Abstract:
An object alignment inspecting apparatus is used to prevent a channeling phenomenon form occurring in an ion implantation process. The apparatus includes a body having the shape of an object to be processed and a series of graduations extending along its outer peripheral edge, a center post protruding from the center of the body; and an indicator having a rotary member freely rotatably mounted to the post and extending from the post to the graduations. In use, the alignment angle inspecting apparatus is placed on the disc of ion implantation equipment that is used to support the object during the ion implantation process. The relative rotational position of the apparatus on the disc is read. This information is used to determine whether the object, when placed on the disc, will assume a relative rotational position which will not give rise to the channeling phenomenon. Also, the object alignment inspecting apparatus may have a plumb mechanism and graduations so that the slope of the disc can be determined as well. The slope of the disc can be adjusted based on the reading taken form the plumb mechanism so as to also ensure that the channeling phenomenon will not occur.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to ion implantation equipment. More particularly, the present invention relates to the orienting of an object, such as a wafer, for ion implantation such that ions will be implanted into the object to a desired depth.  
           [0003]    2. Brief Description of the Related Art  
           [0004]    In general, ion implantation equipment is used to extract ions, accelerate the ions at a high voltage, and inject the accelerated ions to a predetermined depth in an object positioned in the path of the ions. To facilitate the ion implantation process, the ion implantation equipment directs the ion beam onto the surface of the object as well as scans the surface of the object with the ion beam. However, the object must be inclined at a predetermined angle relative to the incoming direction of the ion beam to prevent the ions from being implanted to a depth greater than the desired depth. More specifically, inclining the object increases the possibility that the implanted ions will collide with atomic nuclei of the crystal lattice structure of the object, namely a wafer, whereby the depth to which the ions penetrate the object is restricted by the crystal lattice structure.  
           [0005]    To prevent the ions from penetrating too deeply into the wafer, the wafer (W) must, however, be oriented within an extremely limited range. A channeling phenomenon occurs if the orientation of the wafer is outside a predetermined narrow range whereupon the ions infiltrate the wafer beyond the desired depth. The channeling phenomenon manifests itself as an undesired change in the property of lower layers or an electrically conductive connection of the layers. In other words, the wafer must be oriented accurately relative to the direction of the incoming ion beam (hereinafter referred to as the “implanting direction”) to prevent the channeling phenomenon from occurring. The orientation of the wafer (W) is determined by a combination of the slope (θ) of the wafer as shown in FIG. 1, and a relative rotational position (θ′) of the crystal lattice structure of the wafer, as shown in FIG. 2. The effect of the slope (θ) and relative rotational position (θ′) of the wafer on the results of the ion implantation process will now be described in more detail with reference to FIGS.  1 - 5 .  
           [0006]    The slope (θ) of the wafer is the angle subtended by the plane of the wafer and the ion beam implanting direction (I), whereas the relative rotational position (θ′) of the wafer is the angle subtended by the direction of the crystal lattice structure and the scanning direction (S) of the ion beam. The wafer W is oriented such that the aforementioned slope (θ) and relative rotational position (θ′) of the wafer (W) increase the probability that the implanted ions will collide with the atomic nuclei of the crystal lattice structure. Note, in this case, the silicon crystals of the wafer form a face-centered cubic lattice, as shown in FIG. 3.  
           [0007]    If the slope (′) of the wafer (W) were 90° and the relative rotational position (θ′) of the wafer were 0°, the atomic nuclei of the crystal lattice structure of the silicon wafer (W) would exhibit a wide spacing with respect to the ion implanting and scanning directions, as shown in FIG. 4 a.  In this case, a high percentage of the ions can pass into the wafer (W) without impinging atomic nuclei of the crystal lattice structure, thereby causing the aforementioned channeling phenomenon to occur.  
           [0008]    On the other hand, if the slope (θ) of the wafer were 45° and the rotational angle (θ′) of the wafer were 7°, the aligned atomic nuclei would exhibit a narrower spacing than the case shown in FIG. 4 a.  Nonetheless, as shown in FIG. 4 b,  a high percentage of the implanted ions can still pass freely by the atomic nuclei, whereby the channeling phenomenon may occur.  
           [0009]    Furthermore, if the slope (θ) of the wafer were 35° and the relative rotational position (θ′) of the wafer were 8°, the aligned atomic nuclei would exhibit even a narrower spacing, as shown in FIG. 4 c.  However, even this orientation of the wafer (W) results more or less in a channeling phenomenon, i.e., is not capable of achieving the desired results of the ion implantation process.  
           [0010]    To the contrary, when the slope (θ) of the wafer is about 68°±1 and the relative rotational position (θ′) of the wafer is 7±0.5°, the atomic nuclei exhibit a dense arrangement against which most of the implanted ions will collide, as shown in FIG. 4 d.  Thus, the depth to which the ions can penetrate the wafer (W) is restricted by this orientation of the wafer (W), i.e., the orientation of the crystal lattice structure of the silicon. Accordingly, such an orientation of the wafer is ideal for the ion implantation process.  
           [0011]    The conventional ion implantation equipment for orienting the wafer (W), i.e., for establishing the slope (θ) and relative rotational position (θ′) of the wafer (W), will now be described with respect to FIG. 5. As shown in FIG. 5, a wafer (W) ejected from a load lock (L/L) chamber by a robot (R) is first positioned at an alignment unit (A). There, the wafer (W) is oriented (aligned) at a predetermined relative rotational position (θ′). The robot (R) transfers the aligned wafer (W) from the alignment unit (A) to a disc (D) of a turntable (T) that supports the wafer (W) at a predetermined slope (θ) and in a relative rotational position (θ′).  
           [0012]    However, it is impossible to confirm whether the alignment unit (A) has accurately aligned the wafer (W) In other words, it is impossible to confirm whether the wafer (W) has been oriented by the alignment unit (A) to a relative rotational position (θ′) within a predetermined range.  
           [0013]    In addition, there is another problem in that it is impossible to confirm whether the wafer (W) mounted on the disk (D) is oriented at a desired slope (θ) with respect to the ion beam implanting direction (I).  
           [0014]    As described above, if the values of the slope (θ) and relative rotational position (θ′) of the wafer are outside predetermined ranges, processing defects due to the channeling phenomenon may occur. In this case, the production yield of the semiconductor devices is reduced, and the manufacturing cost of the semiconductor devices is correspondingly increased.  
         SUMMARY OF THE INVENTION  
         [0015]    It is an object of the present invention to solve the aforementioned problems of the prior art. More specifically, it is an object of the present invention to reduce processing defects in the ion implantation process by, for example, preventing the chaneling phenomenon from occurring.  
           [0016]    To achieve these objects, the present invention provides a method of and an apparatus for confirming whether the inclination and/or relative rotational position of an object, when readied for ion implantation, will fall within a predetermined range whereby ions will be implanted into the object no further than to a desired depth.  
           [0017]    An object alignment angle inspecting apparatus according to the present invention comprises a body having the shape of an object, e.g. a wafer, to be processed in the ion implantation equipment, and a series of graduations spaced from one another along a circle so as to represent angles corresponding to relative rotational positions that the apparatus may assume, a center post protruding from the body at the center of the circle, and an indicator for marking a graduation indicative of the relative angular position of the apparatus.  
           [0018]    The indicator includes a rotary member mounted to the post so as to be free to rotate about the body, and extends from the post to the graduations.  
           [0019]    The rotary member may have an annular member extending freely around the center post, a connecting member having a first end fixed to the annular member and a second end disposed adjacent the graduations, and a weight connected to the second end of the connecting member.  
           [0020]    Alternatively, the rotary member may comprises a main plate facing the body and mounted to the post so as to rotate freely about the central axis of the center post parallel to the body. The main plate has an indicator mark adjacent the graduations to mark the graduation indicating the relative rotational position of the apparatus. The main plate preferably is also provided with auxiliary graduations extending alongside the main graduations. The auxiliary graduations are spaced from one another by intervals that are different form the intervals by which the main graduations are spaced for increasing the accuracy of the angle indicated by the apparatus.  
           [0021]    In addition, the indicator may have means by which the slope or inclination of the apparatus can be read. To this end, an indicator of the apparatus includes at least one auxiliary plate extending upright from a rotary member, and an indicating member mounted to the rotary member so as to swing freely relative thereto. The auxiliary plate has graduations spaced along an arc lying in a plane perpendicular to the rotary member. The indicating member extends to the arc, i.e., to the graduations, whereby the graduation of the auxiliary plate indicated by the indicating member is indicative of the angle at which the body is inclined relative to the vertical. The indicating member may comprise a string and a weight, or a plate having an indicating mark.  
           [0022]    In use, the alignment angle inspecting apparatus is placed on the disc of the ion implantation equipment. Once this happens, the relative rotational position of the apparatus on the disc can be read off of the graduations using the indicator. Subsequently, the transportation device of the ion implantation equipment, e.g. the robot, is used to transfer the object alignment angle inspecting apparatus from the disc to the alignment unit of the ion implantation equipment. Once this happens, the relative rotational position of the apparatus in the alignment unit is noted using the graduations of the apparatus. To this end, the alignment unit may be provided with a guide, a slider slidable along the guide, and an indicating pin protruding from the slider to indicate a graduation of the alignment angle inspecting apparatus disposed in the alignment unit. Finally, the relative rotational positions of the object alignment angle inspecting apparatus on the disc and in the alignment unit are compared to determine whether the object transported by the transportation unit from the alignment unit to the disc will assume a rotational position on the disc within a predetermined range relative the direction of scan of the ion beam.  
           [0023]    When the determination reveals that the relative rotational position of the object will be outside the predetermined range, the position of the disc is adjusted appropriately to pre-empt such a misalignment of the object.  
           [0024]    Moreover, the object alignment angle inspecting process repeated, including in reverse, to make sure that the alignment unit and transportation device are providing/maintaining the proper alignment of the object up to the time the object is disposed on the disc. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    These and other objects, features and advantages of the present invention will become clearer from the following detailed description of the preferred embodiments thereof made with reference to the accompanying drawings, of which:  
         [0026]    [0026]FIG. 1 is a sectional view of a wafer, inclined relative to the ion implanting direction;  
         [0027]    [0027]FIG. 2 is a plan view of the wafer showing its angular position relative to an ion-beam scanning direction;  
         [0028]    [0028]FIG. 3 is a perspective view of a unit of the crystal lattice structure of a silicon wafer;  
         [0029]    [0029]FIGS. 4 a  through  4   d  are schematic diagrams illustrating respective relationships between the crystal lattice structure and the rotational position of the wafer;  
         [0030]    [0030]FIG. 5 is a schematic diagram of conventional ion implantation equipment showing a wafer loading apparatus for loading a wafer onto a disc where the ion implantation process takes place;  
         [0031]    [0031]FIG. 6 is a perspective view of a first embodiment of an alignment angle detector in accordance with the present invention;  
         [0032]    [0032]FIG. 7 is a perspective view of another embodiment of an object alignment angle detector in accordance with the present invention; and  
         [0033]    [0033]FIG. 8 is another perspective view of the alignment angle detector of FIG. 7, illustrating the use of the detector in an inspecting method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]    Hereinafter, an object alignment angle detector for use in ion implantation equipment and the method of inspecting an object using the same will be described with reference to accompanying drawings. Note, like reference numerals are used to designate like parts throughout the drawings.  
         [0035]    Referring first to FIG. 6, In accordance with the present invention, an object alignment angle inspecting apparatus  10   a  comprises a generally planar body  12  having the same outer shape as a wafer (W) used for manufacturing semiconductor devices. The entire outer peripheral edge of the body  12  has graduations  16  indicating angles subtended relative to a reference line extending from the center of the body  12 .  
         [0036]    The apparatus  10   a  also comprises a center post  14  disposed at the center of the upper surface of the body  12  so as to be coaxial therewith, and an indicator  18   a  freely rotatably mounted to the center post  14  so as to be free to rotate about the central axis of the post  14 , i.e. so as to act as a pendulum. More specifically, the indicator  18   a  includes: a rotary member  20  in the form of a ring extending freely around the center post  14 , a connecting member  22  having a first end fixed to the outer edge of the rotary member  20  and a second end disposed close to the graduations  16  extending along the outer peripheral edge of the body  12 , and a weight  24  connected at the second end of the connecting member.  
         [0037]    The weight  24  is in the form of a pointer. The graduations  16  are spaced from one another along a circle whose center lies at the central axis of the center post  14 . The indicator  18   a  marks a graduation  16  corresponding to the direction in which a load, i.e., the force of gravity, acts on the weight  24  from the central axis of the body  12 . The graduation thus marked is indicative of the angle subtended between a reference line extending radially from the center of the circle and the indicator  18   a,  i.e., is indicative of the relative rotational position of the detector  10   a.    
         [0038]    The connecting member  22  basically comprises a string. The string is fixed to the rotary member  20  via a through-hole extending through a portion of the rotary member  20  radially from the central axis of the center post  14 . One end of the string passes through the through-hole where it is secured to the inside of the rotary member  20  without any interference from the center post  14 . The other end of the string is connected to the weight  24 .  
         [0039]    In the embodiment of the object alignment angle inspecting apparatus  10   b  shown in FIG. 7, the indicator  18   b  includes a rotary member  26  comprising a plate disposed close to the upper surface of the body  12 . The plate has an overall shape corresponding to a segment of the body  12  as shown in the figure. The rotary member  26  also has an annular portion by which the member  26  is rotatably supported by the center post  14  so as to act as a pendulum. Furthermore, a mark  28  is formed at a predetermined position along the radially outermost edge of the plate of the rotary member  26  to indicate the graduation  16  that corresponds to the direction in which a load, i.e., the force of gravity, acts on the rotary member  26  from the central axis of the body  12 . The mark  28  may take the form of a protrusion.  
         [0040]    In addition, as shown in FIG. 7, the outer peripheral edge of the rotary member  26  is provided with auxiliary graduations  30  indicating angles subtended with respect to the central axis of the body  12 . Preferably, the intervals between the auxiliary graduations  30  differ from, i.e., are larger or smaller than, those between the graduations  16 .  
         [0041]    That is, the graduations  16  of the body  12  and the auxiliary graduations  30  of the rotary member  26  have different intervals like a vernier caliper or micrometer. In other words, the graduations  16  of the body  12  serve as main scale graduations and the auxiliary graduations of the rotary member  26  serve as vernier graduations, so that it is possible to more accurately ascertain the angle indicated by the mark  28 .  
         [0042]    In addition, as shown in FIG. 7, the indicator  18   b  includes at least one auxiliary plate  32  disposed perpendicular to the plate of the rotary member  26  and lying in a plane extending from the location where the mark  28  is formed to the central axis of the body  12 . In this respect, the auxiliary plate(s)  32  enhances the effect of indicating the direction in which the load acts on the rotary member  26 , that is, the function of the mark  28 . The case of two auxiliary plates  32   a,    32   b  will be used in the following description.  
         [0043]    The auxiliary plates  32   a,    32   b  have arcuate peripheral edges that are juxtaposed relative to one another. Graduations  38  are provided along an arc adjacent the peripheral edges of the auxiliary plates  32   a,    32   b.  The arc lies in a plane perpendicular to the body  12  and rotary member  26  and has a radius of curvature emanating from the central axis of the post  14 .  
         [0044]    The indicator  18   b  also includes a connecting string  34  extending between the plates  32   a,    32   b  from a location adjacent the central axis of the post  14 , and a weight  36  connected to the distal end of the connecting string  34 . The weight  36  protrudes form between the plates adjacent the graduations  38  to indicate a slope (θ) subtended by the connecting string  34  and the upper surface of the body  12 .  
         [0045]    In addition, the fixed end of the connecting string  34  is preferably located a predetermined distance above the upper surface of the body  12 , and the graduations  38  are a series of short lines each of which will extend parallel to the connecting string  38  when the weight is  36  is positioned in alignment therewith. Furthermore, the connecting string  38  and the auxiliary plates  32   a,    32   b  may be fixed closer to the center axis  14  and positioned with a roller (not shown) to accurately form the angle that indicates the slope (θ).  
         [0046]    As an alternative, the connecting string  34  may be replaced by a plate similar to that of the rotary body  26 . In this case, the graduations  38  may be main scale graduations and the plate may be provided with an indicating mark and auxiliary graduations.  
         [0047]    Next, a method of confirming the orientation of a wafer (or other object) using the object alignment angle inspecting apparatus  10   a,    10   b  will be described with reference to FIGS.  5 - 8 .  
         [0048]    The object alignment angle inspecting apparatus  10   a,    10   b  is placed in the ion implanting equipment atop the disc (D) that is positioned in the path along which an ion beam is directed. At this time, the indicator  18   a,    18   b  rotates relative to the center post  14  under the force of gravity to indicate the graduation  16  designating the angle corresponding to the relative rotational position of the body  12 . Hence, a graduation  16  representing a relative rotational position of the apparatus is indicated by the pendulum, more specifically, by the weight  24  of the embodiment of FIG. 6 or the mark  28  of the rotary member  26  of the embodiment of FIG. 7. Subsequently, the apparatus  10   a,    10   b  is used to confirm the relative rotational position (θ′) of the wafer (W) on the disc (D) during the ion implantation process, for instance, where a flat zone of the wafer (W) or a mark that shows the orientation of the lattice structure of the wafer (W) will lie on the disc (D) after the wafer (W) has been transported to the disc (D).  
         [0049]    First, the robot (R) is used to transport the alignment angle inspecting apparatus  10   a,    10   b  from the disc (D) onto the alignment unit (A) before the wafer (W) is loaded onto the disc (D). The alignment angle inspecting apparatus  10   a,    10   b  is placed in the alignment unit (A) at the same orientation that will be given to a wafer (W) by the alignment unit (A). Thus, the alignment angle inspecting apparatus (A) can be used to determine whether the wafer (W) will have a relative rotational position (θ′) falling within a predetermined range once the wafer (W) has been transported by the same robot (R) from the alignment unit (A) to the disc (D) by confirming that the graduation  16  indicated when the apparatus  10   a,    10   b  was disposed on the disc (D) arrives at an appropriate location in the alignment unit (A).  
         [0050]    To this end, the alignment unit (A) may be provided with an auxiliary device to confirm exactly where the alignment angle inspecting apparatus  10   a,    10   b  is positioned relative to the aligner of the alignment unit (A). As shown in FIG. 8, the auxiliary device comprises a guide  40 , a slider  42  received on the guide  40  so as to be slidable therealong, and an indicating pin  44  supported by the slider.  
         [0051]    The guide  40  is fixed so as to extend parallel to the diametric direction of the alignment angle inspecting apparatus  10   a,    10   b  when the alignment angle inspecting apparatus  10   a,    10   b  is placed in the alignment unit (A). Opposite sides of the slider  42  protrude from the sides of the guide  40  so as to face the graduations  16 . A through hole extends vertically through one of these protruding sides of the slider  42 . The indicating pin  44  extends through the through hole to a position just above the graduations  16 . Therefore, once the alignment angle inspecting apparatus  10   a,    10   b  is transported by the robot (R) from the disc (D) into the alignment unit (A), the indicating pin  44  is used to check the relative rotational position (θ′) of the alignment angle inspecting apparatus  10   a,    10   b.  A comparison between the graduation  16  indicated by the pendulum when the alignment angle inspecting apparatus  10   a,    10   b  is disposed on the disc (D), and the graduation  16  indicated by the indicating pin  44  when the alignment angle inspecting apparatus  10   a,    10   b  is disposed in the alignment unit (A), thus reveals whether a wafer (W) will be oriented the disc (D) in a desired relative rotational position (θ′).  
         [0052]    If not, an adjustment is made to the ion implantation equipment, e.g., to the position of the disc (D), that ensures that the wafer (W) will be oriented in a relative rotational position (θ′) within a predetermined acceptable range.  
         [0053]    Next, the alignment angle inspecting apparatus  10   a,    10   b  may be transported between the load lock chamber (L/L) and the alignment unit (A) by the robot (R) to once again monitor whether there is any movement of the apparatus  10   a,    10   b  from its relative rotational position (θ′). This action is then compared with the state of movement of the alignment angle inspecting apparatus  10   a,    10   b  from the disc (D) to the alignment unit (A). Accordingly, the operation of the alignment unit (A) within normal parameters can be confirmed and, if necessary, the driving mechanism of the alignment unit (A) can be adjusted.  
         [0054]    If the above-described steps are repeated in reverse, it is possible to check whether the wafers (W) will be misaligned by the transportation device (robot R). If so, the robot (R) of the ion implantation equipment is adjusted. Then, the robot (R) in this adjusted state is used to transport the wafers (W) to the alignment unit (A) and, from there, onto the disc (D). Accordingly, the wafers (W) will assume a proper relative rotational position (θ′) during the ion implantation process.  
         [0055]    Furthermore, when the embodiment of FIG. 7 is disposed on the disc (D), the connecting string  34  acts as a plumb bob to make an angle with the upper surface of the body  12 , as indicated by the weight  36  on the graduations  38  formed along the peripheral edges of the auxiliary plates  32   a,    32   b.  This angle is indicative of the inclination of the alignment angle inspecting apparatus  10   b  relative to the ion beam implanting direction (I), that is, the slope (θ) of a wafer (W) disposed on the disc (D). Also, in this case, the auxiliary graduations  30  of the rotary member  26  and/or the auxiliary graduations provided on a rotary member (not shown) extending between the plates  32   a,    32   b  may be used to more accurately determine the relative rotational position (θ′) and/or slope (θ) that the wafer (W) will assume on the disc (D). If the slope (θ) falls outside of a predetermined range, the position of the turntable (T) is adjusted.  
         [0056]    According to the present invention as described above, the relative rotational position (θ′) and/or the slope (θ) of a wafer (W) on the disc (D) can be confirmed using the object alignment angle inspecting apparatus. If the use of the object alignment angle inspecting apparatus reveals that these angles will not fall within predetermined ranges, the ion implantation equipment is adjusted appropriately. Hence, the wafer (W) will be oriented such that a channeling phenomenon is prevented from occurring in connection with the ion implantation process. As a result, the processing efficiency, manufacturing yield, and productivity of the ion implantation process are improved.  
         [0057]    Finally, although the present invention has been described above with respect to the preferred embodiments thereof, it will be understood that the invention is not limited to the preferred embodiments. Rather, various changes and modifications may be made to the preferred embodiments without departing from the true spirit and scope of the invention as defined in the appended claims.