Shirazi Mahdi, Elliott Simon D
Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland.
Nanoscale. 2015 Apr 14;7(14):6311-8. doi: 10.1039/c5nr00900f.
Atomic layer deposition (ALD) is a technique for producing conformal layers of nanometre-scale thickness, used commercially in non-planar electronics and increasingly in other high-tech industries. ALD depends on self-limiting surface chemistry but the mechanistic reasons for this are not understood in detail. Here we demonstrate, by first-principle calculations of growth of HfO2 from Hf(N(CH3)2)4-H2O and HfCl4-H2O and growth of Al2O3 from Al(CH3)3-H2O, that, for all these precursors, co-adsorption plays an important role in ALD. By this we mean that previously-inert adsorbed fragments can become reactive once sufficient numbers of molecules adsorb in their neighbourhood during either precursor pulse. Through the calculated activation energies, this 'cooperative' mechanism is shown to have a profound influence on proton transfer and ligand desorption, which are crucial steps in the ALD cycle. Depletion of reactive species and increasing coordination cause these reactions to self-limit during one precursor pulse, but to be re-activated via the cooperative effect in the next pulse. This explains the self-limiting nature of ALD.
原子层沉积（ALD）是一种用于制备纳米级厚度保形层的技术，在非平面电子领域有商业应用，并且在其他高科技产业中的应用也越来越多。ALD依赖于自限性表面化学，但其中的机理原因尚未完全清楚。在此，我们通过对由Hf(N(CH3)2)4-H2O和HfCl4-H2O生长HfO2以及由Al(CH3)3-H2O生长Al2O3进行第一性原理计算，证明对于所有这些前驱体，共吸附在ALD中起着重要作用。我们的意思是，一旦在前驱体脉冲期间有足够数量的分子吸附在其附近，先前惰性的吸附片段就会变得具有反应性。通过计算活化能，这种“协同”机制对质子转移和配体解吸有深远影响，而质子转移和配体解吸是ALD循环中的关键步骤。反应物种的消耗和配位增加导致这些反应在前驱体脉冲期间自我限制，但在下一个脉冲中通过协同效应重新激活。这解释了ALD的自限性本质。
