Micross

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Silicon Fabrication Technologies for Micro Filters
Keywords: Silicon microfabrication , microfilters , microfludics
Silicon microfabrication techniques allow for the development of microfludics systems with very accurate control of size and uniformity of structures. In this paper we report on the silicon fabrication process of micro filters for versatile application in fluidics systems. Microfilters are composed of an ordered array of pillars and of supply channels. Depending on pillar pitch, they can be used for, e.g., electrophoresis, chromatography and purification of biological mixtures. The process that we have developed consists in defining initially 1 µm diameter pillars with a pitch of 1 µm or less in an oxide hard mask with a UV stepper and stitching is used to form few cm long patterns across the 200mm wafers. Secondly, supply channels are defined with 1x mask alignment lithography. After definition of supply channels, deep reactive ion etching of silicon is performed with an optimized recipe to etch submicron pillars and supply channels of few millimeters at the same time. The simultaneous etch of both structures avoids complex lithography steps otherwise necessary to protect the pillars while etching the supply channels or vice versa as would be done conventionally. The etch process consists of three different gas chemistry comprising of C4F8/O2/SF6. The addition of oxygen to standard Bosch etch process allow for reduced mask erosion for submicron structures and increased passivation of sidewalls. This help in obtaining deep pillars with aspect ratio greater than 30. At the same time it allows for larger supply channels to be etched without detrimental effect on the profile of pillars. Teflon like residue formed during etching were removed with a specially optimized dry strip recipe. Wafers were then anodically bonded to 200mm Pyrex wafers in order to seal the channels. Pyrex wafer allow the use of optical detection systems. Feed through holes for accessing the supply channels are etched on the backside of Si wafer. This paper report on a simple and novel fabrication process of silicon micro-filters composed of an ordered array of pillars and of supply channels.
Bivragh Majeed, Researcher
IMEC
Leuven, Vlaams Brabant 3001-B,
Belgium


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