This work contributes to the understanding of anisotropic etching of silicon, for microsystems technology, by studying Si/Al selectivity during anisotropic etching of silicon in tetra-methyl ammonium hydroxide (TMAH). By under-etch experiments using a wagon-wheel mask pattern, Si/Al selectivity is studied in relation to trends in etch anisotropy, etched surface morphology, and variations of under-etch behavior with mask-edge angle. TMAH at 5 wt % is used, with or without the additives: dissolved silicon and ammonium persulfate. High Si/Al selectivity is accompanied by obvious changes in the roughness, flatness, and etch rate of the {100} cavity bottoms, by large changes in anisotropy as seen in under-etch rate curves, by lower ratio of {101} to {100} etch rates, and by more regular 〈101〉-oriented steps on non-{111} cavity sidewalls. The conditions are consistent with a low rate of attack of 〈101〉-directed periodic bond chains in the Si lattice.

No abstract

Vibrating beam structures may be used as sensing elements in an angular rate measurement sensor. Achieving a square cross-sectional area with smooth vertical side walls and sharp edges is necessary for these beams. In this work, fabrication of beams with reasonably smooth vertical sidewalls and accurate dimensions, using anisotropic etching of silicon in TMAH, has been investigated. Beams with various thicknesses (500 -100 microns) are fabricated. It is shown that by carefully aligningthemaskat45°fromthe<110> wafer flat, andby maintaining the concentration of TMAH at 25%, it is possible to achieve smooth vertical sidewalls with good uniformity along the length of the beam. Adequate control over the beam lateral dimension is achieved by etching in a 2-step procedure with the second step at a lower temperature (lower etch rate). Single-sided and doublesided masking techniques are investigated in order to fabricate the beams. An alternative design is presented to form the beams using a standard CMOS process.

No abstract

No abstract