chapter 06 ic fabrication - an introduction

8/7/2019 Chapter 06 IC Fabrication - An Introduction

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IC Fabrication


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Semiconductor Applications

3C : Computer--- /Communication / Consumables

Personal Computer--- Desktop Computer (DT) /Notebook (NB)

Communication---ADSL / Cable Modem /

IEEE802.11X / Bluetooth / VoIP

Consumables---Game / DVD / Digital Camera

3C merge--- Digital Home


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Types of Chips

Dynamic Random Access Memory chips (DRAMs) -serve as the primary memory for computers

Microprocessors (MPUs) - act as the brains of computers.

Application Specific Integrated Circuits (ASICs) - arecustom semiconductors designed for very specific functions

Digital Signal Processors (DSPs) - process signals, suchas image and sound signals or radar pulses.

Programmablememory chips (EPROMs, EEPROMs,and Flash) - are used to perform functions that requireprogramming on the chip.


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Semiconductor Fabrication

Processes Front-End Processing (Wafer fabrication)

Back-End Processing (Assembly and

Testing)


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Logic Circuit Design / Layout Design

A logic circuit diagram is drawn to determine theelectronic circuit required for the requested function.

Once the logic circuit diagram is complete,simulations are performed multiple times to test thecircuits operation.


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Photomask Creation

The photomask is a copy of the circuit pattern,drawn on a glass plate coated with a metallic film.

The glass plate lets light pass, but themetallic filmdoes not.

Due to increasingly high integration andminiaturization of the pattern, the size of thephotomask is usually magnified four to ten timesthe actual size.


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Wafer Fabrication A high-purity, single-crystal silicon called

"99.999999999% (eleven-nine)" is grown from aseed to an ingot.

The wafers are generally available in diameters of150 mm, 200 mm, or 300 mm, and aremirror-

polished and rinsed before shipment from thewafer manufacturer.


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Deposition the wafer is placed in a high-temperature furnace to

make the silicon react with oxygen or water vapor, andto develop oxide films on the wafer surface (thermaloxidation).

To develop nitride films and polysilicon films, thechemical vapor deposition (CVD) method is used, in

which a gaseous reactant is introduced to the siliconsubstrate, and chemical reaction produce the depositedlayer material.

Themetallic layers used in the wiring of the circuit arealso formed by CVD, spattering (PVD: physical vapor

deposition)


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Photoresist Coating

A resin called "photoresist" is coated over theentire wafer. (~1m thick coating.)

Photoresist is a special resin similar inbehavior to photography films that changesproperties when exposed to light.


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Masking/Exposure

Placed over the photoresist-coated wafer, whichis then irradiated to have the circuit diagramtranscribed onto it.

An irradiation device called the "stepper" is usedto irradiate the wafer through themask withultraviolet (UV) light.


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Patterning: Development

The photoresist chemically reacts and dissolves in thedeveloping solution, only on the parts that were notmasked during exposure (positivemethod).

Development is performed with an alkalinedeveloping solution.

After the development, photoresist is left on thewafer surface in the shape of themask pattern.


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Etching

"Etching" refers to the physical or chemical etchingof oxide films and metallic films using the resistpattern as a mask.

Etching with liquid chemicals is called "wetetching" and etching with gas is called "dryetching".


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Photoresist Stripping

The photoresist remaining on the wafer surfaceis no longer necessary after etching is complete.Ashing by oxygen plasma or the likes is

performed to remove the residual photoresist.


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Device Insulation Layer (Field-OxideFilm) Formation

After the oxide film and nitride film are developed,a resist pattern is formed on the regions that willbecome the device insulation layer.

Ion implantation is performed on the wafer, forming

a p-type diffusion layer. Next, the oxide film and nitride film on the diffusion

layer areetched. Using the nitride film pattern as themask, the oxide

film that will become the device insulation layer isdeveloped.


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Transistor Formation

A transistor is a semiconductor device with aswitching function and three terminals:source, drain, and gate.

An insulation layer called "gate oxide" is firstformed on the wafer surface.

A polysilicon film is deposited onto the gateoxide, and a polysilicon gate for controllingthe flow of electrons between the sourceregion and the drain region is formed bylithography and etching.

After the polysilicon gate is formed, an n-type diffusion layer consisting of both thesource and the drain regions is formed byimplantation of impurities


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Polysilicon GateCross-Section Image


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Metallization Interconnecting the devices, such as transistors,

formed on the silicon wafer completes the circuit.

the wafer is first covered with a thick and flatinterlayer insulation film (oxide film). Next, contactholes are drilled by lithograph and etching, through

the interlayer insulation film, above the devices tobe connected.

Nine-layer Copper Interconnect Architecture


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Wafer Inspection

Each IC on the completed wafer is electronicallytested by the tester.

After this inspection, the front-end processing iscomplete.


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Mounting

After the IC chips are cut apart, theyare sealed into packages. The ICchips must first be attached to aplatform called the "lead frame.


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Wire bonding

Themounted IC chips are connected to thelead frames.


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Encapsulation

The IC chips and the lead frame islands areencapsulated with molding resin forprotection.


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Characteristic Selection

The packaged IC chips are tested and selected.


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Printing and Lead Finish

The final step of IC chip manufacturing is theprinting onto the package surface and thefinishing of leads. After this step, the ICchips are complete.


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THE END

chapter 06 ic fabrication - an introduction

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