Photo-Assisted RIE of GaN in BCl 3 /Cl 2 /N 2
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N. Medelci, A- Tempez, I. Berishev, D. Starikov, and A.Bensaoula Nitride Materials and Devices Laboratory, SVEC-University of Houston, Houston, TX ABSTRACT
Gallium nitride (GaN) has been under intense investigation due to its unique qualities (wide band gap, chemical and temperature stability) for optoelectronic and high temperature/high power applications. To this end, reactive ion etching (RIE) experiments were performed on GaN thin films using BCI 3/C12/Ar. These resulted in etch rates of 1400 A/min at -400 V dc bias'. However, rough etched surfaces, nitrogen surface depletion and high chlorine content were observed. In order to remedy these shortcomings, a photo-assisted RIE process using a filtered Xe lamp beam was developed, resulting in higher etch rates but again in nitrogen depleted surfaces 2. Preliminary results on using nitrogen instead of argon in the process chemistry show a big improvement in photo-asssisted etch rates (50%) and Ga/N ratio (0.78 versus 1.25). In this paper, the effects of epilayer doping, dc bias, nitrogen flow rate and photo-irradiation flux on GaN etch rates, surface morphology and composition are presented. Finally, preliminary results on the use of a KrF excimer laser beam in the GaN photo-assisted RIE process are presented. INTRODUCTION Wide band gap nI-V nitrides are emerging as the materials of choice for high temperature and high power electronics and blue-UV emitters and detectors. Synthesis of gallium nitride (GaN) is being developed for the fabrication of light emitting diodes, laser diodes and flat panel displays. These characteristics, resulting from their strong chemical strength, become a drawback for their processing and thus for their industrial development. Conventional reactive ion etching (RIE) using halogen-based chemistries achieved relatively low etch rates3-6. High density plasma techniques such as electron cyclotron resonance (ECR), inductively coupled plasma (ICP) and magnetron RIE lead to higher etch rates 7 13. However, these ion-assisted methods cannot avoid ion bombardment damage and
surface roughening at high RF powers. In addition, nitrogen depletion is usually associated with high ion energies. Vertical sidewalls have been realized with chemically assisted ion beam etching (CAIBE) using HC114. Alternative dry etching methods for low lattice damage are low energy electron enhanced etching (LE4)15 and photo-assisted etching. The last technique has already been demonstrated for GaAs and Si'"-?. Photo-assisted etching of GaN has also been tested using an ArF excimer laser in a HCI ambient's. However, the preliminary etch rate was low (optimized etch rates have not yet been reported). Encouraging results for RIE of GaN have been reported using BCI 3/CI2/Ar, with etch rates reaching up to 1,200 A/min at 200 W RF power. Nevertheless, nitrogen depletion, which increases with increasing dc self-bias, was observed after etching. Moreover, higher etch rates are desirable. Therefore, a photo-assisted RIE process using the same chemistry was developed, resulting
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