Thesis presented June 23, 2021

Abstract:
This thesis is dedicated to the study of an alternative and original method to produce strained single-crystal silicon thin film in an effort to develop a strain engineering platform for single crystal semi-conductor. Strain engineering is widely used to boost Si based transistor performance and offers outstanding possibility for the use of Complementary metal–oxide–semiconductor (CMOS) compatible semi-conductor in interesting optoelectronic applications. Usual methods used to fabricate strained semi-conductors are limited in terms of achievable strain value, strain orientation, strained surface and crystalline quality. We aim at proposing a process allowing to tune precisely deformation state (i.e., strain tensor) in a single-crystal. This process is applicable for different semi-conductors and materials and compatible with an industrial environment. The process studied here relies on temporary polymer wafer bonding, mechanical grinding, wet etching and direct bonding to transfer a single crystal silicon thin film from a Silicon On Insulator substrate to a flexible polymer, strain the crystal and bond it back on a rigid substrate. Silicon On Polymer structure were obtained with single crystal silicon thin film with a thickness ranging from 20 to 205 nm. Up to full diameter 200 mm films were transferred as well as patterned wafers. An extensive study of mechanical behavior of Silicon On Polymer (SOP) structures is provided using biaxial and uniaxial tensile test stages combined with Raman spectroscopy, digital image correlation, X-ray diffraction and Micro Laue X-ray Diffraction (μLaue). These results were used to validate a custom mechanical bench test for flexible SOP structures. Corresponding data acquisition and analysis strategies were also developed. The understanding of SOP mechanical behavior enabled the use of a bulge test apparatus to perform a direct bonding between a strained SOP and a silicon oxide die. μLaue allowed for a detailed analysis of the reported crystal. The transfer process was also adapted to functional devices and poly-crystal aluminum nitride thin films. Our custom mechanical bench test allowed the extraction of AlN Raman strain or stress coefficient in different configurations. Promising results showed that direct bonding is a suitable method to maintain a single crystal silicon thin film in a strained state after transfer from a stretched flexible polymer substrate. This can lead to some unprecedented development in strain engineering. Further work can enable the production of strained thin film of different nature, stress orientation and strain level.

Keywords:
strained, semiconductor, films, Wafer bonding