Characterization of Nb surfaces in side-wall spacer passivated Josephson junctions etched with HF vapor
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Journal Title
Journal ISSN
Volume Title
Sähkötekniikan korkeakoulu |
Master's thesis
Authors
Date
2023-08-21
Department
Major/Subject
Micro- and Nanoelectronic Circuit Design
Mcode
ELEC3036
Degree programme
Master’s Programme in Electronics and Nanotechnology (TS2013)
Language
en
Pages
55
Series
Abstract
This thesis aims to characterize the effects of HF vapor etching on the surface of niobium (Nb)-based side-wall spacer passivated Josephson junctions. We study the effects of the etching on Nb thin films, which we use as a proxy for the junctions. From the reaction with HF vapor, undesirable by-products vapor are formed on the surface of Nb. These residue particles are studied and analyzed using various surface, structural, and chemical characterization techniques. Three different types of samples are fabricated and characterized: plain Nb film, Nb/TEOS-based SiO2 and Nb/silane-based SiO2. Characterizing Nb after etching it with HF vapor, the surface gets fluorinated and produces different types of defects depending on the sample and pressure of the etching process. Low pressure recipes cause less damage while high pressure recipes cause blisters. Silane-based oxide produces volatile reaction product (NH4)2SiF6 while TEOS-based oxide does not form but corrodes the surface after the etching process. Water is one of the by-products formed from the reaction of HF vapor with Nb and Nb-oxide which plays an important role in enhancing the formation of residues. Hence, it needs to be controlled and removed from the chamber. The residue particles are concentrated with oxygen and fluorine and are categorized as complex niobium oxy fluoride compounds of the form NbOxFy which occur due to the hydrolysis of Nb pentafluorides. Fluorine-free cleaning techniques are implemented to remove or avoid the residues, but, it turned out that none of the methods were effective. However, aqueous HF (1%) was evidenced to etch the residues completely.Description
Supervisor
Savin, HeleThesis advisor
Ribeiro, MárioKeywords
Josephson junctions, sidewall-passivating spacer structure, HF vapor etching, Nb, Nb oxyfluorides, physical characterization