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

Abstract

The development and optimization of sputtering techniques for the deposition of refractory metal thin films for very large scale integration (VLSI) barrier and encapsulation layers is of significant concern for the microelectronic 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 understanding and simulation of the growth of films deposited by directed sputtering techniques over VLSI topography. In particular the role of high energy neutral gas atoms reflected from the target is investigated as a source of resputtering. Also addressed is the creation of a low density porous film on the sidewalls of vias/contacts due to oblique incident fluxes on these areas. Experimentally Ti and W films are deposited at pressures varying from 0.2 to 12.0 mTorr with and without collimators present. A number of re-emission/resputtering mechanisms were investigated using a Monte Carlo growth simulator and it was found that the model most consistent with the experimental 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.