The effect of varying concentration and spin speed on the thickness of spin-coated PMMA was discussed (for silicon wafers) at: D.B. Hall, P. Underhill, J.M. Torkelson, "Spin coating of thin and ultrathin polymer films", Polymer Engineering and Science, 38(12) 1998, 2039-2045:

http://onlinelibrary.wiley.com/doi/10.1002/pen.10373/abstract

About alternative sovents for PMMA, you may check: https://www.researchgate.net/post/With_PMMA_which_solvent_to_use

Thank you very much. I have already read the first one and I wanted to re-check and to see if another solvent besides toluene has been proved more effective .

I had bad experiences with fast evaporating solvents (low boiling point) for spincoating (rippling structures in spincoated film occurs). For me 2-ethoxy-ethylacetate gives good films (but there is some residual solvent in the spincoated film depending on film thickness > 1000nm which is removed by heating the wafer to about 120°C).

Thank you very much. Indeed, solvents with low boiling point are not that recommended in order to have uniform films.

have you tried anisole? on clean silica or silicon surface this gives pretty good result. and it's relatively safe.

in 4% solution we've got reached ~200 nm film with good uniformity.

what's the purpose of this experiment and what's the expected thickness?