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What is an IC [integrated circuit] - PowerPoint PPT Presentation


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What is an IC ? [integrated circuit]. A IC consists of many functional blocks depending on its functionality. Every block again have its own functionality with sub blocks in it. If we express the same in technical terms Every

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What is an IC ?

[integrated circuit]


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A IC consists of many functional blocks depending

on its functionality.

Every block again have its own functionality

with sub blocks in it


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If we express the same in technical terms Every

block according to its functionality have an internal circuit

Ex # like an op amp

With in every block there will be sub-blocks performing

some functions

Ex # like a gate

This sub block even have individual components connected

in such a way to achieve a specific function

Ex # transistor


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Once a circuit is designed according to its functionality then

we go for the physical implementation.

If the circuit is small and if consists of a few transistors we

can even implement it with hand

But these days every functional circuit consists of a hundreds

of thousands of transistors which is not possible to lay them

out with hand and interconnecting them

So we use a very large scale integrated circuit (VLSI) technology


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This physical implementation of a circuit using then

VlSI technology can be classified in to three categories

1) CUSTOM VLSI DESIGN

2) SEMI CUSTOM VLSI DESIGN

3)PROGRAMABLE LOGIC DESIGN


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CUSTOM VLSI DESIGN then

In CUSTOM VLSI design each and every component

of the circuit will be placed and routed according to the

functionality of the circuit.

This make this design very complex and time consuming

resulting in a very high NRE costs

But the main advantage of this design is maximum

optimization of the circuit which results in less power

consumption and faster speed of functionality


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SEMI-CUSTOM VLSI DESIGN then

In Semi Custom VLSI design we use already built standard

cells or gate arrays

That is the common logic functional blocks which were already built

will be interconnected and used

This results in reducing the design time and layout time

considerably .But the disadvantage of these kind of design

is that maximum optimization of the circuit is not possible

which results in high power consumption and less speed in

performing the function


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PROGRAMABLE LOGIC DEVICE then

In this method we have already built blocks called

programmable logic Device (PLD)

In this method every PLD is connected to each and every gate

present in the block

programming of these kind of IC is done by using a

nonvolatile or volatile memory technology,or by using antifuse

technology

The main disadvantage of this method is that there will be

many unwanted elements which consumes more power

resulting in bad functioning of the circuit


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Now we will look at the way how an IC is laid then

out by using different technologies

EX# 0.18u technology,0.25u,0.35u….etc


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What is a technology ? then

Technology is a set of rules which the designer

follows for laying out a design

This gives all the set of rules which we should

Follow in order to get desiered functionality

This specifies the distance that is to be maintained

Between two layers or two components in a chip


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mask then

Mask layout

mask

Structural

design

mask

Layering

on

silicon

mask

Layout

design

mask

Wafer

resting

mask

Chip cutout/

packaging


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chip then

ingot

Silicon wafer


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Etching of oxide: Wet etching then

  • It employs a liquid solution that dissolves oxide only.

  • Mostly buffered Hydrofluoric acid is used.

  • The wafer is immersed in plastic tank containing HF.

  • It produces sloping sidewalls under photoresist, because of isotropic etching by HF acid.


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Nitride then

Pad

Oxide

Nitride

Window

Thick

Oxide

Bird’s

Beak

Local oxidation of silicon (LOCOS)

  • It allows selective growth of thick oxide layers.

  • A thin pad oxide is grown for protection from mechanical stresses.

  • A nitride film is produced on pad by chemical vapor deposition.

  • The nitride is patterned to expose the regions to be selectively oxidized.

  • Then it is oxidized.

  • The nitride layer is then stripped off.


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Oxide then

Depression

Before Oxidation

After Oxidation

Oxide Step

  • It is the surface discontinuity produced due to difference in oxide thickness and in the depths of the silicon surfaces.

  • The reason being repeated oxidation and etching to form masking layers.


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N-type dopant then

source

Oxide Window

Oxide

Step 2: Deposit dopant

Step 1: Oxide removal

Step 3: Drive in dopant

P-type

silicon

N-type diffusion

Fabrication of diode (planar process)

  • Oxide film is grown and photo lithographically patterned and etched.

  • A dopant source is spun onto the wafer to touch the silicon

  • Wafers are heated in furnace to drive dopant into silicon, which forms shallow counterdoped regions.

  • The finished wafer is diced to form hundreds of diodes.


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Poly then

Oxide

Platinum

Silicon

Silicide

Silicidation (Cont…)

  • Immediately after the contacts are opened, a thin film of platinum is deposited across the entire wafer.

  • Wafer is heated to cause portions of platinum in contact with silicon react to form platinum silicide.

  • The unreacted platinum is removed using a mixture of acids called aqua regia.

  • It silicides both contact openings and any exposed polysilicon.


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Before we go for a Mask layout of any tool.We simulate verify and

Check the design by using Electronic Design Automation(EDA)tools


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Tools for Custom Layout verify and

  • VIRTUOSO

  • Lasi

  • L-Edit

  • Magic




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Tools for SemiCustom Layout verify and

  • Ambit

  • Physically Knowledgeable synthesis (PKS)

  • Silicon Ensemble


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