Post-CMOS Processing for High-Aspect-Ratio

We present a new fabrication sequence for inte- grated-silicon microstructures designed and manufactured in a conventional complentary metal-oxide-semiconductor (CMOS) process. The sequence employs a post-CMOS deep silicon back- side etch, which allows fabrication of high aspect ratio (25:1) and flat (greater than 10 mm radius of curvature) MEMS devices with integrated circuitry. A comb-drive resonator, a cantilever beam array and a -axis accelerometer were fabricated using this process sequence. Electrical isolation of single-crystal silicon was realized by using the undercut of the reactive ion etch (RIE) process. Measured out-of-plane curling across a 120- m-wide 25- m-thick silicon released plate was 0.15 m, which is about ten times smaller than curl of the identical design as a thin-film CMOS microstructure. The -axis DRIE accelerometer structure is 0.4 mm by 0.5 mm in size and has a 25- m-thick single-crystal silicon proof mass. The measured noise floor is 1 mG/ Hz, limited by electronic noise. A vertical electrostatic spring "hardening" effect was theoretically predicted and experimentally verified. (687)

[1]  Dennis C. Ghiglia,et al.  Two-Dimensional Phase Unwrapping: Theory, Algorithms, and Software , 1998 .

[2]  J. Greenwood.  Silicon in mechanical sensors , 1988 .

[3]  G. Fedder,et al.  Laminated high-aspect-ratio microstructures in a conventional CMOS process , 1996 .

[4]  S. Santhanam,et al.  Laminated, sacrificial-poly MEMS technology in standard CMOS , 2000 .

[5]  W. Riethmuller,et al.  Novel Process For A Monolithic Integrated Accelerometer , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[6]  Albert P. Pisano,et al.  Polysilicon integrated microsystems: technologies and applications , 1996 .

[7]  C. Quate,et al.  Fabrication of high-density cantilever arrays and through-wafer interconnects , 1998 .

[8]  R. Howe,et al.  Post-CMOS integration of germanium microstructures , 1999, Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291).

[9]  Christofer Hierold,et al.  Intelligent CMOS sensors , 2000, Proceedings IEEE Thirteenth Annual International Conference on Micro Electro Mechanical Systems (Cat. No.00CH36308).

[10]  G. Fedder,et al.  A lateral capacitive CMOS accelerometer with structural curl compensation , 1999, Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291).

[11]  Gary K. Fedder,et al.  A CMOS z-axis capacitive accelerometer with comb-finger sensing , 2000, Proceedings IEEE Thirteenth Annual International Conference on Micro Electro Mechanical Systems (Cat. No.00CH36308).

[12]  D. M. Freeman,et al.  Nanometer resolution of three-dimensional motions using video interference microscopy , 1999, Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291).

[13]  K. Najafi,et al.  A low-voltage tunneling-based silicon microaccelerometer , 1997 .