Logic gate scanner focus control in high-volume manufacturing using scatterometry

Abstract

Tool matching and optimal process control are critical requirements for success in semiconductor manufacturing. It is imperative that a tool's operating conditions are understood and controlled in order to create a process that is repeatable and produces devices within specifications. Likewise, it is important where possible to match multiple systems using some methodology, so that regardless of which tool is used the process remains in control. Agere Systems is currently using Timbre Technologies' Optical Digital Profilometry (ODP) scatterometry for controlling Nikon scanner focus at the most critical lithography layer; logic gate. By adjusting focus settings and verifying the resultant changes in resist profile shape using ODP, it becomes possible to actively control scanner focus to achieve a desired resist profile. Since many critical lithography processes are designed to produce slightly re-entrant resist profiles, this type of focus control is not possible via Critical Dimension Scanning Electron Microscopy (CDSEM) where reentrant profiles cannot be accurately determined. Additionally, the high throughput and non-destructive nature of this measurement technique saves both cycle time and wafer costs compared to cross-section SEM. By implementing an ODP daily process check and after any maintenance on a scanner, Agere successfully enabled focus drift control, i.e. making necessary focus or equipment changes in order to maintain a desired resist profile.

Usage of profile information obtained with scatterometry

“…Simultaneous focus and exposure control in lithography is effective for CD control [5][6][7][8] . We tried to apply scatterometry to CD control by utilizing the ability of 2D profile monitoring.…”

Application of integrated scatterometry measurements for a wafer-level litho feedback loop in a high-volume 300 mm DRAM production environment

“…Because of the tightened requirement of new technologies, the sampling plan for stand-alone metrology tools, measuring only 2 -4 wafers per lot, will not be sufficient for all kinds of process and tool control and adjustment [3]. Processes using feed-back or feed-forward loops need to be controlled especially tightly [6]. Therefore, integrated metrology (IM) has been identified as necessary to reduce cycle time and load on expensive stand-alone metrology tools.…”