Controllable Si oxidation mediated by annealing temperature and atmosphere

Abstract

The morphology evolution by thermal annealing induced dewetting of gold (Au) thin films on silicon (Si) substrates with a native oxide layer and its dependences on annealing temperature and atmosphere are investigated. Both dewetting degree of thin film and Au/Si interdiffusion extent are enhanced with the annealing temperature. Au/Si interdiffusion can be observed beyond 800 °C and Au–Si droplets form in both argon and oxygen (Ar + O2) and argon and hydrogen (Ar + H2) environments. In Ar + O2 case, the passive oxidation (Si + O2 → SiO2) of diffused Si happens and thick silicon oxide (SiOx) covering layers are formed. A high temperature of 1050 °C can even activate the outward growth of free-standing SiOx nanowires from droplets. Similarly, annealing at 800 °C under Ar + H2 situation also enables the slight Si passive oxidation, resulting in the formation of stripe-like SiOx areas. However, higher temperatures of 950–1050 °C in Ar + H2 environment initiate both the SiOx decomposition and the Si active oxidation (2Si + O2 → 2SiO(g)), and the formation of solid SiOx is absent, leading to the only formation of isolated Au–Si droplets at elevated temperatures and droplets evolve to particles presenting two contrasts due to the Au/Si phase separation upon cooling.

Formation of nanoflowers: Au and Ni silicide cores surrounded by SiOx branches

“…The formation of the circular cavities can be attributed to the decomposition of the SiO 2 layer at high temperature in reducing atmosphere. It has been reported after the annealing of Au thin films deposited on SiO 2 /Si substrates with different thicknesses of the SiO 2 layer [ 3 – 4 36 ]. The active oxidation of Si also occurs once the Si substrate is exposed [ 2 – 3 37 ], which can be proved by the calculated oxygen partial pressure ( Supporting Information File 1 ) and the much greater average depths of cavities (more than 600 nm) compared with the thickness of the SiO 2 layer (300 nm).…”

Fabrication of Platinum Nanoparticles with Different Morphologies by Thermal Dewetting in the Presence of Residual Oxygen and Their Optical Properties

“…To understand the reason why the Pt thin film as thick as 10.8 nm could be fully dewetted to isolated Pt NPs without any substrate perturbation when using Ar or H 2 flow as compared to only partial dewetting occurred for Pt films thicker than 1.4 nm when under vacuum, and the observation that the two different flowing gas of Ar and H 2 had similar effect on the thermal dewetting behavior of Pt thin films, the role of residual O 2 during the thermal dewetting process was investigated. Previous studies have shown that oxidation of the Si substrates occurred in the thermal annealing in ultrapure Ar + H 2 52 and ultrapure N 2 53 environment due to the presence of a small amount of residual O 2 present. To examine whether there is the formation of SiO 2 due to the thermal oxidation in our thermal dewetting processes, a bare Si substrate with a 2.3 nm native SiO 2 surface layer was placed under the similar condition used at 950 °C with 100 sccm H 2 for a duration varying from 15 to 90 min.…”

Estimation of Thermal Stability of Si-SiO2-W Nanolayered Structures with Infrared Spectrometry

“…It is worth noting that, in the presence of air, chemical changes in the W structures are expected to take place at temperatures above 650 °C [ 20 ]. While it is well known that Si-SiO 2 interfacial systems are unstable at high temperatures [ 21 , 22 ], it is also important to monitor low-temperature processes in the context of nanostructured systems. To monitor these temperature-induced changes, Fourier transform infrared spectrometry (FTIR) has been applied as a monitoring method to determine changes in the polar bonds within SiO 2 [ 23 ] and SiO 2 -W structures [ 24 ].…”