Extensive research has been done on porous silicon (PS) and its applications in
optoelectronics since the discovery of its light emitting properties. Porous silicon technology is also
used for silicon micro machining. However, porous films can be seriously strained and this often
causes mechanical curling, fracture and device failures. In the present study an optical apparatus
based on substrate curvature method was developed for intrinsic stress measurement of thin films,
which offered a lot of advantages as overall field, non-contact, high precision, nondestructive, easy
operation and quick response. Using the apparatus, the residual stress in porous silicon layers
prepared by electrochemical etching was obtained. The residual stresses in the films were
determined by measuring the curvature of the Si substrate before and after etching. It is found that
the residual tensile stress tends to increase with the porosity increasing and the doping concentration
of the silicon wafer increasing. The results show that there is a deep connection between the microstructure
PS and the residual stress distribution.
Residual stress measurement of porous silicon thin film by substrate curvature method