Abstract:
A technique for providing a segmented electrostatic lens in an ion implanter is disclosed. In one particular exemplary embodiment, the technique may be realized as an electrostatic lens for use in an ion implanter. The lens may comprise an entrance electrode biased at a first voltage potential, wherein an ion beam enters the electrostatic lens through the entrance electrode. The lens may also comprise an exit electrode biased at a second voltage potential, wherein the ion beam exits the electrostatic lens through the exit electrode. The lens may further comprise a suppression electrode located between the entrance electrode and the exit electrode, the suppression electrode comprising a plurality of segments that are independently biased to manipulate an energy and a shape of the ion beam.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This patent application claims priority to U.S. Provisional Patent Application No. 60/736,293, filed Nov. 15, 2005, which is hereby incorporated by reference herein in its entirety. 

   FIELD OF THE DISCLOSURE 
   The present disclosure relates generally to ion implantation and, more particularly, to a technique for providing a segmented electrostatic lens in an ion implanter. 
   BACKGROUND OF THE DISCLOSURE 
   Ion implanters are widely used in semiconductor manufacturing to selectively alter conductivity of materials. In a typical ion implanter, ions generated from an ion source are directed through a series of beam-line components which include one or more analyzing magnets and a plurality of electrodes. The analyzing magnets select desired ion species, filter out contaminant species and ions having incorrect energies, also adjusting ion beam quality at a target wafer. Suitably shaped electrodes can be used to modify the energy and the shape of the ion beam. 
     FIG. 1  shows a known ion implanter  100  which comprises an ion source  102 , extraction electrodes  104 , a 90° magnet analyzer  106 , a first deceleration (D 1 ) stage  108 , a 70° magnet analyzer  110 , and a second deceleration (D 2 ) stage  112 . The D 1  and D 2  deceleration stages (also known as “deceleration lenses”) are each comprised of multiple electrodes with a defined aperture to allow an ion beam to pass therethrough. By applying different combinations of voltage potentials to the multiple electrodes, the D 1  and D 2  deceleration lenses can manipulate ion energies and cause the ion beam to hit a target wafer at a desired energy. 
   The above-mentioned D 1  or D 2  deceleration lenses are typically electrostatic triode (or tetrode) deceleration lenses.  FIG. 2  shows a perspective view of a conventional electrostatic triode deceleration lens  200 . The electrostatic triode deceleration lens  200  comprises three sets of electrodes: entrance electrodes  202  (also referred to as “terminal electrodes”), suppression electrodes  204  (or “focusing electrodes”), and exit electrodes  206  (also referred to as “ground electrodes” though not necessarily connected to earth ground). A conventional electrostatic tetrode deceleration lens is similar to the electrostatic triode deceleration lens  200 , except that a tetrode lens has an additional set of suppression electrodes (or focusing electrodes) between the suppression electrodes  204  and the exit electrodes  206 . 
   In the electrostatic triode deceleration lens  200 , each set of electrodes may have a space to allow an ion beam  20  to pass therethrough (e.g., in the +z direction along the beam direction). As shown in  FIG. 2 , each set of electrodes may include two conductive pieces electrically coupled to each other to share a same voltage potential. Alternatively, each set of electrodes may be a one-piece structure with an aperture for the ion beam  20  to pass therethrough. As such, each set of electrodes are effectively a single electrode having a single voltage potential. For simplicity, each set of electrodes are referred to in singular. That is, the entrance electrodes  202  are referred to as an “entrance electrode  202 ,” the suppression electrodes  204  are referred to as a “suppression electrode  204 ,” and the exit electrodes  206  are referred to as an “exit electrode  206 .” 
   In operation, the entrance electrode  202 , the suppression electrode  204 , and the exit electrode  206  are independently biased such that the energy of the ion beam  20  is manipulated in the following fashion. The ion beam  20  may enter the electrostatic triode deceleration lens  200  through the entrance electrode  202  and may have an initial energy of, for example, 10-20 keV. Ions in the ion beam  20  may be accelerated between the entrance electrode  202  and the suppression electrode  204 . Upon reaching the suppression electrode  204 , the ion beam  20  may have an energy of, for example, approximately 30 keV or higher. Between the suppression electrode  204  and the exit electrode  206 , the ions in the ion beam  20  may be decelerated, typically to an energy that is closer to the one used for ion implantation of a target wafer. Therefore, the ion beam  20  may have an energy of, for example, approximately 3-5 keV or lower when it exits the electrostatic triode deceleration lens  200 . 
   The significant changes in ion energies that take place in the electrostatic triode deceleration lens  200  can have a substantial impact on a shape of the ion beam  20 .  FIG. 3  shows a top view of the electrostatic triode deceleration lens  200 . As is well known, space charge effects are more significant in low-energy ion beams than in high-energy ion beams. Therefore, as the ion beam  20  is accelerated between the entrance electrode  202  and the suppression electrode  204 , little change is observed in the shape of the ion beam  20 . However, when the ion energy is drastically reduced between the suppression electrode  204  and the exit electrode  206 , the ion beam  20  tends to expand in both X and Y dimensions at its edges. As a result, a considerable number of ions may be lost before they reach the target wafer, and the effective dose of the ion beam  20  is reduced. 
   There have been attempts to reduce the above-described space charge effect in an electrostatic triode lens. In one approach, for example, Pierce geometry, well known to those skilled in the art, is introduced to each electrode in the electrostatic triode deceleration lens. That is, each electrode is bent at its tip to a defined angle such that electric fields inside the electrostatic triode lens are such that they generate focusing forces counteracting the space charge spreading effects at the edge of an ion beam. However, this approach can only achieve a limited success in controlling ion beam shapes. Despite a changed shape, each electrode still remains one conductive piece biased with a single voltage potential. As a result, generation of the focusing forces at the edge of the ion beam is constrained by the overall voltage potential applied to the electrode. In addition, one particular shape of an electrode may be useful for adjustment of only one particular beam shape or the purveyance of the ion beam. 
   In view of the foregoing, it would be desirable to provide a technique for providing an electrostatic lens which overcomes the above-described inadequacies and shortcomings. 
   SUMMARY OF THE DISCLOSURE 
   A technique for providing a segmented electrostatic lens in an ion implanter is disclosed. In one particular exemplary embodiment, the technique may be realized as an electrostatic lens for use in an ion implanter. The lens may comprise an entrance electrode biased at a first voltage potential, wherein an ion beam enters the electrostatic lens through the entrance electrode. The lens may also comprise an exit electrode biased at a second voltage potential, wherein the ion beam exits the electrostatic lens through the exit electrode. The lens may further comprise a suppression electrode located between the entrance electrode and the exit electrode, the suppression electrode comprising a plurality of segments that are independently biased to manipulate an energy and a shape of the ion beam. 
   In accordance with other aspects of this particular exemplary embodiment, a first set of electrostatic fields may be created between the suppression electrode and the entrance electrode, the first set of electrostatic fields accelerating the ion beam to a first electrical potential. A second set of electrostatic fields may be created between the suppression electrode and the exit electrode, the second set of electrostatic fields decelerating the ion beam to a second electrical potential. According to one embodiment, the entrance electrode, the exit electrode, and the suppression electrode may be configured and biased to provide a first (or a second) stage of deceleration for a ribbon-shaped ion beam in the ion implanter. 
   In accordance with further aspects of this particular exemplary embodiment, the plurality of segments may comprise at least one center electrode and at least two side electrodes. The at least one center electrode may be biased to manipulate the energy of the ion beam, and the at least two side electrodes may be biased independently from the at least one center electrode to correct a divergence of the ion beam. The at least two side electrodes may be biased to offset a space-charge effect near edges of the ion beam. The at least two side electrodes may be disposed symmetrically with respect to the at least one center electrode. The at least two side electrodes may also be symmetrically biased. 
   In accordance with additional aspects of this particular exemplary embodiment, the plurality of segments may comprise at least one center electrode and two or more end electrodes that shield out external electrostatic fields. 
   In accordance with a further aspect of this particular exemplary embodiment, the ion beam may be a ribbon-shaped ion beam, and the electrostatic lens may be adapted to accommodate the ribbon-shaped ion beam. 
   In accordance with a yet further aspect of this particular exemplary embodiment, at least one electrode in the electrostatic lens may have a curved edge that further alters electric fields inside the electrostatic lens. 
   In accordance with a still further aspect of this particular exemplary embodiment, the suppression electrode may comprise one center electrode and two side electrodes that are disposed symmetrically on each side of the center electrode. Alternatively, the suppression electrode may comprise one center electrode and two side electrodes that are disposed asymmetrically on each side of the center electrode. 
   The electrostatic lens may further comprise an additional suppression electrode between the suppression electrode and the exit electrode. 
   In another particular exemplary embodiment, the technique may be realized as a method for providing an electrostatic lens for use in an ion implanter. The method may comprise providing an entrance electrode biased at a first voltage potential. The method may also comprise providing an exit electrode and biased at a second voltage potential. The method may further comprise providing a suppression electrode located between the entrance electrode and the exit electrode, the suppression electrode comprising a plurality of segments. The method may additionally comprise independently biasing the plurality of segments in the suppression electrode to create electric fields that manipulate an energy and a shape of an ion beam that enters the electrostatic lens through the entrance electrode and exits the electrostatic lens through the exit electrode. 
   In accordance with other aspects of this particular exemplary embodiment, the electric fields may manipulate an angular shape of an envelope of the ion beam. 
   In accordance with further aspects of this particular exemplary embodiment, the plurality of segments may comprise at least one center electrode and at least two side electrodes. The at least one center electrode may be biased to manipulate the energy of the ion beam, and the at least two side electrodes may be biased independently from the at least one center electrode to correct a divergence of the ion beam. The method may further comprise biasing the at least two side electrodes to offset a space-charge effect near edges of the ion beam. The method may also comprise positioning and biasing the at least two side electrodes symmetrically with respect to the at least one center electrode. 
   In accordance with additional aspects of this particular exemplary embodiment, the method may further comprise providing an additional suppression electrode between the suppression electrode and the exit electrode. 
   The present disclosure will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present disclosure is described below with reference to exemplary embodiments, it should be understood that the present disclosure is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein, and with respect to which the present disclosure may be of significant utility. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only. 
       FIG. 1  shows a conventional ion implanter. 
       FIGS. 2 and 3  show a conventional electrostatic triode lens and illustrate a problem therein. 
       FIG. 4  shows a perspective view of an electrostatic triode lens in accordance with an embodiment of the present disclosure. 
       FIG. 5  shows a top view of an electrostatic lens in accordance with an embodiment of the present disclosure. 
       FIG. 6  shows a top view of another electrostatic lens in accordance with an embodiment of the present disclosure. 
       FIG. 7  shows a perspective view of yet another electrostatic lens in accordance with an embodiment of the present disclosure. 
       FIG. 8  shows a perspective view of still another electrostatic lens in accordance with an embodiment of the present disclosure. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Embodiments of the present disclosure illustrate an improved type of electrostatic lens that has one or more segmented suppression electrodes. These electrodes may comprise multiple segments that are independently or separately biased with respect to one another thereby providing flexible and effective manipulation of an ion beam&#39;s shape as well as its energy. 
   Referring to  FIG. 4 , there is shown a perspective view of an electrostatic lens  400  in accordance with an embodiment of the present disclosure. Somewhat similar to a conventional electrostatic triode lens, the electrostatic lens  400  may comprise an entrance electrode  402  and an exit electrode  406 . Instead of a single suppression electrode, however, the electrostatic lens  400  may comprise a plurality of electrodes (collectively referred to as “suppression electrode  404 ”) between the entrance electrode  402  and the exit electrode  406 . In other words, what used to be a single suppression electrode may be segmented into multiple electrodes (or segments) that may be independently positioned and biased to create desired electric fields in the electrostatic lens  400 . In the exemplary electrostatic lens  400 , the suppression electrode  404  is segmented into or comprises three electrodes: a center electrode  404   a , and two side electrodes  404   b  and  404   c . The side electrodes  404   b  and  404   c  may be symmetrically positioned with respect to the center electrode  404   a . Depending on a shape of an incoming ion beam and a desired shape change, gap  403  between the entrance electrode  402  and the suppression electrode  404  may have a contour with defined curvature(s). Similarly, gap  405  between the suppression electrode  404  and the exit electrode  406  may also have a contour with defined curvature(s). 
     FIG. 5  shows a top view of the electrostatic lens  400  in accordance with an embodiment of the present disclosure. An ion beam  40  may enter the electrostatic lens  400  through the entrance electrode  402 . The ion beam  40  may be a ribbon-shaped ion beam that is wider in an x-direction than its height in a y-direction. The ion beam  40  may have an initial energy of, for example, approximately 10-20 keV. Assuming the ion beam  40  mainly consists of positive ions, the entrance electrode  402  may be biased at a same or similar potential as the incoming ion beam  40 , and the center electrode  404   a  of the segmented suppression electrode  404  may be biased at a much lower potential than the entrance electrode  402 . For example, according to one embodiment, the entrance electrode  402  may be biased at 22 kV and the center electrode  404   a  may be biased at −11 kV. As a result, a strong electric field may be created to accelerate the positive ions as they travel from the entrance electrode  402  towards the suppression electrode  404 . The exit electrode  406  may be biased at a potential that is the same as or similar to a potential of a target wafer which receives the ion beam  40 . In this embodiment, for example, the exit electrode  406  may be biased at ground potential, which decelerates the ions  40  to an energy of approximately 3-5 keV or lower. In another embodiment, the entrance electrode  402  may be biased at −12 kV, the center electrode  404   a  of the segmented suppression electrode  404  may be biased at −2 kV, and the exit electrode  406  may be biased at ground potential. As a result, an ion beam  40  with an initial energy of approximately 15 keV may be decelerated to approximately 3 keV upon exiting the deceleration lens  400 . In addition, the side electrodes  404   b  and  404   c  may be positioned and/or biased independently from the center electrode  404   a  to provide a desired correction to a shape of the ion beam  40 . Depending on the specific usage in an ion implanter (e.g., either as D 1  or as D 2  deceleration lens shown in  FIG. 1 ), the electrostatic lens  400  may be configured to, for example, adjust a divergence angle of the ion beam  40 , or change a width of the ion beam  40 , or do both. The side electrodes  404   b  and  404   c  may be positioned and biased accordingly. In this embodiment, a main purpose of the electrostatic lens  400  is to reduce the divergence angle for the ion beam  40 . Therefore, the side electrodes  404   b  and  404   c  are disposed in the same plane as the center electrode  404   a  and are positioned symmetrically with respect to the center electrode  404   a . Both the side electrodes  404   b  and  404   c  are biased at −8.5 kV, which creates focusing forces along edges of the ion beam  40  to compensate for a defocusing effect of space charges. As a result, the ion beam  40  may have a small divergence or none at all after being decelerated between the suppression electrode  404  and the exit electrode  406 . In addition, curvatures of the electrodes may further tailor electric fields (e.g., in the gaps  403  and  405 ) to produce focusing or defocusing forces as desired. 
   It should be noted that, for illustration purposes, the upper and lower pieces in each electrode of the electrostatic lens  400  are treated as sharing a same shape and bias. However, this is only necessary when an ion beam is symmetric or non-diverging in the y-direction. It is contemplated that the electrostatic lens technique described herein may be applied in the y-direction as well as in the x-direction. In addition, either or both suppression electrodes in an electrostatic tetrode lens may be segmented as described herein. 
     FIG. 6  shows a top view of an electrostatic lens  600  in accordance with an embodiment of the present disclosure. The electrostatic lens  600  may comprise an entrance electrode  602 , a suppression electrode  604 , and an exit electrode  606 . Here, the suppression electrode  604  may comprise five segments: a center electrode  604   a , and four side electrodes  604   b ,  604   c ,  604   d , and  604   e . The side electrodes may be in a same plane as the center electrode  604   a . The side electrodes  604   b  and  604   c  may be positioned symmetrically with respect to the center electrode  604   a . Similarly, the side electrodes  604   d  and  604   e  may be positioned symmetrically with respect to the center electrode  604   a . The center electrode  604   a  may be biased with respect to the entrance electrode  602  to accelerate an incoming ion beam  60 , and with respect to the exit electrode  606  to decelerate the ion beam  60 . According to one embodiment, the side electrodes  604   b  and  604   c  may share a first voltage potential that is independent from the voltage potential on the center electrode  604   a . Similarly, the side electrodes  604   d  and  604   e  may share a second voltage potential that is independent from the first voltage potential or the voltage potential on the center electrode  604   a.    
   In both the 3-segment configuration, as shown in  FIGS. 4 and 5 , and the 5-segment configuration as shown in  FIG. 6 , actual voltage potentials applied to the independently biased electrodes may be either computationally determined based on mathematical models, or experimentally determined based on iterative adjustment of biasing voltages and measurement of angle response function(s). Alternatively, the computational and experimental methods may be combined in determining the biasing voltages. According to one embodiment, it may be desirable to keep the number of segments in the suppression electrode down in order to save computation time or tuning time. 
     FIG. 7  shows a perspective view of an electrostatic lens  700  in accordance with an embodiment of the present disclosure. The electrostatic lens  700  may comprise an entrance electrode  702 , a suppression electrode  704 , and an exit electrode  706 . The suppression electrode  704  may comprise center electrodes  704   a  and end electrodes  704   b . The center electrodes  704   a  may be biased at a first voltage potential while the end electrodes  704   b  may be biased at a second voltage potential. According to one embodiment, this configuration may be used in a D 2  deceleration lens such as the one shown in  FIG. 1 . At the D 2  deceleration lens, an ion beam may be wider and taller than when it is at the D 1  deceleration lens. It may be desirable to adjust both the width and divergence angle of the ion beam. The properly biased end electrodes  704   b  may provide the focusing forces needed to reduce the width and divergence angle of the ion beam. In addition, the end electrodes  704   b  may shield out unwanted electromagnetic interferences. 
     FIG. 8  shows a perspective view of an electrostatic lens  800  in accordance with an embodiment of the present disclosure. The electrostatic lens  800  may comprise an entrance electrode  802 , a suppression electrode  804 , and an exit electrode  806 . The suppression electrode  804  may comprise center electrodes  804   a , side electrodes  804   b  and  804   c , and end electrodes  804   d . Compared with the electrostatic lens  700 , the electrostatic lens  800  have the additional side electrodes  804   b  and  804   c  and therefore may provide more capability to shape electric fields. On the other hand, the additional side electrodes  804   b  and  804   c  may also mean additional variables to deal with. 
   The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.