Abstract:
The present invention provides a substrate-engraving-type chromeless phase-shift mask enabling to adopt a manufacturing method which poses no problem in quality, gives a high operating efficiency, and permits arrangement of characters and symbols, and a manufacturing method thereof. The substrate of the invention has a character/symbol section, on a surface of a transparent substrate, comprising characters and/or symbols engraved in the form of a slit-shaped or lattice-shaped pattern comprising concave grooves only in a prescribed portion corresponding to the characters and/or symbols.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a transparent substrate, used in a phase-shift mask for manufacturing semiconductor, a mask for processing optical products, or other optical products, having a character/symbol section in which a slit-shaped or lattice-shaped pattern comprising concave grooves is provided on one surface of the substrate only in a prescribed area in response to the shapes of the characters and/or the symbols, and a manufacturing method thereof.  
           [0003]    2. Description of the Related Art  
           [0004]    There is recently an increasing demand for a higher density and a finer configuration of semiconductor chip circuits. It is therefore necessary to transfer a finer circuit pattern onto a resist on a wafer. From such a point of view, the conventional binary mask forming a circuit pattern with a light shielding section and a transparent section is insufficient to satisfy requirements.  
           [0005]    More recently, on the other hand, progress in optical lithographic technology is really remarkable, and as a technique for improving resolution of the projecting exposure unit, it is the present common practice to adopt the phase-shift process which increases the pattern resolution by using different phases of light passing through two adjacent transparent portions on the photomask.  
           [0006]    Various types of phase-shift mask used in this phase-shift process have been developed, and are used in response to the purposes of use. Among others, the engraving type phase-shift mask of forming a shifter section by engraving the substrate is becoming more common.  
           [0007]    A substrate-engraving-type chromeless phase-shift mask for processing optical products is now applied for processing optical fibers.  
           [0008]    Because a layer of a chromium-based metal such as chromium, chromium oxide or chromium oxide nitride is usually used as a light shielding layer for various phase-shift masks, a phase-shift mask which does not have a light shielding layer but uses a shifter section comprising concave grooves formed on a surface of a transparent substrate is referred to as a chromeless phase-shift mask of the substrate-engraving type.  
           [0009]    In the above-mentioned photomask, it is required to provide characters or symbols. It therefore becomes necessary to conduct operations for forming characters and symbols on the mask, together with preparation of a circuit pattern on the mask portion, thus requiring more and more complicated manufacture of the mask as a whole.  
           [0010]    It is demanded, not to perform formation of characters and symbols as an independent and separate step, but to form characters and symbols within a photomask preparing step as far as possible. In the conventional manufacturing process of a substrate-engraving-type chromeless phase-shift mask, the problems shown in FIG. 3 are encountered.  
           [0011]    [0011]FIG. 3( a ) is a schematic plan view of the middle of processing of a conventional substrate-engraving-type chromeless phase-shift mask having characters and symbols; FIG. 3( b ) is a schematic view illustrating enlarged characters in B 1  portion of FIG. 3( a ); FIG. 3( c ) is an enlarged view of B 2  portion shown in FIG. 3( b ); FIG. 3( d ) is a sectional view of FIG. 3( c ) cut along the line B 3 -B 4 ; and FIGS.  3 ( c   1 ) and  3 ( d   1 ) illustrate states after processing corresponding to FIGS.  3 ( c ) and  3 ( d ), respectively. In FIG. 3, reference numeral  200  represents a phase-shift mask;  210  represents a transparent substrate;  220  represents a main pattern section;  230  represents a character/symbol section;  231  represents a light shielding film;  232  represents an opening (of the light shielding film); and  215  represents a concave groove section.  
           [0012]    Character “ 2 ” in the B 1  portion of the character/symbol section  230  shown in FIG. 3( a ) is formed by opening the light shielding film  231 , as shown in FIG. 3( b ). An enlarged schematic plan view of B 2  portion thereof is as shown in FIG. 3( c ). The sectional view of FIG. 3( c ) cut along the line B 3 -B 4  is as shown in FIG. 3( d ).  
           [0013]    The conventional manufacture of a substrate of a substrate-engraving-type chromeless phase-shift mask is accomplished simultaneously with the forming step of a circuit pattern which is the main pattern for the formation of a character/symbol section, resulting in the manner shown above.  
           [0014]    However, this manufacturing method of the substrate-engraving-type chromeless phase-shift mask contains a step of wet-etching all or part of the light shielding film, following the forming step of characters and symbols, and patterned characters in this step sometimes disappear as shown in FIGS.  3 ( c   1 ) and  3 ( d   1 ).  
           [0015]    A counter-measure was taken to prevent disappearance of patterned characters and symbols by a method comprising the steps of covering the characters and symbols with a wet-etching-resistant protective film and carrying out wet etching. In this case, however, problems were encountered in that excessive light shielding film remained near the characters, and the addition of a coating step of the protective film led to a lower operating efficiency.  
           [0016]    The present invention was developed to solve the problems as described above, and has an object to provide a substrate-engraving-type chromeless phase-shift mask which poses no problem in quality, gives a high operating efficiency, and permits arrangement of characters and symbols, and a manufacturing method thereof.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention provides a substrate having a character/symbol section, on a surface of a transparent substrate, comprising character and/or symbols engraved in the form of a pattern of concave grooves only in prescribed areas meeting the shapes of the characters and/or symbols.  
           [0018]    In the substrate mentioned above, the transparent substrate is a glass substrate or a resin substrate.  
           [0019]    Also in the above-mentioned substrate, the pattern comprising concave grooves is a slit-shaped or lattice-shaped pattern, and the slit-shaped or lattice-shaped pattern is formed so that the width of a concave groove and the width of the space between two adjacent concave grooves are at a ratio 1:1.  
           [0020]    In the above-mentioned substrate, the character/symbol section is an alignment mark, an area code, a barcode, a scale or a position mark indicating a location.  
           [0021]    Again in the substrate described above, the substrate having the character/symbol section is a photomask, and the photomask includes a substrate-engraving type chromeless phase-shift mask or a phase masks for fiber Bragg grating fabrication as disclosed in Japanese Patent Publication No. H7-140311.  
           [0022]    The processing method of the character/symbol section in the substrate having the character/symbol section comprises (a) resist arranging step of arranging an electron-beam-sensitive resist on a light shielding film provided at least in a character/symbol section forming area of a surface of a transparent substrate; (b) a resist image forming step of forming a resist image opening at portions for forming a pattern comprising concave grooves by developing the resist after selective exposure of the resist by means of an exposing unit such as an electron beam exposing unit; (c) an etching step of forming a light shielding film opening at portions for forming the pattern comprising the concave grooves by etching the light shielding film exposed from the openings of the resist image; (d) a substrate engraving step of engraving the resist and transparent portions of the substrate exposed from the openings of the light shielding film; and (e) a removing step of removing resist and light shielding film.  
           [0023]    In the above-mentioned method, the substrate having the character/symbol section is a chromeless phase-shift mask having no substrate-engraving-type light shielding layer, and the resist arranging step is conducted by simultaneously carrying out, after providing a light shielding film over an entire surface of the transparent substrate and arranging an electron-beam-sensitive resist over the entire surface of the light shielding film, a step for forming the character/symbol section and a step for forming the shifter section, comprising (A) a resist image forming sub-step of selectively exposing the resist to electron beam, and developing the resist, thereby forming a resist image opening at portions for forming the character/symbol section and a portion for forming a shifter section; (B) an etching sub-step of etching the light shielding film opening at portions for forming the character/symbol section and a portion for forming the shifter section; (C) a substrate engraving sub-step of engraving the portions of the substrate exposed from openings of the resist and the light shielding film by etching; and (D) a sub-step of removing remaining resist and light shielding film.  
           [0024]    Also in the method described above, the pattern comprising concave grooves is a slit-shaped or lattice-shaped pattern.  
           [0025]    The method as described above can be applied also in the manufacture of a phase masks for fiber Bragg grating fabrication.  
           [0026]    Manufacturing methods when the transparent substrate is made of a resin include a method comprising the steps of using a glass substrate prepared as above as an original board, making a matrix with reversed convexity-concavity, and preparing a resin product with positive convexity-concavity from the matrix.  
           [0027]    By adopting the configuration as described above, the transparent substrate of the present invention makes it possible to provide a substrate having a character/symbol section permitting recognition of characters and symbols by only forming concave grooves on the transparent substrate.  
           [0028]    Particularly, the invention enables to provide a substrate-engraving-type chromeless phase-shift mask which permits use of a manufacturing method which poses no problem in quality, gives a high operating efficiency, and permits arrangement of characters and symbols, having a character/symbol section.  
           [0029]    More specifically, the aforementioned object is achieved by a substrate having a character/symbol section, on a surface of a transparent substrate, comprising characters and/or symbols engraved in the form of a pattern of concave grooves only in prescribed areas meeting the shapes of the characters, and/or symbols.  
           [0030]    Specifically, identification of characters and symbols by reflected light is made possible by providing a pattern comprising concave grooves only in prescribed areas in response to shapes of characters and/or symbols.  
           [0031]    By preparing the character/symbol section in a mirror image pattern, it is possible to confirm the character/symbol section even from the back.  
           [0032]    Use of a slit-shaped or lattice-shaped pattern comprising concave grooves permits achievement of a simpler and more practical pattern.  
           [0033]    A ratio 1:1 of the groove width to the width of the space between grooves of the slit-shaped or lattice shaped pattern comprising the concave grooves is preferable in terms of visibility.  
           [0034]    The pitch of the groove width and the space between grooves should preferably be within a range of 0.2 to 10 μm.  
           [0035]    The character/symbol section may be an alignment mark necessary when drawing a photomask or a wafer, an area code, a barcode, a scale or a position mark indicating a location. It suffices to provide the same in response to the purpose of use.  
           [0036]    The characters may be alphabet, numerals, Hiragana, Katakana or any other kind of character.  
           [0037]    A photomask may be used as a substrate having a character/symbol section as described above, and particularly, a substrate-engraving-type phase-shift photomask is effective as described above.  
           [0038]    When the substrate having a character/symbol section is a semiconductor manufacturing mask, it is applicable for confirming the type of the mask and other pieces of information upon attaching the mask to a drawing unit.  
           [0039]    The processing method of a character/symbol section in a substrate having the character/symbol section of the invention makes it possible to provide a manufacturing method of a photomask, which poses no problem in quality, gives a high operating efficiency, and permits arrangement of characters and symbols.  
           [0040]    When manufacturing an engraving-type chromeless phase-shift mask, a character/symbol section is formed flush with the photomask circuit pattern. It is therefore possible to obtain a character/symbol section as shown in FIG. 3( b ), which has conventionally required two runs of makeup, by a single run of makeup, because a circuit pattern and the character/symbol section can be prepared simultaneously in a step.  
           [0041]    It is thus possible to manufacture a mask having a character/symbol section permitting identification by reflected light to the substrate without the necessity to leave a light shielding film near the character/symbol section. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]    [0042]FIG. 1( a ) is a schematic plan view of a phase-shift mask which is an embodiment of the substrate having a character/symbol section of the present invention; FIG. 1( b ) is a schematic view illustrating enlarged characters in A 1  portion shown in FIG. 1( a ); FIG. 1( c ) is an enlarged view of A 2  portion of FIG. 1( b ); and FIG. 1( d ) is a sectional view of FIG. 1( c ) cut along the line A 3 -A 4 .  
         [0043]    [0043]FIG. 2 is a processing step diagram of the character/symbol section shown in FIG. 1; and  
         [0044]    [0044]FIG. 3( a ) is a schematic plan view of a conventional substrate-engraving-type phase-shift mask having characters and symbols during processing; FIG. 3( b ) is a schematic view illustrating enlarged characters in B 1  portion shown in FIG. 3( a ); FIG. 3( c ) is an enlarged view of B 2  portion shown in FIG. 3( b ); FIG. 2( d ) is a sectional view of FIG. 3( c ) cut along the line B 3 -B 4 ; and FIGS.  3 ( c   1 ) and  3 ( d   1 ) illustrate states after processing corresponding to FIGS.  3 ( c ) and  3 ( d ). 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]    An embodiment of the present invention will now be described with reference to the drawings.  
         [0046]    [0046]FIG. 1( a ) is a schematic plan view of a phase-shift mask which is an embodiment of the substrate having a character/symbol section of the present invention; FIG. 1( b ) is a schematic view illustrating enlarged characters and A 1  portion shown in FIG. 1( a ); FIG. 1( c ) is an enlarged view of A 2  portion of FIG. 1( b ); and FIG. 1( d ) is a sectional view of FIG. 1( c ) cut along the line A 3 -A 4 ; and FIG. 2 is a processing step diagram of the character/symbol section shown in FIG. 1.  
         [0047]    In FIGS. 1 and 2,  100  represents a substrate having a character/symbol section (also referred to as a phase-shift mask or simply as a substrate);  110  represents a transparent glass substrate;  112  represents a circuit pattern portion;  113  represents a character/symbol section;  115  represents concave grooves;  120  represents a light shielding film;  125  represents an opening (of the light shielding film);  130  represents a resist layer;  130 A represents a resist image; and  135  represents an opening of the resist layer.  
         [0048]    An embodiment of the substrate having a character/symbol section of the present invention will be described with reference to FIG. 1.  
         [0049]    The substrate  100  having the character/symbol section of the embodiment shown in FIG. 1( a ) is a substrate-engraving-type chromeless phase-shift mask having the character-symbol section  113  arranged in an area different from that of the circuit pattern  112 . The character/symbol section  113  has a slit-shaped pattern comprising concave grooves  115  engraved on the transparent glass substrate  110 , as shown in FIGS.,  1 ( c ) and  1 ( d ), provided in only a prescribed area in response to the shapes of the characters and/or symbols.  
         [0050]    The pattern of slits comprising the concave grooves  115  has a ratio 1:1 of the groove width to the width of a space between grooves.  
         [0051]    The pitch of the concave groove width and the space between the concave grooves  115 , of which the minimum manufacturable size is about 0.2 μm, should preferably be 10 μm or smaller from the point of view of visibility.  
         [0052]    A variation of this embodiment is one formed with a pattern having concave grooves  115  of the character/symbol section  113  of a lattice shape, not a slit shape.  
         [0053]    In another variation of this embodiment, an alignment mark, an area code, a barcode, a scale or a position mark indicating a location is provided in the character/symbol section in response to the purpose of use.  
         [0054]    An example of processing of the character/symbol section in the substrate having the character/symbol section of this embodiment will now be briefly described with reference to FIG. 2.  
         [0055]    The light shielding film  120  is formed on an entire surface of the transparent glass substrate  110 , and the resist layer  130  is formed on the entire surface of the light shielding film  120  (FIG. 2( a )).  
         [0056]    Applicable light shielding films usually include chromium-based metal films of chromium, chromium oxide or chromium oxide nitride, but are not limited thereto.  
         [0057]    The light shielding film  120  is formed by sputtering or vapor deposition.  
         [0058]    The resist layer should have a desired resolution and a satisfactory processability, and is usually formed by means of spin coating.  
         [0059]    Then, selective exposure is accomplished by an exposing unit such as an electron-beam drawing unit, and the resist is developed, thereby forming the resist image  130 A opening at portions for forming slit-shaped concave grooves in the character/symbol section forming areas and at the portion for forming the shifter of the main pattern (FIG. 2( b )).  
         [0060]    Then, the light shielding film  120  is etched at the portion exposed from the opening  135  of the resist image  130 A (FIG. 2( c )), and the resist image  130 A and the portion of the transparent substrate exposed from the opening of the light shielding film  120  are engraved by etching (FIG. 2( d )).  
         [0061]    When the light shielding film is a chromium-based metal film, etching of the light shielding film  120  is accomplished through wet etching using an aqueous ceric sulfate ammonium solution or dry etching using a chlorine-based gas, by use of the resist image  130 A as an etching-resistant mask.  
         [0062]    Since forming of the shifter section and forming of the slit-shaped concave grooves  115  of the character/symbol section are simultaneously carried out, etching of the transparent glass substrate is conducted through dry etching using a fluorine-based gas.  
         [0063]    Then, after completing etching, the resist  130 A is stripped off (FIG. 2( e )), and the entire light shielding film  120  is removed through wet etching (FIG. 2( f )).  
         [0064]    It is thus possible to simultaneously perform forming of the circuit pattern and forming of the character/symbol section.  
         [0065]    According to the present invention, as described above, it is possible to provide a substrate having a character/symbol section permitting recognition of characters and symbols by only forming concave grooves on a transparent substrate, and a manufacturing method of such a substrate.  
         [0066]    Particularly, when the substrate having a character/symbol section is a photomask, the characters and symbols are recognizable even when the character/symbol section is not formed by patterning of the light shielding film. It is therefore possible to increase the degree of freedom for the photomask manufacturing method, and as a result, to arrange the characters and symbols at a satisfactory operating efficiency with no problem in quality of the character/symbol section.