KLA Tencor announces Archer 200 overlay metrology system

by M. David Levenson, Editor-in-Chief, Microlithography World

As the semiconductor industry advances toward the 32nm node, overlay specifications have narrowed dramatically, requiring control of high-order grid and field distortions, according to the International Technology Roadmap for Semiconductors (ITRS). Seeking to meet the new requirements is KLA-Tencor’s new Archer 200, the latest version of the company’s imaging overlay measurement tool.

Boasting a total machine uncertainty (TMU) of 1nm (25% better than the Archer 100) and 25% better throughput, Archer 200 will facilitate high order overlay control for all three exposure tool vendors, according to Noam Knoll, VP of marketing for the company’s overlay group, who gave an overview of the new tool for WaferNEWS. The Archer 200 uses the KLA-Tencor AIM grating alignment mark and is compatible with 10μm2 μAIM targets as well.

Example of overlay error. (Source: KLA-Tencor)

Overlay performance good enough for double patterning requires accurate modeling of displacements and distortions, including higher order errors within the field. Accurate modeling requires taking more measurements — for example, Knoll estimated that 3rd order field distortion requires six targets within the exposure field to capture adequately. The use of μAIM targets minimizes the loss of useful real-estate. Capturing the higher-order grid and field distortions (with several hundred measurements/wafer) reduces the residual errors by 40%, according to Knoll. With a move-acquire-measurement (MAM) time of 0.65sec (20% faster), the Archer 200 maintains a throughput of 100 wafers/hr. In a statement, KLA-Tencor listed the redesigned systems’ other improvements, including a 20% improved “tool induced shift” of 0.8nm and 30%-50% better matching, with unspecified “greater measurement repeatability.”

The Archer 200 can also be equipped with a SCOL module for scatterometry-based overlay measurements. The TMU of the SCOL system was even smaller at 0.7nm, but throughput is reduced, Knoll reported. Owners of Archer 100 tools will have an upgrade path to the 200, according to Charles Lewis, KLA-Tencor’s global PR director, and there is extendibility to next-gen products that combine overlay and CD metrology. — M.D.L.

AIM and μAIM alignment marks. (Source: KLA-Tencor)

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