US Patent 10923363 Method for increasing pattern density on a wafer

Techniques herein include a method of patterning semiconductor wafers with improved line edge roughness (LER) and/or line width roughness (LWR), including lines below 12 nm in width. An initial bilayer mandrel is formed. The top layer is trimmed to a particular ratio. A reversal material protects uncovered portions of the lower layer, while a central portion is removed, resulting in two mandrels, each one fifth the initial mandrel width. The resulting mandrels are transferred into two underlying layers to form second bilayer mandrels. Sidewall spacers are formed on the second bilayer mandrels, and a fill material can fill remaining spaces. A planarization step can planarize the substrate to a bottom layer of the second bilayer mandrels, which results in a multi-line layer having square profile lines at 1:1 spacing ratio without spacer rounding.