Specific Processing Steps Research Articles

On the flicker noise in submicron silicon MOSFETs

An overview is given of recent theoretical concepts and experimental findings with respect to the flicker or 1/ f noise in advanced silicon MOSFETs. First, a summary will be given of the theoretical models which to date are being considered for modeling of the flicker noise phenomenon. These will be confronted with experimental evidence, from which the likely validity range of the different models and their possible limitations follow. Next, attention will be paid to the impact of technology scaling to submicron dimensions on the 1/ f noise. Finally, the effect of specific advanced processing steps, typical for submicron CMOS technology will be highlighted and guidelines for low-noise processing will be formulated.

Impact of Processing Parameters on Leakage Current and Defect Behavior of n + p Silicon Junction Diodes

In this study the origin of the leakage current of diodes and the impact of process conditions on the leakage current is investigated. The influence of isolation modules, namely, conventional local oxidation of silicon (LOCOS) vs. polybuffered LOCOS, and different junction annealing conditions, namely, furnace anneal and rapid thermal anneal, on the diode leakage current is discussed. The diode leakage current level distribution over a wafer is very sensitive to specific processing steps, such as active area definition. For large peripheral diodes in p‐type substrate or in p‐well, the leakage current strongly depends on junction annealing conditions. The diodes processed with furnace anneal have one order of magnitude lower leakage currents compared to the diodes with rapid thermal anneal. This difference in leakage current is due to different surface generation velocities at the silicon‐oxide isolation interface. © 1999 The Electrochemical Society. All rights reserved.

Focused ion beam preparation of inclined planes in semiconductor materials : B. Khamsehpour and S. T. Davies. Vacuum, 47 (5), 451 (1996)

A focused-ion-beam (FIB) machine is a versatile tool used extensively in the integrated circuit (IC) industry for conducting failure analysis, prototype fabrication, and device repair. Lithography can also be performed using FIB for direct patterning of photoresists without using a mask. The FIB technique has several advantages over other maskless processes, such as direct-write e-beam lithography; ion-beam patterning of the photoresist offers higher resist sensitivity and lesser backscattering/proximity effects than the e-beam patterning.In this paper, we investigated a new FIB lithography process, called NERIME (negative resist image by dry etching). The NERIME process is a single-layer resist scheme, which implements a Ga+ FIB exposure of DNQ/novolak-based resists, followed by a near-ultraviolet (NUV) flood exposure, silylation, and oxygen dry etching. The NERIME process could not only yield both positive and negative images, but also achieve a nanometer resolution down to 65 nm and a high aspect ratio for the processed patterns. The principle of the negative image formation was also investigated by TEM and found to be due to the creation of a thin gallium oxide mask layer during etching. The NERIME process could be utilized for specific CMOS processing steps for the next generation technology nodes, such as high-resolution lithography over topographical surfaces.

Altered mRNA Splicing and Inhibition of Human E-selectin Expression by an Antisense Oligonucleotide in Human Umbilical Vein Endothelial Cells

We have characterized the mechanism of action of an antisense oligodeoxynucleotide (ASO) targeting human endothelial leukocyte adhesion molecule, E-selectin. ISIS 4730, a 20-base ASO designed to be complementary to a region in the 3'-untranslated region (3'-UTR) of human E-selectin, is a potent and specific inhibitor of both mRNA and protein expression in human umbilical vein endothelial cells. Following treatment with ISIS 4730, a lower molecular weight mRNA (3300 bases) species was detected by Northern blot analysis with a corresponding decrease in the mature E-selectin transcript (3875 bases). The ASO-induced low molecular weight mRNA is stable and remains in the nucleus. We demonstrate that ISIS 4730 targets E-selectin pre-mRNA in the nucleus and promotes cleavage of the pre-mRNA at the hybridization site, resulting in prevention of splicing of the last intron. The change in molecular weight of the E-selectin transcript is the result of loss of the 3'-UTR due to ASO-mediated RNA cleavage and retention of the last intron. Cleavage of the E-selectin pre-mRNA appears to be due to endogenous RNase H or a related enzyme activity.

Selective Cataloging of Federal Documents:

To increase access to federal depository documents, the University of Southern Colorado Library has cataloged selectively approximately one percent of incoming publications, as well as frequently used older ones. Using the OCLC Prism Service, we download bibliographic records to the hard drive of a PC, then transfer records into the on-line catalog. This article describes the specific processing steps developed, the expenses encountered, and the criteria used for selecting documents to catalog.

Modeling the cost of ownership of assembly and inspection

While the semiconductor industry may have the technologies required for the next 15 years of growth, the ability to implement these technologies in cost effective, competitive products is in question. The same impediment may also impact board and system level electronics. Cost of ownership (COO) was developed to address the economic and productive performance of a fabrication tool by estimating the total life-cycle cost of a specific semiconductor process step. Since there are many similarities between wafer fabrications, the methods used for estimating wafer fabrication COO may be applied to estimate device and system assembly COO. COO is also useful for equipment required to support manufacturing such as inspection tools. COO analysis for inspection equipment is more complex than for fabrication equipment, requiring a two-part analysis. First, the cost of operating the inspection tool is estimated. Second, the cost impact of inspection on the processes being measured must be estimated. The benefits of inspection are estimated by considering the impact of inspection on a process or product. Since characterization information improves the process, then inspection is a value added step.

Recent results obtained at IMEC on multicrystalline silicon solar cells

In order to optimize the efficiency of multicrystalline silicon solar cells, the influence of specific process steps and sequences were studied. Therefore clean-room high efficiency as well as industrial screen-printed cells were fabricated. Benefits are found in choosing a substrate with lower base resistivity, using front and rear oxide passivation, using hydrogen passivation for bulk and surfaces, the use of Si 3N 4 with a double function i.e. as an anti-reflection and passivation layer and the use of mechanical V-grooving. Efficiencies of 17% are found on 4 cm 2 clean-room fabricated cells and 15.2% has been obtained on 100 cm 2 V-grooved screenprinted industrial cells.

Tritium Recovery from a Solid Breeder Demo Blanket

The main task of a Tritium Extraction System (TES) for a helium cooled Li{sub 4}SiO{sub 4} DEMO blanket is the tritium recovery from a purge gas stream. On the basis of several TES proposals published for a NET/ITER solid breeder blanket, a new concept has been developed which is especially appropriate to cope with large purge gas streams. As tritium is expected to appear in two chemical forms (HT and HTO) two specific process steps are used for its removal from the primary purge gas loop: a cooler to freeze out Q{sub 2}O at 173 K (Q = H,T), and a molecular sieve bed to absorb Q{sub 2} at 78 K. Only these components including some additional devices for the gas pre-conditioning like a compressor and a precooler, are subjected to the high gas flow rates mentioned above. All further processing is done in relatively small secondary loops during and after warmup of the cooler and the molecular sieve bed. Q{sub 2}O reduction by using the water gas shift reaction, and separation of Q{sub 2} with Pd/Ag diffusors are the main process steps in the secondary loops. The feasibility of the proposed method is very promising as all process stepsmore » are based on well known technical and radiochemical experience. 20 refs., 4 figs., 1 tab.« less

Application of Line Modified-Asymmetric Crystal Topography for Qualitative and Quantitative Evaluation of Integrated Circuits

Abstract X-ray diffraction topography is the name given to several x-ray diffraction techniques where large area x-ray beams diffracted from a crystal provide detailed information about the surface structure and internal perfection of crystal microstructures. Since x-ray topographic techniques are based on Bragg (reflection) or Laue (transmission) diffraction from a crystal lattice, they are extremely sensitive to any atomic lattice imperfections and strains. Alterations of the interplanar spacing as small as one part in ten thousand extending over a reasonable number of atomic ce11 lengths can be recorded as a corresponding change in the diffracted beam intensity. Line Modified-Asymmetric Crystal Topography (LM-ACT) is one such reflection technique that shows particular promise in Che field of microelectronics. The LM-ACT system is designed with low angular divergence in the x-ray beam probe. Low probe beam divergence allows details of device geometries on the order of microns to be resolved in the recorded x-ray intensity variation of the diffracted beam. The LM-ACT system was applied here to the study of integrated circuits (IC) after specific processing steps were accomplished during IC fabrication and in the final product condition. Topographs obtained from specular crystal surfaces that were implanted through a patterned mask showed contrast variations between the implanted and non-implanted regions; details of the mask patterns have been resolved on the order of a few microns. LMACT topographs from annealed, and unannealed, Implanted specimens showed marked differences and as a result it is suggested that LM-ACT would be beneficial in optimizing the processing schedule for a particular wafer/electronic system. A significant feature of the LM-ACT technique is the capability for producing high resolution stereo-pair topographs that provide quantitative information through the depth of individual process layers in an integrated circuit.

A method for 3-D structure retrieval of interfaces by quantitative analysis of HRTEM micrographs

An understanding of many properties of polycrystalline materials requires knowledge of the atomistic structure and composition of grain boundaries (GBs). Recently, Kenway developed atomistic GB models for α-Al2O3 by computer simulation. It is most desirable to determine the atomistic three-dimensional (3-D) GB structure experimentally, not only to check the theoretical calculations but also to investigate the possibilities and limitations of quantitative high-resolution electron microscopy (HREM). The 3-D analysis must be performed on the GB along (at least) two different projections and requires specific image processing steps for micrographs taken along each projection. The experimental micrographs must be compared with simulated images of the refined structure until a “best fit” is achieved. So far, only 2-D optimization procedures have been introduced to do the fitting quantitatively for one projected structure. The basic concept of such analyses is to calculate an objective function and subsequently vary free parameters (in this case atomic positions) until a maximum of the objective function in the multidimensional parameter space is found.

Low-loss beamwidth transformers on InP with reduced requirements on lithographic resolution

An optimized waveguide taper structure is investigated for the efficient spot-size transformation of guided waves on InP-based optoelectronically integrated circuits. The simple two-layer structure is suitable for very low-loss chip-fiber interconnections. Using a special layout and process steps, the earlier strong requirements on lithographic resolution can be reduced to values of 200–300 nm, maintaining, however, the low-loss transformation properties. The quality of different process sequences are compared with respect to their loss properties.

Molecular biology of hydrogen utilization in aerobic chemolithotrophs.

The aerobic bacteria capable of obtaining energy from the oxidation of H2 form a heterogenous group that includes both facultative and obligate chemolithotrophs and representatives of both gram-negative and gram-positive genera. H2-oxidizing aerobes inhabit such diverse biotypes as soil, oceans, and hot springs. The oxidation of H2 in these bacteria is catalyzed by [NiFe] metalloenzymes called hydrogenases. The hydrogenases studied so far belong to two families: dimeric, membrane-bound enzymes (MBH) coupled to electron transport chains and tetrameric, cytoplasmic NAD-reducing enzymes (SH). Ni2+ is an essential component of the active site contained in the large subunit of the MBH enzymes. The genes for the MBH enzymes are located in conserved clusters of accessory genes, some of which encode maturation functions and hydrogenase-related redox proteins. Maturation of both types of hydrogenase is apparently complex, involving specific nickel incorporation and proteolytic processing steps. In Alcaligenes eutrophus and Rhodobacter capsulatus, hydrogenase expression is regulated by transcriptional activators belonging to the response-regulator family.

DIMES-01, a baseline BIFET process for smart sensor experimentation

The DIMES-01 BIFET baseline process is presented. The process and devices are described in relationship to their application in integrated silicon sensor research and development. In particular, the possibilities of introducing special sensor process modules and steps are treated.

Soldering Techniques for Fine‐pitch SMDs

To better understand trends and user experiences with fine‐pitch surface mounted component assembly, the author's company has surveyed a number of manufacturing engineers involved in the processing of such devices, including telecommunications equipment, business equipment, computers and related peripherals, test instruments, automotive electronics and military electronics. This paper summarises the findings of this survey. It reviews the various fine‐pitch devices, the special process steps required to assemble these components, conditions under which mass reflow techniques have proved acceptable, and the reported advantages and limitations of the alternative localised reflow processes.

Application of defect spectroscopy to silicon processing technology

Established defect spectroscopies and silicon characterization techniques are successfully applied to device manufacturing quality control. Deep level transient spectroscopy, DLTS, and photoconducting decay recombination lifetime measurements routinely monitor epitaxial silicon. Fe and Mo are commonly observed contaminants. Processing tools, such as epitaxial reactors and ion-implantation machines, are regularly monitored for trace metals. Dislocations introduced by specific silicon processing steps are selectively studied with DLTS. Dislocation signatures are present in selectively grown epitaxial silicon as well as in shallow junctions created by BF2 implantation. As a final example, defects introduced by reactive ion etching of silicon are examined by DLTS, photol-uminescence and spreading resistance profiling. The near surface displacement damage region is a source of interstitial defects which undergo recombination enhanced diffusion to depths as great as 1 μm. Measurements previously reserved for research are now being successfully employed as monitors and controls to improve the quality of silicon microelectronic manufacturing.

Subsurface Processing of Electronic Materials Assisted by Atomic Displacements

In the early years of doping of semiconductors by ion implantation, atomic displacements and residual lattice damage were considered undesirable byproducts of an otherwise controllable doping process. Steps were taken to minimize disorder during implantation and/or to remove it as completely as possible during a subsequent annealing process. In many cases, such as boron- or phosphorus-implanted silicon, annealing temperatures exceeding 900°C were necessary to achieve the desirable electrical properties. Indeed, removal of implantation damage remains a crucial issue, particularly as device dimensions shrink and the need has arisen for substantially lower processing temperatures. The advent of high-energy (MeV) implantation in specific processing steps and the increasing use of more complex (often multilayer) compound semiconductors has added further to the need to understand and control ion damage and its annealing in semiconductors.Over the past decade, there has been a growing realization that implantation induced atomic displacements and defects can have significant advantages in processing. For example, it was realized early that ion damage, and resultant defect fluxes to and from lattice disruptions, can “getter” and trap undesirable impurities that would otherwise interfere with device operation. More recently, it has been possible to use ion beams to tailor damage structures and form amorphous-crystalline superlattices, to remove pre-existing damage and induce crystallization of amorphous layers at very low temperatures, to form ultrapure amorphous silicon for studying thermodynamic properties of this phase, or to mix films with semiconductors and form stable compounds such as silicides. Indeed, ion damage has been used to electrically isolate devices, to form optical waveguides and cavities, and to improve the junction properties of deeply doped layers. These issues are briefly reviewed in this article.

Size-sensitive multiresolution decomposition of images with rank order based filters

In this paper, the problem of size-sensitive multiresolution decomposition is addressed. It is shown that various decompositions can be achieved using a class of nonlinear filters known as rank order based filters. This class includes, as a special case, classical rank order filters and a large number of morphological filters with flat structuring element. As the notion of size in an image is related to shape, two kinds of decomposition are investigated. In the first one, the object size is assessed by comparison with a set of arbitrary masks (squares) and does not take into account the actual shape of the objects present in the image. This approach leads to a nonadaptive size-sensitive decomposition. In the case of texture images, this nonadaptive decomposition can be attractively replaced by an adaptive scheme. This last approach consists in extracting a set of dominant shapes of given sizes contained in the image and in assessing the size of a specific element by comparison with the various dominant shapes. In both cases, particular attention is paid to the problem of shape preservation in the hierarchy. It is concluded that in the case of nonadaptive decomposition, the shape is far from being preserved. To address this problem, a specific but simple processing step is proposed. It is based on modification and combination of geodesic erosion and dilation. This approach is attractive because of its simplicity and of the very good shape preservation it allows. As applications, multiresolution decomposition is applied to defect detection and grey level segmentation problems. In the case of defect detection, multiresolution decomposition is used as a simplification tool which retains the image components of useful size. A large number of grey level and texture defect detections are described to show the robustness and accuracy of the approach. Decomposition can also be used as a starting point of a grey level segmentation algorithm. Examples of very simple segmentation techniques are described and discussed.

Validation of virus inactivation by heat treatment in the manufacture of diaspirin crosslinked hemoglobin.

Diaspirin crosslinked hemoglobin (DCLHb), a hemoglobin based oxygen carrying solution prepared from outdated human blood, is subjected to a heat treatment step to inactivate viruses in our manufacturing process. To validate the efficacy of this inactivation, we have simulated the heat treatment procedure at a reduced scale using hemoglobin solution spiked with representative viruses. Human Immuno-deficiency Virus (HIV), Cytomegalovirus (CMV), and Duck Hepatitis B Virus (DHBV) were used in this validation. Inoculation with concentrated virus was performed just prior to the heat treatment to determine the effect of that specific process step. Samples were taken before, during, and after heat treatment and assayed for virus titer in an attempt to assess the rate as well as the extent of virus inactivation. CMV was analyzed in a plaque assay using MRC-5 indicator cells. The titer was reduced from 3.3 x 10(6) plaque forming units (PFU) per mL to less than 5 x 10(1) PFU/mL (detection limit) within 30 minutes. DHBV was analyzed by inoculation of serially diluted samples into Pekin ducklings, followed at intervals by screening sera for DHBV DNA by dot blot hybridization. The titer was reduced from 5.0 x 10(6) duck infectious units (DIU) per mL to less than 5 x 10(0) DIU/mL (detection limit) within 1 hour. HIV titers were determined through an ELISA assay for p24 antigen present in peripheral blood lymphocyte cocultivation supernatants. The titer was reduced from 2.0 x 10(4) infectious units (IU) per mL to less than 2 x 10(0) IU/mL (detection limit) within 1 hour. These data indicate that high titers of these blood borne viruses are rapidly inactivated by this heat treatment process.

Self-shift characteristics of single-substrate AC plasma display incorporating suspended electrodes

The suspended-electrode single-substrate AC plasma display, which has low input power and full color capability (because of reduced ion bombardment), has been examined for operation as a self-shift display. The structural symmetry of these devices has been improved by special process steps involving self-aligning and touch-up-etch techniques. The pixel shift has been successfully performed on individual pixels along the suspended electrodes, and the results indicate a shift speed of 2000 characters/s with a resolution of 30 lines/in. No tendency of reverse-shift has been noticed (hence good directivity). However, it was not possible to perform a shift operation perpendicular to the direction of suspended electrodes due to the structural limitation on breakdown voltage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

EFFECT OF PREHYDROGENATION ON HYDROCONVERSION OF MAYA RESIDUUM, PART II: HYDROGEN INCORPORATION

Maya 650{sup 0}F residuum (Maya AR) was prehydrogenated over a standard hydroprocessing catalyst. The 650{sup 0}F residuum of this product (HMaya AR) and Maya AR were then separately hydroprocessed further at selected conditions. The products were examined by elemental, {sup 1}H and {sup 13}C NMR analyses to determine the how hydrogen was incorporated during processing. For all processing steps, hydrogen was incorporated in capping fragments formed during cracking reactions, as well as in hydrogenation reactions, heteroatom removal, and hydrocarbon gas formation, but the distribution of the hydrogen was dependent upon the type and severity of the process. For the direct hydroconversion of Maya AR, 25 to 30% of the total hydrogen was incorporated for heteroatom removal and hydrocarbon gas formation. The remaining hydrogen was incorporated in hydrogenation and cracking reactions. The hydrogen incorporation during each specific processing step is discussed, along with an evaluation of the prehydrogenation step as a residuum conversion process option. These results are compared to previously reported hydrogen incorporation measurements on other feeds and processing methods.