JPH0883916A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE: To prevent the spread of etchant to a surface side and the damage of a beam by preventing the peeling of an etching resistant material in the etching step at the time of manufacturing even by improving the detecting sensitivity. CONSTITUTION: The semiconductor acceleration sensor comprises a single or a plurality of protrusions 7a made of layer regions connected to either a superposed part 4 or a frame 5 in a slit 6 to set the width of the slit 6 to a predetermined value or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor manufactured by using an electrochemical etching (hereinafter abbreviated as ECE) process.

[0002]

2. Description of the Related Art Conventional semiconductor acceleration sensors include those shown in FIGS. 5 and 6, for example. Details are described in Japanese Patent Application No. 5-278032. Here, 1 is a p-type silicon substrate, 2 is an n-type epitaxial layer as a thin layered region having a thickness of several μm to several tens of μm deposited on the p-type silicon substrate 1, 3 is a beam portion, and 4 is a weight portion. Reference numeral 5 is a fixed portion (frame portion), 6 is a slit, and each of these portions is a p-type diffusion that selectively penetrates the n-type epitaxial layer 2 at a portion corresponding to the slit 6 in the n-type epitaxial layer 2. A region is formed and the p-type silicon substrate 1 is biased while biasing the n-type epitaxial layer 2 to a positive potential.
ECE from the back using an alkaline anisotropic etchant
It is formed by performing. The weight portion 4 is suspended and supported by a fixed portion 5 that surrounds the weight portion 4 by a beam 3 formed of one or a plurality of n-type epitaxial layers 2. A plurality of p-type piezoresistors 8 are formed on the surface of the beam portion 3 and they are bridge-connected, and the resistance value change of the piezoresistor 8 due to the stress generated on the surface of the beam portion 3 due to the acceleration applied to the weight portion 4 is changed. The voltage is converted into a voltage, a voltage corresponding to the acceleration is output, and the acceleration is detected. A glass pedestal 9 is a PYRE having a thermal expansion coefficient close to that of silicon.
It is made of X glass or the like and is anodically bonded to the p-type silicon substrate 1.

In the manufacture of such an acceleration sensor, the weight portion 4 and the beam portion 3 are accurately etched after the silicon surface is protected by an etching resistant material such as a silicon resin so that the etching solution does not attack the silicon surface. In order to connect the n-type epitaxial layer 2 forming the beam portion 3 to a power source,
An ECE process is generally used in which the p-type silicon substrate 1 and the p-type diffusion region are etched by immersing the counter electrode in an etching solution and applying an electric field.

[0004]

However, in such a conventional semiconductor acceleration sensor, the width of the beam portion is usually narrowed and the slit widths on both sides thereof are widened in order to increase the acceleration sensitivity. When the slit portion is removed in the ECE process, the etching-resistant material for surface protection, which should be attached so as not to attack the surface by etching, is likely to be peeled off due to the hydraulic pressure of the alkaline anisotropic etching liquid. Figure 7 shows the etching resistant material 1 in the ECE process.
It is a conceptual diagram of 0 peeling. The peeling of the etching resistant material 10 leads to the wraparound of the alkaline anisotropic etching liquid on the surface, and the etching of the surface causes a defect in the semiconductor acceleration sensor. Further, although the etching resistant material 10 has a reinforcing effect on the beam portion with respect to the etching solution, the reinforcing effect disappears when the etching resistant material 10 is peeled off, so that the beam portion may be destroyed.

The present invention has been made by paying attention to such conventional problems. Even if the detection sensitivity is improved, the etching resistant material is prevented from being peeled off in the etching step during the manufacturing process. It is an object of the present invention to provide a semiconductor acceleration sensor capable of preventing the beam from wrapping around to the surface side and breaking the beam portion and dramatically improving the yield.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 forms an opposite conductivity type layered region on the main surface of one conductivity type semiconductor substrate, and corresponds to a slit in the layered region. Forming one conductivity type diffusion region selectively penetrating the layered region in a part, selectively forming an etching mask on the back surface of the semiconductor substrate, and depositing an etching resistant material on the entire surface of the layered region, Electrochemical etching that etches the semiconductor substrate while applying a voltage to the layered region is performed, and the slit corresponding portion is etched so as to penetrate to the surface side while leaving the layered region, thereby forming a slit. A weight portion having a thickness of the semiconductor substrate, a frame portion formed so as to surround the weight portion, and the weight portion formed of the layered region, In a semiconductor acceleration sensor having a single or a plurality of beams supported on and a piezoresistor formed on the beam, and detecting the stress on the beam caused by acceleration application by the piezoresistor, in the slit, The gist of the present invention is to provide a single or a plurality of protrusions that are connected to only one of the weight portion and the frame portion and that are formed of the layered region for setting the width of the slit to a predetermined value or less.

According to a second aspect of the invention, in the semiconductor acceleration sensor according to the first aspect, the width of the slit is
The gist is that the thickness is not less than 100 μm and not less than the thickness of the layered region.

According to a third aspect of the present invention, in the semiconductor acceleration sensor according to the first or second aspect, the semiconductor substrate is p-type and the layered region is an n-type epitaxial layer.

The invention according to claim 4 is the same as claim 1 or claim 2.
Alternatively, in the semiconductor acceleration sensor according to 3, the cantilever structure in which the single beam or the plurality of beams support only one side around the weight portion, or the two sides supporting the opposite two sides around the weight portion on opposite sides to each other. The gist is that it is either a cantilever structure.

[0010]

According to the first aspect of the invention, if the width of the beam is set to be narrow in order to increase the detection sensitivity, the width of the slit tends to be wide, but only one of the weight portion and the frame portion is provided in the slit. By providing a protrusion that is connected and sets the slit width to a predetermined value or less, the width of the slit is narrowed, the adhesion of the etching resistant material to the substrate is increased in the etching step during manufacturing, and peeling is prevented. . As a result, it is possible to prevent the etching solution from wrapping around the surface and breaking the beam. Since the protrusion is not connected to the beam at all, the protrusion does not affect the detection sensitivity.

According to the second aspect of the present invention, generally, the area surrounded by the slit within 100 μm in the surface direction of the substrate has a small thickness of the substrate. Considering the influence of thermal strain, the bipolar circuit associated with the sensor is installed. This is unsuitable, and the wraparound of the etching solution on the surface is allowed in this range. By setting the width of the slit to 100 μm or less, it is possible to make the surface wraparound range within 100 μm. Further, by setting the minimum width of the slit to be the thickness of the layered region, the circulation of the etching solution is improved, and efficient and less variable etching is possible.

In the invention of claim 3, the semiconductor substrate is p-type and the layered region is an n-type epitaxial layer, so that the p-type semiconductor substrate is alkaline from the back surface while biasing the n-type epitaxial layer to a positive potential. By performing selective electrochemical etching using an anisotropic etching solution, the weight portion of the thickness of the semiconductor substrate, the beam including the layered region, the slit, the frame portion, and the like are accurately etched and formed.

In a fourth aspect of the present invention, the semiconductor acceleration sensor is provided with a protrusion for setting the slit width to a predetermined value or less in the slit regardless of the type of cantilever structure or double-supported beam structure. Different structures are applicable.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a first embodiment of the present invention. In FIG. 1 and FIGS. 3 and 4 showing second and third embodiments to be described later, the same or equivalent members and parts as those in FIGS. 5 and 6 are designated by the same reference numerals. A duplicate description will be omitted. In this embodiment, the central weight portion 4
Has a so-called double-supported beam structure in which the beam is suspended and supported from both sides by the four beam portions 3 on the fixed portion 5. Further, in the present embodiment, the n-type for connecting the weight portion 4 and the fixed portion 5 in the slits 6 located on both sides of the weight portion 4 in FIG. 1 respectively and setting the width of the slit 6 to a predetermined value or less Projection made of epitaxial layer, so-called dummy beam 7a
Are formed. Although the dummy beam 7a has the same thickness as the beam portion 3 having the piezoresistor 8 and is connected to the weight portion 4 or the fixed portion 5, the beam portion 3 having the piezoresistor 8 is formed.
Is not connected at all. The size of the dummy beam 7a is defined by the width of the slit 6.

Next, the operation of this embodiment will be described. When the acceleration is applied, the weight portion 4 is vertically displaced according to the acceleration, and stress is generated in the beam portion 3 accordingly, so that the value of the piezoresistor 8 on the beam portion 3 is also changed and the acceleration is increased. To be detected. Here, one method of increasing the sensitivity to acceleration is to reduce the width of the beam portion 3, but the width of the slit 6 beside the beam portion 3 is increased. This causes peeling of the etching-resistant material for surface protection when the slit 6 penetrates in the ECE process, and the etching solution wraps around the surface, corroding the circuit portion and causing a sensor defect. Therefore, a dummy beam 7a having the same thickness as that of the beam portion 3 is provided in the slit 6, and the width of the slit 6 is narrowed to increase the adhesion between the silicon substrate and the etching resistant material and prevent the etching resistant material from peeling off. . This makes it possible to solve problems such as the etching solution sneaking onto the surface. Since the dummy beam 7a is not connected to the beam portion 3 having the piezoresistor 8 at all, the dummy beam 7a has no influence on the acceleration sensitivity. Due to the structure of the dummy beam 7a, it is possible to create the dummy beam 7a only by modifying the mask without complicating the ECE process. FIG. 2 shows the relationship between the slit width and the amount of the etching solution flowing around the surface with respect to the peeling of the etching resistant material. The maximum allowable value of the surface wraparound is set to a region in the vicinity of the slit 6 where no problem occurs in the operation of the circuit formed on the silicon substrate. Generally 1 from the slit 6 in the surface direction
The range surrounded by 00 μm or less is mainly unsuitable for installation of a bipolar circuit considering the influence of thermal distortion and the like, and this part is an area where surface wraparound is allowed. According to the relationship in FIG. 2, it is necessary to set the slit width to 100 μm or less in order to ensure that the surface wraparound is 100 μm or less. Therefore, the maximum allowable slit width is set to 100 μm. Further, the minimum allowable value of the slit 6 is determined by the etching variation of the slit 6 part.
In order to reduce this variation, it is necessary that the etching liquid be well circulated when the slit 6 is etched. In order to efficiently circulate this etching solution,
The ratio of the width of the slit 6 to the thickness of the n-type epitaxial layer is 1
The above is desirable. Therefore, the minimum slit width is the thickness of the n-type epitaxial layer. Also, the dummy beam 7a
Plays a role of blocking dust larger than the slit 6, and also has an effect of preventing clogging of dust and ensuring a normal sensor function.

FIG. 3 shows a second embodiment of the present invention. In this embodiment, the structure of the silicon substrate is the same as that of the first embodiment described above, but the dummy beam 7b is connected to the weight portion 4 side. That is, the slit 6 does not pass through the center of the dummy beam 7b, but is offset to the fixed portion 5 side. By setting the width of the slit 6 in the same manner as in the first embodiment, the same operation and effect as in the first embodiment can be obtained.

FIG. 4 shows a third embodiment of the present invention. In this embodiment, the structure of the silicon substrate is the same as that of the first embodiment, but the dummy beam 7c is connected to the fixed portion 5 side. That is, the slit 6 does not pass through the center of the dummy beam 7c, but is offset to the weight portion 4 side. By setting the width of the slit 6 in the same manner as in the first embodiment, the same operation and effect as in the first embodiment can be obtained.

In each of the above embodiments, the plurality of beam portions 3
The semiconductor acceleration sensor having a double-supported beam structure in which two opposite sides of the weight portion 4 are supported by the fixed portions 5 on the opposite sides has been described. However, in the present invention, a single or a plurality of beam portions are provided around the weight portion. It can also be applied to a semiconductor acceleration sensor having a cantilever structure that is supported by only one side.

[0019]

As described above, according to the first aspect of the invention, the slit is connected to only one of the weight portion and the frame portion to set the width of the slit to a predetermined value or less. Since a single or multiple protrusions consisting of a layered region are provided, even if the detection width is set to be narrow to improve the detection sensitivity, the etching-resistant material is prevented from peeling during the etching process during manufacturing, and the etching solution It is possible to prevent wraparound to the surface side and breakage of the beam portion, and it is possible to dramatically improve the yield.

According to the inventions described in claims 2 to 4, in addition to the effects of the invention described in claim 1, there are the following effects.

According to the second aspect of the present invention, the width of the slit is not less than the thickness of the layered region and not more than 100 μm. Therefore, in the etching process at the time of manufacturing, the etching solution wraps around to the surface side. In addition, the wraparound range can be suppressed within a range of 100 μm from the slit in the surface direction of the substrate, which is unsuitable for installing a bipolar circuit, and the etching solution can be circulated efficiently to perform an efficient etching process with less variation. You can

According to the third aspect of the present invention, the semiconductor substrate is p-type, and the layered region is an n-type epitaxial layer. Therefore, the n-type epitaxial layer is biased to a positive potential in the etching step during manufacturing, and the p-type epitaxial layer is formed. -Type semiconductor substrate is subjected to selective electrochemical etching from the back surface using an alkaline anisotropic etching solution, so that the weight portion of the thickness of the semiconductor substrate, the beam composed of layered regions, the slit and the frame portion can be accurately formed. It can be formed by etching.

According to the fourth aspect of the present invention, the structure in which the protrusion for setting the slit width to a predetermined value or less is provided in the slit is either a cantilever structure or a double-supported beam structure of the semiconductor acceleration. It can also be applied to a sensor.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of a semiconductor acceleration sensor according to the present invention.

FIG. 2 is a diagram showing a relationship between a slit width and an etching solution surface wraparound amount in an ECE process during manufacturing in the first embodiment.

FIG. 3 is a main part plan view showing a second embodiment of the present invention.

FIG. 4 is a plan view of an essential part showing a third embodiment of the present invention.

FIG. 5 is a plan view of a conventional semiconductor acceleration sensor.

6 is a cross-sectional view taken along the line AA of FIG.

FIG. 7 is a diagram for explaining the peeling of the etching resistant material in the ECE process at the time of manufacturing in the above example.

[Explanation of symbols]

 1 p-type silicon substrate (semiconductor substrate) 2 n-type epitaxial layer (layered region) 3 beam 4 weight part 5 fixed part (frame part) 6 slits 7a, 7b, 7c dummy beam (protrusion) 8 piezoresistive 10 anti-etching material

Claims (4)

[Claims] 1. An opposite conductivity type layered region is formed on a main surface of a one conductivity type semiconductor substrate, and a one conductivity type diffusion region penetrating the layered region is selectively formed in a portion of the layered region corresponding to a slit. An etching mask is selectively formed on the back surface of the semiconductor substrate, an anti-etching material is deposited on the entire surface of the layered region, and electrochemical etching is performed to etch the semiconductor substrate while applying a voltage to the layered region. Manufactured by a step of forming a slit by etching so as to penetrate the slit corresponding portion to the surface side while leaving the layered region, and forming a weight portion having a thickness of the semiconductor substrate and surrounding the weight portion. A frame portion, a beam or beams that are formed of the layered region and that support the weight portion on the frame portion, and a piezoresistor formed on the beam. In the semiconductor acceleration sensor having a stress on the beam caused by the acceleration application, which is detected by the piezoresistance, the slit is connected to only one of the weight portion or the frame portion, and the width of the slit is a predetermined value. A semiconductor acceleration sensor, characterized in that it is provided with a single or a plurality of protrusions formed of the layered region for setting below. 2. The semiconductor acceleration sensor according to claim 1, wherein the width of the slit is equal to or larger than the thickness of the layered region and equal to or smaller than 100 μm. 3. The semiconductor acceleration sensor according to claim 1, wherein the semiconductor substrate is p-type, and the layered region is an n-type epitaxial layer. 4. A cantilever structure in which the one or more beams support only one side around the weight portion, or a both-end beam structure in which two opposite sides around the weight portion support each other on opposite sides. It is any one of Claims 1 and 2 characterized by the above-mentioned.
Alternatively, the semiconductor acceleration sensor described in 3 above.