Atomic Layer Deposition of HfO2 Films Using Tetrakis(1-(N,N-dimethylamino)-2-propoxy)hafnium [Hf(dmap)4] for Advanced Gate Dielectrics Applications

Atomic layer deposition (ALD) of HfO2 thin films was studied by using a novel Cl-free hafnium ALD precursor: tetrakis(1-(N,N-dimethylamino)-2-propoxy)hafnium [Hf(dmap)4]. This precursor is a liquid at room temperature and has been shown by differential scanning calorimetry (DSC) analysis to be stable at temperatures as high as 371 °C. Compared with the conventional Hf precursor tetrakis(ethylmethylamido)hafnium(IV) (TEMAH), Hf(dmap)4 exhibits a substantially greater decomposition temperature because of its alkoxide structure. Hf(dmap)4 is a volatile compound that shows a very clean thermogravimetry curve without decomposition or residue formation at 10 Torr. We performed ALD of HfO2 using Hf(dmap)4 with an oxidant of either O3 or H2O as an oxidant. As the wafer temperature was increased from 250 to 400 °C, the film growth rate slightly increased from 0.35 to 0.55 Å/cycle. Therefore, Hf(dmap)4 can be used for ALD at higher deposition temperatures than for TEMAH. However, the film growth rate was lowered by the sterically hindered ligand structure of the precursor. We evaluated the saturation behavior of the growth rate in experiments in which the Hf(dmap)4 supply time was varied from 5 to 30 s. As a result, a constant film growth rate was observed because of ALD saturation when the precursor supply time was 10 s or longer in the temperature range 350–400 °C. This result indicates that Hf(dmap)4 was not decomposed and behaved as an ALD precursor at 400 °C. We concluded that Hf(dmap)4 is a promising precursor for high-temperature ALD of HfO2 film for gate dielectrics, high-K capacitors, and HfO2-based ferroelectrics.