Heating device for heating semiconductor wafers in thermal processing chambers

FIELD OF THE INVENTION

0001[0001] The present invention is generally directed to thermal processing chambers for heating semiconductor wafers using light energy. More particularly, the present invention is directed to improved heating lamp configurations containing tuning devices which are used to more uniformly heat semiconductor wafers.

BACKGROUND OF THE INVENTION

0002[0002] A thermal processing chamber as used herein refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and a light source that emits light energy for heating the wafer. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a preset temperature regime. For monitoring the temperature of the semiconductor wafer during heat treatment, thermal processing chambers also typically include temperature sensing devices, such as pyrometers, that sense the radiation being emitted by the semiconductor wafer at a selected band of wavelengths. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated with reasonable accuracy.

0003[0003] In alternative embodiments, instead of or in addition to using radiation sensing devices, thermal processing chambers can also contain thermocouples for monitoring the temperature of the wafers. Thermocouples measure the temperature of objects by direct contact.

0004[0004] Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical reactions can take place as the wafer is fabricated into a device. During rapid thermal processing, which is one type of processing, semiconductor wafers are typically heated by an array of lights to temperatures, for instance, from about 400° C. to about 1,200° C., for times which are typically less than a few minutes. During these processes, one main goal is to heat the wafers as uniformly as possible.

0005[0005] Problems have been experienced in the past, however, in being able to maintain a constant temperature throughout the wafer and in being able to control the rate at which the wafer is heated. If the wafer is heated nonuniformly, various unwanted stresses can develop in the wafer. Not being able to heat the wafers uniformly also limits the ability to uniformly deposit films on the wafers, to uniformly etch the wafers, beside limiting the ability to perform various other chemical and physical processes on the wafers.

0006[0006] Temperature gradients can be created within the wafer due to various factors. For instance, due to the increased surface area to volume ratio, the edges of semiconductor wafers tend to have a cooling rate and a heating rate that are different than the center of the wafer. The energy absorption characteristics of wafers can also vary from location to location. Additionally, when gases are circulated in the chamber, the gases can create cooler areas on the wafer due to convection.

0007[0007] In the past, various lamp configurations have been proposed in order to overcome the above described deficiencies and improve the ability to heat wafers more uniformly and to control the temperature of the wafers at various locations. These systems, however, have become increasingly complex and expensive to produce. For instance, some systems can contain well over 100 lamps.

0008[0008] As such, a need currently exists for an improved thermal processing chamber that is capable of uniformly heating semiconductor wafers in a relatively simple manner without being as complex as many prior art systems. A need also exists for an improved rapid thermal processing chamber for heating semiconductor wafers that is equipped with controls for varying the amount of energy that is applied to the wafer at different locations based upon the characteristics and properties of the wafer. Such controls are especially necessary due to the increasing demands that are being placed upon the preciseness at which the semiconductor wafers are heat treated and at which semiconductor devices are fabricated.

SUMMARY OF THE INVENTION

0009[0009] The present invention recognizes and addresses the foregoing disadvantages and others of prior art constructions and methods.

0010[0010] Accordingly, it is an object of the present invention to provide an improved thermal processing chamber for heat treating semiconductor wafers.

0011[0011] Another object of the present invention is to provide a thermal processing chamber having an improved lamp configuration for heating the wafers uniformly.

0012[0012] Still another object of the present invention to provide a heating device for use in thermal processing chambers that contains a plurality of lamps which form overlapping heating zones on a wafer being heated.

0013[0013] Another object of the present invention is to provide a heating device for use in thermal processing chambers that contains tuning devices spaced between heating lamps for uniformly heating wafers with high levels of controllability.

0014[0014] It is another object of the present invention to provide a heating device for use in thermal processing chambers that not only contains lamps for heating semiconductor wafers but also contains a tuning device for heating the wafers more uniformly, wherein the tuning device comprises a lamp in operative association with or without a focusing lens which is used to direct light energy being emitted by the lamp onto a determined area of the semiconductor wafer.

0015[0015] Another object of the present invention is to provide a heating device for use in thermal processing chambers containing a plurality of lamps for heating a semiconductor wafer and at least one passive optical element placed amongst the lamps which redirects light energy being emitted by the lamps for heating semiconductor wafers more uniformly.

0016[0016] Still another object of the present invention is to provide a heating device for use in thermal processing chambers that contains passive optical elements having a ruled prismatic surface which is positioned within the heating device in order to redirect light energy being emitted by the heating device onto a semiconductor wafer in a manner that heats the wafer more uniformly.

0017[0017] These and other objects of the present invention are achieved by providing an apparatus for heat treating semiconductor wafers. The apparatus includes a thermal processing chamber adapted to contain a semiconductor wafer. For instance, a substrate holder can be contained within the chamber upon which the wafer is held. A heating device is placed in communication with the thermal processing chamber which emits thermal light energy onto the wafer held on the substrate holder. The heating device can include an assembly of light energy sources which are positioned, for instance, to heat different zones of the wafer. The light energy sources form an irradiance distribution across a surface of the wafer.

0018[0018] More particularly, during the heating process, either the semiconductor wafer can be rotated or the light energy sources can be rotated. In this manner, the light energy sources form radial heating zones on the wafer which aid in heating the wafer uniformly and provide good temporal control during the heating cycle.

0019[0019] In accordance with the present invention, the heating device further includes at least one tuning device positioned amongst the light energy sources. The tuning device is configured to change the irradiance distribution of the light energy sources in a manner for more uniformly heating the semiconductor wafer. The tuning device can be an active device which emits light radiation onto a determined location of the wafer or can be a passive device, which redirects light radiation being emitted by the light energy sources contained in the heating device for adjusting the irradiance distribution of the light energy sources.

0020[0020] In one example of an active device, the tuning device includes a light energy source spaced from one or more focusing lenses. The focusing lens is configured to focus light energy being emitted by the light energy source onto a determined location of the wafer. The light energy source and the focusing lens can be mounted to a movable support structure. The support structure can be movable for directing the light energy being emitted by the tuning device onto different locations as desired depending upon the particular application. In general, the tuning device is used to supply light energy to the wafer in areas where further heating is desired in order to compensate for any nonuniformities in the irradiance distribution of the plurality of light energy sources.

0021[0021] In one embodiment, the support structure to which the light energy source is mounted includes a tiltable lever arm. The lever arm is tiltable for directing light energy being emitted by the tuning device to a particular location.

0022[0022] The system of the present invention can include as many tuning devices as are required for uniformly heating wafers. The number of tuning devices incorporated into a particularly system will generally depend upon numerous factors, including the configuration of the light energy sources. In one embodiment, the light energy sources can be placed in concentric rings and tuning devices can be placed in between the rings of lamps.

0023[0023] In order to control the amount of light energy that is emitted by the plurality of light energy sources, the apparatus of the present invention can include at least one temperature sensing device which senses the temperature of the wafer at a plurality of locations. For instance, the temperature sensing device can be a plurality of pyrometers, one pyrometer with multiple viewing ports, or one or more thermocouples. The temperature sensing devices can be in communication with a controller, such as a microprocessor, which determines the temperature of the wafer. The controller, in turn, can be in communication with the power supply of the light energy sources for controlling the amount of heat being emitted by the light energy sources in response to the temperature of the wafer. The controller can be configured, for instance, to control the amount of light energy being emitted by each light energy source or can control different groups of the light energy sources.

0024[0024] In one embodiment, the controller can be configured to also control the amount of light energy that is being emitted by a tuning device installed in accordance with the present invention. In particular, the controller can be used to control the tuning device independent of the light energy sources. Further, the controller can also be configured to be capable of automatically moving the support structure upon which the tuning device is mounted in order to change and adjust the location of where the light energy being emitted by the tuning device contacts the wafer.

0025[0025] The light energy sources used in the heating device of the present invention can be, for instance, lamps, such as tungsten-halogen lamps. The lamps can be substantially vertically oriented with respect to the semiconductor wafer, or can be oriented horizontally. In order to maintain the lamps in position, the lamps can be connected to a mounting base. The mounting base can include reflective devices for directing the light energy being emitted by the lamps onto the wafer. The reflective devices can be polished annular surfaces surrounding the lamps or, alternatively, can be in the shape of plates that extend adjacent to the lamps. For example, in one embodiment, the heating device includes reflective plates which extend beyond the length of the lamps in a direction perpendicular to the semiconductor wafer.

0026[0026] Besides using active tuning devices that emit light radiation, the present invention is also directed to the use of passive tuning devices which redirect light energy being emitted by the light energy sources. In particular, the light energy is redirected in a manner such that semiconductor wafers are heated more uniformly. In this embodiment, the tuning device can comprise an optical element positioned adjacent to at least one of the light energy sources. The optical element can be designed either to reflect, to absorb, or to refract light energy.

0027[0027] In one embodiment, the optical elements can include a ruled prismatic surface for reflecting light radiation in a specified manner. The ruled prismatic surface can have a fixed pitch and a fixed facet angle or a fixed pitch with a variable facet angle. The ruled prismatic surface can be made from a highly reflective material, such as a dielectric material or a metal, such as gold.

0028[0028] Besides having a ruled prismatic surface, in an alternative embodiment, the optical element can include a diffuse surface, which scatters light energy in all directions. The diffuse surface can be made from, for instance, a rough surface.

0029[0029] Preferably, the passive tuning device has an adjustable position with respect to the light energy sources contained in the heating device. For instance, in one embodiment, the tuning device can be placed at different angles with respect to the light energy sources and at a different height. For instance, the light energy sources can be all attached to a mounting base and can all be substantially vertically oriented. The tuning device can be designed to be insertable in and out of the mounting base so as to be positioned at a different height with respect to the light energy sources. The position of the tuning device can be controlled using a controller if desired.

0030[0030] Other objects, features and aspects of the present invention are discussed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

0031[0031] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended figures in which:

0032[0032]FIG. 1 is a cross-sectional view of one embodiment of a thermal processing chamber that may be used in accordance with the present invention;

0033[0033]FIG. 2 is a plan view of one embodiment of a heating device that may be used in thermal processing chambers made in accordance with the present invention;

0034[0034]FIG. 3 is a cross sectional view of one embodiment of a tuning device for use in the present invention;

0035[0035]FIG. 4 is a plan view of an alternative embodiment of a heating device that may be used in thermal processing chambers in accordance with the present invention;

0036[0036]FIG. 5 is a partial perspective view of an alternative embodiment of a tuning device made in accordance with the present invention;

0037[0037]FIG. 6 is an enlarged portion of the tuning device shown in FIG. 5 illustrating how light energy may be reflected off the surface of the device; and

0038[0038]FIG. 7 is a graphical representation of the results obtained in the Example which follows.

0039[0039] Repeat use of references characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0040[0040] It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary construction.

0041[0041] A rapid thermal processing apparatus uses intense light to heat a semiconductor wafer as part of the manufacturing process of integrated circuits. Exposure to light energy, which is also referred to herein as light energy, causes a rapid increase in the temperature of a semiconductor wafer and allows processing times to be relatively short. In rapid thermal processing systems, it is important to radiate the wafer with very high intensity light in a very uniform and controlled fashion. As stated above, the difficulty with current devices is that the requirements for the intensity of the radiated light and the ability to heat wafers uniformly are very difficult to achieve.

0042[0042] In general, the present invention is directed to an apparatus and method for heating semiconductor wafers uniformly and at a controlled rate. The apparatus includes a thermal processing chamber in communication with a heating device that is used to heat treat semiconductor wafers contained in the chamber. The heating device contains a plurality of lamps that are positioned at preselected locations for heating the wafers. In particular, the lamps emit light energy and form a irradiance distribution over the surface of the wafer.

0043[0043] During heating, the wafer is rotated with respect to the plurality of lamps. In this manner, the lamps form radial heating zones on the wafer. The energy supplied to each heating zone can be controlled while the wafer is being heated.

0044[0044] In one embodiment, the temperature at different locations of the wafer is monitored. Based upon the temperature sensed at the different locations, the energy being emitted by the lamps is selectively controlled.

0045[0045] In accordance with the present invention, the heating device in communication with the thermal processing chamber further contains tuning devices which are designed to modify the irradiance distribution of the heating lamps for more uniformly heating the semiconductor wafer. The tuning devices allow fine adjustments to be made to the wafer irradiance distribution pattern in order to heat the wafer under a more controlled temperature regime and more uniformly. The tuning device can be, in one embodiment, a localized and focused source of light energy that can be directed onto a particular location on the wafer. In an alternative embodiment, however, the tuning device can be a passive device which redirects light energy being emitted by the heating lamps in a manner that heats the wafer more uniformly.

0046[0046] For instance, the tunning device can be an active localized source such as a tungsten halogen bulb in an optical configuration or a laser diode with relatively high power. Alternatively, the tuning device can be a passive device that is used to distort and optimize the radiation of the light energy sources and create a desired uniform illumination.

0047[0047] Referring to FIG. 1, a system generally <b>10</b> made in accordance with the present invention for heat treating a wafer made from a semiconductive material, such as silicon, is illustrated. System <b>10</b> includes a processing chamber <b>12</b> adapted to receive substrates such as a wafer <b>14</b> for conducting various processes. As shown, wafer <b>14</b> is positioned on a substrate holder <b>15</b> made from a thermal insulating material such as quartz. Chamber <b>12</b> is designed to heat wafer <b>14</b> at very rapid rates and under carefully controlled conditions. Chamber <b>12</b> can be made from various materials, including metals and ceramics. For instance, chamber <b>12</b> can be made from stainless steel or quartz.

0048[0048] When chamber <b>12</b> is made from a heat conductive material, preferably the chamber includes a cooling system. For instance, as shown in FIG. 1, chamber <b>12</b> includes a cooling conduit <b>16</b> wrapped around the perimeter of the chamber. Conduit <b>16</b> is adapted to circulate a cooling fluid, such as water, which is used to maintain the walls of chamber <b>12</b> at a constant temperature.

0049[0049] Chamber <b>12</b> can also include a gas inlet <b>18</b> and a gas outlet <b>20</b> for introducing a gas into the chamber and/or for maintaining the chamber within a preset pressure range. For instance, a gas can be introduced into chamber <b>12</b> through gas inlet <b>18</b> for reaction with wafer <b>14</b>. Once processed, the gas can then be evacuated from the chamber using gas outlet <b>20</b>.

0050[0050] Alternatively, an inert gas can be fed to chamber <b>12</b> through gas inlet <b>18</b> for preventing any unwanted or undesirable side reactions from occurring within the chamber. In a further embodiment, gas inlet <b>18</b> and gas outlet <b>20</b> can be used to pressurize chamber <b>12</b>. A vacuum can also be created in chamber <b>12</b> when desired, using gas outlet <b>20</b> or an additional larger outlet positioned beneath the level of the wafer.

0051[0051] During processing, substrate holder <b>15</b>, in one embodiment, can be adapted to rotate wafer <b>14</b> using a wafer rotation mechanism <b>21</b>. Rotating the wafer promotes greater temperature uniformity over the surface of the wafer and promotes enhanced contact between wafer <b>14</b> and any gases introduced into the chamber. It should be understood, however, that besides wafers, chamber <b>12</b> is also adapted to process optical parts, films, fibers, ribbons, and other substrates having any particular shape.

0052[0052] A heat source or heating device generally <b>22</b> is included in communication with chamber <b>12</b> for heating wafer <b>14</b> during processing. Heating device <b>22</b> includes a plurality of lamps <b>24</b>, such as tungsten-halogen lamps. As shown in FIG. 1, lamps <b>24</b> are placed above wafer <b>14</b>. It should be understood, however, that lamps <b>24</b> may be placed at any particular location. Further, additional lamps could be included within system <b>10</b> if desired.

0053[0053] The use of lamps <b>24</b> as a heat source is generally preferred. For instance, lamps have much higher heating and cooling rates than other heating devices, such as electrical elements or conventional furnaces. Lamps <b>24</b> create a rapid isothermal processing system that provide instantaneous energy, typically requiring a very short and well controlled start up period. The flow of energy from lamps <b>24</b> can also be abruptly stopped at any time. As shown in the figure, lamps <b>24</b> are equipped with a gradual power controller <b>25</b> that can be used to increase or decrease the light energy being emitted by any of the lamps.

0054[0054] In order to assist in directing the light energy being emitted by lamps <b>24</b> onto wafer <b>14</b>, the lamps can be associated with a reflector or a set of reflectors. For instance, mounting base <b>34</b> can include a reflective surface that surrounds the lamps. In one embodiment, reflective angular recesses can be formed into a mounting base <b>34</b> for directing the light energy onto the wafer.

0055[0055] Referring to FIG. 2, in one alternative embodiment, heating device <b>22</b> can include arc-shaped reflector plates <b>36</b> which are located in between the concentric rings of lamps <b>24</b>. Reflector plates <b>36</b> are substantially vertically oriented with respect to a wafer placed in communication with heating device <b>22</b> and extend at least a portion of the length of lamps <b>24</b>. More particularly, arc-shaped reflector plates <b>36</b> can extend less than the length of lamps <b>24</b> about the same length as lamps <b>24</b> or beyond the length of lamps <b>24</b>. Reflector plates <b>36</b> serve to direct the light energy being emitted by the concentric rings of lamps. Besides arc-shaped reflector plates <b>36</b>, however, it should be understood that various other reflective devices may be used in heating device <b>22</b>.

0056[0056] In order to monitor the temperature of wafer <b>14</b> during the heating process, in this embodiment, thermal processing chamber <b>12</b> includes plurality of radiation sensing devices generally <b>27</b>. Radiation sensing devices <b>27</b> include a plurality of optical fibers or light pipes <b>28</b> which are, in turn, in communication with a plurality of corresponding light detectors <b>30</b>. Optical fibers <b>28</b> are configured to receive thermal energy being emitted by wafer <b>14</b> at a particular wavelength. The amount of sensed radiation is then communicated to light detectors <b>30</b> which generate a usable voltage signal for determining the temperature of the wafer which can be calculated based, in part, on Planck's Law. In one embodiment, each optical fiber <b>28</b> in combination with a light detector <b>30</b> comprises a pyrometer. In another embodiment, the optical fibers <b>28</b> are routed to a single but multiplexing radiation sensing device.

0057[0057] In general, thermal processing chamber <b>12</b> can contain one or a plurality of radiation sensing devices. In a preferred embodiment, as shown in FIG. 1, thermal processing chamber <b>12</b> contains a plurality of radiation sensing devices that measure the temperature of the wafer at different locations. Knowing the temperature of the wafer at different locations can then be used to control the amount of heat being applied to the wafer as will be described in more detail hereinafter. The amount of heat applied to various zones of the wafer can also be controlled in an open loop fashion. In this configuration the ratios between the various heating zones can be pre-determined after manual optimization. In subsequent processes, these ratios are used with no changes during the heating cycles.

0058[0058] During the process of the present invention, system <b>10</b> should be designed such that optical fibers <b>28</b> only detect thermal radiation being emitted by wafer <b>14</b> and not detect radiation being emitted by lamps <b>24</b>. In this regard, system <b>10</b> includes a filter <b>32</b> which prevents thermal radiation being emitted by lamps <b>24</b> at the wavelength at which light detectors <b>30</b> operate from entering chamber <b>12</b>. Filter <b>32</b> also serves to isolate lamps <b>24</b> from wafer <b>14</b> and prevent contamination of the chamber. Filter <b>32</b> as shown in FIG. 1 can be a window positioned between chamber <b>12</b> and heat source <b>22</b>. In an alternative embodiment, each lamp <b>24</b> can be covered by a separate filter.

0059[0059] In one embodiment, filter <b>32</b> is made from fused silica or quartz. Fused silica is known to absorb thermal radiation very effectively at selected wavelengths. For instance, synthetic fused silica with high concentration of OH ions is very effective at absorbing light at a wavelength of from approximately 2.7 micrometers to about 2.8 micrometers. Thus, in one embodiment, when filter <b>32</b> is made from synthetic fused silica, light detectors <b>30</b> can be configured to detect thermal radiation being emitted by wafer <b>14</b> at a wavelength of about 2.7 micrometers. In other embodiments, the separation between radiation arriving to the sensor from the wafer and lamps is achieved by mechanical means of isolation. In these embodiments, buffers and shields are present to prevent a direct path from forming between a light source and a sensing port.

0060[0060] Besides using radiation sensing devices, other temperature sensing devices may be used in the system of the present invention. For instance, one or more thermocouples may be incorporated into the system for monitoring the temperature of the wafer at a single location or at a plurality of locations. The thermocouples can be placed in direct contact with the wafer or can be placed adjacent the wafer from which the temperature can be extrapolated.

0061[0061] System <b>10</b> further includes a system controller <b>50</b> which can be, for instance, a microprocessor. Controller <b>50</b> receives voltage signals from light detectors <b>30</b> that represent the radiation amounts being sampled at the various locations. Based on the signals received, controller <b>50</b> is configured to calculate the temperature of wafer <b>14</b> at different locations.

0062[0062] System controller <b>50</b> as shown in FIG. 1 can also be in communication with lamp power controller <b>25</b>. In this arrangement, controller <b>50</b> can determine the temperature of wafer <b>14</b>, and, based on this information, control the amount of thermal energy being emitted by lamps <b>24</b>. In this manner, instantaneous adjustments can be made regarding the conditions within reactor <b>12</b> for processing wafer <b>14</b> within carefully controlled limits.

0063[0063] In one embodiment, controller <b>50</b> can also be used to automatically control other elements within the system. For instance, controller <b>50</b> can be used to control the flow rate of gases entering chamber <b>12</b> through gas inlet <b>18</b>. As shown, controller <b>50</b> can further be used to control the rate at which wafer <b>14</b> is rotated within the chamber.

0064[0064] As described above, the present invention is generally directed to a particular heating configuration that is used within thermal processing chamber <b>12</b>. Referring to FIG. 2, one embodiment of a heating device <b>22</b> that can be used in combination with thermal processing chamber <b>12</b> in accordance with the present invention is illustrated. As shown, heating device <b>22</b> includes a plurality of light energy sources, such as lamps <b>24</b> that are secured to a mounting base <b>34</b>. In this embodiment, lamps <b>24</b> are arranged in five concentric rings which each serve to heat a separate radial zone on a wafer. It should be understood, however, that many other lamp configurations may be used without limitation.

0065[0065] In accordance with the present invention, in order to heat a wafer more uniformly, heating device <b>22</b> further includes tuning devices <b>40</b> which, in this embodiment, are generally positioned in between the concentric rings of lamps <b>24</b>. Tuning devices <b>40</b> are designed to emit controlled and focused amounts of light energy onto particular locations of a semiconductor wafer being heated. The tuning devices are provided in order to make fine adjustments to the irradiance distribution produced by lamps <b>24</b> in order to more precisely heat the wafers. For example, tuning devices <b>40</b> can be used to emit controlled amounts of light energy between the radial heating zones located on the wafer.

0066[0066] Tuning devices <b>40</b> as shown in FIG. 2 are active localized sources of focused light energy. The tuning devices can be, for instance, laser diodes having a relatively high power. In an alternative embodiment, as shown in FIG. 3, tuning devices <b>40</b> can be a lamp, such as a tungsten halogen lamp, in operative association with one or more focusing lenses.

0067[0067] As shown particularly in FIG. 3, tuning device <b>40</b> includes a light energy source <b>42</b> that is spaced a predetermined distance from a first focusing lens <b>44</b> and a second focusing lens <b>46</b>. Focusing lenses <b>44</b> and <b>46</b> are designed to focus a beam of light energy being emitted by light energy source <b>42</b> onto a desired location of a semiconductor wafer <b>14</b>. In this embodiment, tuning device <b>40</b> is recessed in relation to lamps <b>24</b> shown in FIG. 2. Thus, as shown, tuning device <b>40</b> is placed behind an opening formed into a wall <b>48</b> of heating device <b>22</b>. Wall <b>48</b> as shown in FIG. 2 is located behind lamps <b>24</b>. It should be understood, however, that tuning device <b>40</b> can also be placed on the other side of wall <b>48</b> in the same plane as lamps <b>24</b>.

0068[0068] As shown in FIG. 3, light energy source <b>42</b> and focusing lenses <b>44</b> and <b>46</b> can be mounted to a support structure <b>60</b>. Support structure <b>60</b> can include a tiltable lever arm which allows for an adjustment to be made in the position of the tuning device. In particular, support structure <b>60</b> can be tilted for focusing light energy being emitted by the light energy source onto desired locations of wafer <b>14</b>.

0069[0069] During operation, heating device <b>22</b> is preferably in communication with a system controller <b>50</b> as shown in FIG. 1. Based upon the temperature of the wafer being heated, system controller <b>50</b> can be designed to vary the amount of light energy being emitted by lamps <b>24</b> and by tuning devices <b>40</b>. Each of the lamps that make up a concentric ring can be controlled together in order to form radial heating zones on the wafer. Tuning devices <b>40</b> on the other hand, can be controlled by system controller <b>50</b> independent of the concentric rings in a manner that enhances temperature uniformity throughout the wafer. System controller <b>50</b> can also be used to control support structure <b>60</b> for automatically directing light energy being emitted by tuning device <b>40</b> onto a desired location of the wafer.

0070[0070] As described above, besides using localized active sources, the tuning devices of the present invention can also comprise passive sources which are used to adjust and vary the irradiance distribution of the heating lamps in a manner that enhances wafer temperature uniformity. One embodiment of a system using passive tuning devices is illustrated in FIG. 4. As shown, a heating device generally <b>122</b> for use in thermal processing chamber <b>12</b> as shown in FIG. 1 is illustrated. Heating device <b>122</b> includes an assembly of lamps <b>124</b> secured to a mounting base <b>134</b>, which includes a base plate <b>148</b>. In this embodiment, lamps <b>124</b> are spaced at various locations on mounting base <b>134</b> and are designed to form many different radial heating zones on a wafer.

0071[0071] In accordance with the present invention, heating device <b>122</b> further includes tuning devices <b>140</b> which are positioned adjacent to selected lamps. In this embodiment, tuning devices <b>140</b> are optical elements designed to redirect a portion of the radiant energy being emitted by the lamp assembly, thereby allowing fine adjustments to the irradiance distribution of the heater device onto a wafer located below the assembly.

0072[0072] In this particular embodiment, the optical elements are rectangular shaped and are inserted into heating device <b>122</b> generally near one or more of the lamps <b>124</b>. Heater device <b>122</b> can be designed such that the depth of insertion of tuning devices <b>140</b> and the azimuthal angle of the tuning devices can be adjusted. For instance, tuning devices <b>140</b> can be inserted through an opening formed into base plate <b>148</b> and can be extended into the heater device any desired length in relation to the length of lamps <b>124</b>. Similarly, in some systems, the angle at which the tuning devices are inserted can be adjusted.

0073[0073] The purpose of tuning devices <b>140</b> is to cause the radiation being emitted from lamps <b>124</b> to deviate from an original azimuthal direction of propagation in order to modify the radial power distribution on the wafer. Desirably, the light energy being emitted by the lamps exits heater device <b>122</b> sooner than it would otherwise without tuning devices <b>140</b> and will hit and contact the wafer at a different radial location than it would otherwise. By selectively varying the location of tuning devices <b>140</b>, the wafer can be heated under a more controlled and uniform temperature regime.

0074[0074] In order to redirect the light energy that is being emitted by lamps <b>124</b>, tuning devices <b>140</b> include at least one surface having desired optical characteristics. In modifying the irradiance distribution of the lamps, tuning devices <b>140</b> can either reflect light energy, refract light energy, or can even absorb light energy.

0075[0075] One preferred embodiment of a tuning device <b>140</b> that can be used to reflect light energy in a desired manner is illustrated in FIG. 5. As shown, tuning device <b>140</b> includes a ruled prismatic surface <b>162</b>. As shown, surface <b>162</b> is serrated and mirrored. The prismatic surface illustrated in FIG. 5 employs a fixed pitch with a fixed facet angle. It should be understood, however, that the surface could also employ a fixed pitch with a variable facet angle.

0076[0076] By including a ruled prismatic surface, tuning device <b>140</b> causes radiant energy contacting the device to exit heater device <b>122</b> sooner than would otherwise occur. This device alters the radial irradiance distribution of the system in a way that can be finely adjusted over some preestablished range.

0077[0077] Referring to FIG. 6, a simplified detail of light energy reflecting off of one facet of tuning device <b>140</b> is illustrated. As shown, horizontal rays incoming from the left of surface <b>162</b> contact the tuning device and exit with a dramatically different vertical orientation. As described above, besides using a fixed facet angle, tuning device <b>140</b> can also be made with a variable angle design. When using a variable angle design, tuning device <b>140</b> can be used to more accurately focus light radiation contacting surface <b>162</b> and more accurately redirect the light energy onto a particular location on the wafer being heated if desired.

0078[0078] It should be understood, however, that numerous other surface structures are possible. For instance, in an alternative design, surface <b>162</b> of tuning device <b>140</b> can be planar and diffusing, causing light energy contacting the surface to scatter in all directions. For instance, a highly diffuse surface may be a rough but highly reflective surface on tuning device <b>140</b>. Using a diffuse surface may be less costly to produce but may not provide a similar amount of control as using a prismatic surface.

0079[0079] As stated above, tuning device <b>140</b> can be designed to either reflect light radiation, refract light radiation or absorb light radiation. When used to reflect light radiation, preferably tuning device <b>140</b> is coated with a highly reflective material, such as a dielectric material or a polished metal, such as gold, copper, or aluminum. When used to refract or absorb light energy, tuning device <b>140</b> can be made, for instance, from quartz.

0080[0080] The present invention may be better understood with reference to the following example.

EXAMPLE

0081[0081] The following example was conducted in order to demonstrate how a tuning device made in accordance with the present invention can be used to change the irradiance distribution of light energy sources.

0082[0082] A prismatic tuning device similar to the one illustrated in FIG. 5 was inserted into an array of light energy sources in a thermal processing chamber. The array of light energy sources included five concentric rings of vertically orientated lamps mounted to a base, similar to the heating device illustrated in FIG. 4. The prismatic tuning device was positioned adjacent one of the lamps located on the second concentric ring from the center of the array of lamps.

0083[0083] Specifically, in this example, only the second concentric ring of lamps was turned on in order to measure its effect. Light intensity was then measured at different radial locations at the same distance from the light source as the semiconductor wafer would be placed. In particular, light intensity was measured when the tuning device was positioned adjacent to one of the light energy sources and when the tuning device was absent from the heating device. The results of the example are illustrated in FIG. 7. Also illustrated in the Figure is a graph of the difference in relative intensity between when the prismatic element was inserted and when it was not. (The scale for the difference is on the Y axis on the right.)

0084[0084] As shown by the figure, inclusion of the tuning device of the present invention changed the irradiance distribution of the light energy sources of particular advantage, the tuning device only slightly modified the irradiance distribution. In this manner, the tuning device of the present invention is well suited to making fine adjustments in the manner in which a wafer is illuminated in order to promote temperature uniformity.

0085[0085] These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.