95-2-semiconductor (1)

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Introduction to

Semiconductor Fabrication Process

Yao-Joe Yang

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Why I have to introduce semiconductor

manufacturing process ?

The most important industry in Taiwan

Both IC and LCD use similar

manufacturing concepts ME play the most important role in the

field (process, equipment, automation,

QC)

The core of the hi-tech in the world

The core of the recent technology

revolution in human history


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Integrated Circuits

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ANALOG ADXL-50 ARCHITECTURE

~ 5 mm

The cover picture of

Micorelectronic Circuit

by Sedra and Smith

Accelerometer

A classic example ofintegration of MEMS

and electronic circuit


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NovaSensor Accelerometer

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MIT/AT&T Micro Motor (Circa 1989)


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Optical Switch

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Micro-robot


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Packaged tactile array: (a) close-up of polyimidesensor array inserted into connector and (b) overview

of tactile sensor, connector and PCB patterned to

interface with card-edge connector.

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Crystal Growth

Yao-Joe Yang


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Crystal Pulling: CZ method

Graphite Crucible

Single Crystal

silicon Ingot

Single Crystal Silicon Seed

Quartz Crucible

Heating Coils1415 C

Molten Silicon

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CZ Crystal Pulling

Source: http://www.fullman.com/semiconductors/_crystalgrowing.html


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CZ Silicon Ingots

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Czochralski Growth Equipnment


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Overview of Wafer Fabrication

Yao-Joe Yang

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Basic Wafer Fabrication Operations

Layering form thin layer/film structures

oxidation, CVD, sputtering, evaporation, epitaxy ..

Patterning (patter transfer) trim layer/film to desired device size

lithography, etching .

Doping skip adjust layer/film/substrate electrical properties

ion implementation, diffusion

Heat treatment skip partially recover the damage after certain processes

diffusion process, annealing .


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Layering

Adding (uniform) thin layers to wafer surfaces

Methods

Growing:

oxidation (grow silicon oxide: SiO2)

nitridation (grow silicon nitride: Si3N4)

Deposition

Epitaxy

chemical vapor deposition physical vapor deposition

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Layering

In terms of final shapes, there are three types oflayering processes:

Conformal

Planar

Stack (not traditional IC process)


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Conformal

original original

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Planar

original original


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Stack

(not traditional IC process)

original original

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Patterning

A series of steps that remove unwanted

patterns from substrate surface layers

Patterns are defined byphoto-masks ( )

Also known as: Photomasking, masking,

lithography, photo-lithography, -lithography


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Etching

Layer 1

Layer 2

Layer 1

Layer 2

Photo-mask

Example:

Layer 1 is etched by an etchant

Pattern is defined by photo-mask (etching mask is not shown)

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FSG

Metal 4 Copper

Passivation 1, USG

Passivation 2, nitride

Lead-tin

alloy bump

FSG

CopperMetal 2

FSG

FSG

CopperMetal 3

FSG

P-epi

P-wafer

N-wellP-well

n+STI p+ p+USGn

+

PSG Tungsten

FSG

Cu Cu

Tantalum

barrier layer

Nitride etch

stop layer

Nitride

seal layer

M 1

Tungsten local

Interconnection

Tungsten plug

PMD nitride

barrier layer

T/TiN barrier &

adhesion layer

Tantalum

barrier layer

CMOS Chip

with 4 Metal

Layers


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CMOS IC

p-Si USGn-Si

Balk Si

Polysilicon

STI

n+ Source/Drain p+ Source/DrainGate Oxide

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Overview of Patterning

Yao-Joe Yang


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Patterning

Patterns transferred from photo-masks to

thin-films on a planar substrate via

lithographic process

Example

Step 1:

Transfer patterns of photo-masks () tophotoresist () by lithography techniques

Step 2:Use etchants () to etch unwanted portionof material defined by etching-masks.

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Pattern Transfer:

Example 1

Spin-coating PR

Photo-lithography

alignment and exposure

Development

Etching

Striping remaining PR


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Example 2:

Starting Material

P-Well

USGSTI

Polysilicon

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Example 2:

Spin-coating PR

P-Well

USGSTI

Polysilicon

Photoresist ()


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Example 2:

Photo-Mask Alignment (using an aligner)

P-Well

USGSTI

Polysilicon

Photoresist

Photomask ()

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Example 2:

Gate Mask Exposure

Gate Mask

P-Well

USGSTI

Polysilicon

Photoresist


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Example 2:

Development

P-Well

USGSTI

Polysilicon

PR

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Example 2:

Etch Polysilicon (not finished yet)

P-Well

USGSTI

PRPR

Polysilicon


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Example 2:

Final Shape of Etched Polysilicon

P-Well

USGSTI

Gate Oxide Polysilicon

PR

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Example 2:

Strip Photoresist

P-Well

USGSTI

Gate Oxide Polysilicon


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Summary of a typical patterning procedure

Spin coating photoresist (PR) on a wafer

Mask alignment with the wafer using an

aligner ( )

Exposure of PR

Development (remove unwanted PR)

With the remained PR as etching masks, etch the

wafer

Striping the remaining PR from the wafer

Patterning

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Lithography

Yao-Joe Yang


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Optical

X-ray (skipped)

electron beam writer (skipped)

non-traditional, no masks

Types of lithography systems

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Optical Lithography

Photo-masks ()

Interface between designers and devices

Designers layout design (mask) on computers (2D patterns)

opaque patterns (chromium) on transparent glass (fused

silica)


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Photomasks ( )

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Photoresist

Photoresist (PR, )

Optical resists:

photosensitive polymers

PR is coated on the whole

substrate surface using spin-

coater

Positive PR:

can be removed by KOH orNaOH solution if it is exposed

most popular for IC process

Negative PR:

can be removed by specificsolution if it is not exposed

not good for feature size < 3 um


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Aligners

Alignment and exposure systems

()

A microscopic system which:

Align the photo-mask and the substrate

Expose PR

Also called:

printers

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Classification of aligners by exposure methods

Contact printer ()

High resolution ( 1m)

Mask deterioration

Proximity printer ()

10 - 25 m gap --> longer mask life

Diffraction effect --> 2 - 4 m resolution

Projection printer ()

Image of mask usually reduced

Scanning or stepping of small field (~ 1cm)

VLSI standard (0.25 m possible with deep-UV source)


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Schematics of Exposure systems

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Contact Printer

Light Source

Lenses

Mask

PhotoresistWafer


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Proximity Printer

Light Source

Lenses

Mask

PhotoresistWafer

~10 m

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Light Source

Lens

Mask

Photoresist

Wafer

Scanning Projection System

Synchronized

mask and wafer

movement

(stepper)

Slit

Lens


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Lithography

Karl Suss Contact Aligner stepper

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Light sources ()

Visible light

Ultraviolet (UV)

Deep ultraviolet (DUV)

Extreme ultraviolet (EUV)


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Coating of Photoresists

Spinning coating

Final thickness of photoresist is a function of rotating speed.

Relationship has been calibrated and formed a look up table

Thickness1

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Photoresist Spin Coating

Spindle

To vacuumpump

PR dispensernozzle

Chuck

PR suck back

Wafer


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Photoresist Spin Coating

Spindle

To vacuumpump

PR dispensernozzle

Chuck

PR suck back

Wafer

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Coater ( )

Spin coater

95-2-semiconductor (1)

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