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Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
Oct. 16, 2006
Photomask TeamSemiconductor R & D Center
Samsung Electronics Co. Ltd &Samsung Advanced Institute of Technology
EFFECT OF CURRENT CLEANING PROCESSES ON REFLECTANCE OF EUV MASK
Jaehyuck Choi,, Sungmin Huh, Segun Moon, Jinhui Kim, Soowan Koh, Eun-jung Kim, Sunghun Chi, Byungcheol Cha,
Dongwan Kim, Jeong-woo Lee, Seongwoon Choi, Woosung Han
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
2/17 Oct. 16, 2006
ContentsContents
1. Oxide Layer and Reflectivity for EUV Mask
2. Sample Preparation
3. Reflectivity Analysis
4. Ellipsometry Analysis
5. Conclusions
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
3/17 Oct. 16, 2006
1. Oxide Layer and Reflectivity for EUV Mask
Interfacial layer of Mo-on-Si is thicker than the Si-on-Mo interface- Atomic weight difference: Mo (95.94) vs. Si (28.09)- The crystalline Mo is more densely packed than amorphous Si.
Factors that affect M/L Reflectivity
Capping layer oxide layer thicknessCapping layer materialsCapping layer thickness
Mo layer thickness / (Mo + Si) layer thicknessMo layer + Si layer thickness (period)
Mo/Si interfacial layer thicknessSi/Mo interface layer thickness
Mo layer + Si layer pair No.
Incident light wavelengthIncident angle
Capping layer surface roughness
Silicide (1.7 nm)
SiO2 (1.2 nm)
Si (2.8 nm)
Mo (2.3 nm)Silicide (0.6 nm)
Si (2.2 nm)
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
4/17 Oct. 16, 2006
EUV Reflectivity vs. TEUV Reflectivity vs. Toxox & T& Tcappingcapping
When the thickness of oxide layerexceeds 2 nm, it starts to affect
the total EUV Reflectivity
In order to understand how the Capping oxide layer &
the Capping layer thicknessesaffect the EUV Reflectivity,
the reflectivity was calculated
We need to find out optimal cleaning processes that
do not affect the Reflectivity
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
5/17 Oct. 16, 2006
Definition of Rmax, FWHM, & CW
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
6/17 Oct. 16, 2006
2. Sample Preparation
EUV mask fabrication
EUV mask blankfrom blank vendor
e-beam writing
absorber etch
resist strip & cleaning
defect inspection
repair
buffer etch
clean
final inspection
EUV mask Cleaning
Bath : SPM, SC-1
Spin :O3 Water, H2 Water
Dry : Asher
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
7/17 Oct. 16, 2006
Ozone Water
00.10.20.30.40.50.60.7
12.8 13 13.2 13.4 13.6 13.8 14 14.2
Wavelength (nm)
Ref
lect
ivity
O3
Direct oxidation by “Ozone”
HO• Indirect oxidation by “Ozone”
C=C C-H C-OH C=O OH-C=O
Olefin Alkane Alcohol KetoneCarboxylic
acid
AlcoholKetone
Carboxylic acid
AlcoholKetone Carboxylic acid Soluble
in DIW
Superior oxidant than “Ozone”
Oxidation
SiO3 Water
Organic contaminant SiO2
A oxide layer is made by O3 water
Change of Reflectivity
Ozone Water3. Reflectivity Analysis
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
8/17 Oct. 16, 2006
Oxidation
SiH2SO4
From SPM
Organic contaminant SiO2
A oxide layer is made by SPM
Change of Reflectivity
Organic contaminants ⇒ CO, CO2, H2O
SPM
00.10.20.30.40.50.60.7
12.8 13 13.2 13.4 13.6 13.8 14 14.2
Wavelength (nm)
Ref
lect
ivity
SPM
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
9/17 Oct. 16, 2006
Ashing
00.10.20.30.40.50.60.7
12.8 13 13.2 13.4 13.6 13.8 14 14.2
Wavelength (nm)
Ref
lect
ivity
Plasma AshingO2
O (1D) O (1D)
Ionizing Radiation
CkHmOn ⇒ Ck’Hm’On’ ⇒ CO, CO2, H2O
O (1D) O (1D)
A oxide layer is made by Ashing
Change of Reflectivity
SiO (1D)
from Ashing
Organic contaminant SiO2
Oxidation
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
10/17 Oct. 16, 2006
Si
-- -------
- - - - - -
-
- - - - - -
OH- from SC-1
OH- from SC-1
H2O2 from SC-1
particle SiO21) Oxidation
2) Lift Off
3) Repulsion
The oxide layer made by H2O2 is etched by NH4OH
Almost no change of Reflectivity
SCI
00.10.20.30.40.50.60.7
12.8 13 13.2 13.4 13.6 13.8 14 14.2
Wavelength (nm)
Ref
lect
ivity
SC-1
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
11/17 Oct. 16, 2006
-- -------
- - - - - -
-
- - - - - -
H2 Water
1) Lift Off
2) Repulsion
H2 Water
No oxide layer is made by H2 Water
Almost no change of Reflectivity
H2 Water
00.10.20.30.40.50.60.7
12.8 13 13.2 13.4 13.6 13.8 14 14.2
Wavelength (nm)
Ref
lect
ivity
H2 Water
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
12/17 Oct. 16, 2006
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
ΔR
max
-0.15
-0.1
-0.05
0
0.05
0.1
ΔFW
HM
, ΔC
W
Rmax FWHM Centroid Wavelength
O3 water
SPM SC-1 Ashing H2 water
O3 water SPM Ashing SC-1 H2 Water
Δ Rmax (%) - 0.51 - 0.37 - 1.12 0.12 - 0.08
CW (nm) - 0.13 0.01 0.083 0.01< ~ 0
FWHM (nm) - 0.01 - 0.01 ~ 0 ~ 0 ~ 0
Serious (oxidation) Moderate (oxidation) Moderate (etching)
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
13/17 Oct. 16, 2006
Oxidant agent4. Ellipsometry Analysis
SPM
O3 Water
Ashing
a-Si(56.4%)+SiO2(43.6%)
ML
97.73 Å
Before Cleaning SiO2
ML
8.44 Å
94.19 Åa-Si(70.9%)+SiO2(29.1%)
After Cleaning
Δ SiO2
Δ a-Si
a-Si
SiO2
ML
41.79 Å
62.30 Å
Before Cleaning
a-Si(56.4%)+SiO2(43.6%)
ML
97.73 Å
After Cleaning
Δ SiO2
Δ a-Si?
a-Si
SiO2
ML
41.33 Å
60.51 Å
Before Cleaning
a-Si(72.3%)+SiO2(36.7%)SiO2
ML
18.43 Å
74.90 Å
After Cleaning
Δ SiO2
Δ a-Si
Δ SiO2
Δ a-SiΔ Rmax Δ SiO2 CW Δ a-Si CW
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
14/17 Oct. 16, 2006
Etching agent
a-Si
SiO2
ML
40.30 Å
62.00 Å
Before CleaningSiO2
ML
38.87 Å
61.96 Åa-Si
After CleaningSC-1
Δ SiO2Δ a-Si
a-Si
SiO2
ML
38.87 Å
61.96 Å
Before Cleaning
a-Si(72.3%)+SiO2(36.7%)
SiO2
ML
34.00 Å
61.00 Å
After CleaningH2 Water
Δ SiO2Δ a-Si
Almost no change in Δ Rmax & CW
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
15/17 Oct. 16, 2006
Δ SiO2
Δ a-SiΔ Rmax Δ SiO2 CW Δ a-Si CW
In order to prove the above relationshipsthe Δ of Rmax & CW vs. the Δ of SiO2 or a-Si was simulated
0
0 .1
0 .2
0 .3
0 .4
0 .5
0 .6
0 .7
0 .8
12 12 .5 13 13 .5 14 14 .5 15
00 .511 .522 .533 .544 .55
0
0 .1
0 .2
0 .3
0 .4
0 .5
0 .6
0 .7
0 .8
12 12 .5 13 13 .5 14 14 .5 15
1010 .51111 .51212 .51313 .51414 .515
ΔRmax & CW vs. SiO2 Thickness ΔRmax & CW vs. a-Si Thickness
As SiO2 thickness increases, ΔRmax decreases and CW increases.
As a-Si thickness increases, Δ Rmax decreases and CW decreases.
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
16/17 Oct. 16, 2006
CONCLUSIONS
• We have investigated the effects of current cleaning processes such as SPM, O3 water, plasma ashing, SC-1, and H2 water on the reflectivity of EUV mask.
• We observed that Rmax increases after cleaning processes with etching effect (e.g. SC-1) while Rmax decreases after cleaning processes with oxidation effect(e.g. O3 water or plasma ashing).
• We also observed that CW moves towards shorter wavelength after O3 water cleaning process but it moves towards longer wavelength after Ashing process.
• Simulation and ellipsometry analysis signify that the thickness increase of either SiO2 or a-Si layer causes Rmax to decrease. Since O3 water process thickens a-Si layer while ashing process thickens SiO2 layer, either process eventually reduces Rmax.
• This analysis also confirmed that the thickness increase of SiO2 layer and a-Si layer causes CW to move towards longer and shorter wavelength, respectively. O3 water process drives CW towards shorter wavelength since it thickens a-Si layer while ashing process towards longer wavelength since it thickens SiO2 layer.
Photomask Team / MEMORY DIVISION
2006 International Symposium on EUVL
AAAAA
17/17 Oct. 16, 2006
FUTURE WORK
• We will select current cleaning processes that do not affect the reflectivity of EUVmask and then combine them into a series of cleaning procedures for better PRE and less damage.
• We are also working on the development of cleaning processes that can significantly reduce chemical contamination on the EUV mask surface for the purpose of reducingany possibilities of progressive defect creation on it during laser exposure.
ACKNOWLEDGEMENT
• We would like to appreciate the help made by Kyongyoon Bang fromSamsung Electronics for the ellipsometry analysis of EUV mask.