Thermal stability studies for advanced Hafnium and Zirconium ALD precursors

The development of novel precursors for advanced semiconductor applications requires molecular engineering and chemical tailoring to obtain specific physical properties and performance capabilities. Having identified promising avenues in ligand design, the first priority when isolating a new compound is to ensure that when used it is safe and will not cause detrimental effects in deposition equipment due to thermal decomposition. We have employed different techniques to study the physical properties and stabilities of highly promising Hafnium and Zirconium compounds particularly suited to the Atomic Layer Deposition technique for fabrication of state-of-the-art metal oxide layers for both logic and memory semiconductor devices to ensure that they may be employed safely. In particular mixed alkyl/alkoxide and alkylcyclopentadienyl. substituted compounds [(MeCp)(2)M(OMe)(x)Me2-x M=Hf and Zrx=0 or 1] were compared to conventional alkylamine sources (M(NEtMe)(4) M=Hf and Zr). The use of thermogravimetric analysis (TGA) to determine evaporation rates under a variety of conditions is employed to determine initial temperature regimes where decomposition may occur. More detailed studies using Nuclear Magnetic Resonance (NMR) are then conducted at fixed temperatures over a prolonged time period with regular monitoring to establish degradation effects more accurately. Our studies show similar trends between both Hf and Zr materials with the Zr derivatives less stable in all cases. Operation temperatures required to achieve suitable vapour transport in the case of MeCP2ZrMe2 have been found to lead to catastrophic decomposition after a relatively short time thus negating the usefulness of this precursor in a production environment. All other sources were deemed safe to employ under standard process conditions. (c) 2007 Elsevier B.V. All rights reserved.