Abstract:
A vaporizer with several novel features to prevent vapor condensation and the clogging of the nozzle is disclosed. The vaporizer is designed such that there is an increase in temperature along the path that the vapor travels as it flows from the crucible to the arc chamber. The vaporizer uses a nested architecture, where the crucible is installed within an outer housing. Vapor leaving the crucible exits through an aperture and travels along the volume between the crucible and the outer housing to the nozzle, where it flows to the arc chamber. In certain embodiments, the aperture in the crucible is disposed at a location where liquid in the crucible cannot reach the aperture.

Description:
FIELD 
       [0001]    Embodiments of the present disclosure relate to a vaporizer for use with an ion source, and more particularly, a vaporizer that may be deployed in various orientations. 
       BACKGROUND 
       [0002]    Ion sources are employed to create the ions used to perform various semiconductor processes, such as ion implantation. In many embodiments, a dopant species, often in the form of a gas is introduced into the arc chamber of an ion source. The dopant species is then excited, such as by high energy electrons that have been accelerated across a potential or by radio frequency (RF) energy, to create ions. These ions are then extracted from the arc chamber in the form of an ion beam. 
         [0003]    In certain embodiments, the dopant species may be in the form of a solid, which is vaporized prior to its use in the arc chamber of the ion source. For example, a solid material may be disposed in a crucible or tube, which is part of a vaporizer. The crucible is then heated, such as by an external heating coil. Vapor then exits the crucible through a nozzle, where it is guided toward the arc chamber of the ion source. In certain embodiments, the crucible may be disposed within the ion source itself. 
         [0004]    One issue associated with vaporizers is condensation. As the crucible is heated, the solid material disposed within reaches a temperature sufficient to produce a needed vapor pressure of the solid material. However, as the vaporized gas exits the crucible, the gas may encounter regions which are at a lower temperature than that inside the crucible. If this lower temperature is less than the temperature of the solid material containing the dopant, the vapor may begin to condense. Condensation may reduce or even inhibit the flow of vapor to the ion source. 
         [0005]    In addition, in certain embodiments, the nozzle of the vaporizer may be positioned lower than other portions of the vaporizer. In other words, the height of the nozzle may be less than other portions of the vaporizer. This may be problematic if the dopant containing species is in the liquid state. In certain applications, the solid material containing the dopant may have a melting temperature lower than the temperature necessary to produce a useable vapor pressure. In this case, the temperature of the crucible may be greater than the melting temperature. In such instances, the material may melt, and the vapor is generated from the liquid. This liquid may then flow toward the nozzle, which is lower in height than these other portions of the tube. This liquid may cause the vaporizer to clog. Also, it may be undesirable for the liquid to enter the arc chamber of the ion source. 
         [0006]    In summary, current vaporizers suffer from two major drawbacks. The first is a temperature gradient across the vaporizer that causes some portions of the vaporizer to be cooler than other portions. This may cause some of the vapor in the vaporizer to condense and block the flow of the remaining vapor. The second issue is spatial orientation. As stated above, if the nozzle is lower in height than the rest of the crucible, liquid may flow toward the nozzle causing clogging. 
         [0007]    Thus, it would be beneficial if there were a vaporizer that addressed these issues associated with condensation. It also would be advantageous if such a vaporizer could be deployed in a number of different orientations without condensed material flowing out of the vaporizer or clogging. 
       SUMMARY 
       [0008]    A vaporizer with several novel features to prevent vapor condensation and the clogging of the nozzle is disclosed. The vaporizer is designed such that there is an increase in temperature along the path that the vapor travels as it flows from the crucible to the arc chamber. The vaporizer uses a nested architecture, where the crucible is installed within an outer housing. Vapor leaving the crucible exits through an aperture and travels along the volume between the crucible and the outer housing to the nozzle, where it flows to the arc chamber. In certain embodiments, the aperture in the crucible is disposed at a location where liquid in the crucible cannot reach the aperture. 
         [0009]    According to one embodiment, a vaporizer is disclosed. The vaporizer comprises a crucible in which a dopant material may be disposed, having an aperture passing through a sidewall of the crucible; an outer housing surrounding the crucible; a vapor channel disposed between the outer housing and the crucible, wherein the aperture is in communication with the vapor channel; and a gas nozzle attached to one end of the outer housing in communication with the vapor channel. In some embodiments, the aperture is disposed in a location so that liquid in the crucible cannot reach the aperture. In certain embodiments, vapor travels in a path from the crucible through the aperture into the vapor channel and to the gas nozzle, and wherein a temperature is increasing as the vapor flows along the path from the aperture to the gas nozzle. In some embodiments, a spacer is disposed between the crucible and the outer housing, separating the crucible and the outer housing. 
         [0010]    According to another embodiment, a vaporizer is disclosed. The vaporizer comprises a crucible in which a dopant material may be disposed; and an outer housing surrounding the crucible and having a gas nozzle; wherein the crucible is thermally isolated from the outer housing. In some embodiments, vapor formed in the crucible travels in a vapor channel located between an outer surface of the crucible and an inner surface of the outer housing. In some embodiments, the crucible comprises an aperture through a sidewall such that the vapor passes through the aperture into the vapor channel, wherein the aperture is disposed at a location having a height equal to or greater than the height of the dopant material. 
         [0011]    According to a third embodiment, a vaporizer is disclosed. The vaporizer comprises a crucible in which a dopant material may be disposed, the crucible being cylindrical, sealed on two ends and having an aperture passing through a sidewall of the crucible; an outer housing surrounding the crucible, wherein a body of the outer housing is cylindrical; and a vapor channel disposed between the crucible and the outer housing, wherein the aperture is in communication with the vapor channel; wherein the outer housing comprises a first end and a second end opposite the first end, with a gas nozzle attached to the first end of the outer housing and in communication with the vapor channel. In certain embodiments, the vaporizer is oriented in an ion source such that the first end is lower than the second end, and wherein the aperture is disposed near the second end. In certain embodiments, the vaporizer is oriented in an ion source such that the first end is higher than the second end, and wherein the aperture is disposed near the first end. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]    For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: 
           [0013]      FIG. 1  is a vaporizer in accordance with one embodiment; 
           [0014]      FIG. 2  is an enlarged view of the crucible of  FIG. 1 ; 
           [0015]      FIGS. 3A-3C  show the vaporizer of  FIG. 1  deployed in different orientations; 
           [0016]      FIGS. 4A-4C  show different configurations of the spacers used in  FIG. 1 ; and 
           [0017]      FIG. 5  shows the vaporizer of  FIG. 1  as employed in an ion source. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As described above, a vaporizer is used to heat a solid to produce a sufficient vapor pressure so that the vapor of a solid material containing a desired dopant species may be introduced into an arc chamber of an ion source. The vaporizer typically comprises a crucible to hold the solid material, a heating element to heat the crucible and a nozzle, through which the vapor exists the vaporizer. 
         [0019]    The present vaporizer incorporates various novel features which reduce the possible of condensation and clogging in a way not previously possible. 
         [0020]      FIG. 1  shows a view of the vaporizer  100  according to one embodiment. The vaporizer  100  includes a heat source  110 , which is used to supply heat to the crucible  130 . The heat source  110  may be a resistive wire heater, where current is passed through the wire, causing the wire to heat. Other types of heat sources may also be used, such as, but not limited to heating lamps. While  FIG. 1  shows the heat source  110  disposed adjacent to one side of the vaporizer  100 , other embodiments are also possible. For example, in certain embodiments, the heat source  110  may wrap around the entirety of the vaporizer  100 , providing heat on all sides. In other embodiments, the heat source  110  may be embedded within the outer housing  120  of the vaporizer  100 . For example, the heat source  110  may be a resistive wire heater that is embedded directly in the outer housing  120 . 
         [0021]    The crucible  130  is used to hold the dopant material, which is typically in solid form. The crucible  130  may be constructed of any suitable material, such as graphite, a refractory metal or ceramic material. The crucible  130  may have a two piece construction, so that the two pieces of the crucible  130  may be separated to allow the solid dopant material to be placed therein. After the solid dopant material has been placed inside the crucible  130 , the two pieces are then joined together. As an example, the crucible  130  may consist of a hollow tube with one closed end and one open end and a cap. The cap and hollow tube may each have threads that allow the two pieces to thread together, creating a crucible  130  where both ends are sealed. 
         [0022]    The crucible  130  is disposed within an outer housing  120 . The outer housing  120  may be constructed of a refractory metal, graphite, or ceramic material. In certain embodiments, the crucible  130  and the outer housing  120  are cylindrical in shape, and share a common major axis such that the spacing between the outer wall of the crucible  130  and the inner wall of the outer housing  120  is constant around the circumference of the crucible  130 . The spacing between the outer wall of the crucible  130  and the inner wall of the outer housing  120  forms a vapor channel  125 , through which vapor may flow. 
         [0023]    In certain embodiments, spacers  140  are used to hold the crucible  130  in place within the outer housing  120 , thus defining the vapor channel  125 . In some embodiments, the spacers  140  are disposed in the vapor channel  125  and hold the crucible  130  such that vapor channel  125  between the crucible  130  and the outer housing  120  may have a uniform thickness. In other words, the spacers  140  cause the crucible  130  and the outer housing  120  to be concentric. However, in other embodiments, the spacers  140  may be configured such that the vapor channel  125  is not uniform thickness around the circumference. For example, the vapor channel  125  may be wider in the region where the vapor is intended to flow. The spacers  140  may be ring-shaped in certain embodiments. As will be described in more detail below, the spacers  140  may have notches, holes or openings to allow for the passage of vapor through the vapor channel  125 . The spacers  140  may be constructed of any suitable material, such as graphite, or a refractory metal. Additionally, in certain embodiments, the spacers  140  may be used to better thermally isolate the crucible  130  from the outer housing  120  so that the outer housing  120  will be higher in temperature than the crucible  130 . In this case, the spacers may be constructed of materials having low thermal conductivity and a high melting point. Suitable materials may include alumina or fused silica. In other words, in certain embodiments, the spacers  140  are constructed of a thermally insulating material. 
         [0024]    In other embodiments, the crucible  130  may be disposed within the outer housing  120  without the use of spacers. For example, the crucible  130  may fit fairly tightly inside the outer housing  120 . In this embodiment, a channel may be created in the inner wall of the outer housing  120 . Alternatively, a channel may be created in the outer wall of the crucible  130 . The channel may be created by removing material from the outer housing  120  or the crucible  130  after the component is created. Alternatively, the channel may be created by an insert in the mold used to create the outer housing  120  or the crucible  130 . 
         [0025]    In each of these embodiments, the channel formed in the outer housing  120  or the crucible  130  serves as the vapor channel  125 . 
         [0026]    In another embodiment, the crucible  130  snugly fits within the outer housing  120  at the two ends, such that the spacing between the sidewalls of the crucible  130  and the outer housing  120  is maintained by a friction fit. This spacing forms the vapor channel  125 . 
         [0027]    As shown in  FIG. 5 , the outer housing  120  may be connected to a mounting base  150 , which attaches the vaporizer  100  to the ion source  200 . For instance, the arc chamber  210  may sit atop an ion source body  220  to which all other components of the ion source, including the vaporizer  100 , are mounted. The mounting base  150  may be constructed using metal or another suitable material. The end of the outer housing  120  nearest the mounting base  150  may be sealed. 
         [0028]    The end of the outer housing  120  that is opposite the mounting base  150  may be in communication with a gas nozzle  160 . Vapor created in the crucible  130  exits the vaporizer  100  through the gas nozzle  160 . In some embodiments, the gas nozzle  160  may be in communication with the arc chamber  210  of the ion source  200 . 
         [0029]      FIG. 2  shows a view of the crucible  130  of  FIG. 1 . As described earlier, spacers  140  may be disposed around the crucible  130  to separate the crucible  130  from the outer housing  120 . While  FIG. 1  and  FIG. 2  show two spacers  140 , any number of spacers  140  may be used and the disclosure does not limit the number of spacers  140  that can be employed. Alternatively, as described above, in certain embodiments, spacers  140  are not used. An aperture  135  is disposed in the side of the crucible  130 . In certain embodiments, the aperture  135  is disposed on the cylindrical sidewall of the crucible  130 . However, the aperture  135  may be disposed on an end of the crucible  130  in other embodiments. The aperture  135  passes through the wall of the crucible  130  and provides a pathway for vapor from the interior of the crucible  130  to the vapor channel  125 . Thus, in certain embodiments, the crucible  130  may be sealed at both ends, with the only opening being the aperture  135  disposed on the cylindrical sidewall of the crucible  130 . 
         [0030]    In certain embodiments, such as that shown in  FIG. 1 , spacers  140  are used to create the vapor channel  125 , which is in communication with the aperture  135  and the gas nozzle  160 . In other embodiments, the vapor channel  125  is created by including a channel or notch along the inner wall of the outer housing  120  or the outer wall of the crucible  130 . In these embodiments, the channel or notch extends from the aperture  135  to the gas nozzle  160 . 
         [0031]    The solid dopant material  131  is disposed within the crucible  130 , and is separated from the aperture  135  through the use of a filter  132 . The filter  132  may be quartz wool or another suitable material. The filter  132  serves as a filter which allows the passage of gasses, but prevents the passage of the solid dopant material  131 . 
         [0032]    Having enumerated the various components in the vaporizer  100 , its operation will now be described with reference to  FIGS. 1-2 . The heat source  110  is used to apply heat to the outer housing  120 , and in some instances, to the gas nozzle  160 . As the outer housing  120  is heated, heat is also radiated to the crucible  130 . Since the crucible  130  is separated from the outer housing  120  through the use of spacers  140 , it heats at a slower rate and may reach a lower final temperature. As the solid dopant material  131  heats, vapor is formed. This vapor passes through the filter  132  and exits the crucible  130  through the aperture  135 . In certain embodiments, the aperture  135  is disposed in the sidewall of the crucible  130  so as be at a height that is greater than or equal to the solid dopant material when the vaporizer  100  is installed in the ion source  200 . In this way, dopant material in the condensed phase will not flow out of the aperture  135 . 
         [0033]    The vapor then moves along the vapor channel  125  between the outer housing  120  and the crucible  130 . Since this vapor channel  125  is adjacent to the outer housing  120 , it is at a higher temperature than the crucible  130 . Thus, the possibility of condensation is greatly reduced. The vapor then exits the vaporizer  100  through the gas nozzle  160 . Again, since the gas nozzle  160  is closer in proximity to the arc chamber  210  of the ion source  200  than other parts of the vaporizer  100 , the gas nozzle  160  will be higher in temperature, further reducing the possibility of condensation. Thus, the temperature of the path travelled by the vapor may be increasing as the vapor moves toward the arc chamber  210  of the ion source  200 . 
         [0034]    Note that the vapor moves along the vapor channel  125  to reach the gas nozzle  160 . To do so, in certain embodiments, the vapor passes through the spacers  140  that are disposed in the vapor channel  125 . To allow for this passage of vapor, the spacers  140  may be designed with one or more notches, holes or openings therein. 
         [0035]      FIG. 4A  shows a spacer  140  according to one embodiment. This spacer  140  has a single opening, in the form of a notch  141 , disposed along its outer circumference. In this embodiment, all of the vapor passes through this notch  141  to reach the gas nozzle  160 . In certain embodiments, the heat source  110  may be disposed along one side of the outer housing  120 , thus making this portion of the outer housing  120  warmer than other portions. In these embodiments, the notch  141  may be disposed near the warmer portion of the outer housing  120 . While  FIG. 4A  shows a notch  141  along the outer circumference, other embodiments are also possible. For example, the spacer  140  may have an opening or hole therethrough. Further, the notch  141  may be disposed along the inner circumference of the spacer  140 . Thus, the type or position of the opening in the spacer  140  is not limited by this disclosure. 
         [0036]    In other embodiments, the heat source  110  may be wrapped around the outer housing  120 . In these embodiments, the entirety of the outer housing  120  may be at or near the same temperature.  FIG. 4B  shows a spacer  145  which may be used with this configuration. The spacer  145  has a plurality of openings, in the form of notches  146 , disposed around its outer circumference, allowing vapor to pass through. Again, openings or holes may be used instead of notches  146 . Further, the notches  146  may be disposed along the inner circumference of the spacer  145 . 
         [0037]      FIG. 4C  shows a spacer  148 , which has no notches, holes or openings. This spacer  148  does not permit the passage of vapor. Its use is described below. 
         [0038]    The vaporizer  100  described herein may be used in a plurality of orientations.  FIG. 3A  shows the vaporizer  100  in an orientation where the gas nozzle is tilted at a downward angle. In  FIGS. 3A-3C , line  300  points in the upward direction. Of course, other angles may also be employed, and  FIG. 3A  is meant to illustrate the operation of the vaporizer  100  when the gas nozzle  160  is at a height lower than the crucible  130 . 
         [0039]    In this embodiment, the aperture  135  is disposed on the sidewall, closer to the end where the mounting base  150  is disposed. This location is selected as it is higher than the level of the solid dopant material that is disposed within the crucible  130 . The location of the aperture  135  has two aspects to it. The first aspect is the location of the aperture  135  along the sidewall in the axial direction. The second aspect is the location of the aperture  135  along the radial direction. In  FIG. 3A , the aperture  135  is shown near the mounting base  150  in the axial direction and disposed near the top of the crucible  130  in the radial direction. This location of the aperture  135  provides a natural flow path for the vapor in the crucible  130 , as the aperture  135  will not be obstructed by condensed dopant material. As the dopant material vaporizes, vapor passes through the filter  132  to the aperture  135 . Once the vapor exits the aperture  135 , it moves along vapor channel  125  and through the openings in spacers  140  toward the gas nozzle  160 . Since the arc chamber  210  is maintained at very low pressure, the vapor is drawn toward the gas nozzle  160 . 
         [0040]      FIG. 3B  shows an embodiment where the vaporizer  100  is installed with the gas nozzle  160  pointing vertically upward. Again, this figure is merely illustrative and the description is applicable to any orientation where the gas nozzle  160  is tilted upward. 
         [0041]    In this embodiment, the aperture  135  is disposed on the sidewall of the crucible  130  closer to the gas nozzle  160  in the axial direction. In this way, the vapor flows upward through the filter  132  and exits through the aperture  135 . The vapor then flows toward the lower pressure arc chamber  210 . In this embodiment, the spacers  140  used may be those shown in  FIG. 4C . These spacers  148  inhibit the flow of vapor through the vapor channel  125  and force the vapor upward toward the gas nozzle  160 . 
         [0042]      FIG. 3C  shows a third orientation where the vaporizer  100  is horizontal. In this orientation, the location of the aperture  135  in the axial direction can vary, as all locations are at the same height. The aperture  135  may be at the highest point in the radial direction. While the location of the aperture  135  may vary, in certain embodiments, the aperture  135  is disposed at one of the two ends of the crucible  130 . These two positions allow the maximum amount of solid dopant material  131  to be disposed in the crucible  130  and allow convenient placement of the filter  132 . However, the selection of one of these two locations may be implementation dependent. 
         [0043]    If the aperture  135  is disposed near the mounting base  150 , as shown in  FIG. 3C , the openings in the spacers  140  may be disposed along the top part of the vapor channel  125 . This further reduces the chances of clogging in case of condensation, as the condensate will flow toward the lower part of the vapor channel  125 . 
         [0044]    The embodiments described above in the present application may have many advantages. In each of these embodiments, several common attributes can be found. 
         [0045]    First, in all of these embodiments, the aperture  135  in the crucible  130  is disposed in a location that is not easily reached by liquid. In other words, even if liquid were to form within the crucible  130 , that liquid cannot reach the aperture  135  and flow into the vapor channel  125  where it may clog that passageway. In this way, the risk of clogging is reduced considerably. 
         [0046]    Second, in each of these embodiments, the path for the vapor is one in which the temperature is increasing as the vapor flows along the path. As described above, the crucible  130  is thermally isolated from the outer housing  120 , and therefore is cooler than the outer housing. As vapor exits the crucible  130 , it enters a vapor channel  125 , which is adjacent to the outer housing  120 , and therefore is warmer than the crucible  130 . Additionally, as the vapor moves toward the gas nozzle  160 , it is further heated as the gas nozzle  160  is also heated by the arc chamber  210 . Thus, the risk of condensation along the path from the crucible  130  to the arc chamber  210  is greatly reduced. 
         [0047]    Third, the crucible  130  may be installed in the outer housing  120  in different configurations. For example, the crucible  130  may be installed such that the aperture  135  is closer to the gas nozzle  160  or closer to the mounting base  150 . The ability to reconfigure the aperture  135  allows the vaporizer  100  to be disposed in a plurality of orientations, including vertical, horizontal, upwardly tilting and downward tilting. Further, the risk of clogging and condensation is minimized in each of these orientations. 
         [0048]    The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. 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.