Area-Selective Etching of Poly(lactic acid) Films via Catalytic Hydrogenolysis and Cracking

Fabrication of future semiconductor devices requires new and inventive self-aligning patterning processes. One such process is area-selective etching (ASE) of polymers, which exploits different catalytic properties of different surfaces. In ASE, a polymer film is decomposed only from the top of catalytically active materials, while the polymer stays intact on catalytically inactive materials. This means that the patterning is self-aligned, thus avoiding edge placement errors. So far, patterning by ASE of polymers has been demonstrated in oxidative atmospheres. Here, we study the ASE of poly(lactic acid) (PLA) in two nonoxidative atmospheres: inert atmosphere where decomposition by cracking occurs, and H2 atmosphere where the polymer is decomposed by hydrogenolysis. Ni, NiO, Ir, and Pt films were identified as hydrogenolysis catalysts in the decomposition of PLA, whereas Co and CoO films catalyzed the decomposition of PLA both under an inert atmosphere and in the presence of H2. Further studies revealed, however, that it is the native Co oxide or hydroxide, rather than metallic Co, that promotes the decomposition of PLA. We also compared a commercially available amorphous PLA and self-synthesized semicrystalline PLA. The semicrystalline PLA showed less flow during the ASE process, due to its higher melting temperature, as compared to the amorphous PLA. The semicrystalline PLA inhibited 1000 atomic layer deposition (ALD) cycles of Cu, whereas clear Cu growth was observed on the amorphous PLA after 1000 cycles. Additionally, the amorphous PLA film was decomposed during the Cu deposition, unlike the semicrystalline PLA film which stayed intact. The results give further confidence that ASE of polymers can be achieved with various surface combinations by carefully choosing the right catalytic material, polymer, and atmosphere.