Characterization of oxynitride hardmask removal processes for refractory x-ray mask fabrication

Silicon oxynitride removal processes are characterized for incorporation into the refractory x-ray mask fabrication sequence as the hardmask removal step. It is essential that this process not alter final image placement, one of the most critical parameters affecting x-ray mask performance. In this paper, we show that 10:1 buffered HF causes large image placement movement when used on refractory x-ray masks. This is because etching in HF has deleterious effects on TaSi, resulting in highly compressive film stress. Materials analysis indicates the presence of hydrogen in the TaSi films after being exposed to HE which is most likely affecting the film stress. Alternative processes being investigated include using a more dilute 100:1 buffered HF solution and a CHF3 plasma dry-etch chemistry. Both of these options completely remove the SiON hardmask without causing any significant image placement movement and result in high quality refractory x-ray masks.