Stiction of surface micromachined structures after rinsing and drying: model and investigation of adhesion mechanisms

The mechanisms causing stiction of polysilicon structures fabricated by surface micromachining techniques have been investigated. It is found that during drying from rinse liquids attractive dynamic apillary forces are responsible for bringing micromechanical structures into contact with the underlying substrate. Measured adhesion energies of sticking microbridges indicate that van der Waals forces are responstble for the stiction of hydrophobic surfaces and that hydrogen bridging is an additional adhesion mechanism for hydrophilic surfaces. Methods to reduce the stiction problem are indicated. Intruduction A notorious problem of surface micromachined struc-tures using the sacrificial ayer etching technique is the permanent attachment of slender structures to the underlying substrate after drying. This phenomenon is known as sticking or stiction [l-6]. It is assumed that during drying attractive capillary forces bring micro-mechanical structures into contact with the substrate