OPTIMIZATION OF Al STEP COVERAGE THROUGH COMPUTER SIMULATION AND SCANNING ELECTRON MICROSCOPY.

Abstract

Minute cracks in integrated circuit metallization at step edges constitute a very real hazard to device reliability. The computer simulations of metal film deposition reported in this study are in excellent agreement with SEM photographs of actual film step coverage obtained on unheated substrates. The use of the simulation technique to optimize step coverage has led to the modification of the planetary system used to support the wafers in the electron beam metal deposition apparatus. However, even with optimization of the planetary-source configuration, small cracks in metal films at steps occur if the step angles are greater than a maximum value determined by the system geometry. For the deposition system used in this work that maximum angle is 40 degree . However, steps with angles of 50 degree have been successfully coated with crack-free films when the substrates are heated above 300 degree C during deposition. We conclude that good step coverage may be obtained by optimization of the source-planetary configuration in the deposition apparatus, by controlling the substrate step profiles and by the use of elevated substrate temperatures.