"Novel Mechanisms on the Growth Morphology of Films"

Random surface roughness very often can occur during the growth or etching of films under non-equilibrium conditions. Several competing mechanisms such as noise, surface diffusion, and shadowing all play a role in the evolution of surface roughness. However, recent results obtained in many growth and etching processes exhibit an unusual tendency: the morphology is very rough where it is expected to be smooth and vice versa. The origin, we believe, is due to the fact that during the deposition and etching processes the atoms very often do not stick to the surface upon their first strikes. Atoms actually bounce around before all settle on surface sites. This non-unity sticking probability can lead to a very rough surface during etching and a very smooth surface during sputter or chemical vapor deposition that cannot be explained by the conventional mechanisms. INTRODUCTION It is common knowledge that during either deposition or etching of a film the surface (growth or etch front), very often tends to become rough under a wide variety of processing conditions. With the recent development of modern characterization tools including real space imaging and diffraction techniques, the growth front roughness evolution can be studied quantitatively [1]. Large amounts of data have been reported in the literature. However, quantitative understanding of the roughening phenomena is far from complete. The conventional models [2,3,4] that include noise, surface diffusion, and shadowing effects cannot explain much of the roughening data obtained by common deposition and etching methods such as sputter deposition, chemical vapor deposition (CVD), and plasma etching. In this work we shall show, in addition to surface diffusion and shadowing, that non-unity sticking coefficient can play a very important role in understanding many roughening phenomena. EXPERIMENTAL SURVEY Figure 1 shows four commonly employed deposition techniques: thermal evaporation, sputter deposition, chemical vapor deposition, and oblique angle deposition. Included also in Fig. 1 is a graph showing the incident flux distribution for various deposition techniques. The θ is defined as the angle between the surface normal and the direction of the incidence beam of atoms. Every often the deposition is performed at sufficiently low temperature and the surface diffusion is not strong enough to completely smoothen the growth front. Any fluctuations at the growth front would therefore cause some initial non-uniformity or roughness across the surface. Mat. Res. Soc. Symp. Proc. Vol. 749 © 2003 Materials Research Society W1.2.1