Planar Inductively Coupled BCl[sub 3] Plasma Etching of III-V Semiconductors

Abstract

Both Ga-based ͑GaAs, AlGaAs͒ and In-based ͑InGaP, InP, InAs, and InGaAsP͒ compound semiconductors were etched in a planar inductively coupled plasma ͑ICP͒ reactor in pure BCl 3 . The Ga-based materials etched at significantly higher rates, as expected from the higher volatilities of their trichloride etch products relative to InCl 3 . In contrast to the more common cylindrical geometry ICP sources, the dc self-bias which controls ion energy is not strongly dependent on source power up to ϳ400 W while etch rates increase rapidly over this power range. The source tunes easily even at very low powers ͑Ͻ100 W͒ but operates inefficiently above ϳ10 mTorr, with a marked decrease in both emission intensity from the discharge and in resulting etch rates of the compound semiconductors. The etched surfaces of both AlGaAs and GaAs have comparable root-mean-square roughness and similar stoichiometry to the unetched control samples, while the surfaces of In-based materials are degraded by the BCl 3 etching.The GaAs/AlGaAs and InP/InGaAsP heterostructures are the basis of most modern compound semiconductor electronic and photonic devices. [1][2][3][4][5] In particular, devices such as high electron mobility transistors ͑HEMTs͒ and heterojunction bipolar transistors ͑HBTs͒ rely on the ability to selectively etch one component of the heterostructure over the other in applications such as microwave power amplifiers and low noise amplifiers. 6-28 Further requirements for this etching are vertical sidewalls and minimal surface disruption. The latter involves both the lattice damage created by ion bombardment and any changes in stoichiometry. High density plasmas have proven attractive for these applications, with the ability to control both ion density and ion energy. [8][9][10][11][12][13] A key point that emerged from past studies with both electron cyclotron resonance ͑ECR͒ and cylindrical geometry inductively coupled plasma ͑ICP͒ etching of these heterostructures is that significant damage can be created even at moderate source powers ͑300-500 W͒, 12,16,18 so it is essential to develop high density sources that can operate efficiently over a broad range of powers and be usable over a continuous range of conditions. Our initial experience with planar ICP sources is that they are continuously tunable at low powers ͑0-200 W͒ and therefore offer a versatile range of operating conditions for applications from through-wafer vias to low damage mesa formation.In this paper we describe the results of etching GaAs, AlGaAs, InP, InGaP, InAs, and InGaAsP in a planar ICP tool with a single BCl 3 chemistry. The system appears well suited to patterning of GaAs/AlGaAs at room temperature, producing clean, vertical profiles. ExperimentalGaAs, InP, and InAs wafers were cut from Czochralski-grown boules and were nominally undoped with ͑100͒ orientation in all cases. The In 0.5 Ga 0.5 P and Al 0.2 Ga 0.8 As were grown lattice-matched to GaAs substrates by either metalorganic molecular beam epitaxy ͑MOMBE͒ or metalorganic chemical vapor deposition ͑...

Nitrogen vibrational excitation in a N2/He pulsed planar-ICP RF discharge

“…Radio frequency ICP discharges using planar coil configurations are largely used as high-density plasma for low pressure applications [1]. ICPs fed with reactive gases are currently employed in microelectronics [2][3][4]. Investigations in pulsed conditions are very useful for studying elementary kinetics [5] since they allow temporal discrimination of electron/ion induced processes from neutral chemistry.…”