Characterization of reactive ion etching of III-V compound semiconductor materials

Abstract

Reactive ion etching (RIE) of III-V compound semiconductor materials such as InP, InGaAs, InAlAs, and InGaAsP in methane (CH$\sb4$) gas mixtures has been investigated. Etch rates of 800, 400 and 600 A are obtained for InP, InGaAs, and InGaAsP, respectively. Optimum processes have been developed for reliable fabrication of uniform short period gratings with smooth etched surfaces and excellent stoichiometry in these compounds. Highly anisotropic structures with dimensions down to 300 A at a pitch of 600 A are demonstrated in InP. A selective RIE process for InGaAs on InAlAs in a CH$\sb4$:H$\sb2$ plasma has been developed and utilized to fabricate 0.26 $\mu$m T-gate modulation doped field-effect transistors (MODFETs). The microwave measurements of reactive-ion-etched and wet-etched devices show identical performance.

The RIE of GaAs and AlGaAs have been characterized in SiCl$\sb4$ plasma chemistry. The optical, electrical and chemical properties of the etched materials have been investigated. The effects of different RIE parameters such as gas chemistry, RF power, and reactor pressure have been studied. The RIE of laser facets in the GaAs/AlGaAs/InGaAs material system and the growth on RIE-patterned GaAs substrates are reported. Selective RIE of GaAs on AlGaAs in SiCl$\sb4$/SiF$\sb4$ plasma is studied. A selectivity ratio of 350:1 has been obtained at low power. A small decrease in the saturation current of gateless MODFET structures has been observed after etching the GaAs cap layer and has been ascribed to low energy ion bombardment of the surface. This process is applied to the fabrication of 0.2 $\mu$m T-gate pseudomorphic MODFETs. The dc and microwave performances of RIE and wet-etched devices are identical. For these short-gatelength devices, a threshold voltage standard deviation of only 30 mV is obtained for the reactive-ion-etched devices as compared to 230 mV for the wet-etched devices. This uniform distribution is essential to the realization of integrated circuits.

Surface analysis methods, such as scanning electron microscopy (SEM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and Fourier transform infra-red spectroscopy (FTIR), have been utilized extensively to determine the chemistry of etched surfaces. Raman spectroscopy, Hall carrier mobility measurement and photoluminescence spectroscopy indicate insignificant electrical damage to the materials under optimal RIE conditions. Results of the surface analysis have been used to delineate optimum processes for the fabrication of the above devices.