Your question is Causes of Non-Uniform Wafer Heating. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
What can cause a heater to supply non-uniform heating to a wafer?
Keep your answer focused on the physical and control reasons a wafer can see temperature variation across its surface. You can mention examples from semiconductor processing equipment, but do not turn it into a troubleshooting checklist.
The interviewer is checking whether you can distinguish heater design issues, wafer-to-heater coupling problems, and control or sensor problems. Stay at the level of thermal fundamentals and practical equipment behavior.