Marion Geidel

Barrier performance optimization of atomic layer deposited diffusion barriers for organic light emitting diodes using x-ray reflectivity investigations

The importance of O3 pulse duration for encapsulation of organic light emitting diodes (OLEDs) with ultra thin inorganic atomic layer deposited Al2O3 layers is demonstrated for deposition temperatures of 50 °C. X-ray reflectivity (XRR) measurements show that O3 pulse durations longer than 15 s produce dense and thin Al2O3 layers. Correspondingly, black spot growth is not observed in OLEDs encapsulated with such layers during 91 days of aging under ambient conditions. This implies that XRR can be used as a tool for process optimization of OLED encapsulation layers leading to devices with long lifetimes.

Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions

Germanium is a promising material for future very large scale integration transistors, due to its superior hole mobility. However, germanium-based devices typically suffer from high reverse junction leakage due to the low band-gap energy of 0.66 eV and therefore are characterized by high static power dissipation. In this paper, we experimentally demonstrate a solution to suppress the off-state leakage in germanium nanowire Schottky barrier transistors. Thereto, a device layout with two independent gates is used to induce an additional energy barrier to the channel that blocks the undesired carrier type. In addition, the polarity of the same doping-free device can be dynamically switched between p- and n-type. The shown germanium nanowire approach is able to outperform previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents. The dielectric and Schottky barrier interface properties of the device are analyzed in detail. Finite-element drift-diffusion simulations reveal that both leakage current suppression and polarity control can also be achieved at highly scaled geometries, providing solutions for future energy-efficient systems.

Investigations on Ru-Mn films as plateable Cu diffusion barriers

In this study Ru-Mn alloys are discussed in terms of some of the major questions that are typically associated with the development of new types of barriers. First, the Cu diffusion barrier performance after annealing at high temperatures and under subsequent bias temperature stress is investigated, on SiO2 and on low-k dielectrics. Second, the origin of the barrier performance - either a self forming barrier caused by segregation of an alloyed element, or the stuffing of grain boundaries - is investigated, since this is of importance with regard to an electromigration barrier at the bottom of a via. Third, Cu plating and Cu adhesion behavior are addressed, since they are also important with regard to electromigration, specifically along the side walls of trenches. Fourth, the blocking of oxygen diffusion is investigated. Furthermore, down-scaling of the Mn content to a lowest possible level is pursued in order to reduce line and via resistances.

Molecular beam deposited zirconium dioxide as a high-κ dielectric for future GaN based power devices

Molecular beam deposited zirconium dioxide (ZrO2) was assessed as high-κ gate dielectric for future GaN based devices. To compare and study electrical and structural properties, thin ZrO2 films were deposited on three different substrates, n++-c-plane GaN, p-(100) Si, and TiN. The films were fabricated by electron beam evaporation from a single stoichiometric ZrO2 target. A substrate-independent phase transition from amorphous ZrO2 to the tetragonal/cubic phase was identified by gracing incidence x-ray diffractometry. Finally, monoclinic ZrO2 emerged with increasing film thickness. As found by x-ray photoelectron spectroscopy, ZrO2 formed an abrupt interface to both GaN and TiN without intermixture. Dielectric constants in the range of 14–25 were extracted from capacitance versus voltage measurements for as-deposited ZrO2 films. The leakage currents of ZrO2 on GaN resembled their counterparts on Si as well as on TiN.

Monitoring atomic layer deposition processes in situ and in real-time by spectroscopic ellipsometry

Depositing ultra-thin metallic films with an accurate control of the film properties (like film thickness, surface roughness and electrical properties) both in the initial and in the progressed film growth regime is a critical challenge. Monitoring atomic layer deposition processes by spectroscopic ellipsometry allows film thickness control in the sub-nanometer range. In addition, ellipsometry serves as a powerful technique for process analysis as it covers many relevant issues, like the evaluation of substrate temperatures as well as the quantification of film properties during the entire ALD process (i. e. in all relevant growth regimes).

In situ XPS investigation of the chemical surface composition during the ALD of ultra-thin aluminum oxide films

Atomic layer deposition (ALD) is the most advanced technique for the fabrication of ultra-thin conformal films. To yield high quality films, the knowledge of chemical reactions and interactions between the substrate surface and the precursors is becoming increasingly important, especially within the very first ALD cycles. In this work, the ALD process of aluminum oxide with trimethylaluminum (TMA) and water is studied by using X-ray photoelectron spectroscopy (XPS) without vacuum break. This allows the investigation of the initial gaseous-solid-reactions, i. e. the chemisorption mechanism of the precursor molecules, with sub-monolayer resolution. The results show the ligand exchange during the ALD reactions and the dependence of the growth mode on the presence of hydroxyl groups and oxygen as adsorption sites on the substrate surface.

Cu passivation with self-assembled monolayers for direct metal bonding in 3D integration

Direct metal bonding is a preferred fine-pitch technology for stacking of Si dies in 3D integration. Cu is a metal of choice for direct metal bonding because it is the most common metal for redistribution layer in advanced semiconductor manufacturing, Cu has high conductivity and it is a low cost candidate. However Cu oxidises very fast in air which makes the bonding procedure challenging. In this study we present the novel technique of Cu passivation with temporary protective self-assembled monolayer (SAM). X-ray photoelectron spectroscopy (XPS) analysis was used in order to carry out the chemical analysis of the Cu surface. Contact angle (CA) measurements provided the information about the monolayer formation. The influence of immersion time and storage conditions on the SAM passivation quality was examined. Storage of a coated Cu surface at low-temperature air conditions was found to be a promising technique for a long-term oxidation retarding. We summarize the key substrate parameters that influence SAM protective capability.

Characterisation of Cu/Cu bonding using self-assembled monolayer

Purpose Cu/Cu diffusion bonding is characterised by high electrical and thermal conductivity, as well as the mechanical strength of the interconnects. But despite a number of advantages, Cu oxidises readily upon exposure to air. To break through the adsorbed oxide-layer high temperature and pressure, long bonding time and inert gas atmosphere are required during the bonding process. This paper aims to present the implementation of an organic self-assembled monolayer (SAM) as a temporary protective coating that inhibits Cu oxidation. Design/methodology/approach Information concerning elemental composition of the Cu surface has been yielded by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy. Two types of substrates (electroplated and sputtered Cu) are prepared for thermocompression bonding in two different ways. In the first case, Cu is cleaned with dilute sulphuric acid to remove native copper oxide. In the second case, passivation with SAM followed the cleaning step with dilute sulphuric acid. Shear strength, fracture surface, microstructure of the received Cu/Cu interconnects are investigated after the bonding procedure. Findings The XPS method revealed that SAM can retard Cu from oxidation on air for at least 12 h. SAM passivation on the substrates with sputtered Cu appears to have better quality than on the electroplated ones. This derives from the results of the shear strength tests and scanning electron microscopy (SEM) imaging of Cu/Cu interconnects cross sections. SAM passivation improved the bonding quality of the interconnects with sputtered Cu in comparison to the cleaned samples without passivation. Originality/value The Cu/Cu bonding procedure was optimised by a novel preparation method using SAMs which enables storage and bonding of Si-dies with Cu microbumps at air conditions while remaining a good-quality interconnect. The passivation revealed to be advantageous for the smooth surfaces. SEM and shear strength tests showed improved bonding quality for the passivated bottom dies with sputtered Cu in comparison to the samples without SAM.

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.