cmp consumables: current challenges and … cour… · ppt file · web view · 1999-10-28title:...

Philipossian

1NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing

Tutorial onChemical Mechanical Polishing (CMP)

Ara Philipossian

Intel Corporation

1999 Arizona Board of Regents for The University of Arizona

Philipossian


Outline of the Tutorial

• Section A: Overview– Generalized schematics of CMP and Post-CMP Clean– Current CMP environment– Evolution of CMP– The CMP Module– The CMP Infrastructure

• Section B: Polishing equipment trends• Section C: Polishing process issues• Section D: Consumables (pads & slurries)

– Quality issues– Factors affecting productivity– Critical pad and slurry parameters

Philipossian


Outline of the Tutorial

• Section E: Industry - University Gaps• Section F: Environmental Health and Safety (EHS)

considerations• Section G: Slurry fluid dynamics• Section H: Slurry re-use• Section I: Post-CMP cleaning

Philipossian


Section A: Overview

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Schematic Diagram ofChemical Mechanical Polishing Process

Carrier

RetainingRing

Slurry

Polish Platen

Pad

Pad Conditioner

Downforce

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Schematic Diagram ofPost-CMP Scrubbing

wafer

PVA brush

Cleaning Fluid

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CMP Environment• CMP has become the widely accepted planarization method of choice

for < 0.5 micron technologies• The overall CMP market is growing at a rate of ~ 50% per year• The current momentum in process integration and scaling far exceeds

the fundamental understanding of complex interactions among:– Equipment– Consumables (i.e. slurry, pad, carrier film)– Process parameters– IC type and density

• Processes and consumables are formulated to provide optimum performance for a given equipment and IC product set

• For a 4 metal layer process with STI, ILD and W CMP steps, approximately 20 polishers are needed ( 60% utilization, 20 wafers per hour, 5000 wafer starts per week factory)

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CMP Environment

• Protection of intellectual property hinders shared learning among IC, equipment and consumables manufacturers, but also provides a technological advantage:

– Internally developed equipment, precision parts and sub-systems

• Morimoto & Patterson, US Patent No. 5,104,828 (1992)• Breivogel, Blanchard & Prince, US Patent No. 5,216,843 (1993)• Breivogel, Louke, Oliver, Yau & Barns, US Patent No. 5,554,064 (1996)

– Internal slurry formulations licensed to suppliers for exclusive use– Customized pads– 3rd party modifications of off-the-shelf consumables and equipment

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Evolution of CMP

0

2

4

6

8

10

12

1994 (0.25to 0.50micron)

1997 (0.25to 0.35micron)

Num

ber o

f Pol

ish

Ste

ps

Tungsten

Oxide

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Evolution of CMP

Generation Application CMPAttributes

Post-CMP CleanAttributes

First

(0.8 to 0.5um)

ILD Single platen, single head,one step polish

Wet station,scrubber, DI water

Second

(0.5 to 0.25um)

ILD, Doped ILD,STI & W

Multiple platens, multipleheads, buffing, end-point

detection & on-boardmetrology

Scrubber, DI water& NH4OH

Third

(0.25 to 0.18um)

ILD, Doped ILD,STI, W, Low KILD, Cu, Al &

polysilicon

Integrated Dry-In Dry-Out,multiple platens, multiple

heads, non-rotary (i.e. orbitaland linear), multiple step

polish, end point detectionand on-board metrology

Integrated Dry-InDry-Out, scrubbing,DI water, NH4OH,HF, novel cleaning

methods andchemistries

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W S

lurr

y 2 3

ILD

Slu

rry 5 6

ILD

Top

Pad

8

Nor

mal

ized

Cos

t per

Waf

er

a - Negotiate Priceb - Insert competitionc - Reduce disposal volumed - reclaim and re-use

a - Negotiate Priceb - Insert competitionc - Increase pad life via better QCd - Increase pad life via better chemistry

Total Cost Chemical Expenditure per fully Processed Product Wafer

(Disposal and Treatments Costs are Included)

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The CMP Module

Polish

In-Situ Measure

Measure & Inspect

Measure & Inspect

Re-work

Product and Test Wafers

Water

Slurry

Pad

Energy

Clean

Product and Test Wafers

Liquid Waste

Energy

Filter

Solid Waste

Carrier Film

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• Polishing: Rotary (single or multiple heads and platens)– Orbital (single or multiple heads and platens)– Linear (multiple heads)

• Cleaning: Mechanical scrubbing (with & without chemistry or megasonics) Wet cleaning (with and without megasonics)

• Measurement and inspection: Removal Rate– Thickness uniformity (wafer-to-wafer, within-die, die-to-die)– Defect density– Dishing– Erosion– Plug recess Planarity– Surface Roughness

The CMP Infrastructure

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• In-situ Measurement:

– End-point detection• Consumables:

Pad (polyurethane, impregnated felt, fixed abrasive) Slurry (silica, alumina or ceria abrasives, organic and inorganic

additives)– Filter (point-of-use or post-slurry-blending)– Conditioning (diamonds)

• Slurry delivery• Water delivery• Waste treatment:

– Off-site disposal– Recycling Re-use

The CMP Infrastructure

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Section B: Polishing Equipment Trends

Philipossian, Morimoto and Cadien, CMP-MIC,Santa Clara, CA (1996)

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Equipment Environment

• In high-volume manufacturing, the balance between high throughput, size and complexity needs to be maintained

Polisher Number ofPolish Heads

Number ofPolish Plattens

A 1 1B 2 1C 3 3D 4 4E 5 1F 6 1

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Equipment Environment• Development of automated dry-in-dry-out systems that:

• Improve throughput• Reduce footprint• Reduce total cost• Reduce ergonomic issues• Reduce number of people

Robot

CleanI/O

Polish 1 Polish 2

Polish

I/O

Clean

• Ability to polish 300-mm wafers• In-situ metrology for device wafers with closed-loop control

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Section C: Polishing Process Issues

Philipossian, Morimoto and Cadien, CMP-MIC,Santa Clara, CA (1996)

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Process Issues• Within-Wafer Non-Uniformity (WIWNU):

– Wafer flatness– Carrier film, pad & slurry type (discussed earlier)– Carrier design– Pad conditioning method– Platen & carrier speeds– Retaining ring design (i.e. extent of pressure discontinuity between wafer

edge and retaining ring)– Slurry injection scheme

• Defect density:– Pad & slurry type– Use of secondary platen– Post-CMP cleaning method

• Removal rate:– Carrier film, pad & slurry type (discussed earlier)– Downforce– Platen & carrier speeds

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Process Issues• Planarity:

– Pad type– Circuit density & structure size– Extent of ILD removed– Downforce, platen speed & carrier speeds

– Step Height Ratio (SHR) = Post Step Height / Pre Step Height– The goal is to minimize SHR and maximize PD thereby minimizing Within-Die Non-

Uniformity (WIDNU)Planarization Distance (PD)

Post

PrePolish

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Effect of Structure Size & Densityon Post Step Height

0

2000

4000

6000

8000

0 4 8 12 16

Structure Size (mm)

Post

Ste

p H

eigh

t (A)

0

500

1000

1500

2000

0 20 40 60 80 100

Structure Density (%)Po

st S

tep

Hei

ght (

A)

• SHR is greater on metal pads compared to isolated narrow lines• Areas with lower circuit density polish faster than areas with dense underlying topography• Each circuit design will have a different WIDNU due to variations in size and density of interconnects

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Effect of Downforce on Removal Rate & Planarity

500

1000

1500

2000

2500

0 2 4 6 8 10

Downforce (psi)

Rem

oval

Rat

e (A

/min

)

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10

Downforce (psi)SH

R

• Increase in downforce (wafer pressure applied to the polishing pad) results in a linear increase in removal rate (i.e. Preston’s Equation)• Increase in downforce degrades planarity due to pad deformation and subsequent increase in local pressure at the ‘valley’ regions (i.e. Hook’s Law)

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Effect of Platen Speed on Removal Rate & Planarity

1000

1500

2000

2500

3000

0 20 40 60 80 100

Platen Speed (RPM)

Rem

oval

Rat

e (A

/min

)

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100

Platen Speed (RPM)SH

R

• Increase in platen speed increases removal rate linearly (i.e. Preston’s Equation)• Increase in platen speed improves planarity• At higher speeds the pad contacts mainly the ‘hill’ regions since it does not have sufficient time to conform to the ‘valley’ regions

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Effect of Carrier Speed onWafer Center & Edge Removal Rates

1000

1500

2000

2500

3000

0 20 40 60 80 100

Carrier Speed (RPM)

Rem

oval

Rat

e (A

/min

)

• Platen speed is maintained at 70 RPM• Center-to-edge removal rate difference increases with increasing carrier speed• Carrier diameter << platen diameter & at low carrier speeds, the linear velocity vector created by the carrier is much smaller than that created by the platen• As carrier speeds approach & exceed platen speed, the linear velocity vector created by the carrier becomes significant

Edge

Center

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Effect of Pad Hardness onPost Step Height and Planarization Distance

0

2000

4000

6000

8000

0 0.5 1 1.5 2 2.5 3 3.5 4

Horizontal Distance (mm)

Post

Ste

p H

eigh

t (A

)

• Harder pads deform less under pressure thus leading to:- Lower SHR, higher PD, and improved WIDNU (i.e in mm range)- Poorer WIWNU (i.e. in cm range)

• Harder pads also result in higher removal rates and higher defect densities

Soft Pad

Hard Pad

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Effect of Pad Compressibilityon Electrical Integrity of ILDKaufman, Proceedings of Spring MRS, CA (1995)

6

7

8

9

10

11E-

Fiel

d at

50%

Fai

ls(M

V/cm

)

As DepositedGlass Bead / PolymerPolymerStacked PolymerFelt

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Section D: CMP Consumables

Philipossian, Sanaulla, and Moinpour, Semicon West Technical Session on CMP, CA (1998)

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CMP Slurries and PadsAreas of Concern

Availability

Design

EHS

Legal

Supplier

Quality & Reliability

Manufacturability

Total Cost

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Quality IssuesIntel Corporation

All Chemicals

Procedural34%

Packaging24%

Intrinsic Material

27%

Delivery & Warehousing

15%

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Quality IssuesIntel Corporation

CMP Slurries

Procedural19%

Packaging19%

Intrinsic Material

43%


19%

70% Abrasive Issues20% Foreign Matter10% Other

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Quality Issues Intel Corporation

CMP Pads

Procedural15%

Intrinsic Material

75%


10%

40% Texture30% Foreign Matter20% Adhesive10% Other

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Impact of Quality IssuesThe Quality Indicator (QI)

QI = 100 - (2) [(a) + (2) (b) + (4) (c) + (8) (d) + (16) (e)]

SCAR: Supplier Corrective Action RequestNote: The Quality Indicator is measured on a quarterly basis for each supplier

e = No. of factory interrupts (i.e. issues resulting in tool or factory downtime, or product loss)

d = No. of near misses (i.e. issues requiring extra Intel resources to keep the factory running)

c = No. of repeat SCARs

b = No. of SCARs (i.e. issues caused by gross supplier negligence)

a = No. of issues (i.e. all issues regardless of impact to Intel)

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Supplier ComparisonCMP Suppliers vs. Photoresist and Wet Chemical Suppliers

(Data Collected Since 1Q96)

0

20

40

60

80

100

Pad & SlurrySuppliers

PhotoresistSuppliers

Wet ChemicalSuppliers

Aver

age

Qua

lity

Indi

cato

r

Challenge

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Equipment - Availability - Reliability

- Integrated Run Rate

Productivity

Factors Influencing Productivity

Labor - EHS

- Ergonomics - Automation

Process Stability & Manufacturability- RR- WIWNU, WTWNU, WIDNU

- Defects- Planarity- Pad life- Pad & slurry quality

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Tool Integration and AutomationIntegrated Run Rate

Robot

R1

CMP#1R2

CMP#2R3

Cleaner

R4

Robot

R1

Wafers Wafers

WafersRobot

R1 R5

CleanerRobot

R1

CMP#3

CMP#1R2

CMP#2

R3

R4

Wafers

Robot Limited

Cleaner Limited

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• Changing pads in high-volume manufacturing poses a serious ergonomic issue:

– Frequency of change– Difficulty of change

• A compromise must be reached between adhesive strength and its effect on the polishing process:

– Hardness– Compressibility– Corrosion resistance– Use of chemicals to remove

adhesive residues• Mechanical pad-pullers are

becoming a requirement in factories

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

WSPW

# of

pad

cha

nges

per

wee

k

Polishing Pad LifeFrequency of Changing Pads as a Function of Pad Life

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Polishing Pad LifeEffect of Pad Life on Tool Availability

• Availability (%) = 100 - Scheduled Downtime - Unscheduled Downtime• Scheduled Downtime:

– Tool PM, facilities PM, monitors, tool qualification and consumables changeout• Unscheduled Downtime:

– Out-of-control conditions, repairs

80

85

90

95

100 200 300 400 500 600Pad Life

Tool

Ava

ilabi

lity

(%)

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• 5000 WSPW• 5 oxide polish steps• Pad life of 500 (i.e. number of

wafers polished before pad change)

• Pad change duration:– Complexity of process

qualification on fresh pad (i.e. pad break-in)

– Other consumable changes (i.e. wafer carrier & pad conditioner)

– Ergonomics of pad change (i.e. pad size and adhesive strength)

5 Layers

0

20

40

60

80

100

120

0 5 10 15 20 25

# of Polishers

% A

vaila

bilit

y

0.5 hours

1 hour

2 hours

4 hours

6 hours

No. of Polishers vs. Tool AvailabilityEffect of Pad Change Duration

(Pad Life & Scheduled and Unscheduled Downtime are Fixed)

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5 Layers

0

20

40

60

80

100

120

0 5 10 15 20 25

# of Polishers

% A

vaila

bilit

y

1 hour

6 hours

12 hours

No. of Polishers vs. Tool AvailabilityEffect of Un-Scheduled Downtime

(Pad Life, Pad Change Duration and Scheduled Downtime are Fixed)

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Oxide Polisher Downtime Pareto Chart

Sch

edul

ed Q

ual

Tool

PM

Rep

air

OO

C

Oth

er

Uns

ched

uled

Qua

l

Faci

litie

s P

M

Nor

mal

ized

Tim

e

C+P

C+P+T

C+P+TC+P

C = ConsumablesP = ProcessT = Tool

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Oxide Polisher Downtime Pareto Chart

Sch

edul

ed Q

ual

Tool

PM

Rep

air

OO

C

Oth

er

Uns

ched

uled

Qua

l

Faci

litie

s P

M

Nor

mal

ized

Tim

e

average pad lifeaverage POU filter life

variability in pad and slurry properties (PSD)

average filter lifevariability in slurry properties (PSD)

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Effect of pH and Abrasive Content on ILD Removal Rate

Scherber et al., Proceedings of the Symposium on Planarization Technology: CMP, Semicon West (1994)

50

60

70

80

90

100

110

9.5 10.5 11.5pH

Rem

oval

Rat

e

9% 12% 15%

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Effect of Trace Metals on ILD Polish Performance

Slurry [Al] [Ca] [Cr] [Fe] [Ni] NormalizedDefect Density

F < 0.2 < 0.2 0.7 1 < 0.2 1

G 99 1.2 3 18 3.2 3 to 11

- All units in ppm- Slurries F & G are identical except for the metal content- Comparable removal rate and uniformity

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Effect of Hydrocarbons onILD Polish Performance

Slurry NormalizedHydrocarbon

Content

NormalizedDefectDensity

H 1 1

I 14 3 to 6

- Slurries H & I are identical except for the hydrocarbon content

- Hydrocarbon contained a polar group- Comparable removal rate and uniformity- Majority of defects were ‘scratches’

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Abrasive Geometry

Primary Particle

Aggregate

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Effect of Abrasive Geometryon ILD Polish Performance

Slurry Appx. PrimaryParticle

Size(nm)

Appx. MeanAggregate

Size(nm)

NormalizedMean

RemovalRate

NormalizedWIWNU

(3-sigma)

A 29 122 86 --B 29 110 100 100C 19 95 82 83D 20 110 79 154E 50 200 94 104

- Fumed silica abrasive- Constant pH and abrasive content- Comparable defect density and planarity

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Effect of Abrasive Geometry on ILD Removal Rate

70

80

90

100

110

0.15 0.2 0.25 0.3

PPS / MAS (unitless)

Rem

oval

Rat

e

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Section E: Industry - University Gaps

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Core Subject Funded UniversitiesPad synthesisPad deformation studies SUNY, Saitama Univ, RPI,

Nagoya Inst of TechBrush synthesisAdhesive developmentAbrasive powder synthesisAbrasive powder and slurry morphology, PSD,geometry and type

Univ of Minnesota, Univ ofCentral Florida

Abrasive powder metrologySlurry and pad fluid mechanics (empirical) Tufts, Georgia Inst of TechSlurry and pad fluid mechanics (modeling) TuftsSlurry consumption reduction TuftsConsumable - tool - process interactions Berkeley, MIT, Tufts, ASUElectrochemistry Univ of NM, Sandia, RPI,

Univ of ArizonaSlurry dispersion and mixingSlurry filtration IMEC

Development of Core Competencies(Industry - University Gaps)

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Core Subject Funded UniversitiesReaction kinetics RPI, Sandia, Clarkson,

Univ of NMCMP process development & modeling IMEC, MIT, Tohoku Univ,

Stevens InstituteSlurry, pad and brush shelf-life studiesAdditives to enhance or retard removal rates Clarkson, RPI, Tohoku

UnivAdditives to modulate removal rate selectivity RPI, ClarksonDispersion and colloidal stability Clarkson, Univ of ArizonaAnti-caking agent developmentSlurry reclaim and re-use Univ of ArizonaDissolution, passivation, adhesion and roughening Univ of Florida, ClarksonSurfactants Univ of Arizona, ClarksonPad and slurry interactions SUNYEnhanced Pourbaix diagrams

Development of Core Competencies(Industry - University Gaps)

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Section F: EHS Hierarchy and Considerations

Philipossian, Moinpour and Poliak, Proceedings of VMIC, Santa Clara, CA (1998)

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EHS Hierarchy & Issues

• Environmental regulations are growing at an amazing rate:– Federal and local initiatives & regulations– International initiatives

• Recycling regulations are extremely complex and require detailed understanding and follow-through

• Many new materials are not designed with EHS in mind. In many cases, suppliers do not even know the potential EHS impact of these materials

• To find out late in the process that a material has a serious EHS impact can delay technology introduction or increase cost

• Most chemical suppliers have committed to ownership from cradle-to-grave, but follow-through is poor

Replace > Reduce > Re-use > Recycle > Abate

Philipossian


RA

IARHAA

CERFA EPAOPA

GCRAPPACAAA

SPAGCPAWQAEPCRA

SARAHSWANWPAAPA

CERCLAUORASWDAA

EAWANCPACWASWDARCRATSCAHMTA

SDWACZMAODA

EQIA CAANPAA NEPAAQA

NESA

WAWA

FIFRA

MVAPCA

WLFMLA

FCAPHSA

TGA RHA

FWCAWRA

FWPCA

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000020

4060

8010

012

014

016

0

Year

Growth of US Environmental Legislation(Cumulative No. of Environmental Laws)

Technology & Environment,Washington DC, National AcademyPress, p. 101 (1989)

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EHS in CMP(Level - I Considerations)

energy inputs

chemical inputs

EHSergonomics

chemical outputs

energy outputs

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energy inputs

chemical inputs

ergonomics

chemical outputs

polish tool

post-polish tool

film type

IC type

slurry type

process recipe

pad type

post-polish consumable

IC density

wafer size

publicly owned treatment works

in-fab discharge treatment methodfab location

wafer starts per week

energy outputs

chemical blending & delivery system

UPW systemEHS

EHS in CMP(Level - II Considerations)

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energy inputs

chemical inputs

ergonomics

chemical outputs

polish toolpost-polish tool

film typeIC type

slurry type

process recipe

pad type


IC density

wafer size

publicly owned treatment worksin-fab discharge treatment methodfab locationwafer starts per week

energy outputs

chemical blending & delivery systemUPW system

pHabrasive typeabrasive size

abrasive shapeabr. morphology

solids contentoxidizer typeadditive type

buffer typebase typeacid type

zeta potentialionic strength

viscositycolor

shelf lifepot life

dispersability

EHS in CMP(Level - III Considerations)

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energy inputs

chemical inputs

ergonomics

chemical outputs

polish toolpost-polish tool

film typeIC type

slurry type

process recipe

pad type


IC density

wafer size


energy outputs


sizematerial

stackthickness

texturemorphology

hardnessspecific gravitycompressibility

hole patterngroove pattern

adhesive strengthlife

shelf life


Philipossian


energy inputs

chemical inputs

ergonomics

chemical outputspolish toolpost-polish tool

film typeIC type

slurry type

process recipe

pad type


IC density

wafer size


energy outputs


automationfootprint

conditionerendpoint detectionwater inj. schemeslurry inj. scheme

effluent segregationPOU filtration

flow dynamicsre-use compatibility

carrier designplaten design

ring designnumber of platens

rotation schemevent design

parts clean req.PPE req.

ease of maint.run rate


Philipossian


energy inputs

chemical inputs

ergonomics

chemical outputspolish tool

post-polish tool

film typeIC type

slurry type

process recipe

pad type


IC density

wafer size

publicly owned treatment worksin-fab discharge treatment method

fab locationwafer starts per week

energy outputs


water flow rateslurry flow rate

chemical flow ratedilution

flow overlapautomation

carrier speedplaten speed

down-forceback-pressure

number of platensconditioning recipe


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Section G: CMP Fluid Dynamics

Coppeta, Roger, Racz, Kaufman & Philipossian, Pad effects on slurry transport beneath a wafer during polishing,

CMP-MIC, Santa Clara (1998)

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Fluid Dynamics• Goal:

– Reduce slurry dispense volume– Increase slurry utilization efficiency– Entrain a uniform layer of new slurry beneath the wafer– Prevent polished material from being re-entrained beneath the wafer

• Key issues which need to be comprehended:– Chemical & mechanical factors which influence polishing– Slurry film thickness between wafer and the pad– Slurry transport mechanism, and factors that influence slurry

transport• Slurry injection scheme• Slurry flow rate• Pad type, conditioning and topography• Platen and carrier speed

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Dual-Emission Laser-Induced Fluorescence

Glass Wafer

Polish Platen

Pad

Camera Laser

Slurry with Fluorescence dye Slurry

Philipossian


http:\\www.tuftl.tufts.edu

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Slurry Transport

InterrogationRegion

Wafer

Post

Examining:- Mean slurry age- Residence time- Slurry Gradients

(flat pads)- Drag on wafer- Fluid thickness measurements

Pad

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Slurry Flow Rate

Flat Pad

Grooved Pad Manufacturer: RodelSlurry Flow Rate: x cc/minWafer Down Force: 4 psiPlaten Speed: 60 rpmX-Y Groove Depth: 20 mils

Time (sec)

Perc

ent N

ew S

lurr

y

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Platen Speed

Manufacturer: FreudenbergSlurry Flow Rate: 35 cc/minWafer Down Force: 4 psiPlaten Speed: x rpmX-Y Groove Depth: 20 mils

Flat Pad

Grooved Pad

Time (sec)

Perc

ent N

ew S

lurr

y

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Static Case

Pad deformation: (4 psi, 0 rpm)

Image of a single pad Thickness profile as determined by ratiometric technique

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Section H: Slurry Reuse

Kodama, A reclaim use of CMP slurry, 29th Symposium on ULSI Ultra Clean Technology, Tokyo, Japan (1996)

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Slurry Re-UseExperimental Setup

Secondary Platen Primary Platen

Slurry Capture Tub

Spent Slurry Reservoir

Pump & Filter

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RR & WIWNU vs. Slurry Reclaim

750

1000

1250

1500

1750

2000

1 2 3 4 5 6No. of Reclaims

Rem

oval

Rat

e (A

/min

)

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6No. of Reclaims

WIW

NU

(% 1

-sig

ma)

fumed 50 / 200 nmcolloidal 102 / 212 nm

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Surface Roughness & pH vs. Slurry Reclaim

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 6No. of Reclaims

Ra

(nm

)

1010.110.210.310.410.510.610.710.810.9

1111.111.211.311.411.5

1 6No. of Reclaims

pH

fumed 50 / 200 nm

colloidal 102 / 212 nm

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Mean Aggregate Size vs. Slurry Reclaim

180

185

190

195

200

205

210

215

220

1 6No. of Reclaims

Mea

n A

ggre

gate

Siz

e (n

m)

fumed 50 / 200 nmcolloidal 102 / 212 nm

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Section I: Post-CMP Cleaning

Moinpour & Burke, Keynote Address, CMP-MIC, Santa Clara (1998)

Jankovsky, 3rd CMP Workshop, Lake Placid, NY (1998)

Busnaina, 3rd CMP Workshop, Lake Placid, NY (1998)

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Post-CMP Clean

• Defects & Contamination:– Abrasive particle residues

(i.e. silica, alumina or ceria)– Chemicals on surface (i.e.

surfactants, or slurry additives)

– Alkali metal contaminants (i.e. K or Na)

– Heavy metals (i.e. Fe)– Pad residues– Pad conditioner (i.e.

diamond) residues

• Requirements:– Quick and repeatable– Cause do damage to devices

or films (i.e. change roughness or planarity)

– No residue or redeposition– Low cost of ownership

(COO)• Environment:

– Mechanical scrubbing (with & without chemistry or megasonics)

– Wet cleaning (with and without megasonics)

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Post-CMP Clean (Defect Reduction Strategies)

• Step - I … Reduce defects during the CMP process:– Use slurry additives

• Step - II … Reduce defects further by performing an additional buffing process:– Use chemicals on the

secondary platen• Step - III … Reduce defects

even further during the post-CMP cleaning process:– Use chemicals in the post-

CMP cleaning tool

Application Process Chemical

Oxide NH4OH & HFW NH4OH & HF

STI NH4OHpolysilicon APM & HCl

Copper ProprietaryChemicals

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Post-CMP Clean(A Sampling of Chemicals or Methods

Cited in the Literature)

0

3

6

9

12

15

18D

I Wat

er

NH

4OH

HF

Citr

ic A

cid

Meg

ason

ics

TMA

H

Surfa

ctan

t

Hot

DI W

ater

KO

H

APM H

Cl

H2O

2

NH

4F Ice

Prop

riete

ry

Philipossian


• 0.35 um, 200mm technology• Effect of post ILD CMP clean

chemistry on end-of-line yield• Process 1 and Process 2 are

identical polish processes• Process 2 uses a different

Post-CMP Clean chemistry• Improved consumable lifetime• No impact on overall run rate

Post-CMP Clean(Process Improvement)

0

0.2

0.4

0.6

0.8

1

Yield Impact

Cum

ulat

ive

Prob

abili

ty

Philipossian


Cleaning Theory• Particles in liquids:

– Primary cause of adhesion is van der Walls forces (DLVO Theory)

– Secondary cause of adhesion is Electric Double Layer (EDL) forces (however, they are usually repulsive and can help in particle removal)

• Particles in solution become charged• Stern Layer + Diffuse Layer = EDL• Potential at shear plane = Zeta Potential• EDL thickness varies as inverse square root of the ionic strength

(i.e. 4X increase in ionic strength will reduce EDL thickness by 2X)

• EDL and the Zeta Potential are a function of pH

Philipossian


Cleaning Theory

• ELECTRIC DOUBLE LAYER

Philipossian


Cleaning Theory

• DLVO THEORY

Philipossian


Post-CMP Cleaning

Al2O3 Pure

-6

-4

-2

0

2

4

6

2 4 6 8 10 12

pH

Mob

ility

(m2/

V/S

)

Mobility

Philipossian


Brush Cleaning• Advantages:

– Most common cleaning methodology

– Double-side and edge cleaning capability

– High energy scrub capability– The contact mechanism can

help clean wafers with topography

– Simple integration with dry-in-dry-out processing

– Compatible with wet chemistry– Compatible with the recent

advances in ‘smart-brushes’ (zeta-potential engineering)

• Disadvantages:– Contact with wafers may be

harmful– Brush loading with particle

and re-deposition– Low throughput– High COO (chemicals, DI

water, consumables parts)– Static build-up which may

increase particle adhesion forces

– Tough for brushes to contact high aspect ratio topography

– Brush shedding– Brush break-in required

Philipossian


Wet Chemical Cleaning• Advantages:

– More chemically intensive compared to brush cleaning

– Residues and foreign matter can be readily dissolved and removed from the surface

– Ability to manipulate zeta potential to remove particles

– Low COO– High throughput– Controlled cavitation (formation of gas

bubbles by ultrasound) and acoustic streaming (steady flow induced by sound field) can be used to detach and remove particles from the surface

– Formation of acoustic boundary layer

• Disadvantages:– Particle saturation in the

recirculating tank– Difficult to integrate

with dry-in-dry-out processing

– Cleaning process must be tailored to each device layer and material

– Uncontrolled cavitation may cause wafer surface damage

cmp consumables: current challenges and … cour… · ppt file · web view · 1999-10-28title:...

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