The microstructure and texture of thin MO films sputtered onto the native oxide of Si(100) wafers were investigated with both conventional reflection x-ray pole figures, and transmission electron microscopy and diffraction. Films were grown at two deposition rates (powers), 34 nm/min (1.5 kW) and 67 mn/min (3.9 kW), onto both moving and stationary substrates, under otherwise identical experimental conditions. The microstructure of the MO films evolved into a zone 2 microstructure within the first 2 pm of growth. The development of both out-of-plane and in-plane textures was found to be influenced by deposition rate and geometry. Films grown at the lower deposition rate exhibited predominantly (110) textures, while films grown at the higher rate exhibited predominantly (110) textures up to a film thickness of-0.5 ,um and (111) textures above a film thickness of-1 ,YAIL Films with the (110) textures developed grains with elongated footprints and faceted surfaces, while films with the (111) textures developed grains with elongated triangular footprints and faceted surfaces. In all of the films deposited onto moving substrates, an alignment of the grains normal to the tangent plane (defined by the substrate normal and the direction of platen rotation) was observed. In all of the films deposited onto stationary substrates, the development of an in-plane texture was suppressed. These results suggest that a combination of geometric, energetic, and kinetic mechanisms are contributing to the evolution of the microstructure and texture in the MO films.-4610

The development of a preferred crystallographic orientation in the plane of growth, an in-plane texture, is addressed in a model that incorporates anisotropic growth rates of a material and self-shadowing. Most crystalline materials exhibit fast growth along certain crystallographic directions and slow growth along others. This crystallographic growth anisotropy, which may be due to differences in surface free energy and surface diffusion, leads to the evolution of specific grain shapes in a material. In addition, self-shadowing due to an obliquely incident deposition flux leads to a variation in in-plane grain growth rates, where the ''fast'' growth direction is normal to the plane defined by the substrate normal and the incident flux direction. This geometric growth anisotropy leads to the formation of elongated grains in the plane of growth. Neither growth anisotropy alone can explain the development of an in-plane texture during polycrystalline thin-film growth. However, whenever both are present ͑i.e., oblique incidence deposition of anisotropic materials͒, an in-plane texture will develop. Grains that have ''fast'' crystallographic growth directions aligned with the ''fast'' geometric growth direction overgrow grains that do not exhibit this alignment. Furthermore, the rate of texturing increases with the degree of each anisotropy. This model was used to simulate in-plane texturing during thin-film deposition. The simulation results are in excellent quantitative agreement with recent experimental results concerning the development of in-plane texture in sputter deposited Mo films.

Reflection high energy electron diffraction ͑RHEED͒ was used to investigate surface roughening during low temperature Si͑100͒ homoepitaxy. The use of RHEED allowed in situ real-time collection of structural information from the growth surface. RHEED patterns were analyzed using a simple kinematic diffraction model which related average surface roughness and average in-plane coherence lengths to the lengths and widths of individual RHEED diffraction features, respectively. These RHEED analyses were quantified by calibrating against cross-section transmission electron microscopy ͑TEM͒ analyses of surface roughening. Both the RHEED and TEM analyses revealed similar scaling of surface roughness with deposited thickness, with RHEED analyses resulting in roughness values a factor of ϳ2 times lower than those obtained from TEM analyses. RHEED was then used to analyze surface roughening during Si͑100͒ homoepitaxial growth in a range of temperatures, 200-275°C. Initially, surface roughness increased linearly with deposited thickness at a roughening rate that decreased with increasing growth temperature. At each growth temperature, near the crystalline/amorphous Si phase transition, the rate of surface roughening decreased. This decrease coincided with the formation of facets and twins along Si͕111͖ planes. Surface roughness eventually saturated at a value which followed an Arrhenius relation with temperature E act ϳ 0.31 Ϯ 0.1 eV. This activation energy agrees well with the activation energy for the crystalline/amorphous Si phase transition, E act ϳ 0.35 eV, and suggests that limited thickness epitaxy is characterized by this saturation roughness. Once the saturation roughness was reached, no significant changes in surface roughness were detected. In addition, the decay of average in-plane coherence lengths was also temperature dependent. Values of average coherence lengths, at the crystalline/amorphous Si phase transition, also increased with growth temperature. All of these data are consistent with a model that links surface roughening to the formation of critically sized Si͕100͖ facets and the eventual breakdown in crystalline growth.

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The evolution of texture in thin films must be fully understood in order to take advantage of favorable crystallographic orientations in a material for a given application. The development of an out-of-plane texture (preferred crystallographic orientation in the growth direction) and an in-plane texture (preferred crystallographic orientation in the plane of growth) in sputter deposited, thin mo films on Si was studied using transmission electron microscopy and diffraction, and conventional x-ray pole figures. For a range of deposition parameters, a strong (110) out-of-plane texture developed within 1000Å, while a strong in-plane texture did not develop until a thickness of about 1 μm.