Determination of the vapour pressure curves and vaporization enthalpies of hafnium alkoxides using thermogravimetric analysis

In order to identify a volatile metallo-organic precursor for the deposition of hafnium oxide (HfO 2 ) films for atomic layer deposition (ALD) applications, the evaporative properties of hafnium alkoxides (hafnium isopropoxide, hafnium n -propoxide and hafnium n -butoxide) were investigated using thermogravimetric analysis. These hafnium alkoxide samples were synthesized by the electrochemical method and characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance and inductively coupled plasma analysis techniques. The characterization results indicated that the products were 99.997% high-purity hafnium alkoxides and could meet the requirement of purity considering the usage of making HfO 2 gate oxide by ALD. Synthesized samples were subjected to a simultaneous thermogravimetric–differential thermal analysis unit at 10 K min −1 in a dry nitrogen atmosphere flowing at 100 ml min −1 . Benzoic acid was used to calculate a calibration constant, which could then be inserted into a modified Langmuir equation to calculate vapour pressure curves for hafnium isopropoxide and hafnium n -propoxide. Detailed vapour pressure data for the HfO 2 precursor hafnium alkoxides were determined. The vapour pressure curve of hafnium isopropoxide was constructed within the first stage, and calculated to be ln p = 31.157 (±0.200)−13130.57 (±56.50)/T. Hafnium n -propoxide and hafnium n -butoxide were simultaneously undergoing evaporation and decomposition, thus making calculations invalid.

An Interesting Feature of the Vapour Pressure Curve

There exists a maximum in the products of the saturation properties such as

Determination of heats of vaporization and some other thermodynamic properties for four substituted hydrocarbons

The temperature dependence of heats of vaporization and some other derived thermodynamic properties were determined for four substituted hydrocarbons, viz. 2,2,4-trimethylpentane,1-octene, ethylbenzene and n-butylbenzene. The temperature dependence of heats of vaporization was measured and, on the basis of these data, the values of standard heats of vaporization, internal and cohesive energies, entropies of vaporization and the difference of heat capacities of liquid and vapour at constant pressure and along the saturated vapour pressure curve were computed.

Relation of the temperature derivative of heat of vaporization to the difference of heat capacities along the saturated vapour pressure curve

A method of calculating the heat capacity difference of liquid and its vapour along saturated vapour pressure curve is discussed. The qualitative course of this difference in dependence on temperature obtained from the data on the temperature dependence of heat of vaporization of pure substances is judged.