Abstract:
One embodiment relates to an ion implanter. The ion implanter includes an ion source to generate an ion beam, as well as a scanner to scan the ion beam across a surface of a workpiece along a first axis. The ion implanter also includes a deflection filter downstream of the scanner to ditheredly scan the ion beam across the surface of the workpiece along a second axis.

Description:
BACKGROUND 
     In ion implantation systems, an ion beam is directed towards a work piece (e.g., a semiconductor wafer, or a display panel) to implant ions into a lattice thereof. Once embedded into the lattice of the workpiece, the implanted ions change the physical and/or chemical properties of the implanted workpiece region. Because of this, ion implantation can be used in semiconductor device fabrication, in metal finishing, and for various applications in materials science research. 
     An ion beam often has a cross-sectional area that is significantly smaller than the surface area of a workpiece to be implanted. Because of this, typical ion beams are scanned over the surface of the workpiece until a desired doping profile is achieved in the workpiece. For example,  FIG. 1A  shows a cross-sectional view of a conventional ion implantation system  100  where an ion beam  102  traces over a scan path  104  to implant ions into the lattice of a workpiece  106 . While scanning the ion beam over the scan path  104 , the ion implanter makes use of a first axis  108  and a second axis  110  that collectively facilitate two-dimensional scanning over the workpiece surface. In this system  100  there are sufficient scans per unit time over the first axis  108  (e.g., fast axis) to ensure that small features (e.g., small feature  150  in  FIG. 1B ) on the second axis  110  (e.g., slow axis) are adequately scanned over the entire workpiece. However, when the fast scan speed is slowed to approach the slow scan speed, it is difficult to ensure dose uniformity when very sharp features are present in the beam profile (e.g., small feature  150 ). 
     Therefore, aspects of the present disclosure relates to techniques for improving beam uniformity using a scanned ion beam. 
     SUMMARY 
     The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. Rather, the purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. 
     One embodiment relates to an ion implanter. The ion implanter includes an ion source to generate an ion beam, as well as a scanner to scan the ion beam across a surface of a workpiece along a first axis. The ion implanter also includes a deflection filter downstream of the scanner to reduce energy contamination and dither the ion beam across the surface of the workpiece along a second axis. 
     The following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a conventional ion scanning technique. 
         FIG. 1B  illustrates a doping profile delivered by a conventional ion scanning technique. 
         FIG. 2  illustrates an ion scanning technique in accordance with some embodiments. 
         FIG. 3  illustrates an ion implantation system in accordance with some embodiments. 
         FIGS. 4A-4B  illustrate voltage waveforms consistent with the scanning technique of  FIG. 4C . 
         FIG. 4C  illustrates an ion scanning technique that makes use of electrical fields in accordance with some embodiments. 
         FIG. 4D  illustrates how the ion scanning technique of  FIG. 4C  works in coordinated fashion with workpiece translation to implant ions into a workpiece, in accordance with some embodiments. 
         FIG. 5  illustrates a side view of another scanned and dithered ion beam. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures are not necessarily drawn to scale. 
       FIG. 2  shows a scanning technique utilizing an improved scan path in accordance with some aspects of the disclosure. As shown, to trace a scan path  204  over a workpiece surface  206  and thereby implant ions into a workpiece, an ion beam  202  is scanned back and forth over a first axis  208  while being simultaneously and ditheredly scanned over a second axis  210 . Thus, rather than scanning the ion beam  202  over the second axis  210  at a fixed unidirectional speed (as was done in the conventional scan technique shown in  FIG. 1A ), the ion beam  202  is scanned over the second axis with a superposition of a constant speed and a small amplitude, rapid oscillation. Most typically, the scanning of the beam along the first axis  208  is done with an electric or magnetic scanner, while the workpiece is mechanically translated along the second axis  210 . However, it is also possible to have the workpiece translated along both axes  208 ,  210 , while the fast oscillation (dither) of the beam is achieved with an electric or magnetic beam scanner. Thus “dither” in this context can refer to the manner in which predetermined, random, or pseudo-random perturbations are used to prevent large-scale patterns such as “banding” or “striping” in the doping profile, which can be objectionable. Sharp features (e.g. sharp feature  150  in  FIG. 1B ) can cause striping and dithering effectively blurs these features, making them less sharp, and thus less detrimental to the uniformity of the implanted doping profile. 
       FIG. 3  illustrates one embodiment of an ion implantation system  300  operable to carry out scanning techniques in accordance with some aspects of the invention. The ion implantation system  300  includes a source terminal  302 , a beamline assembly  304 , a scan system  306 , and an end station  308 , which are collectively arranged so as to inject ions (dopants) into the lattice of a workpiece  310  according to a desired dosing profile. 
     More particularly, during operation, an ion source  316  in the source terminal  302  is coupled to a high voltage power supply  318  to ionize dopant molecules (e.g., dopant gas molecules), thereby forming a pencil ion beam  320 . 
     To steer the pencil beam  320  from the source terminal  302  towards the workpiece  310 , the beamline assembly  304  has a mass analyzer  322  in which a dipole magnetic field is established to pass only ions of appropriate charge-to-mass ratio through a resolving aperture  324 . Ions having an inappropriate charge-to-mass ratio collide with the sidewalls  326   a,    326   b;  thereby leaving only the ions having the appropriate charge-to-mass ratio to pass though the resolving aperture  324  and into the workpiece  310 . The beam line assembly  304  may also include various beam forming and shaping structures extending between the ion source  316  and the end station  308 , which maintain the pencil beam  320  in an elongated interior cavity or passageway through which the pencil beam  320  is transported to the workpiece  310 . A vacuum pumping system  328  typically keeps the ion beam transport passageway at vacuum to reduce the probability of ions being deflected from the beam path through collisions with air molecules. 
     Upon receiving the pencil beam  320 , a scanner  330  within the scan system  306  laterally diverts or “scans” the pencil beam back and forth in time (e.g., in a horizontal direction) to provide the scanned ion beam  332 . In some contexts, this type of scanned pencil beam may be referred to as a ribbon beam. In the illustrated embodiment, the scanner  330  is an electrical scanner that includes a pair of electrodes  334   a,    334   b  arranged on opposing sides of the scanned beam  332 . A control system  336  induces a change in a variable power source  338  to provide a time-varying current or voltage on the electrodes  334   a,    334   b,  thereby inducing an oscillatory time-varying electric field in the beam path region and scanning the ion beam back and forth in time. In other embodiments, the scanner  330  can be a magnetic scanner that provides a time-varying magnetic field in the beam path region, thereby scanning the ion beam in time. In some embodiments, only a single electrode (rather than a pair of electrodes) can be used. 
     A parallelizer  340  in the scan system can redirect the scanned ion beam  332  so that the ion beam strikes a surface of the workpiece  310  at the same angle of incidence over the entire surface of the workpiece. 
     A deflection filter  342 , which is controlled by control system  336  and powered by a variable power source  344 , diverts the parallelized scanned ion beam along a second axis that can be perpendicular to the first axis. For example, in  FIG. 3 , the second axis could extend into the plane of the page or out of the plane of the page. The deflection filter  342  can impart a time-independent deflection and a time-dependent “dithered” deflection. Because the deflection filter  342  is downstream of the parallelizer  340  the working gaps of the corrector and deflection filter  342  are limited compared to solutions where a scanner is used to scan the ion beam in two dimensions before the correctors. This helps to reduce cost of the beam line by simplifying the parallelizer  340  and the deflection filter  342 . Also, because this solution limits the volume to be pumped down to vacuum, it can also in some instances improve the vacuum, which limits collisions between ions and air molecules and thus helps improve the resolution/accuracy of the beam. 
     In some embodiments, a quadrupole can be arranged between the scanner  330  and the deflection filter  342 , as shown by reference number  346  or  348  in  FIG. 3 , for example. 
       FIG. 5  shows another embodiment where scanner electrodes  502 A,  502 B scan an ion beam back and forth, and deflection filter electrodes  504 A,  504 B deflect the beam and also introduce dither to the scanned ion beam. Voltages on the electrodes  502 A,  502 B,  504 A,  504 B change the beam trajectory so that the scanned beam passes through the center of beam resolving slits  506  downstream of the scanner. 
       FIG. 4A  shows an example of a first scan voltage  402  that can be applied to the scanner electrodes (e.g.,  334   a,    334   b  in  FIG. 3 ), while  FIG. 4B  shows a second scan voltage  404  that can be applied to the deflection filter electrodes. In some systems the steady relative motion in the slow scan direction  262  is from mechanically moving the workpiece, while in other systems, these scan voltages can collectively trace the ion beam over the scan path illustrated in  FIG. 4C . In some systems, the first scan voltage  402  scans the ion beam  202  back and forth on the first axis in time (e.g., between points A and G in  FIG. 4C ), while the second scan voltage  404  can introduce dither (e.g., vertical displacement in  FIG. 4C ). As shown in  FIG. 4D , when a workpiece  310  is translated  500  along a second axis (e.g., top edge of workpiece  310  moves from point □ to point □ in  FIG. 4D ) and the first and second scan voltages are concurrently applied to the beam, the ion beam effectively traces over a 2-dimensional scan path that covers the surface of the workpiece. 
     Although  FIG. 4A-4B  depict voltages that establish a time-varying electrical field to scan the beam, it will be appreciated that a time-varying magnetic field could also be used in other embodiments. In some embodiments, the scanner can use a time-varying electric field and the deflection filter can use a time-varying magnetic field, or vice versa. 
     Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, different types of end stations  108  may be employed in the ion implantation system  300 . In some embodiments, a “batch” type end station can simultaneously support multiple workpieces on a rotating support structure, wherein the workpieces are rotated through the path of the ion beam until all the workpieces are completely implanted. A “serial” type end station, on the other hand, can be used in other embodiments. Serial type end stations support a single workpiece along the beam path for implantation, wherein multiple workpieces are implanted one at a time in serial fashion, with each workpiece being completely implanted before implantation of the next workpiece begins. Further, although  FIG. 3  illustrated a ion implantation system where the beam was electrically or magnetically scanned in a first (X or fast scan) direction while the workpiece is mechanically scanned in a second (Y or slow scan) direction to impart the scanned ion beam over the entire workpiece; other systems could mechanically scan the ion beam along two different axes rather than using electrical or magnetic translation. 
     In particular regard to the various functions performed by the above described components or structures (blocks, units, engines, 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 or structure which performs the specified function of the described component (e.g., 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 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. The term “exemplary” as used herein is intended to imply an example, as opposed to best or superior. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.