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The atomic layer deposition of cobalt using Co(DAD) 2 and tertiary-butyl amine (TBA) has nearly infinite selectivity (>1000 cycles) on metal vs. insulator (SiO 2 or low-k SiCOH) planar samples. However, on patterned samples, selectivity under identical ALD conditions is limited, due to the diffusion of molecularly-adsorbed metal precursor from reactive to non-reactive surfaces. Four strategies have been found to improve Co ALD selectivity: adding a passivant to remove insulator defect sites, increasing the purge time, decreasing the precursor dose, and periodic annealing. The periodic annealing technique allows reabsorption of the Co nuclei from the insulator surface to the growth surface and is consistent with a low temperature reflow process.

The dimethylzinc adduct [Me 2 Zn(1,4-dioxane)] has been used for the growth of vertically aligned ZnO nanowires by liquid injection MOCVD. The ZnO nanowires were deposited at temperatures of 450 and 500 °C on Si(1 1 1) and F-doped SnO 2 /glass substrates and XRD data showed that the ZnO nanowires were deposited in the wurtzitic phase. Room temperature PL data for the nanowires showed that they are of high crystalline quality with intense near band-edge emission at 3.28 eV and a very low intensity of defect-related green luminescence at 2.42 eV. Single crystal XRD data showed that the [Me 2 Zn (1,4-dioxane)] adduct is polymeric with repeating [Me 2 Zn] units bridged by monodentate 1,4-dioxane ligands.

NbN films were deposited via plasma-enabled ALD from (tBuN=)Nb(NEt2)3 and N2 plasma. A wide temperature process window (250-350°C) was demonstrated. Films had an atomic ratio of Nb:N0.9-0.95 and showed decreasing carbon contamination as the process temperature was increased.

The development and scaling-up of a process for the growth of large diameter aluminum nitride thick films on 2-in sapphire is described. Optimal growth rates between 10 and 15 μ m/h have been reached by adjustment of the reactor pressure, substrate temperature and gas flows. The layer thickness is determined by in situ laser reflection from the layer surface and ex situ by the curve of reflectivity versus wavelength after growth. The crystal quality is demonstrated by in situ laser reflection, scanning electron microscopy (cross sectional images and thickness) and atomic force microscopy (average roughness before and after polishing in the ranges of 20–50 and 3–8 nm, respectively).

The transport of trimethylindium (TMI) must be highly reliable throughout the lifetime of a bubbler. This study reports stability data and transport rates obtained for a number of alternative bubbler designs when tested under different conditions of use. The best results, with exceptionally stable flux output across a wide range of operating parameters throughout the bubbler lifetime, were obtained using a novel perforated disc design. This design is an extension of the cross dipleg concept which provides multiple gas pathways to minimise channelling effects and allow uniform and efficient depletion of the bubbler contents.

Indium phosphide, gallium arsenide phosphide, and aluminum indium phosphide have been deposited by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and tertiarybutylarsine. The effects of growth temperature and V/III ratio on the amount of silicon, sulfur, carbon, and oxygen in InP have been determined. Minimum incorporation was observed at 565 °C and a V/III ratio of 32. In this case, the material contained a background carrier concentration of 2.7×10 14 cm −3 , and the Hall mobilities were 4970 and 135,000 cm 2 /V s at 300 and 77 K. The oxygen contamination in AlInP was found to be only 9.0×10 15 cm −3 for deposition at 650 °C and a V/III ratio of 35. The relative distribution of arsenic to phosphorus in GaAs y P 1− y was determined at temperatures between 525 and 575 °C. The distribution coefficient [ ( N As / N P ) film / ( P TBAs / P TBP ) gas ] ranged from 25.4 to 8.4, and exhibited an Arrhenius relationship with an apparent activation energy of 1.2 eV.

Precursors for use in metal organic vapour phase epitaxy (MOVPE) of compound semiconductor films are supplied in high integrity stainless steel containers to ensure the highest levels of purity and safety are maintained. However, this means that an accurate level determination is difficult to obtain in situ and growers must rely on usage calculations based on source vapour pressure values quoted in the literature. A number of level sensing systems have been investigated with some degree of success to address this problem, but all have suffered from excessive complexity, being limited to a fixed level indication, fragility and other issues. The most suited technology has been identified as capacitance related and data is reported here obtained from a simple, compact, robust probe fitted to a standard MOVPE bubbler. Results from standard source materials trimethylaluminium (TMA), trimethylgallium (TMG), dimethylzinc (DMZ) and diethylzinc (DEZ) under static and simulated chemical vapour deposition (CVD) operating conditions reported here clearly demonstrate that an accurate continuous level can be measured. Information on the repeatability, material compatibility and temperature dependence of the probe is also presented.

ZnO based transparent conducting oxides (TCOs) offer earth abundant alternatives to conventional indium tin oxide (ITO) films. At the same time, ALD enables discretized doping of substitutional cations at a monolayer level, providing fine and exquisite control over dopant concentration and resultant properties. In this work, we present the ALD of tantalum (Ta) doped ZnO (TZO) films. Compared to dopants such as Al3+ and Ti4+, a Ta cation exists in +5 oxidation state and thus, can ideally transfer 3 electrons by substitutionally doping a Zn2+ site. We show that 30 nm TZO films with 2 at% Ta provides a minimum resistivity of 4 mW.cm at room temperature and optical transmissivity of > 86% in the visible range. The precursors used for Zn, O and Ta are diethyl Zn (DEZ), H2O and pentakis-dimethylamido Ta (PDMAT). The targeted % Ta is varied from 2 to 20% by introduction of PDMAT pulse between DEZ and H2O pulses. The electron concentration and the mobility are measured using Hall measurements. A minimum resistivity of 4 mW.cm with carrier density of 9.0x1019 cm-3 and a mobility of 17.7 cm2/V-sec is observed at 2 at% Ta at room temperature. UV-Vis spectroscopy indicates a monotonic increase in bandgap of TZO from 3.2 to 3.4 eV upon addition of Ta. Photoluminescence (PL) shows a quenching of the green band emission of ZnO associated with oxygen defects upon the addition of 2 at% Ta. Upon further Ta addition, a red shifted defect peak appears which is attributed to formation of new Zn vacancies. This data is supported by X-ray photoelectron spectroscopy (XPS), showing removal of O vacancies and a clear Ta-O-Zn bond formation for higher Ta doping. The conductivity of ZnO and 2% Ta doping ZnO behave differently as a function of temperature. TZO have different activation energy compare to pure ZnO. X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) indicate the crystallinity change with the Ta doping. The results provide a clear understanding on the mechanism of Ta doping in ZnO and its direct impact on vacancies and resulting electronic and optical properties. Finally, ALD TZO is deposited on flexible glass substrates and inside nanoporous anodic alumina templates to demonstrate formation of transparent conducting electrodes, conformally on a variety of platforms of relevance to electrochemical research.

Bis(cyclopentadienyl)magnesium (Cp2Mg) is a common source for p-type doping in GaN and AlInGaP materials. It is a white crystalline solid with very low vapor pressure, leading to transport problems similar to solid trimethyindium (TMI). Some of these problems can be alleviated by a newly developed source-solution magnesocene, Cp2Mg, dissolved in a solvent that is essentially nonvolatile. In this paper, we report the growth and comparative results of Mg-doped GaN grown by OMVPE using solid and solution Cp2Mg. Using both sources, we optimized parameters to obtain high-quality GaN growth with hole concentrations up to 1 1018/cm3.

The reduction in oxygen contamination levels in organometallic precursors has been established as a key requirement in the metal organic vapour-phase epitaxy (MOVPE) of high brightness light emitting diode (LED) and laser devices. A number of different volatile oxygen-containing impurity species have been identified, and both physical and chemical techniques have been developed to eliminate them from a wide range of source materials to produce the next generation grade of high-purity products. In this study conclusive growth results are presented to highlight the significantly improved quality of device structures obtained when higher purity oxygen-free precursors are employed.

Dimethylhydrazine is a potential nitrogen precursor for organometallic vapor-phase epitaxy of GaN-based ternaries and quaternaries at relatively low temperatures. We have measured the vapor pressure of dimethylhydrazine and studied the pyrolysis characteristics of dimethylhydrazine in H 2 ambient. Results of co-pyrolysis with triethylgallium in H 2 ambient are also reported. The vapor pressure of dimethylhydrazine is given by Log P =8.19–1780/ T . Pyrolysis of the dimethylhydrazine is found to proceed by cleavage of the N–N bond followed by elimination of the methyl groups. Co-pyrolysis studies showed that an adduct and an intermediate dimer form at low temperatures then further decomposed at higher temperatures to the final product GaN.

Hydrazine derivatives are attractive low temperature nitrogen sources for use in MOVPE due to their low thermal stability. However their purification and subsequent analysis has not previously been investigated in depth for this application. A detailed study on 1,1-dimethylhydrazine {(CH3)2N-NH2} purified by eight different methods and the subsequent quantitative measurements of water present in the samples obtained is reported here. A correlation between 1H nuclear magnetic resonance spectroscopy (NMR), gas chromatography-atomic emission detection (GC-AED) and cryogenic mass spectroscopy (Cryogenic-MS) has been performed. All three analysis techniques can be used to measure water in the samples and with the best purification the water content can be lowered well below 100 ppm. The high purity of this material has been demonstrated by growth results and the state-of-the-art performance of laser diodes.

Solid trimethylindium (TMI) is the precursor of choice of the vast majority of MOVPE applications for indium containing alloys. However consistent pick up has been a problem under normal operating conditions. Solutions to this problem have included Solution TMI™,1 and dual reverse flow bubblers of solid TMI.2 A detailed investigation of the transport characteristics of Solution TMI has been performed, resulting in an increased understanding of its physical properties. This included the use of an Epison III ultrasonic analyzer to monitor the pick up of TMI in the vapor phase at various flow rates (100–1000 sccm), pressures (0.3 and 1 atm.) and temperatures (10–40°C). Solution TMI was shown to have a more consistent ‘pick up’ than dual reverse flow bubblers containing solid TMI. Side by side growth studies of AlInAs and InAlGaAs from Solution TMI and solid adduct grade TMI have shown that Solution TMI also gives layers with reduced oxygen incorporation.

In0.5Al0.5P lattice-matched to GaAs and In0.5A10.5As lattice-matched to InP epilayers were grown by atmospheric pressure metalorganic chemical vapor deposition (AP-MOCVD). The effect of trimethylindium on the purity of the as-grown layers was systematically studied using secondary ion mass spectroscopy (SIMS), deep level transient spectroscopy (DLTS), and capacitance-voltage (C-V) measurements. The SIMS results showed that oxygen is the main impurity in all layers and the oxygen concentration in InAlP was approximately one to four orders of magnitude higher than the oxygen concentration found in InALAs when the same indium source was used, indicating that more oxygen was introduced by the phosphine source than by the arsine source. Two electron traps in the InAlP epilayers and four electron traps in the InALAs epilayers were observed in this study. When a high-purity indium source was used, the best InAlP epilayer showed only one deep electron trap at 0.50 eV while the best InALAs epilayer showed no deep levels measured by DLTS. In addition, we also found that a high concentration of oxygen is related to the high resistivity in both material systems; this suggests that semi-insulating (SI) materials can be achieved by oxygen doping and high quality conducting materials can only be obtained through the reduction of oxygen. The oxygen concentration measured by SIMS in the best InALAs epilayer was as low as 3 × 1017 cm−3.

The effect of tantalum (Ta) addition to ZnO films has been investigated. The films are synthesized using atomic layer deposition. The precursor for Ta is pentakis-dimethylamino Ta (PDMAT) whereas, diethyl Zn (DEZ) is used for ZnO deposition with H2O as an oxidant. The surface reactions are studied using in situ downstream quadrupole mass spectrometry. X-ray photoelectron spectroscopy and photoluminescence show that at low Ta doping, oxygen vacancies are eliminated from the film, whereas at higher Ta doping, Zn vacancies are formed. These observations are supported by density functional theory calculations. Hall measurements show the lowest resistivity for a 30 nm Ta doped ZnO film to be 4 × 10−3 Ω cm with a peak carrier concentration of 1.2 × 1020 cm−3. The ideal cycle ratio used to achieve these properties is 40:1 of (DEZ+H2O):(PDMAT+H2O) pulses. Optical measurements show an average transmittance of 85% in the visible regime. The efficiency of Ta doping the ZnO, which represents the fraction of Ta5+ contributing to conductivity, is found to be at least 6.3%.

The extension of 193nm technology is desirable due to the magnitude of past investments. Since “optical” advances are increasingly difficult, there is a strong demand for more sophisticated “smart” resists to increase pattern density. Many studies have proven double pattering can be used for the extension of 193nm lithography. In this study, a new class of two stage photobase generators will be introduced along with the synthetic procedure. The characterizations for exposure study by NMR have shown typical characteristics of two stage decomposition under the exposure of 254nm light. GCMS was utilized to indicate the formation of photobase and major products from secondary photochemical reactions. Kinetic simulation was also taken into account to show the consistence of proposed mechanism.

Group III-V compound semiconductor material systems, consisting of Group III elements, such as aluminium (Al), gallium (Ga) and indium (In), and Group V elements, such as nitrogen (N), phosphorus (P), arsenic (As) and antimony (Sb), have semiconducting properties. As a result of the covalent bonding...

Transport of trimethylindium (TMI) must be highly reliable throughout source lifetimes. Bubbler design is a key factor and a number of different designs have been assessed. Significant improvements in output stability are demonstrated.

Solid trimethylindium (TMI) is the precursor of choice for the vast majority of MOVPE applications. However consistent pick up has been a problem under normal operating conditions. Epichem's solutions to this problem have included solution TMI/sup TM/ (TMI suspended in a high boiling point amine adducted to TMI) and dual reverse flow bubblers of solid TMI. A detailed investigation of solution TMI/sup TM/ is being continued at Epichem in order to understand the chemical and physical properties of this indium source. Results have proved solution TMI to have a more consistent 'pick up' than any alternative method and it has been identified as the best precursor for low oxygen applications.

In the MOVPE process a steady, controllable flux of precursor into the reaction chamber is a key factor when fabricating highly complex device structures employing ternary and quaternary layers. Historically a simple bubbler design has been employed to perform this task with carrier gas flow and source temperature control able to provide a suitably stable system. However, with the increasing volume demands placed on MOVPE equipment, increased flows and larger bubblers have become necessary and the simple dip tube (dip leg) approach is no longer 100% suitable. In this study, an investigation of 3 novel bubbler dip tube designs have been performed and a comparison made with the standard approach. An Epison III ultrasonic analyser was employed to monitor the pick up of the precursor from a variety of bubblers across a range of flow rates and temperatures. Flows up to 10 sclm have been investigated and differences observed between bubbler dip leg designs the results of which highlight the improvements achievable using a new crosspiece dip tube design.

Molybdenum trioxide films have been deposited using thermal atomic layer deposition techniques with bis(tert-butylimido)bis(dimethylamido)molybdenum. Films were deposited at temperatures from 100 to 300 °C using ozone as the oxidant for the process. The Mo precursor was evaluated for thermal stability and volatility using thermogravimetric analysis and static vapor pressure measurements. Film properties were evaluated with ellipsometry, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and secondary electron microscopy. The growth rate per cycle was determined to extend from 0.3 to 2.4 A/cycle with

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