Murray Ciaran A, Elliott Simon D, Hausmann Dennis, Henri Jon, LaVoie Adrien
Tyndall National Institute, University College Cork , Lee Maltings, Cork, Ireland.
ACS Appl Mater Interfaces. 2014 Jul 9;6(13):10534-41. doi: 10.1021/am5021167. Epub 2014 Jun 18.
Atomic layer deposition (ALD) of highly conformal, silicon-based dielectric thin films has become necessary because of the continuing decrease in feature size in microelectronic devices. The ALD of oxides and nitrides is usually thought to be mechanistically similar, but plasma-enhanced ALD of silicon nitride is found to be problematic, while that of silicon oxide is straightforward. To find why, the ALD of silicon nitride and silicon oxide dielectric films was studied by applying ab initio methods to theoretical models for proposed surface reaction mechanisms. The thermodynamic energies for the elimination of functional groups from different silicon precursors reacting with simple model molecules were calculated using density functional theory (DFT), explaining the lower reactivity of precursors toward the deposition of silicon nitride relative to silicon oxide seen in experiments, but not explaining the trends between precursors. Using more realistic cluster models of amine and hydroxyl covered surfaces, the structures and energies were calculated of reaction pathways for chemisorption of different silicon precursors via functional group elimination, with more success. DFT calculations identified the initial physisorption step as crucial toward deposition and this step was thus used to predict the ALD reactivity of a range of amino-silane precursors, yielding good agreement with experiment. The retention of hydrogen within silicon nitride films but not in silicon oxide observed in FTIR spectra was accounted for by the theoretical calculations and helped verify the application of the model.
由于微电子器件特征尺寸的持续减小，高保形的硅基介电薄膜的原子层沉积（ALD）变得十分必要。氧化物和氮化物的ALD通常被认为在机理上相似，但氮化硅的等离子体增强ALD存在问题，而氧化硅的则较为直接。为找出原因，通过将从头算方法应用于所提出的表面反应机理的理论模型，对氮化硅和氧化硅介电薄膜的ALD进行了研究。使用密度泛函理论（DFT）计算了不同硅前驱体与简单模型分子反应时消除官能团的热力学能量，这解释了实验中前驱体对氮化硅沉积的反应性低于氧化硅的现象，但未解释前驱体之间的趋势。使用更现实的胺和羟基覆盖表面的团簇模型，通过消除官能团来计算不同硅前驱体化学吸附反应途径的结构和能量，取得了更大的成功。DFT计算确定初始物理吸附步骤对沉积至关重要，因此该步骤被用于预测一系列氨基硅烷前驱体的ALD反应性，与实验结果吻合良好。理论计算解释了傅里叶变换红外光谱（FTIR）中观察到的氮化硅薄膜中氢的保留而氧化硅中没有的现象，并有助于验证模型的应用。
