Abstract
The application of an attenuated PSM for printing contact hole layers is one way to extend the useful lifetimes of an I-line stepper. The development of such a process needs to consider more than just the traditional parameters. Selecting the optimum mask CD bias, stepper NA, sigma, exposure, and focus, is even more critical than for the process using conventional binary masks due to sidelobe printing with attenuated PSM. Using an electrical CD measurement technique, this study was able to evaluated process latitude at various stepper and mask bias settings, at one point and at sixteen points per field. One of the resists tested showed 0.85 micrometers depth of focus and > 20% exposure latitude for 0.30 micrometers contacts on 0.75 micrometers pitch. The overlapping process window at sixteen points per field is much smaller than that at only one point per field, justifying the need for such an evaluation. Full wafer CD mapping allowed us to quantify across wafer and across field CD variation. Though the electrical measurements exhibited excellent correlation with SEM measurements (R2 equals 0.994), it is still necessary to verify a chosen process under SEM inspection to evaluate the resist profile for any artifacts such as sidelobe printing.
