Showing papers by "Varian Associates published in 1991"

Rotating sputtering apparatus for selected erosion

Abstract: A magnetron sputter source providing a predetermined erosion distribution over the surface of a sputter target material is described. When the distribution is uniform, close coupling of the sputter target with the substrate to be coated is achieved, resulting in improved collection efficiency of the sputtered material by the wafer and improved film thickness uniformity. Elimination of erosion grooves provide for greater target consumption and longer target life. The cathode magnetron sputter source includes a rotating magnet assembly of a specific shape and a specific magnetic strength provides the desired erosion distribution. The target may be dished to improve uniformity near the periphery of the wafer. The resulting magnetron cathode is used for the deposition of thin films. Further applications of uniform magnetron erosion or preselected erosion include uniform or preselected magnetron sputter etch or reactive ion etch and concurrent deposition and etch.

Collimated deposition apparatus and method

Abstract: Sputtering apparatus and method which are particularly suitable for forming step coatings. A workpiece is supported in a chamber, particles are emitted from a sputter source in a substantially uniform manner throughout an area of greater lateral extent than the workpiece, the pressure within the chamber is maintained at a level which is sufficiently low to prevent substantial scattering of the particles between the source and the workpiece, and the particles are passed through a collimating filter having a plurality of transmissive cells with a length to diameter ratio on the order of 1:1 to 3:1 positioned between the source and the workpiece to limit the angles at which the particles can impinge upon the workpiece.

Wafer coating system

Abstract: Semiconductor wafers having patterns of steps and grooves defining microcircuit elements thereon are coated with metallic film by supporting the wafers individually adjacent a respective ring-shaped sputtering source in stationary relationship thereto. To effectuate such individual wafer processing on a continuous basis and preserve the evacuated argon environment, a vacuum chamber sputter coating apparatus is provided which has a number of work stations therein, at least one of which includes said ring-shaped sputtering source. Also included is a load lock, and an intermittently rotting vertical plate-like wafer carrier means therewithin positioned closely adjacent the chamber entrance, and carrying wafers in turn from the load lock to the work stations. The carrier includes apertures each accepting a wafer therewithin in an upright position, with the wafers edgewise resiliently supported by clip means, without the use of any externally-originating supports such as platens. Both surfaces of wafer can be accessed by processing equipment, for example, heating or cooling means at some of the work stations. Only a few wafers inside the chamber are at risk at any one time, and introduction of contaminants, debris, as well as disturbances to the chamber environment minimized.

Computed tomography apparatus using image intensifier detector

Abstract: Disclosed is a low cost computer tomographic (CT) scanner system specifically designed for radiation therapy treatment planning. A 512-channel photo-diode array (44) with digitizing electronics converts image intensifier (40) optical projection data directly into digital signals and has a dynamic range on the order of 1000,000:1. The new simulator includes a rotating gantry, an X-ray generator (30) with radiographic and fluoroscopic modes and a therapy style patient support assembly. Results on head and body size phantoms indicate that the simulator X-ray generator and image intensifier tube (IIT) (40) with multi-channel photo-detector (44) can produce photon statistic limited CT images. Software and hardware compensation methods are described which minimize geometrical distortions. Low noise, high input impedance electronics are employed which are phase locked to the line frequency. A dual sample interval method is employed which effectively increases the range of the digital signal produced by the front-end electronics by three additional bits.

Methods For Calculating the Internal Temperature of Capillary Columns During Capillary Electrophoresis

Abstract: The internal temperature, the buffer viscosity and the efficiency of heat removal from a silica capillary can be calculated by measuring the differential electroosmostic mobility at a low voltage and a high voltage. the calculated temperature is plotted vs the power generated by the electrophoretic instrument and yields a linear relationship when the power is below 3.0 W. the temperature can also be calculated using the conductivity of the solution. the two methods provide the same temperature, which compares well with literature values. A rule of thumb for a quick calculation of internal temperatures is that a power of 0.1 W

Method for improving the dynamic range of an imaging system.

Abstract: Disclosed is a method for improving the dynamic resolution of an imaging system. The method employs a dual sampling or exposure technique which samples light from an image intensifier (40) over a long and a short sample interval. When the resulting measurement for the long sample interval exceeds a threshold level, the short sample interval measurement is used, multiplied by a scaling factor (50). Below the treshold the long sample interval is used.

Method for increasing the accuracy of a radiation therapy apparatus

Abstract: Disclosed is a method for increasing the accuracy of images obtained in radiation therapy apparatus, such as computer tomography simulator which employs an image intensifier (40) and a photodiode detector (44) for converting light from the image intensifier to electrical signals for further processing. The method recognizes that a significant amount of crosstalk can exist in the image intensifier and photodiode detector chain and provides a series of steps for adjusting the electrical signals obtained from the photodiode detector to compensate for the crosstalk.

Electronically enhanced x-ray detector apparatus

Abstract: The detector of the present invention is suitable for use in a radiation therapy simulator machine. The detector comprises an X-ray image intensifier tube to convert X-rays into photons, a linear array of photodiodes to convert the photons to electrical signals, optical means for coupling the photons to the linear array of photodiodes, and electronic signal processing means for conditioning the signals from the photodiodes. The conditioning includes the use of low noise, phaselocked sampling electronics, implementation of a dual sampling technique for increasing dynamic range, implementation of a linearizing technique for increasing the accuracy of the measurements, and implementation of techniques for adjusting the measurements for point spread and background noise effects.

Charge neutralization apparatus for ion implantation system

Abstract: Methods and apparatus for neutralization of a workpiece (14) such as a semiconductor wafer in a system wherein a beam of positive ions (12) is applied to the workpiece (14). The apparatus includes an electron source (20) for generating an electron beam (22) and a magnetic assembly (24) for generating a magnetic field for guiding the electron beam (22) to the workpiece (14). The electron beam path (22) preferably includes a first section (34) between the electron source (20) and the ion beam (12) and a second section (36) which is coincident with the ion beam (12). The magnetic assembly (24) generates an axial component of magnetic field along the electron beam path (22). The magnetic assembly (24) also generates a transverse component of the magnetic field in an elbow region (26) between the first (34) and second (36) sections of the electron beam path (22). The electron source (20) preferably includes a large area lanthanum hexaboride cathode (42) and an extraction grid (44) positioned in close proximity to the cathode (42). The apparatus provides a high current, low energy electron beam (22) for neutralizing charge buildup on the workpiece (14).

Method of measuring total ionization current in a segmented ionization chamber

Abstract: Information on radiation dosage from segmented ionization chambers (10) can be incomplete due to the existence of insensitive regions of the chamber. By measuring the total current to the high voltage power supply (16), the total ionization current including that in the insensitive areas can be estimated, thereby providing a measure of the dosage to the insensitive areas.

Apparatus and method for multiple ring sputtering from a single target

Abstract: A source for sputtering from concentric rings (15) on the surface of a single target is shown. The source comprises a rotatable closed-loop magnet (21) having a plurality of curved sections of different average radius interconnected by an equal number of radial sections. In the preferred embodiment the curved sections each have a shape which results in a predetermined erosion profile in the associated concentric ring (15) of the sputter target (17). The relative rate of sputtering from each of the rings (15) may be controlled by adjusting the relative lengths of the curved portions of the closed-loop magnet (21).

High voltage dc source including magnetic flux pole and multiple stacked ac to dc converter stages with planar coils

Abstract: A high voltage high power DC source includes a magnetic flux pole structure responsive to a high frequency, relatively low voltage source inductively coupled to the pole. Multiple AC to DC converters inductively coupled to the pole are connected in series, stacked relationship with each other, to derive the high voltage, high power DC output. Each stage includes a pair of oppositely wound planar coils on opposite sides of a printed circuit board. The printed circuits of the different stages are displaced from each other and a coil driven by the high frequency source.

A high-power Klystrode with potential for space application

Abstract: A 500-kW peak power 50-kW average 425-MHz Klystrode has been designed and built as part of a major program on Klystrode development. The evolution of a high-power Klystrode design is discussed. An attempt was made to determine experimentally if a Klystrode would be a viable device in space applications at a 500-kW power level at 425 MHz. Testing proceeded in three phases. The initial testing was done on a beam simulation device to determine the characteristics of the gridded gun. The second phase consisted of low duty cycle full voltage and current RF testing. The third phase involved full duty cycle and long pulses (11 ms). >

High electron mobility transistor

Abstract: A high-electron mobility transistor or HEMT has a top surface layer (22) between its gate and drain arranged to produce a channel to drain conductance that is close to the ungated channel conductance to lower the output conductance and reduce gate leakage and gate capacitance. The transistor has high band-gap active layer (20) to produce a 2DEG channel (16) in an adjacent layer, and source (38), gate (34) and drain (40) electrodes on the active layer. An undoped or lightly doped surface layer (22) in the region between the gate and the drain produces a low conductance for a region of a few hundred A from the drain-side edge of the gate. This spreads the electric field domain over at least this few hundred A distance.

Chemical and Microbiological Analysis of Vacuum-packed, Pasteurized Flaked Imitation Crabmeat

Abstract: Various procedures were used to attempt to correlated spoilage of imitation crabmeat with sensory analysis after storage at 4 degrees C, 10 degrees C and 22 degrees C. Total volatile acids, total volatile bases, cadaverine, putrescine, histamine, aerobic plate count, and proteolytic count correlated well with product spoilage at 22 degrees C. Even though 22 degrees C is considered abusive, the only pathogenic organism isolated was Bacillus cereus. In contrast, at 4 degrees C and 10 degrees C, neither the chemical nor microbial indicators were adequate to assess quality of the product. Thus sensory analysis, despite its limitations, remained the only method currently available to assess product acceptability after prolonged storage at reduced temperatures.

Potential for localized, adjustable deep heating in soft-tissue environments with a 30-beam ultrasonic hyperthermia system.

Abstract: Initial heating rates (°C/min) along parallel tracks at depths of 1–14 cm in a static, muscle-like phantom were determined from time-temperature profiles obtained with 'Helios', a 30-beam ultrasonic hyperthermia system developed by Varian Associates. Data were taken at a single operating frequency of 556 kHz, for different sets of focal plane ring diameters of the four-ring array applicator, different levels of transducer driving power and two different focal plane depths, 6 cm and 9 cm. In each experiment, at each point of temperature measurement, analysis of temperature versus time data over a 2 min heating interval permitted separation of the desired phantom heating from artefactual heating resulting primarily from absorption of transverse (shear) waves produced at phantom-metal probe catheter interfaces. The results of the studies conducted suggest that in a non-translating carriage mode, Helios can produce axially and laterally localized deep heating in soft tissues for tissue volumes of lateral dime...

Power-combining and injection-locking magnetrons for accelerator applications

Abstract: The authors are investigating a number of approaches to achieve phase locking and power combining without the use of circulators. In the method described, the X-band waveguide 3 dB hybrid coupler provides the avenue for both injection locking and power combining of magnetron pairs. A series of experiments were undertaken where two magnetrons are injection locked and power combined, first operating into a matched load, then into a tunable short, and finally into X-band cavities. It was observed that injection-locked magnetrons can be used to drive a moderate Q cavity at long pulse without a circulator with excellent phase coherency. The cavity transient impedance does not preclude the magnetrons from filling the cavity, at least when the cavity fill time is less than the magnetron phase lock time. >

Fast- and super-fast-warm-up cathodes using novel APG/APBN heaters

Abstract: A fast-warm-up heater/cathode approach for microwave tubes is described. Anisotropic pyrolytic graphite (APG) deposited onto anisotropic pyrolytic boron nitride (APBN) was used to fabricate heater wafers. Both planar and spherical heaters can be produced. APG/APBN characteristics are discussed along with methods for heater fabrication. Measured fast-warm-up thermal cycling data are presented for 4 to 60 mm cathode diameters. Fast warm-up times of 1-2 s for 4.0-6.4-mm-diameter cathodes and less than 20 s for 60-mm-diameter cathodes were demonstrated with highly reliable thermal cycling performance. >

High power NMR probe

Abstract: An NMR probe employs an adjustable RF voltage divider (C 1 , C 2 ') comprising a single capacitive impedance switched into or out of the divider by a single 2-pole switch (SP1', SP2').

Rotor synchronized cross polarization of solid state NMR

Abstract: The cross polarization condition for hetero-coupled NMR spectroscopic investigations for a sample spinning at rate ω R is improved by causing at least one of the RF excitation channels to emit pulses in synchronous relationship to the sample spinner during the cross polarization contact whereby dependence of the NMR signal on mechanical spin rate ω R is reduced.

Stator assembly for a turbomolecular pump

Abstract: In a stator assembly for a turbomolecular pump, each stator is assembled from two semicircular portions mutually aligned and secured in place by tongue and grooves means, each such stator including a plurality of radially directed blades connecting an inner circular edge and outer circular edge of the stator, such edges occupying respective parallel displaced planes. The outer edge of each stator includes regularly outward projected tabs which bear between spacer rings to maintain axial alignment.

Prospects for a 1-THz vacuum microelectronic microstrip amplifier

Abstract: Microstrip amplifiers using vacuum microelectronic technology with 1-50-W output power at frequencies potentially up to 1 THz are discussed. Practical design limitations are described, including loss in the gated field emission microstrip, required field emission current, space-charge limitations on emission current, and heat dissipation. Two possible designs are presented. The vacuum microelectronic microstrip amplifier appears to be feasible, provided field emitters with the required current densities can be fabricated. Higher output power and amplification to frequencies of 1 THz may be possible by separating the electron collector and the output microstrip. Areas for further work are discussed. >

Reduction of gradient coil interaction with room temperature shims

Abstract: A gated amplifier drives a gradient coil when the gate signal is applied and the gate signal also controls an FET switch to disconnect a shim power supply from shim coils and connects the shim power supply instead to a dummy load. When the gate signal is removed, the shim coil is restored to operation from the shim power supply.

High power x-ray tube

Abstract: A high power x-ray generating tube (2) for reducing the effects of excessive heating of the window (16) through which the x-rays (16) are transmitted. The x-ray generating tube consists of a metal center section (6) having a stationary cathode (8) and a rotating anode (10). Various embodiments are employed for deflecting secondary electrons back scattered from the anode away from the window to avoid overheating of the window. A grounded anode simplifes the mechanisms required to prevent overheating.

Clamping a workpiece utilizing polyphase clamping voltage

Abstract: Apparatus for electrostatic clamping of a workpiece such as a semiconductor wafer in a vacuum processing chamber wherein an ion beam is applied to the wafer is provided. In one embodiment, the apparatus includes an electrically conductive platen, a resilient, thermally-conductive dielectric layer affixed to the platen and one or more conductive wires positioned on the clamping surface. The wires protrude at least slightly above the clamping surface except when the wafer is clamped thereon. A clamping voltage is applied between the wires and the platen to firmly clamp the wafer against the clamping surface and depress the wires into the resilient dielectric layer. The clamping voltage preferably comprises a bipolar square wave in the frequency range of less than one Hz to 300 Hz and having a switching rate of about 1000 volts per millisecond or less to limit charging current to the wafer and thereby prevent arcing. In another embodiment, a three-phase wafer clamping apparatus includes a platen divided into three electrically-isolated sections. One phase of a three-phase clamping voltage is connected to each of the platen sections. In the three-phase configuration, the wafer charging current is very small, and the clamping force is essentially constant.

Carm amplifier designs for high power

Abstract: The cyclotron autoresonance maser (CARM) is shown to be capable of extremely high power efficient operation with relatively weak magnetic field requirements. A general description of the CARM traveling wave amplifier is presented. The linear theory is applied to study the stability of the device and a self-consistent numerical simulation code is used to predict the performance. It is found that grazing intersection often gives superior performance, especially for high current electron beams. The designs of two CARM amplifiers for the applications of a high gradient rf linac and electron cyclotron resonance plasma heating as well as a proof of principle experiment are presented.

Partial fan beam tomographic apparatus and data reconstruction method

Abstract: A computed tomography method and apparatus for sequentially projecting partial fan beams through a sample (32), measuring data resulting from each projection, and generating an image of a sample section from the measured data without reordering the measured data to simulate data obtained by projecting parallel ray beams through the sample (32). Partial fan beam radiation received at a detector array (44) is processed to image a larger diameter sample section than could be imaged with full fan beams projected from the same source to the same detector array (44) with the same source-to-detector spacing(s). Preferably, X-ray radiation is transmitted through the sample (32) and the system includes an image intensifier tube (40) for receiving data representing at least a portion of the transmitted radiation. Preferably, the invention includes a linear detector array (44) which receives the image intensifier tube output and an extension detector array (45) which receives partial fan beam radiation which has propagated through the sample but which is not incident at the image intensifier tube. The data measured during each partial fan beam scan are preferably weighted to simulate full fan beam data. The weighted partial fan data signals are then processed in the same way as if they were unweighted data signals resulting from exposure of the sample (32) to full fan beams.