Production of High Purity Functional Water at Point-of-Use for Advanced Mask Cleaning Processes

Transcription

1 purify protect transport Production of High Purity Functional Water at Point-of-Use for Advanced Mask Cleaning Processes 2010 International Workshop on EUV Lithography June 22-24, 2010 Annie Xia, Sr. Applications Engineer Entegris Inc.

2 Abstract 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. In this paper, we describe the design and development of a point-ofuse 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, submicron 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 feature to allow precise control and minimal process variations. Page 2

3 Limitations of Sulfur-based Wet Cleaning Process Organics Removal Particle Removal Rinse Clean Current Chemistry SPM (H 2 SO 4 + H 2 O 2 + H 2 O) APM + Megasonic (NH 4 OH + H 2 O 2 + H 2 O) DIW Rinse Drawbacks Particulates in SPM (SO 4 2- ) residuals -- Haze Contaminants unremovable by SPM Ionic residues -- Haze Too aggressive causing film loss Limited number of cleans Hot DIW rinse may cause wear on masks. Current cleaning processes do not provide mask surfaces that are free from contamination. Adders! Page 3

4 Definition of Functional Water Pure Water + Physical / Chemical Processing Electrolysis Gasification Chemical Addition Light Irradiation Ultrasonic Excitation = Enhanced Cleaning Efficiency! Functional Water: Altered physical / chemical properties: Dielectric constant Viscous force Electrical conductivity Surface tension Oxidation-reduction potential Page 4

5 Sulfur-free Cleaning using Functional Water Organics Removal Particle Removal Rinse Clean New Chemistry O 3 / DI Water ( 5 50 ppm) H 2 / DI Water + Megasonic ( < 3 ppm) DI Water Rinse CO 2 / DI Water (Optional) Advantages of Functional Water * Made at point-of-use * Good cleaning efficiency * Cleaner than SPM * Compatible with existing tools * No waste except H 2 O and gas * Environmentally friendly * Relatively low cost * Can be room temperature Page 5

6 Liquid Gasification using Membrane Contactor Hollow Fiber Membrane Gas Permeate All PFA Membrane Contactor Liquid Inlet Process Liquid In Gas Inlet Conditioning Liquid In Feed Gas Hollow Fiber Membrane Conditioning Liquid Out Gas Outlet Tube Bundle Water Boundary Layer Gas-Liquid Interface Hydrophobic Membrane Gas Membrane Interface Flow Gas Molecule Gas Diffusion Gas Flow Process Liquid Outlet All PFA ultra-clean construction Low extractable and particles Excellent chemical compatibility PFA hollow fiber membrane Only gas permeable, Hydrophobic 2 m 2 membrane surface Low pressure drop < 7 8 Liter/min water flow Page 6

7 Concept of Point-of-Use Ultra-pure Functional Water Polishing and Gasification System Purification Facility DI Water Recirc Pump Organic & Ion Removal UV + Ion Exchangers Particle Removal Filtration To mask clean tool Clean DI Water with controlled: temperature dissolved gas concentration Degas & Re-gas PFA Membrane Contactor Gasification and Control Temperature Control Control (Optional) PFA Heat Exchangers Page 7

8 Typical Ionic Purification and Particle Removal 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. Particle Shedding in DI 1 LPM Cumulative Particles/Liter >= 0.05 um with UDI 50 Page Background Background Install 10 nm Particle Filter 8.7 Particles/L (27 Data Point Average) Time (hours) Outlet DI water Particles < 10 counts / Liter (> 0.05µm)

9 Automated DI Water Gasification Process Degas & Regas in one step Types of Dissolved Gas Sensors MFC Gasified DI Water Outlet Closed Loop Controller Dissolved Gas Sensor O3-DIW: H2-DIW: N2-DIW: - Dissolved O 3 sensor - ORP sensor - Dissolved H 2 sensor - ORP sensor - Dissolved N 2 sensor DI Water Inlet At a constant water temperature: Gas P or flow, Gas solubility Gas P or flow, Gas solubility CO2-DIW: - Dissolved CO 2 sensor -ph meter - Resistivity sensor ORP Oxidation Reduction Potential Gas Exhaust To Single / Batch Type Cleaning Tools How does the control system work: Dissolved gas sensor sends feedback to closed loop controller. Closed loop controller keeps adjusting gas flow until dissolved gas sensor measurement matches the setpoint. Direct Gas Injection! No Gas or Liquid Mixing! Page 9

10 Why do we need to control gas concentration? O3 Concentration vs. Cleaning Efficiency O 3 concentration affects cleaning efficiency! Maintaining stable O 3 concentration Consistent cleaning efficiency Source: Investigation of Sulfur Free Clean Processes for Next Generation Lithography. C. Chovino, et al, AMTC GmbH Auto concentration control minimizes process variability! Without Auto Concentration Control Conductivity (us/cm) Dissolved CO 2 Conc. Water Flow Time (min) DI Water Flow (LPM) Conductivity (us/cm) With Auto Concentration Control Dissolved CO 2 Conc. Water Flow Time (min) DI Water Flow (LPM) Conductivity DI Water Flow Conductivity DI Water Flow Page 10

11 Water Ozonation and Hydrogenation Efficiency Dissolved O 3 Concentration vs. Water Flow (Single Membrane Contactor) Dissolved H 2 Concentration vs. H 2 Pressure (Single Membrane Contactor) Dissolved O3 in Water (ppm) Test condition: Ozone Generator -O 2 : 5 SLPM; g/nm 3 Water temp = 25 o C Dissolved H2 in Water (ppm) Test condition: DI Water Flow = 6 LPM Water temp = 25 o C DI Water Flow (LPM) H2 Pressure (MPa) To adjust dissolved O 3 concentrations: - Inlet O 3 concentration, Dissolved O 3 concentration ; vice versa - Inlet O 2 flow, Dissolved O 3 concentration ; vice versa To adjust dissolved H 2 concentration at a given flow: -H 2 pressure, Dissolved H 2 concentration ; vice versa Page 11

12 Gasification System Control Performance LPM (every 30 seconds) Dissolved CO 2 concentration (Water Resistivity) stability within ± 5% of Setpoint! Resistivity (MOhm-cm) Target Resistivity = 0.05 MΩ-cm DI Water Flow Water Temp = 23 Resistivity = 1/ Conductivity Time (min) o C Conductivity Sensor: Horiba HE-480 Resistivity DIW Flow Dissolved CO 2 Concentration DI Water Flow (LPM) Page 12

13 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. Page 13