Magnetic mirror plasma source

The preferred embodiments described herein provide a magnetic mirror plasma source. While the traditional magnetic/electrostatic confinement method is ideal for many applications, some processes are not best served with this arrangement. The preferred embodiments described herein present a new technique to confine electrons (3) to produce a low pressure, dense plasma directly on a substrate surface (75). With these preferred embodiments, a combination of electrostatic and mirror magnetic confinement is implemented. The result is a novel plasma source that has unique and important advantages enabling advancements in PECVD, etching, and plasma treatment processes.

BACKGROUND

The present invention relates to a magnetic mirror plasma source. Before turning to the detailed description of the presently preferred embodiments, related prior art is discussed below. The related prior art is grouped into the following sections: magnetic confinement and the Penning cell source, facing target sputtering, plasma treatment with a web on a drum, and other prior art methods and apparatuses.

Magnetic Confinement and the Penning Cell Source

A good presentation on magnetic mirror confinement is presented in section 3.4.2 of J. Reece Roth,Industrial Plasma Engineering, Volume1: Principles, IOP Publishing, Ltd. 1995. Confinement of electrons and ions using magnetic mirrors is well known, especially in fusion research.

Facing Target Sputtering

U.S. Pat. No. 4,963,524 to Yamazaki shows a method of producing superconducting material. An opposed target arrangement is used with the substrate positioned between the electrodes in the magnetic field. The magnetic field is symmetrical between the electrodes, and the substrate is in the middle of the gap. With the substrate in this position, the Hall current generated within the magnetic field tends to be distorted and broken. When this happens, the plasma is extinguished and/or the voltage is much higher.

Plasma Treatment with a Web on a Drum

In U.S. Pat. Nos. 5,224,441 and 5,364,665 to Felts et al., a flexible substrate is disposed around an electrified drum with magnetic field means opposite the drum behind grounded shielding. In this arrangement, the shield opposite the drum is either grounded or floating. The substrate is supported by the surface without a mirror magnetic field emanating from the substrate.

In U.S. Pat. No. 4,863,756 to Hartig et al., the substrate is continuously moved over a sputter magnetron surface with the surface facing the magnetron located inside the dark space region of the cathode. In this way, the magnetic field of the magnetron passes through the substrate and is closed over the substrate surface constricting the plasma onto the surface.

Other Prior Art Methods and Apparatuses

U.S. Pat. No. 5,627,435 to Jansen et al. discloses a hollow cathode source operating at high, diode plasma regime pressures (0.1-5 Torr). The plasma is created inside the housing and then is emitted through holes. The plasma is generated in one chamber and then conducted to the substrate with the help of magnets under the substrate.

U.S. Pat. Nos. 6,066,826 and 6,287,687 to Yializis and Yializis et al. disclose a plasma treatment device for web materials. Similar to Jansen et al., a plasma is generated with a hollow cathode array and is ‘focused’ on the web by a magnetic field. As stated in the patent, the web charges up and the treatment stops when DC is used. As will be made clear below, this is different than the presently preferred embodiments. In the presently preferred embodiments, DC can readily be used with an insulating substrate without charge buildup over time. In these referenced patents, the magnetic field lines are not shown.

U.S. Pat. No. 6,077,403 to Kobayashi et al. shows a magnetron in combination with a second magnetic field. In this patent, the second field passes through the substrate to a supplemental electrode. This apparatus is not a stand-alone plasma source—it assists with ionizing and directing sputtered material to the substrate. Also, the first embodiment has the mirror field with a stronger magnetic field at the supplemental electrode than at the surface of the substrate.

In U.S. Pat. No. 4,631,106 to Nakazato et al., magnets are located under a wafer to create a magnetron type field parallel to the wafer. The magnets are moved to even out the process. The opposed plate is grounded, and the wafer platen is electrified.

U.S. Pat. No. 4,761,219 to Sasaki et al. shows a magnetic field passing through a gap with the wafer on one electrode surface. In this case, the electrodes are opposed to each other. The wafer is placed on the less compressed magnetic mirror surface, and the opposed surface across from the wafer is grounded.

U.S. Pat. No. 4,853,102 to Tateishi et al. uses a cusp field to assist sputter deposition into high aspect ratio holes. The flux lines leaving the substrate do not enter a negatively biased electrode.

U.S. Pat. No. 5,099,790 to Kawakami shows a microwave source with a moving magnet below the wafer to even out the coating on the wafer. In another figure, the substrates are moved over a stationary magnet(s). In this source, the plasma is generated in a separate plasma generation chamber and then directed to the wafer substrate with the assistance of the magnet under the substrate.

In U.S. Pat. No. 5,225,024 to Hanley et al., ExB containment is achieved by forcing the B flux into a parallel path over the substrate surface. U.S. Pat. No. 5,437,725 to Schuster et al. discloses a metal web drawn over a drum containing magnets. The web is electrified, and the opposed shield is at ground potential.

The source disclosed in U.S. Pat. No. 5,900,284 to Hu produces several magnetron type confinement traps on the surface above the magnets.

SUMMARY

The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims.

By way of introduction, the preferred embodiments described below relate to a magnetic mirror plasma source. In one preferred embodiment, a plasma source apparatus is provided comprising first and second surfaces with a gap between the surfaces, wherein the first surface comprises a substrate and wherein at least the second surface is connected to a power supply so as to contain electrons; a third surface connected to the power supply; a magnetic field passing through both the first and second surfaces and through the gap between the surfaces, wherein at least a portion of the magnetic field passing through the substrate is at least two times stronger at the substrate surface than at a weakest point along a field line within the gap and is strong enough to magnetize electrons; and an electric field created by the power supply connected between the second surface and the third surface, wherein the electric field penetrates into an electron confining region of the magnetic field so that a created Hall electron current is contained within an endless loop.

Other preferred embodiments are provided, and each of the preferred embodiments can be used alone or in combination with one another. The preferred embodiments will now be described with reference to the attached drawings.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

In the prior art, many magnetically confined plasmas are confined in two dimensions by the magnetic field and electrostatically in the third dimension. A planar magnetron, for instance, confines the electrons in the racetrack with arcing magnetic field lines and the electrostatic potential of the cathode target.

While the traditional magnetic confinement method is ideal for many applications, some processes are not best served with this arrangement. The preferred embodiments described herein present a new technique to confine electrons to produce a low pressure, dense, relatively low voltage plasma. With these preferred embodiments, a combination of electrostatic and mirror magnetic confinement is implemented. The result is a novel plasma source that has unique and important advantages enabling advancements in PECVD, etching, and plasma treatment processes.

FIG. 1Ashows a simple implementation of one preferred embodiment. A non-magnetic substrate1is placed over a magnet5. A high permeability material such as steel serves as the cathode3and is positioned over substrate1at sufficient distance to allow a plasma to form between the cathode3and substrate1. Anode11is a ring of wire positioned around the periphery of cathode3. In this configuration, magnetic field lines12are formed between the magnet5and cathode3. The field strength of these lines is stronger at the surface of the substrate1than at the cathode3forming a mirror magnetic field with the compressed end on the substrate1. When a plasma voltage is impressed between cathode3and anode11, a plasma14lights between the cathode3and substrate1. With this preferred embodiment, rather than the substrate1plasma facing surface being held at cathode potential to reflect electrons, this surface can be left floating. The electron containment is achieved by using the magnetic mirror effect. The result is that electrons are contained in all degrees of freedom by either magnetic and electrostatic Lorentz forces or by the magnetic mirror formed over the substrate.

Please now refer to FIG.1B. The magnetic mirror effect is well understood and has been used to confine plasmas in particle fusion research. As an electron24moves along field line25from a region of weaker magnetic field Bo toward a stronger magnetic field Bm, the electron axial velocity Va is converted to radial gyration velocity Vr around the field line25. If the axial velocity Va component reaches 0 before the electron has passed through the magnetic mirror at substrate22, the electron is reflected back toward the weaker field region. As the ratio of strong to weak magnetic field increases, more electrons are reflected. This magnetic mirror effect is greatly assisted in the preferred embodiments by the electric field surrounding the magnetic field. This is depicted inFIG. 1Aby arrows17and dashed line15. This electric field imposes a radial force on electrons that increases the radial velocity and results in better electron containment by the mirror effect. This can be seen in the plasma as a cone of bright plasma surrounding the inner plasma region, region27in FIG.1B.

This preferred embodiment uses these characteristics to confine a low pressure plasma for the processing of a substrate. In theFIG. 1Asource, a rare earth magnet5is used to create a strong magnetic field region at the plasma facing surface of substrate1. Further from the magnet, the field progressively weakens and spreads out to cathode plate3. When a voltage of ˜400V-800V is impressed between the cathode3and anode11and the chamber pressure is approximately between 3 and 100 mTorr, electrical breakdown occurs, and a plasma is maintained in region14. As electrons are created either by secondary emission from the cathode3or by collisions in the plasma, they are confined within plasma region14and generate an endless Hall current within plasma14. Several features, benefits, and limitations of this new source are discussed below.

When the substrate is floated or connected to the electrode opposed to electrode3, at least a portion of the magnetic mirror created between the plasma facing surface of substrate1and the plasma facing surface of cathode3must exceed a ratio of 2:1. This ratio is defined as the field strength at a point on the plasma facing surface of substrate1versus the strength of the weakest point along that same field line in the gap. A weaker ratio than 2:1 results in too few electrons being reflected by the magnetic mirror, and a low pressure plasma cannot be sustained. The idea of this preferred embodiment is to confine sufficient electrons such that a low pressure plasma is sustained. In trials of many configurations, the ratio of at least 2:1 between the strong field over the substrate and the weaker field in the gap is important. As the ratio increases, the confinement improves. With rare earth magnets and substrates of thicknesses less than ½ inch, it is relatively easy to achieve ratios up to or exceeding 10:1. If the substrate is connected either in parallel to electrode3or to a separate power supply so that the substrate is biased to electrostatically confine electrons, the mirror field can be less than the 2:1 ratio.

The confinement obtained using this preferred embodiment is not as efficient as traditional electrostatic (Lorentz) confinement. While with magnetic mirror ratios exceeding 2:1 and the anode placement accentuating the radial electron velocities produces confinement sufficient for a low pressure plasma, a substantial electron flow out of the plasma into the substrate is apparent. This is deduced from several data points. The pressure required to sustain the plasma is higher than a typical magnetron source. Where a magnetron source operates at 1-5 mTorr, the magnetic mirror source operates at pressures above 3 mTorr with typical pressures of 10 mTorr. The voltage of the mirror source is higher. A modified Penning discharge as shown in U.S. patent application Ser. No. 10/036,067, which is hereby incorporated by reference, can sustain a plasma at less than 400V. The mirror source low voltage operation is closer to 500V. While the effect of reduced plasma confinement efficiency can be negative to some processes, it is a benefit to this preferred embodiment. Looking at the configuration ofFIG. 1A, sufficient electron containment is achieved to create a dense, Hall current contained plasma while the “poor” confinement results in a high electron flow out of the plasma directed at the substrate1. This is an ideal arrangement for many plasma processes. In the dense plasma formed directly over the substrate etching compounds, PECVD reactants, or plasma treatment gases are efficiently activated. Simultaneously, the high electron and ion flow sweeps the activated particles onto the substrate. An analogy is the plasma, constrained by the cathode electrode and the mirror magnetic field, is like a pressurized bottle. At the substrate, the compressed mirror field forms the nozzle on the bottle, both restraining the flow and directing the flow out of the bottle.

Another aspect of this preferred embodiment is that while the particle current to the substrate is high, the particle energy to the substrate is lower than sources energizing the plasma through the substrate. In this preferred embodiment, the substrate is electrically floating. The floating potential of ˜−10V is low enough to largely rule out substrate or coating ablation or substrate damage due to impinging high energy particles. This is critically important to processes involving semiconductor wafers, low temperature substrate materials, and most PECVD processes.

Note that the substrate can also be biased negatively with the same power supply16(in the case of a conductive substrate) or a different power supply. As the substrate is negatively biased, more electrons are repelled from the substrate and contained within the plasma. This can be useful to produce increased ion energies impinging the substrate. For non-conductive substrates, an AC, RF or pulsed DC power supply can be used. The advantage of floating the substrate is that thick, large, non-conductive substrates such as architectural glass or flexible polymer web can be used without the cost or complexity of a backside AC power supply. In particular, when an insulating substrate is too thick to pass even an RF signal, the preferred embodiment can be applied.

The substrate can also be grounded or connected as the anode in theFIG. 1Acircuit. The fundamental containment of the magnetic mirror continues to operate with the substrate as the anode. In this mode, the electron current to the substrate increases. While a sustained glow is maintained, the voltage is higher, a strong magnetic mirror is required, and/or the chamber pressure must be higher than when the substrate is floating or negatively biased. For some substrates, metal sheet for instance, a grounded substrate is much easier to configure. For others, plastic web or glass, the floating option is easier.

In any of these electrical configurations, the electron and ion flow onto the substrate is concentrated into the physical dimensions of the magnet pole as it emanates from the substrate. As the magnet pole is extended for wide substrates, the dense plasma region on the substrate takes the shape of a long bar. To obtain uniformity in the cross direction to the bar, the substrate must move in relation to the plasma. This is shown in later figures.

Only the field lines that pass from the substrate to cathode3are shown. There are other field lines that do not pass through cathode3, but these are not important. Electrons caught in these lines simply are collected at the substrate or swept to the power supply and are not contained long enough to help sustain a plasma.

FIG. 1Ashows a simple arrangement to explain the fundamental preferred embodiment. Later figures depict several sources implementing the preferred embodiment to process wafers, flat substrates, and flexible substrates. While an attempt has been made to show the breadth of applications that can be addressed with the preferred embodiment, many more will be apparent to one skilled in the art. The preferred embodiment presents an entirely new genus of magnetically confined plasma source that will have as many species as the traditional magnetron/Penning confinement method.

FIG. 1Cshows a wafer processing plasma source of a preferred embodiment. Wafer76is placed upon non-magnetic platen75. A magnetic field78is passed through the wafer and through the gap between the wafer and cover72. Cover72is made of a high permeability material such as 400 series stainless steel. The magnetic circuit is formed by cover72, steel shunt circle81, shunt74, and magnet80. Shunt74and magnet80rotate under the stationary platen75. As explained inFIG. 1A, by producing a strong magnetic mirror field over the wafer, a plasma is maintained directly above the wafer. This can be very beneficial because a dense plasma directly on the wafer is produced to etch, plasma treat, or PECVD coat the wafer while at the same time, because the wafer is not at high voltage, the energy of bombarding particles is lower and damage to wafer structures is reduced. Power supply70is connected between cover72and shunt81. This can be a DC, AC or higher frequency supply. If an insulating coating is being deposited, the power supply should be of sufficient frequency to pass current through coating depositing on the plasma facing surface of electrodes72and81. Magnet80is long enough to extend the plasma over the width of the wafer. When shunt74and magnet80are rotated, the plasma is swept over the wafer surface. Other means to sweep the plasma over a surface can be used. For instance, a robot arm can be used to move the magnet80under platen75in a prescribed pattern. In combination with an end point detector, the surface is “painted” with plasma until the detector indicates the process is complete. In this source, the magnet material is a rare earth type. The field produced between the wafer and electrode72is greater than 100 gauss—in other words, the plasma electrons are “magnetized” in the gap. Using today's materials, it is relatively easy to increase the magnetic field strength to also magnetize the plasma ions. This requires a magnetic field strength nearing or greater than 1000 G. The plasma of the method of the preferred embodiment adapts well to ion magnetization because there are no cathode surfaces to interrupt a larger gyro radius as with a planar magnetron type confinement. Where prior art sources have used magnets under the wafer to direct plasma down onto the wafer from another plasma source, the method of the preferred embodiment produces a dense plasma in and of itself, the dense plasma forming directly over the wafer surface. The benefits of focusing the electron and ion flow down on the wafer are fully realized in the method of the preferred embodiment. As shown by switch83and bias power supply82, the inventive method allows for platen75and wafer76being either left floating, grounded or positively or negatively biased by supply82.

FIG. 2is an isometric view of the wafer processing plasma source of FIG.1C. The source in this view is exploded to show the parts for clarity. Magnet80is disposed under platen75and wafer76. The magnetic mirror field between electrode72and the wafer is augmented with shunts74and81. By using a long magnet80that extends to or beyond the edge of wafer76, the uniform Hall current plasma77is swept over the entire wafer as shunt74and magnet80are rotated.

FIG. 3Ais a section view of a plasma source employing the method of the preferred embodiment. Substrate1may be a rigid planar substrate or a web tensioned to be planar between two continuously moving rolls. Substrate1is in proximity to shield8but is far enough away to allow the substrate1to be conveyed without scrapping shield8. A magnetic field12is set up between the substrate and plate3by permanent magnets5,6, and7, magnetic shunts2and4and cathode electrode3. The field12is shaped into a shower head mirror field with the substrate1located at the compressed end. An electric field15is created by power supply16between cathode electrode plate3and the chamber ground. Shields9,10and11are connected to ground. Magnet shunt4and shield8electrically float. Power supply16can be DC even in the case of a dielectric substrate because there is no current flow to shield8. Alternatively, in the case where a dielectric coating is being applied, a pulsed DC or AC power supply16can be used. This is done because coating on electrode3and the grounded surfaces can impede DC current flow. The plasma13is confined by the magnetic field12, electrode3, and the magnetic mirror at the substrate1. The electrons are trapped in the dimension out of or into the paper by electric field lines15that continuously circumvent the magnetic field12all around magnetic field12. The result is that Hall current14created by the electron confinement is trapped into a continuous loop within the magnetic field12. At low powers, this containment ring is readily apparent to the eye. At higher powers, the plasma expands to fill the region13between the substrate and electrode3. Note that the anode is the chamber wall and grounded shields. This provides sufficient electric field penetration into the gap between cathode plate3and substrate1for the plasma confinement effects. The gap between cathode plate3and the substrate must be sufficient to strike a plasma. The gap size is also based upon the necessity to create a strong mirror magnetic field between surfaces3and1, the need for a magnetic field sufficient to magnetize at least electrons and nice-eties such as being able to see the plasma from a view port. A typical gap is 2 inches. A source like that inFIG. 3Awas built with a 4″ long magnet7(out of the paper) and an 8″ long cathode electrode3. With the chamber pressure at 20 mTorr and a voltage of approximately 500V impressed between cathode electrode3and ground, a bright plasma is maintained on substrate1as shown. To start the discharge, the pressure may have to be spiked depending upon the ignition voltage of the power supply. While specific values are given here, different pressures, voltages, frequencies and power levels can be used depending upon the process (PECVD, treatment, etching), process gasses, substrate size and material, magnetic fields and other variables. The values given are intended to provide the engineer with starting values to demonstrate the preferred embodiment. As with traditional magnetron confinement, the operating values can vary widely while still receiving the benefits of the preferred embodiment.

FIG. 3Bis an isometric view of an extendedFIG. 3Aplasma source. In this view, one can see that the plasma Hall current is contained within the dipole magnetic field created by magnets5,6, and7and shunts2and4and electrode3. Note that with this dipole arrangement, magnet pole7simply ends near the edge of the substrate. The magnetic field12in the gap extends from permanent magnet7to cathode plate3to create one extended showerhead mirror magnetic field. Within this field, Hall currents are confined into a racetrack14, and an intense plasma is created in this looping ring. Substrate1is conveyed over magnet poles6and7and shield8. The gap between shields8and9is small to minimize spurious plasma generation while allowing the substrate to pass through unobstructed. Shield10and11may receive enough heat to require water cooling. This is largely dependent upon the type of process, power levels, materials and factors relating to the configuration of the plasma contacting surfaces, fields, etc. For most industrial processes with long process runs and high powers, all electrodes must be water cooled using known techniques.

FIG. 4shows a section view of another planar source implementing this preferred embodiment. This source is composed of two identical sources10and11, connected across a mid-frequency (50-450 kHz) power supply16. This arrangement is similar to two planar magnetrons connected across an AC supply. As with the planar magnetron configuration, this is useful when insulating coatings are produced because each source alternates as both an anode and cathode. In the cathode mode, ion impingement tends to ablate and clean the electrode so that electrode conductivity is maintained over extended production runs. Sources10is composed of a magnetron magnet array with center magnets7, outer ring magnets6and magnet shunt2. Non-magnetic cover8protects the magnets from UV light. Planar substrate1is supported by rollers not shown to pass over cover8without contact. Above substrate1, electrode3is a box following the outline of magnets6. Electrode3is constructed of high permeability material such as mild steel to conduct the magnetic field as shown. Gap magnetic field lines12are shown as they emanate from magnets7, pass through substrate1and end at electrode3. The preferred embodiment is maintained in this arrangement with electrons contained by the magnetic field12, cathode electrode3and the compressive magnetic mirror over the substrate. In this case, rather than a dipole magnetic field, a field more similar to a magnetron is created with the Hall current contained within the “wings” of plasma14within box3. Note that instead of the electric field permeating into the sides of a dipole magnetic field, the electric field penetrates into the top of the magnetic field as shown by schematic electric field lines15. The result is the same, as electrons are confined into an endless Hall current region within magnetic field12. Source11has the identical construction. When power supply16is turned on and process gas is supplied into the source chamber at −5-100 mTorr, plasmas14and34light. Power supply16may be set to a wide range of frequencies. Typically, thin films collecting on electrodes3and23are conductive at frequencies above 20 kHz. This source excels at plasma processes such as plasma treatment, PECVD and plasma etching. It is particularly useful when thick, large substrates such as architectural glass require one of these processes. Because the glass is electrically floating, the difficulty of passing current through thick glass is removed, and a dense plasma is directed onto the substrate. Additionally, by positioning the cathode plates vertically, sputtering of the cathodes is directed away from the substrate. This reduces contamination of the substrate with sputtered material and reduces the heat load on the substrate. Therefore, as a PECVD coating is deposited on a substrate, the cathode surface is sputtering cleaning itself with the sputtered material directed away from the substrate. Vertical positioning of the cathodes is a significant benefit to some applications. Note that in production, the cathode electrodes3and23must be water cooled (not shown), and other surfaces may also require cooling depending upon the process conditions.

Sources10and11can be extended to any width required in the same way a magnetron sputter cathode can be extended. In this case, the magnetron magnet arrangement is lengthened under the substrate and the permeable box over the substrate is equally extended. As with a magnetron cathode, the confined Hall current moving around the “racetrack” provides an inherent uniformity across the length of the source. By moving the substrate orthogonally under the plasma, highly uniform plasma treatment of the surface is obtained.

FIG. 5shows a section view of a web coating apparatus employing the preferred embodiment. In this embodiment, both rolls101and102support web100, and web100is moved continuously over rolling supports101and102. Roll102contains permanent magnet and magnet shunt assembly111. Roll101is a steel roller of sufficient thickness to carry magnetic field108. Magnetic field108is created in the gap between rolls101and102by magnetic assembly111, steel roll101, magnet shunt pieces106and107, permanent magnets104and105and magnetic shunt103. Due to the different pole structures, magnetic field108is not a symmetrical mirror field but takes on the appearance of a showerhead. Roll101is connected to power supply110as the cathode electrode and roll102can either be left electrically floating, connected as an anode in the electrical circuit, or connected in parallel with roll101as the cathode. Different outcomes result and offer different advantages depending upon process requirements. When roll102is left floating, an electron trap of the preferred embodiment is maintained by the magnetic mirror effect as electrons approach the compressed magnetic field108at the roll102surface and by the physical presence of web100on roll102. The magnetic field108is surrounded by electric field118so that Hall currents are contained within magnetic field108, and an intense plasma109is created. When roll102is left floating or connected as the anode, plasma109tends to push up against the web around roll102. In this embodiment, magnetic pole pieces106and107are electrically floating, permanent magnets are ceramic type and are not electrically conductive, and magnetic shunt103is connected to the chamber ground. Per the inventive method, roll101must be connected as a cathode. Roll102, with the stronger magnetic field, can be connected as the anode, cathode or floating.

FIG. 6is another flexible web apparatus with a different type of magnetic field. In the earlier embodiment, the magnetic field lines in the gap between the rolls arced inward toward the center of the field. In this apparatus, the magnetic field108arcs away from the field centerline. Since either case produces magnetic field lines that pass through at least one cathode surface and at least one substrate surface, the advantage of the preferred embodiment is maintained. In this apparatus, roll102contains permanent magnets114and116and shunt115that produce magnet fields108between roll102and ferromagnetic plates101,112and113. Plates101,112and113are curved to generally follow the curvature of roll102. These plates can be flat or another shape. Plate101is connected to power supply110and serves as the cathode of the source. Plates112and113serve as the anode for the source. With this arrangement, electric fields118are set up between the cathode and anode surfaces. Note that because a dielectric web is not disposed over plate surfaces101,112or113, a DC power supply can be used. Alternately, if a dielectric PECVD coating is to be applied that will deposit an insulating coating over plates101,112and113, a pulsed DC or AC power supply can be used. The gap between cathode plate101and anode plates112and113is smaller than the dark space distance to avoid plasma in these gaps. Roll102supports web100and turns to continuously move new web in front of the plasma. Magnets114and116and shunt115do not turn with roll102. In operation, a plasma109is formed within the extended cone of magnetic field lines that pass though cathode plate101and enter roll102. Note that at the end of the source, there are no racetrack magnet turnarounds. Anode plates112and113close around cathode plate101to form the required continuous electric fields118around the magnetic field108.FIG. 7shows more detail on the end of the source. With the end containment of the Hall current in place, the continuous Hall current confinement region is formed within magnetic field108, and uniform and intense plasma109results along the length of the roll102.

FIG. 7shows a top view of the source depicted in FIG.6. In this view, the end containment of Hall currents can be seen. End containment is accomplished by providing continuous electric fields emanating from the roll101cathode surface (in upstream terms) to the anode through magnetic field108. This produces the VxB forces on primary electrons that prevent them from reaching the anode plates112and113. As the electrons move away from the cathode plate101, they move closer to roll102until they are stopped by the diverging electric fields, compressing magnetic fields and the physical surface of the web100on roll102. An advantage of this design is that while web100is in close proximity to plasma109as the web100passes over roll102, the web100is not at cathode potential and does not receive the subsequent intense ion bombardment. By adjusting the magnetic field, electric fields, position of cathode, anode and substrate surfaces and other process dependent variables such as the process gases, many different processes and applications can be successfully accomplished.

FIG. 8shows a section view of another web apparatus. In this embodiment, roll1contains a magnetron magnetic array composed of magnets6and7and shunt8. This magnetron array does not rotate as roll1rotates and supports web3. Roll2is hollow steel conveyor roll thick enough to largely carry the magnetic field emanating from roll1. Magnetic field13is a racetrack field around center field14and is an un-symmetric magnetic mirror from permanent magnet6to steel roll2. Roll2is the cathode electrode and is connected to power supply18while roll1is switch-selectable depending upon the application. With switch24connected to the cathode electrode, the roll pair behave similarly to the magnetron confined Penning discharge described in PCT application serial no. PCT/US02/11473. With the switch in the center and roll1floating, the electric field is between roll2and the chamber walls. Electrons are trapped in the magnetic mirror at roll1as they try and escape cathode roll2. A plasma is formed against roll1contained within the racetrack magnetic field13. While a plasma is present against roll1and therefore web3, the web is not biased and receives relatively lower energy ion bombardment. PECVD films can be produced on web3with this arrangement due to the close proximity plasma16. At the cathode electrode, the web3on roll2receives ion bombardment and some PECVD coating. The third switch setting connects roll1to the anode electrode of power supply18. This produces additional electron current into web3on roll1that may be desirable in some cases. Roll1and/or roll2may be water cooled using known techniques.

FIG. 9is a section view of a planar mirror magnetron device similar to FIG.8. In this embodiment, a planar substrate101is disposed between surfaces112and102, in close proximity to surface112while allowing the substrate101to be conveyed over surface112without hitting surface112. Across the gap between surfaces112and102, two magnetic fields are formed108and110. Magnetic field108is shaped into a racetrack around the periphery of magnetic shunt plates103and102. Magnetic field110is formed inside of magnetic field108also between the two shunt plates102and103. Shunt plate102is connected to the cathode side of power supply107. Surface112can be connected either to the cathode electrode, anode electrode or left floating. When the surface is left floating, a DC power supply may be used even if the substrate is a dielectric. If surface112is connected as the cathode or a dielectric PECVD coating is to be applied to substrate101, the power supply107may be a pulsed DC or AC type supply. In the case where surface112is left floating, a plasma is generated by surface102in conjunction with racetrack shaped magnetic field108. The plasma tends to form within racetrack magnetic field108and push up against the surface of substrate108. With plasma in direct contact with the substrate108, the substrate can be efficiently coated with a PECVD coating, etched or plasma treated.

FIG. 10shows a side view of the source depicted in FIG.9. This view shows that, similar to a magnetron sputtering cathode, the magnetically enhanced plasma of the method of the preferred embodiment can be uniformly extended for large area substrates. Just as this is a major advantage to magnetron sputtering, this is also a major advantage to the presently preferred embodiments. In this view, magnet shunt plate102and magnet assembly103,104and112are separated by a gap. Magnetic field108is disposed across the gap and follows the racetrack shape of permanent magnets104. A plasma109is formed against substrate101during operation.

FIG. 11shows an isometric view of the source depicted in FIG.9. In this view, the racetrack shape of permanent magnets104around permanent magnets105can be seen.

FIG. 12depicts a source of another preferred embodiment. In this source, two magnets are disposed across a gap. Cathode electrode45is located approximately in the center of the gap. Electrode45is constructed of a non-magnetic material such as copper, stainless steel or titanium. As can be seen, a mirror magnetic field is generated with the compressed field passing through the substrate41and the less compressed field passing through the cathode electrode45. When voltage is impressed across the cathode electrode45and a ring anode43such that electric fields penetrate into the magnetic field sufficiently, the electron Hall current is contained within the magnetic field. With sufficient voltage and process gas pressure, a plasma44is formed between the cathode and substrate. The idea of this figure is to show that magnetic arrangements other than a high permeability cathode can be implemented. All the embodiments of the invention show a high permeability member or permanent magnet at the uncompressed, cathode electrode end of the magnetic field. This is because this works well to pull the magnetic field from the magnet under the substrate, through the gap and into the cathode electrode. While this remains true, an alternative is to position only a non-magnetic electrode over the substrate. For instance, inFIG. 12, magnet40could be removed. The magnetic field would primarily loop around from the north pole to south pole of magnet47. A small portion of the field would indeed however pass from the north pole of magnet47and, before arriving at the south pole, pass through cathode surface45. If this field is strong enough to magnetize electrons, a plasma per the inventive method will form. Again, because of the relative simplicity of using a magnetic material in the cathode45‘assembly’ and the benefit of increasing the field lines into the cathode, a magnetic material is preferred.

Note that cathode surface45can be moved closer to magnet40. In this configuration, the electrons moving toward the substrate are moving from a region of weak magnetic field to a stronger field (with a ratio in excess of 1:2). While this does produce a confined plasma, it is not presented in the application figures because the source works much better when the cathode surface45is placed in the region of expanded, weaker magnetic field. The larger electron collection area may play a role in making the source operate with a brighter glow and at lower pressure and voltage.

FIG. 13shows another variation of the preferred embodiment. In this source, the cathode plates52are parallel with substrate51. Magnetron magnet array60is disposed under substrate51and is composed of magnets56,57and59and magnetic shunt50. Magnets59serve to push the field lines emanating from center magnets57up through substrate51so that they enter the top of cathode plate52as shown. Power supply55is connected between cathode electrode52and gas distribution anode electrode53. The result is the same as the previous apparatus—a magnetically confined plasma54is generated within the region confined by magnetic fields61, cathode electrode52and compressed magnetic mirror region62. This figure shows that the magnetic field of the preferred embodiment may take on a variety of forms. Also shown is a method (magnets59) to enhance the mirror effect passing through the substrate. This arrangement can be useful to reduce the amount of material sputtered from cathode52collecting on substrate51.

FIG. 14shows a preferred embodiment using a magnetron sputtering source. Magnet assembly212composed of magnets206and207and shunt200are positioned below planar substrate201. Shunt bars209and202form a box over the substrate, and the magnetic field of the preferred embodiment is formed. Magnetron208is positioned above the mirror source. Plasma210is the sputtering racetrack plasma. The addition of a sputter magnetron over the mirror source can be useful to create PECVD films with metal atoms added to the coating structure. Also, the source of the preferred embodiment can be used to assist with reactive sputtering. In this depiction, an AC power supply is used and is connected between the mirror source and the planar magnetron. Alternately, each can have a separate power supply. As another alternative, two magnetrons can be connected to one AC supply, and the mating two mirror sources can have a separate AC supply as in FIG.4.

Note that in this embodiment, two plasma sources are operated at the same time—a magnetron sputter cathode and a mirror source per the inventive method. In prior art, magnets under the substrate were used to focus the plasma to the substrate from a separate plasma source. In the present invention, the magnetic field and cathode surfaces create a stand alone plasma source that can be operated along with other plasma sources.

FIG. 15shows an activated reactive evaporation source assisted by the preferred embodiments described above. In this implementation, a flexible web301is disposed round a rotating drum302. Magnetron magnet array300is located inside the drum and does not rotate. External high permeability plates304are connected to power supply310as described above. Power supply310is connected to shield307(isolated from304) and ground. A thermal evaporation source303emits condensate308toward web301. Typical of an evaporation process, the required mean free path length for condensate to reach the substrate requires operation below 1 mTorr. This pressure is too low for stand alone mirror magnetron operation. So in this apparatus, the mirror magnetron plasma requires the presence of the evaporant to produce a local high pressure sufficient to ignite the plasma. The mirror magnetron creates a dense plasma on the web greatly assisting in reacting the condensate material. Reactant gas is introduced through distribution tubes305. The gas flow is forced by shields306to largely flow between the web and electrodes304. The gas is then separated from the condensate thermal source by the magnetic field311and subsequent plasma312. The reactive deposition process is assisted also by the electron and ion flow into the substrate through the magnetic mirror nozzle effect as previously described. Note that an electron beam or laser source can be used in place of the thermal evaporation source.

FIG. 16depicts another source useful for treating planar substrates. This source again shows the many forms the inventive method can take. In this source, the closed loop electron Hall current is extended beyond a simple racetrack shape. The mirror magnetic field308is created with magnets306and307and magnet shunt305under the substrate and plates301and302above the substrate. Plates301and302are connected as the cathode. In this case, the chamber wall is the opposed electrode. The plasma304forms Within the mirror magnetic field308per the inventive method and a dense plasma304traces the pole outline. Though different in appearance, the basic criteria of the inventive method is met: 1) A mirror magnetic field emanates up through the substrate, the field passes thru a plasma contain gap and then into an electron containing electrode surface. 2) Electric fields penetrate the magnetic field sufficient to contain the Hall current in an endless loop and 3) A substrate is moved relative to the plasma to uniformly treat the substrate. While more complicated, one possible advantage of this design is that more bands of mirror focused plasma ‘nozzles’ are brought into contact with substrate300.

FIG. 17is a section view of another planar substrate or flexible web plasma source. In this embodiment, a portion of the magnetic field50leaves magnet40and forms a mirror type field in the gap between the substrate41and pole piece45. Shunt46directs the magnetic field over to pole45and down to magnet47. In this way, two plasma ‘cones’ are created with one power supply42. Note that poles45are shorter than magnets40and47so that the magnetic field blooms around the ends of poles45and allows the contained Hall currents to pass around the end of poles45. In operation the plasmas44appear as two cones with poles45penetrating into the base of the cone. Stray magnetic field49does not ‘light up’ because the field lines do not pass through a cathode surface. Poles45are bolted to shunt46with screws48. This subassembly is held in position over the substrate41and magnet assembly with a bracket and fasteners not shown. The substrate in this source is floating as is the magnets40and47and magnet shunt43. The substrate is passed close to magnets40and47to maximize the mirror magnetic field on substrate41. Note that because both the substrate41and magnets40and47are floating, no plasma lights behind the substrate during operation.

As has been described, the combined Lorentz and magnetic mirror electron confinement arrangement traps the Hall current in a racetrack orbit directly over the substrate. Of similar magnitude to Penning's work in the 1930's, this confinement regime opens doors to a wide range of processes and technologies producing results not resembling known prior art. Many applications for PECVD, plasma etching and plasma treatment will be substantially improved or made possible. Also as shown, the new source can be combined with other plasma sources to improve upon or create new plasma sources. While many benefits to this new technology will be found, some of the benefits are:A dense plasma is created in a confined zone directly over a substrate, and a large electron/ion current is directed onto the substrate through the “nozzle” of the magnetic mirror. This results in high rate PECVD or other plasma activity on the substrate.The magnetic and electric field confinement geometry produces a symmetrical, endless racetrack confinement zone similar to a planar magnetron sputtering device or a grid-less ion source. As is known in these technologies, the length of the confinement zone can be extended to accommodate wide substrates while maintaining a uniform plasma. This is a major improvement over unconfined RF or microwave discharges for large substrates at significantly less cost.As a true magnetically enhanced plasma source, the efficient plasma confinement allows operation at low pressures and voltages. Many process advantages are gained by this. Plasma does not light in other parts of the chamber or on electrode surfaces outside of the containment zone. The plasma is characteristically stable and uniform. Lower plasma voltage requirements make the power supplies safer and less costly.A significant advantage of low pressure PECVD operation is that the increased free mean path length allows powder free operation at high powers. Film morphology is also enhanced for many films at lower pressures.The technology is adaptable to different process substrate energy requirements. As shown in the figures, the substrate can be floating, biased negatively, or biased positively to produce different results.

Finally, it should be noted that any of the alternatives discussed above can be used alone or in combination with one another. Some of these alternatives include:The surface of the cathode electrode can be covered with a ‘target’ material that, if sputtered, is either helpful or benign to the process.The surface of the cathode electrode can be positioned relative to the substrate so as to minimize the arrival of sputtered material from the electrode on the substrate.The substrate can be biased positively, tied to ground, left floating, or biased negatively.An AC or RF voltage can be used to bias the substrate.DC, AC, or RF can be used to power the cathode electrode.The magnetic field can be moved relative to the substrate instead of the substrate moving relative to the magnetic field.The cathode and substrate surfaces can be non-parallel, as shown in FIG.4and FIG.17.The magnetic field can be made using a magnetron-type array.Multiple dipole magnetic fields can be created and connected to one power supply.The magnetic field can be made with high permeability materials and magnets both above and below the substrate or just below the substrate.The substrate can be a flexible web supported by a conveyor roll.The substrate can cover both surfaces. A compressed mirror surface is highly preferred. A less compressed surface is optional.The magnetic field can be shaped concave or convex.The mirror field can be shaped into a racetrack with the return field passing through the center of the racetrack.The magnetic field can be produced with permanent magnets or electromagnets.The mirror source can be combined with a sputter magnetron to assist with plasma reaction or substrate treatment.The source can be used to assist a reactive process with a thermal evaporation or electron beam deposition process (or laser ablation).

It is intended that the foregoing detailed description be understood as an illustration of selected forms that the invention can take and not as a definition of the invention. It is only the following claims, including all equivalents, that are intended to define the scope of this invention.