Patent Publication Number: US-2005139233-A1

Title: Cleaning solution and method of cleaning a semiconductor device using the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a divisional of U.S. patent application Ser. No. 10/671,245, filed on Sep. 24, 2003, now pending, which is claims priority from Korean Patent Application 2002-80610, filed on Dec. 17, 2002, the contents of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This disclosure relates to a cleaning solution and a method of cleaning a semiconductor device using the same, and more particularly to a cleaning solution for completely removing various polymers attached to a tungsten wiring of a semiconductor device and a method of cleaning a semiconductor device using the same.  
      2. Description of the Related Art  
      Recently, semiconductor devices have been greatly improved as information processing apparatus such as a computers are rapidly developed. The semiconductor device is required to have rapid response speed and large storage capacity so that a semiconductor manufacturing process is developed to improve integration density and reliability of the semiconductor device.  
      To accomplish high integration density of a semiconductor device, a cell of the semiconductor device should be reduced. In accordance with reduction of the size of the cell, all the patterns formed on a substrate have reduced dimensions and processing margins are also decreased. Hence, the semiconductor device may not have adequate electrical insulation and refresh characteristics. Also, sizes of the patterns are greatly reduced and multi-layered wirings are demanded according as the semiconductor device has high integration density.  
      As design rules for semiconductor devices are reduced, a metal having a relative low electrical resistance is used for metal wirings of the semiconductor device instead of a metal having high electrical resistance. For example, tungsten silicide, rather than tungsten, is employed for the metal wiring of the semiconductor device to be used as a gate electrode or a bit line of a volatile or non-volatile memory device.  
      As processes of forming a metal wiring and a contact hole for multi-layered metal wirings are more frequently employed in a semiconductor manufacturing process, a dry etch process for etching a metal and an ashing process for removing a photoresist pattern are also frequently performed. When the metal wiring is formed using the dry etch and ashing processes, impurities are generated from a dry etch gas, the photoresist pattern, an oxide film, and a tungsten film and the impurities are attached to a sidewall of the metal wiring. The impurities may increase electrical resistance of a semiconductor device or may cause an electrical short between adjacent metal wirings when the impurities remain on the metal wiring. Thus, these impurities should be removed from the metal wiring.  
      Japanese Patent Laid Open Publication No. 10-779366 discloses a method of removing impurities remaining on a substrate using a cleaning solution including about 24 percent by weight of sulfuric acid, about 5 percent by weight of aqueous hydrogen peroxide solution, about 0.02 percent by weight of hydrogen fluoride, about 0.075 percent by weight of N-dodecyl benzene sulfonic acid and water. The impurities on the substrate are removed by immersing the substrate into the cleaning solution for about 10 minutes and rinsing the substrate using deionized water for about 7 minutes.  
      Korean Patent Laid Open Publication No. 2000-61342 discloses a method of removing polymers remaining on a substrate by successively using a cleaning solution of sulfuric acid (H 2 SO 4 ) and aqueous hydrogen peroxide solution (H 2 O 2 ), a cleaning solution of hydrogen fluoric acid (HF) and water (H 2 O), and an SCl cleaning solution. The polymers are generated after a dry etch process for forming a tungsten silicide wiring on the substrate.  
      Meanwhile, an organic stripper including hydroxylamine is generally used in a cleaning process for removing impurities generated after a process of etching a tungsten wiring because the organic stripper may not cause damages of the tungsten wiring and an underlying film. However, the organic stripper may not completely remove the impurities remaining on a substrate. The organic stripper may not effectively remove oxygen-containing polymers (polymeric oxides) generated during etching of the tungsten wiring so that the impurities are not completely removed from the substrate. Additionally, because the impurities attached to the tungsten wiring are adequately removed from the tungsten wiring for more than about 20 minutes, the time required for removing the impurities may be too long when the impurities are removed using the organic stripper.  
      To solve the above-mentioned problems, an improved organic stripper has been developed. The improved organic stripper additionally includes fluorine-containing chemicals like HF or NHF4, an organic solvent, and a corrosion inhibitor. The organic solvent can prevent a metal wiring from being damaged due to the fluorine-containing chemicals. However, the improved organic stripper may not effectively remove polymers generated during etching the metal wiring and the improved organic stripper is very expensive. Also, the improved organic stripper may excessively etch some underlying films to such an extent that the improved organic stripper can hardly be employed for a semiconductor manufacturing process.  
      Embodiments of the invention address these and other disadvantages of the conventional art.  
     SUMMARY OF THE INVENTION  
      Among other advantages, embodiments of the invention provide a cleaning solution that can effectively remove various polymers attached to tungsten wiring without damage to the tungsten wiring and an underlying film. Additionally, the time required for removing the polymers can be greatly reduced, improving the throughput of the semiconductor device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other advantages of the invention will become readily apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings.  
       FIG. 1  is a graph illustrating the etch rate of a tungsten wiring relative to the amount of sulfuric acid contained in a cleaning solution according to embodiments of the invention.  
       FIG. 2  is a graph illustrating the etch rate of an oxide film relative to the amount of sulfuric acid contained in a cleaning solution according to embodiments of the invention.  
       FIG. 3  is a graph illustrating the etch rate of a tungsten wiring relative to the amount of aqueous hydrogen peroxide solution contained in a cleaning solution according to embodiments of the invention.  
       FIG. 4  is a graph illustrating the etch rate of an oxide film relative to the amount of aqueous hydrogen peroxide solution contained in a cleaning solution according to embodiments of the invention.  
       FIG. 5  is a graph illustrating the etch rate of an oxide film relative to the cleaning time using an embodiment of the invention.  
       FIG. 6A  is an electron microscope photograph illustrating a structure including a tungsten wiring cleaned using a conventional cleaning method.  
       FIG. 6B  is an electron microscope photograph illustrating a structure including a tungsten wiring cleaned in accordance with an embodiment of the invention.  
       FIGS. 7A  to  7 D are cross-sectional diagrams illustrating a method of forming a transistor of a semiconductor device according to an embodiment of the invention.  
       FIGS. 8A  to  8 E are cross-sectional diagrams illustrating a method of forming a bit line of a semiconductor device according to another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, the preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In the following drawings, like reference numerals identify similar or identical elements.  
      Cleaning Solution  
      A cleaning solution according to embodiments of the invention includes sulfuric acid (H 2 SO 4 ), aqueous hydrogen peroxide solution (H 2 O 2 ), deionized water (H 2 O), and hydrogen fluoric acid (HF) solution. The hydrogen fluoric solution is prepared by diluting hydrogen fluoric acid with deionized water. The cleaning solution efficiently removes various polymers remaining on a metal wiring formed on a substrate without damages of the metal wiring and an underlying film after a dry etch process is performed to form the metal wiring.  
      In particular, the cleaning solution has the following characteristics.  
      The cleaning solution can prevent damage to a tungsten wiring under an adequately controlled condition even though the sulfuric acid and the aqueous hydrogen peroxide solution contained in the cleaning solution may corrode the tungsten wiring.  
      The cleaning solution can completely remove various polymers including metallic components and oxygen-containing components generated during dry etching the tungsten wiring.  
      The cleaning solution can adequately etch oxygen-containing polymers while simultaneously preventing the lifting of the tungsten wiring due to en excessive etch of an underlying oxide film. In addition, the cleaning solution can prevent an increase in the aspect ratio of the tungsten wiring and the generation of a void in an interlayer dielectric film by reducing the etching of the interlayer dielectric film.  
      To meet the above-mentioned characteristics, cleaning solutions according to embodiments of the invention preferably include about 1 to about 10 percent by weight of sulfuric acid, about 0.5 to about 5 percent by weight of aqueous hydrogen peroxide solution, and about 85 to about 98.5 percent by weight of hydrogen fluoric acid solution. Therefore, the cleaning solution can effectively remove the polymers generated during a formation of a structure including a tungsten wiring.  
      The cleaning solution preferably includes about 1 to about 10 percent by weight of sulfuric acid. If the cleaning solution includes less than about 1 percent by weight of sulfuric acid, the cleaning solution will not cause damage to a tungsten film pattern and an oxide film pattern formed on a substrate. However, the cleaning solution will not easily remove the polymers including metallic by-products and oxides generated during the etching of the tungsten film. When the cleaning solution includes more than about 10 percent by weight of sulfuric acid, although the cleaning solution can easily remove metallic polymers and oxygen-containing polymers generated during a formation of the tungsten film pattern, the cleaning solution may cause damage to the tungsten film pattern and the oxide film pattern. The cleaning solution preferably includes about 1 to about 10 percent by weight, and more preferably, about 3 to about 8 percent by weight of sulfuric acid.  
      Because sulfuric acid can easily corrode the tungsten film pattern, an etched amount of the tungsten film pattern can be controlled in accordance with the amount of the sulfuric acid contained in the cleaning solution. Additionally, the sulfuric acid serves as a catalyst that augments the potential of hydrogen (pH) of the cleaning solution to more rapidly dissolve the hydrogen fluoric acid. Hence, the oxygen-containing polymers are more easily removed from the tungsten film pattern.  
      The cleaning solution preferably includes about 0.5 to about 5 percent by weight of aqueous hydrogen peroxide solution. When the cleaning solution includes less than about 0.5 percent of by weight of aqueous hydrogen peroxide solution, the metallic polymers and the oxygen-containing polymers are not easily removed although the cleaning solution will not cause damage to the tungsten film pattern and the oxide film pattern. In the case where the cleaning solution includes more than 5 percent by weight of aqueous hydrogen peroxide solution, the cleaning solution may cause the damages of the tungsten film pattern and the oxide film pattern although the cleaning solution will easily remove the metallic polymers and the oxygen-containing polymers. Therefore, the cleaning solution preferably includes about 0.5 to about 5, and more preferably about 1 to about 3 percent by weight of aqueous hydrogen peroxide solution. Here, the aqueous hydrogen peroxide solution has a concentration of about 25 to about 30 percent.  
      The amount of hydrogen fluoric acid solution contained in the cleaning solution varies in accordance with the concentration of the hydrogen fluoric acid after dilution with deionized water. The hydrogen fluoric acid solution includes about 1,000 ml of deionized water and about 0.1 to about 2 ml of hydrogen fluoric acid. In this case, the hydrogen fluoric acid solution has a concentration of about 50 percent. The cleaning solution preferably includes about 85 to about 95 percent by weight of hydrogen fluoric acid solution.  
      When the cleaning solution includes less than about 85 percent by weight of hydrogen fluoric acid solution or the amount of hydrogen fluoric acid contained in the hydrogen fluoric acid solution is less than 0.1 ml, the cleaning solution may not remove the oxygen-containing polymers.  
      When the cleaning solution includes more than 95 percent by weight of hydrogen fluoric acid solution or the amount of hydrogen fluoric acid contained in the hydrogen fluoric acid solution is more than 2 ml, the cleaning solution may cause damage to the tungsten film pattern and the oxide film pattern although the cleaning solution can easily remove the oxygen-containing polymers and the metallic polymers.  
      Thus, the cleaning solution preferably includes a hydrogen fluoric acid solution of about 85 to about 95 percent by weight. Here, the hydrogen fluoric acid has a concentration of 50 percent and the hydrogen fluoric acid solution includes about 0.1 to about 2 ml of hydrogen fluoric acid and about 1,000 ml of deionized water.  
       FIG. 1  is a graph illustrating an etch rate of a tungsten wiring relative to the amount of sulfuric acid contained in a cleaning solution according embodiments of the invention.  
      Referring to  FIG. 1 , the etch rate of the tungsten wiring increases from about 70 to about 330 Å/min as the amount of sulfuric acid contained in the cleaning solution is augmented from about 1 to about 10 percent by weight. Here, a substrate including the tungsten wiring was immersed in the cleaning solution having a temperature of about 25° C. for about 10 minutes.  
      When the amount of the sulfuric acid contained in the cleaning solution was more than about 5 percent by weight, the etch rate of the tungsten wiring rapidly increased. In order to easily control the etch rate of the tungsten wiring, the amount of the sulfuric acid contained in the cleaning solution is preferably no more than about 5 percent by weight.  
       FIG. 2  is a graph illustrating an etch rate of an oxide film relative to the amount of sulfuric acid contained a cleaning solution according to embodiments of the invention.  
      Referring to  FIG. 2 , the etch rate of the oxide film increases from about 150 to about 300 Å/min as the amount of sulfuric acid contained in the cleaning solution increases from about 1 to about 10 percent by weight. In this case, a substrate including the oxide wiring was immersed in the cleaning solution having a temperature of about 25° C. for about 10 minutes.  
      Although the sulfuric acid cannot directly etch the oxide film, the sulfuric acid serves as a catalyst that can more rapidly dissociate hydrogen fluoric acid contained in the cleaning solution because the acidity of the cleaning solution increases in accordance with an increase of the amount of sulfuric acid contained in the cleaning solution. When the hydrogen fluoric acid is dissociated, it can more easily etch the oxide film and oxygen-containing polymers.  
       FIG. 3  is a graph illustrating an etch rate of a tungsten wiring relative to the amount of aqueous hydrogen peroxide solution contained in a cleaning solution according to embodiments of the invention.  
      Referring to  FIG. 3 , the etch rate of the tungsten wiring increases from about 50 to about 90 Å/min as the amount of the aqueous hydrogen peroxide solution contained in the cleaning solution increases from about 2.5 to about 5 percent by weight at a temperature of about 25° C. Additionally, at a temperature of about 32.5° C., as the amount of the aqueous hydrogen peroxide solution contained in the cleaning solution increases from about 2.5 to about 5 percent by weight, the etch rate of the tungsten wiring increases from about 120 to about 200 Å/min. Here, the substrate including the tungsten wiring was immersed in the cleaning solution for about 10 minutes.  
      As described above, a temperature variation of the cleaning solution has a greater effect on the etch rate of the tungsten wiring than the amount of the aqueous hydrogen peroxide solution or the sulfuric acid. Accordingly, in order to more easily control the etch rate of the tungsten wiring, the temperature of the cleaning solution is preferably maintained at about 25° C. while the amounts of the aqueous hydrogen peroxide solution and the sulfuric acid are selectively adjusted.  
       FIG. 4  is a graph illustrating an etch rate of an oxide film relative to the amount of aqueous hydrogen peroxide solution contained a cleaning solution according to embodiments of the invention.  
      Referring to  FIG. 4 , at a temperature of about 25° C., the etch rate of the oxide film increases from about 150 to about 170 Å/min as the amount of the aqueous hydrogen peroxide solution contained in the cleaning solution increases from about 2.5 to about 5 percent by weight. In addition, at a temperature of about 32.5° C., as the amount of the aqueous hydrogen peroxide solution contained in the cleaning solution increases from about 2.5 to about 5 percent by weight, the etch rate of the oxide film increases from about 180 to about 210 Å/min. In this case, a substrate including the oxide film was immersed in the cleaning solution for about 10 minutes.  
      When the amount of aqueous hydrogen peroxide solution contained in the cleaning solution increases, the etch rate of the oxide film gradually increases because the aqueous hydrogen peroxide solution does not directly etch the oxide film but serves as a catalyst for etching the oxide film.  
      Because the etch rate of the oxide film is more proportional to the temperature of the cleaning solution than the amount of the aqueous hydrogen peroxide solution contained in the cleaning solution, the temperature of the cleaning solution is maintained at about 25° C. while the amounts of sulfuric acid and aqueous hydrogen peroxide solution contained in the cleaning solution are selectively adjusted in order to easily control the etch rate of the oxide film.  
      According to embodiments of the invention, because the etch rates of the tungsten wiring and the oxide film vary greatly in accordance with the temperature of the cleaning solution and the amounts of the sulfuric acid and the aqueous hydrogen peroxide solution contained in the cleaning solution, the temperature of the cleaning solution and the amounts of etchant and catalyst are advantageously controlled to achieve pertinent etching of a metal wiring or an insulation film.  
      Method for Cleaning a Tungsten Wiring  
      In a process for cleaning polymers that remain on a tungsten wiring, a cleaning solution is provided in a cleaning bath. The cleaning solution includes about 5 percent by weight of sulfuric acid, about 2.5 percent by weight of aqueous hydrogen peroxide solution and about 92.5 percent by weight of hydrogen fluoric acid solution. Here, the hydrogen fluoric acid solution includes about 1,000 ml of deionized water and about 0.1 to about 2 ml of hydrogen fluoric acid. The hydrogen fluoric acid has a concentration of about 50 percent.  
      After a dry etch process is performed on a substrate that includes an oxide film and the tungsten wiring, the substrate is immersed in the cleaning solution. In this case, organic, metallic, and oxygen-containing polymers adhere to the tungsten wiring and the oxide film. The oxygen-containing polymers positioned on an outer sidewall of the tungsten wiring are first removed with the hydrogen fluoric acid contained in the cleaning solution. The tungsten wiring includes, for example, tungsten patterns.  
      When the oxygen-containing polymers are removed, the organic and metallic polymers are exposed. The organic and metallic polymers are removed by the aqueous hydrogen peroxide solution and sulfuric acid contained in the cleaning solution without damage to the tungsten wiring.  
      When a temperature of the cleaning solution is below about 20° C., the time required for completely removing the polymers from the sidewall of the tungsten wiring is greatly increased. To the contrary, when the cleaning solution has a temperature above about 30° C., damage to the tungsten wiring and an underlying layer may be caused even though the polymers may be rapidly removed from the tungsten wiring. Accordingly, the cleaning solution preferably has a temperature of about 25° C. to remove the polymers from the tungsten wiring.  
       FIG. 5  is a graph illustrating the etch rate of an oxide film relative to the cleaning time using a cleaning solution according to an embodiment of the invention. In  FIG. 5 , when the tungsten wiring including the polymers was cleaned, the etched amount of the oxide film formed beneath the tungsten wiring was observed by varying the cleaning time of the tungsten wiring so that the etch rate was measured in order to identify an advantageous cleaning time for the tungsten wiring.  
      Referring to  FIG. 5 , the polymers could be more completely removed from the tungsten wiring as the cleaning time increased, however, the underlying oxide film was excessively etched during removal of the polymers. That is, when the cleaning time increased from about 1 to about 10 minutes, the etch rate of the oxide film increased from about 30 to about 200 Å. Thus, a process for cleaning the tungsten wiring is preferably executed with a cleaning time of below about 9 minutes.  
      After the process for cleaning the tungsten wiring is accomplished, the substrate including the tungsten wiring is taken out of the cleaning solution. Then, the substrate is rinsed using deionized water to remove the cleaning solution remaining on the substrate. When the substrate is taken out of the cleaning solution, most polymers are dissolved in the cleaning solution or detached from the tungsten wiring so that most polymers are removed from the substrate or bond strengths between the polymers and the tungsten wiring are greatly reduced. Therefore, the polymers are cleaned from the substrate and the tungsten wiring when the rinsing process is performed on the substrate.  
      The substrate is dried to remove the remaining deionized water.  
      According to the method for cleaning the tungsten wiring, the polymers can be effectively removed from the tungsten wiring without damage to the tungsten wiring.  
       FIG. 6A  is an electron microscope photograph illustrating a structure including a tungsten wiring that was cleaned using a conventional cleaning method.  FIG. 6B  is an electron microscope photograph illustrating a structure including a tungsten wiring cleaned employing a cleaning method according to an embodiment of the invention.  
      Referring to  FIG. 6A , oxygen-containing polymers are not sufficiently removed from the tungsten wiring and also damage of the tungsten wiring (region A) was caused when the tungsten wiring was cleaned using the conventional method. As shown in  FIG. 6B , however, when the tungsten wiring is cleaned according to an-embodiment of the invention, the polymers generated during etching of the tungsten wiring and during ashing of a photoresist pattern were completely removed from the tungsten wiring. Also, damage to the tungsten wiring and the underlying oxide film are not nearly as severe.  
      Hereinafter, a method of forming a structure of a semiconductor device will be described with reference to the accompanying drawings.  
       FIGS. 7A  to  7 D are cross-sectional diagrams illustrating a method of forming a transistor of a semiconductor device according to an embodiment of the invention.  
      Referring to  FIG. 7A , an isolation process such as a shallow trench isolation (STI) process or a local oxidation of silicon (LOCOS) is performed on a substrate  100  to define an active region and a field region  100   b.  Preferably, the active and field regions  100   b  are defined using the STI process.  
      Particularly, the substrate  100  is partially etched to form a trench at a portion of the substrate  100  corresponding to the field region  100   b.  After a silicon oxide film is formed on the substrate  100  and fills up the trench, the silicon oxide film is etched using a chemical mechanical polishing (CMP) process, thereby forming a filed oxide film in the trench to define the field region  100   b.    
      Referring to  FIG. 7B , after impurities are selectively implanted into portions of the substrate  100  to from a P-type well and an N-type well on the substrate  100 , gate electrodes  110  are formed on the substrate  100 . The gate electrodes  110  include gate oxide film patterns  102   a,  first polysilicon film pattern  104   a,  first tungsten film patterns  106   a,  and first nitride film patterns  108   a,  respectively.  
      Particularly, a gate oxide film  102  having a thickness of about 50 to about 100 Å is formed on the substrate  100 . A first polysilicon film  104  doped with N-type impurities is formed on the gate oxide film  102  to a thickness of about 1,000 to about 1,500 Å. A first tungsten film  106  is formed on the first polysilicon film  104  in order to reduce a resistance of the gate electrode  110 . Alternatively, a first tungsten silicide film can be formed on the first polysilicon film  104  instead of the first tungsten film  106 . A first nitride film  108  is formed on the tungsten film  106 . Alternatively, a barrier layer can be formed between the first polysilicon film  104  and the first tungsten film  106  so as to easily form the first tungsten film  106 . After a photoresist pattern (not shown) is formed on the first nitride film  108  to define a layout of the gate electrodes  110 , the first nitride film  108 , the first tungsten film  106 , the first polysilicon film  104 , and the gate oxide film  102  are successively etched using the photoresist film as an etching mask, thereby forming the gate oxide film patterns  102   a,  the first polysilicon film patterns  104   a,  the first tungsten film patterns  106   a,  and the first nitride film patterns  108   a.  As a result, the gate electrodes  110  serve as word lines for a semiconductor device that is formed on the substrate  100 . The photoresist pattern is removed via a plasma ashing process and a stripping process using sulfuric acid.  
      When the gate electrodes  110  are formed using the etching process, a great quantity of polymers (P) is attached to sidewalls of the gate electrodes  110 . The polymers (P) are generated during the etching of the photoresist pattern, the first nitride film  108 , the first tungsten film  106 , the first polysilicon film  104 , and the gate oxide film  102 . The polymers (P) may increase the electrical resistance of the transistor including the first tungsten film patterns  106   a  so they should be removed from the gate electrodes  110 .  
      Referring to  FIG. 7C , in order to remove the polymers (P) attached to the sidewalls of the gate electrodes  110  including the first tungsten film patterns  106   a,  a cleaning bath including a cleaning solution is provided. The cleaning solution includes about 5 to about 7 percent by weight of sulfuric acid, about 2.5 percent by weight of aqueous hydrogen peroxide solution and about 90.5 to about 92.5 percent by weight of hydrogen fluoric acid solution. In this case, the hydrogen fluoric acid solution includes about 0.1 to about 2 ml of hydrogen fluoric acid and about 1,000 ml of deionized water wherein the hydrogen fluoric acid has a concentration of about 50 percent.  
      The substrate  100  including the polymers (P) attached thereto is immersed in the cleaning solution having a temperature of about 20 to about 30° C. for about 1 to about 9 minutes so that the polymers (P) are removed from the gate electrodes  110 .  
      In particular, the polymers (P) include organic polymers, metallic polymers, and oxygen-containing polymers. The organic and metallic polymers are first attached on the sidewalls of the gate electrodes  110  when the tungsten film patterns  106   a  are formed. The oxygen-containing polymers are attached to the metallic polymers and the sidewalls of the first tungsten film patterns  106   a  when the gate film patterns  102   a  are formed.  
      To remove these polymers (P), the substrate  100  including the gate electrodes  110  is immersed in the cleaning solution bath. The oxygen-containing polymers are first removed from the sidewalls of the gate electrodes  110  using the hydrogen fluoric acid included in the cleaning solution.  
      When the oxygen-containing polymers are removed, the organic polymers and the metallic polymers are exposed. The organic and metallic polymers are removed from the gate electrodes  110  using the aqueous hydrogen peroxide solution and the sulfuric acid contained in the cleaning solution without damage to the first tungsten film patterns  106   a.    
      In cases where the cleaning solution has a temperature of below about 20° C., the time required for removing the polymers (P) attached to the gate electrodes  110  is greatly increased. On the other hand, when the cleaning solution has a temperature of above about 30° C., the gate electrodes  110  and the gate oxide film patterns may be damaged although the polymers (P) are rapidly removed from the gate electrodes  110 . Therefore, the cleaning solution advantageously has a temperature of about 25° C.  
      After the substrate  100  including the gate electrodes  110  is taken out of the cleaning solution, the substrate  100  is rinsed using deionized water to remove the remaining cleaning solution. When the substrate  100  is taken out of the cleaning solution, most polymers (P) are dissolved by components contained in the cleaning solution and removed from the gate electrodes  110 , the polymers (P) are detached from the gate electrodes  110 , or the adhesion strength between the gate electrodes  110  and the polymers (P) is greatly reduced. Hence, the polymers (P) remaining on the substrate  100  are completely removed during the rinsing process using deionized water.  
      Then, a dry process is performed on the rinsed substrate  100  to remove the deionized water remaining on the substrate  100 . In this case, various polymers can be completely removed from the gate electrodes without the damages of the gate oxide film patterns  102  and the first tungsten film patterns  106   a.    
      Referring to  FIG. 7D , nitride spacers  112  are formed on the sidewalls of the gate electrodes  110 . Impurities are implanted into portions of the substrate  100  between the gate electrodes  110  using the gate electrodes  110  as masks, thereby forming source/drain regions  114   a  and  114   b  between the gate electrodes  110 . Thus, transistor structures including the gate electrodes  110 , the spacers  112 , and the source/drain regions  114   a  and  114   b  are formed on the substrate  100 .  
      In this embodiment, the source regions  114   a  of the transistor structures correspond to contact regions of capacitors and the drain regions  114   b  of the transistor structures correspond to contact regions of bit lines.  
       FIGS. 8A  to  8 E are cross-sectional diagrams illustrating a method of forming a bit line of a semiconductor device according to another embodiment of the invention. In this embodiment, the processes for forming transistor structures are identical to those of the embodiment described in  FIGS. 7A-7D .  
      Referring to  FIG. 8A , a first oxide film is formed on the substrate  100  where the transistor structures are formed. The first oxide film is etched using an etch back process or a CMP process until upper faces of the transistor structures are exposed. Thus, a first interlayer dielectric film  120  is formed on the substrate  100  to cover the transistor structures. The first interlayer dielectric film  120  includes boro-phosphor silicate glass (BPSG), undoped silicate glass (USG), or silicon oxide.  
      After a mask pattern (not shown) is formed on the first interlayer dielectric film  120 , a portion of the first interlayer dielectric film  120  is anisotropically etched to form a contact hole  122  using the mask pattern as an etching mask. The contact hole  122  exposes the drain region  114   a  of the transistor structure. The contact hole  122  is formed as a self-aligned contact by the spacer  120  in order to ensure a process margin.  
      Referring to  FIG. 8B , a conductive material like tungsten is formed on the first interlayer dielectric film  120  to fill up the contact hole  122 , and a portion of the conductive material on the first interlayer dielectrics is etched using a CMP process. Hence, a conductive plug  124  is formed in the contact hole  122 . The conductive plug  124  is electrically connected to the drain region  114   b  of the transistor structure.  
      Referring to  FIG. 8C , a bit line  132  is formed on the first interlayer dielectric film  120  where the conductive plug  124  is formed. In a process of forming the bit line  132 , a second polysilicon film  126 , a second tungsten film  128 , and a second nitride film  130  are successively formed on the first interlayer dielectric film  120  in which the conductive plug  124  is formed. Alternatively, a second tungsten silicide film can be formed on the second polysilicon film  126  instead of the second tungsten film  128 . In addition, a barrier layer can be formed between the second polysilicon film  126  and the second tungsten film  128  so as to easily form the second tungsten film  128  on the second polysilicon film  126 .  
      Referring to  FIG. 8D , the second nitride film  130 , the second tungsten film  128 , and the second polysilicon film  126  are successively etched using a mask pattern (not shown) and a dry etch process to form the bit line  132  including a second nitride film pattern  130   a,  a second tungsten film pattern  128   a,  and the second polysilicon film pattern  126   a.  The bit line  132  is positioned on the conductive plug  124 . When the dry etch process is accomplished, a large quantity of polymers (P) adhere to a sidewall of the bit line  132 . The polymers (P) are generated during etching of the second nitride film  130 , the second tungsten film  128 , the second polysilicon film  126 , and the mask pattern. The polymers (P) may increase the electrical resistance of the bit line  132  including the second tungsten film pattern  128   a.  Therefore, the polymers (P) should be completely removed from the sidewall of the bit line  132 .  
      Referring to  FIG. 8E , in order to remove the polymers (P) attached to the sidewall of the bit line  132  having the second tungsten film pattern  128   a,  a bath receiving a cleaning solution is prepared. The cleaning solution includes about 5 percent by weight of sulfuric acid, about 2.5 percent by weight of aqueous hydrogen peroxide solution, and about 92.5 percent by weight of hydrogen fluoric acid solution. In this case, the hydrogen fluoric acid solution has about 1,000 ml of deionized water and about 0.1 to about 2 ml of hydrogen fluoric acid. The hydrogen fluoric acid has a concentration of about 50 percent.  
      The substrate  100  having the resultant structure to which the polymers (P) are attached is immersed in the cleaning solution, which has a temperature of about 20 to about 30° C., for about 1 to about 9 minutes. Thus, the polymers (P) are removed from the bit line  132 . Here, a process for removing the polymers (P) is performed under conditions identical to those of the embodiment described in  FIGS. 7A-7D .  
      After the substrate  100  is taken out of the cleaning solution, the substrate  100  is rinsed using deionized water to remove the cleaning solution remaining on the substrate  100 .  
      The substrate  100  is the dried to remove the remaining deionized water on the substrate. Consequently, the polymers (P) are completely removed from the sidewall of the bit line  132  without damage to the first interlayer dielectric film  120  or the second tungsten film pattern  128   a.    
      A silicon nitride film having a uniform thickness is continuously formed on the first interlayer dielectric film  120  and on the bit line  132 , and then the silicon nitride film is etched using an etch back process to form a spacer  134  on the sidewall of the bit line. Thus, a bit line structure including the bit line  132  and the spacer  134  is completed. In this embodiment, a semiconductor device including the bit line structure can have improved electrical characteristics because the bit line structure can has a second tungsten film pattern  128   a  that is damage-free.  
      According to embodiments of the invention, various polymers attached to metal patterns can be easily removed without damage to the metal patterns or the underlying oxide film. In addition, a throughput of a semiconductor device can be improved by reducing the time required for removing the polymers.  
      Embodiments of the invention will now be described in a non-limiting way.  
      Embodiments of the invention provide a cleaning solution for removing a polymer that includes about 1 to about 10 percent by weight of sulfuric acid, about 0.5 to about 5 percent by weight of aqueous hydrogen peroxide solution, and about 85 to about 98.5 percent by weight of hydrogen fluoric acid solution. The hydrogen fluoric acid solution includes about 1,000 ml of deionized water and about 0.1 to about 2 ml of hydrogen fluoric acid, wherein the hydrogen fluoric acid has a concentration of about 45 to about 55 percent, and preferably about 50 percent.  
      Embodiments of the invention also provide a method of cleaning a semiconductor device. After a cleaning solution is prepared, polymers attached to a metal wiring formed on a substrate are removed. The cleaning solution includes about 1 to about 10 percent by weight of sulfuric acid, about 0.5 to about 5 percent by weight of aqueous hydrogen peroxide solution and about 85 to about 98.5 percent by weight of hydrogen fluoric acid solution. The polymers are removed by immersing (or dipping) the substrate into the cleaning solution after a dry etching process is performed to form the metal wiring on the substrate. Then, the substrate is rinsed to remove the remaining cleaning solution and the substrate is dried. In this case, the cleaning solution has a temperature of about 20 to about 30° C. and the substrate is immersed in the cleaning solution for about 1 to about 9 minutes.  
      In accordance with another embodiment of the invention, there is provides a method of forming a structure of a semiconductor device. A substrate is provided. The substrate includes a polysilicon film, a tungsten film, and a nitride film successively formed thereon. Subsequently, a mask pattern is formed on the nitride film and structure is formed on the substrate. The structure includes a nitride film pattern, a tungsten film pattern, and a polysilicon film pattern formed by dry etching the polysilicon film, the tungsten film, and the nitride film. After the mask pattern is removed, polymers attached to a sidewall of the structure formed on the substrate are removed. The polymers are removed by immersing the substrate into the cleaning solution including about 1 to about 10 percent by weight of sulfuric acid, about 0.5 to about 5 percent by weight of aqueous hydrogen peroxide solution, and about 85 to about 98.5 percent by weight of hydrogen fluoric acid solution. In this case, the hydrogen fluoric acid solution includes about 1,000 ml of deionized water and about 0.1 to about 2 ml of hydrogen fluoric acid, wherein the hydrogen fluoric acid has a concentration of about 45 to about 55 percent, and preferably about 50 percent. Then, the substrate is rinsed to remove the cleaning solution and dried. Alternatively, a barrier layer is formed between the polysilicon film and the tungsten film.  
      Having described several exemplary embodiments of the invention, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made to the particular embodiments of the invention disclosed that are nevertheless within the scope and the spirit of the invention as outlined by the appended claims.