Process resilient overlay target designs for advanced memory manufacture

In recent years, lithographic printability of overlay metrology targets for memory applications has emerged as a significant issue. Lithographic illumination conditions such as extreme dipole, required to achieve the tightest possible pitches in DRAM pose a significant process window challenge to the metrology target design. Furthermore, the design is also required to track scanner aberration induced pattern placement errors of the device structure. Previous workiii, has shown that the above requirements have driven a design optimization methodology which needs to be tailored for every lithographic and integration scheme, in particular self-aligned double and quadruple patterning methods. In this publication we will report on the results of a new target design technique and show some example target structures which, while achieving the requirements specified above, address a further critical design criterion – that of process resilience.