Advanced stress application device for <i>in-situ</i> optical measurement on multiple optical paths under stress in thin films

Abstract This paper proposes a prototype device engineered to measure the optical properties of semiconductor films deposited on Si substrates under controlled stress conditions. Utilizing a four-point bending method enhanced with a displacement conversion mechanism, the device ensures the preservation of necessary optical paths for both reflected and transmitted light, which is essential for optical measurements. The design incorporates an indenter with an inclination of less than 0.02° within the four-point bending apparatus, enabling application of the stress necessary to change optical properties without fracturing the Si substrate. The flexure observed in the Si substrate upon stress application was found to closely align with theoretical predictions for four-point bending. Furthermore, this study established a direct proportionality between the stress dependence of the Raman shift and applied stress, with the proportionality coefficient matching those documented in the literature. The device has been successfully demonstrated to facilitate Raman spectroscopy measurements at a stress level of 600 MPa, doubling the previously reported threshold, without resulting in fractures of the Si wafer. This development presents a powerful tool for the assessment of semiconductor films on Si substrates, offering advanced insights into stress-dependent optical properties.