**Commenced**in January 2007

**Frequency:**Monthly

**Edition:**International

**Paper Count:**31464

##### A CUSUM Control Chart to Monitor Wafer Quality

**Authors:**
Sheng-Shu Cheng,
Fong-Jung Yu

**Abstract:**

C-control chart assumes that process nonconformities follow a Poisson distribution. In actuality, however, this Poisson distribution does not always occur. A process control for semiconductor based on a Poisson distribution always underestimates the true average amount of nonconformities and the process variance. Quality is described more accurately if a compound Poisson process is used for process control at this time. A cumulative sum (CUSUM) control chart is much better than a C control chart when a small shift will be detected. This study calculates one-sided CUSUM ARLs using a Markov chain approach to construct a CUSUM control chart with an underlying Poisson-Gamma compound distribution for the failure mechanism. Moreover, an actual data set from a wafer plant is used to demonstrate the operation of the proposed model. The results show that a CUSUM control chart realizes significantly better performance than EWMA.

**Keywords:**
Nonconformities,
Compound Poisson distribution,
CUSUM control chart.

**Digital Object Identifier (DOI):**
doi.org/10.5281/zenodo.1328390

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