In vacuo studies on plasma-enhanced atomic layer deposition of cobalt thin films

et al. 2020

J. Phys. Chem. C

Cobalt is a potential candidate in replacing copper for interconnects and has been applied in the trenches and vias in semiconductor industry. A non-oxidizing reactant is required in plasmaenhanced atomic layer deposition (PE-ALD) of thin films of metals to avoid O-contamination. PE-ALD of Co has been demonstrated experimentally, but the growth mechanism and key reactions are not clear. In this paper, the reaction mechanism of metal cyclopentadienyl (Cp, C5H5) precursors (CoCp2) and NHx-terminated Co surface is studied by density functional theory (DFT) calculations. The Cp ligands are eliminated by CpH formation via a hydrogen transfer step and desorb from metal surface. The surface facet plays an important role in the reaction energies and activation barriers. The results show that on the NHx-terminated surfaces corresponding to ALD operating condition (temperature range 550K to 650K), the two Cp ligands are eliminated completely on Co(100) surface during the metal precursor pulse, resulting in Co atom deposited on the Co(100) surface. But the second Cp ligand reaction of hydrogen transfer is thermodynamically unfavourable on the Co(001) surface, resulting in CoCp fragment termination on Co(001) surface. The final terminations after metal precursor pulse are 3.03 CoCp/nm 2 on NHxterminated Co(001) surface and 3.33 Co/nm 2 on NHx-terminated Co(100) surface. These final structures after metal precursor pulse are essential to model the reaction during the following Nplasma step.

Section: Discussionmentioning

confidence: 99%

“…This is consistent with the experimental finding of subsurface N atoms in Co metal. 18,[38][39] The study of the plasma step is beyond the scope of this paper. However, we can explore some possible reactions of the surface bound NHx species after CpH elimination on the Co(100) surface, leading to the formation of N2H4, NH3 or N2.…”

Section: Discussionmentioning

confidence: 99%

Reaction Mechanism of the Metal Precursor Pulse in Plasma-Enhanced Atomic Layer Deposition of Cobalt and the Role of Surface Facets

et al. 2020

J. Phys. Chem. C

“…This is consistent with the reported nitrogen incorporation into deposited Co thin films and Cobalt nitride using CoCp2 and NH3 plasma. 30,45 At temperatures of 533K and below, the deposited thin films consist primarily of Co2N. At higher temperature at 573K, the CoxN is a mixture of Co3N and Co.…”

Section: Regeneration Of Surface Nhx Terminations At Post-plasma Stagementioning

confidence: 99%

Self-limiting nitrogen/hydrogen plasma radical chemistry in plasma-enhanced atomic layer deposition of cobalt

et al. 2022

Nanoscale

“…These trench N species on Co(100) surface will be a potential source of N impurities in deposited Co thin films. 30,42 We applied Bader charge analysis to the Co (001) and (100) surfaces in each step of NHx removal.…”

Section: Reactions Of Plasma Generated H Radicals On Nhx-terminated Co(100) Surfacementioning

confidence: 99%

“…This is consistent with the reported nitrogen incorporation into deposited Co thin films and Cobalt nitride using CoCp2 and NH3 plasma. 30,42 At temperatures of 533K and below, the deposited thin films consist primarily of Co2N. At higher temperature at 573K, the CoxN is a mixture of Co3N and Co.…”

Section: Reactions Of Plasma Generated H Radicals On Nhx-terminated Co(100) Surfacementioning

confidence: 99%

Self-limiting Nitrogen/Hydrogen Plasma Radical Chemistry in Plasma-Enhanced Atomic Layer Deposition of Cobalt

Lü

et al. 2021

Preprint

Cobalt (Co) is a potential candidate in replacing copper for interconnects and has been applied in the trenches in semiconductor industry over twenty years. A non-oxidizing reactant is required in plasma-enhanced atomic layer deposition (PE-ALD) of thin films of metals to avoid O-contamination. PE-ALD of Co has been demonstrated experimentally with plasma sources of NH3 or a mixture of N2 and H2, but the growth mechanism and key reactions are not clear. In this paper, we have investigated the reactions of plasma generated radicals H, N, NH and NH2 at metal precursor (CoCp2) terminated Co (001) and (100) surfaces using static DFT calculations at 0 K and molecular dynamics simulations at 600 K. N radicals play an important role in eliminating surface-bound Cp ligand (if any) via pyridine (C5H5N) formation and desorption, whereas H radicals have endothermic reactions for eliminating Cp ligand via CpH formation and desorption. The surface NHx species are eliminated by H radicals via NH3 formation and desorption. The simulations of these key reactions show that on Co(001) surface, the remaining Cp ligand and surface NHx species after the metal precursor pulse will be completely removed with N and H radicals, resulting in Co atoms deposited on Co(001) surface at a coverage of 3.03Co/nm2. Whereas, on Co(100) surface, the surface NH2 species cannot be completely removed via NH3 formation and desorption due to overall endothermic reactions. Instead, H radicals react with trench N species, contributed to H transfer at metal precursor pulse, to form NH. These trench N species cannot be eliminated completely on Co(100) surface, which will be the source of N impurities for the deposited Co thin films. At the post-plasma stage, the metal surface will be covered with NHx-terminations with plasma generated NH radicals, which is then ready for the next deposition cycle. Our results explain why ammonia or H2/N2 plasma, which produce NHx species are required to deposit Co thin films using Co metallocene precursors.