JPH0797644B2 - Semiconductor acceleration sensor and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor acceleration sensor having a stopper structure that can be formed by batch processing.

[Prior art]

A conventional semiconductor acceleration sensor is, for example, the IE Electron Devices (IEEE).
Electron Devices, vol.ED-26, No.12, p.1911, Dec.197
9 "A Batch-Fabricated Silicon Accelerometer")
Are listed in.

FIG. 2 is a perspective view of the above device and AA ′, BB ′.
FIG.

In FIG. 2, 21 is a Si substrate, 22 is a Si cantilever, 23 is a Si weight, 24 is a void, and 25 is a piezoresistor.

In the semiconductor acceleration sensor shown in FIG. 2, when the acceleration is applied, the Si weight 23 is displaced, and thereby the Si cantilever 22 is distorted. A piezoresistor 25 is formed on the surface of the Si cantilever 22, and when strain occurs in the Si cantilever 22, the resistance value of the piezoresistor 25 changes due to the piezoresistive effect. Acceleration can be detected by detecting the change in the resistance value.

Further, as a mounting structure of the above-mentioned sensor chip, a structure as shown in FIG. 3 (perspective view and XX ′ sectional view) is shown. This is a structure to prevent the cantilever from breaking due to excessive acceleration such as dropping.
It has a structure in which the Si substrate 21 having the above is sandwiched by two stoppers, a lower stopper 26 and an upper stopper 27.

[Problems to be solved by the invention]

However, the acceleration sensor having the above structure has the following problems.

First of all, in the above structure, since there is no function of suppressing the displacement of the weight between the formation of the beam and the formation of the stopper, it is necessary to take great care in handling the chip. If the value is bad, there is a problem that the beam is broken and the yield is reduced.

Secondly, there is a problem that the stopper forming process becomes complicated and the cost increases. That is, one of the purposes of forming the acceleration sensor with a semiconductor is to reduce the cost per chip by batch processing. As is clear from IC manufacturing, many chips are formed on a wafer and processed at the same time. By doing so, it is possible to produce a product of stable quality and low cost, but the structure in which the upper and lower stoppers are bonded to each other after forming the beam as shown in FIG. 3 causes a significant increase in cost.

Thirdly, there is a problem of difficulty in forming a stopper. That is, in the structure shown in FIG. 3, the distance between the stopper and the weight must be controlled with an accuracy of several μm to several tens of μm depending on the design of the beam, and high accuracy is required for forming the stopper and adhering to the chip. There is a problem in that a high stopper manufacturing technique and a stopper bonding technique are required, which increases the mounting cost.

Furthermore, in the acceleration sensor as described above, a weight such as a metal may be added to the upper surface of the Si weight 23 in order to reduce the sensitivity of the other axis, but the thickness of such a metal weight inevitably varies. Since it occurs, it is difficult to precisely set the distance between the weight and the stopper (the distance between the metal weight formed on the upper surface of the Si weight 23 in FIG. 3 and the upper stopper 27), and therefore a stopper with a high precision effect can be obtained. There is also the problem that it will be difficult to realize.

The present invention has been made to solve various problems of the prior art as described above, and it is possible to form a stopper during sensor chip formation, that is, during a wafer process,
An object of the present invention is to provide a semiconductor acceleration sensor which has stable and uniform performance, is inexpensive, and is suitable for mass production.

[Means for solving problems]

In order to achieve the above object, in the semiconductor acceleration sensor of the present invention, the plurality of first protrusions provided in a portion of the weight portion facing the support portion and the portion of the support portion facing the weight portion in the above are provided. A plurality of second protrusions formed at positions where the first protrusions and a portion thereof overlap in the vertical direction, and
Some of the plurality of first and second protrusions have the first protrusions in the vertical direction in the vertical direction, and the others have the second protrusions in the upper direction. It is configured to overlap with each other through a predetermined gap. The above-described vertical relationship between the first and second protrusions is set so that, for example, one relationship is upper and the other relationship is lower.

In the manufacturing method of the present invention, a step of forming a high-concentration n-type diffusion layer, which is a void portion between the first protrusion and the second protrusion, at a predetermined position on the surface of the Si substrate, ,the above
A step of forming a Si layer on the surface of the Si substrate, a step of forming a high concentration p-type diffusion layer at a predetermined position of the Si layer so as to contact at least the high concentration n-type diffusion layer, and a back surface of the Si substrate After forming a film to be a mask for Si etching at a predetermined position, a single or a plurality of beam portions and a single weight portion provided at an end portion of the beam portion are formed by using electrochemical etching from the back surface. A step of forming a support portion connected to the other end of the beam portion and surrounding the outer periphery of the weight portion; a step of removing the high-concentration p-type diffusion layer; and an exposure step by the electrochemical etching. Removing the high-concentration n-type diffusion layer by electrolytic etching to form a gap between the first protrusion and the second protrusion, and separating the Si weight portion from the support portion. Like It is.

[Action]

With the above configuration, in the semiconductor acceleration sensor of the present invention, when excessive acceleration is applied and displacement of the mutual position of the weight portion and the support portion becomes large, the first protrusion is formed. Part and the second protrusion part to prevent further displacement, and some of the first protrusion part and the second protrusion part have the first protrusion part on top and the other part. Since the second protrusion is overlapped with the second protrusion facing upward, it is possible to reliably prevent excessive displacement even when acceleration in either the upper or lower direction is applied, and the beam portion is damaged. It can be effectively protected so that it does not exist.

Further, in the manufacturing method of the present invention, since the stopper (projection) can be formed during the wafer process, the yield is improved, and since it is not necessary to form the stopper later, the mounting cost can be reduced. .

In addition, a high-concentration n-type diffusion layer, which serves as a void portion between the first protrusion and the second protrusion, is formed at a predetermined position on the surface of the Si substrate, and is then removed by electrode etching. Since the gap is formed between the first and second protrusions by the above, the size of the gap can be formed with high accuracy, and the protection characteristics of the stopper can be made uniform.

Further, since the formation of the high-concentration n-type diffusion layer serving as the void portion can be performed simultaneously with the step of forming the embedded layer (high-concentration n-type diffusion layer) in the signal processing circuit of the acceleration sensor, etc. Can be simplified and the cost can be reduced.

〔Example〕

FIG. 1 is an embodiment of the present invention, (a) is a plan view,
(B) is an A-B-C sectional view of (a), (c) is an A-B'-C 'sectional view of (a).

First, the structure will be explained. Si having a Si weight portion 12 at one end
A cantilever 13 is fixed to the Si support portion 11, and a piezoresistor 14 is formed on the surface of the Si cantilever 13. The process up to this point is the same as the conventional example shown in FIG.

In addition, in the peripheral portion of the Si weight portion 12 and the predetermined region of the Si support portion 11 on the Si weight portion 12 side, the first protrusion 15 is located on the Si weight side, and the second protrusion 16 is located on the Si support portion side. Is formed as follows. That is, the first protrusion 15 and the second protrusion 16 are formed so as to partially overlap each other with a predetermined gap 17 therebetween. This overlap is the ABC of Fig. 1 (b).
As shown in the cross-section, the first protrusion 15 overlaps with the second protrusion 16 and the second protrusion 16 as shown in the AB′C ′ cross-section of FIG. 1C. Overlaps so that it is on the first protrusion 15, and the structure is such that both overlap.

The above-described vertical relationship between the first and second protrusions is set so that, for example, one relationship is upper and the other relationship is lower. That is, when the first protrusion is at a certain position, the second protrusion may be adjacent to the first protrusion.

Next, the operation will be described.

In the sensor shown in FIG. 1, the Si support portion 11 and the Si weight portion 1
2, Si cantilever 13, first protrusion 15, second protrusion 16 are formed during the wafer process.

When acceleration is applied to this sensor, the Si weight portion 12 is displaced in the α ₁ direction or the α ₂ direction in FIG. And if an excessive acceleration is applied, the displacement will increase,
When the displacement exceeds a predetermined value, the first protrusion 15 and the second protrusion 16 come into contact with each other to stop the displacement.

For example, in the ABC cross section of (b), the first projection 15 is stopped by the second projection 16 against excessive displacement in the α ₂ direction, and the AB′C ′ cross section of (c). In view of the above, the first protrusion 15 is also stopped by the second protrusion 16 with respect to an excessive displacement in the α ₁ direction. Therefore, even if excessive acceleration is applied, excessive stress is not applied to the Si cantilever 13, and damage to the Si cantilever 13 can be prevented.

In addition, since the protrusion that serves as a stopper for preventing Si cantilever bending can be formed during the wafer process, the stopper can be formed with high accuracy, the yield of manufacturing the acceleration sensor is improved, and the stopper is formed during mounting. Implementation cost is reduced because it is not necessary.

Next, FIG. 4 is a second embodiment of the present invention and shows a plan view of an acceleration sensor having a cantilever structure.

In this embodiment, Si beams 131 and 132 are provided on both ends of the Si weight portion 12.
The present invention is applied to an acceleration sensor having a so-called double-supported beam structure having a. The present invention can be applied to the case of such a plurality of beam structures as in the case of FIG.

Next, a method of manufacturing the acceleration sensor shown in FIG. 1 will be described with reference to FIG.

First, in (a), P ⁺ or the like is introduced at a high concentration at a predetermined position on the main surface of the p-type Si substrate 41 of the <111> plane by a high concentration by an ion implantation method or the like, and is thermally diffused to form a high concentration n-type. A diffusion layer 42 is formed.

Next, in (b), by the epitaxial growth method,
On the main surface of the p-type Si substrate 41, the n-type upper Si layer 43 in which the impurities forming the n-type are introduced at a low concentration is formed.

Next, in (c), an impurity (for example, B ⁺⁾ that forms p-type is formed on the upper Si layer 43 so as to be in contact with the high-concentration n-type diffusion layer 42.
Etc.) is introduced at a high concentration by an ion implantation method and thermally diffused to form a p-type diffusion layer 44.

Next, in (d), after forming the piezoresistor 14 using a thermal diffusion method at a predetermined position to be a beam of the acceleration sensor, p
At a predetermined position on the back surface of the Si substrate 41, a SiO ₂ and SiN ₄ film to be a mask for Si etching is formed. Next, the n-type upper Si layer
A predetermined region of the p-type Si substrate 41 and the p-type diffusion layer 44 formed in the upper Si layer 43 are etched by an electrochemical etching method using an alkaline etching solution with 43 as an anode. The electrochemical etching method is described in detail in JP-A-61-97572 (method for manufacturing a semiconductor acceleration sensor). Finally, the high-concentration n-type diffusion layer 42 is etched using 5% HF electrolytic etching to separate the first protrusion 15 and the second protrusion 16 and form a stopper. Further, by this wafer process, the Si support portion 11, the Si weight portion 12, and the Si cantilever 13 are simultaneously formed.

In the current bipolar transistor and manufacturing method, in order to reduce the collector resistance of the npn transistor, a high-concentration n-type diffusion layer, that is, a so-called buried layer is formed at a predetermined position of the p-type Si substrate. After forming the embedded layer,
An n-type epitaxial layer is grown, and an impurity diffused layer such as an emitter, a base and a collector forming a transistor circuit is formed in this portion. Therefore, the formation of the high-concentration n-type diffusion layer 42 shown in FIG. 5 (a) in the manufacturing method of the present invention is performed by the above-mentioned buried layer (high-concentration n-type diffusion layer) in the signal processing circuit of the acceleration sensor. Since it can be performed at the same time as the forming step, the manufacturing process can be simplified and the cost can be reduced.

As described above, the present invention has fewer manufacturing steps than the acceleration sensor described in Japanese Patent Application No. 62-318752, etc., which the present applicant has already filed, and can improve the yield and reduce the cost.

〔The invention's effect〕

With the above-mentioned configuration, in the present invention,
If excessive displacement is applied to the weight part and the support part, the protrusions will hit each other and prevent further displacement.Be careful not to damage the beam part. Can be effectively protected.

In addition, since the protrusion that serves as a stopper can be formed during the wafer process, the yield is improved, and since it is not necessary to form a stopper later, the mounting cost can be reduced.

Furthermore, the accuracy of the voids between the protrusions is determined by the thickness of the high-concentration n-type diffusion layer 42 formed during the wafer process, and therefore can be formed with extremely high accuracy.

Therefore, according to the present invention, a stopper that prevents the beam from being broken during the manufacturing process and the mounting process, and prevents the beam from being broken due to the application of excessive acceleration or the vibration near the resonance frequency after the completion of the batch process. The excellent effect is that it can be realized with high accuracy and low cost.

[Brief description of drawings]

FIG. 1 is a plan view and a sectional view of a semiconductor acceleration sensor of the present invention, FIG. 2 is a perspective view and a sectional view of an example of a conventional semiconductor acceleration sensor, and FIG. 3 is a perspective view showing a mounting example of a conventional semiconductor acceleration sensor. FIG. 4 is a plan view of another embodiment of the present invention, and FIG. 5 is a sectional view showing a manufacturing method of the present invention. <Description of symbols> 11 …… Si support 12 …… Si weight 13 …… Si cantilever 14 …… Piezoresistance 15 …… First projection 16 …… Second projection 17 …… Projection Void between 131, 132 …… Si beam

Claims (2)

[Claims] 1. A single or a plurality of beam portions that are distorted when an acceleration is applied, a single weight portion formed by connecting to one end of the beam portion, and an outer periphery of the weight portion connected to the other end of the beam portion. In a semiconductor acceleration sensor formed on a semiconductor substrate, a support portion formed so as to surround with a predetermined interval and a piezoresistive portion formed on the beam portion, the acceleration detection direction, that is, the beam portion is When the direction of distortion is vertical, a plurality of first protrusions provided on a portion of the weight portion facing the support portion and the first protrusion on a portion of the support portion facing the weight portion. A plurality of second protrusions formed at positions that partially overlap each other in the vertical direction, and a part of the plurality of first and second protrusions is the first protrusion in the vertical direction. The protrusion of 1 is on the top, the others are The semiconductor acceleration sensor, wherein the protrusions are turned on, and is formed so as to overlap with a predetermined gap from each other. 2. A step of forming a high-concentration n-type diffusion layer, which is a void portion between the first protrusion and the second protrusion, at a predetermined position on the surface of the Si substrate, and the surface of the Si substrate. A step of forming a Si layer thereon, a step of forming a high-concentration p-type diffusion layer at a predetermined position of the Si layer so as to contact at least the high-concentration n-type diffusion layer, and a predetermined step on the back surface of the Si substrate. After forming a film to be a mask for Si etching at a position, using electrochemical etching from the back surface, a single or multiple beam portion and a single weight portion provided at the end portion of the beam portion and the beam portion are provided. Forming a support portion connected to the other end so as to surround the outer periphery of the weight portion; removing the high concentration p-type diffusion layer; and the high concentration exposed by the electrochemical etching. Removal of n-type diffusion layer by electrolytic etching Forming a space between the second protruding portions of the first protrusions by Rukoto method of manufacturing a semiconductor acceleration sensor and a step of disconnecting from the support portion to the Si weight portion.