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At least 127 records · Page 7

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NASA NTRS1978

Apparatus for use in examining the lattice of a semiconductor wafer by X-ray diffraction

An improved apparatus for examining the crystal lattice of a semiconductor wafer utilizing X-ray diffraction techniques was presented. The apparatus is employed in a method which includes the step of recording the image of a wafer supported in a bent configuration conforming to a compound curve, produced through the use of a vacuum chuck provided for an X-ray camera. The entire surface thereof is illuminated simultaneously by a beam of incident X-rays which are projected from a distant point-source and satisfy conditions of the Bragg Law for all points on the surface of the water.

Parker, D. L.↗

NASA NTRS1979

Remote manipulator for IC wafers

Mechanical manipulator automatically loads, transports, and unloads silicon wafers between processing stations in large-scale integrated-circuit fabrication facility at Marshall Space Flight Center thus eliminating need for human opeators at various stages in processing cycle. It also reduces possibility of wafer contamination.

Hudgins, J. L.↗

NASA NTRS1980

Automatic inspection of silicon wafers

Laser machine scans wafers for contaminating particles which cause open circuits, short circuits, and other defects in integrated circuits and transfers good wafers to integrated circuit processing equipment. Machine is faster and more accurate than human operator using lightfield/dark field microscope.

Martin, M.↗

NASA NTRS1979

A gas chromatographic air analyzer fabricated on a silicon wafer

A miniature gas analysis system has been built based on the principles of gas chromatography (GC). The major components are fabricated in silicon using photolithography and chemical etching techniques, which allows size reductions of nearly three orders of magnitude compared to conventional laboratory instruments. The chromatography system consists of a sample injection valve and a 1.5-m-long separating capillary column, which are fabricated on a substrate silicon wafer. The output thermal conductivity detector is separately batch fabricated and integrably mounted on the substrate wafer. The theory of gas chromatography has been used to optimize the performance of the sensor so that separations of gaseous hydrocarbon mixtures are performed in less than 10 s. The system is expected to find application in the areas of portable ambient air quality monitors, implanted biological experiments, and planetary probes.

Terry, S. C.↗

NASA NTRS1982

High-Speed Wafer Slicer

Multiblade cutter slices silicon ingots into solar-cell wafers quickly and with little waste. Speed and blade pressure ensure high wafer-production rate. Lightweight, balanced construction minimizes blade vibration and reduces sideways motion that would otherwise widen kerf and waste silicon.

Schmid, F.↗

NASA NTRS1980

Electrostatic bonding of thin (approximately 3 mil) 7070 cover glass to Ta2O5 AR-coated thin (approximately 2 mil) silicon wafers and solar cells

Electrostatic bonding (ESB) of thin (3 mil) Corning 7070 cover glasses to Ta2O5 AR-coated thin (2 mil) silicon wafers and solar cells is investigated. An experimental program was conducted to establish the effects of variations in pressure, voltage, temperature, time, Ta2O5 thickness, and various prebond glass treatments. Flat wafers without contact grids were used to study the basic effects for bonding to semiconductor surfaces typical of solar cells. Solar cells with three different grid patterns were used to determine additional requirements caused by the raised metallic contacts.

Egelkrout, D. W.↗

NASA NTRS1983

Gettering Silicon Wafers with Phosphorus

Silicon wafers subjected to gettering in phosphorus atmosphere have longer diffusion lengths and higher solar-cell efficiencies than untreated wafers. Gettering treatment improves properties of solar cells manufactured from impure silicon and is compatible with standard solar-cell processing.

Daiello, R. V.↗

NASA NTRS1982

LSA project perspective of wafering technology

The economics and techniques for eliminating wafering as a part of ingot technology in the production of silicon sheets for photovoltaic applications are considered. Technical progress in both ingot and non-ingot technologies for the low cost solar array project is described in the context of process economics. The critical areas of research in wafering are delineated and their payoff potential discussed.

Koliwad, K. M.↗

NASA NTRS1985

Stress rate and proof-testing of silicon wafers

Fracture mechanics test methods were applied to evaluate the proof-test characteristics of single-crystal silicon wafers. The results indicate that the strength distribution of silicon wafers is truncated by proof-testing. No subcritical crack growth occurred during proof-loading, as inferred from the lack of a stress-rate effect on strength. Mechanical proof-testing appears to be an effective method for eliminating weak samples before cell processing.

Chen, C. P.↗

NASA NTRS1987

Wafer level reliability for high-performance VLSI design

As very large scale integration architecture requires higher package density, reliability of these devices has approached a critical level. Previous processing techniques allowed a large window for varying reliability. However, as scaling and higher current densities push reliability to its limit, tighter control and instant feedback becomes critical. Several test structures developed to monitor reliability at the wafer level are described. For example, a test structure was developed to monitor metal integrity in seconds as opposed to weeks or months for conventional testing. Another structure monitors mobile ion contamination at critical steps in the process. Thus the reliability jeopardy can be assessed during fabrication preventing defective devices from ever being placed in the field. Most importantly, the reliability can be assessed on each wafer as opposed to an occasional sample.

Root, Bryan J.↗

NASA NTRS1987

Analysis of the interaction of a laser pulse with a silicon wafer - Determination of bulk lifetime and surface recombination velocity

The decay of excess minority carriers produced in a silicon wafer of thickness d by a laser pulse is analyzed. A comprehensive theory based on this analysis is presented for the determination of bulk lifetime Tau(b) and surface recombination velocity S. It is shown that, starting with an exponential spatial profile, the carrier profile assumes a spatially symmetrical form after approximately one time constant of the fundamental mode of decay. Expressions for the spatial average of the carrier density as a function of time are derived for three temporal laser pulse shapes: impulse, square, and Gaussian. Particular attention is paid to the time constants of the fundamental and higher modes of decay. The ratios of the time constants of the higher modes to the fundamental mode, as well as the time constant of the fundamental mode, are presented over wide ranges of values of S and d. For Sd less than about 40 sq cm/s, a two-wafer method is developed to determine Tau(b) and S; it is also shown that the requirement of d/Tau(b) greater than about 20S is sufficient to adequately guarantee that the asymptotic value of the instantaneous observed lifetime differs from the bulk lifetime by no more than 10 percent.

Luke, Keung L.↗

NASA NTRS1988

A chemical/microwave technique for the measurement of bulk minority carrier lifetime in silicon wafers

A chemical/microwave technique for the measurement of bulk minority carrier lifetime in silicon wafers is described. This method consists of a wet chemical treatment (surface cleaning, oxidation in solution, and measurement in HF solution) to passivate the silicon surfaces, a laser diode array for carrier excitation, and a microwave bridge measuring system which is more sensitive than the microwave systems used previously for lifetime measurement. Representative experimental data are presented to demonstrate this technique. The result reveals that this method is useful for the determination of bulk lifetime of commercial silicon wafers.

Luke, Keung L.↗

NASA NTRS1988

On the viscoplastic response of a composite wafer

In the present treatment of a viscoplastic composite wafer formed from a viscoplastic matrix that is reinforced by elastic or viscoplastic fibers attached to its plane surfaces, one constitutive equation is established by considering the viscoplastic behavior of the matrix as determined by an integral-type constitutive law whose intrinsic time-measure is pertinent to endochronic viscoplasticity. Attention is given to asymptotic cases where fiber stiffnesses and the hydrostatic modulus of the wafer are much larger than the latter's shear modulus. An explicit calculation is used when the stress field is uniaxial.

Valanis, K. C.↗

NASA NTRS1990

Growth of high quality 6H-SiC epitaxial films on vicinal (0001) 6H-SiC wafers

Previously reported growth of SiC films on SiC by chemical vapor deposition (CVD) used alpha-SiC crystal substrates. The CVD growth and evaluation of high quality 6H-SiC films on 6H-SiC wafers cut from large boules grown by the modified-sublimation process is reported. The single-crystal 6H-SiC films were grown on wafers oriented 3 to 4 deg off the (0001) plane toward the 11-20 direction. The films, up to 12 microns thick, had surfaces that were smooth and featureless. The high quality of the films was demonstrated by optical and electron microscopy, and low-temperature photoluminescence.

Powell, J. A.↗

NASA NTRS1991

Thermal and structural assessments of a ceramic wafer seal in hypersonic engines

The thermal and structural performances of a ceramic wafer seal in a simulated hypersonic engine environment are numerically assessed. The effects of aerodynamic heating, surface contact conductance between the seal and its adjacent surfaces, flow of purge coolant gases, and leakage of hot engine flow path gases on the seal temperature were investigated from the engine inlet back to the entrance region of the combustion chamber. Finite element structural analyses, coupled with Weibull failure analyses, were performed to determine the structural reliability of the wafer seal.

Tong, Mike T.↗

NASA NTRS1991

Thermal and structural assessments of a ceramic wafer seal in hypersonic engine

Tong, Mike↗

NASA NTRS1992

Evaluation of an innovative high temperature ceramic wafer seal for hypersonic engine applications

A critical mechanical system in advanced hypersonic engines is the panel-edge seal system that seals gaps between the articulating engine panels and the adjacent engine splitter walls. Significant advancements in seal technology are required to meet the extreme demands placed on the seals, including the simultaneous requirements of low leakage, conformable, high temperature, high pressure, sliding operation. In this investigation, the design, development, analytical and experimental evaluation of a new ceramic wafer seal that shows promise of meeting these demands will be addressed. A high temperature seal test fixture was designed and fabricated to measure static seal leakage performance under engine simulated conditions. Ceramic wafer seal leakage rates are presented for engine-simulated air pressure differentials (up to 100 psi), and temperature (up to 1350 F), sealing both flat and distorted wall conditions, where distortions can be as large as 0.15 inches in only an 18 inch span. Seal leakage rates are low, meeting an industry-established tentative leakage limit for all combinations of temperature, pressure and wall conditions considered. A seal leakage model developed from externally-pressurized gas film bearing theory is also presented. Predicted leakage rates agree favorably with the measured data for nearly all conditions of temperature and pressure. Discrepancies noted at high engine pressure and temperature are attributed to thermally-induced, non-uniform changes in the size and shape of the leakage gap condition. The challenging thermal environment the seal must operate in places considerable demands on the seal concept and material selection. Of the many high temperature materials considered in the design, ceramics were the only materials that met the many challenging seal material design requirements. Of the aluminum oxide, silicon carbide, and silicon nitride ceramics considered in the material ranking scheme developed herein, the silicon nitride class of ceramics ranked the highest because of their high temperature strength; resistance to the intense heating rates; resistance to hydrogen damage; and good structural properties. Baseline seal feasibility has been established through the research conducted in this investigation. Recommendations for future work are also discussed.

Steinetz, Bruce M.↗

NASA NTRS1992

Growth and characterizaton of 3C-SiC and 6H-SiC films on 6H-SiC wafers

Single crystal SiC films were grown by CVD on vicinal (0001) SiC wafers cut from boules produced by the modified sublimation method. Wafers with tilt angles less than 0.5 deg yielded 3C-SiC; tilt angles of 3 to 4 deg resulted in 6H-SiC films. The surface morphology of these films, up to 24 microns thick, were investigated as a function of growth parameters such as the Si/C ratio in the input gases and the presence of dopant materials such as nitrogen and trimethylaluminum.

Powell, J. A.↗