Selection Criteria for Small-Molecule Inhibitors in Area-Selective Atomic Layer Deposition: Fundamental Surface Chemistry Considerations

Conspectus Atomically precise and highlyselective surfacereactions are requiredfor advancing microelectronics fabrication. Advanced atomic processingapproaches make use of small molecule inhibitors (SMI) to enable selectivitybetween growth and nongrowth surfaces. The selectivity between growthand nongrowth substrates is eventually lost for any known combinations,because of defects, new defect formation, and simply because of aBoltzmann distribution of molecular reactivities on surfaces. Theselectivity can then be restored by introducing etch-back correctionsteps. Most recent developments combine the design of highly selectivecombinations of growth and nongrowth substrates with atomically precisecycles of deposition and etching methods. At that point, a singleadditional step is often used to passivate the unwanted defects orselected surface chemical sites with SMI. This step is designed tochemically passivate the reactive groups and defects of the nongrowthsubstrates both before and/or during the deposition of material ontothe growth substrate. This approach requires applications of the fundamentalknowledge of surface chemistry and reactivity of small molecules toeffectively block deposition on nongrowth substrates and to not substantiallyaffect deposition on the growth surface. Thus, many of the conceptsof classical surface chemistry that had been developed over severaldecades can be applied to design such small molecule inhibitors. Thisarticle will outline the approaches for such design. This isespecially important now, since the ever-increasing numberof applications of this concept still rely on trial-and-error approachesin selecting SMI. At the same time, there is a very substantial breadthof surface chemical reactivity analysis that can be put to use inthis process that will relate the effectiveness of a potential SMIon any combination of surfaces with the following: selectivity; chemicalstability of a molecule on a specific surface; volatility; sterichindrance, geometry, packing, and precursor of choice for materialdeposition; strength of adsorption as detailed by interdisplacementto determine the most stable SMI; fast attachment reaction kinetics;and minimal number of various binding modes. The down-selectionof the SMI from the list of chemicals that satisfythe preliminary criteria will be decided based on optimal combinationsof these requirements. Although the specifics of SMI selection arealways affected by the complexity of the overall process and willdepend drastically on the materials and devices that are or will beneeded, this roadmap will assist in choosing the potential effectiveSMIs based on quite an exhaustive set of "SMI families"in connection with general types of target surfaces.