Control Charts for Particles in the Semiconductor Manufacturing Process

Particles such as dust have serious negative effects on yield, performance and reliability in the semiconductor manufacturing process. As a result, there is the need to control particles in the manufacturing process, which often is done by means of control charts. The c-chart is a control chart based on the Poisson distribution generally used to monitor the number of defects in statistical process control. However, if the c-chart is used in a semiconductor manufacturing process, the process will often be declared out-of-control although the process is in-control, because the number of particles on a wafer does not follow a Poisson distribution. In this study, we assume that the particle distribution follows a negative binomial distribution, and propose a procedure for the use of a control chart that includes outlier removal. The usefulness of this proposal is then shown by simulation, numerical analysis, and application of the proposed steps to real data.