Characterization of Atomic Layer Deposited Ultrathin HfO 2 Film as a Diffusion Barrier in Cu Metallization
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0990-B09-03
Characterization of Atomic Layer Deposited Ultrathin HfO2 Film as a Diffusion Barrier in Cu Metallization Prodyut Majumder1, Rajesh Katamreddy1, and Christos G. Takoudis1,2 1 Department of Chemical Engineering, University of Illinois at Chicago, 810 S Clinton St, Chicago, IL, 60607 2 Department of Bioengineering, University of Illinois at Chicago, 851 S Morgan St, Chicago, IL, 60607 ABSTRACT Thermally stable, amorphous HfO2 thin films deposited using atomic layer deposition have been studied as a diffusion barrier between Cu and the Si substrate. 4 nm thick as-deposited HfO2 films deposited on Si are characterized with X-ray photoelectron spectroscopy. Cu/HfO2/ samples are annealed at different temperatures, starting from 500 ∞C, in the presence of N2 atmosphere for 5 min and characterized using sheet resistance, X-ray diffraction and scanning electron microscopy. Ultrathin HfO2 films are found to be effective diffusion barrier between Cu and Si with a high failure temperature of about 750 ∫C. INTRODUCTION Copper has drawn much attention as an interconnect material in advanced ultra large scale integration circuits due to its low electrical resistivity (~ 1.7 µΩ.cm) and superior resistance to electromigration when compared with Al. However, the difficulty with Cu is that it reacts with Si at relatively low temperatures (~200 ∞C) to form Cu-silicides [1, 2], leading to the degradation of integrated circuits. Therefore, in order to use Cu interconnects, a diffusion barrier needs to be formed between Cu and Si or inter-level dielectrics to prevent the interdiffusion or reaction between Cu and adjacent materials. Apart from high thermal stability and chemical inertness, a diffusion barrier layer has to fulfill other strict demands [3, 4]. An amorphous (and to some extent nanocrystalline) barrier is the most preferable candidate as it lacks grain boundaries that provides fast diffusion pathway for Cu to react with Si or SiO2. The decreasing device dimensions in microelectronic circuits set high demands for film conformity as the barrier thickness is predicted to decrease from 6.5 nm at the 80 nm technology node (year 2005) to 1.9 nm at the 25 nm node by the year 2015 [5]. Atomic layer deposition (ALD) [6] is one of the most promising techniques to fulfill such future requirements, especially strict conformality and submonolayer thickness control. In ALD, the film growth proceeds via self-limiting surface reactions, it is easy to control the film thickness, and it also offers superior via/trench filling capabilities. There are many barrier materials which have been studied such as transition metals and their alloys, nitrides, carbides and borides, ternary transition metal-Si-N alloys, other ternary alloys, and so on [7, 8]. The transition metal oxides were scarcely studied as a diffusion barrier until Yoon et al. [9] showed that the addition of microcrystalline CeO2 increases the Ta breakdown temperature from 550 to 850 ∞C. The grain boundaries of Ta were stuffed by CeO2 that inhibits the interdiffusion of Cu
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