Metrology and analysis

What is placed on the wafer to measure overlay error?

  1. ABond pads
  2. BNotch
  3. CDedicated overlay measurement marks
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Answer: C. Dedicated overlay measurement marks

To measure overlay accuracy, dedicated marks (targets) combining patterns from the previous and current layers are made in places such as the scribe lines around chips. Optical metrology tools measure their relative positions to determine the misalignment, which is also used to correct the exposure tool.

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More Metrology and analysis questions

  1. Which technique directs X-rays at a very shallow angle and determines thin-film thickness and density from oscillations in reflectivity?
  2. Which method is used to measure wafer bow, warp and flatness?
  3. Which technique evaluates whether a measuring instrument's repeatability and reproducibility are small enough compared with the process variation to be controlled?
  4. What is the main reason fine patterns a few tens of nm wide cannot be observed directly with an optical microscope?
  5. Which equation is used to determine film stress from the change in wafer bow before and after deposition?