Patterning method

A patterning method comprising:

• forming a layer stack comprising in a bottom-up direction a target layer, a lower memorization layer and an upper memorization layer,
• forming above the upper memorization layer a first mask layer, wherein a set of trenches are formed in the first mask layer using lithography and etching,
• patterning a set of upper trenches in the upper memorization layer, the patterning comprising using the first mask layer as an etch mask,
• forming a spacer layer on sidewalls of the set of upper trenches,
• forming a first block pattern, the first block pattern comprising a set of first blocks, each first block extending across an upper trench in the upper memorization layer,
• patterning a first set of lower trenches in the lower memorization layer, the patterning comprising using the patterned upper memorization layer, the spacer layer and the first block pattern as an etch mask, wherein at least a subset of the first set of lower trenches are interrupted by a trench interruption, each trench interruption being formed by a portion of the lower memorization layer preserved under a respective one of the first blocks,
• patterning the patterned upper memorization layer to form a second block pattern comprising a set of second blocks, each second block being formed of a respective remaining portion of the upper memorization layer,
• forming above the patterned lower memorization layer and the second block pattern a second mask layer, wherein a set of trenches are formed in the second mask layer using lithography and etching, wherein each trench of the set of trenches is formed over a respective remaining portion of the patterned lower memorization layer,
• patterning a second set of lower trenches in the patterned lower memorization layer, the patterning comprising using the second mask layer, the spacer layer and the second block pattern as an etch mask, wherein at least a subset of the second set of lower trenches are interrupted by a trench interruption, each trench interruption being formed by a portion of the lower memorization layer preserved under a respective one of the second blocks, and
• wherein the method further comprises patterning in the target layer a first set of target trenches under the first set of lower trenches and a second set of target trenches under the second set of lower trenches.