Abstract:
A physical vapor deposition chamber, which includes a sputtering target, a magnetron disposed on a back side of the sputtering target, a metal sheet disposed between at least a portion of the magnetron and the sputtering target to reduce the effect of the magnetic strength of the portion of the magnetron on the sputtering target and a substrate support for holding a substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     Embodiments of the present invention generally relate to substrate processing systems, such as physical vapor deposition systems.  
         [0003]     2. Description of the Related Art  
         [0004]     Physical vapor deposition (PVD) is one of the most commonly used processes in fabrication of electronic devices, such as flat panel displays. PVD is a plasma process performed in a vacuum chamber where a negatively biased target is exposed to a plasma of an inert gas having relatively heavy atoms (e.g., argon) or a gas mixture comprising such inert gas. Bombardment of the target by ions of the inert gas results in ejection of atoms of the target material. The ejected atoms accumulate as a deposited film on a substrate placed on a substrate pedestal disposed underneath the target within the chamber. Flat panel sputtering is principally distinguished from the long developed technology of wafer sputtering by the large size of the substrates and their rectangular shape.  
         [0005]     Films deposited using current PVD chambers, however, often lack uniform thickness. This phenomenon may be caused by uneven plasma distribution across the target. For example, the plasma density at the edge of the target may be high, while the plasma density at the center of the target may be low, which leads to a deposition of film having uneven thickness.  
         [0006]     Therefore, a need exists in the art for a method for adjusting electromagnetic field across a front side of a sputtering target.  
       SUMMARY OF THE INVENTION  
       [0007]     Embodiments of the invention are directed to a method for adjusting an electromagnetic field across a front side of a sputtering target disposed inside a chamber. The method includes depositing a layer of film on a substrate disposed facing the front side of the sputtering target. The layer of film comprises material from the target. The method further includes identifying one or more areas on the layer of film having an undesired thickness and adjusting one or more magnet pieces that correspond with the areas on the layer of film having the undesired thickness. The magnet pieces are disposed on a back side of the sputtering target and the back side is opposite of the front side.  
         [0008]     Embodiments of the invention are also directed to a physical vapor deposition chamber, which includes a sputtering target, a magnetron disposed on a back side of the sputtering target, a metal sheet disposed between at least a portion of the magnetron and the sputtering target to reduce the effect of the magnetic strength of the portion of the magnetron on the sputtering target and a substrate support for holding a substrate.  
         [0009]     Embodiments of the invention are also directed to a method for processing a substrate in a physical vapor deposition chamber. The method includes providing a sputtering target, providing a magnetron on a back side of the sputtering target and changing the configuration of the magnetron to increase uniformity of deposition on the substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0011]      FIG. 1  illustrates a process chamber that may be used in connection with one or more embodiments of the invention.  
         [0012]      FIG. 2  illustrates a linear magnetron that may be used in connection with one or more embodiments of the invention.  
         [0013]      FIG. 3  illustrates a schematic view of a serpentine magnetron that may be used in connection with one or more embodiments of the invention.  
         [0014]      FIG. 4  illustrates a schematic view of a spiral magnetron that may be used in connection with one or more embodiments of the invention.  
         [0015]      FIG. 5  illustrates a serpentine magnetron that may be used in connection with one or more embodiments of the invention.  
         [0016]      FIG. 6  illustrates a double-digitated magnetron that may be used in connection with one or more embodiments of the invention.  
         [0017]      FIG. 7  illustrates a rectangularized spiral magnetron that may be used in connection with one or more embodiments of the invention.  
         [0018]      FIG. 8  illustrates a flow diagram of a method for adjusting the electromagnetic field across the front side of the sputtering target in accordance with one or more embodiments of the invention.  
         [0019]      FIG. 9A  illustrates a schematic diagram of a metal sheet being disposed between a sputtering target and a magnetron in accordance with one or more embodiments of the invention.  
         [0020]      FIG. 9B  illustrates a schematic diagram of replacing magnet pieces with weaker magnet pieces to reduce the electromagnetic field in accordance with one or more embodiments of the invention.  
         [0021]      FIG. 9C  illustrates a schematic diagram of removing magnet pieces to reduce the electromagnetic field in accordance with one or more embodiments of the invention.  
         [0022]      FIG. 9D  illustrates a schematic diagram of replacing magnet pieces with stronger magnet pieces to increase the electromagnetic field in accordance with one or more embodiments of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0023]      FIG. 1  illustrates a process chamber  100  that may be used in connection with one or more embodiments of the invention. One example of a process chamber  100  that may be adapted to benefit from the embodiments of the invention is a PVD process chamber, available from AKT, Inc., located in Santa Clara, Calif.  
         [0024]     The process chamber  100  includes a chamber body  102  and a lid assembly  106  that define an evacuable process volume  160 . The chamber body  102  is typically fabricated from welded stainless steel plates or a unitary block of aluminum. The chamber body  102  generally includes sidewalls  152  and a bottom  154 . The sidewalls  152  and/or bottom  154  may include a plurality of apertures, such as an access port  156 , a shutter disk port (not shown) and a pumping port (not shown). The access port  156  provides for entrance and egress of a substrate  112  to and from the process chamber  100 . The pumping port is typically coupled to a pumping system that evacuates and controls the pressure within the process volume  160 .  
         [0025]     A substrate support  104  is disposed inside the chamber body  102  and is configured to support the substrate  112  thereupon during processing. The substrate support  104  may be fabricated from aluminum, stainless steel, ceramic or combinations thereof. A shaft  187  extends through the bottom  154  of the chamber body  102  and couples the substrate support  104  to a lift mechanism  188 . The lift mechanism  188  is configured to move the substrate support  104  between a lower position and an upper position. A bellows  186  is typically disposed between the lift mechanism  188  and the chamber bottom  154  and provides a flexible seal therebetween, thereby maintaining vacuum integrity of the process volume  160 .  
         [0026]     Optionally, a bracket  162  and a shadow frame  158  may be disposed within the chamber body  102 . The bracket  162  may be coupled to the sidewall  152  of the chamber body  102 . The shadow frame  158  is generally configured to confine deposition to a portion of the substrate  112  exposed through the center of the shadow frame  158 . When the substrate support  104  is moved to the upper position for processing, an outer edge of the substrate  112  disposed on the substrate support  104  engages the shadow frame  158  and lifts the shadow frame  158  from the bracket  162 . Alternatively, shadow frames having other configurations may optionally be utilized as well.  
         [0027]     The substrate support  104  may be moved into a lower position for loading and unloading the substrate  112  from the substrate support  104 . In the lower position, the substrate support  104  is positioned below the bracket  162  and the access port  156 . The substrate  112  may then be removed from or placed into the chamber  100  through the access port  156 . Lift pins (not shown) may be selectively moved through the substrate support  104  to space the substrate  112  away from the substrate support  104  to facilitate the placement or removal of the substrate  112  by a wafer transfer mechanism disposed exterior to the process chamber  100 .  
         [0028]     The lid assembly  106  generally includes a target  164 , which is configured to provide material that is deposited on the substrate  112  during the PVD process. The target  164  may include a peripheral portion  163  and a central portion  165 . The peripheral portion  163  is typically disposed over the sidewalls  152 . The central portion  165  of the target  164  may protrude, or extend in a direction, towards the substrate support  104 . It is contemplated that other target configurations may be utilized as well. For example, the target  164  may include a backing plate having a central portion of a desired material bonded or attached thereto. The target material may also include adjacent tiles or segments of material that together form the target  164 .  
         [0029]     The target  164  and substrate support  104  may be biased relative to each other by a power source  184 . A gas, such as argon, may be supplied to the process volume  160  from a gas source  182  through one or more apertures (not shown), which may be formed in the sidewalls  152  of the process chamber  100 . The biasing of the target  164  and the substrate support  104  generate an electromagnetic field such that a plasma may be formed between the substrate  112  and the target  164 . Ions within the plasma are accelerated toward the target  164  and cause material to become dislodged from the target  164 . The dislodged material is attracted towards the substrate  112  and deposits a film of material thereon.  
         [0030]     The process chamber  100  may be in communication with a controller  190 , which typically includes a central processing unit (CPU)  194 , support circuits  196  and memory  192 . The CPU  194  may be one of any form of computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory  192  is coupled to the CPU  194 . The memory  192  may be a computer-readable medium or one or more of readily available memory, such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits  196  are coupled to the CPU  194  for supporting the CPU  194  in a conventional manner. These circuits  196  may include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like. The controller  190  may be used to control operation of the process chamber  100 , including any deposition processes performed therein.  
         [0031]     The lid assembly  106  may further include a magnetron  166 , which enhances consumption of the target material during processing. The following paragraphs describe various types of magnetrons that may be used in connection with one or more embodiments of the invention.  
         [0032]      FIG. 2  illustrates a linear magnetron  200  that may be used in connection with one or more embodiments of the invention. The linear magnetron  200  includes a central pole  226  of one vertical magnetic polarity surrounded by an outer pole  228  of the opposite polarity to project a magnetic field within the chamber  100  and parallel to the front side of the target  164 . The two poles  226 ,  228  are separated by a substantially constant gap  230  over which a high-density plasma is formed under the correct chamber conditions and flows in a close loop or track. The outer pole  228  includes two straight portions  232  connected by two semi-circular arc portions  234 . The magnetic field traps electrons and thereby increases the density of the plasma, which in turn increases the sputtering rate. The relatively small widths of the linear magnetron  200  and of the gap  230  produce a higher magnetic flux density. The closed shape of the magnetic field distribution along a single closed track forms a plasma loop generally following the gap  230  and prevents the plasma from leaking out the ends. Although horseshoe magnets may be used, the preferred structure includes a large number of strong cylindrical magnet pieces that may be made from materials, such as, NdBFe arranged in the indicated pole shapes with their orientations inverted between the two indicated polarities.  
         [0033]      FIG. 3  illustrates a schematic view of a serpentine magnetron  300  that may be used in connection with one or more embodiments of the invention. The serpentine magnetron  300  may include multiple long parallel straight portions  342  arranged on a pitch P smoothly joined by end portions  344 , which may be arc shaped or alternatively short straight portions with curved corners connecting to the straight portions  342 .  
         [0034]      FIG. 4  illustrates a schematic view of a spiral magnetron  400  that may be used in connection with one or more embodiments of the invention. The spiral magnetron  400  may include a continuous series of straight portions  452  and  454  extending along perpendicular axes and smoothly joined together in a rectangular spiral. Neighboring parallel straight portions  452  or  454  are separated by a track pitch P. The number of folds in either magnetron  300  or magnetron  400  may be significantly increased. Although it is not necessary, each of the magnetrons may be considered a folded or twisted version of an extended racetrack magnetron of  FIG. 2  with a plasma loop formed between the inner pole and the surrounding outer pole. When the linear magnetron  200  of  FIG. 2  is folded, the poles of neighboring folds may merge.  
         [0035]      FIG. 5  illustrates a serpentine magnetron  500  that may be used in connection with one or more embodiments of the invention. The serpentine magnetron  500  may be formed of a closed serpentine gap  562  between an inner pole  564  and an outer pole  566  completely surrounding the inner pole  564 . The plasma loop includes two closely spaced anti-parallel propagating plasma tracks separated by a track pitch Q and folded to form a structure that is generally periodic in the illustrated x-direction with a period of the track pitch Q. The single folded track and hence the magnetron have a shape generally following long straight portions  568  extending symmetrically in one direction about a medial line M and shorter straight portions  570  extending in the other directions. Curved portions  572 ,  574 , connect the straight portions  568 ,  570 . The inner curved portion  574  curves sharply around 180°. It is understood that the serpentine magnetron  500  may include additional folds of the plasma loop, particularly for larger target sizes. The serpentine magnetron  500  may also include tail portions  582  in which both the inner and outer poles  564 ,  566  have been extended in the region surrounding end curved portions  584  of the gap  572  so that the end curved portions  584  are outside of a rectangular outline of the useful area of the magnetron  500 . It is understood that if the plasma loop has an odd number of folds, the two tail portions  582  occur on opposed lateral sides of the magnetron plate  542 .  
         [0036]      FIG. 6  illustrates a double-digitated magnetron  600  that may be used in connection with one or more embodiments of the invention. The double-digitated magnetron  600  includes an inner pole  692  formed of two opposed rows of generally straight teeth portions  694  and a surrounding outer pole  696  separated from the inner pole  692  by a closed gap  698 . The straight portions of the gap  698  are arranged about two general symmetry lines Q 1  and Q 2 . The serpentine magnetron  500  and double-digitated magnetron  600 , although visually different, are topologically similar and provide similar magnetic field distributions. Both advantageously have straight portions constituting at least 50% and preferably more than 75% of the total track length. The digitated magnetron  600  is, however, distinguished from the serpentine magnetron  500  and the rectangularized spiral (or helical) magnetron  700  (to be described later) by its inner pole  692  having a complex shape with many projections and not describable in terms of a single path. In contrast, the inner pole of the serpentine and helical magnetrons has a nearly constant width that follows a single convolute or folded path extending from one end to the other. Expressed differently, the inner pole of serpentine and helical magnetrons has only two ends defining ends of the closed plasma loop, while the inner pole of the digitated magnetron has three or more ends with many equivalent ends to the plasma loop.  
         [0037]      FIG. 7  illustrates a rectangularized spiral magnetron  700  that may be used in connection with one or more embodiments of the invention. The rectangularized spiral magnetron  700  includes continuous grooves  702 ,  704  formed in a magnetron plate  706 . Unillustrated cylindrical magnets of opposed polarities respectively fill the two grooves  702 ,  704 . The groove  702  completely surrounds the groove  704 . The two grooves  702 ,  704  are arranged on a track pitch Q and are separated from each other by a mesa  708  of substantially constant width. In the context of the previous descriptions, the mesa  708  represents the gap between the opposed poles. The one groove  702  represents the outer pole. The other groove  704  represents the inner pole which is surrounded by the outer pole. Similarly to the racetrack magnetron, whether twisted or not, one magnetic pole represented by the groove  704  is completely surrounded by the other magnetic pole represented by the groove  702 , thereby intensifying the magnetic field and forming one or more plasma loops to prevent end loss. The width of the outermost portions of the groove  702  is only slightly more than half the widths of the inner portions of that groove  702  and of all the portions of the other groove  704  since the outermost portions accommodate only a single row of magnets while the other groove portions accommodate two rows in staggered arrangements. The grooves  702 ,  704  of the magnetron  700  may be modified to include a tail portion around a 180° curved end  710  of the mesa  708 , similar to the tail portions  582  of  FIG. 5 . A single magnetic yoke plate may cover the back of the magnetron plate  706  to magnetically couple all the magnets. Various magnetrons described herein may be further described in more detail in commonly assigned U.S. patent application Ser. No. 10/863,152, filed Jun. 7, 2004 and entitled Two Dimensional Magnetron Scanning for Flat Panel Sputtering, which is incorporated herein by reference.  
         [0038]     Other convolute shapes for the magnetron may be used in connection with one or more embodiments of the invention. For example, serpentine and spiral magnetrons can be combined in different ways. A spiral magnetron may be joined to a serpentine magnetron, both being formed with a single plasma loop. Two spiral magnetrons may be joined together, for example, with opposite twists. Two spiral magnetrons may bracket a serpentine magnetron.  
         [0039]      FIG. 8  illustrates a flow diagram of a method  800  for adjusting the electromagnetic field across the front side of the sputtering target  164  in accordance with one or more embodiments of the invention. The front side may be defined as the side facing the substrate  112 . The back side may be defined as the side facing the magnetron  166 . At step  810 , a layer of film is deposited on the substrate  112 . The layer of film may be made of material that has been dislodged from the sputtering target  164  during a PVD process. At step  820 , the thickness of the film is measured. The thickness of the film may be determined from a two dimensional contour image of the film. However, other means commonly known by persons with ordinary skill in the art may be used to measure the thickness of the film. In addition to or in lieu of measuring the thickness of the film, the sheet resistance of the film may be measured. Sheet resistance is inversely proportional to thickness. At step  830 , one or more areas on the film having an undesired thickness are identified. In one embodiment, one or more areas on the film having a thickness less than a desired thickness are identified. For example, a desired thickness for Al or Mo film is between about 2000 Å and 3000 Å. In another embodiment, one or more areas on the film having a thickness greater than a desired thickness are identified. At step  840 , the electromagnetic field across the front side of the target is adjusted. In one embodiment, the electromagnetic field that corresponds with the identified areas may be adjusted. As such, the electromagnetic field may be adjusted by adjusting one or more magnet pieces that correspond with the identified areas. In another embodiment, the electromagnetic field that corresponds with one or more areas adjacent the identified areas may be adjusted. As such, the electromagnetic field may be adjusted by adjusting one or more magnet pieces adjacent the magnet pieces that correspond with the identified areas.  
         [0040]     In an embodiment in which the areas on the film have a thickness less than a desired thickness, the electromagnetic field across the front side of the sputtering target that corresponds with the identified areas may be increased. In one embodiment, the magnet pieces that correspond with the identified areas may be replaced with stronger magnet pieces. In addition to or in lieu of replacing the magnet pieces with stronger ones, the distance between the magnet pieces that correspond with the identified areas may be decreased. For example, the distance between one or more magnet pieces having opposite polarity may be decreased to increase the electromagnetic field across the front side of the sputtering target that corresponds with the identified areas. Such distance may be illustrated in  FIG. 7  as the mesa  708 , which represents the gap between the opposed poles.  
         [0041]     Alternatively, the electromagnetic field that corresponds with areas adjacent the areas having a thickness less than the desired thickness may be reduced. In one embodiment, a metal sheet may be placed between the sputtering target and one or more magnet pieces adjacent the magnet pieces that correspond with the identified areas.  FIG. 9A  illustrates a schematic diagram of a metal sheet  910  being disposed between a sputtering target  964  and a magnetron  920  in accordance with one or more embodiments of the invention. In one embodiment, the metal sheet  910  is attached to the magnetron  920 , leaving a gap between the metal sheet  910  and the sputtering target  964 . In particular, the metal sheet  910  is disposed between the sputtering target  964  and magnet pieces  930 ,  940 ,  950 ,  960 ,  970  and  980 , which are adjacent to magnet pieces  955  and  965 , which correspond with areas having a thickness less than the desired thickness. In this manner, the electromagnetic field across the front side of the sputtering target  964  that correspond with magnet pieces  930 ,  940 ,  950 ,  960 ,  970  and  980  is reduced such that the areas that correspond with magnet pieces  930 ,  940 ,  950 ,  960 ,  970  and  980  and the areas that correspond with magnet pieces  955  and  965  have substantially the same thickness. The metal sheet may be made of any metallic or magnetic material, such as nickel or cobalt.  
         [0042]     The electromagnetic field that corresponds with areas adjacent the areas having a thickness less than the desired thickness may also be reduced by increasing the distance between one or more magnet pieces adjacent the magnet pieces that correspond with the identified areas. The electromagnetic field may also be reduced by replacing one or more magnet pieces adjacent the magnet pieces that correspond with the identified areas with weaker magnet pieces. In this manner, the thickness of the areas adjacent the identified areas is reduced so that the layer of film has a substantially uniform thickness.  
         [0043]     In an embodiment in which the areas on the film have a thickness greater than a desired thickness, the electromagnetic field across the front side of the sputtering target that corresponds with the identified areas may be reduced. In one embodiment, the electromagnetic field may be reduced by replacing the magnet pieces that correspond with the identified areas with weaker pieces. As an example,  FIG. 9B  illustrates that magnet pieces  930 ,  940 ,  950 ,  960 ,  970  and  980  have been replaced with weaker magnet pieces  931 ,  941 ,  951 ,  961 ,  971  and  981  respectively. In another embodiment, those magnet pieces may be completely removed. As an example,  FIG. 9C  illustrates that magnet pieces  930 ,  940 ,  950 ,  960 ,  970  and  980  have been removed. In yet another embodiment, a metal sheet may be placed between the sputtering target and the magnet pieces that correspond with the identified areas. In still yet another embodiment, the electromagnetic field may be reduced by increasing the distance between the magnet pieces.  
         [0044]     Alternatively, the electromagnetic field that corresponds with areas adjacent the areas having a thickness greater than the desired thickness may be increased. In one embodiment, the electromagnetic field may be increased by replacing one or more magnet pieces adjacent the pieces that correspond with the identified areas with stronger magnet pieces. As an example,  FIG. 9D  illustrates magnet pieces  955  and  965  have been replaced with stronger magnet pieces  956  and  966  respectively. In another embodiment, the distance between the magnet pieces adjacent the pieces that correspond with the identified areas may be decreased.  
         [0045]     Various adjustment embodiments of the invention described above may be used in combination. For example, the electromagnetic field across the front side of the sputtering target that corresponds with areas on the film having a thickness less than a desired thickness may be increased by replacing the magnet pieces that correspond with the identified areas with stronger magnet pieces and decreasing the distance between the stronger magnet pieces. Likewise, the electromagnetic field across the front side of the sputtering target that corresponds with areas of the film having a thickness greater than a desired thickness may be reduced by replacing the magnet pieces that correspond with the identified areas with weaker pieces, placing a metal sheet between the sputtering target and the magnet pieces, and increasing the distance between the magnet pieces.  
         [0046]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.