Results from the recently available TeraScanHR reticle inspection system were published in early 2007. These
results showed excellent inspection capability for 45nm logic and 5xnm half-pitch memory advanced production
reticles, thus meeting the industry need for the mid-2007 start of production. The system has been in production use
since that time. In early 2007, some evidence was shown of capability to inspect reticles for the next nodes, 32nm
logic and sub-50nm half-pitch memory, but the results were incomplete due to the limited availability of such
reticles. However, more of these advanced reticles have become available since that time. Inspection results of
these advanced reticles from various leading edge reticle manufacturers using the TeraScanHR are shown. These
results indicate that the system has the capability to provide the needed inspection sensitivity for continued
development work to support the industry roadmap.
High resolution mask inspection in advanced wafer fabs is a necessity. Initial and progressive mask defect problem still remains an industry wide mask reliability issue. Defect incidences and its criticality vary significantly among the type of masks, technology node and layer, fab environment and mask usage. A usage and layer based qualification strategy for masks in production need to be adopted in wafer fabs.
With the help of a high-resolution direct reticle inspection, early detection of critical and also non-critical defects at high capture rates is possible. A high-resolution inspection that is capable of providing necessary sensitivity to critical emerging defects (near edge) is very important in advanced nodes. At the same time, a way to disposition (make a go / no-go decision) on these defective masks is also very important. As the impact of these defects will depend on not only their size, but also on their transmission and MEEF, various defect types and characteristics have to be considered.
In this technical report the adoption of such a high-resolution mask inspection system in wafer fab production is presented and discussed. Data on this work will include inspection results from advanced masks, layer and product based inspection pixel assignment, defect disposition and overall wafer fab strategies in day-to-day production towards mask inspection.
Progressive mask defect problem is an industry wide mask reliability issue. During the start of this problem when the defects on masks are just forming and are still non-critical, it is possible to continue to run such a problem mask in production with relatively low risk of yield impact. But when the defects approach more critical state, a decision needs to be made whether to pull the mask out of production to send for clean (repair). As this problem increases on the high-end masks running DUV lithography where masks are expensive, it is in the interest of the fab to sustain these problem masks in production as long as possible and take these out of production only when absolutely necessary; i.e., when the defects have reached such a critical condition on these masks that it will impact the process window. During the course of this technical work, investigation has been done towards understanding the impact of such small progressive defects on process window. It was seen that a small growing defect may not print at the best focus exposure condition, but it can still influence the process window and can shrink it significantly. With the help of a high-resolution direct reticle inspection, early detection of these defects is possible, but fabs are still searching for a way to disposition (make a go / no-go decision) on these defective masks. But it is not an easy task as the impact of these defects will depend on not only their size, but also on their transmission and MEEF. A lithographic detector has been evaluated to see if this can predict the criticality of such progressive mask defects.