Gas flow effects on the structure and composition of SiN x /Si/SiN x films prepared by radio-frequency magnetron sputter
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The structure and composition of SiNx /Si/SiNx films were investigated by means of x-ray reflectivity, x-ray photoelectron spectroscopy, and atomic force microscopy. The three-layer films were prepared by radio-frequency magnetron sputtering under the condition of constant nitrogen flow and the argon flow. It was found that the deposition rate and surface structure of the silicon nitride films were mainly determined by the nitrogen flow rather than the argon flow. But the composition of the silicon nitride films was controlled by the gas flow ratio (FAr /FN2) used during sputtering.
I. INTRODUCTION
Silicon nitride thin films have attracted much attention of researchers in various fields. Due to the films’ special properties, such as high chemical stability and dielectric constant, they are used as oxidation masks, gate dielectrics, intermediate insulators, passivation layers, and hard coating materials. Reactive magnetron sputtering has a good potential to fabricate high-quality hydrogen-free silicon nitride films at very low temperatures, and it is easy to prepare silicon nitride films of various structures and properties by this method.1– 4 Several papers discussed the deposition rate of the silicon nitride films prepared by reactive sputtering; however, in most of their conclusions were drawn under the condition of the fixed total pressure. Berg et al.5–7 reported that when the argon flow was fixed, the deposition rate of metal nitride films prepared by reactive sputtering changed in a “Z” style with the increase of nitrogen flow; i.e., the deposition rate decreased slowly in the initial stage, then decreased rapidly, and finally decreased slowly again. Stedile et al.8 have studied the deposition of silicon nitride films prepared by radio-frequency magnetron sputtering under low and constant argon pressure. They found a good agreement between Berg’s theory and their experimental data, including the composition of the film and the relationship between the deposition rate and the nitrogen partial pressure. We investigated the deposition of SiNx /Si/SiNx films by keeping the nitrogen and argon flows constant, and found that with increase in the
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J. Mater. Res., Vol. 16, No. 1, Jan 2001 Downloaded: 18 Mar 2015
nitrogen flow from 0 to 4 sccm, the deposition rate of the silicon nitride films decreased rapidly in the initial stage, then gradually decreased, and finally reached a stable value. X-ray reflectivity (XRR) is a powerful method of analysis, especially in the measurement of thickness and density of thin films. Besides its nondestructive property, its high accuracy has been demonstrated by many researchers.9–11 In this paper, we focus on the gas flow effects on the structure and composition of SiNx /Si/SiNx films. XRR combined with x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was performed to characterize the structure and the composition of the films. II. EXPERIMENTS
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