Abstract:
An apparatus and method for heating substrates, such as semiconductor wafers. A radiation energy source is arranged proximate to a reflector to direct radiation towards a window providing optical access to a processing chamber. A lens positioned outside of the window focuses the radiation emitted from the radiation energy source and reflector and directs it through the window. The focused radiation energy can be used to directly or indirectly heat a semiconductor wafer disposed in the processing chamber.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     This invention generally relates to semiconductor manufacturing equipment and, more particularly, to an apparatus and method used for the processing of semiconductor wafers.  
         [0003]     2. Description of the Related Art  
         [0004]     In the semiconductor industry, advancements in the development of semiconductor devices of decreased dimensions require the development of new processing and manufacturing techniques. One such processing technique is known as Rapid Thermal Processing (RTP). The RTP technique reduces the amount of time that a semiconductor device is exposed to high temperatures during processing. The RTP technique, typically includes irradiating the semiconductor device or wafer with sufficient power to rapidly raise the temperature of the wafer and maintaining the temperature for a time period long enough to successfully perform a fabrication process, but which avoids such problems as unwanted dopant diffusion that would otherwise occur during longer exposure to high processing temperatures.  
         [0005]     Generally, conventional RTP systems use a radiation source and reflectors to heat the bulk of the semiconductor wafer. The radiation source is usually a bank of lamps that emit radiation energy that is focused on the wafer by the reflectors.  
         [0006]     Conventional lamp-based RTP systems have considerable drawbacks with regard to achieving and maintaining a uniform temperature distribution across the active layer of the wafer surface. By applying more power to the filament, the power intensity of the lamp may be increased. However, the power density of direct radiation is limited by the rating of lamps and further by packing density of the lamps.  
         [0007]     Temperature fluctuations occur on the surface of the wafer which may cause crystal defects and slip dislocations in the wafer at high temperatures (e.g. ˜1000° C.). Further, the heating ramp rate and maximum temperature achievable are limited by the power density of the lamps.  
         [0008]     For the above reasons, what is needed is an apparatus and method for uniformly and controllably heating the surface of a semiconductor wafer during rapid thermal processing.  
       SUMMARY  
       [0009]     The present invention includes an apparatus and method for heating substrates, such as semiconductor wafers. In the present invention, a radiation energy source is arranged proximate to a reflector to direct radiation towards a window providing optical access to a processing chamber. A lens positioned outside of the window can efficiently focus the radiation emitted from the radiation energy source and reflector and direct it through the window. The focused radiation energy can be used to directly or indirectly heat a semiconductor wafer disposed in the processing chamber. The use of the lens to focus the intensity of the radiation significantly improves the thermal uniformity and ramp rate of the design.  
         [0010]     The radiation from the radiation energy source can be focused and directed by the lens through the window towards a heat absorbing member on which the wafer is placed. By heating the heat absorbing member, the wafer can be subjected to more uniform heating and thus, the apparatus can provide reproducible results. The intense heating of the heat absorbing member also allows for a high heating ramp rate.  
         [0011]     Since the radiation from the radiation energy source is focused and directed the power density the radiation provides can be tailored without regard for the rating of the radiation energy source. For example, if the radiation energy source is a bank of lamps, the rating of the lamps would not be a substantial factor. Further, the radiation energy source is not limited by packing density. For example, if the radiation energy source is a bank of lamps, the size of the bank would not matter since the radiation is collected from all of the lamps and focused.  
         [0012]     In one aspect of the invention, an apparatus is provided for heating a semiconductor substrate. The apparatus includes a chamber having a window providing optical access to the interior of said chamber. A radiation energy focusing assembly positioned in an optical path with the window is provided to focus radiation energy emitted from a radiation energy source into the window. The focused radiation energy can be used to heat a semiconductor substrate disposed in the chamber.  
         [0013]     In another aspect of the present invention, a method is provided for processing a semiconductor substrate including providing a chamber having a window which allows for optical access along an optical path to an interior of the chamber. The method also includes generating radiation energy from a radiation source; concentrating the radiation energy; and causing the concentrated radiation energy to enter the chamber through the window to change the temperature of a semiconductor substrate disposed in the interior of the chamber.  
         [0014]     These and other features and advantages of the present invention will be more readily apparent from the detailed description of the embodiments set forth below taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0015]      FIG. 1  is a simplified cross-sectional view of one embodiment of the present invention;  
         [0016]      FIG. 2  is a flow diagram illustrating an operational method for using the apparatus of  FIG. 1  in accordance with the present invention;  
         [0017]      FIG. 3  is an embodiment of a lens including a cooling means in accordance with the present invention;  
         [0018]      FIG. 4  is a simplified illustration of a mechanism for cooling the radiation focusing lens in accordance with an embodiment of the present invention; and  
         [0019]      FIG. 5  is a simplified illustration of yet another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]      FIG. 1  is a simplified representation of the wafer heating apparatus of the present invention. Heating apparatus  100  includes a processing chamber  102  defining a processing area  104 . Optionally, disposed within processing area  104  is a heat absorbing member  106  used to support a single wafer  108  during processing. A window  110  is formed or mounted onto processing chamber  102  to provide optical access along an optical path  101  to processing area  104 . External to processing chamber  102  and positioned substantially along optical path  101  are a radiation focusing assembly  112 , a radiation source  114 , and a strategically positioned radiation reflecting device  118 .  
         [0021]     It should be understood that optical path  101  is represented by a line segment merely to provide an illustrative representation of the line-of-sight access through window  110  into process chamber  102  upon which some of the components of heating apparatus  100  are generally aligned. Optical path  101  is shown perpendicular to window  110  only by example and should not be considered as limiting in any manner.  
         [0022]     In accordance with the present invention, processing chamber  102  can be an RTP chamber, such as those used in thermal anneals. In other embodiments, processing chamber  102  may be used for dopant diffusion, thermal oxidation, nitridation, chemical vapor deposition, and similar processes.  
         [0023]     Processing chamber  102  includes an opening (not shown) on one end of processing chamber  102 , which provides access for the loading and unloading of wafer  108  before and after processing. The opening may be a relatively small opening, but large enough to accommodate a wafer of between about 0.5 mm to 2 mm thick and up to 300 mm (˜12 in.) in diameter, and a loading device, such as the arm and end effector of a robot. Processing chamber  102  may be constructed with a minimal internal volume-surrounding wafer  108 . As a result, heating apparatus  100  may be made smaller, requiring less floor space. Preferably, processing chamber  102  is made of a transparent quartz or similar material.  
         [0024]     Wafer  108  is positioned within processing chamber  102  supported on a wafer support device  106 , which supports the single wafer  108  within processing area  104 . In one embodiment, wafer support device  106  allows a substantial amount of the surface of wafer  108  to be exposed along optical path  101  to window  110  or, if provided, to heat absorbing member  106   a.    
         [0025]     In one embodiment, heat absorbing member  106   a  supports wafer  108  spaced therefrom on standoffs (not shown) or in contact therewith. The standoffs may be any high temperature resistant material, such as quartz, which may have a height of between about 50 μm and about 20 mm. Standoffs contact wafer  108  with a minimal amount of surface area thus leaving a substantial amount of the wafer surface area exposed to heat absorbing member  106   a . In most embodiments, processing chamber  102  requires no internal moving parts to position wafer  108 , such as lift-pins, actuators, and the like. Alternatively, in some embodiments, processing chamber  102  may use moveable standoffs or lift-pins to position wafer  108  on heat absorbing member  106   a.    
         [0026]     Heat absorbing member  106   a  can be made of a heat absorbing material, such as graphite, SiC, or a similar material. Heat absorbing member  106   a  and may have a variable thickness, ranging from between about 0.5 mm and about 20 mm.  
         [0027]     In one embodiment, as shown in  FIG. 1 , heat absorbing member  106   a  can be positioned operationally along optical path  101 , in-line with window  110 . In one embodiment, window  110  may be fused silica, quartz, sapphire, or other material, which is sufficiently transparent in the visible and near IR portion of the electromagnetic spectrum. Window  110  may have a thickness of between about 1 mm and about 5 mm and a diameter that is at least as great as or greater than the diameter of wafer  108  or heat absorbing member  106   a.    
         [0028]      FIG. 1  also illustrates radiation focusing assembly  111  positioned external to processing chamber  102  and disposed along optical path  101  between radiation energy source  114  and window  110 . In one embodiment, radiation focusing assembly  111  includes a single radiation focusing lens  112  or, alternatively, a radiation focusing lens group  112  (i.e. a plurality of lenses  112  used in conjunction with one another). Focusing lens  112  may include any conventional type of lenses, the use and function of which are well known in the art. For example, in one embodiment, lens  112  may be a Fresnel lens, which is a thin optical lens consisting of concentric rings of segmental lenses and having a short focal length. In other embodiments, lens  112  is a convex or concave lens (or a combination thereof). Radiation focusing assembly  111  may optionally include a focus mechanism  115  and a radiation collector  116 .  
         [0029]     Focus mechanism  115  can be coupled to radiation focusing assembly  111  to move radiation focusing lens  112  along optical path  101  so that radiation energy from radiation energy source  114  transmitted along optical path  101  into window  110  can vary in magnification within a focus range.  
         [0030]     Focus mechanism  115  is coupled to a support structure, which allows for the automatic or manual movement of radiation focusing assembly  111 . For example, focus mechanism  115  can include a linear actuator assembly, which provides a conventional means for radiation focusing assembly  111  to be operable to move a distance d 1  along optical path  101 , as indicated in  FIG. 1  by arrow  122 , between a position proximate to and a position distant from window  110 . The linear actuator assembly may include, but is not limited to, conventional drivers and motion translation mechanisms, such as linear guides and linear rollers, which can be urged manually, and linear motors, stepper motors, hydraulic drives, and the like, which may be automated using gears, pulleys, chains, and the like. The benefit of being able to move the position of radiation focusing assembly  111  is that the area to be heated can be controlled without modifying any parts internal to processing chamber  102 . In addition, the achievable temperature can be varied.  
         [0031]     Radiation energy source  114  provides radiation energy in accordance with the present invention. In one embodiment, radiation energy source  114  may include a bank of high-intensity lamps of the type conventionally used in lamp heating operations, which generally provide radiation energy as represented by rays  123  in  FIG. 1 . In one embodiment, radiation energy source  114  includes a filament-less lamp, such as a high-power arc lamp. In another embodiment, radiation energy source  114  may include a bank of well-known tungsten-halogen lamps. Typically, the power requirement for each lamp  120  is between about 500 Watts and about 50 kWatts.  
         [0032]     Reflector  118  may be positioned on a side of radiation energy source  114  opposed from radiation lens assembly  111  to efficiently collect the radiation energy emitted from radiation source  114  and direct the reflected energy as desired. As described in greater detail below, in one embodiment, reflector  118  can be used to direct radiation energy from radiation energy source  114  to radiation focusing lens  112 . In this embodiment, radiation energy is reflected as generally indicated by representative rays  124 . It should be understood that radiation energy from radiation energy source  114  is not limited to any specific direction, and rays  123  and  124  indicate only a reasonable approximation.  
         [0033]     In one embodiment, radiation energy source  114  and reflector  118  are moveable along optical path  101  a distance d 2 , as represented by arrow  126 . In this manner, the intensity of the radiation energy can be varied along optical path  101  as a function of the distance d 2  of radiation energy source  114  from radiation focusing assembly  111 . This embodiment may be most beneficial when distance d 1  is fixed or physically limited.  
         [0034]     Referring now to  FIGS. 1 and 2 , in one operational embodiment (S 200 ), a typical semiconductor loading robot (not shown) rotates toward a wafer cassette or other wafer storage device (not shown), picks up wafer  108 , and loads the wafer into processing chamber  102  (S 202 ), which may be at atmospheric pressure or under vacuum. The robot loader places wafer  102  onto wafer support device  106 , such as heat absorbing member  106   a  or, alternatively onto standoffs. The robot loader then retracts and, subsequently, the processing of wafer  108  can begin.  
         [0035]     To raise the temperature of wafer  108  to a processing temperature, such as between a range of about 100° C. and about 1800° C., radiation energy source  114  is activated (S 204 ). Radiation energy along rays  123  and  124  from radiation energy source  114  travel toward radiation focusing assembly  111  (S 206 ). The amount of radiation energy generated can be varied depending on the temperature requirements of the semiconductor wafer processing operation.  
         [0036]     The radiation energy that reaches radiation focusing assembly  111  may be received directly into radiation focusing lens  112 . In addition, radiation energy collector  116  can be used to capture and re-direct radiation energy into radiation focusing lens  112  that would otherwise have gone astray.  
         [0037]     Rays  128  outline a representative beam  130  of focused radiation energy which leaves radiation focusing lens  112  and travels through window  110  of processing chamber  102 . Since radiation focusing assembly  111  is positioned along optical path  101 , a substantial amount of radiation energy which travels through focusing lens  112  will necessarily travel along optical path  101  into window  110 . To increase or decrease the width of beam  130 , radiation focusing assembly  111  can be moved toward window  110  along optical path  101  the desired distance d 1 . Alternatively, in the event distance d 1  is a fixed or limited distance, radiation energy source  114  and reflector  118  can also be moved a distance d 2  along optical path  101  to achieve a similar result.  
         [0038]     In one embodiment, wafer  108  is positioned in processing chamber  102  on wafer support device  106  with unobstructed exposure of wafer  108  along optical path  101 . In this embodiment, focused beam  130  travels through window  110  to impinge directly on at least one surface of wafer  108  (S 208 ). The focused radiation energy causes the temperature of wafer  108  to increase to between about 900° C. and about 1200° C.  
         [0039]     In another embodiment, focused beam  130  travels through window  110  to impinge on heat absorbing member  106   a  (S 208 ). The focused radiation energy causes the temperature of heat absorbing member  106   a  to increase. In one embodiment, the temperature of heat absorbing member  106   a  can be raised up to between about 900° C. and about 1200° C. The temperature of wafer  108  disposed on or near heat absorbing member  106   a  correspondingly increases to allow the desired processing of wafer  108  to commence.  
         [0040]     Heat absorbing member  106   a  provides temperature uniformity through heat diffusion and removes dependency on emissivity. In addition, heat absorbing member  106   a  can reduce gravitational stress from the weight of the wafer.  
         [0041]     In one embodiment, an internal wall surface  138  opposed to window  110  can be coated with a reflective material, such as gold and silver, with or without a UV protection layer, to create a substantially mirror surface. In this manner, any portion of beam  130  which impinges on wall surface  138  can be reflected toward wafer  108 .  
         [0042]     It should be understood that radiation energy provided by radiation energy source  114  can heat lens  112 . In some embodiments, a cooling means can be provided to ensure that lens  112  does not overheat so as to become in operative.  FIG. 4  illustrates one embodiment of a focusing device  300  that includes a cooling means. In this embodiment, focusing device  300  forms an enclosure having a first side  302  of the enclosure including a lens. A second side  304  of the enclosure can be a non-focusing portion or optionally, can also be a lens. The enclosed walls  302 ,  304 ,  306  and  308  of focusing device  300  define a passageway  310 . On either wall  306  and  308  are outlets  312  and  314  through which a fluid can be made to flow.  
         [0043]     In operation as a fluid passes into outlet  312 , through passageway  310 , and out from outlet  314 , heat energy from walls  302 ,  304 ,  306 , and  308  is transferred to the fluid and removed from the enclosure.  
         [0044]      FIG. 4  is a simplified illustration of another embodiment of a mechanism for cooling the radiation focusing lens in accordance with an embodiment of the present invention. In this embodiment, a processing chamber  402  includes a window  404  mounted thereto or formed thereon. The window may be held to processing chamber  402  using, for example, clamps.  
         [0045]     Radiation focusing assembly  406 , including radiation focusing lens  408  is coupled to processing chamber  402 , such that radiation focusing lens  408  and window  404  are aligned along optical path  409 . In this embodiment, distance d 3  between lens  408  and window  404  is fixed. Radiation focusing assembly  406  defines an enclosure around window  404 , which includes ducts  410  and  412  which allow for the flowing of a liquid or gas there through. The flowing liquid or gas removes heat from radiation focusing lens  408  as the fluid or gas passes over the lens. The flowing liquid and gas can be any substance which readily absorbs heat, yet allows the desired wavelength of photon energy to pass, for example, pure water, filtered air and dye liquids.  
         [0046]     It should be understood that a cooling means, such as those described above or any well-known means for removing heat from a lens, can be used with any of the embodiments of the present invention.  
         [0047]      FIG. 5  is a simplified illustration of yet another embodiment of the present invention. In this embodiment, a wafer heating apparatus  500  includes a process chamber  502  having more than one window, for example window  504  and window  506 . Each of the windows can provide optical access to the interior of process chamber  502 . A focusing assembly and radiation energy source can be aligned along an optical path defined by each window. For example, windows  504  and  506  provide optical access to the interior of process chamber  502  and wafer  514 . In this example, a first focusing assembly  508  and a first radiation energy source  510  can be aligned along an optical path  512  defined by window  504  to impinge on a first surface of wafer  514 . A second focusing assembly  516  and a second radiation energy source  518  can be aligned along an optical path  520  defined by window  506  to impinge on a second surface of wafer  514 . In this manner, radiation energy can be allowed to impinge on multiple surfaces of wafer  514 .  
         [0048]     Alternatively, a heat absorbing member (e.g.  FIG. 1 ) can be positioned proximate or in contact with either the first or second surface of wafer  514 . The heat absorbing member can be heated by the radiation energy entering windows  504  or  506  to subsequently heat wafer  514 .  
         [0049]     Radiation focusing assemblies  508  and  516  as well as radiation energy sources  510  and  518  are expected to perform substantially as described with regard to similar components in other embodiments.  
         [0050]     Having thus described the preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Thus the invention is limited only by the following claims.