S. Moisa

Physical and Electrical Characterization of ZrO2 Gate Insulators Deposited on Si(100) Using Zr ( O i ­ Pr ) 2 ( thd ) 2 and O 2

The characteristics of ultrathin ZrO 2 films deposited using molecular oxygen and the zirconium precursor Zr(O i - Pr) 2 (thd) 2 [where O i -Pr is isopropoxide and thd is 2,2,6,6-tetramethyl-3,5-heptanedionate] were investigated. The organometallic was dissolved as a 0.15 M solution in octane and introduced into the deposition chamber using a liquid injection system. The deposition rate was insensitive to molecular oxygen flow but changed with liquid injection rate and was thermally activated in the range 390-550°C. No evidence of Zr-C and Zr-Si bonds were found in the X-ray photoelectron spectroscopy (XPS), spectra, and carbon concentrations, <0.1 atom %, the detection limit of the XPS depth profiling measurements, were obtained at the lowest deposition temperatures and deposition rates. High-resolution transmission electron microscopy showed the ZrO 2 films to be polycrystalline as deposited, with an amorphous zirconium silicate interfacial layer. The effects of postdeposition annealing were also demonstrated. After proper annealing treatments, promising capacitance-voltage and current-voltage characteristics were achieved. A film with an equivalent oxide thickness of 2.3 nm showed current reductions of approximately two orders of magnitude when compared to SiO 2 , but some improvements are required if these films are to be used as a gale-insulator beyond the 100 nm CMOS (complementary metal oxide semiconductor) technology node.

Composition and growth of thin anodic oxides formed on InP (100)

Thin anodic oxides ( < 100 A) were formed on p-InP (100) in phosphate solution (0.3 M NH 4 H 2 PO 4 ) and in sodium tungstate solution (0.1 M Na 2 WO 4 , 2H 2 O) at different temperatures (25 and 80°C) and potentials (1 8 V). Thickness and composition were determined by different surface-analytical techniques including Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. In general, it has been observed that double-layered films are obtained with an outer In-rich layer. The thickness of the outer layer, oxide morphology and roughness as well as the composition of the duplex structure are strongly dependent on the temperature and the composition of the electrolyte. It has been found that oxides formed in phosphate exhibit a higher stability against dissolution compared with oxides formed in tungstate. The latter contain a large amount of In 2 O 3 , which leads to poor electrical properties.

Anodic film growth on InP in sodium tungstate

Abstract Anodic film growth on InP and the wider implications to alloys have been examined, with the aim of probing film composition to gain insight into the ionic transport processes responsible for duplex film formation. For anodizing at relatively high efficiency, the anodic film reveals an outer indium-rich layer, essentially free of phosphorus species, and an inner layer containing both indium and phosphorus species. Growth of such films, on a co-operative transport basis, leading to amorphous film formation, can be explained by the faster outward migration of indium species relative to phosphorus species. The inner layer would then be composed of appropriately arranged In–O and P–O units. However, such an arrangement is difficult to reconcile with the X-ray photoelectron spectroscopy data, which suggest the presence of phosphorus in the form of P 2 O 5 , PO 4 3− , PO 3 − and polyphosphate species. In order to explain fully the transport process for film growth and to understand film composition, further studies using marker and tracer experiments are essential.

Influence of Deuterium and Platinum on the Thermal Oxidation of GaAs

The thermal oxidation of GaAs at 500 degreesC in O-18 labeled O-2 has been studied with gas phase analysis, Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy. The influence of a few hundred atomic parts per million of deuterium in the GaAs substrate and of surface platinum have been evaluated with respect to oxide growth mechanisms and the degree of As buildup. Deuterium increased the transport from the substrate interface of both Ga and As toward the gas interface thereby lowering the degree of preferential Ga oxidation and As buildup at the substrate interface. Platinum, on the other hand, catalyzed the dissociation of the oxygen molecule at the gas interface and thereby facilitated an increased transport of oxygen toward the substrate interface. That results in an increased overall oxidation rate with a high degree of preferential Ga oxidation and concomitant As buildup. When the oxygen pressure was increased from 20 to 720 mbar, a lowered degree of As buildup was observed due to the lower degree of preferential Ga oxidation.

Anodic oxidation of gallium nitride

The anodic oxidation of n-type GaN (carrier concentration 4.6 × 1018 cm−3) under laboratory illumination at a constant current density of 5 mA cm−2 in sodium tungstate electrolyte is examined by high resolution microscopy and surface analysis. The GaN, deposited as a thin layer by molecular beam epitaxy, had an initially faceted surface. Anodic oxidation gives rise to local growth of an amorphous Ga2O3-based reaction product, often, but not exclusively, located in the vicinity of troughs formed by intersecting facets. At these regions dislocations in the GaN intersect the surface. The product is non-uniform in thickness and morphology, with pore-like features. With prolonged anodic treatment, local oxidation progresses as channels, which eventually reach the base of the GaN layer, leaving a porous skeleton. The formation of a uniform and compact film material on GaN is considered to be impeded by generation of nitrogen from the anodic reaction, with the strength of the Ga–N bonding focusing oxidation on regions of increased impurity, non-stoichiometry or defect concentration.

Role of oxygen bubble generation in anodic film growth on InP

The morphologies of barrier-type anodic films grown on InP have been investigated using atomic force microscopy, scanning electron microscopy and transmission electron microscopy in order to gain further understanding of the non-linear voltage–time behaviour and the development of blisters in the films. The films, which are two layered, with an outer layer of In2O3 and an inner phosphorus-rich layer, containing also indium species, were formed at 50 A m−2 in aqueous 0.1 M sodium tungstate electrolyte at 298 K. During the early stages of anodizing, i.e. within the initial region of linear voltage–time response, a relatively compact and uniform film forms, with a comparatively featureless surface. However, as the voltage increases, cavities develop within the film, and in places the anodic film material detaches partially from the substrate. The film surface then discloses fine-textured roughness and coarse protuberances associated with cavity formation and detachment respectively. Such transformation of the film morphology correlates with a decrease in slope of the voltage–time response, which commences at a formation voltage of approximately 17 V, with a film thickness of about 25 nm. The behaviour is explained by generation of oxygen within the anodic film material, which forms high pressure bubbles of gas. Such gas formation is related to the presence of an In2O3 outer layer of the film and the presence of units of In2O3 in the inner layer of the film, which facilitate oxidation of O2− ions of the film material.

Ultrathin Zirconium Silicate Films Deposited on Si(100) Using Zr ( O i ­ Pr ) 2 ( thd ) 2 , Si ( O t ­ Bu ) 2 ( thd ) 2 , and Nitric Oxide

i-Pr)2(tetramethylheptanedione,thd) 2 , Si(O t -Bu)2(thd) 2 and nitric oxide in a pulse-mode metallorganic chemical-vapor deposition apparatus with a liquid injection source. High resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy ~XPS!, and medium energy ion scattering were employed to investigate the structure, surface roughness, chemical state, and composition of the films. The nitric oxide used as oxidizing gas, instead of O2 , not only reduced the thickness of the interfacial layer but also removed the carbon contamination effectively from the bulk of the films. The as-deposited Zr silicate films with a Si:Zr ratio of 1.3:1 were amorphous, with an amorphous interfacial layer 0.3-0.6 nm thick. After a spike anneal in oxygen and a 60 s nitrogen anneal at 850°C, these films remained amorphous throughout without phase separation, but the interfacial layer increased in thickness. No evidence of Zr-C and Zr-Si bonds were found in the films by XPS and carbon concentrations,0.1 atom %, the detection limit, were obtained. The hysteresis, fixed charge density, and leakage current determined from capacitance-voltage analysis improved significantly after postdeposition anneals at 850°C and the films exhibited promising characteristics for deep submicrometer metal-oxidesemiconductor devices.

Composition and Growth of Thermal and Anodic Oxides on InAlP

Abstract Producing insulating layers on III-V semiconductors is crucial for a number of device applications. Al-containing thermal oxides on AlGaAs, InAlAs, and more recently on InAlP have been found to possess good insulating characteristics. This paper presents data on insulating oxides formed on InAlP layers by thermal oxidation at 500°C in moist nitrogen (95°C) or by anodization in sodium tungstate solution. The oxides (20-300nm thick) have been characterized by Auger electron spectroscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, and transmission electron microscopy. Oxides are amorphous and appear to be a mixture of indium phosphates and aluminium oxide. Indium hydroxide is present at the outer surface of anodically grown oxide. Thermal oxide growth follows parabolic kinetics, whereas the thickness of anodic oxides increases linearly with potential up to ~120V. Electrical measurements indicate that the thermal oxides have good electrical properties making the films potentially useful for some device applications.