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Removal of Nano Particles on the Hard Mask Wafer Backside using Brush Cleaning
Hyun-Tae Kima*, Yeo-Ho Kima, Nagendra Prasad Yerriboinab, Tae-Gon Kimc, KyuHwang Wond and Jin-Goo Parka, b, †
a Department of Bio-Nano Technology, b Materials Science and Chemical Engineering, c Smart Convergence Engineering, Hanyang University, Ansan, 15588, Korea
d Samsung Electronics, Hwaseong, 18448, Korea
(E-mail: *[email protected], †[email protected])
As pattern nodes continue to scale down and become more complex, lithography technologies have required many solutions to create extremely small patterns. For a certain process such as, high aspect ratio trench patterning, the hard mask has been chosen for a high etch resistance and selectivity.
Amorphous carbon and siloxane based materials were commonly used as hard mask materials which can be prepared by CVD or spin-on processes. During deposition process, the physical contacts of the wafer backside to pedestals such as chuck or lift pins are necessary to support and transfer the wafer.
The electrostatic chuck (ESC) is widely utilized in deposition process because of its advantages in nonedge exclusion, wafer temperature control and particle defect reduction. However, the pin contact is the protrusion part on ESC that directly contacts wafer backside can make exfoliation of pre-existed
backside film which results in the generation of particle defects. These backside particles may travel to the front side. These backside particles vary in size and materials because of backside particles which were crushed by the chucking pressure. It also greatly affects ESC chucking performance, adhesion
uniformity and flatness stability. Especially, these backside particles were exposed to the thermal energy during the CVD process. It induces deformation of the particles, leading to an increase in adhesion to the substrate. This aging effect results in the reduction of particle removal efficiency. To solve these
particle issues, an effective cleaning process is necessary to remove the contaminated particles on the backside. The adhesion and removal of these particles were first analyzed on backside surfaces. PVA brush cleaning, generally used for post CMP cleaning process, was applied to effectively remove the
particles by physical cleaning in this study.
Abstract
Introduction
Silicon wafer backside
Electrostatic chuck
Contact point
Electrostatic chucking involves contact in
many point between the ECS and backside
of wafer
Delamination of backside film (SiO2)
SEM images
Crushed SiO2 particles
Research Objective
Backside
Particle
Backside particles which were crushed by the chucking pressure
- particle size : nm - 10 µm
- composition : SiO2
- process temp : - 550°C, hard mask coating process
Brush
Cleaning
To remove these particles, Brush cleaning was applied with DIW
Pin-type brush
PVA
brush
Top view
Parameters
- Only DIW use
- Pressure
- Spin speed of brush
- Spin speed of wafer
How much force do we need to remove particles?
Quantification of
Cleaning force
Quantification of
Adhesion force
Process was optimized by
experiential approaching
Optimization
Backside cleaning
condition
Experimental
• Pre-treatment of silicon wafer
1.SC1 (NH4OH:H2O2:DIW=1:2:50) 10min. (dipping) – particle removal
2.Rinse 5min. + Dry N2 blowing
3.DHF (1:100) 3min. (dipping) – native oxide removal
4.Rinse 5min. + Dry N2 blowing
•Deposition of PSL particle on silicon surface (-3㎛)
Colloidal PSL solution (100-500ppm)+ DIW 1min. (dipping)
Back side defect Lateral force analysis
Brush cleaning
① Contamination
particle
Si wafer
② Particle counting
(AFM / OM)③ Brush cleaning ④ Particle counting
(AFM / OM)
• Lab scale brush cleaning (Pin type)
Parameters
- z axis (pressure) ±30mm
- brush rotation speed (500rpm)
- wafer rotation speed (1000rpm)
- DIW flow
- brush type
Quantification of adhesion force using AFM
• C-D signal (a+c)-(b+d)
• Torsional spring constant (kt) = nN/rad
• Angle conversion factor (𝜂)
• Force conversion factor (κ)
• Lateral force(FL)
Results
SPCC 2019 | Portland, Oregon, USA | April 2-3, 2019
• Lateral force (1.0-3.0㎛)
Back side particle
(by ESC chucking)
Standard particle
(PSL particle)
10 20 30 40 50 60 70 80 90 100 1100
5
10
15
20
25
30
35
40
Late
ral fo
rce (
nN
)
Particle size (nm)
10 20 30 40 50 60 70 80 90 100 110
0
5
10
15
20
25
30
35
40
Particle size(nm)
• Lateral force (20, 50, 100nm)
Particle size (nm) Particle size (nm)
2.81nN
6.44nN
13.19nN
2.11nN
8.13nN
26.96nN1day aging 7day aging
A smaller than 100nm size of particle was sensitive to aging time
Back side particle shows higher lateral force than standard particle
Theoretical cal.
0 500 1000 1500 2000 2500 3000
-200
0
200
400
600
800
1000
1200
1400
1600
1800
2000
La
tera
l fo
rce
(nN
)
Particle size (nm)
Theorical calcuation
Experimetal data
Particle size (nm)
Late
ral fo
rce (
nN
)
Experimental data
<1000nm particle : JKR model
>2000nm particle : DMT model
• Lateral force (0.1-3.0㎛)
Measuring of lateral force
using AFM
• Brush cleaning optimization
- with brush usage
30 60 90 120 150 180 21060
65
70
75
80
85
90
95
100
105
PR
E (
%)
Cleaning time (s)Time of brush usage (sec.)
Part
icle
rem
oval effic
iency (
%)
Gap-distance : 0
Wafer rotation speed: 100 rpm
Brush rotation speed: 105 rpm
600nm SiO2
100 120 140 160 180 20060
65
70
75
80
85
90
95
100
105
PR
E (
%)
Brush rotation speed (rpm)Brush rotation speed (RPM)
- with brush rotation speed
600nm SiO2
Gap-distance : 0
Wafer rotation speed: 100 rpm
time: 20s
Optimized condition : >90% removal efficiency (over 600nm SiO2 particle)
JKR model DMT model
http://www.ntmdt.com/spm-basics/view/adhesion-forces
20 30 40 50 600
10
20
30
40
50
60
70
80
90
100
PR
E(%
)
Process time (sec.)Process time (sec.)
Gap-distance : 0
Wafer rotation speed: 100 rpm
Brush rotation speed: 120 rpm
- with process time100nm SiO2
• Particle removal evaluation
Before cleaning (O.M)
After cleaning
1Kx
1Kx20μm
20μm
Part
icle
rem
oval effic
iency (
%)
• Aging effect
0
100
200
300
400
500
600
700
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Tem
pera
ture
(℃
)
Time (hr.)
71.6%90.6%Aging condition : 600°C heating (6hr.)
100nm SiO2 removal efficiency : 90.6% (60sec.)
After aging process, removal efficiency is a 71.6%
Conclusion Acknowledgment
This research was supported by a Semiconductor Industry Collaborative Project
between Hanyang University and Samsung Electronics Co. Ltd.
• To quantify the adhesion force of back side particle attached to the substrate, the lateral force was measured using the AFM
• Because of high temperature aging, back side particles (25.96nN) are harder to remove compared to the standard particle(13.19nN)
• Pin-type brush shows high removal efficiency of 100nm SiO2 particle over 90%. However, after aging process, removal efficiency reduced to
19% decrease. Hence chemical forces are required to remove heat treated particle on backside
Surface force
acts only within
the contact area
Surface force
acts only outside
the contact area
Attracting molecules
Repulsing molecules
Attracting molecules
Repulsing molecules
