Investigation on Ge0.8Si0.2-Selective Atomic Layer Wet-Etching of Ge for Vertical Gate-All-Around Nanodevice

For the formation of nano-scale Ge channels in vertical Gate-all-around field-effect transistors (vGAAFETs), the selective isotropic etching of Ge selective to Ge0.8Si0.2 was considered. In this work, a dual-selective atomic layer etching (ALE), including Ge0.8Si0.2-selective etching of Ge and crystal-orientation selectivity of Ge oxidation, has been developed to control the etch rate and the size of the Ge nanowires. The ALE of Ge in p(+)-Ge0.8Si0.2/Ge stacks with 70% HNO3 as oxidizer and deionized (DI) water as oxide-removal was investigated in detail. The saturated relative etched amount per cycle (REPC) and selectivity at different HNO3 temperatures between Ge and p(+)-Ge0.8Si0.2 were obtained. In p(+)-Ge0.8Si0.2/Ge stacks with (110) sidewalls, the REPC of Ge was 3.1 nm and the saturated etching selectivity was 6.5 at HNO3 temperature of 20 degrees C. The etch rate and the selectivity were affected by HNO3 temperatures. As the HNO3 temperature decreased to 10 degrees C, the REPC of Ge was decreased to 2 nm and the selectivity remained at about 7.4. Finally, the application of ALE in the formation of Ge nanowires in vGAAFETs was demonstrated where the preliminary I-d-V-ds output characteristic curves of Ge vGAAFET were provided.

Automated summary

A dual-selective atomic layer etching technique has been developed to control the etch rate and size of Ge nanowires in vGAAFETs, considering the selectivity between Ge0.8Si0.2 and Ge. Experimental results demonstrate that the etch rate and selectivity of Ge vary with different nitric acid temperatures.