Silicon Nitride Interface Engineering for Fermi Level Depinning and Realization of Dopant-Free MOSFETs

Problems with doping in nanoscale devices or low temperature applications are widely known. Our approach to replace the degenerate doping in source/drain (S/D)-contacts is silicon nitride interface engineering. We measured Schottky diodes and MOSFETs with very thin silicon nitride layers in between silicon and metal. Al/SiN/p-Si diodes show Fermi level depinning with increasing SiN thickness. The diode fabricated with rapid thermal nitridation at 900 ∘C reaches the theoretical value of the Schottky barrier to the conduction band ΦSB,n=0.2 eV. As a result, the contact resistivity decreases and the ambipolar behavior can be suppressed. Schottky barrier MOSFETs with depinned S/D-contacts consisting of a thin silicon nitride layer and contact metals with different work functions are fabricated to demonstrate unipolar behavior. We presented n-type behavior with Al and p-type behavior with Co on samples which only distinguish by the contact metal. Thus, the thermally grown SiN layers are a useful method suppress Fermi level pinning and enable reconfigurable contacts by choosing an appropriate metal.

Rapid Synthesis of Aluminum Nitride Nanopowders from Gaseous Aluminum Chloride

The synthesis of aluminum nitride (AlN) powders is traditionally completed through a thermal nitridation process, in which the reacting aluminum powders are combined with nitrogen at high temperatures with a long reaction time (usually several hours). Moreover, the occurrence of agglomeration within the melting Al particles results in a poor dispersibility of AlN powders, with a low efficiency of nitridation. In this study, an atmosphere-pressure microwave plasma preceded the rapid gas-gas synthesis process. In the reactor, the gaseous aluminum chloride (AlCl3) reactant was fed at different positions (R1, R2, R3) to react with nitrogen at various reaction temperatures (690~1150°C) to rapidly produce AlN nano powders (in several seconds). The process was operated at a total flow rate of 13 slm with NH3 gas content of 0 or 0.77% and an applied power of 1200/1400 W. Results showed that the high purity and dispersibility of AlN powders were found at a AlCl3 feeding position closer to the resonant cavity of the reactor (R3, 1150°C). The AlN particle size was in the range of 25-50 nm. The experiments indicated that the gas-gas reaction for rapidly synthesizing AlN nanopowders can be successfully carried out via an AlCl3-N2 plasma-chemical approach.

Two-Stage Plasma-Thermal Nitridation Processes for the Production of Aluminum Nitride Powders from Aluminum Powders

The synthesis of aluminum nitride (AlN) powders is traditionally done via the thermal nitridation process, in which the reaction temperature reaches as high as 960 °C, with more than several hours of reaction time. Moreover, the occurrence of agglomeration in melting Al particles results in poor AlN quality and a low efficiency of nitridation. In this study, an atmosphere-pressure microwave-plasma preceded the pre-synthesis process. This process operates at 550 °C for 2–10 min with the addition of NH4Cl (Al: NH4Cl = 1:1) for generating a hard AlN shell to avoid the flow and aggregation of the melting Al metals. Then, the mass production of AlN powders by the thermal nitridation process can be carried out by rapidly elevating the reaction temperature (heating rate of 15 °C/min) until 1050 °C is reached. X-Ray Diffractometer (XRD) crystal analysis shows that without the peak, Al metals can be observed by synthesizing AlN via plasma nitridation (at 550 °C for 2 min, Al: NH4Cl = 1:1), followed by thermal nitridation (at 950 °C for 1 h). Moreover, SEM images show that well-dispersed AlN powders without agglomeration were produced. Additionally, the particle size of the produced AlN powder (usually < 1 μm) tends to be reduced from 2–5 μm (Al powders), resulting in a more efficient synthesizing process (lower reaction temperature, shorter reaction time) for mass production.