Patent Publication Number: US-2015070672-A1

Title: Light exposure method, light exposure device, and reflective projection light exposure mask

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-187660, filed on Sep. 10, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a light exposure method, a light exposure device and a reflective projection light exposure mask. 
     BACKGROUND 
     In reflective projection light exposure, light is irradiated on the mask surface of a reflective projection light exposure mask, and the reflected light of that light is projected to the object to be exposed to light. The light is incident on the reflective projection light exposure mask with the main light axis inclined with respect to the mask surface. In order to form a fine pattern, it is necessary that the optical system has a high numerical aperture (NA). 
     When an optical system with a high NA is used, the incident angle of the light with respect to the mask surface is increased. Increasing the incident angle causes a reduction in the transfer performance (pattern image contrast, etc.), due to the effect of a change in reflectance properties according to the incident angle and a shadowing effect due to the thickness of the reflective mask pattern part (absorbent body). In reflective projection light exposure, it is important to improve the transfer performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  and  FIG. 1B  are schematic views illustrating a configuration of a reflective projection light exposure mask according to a first embodiment; 
         FIG. 2A  to  FIG. 2D  illustrate the shadowing effect; 
         FIG. 3  is a schematic view illustrating the projection of the light reflected at the reflective projection light exposure mask; 
         FIG. 4A  and  FIG. 4B  show a comparison between this embodiment and a reference example; 
         FIG. 5A  and  FIG. 5B  show the intensity of optical images; 
         FIG. 6  shows the relationship between the position of the focal point and the shift of the image; 
         FIG. 7A  and  FIG. 7B  illustrate the second embodiment; 
         FIG. 8  is a schematic view illustrating a configuration of a light exposure device according to the third embodiment; and 
         FIG. 9  is a flowchart illustrating the light exposure method according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a light exposure method includes irradiating light on a reflective projection light exposure mask and irradiating an object to be exposed to light with reflected light by reflecting the light by the reflective projection light exposure mask. The reflective projection light exposure mask includes a substrate and a pattern portion. The substrate has a first surface. The pattern portion has a multilayer reflective film provided on the first surface of the substrate. The pattern portion includes a plurality of protruding patterns and depression patterns. The depression patterns are provided between the plurality of protruding patterns. 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. In the following description, the same reference numeral is applied to the same member, and for members that have been described once, the description is omitted as appropriate. 
     First Embodiment 
       FIG. 1A  and  FIG. 1B  are schematic views illustrating a configuration of a reflective projection light exposure mask according to a first embodiment. 
       FIG. 1A  is a schematic cross-sectional view taken along the line A-A illustrated in  FIG. 1B ,  FIG. 1B  is a schematic plan view of a reflective projection light exposure mask  110 . In  FIG. 1A , an enlarged schematic cross-sectional view of a portion of the reflective projection light exposure mask  110  is illustrated. 
     As illustrated in  FIGS. 1A and 1B , the reflective projection light exposure mask  110  according to this embodiment includes a substrate  10  and a pattern portion  20 . Glass, for example, is used as the substrate  10 . The substrate  10  includes a first surface  10   a , and a second surface  10   b  on the opposite side to the first surface  10   a . In this embodiment, the direction normal to the first surface  10   a  is the Z direction. Also, one of the directions normal to the Z direction is defined as the X direction, and the direction normal to the Z direction and the X direction is defined as the V direction. 
     The pattern portion  20  is provided on the first surface  10   a  of the substrate  10 . The pattern portion  20  includes a multilayer reflective film  25 . The pattern portion  20  includes a plurality of protruding patterns  21 , and depression patterns  22  provided between the plurality of protruding patterns  21 . The protruding patterns  21  and depression patterns  22  each extend in, for example, the Y direction. In other words, a line and space pattern configuration is configured by the protruding patterns  21  and the depression patterns  22 . In this embodiment, a line and space pattern configuration is used as an example, but other pattern configurations (for example, an island configuration) may be used. 
     In the reflective projection light exposure mask  110 , the protruding patterns  21  include a multilayer reflective film  25 . The multilayer reflective film  25  is not included in the depression patterns  22 . The first surface  10   a  of the substrate  10  is exposed on the bottom  22   b  of the depression patterns  22 . If an etching stopper film (not shown on the drawings) is provided on the first surface  10   a  of the substrate  10 , the first surface  10   a  includes an etching stopper film. In other words, the etching stopper film included in the first surface  10   a  is exposed on the bottom  22   b  of the depression patterns  22 . 
     The multilayer reflective film  25  is a film that reflects light with a predetermined wavelength. In this embodiment, the multilayer reflective film  25  effectively reflects extreme ultraviolet (EUV). The wavelength of the EUV is, for example, not less than several nanometers (nm) and not more than several tens of nanometers. In this embodiment, EUV of 115 nanometers (nm) is used, for example. 
     The multilayer reflective film  25  includes, for example, a plurality of first films  25   a  and a plurality of second films  25   b  stacked alternately. Molybdenum (Mo) for example is used in the first film  25   a . Silicon (Si) for example is used in the second film  25   b.    
     The multilayer reflective film  25  includes, for example, several tens of pairs of the first film  25   a  and the second film  25   b . In this embodiment, about 40 pairs of the first film  25   a  and the second film  25   b  are included. The film thickness of the first film  25   a  and the second film  25   b  are each, for example, about several nanometers. In this embodiment, the film thickness is not less than about 3 nm and not more than 4 nm. The total thickness of the multilayer reflective film  25  is, for example, 280 nm. Three or more types of films may be stacked alternately in the multilayer reflective film  25 . 
     To manufacture the reflective projection light exposure mask  110 , for example, an etching stopper film is formed on the first surface  10   a  of the substrate  10 , and the multilayer reflective film  25  is formed on the etching stopper film. Then, a portion of the multilayer reflective film  25  is etched to the etching stopper film by, for example, reactive ion etching (RIE). In this way, the portion remaining without being etched becomes the protruding patterns  21 , and the portion where the multilayer reflective film  25  is removed by etching becomes the depression patterns  22 . 
     In the manufacture of the reflective projection light exposure mask  110 , it is not necessary to provide a separate material for the bottom of the depression patterns  22 , so the manufacturing process is simplified. 
     In reflective projection light exposure using the reflective projection light exposure mask  110 , the shadowing effect is suppressed, and a high contrast pattern image is formed. 
       FIGS. 2A through 2D  illustrate the shadowing effect. 
     In  FIG. 2A , a schematic perspective view is illustrated of an example where light is incident at an inclination to the direction normal to the direction in which the pattern extends, and in  FIG. 2B , a schematic perspective view is illustrated of an example where light is incident at an inclination to the direction in which the pattern extends.  FIG. 2C  shows the reflected light intensity as the line L 1  when the light is incident as shown in  FIG. 2A , and  FIG. 2D  shows the reflected light intensity as the line L 2  when the light is incident as shown in  FIG. 2B . The horizontal axis in  FIG. 2C  and  FIG. 2D  represents the position in the direction normal to the pattern, and the vertical axis represents the intensity. 
     A reflective projection light exposure mask  190  as illustrated in  FIG. 2A  and  FIG. 2B  includes the substrate  10 , the multilayer reflective film  25  formed on the substrate  10 , and a light absorbent pattern P provided on a portion of the multilayer reflective film  25 . 
     As illustrated in  FIG. 2A , when light is incident at an inclination to the direction normal to the direction in which the light absorbent pattern P extends, a portion of the light reflected at the multilayer reflective film  25  is blocked by the side surface of the light absorbent pattern P. On the other hand, as illustrated in  FIG. 2B , when light is incident at an inclination to the direction in which the light absorbent pattern P extends, the light reflected at the multilayer reflective film  25  is reflected without being blocked by the side surface of the light absorbent pattern P. Therefore, the intensity of the reflected light shown in  FIG. 2C  (line L 1 ) is lower than the intensity of the reflected light shown in  FIG. 2D  (line L 2 ). 
       FIG. 3  is a schematic view illustrating the projection of the light reflected at the reflective projection light exposure mask. 
       FIGS. 4A and 4B  show a comparison between this embodiment and a reference example. 
       FIG. 4A  shows the relationship between the focal point position and the contrast, and  FIG. 4B  shows the relationship between the position of intersection with the pattern and the contrast. 
     As illustrated in  FIG. 3 , the light C 1  is incident on the reflective projection light exposure mask  110  and  190 . The reflected light of the light C 1  incident on the reflective projection light exposure mask  110  and  190  is the light C 2 . The light C 1  is inclined at an angle of 8° for example with respect to the axis normal to the mask plane (the first surface  10   a  of the substrate  10 ) of the reflective projection light exposure mask  110  and  190 . The reflected light C 2  irradiates the object to be exposed to light via a projection optical system which is a second optical system  530 . The object to be exposed to light is, for example, a wafer W on which a resist is applied. 
       FIG. 4A  shows the results of a simulation of the variation in contrast when the position of the focal point of the light C 1  is varied for the reflective projection light exposure masks  110  and  190 . The horizontal axis of  FIG. 4A  represents the position of the focal point of the light C 1  incident on the reflective projection light exposure masks  110  and  190 , and the vertical axis represents the contrast of the reflected light C 2 . 
     In this embodiment, the position of the focal point is the position on the Z direction relative to the first surface  10   a  of the substrate  10 . A positive position of the focal point represents upward from the first surface  10   a  (the opposite side to the substrate  10 ), and a negative position of the focal point represents downward from the first surface  10   a  (the substrate  10  side). Also, the contrast is represented by the following equation (1). In equation (1), I max  is the maximum value of the light intensity, and I min  is the minimum value of the light intensity. 
       Contrast=( I   max   −I   min )/( I   max   +I   min )  (1)
 
     The line L 10  shown in  FIG. 4A  is the contrast for the reflective projection light exposure mask  110 , and the line L 20  is the contrast for the reflective projection light exposure mask  190 . Here, the thickness of the multilayer reflective film  25  is 280 nm. In the reflective projection light exposure mask  110 , the protruding patterns  21  include the multilayer reflective film  25  with a thickness of 280 nm. The depression patterns  22  do not include the multilayer reflective film  25 . In the reflective projection light exposure mask  190 , the light absorbent pattern P is provided on a portion of the multilayer reflective film  25 . 
     As shown in  FIG. 4A , the position of the focal point of the peak P 1  of the line L 10  of the contrast for the reflective projection light exposure mask  110  is different from the position of the focal point of the peak P 2  of the line L 20  of the contrast for the reflective projection light exposure mask  190 . 
       FIG. 4B  shows the results of simulation of the optical image for the reflective projection light exposure masks  110  and  190 . The horizontal axis of  FIG. 4B  shows the position in the direction normal to the pattern of the reflected light C 2  in the reflective projection light exposure masks  110  and  190 , and the vertical axis shows the intensity. 
     The line L 11  shown in  FIG. 4B  is the intensity for the reflective projection light exposure mask  110 , and the line L 21  is the intensity for the reflective projection light exposure mask  190 . It can be seen that the intensity for the reflective projection light exposure mask  110  as represented by the line L 11  is greater than the intensity for the reflective projection light exposure mask  190  as represented by the line L 21 . In other words, it can be seen that, in the reflective projection light exposure mask  110 , the transfer performance is superior compared with when the reflective projection light exposure mask  190  is used. 
       FIGS. 5A and 5B  show the intensity of optical ages. 
       FIG. 5A  shows the intensity of optical image due to the reflective projection light exposure mask  190 . The horizontal axis of  FIG. 5A  represents the position in the direction normal to the pattern of the reflected light C 2  for the reflective projection light exposure mask  190 , and the vertical axis represents the intensity. 
     The line L 31   a  shown in  FIG. 5A  is an example in which the position of the focal point of the light C 1  is set to 250 nm, the line L 31   b  is an example in which the position of the focal point of the light C 1  is set to 300 nm, and the line L 31   c  is an example in which the position of the focal point of the light C 1  is set to 350 nm. 
       FIG. 5B  shows the intensity of the optical image due to the reflective projection light exposure mask  110 . The horizontal axis of  FIG. 58  shows the position in the direction normal to the pattern of the reflected light C 2  for the reflective projection light exposure mask  110 , and the vertical axis shows the intensity. The line L 32   a  shown in  FIG. 5B  is an example in which the position of the focal point of the light C 1  is set to 250 nm, the line L 32   b  is an example in which the position of the focal point of the light C 1  is set to 300 nm, and the line L 32   c  is an example in which the position of the focal point of the light C 1  is set to 350 nm. 
     It can be seen that each of the lines L 32   a , L 32   b , and L 32   c  shown in  FIG. 5B  have a greater intensity than the lines L 31   a , L 31   b , and L 31   c  shown in  FIG. 5A . 
     Also, it can be seen that the images when the reflective projection light exposure mask  110  and  190  are used shift depending on the position of the focal point, as shown by the lines L 31   a , L 31   b , and L 31   c  of  FIG. 5A  and the lines L 32   a , L 32   b , and L 32   c  of  FIG. 5B . 
       FIG. 6  shows the relationship between the position of the focal point and the shift of the image. 
     The horizontal axis of  FIG. 6  represents the position of the focal point, and the vertical axis represents the amount of deviation of the position of the image in the direction normal to the pattern. The line L 33   a  in  FIG. 6  represents the relationship between the position of the focal point for the reflective projection light exposure mask  190  and the amount of deviation of the position of the image. The line L 33   b  is a line that approximates the line L 33   a  with a straight line. The line L 34   a  represents the relationship between the position of the focal point for the reflective projection light exposure mask  110  and the amount of deviation of the position of the image. The line L 34   b  is a line that approximates the line L 34   a  with a straight line. 
     As shown in  FIG. 6 , in the reflective projection light exposure mask  110 , the amount of deviation of the position of the image with respect to the position of the focal point is larger compared with that for the reflective projection light exposure mask  190 . When the amount of deviation of the position with respect to the position of focal point is large, it is easy to use the position of the focal point as a monitor when setting. 
     In this way, by using the reflective projection light exposure mask  110 , it is possible to improve the transfer performance in reflective projection light exposure. 
     Second Embodiment 
     Next, a reflective projection light exposure mask according to a second embodiment is explained. 
       FIGS. 7A and 7B  illustrate the second embodiment. 
       FIG. 7A  shows a schematic cross-sectional view of an example of the configuration of a reflective projection light exposure mask  120  according to this embodiment.  FIG. 7B  shows the results of simulation of the relationship between the position of the focal point and the normalized image log slope (NILS). 
     As illustrated in  FIG. 7A , the reflective projection light exposure mask  120  according to this embodiment includes the substrate  10  and a pattern portion  30 . The pattern portion  30  is provided on the first surface  10   a  of the substrate  10 . The pattern portion  30  includes a multilayer reflective film  25 . 
     The pattern portion  30  includes a plurality of protruding patterns  31 , and depression patterns  32  provided between the plurality of protruding patterns  31 . The protruding patterns  31  and depression patterns  32  each extend in, for example, the Y direction. In other words, a line and space pattern configuration is configured by the protruding patterns  31  and the depression patterns  32 . In this embodiment, a line and space pattern configuration is used as an example, but other pattern configurations (for example, an island configuration) may be used. 
     In the reflective projection light exposure mask  120 , the protruding patterns  31  include a protruding multilayer reflective film  251  that is a portion of the multilayer reflective film  25 . The depression patterns  32  include a depression multilayer reflective film  252  which is another portion of the multilayer reflective film  25 . The thickness t1 of the protruding multilayer reflective film  251  is greater than the thickness t2 of the depression multilayer reflective film  252 . 
     The depression pattern  32  is a portion that is recessed from the top surface of the protruding multilayer reflective film  251  of the protruding pattern  31  in the Z direction by the depth d1 towards the substrate  10 . In other words, the difference in the thickness t1 of the protruding multilayer reflective film  251  and the thickness t2 of the depression multilayer reflective film  252  is equal to the depth d1. 
     The thickness t2 of the depression multilayer reflective film  252  is for example not more than ½ the thickness t1 of the protruding multilayer reflective film  251 . 
     To manufacture the reflective projection light exposure mask  120 , the multilayer reflective film  25  is formed on the first surface  10   a  of the substrate  10 . Then, a portion of the multilayer reflective film  25  is etched using, for example, RIE. This etching is carried out to a position part way along the multilayer reflective film  25  in the Z direction. In other words, the etching is carried out to a position between the top surface of the multilayer reflective film  25  and the first surface  10   a  of the substrate  10 . The portion that remains without being etched becomes the protruding pattern  31 , and the portion removed by etching down to part way from the top surface of the multilayer reflective film  25  becomes the depression pattern  32 . 
     In the manufacture of the reflective projection light exposure mask  120 , it is not necessary to provide a separate material for the bottom of the depression patterns  22 , so the manufacturing process is simplified. 
     In reflective projection light exposure using the reflective projection light exposure mask  120 , the shadowing effect is suppressed, and a high contrast pattern image is formed. 
     The horizontal axis of  FIG. 7B  shows the position of the focal point, and the vertical axis shows the NILS. Here, the thickness of the multilayer reflective film  25  is 280 nm. Also, the NILS is represented by the following equation (2). In equation (2), W is a required dimension, I th  is an image intensity threshold to give W, and (dI/dx) is the slope of the spatial image. 
         NILS=W ×(1 /I   th )×( dI/dx )  (2)
 
     The line L 41  in  FIG. 7B  is a line that represents an example in which the depth d1 of the depression patterns  32  is 56 nm. The line L 42  is a line that represents an example in which the depth d1 of the depression patterns  32  is 196 nm. The lines L 41  and L 42  are included in the example of the reflective projection light exposure mask  120 . The line L 43  is a line that represents an example of the reflective projection light exposure mask  110  (an example in which the multilayer reflective film  25  is not included in the depression patterns  22 ). The line L 44  is a line that represents an example of the reflective projection light exposure mask  190 . 
     It can be seen that the NILS of the reflected image due to the reflective projection light exposure mask  110  and reflective projection light exposure mask  120  as represented by the lines L 41 , L 42 , and L 43  is greater than the NILS of the reflected image due to the reflective projection light exposure mask  190  as represented by the line L 44 . 
     Also, the NILS in line L 42  is greater than the NILS of lines L 41  and L 43 . In other words, by appropriately setting the depth d1 in the depression patterns  32 , a large NILS can be obtained. 
     In this way, by using the reflective projection light exposure mask  120 , it is possible to improve the transfer performance in reflective projection light exposure. 
     Third Embodiment 
     Next, a light exposure device according to a third embodiment is explained. 
       FIG. 8  is a schematic view illustrating a configuration of a light exposure device according to the third embodiment. 
     As illustrated in  FIG. 8 , a light exposure device  500  according to this embodiment includes a light source  510 , a first optical system  520 , and a second optical system  530 . 
     The light source  510  emits, for example, EUV light C 1 . The first optical system  520  irradiates the reflective projection light exposure mask  110  and  120  with the light C 1  emitted from the light source  510 . The first optical system  520  is an irradiating optical system. The first optical system  520  includes, for example, a plurality of mirrors M 1  through M 5 . Aberration of the light C 1  is corrected by the plurality of mirrors M 1  through M 5 . Also, the light C 1  is focused on a predetermined position of the reflective projection light exposure mask  110  and  120  by the plurality of mirrors M 1  through M 5 . The positions and angles of the plurality of mirrors M 1  through M 5  can be adjusted as appropriate. 
     The second optical system  530  projects light C 2  reflected by the reflective projection light exposure mask  110  and  120  towards an object to be exposed to light (for example, a wafer W on which a resist is applied). The second optical system  530  is a projection optical system. The second optical system  530  includes, for example, a plurality of mirrors M 6  through M 11 . Aberration of the light C 2  is corrected by the plurality of mirrors M 6  through M 11 . Also, the light C 2  is focused on a predetermined position on the wafer W by the plurality of mirrors M 6  through M 11 . The positions and angles of the plurality of mirrors M 6  through M 11  can be adjusted as appropriate. 
     The wafer W is mounted on a stage  540 . The light exposure device  500  projects the light C 2  which is light reflected by the reflective projection light exposure mask  110  and  120  onto the wafer W via the second optical system  530 . When projection onto one region is completed, the stage  540  is moved. Then, the light C 2  is projected onto the next region of the wafer W. By repeating this process, the light C 2  is projected onto a plurality of regions on the wafer W. 
     The first optical system  520  sets the position of the focal point of the light C 1  between the first surface  10   a  and the top surfaces of the protruding patterns  21  and  31  of the reflective projection light exposure mask  110  and  120 . For example, as shown in  FIG. 7B , in the line L 43  that represents the relationship between the position of the focal point and the NILS in the reflective projection light exposure mask  110 , there is a peak P 43   a  near the focal point position 250 nm. Also, in the lines L 41  and L 42  that represents the relationship between the position of the focal point and the NILS in the reflective projection light exposure mask  120 , there are peaks P 41   a  and P 42   a  near the focal point positions 110 nm and 350 nm. The focal point positions are set in accordance with these peaks P 41   a , P 42   a , and P 43   a.    
     Also, the first optical system  520  may set the position of the focal point of the light C 1  on the substrate  10  side of the first surface  10   a  of the reflective projection light exposure mask  110  and  120 . For example, as shown in  FIG. 7B , in the line L 43 , there is a peak P 43   b  near the focal point position −220 nm. Also, in the lines L 41  and L 42 , there are peaks P 41   b  and P 42   b  near the focal point positions −340 nm and −100 nm. The focal point positions are set in accordance with these peaks P 41   b , P 42   b , and P 43   b.    
     By setting the positions of the focal points in this manner, it is possible to increase the contrast of the images of the light C 2  due to the reflective projection light exposure mask  110  and  120  and exhibit sufficient transfer performance. 
     Fourth Embodiment 
     Next, a light exposure method according to a fourth embodiment is explained. 
       FIG. 9  is a flowchart illustrating the light exposure method according to the fourth embodiment. 
     As illustrated in  FIG. 9 , the light exposure method according to this embodiment includes preparing a substrate and mask (step S 101 ), irradiating with light (step S 102 ), and projecting the light (step S 103 ). 
     In preparing the substrate and mask (step S 101 ), an object to be exposed to light, for example a wafer W, is prepared. For example, a resist is applied to the surface of the wafer W. The wafer W is mounted on the stage  540  illustrated in  FIG. 8 . Also, reflective projection light exposure mask  110  and  120  is prepared as a mask. The reflective projection light exposure mask  110  and  120  is fixed in a mask holder (not illustrated on the drawings) of the light exposure device  500  illustrated in  FIG. 8 . 
     Next, in irradiating with light (step S 102 ), the reflective projection light exposure mask  110  and  120  is irradiated with a predetermined light C 1 . The light C 1  is, for example, emitted from the light source  510  illustrated in  FIG. 8 , and irradiated onto the reflective projection light exposure mask  110  and  120  via the first optical system  520 . 
     In this embodiment, when the reflective projection light exposure mask  110  and  120  is irradiated with the light C 1 , the position of the focal point of the light C 1  is set between the first surface  10   a  and the top surface of the protruding pattern  21  and  31  of the reflective projection light exposure mask  110  and  120 . Also, the position of the focal point of the light C 1  maybe set on the substrate  10  side of the first surface  10   a  of the reflective projection light exposure mask  110  and  120 . 
     Next, in projecting the light (step S 103 ), the light C 2  which is the light C 1  reflected by the reflective projection light exposure mask  110  and  120  is projected onto the wafer W which is the object to be exposed to light. The light C 2  is projected onto the wafer W via the second optical system  530  illustrated in  FIG. 8 , for example. In this way, the image of the reflected light is transferred to the resist on the wafer W by the reflective projection light exposure mask  110  and  120 . 
     According to the light exposure method of this embodiment, it is possible to improve the contrast of the image of the light C 2  due to the reflective projection light exposure mask  110  and  120  and exhibit sufficient transfer performance. 
     As explained above, according to the reflective projection light exposure mask, light exposure method, and light exposure device of this embodiment, it is possible to improve the transfer performance of the pattern image. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.