Dual exposure patterning of a photomask to print a contact, a via or a curvilinear shape on an integrated circuit

A method, comprising:

• forming a first square shape with photomask writing equipment, using a first sub-threshold dosage of an energy beam on a photoresist layer of a photomask substrate;
• forming an overlapping second square shape equal in size to the first square shape with the photomask writing equipment using a second sub-threshold dosage on the photoresist layer, the second square shape being rotated relative to the first square shape to form a regular octagonal overlap area, that exposes the photoresist layer to at least a threshold dosage;
• and
• forming a photomask, based on developing the exposed photoresist layer, to provide optical transmission corresponding to the regular octagonal overlap area of at least the threshold dosage, which closely approximates a circle.

A system, comprising:

• integrated circuit (IC) design software that provides a physical layout of any of a contact, a via, and a curvilinear shape;
• and
• photomask writing equipment that:
• forms a first rectangular shape using a first sub-threshold dosage of an energy beam on a photoresist layer of a photomask substrate, based on the physical layout;
• forms an overlapping second rectangular shape using a second sub-threshold dosage on the photoresist layer, the second rectangular shape being rotated relative to the first rectangular shape to form one of:
• a hexagonal overlap area and an octagonal overlap area, that exposes the photoresist layer to at least a threshold dosage, based on the physical layout;
• and
• forms a photomask, based on developing the exposed photoresist layer, to provide optical transmission corresponding to the one of:
• the hexagonal overlap area of at least the threshold dosage and the octagonal overlap area of at least the threshold dosage.