what is film uniformity and why does it matter

Film UNIFORMITY is how even the thickness (and other properties) is across the wafer — center vs edge, wafer to wafer. Why it matters: a non-uniform film means some die get a different thickness, which changes device performance — so a 'good average' can still mean bad die at the wafer edge. Measured with tools like ELLIPSOMETRY (your specialty — you were an SME). The key line: 'A GPS engineer reads the uniformity map like a vital sign — uniformity, not just the average, is what determines yield.' Why GPS cares: drift in uniformity is often the first signal of a chamber problem (temperature drift, target wear, chamber condition) — catching it early prevents a yield hit. Show you know how to measure it and what a drift means. This is a strong place to lead with your measurement background.