Patent Document

BACKGROUND OF THE INVENTION 
     The present invention relates generally to ion implantation systems, and more particularly, to heating assemblies for raising the temperature of a wafer to an elevated level within an evacuated chamber of an ion implantation system. 
     Processing of semiconductor wafers by ion implantation is routinely practiced in manufacturing integrated circuits. Ion implantation is typically performed in an evacuated chamber in which a semiconductor wafer is exposed to a beam of ions having a selected energy. In some ion implantation techniques, the wafer is heated to elevated temperatures during ion implantation steps to dynamically anneal defects generated in the wafer as a result of ion bombardment, and/or during subsequent annealing steps. 
     Heating a substrate within the vacuum environment of an ion implantation chamber has proven difficult. Many materials, especially heating lamps, fail quickly when heated in a vacuum environment, especially if provisions for cooling the lamps are not provided. Typically, metal blocks are utilized to mount the lamps in order to provide a heat sink for dissipating the heat generated by the lamps. It has generally been thought that a metal, such as copper, with very high thermal conductivity is the ideal choice for such a mounting block. Copper is also preferred because it is easy to electroplate, thereby facilitating the deposition of mirror-like reflective coatings. By coating the surface of the block that lies behind the lamp, the efficiency of radiant heat transfer is enhanced. 
     Nonetheless, copper mounting blocks have a number of drawbacks, not the least of which is that copper is difficult to machine. Internal networks for transmitting cooling fluids within the block need to be bored or otherwise machined into the block, but due to the relative softness of copper and copper alloys, the conventional copper mounting block is usually constructed from multiple pieces, each machined with a portion of the required networks. The pieces must then braised together and tested for integrity. Multiple-piece braised components subjected to large-gradient temperatures can be prone to leakage and other structural failures, as well as requiring complex and time-consuming manufacturing and assembly techniques. 
     Accordingly, there is a need for simpler heating devices that can withstand the rigors of a vacuum environment and repeated heating with greater ease of manufacturing. There is also a need for such heating devices that can perform in a vacuum environment without failure over extended time periods. 
     SUMMARY OF THE INVENTION 
     The present invention provides a heating assembly that includes a thermally conductive, lamp-mounting block manufactured from aluminum or a similar material, which can be machined as a single-piece (e.g., unibody) block. The unibody block includes one or more networks of inner passageways bored or otherwise machined within the block for transporting one or more cooling fluids. The mounting block can also have a reflective coating on one or more of its surfaces that face the lamps to efficiently reflect heat and/or light generated by the lamps onto a desired surface, for example, a semiconductor wafer. Thermal isolation devices, e.g., pads, provide for both physical mounting of the heating lamps to the mounting block and also provide thermal isolation between the heating lamp and its electrical connections are also disclosed for protecting heat-sensitive elements of the heating assembly such as seals. 
     In one aspect, the thermally conductive block can include a plurality of openings formed therein that are in fluid communication with at least one of the inner passageways. The openings are preferably formed in proximity of the lamps to allow a flow of a cooling fluid circulating through the passageways onto the lamps, thereby cooling the lamps. The openings can be formed along the length of a heating lamp, for example, in a single row, or in multiple rows each positioned at one side of the lamp. In some embodiments, two rows of openings are utilized in which the openings in one row are offset relative to those in the other row to maximize the area of the lamp that will be in contact with the cooling fluid. Those having ordinary skill in the art will appreciate that other arrangements of openings can also be utilized so long as the flow of a cooling fluid through the openings is substantially directed onto a lamp to be cooled. 
     In a related aspect, the passageway that is in fluid communication with the openings can receive a gaseous cooling fluid (e.g., air or nitrogen) and allow it to expand on and around the heating lamp, via the plurality of openings, to remove heat generated by the lamps. Another passageway can be utilized to circulate a cooling fluid, e.g., water, through the block from an inlet port to an outlet port. 
     In further aspects, the heating assembly can include a cover, for example, a quartz tube, in which the lamp and block can be disposed. One or more seals, for example, O-ring seals, formed in the block can seal the cover, thereby insulating the lamps from an external environment in which the heating assembly is positioned. 
     In another aspect, the thermally conductive block is formed of aluminum, and is coated with a highly reflective material, such as, gold. A primer layer, for example, a nickel layer, can be applied to the aluminum block prior to application of the high reflective coating in order to enhance the adhesion of the reflective coating to the block. The use of aluminum for forming the block is particularly advantageous in that it allows readily forming the inner passageways in the block. 
     Still another aspect of the invention, the thermally conductive block is manufactured as a unibody construction. Internal networks of passageways can be manufactured via “gun-drilling” methods and techniques, for example. 
     The present invention also provides a heating assembly for use in an ion implantation system that includes a heating assembly formed of a lamp and a thermally conductive block holding the lamp. The lamp is capable of heating a silicon wafer during the implantation process for reducing or eliminating surface damage, particularly amorphous layering, of the wafer. The thermally conductive block has a layer of gold over a primer layer to increase efficiency and reduce parasitic heating of the block. Further, the block has a series of passageways through which a cooling fluid can be circulated to remove heat, as well as a series of passageways through which a compressible cooling fluid can be introduced and expanded over and around the lamp. The assembly is surrounded by a cover, e.g., a quartz tube, sealed at each end providing separation of the heating assembly environment from the vacuum of the ion implantation device. The invention also includes a mount supplying a physical attachment for the heating assembly, and also couplings for electrical supplies and cooling fluid inlets and outlets. 
     A heating assembly according to the invention can be utilized in a variety of different applications. For example, such a heating assembly can be employed in an evacuated chamber of an ion implantation chamber to provide heating of semiconductor wafers during ion implantation and/or annealing steps. In such an application, the heating assembly can be coupled to a mount for stable positioning within an end station of the ion implantation chamber. The mount can include inlet and outlet ports to allow flow of cooling fluids from an external source into the inner passageways of the block. 
     Further understanding of the invention can be obtained by reference to the following detailed description in conjunction with associated drawings which are briefly described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a typical ion implantation device in which a heating assembly according to the teachings of the invention is incorporated for heating semiconductor wafers positioned in an end station of the implantation device. 
     FIG. 2 shows a heating assembly according to the teachings of the invention. 
     FIG. 3 illustrates major components of a heating assembly of the invention. 
     FIG. 4 is a cross-sectional view of the heating assembly of FIG. 2 illustrating inner passageways formed in a thermally conductive block of the assembly. 
     FIG. 5 shows cross-sectional views of the assembly of FIG.  2 . 
     FIG. 6 is a detailed view of an end portion of the heating assembly of FIG.  2 . 
     FIGS. 7A-7C are various cross-sectional views of a heating assembly of the invention. 
     FIG. 8 illustrates a heating assembly according to the invention coupled to a mount for positioning in an end station of an ion implantation chamber. 
    
    
     DETAILED DESCRIPTION 
     The present invention provides a heat lamp assembly that can include a heating lamp mounted onto a thermally conductive block that provides efficient reflection of radiation generated by the lamp onto a selected surface, for example, a surface of a semiconductor wafer disposed in an ion implantation chamber. The block can include a plurality of openings that allow ingress/egress of one or more cooling fluids to/from inner passageways allowing for removal of heat from the block. The block can also include further openings that allow a cooling fluid, e.g., a gas, to flow over the lamp to facilitate removal of heat from the lamp. These, and other features, are described herein. 
     FIG. 1 illustrates an exemplary ion implantation apparatus  10  in which a heating assembly  12  coupled with a mount  40  according to the teachings of the invention is used. The ion implantation system  10  includes a beam delivery assembly  14 , a beam-forming device  16 , and an end-station  28 . The beam delivery assembly  14  can include an ion source  18  that generates a beam of ions  24 . The beam delivery assembly  14  can further include an ion analyzer  20 , such as a magnetic analyzer, that selects appropriately charged ions. An accelerator  22  accelerates the selected ions to a desired energy, e.g., about 200 keV, and a beam-forming device  16  shapes the accelerated ions into an ion beam  24  having a selected cross-sectional shape and area. 
     The beam  24  is directed to a plurality of targets, e.g., semiconductor wafers  26 , to implant a selected dose of ions therein. In this exemplary embodiment, the targets are disposed in the end-station  28  with a rotating support structure  30 . A drive mechanism (not shown) can rotate the support structure  30  to sequentially expose one or more of the wafers  26  to the ion beam  24 . During ion implantation, one or more vacuum pumps  34  evacuate the chambers, e.g., the ion source  18 , accelerator assembly  22 , and end-station  28 . 
     The heating assembly  12  formed according to the teachings of the invention is disposed in the end-station  28  to heat the wafers  26  during ion implantation and/or subsequent annealing steps. The assembly is preferably positioned so as not to interfere with the ion beam  24 . In the illustrated embodiment, the assembly  12  is attached to a mount  40  which provides for placement of the assembly  12  within the end-station  28 . The mount  40  also provides for electrical coupling of the assembly  12  via electrical connectors  32 . Cooling fluids can be circulated within the assembly  12  via fluid couplings  36 ,  38  provided by the mount  40  for the removal of heat from the assembly  12  and/or mount  40 . The fluids can be, for example, water or air, or other fluids suitable for dissipating heat from the assembly. Multiple assemblies  12  can be placed within the end-station  28 , and be coupled to a single mount  40 . In some embodiments, multiple mounts  40  can be placed within the end-station  28 . 
     FIG. 2 shows the assembly  12 , with FIG. 3 depicting major components of the assembly  12  according to one embodiment of the invention. The exemplary assembly  12  includes, among other elements, a heating lamp  42 , a thermally conductive block  44  to which the heating lamp is mounted, and a cover  46 . 
     The cover  46  insulates the lamp  42  and block  44  from an external environment, for example, a vacuum environment of the ion implantation chamber. In this embodiment, the cover  46  is in the form of a tube that surrounds the block  44  allowing operation of the heating assembly  12  within the vacuum of the ion implantation device, but the cover can be of different shapes and/or materials that are suitable depending on the external environment. Seals  68  located on end portions  57 ,  56  of the block  44  function with the cover  46  to separate the internal environment of the assembly  12  from the exterior environment. The illustrated seals are of a conventional “O-ring” configuration, but they can be labyrinth or other designs known in the art. 
     The heating lamp  42  has a central portion containing a heat producing material  48 , providing heat upon electrical stimulation. The heating material  48  can be tungsten, quartz or any other material that produces sufficient heat upon electrical simulation for a desired application. In one embodiment, the heating lamp  42  can be approximately 10-12 inches long. In other embodiments, the length of the lamp  42  can vary according to the heating application and/or physical size limitations of a device in which the heat lamp assembly is disposed. Two end portions  50 ,  52  provide electrical coupling of the heat producing material  48  to a source of electrical power, and farther allow physical mounting of the heating lamp  42  to the block  44  via heat-isolation pads  58   a - 58   d  (collectively,  58 ). 
     The heat-isolation pads  58   a ,  58   b ,  58   c , and  58   d , (FIGS. 3,  7 A) are mounted to the block  44  by utilizing, for example, a plurality of fasteners, such as, screws  60 . The heat-isolation pads  58  are preferably positioned in proximity of the end portions  56 ,  57  to enhance isolation of heat generated by the lamp from these end portions, e.g., in proximity with high-temperature gradients, and consequently from the seals  68 , thereby ensuring proper operation of the seals. The heat-isolation pads  58  can be formed of any material having a high coefficient of thermal conductivity. For example, the pads can be formed of aluminum. The pads can have a non-reflective surface facing the lamp to maximize heat transfer from the heating assembly. In some embodiments, the pads have a reflective surface on faces not receiving radiated energy from the heating assembly to increase cooling characteristics of the pads. 
     The thermally conductive block  44  includes a central portion  54  and two end portions  56  and  57 . The end portions  56 ,  57  (FIGS. 2,  3 ,  5 ,  6  and  7 ) allow physical mounting of the lamp  42  to the block  44 , and further allow electrical coupling of the lamp to a source of electrical power (not shown). In addition, the end portions  56 ,  57  include elements for coupling of the heat lamp assembly  12  to a mounting block as described in detail below with reference to FIG.  7  and FIG.  8 . In particular, each end portion  56 ,  57  includes a tab, e.g.,  62 , or other coupling element, that can physically and electrically couple with an end portion  50 ,  52  of the heating lamp  42 . In the illustrated embodiment, the lamp end portion, e.g.,  52 , is extruded or otherwise placed within a channel along a longitudinal axis of a block end portion  56 , and coupled with the tab  62 . 
     FIG.  3  and FIG. 4 depict two reflective sloping surfaces  55   a ,  55   b  which reflect light and heat generated by the lamp  42  onto a desired location, for example, a surface of a semi-conductor wafer  26  (FIG.  1 ). The reflective surfaces  55   a ,  55   b  can have a coating of a high reflectivity material, e.g., gold, that is deposited on the material forming the block  44 , e.g., aluminum, via an intermediate primer layer, e.g., nickel. The primer layer advantageously enhances adhesion of the gold layer to the material forming the block  44 . 
     A plurality of openings  66  formed in the reflective surfaces  55   a  and  55   b  allow flowing a cooling gas, for example, air, introduced into the block  44  via an inner passageway as described below, over the lamp  48  in order to remove heat therefrom. The cooling gas can be nitrogen or other compressible or non-compressible fluids suitable for contact with the heating lamp  48 . In one illustrated embodiment (FIG. 3) the openings are arranged in two rows such that the openings in one row are offset relative to those in the other row to maximize an area of the lamp that will be in contact with the flowing gas. In other embodiments (e.g., FIGS.  4  and  6 A), there can be a single row  66 . 
     With further reference to FIG. 4 (See also FIGS. 5,  7 B- 7 C) the thermally conductive block  44  further includes networks of inner passageways  70 ,  72 , and  74  that extend along a longitudinal axis of the block and provide conduits for flow of fluids, such as, air and water. In this illustrated embodiment, cooling water is circulated through the block via passageways  70  and  72 , for example, by introducing water into the block via passageway  70  and removing water from the block via the passageway  72 , or vice versa. The flow of the cooling water advantageously cools the block to ensure proper operation of various seals, for example seal  68 . Other cooling fluids, such as, ethylene glycol, or other heat-removing fluid suitable for circulation through the block can also be employed. 
     In this embodiment, the inner passageway  74  is in fluid communication with the openings  66  to allow flow of a cooling fluid, e.g., air, introduced via the passageway  74  under pressure, over the lamp  48 . The cooling air is then extracted from the area between the lamp  48  and the interior of the cover  46  via a central coupling of one or both of the end portions  56 ,  57 . 
     With reference to FIGS. 2,  3 ,  4  and  7 A- 7 C, each end portion  57  includes openings that provide ingress and egress of fluids into and out of the inner passageways  70 ,  72 , and  74 . More particularly, cooling water (or other heat-removing fluid) can be introduced and extracted via ports  64  and  84 , and cooling air (or other gaseous fluids) can be introduced into the inner passageway  70  via an inlet port  86  and removed via an outlet port  88 . 
     A variety of materials can be employed to manufacture the thermally conductive block  44 . For example, in one preferred embodiment, aluminum is utilized to form the block  44  as a unibody structure. The use of aluminum is particularly advantageous because it readily allows machining, e.g., boring a network of inner passageways and seal seats in the block. The manufacture can utilize, for example, so-called gun-drilling techniques to generate inner passageways in a unitary block of aluminum instead of braise-joining multiple machined pieces. 
     As described above, a primer coating, e.g., nickel, can be applied to the aluminum surfaces of the block, and a coating of a highly reflective material, such as, gold, can subsequently be applied to the primer so as to generate highly reflective surfaces for directing radiation generated by the lamp to a desired location. 
     With reference to FIG. 8, the heat lamp assembly  90  can be coupled to a mount  92  that allows positioning the heat lamp assembly within an ion implantation chamber. The mount  92  provides electrical couplings  94  cooling water couplings  96  and cooling air couplings  98 ,  100 . The couplings can have a variety of different configurations. For example, the air inlet coupling  98  can be a flange coupling, a nipple coupling, or any other coupling known in the art. Multiple heating lamp assemblies of the invention can be coupled to a single mount, thus enabling a variety of configurations depending on physical shape and dimensions of an ion chamber and desired wafer temperatures to be achieved. 
     In some embodiments, sensors can be attached to the heating assembly and/or mount to control the heat output, cooling water and air flow, and other characteristics of operational parameters. Further, the block can be connected to anti-static or other voltage differential detection/correction equipment to protect the mount and coupled assemblies from electrical damage. In some embodiments, sensors capable of detecting the temperature of a wafer  26  can be used, such as a thermocouple, infrared sensor, or other temperature-sensing device. 
     Those of ordinary skill in the art will appreciate that various modifications can be made to the above embodiments without departing from the scope of the claimed invention as described by claims. For example, the size of the heating assembly can vary, the heating capacity can vary, and the cooling fluids can vary, depending on the requirements of the application.

Technology Category: h