US Patent 7807342 Transmission mask with differential attenuation to improve ISO-dense proximity

An apparatus, system and method to compensate for the proximity effects in the imaging of patterns in a photolithography process. A light exposure of a photoresist layer is effectuated in predetermined patterns through an exposure mask having light-transmissive openings in correspondence to the predetermined patterns. The exposure mask has areas densely populated with the light-transmissive openings and areas sparsely populated with the light-transmissive openings. Light is attenuated through the densely populated light-transmissive openings by a different amount than through the sparsely populated light-transmissive openings.