Projection-microlithography alignment method utilizing mask with separate mask substrates

A method for aligning a mask-pattern image and for projecting a corrected mask-pattern image onto a sensitized surface of a sensitive substrate on a substrate stage using a charged-particle-beam pattern-transfer apparatus, the method comprising the steps of:

• (a) providing a mask comprising a mask-pattern defined by a plurality of mask reticles, wherein each mask reticle comprises a separate respective mask substrate and the pattern defined by each mask reticle being segmented into multiple mask-reticle subfields, the mask further comprising a retention member to which the plurality of mask reticles comprising the separate respective mask substrates are secured, a fiducial mark on the retention member, respective fine-alignment marks formed on the mask reticles at prescribed locations, and a reference mark formed on a substrate stage immediately adjacent to the sensitive substrate;
• (b) before mounting the mask in a pattern-transfer apparatus for the purpose of projection-exposing the pattern defined by the mask reticle onto the sensitive substrate, determining a design position of at least one of the mask reticles relative to the retention member;
• (c) storing data, corresponding to the determined design position of the at least one mask reticle relative to the retention member, in a memory;
• (d) mounting the mask on a mask stage in the pattern-transfer apparatus;
• (e) determining an actual position of the retention member relative the sensitive substrate by detecting positions of the fiducial mark located on the retention member and detecting the position of the reference mark on the substrate stage;
• (f) recalling the design-position data of each mask reticle relative to the retention member, and comparing the actual-position data of the retention member relative to the sensitive substrate with the design-position data of each mask reticle relative to the retention member to obtain data concerning a type and amount of correction required to make the positions of selected mask-reticle subfields coincide with the position of corresponding sensitive substrate subfields, the correction being to at least one of scaling, rotation, and position errors resulting from distortion or movement of the mask reticles;
• (g) based on the data determined in step (f), moving the mask stage, moving the substrate stage, or altering a characteristic of the charged-particle beam to correct the at least one of scaling, rotation, and position errors by the determined correction amount;
• and
• (h) exposing a selected mask subfield using the corrected charged-particle beam to form an image of the mask subfield on the corresponding sensitive substrate subfield.