The Simulation and Inspection for the Starting Phenomenon of Slit Coating Process on Glass Substrate
Ta-Hsin Chou*, Wen-Hsien Yang*, Kuei-Yuan Cheng*,
Yu-Chen Chang**, and Thomas Luo**
*Industrial Technology Research Institute, No. 195, Sec. 4, Chung Hsing Rd., Chutung, Hsinchu, Taiwan 31040, R.O.C.
**Yuan Ze University, 135, Yuan-Tung Road, Chung-Li, Taiwan 32003, R.O.C.
We developed a two-dimensional Computational Fluid Dynamics (CFD) model of a slit nozzle and coating for photoresist, using the Volume Of Fluid (VOF) to calculate the transient free surface. Parameters studied in simulation, including contact angle, liquid feed rate, slit gap, and coating gap. Simulation results yielded information on operation and buildup conditions, enabling us to examine microscopic fluid flows. Experiments used a slit coater (ITRI) having a slit nozzle 370 mm wide and a 100 µm slit gap, and set on a vertical moving table. A glass substrate was fixed on a horizontal moving table by a vacuum pump. Photoresist is pumped from a tank to the slit nozzle by a plunger. During coating, a CCD camera facing the slit gap imaged coating conditions. Experimental parameters studied included substrate speed, coating gap, and photoresist feed rate. The substrate was operated at 10 to 20 mm/second, the coating gap was set at 100 µm, and the photoresist feed rate was from 0.4 to 0.8 ml. Simulation and experimental results confirmed that CFD simulation was possible in designing the slit nozzle and preverifying coating. Photoresist coating was possible below 1.5 µm thick with 5%uniformity.
-  K. J. Rorschach, “Limiting Flow In A Pre-metered Coating Device,” Chemica Engineering Science, Vol.31, pp. 1057-1060, 1976.
-  B. G. Higgins and L. E. Scriven, “Capillary Pressure and Viscous Pressure Drop Set Bounds on Coating Bed Operability,” Chemical Engineering Science, Vol.35, pp. 673-682, 1979.
-  K. Y. Lee and T. J. Liu, “MinimumWet Thickness In Extrusion Slot Coating,” Chemical Engineering Science, Vol.47, No.7, pp. 1703-1713, 1992.
-  C. K. Yang, D. H. Wong, and T. J. Liu, “The Effect of Polymer Additives on The Operating Windows of Slot Coatings,” Polymer Engineering Science, Vol.44, pp. 1970-1976, 2004.
-  K. N. Christodoulou and L. E. Scriven, “Discretization of Free Surface Flows and Other Moving Boundary Problems,” J. of Computational Physics, Vol.99, pp. 39-55, 1992.
-  Y. C. Chang, T. Luo, K. Y. Cheng, S. Yang, and T. H. Chou, “A twodimensional CFD model of slot die coating for larger area coating techniques,” The 2nd Asian Symposium on Nano Imprint Lithography, 2009.