Showing papers by "Varian Associates published in 1988"

Mutileaf collimator for radiotherapy machines

Abstract: In a radiation therapy machine it is desirable to produce irregular radiation field shapes in order to shield critical organs not invaded by the tumor. A multileaf collimator is formed of a multiplicity of heavy metal bar leaves driven relative to frames which are driven relative to jaws of a rectangular field collimator by electric motors and flexible cables.

Mode suppressors for whispering gallery gyrotron

Abstract: A gyrotron interaction resonator 29 operating in a TEn1 cavity mode has an array of longitudinal slots 32 in the conductive wall 30. The slots 32 are spaced to couple to the unwanted TEn1 modes and to other modes of differing n and not to the desired mode. Wave-absorptive material 34 spaced from the inner cavity wall 28 and coupled to slots 32 absorbs the unwanted modes.

Junctions for monolithic cascade solar cells and methods

Abstract: In order to increase the efficiency of solar cells, a monolithic stacked device is constructed comprising a plurality of solar sub-cells adjusted for different bands of radiation. The interconnection between these sub-cells has been a significant technical problem. The invention provides an interconnection which is an extremely thin layer of gold formed between the sub-cells by organometallic chemical vapor deposition. Such a layer tends to form beads which serve as a low resistance shorting interconnect while passing a large fraction of the radiation to the lower sub-cells.

Apparatus for retaining wafers

Abstract: A device for releaseably holding a workpiece includes a resilient collet which is pivotally attached to a base Several fingers for holding the workpiece extend from the collet The fingers are pivoted by actuating a member which elastically deforms the collet and causes the fingers to pivot from a position for engaging the workpiece to a position for releasing the workpiece and vice-versa In one application, the base is a platen for supporting a wafer in a semiconductor processing system and a plurality of such platens and a corresponding plurality of the holding devices are arranged around the periphery of the disk A counterweight ring is attached to the ring-shaped collet to counter-balance the moment generated by the centrifugal force of the wafer pressing against the fingers as the disk is rotated

Methods and apparatus for thermal transfer with a semiconductor wafer in vacuum

Abstract: Thermal transfer between a semiconductor wafer and a platen during vacuum processing is provided through a soft, thermally-conductive polymer layer having a thin, hard surface film. The soft polymer layer, which is preferably silicone rubber containing thermally-conductive particles, conforms to surface irregularities on the wafer and has low thermal resistance. The surface film is preferably silicon dioxide in the form of a multiplicity of flat plates integrally formed on the silicone rubber. Adherence of the wafer and of foreign matter to the polymer layer is prevented by the surface film. In addition, the underlying polymer layer is protected by the surface film. A high purity polymer layer is fabricated by evacuating the mold cavity and the resin container prior to injection of resin. The mold for the polymer layer utilizes a hard, smooth mold release surface and a resilient gasket between the platen and the mold release surface. The gasket establishes the dimensions of the polymer layer and seals the mold cavity. The surface film is formed by oxygen plasma treatment of the silicone rubber layer.

Sputter module for modular wafer processing machine

Abstract: A sputter coating module for a multifunction processing machine is provided in which the supporting mechanism for the workpiece can be isolated from the sputtering source, the pumps and other processing apparatus for cleaning without exposing the entire machine to atmosphere. The supporting mechanism which is rotatable from the horizontal to the vertical is hollow and mounted on hollow vacuum-sealed trunnions to allow passage of water, argon, and dry-nitrogen or air at atmospheric pressure into the interior of the supporting mechanism.

Horizontal laminar air flow work station

Abstract: A load chamber (6) of a load lock is provided with a vertical air curtain which isolates the load chamber (6) from the general clean room environment. Horizontal air flows generated in the load chamber (6) bathe wafers (W) held horizontally in the chamber with filtered air. These horizontal air flows are captured by the air curtain and recirculated to filters (26b,28b) which provide horizontal and vertical air flows in the load chamber (6). If desired, the vertical and horizontal flows may be driven by the air supply mechanism of the clean room itself.

Wafer support assembly

Abstract: An assembly is provided for supporting semiconductor wafers individually within a support while permitting processing of both faces of a wafer as well as facilitating rapid insertion and removal of wafers into the support. Each assembly includes a wire clip having an arcuate tip used to grasp the wafer. The wire clip can be moved in two planes by actuating mechanisms, thereby moving the clip out of the plane of wafer processing and facilitating loading in the wafer processing plane.

Microwave field effect switch

Abstract: A monolithic microwave integrated circuit switch includes a series field effect transistor having a source drain path in series with an inductive transmission line including plural taps. Source drain paths of plural shunt field effect transistors are connected to the taps. The source drain paths of the series and shunt transistors are biased so that the series and shunt source drain paths have complementary low and high impedance states. The high impedance state is capacitive, having a value on the order of magnitude of the inductive transmission line. During a first time interval, the capacitive and inductive impedances form a matched low pass filter to supply current from a microwave source to a load. During a second time interval, current from the microwave source flows through the shunt field effect transistors to be decoupled from the load. The circuit is in stripline form, with source electrodes of field effect transistors including first and second arms respectively having first and second elongated parallel sides. First and second elongated edges of drain electrodes of the transistors extend parallel to the elongated sides. A gate electrode of each transistor includes first and second elongated fingers respectively extending parallel the elongated sides and edges. The first finger is between the first side and first edge; the second finger is between the second side and second edge.

Titamium nitride sputter targets

Abstract: The present invention provides a sputter target for the deposition of titanium nitride films. The sputter target has a target face comprising titanium nitride having a density of at least 90% of the theoretical density of 100% pure titanium nitride. The sputter target is prepared by subjecting titanium nitride powder to hot isostatic pressure.

Modelling of chemical vapor deposition reactors

Abstract: The design and development of chemical vapor deposition reactors has historically been done experimentally. In recent years, however, the performance of these reactors has been pushed to the limit, requiring more time and expense to develop new systems. This paper will review the recent development of mathematical techniques for the modeling of such reactors. Methods for modeling of low-pressure, cold-wall and hot-wall systems will be covered as well as high-pressure reactors (≈ atmospheric). The basic concepts involved in describing the flow of reacting gases, including gas phase and surface reactions, will be presented. The techniques that have been employed (which include surface reactions in the mathematical description so that deposition rates may be calculated) will be reviewed as well.

Quick change sputter target assembly

Abstract: A sputtering target assembly is disclosed having a sputtering gun with an inner and outer annular wall, where the inner annular wall has a plurality of radially projecting set screws, threadably movable within threaded apertures in the inner annular wall. A mounting ring is profiled to fit over the inner annular wall, the mounting ring having a recessed grove, into which the set screws are received, to secure the mounting ring. The mounting ring includes a plurality of radially disposed spring plungers which are threadably installed in threaded apertures in the mounting ring. The target has a grooved inner annular surface for receiving the spring ball plungers, whereby the target is retained to the sputtering gun.

High voltage power supply for a microwave electron tube

Abstract: A power supply for helix and collector electrodes of a traveling wave tube is driven by an AC power source having a frequency of at least 500 KHz. The helix supply includes plural, stacked voltage double AC to DC modules responsive to the 500 KHz source. The collector supply includes plural AC to DC modules, each having a diode full wave rectifier bridge, connected in stacked relation. Each of the modules includes a transformer with a ferrite, toroidal core dimensioned so that it is not driven into saturation by the 500 KHz source. Each module also includes inexpensive, signal switching diodes having a recovery time of approximately 4 nanoseconds. The ratio of the collector to helix DC voltages is maintained constant by threading a common lead through the apertures of the toroidal cores of the helix and collector modules. A separate common lead threaded through the apertures of the toroidal cores in the collector modules is connected directly to the 500 KHz power source. A feedback circuit responsive to the helix-cathode voltage of the TWT controls the helix power supply voltage precisely.

X-ray tube exposure monitor

Abstract: An X-ray tube exposure monitor for recording the emissions from a diagnostic X-ray tube A photo diode is mounted inside the X-ray tube bulkhead and detects radiation from the X-ray tube The photo diode is connected to a high gain amplifier and, in response to radiation being detected, the output of the amplifier sends an electronic signal to a microprocessor The microprocessor records the emission duration and the temperature of oil around the X-ray tube and increments an exposure count The recording and exposure count is stored in non-volatile memory which is read later by a service technician

High voltage DC power supply

Abstract: A DC power supply for a traveling wave tube having cathode, collector and helix electrodes responds to a DC power source and a high frequency switching source. A switch controlled by the switching source is opened and closed at a fixed frequency and variable duty cycle determined by the helix-cathode voltage. A flyback choke is connected to the switch and DC power supply so current flows between the power source via the choke to the switch and a series resonant circuit while the switch is closed. First and second capacitors in separate branch circuits of the resonant circuit are respectively connected to first and second AC to DC converter and voltage multiplier stacks; each multiplier in the stacks includes a pair of branches with oppositely poled plural signal switching diodes and a capacitor. The cathode and helix are respectively connected to output terminals of the first and second stacks, while the collector is connected to a terminal between the first and second stacks. The resonant circuit is connected with the switch, flyback choke and voltage multipliers so that while the switch is closed a half-wave rectified current waveform at the resonant circuit resonant frequency flows in the resonant circuit and a ramping current having a first polarity direction flows in the choke. A ramping current having a second plurality direction flows in the choke and resonant circuit while the switch is open.

Photoelectron sources: Selection and analysis

Abstract: Laser-driven photoemissive cathodes have generated extremely bright pulsed electron beams with normalized brightness of 10 7 A/(cm 2 rad 2 ). Intense beams have been observed with pulse widths of 60 ps and 50 ns, indicating a wide temporal range over which this technology is applicable. Although only Cs 3 Sb and GaAs(Cs, O), both irradiated by a frequency-doubled Nd laser, have, so far, been studied, other semiconductor photoemitters are available and metal, or metal compound, photoemitters, driven by UV lasers, are possible contenders. Proper selection of a photocathode for a specific free electron laser application is outlined. The problem of plasma formation, due to the application of excessive electric fields on the electrodes, is also addressed. Such plasmas limit the maximum current densities that may be extracted at a given accelerating voltage and pulse width. A comparison between photocathodes, thermionic cathodes, and cold cathodes is made in terms of their respective brigthnesses and potential for operation at high current densities.

Compensated scan wave form generator for ion implantation equipment

Abstract: A scan controller for an ion implantation system includes a compensation circuit for generating a scanning signal from a triangle voltage signal. The scanning signal causes an ion beam to be deflected so that, in the variety of geometries describing the orientation of the target in the implantation system, the position of the intersection of the ion beam with the planar target surface changes linearly with time. In one embodiment the scanning signal has the form v(t)=-d -e/(t+c). In other embodiments the compensation circuit approximates the above function by means of polynomials.

Counterflow leak detector with high and low sensitivity operating modes

Abstract: A counterflow helium mass spectrometer leak detector in which a helium sample passes in a reverse direction through a diffusion pump (26) to a mass spectrometer (36) for measurement. The diffusion pump (26) includes a conventional foreline (24) and a second foreline (32) provided with an ejector stage (79). A test sample (8) is coupled from a test port (10) through a bypass valve (22) to the conventional foreline (24) in a high sensitivity mode and is coupled to the second foreline (32) in a low sensitivity mode. In the low sensitivity mode, the bypass valve (22) is closed. An apertured control plate (84) in the diffusion pump (26) controls the relative reverse rates of diffusion from each foreline (24, 32) to the diffusion pump inlet (38) by controlling the rates of vapor flow to annular pumping stages (75, 77) and to the ejector stage (79). The ejector stage (79) includes a nozzle (80) for directing a stream of vapor into the second foreline (32) so as to inhibit flow of helium into the diffusion pump (26) and establish a lower reverse diffusion rate at the second foreline (32). The disclosed configuration permits measurement of a large range of leak rates.

Low deflection force sensitive pick

Abstract: A tactile pick includes a base and a lever attached beneath the base by a pivot. A load sensing device including a strain gauge is located between the base and the portion of the lever on one side of the pivot; the portion of the lever on the other side of the pivot is adapted to receive a semiconductor wafer. Rotation of the lever about the pivot induced by the weight of a wafer causes an actuator to depress a flexible member on which a strain gauge is mounted. The output signal of the strain gauge is processed by a controller to provide an output signal which varies monotonically with the magnitude of the weight placed on the wafer receiving portion of the lever. The pick is employed in connection with the wafer transport system which transfers wafers from a cassette to the pick lever.

Nonresonant multiphoton-ionization yields from Gaussian laser beams

Abstract: The yield of ions from nonresonant multiphoton ionization from a focused laser beam is most intense in the laser beam’s focal plane, where the laser irradiance is most intense. However, appreciable ion yields can exist at significant distances from the focal plane along the laser axis. In many experimental situations ion detectors are sensitive only to limited extents along the laser axis, and ions generated beyond these limits are not detected. We include this effect here and show that for a Gaussian beam this effect can be considerable in realistic situations. We also show that the ion yield can be described by a function of two dimensionless variables, and we present approximate analytic expressions for the yields.

Cryosorption surface for a cryopump

Abstract: A two-stage cryosorption pump has a first stage at a higher temperature and a second stage at a lower temperature. Sorption surfaces of reticulated vitreous carbon formed on the second stage have high rigidity and exceptionally high void volume.

Growth rate monitor for molecular beam epitaxy

Abstract: A light source with appropriate optics focusses light on the wafer surface during deposition, while a nearby collector is biased to collect photoemitted electrons from the growing surface. A pico ammeter can be used to convert the small oscillatory current detected to a substantial voltage signal which can be recorded or processed by computer or other sutiable device. The light must contain wavelengths at energies close to or greater than the energy of the photoemission threshold. The detected photoemitted electron signal has an oscillatory component occurring due to the growth of epitaxial layers. This oscillation has frequency 1/τ, where τ is the monolayer accumulation time.

NMR spinner speed control

Abstract: An NMR sample spinner comprises first rotational torque means to impart a first rotation to a sample rotor and a second rotational torque means for applying a rotational torque of selected magnitude opposite that applied by said first rotational torque means, whereby positive rotational rate control is more precisely and rapidly realized, sense of rotation is controlled, and undesired rotational torques may be compensated.

Millimeter wave circulator

Abstract: A millimeter wave wideband circulator (10) which employs a triangular ferrite prism (36) with symmetrically grooved sides (40) The prism is configured to support a pair of closely-spaced higher order resonance mode sets which function to enlarge the bandwidth of the circulator and to suppress spurious mode resonances in the centre and roll-off portions of the bandpass The simplicity of the junction design combined with the non-critical alignment requirement of the ferrite prism makes practical the fabrication of a multi-junction millimeter wave circulator in a single intergrated housing

Multiple sheet beam gridded electron gun

Abstract: A gun for generating a multiple sheet beams 50 of electrons has a flat surfaced cathode 10 with parallel protruding ridges 12 of non-emitting material forming parallel focus electrodes for the sheet beamlets. A control grid of parallel bars 14 is aligned with the ridges 12 to reduce grid interruption. The beamlets may be focussed between support bars 54 of a foil anode 52 for passing the beam into a high-pressure volume such as a gas laser 48. The ridges are formed by inserting non-emissive bent sheets into grooves 58 in the cathode, which are dovetailed to hold them.

Generic expert system shell for diagnostic reasoning

Abstract: Rule based expert systems provide a modular and uniform approach to representing knowledge, however it has been recognized that rule-based systems become increasingly difficult to understand and maintain as the number of rules grow. Expert systems today are developed on general purpose inference shells that offer general purpose paradigms which do not take into considerations the type of problems being solved. It is up to the users to create the meta level control to prevent rule interference, and for the rules to function properly. This task tends to become increasingly difficult in direct proportion to the size of the accumulated knowledge.The solution is in a new generation of Application Specific Expert System Tools that are designed with specific paradigms and knowledge representation methodology that meet the requirements of a specific domain. This concept is examplified in the work presented here that introduces a generic expert systems shell for diagnostic reasoning. Domain knowledge is represented as five different classes of objects. A paradigm for diagnostic reasoning is built into the inference algorithm to become part of the inference shell, replacing the usual general purpose forward or backward chaining algorithm.

Fluid flow sensor with flexible vane

Abstract: A flow sensor for regulating the air flow rate to a cooling system can be formed as a housing for channeling the flow through a retangular cavity and a one piece vane of bent metal strip which deflects and closes an electrical contact at a predetermined air flow rate and opens when the air flow rate falls below a preset threshold level.

Sputter manufacturing method for superconducting wire

Abstract: A superconducting wire containing brittle super­conducting material is formed by passing a core filament (42) through a sequence of hollow cathode sputtering chambers (26,30) which, in turn, deposit a sequence of layers (44, 46) of superconducting and non-superconducting materials. The hollow cathode sputtering source makes efficient use of precious materials and coats the core uniformly.

Rapid thermal chemical vapour deposition apparatus

Abstract: In a chemical vapor deposition apparatus for coating semiconductor wafers, the wafer is held face down in the reaction chamber. A radiant heat source above the wafer and outside the reaction chamber heats the wafer from its backside of a temperature in excess of 1000°C rapidly. In the selective tungsten process the temperature of the wafer is raised from ambient to about 600°C while flowing process gases. At the upper temperature range the heating source can be rapidly cycled on and off to improve the uniformity of coating.