Martin Plihal

Novel methods for SPC defect monitoring: Normalizable diversity sampling: Defect inspection

The key to robust SPC control is the inline signals provided by metrology tools (e.g. CD-SEM, Overlay, film thickness measurement) and defect inspection tools (e.g. Surfscan, Broadband Plasma (BBP), Laser Scanning). Wafer defect inspection tools like Broadband Plasma find anomalies and provide defect coordinates to report their locations. Defects reported by the inspection tools are then sampled, or in other words, a sub-set of those defects are chosen for Scanning Electron Beam (SEM) Review. Classification of the defect type is provided using SEM. Due to SEM review throughput limitations, not every defect reported by inspection can be sampled for review. Therefore, the theoretical ideal sampling technique would generate an accurate representation of the true defect population on a wafer solely based on a limited review sample. The paper discusses the methodology for selecting such a review sample, termed diversity sampling. This scheme samples defects based on properties (location on wafer / die, design location, optical characteristics) instead of sampling solely based on defect location. Compared to random sampling, this technique demonstrates reduced error between the normalized defect density reported and the true defect density actually present on the wafer.

EUV stochastic defect monitoring with advanced broadband optical wafer inspection and e-beam review systems

As Extreme UltraViolet (EUV) lithography nears high volume manufacturing (HVM) adoption to enable the sub-7nm scaling roadmap, characterizing and monitoring defects that print at wafer level are of critical importance to yield. This is especially true for defects coming from the EUV mask, such as multi-layer defects, added particles or growth on mask, and for defects coming from the pattern formation process itself, also referred to as stochastic printing defects. A “Print Check” solution has been previously described.1 This technique uses full-wafer patterned optical inspection to monitor mask defects that print on the wafer. In this paper we focus on developing metrology solutions for stochastic printing defects, which are random local variations that occur between structures that should, in principle, print identically, but actually occur at significant frequencies with current state-of-the-art processes. Specifically, we discuss the importance of monitoring these defects using broadband plasma optical inspection and e-beam defect review systems. We show extensive characterizations of defects on line space patterns down to a pitch of 36nm, on contact holes at a pitch of 48nm and on logic blocks in a foundry equivalent N5 test vehicle. Analysis methods based on CD SEM and review SEM images have been described.