Amorphous Carbon Nitride Films as a Candidate for Low Dielectric Constant Materials

Abstract

We have succeeded to prepare high resistivity and rather low dielectric constant amorphous carbon nitride films a-CN_x (0.52<x<0.86) by the reactive radio frequency magnetron sputtering of a graphite target using nitrogen molecules as a sputter gas.

The resistivity of a-CN_x are 5×10¹⁶ to 10₁₇ Ω-cm and be estimated to 10²⁰ Ω-cm, when the ratio of the carbon and nitrogen becomes chemically stoichiometry 3 to 4, i.e. C₃N₄. The resistivity of a-CN_x films prepared by a layer-by-layer method, LL-a-CN_x, is 10¹⁸ Ω -cm for x=0.6. The layer-by-layer method is a cyclic process of a deposition by the sputtering and an etching by atomic hydrogen. The sample LL-a-CN_x made by a layer-by-layer method are compared with that of usual method a-CN^x. The dielectric constant of a-CN^x films calculated from the refractive index n are 3.6 to 2.8 corresponds to nitrogen contents, 0.52<x<0.86. The dielectric constants ε of a-CN_x films decrease with the content of nitrogen x. At an ultimate component of a-CN_x, at x=4/3, the dielectric constant is estimated to 1.8.