HfCl4 is the most commonly used halogenated hafnium precursor. It is a moisture reactive white powder, with a high sublimation point of 320°C at atmospheric pressure and a vapour pressure of 1 torr at 190°C. HfCl4 allows carbon-free deposition, but its use in deposition processes results in corrosive by-products, such as HCl, which may affect both the film quality/purity (Cl contamination), and CVD chamber integrity, which can potentially limit its use. HfCl4 is, however, a strategic compound for chemical suppliers, as it is often the starting material to synthesize other metal-organic precursors. Its purity specifications are therefore of significant importance.
It is a conventional precursor for the ALD of hafnium-containing materials for the applicatiuons where the film quality and purity are less critical. Its use in CVD is limited, because it is a low volatility solid which needs substrate temperatures of 800 °C and above for oxide deposition [[i]]
[i] C.F. Powell in Chemically Deposited Nonmetals, edited by C.F. Powell, J.H. Oxley, J.M. Blocher (John Wiley and Sons Inc., New York, 1966), p. 343 - 420, and references thereafter.