Residual oxide detection with automated E-beam inspection

Shrinking contact design rules and increasingly higher aspect ratios have dramatically decreased the process window for photo and etch engineers. Optimizing the proper amount of overetch to clear all contacts while not inducing overetch damage is an ongoing process variable. Production compatible automated E-beam inspections, utilizing voltage contrast (VC) methods, have demonstrated the capability to detect underetched contacts, however the question always remains, "how much remaining oxide is in the underetched contacts?". This proposed method takes inspection results one step further and attempts to measure the gray scale difference between a defect and a known good reference, (KGRef), and associate a remaining oxide thickness to the defective contact. The KGRef in this inspection is a "dark" contact with a lighter background, while defective contacts appear "bright".