nanoscale control and analysis of the cmp process a … · operation. levitronix 2007 cmp ......

College of Nanoscale Science and EngineeringLevitronix 2007 CMP Users’ Conference

Ul-hasan, Geer, Borst February 15, 2007 1

Nanoscale Control and Analysis of the CMP Process

A Case Study: Topographic and Spectroscopic Analysis of Slurry Particle Retention for Cu CMP

Iftikhar Ul-hasan, Robert E. Geer, Christopher L. Borst

College of Nanoscale Science and EngineeringUniversity at Albany - SUNY, Albany, NY, USA



Outline

CNSE OverviewBackground / Problem StatementTechniques for Nanoscale Consumable AnalysisQuantitative ResultsSummary / DirectionsExtendibility of Techniques



NanoFab 300 East

15,000 ft2 300mm cleanroom space

Scheduled to be completed spring 2008

CESTM (NanoFab 200)

4,000 ft2 200 mm cleanroom space

Completed June 1997

NanoFab 300 North


Completed December 2005

NanoFab 300 South


Completed March 2004

CNSE Facilities



CNSE Specifics

750,000 sq. ft cutting edge facilities (~67,000 ft2 300 mm cleanrooms)Over $3B in active programs currently underwayPartners include SEMATECH, IBM, AMD, Sony, Toshiba, Micron, Qimonda, AMAT, Tokyo Electron, ASML, Vistec Lithography, EbaraApproximately 1500 personnel on site 1Q 2007, planning for 2000 by 4Q 2008CNSE is the umbrella organization which includes the NanoCollege and its Albany NanoTech complex

The site is unique in its execution of joint research and development programs with integrated device manufacturers (IDM), equipment suppliers, and university researchers



CNSE Operations

The CNSE Center for Semiconductor Research (CSR) cleanroom will house over 125 state-of-the-art 300mm wafer tools when build out is completed. More than 70 tools currently installedThe CSR cleanroom is designed for the 32nm node R&D & beyond, but is compatible with previous device generationsThe current integration baseline process (e-testable FEOL/BEOL) available for use by partners is at the 90nm node. This baseline will advance to 45nm when process BKMs are deemed commercially availableThe facility is capable of 25 fully-integrated wafer starts per day, with 24/7 operation



CNSE CMP-Specific Toolset

200mm Strasbaugh 6DS-SP (dual-carrier, dual-platen)300mm Ebara F-REX 300S (4 platen)300mm AMAT Reflexion LK Cu (P1 hybrid eCMP)300mm AMAT Reflexion LK STI (P2 fixed abrasive)



Nanoscale Control and Analysis of the CMP Process

A Case Study: Spectroscopic and Topographic Analysis of Slurry Particle Retention for Cu CMP

Christopher L. Borst, Iftikhar Ul-hasan, Robert E. Geer

College of Nanoscale Science and EngineeringUniversity at Albany - SUNY, Albany, NY, USA



CMP: Nanoscale, dynamical process involving material transport, chemical reaction, physically-assisted material removal

• Nature of CMP process typically inferred from post-polish wafer properties • Limited data available documenting state of abrasive/fluid/pad system

• Challenge: How can the nanoscale nature of the CMP process be investigated beyond the characterization of the post-polished wafer?

• Why Bother? Understanding the nanoscale nature of CMP process can enable better extendibility of CMP for future device generations and improved sustainability of current CMP process paradigms



Case in Point: Where does the slurry go?

Slurry Nanoparticle Retention in Polyurethane Pads

• Left: SEM Micrographs of cross-sectioned pad (bottom) and top pad surface (top) showing topographical structure (pores/asperities) of pad.

• Above: SEM micrograph identifies the presence of retained alumina abrasive following Cu CMP –agglomerates and individual particles

SEM x-section Image of a stacked pad



SEM: Direct imaging of nanoabrasives on pad asperities and in open pores• Charging effects dramatically limit high-resolution imaging of abrasives in

polyurethane pads

SEM micrograph of abrasive collected on asperity (post-CMP).

Presence of dense particle distribution can reduce e-beam charging effects

300 nm 300 nm

SEM micrograph of pad away from wafer

Difficult to obtain high-resolution imaging of particle retention

Direct Imaging of Nanoparticle Retention



Environmental SEM – Low-vacuum SEM to reduce charging of pad samples• Enables improved imaging of particles on asperities and pores

ESEM micrograph of abrasive collected on asperity (post-CMP).

Higher-resolution imaging of nanoparticles

ESEM micrograph of pad away from wafer

High-resolution imaging of pad topography and particle retention

500 nm 500 nm

Direct Imaging of Nanoparticle Retention



Example: How does conditioning effect the presence of abrasive in the pad?It is well-established that conditioning (dressing) maintains uniform performance of CMP pad (and overall process)Is it possible to specifically track where abrasive is, or is not, removed during conditioning?

1 - Raymond R. Jin et al. (Applied Materials)

Without conditioning With Ex-Situ Conditioning

SEM Image of diamond disk1

Can Nanoscale Pad Analysis Be Quantitative?



SEM or ESEM is nonspecific – requires spectroscopic technique to confirm abrasives on asperities and pores• X-ray photoelectron spectroscopy (wide area, surface sensitive)• Calibrate surface atomic concentration to particle density (e.g. Al for

alumina abrasives)

300 µm

Area probed via XPS

-2 0 2 4 6 8 10 12 14 16 18 20

0

2

4

6

8 XPS:AluminumExp#2

Atom

ic %

Conditioning Force(Pounds)

2 %H2O2

CMP pad (post-Cu CMP)

CMP pad (post-Cu CMP)

Example: Residual Alumina vs Conditioner Downforce

(pad center)

Nanoabrasive ‘ID’: XPS



SEM or ESEM is nonspecific – requires spectroscopic technique to evaluate abrasives on asperities and in pores• SEM energy dispersive spectroscopy

(EDS) permits local probing of elemental concentration

• Shows relative difficulty of removing abrasive from pores as compared to asperities

17 18 19 20 21 22 23

5

10

15

20

25

30

A

l Int

ensi

ty (x

103 c

ount

s)

Conditioning Time (sec)

17 18 19 20 21 22 23

0

2

4

6

8

10

A

l Int

ensi

ty (x

103 c

ount

s)

Conditioning Time (sec)

SEM image of the pad showing pores, asperities

Amount of Al2O3 in poresinsensitive to conditioning time

Amount of Al2O3 on asperities decreases with conditioning time

Nanoabrasive ‘ID’: SEM-EDS



0 4 8 12 16 200

1x103

2x103

3x103

4x103

6% H2O2

2% H2O2

EDS:Copper-Inside Pore

Cou

nts

Conditioning Force(Pounds)

Inside Pore0 20 40 60 80 100

010002000300040005000600070008000

DF=2 psi 0% H2O2 by vol. 2% H2O2 by vol. 4% H2O2 by vol. 8% H2O2 by vol.

Ring Radius (mm)

Removal Rate vs. Ring Radius

Rem

oval

Rat

e (Å

/min

)

XPS can likewise correlate presence of complexed Cu with slurry retention• Observation of Cu for high-

concentration H2O2 slurries • No Cu observed for higher

removal rates (lower H2O2concentration)

Example: Residual Cu Inside Pores



Nanoscale Analytical Approaches for CMP Process Investigation• Can be used to reconstruct physical (and in some cases chemical)

state of nano-abrasive in pad• Can generate results that may be correlated with CMP parameters to

illuminate dynamics of process

Local compositional analysis for CMP processing• Can be used for particle-specific identification • Permits separate analysis of particle presence on pad asperity and in

open pores to elucidate slurry transport modes

Summary



Expand to STI and barrier processing to elucidate effects of slurry additives on nanoparticle disposition

Nanoscale Analytical Approaches for CMP Process Investigation could potentially be employed to investigate morphology and elemental retention in other CMP-relevant systems• Conditioning disk surfaces• PVA brushes• CMP retaining rings• Point-of-use and loop filter membranes

Extendibility of Techniques

Future Directions

nanoscale control and analysis of the cmp process a … · operation. levitronix 2007 cmp ......

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