AVS 51st International Symposium
    MEMS and NEMS Monday Sessions
       Session MN-MoP

Paper MN-MoP9
Plasma-Free Etch Chemistry to Realize Defect-free GaAs Micromechanical Resonator Structures@footnote 1@

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: S.W. Kang, Seoul National University, Korea
Authors: S.W. Kang, Seoul National University, Korea
S.B. Shim, Seoul National University, Korea
J.H. Kong, Seoul National University, Korea
K.R. Char, Seoul National University, Korea
Y.D. Park, Seoul National University, Korea
Correspondent: Click to Email
We report on the fabrication of GaAs micromechanical resonator structures utilizing plasma-free etch chemistry, by utilizing latticed-matched MOCVD grown GaAs(0.5 µm)/In@sub 0.5@Ga@sub0.5@P(0.5 µm) alloy system patterned by selective wet-etch chemistries. GaAs (100) cap layer was defined with photoresists and patterned in a citric acid/H@sub 2@O@sub 2@ solution, resulting in near vertical side-wall profiles. After GaAs cap patterning and resist removal, HCl solutions of varying concentrations were investigated for selectivity of InGaP over GaAs for various conditions: temperature, agitation, and differing crystallographic directions. For 12 M HCl solution, vertical etch-rate was found to be ~3 µm/min under agitation. Lateral etch of InGaP layer between GaAs layers starts with initial etch fronts of vee, mixed, and dovetail observed by cross-sectional SEM with predominance of dovetail etch front for lateral etch direction 45° from the cleave direction. The lateral etch rate at 20°C for 12 M HCl solution was highly directional dependent with GaAs cap edge patterned parallel to the cleave direction [011] to be nearly zero and edge 45° from the cleave direction to be ~1 µm/min, similar behavior as observed by Cich et al.@footnote 2@ For increasing dilution of HCl, the etch rate, especially lateral etch rate, was drastically reduced, with no observable lateral etch for 1:4 HCl:H@sub 2@O. For all HCl solutions, high selectivity of InGaP over GaAs was observed. Micromechanical GaAs resonator structures with aspect ratios as high as 30 was realized by simply drying in a flow of dry N@sub 2@ gas. Along with the investigation of etch chemistry, expected benefits of plasma-free fabrication of GaAs-based NEMS resonators will be presented. @FootnoteText@ @footnote 1@ This work is partly supported by KOSEF and Samsung Electronics Endowment through CSCMR and by KIST Vision 21 Project.@footnote 2@ M.J. Cich et al., Appl. Phys. Lett. 82, 651 (2003).