Ts. Cale et al., MODEL FOR SURFACE-DIFFUSION OF ALUMINUM-(1.5-PERCENT) COPPER DURING SPUTTER DEPOSITION, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 11(2), 1993, pp. 311-318
Surface diffusion plays a critical role in improving the step coverage
of sputter deposited aluminum-copper (Al-Cu) films, which are widely
used in the microelectronics industry. Unfortunately, values of surfac
e diffusivity as a function of temperature have not been published for
aluminum copper films commonly used. We present a model for surface d
iffusion during sputter deposition of Al-Cu films and show that semiqu
antitative agreement with experimental Al-(1.5%)Cu film profiles can b
e obtained. This modeling and experimental work is a step toward devel
oping a method to estimate diffusivity values using films deposited in
process equipment, which would prove useful in process design. Al-(1.
5%)Cu films were deposited at 303, 423, 523, and 623 K, into ''infinit
e'' trenches which have a variety of initial aspect ratios. No substra
te bias was applied in order to minimize resputtering of deposited mat
erial. Surface diffusivity as a function of temperature was estimated
by comparing experimental film profiles with profiles simulated using
EVOLVE, a physically based low pressure deposition process simulator.
The equations which govern the deposition process and the required con
stitutive models for both curvature driven surface diffusion and depos
ition kinetics are discussed. Assuming a surface-free energy of 1100 e
rg/cm2, the expression for the surface diffusivity is D = 6 X 10(-4) e
xp(-5800/T) cm2/s with temperature in Kelvin. Our model predicts that
step coverage increases with decreasing feature size, if all other dep
osition parameters are held constant, which is consistent with experim
ent.