Abstract:
A method for ashing a semiconductor device is provided. In the method, the semiconductor substrate, on which a metal interconnection and a photoresist pattern are formed, is processed using H 2 O, and then, by using a mixture of O 2 , N 2 , and H 2 O. The process is performed at least twice repeatedly. As a result, corrosion of the metal interconnection is inhibited and a bridge caused by conductive polymer is prevented.

Description:
RELATED APPLICATION 
     This application claims priority from Korean Patent Application No. 2001-48971, filed on Aug. 14, 2001, the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for fabricating a semiconductor device and, more particularly, to a method of ashing a semiconductor device having a metal interconnection. 
     2. Description of the Related Art 
     To complete the formation of integrated circuits, interconnections such as metal interconnections are used to interconnect semiconductor devices formed in the semiconductor substrate. The metal interconnections may be formed by an anisotropic etch process using a chlorine-based chemical material, e.g., Cl 2  and BCl 3 , as an etching gas. After the etch process, chlorine still remains in polymer formed on the sides of the metal interconnections. As a result, when the semiconductor substrate is unloaded from a reaction chamber after the etch process, chlorine reacts with hydrogen in the air, forming HCl which causes corrosion of the metal interconnections. Also, after forming the metal interconnections, the remaining photoresist pattern and polymer can form a bridge between the metal interconnections. Therefore, it is necessary to completely remove the remaining photoresist pattern and polymer. 
     In order to solve the above-mentioned problems, an ashing process has been introduced. In the ashing process, the remaining chlorine is removed in the first step. Then, the remaining photoresist pattern and polymer are removed in the second step. Korean laid-open Patent No. 96-009976 suggests an ashing process using CF 4  gas and O 2  gas during the first step and using O 2  gas and N 2  gas during the second step. However, in this method, the surface of metal interconnections may be attacked. Also, U.S. Patent Publication No. 5,200,031 discloses an ashing method using NH3 gas during the first step and using O 2  gas and NH 3  gas during the second step. However, the foregoing ashing method cannot completely remove the remaining chlorine, photoresist pattern or polymer. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of ashing a semiconductor device, which inhibits corrosion of a metal interconnection and sufficiently removes a photoresist pattern and polymer. 
     According to an embodiment of the present invention, a method of ashing a semiconductor device having a metal interconnection comprises a loop including a first step of using a passivating gas and a second step of using a stripping gas. The process is preferably performed at least two times alternately or repeatedly. The passivating gas preferably includes water vapor and the stripping gas preferably includes a gas mixture of oxygen, nitrogen and water vapor. The stripping gas may include a mixture of only oxygen and nitrogen. It is preferable to proceed with the steps of using the passivating gas and using the stripping gas under a pressure of 0.5 to 3 Torr and at a temperature of 200 to 270° C. It is also preferable to proceed with the steps of using the passivating gas and using the stripping gas successively in the same reaction chamber. 
     A method of forming the metal interconnection comprises the steps of forming a metal layer on a semiconductor substrate; forming a photoresist pattern on the metal layer; and etching the metal layer using the photoresist pattern as an etch mask. The step of etching the metal layer is carried out using a mixture of Cl 2  and BCl 3  as an etch gas. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description, when taken in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a flowchart illustrating the process according to an embodiment of the present invention; and 
     FIG. 2 is a cross-sectional view of an ashing apparatus used in the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a metal layer and a photoresist pattern are successively stacked on a semiconductor substrate. A metal interconnection is formed by etching the metal layer using the photoresist pattern as an etch mask (S 10 ). 
     The metal layer is typically made of aluminum. Alternatively, it can be also made of metals such as copper, titanium and tungsten. An anisotropic etching process is used to form the metal interconnections, preferably, using Cl 2 , BCl 3 , or a mixture thereof as an etch gas. After etching of the metal layer, however, chlorine-containing polymer may remain on the metal interconnection and the sidewalls of the photoresist pattern. 
     According to an embodiment of the present invention, the semiconductor substrate having the metal interconnections is loaded into the chamber of an ashing apparatus having a plasma generator (S 12 ). The interval between steps S 10  and S 12  is preferably reduced. 
     Referring to FIG. 2, an ashing apparatus  50  has a reaction chamber  56  including an upper electrode  51  for generating plasma and a lower electrode  52  on which a semiconductor substrate  60  is loaded. The upper electrode  51  is connected to the plasma generator  55 . Also, the reaction chamber  56  has an injection line  53  for injecting a source gas and an exhausting line  54  for exhausting a reaction gas. 
     Referring again to FIGS. 1 and 2, a value of a variable “N” is allocated to a first register in a controller of the ashing apparatus  50  and is initialized to “0”. Simultaneously, a value “K” allocated to a second register is adjusted to a desired cycle number (S 14 ). “N” is a variable indicating the number of repeated processes and “K” is a desired total cycle number. 
     The inside of the chamber is adjusted to a pressure lower than atmospheric pressure, e.g., a pressure of 0.5 to 3 Torr by exhausting air from the ashing chamber  56  using a vacuum pump (S 16 ). Next, the semiconductor substrate  60  having a metal interconnection and a photoresist pattern is heated to a desired temperature, e.g., 200 to 270° C. (S 18 ). Then, a power and a frequency of the plasma generator  55  are adjusted to 2000-3000W and 2.45 GHz, respectively. 
     The first step is carried out by injecting a passivating gas into the ashing chamber for a first duration (T 1 ), for example, 5 to 40 seconds (S 20 ). The passivating gas preferably includes water vapor, and the water vapor is preferably injected into the ashing chamber at a flow rate of 2000 to 4000 standard cubic centimeters per minute (sccm). 
     Under the pressure, temperature and plasma conditions as mentioned above, the water vapor reacts with aluminum of the metal layer and chlorine remaining in the polymer and this generates a passivation substance such as AlCl x O y . Because the AlCl x O y  is not a volatile substance, it is not exhausted out of the chamber. However, because AlCl x O y  is a compound that prevents Cl 2  from forming HCl, it inhibits corrosion of the metal interconnection. 
     Next, the second step is performed by injecting a stripping gas into the same chamber for a second duration (T 2 ), for example, 5 to 60 seconds (S 22 ). During the second step, the remaining photoresist pattern and the polymer are removed from the semiconductor substrate. The pressure, temperature and plasma conditions in the chamber are similar to or the same as those used in the first step. The stripping gas preferably includes a mixed gas of oxygen, nitrogen and water vapor. Oxygen, nitrogen and water vapor are injected into the reaction chamber preferably at a flow rate of 5000-10000 sccm, 300-800 sccm and 1-1000 sccm, respectively. Alternatively, the stripping gas may be composed of only oxygen and nitrogen. 
     As mentioned above, process time can be reduced by performing the first (S 20 ) and second (S 22 ) steps in the same chamber, and by uniformly maintaining the pressure, temperature and plasma conditions of the chamber. However, it is possible to adjust the temperature of the first step (S 20 ) lower than that of the second step (S 22 ) so as to prevent hardening of the polymer. 
     After blocking injection of the stripping gas, a value of the variable “N” is increased up to “1” (S 24 ). Subsequently, the value “N” is compared with a value “K”(S 26 ). The first (S 20 ) and second (S 22 ) steps are carried out repeatedly until the value “N” is equal to the value “K”. 
     Considering efficiency and stability in the method for-fabricating a semiconductor device, the value “K” is preferably “3”. That is, it is preferable to carry out a process including the first (S 20 ) and second (S 22 ) steps three times repeatedly. In this case, preferable process conditions are as follows: 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Common process conditions 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Temperature 
                 250° C. 
               
             
          
           
               
                   
                 Pressure 
                 1.3 
                 Torr 
               
               
                   
                 Plasma Generating Power 
                 2600 
                 W 
               
               
                   
                 Plasma Frequency 
                 2.45 
                 GHz 
               
               
                   
                   
               
             
          
         
       
     
     Table 1 shows process conditions common to both the first step (S 20 ) and the second step (S 22 ). As mentioned above, temperature conditions of the first step may be adjusted lower than those of the second step to prevent hardening of polymer. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Process conditions of each step 
               
             
          
           
               
                   
                 Used gas 
                 Process time (second) 
               
             
          
           
               
                   
                 Flow rate (sccm) 
                 1 
                 2 
                 3 
               
               
                   
                   
               
             
          
           
               
                   
                 Final step 
                 H 2 O 
                 20 
                 20 
                 20 
               
               
                   
                   
                 3000 
               
             
          
           
               
                   
                 Second step 
                 O 2   
                 N 2   
                 H 2 O 
                 20 
                 20 
                 60 
               
               
                   
                   
                 7500 
                 400 
                 350 
               
               
                   
                   
               
             
          
         
       
     
     Table 2 shows process gases used during the first and second steps (S 20  and S 22 ) and their flow rates. Table 2 also shows process time of each step while performing the first and second steps three times repeatedly. 
     As mentioned above, according to embodiments of the present invention, the ashing process using water vapor in the first and second steps is carried out at least two times. Consequently, the metal interconnection is protected from damage, and problems caused by the remaining photoresist and polymer are remarkably alleviated. 
     Although various preferred embodiments of the present invention have been disclosed herein for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the invention as provided in the accompanying claims.