Photoresist and the photoresist/wafer interface with a local thermal probe

This paper reports the development of local differential thermal analysis and ellipsometry to measure the glass transition temperature (T g ) of thin films of photoresist. We apply the techniques to measure the glass transition temperature as a function of the film thickness of polystyrene and poly(methyl methacrylate) (PMMA). We also study the effect of the duration of post apply bake and the extent of reaction on the T g of films of a negative photoresist, SAL605. Measurements of the T g as a function of film thickness of polystyrene cast on native silicon oxide substrates primed with hexamethyldisiloxane show that the T g is depressed incrementally as thickness decreases to a maximum of T g - 20 degree(s)C for film thicknesses below 80 nm. Films of PMMA cast on native silicon oxide show a similar depression in the T g of 10 degree(s)C for film thicknesses less than 70 nm. Our study of SAL605 photoresist finds that the T g is not influenced by the condensation reaction between the crosslinker and resin. We find that there is a strong plasticizing effect by the residual solvent in SAL605 over short PAB times that can change the T g by as much as 15 degree(s)C. The T g reaches a steady value after 30 seconds of baking at 90 degree(s)C.