Patent Publication Number: US-2011062623-A1

Title: Method of forming a pattern formation template

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-216074, filed Sep. 17, 2009; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a method of forming a pattern formation template for forming a second template from a first template by imprint techniques. 
     BACKGROUND 
     In recent years, optical imprint techniques (step-and-flash imprint lithography [SFIL]) have been proposed as pattern transfer techniques for realizing the microfabrication of a semiconductor integrated circuit. In a template used in optical imprint techniques, a region where a desired transfer pattern has a concave-convex shape is called a mesa region (main pattern region), which differs from a peripheral region in surface height. In the peripheral region, there are provided alignment marks for adjusting the template pressing positions. 
     In the manufacture of semiconductor integrated circuits, a large number of the same patterns must be formed. Consequently, the template is used very often and therefore the risk of the template being broken is high. To overcome this problem, a first template is formed by electron beam lithography and a second template used in actual pattern transfer is formed from the first template by imprint techniques. 
     The pattern on the mesa region of the first template is transferred to the second template. Since the pattern outside the mesa region differs from the pattern on the mesa region in surface height, the pattern outside the mesa region is not transferred to the second template. Therefore, in the second template, after the main pattern and then a mesa structure have been formed, alignment marks must be formed outside the mesa region of the second template by an additional process. 
     However, when an alignment mark is formed outside the mesa region with a laser beam machine, there is a relative displacement of the position of the alignment mark formed outside the mesa region by additional machining from the position of the already formed main pattern because of the processing accuracy of the laser beam machine and the alignment accuracy of the processed position. If the pattern is transferred to a processed substrate using a template with such a positional accuracy error, the transfer positional control accuracy in pattern transfer will decrease. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view schematically showing a structure of a first template used in a first embodiment; 
         FIG. 2  is a sectional view schematically showing a structure of a second template formed in the first embodiment; 
         FIGS. 3A ,  3 B,  3 C,  3 D,  3 E and  3 F are sectional views to explain the steps of manufacturing the first template in the first embodiment; 
         FIGS. 4A ,  4 B,  4 C,  4 D,  4 E,  4 F,  4 G,  4 H and  4 I are sectional views to explain the steps of manufacturing the second template in the first embodiment; and 
         FIGS. 5A and 5B  are sectional views to explain the difference between the presence and absence of the mesa region in pattern transfer. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a concavo-convex pattern of a first template where a concavo-convex main pattern has been formed in a main pattern region and a concavo-convex peripheral pattern has been formed in a peripheral region is transferred to a second template substrate by imprint techniques. Then, a second template with a step between a region corresponding to the main pattern region and a region corresponding to the peripheral region is formed by retreating the peripheral region of the second template substrate by etching. 
     Hereinafter, referring to the accompanying drawings, embodiments of the invention will be explained. 
     First Embodiment 
       FIG. 1  is a sectional view schematically showing a configuration of a first template used in a first embodiment.  FIG. 2  is a sectional view schematically showing a second template formed by imprint techniques using the first template. 
     As shown in  FIG. 1 , a first template  10  is configured by providing patterns  13 ,  14  at one principal surface of a substrate  11 . At the front face (the undersurface in  FIG. 1 ) of the substrate  10 , a mesa region  12  which is convex except for its periphery is formed. In the mesa region  12 , a main pattern  13  and alignment marks (peripheral marks)  14  are formed. The main pattern  13  is formed in a main pattern region  15  of the mesa region  12 . The alignment marks  14  are formed in a peripheral region  16  of the mesa region  12 . Each of the patterns  13 ,  14  is a concave-convex pattern formed by carving the surface of the substrate  11 . 
     The substrate  11  is made of a translucent material, such as quartz, used in imprint techniques. The first template  10  is formed with a high accuracy by electronic beam lithography. 
     As shown in  FIG. 2 , a second template  30  is configured by providing patterns  33 ,  34  at one principal surface of a substrate  31 . At the front face (the undersurface) of the substrate  31 , a mesa region  32  which is convex in its central part is formed. In the mesa region  32 , a main pattern  33  is formed. In a peripheral region  36  outside the mesa region  32 , alignment marks (peripheral patterns)  34  are formed. That is, the mesa region includes only the main pattern region, not the peripheral region  36 . Each of the patterns  33 ,  34  is formed by imprint techniques using the template  10 . Like the substrate  11 , the substrate  31  is made of a translucent material, such as quartz, used in imprint techniques. 
     As described above, the size of the mesa region in the first template  10  differs from that of the mesa region in the second template  30 . In addition, the alignment marks  14  are formed in the mesa region  12  of the first template  10 , whereas the alignment marks  34  are formed in the peripheral region  36  outside the mesa region  32 . 
     Next, a method of manufacturing the first template  10  and second template  30  will be explained. 
     In the embodiment, the alignment marks  14  formed in the mesa region  12  of the first template  10  are transferred to a region outside the mesa region  32  of the second template  30 . Then, while the relative positional accuracy between the main pattern and the alignment marks in processing the first template is maintained, the alignment marks  34  are formed outside the mesa region  32  of the second template  30 . 
       FIGS. 3A to 3F  are sectional views to explain the steps of manufacturing the first template  10  in the first embodiment. 
     First, as shown in  FIG. 3A , a substrate  11  for forming a first template  10  is prepared. In the embodiment, a Qz substrate with dimensions of about 152 mm×152 mm×6 mm thick is used as the substrate  11 . On the substrate  11 , a Cr film  21  about 10 nm thick is formed by sputtering. EB resist  22  is applied onto the Cr film  21 . 
     Then, a pattern used for transfer by imprint techniques is exposed on the EB resist  22  on the substrate  11  with an electron beam lithography system. At this time, the pattern includes not only the main pattern  13  but also the alignment marks  14 . Then, the EB resist  22  in the exposed part is removed by a processing procedure, thereby forming a resist pattern serving as an etching mask as shown in  FIG. 3B . 
     Next, as shown in  FIG. 3C , with the EB resist film  22  as a mask, the Cr film  21  is etched. Thereafter, the EB resist  22  is peeled. 
     Then, as shown in  FIG. 3D , with the Cr film  21  as a mask, carve etching is applied to the surface of the substrate  11 , thereby forming the main pattern  13  and alignment marks  14 . In the embodiment, anisotropic dry etching is used. In the anisotropic dry etching, a fluorine radical is used in carve etching. Thereafter, photosensitive resin (photoresist)  23  is applied to the substrate  11 . 
     Next, as shown in  FIG. 3E , the photoresist  23  in the part excluding the mesa region  12  is exposed. At this time, the mesa region  12  is set so that the region where the alignment marks  14  have been formed may be inside the mesa region  12 . Thereafter, the photoresist  23  in the exposed part is removed by a processing procedure. 
     Then, as shown in  FIG. 3F , with the photoresist  23  as a mask, the Cr film  21  is etched. Then, with the photoresist film  23  and Cr film  21  as a mask, carve etching is applied to the substrate  11 . In the embodiment, anisotropic dry etching using a fluorine radical is used as carve etching. 
     From this point on, the resist  23  and Cr film  21  are peeled, which completes a first template  10  which has the structure shown in  FIG. 1 . 
     As shown in  FIG. 1 , in the first template  10 , the main pattern  13  and alignment marks  14  are both in the mesa region  12 . Since the main pattern  13  and alignment marks  14  are both exposed in the same process, both have the same positional accuracy and therefore there is no relative positional error. 
       FIGS. 4A to 4I  are sectional views to explain the steps of manufacturing a second template  30  by optical imprint techniques. A first template  10  used here is the one formed by the processes shown in  FIGS. 3A to 3F . 
     First, as shown in  FIG. 4A , a substrate  31  for forming a second template  30  is prepared. In the embodiment, a Qz substrate with dimensions of about 152 mm×152 mm×6 mm thick is used as the substrate  31 . On the substrate  31 , a Cr film  41  about 10 nm thick is formed by sputtering. Light curing resin  42  is applied onto the Cr film  41 . 
     Next, as shown in  FIG. 4B , a concave-convex pattern formed at the surface of the first template  10  is pressed against the light curing resin  42  applied onto the substrate  31  in such a manner that the light curing resin  42  spreads over the concavo-convex pattern at the surface of the first template  10 . 
     Then, as shown in  FIG. 4C , a light source  50  is caused to apply light from the back side of the first template  10 , thereby hardening the light curing resin  42 . Thereafter, as shown in  FIG. 4D , the first template  10  is peeled from the substrate  31  for forming a second template. 
     Next, as shown in  FIG. 4E , with the hardened light curing resin  42  as a mask, the Cr film  41  is selectively etched by RIE techniques. Thereafter, the light curing resin film  42  is peeled. 
     Then, as shown in  FIG. 4F , with the Cr film  41  as a mask, carve etching is applied to the surface of the substrate  31 , thereby forming a main pattern  33  and alignment marks  34  at the surface of the substrate  31 . In the embodiment, anisotropic dry etching using a fluorine radical is used to carve the substrate. 
     Next, as shown in  FIG. 4G , photosensitive resin (photoresist)  43  is applied onto the substrate  31 . Then, the photoresist  43  in the part excluding the mesa region  32  is exposed. At this time, the mesa region  32  is set so that the region where the alignment marks  34  have been formed may be in a peripheral region  36  outside the mesa region  32 . Thereafter, as shown in  FIG. 4H , the photoresist  43  in the exposed part is removed by a processing procedure. 
     Next, as shown in  FIG. 4I , with the photoresist  43  as a mask, the Cr film  41  is etched. Then, with the photoresist film  43  and Cr film  41  as a mask, carve etching is applied to the surface of the substrate. In the embodiment, anisotropic dry etching using a fluorine radical is used. At this time, the part where the alignment marks  34  have been formed is also etched. Because of anisotropic dry etching, the substrate surface in the part excluding the mesa region  32  is carved, while the concavo-convex structure before etching is maintained. 
     From this point on, the photoresist  43  and Cr film  41  are peeled, which completes a second template  30  which has the structure shown in  FIG. 2 . 
     In the second template  30 , the alignment marks  34  have been formed outside the mesa region  32 . In this case, some error in the dimensional accuracy and carve depth accuracy of the alignment marks  34  occurs in the process of forming a mesa structure. However, no new error occurs in the relative positional accuracy between the alignment marks  34  and main pattern  33  and therefore the same accuracy as that of the first template  10  is maintained. That is, the alignment marks  34  and main pattern  33  have the same positional accuracy and therefore there is no relative positional error. 
     Forming the second template  30  by the above processes enables the alignment marks  34  to be formed outside the mesa region  32  without degrading the relative positional accuracy between the main pattern  33  and alignment marks  34 . In addition, use of the template  30  formed by the above processes enables a pattern to be transferred with high accuracy by optical imprint techniques. 
     The reason why the mesa structure is needed in the template  30  is to avoid the breakage of the previously transferred patterns due to the interference with adjacent patterns and the template used when a plurality of patterns are transferred to the same processed substrate. 
       FIG. 5A  shows a case where a pattern has been transferred using a template  30 ′ with no mesa structure. It is seen that, when a pattern  61  is formed on a semiconductor substrate  60  using the template  30 ′, a previously transferred pattern  62  has been broken due to the interference with the template  30 ′.  FIG. 6B  shows a case where a pattern has been transferred using a template  30  with such a mesa structure as described in the first embodiment. It is seen that, even when a pattern  61  is formed on a semiconductor substrate  60  using the template  30 , the interference of the mesa structure with adjacent patterns  62  is avoided and therefore the pattern is transferred without breaking the adjacent pattern  62 . 
     As described above, with the embodiment, the alignment marks  34  can be formed outside the mesa region  32  in the second template  30 , while the relative positional accuracy with the main pattern  33  is kept good. Specifically, the second template  30  can be formed from the first template  10  by imprint techniques and the alignment marks  34  can be formed in the peripheral region  36  with high accuracy without impairing the relative positional accuracy between the main pattern  33  and alignment marks  34  in the second template  30 . Accordingly, a pattern is formed by optical imprint techniques using the second template  30 , which makes it possible to form a pattern with good positional accuracy 
     (Modification) 
     This invention is not limited to the above embodiment. 
     The structure and size of the substrate for forming a template explained in the embodiment are illustrative and not restrictive. The size of the template substrate may be different from that described in the embodiment. The substrate for forming a template is not necessarily made of Qz. Any suitable material may be used, provided that the material has a translucency and rigidity that pose no problem in using optical imprint techniques. The Cr layer on the surface of the substrate used in the embodiment is an example of the material suitable for a mask member in etching Qz and the layer may be made of a suitable metal other than Cr or a suitable nonmetal. 
     The processes used in the embodiment do not restrict the scope of the invention. While in the embodiment, an electron beam lithographic system has been used as lithographic means used to form a first template pattern, a laser beam lithographic system, an ion beam lithographic system, or the like may be used, provided that the system satisfies the required specifications, including accuracy. In this case, the type of resist used may be changed according to the lithographic system used. In addition, imprint techniques in forming a second template are not necessarily restricted to optical imprint techniques. For instance, thermal imprint techniques using thermosetting resin instead of light curing resin may be used. 
     While in the embodiment, anisotropic dry etching using a fluorine radical has been used as means for etching Qz, other techniques, including wet etching using fluorine series solution, may be used, provided that a desired processing accuracy is obtained. When isotropic etching has been used in wet etching, the alignment marks will have become deformed and changed in size. If the alignment marks have been etched isotropically and reflected their original shape, they can be used as alignment marks. For instance, if relatively large alignment marks have been formed in the first template, small alignment marks that reflect the shape of the original marks will be left in isotropically etching the second template. In this case, too, an error in the relative position between the main pattern and alignment marks can be prevented. 
     The peripheral pattern is not necessarily limited to the alignment marks and may be any pattern other than the main pattern, such as identifying marks. 
     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 inventions.