JPH03112170A - Acceleration sensor and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an acceleration sensor whose sensitivity is high, which is highly pressure-resistant, which is small-sized and which can be mass-produced by a method wherein a prescribed groove is formed inside a silicon substrate, one pair of strain- causing parts are formed in surface parts and an inertial mass part is suspended and supported between the strain-causing parts. CONSTITUTION:Grooves 2a', 2b' which have a definite interval width and whose cross- section structure is L-shaped are formed inside a silicon substrate 1; one pair of silicon thin strain-causing parts 4a, 4b are formed in surface parts of the substrate 1; a silicon thick inertial mass part 3' is suspended and supported between the strain-causing parts. In this constitution, even when an acceleration is applied to a capacity formation part 11 and the mass part 3' is given an inertial force F in a downward direction, the strain-causing parts 4a, 4b come into contact with corner parts 1a, 1b inside the grooves 2a', 2b' and are supported, even when a larger acceleration and a larger inertial force F' are given additionally, the strain-causing parts 4a, 4b come into contact with the corner parts 1a, 1b by making use of parts 4A, 4B as fulcrums and can be supported up to a range that the bottom face of the mass part 3' comes into contact with a base stand. Thereby, it is possible to prevent this sensor from being destroyed by a further deformation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an acceleration sensor that detects acceleration caused by earthquakes, movement of objects, collisions, etc., and a method for manufacturing the same.

[Conventional technology]

FIG. 6 is a sectional view showing an example of a conventional acceleration sensor. In the figure, 1 is a silicon substrate, 2 is a groove formed by etching on the back side of the silicon substrate 1 over a rectangular shape and has an almost trapezoidal cross section, and 3 is a silicon substrate 1.
4 is a movable part that suspends and supports the inertial mass part 3 by forming the groove 2 on the silicon substrate 1; These silicon substrates have 1° grooves 2.
The inertial mass section 3 and the strain generating section 4 constitute a sensor chip 5. Reference numeral 6 denotes an electrode area projecting portion formed on the surface side of the silicon substrate 1; 7, an upper cap fixedly arranged to cover the inertial mass portion 3 on the surface side of the silicon substrate 1; and 8, an upper cap T. an upper electrode formed on the inner surface of the silicon substrate 1 to face the inertial mass part 3; a lower cap 9 fixedly arranged to cover the inertial mass part 3 on the back side of the silicon substrate 1;
10 is a lower electrode formed on the inner surface of the lower cap 9 to face the inertial mass section 3, and 11 is a capacitance forming section consisting of a gap.

In such a configuration, when acceleration is applied to the sensor,
The position of the inertial mass section 3 is displaced, the capacitance value changes between the opposing upper electrode 8 and lower electrode 10, and acceleration is detected. On the other hand, when excessive acceleration is applied, the upper and lower caps 7.9 act as stoppers to prevent destruction of the strain-generating portion 4 due to excessive deformation.

[Problem to be solved by the invention]

However, the acceleration sensor configured in this way is
It is composed of three main components: a sensor chip 5, an upper cap 7, and a lower cap 9. Since these three components each have dimensional variations, the following There was a problem like this. In other words, (&) it was extremely difficult to align the three components when assembling them.

(b) Since the completed dimensions of the gaps between the upper cap 7 and lower cap 9 and the sensor chip 5 vary greatly,
It was difficult to design a highly sensitive acceleration sensor because it was necessary to provide a margin for pressure resistance.

(,) Since the bottom surface of the inertial mass section 3 is configured to directly contact the stopper, there is little freedom in designing the shape of the inertial mass section 3 and the shape of the lower plate.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and its purpose is to provide an acceleration sensor that has improved sensitivity to acceleration and that can be mass-produced in a shed and with high pressure resistance, and to manufacture the same. The purpose is to provide a method.

[Means to solve the problem]

In order to solve these problems, the acceleration sensor according to the present invention has a groove having an L-shaped cross-sectional structure with a constant gap width formed in a silicon substrate, and a thin silicon layer formed on the surface of the silicon substrate. A pair of strain-generating parts are formed, and a silicon thick-walled inertial mass part is suspended and supported between the strain-generating parts.

Further, in the method for manufacturing an acceleration sensor according to the present invention, after forming a groove on one surface of a first silicon substrate, a second silicon substrate that will become a strain-generating portion is bonded thereon, and the groove is formed on one surface of the first silicon substrate. By forming a groove connected to the groove of , and forming a groove having an L-shaped cross-sectional structure, a thin silicon strain-generating portion is formed on the surface portion of the silicon substrate.

[Effect]

In the present invention, an L-shaped groove is formed with high precision in a silicon substrate with a constant gap width.

〔Example〕 Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of an acceleration sensor according to the present invention, and the same parts as in the previous figures are given the same reference numerals. In the figure, the back surface parallel to the surface of the silicon substrate 10 is the (110) crystal plane, and the back surface has a (112) axis in a direction perpendicular to the (110) crystal plane. The cross section is etched by anisotropic etching.
A pair of L-shaped grooves 2m'+2b' in the shape of an inverted X are formed in parallel with a constant gap. And this inverted character-shaped groove 2a/.

2b/, a pair of strain-generating portions 4th made of thin-walled portions of the silicon substrate 1 are formed on the upper part of the silicon substrate 1.

4b is formed, and this pair of strain-generating parts 4m+4b
An inertial mass part 3' made of a thick part of the silicon substrate 1 having a rectangular parallelepiped shape is supported and formed between the inertial mass part 3' and a lower electrode 10 opposite to the surface of this inertial mass part 3/.
is formed.

According to such a configuration, the inertial mass section 3' is formed not in a mesa shape but in a rectangular parallelepiped shape of an arbitrary size, so that its mass increases and sensitivity can be improved.

Further, by forming the pair of grooves 2a'12b' in an inverted shape in the silicon substrate 1, acceleration is applied to the capacitance forming part 11, and an inertial force F is applied downward to the inertial mass part 3/. As shown in FIG. 2, even if the
b is each corner 1a in the inverted groove 2a'12b'
r1b, and a larger acceleration is applied thereto), and as shown in FIG.
are corner portions 1a and 4A and 4B, respectively, as fulcrums, respectively.
The inertial mass part 3' can be supported to the extent that the bottom surface of the inertial mass part 3' comes into contact with the base. Therefore, even in the case of excessive acceleration, the function as a two-stage final stopper can be obtained, and destruction due to further deformation can be prevented.

FIG. 1 is a sectional view showing another embodiment of the acceleration sensor according to the present invention, and the same parts as in the previous figures are given the same reference numerals. The difference between this figure and FIG. 1 is that the surface of the silicon substrate 10 is a (100) plane, which is the (100) plane of this crystal plane.
The acceleration sensor is constructed by performing anisotropic etching on the 100) plane to form grooves 2&'j2b' along the (110) axis direction of the crystal plane.

Even in such a configuration, effects completely equivalent to those described above can be obtained.

FIGS. 5(a) to 5(a) are cross-sectional views illustrating an embodiment of the method for manufacturing an acceleration sensor according to the present invention.

In the same figure, first, as shown in the same figure (Hata), an etching mask material 21 such as Si3N4 is formed on the surface of a P-type silicon substrate 10, and then the above-mentioned inverted-shaped groove 2m' is formed in this etching mask material 21. A pair of window patterns 21m, 21b corresponding to the portion parallel to the surface of the silicon substrate 1 in +2b' are formed by υ patterning using the 7 otolithography technique, and this pair of window patterns 21m,
21b is anisotropically etched using an etching solution such as KOH to form a pair of #22m, 22
After forming the etching mask material 21, the etching mask material 21 is removed.

Next, as shown in the same figure (b), a pair of grooves 22m, 22
Although not shown, a masking material such as a thermal oxide film is formed on a portion of the inverted grooves 2m'+2b' perpendicular to the surface of the silicon substrate 1 within b, and the surface of the silicon substrate 10 and the pair of grooves 22m are formed. , 22b, for example, by thermally diffusing phosphorus or the like to form an n-type impurity diffusion layer 23. Next, apply 513N to the back side of this silicon substrate 1 in the same manner as described above.
An etching mask material No. 4 is formed, and anisotropic etching is performed using KOH to form a groove 2 in the portion that will become the inertial mass portion 3'.
form 4. Next, as shown in FIG. 2D, a P-type silicon substrate 26 having an n-type epitaxial layer 25 formed on one surface is heated to 1000 to 1100° C. on the silicon substrate 1 having an 11-type impurity diffusion layer 23 formed on its surface. The n-type epitaxial layer 25 side is directly bonded and integrated by performing 7-generation bonding in an oxidizing atmosphere. Next, the silicon substrate 26 on which the n-type epitaxial layer 25 is formed is immersed in, for example, a KOH solution, and etching is performed by applying a positive potential of several to IOV to the silicon substrate 1 on which the n-type impurity diffusion layer 23 is formed. The etching is then stopped at the n-type epitaxial layer 25, as shown in () in the same figure, and the silicon substrate 26 shown in (d) in the same figure is etched away. Next, as shown in FIG. 3(f), after forming the lower electrode 10 and the electrode number protrusion 6 at predetermined positions on the surface of the n-type epitaxial layer 25, the same method as described above is performed on the back side of the silicon substrate 1. An etching mask material with a thickness of 5t3N< is formed and immersed in a KOH solution to form an n-type epitaxial layer 2.
When etching is performed by applying a positive potential of several to ten-odd volts to 5, the etching stops at the n-type epitaxial layer 25 and n-type impurity diffusion layer 23, and the grooves 22m and 22b communicate with each other. A pair of inverted grooves 26m and 26b are formed. Next, the same figure (x
') VC As shown in FIG. 1, a Pyrex cap T having an upper electrode 8 formed in a concave inner surface is bonded to the n-type epitaxial layer 25 by an anodic bonding method to complete an acceleration sensor similar to that shown in FIG.

According to this method, the pair of inverted grooves 2m'+2b', which suspend and support the inertial mass part 3', are etched into the silicon substrate 10 by anisotropic etching of the silicon substrate 1 and electric field stop etching technology. A pair of grooves 2 parallel to the surface
2m, 22b and a communicating vertical groove 26&,
Since it can be formed by etching 26b, a pair of strain-generating parts 4& is formed on the surface of the silicon substrate 1.

4b can be formed with a highly sensitive structure, and the corner parts 1m and 1b that stop excessive displacement of the inertial mass part 3' can be formed with high precision at the exact positions of the pair of strain-generating parts 4m and 4b. In addition, the above-mentioned process can process 500 to 100 pieces at a time from a φ4′ wafer, similar to the normal IC manufacturing process.
Since 0 pieces can be formed, mass production is possible.

〔Effect of the invention〕

As explained above, according to the present invention, a pair of L-shaped grooves having a constant gap width are formed in a silicon substrate, and a pair of thin-walled silicon strain-generating parts are formed in the surface portion of the silicon substrate. By supporting a silicon thick-walled inertial mass part between the pair of strain-generating parts, high sensitivity and high withstand voltage can be achieved, as well as a degree of freedom in designing the contradictory characteristics of high sensitivity and high withstand voltage. will be significantly expanded. In addition, since the sensor chip with the lower electrode formed on the surface and the cap with the upper electrode formed on the inner surface are arranged facing each other, the number of main components can be reduced from the conventional three to two, and the size can be reduced. Extremely excellent effects such as being possible can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the acceleration sensor according to the present invention, FIGS. 2 and 3 are cross-sectional views explaining the operation of the acceleration sensor shown in FIG. 1, and FIG. Cross-sectional views showing other embodiments, FIGS. 5(&) to (X)
6 is a cross-sectional view showing a process of an embodiment of the method for manufacturing an acceleration sensor according to the present invention, and FIG. 6 is a cross-sectional view showing the configuration of a conventional acceleration sensor. 1・e...Silicon substrate, 1 field, 1b----corner, 2
&'+ 2&'+ 2b', 2bla @ @ a groove, 3'@@@・Inertial mass part, 4m, 4b... Strain part, 4A, 4BΦ... Fulcrum, 6... Electrode area projection part, 1-- upper silicon cap, 8-- upper electrode, 10-- lower electrode, 11-- capacitance forming part,
21...Etching mask, 21m. 21b...Window pattern, 22m + 22b...
e groove, 23...eH type impurity diffusion layer, 24@e...groove, 25...n type epitaxial layer, 26m, 2
6b...Inverted groove.

Claims (2)

[Claims] (1) A first groove is provided with a constant gap width in a direction perpendicular to one surface of the silicon substrate, and connected to the bottom of the first groove to extend outward in a direction parallel to the silicon substrate surface. A second groove having a predetermined gap width is provided on the other side of the silicon substrate to form a groove having an L-shaped cross section in a direction perpendicular to the silicon substrate. , a silicon thick-walled inertial mass section suspended and supported between the strain-generating sections, and a lower electrode formed on the other surface of the silicon substrate, which are adhesively arranged on the other surface of the silicon substrate. An acceleration sensor comprising: a cap; and an upper electrode disposed on the inner surface of the cap to face a lower electrode. (2) forming a second groove on one side of the first silicon substrate of the first conductivity type; forming an impurity diffusion layer of a second conductivity type on a surface, and forming a third groove having a predetermined positional relationship with the second groove on the other surface of the first silicon substrate of the first conductivity type; a second silicon substrate of the first conductivity type having an epitaxial layer of the second conductivity type on one surface, and a second silicon substrate of the first conductivity type; A step of adhering a conductivity type impurity diffusion layer formation surface, and a second conductivity type silicon substrate while applying a positive potential to the second conductivity type epitaxial layer of the first conductivity type silicon substrate. a step of etching away the second conductive type epitaxial layer; a step of forming a lower electrode on the surface of the second conductive type epitaxial layer; and a step of removing the first first conductive type silicon substrate while applying a positive potential to the second conductive type epitaxial layer. etching a portion corresponding to the second groove from the surface to form a first groove connected to the second groove;
A method for manufacturing an acceleration sensor comprising the step of bonding a cap having an upper electrode formed in a recessed part on an epitaxial layer of a second conductivity type.