1. Jianfeng Luo, Prof. David Dornfeld
Material Removal Saturation in Chemical Mechanical Polishing: Effects of Abrasive Size Distribution and Wafer-Pad Contact Area
SFR Workshop
May 24, 2001
Jianfeng Luo, Prof. David Dornfeld
Berkeley, CA
2001 GOAL: To build integrated CMP model for basic mechanical and chemical elements. Develop periodic grating metrology by 9/30/2001.
5/24/2001

2. Motivation
Further Identify the Roles of Abrasive Size Distribution and Wafer-Pad Contact Area on Material Removal in CMP
Identify the Relationship between Abrasive Weight Concentration and Material Removal.
Process Optimization based on Understanding of Roles of Abrasive Size Distribution and Wafer-Pad Contact Area
5/24/2001

3. Abrasive Size Distribution Dependence of MRR:
Particle Size Distribution [1]
Five Different Kinds of Abrasive (Alumina) Size Distributions for Tungsten CMP
Mean Size (m)
Standard Deviation (m)
AKP50
0.29
AKP30
0.38
AKP15
0.60
AA07
0.88
AA2
2.00
(%) Frequency
Abrasive Size X (Log Scale)
1. Bielmann et. al., Electrochem. Letter, 1999
5/24/2001

4. Experimental Data[1] of Material Removal Saturation
Contact area A with abrasive
sitting on it before MRR saturation
Contact area A totally
occupied by abrasives
Concentration increased
from 0 to Cs
pad asperity
abrasives
wafer
pad asperity
smaller contact area
larger contact area
large weight concentration of abrasives
small weight concentration of abrasives
Schematic showing the relationship between contact area and material removal saturation
[1]. From D. J. Stein et. al., J. of ElectroChem. Soc., 1999
5/24/2001

5. Proposed Three Regions of Material Removal as
a Function of Abrasive Weight Concentration
Saturation MRR
5/24/2001

6. Relationship between Abrasive Size and Material Removal Rate before Material Removal Saturates
MRR Saturation at Concentration 10% for Smaller Abrasives
S (xavg+3)2/xavg3
Linear Relationship Holds for Larger Abrasives
[1]
[2]
[1]. Experimental data from Bielmann et. al.., Electrochem. Letter, [2]. Modeling and verification from Luo and Dornfeld, to be submitted to IEEE Transaction: Semiconductor Manufacturing
5/24/2001

7. Relationship between Contact Area and Abrasive Size when Material Removal Saturates
Wafer
xavg-a R
R+xavg-a F
(a)
Contact area A’ with active abrasives
Pad Asperity with Young’s modulus Ep
Abrasive layer with effective Young’s modulus Ea
Real contact parts A’’ between wafer & abrasives
(b)
Saturation MRR (1+m1xavg-a)-1/3
=[1+m1(xavg+3)]-1/3 A’–1/2
xavg +3
Saturation
MRR
Schematic of wafer-abrasive-pad contact in the situation
of material removal saturation (a) before force applied to
the wafer and (b) after force applied to the wafer.
5/24/2001

8. Prediction of Material Removal as a Function of Abrasive Weight Concentration
5/24/2001

9. 2002 and 2003 Goals
Integrate initial chemical models into basic CMP model. Validate predicted pattern development by 9/30/2002.
Develop comprehensive chemical and mechanical model. Perform experimental and metrological validation by 9/30/2003.
5/24/2001