Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2000-06-01
2001-11-20
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
Reexamination Certificate
active
06318175
ABSTRACT:
BACKGROUND OF THE INVENTION
German Patent Application No. 40 00 903 shows a micromechanical sensor configured as an acceleration sensor which is manufactured on the basis of silicon micromechanics. The sensor includes a support made of a silicon substrate with an epitaxial layer of silicon applied to the silicon substrate. A part of the epitaxial layer is laid bare by an etching process to provide micromechanical deflection parts in the form of tongues. One or more tongues are suspended for this purpose from one or more webs and are deflected from the rest of the sensor structure under the action of a force on the sensor. Means are furthermore provided for evaluating the deflection.
German Patent Application No. 40 03 473 discusses taking crystallographic angles of a single-crystal silicon wafer into consideration in connection with the development and arrangement, as well as for the etching process. To provide a means for evaluating the deflection of the tongues, individual electrodes, which are each electrically insulated from each other, are provided so that a capacitative change between tongue and electrode is measurable.
The laying bare of the tongues as a component of the epitaxial layer is effected by means of a rear etching.
This constitutes an additional process step as compared with an ordinary bipolar process.
From PCT Application No. WO 92/03740, it is known to apply, on a support made of a silicon substrate, a layer of polycrystalline silicon onto a silicon-oxide layer having contact windows in an LPCVD process (low pressure chemical vapor disposed). The silicon oxide layer is removed by an etching process, as a result of which the polycrystalline silicon layer is present at a distance from the silicon substrate as tongue or electrode on the supports formed in the contact windows. The deposition rate of low voltage LPCVD-poly is about 60 Å/min and is thus very slight as compared with the separation rate of about 1 &mgr;/min of epitactic polysilicon. Due to this, for reasons of process economy, only relatively thin LPCVD layers can be produced. As the result, the working capacity of a lateral acceleration sensor, for example, is limited by the correspondingly small layer thicknesses of the tongues. Furthermore, additional silicon depositions are necessary for this procedure, as compared with a conventional bipolar process.
SUMMARY OF THE INVENTION
In accordance with the present invention, production of the exposed deflection part of polycrystalline silicon, or the mechanically active layer, can be accomplished without additional expense as part of a bipolar or MOS process. Moreover, no additional silicon depositions are necessary.
Epitaxy is a known special process for the production of single-crystal layers of silicon. In accordance with the present invention, epitaxial layers deposited in polycrystalline form (over silicon-oxide), or other non-crystalline layers, are used which are applied in the course of a conventional bipolar process.
Since the epitaxial deposition rate is very high as compared with an LPCVD process, relatively thick layers of 10 to 30 &mgr;m can be produced in accordance with the present invention, thereby increasing the working capacity of the lateral sensor.
In accordance with the present invention, a silicon oxide layer is applied to a silicon substrate at a position where one or more micromechanical deflection parts are to be formed. Contact window openings are formed on the silicon substrate adjacent to the silicon-oxide layer. An epitaxial layer of silicon is then deposited on both the silicon oxide layer and the contact openings. The epitaxial layer grows in polycrystalline form on the silicon oxide layer. However, the epitaxial layer grows in single crystal form on the contact window openings to provide a direct connection to the silicon substrate. Lateral structural limitations of one or more micromechanical deflection parts are then formed by etching through the polycrystalline portion of the epitaxial layer in narrow etch pits to form trenches using, for example, an anisotropic plasma etching technique. Finally, the silicon-oxide layer is removed during an etching process to complete the formation of the one or more micromechanical deflection parts.
One particular advantage of the present invention is that the method according to the present invention can be universally employed for different designs. For example, arrangements of tongues which are supported on one side and plates which are supported on edge regions are both possible. Moreover, several layers can be produced one above the other. Another advantage is that, using the same method steps and without additional expense, integrated electronic circuits, particularly an evaluation circuit for the deflection, can be produced on the same support with the micromechanical sensor. Similarly, electrical insulation of the micromechanical sensor parts from other electronic components on the same support is possible with the customary manufacturing steps.
REFERENCES:
patent: 5095401 (1992-03-01), Zavracky et al.
patent: 5233213 (1993-08-01), Marek
patent: 6076404 (2000-06-01), Muchow et al.
Muchow Joerg
Muenzel Horst
Offenberg Michael
Waldvogel Winfried
Kenyon & Kenyon
Kwok Helen
Robert & Bosch GmbH
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