A dry-etch step is used to etch 1.0 µm of polysilicon. A sample of five wafers is measured each hour. It is expected that over time the lower electrode of the etcher will become contaminated and ohmic contact with the wafer will therefore deteriorate, decreasing the etch rate. The electrode is cleaned before the first and seventh samples. The measured etch rate is given below. Draw a 2σ regression chart for this process.
