Characterization of Thermoset and Thermoplastic Polyurethane Pads, - - PowerPoint PPT Presentation

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Characterization of Thermoset and Thermoplastic Polyurethane Pads, - - PowerPoint PPT Presentation

Jun 27, 2023 19 likes •242 views

Characterization of Thermoset and Thermoplastic Polyurethane Pads, and Molded and Non-Optimized Machined Grooving Methods for Oxide CMP Applications A. Philipossian, Y. Sampurno, L. Borucki, Y. Zhuang, S. Misra, K. Holland and D. Boning

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SLIDE 1

Characterization of Thermoset and Thermoplastic Polyurethane Pads, and Molded and Non-Optimized Machined Grooving Methods for Oxide CMP Applications

  • A. Philipossian, Y. Sampurno, L. Borucki, Y. Zhuang,
  • S. Misra, K. Holland and D. Boning
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SLIDE 2

Objectives

  • Investigate the effect of PU pad synthesis methods (i.e.

thermoplastic and thermoset), grooving methods (i.e. molded and non-optimized machined grooving) and groove types (i.e. concentric and ‘logarithmic – positive – spiral – positive’) on:

– Dynamic Mechanical Analyzer (DMA) – Coefficient of friction (COF) – Variance of shear force – Removal rate (RR) – Removal rate model

  • Perform simulations using a two-step removal rate

mechanism to estimate the chemical and mechanical rate constant

2

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SLIDE 3

Polisher & Tribometer

Normal Shear avg

F F COF =

Diamond Grit Plate with Rotation & Translation Applied Wafer Pressure Sliding Friction Table Strain Gauge

3

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SLIDE 4
  • Diamond disc conditioner : TBW Industries 100 grit
  • Conditioning pressure : 0.5 PSI
  • Conditioning : In-situ at 30 RPM disc speed & 20 per minute sweep frequency
  • Break-in time : 30 minutes
  • Wafers : 100 mm blanket oxide
  • Wafer pressure : 2, 3 and 4 PSI
  • Sliding velocity : 0.32, 0.64, 0.96 and 1.24 m/s
  • Slurry : Fujimi PL-4217
  • Slurry flow rate : 80 cc/min
  • Pad :
  • Thermoplastic non-optimized machined concentric groove
  • Thermoplastic molded concentric groove
  • Thermoset non-optimized machined concentric groove
  • Thermoset non-optimized machined logarithmic spiral positive groove
  • Polishing time: 60 seconds

Experimental Conditions

4

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SLIDE 5

Prepolymer process (Two step synthesis) +

Long chain diol / polyol

Diisocyanate Step 1 Step 2 Chain Extender Low % NCO prepolymer

Domain 1: Hard segment Domain 2: Soft segment Domain 1: Hard segment Domain 2: Soft segment

Single shot synthesis +

Long chain diol / polyol Chain Extender

+

Domain 1: Hard segment Domain 2: Soft segment

+

Long chain diol / polyol Chain Extender

+ +

Long chain diol / polyol Chain Extender

+

Domain 1: Hard segment Domain 2: Soft segment

Diisocyanate

Thermoplastic and Thermoset Synthesis

Thermoplastic Thermoset

5

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SLIDE 6

Logarithmic Positive Spiral Positive (LPSP) Concentric

Pad Grooving Types

6

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SLIDE 7

Lightly cross-linked polymers have a steeper modulus slope than more heavily cross-linked polymer. (Rodriguez, “Principles of Polymer Systems”, 1996)

DMA Results

7

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SLIDE 8

DMA Results (cont...)

The total energy loss during a stick-slip event is proportional to the damping factor (tan δ) of the material and that this energy must be equated to the external work of friction. (Moore, “Principles and Applications of Tribology”, 1975 and Bartenev & Lavrentev, “Friction and Wear of Polymers”, 1981)

8

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SLIDE 9

0.1 1 1.E-04 1.E-03 1.E-02 0.1 1 1.E-04 1.E-03 1.E-02 0.1 1 1.E-04 1.E-03 1.E-02

COF : 0.31

0.1 1 1.E-04 1.E-03 1.E-02

COF : 0.38 COF : 0.32 COF : 0.33

COF Pseudo-Sommerfeld Number

Stribeck Curves

Thermoplastic Non- Optimized Machined Concentric Groove Thermoplastic Molded Concentric Groove Thermoset Non- Optimized Machined Concentric Groove Thermoset Non-

  • ptimized Machined

LPSP Groove

9

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SLIDE 10

Removal Rate

Removal Rate (A/min) Pressure x Velocity (Pa.m/s)

10

Thermoset Non- Optimized Machined Concentric Groove Thermoplastic Non- Optimized Machined Concentric Groove Thermoplastic Molded Concentric Groove Thermoset Non- Optimized Machined LPSP Groove

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SLIDE 11

Pressure x Velocity (Pa.m/s) Variance of Shear Force (N2)

Thermoplastic Non- Optimized Machined Concentric Groove Thermoplastic Molded Concentric Groove Thermoset Non- Optimized Machined Concentric Groove Thermoset Non- Optimized Machined LPSP Groove

Variance of Shear Force

11

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SLIDE 12

Wafer Pad Pad

Non-Optimized Machined Groove Molded Groove

SEM Images and Conceptualization of Burrs

12

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SLIDE 13
  • Oxide removal in the Langmuir-Hinshelwood model:

– n moles of reactant R in the slurry react at rate k1 with oxide film on the wafer to form a product layer L on the surface – Product layer L subsequently removed by mechanical abrasion with rate k2 – Abraded material L is carried away by the slurry

  • The local removal rate in this mechanism therefore is a function of chemical

and mechanical contributions

L nR SiO

k

→  +

1

2

      − ⋅ = kT E A k exp

1

*

2

2

SiO L

k

→ 

V p c k

p

× × =

2

1 2 1 2

k k k k M RR

w

+ = ρ

Removal Rate Model

13

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SLIDE 14

Pressure x Velocity (Pa.m/s) Mean Pad Temperature (C)

Pad Temperature

14

Thermoset Non- Optimized Machined Concentric Groove Thermoplastic Non- Optimized Machined Concentric Groove Thermoplastic Molded Concentric Groove Thermoset Non- Optimized Machined LPSP Groove

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SLIDE 15

pV V p p C T T

k a p p p

µ γ πκρ ζ

2 / 1

) / ( 2 + =

Physical Temperature Model

COF Pad thermal properties Geometric factor Mean asperity tip contact pressure

Surface layer grows at chemical rate k1. Growth is fastest at the flash temperature Flash heating

. .. ....

Asperity removes layer at mechanical rate k2

Fraction of heat conducted to pad Depends on contact area

15

(Borucki, CMPMIC 2005)

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SLIDE 16
  • T ≡ hydrolyzed layer reaction temperature
  • Reaction temperature is due to flash heating by passing slurry particle-laden asperity tips
  • The quantity in brackets depends on V due to fluid dynamic effects. Assuming a power

law dependence:

  • The model has five fitting parameters: A, E, cp, β & e:

( ) ( )

                  + −                   + −

+ +

+ ⋅ ⋅ ⋅ =

pV V T k E p pV V T k E p w

k e p k e p

Ae pV c Ae pV c M RR

µ β µ β

ρ

2 / 1 2 / 1

pV V p p C T T

a p k p p

      + =

2 / 1

) / ( κρ µ γ ζ pV V T T

k e p

µ β

+

+ =

2 / 1

Flash Heating Temperature

16

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SLIDE 17

Polishing pad cp (moles/J) β (K/Pa-(m/s)1-a) RMS Error (Å/min) Thermoplastic machined concentric groove 1.64E-8 2.15E-3 77 Thermoplastic molded concentric groove 1.74E-8 2.15E-3 78 Thermoset machined concentric groove 2.59E-8 1.45E-3 81 Thermoset machined LSP 2.52E-8 1.45E-3 65

E = 0.53 eV from Sorooshian et al., Journal of Tribology, 127, 639 (2005) e = 0.66 A = 1.02 x 105 moles m-2 s-1

Optimized Fitting Parameters

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SLIDE 18

Removal Rate (A/min)

500 1000 1500 2000 2500 10000 20000 30000

Pressure x Velocity (Pa.m/s)

Effect of varying e between 0 and 1 Data Model

Sensitivity of ‘e’

18

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SLIDE 19

10000 20000 30000

Pressure x Velocity (Pa.m/s) Temperature Increment (C)

10 5 15 20 25 30 35 40

e = 1 e = 0 T - Ta Tp - Ta

Contribution of Flash Heating Temperature

19

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SLIDE 20

0.2 0.6 1.0 1.4 20.7 27.6

Pressure (kPa)

13.8

Velocity (m/s)

0.2 0.6 1.0 1.4

Velocity (m/s)

0.2 0.6 1.0 1.4

Velocity (m/s)

0.2 0.6 1.0 1.4

Velocity (m/s)

Thermoplastic Non- Optimized Machined Concentric Groove Thermoplastic Molded Concentric Groove Thermoset Non- Optimized Machined Concentric Groove Thermoset Non- Optimized Machined LPSP Groove

2.0x10-3 3.0x10-3 4.0x10-3 5.0x10-3 6.0x10-3 7.0x10-3

) .s m moles ( k

2 1

Chemical Reaction Rate Constant, k1

20

Thermoplastic pads exhibit higher chemical reaction rate constant than thermoset pads

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SLIDE 21

0.2 0.6 1.0 1.4 20.7 27.6

Pressure (kPa)

13.8

Velocity (m/s)

0.2 0.6 1.0 1.4

Velocity (m/s)

0.2 0.6 1.0 1.4

Velocity (m/s)

0.2 0.6 1.0 1.4

Velocity (m/s)

0.5x10-3 1.0x10-3 1.5x10-3 2.0x10-3 2.5x10-3 3.0x10-3

) .s m moles ( k

2 2

Mechanical Abrasion Rate Constant, k2

21

Thermoplastic Non- Optimized Machined Concentric Groove Thermoplastic Molded Concentric Groove Thermoset Non- Optimized Machined Concentric Groove Thermoset Non- Optimized Machined LPSP Groove

Thermoplastic pads exhibit lower mechanical abrasion rate constant than thermoset pads

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SLIDE 22
  • Thermoplastic pads induce higher COFs than the thermoset

pads due to their inherently higher degree of energy loss.

  • Since thermoplastic pads exhibit more reduction in storage

modulus, the variance of shear force associated with thermoplastic pads is higher than thermoset pads.

  • Un-optimized machined grooves produce rougher edges than

molded grooves, thereby inducing a higher COF and a higher shear force variance.

  • LPSP groove is designed to bring slurry towards the pad

center, resulting in a higher mean pad temperature. In addition, the LPSP pad induces a higher shear force variance.

  • Simulation results indicate that thermoplastic pads produce a

more mechanically controlled removal than thermoset pads.

Summary

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