Applications of Chemical Engineering Principles to Thin Film Deposition Process Development

Applications of Chemical Engineering Applications of Chemical Engineering Principles to Thin Film Deposition Principles to Thin Film Deposition

Process DevelopmentProcess Development

Applications of Chemical Engineering Applications of Chemical Engineering Principles to Thin Film Deposition Principles to Thin Film Deposition

Process DevelopmentProcess Development

Collin MuiCollin MuiChemical Engineering 140 Guest LectureChemical Engineering 140 Guest Lecture

Stanford UniversityStanford UniversityMay 22, 2008May 22, 2008

Novellus Systems Proprietary InformationNovellus Systems Proprietary InformationP. P. 22

Thin Film Deposition Process DevelopmentThin Film Deposition Process Development

Thin film deposition processes• Chemical vapor deposition• Atomic layer deposition• Reactor design and applications• PDL™ Oxide

Make sure it works• Mechanism of thin film deposition• Lesson 1: Chemical kinetics modeling

Make sure it works the same way• Temperature effects on deposition• Lesson 2: Heat transfer

Make sure it works the same way

at high yield and low cost• Defect detection and reduction• Lesson 3: Particle transport

Wafer

TMA

Silanol

Fdrag

Fgrav

Fthermo


Thin Film Deposition Process and ApplicationsThin Film Deposition Process and Applications

Chemical vapor deposition (CVD) Films deposited by CVD

SURFACE REACTION

PrecursorDesorption

Atomic layer deposition (ALD)

Passivation SiO2

Shallow Trench Isolation (STI)

Inter Metal Dielectric (IMD)

Pre Metal Dielectric (PMD)

Deep Trench Isolation


Thin Film Deposition ReactorThin Film Deposition Reactor

Chemical engineering principles Novellus™ deposition reactor

Precursor deliveryFluid dynamics

Reaction kinetics

Temperature controlHeat transfer


1. Capacitor sacrificial layer• Sacrificial oxide layer for subsequent

etch or CMP• Thickness = 500 - 2000Å

PDLPDL™™ Oxide – A Novel Technology Oxide – A Novel Technology

PDL™ Oxide: Enabling technology Conformal insulator layer Thick films (10kÅ) possible Low temperature deposition No plasma damage

PDL™ Oxide: Precise engineering Accurate thickness control Excellent repeatability High productivity and manufacturability

2. 3D-Interconnect: Wafer level packaging• Insulating oxide liner for through wafer

vias (TWVs)• Large CD but high AR structures• Thickness = 2000 – 10000Å

3. Lithography spacer or oxide liner• Reduce CD limit of lithography• Thin oxide spacer or liner film• Thickness = 50Å to 700Å


AR ~ 4.5

AR ~ 8

Conformal Film Deposition via Surface ReactionsConformal Film Deposition via Surface Reactions

Catalytic Monolayer

SurfacePolymerization

Surface Polymerization

Surface Polymerization

SilicaCatalytic Monolayer

Catalytic Monolayer

Catalytic Monolayer

Trench fill mechanism extendable to high aspect ratio structuresTrench fill mechanism extendable to high aspect ratio structures

AR ~ 17


300 mm Handler(WTS)

PDL Module

Catalyst Station

Silanol Station

PDL Process Module Architecture and ProductivityPDL Process Module Architecture and Productivity

PDL™ process module • Novellus™ Multi-Station Sequential

Deposition (MSSD) architecture• Processes 4 wafers at the same time

Novel architecture results in high productivity and accurate controlNovel architecture results in high productivity and accurate control

Separation of half reactions• Each station performs a half reaction• Improves defect performance

Precursor delivery system• Accurate and repeatable thickness control• Tunable thickness with good uniformity• Scalable from thin to thick films


Surface Chemistry of the PDL ProcessSurface Chemistry of the PDL Process

Sequential trimethylaluminum (TMA) and silanol exposure

One monolayer of TMA catalyzes multiple silanol insertions

Cross-linking and diffusion lead to self-limiting deposition

Nucleation

Surface reactions only

Self-limiting process

Wafer

TMA

Cross-Linking

Diffusion limited growth

Conformal gap fill

Wafer

Chain Insertion

Sequential deposition

High deposition rate

Wafer

Silanol


Lesson 1 – Chemical Engineering KineticsLesson 1 – Chemical Engineering Kinetics

Nucleation

Wafer

TMA

Cross-Linking

Wafer

Chain Insertion

Wafer

Silanol

Silanol FilmChain

The process can be modeled as a “consecutive reaction”The process can be modeled as a “consecutive reaction”

R FC


Kinetic Modeling of Consecutive ReactionsKinetic Modeling of Consecutive Reactions

Consecutive reaction Time-dependent concentration

FCR PR kk

00

00

10

FCkdt

dF

CCkRkdt

dC

RRkdt

dR

P

PSR

SR

RP

tkR

tkP

tktk

RP

R

tk

kk

ekektF

eekk

ktC

etR

PR

PR

R

11

Kinetic equations

Solution of differential equations

Temperature dependence

0 5 10 15 20 25 30 35 40 45 500.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Con

cent

ratio

n

Time

Temp

0 1 2 3 4 5 6 7 8 9 100.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Time

R

C

F

Con

cent

ratio

n


Tuning Film Properties by Deposition TemperatureTuning Film Properties by Deposition Temperature

Kinetics at different temperatures

WERR (100:1 HF) Thermal Oxide

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

60 80 100 120 140 160 180 200 220Temperature (°C)

Wet

Etc

h R

ate

Rat

io

WERR (100:1 HF) ~150A/cyc (Thermal Oxide) WERR (100:1 HF) ~250A/cyc (Thermal Oxide)

Process space for thickness control• Deposition temperature• Precursor delivery• Deposition time

Tunable film properties• Tunable film stress • Tunable wet etch rate

Deposition at low temperature

Deposition at high temperature

0 10 20 30 40 50 60 70 80 90 100

0

10

20

30

40

50

Data: 50mol 100oC

Model: ReactionChi squared 3.39593Saturation 50 ±0Reaction order 1.97373 ±0.15802Rate constant 0.00406 ±0.00213N

umbe

r of

mic

rom

oles

dep

osite

d

Time (s)

0 50 100 150 200

0

10

20

30

40

50

Data: 50mol 200oC

Model: ReactionChi squared 0.46714Saturation 41.5151 ±0.92233Reaction order 2.3419 ±0.27046Rate constant 0.00602 ±0.00543N

umbe

r of

mic

rom

oles

dep

osite

d

Time (s)

Deposition at low temperature

Deposition at high temperature


Cycle 1 Cycle 2 Cycle 3

Cycle 1 Cycle 2 Cycle 3

Lesson 2 – Wafer Heating and Heat TransferLesson 2 – Wafer Heating and Heat Transfer

Importance of temperature control Inadequate heating

Temperature controlHeat transfer

Stable Temperature = Stable ProcessStable Temperature = Stable Process

Adequate heating

020406080

100120140160180200

0 30 60 90 120 150 180Time (s)

Waf

er T

empe

ratu

re (

C)

020406080

100120140160180200

0 30 60 90 120 150 180Time (s)

Waf

er T

empe

ratu

re (

C)


Heat Transfer MechanismsHeat Transfer Mechanisms

Conduction

T2

Radiation

x

TTkQcond

12

2, T2

T1 1, T1

k x2

x1

2121

41

4221

TT

Qradi

Thermal conductivity

Pedestal-wafer gap

Temperature

Emissivity

Convection

T2

T1

k

CuL

k

hL

ThQ

p

conv

PrRe

PrRe664.0Nu 31

21

u

Gas velocity

Gas pressure


Heat Transfer by ConvectionHeat Transfer by Convection

LPCVD Reactor• Pressure = 10 mT to 10 T• Gas = N2

• Final temperature = 200 °C• Flow = variable

Effect of gas flow rate on convective heat transfer• For typical CVD reactors, flow rate ~

100 to 5000 sccm

Insignificant heat transfer by convection• Less than 10% of the heat is transferred

by convection• Usually ignore convection in calculating

wafer heating rate

T2

T1

u

Usually ignore convection in calculating wafer heating rate Usually ignore convection in calculating wafer heating rate

Heat Transfer by Convection

0%

2%

4%

6%

8%

10%

0 2000 4000 6000 8000 10000

Gas flow rate (sccm)

% H

eat

tran

sfer

by

con

vect

ion

10 mT100 mT1 T10 T


Heat Transfer by ConductionHeat Transfer by Conduction

LPCVD Reactor• Flow = 100 sccm to 10 slm• Gas = N2

• Final temperature = 200 °C• Pressure = variable

Effect of gas pressure on conductive heat transfer• LPCVD ~ 10 mT to 1 T• APCVD ~ 100 T

Conduction is the major heat transfer mechanism• Mean free path of gas is short at low

pressures• While pressure does not affect thermal

conductivity, the “effective pedestal-wafer gap” is reduced at low pressures

Increasing conduction is key to effective wafer heatingIncreasing conduction is key to effective wafer heating

T2

T1

k x2

x1

Heat Transfer by Conduction

0%

20%

40%

60%

80%

100%

0.001 0.01 0.1 1 10 100

Pressure (torr)

% H

eat

tran

sfer

by

con

du

ctio

n

100 sccm200 sccm500 sccm1000 sccm


Heat Transfer by RadiationHeat Transfer by Radiation

LPCVD Reactor• Flow = 500 sccm• Gas = N2

• Pressure = 10 mT to 10 T• Temperature = variable

Effect of temperature on radiative heat transfer• CVD temperatures ~ 200°C to 700°C

Radiation is important at• High temperatures, because of the

fourth-power dependence• Low pressures, when conduction is

ineffective. (Note: radiation itself is independent on pressure)

Radiative heat LOSS needs to be considered at high temperaturesRadiative heat LOSS needs to be considered at high temperatures

T2

T1

Heat Transfer by Radiation

0%

20%

40%

60%

80%

100%

0 200 400 600 800 1000

Temperature (C)

% H

eat

tran

sfer

by

rad

iati

on

10 mT100 mT1 T10 T


Effective Wafer Heating by Controlling ConductionEffective Wafer Heating by Controlling Conduction

Heat transfer by conduction• High pressure – a lot of gas molecules• Small pedestal-wafer gap

Improving gas conductivity• Helium has higher thermal conductivity• However, it is more expensive

Use of “heat soak” cycle to preheat wafer to process temperatureUse of “heat soak” cycle to preheat wafer to process temperature

k

Wafer Heating with Nitrogen

0

50

100

150

200

0 30 60 90 120 150 180

Time (s)

Waf

er

Te

mp

era

ture

(C

)

N2 100mTN2 1TN2 10T

Improved Wafer Heating with Helium

0

50

100

150

200

0 5 10 15 20 25 30 35 40 45 50 55 60

Time (s)W

afe

r T

em

pe

ratu

re (

C)

N2 10THe 10T


Importance of Defect ReductionImportance of Defect Reduction

Defects in etch processes Defects in CMP processes

CD CD

Etch Etch Etch

CD CD

Defect control is important in high volume manufacturingDefect control is important in high volume manufacturing

CMP


Defect Inspection by Light ScatteringDefect Inspection by Light Scattering

Optical system Particle map

Light scattering signal

US Patent 6888627


Defect Analysis – Size, Shape, Composition, …Defect Analysis – Size, Shape, Composition, …

Size ~ 10 m Size ~ 2 m Size ~ 0.2 m

Combination of “forensics” and chemical analysis techniquesCombination of “forensics” and chemical analysis techniques


Film Accumulation and Particle GenerationFilm Accumulation and Particle Generation

Particle accumulation• The goal of a CVD process is to deposit

film on a wafer.• Unfortunately, film also deposits on the

reactor walls (hopefully at a slower rate), and the film accumulates as more wafers are deposited

• At some point, the accumulated film deliminates and becomes a particle source.

Particle generation• CVD films are usually stressed (why?).• Interface between two different materials

(film and reactor wall) may be weak (adhesion, lattice mismatch)

• As the film deposition becomes thicker on the reactor walls, the film starts to delaminate and land on the wafer as particles.

Film delamination (and particle generation) is promoted by• Interfacial stress increases with film

accumulation thickness• Temperature gradient and fast

temperature cycling• Sharp corners inside the reactor• Gas flow may blow off loose particles


Lesson 3 – Particle TransportLesson 3 – Particle Transport

Particle inside CVD reactor Forces on a particle

FDrag

FGrav

FThermo

T1

T2

Drag force

DragF

Gravitational force

GravF

Thermophoretic force

ThermoF

Drag force n

gasparticleparticleDrag KC

vvdF

3

Gravitational force


gdF gasparticleparticleGrav 3

6

T

TKdF TparticleThermo

3

Temperature Gradient

Weight

Flow


Drag Force on a ParticleDrag Force on a Particle

Derivation of the drag force• Start with fluid mechanics

• Drag coefficient

• Drag force in the continuum limit

• Correction for small particle at low pressures

Effect of particle size

22

8 relativeparticleparticleDDrag vdCF

22

8Re

24relativeparticleparticleDrag vdF

gasparticleparticleDrag vvdF 3

n

gasparticleparticleDrag KC

vvdF

3

particlen dK

2 Mean free path

Particle Size and Drag Force (Pressure = 1T)

1.0E-24

1.0E-22

1.0E-20

1.0E-18

1.0E-16

1.0E-14

1.0E-12

1.0E-10

1.0E-08

1.0E-06

0.1 1 10 100 1000 10000Gas flow (sccm)

Dra

g F

orc

e (

N)

100 um10 um1 um100 nm10 nm1 nm

Effect of pressurePressure and Drag Force (Particle size = 1m)

Gas flow (sccm)

Dra

g F

orc

e (

N)

1 mT10 mT100 mT1 T10 T100 T760 T

1.0E-24

1.0E-22

1.0E-20

1.0E-18

1.0E-16

1.0E-14

1.0E-12

1.0E-10

1.0E-08

1.0E-06

0.1 1 10 100 1000 10000


Gravitational Force on a ParticleGravitational Force on a Particle

Gravitational force depends on particle size and density only

• Important for large particles

gdF gasparticleparticleGrav 3

6

Gravitational Force on a Particle

1.0E-24

1.0E-22

1.0E-20

1.0E-18

1.0E-16

1.0E-14

1.0E-12

1.0E-10

1.0E-08

1.0E-06

1.E-08 1.E-07 1.E-06 1.E-05 1.E-04

Particle size (m)

Dra

g F

orc

e (

N)

WTaNCuAlHfO2Si3N4SiO2Si


Thermophoretic Force on a ParticleThermophoretic Force on a Particle


• Particles move from surfaces at high temperatures to surfaces at low temperatures

• Depends on particle size• Depends on temperature gradient• KT is a function of particle size, mean

free path, and thermal conductivities

Minimizing thermophoresis• Wafer at higher temperature than the

rest of the reactor

Effect of particle size

T

TKdF TparticleThermo

3

Effect of pressurePressure and Thermophoretic Force (Size = 1m)

1 10 100 1000Temperature Gradient (K/m)

Th

erm

op

ho

reti

c F

orc

e (N

)

1.0E-24

1.0E-22

1.0E-20

1.0E-18

1.0E-16

1.0E-14

1.0E-12

1.0E-10

1.0E-08

1.0E-06

1 mT10 mT100 mT1 T10 T100 T760 T

Particle Size and Thermophoretic Force (Pressure = 1T)

100 um10 um1 um100 nm10 nm1 nm

1 10 100 1000Temperature Gradient (K/m)

Th

erm

op

ho

reti

c F

orc

e (N

)

1.0E-24

1.0E-22

1.0E-20

1.0E-18

1.0E-16

1.0E-14

1.0E-12

1.0E-10

1.0E-08

1.0E-06


Chemical Engineering and Thin Film DepositionChemical Engineering and Thin Film Deposition

Thin film deposition processes• Chemical vapor deposition• Atomic layer deposition• Reactor design and applications• PDL™ Oxide

Lesson 1: Chemical kinetics• Mechanism of thin film deposition• Consecutive reaction

Lesson 2: Heat transfer• Temperature effects on deposition• Convection, conduction, and radiation

Lesson 3: Particle transport• Defect detection and reduction• Particle generation mechanisms• Forces on a particle

Wafer

TMA

Silanol

Fdrag

Fgrav

Fthermo

Documents

Applications of Chemical Engineering Principles to Thin Film Deposition Process Development