Abstract:
A producing method according to the invention of an article having an island structure fundamentally includes a step of coating a forming material having the fluidity on a substrate, a step of facing the substrate and a forming mold with the forming material having the fluidity interposed therebetween to pressurize, a step of applying energy such as heat or light in a pressurized state to cure the forming material in the forming mold, and a step of releasing the forming mold. A producing method of a formed article where a non-forming portion is not remained and only a forming portion is remained is provided. After the step of forming, before the step of curing, a step of removing a forming material having the fluidity outside of the forming mold to clean is inserted. A cleaning solution that dissolves a forming material before curing can remove the forming material.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an article having an island structure in which an island body is partially formed on a surface of a substrate, which is mainly used in an optical field such as light communication, light measurement and optical recording, and a producing method thereof.  
         [0003]     2. Related Art  
         [0004]     A forming technology is widely used as a method of producing articles having an identical shape in large quantities. Pressure forming that is one of the forming technologies is a method where a forming mold is pressed against a deformable work deployed on a substrate, that is, a forming material, to apply pressure to transfer a surface shape of the forming mold on the forming material.  
         [0005]     As the forming materials deformable at low temperatures, resin materials are typical. For instance, photocurable materials that have the fluidity at room temperature and can be cured upon irradiation of UV rays are frequently used.  
         [0006]     Furthermore, sol-gel materials that are organic/inorganic composite materials are known as well. A method of producing articles having fine irregular shape on a surface with a sol-gel material is disclosed in, for instance, JP-A 11-314927.  
         [0007]     The sol-gel materials are materials obtained by adding alcohol, water and a catalyst to compounds such as alkylalkoxysilanes to hydrolyze. In general, these are used after heating and partially removing volatilizing components. Raw material compounds can be selected from a variety of kinds of compounds and these can be used in combinations in some cases.  
         [0008]     In the case of a compound containing silicon such as an alkoxysilane material being used as a raw material, when, after the forming, heating is applied to partially remove organic components, a formed body becomes a state close to an inorganic material mainly made of silicon oxide. Accordingly, formed articles superior in the heat resistance and weather resistance to resin materials can be provided.  
         [0009]     A forming method is carried out in such a manner that, as shown in  FIGS. 8A through 8D , on a surface of a substrate  110 , a forming material  120  having the fluidity is coated (coating step,  FIG. 8A ), thereon a forming mold  130  is pressed to pressurize (forming step,  FIG. 8B ), followed under a pressurized state by heating or irradiating UV rays to cure the forming material (curing step,  FIG. 8C ), and further followed by releasing from the mold (mold releasing step,  FIG. 8D ). Thereby, a formed article  150  on which a shape of the forming mold is transferred can be obtained. By contrast, a forming material may be coated on the forming mold so as to fill the forming material and a substrate may be pressed against this.  
         [0010]     According to such a forming technology, a fine irregular shape can be formed on a surface. Accordingly, the technology is suitable as a producing method of various kinds of optical elements necessary in the optical field such as a microlens array and a diffraction grating (for instance, JP-A 2001-9843). Since such optical elements each are small in size in many cases, it is inefficient to produce these one by one according to the forming method. When an element is small in size, without using so large a substrate, many elements can be simultaneously formed on one substrate and by cutting these individual elements can be obtained. That is, in such a case, it is advantageous to produce by one-time forming operation a structure where a plurality of portions having a desired shape is arranged on the substrate.  
         [0011]     Furthermore, in an array element where a plurality of light-emitting elements or light receiving elements is arranged on a substrate or a so-called optical integrated circuit or opto-electronic integrated circuit where semiconductor elements such as electronic elements, light-emitting elements and light receiving elements are integrated, when, in addition to the elements, lens elements as well are integrated, a structure where a plurality of portions having a desired shape is arranged in predetermined positions can be formed by one-time forming.  
         [0012]     In such a case, as shown in  FIGS. 9A through 9D , on a surface of a substrate  210  or on a surface of a substrate on which a semiconductor element and so on have been formed, a forming material  120  having the fluidity is coated (coating step,  FIG. 9A ) and thereon a plurality of forming molds are pressed to pressurize (forming step,  FIG. 9B ). A plurality of forming molds may be individually independent. However, as shown in the drawing, a plurality of forming molds may be disposed on a support  235  to form one forming mold  230  having a plurality of forming portions  233 . Under a pressurized state, heating or UV irradiation is applied to cure the forming material (curing step,  FIG. 9C ) followed by releasing (mold releasing step,  FIG. 9D ) and thereby a formed article  250  thereon a shape of the forming mold is transferred can be obtained.  
         [0013]     However, existing technologies have problems such as shown below.  
         [0014]     A first problem is in that in the case of a structure such as mentioned above being formed, a forming mold used is smaller than a substrate on which a shape of the forming mold is transferred. Accordingly, when a forming material is coated on the substrate, a portion outside of the forming mold is not pressed and remains on the substrate. Furthermore, even when a forming material is filled and coated in the forming mold, the forming material likely to run over in the periphery of the forming mold.  
         [0015]     As shown in  FIG. 10 , when the pressed forming material runs outside of the forming mold, after curing, a non-forming portion  124  of a forming material  122  is formed in a swelling state. Furthermore, a formed portion  126  on which a surface shape of the forming mold is transferred is formed in recess. Accordingly, outside of the formed portion  126  prepared, a non-forming portion  124  remains, and, when the formed portion is used, in some cases, a function thereof is disturbed. Furthermore, there is a case where a once formed body is used as a forming mold (replica) that is used in an actual production, in such a case, the external non-forming portion  124  disturbs to make difficult to use as a forming mold.  
         [0016]     As a second problem, when a thin film is necessarily formed on a surface of a formed body shown in  FIG. 10  by means of a vacuum deposition method, a film on a surface of the non-forming portion is likely to peel. It is assumed due to that since the non-forming portion  124  is not pressurized, the thermal expansion coefficient thereof is large, and thereby, at the layering, a stress is applied on the thin film.  
         [0017]     From the problems mentioned above, it is preferred that, after the forming, the non-forming portion on the substrate is removed and a structure where only a formed portion is remained in island is formed. However, in order to remove the non-forming portion without causing damage on the formed portion, a complicated step is necessary. When such a step is added, an advantage of the forming process that is simple and adequate to the mass production is damaged.  
       SUMMARY OF THE INVENTION  
       [0018]     The invention was carried out in view of the problems of the existing technologies and intends to provide an article having an island structure, in which in the forming step the non-forming portion is not remained and only a formed portion is remained. Furthermore, the other object of the invention is to provide a producing method of an article having an island structure.  
         [0019]     An article according to the invention and having an island structure is one in which, on a surface of a substrate or a surface of a solid material layer formed on a surface of a substrate, a plurality of island bodies is arranged and formed separated from each other island-like, the island body containing a substance obtained by hydrolyzing and curing a sol-gel material, and, in a surrounding portion of a portion where an island body is formed, a surface of a substrate or a surface of a solid material layer being exposed.  
         [0020]     In such a structure, since only an island body portion is formed protruded on a substrate, when the portion is used, a function thereof is not disturbed. Furthermore, when this is used as a forming mold as well, there is no inconvenience.  
         [0021]     In the above configuration, it is preferable that with glass or semiconductor as a substrate and with a semiconductor layer as a solid material layer, a surface of substrate and/or a surface of solid material layer is partially provided with a conductive film to form a plurality of light-emitting elements and/or light receiving elements on a semiconductor layer, on a surface of the semiconductor layer a conductive film is formed processed as an electrode, and an island body is formed at least partially on a light-emitting element and/or a light receiving element.  
         [0022]     According to such a configuration, an optical component where a semiconductor light-emitting element or light receiving element and an optical element such as a lens are integrated can be provided. Since a light-emitting element can be formed only on a predetermined place on the substrate, it can be avoided to adversely affecting on a whole of optical components.  
         [0023]     All island bodies can be formed into substantially same shape. Furthermore, on a surface of the island body, a predetermined irregular structure can be formed. Still furthermore, a linearly or two-dimensional arrangement according to a rule can be adopted.  
         [0024]     A producing method according to the invention of an article having an island structure includes a step of coating a forming material having the fluidity on a substrate or filling/coating the same in a forming mold, a step of facing the substrate and a forming mold with the forming material having the fluidity interposed therebetween to pressurize, a step of removing the forming material having the fluidity outside of the forming mold to clean, a step of applying energy such as heat or light under a pressurized state to cure the forming material in the forming mold and a step of releasing the forming mold.  
         [0025]     According to the above steps, in the forming step, a non-forming portion outside of the forming mold can be removed before curing, and, thereby, only a curing portion can be remained. Furthermore, when the step of cleaning is added, without damaging the substrate, an island structure can be prepared on a surface of the substrate. Still furthermore, when a structure is in advance formed on a surface of the substrate as well, the portion, without covering with a sol-gel film, can be exposed; accordingly, a function of the structure on the surface of the substrate is neither damaged. Furthermore, since a sol-gel material that covers a periphery of the mold can be removed as well, the mold releasing can be readily applied.  
         [0026]     The cleaning step preferably includes a method of dipping a part or a whole of a substrate covered with the forming mold in a cleaning solution that dissolves the forming material having the fluidity. The non-forming portion can be dissolved in a cleaning solution to remove.  
         [0027]     The cleaning solution is preferably wobbled or moved. When the cleaning solution is wobbled or flowed, dissolution of the non-forming portion can be promoted.  
         [0028]     Furthermore, the cleaning step preferably includes a method of ejecting a cleaning solution that dissolves the forming material having the fluidity to a surface of the substrate covered with the forming mold.  
         [0029]     The cleaning solution being ejected is preferably in the form of mist. When the cleaning solution is in the form of mist, it can be delivered over the substrate without causing irregularity.  
         [0030]     Still furthermore, the cleaning step preferably includes a method of ejecting a gas on a substrate surface covered with the forming mold. With ejection pressure of a gas as well, the non-forming portion can be removed.  
         [0031]     In the respective cleaning steps, a cleaning solution remaining on the substrate surface is desirably removed by ejecting a gas. With ejection pressure of a gas, the cleaning solution can be effectively removed.  
         [0032]     The forming material having the fluidity can be a sol-gel material. In this case, the cleaning solution is preferably water.  
         [0033]     The forming material having the fluidity can be a resin material. In this case, the cleaning solution is preferably an organic solvent that dissolves the resin material.  
         [0034]     According to the invention, a producing method where, before a forming material is cured in the forming step, a non-forming portion can be removed, and, without applying a complicated removing step, only a formed portion is remained can be provided. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]      FIGS. 1A through 1E  are diagrams for explaining producing steps of an article having an island structure according to the invention.  
         [0036]      FIGS. 2A and 2B  are schematic diagrams showing an example of an article having an island structure prepared according to a producing method of the invention.  
         [0037]      FIG. 3  is a schematic diagram showing another example of an article having an island structure prepared according to a producing method of the invention.  
         [0038]      FIGS. 4A and 4B  are diagrams showing a configuration example of a plurality of photodiode arrays formed on a substrate.  
         [0039]      FIGS. 5A and 5B  are schematic diagrams showing an island structure formed on a photodiode array.  
         [0040]      FIG. 6  is a schematic diagram of a so-called moth eye structure.  
         [0041]      FIG. 7  is a diagram showing one example of a cleaning method of the invention.  
         [0042]      FIGS. 8A through 8D  are diagrams for explaining producing steps of an existing formed article.  
         [0043]      FIGS. 9A through 9D  are diagrams for explaining another producing step of an existing formed article.  
         [0044]      FIG. 10  is a schematic cross sectional diagram of a formed article prepared according to an existing producing method. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]     In what follows, embodiment of the invention will be detailed.  
       First Embodiment  
       [0046]     In the embodiment, a forming material is a sol-gel material. The sol-gel material is coated on a glass substrate and a forming mold is pressed thereto to prepare a formed body.  
         [0047]     As the glass substrate, a 50 mm square quartz glass substrate having a thickness of 3 mm was used. As the sol-gel material, a material ([a material obtained by adding polyethylene glycol to tetraethoxysilane] and [a material obtained by mixing methyltriethoxysilane to tetraethoxysilane]) that forms an organo-polysiloxane film was used.  
         [0048]     As a forming mold, a quartz glass forming mold having a plurality of parallel linear groove structures (groove width 1 μm, groove depth 1 μm and magnitude of 20 mm square) was used. The groove has a V-character shape in a cross section perpendicular to a linear direction.  
         [0049]      FIGS. 1A through 1E  are diagrams showing producing steps of the invention.  
         [0050]     In the beginning, a spin coating method was used to coat the sol-gel material as the forming material  30  on the glass substrate  10  substantially uniformly at a thickness of substantially 1 μm (coating step,  FIG. 1A ). On the glass substrate  10  on which the sol-gel material was uniformly coated, a forming mold  30  is placed and pressurized (forming step,  FIG. 1B ). The forming steps up to the step are same as that of an existing forming step.  
         [0051]     In the next place, in the step according to the invention, in a pressurized state as is, from above the glass substrate  10 , pure water that is a cleaning solution  40  is ejected from a nozzle  60  in the form of mist to remove a sol-gel film  21  of a portion where a forming mold is not on the glass substrate  10  (cleaning step,  FIG. 1C ). After the removal, dry air is sprayed to remove moisture remaining on a surface of the glass substrate.  
         [0052]     Thereafter, the glass substrate is held at 70° C. for 1 hr and thereby the sol-gel material is substantially completely dehydrated and polycondensated to gelate (curing step,  FIG. 1D ). Finally, the forming mold is removed to release (mold releasing step,  FIG. 1E ).  
         [0053]     Owing to the above steps, only a sol-gel material of a formed portion  26  where a surface shape of the forming mold is reversed is remained on a surface of the glass substrate. The glass substrate is further fired at 300° C. for 30 min. By carrying out thus, on the glass substrate, a film of organosiloxane only a formed portion of which is cured (hereinafter referred to as “sol-gel film”) remains.  
         [0054]     A sol-gel film thus prepared remains, as shown in  FIGS. 2A and 2B , with only a formed portion  26  protruded to the glass substrate  10 .  FIG. 2A  is a sectional diagram vertical to a substrate surface and  FIG. 2B  is a plan view of a formed article  50 . The formed article  50  has a shape appropriate to use as a forming mold once more.  
         [0055]     Furthermore, when the similar cleaning step is used, as shown in  FIG. 3 , a formed article  52  in which a plurality of formed portions  28  is formed on the same substrate can be prepared. This can be used as a forming mold for simultaneously forming a plural, in which a plurality of forming molds is arranged on the same substrate. When the formed body is cut for every formed portion  28  at a portion where the substrate is exposed to separate, by one-time forming, many optical elements can be prepared.  
         [0056]     Furthermore, in the case of a formed article being applied as an optical element, even when an antireflective film (multi-layered film obtained by layering TiO 2  and SiO 2 : total film thickness substantially 2 μm) substantially totally reflective in a wavelength range of 680 to 880 nm is layered on a surface of the formed body by means of the sputtering method, since a film of the non-forming portion assumed to be large in the thermal expansion coefficient is removed, a problem such as peeling can be inhibited from occurring.  
       Second Embodiment  
       [0057]     The embodiment is a case where a UV-curable epoxy resin is used as a forming material.  
         [0058]     In the steps shown in  FIGS. 1A through 1E , as a forming material  20 , a UV-curable epoxy resin is used, and a forming mold  30  is pressed against this to form a formed article.  
         [0059]     As a glass substrate  10 , a quartz glass substrate having a dimension similar to a first embodiment was used. As an epoxy resin material, a material that can be cured by UV rays was used. As a forming mold  30  as well, one having same shape as that of the first embodiment was used.  
         [0060]     In the beginning, an epoxy resin material having the fluidity was coated on a glass substrate by use of a micropipette. On the glass substrate thereon the epoxy resin material was coated, a forming mold is placed and pressurized. In a pressurized state, from an upper portion of the glass substrate, acetone that is an organic solvent is ejected in the form of mist to dissolve and remove an epoxy resin film of a portion where the forming mold is not present on the glass substrate. After removing, acetone remaining on a surface of the glass substrate was removed by spraying dry air.  
         [0061]     In the next place, from a back surface of the glass substrate, UV rays are irradiated to cure the epoxy resin. After that, the forming mold is removed to release and thereby only the epoxy resin on which a surface shape of the mold is transferred is remained on the surface of the glass substrate. The glass substrate is fired at 100° C. for 1 hr. When thus carrying out, on the glass substrate, a formed body where only a formed portion is cured can be formed.  
         [0062]     A formed portion of an epoxy film thus prepared as well remains in a protruded state to the glass substrate as shown  FIGS. 2A and 2B ; accordingly, it has a shape appropriate when the formed body is again used as a forming mold. Furthermore, when a plurality of the formed portions are prepared on a same substrate, as shown in  FIG. 3 , a mold for simultaneously forming a plural, in which a plurality of forming molds are arranged on a same substrate, can be prepared.  
         [0063]     In the embodiment, a case where an epoxy resin material is used as a forming material was described. However, with other resin materials (for instance, acrylic resin), a forming mold having a shape suitable for the press forming can be prepared. In that case, as the cleaning solution, an organic solvent that dissolves the resin material is necessarily used.  
       Third Embodiment  
       [0064]     The embodiment is a case where a formed body is prepared on a semiconductor substrate on which a light receiving element is formed.  
         [0065]     As shown in  FIG. 4A , on a semiconductor substrate (omitted from showing in the drawing), a plurality of photodiode elements are arranged in a plurality of linear lines to form a photodiode array  54 . When it is industrially produced, it is preferable to form a plurality of array elements on one substrate (semiconductor wafer).  FIG. 4A  shows a situation of a part on the substrate on which a plurality of array elements are formed. In order to operate a photodiode, an electrical connection is necessary. In order to secure the portion, a region  92  having a definite area is necessary for one array element. Furthermore, since these are finally separated, a cutting margin  94  is necessary between the respective regions.  
         [0066]      FIG. 4B  is a diagram showing in detail a part of the photodiode array element, which is shown in  FIG. 4A  surrounded by a chain line. A plurality of photodiode elements  80  are linearly arranged on a substrate  14 . Each of the elements is provided with a metal electrode  82  and a bonding pad  90  connecting thereto is formed. To the bonding pad  90 , a metal wire (omitted from showing in the drawing) is bonded and thereby an electrical signal generated when a photodiode element  80  receives incident light through the metal wire is externally transmitted.  
         [0067]     In the invention, a formed body is prepared by positionally aligning on the photodiode array. As a sol-gel material, a material ([a material obtained by adding polyethylene glycol to tetraethoxysilane] and [a material obtained by mixing methyltriethoxysilane to tetraethoxysilane]) that forms an organo-polysiloxane film was used.  
         [0068]     As a forming mold, a quartz glass forming mold having a plurality of conical holes (period 300 nm and hole depth 750 nm) were used.  
         [0069]     In the beginning, a spin coat method was used to substantially uniformly coat on a substrate a sol-gel material as a forming material at a thickness of substantially 1 μm. On a photodiode element of a substrate on which the sol-gel material was uniformly coated, a forming mold such as shown in  FIGS. 9A through 9D  is placed positionally aligned followed by applying pressure.  
         [0070]     In the next place, in the step according to the invention, under a pressurized state as is, from above the substrate, pure water that is a cleaning solution is ejected in the form of mist from a nozzle to remove a sol-gel film of a portion where the forming mold is not present on the substrate, in particular, a bonding pad portion. After the removal, moisture remaining on a surface of the substrate is removed by spraying dry air.  
         [0071]     After that, the substrate is kept at 70° C. for 1 hr, and thereby the sol-gel material is nearly completely dehydrated and polycondensated to gelate. Finally, the forming mold is removed to release.  
         [0072]     According to the above steps, as shown in  FIGS. 5A and 5B , only a sol-gel material  22  of a formed portion where a surface shape of the forming mold is reversed remains on the photodiode array  54 . When the substrate is further fired at 300° C. for 30 min, on the photodiode array, fine conical structures made of organo-polysiloxane of which only a formed portion is cured and having a shape such as schematically shown in  FIG. 6  are formed. The structure is called a moth eye structure and is known to have anti-reflection effect. Owing to the formation of the structure, light incident on the light receiving element can be reduced from reflecting from a surface of the light receiving element and thereby light receiving efficiency can be improved. Furthermore, since the bonding pad portion is free from the sol-gel material and exposed, after cutting and separation, a metal wire can be immediately bonded.  
         [0073]     The embodiment described an example of a photodiode array. However, the invention, without restricting to the light receiving element, can be applied as well to a light-emitting element. To a light-emitting diode array formed on a semiconductor substrate, a formed body similar to the above can be formed. The formed body can be formed into not only an anti-reflective moth eye structure but also into fine lenses or prisms. When a lens is formed on a light-emitting element, since exit light can be condensed, usage efficiency of light can be improved.  
         [0000]     (Cleaning Step)  
         [0074]     In the cleaning step of the embodiment, a method of ejecting the cleaning solution in the form of mist onto the substrate was adopted. However, the cleaning method is not restricted thereto. The cleaning solution may be sprayed not in the form of mist but in the form of liquid as is. Furthermore, as shown in  FIG. 7 , in a state where the substrate  10  and the forming mold  30  are pressurized with a forming material interposed therebetween, a whole or a part of the substrate and the forming mold may be dipped in the cleaning solution  40  in a cleaning tank  70 . In this case, when the cleaning solution  40  is wobbled with a rotary blade  72  or flowed, the cleaning can be efficiently carried out.  
         [0075]     The cleaning solution after the cleaning is desirably removed by ejecting a gas such as dry air or nitrogen as used in the embodiment. However, without applying such methods, it may be heated.  
         [0076]     In all of the above methods, a cleaning solution that dissolves a forming material was used. However, a method where air is sprayed as a high-speed airflow to physically remove the forming material may be adopted.