Abstract:
A method of achieving ion beam uniformity control using ion beam blockers. The method includes generating an ion beam, detecting a current profile of said ion beam with an ion beam blocker unit, wherein said detected current profile is an initial current profile, blocking a portion of said ion beam with said ion beam blocker unit to achieve a second current profile that is different from the initial current profile, and implanting said ion beam into a workpiece after said blocking.

Description:
FIELD OF THE DISCLOSURE 
     This invention relates to ion implantation and, more particularly, to an apparatus and method for improving the uniformity of an ion beam used for ion implantation. 
     BACKGROUND OF THE DISCLOSURE 
     Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity. 
     In one instance, a ribbon ion beam is used to implant the workpiece. A ribbon ion beam cross-section has a long dimension and a short dimension. The long dimension, for example, may be referred to as a width or x-direction, though other orientations are possible. The ribbon ion beam may be formed using a parallelizing lens or may be a scanned spot beam. 
     Occasionally, the ribbon ion beam may not be perfectly uniform. In the case where the ribbon beam is a scanned spot beam, non-uniformities in the ribbon are typically minimized by scanning the spot beam entirely or almost entirely off of the workpiece and by adjusting the time dependence of the scanning of the spot. However, under some circumstances, for instance when the spot beam current is large or the beam energy is small, it is common for the spot size of the ion beam to increase. The requirement of scanning the spot beam entirely or nearly entirely off the workpiece has the consequence that, for a large spot beam, relatively little beam current is utilized on the workpiece, which reduces the productivity of the implanter. The technique of minimizing non-uniformities by adjusting the time dependence of the scanning of the spot is known to be more complicated and less likely to succeed as the spot size increases. 
     Ribbon ion beam uniformity is one factor that affects implantation. Non-uniform ribbon ion beams may result in imprecise doping or implantation. For example, more heavily-doped stripes may be formed on the surface of a workpiece. An incorrect dose may cause deleterious yield effects if the devices are non-functioning due to the increased or decreased dose. Therefore, there is a need in the art for uniformity during implantation and, more particularly, uniformity during implantation on scanned spot beam implanters. It is with respect to these and other considerations that the present improvements have been needed. 
     SUMMARY 
     An exemplary method of achieving ion beam uniformity control using ion beam blockers in accordance with the present disclosure may include the steps of generating an ion beam, detecting a current profile of said ion beam with an ion beam blocker unit, wherein said detected current profile is an initial current profile, blocking a portion of said ion beam with said ion beam blocker unit to achieve a second current profile that is different from the initial current profile, and implanting said ion beam into a workpiece after said blocking. 
     A first exemplary embodiment of an ion implanter in accordance with the present disclosure may include an ion source that generates an ion beam, a scanner downstream of said ion source, an end station downstream of said scanner, and an ion beam blocker unit positioned between said scanner and said angle corrector magnet, said ion beam blocker unit configured to block a portion of said ion beam. 
     A second exemplary embodiment of an ion implanter in accordance with the present disclosure may include a platen, a plurality of blockers upstream of said platen, a scanner upstream of said plurality of blockers, a plurality of drive units, each of said drive units connected to one of said plurality of blockers and configured to translate one of said blockers in a first direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a beam-line ion implanter in accordance with an embodiment of the present disclosure; 
         FIG. 2  is a side cross-sectional view illustrating an ion beam blocker unit in accordance with the present disclosure; 
         FIG. 3  is a front perspective view illustrating an ion beam blocker unit illustrated in  FIG. 2 ; 
         FIG. 4  is a front perspective view illustrating a second embodiment of a blocker in accordance with the present disclosure; and 
     
    
    
     DETAILED DESCRIPTION 
     An apparatus and method for improving the uniformity of an ion beam using mechanical blockers in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the system and method are shown. The apparatus and method, however, may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the system and method to those skilled in the art. In the drawings, like numbers refer to like elements throughout. 
     The apparatus and method of the present disclosure are described herein in connection with an ion implanter and an associated ion implantation process. However, it is contemplated that the disclosed apparatus and method can be similarly implemented in a variety of other systems and processes, such as may be involved in the manufacture of semiconductors, for example. Additionally, while the exemplary ion implanter disclosed herein is described in connection with the implantation of semiconductor wafers, it will be understood that such disclosure is provided merely for illustrative purposes, and that the ion implanter can be similarly implemented for the implantation of other types of workpieces, including, but not limited to, solar cells, light emitting diodes (LEDs), flat panels, silicon-on-insulator (SOI) wafers, and other such components. Furthermore, while a scanned spot beam is disclosed, the embodiments disclosed herein also may be applicable to a non-scanned spot beam or a ribbon ion beam. 
       FIG. 1  is a schematic diagram of an ion implanter  200 . Those skilled in the art will recognize that the ion implanter  200  is merely one of many examples of such implanters and alternative arrangements may be implemented. In general, the ion implanter  200  includes an ion source  201  that generates ions that form an ion beam  202  which may be an ion spot beam  202 . The ion source  201  may include an ion chamber  203 . A gas may be supplied to the ion chamber  203  where the gas is ionized. This gas may be or may include or contain, in some embodiments, a p-type dopant, an n-type dopant, carbon, hydrogen, a noble gas, a molecular compound, or some other species known to those skilled in the art. The ions thus generated are extracted from the ion chamber  203  to form the ion beam  202 . The ion beam  202  may pass through a suppression electrode  204  and ground electrode  205  into a mass analyzer  206 . The mass analyzer  206  may block undesired ion species in the ion beam  202  while allowing desired ion species to pass. The ion implanter  200  may further include a scanner  208  that is configured to receive the spot ion beam  202  and to rapidly scan the spot ion beam  202  in a direction that is orthogonal to the path of the spot ion beam  202  to form a relatively wider ribbon ion beam  212  as further described below. The scanner  208  may be an electrostatic scanner or a magnetic scanner. The electrostatic scanner may be configured to scan the spot ion beam  202  according to a predetermined and/or adjustable scanner waveform that may dictate the amount of time that the ion beam  202  is directed toward a given point or area on a workpiece as further described below. An ion beam blocker unit  216  may be positioned downstream from the scanner  208 . The ion beam blocker unit  216  may be configured to selectively block portions of the scanned ion beam  202  to improve ion beam uniformity as further described below. 
     An angle corrector magnet  210  may be positioned downstream of the ion beam blocker unit  216  and may convert the diverging beamlets of the scanned ion beam  202  into a ribbon ion beam  212  having substantially parallel ion trajectories. An end station  211  supports one or more workpieces, such as workpiece  213 , in the path of ribbon ion beam  212  such that ions of the desired species are implanted into workpiece  213 . The workpiece  213  may be, for example, a semiconductor wafer. The end station  211  may include a platen  214  to support one or more workpieces  213 . The end station  211  also may include a mechanical drive unit (not shown) for moving the workpiece  213  perpendicular to the long dimension of the ribbon ion beam  212  cross-section, thereby distributing ions over the entire surface of workpiece  213 . It will be understood to those skilled in the art that the entire path traversed by the ion beam is evacuated during ion implantation. The ion implanter  200  may include additional components known to those skilled in the art and may incorporate hot or cold implantation of ions in some embodiments. 
       FIG. 2  is a side cross-sectional view of an ion beam blocker unit  216  (shown by the dotted line). The ion beam blocker unit  216  includes at least one blocker  300 . Each blocker  300  is connected to a drive unit  301  to translate the blocker  300  in the y-direction illustrated by arrow  303 . The distance the blocker  300  is translated affects how much of the ribbon ion beam  212  is blocked or trimmed. The drive unit  301  may be a piezo-electric drive or some other system known to those skilled in the art. The blocker  300  may be fabricated of graphite or some other material that does not contaminate the ribbon ion beam  212 . 
       FIG. 3  is a front perspective view of the ion beam blocker unit illustrated in  FIG. 2 .  FIG. 3  still illustrates the ribbon ion beam  212  going in the z-direction, but now the z-direction comes out of the page. Five blockers  300 A-E are illustrated in  FIG. 3 , but other configurations may be used and this embodiment is not solely limited to five. The blockers  300 A-E may be arranged in an array. The drive units  301  translate the blockers  300 A-E in the y-direction. Each blocker  300 A-E may be individually translated. Thus, blocker  300 E blocks or trims more of the ribbon ion beam  212  than blocker  300 A, which blocks or trims more of the ribbon ion beam  212  than blockers  300 B-D. The individual pattern of the blockers  300 A-E depends on the non-uniformity of the ribbon ion beam  212  or how much of the ribbon ion beam  212  needs to be blocked or trimmed. The blockers  300 A-E also may be translated out of the path of the ribbon ion beam  212 . It may be desirable to have a ribbon ion beam  212  where the vertical integration (such as the y-direction) of the beam is the same throughout the entire ribbon ion beam  212 . 
     A controller may be used to dictate the placement or translation of the individual blockers  300 A-E to make the ribbon ion beam  212  more uniform. Such a controller may be connected to a measurement device that is configured to detect the uniformity, profile, and/or current of the scanned ion beam  202  in real time. For example, the blockers  300 A-E of the ion beam blocker unit  216  may be formed of a conductive, non-contaminating material, such as graphite or doped silicon, and may be connected to a ground  217  (see  FIG. 1 ) through current measuring electronics (not shown). The blockers  300 A-E may thereby operate as sensors for detecting the current profile and the uniformity of the scanned ion beam  202  during uniformity setup by inserting the blockers completely into the beam. The beam current at each blocker position that is required to be trimmed in order to produce a uniform beam can be computed once the total current at each blocker position is known. The blockers can be then retracted by appropriate distances so that a uniform, collimated ribbon ion beam  212  is projected onto the workpiece  213 . 
     The controller, which may be operatively connected to the ion beam blocker unit  216 , may receive such information and may thereby adjust the positions of the individual blockers  300 A-E in order to produce a more uniform ribbon ion beam  212  and, resultantly, more uniform ion implantation in the workpiece  213 . It is further contemplated that the controller may adjust the scanner waveform (described above) in conjunction with adjusting the positions of the individual blockers  300 A-E in order to produce a more uniform ribbon ion beam  212 . 
     It has been observed that employing the ion beam blocker unit  216  in the manner described above may result in sharp or abrupt delineations in the current profile of a ribbon ion beam, such as when one of the blockers  300 A-E is moved into an ion beam and an adjacent one of the blockers  300 A-E is not. Such delineations may be detrimental to the quality of an implanted workpiece. The electrostatic scanner  208  may therefore be employed to deflect (i.e., dither) the ion beam  202  a small amount in order to smooth out the uniformity correction provided the blockers  300 A-E. Such deflection may also be employed to make the effective width of the ion beam  202  larger in cases where the size of the ion beam  202  is smaller than the workpiece  213 . 
     While rectangular blockers  300 A-E are illustrated, other shapes are possible. For example, each blocker  300 A-E may have multiple crenellations or teeth that can block or trim the ribbon ion beam  212 . Other patterns or shapes also may be used.  FIG. 4  is a front perspective view of a second embodiment of a blocker. The blocker  300  includes multiple teeth  302 . Thus, each blocker  300  can block multiple portions of the ion beam. 
     The ion beam blocker unit  216  does not affect the angles of the ribbon ion beam  212  or the beamlets within the ribbon ion beam  212 . Instead, the angles may be affected by other electrodes or magnets. Thus, the uniformity adjustment with the ion beam blocker unit  216  and any angle adjustment with electrodes or magnets may be decoupled. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     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. These other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, 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.