ICMCTF1998 Session D3: Electronic and Optical Applications of Diamond and Related Materials

We have investigated the effects of several process parameters on the growth rate, surface roughness, grain size, and microstructure of diamond thin films prepared by microwave plasma-assisted chemical vapor deposition (MPCVD) on (100) Si from a 1% methane (CH₄) precursor in argon (Ar), with and without the addition of molecular hydrogen (H₂). Film deposition was carried out at pressures ranging from 55-150 Torr, plasma hydrogen contents of 0-99% H₂, and input powers of 500-1200 watts. The resulting films were characterized by visible and UV Raman spectroscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Addition of hydrogen to the feed gas produces the most pronounced enhancement in growth rate and modification of film microstructure, up to a total hydrogen content of approximately 50 atomic percent. Pressure is also shown to have a strong effect on the crystallite size and orientation, as well as on the growth rate. The measured growth rates were virtually independent of microwave power in the range from 500-1200 watts. Nanocrystalline diamond films have potential applications in fields ranging from industrial tool and bearing coatings to encapsulation of integrated microelectromechanical (MEMs) flow transducers to cold cathode devices and flat panel display (FPD) applications.

The results presented here demonstrate that these films can be produced economically and with properties optimized for particular applications through precise control of the growth chemistry and conditions during deposition.

ⁿ*Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract W-31-109-ENG-38.

Diamond and diamond-like carbon thin films have been found to be effective cold cathode electron emitters. The emission mechanism however, is not clear, and a number of models have been advanced to explain the process. In general, there are very few reliable "fingerprints" to determine apriori if a given film will or will not emit electrons. We have used transmission electron microscopy (TEM), photoelectron microscopy (PEEM), visible and UV Raman spectroscopy, scanning tunneling and atomic force microscopy, and UV photoelectron yield measurements to characterize a series of diamond thin films grown in a microwave CVD reactor using C₆₀-Ar-H₂, CH₄-Ar-H₂ and CH₄-Ar-N₂ plasmas, and have identified a set of morphological, topographical, electronic and electrical criteria which enable prediction of the cold cathode electron emission properties. For these films, emission appears to originate largely at grain boundaries, and a simple model for grain boundary emission is presented, based on the observed grain morphology and a recent calculation of grain boundary properties by P. Keblinski, D. Wolf, S. Philpot and H. Gleiter¹. For diamond films grown by other methods such as dc plasma and arc jet deposition, there appear to be different emission sites and emission mechanisms which do not fit the model developed for the films deposited by microwave CVD.

¹ P. Keblinski, D. Wolf, S. Philpot and H. Gleiter, J. Mater. Research, in press

*Work supported by the US Dept. of Energy, Office of Basic Energy Sciences under contract W-31-109-ENG-38, and by the Office of Naval Research under contract N00014-96-C0283.