Highly Oriented Diamond Films Grown at High Growth Rate
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Highly Oriented Diamond Films Grown at High Growth Rate Xianglin Li, Ramon Collazo, and Zlatko Sitar Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27606 ABSTRACT Highly oriented diamond (HOD) films were grown at a high growth rate on (100) silicon substrates by microwave plasma chemical vapor deposition (MPCVD), following the standard bias-enhanced nucleation (BEN) process. The growth rate and diamond quality were investigated as a function of methane concentration in hydrogen (2-6%), and air/CH4 ratio (0 to 0.16). A four-fold increase in the growth rate of HOD films and a three times faster expansion and coalescence of (100) facets was observed within the above process window. The films with the best quality were grown under an air/CH4 ratio of 0.11 at methane concentration of 3.5%. The ratio of x-ray intensity between the first order twins and {111} poles was only 1%. A detailed study of the crystalline quality and phase purity as a function of methane concentration and nitrogen addition is presented.
INTRODUCTION Diamond has many technologically interesting properties such as high thermal conductivity, high dielectric strength, optical transparency down to deep UV, and chemical inertness that brings about biocompatibility. However, to date, the size of single crystal diamond thin films is still limited to the size of the homoepitaxial substrates, usually obtained by the HPHT method. Nearly single crystalline, highly oriented diamond (HOD) films have been engineered to obtain large area diamond with properties close to those of single crystalline films. HOD films are grown on silicon substrates, which help in integration of diamond with current semiconductor technology. Although the fraction of initial oriented nuclei is limited to 50% [1], growth can be manipulated to achieve overgrowth of misoriented grains and a coalesced (100) film. One of the challenges associated with HOD growth is the growth rate. The growth of HOD films on silicon substrates was developed for a low-pressure regime of 25-30 Torr, which yielded growth rates around 0.3 µm/hr [2]. This low growth rate has been considered an insurmountable barrier and many researchers concluded that a pressure of 30 Torr yielded a maximum growth rate [3, 4]. Recently, high growth rate of homoepitaxial diamond by chemical vapor deposition (CVD) exceeding 100 µm/hr in the presence of nitrogen [5] and 50 µm/hr in processes without nitrogen [6] has been demonstrated. Our preliminary studies showed that a similar trend could be achieved in the growth of polycrystalline diamond films on silicon substrates under higher pressure (50 to 125 Torr) and higher methane concentration (up to 10%) [7]. Growth rates in excess of 5 µm/hr were demonstrated while maintaining good diamond quality. This study focuses on HOD diamond films grown at high growth rate on (100) silicon substrates under the above conditions. For comparison, HOD films were also grown under the conventional parameters. The following sections provide experimen
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