JPS6340379A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To construct a highly sensitive acceleration sensor by a method wherein a twin beam held structure is adopted and diffusion resistors are connected bridge-wise. CONSTITUTION:An acceleration sensor of this design is built of an overlap section 4 and flexible sections 9 and 10, respectively provided with diffusion resistors R1 and R3, on both sides of the overlap section 4. For the formation of diffusion resistors R1-R4, an approximately 2mum-thick arsenic diffusion layer is formed in an n-shaped Si wafer flexible portion, and each of the resistor is formed after a U shape. The resistors R1 and R3 (R2 and R4) are so formed that the longitudinal extension of the pattern they form is parallel (perpendicular) to the direction of generation of stress, which reverses the sign of the piezoelectric resistance to be presented. Further, input terminals 13 and 14 and measuring terminals 15 and 16 are on an upper substrate 1. They form a wiring pattern 17 for the diffusion resistors R1-R4 for the construction of a bridge of resistors. With flexible sections 9, 10, 11, and 12 being free of influence of inner stress of protecting films, there is an increase in the sensing accuracy.

Description

[Detailed Description of the Invention] [Summary] As a method to eliminate the decrease in accuracy due to residual internal stress,
An acceleration sensor that uses anisotropic etching to provide a plurality of flexible parts around a weight part.

[Industrial application field]

The present invention relates to the configuration of an acceleration sensor with improved measurement accuracy.

Labor-saving or unmanned systems using Electro-X are being promoted in all sectors, including transportation such as aircraft, automobiles, and trains, as well as machinery, equipment, and construction.

Especially for transportation, compactness and weight reduction are necessary conditions.
Various sensors have been put into practical use using the microelectrox technology used to form semiconductor devices.

[Conventional technology]

Silicon (St) single crystal substrates (hereinafter referred to as Si wafers) are often used as substrates for forming semiconductor devices such as ICs and LSIs, and are processed using thin film formation technology and photolithography technology (photolithography or electron beam lithography). Semiconductor integrated circuits are manufactured using this technology, and mechanical elements of similar size are formed on Si wafers using this technology.

Specific examples include pressure sensors and acceleration sensors.

Fine mechanical elements such as chemical concentration sensors, bubbles, nozzles, and printer heads are made using this technology, and this type of formation technology is called micromechanical devices.

Here, the reason why St is used as a substrate is that Si has a diamond structure and has interfold properties, and has the following characteristics.

■ It has a hardness of 7, which is harder than most metals, and it is resistant to mechanical stress and has a higher elastic limit than iron (maximum limit of recovery when force is removed) for both tension and compression.

■ When subjected to repeated tension and compression, stress accumulates in the grain boundaries of polycrystalline metals, causing fatigue and making them more likely to break, whereas Si maintains its strength.

■ It is possible to perform anisotropic etching by selecting an etching solution, and to accurately drill deep holes. In other words, the (110) plane is etched fastest, but the
0) plane is etched slowly, and (111) plane can be hardly etched.

The present invention relates to the configuration of a piezoresistive acceleration sensor that detects changes in diffused resistance formed on a Si substrate.

Figure 4 shows the Si acceleration sensor 5ilicon Acceleron+eter' developed by Roylance.
IEEE TRANSACTION 0NEL
ECTRON DEVICE, VOLJD-26,N
0, 12, DEC, 1979) That is, two Si wafers are subjected to anisotropic etching to form an upper substrate 1 and a lower substrate 2, which are then bonded together using an adhesive 3. .

Here, the upper board 1 has a weight part (Mass) 4 in the center.
With this as the center, three sides are etched to completely punch out, and one side is shallowly etched to provide a flexible part 5, which forms a cantilever beam that supports the weight part 4.
It has a lever-shaped structure.

Furthermore, a diffused resistor 6 is formed by diffusing impurities in the portion of the flexible portion 5 .

Next, the operating principle is that the lower substrate 2 is lower than the upper substrate 1.
When acceleration is applied in the direction of Electrical resistance changes (piezoresistance occurs).

Therefore, acceleration is measured by detecting the magnitude of this piezoresistance.

However, in such a conventional acceleration sensor, a protective film 7 made of silicon dioxide (SiO□) is provided on the upper substrate 1 by a chemical vapor deposition method (abbreviated as CVO method). Since the measurement is carried out at a high temperature, internal stress is generated in the protective film 7, and therefore, even if no acceleration is applied to the weight section 4, the deflection section 5 is bent, making it impossible to perform highly accurate measurements. be.

[Problem that the invention seeks to solve]

As described above, the conventional acceleration sensor is provided with a protective film 7 to protect the thinly formed flexible part 5 and weight part 4 and ensure reliability. The problem is that the bending portion 5 bends due to stress even when no acceleration is applied, producing piezoresistance, which reduces measurement accuracy.

[Means for solving problems]

The above problem can be solved by an acceleration sensor having a structure in which a plurality of bending parts are provided around the weight part by anisotropic etching, and each bending part is provided with a diffused resistor.

[Effect]

The present invention has changed the conventional cantilever structure to a double-supported beam structure with multiple beams centered around the weight part, and by providing a diffusion resistance in each of the bending parts, residual internal stress due to the formation of a protective film can be reduced. This prevents piezoresistance from occurring.

〔Example〕

FIG. 1 is a sectional view of an acceleration sensor according to the present invention, and FIG.
The figure is a plan view of this, and FIG.
It corresponds to the line position.

That is, as shown in FIG. 1, the acceleration sensor according to the present invention has a bending part 9 and 10 on both sides of the weight part 4 in the center, and these bending parts are provided with diffused resistors R1 and R3 as in the conventional case. Take.

Here, the base of the flexure portion 9.10 of the diffused resistors R, , R1 having a thickness of approximately 1Oμ- is provided at the root position. Due to the occurrence of the greatest stress.

Note that the flexible portions are the left and right flexible portions 9.1 as shown in Fig. 2.
Flexible portions 10.11 are provided not only at the top and bottom but also in the shape of a cross.

Here, the diffused resistors R+, Rt, Rs, and R4 are made of n-type Si.
Boron (B) is diffused to a depth of approximately 2 μm in the flexible portion of the wafer, creating a U-shaped pattern, where R and R3 are such that the longitudinal direction of the resistor pattern is the stress generation direction. R2 and R4 are formed so that the longitudinal direction of the resistance pattern is perpendicular to the direction of stress generation, so that the signs of the piezoresistors are opposite to each other.

In addition, the upper substrate 1 has input terminals 13.14 and measurement terminals 15.16, from which the respective diffused resistors R1,
A wiring pattern 17 is formed on R1, R3, and R4, and the third
As shown in the figure, the wires are connected in a resistor bridge type.
I) Formed with a vapor deposited film, the width of the wiring pattern 17 is 20
It was set as p11.

In the acceleration sensor formed in this way, the flexible portions 9, 10, 11, and 12 do not bend due to the internal stress of the protective film, so the sensing accuracy is five times higher than that of the conventional cantilever structure. We were able to achieve higher performance.

〔Effect of the invention〕

As described above, the present invention employs a double-supported beam structure and connects diffused resistors in a bridge-like manner, thereby making it possible to realize an acceleration sensor with higher sensitivity than the conventional cantilever structure.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an acceleration sensor according to the present invention, FIG. 2 is a plan view of an acceleration sensor according to the present invention, FIG. 3 is a wiring diagram of a diffused resistor, and FIG. 4 is a sectional view of a conventional acceleration sensor. It is. Sansukekyoku (24 catties, 1000 poems of Song Dynasty Manli) 2 mouths

Claims (2)

[Claims] (1) In an acceleration sensor that performs anisotropic etching on a silicon wafer to create a weight portion 4 supported by a flexure portion on which a diffused resistance is formed, and measures acceleration by the flexure of the flexure portion, the flexure portion is An acceleration sensor characterized in that a plurality of acceleration sensors are provided in a symmetrical direction with the weight portion 4 as the center. (2) The four flexible parts are provided in symmetrical directions around the weight part 4, and each of the flexible parts 9, 10, 11, 1
Diffused resistors R_3, R_1, R_2, R formed on 2
2. The acceleration sensor according to claim 1, wherein _4 is wire-connected in a resistor bridge type.