Laser Patterning Of Thin Films Research Articles

Polarization-sensitive direct laser patterning of azopolymer thin films with vortex beams.

Laser patterning of thin films of materials is widely used for the fabrication of one-, two- and three-dimensional functional nanomaterials. Using structured laser beams with a complex structure of amplitude, phase, and polarization distributions allows one to significantly simplify and speed up the procedure of manufacturing nano- and microstructures with a complex shape, such as a spiral structure. Here, we demonstrate the use of vortex laser beams with a helical wavefront for the realization of spiral mass transfer in azopolymer films. The polarization sensitivity of this material allows us to demonstrate the formation of different three-dimensional structures in the case of linearly or circularly polarized vortex beams of different orders. The presented theoretical analysis shows that the profile of the fabricated structures is defined by the structure of the longitudinal component of the incident radiation, and thus can be easily controlled with the polarization state of the radiation without the need to change the amplitude-phase structure of the beam.

Ultraviolet Laser Patterning of Fluorine-Doped Tin Oxide with Different Radiation Directions

Selective laser patterning of thin films in a multilayered structure is an emerging technology for fabricating optoelectronics and microelectronics devices. As the application of ultraviolet (UV) lasers is more and more popular in electronics manufacturing, in this study, we compare UV laser patterning of fluorine-doped tin oxide (FTO) films from the front and back sides. We summarize a formula for calculating the focus offset in back-side ablation (BSA) and analyze systematically the relationships between the laser ablation crater size, the damage on glass substrate, and the laser ablation parameters. In addition, the laser ablation process and mechanisms of the BSA and the front-side ablation (FSA) are also elaborated in this paper.

Grey-scale silicon diffractive optics for selective laser ablation of thin conductive films.

Laser beam shaping can play a crucial role in improving many laser processes, especially in selective laser patterning of thin films for display devices and solar cells. Typical Gaussian spatial energy distributions can increase damage to the substrate and lead to large crater edge ridges, which are sub-optimal for typical industrial thin film processes. We report on the design, fabrication, and testing of reflective silicon diffractive optics developed for spatial beam shaping at a wavelength of 355nm. The application of the elements for laser-selective removal of 20nm indium tin oxide thin films on glass substrates is demonstrated. The design of the phase profile is first generated using the numerical method of computer-generated holography. The phase profiles are realized on a silicon substrate using a novel two-step fabrication technique consisting of a calibrated focused ion beam and an inductively coupled plasma etch. This results in truly grey-scale, blazed diffractive optics, which were analyzed using white light interferometry and atomic force microscopy. Using the diffractive elements with 355nm nanosecond pulses shows excellent focused spot profiles with a good reproduction of the intended design with a first-order off-axis diffractive efficiency of approximately 80% at a 45deg angle of incidence.

Patterning of CIGS thin films induced by rear-side laser ablation of polyimide carrier foil

Laser patterning of thin films is essential for the future development of flexible electronic devices. The damage-free scribing of thermally sensitive thin films such as copper–indium–gallium diselenide (CIGS) that is required for solar module fabrication by integrated interconnections is still challenging. In this study a new approach for non-thermal, damage-free scribing of CIGS films on polyimide foil is proposed and demonstrated. In contrast to the usually used direct laser ablation of the thin-film stack, laser ablation of the polyimide carrier foil at laser fluences higher than 3 J/cm2 is utilized to achieve CIGS film delamination and thus the patterning of the thin film. The edges of the patterned CIGS films do not show typical laser-ablation-induced modifications like melting, debris contamination, or crack formation. The mechanism of the thin-film removal is of non-thermal origin and is probably due to stress formation at the CIGS/Mo interface resulting from secondary processes of polyimide laser ablation like shock-wave formation or local sample deformation.

Ultrafast Laser Patterning of Thin Films on 3-D Shaped Surfaces for Strain Sensor Applications

A femtosecond laser patterning process of thin film sensors on component surfaces is reported. This method is particularly useful for patterning of strain sensors which are sputter deposited directly on curved surfaces. The ablation behavior of NiCr film irradiated by femtosecond laser pulses at non-normal angles of incidence is modeled and experimentally verified with linear and circular beam polarization for incidence angles up to 80°. It is shown that the ablation threshold behavior can be described when including polarization and angle dependent Fresnel reflection into the laser ablation model. The laser process is finally demonstrated by patterning NiCr thin film sensors on a non-planar surface of a mechanical component for a machine tool.

A study of stitch line formation during high speed laser patterning of thin film indium tin oxide transparent electrodes

High speed laser patterning of indium tin oxide thin films on glass is part of the production method used to produce transparent conductive electrodes for plasma display panels. Such a design consists of rows of repeating electrode structures which cover the active area of the display. Whilst the patterning process for such electrode structures exceeds the industrial acceptance criteria there are certain features that are yet to be fully understood. The visible line that occurs in-between two adjacent laser processed areas, commonly known as a stitch line, is one such feature. Previously published research claimed that the stitch line was caused by incomplete removal of the thin film however experimental results presented within this paper demonstrate that this cannot be the case and show that the stitch line is formed by redeposition of the plume of ablated material within the area of overlap with the previous pulse, and that heating of the sample by the second pulse plays a key role in stitch line formation.

Femtosecond laser micromachining of an Au/Cr film nanostack

Selective laser patterning of thin films in a multilayer structure is an emerging technology for the fabrication of MEMS devices. A 775-nm Ti:sapphire laser (130 fs, 1 kHz) was used to irradiate thin-film stacks with variations in the process parameters, such as the pulse energy, feed rate, and numerical aperture of the objective lens. The two layers of the Au/Cr film have the same thickness, which is about 1000 nm. They were coated on a glass substrate. By SEM, an AFM and an optical surface profiler, we investigate the morphology of a pattern including the line width, groove depth, and laser-induced periodic surface structures (LIPSSs). The ablation depth was observed to depend on the pulse energy. In addition, from the energy spectrum, we find which layer was removed completely. The experimental results show that precise micromachining with a desired stability and reproducibility can be achieved by controlling the ablation energy and the feed rate. With a different energy and feed rate, we have processed the gating and the circle, which with the smooth cutting edge and groove was consistent with the beam spatial distribution.

Mechanism and characteristics of steam laser patterning

Steam laser patterning of thin films and/or solid surfaces has been studied by jetting a beam of steam, such as water vapor, onto a sample surface to form a thin liquid film on it and patterning the sample by laser etching along predetermined path. In steam laser patterning, bubbles are formed in a thin liquid film on a sample surface irradiated by a pulsed laser. When the collapsed shock wave generated at the moment of bubble collapse and the high-speed liquid jet formed during bubble collapse are strong enough, cavitation erosion of the sample surface takes place. Compared to dry laser patterning, the etching rate can be greatly enhanced and no shoulder-like structure is formed at the rim of the laser-irradiated spot in steam laser patterning due to this cavitation erosion effect.

Femtosecond laser patterning of Ta0.1W0.9Ox/ITO thin film stack

Selective laser patterning of thin films in a multilayered structure is an emerging technology for process development and fabrication of optoelectronics and microelectronics devices. In this work, femtosecond laser patterning of electrochromic Ta0.1W0.9Ox film coated on ITO glass has been studied to understand the selective removal mechanism and to determine the optimal parameters for patterning process. A 775nm Ti:sapphire laser with a pulse duration of 150fs operating at 1kHz was used to irradiate the thin film stacks with variations in process parameters such as laser fluence, feedrate and numerical aperture of objective lens. The surface morphologies of the laser irradiated regions have been examined using a scanning electron microscopy and an optical surface profiler. Morphological analysis indicates that the mechanism responsible for the removal of Ta0.1W0.9Ox thin films from the ITO glass is a combination of blistering and explosive fracture induced by abrupt thermal expansion. Although the pattern quality is divided into partial removal, complete removal, and ITO film damage, the ITO film surface is slightly melted even at the complete removal condition. Optimal process window, which results in complete removal of Ta0.1W0.9Ox thin film without ablation damage in the ITO layer, have been established. From this study, it is found that focusing lens with longer focal length is preferable for damage-free pattern generation and shorter machining time.

High-Speed Maskless Laser Patterning of Thin Films for Giant Microelectronics

Maskless patterning of indium tin oxide (ITO) thin films was studied using a diode pumped Q-switched Nd:YLF laser. The wavelength was systematically varied from infrared to ultraviolet to investigate the effect of different conditions for light absorption by the ITO film and the glass substrate. Electrically isolating lines could be etched at all wavelengths used. However, residue-free removal of the ITO film could be achieved only when the glass substrate was strongly absorbing the incoming laser light. In all other cases, i.e., strong light absorption by the film only, weak absorption by the film and transmission by the substrate, or strong absorption by the film but weak absorption by the substrate, a ripple-like morphology in the etched groove was produced due to incomplete material removal. In case of ITO films on fused quartz substrates, therefore, the ripple-like morphology in the etched groove was observed at all wavelengths used. The results are consistent with thermal vaporization as the mechanism for the material removal which was confirmed by the predictions of numerical computations for the laser-induced temperature rise.