Standing wave reduction of positive and negative I-line resists.

Implantation layers may require smaller resist thickness as chip dimensions decrease. When reducing the thickness below 800 nm, while keeping all other track and exposure settings the same, standing waves in positive and negative I-line resists become more prominent. Bottom antireflective coating helps reducing the amplitude of the waves, but additional efforts, like BARC open RIE steps, or more coater units on the track, will increase the cost of ownership significantly. One may also consider changing the bake settings, which play a critical role in the formation of standing waves. The standard settings used for mid UV resists are 90 deg post apply bake (PAB) and 110 deg post exposure bake (PEB). Although resist suppliers recommend staying within this temperature range, we have used settings outside the range, as part of testing for possible profile ameliorations. Optimized settings for both tones were achieved with a different combination of the two bakes. The overall performances of the tested samples with optimized settings were satisfying in terms of CD range, stability and process window.