Selective Wet Etching of Silicon Germanium in Composite Vertical Nanowires

Abstract

Silicon Germanium (SixGe1-x or SiGe) is an important semiconductor material for the fabrication of nanowire-based gate-all-around transistors in the next-generation logic and memory devices. During the fabrication process, SiGe can either be used as a sacrificial layer to form suspended horizontal Si nanowires or, because of its higher carrier mobility, SiGe can also be used as a possible channel material that replaces Si in both horizontal and vertical nanowires. In both cases, there is a pressing need to understand and develop nanoscale etching processes that enable controlled and selective removal of SiGe with respect to Si. Here, we developed and tested solution-based selective etching processes for SiGe in composite (SiNx/Si0.75Ge0.25/Si) vertical nanowires. The etching solutions were formed by 2 mixing acetic acid (CH3COOH), hydrogen peroxide (H2O2), and hydrofluoric acid (HF). Here, the two chemicals (H2O2 and CH3COOH) react to form highly oxidizing peracetic acid (PAA or). The hydrofluoric acid serves both as a catalyst for PAA formation and as an etchant for oxidized SiGe. Our study shows that an increase in either of the oxidizer concentrations increases the etch rate, and the fastest etch rate of SiGe is associated with the highest PAA concentration. Moreover, using in situ liquid phase TEM imaging, we tested the stability of nanowires during wet etching and identified that SiGe/Si interface to be the weakest plane; we found that once the diameter of the 160-nm-tall Si0.75Ge0.25 nanowire reaches ~15 nm during the etching, the nanowire breaks at or very close to this interface. Our study provides an important insight into the details of the wet etching of SiGe and some of the associated failure modes that are becoming extremely relevant for the fabrication processes as the size of the transistors shrink with every new device-generation.

Selective Digital Etching of Silicon–Germanium Using Nitric and Hydrofluoric Acids

“…To solve these problems, selective etching with accurate etching depth control and high selectivity was essential. Several selective etching methods have been reported, such as dry etchings with HCl 8 or mixtures of CF4/O2/N2 9-10 CF4/O2/He 11 and wet etchings with mixtures of HNO3, HF, H2O (HNA) 12 or H2O2, HF, CH3COOH [13][14] . However, all these methods are continuous etching and etching depth is time-dependent.…”

State of the Art and Future Perspectives in Advanced CMOS Technology

“…SiGe/Si nanowires can be divided into vertical and horizontal nanowires. The vertical nanowire GAA requires more disruptive technological changes, while the horizontal one has less deviation from FinFET process, and the manufacturing is less difficult [ 112 , 115 ].…”

Formation Pathways of Porous Alloy Nanoparticles through Selective Chemical and Electrochemical Etching

“…To address these questions, we track the chemical and electrochemical selective Ag etching in AuAg alloy NPs using in situ liquid‐phase transmission electron microscopy (TEM). [ 20–29 ] We chose these NPs because Au, Ag, and their alloys are among the best‐characterized materials used for NP synthesis. [ 30–33 ] For example, a recent in situ liquid‐phase TEM study by Liu et al, [ 34 ] examining the transformation of solid AuAg alloy NPs to porous ones by chemical etching, found that the NPs shrink in size and their surfaces become denser as small pores form within the NPs.…”