Abstract:
Embodiments described herein generally relate to an aluminum alloy showerhead with a reduced zinc content for use in semiconductor processing chambers. The showerhead may be utilized in processing chambers adapted for making low temperature polysilicon (LTPS) liquid crystal displays (LCD) or LTPS organic light emitting diode (OLED) displays which may be controlled by thin film transistors (TFT). More specifically, embodiments described herein relate to a reduced zinc showerhead.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 61/841,484, filed Jul. 1, 2013, which is herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments described herein generally relate to an aluminum alloy showerhead with a reduced zinc content for use in processing chambers. The showerhead may be utilized in processing chambers adapted for making low temperature polysilicon (LTPS) liquid crystal displays (LCD) or LTPS organic light emitting diode (OLED) displays which may be controlled by thin film transistors (TFTs). More specifically, embodiments described herein relate to a reduced zinc showerhead. 
         [0004]    2. Description of the Related Art 
         [0005]    Current interest in TFT arrays is particularly high because these devices may be used in LCDs of the kind often employed for computer and television flat panels. The LCDs may also contain light emitting diodes (LEDs), such as OLEDs for back lighting. The LEDs and OLEDs require TFTs for addressing the activity of the displays. 
         [0006]    LTPS displays generally require processing at elevated temperatures in order to deposit the polysilicon. A common source of particle creation during processing is copper metal contamination due to the migration of copper in devices. However, other sources of particle contamination may exist during processing. Particles present during processing may degrade TFT device performance. 
         [0007]    Thus, what is needed in the art are apparatuses for reducing particle contamination during TFT device manufacturing. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments described herein generally relate to an aluminum showerhead, or diffuser, with a reduced zinc content for use in semiconductor processing chambers. LTPS based LCDs or LTPS based OLEDs are generally controlled by TFTs. Particle contamination in the processing chamber during fabrication of the TFTs may reduce the performance capability and reliability of the TFTs. The reduced zinc showerhead may reduce the presence of zinc particles within the processing chamber and improve TFT device performance. 
         [0009]    In one embodiment, a diffuser for processing semiconductor substrates is provided. The diffuser may comprise a body comprising an aluminum alloy, wherein the aluminum alloy comprises less than or equal to 0.01 wt % of zinc. 
         [0010]    In another embodiment, a diffuser for use in a plasma enhanced chemical vapor deposition chamber is provided. The diffuser may comprise a body comprising an aluminum alloy containing less than or equal to 0.01 wt % of zinc, wherein the diffuser may be adapted for operation in an environment having a temperature above 400° C. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
           [0012]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0013]      FIG. 1  is a cross-sectional schematic view of a PECVD chamber according to certain embodiments described herein; 
           [0014]      FIGS. 2A-2C  are schematic cross-sectional views of a TFT at various stages of production according to certain embodiments described herein; and 
           [0015]      FIG. 3  is a cross-sectional schematic diagram of a TFT controlling an LCD pixel or OLED according to certain embodiments described herein. 
           [0016]      FIG. 4  is a color photograph of a portion of a backing plate having a zinc material deposited thereon. 
           [0017]      FIG. 5  is a color photograph of a portion of a backing plate having substantially no zinc material deposited thereon. 
           [0018]      FIG. 6  is a graph illustrating elemental analysis of a portion of a chamber having a zinc material deposited thereon. 
       
    
    
       [0019]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
       DETAILED DESCRIPTION 
       [0020]    Embodiments described herein generally relate to an aluminum showerhead, or diffuser, with a reduced zinc content for use in semiconductor processing chambers. LTPS based LCDs or LTPS based OLEDs are generally controlled by TFTs. Particle contamination in the processing chamber during fabrication of the TFTs may reduce the performance capability and reliability of the TFTs. The reduced zinc showerhead may reduce the presence of zinc particles within the processing chamber and improve TFT device performance. 
         [0021]    The invention is illustratively described below utilized in a processing system, such as a plasma enhanced chemical vapor deposition (PECVD) system available from AKT America, a division of Applied Materials, Inc., located in Santa Clara, Calif. However, it should be understood that the invention has utility in other system configurations, including those sold by other manufacturers. 
         [0022]      FIG. 1  is a schematic, cross sectional view of an apparatus that may be used to perform the operations described herein. The apparatus includes a chamber  100  in which one or more films may be deposited onto a substrate  120 . The chamber  100  generally includes walls  102 , a bottom  104  and a showerhead  106  which define a process volume  105 . A substrate support  118  may be disposed within the process volume  105 . The process volume  105  is accessed through a slit valve opening  108  such that the substrate  120  may be transferred in and out of the chamber  100 . The substrate support  118  may be coupled to an actuator  116  to raise and lower the substrate support  118 . Lift pins  122  are moveably disposed through the substrate support  118  to move a substrate to and from a substrate receiving surface. The substrate support  118  may also include heating and/or cooling elements  124  adapted to maintain the substrate support  118  at a desired temperature. The substrate support  118  can also include RF return straps  126  to provide an RF return path at the periphery of the substrate support  118 . 
         [0023]    The showerhead  106  may be coupled to a backing plate  112  by one or more fastening mechanisms  140 . The one or more fastening mechanisms  140  may help prevent sag and/or control the straightness/curvature of the showerhead  106 . The showerhead  106  may be formed from a metal such as aluminum, stainless steel, and alloys thereof. In one embodiment, the showerhead may be a 6061 aluminum alloy having a reduced zinc content. The reduced 6061 aluminum alloy may have a zinc content of less than or equal to 0.01 wt %. It is believed that when the chamber  100  is operated at temperatures above about 400° C. for extended periods of time, such as in an LTPS process, zinc present in the 6061 aluminum alloy may volatilize and deposit on surfaces in the chamber  100 . The relatively high vapor pressure of zinc, in combination with temperature and pressure conditions of the chamber  100  during processing, may cause the volatilization which may ultimately result in zinc particles present in the chamber  100 . It has been found that a 6061 aluminum alloy having less than or equal to 0.01 wt % zinc reduces or eliminates the creation of zinc particles within the chamber  100 . 
         [0024]    A gas source  132  can be coupled to the backing plate  112  to provide process gases through gas passages in the showerhead  106  to process volume  105  between the showerhead  106  and the substrate  120 . The gas source  132  can include a silicon-containing gas supply source, an oxygen containing gas supply source, and a nitrogen-containing gas supply source, among others. Typical process gases useable with one or more embodiments include silane (SiH 4 ), disilane, N 2 O, ammonia (NH 3 ), H 2 , N 2  or combinations thereof. 
         [0025]    A vacuum pump  110  may be coupled to the chamber  100  to control the process volume  105  at a desired pressure. An RF source  128  can be coupled through a match network  150  to the backing plate  112  and/or to the showerhead  106  to provide an RF current to the showerhead  106 . The RF current creates an electric field between the showerhead  106  and the substrate support  118  so that a plasma may be generated from the gases between the showerhead  106  and the substrate support  118 . 
         [0026]    A remote plasma source  130 , such as an inductively coupled remote plasma source  130 , may also be coupled between the gas source  132  and the backing plate  112 . Between processing substrates, a cleaning gas may be provided to the remote plasma source  130  so that a remote plasma is generated. The radicals from the remote plasma may be provided to chamber  100  to clean chamber  100  components. The cleaning gas may be further excited by the RF source  128  provided to the showerhead  106 . 
         [0027]    The showerhead  106  may additionally be coupled to the backing plate  112  by showerhead suspension  134 . In one embodiment, the showerhead suspension  134  is a flexible metal skirt. The showerhead suspension  134  may have a lip  136  upon which the showerhead  106  may rest. The backing plate  112  may rest on an upper surface of a ledge  114  coupled with the chamber walls  102  to seal the chamber  100 . 
         [0028]      FIGS. 2A-2C  are schematic cross-sectional views of a TFT  200  at various stages of production. As shown in  FIG. 2A , a gate electrode  204  is formed over a substrate  202 . Suitable materials that may be utilized for the substrate  202  include, but not limited to, silicon, germanium, silicon-germanium, soda lime glass, glass, semiconductor, plastic, steel or stainless steel substrates. Suitable materials that may be utilized for the gate electrode  204  include, but are not limited to, chromium, copper, aluminum, tantalum, titanium, molybdenum, and combinations thereof, or transparent conductive oxides (TCO) such as indium tin oxide (ITO) or fluorine doped zinc oxide (ZnO:F) which are commonly used as transparent electrodes. The gate electrode  204  may be deposited by suitable deposition techniques such as PVD, MOCVD, a spin-on process and printing processes. The gate electrode  204  may be patterned using an etching process. 
         [0029]    Over the gate electrode  204 , a gate dielectric layer  206  may be deposited. Suitable materials that may be used for the gate dielectric layer  206  include silicon dioxide, silicon oxynitride, silicon nitride, aluminum oxide or combinations thereof. The gate dielectric layer  206  may be deposited by suitable deposition techniques including plasma enhanced chemical vapor deposition (PECVD). 
         [0030]    A semiconductor layer  208  is then formed over the gate dielectric layer  206  as shown in  FIG. 2B . The semiconductor layer  208  comprises LTPS. In practice, the semiconductor layer  208  is oftentimes referred to as the channel layer, the active layer, or the semiconductor active layer. 
         [0031]    As shown in  FIG. 2C , over the semiconductor layer  208 , the source electrode  210  and the drain electrode  212  are formed. The exposed portion of the semiconductor layer  208  between the source and drain electrodes  210 ,  212  is referred to as the slot or trench  214 . Suitable materials for the source and drain electrodes  210 ,  212  include chromium, copper, aluminum, tantalum, titanium, molybdenum, and combinations thereof, or TCOs mentioned above. The source and drain electrodes  210 ,  212  may be formed by suitable deposition techniques, such as PVD followed by patterning through etching. 
         [0032]    A TFT  200  formed in the chamber  100  may be adapted to control LCD or OLED displays. Thus, the TFT  200  may have a polysilicon semiconductor layer  208 . The polysilicon semiconductor layer may comprise amorphous silicon or microcrystalline silicon which may be annealed into polysilicon. The annealing process may be performed at temperatures greater than about 400° C. As previously described, a showerhead  106  comprising a 6061 aluminum alloy may contain impurities, such as zinc, which may volatilize out of the showerhead  106  and deposit on surfaces within the chamber  100  when the showerhead  106  is subjected to elevated temperatures. The volatilized zinc may be in the form of a zinc powder which may deposit on various surfaces of the chamber  100 . The zinc powder or particles may also deposit on the polysilicon semiconductor layer  208  during TFT  200  fabrication. The particles of zinc may degrade the TFT  200  performance. As such, utilizing a reduced zinc showerhead  106  may reduce or eliminate zinc particles within the chamber  100  when forming an LTPS TFT  200 . 
         [0033]      FIG. 3  is a cross-sectional schematic diagram of a TFT controlling an LCD pixel or OLED. The TFT  200  may be adapted to control a display pixel  306 , such as an LCD or OLED display pixel. The display pixel  306  may be electrically coupled to the display pixel electrode  302  which may be electrically coupled via a connector  304  to the drain  212 . The TFT  200  may provide an electrical signal via the connector  304  to the display pixel electrode  302  which may influence the display pixel  306 . The performance of the TFT  200  is important in controlling the display pixel  306  and any particles present in the chamber  100  during formation of the TFT  200  may degrade performance. This is especially important when using polysilicon as the semiconductor layer  208  because of the elevated temperatures needed to form the polysilicon as the elevated temperatures in the chamber  100  may cause impurities in the showerhead  106  to volatilize out of the showerhead  106 . The reduced zinc showerhead  106  as described above may reduce or eliminate the volatilization of zinc from the showerhead  106  and provide for a TFT with an uncontaminated polysilicon semiconductor layer  208 . 
         [0034]      FIG. 4  is a color photograph of a portion of a backing plate having a zinc material deposited thereon. As shown, a bluish gray material is present on the backing plate. The bluish gray material is believed to be zinc particles which have volatilized and deposited on the backing plate after the chamber is operated at temperatures above about 400° C. for extended periods of time. In addition to depositing on the backing plate, the zinc material is also deposited on other chamber components, such as the walls of the chamber. It is believed that the bluish gray zinc material shown in  FIG. 4  volatilized from a diffuser made of 6061 alloy aluminum having a zinc content greater than 0.01 wt %. 
         [0035]      FIG. 5  is a color photograph of a portion of a backing plate having substantially no zinc material deposited thereon. As shown, substantially no bluish gray material is present on the backing plate when compared to the photograph of  FIG. 4 .  FIG. 5  shows the backing plate after the chamber is operated at temperatures above about 400° C. for extended periods of time with a diffuser made from 6061 alloy aluminum wherein the zinc content of the alloy is less than or equal to 0.01 wt %. It is believed that utilizing a diffuser having a zinc content less than or equal to 0.01 wt % substantially reduces or eliminates the potential for zinc volatilization and deposition on the backing plate and other chamber components. 
         [0036]      FIG. 6  is a graph illustrating elemental analysis of a portion of a chamber having a zinc material deposited thereon. For example, the backing plate of  FIG. 4  may be representative of the results obtained in the elemental analysis illustrated in  FIG. 6 . Energy-dispersive X-ray spectroscopy was performed on a chamber component operated at temperatures above about 400° C. for extended periods of time at a pressure of about 2 Torr with a diffuser made from 6061 alloy aluminum wherein the zinc content of the alloy is greater to 0.01 wt %. The resulting elemental analysis of the chamber component with the bluish gray zinc material present proved the existence of carbon, oxygen, and zinc. Table 1 provides numerical representations of the amounts of the elements present from the graph of  FIG. 6 . 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Element 
                 Weight % 
                 Atomic % 
               
               
                   
                   
               
             
             
               
                   
                 C 
                 10.63 
                 23.35 
               
               
                   
                 O 
                 32.61 
                 53.76 
               
               
                   
                 Zn 
                 56.75 
                 22.89 
               
               
                   
                   
               
             
          
         
       
     
         [0037]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.