Abstract:
Embodiments disclosed herein relate to circular lamp arrays for use in a semiconductor processing chamber. Circular lamp arrays utilizing one or more torroidal lamps disposed in a reflective trough and arranged in a concentric circular pattern may provide for improved rapid thermal processing. The reflective troughs, which may house the torroidal lamps, may be disposed at various angles relative to a surface of a substrate being processed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application No. 61/874,552, filed Sep. 6, 2013, the entirety of which is herein incorporated by reference. 
     
    
     FIELD 
       [0002]    An apparatus for semiconductor processing is disclosed herein. More specifically, embodiments disclosed herein relate to circular lamp arrays for use in a semiconductor processing chamber. 
       BACKGROUND 
       [0003]    Epitaxy is a process that is used extensively in semiconductor processing to form very thin material layers on semiconductor substrates. These layers frequently define some of the smallest features of a semiconductor device. The epitaxial material layers may also have a high quality crystal structure if the electrical properties of crystalline materials are desired. A deposition precursor is normally provided to a processing chamber in which a substrate is disposed and the substrate is heated to a temperature that favors growth of a material layer having desired properties. 
         [0004]    It is generally desired that the thin material layers (film/s) have very uniform thickness, composition, and structure. Because of variations in local substrate temperature, gas flows, and precursor concentrations, it is quite challenging to form films having uniform and repeatable properties. The processing chamber is normally a vessel capable of maintaining high vacuum, typically below 10 Torr. Heat is normally provided by heat lamps positioned outside the vessel to avoid introducing contaminants into the processing chamber. Pyrometers or other temperature metrology devices may be provided to measure the temperature of the substrate. 
         [0005]    Control of substrate temperature, and therefore local layer formation conditions, is complicated by thermal absorptions and emissions of chamber components and exposure of sensors and chamber surfaces to film forming conditions inside the processing chamber. In addition, providing substantially equal amounts of radiation across the substrate surface is another challenge when attempting to form thin material layers having a low thickness variation (a high degree of uniformity) across the surface of the substrate. 
         [0006]    Therefore, there is a need in the art for a radiation system and lamphead array having improved radiation uniformity control and thermal processing capabilities. 
       SUMMARY 
       [0007]    In one embodiment, a lamphead apparatus is provided. The lamphead apparatus includes a body having a bottom surface defining a plane. A reflective trough may be formed in the body and a focal axis of the trough may be angled relative to an axis normal to the plane defined by the bottom surface. 
         [0008]    In another embodiment, a lamphead apparatus is provided. The lamphead apparatus may includes a body having a bottom surface defining a plane and a first reflective trough formed in the body. The first reflective trough may have a focal axis positioned at a first angle relative to an axis normal to the plane defined by the bottom surface. A second reflective trough may be formed in the body surrounding the first reflective trough. The second reflective trough may have a focal axis positioned at a second angle relative to an axis normal to the plane defined by the bottom surface different than the first angle. 
         [0009]    In yet another embodiment, a lamphead apparatus is provided. The lamphead apparatus includes a body having a bottom surface defining a plane and a first reflective trough formed in the body. The first reflective trough may have a focal axis positioned at a first angle relative to an axis normal to the plane defined by the bottom surface. A second reflective trough may be formed in the body surrounding the first reflective trough. The second reflective trough may have a focal axis positioned at a second angle relative to an axis normal to the plane defined by the bottom surface different than the first angle. A third reflective trough may be formed in the body surrounding the second trough. The third reflective trough may have a focal axis positioned at a third angle relative to an axis normal to the plane defined by the bottom surface different than the first angle and the second angle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, 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 disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
           [0011]      FIG. 1  is a schematic, cross-sectional view of a process chamber according to one embodiment. 
           [0012]      FIG. 2A  is a schematic, cross-sectional view of a portion of a lamphead according to one embodiment. 
           [0013]      FIG. 2B  is a schematic, cross-sectional, close-up view of a lamp disposed in a trough of the lamphead of  FIG. 2A  according to one embodiment. 
           [0014]      FIG. 2C  is a schematic, cross-sectional, close-up view of a lamp disposed in a trough according to one embodiment. 
           [0015]      FIG. 3A  is a plan view of a torroidal lamp according to one embodiment. 
           [0016]      FIG. 3B  is a cross-sectional view of the torroidal lamp of  FIG. 3A  taken along line A-A according to one embodiment. 
           [0017]      FIG. 3C  is a cross-sectional view of the torroidal lamp of  FIG. 3A  taken along line B-B according to one embodiment. 
           [0018]      FIG. 3D  is a schematic, cross-sectional view of the torroidal lamp of  FIG. 3A  taken along line  3 C- 3 C according to one embodiment. 
           [0019]      FIG. 4A  is a schema plan view of a lamphead according to one embodiment. 
           [0020]      FIG. 4B  is a schematic, plan view representative of a plurality of torroidal lamps arranged in a concentric pattern according to one embodiment. 
           [0021]      FIG. 5A  is a cross-sectional view of a lamphead and a substrate support according to one embodiment. 
           [0022]      FIG. 5B  is a cross-sectional view of a lamphead and a substrate support according to one embodiment. 
           [0023]      FIG. 6  is a graph depicting the amount of irradiance for a lamphead according to one embodiment. 
           [0024]      FIG. 7A  is a plan view of a lamphead according to one embodiment. 
           [0025]      FIG. 7B  is a cross-sectional view of a portion of the lamphead of  FIG. 7A  according to one embodiment. 
       
    
    
       [0026]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
       DETAILED DESCRIPTION 
       [0027]    A chamber capable of zoned temperature control of a substrate while performing an epitaxy process has a processing vessel with an upper portion, a side portion, and a lower portion all made of a material having the capability to maintain its shape when high vacuum is established within the vessel. At least the lower portion is substantially transparent to thermal radiation, and thermal lamps may be positioned in a flat or conical lamphead structure coupled to the lower portion of the processing vessel on the outside thereof. 
         [0028]      FIG. 1  is a schematic cross-sectional view of a process chamber  100  according to one embodiment. The process chamber  100  may be used to process one or more substrates, including the deposition of a material on a device side  116 , or upper surface, of a substrate  108 . The process chamber  100  generally includes a chamber body  101  and an array of radiant heating lamps  102  for heating, among other components, a ring member  104  of a substrate support  107  disposed within the process chamber  100 . The substrate support  107  may be a ring-like substrate support as shown, which supports the substrate  108  from the edge of the substrate  108 , a disk-like or platter-like substrate support, or a plurality of pins, for example, three pins or five pins. The substrate support  107  may be located within the process chamber  100  between an upper dome  128  and a lower dome  114 . The substrate  108  may be brought into the process chamber  100  and positioned onto the substrate support  107  through a loading port  103 . 
         [0029]    The substrate support  107  is shown in an elevated processing position, but may be vertically positioned by an actuator (not shown) to a loading position below the processing position to allow lift pins  105  to contact the lower dome  114 . The lift pins  105  pass through holes in the substrate support  107  and raise the substrate  108  from the substrate support  107 . A robot (not shown) may then enter the process chamber  100  to engage and remove the substrate  108  therefrom though the loading port  103 . The substrate support  107  then may be moved up to the processing position to place the substrate  108 , with its device side  116  facing up, on a front side  110  of the substrate support  107 . 
         [0030]    The substrate support  107 , while located in the processing position, defines the internal volume of the process chamber  100  into a process gas region  156  (above the substrate  108 ) and a purge gas region  158  (below the substrate support  107 ). The substrate support  107  may be rotated during processing by a central shaft  132  to minimize the effect of thermal and process gas flow spatial non-uniformities within the process chamber  100  and thus facilitate uniform processing of the substrate  108 . The substrate support  107  is supported by the central shaft  132 , which moves the substrate  108  in an axial direction  134  during loading and unloading, and in some instances, during processing of the substrate  108 . The substrate support  107  is typically formed from a material having low thermal mass or low heat capacity, so that energy absorbed and emitted by the substrate support  107  is minimized. The substrate support  107  may be formed from silicon carbide or graphite coated with silicon carbide to absorb radiant energy from the lamps  102  and conduct the radiant energy to the substrate  108 . The substrate support  107  is shown in  FIG. 1  as a ring with a central opening to facilitate exposure of the substrate to the thermal radiation from the lamps  102 . The substrate support  107  may also be a platter-like member with no central opening. 
         [0031]    The upper dome  128  and the lower dome  114  are typically formed from an optically transparent material, such as quartz. The upper dome  128  and the lower dome  114  may be thin to minimize thermal memory, typically having a thickness between about 3 mm and about 10 mm, for example about 4 mm. The upper dome  128  may be thermally controlled by introducing a thermal control fluid, such as a cooling gas, through an inlet portal  126  into a thermal control space  136 , and withdrawing the thermal control fluid through an exit portal  130 . In some embodiments, a cooling fluid circulating through the thermal control space  136  may reduce deposition on an inner surface of the upper dome  128 . 
         [0032]    One or more lamps, such as the array of lamps  102 , may be disposed adjacent to and beneath the lower dome  114  in a desired manner around the central shaft  132  to heat the substrate  108  as the process gas passes over the substrate  108 , thereby facilitating the deposition of a material onto the upper surface  116  of the substrate  108 . In various examples, the material deposited onto the substrate  108  may be a group III, group IV, and/or group V material, or may be a material including a group III, group IV, and/or group V dopant. For example, the deposited material may include gallium arsenide, gallium nitride, or aluminum gallium nitride. 
         [0033]    The lamps  102  may be adapted to heat the substrate  108  to a temperature within a range of about 200 degrees Celsius to about 1200 degrees Celsius, such as about 300 degrees Celsius to about 950 degrees Celsius. The lamps  102  may include bulbs  141  surrounded by a reflective trough  143 . Each lamp  102  may be coupled to a power distribution board (not shown) through which power is supplied to each lamp  102 . The lamps  102  are positioned within a lamphead  145  which may be cooled during or after processing by, for example, a cooling fluid introduced into channels  149  located between the lamps  102 . The lamphead  145  conductively cools the lower dome  104  due in part to the close proximity of the lamphead  145  to the lower dome  104 . The lamphead  145  may also cool the lamp walls and walls of the reflective troughs  143 . If desired, the lamphead  145  may be in contact with the lower dome  114 . 
         [0034]    An optical pyrometer  118  may be disposed at a region above the upper dome  128 . This temperature measurement by the optical pyrometer  118  may also be done on substrate device side  116  having an unknown emissivity since heating the substrate support front side  110  in this manner is emissivity independent. As a result, the optical pyrometer  118  senses radiation from the hot substrate  108  that conducts from the substrate support  107  or radiates from the lamps  102 , with minimal background radiation from the lamps  102  directly reaching the optical pyrometer  118 . In certain embodiments, multiple pyrometers may be used and may be disposed at various locations above the upper dome  128 . 
         [0035]    A reflector  122  may be optionally placed outside the upper dome  128  to reflect infrared light that is radiating from the substrate  108  or transmitted by the substrate  108  back onto the substrate  108 . Due to the reflected infrared light, the efficiency of the heating will be improved by containing heat that could otherwise escape the process chamber  100 . The reflector  122  can be made of a metal such as aluminum or stainless steel. The reflector  122  can have machined channels  126  to carry a flow of a fluid such as water for cooling the reflector  122 . If desired, the efficiency of the reflection can be improved by coating a reflector area with a highly reflective coating, such as a gold coating. 
         [0036]    A plurality of thermal radiation sensors  140 , which may be pyrometers or light pipes, such as sapphire light pipes or sapphire light pipes coupled to pyrometers, may be disposed in the lamphead  145  for measuring thermal emissions of the substrate  108 . The sensors  140  are typically disposed at different locations in the lamphead  145  to facilitate viewing different locations of the substrate  108  during processing. In embodiments using light pipes, the sensors  140  may be disposed on a portion of the chamber body  101  below the lamphead  145 . Sensing thermal radiation from different locations of the substrate  108  facilitates comparing the thermal energy content, for example the temperature, at different locations of the substrate  108  to determine whether temperature anomalies or non-uniformities are present. Such non-uniformities can result in non-uniformities in film formation, such as thickness and composition. At least two sensors  140  are used, but more than two may be used. Different embodiments may use three, four, five, six, seven, or more sensors  140 . 
         [0037]    Each sensor  140  views a zone of the substrate  108  and senses the thermal state of a zone of the substrate. The zones may be oriented radially in some embodiments. For example, in embodiments where the substrate  108  is rotated, the sensors  140  may view, or define, a central zone in a central portion of the substrate  108  having a center substantially the same as the center of the substrate  108 , with one or more zones surrounding the central zone and concentric therewith. It is not required that the zones be concentric and radially oriented, however. In some embodiments, zones may be arranged at different locations of the substrate  108  in non-radial fashion. 
         [0038]    The sensors  140  are typically disposed between the lamps  102  and may be oriented substantially normal to the substrate  108 . In some embodiments, the sensors  140  may be oriented normal to the substrate  108 , while in other embodiments, the sensors  140  may be oriented in slight departure from normality. An orientation angle within about 5° of normal is most frequently used. 
         [0039]    The sensors  140  may be attuned to the same wavelength or spectrum, or to different wavelengths or spectra. For example, substrates used in the chamber  100  may be compositionally homogeneous, or they may have domains of different compositions. Using sensors  140  attuned to different wavelengths may allow monitoring of substrate domains having different composition and different emission responses to thermal energy. Typically, the sensors  140  are attuned to infrared wavelengths, for example about 3 μm. 
         [0040]    A controller  160  receives data from the sensors  140  and separately adjusts power delivered to each lamp  102 , or individual groups of lamps or lamp zones, based on the data. The controller  160  may include a power supply  162  that independently powers the various lamps or lamp zones. The controller  160  can be configured with a desired temperature profile, and based on comparing the data received from the sensors  140 , the controller  160  adjusts power to lamps and/or lamp zones to conform the observed thermal data to the desired temperature profile. The controller  160  may also adjust power to the lamps and/or lamp zones to conform the thermal treatment of one substrate to the thermal treatment of another substrate, in the event chamber performance drifts over time. 
         [0041]      FIG. 2A  is a schematic, cross-sectional view of a portion of the lamphead  145 . The lamphead  145  body may comprise one or more reflective troughs  143  formed therein from a material suitable for rapid thermal processing, such as stainless steel, aluminum, or ceramic materials. The reflective troughs  143  may be coated with a highly reflective material, such as gold, or may be polished or processed to produce a reflective surface capable of reflecting radiation from the lamps  102  towards a substrate. The reflective troughs  143  may be sized to accommodate the lamps  102  having a torroidal bulb  141  with a filament  202  disposed therein. The lamps  102  will be discussed in greater detail with regard to  FIG. 3A-3C . The lamphead  145  may have one or more reflective troughs  143  disposed therein, such as 3 or more troughs, for example, between 7 and 13 troughs. As depicted in  FIG. 2A , only one half the lamphead  145  is shown. In this embodiment, 7 reflective troughs  143  are arranged in a concentric circular pattern. Although depicted as forming a semi-circular shaped cross-sectional trough, the reflective troughs  143  may comprise other dimensions, such as a parabolic shape or truncated parabolic shape which will be discuss in greater detail with regard to  FIG. 2C . 
         [0042]      FIG. 2B  is a schematic, cross-sectional, close-up view of a lamp  102  disposed in a trough of the lamphead  145  of  FIG. 2A  according to one embodiment. The reflective trough  143  formed in the lamphead  145  may comprise a semi-circular cross-sectional shape. Here, a distance A between a wall  204  of the reflective trough  143  and the bulb  141  may be between about 0.5 mm and about 5.5 mm depending on the number of reflective troughs  143  formed in the lamphead. For example, if thirteen reflective troughs  143  are utilized, the distance A may be between about 0.5 mm and about 1.0 mm, such as about 0.7 mm. If seven or eight reflective troughs  143  are utilized, the distance A may be between about 3.5 mm and about 5.5 mm, such as about 4.5 mm. 
         [0043]    The distance A may remain substantially constant between the wall  204  and the bulb  141  at any point within the reflective trough  143 . A portion of the lamp  102  may be disposed within the reflective trough  143 . As depicted by the horizontal dashed line, approximately one half of the lamp  102  may be disposed within the reflective trough  143  and the remainder of the lamp  102  may remain outside the reflective trough  143 . However, it is contemplated that more of less of the lamp  102  may be disposed within the reflective trough  143  to suit radiation requirements as the amount of lamp  102  disposed within the reflective trough  143  may alter the radiation characteristics of the lamp  102 . As previously mentioned, the filament  202 , or coil, may be disposed within the bulb  141  and will be discussed in greater detail with regard to  FIG. 3C . 
         [0044]      FIG. 2C  is a schematic, cross-sectional, close-up view of a lamp  102  disposed in a reflective trough  143  having a substantially parabolic shaped cross-section. As depicted, the reflective trough  143  has a parabolic shaped cross-section. The distance A, described with regard to  FIG. 2B , may be a distance between the lamp  141  and the wall  204  of the reflective trough at a first region of the reflective trench  143 . A distance B which may be different than the distance A may be the distance between the bulb  141  and a vertex of the parabola shaped trough along an axis of symmetry of the parabola shaped trough  143 . For example, the distance B may be greater than the distance A or the distance B may be less than the distance A. In either example, the wall  204  of the parabola shaped reflective trough  143  may comprise a curvilinear surface or a plurality of linear surfaces forming a substantially parabola shaped reflective trough  143 . 
         [0045]    In some examples, the vertex of the parabola shaped reflective trough  143  may be truncated, for example, a portion of the wall  204  at the vertex region may be substantially linear along a horizontal plane and curvilinear portions of the wall  204  may extend from the truncated portion of the reflective trough  143 . In other examples, sections of the parabola may curve away from the vertex region and may be replaced by linear line segments, alone or in addition to segments at the vertex. For the sake of simplicity, these elements may be included in the description of a “truncated parabola.” Certain embodiments may include a linear and/or hollow light pipe in linear segments disposed within the reflective trough  143  where the light pipe may be coupled at the vertex of the parabola shaped reflective trough  143 . 
         [0046]    Similar to  FIG. 2B , a portion of the lamp  102  may be disposed within the reflective trough  143 . As depicted by the horizontal dashed line, approximately one half of the lamp  102  may be disposed within the reflective trough  143  and the remainder of the lamp  102  may remain outside the reflective trough  143 . However, it is contemplated that more of less of the lamp  102  may be disposed within the reflective trough  143  to suit radiation requirements as the amount of lamp  102  disposed within the reflective trough  143  may alter the radiation characteristics of the lamp  102 . 
         [0047]      FIG. 3A  is a plan view of a lamp  102 . The lamp  102 , for example, may be a curved linear lamp or torroidal lamp, and may comprise a substantially torus shaped bulb  141  and may have a hollow interior within which one or more filaments  302 ,  304  may be disposed. The lamp  102  may comprise a material suitable for emitting radiation therefrom, such as a quartz material. A first filament  302  may be coupled between a first coupling member  306  and a second coupling member  308 . A second filament  304  may also be coupled between the first coupling member  306  and the second coupling member  308 . The first filament  302  may be formed between the first coupling member  306  and the second coupling member  308 . The second filament  304  may also be coupled between the first coupling member  306  and the second coupling member  308 , however, the second filament  304  may occupy a region of the bulb  141  not occupied by the first filament  302 . The first coupling member  306  may comprise a lead having a first polarity and the second coupling member  308  may comprise a lead having a second polarity opposite the first polarity, for example, a positive charge or a negative charge, respectively. 
         [0048]      FIG. 3B  is a cross-sectional view of the lamp  102  of  FIG. 3A  taken along line  3 B- 3 B. The bulb  141  may comprise the torroidal shaped portion substantially surrounding the second coupling member  308  and a seal  312 . A lead  310  may extend from the second coupling member  308  through the seal  312  and beyond an exit region  314  where the lead may be coupled to a power source (not shown). The lead  310  may carry a positive or negative current depending upon the design of the circuitry of the lamp  102 . Another lead (not shown) may extend from the first coupling member and may carry a current opposite the current carried by the lead  310 . The seal  312  may be formed from an insulative material to ensure the current reaches the second coupling member  308  where the first and second filaments  302 ,  304  are electrically coupled to the second coupling member  308 . An example of an insulative material for the seal may be a quartz material, among others. 
         [0049]      FIG. 3C  is a cross sectional view of the torroidal lamp  102  of  FIG. 3A  taken along line  3 C- 3 C. The torroidal shaped portion of the lamp  102 , for example, the bulb  141 , may occupy a first plane and the seal  312  may occupy a plane angled from the plane of the bulb  141 . In one example, the seal  312  may be in a plane perpendicular to the first plane, however, it is contemplated that the seal  312  may be angled at any suitable angle from the first plane of the torroidal shaped bulb  141  portion of the lamp  102 . 
         [0050]    As depicted, the first filament  302  and the second filament  304  may be coupled to the second coupling member  308 . For example, the first and second filaments  302 ,  304 , may comprise an electrically conductive material, such as a metallic wire, and may contact the second coupling member  308  to electrically couple the filaments  302 ,  304  to a power source (not shown) via the lead  310 . For example, the filaments  302 ,  304  may hook through the second coupling member  308 , which may be a wire ring or the like. The filaments  302 ,  304  may be formed into various shapes suitable for emitting radiation when an electrically current is applied to the filaments  302 ,  304 . For example, the filaments  302 ,  304  may comprise coiled regions  318  and linear regions  320  arranged in a repeating pattern. The coiled regions  318  of the filaments  302 ,  304  may be spaced apart by the linear regions  320  by between about 1 cm and about 5 cm, such as between about 1.5 cm and about 3 cm. Support members  316  may be coupled to the filaments  302 ,  304  at the linear regions  320 . For example, the support members  316  may contact the linear regions  320  and hold the filaments  302 ,  304  in a fixed position within the bulb  141 . In another example, the support member  316  may be coupled with the filaments  302 ,  304  at the coiled regions  318 . The support members may be sized to contact interior surfaces  322  of the bulb  141  which may help position the filaments  302 ,  304  properly within the bulb  141 . In some embodiments, the bulb  141  may have an outer diameter of between about 5 mm and about 25 mm, such as about 11 mm. 
         [0051]      FIG. 3D  is a schematic, cross sectional view of the torroidal lamp  102  of  FIG. 3A  taken along line  3 C- 3 C according to one embodiment. The filaments  302 ,  304  may be spaced apart by a bridge member  330  which may physically separate the filaments to prevent shorting. The bridge member  330  may be disposed within the seal  312 , which may comprise a hermetic seal  340 . One or more foils  332  may be disposed within the hermetic seal  340  and may be coupled to the filaments  304 ,  302 . For example each filament  302 ,  304  may be coupled with its own foil  332 . A first power lead  334  and a second power lead  336  may be coupled to a single foil  332  and may be coupled to a power source. 
         [0052]      FIG. 4A  is a schematic, plan view of the lamphead  145  according to one example. The lamphead  145  may comprise a first torroidal lamp  406 , a second torroidal lamp  404 , a third torroidal lamp  402 , and a plurality of reflective annular troughs  143  within which the first, second, and third torroidal lamps  406 ,  404 ,  402  may be disposed. The shaft  132  of the substrate support may be disposed through a center region of the lamphead  145 . Although only three torroidal lamps  406 ,  404 ,  402  are depicted, a greater or lesser number of torroidal lamps and reflective annular troughs  143  may be utilized to achieve a desired lamphead design for irradiating a substrate. For example, several torroidal lamps may be located between the first torroidal lamp  406  and the second torroidal lamp  404  and several more torroidal lamps may be located between the second torroidal lamp  404  and the third torroidal lamp  402 . As previously mentioned, as many as 7 or more torroidal lamps, such as about 13 torroidal lamps maybe utilized in the lamphead  145 . As such, spacing between the torroidal lamps may be substantially equal or the spacing may not be constant between each lamp. 
         [0053]    The first torroidal lamp  406  may have a radius X (measured from a center of the lamphead  145  to a center of the torroidal lamp which may be approximated by the filament within the bulb) which may be between about 50 mm and about 90 mm, such as about 72 mm. The second torroidal lamp  404  may have a radius Y which may be between about 110 mm and about 150 mm, such as about 131 mm. The third torroidal lamp  402  may have a radius Z which may be between about 170 mm and about 210 mm, such as about 190 mm. It is contemplated that the radii of the torroidal lamps may be reduced or enlarged for irradiating substrates having diameters of about 200 mm, 300 mm, or 450 mm. 
         [0054]      FIG. 4B  is a schematic, plan view representative of a plurality of torroidal lamps  406 ,  404 ,  402  arranged in a concentric pattern. The concentric pattern may comprise the first torroidal lamp  406  encircled by the second torroidal lamp  404 . The second torroidal lamp  404  may be encircled by the third torroidal lamp  402 . Radiation loss regions  412 ,  422 ,  432 ,  414 ,  424 ,  416  may be representative of regions on the torroidal lamps  406 ,  404 ,  402  where the seal (not shown) and coupling members (not shown) are present (See  FIG. 3C  for more detail). The amount of radiation radiating from the radiation loss regions  412 ,  422 ,  432 ,  414 ,  424 ,  416  may affect the uniformity with which a substrate is irradiated. Minimizing the potentially negative effects of the radiation loss regions  412 ,  422 ,  432 ,  414 ,  424 ,  416  may be achieved by the spatial arrangement of each radiation loss region in relation to nearby radiation loss regions. 
         [0055]    For example, the first torroidal lamp  406  may have a first radiation loss region  416  corresponding to the seal  312 . The length of filament which may be energized within the first torroidal lamp  406  may be approximately equal to the circumference of the first torroidal lamp  406 . The second torroidal lamp  404  may have second radiation loss regions  414 ,  424  which may correspond to two seals, respectively. The second radiation loss regions  414 ,  424  may be disposed at positions antipodal to one another such that a length of the filament between the second radiation loss regions  414 ,  424 , may be approximately equal to the length of the filament within the first torroidal lamp  406 . The third torroidal lamp  402  may have third radiation loss regions  412 ,  422 ,  432  which may correspond to three seals, respectively. In this example, the polarities at each seal  312  may correspond to the three phases In a 3-phase alternative current supply. The third radiation loss regions  412 ,  422 ,  432  and associated seals, may be disposed substantially equidistant from one another along the third torroidal lamp  402  such that a length of the filament between the third radiation loss regions  412 ,  422 ,  432  may be approximately equal to the length of the filament within the first torroidal lamp  406  and the length of the two filament segments in the second torroidal lamp  404 . 
         [0056]    Placing the seals at locations along the torroidal lamps  406 ,  404 ,  402  to increase the distance between the resulting radiation loss regions  412 ,  422 ,  432 ,  414 ,  424 ,  416  may ultimately reduce or mask the effect of the radiation loss regions  412 ,  422 ,  432 ,  414 ,  424 ,  416 . Moreover, by approximately equalizing the filament segment lengths, a single controller may be utilized to provide power to the filaments to reduce to complexity of the associated circuitry and reduce the necessity for numerous power sources providing different voltages for individual filament segments. In certain embodiments, each filament segment may be individually controlled. The filament segments may be wire in parallel if an even number of segments per lamp is utilized. If an odd number of segments per lamp is utilized, then a number of phases equal to the number of segments may equal a multiple of the number of phases. 
         [0057]    In one example, the first torroidal lamp  406  may have a radius of about 72 mm and the filament segment length may be about 450 mm. The second torroidal lamp  404  may have a radius of about 131 mm and the length of each of the two filament segments may be about 410 mm. The third torroidal lamp  402  may have a radius of about 190 mm and the length of each of the three filament segments may be about 400 mm. 
         [0058]      FIG. 5A  is a cross-sectional view of the lamphead  145  and the substrate support  107  according to one embodiment. The lamphead  145  may comprise a conical shape and may be angled a first angle θ 1  from a horizontal plane  501  between about 5° and about 25°, such as about 22°. A first annular trough  502  may be formed in the lamphead  145  such that a focal axis  503  of the first annular trough  502  may angle toward a center region  508  of the lamphead  145 . For example, the focal axis  503  of the first annular trough  502  may be positioned at a second angle θ 2  of between about 5° and about 25° from a line  509  normal to a plane defined by a lower surface  520  of the lamphead  145 . A second annular trough  504  may be formed in the lamphead  145  encircling the first annular trough  502 . The second annular trough  504  may have a focal axis  505  that is angled toward an outer edge  510  of the lamphead  145 . For example, the focal axis  505  of the second annular trough  504  may be positioned at a third angle θ 3  of between about 5° and about 25° from the line  509  normal to the plane defined by the lower surface  520  of the lamphead  145 . A third annular trough  506  may also be formed in the lamphead  145  and may encircle the second annular trough  504 . The third annular trough  506  may have a focal axis  507  that is substantially parallel to the line  509  normal to the plane defined by the lower surface  520  of the lamphead  145 . As a result, a fourth angle θ 4  may be about 0°. 
         [0059]      FIG. 5B  is a cross-sectional view of the lamphead  145  and the substrate support  107  according to one embodiment. The lamphead  145  is similar to the lamphead  145  of  FIG. 5A  except that the lamphead  145  of  FIG. 5B  is flat instead of conical. A focal axis  513  of the first annular trough  502  may angle toward the center region  508  of the lamphead  145 . For example, the focal axis  513  of the first annular trough  502  may be positioned at a fifth angle θ 5  of between about 5° and about 25° from the line  509  normal to a horizontal plane occupied by the lower surface  520  of the lamphead  145 . The second annular trough  504  may have a focal axis  515  that is angled toward an outer edge  510  of the lamphead  145 . For example, the focal axis  515  of the second annular trough  504  may be positioned at a sixth angle θ 6  of between about 5° and about 25° from the line  509  normal to the horizontal plane occupied by lower surface  520  of the lamphead  145 . The third annular trough  506  may have a focal axis  517  that is substantially parallel to the line  509  normal to the horizontal plane occupied by the lower surface  520  of the lamphead  145 . As a result, a seventh angle θ 7  may be about 0°. 
         [0060]    The annular troughs  502 ,  504 ,  506  are representative of three troughs within which a lamp may be disposed. The lamp disposed within each of the annular troughs  502 ,  504 ,  506  may be a single torroidal lamp or a plurality of bulbs having a right circular cylindrical coil disposed therein. The lamps may generally radiate toward a substrate at an angle of the focal axis of the trough. A greater or lesser number of troughs may be incorporated into the lamphead, and various combinations of angled troughs may function to achieve a substantially uniform irradiance across the entire surface of a substrate. 
         [0061]      FIG. 6  is a graph depicting the amount of irradiance for a lamphead according to one embodiment. The model calculations of the graph were made utilizing a lamphead with a first trough having a radius of about 72 mm, a second trough having a radius of about 131 mm, and a third trough having a radius of about 190 mm. The three troughs were angled according to the embodiments described with regard to  FIG. 5A-5B . Although the individual troughs provided a wide range of irradiance, the sum irradiance over the surface of the substrate was much more constrained, that is, a much more even amount of irradiance. For example, it can be seen that the sum irradiance across the surface of the substrate only ranged from about 7.0 E 4  to about 1.1 E 5 . Thus, the combination of angled troughs may provide an improved sum irradiance which may provide a relatively equal amount of thermal energy across the surface of the substrate. 
         [0062]      FIG. 7A  is a plan view of a lamphead  145  according to one embodiment. As opposed to previously described embodiments utilizing a torroidal shaped lamp, a plurality of bulbs  702  having a right circular cylindrical coil disposed therein may be disposed within the reflective troughs  143  of the lamphead  145 . Similar to previously described embodiment, the reflective troughs  143  may be semi-circular cross-sectional shaped, or parabola or truncated parabola cross-sectional shaped. The number of bulbs  702  disposed in the lamphead  145  may be between about 100 and about 500 bulbs, such as about 164 bulbs, or 218 bulbs, or 334 bulbs. 
         [0063]      FIG. 7B  is a cross-sectional view of a portion of the lamphead  145  of  FIG. 7A . For clarity, the bulbs  702  having a right circular cylindrical coil disposed therein may be disposed within the reflective troughs  143 . In the example shown, the reflective troughs  143  may have a truncated parabolic cross-section such that the vertex region  704  of the parabolic shape is substantially linear instead of curvilinear. In some embodiments, the bulbs  702  may be coupled to the reflective troughs  143  having truncated parabolic cross-sections at the linear section of the vertex region  704 . 
         [0064]    While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.