Area-Selective\nEtching of Poly(lactic acid) Films\nvia Catalytic Hydrogenolysis and Cracking

Fabrication of future\nsemiconductor devices requires\nnew and inventive\nself-aligning patterning processes. One such process is area-selective\netching (ASE) of polymers, which exploits different catalytic properties\nof different surfaces. In ASE, a polymer film is decomposed only from\nthe top of catalytically active materials, while the polymer stays\nintact on catalytically inactive materials. This means that the patterning\nis self-aligned, thus avoiding edge placement errors. So far, patterning\nby ASE of polymers has been demonstrated in oxidative atmospheres.\nHere, we study the ASE of poly(lactic acid) (PLA) in two nonoxidative\natmospheres: inert atmosphere where decomposition by cracking occurs,\nand H<sub>2</sub> atmosphere where the polymer is decomposed by hydrogenolysis.\nNi, NiO, Ir, and Pt films were identified as hydrogenolysis catalysts\nin the decomposition of PLA, whereas Co and CoO films catalyzed the\ndecomposition of PLA both under an inert atmosphere and in the presence\nof H<sub>2</sub>. Further studies revealed, however, that it is the\nnative Co oxide or hydroxide, rather than metallic Co, that promotes\nthe decomposition of PLA. We also compared a commercially available\namorphous PLA and self-synthesized semicrystalline PLA. The semicrystalline\nPLA showed less flow during the ASE process, due to its higher melting\ntemperature, as compared to the amorphous PLA. The semicrystalline\nPLA inhibited 1000 atomic layer deposition (ALD) cycles of Cu, whereas\nclear Cu growth was observed on the amorphous PLA after 1000 cycles.\nAdditionally, the amorphous PLA film was decomposed during the Cu\ndeposition, unlike the semicrystalline PLA film which stayed intact.\nThe results give further confidence that ASE of polymers can be achieved\nwith various surface combinations by carefully choosing the right\ncatalytic material, polymer, and atmosphere.