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FSCE focused on resist materials and coordinate correction technology for FPD mask and carried out research on underlying technology. The results we obtained are reported.

We have investigated responses of polymers to EUV radiation from laser-produced plasmas beyond ablation thresholds and micromachining. We concentrated on fabricate precise 3D micro-structures of PDMS, PMMA, acrylic block copolymers (BCP), and silica. The micromachining technique can be applied to three-dimensional micro-fluidic and bio-medical devices. The EUV processing is a promising to realize a practical micromachining technique. In the present work, we used two EUV radiation sources; (a) Wide band EUV light in a range of 10{300 eV was generated by irradiation of Ta targets with Nd:YAG laser light at 500 mJ/pulse. (b) Narrow band EUV light at 11 and 13 nm was generated by irradiation of solid Xe and Sn targets, respectively, with pulsed TEA CO2 laser light. The generated EUV light was condensed onto the materials at high power density beyond the ablation thresholds, using ellipsoidal mirrors. We found that through-holes with a diameter of one micrometer an be fabricated in PMMA and PDMS sheets with thicknesses of 4-10 micrometers, at 250 and 230 nm/shot, respectively. The effective ablation of PMMA sheets can be applied to a LIGA-like process for fabricating micro-structures of metals for micro- and nano-molds. PDMS sheets are ablated if it is irradiated with EUV light beyond a distinct threshold power density, while PDMS surfaces were modified at lower power densities. Furthermore, BCP sheets were ablated to have 1-micrometer structures. Thus, we have developed a practical technique for micromachining of PMMA, PDMS and BCP sheets in a micrometer scale.

We have investigated ablation process of silica glass induced by X-ray irradiation. X-rays around 100 eV were generated by irradiation of Ta targets with Nd:YAG laser light. The laser plasma soft X-rays have a pulse duration of 10 ns. The soft X-rays were focused on silica surfaces at up to 10 8 W/cm 2 . We found that silica glass can be ablated by X-ray irradiation. Typically, the ablated surface have a roughness of 1 nm after ablation by 500 nm in depth. Further, trenches with a width of 50 nm can be clearly fabricated on silica surface. Thus, high quality, practical micromachining can be achieved by the X-ray technique. It is remarkable that more precise features can be fabricated on silica surface than the thermal diffusion length. The results implies non-thermal ablation process. We observed ions ejected from silica surfaces during the irradiation and found that ions are almost atomic species such as Si + , O + , Si 2 + , O 2 + , SiO + . The results revealed that silica surfaces are broken into atomic species by X-ray irradiation. Among X-ray ablated species, 0.5-15 % are estimated to be ionized. Even though 0.5 % atoms are ionized in silica surface, the energy density of Coulomb repulsive force is higher than the energy density of binding energy of silica glass. Therefore, we can conclude that Coulomb repulsion between X-ray generated ions are essential for X-ray ablation of silica glass.

We have investigated responses of PDMS, PMMA and acrylic block copolymers (BCP) to EUV light from laserproduced plasma beyond ablation thresholds and micromachining. We generated wide band EUV light around 100 eV by irradiation of Ta targets with Nd:YAG laser light. In addition, narrow band EUV light at 11 and 13 nm were generated by irradiation of solid Xe and Sn targets, respectively, with pulsed CO2 laser light. The generated EUV light was condensed onto samples, using an ellipsoidal mirror. The EUV light was incident through windows of contact masks on the samples. We found that through-holes with a diameter of 1 μm can be fabricated in PDMS sheets with thicknesses of 10 μm. PDMS sheets are ablated if they are irradiated with EUV light beyond a threshold power density, while PDMS surfaces were modified by irradiation with the narrow band EUV light at lower power densities. Effective ablation of PMMA sheets can be applied to a LIGA-like process for fabricating micro-structures of metals using the practical apparatus. Furthermore, BCP sheets were ablated to have micro-structures. Thus, we have developed a practical technique for microma chining of PMMA, PDMS and BCP sheets in a micrometer scale.

We have investigated nano-ablation of silica glass and ablation process using focused laser plasma soft Xrays. Laser plasma soft X-rays were generated by irradiation of a Ta target with Nd:YAG laser light. The soft X-rays were focused on silica glass plates using an ellipsoidal mirror at fluences up to 1 J/cm 2 .I n order to fabricate nano-trenches, a silica glass plate was irradiated with laser plasma soft X-rays through the windows of a line and space mask. We demonstrated fabrication of nano-trenches with a width of 50 nm. It should be noted that the feature size is more precise than that estimated from the thermal diffusion length for the 10-ns X-rays (i.e. 80 nm). Furthermore, the ablated area has a depth of 470 nm and a roughness of 1 nm after ten shots of irradiation. Thus, the X-ray irradiation technique have a significant feature of direct nanomachining. The ablation occurs at fluences F beyond a ablation threshould Fth and ablation depth per pulse D obeys the law D =1 /α ln(F/Fth), where α is an effective absorption coefficient. These results suggest that absorbed energy is accumulated in the absorbed region without energy diffusion until ablation occurs. In addition, time-resolved mass spectroscopy revealed that silica glass is broken into atomic ions and atomic neutrals during ablation. Because Si + and O + ions have kinetic energies of 10–30 eV, non-thermal process such as Coulomb explosion may be driving force behind the ablation. Such non-thermal process enables us to fabricate nano-structures on silica glass.

We have investigated ablation of inorganic materials using pulsed and focused soft X-rays. Soft X-rays in a range of 1-500 eV were produced by irradiation of Ta targets with Q-switched Nd:YAG laser light (532 nm, 0.5-0.8 J/pulse) with a pulse duration of 10 ns in a vacuum chamber. The soft X-rays were focused on the surfaces of inorganic materials using an ellipsoidal mirror at approximately 0.1 J/cm2. The ellipsoidal mirror is designed so as to focus soft X-rays at about 100 eV efficiently, while it can not reflect soft X-rays above 200 eV. We found that synthetic quartz glass, Pyrex, LiF, CaF2, Al2O3 and LiNbO3, can be ablated by focused and pulsed soft X-rays. Typically, synthetic quartz glass is ablated at 50 nm/shot. We found that ablation occurs at X-ray fluences beyond the ablation threshold. Using a nano-scaled contact mask, trenches with a width of 50 nm and an aspect ratio of 1 are formed. The result indicates the diffusion length of absorbed energy during irradiation is less than 50 nm and that the accumulation results in ablation. The technique can also be applied to basic research of the interaction of intense soft X-rays with materials and resulting damage to the materials.

We have investigated micromachining of inorganic transparent materials by direct soft X-ray ablation. The pulsed soft X-rays 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 10 4 J/cm 2 . The laser plasma soft X-rays (LPSX's) were focused on the surfaces of specimens using an ellipsoidal mirror that is made from silica glass and coated with Au. The ellipsoidal mirror is designed so that LPSX's at arount 10 nm are focused efficiently. The fluence of LPSX's on the specimens is roughly estimated to be 0.1 J/cm 2 . We found that quartz glass plates are machined by pulsed LPSX's irradiation at a rate of 48 nm/shot. Furthermore, the quartz plates have smooth surfaces with a roughness less thatn 10 nm after 10 shots of LPSX irradiation and sharp edges with a steepness less than 100 nm. In addition to quartz glass, the LPSX processing can be applied to micromachining of a variety of materials such as Pyrex, CaF 2 , LiF, LiNbO 3 , Si and silicone. We found a transient state induced by LPSX irradiation of quartz glass. The transient state absorbs 266 nm light. We irradiated quartz glass with 266 nm Nd:YAG laser light and LPSX's simultaneously and found that ablation is enhanced to have a rate of 85 nm/shot. With X-ray imaging optics, nanomachining of inorganic transparent materials should be achieved.

We have investigated microfabrication of inorganic transparent materials using laser plasma soft X-rays with the diffraction limit of 10 nm. As a soft X-ray source, we used Ta laser plasma soft X-rays, whch has a light emission band at around 10 nm. A SiO2 film was confirmed to have absorption band in the soft X-ray region. Micromachining a quartz plate was demonstrated by irradiation with focused soft X-rays and pulsed 266 nm Nd:YAG laser light. The quartz plates are ablated smoothly at 85 nm/shots. It is found that more than 40% of 266 nm laser light is absorbed by the quartz plates just after soft X-ray irradiation at room temperature. Thus, it is shown that a transient state such as an X-ray generated exciton (X-ray exciton), which have absorption band in UV region, are generated by soft X-ray irradiation. The micromachining technique (X-ray exciton method) can utilize the high space resolution of soft X-ray and the high energy density of conventional UV/visible laser light. Further, we found that a variety of materials such as SiO2, LiNO3, Si, CaF2, LiF and Al2O3 are ablated smoothly by irradiation of the focused laser plasma soft X-rays without 266 nm laser light.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Erbium (Er)- or phosphorus (P)-doped silicon nanocrystallites (nc-Si) buried in SiO2 layer were fabricated by laser ablation and the subsequent thermal annealing; i.e. solid-phase growth. The doping effects have been studied by measurements of temperature-dependent photoluminescence (PL) of Er from 6 K to 300 K and PL measurements of nc-Si at room temperature, as well as electron-spin-resonance (ESR) measurements of P donors in nc-Si. The results demonstrates that the solid-phase growth method can realize an intense 1.5micrometers Er PL without thermal quenching and P-donor doping can be attained in nc-Si. These results suggest that impurity doping is useful for modifying furthermore quantized properties of Si nanostructures and making them more functionally active.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have utilized pulsed-laser ablation in ambient inert gas to synthesize silicon (Si) nanoparticles and to perform surface modification and impurity doping. The dynamical growing process of Si nanoparticles has been investigated by measuring time-resolved light emission induced by the second pulsed-laser irradiation with a delayed time. It was found from the time-resolved measurements that the onset of the formation of Si nanoparticles appears at around 1 ms, on inert gas pressure and laser fluence. We demonstrate that light emission can be controlled by adding hydrogen or oxygen gas to inert gas. It is also demonstrated that the thermal quenching which has been serious problem in Er-doped semiconductors can be removed in 1.54 micrometers photoluminescence of Er-doped Si nanocrystallites. These results suggest that laser ablation is useful not only for synthesis of nanostructured materials such as nanoparticles and nanowires/nanotubes, but for their surface modification and impurity doping that are important techniques for realizing functional nanostructures.

For studying the material properties of nanostructured group IV materials, we have developed a pulsed laser ablation method into inert background gases. SiGe alloy nanocrystallites have possibility of novel band structure engineering by controlling not only compositions but also particle sizes. An ArF excimer laser was focused onto the surface of the powder-sintered SixGe1-x target. During the laser ablation, He gas was introduced into a vacuum chamber and was maintained at a constant pressure. Size distribution of the SixGe1-x ultrafine particles decreases with decreasing composition x under fixed conditions of deposition such as background gas pressure. Raman scattering spectra of the deposited SiGe ultrafine particles show three peaks ascribed to mixed crystalline SiGe after annealing, and the linewidths of the peaks broaden due to the reduced size of the crystallites. The frequencies and intensities of the peaks depend on the composition x. Visible PL spectra have broad peaks from 2.25 eV to 2.10 eV, at room temperature. The peak positions show blue shifts with increasing x. Electroluminescent diodes with the Si0.8Ge0.2 nanocrystallite active region were fabricated, and emit visible high peaked at around 1.8 3V, at room temperature.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A time-resolved x-ray absorption spectroscopy apparatus on a laboratory scale is being prepared which utilizes a laser plasma as an x-ray source. One of the major aims imposed on this apparatus is to observe x-ray absorption or reflection spectra of various materials in an energy region from 100 eV up to 3 keV. For this purpose, two sets of optical systems are provided, i.e., a toroidal mirror and grazing incidence flat-field grating for the lower-energy region (100-1000 eV), and a toroidal mirror and curved KAP crystal for the higher-energy region (1-3 keV). Detection of x-rays is performed with MCPs for both energy regions. Preliminary experiments on the generation of x-rays have revealed that the intensity of x-rays in the energy region below 300 eV is as high as 10(16) photons/pulse in 2(pi) steradian.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.