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B. Bhushan IBM Research Division, IBM Almaden Research Center, 650 Harry Road, San lose, California 95120-6099 (Received 9 April 1990; accepted 15 June 1990)

Amorphous carbon films were deposited on glass by dc magnetron sputtering from a graphite target in mixtures of argon and hydrogen. Hydrogen flow and other deposition parameters affected the optical and mechanical properties of these films. Increasing hydrogen content caused the average visible transmittance to vary from 16% to 86% for 500-A thick films. Maximum compressive stress and hardness occur between 0 and 1% hydrogen flow, resulting in rapid delamination. Low sputtering power moderately increases transmittance and hardness while relieving stress. Transparency is induced in both the high-hydrogen and low-power films by formation of sp3 C-C bonds. In the case of the hydrogenated films, however, a softer polymeric structure is formed. I. INTRODUCTION

This paper describes the effect of hydrogen content and sputtering power on the optical and mechanical properties of sputtered carbon films. Films having properties resembling those of diamond would have numerous applications as protective optical coatings. Carbon coatings have been used to antiref lect and protect semiconductor optics in the midinfrared1"4 where the coatings are highly transparent. Visible and nearinfrared transmittance of carbon films can also be enhanced by suitable choice of deposition parameters. High visible transmittance alone is not a sufficient criterion for a viable coating. The hardness of diamond as well as good adhesion of the film must also be realized for carbon coatings to have value for optical applications. Amorphous hydrogenated carbon films, designated a-C: H, can have a wide range of properties falling between those of graphite and diamond, as illustrated in a recent review.5 Near the latter extreme, the films may be referred to as "diamond-like". Diamond-like films are often produced by glow-discharge decomposition of methane or other hydrocarbon gases. Diamond-like films have also been produced by direct ion-beam deposition of carbon and by sputtering. Films produced by these methods need not contain hydrogen and can be simply designated as a-C. Reactive dc magnetron sputtering at low temperatures, as used in this study, can produce either a-C:H or simply a-C. In the next section, we describe the sputtering process used to deposit a-C:H films and the optical and mechanical techniques used to characterize them. Then we present the optical transmittance, intrinsic stress, and hardness as a function of such parameters as hy2538

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drogen flow rate and sputtering power. We will show that under some conditions the films will become more diamond-like, but not necessarily in both electronic and mechanical properties. II. FILM GROWTH AND CHARACTERIZATION

The films described herein were deposited by reactive dc magnetron sputtering. The target was a 99.99%pure graphite disk, 75 mm in diameter, bonded to a water-cooled copper backing plate. The sub