Ion beam etching of GaAs and GaAs/AlGaAs heterostructures probed in real time by spectroscopic ellipsometry

Abstract

A rotating polarizer, multichannel spectroscopic ellipsometer, operating over the spectral range from 1.5 to 4.0 eV, has been employed for process characterization during etching of GaAs and GaAs/AlGaAs heterostructures. The purpose of this study is to assess the capabilities of this relatively new ellipsometric technique for characterizing III–V semiconductor materials, surfaces, and interfaces during preparation and processing. In this work, each pair of ellipsometric spectra, {Ψ(hν),Δ(hν)} is acquired in 3 s with a repetition period of 16 s. Such spectra are analyzed by well-established linear regression techniques to deduce the time evolution of photon energy independent parameters. In the simplest case of sputter etching with Ar ions, the damage layer thickness, composition, and an estimate of surface temperature of the material can be obtained. For the heterostructures, instantaneous etch rates for both GaAs and AlGaAs can be obtained under identical conditions, and the extent of ion-induced intermixing can be determined as the interfaces are crossed. Future advances are expected in this area through assessment and optimization of technologically important reactive ion etching processes.