Imaging of NW placement for 10 nm and beyond

Abstract

Understanding of the accuracy of well (here, N-well or NW) placement is a key feature for device characterization and understanding of yield detractors. An analysis technique which provides quick turnaround and allows not only quick examination across large areas but also SEM resolution is needed. Failure analysis of an RX (active) Short in a < 14 nm serpentine/comb test structure indicated a junction problem. A novel yet simple technique for mapping junction profiles based on contrasts observed in low energy e-beam SEM voltage contrast (SEM-VC) was evaluated on carefully delayered samples. The test samples were also characterized by scanning capacitance microscopy (SCM) to correlate with SEM-VC results. The SEM-VC in one case exactly predicted the well image. However, further investigation showed that distinct SEM-VC features on other similarly delayered samples had nothing to do with the underlying junction profiles. For this reason, OBIRCH (Optical Beam Induced Resistance CHange) was used to determine areas of high and low leakage for an SRAM-like test structure.