Layer patterning using double exposure processes in a single photoresist layer

A structure fabrication method, comprising:

• forming a structure which includes (a) a to-be-patterned layer, (b) a photoresist layer on top of the to-be-patterned layer wherein the photoresist layer includes a first opening, and (c) a cap region on side walls of the first opening, wherein a first top surface of the to-be-patterned layer is exposed to a surrounding ambient through the first opening, wherein said forming the structure comprises:
• providing the to-be-patterned layer,
• forming the photoresist layer on and in direct physical contact with the to-be-patterned layer wherein the photoresist layer comprises a photoresist material,
• performing a first lithography process on the photoresist layer by:
• selectively exposing the first region to light to make the first region soluble in a first photoresist developer;
• and exposing the structure to the first photoresist developer to form the first opening in the first region by the first photoresist developer developing away the photoresist material in the first region,
• forming a cap layer on top of the photoresist layer such that the cap layer fills the first opening wherein the cap layer comprises a first portion on the side walls of the first opening, and
• baking the cap layer resulting in residual photo acids diffusing from the photoresist layer into the first portion of the cap layer which transforms the first portion of the cap layer into the cap region;
• and
• after said forming the structure, performing a second lithography process by:
• selectively exposing a second region to light to make the second region soluble in a second photoresist developer and exposing the structure to the second photoresist developer to form a second opening in the second region by the second photoresist developer developing away the photoresist material in the second region, wherein the cap region is insoluble in the second photoresist developer and is not developed away by the second photoresist developer when exposed to the second photoresist developer via said exposing, wherein the first region and the second region are in distinctly different locations within the photoresist layer, and wherein a second top surface of the to-be-patterned layer is exposed to the surrounding ambient through the second opening.