Selective gate recess RIE etching by CHF3+BCl3 in InAlAs/InGaAs HEMTs

The selective dry etching between InGaAs and InAlAs is an essential process for gate recess in InP-based HEMT fabrication, which means that the top n⁺-InGaAs layer must be etched away, and the etching process is terminated at the underline InAlAs Schottky layer. This etching selectivity between two materials can be realized by the reactive ion-etching, which is not always available from the conventional chemical etching approach. In order to achieve this selectivity, the mixture of CHF₃ and BCl₃ gases was proposed in this study to replace the role of CCl₂F₂ , which has an undesirable impact on the environment. This gas mixture approach has been proven in our previous studies that a high selectivity (~30) can be obtained without a significant surface damage in AlGaAs/GaAs heterostructures. The C_xF_y and non-volatile AlF₃ products generated in the RIE chamber can prevent the further etching in the Al-contented layers. In this study, we explored this concept to investigate the etching process of InAlAs and InGaAs materials by using CHF₃+BCl₃ gas mixture, and apply this approach for gate-recess etching in InP HEMT fabrication