Efficient and intense light sources in the vacuum-ultraviolet spectral region and their applications have been reviewed. High-intensity dielectric-barrier-discharge Ar, Kr and Xe excimer lamps were emphasized. Rare gas excimer lasers such as Ar2, Kr2 with electron beam excitations and discharge pumped F2 lasers were briefly mentioned as coherent VUV light sources. Potentialities of ArKr hetero-eximer lasers were also discussed. Applications of VUV light to surface cleanings, SiO2 thin films decompositions and compositions on Si wafers were reviewed.
Measurements of excitation spectra of photoetching of chlorinated Si(111)7×7 surfaces stimulated by ultraviolet nanosecond pulse laser light revealed that there are two distinct spectral peaks, one (α-peak) being located near 290nm and another (β-peak) at 245 nm. The α-peak exhibits a strong supralinear dependence on light intensity above laser fluence of∼100mJ/cm2 pulse, while the β-peak grows linearly with light intensity. The red shift of the α-peak with increasing intensity coincides with the shift of laser abration, which strongly suggests that the origin of the α-peak photoetching is thermal etching enhanced by surface heating due to interband transition in the substrate. The dependence on polarization of the incident light suggests that the β-peak photoetching originates in excitation of hot carriers in the substrate which are captured resonantly by the anti-bonding states of the adsorbate chlorides resulting in destabilization of the molecules.
Rare gas excimer lamps using dielectric-barrier discharge are a new type of compact and high-efficient light source for vacuum ultraviolet wavelength region. Since the lamps produce incoherent and quasi-continuous radiation, uniform processing over large sample areas is expected to be possible without thermal effects and speckling or interference fringes. The purpose of this paper is to exploit a new technique of material processing by use of the newly developed incoherent rare gas excimer lamps. We will describe some findings obtained by applying the excimer lamps to preparation of silica thin films. A photochemical vapor deposition using a Xe2 excimer lamp has made it possible to prepare silica films by means of a single precursor process from tetraethoxyorthosilicate (TEOS) at room temperature. Transparent SiO2 thin films were obtained with a deposition rate of 0.9nm/min. The refractive index was 1.476 at 632.8nm and the surface roughness reached 0.2nm-rms. These findings indicate that the VUV excimer lamp CVD is a promising method for preparing smooth and fine thickness-controllable films of SiO2 at room temperature. We confirmed that, this technique provides a very promising photo-quantum process for the fabrication of semiconductors and opt-electronic devices, and others.
Surface modification of a selective area of plastics was accomplished by using an ArF excimer laser or an excimer lamp. The chemical stability of the plastics is attributed to the presence of C-H, C-F, C-Cl or C=O bonds. Plastic sheets were photochemically modified to be hydrophilic or metallic properties with ultra violet photons and chemical solutions. The chemical solution was sandwiched between the sample surface and a silica glass window. With UV photons, the solutions and sample surfaces were excited. In the case of the hydrophilic modification, the surfaces were dehydrogenated or difluorinated by the H or B atoms which were photodissociated from H2O or B(OH)3 aqueous solution, and replaced the photodissociated OH radicals. In the case of the metal deposition on the plastic surfaces, the copper sulfate aqueous solution was used. As a result conductive circuit patterns Cu thin films were deposited on the sample surfaces.
A novel technique for precision microfabrication of hard materials such as fused quartz and SiC has been developed by using laser ablation with VUV-UV multiwavelength excitation. In this process, VUV laser beam of small laser fluence (several tens mJ/cm2) and UV laser beam of large laser fluence (several J/cm2) are directed to samples at the same time. The essential mechanism for insulators such as fused quartz is strong absorption of UV laser beams to the excited state formed by VUV laser beams (Excited-State Absorption: ESA). However, direct photo-ionization by the VUV laser beam is important for wide bandgap semiconductors such as SiC. Advantages of this process are discussed in comparison of the conventional single wavelength VUV laser ablation.
The semiconductor industry, whose long period of sustained growth is in no small measure due to the optical lithography process, is now on the verge of a dilemma. Optical lithography has arrived at a crossroads, and after many years of steady improvement in device performance, device integration, and cost reduction, the industry is facing a major crisis. In Japan, Europe and the U.S., consortiums comprising the entries from government, business, and the academic world have been formed in an effort to ward off the coming crisis. Their work seeks to extend the useful life of optical lithography as well as to foster the development of post-optical lithographic processes. A particular problem they are confirming is to ascertain how the development of sub-0.1μm lithographic technology will affect the economical manufacturing of semiconductors. This paper discusses the limits of current optical lithography such as VUV lithography, especially F2 excimer laser and worldwide trends in developing post-optical lithographic processes. Future miniaturization trends in semiconductor production are also discussed.
Well-ordered ultrathin β-carotene films were successfully fabricated using Langmuir-Blodgett (LB) method. Molecular orientation of the films was also investigated. Surface pressure-area isotherm suggested that β-carotene oriented perpendiculaly at the air-water interface by compression, and thus enabled to form two-dimensional film. X-ray diffraction indicated the tilt orientations of 55 and 40 degrees in the five and nine layers, respectively. Fourier-transform infrared reflection-absorption spectroscopy revealed ionone rings of β-carotene perpendicular to the substrate. The molecular orientation of the β-carotene LB films greatly depends upon the cohesive force between the conjugated chains. LB films of a mixture of β-carotene and arachidic acid were ill-defined. This is due to the fact that β-carotene thrusts up to the hydrophobic group of arachidic acid.
Combined with thermal annealing, the locally confined low energy electron-beam from a scanning tunneling microscope (STM) tip can be used for nanofabrication of Si oxide film on Si substrate as nano-lithography mask; the oxide layer within the field emission a-beam exposed area can be decomposed, and then evacuated from the surface at elevated temperatures of about 600°C. Different manometer scale patterns of the oxide windows on Si substrate such as dot window arrays, lines, and circles can be formed. The minimum feature size attained so far is 25nm and the rms edge roughness of line patterns is less than 3.5nm. Mechanism and controllability of the STM nanofabrication processing are discussed.