Thickness and concentration control for silicon-germanium (SIGE) films

This paper reports the study of channel SiGe metrology by using Broadband Spectroscopic Ellipsometry (BBSE) and High Resolution X-Ray Diffraction (HRXRD) simultaneous. The thickness and germanium concentration for each layer of SiGe graded stack have been identified by BBSE with regression model recipe, which is carefully built by using HRXRD as the reference of germanium concentration. The measurement is precise and linear in a wide range. Dynamic precision and repeatability of the thickness and germanium concentration measurements are discussed, which meet the inline monitor requirement. And the most advantage for optical is its high throughput, but because it is the model based measurement, the model will become invalid when process largely changes. This paper illuminates the applicable limits for the optical model measurement, and proposes a hybrid metrology method for inline epitaxy process control. We also studied the silicon channel strain by HRXRD, which is a direct method to monitor the SiGe strain and relaxation. With the function of RSM (reciprocal space map), the Si strain in OCD (optical critical dimension) structure pad has been well demonstrated by using (113) asymmetric measurement.