Atomic Layer Deposition of Cobalt Using H₂-, N₂-, and NH₃-Based Plasmas: On the Role of the Co-reactant

Abstract

This work investigates the role of the co-reactant for the atomic layer deposition of cobalt (Co) films using cobaltocene (CoCp2) as the precursor. Three different processes were compared: an AB process using NH3 plasma, an AB process using H2/N2 plasma, and an ABC process using subsequent N2 and H2 plasmas. A connection was made between the plasma composition and film properties, thereby gaining an understanding of the role of the various plasma species. For NH3 plasma, H2 and N2 were identified as the main species apart from the expected NH3, whereas for the H2/N2 plasma, NH3 was detected. Moreover, HCp was observed as a reaction product in the precursor and co-reactant subcycles. Both AB processes showed self-limiting half-reactions and yielded similar material properties, that is, high purity and low resistivity. For the AB process with H2/N2, the resistivity and impurity content depended on the H2/N2 mixing ratio, which was linked to the production of NH3 molecules and related radicals. The ABC process resulted in high-resistivity and low-purity films, attributed to the lack of NHx,x≤3 species during the co-reactant exposures. The obtained insights are summarized in a reaction scheme where CoCp2 chemisorbs in the precursor subcycle and NHx species eliminate the remaining Cp in the consecutive subcycle.

Coverage and Stability of NHx Terminated Cobalt and Ruthenium Surfaces: a First Principles Investigation

“…One is the ultra-high vacuum (UHV) condition (P/P o = 5×10 -14 ) and the second is the standard ALD operating condition, taken from ref. 32 (P/P o = 1.97×10 -6 ); P o is the standard pressure, i.e. 1 atm.…”

“…The ALD of Co uses metal organic precursors such as cyclopentadienyl dicarbonyl cobalt (CoCp(CO)2) and bis-cyclopentadienyl cobalt (CoCp2) [31][32][33] and the other precursors are NH3 or a mixture of N2 and H2. The first ALD of Ru used RuCp2 and O2 as precursors.…”

“…However, H-plasma alone or separate N2 and H2 plasma can produce lower purity and higher resistivity Co thin films. 32,33,38 It has been argued that the NHx-terminated metal surfaces play an important role in Co thin film deposition. 32,39 However, the nature of the NHxterminated metal surfaces is not yet understood and this is the key advance in our present work.…”

Atomic layer deposition of InN using trimethylindium and ammonia plasma

“…10 The use of ammonia plasma as an alternative nitrogen source for InN ALD has not been fully investigated, although briefly mentioned by Ozgit-Akgun et al 12 The approach to InN ALD employing In(CH3)3 is interesting since the NHx species present in the plasma are believed to remove hydrocarbons from the surface. 13 In this work, we report on the self-limiting growth of crystalline InN thin films by ALD using TMI and ammonia plasma.…”

Atomic Layer Deposition of Inn Using Trimethylindium and Ammonia Plasma

“…The approach to InN ALD employing In(CH 3 ) 3 is interesting since the NH x species present in the plasma are believed to remove hydrocarbons from the surface. 11 In this work, we report on the self-limiting growth of crystalline InN thin films by ALD using TMI and ammonia plasma. Additionally, the impact of ammonia plasma power and ammonia flow on film quality has been investigated, analyzed and described in detail.…”