Compositional variations of sputter deposited Ti/W barrier layers on substrates with pronounced surface topography

Sputter deposited Ti/W barrier layers have been found to be Ti deficient wi th respect to the target composition, which is attributed to the preferenti al resputtering of Ti from the deposited films by energetic neutrals or ion s from the discharge. On the other hand the sputtering yield of most materi als is known to be strongly dependent on the angle of incidence of the bomb arding species. Due to this angular dependence the resputtering rate of Ti/ W films will also be a function of the local orientation of the surface. Th e substrates of the IC circuits onto which the Ti/W barrier layers are depo sited normally possess a pronounced surface topography. The purpose of this work is to study the deviation of the expected Ti/W concentrations at slop ed surfaces as a function of the energy of the bombarding species as well a s the atom to ion flux arrival ratio. It is shown that the Ti concentration in the films as a result of the preferential sputtering does exhibit subst antial concentration variations across sloped surfaces at constant discharg e parameters. The experiments are done in an Ar rf discharge, using a Ti/W target with 50 at.% Ti and 50 at.% W. The films have been analysed by Ruthe rford Backscattering Spectrometry (RBS) and energy-dispersive X-ray Spectro scopy (EDS). The experimental results are discussed and compared with dynam ic simulations using the Transport of Ions in Matter (TRIM) code, which ind icate that the loss of Ti in the deposited films is primarily due to ballis tic preferential sputtering effects. (C) 1999 Elsevier Science S.A. All rig hts reserved.