Research Of Fabrication Of Edge Contact And Electrostatic Doping Simulation Of MoS₂ Transistors

In the post Moore era,semiconductor technology is about to enter the 3nm node,and the battle between silicon-based materials and two-dimensional materials is becoming more and more intensifying.However,the intrinsic zero bandgap of graphene and the instability of black phosphorus(BP)in the air make transition metal sulfides(TMDCs)a hot topic.Owing to suitable bandgap,dangling bond-free surface,and an ultrathin body,molybdenum disulfide(MoS2),the typical representative of TMDCs,shows a wide range of application prospects in the fields of transistors,memories,sensors and photodetectors.However,in case of the two-dimensional layered material MoS2 under the method of traditional top electrode contact,only the top layer of MoS2 material contacts the electrode.MoS2 layers in the remaining channels can only transmit current through voltage tunneling,resulting in the tunneling resistance,which causes the total contact resistance of the transistor to increase exponentially and severely restricts the current injection from the metal electrode into the semiconductor materials.In addition,silicon-based doping processes,such as ion implantation and diffusion,cannot be applied directly to the fabrication of two-dimensional materials MoS2 FETs,leading to an ineffective ohmic contact between the metal electrode and the MoS2 material.It also cannot transform N-type MoS2 FETs into P-type MoS2 FETs.For this reason,this thesis focuses on the edge contact and electrostatic doping of MoS2 FETs.To obtain back-gate MoS2 FETs by edge contact,MoS2 flake was transferred onto the silicon dioxide(SiO2)substrate by mechanical stripping firstly.Next,the pattern was transferred to the MoS2 flake by electron beam lithography(EBL)and inductively coupled plasma etching(ICP).Finally,the metal electrode and the high-K protective layer were deposited by magnetron sputtering(Sputter)and atomic layer deposition(ALD).Four sets of back-gate MoS2 FETs were made by this way with different thicknesses of 6 nm,9 nm,11 nm and 16 nm,respectively.The test results show that when Vgs=40 V and Vds=4 V,the saturation leakage current of MoS2 FETs increases with the number of layers,reaching 6.3 uA/um at 16 nm.At the same time,the test results show that the carrier mobility of MoS2 FETs increased firstly and then decreased with the increase of the number of layers,reaching 38 cm2V-1s-1 at 9 nm.In case of MoS2 FETs with less layers,the dielectric screening is weak,so they are affected easily by charged impurities,which leads to a low carrier mobility.In case of MoS2 FETs with more layers,the interlayer coupling is strong,which leads to insufficient control of the upper layer MoS2 by the gate electrode,which leads to a low carrier mobility.This thesis also uses the rectangular transmission line model to extract the edge contact resistance of 21 nm MoS2 FETs with a resistance of 8.9 K?,which significantly reduces the contact resistance of metal semiconductors.This thesis also uses Silvaco's semiconductor process and device simulation(TCAD)simulation module Atlas to simulate and analyze MoS2 FETs from the perspective of doping method,doping concentration and doping region,explaining doping concentration of MoS2 FETs channel,doping of electrical characteristics of source-drain metal-semiconductor contact region in detail.Furthermore,the electrostatic doping of MoS2 FETs is introduced in detail.The simulation results of current-voltage(I-V)characteristics and electron current density of MoS2 FETs showed that there is an edge conduction phenomenon in the contact area of source-drain metal-semiconductor,the transmission length is only nanometers size.MoS2 flake of the source-drain metal-semiconductor contact area is depleted.Electrostatic doping can increase the carrier concentration and transmission length significantly,which makes the current driving capability of MoS2 FETs improved greatly.