abrasive-free copper chemical mechanical polishing in...

Qingjun QinAdvisor: Professor R. Shankar Subramanian

Center for Advanced Materials Processing (CAMP)Department of Chemical & Biomolecular Engineering

Clarkson UniversityPotsdam, New York 13699

Abrasive-free Copper Chemical Mechanical Polishing in an

Orbital Polisher

ObjectiveBackgroundExperimental WorkModel developmentResults and DiscussionConclusionsSuggested future workAcknowledgements

Outline

Objective

To obtain a fundamental understanding of abrasive-free copper Chemical Mechanical Polishing in an orbital tool from both experimental and theoretical perspectives

To develop a model accommodating slurry fluid mechanics, chemical reaction at the wafer surface, and mechanical removal by pad asperities to predict removal rate and radial non-uniformity of removal rates on the wafer surface

To compare predicted removal rate and WIWNU with experimental data obtained from a SpeedFam-IPEC 676

BackgroundSpecial features of orbital tool

Wafer

Pad

Platen

Slurry Flow

Orbit circle of the pad center

Center line of platen/pad

Axis of wafer rotation

Wafer

Pad

Reference: Oliver et al. (2004)

Experimental WorkExperiment conditions

Slurry (liquid) composition: Hydrogen Peroxide - 5.0 wt%; Glycine - 0.2, 0.5, and 1.0 wt%; pH=5.5

Slurry Flow Rate: 200 ml/minPad: IC1000 (XY grooved hard pad)Pressure: 4 psiPad Orbit Speed: 100, 200, and 300 RPMSample: blanket copper waferPolisher: SpeedFam-IPEC AvantGaard 676 CMP System Cu film thickness measurement: Prometrix Omni RS 35E

Experimental WorkGlycine conc. & pad orbit speed Impact

0.20.51.0

Glycine Conc. (wt%)

0 50 100 150 200 250 300 350Pad Orbit Speed (RPM)

400050

100150200250300350

Rem

oval

Rat

e (n

m/m

in) 400

Flow Rate=200 ml/minPressure = 4 psiHydrogen peroxide Conc. = 5.0 wt%

The removal rate increases with both glycine concentration and pad orbit speed

Glycine Concentration (wt%)0.00 0.20 0.40 0.60 0.80 1.00 1.20

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200

250

300

350

100200300

Slurry Flow Rate = 200ml/minPressure = 4 psiH2O2 Concentration = 5.0 wt%Pad Orbit Speed (rpm)

Experimental WorkRemoval rate on radial positions

Orbit Speed (RPM)100200300

200 ml/min1.0 wt% Glycine4 psi

0 5 10 15 20 25 30 35 40 45 50Positions

0

100

200

300

400

500

Rem

oval

Rat

e (n

m/m

in)

Edge Wafer Center Edge

There is a radial non-uniformity of the removal rates on the wafer surfaceThe removal rate is symmetric about the wafer center with higher values in the central and edge areas, but lower values in other regions on the wafer surface

0

100

200

300

400

500

Rem

oval

Rat

e (n

m/m

in)

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49Positions

Wafer Center

Second CircleFirst Circle

Third Circle

200 ml/min1.0 wt% Glycine300 RPM

Model DevelopmentMain idea to predict removal rate

( ) ( ) 3

1 1

g mN Nji

m i ji ji j

lh dMR f C f CV V dA= =

= + +∑ ∑

0.127

0.127−

Y i( )

0.1270.127− X i( )

( ) 3= +m f dMR CdA

Y i( )

X i( )

( ) ( )( ) ( )

0 0

0 0

cos cos

sin sinw o o

w o o

x d t R t

y t R t

ρ β ω θ ω

ρ β ω θ ω

= + + − +

= + − +

Y i( )

X i( )

Y i( )

X i( )

Model DevelopmentThree functional regions on the pad

1η =

region-I

region-II

region-III

ρ-Roρ+Ro

2 2 21 arccos2

o

o

r RrR

ρηπ

⎛ ⎞+ −= ⎜ ⎟

⎝ ⎠

region-I

region-II

region-III

Model DevelopmentAssumptions & Simplifications

The slurry flow rate in a pad groove is proportional to the pressure difference between its two ends Q = K ( P2 - P1 );The constant K is assumed to be the same for all pad grooves;The kinetics of copper removal rate as a function of the glycineconcentration at the wafer surface (Zhang & Subramanian, 2001)

The pressure underneath all the holes in the pad is the same, and is treated as an unknown constant;The resistance to mass transfer in the liquid is neglected; andGlycine is assumed to be consumed instantaneously by reaction with copper ions to form a complex.

( ) ( )2 2 3 21.062 10 4.3 10 /( )reaction glycine glycine glycineR f C C C moles m s− −= = − × + × ⋅

Model DevelopmentSlurry fluid mechanics

Q K P= Δ

, 1 1, 1, , 1 ,

( , ), 1 1, 1, , 1 ,

4 0

4

i j i j i j i j i j

i ji j i j i j i j i j

P P P P P

qP P P P P

K

+ + − −

+ + − −

+ + + − =

+ + + − = −

,( , ) 0i j

h i j dh

qP P

K− − =

i, j i+1, ji-1, j

i, j-1

i, j+1

in source outQ q Q+ =

y

x

z

2 2

3 3 2 21,3,...

sinh128 1 2 2

cosh2

n

n ba ab a aK

n bL n n na

π

ππ μ π π

∞

=

⎧ ⎫⎡ ⎤⎛ ⎞⎜ ⎟⎪ ⎪⎢ ⎥⎪ ⎪⎝ ⎠⎢ ⎥= −⎨ ⎬⎛ ⎞⎢ ⎥⎪ ⎪⎜ ⎟⎢ ⎥⎪ ⎪⎝ ⎠⎣ ⎦⎩ ⎭

∑

( , )i j totalq Q=∑

Reference: Shah and London (1978)

( , )h i jP

dP

pad

Rubber pad backer

steel pad backer

Model DevelopmentPressure Distribution

Pressures near the pad center are much higher than those in the pad edge areaThe pressure drops fast near the pad edge areaSlurry flow rates in each groove can be obtained by using this pressure distribution and Q = K ( P2 - P1 )

Model DevelopmentGlycine concentration in a pad groove

( ) ( )3

3 2

4.3 104.3 10 exp 2 1.062 10 exp 2 1

AB

AB A AB

CCbWL Q C bWL Q

−

− −

×=

× − × −⎡ ⎤⎣ ⎦

'L Lη=

( ) ( ) ( )( )2⎡ ⎤− + Δ =⎣ ⎦ABQ C x C x x Wdxf C x

Model DevelopmentComputation of glycine concentration distribution

1C

Calculation of the glycine concentrations at all intersections from 61 known concentrations at holes is an iterative computation

2C

3C1C

1C

2C

1C 2C

0C

Model DevelopmentGlycine concentration distribution

Glycine is consumed rapidly near the pad centerOn average, glycine concentration is larger at the edge than in the pad central area

Model DevelopmentAverage glycine concentration in path annulus

=∑∑

gi gi

gg

i

C AC

A

Radial Position (m)0.00 0.02 0.04 0.06 0.08 0.10

Gly

cine

Con

cent

ratio

n (m

ol/m

3 )

0

50

100

150

C0 = 26.6 mol/m3

C0 = 66.6 mol/m3

C0 = 133.2 mol/m3

Model DevelopmentMechanical removal by pad asperities

Pad Orbit Speed (rpm)0 50 100 150 200 250 300 350 400

Mec

hani

cal R

emov

al R

ate

(nm

/min

)

0

50

100

150Glycine concentration (wt%)

0.20.51.0

( )mech expt modelR R f C= −


Mec

hani

cal R

emov

al R

ate

(nm

/min

)

0

50

100

150

Pad orbit speed (rpm)100200300

( )model 2.16 model wpR f C C V= +

Results and DiscussionOverall Removal Rate


Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200

250

300

350

100 rpm

200 rpm

300 rpm

100200300

Pad orbit speed (rpm)

Pad Orbit Speed (rpm)0 50 100 150 200 250 300 350 400

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200

250

300

350

0.2 wt%

0.5 wt%

1.0 wt%

0.20.51.0

Glycine concentration (wt%)

The overall removal rate increase linearly with pad orbit speed but non-linearly with glycine concentrationThe increasing slope is attributed to a synergistic action between the chemical reaction and the mechanical removal

Results and DiscussionRadial Variation of Removal Rate on Wafer Surface

Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200

250

wafer center wafer edgewafer edge

Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200

250

300

350

wafer centerwafer edge wafer edge

Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200

250

300

350

400


(a)

(c)

(b)

liquid flow rate = 200 ml/minpressure = 4.0 psiH2O2 concentration = 5.0 wt%glycine concentration = 1.0 wt%(a) 100 rpm(b) 200 rpm(c) 300 rpm


Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150


Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200


Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

50

100

150

200

250

wafer edgewafer centerwafer edge

(a)

(c)

(b)



Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

10

20

30

40

50

60

70

80


Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

10

20

30

40

50

60

70

80


Sites1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Rem

oval

Rat

e (n

m/m

in)

0

20

40

60

80

100


(a)

(c)

(b)


Conclusions

The discrepancy between the experimentally measured removal rateand the predicted chemical removal is attributed to mechanical removal of the reacted film by the pad asperities on the mesas

The overall removal rate of copper from the wafer surface depends approximately linearly on the pad orbit speed and non-linearly on the glycine concentration

There appears to be a synergy between the chemical action and mechanical action during CMP, which reinforces material removal and can be enhanced by increasing the glycine concentration

Conclusions(Continued)

The shape of the radial variation of the removal rate depends on the nominal glycine concentration in the experiment, but is independent of the nominal glycine concentration or the pad orbit speed in the modeling

For glycine concentrations of 0.5 wt% and 1.0 wt%, in most cases, the agreement between the predicted radial variation and the experimental radial variation is good near the wafer edge but not good in the central region of the wafer

Other factors can influence the radial variation of the removal rates

Suggested Future Work

The constant K in the assumption Q = K ( P2 - P1 ) will be different for different pad grooves, and needs to be calculated individually

Mass transport in the groove should be accommodated

For an accurate prediction of the radial non-uniformity of the removal rate on the wafer surface, the incoming-wafer film uniformity, down-force, wafer curvature, backside pressure, wafer-to-retaining-ring protrusion, retaining ring pressure, pad conditioning, etc. should be considered

The mechanical aspects of removal in abrasive-free polishing are worth pursuing in-depth

A better understanding of the slurry delivery system is needed to improve the accuracy of the predictions from the model

Acknowledgements

Professor R. Shankar Subramanian for his guidance throughout this research program both personally and professionally

Novellus Systems, Inc. (SpeedFam/IPEC) and Rohm and Haas Electronic Materials CMP Technologies for supplies and advice

New York State Office of Science, Technology, and Academic Research (NYSTAR) for financial support

Professor Yuzhuo Li and members of his group for their help with the experiments

abrasive-free copper chemical mechanical polishing in...

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