Black poly-silicon: A nanostructured seed layer for sensor applications

• This is the first description and analysis of b-Si fabrication in poly-silicon thin films using deep reactive ion etching.
• Morphology of black poly-Si (BPS) film is studied in terms of etching parameters like temperature, O2 flow and RF power.
• The effect of the grain size of poly-silicon layer on BPS morphology is analyzed and compared to black c-Si references.
• This is the first demonstration of BPS seed layer applied in a basic MEMS application (potential sensor).

Nanostructured silicon surfaces like black-silicon (b-Si) are of great interest in current sensor technology. This paper presents an alternative method to fabricate b-Si in poly-silicon thin film prepared on pre-deposited insulation layer in order to open new door to the integration of silicon nanograss in biosensor application as sensing or seed layer. In our experiment, black poly-silicon (BPS) is formed in LPCVD deposited poly-silicon thin film by deep reactive ion etching (DRIE) at cryogenic temperature in SF6 + O2 plasma. Etching parameters like temperature, O2 flow and RF power is varied and morphology of the resultant thin film is analyzed by scanning electron microscopy. The fabricated samples are subjected to a comparative investigation, which contained pillar density, directionality, etch rate and loading effects. The effect of the grain size of poly-silicon layer is analyzed and compared to samples micromachined in single-crystalline silicon (c-Si). We found that fabrication parameters of BPS morphology significantly differ from that of conventional b-Si realized in c-Si substrate. A simple application example of our BPS layer for increasing specific surface area of potential sensors is also demonstrated. As far as we know, this is the first demonstration and systematic study of b-Si fabrication in poly-silicon thin film.