FinFET-induced Anisotropy in Printing of Implantation Shapes

摘要

In advanced technological nodes, the photoresist absorbs light, which is reflected by underlying topography during optical lithography of implantation layers. Anti-reflective coating (ARC) helps to suppress the reflections, but ARC removal may damage transistors, not to mention its relatively high cost. Therefore ARC is usually not used, and topography modeling becomes obligatory for printing implantation shapes. Furthermore, presence of Fin Field Effect Transistors (FinFETs) makes modeling of non-uniform substrate reflections exceptionally challenging. In realistic designs, the same implantation shape may be found in a vertical or in a rotated horizontal orientation. This creates two types of relationships between the critical dimension (CD) and FinFET, namely parallel to and perpendicular to the fins. The measurement data shows that CDs differ between these two orientations. This discrepancy is also revealed by our Rigorous Optical Topography simulator. Numerical experiments demonstrate that the shape orientation may introduce CD differences of up to 45 nm with a 248 nm illumination for 14 nm technology. These differences are highly dependent on the enclosure (distance between implantation shape and active area). One of the major causes of the differences is that in the parallel orientation the shape is facing solid sidewalls of fins, while the perpendicular oriented shape "sees" only perforated sidewalls of the fin structure, which reflect much less energy. Meticulously stated numerical experiments helped us to thoroughly understand anisotropic behavior of CD measurement. This allowed us to more accurately account for FinFET-related topography effects in the compact implantation modeling for optical proximity corrections (OPC). This improvement is validated against wafer measurement data.