Abstract:
A plasma processing system for providing a uniform erosion of a surface of a target is provided. The system includes a dual plasma source arrangement, wherein each plasma source of the dual plasma source arrangement having a source housing for generating plasma therein. The system further includes a set of antennas, wherein at least one antenna is positioned outside of the source housing of each plasma source, at least one antenna is configured to be excited with RF power to generate the plasma inside the source housing of the each plasma source. The system yet also includes a magnet assembly configured for directing ions of the plasma within the source housing of the each plasma source through an opening of the source housing toward the surface of the target, wherein the target is positioned between a first plasma source of the dual plasma source arrangement and a second plasma source of the dual plasma source arrangement.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Long-throw plasma-enhanced deposition processes have long been employed for plasma processing of substrates (e.g., wafers, flat panel displays, portable device displays, etc.). In a long-throw plasma-enhanced deposition process, a plasma source is positioned some distance away from the target while bombarding the target with ions. The ions from the plasma source sputter material off the target, which causes the sputtered material to be deposited on the surface of a substrate. Typically a controlled bias voltage in the form of straight DC, or pulsed DC, or RF, is applied to the target, so that the ions in the plasma may energetically bombard the target. 
         [0002]    To elaborate, the term “long throw” refers to the fact that the target is located typically (but not always necessarily) at least one wafer diameter away from the target in order to minimize target poisoning. For example, in the case of reactive sputter deposition, the target is a metal target but an oxide film at the substrate may be formed through injection of oxygen in the proximity of the substrate. Long-throw plasma-enhanced deposition is particularly suitable for reactive plasma deposition processes, which facilitate reactive deposition on substrates for semiconductor device manufacturing. 
         [0003]    Embodiments of the invention relate to improving prior art long-throw plasma-enhanced deposition systems and to method steps to improve deposition processes performed via long-throw plasma-enhanced deposition systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0005]      FIG. 1  shows, in accordance with an embodiment of the invention dual-source long throw plasma-enhanced deposition system. 
           [0006]      FIG. 2  shows, in accordance with an embodiment of the invention, the use of steerable magnets, along with the offset of target surface with respect to the common axis of the plasma sources, to improve sputtering of the target. 
           [0007]      FIG. 3  shows, in accordance with an embodiment of the invention, an alternative embodiment wherein the entire source may be tilted relative to the target instead of tilting the magnets themselves. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0008]    The present invention will now be described in detail with reference to a few embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. 
         [0009]    Various embodiments are described herein below, including methods and techniques. It should be kept in mind that the invention might also cover articles of manufacture that includes a computer readable medium on which computer-readable instructions for carrying out embodiments of the inventive technique are stored. The computer readable medium may include, for example, semiconductor, magnetic, opto-magnetic, optical, or other forms of computer readable medium for storing computer readable code. Further, the invention may also cover apparatuses for practicing embodiments of the invention. Such apparatus may include circuits, dedicated and/or programmable, to carry out tasks pertaining to embodiments of the invention. Examples of such apparatus include a general-purpose computer and/or a dedicated computing device when appropriately programmed and may include a combination of a computer/computing device and dedicated/programmable circuits adapted for the various tasks pertaining to embodiments of the invention. 
         [0010]    Embodiments of the invention relate to dual remote plasma source systems and methods for long-throw plasma-enhanced deposition to achieve more full and uniform erosion of the target&#39;s surface. The ability of the dual remote plasma sources to achieve more full and uniform erosion of the target&#39;s surface in long-throw plasma-enhanced deposition applications makes the inventive process ideal for reactive deposition while minimizing target poisoning. 
         [0011]    As the term is employed herein, target poisoning refers to the undesirable reaction of the target surface with the reactive components that are normally employed at the substrate&#39;s surface to achieve reactive deposition. Target poisoning may alter the chemical composition of the target&#39;s surface, severely change the deposition rate resulting in loss of process control, or change the composition of the material that is sputtered from the target and undesirably alter the deposition film on the wafer. 
         [0012]    Embodiments of the invention also relate to the improvements in the target sputter rate by tilting steering magnets and offsetting of target axis with respect to the axes of the plasma sources, in a dual remote plasma source scheme. Other embodiments of the invention also relate to the arrangement of the steerable magnet coils (such as the use of multiple magnet coils) and the tilting of both sources to enable their individual axes to be directed toward the target with or without the tilting of the steering magnets. 
         [0013]    The features and advantages of embodiments of the present invention maybe better understood with reference to the figures and discussions that follow. 
         [0014]      FIG. 1  shows, in accordance with an embodiment of the invention, a plasma source  102  disposed on one side of target  106  and another plasma source  104  disposed on the opposite side of target  106 . Each of sources  102  and  104  includes a source housing, shown as housing  130  of source  102  for example. An antenna  132  is disposed outside of housing  130  and may be excited with RF energy to ignite a plasma inside housing  130 . The ions from the plasma generated inside housing  130  are then steered by a magnet assembly  134  toward target  106  via opening  138 . The plasma ions from source  102  erode one side of target  106  while the plasma ions from source  104  erode the opposite side of target  106 , thereby allowing target  106  to be eroded more uniformly than if only one source were provided. 
         [0015]    In one or more embodiments, the presence of the second plasma source provides significant advantages pertaining to the issues of uniform target erosion which prevents target poisoning in a reactive process, improved process control, improved target current and/or improved deposition uniformity/quality. As seen in  FIG. 1 , a second plasma source  104  having substantially the same above-described components (e.g., housing, magnet assembly, antenna, etc.). The plasma ions from the second plasma source  104  helps erode the opposite side of target  106 , thereby allowing target  106  to be eroded more uniformly than if only one source were provided. Further, the provision of a second source provides additional tuning knobs to allow the process engineer to more finely tune the process by manipulating the various parameters associated with second plasma source  104 . 
         [0016]    In one or more embodiments, a liner may be disposed inside the plasma source housing. The liner may be formed of substantially the same material or the exact same material as of that the oxide of the target, that is intended to be formed at the substrate in the reactive process. Thus, if some of the liner material is sputtered by the high density plasma formed inside housing  130  (which is now with the aforementioned liner), the sputtered liner material would appear to the substrate to be substantially identical to the sputtered target material. Accordingly, substantially the same desired material would reach the surface of the wafer, eliminating contamination concerns. This liner may be made removable, such as in the form of a removable cylindrical insert for example, in order to facilitate rapid maintenance. 
         [0017]    Generally speaking, target  106  may be positioned symmetrically with respect to source  102  and source  104  although this is not a requirement. For example, if one of sources  102  and  104  is configured to generate a denser plasma than the other, target  106  may be positioned further away from the more powerful plasma source to compensate, if desired. There may exist other reasons for unsymmetrical target positioning in a specific chamber. 
         [0018]    A wafer  108  is disposed such that the material sputtered from target  106  is deposited on wafer  108 . The target may be powered through DC, pulsed DC or RF, pulsed RF, or any combination thereof. Generally speaking, the use of the dual remote plasma sources result in more uniform removal of the target material, thereby allowing the erosion of the target to be more uniform and repeatable. 
         [0019]    Target  106  is shown displaced from source axis  110  of source  102  and from source axis  112  of source  104 . Target  106  may be offset tilted at a small distance at any angle relative to the common axis or the individual axes of the plasma sources. The distance from the target to the individual sources may be varied to optimize the target current. 
         [0020]    Magnet assembly  134  is shown comprising two coil magnets although a single magnet may well be employed. Alternatively, more than two magnets may be employed if desired. As will be discussed later herein, magnet assembly  134  may be disposed perpendicular to source axis  110  and/or  112  (as shown in  FIG. 1 ) or the plane of magnet assembly  134  (or of the individual coil magnet) may be disposed at an angle (other than perpendicular) relative to source axis  110  and/or  112 . 
         [0021]    In accordance with one or more embodiments of the invention, one or more of the steerable magnets may comprise multiple segments to allow the magnet to be shaped to further steer the plasma. In other words, an individual magnet does not have to be planar, and the individual constituent parts of a single magnet may be moved relative to other constituent parts of that magnet (manually or via automatic mechanical, electrical, pneumatic, or electrical actuation) to shape the magnetic field, which in turn provides another tuning knob to influence the plasma formed and/or delivered to the target. 
         [0022]    Wafer  108  may be tilted for step coverage in one or more embodiment. Further, wafer  108  may be biased (with an RF signal, for example) to improve specific film properties in one or more deposition applications. Reactive gas may be injected around the wafer to form a reactive environment to enable reactive deposition to be formed on the substrate&#39;s surface. 
         [0023]      FIG. 2  shows, in accordance with an embodiment of the invention, the use of steerable magnets to improve sputtering of the target. As can be seen in  FIG. 2 , a plasma source  202  includes a magnet assembly  210 , which in turn comprises two steerable magnets  212 A and  212  B. Steerable magnet  212 A and  212 B may be tilted relative to source axis  220  as a single unit or each of steerable magnets  212 A and  212 B may be tilted at different angles other than perpendicular (as shown in  FIG. 2 ) relative to source axis  220 . 
         [0024]    Furthermore, there are shown steerable magnets  222 A and  222 B associated with magnet assembly  220  of plasma source  204 . Steerable magnet  222 A and  222 B may be tilted at the same angle relative to source axis  226  or they may tilted at different angles as shown in  FIG. 2  relative to source axis  226 . 
         [0025]    Still further, each of steerable magnets  212 A,  212 B,  222 A, and  222 B may be tilted at different angles relative to one another or groups of steerable magnets associated with each plasma source may mirror the tilting of the group of steerable magnets on the other plasma source, if desired. 
         [0026]    Relative to conventional long-throw plasma-enhanced deposition systems, target  206  is retracted further upward in the direction of arrow  240  away from the common source axis between plasma source  202  and  204 . As such, target  206  is moved further away from wafer  202  to place target  206  further away from the reactive gas(es) injected in the vicinity of wafer  202  reduce at the possibility of target poisoning. Still further, the tilting of the steerable magnets in the magnet assembly allows plasma ions to be steered toward the target thereby enhancing the target current and increases the sputtering rate. 
         [0027]    Generally speaking, deposition rate is directly proportional to the target current. Target current generally has a maximum at some specific distance from the source axis of a given plasma source, with the specific distance depending on the specific parameters of each machine or each recipe and may be determined empirically by moving the target away from the source axis and measuring, directly or indirectly, the target current. If the target is moved too far away, the target current would drop. The optimal target current may be empirically determined in this manner and advantageously taken into account in the formulation of a processing recipe. 
         [0028]    The magnet tilt angle also has an impact on the target current such that there is a typically a maximum at some magnet tilt angle. The optimal magnet tilt angle of each magnet or magnet assembly may also be determined empirically. 
         [0029]    In accordance with one or more embodiments of the invention, adjustments to the target current may also be made by moving the RF antenna closer to or further away from the magnets. The target current may be tuned by moving the antenna closer to the source opening (such as source opening  138  in  FIG. 1 ) or away from that source opening. Likewise, target current may be tuned by moving the magnet assembly as a unit or individual magnets closer to the source opening or away from the source opening. Other method to optimize the target current may involve moving the sources closer or further away from the target along the source axes, for example. The discovery of these tuning steps, individually or in various combinations thereof, comprise method steps of one or more embodiments of the present invention. 
         [0030]      FIG. 3  shows, in accordance with an embodiment of the invention, an alternative embodiment wherein the entire source may be tilted relative to the target instead of tilting the magnets themselves. In the example of  FIG. 3 , both plasma source  302  and  304  are tilted toward target  306  such that the source axes of these plasma sources  302  and  304  are no longer parallel to the planar surface of target  306 . By using two sources and allowing both sources to be tilted, either as a group or individually, relative to the target advantageously improves the degree by which the target may be uniformly eroded and/or to provide additional control knobs in the sputtering of the target and/or deposition of material on the surface of the substrate. 
         [0031]    The tilting of plasma sources  302  and  304  may eliminate the need for tilting the magnets and eliminate the need to offset the target axis from the axes of the plasma sources. However, in one or more embodiments, the tilting of the two plasma sources, either together or individually, may also be performed in addition to the tilting of the magnets relative to each source axis and/or in combination with the offsetting of the target from the source axis. 
         [0032]    As can be appreciated from the foregoing, embodiments of the invention, via various combinations of the above-discussed innovative structural improvements and/or method steps, improve the uniformity of target erosion, reduce the possibility of target poisoning, provide additional tuning knobs to the deposition process, improve the target current, and/or improve deposition rate and/or uniformity. 
         [0033]    While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. For example, although the figures describe the structures and arrangements of various embodiments of the improved long-throw plasma-enhanced deposition system, the invention also covers method steps as described that improve the deposition processes performed via various embodiments of the improved long-throw plasma-enhanced deposition systems. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. Although various examples are provided herein, it is intended that these examples be illustrative and not limiting with respect to the invention. If the term “set” is employed herein, such term is intended to have its commonly understood mathematical meaning to cover zero, one, or more than one member.