Abstract:
In accordance with this disclosure, there are provided several inventions, including an apparatus and method for creating a plasma resistant part, which may be formed of a sintered nanocrystalline ceramic material comprising yttrium, oxide, and fluoride. Example parts thus made may include windows, edge rings, or injectors. In one configuration, the parts may be yttria co-sintered with alumina, which may be transparent.

Description:
BACKGROUND 
       [0001]    This disclosure relates to the use and manufacture of sintered nanograined components in plasma chambers for semiconductor processing. 
         [0002]    Advanced coatings such as yttria (Y 2 O 3 ) are indispensable for state-of-the-art plasma etch chambers. Y 2 O 3  is a widely used plasma facing material due to its chemical inertness and low erosion rate in plasmas. However, advanced Y 2 O 3  coatings cannot cover all the applications. For example, a high-bias etch process in a plasma processing chamber may require an edge ring with a Y 2 O 3  coating as thick as 1 mm. This may not be economical, and there may be engineering constraints that make such a thick coating impractical. For example, a thick coating subjected to high stress may delaminate even prior to chamber service. Therefore, a more useful edge ring might comprise a sintered ring made from solid Y 2 O 3 . 
         [0003]    However, the use of a traditional solid, sintered Y 2 O 3  edge ring, using micrometer-scale Y 2 O 3  powders, has significant problems. There are fundamental technical difficulties in obtaining pore free, pure Y 2 O 3  solid faces. For example, Y 2 O 3  has very high melting point; therefore, pore free sintering of pure Y 2 O 3  is very difficult. In addition, the sinterability of micro-sized Y 2 O 3  powder is poor, and thus the sintering process at high temperature is prolonged. This long sintering process may lead to uncontrolled grain growth which may further deteriorate the mechanical performance of sintering Y 2 O 3  compacts. Y 2 O 3  ceramics are inherently weak compared to alumina (Al 2 O 3 ) and other common ceramic materials that might alternatively be used in plasma chambers, such as sapphire, aluminum oxynitride (AlON), partially stabilized zirconia (PSZ), or spinel, etc., in terms of both flexural strength and fracture toughness. Related yttrium-containing materials may present similar difficulties. 
         [0004]      FIG. 1  illustrates a representative surface morphology of a sintered Y 2 O 3  edge ring  100  with grain size of approximately 5-10 μm. There are some surface pits  101  clearly visible. Without being limited by any particular theory, the origin of the defects could come from porosity in the Y 2 O 3 , or grain pullout during machining due to poor mechanical strength. These surface defects may lead to concerns about the possibility of loose surface Y 2 O 3  particles, especially for those interfaces under rubbing or heavily handling. In other contexts, one approach to increase sintering density and lower sintering temperature might be to add low melting temperature sintering aids such as Mg/Si/Ca oxides. In the plasma processing context, however, this strategy may lead to metal contamination concerns. 
         [0005]    New ways are therefore needed to take advantage of the properties of Y 2 O 3  and related yttrium materials in plasma chambers. 
       SUMMARY 
       [0006]    Disclosed herein are various embodiments, which provide plasma resistant parts adapted for use in a plasma processing chamber which is configured to produce a plasma while in an operating mode. The part comprises a plasma-facing surface configured to face the plasma when the plasma chamber is in the operating mode, wherein the surface is formed of a sintered nanocrystalline ceramic material comprising yttrium in addition to oxide and/or fluoride. 
         [0007]    In another manifestation, an embodiment provides a method of forming a co-sintered nanocrystalline part. A first green compact is formed from a first ceramic material. A second green compact is formed from nanocrystals of a second ceramic material comprising yttrium in addition to oxide and/or fluoride. The first green compact and the second green compact are co-sintered. 
         [0008]    These and other features of the present inventions will be described in more detail below in the detailed description and in conjunction with the following figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The disclosed inventions are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0010]      FIG. 1  is a scanning electron micrograph of a sintered Y 2 O 3  surface with grain size of about 5-10 μm. 
           [0011]      FIG. 2  is a schematic cross-sectional view of a two-layer co-sintered structure facing a plasma in a plasma chamber. 
           [0012]      FIG. 3  schematically illustrates an example of a plasma processing chamber which may be used in an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Inventions will now be described in detail with reference to a few of the embodiments thereof as illustrated in the accompanying drawings. In the following description, specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced without some or all of these specific details, and the disclosure encompasses modifications which may be made in accordance with the knowledge generally available within this field of technology. Well-known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present disclosure. 
         [0014]    As used herein, the term “nanograined” or “nanocrystalline” refers to a material that is formed of grains or crystals in the nanometer size range, meaning smaller than a micron. Sizes in the nanometer range may include, for example, 500 nm, 200 nm, 100 nm, 50 nm, 20 nm, or smaller. The term “microcrystalline” refers to a material that is formed of grains or crystals in the micron size range, meaning at least one micron. 
         [0015]    Nanograined yttrium-containing ceramics such as Y 2 O 3  may be used to fabricate plasma chamber components. Such components may have benefits that include long lifetime in aggressive etch conditions. Such ceramics can be made dense and pure, by sintering. 
         [0016]    Nanograined yttrium-containing ceramics may have many advantages in the context of plasma processing. These include mechanical strength in an inverse relationship to grain size, resistance to particle flaking, plasma resistance, and increased lifetime. In addition, cleaning may be easier, because it may be possible to use aggressive cleaning methods such as mechanical cleaning or polishing. In addition, where surfaces are normally a sink for reactive components, a nanograined ceramic surface may be textured, which may increase surface area and may help the adhesion of etch by-products. In one example, starting from a homogenous green compact of Y 2 O 3  nanopowders, pure and dense solid Y 2 O 3  blanks with enhanced strength can be synthesized through advanced sintering methods. Such a high quality Y 2 O 3  ceramic can be further precision-machined to create standalone plasma chamber components. In one example, they can form hybrid components with Y 2 O 3  as the plasma-facing “skin.” This may occur through, for example, bonding or green state co-firing. 
         [0017]    In another example, such ceramics may be surface textured with a broad spectrum of length scales. In one example, this may be carried out on nanograined Y 2 O 3  solids using dilute roughening acid such as HCl. 
         [0018]    Chamber components made from dense, nanograined solid Y 2 O 3  should offer unique productivity advantages under some extremely challenging applications in etch chambers. 
         [0019]    In one example, non-agglomerated nanometer size Y 2 O 3  powder may be used to synthesize dense, pure, nano-grained Y 2 O 3  for etch chamber applications. This may achieve submicron (or sub-500 nm, sub-200 nm or even smaller range) grain size on final sintering products. Sintering strategies without grain coarsening may be chosen, as the subsequent densification of sintering. The green compact without aggregate of particles may also be used. Large-scale and cost effective synthesis of Y 2 O 3  nanoparticles (for example, through combustion methods known in the art) and novel sintering methods (for example, two-step sintering, hot isostatic pressing (HIP), spark plasma sintering (SPS), etc.) may enable the fabrication of relatively large size and dome-shaped transparent Y 2 O 3  ceramic optics and very strong armor-like materials. 
         [0020]    For use in a plasma chamber application, transparent polycrystalline ceramics may exhibit high density and high purity, superior mechanical robustness, and small nanometer range grains. Nano-size Y 2 O 3  powder may significantly enhance the sinterability of Y 2 O 3  green body, enabling the sintering of pure and dense compacts at lower temperature and shortened time. Reduction in grain size significantly enhance the material strength following a well-known relationship that mechanical strength is proportional to the square root of grain size. With the grain size further shrunk down to nanometer scale (e.g., sub-200 nm), the flexural strength of nanograined Y 2 O 3  may be as strong as the Al 2 O 3  ceramic, which in certain applications may typically be in the range of about 300-400 MPa. 
         [0021]    Thanks to a number of unique benefits of nanograined Y 2 O 3 , some applications in etch chambers can be easily envisioned. First, a solid Y 2 O 3  edge ring or a solid Y 2 O 3  injector may be precision machined from nanograined Y 2 O 3  for better particle performance. The use of solid Y 2 O 3  for an edge ring or injector with large grain size has not been desirable, due to particle concerns in some applications with stringent defect requirements. 
         [0022]    In a second embodiment, a nanograined Y 2 O 3  sheet may be cofired or bonded onto Al 2 O 3  ceramic window to construct laminated TCP window. For example, a green sheet of nanosize Y 2 O 3  powders can be co-sintered with Al 2 O 3  green sheet to form hybrid structures with Y 2 O 3  exposed to plasmas. Alternatively, a fully sintered nanograined Y 2 O 3  sheet may be bonded (for example, through glass frit or polymer adhesive bonding) to an Al 2 O 3  window. In one embodiment, the bonding layer may be designed to be outside the vacuum. Such a hybrid may combine the benefits of Al 2 O 3  ceramic (e.g., high resistivity, low loss tangent, low cost, and/or better thermal conductivity) with the benefits of plasma-facing, nano-grained Y 2 O 3  ceramic sheet (e.g., purity, density, relative thickness). A thicker Y 2 O 3  laminated layer may in one embodiment provide the option of using more aggressive clean chemistries and more aggressive refurbishment process for some very “dirty” etch processes. 
         [0023]    The formation of nanocrystalline layers as described herein has advantages over the formation of such layers by other means, such as plasma spraying, which may result in the formation of a fluffy structure with significant voids and pores, lack of uniformity, and compromised strength and durability. 
         [0024]      FIG. 2  is a schematic illustration of a cross-section of a hybrid part for a plasma chamber. In this example, layer  201  is an Al 2 O 3  window, bonded to a nanocrystalline Y 2 O 3  layer  202  which faces a plasma  204 . The hybrid structure may contain injector holes  203  for injection of a gas into a plasma chamber. These holes may in one embodiment be part of the green part(s) before sintering or co-sintering, or in another embodiment they may be machined into the part after sintering. In this embodiment, the layers  201  and  202  may each be on the order of about 1-10 millimeters in width, of smaller or larger depending on the application and, if the part is sintered, the minimum thickness required to form a sintered product by methods known in the art. Other hybrid parts of a plasma processing chamber may be formed, with similar two-layer structure. 
         [0025]    A third embodiment is a plasma resistant viewport, which may be transparent in a range of interest, such as optical or UV. Plasma resistant, monocrystalline transparent Y 2 O 3 , is a deep UV transmitter. Nanograined Y 2 O 3  may in one embodiment provide superior plasma resistant window materials for endpoint sensors, such as optical emission spectrometers (OES) under aggressive plasma etch conditions. The size and geometry of polycrystalline transparent Y 2 O 3  viewports may not be limited, as single crystal sapphire windows may be. 
         [0026]    In other embodiments, other plasma resistant monolithic ceramic components may also be sintered if the nanosized powders of interest are readily available. Such material candidates may include AlON (which is commercially available for building bullet proof armors), YF 3 , ZrO 2 , YAG, YOF, etc. 
         [0027]    In other embodiments, a nanocrystalline ceramic component may be textured by increasing its roughness and surface area. Because micrograined ceramic materials may have grains in a range such as 5-10 microns, it becomes impractical to create surfaces features at or below that scale. In one particular embodiment, for a grain size in the range of 20-100 nm (for example, around 50 nm), surface roughness features and bumps may be a similar size range, resulting in a finely-textured surface. 
         [0028]    The inventors have determined that HCl acid percolation through grain boundary is a one of the major roughening mechanisms for certain types of nanocrystaline Y 2 O 3 . Without being limited by theory, this roughening mechanism may be applicable on the sintered, nanograined monolithic Y 2 O 3 . 
         [0029]    For example, a nanocrystalline ceramic component can be textured in a controlled manner to a surface roughness (Ra) in the range 0.02-0.1 μm using dilute acids such as HCl. Surface texturing in a highly controlled manner may be important to ensure non-drift etch process and good adhesion of precoat and/or etch byproducts. 
         [0030]    To facilitate understanding,  FIG. 3  schematically illustrates an example of a plasma processing chamber  300  which may be used in an embodiment. The plasma processing chamber  300  includes a plasma reactor  302  having a plasma processing confinement chamber  304  therein. A plasma power supply  306 , tuned by a match network  308 , supplies power to a TCP coil  310  located near a power window  312  to create a plasma  314  in the plasma processing confinement chamber  304  by providing an inductively coupled power. The TCP coil (upper power source)  310  may be configured to produce a uniform diffusion profile within the plasma processing confinement chamber  304 . For example, the TCP coil  310  may be configured to generate a toroidal power distribution in the plasma  314 . The power window  312  is provided to separate the TCP coil  310  from the plasma processing confinement chamber  304  while allowing energy to pass from the TCP coil  310  to the plasma processing confinement chamber  304 . A wafer bias voltage power supply  316  tuned by a match network  318  provides power to an electrode  320  to set the bias voltage on the substrate  364  which is supported by the electrode  320 . A controller  324  sets points for the plasma power supply  306 , gas source/gas supply mechanism  330 , and the wafer bias voltage power supply  316 . 
         [0031]    The plasma power supply  306  and the wafer bias voltage power supply  316  may be configured to operate at specific radio frequencies such as, for example, 33.56 MHz, 27 MHz, 2 MHz, 60 MHz, 400 kHz, 2.54 GHz, or combinations thereof. Plasma power supply  306  and wafer bias voltage power supply  316  may be appropriately sized to supply a range of powers in order to achieve desired process performance. For example, in one embodiment of the present invention, the plasma power supply  306  may supply the power in a range of 50 to 5000 Watts, and the wafer bias voltage power supply  316  may supply a bias voltage of in a range of 20 to 2000 V. In addition, the TCP coil  310  and/or the electrode  320  may be comprised of two or more sub-coils or sub-electrodes, which may be powered by a single power supply or powered by multiple power supplies. 
         [0032]    As shown in  FIG. 3 , the plasma processing chamber  300  further includes a gas source/gas supply mechanism  330 . The gas source  330  is in fluid connection with plasma processing confinement chamber  304  through a gas inlet, such as a gas injector  340 . The gas injector  340  may be located in any advantageous location in the plasma processing confinement chamber  304 , and may take any form for injecting gas. The process gases and byproducts are removed from the plasma process confinement chamber  304  via a pressure control valve  342  and a pump  344 , which also serve to maintain a particular pressure within the plasma processing confinement chamber  304 . The pressure control valve  342  can maintain a pressure of less than 1 Torr during processing. An edge ring  360  is placed around the wafer  364 . The gas source/gas supply mechanism  330  is controlled by the controller  324 . The plasma reactor  302  may have a plasma resistant viewport  357 . A Kiyo by Lam Research Corp. of Fremont, Calif., may be used to practice an embodiment. 
         [0033]    While inventions have been described in terms of several preferred embodiments, there are alterations, permutations, and various substitute equivalents, which fall within the scope of this invention. There are many alternative ways of implementing the methods and apparatuses disclosed herein. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and various substitute equivalents as fall within the true spirit and scope of the present invention.