The use of mahalanobis distance in solving the sputtering process thin-film thickness uniformity quality problem

Sputtering is one of the important processes in color filter (CF) manufacture, and the sputtering coating thin-film thickness uniformity affects the final quality of the products. The present study aims at solving the CF sputtering process thin-film thickness uniformity quality problem. The mean, the standard deviation and the range of the thickness are adopted as the quality characteristics, as opposed to the general approach that only considers the thickness mean in the measurements of thin-film thickness uniformity. The present study proposes Mahalanobis distance (MD) as a method to detect the nonconforming items in the sputtering process. The proposed method is a robust classification technique and has been applied in various fields effectively. In addition, it is applicable to solving the class imbalance problem. A practical case, which reveals very limited numbers of nonconforming items from the sputtering process in CF, is adopted for the empirical illustrations. The solution quality is compared with that of discriminant analysis (DA). By the MD method, the average accuracy of different quality measure criteria is between 91%∼94% and the results of relative sensitivity (RS) of the MD method are better than those of DA. In comparison with DA, the empirical results demonstrate that the MD method is more accurate and efficient in solving a multivariate, class imbalance problem.