All the technical questions were pretty straight forward. If you know your field, it shouldn't be a problem. Some of the interviewers have no interest in leading you/helping you out, which can be a pain if their question is not very clear. The most difficult question: an inspection tool is flagged as generating particles on a wafer. The tool has numerous chambers and the wafer gets charged when chucked. I was asked how I would determine which part of the inspection process was generating particles, whether charging itself caused particles or if the particles were generated on the way in or out. After answering this, he reframed it in such a way as the particle source was ambiguous, making me come up with a means of isolating the real source. I couldn't figure this out on the fly and he explained his logic to me. I tend to process things in my head, but they're looking to hear how you would work through the problem.