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Jeeun Cho
2007 U.S. Student
Advisor: Patrick L. LiKamWa
"Electro-Chemical Etching of
Semiconductor Micro- and Nanostructures"
Electron beam lithography in combination with inductively coupled plasma - reactive ion
etching (ICP-RIE) has been used to obtain sharp straight wall etching for the fabrication of prepatterned
semiconductor micro- and nano-structures. Because of its high handling cost and
complexity, and its associated problems with defect formation in the semiconductor, an
alternative process, electro chemical etching (ECE) is being developed. ECE is very inexpensive
and simple to use with different selection of etchants. InP was chosen as the material of interest
because of its direct bandgap and strong interaction with charge carriers which are crucial in
optoelectronics. The etching processes was achieved using very weak aqueous solutions of HCl,
HBr, and mixture of HCl and HNO3 with varying current level, etching time, and acidic
concentration. The etching rate was observed to be highly dependent on the values of those
variables. Various patterns of different sizes and aspect ratios were fabricated on InP samples to
study the side view profile of etched surface. The cleaved sample showed evidence that the
straight wall could be achieved with current larger than 5mA. The measured vertical to sideways
etching ratio hinted that these acidic solutions’ gave rise to isotropic etching of the
semiconductor. It is believed that this is caused by the electric field changing its direction from
vertical to horizontal during etching process, resulting in inevitable lateral etching. ...full text
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