BRIEF DESCRIPTION OF THE DRAWINGS
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:
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;
FIG. 2 is a perspective view of one example of a silicon wafer diffusion furnace according to a variant of the invention;
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
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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®.
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.
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.
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.
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.
Patent Application
20080079220
