ABSTRACT
This chapter discusses the particles-per-wafer-per-pass (PWP) methodology of measuring particles added to wafers when these wafers are passed through one or more pieces of process equipment. PWP is the number of particles added to wafers in one pass through one or more pieces of process equipment. The principal topics of importance in PWP methodology are calibration and PWP characterization of the counting tool(s), measurement plan structure, analysis of variances, and the calculation of statistical confidences. The uniqueness of the PWP method is its perspective on contamination directly to wafers and its specificity to whole pieces of processing equipment or specifically selected process steps or process segments. Particle measurements on wafers begin with wafers that have an undetermined number of particles. The particles on these wafers originally may have an unknown number distribution (not to mention an unknown size distribution) whose population is certainly different from zero.
