Diameter Substrates Research Articles

Uniformity and Performance Characterization of GaN P-I-N Photodetectors Fabricated From 3-Inch Epitaxy

AbstractGallium nitride wafer epitaxy on large diameter substrates is critical for the future fabrication of large area UV linear or 2D imaging arrays, as well as for the economical production of other GaN-based devices. Typical group III-nitride deposition is now performed on 2-inch diameter or smaller sapphire substrates. Reported here are visible blind, UV GaN p-in photodetectors which have been fabricated on 3-inch diameter (0001) sapphire substrates by RF atomic nitrogen plasma MBE. The uniformity across the wafer of spectral responsivity and shunt resistance (R0) for the p-i-n photodetectors has been characterized. Spectral responsivity and 1/f noise as a function of temperature exceeding 250°C will be presented for the GaN p-i-n photodetectors. Spectral response with >0.17 A/W at peak wavelength and having 4-6 orders of magnitude visible rejection has been achieved. 1/f noise typically less than 10-14 A/Hz1/2 at room temperature also has been achieved with GaN p-i-n photodiodes. The results have been correlated with proposed models for dark current and 1/f noise in GaN diodes.

Diamond coatings for tool shafts by induction plasma deposition

Induction plasma torches have inherent properties such as large plasma volume, generated without electrodes, with high plasma temperatures (10000 K) and axial injection capability, The potential benefits for diamond synthesis are large coverage as well as high growth rate. In this paper, induction plasma was used to synthesise diamond layers, without diamond preseeding and the diamond growth (axially and radially) was investigated as a function of various thermal boundary layers thicknesses determined by emission spectroscopy. The small diameter substrate (4.76 mm) was used to probe the diamond quality as a function of the homogeneity of the generated plasma in order to get data on diamond growth all along the large plasma diameter. The results have shown that the gas velocity strongly influences the thermal boundary layer thickness as well as the radial growth of the diamonds. This was demonstrated by SEM as well as roughness measurements. The reduction of the overall diffusion time by the decrease in the boundary layer thickness can consequently improve the growth of the lateral faces of the diamond which are less directly seen by the plasma gases.

Microfabrication Technology for the Production of Capillary Array Electrophoresis Chips

Improvements in the fabrication, sample handling and electrical addressing of capillary array electrophoresis (CAE) chips have permitted the development of high density, high-throughput devices capable of analyzing 48 samples in about 20 minutes. The fabrication of high density capillary arrays on 10 cm diameter substrates required the characterization of glasses that yield high quality etches and the development of improved sacrificial etch masks. Using these improved fabrication techniques, high-quality, deep channel etches are routinely obtained. Methods for bonding large area substrates and for drilling arrays of 100 or more access holes have also been developed. For easier sample introduction, we use an array of sample wells fabricated from an elastomeric sheet. The practicality of these technologies is demonstrated through the analysis of 12 DNA samples in parallel on a microfabricated CAE chip, the development of methods for injecting multiple samples onto a single capillary without cross contamination, and the operation of a microfabricated array of 12 capillaries with 4 sample injections per capillary that can analyze 48 samples.

In situ pulsed laser deposition of large-area ceramic and multilayer films for applications in industry

High-quality superconducting films have been deposited onto 2 in. diameter substrates in a large-area pulsed laser deposition (PLD) system incorporating a novel pseudoblackbody radiation heater. A KrF laser (λ=248 nm) was rastered across the radius of a rotating target and a slot in the blackbody heater collected the ablation plume onto a rotating substrate holder. Critical temperatures of >90 Kwith critical current densities of 2–4 MA/cm2 were measured across a 2 in. diam YBa2Cu3O7−δ(YBCO) film deposited on an LaAlO3(LAO) substrate. Metal atom concentrations were measured by Rutherford backscattering spectrometry to be nearly stoichiometric and the film thickness uniformity was ±7% about the mean. Purely c-axis orientation was observed in the x-ray diffraction patterns. A multilayer LAO/YBCO film was deposited in situ on an MgO substrate using a large-area target load-lock chamber and exhibited good crystalline quality. YBCO films deposited onto both sides of a 1 in. square by 0.010-in.-thick MgO substrate were patterned and fabricated into a four-channel microwave receiver operating near 10 GHz. The receiver exhibited low loss and good frequency selectivity at 77 K.

An experimental study of high pressure synthesis of diamond films using a microwave cavity plasma reactor

Diamond film deposition on Si “benchmark” substrates is experimentally investigated at high pressures using a microwave plasma disk reactor and CH4/H2 gas mixtures. In this microwave plasma reactor the plasma is formed inside a 12.7 cm diameter disk-like discharge region located at one end of an internally tuned cylindrical cavity applicator. A water cooling stage is employed to control substrate temperature. The input variables of the experimental evaluation are (1) methane concentration, expressed as c = %CH4H2 from 1∼8%, (2) total flow rate, ft, 200∼1400 sccm, (3) substrate temperature TS which varies from 700∼1125°C, (4) deposition time, t, 5 ∼ 100 h, (5) pressure, p, 80 ∼ 140 Torr, (6) incident power, Pinc, 2 ∼ 4.5 kW. The output films deposited on 2 in. diameter substrates were characterized by (1) growth rate in μm/h and mg/h, (2) film morphology, and (3) Raman spectra. In particular film growth rate versus CH4H2, flow rate, TS and t were performed on films deposited uniformly (<15%) over 2 in. diameter Si substrates. 5 h experiments indicated that the average film growth rate (over 2 in. diameter) varied from a few μm/h with c = 1% to 4.3 μm/h at c = 3% and then decreased for high c ratios. Average growth rate also varied with flow rate with a maximum of over 5 μm/h (∼ 35 mg/h). Growth rate increases as deposition time increases and reaches a maximum growth rate of 6.3 μm/h (∼44 mg/h) at t = 100 h. The film growth reaches a maximum around TS = 1100°C for both 2 and 3% chemistries.

Vapor deposited organic thin film in microgravity

Organic thin films have been grown in space by effusive ampoule physical vapor transport technique with different growth parameters for the source temperature, transport flux, substrate, seeding, and backfilling. Results described in this paper are based on data from the two United States Space Shuttle Endeavour flights, STS (Space Transportation System)-59 and STS-69, using the moderate temperature facility (MTF) for materials processing in space. The facility consists primarily of the effusive ampoule, in which the thin film growth process takes place, encased in two concentric aluminum cylinders with a vacuum space between them. The MTF has produced thin films of variable quality and thickness across 12 mm diameter substrates. The results are discussed with reference to the growth parameters.

Industrial metalorganic chemical vapor deposition technology for the growth of YBa 2Cu 3O 7−∂

MOCVD is the established technology for the mass production of compound semiconductors for e.g. opto-electronic devices. To transfer the MOCVD technology for HTS films to the standard MOCVD technology used in semiconductor production two major challenges have to be solved: 1. the Ba-precursor instability and 2. the demonstration of uniform of HTS films onto large area substrates. This paper presents an industrial MOCVD process solving these challenges using a new stable fluorinated Ba-precursor and a Gas Foil Rotation® susceptor. On a 2 inch diameter substrate area state-of-the-art YBCO thin films were fabricated having a thickness uniformity of 1% and compositional uniformity of 2% and 5% for Y/Ba and Cu/Ba, respectively. The films show a surface morphology with low defect density (<5 within 100 μm 2) and excellent superconducting properties ( T c (50%)>90 K, j c ( T=77 K, ( B=0 T)>5×10 6 A cm −2). The residual contamination by fluorine was determined by SIMS to be less than 250 ppm. This gives the strong evidence that this industrial process can be transferred to the Multiwafer Planetary Reactors® for mass production.

Low dislocation density Si-doped GaAs single crystal grown by the vapor-pressure-controlled Czochralski method

Si-doped GaAs substrates have been widely used for optical devices. Recently, as the device fabrication process has changed, larger diameter substrates can be used. Almost dislocation-free Si-doped GaAs crystals of 75 mm diameter, which are suitable for the fabrication of optical devices, have been successfully grown using our vapor-pressure-controlled Czochralski (VCZ) method. The generation of slip dislocations could be suppressed and the growth of the dislocation-free crystal was achieved by decreasing the thickness of B2O3. The VCZ crystals contained a large amount of unintentionally doped boron (B) of about 1018 cm−3. By comparing the electrical data of the VCZ crystals with those of the gradient freeze (GF) crystal free from B, it is found that B acceptors decrease the intrinsic compensation ratio ([SiAs][SiGa]).

Electronic Properties and Device Applications of Hot-Wire CVD Polycrystalline Silicon Films

ABSTRACTPolycrystalline silicon films (5 to 30 μm thick) have been deposited on glass substrates at low temperatures (400–550 °C) with a rate of 15 Å/s by hot-wire chemical vapour deposition (HWCVD). The homogeneity of the deposited layer is ±5% on a 8 cm diameter substrate. The films have columnar microstructure and a textured surface. The undoped films (carrier concentration, 1011 cm−3) have a resistivity of 105-106 Ω-cm, activation energy of 0.50 ± 0.05 eV and Hall mobility of 14 ± 4 cm2 /V.s. By in situ gas phase doping, resistivity can be varied by six to seven orders of magnitude. Incorporation of dopant atoms such as boron into the film, strongly influences its morphological and crystallographic structure. The mobility lifetime product of undoped films is low (10−8 cm2/V), possibly due to the presence of a high density of dangling bonds defects and broad band-tails. This product can be improved by a factor of 5 to 10 by using in-situ hydrogen passivation in the same reactor at lower temperature (350–400 °C) within one hour. The results of many complementary experiments suggest that hydrogen treatment mainly improves carrier mobility by a factor of 3 to 4 by passivating extended defects. Preliminary results on application of these types of materials in unoptimized P-I-N solar cells on c-Si and glass substrates are presented.

Precision manufacture of optical disc master stampers

This paper details a new manufacturing process for compact disc master stamper production. Stamper is an optical disc industry term for the mold used to replicate polymer compact discs (CDs) in an injection molding device. The stamper surface contains a negative image of the CDs more than 1 billion, submicrometer features embossed in a spiral pattern on a 138-mm diameter substrate. In conventional mastering, nickel submaster stampers are generated by electroforming from a glass master. In the proposed process, submaster stampers are not required, and a ceramic master is used directly as a stamper for injection molding. In the new process, ceramic substrates are ion machined through a photoresist mask, resulting in improved productivity, reduced hazardous waste, and lower production costs. All critical process steps have proved feasible in the research reported here. The new stamper production technique replaces the conventional glass master substrate with a tough ceramic and replaces several difficult electrochemical and manual operations with a single precision ion machining step. Processes that precede and follow stamper fabrication remain largely unchanged. In the new process, precision stamper manufacturing (PSM), more than 200 minutes of chemical processing, electroforming, back-polishing, punching, and handling are replaced by fewer than 20 minutes of automatically controlled ion machining. At the same time, PSM eliminates nearly all process steps that produce toxic and hazardous wastes. The process is suitable for production of CD-audio, CD-ROM, and high-density DVD formats. A process flow diagram and a series of proof-of-concept experiments are described.

A new cascade impactor for aerosol sampling with subsequent PIXE analysis

A small deposit area low pressure impactor (abbreviated to SDI) has been developed and tested. The device has been designed specifically to collect size-fractionated aerosol samples in remote locations for subsequent chemical analysis by PIXE. The SDI is a 12-stage, multinozzle device, but the deposit for each stage remains confined to an area with diameter less than 8 mm. It operates at a flow rate of 11 L/min and accepts the same, 25 mm diameter substrate rings as the PIXE International cascade impactor. The experimental cut-points for stages 12 through 1 are 8.50, 4.08, 2.68, 1.66, 1.06, 0.796, 0.591, 0.343, 0.231, 0.153, 0.086 and 0.045 μm equivalent aerodynamic diameter. The SDI has been tested in (and employed for) size-fractionated aerosol sampling in the Finnish Arctic and at Summit in Greenland. The data show that the SDI gives results very similar to those obtained with the PIXE International impactor, but with detection limits that are much lower. This suggests that the SDI can be used with shorter sampling times or in areas where concentrations are smaller to obtain reliable size distribution data. The results also suggest that data for a greater number of elements can be obtained with the SDI.

Fall and Winter Movements of and Habitat Use by Cutthroat Trout in the Ram River, Alberta

Abstract Fall and winter movements of and habitat use by cutthroat trout Oncorhynchus clarki were studied with radiotelemetry in low, mid, and high altitudes of a river system to evaluate the timing and extent of habitat shifts when fish moved from summer feeding areas to overwintering areas. The movements of 20 fish were monitored from August to November 1991, and 17 fish were monitored from October to December 1992. Cutthroat trout moved out of summer habitats in mid-September, and many made a two-stage shift in habitat use from summer to winter that was associated with anchor ice formation. When cutthroat trout were excluded from fall habitats by anchor ice, they moved to overwintering areas less likely to be influenced by frazil and anchor ice: deep pools with ice cover or areas where water temperatures were higher than the rest of the stream because of springs or upwelling warm groundwater. Cutthroat trout used deeper water and smaller diameter substrates in winter than in summer but used less cover ...

Hydraulic conductivity of gravel and sand as substrates in rock-reed filters

Long-term use of a constructed wetland to treat landfill leachate requires that the saturated hydraulic conductivity be maintained and clogging avoided to prevent overland flow, which bypasses the treatment process. This paper describes the application of an equation developed for prediction of cumulative drainage volume from hillslopes to measure the saturated hydraulic conductivity ( K s) of substrates used in rock-reed filters. Outflow was measured at five intervals during the first 26 months of operation. The values of K s) obtained by the drainage equation compared favorably with values calculated from a more dificult method based on Darcy's law. Results indicate that the finest substrate (a sand-and-gravel mixture) became almost completely clogged, and that the presence of reeds ( Phragmites australis) did not maintain or increase the conductivity. Hydraulic conductivity of pea-gravel (0.5-cm diameter) and coarse-gravel (3-cm diameter) substrates with reeds did decrease in the 26-month period.

In situ X-ray topography studies during the molecular beam epitaxy growth of InGaAs on (001) GaAs: effects of substrate dislocation distribution on strain relaxation

We report results from a novel facility constructed to enable in situ X-ray diffraction studies during the molecular beam epitaxy growth of Ill-V strained layer device structures on 50 mm diameter substrates. This new facility, used in conjunction with the Daresbury synchrotron source, permits X-ray topographic imaging of individual misfit dislocations formed during the molecular beam epitaxy growth process. The misfit dislocation growth and interactions can be imaged as a function of layer thickness, strain, growth and post-growth conditions. Our recent results show that the nature and distribution of dislocations threading up from the substrate are crucial in determining the initial pattern of epilayer relaxation. Under certain growth conditions and substrate dislocation distributions, large areas of the epilayer remain free of misfit dislocations at epilayer thicknesses significantly higher than the measured initial critical thickness tc1. We have observed in situ for the first time a second critical thickness tc2 (under certain conditions tc2>2tc1) at which there is a rapid increase in misfit dislocation density as a second misfit dislocation source(s) becomes active.

Ion Beam Assisted Deposition of Si-Diamond-Like Carbon Coatings on Large Area Substrates

AbstractHard, low-friction silicon-containing diamond-like carbon coatings (Si-DLC), were formed by Ar+ ion beam assisted deposition (IBAD), on 5 in. diameter silicon wafers. The diffusion pump oil precursor (tetraphenyl-tetramethyl-trisiloxane: (C6H5)4(CH3)4Si3O2) was evaporated through seven, 3 mm diameter, closely packed apertures (multinozzle/multi-aperture container) arranged in a hexagonal pattern, approximately 5 mm apart according to mathematical model [1[ developed at ARL describing the spatial distribution of film deposition from nozzles and apertures onto inclined substrates.The ion energy was kept at 40 keV whereas the ion current density and the oil evaporation temperature were varied to produce hard, lubricious and adherent films. The multinozzle array allowed the relatively uniform (± 20%) coverage of the entire 5 in. substrate. The thickness and the microhardness of the films were measured along the rectilinear surface coordinates of the substrate area. Depending on the deposition parameters the standard deviation of the coating thicknesses and Knoop micro-hardness varied from 14 to 30 percent respectively over the substrate. This is a significant improvement from the previously used single nozzle set up where the standard deviation of the coating thickness was 50 to 100 percent for 2 in. diameter substrates. The Knoop microhardness and the sliding friction coefficient of these coatings ranged from 10,000 to 20,000 MPa and 0.04 to 0.2 respectively. These values are in agreement with our previously reported single nozzle results [2].

Performance Features for Urea Hydrolysis in A Cstr with Microencapsulated Urease

The factors which influence the steady state performance of a CSTR operation with microencapsulated urease for the regeneration of a dialysated solution have been studied at various enzyme activities. The theoretical model considered the effect of microcapsule diameter, pH-dependent kinetics, and product inhibition and substrate depletion, in relation to urea conversion and the capsule effectiveness factor. The limiting effects of pH, product inhibition and substrate depletion were also studied individually and in combination under eight case studies. The base case which included these three limiting factors in the reaction process, predicted the lowest urea conversion values at the enzyme activities considered. However, the effectiveness factor for each case at a fixed microcapsule diameter depended on the enzyme activity. This behaviour was studied for two different microcapsule diameters, 5 microns and 500 microns. At enzyme activities lower than 1 mM/s, a model considering Michaelis-Menten kinetics alone, predicted the highest effectiveness factors. On the other hand, beyond 1 mM/s enzyme activity, the lowest effectiveness factors were predicted, although higher conversions than that of the base case were achieved. This might be due to the rapid depletion of substrate at high activities when Michaelis-Menten kinetics were considered, leads to residual substrate concentrations (Sr) lower than the Michaelis-Menten constant Km,o; a condition for a dramatic drop in the intraparticle reaction rate. The limiting factors in the base case held Sr at a relatively higher value than Km,o.

Uniformity of Arsenic Dimer and Tetramer Fluxes from a Valved Arsenic Cracking Source in MBE

AbstractWe have studied the uniformity of the arsenic flux from a commercially available valved arsenic cracker source for MBE. There are many epitaxial structures that require a uniform arsenic flux distribution for rotated epitaxial growth and, in the non-rotated case, for RHEED. For non-stoichiometric GaAs growth at low substrate temperatures, which results in arsenic precipitates being formed during the in-situ anneal process, a specific As/Ga ratio must be used to maintain high crystalline quality and to achieve the desired electrical properties. Also, in the growth of InGaAsP the As/P ratio is equally important for lattice match and quality device results. We report on the uniformity of amorphous arsenic (a-As) films condensed on the surface of 3" diameter sapphire wafers slightly below room temperature. Sapphire substrates were used in place of GaAs wafers to facilitate the use of x-ray fluorescence for the measurement of the arsenic film uniformity. Uniformity maps will be presented for rotated and non-rotated a-As depositions of As2 and As4. Results indicate the uniformity of a-As, As4, films to have a standard deviation of &lt; 2.5% across a 3" diameter substrate for the rotated case. Characteristics of the non-rotated case will be presented.

5387067 Direct load/unload semiconductor wafer cassette apparatus and transfer system: Grunes Howard E Santa Cruz, CA, UNITED STATES Assigned to Applied Materials Inc

A UHV compatible deposition system has been constructed for the growth of diamond films by 2.45 GHz microwave plasma chemical vapour deposition (CVD). The system comprises a loadlock and a spherical deposition chamber where the heated 100 mm diameter substrate is exposed to a reactive plasma environment. The design provides ports for in-situ monitoring by ellipsometry, optical emission spectrometry, mass spectrometry, and laser reflectometry and allows for the later addition of analysis chambers such as XPS. Computer control is provided for all major components and operations, including pumps, valves, gas flows, pressure and temperature adjustment. The system has four pumping groups, two for the main growth chamber providing base vacuum and for pumping the process gases, one for evacuating the loadlock and the fourth for the mass spectrometer. Microwaves enter the chamber via an antenna-based microwave applicator with a water-cooled quartz window. A key feature of this design is the ability to have a free standing ball plasma which touches neither the chamber walls nor the substrate.

Substrate heater for large area YBa 2Cu 3O x films growth without electrical feedthroughs

A new substrate heater based on an optical waveguide is demonstrated. The substrate heater is capable of heating a 2″ diameter substrate to 900°C with a temperature uniformity better than +/- 2°C. The substrate heater is ideal for use in reactive atmospheres because the heating source is placed outside the deposition chamber. The substrate heater is used in a laser ablation deposition system. To overcome the problem with the very narrow deposition profile typical for laser ablation, the substrate heater may be scanned 2″ by 2″.

Semiconductor liquid phase epitaxy for solar cell application

This paper describes liquid phase epitaxy techniques which have been developed for growing semiconductor layers on 100 mm diameter substrates for solar cells. We have prepared Si and GaAs layered structures, whose surface textures have the shapes of pyramids, roofs, or mesa facets of different size and periodicity. Microscopic growth mechanisms influence surface and interface morphologies of the layers as well as their electronic and optical properties. Sharp doping profiles are measured at interfaces of grown layers.