Investigating area-selective atomic layer deposition of dielectric on diverse substrate systems
Keywords: Materials Science and Engineering.

The manufacturing process for semiconductor devices has become increasingly complex and costly due to bottlenecks with conventional top-down fabrication methods. Hence, researchers are looking for alternative approaches to address these issues. Area-selective atomic layer deposition (AS-ALD) is attracting growing research interest because of its ability to form patterned materials in a bottom-up fashion. To achieve AS-ALD, self-assembled monolayers (SAMs) are commonly used as inhibitors to block ALD processes. SAM molecules can spontaneously form ordered structures on specific surfaces depending on the headgroup of the molecule. By selecting the right type of SAM headgroup depending on the substrate materials, selective SAM formation on specific areas of patterned substrates can be achieved, leading to successful achievement of AS-ALD. Although SAM-assisted AS-ALD is promising, challenges remain in developing more robust AS-ALD systems with broader applicability. In the first part of this thesis, dodecanethiol (DDT) is used as the inhibitor for AS-ALD on metal/dielectric substrates. We show that a DDT passivation layer forms only on Cu but not on SiO2 or low-k dielectric surfaces, thus allowing AS-ALD of ZnO and Al2O3 on the dielectric regions of metal/dielectric patterned substrates to be achieved. By conducting DDT deposition on slightly oxidized Cu surfaces which consist mainly of Cu2O, we further show that the packing of the DDT SAM can be enhanced, leading to improvement of the ALD blocking ability. In addition, because thiols have been shown to form multilayer structures on CuO-covered Cu substrates, the impact of the DDT structure, i.e., monolayer vs. multilayer, on both the blocking ability and edge effects at the interface of metal/dielectric patterns during AS-ALD is studied. The results indicate that multilayer DDT blocks ZnO ALD more effectively than does monolayer DDT, while monolayer DDT is more efficacious in inhibiting Al2O3 ALD. The study on the interfacial effect in patterns with feature sizes of 20-100 nm shows that multilayer DDT can lead to some undesired effects: inhibition of ZnO at the SiO2 edges and nonuniform ZnO deposition on SiO2 regions (much thinner ZnO film at small pitch sizes). On the other hand, ZnO grows uniformly on SiO2 regions without the above-mentioned issues when monolayer DDT is used. The second part of the thesis focuses on developing new AS-ALD systems. We demonstrate that an octadecyltrimethoxysilane (OTMS) SAM is selectively formed on SiO2 of Cu/SiO2 patterns only when DDT is first used as the protector on Cu surfaces to prevent OTMS adsorption on Cu. After selective removal of the DDT protector by thermal treatment prior to ALD, AS-ALD of Al2O3 and ZnO on Cu regions of the patterns is demonstrated. In addition to selective deposition onto metal-dielectric patterns, AS-ALD on more general material systems, for which chemically similar materials are present on the substrate surface at the same time, is investigated. We achieve the selective formation of octadecylphosphonic acid (ODPA) SAMs on various metal oxide substrates, including Al2O3, HfO2, TiO2 and Ta2O5, over SiO2 by relying on the different reactivity of the ODPA headgroup on these oxide surfaces. AS-ALD is then demonstrated with SiO2 as the growth surface and the other four metal oxides as the nongrowth surface. To further obtain selectivity in more general systems, the solvent and deposition time for ODPA SAM formation are optimized. We show that selective deposition of ZnO and Al2O3 ALD between different metal oxide substrates can be achieved, with especially good selectivity between Al2O3 (growth surface) vs HfO2 (nongrowth surface). In the final part of this thesis, the breakdown behavior of SAM inhibitors in AS-ALD is investigated. The octadecyltrichlorosilane (ODTS) SAM paired with Al2O3 and ZnO ALD is used as the model system for the SAM inhibitor and ALD process, respectively. The results show that no notable changes in the crystallinity and structure (thickness, density and roughness) of ODTS SAMs are observed until a significant amount of ALD nucleation occurs. The study also reveals different morphologies of the ALD materials deposited on top of ODTS SAMs. Al2O3 tends to form a relatively continuous film whereas ZnO forms dispersed nanoparticles. Overall, the studies presented in this thesis provide greater understanding of AS-ALD and open up more opportunities for new applications of AS-ALD