Comparative evaluation of drying techniques for surface micromachining

Abstract Five different procedures commonly used to rinse and dry released microstructures are compared: evaporation drying with deionized (DI) water or methanol, sublimation drying with t -butyl alcohol or p -dichlorobenzene, and supercritical drying with CO 2 . For objective comparison, identical test structures, made by the MCNC Multi-User MEMS Processes (MUMPs), are used in evaluating the drying techniques. The test chips contain arrays of surface-micromachined polysilicon cantilevers (2 (μm thick, 2 μm gap from the substrate) with varying widths and lengths. Some beams feature dimples or tips to quantify their anti-stiction effect. This study reveals, for the first time, that the maximum beam length obtainable increases as the beam width increases for the cases of sublimation and supercritical drying, opposite to the previously known case of evaporation drying. Both sublimation drying methods as well as supercritical drying rendered good results, releasing cantilevers up to 700 μm in length without stiction. We also introduce a new setup that considerably improves the way sublimation is used to dry microstructures.

[1]  Chun‐Sing Lee,et al.  Dry release for surface micromachining with HF vapor-phase etching , 1997 .

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

[3]  H. Fujita,et al.  Design, Fabrication, And Testing Of A C-shape Actuator , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[4]  H. Fujita,et al.  Electrostatic parallelogram actuators , 1991, TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers.

[5]  John Tyler Bonner,et al.  On size and life , 1983 .

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

[7]  B. Bhushan.  Handbook of micro/nano tribology , 1995 .

[8]  H. Tilmans,et al.  Stiction of surface micromachined structures after rinsing and drying: model and investigation of adhesion mechanisms , 1994 .

[9]  Roger T. Howe,et al.  The effect of release-etch processing on surface microstructure stiction , 1992, Technical Digest IEEE Solid-State Sensor and Actuator Workshop.

[10]  Chang-Jin Kim,et al.  Polysilicon surface-modification technique to reduce sticking of microstructures , 1996 .

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

[12]  藤正 巌,et al.  IEEE Micro Electro Mechanical Systems Workshop. , 1989 .

[13]  H. Fujita,et al.  An integrated lateral tunneling unit , 1992, [1992] Proceedings IEEE Micro Electro Mechanical Systems.

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

[15]  C. Mastrangelo,et al.  A dry-release method based on polymer columns for microstructure fabrication , 1993, [1993] Proceedings IEEE Micro Electro Mechanical Systems.

[16]  Roger T. Howe,et al.  Ammonium Fluoride Anti-stiction Treatments For Polysilicon Microstructures , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[17]  H. Fujita,et al.  Photoresist-Assisted Release of Movable Microstructures , 1993 .

[18]  M. Orpana,et al.  Control of residual stress of polysilicon thin films by heavy doping in surface micromachining , 1991, TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers.

[19]  W. Messner,et al.  Effective methods to prevent stiction during post-release-etch processing , 1995, Proceedings IEEE Micro Electro Mechanical Systems. 1995.

[20]  J. J. Sniegowski,et al.  Advances in processing techniques for silicon micromechanical devices with smooth surfaces , 1989, IEEE Micro Electro Mechanical Systems, , Proceedings, 'An Investigation of Micro Structures, Sensors, Actuators, Machines and Robots'.