Quantifying EUV imaging tolerances for the 70, 50, and 35 nm modes through rigorous aerial image simulations

According to the International Technology Roadmap (ITRS) EUV exposure tools are expected to support both logic and memory manufacturing for the 70 nm node and beyond. In order to meet the CD control and overlay requirements at the expected tolerance levels for high volume manufacturing, tool performance from ideal need to be assessed and quantified. The impact of lens aberrations and flare to the aerial image at the system level were studied for three different technology nodes of interest: 70, 50, and 35 nm. This was done by computing the electric field at the mask level by making use of a rigorous mask simulator based on the differential method. The subsequent aerial image was then computed by using a standard scalar imaging model. The effects on critical dimensions (CDs) through focus as well as overlay were investigated in order to arrive at a tolerance level for lens aberration and flare contribution at the system level. It is shown that isolated line CD control requirements set an upper limit on the overall imaging performance while for overlay both feature types seem to play a similar role that defines the tolerance limit. Mandating a 10% CD control range leads to a 30 milli Wave (RMS) aberration requirement. This conclusion was reached by analyzing the response of each of 37 Zernike coefficients separately for both isolated and nested lines. Employing two separate sets of KrF PMI data that were scaled to a range of RMS values seemed to further reinforce the previous aberration tolerancing conclusion. A separate but similar flare analysis indicates that cross field flare variations need to be controlled to within 2% to meet CD control requirements that are consistent with ITRS roadmap.