UV Laser Deposition of Thin Films at 248 NM for Phase Shifting Mask Repair
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variety of different phase-mask technology has been developed [2-7]. Silicon dioxide and thin metallic films have been used in several phase-masks as the phase shifting component. Currently the unavailability of an appropriate phase-mask repair procedure delays the use of this technology indicating a strong need for an efficient repair procedure [1]. This paper addresses this need by studying localized laser-induced deposition of silicon dioxide and metallic thin films. Photo-induced deposition of high quality silicon dioxide films with SiH, and oxidizing coreactants using laser [8,9] and conventional UV sources [10-12] have been described in numerous references. Several other studies have also been reported with different organosilane precursors [9,13,14]. In all reported studies, however, radiation of 193 nm or shorter has been used or a photosensitizer has been applied [11,12]. These relatively short wavelengths had to be used since the investigated silicon compounds and coreactants had very weak adsorption cross sections above 200 nm. These processes, however, have drawbacks for several applications since they require expensive optical elements, compatible with this wavelength to be used. In this study, we report that deposition of high quality silicon dioxide is feasible at 248 nm with appropriate organosilane compounds. The optical properties of the deposits can be "tuned" by appropriately choosing the reactant, coreactants, and proper exposure conditions. From screening of numerous silicon compounds [15,16], three reactants have been identified that produce films of good optical quality at a reasonable rate of growth for practical laser 565 Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
exposures. The results are summarized in this paper, a detailed description of the work will be published elsewhere [15,16]. Laser-induced deposition of metallic films has been widely studied in the literature [17]. However optical properties, such as transmission and phase shift of these films, have received little attention so far. In this work, we concentrated on these optical parameters; the selection of the precursors and the optimization ofthe parameters were driven by matching the desired optical properties. EXPERIMENTAL The experimental setup, described in detail elsewhere [16], is briefly discussed here. A Lambda-Physik 2051 LPX laser operated at 248 nm was used as the radiation source. The light was homogenized with an Image Microsystems beam condenser and homogenizer and
was focused with an Ealing Optics Schwarzshield reflecting objective using either 15X or 36X magnification, depending on the resolution desired. The focused light was coupled into a gas cell through a 250 micron thick, 25 mm diameter quartz window. The size of the spot was varied with a variable aperture in both the x and y dimensions. The gas cell was mounted on a motorized translation stage and pumped with a turbomolecular pump. The base pressure was 5xl0 Torr. Polished quartz plates were typically used as substrates e
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