Ultrafast Aqueous Etching of Gallium Arsenide
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ULTRAFAST AQUEOUS ETCHING OF GALLIUM ARSENIDE A.E. Willner, D.V. Podlesnik,
H. Gilgen, and R.M. Osgood,
Jr.
Microelectronics Sciences Laboratories Columbia University 10027 New York, New York ABSTRACT Very rapid room-temperature photochemical etching of n-type GaAs was achieved in aqueous hydrofluoric acid in The etch conjunction with ultraviolet laser illumination. rates of -500 )am/min represent an order of magnitude increase in etch rates over previously reported results for solutions Furthermore, no hydrofluoric acid. that contained of nitric acid into the hydrofluoric acid incorporation solution resulted in smooth etched surfaces thus allowing This rapid process was used to deep, waveguiding etching. etch deep, large-area structures in GaAs samples. INTRODUCTION etching has photochemical aqueous Laser-induced previously been demonstrated in various semiconductors [1-5]. a useful way to fabricate microstructures This technique is utilizing a stationary or scanned laser writing beam. The process is electrodeless, maskless, single-step, and produces Despite damage-free structures in a nonthermal environment. these advantages, the usefulness of this process to write over large
areas
is
quite limited unless the etching speed can be
increased from the values cited in the literature. Typically, the reported etch rates for the nonthermal regime have been We report here the achievement between 10 and 50 lam/min [6]. of an increase of at least an order of magnitude in the etch rates for n-type GaAs. This process shows promise for large-area micromachining of semiconductors. EXPERIMENTAL SETUP The etching experiments were performed primarily with 257-nm output of a frequency-doubled Ar+ laser, the comparison with etching at a longer although a brief wavelength was done with the Ar+-laser fundamental at 514 ram. The laser light was manipulated by a scannable optical microscope; using a computer controlled stage, we could scan The the sample perpendicular to the axis of the laser beam. semiconductor sample was immersed in an electrolyte solution inside a plastic cell with a sapphire window. Two different aqueous solutions were examined: a binary solution, HF:H 2 0, Etching solutions and a ternary solution, HF:HNO 3 :H 2 0. The deep were diluted and produced negligible dark etching. 257 nm, which has been shown to ultraviolet laser light at etch GaAs efficiently, was focused to a 3-pam spot with a 1OX The incident microscope objective onto the GaAs surface [6]. laser power density ranged from 1 W/cm2 to 3 kW/cm 2 . For Mat. Res. Soc. Symp. Proc. Vol- 75. ' 1987 Materials Research Society
404
range this neglected.
of
laser
intensities
thermal
effects
can
be
n-type, (100) The samples used in our experiments were Before the 1018 cm- 3 . GaAs wafers doped with Si to the samples were photochemical experiments were performed, cleaned by a standard chemical washing procedure and dried An x-ray photoelectron spectrometer (XPS) was used with N2 . Etched chemical composition. the surface to measure microstructures w
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