Stefan De Gendt

Metal-organic chemical vapor deposition of transition metal dichalcogenides is often accompanied by gas-phase reactions, which may lead to metal-based cluster formation in the gas phase and reduced deposition on the substrate surface. This study demonstrates that the cluster formation can be suppressed by keeping the residence time of metal precursor molecules in the reaction chamber significantly shorter than the typical collision time between such molecules. The rate of cluster formation was quantified by a single dimensionless parameter, the reduced residence time τr, which is the ratio of the average residence time to the intermolecular collision time. From an experimental study of WS2 metal-organic chemical vapor deposition using W(CO)6 and H2S precursors, the deposition rate is mass-transport limited at low W(CO)6 concentrations and process pressures, corresponding to τr ≪ 1. However, for τr ≥ 1, the deposition rate drops sharply, indicating cluster formation.

Semiconductor manufacturing is a resource and energy-intensive industry with a substantial environmental footprint. To address the footprint, we present a methodology for quantifying the environmental impact of semiconductor unit processes using the Environmental Footprint 3.1 Life Cycle Impact Assessment (LCIA) framework, focusing on identifying improvement opportunities in process steps with less sensitivity to defects. We apply this methodology to backside wet cleaning by proposing an alternative single-wafer process that adopts ozonated chemistries. The assessment used primary data from imec’s 300 mm pilot line. Results show that the proposed process reduces the total environmental footprint by 55% compared to the baseline Spin Cleaning with Repetitive use of Ozonated water and Diluted HF process. Key reductions include 67% less electricity for cleaning, 59% less HF use, and a 31% reduction in ultrapure water consumption. When scaled to a facility producing N28 Logic wafers at 50,000 wafer starts per month, with 46 backside clean steps per processed wafer, the process achieves annual savings of approximately 4 million kWh of electricity and 28 million liters (28,000 m³) of tap water per year. A sensitivity analysis revealed that replacing fossil-based electricity with hydroelectric power further reduces total environmental impacts by up to 63%, emphasizing the benefit of combining process innovation with renewable energy sourcing.

Semiconducting monolayer transition metal dichalcogenides (TMDs) such as MoS ₂ possess exceptional properties that make them highly desirable in photonic and optoelectronic applications. The photoluminescence (PL) of MoS ₂ is a valuable measure of its electronic and optical properties. Herein, chemical functionalization based on diazonium chemistry is used to modulate the PL of MoS ₂ in a programmed fashion. Using PL mapping, it is demonstrated that binding of aryl units with electron‐donating substituents leads to decreased PL, whereas electron‐withdrawing substituents enhance PL compared to pristine MoS ₂ . This functionalization is utilized to selectively modulate radiative recombination in the basal plane and to demonstrate the dependence of PL on the Fermi level. Raman spectroscopy corroborates the changes in the PL, and cryo‐PL also confirms that the chemical functionalization proceeds without the creation of additional defects in the basal plane of MoS ₂ . The surface morphology of functionalized MoS ₂ is characterized using scanning probe microscopy, which reveals the formation of well‐defined one‐nanometer‐thick films. Electrical characterization of devices incorporating functionalized MoS ₂ as the channel material reveals intriguing contrast to the PL trends, highlighting complex underlying mechanisms. Potential explanations for this divergence are explored, providing new insights into the electronic behavior of functionalized MoS ₂ .

BaBiO₃ has recently gained significant research attention as a parent material for an interesting family of alloyed compositions with multiple technological applications. In order to grow a variety of structures, a versatile deposition tool such as molecular beam epitaxy must be employed. In this work, the molecular beam epitaxy growth of BaBiO₃ on SrTiO₃(001) and MgO(001) substrates is studied. When grown by molecular beam epitaxy on SrTiO₃(001) or MgO(001) substrates, BaBiO₃ is known to have two competing orientations, namely (001) and (011). Characterization of the thin film is carried out by X-ray diffraction, X-ray reflectivity, atomic force microscopy, Rutherford backscattering, and transmission electron microscopy. Pathways to block the growth of BaBiO₃(011) and to grow only the technologically relevant BaBiO₃(001) are described for both substrates. An understanding of the enabling mechanism of the co-growth is established from an epitaxial point of view. This can be beneficially utilized for the growth of different compositions in the BaBiO₃ material family in a more controlled manner.

To achieve further miniaturization of semiconductor devices, extreme ultraviolet lithography is employed for patterning at the cutting-edge nodes. This technique necessitates the use of ultrathin resists (less than 50 nm thick) to maintain pattern stability and meet depth of focus requirements. Typical cold plasmas used for dry etching are rich in vacuum ultraviolet photons, which can cause unintended damage to these resists. This can further reduce the etch budget and complicate pattern transfer. Thus, understanding the impact of these plasma photons on ultrathin resists can be crucial for enabling pattern transfer of sub-10 nm features. Here, we investigate the effects of the vacuum ultraviolet photons on three different models of ultrathin negative tone chemically amplified resists along with polymethyl methacrylate as a reference positive tone baseline resist. The resists were exposed to vacuum ultraviolet photons using a deuterium lamp, to argon ions using an ion beam etch tool, and to argon plasma using an inductively coupled plasma etch tool. Using different characterization techniques, the variations in etch rate, surface roughness, and bulk chemical changes of the resists under different processing conditions were examined. The applicability of the Ohnishi number and ring parameter etch rate models to the resists and processing conditions used was also studied.

This study investigates the direct magnetoelectric effect in thin film composites comprising a 550 nm thick poly(vinylidene fluoride‐trifluoroethylene) (PVDF‐TrFE) layer spin‐coated onto a 500 µm thick Ni foil substrate. Direct measurements of charge accumulation on dot capacitors with Au top electrodes, induced by the rotation of Ni magnetization from in‐plane to out‐of‐plane orientation by an applied magnetic field, reveal pronounced magnetoelectric coupling. Polarization differences between in‐plane and out‐of‐plane magnetization states of up to (13.8 ± 0.8) × 10⁻⁴ µC cm⁻² are derived from charge measurements. This corresponds to a maximum open circuit voltage difference of up to 75 ± 6 mV and a magnetoelectric coupling coefficient with respect to magnetization changes of 310 ± 27 mVA⁻¹. Finite element simulations using COMSOL Multiphysics corroborate experimental findings, indicating near‐independence of generated polarizations and open circuit voltages when lateral capacitor dimensions are reduced into the nanometer range. Simulations of nanoscale pillar devices on rigid substrates, employing materials with optimized piezoelectric and magnetostrictive parameters, predict the potential for generating large open circuit voltage differences exceeding 2 V, highlighting the prospects of such devices for spintronic applications.

Atomic layer etching (ALE) continues to garner wide attention as a technique for controlled patterning of different materials.^1,2 However, a substantial amount of these studies are carried out on blanket films. It is therefore pivotal to investigate the feasibility of ALE for patterning high-density features as it exhibits the potential to be the preferred etching method for novel materials in the semiconductor industry. This talk will focus on the impact of ALE in the patterning of complex metal oxides like InGaZnO and MgZnO. These metal oxides are potential contenders as channel materials in high-performing transistors for memory and compute applications.³ Therefore, several critical criteria need to be followed when ALE conditions are being defined. The channel needs to be patterned with minimal physical and chemical damage such that there is little or no impact on the mobility parameters of the channel. The etching process should not induce redeposition onto the hard mask which also acts as a top contact in an integrated stack within the chip. In the case of InGaZnO, ALE-based patterning down to pitch 36 nm will be discussed in a systematic fashion.⁴ At such scaled pitches, it is observed that the etching challenges highlighted above cannot be resolved completely by ALE itself. Therefore, ALE in conjunction with other patterning approaches such as plasma pulsing needs to be employed to achieve satisfactory etching of the features at pitch 36 nm. On the other hand, when the metal oxide layer comprises a non-volatile element like Mg (in MgZnO), the etching mechanism tends to be both physical and chemical. In this case, it is still seen that the ALE approach provides a more controlled way of removing the layer without damaging the layer composition when compared to its conventional counterpart – reactive ion etching (RIE) at pitch 90 nm.⁵ REFERRENCES (1) Metzler, D.; Bruce, R. L.; Engelmann, S.; Joseph, E. A.; Oehrlein, G. S.; Fluorocarbon Assisted Atomic Layer Etching of SiO₂ Using Cyclic Ar/C₄F₈ Plasma. J. Vac. Sci. Technol. A 2014, 32, 020603. (2) Metzler, D.; Li, C.; Engelmann, S.; Bruce, R. L.; Joseph, E. A.; Oehrlein, G. S.; Fluorocarbon Assisted Atomic Layer Etching of SiO₂ and Si Using Cyclic Ar/C₄F₈ and Ar/CHF₃ plasma. J. Vac. Sci. Technol. A 2016, 34, 01B101. (3) Belmonte, A.; Oh, H.; Rassoul, N.; Donadio, G. L.; Mitard, J.; Dekkers, H.; Delhougne, R.; Subhechha, S.; Chasin, A.; van Setten, M. J.; Kljucar, L.; Mao, M.; Puliyalil, H.; Pak, M.; Teugels, L.; Tsvetanova, D.; Banerjee, K.; Souriau, L.; Tokei, Z.; Goux, L.; Kar, G. S.; Capacitor-Less, Long-Retention (>400s) DRAM Cell Paving the Way towards Low-Power and High-Density Monolithic 3D DRAM. 2020 IEEE International Electron Devices Meeting (IEDM) 2020, pp. 28.2.1-28.2.4. (4) Kundu, S.; Decoster, S.; Bezard, P.; Mehta, A. N.; Dekkers, H.; Lazzarino F.; High-Density Patterning of InGaZnO by CH4: a Comparative Study of RIE and Pulsed Plasma ALE. ACS Appl. Mater. Interfaces 2022, 14, 29, 34029–34039. (5) Ghorbani, L.; Kundu, S.; De Gendt, S.; Manuscript in preparation.

Exploring the ability of atomically precise magnetic Ni ₄ scatterers to augment graphene's spin activity.