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SEMI F55-0600 © SEMI 2000 3 10.2 Become familiar with the safe h a ndling practices associated with the corros ive gas bef ore undertaking this test. 11 Prepar ation of Apparatus 11.1 T he test apparatus is the sourc e o…

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SEMI F55-0600 © SEMI 2000 2
control valve. This output is sometimes called valve
voltage.
6 Summary of Method
6.1 Corrosive gas and moisture-containing N
2
are
alternately flowed through the DUT with intervening
dry N
2
purges. The test MFC is monitored over time
for changes in performance resulting from corrosion.
6.2 This test is intended to be an accelerated
simulation of the effects of alternating corrosive and
moisture-exposure conditions. The test records how
long it takes for corrosion to affect calibration. MFCs
that are more resistant to corrosion failures should last
longer under the test conditions. A dry N
2
purge
separates each MFC's exposure to the corrosive gas and
to the moisture-containing gas. This purging favors
MFC designs that perform well in corrosive service
because those MFCs can be dried out quickly with
limited purging.
6.3 This method is expected to yield data that can be
used to compare the relative performance of
components tested for the purpose of qualification.
7 Interference’s
7.1 Portions of the gas system exposed to HCl may
require replacement or cleaning and refurbishment
between test sequences to avoid invalidating subsequent
tests by prematurely contaminating DUTs. Take care in
the design and maintenance of the system so that
particles shed from upstream piping components as a
byproduct of corrosion are minimized so that they do
not affect the DUT.
8 Apparatus
8.1 Containment System to contain corrosive gas
leaks that may develop in the DUT or gas system. The
portion of the system that contains the corrosive gas
should be operated in a suitable secondary containment
environment.
8.2 Power Supply, Controls, and Data Collection
Devices capable of recording data 20 times per
second. Signals should be measured with a resolution
of one mV or better. Data may be recorded in
convenient units such as volts, sccm, or percent of FS.
For the purpose of analysis and reporting, data should
be converted to percent of FS except for valve drive,
which may be reported in either percent of maximum
drive or volts.
8.3 DUT
8.4 Data Acquisition System — Recommended as a
data collection system to facilitate test sequencing and
data collection.
8.5 Plumbing — with tubing and gas-switching valves
constructed from 316L electropolished stainless steel or
other material that exhibits superior corrosion resistance
compared to 316L. The use of materials such as
plastics, which retain or are permeable to water vapor,
are not appropriate. All-metal sealed valves (no
elastomers) are readily available and must be used.
8.6 The test plumbing is intended to represent the
technology level found in the semiconductor process
gas piping in which a typical DUT will operate.
8.7 A filter has not been specified immediately
upstream of the DUT because it would harbor
contaminates and make it difficult to alternate gas
types.
8.8 Dry N
2
Source — pressure regulated source with a
moisture level no greater than 50 ppbv.
8.9 Dry HCl Source — pressure regulated source with
a moisture level no greater than 500 ppbv.
8.10 Reference Flowmeter — traceable with
calibration certificate, calibrated for N
2
, FS flow 100%
to 125% of the FS N
2
equivalent flow range of the DUT
Accuracy better than 5%, linear to 0.5% FS repeatable
to 0.15% over a three-hour period, and reproducible to
0.3% of the test flow for the duration of the test .
NOTE 2: As this test is concerned with changes in DUT
calibration and not the value of DUT calibration itself, the
accuracy of the reference flowmeter is not paramount.
8.11 Moisture Generator to introduce water vapor
in a concentration of 100 ppmv (µl/l) ± 20% in N
2
.
8.12 Moisture Analyzer to periodically verify the
output of moisture generator.
9 Reagents and Materials
9.1 HCl
9.2 N
2
10 Safety Precautions
10.1 This standard may involve hazardous materials,
operations, and equipment. This standard does not
purport to address all of the safety problems associated
with its use. It is the responsibility of the user of this
standard to establish appropriate safety and health
practices and to determine the applicability of
regulatory limitations prior to use.
NOTE 3: The DUT will be contaminated with corrosive
material at the conclusion of this test. Caution should be
exercised in handling. A contaminated DUT should be
properly decontaminated.
SEMI F55-0600 © SEMI 20003
10.2 Become familiar with the safe handling practices
associated with the corrosive gas before undertaking
this test.
11 Preparation of Apparatus
11.1 The test apparatus is the source of three gases—
dry N
2
, dry HCl, and N
2
containing a known level of
water vapor. Each gas can be valved through the DUT
individually with minimal cross contamination. The
DUT actively controls the gas flow in each case. The
gas then flows into either a scrubbed exhaust system for
safe disposal or a reclamation system. A reference
flowmeter in the dry N
2
supply line is used to detect
changes in calibration of the DUT when dry N
2
is
flowing in series through both devices.
11.2 Setup and Schematic — See Figure 1 for a
schematic of the test apparatus. This schematic may
not show in detail all the components required in an
actual system.
11.3 Supply the manufacturer's reco mmended power
to the DUT. Provide MFC setpoint and purge
command (if available). Monitor the following:
11.3.1 DUT setpoint input.
11.3.2 DUT indicated flow output.
11.3.3 DUT valve drive output (if available)
11.3.4 actual flow (output of reference flowmeter)
11.4 Verify that the proper moisture levels exist in
each of the test gases.
11.5 Provide a purge flow loop that maintains a
constant flow of dry N
2
in the line from the DUT to the
exhaust system. Flow in this loop must be sufficient to
prevent back diffusion into the DUT of moisture
generated in the exhaust system, particularly when flow
into the DUT is shut off for measuring zero.
11.6 If the moisture generator is sup plied from the
same N
2
source that supplies the dry N
2
, take
precautions to avoid the diffusion of moisture from the
moisture generator into the dry N
2
line. Such
precautions may include the use of separate pressure
regulators and other valving.
11.7 Moisture generators typically take time to
stabilize. A continuous flow should be maintained
through the moisture generator during the test to
maintain a stable moisture flow. This may require
diverting the output flow to a vent when not flowing
through the DUT.
11.8 Periodically verify the moisture concentration of
wet N
2
with a suitable moisture analyzer.
11.9 Follow manufacturer set-up procedures for all
equipment.
11.10 Conduct the test at an ambient temperature of 22
± 2°C.
11.11 The DUT moisture generator, flowmeters, and
other instrumentation should have been stabilized at
room temperature for 24 hours before beginning the
tests. It is not necessary to flow gas during this
stabilization time.
11.12 All portions of the plumbing system that could
contain HCl must be helium leak tested per SEMI F1
before introducing HCl into the system. When
changing the DUT or other components, at least those
portions of the system that were changed must be re-
tested.
NOTE 4: Small leaks in a corrosive gas system can become
much larger without warning.
12 Calibration and Standardization
12.1 Calibrate all instrumentation using current
standards that are traceable to an appropriate standards
laboratory. In the absence of appropriate standards, use
manufacturer recommendations for calibration.
13 Procedure
NOTE 5: Refer to Figure 2 for a flowchart of the following
test.
13.1 Set the pressure of each of the HCl and Dry N
2
gas sources at 140 kPa ± 5%. Set the pressure of the
N2 to the moisture generator to the appropriate value
recommended by the manufacturer. If the test must be
run at some other pressure, because of a limitation of
the DUT, report this fact in the test results.
13.2 Start the wet N
2
flow to vent or through the
moisture analyzer. Establish a stable moisture
concentration at 100 ppmv ± 20% before beginning the
test sequence. Set the wet N
2
to flow within ± 5% of
the DUT flow that will be run during the test.
13.3 Place the DUT control valve in the purge or fully
open position by supplying a purge command or a
200% setpoint. Purge with dry N
2
at a rate of one to
two times FS flow for one hour to establish initial
conditions. The purge rate is controlled by adjusting
the supply pressure and is monitored by a purge-rate
flowmeter located in the gas-supply path. Follow the
manufacturer's procedure for fully opening the DUT
control valve.
13.4 Provide a setpoint to the DUT for 80 ± 5% of FS
flow.
13.5 Determining the Test Baseline and Measurement
Repeatability.
SEMI F55-0600 © SEMI 2000 4
NOTE 6: Data throughout this test may be recorded in a
format similar to that found in Table A1.1.
13.6 Open valve V1 and flow dry N
2
at a setpoint of
80% ± 5% of the DUT FS and wait 10 minutes.
13.7 Record:
13.7.1 DUT setpoint
13.7.2 DUT indicated flow
13.7.3 DUT valve drive output (if available)
13.7.4 Actual flow
13.8 Stop flow by closing V1. Drive the MFC control
valve to a closed position by providing a zero setpoint
or as otherwise provided by the manufacturer. Allow
the MFC indicated flow output to stabilize for a
minimum of three minutes.
13.9 Record the DUT indicated flow and the actual
flow during the zero flow condition.
13.10 Repeat Sections 13.6 through 13.9 twelve times.
This will yield 12 data points for each of the six
measured parameters.
13.11 For each of the six parameters recorded,
perform the following calculation on the 12 baseline
data points to determine the repeatability of the
measurement:
(highest value - lowest value) × 100
average of the 12 values
13.12 If each of the six parameters is not repeatable
within 0.2% during these two hours, subsequent test
data may not be valid and the problem should be
resolved before proceeding with the test.
13.13 Baseline
NOTE 7: Use the averaged value of the measurements made
in Section 13.13 for each parameter as the baseline for that
parameter in the following tests.
13.14 Test Sequence — Without changing the DUT
setpoint, repeat the test sequence in Sections 13.19-
13.22 every 30 minutes, continuously, 24 hours per day,
seven days per week until one of the following test
termination conditions is met.
13.15 The test should not be interrupted because the
DUT may continue to corrode during the interruption,
making test results non-repeatable. The output of the
moisture generator should be measured periodically
during the test sequence to ensure that it remains within
the test specifications.
13.16 Terminate the test sequence if:
13.16.1 The DUT fails to function
13.16.2 The actual-flow shift from baseline exceeds
25%
13.16.3 The valve drive exceeds the manufacturer's
limits
13.16.4 The DUT indicated flow differs from
commanded setpoint by > 5%
13.16.5 The test exceeds 5000 cycles
13.17 Flow dry N
2
for five minutes. After five
minutes, record data on the six test parameters as done
in Section 13.7, interrupting flow to record the DUT
indicated flow and reference flowmeter output at zero
flow. After taking measurements, flow dry N
2
again so
that the total length of this step is 10 minutes. Record
data as shown in Figure 3.
13.18 Flow dry HCl for seven minutes.
13.19 Repeat Section 13.19 and then proceed to
Section 13.22.
13.20 Flow wet N
2
for three minutes. If no test
termination condition is met as described in Section
13.18, repeat Sections 13.19 - 13.22. If a test
termination condition is met, proceed to Section 13.23.
13.21 After the test has been completed, place the
DUT control valve in the purge or fully open position.
Purge with dry N
2
for one hour or at least 50 volume
changes. Cycle the purge gas for 15 seconds on and 15
seconds off by opening and closing V1 for the duration
of the purge. Follow the manufacturer's procedure for
fully opening the DUT control valve.
NOTE 8: Verify purge flow with the reference flowmeter or
by using other means. Corrosion may have rendered the
control valve inoperable. An alternate approach for purging
any corrosive material from the system may have to be
followed.
13.22 Alternate Approach to Purging.
13.23 If gas cannot be purged through the DUT, cycle-
purge each end of the DUT separately using Sections
13.26 through 13.28.
13.24 With valves V2 and V3 closed for the duration
of the procedure, close valve V6 and pressurize both
sides of the system by opening V1 and V7 for 15
seconds.
13.25 Vent pressure through the exhaust system by
closing V1 and opening V6 for 15 seconds.
13.26 Repeat pressure and vent cycles for a minimum
of one hour.
13.27 Remove the DUT. Preserve the test system, if
desired, by taking steps to exclude atmospheric
moisture. Such steps could include capping the system
and shutting all valves. Alternately, the DUT may be