Since high-NA extreme ultraviolet (EUV) exposure tools have a half field size, two masks are necessary for exposing a large device which is larger than the half field of 26 mm × 16.5 mm. However, it takes long time until exposing the 2nd half field since the 2nd mask would be loaded after exposing the 1st half fields on many wafers. This may cause poor characteristics at the stitching area. Therefore, an introduction of a two-mask stage is proposed. This can drastically reduce the time until exposing the 2nd half field. However, since a conventional scan with two masks makes two separate exposed areas, a new scan method is necessary in order to contact the two half fields.
|