Low damage etching for fabrication of quantum-effect devices.

Abstract

A low damage and highly controllable dry etching technique that can be applied to the fabrication of quantum effect devices was developed. An electron cyclotron resonance source was used so that a high density plasma with low ion energy can be generated at low pressure to achieve minimal damage and enhanced anisotropy for etching quantum structures. Surface damage induced by etching has been characterized using various electrical and surface analysis techniques. Less electrical degradation was observed on Schottky diodes, unalloyed transmission lines, and conducting wires etched with lower ion energy, lower ion flux, higher etch temperature, lower pressure, addition of reactive species, and with damage removal or passivation using low energy chlorine species. These changes correlate well with the increase in the defect density measured from cross-sectional transmission electron microscopy on GaAs etched with higher ion energy and lower etch temperature. The measured depth of defects, however, has no obvious correlation with the electrical characteristics observed. The presence of these defects on GaAs etched with high ion energy was further verified by photoreflectance measurements which show a shifting of the Fermi-level position towards the As$\sb{\rm Ga}$ defect level. Auger electron spectroscopy shows that etching with Cl$\sb2$/Ar is residue free and is therefore suitable for device fabrication. Besides minimization of the surface damage, good controllability in etch depth is also important for etching quantum effect devices. This has been achieved with a novel layer by layer etching technique with minimal electrical degradation. The use of mass spectrometry to precisely control the end point of deep InP via holes etching was also demonstrated. Based on these results, optimized etch conditions were applied to the fabrication of quantum effect devices including the in-plane gated quantum wire transistors with good device characteristics, $\rm In\sb{0.20}Ga\sb{0.80}As/GaAs$ etched mirrors with reflectivities up to 93%, triangular ring lasers with threshold current as low as 3.7 mA, and 35 nm quantum dots with enhanced photoluminescence intensity and electro-optic effects. These results show that the advantages of quantum effect devices can be realized with low damage etching.