A model is presented for the description of thin films prepared from solution by spinning. Using only the centrifugal force, linear shear forces, and uniform evaporation of the solvent, the thickness of the film and the time of drying can be calculated as functions of the various processing parameters. The model is compared with experimental results obtained on positive photoresists and excellent agreement is obtained. When adequate care are is taken, the liquid forms a level surface during spinning, and the film thickness becomes uniform and independent of the size of the substrate. The film thickness h shows the following dependence on spin speed f, initial viscosity ν0, and evaporation rate e:h∝f−2/3νo1/3e1/3, and e is proportional to f1/2.

Topics
Kinematics, Deformation, Light sensitive materials, Thin films
1.
A. G.
Emslie
,
F. T.
Bonner
, and
L. G.
Peck
,
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29
,
858
(
1958
).
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2.
A.
Acrivos
,
M. G.
Shah
, and
E. E.
Petersen
,
J. Appl. Phys.
31
,
963
(
1960
).
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3.
A recent paper by
B. D.
Washo
, [
IBM J. Res. Develop.
21
,
190
(
1977
)] attempts to calculate the thickness of spun films without taking evaporation into account. This is done by making an unrealistic approximation of no or little outward flow. It results in a radial dependence of the thickness [Eq. (8) of their paper], whereas the exact calculation of the fluid distribution without evaporation predicts a uniform thickness (Ref. 1).
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4.
G. F. Damon, Proceedings of the Second Kodak Seminar on Microminiaturization (Eastman Kodak Co., Rochester, New York, 1967), p. 36.
5.
O. S. Heavens, Optical Properties of Thin Films (Butterworths, London, 1955), Chap. 5.
6.
A. E. Bell (private communication).
7.
L. P. Fox (private communication).
8.
W. G.
Cochran
,
Proc. Cambridge Philos. Soc.
30
,
365
(
1934
).
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© 1978 American Institute of Physics.
1978
American Institute of Physics
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