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SEMI F54-1000 © SEMI 2000 2 6 Summary of Method 6.1 The m easurement is performed u s ing aerosol standards consisting of N aCl particl es sus pended in air. Aeros ols are produced by nebulizing a solu tio n of Na Cl in …

SEMI F54-1000 © SEMI 20001

SEMI F54-1000

TEST METHOD FOR MEASURING THE COUNTING EFFICIENCY OF

CONDENSATION NUCLEUS COUNTERS

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 July 13, 2000. Initially available on SEMI OnLine August 2000; to be published

October 2000. Previously published June 2000.

1 Purpose

1.1 Particle specifications for gases require the use of

condensation nucleus counters (CNCs) having specified

counting efficiencies. This document provides the test

method for determining the counting efficiencies of

CNCs.

2 Scope

2.1 This document provides the method for 1)

generating an aerosol standard consisting of sodium

chloride (NaCl) particles having sizes 0.01 micrometer

and larger suspended in air at atmospheric pressure (1 ×

Pa), 2) controlling the size and concentration of

particles in the aerosol, and 3) using the aerosol to

determine the counting efficiency of a CNC as a

function of particle size. This method is suitable for

CNCs having a lower size sensitivity of 0.01

micrometer or larger.

NOTE

1: Suitable test methods for calibrating optical particle

counters are contained in ASTM F328 and JIS B 9921.

2.2 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 document does not provid e the method for

adjusting the CNC’s counting efficiency.

3.2 This document does not provid e the method for

determining the CNC

’s background noise level,

maximum concentration limit, or maximum detectable

particle size.

4 Referenced Standards

4.1 ASTM standards

ASTM D1193 — Standard Specification for Reagent

Water

1 American Society of Testing and Materials, 1916 Race Street,

Philadelphia, PA 19103, USA

ASTM F328 — Standard Practice for Calibration of an

Airborne Particle Counter Using Monodisperse

Spherical Particles

4.2 JIS standard

JIS B 9921 — Japanese Industrial Standard, Light

Scattering Automatic Particle Counter

NOTE 2: As listed or revised, all documents cited shall be the

latest publications of adopted standards.

5 Terminology

5.1 aerosol electrometer — an instrument that

converts the charge flow in an aerosol stream to an

electrical current signal.

5.2 aerosol standard — an aerosol containing particles

of a known size and concentration.

5.3 coincidence error — the inaccuracy in a measured

particle concentration caused by multiple particles in

the optical sensing volume of an instrument.

5.4 concentration limit — the maximum concentration

of particles in an aerosol to avoid a coincidence error of

10% or greater in an instrument.

5.5 counting efficiency — the ratio of the

concentration of particles reported by the CNC to that

reported simultaneously from the same aerosol by a

reference instrument.

5.6 lower size sensitivity — the particle size

corresponding to 50% counting efficiency for the CNC.

5.7 monodisperse aerosol — an ae rosol having a

narrow distribution of particle sizes. The maximum

band width of a monodisperse aerosol is defined in

Section 8.7.

5.8 particle concentration — the number of particles

per unit volume in a gas.

5.9 polydisperse aerosol — an aerosol having a wide

distribution of particle sizes.

NOTE 3: Additional terminology is contained in ASTM F328

and JIS B 9921.

2 Japanese Standards Association, 1-24, Akasaka 4-chome, Minato-

ku, Tokyo 107, Japan

SEMI F54-1000 © SEMI 2000 2

6 Summary of Method

6.1 The measurement is performed using aerosol

standards consisting of NaCl particles suspended in air.

Aerosols are produced by nebulizing a solution of NaCl

in water. After drying and charge neutralization,

particles of the required size are extracted from the

aerosol using an electrostatic classifier (EC). The

concentration of particles in the resulting monodisperse

aerosol is then recorded by the CNC and compared to

that measured simultaneously by a reference

instrument. Examples of suitable reference instruments

are described in Section 8.8.

NOTE 4: This method has been shown to provide repeatable

results in tests performed in separate laboratories on similar

CNCs. Examples of these tests are found in Agarwal and

Sem

and Bartz, et al

7 Requirements

7.1 The reference instrument must have a proven

counting efficiency

of not less than 95% over the entire

range of particle sizes tested. Low counting efficiency

in the reference instrument results in an error in the

measured particle concentration. The counting

efficiency for the reference instrument must be checked

by the manufacturer against a calibrated standard, such

as a calibrated aerosol electrometer.

7.2 Coincidence error in either the CNC or the

reference instrument causes inaccuracy in the measured

particle concentration. The concentration limit for each

instrument must be obtained from the manufacturer’s

specifications. The particle concentration in the aerosol

standard must be kept below both concentration limits.

7.3 When an aerosol electrometer is used as the

reference instrument, the minimum detectable particle

concentration must be obtained from the manufacturer’s

specifications. A particle concentration below the

minimum detectable value will cause inaccurate results.

The particle concentration in the aerosol standard must

be kept above the minimum detectable particle

concentration.

7.4 The transport loss of particles from the EC to the

CNC, and from the EC to the reference instrument must

be checked. Any disparity in particle transport loss to

the two instruments will cause erroneous results. The

method for calculating the transport loss of particles in

3 Agarwal, J. K. and Sem, G. J. Continuous Flow, Single-Particle-

Counting Condensation Nucleus Counter. Journal of Aerosol

Science, 11: 343-357 (1980)

4 Bartz, H., Fissan, H., Helsper, C., Kousaka, Y., Okuyama, K.,

Fukushima, N., Keady, P. B., Kerrigan, S., Fruin, S. A., McMurry, P.

H., Pui, D. Y. H. and Stolzenburg, M. R. Response Characteristics for

Four Different Condensation Nucleus Counters to Particles in the 3-

50 nm Diameter Range. Journal of Aerosol Science, 16 (5): 443-456

(1985)

sample lines is found in Pui, et al

. The transport loss

must be calculated for each particle size tested. Record

all transport loss calculations.

7.5 When an aerosol electrometer is used as the

reference instrument, a correction must be made for

multiple charging of particles in the aerosol standard.

Multiple charging can cause substantial error when

measuring particles larger than 0.06 micrometer. The

correction factor for multiple charging must be obtained

from the manufacturer of the EC. An example of the

method for calculating the correction factor is found in

Liu and Pui

8 Apparatus

8.1 Atomizer — A sub-micrometer aerosol generator

capable of nebulizing a liquid solution. The atomizer

must be capable of producing a stable aerosol

containing particles as small as 0.01 micrometer after

drying.

8.2 Liquid Trap — A device which allows free

passage of an aerosol stream containing sub-micrometer

particles, but which removes the entrained liquid phase

by gravitational settling into a reservoir.

8.3 Diffusion Drier — A device which allows free

passage of an aerosol stream containing sub-micrometer

particles, but which dries the aerosol by diffusion of

water vapor into a surrounding desiccant medium. The

design flow rate of the diffusion drier must at least

match the output flow rate of the atomizer.

8.4 Aerosol Neutralizer — A bipolar charging device

which neutralizes aerosols by producing both positive

and negative air ions. The neutralizer must reduce the

charge on the particles to the Boltzmann equilibrium

level. The design flow rate of the neutralizer must at

least match the output flow rate of the atomizer.

8.5 Bypass Filter — A high efficie ncy point of use gas

filter. The design flow rate of the bypass filter must at

least match the output flow rate of the atomizer.

8.6 Mixing Vessel — A device which disperses

particles in a flowing aerosol by inducing turbulence.

8.7 Electrostatic Classifier (EC) — A device which

extracts particles from a polydisperse aerosol according

to their electrical mobility. The electrical mobility of a

particle depends upon its size and charge. The

EC must

extract a monodisperse aerosol standard having a

5 Pui, D. Y. H, Ye, Y. and Liu, B. Y. H. Sampling, Transport, and

Deposition of Particles in High Purity Gas Supply System.

Proceedings 9th ICCCS: 287-293, (1988)

6 Liu, B. Y. H. and Pui, D. Y. H. A Submicron Aerosol Standard and

the Primary, Absolute Calibration of the Condensation Nuclei

Counter. Journal of Colloid and Interface Science, 47 (1): 155-171

(1974)

narrow band width. The mobility band width of the

extracted aerosol must be no greater than 20% of the

mean particle mobility. The method for calculating

electrical mobility and mobility band width are found in

Liu and Pui

8.8 Reference Instrument — An instrument which can

measure the concentration of particles in an aerosol.

The calibration of the reference instrument must have

been checked against a calibrated standard within the

past 12 months. Calibration and maintenance records

for the reference instrument must be maintained.

Suitable reference instruments include aerosol

electrometers and CNCs having lower size sensitivities

below 0.01 micrometer.

8.9 Condensation Nucleus Counter (CNC) or

Condensation Particle Counter (CPC) — The particle

counter to be used in process gas particle

measurements, and for which the calibration check is

required. The CNC detects sub-micrometer particles

using nucleation and droplet growth of a super-

saturated working fluid.

8.10 Tubing — In order to minimize particle losses, all

tubing used to transport charged aerosol particles must

be constructed from electrically conductive materials

(e.g., stainless steel) and grounded.

9 Reagents and Materials

9.1 De-ionized or distilled water in accordance with

ASTM D1193, Type 1 is required to dissolve NaCl for

aerosol generation.

9.2 NaCl is required for aerosol generation.

9.3 A supply of dry, oil-free compressed air is

required to generate and transport aerosols in the

apparatus.

10 Preparation of Apparatus

10.1 The test apparatus is shown in Figure 1. The

particle concentration in the aerosol is controlled using

a bypass filter. If the flow rate of the monodisperse

aerosol from the EC is insufficient to supply the CNC

and reference instrument simultaneously, filtered air

must be added to the stream. The air must be added to

the aerosol upstream of a mixing vessel. If the flow

rate of the monodisperse aerosol from the EC is greater

than that required to supply the CNC and reference

instrument simultaneously, the excess aerosol must be

vented.

Compressed

Air

Liquid

Trap

Diffusion

Drier

Bypass Filter

for Dilution

erosol

Neutralizer

tomizer

Sheath Air

Excess Air Vent

Electrostatic

Classifier

Monodisperse

Reference

Instrument

Nucleus

Counter

Filtered

Mixing

Vessel

Filtered Make-Up Air

or Excess Aerosol Vent

erosol Standard

Condensation

Vent

ent

(CNC)

(EC)

Figure 1

Schematic Diagram of Test Apparatus