Patent Application
20240098871
The disclosure relates generally to ion implantation apparatus and more particularly to high energy beamline ion implanters.
Ion implantation is a process of introducing dopants or impurities into a substrate via bombardment. Ion implantation systems may comprise an ion source and a series of beam-line components. The ion source may comprise a chamber where ions are generated. The ion source may also comprise a power source and an extraction electrode assembly disposed near the chamber. The beam-line components, may include, for example, a mass analyzer, a first acceleration or deceleration stage, a collimator, and a second acceleration or deceleration stage. Much like a series of optical lenses for manipulating a light beam, the beam-line components can filter, focus, and manipulate ions or ion beam having particular species, shape, energy, and/or other qualities. The ion beam passes through the beam-line components and may be directed toward a substrate mounted on a platen or clamp.
Implantation apparatus capable of generating ion energies of approximately 1 MeV or greater are often referred to as high energy ion implanters, or high energy ion implantation systems. One type of high energy ion implanter is termed linear accelerator, or LINAC, where a series of electrodes arranged as tubes conduct and accelerate the ion beam to increasingly higher energy along the succession of tubes, where the electrodes receive an powered voltage signal. Known LINACs are driven by an RF voltage of frequency in the 10 MHz-120 MHz range, with many using 13.56 MHz and its harmonics, which frequencies have special permission for industrial, scientific and medical (ISM) usage by the Federal Communication Commission (FCC). A given stage of a linear accelerator is driven by an assembly of RF electrodes (a drift tube assembly) that are arranged as hollow tubes to conduct the ion beam therethrough, where acceleration of the ion beam takes place in gaps between adjacent electrodes of the drift tube assembly.
One issue for operation of RF LINAC ion implanters is that during acceleration of an ion beam, which ion beam is partitioned into ion bunches along a direction of propagation (Z-direction), a natural tendency of an ion bunch is to spread out both transversely (in X-direction and Y-direction) as well as longitudinally (in Z-direction, or equivalently, in time). Thus, besides accelerating an ion beam, a LINAC also has to focus the ion beam to maintain a small lateral dimension that will propagate down the beam ‘pipeline’ without losing ions to the sidewalls. Traditionally this focusing is performed by inserting direct current (DC) quadrupole elements between the acceleration stages. Such quadrupoles may be electromagnetic or electrostatic, while electrostatic quadrupoles are used more often because of compactness, lower cost and the ability to perform almost as well at the energies used in semiconductor processing (<20 MeV). These quadrupoles are often equipped with more than one power supply, allowing them to do double duty as steering elements used to correct for minor sideways deflection of the beam. Because the quadrupoles require extra spacing between adjacent acceleration stages, the inserting of quadrupoles into a LINAC increases the minimum length required for the beamline. As a result, the footprint of the ion implanter is increased, and the ability to transport drift beams (that are not accelerated by the RF fields) through the LINAC is limited.
One approach for reducing the length of the overall linear accelerator involves adding a magnetic quadrupole within a drift tube electrode. This approach is limited to a pulsed beam and a relatively low duty cycle. In ion implantation applications, continuous wave (CW) operation is required, where providing water cooling for electromagnets inside the drift tubes presents a significant challenge. Other approaches employ permanent magnet quadrupoles, which arrangements are relatively bulky.
With respect to these and other considerations the present disclosure is provided.
In one embodiment, an apparatus is provided. The apparatus may include a drift tube assembly having a plurality of drift tubes to conduct an ion beam along a beam propagation direction. The plurality of drift tubes may define a multi-gap configuration corresponding to a plurality of acceleration gaps, wherein at least one powered drift tube of the drift tube assembly is coupled to receive an RF voltage signal. The apparatus may also include a DC electrode assembly that includes a conductor line, arranged within a resonator coil that is coupled to receive a DC voltage signal into the at least one powered drift tube. The DC electrode assembly may also include a DC electrode arrangement, connected to the conductor line and disposed within the at least one powered drift tube.
In another embodiment, a linear accelerator may include a plurality of acceleration stages. At least one acceleration stage of the plurality of acceleration stages may include a drift tube assembly, to conduct an ion beam along a beam propagation direction. The acceleration stage may also include a resonator coil that has a conductive wall that is coupled to deliver an RF voltage to a powered drift tube of the drift tube assembly. The acceleration stage may also include a DC electrode assembly that includes a conductor line, arranged within the resonator coil, and electrically isolated from the resonator coil. The DC electrode assembly may also include a DC electrode arrangement, connected to the conductor line and disposed within the at least one powered drift tube, and electrically isolated from the at least one powered drift tube.
In a further embodiment, an ion implanter may include an ion source, to generate an ion beam; and a linear accelerator, disposed to receive the ion beam. The linear accelerator may include a plurality of acceleration stages, wherein at least one acceleration stage of the plurality of acceleration stages comprises a drift tube assembly, to conduct an ion beam along a beam propagation direction. The acceleration stage may also include a resonator coil that has a conductive wall that is coupled to deliver an RF voltage to a powered drift tube of the drift tube assembly, and may further include a DC electrode assembly. The DC electrode assembly may include a conductor line, arranged within the resonator coil, and electrically isolated from the resonator coil, and may also include a DC electrode arrangement, connected to the conductor line and disposed within the at least one powered drift tube, and electrically isolated from the at least one powered drift tube.
The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict exemplary embodiments of the disclosure, and therefore are not be considered as limiting in scope. In the drawings, like numbering represents like elements.
An apparatus, system and method in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, where embodiments of the system and method are shown. The system and method may be embodied in many different forms and are not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so this disclosure will be thorough and complete, and will fully convey the scope of the system and method to those skilled in the art.
Terms such as “top,” “bottom,” “upper,” “lower,” “vertical,” “horizontal,” “lateral,” and “longitudinal” may be used herein to describe the relative placement and orientation of these components and their constituent parts, with respect to the geometry and orientation of a component of a semiconductor manufacturing device as appearing in the figures. The terminology may include the words specifically mentioned, derivatives thereof, and words of similar import.
As used herein, an element or operation recited in the singular and proceeded with the word “a” or “an” are understood as potentially including plural elements or operations as well. Furthermore, references to “one embodiment” of the present disclosure are not intended to be interpreted as precluding the existence of additional embodiments also incorporating the recited features.
Provided herein are approaches for improved high energy ion implantation systems and components, based upon a beamline architecture, and in particular, ion implanters based upon linear accelerators. For brevity, an ion implantation system may also be referred to herein as an “ion implanter.” Various embodiments entail novel approaches that provide the capability of improved control of an ion beam during acceleration through the acceleration stages of a linear accelerator, and in particular, improved ion beam focusing.
Various embodiments of the disclosure are related to a novel architecture for drift tube assemblies in a linear accelerator (LINAC), and in particular, for linear accelerators used to accelerate ion beams in a beam line ion implanter. In various embodiments, a given acceleration stage of a LINAC may be provided with a drift tube assembly that includes a plurality of drift tubes to conduct an ion beam along a beam propagation direction. The drift tube assembly is equipped with at least one powered drift tube that is coupled to receive an RF voltage signal. Together with grounded drift tubes, the drift tube assembly defines a plurality of acceleration gaps to accelerate the ion beam.
In the present embodiments, a configuration of inner electrode(s) is provided within one or more powered drift tubes of a drift tube assembly, where the configuration of electrodes may be referred to as “DC optics” to denote that the inner electrode provides a static (DC) electric field within the drift tube. In particular, as detailed below, a DC electrode assembly may be provided that includes a conductor line, arranged within a resonator coil that is coupled to deliver RF voltage signal a powered drift tube, as well as a DC electrode arrangement (DC optics) that is connected to the conductor line and is disposed within the powered drift tube.
The drift tube assembly 150 is formed of a plurality of drift tubes, including a first grounded drift tube 160, a second grounded drift tube 180, a first powered drift tube 110, disposed downstream of the first grounded drift tube 160, and a second powered drift tube 110A, disposed downstream of the first powered drift tube 110. It may be understood that the drift tube assembly 150 is coupled to a resonator (shown as resonator 108 in
In the configuration of
Turning to
Returning to
The conductor line 124 is coupled to receive a DC voltage from a DC voltage source 126, and as explained with respect to the figures to follow, may accordingly generate a DC electric field within the first powered drift tube 110. As detailed below, the DC electric field will arise between a given DC electrode of the DC electrode arrangement 122, and a wall of the first powered drift tube 110.
Turning to
In other embodiments, the DC electrode arrangement 122 may be arranged as a quadrupole configuration, as shown in
Thus, a feature of the apparatus 100 is the ability to provide a DC field within a chamber formed by the first powered electrode 110. By appropriate selection of the type of configuration of the DC electrode arrangement 122, and by application of a suitable DC voltage, the apparatus 100 may focus, steer, or otherwise manipulate an ion beam 114 passing through the first powered drift tube 110. The manipulation of the ion beam 114 by the DC electrode arrangement 122 is performed in a manner that is independent from the acceleration of the ion beam 114 that is provided by RF voltage applied to the first powered drift tube 110 by the resonator 108.
Turning to
In addition, according to the embodiment of
Turning to
∇×E=−−iωB (1)
As a result, in accordance with Stoke's theorem
φE.dl=−∫AiωB dA (2)
If we consider a loop 140 that hugs the interior surface of the resonator coil and goes through the DC voltage source 126, no B field will pass through the loop 140. And therefore
φE.dl=0 (3),
such that the voltage Vd (which is a DC voltage) has to appear between the points P and Q of
Turning to
φE.dl=∫AiωB·dA (4).
In various embodiments the value of this parameter may in the range of tens of thousands of volts, and for example, −100 kVRF. Most of this voltage will appear between the points R and S in
Turning to
The ion implanter 300 may include an analyzer 310, functioning to analyze the ion beam 306 as in known apparatus, by changing the trajectory of the ion beam 306, as shown. The ion implanter 300 may also include a buncher 312, and a linear accelerator 314 (shown in the dashed line), disposed downstream of the buncher 312, where the linear accelerator 314 is arranged to accelerate the ion beam 306 to form a high energy ion beam 315, greater than the ion energy of the ion beam 306, before entering the linear accelerator 314. The buncher 312 may receive the ion beam 306 as a continuous ion beam and output the ion beam 306 as a bunched ion beam to the linear accelerator 314. The linear accelerator 3314 may include a plurality of acceleration stages (314-A, 314-B, . . . to 314-Z (not shown)), arranged in series, as shown. In various embodiments, the ion energy of the high energy ion beam 315 may represent the final ion energy for the ion beam 306, or approximately the final ion energy. In various embodiments, the ion implanter 300 may include additional components, such as filter magnet 316, a scanner 313, collimator 320, where the general functions of the scanner 313 and collimator 320 are well known and will not be described herein in further detail. As such, a high energy ion beam, represented by the high energy ion beam 315, may be delivered to an end station 322 for processing a substrate 324. Non-limiting energy ranges for the high energy ion beam 315 include 500 keV-10 MeV, where the ion energy of the ion beam 306 is increased in steps through the various acceleration stages of the linear accelerator 314. In accordance with various embodiments of the disclosure, one or more of the acceleration stages of the linear accelerator 314 may include a drift tube assembly, with integrated DC electrode arrangement, as detailed with respect to the embodiments of
In view of the above, the present disclosure provides at least the following advantages. An advantage provided by an ion implanter incorporating the present DC electrode architecture is that the focusing of the ion beam may take place without the need for external quadrupole structures. In other words, the novel design of the present embodiments allows the focusing and steering of a beam to be done within the length of a drift tube without adding any extra length to the LINAC to achieve these purposes. This result enables the manufacture of a shorter LINAC and hence a more compact high energy ion implanter. One additional advantage of this design is that the size of the DC optics may scale with the ion energy along a LINAC: the shorter drift tubes (near the beginning of the LINAC where the ions are at lower ion energy) just have room for shorter DC focusing optics, but at this point the drift tubes would just need smaller E-field path length integrals because the ions have lower energy. Once the ions have acquired higher energy and require larger field path length integrals, the drift tubes will also be longer and allow for stronger focusing.
While certain embodiments of the disclosure have been described herein, the disclosure is not limited thereto, as the disclosure is as broad in scope as the art will allow and the specification may be read likewise. Therefore, the above descriptions are not to be construed as limiting. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.
