Developing a new lithographic process routinely involves usage of lithographic toolsets and much engineering time to perform data analysis. Process transfers between fabs occur quite often. One of the key assumptions made is that lithographic settings are equivalent from one fab to another and that the transfer is fluid. In some cases, that is far from the truth. Differences in tools can change the proximity effect seen in low k1 imaging processes. If you use model based optical proximity correction (MBOPC), then a model built in one fab will not work under the same conditions at another fab. This results in many wafers being patterned to try and match a baseline response. Even if matching is achieved, there is no guarantee that optimal lithographic responses are met. In this paper, we discuss the approach used to transfer and develop new lithographic processes and define MBOPC builds for the new lithographic process in Fab B which was transferred from a similar lithographic process in Fab A. By using PROLITHTM simulations to match OPC models for each level, minimal downtime in wafer processing was observed. Source Mask Optimization (SMO) was also used to optimize lithographic processes using novel inverse lithography techniques (ILT) to simultaneously optimize mask bias, depth of focus (DOF), exposure latitude (EL) and mask error enhancement factor (MEEF) for critical designs for each level.
Evaluation of contact holes ranging from 0.35 micrometers to 0.7 micrometers for a number of i-line photoresists and attenuated phase-shift reticles has been completed. The study compared the effects of different photoresists patterned with a binary reticle as well as attenuated phase-shift reticles having transmission levels of 6%, 8%, and 12%. The measures of contact performance used to compare resist/reticles are focus budget, exposure latitude, and resolution. From the data collected, a large process window for sub half-micron contacts is demonstrated by using an optimum resist/reticle combination. With phase-shift, an increase in focus budget is realized with the amount of improvement dependent on the resist and transmission of the reticle. The resolution capability of all of the resists is improved by using phase-shift, although, phase-shift did not affect the linearity of the resists. Data collected points to the importance of optimizing the resist process with transmission level and applying the proper bias to maximize the focus budget.
Extending i-line lithography to 0.35 micrometers processing is a realistic possibility because of improvements in photoresists, steppers, track equipment, and reticle technology. The manufacturing of 0.35 micrometers devices can include as many as twenty lithography levels, however, most of the critical issues can be addressed in printing the gate and contact levels. The optimized process for 0.35$ mum gates and contacts is presented in this paper. Even with advanced photoresists, enhancement techniques were needed to meet the processing requirements for these two levels on actual topography. The enhancement techniques used for the gate level were a TARC and modified illumination. A TARC was required to improve linewidth uniformity, and modified illumination to improve focus budget and exposure latitude. For contacts, attenuated phase shift was required to achieve workable focus latitude. The data presented shows that an optimized i-line resist processes with enhancement techniques can meet the requirements of volume production of 0.35 micrometers devices.
Phase shift has been seen by many as a route to increase the resolution capability of optical microlithography beyond the Rayleigh criterion. The initial enthusiasm with which this technology was greeted has been moderated by the realization that prior to its practical application many technical challenges must be overcome. Nevertheless progress has been made. The question to be answered is no longer whether phase shift works, but rather which phase-shift approach and manufacturing technique provide the best practical solutions. We compare three techniques to build alternating phase-shift reticles: (1) deposited spin-on glass (SOG), (2) chemical vapor deposition (CVD) silicon dioxide, and (3) etched quartz. The merits of each approach are judged in terms of lithographic performance, ease of manufacture, and reliability. We condude that the SOG approach offers the best short-term solution to the manufacture of alternating phase-shift masks, although its lithographic performance is somewhat inferior to the other two and its long-term reliability remains to be determined. For deposited oxide to be a viable long-term approach, the oxide must be deposited under the chrome; for etched quartz, the roughness and defect density must be controlled.