ECE_5360_Lab__3 - Lab # 3: Field Oxide Characterization,...

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In this lab, you will receive your wafers back after they have been oxidized in the wet furnace in CNF. You will characterize the oxide by using a spectrophotometer. This will yield the oxide thickness. Then you will then apply photoresist on top of this oxide using the spinner and then pattern the resist with the mask aligner. The TA will then perform a wet oxide etch using a HF solution. You will then strip the photoresist and leave the wafer in the lab for next week’s work. Lab Experiment: (in the lab) 1. Field Oxide Characterization a. Visual Inspection - Color Chart : A crude estimate of oxide thickness can be obtained using the color chart given below in Figure 1. Verfiy your oxide color is correct for a field oxide thickness of 765 nm. b. Filmetrics measurement – Measure the oxide thickness at the usual 5 points, as you did last week. Figure 1. Color Chart of Thermally Grown SiO2 (courtesy of IBM).
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2. Field Oxide Patterning – Background. Defining the Active Areas. First let us examine the full mask layout which is shown in Figure 2. Figure 2. Mask layout with all four levels shown.
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This pattern is repeated 49 times, in a 7 by 7 array on your 4” substrate. The location of transistors, diodes, resistors alignment aids, verniers, etc. is as indicated. In this lab, we will focus on the reproduction of the verniers. Patterning of the field oxide is used to define the active regions for transistors of the gate electrode, and the extent of the source/drain regions. For diodes, the field oxide is etched away to make contacts and define the diode area. Where the probe pads and interconnects exist, the Al metallization is on top of the field oxide. The resulting MOS capacitor from the metallization/field oxide/semiconductor must have a threshold voltage much larger in magnitude than the corresponding MOS capacitor formed on the gate oxide. (Operating the transistor at voltages where the semiconductor under the field oxide is not inverted or driven into accumulation.) This is accomplished making the field oxide roughly ten times thicker than the gate oxide. As a plasma etch would be slow for an oxide of this thickness, we will use a wet HF-based chemical etch to remove the field oxide in selected areas. 3. Field Oxide Patterning – Procedures: a. Resist spinning – same procedure as last week. Measure the resist thickness at the usual 5 points. b. Resist exposure – same procedure as last week. c. Resist development – same procedure as last week. 4. Pattern Inspection and Verification
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ECE_5360_Lab__3 - Lab # 3: Field Oxide Characterization,...

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