Patent Publication Number: US-2004043306-A1

Title: Phase shift mask

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a phase shift mask used for manufacturing a semiconductor device.  
       [0003] 2. Description of the Background Art  
       [0004] Conventionally, a light shield film has been formed on a transparent substrate, and a photomask, that is, a phase shift mask, has been used for transferring a pattern corresponding to a pattern in a region where the light shield film is not formed onto a resist film on a semiconductor substrate. The phase shift mask is provided with a large pattern  1   a  having a relatively large opening width, and a small pattern  1   b  having a relatively small opening width, which are portions where a light shield film  2   a  is not provided on a transparent substrate  1 .  
       [0005]FIG. 16 shows a relation of a cross-sectional configuration of the phase shift mask shown in FIG. 15 with an amplitude and intensity of light. Light passes through a region inside large pattern  1   a , while it is shielded by light shield film  2   a  in a region outside the same. Here, light shield film  2   a  is a halftone film allowing a small amount of light (3 to 8%) to transmit.  
       [0006] Accordingly, the amplitude and intensity of the light is large only in the region inside large pattern  1   a , and is small in the region outside the same. In addition, a lowest light intensity value k appears outside a position where large pattern  1   a  is transferred onto the semiconductor substrate, when light passes only through transparent substrate  1  of large pattern  1   a  of the phase shift mask.  
       [0007] The reason for this is as follows. In spite of a small amount of light passing through light shield film  2   a , a large amount of light passing through large pattern  1   a  diffracts. Therefore, the diffracted light interferes with the light that has passed through light shield film  2   a , and an area where light intensity is close to zero has been produced outside large pattern  1   a.    
       [0008] Because of the relation shown in FIG. 16, in a pattern transferred onto the semiconductor substrate, a dimple is produced in a peripheral region of large pattern  1   a , and not produced in a peripheral region of small pattern  1   b.    
       [0009] A geometry of the pattern on the semiconductor substrate may be deteriorated because of the above-described dimple. Therefore, as shown in FIG. 17, a chrome film 7 having a fall light shield property (close to 100%) is formed in the vicinity of an outer periphery of large pattern  1   a  so as to surround the same. Thus, a problem caused by a fact that light shield film  2   a  is a halftone mask is solved.  
       [0010] In-the phase shift mask as shown in FIG. 17, chrome film  7  with a full light shield property has a different light transmittance from light shield film  2   a  which is a halftone mask. Therefore, when the phase shift mask is irradiated with light using an exposure apparatus, there is an aberration between light passing through transparent substrate  1  inside large pattern  1   a  and light passing through chrome film  7  and transparent substrate  1 . Because of the effect of aberration, an amount of displacement between large pattern  1   a  formed on the phase shift mask and a pattern obtained by transferring large pattern  1   a  onto the semiconductor substrate will be different from that between small pattern  1   b  formed on the phase shift mask and a pattern obtained by transferring small pattern  1   b  onto the semiconductor substrate. In other words, the aberration will cause a relative transfer error between large pattern  1   a  and small pattern  1   b.    
       [0011] The phase shift mask as shown in FIG. 18 is disclosed in Japanese Patent Laying-Open No. 10-31300. In the phase shift mask as shown in FIG. 18, a plurality of light shield films  2   a  are formed on transparent substrate  1 . An outer periphery of light shield film  2   a  having a small opening width among the plurality of light shield films  2   a  forms small pattern  1   b . In addition, on light shield film  2   a  of large pattern  1   a  having an opening width larger than small pattern  1   b , a full light shield film  10  for constituting large pattern  1   a  is formed.  
       [0012]FIG. 19 shows a cross-section along the line XIX-XIX of the phase shift mask shown in FIG. 18. In the phase shift mask having a configuration as shown in FIGS. 18 and 19 as well, light transmittance is significantly different between the region inside large pattern  1   a  and the peripheral region thereof. Consequently, a relative transfer error in the pattern due to the aberration is caused.  
       SUMMARY OF THE INVENTION  
       [0013] An object of the present invention is to provide a phase shift mask, with which a relative transfer error of a pattern formed on a semiconductor substrate due to an aberration is reduced to a minimum.  
       [0014] A phase shift mask according to the present invention includes a transparent substrate provided with a main surface, a first pattern formed to a prescribed depth from the main surface and having a prescribed opening width, and a second pattern formed to a depth similar to the aforementioned prescribed depth from the main surface and having an opening width larger than the aforementioned prescribed opening width. An amplitude of light passing through the first pattern and an amplitude of light passing through the second pattern have a phase opposite to an amplitude of light passing through the main surface in a periphery of the first pattern and light passing through the main surface in a periphery of the second pattern. The phase shift mask is configured such that difference of light transmittance between the second pattern and a periphery of the second pattern is smaller than that between the first pattern and a periphery of the first pattern.  
       [0015] Here, difference of light transmittance between the second pattern and the periphery thereof may be zero.  
       [0016] According to the above-described configuration, the transfer error of the pattern due to the aberration caused by the difference of light transmittance between the inside of the second pattern and the outside thereof can be reduced.  
       [0017] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018]FIG. 1 is a top view of a phase shift, mask of a first embodiment.  
     [0019]FIG. 2 is a cross-sectional view of the phase shift mask of the first embodiment.  
     [0020] FIGS.  3  to  5  illustrate a method of manufacturing the phase shift mask of the first embodiment.  
     [0021]FIG. 6 is a top view of a phase shift mask of a second embodiment.  
     [0022]FIG. 7 is a cross-sectional view of the phase shift mask of the second embodiment.  
     [0023] FIGS.  8  to  10  illustrate a method of manufacturing the phase shift mask of the second embodiment.  
     [0024]FIG. 11 illustrates another example of the phase shift mask of the first embodiment.  
     [0025]FIG. 12 illustrates a relation of a cross-section along the line XII-XII of a configuration shown in FIG. 11 with an amplitude and intensity of light in the other example of the phase shift mask of the first embodiment.  
     [0026]FIG. 13 is a top view of a variation of the phase shift mask of the first embodiment.  
     [0027]FIG. 14 illustrates a relation of a cross-section along the line XIV-XIV in FIG. 13 with an amplitude and intensity of light in the variation of the phase shift mask of the first embodiment.  
     [0028]FIG. 15 is a top view of a conventional phase shift mask.  
     [0029]FIG. 16 illustrates a relation of a cross-section along the line XVI-XVI of the conventional phase shift mask shown in FIG. 15 with an amplitude and intensity of light.  
     [0030]FIG. 17 illustrates a state in which a chrome film is formed in a periphery of a large pattern in the conventional phase shift mask.  
     [0031]FIG. 18 is a top view of a conventional phase shift mask described in Japanese Patent Laying-Open No. 10-31300.  
     [0032]FIG. 19 illustrates a relation of a cross-section along the line XIX-XIX of the conventional phase shift mask shown in FIG. 18 with an amplitude and intensity of light. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0033] In the following, a phase shift mask and a manufacturing method thereof in embodiments of the present invention will be described with reference to the figures.  
     [0034] (First Embodiment)  
     [0035] With reference to FIGS.  1  to  5 , a phase shift mask of the present embodiment and a manufacturing method thereof will be described.  
     [0036] As shown in FIGS. 1 and 2, the phase shift mask of the present embodiment includes a transparent substrate  1  having a main surface, a small pattern  1   b  formed to a prescribed depth from the main surface and having a prescribed opening width, and a large pattern  1   a  formed to a depth similar to the aforementioned prescribed depth from the main surface and having an opening width larger than the aforementioned prescribed opening width.  
     [0037] In addition, an amplitude of light passing through small pattern  1   b  and an amplitude of light passing through large pattern  1   a  have a phase opposite to an amplitude of light passing through the main surface in a periphery of small pattern  1   b  and light passing through the main surface in a periphery of large pattern  1   a . Note that, in the phase shift mask of the present embodiment, phase shift in a range of 175 to 185° is considered as the opposite phase.  
     [0038] Moreover, as will be described later, the phase shift mask of the present embodiment is configured such that difference of light transmittance between large pattern  1   a  and the periphery thereof is smaller than that between small pattern  1   b  and the periphery thereof.  
     [0039] Therefore, the relative transfer error of the pattern onto the semiconductor substrate due to the aberration caused by the difference of light transmittance between the inside of large pattern  1   a  and the outside thereof can be reduced.  
     [0040] Specifically, the phase shift mask of the present embodiment described above has a configuration as follows. As shown in FIG. 1, the phase shift mask includes light shield film  2   a  provided on transparent substrate  1  and surrounding the periphery of small pattern  1   b  when viewed from a direction vertical to the main surface of transparent substrate  1 . In addition, light shield film  2   a  is provided in a region other than the peripheral region of large pattern  1   a  on the transparent substrate.  
     [0041] According to the above-described configuration, presence or absence of light shield film  2   a  can eliminate difference of light transmittance between the inside of large pattern  1   a  and the peripheral region thereof.  
     [0042] The phase shift mask of the present embodiment described above is manufactured in a process as follows.  
     [0043] First, as shown in FIG. 3, a light shield film  2  is formed on transparent substrate  1 . A resist film  3  is then formed on light shield film  2 . Thereafter, a first opening and a second opening having an opening width larger than the first opening are provided on resist film  3 , to form a resist film  3   a . Next, light shield film  2  exposed on the bottom face of the first opening and the second opening is removed. Thereafter, as shown in FIG. 4, transparent substrate  1  exposed on the bottom face of the first opening and the second opening is etched to form small pattern  1   b  and large pattern  1   a . Resist film  3   a  is then removed. Thereafter, a resist film  4  is formed in an upper region of transparent substrate  1 , that is, on an upper portion of a region other than the peripheral region of large pattern  1   a . Thereafter, light shield film  2   a  is removed using resist film  4  as a mask, to obtain a configuration shown in FIG. 5. Finally, resist film  4  is removed, and the phase shift mask shown in FIG. 2 is completed.  
     [0044] (Second Embodiment)  
     [0045] Next, a phase shift mask and a manufacturing method thereof of a second embodiment will be described with reference to FIGS.  6  to  10 .  
     [0046] As shown in FIGS. 6 and 7, as in the phase shift mask of the first embodiment, the phase shift mask of the present embodiment includes a substrate  1  having a main surface, a small pattern  1   b  formed to a prescribed depth from the main surface and having a prescribed opening width, and a large pattern  1   a  formed to a depth similar to the aforementioned prescribed depth from the main surface and having an opening width larger than the aforementioned prescribed opening width.  
     [0047] In addition, an amplitude of light passing through small pattern  1   b  and an amplitude of light passing through large pattern  1   a  have a phase opposite to an amplitude of light passing through the main surface in a periphery of small pattern  1   b  and light passing through the main surface in a periphery of large pattern  1   a . Note that, in the phase shift mask of the present embodiment, phase shift in a range of 175 to 185° is considered as the opposite phase.  
     [0048] Moreover, as will be described later, the phase shift mask of the present embodiment is configured such that difference of light transmittance between large pattern  1   a  and the periphery thereof is smaller than that between small pattern  1   b  and the periphery thereof.  
     [0049] Furthermore, as shown in FIG. 6, in the phase shift mask of the present embodiment, ions are implanted in a region within transparent substrate  1 , surrounding the periphery of small pattern  1   b  when viewed from a direction vertical to the main surface of transparent substrate  1 . As shown in FIG. 7, ions are contained in the region other than the peripheral region of large pattern  1   a  on transparent substrate  1  (the peripheral region of small pattern  1   b , for example) in an amount larger than in the peripheral region of large pattern  1   a  on transparent substrate  1 . Note that, in the phase shift mask of the present embodiment, an amount of the ions implanted into the peripheral region of large pattern  1   a  on transparent substrate  1  is zero.  
     [0050] According to the configuration described above, by controlling an amount of ions contained in transparent substrate  1 , difference of transmittance between the light passing through the inside of large pattern  1   a  and the light passing through the outside thereof can be made smaller than that between the light passing through the inside of small pattern  1   b  and the light passing through the outside thereof.  
     [0051] The phase shift mask of the present embodiment described above is manufactured in a process as follows.  
     [0052] First, ions are implanted into the vicinity of the surface of transparent substrate  1 , to form an ion-implanted region  1   i . Next, as shown in FIG. 8, resist film  3  is formed on ion-implanted region  1   i . A first opening and a second opening having an opening width larger than the first opening are provided in resist film  3 , to form resist film  3   a . Next, as shown in FIG. 9, ion-implanted region  1   i  and transparent substrate  1  exposed on the bottom face of the first opening and the second opening are removed, to form small pattern  1   b  and large pattern  1   a  having an opening width larger than small pattern  1   b  on transparent substrate  1 . Resist film  3  is then removed. Thereafter, the peripheral region of large pattern  1   a , which is also an upper region of transparent substrate  1 , is irradiated with laser in a direction shown with an arrow in FIG. 10, thereby removing the ions implanted in the peripheral region of large pattern  1   a , as shown in FIG. 7.  
     [0053]FIG. 11 schematically shows the phase shift mask of the present embodiment shown in FIG. 1. FIG. 12 shows the cross-section along the line XII-XII in FIG. 11. As can be seen from FIGS. 11 and 12, in the phase shift mask of the present embodiment, a lowest light intensity point k is located on a line drawn vertically from large pattern  1   a  down to the semiconductor substrate.  
     [0054]FIG. 13 shows a variation of the phase shift mask in the embodiment, described corresponding to the phase shift mask disclosed in Japanese Patent Laying-Open No. 10-31300, which is a reference of the conventional art shown in FIGS. 18 and 19 illustrating the conventional technique. FIG. 14 illustrates a relation of a cross-section of the phase shift mask shown in FIG. 13 with an amplitude and intensity of light. In the phase shift mask of the variation shown in FIGS. 13 and 14, light shield film  2   a  is formed on transparent substrate  1 , and an outer periphery of light shield film  2   a  forms small pattern  1   b . In addition, a transparent substrate projection  1   x  is provided on transparent substrate 1, and an outer periphery of transparent substrate projection  1   x  forms large pattern  1   a.    
     [0055] Table 1 shows light transmittance and a phase angle respectively of the region inside small pattern  1   b , the region outside small pattern  1   b , the peripheral region of large pattern  1   a , and the region inside large pattern  1   a , respectively for the phase shift masks according to the conventional art shown in FIGS. 15 and 16 described above, the technique described in Japanese Patent Laying-Open No. 10-31300 shown in FIGS. 18 and 19, the first embodiment, and the variation of the first embodiment.  
                                   TABLE 1                                   Region inside small   Peripheral region of   Peripheral region of   Region inside large           pattern 1b   small pattern 1b   large pattern 1a   pattern 1a                                                    Conventional art   Transmittance: High   Transmittance: Medium   Transmittance: High       shown in FIGS. 15   Phase Angle: 0°   Phase Angle: 180°   Phase Angle: 0°       and 16                                 Technique   Transmittance:   Transmittance: High   Transmittance:   Transmittance: 0       described in No.   Medium   Phase Angle: 0°   Medium   Phase Angle: —       31300 shown in   Phase Angle: 180°       Phase Angle: 180°               Phase shift mask in   Transmittance: High   Transmittance:   Transmittance: High   Transmittance: High       first embodiment   Phase Angle: 0°   Medium   Phase Angle: 180°   Phase Angle: 0°               Phase Angle: 180°       Variation of   Transmittance:   Transmittance: High   Transmittance: High   Transmittance: 0°       technique   Medium   Phase Angle: 0°   Phase Angle: 180°   Phase Angle: —       described in first   Phase Angle: 180°       embodiment shown       in FIGS. 11 and 12                                  
 
     [0056] As can be seen from Table 1, according to the conventional art shown in FIGS. 15 and 16 as well as the technique described in Japanese Patent Laying-Open No. 10-31300 shown in FIGS. 18 and 19, there is a difference of light transmittance between the peripheral region of large pattern  1   a  and the region inside the same.  
     [0057] On the other hand, in the phase shift mask of the first embodiment and the variation thereof shown in FIGS. 11 and 12, light transmittance in the peripheral region of large pattern  1   a  is identical to that inside the same. In other words, difference of light transmittance between the peripheral region of large pattern  1   a  and the region inside the same is smaller than that between the peripheral region of small pattern  1   b  and the region inside the same.  
     [0058] Further, a manufacturing method of a semiconductor device using the phase sift mask described above is as follows.  
     [0059] First, a prescribed pattern formed in the phase sift mask is transcribed into a resist film formed on a wafer by a lithography art, for example, a lithography art using KrF Excimer Laser as light to be used in an abridgement projection exposure step, which is known by people skilled in the art field. Thereafter, an opening corresponding to the prescribed patter described above is formed in the resist by developing the resist film into which the prescribed pattern was transcribed. Further, the resist film in which the opening was formed is used as a mask of the wafer in an etching step of the wafer, and thereby, a pattern corresponding to the opening is formed in the wafer.  
     [0060] Steps described above are conducted when a pattern is formed in each layer on or above the wafer. As a result, a semiconductor device that a desired pattern was formed in each layer on or above the wafer is manufactured.  
     [0061] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.