Elimination of Resist Roisoning in Via-First Dual Damascene Processes

摘要

Resist poisoning in via-first dual damascene was observed after trench lithography. The resist poisoning was more likely to occur when a low-kappa material was used. To examine the relationship between resist poisoning and the amount of basic contaminants, we analyzed basic molecules by capillary electrophoresis (CE), ion chromatography, and thermal desorption-atmospheric pressure ionization-mass spectrometry (CE), ion chromatography, and thermal desorption-atmospheric pressure ionization-mass spectrometry (TD-API-MS). It was found that three amines were adsorbed on a low-kappa wafer. The total amount of amines was related to the resist poisoning. We also conducted TD-API-MS experiments on wafers with a variety of via densities. These experiments well explained why isolated vias are more likely to suffer from resist poisoning. As a process approach towards the elimination of resist poisoning, we confirmed that quick heat treatment at a high temeprature was effective in removing the amines from the low-kappa water. As a material approach, we tried to mke resists with high resistance to resist poisoning. The addition of a quencher (organic base) in the resists effectively reduced the resist posioning. The mechanism was verified by nonaqueous titrations of am odel resist system. It was found from the model experiments that a buffer system composed of the photoacid and its conjugate base was working to keep the pH changes from external basic contaminants small.