The Study Of Reducing Schottky Barrier Height By Inserting Atomic Layer Deposited High κ Dielectrics

As complementary metal-oxide-semiconductor (CMOS) transistor is reaching scaling limitation, the thickness of traditional silicon CMOS transistor’s gate is reduced to the atomic scale, which will induce the leakage current too large due to the quantum tunneling. To solve this problem, Silicon Carbide (SiC) and Indium phosphide (InP) have great potential as alternative channel materials for future high-speed and high-frequency applications due to their extraordinary high carrier mobility. Silicon Carbide (SiC) and Indium phosphide (InP) were widely used in electronic, optoelectronic and photonic devices for its high electron saturation velocity and high thermal conductivity. These excellent properties make SiC and InP suitable for high-temperature and high-frequency applications.For high performance in metal-oxide-semiconductor field effect transistor (MOSFET), Ohmic contact with low contact resistance and high stability is required. However, it is still a challenge to make an Ohmic contact with a small contact resistance at the source/drain (S/D) of SiC MOSFETs and InP MOSFETs because of the Fermi level pinning at metal/SiC interface and InP interface. This pinning issue induced the effective Schottky barrier height (φ>B,eff) hardly to be tuned by metal work functions, which was explained by Metal-Induced Gap States (MIGS) or Bond Polarization Theory. Therefore, the research of the contact and interface issues of metal/SiC and metal/InP is believed to very important for the industry application.We review all the important work of the depinning effect of metal/semiconductor by inserting an ultrathin high-κ dielectric to shift the Fermi level position. Based on those, we demonstrated releasing Fermi level pinning of metal/SiC and metal/InP by using this method. The ultrathin high-κ dielectric was grown by Atomic Layer Deposition. These Metal-Insulator-Semiconductor (MIS) structures were observed by Transmission Electron Microscope; the high-κ/native oxide interfacial characteristic was obtained with X-ray Photoemission Spectroscopy; the electrical properties of MIS structures were characterized by current-voltage technique; the Schottky barrier height and contact resistances were measured as well.Our work consists of two parts:In one part of this work, we successfully realized the depinning effect and the modulation of current density and Schottky barrier height of metal/SiC contact by inserting an ultrathin Al2O3 between the metal and semiconductor. By varying the thickness of Al2O3, we can acquire the ideal contact resistance on our demands and achieve a transfer between Schottky contact and ohmic contact. Since Al2O3’s areal density of oxygen atoms (a) is larger than that of SiO2, the a difference at the interface will be compensated by oxygen transfer from the higher-a to the lower-a oxide which creates oxygen vacancies in higher-σ oxide (Al2O3) and negative charged centers in lower-a oxide (SiO2). The mechanism appears to be the coaction of a dipole decreasing the barrier and the tunneling resistance increasing the barrier.In another part of this work, we successfully realized the Fermi level depinning and the modulation of of,φ,Beff and Rc for Au/n-InP junctions by inserting an ultrathin Al2O3 monolayer dielectric or Al2O3/HfO2 bilayer dielectrics between metal and semiconductor interface. Compared with monolayer dielectric MIS structures, the high-K/high-K bilayer dielectric MIS structures can further shift the Fermi level and reduce φB,eff(from 0.49 eV to 0.22 eV) than the monolayer dielectric (from 0.49 eV to 0.32 eV) even though the overall dielectric thickness was thicker. The a difference of these three materials:Al2O3, HfO2 and InP’s native oxide In2O3 leads to the generation of the dipoles, and the relationship is σAl2O3>σIn2O3. For monolayer dielectric Au/Al2O3/InP MIS structures, only the intrinsic dipole exists at the high-K/native oxide of semiconductor interfaces; for the high-κ/high-K bilayer dielectric Au/Al2O3/HfO2/InP MIS structures, the intrinsic dipole exists at high-K/native oxide of semiconductor interfaces and the additional extrinsic dipole exists at high-K/high-K interfaces. The additional extrinsic dipole can further reduce the barrier height.This method is simple but effective. It provides a more flexible method possible to make ideal source/drain contacts for SiC and InP MOSFETs as well as other wide bandgap semiconductor and Ⅲ-Ⅴ semiconductor MOSFETs and tunable barrier heights for Schottky Barrier FETs. This method is promising both in scientific research and industrial application.