lec05_-_fabrication_process_-_basic - Copy

lec05_-_fabrication_process_-_basic - Copy -...

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1 Microelectronics (Part 2) Chapter 4: Fabrication Technology
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Course Outcomes CO2: to identify the sequences of fabrication process in constructing the physical layout of CMOS circuit Purpose To introduce the technology that is responsible for the semiconductor devices Number of enhancements to the basic CMOS technology are described 2
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CMOS Basics 4 MOS: Metal Oxide Semiconductor Transistors are built on a Silicon (semiconductor) substrate Pure silicon has no free carriers and conducts poorly Dopants are added to increase conductivity: extra electrons (n-type) or extra holes (p-type) MOS structure created by superimposing several layers of conducting, insulating and transistor-forming materials Metal gate has been replaced by polysilicon or poly in modern technologies There are two types of MOS transistors: nMOS : _________ doped silicon, rich in electrons pMOS : _________ doped silicon, rich in holes CMOS : both type of transistors are used to construct any gate
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CMOS Basics 5 nMOS and pMOS Four terminal devices: Source (S), Gate (G), Drain (D), body (substrate, bulk)
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CMOS Basics CMOS Inverter Cross-section
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7 Fabrication Technology
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8 The Elements Periodic Table
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9 The Elements Materials
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Dopants 10 Used to selectively change the conductivity of silicon Silicon: a semiconductorwith resistance between that of conductor and an insulator Adding dopants _________ to pure silicon increases the conductivity Group V: extra electronc (n-type) e.g Phophorous Group III: missing electron or hole (p-type) e.g. Boron Controlled amounts of impurities are added to the melt to enable the proper electrical properties
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11 Silicon Wafer Basic starting material is silicon wafer One side of the wafer is highly polished circuits are etched on this face Wafer is circular, with a flat edge which facilitates initial alignment Made from single crystal silicon, using a seed crystal of appropriate crystal alignment Finally the resulting cylinder of single crystal silicon is sliced into wafers One side of the wafer is processed to obtain several die or instances of the IC per wafer Diameter: 75 to 300 mm Thickness: 0.25 to 1.0 mm Crystal orientation determined by a seed crystals Ingot growth rate: 30 to 180 mm/hour
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