Capacitive vacuum sensor

Details Capacitive vacuum sensor Capacitive vacuum sensor

2001-03-09

2003-07-29

Noori, Max (Department: 2855)

Measuring and testing

Fluid pressure gauge

Diaphragm

C073S724000

Reexamination Certificate

active

06598483

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum sensor, and more particularly to a capacitive vacuum sensor that can measure the degree of vacuum over a wide range, wherein the vacuum sensor comprises a single vacuum sensor device that includes a non-conducting substrate, a plurality of fixed electrodes mounted on the non-conducting substrate, and a diaphragm electrode formed by a plurality of elastic structures each having a different square area and mounted to face opposite each respective one of the plurality of the fixed electrodes.
2. Description of the Prior Art
When electronic components or semiconductor devices are manufactured, the thin film deposition or etching process that is proceeded within the vacuum equipment is indispensable. During the process, the vacuum equipment is usually to be maintained at a constant internal pressure. Typically, this internal pressure may be measured by using a capacitive vacuum sensor that provides the capability of measuring the pressure precisely, regardless of the kind of gases employed.
An example of the capacitive vacuum sensor that is currently commercially available includes a diaphragm electrode that is formed by a single elastic structure. The range of pressures that can be measured by this type of vacuum sensor is limited to those pressures having the magnitude of up to three (3) figures. This is the limit of the existing capacitive vacuum sensor, because the single elastic structure can only be deflected slightly in the lower pressure range, and the change in the capacitance can only occur slightly in response to such slight deflection of the elastic structure. Thus, the vacuum sensor cannot detect such a slight change in the capacitance in the lower pressure range. In the higher pressure range, on the other hand, the elastic structure of diaphragm electrode cannot be deflected in proportion to any change in the pressure, and any change in the capacitance cannot be detected. Thus, the pressure range in which the existing capacitive vacuum sensor can respond to any change in the pressure is limited.
Specifically, one example of the conventional capacitive vacuum sensor is shown in
FIG. 4
, which is described in U.S. Pat. No. 5,515,711. As shown in
FIG. 4
, this sensor includes a reference pressure chamber
1
in which a reference pressure prevails. The reference pressure chamber
1
is partitioned from a region
3
leading to the vacuum equipment
2
by a diaphragm electrode
4
. A fixed electrode
5
is disposed to face opposite the central portion of the diaphragm electrode
4
. The diaphragm electrode
4
is deflected in response to any differential in the pressure between the reference pressure chamber
1
and the region
3
leading to the vacuum equipment
2
, as shown by dot-dash lines in FIG.
4
. When this occurs, the capacitance that develops between the diaphragm electrode
4
and the fixed electrode
5
may change in inverse proportion to the distance between the diaphragm electrode
4
and fixed electrode
5
. This change in the capacitance may be sensed by the vacuum sensor that provides an electrical signal that represents such change from an output terminal. This electrical signal may be fed via a conducting lead
9
to an electric circuit
7
incorporated in the vacuum sensor, where the change in the capacitance may be converted into the corresponding voltage or current. This voltage or current may appear at an output terminal
12
. Then, the current pressure may be determined from the voltage or current.
It is noted that the diaphragm electrode
4
may also be deflected by its own thermal expansion or contraction, which may occur when there is any change in the ambient temperature. This may introduce an error in measuring the actual pressures. To avoid this situation, the conventional capacitive vacuum sensor includes an additional compensation electrode
10
that is located to face opposite the diaphragm electrode
4
but is positioned off the central portion of the diaphragm electrode
4
. The function of the compensation electrode
10
is to cancel out the capacitance detected at the fixed electrode
5
by the capacitance detected at the compensation electrode
10
, and to ensure that the pressures can be measured accurately regardless of any change in the ambient temperature.
To describe this more clearly, the fixed electrode
5
is located opposite the diaphragm electrode
4
such that it is positioned in the central portion of the diaphragm electrode
4
, whereas the compensation electrode
10
is also located opposite the diaphragm electrode
4
but is positioned off the central portion of the diaphragm electrode
4
. Thus, when any change in the pressure occurs, and the corresponding change in the capacitance then occurs, the resulting capacitance change value that may be detected at the fixed electrode
5
will be greater than the value that may be detected at the compensation electrode
10
. When any change in the capacitance is caused by the thermal expansion or contraction, on the other hand, the resulting capacitance change value that may be detected at the fixed electrode
5
will be substantially equal to the value that may be detected at the compensation electrode
10
. Thus, the capacitance as detected at the fixed electrode
5
may be cancelled by the capacitance as detected at the compensation electrode
10
, so that any change in the capacitance that may be caused by the thermal expansion or contraction may be compensated. The conventional capacitive vacuum sensor is so designed that it can measure the pressures accurately as described above.
It is noted, however, that as the portion of the diaphragm electrode
4
that faces opposite the compensation electrode
10
is formed by the elastic structure, the change in the capacitance that may be detected at the compensation electrode
10
contains two components, that is, one component that corresponds to the change in the capacitance due to the change in the gas pressure and the other component that corresponds to the change in the capacitance due to the thermal expansion or contraction. Thus, if the capacitance as detected at the fixed electrode
5
is cancelled by the capacitance as detected at the compensation electrode
10
, the change in the capacitance caused by the change in the gas pressure may also be cancelled. This may degrade the ability or sensitivity of the vacuum sensor to any change in the pressure.
FIG. 5
illustrates another example of the conventional capacitive vacuum sensor that includes a diaphragm electrode based on the dual elastic structure. This capacitive vacuum sensor is built by using the micromachining technology (K. Hatanaka, D. Y. Sim, K. Minami and M. Esahi, Technical Digest of the 13th Sensor Symposium, pp. 37-40 (1995)). In this example, the diaphragm electrode
4
has some portions that are different in the thickness, and the dual elastic structure includes two different size elastic structures, that is, an elastic structure
8
that is 5 &mgr;m in thickness and is 2 mm×2 mm in size, and an elastic structure
18
that is also 5 &mgr;m in thickness but is 4 mm×4 mm in size. Those two elastic structures
8
,
18
are supported by a rigid structure
11
that is 200 &mgr;m in thickness. The diaphragm electrode
4
is mounted on the non-conducting substrate
13
under the vacuum condition. The vacuum sensor thus formed includes two reference pressure chambers
1
,
1
, one for the elastic structure
8
and the other for the elastic structure
18
. Getters
6
,
6
serve to adsorb any gases that remain in the respective reference pressure chambers
1
,
1
, keeping the reference pressure chambers
1
,
1
under high vacuum. A fixed electrode
5
is provided to face opposite the elastic structure
8
on the non-conducting substrate
13
, and another fixed electrode
15
is provided to face opposite the elastic structure
18
. The fixed electrodes
5
,
15
have the same dimensions as the corresponding elastic structures
8
,
18
.
Then, when there is

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