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Reaction Mechanisms and Dynamics in the Early Stage of High-κ Oxide Atomic Layer Deposition : Investigations by In Situ and Operando X-ray Photoemission Spectroscopy

D Acunto, Giulio LU (2022)
Abstract
Atomic layer deposition (ALD) is an outstanding deposition technique to deposit highly conformal and uniform thin films with atomic precision. In particular, ALD of transition metal oxide layers from metal amido complexes and water finds its way in several technological fields, including green energy devices and in the semiconductor industry. These ALD reactions are believed to follow a reaction scheme based on the ligand exchange mechanism, in which the surface on which deposition takes place plays a largely static role and the ligands of the used precursor are chemically unchanged during the reaction. To address the correctness of the model, time-resolved in situ and operando ambient pressure x-ray photoelectron spectroscopy (APXPS)... (More)
Atomic layer deposition (ALD) is an outstanding deposition technique to deposit highly conformal and uniform thin films with atomic precision. In particular, ALD of transition metal oxide layers from metal amido complexes and water finds its way in several technological fields, including green energy devices and in the semiconductor industry. These ALD reactions are believed to follow a reaction scheme based on the ligand exchange mechanism, in which the surface on which deposition takes place plays a largely static role and the ligands of the used precursor are chemically unchanged during the reaction. To address the correctness of the model, time-resolved in situ and operando ambient pressure x-ray photoelectron spectroscopy (APXPS) technique was employed during the ALD of HfO2 on InAs covered by a thermal or native oxide, TiO2(101) and oxidised as well as clean Si(111).
The classic ligand exchange reaction mechanism does not adequately describe the reaction path in any of the investigated sample systems. In particular, ALD of HfO2 on SiO2 follows a bimolecular reaction mechanism based on the insertion of an hydrogen atom of one of the ligands in an amido complex dimer. As a result of its bimolecular nature, this reaction can take place only on a SiO2 surface of a sufficiently high coverage of physisorbed complexes. Similarly, on TiO2 the early stage of the reaction is based on dissociative adsorption, followed by an intra- and inter- molecular reaction path, leading to the formation of new sets of surface species never before identified in any of the previous ALD models.
For easily reducible surfaces, such as InAs oxide and TiO2, evidence is found for HfOx formation already during the first ALD half-cycle, due to the transfer of O atoms from the surface to the metal complex. Clearly, this contradicts the static role of the surface in standard ALD models. Interestingly, in the case of InAs covered by a thermal or native oxide, this phenomenon, which lies behind the so-called self cleaning effect, guarantees a sharp interface between the III-V material and HfO2, which is a prerequisite for next generation MOSFETs.
These results open new doors for improving devices based on ALD. Time-resolved in situ and operando APXPS allows to follow the kinetics and mechanisms involved in ALD, in real time at second time resolution with significant benefit for the further improvement of general understanding of ALD reactions. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Bent, Stacey, Stanford University
organization
publishing date
type
Thesis
publication status
published
subject
keywords
atomic layer depostion (ALD), high-k oxide, in situ and operando study, XPS, APXPS, Fysicumarkivet A:2022:D'Acunto
pages
126 pages
publisher
Lund University
defense location
Rydbergsalen, fysiska institutionen, Professorsgatan 1, Lund. Join via zoom: https://lu-se.zoom.us/j/68020412121?pwd=OGt0SDNRNkFyaXpGOEQyZkJrRnJhdz09 passcode: 400435
defense date
2022-05-20 13:15:00
ISBN
978-91-8039-230-3
978-91-8039-229-7
language
English
LU publication?
yes
id
1c02fe0a-7864-4eae-9a48-38a149b5842a
date added to LUP
2022-04-20 01:08:52
date last changed
2023-09-06 09:59:46
@phdthesis{1c02fe0a-7864-4eae-9a48-38a149b5842a,
  abstract     = {{Atomic layer deposition (ALD) is an outstanding deposition technique to deposit highly conformal and uniform thin films with atomic precision. In particular, ALD of transition metal oxide layers from metal amido complexes and water finds its way in several technological fields, including green energy devices and in the semiconductor industry. These ALD reactions are believed to follow a reaction scheme based on the ligand exchange mechanism, in which the surface on which deposition takes place plays a largely static role and the ligands of the used precursor are chemically unchanged during the reaction. To address the correctness of the model, time-resolved in situ and operando ambient pressure x-ray photoelectron spectroscopy (APXPS) technique was employed during the ALD of HfO2 on InAs covered by a thermal or native oxide, TiO2(101) and oxidised as well as clean Si(111).<br/>The classic ligand exchange reaction mechanism does not adequately describe the reaction path in any of the investigated sample systems. In particular, ALD of HfO2 on SiO2 follows a bimolecular reaction mechanism based on the insertion of an hydrogen atom of one of the ligands in an amido complex dimer. As a result of its bimolecular nature, this reaction can take place only on a SiO2 surface of a sufficiently high coverage of physisorbed complexes. Similarly, on TiO2 the early stage of the reaction is based on dissociative adsorption, followed by an intra- and inter- molecular reaction path, leading to the formation of new sets of surface species never before identified in any of the previous ALD models.<br/>For easily reducible surfaces, such as InAs oxide and TiO2, evidence is found for HfOx formation already during the first ALD half-cycle, due to the transfer of O atoms from the surface to the metal complex. Clearly, this contradicts the static role of the surface in standard ALD models. Interestingly, in the case of InAs covered by a thermal or native oxide, this phenomenon, which lies behind the so-called self cleaning effect, guarantees a sharp interface between the III-V material and HfO2, which is a prerequisite for next generation MOSFETs.<br/>These results open new doors for improving devices based on ALD. Time-resolved in situ and operando APXPS allows to follow the kinetics and mechanisms involved in ALD, in real time at second time resolution with significant benefit for the further improvement of general understanding of ALD reactions.}},
  author       = {{D Acunto, Giulio}},
  isbn         = {{978-91-8039-230-3}},
  keywords     = {{atomic layer depostion (ALD); high-k oxide; in situ and operando study; XPS; APXPS; Fysicumarkivet A:2022:D'Acunto}},
  language     = {{eng}},
  month        = {{04}},
  publisher    = {{Lund University}},
  school       = {{Lund University}},
  title        = {{Reaction Mechanisms and Dynamics in the Early Stage of High-κ Oxide Atomic Layer Deposition : Investigations by <i>In Situ </i>and <i>Operando </i>X-ray Photoemission Spectroscopy}},
  url          = {{https://lup.lub.lu.se/search/files/116979183/e_nailing_ex_Giulio.pdf}},
  year         = {{2022}},
}