Spin coating is a procedure used to deposit uniform

thin film A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...

s onto flat substrates. Usually a small amount of coating material is applied on the center of the substrate, which is either spinning at low speed or not spinning at all. The substrate is then rotated at speed up to 10,000 rpm to spread the coating material by

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...

. A machine used for spin coating is called a spin coater, or simply spinner. Rotation is continued while the fluid spins off the edges of the substrate, until the desired thickness of the film is achieved. The applied solvent is usually volatile, and simultaneously

evaporates Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

. The higher the

angular speed Angular may refer to: Anatomy * Angular artery, the terminal part of the facial artery * Angular bone, a large bone in the lower jaw of amphibians and reptiles * Angular incisure, a small anatomical notch on the stomach * Angular gyrus, a regio ...

of spinning, the thinner the film. The thickness of the film also depends on the

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

and

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', ''number concentration'', an ...

of the solution, and the solvent. Pioneering theoretical analysis of spin coating was undertaken by Emslie et al., and has been extended by many subsequent authors (including Wilson et al., who studied the rate of spreading in spin coating; and Danglad-Flores et al., who found a universal description to predict the deposited film thickness). Spin coating is widely used in

microfabrication Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" o ...

of functional oxide layers on glass or single crystal substrates using sol-gel precursors, where it can be used to create uniform thin films with nanoscale thicknesses. It is used intensively in

photolithography In integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect ...

, to deposit layers of

photoresist A photoresist (also known simply as a resist) is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronic industry. T ...

about 1

micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

thick. Photoresist is typically spun at 20 to 80 revolutions per second for 30 to 60 seconds. It is also widely used for the fabrication of planar photonic structures made of polymers. One advantage to spin coating

thin films A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...

is the uniformity of the film thickness. Owing to self-leveling, thicknesses do not vary more than 1%. However, spin coating thicker films of

polymers A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

and photoresists can result in relatively large edge beads whose planarization has physical limits.Arscott, S
"The limits of edge bead planarization and surface levelling in spin-coated liquid films"
''J. Micromech. Microeng.'' 30, 025003, (2020).

References

External links

*
Spin Coating of Thin and Ultrathin Polymer Films
*
Deposition of polymer films by spin casting: A quantitative analysis
Industrial processes Semiconductor device fabrication Thin film deposition {{Industry-stub

References

Further reading

External links