Selective Wet Etching of Silicon Germanium in Composite Vertical Nanowires

Zhaslan Baraissov; Antoine Pacco; Siddardha Koneti; Geeta Bisht; Federico Panciera; Frank Holsteyns; Utkur Mirsaidov

doi:10.1021/acsami.9b11934

Selective Wet Etching of Silicon Germanium in Composite Vertical Nanowires

ACS Appl Mater Interfaces. 2019 Oct 9;11(40):36839-36846. doi: 10.1021/acsami.9b11934. Epub 2019 Sep 26.

Authors

Zhaslan Baraissov^{1

2}, Antoine Pacco³, Siddardha Koneti^{1

2}, Geeta Bisht^{1

2}, Federico Panciera^{1

2}, Frank Holsteyns³, Utkur Mirsaidov^{1

2

4

5}

Affiliations

¹ Department of Physics , National University of Singapore , Singapore 117551 , Singapore.
² Centre for BioImaging Sciences, Department of Biological Sciences , National University of Singapore , Singapore 117557 , Singapore.
³ imec , Kapeldreef 75 , Leuven B-3001 , Belgium.
⁴ Centre for Advanced 2D Materials and Graphene Research Centre , National University of Singapore , Singapore 117546 , Singapore.
⁵ Department of Materials Science and Engineering , National University of Singapore , Singapore 117575 , Singapore.

PMID: 31525293
DOI: 10.1021/acsami.9b11934

Abstract

Silicon germanium (Si_xGe_1-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 be used either as a sacrificial layer to form suspended horizontal Si nanowires or, because of its higher carrier mobility, 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 (SiN_x/Si_0.75Ge_0.25/Si) vertical nanowires. The etching solutions were formed by mixing acetic acid (CH₃COOH), hydrogen peroxide (H₂O₂), and hydrofluoric acid (HF). Here, CH₃COOH and H₂O₂ react to form highly oxidizing peracetic acid (PAA or CH₃ CO₃H). 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 any of the two oxidizer (H₂O₂ and PAA) 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 the SiGe/Si interface to be the weakest plane; we found that once the diameter of the 160-nm-tall Si_0.75Ge_0.25 nanowire reaches ∼15 nm during the etching, the nanowire breaks at or very close to this interface. Our study provides important insight into the details of the nanoscale 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.

Keywords: chemical etching; in situ TEM; nanofabrication; nanowire; silicon germanium.