Improving wet etch resistance of organic underlayers

The continued miniaturization of integrated circuit features has been made possible through multilayer patterning processes where different etch steps transfer the patterned photoresist image through various hardmasks to the underlying substrate. Wet etchants, such as the aqueous mixture of ammonium hydroxide and hydrogen peroxide known as SC-1 (Standard Clean -1), are often used for the selective removal of metal surfaces (i.e. TiN) from the substrate. To ensure that this metal removal is indeed selective, organic underlayers are used to protect the metal surface in regions where metal removal is unwanted. Unfortunately, these harsh basic and oxidative conditions are often incompatible with many underlayers which result in their delamination from the substrate, exposing and damaging the metal surface. Here we report our work on improving the SC-1 wet etch resistance of an underlayer coated over TiN. By increasing the film’s binding to the metal surface and decreasing its brittleness through polymer design or additive choice, we improve the time for film delamination in an SC-1 bath from 1 minute to over 20 minutes. Furthermore, we have developed a new method to evaluate SC-1 resistance by quantifying TiN removal by measuring the amount of titanium leached into the solution during wet etching by using inductively coupled plasma mass spectrometry (ICP-MS). We demonstrate with this method and XSEM images that TiN can be removed if the film does not act as a sufficient barrier to prevent SC-1 penetration, even if no film delamination is observed, which will be used to optimize future underlayer formulations.