Cmp Tutorial

Tutorial on Chemical Mechanical Polishing (CMP) Ara Philipossian Intel Corporation  1999 Arizona Board of Regents for The University of Arizona

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

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

Section A: Overview

Schematic Diagram of Chemical Mechanical Polishing Process Carrier Retaining Ring Slurry Polish Platen Pad Pad Conditioner Downforce

Schematic Diagram of Post-CMP Scrubbing wafer PVA brush Cleaning Fluid

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)

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

Evolution of CMP

Total Cost Chemical Expenditure per fully Processed Product Wafer (Disposal and Treatments Costs are Included) 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

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

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

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

Section B: Polishing Equipment Trends Philipossian, Morimoto and Cadien, CMP-MIC, Santa Clara, CA (1996)

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

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

Section C: Polishing Process Issues Philipossian, Morimoto and Cadien, CMP-MIC, Santa Clara, CA (1996)

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

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

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

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)

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

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

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

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

Section D: CMP Consumables Philipossian, Sanaulla, and Moinpour, Semicon West Technical Session on CMP, CA (1998)

CMP Slurries and Pads Areas of Concern Availability Design EHS Legal Supplier Quality & Reliability Manufacturability Total Cost

Quality Issues Intel Corporation All Chemicals

Quality Issues Intel Corporation CMP Slurries 70% Abrasive Issues 20% Foreign Matter 10% Other

Quality Issues Intel Corporation CMP Pads 40% Texture 30% Foreign Matter 20% Adhesive 10% Other

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)

Supplier Comparison CMP Suppliers vs. Photoresist and Wet Chemical Suppliers (Data Collected Since 1Q96) Challenge

Factors Influencing Productivity Equipment - Availability - Reliability - Integrated Run Rate Productivity Labor - EHS - Ergonomics - Automation Process Stability & Manufacturability - RR - WIWNU, WTWNU, WIDNU - Defects - Planarity - Pad life - Pad & slurry quality

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

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

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

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)

No. of Polishers vs. Tool Availability Effect of Un-Scheduled Downtime (Pad Life, Pad Change Duration and Scheduled Downtime are Fixed)

Oxide Polisher Downtime Pareto Chart C+P C+P+T C+P+T C+P C = Consumables P = Process T = Tool

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)

Effect of pH and Abrasive Content on ILD Removal Rate Scherber et al., Proceedings of the Symposium on Planarization Technology: CMP, Semicon West (1994)

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

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’

Abrasive Geometry Primary Particle Aggregate

Effect of Abrasive Geometry on ILD Polish Performance - Fumed silica abrasive - Constant pH and abrasive content - Comparable defect density and planarity

Effect of Abrasive Geometry on ILD Removal Rate

Section E: Industry - University Gaps

Development of Core Competencies (Industry - University Gaps)

Section F: EHS Hierarchy and Considerations Philipossian, Moinpour and Poliak, Proceedings of VMIC, Santa Clara, CA (1998)

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

Growth of US Environmental Legislation (Cumulative No. of Environmental Laws) Technology & Environment, Washington DC, National Academy Press, p. 101 (1989) 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 80 100 120 140 160 Year

EHS in CMP (Level - I Considerations) energy inputs chemical inputs EHS ergonomics chemical outputs energy outputs

EHS in CMP (Level - II Considerations) 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 - III Considerations) 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 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) 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 size material stack thickness texture morphology hardness specific gravity compressibility hole pattern groove pattern adhesive strength life shelf life

EHS in CMP (Level - III Considerations) 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 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

EHS in CMP (Level - III Considerations) 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 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

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)

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

Dual-Emission Laser-Induced Fluorescence Glass Wafer Polish Platen Pad Camera Laser Slurry with Fluorescence dye Slurry

http:ww.tuftl.tufts.edu

Slurry Transport Interrogation Region Wafer Post Examining: - Mean slurry age - Residence time - Slurry Gradients (flat pads) - Drag on wafer - Fluid thickness measurements Pad

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) Percent New Slurry

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) Percent New Slurry

Static Case Pad deformation: (4 psi, 0 rpm) Image of a single pad Thickness profile as determined by ratiometric technique

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

Slurry Re-Use Experimental Setup Secondary Platen Primary Platen Slurry Capture Tub Spent Slurry Reservoir Pump & Filter

RR & WIWNU vs. Slurry Reclaim fumed 50 / 200 nm colloidal 102 / 212 nm

Surface Roughness & pH vs. Slurry Reclaim fumed 50 / 200 nm colloidal 102 / 212 nm

Mean Aggregate Size vs. Slurry Reclaim fumed 50 / 200 nm colloidal 102 / 212 nm

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)

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)

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

Post-CMP Clean (A Sampling of Chemicals or Methods Cited in the Literature)

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)

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

Cleaning Theory
ELECTRIC DOUBLE LAYER

Cleaning Theory
DLVO THEORY

Post-CMP Cleaning

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

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 Tutorial

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