The production of high quality optical devices based on porous silicon relies on having precise control over the refractive index and thickness of each porous silicon layer. Until now this has been achieved by pre-calibrating each growth system and making sure that parameters such as wafer doping, electrolyte concentration and temperature are kept constant with each fabrication. However low doped silicon required for IR based silicon photonics has significant non-uniformity in the index and growth rate during formation of the porous silicon. The solution we have developed is based on realtime in-situ monitoring of low-doped silicon during porous silicon growth. This process rapidly measures the optical interference between the porous silicon film and the backside silicon surface. The optical light source comes from six coarse-wavelength-division-multiplexed lasers, with rapid switching between wavelengths achieved using a microelectromechanical switch. The system permits rapid measurement (<1 sec) of the reflection spectra from all lasers, enabling real-time thickness and refractive index of each layer to be determined during growth. Our aim is to enable growth of high quality multi-layer films such as those required for Bragg Reflectors and high-Q Fabry-Perot microcavities. In this paper we briefly describe the instrument, the numerical models developed to gather the measurements, and show preliminary results gathered from this instrument during growth. The results show a good agreement with theoretical optical modelling, and also direct measurements of the porous silicon layers.

Date Published: 30 December 2008
PDF: 9 pages
Proc. SPIE 7267, Smart Materials V, 72670R (30 December 2008); doi: 10.1117/12.817420

Published in SPIE Proceedings Vol. 7267:
Smart Materials V
Nicolas H. Voelcker; Helmut W. Thissen, Editor(s)