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Spin coating is a widely used process for applying a thin uniform filmto a
flat substrate or wafer disc. This technique is used in the electronics
industry to coat photoresist on silicon wafers for integrated circuits,for
magnetic storage disks, and for coating color television scseens andoptical
devices. During the process of spin coating a small quantity of liquid, which
is usually in solution with some volatile solvents, is initially applied
onto a slowly spinning disk, forming a liquid film to wet the whole disk,
and the spinning disk is then accelerated to higher rotating speed.
In this thesis the dynamic properties and uniformity of the spin-coated
film are considered. At first the dynamic film thickness, coating processing
time, skin formation phenomena, dynamic shear stress and max. shear stressin
the film are discussed. We set up a mathematical model of the spin coating
system which includes the governing equations of dynamic film thickness,
fluid continuity, convective/diffusion solvent mass fraction in the film,
fluid momentum and solvent mass transfer in the free surface with the
Garlerkin finite element method dealing with space and solvent mass fraction
variables and finite difference method dealing!with time variable. In the
results the film thickness and coating processing time are functions of
spinning speed, initial solvent mass fraction of coating solution, initial
solvent mass fraction in the gas phase, operating pressure, operating
temperature, material rheological properties, in itial solution viscosity
and initial film thickness. The relation between the film properties and
operation variables is found. The skin formation phenomena is the function
of mass transfer rate, the solvent property of the coating solution,
spinning speed,operation temperature and initial film thickness. Finally
, the max. shear stress depends on spinning speed, initial film thickness
and the radius of substrate. The expression of max. shear stress of
spin-coated film isalso found.
Next the uniformity of spin-coated film for the Newtonian fluid and
non-Newtonian fluid (power law fluid and truncated power law fluid) is
considered.To study the uniformity of spin-coated film, we consider the
continuity equation, equations of motion, average solvent mass fraction
in the film,dynamic film thickness and solvent mass transfer in the free
surface and usethe central difference method dealing with space variable
and average solventmass fraction variable and 4th order Runge-Kutta
method dealing with the ordinary differential equations. In the results
the degree of uniformity of the spin-coated film of Newtonian fluid is
over 99.5 % with ioitial linear film non-uniformity. Therefore initial
wave type film non-uniformityresults in the worse film uniformity and
the degree of film uniformitydecreases with time increasing. For
spin-coated film of non-Newtonian fluid,the degree of film uniformity
can only reach 92 % but the film thickness and degree of film uniformity
does not depend upon the initial film non-uniformity.
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