Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Patent
1999-05-27
2000-12-12
Chaudhari, Chandra
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
438 52, 257415, 3612834, H01L 2100
Patent
active
061597627
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for manufacturing micromechanical sensors, particularly absolute pressure sensors, that are preferably manufactured in the framework of a CMOS process and are arranged on a substrate as a micromechanical component.
2. Description of the Related Art
Capacitative pressure sensors are utilized for measuring absolute pressure. A closed chamber having a reference pressure is terminated by an elastic membrane that is exposed to an external pressure. The electrically conductive membrane, together with the side of this chamber that lies opposite, forms a plate capacitor. The membrane is deformed due to the pressure difference between the external pressure and the internal reference pressure. The capacitance of this capacitor changes due to the changed distance between the membrane and the backside of the chamber acting as a cooperating electrode that, for example, can be formed by a doped region produced in semiconductor material. The external pressure can be identified from this change in capacitance. Such an arrangement is disclosed, for example, by U.S. Pat. No. 5,095,401. One problem in the manufacture of such pressure sensors in the framework of a CMOS process derives in that, after the cavity provided under the membrane has been etched out, this cavity must be closed and the closure layer provided therefor is applied at a pressure of more than 10 mbar. The gas enclosed in the cavity therefore has too high a pressure, this having a negative influence on the sensitivity and temperature stability of the sensor. The relatively dense gas in the cavity heats too greatly given existing membrane oscillations and thereby falsifies the measured result. A corresponding difficulty occurs given encapsulated acceleration sensors wherein a moveable micromechanical mass part is arranged in a cavity that is closed off from the outside.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a manufacturing method for a micromechanical sensor implementable in the framework of a CMOS processor wherein the aforementioned problem does not arise.
This object is achieved with the method comprising the steps:
a) a second layer or layer sequence is applied onto a first layer or layer sequence provided for the manufacture of cavity;
b) using a mask, recesses having a size dimensioned for the following steps c) and d) are produced in the second layer in the region of the projection of the cavity to be manufactured that is perpendicular relative to the layer planes;
c) upon employment of these recesses, a cavity is etched out in the first layer or layer sequence;
d) a closure layer is applied onto the second layer such that the recesses are closed without filling up the cavity;
e) at least one of the recesses in the second layer is re-opened at least to such an extent that the cavity is opened; and
f) this recess is re-closed with a material that differs from the material of the closure layer, so that the cavity is closed.
An improvement of the method provides that the closure layer applied in step d) is composed of borophosphorous silicate glass. In step f, a metal sputtering and/or a deposition of a dielectric ensues. The step f is implemented such that a gas enclosed in the cavity thereafter resides under a pressure of at most 2000 Nm.sup.-2 at room temperature.
Preferably, an electrically conductively doped region is produced at an upper side of a substrate of semiconductor material before step a and the first layer or layer sequence is produced thereover;
in step a, the second layer or layer sequence is produced at least partially electrically conductively; and
in step e, via holes for electrical contacting of the second layer and of the doped region are simultaneously produced.
In step a, the second layer is applied as membrane layer for an absolute pressure sensor;
in step b, the recesses are arranged such that at least one of these recesses is present in a portion of the membrane layer that is not provided f
REFERENCES:
patent: 5095401 (1992-03-01), Zavracky et al.
patent: 5596219 (1997-01-01), Hierold
patent: 5760455 (1998-06-01), Hierold et al.
Howe, "Surface micromachining for microsensors and microactuators", J. Vac. Sci. Technol., 1988 American Vacuum Society, pp. 1809-1813.
Japanese abstracts, Publication No. 01013773, Publication Date Jan. 18, 1989.
Hierold Christofer
Naher Ulrich
Scheiter Thomas
Chaudhari Chandra
Christianson K
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