BCl3/Ar reactive ion etching for gate recessing of GaInP/InGaAs/GaAs pseudomorphic high electron mobility transistors

BCl3 reactive ion etching for gate recessing of GaInP/InGaAs/GaAs pseudomor phic high electron mobility transistors (PHEMTs) is found improved by the a ddition of an appropriate amount of Ar to the gas flow. The influence of th e BCl3/Ar gas flow ratio on GaAs to GaInP etch selectivity, surface roughne ss, and surface damage was studied. The results indicate that the condition s for minimum plasma damage, as determined by photoreflectance (PR) spectro scopy, corresponded with the conditions for minimum surface roughness, as d etermined by atomic force microscopy (AFM). The optimal BCl3/Ar gas flow ra tio for minimum surface damage and roughness was found to be 6:4. Two BCl3: Ar flow rate ratios, 6:4 (optimal ratio) and 10:0 (pure BCl3) were used for gate recess etching in the fabrication of GaInP/InGaAs/GaAs PHEMTs. From d rain-source current to gate-source voltage (I-ds- V-gs) measurements, it wa s found that the plasma-induced damage for the sample S-c dry etched with 6 :4 BCl3/Ar is less than that of the sample S-e dry etch'ed with pure BCl3. The de and small signal rf characteristics of PHEMT S-c were superior to th ose of the wet-etched PHEMT S-o and PHEMT S-e dry etched with pure BCl3. Th e improvement is attributed to the lower parasitic source resistance associ ated with the tighter recess geometry of the BCl3 plasma recess device. The se results show that photoreflectance spectroscopy is a powerful tool for i nvestigating surface damage and can be used to improve the performance of P HEMTs. (C) 1998 American Vacuum Society. [S0734-211X(98)19806-2].