JPS6176961A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To prevent a fault caused by a leak of p-n junction of a diffused resistor by providing a CVD film formed at a low temperature directly on the surface of an Si cantilever, and stabilizing the surface without exposing a ground of Si. CONSTITUTION:An Si cantilever 12 is formed on an Si substrate, and a diffused resistor 17 of p type is formed in the vicinity of a supporting part of said cantilever 12. Also, a thermal oxidation film 13 is removed from the cantilever 12, and a CVD film 14 is formed directly on the cantilever 12. Moreover, an Al wiring 16 for connecting the diffused resistor 17 and the outside is formed. Accordingly, the surface is stabilized in comparison with the case when Si is exposed, and it is scarcely feared that a fault by a leak of p-n junction is generated. Also, an influence of warping by thermal distortion can be reduced, and a temperature characteristic, etc. can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ultra-small semiconductor acceleration sensor using a cantilever formed on a semiconductor substrate.

[Prior art]

Recently, ultra-small semiconductor acceleration sensors formed on semiconductor substrates have been developed.

This semiconductor acceleration sensor is formed on a semiconductor substrate using thin film technology such as etching, and detects acceleration by detecting resistance changes due to the piezoresistive effect of the semiconductor and minute capacitance changes due to deviation. It looks like this.

Since these semiconductor acceleration sensors are formed using thin film technology as described above, the length of the vibrating portion is, for example, 110 mm.
Approximately 0a, thickness is II! It can be formed extremely small, with a total chip size of about 1 mm square, and
An excellent feature of the integrated circuit is that it can be formed on the same substrate as other elements.

As the above semiconductor acceleration sensor, for example, IE
EE Electron Devices, Vol.
, ED-26, No. 12°p, 1911. Dec,
1979 “A Batch-Fabricated S
ilicon Accelerometer".

FIG. 2 is a diagram showing the above semiconductor acceleration sensor (a
) shows a plan view, and (b) shows a cross-sectional view.

In FIG. 2, 21 is a Si acceleration sensor chip, 22
23 is a Si weight, 24 is a p-type diffused resistor, and 25 is a P+ type diffused electrode.

In the semiconductor acceleration sensor shown in FIG.

When acceleration is applied, the Si weight 23 is deflected, thereby causing strain in the Si cantilever beam 22.

A P-type diffused resistor 24 is formed near the support portion of this Si cantilever beam 22, and when the cantilever beam is strained, the resistance value of the diffused resistor 24 changes due to the piezoresistance effect.

By detecting this change in resistance value via the p+ type diffusion electrode 25, acceleration can be detected.

[Problem that the invention seeks to solve]

In conventional semiconductor acceleration sensors such as those described above, the Si thermal oxide film is often removed to facilitate mounting in subsequent steps.

However, as a result, the Si surface is exposed, which increases the leakage current at the PN junction and increases the diffusion resistance 24.
There is a problem that the stability of

In particular, this type of sensor is designed to detect minute changes in resistance due to strain, so when the leakage current increases as described above, it becomes difficult to accurately detect acceleration.

On the other hand, a method of leaving a Si thermal oxide film may also be considered.

In that case, since the surface is covered with a Si thermal oxide film, the leakage current at the PN junction is reduced and the stability of the diffused resistor 24 is increased.

However, if the Si thermal oxide film is left, another drawback arises: thermal distortion occurs.

In other words, since the Si thermal oxide film is formed at a high temperature of 1100 to 1200°C, thermal strain occurs due to the difference in thermal expansion coefficient between SL and Sin, and the cantilever beam becomes deformed when returned to room temperature after manufacturing. The problem arises that the

FIG. 3 is a diagram showing the above-mentioned thermal strain, where 31 is a Si cantilever, and 32 is a thermal oxide film formed on the Si cantilever. Further, Δα is the deflection due to thermal strain.

The warpage due to thermal strain of the cantilever beam shown in Figure 3 is as follows (1)
It is given by Eq.

In the above equation, r is the radius of curvature of warpage, Δt is the temperature difference between the processing temperature and room temperature, α is the coefficient of thermal expansion, E is the elastic constant, and d
is the film thickness, the subscript , is Si, and f is the thermal oxide film (Sin
, ) indicates the value.

Also, if the length of one cantilever beam is 2, the deflection ΔQ at the tip of the cantilever beam is ΔQ=r(1-cos −) ・・・・・・・・・
・・・・・・・・・・・・・・・・・・(2)

In the above equations (1) and (2), dg=10 voices, df
” 1 am, fl = 2 nun, Δt =
Assuming 1200℃, α5=3.5 x 10-', α
f=5X10-', E, = 1.9X1012
dyne/ci, Ef=0.6X10”dyne/c
nf, r=■, 47■, Δ12=136 capes.

If the Si thermal oxide film is used as it is as a surface protective film in this way, thermal distortion will occur, which will cause problems such as an increase in offset voltage and deterioration of temperature characteristics.

As mentioned above, in the conventional semiconductor acceleration sensor, S
Products from which the i-thermal oxide film has been removed have the problem of increased leakage current, and products that use the Si thermal oxide film as it is as a surface protective film have the problem of various failures due to thermal strain. Ta.

The present invention aims to solve the problems of the prior art as described above.

[Means for solving problems]

In order to achieve the above object, the present invention uses a vapor phase growth method (CVD;
Chemical Vapor Depositio
n) to form a protective film.

In addition, as a CVD film, for example, PSG (Phos
ph.

It is possible to use a film such as SL, N, or 5-ilicate glass film.

[Embodiments of the invention]

FIG. 1 is a sectional view of a main part of an embodiment of the present invention.

In FIG. 1, a Si cantilever 12 is formed on a Si substrate 11 (single crystal silicon), and the Si cantilever 12
A p-type diffused resistor 17 is formed near the support portion.

Further, the thermal oxide film 13 is removed from the top of the Si cantilever 12, and the CvD film 14 is directly placed on the Si cantilever 12.
is formed. 4, the manufacturing process of the semiconductor acceleration sensor shown in FIG. 1 will be described with reference to FIG.

In FIG. 4, first, in (a), the Si substrate 11
A p-type impurity is diffused into a part of the n-type layer formed above to form a p-type diffused resistor 17.

Thereafter, the portion of the thermal oxide film 13 that will become the Si cantilever 12 is removed.

Next, in (b), CVD is applied as an intermediate insulating layer to the entire surface.
A film 14 is formed.

Next, in (c), a hole for connecting to the diffused resistor 17 is made in the CVD film 14.

Next, in (d), the M wiring 16 is formed in the above hole.

Next, in (e), CVD is applied as a final protective film to the entire surface.
A film 15 is formed.

Next, in (f), Si etching is performed from the back surface (lower side in the drawing) to form a Si cantilever 12.

In the semiconductor acceleration sensor formed as described above, the surface is covered with a CVD film and the Si is not exposed as a bare surface, so the surface is stabilized and problems such as leakage of the PN junction are eliminated.

Furthermore, since a CVD film can be formed at a significantly lower temperature than a thermal oxide film, thermal distortion can also be significantly reduced.

For example, PH in SiH, -02 as a CVD film.

PSG, which is a doped oxide mixed with and reacted with
When using a membrane, in (1) and (2) above, Δt
is 400℃, so r = 4.4 countries, ΔQ = 46I
! m, and the thermal strain can be reduced to about 1/3 compared to the case of the thermal oxide film described above.

Next, FIG. 5 is a sectional view of main parts of a second embodiment of the present invention.

In the embodiment shown in FIG. 5, a Si cantilever 52 is formed on a Si substrate 51, and a p-type diffused resistor 56 is formed near the support portion of the Si cantilever 52.

Further, a + type diffusion wiring 57 is provided as an electric wire for connecting the p-type diffused resistor 56 to the outside, and both the negative wiring 55 and the thermal oxide film 53 are formed only outside the Si cantilever 52. .

Then, the entire surface is covered with a CVD film 5 as a final protective film.
4 is covered.

Next, the manufacturing process of the above semiconductor acceleration sensor will be explained using FIG. 6.

First, in (a), a thermal oxide film 53 is formed on a Si substrate 51.

Next, in (b), a P-type diffused resistor 56 is formed near the portion that will become the support portion of the Si cantilever.

Next, in (c), a p+ type diffusion wiring 57 is formed so as to be connected to the p type diffusion resistor 56.

Next, in (d), the S1 cantilever beam part and p+
The portion of the thermal oxide film 53 connected to the type diffusion wiring 57 is removed.

Next, in (e), a horizontal wiring 55 is formed so as to be connected to the p-type diffusion wiring 53.

Next, in (f), CVD is applied as a final protective film to the entire surface.
A film 54 is formed.

Next, in (g), the back side of the 81 board 51 (lower part of the drawing)
Then, etching is performed to form a Si cantilever 52.

The semiconductor acceleration sensor configured as described above has a CV
Since the D film is formed of only one layer as the final protective film, the thickness of the CVD film can be made thinner than that of the sensor shown in FIG. It can be made smaller.

In the above example, a PSG film is used as the CVD film, but other Si3N4 films may also be used.

Further, a laminated structure of a PSG film and a Si3N film can also be used.

〔Effect of the invention〕

As described above, according to the present invention, since the CVD film formed at low temperature is directly provided on the surface of the Si cantilever formed on the 81 substrate and having a diffused resistance near the support part,
The surface is more stable than when the bare Si surface is exposed, and problems caused by leakage from the PN junction of the diffused resistor are eliminated.

Furthermore, compared to the case where the Si background is covered with a thermal oxide film, the effect of warping due to thermal strain can be reduced, and excellent effects such as improved temperature characteristics can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view of an embodiment of the present invention, Fig. 2 is a plan view and a sectional view of a conventional device, Fig. 3 is an explanatory diagram of warping due to thermal strain in a two-layer film structure, and Fig. 4 is a FIG. 5 is a sectional view of another embodiment of the present invention, and FIG. 6 is a diagram showing the manufacturing process of the embodiment of FIG. 5. Explanation of symbols

Claims (1)

[Claims] By forming a diffused resistor near the support part of a cantilever beam formed on a semiconductor substrate and supported at one end, and detecting a change in the resistance value that occurs in the diffused resistor according to the deviation of the cantilever beam. In a semiconductor acceleration sensor that detects acceleration, CVD is formed directly on the surface of the cantilever at low temperature.
A semiconductor acceleration sensor characterized by being provided with a film.