Patent Description:
This invention was made with government support under <NUM>, <NUM> and <NUM> awarded by the National Science Foundation. The government has certain rights in the invention.

The present application generally pertains to an ion source and more particularly to a single beam plasma or ion source apparatus.

Thin film processing is widely used for manufacturing semiconductor devices, displays, solar panels, tribological coatings, sensors and micro-electromechanical systems. Conventional physical and chemical vapor depositions generally result in loosely packed atoms <NUM> on a workpiece <NUM> due to their limited kinetic energies, as is shown in <FIG>. The micro-porous structures lead to unstable material properties and device performance. Nevertheless, ion sources have become the essential tools for manufacturing high-quality thin films and devices.

One conventional ion source is of a racetrack design illustrated in <FIG>. This device consists of a racetrack- or ring-shaped anode <NUM>, a pair of center and outer magnetic poles, and magnets <NUM>. The anode is connected to the positive terminal of a DC power supply. The magnetic poles are connected to a ground potential and act as cathodes <NUM>. Electrons attracted toward the anode experience a Lorenz force that drives the electrons in E×B direction (where E is an electrical field vector and B is a magnetic induction field vector). Hence, the electrons drift along the racetrack in an electron trajectory <NUM> instead of directly reaching the anode. The confined electrons ionize the process gases and create ions <NUM>, which are subsequently extracted out of the plasma region.

There are two critical requirements for the racetrack ion sources to operate properly: <NUM>) the electrons must drift in a closed loop (a racetrack or a circular ring) to ensure they are confined; and <NUM>) the gap between the anode and cathode must be small (a few millimeters) to create a strong electrical field to extract the ions. Hence, a racetrack linear source actually produces two beams in the straight section and a circular source generates a ring-shaped beam. Therefore, the emitted ions have a wide distribution of emission angles; research has shown that the associated ion incident angle has a notable effect on the morphology of the treated surfaces. Furthermore, the racetrack ion sources require a voltage greater than <NUM> V to sustain the plasma discharges. This is determined by the electromagnetic fields inbetween the anode and cathode. Therefore, the ion energies could be so high that they can damage the deposited films and undesirably roughen the film surfaces.

The narrow emission slit in the traditional racetrack ion sources results in frequent maintenance due to undesired material deposition and contamination of the anode and cathode adjacent the exit slit. Furthermore, it is troublesome to realign the cathode after cleaning to maintain a uniform emission slit since the traditional racetrack construction mounts the magnetic steel cathode directly onto the magnets. Exemplary racetrack configurations are disclosed in <CIT>, and <CIT>.

Another traditional ion source is disclosed in <CIT>. This approach commonly works at low pressure (for example, <NUM>-<NUM> Torr) which is incompatible with a typical sputtering pressure of at least <NUM>-<NUM> Torr. Furthermore, the Kaufman ion source undesirably uses a filament to thermionically emit electrons which makes it unsuitable for use with reactive gases. Moreover, the design typically employs metal grids across an outlet, thereby disadvantageously being prone to contamination, and requiring frequent downtime and maintenance. <insert page 2a>.

In accordance with the present invention, an ion source apparatus according to present claim <NUM> is provided. Further, a method of using an ion source in a material coating machine according to present claim <NUM> is provided.

<CIT> discloses an ion source which may comprise a base, a first frame and a second frame. The first frame may include:.

<CIT> discloses a closed loop exit hole formed in a magnetically permeable end wall of an enclosure of a closed electron drift ion source. Parts of this end wall separated by the exit hole serve as pole pieces of the magnetic system and define the first pole gap. The magnetic system includes pole pieces, which define the second pole gap made in the form of a closed loop exit hole and arranged along the direction of ion emission. Magnetomotive force sources are located in space between two groups of magnetic terminals. The ratio of width of each pole gap and distance between pole pieces of the first and second magnetic gaps along the direction of ion emission is not less than <NUM>.

<CIT> discloses a cold cathode closed drift ion source provided with segregated gas flow. The first gas may be caused to flow through or along a path around a peripheral portion of the anode so as to pass through the electric gap between the anode and cathode. A second gas (different form the first gas) may be caused to flow toward the ion emitting slit, without much of the second gas having to pass through the electric gap(s). It if is desired to utilize a gas which produces insulative material (e.g., an organosilicon gas), this gas may be used as the second gas.

The present ion source apparatus is advantageous over traditional devices. For example, the present apparatus advantageously emits a single ion beam, the cross-sectional diameter or width of which can be modulated from about <NUM> to at least <NUM>, and it can be made to any length in a single beam linear configuration. Moreover, the beam of the present apparatus can be generated in a wide range of operating pressures (for example <NUM> mTorr to ><NUM> mTorr) which is compatible with simultaneous sputtering. The present apparatus beneficially operates with many different gases including inert and reactive gases since it does not use a filament. Furthermore, the present ion source can operate over a wide range of discharge voltages from <NUM> to greater than <NUM> V that lead to tunable ion energies for optimal ion-surface interactions.

The present apparatus is also advantageous for long-term stable operation since: <NUM>) the anode is unlikely to be contaminated because no direct coating flux can reach the active surfaces; <NUM>) the cathode is not sensitive to the coatings because it can be set at a floating potential and gets automatically biased; and <NUM>) the non-magnetic cap or cover can be easily disassembled and reassembled for maintenance, as compared to conventional devices. It is noteworthy that the present apparatus emits a stable ion beam without interference with other plasma sources that simultaneously operate. Another advantage is the single beam ion source leads to significant decrease in the discharge voltage of a sputtering source and subsequently improves a sputtered film quality. Additional features and benefits will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings.

A preferred embodiment of an ion source apparatus <NUM> can be observed in <FIG> and <FIG>. Ion source apparatus <NUM> includes a vacuum chamber <NUM>, an ion source <NUM>, a deposition source <NUM>, and a specimen or workpiece <NUM>. Ion source <NUM> and deposition source <NUM> are mounted to vacuum chamber <NUM> through vacuum-sealed ports. The apparatus also includes a pumping port connected to a vacuum pump <NUM>, an input gas port connected to a process gas source, pressure gauges and optional heaters. Various configurations of the vacuum chamber exist, depending upon the specific functions desired of the system.

Exemplary ion source <NUM> includes an anode <NUM> and a cathode <NUM>. The anode is mounted upon an insulator <NUM>. The cathode is mounted on a metallic closure plate <NUM>, which in turn is mounted to flange <NUM> on vacuum chamber <NUM>. In this case, cathode <NUM> is set at an electrical ground potential. Cathode <NUM> can be a single piece or two pieces that include an external structural body <NUM> and an end cap <NUM> removeably fastened thereto via screws <NUM>. Cap <NUM> of cathode <NUM> inwardly overhangs anode <NUM> with a single through-opening <NUM> in a center thereof defining an ion emission outlet. In the presently illustrated embodiment, structural body <NUM> and cap <NUM> of cathode <NUM> have circular peripheries and opening <NUM> is circular. Furthermore, the presently illustrated cap <NUM> employs a frustoconically tapered surface <NUM> adjacent through-opening <NUM>.

It is alternately envisioned that other arcuate shapes such as ovals or other single apertured, elongated hole shapes may be employed for these noted components. An alternate embodiment can be observed in <FIG> where a tapered single through-opening <NUM> in a cap <NUM> of a cathode <NUM> is linearly elongated in a lateral direction generally perpendicular to an emission central plane or direction of ions <NUM>. The internal anode components are also laterally elongated surrounding a plasma area below opening <NUM>.

Returning to the exemplary embodiment illustrated in <FIG>, multiple permanent magnets <NUM>, preferably two, and multiple magnetic shunts <NUM>, preferably three, are enclosed in anode <NUM>. An electrically conductive internal cover <NUM> defines an open plasma region or area <NUM> essentially aligned with opening <NUM>. Magnets <NUM> and shunts <NUM> each have coaxially aligned, circular internal edges and circular external edges wherein they are each ring-shaped with a hollow center. Magnets <NUM> are sandwiched or stacked between the shunts <NUM> such that the magnets are spaced apart from each other by the middle shunt. The upper and lower magnets are placed in series, e.g. N-S/N-S or S-N/S-N. Moreover, the cross-section of each side of the magnet and shunt assembly has a generally E-shape with the elongated and internal edges of shunts <NUM> extending toward a centerline axis <NUM> of ion source <NUM>. Magnets <NUM> and shunts <NUM> are internally secured within an anode body <NUM> which is coupled to an anode base <NUM> via screws or other threaded fasteners. An optional incoming gas or cooling fluid inlet <NUM> and associated passageways are disposed through anode base <NUM>, insulator <NUM> and plate <NUM>. It is noteworthy that all of anode <NUM>, including magnets <NUM> and shunts <NUM>, are spaced internally away from all of cathode <NUM> either by a gap or insulator.

In the <FIG> configuration, the cathode is isolated from ground at an electrically floating or biased potential. In the <FIG> version, however, the cathode is connected to ground potential through flange <NUM>.

<FIG> illustrate ion source apparatus <NUM> in operation. When energized, a precursor gas in an open plasma area <NUM> internal to anode <NUM> is converted into a plasma due to the energetic electrons <NUM> moving between the portions of the magnet and shunt assembly as acted upon by the associated electromagnetic fields. Magnetic flux lines <NUM> flow from one top shunt <NUM> to the bottom outer shunt <NUM> or vice versa. Furthermore, a dip <NUM> or outwardly depressed undulation of at least some of the magnet flux lines <NUM> are caused by the magnetic assembly. This dip <NUM> advantageously serves to delay and/or trap adjacent electrons <NUM> as they are otherwise flowing along magnetic flux lines <NUM> and reach the anode. This dip therefore advantageously increases ionization and promotes flux density of ions <NUM> emitted through outlet opening <NUM> of cathode cap <NUM> coaxially aligned with a longitudinal centerline axis <NUM>. In certain configurations, the center shunt <NUM> is optional. Alternately, it is envisioned that multiple dips <NUM> may be provided between originating and terminating ends of the magnetic fields <NUM> within open plasma area <NUM>.

The presently preferred construction of ion source <NUM> allows for adjustability of ion beam <NUM> from <NUM> to at least <NUM> in diameter or lateral width. This can be achieved through different sizing of outlet <NUM>, magnets <NUM>, and shunts <NUM>. Furthermore, a single ion beam <NUM> is emitted from ion source <NUM> with the ions almost uniformly distributed around a center axis when viewed in cross-section, as contrasted to the traditional ring-like and hollow center ion beams generated from the racetrack ion sources. Moreover, while the presently preferred magnets <NUM> and shunts <NUM> are hollow annular rings coaxially aligned with centerline <NUM> in a circular single beam ion source, they may alternately consist of multiple solid rod or bar-like magnets that are arranged about centerline <NUM> in a circular or arcuate pattern, although some of the preferred advantages may not be realized. In a linear single beam ion source, the ends include half of the circular configuration described above and the straight section may consist of multiple solid rod or bar-like magnets. It is also alternately envisioned that more than two stacked magnets or electromagnets may be employed and if so, additional associated shunts may be provided so as to extend the generally E-cross-sectional configuration with more than three inwardly extending teeth or projecting edges.

In one embodiment shown in <FIG>, ion beam <NUM> is transmitted from ion source <NUM> to specimen <NUM>, where target material <NUM> is subsequently deposited onto the surface of specimen <NUM> from source <NUM>. In one structural configuration, specimen <NUM> is coupled to an electromagnetic actuator <NUM>, such as an electrical motor or solenoid. A similar electromagnetic actuator <NUM> is coupled to source <NUM>. These optional electromagnetic actuators <NUM> and <NUM> can impart rotational and/or linear movement to specimen <NUM> and source <NUM>. The present ion source assisted deposition effectively overcomes the conventional loose atom packing problem and advantageously produces dense films with superior stability, smooth film surface, high electric conductivity, and strong coating adhesion, due to dense packing of atoms <NUM>, as illustrated in <FIG>.

<FIG> illustrates an alternate embodiment of the present single beam plasma or ion source apparatus <NUM>. In the present exemplary configuration, ion source <NUM> including its anode <NUM> and cathode <NUM>, are essentially the same as in the prior embodiments of <FIG>. However, a sputtering source <NUM> is employed to operate simultaneously with the ion source <NUM>. Sputtering source <NUM> is a magnetron sputter gun or other type of sputtering device, which generally includes a target <NUM> and an assembly of magnets and shunts that create a proper magnetic field in front of the target surface. In this embodiment, the single ion beam <NUM>, is directly emitted toward specimen or workpiece <NUM> while target material <NUM> is simultaneously sputtered from target <NUM> and deposited on specimen <NUM> to form coating <NUM>. This ion treatment occurs simultaneously with the sputtering deposition at the same vacuum chamber pressure.

In a production setting, the apparatus components can be set vertical or horizontal. Furthermore, the specimen can be rigid or flexible. It is also noteworthy that a conveyor or roller system may be employed with any of the embodiments disclosed in the present application.

Ion beam <NUM> interacts with deposited thin film <NUM>, which is expected to directly improve characteristics of the film such as density, electric conductivity and barrier properties. This ion beam assisted thin-film growth is ideally suited for achieving super-smooth thin films and also to fabricate polycrystalline thin films at low temperatures such as room temperature.

The present ion source apparatus advantageously allows a wide range of operating pressures, such as those from <NUM> mTorr to <NUM> mTorr, which allow the ion creation and emission to be entirely compatible with sputtering. Furthermore, the present ion source apparatus advantageously allows ion creation and emission independent of the operating gas since no filament is used; thus, argon, oxygen and other inert and reactive gases may be used. The present ion source also works in a voltage control mode or a current control mode, and the discharge voltages can be as low as <NUM> volts. Moreover, the narrow focused ion beam advantageously provides a stable discharge without arcing.

In one example, the process gases consist of argon mixed with <NUM>% oxygen and the pressure is maintained at <NUM> mTorr. The power applied to sputtering magnetron <NUM> is fixed at <NUM> Watts. Without ion source <NUM> power on, a five-minute sputtering creates an ITO coating <NUM> of approximately <NUM> thickness, i.e. <NUM> per minute. On the other hand, the same magnetron is powered at <NUM> W and the ion source is turned on with a voltage of approximately <NUM> V. A five-minute deposition produces an ITO film of <NUM> thickness, i.e. <NUM> per minute. Hence, the ion source leads to approximately <NUM>% increase in the deposition rates. Based on the deposition rates and the same deposition parameters, ITO films of about <NUM> thickness were deposited on glass substrates at room temperature with and without the ion source powered on. The sheet resistance of the ITO films decreased to <NUM>/<NUM> as shown in <FIG>.

The creation and emission of ion beam <NUM> from ion source <NUM> simultaneously with a sputtering of target material onto substrate <NUM> beneficially creates a smoother and denser external surface of coating <NUM> on substrate <NUM>. This is achieved by ions <NUM> impacting against the target material atoms as the atoms are being deposited or attaching to the previously deposited target material, and thereby pushing the new atoms into voids in each prior layer in the coating growth and buildup (see <FIG>). This is ideally suited for depositing a coating <NUM> and improving the quality thereof including increased deposition rates and better crystallinity. These improvements based on the present apparatus obtain greater light transmittance through coating <NUM> when the coating is an ITO films, and/or the coating exhibits improved hardness. <FIG> and <FIG> show the atomic force microscopy phase images of indium-tin-oxide ("ITO") films deposited using apparatus <NUM> without and with ion source <NUM> in simultaneous operation, respectively. The results indicate that the ion source assisted deposition leads to dense and smooth ITO films.

Reference should now be made to <FIG>. Another embodiment of a single beam plasma or ion source apparatus <NUM> includes ion source <NUM> with anode <NUM> and cathode <NUM> essentially like that of the prior embodiments. This apparatus emits a chemical precursor gas from inlet <NUM> or another remote entrance into ion source <NUM> such that the plasma generated therein by the electromagnetic fields creates desired chemical species that subsequently deposit as a coating <NUM> on a specimen or workpiece <NUM>. One such gas precursor is CH<NUM>. This chemical vapor deposition process deposits and grows carbon coatings. Alternately, a carbon-based sputter target can be employed as with any of the other embodiments disclosed herein to produce carbon atoms as the specimen coating.

In the present exemplary configuration, specimen <NUM> on a conveyor system moves across the ion source and gets coated. A roll-to-roll coating arrangement <NUM> can also coat a flexible PET film, flexible and thin stainless steel sheet, or the like. Such a film and roller configuration can be employed with any of the embodiments disclosed herein.

<FIG> illustrates a different embodiment single beam plasma or ion source apparatus <NUM>. Anode <NUM> and cathode <NUM> of ion source <NUM> are essentially the same as with the prior embodiments. Additionally, a radio frequency ("RF") induction coil <NUM> is mounted between, and spaced away from, ion source <NUM> and a specimen <NUM>. Radio frequency induction coil <NUM> creates an electromagnetic field during the operation of ion source <NUM> such that a single source ion beam <NUM> passes from outlet hole <NUM> through a hollow center <NUM> of coil <NUM> and onto a coating <NUM> of substrate <NUM>. The RF frequencies are preferably in the range of about <NUM> to <NUM>, and more preferably <NUM>.

While radio frequency induction coil <NUM> is preferably located inside the vacuum chamber along with ion source <NUM> and specimen <NUM>, they may alternately be configured such that radio frequency induction coil <NUM> can be on the opposite side of specimen <NUM> from ion source <NUM>. Radio frequency induction coil <NUM> will advantageously generate additional ions and densify the ions within ion beam <NUM>. It is also envisioned that the radio frequency induction coil shall assist in shaping ion beam <NUM> for better control and focusing when depositing coating or films <NUM> on specimen <NUM>.

Turning now to <FIG>, another embodiment of an ion source apparatus <NUM> includes an ion source <NUM> and a sputtering target <NUM>. Ion source <NUM> is similar to that of the prior embodiments disclosed herein. Furthermore, ion source <NUM> includes a cathode cap <NUM> with a single and central outlet hole <NUM> through which a single ion beam <NUM> is emitted to assist in creation of a coating <NUM> on a specimen or workpiece <NUM> within a vacuum chamber.

An annular pedestal <NUM> of conductive metallic material is mounted upon an insulator <NUM> and serves to mount an annular shaped sputter target <NUM> thereupon. Ion source <NUM> is concentrically and coaxially located within a hollow center of target <NUM> and pedestal <NUM>. This provides an integrated and simultaneously acting sputtering and ion emission sources which advantageously operate at the same internal vacuum chamber pressure. It is beneficially envisioned that the present integrated and concentric sources can more quickly cover a larger specimen area in a shorter amount of time for both sputtered material deposition and ion emission interactions with the deposited atoms, than would otherwise be achieved with remotely offset ion and target sources. It is further envisioned that the present integrated and concentric sources may provide more complete ion-activated sputtering and in a more uniform manner than with conventional devices. More specifically, the present integrated and coaxial sources are expected to more advantageously be aligned with the specimen thereby achieving a more uniform coating versus offset angled sputtering target locations. A similar principle can be extended to a linearly elongated shape single beam ion source integrated with a sputtering magnetron or other deposition sources.

Claim 1:
An ion source apparatus (<NUM>) comprising:
(a) an anode (<NUM>) comprising an anode body (<NUM>), magnetic shunts (<NUM>) inwardly extending from the anode body (<NUM>) toward an ion emission axis (<NUM>), permanent magnets (<NUM>) located between the magnetic shunts (<NUM>) in a stacked arrangement in the direction of the ion emission axis (<NUM>), and an open plasma area (<NUM>) being located within a hollow central area of the anode (<NUM>), the magnetic shunts (<NUM>) and permanent magnets (<NUM>) internally secured within the anode body (<NUM>);
(b) a cathode (<NUM>) comprising a cap (<NUM>) having a single outlet opening (<NUM>) therethrough, the outlet opening (<NUM>) being aligned with the axis (<NUM>), the outlet opening being configured to allow emission of an ion beam from the hollow central area of the anode (<NUM>);
(c) magnetic flux lines (<NUM>) extending between uppermost and lowermost of the magnetic shunts (<NUM>), the magnetic flux lines (<NUM>) including a central outward dip (<NUM>) adjacent a middle of the magnetic shunts (<NUM>), the dip (<NUM>) of the magnetic flux lines (<NUM>) being in the open plasma area (<NUM>), and the dip (<NUM>) changing movement of electrons (<NUM>) adjacent the dip (<NUM>) to increase ionization within a plasma inside the anode (<NUM>);
(d) the permanent magnets (<NUM>) and the magnetic shunts (<NUM>) each being of a closed loop shape; and
(e) the magnetic shunts (<NUM>) inwardly projecting toward the axis (<NUM>) further than the permanent magnets (<NUM>).