Properties of Diamondlike Carbon Films
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PROPERTIES OF DIAMONDLIKE CARBON FILMS K. FUJII, S.H. YOKOTA and N. SHOHATA Fundamental Research Labs., NEC Corporation 1-1, Miyazaki 4-chome, Miyamae-ku, Kawasaki,
Kanagawa 213, Japan
ABSTRACT Hard carbon films have been deposited onto room-temperature silicon The substrates are substrates in a de plasma of methane and hydrogen. A stainless mesh is held at the same potential as placed on the cathode. Although the deposited the cathode and is set above the substrates. films are amorphous and contain 24.4 atomic percent hydrogen, they have the following diamondlike properties: hardness is almost equivalent to that of natural diamond; electrical resistivity is on the order of 10 0-cm; chemical inertness is excellent to acids; thermal diffusivity is stress of 5.2 cm2 /sec. However, the films have a large compressive 10 dyn/cm2. 1.3X10 Annealed films exhibit dehydrogenation, graphitization, an increase in chemical reactivity, volume expansion and stress relaxation above 4000C. The activation energy for the transformation from the diamondlike phase to the graphitic phase is 18 kcal/mole. The dependence of the thermal diffusivity and hydrogen content on both the CH4/H2 gas mix ratio and the total pressure have been measured for the films deposited in a dc plasma without the mesh. INTRODUCTION Much work has been devoted to the deposition of diamond or diamondlike carbon (DLC) films which have properties similar to those of diamond. Recently, these films have been synthesized by chemical vapor deposition [1-4], plasma assisted chemical vapor deposition [5-101, ion the growth of diamond beam deposition [11-14] and spputering [15-18]. films usually requires high substrate temperatures of about 800*C. Furthermore, the surface of the deposited diamond films is usually very rough because it consists of aggregates of diamond crystals a few microns in diameter. Meanwhile, the amorphous carbon films usually have smooth surfaces. However, their properties critically change from graphitic to diamondlike depending on the deposition conditions. The properties of DLC films deposited in a dc plasma of methane and hydrogen were studied. The properties of our DLC films were closely equivalent to those of diamond. The DLC films were heat treated to establish the temperature region over which the DLC films maintained their diamondlike properties. EXPERIMENTAL A modified dc plasma reactor, shown in Fig. 1, was used to deposit DLC films. Stainless steel mesh (#635), held at the same potential as the substrate placed on the stainless steel cathode, was set 2 mm above the substrate. The distance between the tungsten plate anode and the cathode was 2 cm. the reactant gas was a mixture of methane and A Si(100) wafer was used as the substrate. hydrogen. Films were grown under the following conditions: unheated substrate (T~
S1.5
Z)
3 35
L L.L
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