Abstract:
A plasma processing apparatus and method are disclosed which create a uniform plasma within an enclosure. In one embodiment, a conductive or ferrite material is used to influence a section of the antenna, where a section is made up of portions of multiple coiled segments. In another embodiment, a ferrite material is used to influence a portion of the antenna. In another embodiment, plasma uniformity is improved by modifying the internal shape and volume of the enclosure.

Description:
BACKGROUND 
     A plasma processing apparatus generates a plasma in a chamber which can be used to treat a workpiece supported by a platen in a process chamber. In some embodiments, the chamber in which the plasma is generated is the process chamber. Such plasma processing apparatus may include, but not be limited to, doping systems, etching systems, and deposition systems. In some plasma processing apparatus, ions from the plasma are attracted towards a workpiece. In a plasma doping apparatus, ions may be attracted with sufficient energy to be implanted into the physical structure of the workpiece, e.g., a semiconductor substrate in one instance. 
     In other embodiments, the plasma may be generated in one chamber, which ions are extracted from, and the workpiece is treated in a different process chamber. One example of such a configuration may be a beam line ion implanter where the ion source utilizes an inductively coupled plasma (ICP) source. The plasma is generally a quasi-neutral collection of ions (usually having a positive charge) and electrons (having a negative charge). The plasma has an electric field of about 0 volts per centimeter in the bulk of the plasma. 
     Turning to  FIG. 1 , a block diagram of one exemplary plasma doping apparatus  100  is illustrated. The plasma doping apparatus  100  includes a process chamber  102  defining an enclosed volume  103 . A gas source  104  provides a primary dopant gas to the enclosed volume  103  of the process chamber  102  through the mass flow controller  106 . A gas baffle  170  may be positioned in the process chamber  102  to deflect the flow of gas from the gas source  104 . A pressure gauge  108  measures the pressure inside the process chamber  102 . A vacuum pump  112  evacuates exhausts from the process chamber  102  through an exhaust port  110 . An exhaust valve  114  controls the exhaust conductance through the exhaust port  110 . 
     The plasma doping apparatus  100  may further includes a gas pressure controller  116  that is electrically connected to the mass flow controller  106 , the pressure gauge  108 , and the exhaust valve  114 . The gas pressure controller  116  may be configured to maintain a desired pressure in the process chamber  102  by controlling either the exhaust conductance with the exhaust valve  114  or a process gas flow rate with the mass flow controller  106  in a feedback loop that is responsive to the pressure gauge  108 . 
     The process chamber  102  may have a chamber top  118  that includes a first section  120  formed of a dielectric material that extends in a generally horizontal direction. The chamber top  118  also includes a second section  122  formed of a dielectric material that extends a height from the first section  120  in a generally vertical direction. The chamber top  118  further includes a lid  124  formed of an electrically and thermally conductive material that extends across the second section  122  in a horizontal direction. 
     The plasma doping apparatus further includes a source  101  configured to generate a plasma  140  within the process chamber  102 . The source  101  may include a RF source  150  such as a power supply to supply RF power to either one or both of the planar antenna  126  and the helical antenna  146  to generate the plasma  140 . The RF source  150  may be coupled to the antennas  126 ,  146  by an impedance matching network  152  that matches the output impedance of the RF source  150  to the impedance of the RF antennas  126 ,  146  in order to maximize the power transferred from the RF source  150  to the RF antennas  126 ,  146 . 
     In some embodiments, the planar and helical antennas  126 ,  146  comprise a conductive material wound in a spiraling pattern. For example,  FIG. 2A  shows one embodiment of a traditional planar antenna  126 , while  FIG. 2B  shows a second embodiment.  FIG. 3  shows a traditional helical antenna  146 . 
     The plasma doping apparatus may also include a bias power supply  190  electrically coupled to the platen  134 . The plasma doping system may further include a controller  156  and a user interface system  158 . The controller  156  can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller  156  may also include communication devices, data storage devices, and software. The user interface system  158  may include devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the plasma doping apparatus via the controller  156 . A shield ring  194  may be disposed around the platen  134  to improve the uniformity of implanted ion distribution near the edge of the workpiece  138 . One or more Faraday sensors such as Faraday cup  199  may also be positioned in the shield ring  194  to sense ion beam current. 
     In operation, the gas source  104  supplies a primary dopant gas containing a desired dopant for implantation into the workpiece  138 . The source  101  is configured to generate the plasma  140  within the process chamber  102 . The source  101  may be controlled by the controller  156 . To generate the plasma  140 , the RF source  150  resonates RF currents in at least one of the RF antennas  126 ,  146  to produce an oscillating magnetic field. The oscillating magnetic field induces RF currents into the process chamber  102 . The RF currents in the process chamber  102  excite and ionize the primary dopant gas to generate the plasma  140 . 
     The bias power supply  190  provides a pulsed platen signal having a pulse ON and OFF periods to bias the platen  134  and hence the workpiece  138  to accelerate ions  109  from the plasma  140  towards the workpiece  138 . The ions  109  may be positively charged ions and hence the pulse ON periods of the pulsed platen signal may be negative voltage pulses with respect to the process chamber  102  to attract the positively charged ions. The frequency of the pulsed platen signal and/or the duty cycle of the pulses may be selected to provide a desired dose rate. The amplitude of the pulsed platen signal may be selected to provide a desired energy. 
     One drawback of conventional plasma processing is lack of plasma uniformity. In some embodiments, the plasma concentration is greater in a portion of the process chamber, thereby causing unequal implantation of ions. To overcome this, it has been suggested to add a conductive body near the antenna  126 ,  146 . Note in  FIGS. 2 and 3 , the antenna can be viewed as a set of connected nearly circular coiled segments, where the first end of a first coiled segment is connected to the second end of an adjacent coiled segment. For example, both  FIG. 2A  and  FIG. 2B  can be seen to have 4 connected coiled segments. In the case of  FIG. 2A , the shape of each coiled segment  201  is slightly irregular such that the second end of a coiled segment  201  does not meet the first end of that coiled segment. Thus, one end of coiled segment  201   a  connects to an end of coiled segment  201   b . In contrast, the coiled segments  202  of  FIG. 2B  are circular, however, there is a break such that the two ends of the coiled segments  202  do not connect. In this case, a linear segment  203  is used to connect two adjacent coiled segments  202 . For example, linear segment  203   a  is used to connect coiled segment  202   d  and coiled segment  202   c.    
       FIG. 3  shows a helical antenna  146 . The wound coiled segments  204  of a helical antenna  146  can be attached using the mechanisms shown in  FIG. 2A-B  for planar antennas. To improve the plasma uniformity of a chamber utilizing such an antenna, it has been suggested to add a conductive body near one of more coiled segments of the antenna. In other words, referring to  FIG. 2A , a metal object may be shaped and located so as to affect coiled segment  201   d , without little or no impact on the other coiled segments. Stated another way, the conductive body is symmetrical in the radial direction (assuming a polar coordinate system where the origin is the center of the antenna as shown in  FIGS. 2A-B ). The metal object may be circular or annular. For example, an annular metal body may be used to affect coiled segment  201   a , without affecting coiled segments  201   b - d.    
       FIG. 4  shows a block diagram of a conventional ion implanter  300 . Of course, many different ion implanters may be used. The conventional ion implanter may comprise an ion source  302  that may be biased by a power supply  301 . The system may be controlled by controller  320 . The operator communicates with the controller  320  via user interface system  322 . The ion source  302  is typically contained in a vacuum chamber known as a source housing (not shown). The ion implanter system  300  may also comprise a series of beam-line components through which ions  10  pass. The series of beam-line components may include, for example, extraction electrodes  304 , a 90° magnet analyzer  306 , a first deceleration (D 1 ) stage  308 , a 70° magnet collimator  310 , and a second deceleration (D 2 ) stage  312 . Much like a series of optical lenses that manipulate a light beam, the beam-line components can manipulate and focus the ion beam  10  before steering it towards a workpiece or wafer  314 , which is disposed on a workpiece support  316 . 
     In operation, a workpiece handling robot (not shown) disposes the workpiece  314  on the workpiece support  316  that can be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat” (not shown). Meanwhile, ions are generated in the ion source  302  and extracted by the extraction electrodes  304 . The extracted ions  10  travel in a beam-like state along the beam-line components and implanted on the workpiece  314 . After implanting ions is completed, the workpiece handling robot may remove the workpiece  314  from the workpiece support  316  and from the ion implanter  300 . 
     The ion source  302  may be an inductively coupled plasma (ICP) ion source. In some embodiments, such as in  FIGS. 5A-B , the ion source  302  may comprise a rectangular enclosure, having an extraction slit  335  on one side  337 . In certain embodiments, the side  336  opposite the extraction slit  335  may be made of a dielectric material, such as alumina, such that a planar antenna  338  may be placed against the dielectric wall  336  to create a plasma within the enclosure  302 . The enclosure  302  also has a top surface  339 , a bottom surface  341 , and two endwalls  338 ,  340 . 
     In another embodiment, a helical antenna  350  is wrapped around the endwalls  338 ,  340  and the top surface  339  and bottom surface  341  of the ICP ion source  302 , as shown in  FIG. 6 . 
     In these embodiments, due to the irregular shape of the ion source  302 , it is difficult to create a uniform plasma which can be extracted through the extraction slit  335 . Accordingly, there is a need for a plasma processing method that overcomes the above-described inadequacies and shortcomings. 
     SUMMARY 
     A plasma processing apparatus and method are disclosed which create a uniform plasma within an enclosure. In one embodiment, a conductive or ferrite material is used to influence a section of the antenna, where a section is made up of portions of multiple coiled segments. In another embodiment, a ferrite material is used to influence a portion of the antenna. In another embodiment, plasma uniformity is improved by modifying the internal shape and volume of the enclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which like elements are referenced with like numerals, and in which: 
         FIG. 1  is a block diagram of a plasma doping apparatus of the prior art; 
         FIGS. 2A-B  illustrate planar antenna of the prior art; 
         FIG. 3  illustrates a helical antenna of the prior art; 
         FIG. 4  is a block diagram of a ion implantation apparatus; 
         FIG. 5A  is a front view of one embodiment of an ICP source; 
         FIG. 5B  is a rear view of the embodiment of  FIG. 5A ; 
         FIG. 6  is a front view of a second embodiment of an ICP source; 
         FIG. 7A  illustrates one example of plasma non-uniformity; 
         FIG. 7B  illustrates the corrective action required for  FIG. 7A ; 
         FIG. 7C  illustrates a first embodiment to correct the non-uniformity of  FIG. 7A ; 
         FIG. 8A  illustrates a second example of plasma non-uniformity; 
         FIG. 8B  illustrates the corrective action required for  FIG. 8A ; 
         FIG. 8C  illustrates a first embodiment to correct the non-uniformity of  FIG. 8A ; 
         FIG. 9A  illustrates a second embodiment to correct the non-uniformity of  FIG. 7A ; 
         FIG. 9B  illustrates a second embodiment to correct the non-uniformity of  FIG. 8A ; 
         FIG. 10A  illustrates a third embodiment to correct the non-uniformity of  FIG. 7A ; 
         FIG. 10B  illustrates a fourth embodiment to correct the non-uniformity of  FIG. 7A ; and 
         FIG. 11  illustrates a fifth embodiment to correct the non-uniformity of  FIG. 7A . 
     
    
    
     DETAILED DESCRIPTION 
     As described above, traditional ICP ion sources typically produce a plasma which is non-uniform in density. This problem is compounded when a non-symmetric enclosure (such as a rectangular enclosure) is used.  FIGS. 5-6  show several embodiments of rectangular enclosures that may be used by inductively coupling energy to a plasma. This inductive coupling can be attenuated by placing a material that will dissipate energy through either eddy and/or hysteresis losses. Depending on the material used, either or both losses may be made to occur. For example, copper and aluminum will result in eddy losses alone, a non conductive ferrite will result in only hysteresis losses, and a magnetic steel will result in both eddy and hysteresis losses. Therefore, the term “attenuating materials” refer to both conductive materials and ferromagnetic materials. By selectively placing an RF attenuating material near a portion of the antenna for an ICP source, it is possible to control uniformity. In addition to the material&#39;s shape and composition, the magnitude of the attenuation can be controlled by adjusting the distance between the attenuating material and the antenna. To do so, the attenuating material  360  is moved in a direction perpendicular to the plane of the antenna. For example, in  FIG. 7C , the attenuating material  360  is moved in the z direction. In  FIG. 9A , the attenuating material  360  is moved in the y direction. In  FIG. 9B , the attenuating material  360  is moved in the x direction. 
     In some embodiments, the plasma density created by the rectangular ICP source of  FIG. 5  may be greater near the volumetric center of the enclosure.  FIG. 5  shows an enclosure with a planar antenna, having a length, a width, and a depth. where length is defined as the direction parallel to the extraction slit  335 . The length is also referred to as the x dimension, while the width and depth are referred to as the y and z dimensions, respectively.  FIG. 7A  shows a graph of the plasma density as a function of x-axis position, where the origin indicates the center of the extraction slit  335 . As shown in the graph, the plasma density is greatest at the center and decays as one moves from the center toward the endwalls  338 ,  340 . To correct this, it would be advantageous to reduce the density at the center, so as to be closer to the rest of the enclosure  302 , as shown in  FIG. 7B . To achieve this effect, an attenuating material  360  may be placed near the antenna  338  in the region which is to be attenuated.  FIG. 7C  shows an attenuating material  360  placed over antenna  338  in the center of the enclosure  302 . Note that the attenuating material  360  covers the antenna  338  in the y dimension, but covers only a portion of each coiled segment in the x dimension. In other words, unlike prior art embodiments, the coiled segments are partially exposed, and partially covered. The choice of attenuating material  360  may be a conductive material, such as copper; a ferrite, or a combination having both properties, such as steel. The term “covered” as used in this disclosure is not intended to mean that the attenuating material literally covers the antenna. Rather, the term is defined as the attenuating material having the same x and y coordinates (for a planar antenna) as the antenna, while a different z coordinate. For helical antenna, the term refers to the same x, z coordinates for  FIG. 9A  and the same y,z coordinates for  FIG. 9B . 
     In addition to being able to select a portion of the plasma density to attenuate through the use of an attenuating material, the amount of attenuation can also be controlled. As the attenuating material  360  is moved further from the antenna  338 , its ability to attenuate the plasma density in the enclosure is reduced. 
       FIG. 8A  shows a graph of the plasma density as a function of x-axis position, where the origin indicates the center of the extraction slit  335 . As shown in the graph, the plasma density is greatest near the endwalls  338 ,  340  and decays as one moves toward the center. To correct this, it would be advantageous to reduce the density at the ends, so as to be closer to the rest of the enclosure  302 , as shown in  FIG. 8B . To achieve this effect, an attenuating material  360  may be placed near the antenna  338  in the region which is to be attenuated.  FIG. 8C  shows an attenuating material  360  placed over antenna  338  at the ends of the enclosure  302 . Note that, like  FIG. 7C , the attenuating material  360  covers the antenna  338  in the y dimension, but covers only a portion of each coiled segment  371  in the x dimension. 
     A similar mechanism may be used for helical antennas, such as that of  FIG. 6 . For example, if the enclosure of  FIG. 6  had a plasma density profile such as that shown in  FIG. 7A , the attenuating material  360  may be placed over the center of the enclosure  302 , near top surface  339  and bottom surface  341 , as shown in  FIG. 9A . This figure shows that the attenuating material  360  extends over a portion of the x dimension, but across the entire z dimension. Similarly, if the enclosure  302  of  FIG. 6  had a plasma density profile such as that shown in  FIG. 8A , the attenuating material  360  may be placed over the sidewalls  338 ,  340 , as shown in  FIG. 9B . This figure shows that the attenuating material  360  extends over a portion of the y dimension, but across the entire z dimension. 
     While  FIGS. 7C ,  8 C, and  9 A-B show the attenuating material  360  extending beyond the relevant dimension of the enclosure  302 , the disclosure is not limited to this embodiment. In certain embodiments, the attenuating material  360  may extend across only a portion of the relevant dimension. For example, as shown in  FIG. 10A , an attenuating material  360  may be placed in proximity to portions of one or more coil segments  371 , such that it does not cover any coil segment  371  completely. In addition, there are coil segments that are not covered at all. For example, in  FIG. 10A , the outermost coil segment  371   c  is not covered at all, while the inner coil segments  371   a - b  are only covered over a small region. In other words, this figure shows that the attenuating material  360  extends over a portion of the x dimension, and a portion of the y dimension. 
     In other embodiments, shown in  FIG. 10B , the attenuating material  360 , in the form of a ferrite material, is used to completely cover one or more coil segments  371   a - b , while leaving other coil segments  371   c  completely exposed. 
       FIG. 11  shows another embodiment of a mechanism to allow uniform plasma density. In this embodiment, additional structures  400  are added within the enclosure to selectively reduce the volume of the enclosure  302 . For example, the structures of  FIG. 10  would attenuate the plasma density in the center of the enclosure, similar to the effect created by  FIG. 7C  or  FIG. 9A . In another embodiment, the structures  400  can be positioned to reduce the volume nears the ends of the ion source  302 , thereby creating the same effect as  FIG. 8C  or  FIG. 9B . This material can be of the same type as the interior of enclosure  302 , such as aluminum, graphite, alumina ceramic, or silicon carbide. 
     In some embodiments, the additional structures  400  are placed so as to vary the width or depth of the interior of the enclosure  302 . The variation in these dimensions may vary over the length of the enclosure. In other words, as seen in  FIG. 11 , the effective width of the enclosure  302  is widest near the endwalls  338 ,  340  and narrowest in the center of the enclosure. 
     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.