Reactive Ion Etching of AlN, AlGaN, and GaN Using BCl₃

Abstract

The III-V nitrides are promising materials for use in UV-blue-green optoelectronics, high-temperature electronics, and negative-electron-affinity (NEA) electron emitter applications. In order to realize this potential, it is important to develop an etching technology for device fabrication. The stability of the III-V nitrides to harsh chemical environments makes most wet etching extremely difficult, so that dry etching alternatives are desirable. Recent experiments have shown that BCI₃-based chemistries are effective for reactive ion etching of GaN and that KOH-based solutions may preferentially etch AIN from GaN. This paper reports on the use of BCI3 for etching AIN and AlGaN in addition to GaN and the creation of structures such as mesas and lines. It also examines the potential use of potassium Hydroxide (KOH) as a wet etchant of the nitrides. AIN, AlGaN, and GaN films grown by either metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) were patterned with Ni in 250 μm × 250 μm squares and 5 μm wide lines to create mesas and lines for typical light emitting diode (LED) or laser diode applications. Reactive ion etching was performed in a commercial reactor using BCI3 pressures ranging from 5 to 30 mTorr. Gas flow rates of 5 to 50 seem and RF powers of 50 to 150 W were employed. High nitride etch rates of up to 730 Å/min. were observed but lower etch rates were needed to avoid etching of the Ni mask. Smooth mesa surfaces and sidewalls were observed in scanning electron micrographs of the etched nitride structures. Mesas as small as 5 μm × 5 μm were patterned and made in this way. Lines were also made in a similar manner as narrow as 5 μm on GaN/AIN epilayers. Subsequent wet etching of these lines showed that KOH-based solutions such as AZ400K developer attack not only AIN but also GaN depending upon the quality of the film. Possibilities for using this wet etch as a defect etchant or selective etch of nitrides on SiC are discussed.