Defect inspection is one of the major challenges in the manufacturing process of photomasks. The absence of any
printing defect on patterned mask is an ultimate requirement for the mask shop, and an increasing effort is spent in order
to detect and subsequently eliminate these defects. Current DUV inspection tools use wavelengths five times or more
larger than the critical defect size on advanced photomasks. This makes the inspectability of high-end mask patterns
(including strong OPC and small SRAF's) and sufficient defect sensitivity a real challenge. The paper evaluates the
feasibility of inspecting the printed wafer as an alternative way for the high-sensitivity defect inspection of photomasks.
Defects originating in the mask can efficiently be filtered as repeated defects in the various dies on wafer. Using a
programmed-defect mask of 65-nm technology, a reliable detection of the printing defects was achieved with an
optimized inspection process. These defects could successfully be traced back to the photomask in a semi-automated
process in order to enable a following repair step. This study shows that wafer inspection is able to provide a full defect
qualification of advanced photomasks with the specific advantage of assessing the actual printability of arbitrary defects.
With decreasing pattern sizes the absolute size of acceptable pattern deviations decreases. For mask-makers a
new technology requires a review, which mask design variations print on the wafer under production illumination
conditions and whether these variations can be found reliably (100%) with the current inspection tools. As
defect dispositioning is performed with an AIMS-tool, the critical AIMS values, above which a defect prints
lithographically significant on the wafer, needs to be determined. In this paper we present a detailed sensitivity
analysis for programmed defects on 2 different KLA 5xx tools employing the pixel P90 at various sensitivity
settings in die-to-die transmitted mode. Comparing the inspection results with the wafer prints of the mask
under disar illumination it could be shown that all critical design variations are reliably detected using a state-of-the-art tool setup. Furthermore, AIMS measurements on defects with increasing defect area of various defect
categories were taken under the same illumination conditions as for the wafer prints. The measurements were
evaluated in terms of AIMS intensity variation (AIV). It could be shown that the AIMS results exhibit a linear
behavior if plotted against the square-root area (SRA) of the defects on the mask as obtained from mask SEM
images. A consistent lower AIV value was derived for all defect categories.
In case drastic changes need to be made to tool configurations or blank specifications, it is important to know as early as possible under which conditions the tight image placement requirements of future lithography nodes can be achieved. Modeling, such as finite element simulations, can help predict the magnitude of structural and thermal effects before actual manufacturing issues occur, and basic experiments using current tools can readily be conducted to verify the predicted results or perform feasibility tests for future nodes. Using numerical simulations, experimental mask registration, and printing data, the effects on image placement of stressed layer patterning, pellicle attachment, blank dimensional and material tolerances, as well as charging during e-beam writing were investigated for current mask blank specifications. This provides an understanding of the areas that require more work for image placement error budgets to be met and to insure the viability of optical lithography for future nodes.