GaN Etching in BCl 3 /Cl 2 Plasmas
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BCI3 /Ci2
PLASMAS
aR. J. Shul, ac. I. H. Ashby, ac. G. Willison, aL. Zhang, a J. Han, 'M. M. Bridges, bS. J.
Pearton, cJ. W. Lee, and d L. F. Lester aSandia National Laboratories, Albuquerque, NM 87185-0603, [email protected] bUniversity of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611 cPlasma-Therm, Inc., St. Petersburg, FL 33716 d University of New Mexico, Electrical Engineering, Albuquerque, NM ABSTRACT GaN etching can be affected by a wide variety of parameters including plasma chemistry and plasma density. Chlorine-based plasmas have been the most widely used plasma chemistries to etch GaN due to the high volatility of the GaCl, and NCIX etch products. The source of Cl and the addition of secondary gases can dramatically influence the etch characteristics primarily due to their effect on the concentration of reactive C1 generated in the plasma. In addition, high-density plasma etch systems have yielded high quality etching of GaN due to plasma densities which are 2 to 4 orders of magnitude higher than reactive ion etch (RIE) plasma systems. The high plasma densities enhance the bond breaking efficiency of the GaN, the formation of volatile etch products, and the sputter desorption of the etch products from the surface. In this study, we report GaN etch results for a high-density inductively coupled plasma (ICP) as a function of BCI3:C12 flow ratio, dc-bias, chamber pressure, and ICP source power. GaN etch rates ranging from -100 A/min to > 8000 A/min were obtained with smooth etch morphology and anisotropic profiles. INTRODUCTION As 111-V nitride device structures become more complicated and design rules shrink, wellcontrolled etch processes are necessary. To date most of the plasma etch development has been directed toward mesa structures for photonic devices where high-rate, anisotropic, equi-rate etching is required. Recent interest in high power, high temperature electronic devices has added to these etch requirements due to shallower etch depths and smaller critical dimensions than those required for photonic devices. Well-controlled rates, smooth etch morphology, low plasmainduced-damage, and selective etching of one material over another must also be achieved for such devices. Etch requirements are further complicated by the fact that the III-V nitrides etch at much slower rates than conventional III-V compound semiconductors despite similar volatilities of the etch products. Based on the strong bond energies of the III-V nitrides, the rate limiting step of the etch process may be the initial breaking of the group-III-N bonds.' GaN has a bond energy of 8.92 eV/atom, InN 7.72 eV/atom, and AIN 11.52 eV/atom as compared to GaAs which has a bond energy of 6.52 eV/atom. 2 High-density plasma etch systems, including inductively coupled plasmas (ICP), have shown high quality patterning results for group-EIf nitrides due to plasma densities which are 2 to 4 orders of magnitude higher than reactive ion etch (RIE) systems.3" The high plasma flux improves the efficiency of brea
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