Post-processing of Commercial CMOS Chips for the Fabrication of DNA Bio-FET Sensor Arrays
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0951-E05-09
Post-Processing of Commercial CMOS Chips for the Fabrication of DNA Bio-FET Sensor Arrays W. H. Jiang1, D. Landheer1, G. Lopinski2, A. Rankin3, N. G. Tarr3, and M. J. Deen4 1 Institute for Microstructural Sciences, National Research Council of Canada, Ottawa, K1A 0R6, Canada 2 Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, K1A 0R6, Canada 3 Department of Electronics, Carleton University, Ottawa, K1S 5B6, Canada 4 Department of Electrical and Computer Engineering, McMaster University, Hamilton, L8S 4K1, Canada ABSTRACT A BioFET array can be fabricated by post-processing of a standard CMOS chip if temperatures are kept below 450 °C and radiation or ion-bombardment damage is minimized. The processing starts with encapsulation by deposition of a low stress, electrolyte-impermeable silicon nitride layer by PECVD at 375 oC. Anisotropic reactive ion etching with an inductively coupled plasma using C4F8 and Ar was used to remove the silicon nitride and oxide layers above the poly-silicon gates. The poly-silicon was then etched off using a selective wet etch. The effect of the processing was characterized by making current-voltage and capacitance-voltage measurements with MOS capacitor structures at each stage of processing and results showed that trapped charges or interface states could be annealed out at low temperatures. Scanning electron microscopy was used to examine the cross-section of the gate areas after the etching. The results of current-voltage measurements with a Ag/AgCl reference electrode on devices in electrolyte solutions were compared to the results of charge-sheet model calculations including the effect of amphoteric charging sites on the oxide and the potential drops in the electrolyte. Measurements showing the threshold shifts subsequently produced by DNA probe attachment and hybridization will also be presented. INTRODUCTION In the past decade, it has been shown that sensitive detection of DNA fragments should be possible using the field-effect on Si [1-3], raising the possibility of incorporating the sensors on chips using standard commercial metal-oxide-silicon (MOS) processes. This sensitive electrical method for the detection of oligonucleotides could open the path to micro-array technologies, not dependent on bulky optical scanners that are not easy to apply in point-of-use applications, and incorporating all the advantages of complementary MOS (CMOS) technology; low cost, integrated analogue and digital signal processing, and optical or wireless transfer of preprocessed data to a simple hand-held instrument. In this paper, we will report the post processing of standard CMOS chips for the fabrication of field effect device sensor arrays. Preliminary results showing the direct electronic detection of DNA attachment and hybridization on the gate oxide surface will also be presented.
EXPERIMENT The post-processing starts with passivation of the chip by silicon nitride film using an Oxford parallel plate plasma enhanced chemical vapor deposition (
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