Optical double patterning allows for increased quality control over varying film stacks as well as allowing photolithography equipment to image smaller dense features. This is done by splitting dense patterns into two separate masks. A contact cut layer double patterning process was developed, and proved to be successful down to contact density of 4 μm CD by 4 μm density (4x4 μm CD x Density). Conventional dark field double patterning processes use two separate substrate etch steps (one etch step after each pass of lithography). This project developed a dark field double patterning process which incorporated light field double patterning techniques, which in effect eliminated one of the substrate etch steps by thermally curing the first pass of photoresist. Thermal cure temperatures of first pass resist were varied from 125°C to 200°C, finding that temperatures less than 175°C did not sufficiently cross-link the resist enough to stand up to the second pass of lithography, resulting in loss of first resist patterns. Temperatures greater than 175°C caused the first pass lithography to flow, resulting in the elimination/minimizing of contact cut feature densities less than 4x4 μm. A successful contact cut (dark field) double patterning process was developed; however feature densities were limited due to the incorporation of light field double patterning techniques.
Namestnik, William A.
"Process Design & Development of Contact Cut Double Patterning,"
Journal of the Microelectronic Engineering Conference: Vol. 18
, Article 11.
Available at: http://scholarworks.rit.edu/ritamec/vol18/iss1/11