Abstract:
In providing a bottom antireflective coating (BARC) in a semiconductor structure, a primer layer, for example, hexamethyldisilazane (HMDS), is provided on a substrate, and the BARC is formed on the primer. This results in a substantially defect free BARC layer, having a more uniform reflectivity which in turn leads to improve to photolithographic pattern resolution.

Description:
REFERENCE TO RELATED CASE 
     This application is based on and claims the benefit of U.S. Provisional Application Ser. No. 60/249336, filed Nov. 16, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to semiconductor devices and manufacturing processes, and more particularly, to formation of a bottom antireflective coating (BARC) in a semiconductor structure. 
     2. Discussion of the Related Art 
     In semiconductor technology it is well-known to provide a bottom antireflective coating (BARC) on a surface beneath a layer of photoresist, to aid in the patterning of images. The BARC cuts down on light scattering into the resist, which helps in defining images. The BARC also minimizes standing waves effects and improves image contrast. 
     In order to achieve these advantages, the BARC must be relatively defect free. Such a uniform BARC would provide a more uniform reflectivity, in turn leading to better photolithographic pattern resolution. 
     Using a normal spinon technique to apply a BARC on a substrate can result in numerous defects therein in the form of variations in thickness, leading to the problems described above. 
     Therefore, what is needed is a method for forming a low defect BARC layer, so that manufacturing efficiency is increased. 
     SUMMARY OF THE INVENTION 
     In the present method, rather than applying a BARC directly onto a substrate, a primer, for example, vapor deposited hexamethyldisilazane (HMDS) along with a small amount of trimethylsilyldiethylamine (TMSDEA) as an additive, is vapor deposited on the substrate, and the BARC is formed on the primer. Then a layer of photoresist may be formed over the BARC. The inclusion of the primer layer results in a low defect BARC, in fact eliminating defects due to variations in thickness, so that the BARC provide uniform reflectivity to in turn provide improved photolithographic pattern resolution 
     The present invention is better understood upon consideration of the detailed description below, in conjunction with the accompanying drawings. As will become readily apparent to those Gilled in the art from the following description, there is shown and described an embodiment of this invention simply by way of the illustration of the best mode to carry out the invention. As will be realized, the invention is capable of other embodiments and its several details are capable of modifications and various obvious as, all without departing from the scope of the invention. Accordingly, the drawings and detailed description will be regarded as illustrative in nature and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as said preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a sectional view of a semiconductor structure including a substrate having a BARC coating thereon, in accordance with the prior art; 
     FIG. 2 is a plan view of a wafer having a structure as shown in FIG. 1, showing defects there accordance with the prior art; 
     FIG. 3 is a graph showing distribution of defect count indicated in FIG. 2 by size thereof in accordance with the prior art; 
     FIG. 4 is a sectional view of a semiconductor structure including a substrate having a primer and a BARC coating thereon, in accordance with the present invention; 
     FIG. 5 is a plan view of a wafer having a structure as shown in FIG. 4, in accordance with a present invention; 
     FIG. 6 is a graph showing distribution of defect count indicated in FIG. 5 by size thereof, in accordance with the present invention; and 
     FIG. 7 is a sectional view similar to that shown in FIG. 4, and further showing a photoresist layer on the primer layer. 
    
    
     DETAILED DESCRIPTION 
     Reference is now made in detail to a specific embodiment of the present invention which illustrates the best mode presently contemplated by the inventors for practicing the invention. 
     FIG. 1 shows a semiconductor structure  10  including a substrate  12 , the substrate  12  in this illustrative embodiment made up of a silicon layer  14  and layer  16  thereon, for example silicon dioxide (SiO 2 ), silicon oxide (SiON), tetraethyl orthosilicate TEOS), fluorine doped TEOS (FTEOS), low k dielectric, metal, polysilicon, silicon nitride (Si 3 N 4 ), or some other appropriate material The semiconductor structure  10  takes the form of a typical wafer  18  (FIG.  2 ). The substrate  12  has formed thereon a BARC  20  in contact with the layer  16 , being of organic material, for example a polyimide or a polysulfone. The BARC  20  was formed using conventional BARC material, dispensing and casting techniques, along with conventional edge bead removal, backside rinse, drying, baking and cooling. Then, the BARC  20  was scanned for defects using the KLA 2132. As will be seen in FIG. 2, a large number of defects  22  (including thickness variations, non-visual defects, equipment related defects, and bubble/void defects) was indicated, the testing being programmed to cease when the defect count reached 5000, which count was reached prior to the entire wafer  18  being scanned (FIG.  2 ). A distribution of defect count by size is shown in FIG.  3 . As will be seen, a high number of large defects results from this described method, leading to the problems set forth above. 
     FIG. 4 again shows a semiconductor structure  30  including a substrate  32 , the substrate  32  in this embodiment made up of a silicon layer  34  and layer  36  thereon. The material of layer  36  may be as specified as for layer  16 , or any other suitable material. The semiconductor structure  30  again takes the form of a wafer  38  as shown in FIG.  5 . The layer  36  of the substrate  32  has deposited thereon a primer layer  40 . The primer layer  40  is formed of hexamethyldisilazane HMDS), which is commonly used as a primer material on which photoresist is directly deposited The primer layer may include a small amount, for example 1%, trimethylsilyldiethylamine IDEA). The layer  40  is applied by vapor deposition at 130° C. for 60 seconds. The resulting structure is allowed to cool for 60 seconds to 20.5° C. 
     Next, a BARC  42  is applied to the primer layer  40 . Again, the BARC  42  is an organic layer, for example a polyimide or a polysulfone. Using a TEL (Tokyo Electronics limited) Mark VIII track system, the BARC material, in this embodiment AZ&#39;s KrF  17 B, is dispensed m a volume in the range of 3-5 cc, in this embodiment at a dispense rate of 3.5 cc, at 1 cc/second, in the range of from 1000-2000 RPM in this embodiment 1700 RPM The casting speed is in the range of from 2300-2700 RPM in this embodiment 2400 RPM, and casting is undertaken for 30 seconds. The BARC  42  thickness in this embodiment is in the range of 90 nm to 160 nm, in this embodiment approximately 140 nm thick. After edge bead removal and backside rinse, a drying step is undertaken at 3500 RPM for 25 seconds. The resulting sure including the BARC is baked at 185° C. for 60 seconds, and the structure is cooled for 60 seconds to 20.5° C. 
     As will be seen in FIG. 5, a very small number of relatively small defects  44  is indicated. Upon further investigation, it was revealed that all of the defects  44  fall into the category of bubble/void defects. That is, defects due to thickness variations were completely eliminated. 
     A distribution of defect count by size is shown in FIG.  6 . As will be seen, not only are defects lower in number, but they are of generally smaller size than those indicated in the above prior art example. This reduction in defects in the BARC  42  and on of defects due to thickness variations is due to the inclusion of the primer layer  40  on which the BARC is formed. 
     FIG. 7 shows the structure of FIG. 4 with a photoresist layer  46  provided on the BARC  42 . With a uniform (thickness variation defect free) BARC  42 , more uniform reflectivity thereof is achieved, leading to improved photolithographic pattern resolution. 
     The foregoing description of the embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed Other modifications or variations are possible in light of the above teachings. 
     The embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill of the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled