To study the material deterioration at and around the
support contacts during processing of silicon wafers, we used
Rockwell indentation at elevated temperatures as a model.
Cz-silicon was subjected for 30 s to a load of 1.5 N, at
temperatures between 70 °C and 660 °C. The
resulting morphology was checked by Scanning Electron Microscopy.
Micro Raman Spectroscopy was used to monitor residual stress and the
occurrence of silicon polymorphs. We found strong compressive
stress inside the indented area, with a dramatic drop and reversal
to tensile stress at its boundary. The morphology shows a top hat
profile, covered with a mesh of vein-like structures. Crystalline
phases such as Si-III, Si-IV, Si-XII, and amorphous silicon are
observed. Outside the spot, the situation depends strongly on the
indentation temperature. Up to 400 °C the material appears
practically unstressed, with a high density of relaxation cracks.
At 500 °C and 600 °C a transition is found from
strong tensile stress at the boundary to another region of compressive
stress extending over more than 40 μm, associated with a
significantly lower crack density. At still higher temperature
(660 °C) the crack density tends to zero, and comparably weak
stress seams to oscillate between compressive and tensile.