KLA-Tencor goes for 2xnm trifecta
Fabs evaluating lithography technologies for the 2Xnm logic (3Xnm half-pitch memory) node—spacer pitch splitting/pattern cutting, true pitch splitting, inverse lithography (ILT)/source mask optimization (SMO), and even EUV—need a single reticle inspection system that can handle all of them, according to Dan Lopez, senior director of marketing of KLA-Tencor's reticle and photomask inspection division. To address this transition in mask design, the company has launched the Teron 600 Series mask defect inspection system, with a programmable scanner-illumination capability and improvements in sensitivity and computational lithography power over the company's TeraScan XR platform.
Lopez articulated the challenges for each lithography technology addressed by the new platform. With EUV, that means: small linewidths, a reflective imaging technique, no pellicles to protect the mask, and multilayer defects, along with other new defect mechanisms. To handle multilayer defects, the company designed a completely new optics bench, the details of which are proprietary.
The challenges for advanced double-patterning lithography at 2Xnm include critical CDs that are formed between two masks, mask defects that are created by the contribution from two masks, and a ~35% mask contribution to the overlay budget (KLA-Tencor's estimate). To address these, the Teron platform offers: die-to-database inspection, multilayer database processing, context-sensitive defect detection, and an experimental "intensity CDU" which enables correlation to mask CD-SEM results, and more detail for mask process development.
With ILT/SMO, it's no longer straightforward what an important defect might be on the mask. Similarity in sizes of primary and assist features makes defect impact assessment difficult, and with the complex illumination pattern used with SMO, "you don't see the 1:1 correlation between the mask and the wafer," explained Lopez.
To address these issues, the Teron 600 is able to simultaneously inspect with transmitted and reflected light, and context-sensitive defect detection is also essential. Also important is having a programmable scanner source model to predict what the illumination and the mask will "do" at the wafer, said Lopez. And wafer plane inspection (a technology recently introduced by KLA-Tencor) takes the two inputs, scanner illumination and the mask image, and does a rigorous lithography simulation to predict what will happen on the wafer.
The company says the Teron 600 platform has successfully inspected prototype reticles created for ILT/SMO, double-patterning lithography, and EUV (masks and blanks), and is engineered to be extendible to potential 1Xnm optical solutions as well. The new platform can also work with the TeraScan 500 Series reticle defect inspection systems in a mix-and-match strategy. Beta tools are now being shipped, according to Lopez. — D.V.