Abstract:
A cleaning liquid is provided, which comprises an aqueous solution containing nitric acid, sulfuric acid, a fluorine compound, and a basic compound. The concentration of water in the cleaning liquid is 80% by weight or more, and the pH value of the cleaning liquid is from 1 to less than 3. The cleaning liquid is effective for removing etching residues formed in a dry etching process from semiconductor devices and display devices without oxidizing and corroding their metal wirings, particularly, copper wirings and the materials of insulating films.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a cleaning liquid and a cleaning method for removing etching residues formed on the surfaces of semiconductor devices and display devices in the production thereof, and particularly to a cleaning liquid and a cleaning method for removing etching residues, which firmly adhere to the surfaces of semiconductor devices and display devices, without damaging the materials of semiconductor devices and display devices such as metal wirings, interlayer insulation films, etc.  
         [0003]     2. Description of the Prior Art  
         [0004]     At present, semiconductor devices such as highly integrated LSI are generally produced by lithographic methods. The lithographic production of semiconductor devices generally includes sequential step: a step of forming electroconductive thin films, such as metal films, which are finally made into wirings; a step of forming interlayer insulation films such as silicon oxide films for insulating electroconductive thin films and wirings on a substrate such as silicon wafer; a step of forming an overlying photosensitive layer by coating a photoresist uniformly; a step of forming a patterned resist film by a pattern exposure and subsequent development of the photosensitive layer; a step of patterning the underlying thin films by a selective etching utilizing the patterned resist film as a mask; and a step of removing the remaining patterned resist film completely.  
         [0005]     Recently, semiconductor devices come to be integrated more highly, and the formation of a pattern of 0.18 μm or smaller is required. As the processing dimension becomes extremely finer, the dry etching has come to dominate in the selective etching process. In the dry etching process, it is known that residues derived from dry etching gas, resist, film to be etched and materials of the treating chamber of dry etching apparatus (hereinafter, the residues will be referred to as “etching residues”) are formed. The etching residues remaining inside and around via holes unfavorably increase the resistance and cause electric short circuits.  
         [0006]     As the cleaning liquid for removing etching residues formed during the formation of metal wirings, organic amine-containing stripping liquids composed of a mixture of an alkanolamine and an organic solvent have been disclosed (JP 62-49355A and JP 64-42653A). When the proposed stripping liquids are washed with water after removing etching residues and remaining resist, the amine is dissociated by the absorbed water and the stripping liquids become alkaline, to corrode metal films, etc. Therefore, an organic solvent such as an alcohol, in place of water, must be used as the rinsing liquid, to reduce the safety and increase environmental load.  
         [0007]     As the cleaning liquid more powerful in removing etching residues and resist films than the organic amine-containing stripping liquids, fluorine-containing cleaning liquids composed of a fluorine compound, an organic solvent, a corrosion inhibitor, etc. have been disclosed (JP 7-201794A and JP 11-67632A). Under recent severe conditions of dry etching in the production of semiconductor devices, the resists are degraded significantly. The proposed organic amine-containing stripping liquids and fluorine-containing cleaning liquids are less effective for completely removing such degraded resists.  
         [0008]     Since the organic amine-containing stripping liquids and the fluorine-containing cleaning liquids contain a large amount of organic solvents, the use thereof in the production of semiconductor devices necessitates undue precautions for safety and for reducing environmental load, such as the treatment of liquid wastes. To remove such drawbacks, acid-containing cleaning liquids such as an aqueous solution of an organic acid and an aqueous solution of nitric acid, sulfuric acid and phosphoric acid have been proposed (JP 10-72594A and JP 2000-338686A). However, the proposed acid-containing cleaning liquids are less effective for removing firmly adhered etching residues, particularly, etching residues containing silicon, silicon oxides, copper oxides, etc.  
         [0009]     Therefore, there has been a strong demand for a cleaning liquid that removes etching residues, particularly, etching residues containing silicon, silicon oxides, copper oxides, etc. completely without damaging the wiring materials, particularly, copper and that is highly safe and environmentally friend.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention is directed to provide a cleaning liquid and a cleaning method for quickly removing etching residues, particularly etching residues containing silicon, silicon oxides, copper oxides, etc. which are formed during dry etching in the wiring process in the production of semiconductor devices and display devices without oxidizing or corroding the materials of copper wirings, insulating films, etc.  
         [0011]     Thus, the present invention provides a cleaning liquid for semiconductor devices and display devices having metal wirings, which is an aqueous solution containing nitric acid, sulfuric acid, a fluorine compound, and a basic compound, wherein a content of water is 80% by weight or more of the cleaning liquid and a pH value of the cleaning liquid is form 1 to less than 3.  
         [0012]     The present invention further provides a cleaning method of semiconductor devices and display devices having metal wirings, which includes a step of bringing the semiconductor devices and display devices into contact with the cleaning liquid mentioned above. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a partially cross-sectional view of a semiconductor device after subjected to etching and removal of remaining resist, showing the formation of etching residues on the sidewalls of etched portion. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     The concentration of each of nitric acid and sulfuric acid in the cleaning liquid is preferably from 0.001 to 10% by weight, and more preferably from 0.005 to 8% by weight. The concentrations of nitric acid and sulfuric acid may be the same or different. Preferably, the weight ratio of sulfuric acid/nitric acid is from 0.1 to 1000, and more preferably from 1 to 100.  
         [0015]     Examples of the fluorine compounds include hydrofluoric acid, acidic ammonium fluoride, and quaternary ammonium fluorides represented by the following formula 1:  
                         
 
 wherein each of R 1 , R 2 , R 3  and R 4  is independently alkyl group, aralkyl group, alkenyl group, aryl group, hydroxyalkyl group or alkoxyalkyl group. Specific examples of the quaternary ammonium fluorides of the formula 1 include tetramethylammonium fluoride, tetraethylammonium fluoride, triethylmethylammonium fluoride, trimethylhydroxyethylammonium fluoride, tetraethanolammonium fluoride, and methyltriethanolammonium fluoride, with ammonium fluoride and tetramethylammonium fluoride being preferred. 
 
         [0016]     These fluorine compounds may be used alone or in combination of two or more. The content of the fluorine compound in the cleaning liquid is preferably from 0.001 to 15% by weight, and more preferably from 0.005 to 10% by weight.  
         [0017]     Examples of the basic compounds include ammonia, primary amines, secondary amines, tertiary amines, imines, alkanolamines, heterocyclic compounds which may have C 1-8  alkyl, and quaternary ammonium hydroxides represented by the following formula 2:  
                         
 
 wherein each of R 5 , R 6 , R 7  and R 8  is independently alkyl group, aralkyl group, alkenyl group, aryl group, hydroxyalkyl group or alkoxyalkyl group. 
 
         [0018]     Examples of the primary amines include ethylamine, n-propylamine, butylamine, 1-ethylbutylamine, 1,3-diaminopropane, and cyclohexylamine; examples of the secondary amines include diethylamine, di-n-propylamine, di-n-butylamine, and 4,4′-diaminodiphenylamine; examples of the tertiary amines include dimethylethylamine, diethylmethylamine, triethylamine, and tributylamine; examples of the imines include 1-propaneimine and bis(dialkylamino)imine; examples of the alkanolamines include monoethanolamine, diethanolamine, triethanolamine, diethylethanolamine, and propanolamine; examples of the heterocyclic compounds which may have C 1-8  alkyl include pyrrole, imidazole, pyrazole, pyridine, pyrrolidine, 2-pyrroline, imidazolidine, 2-pyrazoline, pyrazolidine, piperidine, piperazine, and morpholine; and examples of the quaternary ammonium hydroxides of the formula 2 include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, trimethylhydroxyethylammonium hydroxide (choline), and tetraethanolammonium hydroxide, with tetramethylammonium hydroxide and trimethylhydroxyethylammonium hydroxide (choline) being preferred because of their strong basicity with no metal ion.  
         [0019]     These basic compounds may be used alone or in combination of two or more. The concentration of the basic compound in the cleaning liquid is preferably selected from a range of 0.01 to 15% by weight so as to regulate the pH of the cleaning liquid within the intended range.  
         [0020]     To enhance the wetting properties, the cleaning liquid may further contain a surfactant such as a cationic surfactant, an anionic surfactant, a nonionic surfactant and a fluorine-containing surfactant, with the anionic surfactant being preferred, and polyoxyethylene alkyl ether phosphate and polyoxyethylene alkylaryl ether phosphate, such as “Plysurf A215C” (tradename of Dai-Ichi Kogyo Seiyaku Co., Ltd.) and “Phosphanol RS-710” (tradename of Toho Chemical Industry Co., Ltd.), being more preferred. The surfactant may be used singly or in combination of two or more. The concentration of the surfactant in the cleaning liquid, if used, is preferably from 0.001 to 5% by weight, and more preferably from 0.01 to 1% by weight.  
         [0021]     To enhance the anti-corrosion properties against copper wirings, the cleaning liquid may further contain an anti-corrosion agent such as, but not limited to, an aromatic hydroxy compound, a triazole compound, a sugar alcohol, and a chelate compound.  
         [0022]     Examples of the aromatic hydroxy compounds include phenol, cresol, xylenol, pyrocatechol, tert-butylcatechol, resorcinol, hydroquinone, pyrogallol, 1,2,4-benzenetriol, salicyl alcohol, p-hydroxybenzyl alcohol, o-hydroxybenzyl alcohol, p-hydorxyphenethyl alcohol, p-aminophenol, m-aminophenol, diaminophenol, a minoresorcinol, p-hydroxybenzoic acid, o-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, and gallic acid. Examples of the sugar alcohols include sorbitol, xylitol and palatinit. Examples of the triazole compounds include benzotriaole, aminotriazole and aminotetrazole. Examples of the chelate compounds include phosphoric acid-based compounds such as 1,2-propanediaminetetramethylenephosphonic acid and hydroxyethanephosphonic acid; carboxylic acid-based compounds such as ethylenediaminetetraacetic acid, dihydroxyethylglycine, nitrilotriacetic acid, oxalic acid, citric acid, malic acid, and tartaric acid; amine compounds such as bipyridine, tetraphenylporphyrin, phenanthroline, and 2,3-pyridinediol; oxime compounds such as dimethylglyoxime and diphenylglyoxime; and acetylene compounds such as phenylacetylene and 2,5-dimethyl-3-hexyne-2,5-diol. These anti-corrosion agents may be used alone or in combination of two or more. The concentration of the anti-corrosion agent in the cleaning liquid, if used, is preferably from 0.001 to 10% by weight, and more preferably from 0.005 to 5% by weight.  
         [0023]     Other additives used in known cleaning liquids may be also usable in the cleaning liquid of the invention, if necessary, as long as the incorporation thereof is not adversely affect the effects of the invention. Such additives may include, but not limited to, organic acids, their salts, nucleophilic amines, and their salts.  
         [0024]     Examples of the organic acids include formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, maleic acid, succinic acid, adipic acid, lactic acid, butyric acid, malic acid, pyruvic acid, citric acid, benzoic acid, 1,4-naphthoquinone-2-sulfonic acid, ascorbic acid, isoascorbic acid, salicylic acid, and aminocarboxylic acids such as ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, 1,3-propanediaminetetraacectic acid, diethylenetriaminepantaacetic acid, triethylenetetraminehexaacetic acid, nitrilotriacetic acid and hydroxyethyliminodiacetic acid. Examples of the nucleophilic amines include hydroxylamine, diethylhydroxylamine, hydrazine, and N,N-dimethylhydrazine. These may be used alone or in combination of two or more. The concentration of such additives in the cleaning liquid, if used, is preferably from 0.001 to 10% by weight and more preferably from 0.005 to 5% by weight.  
         [0025]     The pH of the cleaning liquid is from 1 to less than 3, preferably from 2 to less than 3. The upper limit of each pH range is preferably 2.9. The pH is selected from the above range according to etching conditions and the kinds of materials of semiconductor device components and display device components.  
         [0026]     The cleaning method of the invention is conducted, for example, in a manner described below. An electroconducting thin film to be made into wirings and an insulating film are successively formed on a substrate. Then, a photoresist is applied thereon. The photoresist film is patterned by exposure to a pattern of light and development. Using the patterned photoresist film as a mask, the non-protected area of the insulating film is selectively etched. Thereafter, the remaining photoresist film is removed by ashing. As shown in  FIG. 1 , the etching residues  4  remain on the etched surface and its vicinities even after the removal of the photoresist film. Then, the etching residue are removed by bringing the semiconductor device into contact with the cleaning liquid. The contact treatment is performed by spray, application, immersion, etc., utilizing ultrasonic wave, if needed. The contact temperature and the contact time depend on the etching conditions and the materials of semiconductor device components, and preferably from room temperature to 90° C., and more preferably from 0.5 to 30 min. After removing the etching residues, the rinsing with only water is sufficient in the method of the invention, and the use of organic solvent such as alcohol is not needed.  
         [0027]     The cleaning liquid and cleaning method of the invention is applicable to semiconductor devices and display devices including substrate materials such as silicon, amorphous silicon, polysilicon and glass; insulating materials such as silicon oxide and silicon nitride; barrier materials such as titanium, titanium nitride, tantalum and tantalum nitride; wiring materials such as copper, tungsten, titanium-tungsten, aluminum, chromium and chromium alloys; compound semiconductors such as gallium-arsenic, gallium-phosphorus and indium-phosphorus; and oxide semiconductor such as chromium oxide. Particularly, the cleaning liquid of the invention is effective for removing the etching residues containing silicon, silicon oxides, cupper oxides, etc. from semiconductor devices and display devices having metal wirings made of only copper or laminated metal wirings of copper and a barrier material such as titanium, titanium nitride, tantalum and tantalum nitride.  
         [0028]     The present invention will be explained in more detail by reference to the following examples which should not be construed to limit the scope of the present invention.  
       EXAMPLES 1-10 and COMPARATIVE EXAMPLES 1-3  
       [0029]     On a substrate, a copper wiring film  1  was formed, on which a silicon nitride film  2  and a silicon oxide film  3  were successively formed by CVD. A photoresist was applied onto the silicon oxide film  3 , exposed to a pattern of light and developed, to form a patterned resist. Using the patterned resist as the mask, the silicon nitride film  2  and the silicon oxide film  3  were selectively etched, and then, the remaining resist was removed by ashing, to obtain a semiconductor device. A partially cross-sectional view of the semiconductor device is shown in  FIG. 1  which shows that the etching residues  4  remain on the sidewalls of the etched portion.  
         [0030]     The semiconductor device having copper wirings was cleaned with each of the cleaning liquids shown in Tables 1 and 3 under the conditions shown in Tables 2 and 4, rinsed with super pure water, and dried. The surface of the dried semiconductor device was observed under a scanning electron microscope (SEM) to evaluate the removal of etching residues and the corrosion of copper wirings according to the following ratings. The results are shown in Tables 2 and 4.  
         [0000]     Evaluation Ratings  
         [0031]     Removal of Etching Residues 
        A: Completely removed.     B: Nearly completely removed.     C: Partly remained.     D: Substantial part remained.        
 
         [0036]     Corrosion of Cooper Wirings 
        A: No corrosion.     B: Substantially no corrosion.     C: Apparent crater or pit corrosion.     D: Copper film was roughened over its entire surface and recessed.        
 
         [0041]     As seen from Table 2, in Examples 1 to 10 where the cleaning liquids of the invention were used, the etching residues were completely removed without corroding copper.  
                                                                                                                                     TABLE 1                                       Concentrations (% by weight)                Nitric   Sulfuric               Examples   Acid   Acid   Fluorine Compound   Basic Compound                    1   0.1   4   AF   0.06   TAH   8.8       2   0.1   4   TAF   0.10   TAH   6.5       3   0.1   4   AF   0.15   TAH   7.2       4   1.0   4   TAF   0.10   TAH   8.0       5   0.1   8   TAF   0.10   TAH   10.9       6   0.1   4   AF   0.05   choline   6.5       7   0.1   4   TAF   0.30   TAH   6.4       8   0.1   4   AF   0.05   TAH   6.7       9   0.1   4   TAF   0.10   TAH   2.5       10   0.1   4   AF   0.05   TAH   6.7                        Concentrations (% by weight)                Examples   Anti-corrosion agent/Additive       Water   pH                    1   L-ascorbic acid   1.0   86.04   2.0       2   —   —   89.30   2.0       3   —   —   88.55   2.9       4   EDTA   0.01   86.89   2.9       5   hydroxylamine   0.5   80.40   2.9       6   Phosphanol RS-710   0.1   89.25   2.0       7   Phosphanol RS-710   0.1   89.00   2.9           formic acid   0.1       8   EDTA   0.01   88.64   2.0           hydroxylamine   0.5       9   Phosphanol RS-710   0.1   92.70   2.0           hydrazine   0.5       10   EDTA   0.01   89.04   2.0           formic acid   0.1                 AF—ammonium fluoride            TAF—tetramethylammonium fluoride            TAH—tetramethylammonium hydroxide            Phosphanol RS-710: tradename of Toho Chemical Industry Co., Ltd.            EDTA: ethylenediaminetetraacetic acid             
 
         [0042]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
               
               
                   
                 Cleaning Conditions 
                 Cleaning Results 
               
             
          
           
               
                   
                 Temperature 
                 Time 
                 Removal of 
                 Corrosion of 
               
               
                 Examples 
                 (° C.) 
                 (min) 
                 etching residues 
                 copper 
               
               
                   
               
             
          
           
               
                 1 
                 30 
                 2 
                 A 
                 A 
               
               
                 2 
                 30 
                 2 
                 A 
                 A 
               
               
                 3 
                 30 
                 2 
                 A 
                 A 
               
               
                 4 
                 50 
                 1 
                 A 
                 A 
               
               
                 5 
                 30 
                 2 
                 A 
                 A 
               
               
                 6 
                 30 
                 2 
                 A 
                 A 
               
               
                 7 
                 30 
                 2 
                 A 
                 A 
               
               
                 8 
                 30 
                 2 
                 A 
                 A 
               
               
                 9 
                 30 
                 2 
                 A 
                 A 
               
               
                 10 
                 30 
                 2 
                 A 
                 A 
               
               
                   
               
             
          
         
       
     
         [0043]    
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
               
               
                 Compar- 
                 Concentrations (% by weight) 
                   
               
             
          
           
               
                 ative 
                 Nitric 
                 Sulfuric 
                 Fluorine 
                 Basic 
                   
                   
               
               
                 Examples 
                 Acid 
                 Acid 
                 Compound 
                 Compound 
                 Water 
                 pH 
               
               
                   
               
             
          
           
               
                 1 
                 — 
                 4 
                 AF 
                 0.05 
                 TAH 
                 7.0 
                 88.95 
                 2.9 
               
               
                 2 
                 0.1 
                 — 
                 TAF 
                 0.1 
                 — 
                 — 
                 99.80 
                 2.9 
               
               
                 3 
                 0.1 
                 4 
                 — 
                 — 
                 TAH 
                 7.4 
                 88.59 
                 2.9 
               
               
                   
               
               
                   AF—ammonium fluoride    
               
               
                   TAF—tetramethylammonium fluoride    
               
               
                   TAH—tetramethylammonium hydroxide    
               
             
          
         
       
     
         [0044]    
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                   
               
               
                   
                 Cleaning Conditions 
                 Cleaning Results 
               
             
          
           
               
                 Comparative 
                 Temperature 
                 Time 
                 Removal of 
                 Corrosion of 
               
               
                 Examples 
                 (° C.) 
                 (min) 
                 etching residues 
                 copper 
               
               
                   
               
               
                 1 
                 30 
                 5 
                 C 
                 A 
               
               
                 2 
                 30 
                 5 
                 C 
                 A 
               
               
                 3 
                 30 
                 5 
                 D 
                 A 
               
               
                   
               
             
          
         
       
     
         [0045]     The cleaning liquid of the invention is safe and environmentally friend. Using the cleaning liquid, the etching residues on semiconductor devices and display devices are easily removed within a short period of time. Since the wiring materials are not corroded, the use of the cleaning liquid enables the production of high precision and high quality circuit wirings. In addition, the rinse after treating with the cleaning liquid is effected by using only water without needing an organic solvent such as alcohol.