Methods for detecting incidence orthogonality of a patterned beam in charged-particle-beam (CPB) microlithography, and CPB microlithography systems that perform same

In a charged-particle-beam (CPB) microlithography method, in which a pattern is defined on a segmented reticle divided into multiple subfields, the subfields are illuminated individually by an illumination beam to form a patterned beam, the patterned beam is projected to form corresponding subfield images on a lithographic substrate, and the subfield images are stitched together on the substrate to form a transferred pattern on the substrate, a method for determining an incidence orthogonality of the patterned beam on the substrate, the method comprising:

• (a) placing a first reticle fiducial mark on a movable body located at a reticle plane, the movable body being laterally placeable at each of first and second laterally displaced positions on the reticle plane;
• (b) passing a charged particle beam through the first reticle fiducial mark at each of the two laterally displaced positions to form respective laterally spaced-apart images of the first reticle fiducial mark at each of first and second locations situated near a substrate plane, wherein the first and second locations are separated from each other in an optical-axis direction by a distance (ΔH), and measuring a lateral distance (L1, L2) between the respective first and second images of the first reticle fiducial mark at each of the first and second locations, respectively;
• and
• (c) determining the incidence-orthogonality error (Δθ) at the substrate surface by calculating Δθ=(L1−L2)/2ΔH for the first reticle fiducial mark.

A charged-particle-beam (CPB) microlithography apparatus for transferring a pattern to a substrate from a segmented reticle divided into multiple subfields defining respective portions of the pattern, the apparatus comprising:

• an illumination-optical system situated and configured to direct a charged-particle illumination beam from a source to individual subfields of the reticle, thereby forming a patterned beam propagating downstream from the reticle while carrying an aerial image of an illuminated subfield of the reticle;
• a projection-optical system situated downstream of the illumination-optical system and configured to direct the patterned beam to a lithographic substrate to form respective images, corresponding to the aerial images, stitched together on the substrate to form a transferred pattern on the substrate;
• a reticle stage, situated downstream of the illumination-optical system, for holding the reticle at a reticle plane during illumination of the subfields by the illumination beam;
• and
• an incidence-orthogonality detector, comprising (a) first and second reticle fiducial marks situated on the reticle stage and being spaced apart laterally from each other at the reticle plane;
• (b) a substrate fiducial mark situated downstream of the projection-optical system near a substrate plane, the substrate fiducial mark being placeable selectively at first and second lateral positions at each of first and second locations situated near the substrate plane, wherein the first and second locations are separated from each other in an optical-axis direction by a distance (ΔH);
• (c) a deflector situated and configured to deflect respective patterned beams, produced by passage of the illumination beam through the first and second reticle fiducial marks and to scan the patterned beams, carrying respective images of the first and second reticle fiducial marks, on the substrate fiducial mark at the first and second lateral positions, respectively, at each of the first and second locations;
• (d) measurement means for measuring a lateral distance (L1, L2) between the respective images of the first and second reticle fiducial marks at each of the first and second locations, respectively;
• and (e) determination means for determining, from L1, L2, and ΔH, an incidence orthogonality (Δθ) of the patterned beam at the substrate plane, according to an expression Δθ=(L1−L2)/2ΔH.

A charged-particle-beam (CPB) microlithography apparatus for transferring a pattern to a substrate from a segmented reticle divided into multiple subfields defining respective portions of the pattern, the apparatus comprising:

• an illumination-optical system situated and configured to direct a charged-particle illumination beam from a source to individual subfields of the reticle, thereby forming a patterned beam propagating downstream from the reticle while carrying an aerial image of an illuminated subfield of the reticle;
• a projection-optical system situated downstream of the illumination-optical system and configured to direct the patterned beam to a lithographic substrate to form respective images, corresponding to the aerial images, stitched together on the substrate to form a transferred pattern on the substrate;
• a reticle stage situated downstream of the illumination-optical system, for holding the reticle at a reticle plane during illumination of the subfields by the illumination beam;
• a substrate stage situated downstream of the projection-optical system, for holding the substrate at a substrate plane during transfer of respective images of the subfields to corresponding locations on a lithographic substrate;
• and
• an incidence-orthogonality detector, comprising (a) a first reticle fiducial mark situated on the reticle stage, the reticle stage being laterally movable so as to place the first reticle fiducial mark selectively at each of first and second laterally displaced positions on the reticle plane;
• (b) a first substrate fiducial mark situated on the substrate stage, the substrate stage being laterally movable so as to place the first substrate fiducial mark selectively at each of first and second laterally displaced positions near the substrate plane, the first substrate fiducial mark being placeable selectively at first and second locations near the substrate plane but separated from each other in an optical-axis direction by a distance (ΔH);
• (c) a deflector situated and configured to deflect the patterned beam, produced by passage of the illumination beam through the first reticle fiducial mark, and to scan the patterned beam, carrying an aerial image of the first reticle fiducial mark, on the substrate fiducial mark at the first and second lateral positions, respectively, at each of the first and second locations;
• (d) measurement means for measuring a lateral distance (L1, L2) between the image of the first reticle fiducial mark at each of the first and second locations, respectively;
• and (e) determination means for determining, from L1, L2, and ΔH, an incidence orthogonality (Δθ) of the patterned beam at the substrate plane, according to an expression Δθ=(L1−L2)/2ΔH.