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Unformatted text preview: reached): (2 points) Answer Key We use positive photoresist. The areas exposed to light become weakened and are dissolved in developer. Wet oxidation was used, since we needed a very thick layer that didnt have to be high quality. Wet oxidation grows more quickly, but produces lower quality oxide. We used dry oxidation since we wanted to controllably grow a thin, high quality oxide layer. Dry oxidation is slower, but produces a denser oxide with better electrical performance. Pushing the wafers and boat into the hottest part of the furnace (the middle) too quickly could result in thermal shock, causing warping or cracking of the wafers or the boat due to uneven thermal expansion. HF wet etch is isotropic: lateral etch = vertical etch PR doesnt get etched, and we havent stripped it yet. This leads to undercut and a curved SiO 2 profile. The faster rotation rate creates a thinner coating in the same amount of time....
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- Spring '08