Die-to-Model (D2M) inspection is an innovative approach to running inspection based on a mask design layout data. The
D2M concept takes inspection from the traditional domain of mask pattern to the preferred domain of the wafer aerial
image. To achieve this, D2M transforms the mask layout database into a resist plane aerial image, which in turn is
compared to the aerial image of the mask, captured by the inspection optics.
D2M detection algorithms work similarly to an Aerial D2D (die-to-die) inspection, but instead of comparing a die to
another die it is compared to the aerial image model. D2M is used whenever D2D inspection is not practical (e.g., single
die) or when a validation of mask conformity to design is needed, i.e., for printed pattern fidelity. D2M is of particular
importance for inspection of logic single die masks, where no simplifying assumption of pattern periodicity may be
done. The application can tailor the sensitivity to meet the needs at different locations, such as device area, scribe lines
In this paper we present first test results of the D2M mask inspection application at a mask shop. We describe the
methodology of using D2M, and review the practical aspects of the D2M mask inspection.
Readiness of new mask defect inspection technology is one of the key enablers for insertion & transition of the next
generation technology from development into production. High volume production in mask shops and wafer fabs
demands a reticle inspection system with superior sensitivity complemented by a low false defect rate to ensure fast
turnaround of reticle repair and defect disposition (W. Chou et al 2007).
Wafer Plane Inspection (WPI) is a novel approach to mask defect inspection, complementing the high resolution
inspection capabilities of the TeraScanHR defect inspection system. WPI is accomplished by using the high resolution
mask images to construct a physical mask model (D. Pettibone et al 1999). This mask model is then used to create the
mask image in the wafer aerial plane. A threshold model is applied to enhance the inspectability of printing defects. WPI
can eliminate the mask restrictions imposed on OPC solutions by inspection tool limitations in the past. Historically,
minimum image restrictions were required to avoid nuisance inspection stops and/or subsequent loss of sensitivity to
defects. WPI has the potential to eliminate these limitations by moving the mask defect inspections to the wafer plane.
This paper outlines Wafer Plane Inspection technology, and explores the application of this technology to advanced
reticle inspection. A total of twelve representative critical layers were inspected using WPI die-to-die mode. The results
from scanning these advanced reticles have shown that applying WPI with a pixel size of 90nm (WPI P90) captures all
the defects of interest (DOI) with low false defect detection rates. In validating CD predictions, the delta CDs from WPI
are compared against Aerial Imaging Measurement System (AIMS), where a good correlation is established between
WPI and AIMS<sup>TM</sup>.
Pixelated phase masks rendered from computational lithography techniques demand one generation-ahead mask
technology development. In this paper, we reveal the accomplishment of fabricating Cr-less, full field, defect-free
pixilated phase masks, including integration of tapeout, front-end patterning and backend defect inspection, repair,
disposition and clean. This work was part of a comprehensive program within Intel which demonstrated microprocessor
To pattern mask pixels with lateral sizes <100nm and vertical depth of 170nm, tapeout data management, ebeam write
time management, aggressive pattern resolution scaling, etch improvement, new tool insertion and process integration
were co-optimized to ensure good linearity of lateral, vertical dimensions and sidewall angle of glass pixels of arbitrary
pixelated layout, including singlets, doublets, triplets, touch-corners and larger scale features of structural tones
including pit/trench and pillar/mesa. The final residual systematic mask patterning imperfections were corrected and
integrated upstream in the optical model and design layout.
The volume of 100nm phase pixels on a full field reticle is on the order tera-scale magnitude. Multiple breakthroughs in
backend mask technology were required to achieve a defect free full field mask. Specifically, integration of aerial
image-based defect inspection, 3D optical model-based high resolution ebeam repair and disposition were introduced.
Significant reduction of pixel mask specific defect modes, such as electro static discharge and glass pattern collapse,
were executed to drive defect level down to single digit before attempt of repair. The defect printability and repair yield
were verified downstream through silicon wafer print test to validate defect free mask performance.
Driven by Moore's Law, the quest to double the number of transistors on a given chip every 18-24 months, the density and complexity of patterns on photomasks has increased steadily and significantly. To maintain the fidelity of shrinking features, reticle enhancement techniques such as OPC (Optical Proximity Correction) and Phase Shift Masks are now widely used in optical lithography to extend the lifetime of the existing technology. These techniques (or advanced reticles) provide the desired improvements in spatial resolution, but also complicate the task of reticle defect inspection. In this paper, we present results from ongoing contamination inspections of Embedded (Attenuated) Phase Shift Masks (EPSMs) for 248nm and 193nm lithography. A variety of 248nm masks have been successfully inspected on the KLA-Tencor STARlightTM SL3UV and SL3 tools at Intel Mask Operations (IMO) in Santa Clara, CA. Lessons learned from inspection of 248nm masks are being applied towards inspection of 193nm masks. A representative sample of inspection parameters such as algorithm options, and corresponding inspection results (defect types, capture rates etc.) are presented and discussed in the paper.