Molecule-by-Molecule Writing Using a Focused Electron Beam

The resolution of lithography techniques needs to be extended beyond their current limits to continue the trend of miniaturization and enable new applications. But what is the ultimate spatial resolution? It is known that single atoms can be imaged with a highly focused electron beam. Can single atoms also be written with an electron beam? We verify this with focused electron-beam-induced deposition (FEBID), a direct-write technique that has the current record for the smallest feature written by (electron) optical lithography. We show that the deposition of an organometallic precursor on graphene can be followed molecule-by-molecule with FEBID. The results show that mechanisms that are inherent to the process inhibit a further increase in control over the process. Hence, our results present the resolution limit of (electron) optical lithography techniques. The writing of isolated, subnanometer features with nanometer precision can be used, for instance, for the local modification of graphene and for catalysis.</p

The rational design of a Au(I) precursor for focused electron beam induced deposition

Au(I) complexes are studied as precursors for focused electron beam induced processing (FEBIP). FEBIP is an advanced direct-write technique for nanometer-scale chemical synthesis. The stability and volatility of the complexes are characterized to design an improved precursor for pure Au deposition. Aurophilic interactions are found to play a key role. The short lifetime of ClAuCO in vacuum is explained by strong, destabilizing Au-Au interactions in the solid phase. While aurophilic interactions do not affect the stability of ClAuPMe3\, they leave the complex non-volatile. Comparison of crystal structures of ClAuPMe3 and MeAuPMe3 shows that Au-Au interactions are much weaker or partially even absent for the latter structure. This explains its high volatility. However, MeAuPMe3 dissociates unfavorably during FEBIP, making it an unsuitable precursor. The study shows that Me groups reduce aurophilic interactions, compared to Cl groups, which we attribute to electronic rather than steric effects. Therefore we propose MeAuCO as a potential FEBIP precursor. It is expected to have weak Au-Au interactions, making it volatile. It is stable enough to act as a volatile source for Au deposition, being stabilized by 6.5 kcal/mol. Finally, MeAuCO is likely to dissociate in a single step to pure Au

Focused helium and neon ion beam induced etching for advanced extreme ultraviolet lithography mask repair

The gas field ion microscope was used to investigate helium and neon ion beam induced etching of nickel as a candidate technique for extreme ultraviolet (EUV) lithography mask editing. No discernable nickel etching was observed for room temperature helium exposures at 16 and 30 keV in the dose range of 1 x 10(15)-1 x 10(18) He+/cm(2); however, transmission electron microscopy (TEM) revealed subsurface damage to the underlying Mo-Si multilayer EUV mirror. Subsequently, neon beam induced etching at 30 keV was investigated over a similar dose range and successfully removed the entire 50 nm nickel top absorber film at a dose of similar to 3 x 10(17) Ne+/cm(2). Similarly, TEM revealed subsurface damage in the underlying Mo-Si multilayer. To further understand the helium and neon damage, the authors simulated the ion-solid interactions with our EnvizION Monte-Carlo model, which reasonably correlated the observed damage and bubble formation to the nuclear energy loss and the implanted inert gas concentration, respectively. A critical nuclear energy density loss of similar to 80 eV/nm(3) and critical implant concentration of similar to 2.5 x 10(20) atoms/cm(3) have been estimated for damage generation in the multilayer structure. (C) 2014 American Vacuum Society

The role of electron scattering in electron-induced surface chemistry

Electron-induced chemistry on surfaces plays a key role in focused electron beam induced processing (FEBIP), a single-step lithography technique that has increasingly gained interest in the past decade. It is crucial for the understanding and modelling of this process to know the role of the surface in the electron-induced dissociation of an adsorbed precursor molecule. However, the electron scattering in the underlying solid makes it impossible to determine this directly. In this paper the contribution of electron scattering in the target on the measured deposition yield is calculated for the precursor MeCpPt(IV)Me-3, using the matrix inversion method. The calculation is based on experimental data for the dissociation yield and secondary electron emission. Two trends are observed in the analysis. Firstly, the contribution of electron scattering to the experimentally determined dissociation yield is not dominant for primary electron (PE) energies up to about 50 eV. Therefore, the role of the surface in this energy range can therefore reasonably be deduced from differences between electron-induced dissociation in the gas phase and the adsorbed phase. Secondly, at PE energies above 80 eV the electron scattering contributes significantly to the measured dissociation yield. The cross section that is calculated with the matrix inversion method peaks at 80-150 eV, which is typical for gas phase ionization. This suggests that surface interactions (other than electron scattering) do not dominate the chemistry for energies above PE energies of 80 eV. The obtained result can be used as input for Monte Carlo simulations for focused electron beam induced deposition

Charging effects during focused electron beam induced deposition of silicon oxide

This paper concentrates on focused electron beam induced deposition of silicon oxide. Silicon oxide pillars are written using 2, 4, 6, 8, 10-pentamethyl-cyclopenta-siloxane (PMCPS) as precursor. It is observed that branching of the pillar occurs above a minimum pillar height. The branching is attributed to charging of the deposit by the electron beam. The branching can be suppressed by introducing water into the chamber together with PMCPS. At the same time, the cointroduction of water results in a higher growth rate, which is found to be specific to PMCPS.

The role of electron-stimulated desorption in focused electron beam induced deposition

<p>We present the results of our study about the deposition rate of focused electron beam induced processing (FEBIP) as a function of the substrate temperature with the substrate being an electron-transparent amorphous carbon membrane. When W(CO)(6) is used as a precursor it is observed that the growth rate is lower at higher substrate temperatures. From Arrhenius plots we calculated the activation energy for desorption, E-des, of W(CO)(6). We found an average value for E-des of 20.3 kJ or 0.21 eV, which is 2.5-3.0 times lower than literature values. This difference between estimates for E-des from FEBIP experiments compared to literature values is consistent with earlier findings by other authors. The discrepancy is attributed to electron-stimulated desorption, which is known to occur during electron irradiation. The data suggest that, of the W(CO)(6) molecules that are affected by the electron irradiation, the majority desorbs from the surface rather than dissociates to contribute to the deposit. It is important to take this into account during FEBIP experiments, for instance when determining fundamental process parameters such as the activation energy for desorption.</p>

Acetone and the precursor ligand acetylacetone: distinctly different electron beam induced decomposition?

In focused electron beam induced deposition (FEBID) acetylacetone plays a role as a ligand in metal acetylacetonate complexes. As part of a larger effort to understand the chemical processes in FEBID, the electron-induced reactions of acetylacetone were studied both in condensed layers and in the gas phase and compared to those of acetone. X-ray photoelectron spectroscopy (XPS) shows that the electron-induced decomposition of condensed acetone layers yields a non-volatile hydrocarbon residue while electron irradiation of acetylacetone films produces a non-volatile residue that contains not only much larger amounts of carbon but also significant amounts of oxygen. Electron-stimulated desorption (ESD) and thermal desorption spectrometry (TDS) measurements reveal striking differences in the decay kinetics of the layers. In particular, intact acetylacetone suppresses the desorption of volatile products. Gas-phase studies of dissociative electron attachment and electron impact ionization suggest that this effect cannot be traced back to differences in the initial fragmentation reactions of the isolated molecules but is due to subsequent dissociation processes and to an efficient reaction of released methyl radicals with adjacent acetylacetone molecules. These results could explain the incorporation of large amounts of ligand material in deposits fabricated by FEBID processes using acetylacetonate complexes

Ultrahigh resolution focused electron beam induced processing: the effect of substrate thickness

van Dorp WF, Laczic I, Beyer A, et al. Ultrahigh resolution focused electron beam induced processing: the effect of substrate thickness. Nanotechnology. 2011;22(11): 115303

Area-selective atomic layer deposition of Ru on electron-beam-written Pt(C) patterns versus SiO2 substratum

Area selectivity is an emerging sub-topic in the field of atomic layer deposition (ALD), which employs opposite nucleation phenomena to distinct heterogeneous starting materials on a surface. In this paper, we intend to grow Ru exclusively on locally pre-defined Pt patterns, while keeping a SiO2 substratum free from any deposition. In a first step, we study in detail the Ru ALD nucleation on SiO2 and clarify the impact of the set-point temperature. An initial incubation period with actually no growth was revealed before a formation of minor, isolated RuO x islands; clearly no continuous Ru layer formed on SiO2. A lower temperature was beneficial in facilitating a longer incubation and consequently a wider window for (inherent) selectivity. In a second step, we write C-rich Pt micro-patterns on SiO2 by focused electron-beam-induced deposition (FEBID), varying the number of FEBID scans at two electron beam acceleration voltages. Subsequently, the localized Pt(C) deposits are pre-cleaned in O2 and overgrown by Ru ALD. Already sub-nanometer-thin Pt(C) patterns, which were supposedly purified into some form of Pt(O x ), acted as very effective activation for the locally restricted, thus area-selective ALD growth of a pure, continuous Ru covering, whereas the SiO2 substratum sufficiently inhibited towards no growth. FEBID at lower electron energy reduced unwanted stray deposition and achieved well-resolved pattern features. We access the nucleation phenomena by utilizing a hybrid metrology approach, which uniquely combines in-situ real-time spectroscopic ellipsometry, in-vacuo x-ray photoelectron spectroscopy, ex-situ high-resolution scanning electron microscopy, and mapping energy-dispersive x-ray spectroscopy