Study of alternate hardmasks for extreme ultraviolet patterning
Traditional patterning stacks for deep ultraviolet patterning have been based on a trilayer scheme with an organic planarizing layer, silicon antireflective coating or organic bottom antireflective coating, and photoresist. At an extreme ultraviolet (EUV) wavelength, there is no longer a need for reflectivity control. This offers an opportunity to look at different types of underlayers for patterning at sub-36 nm pitch length scales. An alternate hardmask can be used to develop a low aspect ratio patterning stack that can enable a larger process window at sub-36 nm pitch resolution. The hardmask layer under the resist has the potential for secondary electron generation at the resist/hardmask interface to improve resist sensitivity. This work explores EUV patterning on deposited hardmasks of various types such as silicon oxides and metal hardmasks. It also details the challenges of patterning directly on an alternate underlayer and approaches for improving patterning performance on such layers.