IC Fabrication - An Introduction

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 Jau-Wen Lin, Ph. D.

Integrated circuit showing Integrated circuit showing memory blocks, logic and memory blocks, logic and input/output pads around input/output pads around the periphery

Integrated circuit showing Integrated circuit showing memory blocks, logic and memory blocks, logic and input/output pads around input/output pads around the periphery

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_{ix Level of}

 drain      

IC device

Silicon chip High lead solder die attach

Tin/lead plated copper  leadframe

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_{emiconductor Applications}

 3C : Computer---

/Communication / Consumables

 Personal Computer---

Desktop Computer (DT) / Notebook (NB)



Communication---ADS_{L / Cable Modem /}

IEEE802.11X / Bluetooth / VoIP



Consumables---Game / DVD / Digital Camera

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

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_{pecific Integrated Circuits (A}

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_ICs)

-

are custom semiconductors designed for very specific

functions

 Digital

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_{ignal Processors (D}

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_Ps)

-

_{process signals,}

such as image and sound signals or radar pulses.

 Programmable memory chips (EPROMs,

EEPROMs, and Flash)

- are used to perform functions that require programming on the chip.

 Front-End Processing (Wafer fabrication)

 Back-End Processing (Assembly and

Testing)

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_{emiconductor Fabrication}

A logic circuit diagram is drawn to determine the electronic circuit required for the requested function. Once the logic circuit diagram is complete,

simulations are performed multiple times to test the circuit·s operation.

Logic Circuit Design / Layout

Design

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 the metallic film

does not.

 Due to increasingly high integration and

miniaturization of the pattern, the size of the

photomask is usually magnified four to ten times the actual size.

The

photomask of a RF _IC

Wafer Fabrication

 A high-purity, single-crystal silicon called

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

 The wafers are generally available in diameters of 150 mm, 200 mm, or 300 mm, and are

mirror-polished and rinsed before shipment from the wafer manufacturer.

Deposition

 the wafer is placed in a high-temperature furnace to make the silicon react with oxygen or water vapor, and to develop oxide films on the wafer surface (thermal oxidation).

 To develop nitride films and polysilicon films, the chemical vapor deposition (CVD) method is used, in which a gaseous reactant is introduced to the silicon substrate, and chemical reaction produce the deposited layer material.

 The metallic layers used in the wiring of the circuit are also formed by CVD, spattering (PVD: physical vapor deposition)

Photoresist Coating

 A resin called "photoresist" is coated over the entire wafer. (~1m thick coating.)

 Photoresist is a special resin similar in

behavior to photography films that changes properties when exposed to light.

Masking/Exposure

 Placed over the photoresist-coated wafer, which is then irradiated to have the circuit diagram

transcribed onto it.

 An irradiation device called the "stepper" is used to irradiate the wafer through the mask with

Patterning: Development

 The photoresist chemically reacts and dissolves in the developing solution, only on the parts that were not masked during exposure (positive method).

 Development is performed with an alkaline developing solution.

 After the development, photoresist is left on the wafer surface in the shape of the mask pattern.

Etching

 "Etching" refers to the physical or chemical etching of oxide films and metallic films using the resist

pattern as a mask.

 Etching with liquid chemicals is called "wet etching" and etching with gas is called "dry etching".

Photoresist

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_tripping

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

Device Insulation Layer

(Field-Oxide Film) Formation

 After the oxide film and nitride film are

developed, a resist pattern is formed on the regions that will become 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 are etched.

 Using the nitride film pattern as the mask, the oxide film that will become the device insulation layer is developed.

Transistor Formation

 A transistor is a semiconductor device with a switching function and three terminals:

source, drain, and gate.

 An insulation layer called "gate oxide" is first formed on the wafer surface.

 A polysilicon film is deposited onto the gate oxide, and a polysilicon gate for controlling the flow of electrons between the source

region and the drain region is formed by lithography and etching.

 After the polysilicon gate is formed, an n-type diffusion layer consisting of both the source and the drain regions is formed by implantation of impurities

Polysilicon Gate

Metallization

 Interconnecting the devices, such as transistors, formed on the silicon wafer completes the circuit.  the wafer is first covered with a thick and flat

interlayer insulation film (oxide film). Next, contact holes are drilled by lithograph and etching, through the interlayer insulation film, above the devices to be connected.

Wafer Inspection

 Each IC on the completed wafer is electronically tested by the tester.

 After this inspection, the front-end processing is complete.

Dicing

 In back end processing, a wafer completed in front end processing is cut into individual IC chips and encapsulated into packages.

Mounting

 After the IC chips are cut apart, they are sealed into packages. The IC

chips must first be attached to a platform called the "lead frame´.

Wire bonding

 The mounted IC chips are connected to the lead frames.

Encapsulation

 The IC chips and the lead frame islands are encapsulated with molding resin for

Characteristic

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_election

 The packaged IC chips are tested and selected.