JPH0778800A - Fine processing method, accelerometer and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a means wherein etching is prevented from deteriorating in anisotropy due to the crystal orientation of an Si substrate when the substrate is etched using an SiC film as a mask, wherein the above means is used in a fine processing method and the manufacture of an accelerometer. CONSTITUTION:In a fine processing method in which an SiC film 4 is deposited on an Si substrate 1, and the Si substrate 1 is selectively etched through the SiC film 4 as a mask, a boron diffusion layer 3 is formed in the Si substrate 1 as deep as a point where carbon of the SiC film 4 diffused into the Si substrate 1 reaches when the SiC film 4 is deposited on the Si substrate 1, and then the SiC film 4 is deposited on the Si substrate 1. Using this fine processing method, an accelerometer having such a structure that a weight 12 is suspended from a fixed part 11 by a beam composed of the SiC film 4, a boron diffusion layer 3 of the SiC film 4 and the Si substrate 1, and another boron diffusion layer of a Ta film, the SiC film, and the Si substrate can be accurately and easily manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microfabrication method, an accelerometer and a manufacturing method thereof. In recent years, there has been earnestly developed a technique for manufacturing an accelerometer used for a collision detection sensor or the like used in an airbag for protecting a driver or the like at the time of collision of an automobile by using a fine processing method (micromachine technology).

[0002]

Prior to the description of the present invention, a conventional accelerometer and its manufacturing method will be described. FIG. 8 is a configuration explanatory view of a conventional accelerometer, (A) shows a plane, and (B).
Shows a cross section taken along line XX ′ of (A). In this figure, 61 is a fixed part, 62 is a weight part, 63 is a space,
64 ₁ , 64 ₂ , 64 ₃ , 64 ₄ are beams, 65 ₁ , 6
5 ₂ , 65 ₃ , 65 ₄ are drive electrodes, 66 ₁ , 66 ₂ , 6
6 ₃ and 66 ₄ are detection electrodes, 67 ₁ , 67 ₂ , 67 ₃ and 6
7 ₄ is an upper electrode.

In a conventionally known accelerometer, a frame-shaped fixed portion 61 made of Si and an Si-shaped fixed portion 61 having a reverse trapezoidal cross section and having a flat surface of about 1 mm on a side or a square and a mass of about 1 to 2 mg are used. The weight portion 62 is arranged with a space 63 in between, and the fixed portion 61 and the weight portion 62 are connected at their bottoms by silicon beams 64 ₁ , 64 ₂ , 64 ₃ , 64 ₄ and the upper surface of the fixed portion 61 is driven. Electrodes 65 ₁ , 65 ₂ ,
65 ₃ , 65 ₄ and detection electrodes 66 ₁ , 66 ₂ , 66 ₃ , 6
6 ₄ are formed, and the drive electrodes 65 ₁ and 65 6 are formed thereon.
₂ , 65 ₃ , 65 ₄ and detection electrodes 66 ₁ , 66 ₂ , 6
6 _3, 66 ₄ covering the upper electrode 67 ₁ connecting the fixed portion 61 and the weight portion 62, 67 _2, 67 _3, 67 ₄ are formed.

In this accelerometer, the drive electrode 65₁etc
And the upper electrode 67₁When a voltage is applied between the
67₁Etc. are drive electrodes 65₁Attracted to the side and approached
It Upper electrode 67₁Etc. and drive electrode 65₁Etc. approaching each other
Then, the upper electrode 67₁Etc. and detection electrode 66₁Stillness
The electric capacity increases. Upper electrode 67₁Etc. and detection electrode 66₁
The capacitance between the drive electrode 65₁Etc. and the upper electrode 67₁
When negative feedback is applied to the voltage between₁And so on
Part electrode 67 ₁Continuous at a frequency determined by mechanical constants such as
Can be vibrated.

In this state, when acceleration is applied to this accelerometer horizontally, for example, from the right side to the left side, the weight portion 62 rotates counterclockwise, and as a result, a compressive force acts on the left upper electrode 67 _1. , stretching force acts on the right side of the upper electrode 67 _3,
The mechanical constants of the left upper electrode 67 ₁ and the right upper electrode 67 ₃ change in opposite directions.

Therefore, since the mechanical frequency of the left upper electrode 67 ₁ and the right upper electrode 67 ₃ changes, the acceleration applied to the accelerometer is detected by electrically detecting the change in the mechanical frequency. Sensitive and quick detection is possible.

FIG. 9 is an explanatory view of a manufacturing process of a conventional first accelerometer, and (A) to (D) show each process.
In this figure, 71 is a Si substrate, 71 ₁ is a fixed part, 7
1 ₂ is a weight portion, 72 is a Si oxide film, 72 ₁ and 72 ₂ are openings, 73 ₁ and 73 ₂ are boron diffusion layers, and 74 is new Si.
The oxide films 75 ₁ and 75 ₂ are spaces. A conventional method (1) for manufacturing an accelerometer will be described with reference to the process explanatory drawing.
In this description, the surface above the Si substrate 1 is referred to as the upper surface and the surface below the Si substrate 1 is referred to as the lower surface in each drawing, but there is essentially no upper or lower reference.

First Step (See FIG. 9A) A Si oxide film (SiO ₂ ) 72 is formed on both surfaces of a Si substrate 71 having a (100) surface by thermal oxidation or CVD.

Second step (see FIG. 9B) The Si oxide film 72 on the lower surface of the Si substrate 71 is selectively removed by a photolithography technique, and an opening 72 _{1 in} the shape of a weight portion 71 ₂ and a fixing portion 71 _{1 are formed.} Frame-shaped opening 72 ₂
Forming a boron diffusion blocking pattern. This step has the property that a high-concentration diffusion layer of p ⁺ -type impurities such as boron cannot be dissolved in a crystal axis anisotropic etching solution (May 1991).
March 30 Asakura Shoten Co., Ltd. Light "Encyclopedia of Sensors" 13
(See page 7) is used.

Third step (see FIG. 9 (C)) The openings 72 ₁ , 7 of the diffusion preventing pattern are formed by the diffusion furnace.
Boron is diffused into the Si substrate 71 through 2 _{2 at} a concentration of about 10 ²⁰ cm ^-2 to a depth of several μm to form a boron diffusion layer 73 ₁ .
73 ₂ is formed.

Fourth step (see FIG. 9 (D)) The Si oxide film 72 on the lower surface used as the diffusion blocking pattern for forming the boron diffusion layers 73 ₁ and 73 ₂ and the upper surface contaminated with boron. After removing the Si oxide film 72 and forming a new clean Si oxide film 74 on the upper surface, the Si substrate 71 is subjected to KOH using the boron diffusion layers 73 ₁ and 73 ₂ and the new clean Si oxide film 74 as an etching mask. Anisotropic etching is performed using an aqueous solution or the like to fix the fixing portion 71 ₁ and the weight portion 7.
Frame-shaped spaces 75 ₁ and 75 ₂ for isolating _{1 2} are formed.

In this process, Si contaminated with boron is
The reason why the oxide film 72 is removed and the clean Si oxide film 74 is formed is that this clean S oxide is formed when the detection circuit or the like is formed later.
This is because the i oxide film 74 is used as a gate insulating film.
Although the step of forming the beam that suspends the weight portion 71 ₂ from the fixed portion 71 ₁ is omitted in the description of this manufacturing process, an etching mask corresponding to the shape of the beam is formed and It is formed at the same time as the process.

The above-mentioned steps of FIGS. 9A to 9D are steps for forming only the weight portion, and in fact, before the anisotropic etching of Si, the upper surface of the fixing portion 71 ₁ is formed. As shown in FIG. 8, a drive electrode and a detection electrode are formed, and the fixed portion 71 ₁ and the weight portion 71 are covered with the drive electrode and the detection electrode.
_An accelerometer is completed by forming an upper electrode that spans _two .

FIG. 10 is an explanatory view of a manufacturing process of a conventional second accelerometer, and (A) to (D) show each process. In this figure, 81 is a Si substrate, 81 ₁ is a fixed portion, 81 ₂ is a weight portion, 82 is a Si oxide film, and 83 is β-Si.
C film, 83 ₁ and 83 ₂ are openings, 84 is a carbon diffusion layer, 85
₁ , 85 ₂ is a space. This method of manufacturing the accelerometer is different from the above-described first method of manufacturing the conventional accelerometer in that the Si substrate is anisotropically etched using the SiC film as an etching mask. A conventional method (2) for manufacturing an accelerometer will be described with reference to the process explanatory drawing.

First Step (See FIG. 10A) A Si oxide film 82 is formed on the upper surface of a Si substrate 81. This Si oxide film 82 is formed on the back surface of the Si substrate 81 by S in the second step.
When forming the iC film 83, Si is formed on the upper surface of the Si substrate 81.
It is formed to prevent the C film 83 from being deposited on the upper surface of the Si substrate 81.

Second Step (see FIG. 10B) In the first step, a SiC film 83 is formed by CVD on the lower surface of the Si substrate 81 having the Si oxide film 82 formed on the upper surface.
The carbon diffusion layer 84 shown in this figure will be described later.

Third step (see FIG. 10C) Fixing portion 81₁On the drive electrode 86₁, Detection electrode 86₂
Forming a fixed part 81 ₁And weight 81₂Over the top
Pole 87₁, 87₂To form. Space 85 later₁, 85₂
Of the SiC film 83 where the
83₁, 83₂To form.

Fourth step (see FIG. 10 (D)) Spaces 85 ₁ and 85 ₂ are formed by anisotropically etching the Si substrate 81 with a KOH aqueous solution or the like through the openings 83 ₁ and 83 ₂ formed by removing the SiC film 83. And the fixed portion 81 ₁ and the weight portion 81 ₂ are separated. Although not shown, an etching mask for leaving the beam is formed, and at the same time as this step, a beam connecting the fixing portion 81 ₁ and the weight portion 81 ₂ is formed.

11 and 12 show a third conventional accelerometer.
6A to 6H are explanatory views of the manufacturing process of FIG.
is doing. Since this accelerometer is symmetrical,
The left half is shown. In this figure, 91 is a Si group
Board, 91₁Is the fixed part, 91₂Is the weight, 92₁, 92₂，
92₁₁, 92₁₂, 92_{twenty one}Is a Si nitride film, 93₁₁, 9
Three₁₂, 93₁₃, 93 _{twenty one}, 93_{twenty two}Is oxidized silicon containing boron
Con film, 94₁₁, 94₁₂, 94₁₃, 94_{twenty one}, 94_{twenty two}Is
Ron diffusion layer, 95₁, 95₂Is a non-contaminated Si oxide film,
96 is a silicon nitride film, 97₁Is the drive electrode, 97₂Check
Output electrode, 98 PSG film, 99 upper electrode, 100 protective
It is a protective PSG film. This process diagram is used to add
The manufacturing method (3) of the speedometer will be described.

First step (see FIG. 11A) CVD is performed on both upper and lower surfaces of a Si substrate 91 having a (100) surface.
Thus, Si nitride films 92 ₁ and 92 ₂ are formed. In addition,
The Si nitride films 92 ₁ and 92 ₂ can be replaced with Si oxide films.

Second step (see FIG. 11B) By patterning the Si nitride film 92 ₁ formed on the upper surface of the Si substrate 91, the fixing portion 91 ₁ and the weight portion 91 _{2 are formed.}
Si nitride films 92 ₁₁ and 92 ₁₂ are left in the narrow region where the electrodes are isolated and the region where the drive electrode 97 ₁ is formed.

Further, Si formed on the lower surface of the Si substrate 91
By patterning the nitride film 92 ₂ , a region sandwiched between regions where the fixed portion 91 ₁ and the weight portion 91 ₂ are formed,
Leaving the Si nitride film 92 ₂₁ in the region where to form the beam (not shown).

Si nitride film 92 _{11 on} the upper surface of Si substrate 91,
92 ₁₂ silicon oxide film 93 ₁₁ containing boron in a region not left, 93 _12, 93 and _13, also, silicon oxide containing boron in a region where the lower surface of the Si nitride film 92 ₂₁ of the Si substrate 91 is not left The films 93 ₂₁ and 93 ₂₂ are selectively formed by CVD.

Third step (see FIG. 11C) A silicon oxide film 93 containing boron is formed by using a diffusion furnace.₁₁，
93₁₂, 93₁₃, 93 _{twenty one}, 93_{twenty two}For several days,
Silicon oxide film 93 containing boron on the substrate 91₁₁Included in etc.
The boron is diffused and spread on the upper surface of the Si substrate 91.
Scatter 94₁₁, 94₁₂, 94₁₃Of the Si substrate 91
Boron diffusion layer 94 on the bottom surface_{twenty one}, 94_{twenty two}To form. That
Later, the Si nitride film 92₁₁, 92₁₂, 92_{twenty one}Including and boron
Silicon oxide film 93₁₁, 93₁₂, 93₁₃, 93_{twenty one}, 93
_{twenty two}To remove.

Fourth step (see FIG. 11D) Si oxide film 9 without contamination on the upper and lower surfaces of the Si substrate 91
5 ₁ and 95 ₂ are newly formed, and the Si oxide film 95 ₂ on the lower surface is formed.
Is patterned by a photolithography technique using an exposure mask to which a correction pattern is added to form a frame-shaped etching window 96 for separating the fixed portion 91 ₁ and the weight portion 91 ₂ . This correction pattern is (100)
This pattern is added to the etching mask pattern in order to correct the etching anisotropy due to the crystal orientation on the Si substrate having a plane and form the fixed portion 91 ₁ and the weight portion 91 ₂ having a desired shape.

Fifth step (see FIG. 12 (E)) A Si nitride film 96 is formed on the contamination-free Si oxide film 95 ₁ on the upper surface of the Si substrate 91, and a conductor film is formed thereon. Drive electrode 97 by patterning
₁ and the detection electrode 97 ₂ are formed.

Sixth step (see FIG. 12F) A PSG film 98 is formed on the drive electrode 97 ₁ and the detection electrode 97 ₂ , and the peripheral edge portion is used as a wiring layer on the PSG film 98. An upper electrode 99 reaching the boron diffusion layers 94 ₁₁ and 94 ₁₃ is formed.

Step 7 (see FIG. 12G) In order to protect the detection circuit (not shown), a protective PSG film 100 is formed on the upper surface and the boron diffusion layer 9 is formed.
The Si substrate 91 is anisotropically etched using the masks 4 ₂₁ and 94 ₂₂ and the Si oxide film 95 ₂ which does not contaminate to fix the fixed portion 91.
To remove the region, excluding ₁ and the weight portion 91 ₂ and the beam portion (not shown).

Eighth step (see FIG. 12 (H)) PSG film 98 between the drive electrode 97 ₁ , the detection electrode 97 ₂ and the upper electrode 99, and the detection circuit portion of the protective PSG film 100 (not shown). The area other than the above area is removed by etching to complete the accelerometer.

[0030]

According to the first conventional method of manufacturing an accelerometer described above, a photoresist is applied on the Si oxide film formed on the upper and lower surfaces of the Si substrate,
This photoresist is exposed and developed using an exposure mask in which the fixed portion and the weight portion are integrated and patterned, and the Si oxide film is patterned using the patterned resist film as a mask to diffuse boron through the opening. In order to form a protective mask pattern for etching the Si oxide film by using the exposure mask of the weight portion to which the correction pattern is added, after further removing the Si oxide film used for selective diffusion and forming the Si oxide film. There is a problem that the mask process is required twice to form the weight portion and the beam, and the diffusion process takes several days, so that the manufacturing time becomes long.

When the SiC film is used as a mask for anisotropically etching the Si substrate as in the second conventional method for manufacturing the accelerometer described above, the etching anisotropy due to the crystal orientation of the Si substrate is used. However, there was a problem that the desired etching shape could not be obtained. As a result of analyzing the vicinity of the SiC film by SIMS in order to investigate the cause,
It was detected that carbon constituting the SiC film was diffused in the vicinity of the boundary of the SiC film (see FIG. 10), and due to the influence of the carbon diffusion layer 84, etching due to the crystal orientation was performed. It was found that the anisotropy of was decreased. It is an object of the present invention to provide a microfabrication method, an accelerometer, and a method for manufacturing the same that do not reduce the etching anisotropy due to the crystal orientation of the Si substrate when a SiC film is used as a mask material for etching.

[0032]

According to the present invention, there is provided a fine processing method for depositing a SiC film on a Si substrate and selectively etching the Si substrate using the SiC film as a mask. A step of forming a boron diffusion layer in at least a depth at which carbon constituting the SiC film diffuses into the Si substrate at least when the SiC film is deposited on the Si substrate. In this case, the depth of the boron diffusion layer is set to 1000Å to 4 μm, and the boron diffusion concentration is set to 10 ^19.
/ Cm ² or more.

Further, according to the present invention, S is formed on the Si substrate.
Manufacture of an accelerometer using a process of depositing an iC film and selectively etching the Si substrate using the SiC film as a mask to form a structure in which a weight part subjected to acceleration is suspended from a fixed part by a beam. In the method, the Si
Forming a boron diffusion layer to a depth at which carbon constituting the SiC film diffuses into the Si substrate at least when the SiC film is deposited on the Si substrate in the substrate;
Alternatively, by patterning the SiC film and the boron diffusion layer, the patterned SiC film or the SiC film
A process of selectively etching the Si substrate using the film and the boron diffusion layer as a mask was adopted.

Further, in the accelerometer according to the present invention, the weight portion that receives the acceleration is formed below the fixing portion that surrounds the weight portion with a space between the SiC film or the SiC film and the Si substrate. A structure is adopted in which the structure is such that it is suspended by a beam made of a boron diffusion layer, and the fixing portion is suspended by an upper electrode made of an elastic conductor in the upper part thereof.

In this case, the weight portion that receives the acceleration corrects the etching pattern orientation anisotropy of the Si substrate and the mask pattern for forming the weight portion under the weight portion to realize the etching of a desired shape. Therefore, it is possible to employ a configuration in which the correction mask pattern added for that purpose and the beam including the mask pattern for forming the beam are suspended from the fixed portion. Further, in this case, the depth of the boron diffusion layer is set to 1000Å to 4 μm, and the diffusion concentration of boron is set to 10 ^19.
/ Cm ² or more.

Further, in this case, the oblique side of the beam connected to the correction mask pattern and one side of the weight portion mask pattern can be formed so as not to be orthogonal to each other. Further, the reinforcing mask pattern can be formed in the portion where the correction mask pattern and the weight portion mask pattern are connected. Also,
In this case, the beam can be formed of a composite film of a SiC film and a Ta film, or a SiC film, a Ta film, and a boron diffusion layer of a silicon substrate.

[0037]

The mechanical constant of the beam can be adjusted by forming the beam, which suspends the weight part from the fixed part surrounding the weight part, into a double structure of the SiC film and the boron diffusion layer of the Si substrate as in the present invention. Moreover, since the thickness of the SiC film can be reduced, the deposition time of the SiC film and the etching time for patterning the SiC film can be shortened.

Further, since the boron is previously diffused to the Si substrate on the surface where the SiC film as the etching mask is formed, to a depth greater than the depth of diffusion of the carbon constituting the SiC film, there has been a problem in the conventional technique. To prevent deterioration of etching anisotropy or selectivity due to crystal orientation due to the influence of carbon diffused in a Si substrate when forming a SiC film, and to manufacture a higher precision accelerometer. You can

Further, the SiC film or Si diffused by boron is EDPW (ethylenediamine / pyrocatechol aqueous solution).
Since it has sufficient resistance to etching liquids such as the above, it functions as an etching mask material. Therefore, the thickness of the beam can be set by adjusting the depth of the boron diffusion layer of the Si substrate, and the mechanical constant of the beam can be adjusted.

Further, the etching mask or the beam is made of Si.
If a Ta film is formed on a silicon carbide film to form a triple structure of Ta film, a silicon carbide film, and Si in which boron is diffused, instead of forming a C film and a double structure of Si in which boron is diffused, The mechanical constant of the beam can be adjusted in a wider range to provide an etching mask with higher resistance.

[0041]

EXAMPLES Examples of the present invention will be described below. (First Embodiment) FIGS. 1A to 1C are explanatory views of the manufacturing process of the accelerometer of the first embodiment, and FIGS. 1A to 1E show each process. In this figure, 1 is a Si substrate, ₁₁ is a fixed part, 1
₂ is a weight part, 2 is a Si oxide film, 3 is a boron diffusion layer, 4 is S
iC film 4 ₁ , 4 ₂ , 5 ₁ , 5 ₂ is an opening, 5 is a resist film, and 6 ₁ , 6 ₂ are spaces. A method of manufacturing the accelerometer of the first embodiment will be described with reference to the process explanatory drawings.

First step (see FIG. 1A) A Si oxide film 2 is deposited on the upper surface of a Si substrate 1 by CVD. The Si oxide film 2 may be formed by thermal oxidation instead of CVD. In this description, the surface above the Si substrate 1 is referred to as the upper surface and the surface below the Si substrate 1 is referred to as the lower surface in each drawing, but there is essentially no upper or lower reference.

Second Step (See FIG. 1B) Boron is ion-implanted (I · I) into the lower surface of the Si substrate 1 at a concentration of 10 ²⁰ cm ^-2 to a depth of 1000 Å or more from the surface to form boron. The diffusion layer 3 is formed. Boron can be introduced by thermal diffusion instead of ion implantation.

Third Step (see FIG. 1C) A SiC film 4 having a thickness of several μm is deposited on the boron diffusion layer 3 on the lower surface of the Si substrate 1 by CVD.

Fourth Step (see FIG. 1D) A photoresist is coated on the SiC film 4 on the lower surface of the Si substrate 1, and the photoresist is exposed and developed to separate the fixed portion 1 ₁ and the weight portion 1 ₂ . The openings 5 ₁ , 5 at positions where the spaces 6 ₁ , 6 ₂ are formed.
A resist film 5 having ₂ is formed. This resist film 5
The SiC film 4 and the boron diffusion layer 3 are selectively removed by applying a dry etching process such as RIE to the Si substrate 1 through the openings 5 ₁ and 5 ₂ to form the openings 4 ₁ and 4 ₂ .

Fifth Step (See FIG. 1E) Anisotropic etching liquid such as KOH aqueous solution is used through the openings 4 ₁ and 4 ₂ formed by selectively removing the SiC film 4 and the boron diffusion layer 3. Then, an anisotropic etching process is applied to the lower surface of the Si substrate 1 to form spaces 6 ₁ and 6 ₂ for separating the fixed portion 1 ₁ and the weight portion 1 ₂ .

In this step, the fixed portion 1 ₁ and the weight portion 1 are
The description of the patterning for forming the beam connecting the _two is omitted. After this step, the drive electrode and the detection electrode is formed on the upper surface of the fixed portion 1 _1, to form a straddling upper electrode to the fixed portion 1 ₁ and the weight section 1 ₂ on the drive electrode and the detection electrode acceleration Complete the total.

As described above, before depositing the SiC film 4 on the lower surface of the Si substrate 1, the carbon constituting the SiC film 4 is diffused into the Si substrate 1 at a depth or deeper than that. Actually, 1000 Å ~ 4 μm, 10
Boron is introduced at a concentration of ¹⁹ cm ^-2 or more to form a boron diffusion layer 3
By forming the above, it is possible to eliminate the adverse effect that the anisotropy of etching due to the crystal orientation decreases in the step of anisotropically etching the Si substrate 1 using the SiC film 4 as a mask.

(Second Embodiment) FIGS. 2 and 3 show a second embodiment.
3A to 3G are explanatory views of the manufacturing process of the accelerometer of FIG.
Each step is shown. This accelerometer is symmetrical
Therefore, the left half is shown in this figure. This figure smells
11 is a Si substrate, 11₁Is the fixed part, 11₂Is the weight,
11₃Is space, 12 is Si oxide film, 13 is boron diffusion
Layer, 14 is a SiC film, 14₁, 22 ₁Is opening, 15 is new
17 Si oxide film, 16 Si nitride film, 17₁Is the driving power
Pole, 17₂Is a detection electrode, 18 is a PSG film, and 19 is an upper electrode.
Electrode, 20 is a PSG film for protection, 21 is a Si oxide film, 22
Is a resist film, and 23 is a Si oxide film. Description of this process
A method of manufacturing the accelerometer of the second embodiment will be described with reference to the drawings.
It

First Step (see FIG. 2A) A Si oxide film 12 is deposited on the upper surface of the Si substrate 11.

Second step (see FIG. 2B) Boron is diffused or ion-implanted (II) into the lower surface of the Si substrate 11 to a concentration of 10 ²⁰ cm ^-2 and a depth of 1000 Å or more from the surface. The boron diffusion layer 13 is formed.

Third step (see FIG. 2C) CVD is performed on the boron diffusion layer 13 on the lower surface of the Si substrate 11.
Then, the SiC film 14 is deposited to a thickness of several μm.

Fourth Step (see FIG. 2D) The Si oxide film 12 formed on the upper surface of the Si substrate 11 and contaminated by the previous steps is removed, and a new Si oxide film 15 is formed thereon. The Si nitride film 16 is formed, and the drive electrode 17 ₁ and the detection electrode 17 ₂ are formed on the Si nitride film 16. A PSG film 18 is formed thereon, an upper electrode 19 is formed thereon, and the PSG film 2 for protection is formed on the entire surface.
Form 0.

Fifth Step (See FIG. 3E) A Si oxide film 21 is deposited on the SiC film 14 on the lower surface of the Si substrate 11 by sputtering, a photoresist is applied on the Si oxide film 21, and then fixed. Section 11 ₁ and weight section 11
_The fixed portion 11 ₁ and the weight portion 11 ₂ are exposed and developed by using a photomask having a space shape for separating the _two.
A resist film 22 having an opening 22 _{1 in} the shape of a space for separating is formed.

Sixth step (see FIG. 3F) Using the resist film 22 formed in the fifth step as a mask, RI
The Si oxide film 21 is selectively etched by dry etching such as E, and the SiC film 14 and the boron diffusion layer 13 are selectively etched by using the selectively etched Si oxide film 21 as a mask to obtain SiC. A beam (not shown) composed of the film 14 and the boron diffusion layer 13, and S
The lower surface of the i-substrate 11 is anisotropically etched to fix the fixed portion 11 _1.
An etching mask having an opening 14 ₁ for forming a space 11 ₃ for separating the weight portion 11 ₂ and the weight portion 11 ₂ is formed.

Step 7 (see FIG. 3G) In order to protect the element and the drive circuit exposed on the surface from the EDPW (ethylenediamine-pyrocatechol aqueous solution) etching solution, for example, a Si film having a thickness of 1.5 μm is used. The oxide film 23 is formed by CVD, and the whole is dipped in an EDPW etching solution to anisotropically etch the lower surface of the Si substrate 11, so that the fixed portion 11 ₁ and the weight portion 11 ₂ are formed by etching the beam made of the SiC film and the etching. Separation is performed in a state of being connected with a correction pattern for correcting anisotropy. The boron diffusion layer 1
By increasing the depth of 3 to 1 to 2 μm, the composite film of the boron diffusion layer 13 of the Si substrate and the SiC film 14 is formed into the weight portion 11.
It can also be used as a beam to suspend ₂ .

As in this embodiment, a beam for suspending the weight portion 11 ₂ from the fixed portion 11 ₁ surrounding the weight portion 11 ₂ is attached to the SiC film 14
By using a double structure of the boron diffusion layer 13 of the Si substrate and the Si substrate, the mechanical constant of the beam can be adjusted.
Since the thickness of the iC film 14 can be reduced, SiC
The deposition time of film 14 and the etching time for patterning this SiC film 14 can be shortened.

(Third Embodiment) FIGS. 4 and 5 are explanatory views of the manufacturing process of the accelerometer of the third embodiment, and (A) to (G) show the respective steps. Since this accelerometer is symmetrical, the left half is shown in this figure. In this figure, 31 is a Si substrate, 31 ₁ is a fixed part, 31 ₂ is a weight part,
31 ₃ is a space, 32 is a Si oxide film, 33 is a boron diffusion layer, 34 is a SiC film, 35 is a new Si oxide film, 36 is a Si nitride film, 37 ₁ is a drive electrode, 37 ₂ is a detection electrode, 3
8 is a PSG film, 39 is an upper electrode, 40 is a protective PSG
A film, 41 is a Ta film, 41 ₁ and 42 ₁ are openings, 42 is a resist film, and 43 is a Si oxide film. A method of manufacturing the accelerometer of the third embodiment will be described with reference to the process explanatory drawings.

First Step (see FIG. 4A) A Si oxide film 32 is formed on the upper surface of the Si substrate 31.

Second Step (See FIG. 4B) Boron is diffused or ion-implanted (II) into the lower surface of the Si substrate 31 to obtain a concentration of 10 ²⁰ cm ^-2 and a depth of 1000 Å or more from the surface. And the boron diffusion layer 33 is formed.

Third Step (See FIG. 4C) CVD is performed on the boron diffusion layer 33 on the lower surface of the Si substrate 31.
A SiC film 34 having a thickness of several μm is deposited by.

Fourth Step (see FIG. 4D) The Si oxide film 32 formed on the upper surface of the Si substrate 31 is removed, and a new Si oxide film 35 and a Si nitride film 36 are formed. Drive electrode 37 ₁ and detection electrode 3 on 36
7 ₂ is formed, thereon, to form a PSG film 38, the upper electrode 39 is formed thereon, further, P for protection on the whole surface
The SG film 40 is formed.

Fifth Step (See FIG. 5E) A Ta (tantalum) film 41 is formed by PVD on the SiC film 34 on the lower surface of the Si substrate 31, and a photoresist is applied on the Ta film 41. The fixed portion 31 ₁ and the weight portion 31 ₂ are exposed and developed using a photomask having a shape of a space 31 ₃ for separating the fixed portion 31 ₁ and the weight portion 31 2.
A resist film 42 having an opening 42 _{1 in} the shape of a space 31 ₃ separating ₂ is formed.

Sixth Step (see FIG. 5F) The Ta film 41 is selectively removed by dry etching such as RIE using the resist film 42 having the opening 42 ₁ formed by the above steps as a mask to form an opening. 41 ₁ is formed, which SiC film 34 is etched as a mask, a beam made of SiC film 34, the space 31 ₃ to separate the fixing portion 31 ₁ and the weight section 31 ₂ on the lower surface of the Si substrate 31 is etched In this case, an etching protection mask is formed.

Step 7 (see FIG. 5G) C is used to protect the surface against the EDPW etching solution.
A Si oxide film 43 having a thickness of 1.5 μm is deposited by VD, and the whole is immersed in an EDPW etching solution for anisotropic etching to fix the fixed portion 31 ₁ and the weight portion 31 ₂ to the Ta film 41.
And a beam made of a composite film of the SiC film 34 and the correction pattern can be connected and separated. After this step, if the Ta film 41 is peeled off, a beam having only the SiC film 34 can be formed, and the mechanical constant of the beam can be adjusted.

Here, the mask pattern used in the method of manufacturing the accelerometer of each of the above-described embodiments will be described.

FIG. 6 is an explanatory view of the first mask pattern used in the present invention. In this figure, 51 is a fixed portion mask pattern, 52 is a weight portion mask pattern, 53 is a beam portion mask pattern, and 54 is a correction mask pattern.

Although only the upper right part of the accelerometer is shown in this drawing, the mask patterns 51 to 54 are used to selectively etch the Si substrate to form a square-shaped or rectangular-shaped planar weight. An object of the present invention is to realize a structure in which a part is suspended from two fixed beams separated from each other by a frame-shaped space surrounding the part. The reason for forming the beam part by two parallel beams is to stably suspend the weight part from the fixed part and to etch the Si substrate from the gap between the two parallel beams. This is because.

The first mask pattern is formed by etching the Si substrate and has a shape to be finally formed, that is, the fixed portion mask pattern 51, the weight portion mask pattern 52, and the beam portion mask pattern 53. other,
A correction mask pattern 54 is formed.

In the correction mask pattern 54, since the etching rate varies depending on the crystal orientation, as is conventionally known, the mask pattern is formed to correct the anisotropy of the etching rate. In this case, a correction mask pattern 54 having a right angle portion is used by utilizing the phenomenon that the etching rate of the Si substrate under the acute angle portion of the mask pattern increases, but the Si substrate excessively recedes by the etching. In the portion where it is necessary to prevent the above, for example, in the portion (θ) where the correction mask pattern and the beam mask pattern intersect, the sides of the mask pattern are not orthogonal to each other. This first
The anisotropic etching with the mask pattern proceeds like a thin broken line, and finally becomes a shape like a thick broken line.

In this case, the correction mask pattern 54 added to the weight portion mask pattern 52 can also be used as a part of the beam to adjust the mechanical constant of the beam.

FIG. 7 is an explanatory view of the second mask pattern used in the present invention. In this figure, 51 is a fixed part pattern, 52 is a weight part pattern, 53 is a beam part pattern, and 55 is a reinforcing mask pattern.

The second mask pattern is a modification of the first mask pattern in consideration of mechanical strength.
In the second mask pattern, a reinforcing mask pattern 55 is provided at the connecting portion of the beam portion mask pattern 53 extending from the fixed portion mask pattern 51 and the weight portion mask pattern 52 in consideration of mechanical strength and mechanical constants. Has been formed. The anisotropic etching by the second mask pattern proceeds like a thin broken line, and finally becomes a shape like a thick broken line.

Although the method of manufacturing the accelerometer has been described in each of the above-described embodiments, the present invention uses the SiC film deposited on the Si substrate as an etching mask.
It can be widely applied to a fine processing method for selectively etching an i substrate.

[0075]

As described above, according to the fine processing method of the present invention, when a SiC film is used as an etching resistant mask for adding an etching step to the Si substrate, the Si substrate is deposited before the SiC film is deposited. By diffusing boron therein, particularly good anisotropic etching can be performed without impairing the etching selection ratio of the Si substrate.

Further, in the accelerometer of the present invention, the weight portion subjected to acceleration is suspended by the beam from the fixed portion surrounding the same through the space, and the weight portion and the fixed portion are made of an elastic conductor. Since the beam that is connected by the upper electrode and that suspends the weight part on this fixed part is made of a plate-shaped body made of a SiC film or a composite film of a SiC film and a Ta film, the mechanical constant of the beam part The adjustment is easy, and the mechanical constant of the beam portion can be adjusted more easily by adding a part of the mask pattern used for etching when separating the weight portion from the fixed portion to the beam.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing process of an accelerometer according to a first embodiment, in which (A) to (E) show each process.

FIG. 2 is an explanatory view (1) of a manufacturing process of the accelerometer of the second embodiment.
And (A) to (D) show each step.

FIG. 3 is an explanatory view (2) of the manufacturing process of the accelerometer of the second embodiment.
And (E) to (G) indicate the respective steps.

FIG. 4 is an explanatory view (1) of the manufacturing process of the accelerometer of the third embodiment.
And (A) to (D) show each step.

FIG. 5 is an explanatory view (2) of the manufacturing process of the accelerometer of the third embodiment.
And (E) to (G) indicate the respective steps.

FIG. 6 is an explanatory diagram of a first mask pattern used in the present invention.

FIG. 7 is an explanatory diagram of a second mask pattern used in the present invention.

8A and 8B are configuration explanatory views of a conventional accelerometer, in which FIG. 8A shows a plane and FIG. 8B shows a cross section taken along line XX ′ of FIG.

FIG. 9 is an explanatory view of a manufacturing process of a conventional first accelerometer, and (A) to (D) show each process.

FIG. 10 is an explanatory view of a manufacturing process of a conventional second accelerometer, and (A) to (D) show each process.

FIG. 11 is an explanatory view (1) of a manufacturing process of a conventional third accelerometer, and (A) to (D) show each process.

FIG. 12 is a manufacturing process explanatory diagram (2) of a third conventional accelerometer, and (E) to (H) show each process.

[Explanation of symbols]

1 Si substrate 1 ₁ fixed part 1 ₂ weight part 2 Si oxide film 3 boron diffusion layer 4 SiC film 4 ₁ , 4 ₂ , 5 ₁ , 5 ₂ opening 5 resist film 6 ₁ , 6 ₂ space 11 Si substrate 11 ₁ fixed part 11 ₂ Weight part 11 ₃ Space 12 Si oxide film 13 Boron diffusion layer 14 SiC film 14 ₁ , 22 ₁ Opening 15 New Si oxide film 16 Si nitride film 17 ₁ Drive electrode 17 ₂ Detection electrode 18 PSG film 19 Upper electrode 20 Protection PSG film 21 Si oxide film 22 Resist film 23 Si oxide film 31 Si substrate 31 ₁ Fixed part 31 ₂ Weight part 31 ₃ Space 32 Si oxide film 33 Boron diffusion layer 34 SiC film 35 New Si oxide film 36 Si nitride film 37 _first driving electrode 37 _{and second} detection electrode 38 PSG film 39 upper electrode 40 protective PSG film 41 Ta film 41 _1, 42 ₁ opening 42 the resist film 43 Si oxide film 51 Ma fixing portion Click pattern 52 weight part for mask pattern 53 beam portion for the mask pattern 54 correction mask pattern 55 for reinforcement mask pattern

Claims (6)

[Claims] 1. A SiC film is deposited on a Si substrate and the S
In a microfabrication method of selectively etching the Si substrate using the iC film as a mask, the Si film is deposited in the Si substrate at least when the SiC film is deposited on the Si substrate.
A fine processing method comprising a step of forming a p-type impurity diffusion layer to a depth at which carbon constituting the C film diffuses into the Si substrate. 2. The microfabrication method according to claim 1, wherein the p-type impurity is boron. 3. An SiC film is deposited on a Si substrate and the S
A method for manufacturing an accelerometer, comprising the step of forming a structure in which a weight portion subjected to acceleration is suspended from a fixed portion by a beam by selectively etching the Si substrate using the iC film as a mask. A p-type impurity diffusion layer is formed at least to a depth at which carbon constituting the SiC film diffuses into the Si substrate when the SiC film is deposited on the Si substrate, and SiC
And a step of patterning the film and the p-type impurity diffusion layer, and selectively etching the patterned SiC film or the Si substrate using the SiC film and the p-type impurity diffusion layer as a mask. Accelerometer manufacturing method. 4. A weight portion which receives acceleration is provided at a lower portion thereof from a fixing portion which surrounds the weight portion with a space therebetween, and SiC.
A film or an accelerometer, which is suspended by a beam composed of a SiC film and a p-type impurity diffusion layer of a Si substrate, and is suspended above the fixing portion by an upper electrode made of an elastic conductor. . 5. A weight part subjected to acceleration is provided below the mask part for forming the weight part and the etching crystal orientation anisotropy of the Si substrate so as to realize etching of a desired shape. The accelerometer according to claim 4, wherein the accelerometer is suspended from the fixed portion by a beam including a mask pattern for correction to be added to the beam and a mask pattern for forming the beam. 6. The beam comprises a SiC film and a Ta film, or a SiC film.
The accelerometer according to claim 4, which is formed of a composite film of a film, a Ta film, and a boron diffusion layer of a silicon substrate.