Etch process monitoring possibilities and root cause analysis

Tilt of the shallow trench isolation on the wafer edge with the radial signature is a known issue for all technology nodes. Presence of this tilt was proven by cross-sectional TEM measurements. For advanced nodes, starting from 28 nm, this tilt becomes one of the crucial yield-killer strongly influencing the performance of the edge dies. If this tilt is not corrected for, overlay values of all FEOL layers will include an error on the wafer edge which leads to low performance of the devices and possibly yield loss. The etch process is thought to be responsible for the tilt, however even for the simplest stack the mechanism and reason of the tilt is not clear. The ability to monitor this tilt in production opens a way for understanding this mechanism and even eliminate the root cause. In this paper we will present the opportunity to measure with Spectroscopic critical dimension (SCD) and Overlay-Accuracy flags the asymmetry of tilted etch structures as well as identify the possible root cause of the tilt by monitoring the nanotopography before and after the etch process.