Fundamental studies of titania-based high dielectric constant materials.

摘要

In an effort to increase integrated circuit performance and to achieve higher device density, the dimensions of transistors, particularly the gate oxide, have been continuously scaled down since the advent of integrated circuits 50 years ago. The technology roadmaps predict that the thickness of the SiO 2 gate dielectric needs to be scaled below 2 nm for sub-0.1 mum complimentary metal oxide semiconductor (CMOS) transistors. In spite of its many attributes, SiO2 has reached its minimum thickness limit due to a relatively low dielectric constant (k=3.9). At these dimensions, the concerns regarding high tunneling leakage current and low gate capacitance have lead to the exploration of alternative dielectric materials with higher dielectric constant ( k) that can replace the ultra-thin SiO2. In this regard, growth of titanium-base dielectric materials on Si substrate is being studied due to the fact that TiO2 has high dielectric constants up to 80. Thermal stability and interfacial reaction of high-k dielectrics are of utmost concern for their integration into current CMOS process. Our goal is to establish process-structure-property relationship and obtain Ti-based dielectric films with good fundamental properties, such as high crystallization temperatures, low impurity levels, and negligible interfacial reactions which may lead to low leakage current.; Traditionally, TiNO or TiO2 films are deposited at temperature above 300°C using alkoxide-based Ti precursors, such as titanium tetra-isopropoxide. High temperature induces interfacial SiOx formation and causes film crystallization, which is not desirable. Moreover, Alkoxide-based precursors react with Si substrate, especially for transition metal that acts as catalytic source and further enhances SiOx formation. Thus, it is imperative to find a new Ti-containing precursor. In this study, first time we demonstrate that Tetrakis(diethylamino)titanium (TDEAT), an oxygen-free metal alkylamide Ti-containing precursor, is a very promising precursor for deposition of high quality Ti-based gate dielectric at low temperatures.; Catalytic CVD is also evaluated for both Al2O3 and TiO2 deposition and NH3 is studied as a possible catalyst. Gas phase catalysis is versatile and represents a new strategy for the enhancement of deposition reactions. It is found the effects of NH 3 on the deposition of Al2O3 and TiO2 are different. For TiO2 deposition, besides the catalyst effect, NH3 is also involved in the reaction with TDEAT to form TiNO or TiN. For Al2O3, NH3 mainly acts as a catalyst without introducing any impurities into the films. In either case, the film deposition rate is enhanced by using NH3.; Ti alloy-based dielectrics have received considerable attention, which is expected to overcome the limits of TiO2 while utilize its high k value. In this work, laminated TiO2/Al2O 3 films are deposited by means of cyclic-chemical vapor deposition (Cyclic-CVD) using TDEAT, Trimethylaluminium (TMA) and O2 at 300°C and 0.7 torr. Cyclic CVD offers better composition, thickness control and less gas phase reactions. Our study shows that the properties of TiO2, such as crystallization temperature, roughness and interfacial reaction, improve a lot with the addition of even a few percent of Al2O3. We demonstrated that Cyclic-CVD TiO2/Al2O3 is very promising to be used as alternative gate dielectric.