Process window variation comparison between NTD and PTD for various contact type

As technology node has been shrinking for bit growth, various technologies have been developed for high productivity. Nevertheless, lithography technology is close to its limit. In order to overcome these limits, EUV(Extreme Ultraviolet Lithography) and DSA(Directed Self-Assembly) are being developed, but there still exists problems for mass production. Currently, all lithography technology developments focus on solving the problems related to fine patterning and widening process window. One of the technologies is NTD(Negative Tone Development) which uses inverse development compared to PTD(Positive Tone Development). The exposed area is eliminated by positive developer in PTD, whereas the exposed area is remained in NTD. It is well known that NTD has better characteristics compared to PTD in terms of DOF(Depth of Focus) margin, MEEF(Mask Error Enhancement Factor), and LER(Line End Roughness) for both small contact holes and isolated spaces [1]. Contact hole patterning is especially more difficult than space patterning because of the lower image contrast and smaller process window [2]. Thus, we have focused on the trend of both NTD and PTD contact hole patterns in various environments. We have analyzed optical performance of both NTD and PTD according to size and pitch by SMO(Source Mask Optimization) software. Moreover, the simulation result of NTD process was compared with the NTD wafer level performance and the process window variation of NTD was characterized through both results. This result will be a good guideline to avoid DoF loss when using NTD process for contact layers with various contact types. In this paper, we studied the impact of different sources on various combinations of pattern sizes and pitches while estimating DOF trends aside from source and pattern types.