Electron beam physical vapor deposition

vignette|Evaporateur métallique « E-gun » utilisé au centre de recherche « Thales Research & Technology » du milieu des années 80 jusqu’en 2004 pour l’évaporation des sandwichs métalliques de contact ohmique et de grille. L’évaporation par faisceau d’électrons (aussi évaporation par faisceau électronique ; en anglais : Electron-beam physical vapor deposition / EBPVD, aussi simplement electron-beam evaporation) est une forme de dépôt physique en phase gazeuse, plus spécifiquement d’évaporation sous vide, dans laquelle une anode cible sous vide poussé est bombardée par un faisceau d’électrons émis par un canon à électrons. Le faisceau d’électrons chauffe localement la cible, dont la matière (atomes ou molécules) se vaporise et condense sous forme de couche mince sur le substrat (et les parois de la chambre à vide). Introduction Le dépôt de couches minces est une famille de procédés largement utilisés, notamment :

dans l’industrie des semi-conducteurs, pour la fabrication

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

The fabrication of defined and high-quality metal nanostructures is an ongoing topic of research. Direct-write deposition of copper nanostructures is of great value for many fields of research and industrial applications. Focused electron beam induced deposition (FEBID) is an additive fabrication technique with extremely high resolution and versatility. Physisorbed, gaseous precursor molecules are locally dissociated by a finely focused electron beam resulting in volatile fragments which desorb and non-volatile fragments forming the deposit. When applying suitable deposition parameters, these deposits can be as small as the beam diameter and have ideally little to no contamination. For electron beam induced metal deposition, metal-organic compounds are chosen as precursors. However, organic ligand material is often co-deposited, which is detrimental to the depositâs properties. This work addresses the study of the perfluorinated copper carboxylate [Cu2(ÎŒ-O2CC2F5)4] (Cu2(pfp)4) and its aminated derivatives Cu2(EtNH2)2(pfp)4 and Cu2(tBuNH2)2(pfp)4 as viable FEBID precursors. 25 at.% of copper was achieved with the amine free compound, and 15 at.% with each of the two aminated complexes. Based on the chemical analysis of the deposits, electron-induced dissociation paths were proposed for the adsorbed species, demonstrating the influence of the ligand chemistry and fragmentation on the deposit composition. In parallel, the perfluorinated silver carboxylate Ag2(pfp)2 was reported and compared directly to its copper equivalent. The silver complex yielded up to 74 at.% metal content and exhibited strong susceptibility to varying electron beam densities throughout the deposit. Cu2(pfp)4 did not manifest the same electron sensitivity. Theoretical models, combining analytical solutions with Monte Carlo simulations of primary and backscattered electrons were successfully fitted to the cross sections of deposits from both carboxylates, determining the growth regimes within a single spot deposit. Additionally, two previously reported Î²-diketonates, Cu(hfac)2 and Cu(tbaoac)2, were directly compared to the other Cu(II) precursors with the aim to determine any dependence of the ligand size, electron density or dwell time on the deposit purity. The investigations concluded that the metal content rather depends on the chemistry of the metal-ligand bond than on the ligand size. This applies to both, the variation of ligands and the variation of the metal center. vii Furthermore, two copper complexes, Cu(hfac)2 and Cu2(pfp)4, were investigated in situ with a dedicated, custom-made setup. The âeQCMâ combines a low energy electron source (10- 100 eV) with a quartz crystal microbalance and serves to study fundamental processes occurring during FEBI deposition. First results yielded the total dissociation cross section for each precursor at varying electron energies. Finally, alternative approaches for the electron induced copper deposition from Cu2(pfp)4 were investigated. A two-step post-purification recipe of as-deposited material was reported to yield pure copper crystals (> 97 at.%). Additionally, direct electron beam lithography in a layer of condensed precursor was explored. This room temperature deposition approach yielded in lower metal contents but could potentially produce high resolution deposition.

EPFL2020

Oxygen assisted focused electron beam induced deposition of silicon dioxide

Alexandre Perentes

Focused Electron Beam Induced Deposition (FEBID) is a rapid prototyping technique for the investigation, production and modification of 2 and 3-D nanostructures. The process takes place at room temperature, in the high-vacuum chamber of a Scanning Electron Microscope (SEM). The principle is based on the local FEB decomposition of molecules injected in the chamber and adsorbed on a surface. These molecules, called the precursors, are specifically chosen to contain the element of interest to be deposited. However, the electron induced decomposition results in contaminated materials containing additional parasitic elements from the precursor molecule. These contaminants are incorporated with the element of interest, and downgrade the properties of the materials and prevent therefore their use for many applications. Gas-assisted FEBID, the subject of this thesis, is a promising evolution and solution to the problem that was never extensively studied in literature. It consists in injecting a reactive gas simultaneously to the precursors, which will react in real time with the deposited contaminants to form volatile products, leaving ideally only the interesting material on the surface. This work focused on the Oxygen assisted FEBID of Silicon dioxide (SiO2) and on the understanding of the deposition process. SiO2 it is a high performance material for nano-optic and electronic applications, widely used in research and industry. Modifications were brought to an existing SEM to allow the simultaneous injection of two different and controlled gases, and to allow the in-situ control of growth of optical materials. Si-precursors of three families (alkoxy-, alkyl- and isocyanato-silanes) were compared. The FEBID material could be gradually converted from contaminated Si-materials to pure SiO2, above a [O2]/[precursor] ratio specific to each precursor chemistry and precursor flow. The SiO2 deposited was stoichiometric, C and OH–free, had an estimated density of 2.2, was amorphous and had optical properties close to that of fused silica. Optical structures for nano-optics and plasmonics were produced. Compared to traditional FEBID, O2 assisted FEBID required much lower energy to induce a decomposition reaction, and secondary electrons achieved 90 % of the deposition process in our setup. The electron efficiency could be multiplied by 20 compared to conventional FEBID. O2 assisted FEBID was insensitive to electron density in our setup. The conditions for no C and large deposition rates during O2 assisted FEBID were high molecule reactivity to O2, low sticking coefficient, low acceleration voltage and dwell time (< 6 µs), and large replenishment time (> 60 µs). As function of the precursor chemistry and flow, additional O2 influenced the deposition rate, which could be increased it by a factor of 7. The O2 and precursor molecules co-adsorption resulted in a surface coverage competition, which determined the deposition efficiencies. Limitations due to the residual water in the SEM were demonstrated and characterized. They appeared as Oxygen incorporation in the deposited materials, which influenced the deposition process. Residual water impinging flow was demonstrated to be responsible of the FEBID process deposition efficiency when no Oxygen was injected.

EPFL2007

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

EPFL2020

Oxygen assisted focused electron beam induced deposition of silicon dioxide

Alexandre Perentes

EPFL2007

Electron beam physical vapor deposition

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Deposition of copper structures using focused electron deposition

Oxygen assisted focused electron beam induced deposition of silicon dioxide

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Oxygen assisted focused electron beam induced deposition of silicon dioxide

Deposition of copper structures using focused electron deposition