Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/58—After-treatment
  • C23C14/5826—Treatment with charged particles
  • C23C14/5833—Ion beam bombardment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/221—Ion beam deposition
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C26/00—Coating not provided for in groups C23C2/00 - C23C24/00
  • C23C26/02—Coating not provided for in groups C23C2/00 - C23C24/00 applying molten material to the substrate
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J27/00—Ion beam tubes
  • H01J27/02—Ion sources; Ion guns
  • H01J27/08—Ion sources; Ion guns using arc discharge
  • H01J27/14—Other arc discharge ion sources using an applied magnetic field
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
  • H01J37/317—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation
  • H01J37/3178—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation for applying thin layers on objects
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/30—Electron or ion beam tubes for processing objects
  • H01J2237/31—Processing objects on a macro-scale
  • H01J2237/3142—Ion plating

Definitions

• This invention primarily addresses the general problem of high volume deposition of coating layers for the materials industry.
• the current invention solves the problem of low cost, commercial scale deposition of coating materials with properties enhanced beyond those resulting from unassisted deposition techniques.
• a major problem in the general area of physical deposition of one material upon another has been the difficulty of influencing the final state of the overall structure.
• the primary parameters controlling the results of most physical deposition techniques are the relative heat capacities and thermal conductivities of the substrate material and of the material being deposited. As these material parameters cannot be altered, the most important process control parameter is the substrate temperature, followed closely in importance by the deposition rate.
• one deposits a first layer which exhibits good adhesion to the substrate, then deposits the desired layer on top of the intermediate layer, which also exhibits good adhesion to the top layer.
• adhesion between smooth non-alloyed layers is essentially a function of their surface energy, such that a layer having a low surface energy will adhere strongly to a substrate having a high surface energy.
• the reason for poor adhesion is that the desired coating material has higher surface energy than the substrate. (Other reasons will be discussed later.) If so, and an intermediate layer has even lower surface energy than does the substrate, the naive expectation is that the top coating will exhibit even less adhesion to the intermediate layer than to the substrate. This problem most often appears when the interfaces between materials are'clean and abrupt.
• the deposition rate is set roughly at a value which allows the atoms being deposited to diffuse about the surface, comfortably finding places in the growing crystal structure before being buried by the next layer.
• IBAD Ion Beam Assisted Deposition
• the ion dose per cm 2 of surface required to significantly alter the process of physical deposition must be on the order of 10 1S - 10 16 ions per cm 2 per layer of atoms deposited. If the dose is much smaller, there will be little or no effect evident on the growing structure. If the dose is much greater, amorphization or other forms of degradation of the excited region is common, owing to the combination of large-scale ion damage of the crystal lattice and the rapid quenching of the damaged regions which prevents regrowth of the crystal. As a result, for a typical growth rate of ⁇ lA per second, the ion beam current required for IBAD is about 0J - 1 miliiamp / cm 2 . (This is a relatively high beam current density; accordingly, most experiments to date have actually used lower currents, and hence smaller growth rates.)
• the total thermal load on the structure from this level of irradiation is less that 1 watt / cm 2 .
• the thermal time constant of the excited region is subnanosecond for many materials, it is clear that there is effectively no local increase in temperature in the near-surface region. IBAD thus depends solely on nonthermal collision-induced atomic displacements to attain its benefits.
• IBAD is a nonthermal process, it does not produce alterations in properties of the growing film which depend more upon rapid thermal treatment than on ion beam mixing and densification. Such properties are important for many coating applications, ranging from corrosion-resistant coatings for metals to optical coatings and microelectronics.
• the present invention is directed to a new approach to ion assisted beam deposition, called Pulsed Ion Beam Assisted Deposition (PIBAD), and to apparatus capable of carrying out said new approach, that satisfies the aforementioned needs of the materials industry.
• the essence of the pres nt invention is the periodic thermal treatment of a thin surface layer (-1-10 ⁇ m) during the growth process.
• growth and pulsed ion beam are nearly independent processes, the growth process serving primarily to deposit material on a surface, whereupon the pulsed ion beam then converts that material into the desired final structure.
• PIBAD thus depends on a fundamentally different approach to material deposition than does the IBAD process.
• Figures 1-3 describe an IBEST rapidly repeating pulsed ion accelerator, comprising a
• FIG. 1 is a schematic of the RHEPP pulsed power system
• Figure 1A is a circuit diagram of a pulse compression system 15 utilized in the pulsed power system of Figure 1;
• Figure IB is a cross-sectional view of a pulse forming line element
• Figure IC is a cross-sectional view of the Linear Inductive Voltage Adder (LrVA);
• FIG. 2 is a partial cross-sectional vie of the magnetically-controlled anode plasma (MAP) source 25 of the present invention
• Figure 2A is a modified version of Figure 2 showing the magnetic field lines produced by the fast and slow coils in the MAP source'
• Figure 2B is an expanded view of a portion of Fig. 2 showing the gas inlet valve and the gas inlet channel;
• Figure 2C is a schematic diagram of the electric circuit for the fast coil;
• Figure 3 is a schematic full cross-sectional view of the MAP ion diode.
• Figure 4 is a set of schematic diagrams of various aspects of the PIBAD processes.
• Figure 4A is a schematic diagram of a process by which material ablated from a first material surface is redeposited onto that surface;
• Figure 4B is a schematic diagram of a process by which material ablated from a first material surface is redeposited onto a second material surface; and
• Figure 4C is a schematic diagram of the treatment of a deposited layer. Description
• the essence of the PIBAD process is to apply a rapidly repeated pulsed thermal treatment of a near-surface region concomitant with the process of growing a material on a substrate, thus altering the characteristic structure of the composite structure.
• This thermal treatment is applied by irradiating the growth surface with one or more pulses of high current ions during and/or following the growth process.
• the primary effect of an ion pulse is to dramatically raise the temperature of a thin surface layer, rather than the nonthermal collisional effects associated with ion implantation.
• this thermal energy can be used for three major effects, annealing, melting, or vaporization of the near-surface region of the sample.
• Figure 4C illustrates schematically the process of PIBAD treatment of a film 45 grown on a substrate 42.
• the film is grown by a growth apparatus (not shown).
• the ion pulse generator 40 generates an energetic pulse of ions 41 which intersect the surface of film 45.
• only film 45 may be heated, or both film 45 and substrate 42 may be heated.
• Ion beam pulses having relatively small amounts of energy can be used to provide a rapid thermal anneal to the composite structure.
• the ion pulse surface energy densities for the annealing process should be such as to not melt the target, but should come close enough to the melting point (perhaps 0.6-0.99 T m ) so that the thermal effects are significant during the period in which the target surface remains hot.
• the melting temperature is -1350 °K.
• the desired ⁇ T is -1100 °K.
• the first relation above gives the surface energy density of the ion beam pulse as ⁇ - 1.9 J/cm 2 .
• the thermal time constant of the ion-heated region is ⁇ t - 200 nsec.
• ⁇ is only about 0.1 J/cm 2 , while ⁇ t - 500 nsec.
• a final metallic example is stainless steel, where the same normalized annealing conditions will require ⁇ ⁇ 0.6 J/cm 2 and the time constant, owing to the lower thermal conductivity of alloys, is ⁇ t - 5 ⁇ sec.
• the desired effect will vary over a wide range of pulse energies depending on what the target material is.
• general statements about the amount of energy- required and the thermal time constant associated with a given irradiation condition are not possible, but must be calculated roughly for each situation using the above relations.
• Another important factor is the rate at which the temperature quenches following the heating effects of the ion pulse. This parameter is approximately ⁇ T/ ⁇ t ⁇ ⁇ K /(cp) 2 ⁇ 3 .
• the quench rate for the above examples range from ⁇ 10 t0 °K sec for the copper example to - 10 °K sec for the stainless steel. Note that the value of ⁇ T/ ⁇ t varies as ⁇ "3 , so that the ion penetration depth (or equivalently the ion kinetic energy) is by far the most important parameter in determining the quenching rate.
• the ion beam pulse is then used to melt and regrow this material, thereby greatly improving the character of the material.
• Another application if the ion pulse penetrates deeply enough that the substrate-growth layer interface is melted, is the formation of a highly alloyed region in many material combinations, even when such alloys are not thermodynamically preferred at the intended operating temperatures for the completed composite structure. Note that, since as much as 10 ⁇ m of material may be treated by a single ion pulse, and we shall see that the IBEST system is easily capable of pulse rates of 100 pps, in principle the resulting transformation from highly-defective material to high-quality material would make a deposition rate on the order of 1 mm/sec practical.
• the current invention thus has the potential to deposit material at a rate some 3-4 orders of magnitude faster than existing processes, opening the door to growing machine parts directly by physical deposition, a technique which might be particularly useful for gas turbines and jet engine components.
• the surface layer of the composite structure will be vaporized, again typically to a depth approximating that of the penetration of the ions. This might seem a strange thing to do when the goal is to grow a film.
• a shock wave is transmitted into the surface. If a 10 ⁇ m layer is vaporized in -100 nsec, and the material vaporized has a specific gravity of -10, the inward propagating shock wave has a magnitude on the order of 1 Gpa, or 10 kbar.
• shock wave is strong enough to cause plastic flow and dislocation multiplication in almost any materials, thereby dramatically changing the mechanical properties of the non-vaporized remnant surface. In particular, extreme hardening of the surface would be common.
• ⁇ 1 eV low-temperature
• FIG. 4A This effect is shown schematically in Figure 4A, subfigures 1-4.
• an short pulse of ions 400 approaches the near-surface region 401 of the substrate 402.
• the thickness of 401 is the ion penetration range in the substrate material, and the total energy of the pulse is sufficient to vaporize the material in 401.
• the pulse of ions has been absorbed by the near-surface region 401, which has now vaporized.
• the pulse is of short enough duration (-100 nsec) that the material in 401, although vaporized, has not had time to expand significantly.
• the material in 401 is expanding, although it still has very high pressure and density.
• Another possibility is that one might desire to vaporize a layer of material thicker than the deposited layer.
• the object would be to alter the properties of the original surface while causing as little evaporation of the original surface as possible. This could be accomplished by depositing a sacrificial layer on the 1 surface, and then applying an ion pulse sufficient to vaporize a surface layer somewhat thicker that the sacrificial layer. If the parameters were carefully chosen, the material redeposited on the surface would be substantially that portion of the original surface which was vaporized.
• the surface would have been subjected to a strong shock wave and to a high-pressure high-speed redeposition of the vaporized materials, but would still consist substantially of the original material of the surface, and the location of the final surface would be substantially that of the original surface.
• the properties of the treated surface would be changed in a manner not accessible even through the rapid melt and regrowth which can be produced using weaker ion beam pulses for thermal treatment.
• Another application for the PIBAD process is in the cleaning of volatile materials from surfaces. It is possible to heat a surface sufficiently to remove, for example, a layer of hydrocarbon contaminants without disturbing the underlying structure. Such a cleaning process might be useful in microelectronics, plating, mechanical assembly, and the food industry, removing the problem of using carcinogenic solvents.
• the processes outlined are simple illustrations of the potential of the use of pulsed ion beams combined with conventional growth processes.
• the PEBAD process is primarily controlled by the depth of penetration of the ions and the total energy of the ion pulse. Because there typically are no chemical effects involved in the use of PIBAD, the identity and kinetic energy of the ions are unimportant as long as the desired penetration depth of the ions is attained.
• any accelerator system which can generate pulses of ions having suitable kinetic energy, peak power, and total energy per pulse can be used in the PIBAD processes which make up the present invention.
• the IBEST system which is the subject of a copending U.S. patent application (08 /317,948) will be discussed in some detail., but not the invention is not intended to exclude other pulsed ion accelerator systems.
• IBEST generally uses ion energies above 20 keV (more generally above lO ⁇ 'keV) * and below about 1 MeV, resulting in an ion penetration depth on the order of 1-50 ⁇ m, depending on the identity of the ions and the target atoms. This is in sharp contrast to the few nanometers affected in the IBAD process.
• IBEST apparatus can generate ion energies above 10 MeV, but such energies are not well suited to the present invention.
• IBEST apparatus appropriate for PIBAD applications typically would have an average power of a hundred kilowatts and a pulse repetition rate of about 100 pps.
• the total energy per pulse is thus about a kilojoule.
• the peak power of the ion pulse is about 10 10 watts.
• the MAP diode can irradiate an area ranging from about 5- 1000 cm 2
• the surface energy density of the ion pulse ranges from about 1-200 J/cm 2 when the IBEST system is operating at full power (100 k ⁇ V)- If lower surface energy densities are required, either the ion beam can be defocused or the energy per pulse can be reduced.
• the power and timescales described above are sufficient to anneal a coating, melt and regrow a film, or to vaporize a near surface layer.
• the thermal time constant of the heated layer in metals is about 1-l Otimes that of the ion pulse itself, so the PIBAD treated material quenches at a rate on the order of 10 8 °K sec or greater, fast enough that the high temperature structure is generally preserv ed.
• the near-surface region melts and then regrows using the underlying atomic structure as a substrate.
• Such treatment tends to remove undesired structures (e.g., amorphous structures) and to densify the near-surface region.
• Application of IBEST technology to the problem of material deposition thus provides a previously unknown versatility for controlling the structure of the finished article.
• the total material deposition rate would be so high that the pre-pulse structure would be highly defective on both the atomic and macro levels.
• the only function of the material deposition process is to put material on the growth surface. The material is then altered into the desired structure by the thermal effects of the PIBAD process. This suggests that, using IBEST technology, a high-quality material deposition rate on the order of 0J - 1 mm/sec should be possible for materials which can handle the heat load. This rate is 10 4 to 10 6 times faster than any previously known deposition process capable of yielding high-quality structures.
• the enormous deposition rate made possible using the PIBAD process makes possible the construction of macroscopic products using physical deposition.
• Such a product would be a gas turbine blade for small natural gas generators.
• a gas turbine blade for small natural gas generators.
• such a device should take less than 1 hour to grow, using variable aspect deposition masks to define the structure of the turbine blade.
• the use of multiple PIBAD pulses per growth cycle might make possible formation of a densified quenched high-temperature structure that might outperform conventional turbine blades.
• PIBAD process to make diesel engines for trucks with a deposition period of a few hours, ivfn and advanced IBEST system capable of irradiating larger areas.
• the internal and external structures of the engine would be built up using masks, in a manner similar in principle (if not in detail) to the operation of a 3-D laser pantograph.
• the alloys could be regrown, heat-treated, shock-treated, and high- pressure vapor redeposited in precise locations, it would not be surprising if a process could be developed to meet the DOT goal of producing a diesel engine for trucks having an expected lifetime of a million miles.
• the PIBAD system clearly has great potential for manufacture of large-scale commercial products.
• a pulsed ion source 40 can irradiate portions of a target material 42 with a sufficiently energetic pulse of ions 41 to vaporize the near surface region of substrate 42, forming a plume 43 of vaporized material.
• the growth surface 44 can then be positioned so that the plume 43 of vaporized material from the target is captured thereon.
• a second IBEST system will usually be set up to irradiate the growth surface. This IBEST system will be adjusted to facilitate the PIBAD melt and regrow process, thereby producing high-quality material. It is possible to use a single IBEST system for irradiation of both the deposition source and the growth surface, but this involves additional beam steering hardware.
• the ion pulse has a total delivered energy of 10 kJ (thus, a 1 M ⁇ V IBEST system). Adjust the ion energy and ion identity until a plume having a kinetic energy of about 2 eV results. The vapor then has an effective temperature of about 10000 K.
• the total amount of material vaporized is roughly 0.05 gram-mole, or about 3 gms of steel. Some of the material redeposits on the deposition source surface, but how much is a function of the material and the temperature of the plume. However, the amount redeposited will always be much less than half of the total material vaporized.
• pulsed sources of energy for thermal treatment can include lasers, pulses of plasmas, as from plasma railguns, and pulsed electron beams, all of w hich would be used in a manner similar in essence to the IBEST system.
• ion beam sources A variety of ion beam sources exist. Typical ion beam generators use dielectric surface arcing on an anode as a source of ions and thereafter magnetically or geometrically direct and focus the generated ion beam onto the material of interest. This surface arcing (also called “flashover”) destroys the anode surface in less than 100 pulses, and produces a mixed species of ions that cannot be adjusted. Other difficulties arising from flashover include: production of large quantities of neutral gas that makes high repetition rate difficult, generation of debris which can contaminate surfaces being treated, and non-uniformity and irreproducibility of the beam in some cases due to the localized and difficult to control nature of flashover ion sources.
• State-of-the-art ion beam generators are typically "one shot” devices, i.e., they operate at low repetition rates ( « 1 Hz).
• Existing high intensity ion beam generators cannot be operated at high repetition rates (» 1 Hz) for a number of reasons.
• existing pulsed power supplies are not able to generate electrical pulses at high repetition rates having the voltage, pulse width (i.e., nominal temporal duration), and pulse energy required to generate the ion beams needed for the various beneficial applications described herein. This limitation renders commercial exploitation impractical.
• one shot surface treatments from a robust ion beam source are adequate for some purposes.
• MAP Magneticically-confined Anode Plasma
• MAP ion sources are particularly interesting because of their ability to shield the ion source structure from the destructive effects of the ion plasma by the magnetic shielding created by the magnetic structure of the MAP ion source.
• most of the prior art MAP ion sources were designed to used in a beam line that also included downstream steering and confinement of the produced ion beams by various electric and/or magnetic fields. This steering and confinement was necessary because of the beam rotation created by the magnetic structure of these MAP ion sources which imparted significant rotation to the produced ion beam.
• the downstream electric and/or magnetic fields add complexity, size and expense to a system employing such MAP ion sources.
• the IBEST system described herein includes a new type of magnetically- confined anode plasma ion beam source.
• the gas nozzle is designed to produce a high mach number (supersonic) gas flow rate to efficiently localize the gas puff introduced into the ionizing region proximate the fast coil. Means are also provided to create an adjustable bias field to control the formation position of the plasma.
• a fast ringing field is imposed on the gas puff as it is delivered to the ionizing region to pre-ionize the gas.
• the MAP ion diode when combined with the RHEPP source, yields an ion beam generator system capable of high average power and repetitive operation over an extended number of operating cycles for assisting deposition over large surface areas of materials at commercially attractive costs.
• the ion beam generator of the present invention can produce high average power (l kW-4M ⁇ V) pulsed ion beams at 0.02-20 MeV energies and pulse durations or lengths of from about 10 nanoseconds (ns) - 2 microseconds ( ⁇ s), or longer as necessary for the particular application.
• the first of the components in the pulsed ion beam generating system is a compact, electrically efficient, repetitively pulsed, magnetically switched, pulsed power system capable of 10 9 pulse operating cycles of the type described by H. C. Harjes, et al, Pro 8th IEEE Int. Pulsed Power Conference (1991), and D. L. Johnson et al., "Results of Initial Testing of the Four Stage RHEPP Accelerator” pp. 437-440 and C. Harjes et al., "Characterization of the RHEPP 1 ⁇ s Magnetic Pulse Compression Module", pp.
• FIG. 1 A block diagram of a power system produced according to the teachings of the present application is shown in Figure 1. From the prime power input, several stages of magnetic pulse compression and voltage addition are used to deliver a pulsed power signal of up to 2.5 MV, 60 ns FWHM, 2.9 kJ pulses at a rate of 120 Hz to an ion beam source for this particular system.
• the power system converts AC power from the local power grid into a form that can be used by an ion beam source 25.
• the power system comprises a motor 5 which drives an alternator 10.
• the alternator 10 delivers a signal to a pulse compression system 15 which has two subsystems, a l ⁇ s pulse compressor 12 and a pulse forming line 14.
• the pulse compression system 15 provides pulses to a linear inductive voltage adder (IJTVA) 20 which delivers the pulses to the ion beam source 25.
• IJTVA linear inductive voltage adder
• the alternator 10 is a 600 k ⁇ V, 120 Hz alternator. In the unipolar mode, it provides 210 A rms at a voltage of 3200 V rms with a power factor of 0.88 to the magnetic switch pulse compressor system 15. The alternator is driven by a motor connected to the local 480V power grid.
• the particular alternator used herein was designed by Westinghouse Corporation and fabricated at the Sandia National Laboratories in Albuquerque, New Mexico. It is described in detail in a paper by R. M. Calfo et al., "Design and Test of a Continuous Duty Pulsed AC Generator" in the Proceedings of the 8th IEEE Pulsed Power Conference, pp. 715-718, June, 1991, San Diego, California.
• This reference is incorporated herein in its entirety.
• This particular power system was selected and built because of its relative ease in adaptability to a variety of loads.
• Other power sources may be used and may indeed be better optimized to this particular use.
• a power supply of the type available for Magna-Amp, Inc. comprising a series of step-up transformers connected to the local power grid feeding through a suitably-sized rectifier could be used.
• the present system however has been built and performs reasonably well.
• the pulse compression system 15 is separated into two subsystems, one of which is a common magnetic pulse compressor 12 composed of a plurality of stages of magnetic switches (i.e., saturable reactors) the operation of which is well known to those skilled in the art
• This subsystem is shown in more detail in Fig. 1A.
• the basic operation of each of the stages is to compress the time width (transfer time) of and to increase the amplitude of the voltage pulse received from the proceeding stage. Since these are very low loss switches, relatively little of the power is wasted as heat, and the energy in each pulse decreases relatively little as it moves from stage to stage.
• the specific subsystem used herein is described in detail by H. C.
• the PFL is a triaxial water insulated line that converts the input LC charge waveform to a flat-top trapezoidal pulse with a design 15 ns rise/fall time and a 60 ns FVVHM.
• the construction and operation of this element is described in detail by D. L. Johnson et al. "Results of Initial Testing of the Four Stage RHEPP Accelerator", 9th IEEE International Pulsed Power Conference, pp.437-440, Albuquerque, NM, June, 1993. This paper is also incorporated by reference in its entirety.
• a cross sectional view of the PFL is shown in Figure IB.
• the pulse compression system 15 can provide unipolar, 250 kV, 15 ns rise time, 60 ns full width half maximum (FVVHM), 4 kJ pulses, at a rate of 120 Hz, to the linear inductive voltage adder (LIVA) (20).
• the pulse compression system 15 should desirably have an efficiency >80% and be composed of high reliability components with very long lifetimes (-10 -10 pulses).
• Magnetic switches are preferably used in all of the pulse compression stages, MS1-MS5, because they can handle very high peak powers (i.e., high voltages and currents), and because they are basically solid state devices with a long service life.
• the five compression stages used in this embodiment as well as the PFL 14 are shown in Fig. 1 A.
• the power is supplied to the pulse compression system 15 from the alternator 10 and is passed through the magnetic switches, MS1-MS5, to the PFL 14.
• the PFL is connected to the linear induction voltage adder (LIVA) 20 described below.
• the second and third magnetic switches, MS2 and MS3, are separated by a step-up transformer Tl as shown.
• Switch MS6 is an inversion switch for the PFL.
• the pulse forming line (PFL) element 14 is shown in schematically in Fig. 1A and in cross section in Fig. I B.
• MS6 in Fig. 1A corresponds to the inversion switch 302 shown in Fig. I B located on the input side of the tri-axial section 314 of the PFL.
• Output switches 304 and charging cores 306 are also shown.
• the regions 310 are filled with deionized water as the dielectric.
• the interior region 308 is filled with air and oil coiling lines, not shown, for the output sw itches 304.
• the output of the PFL is fed in parallel to each of the individual LIVA stages 20, with the positive component flowing through conductors 316 and the shell 318 of the PFL serv ing as ground.
• the positive conductors 316 are connected to each of the LIVA stages.
• the LIVA (20) is preferably liquid dielectric insulated. It is connected to the output of the PFL and can be configured in different numbers of stages to achieve the desired voltage for delivery to the ion beam source.
• the LIVA 20 can deliver nominal 2.5 MV, 2.9 kJ, pulses at a rate of 120 Hz to the ion beam source 25 when configured with 10 stages of 250 kV each.
• the LIVA was configured with four stages of 250 kV each, such that the LIVA delivered a total of 1.0 MV to the ion beam source.
• this voltage can be increased or decreased by changing the number of stages in the LIVA to match the particular material processing need.
• the nominal output pulse of the LIVA 20 is the same as that provided to it by the PFL, namely, trapezoidal with 15 ns rise and fall times and 60 ns FVVHM (full width half maximum).
• Figure IC shows a cross section of the four stage LIVA.
• the four stages, 320, 322, 324, and 326, are stacked as shown and fed the positive pulses from the PFL via the cables 321, 323, 325, and 327.
• the stages are separated by gaps 330 and surrounded by transformer oil for cooling.
• the output from each of the LIVA stages adds to deliver a single total pulse to the ion beam source shown here schematically as 25 which is located within a vacuum chamber 332, shown in partial view.
• the outside shell of the LIVA is connected to ground.
• the power system P ( Figure 1) as described, can operate continuously at a pulse repetition rate of 120 Hz delivering up to 2.5 kJ of energy per pulse in 60 ns pulses.
• the specific power system described here can deliver pulsed power signals of about 20-1000 ns duration with ion beam energies of 0.25-2.5 MeV.
• the power system can operate at 50% electrical efficiency from the wall plug to energy delivered to a matched load.
• the power system P uses low loss pulse compression stages incorporating, for example, low loss magnetic material and solid state components, to convert AC power to short, high voltage pulses.
• the ability to produce voltages from 250 kV to 20 MV by stacking voltage using a plurality of inductive adders incorporating low loss magnetic material is a principle feature when high voltages are needed, although it is also possible to use a single stage pulse supply, eliminating the need for the adder.
• the power system can operate at relatively low impedances ( ⁇ 100 ⁇ ) which sets it apart from many other repetitive, power supply technologies, such as transformer-based systems. This feature allows large pulse currents to be attained at reasonable voltages, enabling high treatment rates and the treatment of large ar ⁇ as (5 to more than 1000 cm ) with a single pulse so as to reduce edge effects occurring at the transition between treated and untreated areas.
• the second component of the pulsed ion beam system is the MAP ion beam source 25, shown in Figure 2.
• the MAP ion beam source is capable of operating repetitively and efficiently to utilize the pulsed power signal from the power system efficiently to turn gas phase molecules into a high energy pulsed ion beam. It can also be operated in the single shot mode, as necessary for a particular application.
• a precursor of the ion beam source is an ion diode described generally by J. B. Greenly et al, "Plasma Anode Ion Diode Research at Cornell: Repetitive Pulse and 0.1 TVV Single Pulse Experiments", Proceedings of 8th Intl. Conf. on High Power Particle Beams (1990) all of which is incorporated by reference herein. Although this reference ion diode differs significantly from the ion diode utilized in the present system as discussed above, the background discussion in this reference is of interest.
• the ion beam source 25 is shown in Figure 2.
• the ion beam source 25 is a magnetically-confined anode plasma (MAP) source.
• Figure 2 is a partial cross- sectional view of one symmetric side of the ion beam or MAP source 25.
• the ion beam or MAP source 25 produces an annular ion beam K which can be brought to a broad focus symmetric about the axis X-X 400 shown.
• slow (1 ms rise time) magnetic field coils 414 produce magnetic flux S (as shown in Fig. 2A) which provides the magnetic insulation of the accelerating gap between the cathodes 412 and the anodes 410.
• the anode electrodes 410 also act as magnetic flux shapers.
• the slow coils 414 are cooled by adjacent water lines, not shown, incorporated into the structure 30 supporting the cathodes 412 and the slow coils 414.
• the main portion of the MAP structure shown in this Figure is about 18 cm high and wide.
• the complete MAP ion diode can be visualized as the revolution of the cross-sectional detail of Fig. 2 about the central axis 400 of the device to form a cylindrical apparatus. A full cross sectional view appears in Fig. 3.
• the ion beam or MAP source 25 operates in the following fashion: a fast gas valve assembly 404 located in the anode assembly 35 produces a rapid (200 ⁇ s) gas puff which is delivered through a supersonic nozzle 406 to produce a highly localized volume of gas directly in front of the surface of a fast driving coil 408 located in an insulating structure 420.
• the nozzle is designed to prevent any transverse flow of non-ionized gas into the gap between the anodes 410 and cathodes 412.
• the fast driving coil 408 is fully energized from the fast capacitor 150, inducing a loop voltage of 20 kV on the gas volume, driving a breakdown to full ionization, and moving the resulting plasma toward the anode electrodes 410 in about 1.5 ⁇ s or less, to form a thin magnetically- confined plasma layer.
• the pre-ionization step is a departure from the earlier MAP reference which showed a separate conductor located on the face of a surface corresponding to the insulating structure 420 herein. Since this conductor was exposed to the plasma, it broke down frequently. It was discovered that the separate pre-ionizing structure was unnecessary.
• the gas can be effectively pre-ionized by placing a small ringing capacitor 160 in parallel with the fast coil. The field oscillations produced by this ringing circuit pre-ionize the gas in front of the anode fast coil. A schematic electrical diagram of this circuit is shown in Fig. 2C.
• the bias field capacitor 180 drives a greater than 1 microsecond risetime current in the fast coil before the main capacitor pulse begins. This allows adjustment of the field configuration produced by the fast capacitor current.
• the fast capacitor 150 drives a 1 microsecond risetime pulse in the fast coil.
• the preionizer capacitor 160 causes the voltage across the fast coil to ring with a much less than 1 microsecond period, inducing a large oscillating electric field in the gas to be ionized, leading to partial ionization of the gas.
• the rising magnetic field produced by the fast coil 408 pushes the ionized gas away from the fast coil, stagnating it against the preexisting magnetic field from the slow coil 414.
• the fast coil is then fully energized as described above to completely breakdown the gas into the plasma. After this pulse the field collapses back into the fast coil which is connected to a resistive load which is in turn connected to a heat sink, not shown.
• a heat sink not shown.
• cooling channels in the supporting structure are used, but other solutions are possible and relatively straightforward. In this manner heat build up in the fast coil is avoided.
• the fast coils 408 have been redesigned from the reference fast coils in several ways as well as the heat sinking mentioned above.
• the gap between the fast coil and the anode electrodes 410 has been reduced with the result that the amount of necessary magnetic energy has been decreased by over 50%.
• the lower energy requirement permits repetitive use at higher frequencies and reduces the complexity of the feed system voltages for the fast coils.
• the design of the flux-shaping anode electrode assembly has also contributed to these beneficial results.
• the pulsed power signal from the power system is then applied to the anode assembly 35, accelerating ions from the plasma to form an ion beam K.
• the slow (S) and fast (F) magnetic flux structures, at the time of ion beam extraction, are shown in Figure 2A.
• the definite separation between the flux from the fast coil from the flux from the slow coil is shown therein. This is accomplished by the flux-shaping effects of the anodes 410 and also by the absence of a slow coil located in the insulating structure 420 as was taught in the earlier MAP reference paper.
• the slow coils in the present MAP ion diode are located only in the cathode area of the MAP.
• This anode flux shaping in conjunction with the location of slow coils in the cathode assembly is different from that shown in the MAP reference paper and permits the high repetition rate, sustained operation of the MAP diode disclosed herein.
• FIG 2B is a detailed view of the gas valve assembly 404 and the passage 425 which conducts the gas from the valve 404 to the area in front of the fast coil 408.
• the passage 425 has been carefully designed to deposit the gas in the localized area of the fast coil with a minimum of blow-by past this region.
• the details of the cross sections of the passage 425 were designed for supersonic transport of the gas puff. The design was done with readily available gas flow computer programs and is within the skill in the art.
• the gas valve flapper 426 is operated by a small magnetic coil 428 which opens and closes the flapper 426 upon actuation from the MAP control system.
• the flapper valve is pivoted on the bottom end 427 of the flapper.
• the coil 428 is mounted in a high thermal conductivity ceramic support structure 429 which is in turn heat sinked to other structure, not shown.
• externally cooled wires surrounding the coil could also serve to extract the heat from the coils. This heat sinking is necessary for the sustained operating capability of the MAP.
• the gas is delivered to the valve from a plenum 431 behind the base of the flapper.
• the plenum 431 should be visualized as being connected to a larger plenum located at the central core of the complete MAP ion diode as shown in Fig. 3.
• the vacuum in the nozzle 406 rapidly draws the gas into the MAP once the flapper 426 is opened.
• the function of the nozzle is to produce a directed flow of gas only in the direction of flow and not transverse to it.
• the MAP ion diode described above is distinguished from prior art ion diodes in several ways. Due to its low gas load per pulse, the rate of vacuum recovery within the MAP allows sustained operation up to and above 100 Hz. As discussed above, the magnetic geometry is fundamentally different from previous ion diodes. Prior diodes produced rotating beams that were intended for applications in which the ion beam propagates in a strong axial magnetic field after being generated in the diode. The present system requires that the ion beam be extracted from the diode to propagate in field-free space a minimum distance of 20-30 cm to a material surface.
• the modifications include: the elimination of a slow coil on the anode side of the diode and its associated feeds, better control over the magnetic field shaping and contact of the anode plasma to the a rode electrode structure through use of the partially field- penetrable electrodes, the elimination of the separate pre-ionizer coil from the prior ion diodes, the circuit associated with the fast coil to provide "bias" current to adjust the magnetic field to place the anode plasma surface on the correct flux surface to eliminate beam rotation and allow optimal propagation and focusing of the beam, and the redesign of the gas nozzle to better localize the gas puff which enables the fast coil to be located close to the diode gap which in turn reduces the energy requirements and complexity of the fast coil driver.
• the plasma can be formed using a variety of gas phase molecules.
• the system can use any gas (including hydrogen, helium, oxygen, nitrogen fluorine, neon, chlorine and argon) or vaporizable liquid or metal (including lithium, beryllium, boron, carbon, sodium, magnesium, aluminum, silicon, phosphorous, sulfur, and potassium ) to produce a pure source of ions without consuming or damaging any component other than the gas supplied to the source.
• the ions will be singly ionized in the accelerator, but the MAP diode can be redesigned to supply more power in the ionization cycle to produce multiply ionized ions, thus giving higher ion energies for a given accelerating voltage.
• the ion beam K propagates 20-30 cm in vacuum ( ⁇ 10 *3 ) to a broad focal area (5 - 1000 cm 2 ) at the target plane 195, shown in Fig. 3, where material samples are placed for treatment.
• the ion beam or MAP source 25 is capable of operating at repetitive pulse rates of 100 Hz continuously with long component lifetimes >10 ⁇ .
• the ion beam or MAP source 25, according to the principles of the present invention draws ions from a plasma anode rather than a solid dielectric surface flashover anode used in present single pulse ion beam sources. One therefore has precise control over the components in the ion beam by control of the composition of the gas source.
• the MAP ion diode and the RHEPP source are the essential components of the IBEST pulsed ion beam generator system.
• Such a system is capable of high average power and repetitive operation over an extended number of operating cycles for assisting deposition over large surface areas of materials at commercially attractive costs.

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• 1996
  • 1996-01-23 CA CA002186102A patent/CA2186102A1/en not_active Abandoned
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