EUV Multi-Patterning

**EUV Multi-Patterning SAQP/SALELE** is **an advanced lithographic process technique employing extreme ultraviolet light with multiple exposure and selective etching steps to pattern semiconductor features smaller than the resolution limit of a single EUV exposure — enabling feature definition at sub-wavelength dimensions through sequential self-aligned processes**. Self-aligned quadruple patterning (SAQP) and self-aligned litho-etch-litho-etch (SALELE) represent extensions of self-aligned double patterning (SADP) techniques that have become necessary as feature scaling pushes beyond single-exposure resolution capabilities, requiring multiple sequential exposure and etch cycles to achieve target dimensions. The SAQP process begins with initial feature (typically line or trench) definition through conventional lithography and etching, followed by spacer deposition and selective etching to create multiple smaller features from each original pattern, enabling quadrupling of feature density compared to the original photomask pattern. The selective etch chemistry in multi-patterning processes is critical, requiring excellent selectivity between different materials to enable removal of sacrificial spacer materials while preserving underlying features, necessitating sophisticated plasma etch process development and characterization. The SALELE process extends multi-patterning by incorporating additional lithography exposures between etch steps, enabling more flexibility in final feature patterns compared to purely self-aligned approaches, at the cost of increased process complexity and photomask count. The integration of EUV multi-patterning with advanced gate-all-around and other three-dimensional transistor architectures enables precise definition of complex device geometry patterns that would be impossible with conventional single-exposure processes. Pattern collapse during multi-patterning remains a significant challenge, particularly for dense line patterns where narrow feature widths and high aspect ratios create mechanical instability during critical etch and cleanup steps. **EUV multi-patterning techniques (SAQP, SALELE) enable patterning of features smaller than EUV resolution limits through sequential self-aligned exposure and etch cycles.**