Abstract:
Reticles having reticle patterns suitable for reducing edge of array effects are provided. The reticle patterns may have transmission patterns etched 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.

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]    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  
         [0005]    The present invention relates to reticles and methods of forming and using reticles. In accordance with one embodiment of the present invention, a reticle is provided. The reticle comprises a reticle substrate having a reticle pattern, and the reticle pattern comprises at least one subarray area and at least one periphery area. The at least one subarray area is defined by densely patterned subarray features, and the at least one periphery area is defined by open areas that lie outside the at least one subarray area. The open areas defining the at least one periphery area have a transmission pattern etched therein.  
           [0006]    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 reticle substrate having a reticle pattern, and the reticle pattern comprises at least one subarray area and at least one periphery area. The at least one subarray area is defined by densely patterned subarray features, and the at least one periphery area is defined by open areas that lie outside the at least one subarray area. The open areas defining the at least one periphery area have a transmission pattern etched therein.  
           [0007]    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; patterning the reticle blank to form a reticle pattern, wherein the reticle pattern comprises at least one subarray area and at least one periphery area, the at least one subarray areas is defined by densely patterned subarray features, and the at least one periphery area is defined by open areas that lie outside the at least one subarray area; and etching said open areas defining said at least one periphery area to form a transmission pattern.  
           [0008]    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 transmission 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 transmission pattern in the at least one periphery area. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic illustration of a portion of a reticle in accordance with the present invention.  
         [0010]    [0010]FIG. 2 is a cross-section of a portion of a reticle in accordance with the present invention.  
         [0011]    [0011]FIG. 3 is a schematic illustration of one transmission pattern in accordance with the present invention.  
         [0012]    [0012]FIG. 4 is an illustration of a portion of a reticle blank.  
         [0013]    [0013]FIG. 5 is a schematic illustration of a reticle being used to pattern a radiation sensitive layer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    The present invention provides reticles having reticle patterns that reduce edge of array effects and methods of forming and using the same.  
         [0015]    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.  
         [0016]    Referring to FIG. 1, 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. 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 . For example, the densely patterned subarray features  24  may have a space to feature ratio of about 1:1 to about 4:1. The densely patterned subarray features  24  may be feature patterns for capacitors or transistors or other suitable feature patterns that generally form portions of a memory array.  
         [0017]    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 and because the open areas generally do not contain other densely patterned feature patterns formed near the subarray area  20 . 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 generally separated from the densely patterned subarray features  24 . The feature patterns  26  may include, but are not limited to, feature patterns for sense amplifiers, row decoders, and row drivers.  
         [0018]    The open areas defining the periphery area  22  may contain a transmission pattern  28  etched therein. The presence of the transmission pattern  28  on the reticle  18  may address edge of array effects that may occur in reticle patterns having densely patterned subarray areas and less densely patterned periphery areas. For example, the difference between the critical dimension of subarray features  24  patterned on a radiation sensitive layer near the center of the at least one subarray area  20  and the critical dimension of subarray features  24  patterned on a radiation sensitive layer near the edge of the at least one subarray area  20  is addressed by the presence of the transmission pattern  28 . For example, the presence of the transmission pattern  28  may address the amount of stray light that can cause bulk exposure from less dense areas. Mid-range flare of stepper tools may be addressed by the presence of the transmission pattern  28  on the reticle  18 .  
         [0019]    Referring to FIGS. 1 and 2, the transmission pattern  28  is etched into the reticle substrate  12  in the open areas defining the periphery area  22 . The transmission pattern is generally formed about 4 to about 40 μm from the subarray area  20 , and the transmission pattern is more typically formed about 4 μm from the subarray area. The transmission pattern  28  may be a line pattern as shown in FIG. 1. The line pattern  28  is generally formed by etching a series of trenches  29  in the reticle substrate  12 . The trenches  29  are generally etched to a have a depth between about λ(4(n−1)) to about λ(6(n−1)) where λ is the wavelength of a given patterning radiation in angstroms and n is the index of refraction of the reticle substrate  12 . The depth of the trenches  29  is generally chosen to provide a desired phase shift of patterning radiation that passes through the transmission pattern. The patterning radiation is generally phase shifted less than about 180° upon passing through the transmission pattern  28 , and the patterning radiation is more generally phase shifted about 60° to about 120°. Controlling the phase shift of the patterning radiation allows the intensity of the patterning radiation at the imaging point, such as a radiation sensitive layer, to be effectively reduced after passing through the transmission pattern due to destructive interference. 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.  
         [0020]    The trenches  29  may be formed to have a space to line ratio of between about 1:1 to about 4:1. The space to line ratio is chosen in conjunction with the trench  29  depth to provide a desired intensity of patterning radiation at the imaging point for given optical settings. The transmission pattern  28  may also be an alternating box pattern as shown in FIG. 3 or any other suitable pattern. If the transmission pattern  28  comprises another suitable pattern, the pattern parameters are chosen to provide a desired intensity of patterning radiation at the imaging point.  
         [0021]    The trasmission pattern is generally formed such that the intensity of the patterning radiation incident on a given imaging point is less than the intensity of patterning radiation incident on the transmission pattern  28  due to destructive interference caused by the patterning radiation being phase shifted after passing through the transmission pattern  28 . The transmission pattern  28  may be formed such that the intensity of patterning radiation at a given imaging point after being transmitted through the transmission pattern  28  is approximately equal to the intensity of patterning radiation at a given imaging point after being transmitted through the subarray area  20 . This will reduce the amount of stray light from the periphery area  22  because the background radiation is reduced. For example, the transmission pattern  28  may be formed such that about intensity of the patterning radiation at the imaging point is about 25 to 50% of the intensity of the patterning radiation incident on the transmission pattern  28 , and the transmission pattern  28  is more typically formed such that the intensity of the patterning radiation at the imaging point is about 35% of the intensity of patterning radiation incident on the transmission pattern  28 .  
         [0022]    Referring to FIGS. 1 and 2, the transmission pattern  28  is generally etched such that the transmission pattern  28  comprises a non-printable pattern. As used herein, the term “non-printable pattern” is defined to mean a pattern that will not cause a radiation sensitive layer to be printed upon exposing the non-printable pattern to patterning radiation. Generally, the depth and space to line ratio of the transmission pattern  28  is chosen to provide a phase shift that will cause destructive interference and ensure that the transmission pattern  28  is non-printable for a given set of optical settings. For example, the trenches  29  of the transmission pattern  28  may be formed a distance apart that is at or near the wavelength of the patterning radiation to which the reticle  18  is exposed. Alternatively, the trenches  29  of the transmission pattern  28  may be formed a distance apart that is below the wavelength the patterning radiation to which the reticle  18  is exposed. For example when the transmission pattern  28  comprises a series of alternating trenches  29 , the transmission pattern  28  creates an alternating phase filter wherein patterning radiation is phase shifted less than about 180° upon passing through the alternating phase filter. The phase shift causes destructive interference, and the transmission pattern does not print. Thus, the transmission pattern  28  is highly tunable and not limited to small pattern sizes.  
         [0023]    [0023]FIG. 4 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 silicide, 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.  
         [0024]    Referring to FIGS. 1 and 4, the reticle pattern comprising at least one subarray area  20  and at least one periphery area  22  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 for a positive resist or any unexposed resist  16  is removed for a negative resist. The radiation blocking layer  14  is etched where the resist  16  has been removed, and the rest of the resist  16  is stripped. Generally, there will be no pattern formed in the open areas defining the periphery area  22  and the radiation blocking layer  14  will be removed in those areas.  
         [0025]    Subsequently, the transmission pattern  28  is patterned onto another resist layer and the pattern is developed. The reticle substrate  12  is then etched to form the transmission pattern  28  on the reticle  18 . For example, the reticle substrate  12  may be dry etched to form the transmission pattern. The remaining resist is then removed. Therefore, the densely patterned subarray features  24  defining the subarray area  20  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 . The transmission pattern  28  is formed from etching the reticle substrate  12  in areas that have been exposed.  
         [0026]    Referring to FIGS. 1 and 5, the reticle  18  having a transmission 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 . 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. 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  may be an electromagnetic radiation source. The radiation source  30  may be an on or off axis radiation source, and the radiation source  30  is more generally an off axis radiation source.  
         [0027]    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.  
         [0028]    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 transmission 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 .  
         [0029]    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.