrifice layer of area deposition second (8)；

   E, the second sacrifice layer (8) that will be located at directly over the first middle anchor point (21) etches away；

   F, in the second sacrifice layer (8) disposed thereon mass layer, and mass (3) is etched on mass layer, among second The pattern of anchor point (31), wherein the second middle anchor point (31) is located at the surface of the first middle anchor point (21)；And in mass (3) On etch multiple through holes (6)；

   G, remove the first sacrifice layer (7), the second sacrifice layer (8), form Z axis structure.
9. 9. production method according to claim 8, it is characterised in that：Also including between the step b, step c will be solid Fixed electrode layer (a) it is smooth chemical conversion predetermined thickness the step of.
10. 10. production method according to claim 8, it is characterised in that：In the step f, etched by mass layer Mass (3), the second middle anchor point (31) pattern before, in addition to by mass layer it is smooth chemical conversion predetermined thickness the step of.