Spin coating resist planarization

In this paper the planarizing properties of some commercially available resins and monomers are evaluated. Other important properties such as etching resistance, film absorbance and glass transition temperature Tg are reported and discussed. Some of the materials that we evaluated are not marketed for use in the microelectronics industry. Consequently, they are not available as filtered spin coating solutions and may contain high levels of metal impurities that adversely affect device performance. 

Resist films that are spin-coated over topographic features have a tendency to planarize or smooth out the bumps. The extent to which this occurs is never perfect and depends on both substrate and resist material parameters (27). Two types of planarization influence resolution ... 

For e-beam exposure, the resist films were spin coated on Si02 (2000 Angstroms), prebaked and exposed at 20 kV in a Cambridge e-beam microfabricator. For our initial studies, an IPC 4005 barrel plasma etcher was used to develop the resist patterns. In our recent studies, a Plasma-Therm PK-1250 planar plasma etcher was used to develop the resist patterns. 

The second approach is spin casting polymers onto a substrate surface. Examples include using polyimides and a PR called SU-8. The third method is resist etchback. The wafer is first spin coated with a PR to planarize the surface, followed by a blank plasma etch that has the same approximate etching rate of the PR as that of the underlying material (e.g., Si02) and produces a much more planar surface. 

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