Area-Selective Etching of Poly(methyl methacrylate) Films by Catalytic Decomposition

Valtteri Lasonen, Anton Vihervaara, Georgi Popov, Eva Tois, Lars Mester, Mohammad Karimi, Yoana Ilarionova, Reza Jafari Jam, Jonas Sundqvist and Mikko Ritala

Chemistry of Materials 35, 6097 (2023)
Area-selective etching (ASE) of polymers is a new, inventive, and simple self-aligned patterning technique which has the potential to become an important method for the fabrication of semiconductor devices. A polymer film is etched by using etchant gases, which diffuse through the polymer and are activated by catalytic materials underneath the polymer. The polymer is decomposed locally on top of catalytically active materials, while on top of catalytically inactive materials, the polymer stays intact. This makes the process area-selective and self-aligned, which avoids edge placement errors and other defects. The patterned polymer can be exploited in subsequent area-selective deposition or lift-off processes. In this paper, we study ASE of poly(methyl methacrylate) (PMMA) by using Pt, CeO2, Ti, and Cu as catalytic materials in an O2, H2, or inert atmosphere. Native SiO2 and Al2O3 were used as non-catalytic surfaces. The catalytic decomposition of PMMA on Pt and CeO2 in the air was clean; i.e., no intermediates in the middle of the process or any residue after the process were found on the surface. It was also demonstrated that very small amounts of Pt or CeO2, even down to a fraction of a monolayer, were enough to show the catalytic effect. Ti showed a clear catalytic effect in the H2 and inert atmospheres. Copper oxide, rather than metallic copper, was found to promote the decomposition of PMMA in the H2 and inert atmospheres. Finally, the feasibility of the overall patterning process was demonstrated on a 100 nanometer scale by ASE of PMMA followed by atomic layer deposition of Ni using Pt as the catalytic surface and native SiO2 as the non-catalytic surface.