Method for monitoring lateral encroachment of spacer process on a CD SEM

A process implementing steps for determining encroachment of a spacer structure in a semiconductor device having thick and thin spacer regions, including a transition region formed therebetween. The method steps comprise: obtaining a line width roughness (LWR) measurement at at least one location along each thick, thin and transition spacer regions; determining a threshold LWR measurement value based on the LWR measurements; defining a region of interest (ROI) and obtaining a further LWR measurement in the ROI; comparing the LWR measurement in the ROI against the threshold LWR measurement value; and, notifying a user that either encroachment of the spacer structure is present when the LWR measurement in the ROI is below the threshold LWR measurement value, or that no encroachment of the spacer structure is present when the LWR measurement in the ROI is above the threshold LWR measurement value.