Characterization And Optimization Of Positive Tone Duv Resists On Tin Substrates

Chemically amplified resists are notoriously sensitive to substrate contaminations. Such substrates include Si3N4, SOG, SiO2 and TiN. Contaminations can result in deactivation of the acid catalyst, leading to resist footing for positive tone deep UV resists. In this paper we have tested several state of the art deep UV resists on TiN. Through cross-sectional inspections, it was seen that several of the most advanced resists available still suffer from footing on TiN. By varying the process parameters of the TiN PVD process, TiN layers with various ratios of Ti:N were obtained. Variations in TiN composition result in changes of deactivation of acid catalyst, In addition, optical properties of the TiN layer are changed as well, resulting in different resist performances.For resists suffering from footing on TiN, it was demonstrated that footing is related to the nitrogen saturation of the TiN layer. However, for ARCH2 resist series, no resist footing was seen on different TiN layers. For the optimization of deep UV patterning of 0.25 mu m CMOS metal layers using standard TiN layers, we have tested several resists of the ARCH2 resist series. The series of resists are based on the same resist chemistry. The difference between the formulations is in their absorbance, being 0.21 /mu m, 0.28/mu m and 0.44 mu m for ARCH214, ARCH212 and ARCH200, respectively. It was seen that with transparent resists notching can occur due to substrate roughnesses. By increasing the resist thickness and for the resist absorbance, notching was minimized.