Background: With continuous decrease in the technology node of dynamic random access memories (DRAMs) down to sub-20 nm, the self-aligned double patterning (SADP) is an effective approach to generate two-dimensional (2-D) patterns, particularly contact arrays.

Aim: We demonstrate a patterning scheme using the SADP technique to produce active trim contacts with anisotropic pattern pitches.

Approach: The proposed scheme uses two consecutive spacer-formation processes.

Results: By making the ellipsoidal core pillars and minimizing the spacer thickness, 2-D critical dimensions (CDs) for self-generated contacts match well with those for core contacts. In addition, an interesting cross-dependence of X-CD and Y-CD variations for the core and self-generated contacts is observed.

Conclusion: This patterning approach is useful for forming active trim contacts in sub-20 nm DRAMs using fewer numbers of ArF immersion photolithography steps.