2018年1月30日
六本木 泉ガーデンタワー（東京）第35回無機材料に関する最近の研究成果発表会

ガラス研磨モデルの界面計測に基づく化学機械研磨メカニズムの提案
静岡大学大学院
総合科学技術研究科
須田 聖一
suda@shizuoka.ac.jp
1Ultra-smooth glasses

Removal rate /μmmin-1

Introduction– Application of ultra-smooth glasses –3

CeO2

2ZrO2

1

HOYA HP

Hard disk glass
substrates

AGC HP

Flat paneletc.
displaysFig. 1. Application of ultra-smooth glasses.

CeO2 abrasives

0Al2O3123

Lee M. Cook, J. Non-Crystalline Solids, 120, 152171(1990).

Fig. 2. Removal rate of glasses using
conventional abrasives.

Scratch-free glass surface and high removal rate(Mechanism)

Chemical Mechanical Polishing (CMP)
21

Introduction– High polishing properties of ceria abrasives –Chemical Mechanical Polishing(CMP)
Excellent polishing properties of the ceriabased abrasives are brought by chemicalmechanical polishing (CMP).
Ceria
abrasives

Zirconia or alumina shows superiormechanical strength, but glass polishingproperties are much inferior to ceria
abrasives.
Zirconia
oralumina
Fig. 4. Image view of polishing CP/MP balanceon zirconia or alumina abrasives.

MechanicalPolishing (MP)Glasses polished withalumina or zirconia often
observe relatively deep
scratches.

Fig. 3. Image view of cooperation between
chemical polishing and mechanical polishing.

Fig. 5. AFM image of glass after polishing withconventional zirconia particles.

ChemicalPolishing (CP)3

Introduction– Previously Proposed CP Mechanism –Covalent Bonding Formation CP Mechanism proposed by Dr. Hoshino et.al.
Si-O-Si
BeforepolishingAfterpolishing
After
Washingwith acid

Si-O-Ce？

Ce-OH + Si-O- ←→ Si-O-Ce + OH-CeO
SiCeOSiFig. 7. Image view of removing Si-O on the surfaceof glass by ceria abrasives.

Si-O-SiT. Hoshino, Y. Kurata, Y. Terasaki, K. Susa,Solids, 283, 129-136 (2001).

J. Non-Cryst.

Fig. 6. FT-IR spectra of glasses before and after
polishing with ceria abrasives.

SiO2 surface is first reacted with CeO2
particles and a multiple number ofchemical bondings of Si-O-Ce areformed on the surface.
SiO2 is removed as a lump, which isscraped from the surface. The polishingrate is affected by the formation of CeO-Si bonding.
42Introduction– Proposing CP mechanism with ceria abrasives –Charge Transfer Chemical Polishing (CP) Mechanism
HHO H

O H

Oxygen-defected Ceria abrasive
HCe4+Ce3+OO H
H

Ce3+ → Ce4+ ＋ e-e-O H
Glass Surface

OSiSiFig. 8. Image view of hydration formation of glass
surface according to charge transfer CP mechanism.

1. Electrons formed by oxidation of Ce3+ will transfer to anti-bonding orbital of Si-O
during polishing.
2. The charged electrons in the orbitals extend Si-O bond distance and weaken thebonds.

5Introduction– Overview of glass CMP process –Chemical Process of CMP

Mechanical Process of CMP

Producing hydration layers on glass.

Sweeping softened hydration layers
off glass.

GlassHydration layer

Sweep off

Abrasive slurry
Polishing padFig. 9. Schematic illustration of proposed glass CMP processes.

Polishing properties such as removal rate and surface smoothness wouldmuch depend on formation rate of hydration layer on glass.
Quantitative estimation of hydration layer during CMP is important to clarify
CMP mechanism and to develop novel CMP abrasives.
63Introduction– Proposed hydration layer formation mechanism–
Surface of ceria abrasives Ce3+ →Ce 4+ +ee-e-e-

Challenge 1: Abrasive surface
conditions by estimatingabrasive/water interfacial
resistance.
Challenge 2: Effects of ions inwater solution on hydration
and removal rate.
Challenge 3: Hydration layers
by estimating water/glass
interfacial resistance.

Glass surface

Challenge 4: Hydration layers
by estimating electric
potential between ceria andwater.
7

Challenge 1: Abrasive surface conditions by estimatingabrasive/water interfacial resistance.
Electrodes： SUS304
Height, h： 0.1～1.0 cm

0.1～1.0 cm

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑒𝑠𝑢𝑟𝑒𝑑 𝑤𝑖𝑡ℎ 𝐹𝑅𝐴𝒓
𝑹: 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓𝑤𝑎𝑡𝑒𝑟 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

𝑹 : 𝐼𝑛𝑡𝑒𝑟𝑓𝑎𝑐𝑖𝑎𝑙 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒Fig. 10. Schematic illustration for estimation of electrical properties of abrasive/waterinterfacial resistance during polishing.
84

Challenge 1: Experiments– Estimation of interfacial resistance during polishing –
1.5

0.9

0.3
0.06mm

r

4mm
3mm

3.0
2.0

dL/rA

1.0d/ρL
0.0

0.2 0.4 0.6 0.8 1.0 1.2
Fig. 11. Typical complex impedance
profiles using various electrodes.

𝑹: 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓𝑤𝑎𝑡𝑒𝑟 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

0.02mmZre /kΩ𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑒𝑠𝑢𝑟𝑒𝑑 𝑤𝑖𝑡ℎ 𝐹𝑅𝐴

𝒓1/r /10-3Ω-1-Zim /kΩ

1.2

0.6

4.05mm

0.20.4

0.6

𝑹 : 𝐼𝑛𝑡𝑒𝑟𝑓𝑎𝑐𝑖𝑎𝑙 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒

0.8

Height of electrode / cm
Fig. 12. Relationship between thereciprocal of resistance and heightof electrodes.

Linear relationship enables us to estimate
𝛒 (𝐑𝐞𝐬𝐢𝐬𝐭𝐢𝐯𝐢𝐭𝐲 𝐨𝐟 𝐰𝐚𝐭𝐞𝐫 𝐬𝐨𝐥𝐮𝐭𝐢𝐨𝐧) and 𝒓𝑨 𝑨𝑺𝑹
separately.

1 1 1= +𝑟 𝑅 𝑅′

𝟏𝑑𝑑𝐿
=𝒉+𝒓 𝜌𝐿𝑟

𝜌: 𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
𝑟 : 𝐼𝑛𝑡𝑒𝑟𝑓𝑎𝑐𝑖𝑎𝑙 𝑎𝑟𝑒𝑎 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝐴𝑆𝑅)
9Challenge 1: Results– Change in solution resistivity and abrasives/water ASR –Resistivity of water solution

Fig. 13. Relationship between solution
resistivity and rotation rate.

Interfacial ASR

Fig. 14. Relationship between abrasive/waterinterfacial ASR and rotation rate.

The ASR was doubled by starting rotation of soda-lime glasses. Ceria surface
would be changed by polishing in association with migration of charge carrier.
105

Challenge 2: Results– Effects of NH4NO3 concentration –70085

Removal rate

600

95

500

100

Relative ASR

400
3000.00< 0.05 mol L-1

90

Relative ASR /％Removal rate /nm min-1

800

Hydration layer
Removal rate
> 0.05 mol L-1

105

Hydration layer

110

Removal rate

0.03
0.06
0.09
0.12
NH4NO3 concentration /mol L-1

Fig. 15. Relationship between removal rate or relative ASR and NH4NO3 concentrationin the slurry.
11

Challenge 2: Discussion– Effects of NH4NO3 concentration –NH4NO3 concentration<0.05 mol L-1>0.05 mol L-1

Small amountaddition of NH4NO3
would increaseelectron charge
carrier density inslurry and improves
removal rate
However, excess
addition of charge
carrier ions would
inhibit hydration
reaction by sterichindrance.

Fig. 16. Schematic illustration
Fig. 17. Schematic illustration model ofmodel of promoted hydration inhibited hydration reaction with water
reaction with water solution at solution at more than 0.05 mol L-1 NH NO .
43less than 0.05 mol L-1 NH4NO3.

126

Challenge 3: Experiments– Setup for water/glass interfacial ASR measurement –Ceria pellet

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑒𝑠𝑢𝑟𝑒𝑑 𝑤𝑖𝑡ℎ 𝐹𝑅𝐴

Electrode
Material： SUS304
Height h： 0.1～1.0 cmh𝒓FRAdLGlass

𝑹: 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓𝑤𝑎𝑡𝑒𝑟 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

𝑹 : 𝐼𝑛𝑡𝑒𝑟𝑓𝑎𝑐𝑖𝑎𝑙 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒Abrasive：0, 20, 40% La doped CeO2 (LDC00, 20,40), ZrO2 (ZR), Commercial ceria abrasive (ComCe)
Water solution: 0.02 ～ 0.10 mol L-1NH4NO3solution
Fig. 18. Schematic illustration for estimation of electrical properties of glass/water interfacial
hydration layer during polishing.

13

Challenge 3: Results– Temperature dependence of conductivity and ASR –Conductivity of water solution
Rotation rateof Ceria pellet
3 rpm
5 rpm
10 rpm15 rpm

-2.22
-2.25
-2.28
-2.31
-2.343.15

3.25

3.35

log(ASR-1/10-3 S cm-2)log(σ /S cm-1)-2.19

Interfacial ASR
-0.60
-0.90
-1.20
-1.50
-1.80

Temp.

3.15

3.25

3.35

1/T /10-3K-1

1/T /10-3K-1
Fig. 19. Temperature dependence of water
solution conductivity during polishing.

Rotation rateof Ceria pellet
3 rpm
5 rpm
10 rpm15 rpmFig. 20. Temperature dependence ofInterfacial conduction (1/ASR).

Water solution vs.

Interface147

Challenge 3: Results– Impact of rotation –Interfacial ASR

31050

LDC20
La 20 % doped
CeO2

280

45ASR /kΩ cm2

Electric resistivity/Ω cm

Resistivity of water solution

3 rpm

2502200 rpm

19040

La 20 % doped
CeO2
LDC200 rpm

35303 rpm

25160
00 20 40 60 80 100 120

20 40 60 80 100 120
Polishing load /gf cm-2

Fig. 21. Relationship between water solution
resistivity and load during polishing.

Polishing load /gf cm-2
Fig. 22. Relationship between interfacial ASR
and load during polishing.

Hydration layer would be promoted by polishing (both load
and rotation of ceria pellet).

15

Removal rate

Challenge 3: Discussion– Removal rate vs. Polishing load –ChemicalRemoval rate increases
with increasing polishing load

Both slopes coincide.

CeO2ZrO2

Mechanical

Polishing load
T. SAWANO, T. MARUYAMA, Y. MORIWAKI, Proc. 2013
JSPE Spring Meeting, 655 (2013).

Chemical process of CMP (chemicalpolishing) is independent of load
during polishing.

Fig. 23. Illustration of effect of polishing loadon removal rate for CeO2 and ZrO2 abrasives.

Hydration layer is formed with shear stress during polishing, butamount of hydration would be independent of polishing loads.
168Challenge 3: Results– Impact of ceria abrasive composition –Interfacial ASR
45330
300

LDC40ComCeASR /kΩ cm2

Electric resistivity/Ω cm

Solution resistivity

270240210

ZR

LDC00

LDC2040ZR
LDC00

35

LDC2030ComCe25

LDC4020180

00 20 40 60 80 100 120
Polishing load /gf cm-2
Fig. 24. Relationship between polishing loads
and solution resistivity for various abrasives.

Solution

La dopingslightly resistivity

20 40 60 80 100 120
Polishing load /gf cm-2

Fig. 25. Relationship between polishing loads
and interfacial ASR for various abrasives.

vs.

Interfacial ASR17Challenge 3: Results– La contents vs. removal rate and hydration layer –Relative ASR-1

2.5

3.0

Removal rate

2.0

3.76

1.5

1.14

1.0
0.5

2.5

ASR-1

0.0

2.0
1.5
1.0
0.5

Relative removal rate

3.0

0.0
0.0 0.1 0.2 0.3 0.4 0.5
La content /x : LaxCe1-xO2-x/2

Fig. 26. Relationship between La concentrationin CeO2 and removal rate or ASR.

vs.

La doping

Hydration
layer

Removalrate

Linear relationship between the La
contents and relative ASR-1 .
The slope of hydration formation isapproximately 1 and that of removal
rate is 3.8.
Formation of hydration layer would
be effective to improve polishingproperties.
189

Challenge 4: Experiments– Setup for electric potential measurement –Slip ring

Brush

SUS rod
Ceria plate

P/G
Aluminium board

Fig. 27. SEM image of dense CeO2 ceramic plateused for the estimation of electric potential.

Glass

ElectrodeAbrasive：pure CeO2 (LDC00)
Water solution: 0.05 mol L-1NH4NO3 solution

WaterFig. 28. Schematic illustration for estimationof electric potential voltage during polishing.
19

Challenge 4: Results– Electric potential measurement –Revision of evaluation system led to be
reproducible data on potential change.
ΔE＝ 0.32 V

DE = 0.32 V →DG = -31.1 kJ/mol

Hydration free energy of soda lime glass

C. M. Jantzen, M. J. Plodinec, J. Non-Cryst. Solids, 67,207-223 (1984).

→Fig. 29. Change in potential voltage with time.

-27～

41 kJ/mol

The measured DG is closed to thehydration free energy of soda lime glass.

These ASR and electric potential would directly exhibit hydrationreaction.
2010Discussion
Ceria abrasives

Step 1. Charge transferwith Ce3+/Ce4+.
Step 2. Diffusion of ions(electron carrier).
Step 3. Charge transfer andhydration on the surface of glass.

GlassFig. 30. Schematic illustration of proposed elementary chemical
reactions during chemical polishing.

Step 1 would be rate-limiting of chemical polishing. Abrasive composition andinducing share stress much depend on hydration layer formation on the surface ofglasses.

21

Summary
Quantitative elucidation of CMP isindispensable to improve polishing rate anddevelop novel abrasives. We investigated theestimation of hydration layer during polishing bymeasuring interfacial ASR and electric potential
during polishing.

1. Hydration layer is formed with shear stressduring polishing, but amount of hydration would be
independent of polishing loads.
2. Amount of hydration layer could be estimatedusing reciprocal of ASR. The good linear
relationship was observed between lanthanum
contents and relative value of reciprocal of ASR andremoval rate.
3. The hydration reaction was detected bymeasuring change in electric potential by inducing
share stress.

Charge transfer
Diffusion of
charge carrier
Charge transfer
and hydration
Fig. 31. Schematic illustration of threeelementary reactions by chemical polishing.

2211