U.S. patent application number 14/443904 was filed with the patent office on 2015-11-12 for reference leak generating device and ultra-fine leak testing device using same.
This patent application is currently assigned to NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY. The applicant listed for this patent is NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY. Invention is credited to Kenta ARAI, Tokihiko KOBATA, Hajime YOSHIDA.
Application Number | 20150323408 14/443904 |
Document ID | / |
Family ID | 50775981 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150323408 |
Kind Code |
A1 |
YOSHIDA; Hajime ; et
al. |
November 12, 2015 |
REFERENCE LEAK GENERATING DEVICE AND ULTRA-FINE LEAK TESTING DEVICE
USING SAME
Abstract
There is provided a reference leak generating device capable of
precisely generating an ultra-fine reference leak. The reference
leak generating device adapted to be connected to an upstream side
of a measurement chamber includes a chamber connected to the
measurement chamber through an orifice or a porous plug having a
molecular flow conductance C and a pressure to establish molecular
flow conditions which are known in advance, and is characterized in
that a pressure p.sub.1 of testing gas to be introduced into the
chamber is precisely determined by using a static expansion method
once or more times, and a leak rate of a reference leak at the
pressure p.sub.1 is obtained in accordance with a product of C and
p.sub.1.
Inventors: |
YOSHIDA; Hajime;
(Tsukuba-shi, Ibaraki, JP) ; ARAI; Kenta;
(Tsukuba-shi, Ibaraki, JP) ; KOBATA; Tokihiko;
(Tsukuba-shi, Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND
TECHNOLOGY |
Tokyo |
|
JP |
|
|
Assignee: |
NATIONAL INSTITUTE OF ADVANCED
INDUSTRIAL SCIENCE AND TECHNOLOGY
Tokyo
JP
|
Family ID: |
50775981 |
Appl. No.: |
14/443904 |
Filed: |
November 12, 2013 |
PCT Filed: |
November 12, 2013 |
PCT NO: |
PCT/JP2013/080551 |
371 Date: |
May 19, 2015 |
Current U.S.
Class: |
73/1.58 |
Current CPC
Class: |
G01L 27/002 20130101;
G01M 3/007 20130101; G01M 3/26 20130101; B81B 2201/05 20130101;
B81B 7/0009 20130101; G01M 3/207 20130101 |
International
Class: |
G01L 27/00 20060101
G01L027/00; G01M 3/26 20060101 G01M003/26; B81B 7/00 20060101
B81B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2012 |
JP |
2012-254849 |
Claims
1. A reference leak generating device adapted to be connected to an
upstream side of a measurement chamber, comprising: a chamber
connected to the measurement chamber through an orifice or a porous
plug having a molecular flow conductance C and a pressure to
establish molecular flow conditions which are known in advance,
wherein a pressure p.sub.1 of testing gas to be introduced into the
chamber is precisely determined by a static expansion method of one
time or more, and is set so that testing gas flowing through the
orifice or the porous plug satisfies the molecular flow conditions,
and a leak rate of a reference leak at the pressure p.sub.1 is
obtained in accordance with a product of C and p.sub.1.
2. The reference leak generating device according to claim 1,
wherein the static expansion method is performed by expanding a
volume of testing gas from V.sub.0 to V.sub.0+V.sub.1 between a
second chamber of the volume V.sub.1 which is connected to the
upstream side of the measurement chamber and a first chamber of the
volume V.sub.0 which is connected to an upstream side of the second
chamber.
3. An ultra-fine leak testing device or an outgassing measurement
device comprising a reference leak generating section constituted
of the reference leak generating device according to claim 1, and a
fine leak measuring section, said fine leak measuring section
including a measurement chamber for measuring a leak or an
outgassing from a test piece, a partial pressure analyzer connected
to the measurement chamber, and an entrapment vacuum pump connected
to the measurement chamber and adapted not to trap testing gas,
said reference leak generating section comprising, on the upstream
side of the measurement chamber, the chamber connected to the
measurement chamber through the orifice or the porous plug having
the molecular flow conductance C and the pressure to establish the
molecular flow conditions which are known in advance, wherein the
pressure p.sub.1 of testing gas to be introduced into the chamber
is precisely determined by using the static expansion method once
or more times, and is set so that testing gas flowing through the
orifice or the porous plug satisfies the molecular flow conditions,
the leak rate of the reference leak at this time is obtained in
accordance with the product of C and p.sub.1, an increasing rate of
a partial pressure of testing gas is measured with the partial
pressure analyzer, and an increasing rate of an output signal of
the partial pressure analyzer is compared with the leak rate of the
reference leak to perform calibration.
4. The ultra-fine leak testing device or the outgassing measurement
device according to claim 3, wherein testing gas is inert gas such
as helium or the like.
5. An ultra-fine leak testing device or an outgassing/permeation
measurement device comprising a reference leak generating section
constituted of the reference leak generating device according to
claim 1, and a fine leak measuring section, said fine leak
measuring section including a measurement chamber for measuring a
leak or an outgassing from a test piece, a partial pressure
analyzer connected to the measurement chamber, and a kinetic vacuum
pump connected to the measurement chamber, said reference leak
generating section comprising, on the upstream side of the
measurement chamber, the chamber connected to the measurement
chamber through the orifice or the porous plug having the molecular
flow conductance C and the pressure to establish the molecular flow
conditions which are known in advance, wherein the pressure p.sub.1
of testing gas to be introduced into the chamber is precisely
determined by using the static expansion method once or more times,
and is set so that testing gas flowing through the orifice or the
porous plug satisfies the molecular flow conditions, the leak rate
of the reference leak at this time is obtained in accordance with
the product of C and p.sub.1, and a partial pressure of testing gas
in equilibrium conditions which is measured with the partial
pressure analyzer is compared with the leak rate of the reference
leak to perform calibration.
Description
TECHNICAL FIELD
[0001] The present invention relates to a reference leak generating
device and an ultra-fine leak testing device using the reference
leak generating device, and is used in, for example, an ultra-fine
leak testing for an MEMS package, a crystal oscillator, various
semiconductor packages, an infrared sensor package or the like, for
which a testing of a very fine leak rate has been required in
recent years.
BACKGROUND ART
[0002] Conventionally known Kr85 leak testing can be utilized for a
leak test up to 10.sup.-13 Pam.sup.3/s, but cannot be used in any
mass-production machine because radioactive isotopes are used.
[0003] Further, for an MEMS package, a test of an ultra-fine leak
of 10.sup.-13 Pam.sup.3/s or less is required. However, an existing
technology is not applicable for a highly reliable calibration, and
there is not any standard (reference) for calibration.
[0004] For example, in PTL1, there is described a leak gas
measuring device which uses a cryopump to measure a fine leak rate
from an inspection object filled with helium gas. However, this
device is not provided with any calibration means.
[0005] Additionally, as a national standard of a leak rate in
helium leak testing, 10.sup.-10 Pam.sup.3/s of National Institute
of Standards and Technology (NIST) is minimum. A helium reference
leak having a leak rate of 10.sup.-11 Pam.sup.3/s by extrapolation
of this standard is sold from U.S. corporations or the like.
Therefore, measurement in the range of 10.sup.-10 Pam.sup.3/s to
10.sup.-11 Pam.sup.3/s or less in helium leak testing is an
extrapolation value, and has a low reliability.
[0006] In addition, at present, a calibrated helium standard leak
is attached to a helium leak testing device. However, since
one-point calibration is performed, a linearity of a measuring unit
cannot be confirmed.
[0007] On the other hand, the present inventors have previously
filed applications relating to a calibration method and a
calibration device of a microporous filter for standard mixed gas
leak (PTL2) and to a reference minute gas flow rate introduction
device using a microporous filter (PTL3), concerning the
microporous filter which becomes a molecular flow.
CITATION LIST
Patent Literature
[0008] PTL1: Japanese Unexamined Patent Publication No. 2004-184207
[0009] PTL2: Japanese Unexamined Patent Publication No. 2011-47855
[0010] PTL3: Japanese Unexamined Patent Publication No.
2012-154720
SUMMARY OF INVENTION
Technical Problem
[0011] Therefore, the present invention has been developed to solve
the above problems, and an object thereof is to provide a reference
leak generating device which, instead of an extrapolation value,
actually generates a reference leak of 10.sup.-11 Pam.sup.3/s or
less, and also provide an ultra-fine leak testing device in which
by use of the reference leak generating device, on the spot, a
reference leak is introduced into a measurement chamber of the leak
testing device to calibrate a partial pressure analyzer (a mass
spectrometer) which detects a leak, thereby achieving a high
reliability.
Solution to Problem
[0012] In order to solve the above problems, a reference leak
generating device according to the present invention introduces a
reference leak of 10.sup.-11 Pam.sup.3/s or less into a measurement
chamber or the like through an orifice, a porous plug or the like
having a molecular flow conductance C and pressure conditions to
realize a molecular flow which are known in advance. When
p.sub.1>>p.sub.2 is established where an upstream pressure of
the orifice or the porous plug is p.sub.1 and a downstream pressure
thereof is p.sub.2, a leak rate Q is a product of C and p.sub.1. By
making the upstream pressure p.sub.1 smaller, the ultra-fine leak
rate Q is generated. To precisely determine the upstream pressure
p.sub.1, a static expansion method is used once or several
times.
[0013] Further, the upstream pressure p.sub.1 is set so that
testing gas passing the orifice, the porous plug or the like
satisfies molecular flow conditions. When the molecular flow
conditions are established, C is a constant, which is beforehand
calculated or measured.
[0014] Additionally, the ultra-fine leak testing device according
to the present invention can directly calibrate a partial pressure
analyzer measuring the leak rate, by using the above reference leak
generating device to introduce the reference leak of 10.sup.-11
Pam.sup.3/s or less by testing gas into the measurement chamber of
the leak testing device. When the leak rate is about 10.sup.-11
Pam.sup.3/s, it is possible to carry out a test even while
discharging testing gas by means of a vacuum pump. Furthermore,
there is measured a partial pressure of testing gas when an
introduction flow rate and a discharge rate are equilibrated, to
measure the leak rate. In this case, even when any inert gas is not
used, it is possible to carry out the test.
[0015] However, in the case of the ultra-fine leak of 10.sup.-12
Pam.sup.3/s or less, a method of introducing testing gas into a
vacuum container which is sealed and maintained at a high vacuum to
store and measure testing gas is more advantageous in that a
measurement sensitivity is enhanced. In this case, an entrapment
vacuum pump such as a non-evaporable getter pump or a cryopump is
used as the vacuum pump, and inert gas (helium or the like) for
which the above entrapment vacuum pump does not have any discharge
ability is used as testing gas. When the reference leak is
introduced into a fine leak measuring section evacuated by the
above entrapment vacuum pump, testing gas is not discharged, and is
therefore accumulated in the vacuum container of the fine leak
measuring section. An increasing rate of the partial pressure of
testing gas is measured by means of the partial pressure analyzer.
An output signal of the partial pressure analyzer has a unit of A
(ampere), and hence the increasing rate of the partial pressure to
be obtained has a dimension of A/s. When the increasing rate is
compared with the reference leak having the known leak rate, the
dimension can be converted to a unit (Pam.sup.3/s, g/s, mol/s,
number/s, atm-cc/s or the like) indicating an absolute value of the
leak rate, and calibration can be performed.
[0016] Next, by a vacuum spray method, a vacuum hood method, a
pressure vacuum method (a bombing method) or the like, testing gas
released from a test piece is introduced into a vacuum device
evacuated by the same non-evaporable getter pump or cryopump, and a
partial pressure increase of testing gas at this time is measured
with the calibrated partial pressure analyzer, thereby measuring
the leak rate.
[0017] That is, the reference leak generating device according to
the present invention is a reference leak generating device adapted
to be connected to an upstream side of a measurement chamber, and
includes a chamber connected to the measurement chamber through an
orifice or a porous plug having a molecular flow conductance C and
a pressure to establish molecular flow conditions which are known
in advance, a pressure p.sub.1 of testing gas to be introduced into
the chamber being precisely determined by using a static expansion
method once or more times, and being set so that testing gas
flowing through the orifice or the porous plug satisfies the
molecular flow conditions, and a leak rate of a reference leak at
the pressure p.sub.1 being obtained in accordance with a product of
C and p.sub.1.
[0018] The present invention is also characterized in that in the
reference leak generating device, the static expansion method is
performed by expanding a volume of testing gas from V.sub.0 to
V.sub.0+V.sub.1 between a second chamber of the volume V.sub.1
which is connected to the upstream side of the measurement chamber
and a first chamber of the volume V.sub.0 which is connected to an
upstream side of the second chamber.
[0019] Further, the present invention provides an ultra-fine leak
testing device or an outgassing measurement device including a
reference leak generating section constituted of the above
reference leak generating device and a fine leak measuring section,
the fine leak measuring section including a measurement chamber for
measuring a leak or an outgassing from a test piece, a partial
pressure analyzer connected to the measurement chamber, and an
entrapment vacuum pump connected to the measurement chamber and
adapted not to trap testing gas, the reference leak generating
section comprising, on the upstream side of the measurement
chamber, the chamber connected to the measurement chamber through
the orifice or the porous plug having the molecular flow
conductance C and the pressure to establish the molecular flow
conditions which are known in advance, wherein the pressure p.sub.1
of testing gas to be introduced into the chamber is precisely
determined by using the static expansion method once or more times,
and is set so that testing gas flowing through the orifice or the
porous plug satisfies the molecular flow conditions, the leak rate
of the reference leak at this time is obtained in accordance with
the product of C and p.sub.1, an increasing rate of a partial
pressure of testing gas is measured with the partial pressure
analyzer, and an increasing rate of an output signal of the partial
pressure analyzer is compared with the leak rate of the reference
leak to perform calibration.
[0020] The present invention is also characterized in that in the
ultra-fine leak testing device or the outgassing measurement
device, testing gas is inert gas such as helium or the like.
[0021] Additionally, the present invention provides an ultra-fine
leak testing device or an outgassing/permeation measurement device
including a reference leak generating section constituted of the
above reference leak generating device and a fine leak measuring
section, the fine leak measuring section including a measurement
chamber for measuring a leak or an outgassing from a test piece, a
partial pressure analyzer connected to the measurement chamber, and
a kinetic vacuum pump connected to the measurement chamber, the
reference leak generating section including, on the upstream side
of the measurement chamber, the chamber connected to the
measurement chamber through the orifice or the porous plug having
the molecular flow conductance C and the pressure to establish the
molecular flow conditions which are known in advance, wherein the
pressure p.sub.1 of testing gas to be introduced into the chamber
is precisely determined by using the static expansion method once
or more times, and is set so that testing gas flowing through the
orifice or the porous plug satisfies the molecular flow conditions,
the leak rate of the reference leak at this time is obtained in
accordance with the product of C and p.sub.1, and a partial
pressure of testing gas in equilibrium conditions which is measured
with the partial pressure analyzer is compared with the leak rate
of the reference leak to perform calibration.
Advantageous Effects of Invention
[0022] According to the reference leak generating device of the
present invention, instead of an extrapolation value, a reference
leak of 10.sup.-11 Pam.sup.3/s or less can precisely be generated
on the spot, and according to the ultra-fine leak testing device of
the present invention, the reference leak can be introduced into
the leak testing device on the spot, to carry out a test while
confirming that measurement can be performed, thereby achieving a
high reliability.
[0023] Further, according to the ultra-fine leak testing device of
the present invention, instead of one-point calibration, it is
possible to carry out multipoint calibration, and hence a linearity
of a partial pressure analyzer (a mass spectrometer) which measures
a leak rate can be confirmed.
[0024] In addition, according to the ultra-fine leak testing device
of the present invention, any radioactive substance is not used, a
device constitution is not complicated, and hence the device can be
applied to a mass production machine.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is an explanatory view schematically showing a
reference leak generating device according to the present invention
and an ultra-fine leak testing device using the reference leak
generating device.
[0026] FIG. 2 is a view showing an embodiment of the reference leak
generating device according to the present invention and the
ultra-fine leak testing device using the reference leak generating
device.
[0027] FIG. 3 is a diagram for explaining first expansion of a
static expansion method.
[0028] FIG. 4 is a diagram for explaining second expansion of the
static expansion method.
[0029] FIG. 5 is a diagram showing, in double logarithmic scale, a
relation between an introduction flow rate and an increasing rate
when an expanding operation is repeated.
[0030] FIG. 6 is a diagram showing a ratio between the introduction
flow rate and the increasing rate when the expanding operation is
repeated.
[0031] FIG. 7 is a diagram showing the result of a leak inspection
of five cylindrical MEMS samples each having a diameter of 0.5 mm
and a length of 4 mm by use of the present invention.
DESCRIPTION OF EMBODIMENTS
[0032] FIG. 1 shows a schematic view of a reference leak generating
device according to the present invention, and an ultra-fine leak
testing device according to the present invention which uses the
reference leak generating device as a reference leak generating
section. As shown in the drawing, the ultra-fine leak testing
device has the reference leak generating section and a fine leak
measuring section. The ultra-fine leak testing device includes a
first chamber of a volume V.sub.0, a second chamber of a volume
V.sub.1, and a measurement chamber of a volume V.sub.2 Pressures of
the second chamber and the measurement chamber are represented by
p.sub.1, p.sub.2, and p.sub.0 is an initial pressure of testing gas
before expansion which is measured with a pressure gauge or a
vacuum gauge such as a capacitance diaphragm gauge when the testing
gas (an inert gas such as helium or the like) is introduced into
the first chamber.
[0033] By repeating a static expansion method (in which V.sub.0 is
expanded to (V.sub.0+V.sub.1)) in the reference leak generating
section constituting the reference leak generating section, the
pressure p.sub.1 can precisely be determined to a low pressure, and
Pi can precisely be determined in accordance with:
[0034] p.sub.1={V.sub.0/(V.sub.0+V.sub.1)}.sup.np.sub.0, in which n
is the number of times of expansion. At this time, the pressure
p.sub.1 is set so that the testing gas flowing through an orifice
or a porous plug satisfies molecular flow conditions.
[0035] Testing gas is introduced from the second chamber to the
measurement chamber of the fine leak measuring section through the
orifice or the porous plug in which a molecular flow conductance C
and a pressure to establish the molecular flow conditions are
clarified. C is calculated or measured in advance.
[0036] The pressure of the measurement chamber is measured with a
partial pressure analyzer (QMS or the like), and the measurement
chamber is evacuated by an entrapment vacuum pump (a non-evaporable
getter (NEG) pump, a cryopump or the like) which does not trap
testing gas. At this time, a reference leak rate
Q.sub.R(Pam.sup.3/s) from the second chamber to the measurement
chamber can be obtained in accordance with Equation (1).
Q.sub.R=Cp.sub.1=C{V.sub.0/(V.sub.0+V.sub.1)}.sup.np.sub.0 (1)
[0037] On the other hand, when a leak rate Q.sub.S (Pam.sup.3/s)
from a test piece is measured in the fine leak measuring section,
an ultra-fine leak is measured with the partial pressure analyzer.
At this time, impurity gas other than testing gas is trapped by the
non-evaporable getter pump, and the partial pressure analyzer is
set to be suitably operable, to measure only testing gas (helium or
the like). The reference leak rate Q.sub.R is compared with the
leak rate Q.sub.S from the test piece, to quantitatively measure
Q.sub.S. Helium gas is not trapped by the entrapment vacuum pump
such as the NEG pump or the cryopump, and hence a partial pressure
of testing gas monotonously increases and can therefore be obtained
in accordance with Equation (2).
Q.sub.S=V.sub.2(dp.sub.2/dt) (2)
An increasing rate of the helium partial pressure is measured with
the partial pressure analyzer. At this time, impurity gas released
from the chamber or the like is trapped by the entrapment vacuum
pump (the NEG pump, the cryopump or the like) which does not trap
testing gas, and therefore the partial pressure analyzer can
operate at a suitable pressure.
[0038] It is noted that an ultra-fine leak rate from the test piece
includes, for example, a leak of a filling gas (e.g., helium or the
like) from a gas filling package or the like, and an outgassing
from a material or the like.
EXAMPLE
[0039] FIG. 2 shows an embodiment of a reference leak generating
device according to the present invention, and an ultra-fine leak
testing device according to the present invention which uses the
reference leak generating device as a reference leak generating
section. Abbreviations in the drawing indicate QMS: a quadrupole
mass spectrometer, IG: an ionization gauge, NEG pump: a
non-evaporable getter pump, RP: a rotary pump, TMP: a turbo
molecular pump, DP: a dry pump, and a capacitance diaphragm gauge
(F.S. 133 Pa): a capacitance diaphragm gauge having a full scale of
133 Pa.
[0040] The device is divided into a first chamber of a volume
V.sub.0, a second chamber of a volume V.sub.1, and a measurement
chamber of a volume V.sub.2. The capacitance diaphragm gauge for
measuring a helium pressure before expansion is attached to the
first chamber, the IG for measuring a background pressure is
attached to the second chamber, and the QMS for measuring helium
and the NEG pump for trapping impurity gas other than helium are
attached to the measurement chamber.
[0041] The first chamber can be closed by using two front and rear
valves. The second chamber can be made in a closed state by closing
a valve 1, a valve 2 and a valve 3. Afterward, by opening the valve
1, helium stored in the first chamber is expanded to the second
chamber. The second chamber is connected to the measurement chamber
through a porous plug and the valve 3, and by closing the valve 3,
helium can be introduced from the second chamber into the
measurement chamber only through the porous plug.
[0042] Calibration of the QMS is performed in a state where the
valve 3 is closed. By helium flowing into the measurement chamber
through the porous plug, a helium partial pressure in the
measurement chamber increases, and hence an increasing rate of the
partial pressure is measured with the QMS. On the other hand, a
flow rate of helium flowing into the measurement chamber can
precisely be obtained in accordance with Equation (1):
Q.sub.R=Cp.sub.1=C{V.sub.0/(V.sub.0+V.sub.1)}.sup.np.sub.0.
Therefore, the partial pressure increasing rate of helium which is
measured with the QMS is compared with the introduction flow rate
of helium which is obtained in accordance with the above equation,
so that the QMS can be calibrated. During this calibration,
impurity gas released from a wall or the like in the measurement
chamber is trapped by the NEG pump, and therefore the helium
partial pressure measurement is not disturbed.
[0043] Next, leak testing of a test piece is carried out. As a
method of leak testing, a vacuum spray method, a vacuum hood
method, or a pressure vacuum method (a bombing method) is
applicable. During this testing, the valve 3 is beforehand closed
in the same manner as in the calibration. When there is a leak, the
helium partial pressure in the measurement chamber increases due to
helium leaking out from the test piece. From the increasing rate of
the helium partial pressure and the above calibration result, a
leak rate from the test piece can be measured. Since volumes of the
test piece and a connecting tube also have an influence on the
increasing rate of the helium partial pressure, these volumes
should be separately obtained in advance as required.
[0044] In FIG. 3, the result of first expansion is shown.
[0045] The valve 3 was closed to perform background
measurement.
[0046] The valve 2 was closed to expand He gas from a volume
V.sub.0 to V.sub.0+V.sub.1. At this time, an initial pressure
p.sub.0=114.22 Pa, a pressure p.sub.1 after the expansion=7.77 Pa,
and an expansion ratio=14.69, and He gas passed through the porous
plug to be stored in a volume V.sub.2.
[0047] The valve 1 was closed, the valve 2 was opened, the volume
V.sub.1 was evacuated, and He gas was not introduced into the
volume V.sub.2. Background measurement 2 was performed.
[0048] The valve 3 was opened, He gas stored in the volume V.sub.2
was pumped out, and a zero point was confirmed.
[0049] A leak rate of He gas was
Q.sub.R=3.04.times.10.sup.-9.times.7.77=2.36.times.10.sup.-8
(Pam.sup.3/s),
and the increasing rate (an inclination) of a He gas signal was
1.97.times.10.sup.-8 (A/s). At this time, a secondary electron
multiplier of the QMS was set to ON.
[0050] In FIG. 4, the result of second expansion is shown.
[0051] Similarly to the first time, the valve 3 was closed to
perform the background measurement.
[0052] The valve 2 was closed to expand He gas from the volume
V.sub.0 to V.sub.0+V.sub.1. At this time, an initial pressure
p.sub.0=7.77 Pa (P.sub.0 herein was used to indicate the pressure
of the first chamber before the second expansion), the pressure
p.sub.1 after the expansion=7.77/14.69=0.525 Pa, and He gas passed
through the porous plug to be stored in the volume V.sub.2.
[0053] The valve 1 was closed, the valve 2 was opened, the volume
V.sub.1 was evacuated, and He gas was not introduced into the
volume V.sub.2. The background measurement 2 was performed.
[0054] The valve 3 was opened, He gas stored in the volume V.sub.2
was pumped out, and the zero point was confirmed.
[0055] The leak rate of He gas was
Q.sub.R=3.04.times.10.sup.-9.times.0.525=1.06.times.10.sup.-9
(Pam.sup.3/s),
and the increasing rate (the inclination) of the He gas signal was
1.60.times.10.sup.-9 (A/s).
[0056] FIG. 5 is a graph in which the results obtained when the
expanding operation was repeated six times are plotted on double
logarithmic scale with the vertical axis indicating the increasing
rate (A/s) of the helium signal and the horizontal axis indicating
the introduction flow rate Q.sub.R (Pam.sup.3/s) of helium. It is
shown that the increasing rate of the He gas signal enlarges in
proportion to the introduced leak rate Q.sub.R. Similarly, there
are also plotted in FIG. 5 the results of the measurement in a
state where the secondary electron multiplier (SEM) of the QMS was
set to OFF. It is shown that an obtained ion current (A) becomes
smaller, but similarly, a proportional relation is obtained.
[0057] FIG. 6 is a graph in which the vertical axis indicates a
ratio (A/s)/(Pam.sup.3/s) between the increasing rate of the helium
gas signal and the introduction flow rate, and the horizontal axis
indicates the introduction flow rate Q.sub.R (Pam.sup.3/s) of
helium. It is shown that a relative ratio between Q.sub.R and the
increasing rate of the He gas signal is constant, i.e., results of
an introduction rate and a measurement rate are matched. This also
applies to the result of the measurement in the state where the
secondary electron multiplier of the QMS was set to OFF (the result
multiplied by 100 times is also plotted).
[0058] Therefore, an output signal of the partial pressure analyzer
has a unit of A (ampere), and hence the increasing rate of the
partial pressure to be obtained has a dimension of A/s, but when
the increasing rate is compared with the reference leak with the
known leak rate, the dimension can be converted to a unit
(Pam.sup.3/s, g/s, mol/s, number/s, atm-cc/s or the like)
indicating an absolute value of the leak rate, and this unit can be
utilized as a standard during the calibration process.
[0059] There will be described below the result of a leak
inspection of five cylindrical MEMS samples each having a diameter
of 0.5 mm and a length of 4 mm by use of the present invention. By
using a separate device, MEMS samples were exposed (subjected to a
bombing) in helium gas of three atmospheres for 94 hours after
evacuation. Subsequently, within 50 minutes after opening to the
atmospheric air, Each of the MEMS samples exposed in helium gas was
introduced into the test piece chamber shown in FIG. 2. After the
evacuation, the valve 3 was closed, and an increase of the He gas
signal was measured with the partial pressure analyzer. The result
is shown in FIG. 7. For comparison, there is also shown in FIG. 7
the results of two blank tests (the result when the MEMS sample was
not disposed in the test piece chamber) which were carried out
before and after the measurement of the MEMS sample. The secondary
electron multiplier of the QMS was set to OFF.
[0060] From FIG. 7, it is seen that the increasing rate of helium
obtained from a sample number 3D is clearly larger than those
obtained from the other sample numbers. This is because "a leak"
was present in the sample number 3D, helium gas permeated into the
MEMS during the process of being exposed in helium gas of three
atmospheres, and the penetrating helium gas was released again in
the device of FIG. 2. The increasing rate of helium is
2.88.times.10.sup.-13 A/s, and hence according to the calibration
result (FIG. 5), a size of the leak can quantitatively be
determined as 1.87.times.10.sup.-10 Pa/m.sup.3s. In the results of
the other four samples (1A, 2A, 4A and 5D), as compared with the
test results of the blanks, the increasing rate of helium became
slightly larger, but this is supposedly because helium gas
permeated into glass used in a sealing material of the MEMS.
Consequently, it has been confirmed that by use of the present
invention, a fine leak of order of 10.sup.-10 Pa/m.sup.3s can
easily, quantitatively be measured for an inspection time of about
60 seconds.
[0061] In the above description of the embodiment, the entrapment
vacuum pump is used and the case where helium is used has been
described. However, it is obvious that the present invention is
applicable to the case where another inert gas is used.
[0062] (Modification)
[0063] Further, the reference leak generating device according to
the present invention can be used in combination with a measuring
section in which a kinetic vacuum pump such as a turbo molecular
pump or the like is used instead of the entrapment vacuum pump. As
described above in paragraph 0005, when a leak rate is about
10.sup.-11 Pam.sup.3/s, it is possible to carry out a test while
pumping out testing gas by the vacuum pump, and there is measured a
partial pressure of testing gas when an introduction flow rate and
an effective pumping-out speed are equilibrated, so that the leak
rate can be measured. In this case, testing gas having a known flow
rate is introduced into the measuring section, and there is
measured the partial pressure of testing gas when the introduction
flow rate and the effective pumping-out speed are equilibrated, to
perform the measurement of the leak rate and calibration of a
partial pressure analyzer. In a method in which the kinetic vacuum
pump is used, even when gas other than inert gas is used, it is
possible to measure the leak rate, but a measurement lower limit
becomes higher as compared with the above method of the embodiment
in which the entrapment vacuum pump is used. When an outgassing or
gas permeation from a material or the like is measured, there is a
high possibility that gas other than inert gas is released, and
hence the kinetic vacuum pump is more suitably used.
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