semi合集-English.pdf - 第6598页

SEMI C1-0705 © SEMI 1978, 2005 24 Figure 6 Pressurized Test System 7.14.2.1 The reagent container is placed in a canister suitable for use as a press ure vessel at 4 bar (60 psi), such as a large steel filter housing. Th…

SEMI C1-0705 © SEMI 1978, 2005 23

7.13.4 Evaporation of Samples — Liquid chemical matrix elements may be the source of spectral interferences on

certain target elements e.g. 48SO interferes with 48Ti in a sulfuric acid matrix when using quadrupole-based ICP-

MS. Such spectral interferences may be significantly reduced or eliminated by controlled evaporation of the sample

followed by dissolution and analysis in ultrapure nitric acid or other suitable solvent.

7.13.5 Solution Conditions — The solutions are prepared as given in the procedures for the individual liquid

chemicals or elements.

7.13.6 Working Standard Solutions — Working standard solutions are prepared daily by dilution of stock standard

solutions. Internal standard solutions, if used, are prepared similarly.

7.13.7 Quantification — Quantification may be performed by the method of standard additions or by external

calibration. External standards may also be matrix matched in ultra pure liquid chemicals to assure that plasma

conditions during the analysis are similar for both standards and samples. For those liquid chemicals, which require

matrix removal, the preferred matrix after preparation is dilute nitric acid (typically 1–3%.) The working standard

solutions are prepared to cover the expected range of trace element concentration. Background subtraction by use of

a reagent blank solution is may be used for sample analysis by this technique.

7.13.8 One or more internal standards (such as indium or rhodium) may be used for drift correction during the

analysis.

7.13.9 Remarks — The manufacturer’s manual should be consulted for details specific to the operation of the

instrument. Performance checks on the instrument should be made from time to time to assure adequate mass

resolution, performance, and sensitivity.

7.14 Calibration and Measurement Method for Particles in Liquids — This standard describes the apparatus and

methods used to calibrate optical particle counters (OPCs) and to count hard particles in liquid reagents. The

procedures in this standard provide a means of comparison of particle levels in various reagents using pressurized

sampling and counted using the various available instruments. While the procedures in this standard are primarily

directed at off-line sampling or sampling from containers, OPCs can also be used for continuous on-line particle

measurement. While some substantial technical difficulty may accompany the implementation of the pressurized

sampling technique for containers of more than 10 L, the method should be followed as closely as possible to

maximize the integrity of the data. The following procedures are partially based on the publications in the attached

bibliography, which should be consulted for further details.

7.14.1 Apparatus — The apparatus used to measure the concentration of particles in reagents is comprised of a

sample supply system, a particle counter, and a flow measurement and control system. Two manual flow

measurement and control systems are presented in Figures 4 and 5. Several manufacturers have developed

automated pressurized sampling systems.

7.14.2 Discrete Sample Supply System — In the method specified in this standard, the pressure in the reagent

container is raised sufficiently above atmospheric pressure to produce the required flow and to reduce microbubble

formation, which causes falsely high counts. Pressurizing containers of reagents presents a substantial safety

hazard. Several systems have been developed for pressurizing the contents of a reagent container without placing a

pressure differential across the reagent container wall. A pressurized sampling system is required for all reagents.

Figure 5

Pressurized Test System

SEMI C1-0705 © SEMI 1978, 2005 24

Figure 6

Pressurized Test System

7.14.2.1 The reagent container is placed in a canister suitable for use as a pressure vessel at 4 bar (60 psi), such as a

large steel filter housing. The interior of the canister should be resistant to corrosion by the reagents being tested.

This canister is fitted with a relief valve set at 3.5 bar (50 psi), a nitrogen inlet, and a sealed feed-through for the

sample tube. The reagent container is fitted with a perfluoroalkoxy (PFA) cap to which is attached a hydrophobic

polytetrafluoroethylene (PTFE) nitrogen inlet filter. This permits the nitrogen pressures inside and outside the

reagent container to equilibrate when the vessel is pressurized and prevents particles from the pressure canister from

entering the sample reagent container.

7.14.2.2 Either of two sample and dip tube configurations may be used. In the first, a PFA dip tube, which extends

to 5 cm from the bottom of the reagent container, is attached to the cap. The sample tube, which consists of a single

continuous piece of PFA tubing to reduce the chance of incidental contamination during measurement, is connected

to the cap and the particle counter. This configuration has the advantage that it allows the sample tube to be

disconnected from the cap and dip tube, reducing the risk of splashing and of cross-contaminating samples. The

disadvantage of placing a fitting between the sample and the counter is that the fitting may compromise the integrity

of the sample.

7.14.2.3 In the second configuration, a single tube, without valves, fittings, or discontinuities extends from the

counter, through the cap to 5 cm from the bottom of the reagent container. This has the advantage that it ensures the

integrity of the sample but the disadvantage is that the risk of splashing and cross-contamination is increased.

7.14.3 Particle Counter — Laser light scattering OPCs from any of several suppliers may be used provided they are

in calibration, and used subject to the limitations described in ¶7.14.3.1.

7.14.3.1 Limitations on Counting Particles in Liquid Reagents using OPCs — OPCs are calibrated using

polystyrene latex (PSL) beads suspended in high purity water. The optical properties of naturally occurring particles

in liquid reagents are different from the optical properties of PSL and water. OPCs detect “light-scattering centers”

and calculate particle size and concentration based on the assumption that the light-scattering centers are equivalent

to PSL in water. In reality, light scattered by a particle is dependent upon particle size, particle shape and the

difference between the particle’s refractive index and the refractive index of the surrounding medium. When

properly calibrated OPCs from different manufacturers are used to measure particles in high purity water, they give

comparable size and concentration data.

7.14.3.1.1 Commercially, OPCs are manufactured with different illuminating wavelengths and a variety of optical

arrangements for collecting light scattered by particles. Because of the significant difference in the refractive index

of particles relative to the refractive index of water, the resulting scattered light profile is readily detected by all

OPCs. Hence there is relatively good comparative agreement between OPCs when used to detect particles in high

purity water.

7.14.3.1.2 When calibrated OPCs are used to measure particles in semiconductor liquid reagents, a totally different

situation is encountered. The refractive index of liquid reagents varies significantly from water and is, in general,

greater than water. While the refractive index of reagents is known and can be adjusted for, the refractive index of

particles is unknown and, in many circumstances, is expected to be very close to the refractive index of reagents.

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