JPH1117195A - Manufacture of acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the dispersion of the film thickness of a diaphragm by forming the second embedded layer using the material having the large etching selection ratio for the diaphragm at a position connected to the first embedded layer. SOLUTION: A first embedded layer 6a, wherein high-concentration impurities are injected, is formed at a position where a first diaphragm 2a is constituted at the upper part of a silicon substrate 5. A second embedded layer 6b comprising a silicon oxide film is formed at a position where a second diaphragm 2b is formed at the upper part. This silicon oxide film is etched by etching solution based on hydrogen fluoride. Therefore, the etching of the part other than the second embedded layer 6b seldom occurs, and there is no dispersion of the film thickness of the second diaphragm 2b. Furthermore, since a piezoelectric resistor R is formed on the first diaphragm 2a comprising a single crystal, the piezoelectric coefficient is high in comparison with the case of the formation on a polycrystal, and the reduction of sensitivity can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an acceleration sensor formed by processing a silicon substrate.

[0002]

2. Description of the Related Art FIG. 4 is a side sectional view of a conventional acceleration sensor. A conventional acceleration sensor has a rectangular frame-shaped support portion 1.
And a weight 3 having an inverted trapezoidal cross section, which is swingably supported by a thin diaphragm 2 formed in a cross shape on the upper surface of the support portion 1. The weight 3 and the diaphragm 2 are adjacent to each other with a slight gap.

A plurality of piezoresistors R are provided on the diaphragm 2 formed in a cross shape by diffusion. These piezoresistors R are for detecting acceleration as an electrical output. Piezo resistance R
Are connected in a bridge (not shown), and a voltage is applied to the bridge of each piezoresistor R from an external power supply. The bridge is balanced in a state where no acceleration is applied to the weight 3.

In the acceleration sensor described above, when an acceleration is applied, the weight 3 swings and the diaphragm 2 bends. As a result, a strain is generated in the diaphragm 2 by the stress corresponding to the acceleration, and the resistance value of the piezo resistor R changes according to the strain. The voltage output according to the acceleration is obtained.

When a piezoresistor R is formed on a single crystal and a piezoresistor R is formed on a polycrystal, a piezoresistor formed on a single crystal has a higher piezo coefficient.
Since the output of the piezo resistor R increases, the piezo resistor R is generally formed on a single crystal.

Next, a method of manufacturing the above-described conventional acceleration sensor will be described with reference to FIG. First, in a buried layer forming step, an impurity such as boron is ion-implanted at a high concentration at a predetermined position on one surface surrounding a central portion of the silicon substrate 5 using an N-type silicon substrate 5. Then, a P + buried layer 6 having a high impurity concentration is formed. (FIG. 5
(Refer to (a).) Next, in the epitaxial layer forming step, an epitaxial layer 7 having a thickness corresponding to the diaphragm 2 which bends when an acceleration is applied and having a conductivity type of N-type is formed on one surface side of the silicon substrate 5. (See FIG. 5B.) Next, in the piezoresistive formation step, an impurity such as boron is diffused into a portion of the epitaxial layer 7 corresponding to the diaphragm 2, and the conductivity type is a P-type opposite to the epitaxial layer 7. , A piezoresistor R for converting a resistance change due to deflection into an electric signal is formed. (Refer to FIG. 5C.) Next, in a notch forming step, after forming a wiring portion electrically connected to the piezoresistor R by sputtering or vapor deposition, one surface side of the epitaxial layer 7 and the silicon substrate 5 are formed.
A silicon nitride film 10 is formed on the other side. (FIG. 5
(See (d).) Next, from the other side of the outer peripheral edge plate of the weight portion, anisotropic etching is performed using an alkaline aqueous solution such as potassium hydroxide to form a cut portion 8 reaching the buried layer 6. Forming an outer peripheral edge of the part. (See FIG. 5 (e).) Next, in the diaphragm forming step, an electrode electrically connected to the piezoresistor R via the wiring portion is formed on one surface side, and isotropically etched in all directions. The buried layer 6 is removed, and both ends are epitaxial layers 7.
The diaphragm 2 supported by the support portion 1 and connected to the center of the weight portion is formed on the epitaxial layer 7. As the etching solution, an acidic solution containing hydrofluoric acid is used.
(See FIG. 5 (f))

[0007]

In the acceleration sensor having the above-described structure and manufacturing method, when removing the buried layer 6 by etching, depending on the members of the buried layer 6, the composition of the solution used for etching, the etching time, and the like. The diaphragm 2 is slightly etched. In particular, when a single crystal is used for the diaphragm 2 in consideration of the sensitivity of the acceleration sensor, when the buried layer 6 is removed, other portions are also slightly etched at the same time. However, when the diaphragm 2 is etched, the film thickness of the diaphragm 2 varies, and since the diaphragm 2 is sufficiently thin as compared with the weight portion or the like, it becomes impossible to obtain an acceleration sensor having desired sensitivity characteristics. There is a problem that the yield decreases due to a decrease in the strength of the diaphragm 2 or the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to suppress variations in the film thickness of a diaphragm without deteriorating the sensitivity characteristics of an acceleration sensor and to stabilize the characteristics. Another object of the present invention is to provide a method of manufacturing an acceleration sensor with improved yield.

[0009]

According to the first aspect of the present invention,
A weight part, a thin diaphragm, and a support part for swingably supporting the weight part by the diaphragm are formed by processing a silicon substrate, and the method for manufacturing an acceleration sensor having a piezoresistor in the diaphragm, Forming a first buried layer having a high impurity concentration at a predetermined position on the silicon substrate; and forming a second buried layer using a material having a large etching selectivity with respect to the diaphragm at a position connected to the first buried layer. Forming a thin diaphragm on the first buried layer and the second buried layer using epitaxial growth; and forming the piezoresistor on the diaphragm formed on the first buried layer. Forming and cutting the outer peripheral edge of the weight portion from the back surface of the silicon substrate using anisotropic etching. Forming a saw unit, a step of removing only the second buried layer by isotropic etching,
Removing the first buried layer by isotropic etching.

According to a second aspect of the present invention, in the method for manufacturing an acceleration sensor according to the first aspect, a silicon oxide film is used for the second burying layer, and the second burying layer is formed by using a hydrofluoric acid-based etching solution. It is characterized in that it is removed by isotropic etching.

According to a third aspect of the present invention, in the method for manufacturing an acceleration sensor according to the first or second aspect, the first method is provided.
After the buried layer is removed, etching is performed so that the diaphragm has a beam structure.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described based on FIGS. FIG. 1A is a top view of a semiconductor acceleration sensor according to one embodiment of the present invention, and FIG. 1B is a side sectional view. Reference numeral 1 denotes a support, which supports the weight 3 via a thin diaphragm 2. Reference numeral 4 denotes a notch groove. By providing the notch groove 4, the thin portion of the diaphragm is increased, and the sensor sensitivity is improved.

A piezoresistor R is disposed on the diaphragm 2, and electrically detects the distortion of the diaphragm 2 caused by the movement of the swingable weight 3. On this occasion,
In view of the fact that forming a piezo resistor R on a single crystal has a larger piezo coefficient and a larger output, in the present embodiment, a diaphragm made of single crystal silicon or the like (hereinafter referred to as a first diaphragm 2a). Formed on top.

On the other hand, the portion of the diaphragm 2 where the piezoresistor R is not formed (hereinafter referred to as the second diaphragm 2b) does not need to be particularly formed of a single crystal. Therefore, in the present embodiment, the second diaphragm 2b is formed of a semiconductor or an insulator other than single crystal silicon such as polycrystalline silicon. This prevents the diaphragm 2 from being etched more than necessary and causing a variation in film thickness in a later-described step of forming the diaphragm 2.

Next, a method of manufacturing the acceleration sensor having the above configuration will be described with reference to FIG. First, in the step of forming the buried layer 6, a silicon substrate 5 having a plane orientation (100) is used, and a high concentration impurity is implanted at a position where the first diaphragm 2a is to be formed in a later step. A buried layer 6a is formed, and a second buried layer 6b made of a silicon oxide film is formed at a position where the second diaphragm 2b is to be formed. (See FIG. 2A.) Next, in the epitaxial layer forming step, the epitaxial layer 7 is formed on one surface side of the silicon substrate 5 with a thickness corresponding to the diaphragm 2 which bends when an acceleration is applied. By this step, the first diaphragm 2a on the first buried layer 6a
Is formed on the portion corresponding to the second diaphragm 2b on the second buried layer 6b, and polycrystalline silicon is formed on the portion corresponding to the second diaphragm 2b. (See FIG. 2B.) Next, in the piezoresistor forming step, a piezoresistor R for converting a resistance change due to bending into an electric signal at a portion corresponding to the first diaphragm 2a made of single crystal silicon and a diffusion wiring (shown in FIG. ) Are formed. (See FIG. 2C.) Next, in the weight portion forming step, anisotropic etching is performed from the other surface side of the outer peripheral edge plate of the weight portion 3 using an alkaline aqueous solution such as potassium hydroxide to form the buried layer 6. The notch 8 which reaches is formed, and the outer peripheral edge of the weight 3 is formed. (Figure 2
Next, in the second diaphragm formation step, the second buried layer 6b made of a silicon oxide film is removed by isotropic etching using buffered hydrofluoric acid or the like, and the cut groove 4 is formed.
(A groove formed in this step is referred to as a second cut groove 4b). (Refer to FIG. 2E.) At this time, since the second buried layer 6b formed of the silicon oxide film is etched using the hydrogen fluoride-based etching solution, most portions other than the second buried layer 6b are etched. Therefore, the film thickness of the second diaphragm 2b does not vary.

In this embodiment, polycrystalline silicon is used for the second diaphragm 2b and a silicon oxide film is used for the second buried layer 6b. However, the present invention is not limited to this, and the second buried layer 6b is most suitable. A member to be etched and an etching solution may be used.

Next, in a first diaphragm forming step, the first buried layer 6a is removed with hydrofluoric nitric acid or the like,
A notch 4 (a groove formed in this step is referred to as a first notch 4a) is formed. A solution having a ratio of hydrofluoric acid: nitric acid: acetic acid = 1: 3: 8 is used for the etching here. (See FIG. 2F.) At this time, the etching rate of the isotropic etching is higher in the first buried layer 6a having a higher impurity concentration than in the epitaxial layer 7 having a lower impurity concentration, and Only selective removal.

Finally, wiring for external connection is formed of aluminum or the like. According to the present embodiment, when the second diaphragm 2b occupying most of the diaphragm 2 is formed, a silicon oxide film is used as the buried layer 6 (second buried layer 6b), and this is replaced with hydrogen fluoride. Since the etching is performed with the system etching solution, the portions other than the second buried layer 6b are hardly etched, and the thickness of the second diaphragm 2b does not vary. In addition, the first single crystal
Since the piezoresistor R is formed on the diaphragm 2a, the piezoresistor R has a higher piezocoefficient than that formed on a polycrystal, and there is no decrease in sensitivity. Furthermore, since the first buried layer 6a removed for forming the first diaphragm 2a is slightly smaller than the first buried layer 6a removed for forming the second diaphragm 2b, the etching time can be shortened. It is possible to reduce the influence of removing the first buried layer 6a on other portions.

In the acceleration sensor described above,
The diaphragm 2 may have a beam structure as shown in FIG. 3 (hereinafter, referred to as a beam portion 9). Thereby, the deflection generated by the swinging of the weight portion 3 becomes larger than that in the case of the diaphragm 2, so that a more sensitive acceleration sensor can be configured. The beam portion 9 is formed by adding a step of processing the diaphragm 2 into a beam structure using reactive ion etching or the like in the above-described manufacturing process.

[0020]

As described above, according to the first aspect of the present invention, a silicon substrate is formed by processing a weight portion, a thin diaphragm, and a support portion for swingably supporting the weight portion by the diaphragm. Forming a first buried layer having a high impurity concentration at a predetermined position on a silicon substrate; and forming a diaphragm at a position connected to the first buried layer at a predetermined position on the silicon substrate. Forming a second buried layer using a material having a large etching selectivity with respect to the first buried layer, forming a thin diaphragm on the first buried layer and the second buried layer by epitaxial growth, A step of forming a piezoresistor on a diaphragm formed on the layer, and a step of anisotropic etching from the back surface of the silicon substrate to the outside of the weight portion The method includes a step of forming a cut portion serving as an edge, a step of removing only the second buried layer by isotropic etching, and a step of removing the first buried layer by isotropic etching. Since the piezoresistor can be formed on the single crystal and the second buried layer removed when forming most of the diaphragm can be selectively removed, the acceleration sensor can be formed on the single crystal. Without lowering the sensitivity characteristics of
It is possible to provide a method for manufacturing an acceleration sensor that suppresses variations in the film thickness of the diaphragm and improves the stability and the yield of the characteristics.

According to the second aspect of the present invention, the first aspect is provided.
In the described invention, a silicon oxide film is used for the second buried layer, and the second buried layer is removed by isotropic etching using a hydrofluoric acid-based etching solution, so that most of the diaphragm is formed. It is possible to remove only the second buried layer that is removed when performing.

According to the third aspect of the present invention, there is provided the first aspect.
According to the first aspect of the present invention, in the first aspect of the present invention, the first buried layer is removed, and then the diaphragm is formed into a beam structure by etching, so that the deflection caused by the swinging of the weight portion. Is larger than in the case of the diaphragm, so that a more sensitive acceleration sensor can be configured.

[Brief description of the drawings]

FIG. 1A is a side sectional view and FIG. 1B is a top view of an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a method for manufacturing an acceleration sensor according to an embodiment of the present invention.

FIG. 3 is a top view of an acceleration sensor according to another embodiment of the present invention.

FIG. 4 is a side sectional view of a conventional acceleration sensor.

FIG. 5 is a diagram illustrating a method of manufacturing a conventional acceleration sensor.

[Explanation of symbols]

 R Piezoresistor 1 Support part 2 Diaphragm 2a First diaphragm 2b Second diaphragm 3 Weight part 4 Notch groove 4a Second notch groove 4b Second notch groove 5 Silicon substrate 6 Embedded layer 6a First embedded layer 6b Second embedded layer 7 Epitaxial Layer 8 Notch 9 Beam

Claims (3)

[Claims] 1. An acceleration sensor comprising a weight portion, a thin diaphragm, and a support portion for swingably supporting the weight portion by a diaphragm formed on a silicon substrate, wherein the diaphragm has a piezoresistor. In the manufacturing method, a step of forming a first buried layer having a high impurity concentration at a predetermined position of the silicon substrate, and using a material having a large etching selectivity with respect to the diaphragm at a position connected to the first buried layer Forming a second buried layer by epitaxial growth on the first buried layer and the second buried layer, and forming a thin diaphragm on the first buried layer by using epitaxial growth. Forming the piezoresistor on the outer periphery of the weight portion by using anisotropic etching from the back surface of the silicon substrate. A step of forming a notch serving as an edge; a step of removing only the second buried layer by isotropic etching; and a step of removing the first buried layer by isotropic etching. A method for manufacturing an acceleration sensor. 2. The method according to claim 1, wherein a silicon oxide film is used for the second buried layer, and the second buried layer is removed by isotropic etching using a hydrofluoric acid-based etching solution. Item 7. A method for manufacturing an acceleration sensor according to Item 1. 3. The method for manufacturing an acceleration sensor according to claim 1, wherein the first buried layer is removed and then the diaphragm is formed into a beam structure by etching.