Dielectric Properties of Amorphous Carbon Nitride Films
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ABSTRACT Dielectric properties of amorphous carbon nitride films made by the layer-by-layer method, (LLa-CNx) consisting of a cyclic process with (A) the deposition of an amorphous carbon nitride layer by sputtering and with (B) the etching by atomic hydrogen, have been compared with that of amorphous carbon nitride (a-CNx) films prepared without the hydrogen etching process. It is found that the nitrogen in a-CN× and LLa-CNx could decrease the refractive index n and the dielectric constant E at 1 MHz. The nitrogen could create less dense structure in aCNx and LLa-CNx compared to diamond-like carbon (DLC). The sp3 bonds between carbon atoms seem to increase by the atomic hydrogen treatment in LLa-CNx. The refractive index of LLa-CNx increases with sp3 content. Preliminary experiments adding oxygen in amorphous carbon nitride to create a-CNxOy film are tried and discussed briefly. INTRODUCTION The fundamental methods to obtain low dielectric constant materials for the insulator of the integrated circuit are to design materials with (a) small polarization and (b) small density [1]. Amorphous carbon nitride films a-CNx were proposed recently as a candidate for low dielectric constant materials for ULSI [2]. We have prepared amorphous carbon nitride by the layer-bylayer method LLa-CN, to refine the materials 13]. This method is consist of cyclic process of (A) the deposition of thin a-CN× by reactive sputtering and of(B) the etching by the atomic hydrogen. Dielectric properties and effects of chemical bonding of a-CNx and LLa-CNx are studied and discussed including preliminary experiments on amorphous oxidized carbon nitride film a-CNxOy which is obtained by a oxidation of amorphous carbon nitride a-CN×. EXPERIMENTS Three different preparation methods were used in this paper to obtain amorphous carbon nitride films where (1) a-CNx was prepared by a reactive radio frequency magnetron sputtering using a graphite target and sputter gas of molecular nitrogen gas, (2) LLa-CNx was prepared by the layer-by-layer method using a cyclic process of(A) the deposition of a-CNx thin layer and of(B) the etching by the atomic hydrogen to reduce defects and weak bonds in a-CNx and (3) the surface of amorphous carbon nitride was treated with oxygen radicals made by the glow discharge of oxygen molecular gas to obtain a-CNxOy. Various LLa-CNx films, of similar thickness, were prepared by changing the number of cycles K for the layer-by-layer process. In preparation conditions, nitrogen molecular gas pressure of 0.12 Torr, hydrogen molecular gas pressure of 0.5 Torr, rf-power of 85 W at 13.56 493 Mat. Res. Soc. Symp. Proc. Vol. 593 © 2000 Materials Research Society
MHz and substrate temperature of 200 °C were kept constant. Substrates were Corning 7059 glass for general purpose and crystalline silicon wafer for to measure infrared-absorption and Raman spectra. Refractive index and film thickness were obtained by UV-visible transmittance spectra. Capacitances and dielectric constants were obtained by using a Hewlett-Packered LCR meter HP
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