Advanced Patterning

Multi-Patterning Techniques

When single-exposure resolution isn't sufficient, multi-patterning divides the pattern into multiple simpler exposures:

• LELE (Litho-Etch-Litho-Etch): Two separate lithography and etch steps with different masks. Simple concept, but alignment between exposures is challenging.
• SADP (Self-Aligned Double Patterning): Deposits a spacer on the sidewalls of a sacrificial mandrel, then removes the mandrel. The spacers define features at half the original pitch — no alignment needed.
• SAQP (Self-Aligned Quadruple Patterning): Applies SADP twice to achieve 4× density. Used for the tightest metal pitches at 7nm and 5nm nodes with 193i lithography.

EUV and Beyond

EUV lithography simplifies patterning by replacing multi-patterning with single exposure for critical layers. But even EUV has limits:

• Current EUV (0.33 NA): Single exposure down to ~26 nm pitch
• High-NA EUV (0.55 NA): ASML's next-generation tool (EXE:5000 series), enabling single exposure at ~16 nm pitch. First tools delivered in 2024.
• EUV with multi-patterning: Even tighter pitches still require combining EUV with double patterning

The future may bring even more exotic patterning techniques like directed self-assembly (DSA) using block copolymers, or multi-beam e-beam lithography for mask making.