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SEMI F58-1000 © SEMI 2000 2 SEMI F33 — Method for Calib ration of Atmospheric Pressure Ioni zation Mass Spectrom eter (APIMS) 4.2 AST M Standards 1 ASTM-F1397- 93 — Standard Test Method for Determination of Moist ure Con…
SEMI F58-1000 © SEMI 20001
SEMI F58-1000
TEST METHOD FOR DETERMINATION OF MOISTURE DRY-DOWN
CHARACTERISTICS OF SURFACE-MOUNTED AND CONVENTIONAL
GAS DISTRIBUTION SYSTEMS BY ATMOSPHERIC PRESSURE
IONIZATION MASS SPECTROMETRY (APIMS)
This test method was technically approved by the Global Facilities Committee and is the direct responsibility
of the North American Facilities Committee. Current edition approved by the North American Regional
Standards Committee on August 28, 2000. Initially available on SEMI OnLine August 2000; to be published
October 2000.
1 Purpose
1.1 This document describes the p rocedure for
determination of the moisture dry-down characteristics
(quantity of removable moisture) of surface mounted
and conventional gas distribution systems (integrated
gas distribution systems). APIMS is currently the
method of choice for such dynamic tests because it is
the commercially available technique capable of ppt
moisture analysis with the fastest response time. This
test method may provide guidelines for the application
of other techniques with similar detection limits and
response time to APIMS which are not commercially
available at this time.
1.2 The results of this test can be u sed for qualitative
ranking of gas delivery based on the design. It can also
be used by a sufficiently sophisticated user as input for
numerical simulation of distribution system behavior.
2 Scope
2.1 This test method applies to all types of surface
mounted and conventional gas distribution systems
used in semiconductor processing.
2.2 Test Medium — The test proce dure will be carried
out in nitrogen. Other “inert” gases will have different
purging characteristics and may dry a system more
quickly or slowly. Reactive gases may react chemically
with moisture. Considerations relating to corrosion
resistance are outside the scope of the present
document, although the test procedure may prove useful
in corrosion studies. The results will provide a ranking
with respect to moisture contribution arising as a result
of differences in design, which may be applied with due
caution to systems intended for use in other gas
applications.
2.3 Operating Situations — Moist ure contribution
from a gas delivery system may be the result of
contamination arising in its manufacture, or from
subsequent exposure to ambient air or non-dry gas.
Thus, it is necessary to consider two main situations:
2.3.1 The “initial dry-down” situatio n, which is
determined by the moisture content of the components
in the system (as received) with the effects of
manufacturing process and design, surface quality, pre-
treatment and packaging convoluted together.
2.3.2 The “response to upset” situati on, which is
determined by the amount of moisture taken up by the
system and subsequently released in any exposure after
receipt.
2.4 Safety Issues — 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 limitations
prior to use.
3 Limitations
3.1 This test method allows the de termination of
moisture interactions which can be used, for example,
to rank systems in order of decreasing moisture
interaction. Because different degrees of moisture
interaction are permissible in different situations,
selecting the “best” system requires consideration of
how they will be used, either qualitatively or through a
numerical simulation of distribution system behavior.
The results of this test can only be used for qualification
for gas delivery systems based on different designs. It
cannot be used for production purposes and/or
certification/testing.
4 Referenced Standards
NOTE 1: As listed or revised, all documents cited shall be the
latest publications of adopted standards.
4.1 SEMI Standards
SEMI C15 — Test Method for ppm and ppb Humidity
Standards
SEMI F27 — Test Method for Moisture Interaction and
Content of Gas Distribution Systems and Components
by Atmospheric Pressure Ionization Mass Spectrometry
(APIMS)
SEMI F58-1000 © SEMI 2000 2
SEMI F33 — Method for Calibration of Atmospheric
Pressure Ionization Mass Spectrometer (APIMS)
4.2 ASTM Standards
1
ASTM-F1397-93 — Standard Test Method for
Determination of Moisture Contribution by Gas
Distribution System Components
5 Summary of Test Method
5.1 This test method consists of in itial drydown and
moisture input tests for both surface-mounted and
conventional gas delivery systems.
6 Terminology
6.1 Abbreviations and Acronyms
6.1.1 APIMS — Atmospheric Pressure Ionization
Mass Spectrometry.
6.1.2 EPSS — electropolished stain less steel.
6.1.3 ppm — molar parts per million (µmole/mole).
The same as ppmv.
6.1.4 ppb — molar parts per billion (nmole/mole). The
same as ppbv.
6.1.5 ppt — molar parts per trillion (p mole/mole). The
same as pptv.
6.1.6 slpm — standard liters per minute, the gas
volumetric flow rate measured in liters per minute at
0°C and 1 atm.
6.2 Definitions
6.2.1 baseline — an instrument response under steady
state conditions.
6.2.2 glove box — an enclosure that contains a
controlled atmosphere, usually inert.
6.2.3 induction time — the elapsed time between when
humidified gas is introduced to the test system and
when moisture is detected at the moisture analyzer. For
a test system which is perfectly transparent to moisture,
the induction time is equal to the residence time of the
gas in the system.
6.2.4 peak height — the maximum moisture
concentration recorded when a moisture input of pre-
defined length and concentration is introduced to a test
system.
6.2.5 response time — the time required for the test
system to reach steady state after a change in
concentration.
1 Available from American Society for Testing and Materials, 100
Barr Harbor Dr, West Conshohocken, PA 19428. Fax: 1-610-832-
9555. World Wide Web: http://www.astm.org.
6.2.6 test system — the gas delivery system under test
7 Required Equipment
7.1 APIMS — The APIMS used fo r moisture detection
can be of any type. Calibration of the APIMS shall be
performed as per SEMI F33, one at the beginning and
one at the end of the series. These calibrations shall
both be made under the same analytical conditions
(flow, pressures, plate voltages, etc.) as the tests and the
results shall be within 5% of each other. Provided this
condition is met, the interval between calibrations may
be left to the discretion of the operator; however, it is
suggested that calibration should be carried out
whenever the equipment is moved and/or every two
weeks of operation.
7.2 Dry Gas and Moisture Generator — A source of
extremely dry nitrogen (less than 200 ppt moisture) and
a moisture generator capable of delivering up to 13
slpm nitrogen doped with 200 ppb moisture is required.
This generator may be the same as used to calibrate the
APIMS. The output of the generator shall be verified
according to SEMI C15.
7.2.1 Most ultra-high purity gas panels are currently
fitted with metal gasket type connectors. The same type
of connector should, therefore, be incorporated into the
test bench for connection to the test system.
7.3 Test Blank — Any series of tes ts shall include the
results of testing a blank. The blank shall be the shortest
convenient length (no more than 1 m) of 1/4" EPSS tu-
bing with suitable fittings and/or adapters at either end
to enable it to be inserted in place of the test system.
7.4 Moisture Pulse Generator — A valve arrangement
capable of switching instantaneously between dry and
humidified nitrogen is also required. An example of
such a design is shown in Figure 1. In this design, flow
is maintained in both the humidified and dry gas lines at
all times. By simultaneously switching valves V
1
and
V
3
, or V
2
and V
3
, either humidified or dry gas is
directed through the test system while the other gas
stream is directed to vent. Note that there is a bypass
loop so that flow can be maintained to the APIMS when
the test system is removed. In this design, all gas lines,
but especially those lines between V
1
and V
3
and
between V
2
and V
3
, should be as short as possible and
constructed of EPSS tubing of high quality.
Maintaining gas lines at a constant temperature between
50 and 80ºC wherever possible is also recommended.
7.4.1 The bypass loop will contain a stagnant volume
of gas during testing. To avoid exposing the APIMS to
a large moisture upset whenever it is fed with the gas
contained in the bypass loop, the loop should be
thoroughly baked out (at ≥ 200°C) and protected from
atmospheric contamination thereafter. Valve V
4
should
SEMI F58-1000 © SEMI 20003
be such that some flow can be maintained through the
bypass loop and the test system simultaneously as well
as through each separately. Use of pneumatic valves to
facilitate rapid and simultaneous switching is
recommended.
7.4.2 Other arrangements than that s hown may also be
used. The moisture pulse generator should be designed
so as to give the fastest possible response of the blank
to a change in input moisture level.
7.5 Temperature Control and Measurement — A
stable temperature during the test is of critical import-
ance. The test system shall be kept at 30ºC. TESTS AT
DIFFERENT TEMPERATURES CANNOT BE
COMPARED. Ideally, the blank and test system should
be maintained in a temperature-controlled chamber.
However, if this is impractical, a heating tape can be
used. Temperature control should be to ± 1ºC. A
continuous record of temperature during the test shall
be maintained.
8 Procedure
8.1 Blank Tests — A blank test sha ll be carried out
after each calibration. If initial dry-down testing of
system is not of interest, the initial dry-down test of the
test blank may be omitted and the test blank brought to
equilibrium with zero gas in whatever manner is most
convenient, except that the test blank should not be
heated above 200ºC. Permanent changes in moisture
interaction have been observed at temperatures above
this level.
8.1.1 Initial Dry-down — Start the experiment with the
blank in place of the test system and a flow of dry gas
through the APIMS. The APIMS output should be at
equilibrium with the lowest moisture level of interest,
and in any case no higher than 200 ppt.
8.1.1.1 Switch the gas flow to pass pri marily through
the bypass loop while maintaining a small flow through
the test blank. Remove the test blank completely from
the system. If a glove box or other such enclosure is
used, do not remove the test blank from the glove box.
Immediately reconnect the test blank to V
4
, leaving it
disconnected from V
5
. Allow dry nitrogen to flow
through the test blank for five minutes to purge the air
from inside before reconnecting to V
5
. Switch the gas to
flow only through the blank and not through the bypass
loop. The APIMS will show an increase in moisture
concentration. Record the APIMS output until it
reaches 800 ppt or 48 hours, whichever is less.
8.1.1.2 Repeat the above test twice for a total of three
data sets.
8.2 Tests on Actual Test System
8.2.1 Initial Dry-down — This porti on of the test is
designed to determine the quantity of removable
moisture on the wetted surfaces of the system in the
condition in which it is typically supplied. Thus, the
results of this test will reflect, by design, any
precautions which the supplier has taken to remove
moisture and maintain its dryness during shipping.
8.2.1.1 Start the test as in Section 8.1. 1. The test
system should not be unpacked until after the APIMS
has equilibrated with the background moisture level. If
a glove box or other such enclosure is used, unpack the
system in the glove box. Switch the dry nitrogen flow
to pass through the bypass loop while maintaining a
small flow through the test blank. Bake the sample line
to APIMS at 170°C for 10 min and the APIMS ion
chamber at 150°C for 10 min. Undo the final layer of
packing and any shipping caps or plugs on the system at
this point. Remove the sample blank and connect the
test system to valve V
4
as quickly as possible. Ensure
that the gas lines going to APIMS will be under N
2
purge during the removal of test blank and installation
of test system. Allow the dry nitrogen flow to purge out
any ambient air in the system for five minutes, then
connect the system to V
5
. Switch the gas to flow (1.2
slpm) only through the test system and not through the
bypass loop. The APIMS will show an increase in
moisture concentration. Record the APIMS output until
it reaches 200 ppt or for 24–48 hours, whichever is less.
8.2.1.2 After 24–48 hours, the initial d ry-down part of
the test can be terminated. Remove the filters from the
test system and install special spool pieces. This is done
since filters have a large surface area and would
dominate the dry-down performance.
8.2.2 Moisture Input Test — Flow 1 .2 slpm of dry
nitrogen gas (200 ppt moisture) through appropriate
process channels of the test system. Connect the outlet
of the gas panel to the sample line connecting to the
APIMS. Bake the appropriate process channels using
heater tapes at 60°C for 12 h to remove atmospheric
contamination.
8.2.2.1 At the conclusion of baking, equilibrate the test
system to 30°C. Bake the sample line at 170°C for 10
min and ion source of APIMS at 150°C for 10 min.
Perform a leak check at the inlet and outlet connections
of the test system using 1% methane gas in nitrogen,
after warming up the APIMS for 30 min. Switch the
input gas to nitrogen with 200 ppb moisture (by
switching valves V
1
, V
2
, and V
3
simultaneously, if the
arrangement shown in Figure 1 is used) while recording
the APIMS response. Maintain this input for 20 min
and then switch the input gas to dry nitrogen (200 ppt
moisture) and monitor the dry-down.