Konstantin Karavaev

The initial atomic layer deposition of HfO2∕Si(001) as followed in situ by synchrotron radiation photoelectron spectroscopy

We have grown HfO2 on Si(001) by atomic layer deposition (ALD) using HfCl4 and H2O as precursors. The early stages of the ALD were investigated with high-resolution photoelectron spectroscopy and x-ray absorption spectroscopy. We observed the changes occurring in the Si2p, O1s, Hf4f, Hf4d, and Cl2p core level lines after each ALD cycle up to the complete formation of two layers of HfO2. From the analysis of those variations, we deduced the growth properties of HfO2. The first layer consists of a sparse and Cl-contaminated oxide because of the incomplete oxidation, and the second layer is denser than the first one and with an almost stoichiometric O∕Hf ratio. At the completion of the second layer, the x-ray absorption spectra revealed the change of the Hf-oxide chemical state due to the transition from the thin Hf-oxide to the bulklike HfO2.

HfO2∕Si interface formation in atomic layer deposition films: An in situ investigation

The authors have studied the initial stages of the atomic layer deposition (ALD) of HfO2 onto Si by means of x-ray photoelectron spectroscopy using synchrotron radiation. The ALD was obtained using HfCl4 and H2O as precursors. The investigation was carried out in situ giving the possibility to determine the properties of the grown film after each ALD cycle. The Si 2p, O 1s, and Hf 4d+Cl 2p spectra show the growth of HfO2 in a smooth way until the complete formation of two oxide layers. The averaged growth rate is found to be 0.33 (one layer after three cycles) in accordance with previous works but, within the formation of one oxide layer, each ALD cycle behaves in a distinct way: the oxidation step in the various cycles shows a different efficiency leading to the inclusion of Cl impurities into the Hf oxide. In relation to the experimental results we discuss the origin of the Cl contamination proposing a mechanism based on the adsorption geometry of HfCl4 onto the–OH terminated substrate.

Al-oxynitride interfacial layer investigations for PrXOY on SiC and Si

We investigate the dielectric properties of Praseodymium based oxides PrXOY by preparing MIS (metal insulator semiconductor) structures consisting of PrXOY as a high-k insulating layer and silicon (Si) or silicon carbide (SiC) as semiconductor substrates. The use of a buffer layer between PrXOY and the semiconductor is necessary as we found deleterious reactions between these materials such as silicate and graphite formation. Possessing a higher permittivity value (er) than silicon dioxide (SiO2) and good lattice matching in conjunction with similar thermal expansion coefficient to SiC, we focus on aluminum oxynitride (AlON) as a suitable buffer layer for this high-k/wide-bandgap system. In our spectroscopic investigations we found a decrease or indeed prevention of silicon diffusion into the oxide and an increased Pr2O3 fraction after deposition. In electrical characterizations of PrXOY/AlON stacks we found considerable improvements in the leakage current by several orders on both substrates, especially on silicon where we obtain values down to 10−7A/cm2 at a CET (capacitance equivalent thickness) of 4nm. We observed interface state densities in the range of 5 × 1011-1 × 1012/eVcm2 and 1-5 × 1012/eVcm2 on Si and SiC, respectively.

Optimization of the AlON buffer layer for PrXOY/Si stacks

The authors investigated an aluminum oxynitride buffer layer for PrXOY/Si metal-insulator-semiconductor stacks. The buffer layer limits unintentional interfacial layer formations and improves the electrical parameters as determined by combined electrical and spectroscopic characterization methods. These benefits are attributed to an interaction of the oxygen of the buffer layer with the PrXOY. As essential parameters for the improved performance of the buffer layer the authors find an O:N ratio of 1 and a thickness of 1 nm.

In situ measurements of the atomic layer deposition of high-k dielectrics by atomic force microscope for advanced microsystems

We investigated in situ the atomic layer deposition (ALD) of high-k dielectrics for advanced microsystems by ultra high vacuum (UHV) atomic force microscope (AFM). With our equipment we examined the surface topography of the substrate and the thin high-k films without breaking the vacuum and therefore without contaminating the sample with external agents. Following the full analysis of the Si(001)/SiO2 substrates we started the ALD process. After each ALD cycle using tetrakis-di-methyl-amido-Hf (TDMAHf), and H2O as precursors, we studied the relation between the film growth and the root mean square surface roughness, surface fractal dimension and correlation length. Additional information about the ALD was extracted from the statistical description of the surface by the height histogram together with the surface skewness and kurtosis parameters. The in situ studies of the ALD process with the UHV/AFM system were correlated with the experiments performed by means of synchrotron radiation photoelectron spectroscopy for understanding the fundamental properties of the ALD of high-k thin films on Si(001)/SiO2 substrates.