XeF Excimer Laser Research Articles

P‐77: Novel and Highly Reliable XeF and KrF Excimer Laser Annealing for Reducing the Cost of Flat Panel Display Equipment

One of the most important goals of flat panel display (FPD) manufacturing is to reduce the cost of excimer laser annealing (ELA) processes of low‐temperature poly‐Si (LTPS) technology. We developed novel XeF (351 nm) and KrF (248 nm) excimer lasers specially designed for ELA. The semiconductor‐field‐proven excimer laser technologies are applied to stabilize the operation and to reduce the cost.

P-25: Super Low Temperature Doping of Phosphorus to Poly-Si Thin Films Using XeF Excimer Laser Irradiation in Phosphoric Acid Solution

In this paper, we report on super low temperature doping of phosphorus to poly-Si thin films using XeF excimer laser irradiation in a phosphoric acid solution. In this method, the implantation of P atoms and dopant activation can be performed simultaneously. We prepared poly-Si films with a thickness of 50 nm, and these films were crystallized using XeF excimer laser annealing. After laser doping, the concentration of P atoms in the poly-Si films was approximately 3.5 × 1018 cm−3, and the resistance of the poly-Si films decreased by approximately 0.003 times as compared with that before laser doping.

Laser ablation in liquids of germanium in externally applied electric fields

Ultraviolet light from a XeF excimer laser was used to ablate a germanium target which was immersed in either distilled water or ethanol. Two electrodes in the processing container were used to produce an electric field with the strength ranging from 0 to 9.5 V/cm. The effect of externally applied electric fields on the fabricated nanoparticles was studied. The size and morphology of the obtained products were investigated using transmission electron microscopy. In each liquid, spherical nanoparticles were fabricated. It was observed that the electric field affects their size distribution. With increased electric field strength, the fabricated particles were smaller. However, in the same electric field, particles obtained in water were larger than those in ethanol, except for the 9.5 V/cm field. Additionally, spindle-shaped ablation products have been observed for ablation in ethanol under an electric field of 9.5 V/cm, while ablation in water in all studied fields resulted in filamentary webs.

Formaldehyde LIF detection with background subtraction around single igniting GTL diesel droplets

Formaldehyde is an important combustion intermediate, which is often used for the analysis of turbulent flames, internal combustion engines or droplet/spray ignition processes. Due to its high concentration in hydrocarbon fuel combustion, laser induced fluorescence (LIF) of formaldehyde can easily be excited (e.g. 339, 343, 353 and 355nm) and measured (360–550nm). However, it is often superimposed by background emission from other combustion intermediates as, e.g. polycyclic aromatic hydrocarbons (PAHs).We present formaldehyde LIF excitation spectra obtained with a XeF excimer laser in combination with a spectrometer and an ICCD camera in dependence of pressure (50mbar to 20bar). For formaldehyde LIF and background excitation, we selected the wavelengths 353.373 and 353.386nm, respectively. LIF measurements at the background wavelength contain a rising formaldehyde contribution with increasing pressure. We present a novel method for the calculation of the real background. This method is applied to the ignition of single gas-to-liquid (GTL) diesel droplets. However, the method can also be applied to other fuels. In the case of a GTL diesel ignition experiment (628K, 3bar) the real background amounted to only 30% of the emission which was measured at the background excitation wavelength (353.386nm).

Laser-induced front side and back side etching of fused silica with KrF and XeF excimer lasers using metallic absorber layers: A comparison

Laser-induced front side (LIFE) and back side etching (LIBDE) are methods for nanometer-precision laser etching of transparent materials using thin absorber layers. The etching behaviour of fused silica at a laser wavelength of 248nm (KrF) and 351nm (XeF excimer laser) with a pulse duration of 25ns using a chromium absorber layer was analysed and compared for front and back side etching geometry. For both wavelengths as well as for both processes the etching depth d increases almost linearly in dependence on the laser fluence (it is: d≈δ*(Φ−Φth)). The etching depth at the same laser fluence is higher for 248nm compared to 351nm as well as for back side etching compared to the front side etching process (LIFE: δ(248nm)=20nm/(J/cm2), δ(351nm)=15nm/(J/cm2), LIBDE: δ(248nm)=38nm/(J/cm2), δ(351nm)=8nm/(J/cm2) with Φth,m from 0.3 to 2.65J/cm2). Furthermore, the measured depths were evaluated with the estimated etching depth calculated by a thermal model. The simple thermodynamic model allows a good qualitative description of the etching depth behaviour; however, the model does not allow the quantitative calculation of the etching depth.

Laser-induced front side etching of fused silica with XeF excimer laser using thin metal layers

Laser-induced front side etching (LIFE) is a method for laser etching of transparent materials using thin absorber layers, e.g., for precision engineering or even optical applications.Aluminium, chromium, molybdenum, silver as well as titanium with various layer thicknesses (5–100nm) were applied as absorber for etching trenches in fused silica with nanosecond XeF excimer laser radiation. The sample surfaces were processed at laser fluences up to 10J/cm2 and laser pulse numbers from 1 to 10 pulses.A linear growth of the etching depth at rising laser fluence was found. The film thickness dependency is more complex and mostly influenced by the optical properties of the thin metal films.The influence of the laser fluence, the number of pulses, the absorber material as well as the absorber layer thickness on the etching process, the etching depth, and the surface modification were presented and discussed.A simple model is given that allows the discussion of the etching depth in dependency on the laser fluence and the metal film thickness.The measurements represented a good agreement with the calculated results by a thermal model.The LIFE method allows nm-precision etching of fused silica with etching depths up to 150nm.

High Resolution ITO Lithography Using Excimer Laser for Flat-Panel Display Fabrication

As the higher and higher demand for image definition of flat-panel display (FPD), the minimum linewidth of pixel electrode, which is based on the Indium-Tin-Oxide (ITO) glass, has become narrower and narrower. The feature size of sub-pixel electrode has been narrowed from about 60~100 µm to below 20 µm in recent years. Hence the lithography technology has played a more and more important role in the fabrication of FPD. The laser projection imaging (LPI) technology can solve the problems obviously. In this paper, by using of the 351nm XeF excimer laser projection imaging system we can obtain developed pictures at the resolution between 10 and 20 µm on the ITO glass. In addition, the relation graphs between 10~20 µm linewidth and the modulation transfer function（MTF）of the projection system are simulated and analyzed by the ZEMAX and MATLAB software. Consequently, our system can satisfy the linewidth of the sub-pixel electrode at the resolution between 10 and 20 µm in the production of FPD.

Effect of XeF laser treatment on structure of nanocrystalline diamond films

Nanocrystalline diamond (NCD) films were deposited on Si substrates by microwave plasma-enhanced chemical vapor deposition (MPECVD) using methane/hydrogen/oxygen (30/169/0.2 sccm) as process gases. Subsequently a thin (0.33 μm) and a thick (1.01 μm) NCD films were irradiated with XeF excimer laser ( λ = 351 nm) with 300 and 600 mJ cm − 2 of energy densities in air. The NCD films became rougher after laser irradiations. Fraction of graphitic clusters decreased but oxygen content increased in the thin NCD film after laser irradiation. Opposite phenomena were observed for the thick NCD films. Effect of laser irradiation to oxygenation and graphitization of NCD films was correlated with structural properties of free surface and grain boundaries of the thin and thick NCD films.

Influence of multi-photon ionization of Xe on a XeF discharge induced by KrF laser irradiation

Excimer laser preionization induced by an external laser was investigated for XeF excimer laser discharge induced by a KrF laser, paying attention to the ionized species in the gas. Enhancement of amplified spontaneous emission (ASE) was observed for XeF gas discharge preionized by a KrF laser with and without its irradiation. In contrast, no ASE enhancement was observed for KrF gas discharge with KrF laser preionization. ASE enhancement was larger for the longer wavelength, which was close to the two-photon resonance of the Xe atom, when tunable KrF laser irradiation was used. These results indicate that multi-photon ionization of Xe atoms supplied the initial electrons to the laser-induced preionization.

High-pulse-repetition-rate UV lasers with the inductance-capacitance discharge stabilisation

Compact high-pulse-repetition-rate XeF and KrF excimer lasers and an N2 laser with plate electrodes and the inductive-capacitance discharge stabilisation are studied. The composition and pressure of the active medium of lasers are optimised for obtaining the maximum output energy and maximum pulse repetition rate at comparatively low (no more than 19 m s-1) active-medium flow rates in the interelectrode gap. The pulse repetition rate achieved 4–5 kHz for the relative root-mean-square deviation of the laser pulse energy less than 2%. It is found that the energy of the N2-laser pulses changes periodically under the action of acoustic perturbations appearing at high pulse repetition rates. It is shown that the use of the inductance-capacitance stabilisation of the discharge provides the increase in the maximum pulse repetition rate by 0.5–1.5 kHz (depending on the active medium type). It is found that the stability of the output energy and maximum pulse repetition rate depend on the location of preionisation sparks with respect to the gas flow direction. Some ways for the development of the technology of plate electrodes and inductance-capacitance discharge stabilisation are proposed.

Fabrication of large-grain polycrystalline Ge films using absorptive films

Amorphous germanium (a-Ge) films in samples with or without an absorptive film are crystallized by short-pulse XeF excimer laser crystallization (ELC). An in situ time-resolved optical reflection and transmission (TRORT) monitoring system combining a cw He-Ne probe laser, a digital oscilloscope and two photodetectors is developed to investigate the melting and resolidification dynamics of Ge films during ELC. TRORT measurements reveal that the longest melt duration is prolonged from 250 to 1000 ns by adding absorptive films in the samples. Absorptive films are shown to be effective in improving the melt duration of the molten state and the grain size of polycrystalline Ge films. The grain size with a diameter of approximately 12 μm can be fabricated in the superlateral growth regime for 90-nm-thick a-Ge films at room temperature in air by single-shot ELC.

Characterization of polycrystalline Ge thin films fabricated by short-pulse XeF excimer laser crystallization

XeF excimer laser-induced melting and recrystallization dynamics of amorphous germanium are investigated using time-resolved optical reflection and transmission measurements with a nanosecond time resolution, field-emission scanning electron microscopy, and micro-Raman spectroscopy. It is found that the disc-shaped grain with a diameter of approximately 0.8 µm is located in the complete melting regime with a melt phase duration of approximately 141–200 ns. The significant change of transmissivity is a key phenomenon revealing the excessive excimer laser fluence during excimer laser crystallization by in-situ optical measurements. Differences between the melting and recrystallization phenomenon for Si and Ge thin films are also discussed.

In-Situ and Ex-Situ Measurements on Silicon Thin Films Fabricated by Excimer Laser Annealing

The phase transitions occurring at the surface of amorphous silicon and a-Si/SiO2interface of the sample during XeF excimer laser annealing has been investigated by nonintrusive in-situ real-time optical reflectivity and transmissivity measurements with nanosecond time resolution. Five distinct regimes were demonstrated on the basis of various excimer laser fluences. The structural transformation scenario of silicon films based on the recrystallization mechanism is proposed to interpret the formation of the grain microstructure. The ex-situ microstructural characterizations of excimer laser-irradiated region as a function of various excimer laser energy densities were characterized by scanning electron microscopy and micro-Raman scattering measurements. A super-lateral growth length of approximately 1μm was obtained in a 90-nm-thick a-Si film by a single excimer laser pulse without any substrate heating. Micro-Raman scattering measurements as a function of various excimer laser energy densities were also carried out.

Monitoring explosive crystallization phenomenon of amorphous silicon thin films during short pulse duration XeF excimer laser annealing using real-time optical diagnostic measurements

Melting and crystallization scenario of amorphous silicon (a-Si) thin films have been investigated using in situ time-resolved optical reflection and transmission measurements. The explosive crystallization phenomenon is observed using a single-mode continuous wave He–Ne probe laser for thickness of 50 nm and 90 nm a-Si thin films upon 25 ns pulse duration of XeF excimer laser irradiation, respectively. The explosive crystallization phenomenon is easier to observe in the large thickness of a-Si thin films, a sample with pure a-Si microstructure and under longer pulse duration of excimer laser irradiation by time-resolved optical reflection and transmission measurements.

Nanosecond Time Resolution In Situ Optical Reflection and Transmission Measurements during XeF Excimer Laser Interaction with Amorphous Silicon Thin Films

XeF excimer laser-induced melting and recrystallization of amorphous silicon was studied using in-situ online time-resolved reflection and transmission measurements with a nanosecond time resolution. The explosive crystallization was observed for 50nm thick amorphous silicon on SiO2 deposited on non-alkali glass substrate upon 25ns pulse duration of excimer laser. Three distinct regrowth regimes were found using various excimer laser fluences. Scanning electron microscopy, Raman spectroscopy and atomic force microscopy were used to evaluate the excimer laser- irradiated region of the sample. Grain size, surface roughness and melt duration as a function of different laser fluences are also determined.

P-60: Thin-beam Directional X'tallization Method for SOP and OLED Application

We propose a Thin-beam Directional X' tallization (TDX) method, based on a high power, high repetition rate XeF excimer laser source and special optics, to produce a long, narrow (∼ 5 micron) beam with sharp edge slope. We present experimental results from a prototype TDX system that demonstrates very uniform directional laterally grown poly-Si films without any grain boundary protrusions.

Laser Measurement of Polycyclic Aromatic Hydrocarbons (PAHs) in a Flame (2nd Report, Presumption of PAHs by Laser-Induced Fluorescence Spectrum)

Laser induced fluorescence (LIF) method was applied to the measurement of PAHs (Polycyclic Aromatic Hydrocarbons) in a propane diffusion flame. Various PAHs were excited by a KrF excimer laser and a dye-laser pumped by the XeF excimer laser. By measuring the enission spectra of various PAHs vapors, it was found that the peak wavelength in the emission spectrom of LIF shifted to the longer wavelength side with an increase of PAHs carbon numbers. The carbon numbers of PAHs in a diffusion flame was presumed from the data of peak wavelength of emission spectrum. It was confirmed that the carbon numbers of PAHs in the diffusion flame increased as approaching to the flame surface. The maximum carbon number was about 26 at the layer close to the flame surface.

Reductive total chlorine free photochemical bleaching of cellulosic fabrics, an energy conserving process

Water-insoluble natural colored compounds adsorbed or chemically bound on cellulosic fabrics were bleached effectively at room temperature by a selective photolysis of the colored compounds using various excimer lasers (ArF, KrF, XeCl, XeF), a low-pressure mercury lamp, and a black-light fluorescent lamp in the presence of aqueous solutions of various reducing reagents. Sodium borohydride gave the best efficiency on the bleaching when KrF, XeCl, XeF excimer lasers or a low-pressure mercury lamp were used as light sources and the efficiency of the bleaching was found to be comparable to that of the conventional thermal bleaching processes.

Upconverted VUV luminescence of Nd 3+ and Er 3+ doped into LiYF 4 crystals under XeF-laser excitation

The upconverted VUV (185 nm) and UV (230 and 260 nm) luminescence due to 5d–4f radiative transitions in Nd 3+ ions doped into a LiYF 4 crystal has been obtained under excitation by 351/353 nm radiation from a XeF excimer laser. The maximum upconversion efficiency, defined as the ratio of intensity for 5d–4f luminescence to overall intensity for 5d–4f and 4f–4f luminescence from the 4D 3/2 Nd 3+ level, has been estimated to be about 70% under optimal focusing conditions for XeF laser radiation. A redistribution of intensity between three main components of 5d–4f Nd 3+ luminescence is observed under changing the excitation power density, which favors the most long-wavelength band (260 nm) at higher excitation density level. The effect is interpreted as being due to excited state absorption of radiation emitted. The upconverted VUV and UV luminescence from the high-lying 2F(2) 7/2 4f level of Er 3+ doped into a LiYF 4 crystal has also been obtained under XeF-laser excitation the most intense line being at 280 nm from the spin-allowed transition to the 2H(2) 11/2 4f level of Er 3+, but the efficiency of upconversion for Er 3+ emission is low, less than 5%.

Photosensitive GeO2-SiO2 films for ultraviolet laser writing of channel waveguides and bragg gratings with Cr-loaded waveguide structure.

Irradiation with intense ultraviolet laser pulses induced a large refractive-index change in 30GeO2-70SiO2 waveguide-grade thin films prepared by the plasma-enhanced chemical vapor deposition method, which contained a large amount of photoactive Ge2+ defects. The maximum index change in the as-deposited films by KrF and XeF excimer laser irradiation was estimated to be 1.2 x 10(-3) and 0.28 x 10(-3), respectively. These results clearly indicate that the photorefractivity of GeO2-SiO2 glasses is due to a Ge2+ defect in origin. The channel waveguide and the planar Bragg gratings were directly written in the photoactive Ge(2+)-enriched GeOs-SiO2 thin films by pulsed ultraviolet laser irradiation with a Cr-metal-loaded-type waveguide structure.