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Tuning the Thermal Properties of Hafnium Precursors by Tailoring the Ligands

Group IV metal oxide thin films materials (TiO2, ZrO2 and HfO2) find a range of potential applications such as alternative gate oxide materials for CMOS devices, optical fibers, sensors, thermal barrier coatings, waveguides etc. [1,2] owing to their advantageous physical properties (high permittivity, refractive index, hardness etc.). Metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) are considered as most attractive thin film deposition methods where conformality, uniformity are crucial. One of the major challenges for a successful vapor deposition process such as MOCVD or ALD is the availability of suitable precursors exhibiting appropriate thermal and physical properties. Recently it has been shown that guanidinate-based transition metal and rare-earth metal complexes exhibit promising thermal properties and can successfully be employed as precursors for MOCVD and ALD of oxide and nitride thin films [3-6]. This study explores the effect of the ligand sterical bulk of the chelating ligand on the resulting thermal properties of hafnium guanidinato and amidinato based precursors. In this context, the physical properties of a series of Hf precursors have been studied in detail by thermal analysis. Our efforts concentrate on the use of thermogravimetric (TG) analysis to investigate the onset temperature of volatilization and temperature regime where precursor decomposition takes place. Detailed isothermal TG studies were carried out to determine the evaporation rates and analyse the long term thermal stability of the individual complexes when maintained at different set temperatures for long periods of time. Figure 1 shows the comparative TG data for the four different hafnium compounds that have been investigated.