Study and Fabricate of Reflectance Coating for UV Lithography Machine Arc Lampshade

Abstract

As one of the key components in lithography, the UV light source has very high demands for wavelength of source and energy. To meet the requirements of UV light source, it demands UV reflectance coating prepared on 78mm Mg-Al alloy paraboloid lampshade . Based on design theory of film, H4 and SiO2 were selected as high and low refractive index materials respectively, and with the help of TFCalc, adopting electron beam vacuum coating method, the reflectance coating was prepared, which satisfied the requirements of reflectivity greater than 98.5% within band of 365-436nm in the case of 0o-45o incident angles. First the reflective band width was broadened through the coating stack; then according to the thickness distribution of film, compensation baffle was designed and modified, which ensured the uniformity of reflectance coating in the lampshade. And last, firmness of coating was strengthened and the reflectivity in the required band was improved by depositing one bonding layer of metal between Mg-Al alloy and dielectric film. By repeated trials, coating absorption problem was solved by changing the process parameters and coating quality of film was improved with the use of ion source assisted deposition, finally the UV film meets the requirements for use.