Dry Etch Damage in InN, InGaN and InAlN
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ABSTRACT Damage introduction in rnI-V nitrides during dry etching can be simulated by exposing the samples to pure Ar plasmas for study of the physical (ion-bombardment) effects. Changes in conductivity of InN, In 0.5Ga 0.5N and In 0.5Al0 5N layers exposed to Ar plasmas under both Electron Cyclotron Resonance and reactive ion etching conditions have been measured as a function of rfpower, pressure and exposure time. The combination of high microwave and high rf powers produces large increases (10-_10 times) in sheet resistance of the nitrides, but conditions more typical of real etching processes (rf power < 150W) do not change the bulk electrical properties. The nitrides are more resistant to damage introduction than other III-V semiconductors. The removal of damage-related traps occurs with an activation energy of -2.7eV. High ion currents during ECR etching can produce substantial conductivity changes, whereas the lower currents under RIE conditions do not affect the nitrides. It is difficult to avoid preferential loss of N in the near-surface of these materials, which leads to leakage currents in rectifying metal contacts deposited on these surfaces. INTRODUCTION
The wide bandgap InGaAIN alloys are attracting interest for use in blue/UV light emitters and detectors, and for field effect transistors capable of high temperature operation.[1-3] The chemical stability of all of the binary, ternary and quaternary components of this materials system has demanded that dry etching be employed for patterning of device structures. A variety of different plasma chemistries have proven successful, inducing CII4/11 2, BC13/Ar, C12/H2 , C12/CII4/H 2/Ar and SiCh4.[4-7]. A consistent feature with all of these mixtures is that the II-V nitride etch rates are considerably slower than for more conventional compound semiconductors such as GaAs and InP under the same conditions.[5,7,8] In the reactive ion etching (RIE) mode etch rates for GaN up to -I OOA/min have been obtained,[6] but higher ion density techniques like magnetron or Electron Cyclotron Resonance (ECR) produce rates up to -4000A/min at lower pressures and dc self biases( 7' 8). It is also clear that the etch rates are invariably limited by sputter removal of the etch products(4 ), and therefore the study of ion-induced damage into the nitrides is a necessary step in optimizing device fabrication processes. We have examined ion-induced changes in conductivity of InN, InGaN and InAlN under both ECR and RIE etching conditions. In both cases we employed pure Ar discharges in order to simulate the ion bombardment received by the nitrides during plasma etching. 163 Mat. Res. Soc. Symp. Proc. Vol. 423 0 1996 Materials Research Society
EXPERIMENTAL The InN, In 0.5Ga 0.5N and In0 .5A10.5N were grown on semi-insulating GaAs substrates by Metal Organic Molecular Beam Epitaxy at 500'C in an Intevac Gas Source Gen II systemn[9] Triethylgallium, trimethylindium and dimethyl ethylamine alane were transported by the carrier gas, while the nitrogen flux was provided by an ECR sour
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