Luminescence Measurement of Fused Silica in the Presence of Excimer Laser Radiation
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ABSTRACT Exicimer laser induced luminsecence characteristics of type The luminescence characterisIII fused silica was investigated. tics in the ultraviolet wavelength region are strongly depending on the intensity of red luminescence at 650 nm. A sample without red luminescence shows a strong emission band at 280 nm. We found that the 280 nm band is corresponds to a absorption band at 225 nm. To clearfy the nature of the 280 nm band, we studied the difference of luminescence of samples which had been kept on heating under various atmosphares, i.e., N,, 0,, He, H,, and air. By these results we suspect that the 280 nm band is related to hydrogen atom which are weakly bounded to the glass network.
INTRODUCTION Type III fused silica is formed in hydrogen-oxygen flame hydrolys of silicon tetra chloride, and it contains OH about 1000 ppm. This material have high optical transmission in UV region. Because of such transmission properties, this material is widely used in the UV lithograpy such as the photomasks and the lenses. The type III fused silica has high resistivity to radiations, but color centers are created by the irradiation of y-ray, X-ray, excimer laser beam, and R.F. plasma[i-5]. The color centers are unfaverable to optical materials for the lithography, because it causes the absorption and emission bands in UV region. We have been investigated the characteristics of the luminescence by excimer laser to find the optimum conditions to produce the optical materials for excimer laser lithography. By the KrF laser irradiation, we had found that the intensity of the red luminescence at 650 nm is proprotional to the i•7-th power of the laser fluence per pulse, and to the 0.6-th *power of the repetition rate[6]. In the case of ArF laser irradiation, the red luminescence is also appeared, but -the relation between the intensity and the condition of irradiation, laser fluence and repetition rate, is not so simple as in KrF laser irradiation[7] In gaeneral, by the KrF laser irradiation, the faint luminescence are observed in UV region, but by the ArF laser Mat. Res. Soc. Symp. Proc. Vol. 172. 01990 Materials Research Society
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irradiation strong luminescence was observed near by 300 nm. To clearfy the nature of these luminescence, we studied the difference of luminescence of samples which are kept on heating under various atmosphares, i.e., N2 , 02, He, H2 , and air. EXPERIMENTAL Samples Three samples with different intensity of red luminescence was used.
A:
a
sample
without
red
luminescence,
B:
weak
red
luminescence, and C: strong red luminescence. The size of samples are 10X10x30 mm3 . These samples are polished to every surface. Lumisescence measurement The system of luminescence measurement is shown in Fig. 1. The laser fluence was controled by using a fused silica lens. Diameter of the beam was adjusted to 3mm by using a iris. In the present measurement, laser beam with the laser fluence of 200 mJ/cm' and the repetition rate of 100 H1zwas used. The luminescence of any sample was detected from the di
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