Laser Annealing Research Articles

Post-fabrication frequency trimming of coplanar-waveguide resonators in circuit QED quantum processors

We present the use of a set of airbridges to trim the frequency of microwave coplanar-waveguide (CPW) resonators post-fabrication. This method is compatible with the fabrication steps of conventional CPW airbridges and crossovers and increases device yield by allowing compensation of design and fabrication uncertainty with 100 MHz range and 10 MHz resolution. We showcase two applications in circuit QED. The first is the elimination of frequency collisions between resonators intended to readout different transmons by frequency-division multiplexing. The second is frequency matching of readout and Purcell-filter resonator pairs. Combining this matching with transmon frequency trimming by laser annealing reliably achieves fast and high-fidelity readout across 17-transmon quantum processors.

Fabrication of Ohmic Contact on N-Type SiC by Laser Annealed Process: A Review

In recent years, because of stringent needs in the fabrication of silicon carbide (SiC) power devices, laser annealing has been introduced to achieve local ohmic contact. In this paper, the laser annealing research for the ohmic contact process of SiC power devices is reviewed, which is mainly divided into four aspects: laser process mechanism, ohmic contact electrode materials, and substrate materials. The effect of laser parameters on ohmic contact and the annealing process on SiC diode devices is also reviewed. Progress of other substrate materials, namely 6H-SiC and semi-insulating 4H-SiC-based devices with laser annealed ohmic contacts, is also briefly discussed, in which formation of semi-insulating SiC ohmic contacts is derived from laser irradiation at the interface to produce 3C-SiC. Some experiment results have been shown in the passage, such as XRD, SEM, TEM, etc. In the review, it points out that the direction of application and development of the laser annealing process for improving the ohmic contact of SiC power devices is highly encouraging.

Room temperature magnetron sputtering and laser annealing of ultrathin amorphous sulfur-rich MoSx films

Room temperature magnetron sputtering of an ultra-thin transition-metal dichalcogenide amorphous precursor and subsequent laser annealing-induced phase transformations were investigated for the synthesis of polycrystalline 2H-MoS2 semiconducting thin films. Radio frequency magnetron sputtering of a MoS3.6 target was used to produce amorphous precursors with S to Mo ratios greater than 2:1 on thermally annealed SiO2 substrates, glass, indium tin oxide coated glass, and amorphous boron-oxy-nitride. The influence of working pressure on the MoS2 and MoS3 interatomic bonding arrangements in amorphous MoSx films was explored with x-ray photoelectron spectroscopy. A 248 nm pulsed laser was used for annealing 1 cm2 sized areas of the amorphous precursor in an ambient atmosphere at fluences of 100–450 mJ for 1, 5, and 10 pulses to form a crystalline 2H-MoS2 phase. The role of laser fluence and substrate choice on phase transformation from the amorphous precursor to the 2H phase, as well as the competition between oxidation, elemental sulfur segregation, and ablation is discussed. Hall effect measurements confirmed p-type behavior of the produced semiconducting films and established mobility and charge carrier density characteristics of the laser-annealed films. The feasibility of scalable processing by combining sputtering from sulfur-rich targets and laser annealing for production of p-type 2H-MoS2 ultrathin films on various substrates is presented.

Experimental and numerical study of Si annealed by laser sources of the visible spectrum (red and blue wavelength)

Laser annealing (LA) is an increasingly important process in the semiconductor manufacturing industry. So far, lasers of nonvisible spectrum have been mostly used for semiconductor applications. The study using a visible wavelength laser is not nearly found though it could be a potential tool to expand applications of the LA. In this study, the silicon (Si) deposited on oxide was annealed using laser sources of visible spectrum. LA of Si was performed using a single laser source of either red or blue wavelengths or a dual-laser source using both wavelengths. The surface morphology and microstructure of the annealed Si were analyzed. A numerical simulation was also conducted to predict the temperature and melt pool characteristics of Si during the annealing process. Surface roughness increased with increasing heat input (or power density) of the laser beam, owing to the considerable melting of Si. The dual laser using a relatively high power density produced Si with high polycrystallinity and large grains. However, the Si lattice constant difference induced by different annealing conditions was negligible. Simulation results showed that temperature, melt pool length, and duration increased with the power density of the dual-laser beam. This contributed to the growth of large Si grains.

Effects of Polycrystalline Silicon Plug Defect on DRAM Characteristics

This study first demonstrates the effect of polycrystalline silicon plug defects, including voids and seams in dynamic random access memory (DRAM) storage node contact (SNC), on product characteristics. The defect portion of SNC has increased continually due to a reduction in the contact area, an increase in the doping concentration, and low-pressure chemical vapor deposition (LPCVD) process limitations. We validate the effect through defect removal experiments. Numerous methods, such as the cyclic deposition/etch/deposition process of silicon, ion implantation, and laser annealing, are used. The experiments are successful without any side effects using a high-density laser annealing process. The contact resistance of the sample-removed polysilicon defect decreases by 59% and the cell drain current increases by 6%. In addition, the overlap capacitance of the drain node and cell gate edge (Cov) variations by the SNC dopant diffusion forming the source and drain junction of the cell transistor is improved by 6%. Finally, we conduct the row precharge delay from the last data-in (tRDL) time delay reliability test using mass production test technology and it was confirmed that the contact area standard that satisfies the product quality target is improved by 10%. We propose a new direction for polycrystalline silicon SNC development for a sub-20-nm DRAM device based on this experiment.

Pulsed laser annealed rare earth doped TiO2 thin films for luminescence and sensing applications

Many research activities target functional luminescent materials based on metal oxides activated with trivalent rare earth ions. Specific applications necessitate optimization of material preparation, annealing and excitation-detection techniques. Hereby we utilized pulsed laser deposition to obtain thin (150 nm) TiO2 films containing 1at% of samarium (Sm) or neodymium (Nd) impurity ions. The effect of pulsed laser annealing (ArF excimer laser, wavelength 193 nm, pulse duration 20 ns) on their structural and luminescent properties was investigated. It was found that, compared to conventional thermal annealing at 700 °C, proper laser annealing (fluence 50 mJ/cm2, 5–15 shots) induced much better crystallization (nearly phase-pure anatase) along with respective improvement of host-sensitized trivalent rare earth fluorescence. The outcome significantly depends on the applied fluence and number of laser shots. Effects of under- and overannealing were witnessed (poor or mixed phase crystallization, weak luminescence and melting/dewetting of the film). A strong luminescence from optimally annealed samples was detected under excitation of 365 nm light emitting diode, which is favorable for potential applications of such thin films. As an example, trace oxygen sensing is demonstrated with the laser annealed TiO2:Sm film.

EXTRAORDINARY MAGNETORESISTANCE OF LASERANNEALED NANO BORON DEPOSITEDON OXIDIZED POROUS SILICON

This study explores the impact of laser annealing on the electrical and magnetic properties of nano boron deposited on oxidized porous silicon (n-B/PSiO2) and its potential for spintronic applications. The Nd: YAG laser was used at varying energies to anneal the n-B thin films. Increasing the laser energy increased grain size and more ordered grain structures. It also increased surface roughness due to forming new grain boundaries and secondary phases. The electrical properties of the material were also affected by the laser annealing, with an increase in forward and reverse current and an increase in electrical resistivity with increased annealing temperature. The study also found that the magnetoresistance of the material increased with increasing laser temperature, attributed to tunnel injection through the thin silicon dioxide layer, and could be up to 7 times higher than non-annealed n-B/PSiO2in a magnetic field. The study highlights the importance of controlling materials’ grain size and structure for their physical and electrical properties. In addition, it provides insights into the electronic properties of n-B/PSiO2and the behavior of charge carriers in a magnetic field.

Active sites of Te-hyperdoped silicon by hard x-ray photoelectron spectroscopy

Multiple dopant configurations of Te impurities in close vicinity in silicon are investigated using photoelectron spectroscopy, photoelectron diffraction, and Bloch wave calculations. The samples are prepared by ion implantation followed by pulsed laser annealing. The dopant concentration is variable and high above the solubility limit of Te in silicon. The configurations in question are distinguished from isolated Te impurities by a strong chemical core level shift. While Te clusters are found to form only in very small concentrations, multi-Te configurations of type dimer or up to four Te ions surrounding a vacancy are clearly identified. For these configurations, a substitutional site location of Te is found to match the data best in all cases. For isolated Te ions, this matches the expectations. For multi-Te configurations, the results contribute to understanding the exceptional activation of free charge carriers in hyperdoping of chalcogens in silicon.

High-Quality Recrystallization of Amorphous Silicon on Si (100) Induced via Laser Annealing at the Nanoscale

At sub-3 nm nodes, the scaling of lateral devices represented by a fin field-effect transistor (FinFET) and gate-all-around field effect transistors (GAAFET) faces increasing technical challenges. At the same time, the development of vertical devices in the three-dimensional direction has excellent potential for scaling. However, existing vertical devices face two technical challenges: “self-alignment of gate and channel” and “precise gate length control”. A recrystallization-based vertical C-shaped-channel nanosheet field effect transistor (RC-VCNFET) was proposed, and related process modules were developed. The vertical nanosheet with an “exposed top” structure was successfully fabricated. Moreover, through physical characterization methods such as scanning electron microscopy (SEM), atomic force microscopy (AFM), conductive atomic force microscopy (C-AFM) and transmission electron microscopy (TEM), the influencing factors of the crystal structure of the vertical nanosheet were analyzed. This lays the foundation for fabricating high-performance and low-cost RC-VCNFETs devices in the future.

Tuning the giant magnetoimpedance response of a glass-coated microwire reinforced polymer by in-situ laser annealing

The ability to modify the giant magnetoimpedance (GMI) effect in amorphous glass-coated ferromagnetic Co-based microwire reinforced polymer via laser irradiation is presented. Through in-situ laser annealing of microwires embedded into a polymer matrix, a 25 % improvement in the GMI response is demonstrated after only 4.9 min of annealing. This improvement is compared to a conventional oven anneal technique, requiring an hour of oven annealing, subsequent sample cooling and polymer casting. This unique in-situ technique offers a novel and expedient path toward tailorable multi-functional composites in the areas of tunable electromagnetic shielding, structurally integrated antennas and magnetic sensors.

Excellent corrosion resistance of Al0.3CoCrFeNiCu high-entropy alloy fabricated by selective laser melting and annealing treatment

The compared microstructure and corrosion resistance of as-cast, as-SLMed (selective laser melting) and as-annealed Al0.3CoCrFeNiCu high-entropy alloy were investigated in this work. The results revealed that the SLM technique could effectively reduce the Cu segregation, and the beneficial nano-sized L12 ordered phase were precipitated in as-annealed samples (annealing treatment at 600 °C/10 h). Corrosion performance of three samples in 3.5% NaCl solution were improved with the order of as-cast < as-SLMed < as-annealed. As the elimination of Cu-rich phase and the fine microstructure occurring as-SLMed sample, resulting in the trivial micro-galvanic corrosion, and thus the corrosion performance of as-SLMed sample was enhanced. In addition, the precipitated L12 ordered phases in as-annealed sample further dramatically improved the corrosion resistance of as-SLMed sample.

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.

Ni-Silicide Ohmic Contacts on 4H-SiC Formed by Multi Pulse Excimer Laser Annealing

The formation of ohmic contacts by laser annealing approach is of great importance for SiC power devices, since it allows their fabrication on thin substrates, that is of crucial significance to reduce power dissipation. Ni silicide reaction under UV laser irradiation has been studied in detail with particular focus on single pulse approach, in order to describe the early stage of reaction process. The use of a multi pulse approach, for the formation of Ni silicide-based ohmic contacts by means of excimer laser annealing, has been investigated in this work. The reaction process has been characterized, as a function of number of pulses, by means of X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis. Laser process simulations, formulated in the framework of phase field theory, have been performed in order to predict the evolution of material during reaction under annealing. Simulations show that reaction moves to Si-reach phases with the increasing on pulses, with a co-existence of Ni2Si and Ni3Si2 phases for the three pulses process. Moreover, simulations show critical differences, in terms of the uniformity of the distribution of the silicide phases along the film, between the single pulse and the multi pulses cases and the increasing of thickness of silicide phases with the pulse sequence. These predictions are in good agreement with the findings of XRD and TEM analyses. The electrical properties of the reacted layer have been evaluated on Schottky Barrier Diodes (SBD) devices, confirming the ohmic behaviour of multi pulse annealed samples.

P‐41: Experimental Study of Intrinsic Melting Mechanism and Behavior During Laser Annealing of Si Films

To experimentally investigate the intrinsic nature of how melting initiates and propagates in laser annealing processes involving polycrystalline thin films, polycrystalline Si obtained by ELA was planarized and then single‐pulse irradiated at various energy densities. AFM analysis of the irradiated films reveals definitively that melting initiates predominantly at grain‐boundary vertices and junctions. Important implications for ELA and SBA (Spot‐Beam‐ Annealing) methods are discussed.

Investigation on Recrystallization Channel for Vertical C-Shaped-Channel Nanosheet FETs by Laser Annealing.

Transistor scaling has become increasingly difficult in the dynamic random access memory (DRAM). However, vertical devices will be good candidates for 4F2 DRAM cell transistors (F = pitch/2). Most vertical devices are facing some technical challenges. For example, the gate length cannot be precisely controlled, and the gate and the source/drain of the device cannot be aligned. Recrystallization-based vertical C-shaped-channel nanosheet field-effect transistors (RC-VCNFETs) were fabricated. The critical process modules of the RC-VCNFETs were developed as well. The RC-VCNFET with a self-aligned gate structure has excellent device performance, and its subthreshold swing (SS) is 62.91 mV/dec. Drain-induced barrier lowering (DIBL) is 6.16 mV/V.

47‐4: Highly Sensitive Lateral Poly‐Si PIN Photodiode by Blue Laser Annealing of 400 nm Amorphous Si for Near Infrared Light Sensing

We report a novel low‐temperature poly‐Si (LTPS) lateral PIN photodiode fabricated using blue laser annealing (BLA) of amorphous Si. The diode exhibits the low off current density of ~ 2.5×10 ‐5 A/cm 2 in dark and a diode factor of 1.47. Under near‐infrared (850 nm) illumination with a power density of 20 mW/cm 2, the photocurrent increases by 1.5×10 3 times at ‐1 V. In addition, we demonstrate that the generated photocurrent can be effectively amplified by a LTPS oxide (LTPO) operational amplifier, yielding the output signal of 17.60 V. Our results suggest that the proposed LTPS‐based photodiode has a great potential for applications in highly sensitive optoelectronic devices.

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.

Surface-Localized 15R Formation on 4H-SiC (0001) Si-Face by Laser Annealing for Power N-Type MOSFETs

A SiC MOSFET fabricated on a thin 15R-SiC layer on top of a 4H-SiC would benefit from both the higher inversion channel mobility of 15R-SiC and higher bulk mobility of 4H-SiC. In this work, a method based on Al implantation followed by UV laser annealing (UV-LA) to form 15R-SiC on 4H is shown. Evaluation of crystal quality and SiC polytype identification are performed by Raman spectroscopy. We show that UV-LA is able to grow 15R-SiC and cure the crystal damaged by ion implantation until a level close to the pristine substrate. This opens new perspectives for fabrication of SiC n-type MOSFETs.

Exploring UV-Laser Effects on Al-Implanted 4H-SiC

In this paper, we explore the effects of excimer laser irradiation on heavily Aluminum (Al)-implanted silicon carbide (4H-SiC) layer. 4H-SiC layers were exposed to UV-laser radiation (308 nm, 160 ns), at different laser fluences and the effects of the laser exposure surface were evaluated from morphological, micro-structural and nano-electrical standpoints. Depending on the irradiation condition, significant near-surface changes were observed. Moreover, the electrical characteristics of the implanted layer, evaluated by means of transmission line method, gave a sheet-resistance of 1.62×104 kW/sq for the irradiated layer, linked to a poor activation of the p-type dopant and/or a low mobility of the carriers in the laser-modified 4H-SiC layer. This study can be useful for a fundamental understanding of laser annealing treatments of 4H-SiC implanted layers.

Rapid laser-induced low temperature crystallization of thermochromic VO2 sol-gel thin films

The thermochromic properties of vanadium dioxide (VO2) offer great advantages for energy-saving smart windows, memory devices, and transistors. However, the crystallization of solution-based thin films at temperatures lower than 400°C remains a challenge. Photonic annealing has recently been exploited to crystallize metal oxides, with minimal thermal damage to the substrate and reduced manufacturing time. Here, VO2 thin films, obtained via a green sol–gel process, were crystallized by pulsed excimer laser annealing. The influence of increasing laser fluence and pulse number on the film properties was systematically studied through optical, structural, morphological, and chemical characterizations. From temperature profile simulations, the temperature rise was confirmed to be confined within the film during the laser pulses, with negligible substrate heating. Threshold laser parameters to induce VO2 crystallization without surface melting were found. With respect to furnace annealing, both the crystallization temperature and the annealing time were substantially reduced, with VO2 crystallization being achieved within only 60 s of laser exposure. The laser processing was performed at room temperature in air, without the need of a controlled atmosphere. The thermochromic properties of the lasered thin films were comparable with the reference furnace-treated samples.