Patent Publication Number: US-2010126854-A1

Title: Sputtering target

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to a sputtering target for use in physical vapor deposition (PVD) equipment. 
     2. Description of the Related Art 
     Typical PVD, or sputtering, equipment includes a vacuum chamber, a target containing the material to be sputtered, a process gas source that provides a process gas to the vacuum chamber, and equipment to generate an electric field. Additionally, a substrate is positioned on a susceptor within the vacuum chamber. The electric field generating equipment is connected to both the susceptor and the target such that an electric field is generated therebetween. In operation, the electric field ionizes the process gas, i.e., the electric filed generates plasma between the target and the susceptor, and accelerates the ionized gas atoms towards the target. As a result, the ionized gas atoms impact the target and dislodge particles from the target material. Once free from the target, these dislodged particles eventually deposit themselves on the substrate as a thin-film. 
     Magnetron sputtering employs equipment that generates a magnetic field orthogonal to the electric field generated between the target and the susceptor. This magnetic field exploits cycloid motion of electrons within the electric field to increase the plasma density proximate the target. As a result, an increased number of ion generating electrons remain proximate the target, and a greater number of process gas ions impact the target. However, slight nonuniformities in the magnetic field add up over time to create nonuniform erosion of the surface of the target. 
       FIG. 1  provides a pair of side-by-side cross-sectional views of a typical planar sputtering target  100  designated as ‘before’  101  and ‘after’  102 . These views  101 ,  102  illustrate the profile of a target&#39;s sputtering surface  105  at the start and end of the target&#39;s useful life, respectively. Line  111  represents an axial centerline of the target  100 . Line  112  is a reference line for noting differences between the before and after conditions. 
     At the start of the target&#39;s operational life, the target  100  has an essentially planar sputtering surface  113  as seen on the ‘before’ view  101 . At or near the end of its useful life, the target  100  has developed a nonplanar sputtering surface  115  characterized by grooves  114 ,  118  and by peaks  116 . Such grooves  118  and peaks  116  tend to undesirably interfere with the edge-to-edge uniformity of deposition rate. At some point, the disparity between the target&#39;s grooves  118  and peaks  116  causes too much edge-to-edge variation in the thickness of the film deposited on the substrate, and the eroded target must be replaced. 
     The length of the commercially useful life of a given target may be cut short by a number of mechanisms including the development of a severely nonuniform erosion profile in the sputtering surface of the target. Of course, any material not consumed from the target is wasted because it is not deposited onto the substrate during the sputtering process. Frequently, as much as 70% of the sputtering material contained in a typical planar sputtering target may be wasted. 
     Therefore, a need exists for a sputtering target that minimizes the waste associated with conventional planar sputtering targets. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the present invention, a sputtering target comprises a fluidized sputtering medium, a tray member for containing the fluidized sputtering medium, and a leveling member for maintaining a substantially planar sputtering surface on the fluidized sputtering medium. 
     In one embodiment, a sputtering target comprises a fluidized sputtering medium, a tray member for containing the fluidized sputtering medium, a leveling member for maintaining a planar sputtering surface on the fluidized sputtering medium, and a loading mechanism for replenishing the fluidized sputtering medium as the fluidized sputtering medium is consumed during a sputtering process. In one embodiment the tray member has a plurality of orifices extending therethrough. 
     In yet another embodiment of the present invention, a sputtering target comprises a fluidized sputtering medium, a tray member for containing the fluidized sputtering medium, a leveling member comprising a vibrational component for maintaining a planar sputtering surface on the fluidized sputtering medium, and a loading mechanism for replenishing the fluidized sputtering medium as the fluidized sputtering medium is consumed during a sputtering process. In one embodiment, the fluidized sputtering medium includes a plurality of spherical pellets of sputtering material. In one embodiment, the tray member has a plurality of orifices extending therethrough. In one embodiment, the orifices are connected to a supply of process gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  (Prior Art) is a before and after cross-sectional view demonstrating a typical erosion profile of a planar sputtering target. 
         FIG. 2  is a schematic cross-sectional view of a planar sputtering target according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention generally include a sputtering target capable of substantially reducing the amount of wasted material associated with conventional sputtering targets. In one embodiment, the sputtering target includes a fluidized bed of sputtering material that constantly maintains a planar sputtering surface throughout the sputtering process. In one embodiment, the fluidized bed of sputtering material is either periodically or constantly supplied with sputtering material to both maintain a planar sputtering surface and reduce downtime of the sputtering equipment. 
       FIG. 2  is a schematic cross-sectional view of a planar sputtering target  200  according to one embodiment of the present invention. The sputtering target  200  includes a tray  210  that contains pellets  220  of sputtering material. The pellets  220  of sputtering material may be comprised of any sputtering material known in the art, such as aluminum or molybdenum. In one embodiment, the pellets  220  of sputtering material are formed from material salvaged from spent traditional sputtering targets that have been cut or ground into granules or pellets. In one embodiment, the pellets  220  are spheres of sputtering material. The spheres of sputtering material may have a diameter ranging from about 0.5 mm to about 15 mm. In one embodiment, the spheres are substantially the same size. In one embodiment, the spheres are of varying size. 
     In one embodiment, the pellets  220  of sputtering material are extruded rods of sputtering material. In one embodiment, the rods of sputtering material have a diameter ranging from about 0.5 mm to about 15 mm. In one embodiment, the rods have a length ranging from about 1 mm to about 25 mm or more. In one embodiment, the rods are substantially the same size. In one embodiment, the rods are of varying size. 
     In one embodiment of the present invention, the pellets  220  of sputtering material are any of a number of cross-sectional shapes, including triangular, quadrilateral, hexagonal, octagonal or some other polygonal shape. In one embodiment, the pellets  220  of sputtering material are all of substantially the same shape and/or size. In one embodiment, the pellets  220  of sputtering material are of varying shapes and/or sizes to improve electrical and thermal conductivity and packing efficiency. In one embodiment, the pellets  220  of sputtering material are granules of sputtering material having irregular shapes. 
     In one embodiment, the sputtering target  200  has a leveling mechanism  230 . In one embodiment, the leveling mechanism  230  is a mechanical vibration mechanism. The mechanical vibration mechanism constantly or periodically vibrates the tray  210  in order to level the pellets  220  as they are consumed during the sputtering process and keep the sputtering surface of the sputtering target  200  substantially planar. 
     In one embodiment, the sputtering target  200  includes one or more gas supply orifices  240  connected to a gas supply source (not shown). The gas supply source supplies a process gas, such as argon, through the orifices  240  to the pellets  220  in the tray  210 , and into a process area  205 . The process gas functions both to level the pellets  220  in the tray  210  as well as to supply process gas for ionization into plasma for sputtering the pellets  220  of sputtering material onto a substrate. In one embodiment, the process gas is a mixture of gasses, such as helium and argon. In one embodiment, the process gas includes oxygen gas. In one embodiment, the process gas includes methane. In one embodiment, the process gas provides cooling or temperature control for the sputtering target  200 . In one embodiment, the process gas provides enhanced plasma deposition efficiency. 
     In one embodiment, the sputtering target  200  includes a cooling means  250  positioned beneath the tray  210 . In one embodiment, the cooling means  250  is a volume of coolant that is in contact with a portion of the tray  210 . The cooling means  250  prevents overheating of the sputtering target  200 . 
     In one embodiment, the target  200  includes an integrated pattern magnet set  260  positioned beneath the tray  210 . In one embodiment, the magnet set  260  may include moving and/or stationary permanent and/or electromagnets. A spacing between the magnet set  260  and the tray  210  may be provided by nonmagnetic shims or other nonmagnetic spacing means. The magnet produces a flux field of a given intensity. At least a portion, if not all, of the produced flux may pass through the target  200  into the process area  205  to ionize the process gas into plasma for sputtering the pellets  220  of sputtering material. 
     In one embodiment, pellets  220  of sputtering material are added to the tray  210  as the pellets  220  are consumed in the sputtering process via a loading means  270 . In one embodiment, loading means  270  includes a sensor  272 , a loader  274 , and a controller  276 . 
     The sensor  272  senses the loss of target material consumed by the sputtering process. In one embodiment, the sensor  272  is a weight sensor, such as a load cell built into the target  200 . In one embodiment, the sensor  272  light sensor, ultrasonic sensor, or radar sensor that senses the loss of volume of the pellets  220  of sputtering material consumed in the sputtering process. 
     The loader  274  replaces the pellets  220  into the tray  210  as the sputtering material is consumed. In one embodiment, the loader  274  is a screw auger or bucket scoop that transports the pellets  220  from a storage bin  278  to the tray  210  as the sputtering material is consumed. 
     In one embodiment, the controller  276  is an on-board or central computer that receives signals from the sensor  272  and provides signals to the loader  274  to transfer the pellets  220  of sputtering material from the storage bin  278  to the tray  210  as the sputtering material is consumed. 
     Therefore, embodiments of the present invention provide a planar sputtering target capable of extended or continuous, which substantially reduces the amount of waste material associated with prior art sputtering targets. Embodiments of the present invention provide a sputtering target with a fluidized bed of sputtering material. The fluidized bed may be continuously leveled to continuously provide a planar sputtering surface. Additionally, the fluidized bed may be continuously renewed with sputtering material as sputtering material is consumed in the sputtering process. 
     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.