Abstract
In the past few decades, gate insulators with a high dielectric constant (high-k dielectric) enabling a physically thick but dielectrically thin insulating layer, have been used to replace traditional SiOx insulator and to ensure continuous downscaling of Si-based transistor technology. However, due to the non-silicon derivative natures of the high-k metal oxides, transport properties in these dielectrics are still limited by various structural defects on the hetero-interfaces and inside the dielectrics. Here, we show that another insulating silicon compound, amorphous silicon nitride (a-Si3N4), is a promising candidate of effective electrical insulator for use as a high-k dielectric. We have examined a-Si3N4 deposited using the plasma-assisted atomic beam deposition (PA-ABD) technique in an ultra-high vacuum (UHV) environment and demonstrated the absence of defect-related luminescence; it was also found that the electronic structure across the a-Si3N4/Si heterojunction approaches the intrinsic limit, which exhibits large band gap energy and valence band offset. We demonstrate that charge transport properties in the metal/a-Si3N4/Si (MNS) structures approach defect-free limits with a large breakdown field and a low leakage current. Using PA-ABD, our results suggest a general strategy to markedly improve the performance of gate dielectric using a nearly defect-free insulator.
Highlights
We demonstrate a-Si3N4 prepared via a one-step, two atomic beams (Si evaporated beam and N2-plasma) method called plasma-assisted atomic beam deposition (PA-ABD) for use as a long expected and versatile insulating layer that meets a wide range of requirements for high-performance gate dielectrics
In contrast to the strong defect emissions from the typical plasma-enhanced chemical vapor deposition (PECVD) grown a-SiNx, the PL spectra from the PA-ABD grown a-Si3N4 on both (111) and (100) substrates are almost identical to the PL spectra of their substrates, demonstrating that the electrically active defects with atomic configurations that give rise to the electronic states in the a-Si3N4 band gap was substantial reduced by the absence of Si-H and N-H bonding during deposition[20]
To our knowledge, this work is the first demonstration of the defect-free a-Si3N4 insulating layer for use as a gate dielectric on Si with an extremely large band gap energy and a low leakage current
Summary
We demonstrate a-Si3N4 prepared via a one-step (without a post-annealing process), two atomic beams (Si evaporated beam and N2-plasma) method called plasma-assisted atomic beam deposition (PA-ABD) for use as a long expected and versatile insulating layer that meets a wide range of requirements for high-performance gate dielectrics. We show that the use of PA-ABD enables the formation of an atomically abrupt interface and a smooth surface a-Si3N4/Si heterojunction with excellent insulating properties such as a large dielectric band gap (~6 eV) and large heterojunction valence/conduction band offset (VBO/CBO) values for blocking mobile carriers while applying gate voltage. Under the current-voltage (I-V) characteristic measured on the metal/a-Si3N4/Si (MNS) heterostructure, the nearly defect-free nature inherent to the UHV PA-ABD process shows the scalability of the high-quality a-Si3N4 insulating layer with a large breakdown field and a low leakage current
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