PRODUCTION OF HIGH-PURITY FUNCTIONAL WATER AT
POINT-OF-USE FOR ADVANCED MASK CLEANING PROCESSES
Annie Xia, Entegris, Inc.
Abstract
Typical Ionic Purification and Particle Removal
Without the use of traditional pellicles, EUV masks demand high purity and effective but mild cleaning
techniques for protection from defects. Recently, trends towards dilute chemistries and progress in
megasonic cleaning have brought renewed interest in gasified DI water.
Current
Chemistry
Particle Removal
SPM
(H2SO4 + H2O2 + H2O)
Cumulative Particles/Liter
≥0.05 µm with UDI 50
1000
Background
100
10
1
2
How does the control system work?
4
6
8
10
12
Time (hours)
16
18
20
MFC
Closed loop
controller
DIW Rinse
Gasified DI
water outlet
Types of Dissolved Gas Sensors
Dissolved gas
sensor
Dissolved O3 sensor
ORP sensor
Dissolved H2 sensor
ORP sensor
Dissolved N2 sensor
Dissolved CO2 sensor
pH meter
Resistivity sensor
H2-DIW
• Hot DIW rinse may cause
wear on masks
Current cleaning processes do not provide mask surfaces that are free from contamination.
14
Degas and regas in one step
• Dissolved gas sensor sends feedback to closed loop controller
• Closed loop controller keeps adjusting gas flow until dissolved
gas sensor measurement matches the setpoint
• Ionic residues – Haze
• Too aggressive causing film loss
• Limited number of cleans
Outlet DI
water particles
<10 counts/Liter
(>0.05 µm)
8.7 Particles/L
(27 data point average)
Automated DI Water Gasification Process
O3-DIW
Drawbacks
10000
0
Rinse Clean
APM + Megasonic
(NH4OH + H2O2 + H2O)
• Particulates in SPM
• (SO42-) residuals – Haze
• Contaminants unremovable by SPM
Install 10 nm particle filter
100000
0.1
Limitations of Sulfur-based Wet Cleaning Process
Organics Removal
1000000
• Typical outlet DI water contains PPQ levels
of ionic species:
– Less than 0.5 ppt/each element:
Li, Na, Mg, Al, K, Ca, Ti, Cr,
Fe, Mn, Ni, Cu, …
• Typical outlet DI water contains single digit
particles per liter
In this paper, we describe the design and development of a point-of-use functional water treatment
system, specifically for advanced mask cleaning applications. The system is comprised of two modules —
the purification module and the gasification module. The purification module provides treatment features
including TOC reduction, sub-micron particle retention, as well as thermal and pressure control. The
gasification module is capable of delivering bubble-free DI water with various gases (O3, N2, H2, CO2,
NH3, etc.) over a wide concentration range. The gasification module is also equipped with automatic
dissolved gas concentration control features to allow precise control and minimal process variations.
Particle Shedding in DI Water @ 1 L/min
N2-DIW
CO2-DIW
Adders
At a constant water temperature:
Gas P or flow , Gas solubility
Gas P or flow , Gas solubility
To single/batch type
cleaning tools
DI water inlet
ORP – Oxidation Reduction Potential
Gas exhaust
Direct gas injection. No gas or liquid mixing.
Definition of Functional Water
Why do we need to control gas concentration?
Remaining Counts (-)
100000
10000
1000
DIO3
100
SPM
10
1
Pure Water
0
Enhanced Cleaning Efficiency
O3 /DI Water
( 5 – 50 ppm)
H2 /DI Water + Megasonic
(<3 ppm)
DI Water Rinse
CO2 /DI Water (Optional)
Water flow
Dissolved CO2
concentrate
0.5
0
0
1
Conductivity
2
3
Time (min)
60
50
40
30
20
Test condition:
Ozone generator — O2: 5 SLPM; 250 g/Nm3
Water temperature — 25°C
10
10
15
DI Water Flow (L/min)
20
Gas outlet
1.5
Gas diffusion
3
PFA hollow fiber membrane
• Only gas permeable, hydrophobic
• 2 m2 membrane surface
6
10.5
25
To mask clean tool
Clean DI Water with Controlled
• Temperature
• Dissolved gas concentration
DI water flow
1.0
Test condition:
DI water flow – 6 L/min
Water temperature – 25°C
0
18
10.5
6
0.02
0.04
0.06
H2 Pressure (MPa)
0.08
0.1
0.090
0.080
Degas and Regas
PFA Membrane Contactor
Temperature Control
(Optional)
PFA Heat Exchangers
Gasification and Control
1.5 L/min (every 30 seconds)
20
18
16
0.070
14
0.060
12
0.050
10
0.040
8
0.030
6
4
Water flow
0.010
2
0
0.000
0
1
Resistivity = 1/ Conductivity
Conductivity Sensor: Horiba HE-480
Particle Removal
Filtration
3
Dissolved CO2
concentration
0.020
2
3
Time (min)
4
5
Water Temp = 23°C
DI water flow
Summary
• A point-of-use functional water delivery system using membrane contacting technology enables:
– Purification and filtration at point-of-use
– Precise control at point-of-use
– Less chance of contamination at point-of-use
• Automatic control of dissolved gas concentration brings added benefit of ensuring a stable and
seamless cleaning process
5853 EUV Symposium
0.12
To adjust dissolved H2 concentration at a given flow:
• H2 pressure , Dissolved H2 concentration ; vice versa
Target Resistivity = 0.05 MΩ-cm
Resistivity
Organic and Ion Removal
UV + Ion Exchangers
5
1.5
30
0.100
Low pressure drop
• <7 kPa @ 8 L/min water flow
Purification
Recirc
Pump
4
Dissolved CO2 Concentration (Water Resistivity)
Stability within ±5% of Setpoint
Concept of Point-of-Use Ultra-pure Functional Water
Polishing and Gasification System
Facility
DI Water
2
3
Time (min)
Gasification System Control Performance
Liquid outlet
All PFA ultra-clean construction
• Low extractable and particles
• Excellent chemical compatibility
1
Tube bundle
Gas inlet
Gas flow
5
Resistivity (MOhm-cm)
Hollow
fiber
membrane
0
2.0
To adjust dissolved O3 concentrations:
• Inlet O3 concentration , Dissolved O3 concentration ; vice versa
• Inlet O2 flow , Dissolved O3 concentration ; vice versa
Gas-liquid interface
Feed gas
0
0
0
Boundary layer
Hydrophobic
membrane
Gas molecule
Gas
0.5
(Single Membrane Contactor)
0.5
1.0
Water flow
Dissolved CO2
concentrate
Conductivity
2.5
70
All PFA Membrane Contactor
Flow
1.5
Dissolved H2 Concentration vs. H2 Pressure
(Single Membrane Contactor)
Liquid inlet
Water
DI water flow
Dissolved O3 Concentration vs. Water Flow
Liquid Gasification Using Membrane Contactor
Gas permeate
5
2.0
Water Ozonation and Hydrogenation Efficiency
• Good cleaning efficiency
• Compatible with existing tools
• Environmentally friendly
• Can be room temperature
Membrane Interface
4
2.5
Auto concentration control
minimizes process variability
0
Hollow Fiber Membrane
1.0
3.0
Consistent cleaning efficiency
Advantages of Functional Water
• Made at point-of-use
• Cleaner than SPM (sulfuric
peroxide mixture)
• No waste except H2O and gas
• Relatively low cost
1.5
10.00
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
DI Water Flow (L/min)
New
Chemistry
2.0
Dissolved H2 in Water (ppm)
Rinse Clean
60
2.5
O3 concentration affects cleaning efficiency
Maintaining stable O3 concentration
Dissolved O3 in Water (ppm)
Particle Removal
20
30
40
50
DI03 Concentration (ppm)
3.0
Source: Investigation of Sulfur Free Clean Processes for
Next Generation Lithography. C. Chovino, et al, AMTC GmbH.
Sulfur-free Cleaning Using Functional Water
Organics Removal
10
10.00
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
With Auto Concentration Control
DI Water Flow (L/min)
• Dielectric constant
• Viscous force
• Electrical conductivity
• Surface tension
• Oxidation-reduction potential
Without Auto Concentration Control
Conductivity (µS/cm)
• Electrolysis
• Gasification
• Chemical Addition
• Light Irradiation
• Ultrasonic Excitation
O3 Concentration vs. Cleaning Efficiency
Altered physical/chemical properties:
DI Water Flow (L/min)
Functional Water
Conductivity (µS/cm)
Physical/Chemical
Processing