Patent Abstract:
In an ion implanter, a detector assembly is employed to monitor the ion beam current and incidence angle at the location of the work piece or wafer. The detector assembly includes a plurality of pairs of current sensors and a blocker panel. The blocker panel is disposed a distance away from the sensors to allow certain of the beamlets that comprise the ion beam to reach the sensors. Each sensor in a pair of sensors measures the beam current incident thereon and the incident angle is calculated using these measurements. In this manner, beam current and incidence angle variations may be measured at the work piece site and be accommodated for, thereby avoiding undesirable beam current profiles.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention relate to the field of semiconductor device fabrication. More particularly, the present invention relates to an apparatus and method for measuring the incidence angle for an ion beam in an ion implanter. 
     2. Discussion of Related Art 
     Ion implantation is a process used to dope impurity ions into a semiconductor substrate to obtain desired device characteristics. A precise doping profile in a semiconductor substrate and associated thin film structure is critical for proper device performance. An ion beam is directed from an ion source chamber toward a substrate. The depth of implantation into the substrate is based on the ion implant energy and the mass of the ions generated in the source chamber. In addition, the beam dose (the amount of ions implanted in the substrate) and the beam current (the uniformity of the ion beam) can be manipulated through the use of a mass analyzing magnet, a corrector magnet and one or more acceleration and deceleration stages along the ion beam path to provide a desired doping profile in the substrate. However, throughput or manufacturing of semiconductor devices is highly dependent on the uniformity of the ion beam on the target substrate to produce the desired device characteristics. 
     Generally, beam current, energy contamination and uniformity both of ion beam current density and angle of implantation are the parameters that jeopardize device throughput during semiconductor manufacturing processes. For example, if the beam current is too low, this will reduce the throughput of the implanter for a given total ion dose. Energy contamination occurs when there is a small fraction of the ion beam that is at a higher energy than desired. This small fraction of the ion beam at a higher energy level will rapidly increase the depth of the desired junction that is formed in the substrate when creating an integrated circuit and lead to degraded performance of the desired circuit profile. If the ion beam current density and angle of implantation are not uniform, there will be variations in the device properties formed across the semiconductor substrate. These variations in beam current and angle of implantation can compromise the desired device characteristics which could produce lower manufacturing yields and lead to higher processing costs. Thus, there is a need to control at least one or more of these parameters to provide current uniformity for ion implantation systems when manufacturing semiconductor devices. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention are directed to an apparatus for measuring the incidence angles of an ion beam in an ion implanter. In an exemplary embodiment, an ion beam detector assembly includes a plurality of pairs of ion current sensors disposed along a path of an ion beam in an ion implanter. Each of the pairs of ion current sensors is disposed on a detector array along a perpendicular axis with respect to the ion beam. The detector assembly starts from a position outside of the ion beam path and moves across the beam and terminates outside the beam path on the opposite side. As the detector assembly moves across the beam a first of the current sensors detects a first beam current, and a second of the current sensors detects a second beam current where each of the first and second detected beam currents are used to determine an angle of incidence of the ion beam. A blocker panel is disposed a distance ‘d’ upstream from the plurality of pairs of ion current sensors. The blocker panel is configured to block portions of the ion beam having a first group of angles of incidence from reaching a first section of each of the ion current sensors and allowing portions of the ion beam having a second group of angles of incidence to reach a second section of each of the ion current sensors. 
     In an exemplary method of measuring angles of incidence of an ion beam includes replacing a target wafer with an ion beam detector assembly having a plurality of current sensors. An ion beam is provided which is incident on the detector assembly. The beam current associated with the ion beam is detected by the plurality of current sensors. The detector assembly moves across the ion beam measuring beam currents. The angle of incidence of the ion beam is calculated using the detected beam currents from the plurality of current sensors. The angles of incidence are analyzed to determine the uniformity of the ion beam. The beam current is adjusted based on the calculated incidence angles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of a representative ion implanter including an incident angle detector assembly in accordance with an embodiment of the present invention. 
         FIG. 1A  is a schematic view of the movement of the detector assembly with respect to the ion beam path in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an exemplary detector assembly in accordance with an embodiment of the present invention. 
         FIG. 3A  is a front view of the detector assembly of  FIG. 2  in accordance with an embodiment of the present invention. 
         FIG. 3B  is an end view of the detector assembly of  FIG. 2  in accordance with an embodiment of the present invention. 
         FIG. 3C  is a side view of the detector assembly of  FIG. 2  in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow diagram illustrating an exemplary method of monitoring uniformity of ion implantation in accordance with an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention, however, may be embodied in many different forms and should not be construed as 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 invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout. 
       FIG. 1  is a block diagram of an exemplary ion implanter  100  including an ion source chamber  102 . A power supply  101  supplies the required energy to source  102  which is configured to generate ions of a particular species. The ion source chamber  102  typically includes a heated filament which ionizes a feed gas introduced into the chamber to form charged ions and electrons (plasma). The heating element may be, for example, a Bernas source filament, an indirectly heated cathode (IHC) assembly or other thermal electron source. Different feed gases are supplied to the ion source chamber to obtain ion beams having particular dopant characteristics. For example, the introduction of H 2 , BF 3  and AsH 3  at relatively high chamber temperatures are broken down into mono-atoms having high implant energies. High implant energies are usually associated with values greater than 20 keV. For low-energy ion implantation, heavier charged molecules such as decaborane, carborane, etc., are introduced into the source chamber at a lower chamber temperature which preserves the molecular structure of the ionized molecules having lower implant energies. Low implant energies typically have values below 20 keV. 
     The generated ions are extracted from the source through a series of electrodes  104  and formed into a beam  105  which passes through a mass analyzer magnet  106 . The mass analyzer is configured with a particular magnetic field such that only the ions with a desired mass-to-charge ratio are able to travel through the analyzer for maximum transmission through a mass resolving slit and onto deceleration stage  108 . The deceleration stage comprising multiple electrodes with defined apertures that allow the ion beam to pass. By applying different combinations of voltage potentials to these electrodes, the deceleration stage manipulates the ion energies in the beam. 
     Corrector magnet  110  is disposed downstream of the deceleration state and is energized to deflect ion beamlets in accordance with the strength and direction of the applied magnetic field to provide a ribbon beam targeted toward a work piece or substrate  114  positioned on a support or platen. In other words, the corrector magnet shapes the ion beam generated from the deceleration stage into the correct form for deposition onto the workpiece. In addition, the corrector magnet filters out any ions from the beam that may have been neutralized while traveling through the beam line. In some embodiments, a second deceleration stage  112  may be disposed between corrector magnet  110  and target work piece  114 . This second deceleration stage comprising a deceleration lens receives the ion beam from the corrector magnet and further manipulates the energy of the ion beam before it hits the workpiece  114 . 
     As the beam hits the work piece  114 , the ions in the beam penetrates the work piece coming to rest beneath the surface to form a region of desired conductivity, whose depth is determined by the energy of the ions. In order to ensure that the ions penetrate the work piece at a desired incident angle and beam current, system  100  includes detector assembly  116  having a plurality of sensors such as, for example Faraday cups, configured to detect the beam current measured at various points along the path through the ion beam  105 . The changes in beam current relative to the various measured points using the detector assembly  116  yields a measurement of the ion beam incident angle as described with respect to the process outlined below. The detector assembly  116  replaces work piece  114  and the profile measured at each of these sensors is used to determine the angle of incidence of the beam  105 . Based on these measurements, the profile may be modified to improve implant uniformity. Once the desired beam current and incident angle is obtained, the detector assembly  116  is replaced with work piece  114  and the detector assembly is removed from the beam line. In this manner, feedback from the detector assembly may be used to manipulate electromagnets along the beam line to provide a desired beam profile. 
       FIG. 1A  is a schematic drawing illustrating the movement of detector assembly  116  from a starting position A to an end position B. Detector assembly  116  starts from a position A outside of the ion beam path, moves horizontally across the beam  105  and terminates at a position B outside the beam path on the opposite side thereof. As the assembly moves across the beam  105  and the current values detected by each of the detector elements is recorded. The position of the detector assembly  116  as it moves across the beam is also recorded and associated with the corresponding current value detected by the respective detector element. 
       FIG. 2  is a perspective view of detector assembly  116  including a blocker panel  210  and a graphite array  220  having Faradays defined by Faraday pixels  220   1  . . .  220   N  and Faraday bodies  221   1  . . .  221   N  disposed therein. The blocker panel  210  is disposed a given distance “d” away from the array  220 . The Faradays are arranged in pairs along the X axis and are configured to receive a portion of the ion beam not blocked by panel  210 . Each Faraday measures the beam current as the assembly  200  is moved in direction X. In particular, each Faraday receives a portion of the analyzed beam  105  and produces an electrical current based on the representative current thereof. Each Faraday is connected to a current meter to detect the amperage (e.g. mA) and based on the area of the respective Faraday pixel  220   1  . . .  220   N , determines the current (e.g. mA/cm2) of the ion beam received by the Faraday. For explanation purposes, the beam  105  shown in  FIG. 2  is a portion of the beam typically incident on a work piece. The body portions  221   1  . . .  221   N  of the Faradays extend a distance in direction Z in order to prevent the beamlets of beam  105  which enter pixels  220   1  . . .  220   N  froth escaping. As beam  105  is incident on Faraday pixels  220   1  and  220   2 , the beam current is measured by the respective Faradays and the incident angle A of the beam  105  on the particular pixels is calculated by using the following equation:
 
 A =ArcTan((( Ia−Ib )* w )/(( Ia+Ib )*2 d ))  (Equation 1)
 
where Ia and Ib are the beam currents measured at a first and second of a pair of Faraday pixels (e.g. Faraday pixels  220   1  and  220   2 ), ‘w’ is the width of a particular one of the array of Faraday pixels  220   1  . . .  220   N  and d is the distance from blocker panel  210  to array  220  (as illustrated in  FIGS. 3A-3C ). Because of the different positions of each of the pixels  220   1  . . .  220   N  along the array  220 , each measures different amounts of the beam current depending on the angle of incidence for the particular Faraday. In this manner, N/2 pairs of Faradays are used to provide a two-dimensional array of incident angles of beam  105  in direction Y based on the number of detectors in direction X. The two dimensional array of angles is used to adjust the lenses and magnets in the ion implanter to obtain the desired beam angles incident on a work piece. In addition, the larger the distance d, the greater the resolution of the incident angles. However, a process trade off exists between greater angle resolution versus detection of smaller incident angles. The calculation of incidence angles can be repeated and the until the array of incidence angles is acceptable for a particular implantation profile.
 
       FIG. 3B  is a front view of the detector assembly  116  shown in  FIG. 2  including a blocker panel  210  and graphite array  220  housing pairs of Faraday pixels  220   1  . . .  220   N . Each of the pixels  220   1  . . .  220   N  has a width “w”, a first portion of which is disposed behind blocker panel  210  and a second portion of which is not disposed behind blocker panel  210 . Although part of a pixel is behind blocker panel  210 , each pixel is configured to detect a portion of ion beam  105  incident thereon. The pixels  220   1  . . .  220   N  are shown in pair-wise linear columns where the current detected by each pixel pair used to determine the incident angle in accordance with Equation 1 above. A first blocker support post  240   1  is connected to graphite array  220  and blocker panel  210  at a first end of detector assembly  116 . A second blocker support post  240   2  is connected to graphite array  220  and blocker panel  210  at a second end of detector assembly  116 . Blocker panel  210  is a substantially rectangular piece of graphite, however alternative conductive materials and shapes may be employed. In addition, blocker panel  210  may also be capable of rotation away from array  220  about one of the support posts  240 . This may be done to allow calibration of the detectors in the array. 
     Blocker panel  210  is configured to block beamlets of the incident ion beam  105  from reaching the first portion of each Faraday pixel  220   1  . . .  220   N . For example, a first portion  220   a  of pixel  220   2  which has a width approximately w/2 is disposed behind blocker panel  210  and can only receive beamlets of ion beam  105  which are incident thereon at an angle with respect to the planar surface of the array  220 . In other words, beamlets of the ion beam  105  which are perpendicular to first portion  220   a  of pixel  220   2  will be blocked by blocker panel  210 . Similarly, beamlets of the ion beam  105  which are less than orthogonal on pixel portion  220   a  (i.e. toward pixel  220   1 ) will likewise be blocked from reaching pixel portion  220   a  by blocker panel  210 . However, second pixel portion  220   b  of pixel  220   2  which is also has a width of approximately w/2 is not disposed behind blocker panel  210  and therefore is configured to receive beamlets of the ion beam  105  which are substantially orthogonal to pixel portion  220   b  and beamlets of the ion beam  105  which are less than orthogonal to pixel portion  220   b . The width of each of the pixel portions  220   a  and  220   b  may have alternative dimensions depending on the range of incident angles being detected. 
     The relationship of the Faraday pixels and the ion beam  105  is illustrated more clearly in  FIG. 3B  which is an end view of detector assembly  116  taken in direction A.  FIG. 3B  illustrates blocker panel  210 , blocker support post  240   2  array  220 , pixel pair  220   1  and  220   2  and pixel bodies  221   1  and  221   2 , respectively. By way of example, beamlets  105   1  . . .  105   4  are incident on Faraday pixels  220   1  and  220   2  of detector assembly  116 . Beamlet portion  105   1  of ion beam  105  is incident on and received by pixel  220   2  at an incident angle. Beamlet portion  105   2  is orthogonal to pixel  220   2  and is blocked by blocker panel  210 . Beamlet portion  105   3  of ion beam  105  is orthogonal to pixel  220   1  and is blocked by blocker panel  210 . Beamlet portion  105   4  of ion beam  105  is incident on and received by pixel  220   1  at an incident angle. In this example, each of the Faraday pixels  220   1  and  220   2  detects the current density of the incident ion beam and the detector determines the incident angles in accordance with Equation 1 above. 
       FIG. 3C  is a side view of detector assembly  116  illustrating the distance d between blocker panel  210  and array  220 . In particular, distance d is measured from first surface  210   a  of blocker panel  210  to first surface  220   a  of array  220 . Support posts  240   1  and  240   2  are disposed between first surface  220   a  of array  220  and second surface  210   b  of blocker panel  210 . Each of the support posts may extend into respective bores (not shown) in blocker panel  210 . Alternatively, support posts  240   1  and  240   2  may be adjustably configurable to vary the distance d between blacker panel  210  and array  220 . Faraday bodies  2211  . . .  221 N extend from array  220  in order to prevent the beamlets of beam  105  which enter pixels  220   1  . . .  220   N  from escaping and thereby detecting the received beam current. 
       FIG. 4  is a flow diagram illustrating an exemplary method  300  of monitoring uniformity of an ion beam in an ion implantation system. At step  310 , a target work piece is moved away from the ion beam and the detector assembly replaces the work piece to tune a desired implant profile. The detector is provided with a plurality of pairs of Faraday pixels to detect beam currents incident on the pixels. At step  320 , the detector assembly is moved horizontally through the ion beam. The current values of the beam incident on each of the pairs of Faraday pixels are recorded and stored at step  330 . For example, the current associated with detector  220   1  is recorded and stored and the current associated with the corresponding other of the pair of detectors  220   2  is recorded and stored. At step  340 , the position of the detector assembly for each of the current values in step  330  is recorded. The positions of the current measured at step  340  is adjusted to compensate for the distance between the detector pairs at step  350 . In other words, the detected currents will have positions that differ by the horizontal separation of each of the detectors in a pair. Once the detector assembly has passed completely through the ion beam at step  360 , the assembly is stopped and the beam angles are calculated. In particular, the angle of incidence of the beam on each pair of the plurality of pairs of detectors is calculated at step  370  using the formula A=ArcTan(((Ia−Ib)*w)/((Ia+Ib)*2d)) where A is the incident angle, Ia and Ib are the beam currents measured at a first and second of a pair of Faraday pixels, ‘w’ is the width of a particular one of the array of Faraday pixels and d is the distance from a blocker panel  210  to the Faraday array  220 . This calculation at provides a two dimensional array of angles in the Y direction based on the number of detectors in the X direction based on the number of current measurements performed as the detector assembly  116  moved across the ion beam. The angles of incidence are analyzed to determine the uniformity of the ion beam at step  380 . At step  390 , the beam current is adjusted based on the two dimensional array of angles calculated by adjusting the lenses and magnets to obtain the desired beam profile. This procedure may be repeated until the array of angles is acceptable indicating that the lenses and magnets in the ion implanter is appropriate for the given profile. 
     While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.

Technology Classification (CPC): 7