Nanoscalein situinvestigation of ultrathin silicon oxide thermal decomposition by high temperature scanning tunneling microscopy

Abstract

A surface chemical reaction—the thermal decomposition of ultrathin silicon oxide (∼1 nm) by ultrahigh vacuum (UHV) thermal annealing at 600–800 °C—is in situ investigated on a nanometer scale by high temperature scanning tunneling microscopy (STM). The reaction is initiated by the creation of circular voids which expose the underlying silicon substrate. Growth kinetics of the voids is scrutinized via time-lapse STM movies. It is verified that the void perimeters grow linearly with time before coalescence and the reaction occurs peripherally around the void perimeters. It is also demonstrated that the decomposition rate varies concomitantly with the local environment near the reaction fronts. The observed low–high–low rate evolution is qualitatively explained. Increased reaction activation energy is found in the final decomposition stage and the origin of the increase is proposed to be due to the local morphological evolution.

Chemical inhomogeneity of SiOx dissociation by catalytic Au at a relatively low temperature

“…It is known that the removal of native oxide layer through thermal dissociation Si(s) + SiO 2 (s) → 2SiO(g) requires high T (>750 °C) and this mechanism shows formation of voids through removal in gaseous form of SiO(g) . Our work has led us to conclude that the presence of Au grains with low N C number acts as catalyst and reduced the dissociation temperature of SiO x to 500 °C.…”

Low temperature selective growth of GaN single crystals on pre-patterned Si substrates

“…Subsequently, the samples were transferred into the complex UHV apparatus with a base pressure of 3 × 10 −8 Pa and thermally annealed by direct resistive heating at 500°C (>120 min) under UHV conditions. This temperature was sufficient for removal of contaminants from the sample surface, but not high enough for decomposition of the native SiO 2 layer [25]. The structure and cleanness of the substrate were checked in situ by XPS.…”

Chemical and kinetic insights into the Thermal Decomposition of an Oxide Layer on Si(111) from Millisecond Photoelectron Spectroscopy

“…Indeed, volatile SiO (SiO g ) production is a key feature of nanoelectronics processes, naturally relative to silicon surface cleaning 22 , 23 , but also to nano-fabrication 24 – 28 . Microscopy studies pointed to a spatially inhomogeneous process both on Si(001) 9 – 11 , 14 , 15 , 13 and (111) surfaces 12 , 16 . Clean voids appear randomly on the oxidized surface, leaving oxide patches whose thickness does not change, while surface pitting is observed in the clean areas.…”

“…Consequently, four steps for oxide decomposition are envisaged 9 , 10 , 13 , 16 : creation of a mobile Si monomer (step 1); diffusion to the void boundary (step 2); reaction of mobile Si with SiO 2 at the void boundary to form SiO x suboxide species precursor to desorption (step 3); desorption of SiO g (step 4). …”

“…The thermal decomposition of ultra-thin oxidized layers (<1 ML of oxygen) may be limited by step 1 9 , 10 , while thicker thermal oxide layers are apparently limited by steps 3 or 4 13 , 16 , 29 . The void nucleation process itself may depend on the oxide thickness: the density can be constant with time (ultra-thin films 9 ), or increase with time for nm-thick thermal films 13 .…”