impact seminar - university of california, san diego

March 17, 2008 CMP

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IMPACT

Title: Past, present, and future of CMP

Faculty: David Dornfeld

Department: Mechanical Engineering

University: Berkeley

IMPACT Seminar

March 17, 2008 CMP

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IMPACT

• CMP Overview

• CMP History and Future Development (courtesy

of Ken Cadien, formerly of Intel (Fellow Emeritus)

and now Professor and Canada Research Chair in

Nanofabrication, University of Alberta, Department

of Chemical & Materials Engineering)

- slurries and pads

• Towards design for manufacturing (DFM) for CMP

in IMPACT

Outline

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IMPACT

Mechanical

Phenomena

Chemical

Phenomena

Interfacial and

Colloid

Phenomena

Components of Chemical Mechanical Planarization

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Scale Issues in CMP

From E. Hwang, 2004

Scale/sizenm !m mm

Material

Removal

Mechanical particle forces

Particle enhanced chemistry

Chemical

Reactions

Active

AbrasivesPores,

WallsGrooves

Tool mechanics,

Load, Speed

critical features dies

Pad

Mechanism

Layoutwafer

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IMPACT

“GoogleEarth” view of CMP process

We are here

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Head

Plate

n

Pad

do

wn

-

forc

e

slurry

supply

rotation

of wafer

head

Wafe

r 4-

12”

Copper

Featur

e

pad asperity

abrasive

particles

100nm-10!m

~1!

m1-10!m

Pad asperity

Abrasive

Pad/Wafer

Die

Feature/Asperity

Abrasive Contact

CMP phenomena at different scales

March 17, 2008 CMP

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IMPACT

Cadien Cadien OutlineOutline

•• History 1984-2008History 1984-2008

•• Challenges andChallenges and

solutions: slurries andsolutions: slurries and

padspads

–– Next 10 yearsNext 10 years

•• Very long TermVery long Term

•• ConclusionsConclusionsSource: K. Cadien, “The Future of CMP: Slurries and pads,” Keynote

presentation, CMP-MIC, Fremont, March 4, 2008.

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IMPACT

History circa 1984History circa 1984

The semiconductor industry thought that scaling was done

at the 1.0 mm dimension due to topography

Topography 3 µm

Topography > DOF !

Source: K. Cadien, “The Future of CMP: Slurries and pads,” Keynote


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IMPACT

History 1984History 1984

“Karey Holland remembers her reaction one day

in 1984 when a colleague, Bill Cote, at IBM

recommended that she use what seemed for all

the world like a scrub pad and a scouring liquid for

one of the critical steps in processing the silicon

wafers that contained the next-generation

memory chips”.

“The idea of exposing the wafer surface to billions

of abrasive particles did not sit well with her.

‘You’re not going to put that dirt on my wafer,’ she

protested”.Source: Scientific American Magazine, February 1998

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IMPACT

Interconnect Scaling

500 nm

ILD planarization, W plugs w etch

back

130 nm

Six Cu Layer

350 nm

Four Al metal layers, W polish, PSG

180 nm

Six Al Metal layers

250 nm

Five Al metal layers,

SiOF

65 nm

Eight Cu

Layer

90 nm

Seven Cu

Layer

1000 nm

Two Al Metal layers,

BPSG

Oxide PolishSTI PolishPoly PolishTungsten PolishCopper PolishBarrier PolishWet Station CleanDSS cleanDry in/Dry out

Manymilestones

Enable

d by

CMP



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IMPACT

Transistors have also been enabled by CMPTransistors have also been enabled by CMP

Don Scansen, “Under the hood of Intel’s 45nm technology”, WWW.semiconductor.com



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IMPACT

CMP’s Attributes• CMP improved yield

•Removes defects

• CMP reduced electromigration

• CMP enabled optical lithography

• CMP enabled novel integration

schemes•Cu damascene technology

• Enabled upstream modules•CVD

•EPSource: K. Cadien, “The Future of CMP: Slurries and pads,” Keynote


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IMPACT

5-inch FSM5-inch FSM

The Future (next 10 years)

CMP Applied to Many Non-IC

Applications (Courtesy Cabot Microelectronics)

Ref: K. Cadien, “The Future of CMP: Slurries and pads,”

Keynote presentation, CMP-MIC, Fremont, March 4, 2008.

March 17, 2008 CMP

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IMPACT

Challenges for the IC IndustryChallenges for the IC IndustryThe next 10 yearsThe next 10 years

•• Integrating porous Integrating porous ILDsILDs

•• Improving copper dishing, erosion, defects;Improving copper dishing, erosion, defects;

many more metal layersmany more metal layers

•• More tune ability for STI, W, barrierMore tune ability for STI, W, barrier

•• Polishing novel materialsPolishing novel materials

•• 450 mm wafers?450 mm wafers?

•• 1.5 mm edge exclusion?1.5 mm edge exclusion?

Source: K. Cadien, “The Future of CMP: Slurries and pads,”


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IMPACT

ITRS 2007ITRS 2007

PLANARIZATION POTENTIAL SOLUTIONS, pg 24PLANARIZATION POTENTIAL SOLUTIONS, pg 24

Slurries and

Pads

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IMPACT

250 nm

chip 32 nm chip

Oxide

SiON

Poly

Nitride

Doped Ox

Doped Si

W

Ti(N)

Cu

Low K

High K

Ni Silicide

Ru +Ta(N)

ULK

Al(Cu)

A Variety of Materials

Make Up Chip Surfaces

Source: Spiro et al, Proceedings 2007 ICST Conference, Shanghai.

60 Elements (Potential)

15 Elements

Smaller Traces; New Materials,

Processes and Designs

Semiconductors Have Changed

Source: K. Cadien, 2008.

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IMPACT

Oxide Rate2500

NitrideRate

1000

0 0

2500

0 Å/min

Poly

Rate

Fully Tunable Oxide, Nitride, and Poly Polish( Courtesy Cabot Microelectronics)



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IMPACT

Designers Are Demanding More Choice:Example – Tungsten Tunability

SIN

Ti/TiN

PETEOS

Pad Ox

AP-USG

SIN

PETEOS

Pad Ox

AP-USG

Non-Selective

W

SIN

PETEOS

Pad Ox

AP-USG

Selective

i.e.W2000 i.e. W7300Courtesy Cabot Microelectronics

March 17, 2008 CMP

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IMPACT

CMCCMC’’s Epic® D100 Pad - New Pad Process:s Epic® D100 Pad - New Pad Process:

Continuous Extrusion, Supercritical CO2, High Density Continuous Extrusion, Supercritical CO2, High Density

Courtesy Cabot MicroelectronicsSource: K. Cadien, “The Future of CMP: Slurries and pads,”


March 17, 2008 CMP

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IMPACT

• Material Selection and Control– Interspersed Long/Short Chain Polymers

– Optimize Number and Regularity of Hard/Soft Domains

– Control Phase and Void Composition

• Material Processing: Liquid Casting

– Custom Tuned Texture Across the Pad

– Unique Elastic, Viscoelastic and Thermal Properties

Both material and processing knobs allowtunability and extensibility of pad properties

CMP Pads Optimized for Application PerformanceCMP Pads Optimized for Application Performance



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IMPACT

Materials/Process Design: RationaleMaterials/Process Design: Rationale

•• Numerous small hard and soft domainsNumerous small hard and soft domains

–– control tribological and thermal propertiescontrol tribological and thermal properties

–– stable and extended boundary lubrication regimestable and extended boundary lubrication regime

•• Specific curativesSpecific curatives

–– control elastic and control elastic and viscoelastic viscoelastic propertiesproperties

•• GradingGrading

–– improve across the wafer uniformity w/o compromisingimprove across the wafer uniformity w/o compromisingplanarization efficiencyplanarization efficiency

•• Solid lubricantSolid lubricant

–– reduce motor torque during polishreduce motor torque during polish

–– lower friction and lower shear w/o compromising RRlower friction and lower shear w/o compromising RR

•• Extended & lower COFExtended & lower COF

–– lower dishing/erosion and stacking faultslower dishing/erosion and stacking faults

–– lower stress on low k dielectrics during CMPlower stress on low k dielectrics during CMP

Neopad, Ra ~2.35um



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IMPACT

Innovative Pad Design Enhanced Performance

•• Solo pad technology Solo pad technology w/ w/ soft & hard segments in the polymer matrix:soft & hard segments in the polymer matrix:–– Improved planarity within die and within waferImproved planarity within die and within wafer

–– Improved non-uniformity and low edge exclusionImproved non-uniformity and low edge exclusion

–– Reduce Reduce microscratches microscratches and lower defectsand lower defects

–– Competitive material polish ratesCompetitive material polish rates

•• Pad technology designed Pad technology designed w/ w/ ““tunabilitytunability”” feature for each application: feature for each application:–– Provides a novel key process parameter to improve CMP processProvides a novel key process parameter to improve CMP process

performance for current and advanced technologiesperformance for current and advanced technologies

•• Differentiated Pad Manufacturing Concept: Compression moldedDifferentiated Pad Manufacturing Concept: Compression molded– In-situ pad grooves ensure uniform, high integrity profiles and provide

better slurry distribution and efficiency

– Enables significant batch-to-batch process control

•• Lower CoO:Lower CoO:– Material cross-linking: lower wear rates and >2X extended pad life

– Reduced slurry usage (20-30% reduction)

– Less defect addersSource: K. Cadien, “The Future of CMP: Slurries and pads,”


March 17, 2008 CMP

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IMPACT

Very long term - circa 2030

•• There is definitely an inflection pointThere is definitely an inflection point

occurring in the next 20 yearsoccurring in the next 20 years

• Both transistors and interconnects

face fundamental change



Running out of elements for both

transistors and interconnects

March 17, 2008 CMP

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IMPACT

ITRS 2007 Emerging Research DevicesITRS 2007 Emerging Research Devices



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IMPACT

Cu interconnect scaling is an issue long term

Source: S. M. Rossnagel and T. S. Kuan, “Alteration of Cu conductivity in the size effect regime”, J. Vac.

Sci. Technol. B 22.1., Jan-Feb 2004



Resistivity increases with

reduced film thickness

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IMPACT

Could Al replace Cu?

Source: P. Kapur, J. P. McVittie, and K. C. Saraswat, “Technology and

Reliability Constrained Future Copper Interconnects—Part I: Resistance

Modeling”, IEEE Trans. On Electron Devices, 49, (2002) 590-597

Timing depends on barrier

thickness, resistivity

March 17, 2008 CMP

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IMPACT

500 nm

ILD planarization, W

plugs w etch back

130 nm

Six Cu Layer

350 nm

Four Al metal

layers, W polish,

PSG?

180 nm

Six Al Metal layers

250 nm

Five Al metal

layers, SiOF

1000 nm

Two Al Metal

layers, BPSG

Interconnect Scaling & Future Options

65 nm

Eight Cu

Layer

90 nm

Seven Cu Layer

Laser

µP

Optical

modulator

Receiver

circuit

Transmitte r

circuit

Optical WG

Photodetector

Optical

Coupler

Laser

µP

Optical

modulator

Receiver

circuit

Transmitte r

circuit

Optical WG

Photodetector

Optical

Coupler

CNT

?

Optical

3D

Options

After severalgenerations of scaling

Source: K. Cadien, “The Future of CMP: Slurries

and pads,” Keynote presentation, CMP-MIC,

Fremont, March 4, 2008.

March 17, 2008 CMP

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IMPACT

What does all of this mean for CMP?What does all of this mean for CMP?

• Hard to predict

– Depends on integration scheme

• CMP’s attributes will be relevant

– CMP does improve yield so whatever the

scheme this may be useful

– Scattering in interconnects is due partially to the

roughness of the interconnect...CMP does

smooth...Cu and optical

• There is some hope that CMP will be around

in 2030Source: K. Cadien, “The Future of CMP: Slurries



March 17, 2008 CMP

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IMPACT

Summary

Next 10+ years

Continuous improvement

Pad & slurry tunability

New materials

2030 and beyond

3D then optical

Transition/paradigm

shift in 10-20 years

Depends on design,

architecture, etc.

Source: K. Cadien, “The Future of CMP: Slurries



March 17, 2008 CMP

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IMPACT

Cadien’s Summary

• For the next decade or more

- CMP will need to do continuous improvement

•Improved defects, dishing and erosion

•Increased tunability for slurries

•New slurries for new materials

•Novel pads with more tunability to enable the

above

• How is IMPACT addressing these?- process understanding embedded in process model

- stress-induced failures and reduced force polishing

- slurry behavior and slurry “design” based on mechanics

- revive “SMART pad?”

March 17, 2008 CMP

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IMPACT

Pad asperity

Abrasive

Abrasive Contact

Let’s zoom in…

Slurry agglomeration

Charging issues in lapping

Tribo-chemical removal

CMP induced stress

March 17, 2008 CMP

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IMPACT

• Present methods treat CMP process as a black box; are blind toprocess & consumable parameters

• Need detailed process understanding

– For modeling pattern evolution accurately

• Present methods do not predict small feature CMP well

– For process design (not based on just trail and error)

• Multiscale analysis needed to capture different phenomena:

– At sufficient resolution & speed

• CMP process less rigid than other processes: possibility of optimizingconsumable & process parameters based on chip design

– MfD & DfM

• Source of pattern dependence is twofold:

– Asperity contact area (not addressed yet)

– Pad hard layer flexion due to soft layer compression (addressed byprevious models)

CMP Modeling Challenges - IMPACT

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IMPACT

Removal Rate (RR)

Adding the electro-chemical effects

Slurry chemistry(pH, conc. of oxidizer, inhibitor

& complexing agent)

Pad propertieslayers’ hardness, structure

AbrasiveType, size & conc.

Polishing conditions(pressure P, velocity V)

• Develop a transient tribo-electro-chemical model for material removal

during copper CMP

– Experimentally investigate different components of the model

• Using above model develop a framework for pattern dependency

effects.

Polished material

Planarization,

Uniformity, Defects

Incoming topography

CMP

Model1. Passivation Kinetics

2. Mechanical Properties

of Passive Film

3. Abrasive-copper Interaction

Frequency & Force

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IMPACT

Conclusion

• Continuing evolution of devices and materials

• CMP offers interesting challenges at manydifferent scales

– Defect reduction

– “Predictability” for slurry/pad development

• Modeling provides driver for DfM (and MfD)

• Accommodate new applications of CMP

• Strategy must allow appropriate detail at anylevel

• Data structure should allow inheritance to linkhigher views to lower views, rapidly

• Must be well validated/calibrated

• Needs to be “user friendly”

• Requires close interaction with industry drivers

March 17, 2008 CMP

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IMPACT

Thank you for your attention!

impact seminar - university of california, san diego

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