Detailed placement for improved depth of focus and CD control

Sub-resolution assist features (SRAFs) provide an absolutely essential technique for critical dimension (CD) control and process window enhancement in subwavelength lithography. However, as focus levels change during manufacturing, CDs at a given "legal" pitch can fail to achieve manufacturing tolerances required for adequate yield. Furthermore, adoption of off-axis illumination (OAI) and SRAF techniques to enhance resolution at minimum pitch worsens printability of patterns at other pitches. This paper describes a novel dynamic programming-based technique for assist-feature correctness (AFCorr) in detailed placement of standard-cell designs. For benchmark designs in 130 nm and 90 nm technologies, AFCorr achieves improved depth of focus and substantial improvement in CD control with negligible timing, area, or CPU overhead. The advantages of AFCorr are expected to increase in future technology nodes.