An ion source is a device that causes gas molecules to be ionized and then accelerates and emits the ionized gas molecules and/or atoms in a beam towards a substrate. Such an ion beam may be used for various purposes, including but not limited to cleaning a substrate, activation, polishing, etching, and/or deposition of thin-film coatings/layer(s). Example ion sources are disclosed, for example, in U.S. Pat. Nos. 7,030,390; 6,988,463; 6,987,364; 6,815,690; 6,812,648; 6,359,388; and application Ser. No. 10/986,456, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional cold-cathode type ion source. In particular, FIG. 1 is a side cross-sectional view of an ion beam source with an ion beam emitting slit defined in the cathode, and FIG. 2 is a corresponding sectional plan view along section line II-II of FIG. 1. FIG. 3 is a sectional plan view similar to FIG. 2, for purposes of illustrating that the FIG. 1 ion beam source may have an oval and/or racetrack-shaped ion beam emitting slit as opposed to a circular ion beam emitting slit. Any other suitable shape also may be used.
Referring to FIGS. 1-5, the ion source includes a hollow housing made of a magnetoconductive material such as steel, which is used as a cathode 5. Cathode 5 includes cylindrical or oval side wall 7, a closed or partially closed bottom wall 9, and an approximately flat top wall 11 in which a circular or oval ion emitting slit and/or aperture (also sometimes referred to as a “discharge gap”) 15 is defined. The bottom wall 9 and side walls 7 of the cathode 5 are optional. Ion emitting slit/aperture 15 includes an inner periphery as well as an outer periphery. Deposit and/or maintenance gas supply aperture or hole(s) 21 is/are formed in bottom wall 9. Flat top wall 11 functions as an accelerating electrode. A magnetic system including a cylindrical permanent magnet 23 with poles N and S of opposite polarity is placed inside the housing between bottom wall 9 and top wall 11. The N-pole faces flat top wall 11, while the S-pole faces bottom wall 9. The purpose of the magnetic system with a closed magnetic circuit formed by the magnet 23 and cathode 5 is to induce a substantially transverse magnetic field (MF) in an area proximate to ion emitting slit 15.
The ion source may be entirely or partially within conductive wall 50, and/or wall 50 may at least partially define the deposition chamber. In certain instances, wall 50 may entirely surround the source and substrate 45, while in other instances the wall 50 may only partially surround the ion source and/or substrate.
A circular or oval shaped conductive anode 25, electrically connected to the positive pole of electric power source 29, is arranged so as to at least partially surround magnet 23 and be approximately concentric therewith. Anode 25 may be fixed inside the housing by way of insulative ring 31 (e.g., of ceramic). Anode 25 defines a central opening therein in which magnet 23 is located. The negative pole of electric power source 29 may be grounded and connected to cathode 5, so that the cathode is negative with respect to the anode. Generally speaking, the anode 25 is generally biased positive by several thousand volts. Meanwhile, the cathode (the term “cathode” as used herein includes the inner and/or outer portions thereof) is generally held at ground potential although it need not be. This is the case during aspects of source operation, including during a mode in which the source is being cleaned.
The conventional ion beam source of FIGS. 1-5 is intended for the formation of a unilaterally directed approximately tubular ion beam, flowing in the direction toward substrate 45. Substrate 45 may or may not be biased in different instances. The ion beam emitted from the area of slit/aperture 15 is in the form of a circle in the FIG. 2 embodiment and in the form of an oval (e.g., race-track) in the FIG. 3 embodiment.
The conventional ion beam source of FIGS. 1-5 operates as follows in a depositing mode when it is desired that the ion beam from the source deposit at least one layer on substrate 45. A vacuum chamber in which the substrate 45 and slit/aperture 15 are located is evacuated, and a depositing gas (e.g., a hydrocarbon gas such as acetylene, or the like) is fed into the interior of the source via aperture(s) 21 or in any other suitable manner. A maintenance gas (e.g., argon) may also be fed into the source in certain instances, along with the depositing gas. Power supply 29 is activated and an electric field is generated between anode 25 and cathode 5, which accelerates electrons to high energy. Anode 25 is positively biased by several thousand volts, and cathode 5 may be at ground potential as shown in FIG. 1. Electron collisions with the gas in, and/or proximate to, aperture/slit 15 leads to ionization and a plasma is generated. “Plasma” herein means a cloud of gas including ions of a material to be accelerated toward substrate 45. The plasma expands and fills (or at least partially fills) a region including slit/aperture 15. An electric field is produced in slit 15, oriented in the direction substantially perpendicular to the transverse magnetic field, which causes the ions to propagate toward substrate 45. Electrons in the ion acceleration space in and/or proximate to slit/aperture 15 are propelled by the known E×B drift in a closed loop path within the region of crossed electric and magnetic field lines proximate to slit/aperture 15. These circulating electrons contribute to ionization of the gas (the term “gas” as used herein means at least one gas), so that the zone of ionizing collisions extends beyond the electrical gap between the anode and cathode and includes the region proximate to slit/aperture 15 on one and/or both sides of the cathode 5. For purposes of example, consider the situation where a silane and/or acetylene (C2H2) depositing gas is/are utilized by the ion source of FIGS. 1-3 in a depositing mode. The silane and/or acetylene depositing gas passes through the gap between anode 25 and cathode 5.
Magnet 23 will now be described in more detail with reference to FIGS. 4 and 5. In conventional systems, magnet 23 typically is a magnet system comprising multiple magnets. One known magnet system comprises a plurality of stacked magnets 24, with multiple stacks being disposed throughout the ion source. For example, FIG. 4 shows a stack of magnets 24 used in a known magnet system. As shown in FIG. 4, each magnet stack 24 is comprised of six cylindrically-shaped magnets 24a, 24b, 24c, 24d, 24e and 24f stacked on top of each other so as to form a cylinder. In one commercially available source, each magnet stack 24 in the magnet system is comprised of a plurality of 0.25×0.75″ Dia. magnets, stacked six deep.
FIG. 5 is a sectional view similar to FIG. 3, taken along section line II-II in FIG. 1, showing in detail how the stacks of magnets included in the magnet system are disposed throughout the ion source. A series of bores 27a, 27b, 27c, 27d, 27e and 27f are disposed throughout the length of the ion source, and each bore is configured to receive a magnet stack 24 comprising cylindrical magnets 24a-f. It will be appreciated that the size, location, and number of bores shown in FIG. 5 are provided by way of example only and are not limiting. The number of bores 27 may vary based on, for example, the desired geometry of the ion source, etc. Typically, each magnet stack 24 is placed into a bore 27. It is noted that the magnets 24a-f of a magnet stack 24 are not attached to one another (e.g. they are not bonded, adhered, or screwed together, etc.).
Unfortunately, the ion source of FIGS. 1-5 suffers several drawbacks. For example, the design is difficult to produce. Each magnet 24a-f in the magnet stack 24 is small and round. Thus, a considerable amount of material is sacrificed during machining to make these parts. It similarly may be difficult and/or costly to create a large number of appropriately shaped bores 27 into which the magnet stacks 24 can be received.
Also, as a result of the operation of the ion source, the magnets may move around within the bores. Unfortunately, this may tend to damage the magnets in certain instances, ultimately affecting the magnetic flux density produced by the ion source (e.g. as a result of air gaps created by damaged magnets which are soft and fragile). Similarly, because the magnets may move around and are not fixed to one another (or fixed to any other more permanent structure in the ion source such as, for example, the anode 25), foreign material may enter the bores. Again, resulting air gaps may affect (e.g., reduce) the magnetic flux density in the effected area which is not desirable. The need to keep the ion source and the surrounding environment clean thus may be desirable to ensure that the ion source functions properly.
Thus, it will be appreciated that there exists a need in the art for an ion source that overcomes one or more of thee above problems and/or other disadvantages.
Certain example embodiments provide a magnet yoke assembly for use in an ion source. In certain example embodiments, the magnet yoke may be made of or include a lower yoke and an upper yoke. At least one magnet may be disposed between the lower yoke and the upper yoke. The at least one magnet may have a substantially rectangular prism shape in certain example embodiments. The at least one magnet may be adhered to the lower yoke and/or the upper yoke in certain example embodiments of this invention.
Certain other example embodiments provide an ion source capable of emitting an ion beam. Such example embodiments may comprise an anode and a cathode, with one of the anode and cathode having a discharge gap defined therein. A power supply may be in electrical communication with the anode and/or the cathode. At least one magnet yoke assembly may be operable to generate a magnetic field proximate to the discharge gap. The at least one magnetic yoke assembly may comprise a lower yoke and an upper yoke. At least one magnet may be disposed between the lower yoke and the upper yoke, and the at least one magnet may have a substantially rectangular prism shape. The at least one magnet may be adhered to the lower yoke and/or the upper yoke.
In certain non-limiting embodiments, two, three or more magnets may be disposed between the lower yoke and the upper yoke.
In certain other example embodiments, the magnet yoke assembly may further comprise at least two screw holes formed in each of the lower yoke and the upper yoke. A plate may be aligned with each screw hole, with each plate (e.g., screw plate) being disposed on a magnet-facing surface of the lower yoke and/or upper yoke. The screw holes and the plates may be configured to receive bolts or other types of fasteners. Each plate on the lower yoke and each screw hole on the lower yoke may be threaded in certain example embodiments. Each screw plate on the upper yoke may protrude therefrom forming protrusions and recessions, and each screw plate on the lower yoke may protrude therefrom forming protrusions and recessions. At least one magnet may be disposed between and/or outside of the recessions in certain example embodiments of this invention.
Certain other example embodiments may provide a method of assembling a magnet yoke for an ion source. Such example methods may comprise providing a lower yoke and an upper yoke. At least one substantially rectangular prism-shaped magnet may be positioned between the upper yoke and the lower yoke. The at least one magnet may be adhered to the upper yoke and/or the lower yoke. In certain example embodiments, the upper yoke and the lower yoke may be bolted or otherwise coupled through at least two fastener holes or the like formed in the lower yoke and at least two fastener holes formed in the upper yoke, the at least two fastener holes of the lower yoke and the at least two fastener holes of the upper yoke being aligned. In certain example instances, the magnet yoke may be inserted such that a bottom of an inner cathode of the ion source rests on top of the upper yoke of the magnetic yoke.