Abstract:
According to an aspect of the present invention, there is provided a method for forming a pattern including: applying a photosensitive resin onto a film on a wafer substrate; partly exposing the photosensitive resin to light and developing the photosensitive resin to form a first pattern having an opening portion; applying a photo-curable material onto the film exposed by the opening portion of the first pattern; bringing one face of an optically-transmissive template having a second pattern formed on the one face into contact with the photo-curable material, the second pattern including projections and reentrants; irradiating the photo-curable material with light; and separating the template from the photo-curable material.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Intention 
         [0002]    An aspect of the present invention relates to a method for forming a pattern and a method for manufacturing a semiconductor device. 
         [0003]    2. Description of the Related Art 
         [0004]    With the progress of scaling-down of semiconductor integrated circuits and increase in scale of the integration, it has been demanded to increase the accuracy of photolithography apparatus in the field of a pattern transfer technique to realize microfabrication. On this account, the cost involved in such apparatus has been increasing, which has been a disadvantage. 
         [0005]    As a technique to form a fine pattern at low cost, the photo-nanoimprint technique has been proposed (see e.g. JP-2000-194142-A). This is a technique to transfer a resist pattern by: pressing a stamper, i.e. a template having the projection-and-reentrant pattern that corresponds to a pattern to be formed on a substrate, against a photo-curable organic material layer formed on a surface of a substrate targeted for transfer; applying rays of light through the template to cure the organic material layer in this condition; and then separating the template from the organic material layer. 
         [0006]    The organic material layer, which serves as a resist, is applied to the targeted surface, during which the operation is controlled so that the organic material is spread reaching every nook and cranny of the projection-and-reentrant pattern on the template. In an area where the template overlaps with an edge of a substrate when the template is pressed against the substrate, it is usually difficult to keep the template in parallel with the surface of the substrate. Therefore, the organic material is not put on such area, to which no pattern is transferred. 
         [0007]    In regard to the vicinity of the periphery of a pattern transfer area, no pattern is formed in a peripheral area of a wafer substrate, which poses problems including the following defects. The first is the abnormality in a processing form arising near the periphery of the pattern transfer area under the influence of the change in pattern coverage in an etching step after imprinting. The second is the exfoliation of a wire in a process of CMP (Chemical Mechanical Polishing) after burying the wire in position. 
       SUMMARY OF THE INVENTION 
       [0008]    According to an aspect of the present invention, there is provided a method for forming a pattern including: applying a photosensitive resin onto a film on a wafer substrate; partly exposing the photosensitive resin to light and developing the photosensitive resin to form a first pattern having an opening portion; applying a photo-curable material onto the film exposed by the opening portion of the first pattern; bringing one face of an optically-transmissive template having a second pattern formed on the one face into contact with the photo-curable material, the second pattern including projections and reentrants; irradiating the photo-curable material with light; and separating the template from the photo-curable material. 
         [0009]    According to another aspect of the present invention, there is provided a method for manufacturing a semiconductor device including: applying a photosensitive resin onto a film on a wafer substrate; partly exposing the photosensitive resin to light and developing the photosensitive resin to form a first pattern having an opening portion; applying a photo-curable material onto the film exposed by the opening portion of the first pattern; bringing one face of an optically-transmissive template having a projection-and-reentrant pattern formed on the one face into contact with the photo-curable material; irradiating the photo-curable material with light; separating the template from the photo-curable material; etching the film by using of a combination of the photosensitive resin and photo-curable material as a mask; and forming a device pattern on the wafer substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments may be described in detail with reference to the accompanying drawings, in which: 
           [0011]      FIGS. 1A to 1F  are sectional views for explaining the steps of a method for forming a pattern according to a first embodiment of the present invention; 
           [0012]      FIG. 2  is a top view of a wafer substrate formed by the method according to the first embodiment; 
           [0013]      FIGS. 3A to 3D  are sectional views for explaining the steps of a method for forming a pattern according to a comparative example; 
           [0014]      FIG. 4A  is an illustration partly showing a top face of a wafer substrate formed by the method according to the comparative method; 
           [0015]      FIG. 4B  is an illustration partly showing a cross section of the wafer substrate; 
           [0016]      FIGS. 5A to 5G  are sectional views for explaining the steps of a method for forming a pattern according to a second embodiment of the present invention; 
           [0017]      FIGS. 6A to 6C  are top views of wafer substrates formed by the method according to the second embodiment; 
           [0018]      FIGS. 7A to 7C  are sectional views for explaining a method for forming a pattern according to a variant of the embodiment; 
           [0019]      FIGS. 8A to 8F  are sectional views for explaining the steps of a method for forming a pattern according to a third embodiment of the present invention; and 
           [0020]      FIG. 9  is a top view of a wafer substrate formed by the method according to the third embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Embodiment of the present invention will be described below with reference to the drawings. 
       First Embodiment  
       [0022]      FIGS. 1A to 1F  are sectional views for explaining the steps of a method for forming a pattern according to the first embodiment. As shown in  FIG. 1A , a resist  2  is applied onto a wafer substrate  1  with a film (not shown) formed thereon. The resist  2  is a positive type photoresist. 
         [0023]    The wafer substrate  1  is irradiated with light, thereby exposing the resist  2  to light as shown in  FIG. 1B . The area to be exposed to light is an area A, in which a desired fine pattern is to be formed to make a chip by the photo-nanoimprint technique in a later step. In this case, the exposure was performed by a KrF (krypton fluoride) scanner, which is a scanning-type aligner, using a photomask with its whole effective area opening. 
         [0024]    Then, the development of the wafer substrate  1  is performed, leaving only a part of the resist  2  on an area (wafer peripheral area) B, which has not undergone the exposure, as shown in  FIG. 1C . 
         [0025]    After that, a liquid photo-curable organic material  3  is applied onto the wafer substrate  1 , as shown in  FIG. 1D . The photo-curable organic material is acrylic monomer, for example. 
         [0026]    Next, a template  4  having the projection-and-reentrant pattern that correspond to the pattern to be formed on the water substrate  1  is brought into contact with the photo-curable organic material  3 , as shown in  FIG. 1E . Then, the liquid photo-curable organic material  3  is forced to flow expanding along the projection-and-reentrant pattern on the template  4  and fill the space inside the template. After that, the substrate thus prepared is subjected to irradiation with light, and then the photo-curable organic material  3  is cured. The light used for the irradiation may be any kind of light as long as it is capable of curing the photo-curable organic material  3 , and for example, light emitted by a lamp may be used. The template  4  is formed from a material which allows the light to pass through it, e.g. quartz glass. 
         [0027]    Subsequently, the template  4  is separated from the photo-curable organic material  3  as shown in  FIG. 1F . At this point, the photo-curable organic material  3  has been cured, and therefore the material  3  is kept in the condition (i.e. shape) when it is in contact with the template  4 . Here, a central portion of the photo-curable organic material  3  having a smaller pitch is termed a device chip-forming area A 1 , and an edge portion having a larger pitch is termed a chip peripheral area A 2 . 
         [0028]    After that, the steps shown with reference to  FIGS. 1D to 1F  are repeated, thereby forming a layer of the photo-curable organic material  3  having a desired projection-and-reentrant pattern in two or more areas on the wafer substrate  1 . The top view of the wafer substrate  1  thus formed is shown in  FIG. 2 . On the wafer peripheral area B, on which the pattern transfer by using of the template  4  has not been performed, the resist  2  still remains. 
         [0029]    Subsequently, the resist pattern formed by using of the template  4 , and the resist  2  is used as a mask to etch the film (not shown) on the wafer substrate  1 . After that, a burying of a wire in a groove of the pattern formed by the etching, CMP and other processes are performed, whereby a device is formed. 
         [0030]    As the resist  2  remains on the wafer peripheral area B, the difference in coverage of the wafer substrate  1  between the area (A 1  and A 2 ) to which the pattern is transferred by using of the template  4  and the wafer peripheral area (B) can be made smaller. Thus, the defects, such as the abnormality of a processing form arising the periphery of the pattern-forming area in the etching step, and the exfoliation of a wire in the step of CMP, can be prevented. 
       COMPARATIVE EXAMPLE  
       [0031]      FIGS. 3A to 3D  are sectional views for explaining the steps of a method for forming a pattern according to a comparative example. As shown in  FIG. 3A , a liquid photo-curable organic material  32  is applied onto a wafer substrate  31  with a film (not shown) formed thereon. 
         [0032]    Next, a template  33  having the projection-and-reentrant pattern that corresponds to the pattern to be formed on the wafer substrate  31  is brought into contact with the photo-curable organic material  32 , as shown in  FIG. 3B . Then, the liquid photo-curable organic material  32  is forced to flow expanding along the projection-and-reentrant pattern on the template  33  and fill the space inside the template. After that, the substrate thus prepared is irradiated with light from above the template  33 . The light used for the irradiation may be any kind of light as long as it is capable of curing the photo-curable organic material. The template  33  is formed from a material which allows the light to pass through it, e.g. quartz glass. 
         [0033]    In this way the photo-curable organic material  32  is cured as shown in  FIG. 3C . 
         [0034]    The template  33  is thereafter separated from the photo-curable organic material  32  as shown in  FIG. 3D . At this point, the photo-curable organic material  32  has been cured, and therefore the material  32  is still kept in the condition (i.e. shape) when it was in contact with the template  33 . 
         [0035]    After that, the steps shown with reference to  FIGS. 3A to 3D  are repeated, thereby forming a layer of the photo-curable organic material  32  having a desired projection-and-reentrant pattern in two or more areas on the wafer substrate  31 .  FIG. 4A  shows a part of the top face of the resultant wafer substrate  31 , and  FIG. 4B  shows a cross section taken along the line C-C′ shown in  FIG. 4A . The organic material is not put on an area on the substrate, which is not subjected to the pattern transfer by using of the template  33 , i.e. an area where the template  33  overlaps with an edge L of the wafer substrate  31  (hereinafter referred to as “wafer peripheral area S”). 
         [0036]    Subsequently, the patterns thus formed by using of the template  33  are used as a mask to etch the film (not shown) on the wafer substrate  31 . After that, a burying of a wire in a groove of the pattern formed by the etching, CMP and other processes are performed. 
         [0037]    In this comparative example, the difference in the coverage of the wafer substrate  31  between the area to which the pattern is transferred by using of the template  33  and the wafer peripheral area S (having no pattern) is so large that the abnormality in a processing form such as a tapered shape of a groove of the pattern formed in the etching step can be caused. Further, the exfoliation of a wire can be caused in the step of CMP. If a device is formed on a substrate having such defect, a trouble such as the deterioration in electric property will come up. 
         [0038]    In contrast, with the method for forming a pattern according to the embodiment, it is possible to reduce the difference in the coverage of the water substrate  1  between the area to which the pattern is transferred by using of the template  4  and the wafer peripheral area where the remaining resist  2  is used as a dummy pattern. Therefore, it is possible to prevent a defect concerning a pattern processing form and the like from being caused in the later etching step and the like. In addition, when a device is formed on a substrate with a pattern formed according to this method, good electrical properties can be achieved. 
       Second Embodiment  
       [0039]      FIGS. 5A to 5G  are sectional views for explaining the steps of a method for forming a pattern according to the second embodiment. While in the first embodiment, the remaining resist having a coverage of 100% is used as a dummy pattern on the wafer peripheral area, in the second embodiment a dummy pattern having a desired aperture ratio is formed. As shown in  FIG. 5A , a resist  52  is applied onto a wafer substrate  51  with a film (not shown) formed thereon. The resist  52  is a positive type photoresist. 
         [0040]    A 100%-opening mask (not shown) is used to expose an area (chip-forming area) A to light as shown in  FIG. 5B , provided that on the chip-forming area A, a desired fine pattern is formed by the photo-nanoimprint technique to form a chip in a later step. Here, the exposure is performed using a KrF (krypton fluoride) scanner. 
         [0041]    Then, as shown in  FIG. 5C , a mask (not shown) having a dummy pattern for adjusting the coverage is used to perform exposure to light on an area B where formation of the desired fine pattern by the photo-nanoimprint technique in the later step is not performed. The area B is a wafer peripheral area of the wafer substrate  51 , for example. The dummy pattern is determined based on the projection-and-reentrant pattern of a template  54  used in a later step of photo-nanoimprint. The aperture ratio of the dummy pattern is arranged to be equal to the percentage of projecting portions of the template  54  (corresponding to reentrant portions of the pattern transferred to the wafer substrate  51 ). 
         [0042]    After that, the development of the wafer substrate  51  is performed, leaving a part of the resist  52  on the wafer peripheral area, which is to be used as a dummy pattern, as shown in  FIG. 5D . 
         [0043]    Subsequently, a liquid photo-curable organic material  53  is applied to a chip-forming area of the wafer substrate  51  as shown in  FIG. 5E . The photo-curable organic material  53  is e.g. acrylic monomer. 
         [0044]    Next, a template  54  having the projection-and-reentrant pattern that corresponds to the pattern to be formed on the wafer substrate  51  is brought into contact with the photo-curable organic material  53 , as shown in  FIG. 5F . Then, the liquid photo-curable organic material  53  is forced to flow expanding along the projection-and-reentrant pattern on the template  54  and fill the space inside the template. After that, the substrate thus prepared is irradiated with light from above the template  54  to cure the photo-curable organic material  53 . The light used for the irradiation may be any kind of light as long as it is capable of curing the photo-curable organic material  53 , and for example, light emitted by a lamp may be used. The template  54  is formed from a material which allows the light to pass through it, e.g. quartz glass. 
         [0045]    The template  54  is thereafter separated from the photo-curable organic material  53  as shown in  FIG. 5G . At this point, the photo-curable organic material  53  has been cured, and therefore the material  53  is still kept in the condition (i.e. shape) when it was in contact with the template  54 . 
         [0046]    After that, the steps shown with reference to  FIGS. 5E to 5G  are repeated, thereby forming a layer of the photo-curable organic material  53  having a desired projection-and-reentrant pattern in two or more areas on the wafer substrate  51 .  FIGS. 6A to 6C  each present a top view of the wafer substrate  51  which can be formed in this process. As shown in the drawings, on each wafer peripheral area, on which the pattern transfer by using of the template  54  has not been performed, the resist  52  shaped into a dummy pattern still remains. 
         [0047]    Subsequently, a combination of the pattern  53  formed by using of the template  54 , and the resist  52  shaped into a dummy pattern is used as a mask to etch the wafer substrate  51 . After that, a burying of a wire in a groove of the pattern formed by the etching, CMP and other processes are performed, whereby a device is formed. 
         [0048]    The dummy pattern suffices as long as the aperture ratio of the dummy pattern is equal to the percentage of projecting portions of the template  54  (corresponding to reentrant portions of the pattern transferred to the wafer substrate  51 ). Examples of a dummy pattern having an aperture ratio of 50% include a checkered pattern as shown in  FIG. 6A , and a stripe pattern as shown in  FIG. 6B . Also, the dummy pattern may be a pattern having two or more holes H as shown in  FIG. 6C . 
         [0049]    As the resist  52  remains in the form of a dummy pattern on the wafer peripheral area (Area B), the area to which the pattern is transferred by using of the template  54  and the wafer peripheral area are arranged to have a pattern aperture ratio common to them. As a result, the difference in coverage of the wafer substrate  51  between these areas can be reduced remarkably, and therefore the defects including the abnormality of a processing form arising in the etching step, and the exfoliation of a wire in the step of CMP can be prevented more efficiently. 
         [0050]    The resist  52  may be negative type one. An example of using a negative type resist as the resist  52  will be described with reference to  FIGS. 7A to 7C  as a variant of the embodiment. 
         [0051]    As shown in  FIG. 7A , a negative type resist  72  is applied onto a wafer substrate  71  with a film (not shown) formed thereon. 
         [0052]    Then, as shown in  FIG. 7B , a mask (not shown) having a dummy pattern for adjusting the coverage is used to perform exposure to light on an area B where formation of the desired fine pattern by the photo-nanoimprint technique in the later step is not performed. The area B is a peripheral area of the wafer substrate  71 , for example. The dummy pattern is determined based on the projection-and-reentrant pattern of a template used in the later photo-nanoimprint step. 
         [0053]    Then, the development of the wafer substrate  71  is performed, leaving only a part of the resist  72  on an area, which has undergone the exposure, as shown in  FIG. 7C . The later steps are the same as the steps which have been described with reference to  FIGS. 5E to 5G , and the their descriptions are omitted here. 
         [0054]    In the case of using a positive type photoresist, two photomasks are needed to partly leave the resist  52  according to a dummy pattern on the wafer substrate  51  as shown  FIGS. 5B and 5C . However using a negative type resist can decrease the number of photomasks used to partly leave the resist on the wafer substrate according to a dummy pattern to one as shown in  FIGS. 7B and 7C , whereby the cost can be reduced. 
       Third Embodiment  
       [0055]      FIGS. 8A to 8F  are sectional views for explaining the steps of a method for forming a pattern according to the third embodiment. As shown in  FIG. 8A , a resist  82  is applied onto a wafer substrate  81  with a machining-target film (not shown) formed thereon. The resist  82  is a positive type photoresist. 
         [0056]    Exposure to light on a wafer substrate is performed using a mask (not shown) having; an opening in a place corresponding to a device chip-forming area A 1 , on which a desired fine pattern is formed by the photo-nanoimprint technique in a later step; a peripheral device pattern in a place corresponding to a chip peripheral area A 2 ; and a dummy pattern in a place corresponding to a wafer peripheral area S as shown in  FIG. 8B . Here, the exposure is performed using a KrF (krypton fluoride) scanner. The dummy pattern is determined based on the projection-and-reentrant pattern of a template  84  used in the later photo-nanoimprint step, and the peripheral device pattern. The aperture ratio of the dummy pattern is arranged based on the percentage of projecting portions of the template  84  (corresponding to reentrant portions of the pattern transferred to the wafer substrate  81 ), and the aperture ratio of the peripheral device pattern so that the chip-forming area (A 1  and A 2 ) and the wafer peripheral area (S) are identical to each other in the percentage of exposed portions of the wafer substrate  81 . 
         [0057]    Then, the development of the wafer substrate  81  is performed, leaving only a part of the resist  82  on an area, which has not undergone the exposure, as shown in  FIG. 8C . The remaining resist  82  is used to form a dummy pattern. 
         [0058]    Subsequently, a liquid photo-curable organic material  83  is applied onto the wafer substrate  81  as shown in  FIG. 8D . The photo-curable organic material is e.g. acrylic monomer. 
         [0059]    Next, a template  84  having the projection-and-reentrant pattern that corresponds to the pattern to be formed on the wafer substrate  81  is brought into contact with the liquid photo-curable organic material  83 , as shown in  FIG. 8E . Then, the liquid photo-curable organic material  83  is forced to flow expanding along the projection-and-reentrant pattern on the template  84  and fill the space inside the template. After that, the substrate thus prepared is irradiated with light from above the template  84  to cure the photo-curable organic material  83 . The light used for the irradiation may be any kind of light as long as it is capable of curing the photo-curable organic material  83 , and for example, light emitted by a lamp may be used. The template  84  is formed from a material which allows the light to pass through it, e.g. quartz glass. 
         [0060]    The template  84  is thereafter separated from the photo-curable organic material  83  as shown in  FIG. 8F . The photo-curable organic material  83  has been cured, and therefore the material  83  is still kept in the condition (i.e. shape) when it was in contact with the template  84 . 
         [0061]    After that, the steps shown with reference to  FIGS. 8D to 8F  are repeated, thereby forming a layer of the photo-curable organic material  83  having a desired projection-and-reentrant pattern in two or more areas on the wafer substrate  81 . 
         [0062]    The top view of an example of the wafer substrate  81  which can be formed in this process is presented by  FIG. 9 . As shown in the drawings, on the wafer peripheral area S, the resist  91  shaped into a dummy pattern (having two or more holes) remains; on the chip-forming area (A 1  and A 2 ), the resist  92  shaped in a peripheral device pattern and the photo-curable organic material  93  having forms of projections shaped by using of the template  84  are arranged. 
         [0063]    Subsequently, a combination of the pattern  83  formed by using of the template  84 , and the remaining resist  82  is used as a mask to etch the wafer substrate  81 . After that, a burying of a wire in a groove of the pattern formed by the etching, CMP and other processes are performed, whereby a device is formed. 
         [0064]    As the resist  82  remains in the form of a dummy pattern on the wafer peripheral area, the difference in coverage of the wafer substrate  81  between the chip-forming area and wafer peripheral area can be reduced remarkably, and therefore the defects including the abnormality of a processing form arising in the etching step, and the exfoliation of a wire in the step of CMP can be prevented efficiently. 
         [0065]    The method for forming a pattern according to this embodiment is suitable for pattern formation by using of a combination of the photo-nanoimprint and photolithography such that only a resist pattern for an area with a narrow pitch (line/space) like a device chip-forming area is formed by using of a template according to the photo-nanoimprint technique, and a pattern for an area whose pitch is not narrow like a chip peripheral area, and a pattern for a wafer peripheral area are formed by the publicly known photolithography technique. 
         [0066]    According to this method, the size of a template can be made smaller, and therefore the cost required to fabricate the template can be reduced. 
         [0067]    The above-described embodiments are each just an example, and should not be regarded as imposing restrictions on the present invention. While in the above embodiments a resist designed for KrF exposure is adopted as the resist to be put on a wafer substrate, other resists which are sensitive to other kinds of light including EB (Electron Beam) and EUV (Extreme Ultraviolet Radiation) may be used instead. The technical field of the present invention is specified by the Claims hereof, and it is intended that any changes and modifications in the sense of being on a parity with the Claims and within the scope thereof are included herein.