Papers by Author: Mei Liu

Abstract: To meet different electrical or optical functionalities, thin films are often of multiple layers processed at high temperatures. Substantial residual stresses can therefore develop in such thin film systems due to the disparate thermal properties of the individual material layers. High stresses can lead to mechanical failure of the systems and thus understanding the residual stresses in thin film systems is important. This paper presents a systematic way to characterize the residual stresses in epitaxial, polycrystalline and amorphous layers by using X-ray diffraction (XRD) techniques. The single-point XRD pattern renders the stresses of crystalline layers and the scanning XRD gives the curvature of the whole film. Based on the newly-developed analytical model, the residual stresses of each layer can all be determined.

Abstract: This paper investigates residual stress of epitaxial silicon film on SOS thin film systems. The emphasis was to develop a method to obtain accurately the complete residual stress tensors. It was found that using the multiple asymmetric X-ray diffraction method to measure strains in 13 [hkl] directions, the complete residual stress tensors can be determined reliably. The results were verified by both the Raman Backscattering and the substrate curvature methods.

Abstract: Silicon-on-sapphire (SOS) thin film systems have had specific electronic applications because they can reduce noise and current leakage in metal oxide semiconductor transistors. However, there are some issues in producing defect-free SOS wafers. Dislocations, misfit, micro twins and residual stresses can emerge during the SOS processing and they will reduce the performance of an SOS product. For some reasons, research publications on SOS in the literature are not extensive, and as a result, the information available in the public domain is fragmentary. This paper aims to review the subject matter in an as complete as possible manner based on the published information about the production, characterization and application of SOS wafers.