Differences in the Modification Effect in the Depth Direction on the Surface of Epoxy Resin Irradiated with Vacuum Ultraviolet Light

We used a vacuum ultraviolet (VUV) spectrophotometer to measure the spectral transmittance of epoxy resin in the 140–220-nm region. This study used dielectric materials that are commonly used in electronic devices. We assessed the penetration of VUV light with a central wavelength of 172 nm from an excimer lamp into the depth direction of the resin and evaluated it based on the absorption coefficient. The epoxy resin was irradiated with a consistent amount of VUV light. Subsequently, attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR) was used to observe the changes in the internal chemical state. By measuring the decrease in the peak at 1100 cm⁻¹ on FTIR-ATR, we identified the relationship between the quantity of 172-nm photons absorbed and the number of reacting ether bonds. Further, the surface of the irradiated epoxy resin was analyzed by x-ray photoelectron spectroscopy (XPS) to evaluate the functional group concentration after exposure to different doses of VUV light. The difference in principle between FTIR-ATR and XPS analyses was used as the basis to examine the depth-wise effects of epoxy resin irradiated with VUV light.