New approaches in diffraction based optical metrology

Abstract

Requirements for on-product overlay, focus and CD uniformity continue to tighten in order to support the demands of 10nm and 7nm nodes. This results in the need for simultaneously accurate, robust and dense metrology data as input for closed-loop control solutions thereby enabling wafer-level control and high order corrections. In addition the use of opaque materials and stringent design rules drive the need for expansion of the available measurement wavelengths and metrology target design space.Diffraction based optical metrology has been established as the leading methodology for integrated as well as standalone optical metrology for overlay, focus and CD monitoring and control in state of the art chip manufacturing. We are presenting the new approaches to diffraction based optical metrology designed to meet the ≤10nm node challenges. These approaches have been implemented in the latest addition to the YieldStar metrology platform, the YS350E introducing a new way of acquiring and processing diffraction based metrology signals.In this paper we will present the new detection principle and its impact on key performance characteristics of overlay and focus measurements. We will also describe the wide range of applications of a newly introduced increased measurement spot size, enabling significant improvements to accuracy and process robustness of overlay and focus measurements.With the YS350E the optical CD measurement capability is also extended, to 10x10µm 2 targets. We will discuss the performance and value of small targets in after-develop and after-etch applications.

Non-integral model-based scatterometry for CD metrology of single high-aspect-ratio microstructures

“…In practice, scatterometry measurements were usually performed on unique periodic test structures situated on the scribe lines of the wafer. As the device scale continues to shrink, these metrology targets no longer provide a good correlation to the in-die structures [18][19][20][21]. More importantly, performing measurements on periodic structures instead of non-periodic structures could lead to additional measurement errors [22].…”