The Theoretical Analysis of Spin Coating Process

• Main Authors: Chen, Chung-Tsien, 陳崇憲
• Other Authors: Shi-Chern Yen
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/46815783541558073179

碩士 === 國立臺灣大學 === 化學工程學系研究所 === 86 === 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.