Abstract:
Reticles having reticle patterns suitable for reducing edge of array effects are provided. The reticle patterns may have sub-resolution patterns or a transmissive block fill formed in the periphery areas of the reticle patterns. Systems incorporating the reticles are also provided. Additionally, methods of forming and using the reticles are provided. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that is will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention is directed toward reticles and methods of forming and employing the reticles.  
           [0002]    Reticles are used in the semiconductor industry to form semiconductor devices having device features. There is a continuing effort to increase device density by scaling down device size, and state of the art devices currently have device features with dimensions well below one micron. Most reticles contain subarray areas containing the patterns for the memory features of the device. As the features size decreases, edge of array effects are observed. The edge of array effects are generally seen as critical dimension differences between the edge or corner of the subarray area and the subarray area a distance from the edge.  
           [0003]    The edge of array effects may be caused by a number of factors. For example, process loading during the manufacture of a reticle may occur. Process loading during reticle manufacture may introduce error into the subarray area because the entire reticle pattern may contain dense and less dense or open areas. Similarly, process loading during wafer processing may occur that causes error to be introduced into the subarray area on the wafer. Stray light from less dense areas of a reticle can cause bulk exposure in a clear field reticle. Additionally, reticles may suffer from underexposure due to large dark areas of a dark field reticle to prevent underexposure.  
           [0004]    The critical dimension difference has been addressed in a number of ways. For example, U.S. patent application Ser. No. 09/748,168 addresses the critical dimension difference by providing a process of manufacturing a photomask that includes forming a dummy pattern in less dense areas of the reticle and subsequently etching the dummy pattern away. The reticle provides improved critical dimension control. However, the reticle may not be easily inspected for defects and is process intensive.  
           [0005]    Thus, there remains a need in the art for reticle patterns that address edge of array effects, and there remains a need in the art for methods of forming and using such reticle patterns.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention relates to reticles and methods of forming and using reticles.  
           [0007]    In accordance with one embodiment of the present invention, a reticle is provided, and the reticle comprises a transparent reticle substrate having a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a sub-resolution pattern formed therein.  
           [0008]    In accordance with another embodiment of the present invention, a system for patterning a radiation sensitive layer comprising a source of electromagnetic radiation and a reticle is provided. The reticle comprises a transparent reticle substrate having a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a sub-resolution pattern formed therein.  
           [0009]    In accordance with yet another embodiment of the present invention, a method of forming a reticle is provided. The method comprises providing a reticle blank and patterning the reticle blank to form a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a sub-resolution pattern formed therein.  
           [0010]    In accordance with another embodiment of the present invention, a method of patterning a radiation sensitive layer is provided. The method comprises providing a reticle, and the reticle comprises a transparent reticle substrate having a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a sub-resolution pattern formed therein. The method further comprises exposing a radiation sensitive layer with the reticle such that the radiation sensitive layer is exposed the reticle pattern. The densely patterned subarray features defining the at least one subarray area are patterned on the radiation sensitive layer in areas exposed to the at least one subarray area, and the radiation sensitive layer is not patterned in areas exposed to the sub-resolution pattern in the at least one periphery area.  
           [0011]    In accordance with one embodiment of the present invention, a reticle is provided, and the reticle comprises a transparent reticle substrate having a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a transmissive block fill formed therein.  
           [0012]    In accordance with another embodiment of the present invention, a system for patterning a radiation sensitive layer comprising a source of electromagnetic radiation and a reticle is provided. The reticle comprises a transparent reticle substrate having a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a transmissive block fill formed therein.  
           [0013]    In accordance with yet another embodiment of the present invention, a method of forming a reticle is provided. The method comprises providing a reticle blank and patterning the reticle blank to form a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a transmissive block fill formed therein.  
           [0014]    In accordance with another embodiment of the present invention, a method of patterning a radiation sensitive layer is provided. The method comprises providing a reticle, and the reticle comprises a transparent reticle substrate having a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain a transmissive block fill formed therein. The method further comprises exposing a radiation sensitive layer with the reticle such that the radiation sensitive layer is exposed the reticle pattern. The densely patterned subarray features defining the at least one subarray area are patterned on the radiation sensitive layer in areas exposed to the at least one subarray area, and the radiation sensitive layer is not patterned in areas exposed to the transmissive block fill in the at least one periphery area.  
           [0015]    In accordance with one embodiment of the present invention, a reticle is provided, and the reticle comprises a transparent reticle substrate having a reticle pattern. The reticle pattern comprises at least one subarray area defined by densely patterned subarray features and at least one periphery area defined by open areas. The open areas defining the at least one periphery area lie outside the at least one subarray area, and the open areas defining the at least one periphery area contain an unresolvable pattern formed therein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIGS. 1 a - 1   c  are schematic illustrations of portions of reticles in accordance with the present invention.  
         [0017]    [0017]FIGS. 2 a - 2   b  are schematic illustrations of sub-resolution patterns.  
         [0018]    [0018]FIG. 3 is an illustration of a portion of a reticle blank.  
         [0019]    [0019]FIG. 4 is a schematic illustration of a reticle being used to pattern a radiation sensitive layer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    The present invention provides reticles having reticle patterns that may address edge of array effects and methods of forming and using the same.  
         [0021]    In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. In the drawings, like numerals describe substantially similar components throughout the several views.  
         [0022]    Referring to FIG. 1 a , a portion of a reticle  18  is illustrated schematically. The reticle  18  may be used to form patterns on radiation sensitive layers when the reticle is exposed to patterning radiation. The reticle  18  generally comprises a transparent reticle substrate  12  having a reticle pattern. The reticle pattern comprises at least one subarray area  20  and at least one periphery area  22 . It will be understood by those having skill in the art that the reticle pattern generally has a plurality of subarray areas  20  and periphery areas  22  in a desired configuration, and that the reticle may be a clear field or dark field reticle. The subarray area  20  is defined by densely patterned subarray features  24 . The densely patterned subarray features  24  are generally patterns for subarray components that are formed in a tightly packed configuration in the subarray area  20 . The densely patterned subarray features  24  may have a space to feature ratio of between about 1:1 to about 4:1. For example, the densely patterned subarray features  24  may be feature patterns for capacitors or transistors that generally form portions of a memory of array.  
         [0023]    The periphery area  22  is defined by open areas that lie outside the subarray area  20 , and the open areas generally begin adjacent to the subarray area  20 . The periphery area is defined by open areas because there are no densely patterned subarray features  24  in the open areas. However, the open areas defining the periphery area  22  may have feature patterns  26  formed in the open areas. The feature patterns  26  formed in the periphery area  22  are not formed near the subarray area  20 . The feature patterns  26  may include, but are not limited to, feature patterns for sense amplifiers, row decoders, and row drivers.  
         [0024]    Referring to FIG. 1 b , the open areas defining the periphery area  22  may contain a sub-resolution pattern  28  formed therein. As used herein, the term “sub-resolution pattern” is defined to mean a pattern dimensioned or configured such that the sub-resolution pattern will not print when the densely patterned subarray features will print on a radiation sensitive layer using a given printing system. For example, the resolution limit of a given process may be expressed mathematically by the following (Raleigh Criterion):  
           R=k   1 (λ)/ NA    
         [0025]    where  
         [0026]    R is the process resolution limit;  
         [0027]    k 1  is the process capability factor;  
         [0028]    λ is the wavelength of the exposure source; and  
         [0029]    NA is the numerical aperture of the lens for the exposure tool. Thus, the sub-resolution pattern  28  will generally be formed such that the features of the sub-resolution pattern  28  are below the R for the given process. The presence of the sub-resolution pattern  28  may address edge of array effects. For example, the presence of the sub-resolution pattern  28  may address stray light that can cause bulk exposure from less dense areas in a clear field reticle or increase the amount of light to prevent underexposure in a dark field reticle.  
         [0030]    The sub-resolution pattern  28  may be a line pattern as shown in FIG. 1 b . Alternatively, the sub-resolution pattern  28  may be a grid pattern as shown in FIG. 2 a , a box pattern as shown in FIG. 2 b , or any other suitable pattern that is sub-resolution in comparison to the densely patterned subarray features  24 . The sub-resolution pattern is generally formed about 4 to about 40 μm from the subarray area  20 , and the sub-resolution pattern is typically formed about 4 μm from the subarray area. The sub-resolution pattern  28  may be formed such that the pitch of the sub-resolution pattern  28  is approximately equal to the pitch of the densely patterned subarray features  24  defining the subarray area  20 . When the pitch of the sub-resolution pattern  20  is approximately equal to the pitch of the densely patterned subarray features  24 , the distance between the components of sub-resolution pattern  28  will be approximately equal to the distance between the densely patterned subarray features  24 . Alternatively, the sub-resolution pattern  28  may be formed such that the density of the sub-resolution pattern  28  is approximately equal to the density of the densely patterned subarray features  24  defining the subarray area  20 .  
         [0031]    The sub-resolution pattern  28  may be formed such that the percentage of patterning radiation transmitted through the sub-resolution pattern  28  is approximately equal to the percentage of patterning radiation transmitted through the subarray area  20 . For example, the sub-resolution pattern  28  may be formed such that about 25 to 50% of the patterning radiation incident on the sub-resolution pattern  28  is transmitted therethrough, and the sub-resolution pattern is more typically formed such that about 35% of the patterning radiation incident on the sub-resolution pattern  28  is transmitted therethrough.  
         [0032]    Referring to FIG. 1 c , the open areas defining the periphery area  22  may alternatively contain a transmissive block fill  29  formed therein. The transmissive block fill  29  is formed to permit partial transmission of patterning radiation incident on the transmissive block fill  29 . The presence of the transmissive block fill  29  may address edge of array effects.  
         [0033]    The transmissive block fill  29  generally comprises a block fill that allows some patterning radiation to pass therethrough. The transmissive block fill  29  may be formed to permit transmission of an amount of patterning radiation that is the approximately equal to the percentage of patterning radiation transmitted through the subarray area  20 . The transmissive block fill  29  may be formed such that the about 25% to about 50% of the patterning radiation incident on the transmissive block fill  29  is transmitted therethrough, and the transmissive block fill  29  is more typically formed such that the about 35% of the patterning radiation incident on the transmissive block fill  29  is transmitted therethrough. Generally, the transmissive block fill is formed about 4 to about 40 μm from the subarray area  20  on the reticle. The transmissive block fill  29  allows the reticle  18  to be more easily inspected for defects than if a sub-resolution pattern is present.  
         [0034]    Referring to FIGS. 1 b  and  1   c , the sub-resolution pattern  28  and the transmissive block fill  29  comprise unresolvable patterns. The patterns  28 ,  29  are unresolvable because presence of the sub-resolution pattern  28  or the transmissive block fill  29  on a reticle  18  does not cause a pattern corresponding to the sub-resolution pattern  28  or the transmissive block fill  29  to be formed at a given imaging point. For the purposes of defining and describing the present invention, it is noted that an imaging point is defined by a point, line, or plane at which an image of a subject pattern may be formed. For example, the imaging point may correspond to the focal point or focal plane of a given imaging system. The imaging point may also correspond to some point, line or plane displaced from the focal point or focal plane of a given imaging system, as long as a useful image of the subject pattern is formed at the displaced point or plane. It will be understood by those having skill in the art that other suitable unresolvable patterns may be employed in the periphery areas  22 .  
         [0035]    The periphery area  22  may contain areas having a sub-resolution pattern  28  and areas containing a transmissive block fill  29 . Additionally, the reticle  18  may have a plurality of periphery areas  22 , and some of the periphery areas  22  may have a sub-resolution pattern  28  while other periphery areas  22  have a transmissive block fill  29 .  
         [0036]    [0036]FIG. 3 shows a portion of a reticle blank  10  that may be used in forming the reticles of the present invention. The reticle blank  10  has a transparent reticle substrate  12 , a radiation blocking layer  14 , and a resist layer  16 . The transparent reticle substrate  12  may be formed from any suitable material such as quartz, and the transparent reticle substrate  12  may be of any suitable thickness and size. The radiation blocking layer  14  may be formed from one or more radiation blocking materials. For example, the radiation blocking layer  14  may be formed from chromium, molybdenum silicon, and combinations thereof. The resist layer  16  may be any suitable resist. It will be understood by those having skill in the art that other suitable reticle blanks and layer configurations may be used.  
         [0037]    Referring to FIGS. 1 b  and  3 , the reticle pattern comprising at least one subarray area  20  and at least one periphery area  22  having a sub-resolution pattern  28  may be formed using any suitable method. Generally, the desired reticle pattern is written onto the reticle blank  10 . The reticle pattern may be written onto the reticle blank  10  using any suitable method. For example the reticle pattern may be written onto the reticle blank using an electron beam. Once the reticle pattern has been written on the reticle blank  18 , the reticle blank  18  is developed and any exposed resist  16  is removed. Finally, the radiation blocking layer  14  is etched where the resist  16  has been removed, and the rest of the resist  16  is stripped. Therefore, the densely patterned subarray features  24  defining the subarray area  20 , the sub-resolution pattern  28  in the open areas defining the periphery area  22 , and the features  26  in the periphery area  22  are formed from at least one radiation blocking layer  14  on a transparent reticle substrate  12 .  
         [0038]    Referring to FIGS. 1 c  and  3 , the reticle pattern comprising at least one subarray area  20  and at least one periphery area  22  having a transmissive block fill  29  may be formed using any suitable method. Generally, the desired reticle pattern is written onto the reticle blank  10 . The reticle pattern may be written onto the reticle blank  10  using any suitable method. For example the reticle pattern may be written onto the reticle blank using an electron beam. The pattern may include block fill areas in the periphery  22  or the pattern may written to expose areas of the reticle substrate  12  in the periphery  22 .  
         [0039]    Once the reticle pattern has been written on the reticle blank  18 , the reticle blank  18  is developed and any exposed resist  16  is removed. Finally, the radiation blocking layer  14  is etched where the resist  16  has been removed, and the rest of the resist  16  is stripped. In the case where the pattern includes block fill areas in the periphery  22 , a subsequent resist layer is formed over the reticle and removed in areas containing the block fill  29 , the block fill  29  is partially etched using any suitable method until the desired transmission or thickness is acheived, and the subsequent resist layer is then removed. In the case where the pattern has exposed areas of the reticle substrate  12  in the periphery, a transmissive radiation blocking layer may be formed over the exposed areas by any suitable method. Therefore, the densely patterned subarray features  24  defining the subarray area  20 , the transmissive block fill  29  in the open areas defining the periphery area  22 , and the features  26  in the periphery area  22  are formed from at least one radiation blocking layer  14  on a transparent reticle substrate  12 .  
         [0040]    Referring to FIGS. 1 b  and  4 , the reticle  18  having a sub-resolution pattern  28  may be used to pattern at least a portion of a radiation sensitive layer  38 . Generally, the reticle  18  is positioned over at least a portion of a radiation sensitive layer  38 . The radiation sensitive layer  38  is exposed with the reticle  18 , and a pattern  40  is formed on the radiation sensitive layer  38 . Generally, a radiation source  30  that produces patterning radiation is used to expose radiation sensitive layer  38  with the reticle  18 , and the radiation source  30  is generally an electromagnetic radiation source. The reticle  18  may be used in conjunction with a lithographic printer, and a condenser  32  and reduction lens  36  may be used during the exposure of the radiation sensitive layer  38  to focus and reduce the reticle pattern onto the radiation sensitive layer  38 . The reticle  18  may be used in a step and repeat system, a step and scan system, or any other suitable system.  
         [0041]    Upon exposing the radiation sensitive layer  38  with the reticle  18 , the pattern  40  on the radiation sensitive layer  38  comprises the densely patterned subarray features  24  defining the subarray area  20  in areas exposed to the subarray area  20 . The radiation sensitive layer  38  is not patterned in areas exposed to the sub-resolution pattern  28  in the periphery area  22 . However, pattern  40  further comprises patterns in areas of the radiation sensitive layer  38  exposed to the feature patterns  26  in the periphery area  22 . The use of the reticle  18  having a sub-resolution pattern  28  may address edge of array effects. The radiation sensitive layer  38  may be a part of a semiconductor substrate. As used herein, the term “semiconductor substrate” is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials.  
         [0042]    Referring to FIGS. 1 c  and  4 , the reticle  18  having a transmissive block fill  29  may be used to pattern at least a portion of a radiation sensitive layer  38 . Generally, the reticle  18  is positioned over at least a portion of a radiation sensitive layer  38 . The radiation sensitive layer  38  is exposed with the reticle  18 , and a pattern  40  is formed on the radiation sensitive layer  38 . A radiation source  30  that produces patterning radiation is used to expose radiation sensitive layer  38  with the reticle  18 , and the radiation source  30  is generally an electromagnetic radiation source. The reticle  18  may be used in conjunction with a lithographic printer, and a condenser  32  and reduction lens  36  may be used during the exposure of the radiation sensitive layer  38  to focus and reduce the reticle pattern onto the radiation sensitive layer  38 . The reticle  18  may be used in a step and repeat system, a step and scan system, or any other suitable system.  
         [0043]    Upon exposing the radiation sensitive layer  38  with the reticle  18 , the pattern  40  on the radiation sensitive layer  38  comprises the densely patterned subarray features  24  defining the subarray area  20  in areas exposed to the subarray area  20 . The radiation sensitive layer  38  is not patterned in areas exposed to the transmissive block fill  29  in the periphery area  22 . However, pattern  40  further comprises patterns in areas of the radiation sensitive layer  38  exposed to the feature patterns  26  in the periphery area  22 . The use of the reticle  18  having a transmissive block fill  29  may reduce edge of array effects. The radiation sensitive layer  38  may be a part of a semiconductor substrate.  
         [0044]    It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention, which is not to be considered limited to what is described in the specification. It shall be observed that the present invention can be practiced in conjunction with a variety of integrated circuit fabrication and reticle fabrication techniques, including those techniques currently used in the art and any other suitable, yet to be developed techniques. Additionally, it is contemplated that the reticle designs disclosed herein are not limited to applications where edge of array effects are addressed.