Transistor layout configuration effect on actual gate LER

Abstract

ABSTRACT The importance of Line Edge Roughness (LER) and Line Width Roughness (LWR) has long surpassed its effect on process control. As devices scale down, the roughness effects have become a major hindrance for further advancement along Moore’s law. Many studies have been co nducted over the years on the sensitivity of LER to various changes in the materials and the process, which have been c onsidered the main way to tack le the problem – especially through Photoresist improvement. However, despite the incr eased development of DFM tools in recent years, limited research was done as to LER sensitivity to layout, and th e research that was done was limited to proximity effects. In this paper, we study the sensitivity of LER to the layout around the transistor, defined by the gate structure of poly over AA (Active Area). Using different types and geometries of transistors, we found that the poly-gate LER is sensitive to the structure of the Active Area around it (source/dr ain from gate to contact, both shape and length). Using local LER measurement (moving standard deviation of poly edge location), we found a clear correlation between LER value and the length of the AA/STI boundary located at a close range. Longer AA edges yield higher LER, as proved by comparing gate LER of dog-bone transistor with classical transistor. Based on these results, we suggest that LER is sensitive not only to proximity effects, but also to the layout of underlying layers, through the effect of light scattering of the edges during the lithographic process.