SURFACE ROUGHENING DURING LOW-TEMPERATURE SI(100) EPITAXY

Reflection high energy electron diffraction (RHEED) was used to invest igate surface roughening during low temperature Si(100) homoepitaxy. T he use of RHEED allowed in situ real-time collection of structural inf ormation from the growth surface. RHEED patterns were analyzed using a simple kinematic diffraction model which related average surface roug hness and average in-plane coherence lengths to the lengths and widths of individual RHEED diffraction features, respectively. These RHEED a nalyses were quantified by calibrating against cross-section transmiss ion 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 v alues a factor of similar to 2 times lower than those obtained from TE M analyses. RHEED was then used to analyze surface roughening during S i(100) homoepitaxial growth in a range of temperatures, 200-275 degree s C. Initially, surface roughness increased linearly with deposited th ickness st a roughening rate that decreased with increasing growth tem perature. At each growth temperature, near the crystalline/amorphous S i phase transition, the rate of surface roughening decreased. This dec rease coincided with the formation of facets and twins along Si{111} p lanes. Surface roughness eventually saturated at a value which followe d an Arrhenius relation with temperature E-act similar to 0.31 +/- 0.1 eV. This activation energy agrees well with the activation energy for the crystalline/amorphous Si phase transition, E-act similar to 0.35 eV, and suggests that limited thickness epitaxy is characterized by th is 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 d ependent. Values of average coherence lengths, at the crystalline/amor phous Si phase transition, also increased with growth temperature. All of these data sue consistent with a model that links surface rougheni ng to the formation of critically sized Si{100} facets and the eventua l breakdown in crystalline growth. (C) 1997 American Institute of Phys ics.