Pulsed laser annealing is a relevant alternative to conventional thermal processes for future technology nodes as it enables the application of a fast and local thermal budget. Such high-energy process can lead to the formation of a liquid phase that recrystallizes upon heat dissipation, through a high velocity liquid/solid interface moving towards the surface. Here, we report on the evolution of the liquid/solid interface roughness and its influence on the crystallinity of Si1-xGex layers depending on multiple parameters (strain state, doping level, Ge content, and pulse duration). This has been conducted with a roughness quantification method based on cross-section STEM-HAADF micrographs. It has been established that the liquid/solid roughness can be decreased by: (i) a compressive strain decrease, (ii) the use of short duration laser pulses or (iii) a reduction of the initial Ge content. The Ge content and strain must correspond to suitable values for optimized MOSFET performances. Consequently, strain and pulse duration were found to be pertinent levers for liquid/solid interface roughness reduction. Increasing the amount of boron atoms in s-Si1-xGex:B/Si systems is another relevant strategy, as compressive strain decrease would then be associated with a beneficial contact resistance lowering in the source-drain regions of p-type MOSFET devices.

The CMOS scaling beyond 10 nm technology node requires high active dopant concentrations in source/drain modules to minimize contact resistance. Pulsed laser annealing has been targeted by chip manufacturers as a future option to enhance the activation level inside highly doped SiGe:B and Si:P regions, mostly used in PMOS and NMOS transistor fabrication, respectively. Indeed, this annealing process allows reaching high temperatures (above melt threshold), locally (~100nm below the surface) and with extremely fast temperature ramp rates (>10 9 °C/s), so that high doping levels have been demonstrated both in pure Si and Ge [1]. In a recent study, structural investigations allowed identifying the best conditions to obtain fully strained and defect-free undoped SiGe layers by liquid phase epitaxial regrowth (LPER) [2]. In this work, we report an analysis on the activation of boron dopants in similar layers. In-situ boron-doped 30 nm thick pseudomorphic Si 0.7 Ge 0.3 layers were grown on p-type bulk Si (100) by CVD. Three different boron concentrations were incorporated inside these layers: 7.8x10 19 (A), 1.4x10 20 (B) and 2.3x10 20 cm -3 (C). By combining the boron chemical profiles with the corresponding Hall effect measurements (Hall scattering factor: 0.35), it was possible to estimate the activation rate inside the as-grown strained SiGe layers and the impact of the possible inactive dopants on the transport properties. From the lowest to the highest boron chemical concentration, we found activation rates of ~100%, ~80% and ~60%, with no significant carrier mobility degradation, even in the sample with the highest fraction of inactive dopants. The SiGe layers were subsequently laser annealed in a SCREEN-LT3100 platform operating at 308 nm (XeCl laser) with a pulse duration around 160 ns. The laser energy densities (ED) ranged from 1.20 to 2.40 J/cm 2 in order to investigate all the various annealing regimes. Results obtained using several characterization techniques were combined to determine the laser annealing regimes, quantify surface roughness and assess the layers’ composition, strain and crystalline quality. These results were compared to electrical measurements performed to analyse the evolution of the electrical parameters as a function of the laser anneal conditions, particularly the activation rate. For the lowly-doped and fully activated layer (A), the sheet resistance increases rapidly at the melt threshold (1.5 J/cm 2 , cf. Fig. 1, red curve), concomitantly with the appearance of a partial relaxation inside the layer (Fig. 2) and the formation of extended defects. The defects may induce a local dopant deactivation, while strain relaxation can result in a modification of the transport properties of the material (modified Hall scattering factor). Both phenomena can be therefore responsible for the observed increase of the sheet resistance. In contrast, for laser EDs allowing complete melt of the layer (i.e. beyond 2.0 J/cm 2 ), the sheet resistance decreases with increasing ED and full activation is achieved (Fig. 3, red curve) together with strain recovery (Fig. 2) and no observable defects. For the highly-doped and partially activated layer (C), partial relaxation also occurs at the melt threshold (Fig. 2). However, thanks to the strain compensation effect of the small boron atoms, the relaxation level is lower compared to the lowly-doped sample and more quickly recovered when increasing the ED (no defects observed at 1.95 J/cm 2 , Fig. 4). In addition, the sheet resistance is found to continuously decrease as a function of the ED (Fig. 1, blue curve) independently of the strain state of the structure. This suggests that, in addition to the previously described phenomena, the initially inactive dopants are progressively incorporated into substitutional positions by LPER. Indeed, when full melt and strain recovery is achieved, a 100% dopant activation is also observed (Fig. 3, blue curve). Characterizations made on sample B suggest a similar behaviour to that of sample C. Finally, further results will be reported from additional experiments aiming at (i) better understanding the impact of strain relaxation on dopant activation and (ii) optimizing the laser annealing process to avoid relaxation. These experiments include the use of a shorter laser pulse for the annealing of the strained SiGe layers, as well as the comparison with results obtained from fully-relaxed boron-doped SiGe annealed under similar laser conditions. Acknowledgements: This work was supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 871813 MUNDFAB. References: [1] F. Cristiano, A. La Magna, Laser annealing processes in semiconductor technology: Theory, modeling, and applications in nanoelectronics , Elsevier 2021 (9780128202555). [2] L. Dagault & al., Investigation of recrystallization and stress relaxation in nanosecond laser annealed Si 1−x Ge x /Si epilayers , ASS, Vol. 527, 146752 (10.1016/j.apsusc.2020.146752). Figure 1

The need of surface-localized thermal processing is strongly increasing especially w.r.t three-dimensionally (3D) integrated electrical devices. UV laser annealing (UV-LA) technology well addresses this challenge. Particularly UV-LA can reduce resistivity by enlarging metallic grains in lines or thin films, irradiating only the interconnects for short timescales. However, the risk of failure in electrical performance must be correctly managed, and that of UV-LA has not been deeply studied yet. In this work microsecond-scale UV-LA is applied on a stack comparable to an interconnect structure (dielectric/Cu/Ta/SiO2/Si) in either melt or sub-melt regime for grain growth. The failure modes such as (i) Cu diffusion into SiO2, (ii) O incorporation into Cu, and (iii) intermixing between Cu and Ta are investigated.

Si 1-x Ge x alloys took a major place in the microelectronic field because of their potential for MOSFETs devices. These last decades, the miniaturisation of these electronic devices allowed optimising their performances. However, this also highlighted new issues concerning the use of conventional Rapid Thermal Annealing for the fabrication processes of such materials. Nowadays, Nanosecond Laser Annealing (NLA) has attracted considerable attention thanks to its low thermal budget. It has been showed that NLA allows performing high temperature annealing localised at the surface, keeping the underlying material at low temperature, which may allow a diversification of device architectures such as 3D integration schemes. Moreover, this process is interesting for the formation of source/drain junctions as dopant concentrations higher than their solubility limit can be incorporated in Si or Ge. However, the impact of NLA on the structure of Si 1-x Ge x materials is not fully understood, especially concerning the melting regime of NLA. Recently, we have investigated the structural evolution induced by NLA in 30 nm-thick strained Si 1-x Ge x layers, elaborated by RPCVD [1]. These investigations have highlighted a strong correlation between the roughness exhibited by the interface between the melted and unmelted areas (referred to as liquid/solid (l/s) interface) and the strain state of the Si 1-x Ge x layers. In particular, in the case of a flat l/s interface, the strain state is determined by the elastic energy stored in the Si 1-x Ge x layer. In contrast, a rough l/s interface always leads to the layer relaxation. In the present study, we carried out a detailed investigation of the evolution of the l/s interface roughness as a function of several experimental parameters (Ge content, doping level, pulse duration). The objective is twofold: (i) to improve our understanding of the origin of the l/s interface roughness and its impact on the strain state of Si 1-x Ge x layers and (ii) to identify the best process conditions to achieve fully strained layers after NLA in the melt regime. As a first step, B-doping has been used to modify the initial strain state of the Si 1-x Ge x layers. Indeed, due to the low covalent radius of B atoms, the introduction of high B concentrations results in strain compensation. To achieve that, strained Si 0.7 Ge 0.3 layers were doped with B atoms during grown. The Z-contrast observed on STEM-HAADF images allowed to quantify the l/s interface roughness and determine its evolution depending on the B-doping level. As shown in Fig.1, it has been evidenced that the flattening of the l/s interface at high B-doping allows to avoid the formation of strain relieving defects in the whole layer. Here, the B-doping is expected to reduce the elastic energy density stored in the Si 1-x Ge x layer, preventing the formation of defects. As a second step, to understand the connection between the l/s interface roughness and the formation of defects, similar investigations have been made using 700 nm-thick fully relaxed Si 1-x Ge x layers. Removing the initial strain may allow to decorrelate the different phenomena inducing the formation of a rough l/s interface. The firsts results evidenced a similar Ge redistribution as in strained Si 1-x Ge x for melt depth up to 115 nm (Fig.2), while the l/s interface roughness was low regardless of the melt depth. However, at deeper melt depths, the structure of these layers is strongly modified. In particular, the roughness of the l/s interface induces lateral Ge segregation during resolidification, leading to pure Ge “walls” in the regrown layers. The origin of such laser-induced self-organisation will be discussed in terms of the elastic energy accumulated in these Si 1-x Ge x layers during resolidification and compared to the physical models proposed in the litterature [2]. As a last step, effects of NLA on strained Si 1-x Ge x layers will be investigated for different laser pulse durations. Indeed, the formation of a rough l/s interface may also be linked to the nano-structuration of the surface during the so-called surface melt regime. Lowering the pulse duration is expected to minimize the size of these structures and avoid the strain relaxation of the Si 1-x Ge x layers. In summary, the results obtained are expected to provide a better insight on the different phenomena occurring when a melt laser process is carried out on Si 1-x Ge x layers and contribute to the optimisation of this annealing technique in view of its application in the fabrication of future nanoelectronics devices. Acknowledgements: This work was supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 871813 MUNDFAB. References: [1] Dagault et al. App. Surf. Sci. 527, 146752 (2020) [2] Weizman et al. J. Appl. Phys. 103, 093536 (2008) Figure 1

In this work, we present a comprehensive investigation of impurities contamination in silicon during UV Nanosecond Laser Annealing at high energy density. By investigating in detail the impact of the annealing ambient and of the surface preparation prior to UV-NLA (including the variation of the surface oxide thickness), we show that the observed oxygen penetration originates from the surface oxide layer. It is proposed that, at high energy UV-NLA, the prolonged contact of SiO2 with high temperature liquid Si induces a partial degradation of the SiO2/Si interface, leading to bond breaking and subsequent injection of O atoms into the substrate. A degradation involving less than 5% of the O atoms contained in the 1st SiO2 mono-layer is sufficient to account for the measured amount of in-diffused O in all of the analysed samples.

Defect evolution and dopant activation are intimately related to the use of ion implantation and annealing, traditionally used to dope semiconductors during device fabrication. However, during the last decade, the increased difficulties to maintain the transistor miniaturization pace have led to a diversification of both the basic device architecture and processes. In this context, the recent advances in nanosecond laser annealing have opened the way to solve a wide spectrum of difficult challenges in semiconductor technology, well beyond the traditional source/drain fabrication issues. Indeed, thanks to its low thermal budget, laser annealing is very attractive not only for the achievement of abrupt and highly doped junctions, but more generally for all semiconductor technologies in which dopants need to be activated while preserving the integrity of the surrounding areas, as in the case of CMOS backside imagers or 3D integration technologies.After giving an overview of some relevant published studies in this domain [1], we will present our recent investigations focused on damage and strain evolution in SiGe and their impact on dopant distribution and electrical activation during nanosecond laser thermal annealing. These will concern compressively strained SiGe layers (with Ge fraction, x, ranging from 0 to 0.4), which were submitted to Ultraviolet Nanosecond Laser Anneal (UV-NLA) at different energies. The impact of the process parameters on the annealing regimes and on the relaxation of the initial compressive strain are investigated in detail. Optimised conditions to achieve pseudomorphic, defect-free structures are identified, which depend on the elastic energy stored in the recrystallized structure (Fig. 1). The impact of the structural modifications induced by UN-NLA on the efficiency of dopant activation is also discussed. Finally, Ge segregation towards the surface occurs during melt laser annealing, resulting in the formation of a Ge-rich surface layer (Fig. 2). Such pseudomorphic SiGe layers with a graded composition and a Ge-rich surface may find promising applications such as contact resistance lowering in doped layers.In the last part, some recent investigations of phosphorus-doped ultra-thin SOI layers submitted to UV-NLA will be presented. Their recrystallization is investigated as a function of the implanted dose as well as the laser energy density, while the best conditions to achieve high dopant activation (up to ~2 % at.) are identified.

The dielectric properties of aluminium oxide (Al2O3) thin films obtained by plasma-enhanced atomic layer deposition (PEALD) from Al(CH3)3/O2 precursors were investigated while focusing on the influences of thermal annealing under a dioxygen (O2) ambient. PEALD-Al2O3-based metal-insulator-silicon structures/capacitors and pH-sensitive chemical field effect transistors were fabricated to deal respectively with microelectronic applications and measurement in liquid phase. Antagonist results were thus evidenced. On the one hand, dealing with high-k gate materials, optimized dielectric properties, i.e. low fixed charge density (4 x 1012 cm-2), high dielectric constant (epsilon r =10.2), Fowler-Nordheim conduction and high breakdown electric fields (Ebd = 8.75 MV/ cm) were obtained for polycrystalline PEALD Al2O3 films annealed at high temperature (T 1 mV/day) and long lifetime ( 180 days), were optimized for unannealed amorphous PEALD Al2O3 films. These phenomena were associated germination/crystallization phenomena in the deposited amorphous alumina structure as well as to related charge trapping and leakage currents in water-based solutions related to the final Al2O3 polycrystalline structure.

UV nanosecond pulsed laser annealing (UV NLA) enables both surface-localized heating and short timescale high temperature processing, which can be advantageous to reduce metal line resistance by enlarging metal grains in lines or in thin films, while maintaining the integrity and performance of surrounding structures. In this work UV NLA is applied on a typical Cu thin film, demonstrating a mean grain size of over 1 μm and 400 nm in a melt and sub-melt regime, respectively. Along with such grain enlargement, film resistivity is also reduced.

30 nm-thick pseudomorphic Si1-xGex layers with Ge concentrations x ranging from 0 to 0.4 were submitted to Ultraviolet Nanosecond Laser Annealing (UV-NLA). The impact of UV-NLA on the various regimes and on the layer crystallinity was assessed for each Ge concentration. This study highlighted the existence of four annealing regimes, with notably a surface melt regime with isolated molten islands on the surface. The strain in the layer depended on the liquid/solid interface roughness and on the stored elastic energy in the layers. In the case of smooth liquid/solid interfaces, a limit for perfect recrystallization was estimated near 750 mJ/m(2).

In this work, we studied the rapid crystallization and the rapid thermal oxidation of amorphous silicon films deposited at 465°C by low-pressure chemical vapor deposition (LPCVD) from disilane. The crystallization is well-controlled and the thermal bugdet is reduced compared to conventional processes. Results concerning the electrical and structural characteristics of poly-Si thin film transistors (TFT) are given. Furthermore, we obtained after plasma hydrogenation better mobilities in the case of rapid thermal processing (RTP) (μp-61 cm2/V.s, VT=-8.3 V, subthreshold slope=-0.8 V/decade, ION/IOFF=1.106 for p-type and μn=80 cm2/V.s, VT=3.7 V, subthreshold slope=1.4 V/decade, ION/IOFF=5.104 for n-type) compared to conventional processing performed at 600°C. The mobilities are improved by a factor of 2 to 3 despite the smaller grain size in the silicon films. We also showed a correlation between the optical absorption coefficient k (at 405nm) and the mobility which appears not only dependent upon, the grain size but also upon the grain quality (grain boundaries and defects inside the grain). This study shows that the structural and electrical properties of thin-films and oxides fabricated by RTP are at least as good as those obtained by conventional techniques.

The initial substrate inhibiting island growth and the formation of an interfacial layer with uncontrollable characteristics are the two main drawbacks of the Atomic Layer Deposition (ALD) of high-k metal-oxide gate dielectrics on silicon (Si). In this paper, we investigate the ALD of Al2O3 films from trimethyl aluminum and H2O, on fluorhydric acid (HF) cleaned, as well as on HF-cleaned and in situ N-2-NH3 plasma pretreated Si between 0 and 75 cycles. The films and their interface were characterized via Scanning Transmission Electron Microscopy coupled to Energy-Dispersive X-ray spectroscopy. The initial deposition is clearly increased on the pretreated surfaces, obtaining a linear ALD regime even after 5 ALD cycles, compared to several tens of cycles needed on HF-cleaned Si. Furthermore, a SixNy layer is formed by the N-2-NH3 plasma pretreatment, which acts as a barrier layer, reducing the oxidation of the Si substrate beneath it. This analysis provides a general framework for the understanding and determination of adequate surface pretreatments, able to combat the substrate inhibited initial growth and the Si oxidation during metal-oxide ALD on Si.

During the first stages of Atomic Layer Deposition (ALD) of Al2O3 on silicon (Si), the substrate nature affects the surface chemistry, leading to an initial island growth mode. Furthermore, an interfacial zone develops between the Si surface and the dielectric, thus damaging the physical properties of the deposited structure. In this work, these two main shortcomings are investigated for the ALD of Al2O3 films on Si from TMA and H2O. The film and the interfacial zone are characterized by a complete range of techniques, including XRR, TEM, XPS, EDX and ToF-SIMS. In parallel, a computational model is developed to study the initial nucleation and growth steps of the film. An induction period is experimentally evidenced and numerically reproduced, together with the island growth and coalescence phenomena. The chemical composition of the (Al, O, Si) interfacial layer is precisely analyzed to get insight in the mechanisms of its formation. We show that Si oxidation occurs during the island growth, catalyzed by the presence of Al, while it is also fed by species interdiffusion through the ALD film.

We report on the optimisation of precursor gas composition for the repeatable preparation of large area highly conductive boron doped nano-crystalline diamond layers with low sp(2) content using microwave plasma enhanced linear antenna chemical vapour deposition apparatus. The precursor gas composition parameter space was probed by varying the boron, oxygen and carbon atomic ratios whilst fixing all other parameters constant. By radically increasing the B content and careful consideration of the B and O content in the gas phase, thin B-NCD layers (similar to 300 nm) were prepared over large areas, repeatable, with high boron concentrations (similar to 2 x 10(21) at/cm(3)) and electrical conductivity levels akin to B-NCD layers prepared in conventional MW PECVD systems (> 35 S cm(-1)) with electrochemical properties suitable for industrial applications. (C) 2017 Elsevier Ltd. All rights reserved.

The surface mechanisms involved in the Atomic Layer Deposition of Al2O3 from TMA and H2O are investigated by means of combined experimental and computational analyses. Reactant adsorption, desorption and surface reaction are taken into account by a surface chemistry model, coupled to a CFD model for an industrial reactor treating 200 mm substrates. Once the model validated by comparison with experimental deposition rates, the relative contribution of each surface phenomenon is quantitatively determined between 100 and 300 degrees C through original reaction probability calculations. It is revealed that the competition between surface reactions and desorption of H2O plays a crucial role in the ALD growth of alumina. The H2O desorption is the limiting factor for the growth at low process temperature whereas it is the OH group surface concentration at higher temperature. This integrated (surface chemistry/kinetics and CFD) model shows a direct link between transport phenomena, such as gas flow recirculation and low temperature zones in the reactor, and film uniformity. (C) 2018 Elsevier Ltd. All rights reserved.

In this paper, we present an enhanced differential Hall effect measurement method (DHE) for ultrathin Si and SiGe layers for the investigation of dopant activation in the surface region with sub-nanometre resolution. In the case of SiGe, which constitutes the most challenging process, we show the reliability of the SC1 chemical solution (NH4OH/H2O2/H2O) with its slow etch rate, stoichiometry conservation and low roughness generation. The reliability of a complete DHE procedure, with an etching step as small as 0.5 nm, is demonstrated on a dedicated 20 nm thick SiGe test structure fabricated by CVD and uniformly doped in situ during growth. The developed method is finally applied to the investigation of dopant activation achieved by advanced annealing methods (including millisecond and nanosecond laser annealing) in two material systems: 6 nm thick SiGeOI and 11 nm thick SOI. In both cases, DHE is shown to be a uniquely sensitive characterisation technique for a detailed investigation of dopant activation in ultrashallow layers, providing sub-nanometre resolution for both dopant concentration and carrier mobility depth profiles.

The reduction of the contact resistance RC is one of the most challenging issues related to the miniaturisation of advanced MOSFET architectures, including FDSOI technology (Fully Depleted Silicon-On-Insulator). RC strongly depends on the active dopant concentration at the semiconductor/salicide interface. It is therefore essential that electrical activation at different depths within a doped layer is reliably determined to optimise the fabrication processes. In this paper, we firstly present a Differential Hall Effect (DHE) method which allows measuring the active dopant concentration profile close to the surface with nm resolution for ultra-shallow doped Si1-xGex and Si layers. Then, we present DHE measurements made on junctions processed with advanced techniques, including nsec LTA and msec DSA anneals.

Aluminium oxide (Al2O3) films were deposited on silicon substrates using plasma-enhanced atomic layer deposition (PE-ALD) technique with tri-methyl-aluminium TMA (Al(CH3)(3)) and dioxygen (O-2) as precursors. PEALD experiments were performed in order to (i) investigate the interfacial properties between the silicon substrate and the alumina layer, and (ii) understand the impact of growth and crystallization phenomena on the Al2O3 films properties (structural, optical, mechanical, dielectric and etch). The formation of oxide-based transition layers, either silicon oxide SiO2 and/or aluminosilicate AlxSiyO, was evidenced for the TMA/O-2 PEALD process. Based on these results, it appears that no substrate-enhanced growth occurs at the early stages of the growth process, as assumed in previous reports. Thus, constant growth rate (0.08 nm per cycle) and refractive index (1.64 at a 450 nm wavelength) were obtained for the Al2O3 layer deposited at 300 degrees C. Finally, thermal annealing experiments were performed on these films, evidencing the influences of atomic structural rearrangement and crystallization on the Al2O3 film main characteristics: interface steepness, atomic structure, refractive index, residual stress, dielectric constant and etch rate.

A three-dimensional Computational Fluid Dynamics model is built for a commercial Atomic Layer Deposition (ALD) reactor, designed to treat large area 20cm substrates. The model aims to investigate the effect of the reactor geometry and process parameters on the gas flow and temperature fields, and on the species distribution on the heated substrate surface, for the deposition of Al2O3 films from trimethyl aluminum and H2O. The investigation is performed in transient conditions, without considering any surface reaction. A second CFD model is developed for the feeding system of the reactor, in order to calculate the unknown reactant inlet flow rates. The two models are coupled via a computational strategy dictated by the available experimental measurements. Results show that a purging flow entering the reactor through its loading door affects the flow field above the substrate surface and causes non-uniformity in the temperature and reactants concentration on the substrate surface. During the TMA pulse, a recirculation sets in above the substrate surface, leading to a non-uniform distribution of species on the surface.

Ti/Al2O3 bilayer stacks are used as model systems to investigate the role of atomic layer deposition (ALD) and chemical vapor deposition (CVD) to prepare 30–180 nm thick amorphous alumina films as protective barriers for the medium temperature oxidation (500–600 °C) of titanium, which is employed in aeronautic applications. X‐ray diffraction (XRD), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), and X‐ray photoelectron spectroscopy (XPS) results show that the films produced from the direct liquid injection (DLI) CVD of aluminum tri‐isopropoxide (ATI) are poor oxygen barriers. The films processed using the ALD of trimethylaluminum (TMA) show good barrier properties but an extensive intermixing with Ti which subsequently oxidizes. In contrast, the films prepared from dimethyl aluminum isopropoxide (DMAI) by CVD are excellent oxygen barriers and show little intermixing with Ti. Overall, these measurements correlate the effect of the alumina coating thickness, morphology, and stoichiometry resulting from the preparation method to the oxidation barrier properties, and show that compact and stoichiometric amorphous alumina films offer superior barrier properties.

A Differential Hall Effect method has been developed that allows to determine of the dopant activation level of SiGe alloys in the surface region. The technique is first optimised in terms of etch rate (~ 1Å/min), surface roughness, strain and stoichiometry stability during etch. We then show that this DHE method allows to experimentally access the dopant activation of ultra-shallow surface layers of less than 0.5 nm.