Abstract:
An anti-electron reflector is constructed to include a substrate, an electron resistant layer formed on a top side of the substrate, and an anti-electron reflective layer provided in between the substrate and the electron resistant layer for enabling an electron beam to pass to the inside of the substrate in an incident direction and minimizing the amount of electrons of the electron beam that return to the electron resistant layer after reflection by the substrate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an anti-electron reflector and, more particularly, to an anti-electron reflector for use in electron-beam lithography to improve electron-beam lithography precision.  
           [0003]    2. Description of Related Art  
           [0004]    When incident electrons penetrate an electron resistant layer to collide with substrate atoms, a number of incident electrons return to the substrate surface through a relatively greater angle of scattering, thereby causing the electron resistant layer around the exposed area to receive an extra exposure dosage that affects the profile and depth of the surrounding exposure pattern. This phenomenon is called the electron beam proximity effect.  
           [0005]    In detail, as shown in FIG. 1, when an incident electron beam  1  strikes the electron resistant layer  3 , a number of incident electrons collide with atoms of the electron resistant layer  3 . Because the arrangement of the electron resistant layer is sparse and the atomic spacing of the electron resistant layer is broad, a number of incident electrons falls at a relatively smaller forward scattering angle θ f , thereby causing the diameter of the incident electron beam  1  to be increased after passing through the electron resistant layer. When the incident electron beam  1  passes the electron resistant layer  3  to the substrate  4 , a number of incident electrons falls at a relatively greater backward scattering angle θ b  due to relatively smaller atomic spacing of the substrate  4 , and a number of incident electrons may return to the electron resistant layer  3 . As illustrated in FIG. 1, the incident electron beam  1  originally has an incident diameter d, however the diameter of the reflected electron beam  2  becomes D after forward scattering and backward scattering, which is much greater than incident diameter d. This condition directly affects the dimensions of the pattern of the surrounding exposure. Due to different electron beam proximity effects, it is difficult to control the accuracy of pattern dimensions.  
           [0006]    When proceeding with photo mask fabrication by an E-beam writer according to conventional methods, increasing electron beam accelerating voltage and changing exposure resistant layers and substrate material so as to reduce the formation of backward scattering electrons and lower the effect of backward scattering electrons is a priority. There are known conventional methods using an E-beam recorder to fabricate compact disk molds. These methods are used to improve electron beam proximity effect by increasing electron beam accelerating voltage. However, since such accelerating voltage must be as high as 100 KV, much higher than the accelerating voltage a regular 30˜40 KV electron gun can provide, it results in high E-beam recorder costs. Therefore, these methods are still not perfect. Further, increasing electron beam accelerating voltage to 100 KV will lower the sensitivity of the electron resistant layer to electrons, resulting in low E-beam recorder productivity levels.  
           [0007]    Therefore, it is desirable to provide an anti-electron reflector that improves electron beam proximity effect.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention has been accomplished under the circumstances in view.  
           [0009]    The main object of the present invention is to provide an anti-electron reflector that improves problems resulting from electron beam proximity effects during electron beam lithography.  
           [0010]    Another object of the present invention is to provide an anti-electron reflector that improves the problem of electron beam proximity effects, and greatly reduces equipment cost and increases productivity.  
           [0011]    To achieve this and other objects of the present invention, the anti-electron reflector comprises a substrate, an electron resistant layer formed on a top side of the substrate, and at least one anti-electron reflective layer provided in between the substrate and the electron resistant layer. Each of said at least one anti-electron reflective layer comprises a composition having an atomic number smaller than that of said substrate, and atoms in said at least one anti-electron reflective layer have an arrangement sparser than that of atoms in said substrate, i.e., atoms in said at least one anti-electron reflective layer have an atomic spacing greater than that of said substrate so that the amount of backward scattering electrons is minimized when the electron beam strikes the substrate.  
           [0012]    Further, in the anti-electron reflective layer, the atomic spacing in the incident direction of the electron beam is greater than that in the reflective direction, i.e., at least one anti-electron reflective layer is directional so that the arrangement of atoms in the electron beam incident direction is sparser to facilitate the incidence of the electron beam; the arrangement of atoms in the oblique reflective direction is relatively denser to harden the return of reflected electrons to the electron resistant layer.  
           [0013]    Each anti-electron reflective layer can be formed on the substrate by deposition coating, for example, sputtering deposition, evaporation deposition, or any other equivalent deposition method. In one embodiment of the present invention, two anti-electron reflective layers are provided wherein the first anti-electron reflective layer is composed of carbon or aluminum while neighboring the substrate; the second anti-electron reflective layer is composed of silicon dioxide or silicon nitride while neighboring the electron resistant layer.  
           [0014]    Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic drawing showing an electron beam proximity effect.  
         [0016]    [0016]FIG. 2 a  is a sectional view of the first embodiment of the present invention.  
         [0017]    [0017]FIG. 2 b  is a microscopic view of the first embodiment of the present invention.  
         [0018]    [0018]FIG. 3 a  is a schematic drawing of the second embodiment of the present invention.  
         [0019]    [0019]FIG. 3 b  is a schematic drawing of the third embodiment of the present invention.  
         [0020]    [0020]FIG. 4 is a schematic drawing of the fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    With reference to FIGS. 2 a  and  2   b , the first embodiment of the present invention comprises a directional anti-electron reflective layer  15  provided in between an electron resistant layer  13  and a silicon substrate  14 . As illustrated in FIG. 2 a , when an incident electron beam  11  strikes the substrate directly vertical, the so-called “directional” anti-electron reflective layer  15  has an atomic spacing a in the direction of the incident electron beam  11 . When the incident electron beam strikes substrate atoms and causes a reflection, two different electron backward scattering paths might be happened, greater backward scattering angle, electron beam  121 , and small backward scattering angle, electron beam  122  might be produced. Because the backward scattering electron beam  121  does not affect the shape of exposure significantly and its return direction is close or almost equal to the direction of the anti-electron reflective layer, the directional anti-electron reflective layer does not block the reflection of the incident electron beam onto the electron resistant layer.  
         [0022]    Referring to FIG. 2 b  again, assume the angle θ b  of the backward scattering electron beam  122  is 45°, at this time the atomic spacing of the directional anti-electron reflective layer in this direction is relatively smaller, or about  
             2      a       2     .                         
 
         [0023]    This smaller atomic spacing limits the angle of backward scattering, thereby causing the forward path for backward scattering electrons  122  to be narrowed and the possibility of the return of backward scattering electrons to the electron resistant layer to be reduced, and therefore unnecessary exposure is eliminated and, the accuracy of electron beam exposure is greatly improved. The angle θ b  of the backward scattering electron beam  122  is an assumed angle for explanation only but not a fixed value.  
         [0024]    The material of the substrate can be metal, glass, or any manufacturing material using electron beams as an exposure light source. According to this embodiment, the silicon substrate is used to make a compact disk molds.  
         [0025]    [0025]FIG. 3 a  is a schematic drawing of the second embodiment of the present invention. According to this embodiment, the atomic number of the composition of the anti-electron reflective layer is smaller than that of the composition of the silicon substrate. Therefore, the atomic radius of the composition of the anti-electron reflective layer is relatively smaller. As illustrated, under the same arrangement of atoms, the atomic spacing is relatively greater if the atomic number is relatively smaller. Therefore, a relatively smaller amount of backward scattering electrons is produced when incident electrons strike the anti-electron reflective layer. When incident electrons pass the anti-electron reflective layer to strike the substrate, , a lesser amount of backward scattering electrons is allowed to return to the electron resistant layer due to the blocking effect of the anti-electron reflective layer.  
         [0026]    According to this embodiment, the anti-electron reflective layer is composed of atomic number 6 carbon or atomic number 13 aluminum that is smaller than the atomic number 14 silicon.  
         [0027]    The material for the substrate can be metal, glass, or any of a variety of manufacturing materials using electron beams as the exposure light source. According to this embodiment, the silicon substrate is used to make compact disk molds.  
         [0028]    [0028]FIG. 3 b  is a schematic drawing of the third embodiment of the present invention. According to this embodiment, an anti-electron beam reflective layer  35  is provided in between an electron resistant layer  33  and a silicon substrate  34 . As illustrated, the arrangement of atoms of the composition of the anti-electron reflective layer is more sparse than the arrangement of the atoms of the composition of the silicon substrate, i.e., the atomic spacing of the composition of the anti-electron reflective layer is relatively greater, therefore only a small amount of backward scattering atoms is produced when an incident electron beam strikes the anti-electron reflective layer. When incident electrons pass the anti-electron reflective layer to strike the substrate, a greater amount of backward scattering electrons are produced, however due to the blocking effect of the anti-electron reflective layer, the amount of backward scattering atoms capable of returning to the electron resistant layer is greatly reduced.  
         [0029]    According to this embodiment, the anti-electron reflective layer is composed of silicon dioxide or silicon nitride.  
         [0030]    The material for the substrate can be metal, glass, or any of a variety of manufacturing materials using an electron beam as the exposure light source. According to this embodiment, the silicon substrate is used to make a master compact disk.  
         [0031]    [0031]FIG. 4 is a schematic drawing of the fourth embodiment of the present invention. According to this embodiment, two anti-electron reflective layers  451  and  452  are provided in between an electron resistant layer  43  and a silicon substrate  44 . One anti-electron beam reflective layer  451  is a directional anti-electron resistant layer similar to the aforesaid first embodiment, which neighbors the electron resistant layer  43 . The other anti-electron reflective layer  452 , similar to the aforesaid second embodiment and third embodiment, has a relatively greater atomic spacing and, neighbors the silicon substrate  44 . As to the exposure pattern by the electron beam, backward scattering electrons vertical or approximately vertical to the electron resistant layer are acceptable. What should be prohibited are backward scattering electrons in a particular angle. Therefore, the first layer of the directional anti-electron reflective layer  461  does not affect the forwarding of electrons in the incident direction and the loose atomic spacing in the second layer of the anti-electron reflective layer  452  reduces the amount of backward scattering electrons, achieving the first effect of this fourth embodiment; the directional anti-electron reflective layer limits the scattering angle of backward scattering electrons when backward scattering electrons return to the first layer of the anti-electron reflective layer, achieving the second effect of this fourth embodiment. By means of the aforesaid two effects, the amount of backward scattering electrons returning to the electron resistant layer is minimized and its distribution is limited.  
         [0032]    The material for the substrate can be metal, glass, or any of a variety of manufacturing materials using an electron beam as an exposure light source. According to this embodiment, the silicon substrate is used to make compact disk molds.  
         [0033]    A prototype of the anti-electron reflector has been constructed with the features of FIGS.  2 ˜ 4 . The anti-electron reflector functions smoothly to provide all of the features discussed earlier.  
         [0034]    Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.