Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-04-29
2001-11-20
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
Reexamination Certificate
active
06318177
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a micromechanical component and to a method for producing the micromechanical component (e.g., a capacitive acceleration sensor) having one or several electrical or mechanical function variables dependent on at least one geometric design parameter. The micromechanical component is produced by an etching process via which a structure with bars and trenches is formed.
BACKGROUND INFORMATION
Using processes of surface micromachining technology, it is possible to produce sensors, actuators and other miniaturized components according to methods that are known from a production of microelectronic components.
It is known that such processes used in surface micromachining technology for producing mechanical and/or electrical functional elements are subject to production process tolerances. In this manner, the term production tolerance is intended to designate the deviation from a setpoint which is expediently selected as the process mean value. As a rule, these production process tolerances result in high variations in the characteristic data of the mechanical or electrical functional elements in question, which must be provided for by balancing, compensation or calibration.
Examples for this are the sensitivity and the resonance frequency of the mentioned micromechanical capacitive acceleration sensor as a function of the trench etching process. In this trench etching process, the sensor is subdivided into a structure having trenches and bars, which contains the necessary functional elements, in this case, capacitor devices and spring devices.
Such production process tolerances, or process tolerances in short, are known to arise in trench etching (e.g., dry etching) due to varying process temperatures or process gas compositions or process gas flow rates, etc.
In general, it is desirable to produce micromechanical components with low characteristic data variation in order to avoid time-consuming and costly calibration processes, balancing processes or the like.
Consequently, one of the objects of the present invention is to keep the characteristic data variations as a function of process tolerances at a low level or to reduce them by a suitable arrangement of certain geometric design parameters.
SUMMARY OF THE INVENTION
A method according to the present invention for producing a micromechanical component, and the micromechanical component have an advantage that, in a specified process tolerance range, a dependency of the characteristic data on the present process situation in the process tolerance range (e.g., 3&sgr; range) is minimized; thus a compensation of the influences occurs simultaneously.
For example, this compensation brings about an increase of the wafer and product yield, a uniform reliability with low balancing outlay (expenses for evaluation electronics are reduced) as well as a smaller possible size of the component.
The present invention provides that the drafting of a design for the micromechanical component proceeds in such a way that the geometric design parameter within the local area of the micromechanical component is subject to a predetermined process-related regularity, the design parameter being essentially constant in relation to function blocks in particular, so that in the etching process, the process tolerance of the design parameter within the micromechanical component shows essentially no locus dependency.
According to another embodiment of the present invention, a determination of an essential dependency of at least one of the electrical or mechanical function variables of the component on the process tolerance of the design parameter or design parameters in question takes place in the etching process. Then, a relationship for the design parameter or design parameters is derived in order to minimize the dependency and finally, the design parameter is determined in such a way that the derived relationship is fulfilled with the expected process tolerance. This procedure is expedient when several design parameters exert a substantial influence and therefore cannot be selected independent of one another.
According to another embodiment of the present invention, the micromechanical component is a capacitive acceleration sensor having a seismic mass device suspended on a torsion spring device, a movable capacitor plate device attached to the seismic mass device and a fixed capacitor plate device interacts with the movable capacitor plate device. In this embodiment, the function variable is the sensitivity of the acceleration sensor, the essential dependency being stated by the following equation:
S
=
C
·
(
b
m
-
Δ
)
(
b
f
-
Δ
)
3
·
(
d
+
Δ
)
where C is a constant, &Dgr; is a process tolerance, b
m
is a width of the seismic mass device, b
f
is a width of the torsion springs of the torsion spring device, and d is a plate distance of the particular capacitor plate device in the unaccelerated state.
According to another embodiment of the present invention, the relationship is formed by forming the derivation of the dependency according to the process tolerance. This may occur either numerically or, if possible, analytically.
According to an additional embodiment, the regularity is specified in such a way that the etching density is held within certain limits of a specified value.
REFERENCES:
patent: 5495761 (1996-03-01), Diem et al.
patent: 5563343 (1996-10-01), Shaw et al.
patent: 5744719 (1998-04-01), Werner
patent: 5756901 (1998-05-01), Kurle et al.
patent: 5880369 (1999-03-01), Samuels et al.
patent: 5987989 (1999-11-01), Yamamoto et al.
patent: 6151966 (2000-11-01), Sakai et al.
Buchan Nicholas
Fehrenbach Michael
Schubert Dietrich
Kenyon & Kenyon
Kwok Helen
Robert & Bosch GmbH
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