INTEGRATED CIRCUITS

INTEGRATED CIRCUITSINTEGRATED CIRCUITS

In electronics, an integrated circuit (also In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon known as IC, microcircuit, microchip, silicon chip, or chip) is a miniaturized electronic chip, or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor circuit (consisting mainly of semiconductor devices, as well as passive components) that devices, as well as passive components) that has been manufactured in the surface of a thin has been manufactured in the surface of a thin substrate of semiconductor material. substrate of semiconductor material. Integrated circuits are used in almost all Integrated circuits are used in almost all electronic equipment in use today and have electronic equipment in use today and have revolutionized the world of electronics.revolutionized the world of electronics.The first integrated circuit

was developed in the 1950s by Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductor.

ADVANTAGES OF IC’SADVANTAGES OF IC’S

SMALL SIZESMALL SIZE LOW COSTLOW COST IMPROVED PERFORMANCEIMPROVED PERFORMANCE HIGH RELIABILITY AND RUGGEDNESSHIGH RELIABILITY AND RUGGEDNESS LOW POWER CONSUMPTIONLOW POWER CONSUMPTION LESS VULNERABILITY TO PARAMETER LESS VULNERABILITY TO PARAMETER

VARIATIONVARIATION EASY TROUBLESHOOTINGEASY TROUBLESHOOTING INCREASED OPERATING SPEEDINCREASED OPERATING SPEED LESS WEIGHT,VOLUMELESS WEIGHT,VOLUME EASY REPLACEMENTEASY REPLACEMENT

DISADVANTAGES OF DISADVANTAGES OF IC’SIC’S

AS IC IS SMALL IN SIZE ITS UNABLE TO AS IC IS SMALL IN SIZE ITS UNABLE TO DISSIPATE LARGE AMOUNT OF POWER. DISSIPATE LARGE AMOUNT OF POWER. INCREASE IN CURRENT MAY PRODUCE INCREASE IN CURRENT MAY PRODUCE ENOUGH HEAT WHICH MAY DESTROY THE ENOUGH HEAT WHICH MAY DESTROY THE DEVICE.DEVICE.

AT PRESENT COILS, INDUCTORS AND AT PRESENT COILS, INDUCTORS AND TRANSFORMERS CAN NOT BE PRODUCED IN TRANSFORMERS CAN NOT BE PRODUCED IN IC FORM.IC FORM.

CLASSIFICATION OF CLASSIFICATION OF IC’SIC’S

On the basis of On the basis of fabrication techniques usedused

On the basis of the On the basis of the chip size

On the basis of On the basis of applications

ON BASIS OF FABRICATIONON BASIS OF FABRICATION

Monolithic IC’sMonolithic IC’s

Thin and Thick Film IC’s.Thin and Thick Film IC’s.

Hybrid or Multi-chip ICs.Hybrid or Multi-chip ICs.

MONOLITHIC IC’SMONOLITHIC IC’S

Monolithic circuit is built into a single stone or single crystal i.e. in monolithic ICs, all circuit components, and their interconnections are formed into or on the top of a single chip of silicon. Monolithic ICs are by far the most common type of ICs used in practice, because of mass production , lower cost and higher reliability.

THIN AND THICK FILM THIN AND THICK FILM IC’SIC’SThese devices are larger than monolithic ICs but smaller than discrete circuits. These ICs can be used when power requirement is comparatively higher. With a thin-or thick-film IC, the passive components like resistors and capacitors are integrated, but the transistors and diodes are connected as discrete components to form a complete circuit. The essential difference between the thin- and thick-film ICs is not their relative thickness but the method of deposition of film. Both have similar appearance, properties and general characteristics.

HYBRID IC’SHYBRID IC’S

The circuit is fabricated by interconnecting a number of individual chips.

Hybrids ICs are widely used for high power audio amplifier applications .

Have better performance than monolithic ICs

Process is too expensive for mass production

ON BASIS OF CHIP SIZEON BASIS OF CHIP SIZE

SSI (small-scale integration)

MSI (medium-scale integration)

LSI (large-scale integration)

VLSI (very large-scale integration)

ULSI (ultra large-scale integration)

Small scale integration (SSI) has 3 to 30

gates/chip orUp to 100 electronic components

per chip

Medium scale integration (MSI) has

30 to 300 gates/chip or 100 to 3,000 electronic components per chip

SSI AND MSISSI AND MSI

LSI AND VLSILSI AND VLSI

Large scale integration (LSI)-300 to 3,000

gates/chip or 3,000 to 100,000 electronic

components per chip Very large scale

integration (VLSI)-more than 3,000 gates/chip or

100,000 to 1,000,000 electronic components per

chip

ULSIULSIUltra Large-Scale Integration (ULSI)- More than 1 million electronic components per chip The Intel 486 and Pentium microprocessors, for example, use ULSI technology. The line between VLSI and ULSI is vague.

ON BASIS OF ON BASIS OF APPLICATIONSAPPLICATIONS

LINEAR INTEGRATED CIRCUITSLINEAR INTEGRATED CIRCUITS

DIGITAL INTEGRATED CIRCUITSDIGITAL INTEGRATED CIRCUITS

LINEAR INTEGRATED LINEAR INTEGRATED CIRCUITSCIRCUITS

When the input and output When the input and output relationship of a circuit is relationship of a circuit is linear, linear, linear ICslinear ICs are used. are used. Input and output can take place Input and output can take place on a continuous range of values.on a continuous range of values.

Example operational Example operational amplifiers, power amplifiers, amplifiers, power amplifiers, microwave amplifiers microwave amplifiers multipliers etc.multipliers etc.

DIGITAL INTEGRATED DIGITAL INTEGRATED CIRCUITSCIRCUITS

When the circuit is either in on-state or off-state and not in between the two, the circuit is called the digital circuit. ICs used in such circuits are called the digital ICs. They find wide applications in computers and logic circuits.Example logic gates, flip flops, counters, microprocessors, memory chips etc.

FABRICATION STEPSFABRICATION STEPS

The base on which ic is formed is a The base on which ic is formed is a p-type substrate.p-type substrate.

The 2The 2ndnd layer is a thin layer grown as layer is a thin layer grown as single n-type crystal and also known single n-type crystal and also known as epitaxial growth. Active and as epitaxial growth. Active and passive devices of the circuits are passive devices of the circuits are formed in this layer by diffusion.formed in this layer by diffusion.

Selective diffusion is needed at each Selective diffusion is needed at each diffusion stage. diffusion stage.

SiO2 layer is formed on the top of SiO2 layer is formed on the top of epitaxial layer.epitaxial layer.

n+ emitter is diffused into p-type base n+ emitter is diffused into p-type base by photolithographic masking and by photolithographic masking and etching.etching.

Another SiO2 layering , masking and Another SiO2 layering , masking and etching exposes n+ and p areas for etching exposes n+ and p areas for forming metallic contacts.forming metallic contacts.

A thin Al layer is then deposited over A thin Al layer is then deposited over entire chip surface leaving inter & entire chip surface leaving inter & external connections, the rest of Al is external connections, the rest of Al is etched away.etched away.

EPITAXIAL GROWTHEPITAXIAL GROWTH

Epitaxial growth is the formation of layer of Si crystal with n-type doping as an extension of the existing p-type Si substrate. The process is carried in a reactor at 1000 C where finished wafers the inserted.

Si is obtained by breaking SiCl4 in presence of H2 :

SiCl4 + 2 H2 --> Si + 4 HCl

For n-type doping of epitaxial layer PH4 & N2 is fed to the reactor .

OXIDE GROWTHOXIDE GROWTH

SiO2 layer is grown and removed from surface of SiO2 layer is grown and removed from surface of silicon slice many times during manufacture of IC’ssilicon slice many times during manufacture of IC’s

Characteristics of SiO2 layer :Characteristics of SiO2 layer :• Acts as diffusion mask permitting selective Acts as diffusion mask permitting selective

diffusions into Si waferdiffusions into Si wafer• Used for surface passivation i.e. protecting Used for surface passivation i.e. protecting

junction from moisture and other atmospheric junction from moisture and other atmospheric contaminantscontaminants

• Used for insulating the metal interconnections Used for insulating the metal interconnections from Si from Si

The silicon wafers are kept in quartz boat and inserted into a quartz tube. the tube is heated to 1000-1200 C such that temperature is uniform along the length of tube. Nitrogen,dry oxygen, steam is passed over the slices to grow the oxide layer .

Si +O2 SiO2

The Process…The Process…

PHOTOLITHOGRAPHYPHOTOLITHOGRAPHY

Photolithography or Optical lithography, is a process used in micro fabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photo mask to a light-sensitive chemical photo resist, or simply "resist," on the substrate. A series of chemical treatments then engraves the exposure pattern into the material underneath the photo resist.

MASKING AND MASKING AND ETCHINGETCHING

During the photolithographic process the wafer is coated with a uniform film of a photosensitive emulsion such as KPR (Kodak photo resist). A large black-n-white layout of the desired pattern of opening is made and then reduced photographically. This negative (or stencil) of the required dimensions is placed as a mask over the photo resist. By exposing the KPR to UV light through the mask , the photo resist becomes polymerized under the transparent regions of the stencil .

The mask is now removed and wafer is developed using chemical (such as trichloroethylene) which dissolves the unexposed portion of the photo resist film. Now the chip is immersed in an etching solution of HCl, which removes the oxide from the areas through which dopants are to be diffused. After etching and diffusion of impurities , the resist mask is removed with a hot H2SO4.

FABRICATNG A FABRICATNG A MONOLITHIC CIRCUITMONOLITHIC CIRCUIT

1)1) Epitaxial Growth Epitaxial Growth

2)2) Isolation DiffusionIsolation Diffusion

3)3) Base DiffusionBase Diffusion

4)4) Emitter diffusionEmitter diffusion

5)5) Aluminum MetallizationAluminum Metallization

Fabrication steps involved are:

ISOLATION DIFFUSIONISOLATION DIFFUSION

Using photolithographic etching process , oxide is removed at four different places.The wafer is now subjected to so-called isolation diffusion where p-type impurities penetrate the n-type epitaxial layer from the above four places and reach the p-type substrate. N-type region left is known as isolated region because they are separated by two back-to-back p-n junctions. Their purpose is to allow electrical isolation between different circuit components.

BASE DIFFUSIONBASE DIFFUSION

During this process a new layer of oxide is formed over the wafer and the photolithographic process is used again to create the pattern of openings to diffuse p-type impurities (boron). In this way transistor base regions such as resistors , the anode of diodes , and junction capacitors are formed. The resistivity of base layer should be higher than that of the isolated regions.

EMITTER DIFFUSIONEMITTER DIFFUSION

A layer of oxide is again formed over the entire surface, and the masking and etching processes are used again to the windows in p-type region. Through these openings are diffused n-type impurities (phosphorus) for the formation of transistor emitter , the cathode regions for diode ,and junction capacitors.

ALUMINIUM ALUMINIUM METALIZATIONMETALIZATION

Metalisation is used to interconnect the various components of the IC. to make these connections, a fourth set of window is opened into a newly formed SiO2 layer at the points where contact is to be made. The interconnections are made using vacuum deposition of a thin even coating of Al over the entire wafer and undesirable Al areas are removed using photoresist technique.

VACUUM DEPOSITIONVACUUM DEPOSITION

MONOLITHIC DIODEMONOLITHIC DIODE

MONOLITHIC RESISTORMONOLITHIC RESISTOR

MONOLITHIC MONOLITHIC CAPACITORCAPACITOR

THIN FILM THIN FILM FABRICATIONFABRICATION

Vacuum evaporationVacuum evaporationPlating technique--Electroplating and ElectrolessplatingPlating technique--Electroplating and ElectrolessplatingSputtering-- material to be deposited on substrate is subjected to heavy Sputtering-- material to be deposited on substrate is subjected to heavy bombardment by the ions of a heavy inert gas.the atoms are given out from cathode, bombardment by the ions of a heavy inert gas.the atoms are given out from cathode, migrate away from cathode through low pressure inert gas and finally land on migrate away from cathode through low pressure inert gas and finally land on substratesubstrateScreening – uses screen woven from very fine silk threads and mounted on Al Screening – uses screen woven from very fine silk threads and mounted on Al frames. The screen is coated with photo sensitive emulsions. The screen is placed on frames. The screen is coated with photo sensitive emulsions. The screen is placed on substrate and components are deposited by driving squeegee across the patterned substrate and components are deposited by driving squeegee across the patterned screen.screen.

Thin films provide greater precision in component values. The film deposition can be done using any of the following methods:

Advantages of thin filmAdvantages of thin film

Good high frequency responseGood high frequency response

High component package densityHigh component package density

Resistors can be trimmed to Resistors can be trimmed to precisionprecision

Simple processing techniquesSimple processing techniques

THICK FILM THICK FILM FABRICATION FABRICATION

Thick film technology is used to Thick film technology is used to fabricate high density circuits fabricate high density circuits containing resistors, conductors and containing resistors, conductors and capacitors at low cost.capacitors at low cost.

The technique used for depositing The technique used for depositing thickfilmsthickfilms

over substrate involves:over substrate involves:

Screen printingScreen printing

Substrate firingSubstrate firing

Advantages of thick filmAdvantages of thick film

Low fabrication costLow fabrication cost Good high frequency responseGood high frequency response Very low tolerance cause of Very low tolerance cause of

trimmingtrimming Highly stable and reliableHighly stable and reliable Simple fabrication stepsSimple fabrication steps

DIFFUSIONDIFFUSION

Sputtering apparatusSputtering apparatus

HERE WE SIGN OFF...

WITH: