Nanoscale Schottky Barrier Visualization Utilizing Computational Modeling and Ballistic Electron Emission Microscopy
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ballistic electron emission microscopy (BEEM)
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AbstractUnderstanding the properties and performance of semiconductor interfaces on the nanoscale advances semiconductor device technology which has had tremendous impact on nearly all aspects of our daily lives. Investigating the nanoscale fluctuations in the electrostatics of metal-semiconductor, or Schottky, interfaces is crucial. However, techniques for directly measuring the electrostatics at an interface are limited. Current state-of-the-art finFETs use metal-semiconductor silicides, such as Ti-Si/Si, for Schottky source-drain contacts. Studying the underlying physics of the Schottky barrier interface of silicides and other metal-semiconductor systems is critical for measuring the Schottky barrier accurately, which can be accomplished with ballistic electron emission microscopy (BEEM), a scanning tunneling microscopy (STM) based technique. In this work, the visualization of the interface to nanoscale dimensions is enhanced by computational modelling of threshold histograms acquired by the BEEM measurement technique. Modelling using a kinetic Monte-Carlo approach is utilized to simulate the distributions of barrier heights that includes effects from the interface and transport of the hot electrons as well as indication of a multi-barrier heights present at the interface. The aid of this modelling enables the discovery of several underlying properties of the interface. Analyzing the parameters of the modelling and comparing to measured data provides detailed insight into the effects that both electron scattering and incomplete silicide formation in W/Si(001) and WSi2/Si(001) have upon the transport of electrons through these structures, which is difficult to detect with conventional current-voltage measurements. The modelling also includes simulation of multiple barriers present at the interface due to the intermixing of similar metals such as Au and Ag at the interface of Si(001) In this regard, Schottky barrier visualization as the combination of histograms, mapping, and modelling provides a new insight into the local nanoscale phenomenon of the Schottky barrier. This thesis investigates the modelling of these metal-semiconductor systems and uses modelling to look at metal thickness dependent effects on the Schottky barrier from Fermi-level pinning in Au/Cr-Si/Si(001) and Au/Cr-Si/Si(111) silicide.