Characterization of amorphous and crystalline silicon nanoclusters in ultra thin silica layers

Abstract

The nucleation and structure of silicon nanocrystals formed by different preparation conditions and silicon concentration (28 -70 area %) have been studied using Transmission Electron Microscopy (TEM), Energy Filtered TEM (EFTEM) and Secondary Ion Mass Spectroscopy (SIMS). The nanocrystals were formed after heat treatment at high temperature of a sputtered 10 nm thick silicon rich oxide on 3 nm SiO2 layer made by Rapid Thermal Oxidation (RTO) of silicon. Nanocrystals precipitate when the excess silicon concentration exceeds 50 area %. Below this percentage amorphous silicon nanoclusters were found. In-situ heat treatment of the samples in the TEM showed that the crystallization requires a temperature above 800 o C. The nanocrystals precipitate in a 4 nm band, 5 nm from the Si substrate and 4 nm from the SiO2 sample surface. The silicon nucleates where the excess Si concentration is the highest. The top surface has less excess Si due to reaction with oxygen from the ambient during annealing. The SiO2-RTO layer is more Si rich due to Si diffusion from the SiO2-Si layer into RTO. Twinning and stacking faults were found in nanocrystals with 4-10 nm in diameter. These types of defects may have large effects upon the usability of the material in electronic devices. Both single and double twin boundaries have been found in the nanocrystals by high resolution transmission electron microscopy (HRTEM). Image simulations were carried out in order to obtain more information about the defects and nanocrystals. The stacking faults are extrinsic and located in the twin boundaries.

The formation of Er-oxide nanoclusters in SiO2 thin films with excess Si

“…The nanoclusters were amorphous and precipitate throughout the whole oxide thickness, except for the RTO-SiO 2 and the SiO 2 top layer. At a very short electron beam exposure time (less than 20 seconds), the Si-Er-rich SiO 2 appears darker than pure SiO 2 observed in previous studies 16,17 , and only a few small nanoclusters were observed. This is attributed to the Er atoms being evenly distributed in the oxide before exposure to an intense electron beam.…”

“…In previous studies the nucleation, growth and the crystal and electronic structure of Si nanoclusters in a thin SiO 2 layer have been studied by various microscopy and spectroscopy techniques 16,17 . In the present work, we studied the nucleation, composition and distribution of Er clusters in SiO 2 with low doses of Si, by means of High Resolution Transmission Electron Microscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS) mapping, Energy Filtered TEM (EFTEM), Scanning Transmission Electron Microscopy (STEM) and X-ray Photoelectron Spectroscopy (XPS).…”

Composition and structure of Pd nanoclusters in SiO$_x$ thin film

“…Then a ∼10 nm layer of silicon rich oxide (46 at. %) was sputtered from a SiO 2 :Si composite target onto the RTO-SiO 2 and heat treated in a N 2 atmosphere at 1000 • C for 30 min, as described in our previous article 11,12 . A ∼20nm SiO 2 layer containing 0.5 at.…”

Calculate IR optical constants of Si substrate under high temperature condition

“…Single-crystalline silicon is a high refractive index material and can be used as thin film substrates from near infrared (~1 μm) to far-infrared (~15 μm) regions [1][2][3]. The calculation of optical constants (refractive index, extinction coefficient) of substrate is of great importance for the design of optical coatings.…”