Focused ion beam direct patterning of hardmask layers

Abstract

Inorganic hardmasks are routinely employed in reactive ion etching (RIE) processes due to their excellent etch resistance. However, since pattern definition is commonly performed using organic resist materials, the enhanced etch resistance provided by the inorganic hardmasks comes at the expense of added process complexity. In this work, the authors introduce the method of direct patterning of hard masks (DPHM) utilizing milling and gas assisted deposition (GAD) with a focused ion beam (FIB). DPHM by FIB allows to structure hardmask materials, which are otherwise not accessible with standard processes. Further, it reduces the high number of (typically seven) processing steps required for resist based patterning down to only three using FIB milling of hardmasks or even two using FIB GAD for patterning. The authors found that by FIB milled hard masks made of oxide such as aluminum zinc oxide exhibited excellent pattern clarity. For other materials, effects such as ion beam induced dewetting were found to affect the patterning result and must be considered in the choice of hardmask materials. Comparing DPHM and RIE to pure FIB milling of bulk material a speed enhancement of at least 755 times has been achieved. DPHM by FIB milling offers the highest versatility in material choice while FIB GAD enables faster patterning of selected hardmask materials.