New photomask patterning method based on KrF stepper

To solve the very low throughput of an e-beam writer in mask fabrication, a new patterning method based on a step-and-repeat exposure system, that is a photomask repeater, has been developed. In this paper, we intended to clarify the feasibility of 0.15 micrometers generation mask fabrication with the KrF photomask repeater. Inter-field registration accuracy (3sigma) in the photomask repeater is 14.9 nm in X direction and 29.1 nm in Y direction and can meet the registration specification (30 nm) of a 0.15 micrometers generation mask. Intra-field mis-registration caused by stepper lens distortion is 14 nm (3sigma) in X direction and 12 nm in Y direction for a 12 mm X 12 mm field and gets larger with an increase of a field size. Inter-field CD uniformity (3sigma) is 15.7 nm in 122.5 mm X122.5 mm mask area and intra-field CD uniformity is 10.3 nm in 12 mm X 12 mm field area. The sum of inter-field and intra-field value in the KrF photomask repeater don't currently satisfy the 30 nm registration and 15 nm CD uniformity specification of a 0.15 micrometers generation mask. So we need to reduce the registration and CD errors with optimizing PR coating and development process, using a small field size and compensating the errors of intra-field factors to a mother mask.