Heta-Elisa Nieminen

This study investigates the use of pinacolborane as a small molecule inhibitor for the area selective atomic layer deposition (ALD) of Ru on oxide, nitride, and metal surfaces. Pinacolborane selectively chemisorbs and blocks the Ru film growth on native SiO2, TiN, Co, Cu, HfO2, and ZrO2 surfaces while Ru film grows solely on a Pt surface. The surfaces were subjected to eight exposures of 10 s pulses of pinacolborane separated by 30 s of N2 purging, followed by Ru film deposition with bis(cyclopentadienyl)ruthenium (RuCp2) and O2 at 340 °C. The process was tested at various temperatures, and the difference between the growth surface and nongrowth surfaces was the most evident at 340 °C. Energy dispersive x-ray spectroscopy confirmed the selective deposition of Ru film on Pt surfaces. X-ray photoelectron spectroscopy revealed the presence of boron on the HfO2 surface after the pinacolborane exposures. Selectivity of the Ru growth on Pt is greater than 0.9 with respect to native SiO2 up to 300 Ru ALD cycles; TiN, HfO2, and ZrO2 up to 900 Ru ALD cycles; Co up to 700 Ru ALD cycles; and Cu up to 1000 Ru ALD cycles. Additionally, in an ABC-type process where pinacolborane is dosed in every ALD cycle, Ru film grows only on Ru while being effectively suppressed on native SiO2 and Pt surfaces. Our findings can serve as a valuable resource in the fabrication of next-generation interconnects.

The growing demands of artificial intelligence and big data require semiconductor technologies that enable high-performance computing with low power consumption. Ferroelectric materials combined with semiconductors are one intriguing alternative for the future needs. For example, thin ferroelectric doped hafnium dioxide, deposited by atomic layer deposition (ALD), is already well integrated and scaled up in current semiconductor device processing. This study investigates ALD growth of HfO2 thin films using CpHf(NMe2)3 and O3 as precursors focusing on interface evolution through low energy ion scattering and x-ray photoelectron spectroscopy (XPS). A flow-type ALD reactor that is in vacuo connected to the surface-sensitive techniques was used allowing for in-depth analysis without air exposure. The study highlights that the full coverage of oxidized TiN substrate is achieved after approximately 30 ALD cycles. The XPS spectra demonstrate interaction between the substrate and the hafnium oxide film suggesting valence and conduction band bending in the films. The findings contribute to the understanding of the deposition, growth, and interface changes for developing thin ferroelectric HfO2.

The initial adsorption of MeCpPtMe3 is investigated using synchrotron-based ambient pressure x-ray photoelectron spectroscopy (XPS). The experiments are done on a native oxide-covered Si substrate. In addition, a reaction with O2 and the created Pt surface was investigated. Inspiration for the reaction studies was found from atomic layer deposition of metallic Pt, process that uses the same compounds as precursors. With time-resolved XPS, we have been able to observe details of the deposition process and especially see chemical changes on the Pt atoms during the initial deposition of the Pt precursor. The change of the binding energy of the Pt 4f core level appears to occur on a different timescale than the growth of the active surface sites. The very long pulse of the Pt precursor resulted in a metallic surface already from the beginning, which suggest chemical vapor deposition-like reactions occurring between the surface and the precursor molecules in this experiment. Additionally, based on the XPS data measured after the Pt precursor pulse, we can make suggestions for the reaction pathway, which point toward a scenario that leaves carbon from the MeCpPtMe3 precursor on the surface. These carbon species are then efficiently removed by the subsequent coreactant pulse, leaving behind a mostly metallic Pt film.

In this paper, we introduce a vacuum cluster tool designed specifically for studying reaction mechanisms in atomic layer deposition (ALD) and atomic layer etching (ALE) processes. In the tool, a commercial flow-type ALD reactor is in vacuo connected to a set of UHV chambers so that versatile surface characterization is possible without breaking the vacuum environment. This way the surface composition and reaction intermediates formed during the precursor or etchant pulses can be studied in very close to true ALD and ALE processing conditions. Measurements done at each step of the deposition or etching cycle add important insights about the overall reaction mechanisms. Herein, we describe the tool and its working principles in detail and verify the equipment by presenting results on the well-known trimethyl aluminum–water process for depositing Al2O3.

In this work, we developed an atomic layer deposition (ALD) process for gold metal thin films from chloro(triethylphosphine)gold(I) [AuCl(PEt₃)] and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine [(Me₃Ge)₂DHP]. High purity gold films were deposited on different substrate materials at 180 °C for the first time with thermal reductive ALD. The growth rate is 1.7 Å/cycle after the film reaches full coverage. The films have a very low resistivity close to the bulk value, and a minimal amount of impurities could be detected. The reaction mechanism of the process is studied in situ with a quartz crystal microbalance and a quadrupole mass spectrometer.

In this work, the reaction mechanism in the atomic layer deposition (ALD) process of AlF3 thin films is studied with in situ quartz crystal microbalance and quadrupole mass spectrometer. The depositions are done with AlCl3 and TiF4 as precursors. Similar to many metal fluoride films deposited by ALD, the growth rate of the AlF3 is strongly temperature dependent. In addition, at low temperatures, the growth rate is exceptionally high for a traditional ALD process. In this study, the reasons behind these characteristics are studied and a detailed step-by-step mechanism for the AlF3 film growth process is presented.

An ambient pressure cell is described for conducting synchrotron-based x-ray photoelectron spectroscopy (XPS) measurements during atomic layer deposition (ALD) processes. The instrument is capable of true in situ and operando experiments in which it is possible to directly obtain elemental and chemical information from the sample surface using XPS as the deposition process is ongoing. The setup is based on the ambient pressure XPS technique, in which sample environments with high pressure (several mbar) can be created without compromising the ultrahigh vacuum requirements needed for the operation of the spectrometer and the synchrotron beamline. The setup is intended for chemical characterization of the surface intermediates during the initial stages of the deposition processes. The SPECIES beamline and the ALD cell provide a unique experimental platform for obtaining new information on the surface chemistry during ALD half-cycles at high temporal resolution. Such information is valuable for understanding the ALD reaction mechanisms and crucial in further developing and improving ALD processes. We demonstrate the capabilities of the setup by studying the deposition of TiO₂ on a SiO₂ surface by using titanium(IV) tetraisopropoxide and water as precursors. Multiple core levels and the valence band of the substrate surface were followed during the film deposition using ambient pressure XPS.

An experimental approach is described in which well-defined perturbations of the gas feed into an Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) cell are fully synchronized with the time-resolved x-ray photoelectron spectroscopy data acquisition. These experiments unlock new possibilities for investigating the properties of materials and chemical reactions mediated by their surfaces, such as those in heterogeneous catalysis, surface science, and coating/deposition applications. Implementation of this approach, which is termed perturbation-enhanced APXPS, at the SPECIES beamline of MAX IV Laboratory is discussed along with several experimental examples including individual pulses of N₂ gas over a Au foil, a multi-pulse titration of oxygen vacancies in a pre-reduced TiO₂ single crystal with O₂ gas, and a sequence of alternating precursor pulses for atomic layer deposition of TiO₂ on a silicon wafer substrate.