Abstract:
The present invention involves a beam energy identification system, comprising an accelerated ion beam, wherein the accelerated ion beam is scanned in a fast scan axis within a beam scanner, wherein the beam scanner is utilized to deflect the accelerated ion beam into narrow faraday cups downstream of the scanner, wherein a difference in scanner voltage or current to position the beam into the Faraday cups is utilized to calculated the energy of ion beam.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates generally to ion implantation, and particularly to systems and methods for identifying beam energy. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ion implantation is a physical process, as opposed to diffusion, which is a chemical process that is employed in semiconductor apparatus fabrication to selectively implant dopant into a semiconductor workpiece and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and the semiconductor material. For ion implantation, dopant atoms/molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and swept across a workpiece or wafer. The dopant ions physically bombard the workpiece, enter the surface and typically come to rest below the workpiece surface in the crystalline lattice structure thereof. 
         [0003]    In RF based accelerators, ions are repeatedly accelerated through multiple RF voltage driven acceleration gaps. Due to the time varying nature of RF acceleration fields and the multiple numbers of acceleration gaps (usually greater than 20) there are a large number of parameters which influence the final beam energy. Although it may not be technically impossible, “set and forget” techniques can not be used in setting up the final beam energy and fine adjustments have to be performed on the parameters to maximize beam transmission through a filter with known passband. 
         [0004]    An energy filter is used not only as a simple filter to reject unwanted portions of the energy spectrum, but also and more importantly as an energy standard to which all the acceleration parameters are tuned. In this sense, the energy filter plays the ultimate role in determining the final beam energy. However, quite often the design of the energy filter has to be compromised, mostly because of space restrictions or some other imposed conditions limiting proper functioning and as a result, precision in the final beam energy is uncertain. There have been several attempts to develop an independent measurement system of beam energy, but no particular method has been incorporated into production machines. 
         [0005]    Accordingly, suitable systems or methods for identifying beam energy are desired, that accurately measures the final beam energy. 
       SUMMARY OF THE INVENTION 
       [0006]    The following presents a simplified summary of the invention in order to provide a basic understanding of one or more 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 thereof. Rather, the primary 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. 
         [0007]    The present invention according to one or more embodiments creates a beam energy identification system utilizing a beam scanner which scans an accelerated ion beam at a frequency to create a wide uniform ion beam in one direction for uniform ion implantation on a workpiece, or a semiconductor wafer. One embodiment of this invention comprises two narrow Faraday cups placed at a distance downstream of scanner and a difference in scanner voltage (or current if the scanner is electromagnetic) to deflect the ion beam into each of the two narrow Faraday cups is used to calculate the energy of ion beam. 
         [0008]    According to yet another aspect of the invention, two narrow Faraday cups are placed downstream of a scanner after going through a beam parallelizing lens (e.g., an electromagnetic lens, called an angle corrector magnet) to parallelize the fanning-out beam exiting the scanner. Again, a measured difference in scanner voltage (or current if the scanner is electromagnetic) to deflect the ion beam into each of the two Faraday cups is used to calculate the energy of the ion beam. 
         [0009]    To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a simplified top view illustrating an ion implantation system in accordance with an aspect of the present invention; 
           [0011]      FIG. 2  is a top view illustrating an embodiment of a beam energy identification system in accordance with an aspect of the present invention; 
           [0012]      FIG. 3  is a top view illustrating yet another embodiment of a beam energy identification system in accordance with an aspect of the present invention; 
           [0013]      FIG. 4  is a functional block diagram illustrating a beam energy identification method according to yet another embodiment of the present invention; and 
           [0014]      FIG. 5  is a functional block diagram illustrating a beam energy identification method according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout. It will be appreciated by those skilled in the art that the invention is not limited to the exemplary implementations and aspects illustrated and described hereinafter. For the sake of providing a clear description of the invention, the systems and the methods will be described in connection with scanned pencil ion beam implantation. However, it is to be expressly understood that these descriptions are not intended to be self-limiting in any manner Referring now to the figures, in accordance with one exemplary aspect of the present invention,  FIG. 1  illustrates a typical hybrid parallel scan single wafer ion implantation system  100 . The implantation system  100  is also a type referred to as a post acceleration implanter, since a main accelerator  113  is placed after a mass analyzer  104  and before an energy filter  130 . Most ion implanters of this type have the energy filter  130  after the accelerator  113  to remove unwanted energy spectrum in the output of accelerator  113 . The filtered ion beam goes through a beam scanner  119  and then through an angle corrector lens  120  to convert the fanned-out beam  111  into a parallel shifted ion beam  115 . 
         [0016]    A workpiece and/or substrate  134  is moved orthogonal (shown as moving in and out of the paper) to the ion beam  115  in the hybrid scan scheme to irradiate the entire surface of the workpiece  134  uniformly. As stated above, various aspects of the present invention may be implemented in association with any type of ion implantation system, including, but not limited to the exemplary system  100  of  FIG. 1 . 
         [0017]    The exemplary hybrid parallel scan single wafer ion implantation system  100  comprises a source chamber assembly  112  which includes an ion source  102  and an extraction electrode assembly  121  to extract and accelerate ions to an intermediate energy. A mass analyzer  104  removes unwanted ion mass species; the accelerator assembly  113  accelerates the ions to a final energy. The beam scanner  119  scans a pencil beam exiting from the accelerator assembly  113  back and forth at a fast frequency into the angle corrector lens  120  to convert the fanning out scanned beam  111  from the beam scanner  119  to the parallel shifted beam  115  and the workpiece  134  which is housed in a process chamber. 
         [0018]    The accelerator assembly  113 , for example, can be RF linear particle accelerator (LINAC) in which ions are accelerated repeatedly by an RF field, or a DC accelerator, for example, a tandem electrostatic accelerator, which accelerates ions with a stationary DC high voltage. The beam scanner  119 , either electrostatically or electromagnetically scans the ion beam  110  left to right into the angle corrector lens  120 , which converts the fanning-out beam  111  into the parallel shifted ion beam  115 . The angle corrector lens  120  is most likely to be an electromagnetic magnet as shown, but there is also an electrostatic version, for example. The final parallel shifted ion beam  115  out of the angle corrector lens  120  is directed onto the workpiece  134 . 
         [0019]      FIG. 2  illustrates a beam energy identification system  200  utilized in an exemplary hybrid parallel scan single wafer ion implantation system  100  (e.g.,  FIG. 1 ), wherein a stationary pencil ion beam  202  is scanned with an electrostatic beam scanner  204  in one axis, the fast scan axis (usually greater than 100 Hz), a fanned out beam  211  can be converted to a parallel shifted beam  215  by an angle corrector lens  220 , typically an electromagnet (e.g., angle corrector magnet) and a wafer or workpiece  234  is mechanically moved orthogonal to the beam scanning axis. In this type of ion implantation system  100  the electrostatic beam scanner  204  is most often positioned after the ion beam  202  acquires full acceleration energy. The beam scanner  204  can be either electrostatic or electromagnetic, but for simplicity of discussion, it is assumed that the scanner  204  is an electrostatic scanner. For an electromagnetic scanner, the mathematical relationship is slightly more complex than for the electrostatic scanner  204  and it requires knowing the mass of the ions. 
         [0020]    For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam  202  by the electrostatic scanner  204  is a linear function of scan voltage (for an electrostatic scanner) and the inverse of beam energy. The calculation for a deflection angle (Δθ 1S ) is shown below as Equation 1. In this embodiment of the present invention the angle corrector magnet  220  is deactivated which allows the deflected beam  211 , deflected by the scanner to  25  pass through the angle corrector magnet  220  without deflection. 
         [0000]      Δθ 1S =( K   1S )(Δ V   1S )/( E/q ) (electrostatic equation)   (Eq. 1) 
         [0021]    wherein:
       Δθ 1S  is a change of deflection angle   K 1S  is a constant (of the 1st order) throughout the ranges of the beam energy (E) and scanner voltage (V 1S )   ΔV 1S  is the change in electrostatic scanner voltage   E is the beam energy   q is the charge value of the ions       
 
         [0027]    Rearranging the terms described above can be done to determine the beam energy (E), shown below as Equation 2: 
         [0000]        E =(Δθ 1S )( q )/(( K   1S )(Δ V   1S )) (electrostatic equation)   (Eq. 2) 
         [0028]    Now referring to an electromagnetic scanner  215  (as opposed to an electrostatic scanner  204 ) the change of beam deflection angle (Δθ 1M ) is shown below as Equation 3. In this embodiment of the present invention the angle corrector magnet  220  is deactivated which allows the scanner deflected beam  211  to pass through the angle corrector magnet  220  without deflection. 
         [0000]      Δθ 1M =( K   1M )( q )(Δ B   1M) /(sqrt( Em )) (electromag. eq.)   (Eq. 3) 
         [0029]    wherein:
       Δθ 1M  is the change of beam deflection angle;   K 1M  is constant (of the 1st order) throughout the ranges of the beam energy (E) and a magnetic field in the electromagnetic scanner;   ΔB 1M  is the change in the electromagnetic scanner magnetic field;   E is the beam energy;   q is the charge value of the ions; and   m is the mass of ions.       
 
         [0036]    Rearranging terms to determine the beam energy (E) is shown below as Equation 4: 
         [0000]        E =( K   1M   ΔB   1M    q Δθ   1M ) 2   /m  (electromag. eq.)   (Eq. 4) 
         [0037]    Yet another embodiment of the present invention is an ion beam energy identification system  300 ; depicted in  FIG. 3  that can also be used in a hybrid scan single wafer ion implantation system  100 . In this kind of system a beam scanner is most often situated after the ion beam  302  acquires full acceleration energy. The primary angle of deflection of the ion beam  202  by the scanner  204  is a linear function shown as Equation 5 that adds an additional correction factor f 1M . 
         [0038]    The system  300  can be utilized in an exemplary hybrid parallel scan single wafer ion implantation system  100  (e.g.,  FIG. 1 ), wherein a stationary pencil ion beam  302  is scanned (usually at a frequency greater than 100 Hz) with an electrostatic beam scanner  304  in one axis. In the fast scan axis, a fanned out beam  311  is converted to a parallel shifted beam  315  by activating an angle corrector lens  320 , typically an electromagnet (e.g., angle corrector magnet) and a wafer or workpiece  334  is mechanically moved orthogonal to the beam scanning axis. In this type of ion implantation system the beam scanner  304  is most often positioned after the ion beam  302  acquires full acceleration energy. The beam scanner  304  can be either electrostatic or electromagnetic, but for simplicity of discussion, it is first assumed that the scanner  304  is an electrostatic scanner. For an electromagnetic scanner as discussed supra, the mathematical relationship is slightly more complex than for an electrostatic scanner and it requires knowing the mass of the ions. 
         [0039]    For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam  302  by the electrostatic scanner  304  is a linear function of scan voltage (for an electrostatic scanner) and the inverse of the ion beam energy. The calculation for the shift of beam position (Δθ 2S ) is shown below as Equation 5. In this embodiment of the present invention the angle corrector magnet  220  is activated which allows the fanned out beam  211  to be converted into a parallel ion beam  315  as illustrated in  FIG. 3 . 
         [0000]      Δθ 2S =( f   2S )( k   2S )(Δ V   2S )/( E/q )   (Eq. 5) 
         [0040]    wherein:
       Δθ 2S  is the shift of beam position;   f 2S  is a correction factor to account for effect of corrector magnet;   K 2S  is approximately constant throughout ranges of the beam energy and electrostatic scanner voltage;   ΔV 2S  the change in electrostatic scanner voltage;   E the beam energy; and   q is the charge value of the ions.       
 
         [0047]    Rearranging terms: 
         [0000]        E =(Δθ 2S )( q )/(( f   2S )( k   2S )(ΔV 2S ))   (Eq. 6) 
         [0048]    Now referring to another embodiment of the present invention is an electromagnetic scanner  315  (as opposed to the electrostatic scanner  204 ) the shift of beam position (Δθ 2M ) is shown below as Equation 7. In this embodiment of the present invention the angle corrector magnet  320  is activated which allows the deflected beam by the scanner  311  to pass through the angle corrector magnet  320  and to be deflected into a parallel ion beam  315 . 
         [0000]      Δθ 2M =( f   2M )( k   2M ) q (Δ B   2M )/sqrt( Em )   (Eq. 7) 
         [0049]    wherein:
       Δθ 2M  is the shift of beam position;   f 2M  is a correction factor to account for effect of corrector magnet;   K 2M  is approximately constant throughout ranges of the beam energy and electromagnetic scanner current;   ΔB 2M  the change in magnetic field in the electromagnetic scanner;   E the beam energy;   m is the mass of ions; and   q is the charge value of the ions.       
 
         [0057]    Rearranging terms: 
         [0000]        E =( q K   2M    f   2M    ΔB   2M  Δθ 2M ) 2   /m    (Eq. 8) 
         [0058]      FIG. 4  illustrates an exemplary method of beam energy identification  400  that will be described in detail with respect to  FIG. 2 . Although the methodology  400  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. 
         [0059]    The method  400  begins at  404  with generating an ion beam  202  and scanning the ion beam  202  in a fast scan axis with an ion beam scanner  204  (e.g.,  FIG. 2 ), for example. The ion beam  202  ( FIG. 2 ) is extracted at  404  and scanned at a frequency of greater than 100 Hz. The ion beam  202  in this example is a pencil ion beam; however potential ion beams can be a divergent beam, a ribbon beam, and the like. The ion beam scanner  204  can be an electrostatic ion beam scanner  215  ( FIG. 2 ) or an electromagnetic ion beam scanner  217 . 
         [0060]    Two or more Faraday cups and/or other type detection mechanism(s) and/or sensors can be employed to detect a deflected ion beam  211  ( FIG. 2 ) and thus ascertain the ion beam energy associated therewith. At  406  a first Faraday cup  216  is located to capture a first deflected ion beam peak  211   a  and a second Faraday cup  218  is located to capture a second deflected ion beam peak  211   b.  It is determined at  408  if the scanner is an electrostatic scanner  215  or an electromagnetic scanner  217 . If the scanner is the electrostatic scanner  215  the voltage is varied to obtain peak of a first deflected ion beam  211   a  ( FIG. 2 ) in the first Faraday cup  216  ( FIG. 2 ) and a second deflected ion beam peak  211   b  ( FIG. 2 ) in the second Faraday cup  218  ( FIG. 2 ). An angle corrector magnet  220  ( FIG. 2 ) is deactivated so that the deflected ion beam  211  by the scanner travels to the Faraday cups  216  and  218  un-deflected. The beam energy (E) is calculated at  414  ( FIG. 4 ) utilizing the change in voltage. Referring to the equation derived previously as Eq. 2. 
         [0000]        E =(Δθ 1S )( q )/(( K   1S )(Δ V   1S )) (electrostatic equation)   (Eq. 2) 
         [0061]    wherein:
       Δθ 1S  is an shift of beam angle;   K 1S  is a constant (of the 1st order) throughout the ranges of beam energy (E 1S ) and scanner voltage (V 1S );   ΔV 1S  is the change in electrostatic scanner voltage;   E is the beam energy; and   q is the charge value of the ions.       
 
         [0067]    If it is determined at  408  that the scanner is the electromagnetic scanner  217  the current is varied to obtain the peak of a first deflected ion beam peak  211   a  ( FIG. 2 ) in the first Faraday cup  216  ( FIG. 2 ) and a second deflected ion beam peak  211   b  ( FIG. 2 ) in the second Faraday cup  218  ( FIG. 2 ). The angle corrector magnet  220  ( FIG. 2 ) is deactivated so that the deflected ion beam  211  by the scanner travels to the cups  216  and  218  un-deflected. The beam energy (E) is calculated utilizing the change in magnetic field in the scanner at  25   414 . Referring to the equation derived previously as Eq. 4. 
         [0000]        E =( K   1M    ΔB   1M    q Δθ   1M ) 2   /m    (Eq. 4) 
         [0068]    wherein:
       Δθ 1M  is shift of beam angle;   K 1M  is a constant (of the 1st order) throughout the ranges of the beam energy (E) and scanner current;   ΔB 1M  is the change in the magnetic field in electromagnetic scanner;   E is the beam energy   m is the mass of ions; and   q is the charge value of the ions.       
 
         [0075]      FIG. 5  illustrates yet another exemplary method for beam energy identification  500  that will be described in detail with respect to  FIG. 3 . Although the methodology  500  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. 
         [0076]    The method  500  begins at  504  with generating an ion beam  302  and scanning the ion beam  302  in a fast scan axis with an ion beam scanner  304  (e.g.,  FIG. 3 ), for example. The ion beam  302  ( FIG. 3 ) is extracted at  504  and scanned at a frequency of greater than 100 Hz. The ion beam  302  in this example is a pencil ion beam; however potential ion beams can be a divergent beam, a ribbon beam, and the like. The ion beam scanner  304  can be an electrostatic ion beam scanner  315  ( FIG. 3 ) or an electromagnetic ion beam scanner  317 . 
         [0077]    Two or more Faraday cups and/or other type detection mechanism(s) and/or sensors can be employed to detect a parallel ion beamlets created from the parallel ion beam  315  ( FIG. 3 ) and thus ascertain the ion beam energy associated therewith. At  506  a first faraday cup  322  is located to capture a first parallel ion beam peak  315   a  and a second faraday cup  324  is located to capture a second parallel ion beam peak  315   b.  It is determined at  508  if the scanner  304  is an electrostatic scanner  313  or an electromagnetic scanner  317 . If the scanner  304  is an electrostatic scanner  313  the voltage is varied to obtain a first parallel ion beam peak  315   a  ( FIG. 3 ) in the first Faraday cup  322  ( FIG. 3 ) and a second parallel ion beam peak  315   b  ( FIG. 3 ) in the second Faraday cup  324  ( FIG. 3 ). An angle corrector magnet  320  ( FIG. 3 ) is activated so that the parallel ion beam  315  travels to the cups  322  and  324 . The ion beam energy (E) is calculated at  514  ( FIG. 5 ) utilizing the change in scanner voltage. Referring to the equation derived previously as Eq. 6. 
         [0000]        E =(Δθ 2S )( q )/(( f   2S )( k   2S )(Δ V   2S )) (electrostatic equation)   (Eq. 6) 
         [0078]    wherein:
       Δθ 2S  is the second electrostatic shift of beam position;   f 2S  is a correction factor to account for effect of corrector magnet;   K 2S  is approximately constant throughout ranges of the second electrostatic beam energy 2and electrostatic scanner voltage;   ΔV 2S  the second change in electrostatic scanner voltage;   E the beam energy; and   q is the charge value of the ions.       
 
         [0085]    Wherein, the method  500  ends if the scanner was the electrostatic scanner  313 . 
         [0086]    If it is determined at  508  that the scanner  304  ( FIG. 3 ) is an electromagnetic scanner  317  the current is varied to obtain a parallel ion beam peak  315   a  ( FIG. 3 ) in the first Faraday cup  322  ( FIG. 3 ) and a second parallel ion beam peak  315   b  ( FIG. 3 ) in the second Faraday cup  324  ( FIG. 3 ). The angle corrector magnet  320  ( FIG. 3 ) is activated so that the parallel ion beam  315  travels to the cups  322  and  324 . The beam energy (E) is calculated utilizing the change in current at  514 . Referring to the equation derived previously as Eq. 8. 
         [0000]        E =( K   2M    ΔB   2M    q Δθ   2M ) 2   /m  (electromagnetic equation)   (Eq. 8) 
         [0087]    wherein:
       Δθ 2M  is the shift of beam position;   K 2M  is a constant (of the 1st order) throughout the ranges of a beam energy (E) and scanner current;   ΔB 2M  is the change in a magnetic field of the electromagnetic scanner;   E is a beam energy; and   q is a charge value of the ions.       
 
         [0093]    Wherein, the method  500  ends if the scanner is an electromagnetic scanner  317 . 
         [0094]    Although the invention has been illustrated and described with respect to one or more implementations, 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, apparatus, 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 (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. 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.”