Properties of Molybdenum Nitride Thin Film Deposited by Reactive Sputter Deposition
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Properties of Molybdenum Nitride Thin Film Deposited by Reactive Sputter Deposition Yimin Wang, Jin W. Seok and Ray Y. Lin Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0012, U.S.A. ABSTRACT Molybdenum nitride thin film was deposited on silicon wafer with the reactive sputter deposition. γ-Mo2N thin film was obtained with nitrogen content in sputtering gas varying from 10% to 30%. An amorphous structure was observed in the thin film deposited at 50% nitrogen. Crystallinity of Mo-N thin film decreased as the total sputtering gas pressure increased. SEM examinations showed that the surface morphology of Mo-N thin films varies with the nitrogen content in the sputtering gas. The sheet resistivity of as deposited thin film increases with increasing nitrogen content in sputtering gas. The amorphous thin film deposited at 50% nitrogen survived 700°C/5min thermal annealing without obvious crystallization but failed after 800°C/5min thermal annealing, in which the crystalline γ-Mo2N and h-MoSi2 phases were observed. Sheet resistivity measurement showed a decrease in thin film resistivity with increasing thermal annealing temperatures. INTRODUCTION With a lower electric resistivity and better resistance to electromigration than those of aluminum, Cu is highly attractive for interconnections for ultra-large scale integration device applications. However, Cu is mobile, creates a deep trap level in Si and causes degradation of device reliability. It is necessary to use a diffusion barrier between Si and Cu to retard the interdiffusion between Cu and Si [1, 2]. Molybdenum nitride thin film is one of the promising materials for diffusion barrier. Polycrystalline γ-Mo2N has been prepared by various reactive sputter deposition methods [4-8] for potential application as copper diffusion barriers by sputtering Mo target in N2 and Ar mixture gas atmosphere under different nitrogen contents. Mo-N thin films with various properties are obtained. However, all reports [3-7] related to reactive sputtered Mo-N thin film observed polycrystalline structure. No amorphous Mo-N diffusion barriers prepared by sputter deposition and their properties have been documented by now. Amorphous structure is a desired structure for diffusion barrier due to lack of fast diffusion path, e.g., grain boundaries. In this research, we present the formation of an amorphous Mo-N diffusion barrier by pulsed DC reactive magnetron sputter deposition. The phase structures and sheet resistivity of the Mo-N thin film deposited under different nitrogen contents will be reported. The stability of the amorphous diffusion barrier will also be discussed. EXPERIMENTAL DETAILS The Si substrate used in this experiment was a p-type Si(100) wafer with the sheet resistivity in the range of 7∼14 Ω cm. The Si(100) wafer was etched by immerging in 10% HF solution for 1.5 minutes to remove the native oxide layer on the surface. A sputter deposition system with
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