85 arranged in rows and columns each of the patterns 82 to 85 corresponds to a complete display device not to a portion of a display device the patterns 82 to 85 are transferred to the substrate 4 by a photolithography technique the mask 81 includes gap measuring windows 2 near the corners thereof around the array of the patterns 82 to 85 the windows 2 are transparent regions that allow the laser beams 7 to pass therethrough to determine the gaps between the mask 81 and the substrate 4 near the corners thereof a gap measuring windows 2 d through 2 h are additionally disposed on the mask 81 to allow laser beams to pass therethrough to determine the gaps between the mask 81 and the substrate 4 in the middle region thereof the gap measuring window 2 d is disposed in a non patterned region between patterns 82 and 83 and the gap measuring window 2 e is disposed in a non patterned region between patterns 84 and 85 the gap measuring window 2 f is disposed in a non patterned region between patterns 82 and 84 and the gap measuring window 2 g is disposed in a non pattern region between patterns 83 and 85 the gap measuring window 2 h is disposed at.