Nanosecond Laser Ablation Of Silicon Research Articles

Deposition of oxide nanostructures by nanosecond laser ablation of silicon in an oxygen-containing background gas

Deposition of oxide nanostructures by nanosecond laser ablation of silicon in an oxygen-containing background gas

Laser Formation of Colloidal Sulfur- and Carbon-Doped Silicon Nanoparticles

Unique sulfur- and carbon- doped silicon nanoparticles, as well as partially oxidized, are obtained by nanosecond laser ablation of silicon in liquid carbon disulfide. Detailed structural, chemical, and optical characterization of these particles was performed by scanning and transmission electron microscopy, IR spectroscopy, energy dispersive X-ray spectroscopy, and Raman scattering spectroscopy. It is shown that the sulfur concentration in particles is on the order of 1 at %, owing to which they demonstrate a considerable absorption in the mid-IR region.

Лазерная генерация коллоидных кремниевых наночастиц, легированных серой и углеродом

Unique silicon nanoparticles doped with sulfur and carbon, as well as partially oxidized, were obtained by nanosecond laser ablation of silicon in liquid carbon disulfide. Their detailed structural, chemical and optical characterization was carried out by scanning and transmission electron microscopy, IR spectroscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. Studies have shown that the sulfur content in the particles is about 1 at. %, due to which they show significant absorption in the mid-IR range.

Photoluminescence analysis of colloidal silicon nanoparticles in ethanol produced by double-pulse ns laser ablation

Silicon nanoparticles (SiNPs) have attracted much attention for optoelectronic devices as well as biomedical applications due to their wide range of visible emissions, which are greatly influenced by their surface characteristics. This paper presents photoluminescence properties of colloidal SiNPs produced by using single-pulse and double-pulse nanosecond laser ablation of silicon in ethanol. The laser ablation processes were performed under the same experimental conditions, but the experiments result in production of the colloidal SiNPs with different size and surface characteristics. The structural and optical properties of colloidal SiNPs were investigated, with the aim of clarifying the role of surface characteristics on the photoluminescence emissions. The SiNP colloids exhibit similar luminescence behavior to the pure ethanol at the spectral range of 300–600nm, with a slight enhancement of intensity. The results indicate that the excitation-dependent photoluminescence spectra of the colloids are associated with the Raman scattering of pure ethanol which are enhanced due to the presence of SiNPs with different OH related surface characteristics.

Double-pulse nanosecond laser ablation of silicon in water

This work was conducted experimentally to investigate the material removal rate and its mechanisms during the single-pulse and double-pulse nanosecond laser ablation of a silicon wafer in distilled water. The laser ablation processes were performed under the same experimental conditions with the same total pulse energy (Esingle pulse = Edouble pulse). The amount of ablated material was estimated for all of the processes based on measuring the dimensions (depths and widths) and volumes of the laser-induced craters on the silicon wafer. The results indicate that double-pulsed laser processing can result in a higher material removal rate compared to the more common single-pulse process, when the inter-pulse delay time is less than the pulse duration. The higher ablation yield in the double-pulse process can be due to the higher coupling efficiency of the second laser pulse with the melted target induced by the laser pre-pulse, leading to the more efficient laser energy absorption and deposition within the irradiated region. The double-pulse nanosecond laser processing with delay time of ~5 ns not only results in a higher material removal rate, but also leads to preparation of silicon nanoparticles with a greater mean particle size compared to that of the more common single-pulse laser ablation process.

A unified model to determine the energy partitioning between target and plasma in nanosecond laser ablation of silicon

In semiconductor industry, pulsed nanosecond lasers are widely applied for the separation of silicon wafers. Here, the high intensities employed activate a cascade of complex multi-physical and multi-phase mechanisms, which finally result in the formation of a laser induced plasma, shielding the target from the incoming laser beam. Such induced plasma plume, by preventing the laser to effectively reach the target, reduces the overall efficiency and controllability of the ablation process. Modelling can be a useful tool in the optimization of industrial laser applications, allowing a deeper understanding of the way the laser energy distributes between target and induced plasma. Nevertheless, the highly multi-physical character of laser ablation poses serious challenges on the implementation of the various mechanisms underlying the process within a common modelling framework. A novel strategy is here proposed in order to simulate in a simplified, yet physically consistent way, a typical industrial application as laser ablation of silicon wafers. Reasonable agreement with experimental findings is obtained. Three fundamental mechanisms have been identified as the main factors influencing the accuracy of the numerical predictions: the transition from evaporative to volumetric mass removal occurring at critical temperature, the collisional and radiative processes underlying the initial plasma formation stage and the increased impact of the liquid ejection mechanism when a sub-millimeter laser footprint is used.

Laser-Induced Liquefaction of Tetrafluoroethane and Sulfur Hexafluoride Gases

Laser ablation is a significant industrial tool for material structuring; however, the quality of such physical processes is often hindered by the redeposition of ablated matter in the laser interaction zone. Laser-induced liquefaction (LIL) offers a novel approach to minimizing material redeposition by irradiating the target in a dry ambient and transporting the material away in a liquid medium. SEM, EDX, and real-time imaging provided evidence of the decomposition of the assist gases, tetrafluoroethane (C2H2F4) and sulfur hexafluoride (SF6), during nanosecond laser ablation of silicon and confirmed the presence of a transient liquid phase in the vicinity of the trench during laser ablation. The elemental composition and spatial characteristics of the redeposited ablated matter indicate that the liquefied species and chemistry of the ablated matter are important in the enhancement of the material removal processes. As a result, high aspect ratio trenches with low redeposition of material in the ablated f...

Thermal modeling and experimental study of infrared nanosecond laser ablation of silicon

Nanosecond (ns) laser ablation of silicon has important applications in electronics, photovoltaics, and many other areas. However, most of the previous work is mainly focused on ultraviolet (UV) or visible ns lasers, and the investigation is very limited for infrared lasers (e.g., at 1064 nm), which have the advantage of much lower cost and external energy consumption. In this paper, a thermal model has been developed and experimentally verified for ablation of silicon by 200 ns and 1064 nm laser pulses. This kind of work has been rarely reported in literature. The model predictions agree reasonably well with experimental measurements. The investigation indicates that surface evaporation should be the dominant physical mechanism of material removal for laser silicon ablation under the studied conditions. It has also been found that the physical processes of multipulse laser-silicon interaction at 1064 nm may strongly depend on laser pulse number and repetition rate (the pulse-to-pulse temporal distance).

Experimental study of infrared nanosecond laser ablation of silicon: The multi-pulse enhancement effect

Experimental study has been performed on nanosecond (ns) laser ablation of silicon at 1064 nm, through which a so-called “multi-pulse enhancement effect” has been revealed, which has been rarely reported in literature. The major features of this effect are: (1) for multi-pulse laser ablation at the same spatial location, the ablation efficiency increases as the pulse number increases and the pulse-to-pulse temporal distance decreases; (2) for multi-pulse ablation performed sequentially at a group of locations, the ablation quality and efficiency starting from the second location can be significantly enhanced if the distance between adjacent locations is sufficiently small. Further study is needed to confirm and understand the underlying physical mechanism for the multi-pulse enhancement effect, which can be utilized to significantly improve the quality and efficiency of laser silicon micromachining using the low-cost and low-energy-consumption infrared ns lasers. This may decrease the cost and energy consumption of many relevant areas, such as the solar cell industry.

Absence of amorphous phase in high power femtosecond laser-ablated silicon

As femtosecond lasers emerge as viable tools for advanced microscale materials processing, it becomes increasingly important to understand the characteristics of materials resulting from femtosecond laser microablation or micromachining. We conducted transmission electron microscopy experiments to investigate crater structures in silicon produced by repetitive high power femtosecond laser ablation. Comparable experiments of nanosecond laser ablation of silicon were also performed. We found that an amorphous silicon layer that is typically produced in nanosecond laser ablation is absent when the material is irradiated by high power femtosecond laser pulses. Instead, only a defective single crystalline layer was observed in the high power femtosecond laser-ablated silicon crater. Possible mechanisms underlying the formation of the defective single crystalline phase are discussed.

Vaporization and Plasma Shielding during High Power Nanosecond Laser Ablation of Silicon and Nickel

A thermal model to describe the high-power nanosecond pulsed laser ablation is presented. It involves the vaporization and the following plasma shielding effect on the whole ablation process. As an example of Si target, we obtain the time evolution of the calculated surface temperature, ablation rate and ablation depth. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the ablation depth with laser fluence based on different models is shown. Moreover, we simulate the pulsed laser irradiation Ni target. The evolution of the transmitted intensity and the variation of ablation depth per pulse with laser fluence are performed. Under the same experimental conditions, the numerical results calculated with our thermal model are more in agreement with the experimental data.

Realtime study of plume ejection dynamics in silicon laser ablation under 5ns pulses

We present results of nanosecond laser ablation of silicon over a broad range of laser intensities, investigated by studying the time evolution of the ablation plume ejection, which, as measured by transmission of a probe beam, consists of a fast ejection phase followed by a delayed slow ejection phase. Experimental results indicate that different physical processes dominate at different ablation stages. The laser intensity threshold for the appearance of the slow ejection is ∼30GW∕cm2. The plume kinetics parameters extracted from our experiments agree well with estimations based on blast wave and homogeneous nucleation theories, providing a physical explanation for the observed ablation rate dependence on the laser light intensity.

Experimental investigation of ablation efficiency and plasma expansion during femtosecond and nanosecond laser ablation of silicon

Femtosecond laser (Ti:sapphire, 100 fs pulse duration) ablation of silicon in air was compared with nanosecond laser (Nd:YAG, 3 ns pulse duration) ablation at ultraviolet wavelength (266 nm). Laser ablation efficiency was studied by measuring crater depth as a function of pulse number. For the same number of laser pulses, the fs-ablated crater was about two times deeper than the ns-crater. The temperature and electron number density of the laser-induced plasma were determined from spectroscopic measurements. The electron number density and temperature of fs-induced plasmas decreased faster than ns-induced plasmas due to different energy deposition mechanisms. Images of the laser-induced plasma were obtained with femtosecond time-resolved laser shadowgraph imaging. Plasma expansion in both the perpendicular and the lateral directions were compared.

Analysis of recoil force during Nd:YAG laser ablation of silicon

Recoil force exerted on the substrate during a nanosecond laser ablation of silicon is measured. The ablation sample is placed at the end of a 400-μm-thick and 13-mm-long silicon cantilever. The vibration amplitude of the cantilever induced by the recoil force is measured in real time with a probe beam. By comparing the deflection amplitude of the cantilever with a theoretical model, the recoil momentum is estimated. For laser irradiance in the order of 1011 W/cm2, the recoil pressure reached a value of over 40×109 Pa.

Delayed phase explosion during high-power nanosecond laser ablation of silicon

An important parameter for high-irradiance laser ablation is the ablation crater depth, resulting from the interaction of individual laser pulses on a targeted surface. The crater depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 2×1010 W/cm2, above which, large (micron-sized) particulates were observed to eject from the target. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of the laser pulse is a possible mechanism for the observed dramatic increase of the ablation depth. Calculations based on this delayed phase explosion model provide a satisfactory estimate of the measurements. In addition, we find that the shielding of an expanding mass plasma during laser irradiation has a profound effect on this threshold phenomenon.

Laser-induced explosive boiling during nanosecond laser ablation of silicon

The surface morphology of single crystal (1 0 0) Si wafers irradiated by 266 and 1064 nm laser pulses emitted by a Nd:YAG laser has been investigated. The morphology of the bottom of craters formed as a result of single or multipulse laser irradiation by the 266 nm wavelength, which is well absorbed by Si (optical absorption coefficient, α ∼10 6 cm −1), remained flat and almost featureless up to the maximum fluence of 18 J/cm 2 used in this study. The rims of the craters showed signs of radial liquid flow but it is apparent that the vaporization process was confined to the surface region. A different morphology was observed at the bottom of the craters formed by the 1064 nm wavelength laser pulses. Because this wavelength is absorbed in volume, α<10 4 cm −1 , a rather thick liquid Si pool formed at the surface. For laser fluences higher than 3 J/cm 2 evidence of boiling sites were observed at the bottom of the crater. By analyzing their formation mechanisms, density and shape, we suggest that they were induced by heterogeneous boiling and not homogeneous boiling, also known as phase explosion.

Comment on “Evidence for phase-explosion and generation of large particles during high power nanosecond laser ablation of silicon” [Appl. Phys. Lett. 76, 783 (2000)

Comment on “Evidence for phase-explosion and generation of large particles during high power nanosecond laser ablation of silicon” [Appl. Phys. Lett. <b>76</b>, 783 (2000)

Response to “Comment on ‘Evidence for phase explosion and generation of large particles during high power nanosecond laser ablation of silicon’ ” [Appl. Phys. Lett. 79, 442 (2001)

Abstract

Explosive change in crater properties during high power nanosecond laser ablation of silicon

Mass removed from single crystal silicon samples by high irradiance (1×109 to 1×1011 W/cm2) single pulse laser ablation was studied by measuring the resulting crater morphology with a white light interferometric microscope. The craters show a strong nonlinear change in both the volume and depth when the laser irradiance is less than or greater than ≈2.2×1010 W/cm2. Time-resolved shadowgraph images of the ablated silicon plume were obtained over this irradiance range. The images show that the increase in crater volume and depth at the threshold of 2.2×1010 W/cm2 is accompanied by large size droplets leaving the silicon surface, with a time delay ∼300 ns. A numerical model was used to estimate the thickness of the layer heated to approximately the critical temperature. The model includes transformation of liquid metal into liquid dielectric near the critical state (i.e., induced transparency). In this case, the estimated thickness of the superheated layer at a delay time of 200–300 ns shows a close agreement with measured crater depths. Induced transparency is demonstrated to play an important role in the formation of a deep superheated liquid layer, with subsequent explosive boiling responsible for large-particulate ejection.

Evidence for phase-explosion and generation of large particles during high power nanosecond laser ablation of silicon

The craters resulting from high-irradiance (1×109–1×1011 W/cm2) single-pulse laser ablation of single-crystal silicon show a dramatic increase in volume at a threshold irradiance of 2.2×1010 W/CM2. Time-resolved shadowgraph images show ejection of large particulates from the sample above this threshold irradiance, with a time delay ∼300 ns. A numerical model was used to estimate the thickness of a superheated layer near the critical state. Considering the transformation of liquid metal into liquid dielectric near the critical state (i.e., induced transparency), the calculated thickness of the superheated layer at a delay time of 200–300 ns agreed with the measured crater depths. This agreement suggests that induced transparency promotes the formation of a deep superheated layer, and explosive boiling within this layer leads to particulate ejection from the sample.