Mechanism of Diamond Growth on Carbide Substrates Using Fluorocarbon Gases
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KJ. GRANNEN AND R.P.H. CHANG Northwestern University, Department of Materials Science & Engineering, Evanston, IL 60208-3108.
ABSTRACT The etching and growth behavior of diamond in C Fy / 02 / H 2 plasmas have been investigated. Using this gas mixture, diamond can nucleate on untreated tungsten carbide and silicon carbide substrates up to a density of 108 crystallites/cm 2. This compares to a density of 102 crystallites/cm 2 when using a methane gas mixture and these same substrates. The increase in nucleation density is attributed to the selective etching of the non-carbon component of the carbide with subsequent nucleation on the carbon enriched surface. The effect of temperature on the nucleation rate has been studied with a lower nucleation density at higher growth temperatures. INTRODUCTION Due to its impressive array of physical and mechanical properties, thin film diamond is being investigated aggressively. One of the main problems in thin film diamond growth is the need to abrade/seed the substrate with diamond in order to have sufficient nucleation density'. To circumvent this seeding 'step, various alternatives have been investigated. These include carbon ion implantation2 4 , the use of fullerenes , buffer layers 710, or bias-enhanced nucleation1 ' 2. Most of these investigations rely on the placement of non-diamond carbon on the substrate to start the nucleation process. In our research, we study the growth of diamond on carbide substrates using the carbon already in the substrate as the starting point for nucleation. The unique etching and growth chemistry of a CxFI / H2 / 02 is responsible for diamond growth, and a model is proposed to explain the rapid growth of diamond on carbide substrates. EXPERIMENTAL The samples were grown in a microwave plasma chemical vapor deposition system described previously 13. Table I lists the growth conditions. Substrates were tungsten carbide and silicon carbide powders ranging from -325 mesh to + 10 microns with a typical purity of 99%. These powders were loaded directly into the chamber and grown for one hour at the parameters listed below. 511 Mat. Res. Soc. Symp. Proc. Vol. 317. ©1994 Materials Research Society
Table I. Typical diamond growth conditions Substrate: Feed Gases: Total Flow Rate: Pressure: Microwave Power: Substrate Temperature:
WC or SiC powder CF4, C2F 6, C3F 8, or C4 F8 all at 1/2% - 3%, 1% 02, balance H2 200 sccm 40 mBar 350-400 W 850 - 900 C
During growth, emissions from the plasma are monitored via optical emission spectroscopy. The optical emission setup is composed of an EG&G PARC Model 1470 A Process Monitor, and a Model 1455 silicon photodiode array detector coupled to a 0.5 m grating monochromator. Light is collected from the plasma without a focussing lens with and without the tungsten carbide substrates present. To detect the presence of tungsten, atomic tungsten emission peaks at 400.9 nm and 413.7 nm Post-growth examination was via scanning electron microscopy are monitored. (SEM) to determine whether diamond was present as well as
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