Influence of the nucleation process on the azimuthal misorientation of heteroepitaxial diamond films on Si(001)

In order to clarify the mechanisms that limit the alignment for diamond heteroepitaxy on Si(001) the influence of different process parameters during the bias enhanced nucleation step on the misorientation of diamond on Si(001) was evaluated using x-ray diffraction texture measurements, It is shown that the azimuthal width of the {220} pale density maxima in the substrate plane measured in transmission is a quantity that allows a systematic study of the parameter space for oriented nucleation. From the negligible influence of the substrate surface roughness and of the substrate temperature between 675 and 905 degrees C it is concluded that the migration, rotation, and rearrangement processes of nucleated diamond clusters do not control alignment in the temperature range studied. In contrast, the duration of the biasing procedure, the process pressure, and the absolute value of the bias voltage can strongly vary the azimuthal distribution between a full width at half-maximum of 3.9 degrees and more than 15 degrees. Low bias voltages favor narrow distributions whereas high bias voltages are accompanied by extremely low biasing: times (down to 20 s), When the optimum biasing time is exceeded, the orientation is lost via two different routes. Several models for the underlying mechanisms are proposed with those that are most probable pointing to a detrimental influence by ion bombardment. (C) 1997 American Institute of Physics.