Si3N4 Deposition & the Virtual Chemical Vapor Deposition Lab · Milo Koretsky Chemical Engineering...

Si3N4 Deposition & the Virtual

Chemical Vapor Deposition Lab

Making a transistor, the general process

A closer look at chemical vapor deposition and the virtual lab

Images courtesy Silicon Run Educational Video, VCVD Lab Screenshot

On a wafer, billions of transistors are housed on a single square chip. One malfunctioning transistor could cause a chip to short-circuit, ruining the chip. Thus, the process of creating each microscopic transistor must be very precise.

Wafer image: http://upload.wikimedia.org/wikipedia/fr/thumb/2/2b/PICT0214.JPG/300px-PICT0214.JPG

Why Si3N4 Deposition…Making

Microprocessors

http://vista.pca.org/yos/Porsche-911-Turbo.jpg

http://www.sonyericsson.com/cws/products/mobilephones

/overview/x1?cc=us&lc=en

What size do you think an

individual transistor being

made today is?

Size of Transistors

Scaling of successive generations of MOSFETs into the nanoscale regime (from Intel).

One chip is made of millions or billions of transistors

packed into a length and width of less than half an

inch. Channel lengths in MOSFET transistors are

less than a tenth of a micrometer. Human hair is

approximately 100 micrometers in diameter.

Transistor: MOS

We will illustrate the process sequence of

creating a transistor with a Metal Oxide

Semiconductor(MOS) transistor.

Wafers – 12” Diameter

p-Si

Insulatorconductor

n-Si

Source DrainGate

n-Si

½” to ¾”

Image courtesy: Pro. Milo Koretsky

Chemical Engineering Department at OSU

IC Manufacturing ProcessIC Processing consists of selectively

adding material (Conductor, insulator,

semiconductor) to, removing it from or

modifying it

Wafers

Deposition /

OxidationEtching / CMP

Loop

Photo/

Pattern

Transfer Cle

an

Cle

an Ion Implant /

Anneal

Graphics copy-write Pro. Milo Koretsky


(Note that these steps are not all the steps to create

a transistor. Some steps are skipped. This is purely to

show the various stages in the loop to create a transistor.)

Making a Transistor:

Starting Silicon Wafer

Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Si

Wafers



Clean substrate

Si

Polished Silicon Wafer



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Chemical Vapor Deposition: Si3N4

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Process 200 Wafers at a Time

Spin Coating of Photoresist

Si

mask



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Develop Photoresist

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Plasma Etch Si3N4

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Plasma Etch: Strip Photoresist

Si



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Ion Implantation

Si

IONS IONSIONS

1.75 u

1/50th of a human hair



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

Anneal

Si

HEAT HEATHEAT

Activate (& diffuse) the dopant

• Clean before anneal



Dep

os

ition

/

Oxid

atio

n

Lo

op

Ph

oto

/

Patte

rn

Tra

ns

fer

Etc

hin

g /

CM

P

Clean

Ion

Imp

lan

t /

An

ne

al

The Final Steps…a completed transistor

Gate: +

e- e-

Source - Drain: +

Si



Chemical Vapor Deposition A Closer Look: Si3N4



Reactions:

__SiCl2H2 (g)Dichlorosilane

++ Si3N4 (s)Silicon

nitride

__NH3 (g)Ammonia

H2 (g)Hydrogen

HCl (g)Hydrogen chloride

+

DCS (gas)

NH3 (gas)

Silicon

nitride

NH4Cl (gas)H2 (gas)

NH3 (gas)

DCS (gas)

__HCl (g)Hydrogen chloride

+ ___NH4 Cl(g)Ammonium chloride

__NH3 (g)Ammonia

Chemical Vapor Deposition A Closer Look: Si3N4



Reactions:

3 SiCl2H2 (g)Dichlorosilane

++ 1 Si3N4 (s)Silicon

nitride

4 NH3 (g)Ammonia

6 H2 (g)Hydrogen

6 HCl (g)Hydrogen chloride

+

DCS (gas)

NH3 (gas)

Silicon

nitride

NH4Cl (gas)H2 (gas)

NH3 (gas)

DCS (gas)

1 HCl (g)Hydrogen chloride

+ 1 NH4 Cl(g)Ammonium chloride

1 NH3 (g)Ammonia

Overall Reaction:

3 SiCl2H2 (g)Dichlorosilane

(DCS)

++ Si3N4 (s)Silicon

nitride

10 NH3 (g)Ammonia

6 H2 (g)Hydrogen

6 NH4Cl (g)Ammonium chloride

+

What factors do you think

affect the reaction and film

growth?

Temperature

Concentration

Reaction/Deposition Time

Virtual CVD OverviewChoosing the Virtual CVD reactor parameters

Pressure

is Fixed

Factors that Effect Reaction and Film Growth:

Concentration

SiCl2H2 (gas)

NH3 (gas)

NH4Cl (gas)H2 (gas)

NH3 (gas)

SiCl2H2 (gas)

Absolute flow rates of

NH3 to SiCl2H2

Ratio of NH3 to SiCl2H2

Pressure (fixed)

PV = nRT

Graphics copy-write Pro. Milo Koretsky, Chemical Engineering Department at OSU and Silicon Run Educational Video

There are 5

temperature zones

Remember (18.12, Addison-Wesley, Chemistry)

Rate = k[A]1


Temperature

k k0 exp Ea, f

RT

The Arrhenius Equation

En

erg

y

Reaction coordinate

Ea,f

A

B

First order reaction (thermal):

A B

What can you do with the 5 temperature

zones???


Temperature

SiCl2H2 (gas)

NH3 (gas)

NH4Cl (gas)H2 (gas)

NH3 (gas)

SiCl2H2 (gas)

PV = nRT

Graphics copy-write Pro. Milo Koretsky, Chemical Engineering Department at OSU and Silicon Run Educational Video


Deposition Time aka Reaction Time

Reaction/Deposition Time = the

amount of time the reactor runs

How do you think deposition time

effects the film thickness???

Virtual CVD Overview

Each run costs $

Choosing the Virtual CVD reactor parameters

Pressure

is Fixed

0

200

400

600

800

1000

-150 -50 50 150

Fil

m T

hic

kn

es

s [

A]

Film thickness is determined by the amount of material

that reacts and is grown on the wafer

Uniformity describes the evenness of film thickness on

the wafer

Measurement – Thickness & Uniformity

45% Uniformity 100% Uniformity

0

200

400

600

800

1000

-150 -50 50 150

Fil

m T

hic

kn

es

s [

A]

x position x position

Film thickness is determined by the amount of material

that reacts and is grown on the wafer

Uniformity describes the evenness of film thickness on

the wafer

Measurement – Thickness & Uniformity

SiCl2H2 (gas)

NH3 (gas)

NH4Cl (gas)H2 (gas)

NH3 (gas)

SiCl2H2 (gas)

0

50

100

150

200

0 2000 4000 6000 8000 10000

Waf

er #

Thickness [A]

79% Overall Efficiency

50% Overall Efficiency

Measurement via Ellipsometer

The ellipsometer is used to measure the

thickness and refractive index of

transparent films.

It is made of a light source and polarizer

on one side and a analyzer and detector

on the other side.

Light from the source is polarized

and reflected off the film.

The analyzer is rotated till no light

passes through it.

The angle of rotation depends on the

thickness of the film.

Analyzer &

Detector

Light Source,

Control &

Polarizing

Sheet

Light Source

Light Control

Polarizing

Sheet

Analyzing

Polarizer

Detector

Substrate

Virtual CVD Overview

Each measurement costs $

Choosing the locations on the wafer to measure

Virtual Chemical Vapor Deposition

(VCVD) Program

Photo Courtesy of http://webmedia.national.com/gallery/06/06_rgb.jpg

VCVD Program

Semiconductor Manufacturing Fab

Your Objectives:

Determine how temperature, flow rates, and

reaction time impact deposition of Si3N4

Minimize cost of testing process used to

determine the impact of these parameters

Extra Credit: Find an optimized “recipe” that

produces high uniformity (within wafer and

between wafers) and meets a target

thickness of 1000 Angstroms

Economy of Transistors

~$300 /chip

X ~200 chips/wafer

X 200 wafers/furnace

load =

$12 Million

per furnace

loadhttp://www.dvhardware.net/article16696.html

http://www.nitride.co.jp/english

/products/wafer.html

Let’s Get Started

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Si3N4 Deposition & the Virtual Chemical Vapor Deposition Lab · Milo Koretsky Chemical Engineering...

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