JPH063369A - Accelerometer - Google Patents

Abstract

PURPOSE:To obtain such a highly efficient accelerometer that the stress of a beam from which a weight section is hung can be efficiently controlled and the material constituting the beam effectively functions as an etching mask. CONSTITUTION:In the title accelerometer, a weight section 15 which receives acceleration is hung from a beam 16 in a fixing section 14 which surrounds the section 15 with a space in between and the sections 15 and 14 are connected to each other through an upper electrode 6 composed of an elastic conductor. In addition, a detection electrode 4 is provided on the section 14 in a state where the electrode 4 is in contact with the electrode 6. The beam 16 is composed of a platy body manufactured by coating a metallic thin film 9 with thin films 8 and 11 of silicon carbide, silicon nitride, titanium nitride, or silicon oxide or a platy body consisting of a composite film of the metallic thin film 9 and thin film 8 of silicon carbide, silicon nitride, titanium nitride, or silicon oxide.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improvements in accelerometers. 2. Description of the Related Art In recent years, there has been developed a technique for manufacturing an accelerometer used for a collision detection sensor of an airbag that operates to protect a human body in the event of a vehicle collision using a micromachine technology.

[0002]

2. Description of the Related Art A back view of an accelerometer is shown in FIG.
FIG. 7B shows a cross-sectional view taken along the line AA ′ of FIG. In the figure, 15 is a weight portion, 14 is a fixed portion, 16 is a beam on which the weight portion 15 is suspended by the fixed portion 14, and 6 is a weight portion 15.
An upper electrode that detects the acceleration received by the detection electrode. The detection electrode (not shown) that detects the capacitance between the upper electrode and the lower electrode, which depends on the detection method, and the drive electrode that resonates the upper electrode (not shown). No.) is formed.

Since the accelerometer shown in FIG. 7 is bilaterally symmetric, a conventional method for manufacturing an accelerometer will be described below with reference to a sectional view showing only the left half of the AA 'section.

As shown in FIG. 8A, the silicon substrate 1
A silicon nitride film or a silicon oxide film 21 is formed on the surface, and this is patterned, and in the lower surface, the area between the fixing portion 14 and the weight portion 15 excluding the area where the beam 16 is formed, and the upper surface. In the above, the fixed portion 14 and the weight portion 15 remain in the area where they are separated from each other and the detection electrode forming area.

The solid diffusion source is heated by using a diffusion furnace, and the silicon nitride film or the silicon oxide film 21 of the silicon substrate 1 is heated.
A boron oxide film is formed in a region not covered with the silicon oxide film, and the boron oxide film is used as a diffusion source for diffusion over a period of several days to form a boron diffusion layer 22 as shown in FIG. 8B. Then, the silicon nitride film or the silicon oxide film 21 is removed.

As shown in FIG. 8C, an oxide film 23 free from contamination is newly formed and patterned to fix the fixing portion 14.
An etching window 24 for separating the weight portion 15 from the weight portion 15 is formed.

As shown in FIG. 9A, a silicon nitride film 25 is formed on the upper surface to form a detection electrode 26 and a drive electrode 27, and an upper electrode 29 is formed via a PSG film 28, and then, A PSG film 30 is formed on the entire surface to protect the detection circuit section (not shown).

As shown in FIG. 9 (b), the crystal anisotropic etching is performed to remove the region 13 between the fixed portion 14 and the weight portion 15 except the beam portion 16. And detection electrode
26. The PSG film 28 between the drive electrode 27 and the PSG film 30 that protects the detection circuit portion are removed by etching.

[0009]

Although a beam is formed by diffusing boron into a silicon substrate in a beam forming region and then etching the beam, the stress in the boron diffusion layer cannot be measured. Therefore, the silicon substrate is etched. The stress state of the beam is not known until the beam is formed. However, it is difficult and a lot of time is required to correct the stress of the beam after the beam is formed.

An object of the present invention is to eliminate this drawback, the stress of the beam that suspends the weight portion is efficiently controlled, and the material constituting the beam effectively functions as an etching mask. To provide a high performance accelerometer.

[0011]

[Means for Solving the Problems] The above-mentioned object is that a weight portion (15) subjected to acceleration is suspended by a beam (16) on a fixing portion (14) surrounding the weight portion through a space. The weight portion (15) and the fixing portion (14) are connected by an upper electrode (6) made of an elastic conductor, and the fixing portion (14) is in contact with the upper electrode (6). In the accelerometer provided with a detection electrode (4) on the beam (16), the beam (16) is covered with a metal thin film (9) of silicon carbide, silicon nitride, titanium nitride or silicon oxide thin film (8/11). It is achieved by an accelerometer which is a plate-shaped body that is formed or a composite film of a metal thin film (9) and a thin film (8) of silicon carbide, silicon nitride, titanium nitride or silicon oxide. The metal of the metal thin film (9) is preferably tantalum, titanium, gold, tungsten or nickel.

[0012]

The beam 16 for suspending the weight portion 15 is constituted by a plate-shaped body in which the metal thin film 9 is covered with the nitride film 8/11 or a plate-shaped body made of a composite film of the nitride film 8 and the metal thin film 9. The stresses of the beams can be balanced by selecting the stresses of the nitride film 8/11 and the metal thin film 9 such that one is tensile stress and the other is compressive stress. For example, since titanium nitride has a compressive stress and tantalum has a tensile stress, a tantalum thin film may be covered with a titanium nitride film to form a beam, or a beam having a two-layer structure of a tantalum thin film and a titanium nitride film may be formed. If so, the stress of the beam can be balanced. The stress in the beam portion can be controlled by changing the film thickness of the nitride film or the metal thin film. Further, since these materials have sufficient resistance to etching solutions such as caustic potash and EDPW (ethylenediamine / pyrocatechol aqueous solution), they also function as etching mask materials.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing an accelerometer according to two embodiments of the present invention will be described below with reference to the drawings. In addition,
The manufacturing process will be described with reference to the cross-sectional view corresponding to the BB ′ cross section of FIG.

First Embodiment See FIG. 2 (a) Using a well-known method, a silicon oxide film 2 and a silicon nitride film 3 are formed on a silicon substrate 1, and then a lower electrode 4 is formed on the silicon oxide film 2. Then, the upper electrode 6 is formed via the PSG film 5, and the PSG film 7 is further formed on the entire surface.

Referring to FIG. 2B, the silicon oxide film 2 and the silicon nitride film 3 on the back surface are removed.

Referring to FIG. 2 (c), a titanium nitride film 8 having a compressive stress is formed to a thickness of 500 to 3000 Å by using a plasma CVD method, and then,
Using physical vapor deposition (PVD), the tantalum film 9 is formed to a thickness of 5000 Å to 2 μm so as to have a tensile stress. A tensile stress film can be easily formed by controlling the growth power and the growth pressure.

Referring to FIG. 3A, a resist film 10 is formed and patterned by using a photolithography method to remain on the regions where the beam portion, the fixed portion and the weight portion are formed.

Referring to FIG. 3B, the tantalum film 9 is etched using a method such as isotropic chemical etching, isotropic plasma etching, anisotropic and isotropic etching. At this time, the tantalum film 9 is side-etched as shown in the figure.

Referring to FIG. 3C, the resist film 10 is removed and a titanium nitride film 11 is formed again.

Referring to FIG. 1A, a resist film 12 is formed and exposed and developed using the same mask as that used for forming the resist pattern 10 shown in FIG. And remains on the formation area of the fixed portion.

Referring to FIG. 1B, the titanium nitride film 8/11 is etched using an anisotropic etching technique such as a reactive ion etching (RIE) method. As a result, the tantalum thin film 9 becomes the titanium nitride film 8.
A beam 16 covered by 11 is formed.

Referring to FIG. 1C, the silicon substrate 1 is subjected to crystal anisotropic etching to remove a region 13 between the fixed portion and the weight portion except the beam 16.

Referring to FIG. 4, the PSG film 5 between the lower electrode 4 and the upper electrode 6 and the PSG film 7 for protecting the electrode are removed by etching, and this is taken along the line AA 'in FIG. 7 (a). The view seen in the corresponding section is shown in FIG. In the figure, 14 is a fixed part, 15 is a weight part, 13 is a space between the fixed part and the weight part 15, 6
Is an upper electrode, and 4 is a lower electrode. The weight portion 15 is a beam 16 in which the tantalum thin film 9 is covered with the titanium nitride films 8/11.
Is suspended from the fixed portion 14 by.

Second Embodiment See FIG. 2 (a) Using a well-known method, a silicon oxide film 2 and a silicon nitride film 3 are formed on a silicon substrate 1, and then a lower electrode 4 is formed. The upper electrode 6 via the PSG film 5
And the PSG film 7 is formed on the entire surface.

Referring to FIG. 2B, the silicon oxide film 2 and the silicon nitride film 3 on the back surface are removed.

Referring to FIG. 2 (c), a titanium nitride film 8 which is a film of compressive stress is formed to a thickness of 500 to 3000 Å using a plasma CVD method, and then,
Using physical vapor deposition (PVD), the tantalum film 9 is formed to a thickness of 5000 Å to 2 μm so as to have a tensile stress. A tensile stress film can be easily formed by controlling the growth power and the growth pressure.

Referring to FIG. 5A, a resist film 10 is formed and patterned by using a lithography method to remain on the formation regions of the beam portion, the fixed portion and the weight portion.

Referring to FIG. 5B, the tantalum film 9 and the titanium nitride film 8 are etched by using a method such as isotropic chemical etching, isotropic plasma etching, isotropic and anisotropic etching.

Referring to FIG. 5C, the crystal anisotropic etching of the silicon substrate 1 is performed to remove the region 13 between the fixed portion and the weight portion except the beam 16.

Referring to FIG. 6, the PSG film 5 between the lower electrode 4 and the upper electrode 6 and the PSG film 7 for protecting the electrode are removed by etching, and the PSG film 5 is cut along a section corresponding to the section AA 'in FIG. The view seen at is shown in FIG. In the figure, 14 is a fixed part, 15 is a weight part, 13 is a space between the fixed part 14 and the weight part 15, 6 is an upper electrode, and 4 is a lower electrode. The weight portion 15 is suspended from the fixed portion 14 by a beam 16 which is a plate-like body made of a composite film of the tantalum thin film 9 and the titanium nitride film 8.

[0031]

As described above, in the accelerometer according to the present invention, the beam for suspending the weight portion from the fixed portion is a plate-shaped body in which a metal thin film is covered with a nitride film or the like, or a metal thin film and a nitride film. Since it is composed of a plate-like body composed of a composite film with a film, etc., and is selected so that the stress directions (compression or tension) of the metal thin film and the nitride film are reversed, it saves a lot of time and labor. It is possible to control the stress of the beam portion to a predetermined value without needing it, and it is possible to manufacture a high-performance accelerometer.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing process of an accelerometer according to the present invention.

FIG. 2 is an explanatory view of the manufacturing process of the accelerometer according to the present invention.

FIG. 3 is an explanatory view of the manufacturing process of the accelerometer according to the present invention.

FIG. 4 is an explanatory view of the manufacturing process of the accelerometer according to the present invention.

FIG. 5 is an explanatory view of the manufacturing process of the accelerometer according to the present invention.

FIG. 6 is a diagram illustrating the manufacturing process of the accelerometer according to the present invention.

FIG. 7 is a configuration diagram of an accelerometer.

FIG. 8 is a manufacturing process diagram of an accelerometer according to a conventional technique.

FIG. 9 is a manufacturing process diagram of an accelerometer according to a conventional technique.

[Explanation of symbols]

 1 Silicon substrate 2 Silicon oxide film 3 Silicon nitride film 4 Lower electrode 5.7 PSG film 6 Upper electrode 8/11 Titanium nitride film 9 Tantalum thin film 10/12 Resist film 13 Space between fixing part and weight part 14 Fixing part 15 Weight 16 beams

Claims (3)

[Claims] 1. A weight part (15) subjected to acceleration is suspended by a beam (16) on a fixing part (14) which surrounds the weight part (15) through a space, and the weight part (15) and the fixing part (15). 14) is connected to an upper electrode (6) made of an elastic conductor, and a detection electrode (4) is provided on the fixed portion (14) so as to be in contact with the upper electrode (6). In the accelerometer, the beam (16) has a metal thin film (9) made of silicon carbide, silicon nitride, titanium nitride or silicon oxide (8.
An accelerometer, which is a plate-shaped body covered with 11). 2. A weight part (15) subjected to acceleration is suspended by a beam (16) on a fixing part (14) which surrounds the weight part (15) through a space, and the weight part (15) and the fixing part (14). ) Is connected by an upper electrode (6) made of an elastic conductor, and the detection electrode (4) is provided on the fixed portion (14) so as to be in contact with the upper electrode (6). In the beam (16), the metal thin film (9) is a silicon carbide, silicon nitride, titanium nitride or silicon oxide thin film (8).
An accelerometer, which is a plate-shaped body made of a composite film of and. 3. Accelerometer according to claim 1 or 2, characterized in that the metal of the metal thin film (9) is tantalum, titanium, gold, tungsten or nickel.