Modeling of the surface roughness of thin TiSi2 films at the point of rupture

When a polycrystalline thin film on a substrate is annealed, grooving at grain boundaries will eventually lead to film rupture, followed by island formation. Two models were developed to predict the surface roughness at the point of rupture (interface roughening effect included) of polycrystalline thin films of TiSi2 on Si based on 2-D and 3-D film analysis. The modeling results predicted that the rms roughness at rupture (RMS*) is essentially linear with film thickness (verified for thickness up to 150 nm), and that RMS* is not sensitive to grain size, 2R (for R=1–10 μm). Comparison is made with experimental data obtained with the atomic force microscope from thermal stability testing of two TiSi2 thin film specimens on (111)-Si, for annealing treatments carried out at 950°C in argon gas. The two specimens had the same thickness of about 150 nm but were formed under different silicide formation schemes. The experimental rms roughness values at rupture were approximately two times higher than predictions of the 3-D film model. The positive deviation is attributed to one or more of the following possibilities: initial film roughness due to intrinsic roughness of the silicide grains and presence of film defects like hillocks, faceting and relative subsidence of grains due to anisotropy and grain orientation effects, and hole formation and impingement.