Determination of diamond growth rate in a flow tube geometry as a function of measured atomic hydrogen density

Abstract

Present diamond deposition reactors have been very successful in furthering 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, and CH4:H2 concentration ratio in methane-based reactors) change all chemical species and their relationships. Changes in diamond growth created by independent changes to a single species are not directly accessible. 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 atomic hydrogen sensor was used to measure atomic hydrogen density output as a function of both power and pressure. Diamond was then grown as a function of atomic hydrogen density, and growth rate was shown to be linear with density with a lower bound relationship of 0.27 μm/h/1016 cm−3. Since the magnitude and trend of the data appear to be inconsistent with other reported results, they are analyzed with respect to a simplified growth model. Based on reasonable assumptions, we conclude that the data are consistent with growth rate being independent of surface atomic hydrogen concentration and linear with methyl radical concentration. Because sufficient methyl radical density is produced through the interaction of atomic hydrogen with methane with correspondingly negligible reduction in total atomic hydrogen density, it is inferred that growth rate linearity with atomic hydrogen enters only through the production of methyl radical.