Abstract:
An environmental seal incorporated into a diffusion furnace having a heated chamber including a rotatable susceptor and integrally formed shaft support. A plurality of silicon wafers are supported on an associated carrier centered upon the turntable and rotated at a selected velocity. The processing chamber is heated to a selected temperature range and, corresponding to a desired (typically subatmospheric pressure) environment established within the interior and the introduction to a desired recipe of gaseous components/dopants, facilitates a wafer material treatment within the furnace. The use of a nonmetallic environmental seal, typically in the form of a spring-loaded rotary seal or multiple O-ring arrangement, prevents the escape of heat or introduction of pressure/particle contaminants into the chamber. One or more mirror surfaces further assist in retarding heat loss.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention deals generally with wafer substrate thermal processing. Specifically, the present invention discloses a nonmetallic rotary seal for use with a wafer carrying and rotatable platform associated with a heat diffusion furnace for performing any of a number of treatment operations such as chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), rapid thermal processing (RTP), and dry plasma etching. 
         [0003]    2. Description of the Prior Art 
         [0004]    The prior art is well documented with varying examples of furnaces in use with the treatment of wafer substrates, such as are utilized in the semiconductor industry. In practice, any of a number of heat treatment applications, such as chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), rapid thermal processing (RTP), and dry plasma etching, can be performed on a single wafer or batch of supported and spatially separated wafers. 
         [0005]    In a preferred application, the wafer batch is supported upon a carrier in an incrementally spaced-apart fashion, and typically in multiple stacked fashion. Variations in processing environment are increased by the high temperatures often associated with many wafer processing procedures, usually well above 200° C. Temperature variations, combined in many instances with low interior pressures and the necessity of performed uniform within-wafer (WIW) and wafer-to-wafer (WTW) reaction processing within the furnace interior, and the requirements of maintaining an even temperature and reaction profile within the furnace typically require that a single wafer or batch be supported upon a rotatable platform and that the same be rotated at a speed anywhere up to a dozen revolutions per minute to enhance uniformity. 
         [0006]    In practice, a single wafer or wafer batch is placed on a carrier or boat placed within the diffusion furnace. In order to retain chamber integrity and lessen contamination concerns, a chamber platform surface, carrier or boat is often formed of the same material such as quartz. A mechanism is provided for accurate temperature control. As is known in the art, maintaining effective temperature control is critically important as rates of diffusion of the various silicon dopants, deposition, etch and other reaction rates are primarily a function of temperature and which may range in use upwards of 1300° C. 
         [0007]    Existing rotary seals associated with such processing chambers with rotatable platforms often incorporate ferromagnetic and other metallic based composition seals. Experience has determined that such metallic seals tend to emit contaminates into a chamber when a seal is heated. Given the precise compositional requirements which must be maintained in wafer processing, the introduction of contaminants such as those deriving from compromised magnetic/ferrofluidic seals can quickly compromise the processing chamber components and poison any wafer held within the processing chamber. 
       SUMMARY OF THE PRESENT INVENTION 
       [0008]    The present invention discloses an improved and nonmetallic rotary seal for use with a wafer carrying and rotatable platform associated with a heat diffusion furnace. In particular, the present invention contemplates replacing traditional metallic (e.g. ferrofluidic) seals with any of a number of typically spring-loaded and nonmetallic seals, including those constructed of fluoropolymers, to prevent both the passage of gases into or out of the furnace processing chamber. Teflon® is a registered trademark of E.I. DuPont De Nemours and Company and is representative of synthetic resinous fluoropolymers in the form of molding and extruding compositions and fabricated shapes such as sheets, rods, tubes, tapes and filaments. 
         [0009]    A conventional wafer processing chamber typically includes a heated vessel including a rotatable susceptor, typically further provided by a quartz turntable and integrally formed shaft support. As previously described, a single wafer or batch of wafers are held within a carrier centered upon the turntable and rotated at a selected velocity. The vessel is heated to a selected temperature range and, corresponding to a desired (typically subatmospheric) environment established within the vessel interior and the introduction to a desired recipe of gaseous reagents, facilitates a given treatment chemistry occurring to a wafer substrate within the processing chamber. 
         [0010]    Additional variants of the present invention include the substitution of one or more dynamic O-rings constructed of a durable and high temperature resistant elastomer, such as further known under the commercial names Calrez® (Lumaco) or Kalrez® (DuPont Performance Elastomers) for the spring-loaded and fluoropolymer seal. One or more mirrored surfaces may also be incorporated into the diffusion furnace construction, such as underside of the quartz turntable or associated door, as well as at a lowermost location associated with the integrally formed quartz shaft. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Reference will now be made to the attached drawings, when read in combination with the following detailed description, wherein like reference numerals refer to like parts throughout the several views, and in which: 
           [0012]      FIG. 1  is a partial cutaway view of a diffusion oven interior according to the present invention and illustrating the features of the integrally formed and rotatable turntable and support shaft, mirrored and heat reflective lower surface, and spring-loaded fluoropolymer seals to prevent the occurrence of volatile emissions associated with conventional ferrofluidic type seals; 
           [0013]      FIG. 2  is a perspective view of one example of a silicon wafer diffusion furnace according to a variant of the invention; 
           [0014]      FIG. 3  is a partial cutaway view illustrating an alternate embodiment of the invention and by which the spring-loaded Teflon® seals are substituted by one or more dynamic O-rings of a high temperature resistant elastomer, as well as illustrating another variant for incorporating a heat reflective mirrored surface to an underside of the quartz shaft; and 
           [0015]      FIG. 4  is a partial view of a further alternate variant of a spring-loaded seal arrangement incorporated into a diffusion type furnace according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    The present invention has utility in the formation of a rotary seal in a wafer processing chamber. An inventive seal lacks the catastrophic failure mode associated with conventional ferrofluidic seals. 
         [0017]    Referring now to  FIG. 1 , a partial cutaway view is illustrated at  10  of a diffusion furnace interior according to a variant of the present invention. As previously described, the present invention teaches the incorporation of an improved environmental seal, primarily to avoid the introduction of contaminants within the chamber interior. As also described, the environmental sealing features associated with the prior art suffer from the emission of particulate associated with thermal failure of conventional ferrofluidic (metallic) seals, as well as the escape of heat or introduction of external pressurization into the carefully created environmental conditions associated with the furnace interior. 
         [0018]    Reference is generally made in  FIG. 2  at  12  of an example of a diffusion furnace according to one desired illustration. The furnace  12  is intended only to show one generally representative and nonlimiting example of a typical diffusion furnace for use in the wafer processing technology, and which is intended to provide continuous operating conditions at elevated temperatures (upwards of several hundred degrees Celsius) for such as chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), rapid thermal processing (RTP), and dry plasma etching and the like. The representation  12  of  FIG. 2  is further intended only to be representative of a desired three-dimensional enclosure environment that provides such components as controls for admitting a desired gas or vapor into the chamber concurrent with establishing a desired elevated temperature. 
         [0019]    As will be described in further reference to  FIG. 1 , the essential aspects of a diffusion furnace for purposes of the present disclosure are the existence of a rotatable susceptor or turntable surface, see at  14  in  FIG. 1 , associated with an integrally defined and extending shaft portion  16 , and upon which is supported one or more wafer substrates as depicted at  18 ,  20 ,  22 , et seq. in  FIG. 1 . The wafers are typically supported in a closely spaced fashion upon a carrier  24 , centered relative to a rotational axis  26  associated with the rotatable platform  14 . It is appreciated that workpieces other than wafer substrates are processed herein and include industrial pieces subject to oxidation, nitrification, or other coating process. 
         [0020]    It is desired to treat one or more wafers  18 ,  20  and  22  (ranging in multiple stacked fashion up to a hundred or more) within a desired internal environment selected from a desired, temperature, pressurization and varying chemical makeup. In order to maintain a consistent heat and chemical pattern across all of the waters, the same are made to rotate upon the platform  14  at a velocity from one or two to upwards of several to ten or more revolutions per minute, the same preventing localized heat spots or inconsistent reagent flow patterns across a wafer. 
         [0021]    The integrally formed and rotatable susceptor  14  and integrally formed support shaft  16  are typically constructed of a heat insulating surface, which may include any of a number of different materials including quartz, silicon carbide, silicon nitride, polycrystalline silicon material, stainless steel or oxide-containing ceramic compositions. A quartz or other insulating material, such as that from which door  28  is constructed, is provided between the rotatable platform  14  and an underlying stainless steel layer  30 . Optionally, a ceramic coating is applied directly onto the stainless steel. 
         [0022]    A process chamber seal  32  is arranged at an outer circumferential location associated with the platform and incorporated into the underside positioned door  28 . Additional components associated with the furnace enclosure include a housing  34  surrounding the shaft  16  and incorporating a static seal  36  in abutting fashion with a surface of the door  28  located opposite the process chamber seal  32 . 
         [0023]    Supported at a lower end of the housing  34  is an input drive shaft  38 , the same including an upwardly extending sleeve  40  portion for seating and rotatably slaving the integral shaft portion  16  of the rotating susceptor  14 , as well as an associated and end support bearing  42  positioned between the outer annular end of the sleeve  40  and the inner annular surface of the housing  34 . A plurality of annularly positioned clamps  44  and  46  assist in securing the housing  34  to the underside positioned door  30 . 
         [0024]    Sealing the underside location of the rotating susceptor  14 , from which the shaft  16  extends, is accomplished by substituting the ferrofluidic or other metallic-based seals of the prior art with, in the instance of one variant, a nonmetallic and chemically inert material in the form of a spring-loaded rotary seal  48  which is biased at an outer annular location against an inner annular location of the door  30  (typically a stainless steel material) and at an opposite and inner end biased against the outer circumference of the rotating shaft  16  prior to the same seating within the sleeve  40  of the input shaft drive. 
         [0025]    In a preferred embodiment, the spring-loaded rotary seal  48  is constructed of synthetic resinous fluoropolymer such as polytetrafluoroethylene, perfluoro alkoxy polymer resins, fluorinated ethylene-propylene, ethylene tetrafluoroethylene, ethylene chlorotrifluoroethylene, polyvinylidene difluoride, polychlorotrifluoroethylene, fluorocarbon rubber chlorotrifluoroethylene, perfluoro elastomers (FFKM), and fluoroelastomers (FKM). An advantage of utilizing an inventive seal in place of a ferrofluidic or like metallic based seal is to prevent the drawing of metal-containing particulate into the chamber as volatile materials, such as which currently occurs with seal temperatures in excess of 200° C. 
         [0026]    Referring to the partial view of  FIG. 4 , a further alternate variant of a spring-loaded seal arrangement incorporated into a processing chamber is shown according to the present invention. This includes the substation of the rotary seal  48  with a modified arrangement including a fixed annularly spaced component  50 , from which a biasing component  52  projects inwardly against the exterior circumferential surface of the shaft  16  and is biased in its inwardly directed fashion by an alternately configured spring component  54 . Other and potentially differently configured rotary seal designs are envisioned within the scope of the invention, each incorporating a chemically inert and heat-resistant material in the manner previously described. 
         [0027]    Referring further to  FIG. 3 , a partial cutaway view is shown at  56  illustrating an alternate embodiment of the invention, and by which the spring-loaded seals of  FIGS. 1 and 4  are substituted by one or more dynamic O-rings, see further at  58  and  60 , interposed between upper and lower exterior circumferential locations associated with the shaft  16  and an associated inner location associated with a housing or shaft support location  62  extending downwardly from the rotating platform (not shown in this illustration). The O-rings  58  and  60  are also constructed of a chemically inert and durable temperature-resistant elastomer, such as FFKM or FKM which are known under the commercial names Calrez® or Kalrez®. 
         [0028]    Additional features include a modified configuration of an insulating door  58 , including inner static seals  64  and  66 , and bearing  68  supporting the outer location of the shaft support  62 . An interposed and lengthwise extending collar or support is shown in reduced fashion at  70  in  FIG. 3  and is understood to spatially arrange and support the dynamic O-rings  58  and  60  at desired locations relative to the shaft  16  and relative outer annular housing/support components  62 . 
         [0029]    An additional feature of the invention, additional to the chemically inert and heat resistant elastomeric sealing components, is the incorporation of at least one heat reflective and mirrored surface for the purpose of further reducing heat loss from furnace enclosure to the outside environs. In the illustration of  FIG. 3 , a first selected mirrored surface is illustrated at  72  and which may be incorporated either into a fixed or rotatably associated portion of a lowermost and end positioned shaft drive support  74 . 
         [0030]    Experimentation has determined that one pathway of heat loss exists along the extending shaft  16  and the provision of a mirroring surface at the end cap location will tend to redirect and reduce thermal heat loss at this location. Referring again to  FIG. 1 , a further mirrored surface location is referenced at  76  and such as which may exist at the junction between the quartz (or other heat insulating) door  28  and the succeeding stainless steel  30  layer, the provision of a mirroring surface at this location further interrupting heat losses from the furnace. 
         [0031]    Having described our invention, other and additional preferred embodiments will become apparent to those skilled in the art to which it pertains and without deviating from the scope of the appended claims.