Elena comprises 15 Early Stage Researchers, which all pursue individual PhD projects;
Objectives: The current project aims to establish branching ratios and cross sections for low energy electron induced fragmentation of selected FEBID precursor molecules in the gas phase. The target molecules will be gold complexes delivered by our collaborators. The reactions of these molecules with low energy electrons will be studied in the gas phase through sublimation into HV where they are exposed to low energy electrons generated by a throchoidal monochromator (TEM) in a crossed beam instrument and the influence of incident electron energy on fragmentation is studied by mass spectrometry. The ligand structure of these Au containing complexes will be chosen with regards to their expected susceptibility to the different low energy induced dissociation processes. The energy range explored will be 0-150 eV with an achievable energy resolution < 100 meV.
Our main objective is to help establish a fundamental understanding of the mechanisms behind FEBID, especially the role of low energy (0-50 eV) secondary electrons. In the long run we expect this understanding, in conjunction with surface experiments conducted by participants (UBre, CNRS, JH) and actual FEBID experiments through e.g. participants (EMPA, UErl, TUD), to contribute to rational design of superior FEBID precursors suitable for testing under processing conditions (Tescan, Zeiss, PhW). Long-term objective is to use new chemical and physical insights into FEBID to realize its technical and economical potential as commercial nanofabrication method.
The ESR will have training in state of the art techniques to study electron-molecule interactions and in supporting structural and dynamics calculations carried out in collaboration with Dr. Ragnar Björnsson at UIce.
Objectives: The current project aims to establish gas phase branching ratios and cross sections for low energy electron induced fragmentation of monomer units from typical EUVL resist polymers. The reactions of resist molecules with low energy electrons will be studied in the gas phase through sublimation into high vacuum where they are exposed to low energy electrons generated by a trochoidal electron monochromator and the influence of incident electron energy on fragmentation is studied by means of mass spectrometry. Special emphasis will be on halogenated, derivatives to study possible means of activating local radical reactions in such resist materials. The energy range explored will be 0-150 eV with an achievable resolution better than 100 meV.
Our main objective is to aid the possible utilization of low energy (0-50 eV) secondary electrons in EUVL to induce controlled chemistry in the resist material. The ESR will be trained in state of the art techniques to study electron-molecule interactions. Under the hands on supervision of a research associate ESR2 will also adapt a supporting structural and dynamics calculations carried out in collaboration with Dr. Ragnar Björnsson at UIce.
Expected Results: Absolute cross sections for dissociative electron attachment and dissociative ionization, and qualitative assessment of neutral dissociation of a set of native and halogenated monomers from polymer components of potential, EUVL resist material (energy range from 0-100) eV).
The fabrication of nanostructures by FEBID and EUV lithography is based on common principles. This concerns not only the fact that in both processes low-energy electron play a major role in initiating chemical reaction that will yield the desired structures. They are released in FEBID as secondary electrons by scattering of the impinging high energy electron beam and in EUVL as photoelectrons resulting from absorption of an EUV photon. As another factor, similar chemical species produced from the initial electron interactions in a FEBID precursor or EUVL resist trigger or assist subsequent reactions. These processes need to be understood to achieve better control over nanostructure formation in both FEBID and EUVL. As an example, reactive species or sites produced on surfaces under the effect of an electron beam may trigger the autocatalytic decomposition of specific FEBID precursors. This effect is exploited as electron beam induced surface activation (EBISA) to predefine with the electron beam surface areas where a deposit will growth will occur.
This project investigates the fundamental chemical processes initiated in molecular layers or coordination polymers grown on surfaces. The results will provide insight in how the chemical species produced under the effect of the impinging radiation contribute to or assist in the formation of nanostructures. This is complemented by studies of model systems in the gas phase as well as applications in FEBID technology performed during the secondments.
"The current project exploits the novel experimental technique of Velocity Map Imaging (VMI) to explore the dissociation dynamics of FEBID and EUVL precursor molecules. The host group has been at the forefront of developing VMI from its study of photon-induced processes to authoritative studies of DEA. In DEA anionic products are identified and their routes of formation and branching ratios characterised. The method has recently been extended to higher energies to explore the previously little studies process of Dipolar Dissociation revealing new fragmentation pathways."
Objectives: Secondary electrons generated through the ionization of a polymer play a major role in the sensitization in EUV resists. This means that the absorption strength of EUV resists should be optimized by an adjustment of the polymer absorption coefficient. Even though oxide nanoparticles have already been proven to enhance mechanical properties towards etching process, i.e. etch resistence, the use of well-defined organometallic building blocks of a specific size (clusters of approx. 1.5 nm diameter) and functionalised surfaces is not well established. In resist formulations for Extreme UV Lithography (EUVL), homogeneously dispersible clusters with functional groups as small inorganic building blocks should enhance the etch resistance and the resolution as well as the line etch roughness. We envision the incorporation of metal oxide clusters (mainly zirconium-based) with 4-8 metal atoms per cluster and variable number of cross-linkable ligands in a monomer matrix, which enables the resist materials to form a rigidified structure and therefore become relatively difficult to be dissolved by most of the solvents. The incorporation of such entities in resists will not only increase the refractive index, but also allows controlling the number of crosslinking ligands coordinated to this metal-oxo cluster. Such cluster reinforced hybrid materials are well known in sol-gel and polymer chemistry, however resists containing these building blocks have been neglected to date. The clusters will be characterised by state of the art NMR, IR and X-ray techniques as well as thermogravimetry (TGA) to gain information about the outgassing of the coatings, which will have large impact on their use in EUVL under vacuum conditions. Spin and dip coating of the resists will be performed and the resulting films characterised to tailor the coating thickness. The ESR will be trained in organometallic chemistry under inert atmospheres (e.g. argon and nitrogen), basic polymer chemistry as well as coating techniques to achieve the optimal resist design. Expected Results: New resist formulations containing metal-oxo-based clusters for optimised formulation in inorganic-organic hybrid resists in respect to line edge roughness, etch resistance and resolution. Understanding of the interactions within such resist films and evaluation of commercial suitability of such resists containing inorganic clusters with defined branching sites and refractive indices.
Objectives: We will use a focused electron beam in combination with certain precursor molecules for the controlled fabrication of nanostructures as a part of focused electron beam induced deposition (FEBID) technique. In a more vivid picture, one might think of the electron beam as a pen and the precursor molecules as ink to write nanostructures. The basis of the targeted investigations is the electron beam induced surface activation (EBISA) a novel FEBID method. Thereby, a highly focused electron beam of a scanning electron microscope (SEM) is used to directly modify the substrate itself without the presence of precursor molecules, then the surface is exposed to precursor molecules which catalytically decompose at the pre-irradiated areas for the formation of a nanoscaled deposit in our unique ultra-high vacuum (UHV) system. The systematic variation of experimental parameters and comparison the experimental results with high quality simulations allows for a detailed insight into the role of scattered electrons in solids such as forward scattered or backscattered electrons. The investigations will comprise detailed high resolution microscopic (STM, SEM, HRTEM) and spectromicroscopic (AES, SAM) characterization of the electron beam irradiated substrates and the initial states of electron beam induced deposition. The main objective of the study is to gain detailed understanding of the physics and chemistry involved in FEBID processes with the aim to improve the fabrication of the nanoscaled deposits. Expected Results: We expect to gain new insights into the nature of electron scattering in the substrate (proximity effects!) via the EBISA method. Furthermore, we anticipate learning how to use our knowledge to improve the fabrication of nanostructure.
The project aims at understanding the EBID process, the effect of various parameters on the growth, having a good control over the deposition and achieving a reproducible growth process at the highest possible resolution. This allows to use EBID for reliable fabrication of nano-structures and nano-devices and can also be complementary with other existing lithography processes. Several metrology tools will be used to measure and characterize the shapes of the deposits. Deposition of 3D structures will be investigated as well. Various novel precursors will be tested, some of which will be synthesized by other ELENA partners or ESRs, to find precursors with better deposition properties such as growth rates and purity. During a secondment at Phenom World, instrumentation will be developed to introduce EBID into their microscopes and the merits of this will be investigated.
Focused Electron Beam Induced Deposition (FEBID) is a novel and promising method of printing three-dimensional structures at nanometer scale. It allows to directly manufacturing objects in nearly every desired shape, using a variety of materials. Although its advantages, there are still many challenges and unanswered questions regarding creating of high shape- fidelity and pure nanostructures. One of the most important is to design a proper precursor, which not only allows us to grow pure metal 3D-objects, but also will be stable in vacuum and volatile at room or moderately elevated temperature. The typical FEBID precursor molecule contains a central metal atom surrounded by non-metallic (in most cases organic) ligands. As the electron induced dissociation of molecules is not selective, the ligands can also be dissociated and incorporated into deposit causing impurities in the grown structures.
My studies will uncover electron induced surface processes occurring during e-beam induced deposition with various novel precursor classes. The focus is mostly on molecules containing gold, silver, and ruthenium coordinated with NHC- halogene, fluorinated and non-fluorinated carboxylate, and allyl-carbonyl halogene complexes. The control of FEBID material purity by electron irradiation dose rate and through substrate temperature variation will be studied using chemical and electrical analysis. By tuning deposition process parameters, we want to achieve fully 3 dimensional deposits with different metal to non-metallic matrix ratios. The thorough investigation of deposited material composition and internal structure will enable us to fundamentally investigate the role of incomplete dissociation vs. ligand co-deposition pathways of adsorbed molecules and to expand existing FEBID models.
EUV lithography, which is still in the research phase, is deemed to be the future of the semiconductor industry. However, as we reduce the wavelength to 13.5 nm, the energy of the photons becomes so high, that we move from excitation chemistry (in DUV lithography) to radiation chemistry (in EUV lithography). This changes the chemical interactions happening between the photons and the photoresist. The obscure change in the chemistry results in the underperformance of the currently available state-of-the-art photoresists. The major problem associated with the current systems of EUV resist is something known as RLS tradeoff. R stands for the resolution, which is the smallest feature size that can be printed using that material. L stands for line-edge-roughness, which is the deviation of line-space feature from an ideal smooth shape. And S stands for sensitivity, which is the minimum exposure dose required to reach the resolution. It is proving to be impossible to improve two of the parameters without exacerbating the third (hence, a trade-off). This RLS trade-off is caused due to chemical variability at nanoscale level. Only through the fundamental understanding of the chemistry of the process, it will be possible to produce robust photoresist systems that can work efficiently for EUV lithography. The objective of this research project is to bridge this understanding. The approach of this project is a combination of two ways: 1) To enhance our knowledge of fundamental chemistry happening at the nanoscale level during EUV-patterning (through fundamental experiments such as solid- and gas-phase reactions) and 2) To use that understanding to design and characterize novel and robust EUV photoresists systems (through understanding synthesis of novel EUV systems, EUV patterning using NXE scanner, CD-SEM analysis and RLS characterization). Expected results from the project is to get a better understanding of the fundamental chemistry and correlating that to the critical parameters of novel EUV resist systems.
The project aims to give fundamental and detailed answers to the question of how novel precursors (i.e., a chemical compound containing metal atoms, brought to the gas phase) can be used in order to create nanostructures in the 3D domain by means of electron irradiation. Starting from rather simple structures, the project will elucidate the physical mechanisms decisive for creating reproducible arbitrary complex structures and the obstacles which have to be overcome in order to create such structures. The deposited 3D nanostructures are furthermore studied for their optimum deposition parameters (e.g., beam energy, beam current) and the performance and quality of the deposited structure (e.g., growth rate, material composition, shape fidelity) as well as processing influences. These findings will then be used to generalise the deposition procedure in such a fashion that any arbitrary precursor can be employed to generate any arbitrary 3D nanostructure. Expected Results: A set of optimized parameters for deposition of each tested FEBID precursor; Automated procedures for depositing nanostructures using a focused electron beam; An established relation between material composition of the nanostructures and FEBID deposition parameters.
For lithography processes in the semiconductor production, photomasks, opaque plates with transparent regions, are used to create defined patterns on wafers. Their tremendous production cost in case of high-end masks makes it mandatory to optimize their fabrication by repairing their defects.
EUV photomask repair
For EUV lithography a new classe of mask with smaller structures enter the stage, that drives mask complexity and cost. In order to achieve a high mask repair yield, the nanometer-accurate removal of undesired and deposition of missing material by etching and depositing, respectively, is essential. For this, focused electron beam induced etching and deposition is applied in order to correct the pattern on masks. Critical performance indicators for a successful repair application are for example processing resolution, minimum repairable feature size and optical CD ("critical dimension") variations.
The main goal of this research is to gain insight on the physical and chemical mechanisms governing focused electron beam induced processes and so derive key parameters to control and optimize the mask repair performance. This includes the investigation of new precursors and process parameters related to the electon beam.