Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1995-12-04
2001-05-08
Williams, Hezron (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514320, C073S514360
Reexamination Certificate
active
06227049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acceleration sensor, and more specifically, a semiconductor type acceleration sensor suitable for a air-bag system, a suspension control system, or the like, for automobiles.
2. Description of the Related Art
In producing a semiconductor type acceleration sensor, the movable part thereof has hitherto been prepared in such a way that it penetrates a single crystal silicon wafer. Accordingly, the movable part must be sized so as to penetrate through the thickness of a wafer, and therefore, it has been difficult to miniaturize the acceleration sensor. In addition, in order to incorporate this sensor into a package, a relaxation part, have been required such as a pedestal, in order to release the stress caused by the difference in coefficients of thermal expansion or the like.
However, in Nikkei Electronics, Nov. 11, 1991 (No. 540), pp 223 to 231, there is illustrated an acceleration sensor produced by use of a surface micro-machining technique. According to this technique, a thin polysilicon film is laminated on a silicon substrate, and this polysilicon film is etched, whereby a beam movable parallel to the surface of the substrate is formed, so as to form a differential capacity type acceleration sensor. However, when a beam structure is formed by use of polysilicon, if a signal processing circuit is formed around the formed beam structure, the sensor characteristics become unstable. This is because the beam structure is formed of a polycrystalline and amorphous material, resulting in noticeable variation for every production lot. Accordingly, it is still desirable to form an acceleration sensor by surface micro-machining single crystal silicon.
Under such circumstances, the purpose of the present invention is to provide an acceleration sensor having a novel structure, by which high precision and high reliability can be realized.
In addition, another purpose of the present invention is to produce this acceleration sensor with a good yield rate during the production process thereof.
SUMMARY OF THE INVENTION
The gist of a first embodiment of the present invention resides in an acceleration sensor, comprising a second single crystal silicon substrate bonded onto a first single crystal silicon substrate with an insulating film interposed therebetween, the second single crystal silicon substrate being made of a thin film, a beam formed on at least either of said first and second single crystal silicon substrates and movable in a direction parallel to the surface thereof, and a signal-processing circuit formed on at least one of said first and second single crystal silicon substrates for performing processing of signals produced by a movement of beam, caused by an acceleration.
In addition, the gist of a second embodiment of the present invention resides in a process for producing an acceleration sensor, comprising; a first step of forming, on a main surface of a first single crystal silicon substrate, a groove with a predetermined depth for formation of a beam; a second step of forming, on the main surface of said first single crystal silicon substrate, a film of a polycrystaline silicon, an amorphous silicon or a mixture thereof so as to fill said groove with said silicon film, and smoothing (flattening) the surface of said silicon film; a third step of bonding the main surface of said first single crystal silicon substrate to a second single crystal silicon substrate with an insulating film formed thereon, said insulating film being interposed between said first and second single crystal silicon substrates; a fourth step of polishing the reverse side of said first single crystal silicon substrate to a predetermined degree, so as to make said first single crystal silicon substrate a thin film; and a fifth step of forming a signal-processing circuit on at least either of said first and second single crystal silicon substrates, and thereafter, removing by etching said silicon film of a polycrystal silicon, an amorphous silicon or a mixture thereof from said reverse side of said first single crystal silicon substrates, to form a beam.
In addition, the gist of a third embodiment of the present invention resides in a process for producing an acceleration sensor, comprising; a first step of bonding a main surface of a first single crystal silicon substrate to a second single crystal silicon substrate with an insulating film formed thereon, said insulating film being interposed therebetween; a second step of polishing the reverse side of said first single crystal silicon substrate to a predetermined degree, so as to make the first single crystal silicon substrate a thin film; a third step of forming a groove with a predetermined depth for formation of a beam; a fourth step of forming, on the reverse side of said first single crystal silicon substrate, a film of a polycrystal silicon, an amorphous silicon or a mixture thereof, so as to fill said groove with said silicon film, and smoothing the surface of said silicon film; and a fifth step of forming a signal-processing circuit on at least one of said first and second single crystal silicon substrates, and thereafter, removing by etching said film of polycrystal silicon, amorphous silicon or a mixture thereof from the reverse side of the first single crystal silicon substrate, to form a beam.
In the first embodiment, when an acceleration is applied in a direction parallel to the surface of the bonded single crystal silicon substrates, the beam formed on the first or second single crystal silicon substrate moves. As this beam moves, signal processing is performed in the signal-processing circuit formed on the first or second single crystal silicon substrate.
In the second embodiment, as a first step, a groove of a predetermined depth for formation of a beam is formed on the main surface of the first single crystal silicon substrate, and as a second step, a film of a polycrystalline silicon, an amorphous silicon or a mixture thereof is formed on the main surface of the first single crystal silicon substrate, whereby the groove is filled with the silicon film, and the surface of this silicon film is flattened. Subsequently, as a third step, the main surface of the first single crystal silicon substrate is bonded to a second single crystal silicon substrate having an insulating film formed thereon, said insulating film being interposed between the first and second single crystal substrates, and, as a fourth step, the reverse side of the first single crystal silicon substrate is polished to a predetermined degree, whereby the first single crystal silicon substrate is made into a thin film. Subsequently, as a fifth step, a signal-processing circuit is formed on the first or second single crystal silicon substrate, thereafter the polycrystalline, amorphous or mixed silicon film is removed by etching from the reverse side of the first single crystal silicon substrate, and a beam is formed. As a result, an acceleration sensor according to the first invention is produced.
In the third embodiment, as a first step, the main surface of a first single crystal silicon substrate is bonded to a second single crystal silicon substrate with an insulating film formed thereon, said insulating film being interposed between the first and second substrates, and as a second step, the reverse side of the first single crystal silicon substrate is polished to a predetermined degree, so that the first single crystal silicon substrate is made into a thin film. Subsequently, as a third step, a groove of a predetermined depth for formation of a beam is formed on the reverse side of the first single crystal silicon substrate, and as a fourth step, a film of polycrystalline silicon, an amorphous silicon or a mixture thereof is formed on the reverse side of the first single crystal silicon substrate, whereupon the groove is filled with the silicon film, and the surface of the silicon film is flattened. Subsequently, as a fifth step, a signal-processing circuit is formed on the first or
Denso Corporation
Kwok Helen C.
Pillsbury Madison & Sutro LLP
Williams Hezron
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