Adhesion of polysilicon microbeams in controlled humidity ambients

The authors characterize in-situ the adhesion of surface micromachined polysilicon beams subject to controlled humidity ambients. Beams were freed by supercritical CO{sub 2} drying. Consistent adhesion results were obtained using a post-treatment in an oxygen plasma which rendered the microbeams uniformly hydrophilic. Individual beam deformations were measured by optical interferometry after equilibration at a given relative humidity (RH). Validation of each adhesion measurement was accomplished by comparing the deformations with elasticity theory. The data indicates that adhesion increases exponentially with RH from 30% to 95%, with values from 1 mJ/m{sup 2} to 50 mJ/m{sup 2}. Using the Kelvin equation, the authors show that the data should be independent of RH if a smooth interface is considered. By modeling a rough interface consistent with atomic force microscopy (AFM) data, the exponential trend is satisfactorily explained.

[1]  A. Adamson.  Physical chemistry of surfaces , 1960 .

[2]  J. Greenwood,et al.  Contact of nominally flat surfaces , 1966, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[3]  Hiromitu Naono,et al.  Determination of physisorbed and chemisorbed waters on silica gel and porous silica glass by means of desorption isotherms of water vapor , 1980 .

[4]  J. Israelachvili.  Intermolecular and surface forces , 1985 .

[5]  E. Fuller,et al.  Closure and Repropagation of Healed Cracks in Silicate Glass , 1985 .

[6]  C. Hsu,et al.  Mechanical stability and adhesion of microstructures under capillary forces. II. Experiments , 1993 .

[7]  C. Hsu,et al.  Mechanical stability and adhesion of microstructures under capillary forces. I. Basic theory , 1993 .

[8]  Carlos H. Mastrangelo,et al.  Adhesion release and yield enhancement of microstructures using pulsed Lorentz forces , 1995 .

[9]  R. J. Collins,et al.  Performance impact of monolayer coating of polysilicon micromotors , 1995, Proceedings IEEE Micro Electro Mechanical Systems. 1995.

[10]  Ernest J. Garcia,et al.  Surface micromachined microengine , 1995 .

[11]  B. Bhushan,et al.  The micro-meniscus effect of a thin liquid film on the static friction of rough surface contact , 1996 .

[12]  A. Sunol,et al.  Supercritical fluids : extraction and pollution prevention , 1997 .

[13]  R. Maboudian,et al.  Self-assembled fluorocarbon films for enhanced stiction reduction , 1997, Proceedings of International Solid State Sensors and Actuators Conference (Transducers '97).

[14]  Roger T. Howe,et al.  Effect of hydrogen termination on the work of adhesion between rough polycrystalline silicon surfaces , 1997 .