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 micrometers 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/micrometer, 0.28/micrometer and 0.44/micrometer 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/or the resist absorbance, notching was minimized.
In this work we have investigated the photoresist thin film interference effect on different reflective substrates. Using computer simulated and experimental swing curves, the fitting parameters of an empirical formula based on the two mirror Fabry-Perot etalon are correlated to the reflectivity and resist characteristics. In particular, the phase of the swing curve which corresponds to the phase shift of the light wave at the resist/substrate interface was studied in detail. Therefore, the swing behavior on different reflective substrates (Si, Al, etc.) as well as on oxidized wafers was measured. It is postulated that this difference in phase shift is due to the different nature of the substrates, i.e. the complex refractive index in addition to the thickness. Simulations of the latent image of the photoresist predict that the axial shift of the latent image is also connected to the phase shift of the light wave at the resist/substrate interface and therefore related to the swing curve phase. To illustrate the axial shift of the latent image of the photoresist an improved cross section development technique based on a top coating before cleaving and development is proposed. Possible effects of this phase on the standing waves and on the profile at the resist/substrate interface are also examined with this improved method. Furthermore, Al substrates with a smaller grain size were used in order to explore this influence of diffuse reflectivity on the swing effect.