Process window monitoring: an emerging requirement for efficient low-k1 lithography

Abstract

There are practical challenges associated with manufacturing implementation of optical photolithography at aggressive design rules. As k 1 factors decrease, lithographic focus-exposure process windows have collapsed from a comfortable several-micron depth of focus (DOF) at the 1um technology node, to a challenging 0.3-to-0.4um at the 0.13um node. As a consequence, the monitoring, management, and control of lithography tool process windows are increasingly important to efficient semiconductor manufacturing.A standard method to deduce lithography-tool process window position and size is based on data from a focus-exposure matrix (FEM) wafer. Unfortunately, the data transfer, analysis, and fab-wide reporting of best focus and other important tool parameters can require a large amount of engineering time and effort, effectively making it impossible in a largescale production-fab environment.In this work, we present results obtained with a new automated CD-SEM system used to monitor the 0.15um and 0.13um tools and processes in TSMC Fab 6 (70k wafer starts per month). To enable daily FEM-based tool monitoring in this high-volume production fab, these systems provide full "hands-off" automation of data analysis and web-based reporting of best focus, best energy, DOF, image tilt and other significant performance parameters and metrics for each cell. Using these systems, we demonstrate detection of fluctuations in single-tool best focus as small as approximately 20nm using an FEM with focus steps of 200nm. This capability is then used to detect and diagnose process window drifts in single exposure tools as well as mismatches in best focus between multiple exposure tools of several hundred nanometers. The monitoring and reduction of these lithography process window variations have allowed us to increase the performance and efficiency of our advanced lithography manufacturing lines.

Process Window Centering for 22 nm lithography

“…The most common lithography learning methods are FEM (Focus Exposure Matrix) [1,2] and PWQ (Process Window Qualification) [2][3][4][5]. Traditionally FEM utilizes a few locations per die to define the best dose and focus based on CD (critical dimension) measurements analyzed on a Bossung plot.…”