Investigation of attractive forces between PECVD silicon nitride microstructures and an oxidized silicon substrate

A troublesome phenomenon encountered durmg the reahzatlon of free-standmg mlcrostructures, for example, beams, diaphragms and micromotors, IS that mltlally released structures afterwards stick to the substrate This effect may occur durmg wafer drying after the etching process has been completed, as well as during normal operation as soon as released structures come mto contact with the substrate In this paper the most Important types of attractive forces are dIscussed with respect to thetr possible influence on the performance of mtcromachmed structures It IS concluded that the mam reason for stlckmg of PECVD slhcon mtnde mlcromachmed structures IS adsorptron of water molecules The water molecules, adsorbed on both surfaces, attract each other as soon as the surfaces come mto contact It IS shown that a chemical surface modlficatlon, m order to achieve hydrophobic surfaces, IS an effective method for avoldtng adsorption of water, and therefore reduces sticking Sticking of mlcromachmed structures during drying IS reduced by rmsmg \nth a non-polar hqmd before wafer drying