Self-aligned patterning by area-selective etching of polymers and area-selective atomic layer deposition: Decreasing polymer flow and activating noncatalytic surface

Future semiconductor device architectures necessitate innovative patterning processes. Area-selective etching (ASE) of polymers is a self-aligned patterning technique with significant potential for the future semiconductor fabrication. In the ASE process, etchant gas penetrates the polymer film and becomes activated by the underlying catalytic material. Consequently, at the correct temperature, the polymer layer is selectively decomposed above the catalytically active areas, while it remains unaltered above catalytically inactive areas. This area-selective process ensures self-alignment, thus preventing edge placement errors. The resulting patterned polymer can be utilized in subsequent area-selective deposition or lift-off processes. In this article, we study ASE of poly(methyl methacrylate) (PMMA) and poly(lactic acid) by first testing several metal oxide and nitride surfaces, namely, Al2O3, HfO2, ZrO2, Ta2O5, CeO2, NiO, TiO2, TiN, and Si3N4, for their catalytic effect in an O2, H2, and inert atmosphere. The experiments reveal that most of these surfaces are noncatalytic, therefore requiring activation. We demonstrate that a noncatalytic surface (HfO2) can be easily converted to catalytic by depositing a small amount of catalytic material (CeO2) on top. We then create a test structure by patterning another noncatalytic material (TiO2) on top with direct atomic layer processing, after which we use ASE of PMMA to create a patterned inhibition layer. This inhibition layer is then used in area-selective atomic layer deposition of ZrO2. Additionally, we show that the polymer flow during the ASE process can be significantly reduced by increasing the molecular weight of the polymer.