Abstract:
A reticle includes a reticle body having a first surface, a pattern disposed on the first surface of the reticle body, and at least a protection layer disposed on the first surface of the reticle body. The protection layer is in contact with the first surface of the reticle body.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a reticle having a protection layer thereon, and more particularly, to a reticle that has a passivation layer disposed thereon to isolate the pattern of the reticle from the environment.  
         [0003]     2. Description of the Prior Art  
         [0004]     In a photolithography process, a reticle (photomask) plays an important role. The reticle, like a mold in a printing process, has a predetermined pattern thereon, and the pattern can be transferred to a photoresist layer by an exposure process. Therefore, the pattern of the reticle is critical to the accuracy of pattern transfer. If particles (referred to as the haze defect) appear in the reticle, the transferred pattern will be influenced.  
         [0005]     Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  illustrates a schematic view of a conventional reticle  10 , and  FIG. 2  illustrates the conventional reticle  10  during an exposure process. As shown in  FIG. 1  and  FIG. 2 , the conventional reticle  10  includes a reticle body  12 , a pattern  14  disposed on the surface of the reticle body  12 , a frame  16  disposed in the reticle body  12 , and a pellicle  18  mounted on the frame  16 . The reticle body  12  is made of transparent materials, e.g. glass or quartz, and the pattern  14  is made of opaque materials, e.g. chromium, to shield the exposure light. In the exposure process, the exposure light, which is not shielded by the pattern  14 , passes through to a lens  30  to be focused on a wafer  40 . Consequently, the pattern  14  disposed on the reticle body  12  can be transferred to the wafer  40 . The pellicle  18  is mounted on the reticle body  12  with the frame  16 , and the purpose of the pellicle  18  is to keep away particles that may influence the accuracy of pattern transfer. As shown in  FIG. 2 , unexpected external particles  20  may appear during the exposure process. With the pellicle  18 , the particles  20  do not influence the accuracy of pattern transfer since the exposure light shielded by the particles adhered to the pellicle  18  does not focus on the wafer.  
         [0006]     The pellicle  18  may be able to ensure the accuracy of pattern transfer if the particles  20  appear on the surface of the pellicle  18 . However, since the pellicle  18  does not completely surround the pattern  14 , particles  20  may still appear on the surface of the reticle body  12  and the pattern  14 . This is commonly referred to as the haze defect. Please refer to  FIG. 3 .  FIG. 3  illustrates a schematic view of the reticle  10  when particles  20  appear on the reticle body  12 . As shown in  FIG. 3 , the reticle  10  needs to be cleaned regularly. The clean solution normally contains sulfuric acid, and the sulfuric acid may react with ammonia that commonly exists in the reaction chamber. Consequently, ammonium sulfate particles  20  will appear on the surface of the pattern  14  and the reticle body  12 . When particles  20  exist on the surface of the reticle body  12 , the accuracy of pattern transfer will be reduced.  
       SUMMARY OF THE INVENTION  
       [0007]     It is therefore one of the objectives of the claimed invention to reduce the haze defect in reticles.  
         [0008]     According to the claimed invention, a reticle is disclosed. The reticle includes a reticle body having a first surface, a pattern disposed on the first surface of the reticle body, and at least a protection layer disposed on the first surface of the reticle body. The protection layer covers the first surface of the reticle body, and has high transparency and refraction rate for any wavelength of exposure light. The refraction rate of the protection layer should be higher than that of air.  
         [0009]     Since the protection layer covers the surface of the reticle body, the haze defect due to particles adhered to the surface of the reticle body is reduced. In addition, the protection layer is also able to protect the pattern from being damaged by external forces.  
         [0010]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  illustrates a schematic view of a conventional reticle.  
         [0012]      FIG. 2  illustrates the conventional reticle during an exposure process.  
         [0013]      FIG. 3  illustrate a schematic view of the reticle when particles appear on the reticle body.  
         [0014]      FIG. 4  illustrates a schematic view of a reticle according a first preferred embodiment of the present invention.  
         [0015]      FIG. 5  illustrates the chemical structure of ring opening metathesis polymer (ROMP).  
         [0016]      FIG. 6  illustrates a schematic view of a reticle according a second preferred embodiment of the present invention.  
         [0017]      FIG. 7  illustrates a schematic view of a reticle according a third preferred embodiment of the present invention.  
         [0018]      FIG. 8  illustrates a schematic view of a reticle according a fourth preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     Please refer to  FIG. 4 .  FIG. 4  illustrates a schematic view of a reticle  50  according a first preferred embodiment of the present invention. As shown in  FIG. 4 , the reticle  50  of the present invention includes a reticle body  52 , a pattern  54  disposed on a first surface of the reticle body  52 , and a protection layer  56  disposed on the first surface of the reticle body  52 . The reticle body  52  is made of transparent materials, e.g. glass or quartz, and the pattern  54  is made of opaque materials, e.g. chromium, to shield the exposure light. The protection layer  56  disposed on the first surface of the reticle body  12  is to reduce the haze defect that influences the accuracy of pattern transfer. In this embodiment, since the protection layer  56  further covers the pattern  54 , it also works to isolate the pattern  54  and the reticle body  52  so that the reticle  50  is well protected. By virtue of the protection layer  56 , the pattern  54  can be correctly transferred to the photoresist layer disposed on the wafer.  
         [0020]     The protection layer  56  is penetrable by light of any wavelength, particularly by exposure light, so that the exposure light is not shielded. Generally, exposure light is UV light with a wavelength of 248 nm, 193 nm, or 157 nm, EUV light, or X-rays. The light transmittance for these types of exposure light is preferably larger than 90%, and the refraction rate of the protection layer  56  should be higher than the refraction rate of air. The material of the protection layer  56  can be any suitable transparent material that allows the exposure light to pass. The material of the protection layer  56  can be an organic material, an inorganic material, a polymer, a copolymer, a hybrid polymer, or any combination of the aforementioned materials. In this embodiment, the material of the protection layer  56  is ring opening metathesis polymer (ROMP). Please refer to  FIG. 5 .  FIG. 5  illustrates the chemical structure of ring opening metathesis polymer (ROMP). Since ROMP is penetrable by light of any wavelength, the exposure light is not shielded.  
         [0021]     It is to be noted that the material of the protection layer  56  can also be cyclo-olefin, methacrylate, or other suitable materials. In addition, the glass transition temperature of the protection layer  56  is preferably larger than 90 degree Celsius so that the protection layer  56  can remain stable during the exposure process. For the same reason, the molecular weight of the protection layer  56  is preferably larger than 3000 if a polymer is adopted. The protection layer  56  can also be a conductive material so as to provide electrostatic discharge protection. In addition, in this embodiment the protection layer  56  has a smooth surface, and can be formed by depositing techniques, coating techniques, or any suitable thin-film techniques.  
         [0022]     Please refer to  FIG. 6 .  FIG. 6  illustrates a schematic view of a reticle  60  according a second preferred embodiment of the present invention. As shown in  FIG. 6 , the reticle  60  of the present invention includes a reticle body  62 , a pattern  64  disposed on a first surface of the reticle body  62 , and a protection layer  66  disposed on the first surface of the reticle body  62 . In contrast with the first preferred embodiment, the protection layer  66  in this embodiment only covers the first surface of the reticle body  62 .  
         [0023]     Please refer to  FIG. 7 .  FIG. 7  illustrates a schematic view of a reticle  70  according a third preferred embodiment of the present invention. As shown in  FIG. 7 , the reticle  70  of the present invention includes a reticle body  72 , a pattern  74  disposed on a first surface of the reticle body  72 , and a protection layer  76  disposed on the first surface of the reticle body  72 . In this embodiment, the protection layer  76  covers both the first surface of the reticle body  72  and the pattern  74 , but the protection layer  76  has a bumpy surface.  
         [0024]     Please refer to  FIG. 8 .  FIG. 8  illustrates a schematic view of a reticle  80  according a fourth preferred embodiment of the present invention. As shown in  FIG. 8 , the reticle  80  of the present invention includes a reticle body  82 , a pattern  84  disposed on a first surface of the reticle body  82 , and a protection layer  86  disposed on the first surface of the reticle body  82 . In this embodiment, the reticle  80  further includes a frame  88  mounted on the reticle body  82 , and a pellicle  90  mounted on the frame  88 . In this embodiment, the reticle  80  includes both the protection layer  86  and the pellicle  90 , and the protection layer  86  can have any form disclosed in the aforementioned embodiments.  
         [0025]     By virtue of the protection layer being directly disposed on the reticle body, exposure light shielded by the haze defect will no longer focus on the photoresist layer. Consequently, the accuracy of pattern transfer is ensured.  
         [0026]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.