Abstract:
A phase shift mask including a first phase shifter through which light passes by a first optical path length; a second phase shifter through which light passes by a second optical path length inverted in an optical phase from the first optical path length, the second phase shifter formed away from the first phase shifter by a predetermined distance; a light-blocking part formed around the first phase shifter and second phase shifter; and a correction pattern provided at a part of at least one of the first phase shifter and second phase shifter for correcting a distribution of light intensity between light passing through the first phase shifter and light passing through the second phase shifter, and method of exposure and method of producing a semiconductor device using the phase shift mask.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a phase shift mask used in a photolithography process for forming a miniaturized pattern on a semiconductor device etc. and to a method of exposure and a method of producing a semiconductor device using the same, in particular a phase shift mask, a method of exposure, and a method of producing a semiconductor device able to make a line width of a miniaturized pattern uniform. 
     2. Description of the Related Art 
     Along with improvements in the performance of semiconductor devices, greater miniaturization and higher density packaging have become demanded in the semiconductor production process. Therefore, when forming resist patterns by photolithography, it is also required to form miniaturized patterns exceeding the resolution limit determined by the wavelength of the light and optical system. 
     In recent years, as a method for forming a miniaturized pattern of less than the exposure wavelength, a multiple exposure method using a Levenson phase shift mask has been employed. This method of exposure comprises exposure using a Levenson phase shift mask and exposure using a mask other than a Levenson phase shift mask. 
     As a mask other than a Levenson phase shift mask, usually a binary mask comprised of a light-blocking film formed with apertures passing light is used. However, it is also possible to perform the multiple exposure by combining a half-tone type phase shift mask using a material having a certain transmittance as a light-blocking film etc. together with a Levenson phase shift mask. 
     When performing exposure using a Levenson phase shift mask, miniaturized patterns exceeding the resolution limit determined by the wavelength of the light and optical system can be transferred, but unnecessary patterns are generated between regions opposite in phase because of the decrease in light intensity. To eliminate the unnecessary patterns and form patterns not requiring as high a resolution as with a Levenson phase shift mask, at least two exposures are performed. 
     The multiple exposure method using a Levenson phase shift mask has already been applied commercially for forming gate layers of a high-speed LSI or ULSI etc. A gate layer of a ULSI requires a high controllability of line width in the patterns forming the gate electrodes, so a phase shift mask comprised of an array of phase shifters is used at the pattern forming parts. 
       FIG. 1A  shows an example of the gate layer of a ULSI. As shown in  FIG. 1A , an active region  101  of a PMOS and an active region  102  of an NMOS are formed in a substrate. A gate layer  103  is formed on the substrate. The gate layer  103  is comprised of for example polysilicon. The miniaturized pattern parts on the active regions  101  and  102  are the gate electrodes  103   a  and  103   b . A channel is formed below them. 
     The gate layer  103  at the portions other than the active regions  101  and  102  is formed with a gate contact. For decreasing the resistivity of interconnections, facilitating fabrication of the pattern, etc., the gate layer  103  is made a relatively thick line width at portions other than the gate electrodes  103   a  and  103   b . The portions other than the active regions  101  and  102  and gate layer  103  are element isolation regions. 
       FIG. 1B  shows mask patterns when forming resist patterns for forming the gate layer  103  of  FIG. 1A  by the multiple exposure method. Here, an example of multiple exposure using a Levenson phase shift mask and binary mask is shown. The resist is assumed to be a positive type resist. 
     The solid lines in  FIG. 1B  show the patterns of the Levenson phase shift mask. The hatched portion shows a light-blocking part  104  of the Levenson phase shift mask. Light passes through the phase shifters  105   a ,  105   b ,  106   a , and  106   b  other than the light-blocking part  104 . The phase shifters  105   a  and  105   b  differ from each other in thickness (or optical path length). Due to this, the phase of the light passing through the phase shifters  105   a  and  105   b  is inverted. Between the phase shifters  105   a  and  105   b , the light intensity becomes smaller and the resist remains in a narrow line width. 
     In the same manner, the phase shifters  106   a  and  106   b  differ from each other in optical path lengths. Due to this, between the phase shifters  106   a  and  106   b , the resist remains in a narrow line width. 
     On the other hand, the dotted lines of  FIG. 1B  show the pattern of the binary mask. This corresponds to the pattern of the gate layer  103  of  FIG. 1A  in the portion other than the gate electrodes  103   a  and  103   b  of FIG.  1 A. 
     The exposure using the Levenson phase shift mask of FIG.  1 B and exposure using the binary mask can be performed in any sequence. After the multiple exposure, the resist is developed to form the resist patterns. Using the resist patterns as a mask, the for example polysilicon layer is dry etched to obtain the gate layer  103  shown in FIG.  1 A. 
     However, when using the conventional Levenson phase shift mask described above for exposing the resist, it is not possible to make the line width of the resist constant at the miniaturized patterns of the gate electrodes. A resist for forming the circled part in the gate layer  103  shown in  FIG. 2A  is shown enlarged in FIG.  2 B. 
     As shown in  FIG. 2B , the line width of the resist  107  becomes narrower in the longitudinal direction of the gate electrode (gate width direction) from the center part toward one end. On the other hand, at the end of the gate electrode in the gate width direction, the line width of the resist  107  sharply increases. When forming the gate electrode  103   a  (see  FIG. 2A ) by using such a resist  107  as a mask, the gate electrode  103   a  becomes locally narrow near that one end. 
     In the same way, the resist line width fluctuates at the other end of the gate electrode  103   a  or both ends of the gate electrode  103   b  of FIG.  2 A. Therefore, a gate electrode  103   a  with a uniformly narrow line width cannot be obtained on the active region  101  such as shown in FIG.  2 A. The gate electrode  103   b  on the active region  102  also does not have a uniform line width. 
     For example, in the case of a CMOS circuit shown in  FIG. 2A , due to the local thinning in the line widths of the gate electrodes  103   a  and  103   b , leakage etc. is easily induced and the circuit no longer functions as a CMOS circuit. 
     Japanese Patent No. 2892014 (Japanese Unexamined Patent Publication (Kokai) No. 2-39152) discloses a method of exposure able to improve the uniformity of line width when forming adjacent slit-type patterns by photolithography. According to this method of exposure, as shown in  FIG. 3 , a mask  114  comprising rectangular patterns  112  and  113  on a support  111  is used for exposure. At the corners of the mask patterns  112  and  113 , jog parts  114  and  115  are provided. 
     If the jog parts  114  and  115  were not formed at the mask patterns  112  and  113 , the distribution of light intensity in the part enclosed by the dotted line of  FIG. 3  would become as shown in FIG.  4 A. As shown in  FIG. 4A  by the arrow, the light intensity would locally increase near the corners of the patterns and the line width of the resist would fluctuate at these parts. 
     On the other hand, as shown in  FIG. 3 , due to the provision of the jog parts  114  and  115  on the mask patterns  112 ,  113 , it becomes possible to make the distance between the transferred patterns constant as shown in FIG.  4 B. 
     However, since the above mask is a binary mask, it cannot be applied to form a miniaturized pattern exceeding the resolution limit determined by the wavelength of the light and the optical system. Also, in the case of the above method of exposure, along with the distance between the patterns becoming constant, rounded shapes at the ends of the patterns become more prominent. Therefore, when miniaturizing patterns, this is sometimes conversely disadvantageous in forming patterns with a high precision. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a phase shift mask able to correct the distribution of light intensity between phase shifters and prevent fluctuation in line width of a miniaturized pattern. 
     Another object of the present invention is to provide a method of exposure able to prevent fluctuation in line width in formation of a miniaturized pattern including exposure using a Levenson phase shift mask. 
     Another object of the present invention is to provide a method of producing a semiconductor device able to form a miniaturized pattern with a uniform line width in a photolithography process. 
     According to a first aspect of the present invention, there is provided a phase shift mask comprising a first phase shifter through which light passes by a first optical path length; a second phase shifter through which light passes by a second optical path length inverted in an optical phase from the first optical path length, the second phase shifter formed away from the first phase shifter by a predetermined distance; a light-blocking part formed around the first phase shifter and second phase shifter; and a correction pattern provided at a part of at least one of the first phase shifter and second phase shifter for correcting a distribution of light intensity between light passing through the first phase shifter and light passing through the second phase shifter. 
     Preferably, the first phase shifter and second phase shifter are shaped so that the light intensity is canceled out in a line shape between the light passing through the first phase shifter and the light passing through the second phase shifter; and the correction pattern is shaped so that a line width of the line-shaped part becomes constant. 
     Preferably, the correction pattern is shaped to cut away at least one corner of the first and/or second phase shifter. 
     Preferably, a length of a portion where the first phase shifter and second phase shifter face each other is longer than a desired length of the line-shaped portion. More preferably, the facing portion includes parts outside of the two ends of the line-shaped portion in a longitudinal direction. 
     Preferably, the phase shift mask of the present invention has a plurality of at least the first phase shifter, and the first phase shifters are arranged via the second phase shifter. 
     Due to this, it becomes possible to prevent a fluctuation in line width of a miniaturized pattern formed by light passing through the first and second phase shifters. Specifically, it is possible to prevent the line width from becoming narrower from the center to the end of the phase shifter in the longitudinal direction. Further, it is possible to prevent the line width from becoming sharply thicker near an end of the phase shifter in the longitudinal direction. 
     According to a second aspect of the present invention, there is provided a method of exposure performing a first exposure via a phase shift mask comprising using a phase shift mask comprising a first phase shifter through which light passes by a first optical path length; a second phase shifter through which light passes by a second optical path length inverted in an optical phase from the first optical path length, the second phase shifter formed away from the first phase shifter by a predetermined distance; a light-blocking part formed around the first phase shifter and second phase shifter; and a correction pattern provided at a part of at least one of the first phase shifter and second phase shifter for correcting a distribution of light intensity between light passing through the first phase shifter and light passing through the second phase shifter. 
     Preferably, the first phase shifter and second phase shifter are shaped so that the light intensity is canceled out in a line shape between the light passing through the first phase shifter and the light passing through the second phase shifter; and the correction pattern is shaped so that a line width of the line-shaped part becomes constant. 
     Preferably, the method of exposure further comprises, before or after the first exposure, a step of second exposure via a second mask formed with a different pattern from the phase shift mask. 
     Preferably, the correction pattern is shaped to cut away at least one corner of the first and/or second phase shifter. Preferably, a length of a portion where the first phase shifter and second phase shifter face each other is longer than a desired length of the line-shaped portion. More preferably, the facing portion includes parts outside of the two ends of the line-shaped portion in a longitudinal direction. 
     Due to this, it becomes possible to prevent a fluctuation in line width in fabrication of a miniaturized pattern formed exposure using a Levenson phase shift mask. Specifically, it is possible to prevent the line width from becoming narrower from the center to the end of the phase shifter in the longitudinal direction. Further, it is possible to prevent the line width from becoming sharply thicker near an end of the phase shifter in the longitudinal direction. 
     Further, if performing the second exposure in addition to the exposure using the Levenson phase shift mask, it is possible to cover over a change of shape of the end of a pattern caused by lengthening the shape of a phase shifter in the longitudinal direction. 
     According to a third aspect of the present invention, there is provided to a method of producing a semiconductor device including a step of focusing light on a substrate via a phase shift mask to transfer a pattern to the substrate comprising using a phase shift mask comprising a first phase shifter through which light passes by a first optical path length; a second phase shifter through which light passes by a second optical path length inverted in an optical phase from the first optical path length, the second phase shifter formed away from the first phase shifter by a predetermined distance; a light-blocking part formed around the first phase shifter and second phase shifter; and a correction pattern provided at a part of at least one of the first phase shifter and second phase shifter for correcting a distribution of light intensity between light passing through the first phase shifter and light passing through the second phase shifter. 
     Due to this, it becomes possible to prevent a fluctuation in line width in fabrication of a miniaturized pattern formed exposure using a Levenson phase shift mask. Specifically, it is possible to prevent the line width from becoming narrower from the center to the end of the phase shifter in the longitudinal direction. Further, it is possible to prevent the line width from becoming sharply thicker near an end of the phase shifter in the longitudinal direction. Therefore, it becomes possible to form a miniaturized pattern of for example a gate layer at a high precision. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the accompanying drawings, in which: 
         FIG. 1A  shows an example of the layout of a gate layer; 
         FIG. 1B  shows a mask pattern used for multiple exposure for forming the pattern of  FIG. 1A ; 
         FIG. 2A  shows an example of the layout of a gate layer; 
         FIG. 2B  shows a resist for forming a part of the gate layer inside a dotted line of  FIG. 2A ; 
         FIG. 3  shows a conventional mask having correction patterns; 
         FIGS. 4A and 4B  show the results of simulation of the light intensity at the part inside of the dotted line of  FIG. 3 , wherein  FIG. 4A  shows a case without correction patterns and  FIG. 4B  shows a case with correction patterns (jogs); 
         FIG. 5A  shows the layout of a gate layer according to a first embodiment of the present invention; 
         FIG. 5B  shows phase shifters for forming the pattern of  FIG. 5A ; 
         FIG. 6  shows the results of simulation of the light intensity at the phase shifters of  FIG. 5B ; 
         FIG. 7  shows the extracted distribution of light intensity when a line width at the center parts of the phase shifters becomes 100 nm from  FIG. 6 ; 
         FIG. 8A  shows the layout of a gate layer according to the first embodiment of the present invention; 
         FIG. 8B  shows phase shifters of a comparative example for forming the pattern of  FIG. 8A ; 
         FIG. 9  shows the results of simulation of the light intensity at the phase shifters of  FIG. 8B ; 
         FIG. 10  shows the extracted distribution of light intensity when a line width at the center parts of the phase shifters becomes 100 nm from  FIG. 9 ; 
         FIG. 11A  shows the layout of a gate layer according to a second embodiment of the present invention; 
         FIG. 11B  shows phase shifters for forming the patterns of  FIG. 11A ; 
         FIG. 12  shows the results of simulation of the light intensity at the phase shifters of  FIG. 11B ; 
         FIG. 13  shows the extracted distribution of light intensity when a line width at the center parts of the phase shifters becomes 100 nm from  FIG. 12 ; 
         FIG. 14A  shows the layout of a gate layer according to the second embodiment of the present invention; 
         FIG. 14B  shows phase shifters of a comparative example for forming the patterns of  FIG. 14A ; 
         FIG. 15  shows the results of simulation of the light intensity at the phase shifters of  FIG. 14B ; and 
         FIG. 16  shows the extracted distribution of light intensity when a line width at the center parts of the phase shifters becomes 100 nm from FIG.  15 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Below, preferred embodiments will be described with reference to the accompanying drawings. 
     The technique of multiple exposure using a Levenson phase shift mask is generally applied to the fabrication of a gate layer or other line-type pattern of an ULSI. The following embodiments show examples of application of the present invention to a 0.13 μm generation logic test pattern. Two patterns were sampled as representative patterns and set as first and second embodiments. 
     First Embodiment 
       FIG. 5A  shows the layout of a test pattern of the present embodiment. The pattern shown in  FIG. 5A  is assumed here to be an isolated pattern with no other gate in its surroundings. 
     As shown in  FIG. 5A , an active region  201  is formed in a substrate. A gate layer  202  is formed on the substrate. The gate layer  202  is composed of for example polysilicon. The miniaturized pattern portion on the active region  201  is a gate electrode  202   a . Below this, a channel is formed. In the pattern shown in  FIG. 5A , a gate length L G  is assumed to be 0.10 μm and a gate width W G  1.0 μm. 
       FIG. 5B  shows phase shifters for forming the test pattern shown in FIG.  5 A. The optical path lengths of a phase shifter  203   a  and a phase shifter  203   b  are different from each other. Therefore, the phases of the light passing through the phase shifters  203   a  and  203   b  are inverted. As shown in  FIG. 5B , the phase shifters  203   a  and  203   b  are longer at both ends in the longitudinal direction by 160 nm from the gate width W G  of FIG.  5 A. Therefore, the lengths of the phase shifters  203   a  are  203   b  are 1.32 μm. Further, the widths of the phase shifters  203   a  and  203   b  are 160 nm. The distance between the phase shifter  203   a  and the phase shifter  203   b  is 100 nm. 
     As shown in  FIG. 5B , the phase shifters  203   a  and  203   b  have jog part  204   a ,  204   b ,  204   c , and  204   d . The jog parts are located facing each other. Based on the results of optimization by simulation of the light intensity explained later, the jog parts are formed 100 nm in length and 40 nm in width. 
       FIG. 6  shows the results of simulation of the light intensity for light passing through the phase shifters  203   a  and  203   b  in FIG.  5 B. The simulation conditions were a wavelength of the light source of set at 248 nm, a numerical aperture NA of 0.60, and a coherence factor a of 0.53. The coherence factor a expresses the interference of light of an exposure apparatus. 
     By increasing the length of the phase shifter and providing the jog parts at the ends of the phase shifters, as shown in  FIG. 6 , unevenness of line width is prevented. Also, at the ends of the phase shifters in the longitudinal direction, the corner parts of the transferred image are rounded, but these rounded parts are outside of the active regions. Therefore, the influence of the rounded parts on the line width can be decreased. 
     Also, normally, some of the interconnections are formed so as to perpendicularly intersect the longitudinal direction of the gate electrode. Therefore, the ends of the transferred image of a Levenson phase shift mask can be covered and concealed by further exposure using for example a binary mask or half-tone type phase shift mask. 
       FIG. 7  shows an extracted pattern having a line width at the center parts of the phase shifters of 100 nm based on results of simulation of the light intensity of FIG.  6 . As shown in  FIG. 7 , when the line width is determined by the threshold of the light intensity where the line width at the center parts becomes 100 nm, the minimum line width is 97 nm. 
     As explained above, according to the patterns of the phase shifters of a Levenson phase shift mask of the present embodiment, it is possible to form a narrow gate electrode on an active region by a substantially constant line width. 
       FIG. 8A  shows a test pattern the same as in  FIG. 5A , while  FIG. 8B  shows conventional phase shifters for fabricating the test pattern of  FIG. 8A  as comparison. The optical path lengths of the phase shifter  205   a  and phase shifter  205   b  are different from each other. Due to this, the phases of the light passing through the phase shifters  205   a  and  205   b  are inverted. The phase shifters  205   a  and  205   b  have rectangular shapes of 1.0 μm length and 160 nm width. The distance between the phase shifter  205   a  and phase shifter  205   b  is 100 nm. 
       FIG. 9  shows the results of simulation of the light intensity for the phase shifters of  FIG. 8B  using the same conditions as described above. As shown in  FIG. 9 , at the center parts of the phase shifters in the longitudinal direction, the light intensity between the phase shifter  205   a  and phase shifter  205   b  becomes smaller compared with the ends in the longitudinal direction. Also, at the ends in the longitudinal direction, the distribution of light intensity becomes rounded, so the light intensity at the corner parts becomes weak. As explained above, peanut-shaped distributions of light intensity are observed in FIG.  9 . 
       FIG. 10  shows an extracted pattern having a line width at the center parts of the phase shifters of 100 nm based on the results of simulation of the light intensity of FIG.  9 . As shown in  FIG. 10 , when the line width is determined by the threshold of light intensity where the line width at the center parts becomes 100 nm, the line width becomes narrower toward the ends in the longitudinal direction. The line width becomes 94 nm at the minimum. 
     Comparing  FIG. 10  with  FIG. 7 , it is found that the evenness of line width of a miniaturized pattern on an active region is improved by the Levenson phase shift mask of the present embodiment. 
     The method of exposure and method of producing a semiconductor device of the present embodiment include a step of photolithography using a Levenson phase shift mask formed with the phase shifters of the present embodiment. Due to this, it becomes possible to form a miniaturized pattern exceeding a resolution limit determined by the wavelength of the light and optical system by a uniform line width. 
     Second Embodiment 
       FIG. 11A  shows the layout of test patterns of the present embodiment. The patterns shown in  FIG. 11A  are assumed to gates adjoining each other by a 0.10 μm generation minimum pitch of 0.26 μm. 
     As shown in  FIG. 11A , an active region  211  is formed in a substrate and a gate layer  212  is formed on the substrate. The gate layer  212  is comprised of for example polysilicon in the same manner as the gate layer  202  of FIG.  5 A. 
     The miniaturized patterns on the active region  211  are the gate electrodes  212   a  and  212   b . Channels are formed immediately below them. In the patterns shown in  FIG. 11A , a gate length L G  is set at 0.10 μm and the gate width W G  at 1.0 μm. Also, a distance S between the gate electrodes  212   a  and  212   b  is 0.16 μm. 
       FIG. 11B  shows phase shifters for forming the test patterns of FIG.  11 A. The optical path, lengths of the phase shifters  213   a  and  213   b  are different from each other. Due to this, the phases of light passing through the phase shifters  213   a  and  213   b  are inverted. On the other hand, the optical path length of the phase shifter  213   c  is equal to the optical path length of the phase shifter  213   a . Due to this, the phases of light passing through the phase shifters  213   b  and  213   c  are inverted. 
     The phase shifters  213   a ,  213   b , and  213   c  are lengthened at both ends in the longitudinal direction by 0.16 μm each compared with the gate width W G  of FIG.  11 A. Therefore, the length of the phase shifters  213   a ,  213   b , and  213   c  is 1.32 μm. Also, the width of the phase shifters  213   a ,  213   b , and  213   c  is 160 nm. A distance between adjacent phase shifters is 100 nm. 
     As shown in  FIG. 11B , the phase shifters  213   a ,  213   b , and  213   c  have jog parts  214   a,    214   b ,  214   c ,  214   d ,  214   e ,  214   f ,  214   g , and  214   h  at both ends in the longitudinal direction. The jog parts are arranged facing each other. Based on results of optimization by simulation of the light intensity described later, the jog parts are formed to 100 nm in length and 40 nm in width. 
       FIG. 12  shows the results of simulation of the light intensity for light passing through the phase shifters  213   a ,  213   b , and  213   c  of FIG.  11 B. The simulation conditions were the same as with the simulation of the light intensity of the first embodiment. 
     Since the phase shifters are made longer and the jog parts are provided at the ends of the phase shifter, unevenness of line width is prevented as shown in FIG.  12 . Also, at the ends of the phase shifters in the longitudinal direction, the corner parts of the transferred images become rounded, but these rounded parts are outside of the active region. Therefore, the influence of the rounded parts on the line width can be decreased. 
     Also, in this portion, normally some of the interconnections are formed perpendicularly intersecting the longitudinal direction of the gate electrodes. Therefore, the ends of the transferred image of the Levenson phase shift mask can be covered and concealed by further exposure using for example a binary mask or half-tone type phase shift mask. 
       FIG. 13  shows extracted patterns where line widths at center parts of the phase shifters become 100 nm based on the results of simulation of the light intensity of FIG.  12 . As shown in  FIG. 13 , when the line width is determined by the threshold of light intensity where the line width at the center part is 100 nm, the line width becomes 97 nm at the minimum. 
     As explained above, according to the patterns of the phase shifters of the Levenson phase shift mask of the present embodiment, it is possible to form miniaturized gate electrodes on the active region by substantially constant line widths. 
       FIG. 14A  shows the same test patterns as in FIG.  11 A.  FIG. 11B  shows conventional phase shifters for forming the test patterns of  FIG. 14A  for comparison. The optical path lengths of the phase shifters  215   a  and  215   b  are different from each other. Due to this, the phase of the light passing through the phase shifters  215   a  and  215   b  is inverted. 
     On the other hand, the optical path length of the phase shifter  215   c  is equal to the optical path length of the phase shifter  215   a . Due to this, the phases of light passing through the phase shifters  215   b  and  215   c  are inverted. The phase shifters  215   a ,  215   b , and  215   c  have a rectangular shape of 1.0 μm length and 160 nm width. A distance between adjacent phase shifters is 100 nm. 
       FIG. 15  shows the results of simulation of the light intensity for the phase shifters of  FIG. 14B  under the same conditions as described above. As shown in  FIG. 15 , at the center parts of the phase shifters in the longitudinal direction, the light intensity between the adjacent phase shifters becomes smaller compared with the ends in the longitudinal direction. Also, at the ends in the longitudinal direction, the distribution of light intensity becomes rounded, so the light intensity at the corner parts becomes weak. As explained above, peanut-shaped distributions of light intensity are observed in FIG.  15 . 
       FIG. 16  shows extracted patterns where line widths at center parts of the phase shifters become 100 nm based on the results of simulation of the light intensity of FIG.  15 . As shown in  FIG. 16 , when the line widths are determined by the threshold of light intensity where the line widths at the center parts become 100 nm, the line widths becomes narrower at the ends in the longitudinal direction. The line widths become 94 nm at the minimum. 
     Comparing  FIG. 16  with  FIG. 13 , it is found that the evenness of line widths of the miniaturized patterns on the active region is improved by the Levenson phase shift mask of the present embodiment. 
     A method of exposure and method of producing a semiconductor device of the present embodiment include a step of photolithography using a Levenson phase shift mask formed with the phase shifters of the present embodiment. Due to this, it becomes possible to form a miniaturized pattern exceeding a resolution limit determined by the wavelength of the light and optical system by a uniform line width. 
     According to the phase shift mask, method of exposure, and method of producing a semiconductor device of the above embodiment of the present invention, it is possible to form a miniaturized pattern by a uniform line width. 
     Note that the present invention is not limited to the above embodiments and includes modifications within the scope of the claims. For example, it is possible to change the shape and size of the correction pattern in accordance with the results of simulation of the light intensity. 
     Summarizing the effects of the invention, according to the phase shift mask of the present invention, it is possible to prevent a fluctuation in line width of a miniaturized pattern on an active region. 
     According to the method of exposure of the present invention, it becomes possible to prevent a fluctuation in line width in a process of production of a miniaturized pattern including exposure using a Levenson phase shift mask. 
     According to the method of producing a semiconductor device of the present invention, it is possible to form a miniaturized pattern by a uniform line width in a photolithography process.