Demonstration of ACO-Based Freeform Source for ArF Laser Immersion Lithography System

This paper describes the use of ArF immersion lithography to verify the feasibility of a self-developed freeform illumination source that exposes features on masks and forms resist patterns. After development inspection (ADI) was used to measure the results and inspect whether the critical dimension (CD), process window, line-edge roughness (LER), and line-width roughness (LWR) of the resist pattern attained the standards of existing manufacturing processes. The testing features include nine horizontal and eight vertical features. Ant colony optimization (ACO) can provide optimal freeform illumination sources for these horizontal and vertical features. This paper considers each feature's particular weighting in order to test the complexity and adaptability of the ACO algorithm applied to semiconductor manufacturing processes. The results of source calculations show that all 17 testing features can be satisfied with the X symmetry freeform source. When using this freeform source in an ArF lithography system, the ADI resist CD of all testing features is located within ±10% target CD tolerance. The ADI target CD set by dense patterns is 40 nm. Resist pattern ADI CD measurements show that, under a through-focus condition, the resist pattern CD between 40 and 42 nm is within tolerance, the depth of focus can reach up to 0.1 μm , LER is approximately 5 nm, and LWR is approximately 7 nm. These ADI CD measurements show that this ACO-based freeform source can be integrated into existing advanced semiconductor lithography processes.