Utilizing photosensitive polymers to evaluate UV radiation exposures in different plasma chamber configurations
Monitoring vacuum ultraviolet (UV/VUV) emission in plasma systems is challenging as it requires specialized diagnostic systems or sensors to be compatible with these devices. This study addresses different reactor configurations and plasma chemistries with various levels of UV emission and their effects on a known set of polymers. First, the effect of He plasma treatment of organic underlayer (NFC-1400) and e-beam resist (hydrogen silsesquioxane) on line-space patterning of polysilicon at sub-100 nm pitch was investigated. By applying He plasma exposure, both before and after patterning of the optical underlayer, a significant improvement in line edge roughness (LER) from 2.5 to 1.4 nm was observed. To understand the plasma treatment mechanisms, polymers were exposed to synchrotron VUV light at 62 nm (or 20.0 eV), which coincides with the He VUV emission range (50-60 nm), followed by etching of poly-Si, and were found to have similar LER results. The refraction index measurements for both the optical underlayer and the e-beam resist revealed the key finding that the polymers absorption maxima corresponded exactly to the wavelength of ∼60 nm. Second, the impact of inductively coupled and microwave plasma configurations on etch rates and chemical properties of photoresists were investigated. Identifying specific photon-induced modifications on polymers can help detect UV/VUV emission in the plasma and decouple ion and photon effects on materials. Poly(methyl methacrylate) and poly(4-vinylphenol)-based photoresists were exposed to argon (Ar) and nitrogen (N2) plasmas. Surface and elemental analyses confirmed that plasma effects on chemical modifications, surface roughness, and etch rate were significantly higher for poly(methyl methacrylate) compared to poly(4-vinylphenol)-based photoresists. Detailed elemental and molecular structure analyses of these polymers showed relatively higher damage to both species caused from the inductively coupled plasma, which is ultimately correlated with a higher UV/VUV emission.