Electricity: measuring and testing – Using ionization effects – For monitoring pressure
Reexamination Certificate
2001-01-29
2003-02-04
Oda, Christine (Department: 2858)
Electricity: measuring and testing
Using ionization effects
For monitoring pressure
C324S459000, C313S293000
Reexamination Certificate
active
06515482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns an ionization vacuum gauge, and in particular a hybrid ionization vacuum gauge which incorporates another measurement part into an ionization vacuum gauge.
2. Description of Related Art
In various conventional semiconductor manufacturing systems and electronic device manufacturing systems which employ high vacuums, upon system startup, during maintenance, and as conditions for various processes, pressure measurements must be performed over a wide range ranging from atmospheric pressure to high vacuum regions. Diverse vacuum gauges are used selectively in different measurement applications.
In general, a Pirani vacuum gauge or other thermal conduction vacuum gauge, quartz friction vacuum gauge, or rotation-type viscosity vacuum gauge other vacuum gauge based on gas transport phenomena is used in high-pressure regions (low vacuum regions) from approximately 1 Pa to 10
5
Pa. For pressure measurements during processes, diaphragm-type vacuum gauges are primarily used in response to demands for ease of pressure control and high accuracy. On the other hand, in low-pressure ranges (high vacuum ranges) of 1 Pa or below, ionization vacuum gauges, of which the Bayard-Alpert ionization vacuum gauge (hereafter called “B-A ionization vacuum gauge”) is representative, are widely used. In addition, hybrid type vacuum gauges, which combine a vacuum gauge for measurements in high-pressure regions (low vacuum regions) with a vacuum gauge for measurements in low-pressure regions (high vacuum regions), have been developed as vacuum gauges to perform pressure measurements over a broad range extending from atmospheric pressure to high vacuum regions.
As an example of such a hybrid type vacuum gauge, Japanese Patent Application Laid-open No. 62-218834 discloses a vacuum gauge in which a quartz friction vacuum gauge used for measurements in high-pressure regions (low vacuum regions) from approximately 1 Pa to 10
5
Pa, and a B-A ionization vacuum gauge used for measurements in low-pressure regions (high vacuum regions) of 1 Pa or lower, are installed on the same flange.
The structure and principle of operation of this vacuum gauge are explained referring to FIG.
4
and FIG.
5
.
FIG. 4
is a cross-sectional diagram showing the structure of an ionization vacuum gauge of the prior art;
FIG. 5
is a block diagram showing the control circuitry of an ionization vacuum gauge of the prior art.
This vacuum gauge installs a B-A ionization vacuum gauge and a quartz friction vacuum gauge on a common flange
2
b
, connected by an O-ring
5
to the vacuum vessel
1
. The B-A ionization vacuum gauge part consists of three electrodes, namely an ion collector
8
, filament
3
, and grid
4
; each is connected to a current introduction terminal mounted on the flange
2
b
. The installed quartz friction vacuum gauge consists of a quartz oscillator
18
, connected to the current introduction terminal mounted on the flange
2
b
, and a quartz oscillator vessel
19
.
Pressure regions of 10
−1
Pa or lower are measured using the B-A ionization vacuum gauge.
In low-pressure regions (high vacuum regions), when a positive grid voltage is applied to the grid
4
while simultaneously heating the filament
3
by passing a current, thermal electrons are emitted from the filament
3
toward the grid
4
. Before arriving at the grid
4
, these thermal electrons are accumulated within the grid
4
while undergoing oscillating motion in the vicinity of the grid, and collide with residual gas molecules within the vacuum vessel, which are ionized to create positive-charged ions.
When a thermal electron finally arrives at the grid
4
, an emission current flows between the filament
3
and grid
4
. On applying to the ion collector
8
a voltage (negative voltage) opposite the filament potential, positively-charged ions are captured by the ion collector
8
, and consequently an ion current flows into the ion collector
8
. At this time, if the voltages applied to each electrode are held constant and the emission current is fixed, then the density of thermal electrons undergoing oscillating motion in the vicinity of the grid
4
is constant. Hence the quantity of ions created is proportional to the concentration of gas molecules within the vacuum vessel
1
and therefore proportional to the pressure, so that by measuring the magnitude of the ion current flowing into the ion collector
8
, the pressure within the vacuum vessel
1
can be measured.
On the other hand, pressures in the region from 1 Pa to atmospheric pressure are measured using a quartz friction vacuum gauge.
The oscillator vessel
19
is of a construction which envelops the quartz oscillator
18
. Hence charged particles and thermal radiation emitted from the B-A ionization vacuum gauge are blocked, and adhesion of evaporated and sputtered material on the quartz oscillator
18
is prevented. The aperture part
50
exposes the quartz oscillator
18
to the gas pressure within the vacuum vessel
1
.
When a constant AC voltage is applied to the quartz oscillator
18
to cause oscillation at a resonance frequency, the resistive component of the AC impedance changes with the gas pressure. Hence by measuring the resistive component of the AC impedance, the pressure within the vacuum vessel
1
can be measured.
Next, the operation of this vacuum gauge is explained, referring to FIG.
5
.
The filament
3
of the B-A ionization vacuum gauge is connected to pins
12
a
and
12
b
, the ion collector
8
is connected to pin
9
, and the grid
4
is connected to pin
10
. The lead wires
21
of the quartz oscillator
18
are connected to pins
22
a
and
22
b
. A power supply for filament operation (abbreviated to “FOPS”)
27
is connected to the pins
12
a
and
12
b
via a filament shutoff switch (FSS)
39
, to heat the filament
3
and cause emission of thermal electrons. When it is confirmed that the pressure within the vacuum vessel
1
, measured by means of the quartz oscillator
18
, has reached a prescribed pressure, the filament shutoff switch
39
is turned on, the power supply for filament operation
27
supplies a current to the filament
3
, and the B-A ionization vacuum gauge is operated. The collector potential power supply (CPPS)
51
is connected to pin
9
, and by holding the collector potential at, for example, −50 V, ions which have been generated are collected. An ion collector ammeter (ICA)
33
is connected between the collector potential power supply
51
and ground, to measure the ion current value. The ion current is converted into a pressure by the ion current-pressure conversion circuit (ICPCC)
34
, and the result is displayed on a display device (DD)
25
. The grid potential power supply (GPPS)
29
is connected to pin
10
, to maintain a positive voltage (for example, +150 V) at the grid
4
. As a result, thermal electrons emitted from the filament
3
can be captured.
A phase-locked loop (PLL) circuit
36
is connected between pins
22
a
and
22
b
, to cause stable oscillation of the quartz oscillator
18
at a characteristic frequency. A resonance voltage signal corresponding to the resonance impedance is converted into a pressure value by a resonance impedance-pressure conversion circuit (RIPCC)
37
, and the result is displayed on the display device
25
.
The control circuit (CC)
38
is connected to the resonance impedance-pressure conversion circuit
37
; when it is detected that the pressure measured by the quartz oscillator
18
has fallen below a prescribed value (for example, 1 Pa), a control signal is sent to the filament shutoff switch
39
and to the pressure display device
25
. As a result of toggling of the filament shutoff switch
39
by this control signal, the B-A ionization vacuum gauge operation is switched, and a wide range of pressures, from atmospheric pressure to high vacuum, is measured.
However, the conventional technology described above has problems such as the following.
As a first problem, by combining a B-A ionization vacuum
Anelva Corporation
Burdett James R.
Kerveros James C.
Oda Christine
Venable
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