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SEMI E104-0303 © SEMI 2000, 2003 11 9.3.5.2 Zero Counting NOTE 14: The intent of this procedure is not to adjust the thresholds for the zero count ra te but to ver ify whether the LPPD is within its specification. 9.3.5.…

SEMI E104-0303 © SEMI 2000, 2003 10

9.3.3.5 Fixed velocity at the LPPD: v

= 1 m/s

(independent of line diameter at the LPPD).

9.3.3.5.1 Some LPPDs, e.g. a scanning LPPD for the

use inside a process chamber, require a different

velocity than 1 m/s for calibration. In such cases the

used aerosol velocity at the location of the LPPD shall

be reported in the calibration report form.

9.3.4 Initial Setup

9.3.4.1 Connect the aerosol generator to a supply of

filtered, dried, and compressed zero gas (see Figure 1).

Connect a dryer, neutralizer, and size separator (if

necessary) to the aerosol outlet of the particle generator.

If a dilution of the aerosol before the injection in the

calibration line is necessary, install a dilution stage

behind the size separator.

9.3.4.2 Connect the aerosol line to the calibration line.

Mount the LPPD under test behind the injection and

mixing device. Install the sample acquisition device and

the velocity or flow meter into the calibration line.

9.3.4.3 Connect a PHA to the sensor calibration output

if an appropriate built-in PHA is not available.

9.3.4.4 Before starting the following procedures, make

sure all instruments are turned on and allow a certain

time for warm-up and temperature stabilization.

9.3.4.5 Purge the aerosol line and the calibration line

with filtered and dried air for a minimum of 30 minutes.

9.3.4.6 Check the quality of the zero gas and the

condition of the calibration line using the RPC. Collect

counts for three one-minute periods and determine the

average number of particles reported in counts per

minute. The volume flow of the zero gas shall be

enough for correct operation of the RPC. Record the

cumulative particle count reported for the zero gas for

particles equal to and larger than the LDL of the LPPD

under test.

9.3.4.7 Clean the aerosol generator liquid reservoir and

fill it with clean diluent (particle-free deionized or

destilled water or Isopropanol). Run the aerosol

generator and adjust the pressure and flow rates as

recommended by the aerosol generator manufacturer.

Check the condition of the aerosol line using the RPC.

Collect counts for three one-minute periods and

determine the average number of particles reported per

liter of air. If the number exceeds 1 particle per liter air,

the diluent shall be refiltered before further use. The

average number of particles (counts per minute) should

be reported in the calibration report form.

9.3.4.8 Adjust the volume flow through the calibration

line for the stipulated aerosol velocity at the LPPD

under test.

9.3.4.9 Allow a certain time for stabilization of the

adjusted calibration parameters before any test is

performed.

9.3.5 Sizing LPPD

NOTE 11: For more information and background see

Appendix 2.

9.3.5.1 Size Calibration

NOTE 12: To define the calibration settings either the mode

or median of the voltage pulse distribution could be used. The

use of the modal procedure is common. The calibration report

form should identify the used method.

9.3.5.1.1 By running different monodisperse aerosols

(with v

and V´

= V´

+ V´

), size calibration is

performed. Begin with the largest particles for which a

calibration value is required. Select the particle size

range for which calibration is required. Be sure that the

particle concentration is low enough that predominantly

individual pulses are generated by the LPPD.

Accumulate enough data to avoid statistical errors. The

procedure is repeated for each particle size of interest.

Determine the average LPPD pulse voltage amplitude

with the PHA.

9.3.5.1.2 The mode of the voltage pulse distribution is

determined by the highest point in the distribution. If

the distribution is interfered with noise near the peak

and the peak is not well defined, the data should be

averaged and the peak of the averaged distribution

should be used defining the mode.

9.3.5.1.3 The median voltage is determined by defining

a “Region of Interest” (ROI) which includes the peak

representing the voltage pulses from single polymer

spheres. The PHA determines the total number of

pulses under this peak. The median voltage is that

voltage which devises the number of pulses in the

region such that half are greater and half are less than

the median.

NOTE 13: If the procedure is carried out for the smallest size

of which the LPPD is specified, record the noise level of the

LPPD. The average voltage for this size should be at least

10% higher than stated noise level voltage at which one noise

pulse occurs in one minute.

9.3.5.1.4 The particle size and the average voltage

should be reported in the calibration report form.

9.3.5.1.5 For calibration checks, a reference particle

counter (RPC) with a good sizing capability could be

used. The counting efficiency of the RPC is defined as

100% for the particle sizes used in test. The counts of

the RPC and the LPPD under test in the corresponding

channel should be normalized to a standard detection

area (mm

). The ratio of these counts (in %), the

employed particle size and the threshold settings should

be recorded in the calibration report form.

SEMI E104-0303 © SEMI 2000, 2003 11

9.3.5.2 Zero Counting

NOTE 14: The intent of this procedure is not to adjust the

thresholds for the zero count rate but to verify whether the

LPPD is within its specification.

9.3.5.2.1 By running zero gas (with v

and V´

= V´

)

through the system the zero count rate, specified by the

sensor manufacturer, is checked. The reference particle

counter is used to check the quality of the zero gas. The

minimum acceptable sample time is 10 minutes. The

sampling time shall be long enough to provide adequate

sampling statistics. The zero count rate (average counts

per minute) should be recorded in the calibration report

form.

9.3.5.3 Counting Efficiency

NOTE 15: The actual particle concentration is determined

with a reference particle counter with a 100% counting

efficiency for the employed particle size. It is important that

there are no differences between the concentration within the

detection area of the LPPD and the concentration monitored

by the RPC.

9.3.5.3.1 By running a monodisperse aerosol (with v

and V´

= V´

+ V´

), the maximum of detected

particles is counted. The ratio of the counts of the

LPPD standardized per mm

to the counts of the

reference particle counter per mm

detection area (in %)

for each particle size should be recorded in the

calibration report form.

9.3.5.4 Sensitivity

9.3.5.4.1 By running different monodisperse aerosols

(with v

and V´

= V´

+ V´

) with particle sizes at the

expected sensitivity where the counting efficiency is

between 40% and 60%, the sensitivity is verified. The

counts of the LPPD per mm

detection area compared

to the counts of the reference particle counter per mm

detection area (in %) should be determined. The

determined particle size shall have a counting

efficiency between 40% and 60% and should be

recorded in the calibration report form.

9.3.5.5 Particle Size Resolution

NOTE 16: The particle size shall be at least twice the lower

counting limit to ensure measurement of the entire

distribution and accurate characterization of the calibration

response curve below the particle size of interest. The

resolution is specified by the coefficient of variation (in %)

obtained by dividing the portion of the standard deviation of

the distribution σ

LPPD

that is contributed by the LPPD by the

mean size of the distribution d

9.3.5.5.1 Record the size d

and the standard deviation

d,p

of the used particles in the calibration report form.

By running a monodisperse aerosol (with v

and V´

V´

+ V´

), determine the standard deviation of the

observed particle distribution σ

p,LPPD

. To determine the

standard deviation of the pure sensor signal σ

V,LPPD

, a

pulse height analyzer can measure the voltage peaks at

the analog sensor calibration output. The portion of the

standard deviation of the distribution σ

LPPD

that is

contributed by the LPPD is calculated by the following

formula:

(

)()

, pdLPPDpLPPD

σσσ

−=

9.3.5.5.2 The value of the standard deviation of the

observed distribution σ

p,LPPD

, the standard deviation of

the sensor signal σ

V,LPPD

, and the coefficient of

variation (in %) should be recorded in the calibration

report form.

9.3.6 Non-Sizing LPPD

NOTE 17: For more information and background see

Appendix 2.

9.3.6.1 Zero Counting

9.3.6.1.1 See Section 9.3.5.2.

9.3.6.2 Counting Efficiency

NOTE 18: The actual particle concentration is determined

with a reference particle counter with a 100% counting

efficiency for the employed particle size. It is important that

there are no differences between the concentration within the

detection area of the LPPD and the concentration monitored

by the RPC.

9.3.6.2.1 By running a monodisperse aerosol (using the

smallest particles size which can be counted with v

and V´

= V´

+ V´

), the maximum of detected

particles is counted. The counts of the LPPD per mm

detection area compared to the counts of the reference

particle counter per mm

detection area (in %) and the

employed particle size should be recorded in the

calibration report form. These measurements should be

executed for the defined set of particle sizes including

one size no larger than 1.3 times the sensitivity limit as

specified by the manufacturer.

9.3.7 Interim Procedure

9.3.7.1 Between the settings of the separate thresholds

or the runs with different particle sizes, the system

should be purged with zero gas for a sufficient time.

The aerosol generator should be rinsed with clean

diluent for a sufficient time before adding new

suspension of particles with other size.

10 Calibration Report Form

10.1 The calibration report form shall contain the

following information:

10.1.1 General part:

• Date and time of calibration

• Name of the operator

• Manufacturer of the LPPD

• Model and serial number of the LPPD to be

calibrated (if sensor and counter are separate,

model and serial number for each)

• Size of the detection area (if detection area is

dependent on the particle size, all established

values)

• Model, serial number, manufacturer, and date of

last calibration of the reference particle counter

• Performance of the reference particle counter

(volume flow, sensitivity, zero count rate)

• Environmental conditions: temperature T

, relative

humidity RH, pressure p

• Quality of zero gas as measured with the reference

particle counter (counts per minute)

• Specifications of the particles used for calibration

(manufacturer, certified size and tolerance,

standard deviation σ

d,p

, coefficient of variation,

refractive index, lot number)

• Calibration parameters: particle concentration C

particle velocity v

at the location of the LPPD,

line diameter D

opening area A

of the probe

inlet for each particle size

• Calibration procedure: sizing or non-sizing

10.1.2 For sizing LPPD:

• Size calibration: value of the average voltage of the

different particle sizes, employed particle sizes,

mode or median method

• Size calibration check: values of the thresholds,

employed particle sizes, ratio of the normalized

counts in the corresponding channel (in %)

• Zero counting: value of the zero count rate

(average counts per minute), sampling time

• Particle size resolution: value of coefficient of

variation, value of standard deviation of the

observed distribution, mean size of the distribution,

value of standard deviation of the sensor signal,

employed particle sizes

• Counting efficiency: value of the counting

efficiency (in %), employed particle sizes

10.1.3 For non-sizing LPPD:

• Zero counting: value of the zero count rate

(average counts per minute), sampling time

• Counting efficiency: value of the counting

efficiency (in %), employed particle sizes

10.2 Report significant variations from data reported

from the previous calibration.

11 Related Documents

NOTE 19: These publications related to particle

measurement, vacuum ISPM, and calibration are just

informative to improve understanding of these standard.

Raasch, J.; Umhauer, H.: “Errors in Determination of

Particle Size Distributions Caused by Coincidence in

Optical Particle Counters” Particle Characterization 3,

1990, 424-427

Jaenicke, R.: “The Optical Particle Counter: Cross

Sensitivity and Coincidence” J. Aerosol Sci., 30(5),

1972, 95-111

Borden, P.: “Monitoring Vacuum Process Equipment:

In Situ Monitors – Design and Specification”

Microcontamination, 1991, 43-47

Raabe, O.G.: “The Generation of Aerosols of Fine

Particles” Fine Particles, Ed. Liu, B.; Academic Press,

New York, 1976, 57-110