Evolution of surface morphology during growth and ion erosion of thin films 

R. Schlatmann, J. D. Shindler and J. Verhoeven 
FOM Institute for Atomic and Molecular Physics, 
Kruislaan 407, 1098 SJ Amsterdam, The Netherlands. 

A model is presented to describe the evolution of thin film surface morphology
during growth and ion erosion.  In our model, w e closely follow the
derivation and terminology of the growth model of Stearns [1, 2] and Spiller
[3], Our inclusion of smoothing and roughening mechanisms differs from theirs,
but is equivalent to the treatment by Mayer [4].  Thus, roughness is
introduced by shot noise in the deposition rate, and by variations in the ion
erosion rate with surface curvature.  Smoothing mechanism s in our model are
surface diffusion and viscous flow.  The latter is only taken in to account
during ion erosion.

The behaviour is studied of characteristic in-plane length scales and over-all
amplitude of the roughness, given the certain competing roughening and
smoothing mechanisms.  Particular attention is paid to the deposition method
of growth followed by ion erosion of an excess layer thickness ("ion p
olishing").  The model is extended to the case of multilayers, to include
roughness correlations between different interfaces.  Specular and diffuse
X-ra y scattering measurements on four ion polished Mo/Si multilayers are
presented.  In these samples, the excess layer thickness was varied.  As
measured before [5], the diffusely scattered X-ray in tensity falls off
exponentially in all q_perp ("transverse"-) scans from these samples.
Quantitative agreement between the model and the experimental data can be
achieved if we assume viscous flow (rather than surface diffusion) to be the
dominant smoothing mechanism during ion erosion of the Si layers.

References

[1] D. G. Stearns, J. Appl. Phys., 4286 (1992)
[2] D. G. Stearns, Appl. Phys. Lett., 1745 (1993)
[3] E. Spiller, D. G. Stearns, and M. Krumrey , J. Appl. Phys., 107 (1993)
[4] T. M. Mayer, E. Chason, and A. J. Howard, J. Appl. Phys., 1633 (1994)
[5] R. Schlatmann, J. D. Shindler, and J. Verhoeven, Phys. Rev. B, 5345 (1995)