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

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Atomically precise and highly selective surface reactions are required for advancing microelectronics fabrication. Advanced atomic processing approaches make use of small molecule inhibitors (SMI) to enable selectivity between growth and nongrowth surfaces. The selectivity between growth and nongrowth substrates is eventually lost for any known combinations, because of defects, new defect formation, and simply because of a Boltzmann distribution of molecular reactivities on surfaces. The selectivity can then be restored by introducing etch-back correction steps. Most recent developments combine the design of highly selective combinations of growth and nongrowth substrates with atomically precise cycles of deposition and etching methods. At that point, a single additional step is often used to passivate the unwanted defects or selected surface chemical sites with SMI. This step is designed to chemically passivate the reactive groups and defects of the nongrowth substrates both before and/or during the deposition of material onto the growth substrate. This approach requires applications of the fundamental knowledge of surface chemistry and reactivity of small molecules to effectively block deposition on nongrowth substrates and to not substantially affect deposition on the growth surface. Thus, many of the concepts of classical surface chemistry that had been developed over several decades can be applied to design such small molecule inhibitors. This article will outline the approaches for such design. This is especially important now, since the ever-increasing number of applications of this concept still rely on trial-and-error approaches in selecting SMI. At the same time, there is a very substantial breadth of surface chemical reactivity analysis that can be put to use in this process that will relate the effectiveness of a potential SMI on any combination of surfaces with the following: selectivity; chemical stability of a molecule on a specific surface; volatility; steric hindrance, geometry, packing, and precursor of choice for material deposition; strength of adsorption as detailed by interdisplacement to determine the most stable SMI; fast attachment reaction kinetics; and minimal number of various binding modes.The down-selection of the SMI from the list of chemicals that satisfy the preliminary criteria will be decided based on optimal combinations of these requirements. Although the specifics of SMI selection are always affected by the complexity of the overall process and will depend drastically on the materials and devices that are or will be needed, this roadmap will assist in choosing the potential effective SMIs based on quite an exhaustive set of "SMI families" in connection with general types of target surfaces.

Unfolding an Elusive Area-Selective Deposition Process: Atomic Layer Deposition of TiO2 and TiON on SiN vs SiO2

“…Details are available in the Methods section. The etching step was followed by 5 “cycles” of DMATMS as a small molecule inhibitor (SMI; Figure c). ,, Finally, the substrates were exposed to alternating doses of titanium tetrachloride, TiCl 4 , and water, for t-TiO 2 AS-ALD (Figure d,e) and TiCl 4 and N 2 /H 2 plasma for p-TiON AS-ALD (Figure f,g). A total of 100 and 250 ALD cycles were applied for t-TiO 2 and 250 to 450 cycles for p-TiON.…”

“…An overview of such modification strategies can be found elsewhere. 12 Several area-selective ALD (AS-ALD) processes have been developed so far, 9−11,13−15 yet the selective deposition of hardmask materials on SiN as GS with respect to SiO 2 as NGS has been an extremely challenging target to achieve. AS-ALD of TiN, TiO 2 , and other typical hard-mask materials on SiN vs SiO 2 materials that are ubiquitous in almost every device patterning step, could dramatically expand the processing window of several patterning processes employed in semiconductor manufacturing.…”

“…ALD can offer the optimal conditions to control each individual surface (half-)­reaction at the atomic level, during the precursor or the coreactant steps. − If sufficiently large differences in thermodynamics or kinetics of surface reactions exist on growth vs nongrowth surfaces, selective deposition can be naturally obtained, referred to as inherently selective ALD. , Often, however, the NGS needs to be selectively modified so that thermodynamic or kinetic control can be achieved. An overview of such modification strategies can be found elsewhere …”

Reactive Vapor-Phase Inhibitors for Area-Selective Depositions at Tunable Critical Dimensions

“…In another approach, the modification of a surface with an organic material can be used to deactivate it and inhibit film growth. − The latter strategy may offer the versatility of selectively coating a broad number of metal or dielectric surfaces commonly encountered in device builds. Organic inhibiting materials can be deposited either by solution or vapor-phase methods, generally dependent on the vapor pressure of the molecule. , Solution deposition methods often use self-assembled monolayers (SAMs) to form densely packed inhibiting layers, driven in large part by headgroup chemistry, which presents a strong enthalpic driving force to bind with a surface (such as thiols, phosphonic, and hydroxamic acids). Formation of the monolayer is further aided by interactions between aliphatic side chains through van der Waals forces to form crystalline monolayers (the magnitude of the interaction depends on the length of the side-chain) .…”

Low-Temperature Dechlorosilylation Chemistry for Area-Selective Deposition of Ge2Sb2Te5 and Its Mechanism in Nanopatterns

“…Few papers have reported ASD processes for GST and Sb 2 Te 3 ASD by ALD and CVD . Pore et al reported the ALD of GST at the low temperature of 70 °C by utilizing dechlorosilylation chemistry, and several research groups have demonstrated ALD of GST based on this chemistry. − , Low-temperature ALD in principle creates opportunities to utilize a wide range of small molecule inhibitors (SMIs), polymers, or self-assembled monolayers (SAMs) to enable ASD, as thermal degradation of the passivation can be minimized. , However, no in-depth investigation of ASD by means of the dechlorosilylation chemistry has been reported, to the best of our knowledge.…”