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SEMI E67-0304 © SEMI 1997, 2004 1 SEMI E67-0304 TEST METHOD FOR DETERMININ G RELIABILITY OF MASS FLOW CONTROLLER This test method was technically approved by the Global Gases Committee and is the dire ct responsibility o…
SEMI E66-1103 © SEMI 1997, 2003 14
A2-1.4 The degrees of freedom (dof) is n
1
+ n
2
- 2. For example, if n
1
= n
2
= 8, then dof = 14.
A2-2 Interpretation
A2-2.1 If |t| > t
.975
, then the two means are significantly different at the 95% level. If |t| > t
.995
, then the two means
are significantly different at the 99% level (e.g., by “95% confidence,” it is meant that the difference/no-difference
decision based on the t-test will be correct 95% of the time).
t
.975
= 2.145 (2-sided)
t
.995
= 2.977 (2-sided)
NOTE:
• All readings are log particle counts, not particle counts.
• Since logs are used, zeros have to be replaced by positive values (e.g., 1/2).
• To determine t value for a particular confidence level and (dof), refer to any statistical reference book.
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SEMI E67-0304 © SEMI 1997, 2004 1
SEMI E67-0304
TEST METHOD FOR DETERMINING RELIABILITY OF MASS FLOW
CONTROLLER
This test method 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 December 4, 2004. Initially available at www.semi.org February 2004; to be published March
2004. Originally published September 1997.
1 Purpose
1.1 This document describes a method to help
determine the ability of an MFC to meet the
manufacturer’s published specifications over its life
time. The results of the test will also be useful in the
comparison of MFCs.
2 Scope
2.1 This procedure applies to MFCs used in
semiconductor gas systems.
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 procedure is to be used only in conjunction
with another existing parametric test for mass flow
controllers to obtain the reliability data for that
particular parametric test.
3.2 New MFCs shall be used for reliability testing. An
MFC that has been put through this test method may be
tested for reliability again.
3.3 In addition to this procedure, the parametric test
may also cycle the valve. These cycles should be
ignored for determining the cumulative cycles that are
described in the data table.
3.4 This test will not address root cause analysis of
failures.
3.5 Read points have been selected for this test
procedure so that the test will take approximately six
months to complete. The read point schedule given is
only a suggested schedule and if the user feels that a
different read point schedule would better suit his
needs, this test method can still be used to obtain
reliability data.
4 Referenced Standards
4.1 SEMI Standards
SEMI E17 — Guideline for Mass Flow Controller
Transient Characteristics Tests
SEMI E66 — Test Method for Determining Particle
Contribution by Mass Flow Controllers
SEMI E69 — Test Method for Determining
Reproducibility and Zero Drift for Thermal Mass Flow
Controllers
SEMI F1 — Specification for Leak Integrity of High-
Purity Gas Piping Systems and Components
4.2 SEMASPECs
1
NOTE 1: The SEMASPECs noted here will be superceded by
the comparable SEMI documents when available.
90120391B-STD — SEMATECH Test Method for the
Determination of the Helium Leak Rate for Gas
Distribution System Components
92071220B-STD — SEMATECH Guide to Provisional
Test Methods for Mass Flow Controllers
4.3 Other Document
Nelson, Wayne, Applied Life Data Analysis, New
York, NY Wiley, 1982 (see Annex)
NOTICE: Unless otherwise indicated, all documents
cited shall be the latest published versions.
5 Terminology
5.1 Acronyms and Abbreviations
5.1.1 MFC — Mass flow controller
5.1.2 UHP — Ultra-high purity
5.2 Definitions
5.2.1 cycle — a repeating sequence of setpoints applied
to the MFC.
5.2.2 hard failure — a catastrophic mechanical failure
or electrical failure that results in an inoperable MFC,
1 SEMATECH, 2706 Montopolis Drive, Austin, TX 78741, USA
website: www.sematech.org.
SEMI E67-0304 © SEMI 1997, 2004 2
or a deviation from a user-defined specification that
results in a condition that makes the MFC inadequate
for the user’s process.
5.2.3 parametric test — the test method that deter-
mines the data for which reliability information is
sought (e.g., accuracy test or particle test, SEMI E66).
5.2.4 readpoint — cumulative cycles applied to the
MFC.
5.2.5 reliability — the probability that the equipment
will perform its intended function, within stated
conditions, for a specified period of time.
5.2.6 soft failure — failure that occurs when an MFC
no longer meets the manufacturer' s specification for the
parameter under test.
6 Summary of Test Method
6.1 The MFC is installed in a fixture capable of
applying and recording a number of flow cycles. When
the number of cycles specified in the readpoint schedule
is reached, cycling is suspended, parametric tests are
per-formed, and the cycling is resumed until either the
next readpoint is reached, or the MFC experiences a
hard failure. After the cycling is completed, the
parametric test data is analyzed to determine the
reliability of each parameter.
7 Significance and Use
7.1 This test provides an estimate of the reliability of a
mass flow controller. The results of the test will also be
useful in the comparison of MFCs. The data provided
by this test can help end users determine the reliability
of equipment that uses MFCs.
7.2 The following parameters and associated test
methods should be tested with this test method to obtain
reliability data:
Parameter Test Method
Particle Contribution SEMI E66
Reproducibility & Zero Drift SEMI E69
Helium Leak Rate SEMASPEC
90120391B-STD
Step Response SEMI E17
7.3 The following modifications to the preceding para-
metric test methods are suggested to abbreviate the time
required to complete the reliability test:
7.3.1 SEMI E66 (Particle Contribution) — Abbreviate
this test method to perform only the dynamic control
mode test. Perform Sections 12.1.3 and 12.1.7, and
eliminate Sections 12.1.2, 12.1.4, 12.1.5, 12.1.6, 12.1.8,
12.1.9, and 12.1.10. Refer to Sections 5.2.1
(Background), 5.2.3 (Dynamic), and Figure 5 (Particle
Test Flow Chart).
7.3.2 SEMI E69 (Reproducibility & Zero Drift) —
Omit Sections 12.1 and 12.2.
7.3.3 SEMI F1 (Leak Integrity) — The intent of the
reliability test method is to detect the development of
gross leaks in the DUT due to cycling of the DUT
valve. The inboard component leak test portion of this
standard should be performed.
7.3.4 SEMI E17 (Step Response) — No abbreviation is
necessary for this test. However, perform this test with
the modifications noted in the SEMATECH Guide to
Provisional Test Methods for Mass Flow Controllers,
SEMASPEC 92071220B-STD.
7.4 Change in the performance characteristics of the
MFC, as measured by the above tests, may also be
monitored and analyzed as indicative of drift.
8 Apparatus
8.1 In addition to the apparatus listed below, the user
must also acquire any apparatus required to perform the
parametric test for which reliability data is needed. (See
documents cited in Section 7.2.)
8.1.1 Power supply
8.1.2 NIST (or equivalent recognized standards
agency) — traceable flow calibration system
8.1.3 MFC control cables, as many as required in
Section 8.1.4
8.1.4 Mass flow controllers for controlling test flows in
addition to the DUT MFCs, as many as required for the
test setup
8.1.5 Cycling fixture
9 Materials
9.1 In addition to the materials listed below, the user
must also acquire any materials required to perform the
parametric test for which reliability data is needed. (See
documents cited in Section 7.2.) Since reliability data
for leak integrity is being sought, helium cannot be used
during the cycling procedure.
9.1.1 Source of nitrogen (99.999%)
10 Sampling, Test Specimens, and Test Units
10.1 Three MFCs are required for meaningful data
analysis. However, 20 to 30 MFCs are a recommended
minimum. A larger sample size provides a more precise
estimate of reliability.