Continuous Improvement of Material Characterization Methodology through Gage
Keywords: Gage R&R, pHEMT, XRD, sheet resistance, PL
Reliable metrology data such as layer thickness and composition measured by X-ray diffraction (XRD), sheet resistance measured by Eddy current, and qualitative pHEMT
epi parameters measured by photoluminescence (PL) are essential in a large-scale epitaxial wafer manufacturing process. In this paper, we present the use of ANOVA-based “Gage R&R” (repeatability and reproducibility) studies as the main analytical tool for the evaluation of our XRD, sheet resistance, and PL measurement processes. The results of early Gage studies for some of the measured material parameters revealed that the measurement process was only marginally reliable in the detection of product variation. We proposed experiments for the purpose of identifying the source(s) of the appraiser-toappraiser measurement variation. Each experiment involved first hypothesizing a source of variation, followed by implementation of a Gage study with one or two variables to test the hypothesis. The series of Gage studies showed that enhancement of the x-ray incident beam intensity and increasing standardization of x-ray simulation procedures result in improved measurement reproducibility. For the case of sheet resistance measurement, by implementing an appropriate temperature compensation factor in the measurement process, the variation can be greatly reduced. For our PL measurement process, a preliminary Gage study revealed high appraiser bias for some of the measured peak parameters which allowed us to identify the need for improvement in our operator training system. After modifying the training system, a follow-up PL Gage study to test the effectiveness of the change showed significantly improved measurement repeatability.