High-Density Plasma-Induced Etch Damage of GaN
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"SandiaNational Laboratories, Albuquerque, NM 87185-0603, [email protected] "Universityof Florida, Department ".Office of Materials Science and Engineering, Gainesville, FL 32611
of Naval Research, Arlington, VA 22217 ....University of New Mexico, Center for High Technology Materials, Albuquerque, NM 87106
ABSTRACT Anisotropic, smooth etching of the group-Ill nitrides has been reported at relatively high rates in high-density plasma etch systems. However, such etch results are often obtained under high dc-bias and/or high plasma flux conditions where plasma induced damage can be significant. Despite the fact that the group-III nitrides have higher bonding energies than more conventional 11-V compounds, plasma-induced etch damage is still a concern. Attempts to minimize such damage by reducing the ion energy or increasing the chemical activity in the plasma often result in a loss of etch rate or anisotropy which significantly limits critical dimensions and reduces the utility of the process for device applications requiring vertical etch profiles. It is therefore necessary to develop plasma etch processes which couple anisotropy for critical dimension and sidewall profile control and high etch rates with low-damage for optimum device performance. In this study we report changes in sheet resistance and contact resistance for n- and p-type GaN samples exposed to an Ar inductively coupled plasma (ICP). In general, plasma-induced damage was more sensitive to ion bombardment energies as compared to plasma flux. In addition, pGaN was typically more sensitive to plasma-induced damage as compared to n-GaN.
INTRODUCTION Plasma-induced damage has become more relevant to the group-Ifi nitride materials as interest in electronic devices has increased. For example, with the recent reports of GaN/AlGaN heterojunction bipolar transistors (HBTs) 1-3 low damage etch processes are required to form the collector and base contacts. For HBTs, plasma-induced damage can increase surface recombination currents in the base-emitter junction and surface generation currents in the basecollector junction. Furthermore, the active regions of many electronic devices of interest are often shallow thus requiring low damage plasma processes to ensure optimum device performance. To date, the majority of plasma etch development for the group-Ell nitrides has been for optoelectronic devices where mesa structures are etched to depths often greater than 1 gm. The etch requirements typically include high rate (- 1 lim/min), smooth sidewall morphologies, and anisotropic profiles. With the increased interest in electronic devices, etch requirements must also include slow, controlled etch rates, selectivity of one material over another, and lowdamage. High-density plasma (HDP) etch systems, and in particular inductively coupled plasma (ICP) etch systems, have shown encouraging results for the development of versatile, wellcontrolled etch processes. For example, GaN etch rates ranging from -100 A/min to >1 pm/min have been reported in ICP etch systems with
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