Surface roughening during low temperature Si(100) epitaxy

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Abstract
Reflection high energy electron diffraction (RHEED) was used to investigate surface roughening during low temperature Si(100) 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 (TEM) 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 ∼2 times lower than those obtained from TEM analyses. RHEED was then used to analyze surface roughening during Si(100) 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 Si{111} planes. Surface roughness eventually saturated at a value which followed an Arrhenius relation with temperature Eact∼0.31±0.1 eV. This activation energy agrees well with the activation energy for the crystalline/amorphous Si phase transition, Eact∼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 Si{100} facets and the eventual breakdown in crystalline growth.