Paper TF-TuA11
Branched Interfacial Organic Layers: Controlling Nucleation and Growth of Thin Films

Tuesday, October 16, 2007, 5:00 pm, Room 613/614

Organic layers hold great potential for use in modern electronic and optoelectronic devices, owing to both their unique material properties, and their processing properties, such as their tendency towards self-assembly. In the work we describe here we have investigated the use of self-assembled monolayers (SAMs), or more accurately interfacial organic layers (IOLs), that possess a branched backbone for use as nucleation site multipliers and amplifiers. Here we describe the synthesis and characterization of two branched IOLs, their reactivity with precursors for atomic layer deposition (ALD), and the subsequent nucleation and growth of ALD thin films of TiN on these layers. The first IOL we consider is a layer that possesses a regular branched backbone with terminal -NH₂ groups, based on a sequential chemical reactions and application of polyamidoamine (dendrimer) chemistry. Here, an appropriately chosen -NH₂ terminated SAM serves as the anchor, from which additional growth is seeded, forming an IOL with a "Y" backbone and -NH₂ termination. A second IOL we consider is a randomly branched organic film, possessing -OH groups both at terminal points and along the backbone, which have been grown using anionic ring-opening polymerization of glycidol. In both cases the IOLs themselves have been characterized using X-ray photoelectron spectroscopy (XPS), ellipsometry and contact angle measurements. Furthermore, the layers have been characterized concerning their reactivity with two precursors for ALD, Ti[N(CH₃)₂]₄ and Ta[N(CH₃)₂]₅, using XPS. For the dendrimer we find that the adsorptive capacity of the surface scales with the generation of the dendrimer, i.e., the branching step effectively doubles the reactivity of the surface. For the poly-G layer, however, we find that sufficiently thick layers can virtually strip the Ta complex of all of its ligands, forming a TaO_x core. These observations are borne out in the subsequent growth of ALD thin films of TiN on these layers. Nucleation on the dense -NH₂ terminated dendrimer is relatively facile, and STEM shows a highly conformal layer. Growth on poly-G depends sensitively on its thickness-thin layers behave in a manner similar to the dendrimer IOL, whereas thicker poly-G layers behave more akin to unreactive long-chain -CH₃ layers. We will conclude with a discussion of our results on porous low-κ materials.