Abstract:
A radiative heater for substrates in a physical vapor deposition process for fabricating films of materials in a wide dynamic range of process temperatures and gas pressures includes a heat radiating member made from a high-temperature and oxidation resistant material tolerant to vacuum conditions which separates a heater volume containing heating filaments from a process volume which contains a deposition substrate heated by radiation of the walls of the heat radiating member. The heating elements extend through the body of the heat radiating member as well as in proximity to its surface to provide delivery of the heat to the substrate. The heat radiating member is shaped to form a cavity containing the substrate. The walls of the cavity envelope the substrate and radiate heat towards the substrate. Alternatively, the substrate is adhered to the flat surface of the heat radiating member.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to coating deposition; and in particular, to a substrate heater in a vapor deposition system. 
         [0002]    More in particular, the present invention is directed to a substrate heater capable of uniformly heating substrates over a wide range of temperatures and is capable of operating under limitations of a multi-step deposition process. 
       BACKGROUND OF THE INVENTION 
       [0003]    In material deposition, specifically in coating deposition, a condensable material is provided in a process chamber which condenses onto a substrate so that the thickness of the coating increases with time. The condensable materials may be provided, at least in vicinity of the substrate surface, through variety of mechanisms. For example, a gas containing at least a fraction of the condensable matter, e.g., material&#39;s vapor, may serve as the condensation material source. The gas may also be supplied in a partially ionized (plasma) state. A condensable component may also be generated at the surface of the substrate. The essential requirement of the deposition process is that the condensable component remains on the surface of the substrate to permit the thickness growth of the deposited material during the process. 
         [0004]    Delivery of a condensable material to a substrate may be accomplished through a Physical Vapor Deposition process in which a stream of atoms or ions, containing the material to be deposited is directed towards the substrate. The stream of particles is created by a source located in the process chamber or externally thereto. Kinetic energy of the particles, e.g., the energy range of the atoms or ions, may be within a wide range, from 1 eV to 100 keV. A particle stream of 1 eV to 300 eV energy can be generated, for example, via ablation of a solid tablet of the desirable material under impact of a powerful laser or electron beam. Such particles can condense on the substrate. 
         [0005]    If the stream of particles contains a large amount of highly energetic particles (&gt;300 eV), the coating formation starts from the accumulation of the particles under the substrate surface, e.g., the sub-plantation process, in which the initial accumulation is followed by coating of at yet a larger amount of the material delivered by the stream. 
         [0006]    The coating properties dependent on temperature of the substrate, and on composition of the gas present in the process chamber. Frequently, a rather high temperature of several hundred ° C. is required at the substrate surface to facilitate formation of the coating with desired properties. The pressure and nature of a gas in the process chamber also affects the coating properties. These factors are especially important for complex, multi-component coating materials such as, for example, oxides and nitrides, which also may contain non-condensable elements. Incorporation of these elements, present in the process chamber in the gaseous state, in the coating process occurs via reaction on the surface. The reaction kinetics depends on the surface temperature and the process gas concentration. Optimal concentration of the gas may vary in a wide range, e.g., from a very low (vacuum) to atmospheric pressure (750 Torr). 
         [0007]    Often the coating deposition process includes several steps with considerably different optimal temperature/pressure/gas requirements. For example the coating process sequence may include deposition of layers of several different materials, or annealing in the post-deposition processing. It is frequently required or desirable to perform the sequence within one “vacuum cycle”, that is without exposing the substrate to air or even without cooling it down between the layers deposition. 
         [0008]    These conditions set significant limitations on the choice and design of a heater for heating the substrate up to the required temperature during each process step. A substrate heater desirably functions in specific narrow conditions of a single-step process, and also is to be able to provide heating in a wide variety of conditions for the multi-step deposition process. It is highly desirable to use a single heater for cooling/heating in all process steps. Operational conditions of such a “universal” heater must cover the gas pressure in the range from vacuum (&lt;10 −5  Torr) to 750 Torr and further be compatible with process gases, including oxygen and nitrogen. In addition to operating in the wide dynamic range of process parameters, the heater must meet such operational requirements as the process purity, heater lifetime, etc. Substrate heaters used in the industry, are generally able to operate only in a narrow range of specific conditions. 
         [0009]    For heating a substrate to a temperature T, energy has to be transferred thereto by conduction, or radiation, or convection from an energy source (heater) whose surface temperature To&gt;T. Transfer by convection is not applicable in most film deposition conditions, since density of particles in the chamber atmosphere is too small at a low pressure (&lt;10 Torr) or vacuum conditions. Conduction of heat is effective only if a satisfactorily thermal contact can be established between the heater and the wafer. Often mechanical clamping does not produce good thermal contact, and then a soft, conformal to the heater and wafer surface material is used to fill the gap therebetween. Silver-loaded vacuum grease, or even soldering (with a low-temperature metal such as Indium, as example) may be used as the gap filler. This approach has a limited applicability however due to the facts that: (a) silver starts evaporating at temperature above ˜900° C., and contaminates the wafer surface; (b) wafers of a size greater than ˜20 mm may be damaged when removed from the heater after processing. 
         [0010]    Heating by radiation is a convenient approach free from the drawbacks of conduction and convection. In radiation heating, the source of radiation is usually an electrically resistive hot wire (filament) heated by electrical current. For vacuum processing, Tungsten is an example of the suitable filament material as it is highly resistive, and has a high melting/evaporation temperature. The filament, however, cannot be used in a low vacuum, or in an oxidizing ambient gas in chamber since Tungsten oxidizes quickly and loses it&#39;s electrical conductivity. 
         [0011]    Precious metals, like Platinum, do not oxidize even at a high temperature, and can be used as a radiative filament both in a vacuum and in oxygen processing. However, Platinum has very low emissivity, e.g., it radiates much less than a black material at the same temperature. Further, the platinum wire heater cannot be used as a contact heater. In addition, Platinum is prohibitively expensive for use in such applications. 
         [0012]    Silicon Carbide (SiC) filament can be used in both vacuum and oxidizing process gas. The material, however, is known as producing contaminating particles in the process chamber, and therefore it cannot be used as a contact heater. In addition, maximum temperature of SiC stability in vacuum is limited to ˜1200° C. However, SiC is a suitable material for filaments to operate up to ˜1600° C. in oxygen. 
         [0013]    Generally, it is beneficial to separate the volume containing filament and the process volume with a wall in order to protect filament from the process environment. Specifically, a metallic filament has to be protected from oxidizing environment, and SiC filament—fro vacuum environment. 
         [0014]    To facilitate maximum radiation heat transfer from filament to substrate, it is generally desirable to have the wall to be transparent for the filament radiation. 
         [0015]    To protect the filament from oxidation (if the filament is metallic, like Tungsten) it may be placed inside at least partially transparent envelope to provide different gas environments in the volume internal the envelope and the processing volume external the envelope. Tungsten-halogen radiant heaters have the envelope filled with a halogen gas. By using quartz as the enveloping material, maximum transparency for the filament radiation may be attained. These heaters have been widely used in the semiconductor industry for radiative heating of wafers during annealing. In contrast, in film deposition processes, the transparency requirement is a major drawback of these heaters. During deposition, some deposition material can unavoidably reach the envelope, deposit on the envelope, and may react with the envelope material. The envelope then loses its transparency, thus resulting in decrease in the wafer temperature, and an increase in the envelope temperature which leads to envelope failure. For this reason, the transparent envelope (separating wall) generally does not work well in film deposition. 
         [0016]    Transparent envelope may be replaced in radiative heater designs with a metallic envelope, as it is found in Thermocoax heating coaxial cable, where the envelope is made from a high-temperature, oxidation-resistant material, for example Inconel. In this design, a ceramic powder isolates a hot filament wire from the envelope. The envelope outer surface serves as the surface for radiating energy to a wafer. Although this heater is tolerant to deposition of materials on the surface since it does not change the metal emissivity significantly. The cable-based heater, however, suffers from some drawbacks. First, the surface of the cable-made heaters is not flat, making the contact heating nearly impossible. Second, a chemical reaction between the hot filament material and the isolator material leads to failure of the filament. The reaction rate is higher at high temperatures which limits the operational temperature of the filament, as well as the maximum temperature of the radiating envelope, typically to 1000-1050° C. 
         [0017]    A “universal” heater capable of providing the uniform heating of the substrate in a wide dynamic range of temperatures, pressure and process gases, which permits use in a multi-step coating process is a long-lasting need in the industry. 
       SUMMARY OF THE INVENTION 
       [0018]    It is therefore an object of the present invention to provide a “universal” substrate heater for a Physical Vapor Deposition process capable of wide dynamic ranges of operational parameters. 
         [0019]    It is another object of the present invention to provide a substrate heater permitting uniform heating of a substrate to sufficiently high temperatures. 
         [0020]    It is a further object of the present invention to provide a substrate heater usable for multi-layered vapor deposition. 
         [0021]    The present substrate heater includes a heating assembly positioned in a heater volume and radiating heat to the substrate. The heating assembly includes a heat radiating member having walls defined between a heated surface and a radiating surface of the heat radiating member and an array of heating elements distributed in thermal communication with the heated surface of the heat radiating member. The substrate is positioned to be in thermal communication with the radiating surface. 
         [0022]    The walls of the heat radiating member are shaped to form heater channels extending through the body of the heat radiating member. A portion of the heating surface of the heat radiating member defines a central cavity filled with a process media. The cavity accommodates the substrate therein. The heating elements are positioned in the heater channels as well as distributed over the heated surface of the heat radiating member, thereby providing a substantially uniform surrounding radiation towards the substrate. 
         [0023]    Alternatively, the substrate may be glued to the radiating surface of the heat radiating member. It is preferred that the walls of the heat radiating member forming the heater channels, be curved to avoid mechanical stress and to reduce thermal loss. 
         [0024]    The heat radiating member is shaped to conform with a shape of the substrate. For example, if the substrate is circularly shaped, then the walls of the heat radiating member are cylindrically contoured to form annularly shaped heater channels. If, however, the substrate is an elongated substrate, then heater channels extend substantially parallel each to the other along the sides of the substrate. 
         [0025]    The walls of the heat radiating member separate the process volume filled with the process media from the heater volume. Preferably, side walls of the heat radiating member include heated wall portions exposed to heat radiation from the array of heating elements and unheated wall portions distant from the substrate. 
         [0026]    An isolation element (member) is attached to the unheated wall portions of the side walls in order to thermally isolate the heated wall portions of the heat radiating member from an external area where an electrical contact array may be positioned. The isolation element also functions as a support for the electrical elements. 
         [0027]    A thermoshield is positioned in enveloping relationship with the heat radiating member. The substrate may be supported by bottom walls of the thermoshield for rotational displacement. Alternatively, the substrate may be held by a shaft supported by the isolation element for rotational or linear displacement of the substrate within the heat radiating member. 
         [0028]    Preferably shield plates are located between the isolation element and the heating elements to further improve the heat distribution in the system. 
         [0029]    The heat radiating member may be formed from Inconel, while the heating elements may be formed from silicon carbide. A thermocouple (or another thermo-sensor) measures the temperature of the heat radiating member and communicates the data to an automatic temperature control loop which functions to control the temperature of the heat radiating member. 
         [0030]    These and other features and advantages will become apparent after reading a further description of the preferred embodiment in conjunction with the accompanying patent drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a schematic representation of operating principles of the present substrate heater in a vapor deposition apparatus; 
           [0032]      FIG. 2  is a schematic representation of the present substrate heater; 
           [0033]      FIG. 3  is a schematic representation of an alternative embodiment of the present substrate heater; 
           [0034]      FIGS. 4A and 4B  show a cross-section A-A of the substrate heater shown in  FIGS. 2 ,  3  for a circular wafer ( FIG. 4A ) and a tape-like substrate ( FIG. 4B ); and 
           [0035]      FIG. 5  is a schematic representation of another alternative embodiment of the present substrate heater. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    Referring to  FIG. 1 , illustrating the concept of the present substrate heater, a system  10  for material deposition includes a process chamber  32  and a heater chamber  34  separated each from the other by a high-temperature and oxidation resistant material which is tolerant to vacuum conditions. The heater chamber  34  contains a heating filament  36  and is filled with a gas suitable for the heating filament or it may be open to air. 
         [0037]    A substrate  38  is positioned in the process chamber  32  which is filled with a process gas  40 . The condensable particles (atoms/ions)  42  in the process chamber  32  flow to the substrate  38  and condense on the surface thereof to form a deposited material  44 . The heat from the filament  36  is transferred to the substrate  38  through a hot (radiating) surface  46  formed from a high-temperature and oxidation resistant material, such as, for example, Inconel. By using the radiating surface  46 , a uniform heating of the substrate  38  to high process temperatures may be attained. 
         [0038]    The filament  36  and the radiating surface  46  constitute the substrate heater  48  of the present invention. The operational conditions of the heater  48  cover all or any combination of the following conditions:
       Temperature of the hot surface  46  between 20 to 1150° C.   A flat shape of the hot surface exposed to the process volume  32     A flat-surface substrate can be directly attached to the heater surface   Capability to function in vacuum ambient (&lt;10 −5  Torr)   Capability to function at high pressure (up to 750 Torr) of process gas   Capability to function in the atmosphere of a process gas including oxygen or/and nitrogen   Capability to accept a directed stream of coating material   The heater surface does not produce contaminating particles in the process volume  32     Tolerance of the heater with respect to deposition of some material on surface  46     Filling the heater volume  34  with an optimal gas   Heater lifetime&gt;5000 Hrs.       
 
         [0050]    Referring to  FIGS. 2-3 , illustrating more in detail a cavity-like heater  50 , the same includes a heating assembly  52  formed of a heat radiating member  54  and an array of heating elements  56 . The heat radiating member  54  has side walls  58  shaped to form heat channels  60  and a bottom wall  62 . The heat radiating member  54  is contoured specifically to form a cavity  64  defined by the side walls  58  and the bottom wall  62 . 
         [0051]    A substrate  66  is located inside the cavity  64  and thus is enveloped by the walls  58 ,  62  made of high-temperature, oxidation resistant metal. The walls  58 ,  62  have a heated surface  68  and a radiating surface  70 . In this manner the substrate  66  receives the radiation from the hot radiating surface  70  of the walls  58 ,  62  except the opening  72  of the cavity  64 . The opening  72  serves as an inlet port for the stream  74  of depositing material into the cavity  64 . 
         [0052]    The design of the present substrate heater  50  is intended to maximize the amount of the radiation received by the substrate as well as to minimize the amount of the radiation escaping. The radiation intensity Q depends strongly on the temperatures of the T radiating surface (as Q˜T 4 ). Thus, increase of the maximal temperature of the walls  58 ,  62  of the heat radiating member which is of primary importance. 
         [0053]    As can be seen in  FIGS. 2-3 , the heat radiating member  54  separates the heater volume  34  from the process volume (e.g., cavity  64 ). The heat radiating member  54  is at least partially, fabricated from Iconel©  600  (preferably, from Iconel  601 ). This material is chosen due to its stability in both vacuum and oxidizing environment up to 1200° C., and therefore may be used as the material separating the material deposition volume of the cavity  64  from the volume  34  containing the heating elements  56 . 
         [0054]    The heating elements  56  are arranged in sub-arrays including: (a) a sub-array  76  of the heating elements  56  which extend within the heater channels  60  defined between the side walls  58 . It is important that the heater channels extend substantially through the entire “depth” of the heat radiating member  54  and that the heating elements  56  extend through the entire depth of the heater channels. It is also important, that the heating elements  56  are distributed uniformly along the length of the heater channels in order to provide uniform heating of the material of the side walls  68  and optimal conditions for the heat radiation from the heating surface  70  into the cavity  64 ; and (b) another sub-array  78  of the heating elements  56  is positioned in proximity to the heated surface  68  of the bottom wall  62 . In this arrangement, the substrate  66  is enveloped by the radiating surface  70  which radiates heat thereto. 
         [0055]    As shown in  FIGS. 4A and 4B , presenting cross-section A-A of the arrangements shown in  FIG. 2  or  FIG. 3 , the heat radiating member  54  is shaped in conformance with the substrate  66 . As can be seen in  FIG. 4A , if the wafer  66  is of a circular shape, then the heat radiating member  54  has cylindrically contoured side walls  58  which define annularly shaped heater channels  60  along which the heating elements  56  are circumferentially distributed. 
         [0056]    If the substrate has an elongated tape-like shape, then the heat radiating member  54  is shaped accordingly. In this embodiment, the heater channels  60  extend in parallel each to the other along the substrate. The heating elements  56  are uniformly distributed along the parallel heater channels  60 , as shown in  FIG. 4B . 
         [0057]    The heating elements  56  of the heater  50  may be fabricated, for example, from silicon carbide, SiC. The maximum temperature the SiC heating element can attain is ˜1550° C. when the element is in the air or at least in a partially oxidizing atmosphere. Air may be used as the ambient atmosphere in the heater volume  34 , thereby facilitating the operation of the SiC heating elements  56  at their maximum temperature limited only by the SiC material intrinsic properties. 
         [0058]    The radiation from the SiC element at 1550° C. could in principle heat up the Iconel walls  58 ,  60  to temperatures above 1200° C. However, there are two important factors that limit the usable temperature of Inconel for the application in vacuum film deposition process. The first factor is the gradual oxidation of the Inconel surface, accompanied by the oxidized layer flaking. This phenomena is observed at temperatures higher ˜1200° C. Flaking is not acceptable in film deposition. Another limitation is set by mechanical properties of Inconel. At high temperatures, and under pressure (force) load, the material softens and usually undergoes deformation. The heater may experience maximum mechanical load due to the outside atmospheric pressure when the process volume is at zero pressure (vacuum). The Inconel deformation rate increases quickly with temperature. At 1150° C. and under load of ˜170 PSI, the material deformation due to the changes in shape is ˜0.1% for 1000 Hrs of operation. This deformation level may be accepted for the operation of the substrate heater. Required material thickness to maintain the stress associated with the load of ˜170 PSI is also within reasonable limits. Thus, temperature of the walls in the heater is limited to 1150° C. 
         [0059]    Thickness of the walls in the heat radiating member  54  has been optimized using simulation software for maintaining the mechanical stress below 170 PSI. An important feature of the embodiment is that there are no sharp angles created by the walls of the least radiating member. For example, rounded transitions  80  are formed between the cavity walls  58 , as shown in  FIGS. 2-3 , to avoid the corner stress, thus permitting a reduction of the walls thickness and associated conduction heat losses. 
         [0060]    The side walls  58  have a heated wall portion  82  and an unheated wall portion  84  which is not subjected to direct radiation of the SiC heating elements. The temperature of the unheated wall portion  84  is significantly lower than the temperature of the heated wall portion  82 . The unheated wall portion  84  may sustain a significant stress, and it may have a reduced thickness of 2-3 mm thus further reducing conductive heat losses from the cavity  64 . The heated wall portion  82  is thicker than the portion  84 . For example, for the characteristic size S (diameter) of the cavity  64  (S≧25 mm), the thickness T of the heated wall portion  82  is approximately 2-3 mm&lt;T&lt;0.2 S. Preferably, the characteristic size of the cavity  64  is equal to the “depth” of the cavity. 
         [0061]    The SiC heating elements  56  are located in the heater volume  34 , and surround the cavity  64 . At a heating element temperature of &gt;700° C., the main channel of the heat transfer from the heating element to the cavity  64  is through radiation. For any given heating element temperature, the heating power density [W/cm 2 ] received by the cavity  64  is proportional to the radiating area of the heating element  56 . In other words, not only the SiC heating element has to be at sufficiently high temperature, but also its design has to facilitate dense heating elements packaging. For this purpose, the heating elements in the present substrate heater are configured in such a way so as to maximize the radiating element area whereby the cavity  62  receives radiation from all sides except the open side of the cavity. In the embodiment shown in  FIGS. 2 ,  3 , the cavity of inner diameter of ˜25 mm can receive a power of up to 2000 W from the SiC heating elements  56 . Each heating element  56  is connected to a power supply  86  through electrical leads  88  which are made thin enough to make conduction losses negligible. 
         [0062]    An isolation member  90  is attached between the unheated walls portion  84  and the heated wall portion  82  of the side walls  58  to thermally isolate the heater volume  34  from the unheated wall portion  84  and a volume  92  in which contacts  94  for the electrical leads  88  are disposed. Another function of the isolation member  90  is to mechanically support the heating elements  56 . The isolation member  90  is formed as a ceramic fiberboard, fabricated from SiO 2 —Al 2 O 3  based material able to work at temperatures up to ˜1800° C. At the same time it has very low thermal conductivity, which reduces conductive heat losses from the SiC heating elements  56 . 
         [0063]    At least one shield plate  96  is located between the SiC heating element  56  and the ceramic isolation member  90 . The shield plate  96  intercepts radiation of the SiC heating element in the direction of the isolation member board  90 , and thus is heated to further radiate a significant amount of radiation towards the cavity  62 . The shield plate  96  thus increases efficiency of the substrate heater by attaining a higher cavity temperature at the same power of the SiC heating elements. The shield plate is formed of Inconel  601  foil. Several layers of similar shields  96  may surround the cavity  62 . Front shields are formed with openings for deposition material access into the cavity  62 . 
         [0064]    A thermocouple  98  measures the temperature of the heat radiating member  54 . The readout voltage of the thermocouple is used as a feedback signal for an automatic temperature control loop  100  in the heater power supply electronics  86 . This mechanism does not constitute the inventive concept of the present invention and since it is known to those skilled in the art is not discussed herein in detail. 
         [0065]    As shown in  FIGS. 2 and 3 , a substrate carrier  102  supports the substrate  60  at a pre-defined position in the cavity. The carrier  102  preferably has limited thickness in order to avoid (or limit) the “shadowing” of the substrate from the cavity walls radiation. Since the substrate thickness is small, the carrier having a thickness in the range of several mm would not make a significant difference in the amount of wall radiation received by the substrate laterally. The carrier  102  may be shaped as a disk or as a tape with a recessed central opening to receive the substrate. 
         [0066]    In the embodiment shown in  FIG. 2 , the substrate carrier  102  is supported by stands  104  which are designed to cause a negligible “shadowing” of the substrate from the cavity wall radiation. For example, three rod-like stands of ˜3 mm diameter would obscure less than 5% of radiation of the lower section of the cavity  62 . The stands  104  are preferably made from a low-thermal conductivity material, for example, quartz, and have a small cross-section to reduce conductive heat loss from the substrate carrier  102 . To further reduce the conductive loss, the contact area between the substrate carrier  102  and the stand  104  is minimized by means of including a ball shaped spacer  106  between carrier  102  and stands  104 . The spacer  106  has a negligible ring-like contact area with both the substrate carrier  102  and the stand  104 . 
         [0067]    A support member  108  supports the stands  104 . At the same time, the support member  108  is one of the layers of the radiation shields  96 . The support member  108  may be rotated to permit rotating of the substrate  66  for improved uniformity of the deposition. 
         [0068]    An alternative design for the substrate support is shown in  FIG. 3 . A rotating shaft  110  passes through aligned openings in a cavity top (not shown), the isolation member  90  and the shield plate  96 . The shaft  110 , at least partially, is made from a low-thermal conductivity material, for example, quartz or porous alumina. Arctuated members  112  secure the substrate carrier  102  to the shaft  110 . The members  112  have small cross-section to avoid the obscureness of the substrate to the cavity wall radiation. The shaft is enclosed in a vacuum tight envelope  114  which may be closed at its upper end by a cap  116 . The shaft can rotate or translate laterally in z-direction to provide azimuthal and/or axial movement to the substrate. Rotation may be transferred to the shaft  114  magnetically through the envelope wall via a rotation/translation magnetic drive  118  and at least the upper part of the shaft length is magnetic. The substrate heater shown in  FIG. 3  has the advantage of small size and does not necessitate rotation of large components such as the support member  108  in  FIG. 2 . 
         [0069]    Numerical modeling of the heaters using RadTherm software shows that, in the substrate heater shown in  FIG. 3 , the wafer may be heated to the temperature of ˜1070° C. with the temperature of the walls in the range of 1150° C. Thus, the substrate temperature is approximately ˜80° C. lower than the cavity temperature in the cavity-like heater  50 . The 1150° C. wall temperature may be attained with the SiC heating elements maintained at the temperature of 1500° C. 
         [0070]    In the alternative embodiment shown in  FIG. 5 , the substrate heater  120  is “filled” with Inconel bulk material, and the substrate  66  is located in parallel (or in contact) to a flat surface  122  of the heater. The heater channels  60  extend through the bulk heater material  124 . Heat transfer from the SiC heating elements  56  to the hot surface  122  is facilitated via conductance of the bulk heater material  124 . The bulk material provides uniformity of the temperature over the area of the hot surface  122 . The oxidized Inconel surface serves as the source of wide-spectrum radiation close to that of a black body. Temperatures of ˜950° C. was attained for the Si substrate located ˜3 mm apart from the hot surface  122  heated to a temperature of ˜1150° C. Although delivering a lower substrate temperature than in the cavity-like design presented in  FIGS. 2 ,  3 , the flat-plate open design shown in  FIG. 5 , however, permits the placing of the substrate  66  in close contact to the hot surface  122 , or even adhering of the substrate thereto with a heat-conductive media/member  126  when needed. 
         [0071]    Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention as defined in the appended claims. For example, equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular applications of elements may be reversed or interposed, all without departing from the spirit or scope of the invention as defined in the appended claims.