J. M. Howard

Interfacial layer formation during high-temperature annealing of ZrO2 thin films on Si

High-k materials deposited directly on silicon exhibit an interfacial layer between the grown layer and the underlying substrate. This is of particular concern in metal–oxide–semiconductor technologies where these layers have a deleterious effect on the overall capacitance of the resulting devices. In this letter, the growth and properties of this silicatelike interfacial layer are examined after postdeposition anneals in a vacuum, inert, and oxidizing atmospheres. X-ray reflectivity, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy have been used to characterize the growth and properties of this interfacial layer.

Enhanced electrical properties of Ba0.5Sr0.5TiO3 thin films grown by ultraviolet-assisted pulsed-laser deposition

In this letter, we report enhanced electrical performance of high-dielectric-constant barium strontium titanate (BST) thin films grown by an in situ ultraviolet (UV)-assisted pulsed-laser deposition (UVPLD) technique. In comparison with conventional pulsed-laser deposition (PLD) BST (i.e., films grown under similar conditions but without UV illumination) and films grown by other techniques, the UVPLD-grown films exhibited improved structural and electrical properties. The dielectric constant of 40-nm-thick films deposited at 650 °C by PLD and UVPLD were determined to be 172 and 281, respectively. The density of interface states at the flat-band voltage was found to be approximately 5.6×1011 eV−1 cm−2 for the UVPLD-grown BST films, which was almost an order of magnitude lower than that obtained for conventional PLD films. The leakage current density of the UVPLD-grown films was approximately 4×10−8 A/cm2 at 100 kV/cm, which was nearly 1.5 times lower than that obtained from the PLD deposited films. The equ...

Low-temperature growth of high-k thin films by ultraviolet-assisted pulsed laser deposition

Thin Y2O3 films have been grown on (100) Si using an in-situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique. When compared to conventional pulsed laser deposited (PLD) films under similar conditions, the UVPLD-grown films exhibited better structural and optical properties, especially those grown at lower substrate temperatures, from 200 °C to 400 °C. X-ray diffraction investigations showed that the films grown were highly crystalline and textured. According to X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry investigations, UVPLD-grown Y2O3 films have a better overall stoichiometry and contain less physisorbed oxygen than the conventional PLD-grown films. The refractive index values, measured in the range 300–750 nm by using variable-angle spectroscopic ellipsometry, were similar to those of a reference Y2O3 film.

Effect of silicon pre-nitridation on the formation of the interfacial layer during pulsed laser deposition of thin dielectric oxide films

Abstract Thin high- k dielectric Y 2 O 3 and ZrO 2 films were grown directly on Si by the pulsed laser deposition (PLD) technique. The interfacial layer formed between the Si and the deposited oxide film was characterized. Since this layer has a detrimental effect on the MOS capacitance of the films, an attempt to modify its characteristics was performed through UV-assisted low-temperature nitridation of the surface to create a barrier layer that suppresses Si diffusion through the interface. It was confirmed by structural characterization that this surface pretreatment results in a thinner interfacial layer.

Oxygen trapping during pulsed laser deposition of oxide films

Abstract Ba0.5Sr0.5TiO3, indium tin oxide (ITO), ZnO, and ZrO2 thin films were grown directly on Si substrates by the pulsed laser deposition technique. X-ray photoelectron spectroscopy investigations showed that these films contain oxygen species that are loosely bound, corresponding to what can be described as physisorbed oxygen. This oxygen is responsible for the formation of an interfacial layer at the interface between the Si substrate and the deposited oxide layer during the deposition process. The chemical composition of this interfacial layer consists of SiOx partially mixed with the grown oxide. The trapped oxygen can ensure further growth of the interfacial layer during any post-deposition anneals even when performed in vacuum or inert atmospheres.

Pulsed laser deposition of Y2O3 on Si: characteristics of the interfacial layer

Thin Y2O3 films were directly grown on (100) Si substrates by the pulsed laser deposition technique. It has been found by high resolution cross-section transmission electron microscopy, x-ray reflectometry and x-ray photoelectron spectroscopy (XPS) that at the interface between Si and the grown layer, an interfacial layer always formed. Depth-profiling and angle-resolved XPS investigations showed that this layer consists of a mixture of substoichiometric SiOx(x<2) and the deposited Y2O3 layer, without forming an yttrium silicate. The thickness of this interfacial layer depended on the oxygen pressure and temperature used during the deposition. The main oxygen source for its formation is the physiosorbed oxygen which is trapped inside the grown layer during the laser ablation process. When the thickness of this low-k SiOx was reduced by decreasing the oxygen pressure during laser ablation below the optimum value, a marked degradation of the electrical properties of the structure was noticed.

Characterization of the interfacial layer formed during pulsed laser deposition of oxides on Si

Medium-k dielectric Y 2 O 3 films were directly grown on (100) Si substrates by the pulsed laser deposition (PLD) technique. X-ray photoelectron spectroscopy, variable angle spectroscopic ellipsometry, current-voltage, capacitance-voltage, and high-resolution transmission electron microscopy were used to investigate the composition, thickness, and electrical properties of the grown structures. It has been found that at the interface between the Si substrate and the grown dielectric layer, a SiO x interfacial layer, whose thickness depended on the oxygen pressure used during the PLD growth, was always formed. The main oxygen source for this interfacial layer formation is the physisorbed oxygen trapped inside the grown layer during the laser ablation-deposition process. When trying to reduce the thickness of this low-k interfacial layer by decreasing the oxygen pressure during laser ablation, a marked degradation of the electrical properties of the structures was noticed.

ZrC Thin Films Grown by Pulsed Laser Deposition

ZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique. X- ray photoelectron spectroscopy, x-ray diffraction and reflectivity, variable angle spectroscopic ellipsometry, and four point probe measurements were used to investigate the composition, density, thickness, surface morphology, optical and electrical properties of the grown structures. It has been found that crystalline films could be grown only by using fluences above 6 J/cm 2 and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm 2 and a substrate temperature of 700 °C, highly (100)-textured ZrC films exhibiting a cubic structure (a=0.469 nm) and a density of 6.7 g/cm 3 were deposited. The use of a low-pressure atmosphere of C 2 H 2 had a beneficial effect on crystallinity and stoichiometry of the films. All films contained high levels of oxygen contamination, especially in the surface region, because of the rather reactive nature of Zr atoms.

Ultraviolet-assisted pulsed laser deposition: a new technique for the growth of thin oxide films at medium and low temperatures

The crystallinity, stoichiometry and optical and electrical properties of thin Y2O3, ZnO and Ba0.5Sr0.5TiO3 films grown using an in situ ultraviolet (UV)- assisted pulsed laser deposition (UVPLD) technique have been studied. With respect to films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD grown films exhibited better quality, especially for lower substrate temperatures. They also contained less physisorbed oxygen than the conventional PLD grown layers. These improvements can be explained by the action of several factors. Firstly, deep UV photons and ozone ensure a better in situ cleaning of the substrate. Secondly, the presence during the ablation-growth process of more reactive gaseous species like ozone and atomic oxygen formed by photodissociation of molecular O2 promotes the oxygenation of the films. Thirdly, absorption of UV photons by adatoms could result in an increased surface mobility. All these factors have a beneficial effect upon crystalline growth, especially for moderate substrate temperatures, where the thermal energy available for the process is rather limited.

Application of ultraviolet radiation to minimize interfacial layer formation during the growth of alternate high-k gate dielectrics on Si

Yttrium oxide and barium strontium titanate (BST) thin films were grown directly on Si substrates by the pulsed laser deposition (PLD) technique. Because the optimum oxygen pressure during PLD process is of the order of 10 mTorr, some of the oxygen atoms are trapped inside the grown films and contribute to the growth of a silicon oxide interfacial layer. The use of an UV source during the growth resulted in the reduction of the optimum oxygen pressure and, as a consequence, the amount of trapped oxygen and thickness of the interfacial layer. In addition to that, UV radiation influenced the film morphologies and electrical properties. A further reduction of the interfacial layer was obtained on substrates that were exposed prior to deposition to NH 3 for short periods of time under UV radiation.