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We developed an alternating phase shift mask that offers a sufficient phase accuracy for manufacturing sub-0.18 im devices with 248 nm deep-UV lithography. This mask has a Cr/spin-onglass/quartz structure. Our mask fabrication process utilizes some new techniques which include the use of an SOG shifter with extra thickness, a two step SOG etching, and an additional wet etching process for phase adjustment.Our process showed a good performance, and a phase controllability of 180 0.7 degree was achieved. Phase uniformity was less than 3 degrees over a 100 mm square area. It was nearly equal to the uniformity of the SOG thickness. These results prove that the additional etching process is very effective at improving phase accuracy.