Highly Chemical Reactive Ion Etching of Gallium Nitride
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COBRA Inter-University Research Institute on Communication Technology Eindhoven University of Technology - Department of Electrical Engineering P.O.Box 513, NL-5600 MB Eindhoven, Netherlands 2 Department of Information Technology (INTEC), University of Ghent, Sint Pieternieuwstraat 41, 9000 Ghent, Belgium 3 High Pressure Research Center, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw – Poland 4 Experimental Solid State Physics III, RIM, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, Netherlands
Abstract: A highly chemical reactive ion etching process has been developed for MOVPE-grown GaN on sapphire. The key element for the enhancement of the chemical property during etching is the use of a fluorine containing gas in a chlorine based chemistry. In the perspective of using GaN substrates for homo-epitaxy of high quality GaN/AlGaN structures we have used the above described RIE process to smoothen Gapolar GaN substrates. The RMS value, measured by AFM, went from 20 Å (after mechanical polishing) down to 4 Å after 6 minutes of RIE. Etching N-polar GaN resulted in a higher etch rate than Ga-polar materials (165 vs. 110 nm/min) but the resulting surface was quite rough and suffers from instability problems. Heat treatment and HCl dip showed a partial recovery of Schottky characteristics after RIE.
Introduction GaN materials are very interesting for optoelectronic and microelectronic applications like blue and green LEDs, blue lasers, UV photodetectors, high power and high temperature HEMTs. GaN and its related materials (AlGaN, InGaN, InAlGaN) are most commonly grown, using metal organic vapour phase epitaxy (MOVPE) or molecular beam epitaxy (MBE), on α-Al2O3 substrates. For specific applications like high power transistors, silicon carbide substrates are used because of their higher thermal conductivity. The lattice mismatch remains high in both cases with an advantage for SiC, and hence epitaxial layers suffer from stress induced by the lattice mismatch which results in a very high dislocation density (in the range of 108-1010 cm-2). GaN bulk materials form an attractive solution to circumvent the problems of lattice mismatch encountered in hetero-epitaxy by allowing a perfect lattice-matched epitaxy. Dry etching of GaN has been extensively investigated using numerous plasma-based machines and sources. High etch rate (1.3 µm/min) was reported using an electron cyclotron resonance (ECR) [1]. Conventional reactive ion etching (RIE) generally shows lower etch rates and leads to higher level of induced damages. We have developed a highly
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chemical reactive ion etching process using a conventional parallel plate reactor. In a previous work [2] we reported a fourfold increase in etching rate when simply adding SF6 to SiCl4 + Ar. This highly chemical
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