Laser Processing Of Thin Films Research Articles

Analysis of the Polarization Distribution and Spin Angular Momentum of the Interference Field Obtained by Co-Planar Beams with Linear and Circular Polarization

Interference of two and four light beams with linear or circular polarization is studied analytically and numerically based on the Richards–Wolf formalism. We consider such characteristics of the interference fields as the distribution of intensity, polarization, and spin angular momentum density. The generation of light fields with 1D and 2D periodic structure of both intensity and polarization is demonstrated. We can control the periodic structure both by changing the polarization state of the interfering beams and by changing the numerical aperture of focusing. We consider examples with a basic configuration, as well as those with a certain symmetry in the polarization state of the interfering beams. In some cases, increasing the numerical aperture of the focusing system significantly affects the generated distributions of both intensity and polarization. Experimental results, obtained using a polarization video camera, are in good agreement with the simulation results. The considered light fields can be used in laser processing of thin films of photosensitive (as well as polarization-sensitive) materials in order to create arrays of various ordered nano- and microstructures.

Laser fabrication of lead selenide infrared focal plane array devices

The motivation of this work is to demonstrate the versatility and potential of laser processing in the fabrication of PbSe thin films and focal plane array devices. This work fabricates an FPA device with any need for the suite of equipment and chemicals necessary for photolithography and etching. Advances in laser technologies and the vast number of laser parameters available are enabling the huge potential for laser processing of thin films and device fabrication. This can be accomplished faster using lasers with fewer steps than using conventional thin film deposition and photolithography methods. This work presents the fabrication and simple operation of a proof-of-concept PbSe-based, 120-pixel PFA (10 × 12 pixel) focal plane array using only laser processing for film deposition and device patterning. Lasers were used to both deposition and pattern a PbSe film with 60 × 70 µm pixels with 100 µm pitch with a unit cell photoresponse of 17% DelR. Additional results, challenges, limitations, and suggested future improvements are presented.

Laser machined ultrathin microscale platinum thermometers on transparent oxide substrates

Ultrathin microscale platinum resistive thermometers are of key value to transient temperature measurements. Neither transparent oxide substrates nor femtosecond laser patterning have been investigated for the fabrication of Pt thin film thermometers. Here, we have fabricated a laser machined, 50 μm wide and 50 nm thick, serpentine, Pt thin film sensor capable of sensing temperatures up to 650 °C over multiple heating and cooling cycles. Various materials and associated processing conditions were studied, including both sapphire and silica as transparent substrates, alumina and titanium dioxide as adhesion layers, and lastly alumina and silicon dioxide as capping layer. In-situ resistance monitoring helps verify the multi-cycle stability of the sensor and guide the optimization. 10 μm sized sensors could be laser-machined, but did not survive multiple heating and cooling cycles. We demonstrate that sensors with amorphous Ge thin layers can also repeatably measure temperatures up to 650 °C. It is anticipated that this sensor can be used for fast, high spatial resolution temperature probing for laser processing of thin films.

Sintering of thin titanium dioxide nanoparticle films via photothermal processing with ultraviolet continuous-wave lasers

Photothermal laser processing of thin films of anatase titania nanoparticles (TiO2 NPs, diameter: 8–10nm) with a thickness of about 500nm is addressed. Laser processing in ambient air is carried out using a microfocused continuous-wave laser setup operating at a wavelength of 355nm and a 1/e laser spot size of 1.6μm. In conjunction with scanning electron microscopy, this approach provides a highly reproducible and convenient means in order to modify the local film structure and study the dependence of the resulting film morphology on the laser parameters. Generally, sintering of the nanoparticles is observed. At high laser power densities and/or long irradiation times the average particle/grain size increases reaching values of 200nm and more. This opens up an opportunity to introduce scattering centers and optimize light trapping within the film, e.g., targeting photovoltaic or photocatalytic applications.

Photothermal laser processing of thin silicon nanoparticle films: on the impact of oxide formation on film morphology

Photothermal laser processing of thin films of H-terminated silicon nanoparticles (Si NPs) is investigated. Ethanolic dispersions of Si NPs with an average diameter of 45 nm are spin-coated on silicon substrates yielding films with thicknesses ≤500 nm. Small-area laser processing is carried out using a microfocused scanning cw-laser setup operating at a wavelength of 532 nm and a 1/e laser spot size of 1.4 μm. In conjunction with microscopic techniques, this provides a highly reproducible and convenient approach in order to study the dependence of the resulting film morphology and composition on the experimental parameters. Processing in air results in strongly oxidized granular structures with sizes between 100 and 200 nm. The formation of these structures is dominated by surface oxidation. In particular, changing the processing parameters (i.e., laser power, writing speed, and/or the background air pressure) has little effect on the morphology. Only in vacuum at pressures <1 mbar, oxygen adsorption, and hence oxide formation, is largely suppressed. Under these conditions, irradiation at low laser powers results in mesoporous surface layers, whereas compact silicon films are formed at high laser powers. In agreement with these results, comparative experiments with films of H-terminated and surface-oxidized Si NPs reveal a strong impact of the surface oxide layer on the film morphology. Mechanistic aspects and implications for photothermal processing techniques, e.g., targeting photovoltaic and thermoelectric applications, are discussed.

Laser Processing of Thin Films for Photovoltaic Applications

This paper discusses the structuring of several thin film materials used for solar cells, e.g. SiNx, SiO2 and Transparent Conductive Oxides (TCOs). The focus of the experiments is to obtain an optimal edge quality without damaging the substrate below the structured region. Two important laser parameters are wavelength and pulse duration which determine the absorption of the laser radiation in the processed material and the extent of heat influence on the surrounding material. Processing with several wavelengths (e.g. 532 nm and 1064 nm) and pulse durations especially in the picoand nanosecond range is studied. The results obtained with the different laser parameters are compared by considering ablation threshold, debris, and damage due to heat conduction. The quality of laser processing is determined by optical and scanning electron microscopy. Results from the structuring of TCOs and organic layers are acquired with different laser types. Additionally, comparisons are made regarding the achievable structuring quality for mass production, relevant speeds around 1 m/s for thin films and 1-2 seconds processing time for wafer based cells.

Excimer laser processing of inkjet-printed and sputter-deposited transparent conducting SnO 2:Sb for flexible electronics

The feasibility of low-temperature fabrication of transparent electrode elements from thin films of antimony-doped tin oxide (SnO 2:Sb, ATO) has been investigated via inkjet printing, rf magnetron sputtering and post-deposition excimer laser processing. Laser processing of thin films on both glass and plastic substrates was performed using a Lambda Physik 305i excimer laser, with fluences in the range 20–100 mJ cm − 2 reducing sheet resistance from as-deposited values by up to 3 orders of magnitude. This is consistent with TEM analysis of the films that shows a densification of the upper 200 nm of laser-processed regions.

Numerical simulation of thermal wave propagation during laser processing of thin films

A numerical model is developed to represent the thermal wave propagation during ultrashort pulsed laser processing of thin films. The model developed is based on the solution of non-Fourier heat conduction problem with temperature and thermal flux delays using discontinuous finite-element method. The mathematical formulation is described and computational procedures are given. The computer model is validated using the analytical solution for one-dimensional (1-D) thermal wave equations. Numerical simulations are performed to study the thermal wave propagation in a GaAs thin film exposed to ultrashort laser pulses. A wavelike behavior of the thermal signal propagation is observed, and the diffusive effect of the time relaxation in the temperature gradient is calculated and discussed. The thermal behavior of thin films under laser radiation is also studied as a function of various process parameters including pulse duration, laser pulse shapes and characteristic times of heat fluxes.

HEAT TRANSFER IN LASER PROCESSING OF THIN FILMS

HEAT TRANSFER IN LASER PROCESSING OF THIN FILMS

Laser Processing of Thin Films and Microstructures: Oxidation, Deposition and Etching of Insulators

Laser Processing of Thin Films and Microstructures: Oxidation, Deposition and Etching of Insulators

Book Reviews

The High-Tech Industry Manual: Conversion of U.S. Industry to High Technology Through Technology Transfer-Reviewed by Raymond J. Mataloni; Laser Processing of Thin Films and Microstructures-Reviewed by Richard Lee

Thermally Induced Stresses and Strains in Laser Processing of Thin Films

AbstractThe stresses and strains induced in thermal laser processing of substrates and thin films on substrates, are obtained in terms of single integrals by solving the thermoelastic equations using a Gaussian profile laser as the heating source. This analysis is applied to silicon thin films on fused silica and sapphire substrates. In part, this study shows that defects can form in the films because the stresses induced during high temperature laser processing of silicon and similar materials can exceed the yield stress under certain experimental conditions.

Laser processing of thin films (review)

A review is given of technological developments and physical investigations relating to laser processing of thin films. It is pointed out that this application is one of the most promising in modern laser technology. Special attention is paid to special features of the action of laser radiation on thin-film objects and to general relationships governing the destructive effects. This is used as a basis for the formulation of the criteria which should govern the choice of the laser, optical system, and optimal characteristics of the laser beam.