DETERMINATION OF DIAMOND GROWTH-RATE IN A FLOW TUBE GEOMETRY AS A FUNCTION OF MEASURED ATOMIC-HYDROGEN DENSITY

Present diamond deposition reactors have been very successful in furth ering our understanding of how diamond grows at low pressures. However , their primary disadvantage is that changes in reactor conditions (e. g., filament temperature or microwave power, substrate temperature, an d CH4:H-2 concentration ratio in methane-based reactors) change all ch emical species and their relationships. Changes in diamond growth crea ted by independent changes to a single species are not directly access ible. For example, it is known that making atomic hydrogen is required for the growth of diamond films. However, changes to film growth rate have not been tied quantitatively to changes in the amount of atomic hydrogen available. A high-yield atomic hydrogen source was fabricated and pretested in a diamond growth setup. A previously developed atomi c hydrogen sensor was used to measure atomic hydrogen density output a s a function of both power and pressure. Diamond was then grown as a f unction of atomic hydrogen density, and growth rate was shown to be li near with density with a lower bound relationship of 0.27 mu m/h/10(16 ) cm(-3). Since the magnitude and trend of the data appear to be incon sistent with other reported results, they are analyzed with respect to a simplified growth model. Based on reasonable assumptions, we conclu de that the data are consistent with growth rate being independent of surface atomic hydrogen concentration and linear with methyl radical c oncentration. Because sufficient methyl radical density is produced th rough the interaction of atomic hydrogen with methane with correspondi ngly negligible reduction in total atomic hydrogen density, it is infe rred that growth rate linearity with atomic hydrogen enters only throu gh the production of methyl radical. (C) 1996 American Vacuum Society.