An analysis of the role of high energy neutral bombardment in longthrow/collimated sputtering of refractory metal barrier layers

The development and optimization of sputtering techniques for the depositio n of refractory metal thin films for very large scale integration (VLSI) ba rrier and encapsulation layers is of significant concern for the microelect ronic fabrication industry. A number of directed sputtering techniques such as collimation and low pressure longthrow configurations have been applied to this problem. This paper addresses a number of issues present in the un derstanding and simulation of the growth of films deposited by directed spu ttering techniques over VLSI topography. In particular the role of high ene rgy neutral gas atoms reflected from the target is investigated as a source of resputtering. Also addressed is the creation of a low density porous fi lm on the sidewalls of vias/contacts due to oblique incident fluxes on thes e areas. Experimentally Ti and W films are deposited at pressures varying f rom 0.2 to 12.0 mTorr with and without collimators present. A number of re- emission/resputtering mechanisms were investigated using a Monte Carlo grow th simulator and it was found that the model most consistent with the exper imental films was an assumption of resputtering due to reflected neutrals. A significant result is a dramatic increase in the resputtering rate when a collimator was present due to a relative increase in the reflected neutral flux. Finally, the paper presents an analysis of the effect of pressure on bottom and step coverage in high aspect topography. (C) 1998 American Inst itute of Physics. [S0021-8979(98)00621-5].