JPH04102066A - Acceleration sensor and its manufacture - Google Patents

Abstract

PURPOSE:To simplify management of a position of a weight and thickness of a thin part and also to stably realize desired sensitivity in batch processing by integrating a mount, a cantilever, the weight and the thin part by means of etching of a desired part of a silicon substrate. CONSTITUTION:An HI groove 1b which is formed by anisotropic etching HI from a rear of a silicon substrate 1 and an HI groove 1c which is formed by plasma HI from a surface form a through groove 1a communicating through the surface and the rear. The groove 1a separates the substrate 1 into a peripheral part and an inner part except a coupling portion, while a mount 3 is structured on the peripheral part and a weight 5, a cantilever 4 and a thin part 2 are integrally structured on the inner part. The grooves 1b, 1b located on both sides of the coupling portion are subjected to side etching to form a recess 16, while the thin part 2 is formed between the bottom of the recess and the surface of the substrate 1. Therefore at the time of anisotropic HI, it is easy to manage thickness of the thin part by means of optimization of HI width. In addition, an integral structure permits easy placement of the weight to an optimum position so that stable acquisition of desired sensitivity in batch processing is possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is widely used as an acceleration sensor particularly for automobiles, and is an acceleration sensor (semiconductor acceleration sensor) that detects acceleration by strain generated in a silicon cantilever. and its manufacturing method.

[Conventional technology]

A semiconductor acceleration sensor has a pedestal at its base end, a silicon cantilever with a thin wall in the middle, and a weight fixed to the tip of the cantilever. is detected as the output of a brifuge made up of a diffused resistor on its surface.It is easy to downsize and can be used in harsh environments, so it is suitable for use in automobiles, etc., where the installation space is small. It is widely used as it is optimal for limited uses. Conventionally, this type of acceleration sensor is made by creating a cantilever made by thinning the middle part of a silicon substrate, using the base end of this thin part as a pedestal, or fixing it to the pedestal, and attaching a weight to the tip end. Manufactured with installation instructions.

FIG. 12 to FIG. 14 are explanatory diagrams of the manufacturing procedure of a conventional acceleration sensor. First, as shown in FIG. 12, the surface of a silicon substrate 1 as a raw material is coated with a silicon oxide film 10, and a diffused resistor 11 constituting a bridge for strain detection is formed in the missing part of the silicon oxide film 10. Person, output electrode 1
2, these surfaces, together with the surface of the silicon oxide film 10, are covered with a glass coat of a passivation film 13. Next, as shown in FIG. 13, the back side of the silicon base [1 is covered with an etching mask 14 having etching holes 15 at positions corresponding to the diffused resistors 11 on the front side, and the etching holes 15 are etched from the back side. A recess 16 of a predetermined depth is formed at a position corresponding to . As a result, as shown in FIG. 14, a thin part 2 is obtained between the bottom surface of the recess 16 and the surface of the silicon substrate 1, and a pedestal 3 is placed on one side (the left side in the figure) of the thin part 2, and a pedestal 3 is placed on the other side (the left side in the figure). A cantilever 4 is obtained on each side, and an acceleration sensor is constructed by fixing a weight 5 to the tip of the cantilever 4 by bonding means such as adhesive.

[Problem to be solved by the invention]

Now, the detection sensitivity of the acceleration sensor manufactured as described above is
The weight of the cantilever 4 and the weight 5, the fixed position of the weight 5,
It also depends on the thickness and planar area of the thin section 2. However, in the conventional method, as described above, the workability of fixing the weight 5 after forming the thin wall portion 2 is extremely poor, and there is a possibility that the weight 5 may not be fixed at a predetermined position.
The thickness of the recess 16 is controlled by the etching time of the recess 16 performed from the back side of the silicon substrate 1, but since this etching is a hatch process in which many wafers are treated as one unit, the thickness is controlled within the plane of each wafer and between the wafers. There is an unavoidable problem that variations in the thickness of the thin section 2 occur due to differences in etching rates between there were.

The present invention has been made in view of the above circumstances, and provides an acceleration sensor and its manufacture in which the position of the weight and the thickness of the thin film part can be easily controlled, and desired sensitivity can be stably achieved through badge processing. The purpose is to provide a method.

[Means to solve the problem]

The acceleration sensor according to the present invention has a pedestal, a cantilever, a weight, and a thin wall portion integrally formed by etching required parts of a silicon substrate. By anisotropic etching from the back side of the silicon substrate, an etching groove is formed that isolates the periphery of the back side from the inside except for some connecting areas, and side etching is performed between the etched grooves on both sides of the connecting area. A part of the connection part is thinned by etching to form a thin part, and a corresponding part of the etching groove is plasma etched from the surface side of the silicon substrate to make the etching groove penetrate to the surface side, and the peripheral edge side of this is made by plasma etching from the surface side of the silicon substrate. It is used as a pedestal, and the inside is used as a cantilever and a weight.

[Effect]

In the present invention, taking advantage of the fact that anisotropic etching of a silicon substrate hardly progresses in the <111> direction, etching is first performed in the H00> direction from the back side, depending on the size of the etching mask used at this time. An etching groove with a predetermined depth is formed to isolate the peripheral edge of the silicon substrate from the inside except for a part of the connecting area, and then etching proceeds in the H'lO) direction between the etching grooves on both sides of the connecting area. A recess with a depth corresponding to the depth of the etching groove is formed by the side etching groove, a thin wall portion with a constant thickness is formed in this forming area, and the etching groove is communicated with the surface side by plasma etching. Then, the peripheral part separated by the etched groove is used as a pedestal, and the same inner part is separated as a cantilever and a weight integrated with it, and the cantilever and the weight are separated from the peripheral part through the thin part. Obtain an acceleration sensor with a structure supported by a pedestal.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof. FIG. 1 is a plan view of an acceleration sensor according to the present invention, and FIG. 2 is a longitudinal sectional view taken along line nn in FIG. 1.

The acceleration sensor according to the present invention is made of a silicon substrate 1 which is rectangular in plan view, and as shown by crosshatching in FIG. It is separated into a peripheral part and an inner part except for the connection part, and the pedestal 3 is integrally formed on the peripheral part, and the weight 5, cantilever 4 and thin part 2 are integrally formed on the inside. The inner portion separated from the pedestal 3 at the peripheral edge by the through groove 1a has a T-shape in plan view, and the tip of the portion corresponding to the vertical bar of this T-shape is the connecting end with the pedestal 3. In the method for manufacturing an acceleration sensor according to the present invention (hereinafter referred to as the method of the present invention), the vicinity of this connecting end is made into a thin portion 2 by the process described below, and the cantilever 4 is formed by the remaining portion corresponding to the vertical bar of the T-shape. Further, the weight 5 is integrally constituted by the portion corresponding to the horizontal bar.

As will be described later, the through groove 1a is an etching groove 1b having a triangular cross section formed by anisotropic etching from one side (back side) of the silicon substrate 1 toward the other side (front side), and is etched by plasma etching from the front side. An etching groove IC of a certain width is formed by etching to penetrate the surface side, and the second
It has a cross-sectional shape as shown in the figure. FIG. 1 is a plan view from the side where the inclined surface of the etched groove 1b is visible, that is, from the back side, and the crosshatching in the figure is applied only to a corresponding portion of the etched groove IC. The thin portion 2 has etched grooves 1b and lb located on both sides of the connection portion that communicate with each other by side etching that progresses as described below, and forms a recessed portion having a trapezoidal cross section as shown in FIG. 16, and the bottom surface of this recess 16 and the silicon substrate 1
is constructed between the surface of

As described above, the acceleration sensor according to the present invention has a structure in which the cantilever 4 and the weight 5 are supported only by the thin part 2 inside the rectangular frame-shaped pedestal 3, and the pedestal 3 is placed at an appropriate measurement position. The acceleration at this measurement position is applied to the cantilever 4 and the weight 5, and the acceleration is detected using the strain generated in the thin portion 2 as a medium.

Next, the procedure for implementing the method of the present invention for obtaining the acceleration sensor configured as described above will be explained.

3 to 7 are explanatory diagrams of the construction procedure of the thin portion 2 in a cross section taken along the line mm in FIG. 1. First, as shown in FIG.
0, a diffused resistor 11 constituting a bridge for strain detection is formed in the missing part of the resistor 11, and the bridge electrode 12 and output electrode 12 are attached to this, and then these surfaces are coated with silicon oxide. Along with the surface of the film 10, the passivation film 1
Cover with glass coat from step 3. The above procedure is similar to the conventional method, but in the method of the present invention, the thin part 2 is
In order to form a through groove 1a that blocks the diffusion resistor 1 from
The silicon oxide film 10 and the passivation film 13 are removed by etching on both sides of the silicon oxide film 1. This removal is carried out over the entire formation range of the through groove 1a on the surface side of the silicon substrate 1, and as will be described later, the width of the removed portion is equal to the width of the etched groove 1c formed by plasma etching from the surface side. Become.

Next, an etching mask 14 is formed on the back side of the silicon substrate 1 in order to carry out anisotropic etching from the back side of the silicon substrate 1. A plan view of this etching mask 14 is shown in FIG. As shown in this figure, the etching mask 14 includes a peripheral portion 14a corresponding to the pedestal 3, and a T-shaped inner portion 14 corresponding to the cantilever 4 and the weight 5.
It has a planar shape in which the connecting portion 14c corresponding to the thin wall portion 2 is separated from the connecting portion 14c by an etching hole 15 formed corresponding to the formation position of the through groove 1a. Due to the formation of this etching mask 14, in the cross section taken along the line 1--2, as shown in FIG.
The back side of the region where I is formed is covered with the connecting portion 14c, and the silicon oxide film 10 and the passivation film 1 are covered with the connecting portion 14c.
An etching hole 15 is located at a position corresponding to the back side of the removed portion of No. 3, and the outside of the etching hole 15 is located on the peripheral edge portion of
4a, it is in a covered state.

After etching mask 14, etching is performed from the back side of silicon substrate 1 using an anisotropic etchant such as KOH. At this time, the etch rate in the H11> direction is HOO)
Since the etching is significantly smaller than that in the direction, the etching that occurs at the portion where the etching hole 15 is formed on the back side of the silicon substrate 1 is inclined at a predetermined angle (specifically, 54.3°) with respect to the back side. The etching progresses along the slope and almost stops at a position where the slopes starting from both widthwise sides of the etching hole 15 intersect, and as shown in FIG. Etched grooves 1b are formed. The depth h of the etched groove 1b obtained in this way is the width dimension D (the eighth width) of the etched hole 15.
When forming the etching mask 14, the depth h of the etching groove 1b can be accurately controlled by simply providing an etching hole 15 with a width calculated by the following formula. can do.

D = 2 ・h / jan54.3°
-(1) Now, after completing the etching in the <100> direction,
When etching is continued further, the etching in the H11) direction hardly progresses, but the etching in the H10> direction progresses relatively quickly, and the side etching progresses as shown by the broken line in FIG. 5, resulting in the formation of the diffused resistor 11. The portion between the etched grooves 1b and Ib on both sides of the position is etched over the entire back side of the position where the first diffused resistor is formed, and finally, as shown in FIG. A continuous recess 16 having a trapezoidal cross section is formed, and the recess 16
A thin portion 2 having a diffused resistor 11 on the surface side is formed between the bottom surface of the silicon substrate 1 and the surface of the silicon substrate 1 . At this time, the side etching progresses only within the depth range of the etching groove 1b, and the depth of the resulting recess 16 is approximately equal to the depth h of the etching groove 1b previously obtained.
Since this depth h can be easily and accurately controlled as described above, the thin portion 2 having a desired constant thickness can be stably obtained.

After completing the anisotropic etching from the back side as described above, plasma etching is performed from the front side of the silicon substrate 1 to remove the pansivation film 13 and the silicon oxide film 10.
The removed portions are etched to form etching grooves 1c and lc. As a result, the etching grooves 1b, Ib formed from the back side at positions corresponding to the removed portions penetrate to the front side, and the thin wall portion 2 formed between these grooves 1b and 1c are formed on the outside of the etching grooves 1c. It is separated from the pedestal 3.

9 to 11 are explanatory diagrams of the construction procedure of the weight 5 in a cross section taken along the line IX-IX in FIG. 1. In the component parts of the weight 5, first, as shown in FIG.
After forming the diffused resistor 11 and attaching the electrode 12 as described above, the surface of the silicon oxide film 10 is glass-coated with a scivation film 13, and the covering layer of these films 13 and 10 is coated with the through-hole film 13. 'a1a is removed by etching. Next, the back surface of the silicon substrate 1 is covered with an etching mask 14. Since the etching mask 14 has the shape described above, the through hole a1a is
In FIG. 9, which is a cross-sectional view taken along the line IX--IX in FIG.
The outer side of 5.15 is covered with the peripheral edge portion 14a of the etching mask 14, and the inner side is covered with the inner portion 14b.
It becomes covered with.

After being covered with the etching mask 14 in this way,
As in the case of the structure of the thin film portion 2, etching is performed from the back side of the silicon substrate 1 using an anisotropic etchant such as KOH. As mentioned above, this etching progresses along the inclined surface that is inclined at a predetermined angle with respect to the back surface, and the 10th etching
As shown in the figure, an etching groove 1b having a triangular cross section having an apex at a position where the slopes starting from both widthwise sides of the etching hole 15 intersect is formed and then stopped. In this case, the width of the etching hole 15 may be appropriately set so that the apex does not reach the surface of the silicon substrate 1, and
Etching holes 15 for forming etching grooves 1b on both sides
It doesn't have to be the same width.

After completing the etching from the back side in this way, plasma etching is performed from the front side of the silicon substrate 1.
The removed portions of the passivation film 13 and the silicon oxide film 10 are etched to form an etched groove IC, and the etched groove 1b is communicated with the surface side to form a through groove 1a. Separate and form. It should be noted that the cantilever 4 between the weight 5 and the thin portion 2 is also formed by the same procedure. That is, by the above procedure, the thin wall portion 2, the cantilever 4, and the weight 5 are integrated with the base 3, so that the weight 5 can be easily and reliably positioned.

〔Effect of the invention〕

As described in detail above, in the present invention, anisotropic etching is performed from the back side of the silicon substrate to form an etching groove that isolates the periphery of the back side from the inside except for some connecting parts, and Since a part of the connection part is thinned by side etching between the etching grooves on both sides to form a thin part, the thin part can be formed by optimizing the etching width during the anisotropic etching. The thickness of the etched groove can be easily and accurately controlled, and a considerable portion of the etched groove can be penetrated to the surface side by plasma etching.
Since the pedestal on the peripheral side, the inner cantilever, the weight, and the thin part are integrally constructed, the weight can be easily placed in the appropriate position, and the acceleration sensor has the desired sensitivity. The present invention has excellent effects, such as being able to stably obtain it by batch processing.

[Brief explanation of drawings]

FIG. 1 is a plan view of an acceleration sensor according to the present invention, FIG. 2 is a vertical cross-sectional view taken along line nn in FIG. Figure 8 is a plan view of an etching mask used in carrying out the method of the present invention;
FIGS. 9 to 11 are explanatory diagrams of the construction procedure of a weight according to the method of the present invention, and FIGS. 12 to 14 are explanatory diagrams of a conventional method of manufacturing an acceleration sensor. Engineering...Silicon substrate 2...Thin wall part 3...
Pedestal 4... Cantilever 5... Weight 1a.
...Through grooves lb, lc...Etching grooves In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A weight is provided at the tip of a silicon cantilever with a pedestal at the base end, and a thin part is provided in the middle, and acceleration is detected by the strain generated in the thin part as the weight swings. 1. An acceleration sensor, wherein the pedestal, cantilever, weight, and thin portion are integrally formed by etching a required portion of a silicon substrate. (2) Perform anisotropic etching from the back side of the silicon substrate to form an etching groove of a predetermined depth that isolates the periphery of the back side from the inside except for some connecting parts, and then After side etching is performed between the etching grooves on both sides of the connection part to form the thin part in a part of the connection part, plasma is applied from the surface side of the silicon substrate over the entire length of a considerable portion of the etching groove. 2. Manufacturing the acceleration sensor according to claim 1, wherein etching is performed to penetrate the etched groove on the surface side, and the pedestal is formed on the peripheral side of the pedestal, and the cantilever and the weight are formed on the inside. Method.