Abstract:
A phase shifting mask capable of decreasing the optical proximity effect comprises a substrate and at least one phase shifting pattern positioned on the substrate, wherein the phase shifting pattern surrounds at least one optical correction pattern. Preferably, the optical correction pattern is an aperture exposing the substrate, and positioned on an intersection or a corner of the phase shifting pattern. The method for preparing the phase shifting mask comprises steps of forming a polymer layer on a substrate, illuminating a first predetermined region of the polymer layer by an electron beam to change the molecular structure of the polymer layer in the first predetermined region, which surrounds at least one second predetermined region. Subsequently, the polymer layer outside the first predetermined region is removed to form a phase shifting pattern, while the second predetermined region forms an optical correction pattern.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    (A) Field of the Invention 
         [0002]    The present invention relates to a phase shifting mask and method for preparing semiconductor devices using the same, and more particularly, to a chromeless phase shifting mask and method for preparing semiconductor devices using the same. 
         [0003]    (B) Description of the Related Art 
         [0004]    As sizes of critical dimensions (CD) of desired patterns are reduced and approach the resolution limit of lithography equipment, the consistency between the mask pattern and the actual layout pattern developed in the photoresist on the silicon wafer is significantly reduced. Proximity effect in a lithographic process can arise during exposing, photoresist pattern formation and subsequent pattern transferring steps such as etching. To solve the proximity effect, an opaque chrome pattern that reduces this effect is added to certain regions having more serious proximity effects, such as corners of mask patterns. 
         [0005]      FIG. 1(   a ) illustrates a chromeless phase shifting mask  40  according to the prior art, and  FIG. 1(   b ) shows a simulated optical intensity distribution on a portion of the chromeless phase shifting mask  40  (i.e., the dash-lined region) using an optical simulation software called SOLID-E. As shown in  FIG. 1(   b ), there is a discontinuity at the intersection of the line-shaped pattern  42  of the chromeless phase shifting mask  40 , which is not the same as the desired pattern with continuous line-shaped pattern  42 . 
         [0006]      FIG. 2(   a ) illustrates a partial chromeless phase shifting mask  40 ′ according the prior art, and  FIG. 2(   b ) shows a simulated optical intensity distribution on a portion of the partial chromeless phase shifting mask  40 ′ using the SOLID-E. In comparison with the chromeless phase shifting mask  40  in  FIG. 1(   b ), the partial chromeless phase shifting mask  40 ′ in  FIG. 2(   a ) has an auxiliary pattern  44  made of chrome material at the intersection of the line-shaped pattern  42 . The shading effect of the auxiliary pattern  44  can avoid the occurrence of the discontinuity at the intersection of the line-shaped pattern  42 , as shown in  FIG. 2(   b ). 
         [0007]    The preparation of the partial chromeless phase shifting mask  40 ′ requires performing the lithographic process twice for patterning photoresist layers used to define positions of the phase shifting patterns such as the line-shaped pattern  44  and the position of some auxiliary patterns such as the auxiliary pattern  44 , respectively. However, performing the lithographic process twice not only increases the alignment control difficulty, but also limits the throughput of the mask. 
       SUMMARY OF THE INVENTION 
       [0008]    One aspect of the present invention provides a phase shifting mask capable of reducing the optical proximity effect. 
         [0009]    A phase shifting mask according to this aspect of the present invention comprises a substrate, at least one phase shifting pattern positioned on the substrate and at least one optical correction pattern being a transparent region of the substrate, wherein the phase shifting pattern surrounds the optical correction pattern. Preferably, the optical correction pattern is an aperture exposing the substrate, and the phase shifting pattern has a corner or an intersection and the optical correction pattern is positioned at the corner or at the intersection. 
         [0010]    Another aspect of the present invention provides a method for preparing a semiconductor device using a chromeless phase shifting mask capable of reducing the proximity effect. The chromeless phase shifting mask comprises a phase shifting pattern including polymer material, and the preparation of the chromeless phase shifting mask does not need to perform the lithographic process or the etching process for patterning the opaque chrome pattern, solving the problems of mask inspection, phase error and alignment originating from performing the lithographic process twice and etching process at least twice. 
         [0011]    In comparison with the prior art using the auxiliary pattern made of chrome to reduce the optical proximity effect, the chromeless phase shifting mask in accordance with one embodiment of the present invention comprises an optical correction pattern in phase shifting patterns to reduce the optical proximity effect. Further, the preparation of the conventional chromeless phase shifting mask needs to perform the lithographic process twice and etching process, while the preparation of the phase shifting mask according to one embodiment of the present invention does not to perform the lithographic process or etching process such that the throughput of the mask can be increased. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The objectives and advantages of the present invention will become apparent upon reading the following description and upon reference to the accompanying drawings in which: 
           [0013]      FIG. 1(   a ) illustrates a chromeless phase shifting mask according to the prior art; 
           [0014]      FIG. 1(   b ) shows a simulated optical intensity distribution on a portion of the chromeless phase shifting mask using an optical simulation software called SOLID-E according to the prior art; 
           [0015]      FIG. 2(   a ) illustrates a partial chromeless phase shifting mask according to the prior art; 
           [0016]      FIG. 2(   b ) shows a simulated optical intensity distribution on a portion of the partial chromeless phase shifting mask using the SOLID-E according to the prior art; 
           [0017]      FIG. 3  to  FIG. 5  illustrates a chromeless phase shifting mask according to one embodiment of the present invention; 
           [0018]      FIG. 6  shown a simulated optical intensity distribution on a portion of the chromeless phase shifting mask using the SOLID-E according to one embodiment of the present invention; 
           [0019]      FIG. 7  is a diagram showing the variation of the reflection index of the phase shifting pattern under different wavelengths according to one embodiment the present invention; 
           [0020]      FIG. 8  is a diagram showing the variation of the extinction coefficient of the phase shifting pattern under different wavelengths according to one embodiment the present invention; 
           [0021]      FIG. 9  is a schematic diagram showing the application of the phase shifting mask to pattern the shapes of semiconductor devices on a semiconductor substrate according to one embodiment of the present invention; 
           [0022]      FIG. 10(   a ) illustrates a chromeless phase shifting mask  90  according to the prior art; 
           [0023]      FIG. 10(   b ) shows simulated optical intensity distribution of the chromeless phase shifting mask using the SOLID-E according to the prior art; 
           [0024]      FIG. 11(   a ) illustrates a phase shifting mask according to the prior art; 
           [0025]      FIG. 11(   b ) shows simulated optical intensity distribution of the phase shifting mask using the SOLID-E according to the prior art; 
           [0026]      FIG. 12(   a ) illustrates a chromeless phase shifting mask according to another embodiment of the present invention; and 
           [0027]      FIG. 12(   b ) shows a simulated optical intensity distribution of the chromeless phase shifting mask using the SOLID-E according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]      FIG. 3  to  FIG. 5  illustrate a chromeless phase shifting mask  50  according to one embodiment of the present invention, wherein  FIG. 4  and  FIG. 5  are cross-sectional diagrams along a cross-sectional line A-A in  FIG. 3 . A polymer layer  62  is formed on a substrate  52  by a spin-coating process, and energy is then selectively transferred to the polymer layer  62  in a first region  66 , such as irradiating an electron beam  64  to the first region  66 , to change the chemical properties of the polymer layer  62  in the first region  66 , i.e., to generate cross-linking of the polymer layer  62  in the first region  66 , as shown in  FIG. 4 . Particularly, the irradiation of the electron beam  64  will change the molecular structure of the polymer in the first region  66 . The first region  66  surrounds a second region  68  and the electron beam  64  does not irradiate on the second region such that the molecular structure of the polymer layer  62  in the second region  68  substantially remains the same. 
         [0029]    Referring to  FIG. 5 , a developing process is performed to remove a portion of the polymer layer  62  not irradiated by the electron beam  64 , i.e., the polymer layer  62  outside the first region  66 , while the polymer layer  62  inside the first region  66  remains to form a phase shifting pattern  70  on the substrate  52 , as shown in  FIG. 3 , which is a top view of the chromeless phase shifting mask  50 . Particularly, the phase shifting pattern  70  surrounds at least one optical correction pattern  72 , whose position corresponds to the second region  68 . Preferably, the optical correction pattern is an aperture exposing the substrate  52 , i.e., a transparent region, and the refraction index of the phase shifting pattern  70  is different from that of the optical correction pattern  72 . Taking a portion of the substrate  52  not occupied by the phase shifting pattern  70  and the optical correction pattern  72  as a zero-degree region  54 , the optical correction pattern  72  does not contact the zero-degree region  54 , i.e., the peripheral of the optical correction pattern  72  is the phase shifting pattern  70 . In other words, the optical correction pattern  72  is positioned inside the phase shifting pattern  70 , and does not connect to the outer border of the phase shifting pattern  70 . 
         [0030]    In a preferred embodiment, the phase shifting pattern  70  has a corner or an intersection and the optical correction pattern  72  is positioned at the corner or the intersection to avoid the occurrence of the corner rounding or discontinuity of the phase-shifting pattern  70  due to the optical proximity effect. In addition, the optical correction pattern  72  can be optionally positioned on a free end of the phase shifting pattern  70  to avoid the occurrence of line-end rounding or line-end shorting. 
         [0031]    Since the electron beam  64  provides energy for the polymer to change the molecular structure, the solubility to a developer of the polymer irradiated by the electron beam  64  is different from that of the polymer not irradiated by the electron beam  64 . Consequently, the developing process can selectively remove the portion of the polymer layer  62  not irradiated by the electron beam  64 , i.e., removing the portion of the polymer layer  62  outside the first region  66 , while maintaining the other portion of the polymer layer  62  in the first region  66 . In addition, the substrate  52  can be quartz substrate, or a substrate with an interface layer thereon, wherein the interface layer can be a conductive layer made of conductive polymer such as cis-polystyrene and polyaniline, or a glue layer made of hexamethyldisilazane. 
         [0032]    The polymer layer  62  may be made of material including silsesquioxane. For example, the silsesquioxane can be hydrogen silsesquioxane (HSQ), and a developing process using alkaline solution can be performed to remove the polymer layer  62  not irradiated by the electron beam  64 , wherein the alkaline solution is selected from the group consisting of sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution, and tetramethylamomnium hydroxide (TMAH) solution. In addition, the silsesquioxane can be methylsilsesquioxane (MSQ), and a developing process using an alcohol solution such as an ethanol solution is performed to remove the polymer layer  62  not irradiated by the electron beam  64 . Further, the polymer layer  62  can be made of material including hybrid organic siloxane polymer (HOSP), and a developing process using a propyl acetate solution is performed to remove the polymer layer  62  not irradiated by the electron beam  64 . The irradiation of the electron beam  64  will change the molecular structure of the polymer layer  62 , for example, the molecular structure of hydrogen silsesqnioxane will transform into a network structure from a cage-like structure and chemical bonds will be formed between the polymer layer  62  and the quartz substrate  52 . As a result, it is possible to selectively remove the polymer layer  62  outside the first region  66  by a developing process using the alkaline solution. 
         [0033]      FIG. 6  shows a simulated optical intensity distribution on a portion of the chromeless phase shifting mask  50  (i.e., the dashed-line region) using the SOLID-E according to one embodiment of the present invention. In comparison with the chromeless phase shifting mask  40  in  FIG. 1(   a ), the chromeless phase shifting mask  50  in  FIG. 3  has one optical correction pattern  72  at the intersection of the phase shifting pattern  70  including polymer material such that the occurrence of the discontinuity at the intersection of the phase shifting pattern  42  can be avoided, as shown in  FIG. 6 . 
         [0034]      FIG. 7  is a diagram showing the variation of the reflection index of the phase shifting pattern  70  under different wavelengths according to one embodiment the present invention. According to the known phase shifting formula: P=2π(n−1)d/mλ, where, P represents phase shifting angle, n represents the reflection index, d represents the thickness of the phase shifting pattern, m represents an odd number, and λ represents the wavelength of the exposure beam. When the wavelength of the exposure beam is set to be 193 nanometer, the corresponding reflection index is about 1.52, and the thickness of the phase shifting pattern  70  calculated according to the phase shifting formula should be 1828 Å. If the tolerance of the phase shifting angle is set to be 177° to 183°, the thickness of the phase shifting pattern  70  should be 1797 to 1858 nanometers. When the wavelength of the exposure beam is set to be 248 nanometer, the corresponding reflection index is about 1.45, and the thickness of the phase shifting pattern  70  calculated according to the phase shifting formula should be 2713 Å. If the tolerance of the phase shifting angle is set to be 177° to 183°, the thickness of the phase shifting pattern  70  should be 2668 to 2759 nanometers. 
         [0035]      FIG. 8  is a diagram showing the variation of the extinction coefficient of the phase shifting pattern  70  under different wavelengths according to one embodiment the present invention. The extinction coefficient of the phase shifting pattern  70  is substantially zero as the wavelength of the exposure beam is between 190 and 900 nanometer. Therefore, the polymer layer  62  is transparent after the irradiation of the electron beam  64 , which can be used to prepare the phase shifter for the phase shifting mask. 
         [0036]      FIG. 9  is a schematic diagram showing the application of the phase shifting mask  50  to pattern the shapes of semiconductor devices on a semiconductor substrate  80  according to one embodiment of the present invention, wherein the phase shifting mask  50  is a cross-sectional view along a cross-sectional line B-B in  FIG. 3 . The thickness of the phase shifting pattern  70  is designed such that the phase of a transmission beam  76  penetrating through the phase shifting pattern  70  will be lagged by 180 degrees from phase of an exposure beam  74 , while the phase of a transmission beam  78  directly penetrating through the substrate  52  maintains the same as that of the exposure beam  74  without lagging, i.e., 0 degrees. As a result, the transmission beam  76  and the transmission beam  78  will form a destructive interference and the optical intensity of the transmission beam  76  counteracts that of the transmission beam  78 . Consequently, a lithographic process using the phase shifting mask  50  having the phase shifting pattern  70  can form a plurality of corresponding line-shaped patterns  84  on the photoresist layer  82 . The optical correction pattern  72  can be made of material other than that consisting of the polymer layer  62  so long as the difference between the optical correction pattern  72  and the phase shifting pattern  70  can cause phase-lagging between the transmission beams such that the transmission beam  76  can form interference with the transmission beam  78 . 
         [0037]      FIG. 10(   a ) illustrates a chromeless phase shifting mask  90  according to the prior art, and  FIG. 10(   b ) shows simulated optical intensity distribution of the chromeless phase shifting mask  90  using the SOLID-E. The chromeless phase shifting mask  90  comprises a substrate  92  and a rectangular phase shifting pattern  94 . The phase shifting pattern  94  is designed such that the phase of an exposure beam penetrating through the phase shifting pattern  94  will be lagged by 180 degrees, while the phase of the exposure beam penetrating through the substrate  52  maintains the same without lagging, i.e., 0 degrees. However, the simulated optical intensity distribution of the chromeless phase shifting mask  90  does not show the desired rectangle, but a rectangular frame, as shown in  FIG. 10(   b ). 
         [0038]      FIG. 11(   a ) illustrates a phase shifting mask  90 ′ according to the prior art, and  FIG. 11(   b ) shows simulated optical intensity distribution of the phase shifting mask  90 ′ using the SOLID-E. In comparison with the chromeless phase shifting mask  90  in  FIG. 10(   a ), the phase shifting mask  90 ′ further includes an opaque chrome layer  94 ′ on the rectangular phase shifting pattern  94 . The phase shifting mask  90 ′ can provide a rectangular simulated pattern, i.e., the optical intensity distribution, similar to the designed rectangular phase shifting pattern  94 ; however, there is a certain difference in size between simulated pattern and the designed rectangular phase shifting pattern  94 , as shown in  FIG. 11(   b ). 
         [0039]      FIG. 12(   a ) illustrates a chromeless phase shifting mask  100  according to another embodiment of the present invention, and  FIG. 12(   b ) shows a simulated optical intensity distribution of the chromeless phase shifting mask  100  using the SOLID-E. The chromeless phase shifting mask  100  comprises a substrate  102 , a phase shifting pattern  104  and a plurality of optical correction patterns  106 , wherein the phase shifting pattern  104  surrounds the optical correction pattern  106 . The chromeless phase shifting mask  100  provides a simulated pattern, i.e., the optical intensity distribution, similar to the designed phase shifting pattern  104 , and the border of the simulated pattern substantially aligns with that of the designed phase shifting pattern  104 , i.e., the size of the simulated pattern is substantially the same as that of the designed phase shifting pattern  104 , as shown in  FIG. 12(   b ). 
         [0040]    In comparison with the prior art using the auxiliary pattern made of chrome to reduce the optical proximity effect, the phase shifting mask in accordance with one embodiment of the present invention comprises an optical correction pattern in the phase shifting pattern to reduce the optical proximity effect. Further, the conventional technique uses the auxiliary pattern made of opaque chrome on the phase shifting pattern to reduce the optical proximity effect. In contrast, rather than using the conventional opaque chrome pattern, one aspect of the present invention solves the pattern distortion issue due to the optical proximity effect by setting transparent optical correction patterns, such as the aperture exposing the substrate, in the phase shifting pattern, with the pattern being made of material including polymer for instance. 
         [0041]    Further, the preparation of the conventional chromeless phase shifting mask requires performing the lithographic process twice and etching process, while the preparation of the phase shifting mask according to one embodiment of the present invention does not require performing the lithographic process or etching process such that the throughput of the mask can be increased. 
         [0042]    The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.