Ion Source Containing a Sputter Target

An ion source with a sputter target located at the end of the ion source is disclosed. The ion source may include an indirectly heated cathode and the sputter target may be disposed on the end opposite the cathode. The ion source may contain one or more side electrodes, wherein at least one of these electrodes is electrically biased relative to the arc chamber. In one embodiment, the second end of the ion source is made of a dopant containing material and serves as the sputter target. In another embodiment, there is an opening in the second end, and an insert is disposed in this opening. The insert is made of a dopant containing material and serves as the sputter target.

FIELD

Embodiments of the present disclosure relate to an ion source that includes a dopant containing material located on the wall opposite the cathode.

BACKGROUND

Various types of ion sources may be used to create the ions that are used in semiconductor processing equipment. For example, an indirectly heated cathode (IHC) ion source operates by supplying a current to a filament disposed behind a cathode. The filament emits thermionic electrons, which are accelerated toward and heat the cathode, in turn causing the cathode to emit electrons into the arc chamber of the ion source. The cathode is disposed at one end of an arc chamber. A repeller is typically disposed on the end of the arc chamber opposite the cathode. The cathode and repeller may be biased so as to repel the electrons, directing them back toward the center of the arc chamber. In some embodiments, a magnetic field is used to further confine the electrons within the arc chamber.

In certain embodiments, electrodes are also disposed on one or more side walls of the arc chamber. These electrodes may be positively or negatively biased so as to control the position of ions and electrons, so as to increase the ion density near the center of the arc chamber. An extraction aperture is disposed along another side, proximate the center of the arc chamber, through which the ions may be extracted. These biased side electrodes may also negate the need for a repeller on the end wall for electron confinement.

In certain embodiments, it may be desirable to utilize a feed material that is in solid form as a dopant species. However, there are issues associated with using solid feed materials with IHC ion sources. For example, vaporizers used with ion sources are difficult to operate at temperatures greater than 1200 Celsius. Further, there may be issues with heat shielding and condensation in the tubes that connect the vaporizer with the arc chamber. These issues may prevent the use of many solids in a vaporizer because their vapor pressure is too low at 1200 Celsius.

Further, solid sputter targets disposed within the arc chamber may have limited feasibility due to low melting temperatures and limited life due to size constraints.

Therefore, it would be advantageous if there were an ion source that allows for a larger solid sputter target to be disposed within the arc chamber.

SUMMARY

An ion source with a sputter target located at the end of the ion source is disclosed. The ion source may include an indirectly heated cathode and the sputter target may be disposed on the end opposite the cathode. The ion source may contain one or more side electrodes, wherein at least one of these electrodes is electrically biased relative to the arc chamber. In one embodiment, the second end of the ion source is made of a dopant containing material and serves as the sputter target. In another embodiment, there is an opening in the second end, and an insert is disposed in this opening. The insert is made of a dopant containing material and serves as the sputter target.

According to one embodiment, an indirectly heated cathode (IHC) ion source to create an ion beam comprising a dopant species is disclosed. The IHC ion source comprises an arc chamber, comprising a plurality of electrically conductive side walls connecting a first end and a second end; an indirectly heated cathode disposed on the first end of the arc chamber; an electrode disposed on one of the plurality of electrically conductive side walls, wherein a voltage is applied to the electrode relative to a voltage applied to the plurality of electrically conductive side walls of the arc chamber; and wherein the second end is electrically connected to the side walls and is made of a dopant containing material. In some embodiments, the indirectly heated cathode is electrically connected to the side walls. In some embodiments, the dopant containing material has a melting point greater than a melting point of the dopant species. In some embodiments, the dopant species is a metal and the dopant containing material is a ceramic containing the dopant species or an alloy containing the dopant species. In some embodiments, the second end is at least 0.5 inches thick. In some embodiments, the dopant species is aluminum and the dopant containing material is a ceramic containing aluminum or an aluminum alloy.

According to another embodiment, an ion implanter is disclosed. The ion implanter comprises any of the IHC ion sources described above, and one or more beamline components to direct the ion beam toward a workpiece. In some embodiments, the indirectly heated cathode is electrically connected to the side walls. In some embodiments, the dopant species is aluminum and the dopant containing material is a ceramic containing aluminum or an aluminum alloy.

According to another embodiment, an indirectly heated cathode (IHC) ion source to generate an ion beam comprising a dopant species is disclosed. The ion source comprises an arc chamber, comprising a plurality of electrically conductive side walls connecting a first end and a second end; an indirectly heated cathode disposed on the first end of the arc chamber; an electrode disposed on one of the plurality of electrically conductive side walls, wherein a voltage is applied to the electrode relative to a voltage applied to the plurality of electrically conductive side walls of the arc chamber; and wherein an opening is disposed in the second end, and an insert made from a dopant containing material is disposed in the opening and electrically connected to the second end. In some embodiments, the indirectly heated cathode is electrically connected to the side walls. In some embodiments, the dopant containing material has a melting point greater than a melting point of the dopant species. In some embodiments, the dopant species is a metal and the dopant containing material is a ceramic containing the dopant species or an alloy containing the dopant species. In some embodiments, the insert is at least 0.5 inches thick. In some embodiments, the dopant species is aluminum and the dopant containing material is a ceramic containing aluminum or an aluminum alloy. In some embodiments, the insert completely fills the opening. In some embodiments, a gap exists between the opening and the insert. In some embodiments, a holder is disposed at an exterior surface of the second end to retain the insert in position within the opening.

According to another embodiment, an ion implanter is disclosed. The ion implanter comprises any of the IHC ion sources described above, and one or more beamline components to direct the ion beam toward a workpiece.

According to another embodiment, an ion implanter is disclosed. The ion implanter comprises an ion source; and one or more beamline components to direct an ion beam toward a workpiece, wherein the ion source comprises: an arc chamber, comprising a plurality of electrically conductive side walls connecting a first end and a second end; a plasma generator disposed on the first end of the arc chamber; an electrode disposed on one of the plurality of electrically conductive side walls, wherein a voltage is applied to the electrode relative to a voltage applied to the plurality of electrically conductive side walls of the arc chamber; and wherein the second end is electrically connected to the side walls and is made of a dopant containing material or wherein an opening is disposed in the second end, and an insert made from the dopant containing material is disposed in the opening.

DETAILED DESCRIPTION

As described above, vaporizers may be problematic at very high temperatures due to condensation and low vapor pressure.

FIG.1shows an IHC ion source10that overcomes these issues. The IHC ion source10includes an arc chamber100, comprising two opposite ends, and side walls101connecting to these ends. The arc chamber100also includes a bottom wall and a top wall. The walls of the arc chamber100may be constructed of an electrically conductive material and may be in electrical communication with one another. In some embodiments, the walls are made of graphite or tungsten. A cathode110is disposed in the arc chamber100at a first end104of the arc chamber100. A filament160is disposed behind the cathode110. The filament160is in communication with a filament power supply165. The filament power supply165is configured to pass a current through the filament160, such that the filament160emits thermionic electrons. Cathode bias power supply115biases filament160negatively relative to the cathode110, so these thermionic electrons are accelerated from the filament160toward the cathode110and heat the cathode110when they strike the back surface of cathode110. The cathode bias power supply115may bias the filament160so that it has a voltage that is between, for example, 200V to 500V more negative than the voltage of the cathode110. The cathode110then emits thermionic electrons on its front surface into arc chamber100.

Thus, the filament power supply165supplies a current to the filament160. The cathode bias power supply115biases the filament160so that it is more negative than the cathode110, so that electrons are attracted toward the cathode110from the filament160. In certain embodiments, the cathode110may be electrically connected to the arc chamber100, so as to be at the same voltage as the side walls of the arc chamber100. In these embodiments, the cathode110may be electrically connected to the side walls of the arc chamber100. In certain embodiments, the arc chamber100is connected to electrical ground.

In this embodiment, the second end105of the arc chamber100opposite the cathode110is constructed from a dopant containing material. The dopant containing material is a solid material and may have a melting temperature that is greater than the temperatures experienced within the arc chamber100. Further, the dopant containing material may have a higher melting point than the dopant species. For example, if the desired dopant species is aluminum, the second end105may be constructed from an aluminum containing ceramic, such as AlN, or an aluminum containing alloy, such as aluminum tantalum. Other dopants may be used. For example, the dopant species may be a metal, such as gallium, lanthanum, indium and others. If these other dopant species are used, ceramics that include the dopant species or alloys that include the dopant species may be used. In this embodiment, the entirety of the second end105is made of the dopant containing material. Thus, in this embodiment, the second end105serves as the sputter target. This second end105may be secured to the arc chamber100in the manner typically used, such as by compression or clamping forces. The second end105is electrically connected to the rest of the walls of the arc chamber100. Thus, in certain embodiments, the second end105is electrically grounded.

In certain embodiments, a magnetic field190is generated in the arc chamber100. This magnetic field is intended to confine the electrons along one direction. The magnetic field190typically runs parallel to the side walls101from the first end104to the second end105.

In the embodiment shown inFIG.1, first electrode130aand second electrode130bmay be disposed on respective opposite side walls101of the arc chamber100, such that the first electrode130aand the second electrode130bare within the arc chamber100. The first electrode130aand the second electrode130bmay be configured so as to be electrically isolated from the side walls101. The first electrode130aand the second electrode130bmay each be biased by a respective power supply. In certain embodiments, the first electrode130aand the second electrode130bmay be in communication with a common power supply. However, in other embodiments, to allow maximum flexibility and ability to tune the output of the IHC ion source10, the first electrode130amay be in communication with a first electrode power supply135aand the second electrode130bmay be in communication with a second electrode power supply135b.

The first electrode power supply135aand the second electrode power supply135bserve to bias the first electrode130aand the second electrode130b, respectively, relative to the side walls101of the arc chamber100. In certain embodiments, the first electrode power supply135aand the second electrode power supply135bmay bias the first electrode130aand the second electrode130bpositively or negatively relative to the side walls101of the arc chamber100. In certain embodiments, at least one of the electrodes may be biased at between 40 and 500 volts relative to the side walls101of the arc chamber100.

WhileFIG.1shows two electrodes130a,130b, it is understood that one of these electrodes, such as second electrode130band its associated second electrode power supply135bmay be eliminated in some embodiments. In another embodiment, the second electrode130bis disposed within the arc chamber100, but is electrically connected to the side walls101of the arc chamber100. Thus, in this embodiment, the second electrode power supply135bmay be eliminated.

The cathode110and the electrodes130a,130bare made of an electrically conductive material, such as a metal or graphite.

Disposed on another side of the arc chamber100, referred to as the top wall103, may be an extraction aperture140. InFIG.1, the extraction aperture140is disposed on a side that is parallel to the page. Further, the IHC ion source10also comprises a gas inlet106through which the gas to be ionized is introduced to the arc chamber100.

During operation, the filament power supply165passes a current through the filament160, which causes the filament160to emit thermionic electrons. These electrons strike the back surface of the cathode110, which may be more positive than the filament160, causing the cathode110to heat, which in turn causes the cathode110to emit electrons into the arc chamber100. These electrons collide with the molecules of gas that are fed into the arc chamber100through the gas inlet106. A carrier gas, such as argon, or an etching gas, such as fluorine-based or chlorine-based gasses, may be introduced into the arc chamber100through a suitably located gas inlet106. The combination of electrons from the cathode110, the gas and the positive potential creates a plasma. The plasma may be confined and manipulated by the electrical fields created by the first electrode130aand the second electrode130b. Further, in certain embodiments, the electrons and positive ions may be somewhat confined by the magnetic field190. In certain embodiments, the plasma is confined near the center of the arc chamber100, proximate the extraction aperture140. In some embodiments, the plasma may be biased at a voltage which is close to the average of the voltages applied to the first electrode130aand the second electrode130b. Chemical etching or sputtering by plasma transforms the second end105into the gas phase and causes ionization. The ionized feed material can then be extracted through the extraction aperture140and used to prepare an ion beam that comprises the dopant species.

In certain embodiments, the voltage of the cathode110is less positive than the voltage of the plasma. For example, in one embodiment, the cathode110may be at the same voltage as the side walls of the arc chamber100. The first electrode130amay be biased at 150V, while the second electrode130bmay be biased at 0V or 20V. Thus, the electrons generated by the cathode110are attracted toward the plasma. In some embodiments, these emitted electrons or other particles may also strike the second end105, causing it to sputter.

Neutral atoms that are sputtered or otherwise released from the second end105are launched toward the plasma, where they can be ionized by the confined electrons and extracted through the extraction aperture140.

In this embodiment, the second end105may be manufactured to have a desired initial thickness. For example, in certain embodiments, the arc chamber100is dimensioned such that the second end105may have a thickness of 0.5 inches or more. Specifically, the outer surface of the second end105(which is opposite that facing the arc chamber100), may extend outward significantly, limited only by the configuration of components outside the arc chamber100. This may provide extended lifetime of the IHC ion source10before the second end is replaced. As the second end105is sputtered, its thickness decreases, slightly increasing the volume of the arc chamber100.

FIG.2shows a second embodiment. Many of the components in this embodiment are identical to those inFIG.1and have been given identical reference designators.

In this embodiment, the second end105may be constructed from the same material as the other walls, which may be graphite or tungsten. The second end105is electrically connected to the side walls101and in certain embodiments, may be grounded.

An opening107is created in the second end105, such as in the center of the second end105, aligned with the cathode110. An insert180may then be disposed into this opening107such that a portion of the insert180is disposed within the arc chamber100. Since the insert180is affixed to the second end105, it is at the same voltage as the second end and may also be grounded. The insert180is made from the dopant containing material. As described above, the dopant containing material may be a solid and may have a higher melting temperature than the temperatures experienced within the arc chamber100. Further, the dopant containing material may have a melting temperature greater than that of the dopant species. If aluminum is the dopant species, the dopant containing material may be an aluminum alloy or a ceramic made from aluminum. Further, as described above, the dopant species may be a metal, such as gallium, lanthanum, indium and others. If these other dopant species are used, ceramics that include the dopant species or alloys that include the dopant species may be used. Thus, in this embodiment, the insert180serves as the sputter target.

In some embodiments, the opening107may be circular, and the insert180may be a cylindrical shape. As shown inFIG.3A, in certain embodiments, the opening107may be threaded. Similarly, the insert180may also be threaded, allowing the insert180to be easily installed and removed from the arc chamber100without having to disassemble the IHC ion source10. Further, the insert180may be longer than 0.5 inches, where a portion of the insert180is disposed within the arc chamber100, and a second portion is disposed outside the arc chamber100. Thus, if it is threaded, as the insert180is consumed, it may be rotated so as to further extend the insert180into the arc chamber100such that the second portion is now inside the arc chamber100.

In other embodiments, the opening107and the insert180may have a different shape, such as rectangular, hexagonal, triangular or any other shape. Furthermore, other mechanisms for holding the insert180may be used. In one embodiment, as shown inFIG.2, a holder108may be installed on the exterior surface of the second end105, which is used to position and retain the insert180. The holder108may be adjustable such that the portion of the insert180that remains outside the arc chamber100may be modified as the insert180is consumed. The holder108may be in the form of a bracket, a clamp, a bolt, or another fastener. In some embodiments, such as that shown inFIG.2, the insert180may have the same cross-section through its length such that all portions of the insert180can pass through the opening107.

In another embodiment, shown inFIG.3B, the insert180may have a head181with a larger outer dimension than the body182. In this way, the insert180may be installed such that the head181is disposed in the arc chamber100. The head181, since its outer dimension is larger than the opening107, retains the insert180in the arc chamber100. In this embodiment, the insert180may be cylindrical, hexagonal, a rectangular prism or a cube. This embodiment may not utilize a holder108. In all instances, the insert180and the second end105may be electrically connected and may be grounded.

In certain embodiments, the insert180may completely fill the opening107so as to seal the arc chamber100. However, in some embodiments, there may be a gap between the insert180and the second end105at the opening107. However, the insert180remains at the same potential as the second end105, regardless of whether there is a gap or not.

While the above disclosure describes the use of a sputter target with an indirectly heated cathode ion source, it is understood that the disclosure is not limited to this embodiment. The ion source may be any type of ion source, such as an RF ion source, a Bernas ion source or any other type.

FIG.4shows an ion implanter that may utilize any of the ion sources described herein. The ion implanter includes an ion source400, which may be any of the ion sources described above. As noted above, in certain embodiments, the ion source400may be an IHC ion source. In another embodiment, the ion source400may be an RF ion source. In this embodiment, an RF antenna may be disposed against a dielectric window. This dielectric window may comprise part or all of one of the chamber walls. The RF antenna may comprise an electrically conductive material, such as copper. An RF power supply is in electrical communication with the RF antenna. The RF power supply may supply an RF voltage to the RF antenna. The power supplied by the RF power supply may be between 0.1 and 10 kW and may be any suitable frequency, such as between 1 and 100 MHz. Further, the power supplied by the RF power supply may be pulsed. Other embodiments are also possible. For example, the plasma may be generated in a different manner, such as by a Bernas ion source, a capacitively coupled plasma (CCP) source, microwave or ECR (electron-cyclotron-resonance) ion source. The manner in which the plasma is generated is not limited by this disclosure.

One chamber wall, referred to as the extraction plate, includes an extraction aperture. The extraction aperture may be an opening through which the ions401generated in the ion source chamber are extracted and directed toward a workpiece490. The ions401may be of the desired dopant species, wherein the dopant containing material is part of or proximate to the second end of the ion source400, as described above. The extraction aperture may be any suitable shape. In certain embodiments, the extraction aperture may be oval or rectangular shaped.

Disposed outside and proximate the extraction aperture of the ion source400are extraction optics410. In certain embodiments, the extraction optics410comprise one or more electrodes. In certain embodiments, the extraction optics410comprises a suppression electrode411, which is negatively biased relative to the plasma so as to attract ions through the extraction aperture. The suppression electrode411may be electrically biased using a suppression power supply. The suppression electrode411may be biased so as to be more negative than the extraction plate of the ion source400.

In some embodiments, the extraction optics410includes a ground electrode412. The ground electrode412may be disposed proximate the suppression electrode411. The ground electrode412may be electrically connected to a second electrode power supply. In other embodiments, the ground electrode412may be electrically grounded so that the second electrode power supply is not used.

In other embodiments, the extraction optics410may comprise in excess of two electrodes, such as three electrodes or four electrodes. In these embodiments, the electrodes may be functionally and structurally similar to those described above, but may be biased at different voltages.

Located downstream from the extraction optics410is a mass analyzer420. The mass analyzer420uses magnetic fields to guide the path of the extracted ions401. The magnetic fields affect the flight path of ions according to their mass and charge. A mass resolving device430that has a resolving aperture431is disposed at the output, or distal end, of the mass analyzer420. By proper selection of the magnetic fields, only those ions401that have a selected mass and charge will be directed through the resolving aperture431. Other ions will strike the mass resolving device430or a wall of the mass analyzer420and will not travel any further in the system.

One or more beamline components may be disposed downstream from the mass resolving device430to direct the ions401toward the workpiece490. For example, a collimator440may be disposed downstream from the mass resolving device430. The collimator440accepts the extracted ions401that pass through the resolving aperture431and creates a ribbon ion beam formed of a plurality of parallel or nearly parallel beamlets. In other embodiments, the ion beam may be a spot beam. In this embodiment, an electrostatic scanner is used to move the spot beam in the first direction, as defined below.

Located downstream from the collimator440may be an acceleration/deceleration stage450. The acceleration/deceleration stage450may be an electrostatic filter. The electrostatic filter is a beam-line lens component configured to independently control deflection, deceleration, and focus of the ion beam. Located downstream from the acceleration/deceleration stage450is the workpiece holder460.

The workpiece490, which may be, for example, a silicon wafer, a silicon carbide wafer, a gallium nitride wafer or another type of substrate, is disposed on the workpiece holder460.

The present system has many advantages. First, this configuration, wherein at least one of the electrodes130a,130bare biased relative to the arc chamber100, eliminates the need for a repeller. Consequently, a sputter target positioned at the second end105may be maintained at the same potential as the arc chamber100. This simplifies the design and eliminates any connection between the sputter target and a power supply. Additionally, many prior art systems utilize a sputter target disposed on or around the repeller, which is either biased or floating. Since the sputter target of the present disclosure is not biased or floating, like these prior art implementations, its temperature may be lower, allowing more options of dopant containing material with low melting temperatures than may otherwise be used.

Furthermore, when using a sputter target disposed around a repeller, the repeller is typically located at the magnetic axis of the ion source, which also corresponds to the region of highest plasma density. Consequently, the sputter target material is not exposed to the highest density plasma, making it less effective at sputtering or etching material from the target. In the present disclosure, since a repeller is not used, the surface area of the sputter target that is exposed to the plasma may be maximized and the region of highest plasma density and highest etching rates can be utilized for the sputter target. For example, in one embodiment, the entirety of the second end serves as the sputter target.

Additionally, by using the entirety of the second end105as the sputter target, the life of the sputter target may be made significantly longer than other prior art implementations. Not only is the exposed surface area larger, but the thickness of the sputter target may be much thicker than conventional systems. Similarly, the insert180shown inFIG.2may also have extended life, since it may be screwed further into the arc chamber100as it is consumed.