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3. Production Process Characterization
3.1. Introduction to Production Process Characterization
3.1.3. Terminology/Concepts Process Variability

Controlled/Uncontrolled Variation

Two trend plots The two figures below are two trend plots from two different oxide growth processes. Thirty wafers were sampled from each process: one per day over 30 days. Thickness at the center was measured on each wafer. The x-axis of each graph is the wafer number and the y-axis is the film thickness in angstroms.
Examples of"in control" and "out of control" processes The first process is an example of a process that is "in control" with random fluctuation about a process location of approximately 990. The second process is an example of a process that is "out of control" with a process location trending upward after observation 20.
This process exhibits controlled variation. Note the random fluctuation about a constant mean. process exhibiting controlled variation
This process exhibits uncontrolled variation. Note the structure in the variation in the form of a linear trend. process exhibiting uncontrolled variation
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