Band Engineering of Rutile TiO2 by Cobalt Doping in Ru/Rutile-TiO2/Ru Capacitor aiming 40-nm DRAM and Beyond

Abstract

A Feasible fabrication process of Ru/rutile-Co-doped TiO2/Ru capacitor for 40-nm DRAM and beyond is developed. As-deposited Ru lower electrode is found out to crystallize Co-doped TiO2 overlayer into rutile having relative permittivity beyond 90 owing to lattice matching. Furthermore, we predicted doping of element having small ionic radius, such as Co, increase Schottky barrier, leading to decrease in leakage current. Temperature dependence of leakage current of RIR-Co-doped-TiO2 capacitor and band structure analysis with X-ray photoelectron spectroscopy shows that leakage current is determined by balancing between thermionic current and tunneling current through Schottky barrier. By doping of Co, the thermionic current decreases, whereas the tunneling current increases. With calculation using theoretical dependence of amount of doped element on leakage current, optimum percentage of Co is estimated as 0.3-0.6 % to achieve a sufficiently low leakage-current. This technology opens possibility to utilize 40-nm DRAM and beyond.

Liquid Injection Atomic Layer Deposition of Metallic Ru Thin Films from Ru(tmhd)3 and of High-k TiO2 Thin Films from Ti(O-i-Pr)2(tmhd)2

“…The growth of TiO 2 thin films by ALD has been extensively investigated (3,4,15). There are several Ti precursors for growing TiO 2 films by ALD.…”

“…Among possible metals which are studied for electrode applications ruthenium is a very interesting material because it has a high work function and a low resistance, it is easily dry etched, and the corresponding oxide is a conducting material, too. The structural compatibility of Ru and Ta 2 O 5 leads to an enhanced capacity of tantalum oxide based capacitors (2) and the growth of higher-k rutile-type TiO 2 films on Ru electrodes is attributed to the formation of an interfacial RuO 2 layer which stabilizes the TiO 2 rutile phase (3)(4). Among possible dielectrics which are studied for high-k layers TiO 2 has received great attention due to its high permittivity which is about 30-40 for an anatase structure and above 80 for a rutile structure (3)(4)(5).…”

“…The structural compatibility of Ru and Ta 2 O 5 leads to an enhanced capacity of tantalum oxide based capacitors (2) and the growth of higher-k rutile-type TiO 2 films on Ru electrodes is attributed to the formation of an interfacial RuO 2 layer which stabilizes the TiO 2 rutile phase (3)(4). Among possible dielectrics which are studied for high-k layers TiO 2 has received great attention due to its high permittivity which is about 30-40 for an anatase structure and above 80 for a rutile structure (3)(4)(5). Resistive switching phenomena in TiO 2 films have recently attracted great interest for potential application in nonvolatile memory devices (6,7).…”