Photoresist Material Gap Filling Loading Improvement from Pattern Density Perspective

As the advanced technology node driven forward and critical dimension (CD) reduction, the critical pattern process window decreases drastically, mainly for the depth of focus (DOF). In the development of process, pattern peeling always occurred due to pattern best focus shift which best focus is different from the critical pattern or exceed the common DOF. The fluctuant substrate tends to be the root cause. Usually, the incoming substrate topography local pattern density affects the photoresist materials gap filling performance, further leads to best focus shift, and this loading variation can't be compensated by the Scanner or covered by the small DOF. Therefore, photoresist materials planarization improvement is very important. In this paper, we studied the effect of pattern density dependent spin-on carbon (SOC) loading on best focus, the result was SOC loading improved and the pattern peeling issue solved by optimizing the pattern design, while only improving process condition seems difficult to improve the SOC loading or planarization. Various types of SOC with different planarization capability and coating process optimization study showed SOC planarization had its limit. In the aspect of SOC planarization improvement, holistic pattern design must be considered to avoid the process issue.