Back Illumination Research Articles

The Effect of Multilayer Patterns on Temperature Uniformity during Rapid Thermal Processing

This work aims to systematically gain an understanding of the effects of multilayer patterns on wafer temperature uniformity during rapid thermal processing (RTP) and to explore possible solutions to the problem. The radiative properties of patterned wafers are predicted using electromagnetic multilayer theory, including a model for the temperature‐dependent optical constants of silicon for wavelengths greater than 0.4 μm. The model for predicting radiative properties is coupled to a finite element‐based reactor transport model to predict steady‐state and transient wafer temperature distributions. A generic two‐dimensional axisymmetric single‐side illumination RTP system is used as a test bed to explore pattern effects. Realistic examples of shallow junction annealing and titanium silicidation are simulated. Results show that pattern effects are an important consideration for rapid thermal processes and that wafer processing, front and back side illumination, and reactor design all have significant effects on pattern‐induced temperature nonuniformity.

Optical windows for a flow cell to contain aqueous solutions at high pressure and temperature

A flow cell to contain aqueous solutions at pressures up to 40 MPa and temperatures up to 600 °C that is equipped with sapphire windows for the transmission of visible light is described. There are four windows, two for the entrance and exit of a laser beam, and two located at 90° that feature f/1 (53° included angle) collection apertures with a 9 mm diameter unobstructed view for Raman spectroscopy, absorption measurements, or studies using full-field back illumination. The window-to-metal seals are gold o-rings; the metal-to-metal seals are gaskets prepared by pressing a gold o-ring onto a gold foil washer. This cell has been used for two years for Raman studies of aqueous solutions at high pressures and temperatures both below and above the supercritical point of water.

Strobe versus Incandescent Lighting for Egg Crack Detection Using Machine Vision

A strobe light was used as a light source for the acquisition of images for the detection of cracks in eggs using machine vision. This light source would potentially enable a camera to obtain a good quality image in a shorter time frame than required by constant incandescent lighting. A circuit was developed to synchronize the firing of the strobe light with the acquisition of the image by the camera. Success rates for egg inspections using the two lighting methods (strobe and incandescent) were compared for a mixture of egg sizes and for medium, large, and extra large eggs. The response surfaces were visibly different depending on type of back illumination of eggs used. However, very little difference was found between the maximum success rates for each lighting method. Maximum success rates were approximately 90% for each illumination method (95% for medium eggs.) Range of values for optimization of the two software constants was also very similar for both types of lighting. Optimum success rates were obtained by defining crack length as 150 to 190 pixels and filter factor as 35 to 40.

Photoelectrolysis of water at bare and electrocatalyst covered thin film iron oxide electrode

Abstract The photoelectrochemical effect on bare and electrocatalyst covered iron oxide thin film electrodes for water splitting reaction has been studied under both front and back illumination conditions. The semiconducting iron oxide films of optimum thickness of ∼33 nm, produced spray pyrolytically by 20 s spray time, gave the maximum photocurrent density of 0.7 mA cm−2. The band gap of the optimum thick film was found to be 2.3 eV. Importantly, the photocurrent density under back illumination was found comparable to that under front illumination. The electrocatalyst ruthenium oxide reduced the onset potential of the iron oxide film by 120 mV but did not increase the limiting photocurrent density. Lead oxide, manganese oxide and cobalt oxide deposited on the iron oxide thin film did not show any electrocatalytic effect but rather reduced the photocurrent density compared to the bare iron oxide film.

A three wavelength infrared focal plane array detector element

We have demonstrated a novel three wavelength InGaAs focal plane array pixel element for detection at wavelengths from 0.9-2.6 μm, where each of three wavelength sensitive detectors are individually addressable. This device consists of successively smaller bandgap layers of In/sub x/Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> spl minus/x/As (x/spl ges/0.53), separated by compositionally graded layers of InAs/sub y/P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> spl minus/y/ to decrease defects induced by lattice mismatch strain with the InP substrate. The various layers were selectively removed so that p-n junctions with different wavelength response are formed. The three detectors have quantum efficiencies between 55 and 95% for front illumination and 15 and 60% for back illumination, and dark currents from 0.01 to 10 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Photocurrents in poly-Si TFTs

Steady-state photocurrents have been measured in poly-Si TFTs fabricated from columnar poly-Si as well as from material crystallised from amorphous LPCVD and PECVD precursors. With top face white light illumination, through the poly-Si gate, the photocurrents from all three technologies were comparable and showed similar trends of increasing photocurrent with film thickness. The photocurrents measured in the thinnest films (600 AA thick) were approximately 7*10-14 A/ µm of channel width/klux. With back face illumination the currents were approximately four times larger. When compared with dark current values of approximately 4*10-14 A/ µm in high quality TFTs, it is apparent that in high light environments, such as LCTV projectors, the photocurrents in unshielded TFTs can be two to three orders of magnitude greater than the dark currents. From the channel length and gate and drain bias dependences, the photocurrent was identified as arising from both optical generation in the drain space charge region and diffusion from the bulk channel. The weak dependence of the photocurrent on drain bias meant that field relieving structures, used for the reduction of dark currents, had a more limited effect upon photocurrents. Spectral photocurrent measurements yielded a value for the recombination lifetime, in a columnar poly-Si TFT, of approximately 2*10-10 s. The detailed spectral response was shown to be due to interference effects in the multiple layer thin film structure.

A Non-Invasive Technique to Quantify In Vitro Bioprosthetic Valvular Coaptation

The functional relationship between valvular leaflet stress and coaptive geometry may provide insight into a bioprosthetic heart valve's ability to maintain coaptation under a broad range of physiologic operating conditions. Previous investigators have only indirectly measured coaptation geometry. A non-invasive in vitro technique is demonstrated to directly quantify the coaptive geometry of bioprosthetic heart valves. A discussion is provided detailing the use of this information in a finite element model to determine the functional relationship between valvular leaflet stress and coaptation geometry. Video images of the stent post deflections and coaptive geometry for size 21 mm, 23 mm, and 25 mm Hancock Aortic Pericardial heart valves are obtained based on back light illumination of each valve's coaptive area at discrete back pressures. The resulting images are analyzed using image processing and motion analysis techniques. Results indicate that at back pressures greater than 50-75 mmHg the coaptive area remains constant. There is a decrease in coaptive depth at the valve's periphery, whereas the point of maximum coaptation maintains position approximately midway along the free margin. Good agreement is found between the experimentally determined and finite element model's predicted coaptation geometry.

Effects of medial septal lesions on an operant delayed go/no-go discrimination in rats

Male hooded rats received either a medial septal lesion or a control operation. The rats were then tested on an operant go/no-go discrimination task, first without a delay contingency (20 days), followed by 25 days under an 8-s delay. A discrete trial procedure with symmetrical reinforcement was used. Each trial began with the operant chamber darkened, except for back illumination of a centrally located press panel. Depression of this panel extinguished the back light and initiated a random presentation of either the go stimulus (2800 Hz tone) or the no-go stimulus (10 Hz pulsing light) for 3 s. Stimulus termination initiated the appropriate delay contingency (0 s or 8 s), which was followed by the cued availability of a lever for 2 s. If the rat pressed the lever on go trials, or refrained from pressing the lever on no-go trials, a food pellet was delivered. The data (% correct responses) were averaged over 5-day blocks. Overall, the septal-lesioned rats performed significantly better than the control rats under both 0-s delay ( p < 0.025) and 8-s delay ( p < 0.001) contingencies. Although there was not a significant difference between the groups during the last block of the 0-s delay (septals 93% correct, controls 89% correct, p > 0.05) or the first block of the 8-s delay (septals 54% correct, controls 53% correct, p > 0.05), the septal-lesioned animals performed significantly better than the controls during all the remaining phases of the experiment. For example, during the final 5-day block of the 8-s delay, the septal-lesioned rats averaged 71% correct and the control rats averaged 61% correct ( p < 0.001). The results support the hypothesis that damage to the septal area produces a deficit in response memory which, in turn, induces a compensatory enhancement of stimulus memory. Medial septum Hippocampus Go/No-go discrimination Working memory Multiple memory systems

Internal photoemission in CoGa/GaAs Schottky barriers, possible injection of electrons into the L valley

Internal photoemission in epitaxially grown films of CoGa/GaAs Schottky barriers by back illumination is used to study the injection of electrons into L and X valleys of the conduction bands of n-type GaAs. The general theory of Fowler predicts that the photocurrent per absorbed photon should vary as the square of the photon energy hν for [(hν−Φb/kT]≥0, where Φb is the difference between the Fermi level and Γ point in the GaAs conduction band. Unlike the case for Au/GaAs Schottky barriers, we observe two thresholds in the photocurrent measurements of uniform epitaxial CoGa/GaAs contacts. The second threshold formed at ≊0.3 eV higher than the first threshold (Γ point) is interpreted as the injection of carriers into the L valley of the GaAs from the metal side. A third threshold at ≊0.5 eV above the Γ point requires a photon energy greater than the energy gap of GaAs (1.4 eV) and hence cannot be observed in the back illumination mode.

Luminance range compression for video film digitizers

Video cameras are used in many film digitization and teleradiology systems. However, the density range of medical radiographs often exceeds the dynamic range of the camera, and all diagnostic information in the original image may not be captured. Information in both the high and low density areas of the film can be captured in a single video frame if the transmitted luminance range of the radiograph is reduced. This can be accomplished by spatially modulating the back illumination of the film such that areas of lesser density receive less illumination while areas of greater density receive greater illumination. In this work, the use of a video monitor is shown to be an effective means to provide spatially modulated light for compressing the transmitted luminance range and thereby expanding the apparent dynamic range of the video camera. A simple computer-interfaced video feedback system that determines the appropriate compression mask and a scheme for linearization of system response are described. This system provides an interactive means for control of the degree of range compression.

An experimental study of the strain field development prior to failure of a marble plate under compression

The strain field development prior to failure of a uniaxially compressed marble plate with an inclined central slot is studied experimentally. The whole process of failure development of the specimen is directly monitored and photographed by back illumination. The displacement fields at different stages are recorded with the moire technique and corresponding strain fields are calculated. Test results show that when the specimen is loaded to a certain level, its strain will become concentrated in relatively narrow belts which are potential locations of the impending ultimate failure. The failure process can be roughly divided into five stages: (1) initiation and propagation of primary forward tensile cracks, also known as wing cracks, (2) initiation and propagation of secondary forward tensile cracks, (3) initiation and intensification of shear belts starting from the slot tips and extending in an “X” form toward the four comers of the specimen, (4) initiation and propagation of backward tensile cracks, and finally (5) the ultimate failure. The forward tensile cracks are similar to those previously described in the literature ∗∗ but the backward cracks run in an opposite direction. In this study, four types of ultimate failure are identified: (i) axial splitting along tensile cracks, (ii) shear fracture along shear belts having a similar trend as the slot, (iii) shear fracture along shear belts sub-conjugate to the slot, and (iv) various combinations of splitting and shear fracture. Specimens with infill mortar material in the slot are also tested, where it is found that the mortar suppresses axial splitting. The geophysical and seismological implications of the test result are also briefly discussed.

The effect of doping density and injection level on minority-carrier lifetime as applied to bifacial dendritic web silicon solar cells

The measured short-circuit current density in bifacial dendritic web silicon solar cells has been found to decrease with decreasing base resistivity, particularly under back illumination. In addition, the ratio of short-circuit current under back illumination to short-circuit current under front illumination was observed to vary with light intensity. These observations reflect the fact that the minority-carrier lifetime in the base of these cells is a function of the base resistivity and the illumination level. The dopant was assumed to play only an indirect role in determining lifetime. This decrease in lifetime is shown to follow from a distribution of defect levels in the bandgap. These levels are a consequence of extended defects that have been observed in the web material, namely oxide precipitates and the dislocation cores that they decorate. The dopant, acts only in the indirect role of moving the Fermi level over an existing background distribution of defect levels that arise from the extended defects. Assuming a parabolic distribution of defect levels in the bandgap, the minority-carrier lifetime was calculated as a function of doping density and excess carrier concentration (illumination level) using the Shockley-Reed-Hall theory. The short-circuit current densities that were calculated using these lifetimes agreed reasonably well with measured values for bifacial dendritic web silicon solar cells. The measurements were made over a range of doping densities (6*10/sup 14/ to 3*10/sup 16/ cm/sup -3/) and illumination levels (0.001 to 1 sun) for both front and back illumination of the bifacial cells. >

The Fabrication and Analysis of Bifacial Solar Cells from Dendritic Web Silicon Substrates

Bifacial solar cells, which respond to light incident on either the front or the back surface, have been fabricated using dendritic web silicon as the substrate material. Both p‐type and n‐type substrates have been used, with resistivity ranging from 0.2 to 100 Ω‐cm for p‐type and from 0.2 to 10 Ω‐cm for n‐type. The thickness of the web substrates varied from 100 to 160 μm. The performance of the cells was found to depend strongly on substrate resistivity, with the highest resistivity giving the best results. Efficiencies in excess of 15% under front illumination, and approaching 15% under back illumination, have been measured. The efficiency under back illumination decreases dramatically with resistivity because of a decrease in minority carrier diffusion length, as deduced from measurements of internal quantum efficiency. The ratio of short‐circuit current under back illumination to short‐circuit current under front illumination also decreases with illumination level below 1 sun. The observed effects of resistivity and illumination level on cell performance are throught to be a consequence of the presence of extended defects (dislocations decorated with precipitates) in web material.

Semiconductor electrodes. 50. Effect of mode of illumination and doping on photochemical behavior of phthalocyanine films

Abstract : The behavior of photoelectrochemical (PED) cells composed of Sno2 or Pt electrodes with coatings of different phthalocyanines (Pc) -H2PC, ZnPc, MgPc, (CuPc, InPc) 1 was investigated. Spectral sensitization at the Sn02/Pc interface leads to photooxidation currents, while efficient photoreduction occurs at the Pc/solution interface through bulk generation of charge carriers. The presence of both anodic and cathodic photocurrents leads to different net photocurrent responses for back and front side illumination, especially with thicker films. The efficiency of the reduction process was sensitive to the potential of the redox couple in solution and maximized when E redox was about 0.37V for N2Pc, ZnPc and -MgPc. A dramatic improvement of the photoelectrochemical behavior of the coating results from doping with an electron acceptor (e.g.,o-chloranil) and quantum yields as high a s 4.6% were measured for Pt/H2Pc electrodes.

Photovoltaic effect in cuprous oxide-copper junctions in relation to the optical absorption spectrum of cuprous oxide

The spectral dependence of the photovoltaic effect (PVE) of Cu 2O-Cu cells, annealed in three distinct ways, was measured. The copper contact was formed by high temperature reduction of the surface of the oxide. The measurements were made for different thicknesses of oxide, and with front wall and back wall illumination. Two types of absorption constant were calculated from PVE measurements and compared with directly measured absorption constants from transmission data. The results allow us to distinguish between electronically active absorption near the bandgap and electronically inactive absorption at longer wavelengths.

The accuracy of Schottky-barrier-height measurements on clean-cleaved silicon

Schottky-barrier diodes have been realized by cleaving n-type Si in ultrahigh vacuum (UHV) in a stream of evaporating metal atoms. The properties of these Al, Mg, and Fe diodes are studied by means of standard I-V, C−2-V, and photoemission threshold measurements in the same UHV. With an error analysis it is shown that the barrier height is most accurately obtained from C−2-V measurements. This is in contrast to the prevailing opinion that the barrier height from photoemission measurements is the most reliable measure of the barrier height. It will be shown that a correct value from the photoemission experiments is obscured by the difficulty in determining the exact number of absorbed photons in the metal (back illumination). Finally, reported large systematic discrepancies between barrier heights from photoemission measurements and those from C−2-V measurements were not observed. All observed differences remain within the experimental error.

A high-pressure ionization chamber

An ionization chamber has been constructed which enables electrode separations up to 100 mm and gas number densities up to 252*1024 m-3 to be employed. The initial photoelectric current was produced by back illumination of a thin metallic film evaporated on to a quartz disc inserted into the cathode. Values of the attachment coefficients for carbon dioxide for gas number densities between 26.5 and 48*1024 m-3 and E/N (electric field/gas number density) values of 84.3, 90.3 and 96.3*10-21 V m2 are given and show that the experimental errors associated with the attachment coefficients are reduced from the +or-160% that would be typical for conventional systems to +or-50% for the present system.

Photoelectrochemical effects in the electrolyte-pigment-metal system

The electrolyte-pigment-metal system can be described as analogous to a photosensitive junction region. When the thickness of the pigment film is increased, the action spectra of the maximum short-circuit photo-current under continuous illumination differ from the absorption spectra both in direct illumination (pigment-electrolyte) and in back illumination (metal-pigment). One is led to believe that there exist two photoactive regions in the system for the production of the short-circuit photocurrent; these two active regions are associated respectively with each interface. When the metallic semitransparent electrode is made of aluminum the two interfaces have opposite sign contributions to the photocurrent; this allows the determination of conditions in which one can observe specifically the contribution of the pigment-electrolyte interface, that is the interactions between excited pigment molecules and the redox system in the electrolyte.

Discussion of “A Simplified Method of Measuring Lifetime Using Steady‐State Back Illumination of an MOS Capacitor” [C. St. L. Rhodes and C. A. T. Salama (pp. 1219–1222, Vol. 121, No. 9)

not Available.

Closure to “Discussion of ‘A Simplified Method of Measuring Lifetime Using Steady‐State Back Illumination of an MOS Capacitor’ [C. St. L. Rhodes and C. A. T. Salama (pp. 1219–1222, Vol. 121, No. 9)

not Available.