In this paper advanced OPC (Optical Proximity Correction) methods, additional with assistant features, and non-obvious
methods were implemented to correct aberrations caused by aggressive illuminations in order to optimize the shape of
the finger tips. OPC model and simulations were verified using 2D verification method.
Inverse Lithography Technology (ILT), a mask creation technique with a decades-long history, has the potential for improving pattern fidelity and lithographic process window for features in dense memory ce lls (such as SRAM) for 100nm and 65nm nodes and beyond. Currently, the quality of OPC/RET/DfM/DfY methodology is verified based on CD
measurements. However, these measurements are not comprehensive enough, limited to a very few layout features. It is desirable to confirm lithographic process window robustly, for all the cell design features of interest, to ensure full functionality of the cell. In this work, we propose for the first time to focus on the electrical deliverables after ILT pattern quality has been initially verified by SEM visual inspection. We designed an electrically measurable SRAM
structure for a 65 nm process, to extract device and interconnect parameters depending on the lithographic process conditions, as a means to compare pattern quality of the conventional mask creation technique, Optical Proximity Correction (OPC) with ILT. We present the drawn layout, the masks created by the two technologies, and the
corresponding image simulation and silicon pattern.
In spite of the advantages of low cost and resistance, dual damascene process has some problems. When contact holes are patterned within the trench patterns, the contact holes are frequently found to be unopen and are bent toward trench side wall (TSW). These cause CD variation and small depth of focus. We can explain this phenomenon in view of limited resolution of photoresist (PR) and the light reflected from the TSW. The deeper the trench depth is, the thicker the thickness of the photoresist for contact hole patterns is, which leads to decreased resolution. And the light reflected off the TSW makes the contact hole's profile bent toward TSW. This reflected light influences on both sides. One is helpful in defining the contact holes near the TSW, and the other causes CD variations according to distance between the contact holes and TSW. If the contact holes and trench patterns are exactly the same sizes, it is possible to decrease the CD variation and to prevent PR contact holes from unopening within the trench patterns. Also it is of help to improve resolution at the bottom of the PR.