An exposure apparatus includes an exposure unit for exposing a wafer. The exposure unit includes an illumination system and masks. The illumination system includes a light-homogenizing unit. The light-homogenizing unit includes a light-homogenizing quartz rod having a regular hexagonal cross section. Each of the masks has a regular hexagonal shape matching with the cross section of the light-homogenizing quartz rod. A field of exposure resulting from this arrangement is less affected by objective field of view distortion and allows a higher useful depth of focus (UDoF) when compared to other fields of exposure of the same size. In addition, with the same projection objective DoF, a greater field of exposure can be obtained.