HfSiO4 dielectric layers deposited by ALD using HfCl4 and NH2(CH2)3Si(OC2H5)3 precursors

The physical and electrical properties of HfSiO4 dielectric layers deposited by atomic layer deposition (ALD) are reported. The precursor chemistries used for deposition were HfCl4/H2O for HfO2 and NH2(CH2)3Si(OC2H5)3/O3 for SiO2. Two processes with HfCl4:NH2(CH2)3Si(OC2H5)3 precursor pulse ratios of 5:1 ("HfO2-rich") and 1:1 ("SiO2-rich") are investigated. Measurements with X-ray photoelectron spectroscopy and channeling Rutherford backscattering spectrometry show that these processes result in layers with Hf/(Hf + Si) ratios of 0.56 and 0.34-0.37, respectively. X-ray diffraction measurements showed formation of a HfO2 cubic phase in HfO2-rich layers starting at 850DGC. In SiO2-rich layers, no crystallization was detected up to 1100DGC. Metal oxide semiconductor (MOS) capacitors with polysilicon electrodes were used for electrical characterization. The k-value of the SiO2-rich layers was found to be 4.8-5.4 and that of the HfO2-rich layers 12.5-15.1, both with an experimental error of 10%. The leakage currents of both types of layers were comparable to SiO2 reference data and increased with polysilicon activation anneal. A high-resolution transmission electron microscopy study revealed phase segregation in thick SiO2-rich layers. In HfO2-rich layers, the phase segregation was less clear, but upon annealing, composition variations at the interfaces were detected. Given the experimental errors, no impact of phase segregation on the k-values of both types of layers could be detected. It is concluded that postdeposition annealing of HfSiO4 layers for application as gate dielectrics applications in advanced complementary MOS technologies is essential to optimize stoichiometry and reduce leakage currents.