Abstract:
An apparatus related to plasma chambers used for processing semiconductor substrates and specifically to improvements in pumping baffle plates used in plasma sources. An apparatus and method for making a baffle plate assembly formed from a modified baffle plate blank wherein a variety of pumping features are formed in the baffle plate blank and opened in a planar material removal operation.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method and apparatus for utilizing a baffle plate in a plasma processing system, and methods of making the same. 
   BACKGROUND OF THE INVENTION 
   The fabrication of integrated circuits (IC) in the semiconductor industry typically employs plasma to create and assist surface chemistry within a vacuum processing system necessary to remove material from and deposit material to a substrate. In general, plasma is formed within the processing system under vacuum conditions by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the system (e.g., etching processes where materials are removed from the substrate or deposition processes where materials are added to the substrate). 
   In the prior art, plasma has been attenuated in the process chamber utilizing various baffle plates. One function of the attenuation has been to improve the confinement of the plasma in the process chamber. Another function of these plates has been to keep plasma from entering areas where harm could occur to mechanical components. Prior baffle plate designs utilize slots or orifices of various configurations to attenuate or confine the plasma. Typical baffle plates utilize hundreds of slot features or thousands of orifice features. These slot and orifice features add considerable cost to produce the typical baffle plate. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a method of fabricating a baffle plate assembly, surrounding a substrate holder in a plasma processing system comprised of forming a baffle plate blank and subsequently forming one or more pumping passageways wherein one or more features of the baffle plate blank are modified by planar material removal forming the pumping passages. 
   The present invention also relates to a baffle plate assembly, which surrounds a substrate holder in a plasma processing system and comprises a baffle plate blank having one or more pumping passages wherein one or more features of the baffle plate blank are modified by planar material removal forming the pumping passages. 
   The present invention also relates to a plasma process apparatus with baffle a plate assembly comprising a process chamber, a plasma generating system configured and arranged to produce a plasma in the process chamber, a gas source configured to introduce gases into the process chamber, a pressure control system to maintain a selected pressure within the process chamber, a substrate holder configured to hold a substrate during substrate processing, and a baffle plate assembly. The baffle plate assembly is disposed radially outward from the substrate and formed from a baffle plate blank with one or more pumping passages formed from planar material removal from the baffle plate blank. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention wherein: 
       FIG. 1  illustrates a schematic block diagram of a plasma processing system according to an embodiment of the present invention; 
       FIG. 2  presents a method of fabricating a baffle plate assembly, surrounding a substrate holder in a plasma processing system; 
       FIG. 3A  presents a plan view of a baffle plate blank according to the present invention; 
       FIG. 3B  presents a cross-sectional view of the baffle plate blank of  FIG. 3A ; 
       FIG. 3C  presents a cross-sectional view of the baffle plate blank of  FIG. 3B , after planar material removal; 
       FIG. 4A  presents a plan view of a baffle plate according to another embodiment of the present invention; 
       FIG. 4B  presents a plan view of a baffle plate according to another embodiment of the present invention; and 
       FIG. 4C  presents a plan view of a baffle plate according to another embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In plasma processing, a baffle plate can be employed to aid in confining the plasma to the processing region adjacent to the substrate, as well as to effect the uniformity of fluid mechanic properties in the processing region adjacent to the substrate. For conventional plasma processing systems, the baffle plate is configured to surround the substrate holder and, in many cases, the baffle plate is physically coupled to the substrate holder using fasteners. In general, the baffle plate comprises a plurality of openings to permit the passage of process gasses, reactants and reaction products to the vacuum pumping system. 
   According to an embodiment of the present invention, a plasma processing system  1  is depicted in  FIG. 1  comprising a plasma processing chamber  10 , an upper assembly  20 , an electrode plate assembly  24 , a substrate holder  30  for supporting the substrate  35 , and a pumping duct  40  coupled to a vacuum pump (not shown) for providing a reduced pressure atmosphere  11  in plasma processing chamber  10 . Plasma processing chamber  10  can facilitate the formation of a process plasma in process space  12  adjacent to the substrate  35 . The plasma processing system  1  can be configured to process substrates of any size, such as 200 mm substrates, 300 mm substrates, or larger. 
   In the illustrated embodiment, electrode plate assembly  24  comprises an electrode plate  26  and an electrode  28 . In an alternate embodiment, upper assembly  20  can also comprise a cover, a gas injection assembly, and/or an upper impedance match network. The electrode plate assembly  24  can be coupled to an RF source. In another alternate embodiment, the upper assembly  20  comprises a cover coupled to the electrode plate assembly  24 , wherein the electrode plate assembly  24  is maintained at an electrical potential equivalent to that of the plasma processing chamber  10 . For example, the plasma processing chamber  10 , the upper assembly  20 , and the electrode plate assembly  24  can be electrically connected to ground potential. 
   Plasma processing chamber  10  can further comprise an optical viewport  16  coupled to a deposition shield. Optical viewport  16  can comprise an optical window  17  coupled to the backside of an optical window deposition shield  18 , and an optical window flange  19  can be configured to couple the optical window  17  to the optical window deposition shield  18 . Sealing members, such as O-rings, can be provided between the optical window flange  19  and the optical window  17 , between the optical window  17  and the optical window deposition shield  18  and the plasma processing chamber  10 . Optical viewport  16  can permit monitoring of optical emission from the processing plasma in process space  12 . 
   Substrate holder  30  can further comprise a vertical translational device  50  surrounded by a bellows  52  coupled to the substrate holder  30  and the plasma processing chamber  10 , and configured to seal the vertical translational device  50  from the reduced pressure atmosphere  11  in plasma processing chamber  10 . Additionally, a bellows shield  54  can be coupled to the substrate holder  30  and configured to protect the bellows  52  from the processing plasma. Substrate holder  10  can further be coupled to a focus ring  60 , and/or a shield ring  62 . Furthermore, a baffle plate  64  can extend about a periphery of the substrate holder  30 . 
   Substrate  35  can be transferred into and out of plasma processing chamber  10  through a slot valve (not shown) and/or a chamber feed-thru (not shown) via a robotic substrate transfer system where it is received by substrate lift pins (not shown) housed within substrate holder  30  and mechanically translated by devices housed therein. Once substrate  35  is received from substrate transfer system, it is lowered to an upper surface of substrate holder  30 . 
   Substrate  35  can be affixed to the substrate holder  30  via an electrostatic clamping system, or a mechanical clamping system. Furthermore, substrate holder  30  can further include a cooling system including a re-circulating coolant flow that receives heat from the substrate holder  30  and transfers heat to a heat exchanger system (not shown), or when heating, transfers heat from the heat exchanger system. Moreover, gas can be delivered to the back-side of substrate  35  via a backside gas system to improve the gas-gap thermal conductance between substrate  35  and substrate holder  30 . Such a system can be utilized when temperature control of the substrate is required at elevated or reduced temperatures. In other embodiments, heating elements, such as resistive heating elements, or thermo-electric heaters/coolers can be included. 
   In the illustrated embodiment shown in  FIG. 1 , substrate holder  30  can comprise an electrode through which RF power is coupled to the processing plasma in process space  12 . For example, substrate holder  30  can be electrically biased at a RF voltage via the transmission of RF power from a RF generator (not shown) through an impedance match network (not shown) to substrate holder  30 . The RF bias can serve to heat electrons to form and maintain plasma. In this configuration, the system can operate as a reactive ion etch (RIE) reactor, wherein the chamber and upper gas injection electrode serve as ground surfaces. A typical frequency for the RF bias can range from approximately 1 MHz to approximately 100 MHz and can be approximately 13.56 MHz. RF systems for plasma processing are well known to those skilled in the art. 
   Alternately, the processing plasma in process space  12  can be formed using a parallel-plate, capacitively coupled plasma (CCP) source, or an inductively coupled plasma (ICP) source, or any combination thereof, and with or without magnet systems. Alternately, the processing plasma in process space  12  is formed from the launching of a Helicon wave. In yet another embodiment, the processing plasma in process space  12  is formed from a propagating surface wave. 
   Referring now to  FIG. 2 , a method of fabricating a baffle plate assembly, surrounding a substrate holder in a plasma processing system is described. As shown in  FIG. 2 , the method begins in  201  with first forming a baffle plate blank. The baffle plate blank is configured with one or more features that when modified by planar material removal form pumping passageways in the baffle plate blank, thus forming a baffle plate assembly. The baffle plate blank, including features to be modified, can be formed by metal casting, metal stamping, machining, ceramic fabrication, molding, or quartz fabrication, or any combination thereof. In  202 , one or more pumping passageways are formed in the baffle plate blank by planar surface removal of the baffle plate blank. Planar material removal can be performed on at least one portion of one surface of the baffle plate blank. Planar surface removal to baffle plate blank can be performed by milling, grinding, lapping, sanding, planning and/or etching. The planar surface removal process can be a single operation. 
   Referring now to an illustrated embodiment of the present invention as depicted in  FIG. 3A ,  FIG. 3B  and FIG  3 C. Baffle plate blank  300  is configured to be capable of surrounding a substrate holder in a plasma processing system. The baffle plate blank  300  is made from aluminum, alumina, silicon, quartz, carbon, silica nitride, and/or ceramic. The baffle plate blank  300  is configured with one or more closed pumping features  301 .  FIG. 3B  identifies a cross-sectional view of baffle plate blank  300  illustrating several closed pumping features  301 . As shown in  FIG. 3B , the baffle plate blank  300  has a profile with multiple variations in a direction perpendicular to a surface of the baffle plate blank  300 . Baffle plate blank  300  has an upper surface  306  and a lower surface  307 . As shown in.  FIG. 3B , the thickness of the variations (e.g., the distance, between upper surface  306  and lower surface  307 ) is greater than the thickness  312  of a plate from which the baffle plate blank  300  is formed. As illustrated in  FIG. 3C , when lower surface  307  is modified, i.e. at least some of the multiple variations are modified, by planar material removal to form a new lower surface  308 , open pumping passages  302  are formed in the baffle plate blank  300 , thus forming a baffle plate assembly  310 . As shown in  FIG. 3C , the walls of the. open pumping passages  302  protrude from the planar surface  309  of the plate  300 . These protrusions are remnants of the multiple variations in the direction perpendicular to the surface  306  of the baffle plate blank  300  after planar removal of material to form the new lower surface  308 . 
   Furthermore a protective barrier can be formed on any surface of the baffle plate assembly  310 . The protective barrier can, for example, facilitate the provision of an erosion resistant surface when the baffle plate assembly  310  is exposed to harsh processing environments, such as plasma. The protective barrier can be formed by providing a surface anodization on one or more surfaces, providing a spray coating on one or more surfaces, and/or subjecting one or more surfaces to plasma electrolytic oxidation. The protective barrier can comprise a layer of a III-column element and/or a Lanthanon element. The protective barrier can comprise Al 2 O 3 , Yttria (Y 2 O 3 ), Sc 2 O 3 , Sc 2 F 3 , YF 3 , La 2 O 3 , CeO 2 , Eu 2 O 3 , and/or DyO 3 . Methods of anodizing aluminum components and applying spray coatings are well known to those skilled in the art of surface material treatment. 
   All surfaces on the baffle plate assembly  310  can be provided with the protective barrier, applied using any of the techniques described above. In another example, all surfaces on the baffle plate  310 , except for a selected portion of a surface or surfaces, can be provided with the protective barrier, applied using any of the techniques described above. Prior to the application of the protective barrier to the surfaces of the baffle plate assembly  310 , any region can be masked in order to prevent the formation of the barrier layer thereon. Alternatively, following the application of the protective barrier to the surfaces of the baffle plate assembly  310  any region can be processed to remove the barrier layer formed thereon. 
   In the embodiment shown in  FIG. 3A ,  FIG. 3B , and  FIG. 3C , the one or more pumping passages  302  can comprise slots aligned in a radial direction. As shown, the slots can be spaced evenly azimuthally. In an alternate embodiment of the present invention, the slots can be spaced unevenly azimuthally. In an alternate embodiment of the present invention, the slots can be slanted and, therefore aligned, evenly partially in a radial direction and an azimuthal direction. In an alternate embodiment of the present invention, the slots can be slanted and, therefore aligned, unevenly partially in a radial direction and an azimuthal direction. In an alternate embodiment of the present invention the slots can be complex geometries aligned radially, slanted, evenly spaced and/or unevenly spaced. Indeed, the slots or other openings can be of any desired configuration. For example,  FIG. 4A  identifies a baffle plate assembly  410  with pumping passages  420  configured in a complex slot configuration, centered with respect to the baffle plate assembly  410  and evenly spaced azimuthally. 
   Alternately the pumping passages can include at least one orifice. Alternately, as shown in  FIG. 4B , the pumping passages  440  comprise a plurality of orifices having a constant size and uniform distribution on the baffle plate assembly  430 . Alternately the pumping passages can comprise a plurality of orifices, wherein the orifice size, distribution (or number density), and/or orifice shape varies across a baffle plate assembly. For example, when a vacuum pump (not shown) accesses a processing chamber  10  through a pumping duct  40 , as shown in  FIG. 1 , the number of pumping passages can be reduced local to the entrance to the pumping duct  40  in order to correct for the non-uniform pressure field inherent to such an arrangement. 
   Alternately pumping passages can include at least one slot and at least one orifice. Varieties of alternate arrangements of these pumping features can utilize any of the alternates described above or any other shape or configuration. 
   The orifice described above can be a round hole, a polygon, an icon, letters of any language and/or any open geometric shape. For example,  FIG. 4C  identifies a baffle plate assembly  450  with multiple orifices  460 , comprised of English language characters. 
   Although only certain exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.