We have developed a 4-kHz ArF excimer laser with ultra-narrow bandwidth, which is applicable to high-NA scanners for sub-0.13-micrometers microlithography. In this paper, we describe a 4-kHz ArF excimer laser for mass production: the model G40A, which has an output power of 20 W and energy dose stability of less than +/- 0.3% (20-ms window) at 4 kHz. This dose stability is comparable to the performance of an existing 2-kHz ArF excimer laser, the model G20A. The new laser also has the following specifications: a long pulse duration of over 40 ns, spectral bandwidth of less than 0.35 pm (FWHM), and spectral purity of less than 1.0 pm (95%). These characteristics are better than those of the G20A. A lifetime test of over 7 billion pulses has been conducted at 4-kHz operation. The new laser has maintained an energy dose stability of less than +/- 0.3% (20-ms windows) and demonstrated performance suitable for mass production even after over 7 billion pulses.
A 3-D numerical model is developed for predicting properties of high-intensity-discharge (HID) lamps. The developed model is based on the powerful and globally suitable, irrespective of optical thickness, discrete ordinates (DO) method for evaluating radiation transfer and predicting the properties of all sections of an HID lamp between two power-supply ends (viz., plasma, electrodes, glass bulb, stem, and lamp house) as a single entity. A test lamp is studied using this model, and the theoretically predicted electrode temperatures are compared with the experimentally measured values for realizing the model performance. The horizontally oriented lamp is operated at a discharge pressure of 2.5 MPa and a direct current (dc) of 2.69 A. In the plasma or gas-filled region, the developed 3-D model solves the complete set of magnetohydrodynamics: transport equations of mass, momentum, and energy along with the vector potential form of Maxwell's equations to account for the electromagnetic effects, and in the solid regions, it solves the energy balance equation with or without radiation transfer. Radiation transfer equation is solved using the DO method by dividing the electromagnetic spectrum into several gray bands. The model has been applied for calculating the properties of the test lamp. Calculations have been done for the electrodes and gas-filled or discharge region, but it is useful for the whole lamp. Output results give clear picture of distributions for temperature, velocity, electromagnetic fields, and radiation. Temperature of plasma near the cathode tip has been found as the maximum of 13 000 K, and it is about 8300 K near the anode tip. For an input power of 145 W, 67% has been dissipated in the bulk plasma as Joule heating, and the rest has been lost in the near-electrode regions or sheaths. The lamp converts 54% of the total input into radiation energy. Electrodes' surface temperatures have been measured experimentally using a two-color radiation thermometer. Comparison of experimentally measured temperature and theoretically predicted temperature is found to agree convincingly (within 8%)
For the prevention of surgical site infection (SSI), continuous disinfection could be helpful. Short wavelength ultraviolet radiation C (UVC) is highly bactericidal but shows cytotoxicity. Radiation of UVC with a wavelength of 222 nm to the skin is considered to be safe because it only reaches the stratum corneum. However, the safety of 222 nm irradiation to the surgical field not covered with skin is unknown. The purpose of this study was to examine the safety of 222 nm UVC irradiation on a surgical field in a rabbit model. Five types of tissue were surgically exposed and irradiated with 222 or 254 nm UVC. Immunohistological assessment against cyclobutane pyrimidine dimer (CPD), an index of DNA damage by UVC, was performed. The CPD-positive cell rate was significantly higher in the 254 nm group than in the other groups in all tissues. A 222 nm group showed significantly more CPD than control in fat tissue, but no significant difference in all other tissues. In fat tissue collected 24 h after irradiation, the 254 nm group showed higher CPD than the other groups, while the 222 nm group had reduced to the control level. These data suggest that 222 nm UVC irradiation could be a new method to safely prevent SSI.
We have developed a new xenon excimer light source in vacuum ultraviolet (VUV). The use of a pulsed gas jet discharge realized efficient cluster excitation and spatially localized emission in VUV with an extremely long pulse duration. An output power of 1.5 W was obtained with a pulse width of 5 ms at 176 nm, corresponding to an efficiency of 3.0%.
Surgical site infections (SSIs) represent an important clinical problem associated with increased levels of surgical morbidity and mortality. UVC irradiation during surgery has been considered to represent a possible strategy to prevent the development of SSI. 254-nm UVC induces marked levels of DNA damage by generating cyclobutyl pyrimidine dimers (CPD) in microorganisms. However, this effect is elicited not only in microorganisms, but also in human cells, and chronic exposure to 254-nm UVC has been established to represent a human health hazard. In contrast, despite short wavelength-UVC light, especially 222-nm UVC, having been demonstrated to elicit a bactericidal effect, single irradiation with a high dose of 222-nm UVC energy has been reported to not induce mutagenic or cytotoxic DNA lesions in mammalian cells. However, the effect of chronic irradiation with a high dose of 222-nm UVC to mammalian cells has not been determined. In this study, it was demonstrated that large numbers of CPD-expressing cells were induced in the epidermis of mice following treatment with a small amount of single exposure 254-nm UVC, and then less than half of these cells reduced within 24 h. Chronic 254-nm UVC irradiation was revealed to induce sunburn and desquamation in mouse skin. Histological analysis demonstrated that small numbers of CPD-expressing cells were detected only in hyperkeratotic stratum corneum after chronic irradiation with a high dose of 254-nm UVC, and that significant hyperplasia and intercellular edema were also induced in the epidermis of mice. In contrast, chronic irradiation with 222-nm UVC light was revealed not to induce mutagenic or cytotoxic effects in the epidermis of mice. These results indicated that 222-nm UVC light emitted from the lamp apparatus (or device), which was designed to attenuate harmful light present in wavelengths of more than 230 nm, represents a promising tool for the reduction of SSI incidence in patients and hospital staff.
