Patterning III-N Semiconductors by Low Energy Electron Enhanced Etching (LE4)
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H.P. Gillis*, M.B. Christopher*, K.P. Martin#, and D.A. Choutov#@ *Departmentof Chemistry and Biochemistry, UCLA, Los Angeles, CA 90095. #MicroelectronicsResearch Center, Georgia Tech, Atlanta, GA 30332 @PresentAddress: NationalSemiconductor, San Jose, CA
Cite this article as MRS Internet J. Nitride Semicond. Res. 4S1, G8.2(1999)
ABSTRACT Fabricating device structures from the III-N wide bandgap semiconductors requires anisotropoic dry etching processes that leave smooth surfaces with stoichiometric composition after transferring high-resolution patterns with vertical sidewalls. The purpose of this article is to describe results obtained by a new low-damage dry etching technique that provides an alternative to the standard ion-enhanced dry etching methods in meeting these demands for processing the HI-N materials. INTRODUCTION The Group II nitride wide bandgap semiconductors hold the potential for important technological innovations in optoelectronics and in high power, high frequency microelectronics.1
Blue and green Light Emitting Diodes (LEDs) are available,4 5 and blue
Laser Diodes have been reported. 6 Moreover, transistors fabricated from the 1I-N materials operate at much higher temperatures and under more adverse conditions than similar devices based on more familiar materials, because of the combination of wide bandgap, strong chemical bonds, and relative chemical inertness.
These same properties of high chemical bond
energies and relative chemical inertness lead to difficulties in processing the TII-N materials by standard lithographic and etching processes.8 Since only very limited wet etching reactions have been identified for these materials, 9 10fabrication of even large structures requires dry etching. Reactive Ion Etching (RIE) gives very slow rates and requires unusually high ion energies; the results are ion bombardment damage, modified stoichiometry in surface and near-surface G8.2 Mat. Res. Soc. Symp. Proc. Vol. 537 © 1999 Materials Research Society
regions, anddry a tendency toward the11 overcut profiles and trenching effects Resonance familiar in (ECR) iondominated etching processes. 121314etch High-density Electron Cyclotron microwave plasmas at modest power, sometimes accompanied by heating the sample to 200°C, produce acceptable etch rates; however, further increase of plasma power and rf bias on the sample to increase etch rate again creates ion-induced damage, alters stoichiometry, and roughens the surface.•S 16 17 Depending on plasma power and rf bias, ECR etching of GaN produces RMS surface roughness from 4 nm to 85 nmJ8 Chemically Assisted Ion Beam Etching (CAIBE), in which Ar+ ion beams at 500 eV are directed to the etching surface through a background pressure of reactive gases, has produced vertical profiles on features 2.0 •tm wide (but not on sub-micrometer features), but with N depletion at the etched surfacesJ9 20 2122 Two recent comprehensive reviews summarize results achieved for the HI-N materials with these standard ion-enhanced dry etching techniques and provide ref
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