Abstract:
Adhesion of high fluorine content films to semiconductor substrates may be improved by forming an intervening inherence layer. The inherence layer may be formed from a plasma gas. In one embodiment, the inherence layer may be a fluoropolymer film. In some cases, the fluoropolymer film may be used to adhere photoresist for advance photolithography processes to silicon substrates.

Description:
BACKGROUND  
         [0001]    This invention relates generally to the processing of semiconductor integrated circuits.  
           [0002]    High fluorine content solutions do not wet conventional semiconductor substrates, and high fluorine content polymers do not adhere well to conventional semiconductor substrates. High fluorine content polymers and polymer solutions may include photoresist for 157-nanometer lithography, as one example.  
           [0003]    To improve the adherence of such high fluorine content materials to semiconductor substrates, a reactive chemical precursor in liquid or vapor phase is reacted with a substrate to covalently bond the precursor functional group to the substrate. The presence of a new functional group at the surface of a substrate changes the surface properties, promoting wetting of material spread, cast or sprayed onto the surface that now has chemical functionality similar to the end groups of the reactive chemical precursor.  
           [0004]    Generally, liquid/vapor phase processing involves expensive, specially designed surface active molecules. Moreover, the chemicals are effective only on the surfaces that the precursor molecules are specifically designed for. Thus, the existing surface modification technique may be inflexible and relatively expensive.  
           [0005]    Thus, there is a need for better ways to adhere high fluorine content materials to a wider range of semiconductor substrates. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is an enlarged, cross-sectional view at an early stage of manufacture in accordance with one embodiment of the present invention;  
         [0007]    [0007]FIG. 2 is an enlarged, cross-sectional view at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0008]    [0008]FIG. 3 is an enlarged, cross-sectional view at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0009]    [0009]FIG. 4 is an enlarged, cross-sectional view at a subsequent stage of manufacture in accordance with one embodiment of the present invention; and  
         [0010]    [0010]FIG. 5 is an enlarged, schematic depiction of an etcher useful in connection with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]    A polymer film with high fluorine content may be produced by plasma polymerization and deposition. A polymer film may be grown from a substrate surface in a microwave plasma with the appropriate feed gases and process conditions in one embodiment. The film is adherent since it is covalently bound to the substrate during polymerization. The polymer film promotes wetting during subsequent spin casting, dip coating or spray coating of high fluorine content polymer solutions, and adhesion of the dried high fluorine content polymer film once the solvent evaporates from solution.  
         [0012]    An example of a high fluorine content polymer is the fluoropolymer photoresist used in photolithography with light having a wavelength of 157 nanometers. Adhesion may be facilitated by the favorable surface energy between the plasma polymerized fluoropolymer film and the high fluorine content coated film.  
         [0013]    Thus, referring to FIG. 1, the fluoropolymer film  14  may be grown or otherwise formed on a semiconductor substrate  12 , which may be a silicon substrate in one embodiment of the present invention. Other examples of substrate  12  include silicon-oxy-nitride, silicon nitride, silicon carbide, and polysilicon. The fluoropolymer film  14  may be grown in a microwave plasma, for example. Next, the layer  16  to be adhered to the substrate  12  may be formed as shown in FIG. 2. Adhesion is facilitated by the intervening film  14 . In some embodiments, the layer  16  is formed of a high fluorine content polymer or polymer solutions such as photoresist.  
         [0014]    In some embodiments, for example where the layer  16  is a photoresist, the layer  16  may be patterned. The patterning may result in exposure and removal of a portion of the layer  16  to form the opening  18 , exposing the portion  14   a  of the film  14 , as shown in FIG. 3.  
         [0015]    Subsequently, the film  14   a  may be removed where exposed to result in the structure shown in FIG. 4. For example, a short O 2  plasma etch may be used to remove the film  14   a.    
         [0016]    The fluoropolymer film  14  may be grown from the plasma state on a silicon substrate  12 , for example, using a Tokyo Electron Limited (Tokyo, Japan) radio frequency plasma oxide etcher  50 , shown in FIG. 5. The etcher  50  may have a chamber  40  that is hermetically sealed.  
         [0017]    An upper electrode  34  and a lower electrode  38  may be spaced a predetermined distance from one another within the chamber  40 . A radio frequency voltage is applied to the electrodes  34  and  38  from a radio frequency power source  44 . A number of fine holes  32  are formed in the upper electrode  34  to admit process or reaction gas. The lower electrode  38  acts as a susceptor having an upwardly facing surface on which a semiconductor wafer  36  or an object to be processed is placed. The opposed surfaces of the upper and lower electrodes  34  and  38  are substantially parallel.  
         [0018]    A top wall of the chamber  40  has a gas introduction port  30  coupled to a gas source. The chamber  40  bottom wall has an exhaust port  42  coupled to an exhaust device. The process gas or an etching gas is introduced into the chamber  40  through the port  30 , flowing through the holes  32  in the upper electrode  34  into the space between the electrodes  34  and  38 . There the etching gas is converted into a plasma. As a result, the film  14  may be formed on the semiconductor wafer  36 . During that process, the chamber  40  is exhausted through the exhaust pipe  42  to maintain a predetermined vacuum level.  
         [0019]    The etcher  50  may have the following settings in one embodiment: a gap between electrodes  34  and  38  of 27 millimeters; a chamber pressure of 62 milliTorr; a radio frequency power of 100 Watts; an inert gas flow of 230 standard cubic centimeters per minute (sccm); an upper electrode temperature of 60° C.; a wall temperature of 60° C.; and a lower electrode temperature of 20° C.  
         [0020]    In some embodiments, various proportions of gases containing carbon, hydrogen, fluorine, and oxygen may be utilized. Suitable gases include C 4 F 8 , CH 2 F 2 , and CF 4 . The flow rates for C 4 F 8  may be in the range of from 0 to 30 sccm in some embodiments. For CH 2 F 2 , the flow rate may be between 10 and 50 sccm in some embodiments. For CF 4 , the flow rate may be from 0 to 100 sccm in some embodiments.  
         [0021]    The film  14 &#39;s thickness is directly dependent on plasma time, with typical growth rates on the order of 10 Angstroms per second, measured by X-ray reflectivity. Film composition, measured by XPS, may show the presence of fluorine, and water contact angles ranging from 80 to 104 degrees. Fluorinated 157 nanometer lithography photoresists were found to adhere to and develop on plasma polymerized silicon substrates, where adhesion has been shown to be poorer on non-modified silicon substrates.  
         [0022]    Thus, in some embodiments, surface modification is achieved in a dry state in a plasma in a single step from bulk gases onto any surface. This may avoid the need for a liquid/vapor phase processing of expensive, specially designed surface active modules onto only the surfaces for which precursor molecules or specifically designed for.  
         [0023]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.