Direct Exfoliation of Large-area and Ultra-Thin Porous Si Layer from Si Wafer
Ru-Chi, Tsai1*, Tze-Chih, Chang1, Yi-Jung, Wang1, Jian-Chiun, Chen2, Yu-Lun, Cheuh1
1Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan
2Industrial Technology Research Institute, Hsinchu, Taiwan
* presenting author:RuChi Tsai,
Recently, many research move on to the porous thin film of silicon. In the cases of crystalline silicon-based solar cells, a μm-thick silicon layer is enough to absorb the required power from solar energy. As a result, to reduce the manufacturing cost by introducing thinner silicon thin film materials has attracted much attention. And for the porous structure, its absorption is better than the usual, it can also apply on some gas sensor, such as CO2 sensor.
We use the electrochemical etching processes to get the porous thin film. We use the hydrofluoric acid and alcohol as electrolyte, and try different current density to controlling the porosity. Now, we can have a porous film in 10 cm2 and the porous structure on the substrate in 15*15cm2 . For the flexible porous thin film, we use two step etching process to form the triple film, the different mechanical properties caused by their porosity let the top layer pill of from the substrate. And the large size etching process, although we can successfully pill off the top layer, we still can form a uniform porous structure.

Keywords: porous silicon, ultra-thin silicon films, thin film epitaxy, electrochemical etching