TFTs as photodetectors for optical interconnects

In this work we are looking at the prospect of using poly-silicon based Thin Film Transistors (TFTs) as photodetectors for optical interconnects that can detect light effectively at 1100nm wavelength from silicon based Light Emitting Diodes (LEDs). These TFTs were fabricated from laser crystallized silicon and were characterized under darkness and illumination. The photosensitivities of these devices were limited due to the presence of aluminium as their gate electrode but have shown us the possibility of a new approach to photodetection

Growth and properties of subnanometer thin titanium nitride films

This research brings new insights into the relation between properties of ultra-thin conductive metal nitrides made by atomic layer deposition (ALD) and their possible industrial applications. The advantage of conductive nitrides over pure metals is (i) better established ALD processes allowing depositing high-quality films and (ii) the presence of nitrogen as an extra tool to manipulate the electron transport properties. In this work, we study titanium nitride (TiN) films with the aim to investigate the growth mechanism in combination with physical and electrical properties as a function of the layer thickness. In microelectronic devices, thin continuous TiN films are commonly used as diffusion barriers and metal gate material. Scaling electronic devices to nanometer dimensions requires a close look at electrical material properties as ultra-thin conductive materials encounter an insulating regime due to the depletion of carriers

Electrical characterization of hot-wire assisted atomic layer deposited Tungsten films

In this work, we applied conventional Van der Pauw and circular transmission line method (CTLM) test structures to determine the sheet and contact resistance of ultra-thin (1-10 nm) tungsten films grown by Hot Wire assisted Atomic Layer Deposition, as well as their temperature coefficient of resistance (TCR). We finally explored the field effect (FE) in these layers

Area-Selective Low-Pressure Thermal Atomic Layer Deposition of Aluminum Nitride

This work demonstrates intrinsic area-selective deposition of AlN films by thermal atomic layer deposition (ALD). Using sequential pulses of trimethylaluminum and NH3 at a substrate temperature of 623 K, polycrystalline AlN was selectively formed on a thin layer of sputtered AlN that was patterned on thermal SiO2 grown on Si substrates. A pretreatment to remove native AlOxNy facilitated the selective growth of ALD-AlN. Transmission electron microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and atomic force microscopy examined the interfaces and layer thickness. As reported in this article, the deposition of AlN exhibits intrinsic selectivity, a trait that can be exploited to grow other III-nitrides selectively, such as GaN.</p

Effects of Oxygen, Nitrogen and Fluorine on the Crystallinity of Tungsten by Hot-Wire Assisted ALD

A heated tungsten filament (wire) is well known to generate atomic hydrogen (at-H) by catalytically cracking molecular hydrogen (H2) upon contact. This mechanism is employed in our work on hot-wire (HW) assisted atomic layer deposition (HWALD), a novel energy-enhancement technique. HWALD has been successfully utilized to deposit tungsten (W) films using alternating pulses of WF6 and at-H. Depending on the conditions, either low-resistivity α- or higher-resistivity β-crystalline phases of W can be obtained. This work aims to clarify (i) which factors are decisive for the formed crystal phase and (ii) the role of the residual gases in the film growth mechanism. In this light, the effects of adding impurities (N2O, O2, NH3 and H2O) were investigated. Oxidizing species have a retarding effect on W growth but the process can be re-initiated after stopping their supply. In contrast, nitridizing species have a permanent inhibition effect. Further, the effects of WF6 overdose were studied. The surplus of WF6 appeared to be crucial for the process: in many cases this led to the formation of β-phase W instead of the α-phase, with a memory effect lasting for several deposition runs. Extra fluorine-containing species were thus identified as the likely cause of β-phase formation

Hot-Wire Assisted ALD: A Study Powered by In Situ Spectroscopic Ellipsometry

Hot-wire assisted atomic layer deposition (HWALD) is a novel energy-enhancement technique. HWALD enables formation of reactive species (radicals) at low substrate temperatures, without the generation of energetic ions and UV photons as by plasma. This approach employs a hot wire (tungsten filament) that is heated up to a temperature in the range of 1300–2000 °C to dissociate precursor molecules. HWALD has the potential to overcome certain limitations of plasma-assisted processes. This work investigates the ability of a heated tungsten filament to catalytically crack molecular hydrogen or ammonia into atomic hydrogen and nitrogen-containing radicals. The generation of these radicals and their successful delivery to the wafer (substrate) surface are experimentally confirmed by dedicated tellurium-etching and silicon-nitridation experiments. It further reports on deposition of low-resistivity oxygen-free tungsten films by using HWALD, as well as on the effect of hot-wire-generated nitrogen radicals and atomic hydrogen in deposition of aluminum nitride and boron nitride films. In parallel, this work provides important illustrative examples of using in situ real-time monitoring of deposition and etching processes, together with extracting a variety of film properties, by spectroscopic ellipsometry technique