One of the process types etches material from the wafer surface (we are talking about a material layer thickness measured in atoms). If the etching is not stopp

One of the process types etches material from the wafer surface (we are talking about a material layer thickness measured in atoms). If the etching is not stopped or quenched in time due to a control system failure, the wafer is 'over etched' and unrecoverable. One former employer, a semi equipment company, had a weekly Monday Morning 'Crash Report'. Our tools performed a wet chemistry etch step on 25 wafers at at time. If the control system failed, the entire lot was in peril. So Monday AM, we'd hear from the CEO which fab managers had called him over the weekend, screaming about the value of the wafers our tools had destroyed. Usually in the $50,000 - $250,000 range. Fun times.