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SEMI F27-0997 © SEMI 1997, 2003 3 6.4 Moisture Pulse Generato r — A valvi ng arrangement capa ble of swit ching rapidly between dry and humidifi ed nitrogen is also required . An example of su ch a design i s shown i n F…
SEMI F27-0997 © SEMI 1997, 2003 2
ambient air or non-dry gas. Thus, it is necessary to
consider two main situations:
1. The “initial dry-down” situation, which is
determined by the moisture content of the
component as received with the effects of
manufacturing process and design, surface quality,
pretreatment and packaging convoluted together.
2. The “Response to upset” situation, which is
determined by the amount of moisture taken up by
the component and subsequently released in any
exposure after receipt.
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 Limitations
3.1 This test method allows the determination of
moisture interactions which can be used, for example,
to rank components in order of decreasing moisture
interaction. Because different degrees of moisture
interaction are desirable in different situations, selecting
the “best” components requires consideration of how
they will be used in a given distribution system, either
qualitatively or through numerical simulation of
distribution system behavior.
4 Referenced Standard
4.1 SEMI Standard
SEMI C15 — Test Method for ppm and ppb Humidity
Standards
NOTICE: Unless otherwise indicated, all documents
cited shall be the latest published versions.
5 Terminology
5.1 Acronyms and Abbreviations
5.1.1 APIMS — Atmospheric Pressure Ionization Mass
Spectrometry
5.1.2 EPSS — Electropolished Stainless Steel
5.1.3 MFC — Mass Flow Controller
5.1.4 ppm — molar parts per million (µmole/mole).
The same as ppmv.
5.1.5 ppb — molar parts per billion (nmole/mole). The
same as ppbv.
5.1.6 ppt — molar parts per trillion (pimole/mole). The
same as pptv.
5.2 Definitions
5.2.1 induction time — the elapsed time between when
humidified gas is input to the test component and when
moisture is detected at the moisture analyzer. For a
component and test system which are perfectly
transparent to moisture the induction time is equal to
the residence time of the gas in the system.
5.2.2 peak height — the maximum moisture
concentration recorded when a moisture input of
predefined length and concentration is introduced to a
test component.
6 Required Equipment
6.1 APIMS — The APIMS used for moisture detection
can be of any type. In order to be considered valid, any
series of moisture tests shall reference two single point
calibrations, 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.
6.2 Dry Gas and Moisture Generator — A source of
extremely dry nitrogen (less than 100 ppt moisture) and
a moisture generator capable of delivering up to 13 slm
nitrogen doped with 50 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.
6.2.1 Most ultra-high purity components 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 components.
6.3 Test Blank — Any series of tests shall include the
results of testing a blank. The blank shall be the shortest
convenient length (no more than 1 m) of 1/4"
electropolished stainless steel (EPSS) tubing with
suitable fittings and/or adapters at either end to enable it
to be inserted in place of the test specimen.
SEMI F27-0997 © SEMI 1997, 2003 3
6.4 Moisture Pulse Generator — A valving arrangement capable of switching rapidly 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 specimen 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 specimen 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 80°C wherever possible is also recommended.
Figure 1
Moisture Test Schematic
6.4.1 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 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 be such that some flow can be
maintained through the bypass loop and the test specimen simultaneously as well as through each separately. Use of
pneumatic valves to facilitate rapid and simultaneous switching is recommended.
6.4.2 Other arrangements than that shown 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.
6.4.3 Use of a glove box or other such enclosure about the test specimen and adjacent piping, to minimize exposure
of the system to ambient contamination when removing and introducing the test specimen, will improve the
precision of moisture content measurements but not of moisture interaction measurements. Use of such an enclosure
is, therefore, left to the discretion of the operator.
6.5 Temperature Control and Measurement — A stable temperature during the test is of critical importance. The
test component shall be kept at 35°C. TESTS AT DIFFERENT TEMPERATURES CANNOT BE
COMPARED. Ideally, the blank and device under test should be maintained in a temperature-controlled chamber.
However, if this is impractical, heating tape can be used. Temperature shall be measured at 1 m intervals on tubing.
Measurement at one point is adequate for small components. Temperature control should be to ± 1°C. A continuous
record of temperature during the test shall be maintained.
7 Procedure
7.1 Blank Tests — A blank test shall be carried out after each calibration. If initial dry-down testing of components
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 200°C.
Permanent changes in moisture interaction have been observed at temperatures above this level.
SEMI F27-0997 © SEMI 1997, 2003 4
7.1.1 Initial Dry Down — Start the experiment with the
blank in place of the test specimen 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 500 ppt. The flow rate
through the test blank should be set according to the
Flow Table (see Table 1).
7.1.1.1 Switch the gas flow to pass primarily 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 500 ppt or for 24 hours, whichever is less.
7.1.1.2 Repeat the above test twice for a total of three
data sets.
7.1.2 Moisture Input Test — After the APIMS has
returned to equilibrium with its initial moisture level,
switch the input gas to 50 ppb moisture (by switching
valves V
1
, V
2
, and V
3
simultaneously, if the
arrangement of Figure 1 is used) while recording the
APIMS response. Maintain this moisture input for 20
minutes. Switch the input to the test blank back to dry
nitrogen and record the decease in moisture level until
the initial background is again reached.
7.1.2.1 Repeat the above test twice for a total of three
data sets.
7.2 Tests on Actual Specimen
7.2.1 Initial Dry Down — This portion of the test is
designed to determine the quantity of removable
moisture on the wetted surfaces of a component 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.
7.2.1.1 Start the test as in Section 7.1.1. The test
specimen 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
component in the glove box. Switch the dry nitrogen
flow to pass through the bypass loop while maintaining
a small component through the test blank. Undo the
final layer of packing and any shipping caps or plugs on
the component at this point. Remove the sample blank
and connect the test specimen to valve V
4
as quickly as
possible. Allow the dry nitrogen flow to purge out any
ambient air in the specimen for five minutes, then
connect the specimen to V
5
. Switch the gas to flow only
through the test specimen and not through the bypass
loop. The APIMS will show an increase in moisture
concentration. Record the APIMS output until it
reaches 500 ppt or for 24 hours, whichever is less.
7.2.1.2 After 24 hours, the dry-down part of the test
can be terminated. If necessary, the moisture level can
be reduced below 500 ppt by baking the component at
200°C or the maximum temperature allowed by the
manufacturer for six hours and/or purging at the highest
flow of dry gas available. If this is not sufficient to
reduce the moisture concentration below 500 ppt, the
test may be abandoned.
7.2.2 Moisture Input Test — After the APIMS has
returned to equilibrium with its initial moisture level,
switch the input gas to 50 ppb moisture (by switching
valves V
1
, V
2
, and V
3
simultaneously, if the
arrangement of Figure 1 is used) while recording the
APIMS response. Maintain this moisture input for 20
minutes. Switch the input to the test blank back to dry
nitrogen and record the decease in moisture level until
the initial background is again reached.
7.2.2.1 Repeat the above test twice for a total of three
data sets.
7.2.2.2 In case the moisture level recorded by the
APIMS does not reach 50 ppb within 20 minutes, an
additional test should be performed in which the
moisture input should be continued until equilibrium is
reached. Then switch the input to the test specimen
back to dry nitrogen and record the decease in moisture
level until the initial background is again reached.
This test should be repeated once (two data sets total).
7.2.3 Bake-Out Test — Heat component to maximum
bake temperature, according to manufacturer’s
specifications, for three hours. Allow it to return to
room temperature. Continue by repeating the moisture
input test, after baking, as in Section 7.2.2.
7.3 Temperature, Flow Rate, and Pressure
Specification — The recommended test pressure is 700
kPa (7 bar). However, lower test pressures are
appropriate for some models of APIMS. Also, the
maximum pressure rating of the test components should
not be exceeded. The component temperature shall be
maintained at 35 ± 1°C during the test.
7.3.1 In the case of tubing, the test shall be carried out
at a single flow determined by the tubing diameter
according to the following table. In the case of valves,
regulators, mass flow controllers (MFC’s), and passive
components (gauges, flow meters, and fittings), the test
will be carried out at a single flow determined by the
table according to the size of the connecting tube stubs.