ORIGIN OF COMPOSITIONAL VARIATIONS IN SPUTTER-DEPOSITED TIXW1-X DIFFUSION BARRIER LAYERS

Sputter-deposited Ti1-xWx diffusion barriers in microelectronic device s have been reported by many groups to be Ti deficient with respect to the target composition. In the present experiments, polycrystalline T ixW1-x alloys were grown on oxidized Si(001) substrates at temperature s T-s between 100 and 600 degrees C by ultrahigh-vacuum magnetron cosp utter deposition from purl W and Ti targets in 5 mTorr (0.65 Pa) Ar an d Xe discharges. Films deposited in Ar were found by Rutherford backsc attering and Auger electron spectroscopies to be increasingly Ti defic ient with increases in the Ti sputtering rate and/or T-s at a constant W sputtering rate. TRIM calculations and Monte Carlo gas-transport si mulations were used, in combination with the experimental results, to show that the Ti loss was due primarily to differential resputtering o f the growing film by energetic Ar particles backscattered from the he avier W target. This effect is exacerbated at elevated film growth tem peratures by Ti surface segregation in the alloy. The use of Xe, rathe r than Ar, as the sputtering gas greatly reduces both the flux and the average energy of backscattered particles incident at the substrate s uch that measurable Ti loss is no longer observed. (C) 1995 American I nstitute of Physics.