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GROWTH AND CHARACTERIZATION OF PECVD DIAMOND FILMS

J. A. MUCHA AND L. SE1BLES AT&T Bell Laboratories, Murray Hill, N.J. 07974

ABSTRACT Polycrystalline diamond films have been deposited on (100) silicon wafers by plasma enhanced chemical vapor deposition (PECVD) using a 1.5 kW microwave source to dissociate dilute gas mixtures of CH 4 and 02 in H 2 . Films as thick as 20pm covering a 2" diameter area were deposited at 925 * C, 40 Torr total pressure, and 500 sccm total flow. These have been characterized as a function of CH 4 [0.24%] and 02 [0-3%] concentrations by measurements of deposition rate, stress, surface roughness, morphology, and impurity levels (C-H and amorphous-graphitic carbon). Addition of oxygen to the discharge tends to reduce impurity levels in the diamond films; however, this is accompanied by a reduction in deposition rate. When an effective CH 4 concentration [= %CH 4 - %021 is used as a metric for 0 2 -containing feed compositions, deposition rates as well as film properties are found to agree well with those obtained in the absence of 02. Thus, 1% CH 4 in hydrogen is nearly equivalent to 4% CH 4 , 3% 02 in hydrogen as feed compositions for depositing diamond.

INTRODUCTION CVD diamond research which began in earnest in Japan in the 1970's has expanded considerably in the 1980's with large efforts in Japan, the United States, and Europe.

Most of the early Japanese work demonstrated that diamond was

indeed the dominant phase that formed using hot-filament dissociation of dilute mixtures of methane in hydrogen.

During the 1980's, U.S. researchers focused on

confirming these results and elucidating the mechanism of diamond formation while their Japanese cohorts focused mainly on developing novel sources for diamond deposition. As a result, DC and microwave plasmas, oxy-acetylene flames, and DC and RF thermal plasmas have all been found to produce diamond and the Japanese have virtually cornered the market on patents relating to sources for the production of polycrystalline, CVD diamond thin films.

It was not until the late 80's that

attention began to be focused on determining the properties of these materials. Perhaps the most important were the demonstration that CVD diamond can exhibit a thermal

2

conductivity"1

near

that of bulk diamond at room

temperature

3 (- 10 W/cm K) and resistivities near 1016 fQ- cm suggesting that CVD diamond Mat. Res. Soc. Symp. Proc. Vol. 250. 01992 Materials Research Society

358

might be a useful dielectric material in electronic applications.

However, none of

these studies were comprehensive and it remains unclear whether desirable properties can be achieved in the same film or whether trade-offs might be required in incorporating diamond films in device applications.

Furthermore, there has been

little information regarding stress, adhesion, surface roughness, cutting, dicing, and etching; all of which are of paramount importance to using CVD diamond in practical applications.

Recently, we have established a program to evaluate CVD dia-

mond