This example uses experimental data published in Czitrom and Spagon, (1997), Statistical Case Studies for Industrial Process Improvement. The material is copyrighted by the American Statistical Association and the Society for Industrial and Applied Mathematics, and is used with their permission. Specifically, Chapter 15, titled “Elimination of TiN Peeling During Exposure to CVD Tungsten Deposition Process Using Designed Experiments”, describes a semiconductor wafer processing experiment (labeled Experiment 2).
Goal, response variables, and factor variables
The goal of this experiment was to fit response surface models to the two responses, deposition layer Uniformity and deposition layer Stress, as a function of two particular controllable factors of the chemical vapor deposition (CVD) reactor process. These factors were Pressure (measured in torr) and the ratio of the gaseous reactants H2 and WF6 (called H2/WF6). The experiment also included an important third (categorical) response – the presence or absence of titanium nitride (TiN) peeling. The third response has been omitted in this example in order to focus on the response surface aspects of the experiment.
To summarize, the goal is to obtain a response surface model for two responses, Uniformity and Stress. The factors are: Pressure and H2/WF6.