View
7
Download
0
Category
Preview:
Citation preview
Accelerating the next technology revolution
Copyright ©2009
SEMATECH, Inc. SEMATECH, and the SEMATECH logo are registered servicemarks of SEMATECH, Inc. International SEMATECH Manufacturing Initiative, ISMI, Advanced Materials Research Center
and AMRC are servicemarks of SEMATECH, Inc. All other servicemarks and trademarks are the property of their respective owners.
Mechanisms of EUV reflectivity loss
from the multiple cleanings
Abbas Rastegar
Byunghoon Lee,
Arun John Kadaksham,
SEMATECH Albany
October 2011
Special thanks to Thomas Laursen (ASML)
SEMATECH Confidential
Outline
• EUV reflectivity loss from multiple cleanings
• Mask blank surface changes from cleaning
– Si diffusion and oxidation
– Ru oxidation
• Contribution of cleaning processes to EUV
reflectivity loss
– Radiation effects
– Chemistry effects
– Megasonic effects
– Combined effects
25 October 2011 2
SEMATECH Confidential
How many times can an EUV mask be
cleaned?
25 October 2011 3
• EUV reflectivity (Rmax) dropped below target after cleaning 20X
±0.5%
Ru layer
+ 4 ML
removed
• What is the mechanism of EUV reflectivity loss?
SEMATECH Confidential 25 October 2011 4
Which cleaning steps oxidize/remove Ru?
• Which steps oxidize Ru and/or Si?
• Which steps remove Ru or Si?
• Is there any combined effects?
– (VUV+ SPM), (VUV+ APM), (SPM+APM)
• Does megasonic contribute to the chemistry effects?
• Verification method:
– Change in EUV reflectivity at each step
Oxidizing steps Etching steps
Physical interactions
APM: (NH4OH/H2O2/H2O)
SPM: (H2SO4/H2O2)
VUV: ( Vacuum UV =172 nm)
SEMATECH Confidential 25 October 2011 5
EUV reflectivity loss from individual
cleaning steps (50X)
• EUV reflectivity loss is maximum when SPM follows VUV
exposure
After 50 x clean
0 0.5 1 1.5 2 2.5 3 3.5
VUV
SPM
VUV+APM
VUV+SPM
VUV+SPM+APM
EUV Reflectivity loss (%)
VUV+SPM+ APM
VUV+SPM+ APM
VUV+SPM+ APM
VUV+SPM+ APM
Standard process
+ Megasonic
+ Megasonic
SEMATECH Confidential 25 October 2011 6
EUV reflectivity loss by individual cleaning
steps (50X)
• EUV reflectivity drops linearly with exposure time
After 50 x clean
0 0.5 1 1.5 2 2.5 3 3.5
VUV
SPM
VUV+APM
VUV+SPM
VUV+SPM+APM
EUV Reflectivity loss (%)
VUV+SPM+ APM
VUV+SPM+ APM
VUV+SPM+ APM
VUV+SPM+ APM
Standard process
+ Megasonic
+ Megasonic
y = -0.0577x - 0.5037
R2 = 0.7154
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
5X 10X 15X 20X 25X 30X 35X 40X 45X 50X
Cleaning Cycle
Ch
an
ge
in
EU
V R
efl
ec
tiv
ity
(%
)VUV(Ar)
SEMATECH Confidential 25 October 2011 7
Si oxidation on top of Ru from
exposure to VUV( =172 nm)
TOFSIMS
Surface oxidation
• Diffused Si on top of Ru is further oxidized by VUV radiation
( ratio of SiO2 / SiO increases)
SEMATECH Confidential 25 October 2011 8
VUV(172 nm)+ NH4OH/H2O2/H2O
(APM)
• VUV + APM is more aggressive than VUV alone.
• Why EUV reflectivity loss is less for (VUV+APM)?
SEMATECH Confidential
Si oxidation from cleaning process
25 October 2011 9
• Greater Si oxidation from (VUV+ APM) than VUV
• APM oxidizes Si and etches SiO2
VUV+SPM
SPM
VUV+ APM
VUV
No clean
SiO2 increase
deeper by
VUV+SPM
With contribution of Thomas Laursen
SEMATECH Confidential
Study of Ru oxidation by TOFSIMS and Auger
( freshly deposited Ru cap multilayer)
25 October 2011 10
• Auger depth profile analysis shows Ru, Si, and O on the
surface, indicative of both Ru and Si oxides
• Ru oxide in all 3 oxidation valances is found on surface of the
fresh Ru blank after deposition (RuO2>Ru2O3>RuO): (9.5:8:1)
Auger TOFSIMS
With c contribution of Thomas Laursen
SEMATECH Confidential
Ru oxidation from the cleaning process
25 October 2011 11
• (VUV+ SPM) leaves the most Ru2O3 on the surface
• All steps with wet chemistry oxidized the Ru surface
• VUV in Ar atmosphere has a small contribution to Ru oxidation
VUV+SPM
SPM
VUV+ APM
VUV No clean
With contribution of Thomas Laursen
SEMATECH Confidential 25 October 2011 12
• Megasonic cleaning of blanks creates pits on the blank
surface
Megasonic induced pits
Average EUV Reflectivity Change by Cleaning
60
61
62
63
64
65
66
3 9 15 24 30 36 42 48 54 60 66 72
Cleaning Cycle
Pe
ak
Re
fle
cit
vit
y (
Rm
ax
av
era
ge
)
Megasonic contribution to EUV reflectivity loss
F/B process
TEM: Jena Harris Jones
SEMATECH Confidential 25 October 2011 13
Dependence of Megasonic pits on Megasonic Power
y = 11.005e0.163x
y = 17.691e0.1076x
0
500
1000
1500
2000
2500
3000
3500
4000
0 10 20 30 40 50 60
Cleaning cycle
Ad
de
r (p
it)
co
un
t
High power MS
Low Power MS
Cleaning-induced pit dependency on
megasonic power
• Higher megasonic powers result in faster pit creation
F/B process
SEMATECH Confidential
Improvement in mask lifetime using softer
cleaning processes
25 October 2011 14
• Softer cleaning processes can clean the mask up to 80X
• Softer clean processes:(no VUV) + lower megasonic powers
±0.5%
SEMATECH Confidential
Chemistry vs. megasonic contributions
25 October 2011 15
• VUV( =172 nm) and megasonic contribute the most to EUV
reflectivity loss
SEMATECH Confidential
Summary • The top surface of the Ru cap is a mixture of Ru, oxygen, Si and all
possible combined oxides and silicides (RuxOy, SixOy,RuxSiyOz)
• VUV radiation
– Oxidizes Si; therefore, EUV reflectivity drops when the Si oxide layer
becomes thicker
– Oxidizes Ru slightly
• (VUV+APM)
– APM will etch the silicon oxide layer formed by VUV radiation; therefore,
EUV absorption will be minimal
• SPM
– Mainly oxidizes Ru
• (VUV+SPM)
– Strongly oxidizes Ru and severely impacts EUV reflectivity
– Not clear which Ru-containing compound has highest EUV absorption
• Megasonic exposure compromises Ru layer integrity, which results in
oxidizing chemistries attacking the multilayer
25 October 2011 16
SEMATECH Confidential
Conclusions • UV light radiation and cleaning chemistries modify the surface of the
Ru-capped multilayer, increasing both the scattering and absorption of
EUV light
• VUV light not only oxidizes the Si on the top surface but also modifies
Ru oxides and silicides such that it will be further oxidized by strong
oxidant agents such as sulfuric acid and hydrogen peroxide
• At this time, it is not clear which chemical compound (Ru oxides, Ru
silicides, or a combination) severely reduces EUV reflectivity
• Therefore, the combined effects of VUV+ chemistry and exposure to megasonic are responsible for degrading capping layer integrity
25 October 2011 17
SEMATECH Confidential 25 October 2011 18
Thank You
Acknowledgement:
Cleans Program: Matt House, Zak Robinson, Thomas Laursen (ASML)
Metrology: CC. Lin, Tonmoy Chakraborty, Jana Harris Jones,
Steve Novak (CNSE)
Operation Support: Anne Rudack and all MBDC technicians
SEMATECH Confidential 25 October 2011 19
EUV reflectivity loss by individual steps
• Only VUV in Ar atmosphere and VUV+ SPM reduce reflectivity
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
5X 10X 15X 18X 23X 28X 33X 38X 43X 48X
Cleaning Cycle
EU
V r
efl
ec
tiv
ity
Ch
an
ge
(%
)SPM VUV(Ar)+APM
y = -0.0577x - 0.5037
R2 = 0.7154
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
5X 10X 15X 20X 25X 30X 35X 40X 45X 50X
Cleaning Cycle
Ch
an
ge
in
EU
V R
efl
ec
tiv
ity
(%
) VUV(Ar) VUV(Ar)+SPM
Recommended