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SEMI E104-0303 © SEMI 2000, 2003 10 9.3.3.5 Fixed vel ocity at the LPPD: v L = 1 m/s (independent of line diam eter at the LPPD). 9.3.3.5.1 Som e LPPDs, e.g. a scanni ng LPPD for the use inside a process cha mber, requir…

SEMI E104-0303 © SEMI 2000, 2003 9

9.2.2.15 All instruments used for the reference calibration procedure shall have been checked for valid calibration

in accordance with ISO 10012-1 and 10012-2. Record all calibration data.

9.2.3 Setup and Schematic

9.2.3.1 See Figure 1.

Neutralizer

Dryer

Aerosol

Generator

ULPA

Filter

Compressed,

Dried Air

Dilution

Aerosol Size

Separator

PHA

Fan

ULPA

Filter

LPPD

Analog Output

Reference

Particle

Counter

Injection and

Mixing Device

V´

, C

, v

V´

Velocity or Flow

Meter and Control

Sample

Acquisition

Device

Figure 1

Calibration setup and schematic

9.3 Calibration Procedure

NOTE 10: Specific procedures for calibrating different

LPPDs can vary considerably not only between manufacturers

but between instrument models. For this reason, this

document cannot provide detailed procedures for calibrating

every LPPD. For detailed procedures for calibrating a specific

LPPD, contact the manufacturer. The calibration should be

performed by a skilled technician.

9.3.1 If the aerosol flow rate is varied, then particle

residence time in the detection area A

will also vary.

This results in pulses of varying duration. Therefore,

the particle velocity v

at the LPPD should be constant

and independent of the line diameter D

. The fan has to

be regulated so that the aerosol velocity at the velocity

meter is v

= v

/ D

. At a constant volume

flow rate V´

(depending on the pressure of the

compressed air) and constant number concentration C

the level of number concentration C

reaches a value

dependent on line diameter D

at constant velocity v

With the known detection area A

of the LPPD, the

number of particles per time (counts per mm

detection

area per time) is defined. The RPC monitors the number

of particles C

of the aerosol generator and the zero air

inside the line.

9.3.2 If the response signal for the used particle size

does not meet the expectations, the operator might use

another particle size within the required size range.

9.3.3 Calibration Parameters

9.3.3.1 The sample measurement time for the

calibration with each particle size should be at least 30

seconds to avoid statistical errors.

9.3.3.2 The calibration is to be performed at ambient

atmospheric pressure in a controlled environment

(temperature, humidity, vibrations).

9.3.3.3 The calibration of the LPPD is to be executed

in a line diameter D

in which the LPPD should be

installed by the user.

9.3.3.4 Fixed particle concentration at the LPPD C

ensure that the coincidence error is always less than

10%.

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: