Laser-assisted CD correction system for EUV masks is developed in order to satisfy the enhanced uniformity requirement for EUV layers. Based on the very nature of chemical reactions, the reaction rate between the EUV mask absorber and wet etchant is controlled to develop EUV mask CD correction system. The CD correction facility is developed by selective temperature control through local laser illumination including considerations on laser wavelength, beam size, position precision under wet etching solution environment, resulting in ultra-fine control of wet etch rate to obtain a process. The process developed is expected to play an important role in EUV productivity as it is the only technology that can respond to specification requiring extreme CD quality control of EUV masks.
We have observed a new type haze of which formation deviates from the generally accepted models with respect to the size, shape, and removability by chemicals. It has very small size of 50~100nm and are crowded around the cell boundary, while the typical haze doesn’t prefer a special region on mask in the majority of cases. It is hard to remove by general cleaning, while the typical haze is easily removed by general cleaning process and even de-ionized water. It is confirmed that the source of the haze is blank material related ions which are formed by chemical etching of blanks during mask cleaning process or the photomask blanks itself.
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