multipatterning

Multipatterning is a group of lithography techniques used to extend the printable density of features beyond the resolution of a single exposure tool, typically by splitting a pattern into multiple masks or processing steps. It arose as semiconductor devices scaled beyond the capabilities of conventional 193 nm immersion lithography, where tighter overlay control and smaller feature sizes were required.

The main approaches include spacer-based self-aligned patterning, self-aligned double patterning (SADP) and higher-order variants, and litho-etch-litho-etch (LELE) double patterning. In spacer-based methods, a conformal layer is deposited and anisotropically etched to form sidewall spacers that define a second pattern offset from the original mask, effectively halving the feature pitch. SADP uses the spacer method to generate two closely spaced patterns from one initial feature, enabling double or triple patterning. LELE relies on two separate lithography steps and etch steps to realize two independent patterns on the same area.

Cut-and-stack or pitch-splitting techniques divide a dense pitch into multiple lithographic masks that are later stacked to form the final layout. Implementation challenges include overlay accuracy, defectivity, software mask design complexity, and equipment cost. As extreme ultraviolet (EUV) lithography matured, some multipatterning layers migrated away from these methods, but multipatterning remains used for certain critical layers where EUV tool availability or cost is prohibitive.

Applications and status: multipatterning has been widely employed in advanced memory and logic manufacturing, particularly during the 2000s and 2010s to push sub-100 nm features before EUV became mainstream. The field continues to evolve with ongoing advances in materials, metrology, and process integration for limited-node needs where single-exposure resolution is insufficient.