Electron microscopic characterization of diamond films grown on Si by bias-controlled chemical vapor deposition
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Diamond films grown by Bias-Controlled Hot Filament Chemical Vapor Deposition (BCCVD) on silicon (Si) substrates were characterized by Transmission Electron Microscopy (TEM). Both plan-view and cross-sectional TEM samples were made from diamond films grown under different biasing conditions. It was found that defect densities in the films were substantially reduced under zero and reverse bias (substrate negative relative to the filament) as compared to forward bias. Furthermore, the diamond/Si interface of the reverse arid zero bias films consisted of a single thin interfacial layer whereas multiple interfacial layers existed at the diamond/Si interface of films grown under forward (positive) bias. Tungsten (W) contamination was also found in the interfacial layers of forward bias films. It is concluded that forward biasing in the present condition is not favorable for growing high quality, low defect density, diamond films. The possible mechanisms which induced the microstructural differences under different biasing conditions are discussed.
I. INTRODUCTION
Diamond film and particle synthesis from the vapor phase under low pressure has been demonstrated by at least 10 different methods since it was first achieved at reasonable growth rates in 1981.x Currently, intensive research activities around the world are aimed at developing a new era in diamond technology which will fully utilize the unique properties of diamond in applications ranging from coatings for wear resistance and cutting tools to optical windows for visible and infrared (IR) transmission, as well as thin films for high temperature, high power semiconductor devices. A decade of research has now led in the general direction of controlling nucleation, increasing the growth rate, reducing defects, and eliminating graphite codeposition. Uniform, large area deposition, and the ultimate goal of heteroepitaxial growth of single crystal films are also major concerns of the research community.2 Unfortunately, little has been known about the mechanisms of diamond nucleation and growth which would be very helpful in achieving these goals.3'4 Therefore, any correlation of process parameters to film properties which aids in furthering the understanding of potential nucleation and growth mechanisms is very beneficial in providing efficient guidelines for advancing the diamond technology. The present research correlates biasing conditions in a hot filament chemical vapor deposition system with film quality and defect density. This, in turn, allows speculation of the role of charged species in the mechanism of diamond growth. Hot filament chemical vapor deposition is one of the most common diamond growth techniques due to J. Mater. Res., Vol. 5, No. 11, Nov 1990
its simplicity and low cost.5 8 A heated filament above the substrate surface is utilized to thermally crack the hydrogen gas into atomic hydrogen. It also activates and dissociates the methane molecules as well as enhances surface processes via thermal excitation and electron bombardment. It has been fo
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