MICROSTRUCTURE EVOLUTION IN AMORPHOUS GE SI MULTILAYERS GROWN BY MAGNETRON SPUTTER-DEPOSITION/

Microstructure evolution in amorphous Ge/Si multilayers grown by dual- target de magnetron sputtering was investigated by cross-sectional tra nsmission electron microscopy, x-ray diffraction, and growth simulatio ns. In films grown under low intensity ion-irradiation conditions, the structure is columnar with low-density regions along column boundarie s where layer intermixing was observed. By increasing the low-irradiat ion intensity (controlled by an applied negative substrate-bias), stru ctures with smooth and well-defined layers could be grown. This was ac hieved at bias voltages between 80 and 140 V, depending on the sputter ing gas pressure. As the ion-irradiation intensity is further increase d, ion-induced intermixing degrades the layer interfaces and finally a n amorphous Si1-xGex alloy forms. The combination of x-ray diffraction measurements and reflectivity calculations reveals an asymmetry betwe en the Ge/Si and Si/Ge interface widths due, primarily, to a correspon ding asymmetry in incident particle energies during the growth of alte rnate layers.