Thermal cyclic atomic-level etching in 3D ULSI device fabrication

Memory and logic device developments are going to three-dimensional structure for higher integration. They are 3D NAND, 3D DRAM, Gate-all-around transistor and back-side power delivery. For generating 3D structure, lateral etching technology is definitely needed. Recently many researchers and engineers have focused on atomic-layer-etching, ALE. But most evaluations were done by dry etchers, which is for anisotropic etchings. We need other technologies with completely uniform lateral etchings.

In this talk, I would like to summarize the history of atomic layer etching development and introduce our technology. For realizing the completely uniform lateral etchings, I think we might have two options: 1) self-limited modification, 2) high etchant density for surface reaction limitation. Regarding option 1, Prof. S. M. George team has evaluated various material ALEs by the ligand-exchange process. But they are very slow etching and cannot be applied to volume fabrication easily. Vapor etching can realize the option 2, however, they are also very slow because of low reaction rate. To meet the practical etching rates with completely uniform etching performances, I believe that we should consider the combination of thermal cyclic process and plasma process with unique gases.

We have developed a new etch tool which has IR lamp and ESC, which achieved reasonably quick heat-up to 300 deg.C in a few ten seconds and quick cooling-down to negative temperature. It also has a plasma source which can deliver enough amount of radicals through the ion shielding plate. In silicon etching, cyclic process of oxidation and oxide removal achieves precisely controlled and conformal removal. For oxide, vapor HF works well for uniform recess in high aspect ratio structure. Hydrofluorocarbon ALE is available in SiN etching. The new tool also provides the cyclic process of deposition and etching for good top-to-bottom uniformity in metal etching by using the plasma.