KrF photolithography is difficult to attain usable process window for sub-100nm patterning due to the limitation from both the illumination and resist chemistry. For sub-0.15um FLASH process, sub-100nm trench, which is the smallest critical dimension to be resolved, becomes a real challenge to use conventional KrF lithography. REAPS (Resolution Enhance Assisted by Physical Shrinkage) process, utilizing the physical reaction catalyzed by the temperature in the patterned resist, is originally developed to enhance the resolution for contact hole in DRAM process. Instead of direct printing desirable feature using KrF process, REAPS treats the printed pattern by coating a water-soluble polymer upon patterned resist. This applying polymer layer provides a physical drive force to iso-tropically deform the resist patterns through controlled thermal process. Although REAPS process is an effective resolution enhancement technology to extend KrF lithography capability to even smaller dimension, its shrinkage performance and process window heavily depend on accurately temperature control of hot plate. To overcome the drawbacks of high temperature sensitivity of pattern shrinkage and achieve stable process control ability, a study on appropriate temperature setting and multi-step REAPS was carried out, and our results illustrate REAPS is applicable to isolated trench process and a sub-100nm trench can be achieved by this approach.
A double exposure technology, SPADE (Single Photo-resist And Double Exposure), utilizes the total accumulation resist energy exposing by different masks for pattern development. This "SPADE" process is a double exposure procedure that including resist coating, baking, first mask exposure, and second mask exposure and developer. This paper examines the process condition affecting the performance of ROM codes. We found that the first exposure with pre-code dense pattern is one of most critical parameters to affect the performance of the CD bias and resolution. Additionally, the second mask for real code pattern developer was also investigated in different mask CD size split. The final ROM code CD behavior is determined by both of the two masks. The results of these studies are discussed in term of mask type, exposure dosage, mask sizing and overlay sensitivity. Experimental results indicate that the iso-dense CD bias is smaller than traditional method. The energy latitude (E.L.%) also shows double than that of traditional ones.