ETCHING TECHNOLOGY FOR CHROMATOGRAPHY MICROCHANNELS

Half-circular channels, to be used for gas chromatography, were etched isotropically using a mixture of HF, HNO3 and H2O. Two wafers with ha lf-circular channels were bonded on top of each other to yield channel s with a circular cross-section. During etching the so-called ''loadin g effect'' was encountered: the etch rate depends on the local structu re density. To solve this, extra structures were placed around the cha nnels to create an equal structure density over the wafer and so preve nt irregularities in channel width. To eliminate the alignment problem s that arise when bonding two wafers with isotropically etched channel s together, a method which combines deep trench etching, passivation a nd isotropic etching was developed to construct channels under the sur face of a wafer. (C) 1997 Published by Elsevier Science Ltd.