semi合集-English.pdf - 第6600页

SEMI C1-0705 © SEMI 1978, 2005 26 7.14.9.2 The smallest particle counter threshold should deliver at least 50% particle counting efficiency at the control size limit. The control size limit is the particle size agreed up…

SEMI C1-0705 © SEMI 1978, 2005 25

Particles therefore have a tendency to become invisible to an OPC. The degree of invisibility will depend on the

optical arrangement of each OPC. A study carried out in 1999

found that particle concentrations reported by

different sensors varied significantly. Chemical-to-chemical comparison indicated that there was no sensor that

consistently reported higher or lower concentrations than other sensors.

7.14.3.2 Using OPCs in Semiconductor Liquid Reagents — OPCs have a critical role to play in monitoring particles

in liquid reagents. OPCs can detect low concentrations of small particles in real-time and can be easily calibrated

using PSL beads. However, the current state of OPC technology limits their use to claim that a liquid reagent meets

a standard particle concentration at a particular particle size.

7.14.3.2.1 When a supplier of a liquid reagent uses an OPC to specify that reagent’s particle concentration, for

example on a Certificate of Analysis, the make and model of OPC must also be specified. If the customer of the

liquid reagents wishes to check whether the incoming reagent meets the claimed level of cleanliness, the customer

must use an OPC of the same make and model number. However, it has also been shown that even two calibrated

“identical” OPCs can differ by 10–20% when measuring particles in liquid reagents.

7.14.4 Flow Control and Measurement System — A discrete or a continuous method may be used to control and

measure the flow of the sample through the particle counter. In both procedures, a needle valve, downstream of the

counter, is used to control the flow rate. In the discrete procedure, a measured volume of fluid is counted and

collected in a graduated container. Automatic level detection may be used to start and stop the counter. In the

continuous procedure, the flow rate is set and the count is accumulated for a measured time period.

7.14.5 Calibration — Each particle counter (sensor and signal analysis unit) must be calibrated at least once every

twelve months.

7.14.5.1 It is recommended that the calibration be performed by the instrument manufacturer or a metrology

laboratory certified by the instrument manufacturer. Calibration is performed by counting polystyrene latex (PSL)

beads suspended in water. PSL beads of known size (characterized by transmission electron microscopy (TEM) and

concentration (characterized by a scanning electron microscope SEM) must be used. In addition most instrument

manufacturers use a working standard or “gold standard” OPC as a reference against which all OPCs of the same

Model are compared.

7.14.5.2 The determination of size correction factors for particle counters is not recommended. Particle counters

should be calibrated with PSL beads in accordance with the manufacturer’s recommendation.

7.14.6 Coincidence Correction Factors — The determination of coincidence correction factors for particle counters

is not recommended. Particle counters should be calibrated with PSL beads as per the manufacturer’s

recommendation. Coincidence correction factors are only valid for monodispersed concentration of particles.

7.14.7 Efficiency Correction Factors — The determination of efficiency correction factors for particle counters is

not recommended. Particle counters should be calibrated with PSL beads as per the manufacturer’s

recommendation.

7.14.8 Monthly Check — It is desirable to check the OPCs size calibration once a month. PSL beads of known size

and approximate concentration can be purchased from several suppliers. Prepare a stock suspension of a

combination of about 10

particles/L of each of the three sizes of PSL beads. Several solutions have been found to

provide acceptably stable suspensions. Among them are: 25:1 ethanol/: water, and water with 0.01% surfactant and

0.05% bactericide. Dilute 10 mL of stock suspension to 1 L and measure the particle concentration using the

procedure specified for reagents. If the results of this check are not within 10% of the expected PSL bead size, the

OPC shall be recalibrated.

7.14.9 Measurement Procedure

7.14.9.1 Setup — Gently invert the sample reagent container three times to homogenize the particle distribution,

then set it aside for 30 minutes to remove the bubbles formed during mixing. Under no circumstances must the

sample reagent container be vigorously shaken or sonicated as this would generate numerous particles.

8 Carrieri, D., D.C.Grant and W.Kelly, “A Comparison of Optical Particle Sensors Used to Measure Particle Concentration in High-Purity

Process Chemicals” Proceedings SEMICON West 1999

SEMI C1-0705 © SEMI 1978, 2005 26

7.14.9.2 The smallest particle counter threshold should deliver at least 50% particle counting efficiency at the

control size limit. The control size limit is the particle size agreed upon between supplier and customer that

represents an acceptable size level. In general this size will be between 0.1 and 0.5 m.

7.14.9.3 Attach the cap with the gas inlet filter and sample tube to the reagent container to be sampled. Place the

reagent container in the canister, and seal the canister so that it may be pressurized. With the sample flow control

valve open, gradually (< 3 bar/min) pressurize the sample to 3 bar for H

and NH

OH or as necessary to obtain

the required flow for other fluids. Allow at least 250 mL of the sample to pass through the sensor before counting.

7.14.9.4 For each sample, after 5 aliquots have been measured, perform a chi-squared test to determine if the data

are statistically valid. If the chi-squared test fails, examine the apparatus for defects, such as loose or cracked

fittings, repair as necessary, and repeat the counting of 5 aliquots. If the sample fails both the second and third chi-

squared tests, it is considered to be immeasurable and should be discarded. If a second sample gives similar results,

the apparatus, including the OPC, may be defective and should be checked with a well-characterized sample and

repaired if necessary.

7.14.10 Measurement

7.14.10.1 Discrete Sampling — Measure multiple aliquots of the same sample. The flow rate must be the same as

that at which the instrument was calibrated. The statistical significance of any count data must be taken into

consideration. Some OPCs inspect as little as 1/1000

of the available sample flow, and may require a greater

number of aliquots and larger sampling volume to ensure good statistics. For example, to obtain a coefficient of

variation (standard deviation/mean) of 10%, it is necessary that at least 100 particles greater than the control size

limit be counted.

7.14.10.2 Continuous Sampling — If continuous sampling apparatus is being used, adjust the needle valve on the

rotameter to obtain a flow rate consistent with the instrument manufacturer’s recommendations. This flow rate must

be the same as that at which the instrument was calibrated. Correct the indicated value for the effect of the fluid

density and viscosity on the rotameter reading. Allow the first minutes’ fluid to flow to drain, then count the

particles in each of five, 15 second intervals. The statistical significance of any count data must be taken into

consideration. Some OPCs inspect as little as 1/1000

of the available sample flow, and may require a greater

number of aliquots and larger sampling volume to ensure good statistics. For example, to obtain a coefficient of

variation (standard deviation/mean) of 10%, it is necessary that at least 100 particles greater than the control size

limit be counted.

7.14.11 Shutdown — As in all portions of this procedure, appropriate safe liquid chemical handling practices must

be used. In particular, attention should be paid to the reactions between different reagents and between reagents and

diluents, including water, and to the inherent hazards of these materials.

7.14.11.1 After the measurement has been completed, vent the pressure vessel to atmospheric pressure through an

appropriate scrubber or exhaust hood, then flush the vessel with nitrogen to remove residual reagent vapors.

7.14.11.2 Flush the OPC and sample system with water or an appropriate solvent to remove the remaining fluid.

7.14.12 Coincidence and Efficiency Corrections — The determination of coincidence and efficiency correction

factors for particle counters is not recommended. If an OPC’s maximum concentration is exceeded, a different OPC

should be selected, or the sample diluted. However any sample dilution will impose additional error and is not

recommended.

7.14.13 Index of Refraction Correction — The determination of an index of refraction correction factor for particle

counters is not recommended, as the refractive index of the contaminating particle is unknown.

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 the responsibility of the user.

Users are cautioned to 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

notice.

By publication of this standard, Semiconductor Equipment and Materials International (SEMI) takes no position

respecting the validity of any patent rights or copyrights asserted in connection with any items mentioned in this

standard. Users of this standard are expressly advised that determination of any such patent rights or copyrights, and

the risk of infringement of such rights are entirely their own responsibility.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction of

the contents in whole or in part is forbidden without express written

consent of SEMI.