A Comparison of Endpoint Methods in Advanced Photomask Etch Applications

摘要

To achieve and eventually surpass the 90 nm design rules described in the ITRS roadmap, precise control of etch process endpoint is necessary. To this end, the authors have conducted a study comparing various photomask endpoint schemes, including reflectance laser endpoint, traditional optical emission spectroscopy (OES) endpoint, and OES endpoint employing various statistical techniques. A series of experiments were performed to determine the best combination of process and spectrometer to optimize the signal to noise ratio. Using this combination, a series of masks with exposed Cr loads ranging from 0.5% to 20% were etched. Sensitivity (represented by signal-to-noise ratio) and repeatability was analyzed for each endpoint technique. A discussion of the relative strengths and weaknesses of each technique is included.