Research On Key Technologies Of Gasb MOS Devices With High-k Dielectric And Metal Gate Stacks

As the integrated circuit (IC) industry develops, the feature size of transistors isscaling down. However, the physical limitation of the scaling for silicon basedtransistors is approaching. High-k/Metal Gate III-V MOSFETs are promising for thefurther development of IC industry, due to the high carrier mobility and low gateleakage current. Most III-V compound semiconductors have very high electron mobility,while their hole mobility is relatively low. For the all III-V CMOS application, researchon p-channel devices is of great importance. Antimonide based III-V materials are theonly materials with high hole mobility among all III-V materials. Consequently,research on GaSb MOS devices is crucial for the all III-V CMOS technology.The improvements in the interfacial properties of high-k/GaSb stacks are veryimportant to fabricate high performance GaSb MOS devices. There are manydifferences between high-k dielectric/III-V substrate system and SiO2/Si system. As aresult, interfacial property characterization methods for SiO2/Si system cannot beapplied to high-k dielectric/III-V substrate system directly. In this thesis, manyinterfacial property characterization methods were analyzed, such as the capacitancemethod and the conductance method, and the method most suitable for high-kdielectric/III-V substrate was determined. A low-temperature measurement equipmentbased on liquid nitrogen was built up for the interfacial property characterization. Manynovel methods for the improvements of the interfacial properties were proposed, such asALD in-situ ozone post deposition treatment, neutralized and acidic (NH4)2S solutionbased sulfur treatment. ALD in-situ ozone post deposition treatment can improve theinterfacial properties, as well as the quality of high-k films deposited at lowtemperatures, which is required by the thermal budget of GaSb. Neutralized and acidic(NH4)2S solution based sulfur treatment can avoid many drawbacks of the traditional(NH4)2S treatment, such as high surface roughness and low efficiency of surface oxideremoval. An interface trap density of7×1012eV-1cm-2has been achieved in this thesis.GaSb MOSFET fabrication process and key technologies were also investigated inthis thesis. GaSb p-channel MOSFETs were fabricated using a self-aligned gate-firstflow. High-k dielectric was deposited using atomic layer deposition technique, gate and source/drain metal were patterned using lift-off technique, source/drain doping wereachieved by ion implantation and activated by rapid thermal anneal. Furthermore,temperature dependent characteristics of the fabricated GaSb MOSFETs weresystematically investigated. Different behaviors were observed in different temperatureregions and the mechanisms underneath were proposed. It is found that the off-statedrain leakage current is generation current dominated in low temperature regions and isdiffusion current dominated in high temperature regions. These works are of greatimportance for the wide application of GaSb MOSFETs in the future.