FIELD OF THE INVENTION [002] This invention relates to methods and apparatus for plasma-assisted processing, and in particular to plasma processing control.

BACKGROUND OF THE INVENTION [003] In some plasma-assisted processes, such as joining or coating parts, precise control of the temperature of those parts can be important. For example, when brazing two parts together, it can be important to know when the brazing interlayer melts. Such knowledge would permit an operator or a computer program to stop further heating of the joint and allow it to freeze, without overheating the part or wasting energy.

[004] Conventional control of plasma-assisted processes, however, can be imprecise. Moreover, some of these processes require extensive calibration.

Furthermore, many of these processes require the use of a temperature sensor, such as a pyrometer, to monitor the temperature.

[005] It is also known that a plasma can be ignited by subjecting a gas at reduced pressure to a sufficient amount of microwave radiation. However, vacuum equipment, which is required to lower the gas pressure, can be expensive, as well as slow and energy-consuming. Moreover, the use of such equipment can limit manufacturing flexibility.

BRIEF SUMMARY OF A FEW ASPECTS OF THE INVENTION [006] Consistent with the present invention, methods and apparatus for controlling plasma-assisted processes are provided.

[007] In one embodiment, a method for determining a condition of a plasma-heated object is provided. The method can include identifying a correlation between a temperature spike associated with an object and a condition of the object, storing trigger information reflecting the correlation, locating the object within a cavity and supplying a gas to the cavity, directing electromagnetic radiation into the cavity in an amount sufficient to establish plasma in the cavity, monitoring an actual temperature spike associated with the object in the cavity, comparing the actual temperature spike of the object with the stored trigger information, and adjusting a temperature control parameter when the actual temperature spike is within a predetermined proximity to the stored trigger information.

[008] In another embodiment, a method is provided for determining a condition of at least one object in a cavity containing gas, where sufficient electromagnetic radiation is directed into the cavity to maintain (e. g., modulate or sustain) a plasma from the gas. The method can include monitoring a temperature of the object and detecting a temperature spike associated with the at least one object.

[009] In a yet another embodiment, an apparatus is provided for controlled heating of an object. The apparatus can include a cavity for containing at least a portion of the object, at least one conduit for supplying a gas to the cavity, at least one radiation source configured to radiate into the cavity, memory for storing trigger information correlating a temperature characteristic associated with the object and a condition of the object, and a controller for receiving information from the sensor and comparing the sensor information with the stored trigger information. The controller can be configured to adjust a temperature control parameter (e. g., regulate the radiation source and the supply of gas) when the sensor information signals a temperature characteristic that is within a predetermined proximity to the stored trigger information.

[010] In a still another embodiment, a method is provided for estimating a temperature of at least one object in a cavity containing gas, where sufficient radiation is directed into the cavity to maintain a plasma from the gas. The method can include measuring a forward power of the radiation, measuring a reflected power of the radiation, estimating an amount of energy consumption by the at least one object by integrating a difference between the forward power and the reflected power over a time period. This estimate can be used control a plasma-assisted process.

[011] Plasma catalysts, and methods and apparatus for igniting, modulating, and sustaining a plasma consistent with this invention are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS [012] Further aspects of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: [013] FIG. 1 shows a schematic diagram of an illustrative apparatus consistent with this invention; [014] FIG. 2 shows an illustrative embodiment of a portion of a plasma system for adding a powder plasma catalyst to a plasma cavity for igniting, modulating, or sustaining a plasma in a cavity consistent with this invention; [015] FIG. 3 shows an illustrative plasma catalyst fiber with at least one component having a concentration gradient along its length consistent with this invention; [016] FIG. 4 shows an illustrative plasma catalyst fiber with multiple components at a ratio that varies along its length consistent with this invention; [017] FIG. 5A shows another illustrative plasma catalyst fiber that includes a core underlayer and a coating consistent with this invention; [018] FIG. 5B shows a cross-sectional view of the plasma catalyst fiber of FIG. 5A, taken from line 5B-5B of FIG. 5A, consistent with this invention; [019] FIG. 6 shows an illustrative embodiment of another portion of a plasma system including an elongated plasma catalyst that extends through ignition port consistent with this invention; [020] FIG. 7 shows an illustrative embodiment of an elongated plasma catalyst that can be used in the system of FIG. 6 consistent with this invention; [021] FIG. 8 shows another illustrative embodiment of an elongated plasma catalyst that can be used in the system of FIG. 6 consistent with this invention; [022] FIG. 9 shows an illustrative embodiment of a portion of a plasma system for directing ionizing radiation into a radiation chamber consistent with this invention; [023] FIG. 10 shows a portion of a simplified schematic diagram of an illustrative apparatus for controlled plasma-assisted processing consistent with this invention; [024] FIG. 11 shows a graph of actual power, temperature, and current data as a function of time during a brazing operation consistent with this invention; [025] FIG. 12 shows an illustrative front panel diagram of a virtual instrument for inputting various control parameters and displaying process data consistent with this invention; [026] FIG. 13 shows an illustrative front panel diagram of another virtual instrument that includes various indicators and controls to display live data and to allow a user to manipulate a plasma-assisted process consistent with this invention; [027] FIG. 14 shows an illustrative functional block diagram of the virtual instruments of FIGS. 12 and 13 consistent with this invention; [028] FIG. 15 shows a flow chart of an exemplary method for determining a condition of a plasma-heated object consistent with this invention; [029] FIG. 16 shows a flow chart of an exemplary method for controlling a plasma-assisted process consistent with this invention; and [030] FIGS. 17A and 17B show a flow chart of an exemplary method for estimating and controlling the temperature of at least one object in a cavity consistent with this invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS [031] Consistent with the present invention, methods and apparatus for controlling plasma-assisted processes are provided. In one embodiment, the total energy absorbed (e. g. , by a ceramic processing cavity and an object being heated in the cavity) can be used to estimate a temperature of the object or some other associated temperature. To measure the temperature precisely, energy absorption <BR> <BR> can be calibrated for a particular configuration (e. g. , a particular cavity and object).

Once calibrated, the method can be used to estimate the temperature of the object when similar configurations (e. g., similar objects and cavities) are used in subsequent runs, even without a pyrometer or temperature sensor of any kind.

[032] This pyrometerless method is based on the realization that the absorbed radiation power is equal to the difference of the forward radiation power and the reflected radiation power. If this difference is integrated over a processing time period, the total amount of absorbed energy can be calculated. If the thermal mass is known (and, if significant, the loss of energy by the cooling/processing gas is known), the absolute temperature or relative temperature change can be analytically or statistically determined. This knowledge can be wholly or partially based on empirical data such as prior runs with similar objects, cavities, and operating conditions.

[033] Thus, this invention can be used to precisely control plasma-assisted processes (e. g. , heating) to lower energy costs and increase heat-treatment efficiency and plasma-assisted manufacturing flexibility.

[034] Additional methods for controlling plasma-assisted processes are also provided.

[035] A plasma catalyst for initiating, modulating, and sustaining a plasma is also provided. The catalyst can be passive or active. A passive plasma catalyst can include any object capable of inducing a plasma by deforming a local electric field (e. g. , an electromagnetic field) consistent with this invention without necessarily adding additional energy through the catalyst, such as by applying a voltage to create a spark. An active plasma catalyst, on the other hand, may be any particle or high energy wave packet capable of transferring a sufficient amount of energy to a gaseous atom or molecule to remove at least one electron from the gaseous atom or molecule, in the presence of electromagnetic radiation.

[036] The following commonly owned, concurrently filed U. S. patent applications are hereby incorporated by reference in their entireties: U. S. Patent Application No. 10/, (Atty. Docket No. 1837.0008), No. 10/, (Atty.

Docket No. 1837.0009), No. 10/, (Atty. Docket No. 1837.0010), No. 10/, (Atty. Docket No. 1837.0011), No. 10/, (Atty. Docket No. 1837.0012), No. 10/, (Atty. Docket No. 1837.0013), No. 10/ (Atty. Docket No. 1837.0015), No. 10/, (Atty. Docket No. 1837.0016), No. 10/, (Atty. Docket No. 1837.0017), No. 10/, (Atty. Docket No. 1837.0018), No. 10/, (Atty. Docket No. 1837.0020), No. 10/ (Atty. Docket No. 1837.0021), No. 10/, (Atty. Docket No. 1837.0023), No. 10/, (Atty. Docket No. 1837.0024), No. 10/, (Atty. Docket No. 1837.0025), No. 10/, (Atty. Docket No. 1837.0026), No. 10/, (Atty. Docket No. 1837.0027), No. 10/, (Atty. Docket No. 1837.0028), No. 10/, (Atty. Docket No. 1837.0029), No. 10/, (Atty. Docket No. 1837.0030), and No. 10/, (Atty. Docket No. 1837.0032).

[037] Illustrative Plasma System [038] FIG. 1 shows illustrative plasma system 10 consistent with one aspect of this invention. In this embodiment, cavity 12 is formed in a vessel that is positioned inside radiation chamber (i. e. , applicator) 14. In another embodiment (not shown), vessel 12 and radiation chamber 14 are the same, thereby eliminating the need for two separate components. The vessel in which cavity 12 is formed can include one or more radiation-transmissive insulating layers to improve its thermal insulation properties without significantly shielding cavity 12 from the radiation.

[039] In one embodiment, cavity 12 is formed in a vessel made of ceramic.

Due to the extremely high temperatures that can be achieved with plasmas consistent with this invention, a ceramic capable of operating at about 3,000 degrees Fahrenheit can be used. The ceramic material can include, by weight, 29.8% silica, 68.2% alumina, 0.4% ferric oxide, 1 % titania, 0. 1 % lime, 0. 1 % magnesia, 0.4% alkalies, which is sold under Model No. LW-30 by New Castle Refractories Company, of New Castle, Pennsylvania. It will be appreciated by those of ordinary skill in the art, however, that other materials, such as quartz, and those different from the one described above, can also be used consistent with the invention. It will also be appreciated that because the operating temperature can be different for different types of plasma-processing, the material used to make the vessel may only need to withstand temperatures substantially below 3,000 degrees Fahrenheit, such as about 1000 degrees, or about 500 degrees Fahrenheit, or even lower.

[040] In one embodiment, plasma was formed in a partially open cavity inside a first brick and topped with a second brick. The cavity had dimensions of about 2 inches by about 2 inches by about 1.5 inches. At least two holes were also provided in the brick in communication with the cavity: one for viewing the plasma and at least one hole for providing the gas. The size of the cavity can depend on the desired plasma process being performed. Also, for some applications, the cavity can be configured to prevent the plasma from rising/floating away from the primary processing region.

[041] Cavity 12 can be connected to one or more gas sources 24 (e. g. , a source of argon, nitrogen, hydrogen, xenon, and krypton) by line 20 and control valve 22, which may be powered by power supply 28 or any other supply. Line 20 may be tubing (e. g. , between about 1/16 inch and about 1/4 inch, such as about 1/8"), but can be any channel or device capable of supplying a gas to cavity 12.

Also, if desired, a vacuum pump (not shown) can be connected to chamber 14 to remove any undesirable fumes that may be generated during plasma processing.

[042] A radiation leak detector (not shown) can be installed near source 26 and waveguide 30 and connected to a safety interlock system to automatically turn off the radiation (e. g. , microwave) power supply if a leak above a predefined safety<BR> limit, such as one specified by the FCC and/or OSHA (e. g. , 5 mW/cm2), was detected.

[043] In one embodiment, the radiation apparatus may include radiation source 26 for directing radiation into the cavity. The radiation apparatus may further include other radiation sources (not shown) for directing additional radiation into the cavity. Radiation source 26, which may be powered by electrical power supply 28, can direct radiation into chamber 14 or cavity 12 through one or more waveguides 30. It will be appreciated by those of ordinary skill in the art that source 26 can be connected directly to chamber 14, thereby eliminating waveguides 30.

The radiation energy entering cavity 12 can be used to ignite a plasma within the cavity. This plasma can be modulated or substantially sustained and confined to the cavity by coupling additional radiation with the catalyst.

[044] Radiation source 26 may be a magnetron, a klystron, a gyrotron, a traveling-wave tube amplifier, or any other device capable of generating radiation.

Radiation having any frequency less than about 333 GHz can be used consistent with this invention. For example, frequencies, such as power line frequencies (about 50 Hz to about 60 Hz), can be used, although the pressure of the gas from which the plasma is formed may be lowered to assist with plasma ignition. Also, any radio frequency or microwave frequency can be used consistent with this invention, including frequencies greater than about 100 kHz. In most cases, the gas pressure for such relatively high frequencies need not be lowered to ignite, modulate, or sustain a plasma, thereby enabling many plasma-processes to occur over a broad range of pressures, including atmospheric pressure and above.

[045] For example, the invention may be practiced by employing microwave sources at both 915 MHz and 2.45 GHz provided by Communications and Power Industries (CPI), although radiation having any frequency less than about 333 GHz can be used. A 3-stub tuner may allow impedance matching for maximum power transfer and a dual directional coupler (not shown) may be used to measure forward and reflected powers.

[046] Radiation energy can be supplied by radiation source 26 through circulator 32 and tuner 34 (e. g. , 3-stub tuner). Tuner 34 can be used to minimize the reflected power as a function of changing ignition or processing conditions, especially before the plasma has formed because microwave power, for example, will be strongly absorbed by the plasma, although the use of a circulator and a tuner is optional.

[047] As explained more fully below, the location of radiation-transmissive cavity 12 in chamber 14 may not be critical if chamber 14 supports multiple modes, and especially when the modes are continually or periodically mixed. As also explained more fully below, motor 36 can be connected to mode-mixer 38 for making the time-averaged radiation energy distribution substantially uniform throughout chamber 14. Furthermore, window 40 (e. g. , a quartz window) can be disposed in one wall of chamber 14 adjacent to cavity 12, permitting temperature sensor 42 (e. g. , an optical pyrometer) to be used to view a process inside cavity 12.

In one embodiment, the optical pyrometer output can decrease from a maximum of five volts, for example, as the temperature rises to within the tracking range. In other embodiments, optical pyrometers are not required.

[048] Sensor 42 can develop output signals as a function of the temperature or any other monitorable condition associated with a work piece (not shown) within cavity 12 and provide the signals to controller 44. Dual temperature sensing and heating, as well as automated cooling gas flow control, can also be used. Controller 44 in turn can be used to control operation of power supply 28, which can have one output connected to source 26 as described above and another output connected to valve 22 to control gas flow into cavity 12.

[049] The equipment may be computer controlled using LabView 6i software, which may provide real-time temperature monitoring and radiation (e. g., microwave) power control. Noise may be reduced by using sliding averages of suitable number of data points. Also to improve speed and computational efficiency, the number of data points in the buffer array may be limited by using shift registers and buffer sizing. The pyrometer may measure the temperature of a sensitive area of, for example, about 1 cm2, which may be used to calculate an average temperature. The pyrometer may sense radiant intensities at two wavelengths and fit those intensities using Planck's law to determine the temperature. It will be appreciated, however, that other devices and methods for monitoring and controlling temperature are also available and can be used consistent with this invention. Control software that can be used consistent with this invention is described further below.

[050] Chamber 14 may have several glass-covered viewing ports with radiation shields and a quartz window for pyrometer access. Several ports for connection to a vacuum pump and a gas source may also be provided, although not necessarily used.

[051] The exemplary radiation apparatus may also include a closed-loop deionized water cooling system (not shown) with an external heat exchanger cooled by tap water. During operation, the deionized water may first cool the magnetron, then the load-dump in the circulator (used to protect the magnetron), and finally the microwave chamber through water channels welded on the outer surface of the chamber.

[052] Plasma Catalysts [053] A plasma catalyst consistent with this invention can include one or more different materials and may be either passive or active. A plasma catalyst can be used, among other things, to ignite, modulate, and/or sustain a plasma at a gas pressure that is less than, equal to, or greater than atmospheric pressure.

[054] One method of forming a plasma consistent with this invention can include subjecting a gas in a cavity to electromagnetic radiation having a frequency less than about 333 GHz in the presence of a passive plasma catalyst. A passive plasma catalyst consistent with this invention can include any object capable of <BR> <BR> inducing a plasma by deforming a local electric field (e. g. , an electromagnetic field) consistent with this invention, without necessarily adding additional energy through the catalyst, such as by applying an electric voltage to create a spark.

[055] A passive plasma catalyst consistent with this invention can be, for example, a nano-particle or a nano-tube. As used herein, the term"nano-particle" can include any particle having a maximum physical dimension less than about 100 nm that is at least electrically semi-conductive. Also, both single-walled and multi- walled carbon nanotubes, doped and undoped, can be particularly effective for igniting plasmas consistent with this invention because of their exceptional electrical conductivity and elongated shape. The nanotubes can have any convenient length and can be a powder fixed to a substrate. If fixed, the nanotubes can be oriented randomly on the surface of the substrate or fixed to the substrate <BR> <BR> (e. g. , at some predetermined orientation) while the plasma is ignited or sustained.

[056] A passive plasma catalyst can also be a powder consistent with this invention, and need not comprise nano-particles or nano-tubes. It can be formed, for example, from fibers, dust particles, flakes, sheets, etc. When in powder form, the catalyst can be suspended, at least temporarily, in a gas. By suspending the powder in the gas, the powder can be quickly dispersed throughout the cavity and more easily consumed, if desired.

[057] In one embodiment, a powder catalyst can be carried into the cavity and at least temporarily suspended with a carrier gas. The carrier gas can be the same or different from the gas that forms the plasma. Also, the powder can be added to the gas prior to being introduced to the cavity. For example, as shown in FIG. 2, radiation source 52 can supply radiation to radiation cavity 55, in which plasma cavity 60 is placed. Powder source 65 can provide catalytic powder 70 into gas stream 75. In an alternative embodiment, powder 70 can be first added to <BR> <BR> cavity 60 in bulk (e. g. , in a pile) and then distributed in the cavity in any number of ways, including flowing a gas through or over the bulk powder. In addition, the powder can be added to the gas for igniting, modulating, or sustaining a plasma by moving, conveying, drizzling, sprinkling, blowing, or otherwise, feeding the powder into or within the cavity.

[058] In one experiment, a plasma was ignited in a cavity by placing a pile of carbon fiber powder in a copper pipe that extended into the cavity. Although sufficient radiation was directed into the cavity, the copper pipe shielded the powder from the radiation and no plasma ignition took place. However, once a carrier gas began flowing through the pipe, forcing the powder out of the pipe and into the cavity, and thereby subjecting the powder to the radiation, a plasma was nearly instantaneously ignited in the cavity.

[059] A powder plasma catalyst consistent with this invention can be substantially non-combustible, thus it need not contain oxygen or burn in the presence of oxygen. Thus, as mentioned above, the catalyst can include a metal, carbon, a carbon-based alloy, a carbon-based composite, an electrically conductive polymer, a conductive silicone elastomer, a polymer nanocomposite, an organic- inorganic composite, and any combination thereof.

[060] Also, powder catalysts can be substantially uniformly distributed in the plasma cavity (e. g. , when suspended in a gas), and plasma ignition can be precisely controlled within the cavity consistent with this invention. Uniform and controllable ignition can be important in certain applications, including those applications requiring brief plasma exposures, such as in the form of one or more bursts. Still, a certain amount of time can be required for a powder catalyst to distribute itself throughout a cavity, especially in complicated, multi-chamber cavities. Therefore, consistent with another aspect of this invention, a powder catalyst can be introduced into the cavity through a plurality of ignition ports to more rapidly obtain a more uniform catalyst distribution therein (see below).

[061] In addition to powder, a passive plasma catalyst consistent with this invention can include, for example, one or more microscopic or macroscopic fibers, sheets, needles, threads, strands, filaments, yarns, twines, shavings, slivers, chips, woven fabrics, tape, whiskers, or any combination thereof. In these cases, the plasma catalyst can have at least one portion with one physical dimension substantially larger than another physical dimension. For example, the ratio between at least two orthogonal dimensions should be at least about 1: 2, but could be greater than about 1: 5, or even greater than about 1: 10.

[062] Thus, a passive plasma catalyst can include at least one portion of material that is relatively thin compared to its length. A bundle of catalysts (e. g., fibers) may also be used and can include, for example, a section of graphite tape.

In one experiment, a section of tape having approximately thirty thousand strands of graphite fiber, each about 2-3 microns in diameter, was successfully used. The number of fibers in and the length of a bundle are not critical to igniting, modulating, or sustaining the plasma. For example, satisfactory results have been obtained using a section of graphite tape about one-quarter inch long. One type of carbon fiber that has been successfully used consistent with this invention is sold under the trademark MagnamiteO, Model No. AS4C-GP3K, by the Hexcel Corporation, of Anderson, South Carolina. Also, silicon-carbide fibers have been successfully used.

[063] A passive plasma catalyst consistent with another aspect of this invention can include one or more portions that are, for example, substantially spherical, annular, pyramidal, cubic, planar, cylindrical, rectangular or elongated.

[064] The passive plasma catalysts discussed above include at least one material that is at least electrically semi-conductive. In one embodiment, the material can be highly conductive. For example, a passive plasma catalyst consistent with this invention can include a metal, an inorganic material, carbon, a carbon-based alloy, a carbon-based composite, an electrically conductive polymer, a conductive silicone elastomer, a polymer nanocomposite, an organic-inorganic composite, or any combination thereof. Some of the possible inorganic materials that can be included in the plasma catalyst include carbon, silicon carbide, molybdenum, platinum, tantalum, tungsten, carbon nitride, and aluminum, although other electrically conductive inorganic materials are believed to work just as well.

[065] In addition to one or more electrically conductive materials, a passive plasma catalyst consistent with this invention can include one or more additives (which need not be electrically conductive). As used herein, the additive can include any material that a user wishes to add to the plasma. For example, in doping semiconductors and other materials, one or more dopants can be added to the plasma through the catalyst. See, e. g. , commonly owned, concurrently filed U. S. Patent Application No. (Atty. Docket No. 1837.0026), which is hereby incorporated by reference in its entirety. The catalyst can include the dopant itself, or it can include a precursor material that, upon decomposition, can form the dopant. Thus, the plasma catalyst can include one or more additives and one or more electrically conductive materials in any desirable ratio, depending on the ultimate desired composition of the plasma and the process using the plasma.

[066] The ratio of the electrically conductive components to the additives in a passive plasma catalyst can vary over time while being consumed. For example, during ignition, the plasma catalyst could desirably include a relatively large percentage of electrically conductive components to improve the ignition conditions.

On the other hand, if used while modulating or sustaining the plasma, the catalyst could include a relatively large percentage of additives. It will be appreciated by those of ordinary skill in the art that the component ratio of the plasma catalyst used to ignite, modulate and/or sustain the plasma could be the same.

[067] A predetermined ratio profile can be used to simplify many plasma processes. In many conventional plasma processes, the components within the plasma are added as necessary, but such addition normally requires programmable equipment to add the components according to a predetermined schedule.

However, consistent with this invention, the ratio of components in the catalyst can be varied, and thus the ratio of components in the plasma itself can be automatically varied. That is, the ratio of components in the plasma at any particular time can depend on which of the catalyst portions is currently being consumed by the plasma. Thus, the catalyst component ratio can be different at different locations within the catalyst. And, the current ratio of components in a plasma can depend on the portions of the catalyst currently and/or previously consumed, especially when the flow rate of a gas passing through the plasma chamber is relatively slow.

[068] A passive plasma catalyst consistent with this invention can be homogeneous, inhomogeneous, or graded. Also, the plasma catalyst component ratio can vary continuously or discontinuously throughout the catalyst. For example, in FIG. 3, the ratio can vary smoothly forming a gradient along a length of catalyst 100. Catalyst 100 can include a strand of material that includes a relatively low concentration of a component at section 105 and a continuously increasing concentration toward section 110.

[069] Alternatively, as shown in FIG. 4, the ratio can vary discontinuously in each portion of catalyst 120, which includes, for example, alternating sections 125 and 130 having different concentrations. It will be appreciated that catalyst 120 can have more than two section types. Thus, the catalytic component ratio being consumed by the plasma can vary in any predetermined fashion. In one embodiment, when the plasma is monitored and a particular additive is detected, further processing can be automatically commenced or terminated.

[070] Another way to vary the ratio of components in a modulated or sustained plasma is by introducing multiple catalysts having different component ratios at different times or different rates. For example, multiple catalysts can be introduced at approximately the same location or at different locations within the cavity. When introduced at different locations, the plasma formed in the cavity can have a component concentration gradient determined by the locations of the various catalysts. Thus, an automated system can include a device by which a consumable plasma catalyst is mechanically inserted before and/or during plasma igniting, modulating, and/or sustaining.

[071] A passive plasma catalyst consistent with this invention can also be coated. In one embodiment, a catalyst can include a substantially non-electrically conductive coating deposited on the surface of a substantially electrically conductive material. Alternatively, the catalyst can include a substantially electrically conductive coating deposited on the surface of a substantially electrically non-conductive material. FIGS. 5A and 5B, for example, show fiber 140, which includes underlayer 145 and coating 150. In one embodiment, a plasma catalyst including a carbon core is coated with nickel to prevent oxidation of the carbon.

[072] A single plasma catalyst can also include multiple coatings. If the coatings are consumed during contact with the plasma, the coatings could be introduced into the plasma sequentially, from the outer coating to the innermost coating, thereby creating a time-release mechanism. Thus, a coated plasma catalyst can include any number of materials, as long as a portion of the catalyst is at least electrically semi-conductive.

[073] Consistent with another embodiment of this invention, a plasma catalyst can be located entirely within a radiation cavity to substantially reduce or prevent radiation energy leakage. In this way, the plasma catalyst does not electrically or magnetically couple with the vessel containing the cavity or to any electrically conductive object outside the cavity. This prevents sparking at the ignition port and prevents radiation from leaking outside the cavity during the ignition and possibly later if the plasma is sustained. In one embodiment, the catalyst can be located at a tip of a substantially electrically non-conductive extender that extends through an ignition port.

[074] FIG. 6, for example, shows radiation chamber 160 in which plasma cavity 165 is placed. Plasma catalyst 170 is elongated and extends through ignition port 175. As shown in FIG. 7, and consistent with this invention, catalyst 170 can include electrically conductive distal portion 180 (which is placed in chamber 160) and electrically non-conductive portion 185 (which is placed substantially outside chamber 160, but can extend somewhat inside the chamber). <BR> <BR> <P>This configuration prevents an electrical connection (e. g. , sparking) between distal portion 180 and chamber 160.

[075] In another embodiment, shown in FIG. 8, the catalyst can be formed from a plurality of electrically conductive segments 190 separated by and mechanically connected to a plurality of electrically non-conductive segments 195.

In this embodiment, the catalyst can extend through the ignition port between a point inside the cavity and another point outside the cavity, but the electrically discontinuous profile significantly prevents sparking and energy leakage.

[076] Another method of forming a plasma consistent with this invention includes subjecting a gas in a cavity to electromagnetic radiation having a frequency less than about 333 GHz in the presence of an active plasma catalyst, which generates or includes at least one ionizing particle.

[077] An active plasma catalyst consistent with this invention can be any particle or high energy wave packet capable of transferring a sufficient amount of energy to a gaseous atom or molecule to remove at least one electron from the gaseous atom or molecule in the presence of electromagnetic radiation.

Depending on the source, the ionizing particles can be directed into the cavity in the form of a focused or collimated beam, or they may be sprayed, spewed, sputtered, or otherwise introduced.

[078] For example, FIG. 9 shows radiation source 200 directing radiation into radiation chamber 205. Plasma cavity 210 can be positioned inside of chamber 205 and may permit a gas to flow therethrough via its gas ports. Source 200 directs ionizing particles 225 into cavity 210. Source 200 can be protected, for example, by a metallic screen which allows the ionizing particles to pass through but shields source 220 from radiation. If necessary, source 200 can be water- cooled.

[079] Examples of ionizing particles consistent with this invention can include x-ray particles, gamma ray particles, alpha particles, beta particles, neutrons, protons, and any combination thereof. Thus, an ionizing particle catalyst can be charged (e. g. , an ion from an ion source) or uncharged and can be the product of a radioactive fission process. In one embodiment, the vessel in which the plasma cavity is formed could be entirely or partially transmissive to the ionizing particle catalyst. Thus, when a radioactive fission source is located outside the cavity, the source can direct the fission products through the vessel to ignite the plasma. The radioactive fission source can be located inside the radiation chamber <BR> <BR> to substantially prevent the fission products (i. e. , the ionizing particle catalyst) from creating a safety hazard.

[080] In another embodiment, the ionizing particle can be a free electron, but it need not be emitted in a radioactive decay process. For example, the electron can be introduced into the cavity by energizing the electron source (such as a metal), such that the electrons have sufficient energy to escape from the source. The electron source can be located inside the cavity, adjacent the cavity, or even in the cavity wall. It will be appreciated by those of ordinary skill in the art that the any combination of electron sources is possible. A common way to produce electrons is to heat a metal, and these electrons can be further accelerated by applying an electric field.

[081] In addition to electrons, free energetic protons can also be used to catalyze a plasma. In one embodiment, a free proton can be generated by ionizing hydrogen and, optionally, accelerated with an electric field.

[082] Multi-mode Radiation Cavities [083] A radiation waveguide, cavity, or chamber can be designed to support or facilitate propagation of at least one electromagnetic radiation mode. As used herein, the term"mode"refers to a particular pattern of any standing or propagating electromagnetic wave that satisfies Maxwell's equations and the applicable boundary conditions (e. g. , of the cavity). In a waveguide or cavity, the mode can be any one of the various possible patterns of propagating or standing electromagnetic fields. Each mode is characterized by its frequency and polarization of the electric field and/or the magnetic field vectors. The electromagnetic field pattern of a mode depends on the frequency, refractive indices or dielectric constants, and waveguide or cavity geometry.

[084] A transverse electric (TE) mode is one whose electric field vector is normal to the direction of propagation. Similarly, a transverse magnetic (TM) mode is one whose magnetic field vector is normal to the direction of propagation. A transverse electric and magnetic (TEM) mode is one whose electric and magnetic field vectors are both normal to the direction of propagation. A hollow metallic waveguide does not typically support a normal TEM mode of radiation propagation.

Even though radiation appears to travel along the length of a waveguide, it may do so only by reflecting off the inner walls of the waveguide at some angle. Hence, depending upon the propagation mode, the radiation (e. g. , microwave) may have either some electric field component or some magnetic field component along the axis of the waveguide (often referred to as the z-axis).

[085] The actual field distribution inside a cavity or waveguide is a superposition of the modes therein. Each of the modes can be identified with one or more subscripts (e. g., TE10 ("tee ee one zero"). The subscripts normally specify how many"half waves"at the guide wavelength are contained in the x and y directions. It will be appreciated by those skilled in the art that the guide wavelength can be different from the free space wavelength because radiation propagates inside the waveguide by reflecting at some angle from the inner walls of the waveguide. In some cases, a third subscript can be added to define the number of half waves in the standing wave pattern along the z-axis.

[086] For a given radiation frequency, the size of the waveguide can be selected to be small enough so that it can support a single propagation mode. In such a case, the system is called a single-mode system (i. e. , a single-mode applicator). The TE10 mode is usually dominant in a rectangular single-mode waveguide.

[087] As the size of the waveguide (or the cavity to which the waveguide is connected) increases, the waveguide or applicator can sometimes support additional higher order modes forming a multi-mode system. When many modes are capable of being supported simultaneously, the system is often referred to as highly moded.

[088] A simple, single-mode system has a field distribution that includes at least one maximum and/or minimum. The magnitude of a maximum largely depends on the amount of radiation supplied to the system. Thus, the field distribution of a single mode system is strongly varying and substantially non- uniform.

[089] Unlike a single-mode cavity, a multi-mode cavity can support several propagation modes simultaneously, which, when superimposed, results in a complex field distribution pattern. In such a pattern, the fields tend to spatially smear and, thus, the field distribution usually does not show the same types of strong minima and maxima field values within the cavity. In addition, as explained more fully below, a mode-mixer can be used to"stir"or"redistribute"modes (e. g., by mechanical movement of a radiation reflector). This redistribution desirably provides a more uniform time-averaged field distribution within the cavity.

[090] A multi-mode cavity consistent with this invention can support at least two modes, and may support many more than two modes. Each mode has a maximum electric field vector. Although there may be two or more modes, one mode may be dominant and has a maximum electric field vector magnitude that is larger than the other modes. As used herein, a multi-mode cavity may be any cavity in which the ratio between the first and second mode magnitudes is less than about 1: 10, or less than about 1: 5, or even less than about 1: 2. It will be appreciated by those of ordinary skill in the art that the smaller the ratio, the more distributed the electric field energy between the modes, and hence the more distributed the radiation energy is in the cavity.

[091] The distribution of plasma within a processing cavity may strongly depend on the distribution of the applied radiation. For example, in a pure single mode system, there may only be a single location at which the electric field is a maximum. Therefore, a strong plasma may only form at that single location. In many applications, such a strongly localized plasma could undesirably lead to non- uniform plasma treatment or heating (i. e., localized overheating and underheating).

[092] Whether or not a single or multi-mode cavity is used consistent with this invention, it will be appreciated by those of ordinary skill in the art that the cavity in which the plasma is formed can be completely closed or partially open.

For example, in certain applications, such as in plasma-assisted furnaces, the cavity could be entirely closed. In other applications, however, it may be desirable to flow a gas through the cavity, and therefore the cavity must be open to some degree. In this way, the flow, type, and pressure of the flowing gas can be varied over time. This may be desirable because certain gases with lower ionization potentials, such as argon, are easier to ignite but may have other undesirable properties during subsequent plasma processing.

[093] Mode-mixing [094] For many applications, a cavity containing a uniform plasma is desirable. However, because radiation can have a relatively long wavelength (e. g., several tens of centimeters), obtaining a uniform distribution can be difficult to achieve. As a result, consistent with one aspect of this invention, the radiation modes in a multi-mode cavity can be mixed, or redistributed, over a period of time.

Because the field distribution within the cavity must satisfy all of the boundary conditions set by the inner surface of the cavity, those field distributions can be changed by changing the position of any portion of that inner surface.

[095] In one embodiment consistent with this invention, a movable reflective surface can be located inside the radiation cavity. The shape and motion of the reflective surface should, when combined, change the inner surface of the cavity during motion. For example, an"L"shaped metallic object (i. e.,"mode-mixer") when rotated about any axis will change the location or the orientation of the reflective surfaces in the cavity and therefore change the radiation distribution therein. Any other asymmetrically shaped object can also be used (when rotated), but symmetrically shaped objects can also work, as long as the relative motion (e. g. , rotation, translation, or a combination of both) causes some change in the location or orientation of the reflective surfaces. In one embodiment, a mode-mixer can be a cylinder that is rotatable about an axis that is not the cylinder's longitudinal axis.

[096] Each mode of a multi-mode cavity may have at least one maximum electric field vector, but each of these vectors could occur periodically across the inner dimension of the cavity. Normally, these maxima are fixed, assuming that the frequency of the radiation does not change. However, by moving a mode-mixer such that it interacts with the radiation, it is possible to move the positions of the maxima. For example, mode-mixer 38 can be used to optimize the field distribution within cavity 12 such that the plasma ignition conditions and/or the plasma sustaining conditions are optimized. Thus, once a plasma is excited, the position of the mode-mixer can be changed to move the position of the maxima for a uniform time-averaged plasma process (e. g. , heating).

[097] Thus, consistent with this invention, mode-mixing can be useful during plasma ignition. For example, when an electrically conductive fiber is used as a plasma catalyst, it is known that the fiber's orientation can strongly affect the minimum plasma-ignition conditions. It has been reported, for example, that when such a fiber is oriented at an angle that is greater than 60° to the electric field, the catalyst does little to improve, or relax, these conditions. By moving a reflective surface either in or near the cavity, however, the electric field distribution can be significantly changed.

[098] Mode-mixing can also be achieved by launching the radiation into the applicator chamber through, for example, a rotating waveguide joint that can be mounted inside the applicator chamber. The rotary joint can be mechanically <BR> <BR> moved (e. g. , rotated) to effectively launch the radiation in different directions in the radiation chamber. As a result, a changing field pattern can be generated inside the applicator chamber.

[099] Mode-mixing can also be achieved by launching radiation in the radiation chamber through a flexible waveguide. In one embodiment, the waveguide can be mounted inside the chamber. In another embodiment, the waveguide can extend into the chamber. The position of the end portion of the <BR> <BR> flexible waveguide can be continually or periodically moved (e. g. , bent) in any<BR> suitable manner to launch the radiation (e. g. , microwave radiation) into the chamber at different directions and/or locations. This movement can also result in mode- mixing and facilitate more uniform plasma processing (e. g. , heating) on a time- averaged basis. Alternatively, this movement can be used to optimize the location of a plasma for ignition or other plasma-assisted process.

[0100] If the flexible waveguide is rectangular, a simple twisting of the open end of the waveguide will rotate the orientation of the electric and the magnetic field vectors in the radiation inside the applicator chamber. Then, a periodic twisting of the waveguide can result in mode-mixing as well as rotating the electric field, which can be used to assist ignition, modulation, or sustaining of a plasma.

[0101] Thus, even if the initial orientation of the catalyst is perpendicular to the electric field, the redirection of the electric field vectors can change the ineffective orientation to a more effective one. Those skilled in the art will appreciate that mode-mixing can be continuous, periodic, or preprogrammed.

[0102] In addition to plasma ignition, mode-mixing can be useful during subsequent plasma processing to reduce or create (e. g. , tune) "hot spots"in the chamber. When a cavity only supports a small number of modes (e. g., less than 5), one or more localized electric field maxima can lead to"hot spots" (e. g. , within cavity 12). In one embodiment, these hot spots could be configured to coincide with one or more separate, but simultaneous, plasma ignitions or processing events. Thus, the plasma catalyst can be located at one or more of those ignition or subsequent processing positions.

[0103] Multi-location ignition [0104] A plasma can be ignited using multiple plasma catalysts at different locations. In one embodiment, multiple fibers can be used to ignite the plasma at different points within the cavity. Such multi-point ignition can be especially beneficial when a uniform plasma ignition is desired. For example, when a plasma is modulated at a high frequency (i. e. , tens of Hertz and higher), or ignited in a relatively large volume, or both, substantially uniform instantaneous striking and restriking of the plasma can be improved. Alternatively, when plasma catalysts are used at multiple points, they can be used to sequentially ignite a plasma at different locations within a plasma chamber by selectively introducing the catalyst at those different locations. In this way, a plasma ignition gradient can be controllably formed within the cavity, if desired.

[0105] Also, in a multi-mode cavity, random distribution of the catalyst throughout multiple locations in the cavity increases the likelihood that at least one of the fibers, or any other passive plasma catalyst consistent with this invention, is optimally oriented with the electric field lines. Still, even where the catalyst is not optimally oriented (not substantially aligned with the electric field lines), the ignition conditions are improved.

[0106] Furthermore, because a catalytic powder can be suspended in a gas, it is believed that each powder particle may have the effect of being placed at a different physical location within the cavity, thereby improving ignition uniformity within the cavity.

[0107] Dual-Cavity Plasma Iqniting/Sustainina [0108] A dual-cavity arrangement can be used to ignite and sustain a plasma consistent with this invention. In one embodiment, a system can include at least a first ignition cavity and a second cavity in fluid communication with the first cavity.

To ignite a plasma, a gas in the first ignition cavity can be subjected to electromagnetic radiation having a frequency less than about 333 GHz, optionally in the presence of a plasma catalyst. In this way, the proximity of the first and second cavities may permit a plasma formed in the first cavity to ignite a plasma in the second cavity, which may be sustained with additional electromagnetic radiation.

[0109] In one embodiment of this invention, the first cavity can be very small and designed primarily, or solely for plasma ignition. In this way, very little radiation energy may be required to ignite the plasma, permitting easier ignition, especially when a plasma catalyst is used consistent with this invention.

[0110] In one embodiment, the first cavity may be a substantially single mode cavity and the second cavity is a multi-mode cavity. When the first ignition cavity only supports a single mode, the electric field distribution may strongly vary within the cavity, forming one or more precisely located electric field maxima. Such maxima are normally the first locations at which plasmas ignite, making them ideal points for placing plasma catalysts. It will be appreciated, however, that when a plasma catalyst is used, it need not be placed in the electric field maximum and, many cases, need not be oriented in any particular direction.

[0111] Illustrative Plasma Processing Control [0112] Methods and apparatus for plasma processing control may be provided consistent with this invention. Such processing control, can include <BR> <BR> monitoring a temperature associated with at least one object (e. g. , being heated by plasma) and detecting a temperature spike. Detection of the temperature spike may be used to trigger further control actions, such as turning off a radiation source, mode-mixing, flowing gas at a different rate, etc. A plasma catalyst can be used to facilitate the igniting, modulating, or sustaining of the plasma at gas pressures less than, equal to, or greater than atmospheric pressure.

[0113] FIG. 10 shows a simplified schematic diagram of illustrative apparatus <BR> <BR> 240 for controlling a plasma-assisted process (e. g. , heating of an object) consistent with this invention. As used herein, the term"object"broadly refers to a single part or component, as well as multiple parts or components, regardless of shape, size, construction, or composition. For example, the term"object"may collectively encompass multiple parts to be joined to each other, together with any material used to join the parts. For example, if a tube is to be brazed to a collar using a brazing ring, the term"object"may collectively encompass at least one portion of the tube, the collar, and the brazing ring, but could include multiple portions or multiple objects, in their entireties.

[0114] The apparatus of FIG. 10 may include controller 244 coupled to memory 246. Controller 244 may be a microprocessor, or any other type of controller capable of executing instructions stored in a memory (which may be part of the controller itself). Memory 246 can include any of correlation module 247, control module 249, and stored temperature information 251. Correlation module 247, which may be implemented in hardware, software, or firmware, can be used to identify a correlation between a temperature spike associated with a plasma-heated object and the object's physical condition.

[0115] Control module 249, which can also be implemented in hardware, software, or firmware, can be used to compare the object's actual condition (e. g., exhibited by a temperature spike) with temperature information 251. Temperature information 251 can include trigger information indicative of a correlation, for example, between a temperature spike associated with the object and its actual condition.

[0116] Control module 249 can compare an actual (measured) temperature spike with the stored trigger information. Control module 249 can be used to alter heating and/or cooling conditions when the actual temperature spike is detected within a predetermined proximity to the stored trigger information. For example, control module 249 can alter a supply of gas to the cavity and/or the radiation directed to the cavity when the actual temperature spike is within a predetermined proximity to the stored trigger information. One skilled in the art will appreciate that although FIG. 10 shows separate correlation and control modules, they could be combined into one module or can be subdivided into further sub-modules. Also, the various modules may be stored in different memories.

[0117] A temperature spike can be considered to be within a predetermined proximity to the stored trigger information when a spike of sufficient magnitude occurs within a particular temperature range. Alternatively, a predetermined proximity can mean that the temperature spikes at a predetermined rate or within a predetermined rate range. In another embodiment, predetermined proximity can simply mean attaining a predetermined elevated temperature or temperature range.

[0118] The actual physical condition of a plasma-heated object may relate to the condition of the object during different plasma-heated processes, such as brazing, welding, sintering, soldering, bonding, or any other joining process.

FIG. 11, for example, shows illustrative graph 252, which includes reflected radiation power data 253, measured temperature (°C) data 254, and magnetron current data 255 as a function of time during a brazing operation consistent with this invention (only temperature scale is shown on the Y-axis). As shown in FIG. 11, the physical condition of an object can relate to the phase (e. g., melting point) of a brazing ring. In one embodiment, the actual physical condition of an object may be stored as part of temperature information 251 and correlated to a known temperature.

[0119] Temperature information 251 can thus include a predetermined temperature. The predetermined temperature can relate to a desirable target temperature or temperature profile. Trigger information can also be related to a temperature or temperature profile of an object. For example, a temperature profile may relate to a range of temperatures of the object over a time period. As used herein, the term"temperature profile"broadly encompasses any time or milestone dependent temperature characteristic that correlates to the physical condition an object. For example, the temperature profile may be a single temperature at which a phase transition is expected to occur. It may alternatively be a series of separate target temperatures, a continuous temperature profile, a time period for achieving a predetermined heating condition, a temperature spike, or any other schedule or target for measuring or controlling a temperature.

[0120] For example, a particular temperature profile may be correlated to a condition that occurs when the object reaches temperature X. Or, the profile may be correlated to a condition related to a sudden spike in temperature, for example, after approximately Y seconds. Alternatively, the profile could be correlated to a condition is predicted to occur when the shape of the time-dependent profile occurs. It will be appreciated that the correlated temperature profile can vary significantly depending upon the plasma-assisted process, the equipment used to perform the process, the correlated condition, the physical characteristics of the object, and a host of other factors. Thus, the invention, in its broadest sense, is not limited to any particular temperature profile.

[0121] Temperature information 251 can include information identifying a temperature spike, such as spike 256 of FIG. 11. Additionally, temperature information 251 can include information related to a particular energy distribution in the cavity. This may be useful where one or more objects are being processed in one or more cavities. For example, a distribution can be empirically based on prior trial runs of the one or more similar objects. The prior runs can be made with a particular amount of radiation and particular gas flow pattern. Then, based on those runs, it may be determined that the energy distribution in the cavity may need to be modified at a certain time during the plasma process.

[0122] For example, energy distribution in the cavity may need to be changed to ensure that the various objects being processed are uniformly or selectively heated. As discussed above, a mode mixer may be used to redistribute the electromagnetic energy in the cavity. Gas flow may also be adjusted in certain parts of the cavity to adjust the plasma distribution and temperature in the cavity.

[0123] In one embodiment, empirically established energy distribution may be compared against an actual measured energy distribution. For example, because the transition probabilities of various atoms are known, this knowledge can be used to determine the status of the plasma. That is, the intensities of the radiation from the various types of atoms can be interpreted using Boltzman's law to determine the actual energy distribution of the radiation in a plasma-processing cavity.

[0124] As discussed above, an object located in a cavity may undergo a plasma-assisted process by directing radiation into the cavity. An actual condition (e. g. , temperature, phase, etc. ) of the object, may be monitored using any appropriate sensor (such as pyrometer 42 of FIG. 1). In addition, exemplary sensors could be a hollow cathode lamp or other type of temperature detection device. For example, a hollow cathode lamp may monitor the actual temperature of a copper brazing ring by detecting a signature melting event associated with the copper. In this case, a current output of the lamp could increase when even a small number of copper atoms become part of the gas or plasma in the cavity. Such an increase could be correlated to the melting of the brazing ring and therefore a temperature. Hollow cathode lamps are available, for example, from Perkin Elmer Incorporated of Shelton, Connecticut. As explained below, any narrow band sensor can also be used to detect melting of the copper brazing ring.

[0125] Narrow band filters may also be used to detect radiation having a particular selected wavelength. Such radiation could be gradually or suddenly emitted when an object achieves a particular temperature. Narrow-band filtered detection may involve the use of a photo-diode, for example. The output of the photo-diode can indicate the intensity of the emission and be used to empirically or analytically determine the actual temperature of the object being processed. As discussed above, one way to measure the actual temperature of an object may rely on a calibration procedure. Once calibrated, the temperature of one or more objects can be determined using any calibrated, correlated event.

[0126] As discussed above, control module 249 of FIG. 10 can be used to compare a measured temperature of an object with temperature information 251.

Based on the comparison, control module 248 can alter any available temperature control parameter, such as a gas flow or a radiation intensity, when the measured temperature meets one or more criteria. For example, when an actual temperature spike is detected within a predetermined proximity to stored trigger information, control module 249 may adjust the rate of gas flow by controlling valve 22 of FIG. 1.

In some circumstances, control module 249 may turn off the radiation source and thereby extinguishing the plasma. Other temperature control parameters include the position of a mode-mixer, the shape of a plasma cavity, the distance between the plasma and the object, etc.

[0127] In one embodiment, a LabVIEW (D graphical development environment was used to automate data acquisition, instrument control, measurement analysis, and data presentation. LabVIEW is available from the National Instruments Corporation, of Austin, Texas. As described below, LabVIEWO can be used to graphically develop a control program. The program can include at least one front panel (such as, described below with respect to FIGS.

12 and 13). It can also include various development representations, such as a hierarchy flow chart representing relationships among various control functions, and a functional diagram interconnecting the various components of the control program. One skilled in the art will appreciate that the description below of the control program is merely exemplary and other development tools and/or programming languages can be used to implement the control program.

[0128] FIG. 12 shows an illustrative front panel diagram of a virtual instrument for inputting various control parameters and displaying process data consistent with this invention. The virtual instrument can be used to operate systems in automated or manual modes. In one automated embodiment, the initial, intermediate, and final radiation power levels can be entered at"Power1"control 260,"Power2"control 262, and"Power3"control 264, respectively, as shown in FIG. 12. Two intermediate temperature set-points"Temp1"and"Temp2"can be entered at controls 265 and 267, respectively. These temperature set-points can be used to trigger further processes and temperature control functions, as desired.

As also shown in FIG. 12,"Sample Interval [mS]"control 266 allows a user to enter a signal-sampling interval and"Max. Interval [min]"control 268 allows a user to enter a maximum time limit that the process may proceed.

[0129] If the processing is not stopped manually before the specified maximum time limit, the radiation power can be turned off automatically and the process stopped. Those skilled in the art will appreciate that this stopping feature can be used as a safety feature as well. The front panel of the virtual instrument shown in FIG. 12 also includes two plots for displaying time-power and time- temperature profiles in windows 270 and 272, respectively. In one embodiment, the program plotted the profile data after the process was complete, although those skilled in the art will appreciate that the profile can also be plotted in real-time.

[0130] During operation in the automatic mode, radiation power can be programmed to start at a power level defined by parameter Power1. When the sample temperature reaches a temperature defined by Temp1, the radiation power can be automatically changed to a power defined by parameter Power2. Similarly, when the sample temperature reaches a temperature defined by Temp2, the radiation power can be changed to a power level defined by parameter Power3.

Thus, during operation in the automatic heating mode, the user was able to use three different heating rates. If necessary, the number of temperature thresholds may be greater or less than two. As a result, any desired temperature profile for heating and cooling can be obtained consistent with this invention.

[0131] FIG. 13 shows an illustrative front panel diagram of another virtual instrument that includes various indicators and controls to display live data and to allow a user to control and manipulate a plasma process consistent with this invention. In an automatic mode, as discussed above with respect to FIG. 12, the preset power and temperature parameters could not be modified once the heating process starts. However, during operation in the manual mode, as shown on the left lower side of the front panel of FIG. 13, radiation power can be increased or decreased manually at any time during the process.

[0132] The front panel of FIG. 13 was programmed to display live sample temperature data in display window 273. The system provides a user live, real-time control of the radiation power with sliding control bar 275 when the"LIVE CTRL YES/NO"control button 276 is used to activate the manual operational mode.

[0133] Further, the front panel of the virtual instrument shown in FIG. 13 can also include a number of controls that enable a user to design a customized temperature profile. Exemplary controls, shown in FIG. 13, include : (i)"Ready/Stop"toggle control 274, which allows a user to start or stop a process, <BR> <BR> (ii) "Live Cntrl"input control 276, which allows a user to select the power level<BR> between 0.5 kW and 5.0 kW, (iii) "Power P2/Power P3"toggle control 280 for<BR> selecting power levels P2 or P3 (which overrides"Auto Set to P3 at (S) "), (iv) "Cooldown"indicator/control button 278, which turns off the radiation power in automatic mode, but keeps the clock running to record the cooling profile (when <BR> <BR> active, the embedded indicator light also turns on), (v)"Pyro Delay (S) "input control<BR> 294, which allows a user to enter a desired pyrometer delay time, (vi) "Braze Temp" input control 296, which allows a user to select a desired brazing temperature, (vii) "Auto set to P2 at (S)"input control 298 and"Auto set to P3 at (S)"input control 300, which enable a user to define two time periods at which the applied power changes to P2 and P3 power levels, respectively, (viii) "No. Ave"input control 310, which allows a user to enter a desired number of data points to be used in the sliding average for the temperature and radiation forward/reflected power channels, and (ix) "Buffer Size"input control 312, which allows a user to enter the size of the buffer memory. One skilled in the art will appreciate that the controls shown in FIG. 13 are exemplary and fewer or more controls may be used consistent with this invention.

[0134] The front panel of FIG. 13 also includes additional indicators that can indicate the status or value of various control parameters associated with <BR> <BR> temperature control. Exemplary indicators shown in FIG. 13 include: (i) "Run Time:<BR> S"indicator 302, which indicates the current run-time in seconds; (ii) "Temp. C"<BR> indicator 304, which indicates the current part temperature in Celsius, (iii) "Forward P"indicator 306, which indicates the current applied power radiation level, (iv) "Reflected P"indicator 308, which indicates the reflected radiation power level, (v) "Magnetron"indicator 286, which indicates the operating status of a radiation power source, such as a microwave power source, (vi)"Auto Cool"indicator 288, which <BR> <BR> indicates the cooling status, (vii) "Auto P2"and"Auto P3"indicators 290 and 292, which indicate whether P2 and P3 power levels are being used (see below), and (viii)"Cooldown"control/indicator 278, which indicates whether the temperature is decreasing. One skilled in the art will appreciate that the indicators shown in FIG.

13 are exemplary and fewer or more indicators may be used consistent with this invention. Some of these indicators are described further below.

[0135] In one embodiment, initiation of a plasma-assisted process can be prepared when"Ready/Stop"toggle control 274 is in the"ready"position (as shown). Similarly, the process can be stopped when toggle 274 is in the"stop" position (not shown). Magnetron indicator 286 can turn on when a source of <BR> <BR> radiation, such as a source of radiation power is turned on."Pyro Delay (S) "input control 294 allows a user to provide a time delay for the pyrometer to stabilize before the system takes automated control of the process.

[0136] Some processes consistent with this invention involve the automatic changing between different power levels, such as power levels P2 to P3. In one embodiment, switching can occur from power level P2 to power level P3 after a time specified by"Auto Set to P2 (S)"input control 298. Similarly, switching can occur from power level P3 to power level P2 after another time specified by"Auto <BR> <BR> Set to P3 (S) "input control 300. When the temperature is controlled using power<BR> level P2, "Auto P2"indicator 290 can be programmed to light up. Similarly, when<BR> the temperature is controlled using power level P3, "Auto P3"indicator 292 can be programmed to light up.

[0137] "Braze temp"control input 296 can be used to automatically turn off the radiation power, such as microwave power, when a desired temperature is reached. In one embodiment, the process clock is allowed to run to record the cooling profile, if desired. Thus, in contrast to manually stopping the system using "Ready/Stop"toggle control 274, activating"Cooldown"control/indicator 278 turns off the radiation power, such as microwave power, but keeps the system clock running to record the cooling profile. When the radiation power is automatically turned off, the front panel can indicate this status by lighting up"Auto Cool" indicator 288. In the automatic mode, selecting"Cooldown"control/indicator 278 turns off and lights up.

[0138] Forward and reflected radiation powers can be measured by dual directional couplers and diodes. The output voltages of the diodes can be converted to actual powers by using look-up tables from calibration charts and spline interpolation. Those skilled in the art will appreciate that other empirical techniques can also be used to measure forward and reflected radiation powers, as well as various analytical techniques, to further process the measured power values.

[0139] If the system is already in an automatic operational mode, selecting "Live Ctrl Yes/No"control 276 places the system into a manual operational mode.

Alternatively, if the system is already in the manual operational mode, selecting "Live Ctrl Yes/No"control 276 puts the system into the automatic operational mode.

In manual mode, vertical sliding control 275 is used to vary the radiation power level.

[0140] "No. Ave. "input control 310 controls the number of data points used in the sliding average calculation. The data points used in the calculation originate from the temperature and radiation power data streams. Those skilled in the art will appreciate that one stream of data, or additional streams of data, may be used consistent with this invention. Because averaging can be carried out using shift registers, the stored data can be purged when its number of data points equals the value of the buffer size specified by"Buffer Size"input control 312. This sliding average calculation technique permits efficient use of available memory and can increase processing speeds and improve temperature control.

[0141] FIG. 14 shows an illustrative block diagram of various functions that can be controlled by software consistent with this invention. On the far left-hand side of FIG. 14, input control data is provided, including, as described above, "Sample Interval [mS],""P1,""P2,""P3,""Temp1,""Temp2,"and"Max. Interval <BR> <BR> [min], "which correspond to objects 400-406, respectively. This control data can be entered through the front panel shown in FIG. 12. Those skilled in the art will appreciate that these objects are outside of the"while-loop,"which is marked by thick rectangular line 330. In other words, input control data is not the data, acquired by the virtual instruments, such as temperature, forward power of the radiation, and the reflected power of the radiation, discussed further below.

Further, such acquired data can be used to calibrate and control the process.

[0142] Thus, FIG. 14 can be used to visualize control of a plasma-assisted process consistent with this invention. For example,"GetVals2. vi" object 332 can retrieve experimental data from eight channels shown (Numbers 0-7) at a rate specified by"sample interval [mS] "control 266, shown in FIG. 12, although a different number of channels can also be used, if desired. In addition to the data that may be relevant to the particular plasma-assisted process, other types of data can also be acquired and used, including information resulting from the monitoring of the magnetron, such as the internally measured power of the magnetron, the magnetron solenoid current, and the magnetron voltage. Temperature, forward radiation power, and reflected radiation power (e. g. , data channels 0,1 and 2, respectively) can also be extracted and separated into three different processing branches.

[0143] Data may be processed after acquisition. For example, units can be converted as needed. Temperature data, for example, was multiplied by a factor of 1,000 to convert from volts to mVolts. In this way, the processed temperature data can correspond to degrees Celsius (the output of the pyrometer used was 1 mV/Celsius). All three processing branches were bundled together again in "Build. Array" object 336 and then fed to SlidingAve. MuItipleChan. vi" object 354 to calculate a sliding average. The output of"Build. Array" object 336 can also also be sent to shift register terminal 444, which is further coupled with"Buffer. sizing" object 338. As a result, each new set of data points is added to the top of"Build. Array" object 336, which facilitates computing of sliding averages. Control"No. Ave." 340 can set up a number of measurements, taken every 100 millisecond, for example <BR> <BR> (based on the value of"Sample Interval [mS] "), which may be averaged. Thus, for example, if the value of control"No. Ave." 340 is 20, then 20 temperature measurements can be used to generate a sliding average temperature.

[0144] As shown in FIG. 14, the data can be further processed by separating it again into different branches for display and control purposes. Radiation power levels (such as microwave power levels in units of kW) were retrieved by interpolation of the diode voltage-power tables before being displayed on the screen. Thus, for example, forward radiation power may be retrieved via"F. Diode- P table-vi"object 376 before being displayed as"Forward P"by object 370.

Similarly, reflected forward power may be retrieved from"R-Diode-P table-iv"object 378 before being displayed as"Reflect P"object 372.

[0145] The temperature, forward radiation power, and reflected radiation power averaged data can replace the corresponding individual data values in "Replace Array Subset"object 356. Time information can be added to the array in "Build Array"object 358. In one embodiment, for example,"Build Array"object 358 may include columns of data reflecting time, temperature, forward radiation power, and reflected radiation power. One skilled in the art will appreciate that the array may also include additional data columns for other types of performance data. The data in the array can then be sent out of the"While Loop"defined by rectangle 330 to"samples"object 360 for storage in memory, such as a computer's hard drive.

[0146] The radiation power preset control values"P1,""P2,"... etc. were monitored to ensure that they fell within a range between a minimum value and a maximum value (e. g. , 0.5-5. 0 KW) by"HighLowLimit. vi" object 340. These values were then converted to appropriate control voltages for the radiation power supply, such as a radiation power supply by"PowerTable. vi" objects 342, which use spline interpolation."Sample Interval"object 400 and"Wait Until Next ms Multiple"object 408 provided timing information in milliseconds, which was converted to seconds at object 441.

[0147] In one embodiment, transition from one power level to another power level, such as P1 to P2 can be based on time. Thus, for example, after a predetermined time, such as 30 seconds, the radiation power associated with a magnetron, can be increased from a value set through P1 control object 401 to a value set P2 through control object 402. To accomplish this, in one embodiment, as shown in FIG. 14, a run time measured the point at which the process began (obtained from"Run Time: S"object 414) may be compared, using compare object 424, with a time value provided by"AUTO SET TO P2 AT (S) "object 426 (e. g., having the time value in seconds at which the power level is programmed to change).

[0148] If the run time is less than the time obtained from object 426, then compare object 424 may generate a logic value 1, which may be fed as a control variable to select object 418. Select element 418 may, depending on the control variable value, produce an output value corresponding to its top input or to its bottom input. Thus, where the control variable is logic value 1, select object 418 may generate a P1 power value, which as shown in FIG. 14, corresponds to the top input. Alternatively, when run time is higher than the time obtained from object 426 (e. g. , specifying the time at which power is programmed to change from level P1 to P2, for example), output of compare object 424 may be logic value 0 causing select object 418 to generate P2 power value at its output. Thus, when the run time exceeds the time at which power needs to be increased from P1 to P2, the power may be automatically changed from P1 to P2. One skilled in the art will appreciate that the various objects and their connections are merely exemplary and other logic elements arranged differently may be used to achieve the above functionality.

[0149] As long as then, the control variable of select object 420 is set to logic value 0, one of P1, P2, or P3 power value may be passed to the next select object 422, depending upon the status of select objects 418 and 442. Select object 422 may then pass that power level value to the radiation power source current control object 416. The power supply associated with the radiation source, such as a Magnetron may then adjust its current accordingly so as to generate the correct radiation power level. Select object 422 can be controlled by"LIVE CTRL YES/NO" object 412. Object 412 may be set to logic value 1, when"live"control is turned on or logic value 0 when turned off.

[0150] In another embodiment, a braze temperature may be set using "BRAZE TEMP (C)"object 436. In this way, a source of radiation, such as a Magnetron, may be turned off once an object whose temperature is being monitored reaches the braze temperature. In one embodiment, where a user has set a pyrometer delay time stored at"PYRO DELAY (S) "object 430, the delay value may be compared with the current run time using compare object 432. When the run time exceeds the delay value, compare object 432 may generate a logic value 1. That logic value then may be fed as a control variable to select object 434.

Select object 434 may produce a value on its output corresponding to it top input when its control variable value is 1 or a value corresponding to its bottom input when its control variable value is 0.

[0151] When the current run time exceeds the pyrometer delay, select object 434 may provide an actual temperature value at its output. The real time temperature value may then be compared with the braze temperature setting stored at"BRAZE TEMP (C) "object 436 and, when it exceeds the braze temperature, compare object 436 may generate a logic value 1 at its output. Otherwise, compare element 436 may generate a logic value 0 at its output. Thus, if the object being heated has not reached the braze temperature, then the output of select object 436 (logic value 0) may be combined with an input from"COOLDOWN" object 440 by using a Boolean logic"OR"operation (object 438). Thus, if no manual cool down command has been given, then the output of object 438 may be logic value 0 (if the output of compare object 436 is logic value 0). The output of object 438 may be used as an input control variable for select object 420, which may provide a power value"0. 00" or a power value higher than zero (such as, P1, P2, or P3). As discussed above, the radiation source current may be controlled accordingly.

[0152] Those skilled in the art will appreciate that the above-listed indicators and controls and the detailed operation described could be different from above and consistent with this invention. For example, those skilled in the art will appreciate that the time and averaged temperature data were processed with various logic objects/gates to generate the desired control functionality. Although the radiation power levels described herein were controlled by time (except the final cooldown step), the radiation power can also be controlled with temperature data by using appropriate combinations of logic gates that process temperature data rather than time data. Further, although some of the above examples refer to magnetron, any other source of radiation, such as a klystron, gyrotron, traveling wave tube amplifier, a solid state source, or any other source of radiation could supply radiation and could be controlled as discussed above.

[0153] FIG. 15 shows a flow chart for exemplary method 450 for determining a condition of a plasma-heated object consistent with this invention. In step 452 a correlation between a temperature spike (such as shown in FIG. 11) associated with an object and a condition of the object can be identified. In one embodiment, the condition may be associated with the melting of a brazing material. In step 454, trigger information reflecting the correlation can be stored, for example, as part of temperature information 251 in memory 246. In step 456, the object may be located within the cavity. In step 458, a gas can be supplied to the cavity and, in step 460, radiation can be directed into the cavity in an amount sufficient to establish a plasma in the cavity.

[0154] In step 462, a temperature spike can be detected by monitoring the temperature of the object using for example, any of the sensors mentioned above.

For example, a pyrometer may be used to detect a temperature spike. It will be appreciated that a lock-in-amplifier may be used to improve the signal-to-noise ratio of the temperature measurement. Also, temperature data may be fed to a radio frequency or other wireless-type transmitter, for transmission to a receiver.

[0155] In step 464, the measured temperature data (e. g. , spike) may be compared with the stored trigger information. As previously described, the trigger information may be stored, for example, as part of temperature information 251.

[0156] In step 466, a temperature control parameter can be adjusted when a measured temperature spike is within a predetermined proximity to the stored trigger information. A supply of gas to the cavity and/or radiation directed to the cavity can be altered. A plasma control program, such as the one described above with respect to FIGS. 12-14, may be used.

[0157] FIG. 16 shows a flow chart for exemplary method 500 that can be used to control a plasma-assisted process consistent with this invention. In step 502, a temperature associated with at least one object can be monitored. The <BR> <BR> temperature may be monitored by direct measurement (e. g. , by using a pyrometer) or estimated using the method of FIGS. 17A and 17B, described below. Other temperature measurement methods can also be used.

[0158] In step 504, a temperature spike can be detected in the acquired temperature data. As used herein, a"spike"can include an increasing portion followed by a decreasing portion. It will be appreciated, however, that different types of spikes, including various types of shapes, can also be detected, depending on the particular process being performed. Also, although FIG. 16 shows a starting point and an ending point, it will be appreciated that additional steps could be added before or after these points, if desired.

[0159] FIG. 17A shows a flow chart of exemplary method 510 for estimating and controlling a temperature during a plasma-assisted process consistent with this invention. The method can include measuring a forward power of radiation in step 522. In one embodiment, forward and reflected powers can be measured using dual-directional couplers and diodes. The output voltage of the diodes can be converted to actual power values, for example, by using look-up tables from calibration charts and spline interpolation. As described above with respect to FIG.

14,"F-Diode-Ptable-vi"object 376 may correlate the output voltage of a diode and a power value. Other analytical or statistical techniques may also be used. Method 522 can further include measuring a reflected radiation power in step 524. In one embodiment, like measurement of forward power, reflected power can be measured using"R-Diode-Ptable-vi"object 372 shown in FIG. 14.

[0160] Method 510 can further include estimating an amount of energy absorbed by at least one object in the cavity step 526. In one embodiment, the amount of energy absorbed may be determined by integrating a difference between the forward power and the reflected power over time to determine the total (net) amount of energy dumped into the cavity during a certain time period. Thus, for example, referring now to FIG. 14, the AP object 374 displays the difference between forward power 370 and reflected power 372 over a processing time.

[0161] A shift register and a summing device can be used to add the AP values for each interval during data acquisition. The net amount of energy absorbed can be displayed in an appropriate unit of measurement (such as kilo Joules) in indicator 443 of FIG. 14, for example. Once the net amount of energy deposited in the cavity is determined, the absolute or relative temperature of the object can also be determined. If the thermal properties of the cavity (such as the heat capacity) are known, these can also be used to refine the calculation.

[0162] FIG. 17B shows some of the additional steps that may be performed consistent with method 510. The additional steps may include receiving a first power level value in step 530. For instance, as shown in FIG. 14, a first power level can be provided as input via the front panel of FIG 12 using Power 1 control 260.

Next, a second power level value can be received in step 532, for example, through Power 2 control 262. In step 534, the forward power level can be set at the first power level value.

[0163] Next, the temperature may be monitored for example, using a pyrometer and, when it reaches a first predetermined value in step 536, the forward power may be automatically changed from a first power level (e. g., P1) to a second power level (e. g. , P2) in step 538. Further, when the temperature reaches a second predetermined value in step 540, the forward power may be automatically <BR> <BR> changed from the second power level to a third power level (e. g. , P3) in step 542.

One skilled in the art will appreciate that the above temperature control sequence is only exemplary, and the power levels may be varied to meet any time/temperature profile.

[0164] In the foregoing described embodiments, various features are grouped together in a single embodiment for purposes of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description of Embodiments, with each claim standing on its own as a separate preferred embodiment of the invention.