Mastering double exposure process window aware OPC by means of virtual targets

Abstract

This paper addresses a challenge to the concept of process window OPC (PWOPC) by investigating the dimensional control of effectively non-printing features to improve the process window (PW) of the primary layout. It is shown based on a double exposure (DE) alternating phase-shift mask (altPSM) process that neglecting the impact of final mask dimensions forming intermediate images in resist (which are subsequently removed with a second exposure) potentially leads to a significant variation in the available focus budget of neighboring linewidth-critical feature dimensions. Various rules-based and model-based options of introducing virtual OPC targets into the OPC flow are discussed as an efficient mean to allow the OPC to take process window considerations into account. The paper focuses especially on the mechanics of how in detail those virtual targets support the beneficial OPC convergence of affected edges. Finally, experimental proof is shown that introducing non-printing, virtual targets being considered as actual targets during OPC ensures enhanced through focus line width stability and hence making the OPC solution well aware of process window aspects.