Basic Photo Process Steps
Spin-Coat Resist Usage/Waste
Chemical Usage in the Photolithography Process
Photoresist
Resin (e.g. Cresol-formaldehyde {Novolac} )
Solvents
Ethyl lactate (EL) (b.p 154C)
Ethyl 3-ethoxypropionate (EEP)
Cellosolve Acetate
Photo-active Compounds
Developer
Edge Bead Remover
Solvents
Reducing VOC Emissionsfrom Photolithography Process
Switch to Water-Based Resists
Advantage: no VOC emissions
Disadvantage: line width resolution, “speed”
Optimize Use of Current Solvent-Based Resists
Advantage: utilize current formulations, equipment
Disadvantage: no hope for eliminating VOC emissions
Benefits to Minimizing Resist Usage
Resist Costs (~$500/gallon)
Environmental Impact
Most of the Resist is “wasted”, in the sense that it is spun off the wafer. The high “waste” is required to achieve uniformity in thickness and proper coverage.
Because of precise resist formulations, solvent evaporation during spinning, and contamination concerns, it is impossible to recycle resist that is spun from the wafer.
Typically, Organic Solvents are used to clean the photoresist “cups” into which the excess resist is spun. Less solvent usage leads to less emissions of Volatile Organic Compounds (VOCs).
Photoresist Dispense Optimization
Objective
Coverage of given thickness
Coverage of given uniformity
Control Variable(s)
Resist properties (viscosity, solvent mass fraction, amount dispensed)
Spin speed
Spin recipe
Temperature, RH
Three Steps to Coating Process
Spin-Coat Operating Parameters
Spin Speed (rpm)
Spin Time (sec)
Surface Temperature
Room Temperature
Room Humidity
Resist Volume
Resist Viscosity
Resist Solid Mass Fraction
Properties of Photoresist
Initial Viscosity: 5 to 100 cP
Solvent Mass Fraction: 70-90%
Photoresist viscosity for these experiments:
560 Resist - 17 cP
500 Resist - 40 cP
Typical Viscosity Changes: 0.01 to 10,000 Poise as SMF goes from 1.0 to 0.0
Typical Diffusivity Changes: 10-6 to 10-12 cm2/sec as SMF goes from 1.0 to 0.0
Process Overview
Current Practice
At slow speed (usually ~2000 rpm) dispense 3-5 cc resist and spin for less than 2 seconds
Ramp up speed (~3000 rpm) and spin for 20-30 seconds
Apply Edge Bead Remover
Fraction Resist “spun off”: typically 97-99%
Ultra Casting Predispense
At very high speed (6000 rpm) dispense 1 cc resist and spin for 1 second
Decelerate to 2000 rpm and apply second dispense of 1 cc
Accelerate to 3000 rpm and spin for 20-30 seconds
Apply Edge Bead Remover
Fraction Resist “spin off”: typically 95-97%
How Fast Does the Solvent Evaporate?
Solid and Solvent Mass Remainingon Wafer
Flow Characteristics:Resist Dispense Nozzle
Resist Flows vs. Pressure Dropin TRACK Pump
Dispense Rate vs. Temperature
Temperature Dependence of Resist Viscosity
Theory of Spin Coating
Effect of Evaporation on Film Height During Spinning
Final Film Thickness:Single Dispense
Ultra Casting Predispense Technique
UCP Resist Coating - 2 Layer Model
Resist Thickness vs RPM
Resist Thickness vs. RPMALL DATA
Final Film Thickness:Double Dispense Data
Final Height:Single and Double Dispense
Conclusions Future Work
Resist Usage:
~5ml for single dispense
~2ml for ucp method
Resist Thickness and Uniformity: Identical for both methods
Comparison to theoretical Models: Identical for both methods; slightly stronger viscosity dependence than predicted theoretically
Resist and solvent usage reduction yields substantial reduction in VOC emissions
Experimental verification for other resists
Further measurements on relative rates of evaporation and viscous thinning as function of RPM, T, t
Inclusion of surface tension effects in model
Further Model development to predict local resist thickness as function of viscosity, solids fraction, wafer position
Acknowledgments
Motorola
Tom Roche
Melissa Masteller
Frank Fischer
Michelle Demumbrum
University of Arizona
Chris Doty
ua master.pot
Basic Photo Process Steps
Spin-Coat Resist Usage/Waste
Chemical Usage in the Photolithography Process
Photoresist
Resin (e.g. Cresol-formaldehyde {Novolac} )
Solvents
Ethyl lactate (EL) (b.p 154C)
Ethyl 3-ethoxypropionate (EEP)
Cellosolve Acetate
Photo-active Compounds
Developer
Edge Bead Remover
Solvents
Reducing VOC Emissionsfrom Photolithography Process
Switch to Water-Based Resists
Advantage: no VOC emissions
Disadvantage: line width resolution, “speed”
Optimize Use of Current Solvent-Based Resists
Advantage: utilize current formulations, equipment
Disadvantage: no hope for eliminating VOC emissions
Benefits to Minimizing Resist Usage
Resist Costs (~$500/gallon)
Environmental Impact
Most of the Resist is “wasted”, in the sense that it is spun off the wafer. The high “waste” is required to achieve uniformity in thickness and proper coverage.
Because of precise resist formulations, solvent evaporation during spinning, and contamination concerns, it is impossible to recycle resist that is spun from the wafer.
Typically, Organic Solvents are used to clean the photoresist “cups” into which the excess resist is spun. Less solvent usage leads to less emissions of Volatile Organic Compounds (VOCs).
Photoresist Dispense Optimization
Objective
Coverage of given thickness
Coverage of given uniformity
Control Variable(s)
Resist properties (viscosity, solvent mass fraction, amount dispensed)
Spin speed
Spin recipe
Temperature, RH
Three Steps to Coating Process
Spin-Coat Operating Parameters
Spin Speed (rpm)
Spin Time (sec)
Surface Temperature
Room Temperature
Room Humidity
Resist Volume
Resist Viscosity
Resist Solid Mass Fraction
Properties of Photoresist
Initial Viscosity: 5 to 100 cP
Solvent Mass Fraction: 70-90%
Photoresist viscosity for these experiments:
560 Resist - 17 cP
500 Resist - 40 cP
Typical Viscosity Changes: 0.01 to 10,000 Poise as SMF goes from 1.0 to 0.0
Typical Diffusivity Changes: 10-6 to 10-12 cm2/sec as SMF goes from 1.0 to 0.0
Process Overview
Current Practice
At slow speed (usually ~2000 rpm) dispense 3-5 cc resist and spin for less than 2 seconds
Ramp up speed (~3000 rpm) and spin for 20-30 seconds
Apply Edge Bead Remover
Fraction Resist “spun off”: typically 97-99%
Ultra Casting Predispense
At very high speed (6000 rpm) dispense 1 cc resist and spin for 1 second
Decelerate to 2000 rpm and apply second dispense of 1 cc
Accelerate to 3000 rpm and spin for 20-30 seconds
Apply Edge Bead Remover
Fraction Resist “spin off”: typically 95-97%
How Fast Does the Solvent Evaporate?
Solid and Solvent Mass Remainingon Wafer
Flow Characteristics:Resist Dispense Nozzle
Resist Flows vs. Pressure Dropin TRACK Pump
Dispense Rate vs. Temperature
Temperature Dependence of Resist Viscosity
Theory of Spin Coating
Effect of Evaporation on Film Height During Spinning
Final Film Thickness:Single Dispense
Ultra Casting Predispense Technique
UCP Resist Coating - 2 Layer Model
Resist Thickness vs RPM
Resist Thickness vs. RPMALL DATA
Final Film Thickness:Double Dispense Data
Final Height:Single and Double Dispense
Conclusions Future Work
Resist Usage:
~5ml for single dispense
~2ml for ucp method
Resist Thickness and Uniformity: Identical for both methods
Comparison to theoretical Models: Identical for both methods; slightly stronger viscosity dependence than predicted theoretically
Resist and solvent usage reduction yields substantial reduction in VOC emissions
Experimental verification for other resists
Further measurements on relative rates of evaporation and viscous thinning as function of RPM, T, t
Inclusion of surface tension effects in model
Further Model development to predict local resist thickness as function of viscosity, solids fraction, wafer position
Acknowledgments
Motorola
Tom Roche
Melissa Masteller
Frank Fischer
Michelle Demumbrum
University of Arizona
Chris Doty
Basic Photo Process Steps
Spin-Coat Resist Usage/Waste
Chemical Usage in the Photolithography Process
Photoresist
Resin (e.g. Cresol-formaldehyde {Novolac} )
Solvents
Ethyl lactate (EL) (b.p 154C)
Ethyl 3-ethoxypropionate (EEP)
Cellosolve Acetate
Photo-active Compounds
Developer
Edge Bead Remover
Solvents
Reducing VOC Emissionsfrom Photolithography Process
Switch to Water-Based Resists
Advantage: no VOC

Free register and download UseNet downloader, then you can free download from UseNet.
Download "VOC Emissions Reduction from Photolithography" from Usenet!