A Combined Experimental and Theoretical Investigation of the Plasma-Surface Interactions in Plasma Deposition of Hydrogenated Amorphous and Nanocrystalline Silicon Films

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

0078711 Aydil Chemically reactive gas plasmas are used widely for etching and deposition of thin films and enable a whole class of technologies in the microelectronics industry. Despite the wide spread use and importance of such plasmas, optimization of plasma processes and design of plasma reactors rely heavily upon trial-and-error experimentation. There is a strong need for fundamental understanding of the intricate and complex coupling between plasma physics, homogeneous and heterogeneous chemistry, and species transport in plasma reactors. In particular, interactions of ions and radicals produced in chemically reactive gas plasmas with surfaces exposed to the discharge remain among the least understood aspects of plasma processing technologies. This lack of knowledge on surface reaction mechanisms and kinetics is a major limitation to the predictive capabilities of plasma reactor models that aim to integrate the plasma physics with gas phase and surface chemistry. A research strategy that integrates plasma and surface diagnostics with atomistic simulations is proposed to provide definitive conclusions about plasma-surface interactions during deposition of hydrogenated amorphous and nanocrystalline silicon films from SiH4/H2,/Ar glow discharges. Si film deposition is chosen as a prototypical chemical process because of its technological importance in the semiconductor industry. The proposed study aims at identifying the elementary surface chemical reactions that govern the plasma deposition mechanism, determining the corresponding reaction rates, and elucidating how these surface kinetic processes affect the evolution of the structure and composition of the surface. Such knowledge can only be achieved through synergistic analysis of the experimental and simulation results. To this end, atomic-scale computer simulations will be employed to study the interactions of silane molecular fragments, H atoms, and energetic ions from the plasma with the deposition surfaces. For detailed mechanistic study of plasma-surface interactions, molecular-dynamics, molecular-statics, and Monte Carlo simulators have been developed based on interatomic potential-energy functions, which have been tested exhaustively to assess their validity in comparison with ab initio calculations and experimental data. In addition, ab initio calculations within density functional theory will be used to generate accurate chemical reaction energy surfaces and variational rate theory will be employed to calculate the corresponding reaction rates. Furthermore, hybrid off-lattice kinetic Monte Carlo simulations will be implemented for full-scale dynamical modeling of the plasma deposition process over realistic time scales. These computational studies will identify surface chemical reactions that occur on surfaces exposed to a chemically reactive plasma, analyze quantitatively the energetics and kinetics of these reactions, and elucidate the elementary steps of the plasma deposition mechanism. The results of the computer simulations will be compared with experimental data and the insights gained from the simulations will be used to guide new experimental studies and design new plasma deposition strategies. In situ surface and plasma diagnostic methods will be used to study the phenomena occurring in the gas phase and on surfaces during film growth. Surface diagnostics will include in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and in situ spectroscopic ellipsometry. ATR-FTIR will be at the heart of our experimental plan: The PI's have developed this technique in order to study surface physics and chemistry in a plasma environment. ATR-FTIR will be used to determine the growth surface composition as a function of the fluxes and energies of species incident onto the surface. The plasma gas-phase diagnostics will include various spectroscopic methods, such as infrared and visible emission spectroscopy, and line-of-sight threshold-ionization mass spectroscopy to detect and measure the radical energies and fluxes impinging on the surface. The proposed research is pioneering in linking experimental in situ plasma and surface diagnostics with atomic-scale dynamical modeling and theoretical surface reaction analysis to establish fundamental mechanistic and quantitative understanding of deposition surface interactions with chemically reactive plasmas and how this interactions evolve during the deposition process. In addition, the proposed research will set the stage for developing an accurate chemical reaction database that can be utilized for equipment-scale plasma reactor modeling. Undertaking such a challenging research effort is particularly timely given the recent experimental and theoretical advances in the field. The scientific underpinnings of plasma processing are multidisciplinary and cut across traditional boundaries between different disciplines including physics, chemistry, chemical and electrical engineering. Thus, the proposed fundamental study in plasma-surface interactions provides an ideal educational tool for training students and postdoctoral scholars in addressing technologically important research problems using an integrated experimental and theoretical approach. ***