JPH0945937A - Fabrication of triaxial acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a trixial acceleration sensor which can be fabricated easily with high yield while preventing generation of void by eliminating a step for pasting single crystal silicon layers. SOLUTION: Silicon oxide 20 is deposited on the surface of a single crystal silicon layer 13 having a partially overlapped part 14. It is then etched to leave the silicon oxide 20 only at a predetermined region on the periphery of jointing face between a flexible part 15 and overlapped part 14 and a polysilicon layer 19 is formed on the silicon oxide. Subsequently, an epitaxial growth layer 22 of single crystal, and a piezoelectric resistance layer 16 are formed on another surface region before the single crystal silicon layer 13 is removed by anisotropic etching from the rear side until the silicon oxide 20 is reached. When the silicon oxide exposed to the rear side of single crystal silicon layer is removed by etching through the use of hydrofluoric acid, the step for pasting the single crystal silicon layers can be eliminated and the yield can be increased because the void is not generated.

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 a three-axis acceleration sensor applying a silicon wafer and a semiconductor process.

[0002]

2. Description of the Related Art A three-axis acceleration sensor is a piezo device which is formed in a portion for detecting acceleration (a weight portion and a bending portion which is distorted by the displacement of the weight portion) and the bending portion, and which converts the distortion of the bending portion into an electric signal. A sensor that includes a resistor and that converts acceleration in the three axial directions acting on the weight portion into an electric signal and outputs the electric signal.

An example of a conventional triaxial acceleration sensor will be described with reference to the sectional view of FIG. In the figure, reference numeral 1 denotes a substantially flat plate-shaped single crystal silicon layer, 2 denotes a weight separated from the surrounding single crystal silicon layer 1, and supported by a substantially thin film-shaped flexible portion 3 formed on the surface of the single crystal silicon layer 1. The peripheral portion of the flexible portion 3 is supported by the single crystal silicon layer 1.
On the surface of the flexible portion 3, a piezoresistive layer 4 for converting the strain of the flexible portion 3 into an electric signal, a high impurity region 5 connected to the piezoresistive layer 4 and serving as a wiring layer, and a high impurity region 5 are connected. The formed electrode layer 6 is formed. The surface of the flexible portion 3 other than the portion where the electrode layer 6 is formed is covered with the silicon oxide film 7. The layer formed on the back surface of the single crystal silicon layer 1 and the bottom surface of the weight portion 2 is a silicon nitride film 8. When the acceleration acts on the weight portion 2 in the thus configured triaxial acceleration sensor, the flexure portion 3 is distorted by the displacement of the weight portion 2, and an electric signal corresponding to the distortion is output from the piezoresistive layer 4.

3 shown in FIG. 5 based on the cross-sectional view of FIG.
An example of a method of manufacturing the axial acceleration sensor will be described. First, as shown in (a), a silicon nitride film 9 is formed on the front surface side of the single crystal silicon layer 1, and a silicon nitride film 8 is formed on the back surface side of the single crystal silicon layer 1. This time,
A silicon nitride film is also formed on the side surface portion of the single crystal silicon layer 1. Next, as shown in (b), the silicon nitride film 9 around the portion that becomes the root of the weight portion 2 (joint portion with the bending portion 3) is removed by photoetching. Further, the silicon nitride film 8 around the lower surface of the weight portion 2 (where the groove for separating the single crystal silicon layer 1 and the weight portion 3 is formed) is removed by photoetching. Further, the single crystal silicon layer 1 is etched to a predetermined depth using the silicon nitride films 9 and 8 as a mask. Next, as shown in (d), the silicon nitride film 9 on the surface of the single crystal silicon layer 1 is removed,
As shown in (e), another single crystal silicon layer 10 is attached to the surface of the single crystal silicon layer 1, and as shown in (f), the thickness of the attached single crystal silicon layer 10 is several tens. The single crystal silicon layer 10 is polished to have a thickness of μm.

Next, as shown in (g), a silicon oxide film 11 is formed on the polished surface, and as shown in (h), the surface of the single crystal silicon layer 10 to be the flexure 3 is formed.
The piezoresistive layer 4 is formed by photoetching and thermal diffusion. In the step shown in (g), the silicon oxide film 12 is also formed on the surface of the single crystal silicon exposed on the back surface side of the single crystal silicon layer 1. Furthermore, as shown in (i),
A high impurity region 5 for connecting the piezoresistive layer 4 and the electrode layer 6 is formed. Next, as shown in (j), the electrode layer 6 is formed on the high impurity region 5 connected to the piezoresistive layer 4, and as shown in (k), the back surface side of the single crystal silicon layer 1 is formed. The silicon oxide film 12 is removed by etching,
Etching is performed from the back surface of the single crystal silicon layer 1 by anisotropic etching to separate the weight portion 2 from the surrounding single crystal silicon layer 1 to complete the triaxial acceleration sensor.

[0006]

In the method for manufacturing the triaxial acceleration sensor described above, the predetermined portion on the surface side of the single crystal silicon layer 1 is removed by etching in the step shown in FIG. 6 (c). Therefore, in the bonding step shown in FIG. 6E, the single crystal silicon layer 10 is bonded to the surface of the single crystal silicon layer 1 in which the concave shape is formed, which is applied in the bonding step. When heat is applied to the single crystal silicon layers 1 and 10, the single crystal silicon layers 1 and 10 are likely to warp, the adhesiveness is deteriorated, and voids are easily generated, resulting in poor yield and technical development. There was a problem that it was difficult.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of manufacturing a triaxial acceleration sensor which can be easily manufactured and has a high yield.

[0008]

In order to achieve the above object, a method of manufacturing a triaxial acceleration sensor according to a first aspect of the present invention comprises a substantially thin film-shaped flexure portion and a weight joined to one surface of the flexure portion. And a step of forming a silicon oxide film on the surface of the single crystal silicon layer, a part of which serves as a weight, and a surface region of the single crystal silicon layer. A step of etching away the silicon oxide film so that the silicon oxide film is left only in a predetermined region around a region serving as a joint surface between the flexure portion and the weight portion, and a plurality of layers are formed on the silicon oxide film by epitaxial growth. Forming a crystalline silicon layer and forming an epitaxial growth layer of single crystal silicon in a surface region other than the region where the polycrystalline silicon layer is formed; Forming a piezoresistive layer on the epitaxial growth layer; etching away the single crystal silicon layer from the back surface side of the single crystal silicon layer by anisotropic etching until the silicon oxide film is reached; And a step of etching away the silicon oxide film exposed on the back surface side of the crystalline silicon layer with hydrofluoric acid.

In the method of manufacturing the triaxial acceleration sensor according to the first aspect, there is no step of bonding the single crystal silicon layers to each other, and voids due to the bonding are not generated, so that the yield can be improved.

A method of manufacturing a triaxial acceleration sensor according to a second aspect of the present invention is a method of manufacturing a triaxial acceleration sensor having a substantially thin-film flexure portion and a weight portion joined to one surface of the flexure portion. And a step of forming a silicon oxide film on the surface of the single crystal silicon layer, a part of which becomes the weight portion, and the surface area of the single crystal silicon layer, which becomes the joint surface of the flexible portion and the weight portion. Etching away the silicon oxide film in a predetermined region around the region; implanting oxygen ions from the surface side at a high acceleration voltage; removing the silicon oxide film after ion implantation; A step of laminating a single crystal silicon layer for forming a flexure portion on the surface of the crystalline silicon layer and polishing the single crystal silicon layer for forming the flexure portion to a predetermined thickness; and forming a piezoelectric film on the single crystal silicon layer for forming the flexure portion. A diffusion resistance layer serving as an anti-layer is formed by thermal diffusion, and a buried silicon oxide film is formed in a region where oxygen ions are implanted, and the buried silicon oxide film is anisotropically etched from the back surface side of the single crystal silicon layer. A step of etching away the single crystal silicon layer until reaching the film, and a step of etching away the embedded silicon oxide film exposed on the back surface side of the single crystal silicon layer with hydrofluoric acid. It is a thing.

In the method for manufacturing a triaxial acceleration sensor according to the second aspect, since the single crystal silicon layers are bonded to each other over the entire surface of the mirror-like flat surface, the adhesion is high, so that voids do not occur and the bonding is stable. You can

A method for manufacturing a triaxial acceleration sensor according to a third aspect of the present invention is a method for manufacturing a triaxial acceleration sensor having a substantially thin film-shaped flexure portion and a weight portion joined to one surface of the flexure portion. And a step of forming a silicon oxide film on the surface of the single crystal silicon layer, a part of which becomes the weight portion, and the surface area of the single crystal silicon layer, which becomes the joint surface of the flexible portion and the weight portion. Etching away the silicon oxide film in a predetermined region around the region; implanting oxygen ions from the surface side at a high acceleration voltage; removing the silicon oxide film after ion implantation; Forming an epitaxial growth layer on the surface of the crystalline silicon layer, forming a buried silicon oxide film in the region into which oxygen ions are implanted, and forming a piezoresistive layer on the epitaxial growth layer. And a step of etching away the single crystal silicon layer from the back surface side of the single crystal silicon layer by anisotropic etching until the buried silicon oxide film is reached, and exposing the back surface side of the single crystal silicon layer. And a step of etching away the embedded silicon oxide film with hydrofluoric acid.

In the method for manufacturing a triaxial acceleration sensor according to the third aspect, there is no step of bonding the single crystal silicon layers to each other, and voids due to the bonding are not generated, so that the yield can be improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A triaxial acceleration sensor formed by an embodiment of a method for manufacturing a triaxial acceleration sensor of the present invention will be described with reference to the sectional view of FIG. In the figure, 13
Is a substantially flat plate-shaped single crystal silicon layer, and 14 is a weight portion which is separated from the surrounding single crystal silicon layer 13 and is supported by a substantially thin film-shaped flexible portion 15 formed on the surface side of the single crystal silicon layer 13. The peripheral portion of the flexible portion 15 is supported by the single crystal silicon layer 13. On the surface of the single crystal silicon layer 13, a piezoresistive layer 16 for converting the strain of the flexure 15 into an electric signal and an electrode layer 17 connected to the piezoresistive layer 16 are formed. The surface of the single crystal silicon layer 13 other than the portion where the electrode layer 17 is formed is covered with a silicon oxide film 18. In addition, in the region of the substantially thin film-shaped flexible portion 15, in the portion around the joint portion with the weight portion 14,
A polycrystalline silicon layer 19 is formed.

3 shown in FIG. 2 based on the sectional view of FIG.
An embodiment of a method of manufacturing the axial acceleration sensor will be described. First, as shown in (a), the single crystal silicon layer 13
A silicon oxide film 20 is formed on the front surface side of the single crystal silicon layer 13 and a silicon oxide film 21 is formed on the back surface side of the single crystal silicon layer 13, and as shown in FIG. A predetermined region around a region that serves as a joint surface between the portion 15 and the weight portion 14 (a region between a region that serves as a joint surface between the flexure portion 15 and the weight portion 14 and a region of the single crystal silicon layer 13 that finally remains as a substrate portion) Silicon oxide film 2 only
The silicon oxide film 20 is removed by etching so that 0 remains.

Next, as shown in (c), a polycrystalline silicon layer 19 is formed on the silicon oxide film 20 by epitaxial growth to a thickness of several tens of μm, and a region where the polycrystalline silicon layer 19 is formed. An epitaxial growth layer 22 of single crystal silicon is formed in the surface region of the single crystal silicon layer 13 other than the above. Further, as shown in (d), a silicon oxide film 18 is formed on the epitaxial growth layer 22 by thermal oxidation, and as shown in (e), a photolithography process, an etching process, and a thermal diffusion process are performed, and then the piezoresistive process is performed. A diffusion resistance layer to be the layer 16 is formed.

Next, after a photolithography process and an etching process, a contact window of the piezoresistive layer 16 is opened, an Al sputtering process, a photolithography process and an etching process are performed, and then the piezoresistive layer 1 is formed as shown in FIG.
The electrode layer 17 is formed on the electrode 6. Further, the front surface side is entirely covered with a resist (not shown), and as shown in (g),
A window 23 is formed in the silicon oxide film 21 on the back surface in order to form a groove for separating the weight portion 14 from the single crystal silicon layer 13 to be the substrate portion by a photolithography process and an etching process, and a window 23 is formed through this window 23. , (H)
As shown in, the single crystal silicon is removed by dry etching until the silicon oxide film 20 is reached. Finally, while leaving the whole surface resist (not shown) on the front surface side, the silicon oxide film 21 on the back surface and the silicon oxide film 20 buried by epitaxial growth and exposed on the back surface side are removed with a thin buffered hydrofluoric acid, By removing the entire surface resist, the triaxial acceleration sensor as shown in (i) is completed.

A different embodiment of the method of manufacturing the triaxial acceleration sensor of the present invention will be described with reference to FIG. However,
The same components as those shown in FIG. 1 are designated by the same reference numerals. First, as shown in (a), the silicon oxide film 20 is formed on the front surface side of the single crystal silicon layer 13, and the silicon oxide film 2 is formed on the back surface side of the single crystal silicon layer 13.
1 to form a single crystal silicon layer 1 as shown in FIG.
Of the surface areas of No. 3, a predetermined area around the area serving as the joint surface between the bending portion 15 and the weight portion 14 (the bending portion 15 and the weight portion 1).
The silicon oxide film 20 in the region to be the junction surface of No. 4 and the region between the regions of the single crystal silicon layer 13 that finally remains as the substrate portion) is removed by etching to form the window 24 for ion implantation.

Next, as shown in (c), oxygen ions are injected into the single crystal silicon layer 13 through the window 24 at an accelerating voltage of several hundred keV to several hundred MeV to form the oxygen ion-implanted layer 25.
Is formed, a resist (not shown) is applied to the entire back surface, and as shown in (d), the silicon oxide film 20 on the front surface side is formed.
Are removed by etching with hydrofluoric acid. Further, as shown in (e), another single crystal silicon layer (single crystal silicon layer 26 for forming the flexure portion) is attached to the surface of the single crystal silicon layer 13 by heat treatment to have a thickness of about several tens of μm. The surface of the single crystal silicon layer 26 for flexure formation is polished and etched to form the single crystal silicon layer 26 for flexure formation.
The surface of is processed into a mirror surface.

Next, as shown in (f), a silicon oxide film 18 is formed on the surface, and a photolithography process, an etching process, and a thermal diffusion process are performed, and then the surface of the single crystal silicon layer 26 for forming the flexure is formed. A diffusion resistance layer to be the piezoresistive layer 16 is formed. In this thermal diffusion step, oxygen in the oxygen ion implantation layer 25 reacts with silicon, so that the buried silicon oxide film 27 is formed in the region of the oxygen ion implantation layer 25.

Next, after a photolithography step and an etching step, a contact window of the piezoresistive layer 16 is opened, an Al sputtering step, a photolithography step, and an etching step are performed, and as shown in FIG.
The electrode layer 17 is formed on the electrode 6. Further, the front surface side is entirely covered with a resist (not shown), and as shown in (h),
A window 23 is formed in the silicon oxide film 21 on the back surface in order to form a groove for separating the weight portion 14 from the single crystal silicon layer 13 to be the substrate portion by a photolithography process and an etching process, and a window 23 is formed through this window 23. , (I)
As shown in, the single crystal silicon is removed by dry etching until the embedded silicon oxide film 27 is reached. Finally, while leaving the entire surface resist (not shown) on the front surface side, the silicon oxide film 21 on the back surface and the embedded silicon oxide film 27 exposed on the back surface side are removed with a thin buffered hydrofluoric acid, and the entire surface on the front surface side is removed. By removing the resist, the triaxial acceleration sensor as shown in (j) is completed.

A further different embodiment of the method for manufacturing the triaxial acceleration sensor of the present invention will be described with reference to FIG.
However, the same components as those shown in FIG. 3 are designated by the same reference numerals. First, as shown in (a), a silicon oxide film 20 is formed on the front surface side of the single crystal silicon layer 13, and a silicon oxide film 21 is formed on the back surface side of the single crystal silicon layer 13, and then shown in (b). As described above, in the surface region of the single crystal silicon layer 13, a predetermined region (a region serving as a joint surface between the flexure portion 15 and the weight portion 14) around a region serving as a joint surface between the flexure portion 15 and the weight portion 14 and finally The silicon oxide film 20 in the region between the regions of the single crystal silicon layer 13 that remains as the substrate portion) is removed by etching, and the window 2 for ion implantation is formed.
4 is formed.

Next, as shown in (c), oxygen ions are implanted into the single crystal silicon layer 13 through the window 24 at an accelerating voltage of several hundred keV to several hundred MeV to form the oxygen ion implanted layer 25.
Is formed, a resist (not shown) is applied to the entire back surface, and as shown in (d), the silicon oxide film 20 on the front surface side is formed.
Are removed by etching with hydrofluoric acid. Further, as shown in (e), an epitaxial growth layer 28 having a thickness of about several tens of μm is formed on the surface of the single crystal silicon layer 13 by epitaxial growth. In this epitaxial growth process, oxygen in the oxygen ion implanted layer 25 reacts with silicon to form a buried silicon oxide film 29.

Next, as shown in (f), a silicon oxide film 18 is formed on the surface, and a piezoresistive layer 16 is formed on the surface of the epitaxial growth layer 28 through a photolithography process, an etching process, and a thermal diffusion process. A diffusion resistance layer is formed.

Next, through a photolithography process and an etching process, a contact window of the piezoresistive layer 16 is opened, and after an Al sputtering process, a photolithography process and an etching process, the electrode layer 17 is formed as shown in FIG. Form. Further, the entire surface is covered with a resist (not shown), and as shown in (h), the weight portion 14 is separated from the single crystal silicon layer 13 to be the substrate portion by a photolithography process and an etching process. In order to form a groove, a window 23 is formed in the silicon oxide film 21 on the back surface, and through this window 23, as shown in (i), single crystal silicon is removed by dry etching until the buried silicon oxide film 29 is reached. Remove by etching. Finally, leaving the entire surface resist (not shown),
With thin buffered hydrofluoric acid, silicon oxide film 21 on the back surface
Then, the embedded silicon oxide film 29 exposed on the back surface side is removed, and the entire surface resist is removed, whereby the triaxial acceleration sensor as shown in (j) is completed.

[0026]

According to the method of manufacturing a triaxial acceleration sensor of claim 1 or 3, there is no step of bonding the single crystal silicon layers to each other, and voids due to the bonding do not occur, so that the yield is improved. Can be improved.

According to the method of manufacturing a three-axis acceleration sensor of claim 2, since the single crystal silicon layers are bonded to each other over the entire surface of a mirror-like flat surface, the adhesion is high, and thus voids are stable and stable. Bonding is possible and yield can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a method for manufacturing a triaxial acceleration sensor of the present invention.

FIG. 2 is a cross-sectional view showing a triaxial acceleration sensor formed by an embodiment of a method for manufacturing a triaxial acceleration sensor of the present invention.

FIG. 3 is a cross-sectional view showing a different embodiment of the method for manufacturing the triaxial acceleration sensor of the present invention.

FIG. 4 is a cross-sectional view showing a further different embodiment of the method for manufacturing the triaxial acceleration sensor of the present invention.

FIG. 5 is a sectional view showing an example of a conventional triaxial acceleration sensor.

FIG. 6 is a cross-sectional view showing an example of a method for manufacturing a conventional triaxial acceleration sensor.

[Explanation of symbols]

 13 Single Crystal Silicon Layer 14 Weight 15 Deflection 16 Piezoresistive Layer (Diffusion Resistive Layer) 19 Polycrystalline Silicon Layer 20 Silicon Oxide Film 22, 28 Epitaxial Growth Layer 26 Single Crystal Silicon Layer for Deflection Forming 27, 29 Embedded Silicon Oxide Film

Claims (3)

[Claims] 1. A method for manufacturing a triaxial acceleration sensor, comprising: a substantially thin film-shaped flexure portion; and a weight portion joined to one surface of the flexure portion, a part of which serves as the weight portion. A step of forming a silicon oxide film on the surface of the crystalline silicon layer,
Of the surface region of the single crystal silicon layer, a step of etching away the silicon oxide film so that the silicon oxide film remains only in a predetermined region around a region serving as a bonding surface between the bending portion and the weight portion, Forming a polycrystalline silicon layer on the silicon oxide film by epitaxial growth and forming an epitaxial growth layer of single crystal silicon in a surface region other than the region where the polycrystalline silicon layer is formed; A step of forming a piezoresistive layer, a step of etching away the single crystal silicon layer from the back surface side of the single crystal silicon layer by anisotropic etching until the silicon oxide film is reached, and a back surface of the single crystal silicon layer A step of etching away the silicon oxide film exposed on the side with hydrofluoric acid. 3 method for producing a-axis acceleration sensor according to symptoms. 2. A method for manufacturing a triaxial acceleration sensor, comprising: a substantially thin film flexure portion; and a weight portion joined to one surface of the flexure portion, a part of which serves as the weight portion. A step of forming a silicon oxide film on the surface of the crystalline silicon layer,
Of the surface area of the single crystal silicon layer, a step of etching away the silicon oxide film in a predetermined area around the area that will be the bonding surface of the flexible portion and the weight portion, and oxygen ions from the surface side to a high acceleration voltage. And a step of removing the silicon oxide film after the ion implantation, and a single crystal silicon layer for forming a flexible portion is attached to the surface of the single crystal silicon layer to form the single crystal silicon for forming the flexible portion. A step of polishing the layer to a predetermined thickness, a diffusion resistance layer to be a piezoresistive layer is formed by thermal diffusion on the single crystal silicon layer for forming the flexure portion, and a buried silicon oxide film is formed in a region where oxygen ions are implanted. And etching the single crystal silicon layer from the back surface side of the single crystal silicon layer by anisotropic etching until the buried silicon oxide film is reached. Process and method for producing a 3-axis acceleration sensor, characterized in that the buried silicon oxide film is exposed on the back side of the monocrystalline silicon layer and a step of etching away with hydrofluoric acid to remove. 3. A method for manufacturing a triaxial acceleration sensor, comprising: a substantially thin film-shaped flexure portion; and a weight portion joined to one surface of the flexure portion, a part of which serves as the weight portion. A step of forming a silicon oxide film on the surface of the crystalline silicon layer,
Of the surface area of the single crystal silicon layer, a step of etching away the silicon oxide film in a predetermined area around the area that will be the bonding surface of the flexible portion and the weight portion, and oxygen ions from the surface side to a high acceleration voltage. Implantation step, a step of removing the silicon oxide film after ion implantation, an epitaxial growth layer is formed on the surface of the single crystal silicon layer, and a buried silicon oxide film is formed in a region where oxygen ions are implanted. A step, a step of forming a piezoresistive layer in the epitaxial growth layer, and a step of etching away the single crystal silicon layer from the back surface side of the single crystal silicon layer by anisotropic etching until the buried silicon oxide film is reached. , The embedded silicon oxide film exposed on the back surface side of the single crystal silicon layer is removed by etching with hydrofluoric acid. 3, characterized in that a step
Axial acceleration sensor manufacturing method.