In‐Situ Studies of ALD Growth of Hafnium Oxide Films

Abstract

Hafnium oxide (HfO 2 ), with its dielectric constant of about 20, large band gap of about 5.6 eV, and band offset with Si of at least 1.5 eV on both valence and conduction band sides, [1] is the material of choice for the current and future generation of CMOS transistor and non-volatile-memory technologies. For an effective implementation of HfO 2 , an issue related to the formation of an interfacial layer with poor dielectric properties needs to be solved. That interfacial layer, in fact, increases the equivalent oxide thickness (EOT) of the oxide stack in the MOS structure. [1] As the EOT for future technology nodes should scale to values lower than 1 nm, the formation of the interfacial layer must be reduced to the monolayer range. A way to achieve this is to control the early stages of the film growth and to reduce the reaction with the substrate by decreasing the growth temperature. In order to decrease the EOT values, atomic layer deposition (ALD) of the high-k oxide was implemented, as the ALD method is capable of delivering very homogeneous thin films of the targeted stoichiometry at low temperatures, although it has often been observed that the ALD growth of HfO 2 is accompanied by an increase in the interfacial layer. [2] No definitive explanation of the mechanism leading to that increase has yet been found. In this contribution, we show a study of the interfacial layer during the formation of the oxide, making use of our in situ approach that permits investigation of the ALD growth by means of X-ray photoelectron spectroscopy (XPS) after each deposition cycle. We also characterized the initial surface of the substrate before the ALD cycles by means of ultra high vacuum (UHV) atomic force microscopy (AFM). XPS is a very powerful tool technique for investigating interfaces, as one can get important chemical and physical information over a region of a few nanometers underneath the thin film surface. The photoemission experiments, when carried out with synchrotron radiation, take advantage of the high photon energy resolution and the possibility of tuning the photon energy over a wide range, allowing either surface or bulk-sensitive spectra to be recorded. We have used such techniques to identify substrate induced silicate formation for both Pr 2 O 3 and HfO 2 dielectric films. [3] AFM delivers the local topographical information of the substrate. The main advantage of using the UHV-AFM system is the ability to control the surface perfection of the initial substrate and to investigate clean and artifact-free surfaces. Correlating the information obtained during the initial growth of HfO 2 films obtained with the two techniques, we are able to get an insight into the mechanisms leading to the interfacial growth during the ALD. ExperimentalTwo different oxidized Si (001) samples were used, with initial oxide thicknesses of 2.2 and 1.5 nm (Sample A and B, respectively). Both samples were etched in a diluted HF solution and then introduced into the fast entry of the equipment. For both substrates, the time of ...

PrOAlN dielectrics for metal insulator semiconductor stacks

“…Shrinking the thickness of the high‐ k more and more this might be questionable, because then the growth of the IL and the high‐ k are consequently influencing each other in a more competing way than it might be the case in thick high‐ k layers. Here, the Ansatz, started in our group to investigate by in situ XPS and atomic force microscopy (AFM) the initial ALD growth cycle by cycle, is a very promising method to analyse the very near interface region 48–50. Nevertheless based on our spectroscopic results and because the smallest electrically investigated thickness is about 5 nm, these fits are applied to the data of this work.…”

“…The results are significant not only for the specific material system but potentially also for studies of the diffusion barrier at the interface of other dielectrics such as HfO 2 , where similar mechanisms can be expected. As our group started already to study the initial layer formation of Hf‐based dielectrics deposited by ALD 48–50, which is considered to be a more controlled deposition method than E‐beam evaporation, these results are important for the further work of our group in this field as well.…”

Elastic Modulus of HfO2 Thin Film Grown by Atomic Layer Deposition with Wrinkle‐based Measurement

“…10 There are several HfO 2 deposition technologies, i.e., physical layer deposition (PLD), 11,12 chemical vapor deposition (CVD), 13,14 atomic layer deposition (ALD). [15][16][17] Among them, ALD is more used recently because high quality deposition is possible under relatively lower temperature, and the layer thickness at atomic level can be easily controlled as self-limiting surface reaction occurs by gradual supply of chemical species. Therefore, uniform thickness of large area in ALD can be formed compared to the existing PLD and CVD processes.…”

“…Moreover, it becomes more popular owing to its quantum tunneling effect that might arise from decrease in the insulation film thickness and expected minimum leakage current . There are several HfO 2 deposition technologies, i.e., physical layer deposition (PLD), chemical vapor deposition (CVD), atomic layer deposition (ALD) . Among them, ALD is more used recently because high quality deposition is possible under relatively lower temperature, and the layer thickness at atomic level can be easily controlled as self‐limiting surface reaction occurs by gradual supply of chemical species.…”

Hf x Zr 1− x O 2 thin films from chemical vapor deposition of fluorinated β-ketoenamine precursors

“…Achieving high-quality HZO thin films with precise control over both composition and thickness often relies on atomic layer deposition (ALD). 6 Atomic layer deposition (ALD) of ZrO 2 and HfO 2 thin films is commonly performed using metal-organic precursors such as tetrakis(dimethylamido)zirconium (TDMAZr), 7 tetrakis(ethylmethylamido)zirconium (TEMAZr), [8][9][10] Zr[Cp(NMe 2 ) 3 ], 11,12 and their hafnium analogues TDMAHf, 13 TEMAHf, 14 and Hf[Cp(NMe 2 ) 3 ], 15 in combination with oxidizing co-reactants including O 2 , O 3 , or H 2 O. Beyond amide-based chemistries, metal alkoxides serve as attractive precursors to high-purity oxides due to their well-defined molecular structures and relatively high volatility, which facilitate efficient gas-phase transport and controlled surface reactions rendering them well suited for both CVD and ALD processes.…”