Ion-Beam Polishing of Diamond Thin Films
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DONG-GU LEE AND RAJIV K. SINGH University of Florida, Department of Materials Science and Engineering, Gainesville, FL32611
ABSTRACT Planarization of diamond thin films has been carried out using a remote electron cyclotron resonance (ECR) oxygen plasma under a negative bias. Diamond thin films were synthesized by hot filament chemical vapor deposition (HFCVD). The surface roughness (Ra) of the diamond films could be considerably reduced from 0.2 gtm to 0.05 gtm using the ECR oxygen plasma. Low planarization and a high etching rate of diamond films were observed for an incident angle of the ion beam to the film surface normal below 45 degrees. High applied bias above -600 V caused secondary discharge effects, resulting in inhomogeneous etching. With an increase in incident angle, needlelike morphology was observed in the diamond film.
INTRODUCTION CVD diamond thin films have been a subject of strong interest because of diamond's excellent properties such as wear resistance, inertness, wide bandgap, thermal conductivity, and optical transparency. On the other hand, since a diamond film is normally grown with a pyramidal shape of { 111 }, the surface of the diamond film is very rough. Therefore, a smooth and flat surface is essential for many mechanical, optical, and electrical applications of CVD diamond films. There have been several reports on planarization of CVD diamond films using gas ion beam [1,2], hot metal plate [3], and laser irradiation [4-8]. Most ion beam planarization of diamond films have been conducted at low pressure (-10-'-10` Torr) to generate a strong ion beam. In this experiment, we report remote-plasma planarization of diamond thin films using oxygen gas at 65 mTorr. Effects of incident angle, temperature, and applied bias have been studied.
EXPERIMENTAL The electron cyclotron resonance (ECR) system used to produce an oxygen plasma for the planarization of diamond films is shown in Fig. 1. This is the same apparatus as described in previous work for diamond deposition [9]. Oxygen gas was introduced at the top of the ECR plasma region with a flow rate of 20 sccm. CVD diamond films were positioned 8 cm downstream from the ECR plasma source and were placed on a ceramic heater. The diamond films were negatively biased relative to ground during etching to attract O and 02' ions from the oxygen plasma [10]. The total gas pressure was 65 mTorr. The applied microwave power (2.45 GHz) was 950 W and the reflected power was 130+20 W. Diamond films were synthesized by hot filament CVD on (100) silicon substrates from 1% methane-99% hydrogen gases. The other growth conditions were as follows: filament temperature 25000 C, substrate temperature 910 0C, filament-substrate distance 10 mm, gas flow rate 100 sccm, total pressure 40 Torr, and growth time 3 hrs. The CVD diamond films had a thickness of 4 rim, 699
Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
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Fig. 2. SEM image of a as-grown polycrystalline diamond film synthesized by HFCVD.
Fig. 1. Schematic diagr
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