NANOPOROUS SILICON MEMBRANE FOR BIOMOLECULAR SEPARATION

Abstract

Separation of biomolecules based on their size and charge is an important procedure employed in biomolecular analysis. Nanosieve comprising of a semi-permeable membrane with nanometer-sized pores is used for this purpose. Described here is the fabrication of ultra thin nanoporous silicon membrane, which can be used as nanosieve, making use of standard microelectronics fabrication techniques. Lithography and bulk silicon etching is used to initially create a 10 μm thick sacrificial membrane in the center of a 200 μm thick silicon substrate. A three-layer stack of SiO2 , amorphous silicon ( a-Si ) and SiO2 is then deposited using chemical vapor deposition technique. The sample is subjected to rapid thermal annealing during which pores are formed in the a-Si layer. Finally, the 15 nm thick nanoporous silicon membrane is released using reactive ion etching of the sacrificial membrane. The formation of the pores is confirmed by transmission and scanning electron microscope images. At present the pore formation is random; our future work will focus on controlled nucleation of silicon nanocrystals so as to get pores at desired locations.