Hcm Harm Knoops

Surface reactions during atomic layer deposition of Pt derived from gas phase infrared spectroscopy

Infrared spectroscopy was used to obtain absolute number information on the reaction products during atomic layer deposition of Pt from (methylcyclopentadienyl)trimethylplatinum [(MeCp)PtMe3] and O2. From the detection of CO2 and H2O it was established that the precursor ligands are oxidatively decomposed during the O2 pulse mainly. Oxygen atoms chemisorbed at the Pt lead to likewise ligand oxidation during the (MeCp)PtMe3 pulse however the detection of a virtually equivalent density of CO2 and CH4 also reveals a concurrent ligand liberation reaction. The surface coverage of chemisorbed oxygen atoms found is consistent with the saturation coverage reported in surface science studies.

Conformality of plasma-assisted ALD: physical processes and modeling

For plasma-assisted atomic layer deposition (ALD), reaching conformal deposition in high aspect ratio structures is less straightforward than for thermal ALD due to surface recombination loss of plasma radicals. To obtain a detailed insight into the consequences of this additional radical loss, the physical processes in plasma-assisted ALD affecting conformality were identified and investigated through Monte Carlo simulations. The conformality was dictated by the recombination probability r, the reaction probability s, and the diffusion rate of particles. When recombination losses play a role, the saturation dose depended strongly on the value of r. For the deposition profiles, a minimum at the bottom of trench structures was observed (before reaching saturation), which was more pronounced with larger values of r. In turn, three deposition regimes could be identified, i.e., a reaction-limited regime, a diffusion-limited regime, and a new regime that is recombination-limited. For low values of r, conformal deposition in high aspect ratio structures can still be achieved, as observed for several metal oxides, even for aspect ratios as large as 30. For high surface recombination loss probabilities, as appears to be the case for many metals, achieving a reasonable conformality becomes challenging, especially for aspect ratios >10.

Optical emission spectroscopy as a tool for studying, optimizing, and monitoring plasma-assisted atomic layer deposition processes

In this note it is demonstrated that optical emission spectroscopy (OES) is an easy-to-implement and valuable tool to study, optimize, and monitor thin film growth by plasma-assisted atomic layer deposition (ALD). The species in the plasma can be identified through the analysis of the light emitted by the plasma. OES provides therefore information on the reactant species delivered to the surface by the plasma but it also yields unique insight into the surface reaction products and, as a consequence, on the reaction mechanisms of the deposition process. Time-resolved measurements reveal information about the amount of precursor dosing and length of plasma exposure needed to saturate the self-limiting half reactions, which is useful for the optimization of the ALD process. Furthermore, time-resolved OES can also be used as an easy-to-implement process monitoring tool for plasma-assisted ALD processes on production equipment; for example, to monitor reactor wall conditions or to detect process faults in real time.

Remote Plasma ALD of Platinum and Platinum Oxide Films

Platinum and platinum oxide films were deposited by remote plasma atomic layer deposition (ALD) from the combination of (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe 3 ) precursor and O 2 plasma. A short O 2 plasma exposure (0.5 s) resulted in low resistivity (15 μΩ cm), high density (21 g/cm 3 ), cubic Pt films, whereas a longer O 2 plasma exposure (5 s) resulted in semiconductive PtO 2 films. In situ spectroscopic ellipsometry studies revealed no significant nucleation delay, different from the thermal ALD process with O 2 gas which was used as a benchmark. A broad temperature window (100―300°C) for remote plasma ALD of Pt and PtO 2 was demonstrated.

Atomic layer deposition for nanostructured Li-ion batteries

Nanostructuring is targeted as a solution to achieve the improvements required for implementing Li-ion batteries in a wide range of applications. These applications range in size from electrical vehicles down to microsystems. Atomic layer deposition (ALD) could be an enabling technology for nanostructured Li-ion batteries as it is capable of depositing ultrathin films (1–100 nm) in complex structures with precise growth control. The potential of ALD is reviewed for three battery concepts that can be distinguished, i.e., particle-based electrodes, 3D-structured electrodes, and 3D all-solid-state microbatteries. It is discussed that a large range of materials can be deposited by ALD and recent demonstrations of battery improvements by ALD are used to exemplify its large potential.

Synthesis and in situ characterization of low-resistivity TaNx films by remote plasma atomic layer deposition

Remote plasma atomic layer deposition (ALD) of TaNx films from Ta[N(CH3)2]5 and H2, H2-N2, and NH3 plasmas is reported. From film analysis by in situ spectroscopic ellipsometry and various ex situ techniques, data on growth rate, atomic composition, mass density, TaNx microstructure, and resistivity are presented for films deposited at substrate temperatures between 150 and 250°C. It is established that cubic TaNx films with a high mass density (12.1gcm−3) and low electrical resistivity (380μΩcm) can be deposited using a H2 plasma with the density and resistivity of the films improving with plasma exposure time. H2-N2 and NH3 plasmas resulted in N-rich Ta3N5 films with a high resistivity. It is demonstrated that the different TaNx phases can be distinguished in situ by spectroscopic ellipsometry on the basis of their dielectric function with the magnitude of the Drude absorption yielding information on the resistivity of the films. In addition, the saturation of the ALD surface reactions can be determined...

Remote Plasma Atomic Layer Deposition of Co3O4 Thin Films

Cobalt oxide thin films have been deposited with remote plasma atomic layer deposition (ALD) within a wide temperature window (100-400 degrees C), using CoCp2 as a cobalt precursor and with remote O-2 plasma as the oxidant source. The growth rate was 0.05 nm/cycle and both the precursor dosing and plasma exposure exhibit saturation after 2 s, all independent of the substrate temperature. This novel combination resulted in the deposition of high density (similar to 5.8 g/cm(3)), stoichiometric Co3O4 showing a preferential (111) orientation for all temperatures. X-ray diffraction, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy independently indicate an increasing crystallinity with increasing substrate temperature, whereas the surface roughness remains low (

Deposition of TiN and TaN by Remote Plasma ALD for Cu and Li Diffusion Barrier Applications

TaN and TiN films were deposited by remote plasma atomic layer deposition (ALD) using the combinations of Ta[N(CH 3 ) 2 ] 5 precursor with H 2 plasma and TiCl 4 precursor with H 2 -N 2 plasma, respectively. Both the TaN and TiN films had a cubic phase composition with a relatively low resistivity (TaN: 380 μΩ cm; TiN: 150 μΩ cm). Dissimilar from the TiN properties, the material properties of the TaN films were found to depend strongly on the plasma exposure time. Preliminary tests on planar substrates were carried out revealing the potential of the TaN and TiN films as Cu and Li diffusion barriers in through-silicon via and silicon-integrated thin-film battery applications, respectively. For the specific films studied, it was found that TiN showed better barrier properties than TaN for both application areas. The TiN films were an effective barrier to Cu diffusion and had no Cu diffusion for anneal temperatures up to 700°C. The TiN films showed low Li intercalation during electrochemical charging and discharging.

Electrical transport and Al doping efficiency in nanoscale ZnO films prepared by atomic layer deposition

In this work, the structural, electrical, and optical properties as well as chemical bonding state of Al-doped ZnO films deposited by atomic layer deposition have been investigated to obtain insight into the doping and electrical transport mechanisms in the films. The range in doping levels from 0% to 16.4% Al was accomplished by tuning the ratio of ZnO and Al 2O3 ALD cycles. With X-ray photoelectron spectroscopy depth profiling and transmission electron microscopy, we could distinguish the individual ZnO and AlOx layers in the films. For films with a thickness of 40 nm, the resistivity improved from 9.8 mΩ cm for intrinsic ZnO to an optimum of 2.4 mΩ cm at 6.9 at. % Al. The binding energy of Zn 2p3/2 increased by 0.44 eV from the intrinsic ZnO to the highest Al-doped ZnO. This shift can be ascribed to an increase of the Fermi level. Ex-situ spectroscopic ellipsometry and Fourier transform infrared spectroscopy were used to measure the optical properties from which the carrier concentration and intra-grain mobility were extracted. The results showed that with increasing Al content, the grain boundary mobility increased at first due to an increased Fermi level, and then decreased mainly due to the scattering at AlOx/ZnO interfaces. For the same reasons, the doping efficiency of Al for highly Al-doped ZnO dropped monotonically with increasing Al. Furthermore, a blue shift of the optical band-gap ΔEg up to 0.48 eV was observed, consistent with the shifts of the Fermi level and the binding energy of the Zn 2p3/2 state.

Redeposition in plasma-assisted atomic layer deposition: Silicon nitride film quality ruled by the gas residence time

The requirements on the material properties and growth control of silicon nitride (SiNx) spacer films in transistors are becoming ever more stringent as scaling of transistor structures continues. One method to deposit high-quality films with excellent control is atomic layer deposition (ALD). However, depositing SiNx by ALD has turned out to be very challenging. In this work, it is shown that the plasma gas residence time τ is a key parameter for the deposition of SiNx by plasma-assisted ALD and that this parameter can be linked to a so-called “redeposition effect”. This previously ignored effect, which takes place during the plasma step, is the dissociation of reaction products in the plasma and the subsequent redeposition of reaction-product fragments on the surface. For SiNx ALD using SiH2(NHtBu)2 as precursor and N2 plasma as reactant, the gas residence time τ was found to determine both SiNx film quality and the resulting growth per cycle. It is shown that redeposition can be minimized by using a sh...