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Aerial Imaging Simplifies Mask Inspection
April 15, 2008
Mask inspection certainly has not been made any easier by the continuing complexity being designed into masks to enable them to print the desired features on the wafer. Low k1 lithography, for example, requires aggressive OPCs, phase-shift masks, combined with extreme off-axis illumination. These and other factors have combined to create major inspection hurdles. Each generation of photomasks incorporates increasingly sophisticated resolution enhancement techniques that reduce the correlation between the pattern on the mask and that on the printed wafer. This can present a problem for traditional inspection systems because they can only produce an image of the mask itself, and it has been a while since there was a connection between the mask pattern and the wafer pattern sufficiently significant to be used for reliable mask inspection.
Source: Applied Materials
Today, at SPIE’s Photomask Japan conference held in Yokohama, Applied Materials (San Jose, California), unveiled its new platform, the Aera2 Mask Inspection system, which has been designed to deliver what the company describes as “the fastest, most powerful inspection and qualification solution for all advanced photomasks.” The system uses aerial imaging technology and is designed to meet mask inspection requirements for defect detection of immersion and double patterning masks for the 45-nm node and beyond. It is expected to address all mask shop inspection applications, while providing over double the throughput of any competing system.
The tool is touted as the first mask inspection system that enables the user to immediately see how a pattern on the mask will appear on the wafer; the system’s software processes the defects detected on the mask by estimating what effect they would have on the wafer. It then filters out the large number of non-printing defects that some other conventional mask inspection systems might label as being printable. By emulating the optical system of 193 mm lithography scanners and placing an image sensor in the wafer plane, the Aera2 system is capable of inspecting the mask under optical conditions that are identical to those when it is exposed in an actual stepper. This provides the user with a “what-you-see-is-what-you-print” result.
Source: Applied Materials
The tool’s aerial inspection technology also creates an entire set of enabling capabilities that strengthen the link between the mask shop and lithography cell by ensuring the printability of a mask before delivery. The platform has an optional application, IntenCD, which leverages the aerial imaging data to create high-precision, high-density CD uniformity maps of an entire mask. These maps can reveal subtle manufacturing defects, helping the mask maker to fine-tune the mask manufacturing process.
Posted by Alexander E. Braun on April 15, 2008 | Comments (0)
