Title

Fundamental studies on selective area laser deposition of graphite, silicon carbide and silicon nitride for in situ device fabrication

Date of Completion

January 1999

Keywords

Engineering, Metallurgy|Engineering, Materials Science

Degree

Ph.D.

Abstract

The goals of this dissertation were to demonstrate the feasibility of fabricating in-situ sensors using the selective area laser deposition (SALD) technique and to understand the SALD process. SiC/C thermocouple sensor was selected to be embedded within a silicon carbide or SiC/Si3N 4 composite matrix and electrically insulated with the silicon nitride layers. To achieve the purposed goals, a systematic methodology was applied in this study. First, the various chemical systems related to the thermal vapor deposition were thermodynamically modeled by direct minimization of the total Gibbs free energy method. Second, the detailed experiments were designed to evaluate the validity of the theoretical predictions and to fundamentally understand the SALD process such as effects of processing parameters on morphology, microstructure and composition of the deposits. Third, based on the understanding achieved during the first and second stage of this study, the in-situ thermocouple sensor device was fabricated and functionally tested. ^ It was found that the experimental results are in excellent consistence with the theoretical predictions. With the use of acetylene (C2H 2), tetramethylsilane (TMS, Si(CH3)4) and a mixture of TMS and ammonia (NH3) graphite, SiC and Si3N 4 were successfully deposited respectively. Strong temperature dependency of SALD products in morphology, composition, crystal structure and size, growth kinetics and relevant properties were revealed. The predicted carbon co-deposition and hydrogen's role in eliminating this co-deposition in SiC or Si3N 4 were experimentally confirmed by the Raman scattering study. The functional test on the fabricated device showed that the embedded SiC/C thermocouples exhibited stable and repeatable response to temperature variation. Thus, the overall results indicated that it is feasible to embed the in-situ sensors within a ceramic matrix using the SALD technique. ^