Surface reaction mechanisms of SiH4 and Si2H6 for epitaxial silicon growth on Si(100): Effects of hydrogen coverage

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The increasing thermal-budget constraints in advanced semiconductor fabrication have intensified the demand for low-temperature Si and SiGe epitaxy. Silane (SiH 4 ) and disilane (Si 2 H 6 ) are attractive Si precursors for low-temperature growth because of their high reactivity; however, their surface reaction mechanisms, particularly on H-covered Si(100), remain insufficiently understood. Herein, density functional theory calculations were performed to investigate the chemisorption and decomposition pathways of SiH 4 and Si 2 H 6 on clean and H-covered Si(100) surfaces, together with H 2 desorption. On clean Si(100), both precursors readily chemisorb at available open sites. For Si 2 H 6 , Si–H bond cleavage exhibits lower energy barriers than Si–Si bond cleavage for both chemisorption (0.01 versus 0.67 eV) and subsequent decomposition (0.44 versus 1.09 eV), identifying Si–H bond cleavage as the minimum-energy pathway. These barriers are substantially lower than the 2.07–2.24 eV required for H 2 desorption, indicating that open-site regeneration is energetically more demanding than precursor reaction. On H-covered surfaces, direct SiH 4 chemisorption and Si 2 H 6 reactions on the fully H-terminated surface provide no energetic advantage over H 2 desorption. In contrast, on the examined partially H-covered surface ( θ H = 0.5), Si 2 H 6 follows an alternative Si–H bond cleavage pathway with a 1.59 eV barrier for chemisorption, followed by 1.11 and 1.18 eV barriers for subsequent decomposition, all lower than H 2 desorption. For these calculated pathways, the total number of open sites is conserved before and after each reaction. These results demonstrate that hydrogen coverage critically affects the reaction mechanism of Si 2 H 6 and helps explain its favorable low-temperature reactivity.