We explore the capability of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) to study nanoscale Si(100) device layers in silicon-on-insulators (SOIs). These device layers are a macroscopic 2D silicon sheet, and understanding the effective coupling of charge in and out of this sheet allows the determination of whether it is possible to accurately measure the electronic properties of the sheet. Specifically, we examine how the spreading resistance is manifested following the processing of SOI device layers with various doping levels. Depending on the doping level, ultra-thin SOI can exhibit significant blue shifts of the peaks in the tunneling and field emission spectra. By comparing these peak shifts with the film resistivity, it is possible to estimate the contribution of the spreading resistance in STM and STS. We show that STM can be used to study the effective n-type dopant concentrations in the 1013–1016 cm−3 range. Furthermore, we demonstrate that with a sufficiently high doping level, 5 nm thick SOI device-layers can be measured and exhibit bulk like electronic characteristics.
Removing the ultrathin native oxide layer from silicon-on-insulator (SOI) without damaging the Si device layer poses several processing challenges, the main one being the maintenance of the device layer integrity during oxide layer removal. In order to address this challenge and find a low thermal budget process, the thermal decomposition of the ultrathin native oxide in ultrahigh vacuum has been investigated using scanning electron microscopy, atomic force microscopy, scanning tunneling microscopy, and x-ray photoelectron spectroscopy. The evolving morphology and chemical composition of the ultrathin oxide and the SOI device layer were investigated as a function of anneal temperature and duration. Multiple anneal cycles at 750 °C, each lasting for 30–90 s, was found to be an effective method of desorbing the oxide without causing dewetting of the device layer. The total amount of carbon present on the sample was not altered significantly by thermal treatment; however, a change in the chemical composition of the carbon was noted. A simple oxygen plasma-based ex situ cleaning step before annealing was found to be effective in reducing the density of SiC on the annealed sample while keeping the annealed surface atomically smooth.
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