Nanosecond Laser Annealing Research Articles

Room-temperature ferromagnetic MnGa nanoparticles in dilute magnetic semiconductor (Ga, Mn)As thin film: preparation and characterization

The GaAs based diluted magnetic semiconductor, (Ga, Mn)As, with the unique advantage of manipulating the spin and charge was widely investigated in the scientific community and considered as a potential material for the spintronic devices. However, its Curie temperature (Tc), which is limited to around 200 K, hinders the research progress of diluted magnetic semiconductors for potential device applications. Herein, we propose an approach to prepare the MnGa nanoparticles embedded in (Ga, Mn)As matrix using the magnetron sputtering deposition of Mn on GaAs surface, followed by the nano-second pulsed laser annealing (PLA), which gives aTcabove 400 K. We demonstrate that the MnGa nanoparticles are only formed in (Ga, Mn) As thin film during the nano-second PLA under a critical range of energy density (0.4-0.5 J cm-2). The highest achieved coercivity, saturation magnetization and remanent magnetization are 760 Oe, 11.3 emu cm-3and 9.6 emu cm-3, respectively. This method for preparing the hybrid system of ferromagnetic metal/dilute magnetic semiconductor builds a platform for exploring the interesting spin transport phenomenon and is promising for the application of spintronic devices.

Ferroelectricity in Ultrathin HfO2-Based Films by Nanosecond Laser Annealing.

Nonvolatile memory devices based on ferroelectric HfxZr1-xO2 (HZO) show great promise for back-end integrable storage and for neuromorphic accelerators, but their adoption is held back by the inability to scale down the HZO thickness without violating the strict thermal restrictions of the Si CMOS back end of line. In this work, we overcome this challenge and demonstrate the use of nanosecond pulsed laser annealing (NLA) to locally crystallize areas of an ultrathin (3.6 nm) HZO film into the ferroelectric orthorhombic phase. Meanwhile, the heat induced by the pulsed laser is confined to the layers above the Si, allowing for back-end compatible integration. We use a combination of electrical characterization, nanofocused scanning X-ray diffraction (nano-XRD), and synchrotron X-ray photoelectron spectroscopy (SXPS) to gain a comprehensive view of the change in material and interface properties by systematically varying both laser energy and the number of laser pulses on the same sample. We find that NLA can provide remanent polarization up to 2Pr= 11.6 μC/cm2 in 3.6 nm HZO, albeit with a significant wake-up effect. The improved TiN/HZO interface observed by XPS explains why device endurance goes beyond 107 cycles, whereas an identical film processed by rapid thermal processing (RTP) breaks already after 106 cycles. All in all, NLA provides a promising approach to scale down the ferroelectric oxide thickness for emerging HZO ferroelectric devices, which is key for their integration in scaled process nodes.

Nanosecond laser annealing processed surface-structured hyperdoped silicon for efficient near-infrared detection

Surface-structured engineering of hyperdoped silicon can effectively facilitate the absorption of sub-bandgap photons in pristine single-crystal silicon (sc-Si). Here, we conducted different annealing approaches of ordinary thermal annealing (OTA) and nanosecond laser annealing (NLA) on modification of titanium-hyperdoped silicon (Si:Ti) surface structure, to achieve efficient near-infrared detection. It is presented that both OTA and NLA processes can improve the crystallinity of Si:Ti samples. In detail, atomic-resolved STEM characterization illustrates that NLA treatment will further eliminate the amorphous phase on Si:Ti surface to varying degrees. While one-dimensional periodic stacking fault structure of 9R-Si phase is formed at the surface of sc-Si and embedded in the Si matrix during the OTA process, which reveals the seamless interface of 9R-Si/sc-Si along with [11¯0] direction. Due to the high sub-bandgap light absorption and good crystal structure, the Si:Ti photodetector after NLA treatment with an energy density of 2.6 J cm-2exhibited the highest responsivity, reaching 151 mA W-1at 1550 nm even at a low operating voltage of 1 V. We assume the performance enhancement of NLA processed Si:Ti photodetectors can be attributed to two aspects, the one is NLA can reduce the recombination of photo-generated charge carriers in amorphous surface layer by improving crystallization, and the other is that NLA process can weaken the diffusion of titanium impurities due to the extremely rapid heating and cooling rates. This study presents prospects towards surface-structured silicon in infrared light detection.

Hyperdoping of germanium with argon toward strain-doping-induced indirect-to-direct bandgap transition in Ge

The first-principles calculations have recently shown that implanting sufficient noble gas atoms into germanium (Ge) can expand its lattice to achieve the desired tensile strain for indirect-to-direct bandgap transition to develop the on-chip high-efficient light emitter. Here, to experimentally prove this strain-doping concept, we implant argon (Ar) ions into Ge and then recrystallize the Ar-doped amorphous Ge (a-Ge) layer using nanosecond laser annealing (NLA) and furnace thermal annealing (FTA), respectively. The NLA effectively recrystallizes the 12 nm thick a-Ge layer with minimal loss of Ar dopants, while FTA fails to fully recrystallize it and results in significant loss of Ar dopants. The regrown Ge layer with Ar concentration above the critical value (0.8%) for bandgap transition is 3.8 nm thick, making it a challenge to distinguish the photoluminescence signal of strain-doped layer from the substrate. To overcome this, increasing the implantation energy and adding a capping layer may be necessary to further prevent Ar loss and achieve a strain-doped layer with sufficient depth. These findings provide promising view of the strain-doping concept for direct-bandgap emission from Ge.

Tuning Superconductivity in Nanosecond Laser‐Annealed Boron‐Doped Si1–xGex Epilayers

Superconductivity in ultradoped Si1−xGex:B epilayers is demonstrated by nanosecond laser doping, which allows introducing substitutional B concentrations well above the solubility limit and up to 7 at%. A Ge fraction x ranging from 0 to 0.21 is incorporated in Si:B: 1) through a precursor gas, by gas immersion laser doping; 2) by ion implantation, followed by nanosecond laser annealing; and 3) by ultrahigh‐vacuum‐chemical vapor deposition growth of a thin Ge layer, followed by nanosecond laser annealing. The 30 and 75 nm‐thick Si1−xGex:B epilayers display superconducting critical temperatures Tc tuned by B and Ge between 0 and 0.6 K. Within Bardeen Cooper Schrieffer (BCS) weak‐coupling theory, Tc evolves exponentially with both the density of states and the electron–phonon potential. While B doping affects both, through the increase of the carrier density and the tensile strain, Ge incorporation allows addressing independently the lattice deformation influence on superconductivity. To estimate the lattice parameter modulation with B and Ge, Vegard's law is validated for the ternary SiGeB bulk alloy by density functional theory calculations. Its validity is furthermore confirmed experimentally by X‐ray diffraction. A global linear dependence of Tc versus lattice parameter, common for both Si:B and Si1−xGex:B, with δTc/Tc ≈ 50% for δa/a ≈1%, is highlighted.

Vis-IR black nano-silicon produced by wet femtosecond-laser nanotexturing/hyperdoping and nanosecond-laser annealing

Compared to conventional oven-based annealing in ambient air of a silicon surface layer nanotextured and hyperdoped in CS2 fluid by femtosecond laser (black nano-silicon), low-intensity nanosecond laser annealing facilitated its delicate recrystallization, preserving quasi-regular nanoscale topography and high n-doping concentration by sulfur donor impurities. The retained and recrystallized topography of the laser-annealed nano-silicon with a few-percent doping level exhibits broadband optical absorption in the visible−near-infrared (vis−NIR) range, rendering this optical material promising for photovoltaic and IR-photonic applications.

C54-TiSi2 formation using nanosecond laser annealing of A-Si/Ti/A-Si stacks

Low resistive Ti-based contacts are required to reach the targeted performances of 3D imaging devices. To fulfill this request, the C54-TiSi2 phase appears to be the most efficient. However, in view of monolithic integration, the temperature needed to form C54-TiSi2 must be drastically reduced by at least 100 °C in order to avoid damage in other parts of the device. Indeed, as these 3D imaging devices require the co-integration of Ti and Ni based silicides, it is crucial to develop a thermal treatment which allows to form the C54-TiSi2 phase without agglomerating the NiSi layer (i.e. at temperatures lower than 600 °C). In this work, a three-layer stack made of a Ti layer in between two amorphous Si thin films deposited on (100) Si substrate has been studied. Nanosecond laser annealing (NLA) followed by rapid thermal annealing (RTA) from 500 to 800 °C were performed on those stacks. Sheet resistance and X-Ray Diffraction measurements showed that the C54-TiSi2 phase could be formed with a RTA treatment at a temperature as low as 600 °C in this case. In line with some previous work, this was due to another phase sequence involving the C40-TiSi2 during the laser annealing. The most favorable microstructure to form C54-TiSi2 by a subsequent RTA treatment seemed to be a matrix made of amorphous titanium silicide containing grains of the C40-TiSi2 template phase. This hypothetical microstructure was formed by laser annealing at a lower energy density when layers of amorphous Si were used.

Laser‐Annealed SiO2/Si1−xGex Scaffolds for Nanoscaled Devices, Synergy of Experiment, and Computation

Laser‐Annealed SiO₂/Si_1−<i>x</i>Ge_<i>x</i> Scaffolds for Nanoscaled Devices, Synergy of Experiment, and Computation

Evaluation of the chemical states and electrical activation of ultra-highly B-doped Si1-xGex by ion implantation and subsequent nanosecond laser annealing

Given that transistordimensions are approaching atomic scale in metal–oxide–semiconductor field-effect-transistors (MOSFETs), attaining low-contact resistivity (ρc) between contact-metal and Si is a primary challenge for source/drain (S/D) fabrications. To reduce ρc, it is necessary to increase active dopant concentration in the semiconductor region underneath the contact-metal. High-dose ion-implantation and nanosecond laser-annealing (NLA) have been intensively investigated to produce highly activated layers in S/D regions. Particularly for the B-doped SiGe layers, which are used as S/D stressor for p-MOSFETs, non-substitutional B species are generated in the highly doped films at concentrations exceeding ∼ 1021 cm−3. These non-substitutional B are electrically non-activated and thus should be minimized to reduce ρc. In this study, we investigated the chemical states and electrical activation in highly B-doped SiGe layer. Using X-ray photoelectron spectroscopy (XPS), we examined the substitutionality of B-atoms and identified new chemical states of Si-B and Ge-B bonds in Si 2p and Ge 3d peaks. In the B 1s spectra, electrical activation states are determined by quantifying relative area ratios of the active/inactive B peaks, which are well matched with activation rates calculated by Hall measurements. Our findings systematically explained the activation behavior of NLA-treated B-doped SiGe films in high B-concentration ranges.

Nanosecond Laser Irradiation for Interface Bonding Characterization

Hydrophilic direct bonding is nowadays widely used in microelectronics for SOI substrate fabrication and 3D integration. Trapped water at the bonding interface plays a key role in the adhesion and adherence mechanisms [1]. Previous studies also reported that water could penetrate the bonding interface. This may modify the radial inhomogeneity of water [2]. However, this reported technique requires specific Silicon-to-Silicon bonding, lacks precision and needs additional characterizations (XRR, FTIR) to quantify the amount of trapped water at the bonding interface. In this work, we present an original methodology that can both accurately characterize and quantify water imbibition.Pulsed nanosecond laser annealing enables to reach extremely high temperatures, above the silicon melting point (1414°C), for very short durations (from a few tens of ns to a few hundred ns). These annealing conditions result in silicon surface melt. The beginning of melting is heterogeneous and leads to a particular surface topology with the formation of molten islands during laser annealing [3]. Recrystallization of these molten islands results in a localized increase of roughness (see fig. 1a). This roughness can exceed the direct bonding critical roughness. Non-bonded areas, i.e. bonding defects, can then be intentionally and precisely placed at the direct bonding interface.In a first step, bonding defects were thus formed along a wafer diameter with a 2 mm pitch. Then, using high-resolution acoustic microscopy, the bonding defects radii evolution was measured over time after direct bonding and without annealing (see fig. 1b). A progressive growth of defect radii was evidenced when getting closer and closer to the wafer edge. An additional water amount coming from the clean room atmosphere resulted in silicon oxidation at room temperature and di-hydrogen generation. Di-hydrogen was then trapped by bonding defects. In other words, bonding defects acted as humidity sensors. We could then record the penetration length and plot it as a function of the square root of time (fig. 1c). The penetration rate is the equivalent of a diffusion coefficient that could be calculated for both Silicon-to-Silicon and Silicon-to-Oxide bonding. We noted a very good agreement with Tedjini’s results for Silicon-to-Silicon bonding [2]. Meanwhile the calculated diffusion coefficient for Silicon-to-Oxide bonding was surprisingly about twice higher.Second, a bonding defect network with the same 2 mm pitch in both X and Y direction was created. After direct bonding, various duration 500°C temperature anneals were performed. The defects radii evolution was once again measured. As it increased over time, we could write the Griffith equilibrium between elastic (due to defect pressure) and surface (γ) energies. Describing defects as circular blisters, the amount of di-hydrogen trapped molecules could then be calculated. Plotting this number of H2 molecules, N, as a function of the annealing time (fig. 1d), we observe that a plateau was reached, meaning that all the di-hydrogen produced in the network was collected in the bonding defects. The water amount responsible for this di-hydrogen generation could then be evaluated and compared to data from other measurements. REFERENCES [1] F. Fournel, C. Martin-Cocher, D. Radisson, V. Larrey, E. Beche, C. Morales, P. A. Delean, F. Rieutord, and H. Moriceau, “Water Stress Corrosion in Bonded Structures”, ECS Journal of Solid State Science and Technology, 4 (5) P124-P130 (2015)[2] Tedjini M, Fournel F, Moriceau H, Larrey V, Landru D, Kononchuk O, et al. Interface water diffusion in silicon direct bonding. Appl Phys Lett. 12 sept 2016;109(11):111603.[3] L. Dagault, S. Kerdilès, P. Acosta Alba, J.-M. Hartmann, J.-P. Barnes, P. Gergaud, E. Scheid, and F. Cristiano, Investigation of Recrystallization and Stress Relaxation in Nanosecond Laser Annealed Si1−xGex/Si Epilayers, Appl. Surf. Sci. 527, 146752 (2020). Figure 1

Impact of nanosecond laser annealing on vacancies in electroplated Cu films studied by monoenergetic positron beams

Positron annihilation was used to probe vacancy-type defects in electrodeposited Cu films after nanosecond pulse laser annealing. For the as-deposited Cu film, we identified the coexistence of two different vacancy-type defects, vacancy clusters (such as V16) and monovacancy-type defects, coupled with impurities. An enlargement in the vacancy size was observed after the laser annealing process. The size of these defects was estimated to be close to V30, and such defects could not be formed by conventional furnace annealing. After furnace annealing at 400 °C, the size of the larger vacancy clusters decreased, but that of the smaller vacancies increased. The observed change in the sizes of vacancies is considered to be related to interactions between vacancies and impurities. The depth profile of the defects varied by changing the laser energy density and the number of laser shots. The impact of laser annealing on the vacancy-type defects was observed even after furnace annealing at 800 °C. Because the presence of point defects in electroplated Cu directly correlates with electromigration and grain growth, the ability of laser annealing to introduce large vacancy clusters in the localized region shows the potential of nanosecond laser annealing as a low-thermal budget process tool for back-end-of-line materials.

Impact of surface reflectivity on the ultra-fast laser melting of silicon-germanium alloys

Ultraviolet nanosecond laser annealing (LA) is a powerful tool where strongly confined heating and melting are desirable. In semiconductor technologies the importance of LA increases with the increasing complexity of the proposed integration schemes. Optimizing the LA process along with the experimental design is challenging, especially when complex 3D nanostructured systems with various shapes and phases are involved. Within this context, reliable simulations of laser melting are required for optimizing the process parameters while reducing the number of experimental tests. This gives rise to a virtual Design of Experiments (DoE). Si1−xGex alloys are nowadays used for their compatibility with silicon devices enabling to engineer properties such as strain, carrier mobilities and bandgap. In this work, the laser melting process of relaxed and strained Si1−xGex is simulated with a finite element method/phase field approach. Particularly, we calibrated the dielectric functions of the alloy for its crystalline and liquid phase using experimental data. We highlighted the importance of reproducing the exact reflectivity of the interface between air and the material in its different aggregation states, to correctly mimic the process. We indirectly discovered intriguing features on the optical behaviour of melt silicon-germanium.

Laser induced crystallization of sputtered MoS2 thin films

The integration of transition metal dichalcogenides (TMDs) thin films into Si CMOS-based devices requires the development of new bottom-up material growth approaches producing high crystallinity films without affecting the SiO2/Si substrate. For this purpose, sputtering is a suitable deposition method due to its simplicity, jointly with high reliability and large area deposition capabilities. However, sputtered layers are amorphous and require a post-deposition thermal treatment to obtain a highly crystalline film. Nanosecond pulsed laser annealing (PLA) has recently emerged as promising route to achieve large-scale crystalline TMDs films without significantly heating or affecting the underlying substrate. The aim of this work is to explore the possibility to produce crystalline 2H–MoS2 on large areas directly on a SiO2-on-Si substrate. The film structure, composition and morphology were monitored as a function of the laser pulse energy density by Raman spectroscopy, X-rays diffraction, Rutherford backscattered spectroscopy (RBS), scanning transmission electron microscopy (STEM) and atomic force microscopy (AFM). The electrical properties of the film with optimized crystallinity were finally investigated through deposition of Cr/Au contacts using shadow masks. This approach can be scaled to other TMDs materials and substrates, also paving the way for the fabrication of heterostructures and electrical devices on the top of a single substrate.

Nanosecond laser annealing of pseudomorphic GeSn layers: Impact of Sn content

Interactions between nanosecond laser pulses and various Sn content pseudomorphic GeSn layers were investigated. The aim was to evaluate the suitability of Ultraviolet Nanosecond Laser Annealing (UV-NLA), with an excimer laser emitting at 308 nm and a pulse duration of 160 ns, for the fabrication of performant contacts in GeSn devices such as electrically pumped lasers. Atomic Force Microscopy (AFM) and X-Ray Diffraction (XRD) revealed similar melt regimes for GeSn on Ge and SiGe on Si. At the melt threshold, surface structures formed where small areas melted. We were then in the so-called surface melt regime. The surface structures’ shape changed with the Sn content. A similar trend was recently evidenced when submitting SiGe layers on Si to UV-NLA. The shape change was more drastic in GeSn than in SiGe. A larger built-in compressive strain because of a much larger size difference between Ge and Sn than Si and Ge might be the reason why. Time Resolved Reflectivity maps showed a more reflective plateau after the melt peak at an Energy Density (ED) of around 1.00 Jcm−2, stemming from the presence of a smooth Sn rich surface layer, as revealed by AFM images at the same ED. Stacked XRD maps outlined that this ED corresponded to the formation of rather high Sn content layers with Sn contents of up to 6.3%, i.e., concentrations significantly above the solid solubility limit, which is below 1%, at variance with conventional annealing processes at 450 °C. UV-NLA has thus opened a new processing window that might be useful for contact formation.

Nanosecond pulsed laser annealing of Cu/Ag/AZO multilayer thin films for performance improvement and transparent heater application

Nanosecond pulsed laser annealing was performed to improve optical and electrical properties of the Cu/Ag/AZO multilayer films. Different laser fluences (L) and scanning speeds (S) were selected to investigate their influences on optical transparency and electrical conductivity of the films. The results revealed that laser annealing under L = 1.0 J/cm2 and S = 10 mm/s effectively promoted grain growth in the film and caused formation of significantly enlarged particles with a more uniform distribution on the film surface. The as-obtained Cu/Ag/AZO multilayer film possessed the optimal comprehensive property with the highest figure of merit of 3.58 × 10–2 Ω−1, far outperforming the unannealed Cu/Ag/AZO multilayer film (1.92 × 10–2 Ω−1). Subsequently, this film was chosen to fabricate a transparent heater, which exhibited excellent heating performance (saturated temperature: 104.9 ℃; response time: 120 s; applied voltage: 5 V) and heating stability. Its deicing availability was also shown by a deicing test.

Formation of Highly-Activated N-Type Shallow Junction in Germanium Using Nanosecond Laser Annealing and Fluorine Co-Doping

By employing a 355-nm nanosecond (ns) ultraviolet (UV) laser annealing, the impact of fluorine (F) co-doping on the formation of a highly activated N-type shallow junction in germanium (Ge) is investigated. Secondary ion mass spectrometry (SIMS) depth profiling of phosphorus (P) demonstrated that an ultra high P concentration of 9 × 1020 cm−3 at a shallow junction of 55 nm with less dopant diffusion can be obtained using ns laser annealing. F co-doping was confirmed to be an efficient way to improve the activation of the P dopants, but show less influence on the redistribution of P dopants within the NLA melted region. However, the activation level of the shallow junction could be increased to approximately 1 × 1020 cm−3 in the presence of F at an optimized concentration.

Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing.

A new approach for the stabilization of the ferroelectric orthorhombic ZrO2 films is demonstrated through nanosecond laser annealing (NLA) of as-deposited Si/SiOx /W(14nm)/ZrO2 (8nm)/W(22nm), grown by ion beam sputtering at low temperatures. The NLA process optimization is guided by COMSOL multiphysics simulations. The films annealed under the optimized conditions reveal the presence of the orthorhombic phase, as confirmed by X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of 12.8µC cm-2 , remnant polarization of 12.7µCcm-2 and coercive field of 1.2MVcm-1 . The films exhibit a wake-up effect that is attributed to the migration of point defects, such as oxygen vacancies, and/or a transition from nonferroelectric (monoclinic and tetragonal phase) to the ferroelectric orthorhombic phase. The capacitors demonstrate a stable polarization with an endurance of 6.0× 105 cycles, demonstrating the potential of the NLA process for the fabrication of ferroelectric memory devices with high polarization, low coercive field, and high cycling stability.

Nanosecond Laser Annealing of NMC 811 Cathodes for Enhanced Performance

Improved performance of lithium-ion batteries (LIBs) plays a critical role in the future of next- generation battery applications. Nickel-rich layered oxides such as LiNi0.8Mn0.1Co0.1O2 (NMC 811), are popular cathodes due to their high energy densities. However, they suffer from high surface reactivity, which results in the formation of Li2CO3 passive layer. Herein, we show the role of nanosecond pulsed laser annealing (PLA) in improving the current capacity and cycling stability of LIBs by reducing the carbonate layer, in addition to forming a protective LiF layer and manipulating the NMC 811 microstructures. We use high-power nanosecond laser pulses in a controlled way to create nanostructured surface topography which has a positive impact on the capacity retention and current capacity by providing an increased active surface area, which influences the diffusion kinetics of lithium-ions in the electrode materials during the battery cycling process. Advanced characterizations show that the PLA treatment results in the thinning of the passive Li2CO3 layer, which is formed on as-received NMC811 samples, along with the decomposition of excess polyvinylidene fluoride (PVDF) binder. The high-power laser interacts with the decomposed binder and surface Li+ to form LiF phase, which acts as a protective layer to prevent surface reactive sites from initiating parasitic reactions. As a result, the laser treated cathodes show relative increase of the current capacity of up to 50%, which is consistent with electrochemical measurements of LiB cells.

Use of Nanosecond Laser Annealing for Thermally Stable Ni(GeSn) Alloys

Use of Nanosecond Laser Annealing for Thermally Stable Ni(GeSn) Alloys

Optimization of solid-phase epitaxial regrowth performed by UV nanosecond laser annealing

Optimization of solid-phase epitaxial regrowth performed by UV nanosecond laser annealing