Defects spin coating

To prepare ultrathin polymer films on the surface of wafers, especially those of large diameter (6 or 8 inch), uniformity and defect density become important factors in determining the resist quality. The conventional spin coating method has been reported to introduce interference striations (11) and high defect densities (2.31 when used to prepare ultrathin polymer films. As an alternative approach, the LB technique has been proposed as being suited to the preparation of more uniform ultrathin polymer films (2). Using this technique monolayer polymer films can be transferred layer by layer to the surface of a solid substrate from the water surface. An important feature of the LB technique is that the accumulation of monolayer films allows the thickness of the built-up film to be controlled in a precise manner. Consequently, extremely uniform and ultrathin polymer films can be prepared. 

One of the major sources of problems encountered in spin-coating hardware is the dispensing equipment. Frequently it has been recommended that the resist be dispensed directly from the bottle thereby avoiding all mechanical pumps, syringes, or additional filtering equipment. Provided the resist solution has been adequately filtered prior to dispensing, direct application from the bottle should yield the lowest defect films possible. 

A recently reported alternative to spin or spray coating is screen printing of polyimide solutions (82, 85, 90). Screen printing is a low-cost, high-throughput process capable of directly patterning the polyimide films as they are deposited. Another alternative is the vapor deposition of polyimides, which was reported by researchers who co-evaporated the diamine and dianhydride monomers at stoichiometric rates (140). The evaporated films had better adhesion, a lower dielectric constant, and a lower dissipation factor compared with spin-coated polyimides. With this process, uniform, defect-free, conformal films can be cured in situ during deposition. 

Chemical Control of Defect Formation During Spin-Coating of Sol-Gels... 

Typically, SEM is used to determine the continuity and the thickness of the film. Large-scale cracks and defects of the film can be determined by top view SEM images, and film thickness is easily obtained from cross-sections. It has been used extensively with powdered samples of mesoporous silica to determine morphology and thus assist in phase determination. However, thin films produced by dip and spin coating typically have a scarcity of features that may be resolved in SEM. This can be seen in Figs. 6A and 6B, SEM images of a mesoporous films templated with P123. 

T.G. Strange, R. Mathews, D.F. Evans, and W.A. Hendrickson, Scanning tunneling microscopy and atomic force microscopy characterization of polystyrene spin coated onto silicon surfaces, Langmuir 8, 920 (1992) U. Okoroanyanwu, J. Cobb, P. Dentinger, P, C. Henderson, V. Rao, and C. Pike, Defects and metrology of ultrathin resist films, Proc. SPIE 3998, 515 (2000). 

Fleischhaker F, Arsenault AC, Schmidtke J, Zentel R, Ozin G (2006) Spin-coating of designed functional planar defects in opal film generalized synthesis. Chem Mater 18 5640... 

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