Abstract:
Techniques for improving extracted ion beam quality using high-transparency electrodes are disclosed. In one particular exemplary embodiment, the techniques may be realized as an apparatus for ion implantation. The apparatus may comprise an ion source for generating an ion beam, wherein the ion source comprises a faceplate with an aperture for the ion beam to travel therethrough. The apparatus may also comprise a set of extraction electrodes comprising at least a suppression electrode and a high-transparency ground electrode, wherein the set of extraction electrodes may extract the ion beam from the ion source via the faceplate, and wherein the high-transparency ground electrode may be configured to optimize gas conductance between the suppression electrode and the high-transparency ground electrode for improved extracted ion beam quality.

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to semiconductor manufacturing equipment and, more particularly, to techniques for improving extracted ion beam quality using high-transparency electrodes. 
     BACKGROUND OF THE DISCLOSURE 
     Ion implantation is a process of depositing chemical species into a substrate by direct bombardment of the substrate with energized ions. In semiconductor manufacturing, ion implanters are used primarily for doping processes that alter a type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is often crucial for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energy levels. 
       FIG. 1  depicts a conventional ion implanter system  100 . The ion implanter  100  includes a source power  101 , an ion source  102 , extraction electrodes  104 , a 90° magnet analyzer  106 , a first deceleration (D 1 ) stage  108 , a 70° magnet analyzer  110 , and a second deceleration (D 2 ) stage  112 . The D 1  and D 2  deceleration stages (also known as “deceleration lenses”) each comprising multiple electrodes with a defined aperture to allow an ion beam  10  to pass therethrough. By applying different combinations of voltage potentials to the multiple electrodes, the D 1  and D 2  deceleration lenses can manipulate ion energies and cause the ion beam  10  to hit a target workpiece  114  at a desired energy. A number of measurement devices  116  (e.g., a dose control Faraday cup, a traveling Faraday cup, or a setup Faraday cup) may be used to monitor and control the ion beam conditions. 
     The ion source  102  and extraction electrodes  104  are critical components of the ion implanter system  100 . The ion source  102  and extraction electrodes  104  are required to generate a stable and reliable ion beam  10  for a variety of different ion species and extraction voltages. 
       FIG. 2  depicts a conventional ion source and extraction electrode configuration  200 . Referring to  FIG. 2 , which is a schematic diagram of the conventional ion source and extraction electrode configuration  200 , the ion source  102  is provided in a housing  201 . The ion source  102  has a faceplate  203 , which has an aperture from which the extraction electrodes  104  may extract ions from plasma in the ion source  102 . The extraction electrodes  104  include a suppression electrode  205  and a ground electrode  207 . As depicted in  FIG. 2 , the suppression electrode  205  and the ground electrode  207  are often double-slotted with different slot dimensions, large slot for high-energy implant application (e.g., &gt;20 keV), and small slot for low-energy application (e.g., &lt;20 keV). 
     It should be appreciated that arrows are shown in  FIG. 2  to represent vacuum pumping directions. Vacuum pumping, as depicted by the arrows, is required to provide pressure level low enough for stable beam-extraction operation between the suppression electrode  205  and the ground electrode  207  for ion beam extraction. 
       FIGS. 3A-3B  depict a conventional ground electrode  207 .  FIG. 3A  depicts a three-dimensional view  300 A of a conventional ground electrode  207 . In this example, the ground electrode  207  is double-slotted, having a first slot  309   a  and a second slot  309   b .  FIG. 3B  depicts a cross-sectional view  300 B of the conventional ground electrode  207 . The ground electrode  207  has a overall height H, which includes a base height b and a slot height a. The ground electrode  207  also has a base angle α and a slot angle β. In the conventional ground electrode  207 , the base height b is greater than the slot height a and the base-to-slot height ratio may be expressed as b/a&gt;1. 
     A problem that currently exists in conventional ion implantation is that as extraction current from the ion source  102  increases, undesirable beam shape may be observed at the target workpiece  114 . This undesirable beam shape may provide “beam wiggles” that ultimately reduce uniformity in the ion beam  10 . Although this problem may be associated with plasma instability and/or plasma oscillation inside the ion source  102 , the extraction electrodes  104  play a critical role and may add to the problem. For example, mechanical imperfections and high background pressure at the extraction electrodes  104  may greatly amplify the “beam wiggles” and degrade ion beam quality. 
       FIG. 4  depicts an illustrative graph  400  of an extracted ion beam profile. In this example, a wiggle-shaped extracted ion beam profile  410  is depicted. As depicted in dotted lines, an ideal extracted ion beam profile  420  is provided. Although both the wiggle-shaped extracted ion beam profile  410  and the ideal extracted ion beam profile  420  have similar profiles, the ideal ion beam profile  420  has a smooth profile, which may be transported and tuned as a high quality ion beam at the target. 
     As described above, “beam wiggles” generated and/or amplified by the extraction electrodes  104  may lead to degraded beam uniformity and poor quality of the ion beam  10  at the target workpiece  114 . In order to improve ion beam quality, the “beam wiggles” in the extracted ion beam profile  410  should be reduced to resemble more closely the ideal extracted ion beam profile  420 . However, conventional systems and methods do not provide an adequate solution to reduce “beam wiggles” in an extracted ion beam profile. 
     In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current ion beam extraction technologies. 
     SUMMARY OF THE DISCLOSURE 
     Techniques for improving extracted ion beam quality using high-transparency electrodes are disclosed. In one particular exemplary embodiment, the techniques may be realized as an apparatus for ion implantation. The apparatus may comprise an ion source for generating an ion beam, wherein the ion source comprises a faceplate with an aperture for the ion beam to travel therethrough. The apparatus may also comprise a set of extraction electrodes comprising at least a suppression electrode and a high-transparency ground electrode, wherein the set of extraction electrodes may extract the ion beam from the ion source via the faceplate, and wherein the high-transparency ground electrode may be configured to optimize gas conductance between the suppression electrode and the high-transparency ground electrode for improved extracted ion beam quality. 
     In accordance with other aspects of this particular exemplary embodiment, the high-transparency ground electrode may be configured with an overall height H, one or more slot portions, a base angle θ, and a slot angle δ, wherein the overall height may comprise a base height y and a slot height x such that the base height y may be less than the slot height x and the base-to-slot height ratio y/x may be equal to or less than 1. 
     In accordance with further aspects of this particular exemplary embodiment, the base angle θ may be 20°. 
     In accordance with additional aspects of this particular exemplary embodiment, the base angle θ may be greater than 20°, such as 40°. 
     In accordance with other aspects of this particular exemplary embodiment, the high-transparency ground electrode may be a single-slot high-transparency ground electrode or a double-slot high-transparency ground electrode. 
     In accordance with further aspects of this particular exemplary embodiment, the ion source may be encased in a housing having a tapered configuration. 
     In accordance with additional aspects of this particular exemplary embodiment, the faceplate may be a protruded faceplate. 
     In accordance with other aspects of this particular exemplary embodiment, the suppression electrode may be a protruded suppression electrode. 
     In accordance with further aspects of this particular exemplary embodiment, the high-transparency ground electrode may further comprise one or more anchor portions positioned near one or more extraction slots of the high-transparency ground electrode for defining stable plasma boundaries inside of the high-transparency ground electrode. 
     In another particular exemplary embodiment, the techniques may be realized as a method for improving ion beam quality. The method may comprise providing an ion source comprising a plasma generator for generating an ion beam and a faceplate with an aperture for the ion beam to travel therethrough. The method may also comprise providing a set of extraction electrodes comprising at least a suppression electrode and a high-transparency ground electrode, wherein the set of extraction electrodes may extract the ion beam from the ion source via the faceplate, and wherein the high-transparency ground electrode may be configured to optimize gas conductance between the suppression electrode and the high-transparency ground electrode for improved ion beam quality. 
     The present disclosure will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present disclosure is described below with reference to exemplary embodiments, it should be understood that the present disclosure is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein, and with respect to which the present disclosure may be of significant utility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only. 
         FIG. 1  depicts a conventional ion implanter system. 
         FIG. 2  depicts a conventional ion source and extraction electrode configuration. 
         FIGS. 3A-3B  depict a conventional ground electrode. 
         FIG. 4  depicts an illustrative graph of a wiggle-shaped extracted ion beam profile and an ideal extracted ion beam profile. 
         FIG. 5  depicts an ion source and extraction electrode configuration, according to an exemplary embodiment of the present disclosure. 
         FIGS. 6A-6B  depict a double-slot high-transparency ground electrode, according to an exemplary embodiment of the present disclosure. 
         FIG. 7  depicts an ion source and extraction electrode configuration, according to another exemplary embodiment of the present disclosure. 
         FIG. 8  depicts an ion source and extraction electrode configuration, according to another exemplary embodiment of the present disclosure. 
         FIG. 9  depicts an ion source and extraction electrode configuration with a high-transparency ground electrode using anchors, according to another exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the present disclosure improve extracted ion beam quality by using high-transparency electrodes. More specifically, various geometric schemes and/or configurations for an ion source and extraction electrodes may provide improved vacuum characteristics for reducing “beam wiggles” in an extracted ion beam profile and improve overall ion beam quality. 
       FIG. 5  depicts an ion source and extraction electrode configuration  500  according to an exemplary embodiment of the present disclosure. Referring to  FIG. 5 , which depicts a schematic diagram of the ion source and extraction electrode configuration  500 , an ion source  502  may be provided in a housing  501 . The ion source  502  may have a faceplate  503  that includes an aperture from which extraction electrodes  504  may extract ions from plasma inside the ion source  502 . The extraction electrodes  504  may include at least a suppression electrode  505  and a ground electrode  507 . 
     In some embodiments, as depicted in  FIG. 5 , the suppression electrode  505  and the ground electrode  507  may be double-slotted. In this example, it should be appreciated that one slot may be for high-energy ion beam application (e.g., &gt;20 keV) and another slot may be for low-energy ion beam application (e.g., &lt;20 keV). However, unlike the conventional ground electrode  207  described above, the ground electrode  507  of  FIG. 5  may be a high-transparency ground electrode  507  having a geometry that optimizes gas conductance in an extraction region (e.g., a region between the suppression electrode  505  and the ground electrode  507 ). It should be appreciated that large arrows are shown in  FIG. 5  to represent vacuum pumping directions. As depicted by the large arrows, using the high-transparency ground electrode  507  may provide improved gas conductance in the extraction region (e.g., due to a large opening area) in a direction toward a turbo pump (not shown) (vertical) and an analyzer magnet (not shown) (horizontal). 
       FIGS. 6A-6B  depict views of the high-transparency ground electrode  507  according to an exemplary embodiment of the present disclosure. For example,  FIG. 6A  depicts a three-dimensional view  600 A of the high-transparency ground electrode  507  according to an exemplary embodiment of the present disclosure. The high-transparency ground electrode  507  of  FIG. 6A  may be a double-slot high-transparency ground electrode  507  having a first slot  609   a  and a second slot  609   b.    
     However, unlike the conventional ground electrode  207  described above, the double-slot high-transparency ground electrode  507  of  FIGS. 6A-6B  may have dimensions that provide improved gas conductance in the extraction region, especially between the suppression electrode  505  and the double-slot high-transparency ground electrode  507 . In particular, the double-slot high-transparency ground electrode  507  may have a substantially reduced base portion.  FIG. 6B  depicts a cross-sectional view  600 B of the double-slot high-transparency ground electrode  507 . In this example, the double-slot high-transparency ground electrode  507  may have an overall height L, which includes a base height y and a slot height x. The double-slot high-transparency ground electrode  507  may also have a base angle θ and a slot angle δ. In some embodiments, the base angle θ may be 20°. It should be appreciated that the base height y may be lesser than the slot height x. Therefore, the base-to-slot height ratio may be expressed as y/x&lt;1. It should also be appreciated that in some embodiments, the slot angle δ may be reduced as well. 
     The above-described double-slot high-transparency ground electrode  507  has a geometry that may provide improved gas conductance. More specifically, the overall volume of the ground electrode  507  may be reduced and therefore provide more room for effective vacuum pumping, which may improve gas conductance. Additionally, the double-slot high-transparency ground electrode  507  may be utilized in existing systems without additional alterations and/or modifications. Thus, using the double-slot high-transparency ground electrode  507  may provide a cost-effective way to optimize gas conductance and improve extracted ion beam quality. 
       FIG. 7  depicts an ion source and extraction electrode configuration  700  according to another exemplary embodiment of the present disclosure. Similar to  FIG. 5 ,  FIG. 7  depicts a schematic diagram of an ion source and extraction electrode configuration  700 . Here, an ion source  702  may be provided in a housing  701 . The ion source  702  may also have a faceplate  703  having an aperture from which extraction electrodes  704  may extract ions from plasma in the ion source  702 . The extraction electrodes  704  may include a suppression electrode  705  and a high-transparency ground electrode  707 . 
     However, unlike  FIG. 5 , the suppression electrode  705  and the high-transparency ground electrode  707  of  FIG. 7  may be single-slotted. For similar reasons stated above, such geometric configurations may optimize gas conductance in the extraction region. 
     It should be appreciated that large arrows are shown in  FIG. 7  to represent pumping directions. As depicted by the large arrows, using the single-slotted high-transparency ground electrode  707  may provide improved gas conductance in the extraction region (e.g., between the suppression electrode  705  and the ground electrode  507 ) in a direction toward a turbo pump (not shown) (vertical) and an analyzer magnet (not shown) (horizontal). Similar to  FIG. 5 , overall volume of the high-transparency ground electrode  707  may be reduced in a single-slot configuration and therefore provide more room for vacuum pumping and an improve ion beam profile. 
     A variety of additional geometric configurations may also be provided. For example,  FIG. 8  depicts an ion source and extraction electrode configuration  800  according to another exemplary embodiment of the present disclosure. Similar to  FIG. 7 ,  FIG. 8  depicts a schematic diagram of an ion source and extraction electrode configuration  800 . In this example, an ion source  802  may be provided in a housing  801 . The ion source  802  may also have a faceplate  803  having an aperture from which extraction electrodes  804  may extract ions from the plasma in the ion source  802 . The extraction electrodes  804  may include a suppression electrode  805  and a ground electrode  807 , which in turn may be single-slotted. 
     However, unlike  FIG. 7 , the housing  801 , the faceplate  803 , the suppression electrode  805 , and the ground electrode  807  of  FIG. 8  may each have different geometric schemes and/or configurations. For instance, the housing  801  may have a tapered configuration (e.g., a tapered top hat configuration) and each of the faceplate  803 , the suppression electrode  805 , and the ground electrode  807  may have a protruded configuration. For similar reasons stated above, these various geometric configurations, independently or altogether, may optimize gas conductance and improve an extracted ion beam profile. 
     The tapered housing  801 , as opposed to the conventional configuration (e.g., non-tapered configuration), may improve gas conductance between the faceplate  803  and the suppression electrode  805 . A tapered shape may provide more room for gas conductance and may therefore minimize gas pressure for improved extracted ion beam quality. The protruded faceplate  803  may also improve gas conductance between the faceplate  803  and the suppression electrode  805 . 
     According to an exemplary embodiment of the present disclosure, the protruded ion source faceplate  803  may be provided. In this example, rather than a conventional planar configuration, the protruded faceplate  803  may be sloped such that an extraction aperture of the protruded faceplate  803  may “protrude” towards the extraction electrodes. 
     It should be appreciated that while beam optics of the protruded faceplate  803  remain the same or similar to that of a conventional faceplate, the shape of the protruded faceplate  803  may provide an improved geometric scheme. Ultimately, a protruded shape may provide more space for improved gas conductance and may therefore lower gas pressure for improved extracted ion beam quality. 
     Referring back to  FIG. 8 , protruded extraction electrodes  804  may also improve gas conductance between the faceplate  803  and the suppression electrode  805 . For example, the protruded suppression electrode  805  may extend further toward the faceplate  803  to improve gas conductance at a region between the faceplate  803  and the suppression electrode  805 . 
     Additionally, in this configuration, the high-transparency ground electrode  807  may be protruded and widened to improve gas conductance as well. For example, in  FIG. 8 , the high-transparency ground electrode  807  may also have widened base angle θ′. In some embodiments, the widened base angle θ′ may be twice that of the base angle θ from previous embodiments. For instance, in one embodiment, base angle θ′ may be 40°. Other various embodiments may also be provided. 
     By using a protruded and widened high-transparency ground electrode  807 , gas conductance may be improved in the region between the suppression electrode  805  and the ground electrode  807 . It should be appreciated that improvements in gas conductance may also be provided in a (horizontal) direction toward an analyzer magnet (not shown). 
     It should be appreciated that anchors may also be provided at the high-transparency ground electrode  807  to alter pressure distribution in an extraction region (e.g., between the suppression electrode  805  and the high-transparency ground electrode  807 ). For example,  FIG. 9  depicts an ion source and extraction electrode configuration  900  with a high-transparency ground electrode  907  using anchors  909  according to another exemplary embodiment of the present disclosure. In some embodiments the high-transparency ground electrode  907  using anchors  909  may better define stable plasma boundaries inside an extraction slot of the ground electrode  907 . In other embodiments, the high-transparency ground electrode  907  using anchors  909  may provide a pressure gradient in a downstream region of an extracted ion beam path. This may provide increased pressure between the suppression electrode  905  and the high-transparency ground electrode  907  and reduce pressure within the high-transparency ground electrode  907  and in regions further downstream. 
     Embodiments of the present disclosure may provide improved extracted ion beam quality by optimizing gas conductance at an ion source and extraction electrodes. These techniques may separately or conjunctively reduce “beam wiggles” in an extracted ion beam profile. In doing so, desired correction to a shape of the ion beam may be provided. More specifically, greater ion beam uniformity, reliability, and predictability may be achieved and effected for improved ion implantation process. 
     It should be appreciated that while certain geometries have been described (e.g., protruded shapes, sizes, changes in angles/ratios, etc.), other geometric configurations for improving gas conductance and improving ion beam quality may also be provided. 
     It should be appreciated that while these embodiments of the present disclosure may be depicted and described as having certain shapes, cross-sectional shapes, numbers, angles, and sizes, other various shapes, cross-sectional shapes, numbers, angles, and sizes may also be considered. 
     It should also be appreciated that while embodiments of the present disclosure are directed to a high-transparency electrode configuration having a single slot or a double slot, other various configurations may also be provided. For example, a high-transparency electrode configurations having smaller or larger numbers of slots (e.g., configurations having single, multiple, or segmented electrodes) may also be provided. 
     It should also be appreciated that operation of the geometric configurations in the embodiments described above should not be restricted to ion source and extraction electrode configurations. For example, the various techniques and geometric configurations described above may also be applied to other ion implantation components as well. 
     It should be also appreciated that while embodiments of the present disclosure are directed to improving gas conductance and extracted ion beam quality, other implementations may be provided as well. For example, the disclosed techniques for utilizing various geometric ion source and extraction electrode configurations may also apply to other various ion implantation systems that use electric and/or magnetic deflection or any other beam collimating systems. Other various embodiments may also be provided. 
     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. Further, 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.