Patent Publication Number: US-2013252141-A1

Title: Method for manufacturing a photomask

Description:
This application claims priority to Korean Patent Application No. 2012-28402, filed on Mar. 20, 2012, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which in its entirety is herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments of the present invention relate to a method for manufacturing a photomask. More particularly, example embodiments of the present invention relate to a method for manufacturing a photomask used for photolithography. 
     2. Description of the Related Art 
     Generally, a photomask is a mask used in photolithography to form a predetermined pattern. Since a distance between adjacent wirings may be decreased and a manufacturing process may be flexible in the photolithography, the photolithography is mainly used for a patterning process both in the present and in the future. Thus, manufacturing the photomask used for the photolithography is very important. 
     The photomask is also manufactured through the photolithography. The manufacturing process for the photomask includes depositing a metal on a base substrate, cleaning the base substrate on which the metal is deposited, coating a photoresist, exposing the photoresist, developing the exposed photoresist, etching the metal layer, stripping the photoresist, cleaning the metal pattern formed on the base substrate, and so on. 
     As mentioned above, many processes are necessary to form the photomask using the photolithography, and most are processed in a vacuum state using relatively expensive equipments, so that a cost price may be increased. In addition, harmful substance may be generated in the photolithography and thus additional cleaning equipment is necessary. 
     BRIEF SUMMARY OF THE INVENTION 
     Example embodiments of the present invention provide a method for manufacturing a photomask capable of increasing productivity and having eco-friendly processes. 
     In an example embodiment of a method form manufacturing a photomask according to the present invention, the method includes coating an organometallic ink on a base substrate to form a solution layer. The base substrate is heat-treated on which the solution layer is formed, to self-produce a nanoparticle in the solution layer. A laser is irradiated to the solution layer, to form a metal pattern. The solution layer having the metal pattern is cleaned. The metal pattern is heat-treated. The metal pattern is covered using an encapsulant. 
     In an example embodiment, the organometallic ink may be coated via one of a slot die coating, a roll coating, a blade coating, a spin coating, a spray coating and an inkjet coating. 
     In an example embodiment, a size of the nanoparticle may be same as or less than about 100 nm. 
     In an example embodiment, the base substrate may be heat-treated before the nanoparticles are combined to be a metal layer. 
     In an example embodiment, the base substrate may be heat-treated using one of a heat source, a heating oven, a microwave oven and a light lamp. 
     In an example embodiment, the nanoparticles into which the laser is irradiated may be sintered to be a metal layer, in forming the metal pattern. In addition, the laser may be irradiated in a chamber in which oxygen, humidity and light are blocked, in forming the metal pattern. 
     In an example embodiment, the solution layer into which the laser is not irradiated may be removed, in cleaning the solution layer, so that a transmissive portion is formed. 
     In an example embodiment, the metal pattern may be heat-treated using one of a heat source, a heating oven, a microwave oven and a light lamp, so that an organic material inside of the metal pattern may be evaporated and an optical density of the metal pattern is increased to enhance optical characteristics of the metal pattern and to enhance an adhesive force between the base substrate and the metal pattern. 
     In an example embodiment, the encapsulant may have a relatively high transmittance, and may include a high polymer film or silicon dioxide (SiO 2 ). 
     According to the example embodiments of the present invention, an organometallic ink in which a nanoparticle is self-produced through heating is used to manufacture a photomask, and thus manufacturing processes are performed in a normal state without using expensive equipments in a vacuum state, compared to a conventional manufacturing process. Thus, productivity of the photomask may be enhanced and the cost price may be decreased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detailed example embodiments thereof with reference to the accompanying drawings, in which: 
         FIGS. 1A to 1H  are processing diagrams illustrating a method for manufacturing a photomask according to an example embodiment of the present invention; and 
         FIG. 2  is a graph illustrating a relation between a frequency and a particle diameter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, example embodiments of the present invention will be described in further detail with reference to the accompanying drawings. 
       FIGS. 1A to 1H  are processing diagrams illustrating a method for manufacturing a photomask according to an example embodiment of the present invention. 
     Referring to  FIG. 1A , in manufacturing a photomask according to the present example embodiment, first, the base substrate  10  is cleaned. The base substrate  10  may include a material having a high transmittance, such as soda-lime glass, quartz and so on. A method for cleaning the base substrate  10  may include one of generating a supersonic wave to the base substrate  10  within cleaning water, injecting a liquid like cleaning water or a gas like a nitrogen gas to the base substrate  10  using a cleaning unit  15 . 
     Referring to  FIG. 1B , an organometallic ink is coated on the cleaned base substrate  10  to form a solution layer  20 . In the present example embodiment, the organometallic ink coated on the base substrate  10  exists with a transparent liquid state like an ink at a room temperature, and includes a metallic ion such as gold (Au), silver (Ag), copper (Cu) and so on, and an organic material combined with each other. The organometallic ink does not include a metallic ion with a solid state, and thus is transparent at a room temperature. However, when a heat is applied to the organometallic ink from outside, the combination of the metallic ion and the organic material is broke down to be deoxidized, and thus a nano-sized metallic particle with the solid state is educed. In the present example embodiment, the organometallic ink having above-mentioned characteristics is used to manufacture the photomask. 
     In addition, the metal included in the organometallic ink may be all kinds of metals which may be combined with the organic material to exist with a liquid state at the room temperature, in addition to gold, silver and copper. 
     A method of coating the organometallic ink on the base substrate  10  includes slot die coating, roll coating, blade coating, spin coating, spray coating, inkjet coating and so on. 
     Referring to  FIG. 1C , the base substrate  10  on which the solution layer  20  is formed is pre-baked. Here, as for a method for heat-treating the base substrate  10 , as illustrate in  FIG. 1C , a heat source  30  is disposed under the base substrate  10  and applies the heat to the base substrate  10 . Alternatively, although not shown in figure, the heat source may be disposed adjacent to the base substrate  10  to apply the heat to the base substrate  10 . In addition, the base substrate  10  on which the solution layer  20  is formed may be disposed in a heating chamber such as a heating oven, a microwave oven and so on to apply the heat to the base substrate  10 . Further, a light lamp may be disposed over or under the base substrate  10  to apply the heat to the base substrate  10 . 
     Accordingly, when the heat is applied to the solution layer  20 , a nanoparticle  25  is self-produced inside of the solution layer  20  formed by the organometallic ink. Here, the self-production of the nanoparticle means that the combination between the metallic ion and the organic material inside of the organometallic ink is broke down to be deoxidized so that a nano-sized metallic particle with the solid state is educed. The self-production of the nanoparticle is proportionate to a temperature of the heat, and the educed nanoparticles  25  are combined to be a metal layer. 
     In the present example embodiment, when the metal layer starts to be formed, a metal pattern is hard to be formed using a laser. Thus, a temperature of the heat applied to the solution layer  20  through the heat source  30  should be limited under the temperature at which the nanoparticles start to be combined with each other to form the metal layer. For example, the temperature is between a minimum temperature at which the nanoparticle  25  starts to be self-produced in the organometallic ink and a maximum temperature at which the nanoparticles  25  start to be combined with each other. 
     Referring to  FIG. 1D , a laser  36  is irradiated to the solution layer  20  in which the nanoparticle  25  is self-produced. For example, the laser  36  is generated from a laser generator  35  and a scanner  32  makes a predetermined pattern, and then the laser having the predetermined pattern is irradiated to the solution layer  20 . Alternatively, although not shown in the figure, the laser  36  is generated from the laser generator  35 , and a stage on which the base substrate  10  is disposed moves with a predetermined pattern, and then the laser having the predetermined pattern is relatively irradiated to the solution layer  20 . Further, although not shown in the figure, the laser  36  is generated from the laser generator  35 , and the scanner and the stage relatively move with a predetermined pattern at the same time, and then the laser having the predetermined pattern is irradiated to the solution layer  20 . 
     Here, a light and heat chemical reaction occurs in the solution layer  20  into which the laser  36  is irradiated, and thus the self-produced nanoparticles  25  are sintered with each other to form a nano metal layer. For example, the solution layer  20  into which the laser  36  is irradiated is not removed via a cleaning process, and remains on the base substrate  10 . Thus, a light blocking portion may be formed. 
     Referring to  FIG. 1E , when the laser  36  is irradiated to the solution layer  20 , the nanoparticles  25  are sintered with each other to be the nano metal layer at a portion of the solution layer  20  into which the laser  36  is irradiated, and thus a predetermined metal pattern  21  is formed. 
     For example, in the laser irradiating process as illustrated in  FIGS. 1D and 1E , the laser is absorbed by the solution layer  20 , and a portion of the solution layer  20  absorbing the laser is sintered to be the metal pattern  21 . For example, the solution layer  20  may be the organometallic ink, and thus nano particles may be generated and the nano particles may be sintered to be the metal pattern  21  in the portion of the solution layer  20  absorbing the laser. 
     The laser irradiation process may be formed in a chamber (not shown) in which oxygen, humidity and light are blocked. For example, the chamber is in a vacuum state, nitrogen or argon filled state, or a darkroom state, and thus the oxygen, the humidity and the light may be completely blocked. 
     Thus, the metal pattern  21  formed via the laser irradiation process may have increased uniformity or quality. 
     Accordingly, the solution layer  20  into which the laser  36  is irradiated remains and the light passes through the solution layer  20  into which the laser  36  is not irradiated, so that the laser  36  is irradiated to form a pattern reversely considering a final pattern formed through the photomask which is manufactured via the method according to the present example embodiment. 
     Referring to  FIG. 1F , the solution layer  20  into which the laser  36  is not irradiated. is cleaned. Thus, a portion of the solution layer  20  at which the nano metal layer is not formed and which the light passes through, is removed. Thus, the solution layer  20  is formed as a metal pattern  21  having a predetermined pattern, and the organometallic ink coated on the base substrate into which the laser  36  is not irradiated is totally removed. 
     In addition, the base substrate  10  and the solution layer  20  are both cleaned using the cleaning unit  15 , and thus foreign substance formed on the base substrate  10  or the solution layer  20  is cleanly removed. 
     Referring to  FIG. 1G , the base substrate  10  and the metal pattern  21  formed on the base substrate  10  are heat-treated. Here, as for the method of the heat-treatment, as mentioned referring to  FIG. 1G , a heat source  30  is disposed under the base substrate  10 , and the heat is applied to the base substrate  10 . Alternatively, although not shown in figure, the heat source may be disposed adjacent to the base substrate  10  to apply the heat to the base substrate  10 . In addition, the base substrate  10  on which the solution layer  20  is formed may be disposed in a heating chamber such as a heating oven, a microwave oven and so on to apply the heat to the base substrate  10 . Further, a light lamp may be disposed over or under the base substrate  10  to apply the heat to the base substrate  10 . 
     Accordingly, the heat source  30  applies the heat, so that the organic material inside of the metal pattern  21  may be evaporated and the nano metal layer inside of the metal pattern  21  may be more densified. In addition, an optical density of the metal pattern is increased to enhance optical characteristics of the metal pattern and to enhance an adhesive force between the base substrate and the metal pattern. For example, a transmissivity of the metal pattern may be decreased. The metal pattern  21  formed as mentioned above may be used as a photomask. Here, the metal pattern  21  may be a light blocking portion blocking a light when used as the photomask, and a portion at which the metal pattern  21  is not formed may be a light transmissive portion transmitting the light. 
     Referring to  FIG. 1H , the metal pattern  21  is covered by an encapsulant  40 . The encapsulant  40  covers all of the metal pattern  21  as illustrated, and may partially cover the base substrate  40 . Alternatively, the encapsulant  40  covers all of the metal pattern  21  and the base substrate  40 . 
     For example, the encapsulant  40  may have a relatively high transmittance, and may include a pellicle having a high polymer film or silicon dioxide (SiO 2 ). The encapsulant  40  has high transparency and relatively harder material, to increase durability of the photomask and to prevent the photomask from be oxidized due to oxygen or humidity of an atmosphere. A thickness of the encapsulant  40  may be about several hundred nanometers. 
       FIG. 2  is a graph illustrating a relation between a frequency and a particle diameter. When the heat is applied to the solution layer  20  and the nanoparticle  25  is self-produced inside of the solution layer  20  including the organometallic ink, a frequency of the self-production of the nanoparticle  25  is illustrated in  FIG. 2 . 
     Referring to  FIG. 2 , when the temperature of the heat from the heat source  30  is between a first temperature at which the nanoparticle  25  starts to be self-produced in the solution layer  20  and a second temperature at which the nanoparticles  25  are sintered with each other, the nanoparticles  25  having a diameter substantially same as or less than about 100 nm occupies substantially same or more than about 80% in the solution layer  20  including the organometallic ink. For example, most of the nanoparticles  25  self-produced in the solution layer  20  may be between about 2 nm and about 3 nm. 
     According to the example embodiments, an organometallic ink in which a nanoparticle is self-produced through heating is used to manufacture a photomask, and thus manufacturing processes are performed in a normal state without using expensive equipments in a vacuum state, compared to a conventional manufacturing process. Thus, productivity of the photomask may be enhanced and the cost price may be decreased. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few example embodiments of the present invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific example embodiments disclosed, and that modifies to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the appended claims. The present invention is defined by the following claims, with equivalents of the claims to be included therein.