Spin Coating Study for Thick Layers with High Viscosity Polyimide Available to Purchase

Polyimide deposition of thick layers (50‐60 μm after soft‐bake) is very important in the field of microelectronics; in particular for fabrication of microwave circuits for telecommunications, micromachining applications, MCM‐D and, in general, for pattern transfer. Spin coating is, even in this case, the only method that can provide good results in terms of quality, repeatability and reliability. This paper discusses problems concerning the polyimide deposition process for obtaining thick layers with an uniformity value within 10% and studying the process itself from a mathematical point of view. In particular, the thickness variation versus frequency has been analysed, checking the mathematical model in which the dependence is ω^−K(K=0.5). It is shown that the polyimide behaves differently depending on the residual solvents at the end of the process and that the model is verified only if the solvents are completely evaporated at the end of the process also. This resolves a certain confusion in the literature where the value of K changes from 0.5 to 1 with different justifications.