Laser Annealing Research Articles

Crystallization of Hydrogenated Amorphous Silicon Thin Films Using Combined Continuous Wave Laser and Thermal Annealing

Crystallization of Hydrogenated Amorphous Silicon Thin Films Using Combined Continuous Wave Laser and Thermal Annealing

Nanosecond pulsed laser etching anti-reflective gratings and synchronous laser annealing for performance optimization of Ag/AZO thin films

Nanosecond pulsed laser etching for fabricating anti-reflective gratings and inducing synchronous laser annealing was performed on Ag/AZO films. The optimum grating pitch was determined by performance analyses of laser-etched unidirectional gratings, based on which laser-etched bidirectional gratings were fabricated to further determine the optimum grating tilt angle. The results revealed that with the increase of grating pitch, the grating ridge total-side-area was gradually decreased to cause a gradually weakened anti-reflective effect, but the superimposed heat-affected zones between adjacent grooves became smaller or even disappeared, which brought about different synchronous laser annealing effects. The unidirectional grating-textured film with a medium grating pitch of 200 μm showed the best overall performance under the combined influence from anti-reflective gratings and synchronous laser annealing. For the bidirectional gratings, although increasing the grating tilt angle did not change the grating ridge total-side-area, it would enable the laser energy to be more uniformly distributed on the whole film surface, producing a better synchronous laser annealing effect. The bidirectional grating-textured film with a grating tilt angle of 90° had the best overall performance with the highest FOM value of 2.18 × 10−2 Ω−1 that was ∼3.2 times that of the as-prepared film. The results are instructive for preparing high-performance TCO-based films.

Optimization of laser annealing parameters based on bayesian reinforcement learning

AbstractDeveloping new semiconductor processes consumes tremendous time and cost. Therefore, we applied Bayesian reinforcement learning (BRL) with the assistance of technology computer-aided design (TCAD). The fixed or variable prior BRL is tested where the TCAD prior is fixed or is changed by the experimental sampling and decays during the entire RL procedure. The sheet resistance (Rs) of the samples treated by laser annealing is the optimization target. In both cases, the experimentally sampled data points are added to the training dataset to enhance the RL agent. The model-based experimental agent and a model-free TCAD Q-Table are used in this study. The results of BRL proved that it can achieve lower Rs minimum values and variances at different hyperparameter settings. Besides, two action types, i.e., point to state and increment of levels, are proven to have similar results, which implies the method used in this study is insensitive to the different action types.

Activation of telecom emitters in silicon upon ion implantation and ns pulsed laser annealing

Recent demonstrations of optically active telecom emitters show that silicon is a compelling candidate for solid-state quantum photonic platforms. In particular, the fabrication of a defect known as the G center has been shown in carbon-rich silicon upon conventional thermal annealing. However, the high-yield controlled fabrication of these emitters at the wafer scale still requires the identification of a suitable thermodynamic pathway enabling its activation following ion implantation. Here we demonstrate the activation of G centers in high-purity silicon substrates upon nanosecond pulsed laser annealing. The proposed method enables non-invasive, localized activation of G centers by the supply of short non-stationary pulses, thus overcoming the limitations of conventional rapid thermal annealing related to the structural metastability of the emitters. A finite-element analysis highlights the strong non-stationarity of the technique, offering radically different defect-engineering capabilities with respect to conventional longer thermal treatments, paving the way to the direct and controlled fabrication of emitters embedded in integrated photonic circuits and waveguides.

Organic pollutants photodegradation increment with use of TiO2 nanotubes decorated with transition metals after pulsed laser treatment

Among various titanium(IV) oxide (TiO2, titania) structures, 1D nanotubes (TiO2 NTs) produced during the two-electrode anodization process, are extensively utilized in sensors or supercapacitors as well as in photo(electro)catalytic water splitting. However, due to wide bandgap and fast electron-hole recombination additional modifications, mostly concerned on materials surface, are required. According to the recent research, TiO2 NTs photo(electro)catalytic characteristic were markedly improved by the combination of surface decoration with transition metal nanoparticles further treated with the laser beam. Nevertheless, until recently, the photocatalytic ability of laser-treated TiO2 NTs for recalcitrant chemicals degradation were hardly described. In this regard, our work focuses on obtaining long, about 7.3 μm TiO2 NTs (L-TiO2 NTs), together with their photoactivity and physicochemical characteristics, as well as their alterations following surface modification utilizing transition metals (tungsten, chromium and nickel) together with laser treatment. Obtained L-TiO2 NTs are characterized by over 13.5 times larger BET surface area in comparison to reference spaced TiO2 NTs with approximately 2 μm length (0.61 m2 g−1 and 0.05 m2 g−1, respectively). This allowed for increasing of the materials photocatalytic activity in both UV–vis and vis light. Additionally, phenol photodegradation reached up to 34% (0.21·10−2 min−1) for tungsten-modified titania after laser annealing at 20 mJ cm2 fluence. The reaction mechanism research revealed that reduction of organic pollutants concentration was primarily caused by superoxide radical anions •O2−. Furthermore, obtained modified L-TiO2 NTs showed remarkable durability without losing their initial activity over ten photocatalytic cycles.

Solution-processed IGZO field-effect transistors with a three-step laser annealing process

Solution-processed IGZO field-effect transistors with a three-step laser annealing process

The influence of laser-annealing pulse width on optical transparency and carrier dynamics of ITO thin films

Indium tin oxide (ITO) has important application in photoelectronic and photonic devices, demanding effective approach and appropriate parameters to modulate the ITO properties. The effects of laser annealing at 1064 nm with different pulse width (875 ps, 10 ns, and 300 ns) on optical and nonlinear optical properties of ITO films were investigated. Compared with 875 ps and 10 ns, laser annealing at 300 ns significantly improved the near-infrared transmittance of ITO films. The change arises from the elimination of oxygen vacancies and reduction of tin oxides, resulting in the decrease of carrier concentration. Finite element simulations indicate that laser annealing with pulse width of 875 ps and 10 ns have high instantaneous peak temperatures of 1128.5 K and 783 K, respectively, while the temperature accumulation between pulses is negligible. On the contrary, the laser annealing with a pulse width of 300 nshas lower peak transient temperature of 343 K but high static residence temperature of 973 K. The results reveal that the modification of ITO films depends more on the static average temperature rather than the instantaneous peak temperature. The modulation of carrier dynamics in both amplitude and temporal domain was demonstrated after 300 ns laser annealing, achieving ultrafast transient response approximately 150 fs. This work provides theoretical and experimental basis for us to select suitable laser conditions for directional annealing of ITO film to make it suitable for the applications of broad optical spectrum photovoltaic devices or ultrafast optical exchange for high-speed data processing.

High-Performance Organic Field-Effect Transistors of Liquid Crystalline Organic Semiconductor by Laser Mapping Annealing.

Organic semiconductors (OSCs), especially small molecule semiconductors, have received increasing attention due to their good designability and variability. Phase transitions and interfacial properties have a decisive influence on device performance. Here, 2-Dodecyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-12) devices are treated with low-power laser annealing, which is able to avoid the influence of the dewetting effect on the hole mobility of organic semiconductor materials. Ultraviolet ozone treatment and self-assembled monolayer treatment can improve the performance and stability of the device. Moreover, after low-temperature thermal annealing, the hole mobility of the device can even reach as high as 4.80 cm2 V-1 s-1, and we tested the optical response of the device to the ultraviolet wavelength and found that its maximum optical responsivity was 8.2 AW-1.

Laser Technology for Perovskite: Fabrication and Applications

AbstractPerovskite has attracted considerable attention in the electronic and optical fields in recent years, fulfilling the requirements of the ever‐growing demand in energy, environment, security, and big data storage. Laser direct writing technology is a flexible and mask‐free approach for fabricating, structuring, modifying, and patterning perovskites. Laser irradiation can directly induce perovskites from precursors due to the photothermal and photochemical effects of laser. Therefore, various laser‐induced perovskites, such as perovskite quantum dots, nanowires, nanocrystals, and films, are summarized. In particular, the laser‐induced perovskites in glass are intensively investigated for their high stability and flexibility in 3D printing. The second part of this review examines various applications of perovskites based on laser technology, such as solar cells, flat lenses, microlasers, photoluminescence, lithography, sensors, optical encryption, and data storage. Diverse laser treatments employed for modulating and patterning perovskite devices, such as laser annealing, laser ablation, and laser‐induced defects, are discussed. Prospective challenges and future trends in this research field are also concluded.

Preparation of Large Grain Size Polysilicon Using Long-Pulse Green Laser Annealing for 3-D Integration Technology

Preparation of Large Grain Size Polysilicon Using Long-Pulse Green Laser Annealing for 3-D Integration Technology

Stress Analysis and Optimization on Saddle-shape Warpage by Direct Patterning of Stressed Film

As the stacks of the three-dimensional integrated circuits (3D-ICs) increases, the mechanical stress issues are challenging due to the increases in the asymmetry saddle-shape warpage. Various approaches to decrease asymmetric warpage were proposed by forming trenches of tens of micrometers or laser annealing treatment on the backside of wafer, but they had low throughput or lack of improved value. In this paper, we present a novel method to decrease the mechanical stress depending on the shape of the warpage by applying direct coating to the backside of wafer. The proposed method is to release the warpage by patterning a photo-sensitive polyimide (PSPI) with the inkjet-printing to adjust the surface characteristics and the steps, and then depositing tetraethylorthosilicate (TEOS) film with high compressive stress. We measured the changes in the asymmetric bow alongside the x-axis and y-axis before and after the process on the bare wafer by a finite element analysis using ABAQUS. Through the experiment and simulation, the x-y skew of about 230μm was obtained when 10μm-thick TEOS film was partially deposited on a 300mm wafer. In addition, by taking advantage of this process, the localized bow (warpage) can be released according to the changes in the thickness and area of the TEOS film. These results provide an effective guideline to solve unusual warpage caused by stacking process and can be applied to 3D integration in advanced packaging.

Patterning Magnonic Structures via Laser Induced Crystallization of Yittrium Iron Garnet

AbstractThe fabrication and integration of high‐quality structures of Yttrium Iron Garnet (YIG) is critical for magnonics. Films with excellent properties are obtained only on single crystal Gadolinium Gallium Garnet (GGG) substrates using high‐temperature processes. The subsequent realization of magnonic structures via lithography and etching is not straightforward as it requires a tight control of the edge roughness, to avoid magnon scattering, and planarization in case of multilayer devices. In this work a different approach is described based on local laser annealing of amorphous YIG films, avoiding the need for subjecting the entire sample to high thermal budgets and for physical etching. Starting from amorphous and paramagnetic YIG films grown by pulsed laser deposition at room temperature on GGG, a 405 nm laser is used for patterning arbitrary shaped ferrimagnetic structures by local crystallization. In thick films (160 nm) the laser induced surface corrugation prevents the propagation of spin‐wave modes in patterned conduits. For thinner films (80 nm) coherent propagation is observed in 1.2 µm wide conduits displaying an attenuation length of 5 µm that is compatible with a damping coefficient of ≈5 × 10−3. Possible routes to achieve damping coefficients compatible with state‐of‐the art epitaxial YIG films are discussed.

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.

Luminescence and temperature properties of Y2O3: Ho3+/Yb3+ millimeter crystals obtained by laser annealing

Luminescence and temperature properties of Y2O3: Ho3+/Yb3+ millimeter crystals obtained by laser annealing

Drastic enhancement of stable and fast domain wall motion in GdFe nanowires through laser-annealing treatment at wire edges

One of the key challenges in racetrack memory (RM) technology is achieving stable and high velocities for domain walls (DWs) while maintaining low power consumption. In our study, we propose a novel laser-annealing (LA) process to modify wire edges for a smoother DW movement along the nanowire. In this regard, a film stack of Pt (5 nm)/Gd26Fe74(20 nm)/SiN(10 nm) was deposited by magnetron sputtering. The DW velocity in the wire was measured by applying single voltage pulses and then observing the DW motion using a Kerr microscope. The current-induced domain walls motion measurements have shown that the LA process significantly enhances the velocity of DW motion. The LA of both edges of the nanowire results in a threefold increase in DW velocity compared to non-LA conditions. Further experiments illustrated that the DW velocity remains stable for the laser-annealed condition across a wide range of applied currents, spanning from 3 × 1011 to 7 × 1011 A/m2. Additionally, our investigation into the magnetic characteristics of laser-annealed nanowire regions exhibited a notable reduction of Hc at the laser-annealed edges. This decrease in Hc indicates greater ease in manipulating the material’s magnetization, which is essential for efficient DW motion. Furthermore, we explored the influence of LA on the Dzyaloshinskii–Moriya Interaction (DMI) field. The DMI finding underscores the strong correlation between DMI fields and DW speed. This achievement, i.e. the stability and consistency of the domain’s velocity (as the components of an RM) in a wide range of applied current, is significant progress in the field of operation and industrialization of RM.

Performance Improvement of In-Ga-Zn Oxide Thin-Film Transistors by Excimer Laser Annealing.

We applied excimer laser annealing (ELA) on indium-zinc oxide (IZO) and IZO/indium-gallium-zinc oxide (IGZO) heterojunction thin-film transistors (TFTs) to improve their electrical characteristics. The IZO and IZO/IGZO heterojunction thin films were prepared by the physical vapor deposition method without any other annealing process. The crystalline state and composition of the as-deposited film and the excimer-laser-annealed films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. In order to further enhance the electrical performance of TFT, we constructed a dual-heterojunction TFT structure. The results showed that the field-effect mobility could be improved to 9.8 cm2/V·s. Surprisingly, the device also possessed good optical stability. The electron accumulation at the a-IZO/HfO, HfO/a-IGZO, and a-IGZO/gate insulator (GI) interfaces confirmed the a-IGZO-channel conduction. The dual-heterojunction TFT with IZO/HfO/a-IGZO-assisted ELA provides a guideline for overcoming the trade-off between high mobility (μ) and positive VTh control for stable enhancement mode operation with increased ID.

Progress and Outlook of 10% Efficient AlGaN‐Based (290–310 nm) Band UVB LEDs

Eco‐friendly and low‐cost aluminum gallium nitride (AlGaN) for the epitaxial growth of ultraviolet‐B (UVB) light‐emitting diodes (LEDs) on c‐Sapphire has the possibility of high external‐quantum efficiency (EQE). In this review paper a special growth techniques for 50% relaxed and 4 μm thick AlGaN buffer layer underneath the multi‐quantum wells (MQWs) are challenged to achieve a maximum internal‐quantum efficiency of 50–57% in 310–290 nm band UVB LEDs. The influence of a thin “Valley” layer in p‐type multi‐quantum barrier electron‐blocking layer on 2D hole generation and injection via intraband tunneling was attempted. Finally, the influence of soft polarized Mg‐doped p‐type Al‐graded AlGaN hole injection layer assisted by excimer laser annealing for better hole injection toward the MQWs was investigated and quite high hole concentration of 2 × 1016 cm−3 and resistivity of 24 Ω‐cm at room temperature was achieved. Consequently, the EQE of transparent 310 and 304 nm UVB LEDs, respectively, reached to a confirmed world record values of ≈5% and ≈10% with light powers of 29 and 40 mW on wafer. This EQE value can surpass 21% if flip‐chip, nanoPSS, photonic crystal, and lens with highly reflective p‐electrodes are incorporated in LED.

One-step additive LIFT printing of conductive elements

The feasibility of printing silver and copper conductive elements on a glass substrate in a one- step through the laser-induced forward transfer method has been successfully demonstrated. The topography of the resulting elements was analyzed, using scanning electron microscopy. Investigation of their chemical composition was conducted by means of energy-dispersive x-ray spectroscopy and x-ray diffraction, revealing that both silver and copper in their metallic nanocrystalline state. The maximum specific conductivity of ≈6 kS cm−1 was achieved for both silver and copper at the optimal scanning speed of 3800 mm s−1, providing two-pulse printing with the laser transfer by the first pulse and laser annealing by the second one. The proposed method facilitates the technological additive printing process of conductive elements and rises its throughput.

Plasmonic Nanocomposites of ZnO-Ag Produced by Laser Ablation and Their Photocatalytic Destruction of Rhodamine, Tetracycline and Phenol.

Hydrosphere pollution by organic pollutants of different nature (persistent dyes, phenols, herbicides, antibiotics, etc.) is one of the urgent ecological problems facing humankind these days. The task of water purification from such pollutants can be effectively solved with the help of modern photocatalytic technologies. This article is devoted to the study of photocatalytic properties of composite catalysts based on ZnO modified with plasmonic Ag nanoparticles. All materials were obtained by laser synthesis in liquid and differed by their silver content and preparation conditions, such as additional laser irradiation and/or annealing of produced powders. The prepared ZnO-Ag powders were investigated by electron microscopy, X-ray diffraction and UV-Vis spectroscopy. Photocatalytic tests were carried out with well- known test molecules in water (persistent dye rhodamine B, phenol and common antibiotic tetracycline) using LED light sources with wavelengths of 375 and 410 nm. The introduction of small concentrations (up to 1%) of plasmonic Ag nanoparticles is shown to increase the efficiency of the ZnO photocatalyst by expanding its spectral range. Both the preparation conditions and material composition were optimized to obtain composite photocatalysts with the highest efficiency. Finally, the operation mechanisms of the material with different distribution of silver are discussed.

Diamond deposition on AlN using Q-carbon interlayer through overcoming the substrate limitations

Q-carbon, a quenched form of carbon, is a recently discovered carbon structure that has tremendous properties, compatibility, and potential for use in device fabrication and other electronic and mechanical applications. However, the non-equilibrium nature of the synthesis process and a very small window of growth parameters have limited the formation of Q-carbon to only low thermal conductive substrates. This study aims to overcome these limitations through extensive tuning of the parameters of diamond-like-carbon (DLC), the base structure required for the formation of Q-carbon. The as-deposited DLC films demonstrate ID/IG ratios ranging from 0.12 to 1.67, which are obtained through the optimization of laser energy density, rep rate, and deposition temperature during pulsed laser deposition. Utilizing Simulation of Laser Interaction with Materials, pulsed laser annealing (PLA) was used to directly transform the DLC films into Q-carbon while varying the PLA energy density from 0.3 J/cm2 to 1.2 J/cm2. Findings of Q-carbon formation on sapphire using different DLC films assisted in the preparation of a roadmap for overcoming the substrate limitations for Q-carbon formation. Further, Q-carbon is formed on AlN substrates for the direct deposition of diamond films without the requirement of a non-carbon interfacial layer or nanodiamond seeding layer. The large-area and uniform diamond growth on Q-carbon shows well-faceted and five-fold twinned growth with a 70 % improvement in the residual compressive stress of diamond on AlN. Such a method of diamond deposition on AlN provides the opportunity to address the thermal management issues in wide- and ultra-wide bandgap high-power electronic devices.