Abstract:
A novel embedded fastener apparatus and method for fastening components to the interior of a process chamber of a semiconductor fabrication apparatus. In one embodiment, an apparatus having a showerhead or gas distribution plate which is mounted to the interior of the process chamber using multiple fasteners which are embedded in respective fastener openings in the showerhead. In another embodiment, an apparatus having a showerhead which is mounted to the interior of the process chamber using multiple exterior fasteners which extend into the showerhead through the walls of the process chamber. Accordingly, the regions of the showerhead which surround the fasteners are physically separated from the interior of the process chamber.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to apparatus for fabricating semiconductor integrated circuits on semiconductor wafer substrates. More particularly, the present invention relates to apparatus having embedded fasteners and an embedded fastener method for the fastening of components in a semiconductor fabrication apparatus.  
       BACKGROUND OF THE INVENTION  
       [0002]     Generally, the process for manufacturing integrated circuits on a silicon wafer substrate typically involves deposition of a thin dielectric or conductive film on the wafer using oxidation or any of a variety of chemical vapor deposition processes; formation of a circuit pattern on a layer of photoresist material by photolithography; placing a photoresist mask layer corresponding to the circuit pattern on the wafer; etching of the circuit pattern in the conductive layer on the wafer; and stripping of the photoresist mask layer from the wafer. Each of these steps provides abundant opportunity for organic, metal and other potential circuit-contaminating particles to accumulate on the wafer surface as well as on the interior surfaces of the process chambers in which the processes are carried out.  
         [0003]     As an example, CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. However, in plasma process chambers used to carry out these various CVD processes, materials such as polymers are coated onto the chamber walls and other interior chamber components and surfaces during the processes. These polymer coatings frequently generate particles which inadvertently become dislodged from the surfaces and contaminate the wafers.  
         [0004]     In semiconductor production, the quality of the integrated circuits on the semiconductor wafer is directly correlated with the purity of the fabricating processes, which in turn depends upon the cleanliness of the manufacturing environment. Furthermore, technological advances in recent years in the increasing miniaturization of semiconductor circuits necessitate correspondingly stringent control of impurities and contaminants in the plasma process chamber. When the circuits on a wafer are submicron in size, the smallest quantity of contaminants can significantly reduce the yield of the wafers. For instance, the presence of particles during deposition or etching of thin films can cause voids, dislocations, or short-circuits which adversely affect performance and reliability of the devices constructed with the circuits.  
         [0005]     Due to the small geometries of components in modern semiconductor integrated circuits, particles having a size larger than about 0.02 m can significantly adversely affect semiconductor processing. Current geometry sizes for semiconductor integrated circuits have reached less than half a micron, and those circuits are adversely affected by particles having a size as small as 0.01 m. In the future, semiconductor integrated circuits will be marked by increasingly smaller geometry sizes, requiring protection from contamination by correspondingly smaller particles.  
         [0006]     Particle and film contamination has been significantly reduced in the semiconductor industry by improving the quality of clean rooms, by using automated equipment designed to handle semiconductor substrates, and by improving techniques used to clean the substrate surfaces. However, as deposit of material on the interior surfaces of the processing chamber remains a problem, various techniques for in-situ cleaning of process chambers have been developed in recent years. Cleaning gases such as nitrogen trifluoride, chlorine trifluoride, hexafluoroethane, sulfur hexafluoride and carbon tetrafluoride and mixtures thereof have been used in various cleaning applications. These gases are introduced into a process chamber at a predetermined temperature and pressure for a desirable length of time to clean the surfaces inside a process chamber. However, these cleaning techniques are not always effective in cleaning or dislodging all the film and particle contaminants coated on the chamber walls. The smallest quantity of contaminants remaining in the chamber after such cleaning processes can cause significant problems in subsequent manufacturing cycles.  
         [0007]     A typical conventional CVD (chemical vapor deposition) system is illustrated schematically by reference numeral  10  in  FIG. 1 . The CVD system  10  generally includes an enclosure assembly  6 , having a vertically-movable wafer support pedestal  12  disposed beneath a showerhead  30 , through which process gases enter a vacuum chamber  15 . A pumping plate  17  may extend around the wafer support pedestal  12  for discharging process gases and other plasma residue from the chamber  15  and into a pumping channel  14  partially circumscribing the chamber  15 , as indicated by the arrows  21 .  
         [0008]     The enclosure assembly  6  is typically an integral housing constructed of a process-compatible material such as anodized aluminum. The enclosure assembly  6  includes a continuous sidewall  11  and a top  7  that includes a top opening (not illustrated) sealed by a removable lid  18 . The lid  18  is typically provided with an inlet tube  16  for allowing deposition gases to enter the showerhead  30 , where the gases are uniformly dispersed throughout the chamber  15  onto a wafer (not illustrated) supported on the wafer support pedestal  12 . The deposition process performed in the apparatus  10  may be a thermal process, a plasma-enhanced process or other chemical vapor deposition process.  
         [0009]     In a typical metal deposition process such as that used in the formation of a tungsten plug (not shown) in an opening formed in a dielectric layer on a wafer (not shown), deposition gases are introduced into the chamber  15  through the inlet tube  16  and the showerhead  30 , respectively, where the gases are deposited into the opening (not illustrated) in the dielectric layer on the wafer. Upon completion of the CVD process, the gases are evacuated from the chamber  15  by operation of a pump (not illustrated) which induces vacuum pressure in the pumping channel  14  to draw the gases out of the chamber  15  and through the pumping channel  14 , where the gases are discharged from the apparatus  10  through a discharge conduit  31  and throttle valve  32 .  
         [0010]     During the chemical deposition process, solid residues frequently form on the sidewalls  11 , wafer support pedestal  12  and other interior surfaces of the chamber  15 . Accordingly, regular periodic cleanings of the chamber  15  between CVD process cycles is necessary for maintaining performance of the CVD system  10  at optimum levels in the production of high-quality integrated circuit devices. Such periodic chamber cleanings are facilitated by introducing cleaning gases and chemicals into the chamber  15  through the inlet tube  16  and showerhead  30 , respectively, while maintaining a vacuum in the chamber  15  by evacuating the gases through the discharge conduit  31  and throttle valve  32 . While such periodic chamber cleaning cycles are effective in removing much of the residues from the interior surfaces of the CVD system  10 , the residues tend to accumulate on the surfaces over time, and these must be removed using periodic preventative maintenance (PM) cleanings. In a PM cleaning, the lid  18  and showerhead  30  components of the CVD system  10  are removed and the vacuum pressure inside the chamber  15  is dispelled to facilitate manually wiping down the interior surfaces of the chamber  15  in order to remove the accumulated residues from the surfaces. Upon commencing the PM cleaning process, however, some toxic, corrosive and/or flammable residual deposition gases may remain in the chamber  15 , and additional potentially harmful gases such as HF may be formed upon contact of hydrogen peroxide, a common cleaning agent, or water with the residues. These potentially harmful gases tend to escape from the open chamber  15  and into the ambient environment of the CVD system  10 , where the gases may injure persons involved in the chamber-cleaning operation or other persons in the vicinity of the CVD system  10 .  
         [0011]     Particles which may contribute to contamination of substrates during semiconductor fabrication have generally two sources. As one source, the intrinsic process design parameters may contribute to excess particle production. As another source, the design of the hardware or equipment used to carry out the processing may contribute to excess particle production. Because it is difficult to modify the process parameters in a satisfactory manner to reduce excess particle production, hardware re-design or modification remains the more effective and practical method for minimizing particle production and contamination of substrates during processing.  
         [0012]     A common characteristic of a conventional CVD system, as well as other types of semiconductor processing systems extensively used in the semiconductor fabrication industry such as PVD (physical vapor deposition) chambers, etching chambers and ashing chambers, for example, is that the showerhead on the interior of the chamber is mounted in place using screws or other fasteners which protrude beyond the interior surface of the showerhead. The region of the showerhead surrounding the fastener tends to become damaged by thermal expansion cycling or plasma arcing, and this causes the accumulation of particles in the damaged area. It has been found that mounting the showerhead in place using fasteners which are embedded in the surface of the showerhead or extend from the process chamber exterior, through the wall of the chamber and into the showerhead significantly reduces thermal cycling damage which may otherwise facilitate the accumulation of contaminating particles thereon.  
         [0013]     Accordingly, an object of the present invention is to provide an embedded or recessed fastener technique for mounting components in a process chamber.  
         [0014]     Another object of the present invention is to provide an embedded or recessed fastener technique which is suitable for mounting components in any type of process chamber including but not limited to a CVD, PVD, etching or ashing chamber.  
         [0015]     Still another object of the present invention is to provide an apparatus having a showerhead or gas distribution plate which is mounted in a chamber using embedded or recessed fasteners.  
         [0016]     Yet another object of the present invention is to provide an apparatus having a showerhead or gas distribution plate which is mounted in a chamber using exterior fasteners.  
         [0017]     A still further object of the present invention is to provide a method for preventing or reducing particle contamination of a showerhead or gas distribution plate, which method includes fastening the showerhead or gas distribution plate to a chamber interior using multiple embedded fasteners.  
         [0018]     Another object of the present invention is to provide a method for preventing or reducing particle contamination of a showerhead or gas distribution plate, which method includes fastening the showerhead or gas distribution plate to a chamber interior using multiple exterior fasteners.  
       SUMMARY OF THE INVENTION  
       [0019]     In accordance with these and other objects and advantages, the present invention is generally directed to a novel embedded fastener apparatus and method for fastening components to the interior of a process chamber of a semiconductor fabrication apparatus. In one embodiment, the invention includes an apparatus having a showerhead or gas distribution plate which is mounted to the interior of the process chamber using multiple fasteners which are embedded in respective fastener openings in the showerhead. In another embodiment, the invention includes an apparatus having a showerhead which is mounted to the interior of the process chamber using multiple exterior fasteners which extend into the showerhead through the walls of the process chamber. Accordingly, the regions of the showerhead which surround the fasteners are physically separated from the interior of the process chamber. Consequently, accumulation of particles inside the process chamber due to thermal-induced damage of the showerhead in the areas surrounding the fastener is eliminated or significantly reduced.  
         [0020]     The invention further contemplates methods for reducing particle contamination of a showerhead or gas distribution plate in a process chamber. In one embodiment, the method includes providing fastener openings in the showerhead, extending fasteners such as screws through the fastener openings and into a structural member of the chamber, and embedding the fasteners in the fastener openings. In another embodiment, the method includes providing fastener openings through the chamber wall and into the showerhead and extending fasteners through the fastener openings to mount the showerhead in the chamber, with the respective fastener openings facing the exterior of the process chamber. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0022]      FIG. 1  is a schematic of a typical conventional CVD process chamber;  
         [0023]      FIG. 2  is a schematic of a process chamber with multiple exterior fasteners mounting a showerhead in the chamber according to one embodiment of the present invention;  
         [0024]      FIG. 3  is a top view of the process chamber of  FIG. 2 ;  
         [0025]      FIG. 4  is a schematic of a process chamber with multiple embedded fasteners mounting a showerhead in the chamber according to another embodiment of the present invention;  
         [0026]      FIG. 5  is an exploded, perspective view of a showerhead assembly in accordance with the embedded-fastener embodiment of  FIG. 4 ; and  
         [0027]      FIG. 6  is a cross-sectional view of a portion of a showerhead, illustrating a typical shape of a fastener opening in the showerhead according to the embodiment of  FIG. 4 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     The present invention has particularly beneficial utility in the mounting of a showerhead or gas distribution plate (GDP) in a CVD (chemical vapor deposition) chamber used to deposit material layers on a semiconductor wafer substrate. However, while references may be made to such CVD chamber, the invention may be equally applicable to mounting a showerhead or GDP in any type of process chamber such as a PVD (physical vapor deposition) chamber, an etching chamber or a plasma ashing chamber.  
         [0029]     Referring to  FIGS. 2 and 3 , a typical CVD system  34  in implementation of one embodiment of the present invention includes a process chamber  36  having a chamber wall  38  and a chamber bottom  40  which together define a chamber interior  42 . A gas mix plate  48  is typically provided in the upper end of the process chamber  36  for receiving and mixing a flow of deposition gases  62 . A showerhead  44  is mounted beneath the gas mix plate  48  in a manner to be hereinafter described and receives the gas  62  from the gas mix plate  48  and disperses the gas  62  into the chamber interior  42 , typically through an underlying confine ring  46 , in conventional fashion. In operation of the CVD system  34 , a wafer  50  is placed on a wafer support (not shown) provided in the chamber interior  42  for the deposition of material layers on the wafer  50 , as is well-known by those skilled in the art. It is understood that the process chamber  36  heretofore described with respect to  FIG. 2  represents one example of a process chamber which is suitable for the present invention and that process chambers of various description which may have features that depart from those heretofore described are equally suitable for implementation of the invention.  
         [0030]     According to the present invention, the showerhead  44  is mounted in the process chamber  36  using multiple exterior fasteners  56 . Each of the exterior fasteners  56  typically includes a fastener head  58  from which extends a threaded shank  60 . As shown in  FIG. 2 , the showerhead  44  is mounted in the process chamber  36  by extending the threaded shank  60  of each exterior fastener  56  through a corresponding chamber wall fastener opening  52  which extends laterally through the chamber wall  38 , and threading the threaded shank  60  into a registering showerhead fastener opening  54  which extends into the lateral surface of the showerhead  44 .  
         [0031]     As shown in  FIG. 3 , multiple exterior fasteners  56  are used in the manner heretofore described to mount the showerhead  44  in the process chamber  36 . The exterior fasteners  56  may be equally spaced from each other along the circumference or perimeter of the chamber wall  38 . In a preferred embodiment, eight of the exterior fasteners  56  are used to mount the showerhead  44 , as shown, although a lesser or greater number of exterior fasteners  56  may be used, as desired.  
         [0032]     In typical operation of the CVD system  34 , deposition gases  62  are introduced into the chamber interior  42  through the gas mix plate  48 , the showerhead  44  and the confinement ring  46 , respectively, where the gases  62  flow into contact with the wafer  50  and materials carried by the gases  62  are deposited onto the wafer  50 . Upon completion of the CVD process, the gases  62  are evacuated from the chamber interior  42  by operation of a pump (not illustrated) to draw the gases  62  out of the chamber interior  42 , typically in conventional fashion.  
         [0033]     It will be appreciated from a consideration of  FIG. 2  that each showerhead fastener opening  54  in the showerhead  44  is substantially sealed off from the chamber interior  42  by abutment of the showerhead  44  against the chamber wall  38 . Consequently, the exterior fasteners  56  extend into the showerhead  44  in such a manner that each of the exterior fasteners  56 , as well as the regions of the showerhead  44  which contact the exterior fasteners  56 , is substantially isolated from the chamber interior  42  in which processing of the wafer  50  is carried out. Accordingly, particles generated by friction between the showerhead  44  and the threaded shank  60 , induced by thermal expansion and contraction cycling of the showerhead  44  during processing, are incapable of inadvertently falling into the chamber interior  42  and contaminating a wafer  50  being processed therein.  
         [0034]     Referring next to  FIGS. 4-6 , a typical CVD system  64  in implementation of another embodiment of the present invention includes a process chamber  66  having a chamber wall  68  and a chamber bottom  70  which define a chamber interior  72 . A gas mix plate  78  is typically mounted in the upper end of the process chamber  66 , and a showerhead  74  is mounted in the process chamber  66  in a manner to be hereinafter described. A spacer  86  is typically interposed between the gas mix plate  78  and the showerhead  74 . A confine ring  76  is typically mounted in the chamber interior  72 , beneath the showerhead  74 . In operation of the CVD system  64 , a wafer  80  is placed on a wafer support (not shown) provided in the chamber interior  72  for the deposition of material layers on the wafer  80 . It is understood that process chambers of various description which may have features that depart from those heretofore described with respect to  FIG. 4  are equally suitable for implementation of the invention.  
         [0035]     According to the present invention, the showerhead  74  is mounted in the process chamber  66  using multiple embedded fasteners  92 . Each of the embedded fasteners  92  typically includes a fastener head  94  from which extends a threaded shank  96 . As shown in  FIG. 4 , the showerhead  74  is mounted in the process chamber  66  by extending the threaded shank  96  of each embedded fastener  92  through a corresponding ring fastener opening  77  which extends through the confine ring  76 , a showerhead fastener opening  82  which extends through the showerhead  74 , a spacer fastener opening  88  which extends through the spacer  86  provided between the gas mix plate  78  and the showerhead  74 . The threaded shank  96  of each embedded fastener  92  is then threaded into a registering plate fastener opening  90  which extends into the bottom surface of the gas mix plate  78 . As shown in  FIG. 6 , the bottom end of the ring fastener opening  77  is typically characterized by a circumferential expansion which defines a fastener head cavity  84  in the confine ring  76 . Accordingly, as shown in  FIG. 4 , the fastener head  94  of each embedded fastener  92  is contained in the corresponding fastener head cavity  84  in such a manner that the flat surface of the fastener head  94  is substantially flush with the bottom surface of the confine ring  76 .  
         [0036]     As shown in  FIG. 5 , multiple embedded fasteners  92  are typically used to mount the showerhead  74  in the process chamber  66 . The embedded fasteners  66  may be equally spaced from each other along the circumference or perimeter of the confine ring  76  and the showerhead  74 . In a preferred embodiment, eight of the embedded fasteners  92  are used to mount the showerhead  74  in the process chamber  66 , as shown, although a lesser or greater number of the embedded fasteners  92  may be used, as desired.  
         [0037]     In typical operation of the CVD system  64 , deposition gases  98  are introduced into the chamber interior  72  through the gas mix plate  78 , the showerhead  74  and the confinement ring  76 , respectively, and flow into contact with the wafer  80 . Various materials carried by the deposition gases  98  are deposited onto the wafer  80 . Upon completion of the CVD process, the gases  98  are evacuated from the chamber interior  72 , typically in conventional fashion.  
         [0038]     It will be appreciated from a consideration of  FIG. 4  that the fastener head  94  of each of the embedded fasteners  92  is recessed into the confine ring  76  in such a manner that the threaded shank  96  each of the embedded fasteners  92  is substantially isolated from the chamber interior  72  in which processing of the wafer  80  is carried out. Accordingly, particles generated by friction between the showerhead  74  and/or the confine ring  76  and the threaded shank  96 , induced by thermal expansion and contraction cycling of the showerhead  74  and confine ring  76  during processing, are incapable of inadvertently falling into the chamber interior  72  and contaminating a wafer  80  being processed therein.  
         [0039]     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.