Raman investigation of stress and phase transformation induced in silicon by indentation at high temperatures

¹ BTU Cottbus, LS Experimentalphysik II, Universitätsplatz 3-4, 03044 Cottbus, Germany
² IHP/ BTU JointLab, Universitätsplatz 3-4, 03044 Cottbus, Germany
³ Institute of Solid State Physics of RAS, 142432 Chernogolovka, Moscow distr., Russia
⁴ IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany

Corresponding author: kouteva@tu-cottbus.de

Received: 4 July 2003
Accepted: 9 December 2003
Published online: 15 July 2004

Abstract

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.