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EE143quiz1-fri-ans - .renniht ti sekam gnihcte-revo...

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EE 143: Lab Quiz 1 Fall 2008, University of California, Berkeley Name: Section: Fri 9-12 1. Why was it important to soak the wafers in Piranha before putting them in the oxidation furnace? (2 points) 2. a) Which type of oxidation (wet or dry) was used to grow the field oxide on the bare wafer? Why? (1 point) b) Which type did we use to grow the gate oxide ? Why? (1 point) 3. Suppose the (dark field) mask shown below is used to expose a negative resist on a wafer, which is then developed, etched, and stripped of PR. If the resulting line is thinner than it was supposed to be, then the wafer was probably: (2 points) over-etched under-etched 4. During oxidation, we pushed wafers into the furnace very slowly. Why should we do this? (2 points) 5. Given the following mask and wafer cross section, draw a single cross section showing the final state after all of the following (and only the following) have been done: exposing, developing, hard bake, HF wet etching (at least until bare Si is reached):
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