Area selective atomic layer deposition of Si-based materials

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Filatova, Ekaterina A.
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University College Cork
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Modern electronics are very small and light yet extremely powerful. This is possible due to the constant integration of new techniques and novel materials into the electronics fabrication process. In the current project we are focusing on one of the most precise deposition fabrication techniques for microchip fabrication, called atomic layer deposition (ALD). In particular, we are interested in the applications of ALD for area-selective deposition, where the material is deposited only where it is needed allowing the lateral control of the grown film. We are using the quantum mechanical modelling, density functional theory (DFT) to investigate the chemical mechanism of the area-selective ALD processes for Si-based materials (SiC, SiO2 and SiNx ), which are widely used in the semiconductor microchip fabrication process. We are also focusing on the possible SiC ALD mechanism in more detail, as this mechanism is very challenging and still not implemented in high-volume manufacturing in the semiconductor industry. In order to investigate the possibility of area-selective deposition of Si-based materials on Si, SiC, SiO2 and SiNx substrates, the difference in adsorption energies of various aminosilane precursors was first analyzed by DFT. From DFT calculations we found that it is thermodynamically favorable for aminosilane precursors to react with SiNx and SiO2 substrates but not with SiC and Si. We further experimentally corroborate these results by depositing SiNx on Si, SiO2 and SiC substrates using di(sec-butylamino)silane precursor and N2 plasma ALD and measuring the apparent SiNx thickness by spectroscopic ellipsometry. Both DFT calculations and experiment show that the aminosilane precursor adsorbs selectively on SiO2 not on Si and SiC substrates, however, after N2 plasma pulse this selectivity is lost. Further, we investigated the possibility of the ALD of SiC. First, we used DFT to screen various precursors in order to select the most favourable for SiC ALD. Then we expanded this study by analyzing how these precursors react with H-terminated and bare SiC surfaces. We predicted that precursors disilane (Si2H6 ), silane (SiH4 ) or monochlorosilane (SiH3Cl) with ethyne (C2H2 ), carbontetrachloride (CCl4 ) or trichloromethane (CHCl3 ) are the most promising for ALD of SiC. All of these precursors are predicted to react thermodynamically with bare SiC but not with the passivated surface. An additional activation step would be needed to sustain an ALD process. In order to analyze how silane plasma fragments will react with the passivated surface, the reaction pathways of neutral silane plasma fragments SiH3 and SiH2 with the H-terminated surface were analyzed. Counterintuitively, it was found that silane plasma fragments SiH3 and SiH2 react selectivity with the Si-H bond rather than with the C-H bond of the H-terminated SiC surface. Lastly, as a part of collaboration with Prof. Adrie Mackus from Plasma Materials Process group in Eindhoven Technological University, Netherlands, we used a DFT screening approach to determine the non-growth surface during ALD of transition metal oxides via a ligand-exchange mechanism in the precursor pulse. Two different precursors reacting with various OH-terminated metal surfaces were compared: a heteroleptic amidometallocene and a homoleptic alkoxide. A sample result is that HfO2 , SiO2 and GeO2 are predicted to show nucleation delay in ALD on OH-terminated W, Co and Cu surfaces. Depending on the ligands used in the ALD precursor, Ru-based or W-based substrates were predicted to resist the nucleation of all the metal oxides that were studied.
ALD , DFT , ALD mechanism , Atomic layer deposition , Ab-initio modelling , Area selective ALD , Silicon materials , Semiconductor
Filatova, E. 2019. Area selective atomic layer deposition of Si-based materials. PhD Thesis, University College Cork.