Tutorial on Chemical Mechanical Polishing (CMP)cmpconsulting.org/wa_files/CMP_20Tutorial.pdf ·...

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

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Tutorial on Chemical Mechanical Polishing (CMP)

Ara Philipossian

Intel Corporation

© 1999 Arizona Board of Regents for The University of Arizona


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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


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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


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Section A: Overview


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Schematic Diagram of Chemical Mechanical Polishing Process

Carrier

Retaining Ring

Slurry

Polish Platen

Pad

Pad Conditioner

Downforce


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Schematic Diagram of Post-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


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Evolution of CMP


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a - Negotiate Price b - Insert competition c - Reduce disposal volume d - reclaim and re-use

a - Negotiate Price b - Insert competition c - Increase pad life via better QC d - 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


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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

Clean I/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

Pre Polish


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Effect of Structure Size & Density on Post Step Height

•  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

•  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

•  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 on Wafer Center & Edge Removal Rates

•  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 on Post Step Height and Planarization Distance

•  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 Compressibility on Electrical Integrity of ILD Kaufman, Proceedings of Spring MRS, CA (1995)


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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 Pads Areas of Concern

Availability

Design

EHS

Legal

Supplier

Quality & Reliability

Manufacturability

Total Cost


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Quality Issues Intel Corporation

All Chemicals


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CMP Slurries

70% Abrasive Issues 20% Foreign Matter 10% Other


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CMP Pads

40% Texture 30% Foreign Matter 20% Adhesive 10% Other


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Impact of Quality Issues The Quality Indicator (QI)

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

SCAR: Supplier Corrective Action Request Note: 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 Comparison CMP Suppliers vs. Photoresist and Wet Chemical Suppliers

(Data Collected Since 1Q96)

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 Automation Integrated Run Rate

Robot

R1

CMP#1 R2

CMP#2 R3

Cleaner

R4

Robot

R1

Wafers Wafers

Wafers Robot

R1 R5

Cleaner Robot

R1

CMP#3

CMP#1 R2

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

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


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Polishing Pad Life Effect 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


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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)

No. of Polishers vs. Tool Availability Effect of Pad Change Duration

(Pad Life & Scheduled and Unscheduled Downtime are Fixed)


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No. of Polishers vs. Tool Availability Effect of Un-Scheduled Downtime

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


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Oxide Polisher Downtime Pareto Chart

C+P

C+P+T

C+P+T C+P

C = Consumables P = Process T = Tool


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Oxide Polisher Downtime Pareto Chart average pad life average POU filter life

variability in pad and slurry properties (PSD)

average filter life variability 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)


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Effect of Trace Metals on ILD Polish Performance

- 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 on ILD Polish Performance

- 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 Geometry on ILD Polish Performance

- 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


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Section E: Industry - University Gaps


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Development of Core Competencies (Industry - University Gaps)


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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


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RA

IA RHAA

CERFA EPA OPA

GCRA PPA CAAA

SPA GCPA WQA EPCRA

SARA HSWA NWPA APA

CERCLA UORA SWDAA

EAWA NCPA CWA SWDA RCRA TSCA HMTA

SDWA CZMA ODA

EQIA CAA NPAA NEPA AQA

NESA

WA WA

FIFRA

MVAPCA

WL FMLA

FCA PHSA

TGA RHA

FWCA WRA

FWPCA

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 0 20

40

60

80

10

0 12

0 14

0 16

0

Year

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

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


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EHS in CMP (Level - I Considerations)

energy inputs

chemical inputs

EHS ergonomics

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 method fab location

wafer starts per week

energy outputs

chemical blending & delivery system

UPW system EHS

EHS in CMP (Level - II Considerations)


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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


IC density

wafer size

publicly owned treatment works in-fab discharge treatment method fab location wafer starts per week

energy outputs

chemical blending & delivery system UPW system

pH abrasive type abrasive size

abrasive shape abr. morphology

solids content oxidizer type additive type

buffer type base type acid type

zeta potential ionic strength

viscosity color

shelf life pot life

dispersability

EHS in CMP (Level - III Considerations)


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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


IC density

wafer size


energy outputs


size material

stack thickness

texture morphology

hardness specific gravity compressibility

hole pattern groove pattern

adhesive strength life

shelf life



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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


IC density

wafer size


energy outputs


automation footprint

conditioner endpoint detection water inj. scheme slurry inj. scheme

effluent segregation POU filtration

flow dynamics re-use compatibility

carrier design platen design

ring design number of platens

rotation scheme vent design

parts clean req. PPE req.

ease of maint. run rate



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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


IC density

wafer size

publicly owned treatment works in-fab discharge treatment method

fab location wafer starts per week

energy outputs


water flow rate slurry flow rate

chemical flow rate dilution

flow overlap automation

carrier speed platen speed

down-force back-pressure

number of platens conditioning 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


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http:\\www.tuftl.tufts.edu


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Slurry Transport

Interrogation Region

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: Rodel Slurry Flow Rate: x cc/min Wafer Down Force: 4 psi Platen Speed: 60 rpm X-Y Groove Depth: 20 mils

Time (sec)

Perc

ent N

ew S

lurr

y


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Platen Speed

Manufacturer: Freudenberg Slurry Flow Rate: 35 cc/min Wafer Down Force: 4 psi Platen Speed: x rpm X-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-Use Experimental Setup

Secondary Platen Primary Platen

Slurry Capture Tub

Spent Slurry Reservoir

Pump & Filter


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RR & WIWNU vs. Slurry Reclaim

fumed 50 / 200 nm colloidal 102 / 212 nm


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Surface Roughness & pH vs. Slurry Reclaim

fumed 50 / 200 nm

colloidal 102 / 212 nm


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Mean Aggregate Size vs. Slurry Reclaim

fumed 50 / 200 nm colloidal 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


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Post-CMP Clean (A Sampling of Chemicals or Methods

Cited in the Literature)


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•  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)


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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


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Cleaning Theory

•  ELECTRIC DOUBLE LAYER


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Cleaning Theory

•  DLVO THEORY


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Post-CMP Cleaning


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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


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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

Tutorial on Chemical Mechanical Polishing (CMP)cmpconsulting.org/wa_files/CMP_20Tutorial.pdf ·...

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Transcript of Tutorial on Chemical Mechanical Polishing (CMP)cmpconsulting.org/wa_files/CMP_20Tutorial.pdf ·...