semi合集-English.pdf - 第123页

SEMI E16-90 © SEMI 1990, 2004 2 the actual leak rate is to be reported, th e sensitivity shall be five times smaller than the leak to be measured. If the sensitivity is not fiv e times smaller, the actual leak rate may b…

100%1 / 7923
SEMI E16-90 © SEMI 1990, 2004 1
SEMI E16-90 (Reapproved 1104)
GUIDELINE FOR DETERMINING AND DESCRIBING MASS FLOW
CONTROLLER LEAK RATES
This guideline was technically approved by the Global Gases Committee and is the direct responsibility of
the North American Gases Committee. Current edition approved by the North American Regional Standards
Committee on July 11, 2004. Initially available at www.semi.org September 2004; to be published
November 2004. Originally published in 1990, last published June 1999.
1 Purpose
1.1 The purpose of this guideline is to establish a
uniform, worldwide means for describing and
measuring leak rates of mass flow controllers. The leak
integrity of a gas delivery system is important to
maintaining product quality and performance. This
guideline is intended to prevent confusion and
misunderstanding between manufacturers and users. In
particular, it distinguishes between mechanical and
diffusion leak rates.
2 Scope
2.1 This guideline contains definitions of terms and
procedures for determining the Leak Rates of mass flow
controllers as used in the semiconductor industry.
NOTICE: This standard does not purport to address
safety issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety and health practices and determine
the applicability of regulatory or other limitations prior
to use.
3 Terminology
3.1 Definitions
3.1.1 leak a path or paths in a sealed system which
will pass helium when a partial pressure differential
exists. A partial pressure differential can exist for
helium even though a total gas pressure differential may
not exist. There are two major leak mechanisms, a
mechanical passage or a material through which gas can
diffuse or permeate. In a real system, a leak may have
both mechanisms operating in parallel.
3.1.1.1 A mechanical leak may be a physical crack, pit,
scratch or other imperfection in a sealing surface, or
contamination or debris on the seals. A diffusion or
permeation leak is caused by the movement of helium
through gaskets, O-rings, polymers, or other materials
through which helium can diffuse.
3.1.2 measured leak rate the leak rate of a given
system measured under specified conditions and
employing a specified test gas (helium). For the
purposes of comparison with rates determined by other
methods of testing, measured leak rates must be
converted to equivalent standard leak rates.
3.1.3 sensitivity (minimum detectable leak rate) the
smallest standard leak rate that an instrument, method
or system is capable of measuring under specified
conditions.
3.1.3.1 For the purposes of this document, the
Measured Leak Rate shall be corrected to Standard
Leak Rate by multiplying by the ratio of 101.32 kPa to
the absolute value of the pressurizing helium unless
otherwise called for by the MFC specifications.
RateLeak Standard
Pressure Actual He
kPa32101RateLeak Measure
.
3.1.4 standard leak rate the quantity of helium at
25C and 101.3 kPa (760 Torr) flowing through a leak
when the high pressure side is at 101.32 kPa and the
low pressure side is below 100 Pa (approximately 1
Torr). Standard Leak Rate shall be expressed in the
following units:
Pa-m
3
/s (He) = “Pascal cubic meters per second,
helium”
or, alternatively,
atm-cc/s (He) = “atmospheric cubic centimeters per
second, helium”
3.1.4.1 The “mass spectrometer helium leak detector”
is generally used for leak rate testing of high and
medium level vacuum apparatus. Units of sccs, Torr-
L/s, and m bar-L/s, have been used in the past but are
not encouraged. Reference materials include MIL
STD-202E, C-1.
NOTE 1: The Pascal (1Pa = 1 N/m
2
) is defined as the
pressure unit of the international unit system SI. Therefore,
the SI units above are preferred. Atm-cc/s is acceptable, as it
is widely used in the semiconductor industry.
4 Testing
4.1 General Requirements
4.1.1 Leak Detector The leak detector shall be of
the helium mass spectrometer type. It shall have
sensitivity at least equal to or smaller than the specified
leak rating of the mass flow controller to be tested. If
SEMI E16-90 © SEMI 1990, 2004 2
the actual leak rate is to be reported, the sensitivity shall
be five times smaller than the leak to be measured. If
the sensitivity is not five times smaller, the actual leak
rate may be reported if the sensitivity of the detector is
also reported.
4.1.2 Helium must have access to all primary seals.
4.1.3 Connections between the MFC and the leak
detector must be leak-tight.
4.1.4 The ambient temperature of the MFC should be
25 ± 5C unless otherwise specified. If another test
temperature is used, it must be recorded during the test.
4.2 Test Procedures There are two basic setups
which may be used to measure the leak rate from the
external environment to the internal gas passages of the
MFC or from the internal passages to the external
environment. Results for either test method may be
reported. The method used must be reported as well. A
third test, the through-the-valve setup, is intended to
measure the quality of the valve seat shutoff.
4.2.1 Internally-Pressurized Leak Test The purpose
of this test set-up is to simulate operation of the MFC
under conditions where the internal pressure is above
ambient. The recommended internal pressure is 300
kPa absolute (30 psig) of helium (see Figure 1).
Regulator
Pressure Gauge
Helium
Temp
MFC
Leak Tight Enclosure
Pressure
Leak Rate
Mass Spec.
Gauges and
Vacuum Pumps
Leak Detector
Figure 1
Internally-Pressurized Leak Test
4.2.2 Externally-Pressurized Leak Test The purpose
of this test is to simulate operation of the MFC under
conditions where the internal pressure is at vacuum.
The external pressure should be equal to atmospheric
pressure. The internal pressure should be less than 100
kPa (see Figure 2).
Regulator
Pressure Gauge
Helium
Temp
MFC
Leak Tight Enclosure
Pressure
Leak Rate
Mass Spec.
Gauges and
Vacuum Pumps
Leak Detector
Figure 2
Externally-Pressurized Leak Test
4.2.3 Control Valve Seat Leak Test The purpose of
this test is to determine the leakage through the control
valve under simulated operation in the closed control
mode. The MFC should be electrically energized for
normal operation and placed in the closed position as
specified for the operation of the MFC. The input
pressure to the MFC should be 100 kPa ± 20%. The
outlet should be connected directly to the helium leak
detector, and pressure should be as low as possible
using good leak detector practice (see Figure 3).
Regulator
Pressure Gauge
MFC
Pressure
Leak Rate
Mass Spec.
Gauges and
Vacuum Pumps
Leak Detector
Helium
Figure 3
Control Valve Seat Leak Test
4.2.3.1 In the case of MFCs which are not designed for
positive shutoff at the control valve, alternative
methods may be employed if documented and reported.
4.3 Reporting Results The example shown in Figure
4 is a plot of leak detector output value vs. time for a
representative elastomer-sealed MFC. This curve is the
sum of mechanical and permeation leak components.
NOTE 2: All times are from application of helium, starting
with a leak detection system pumped down to base reading.
SEMI E16-90 © SEMI 1990, 2004 3
Interval Rate Example
t1 Initial System Response Less than 10 seconds
t2 Leak Prior to Onset of
Permeation
w1 10 seconds to 1 minute
t3 Increasing Permeation 1 minute to 30 minutes
t4 Total Saturation w2 Beyond 30 minutes
Figure 4
Leak Detector Output Value vs. Time
4.3.1 The actual shape of these curves and time
intervals is dependent on the design of the MFC under
test, the elastomer used, if any, and the characteristics
of the leak detection system. These time intervals must
be determined using sound engineering judgment
following qualification testing of the specific MFC
model and test set-up. Once determined, it is
recommended that receiving inspection consist of
measuring for leak rate value w1 at the end of interval
t2.
4.3.2 Following qualification testing, report typical
values for t1 through t4 and w1 and w2. w1 is primarily
the mechanical portion of the leak, and w2 is
mechanical plus permeation. In the case where w2 is
significantly greater than w1, w2 is primarily
permeation. In the case of a gross mechanical leak, w1
could greatly exceed, and thereby mask, w2.
NOTE 3: This test must be performed with elastomers that
are devoid of helium. Such elastomers have either not been
previously exposed to helium or have been degassed
following exposure. Once this test has been performed, the
elastomers must be purged of helium by the passage of time
and/or baking.
4.3.3 In good leak testing practice, the background
level should be verified before the application of helium
to ensure that the elastomers are in a helium degassed
state and that the leak detecting system is in proper
operation.
NOTICE: SEMI makes no warranties or
representations as to the suitability of the standards set
forth herein for any particular application. The
determination of the suitability of the standard is solely
the responsibility of the user. Users are cautioned to
refer to manufacturer's instructions, product labels,
product data sheets, and other relevant literature,
respecting any materials or equipment mentioned
herein. These standards are subject to change without
notice.
By publication of this standard, Semiconductor
Equipment and Materials International (SEMI) takes no
position respecting the validity of any patent rights or
copyrights asserted in connection with any items
mentioned in this standard. Users of this standard are
expressly advised that determination of any such patent
rights or copyrights, and the risk of infringement of
such rights are entirely their own responsibility.
Copyright by SEMI® (Semiconductor Equipment and Materials
International), 3081 Zanker Road, San Jose, CA 95134. Reproduction of
the contents in whole or in part is forbidden without express written
consent of SEMI.