Publications by authors named "Harm C M Knoops"

8 Publications

  • Page 1 of 1

Reaction Mechanisms during Atomic Layer Deposition of AlF Using Al(CH) and SF Plasma.

J Phys Chem C Nanomater Interfaces 2021 Feb 10;125(7):3913-3923. Epub 2021 Feb 10.

Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

Metal fluorides generally demonstrate a wide band gap and a low refractive index, and they are commonly employed in optics and optoelectronics. Recently, an SF plasma was introduced as a novel co-reactant for the atomic layer deposition (ALD) of metal fluorides. In this work, the reaction mechanisms underlying the ALD of fluorides using a fluorine-containing plasma are investigated, considering aluminum fluoride (AlF) ALD from Al(CH) and an SF plasma as a model system. Surface infrared spectroscopy studies indicated that Al(CH) reacts with the surface in a ligand-exchange reaction by accepting F from the AlF film and forming CH surface groups. It was found that at low deposition temperatures Al(CH) also reacts with HF surface species. These HF species are formed during the SF plasma exposure and were detected both at the surface and in the gas phase using infrared spectroscopy and quadrupole mass spectrometry (QMS), respectively. Furthermore, QMS and optical emission spectroscopy (OES) measurements showed that CH and CH F ( ≤ 3) species are the main reaction products during the SF plasma exposure. The CH release is explained by the reaction of CH ligands with HF, while CH F species originate from the interaction of the SF plasma with CH ligands. At high temperatures, a transition from AlF deposition to AlO etching was observed using infrared spectroscopy. The obtained insights indicate a reaction pathway where F radicals from the SF plasma eliminate the CH ligands remaining after precursor dosing and where F radicals are simultaneously responsible for the fluorination reaction. The understanding of the reaction mechanisms during AlF growth can help in developing ALD processes for other metal fluorides using a fluorine-containing plasma as the co-reactant as well as atomic layer etching (ALE) processes involving surface fluorination.
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http://dx.doi.org/10.1021/acs.jpcc.0c10695DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8016095PMC
February 2021

Low-temperature plasma-enhanced atomic layer deposition of 2-D MoS: large area, thickness control and tuneable morphology.

Nanoscale 2018 May;10(18):8615-8627

Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

Low-temperature controllable synthesis of monolayer-to-multilayer thick MoS2 with tuneable morphology is demonstrated by using plasma enhanced atomic layer deposition (PEALD). The characteristic self-limiting ALD growth with a growth-per-cycle of 0.1 nm per cycle and digital thickness control down to a monolayer are observed with excellent wafer scale uniformity. The as-deposited films are found to be polycrystalline in nature showing the signature Raman and photoluminescence signals for the mono-to-few layered regime. Furthermore, a transformation in film morphology from in-plane to out-of-plane orientation of the 2-dimensional layers as a function of growth temperature is observed. An extensive study based on high-resolution transmission electron microscopy is presented to unravel the nucleation mechanism of MoS2 on SiO2/Si substrates at 450 °C. In addition, a model elucidating the film morphology transformation (at 450 °C) is hypothesized. Finally, the out-of-plane oriented films are demonstrated to outperform the in-plane oriented films in the hydrogen evolution reaction for water splitting applications.
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http://dx.doi.org/10.1039/c8nr02339eDOI Listing
May 2018

Tuning Material Properties of Oxides and Nitrides by Substrate Biasing during Plasma-Enhanced Atomic Layer Deposition on Planar and 3D Substrate Topographies.

ACS Appl Mater Interfaces 2018 Apr 9;10(15):13158-13180. Epub 2018 Apr 9.

Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven , The Netherlands.

Oxide and nitride thin-films of Ti, Hf, and Si serve numerous applications owing to the diverse range of their material properties. It is therefore imperative to have proper control over these properties during materials processing. Ion-surface interactions during plasma processing techniques can influence the properties of a growing film. In this work, we investigated the effects of controlling ion characteristics (energy, dose) on the properties of the aforementioned materials during plasma-enhanced atomic layer deposition (PEALD) on planar and 3D substrate topographies. We used a 200 mm remote PEALD system equipped with substrate biasing to control the energy and dose of ions by varying the magnitude and duration of the applied bias, respectively, during plasma exposure. Implementing substrate biasing in these forms enhanced PEALD process capability by providing two additional parameters for tuning a wide range of material properties. Below the regimes of ion-induced degradation, enhancing ion energies with substrate biasing during PEALD increased the refractive index and mass density of TiO and HfO and enabled control over their crystalline properties. PEALD of these oxides with substrate biasing at 150 °C led to the formation of crystalline material at the low temperature, which would otherwise yield amorphous films for deposition without biasing. Enhanced ion energies drastically reduced the resistivity of conductive TiN and HfN films. Furthermore, biasing during PEALD enabled the residual stress of these materials to be altered from tensile to compressive. The properties of SiO were slightly improved whereas those of SiN were degraded as a function of substrate biasing. PEALD on 3D trench nanostructures with biasing induced differing film properties at different regions of the 3D substrate. On the basis of the results presented herein, prospects afforded by the implementation of this technique during PEALD, such as enabling new routes for topographically selective deposition on 3D substrates, are discussed.
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http://dx.doi.org/10.1021/acsami.8b00183DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5909180PMC
April 2018

Atomic Layer Deposition of Wet-Etch Resistant Silicon Nitride Using Di(sec-butylamino)silane and N Plasma on Planar and 3D Substrate Topographies.

ACS Appl Mater Interfaces 2017 Jan 6;9(2):1858-1869. Epub 2017 Jan 6.

Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

The advent of three-dimensional (3D) finFET transistors and emergence of novel memory technologies place stringent requirements on the processing of silicon nitride (SiN) films used for a variety of applications in device manufacturing. In many cases, a low temperature (<400 °C) deposition process is desired that yields high quality SiN films that are etch resistant and also conformal when grown on 3D substrate topographies. In this work, we developed a novel plasma-enhanced atomic layer deposition (PEALD) process for SiN using a mono-aminosilane precursor, di(sec-butylamino)silane (DSBAS, SiHN(Bu)), and N plasma. Material properties have been analyzed over a wide stage temperature range (100-500 °C) and compared with those obtained in our previous work for SiN deposited using a bis-aminosilane precursor, bis(tert-butylamino)silane (BTBAS, SiH(NHBu)), and N plasma. Dense films (∼3.1 g/cm) with low C, O, and H contents at low substrate temperatures (<400 °C) were obtained on planar substrates for this process when compared to other processes reported in the literature. The developed process was also used for depositing SiN films on high aspect ratio (4.5:1) 3D trench nanostructures to investigate film conformality and wet-etch resistance (in dilute hydrofluoric acid, HF/HO = 1:100) relevant for state-of-the-art device architectures. Film conformality was below the desired levels of >95% and attributed to the combined role played by nitrogen plasma soft saturation, radical species recombination, and ion directionality during SiN deposition on 3D substrates. Yet, very low wet-etch rates (WER ≤ 2 nm/min) were observed at the top, sidewall, and bottom trench regions of the most conformal film deposited at low substrate temperature (<400 °C), which confirmed that the process is applicable for depositing high quality SiN films on both planar and 3D substrate topographies.
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http://dx.doi.org/10.1021/acsami.6b12267DOI Listing
January 2017

Role of Surface Termination in Atomic Layer Deposition of Silicon Nitride.

J Phys Chem Lett 2015 Sep 2;6(18):3610-4. Epub 2015 Sep 2.

Department of Applied Physics, Eindhoven University of Technology , Den Dolech 2, 5600 MB Eindhoven, The Netherlands.

There is an urgent need to deposit uniform, high-quality, conformal SiN(x) thin films at a low-temperature. Conforming to these constraints, we recently developed a plasma enhanced atomic layer deposition (ALD) process with bis(tertiary-butyl-amino)silane (BTBAS) as the silicon precursor. However, deposition of high quality SiNx thin films at reasonable growth rates occurs only when N2 plasma is used as the coreactant; strongly reduced growth rates are observed when other coreactants like NH3 plasma, or N2-H2 plasma are used. Experiments reported in this Letter reveal that NH(x)- or H- containing plasmas suppress film deposition by terminating reactive surface sites with H and NH(x) groups and inhibiting precursor adsorption. To understand the role of these surface groups on precursor adsorption, we carried out first-principles calculations of precursor adsorption on the β-Si3N4(0001) surface with different surface terminations. They show that adsorption of the precursor is strong on surfaces with undercoordinated surface sites. In contrast, on surfaces with H, NH2 groups, or both, steric hindrance leads to weak precursor adsorption. Experimental and first-principles results together show that using an N2 plasma to generate reactive undercoordinated surface sites allows strong adsorption of the silicon precursor and, hence, is key to successful deposition of silicon nitride by ALD.
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http://dx.doi.org/10.1021/acs.jpclett.5b01596DOI Listing
September 2015

Low-Temperature Plasma-Assisted Atomic Layer Deposition of Silicon Nitride Moisture Permeation Barrier Layers.

ACS Appl Mater Interfaces 2015 Oct 30;7(40):22525-32. Epub 2015 Sep 30.

Department of Applied Physics, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

Encapsulation of organic (opto-)electronic devices, such as organic light-emitting diodes (OLEDs), photovoltaic cells, and field-effect transistors, is required to minimize device degradation induced by moisture and oxygen ingress. SiNx moisture permeation barriers have been fabricated using a very recently developed low-temperature plasma-assisted atomic layer deposition (ALD) approach, consisting of half-reactions of the substrate with the precursor SiH2(NH(t)Bu)2 and with N2-fed plasma. The deposited films have been characterized in terms of their refractive index and chemical composition by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The SiNx thin-film refractive index ranges from 1.80 to 1.90 for films deposited at 80 °C up to 200 °C, respectively, and the C, O, and H impurity levels decrease when the deposition temperature increases. The relative open porosity content of the layers has been studied by means of multisolvent ellipsometric porosimetry (EP), adopting three solvents with different kinetic diameters: water (∼0.3 nm), ethanol (∼0.4 nm), and toluene (∼0.6 nm). Irrespective of the deposition temperature, and hence the impurity content in the SiNx films, no uptake of any adsorptive has been observed, pointing to the absence of open pores larger than 0.3 nm in diameter. Instead, multilayer development has been observed, leading to type II isotherms that, according to the IUPAC classification, are characteristic of nonporous layers. The calcium test has been performed in a climate chamber at 20 °C and 50% relative humidity to determine the intrinsic water vapor transmission rate (WVTR) of SiNx barriers deposited at 120 °C. Intrinsic WVTR values in the range of 10(-6) g/m2/day indicate excellent barrier properties for ALD SiNx layers as thin as 10 nm, competing with that of state-of-the-art plasma-enhanced chemical vapor-deposited SiNx layers of a few hundred nanometers in thickness.
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http://dx.doi.org/10.1021/acsami.5b06801DOI Listing
October 2015

Atomic Layer Deposition of Silicon Nitride from Bis(tert-butylamino)silane and N2 Plasma.

ACS Appl Mater Interfaces 2015 Sep 28;7(35):19857-62. Epub 2015 Aug 28.

Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, Netherlands.

Atomic layer deposition (ALD) of silicon nitride (SiNx) is deemed essential for a variety of applications in nanoelectronics, such as gate spacer layers in transistors. In this work an ALD process using bis(tert-butylamino)silane (BTBAS) and N2 plasma was developed and studied. The process exhibited a wide temperature window starting from room temperature up to 500 °C. The material properties and wet-etch rates were investigated as a function of plasma exposure time, plasma pressure, and substrate table temperature. Table temperatures of 300-500 °C yielded a high material quality and a composition close to Si3N4 was obtained at 500 °C (N/Si=1.4±0.1, mass density=2.9±0.1 g/cm3, refractive index=1.96±0.03). Low wet-etch rates of ∼1 nm/min were obtained for films deposited at table temperatures of 400 °C and higher, similar to that achieved in the literature using low-pressure chemical vapor deposition of SiNx at >700 °C. For novel applications requiring significantly lower temperatures, the temperature window from room temperature to 200 °C can be a solution, where relatively high material quality was obtained when operating at low plasma pressures or long plasma exposure times.
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http://dx.doi.org/10.1021/acsami.5b06833DOI Listing
September 2015

Electron Scattering and Doping Mechanisms in Solid-Phase-Crystallized In2O3:H Prepared by Atomic Layer Deposition.

ACS Appl Mater Interfaces 2015 Aug 23;7(30):16723-9. Epub 2015 Jul 23.

†Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

Hydrogen-doped indium oxide (In2O3:H) has recently emerged as an enabling transparent conductive oxide for solar cells, in particular for silicon heterojunction solar cells because its high electron mobility (>100 cm(2)/(V s)) allows for a simultaneously high electrical conductivity and optical transparency. Here, we report on high-quality In2O3:H prepared by a low-temperature atomic layer deposition (ALD) process and present insights into the doping mechanism and the electron scattering processes that limit the carrier mobility in such films. The process consists of ALD of amorphous In2O3:H at 100 °C and subsequent solid-phase crystallization at 150-200 °C to obtain large-grained polycrystalline In2O3:H films. The changes in optoelectronic properties upon crystallization have been monitored both electrically by Hall measurements and optically by analysis of the Drude response. After crystallization, an excellent carrier mobility of 128 ± 4 cm(2)/(V s) can be obtained at a carrier density of 1.8 × 10(20) cm(-3), irrespective of the annealing temperature. Temperature-dependent Hall measurements have revealed that electron scattering is dominated by unavoidable phonon and ionized impurity scattering from singly charged H-donors. Extrinsic defect scattering related to material quality such as grain boundary and neutral impurity scattering was found to be negligible in crystallized films indicating that the carrier mobility is maximized. Furthermore, by comparison of the absolute H-concentration and the carrier density in crystallized films, it is deduced that <4% of the incorporated H is an active dopant in crystallized films. Therefore, it can be concluded that inactive H atoms do not (significantly) contribute to defect scattering, which potentially explains why In2O3:H films are capable of achieving a much higher carrier mobility than conventional In2O3:Sn (ITO).
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http://dx.doi.org/10.1021/acsami.5b04420DOI Listing
August 2015