Tailoring the Properties of Polyurethane Coatings with Epoxidized Bio-Polyol Spin-Coated onto Glass and P-Type Si(100) Substrates

Abstract

High-performance plastics or engineering polymers have been actively studied for various microelectronic applications as the demand for faster processing speeds increases. Taking advantage of its high Young’s modulus ideal for inter-layer dielectric applications, polyurethane (PU), a class of linearly-segmented polymer primarily made by reacting isocyanate and polyol, were deposited on borosilicate glass and p-type Si (100) substrates via spin coating method utilizing epoxidized soybean oil as a bio-polyol replacement. Optical micrographs showed that 100% ESBO-based PU coatings exhibited homogeneous and superior quality coatings in contrast to 50% ESBO-and 100% petroleum-based PU coatings as confirmed by scanning electron micrographs and EDX analysis. Based on the surface profilometry data, we found out that PU coatings with film thickness ranging from 6 μm to 28.5 μm can be achieved. FTIR-ATR analysis revealed that maintaining the stoichiometric ratio between O–H and N–C–O vibrational modes closer to unity is a vital factor to produce a high-quality PU coating regardless of the choice of substrate. The average bandgap energy of 4.35 ± 0.03 eV was estimated from the UV-vis reflectance spectra, and the electrical resistance of 107–1010 orders of magnitude was measured using a two-probe method which are typical for dielectric materials. Preliminary insights about the dielectric response of the fabricated PU coatings were investigated using electrochemical impedance spectroscopy and a low κ-value of 2.749 was calculated from the Nyquist plot of the 7.9-μm thick 100% ESBO-based PU coating deposited at 6000 rpm for 45 seconds. These promising results proved that PU coatings from bio-polyols can be tailored to achieve desired coating properties that are amenable for next-generation microelectronic packaging and curable photoresists.