post cmp cleans evolution - linx consulting

Post CMP Cleans Evolution and

Defect Improvement Approaches

Business of Cleans / SPCC Conference

Katrina Mikhaylichenko, Ph.D.

Applied Materials

April 9th, 2017

Applied Materials Confidential

2 Applied Materials | Presented at Business of Cleans / SPCC 2018

CMP Mechanism and Cleaning Challenges

Three-body interaction: Wafer, Pad, Slurry

Slurry: Complex suspensions containing

abrasive particles, stabilizing agents and

inhibitors

Pad & abrasive remove inhibitor(a) from high

pressure areas

Remaining inhibitor(a) protects low areas.

After polish layer cleared from stop layer,

inhibitor(b) protects stop area and inhibitor(a)

represses dishing of oxide in trenches

Polishing by-products (chemical reactants,

agglomerated slurry and pad/conditioner

debris) are present on wafer after polish and

needs to be removed during post-CMP cleans

2


Post CMP Cleaning Challenges

3

Difficult to remove

contaminants:

► Slurry particles and polish residues

► Organic components of the slurry

► Pad debris

Corrosion

Multiple film materials

exposed and new

metals/liners/barriers

(W, TiN, Co, Ru, ULK)

Particle removal is more

difficult with time

Hydrophobic films, Philic /

phobic surface combination

Scratches on softer films

Secondary contamination

due to the “Loading” of the

cleaning media

Wafer edge cross-

contamination

Small particles become

“visible” to metrology tools

only after next film deposition


Particle Removal and Re-Deposition

Particle removal: interaction force between the particle and the substrate has to be eliminated by shear force:

► Fluid shear flow, Brush scrub, Megasonic cleaning, Fluid jet

Chemical etching is used to assist with breaking the particle-surface bond

► Undercut on the substrate and/or wet etch of the particle

After breaking the bond, the particle has to be removed away from the surface to prevent re-attachment

4

Particle attached on wafer

surface

Breaking van der Walls forces:

Undercutting by HF

Shear force by brush scrub,

Megasonics, Fluid jet…

Lift off by repulsive forces:

Shear force by brush scrub,

Megasonics, Fluid jet…

Electrostatic forces

Diffusion of particles to surface

due to overall attraction force

and electrostatic force

Van der Walls interactions:

rapid deposition of particles

close to the surface

Particle Removal

Particle Deposition


Addressing Post CMP Cleaning Challenges in LKP System

Cleaner: 5x Side-by-Side Cleaner Stations

► Megasonics

− Provides physical force to remove contamination form the features

− Provides full wafer immersion tank for bevel contamination removal

► Pre-Clean

− Provides means to perform chemical buff in a dedicated slurry-free module

− Vertical buff enables effective contamination removal off the surface

− Enable cleaning of top surface of the wafer bevel

► Two consecutive brush boxes provide high particle removal efficiency

and precise brush pressure control

► Vapor Dryer provides defect-free drying of hydrophilic, hydrophobic and

mixed surfaces

► Cleaner Chemical Flexibility enables particle undercut and lift-off

− HF-compatible brush box enables SiO2 substrate etching

− Proprietary chemicals often include particle etch capability

5


Po

st

CM

P C

lean

Defe

ct

Imp

rove

me

nt

Ap

pro

ach

es

6

Post Polish Rinse Chemical Rinse in Polisher Load/Unload Station

Chemical Mechanical Buff PreClean Module High Shear Force Clean for Dielectric and Metal CMP

Brush Box Advanced Cleaning Features Chemical Coverage Uniformity Improvement

SteadyClean Brush Torque (Shear Force) Control for Consistent Roller Brush PRE

Ozonated Water Rinse for Organic Defect Reduction

BB2.0 Brush Conditioning for Extended Brush Life

Dryer High Speed Dry in VD1.5


Post Polish Chemical Rinse Optimization for Poly CMP

Strategy:

Convert hydrophobic wafer surface to hydrophilic as soon as possible after polish step to prevent strong

bonding of residues onto surface

7

Using AMAT post polish rinse station design, wafer surface is converted from

hydrophobic to hydrophilic with very short chemical exposure


Post Polish Rinse Effect on Poly Defects

8

Process SP2 Maps SP2 Maps SP2 Maps SP2 Maps Ave.

Counts@80nm

Optimized Post Polish Rinse

X

Un-optimized Post Polish Rinse

10X

About 10X improvement in defects from adding post polish chemical rinse

Polish: Silica poly slurry; PreClean buff: acidic cleaning solution, soft pad;

Brush scrub: acidic cleaning solution


Po

st

CM

P C

lean

Defe

ct

Imp

rove

me

nt

Ap

pro

ach

es

9









PreClean Chemical Mechanical Buff Module

Control parameters

► Wafer RPM: recipe programmable by step

► Pad RPM: recipe programmable by step

► Pad Pressure: recipe programmable by step

► Fully programmable sweep profile control on

wafer and conditioner

► Chemical and water CLC to chemical nozzle

► DIW CLC to rinse bars

► Broad range of chemical compatibility (not HF)

10

Wafer

Holder

DIW

Spray bar

PreClean has a wide range of processing capability

Vacuum

Chuck

Swing

Arm

Pad

conditioner

Chem

nozzle

Buff

pad


Ce Slurry Cleaning Challenge for High Oxide Removal CMP

11

Ceria abrasive have significant surface

chemical action during SiO2 film polish

Oxide removal rates are tunable by

controlling ceria particle characteristics

and the surface activation components

High oxide removal characteristics of the

slurry represent significant challenge for

post CMP clean

Pad

SiO2 Film

CeO2

particle

Si(OH)3

H2O

Si(OH)4

O Ce

O

O Ce O bonding

Dissolution

of Si(OH)4

Pad direction

Polish + B1/B2

Saturated

Problem Statement:

High Ceria surface Contamination after CMP

Without Chemical Buff, ceria surface contamination remains high after conventional Brush Scrub


PreClean for FEOL: ILD0 PreClean vs. Platen Chemical Buff

12

Polish: Ceria slurry polish; Platen buff /PreClean buff: acidic cleaning solution, soft pad;

Brush scrub: acidic cleaning solution

0

20

40

60

80

100

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

Sc

ale

d M

TM

Ad

de

rs,

Bla

nk

et

TE

OS

@ 9

0n

m

Wafer Count

Polish + Platen buff

Polish + Pre-Clean

0

10

20

30

40

Rela

tive

Ad

ders

ILD0 CMP

oxide stop on nitride

FEOL advantage: Move platen chemical buff to pre-clean module in the cleaner

Pre-clean extended run performance more stable than platen buff


PreClean for BEOL: Small Defect Removal on Oxide Wafers Polished with Cu

Alkaline Barrier Slurry

For defect threshold of 90nm (SP5): No significant difference in post-CMP defect count was observed with and without PreClean.

For defect threshold of 45nm (SP5): Adding PreClean significantly reduced post-CMP defect count

Oxide Wafers

PreClean is effective for small, sub 50 nm, particle reduction in BEOL N

orm

ali

ze

d P

ost

Co

un

ts @

>4

5 n

m

P3 Polish + B1B2 P3 Polish + PreClean + B1B2

No

rma

lize

d P

ost

Co

un

ts @

>9

0 n

m

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0


Polish: Alkaline Cu barrier slurry, soft pad

PreClean: Alkaline cleaning solution, soft pad

Brush Scrub: Alkaline cleaning solution


PreClean for BEOL: Small Defect Removal on Low-K Wafers Polished with Cu

Alkaline Barrier Slurry

Adding PreClean significantly reduced post-CMP defect count

through removing organic residues from hydrophobic BD3 wafers

BD3 Wafers

(SP5 at 65nm)


No

rma

lize

d P

ost

Co

un

ts @

>6

5 n

m

8.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Polish: Alkaline Cu barrier slurry, soft pad

PreClean: Alkaline cleaning solution, soft pad

Brush Scrub: Alkaline cleaning solution


PreClean for W CMP: Small Defect Removal on Oxide Wafers Polished with W

Silica Slurry

For defect threshold of 65nm (SP2): No significant difference in post-CMP defect count was observed with and without PreClean.

For defect threshold of 45nm (SP5): Adding PreClean significantly reduced post-CMP defect count

PreClean is effective for small, sub 50nm, particle reduction in W CMP

SP5 at 45 nm SP2 at 65 nm Defect Adders on Blanket Oxide Wafers

No

rma

lize

d M

TM

Ad

ders

@>

65

nm

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

No

rma

lize

d M

TM

Ad

ders

@>

45

nm

Polish: W Silica Slurry

PreClean: NH4OH cleaning solution, soft pad

Brush scrub: alkaline cleaning solution

P3 Polish + B1B2 P3 Polish + PreClean+ B1B2 P3 Polish + B1B2 P3 Polish + PreClean+ B1B2


PreClean Module Flexibility: Particle Removal from Edge

16

TEOS Blanket

Polished with SS12

+ Pre-Clean with no

edge contact > 20mm

+ VD

Re-cleaned with

Pre-Clean +

BB1/BB2/VD

Edge overloaded

Small and

large defects

Re-cleaned with

BB1/BB2/VD

Re-cleaned with

Meg +

BB1/BB2/VD

61

@90nm

Edge counts

still high

Large defects

removed

Low counts & only

film defects observed

Pre-Clean effective in removing nano particles and edge defects


PreClean Module Flexibility Edge Cleaning Capability near Bevel

17

Contaminated Bevel Pre Clean + B1/B2 + VD B1/B2 + VD

Residue belt observed at the Apex

Slurry residue on top surface near bevel

Slurry on top and bottom of bevel

Most of the residue belt is removed

Few isolated, small slurry particles on

top surface near bevel and on top and

bottom of bevel

Most of the residue belt is removed

No slurry on top surface near bevel

Remaining slurry only on bottom

portion of bevel

Pre-Clean effective in removing nano particles and edge defects


Po

st

CM

P C

lean

Defe

ct

Imp

rove

me

nt

Ap

pro

ach

es

18









Brush Box Chemical Uniformity Improvement

Shower style HVM spray bar improves range by 3X

19

Problem Statement

Chemical etch (coverage) non-

uniformity with brush-closed

process due to brush and

chemical spray interferences

Solution

Optimized shower style spray bar

0

10

20

30

40

50

60

-150 -100 -50 0 50 100 150

Ox

ide

re

mo

ve

d (

A)

Position (mm)

POR 1500ml 50rpm

SA HVM 3.0 1500ml 30 rpm

Old Spray bar; 1500 mL/min chem flow

Shower Style HVM bar; 1500 mL/min chem flow

TOX Removal with Brush-Closed Process


Ozonated Water Clean for Oxide and Poly Polish Organics Reduction

Objective:

► Remove organic contamination

Strategy:

► Implement DIO3 rinse in a dedicated cleaner module

Current test methodology:

► Implement Brush-open rinse with DIO3

Circular

Scratches

Defect reduction with DIO3 is due to reduction

in surface Carbon

DIW Rinse

DIO3 Rinse

in BB1

DI Water Rinse

in BB1

DIO3 Rinse

3x improvement observed with DIO3 rinse

No

rma

lize

d M

TM

Ad

de

rs

@>

65

nm

1.50

1.25

1.00

0.75

0.50

0.25

0.00


DIO3: Surface Carbon Reduction Mechanisms on Si

21

Reduction in surface organics is due to surface conversion hydrophilic and direct oxidation reaction

BB1: HF BB2: DIO3 or DIW (brushes Open in both brush boxes)

DIO3 Rinse Effect on Surface Contact Angle DIO3 Rinse Time Effect on Oxide Film Growth on Si Substrate

60 sec DIO3 Rinse 5 sec DIO3 Rinse

60 sec DI Water Rinse

DIO3 rinsed surface shows lower

contact angle due to surface

oxidation with DIO3 exposure

Effective chemical oxide growth on

bare Si with DIO3 rinse

Contact angle >30

Contact angle <5 Contact angle <5


Challenge :

► For small brush gap compression processes (<0.5mm),

variations in roller brushes & mechanical setup lead to

unstable particle cleaning and/or short brush lifetimes.

Approach:

► Maintain consistent brush shear force on wafer surface by

dynamically changing brush spacing to keep brush motor

torque consistent

Benefit:

► Consistent brush PRE for stable particle defect

performance and longer brush lifetimes.

SteadyClean Advanced Brush Torque Control

22

Control Shear Force for Consistent Roller Brush PRE

With SteadyClean Active

Z

z

R R

Brush Compression

Controlled by Gap motor

Challenge: Brush Shear Force Fluctuations

Approach: Consistent Brush Motor Torque


SteadyClean Brush Torque Control – Examples

23

Keeps net brush torque stable over 2000+ wafers

Steady Clean Brush Torque Control compensates for environmental changes and brush wear by dynamically changing brush spacing

Fast Error Correction

Manually

decreased

brush gap


BB2.0: Brush Conditioning Defect Adder Reduction

Objective:

– Extend brush life and reduce brush break-in time to reduce brush

generated defects

Strategy:

– Add conditioning plates to clean brush

– Ex-situ brush cleaning after brush-closed wafer cleaning step and wet idle

– Brush position control during conditioning

– DIW spray on conditioning bar

Status:

– Released on LK and LKP

Circular

Scratches


Po

st

CM

P C

lean

Defe

ct

Imp

rove

me

nt

Ap

pro

ach

es

25









Weight Percent IPA

0 10 20 30 40 50 60 70 80 90 100 15

20

25

30

35

40

45

50

55

60

65

70

75

Su

rfac

e t

en

sio

n (

dyn

es

/cm

)

Water – IPA Surface Tension at 20C

DIW

Basic Principle of Surface Tension Gradient Drying Surface tension difference caused by surface IPA concentration gradient in DIW helps pull DIW from wafer surface

Marangoni drying requirement: refreshing of IPA and DIW to keep the gradient

26

[IPA]A > [IPA]B

gA(IPA+DIW) < gB(IPA+DIW) < g(DIW)

IPA

gB

g A

DIW

N2 + IPA Spray Bar

gB

g A

DIW

N2 + IPA Spray Bar

Wafer motion

IPA-rich atmosphere

near liquid-air interface – Gravity removes bulk of the liquid from the

wafer

– Tank volume exchanged with fresh DIW

(Overflow)

– IPA vapor is continuously fed to the DIW-

air interface

– Interface is kept saturated with IPA to

produce surface tension gradient drying

effect

Vertical Marangoni Tank

Vertical Marangoni Dryer provides defect-free drying of hydrophilic, hydrophobic and mixed surfaces


Vapor Dry 1.5

Optimized IPA spray bar (VD1.5) enables high speed dry on hydrophilic substrates

Objective:

– Develop high speed vapor drying process to support short polish times

– Improve robustness of drying process

Strategy:

– Made prototype setup with which bars adjustable in position and angle

– Optimized spray bar position based on visual observation of droplets on front and back

– Validated optimal position and N2-IPA flow for defectivity on Si, TEOS and BD and FCVD

Status:

– Optimized spray bar position and N2/IPA flow for good defectivity and no residual water

– 29 sec BKM with new bars equivalent to 52 sec BKM with old bars

– Required change in angle, height and spacing of spray bars to front and back

– New geometry implemented: available on LK and LKP

Residual water

Inputs

• Angle

• Height

• Distance

• N2/IPA flow rate

H

DBS DFS

bBS bFS

Outputs

• Defects

• Wetness

• Touch-point

27


VD1.5 Defect Validation on LKP

Demonstrated increased drying robustness

TEOS @ 65nm Si @ 45nm

28

46sec BKM 29sec BKM

0.40

0.35

0.30

0.25

0.20

0.15

0.1 N

orm

ali

ze

d M

TM

Ad

ders

on

Si

@>

45

nm

46sec BKM 29sec BKM

BSLN Short Dry

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.1

No

rma

lize

d M

TM

Ad

ders

on

TE

OS

@>

65

nm

29 Applied Materials | Presented at Business of Cleans / SPCC 2018 29

Addressing Post CMP Cleaning Challenges in LKP System

Difficult to remove

contaminants:

► Slurry particles and polish residues

► Organic components of the slurry

► Pad debris

Corrosion

Multiple film materials

exposed and new

metals/liners/barriers

(W, TiN, Co, Ru, ULK)

Particle removal is more

difficult with time

Hydrophobic films, Philic /

phobic surface combination

Scratches on softer films

Secondary contamination

due to the “Loading” of the

cleaning media

Wafer edge cross-

contamination

5 consecutive cleaning stations

High shear force Pre-Clean

Megasonic option

Two Brush Boxes

Dryer

Flexible chemistries

Inter-Platen Clean

Chemistry in HCLU Option

Flexible chemistries

Brush box recipe flexibility

Vertical Marangoni Dryer

VD1.5 Dryer enhancement

Contamination removal in Pre-Clean

Advanced brush pressure control

Buff pad conditioning in Pre-Clean

BB2.0 brush conditioning in brush box

Wafer top-bevel Clean in Pre-Clean

Bevel clean in immersion Meg tank


Summary

Geometry shrinking and new material implementation in advanced nodes demand the

achievement of high particle removal efficiency.

To address cleaning challenges in various nodes, Applied CMP Clean technology continues to

evolve and includes broad portfolio of cleaning techniques

► Optimized post polish rinse

► High shear force Pre-Clean module for high particle removal efficiency in Dielectric and Metal CMP

► Single wafer Megasonic module for improving defect removal efficiency

► HF-compatible dual brush box module with

− Improved chemical coverage uniformity

− SteadyClean Brush Torque (Shear Force) Control for Consistent Roller Brush PRE

− Ozonated Water Rinse for Organic Defect Reduction

− BB2.0 Brush Conditioning for Extended Brush Life

► Single wafer IPA dryer for achieving water-mark free drying at high speed (with VD1.5 option)

30

post cmp cleans evolution - linx consulting

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