An exposure system with group compensation. The exposure system includes a lot
classification database, a compensation unit and a first exposure device. The lot
classification database records a group classification of at least one lot wafer.
The compensation unit obtains the group classification of the lot wafer from the
lot classification database, retrieves a group compensation value according to
the group classification, and compensates overlay parameters according to the group
compensation value. The first exposure device performs a back-end process including
overlay and exposure processes on the lot wafer using the compensated overlay parameters.