|
Implementation of DUV (248 nm) into 0.25 micrometers production requires an understanding of the associated process complexity. With DUV resists, this encompasses addressing issues of profile integrity on various substrates, etch resistance, and adequate process margin to achieve optimum performance in production. A goal of implementing DUV processes directly into already established flows without modifications to substrates, forces the resolution to these issues. To investigate the ability of accomplishing this with DUV resists, this study concentrates on pattern capability over various bottom organic ARL (gate level) and TiN (metal) substrates. The first part of this study explores issues of resist profile integrity at the resist/ARL interface, resist and ARL etch rates and the resist/ARL systems are used. Improved performance over topography is also noted for specific resist/ARL combinations. Simulations of resist linewidth versus resist thickness show a large reduction in the swing curve amplitude for all ARLs with little difference in switch ratio between ARL materials. Experimental resist swing curves also demonstrate a large reduction in the resist swing curve for all ARLs. However, the resist profile at the ARL interface transitions from a very slight foot to a small undercut as resist thickness show similar capability between each ARL in suppressing standing waves, modeling shows that at least part of this profile change can be attributed to the phase and amplitude of the residual standing wave at the resists/ARL interface. Regarding process performance, a focus latitude of up to 1.0 micrometers with nearly vertical profiles is achieved for 0.25 micrometers equal lines and spaces. Etch rate results show a large difference between the materials with the ARL to resist ratios range from 0.7 to 1.2. The second part of this evaluation addresses patterning DUV resists on TiN/metal substrates. The amount of footing depends on the resist used and can be reduced for a given resist through process optimization. Using an optimized process for a given resist, a k1 factor of 0.53 is achieved with 1.1 micrometers of resist on TiN. Etch rate tests demonstrate adequate resist remaining after etching the full metal stack. These results demonstrate significant improvements in compatibility between DUV resist and new bottom organic ARLs or TiN. While fundamental issues that caused degradation of resist profiles have been reduced or eliminated, process flexibility is still limited by resist/substrate combinations that lead to poor performance. New generations of resists that overcome these compatibility issues allow for integration into existing flows without flow or substrate modifications. However, until more substrate tolerant DUV resists are developed, manufacturing with DUV will require layer specific resist processes.
|
