Wafer scale heteroepitaxy of silicon carbon and silicon carbide thin films and their material properties

Abstract

For years now, many have believed the solution to reducing the cost of the wide bandgap compound semiconductor silicon carbide (SiC) is to grow its cubic form (3C-SiC) heteroepitaxially on silicon (Si). This has the potential to reduce cost, increase wafer size and integrate SiC with Si technology. After decades of research, 3C-SiC grown on Si is still yet to penetrate the commercial market as the process is plagued with various issues such as very high growth temperatures, thermal stresses, high cost, poor epitaxial material quality and poor scalability to wafer sizes beyond 100 mm diameter. The first section of this thesis starts with a focus on the traditional, high temperature growth of 3C-SiC carried out in the first industrial type SiC based reduced pressure chemical vapour deposition (RP-CVD) reactor installed in a UK University. After the process demonstrated little promise for mass scale implementation into the semiconductor industry, a radical change in strategy was made. The research pivoted away from SiC and instead focussed on silicon carbon alloys (Si1-yCy) with carbon (C) contents in the range of 1-3%. Si1-yCy has a range of applications in strain engineering and reducing contact resistance, differing from 3C- SiC quite significantly. Crystalline alloys with C contents around 1.5% were achieved using an industry standard Si based RP-CVD growth system. Analysis was carried out on the defects that form due to the saturation of C in higher content alloys. The high temperature annealing of Si1-yCy resulted in out diffusion of C and traces of 3C-SiC growth which presented itself as a potential buffer layer for 3C-SiC epitaxy. Through the careful selection of growth precursors and process optimisation, high crystalline quality 3C-SiC was grown heteroepitaxially on Si within the industry standard Si based RP-CVD and in-depth material characterisation has been carried out using a vast range of techniques. High levels of electrically active dopants were incorporated into the 3C-SiC and its electrical properties were investigated. Various investigations were carried out on suspended 3C-SiC and Si1-yCy films including strain and tilt measurements through micro X-ray diffraction and the effect of thickness and doping on their optical properties. The results led to a greater understanding of suspended films and provide a foundation for a number of applications in microelectromechanical systems (MEMS) and optical devices. Further material growth research was carried out on Si1-yCy multilayers, selective epitaxy of 3C-SiC and the growth of 3C-SiC on suspended growth platforms. Each topic presents an interesting area for further research. The research presented demonstrates new, state of the art 3C-SiC heteroepitaxial material and its basic structural, electrical and optical properties. A new low-cost and scalable process has been developed for the heteroepitaxial growth of 3C-SiC on Si substrates up to 100 mm with a clear path to scaling the technology up to 200 mm and beyond. Not only does the developed technology have a high commercial impact, it also paves the way for many interesting future research topics, some of which have been briefly investigated as part of this work