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MATERIALS RESEARCH

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TiN prepared by plasma source ion implantation of nitrogen into Ti as a diffusion barrier for SiyyCu metallization W. Wang, J. H. Booske, H. L. Liu, S. S. Gearhart, and J. L. Shohet Engineering Research Center for Plasma-aided Manufacturing, University of Wisconsin-Madison, 1410 Engineering Drive, Madison, Wisconsin 53706

S. Bedell and W. Lanford Department of Physics, State University of New York-Albany, Albany, New York 12222 (Received 24 January 1997; accepted 28 July 1997)

A method of forming TiN films for SiyCu metallization by using plasma source ion implantation (PSII) of nitrogen into Ti is described. The PSII process utilizes a dose of 1 3 1017 ionsycm2 and peak voltages of 210, 215, and 220 kV. The properties of such TiN films as diffusion barriers between Cu and Si were investigated by annealing Cu(2000 A)yTiNyTiySi films in vacuum from 500 ±C to 700 ±C, and by analyzing with four-point probe sheet resistance measurements, Rutherford backscattering spectrometry (RBS), and Auger electron spectroscopy (AES). The TiN films made at peak voltages of 215 and 220 kV were stable barriers against Cu diffusion after annealing at temperatures higher than 600 ±C.

I. INTRODUCTION

As integrated circuit device sizes are continuously scaled down, the present metallization technology based on Al and Al alloys as interconnect materials becomes problematic due to poor reliability against electromigration and stress migration, and longer delay for signal transmission because of larger RC constant.1 New metallization technology with higher reliability and smaller RC constants is required. Cu because of its low resistivity and higher resistance against electromigration and stress migration compared to Al and Al alloys is attractive as an interconnect metal for sub-0.5 and sub0.25 mm device metallization.1,2 However, Cu is a fast diffuser in Si and SiO2 and forms deep levels in the silicon band gap.3 Cu also has poor adhesion to Si and SiO2 . An interfacial layer is needed between Cu and Si and SiO2 to promote adhesion and to inhibit Cu from diffusing into the device active area during thermal cycle processes. Among the materials being studied for diffusion barriers between Cu and Si, nitrides of refractory metals such as Ti, Nb, Ta, and W are attractive because of their high thermal stability and chemical inertness with Cu.4 TiN is particularly interesting as a diffusion barrier between Cu and Si because of its relative low resistivity (20 –100 mVcm) and good adhesion to Si and SiO2 substrates.5–7 Most of the TiN films were prepared in these prior investigations by using reactive sputtering of Ti in a mixture of argon and nitrogen. The sputterdeposited TiN films were polycrystalline phases and failed as Cu diffusion barriers as Cu diffused through 726

http://journals.cambridge.org

J. Mater. Res., Vol. 13, No. 3, Mar 1998

Downloaded: 16 Mar 2015

the grain boundaries to react with Si forming Cu3 Si at temperatures of 500 ±C to 600 ±C.4 A more serious concern for sputter depos