Date of Award


Document Type

Open Access Dissertation


Computer Science and Engineering


Electrical Engineering

First Advisor

Tangali S Sudarshan


High quality, thick (~100µm), low doped and low defect density SiC epitaxial films are essential for high voltage (blocking voltage >10kV), light, compact and reliable next generation power devices. One of the significant challenges in obtaining high quality thick SiC epitaxial films is to restrict/eliminate the Si gas-phase nucleation or aerosol formation during growth. The generated aerosol particles adversely influence growth by reducing the growth rate due to precursor losses, and also affect crystal quality, since the Si droplets are carried to the crystal growth surface. Moreover, liquid aerosol particles adhere to the various reactor parts (parasitic deposition), and contribute to their severe degradation during epitaxial growth. These parasitic depositions are generally loosely bound, and can be carried to the growth surface during growth as particulates, resulting in degradation of crystal quality by introducing defects in the growing epitaxial layers. The aforesaid condition is specifically severe at higher precursor gas flow rates or in long duration growth required to achieve high quality thick epitaxy since parasitic deposition and related particulate formation are also increased at these growth conditions. At this parasitic deposition enhanced condition, the cost of growth is also expected to increase due to frequent replacement of degraded reactor parts. Hence, cost effective, high quality thick epitaxy is not achievable until the particle generation in the reactor is suppressed effectively in high temperature SiC CVD. To investigate the critical issues of parasitic deposition and nucleation related particle generation, intensive comparative study was performed for the first time for different conventional silane and chloro-silane gases. Based on the study of these precursors, a novel Si precursor gas tetrafluorosilane (SiF4) was proposed to be a superior Si precursor gas specifically suitable for high temperature SiC CVD. Initially, SiF4 is compared to DCS without any propane addition during growth. It was found that without propane SiF4 with only hydrogen, no Si deposition takes place in the reactor (only etches the SiC), whereas DCS deposits severe Si on the surface making the reactor parts unusable. The ability of SiF4 not to deposit Si in the reactor is unique and found to be very useful to achieve high quality SiC epitaxy at high temperatures in the cleanest possible growth environment. The chemistry of SiF4 gas precursor is utilized to eliminate Si gas phase nucleation and Si parasitic deposition during silicon carbide (SiC) epitaxial growth, otherwise unachievable in similar growth conditions using conventional silane (SiH4) and dichlorosilane (SiCl2H2/DCS) precursors. Higher Si-F bond strength (565 kJ/mol) in SiF4 prevents early gas decomposition and Si cluster formation, essential for high temperature SiC CVD, and yet enables growth of high quality epitaxy in an improved particulate suppressed growth condition. High quality, thick 4H-SiC epilayers >100 um have been demonstrated using SiF4 with excellent surface morphology, polytype uniformity, crystallinity and low defect density needed for reliable high power devices.


© 2013, Tawhid Rana