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SEMI F38-1104 © SEMI 1999, 2004 1 SEMI F38-0699 (Reapproved 1104) TEST METHOD FOR EFFICIENCY QU ALIFICATION OF POINT-OF-USE GAS FILTERS This test method was technically reapproved b y th e Global Gases Com mittee and is …

12 Precision and Accuracy

12.1 Some variance in Roughness Average is to be

expected on a single surface from measurement to

measurement. No two measurements (as taken by

different operators, on different instruments, or at

different locations on the surface of a component) will

contain the same data points. Because different

instruments will acquire data points at different rates,

and evaluation lengths may differ, a typical Roughness

Average measurement can include hundreds to tens of

thousands of data points. Reported measurements on

the same surface can be expected to deviate up to 20%.

13 Related Documents

13.1 ANSI Standard

Y14.36  Surface Texture Symbols

13.2 BSI Standard

BS 1134  Assessment of Surface Texture, Part 1:

Methods and Instrumentation and Part 2: Guidance and

General Information

13.3 DIN Standard

DIN 4768  Determination of Surface Roughness

Values R

, R

max

with Electric Stylus Instruments

13.4 ISO Standard

ISO 4288  Rules and Procedures for the Mea-

surement of Surface Roughness Using Stylus

Instruments

13.5 JIS Standard

JIS B 0651  Instruments for the Measurement of

Surface Roughness by the Stylus Method

4 American National Standards Institute, Headquarters: 1819 L

Street, NW, Washington, DC 20036, USA. Telephone: 202.293.8020;

Fax: 202.293.9287, New York Office: 11 West 42nd Street, New

York, NY 10036, USA. Telephone: 212.642.4900; Fax:

212.398.0023, Website: www.ansi.org

5 British Standards Institution, 389 Chiswick High Road, London,

W4 4AL, United Kingdom, +44 (0)20 8996 9000, http://www.bsi-

global.com/

6 DIN Deutsche Institut für Normung, (DIN German Institut for

standardization e.V. ), Castle count road 6, 10787 Berlin, Germany,

+49 30 2601-0, +49 30 2601-1231, http://www2.din.de/

7 International Standards Organization, 1, rue de Varembé, Case

postale 56, CH-1211 Geneva 20, Switzerland, +41 22 749 01 11; Fax

+41 22 733 34 30, http://www.iso.org

8 Japanese Standards Association, 4-1-24 Akasaka Minato-ku,Tokyo

107-8440 Japan, +81-3-3583-8005, Fax: +81-3-3586-2014,

http://www.jsa.or.jp/default_english.asp

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

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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

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position respecting the validity of any patent rights or

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mentioned in this standard. Users of this standard are

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SEMI F37-0299 © SEMI 1999, 2004 3

SEMI F38-1104 © SEMI 1999, 2004 1

SEMI F38-0699 (Reapproved 1104)

TEST METHOD FOR EFFICIENCY QUALIFICATION OF POINT-OF-USE

GAS FILTERS

This test method was technically reapproved 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 August 16, 2004. Initially available on www.semi.org September 2004; to be

published November 2004. Originally published June 1999.

1 Purpose

1.1 The purpose of this document is to define a

comprehensive standard test sequence to qualify the

particle filtration efficiency achievable using Point-of-

Use (POU) gas filters.

2 Scope

2.1 This test method defines an evaluation method for

Point-of-Use filters of various media (e.g., metallic,

ceramic, and polymeric) typically used for filtering

inert and process gases in semiconductor applications.

Point-of-Use filters are designed to handle relatively

low flow rates (0.5 – 50 slm.) and moderately high

pressure drops. The filter housing and filtration

element are combined into one sealed and inseparable

unit.

2.2 This test method is intended to demonstrate the

ability of a Point-of-Use gas filter to equal or exceed a

specific particle filtration efficiency class when

challenged with a monodispersed aerosol in the size

range described in Section 6.6.

2.2.1 The efficiency class of the test method is defined

as the log reduction value (LRV), where LRV is the

Log [Input Concentration/System Background Level].

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 These test methods do not apply to gas filter

cartridges.

3.2 These test methods do not apply to bulk gas filters.

3.3 The various media (e.g., metallic, ceramic, and

polymeric) may have slightly different critical particle

sizes (most penetrating particle sizes). Therefore, many

challenge tests have to be performed over a range of

particle sizes to assure that the “worst case” challenge

has been performed.

3.4 The efficiency test is for steady state flow and

room temperature only. Comparison to efficiency in

pulsed flow, elevated temperature etc., will have to be

developed separately.

3.5 Statistical evaluation on the variability in efficiency

of a media type should be done with a valid sample

size. This evaluation is not within the scope of this test

method.

3.6 The upper concentration limit of the CNC as

specified by the manufacturer should not be exceeded.

Exceeding the CNC concentration will understate the

challenge concentration due to coincidence counting,

thus affecting filter efficiency calculations.

3.7 This is not intended as a method for precise

determination of filter efficiency. It is intended as a

means for determining if a filter has an efficiency equal

to or better than an approximate nominal value.

3.8 Commercially available radioactive neutralizers

have pressure limitations. Users should be aware of

these limits.

4 Referenced Standards

4.1 None.

5 Summary of Method

5.1 The test sequence consists of three steps:

5.1.1 Static background with filter.

5.1.2 Filter challenge with first monodispersed particle

size (see Section 6.6 for particle size test sequence).

5.1.3 Filter challenge with subsequent monodispersed

particle sizes.

6 Apparatus and Facility

6.1 Gas Source — Clean, dry gas (nitrogen or air) with

less than 0.5 ppm moisture and less than 0.5 ppm total

hydrocarbons.

6.2 Particle Detector — A condensation nucleus

counter (CNC) with a counting efficiency of 50% at

0.01 micron, as reported by the manufacturer, is

recommended to measure total particle concentration of

particles greater than 0.01 micron. The CNC must meet

SEMI F38-1104 © SEMI 1999, 2004 2

a background level as specified in Section 7.1.2.

6.3 Test Environment — Particle challenge testing does

not require a clean area. Testing in a Class 100 area is

recommended but not required. Refer to Section 6.7 for

installation precautions.

6.4 Configuration for Efficiency Test — One example

of the configuration is shown in Figure 1. The setup

shown in Figure 1 is intended only as a guideline. This

system consists of:

 an aerosol generation system,

 aerosol concentration detectors,

 an air flow measuring system,

 a filter pressure drop sensor, and

 the test filters.

6.5 Test Flow Rate — Maximum manufacturer’s rated

flow rate.

6.6 Challenge Particle Sizes — Experimentation of

various media (e.g., metallic, ceramic, and polymeric)

have resulted in most penetrating particle sizes ranging

from 0.05–0.11 micron.

6.6.1 Several monodispersed particle challenge tests

shall be done over a range of particle sizes so that

testing at the most penetrating particle size is

performed. An electrostatic classifier must be used to

produce a monodispersed challenge.

6.6.2 Due to the effects of particle loading in relation

to filtration efficiency, a clean filter should be used for

each particle size challenge. The differential pressure

across the test filter should be continuously monitored

to eliminate the possibility of particle loading. The

following particle increments are a guideline. Smaller

increments are achievable and are desirable.

6.6.2.1 Challenge Particle Size In Microns:

1 Rubow, K.L., C.B. Davis (1991) "Particle Penetration

Characteristics of Porous Metal Filter Media for High Purity Gas

Filtration", Proceedings of Institute of Environmental Sciences

Annual Technical Meeting

2 Rubow, K.L., and Liu, B.Y.H., Evaluation of Ultra-High Efficiency

Membrane Filters, Proceedings of the 30th Annual Technical

Meeting, Institute of Environmental Sciences, 1984.

3 Rubow, K.L., Liu, B.Y.H., and Grant, D.C., Characteristics of

Ultra-High Efficiency Membrane Filters in Gas Applications; Journal

of Environmental Sciences, May/June, 1988.

4 B. Gotlinsky, P. Conner, D. Capitanio, L. Johnson, and S. Tousi,

Testing of All-Metal Filters for High Purity Semiconductor Process

Gases, Proceedings of the 37th Annual Technical Meeting, Institute

of Environmentak Sciences, 1991.

 0.05

 0.07

 0.10

6.7 Sample Installation — Reasonable precautions

shall be taken when installing the test filter to avoid

particle contamination of the system from ambient.

These precautions may include, but are not limited to:

installation in a Class 100 laminar flow area,

installation in a purged glove bag or other controlled

ambient enclosure, use of a purge flow downstream of

the sample point so that all parts of the system are

under purge, isolation, or termination of the CNC

sample flow, and isolation of the isokinetic sampler

exhaust from ambient.

6.8 Customary practices shall be employed for the

design of the sampling system. This includes any

specialized equipment or procedures recommended by

the CNC manufacturer. Every effort should be taken to

minimize differences in the particle concentrations of

the sampling volume relative to the actual test volume.

Care should be taken to provide an adequate exhaust

length so that back diffusion of particles does not affect

background at 2 times the sampling flow rate. This

length will depend upon the particle concentration in

the ambient environment and on other factors.

6.9 Test Particle — Solid non-volatile particles.

Sodium chloride is recommended, but other particles

could be used such as polystyrene latex beads (PSL) if

sufficiently high concentrations can be generated.

7 Procedure

7.1 Static Background Test

7.1.1 Purge the system at a high velocity flush of 100

slm or the maximum flow rate that the system

components will allow.

7.1.2 Purge the system at test flow rate (Section 6.5).

Measure the particle concentration with clean gas to

determine the background concentration. The

background count is established when the counter has

sampled a minimum of 3 scf (85 sl), and the arithmetic

average during the last 3 scf (85 sl) of gas sampled is

<2 particles/scf (<0.07 particles/sl). The sample

interval shall be 1 minute in duration. Ensure that the

background counts are stable or decreasing. If

background cannot be achieved after 6 scf (170 sl) have

been sampled, there may be a problem with the counter

or test apparatus. Past experience has shown this to be

an adequate volume of gas to give a satisfactory low

level background particle counts.

7.2 Penetration Test