Grazing incidence reciprocal space mapping of partially relaxed SiGe films

Epitaxially grown lattice mismatched semiconductor structures are increasin gly important for microelectronic and optoelectronic applications. Recently , a great deal of research has been carried out on strain relaxation mechan isms in lattice mismatched epitaxial films. Here, we describe triple-axis x -ray diffraction measurements that were performed to study strain relaxatio n mechanisms and dislocation formation in Si1-xGex alloys grown on (0 0 1) Si substrates. At low growth temperature (T-g less than or equal to 600 deg rees C) and small lattice mismatch (< 2%), two different mechanisms of stra in relaxation are observed, depending on the growth temperature and the mag nitude of the strain. At Higher growth temperatures or larger lattice misma tch, strain relaxation occurs initially by surface roughening. Subsequently , 60 degrees misfit dislocations nucleate in regions of high strain. At sma ller lattice mismatch or lower growth temperature, the surface of the film does not roughen and the 60 degrees misfit dislocations are formed primaril y by Frank-Read multiplication. Triple-axis x-ray diffraction reciprocal sp ace maps taken at grazing incidence on very thin epitaxial films can easily distinguish between these two mechanisms. Here, the lattice planes perpend icular to the interface are measured, whereas conventional diffractometry l ooks either at the planes parallel to the wafer surface or at planes having components both parallel and perpendicular to the surface. In the grazing incidence geometry, thickness broadening of the x-ray peak is eliminated, s ince the film is essentially infinitely thick parallel to the surface.