Abstract:
A physical vapor deposition target assembly is configured to isolate a target-bonding layer from a processing region. In one embodiment, the target assembly comprises a backing plate, a target having a first surface and a second surface, and a bonding layer disposed between the backing plate and the second surface. The first surface of the target is in fluid contact with a processing region and the second surface of the target is oriented toward the backing plate. The target assembly may include multiple targets.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention generally relate to an apparatus and method for physical vapor deposition (PVD) and particularly to an improved PVD target and method of operating the same. 
         [0003]    2. Description of the Related Art 
         [0004]    The manufacture of flat panel displays, solar panels, and semiconductor devices relies on methods for the deposition of metallic and non-metallic thin films on a substrate. PVD is one such method. 
         [0005]    PVD is generally performed in a high vacuum chamber and typically involves a magnetron sputtering process. Sputtering is performed by placing a target above the substrate, introducing a gas, such as argon, between the target and the substrate, and exciting the gas with a high-voltage DC signal to create ions that strike the target. The target consists of a material that is to be deposited as a thin film on the substrate. As the target is bombarded by ions, target atoms are dislodged and become deposited onto the substrate. The dislodged target atoms generally have substantial kinetic energy and when they impact the substrate the atoms tend to strongly adhere to the substrate. Magnetron sputtering further involves the placement of rotating or linearly translating magnets or magnet assemblies adapted to increase the plasma density in the PVD chamber and, hence, the deposition rate of the target material onto the substrate. 
         [0006]    In some applications, e.g., the processing of large-area substrates, the PVD target is mounted onto a backing plate, for example to enhance the structural rigidity of the target. PVD target assemblies adapted to process large-area substrates are significantly different in design from target assemblies adapted to process 200 mm and 300 mm silicon wafers, due to factors related to substrate size. For example, target bowing, deposition uniformity, and thermal issues are considerations related to processing large-area substrates. As used herein, the term “large-area substrates” refers to substrates with a surface area, or “footprint” of about 1,000,000 mm 2  and larger and/or having one side that is at least 1 meter in length. The term “footprint”, as used herein, refers to the nominal surface area of a substrate or target and not to the wetted surface area, i.e., the total surface area of all sides and surfaces combined. For example, a 1,000 mm×1,000 mm target has a nominal size of 1,000,000 mm 2 , but a substantially higher wetted surface area, which includes the top and bottom surfaces and side edges. 
         [0007]    The target is typically mounted to the backing plate via a bonding layer disposed therebetween, such as an adhesive elastomeric layer or a layer of solder. Issues associated with using a bonding layer to mount a PVD target to a backing plate include exposure of sensitive regions of the interior of the chamber to unwanted contamination, the presence of arc-inducing features related to the bonding layer, and poor electrical conductivity of the bonding layer affecting flow of electrical energy to the target. 
         [0008]      FIG. 1  illustrates a conventional PVD chamber  100  in a schematic cross-sectional view. PVD chamber  100  includes a target assembly  110 , a chamber body  120 , a substrate support  130 , a shield  140 , a magnet assembly  150  and a processing region  160 . 
         [0009]    Target assembly  110  includes a target  111 , which is bonded to a backing plate  112  by a bonding layer  113 . A DC power connection  114  is electrically coupled to backing plate  112 . Bonding layer  113  bonds target  111  to backing plate  112  and provides an electrically conductive path therebetween, allowing target  111  to be energized through backing plate  112  during the PVD process. Bonding layer  113  may be an elastomeric bond or a solder bond. 
         [0010]    Substrate support  130  positions a substrate  131  adjacent the processing region  160  of PVD chamber  100  during PVD processing. Shield  140 , also referred to as a dark space shield, is positioned inside PVD chamber  100  and proximate target sidewall  115  to protect the inner surfaces of body  120  and target sidewall  115  from unwanted deposition. Shield  140  is positioned very close to target sidewall  115  to minimize re-sputtered material from being deposited thereon. In addition, shield  140  is generally grounded electrically. Because of this, arcing between target  111 , which is at a high voltage, i.e., approximately 300 to 500 V, and shield  140  can easily occur. Arcing is more likely to occur when any sharp point is present on the surface of target sidewall  115 , since the charge density of an electric field proximate a charged conductor, i.e., the intensity of the electric field, is much higher near a sharp point on the charged conductor. Arcing is to be avoided at all times in a PVD chamber due to the large number of substrate-contaminating particles generated thereby as well as the potential for damaging conductive pathways already formed on a substrate. 
         [0011]      FIG. 2A  is a partial cross-sectional view of the region indicated in  FIG. 1  of PVD chamber  100 . In the example shown, bonding layer  113  is an elastomeric bonding layer, which may be used for mounting target  111  to backing plate  112 . The inventors have discovered one problem with using an elastomeric material for bonding layer  113 , namely the presence of voids  117 ,  118  that are typically inside bonding layer  113 . When PVD chamber  100  is pumped down to vacuum, voids  117 ,  118 , which contain air and/or other gases at atmospheric pressure, may burst into PVD chamber  100 , contaminating both the processing region  160  and surfaces exposed thereto, including target sidewall  115 , shield face  141 , and substrate  131 . Void bursting may take place during the initial pump-down of PVD chamber  100  or, due to the thermal cycling of target assembly  110  associated with processing substrates, throughout the life of target assembly  110 . 
         [0012]    Contamination of processing region  160  during PVD processing of a substrate may deleteriously affect the substrate by damaging devices formed thereon or by encouraging subsequent delamination of the PVD-deposited layer from the substrate. In addition, contamination of other surfaces in PVD chamber  100  may result in contamination of many substrates over the life of target assembly  110 . This longer-term contamination problem is caused by particles of PVD-deposited material flaking off of shield face  141  and target sidewall  115  when a layer of bonding layer contaminants are present thereon. 
         [0013]    During the PVD process, any surfaces in line-of-sight of the target face  119  of target  111  will have target material deposited thereon, such as substrate  131  and shield  140 . In addition, surfaces not directly in line-of-sight of target face  119  may also undergo PVD deposition due to “re-sputtering” of material from surfaces such as shield face  141 . In this way, target sidewall  115  also has material from target  111  deposited thereon although not in line-of-sight of target face  119 . In either case, adhesion between a surface, e.g., shield face  141  or target sidewall  115 , and the layer of deposited PVD material must be maximized. The presence of any contaminant on such surfaces, for example from void bursting, substantially reduces the adhesion between said surfaces and the deposited material, thereby producing substrate-contaminating particles. 
         [0014]    The inventors have discovered another problem associated with the bonding layer  113 , which is arcing between target  111  and shield face  141 . The presence of a sharp point or feature on the surface of a charged conductor results in a relatively intense electric field. In the case of target  111 , which is maintained at a high voltage during the PVD process, this may result in arcing between the sharp feature on target  111  and shield face  141 , which is typically grounded. When a bonding layer  113  is used to mount target  111  to backing plate  112 , it is difficult to provide a smooth transition surface between target  111  and backing plate  112  and, hence, may include arc-inducing features. 
         [0015]    For example, void bursting from bonding layer  113  may form a sharp point near shield face  141 .  FIG. 2B  is a partial cross-sectional view of the region indicated in  FIG. 1  of PVD chamber  100  after void  117  (shown in  FIG. 2A ) has burst into processing region  160 . A gap  117 A is formed thereby between target  111  and backing plate  112 , creating a sharp point  116  proximate shield face  141 , which encourages arcing. When bonding layer  113  is a solder bond, arcing may be caused by rugosities in the surface of the solder bond. Arcing may also be caused by regions of incomplete solder coverage between target  111  and backing plate  112 , which may form a gap similar to gap  117 A and a sharp point  116 . 
         [0016]    Therefore, there is a need for an improved PVD target and method of operating the same. 
       SUMMARY OF THE INVENTION 
       [0017]    Embodiments of the present invention generally relate to an apparatus for PVD and particularly to a PVD target assembly. In one embodiment, a PVD target assembly comprises a backing plate, a target with a sealing member disposed on a first surface, and a bonding layer disposed between the backing plate and a second surface of the target. The target may further comprise a side surface exposed to atmosphere with an electrical power connection disposed thereon. The target assembly may further comprise a backing plate extension member, a second target with a second sealing member disposed on a surface thereof, and a bonding layer disposed between the backing plate and a surface of the target on which the sealing member is not disposed. 
         [0018]    According to a second embodiment, a PVD target assembly comprises a first target and a second target, each of which is bonded to a respective backing plate with a bonding layer. Each target has a sealing member receiving area on a surface oriented away from its respective backing plate. The target assembly further comprises a target support member having a sealing member receiving area proximate the sealing member receiving area of the first target and the sealing member receiving area of the second target. 
         [0019]    According to a third embodiment, a method comprises providing a target having a first face and a second face, positioning a substrate proximate and substantially parallel to the first face, sealing an edge portion of the first face of the target, coupling a backing plate to the second face of the target with a bonding layer, flowing a process gas into a processing region defined between the first face of the target and the substrate, and generating a plasma in the processing region to sputter the first surface of the target to deposit a layer on the substrate. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    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. 
           [0021]      FIG. 1  (Prior Art) illustrates a conventional PVD chamber in a schematic cross-sectional view. 
           [0022]      FIGS. 2A ,  2 B (Prior Art) are partial cross-sectional views of a region indicated in  FIG. 1  of a PVD chamber. 
           [0023]      FIG. 3  is a schematic cross-sectional view of a PVD chamber according to one embodiment of the invention. 
           [0024]      FIG. 4  is a partial cross-sectional view of the region indicated in  FIG. 3  of a PVD chamber. 
           [0025]      FIG. 5A  illustrates a schematic plan view of a PVD chamber according to one embodiment of the invention and having a multi-piece target. 
           [0026]      FIG. 5B  illustrates a schematic cross-sectional view of a PVD chamber according to one embodiment of the invention and having a multi-piece target. 
       
    
    
       [0027]    For clarity, identical reference numerals have been used, where applicable, to designate identical elements that are common between figures. 
       DETAILED DESCRIPTION 
       [0028]      FIG. 3  is a schematic cross-sectional view of a PVD chamber  300  according to one embodiment of the invention. PVD chamber  300  may include a target assembly  310 , a chamber body  320 , a substrate support  330 , a shield  340 , and a processing region  360 . 
         [0029]    Target assembly  310  includes a magnet assembly  350 , which is housed in a magnetron chamber  309 , and a target  311 , which is bonded to a backing plate  312  by a bonding layer  313 . Magnet assembly  350  may be an array of a plurality of magnets that rotates or linearly translates parallel to target  311  in order improve deposition rate and uniformity of a PVD-deposited film on substrate  331 . Magnetron chamber  309  may be at atmospheric pressure, evacuated to a pressure below atmospheric pressure, or filled with an electrically insulative cooling fluid, such as deionized water. Power is provided to target  311  via an electrical connection. In one aspect, an electrical connection  314 A may be electrically coupled to backing plate  312  to energize target  311 . In another aspect, an electrical connection  314 B may be electrically coupled to target  311  directly. Power may be DC, AC, or pulsed power. Target  311  consists of the material, typically in a highly purified state, that is to be deposited on substrate  331  in PVD chamber  300 . Bonding layer  313  may be an elastomeric bond or a metallic adhesive bond, such as an indium-containing bonding layer. In the latter case, a surface of a target and a surface of a backing plate are deposited with an indium-based coating, also referred to as indium solder, and pressed together at an elevated temperature. Upon cooling, the indium-containing layer solidifies and bonds the target  311  to the backing plate  312 . 
         [0030]    In one configuration, wherein power is provided to target  311  by electrical connection  314 A and bonding layer  313  is an elastomeric bonding material, bonding layer  313  may contain an additional conductive member (not shown for clarity), such as a copper mesh, to provide improved electric contact between the backing plate and the target. In a preferred embodiment, however, target  311  is energized directly via electrical connection  314 B in order to obviate the need for energizing target  311  indirectly via backing plate  312  and bonding layer  313 . 
         [0031]    Substrate support  330  is disposed inside PVD chamber  300  and positions a substrate  331  adjacent the processing region  360  of PVD chamber  300  during PVD processing. Shield  340 , also referred to as a dark space shield, may be mounted inside PVD chamber  300  and proximate target sidewall  315  to protect the inner surfaces of body  320  and target sidewall  315  from unwanted deposition during PVD processing and/or to provide an electrically grounded anode region. Processing region  360  is the region in PVD chamber  300  that includes the volume bounded by substrate support  330 , target  311 , and shield  340 . 
         [0032]    Target assembly  310  is sealably mounted on upper surface  323  of body  320  in a vacuum-tight manner. By mounting target assembly  310  via a sealable mount on upper surface  323 , target assembly  310  may be removed for repair or replacement with minimal disassembly of PVD chamber  300 . The vacuum-tight seal is typically formed by means of a sealing member  321 , such as an O-ring, positioned in or against sealing surface  322 , such as an O-ring groove.  FIG. 3  depicts sealing surface  322  as an O-ring groove formed as a feature of upper surface  323  of body  320 . In an alternative configuration, sealing surface  322  may instead be a feature on the corresponding surface of target  311 . In either case, a vacuum-tight seal is formed between upper surface  323  and target  311 . In this way, backing plate  312  is not used to form the vacuum-tight seal between target assembly  310  and body  320 , thereby eliminating the need for exposing bonding layer  313  to the processing region  360 . Hence, target assembly  310  is configured so that the only surfaces thereof that are exposed to processing region  360  are surfaces of target  311 . 
         [0033]    Alternatively, aspects of the invention contemplate configurations of sealably mounting target assembly  310  on upper surface  323  wherein sealing member  321  is not an O-ring and sealing surface  322  is not an O-ring groove. For example, target  311  may be sealably mounted to upper surface  323  using an all-metal vacuum seal, wherein sealing member  321  may be a metal gasket, such as a copper strip, compressed against sealing surface  322 , which is a stainless steel knife-edge seat. In another example, sealing member  321  may be a polymeric seal, such as a gasket-like G-10 material. 
         [0034]    In one configuration, target  311  is fabricated from a single piece of material. In this way the only surface of target  311  in fluid contact with processing region  360  is a single machined surface, i.e., there is no transition between two or more materials to create sharp, arc-inducing features.  FIG. 4  is a partial cross-sectional view of the region indicated in  FIG. 3  of PVD chamber  300 . Because backing plate  312  and bonding layer  313  are not exposed to process region  360 , there is no abrupt transition between target material, bonding layer, or backing plate material. Instead, a smoothly machined radius  325  or other appropriate transition may be implemented between target sidewall  315  and target surface  326 , thereby minimizing the possibility of arcing between target sidewall  315  and shield face  341 . And because bonding layer  313  is not exposed to process region  360 , there is no potential for bonding layer material to contaminate said region. 
         [0035]    Aspects of the invention further contemplate the use of a direct electrical connection  314 B (see  FIG. 3 ) for energizing target  311  during processing. Because a side surface of target  311  is exposed to atmosphere, power may be provided directly to target  311  without being routed through backing plate  312  and bonding layer  313 , reducing electrical resistance of the DC circuit. 
         [0036]    In one aspect of the invention, backing plate  312  contains a plurality of cooling conduits  308  through which a cooling fluid may be flowed to prevent overheating of target  311  and backing plate  312  during processing. 
         [0037]    Aspects of the invention may likewise be used to advantage for a PVD chamber whose target assembly includes a multi-piece target.  FIG. 5A  illustrates a schematic plan view of a PVD chamber  500  according to one embodiment of the invention and having a multi-piece target. In this aspect, PVD chamber  500  includes a multi-piece target assembly  510  having three targets  511 A,  511 B,  511 C, however aspects of the invention may be beneficially applied to multi-piece target assemblies having two, three, or more targets. For clarity, only multi-piece target assembly  510  and targets  511 A,  511 B,  511 C are shown in  FIG. 5A .  FIG. 5B  illustrates a schematic cross-sectional view at section A-A in  FIG. 5A  of PVD chamber  500 . Referring to  FIG. 5B , PVD chamber  500  is substantially similar in organization to PVD chamber  300 , described above in conjunction with  FIGS. 3 and 4 . In addition to the multi-piece target, differences therebetween include multiple backing plates  512 A-C, target support members  513 A,  513 B, center shields  540 , and sealing members  521 A-C. 
         [0038]    In the configuration illustrated in  FIG. 5B , each of targets  511 A-C is mounted to a separate backing plate, i.e., backing plates  512 A-C, respectively. Target support member  513 A supports the interior sidewalls  550 A,  550 B, of targets  511 A,  511 B, respectively. Similarly, target support member  513 B supports the interior sidewalls  551 B,  551 C, of targets  511 B,  511 C, respectively. Target support members  513 A, B may be structurally coupled to chamber walls  527 ,  528 . Chamber walls  527 ,  528  are shown in  FIG. 5A . Backing plates  512 A-C may be supported by chamber walls  527 ,  528 , or by body  320  and target support members  513 A, B, and/or a combination of both, depending on the structural requirements of the chamber. Targets  511 A-C are each energized via electrical connections  514 A-C, respectively, as shown in  FIG. 5A . 
         [0039]    Referring to  FIG. 5B , target support members  513 A, B allow a seal to be formed peripherally around each of targets  511 A-C, even though each of targets  511 A-C, has one or more sides that is not supported by an upper surface  323  of body  320 . Interior sidewall  550 A of target  511 A, interior sidewalls  550 B and  551 B of target  511 B, and interior sidewall  551 C of target  511 C are not supported by body  320 . But a multi-target chamber configured with target support members  513 A, B may have a sealing member positioned peripherally against a surface of each target  511 A-C, circumscribing each target with an unbroken seal or closure. For example, a portion of the peripheral seal circumscribing target  511 A is formed by sealing member  521 A between target support member  513 A and a surface of interior edge  550 A. The remainder of this seal is formed by sealing member  521 A between upper surface  323  and target surface  326  of target  511 A. In a similar manner, sealing member  521 C forms a peripheral vacuum-tight seal against target  511 C. In the case of target  511 B, two portions of the peripheral seal circumscribing target  511 B are formed by sealing member  521 B between a surface of an interior edge and a surface of a target support member. 
         [0040]    The peripheral seal formed around each of targets  511 A-C may be a vacuum-tight seal, for example the portions of the seal formed between upper surface  323  and target surface  326 , preventing leakage from atmosphere into processing region  360 . Other portions of said seals may not be vacuum-tight seals, for example when the volumes on each side of the seal are at vacuum. This may be the case when regions  581  are evacuated regions and the seals between regions  581  and processing region  360  are only required to prevent contamination from entering processing region  360 . It is important to note that the peripheral seal formed by sealing members  521 A-C against targets  511 A-C, respectively, isolates bonding layer  313  from processing region  360 . This configuration eliminates contamination of processing region  360  from bonding layer  313  as well as arcing due to sharp points and/or rugosities associated with bonding layer  313 . 
         [0041]    Center shield  540  protects surfaces from unwanted deposition, for example target center sidewalls  515 A,  515 B and target support members  513 A, B. As described above for target  311  in conjunction with  FIG. 4 , targets  511 A-C may each be fabricated from a single piece of material, removing the abrupt transition between bonding layer, target, and backing plate from the processing region. 
         [0042]    For a multi-target configuration, the inventors have learned that a normal orientation of the target sidewall minimizes deposition thereon and reduces subsequent particle contamination of substrates. Therefore, in one aspect, one or more sidewalls of targets  511 A,  511 B, such as interior sidewalls  550 A,  551 B, respectively, are oriented substantially normal to the surface of substrate support  330 . 
         [0043]    The inventors have also learned that aspects of the invention may be used to advantage for PVD chambers adapted to process large-area substrates. Processing large-area substrates requires larger PVD target assemblies. Larger PVD target assemblies are more likely to benefit from the structural rigidity provided by a backing plate bonded to the target, and therefore may benefit from aspects of the invention. In addition, large-area substrates may require multi-piece target assemblies, which may also benefit from aspects of the invention. 
         [0044]    Substrates of the invention can be of any shape (e.g., circular, square, rectangle, polygonal, etc.) and size. Also, the type of substrate is not limiting and can be any substrate comprised of a material of silicon, carbon-containing polymer, composite, metal, plastic, or glass. 
         [0045]    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.