(a) 100 µm - Helmholtz-Zentrum Berlin

4 Results
In order to understand and optimize the aluminum-induced layer exchange pro-
cess (ALILE) two main process parameters were modified. The role of an interlayer
between aluminum and silicon was intensely studied (sec. 4.1). Therefor different
types of oxidation conditions were tested. The thickness of the oxide layer was
varied in a wide range from just about 1 nm to several 10 nm. On the one hand
thick oxide layers and high annealing temperatures leads to large grain sizes in
short process times. On the other hand thin oxide layers and low annealing tem-
peratures enhances the formation of (100) orientated grains. Molybdenum as an
alternative interlayer was investigated. It is shown that molybdenum interlayers
enable the layer exchange process as well. They even facilitate the lift-off process
of the silicon islands.
In a thermal annealing process the process temperature is a crucial parameter. So
far only isothermal annealing experiments have been reported in the ALILE pro-
cess. Here the influence of different temperature profiles was studied (sec. 4.2).
Experiments on increasing and decreasing the temperature during annealing were
performed. The heating step experiments show that after a certain point in the
annealing process the temperature can be increased without causing additional
nucleation but resulting in shorter process time. This reinforces the existence of
depletion regions around the growing grains. Once the depletion regions over-
lap the temperature can be increased. The depletion regions become apparent in
cooling step experiments where additional nucleation is caused by supercooling.
Zones without additional nucleation around existing grains are direct experimen-
tal proof of the existence of concentration profiles, namely the depletion regions.