BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view illustrating a prior art broad ribbon beam ion implantation system that employs two magnets;
FIG. 2 is a schematic view illustrating another prior art ribbon beam ion implantation system that employs a single magnet;
FIG. 3 is a isometric view illustrating another exemplary prior art broad ribbon beam system that employs a single magnet with two magnet coils wrapping around two return yokes;
FIG. 4 is a cross sectional view, illustrating a prior art window frame magnet assembly;
FIG. 4
a is a prior art conventional dipole magnet stretched for broad beam.
FIG. 4
b is another type of prior art window frame magnet used in FIG. 3 with wrap-around coils for broad beam;
FIG. 4
c is a prior art window frame magnet configured to have wide uniform field for broad beam;
FIG. 5 is an isometric view illustrating a prior art broad beam mass analysis system using a window frame magnet shown in FIG. 4c;
FIG. 6 is a block diagram illustrating one implementation of an ion ribbon beam assembly system, according to one aspect of the invention;
FIG. 7 is a simplified isometric view of a deflected broad ribbon beam resulting from employing the prior art assembly depicted in FIG. 2;
FIG. 8 is an isometric view illustrating a deflected and mass analyzed ribbon beam according to yet another aspect of the invention;
FIG. 9
a is a simplified cross sectional view of a cross field magnet, according to yet another aspect of the invention;
FIG. 9
b is a cross sectional view of a cross field magnetic field employing two pairs of coils have a same current density, according to an aspect of the current invention;
FIG. 10
a is a simplified isometric view schematically illustrating the cross field window frame magnet assembly shown in cross section in FIG. 9, according to yet another aspect of the invention;
FIG. 10
b is an alternative way to make cross field within a single magnet, using two pairs of coils wrapping around 4 legs of return yokes.
FIG. 11 is a block diagram of an exemplary method for improving an ion ribbon beam of an ion implantation system according to another exemplary aspect of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout. The invention provides an ion source apparatus for creating elongated ion beams in an ion implantation system having a controllable density profile and other novel features for enhancing uniformity of ionized plasma within the source. One implementation of the various aspects of the invention is hereinafter illustrated and described. However, it will be appreciated that the illustrations and descriptions thereof are exemplary in nature, and that one or more aspects or novel features of the present invention may be carried out in other systems apart from those illustrated and described herein.
Referring initially to FIGS. 6, 7, 8 and 9a, an ion broad beam implantation system 600 is generally illustrated in accordance with the present invention, which may be used to create a wide ribbon and/or broad ion beam. The ion beam source 602 comprises a plasma source 604 and an extraction component 606, wherein plasma can be generated by ionizing a source material, for example, phosphine (PH3), phosphorous (P), arsenic (As), Boron (B), and the like. The ion beam source 602 comprises an extraction slit through which an ion beam may be extracted utilizing the extraction apparatus 606, wherein the ion beam is extracted as a uniform diverging beam. The ion beam then enters the window frame magnet assembly 610, which comprises a first pair of coils 902, coil 904 and 906 in FIG. 9a, to produce uniform vertical field over a wide area, a second pair of coils 908, coil 910 and 912 in FIG. 9, to produce an uniform horizontal field across the entire width of the broad beam, a yoke assembly 612 to act as return path for both pairs of coils, 902 and 908. The first magnetic coil 614 is configured so that the magnetic field flux 704, shown in FIG. 7, or 804 in FIG. 8, is orthogonal to the plane of the divergent beam and the resultant ribbon beam 702 is deflected in a vertical Y direction 710. The entire field in FIG. 7 is referred to as a vertical B field 708 and the exiting beam 706 is deflected as shown.
The second magnetic coil 616 depicted in FIG. 6 creates a second magnetic flux 806, as shown in FIG. 8, that is orthogonal to the magnetic field flux 704 generated by the first magnetic coil 614 and the entire field is referred to as a horizontal B field 810. One aspect of the invention provides that by the addition of the uniform horizontal B field 810 across the plane of the ion ribbon beam can create an improved mass dispersion, since the beam size in vertical dimension is thin (e.g., much thinner than its width). Therefore, the mass resolving power of the magnet assembly 610 and the ion implantation system 600 can be greatly enhanced, as well. The magnetic fields 810 and 812 induce orthogonal Lorentz forces to the in coming ion beam to deflect the beam in two directions, horizontally and vertically to form a ribbon beam 808, as a result. In other words, the vertical magnetic field, 804, is used to convert the diverging beam out of ion source into a parallel beam, and the horizontal magnetic field, 810, is used to deflect the sheet of broad beam vertically to provide vertical position dispersion according to ion mass properties of the incoming ion beam.
FIG. 9
a illustrates a cross section of a cross field window frame magnet assembly 900 employed to create the required uniform cross magnetic field utilizing a single magnet. Another aspect of the present invention is illustrated in FIG. 9a, wherein the window frame magnet assembly 900, shown in cross section, can be constructed in order to create a magnetic cross field. In order to achieve the cross-field X-Y, illustrated in FIG. 8, an orthogonal vertical B field can be added by utilizing a second pair of coils 908, coil 910 and coil 912, in addition to the first pair of coils 902, coil 904 and coil 906. The coils can be contained within a rectangular cross sectional housing 950, for example. Those of ordinary skill in the art will recognize many modifications that may be made to housing shape and design configuration without departing from the scope or spirit of what is described herein in this invention.
FIGS. 9
a and 9b 2D simulation results 900 and 920 with “POISSON” software to show the resulting cross field within the gap 914. Coils 910 and 912 are a pair and their current densities are equal, but the direction of their currents are directly opposite each other, for example, the current for coil 910 is into the paper in FIG. 9b, whereas for coil 912 the current direction is out of paper. The same configuration can be utilized for the other coils 904 and 906, for example. As shown in the simulation, the magnetic field within each coil pairs 902 and 908 is approximately uniform in both the vertical Y direction 930 and the horizontal X direction 932. In this simulation, the current density on all four coils was selected to be the same and the result is an identical field strength in horizontal 932 and vertical direction 930, for example. Of course, different current densities can be employed between coil pair 902 and coil pair 908 to allow two independent controls over bending the ion beam in both directions, as illustrated in FIG. 9b shows an exemplary illustration, in which the current density of the coil pair 902 is reduced to 50% of the current density for the other coil pair 908. As shown in the simulation, the field in the gap 914 has a larger horizontal 932 magnetic component than a vertical 930 magnetic component. Of course, those of ordinary skill in the art will recognize many modifications that may be made to this magnetic coil design configuration, without departing from the scope or spirit of the invention described herein.
FIG. 10
a is an isometric view of yet another aspect of the present invention, illustrating a cross field window frame magnet assembly system 1000. A divergent ion beam 1002 can be directed into the magnet assembly 1004, for example. The single window frame cross field magnet assembly 1004 can bend the ion beam 1002 in two directions, horizontally and also vertically, as it traverses the inside of the magnet assembly 1004. Bending the beam in the horizontal plane can result in parallelizing the divergent ion beam 1002 out of the assembly 1004. The vertical plane magnetic field can be employed to obtain mass dispersion in the vertical direction, depending upon the mass of ions within the ion beam 1002, in order to obtain better mass analysis than that currently available in ion implantation systems.
A broad ribbon beam ion implantation system with this magnetic architecture can be both shorter than conventional systems like the one shown in FIG. 1 and provides more mass resolving power than the architecture shown in FIG. 2 because the final beam 1006 has been magnetically resolved in two directions and unlike the architecture shown in FIG. 3 which requires a wide parallel-beam producing ion source, t this architecture allows to use much smaller size ions source producing a diverging beam. An alternative magnet assembly to produce the required uniform cross field is shown in FIG. 10b. The coils in FIG. 10b wrap around 4 legs of return yokes instead of being contained in the rectangular return yoke in FIGS. 9a and 10. This magnet system, like a magnet shown in FIG. 3, produces large leakage field outside of the system and suffers poor efficiency. However, it will produce the required uniform cross field within the gap. Although the exemplary magnetic assembly 1004 comprises a rectangular window frame magnet structure, other elongated general shapes are possible within the scope of the present invention, for example, ovals, cylinders, and the like. As used herein, the term general shapes include such other shapes distributed along a curvilinear path configured to provide an elongated ribbon-shaped ion beam with adequate mass resolution. It will be appreciated that magnetic coils within the scope of the present invention can include any combination of magnetic coils greater than one, configured in a single magnet assembly 1004.
In accordance with yet another aspect of the present invention, a method of mass analyzing a ribbon beam is provided, as illustrated in FIG. 11 and designated at reference numeral 1100. Although the methodology 1100 is illustrated and described hereinafter as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with one or more aspects of the present invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methodologies according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated.
The method 1100 begins at 1110 with the generation of ion plasma utilizing the plasma source within the ion beam source, for example. An ion beam is extracted at step 1120 and directed toward a window frame magnet assembly. The ion beam can be a divergent beam, a ribbon beam, and the like. At least two magnetic coils are located within the magnet assembly and they can create both a magnetic vertical and magnetic horizontal field. The at least two magnet coils can be enclosed within a housing. In one example, the ion beam is parallel resolved by a first magnetic coil within the magnetic assembly at 1130. In one example, the ion beam entering the magnet assembly can be a diverging beam, wherein the first magnetic coil bends the magnetic coil in a vertical direction.
At 1140 the ribbon beam can be mass analyzed employing a second magnetic coil within the window frame magnet assembly. The second magnetic coil can bend the ribbon beam in the horizontal plane, and thus further mass analyze the ribbon beam. The ribbon beam can then be directed to a workpiece at 1150. For example, one or more faraday cups or other type detection mechanism(s) may be employed to detect the ribbon beam across it width and thus ascertain uniformity associated therewith. The process ends at 1150.
Although the invention has been illustrated and described above with respect to a certain aspects and implementations, it will be appreciated that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary implementations of the invention. In this regard, it will also be recognized that the invention includes a computer-readable medium having computer-executable instructions for performing the steps of the various methods of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes”, “including”, “has”, “having”, “with” and variants thereof are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term “comprising”.
Patent Application
20080078956
