Download - Spin Coating
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Prof. V.KrishnakumarProfessor and Head
Department of PhysicsPeriyar UniversitySalem – 636 011
India
Introduction to Spin Coating
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Agenda
• Introduction to spin coating– Definition and brief history of spin coating– Uses of spin coating technology– Common spin coating defects
• Spin Coating process
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What is Spin Coating?
• A process in which solution is spread evenly over a surface using centripetal force.
• Spin coating will result in a relatively uniform thin film of a specific thickness.
• Spin coating is an important way of creating thin films in the microelectronics industry.
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Brief History of Spin Coating
• Spin coating was first used to apply coatings of paint and pitch around seventy years ago.
• In 1958 Emslie et. al. developed the first spin coating model.
• This model has been used as a basis for future more specific or complicated models.
Lawrence and Zhou: “Spin Coating of Non-Newtonian Fluids”
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Spin Coater Schematic
• Wafer is held to chuck with vacuum pump.
• Lid is placed over spinning basin before spin is initiated.
Vacuum
Wafer
Chuck
Basin
Lid
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Basic Physics of Spin Coating
• Centripetal force is responsible for the spread of liquid across the wafer.
• At long times the fluid will flow only negligibly, resulting in a lower limit of the final thickness.
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Industrial Uses of Spin Coating
• Photoresist for patterning wafers in microcircuit production.
• Insulating layers for microcircuit fabrication such as polymers.
• Flat screen display coatings. Antireflection coatings and conductive oxide.• DVD and CD ROM• Television tube antireflection coatings.
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Common Spin Coating Defects
•Bubbles on the surface of the coated wafer.
•This occurs when fluid is deposited as the wafer is spinning, and may be caused by a faulty dispense tip.
•A swirling pattern may be observed.
•Causes:
•Fluid deposited off center
•Acceleration too high
•Spin time to short
•Exhaust rate too highhttp://www.cise.columbia.edu/clean/process/spintheory.pdf
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Common Spin Coating Defects
•A mark or circle in the center of the wafer could indicate a chuck mark.
•If a chuck mark occurs the type of chuck should be changed.
•Streaks can occur on the wafer for a number of reasons including:
•Acceleration too high
•Fluid deposited off center
•Particles on surface prior to spin
http://www.cise.columbia.edu/clean/process/spintheory.pdf
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Common Spin Coating Defects
•Uncoated areas on wafer occur when to little fluid is deposited on the wafer.
•Pinhole defects can be caused by:
•Air bubbles
•Particles in fluid
•Particles on substrate.
http://www.cise.columbia.edu/clean/process/spintheory.pdf
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Agenda
• Introduction to spin coating– Definition and brief history of spin coating– Uses of spin coating technology– Common spin coating defects
• Spin Coating Process
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Spin Coating Process
• Four main processing steps:
– Step 1: Deposit fluid onto substrate.
– Step 2: Accelerate wafer to final radial velocity.
http://www.mse.arizona.edu/faculty/birnie/Coatings/
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Spin Coating Process
• Four main processing steps:
– Step 3: The coating thins at a rate that depends on the velocity at which the wafer is spinning and the viscosity of the fluid.
– Step 4: Solvent is evaporated from the film, resulting in further thinning.
http://www.mse.arizona.edu/faculty/birnie/Coatings/
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References
Lawrence, C.J, Zhou, W. “Spin coating of non-Newtonian Fluids”. Journal of Non-Newtonian Fluid Mechanics, 39 (1991) 137-187
Middleman, S. An Introduction To Fluid Dynamics. John Wiley and Sons. New York. 1998
http://www.cise.columbia.edu/clean/process/spintheory.pdf
http://www.mse.arizona.edu/faculty/birnie/Coatings
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Questions?