Density functional theory study on the full ALD process of silicon nitride thin film deposition via BDEAS or BTBAS and NH₃

Abstract

A detailed reaction mechanism has been proposed for the full ALD cycle of Si3N4 deposition on the β-Si3N4(0001) surface using bis(diethylamino)silane (BDEAS) or bis(tertiarybutylamino)silane (BTBAS) as a Si precursor with NH3 acting as the nitrogen source. Potential energy landscapes were derived for all elementary steps in the proposed reaction network using a periodic slab surface model in the density functional approximation. Although the dissociative reactivity of BTBAS was slightly better than that of BDEAS, the thermal deposition process was still found to be an inherently high temperature process due to the high activation energies during the dissociative chemisorption of both precursors and the surface re-amination steps. These results underline the need to develop new precursors and alternative nitrogen sources when low temperature thermal silicon nitride films are targeted.

Modeling Mechanism and Growth Reactions for New Nanofabrication Processes by Atomic Layer Deposition

“…Amorphous Si 3 N 4 thin fi lms are widely used as passivation layers, masking layers to prevent oxidation in underlying materials and as a fi nal protection layer due to their hardness and radiation resistance. [57][58][59] There is great interest in developing new ALD processes for SiC and elemental Si itself.…”

“…[ 65 ] Although chlorosilanes (e.g., SiCl 4 , SiH 2 Cl 2 and Si 2 Cl 6 ) are currently used for ALD of silicon nitride with NH 3 or N 2 as nitrogen source, [57][58][59]66,67 ] a chlorine-free low-temperature CVD or, ideally, ALD process would be preferred for many applications. Finding alternative Si precursors, and optimizing existing families such as aminosilanes, is therefore the motivation for some of the theoretical work presented here and for ongoing research.…”

“…[ 57 ] Adsorption is considered at sites corresponding to a continuation of the crystalline lattice or at sites that produce a strained (potentially amorphous) overlayer, so as to obtain an indication of how growth reactions may direct the morphology of the fi lm. For both BDEAS and BTBAS, it is found that activation energies to chemisorb and lose ligands are high.…”

Atomic Layer Deposition of Silicon Nitride Thin Films: A Review of Recent Progress, Challenges, and Outlooks

“…Later in 2004, Mui et al investigated SiN x ALD with SiH 4 and NH 3 using DFT calculations [126]. This pioneering work has revealed that the reactions have to overcome high activation barriers which is challenging for thermal ALD [127]. Recently, the collaboration between academia and industry has contributed to the surge of theoretical simulation studies of SiN x ALD [34,54,57,127,128,129].…”

“…This pioneering work has revealed that the reactions have to overcome high activation barriers which is challenging for thermal ALD [127]. Recently, the collaboration between academia and industry has contributed to the surge of theoretical simulation studies of SiN x ALD [34,54,57,127,128,129]. Murray et al found that the orientation of hydrogen atoms connected to the hydroxyl (–OH) and amine (–NH 2 ) groups is quite different [128].…”