The control of edge placement error (EPE) is playing key role in the patterning of advanced technology node in semiconductor industry. EPE is evaluated by the metric of overlay, distance of patterns between two layers in multi patterning, and patterning error in local area. In past instance, overlay between upper layer and underlayer was measured by electron beam (e-beam) metrology system with scanning electron microscopy (SEM) image.
EPE which is caused by local patterning error on photoresist layer is influenced by scanner tool parameters such as focus and exposure. Technology and method of EPE measurement on photoresist layer is highly required to optimize scanner tool performance.
This study provides the measurement method of EPE on photoresist layer resulting from variation of scanner tool condition. Definition of EPE in this study is the distance between contour of SEM pattern and contour of target layout. Die to Database (D2DB) technology which compares image and layout data was applied to this study with large image size which include huge number of patterns. The advantage of the method was confirmed by the experiment on the verification of local patterning error.
The result of the experiment shows scanner tool conditions are well represented by these local patterning errors. In addition, optimizing scanner parameters and monitoring scanner condition by these local patterning errors are proposed.
Severe process margin in advanced technology node of semiconductor device is controlled by e-beam metrology system and e-beam inspection system with scanning electron microscopy (SEM) image. By using SEM, larger area image with higher image quality is required to collect massive amount of data for metrology and to detect defect in a large area for inspection. Although photoresist is the one of the critical process in semiconductor device manufacturing, observing photoresist pattern by SEM image is crucial and troublesome especially in the case of large image. The charging effect by e-beam irradiation on photoresist pattern causes deterioration of image quality, and it affect CD variation on metrology system and causes difficulties to continue defect inspection in a long time for a large area. In this study, we established a quantitative approach for optimizing e-beam condition with “Die to Database” algorithm of NGR3500 on photoresist pattern to minimize charging effect. And we enhanced the performance of measurement and inspection on photoresist pattern by using optimized e-beam condition. NGR3500 is the geometry verification system based on “Die to Database” algorithm which compares SEM image with design data . By comparing SEM image and design data, key performance indicator (KPI) of SEM image such as "Sharpness", "S/N", "Gray level variation in FOV", "Image shift" can be retrieved. These KPIs were analyzed with different e-beam conditions which consist of “Landing Energy”, “Probe Current”, “Scanning Speed” and “Scanning Method”, and the best e-beam condition could be achieved with maximum image quality, maximum scanning speed and minimum image shift. On this quantitative approach of optimizing e-beam condition, we could observe dependency of SEM condition on photoresist charging. By using optimized e-beam condition, measurement could be continued on photoresist pattern over 24 hours stably. KPIs of SEM image proved image quality during measurement and inspection was stabled enough.