With the reduction of feature size, until probably 0.13 micrometer generations, it is going to be patterned using a DUV illumination source at 248 nm. In these conditions, device development and manufacturing are occurring at ever decreasing k1 factor [k1 equals CD(NA/(lambda) )]. In this low-k1 region, degradation of image contrast brings about nonlinear amplification of mask CD error during image transferring on wafer. This phenomenon (ER; Error Ratio) is severely occurred when critical dimension is smaller than 0.5((lambda) /NA). In this paper, we investigated this phenomena with various condition such as critical dimension, density of L/S, mask type, and phase shift mask. Error ratio at defocused condition is also investigated. From this viewpoint, we discussed effect of mask CD error on wafer CD error and presented newly revised CD control criteria in each device generation. In addition, several strategy which should be considered for reducing error ratio and a photomask process technology for making next generation photomask satisfying high resolution and good CD control requirements has been described in view of low k1 lithography era.