Statistical Analysis: Liquid-Borne Particles
The impact of statistics on choosing and using a liquid particle counter is reviewed. The statistical techniques used with liquid particle counters are well known and relatively simple, but the simultaneous impact of both sample volume and size sensitivity on liquid particle data has not been fully explored in the literature. Both sample volume and sensitivity effect the total number of particles counted per unit time, and when more particles are counted the statistical variation in the data is reduced. For a given sample volume there will always be more particles counted by a particle counter sensitive to smaller particles.
In addition, the concentration of small particles is almost always greater than the concentration of larger particles. The particle size distribution of the particular liquid system will determine whether an instrument optimized for sensitivity produces more information than one optimized for sample volume. A number of liquid systems’ size distribution will be examined and the implications about which particle counter would produce the most information will be discussed.
Further, the paper will review different statistical approaches used for qualifying a bulk chemical delivery system a semiconductor factory, and the impact of using different particle counters to qualify the system to a particular particle concentration.
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