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The effect of laser-induced heat on Cu(In,Ga)Se2 solar cells was evaluated by scanning spreading resistance microscopy (SSRM) to improve the laser scribing (LS) quality. Two types of LS were examined for electrical isolation; that using transparent conductive oxide (TCO) lift-off resulted in a higher conversion efficiency of 17.4% and shunt resistance of 5 × 103 Ωcm2. SSRM images confirmed the absence of shunt paths between the laser-induced low-resistance layer at the trench bottom and the top TCO layer, which resulted in the high shunt resistance. Ultrashort-pulse LS would be a promising tool for reducing the dead area and increasing the throughput by high-speed scribing.

By using laser-induced backside wet etching (LIBWE), we have fabricated very deep micro-trenches in silica glass of 9-μm width and 300-μm depth (aspect ratio ≈ 33). In this paper, we present the details of fabricating the micro-trenches, and discuss why such a deep micro-trench is available by the LIBWE method.

We have investigated micromachining of a variety of materials by irradiation with laser plasma soft X-rays (LPSXs) at around 10 nm. The pulsed LPSXs were generated by irradiation of a Ta target in a vacuum chamber with Nd:YAG laser light at 532 nm, with a pulse duration of 7 ns, at a fluence of ~104 J/cm2. The LPSXs were focused on the surfaces of samples using an ellipsoidal mirror that is designed so that LPSXs at around 10 nm are focused efficiently. We found that quartz glass plates are ablated by LPSX irradiation at a typical rate of 48 nm/shot. Furthermore, the ablated regions have smooth surfaces with a roughness less than 10 nm after 10 shots of LPSX irradiation. It is demonstrated that quartz glass is machined with a lateral resolution higher than 100 nm. In addition to quartz glass, the LPSX processing can be applied to micromachining of a variety of materials such as Pyrex, CaF2, LiF, LiNbO3, Si and silicone.

We have investigated direct nanomachining of inorganic materials using laser plasma soft X-rays. Soft X-rays (X) were generated by irradiation of Ta targets (Ta) with 532 nm Nd:YAG laser light(Y) with a pulse duration of 7 ns, at an energy density of about 10/sup 4/ J/cm/sup 2/. Under the condition, Ta plasma emit soft X-rays at around 10 nm. The soft X-rays were focused on samples (Q) with a spot size of 150 /spl mu/m, using an ellipsoidal mirror (M) that we designed so as to focus soft X-rays at around 10 nm efficiently. It was confirmed that SiO/sub 2/ has optical absorption at around 10 nm. We found that synthetic quartz glass, fused silica, Pyrex, HF, CaF/sub 2/, Al/sub 2/O/sub 3/ and LiNbO/sub 3/ can be machined smoothly by irradiation with laser plasma soft X-rays. Typically, quartz glass is ablated at 40 nm/shot, and has a surface roughness less than 10 nm after 10 shots. In order to investigate lateral resolution, we fabricated a WSi contact mask with 200-nm-pitch line-and-space patterns on quartz glass. We found that quarts glass plates can be machined at a resolution less than 100 nm. In conclusion, we have established a technique for nanomachining a wide variety of inorganic materials using laser plasma soft X-rays at a precision less than 100 nm.

For crack-free marking of glass materials, a beam-scanning laser-induced backside wet etching (LIBWE) process by a beam spot with a fine periodic structure was examined. The fine periodic structure was produced within a beam spot by means of a Mach–Zehnder interferometer incorporated to the optical setup for the beam-scanning LIBWE. A fine structure with a period of 9 µm was observed within the microstructures with a diameter of ca. 40 µm fabricated by a laser shot under double-beam irradiation, and they could be homogeneously fabricated within an area of 800 × 800 µm. The area filled with the microstructures, including fine periodic structures, could be observed in high contrast under a diffuse, on-axis illumination that was used in commercial QR code readers.

The resistance of LiCaAlF6 single crystals against F2 laser irradiation was studied to examine the possible use of LiCaAlF6 as optical components for F2 laser lithography. After the initial increase by F2 laser cleaning, transmittance of LiCaAlF6 at 157 nm remains relatively unchanged even after irradiation with an F2 laser beam up to 105 pulses at a fluence of approximately 160 mJcm-2pulse-1, indicating good tolerance against the cumulative irradiation. We also discuss the mechanism of the initial increase in transmittance with the results of X-ray photoelectron spectroscopy (XPS). The threshold fluence for the onset of optical damage of LiCaAlF6 is approximately 2 Jcm-2pulse-1, similar to that of vacuum ultraviolet (VUV) grade CaF2.

Sapphire plates were etched with the approach of laser-induced backside wet etching (LIBWE) using neat toluene or saturated pyrene/acetone solutions as the etching medium. Using this approach, flexible patterns on the scale of 4-µm can be fabricated on the surface of the plates. The etching process was observed in situ by a CCD camera, which revealed the deposition of black particles and the formation thereafter of a laser-absorbing film in the etched area. By Raman spectroscopic analysis, the film was characterized to be amorphous carbon resulting from the decomposition of toluene or pyrene upon laser irradiation, which is an essential factor contributing to the etching process.

Laser-induced dot transfer is an innovative micropatterning technique that realizes on-demand microdot deposition under room-temperature atmospheric conditions. Based on this method, we have developed site- and size-controlled micropatterning of oxide materials. As a model case, indium tin oxide (ITO) microdots were arrayed on a receiver substrate. A nanosecond, 266 nm laser pulse was focused onto the interface between the ITO film and transparent support, causing the ejection of a single ITO microdroplet. The dependence of the transferred structures on the film thickness as well as the laser-induced film temperature distribution has been investigated by both experimental and finite elemental approaches.

Indium tin oxide films were fabricated by pulsed laser deposition on electric-field-applied substrates. The volume resistivity was effectively reduced when the electric current passing through films showed a drastic increase accompanied by a subsequent small decrease. According to X-ray diffraction (XRD) measurements, the peculiar behavior of electric current is attributable to the electric-field-induced crystallization.

We have investigated direct etching of poly(methyl methacrylate) (PMMA) using laser plasma soft X-rays. We focused soft X-rays of 6–25 nm on PMMA sheets efficiently using an Au coated ellipsoidal mirror. 7×10-2% of laser energy is estimated to be converted to soft X-rays that was incident to the PMMA sheets. We found that PMMA surfaces are etched beyond a threshold power density. The energy density of absorbed soft X-rays at the threshold is 7 kJ/cm3. The results suggest that etching is governed by decomposition into fragments.

Fabrication of FeSi2 nano- and microdot array was performed by utilizing droplet ejection through nanosecond laser-induced forward transfer (ns-LIFT). An amorphous FeSi2 source film on a transparent support was illuminated from the support by a nanosecond excimer laser pulse patterned into migcrogrid form, resulting in size- and site-controlled deposition of microdot array onto a silicon substrate. Micro-Raman spectroscopy confirmed β-FeSi2 crystalline phase even on unheated substrates. Moreover, the dot size was successfully reduced to approximately 500 nm in diameter, smaller than any previously reported by ns-LIFT. This technique is useful for integrating functional nano- and microdots under atmospheric room-temperature conditions.

We have successfully fabricated a deep micro-trench about 7 µm wide and 420 µm deep on silica glass with a maximum aspect ratio of 60 bylaser induced backside wet etching(LIBWE) via KrF laser ablation of a saturated pyrene/acetone solution. The processing time for the microetching was as short as 5 min at a repetition rate of 80 Hz and a fluence ofF= 1.0 J·cm-2·pulse-1. The etch rate was calculated to be approximately 17 nm·pulse-1. The LIBWE method is shown to be very useful for surface microstructuring of silica glass with high aspect ratio and high throughput.

The optical tolerance of annealed LiCaAlF6 single crystals against F2 laser irradiation was investigated. Annealed LiCaAlF6 (t=1.45 mm) shows an improved transmittance at 157 nm, 94.4% after the compensation of the surface reflection loss. Furthermore, after the initial increase by F2 laser cleaning, transmittance at 157 nm remains almost unchanged even after irradiation with a F2 laser beam up to 105 pulses at a fluence of approximately 160 mJ cm-2 pulse-1.

TiO2, PbO and PbTiO3 thin films were prepared using the Titanium-2-ethylhexanolate and lead-2-ethylhexanoate coating photolysis process with ArF excimer laser irradiation. The photolysis of Ti-2-ethylhexanolate, Pb-2-ethylhexanoate and mixed Ti-2-ethylhexanolate and Pb-2-ethylhexanoate was investigated by Fourier transform infrared (FT-IR) absorption spectroscopy and X-ray diffraction (XRD). In the case of the one-step ArF irradiation method at 50 mJ/cm2 with a repetition rate of 10 Hz for 5 min, rutile TiO2 and PbTiO3 perovskite phase along with a pyrochlore phase were obtained, while PbO was not obtained. On the other hand, in the case of the two-step ArF irradiation method consisting of preliminary weak irradiation at 10 mJ/cm2 with a repetition rate of 50 Hz for 0.5 min and a stronger irradiation at 50 mJ/cm2 with a repetition rate of 10 Hz for 5 min, anatase TiO2, β-PbO and a single phase of perovskite PbTiO3 were successfully obtained. The crystallization mechanism of PbTiO3 films from the metallorganic precursor is also discussed.

Neutral fragments from the 248 nm laser ablation of polyarylsulfone (PAS) were investigated using laser post ionization (193 nm) time-of-flight (TOF) mass spectroscopy. Three regimes of ablation fluence were distinguished with respect to detected fragments and differences in their velocity distributions. Over the entire fluence range the arrival profiles of the products matched with a shifted Maxwell-Boltzmann distribution. Interestingly, average translational velocities revealed a non-monotonical dependency on ablation fluence. This is probably be due to screening effects of the ablation pulse by the plume, or to non-thermal effects that may contribute to the ablation process at high fluences. The dependencies of both the flight velocities and the Knudsen layer temperature of the fragments on fluence suggest that PAS ablation is photothermally driven. However, the excessively high values for average translational energies (up to 34 eV at high fluences) and their increases with increasing fragments amu indicate that the process also has some non-thermal features.

Metal oxide films of TiO2, In2O3, ZrO2, ZnO, SnO2 and Fe2O3 have been successfully prepared by the coating photolysis process using ArF excimer laser irradiation at room temperature. When using metal acetylacetonates (acac) as the starting material, TiO2, In2O3 and ZrO2 were obtained with ArF laser irradiation at 50 mJ/cm2 at a repetition rate of 5 Hz for 5 min. When using Zn-acac, Fe, Sn, or In 2-ethylhexanoate as the starting material, a two-step process consisting of preliminary weak and sufficiently strong irradiation was found to be effective for obtaining ZnO, Fe2O3, SnO2 and In2O3 films.

The surface of a fluoropolymer film was fabricated with micron-sized features by laser-induced backside wet etching (LIBWE), using a nanosecond XeCl excimer laser at 308 nm. The etch rate ranged from 5 to 20 nm/pulse by laser irradiation at fluences varying from 160 to 500 mJ/cm2. The threshold fluence for etching was about 100 mJ/cm2 in the case of a tetrahydrofuran (THF) solution containing pyrene. The mechanism of LIBWE is explained by the formation of superheated liquid in a cyclic multiphotonic absorption process.

TiO2 (rutile) films have been successfully prepared by the coating photolysis process using ArF excimer laser irradiation at room temperature. The choice of the Ti-alkoxide type as the starting material and the effects of atmosphere on the product films have been studied by Fourier transformation infrared (FT-IR) and X-ray diffraction (XRD). When using Ti(O-i-C3H7)4 as the starting material, rutile films were obtained by the irradiation in a dry N2 atmosphere, whereas amorphous films were obtained by irradiation in air. When using Ti(OCH2CH(C2H5)-n-C4H9)4 as a starting material, rutile films were obtained by the irradiation even in the air atmosphere. Crystallization mechanism is also discussed.

Laser ablation of composite material consisting of elastomer and carbon black was performed using a KrF excimer laser. Remarkable sensitization of polymer ablation with carbon black was observed and cone-like microstructures were produced on the ablated surface. The development of large cones was due to the aggregation of carbon-rich cones by repeated etching and melting upon further laser irradiation. The cone-like microstructures revealed a visco-elastic property that could be useful in the applications of sealing and packing materials.

Irradiation of poly(tetrafluoroethylene) (PTFE) and poly(tetrafluoroethylene- co-hexafluoropropylene) (FEP) polymer films in an ammonia or hydrazine atmosphere with vacuum UV light resulted in a hydrophilic surface, where abstraction of fluorine atoms and introduction of nitrogen, oxygen, and hydrogen atoms occurred. We used Kr2 * and Xe2 * excimer lamps at wavelengths of 172 nm and 146 nm, respectively. The reaction mechanism for chemical surface modification is discussed on the basis of the results of X-ray photoelectron spectroscopy, secondary ion mass spectrometry, scanning electron spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy analyses.

Chemical vapor deposition of three kinds of 4-[ω(2-methylpropenoyloxy)alkyloxy]-4′-cyanobiphenyls (alkyloxy; ethyloxy, propyloxy and hexyloxy) was carried out using a polarized KrF excimer laser. The films deposited from the hexyloxy monomer, whose radical polymerization gave a side-chain-type liquid crystalline polymer, showed birefrengence and IR dichroism. The anisotropy of IR absorbance suggests that the direction of side chains of the polymer is parallel to the electric vector of the laser beam. The deposition of two other monomers, which yielded amorphous polymers because of the shortness of side chains, induced no molecular orientation. It was concluded that the molecular orientation took place due to an interaction between the liquid crystalline phase of the deposited polymer film and the polarized laser beam.

Poly(o-trimethylsllyl)-phenylacetylene (PTP) film, which was swollen in acetone under a high magnetic field of 15 T, showed birefringence and dichroism. Comparing the IR dichroism of magnetic-field-treated film with that of mechanically stretched film, it was found that the polymer long chain was aligned perpendicularly to the magnetic field. This alignment originated from the magnetic anisotropy of crystalline structures in PTP film.

Excellent critical current behavior at 77 K in magnetic fields up to 14 T has been obtained for Ba2YCu3O7-y (BYCO)-Ag films prepared by dipping-pyrolysis process. The films were epitaxially grown on SrTiO3(100) substrates using a two-step annealing (low-p(O2)/pure O2) method at 770°C. The best values of critical current density at 77 K under a 2-µV/cm criterion were 1.2×106 A/cm2 in a self field and 1.0×105 and 3.8×104 A/cm2 at 8 T and 14 T, respectively, when the field was applied parallel to the a-b plane.

Thick noncentrosymmetric LB films of more than 200 bilayers (thickness of more than 1 µm) were successfully fabricated with an alternating deposition of a phenylpyrazine derivative and arachidic acid monolayers. The alternating LB films were transparent from visible to near infrared region. Spectroscopic and X-ray diffraction studies on the alternating LB films proved that molecules were predominantly oriented normal to the film plane in the LB film. Further, the quadratic dependence of second-harmonic (SH) intensity on film thickness was confirmed in the LB films in the wide range of thickness from 1 to 200 bilayers. From the SH generation measurement, the alternating LB films were found to have fairly large second-order nonlinear susceptibility, which was estimated to be 1×10-7 esu.

In view of applications for excimer laser ablation, it was found that the highly periodic microstructure on polyethersulfone, which was produced by XeCl excimer laser ablation, was effective for alignment of nematic liquid crystals. The alignment of the liquid crystal molecule depends on the orientation of the microstructure, which is easily controlled.