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

Benjamin Richstein,Lena Hellmich,Joachim Knoch

doi:10.3390/micro1020017

Abstract

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.

Highlights

The ability to modify the conductivity of semiconductors with impurity doping is one of the central ingredients of modern complementary metal-oxide-semiconductor (CMOS)
A mere replacement of doped regions with metals appears attractive, the Schottky barrier that forms at metal-semiconductor contacts due to Fermi level pinning severely impacts the electrical behavior of fieldeffect transistors (FETs): So-called Schottky barrier devices exhibit a deteriorated off-state with impaired switching and high leakage, as well as a lower on-state performance compared to conventional FETs with doped source/drain electrodes
This interlayer strongly reduces the density of so-called metal-induced gap states (MIGS) that are the main reason for Fermi level pinning [11,12,13]

Summary

Introduction

The ability to modify the conductivity of semiconductors with impurity doping is one of the central ingredients of modern complementary metal-oxide-semiconductor (CMOS). A promising approach to replace impurity doping with metals is to reduce the impact of the Schottky barrier by depinning the Fermi level. This can be accomplished by inserting an ultrathin insulator in-between the metal and the semiconductor [1,7,8,9,10]. Micro 2021, 1 mechanical stress of the contact metal in use (Al) is small for our measurement conditions at room temperature Because of that, these effects are not explained in more detail. Metallurgical reactions [18] are considered as they change the electrical behavior of the semiconductor device

Methods

Results

Conclusion