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課程名稱：微製造技術Microfabrication Technology

授課教師：王東安Lecture 1

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Course Overview

•Lecture 1 Introduction to microfabrication•Lectures 2-4 Lithographic techniques•Lectures 5-6 Vacuum science and etching•Lectures 7-10 Thin film processes•Lectures 11-12 Micromachining processes•Lecture 13 MEMS devicesTextbook: Stephen A. Campbell, The Science and Engineering of

Microelectronic Fabrication, Oxford University Press, 2001Reference: M. J. Madou, Fundamentals of Microfabrication,

CRC, 2002

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Goals of this course

•Introduce microfabrication techniques•Perspective on MEMS research and devices

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Related Courses at IPE

•Thin film engineering 薄膜工程•Nano fabrication technology 奈米加工技術•Epitaxy engineering 磊晶工程

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Course Mechanics

•Lectures: Monday 9:10-noonM106 精密館

•Homework: Due the following Monday at 9:10am•Exam: Two midterms and Final exam•Oral Report: Select one research paper related to

microfabrication, approved by the instructor. Present the paperat the end of the term.

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Course Mechanics (Cont.)

•Office hours: R358 電機大樓 Mondays 2-3pm•Credit breakdown (approximate)

20% homework20% midterm I20% midterm II20% final exam20% oral report

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Lecture Outline

•Reading Campbell: Chapter 1•Today’s lecture

–Definition of MicroFabrication–Historical tour of microfabrication–Fabrication process of microelectronics–Substrate material

•Phase diagram•Crystal structure•Czochralski growth•Wafer specifications

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Definition of MicroFabrication

•Fabrication of devices with at least some oftheir dimensions in the micrometer range.

•Techniques:–IC methods–Micromolding–Wire electrodischarge machining–Laser machining–Ion- and electron-beam machining–CNC milling

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History of Batch Fabrication Technology

•Planar integrated circuit technology 1958 –•Thin film deposition and etching•A few m on top of the substrate

•CMOS integrated circuits technology enables thedevelopment of MEMS by 1980

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Progress of Silicon Microelectronics

• Density increase by increments of4X every 3 years.

• Most fundamental changes in thefabrication process: Minimumfeature size can be printed in thechip.

• Shorter distances that electronsand holes travel improvetransistor speed.

• Pack transistors together, decreasethe parasitic capacitance.

• ICs progressed from 10 um tounder 1 um.

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Example-A Resistor Voltage Divider

•A re

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Example-Fabrication Process

•Substrate: Siliconwafer

•Grow a thermal oxideof Silicon to preventleakage betweenresistors

•Deposit a conductinglayer for resistors

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Photolithography

•Transfer pattern fromphotomask to wafer

•Optical lithography: spreadphotoresist on wafer,expose photoresist, develop,Etch the film withoutsignificantly attack theresist.

•After etching, rinse wafer,remove resist.

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Unit Processes for Thin FilmDeposition

•Sputtering: using charged articles of ions to bombarda target containing the deposition material. The targeterodes and falls onto the wafer.

•Evaporation: Heating material to be deposited tocreate a vapor stream, coating wafer placed in thestream.

•Chemical vapor deposition: Gasses are flown into achamber containing heated wafer. A chemicalreaction occurs that leaves the desired film on wafer.

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Doping –n-channel MOSFET

•A blanket insulator•A patterned metal

layer•Selectively dope

source and drainregions.

•Dopants are donors(n-type) oracceptors (p-type)

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Doping Techniques

•Diffusion: introduce impurities by exposingheated wafer to a dopant containing gas.

•Ion implantation: Accelerate a beam of ionizedatoms/molecules toward the wafer.

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Epitaxial Growth

•Grow thin layers of semiconductor on top ofthe wafer.

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Roadmap of the Course

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Why Substrate Matters?

•Diffusion depends on crystalline perfection inwafer, which in tern depends on processtemperature.

•Solid solubility and the doping ofsemiconductors crystals

•Crystal structures and defects in crystallinematerials

•Three classes of materials: single crystal,amorphous materials, polycrystalline

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Phase Diagram

•Most materials aremixtures of materials.

•Phase diagram: away to presentproperties ofmixtures of materials

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Ex. 2.1 Calculate fraction of 50%charge that is molten at 1150oC

•x: fraction of thecharge that is molten

•1-x: fraction of thecharge that is solid

•0.5=0.22*x+0.58*(1-x)

•x=0.22•22% of the charge is

molten, 78% is solid

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Phase diagram for GaAs

•Intermetallics: twosolid phases thatmelt to form asingle liquid phase

•Compound GaAs

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Phase diagram for As-Si

•Solid solubility: Maximumconcentration of an impuritythat can be dissolved inanother material underequilibrium conditions

•Solvus curve•Solid solubility of As in Si

is comparatively large->Ascan be used to form veryheavily doped and lowresistance regions such assource and drain contactsfor MOS transistors

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Solid solubility of Si impurities•Doping concentration exceed solid solubility by

quenching.

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Three types of cubic crystals

•Direction: [xyz]•Plane: (xyz)•Equivalent

planes: {xyz}

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Three types of cubic crystals

•Cubic symmetry: witheach edge of the unitcell being the samelength.

• In a crystal with cubicsymmetry, (100) (010)(001) planes have thesame properties, theonly difference is anarbitrary choice ofcoordinate system.

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Diamond structure: Si, Ge

•Group IV elements:need 4 morevalence electronsto complete theirvalence shell. Incrystal, this is doneby formingcovalent bondswith 4 nearestneighbor atoms.

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Semiconductor defects

•Four types of defects–Point

•Vacancy•Interstitial•Substitution impurity•Dislocation: sign of stress

–Line–Area–Volume

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Movement of edge dislocation•Result of shear stress

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Area defect

•Stacking fault

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Czochralski growth

•The technique to producemost of the crystals fromwhich wafers are cut–Solidification of a crystal

from a melt

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Bridgman growth of GaAs

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Wafer specification•Primary flat: perpendicular to <110> direction•Minor flat:

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