Process for producing a speed of rotation coriolis sensor

Details Process for producing a speed of rotation coriolis sensor Process for producing a speed of rotation coriolis sensor

1998-10-20

2001-04-10

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Etching of semiconductor material to produce an article...

C216S057000, C073S504120, C073S504130, C073S514290, C073S777000, C073S862626, C361S280000

Reexamination Certificate

active

06214243

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for the manufacture of a Coriolis rate-of-rotation sensor.
BACKGROUND INFORMATION
Sensors designed as Coriolis rate-of-rotation sensors are known. These sensors have deflectable oscillating (e.g., resonator) masses, spring-suspended (or resiliently-suspended) on a substrate, which support evaluators for the determination of Coriolis accelerations.
It is know to structure such Coriolis rate-of-rotation sensors through the plasma etching of the substrate structure (resonator or vibrating structure) using a bulk silicon membrane previously produced through time-controlled wet etching of the back side. A disadvantageous aspect of this approach is that exact process conditions must be maintained as a result of the time-controlled wet etching of the membrane, since otherwise membrane thicknesses, and thus structure heights, that is, the etching times required in the plasma etching process for etching-through from the front side, cannot be controlled.
SUMMARY OF THE INVENTION
The process according to the present invention is advantageous in.
The process, according to this invention, with the features cited in claim
1
, has the advantage over the background art that the oscillatable substrate structures which support the structured acceleration sensors for measuring Coriolis acceleration can be easily and precisely structured. Since the oscillatory substrate structure, which supports both the evaluation means (arrangement) and the driving means, (arrangement) is structured by plasma etching from a silicon-on-insulator (SOI) wafer substrate, it is advantageously possible to conduct structuring generally independently of etching times. The process of etching, both wet etching from the back side of the wafer, as well as plasma etching from the front side of the wafer, stops automatically at the buried oxide, so that the set structure heights are exclusively determined by the thickness of the SOI layer, thus making it possible to conduct an over-etching, procedure that is, the respective etching process can be conducted for a longer period of time than would have been necessary, so that overall process reliability is increased in the course of structuring. The buried oxide simultaneously ensures the protection of the bottom side of the structure in the course of the process of plasma etching in addition to its stopping function of the etching process. Otherwise, the bottom side of the structure would be attacked after etch-through of the membrane window by the etching gases (fluorine radicals) which flow around the edges. It is also advantageously possible to initially structure the front side of the wafer in plasma on the wafer substrate so that a stable wafer is maintained to the last minute in the course of manufacture. The membranes can advantageously be produced-as a subsequent, final step—by means of process of wet or dry etching from the back side of the wafer, with the buried oxide, as described above serving as a seal for the already produced structured front side of the wafer. Through the buried oxide a quasi-sealing of the front side of the wafer from the back side of the wafer is achieved, which can be additionally supported by additional front side painting.
Another advantageous embodiment of the process according to the present invention is that the buried oxide can be easily removed without additional effort in the course of the sacrificial layer etching of the Coriolis acceleration recorder.
In another embodiment of the present invention simultaneously with the oscillating resonator masses which support the Coriolis acceleration sensors, overload limit stops integrated on the sensors are also structured. The integrated overload limit stops can be advantageously jointly structured out from the front side of the wafer from the SOI wafer substrate along with the oscillating masses and their springs by means of the process of plasma etching, without the need for complex additional measures for establishing external overload limit stops. In general through a process of plasma deep etching from the front side of the wafer it is possible to very easily structure a highly compact substrate structure for a rate-of-rotation sensor with integrated overload limit stops.


REFERENCES:
patent: 5447067 (1995-09-01), Biebl et al.
patent: 5484073 (1996-01-01), Erickson
patent: 5488862 (1996-02-01), Neukermans et al.
patent: 5600065 (1997-02-01), Kar et al.
patent: 5640133 (1997-06-01), MacDonald et al.
patent: 5734105 (1998-03-01), Mizukoshi

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