ECE_5360_Lab__5 - Lab 5 Patterning the Source/Drain Contact...

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Lab # 5 Patterning the Source/Drain Contact Windows In this lab, you will receive your wafers back after a series of process steps have been completed for you. Since lab #4, these wafers have undergone: i) ion implantation, ii) a resist strip in a remote plasma “resist asher” system, and finally, iii) gate oxidation in a dry furnace. Today you will apply photoresist on top of your patterned field oxide/ implanted wafer and pattern the resist with the mask aligner. Now mask Level 3 must be aligned to the pattern of the ion implant (Level 2). A new set of alignment aids and verniers will be used. Once developed, the resist pattern on a transistor will be examined under the microscope in relationship to the etched Field Oxide pattern and the ion implant pattern. Finally, the Level 2 to 3 alignment error will be measured (at the wafer center) using the verniers on the masks. Depending on the Reactive Ion Etcher (RIE) status we will either wet etch or RIE etch the windows in the gate oxide. The wet etch instructions appear below. The dry RIE etch instructions will be provided if the tool comes on line in time! Lab Preparation:(prior to entering lab) 1) Review instructions given on the MA-6 alignment procedures from Lab #4. 2) Anticipate what the microscope images (Level 2 implant pattern + Level 3 resist pattern) on the transistor. 3) Locate the correct sets of verniers for Level 3 placement accuracy (see Figure 2). 4) Estimate the etch time of the gate oxide assuming it is 70 nm in thickness. Use the etch rate of the BOE solution obtained in Lab # 3 when the field oxide was wet etched. Lab Experiment: (in the lab) 1. Ion Implantation - Performed by an outside vendor. And even the TAs aren’t allowed to handle PH 3 . The wafers were processed with the following specifications. a. NMOS Wafers on p-type substrates were implanted with Phosphorous: - Acceleration Potential - 150 keV - Implant Dose – 1 x 10 -16 cm −2 - Beam Tilt - 7 o PH 3 is the phosphorous source of the P +31 species. The beam tilt minimizes the effects of ion channeling. 2. Resist Removal - Performed by the TAs a. After exposure to the extreme heat generated in the ion implantation process, the photoresist will no longer dissolve in most laboratory solvents. At this point, a plasma process is the most effective way to remove the resist. The wafers were loaded into an Aura 1000 resist asher. This tool has two chambers. In the first chamber, an O 2 plasma is generated with a microwave source; this generates oxygen radicals and ozone. The
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second chamber is where the wafer sits, and is connected to the first via a pipe and valve.
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ECE_5360_Lab__5 - Lab 5 Patterning the Source/Drain Contact...

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