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Details of the FACTEX Procedure 
See FACTEX16 in the SAS/QC Sample Library 
Yin and Jillie (1987) describe an experiment on a nitride etch process for a single wafer plasma etcher. The experiment was run using four factors: cathode power (POWER), gas flow (FLOW), reactor chamber pressure (PRESSURE), and electrode gap (GAP). A single replicate of a 2^{4} design was run, and the etch rate (RATE) was measured.
You can use the following statements to construct a
16run design in the four factors:
proc factex; factors power flow pressure gap; output out=desgndat power nvals=(0.80 1.20) flow nvals=(4.50 550 ) pressure nvals=(125 200 ) gap nvals=(275 325 ); run;
The design with the actual (decoded) factor levels is saved in the data set DESGNDAT. The experiment using the 16run design is performed, and the etch rate is measured. The following DATA step updates the data set DESGNDAT with the values of RATE:
data desgndat; set desgndat; input rate @@; datalines; 550 669 604 650 633 642 601 635 1037 749 1052 868 1075 860 1063 729 ;
The data set DESGNDAT is listed in Output 15.15.1.
Output 15.15.1: A 2^{4} Design with Responsesproc glm data=desgndat; class power flow pressure gap; model rate=powerflowpressuregap@2 / ss1; run;The factors are listed in both the CLASS and MODEL statements, and the response as a function of the factors is modeled using the MODEL statement. The MODEL statement requests Type I sum of squares (SS1) and lists all effects that contain two or fewer factors. It is assumed that threefactor and higher interactions are not significant.
Part of the output from the GLM procedure is shown in Output 15.15.2. The main effect of the factors POWER and GAP and the interaction between POWER and GAP are significant (their pvalues are less than 0.01).
Output 15.15.2: Analysis of Variance for the Nitride Etch Process Experiment

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