Effects of Pad Properties on Cu Dishing During CMP

Caprice GrayPhD Student, Mechanical Engineering

Tufts University, Medford, MAIntel Intern Presentation

8/18/05

Overview

• Goal: Investigate Cu line dishing during CMP using polishing pads with varying properties

• Motivation: How do pad properties affect dishing as design rules shrink?

• Topics Covered:– Automated dishing analysis for higher data throughput– Evaluated 9 different pad– Pad Properties Evaluated

• Fiber size• Pad hardness• Hydrophobicity (Surface Tension)• Fibrous vs. Porous

Experimental OverviewCu

Ta

Silicon

Cu FW

ILD up region

Constants Variables Responses•Platen/Wafer Rotation Rate

•Slurry Flow

•Slurry Type

•Starting Cu/Ta layer thickness and topography

•Pad Type (9 types)

•Pattern Density (20%-70%)

•Feature Width (0.16-20um)

•Polish time

(0-6min)

•Dishing/Dishing Rate

•Erosion

Polishing Pads

Polyurethane impregnatedPolyester felt

Felt

Nylon

Microporouspolyurethane

Silk

TangledPolyester

Fibrous Porous

Soft

Soft

Hard

Polyurea/PolyurethaneNanocomposit

Elastomer/WSP Alloy

Mohair Microfiber

Analysis Process

Polish Wafers(vary polish time)

Profile features and save data Data Evaluationattain average dishing

Change PadsData Modeling and effect screening

Automated Data Evaluation

Import Raw Data Isolate region of interest and apply data smoothing filter

Isolate features andcalculate dishing

Isolate feature width region

Calculate average dishing and Erosion for each feature width

0

Dishing

Erosion

Dishing Rate Results

0

100

200

300

400

500

600

700

800

900

1000

0.1 1 10 100

Feature Width (mm)

Dis

hin

g R

ate

(A

/min

)

Polyurethane

Microfiber

Nylon

Porous Felt

Tangled Polyester

Silk

Fibrous Felt

Nanocomposit

WSP elastomer

QuestionableData

Most Pads have similardishing rates for features

smaller than 2 um

Distict Dishing ratesfor large features

Dishing is Predictable

Dishing Rate is a function of:Feature WidthFeature DensityPad

“Pad” is a convolution of many material

properties

HardnessFiber/Pore SizeHydrophobicityAsperity GeometryGroovingCompressibilityDensityMaterial

Evaluation of VariablesFeature Width > 2umFeature Width < 2um

Contact Angle*(Hydrophobicity)

Fiber/Pore Size(um)

Pad Hardness(Shore D)

Feature Density

0

20%

70%

70

20

0

20

0

100

Dishing Rate (A/min)800

Dishing Rate (A/min)800 0

Pores

Fibers

*Soft Fibrous Pads Only

No Effect No Effect

No Effect

Summary and Conclusions• A LabView interface was developed to automate data analysis• Summary of design rule affects on Dishing Rates (DR)

– Feature Width↓ DR↓– Large Features Large DR variation pad to pad– Small Features Small DR variation pad to pad– Feature Density has minimal affect on DR

• Summary of pad property affects on DR– Hardness↓ DR↑ for large features– Fiber size↑ DR↓ more so for large features– Hydrophobicity↑ DR↓ for porous pads, for large features– Hydrophobicity↑ DR↑ for fiberous pads, more so for large features

• Recommendations– Large Features (FW > 2 um): Allied, JSR – Small Features (FW < 2 um): Allied, SUBA IV, TWI 711, (Polytex)– All Feature Scales (0.32um – 20 um): Allied, TWI 711, SUBA IV

• Future Work– Determine the relationship between other pad properties and dishing– Examine erosion data– Is there different selectivity on the pads? (Cu vs. Ta vs. Oxide polish rates)

Dishing Rate Normalized to Bulk Rate

0%

5%

10%

15%

20%

25%

30%

0.1 1 10 100

Feature Width (um)

Dis

hin

g R

ate

/Bu

lk R

ate

Polyurethane

Microfiber

Nylon

Porous Felt

Tangled Polyester

Silk

Fibrous Felt

Nanocomposit

WSP Elastomer

QuestionableData

Most Pads have similardishing rates for features

smaller than 2 um

Distict Dishing ratesfor large features

Oxide Polishing Pad

Dishing Rate and Feature Density

0

100

200

300

400

500

600

700

0.1 1 10 100

Feature Width (um)

Dis

hin

g R

ate

(A

/min

)

FD=50%

FD=70%

FD=20%

Effect of Feature Density by Pad

0

10

20

30

40

50

60

70

80

Re

lati

ve

Aff

ec

t o

f F

D o

n D

ish

ing

(a

u)

Increasing Fiber Diameter

Porous Pads

Fiberous Pads

Dishing Rate and Pad Hardness

0

100

200

300

400

500

600

700

800

900

10 20 30 40 50 60 70

Hardness (Shore D)

Dis

hin

g R

ate

(A

/min

)

FW=20um

FW=5um

FW=1um

FW=0.32um

Fibrous Felt

Tangled Polyesters

Porous Felt

Polyurethane

Nanocomposit

WSPElastomer

Normalized Dishing Rate with Pad Hardness

0%

2%

4%

6%

8%

10%

12%

14%

10 20 30 40 50 60 70

Hardness (Shore D)

Dis

hin

g R

ate

\Bu

lk R

ate

FW=20um

FW=5um

FW=1um

FW=0.32um

Fibrous Felt

Tangled Polyester

Porous Felt

Polyurethane

Nanocomposit

WSPelstomer

Dishing Rate and Fiber Size

Dishing Rate and Contact Angle

Soft FiberousPorous

Brushlon and TWI 711 behave completely differentlyBrushlon- fiberous, high dishing rate, contact angle = 0TWI 711 – intermediate dishing rate (between allied and SUBA,90+ contact angle

Soaks in near different grove-drop locations. Otherwise, no soak.

Contact Angle Images

Polyurethane

WSP ElastomerTangled Polyester Nanocomposit Microfiber-initial

Porous FeltMicrofiber – 1 minFibrous Felt

Soaks in

Soaks in quickly

Soaks inSoaks in quickly

Soaks in Does not soak in

Processing Interface

Evaluating Erosion Data

• Long Scans Length Scan Leveling Drift Inaccurate Erosion Data

• Can examine erosion amplitude– See planarity in time

across entire structure– Lose information about

feature width effects

• Must Evaluate shorter scans for accurate erosion data

Erosion Amplitudes

100

300

500

700

900

1100

1300

1500

1700

0 1 2 3 4 5 6

Time (min)

Ero

sio

n A

mp

litu

de

(A

)

polyurethane

fibrous felt

Silk

Tangled Polyester

Porous Felt

Microfiber

Erosion v Dishing

SUBA IVTWI 711

Erosion Through Material Layers

Unpolished Ta no Cu No Ta or Cu Overpolished Wafer

• Can optically identify the presence on Ta inside Cu lines, but not outside the lines