Study of trimethylgallium-ammonia-nitrogen system using in situ Raman spectroscopy.

摘要

The rapid growth of the semiconductor industry has demanded the shortening of process development time, particularly in chemical vapor deposition (CVD) technology. This poses challenges on two major fronts: developing new CVD chemical precursors and optimizating reactor designs and growth conditions. The objective of this dissertation is to demonstrate the combination of in situ Raman spectroscopy, ab initio calculations for product properties, numerical CVD reactor modeling and inverse problem solution, to identify reaction mechanisms, reaction rate constants and species diffusivities.; 3-Dimentional, spatially resolved gas phase temperature and species concentration profiles were obtained by using in situ Raman spectroscopy in an inverted, vertical impinging flow reactor. Analytical methods for were developed to reduce experimental data. For concentration measurement, modification of the “Relative normalized differential Raman scattering cross section “Σ_j” formula was proposed.; An inverse problem solution code was developed based on Tikhonov regularization for identifying species diffusivity and gas phase homogeneous reaction rate constants. The gas phase binary mass diffusion coefficient of TMGa in N ₂ was found to be 0.08 [cm2s−1]. The rate constant of TMGa homogeneous decomposition in N₂ environment was found to be 3.4 × 1015 exp(60.1 kcal/RT) [s −1]. The rate constant of NH₃ homogeneous decomposition in N₂ environment was found to be 1.4 × 1016 exp(90.11 kcal/RT) [cm3 mol−1 s −1]. The identified values matches literature values very well.; For the first time, TMGa-NH₃-N₂ reaction system was studied at conditions close to the actual GaN MOCVD conditions. A gas phase reaction mechanism was proposed based on measured gas phase temperature and the species concentration profiles of the key components in the TMGa-NH ₃-N₂ reaction system.; Given the proposed TMGa-NH₃-N₂ reaction mechanism, a scale analysis and operating window calculation for GaN MOCVD was performed to a provided qualitative understanding of the growth process. An analytical form of the GaN growth rate was deduced. An optimized operating window for GaN growth was also suggested. Both agree very well with the operating conditions provided by commercial reactor manufacturers.; Numerical simulation of TMGa:NH₃-NH₃-N₂ gas phase reaction system was successfully carried out. Simulated gas phase temperature and NH₃ concentration profiles agree well with the in situ Raman experimental results. The simulated concentration profiles of the reaction products were in agreement with of the in situ Raman experimental results.