Patent Publication Number: US-2007114436-A1

Title: Filament member, ion source, and ion implantation apparatus

Description:
PRIORITY CLAIM  
      A claim of priority is made under 35 U.S.C. § 119 to Korean Patent Application 2005-110002 filed on Nov. 17, 2005, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND  
      1. Field  
      The present invention Example embodiments may relate to an apparatus for manufacturing a semiconductor device, and more particularly, to a filament member, an ion source, and an ion implantation apparatus.  
      2. Description of the Related Art  
      Ion implantation is a semiconductor device manufacturing process used to dope a silicon wafer with impurities, for example, a P-type dopant, boron (B), aluminum (Al) and indium (In), and a N-type dopant, antimony (Sb), phosphorus (P), and arsenic (As). The impurities may be implanted into the silicon wafer in the form of a plasma ion beam. Ion implantation techniques have been widely used to manufacture semiconductor devices, because controlling the concentration of impurities injected into a wafer may be easier.  
      An ion implantation apparatus may include an ion source for generating an ion beam.  FIG. 1  is a schematic view illustrating a conventional ion source  900 . Referring to  FIG. 1 , the ion source  900  may include an arc chamber  920  and a filament  940  disposed in the arc chamber  920  for emitting thermoelectrons. The arc chamber  920  may include an inlet  922  through which source gas may be introduced and an ion beam outlet  924  through which positive ions may be extracted. When the filament  940  and the arc chamber  920  are powered, the filament  940  may heat-up to a desired temperature to emit electrons. The emitted electrons may collide with gas molecules distributed inside the arc chamber  920  to ionize the gas molecules. During this process, gaseous plasma including various ions and electrons may be generated, and ions may be discharged through the ion beam outlet  924 . The generated ions may be emitted through the ion beam outlet  924  and implanted onto a wafer.  
      Positive ions produced near the filament  940  may be directed to and collide with the filament  940 , which may damage the filament surface (sputter etching). The sputter etching may wear the filament  940  and eventually cause a short. In other words, the lifespan of the filament  940  may be shortened due to the sputter etching. The sputter etching may occur at a high rate when positive ions are incident to the filament  940  at an angle of about 30° to 60°. Most of the positive ions hit the filament  940  at an angle, because wire filaments may be commonly used.  
      As illustrated in  FIG. 2 , the filament  940  may be formed as a coil to allow electrons to flow in a longer path. In the coil filament, however, thermoelectrons emitted at a rear portion of the filament may collide with a front portion, which may damage the front portion. The damage may shorten the lifespan of the coil filament.  
      Furthermore, electrons flow through a single path in the wire filament arrangement. Therefore, if the wire filament breaks at any point, for example, by the sputter etching, the operation of an ion implantation apparatus must be stopped to replace the broken wire filament.  
      In addition, the wire filament may be formed with a tungsten wire by heating the tungsten wire to a high temperature and applying a force to bend the tungsten wire into coil shape, for example, a pig&#39;s tail. However, it may be difficult to manufacture the pig&#39;s tail shaped coil. Moreover, the characteristic features of tungsten may change when tungsten is heated to a high temperature. The dimension of the pig&#39;s tail filament may be easily affected by bending conditions, because the pig&#39;s tail filament may be formed by bending. It may also be difficult to manufacture a pig&#39;s tail filament having a large diameter.  
     SUMMARY  
      In an example embodiment, a filament member may be configured to discharge thermoelectrons and may include a cathode, an anode, and a thermoelectron emitter disposed between the cathode and the anode. The thermoelectron emitter may be disposed between the cathode and the anode, and the thermoelectron emitter may include slots and a plurality of conductive paths disposed around the slots to emit thermoelectrons. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide further understanding of example embodiments and are incorporated in and constitute a part of this application, may illustrate example embodiments. In the drawings:  
       FIG. 1  is a schematic view illustrating a conventional ion source;  
       FIG. 2  is a perspective view of a filament of the conventional ion source illustrated in  FIG. 1 ;  
       FIG. 3  illustrates a schematic structure of an ion implantation apparatus according to an example embodiment;  
       FIG. 4  illustrates a schematic structure of an ion source illustrated in  FIG. 3 ;  
       FIG. 5  is a perspective view of a filament member illustrated in  FIG. 4 ;  
       FIG. 6  is a front view of  FIG. 5 ;  
       FIGS. 7 and 8  are front views of a filament member according to another example embodiment;  
       FIGS. 9A and 9B  illustrate an incident angle of positive ions to a conductive path having a flat front surface and a conductive path having a circular front surface, respectively;  
       FIG. 10  is a perspective view of a filament member according to another example embodiment;  
      FIG. 11  illustrates traveling paths of ions emitted from the filament member illustrated in  FIG. 10  into an arc chamber;  
       FIG. 12  is a perspective view of a filament member according to another example embodiment; and  
       FIG. 13  illustrates traveling paths of ions emitted form the filament member illustrated in  FIG. 12  into an arc chamber. 
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS  
      Example embodiments will be described below in more detail with reference to the accompanying drawings. Example embodiments may, however, be embodied in different forms and should not be constructed as limited to example embodiments set forth herein. Rather, example embodiments are provided so that this disclosure will be thorough, and will convey the scope of the example embodiments to those skilled in the art.  
      It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it may be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.  
      It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.  
      Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.  
      The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.  
      Example embodiments may be described herein with reference to cross-section illustrations that may be schematic illustrations of idealized embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, the example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the drawings are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the example embodiments.  
      Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.  
      Reference will now be made in detail to example embodiments, with references to  FIGS. 3 through 13 .  
      Referring to  FIG. 3 , an ion implantation apparatus  1  may include an ion source  10 , an analyzer  20 , an accelerator  30 , a concentrator  40 , a scanner  50 , and an end station  60 .  
      The ion source  10  may produce ions. The analyzer  20  may select specific ions having a desired atomic weight to be implanted into a wafer. The accelerator  30  may accelerate the selected ions to implant the ions to a desired depth on the wafer. When neutral ions ionize and move, positively charged ions may cluster together. Therefore, the ion beam may diverge due to repulsion force of the positively charged ions. Thus, the concentrator  40  may focus the ion beam to a scanner  50 . The scanner  50  may vary the direction of the ion beam to all directions to uniformly scan the wafer. The ions may be implanted into the wafer at the end station  60 .  
       FIG. 4  is a sectional view of the ion source  10  of the ion implantation apparatus  1  illustrated in  FIG. 3 . Referring to  FIG. 4 , the ion source  10  may include an arc chamber  100 , a filament member  200 , and a repeller  300 .  
      The arc chamber  100  may have a substantially rectangular shape with a first sidewall  120 , a second sidewall  140 , a third sidewall  160 , a fourth sidewall  180 , a fifth sidewall (not shown), and a sixth sidewall (not shown). The first and second sidewalls  120  and  140  may face each other, and the third and fourth sidewalls  160  and  180  may face each other. The third and fourth sidewalls  160  and  180  may be perpendicular to the first and second sidewalls  120  and  140 . The first sidewall  120  of the arc chamber  100  maybe formed with an inlet  122  for introducing source gas. The second sidewall  140  of the arc chamber  100  may be formed with an ion beam outlet  142  for extracting positively charged ions produced inside the arc chamber  100 . The inlet  122  may be a circular hole, and the ion beam outlet  142  may have a slit shape. The arc chamber  100  may receive a positive voltage from an arc power supply  484 .  
      The filament member  200  and the repeller  300  may be installed in the arc chamber  100 . The filament member  200  may be near and in parallel with the third sidewall  160 , and the repeller  300  may be near and in parallel with the fourth sidewall  180 . The filament member  200  may emit thermoelectrons to separate the source gas into positively charged ions and electrons.  
      The repeller  300  may receive a negative voltage. Thermoelectrons emitted from the filament member  200  that do not ionize with the source gas may be pushed back to the source gas by the repeller  300 . The filament member  200  may be supported by filament fixing blocks  420 , and the repeller  300  may be supported by a repeller fixing block  440 . The filament fixing blocks  420  may penetrate through the third sidewall  160 . The filament fixing block  420  may be formed of an insulating material in order to support the filament member  200  and insulate the filament member  200  from the arc chamber  100 . Conductive projections  422  (denoted by reference numerals  422   a  and  422   b  in  FIG. 5 ) may be connected to the filament member  200  and inserted into the filament fixing block  420 . The conductive projections  422  may receive a filament current from a filament power supply  482 . The repeller fixing block  440  may penetrate the fourth sidewall  180  of the arc chamber  100 . The repeller fixing block  440  may support the repeller  300  and insulate the repeller  300  from the arc chamber  100 . A conductive projection  442  may be connected to the repeller  300  and inserted into the repeller fixing block  440 .  
      Referring to  FIGS. 4, 5 , and  6 , a cathode plate  290  may be disposed between the filament member  200  and the third sidewall  160 . The cathode plate  290  may push thermoelectrons emitted from conductive paths  262  of the filament member  200  toward the source gas (e.g., toward the fourth sidewall  180 ). The cathode plate  290  may include holes  292  and  294 . The hole  292  may receive the conductive projection  422   a  coupled to an anode  220  of the filament member  200 , and the hole  294  may receive the conductive projection  422   b  coupled to a cathode  240  of the filament member  200 . The hole  292  may be sufficiently large such that the conductive projection  422   a  coupled to the anode  220  does not make contact with the cathode plate  290 . The hole  294  may be of size such that the conductive projection  422   b  coupled to the cathode  240  contacts the cathode plate  290 .  
      With reference to  FIGS. 5 and 6 , the filament member  200  will now be described.  FIG. 5  is a perspective view of the filament member  200 , and  FIG. 6  is a front view of  FIG. 5 . The filament member  200  may include the anode  220 , the cathode  240 , and a thermoelectron emitter  260 .  
      A positive terminal of the filament power supply  482  may be connected to the conductive projection  422   a , and the anode may be connected to the conductive projection  422   a . A negative terminal of the filament power supply  482  may be connected to the conductive projection  422   b , and the conductive projection  422   b  may be connected to the anode  220 . The thermoelectron emitter  260  may include the conductive paths  262 . The conductive paths  262  may have one end connected to the anode  220  and the other end connected to the cathode  240 . Electrons may flow from the cathode  240  to the anode  220  through the conductive paths  262 . A current of about  200  amps may be applied to the conductive paths  262 , and thermoelectrons may be emitted from the conductive paths  262  due to heat generated by the current.  
      In an example embodiment, the thermoelectron emitter  260  may include at least two conductive paths  262 . Each of the conductive paths  262  may be sufficiently narrow such that thermoelectrons may be emitted. However, the conductive paths  262  may break if the conductive paths  262  are too narrow, therefore, the width of the conductive paths  262  should be accordingly considered. Further, each of the conductive paths  262  should be of sufficient length to emit thermoelectrons. Each of the conductive paths  262  may also be formed into a zigzag shape, such that each of the conductive paths  262  may have a longer length in a limited region in the thermoelectron emitter  260 . The zigzag configured conductive paths  262  may be formed by defined plate slots  264  as illustrated in  FIG. 6 . Die casting, electrical discharge machining, or wire cutting may be used to form the plate slots  264  in a tungsten plate.  
      The conductive paths  262  may have the same shape with respect to each other. If the conductive paths  262  have different shapes, the conductive paths  262  may have different resistances, resulting in different currents flowing through the conductive paths  262 . In this case, the conductive paths  262  may emit different amount of thermoelectrons, and thus thermoelectron emission rates may vary across the thermoelectron emitter  260 .  
      In an example embodiment, as shown in  FIG. 6 , the filament member  200  may have a rectangular plate shape with a first side  202 , a second side  204 , a third side  206 , and a fourth side  208 . The first and second sides  202  and  204  may face each other, and the third and fourth sides  206  and  208  may face each other. The anode  220  may be disposed on the first side  202 , the cathode  240  may be disposed on the second side  204 , and the thermoelectron emitter  260  may be formed between the anode  220  and the cathode  240 . The plate slots  264  may be formed in the thermoelectron emitter  260  between the anode  220  cathode  240 . For example, one of the plate slots  264  may be formed inwardly from the third side  206  between the anode  220  and the thermoelectron emitter  260  in a direction parallel with the first side  202 . Further, another of the plate slots  264  may be formed inwardly from the fourth side  208  between the anode  220  and the thermoelectron emitter  260  in a direction parallel with the first side  202 . In other words, the plate slots  264  may form an “H” shape in the thermoelectron emitter  260 . These plate slots  264 , formed from the third side  206  and the fourth side  208 , may have the same length and face each other. In the same way, some of the other plate slots  264  may be formed between the cathode area  240  and the thermoelectron emitting area  260 .  
      By forming the plate slots  264  in a configuration as described above, the thermoelectron emitter  260  may include the two conductive paths  262  symmetrically formed on upper and lower sides therein, and each of the two conductive paths  262  may have a zigzag shape. Specifically, the zigzag shape of each of the conductive paths  262  may be configured using first paths arranged in parallel and a second path arranged perpendicular and connected to the first paths. The plate slots  264  may be formed such that each of the conductive paths  262  may have a uniform width throughout its length.  
      In the above-described example embodiment, the conductive paths  262  may be symmetric with respect to each other. However, the conductive paths  262  do not have to be symmetric with respect to each other. The conductive paths  262  may have the same width and length. Thus, the conductive paths  262  may have similar resistances. The conductive paths  262  may have other shapes, for example, a straight or curved shape.  
      In the above-described example embodiment, the thermoelectron emitter  260  may include two conductive paths  262 . However, in another example embodiment, a filament member  200   a  may include a thermoelectron emitter  260   a  configured with more than two conductive paths  262 , as illustrated in  FIG. 7 .  
      In another example embodiment illustrated in  FIG. 8 , a filament member  200   b  may include a thermoelectron emitter  260  configured with conductive paths  262   a  and  262   b  having different widths and lengths. In this case, the conductive paths  262   a  and  262   b  may have different resistances. For example, the thermoelectron emitting area  260   b  may include two symmetrical zigzag conductive paths  262   a  and one relatively straight conductive path  262   b . Thermoelectrons emitted from the straight conductive path  262   b  may be more intensive than the two symmetrical zigzag conductive paths  262   a , because the straight conductive path  260   b  may have a relatively smaller resistance. As the thermoelectrons are emitted, the straight conductive path  262   b  may become narrower and thus the resistance of the straight conductive path  262   b  may increase. Therefore, after a time, the resistance of the zigzag conductive paths  262   a  may become smaller than that of the straight conductive path  262   b , and thermoelectrons emitted from the zigzag conductive path  262   a  may be more intensive than from the straight conductive path  262   b . This thermoelectron emitting pattern may repeat. Although the thermoelectron emitting rate of the conductive paths  262   a  and  262   b  are at times different, the average thermoelectron emitting rate of the conductive paths  262   a  and  262   b  may be similar over a period of time. Thus, the life span of the conductive paths  262   a  and  262   b  may be similar.  
      As illustrated in  FIG. 8 , the cathode  240  and the anode  220  may be connected by the plurality of conductive paths  262   a  and  262   b . Therefore, even if one of the conductive paths  262   a  and  262   b  breaks, the filament member  200   b  may function until all the conductive paths are broken.  
      Referring again to  FIG. 5 , the filament member  200  may be formed of a relatively flat plate such that thermoelectrons may be emitted from a flat surface of the filament member  200  onto gases in the arc chamber  100 . When positive ions generated near the conductive paths  262  collide onto the conductive paths  262 , most of the positive ions may be incident at a right angle to the conductive paths  262 . Therefore, damage by the positive ions (sputter etching) may be reduced.  
       FIG. 9A  illustrates the incident angle of positive ions to a conductive path  262  having a flat front surface  261 , and  FIG. 9B  illustrates the incident angle of positive ions to a conductive path  262 ′ having a circular front surface  261 ′. Referring to  FIG. 9B , because positive ions may collide onto the circular front surface  261 ′ of the conductive path  262 ′, most of the positive ions may be incident on the circular surface  261 ′ at non-perpendicular angles. Therefore, sputter etching rate may be high. However, referring to  FIG. 9A , positive ions may collide onto the flat front surface  261  of the conductive path  262 . Therefore, most of the positive ions may be incident on the flat front surface  261  at a right angle, and thus sputter etching rate may be lower.  
       FIG. 10  is a perspective view of a filament member  200   c  according to another example embodiment. Referring to  FIG. 10 , a filament member  200   c  may be formed of a convex plate. The convex plate may include a first side  202 , a second side  204 , and a convex surface formed between the first side  202  and the second side  204 . Thermoelectrons may be emitted from the convex surface toward gases in the arc chamber  100  Referring to  FIG. 10 , when the filament member  200   c  shown in  FIG. 10  is used as compared with a flat filament, thermoelectrons may be emitted to a wider area. The convex plate may have a sufficiently large radius of curvature to reduce a sputter etching rate. Alternatively, the filament member  200   c  may curve convexly from its four sides  202 ,  204 ,  206 , and  208  toward the center thereof.  
       FIG. 12  is a perspective view of a filament member  200   d  according to another example embodiment. Referring to  FIG. 12 , the filament member  200   d  may be formed of a concave plate. The concave plate may include a first side  202 , a second side  204 , and a concave surface formed between the first side  202  and the second side  204 .  
      Thermoelectrons may be emitted from the concave surface toward gases in the arc chamber  100 . Referring to  FIG. 13 , when the filament member  200   d  illustrated in  FIG. 12  is used, thermoelectrons emitted from the filament member  200   d  may converge to a narrower area in the arc chamber  100 . The concave plate may have a sufficiently large radius of curvature to reduce sputter etching rate. Alternatively, the filament member  200   d  may curve concavely from its four sides  202 ,  204 ,  206 , and  208  toward the center of the arch chamber  100 .  
      In example embodiments, as illustrated in  FIGS. 5-8 ,  10  and  12 , an anode and at least one of a first conductive path and/or a cathode and at least one of a second conductive path are coplanar; that is a plane exists in a direction substantially parallel to a major axis of a filament member that cuts through the anode and at least one of the conductive paths and/or the cathode and at least one of the second conductive paths.  
      In the above-described example embodiments, the filament member may have a rectangular plate shape. However, the filament member may have other shapes, for example, a circular plate shape, a polygon plate shape, etc.  
      According to the filament member of example embodiments, conductive paths may be provided by forming slots in a tungsten plate. Therefore, conductive paths having various shapes and widths may be provided.  
      Further, since the filament member may include a plurality of conductive paths, the filament member may continuously be used even when one of the conductive paths is shorted. Therefore, the lifespan of the filament member can be increased.  
      Furthermore, when the filament member may be formed of a flat plate according to example embodiments, sputter etching caused by positive ions colliding into the filament member may be reduced. Therefore, the lifespan of the filament member may increase.  
      In addition, when the filament member may be formed of a convex plate according to another embodiment, thermoelectrons may be emitted from the filament member to a wide area in an arc chamber. Therefore, the thermoelectrons may ionize gases throughout the arc chamber.  
      Further, when the filament member may be formed of a concave plate according to a further another example embodiment, thermoelectrons emitted from the filament member may converge on an area of an arc chamber. Therefore, the ionization of gases in the arc chamber may increase at the area.  
      It will be apparent to those skilled in the art that various modifications and variations may be made in example embodiments. Thus, it is intended that example embodiments may cover the modifications and variations provided they come within the scope of the appended claims and their equivalents.