Laser spectrum requirements for tight CD control at advanced logic technology nodes

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Tight circuit CD control in a photolithographic process has become increasingly critical particularly for advanced process nodes below 32nm, not only because of its impact on device performance but also because the CD control requirements are approaching the limits of measurement capability. Process stability relies on tight control of every factor which may impact the photolithographic performance. The variation of circuit CD depends on many factors, for example, CD uniformity on reticles, focus and dose errors, lens aberrations, partial coherence variation, photoresist performance and changes in laser spectrum. Laser bandwidth and illumination partial coherence are two significant contributors to the proximity CD portion of the scanner CD budget. It has been reported that bandwidth can contribute to as much as 9% of the available CD budget, which is equivalent to ~0.5nm at the 32nm node. In this paper, we are going to focus on the contributions of key laser parameters e.g. spectral shape and bandwidth, on circuit CD variation for an advanced node logic device. These key laser parameters will be input into the photolithography simulator, Prolith, to calculate their impacts on circuit CD variation. Stable though-pitch proximity behavior is one of the critical topics for foundry products, and will also be described in the paper.