Abstract:
Provided is a method of reducing resist residue on a semiconductor substrate surface in a step of performing resist stripping, by introducing ozone gas into a chemical solution. Circulation lines are arranged for a tank ( 12 ) for performing processing on the semiconductor substrate ( 1 ), and two circulation pumps ( 131, 132 ) and two filters ( 141, 142 ) are arranged on those circulation lines. Further, a gas introducing jig ( 34 ) configured to dissolve the ozone gas into the chemical solution is incorporated in those circulation lines.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor-substrate processing apparatus used in photolithography, which is a process of manufacturing a semiconductor device, and mainly in a step of stripping a photoresist that is applied onto a semiconductor substrate surface and a step of removing organic substances adhered onto the semiconductor substrate surface. 
         [0003]    2. Description of the Related Art 
         [0004]    In the manufacturing of a semiconductor device through use of a semiconductor substrate, there has been performed a step of stripping a photoresist applied onto a semiconductor substrate surface off from the substrate surface. There has also been performed processing of immersing the semiconductor substrate into a chemical solution, which is made by heating a mixed liquid of sulfuric acid and a hydrogen peroxide solution up to a temperature of 120 degrees Celsius or more, in order to remove organic substances adhered onto the semiconductor substrate surface, and then performing cleaning using pure water and drying. This is a technology using the fact that substances on the semiconductor substrate surface, e.g., the photoresist are dissolved or stripped by substances having extremely high oxidizability, e.g., peroxydisulfuric acid that is generated through reaction between the sulfuric acid and the hydrogen peroxide solution. 
         [0005]    Further, as an alternative measure, there has been proposed a technology that attains the same effect as that achieved by the mixed liquid formed of the sulfuric acid and the hydrogen peroxide solution. In this technology, there is used a substance having high oxidizability, e.g., peroxydisulfuric acid that is generated through reaction between sulfuric acid and ozone gas. The reaction is caused by injecting the ozone gas into a high-temperature sulfuric acid and then introducing the sulfuric acid and the ozone gas into a processing tank (see, for example, Japanese Patent Application Laid-open H11-174692). 
         [0006]    However, when processing is performed to the semiconductor substrate in the apparatus disclosed in Japanese Patent Application Laid-open H11-174692, a problem arises as described below. In particular, at first, the photoresist film that is stripped is collected by a filter, but a large amount of resist peels off right after the stripping. Therefore, there is a fear in that the filter maybe contaminated by the resist, thereby lowering its collecting performance. This leads to resist that cannot be collected being adhered to the wafer again in form of fine particles. Further, there is a limit on concentration in which ozone can be dissolved in the chemical solution using a permeation membrane. Therefore, there is a problem in that parts of the resist may be difficult to strip depending on the pattern that is transferred onto the semiconductor substrate surface, and that the resist may remain on the substrate surface even when the processing is continued for a long time. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is provided in order to solve the problems described above, and an aim thereof is to prevent a semiconductor substrate surface from being affected by contamination of a filter, while diffusing ozone directly into a processing tank and securing a sufficient concentration of a chemical solution in a semiconductor-substrate processing apparatus. 
         [0008]    According to one embodiment of the present invention, circulation lines are arranged for a tank for performing processing on a semiconductor substrate, and two circulation pumps and two filters are arranged on those circulation lines. Further, a gas introducing jig configured to dissolve ozone gas into a chemical solution is incorporated in those circulation lines. 
         [0009]    Through use of the measures described above, the number of fine particles that remain on the semiconductor substrate surface after the resist stripping processing can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic view of a semiconductor-substrate processing apparatus according to an embodiment of the present invention. 
           [0011]      FIG. 2  is a schematic view of the semiconductor-substrate processing apparatus according to the embodiment of the present invention with a first circulation direction of a chemical solution. 
           [0012]      FIG. 3  is a schematic view of the semiconductor-substrate processing apparatus according to the embodiment of the present invention with a second circulation direction of the chemical solution. 
           [0013]      FIG. 4  is a diagram for showing a comparison of the number of remaining fine particles between a case where processing is performed using the semiconductor-substrate processing apparatus according to the embodiment of the present invention, and a case using the related art. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Now, referring to the drawings, an embodiment of the present invention is described. 
         [0015]      FIG. 1  is a schematic view of a semiconductor-substrate processing apparatus according to an embodiment of the present invention. 
         [0016]    A processing tank  12  which is used to hold chemical solutions for processing includes a heater  40 , an ozone gas diffusing jig  31 , and a duckboard-shaped jig  15 . A wafer-holding jig  16  configured to accommodate a semiconductor substrate  1  may be placed on the duckboard-shaped jig  15  to perform chemical solution processing. A chemical solution injecting device  10  configured to perform injection of the chemical solution is connected to the processing tank  12  via a chemical solution injecting valve  111  and a pipe. A plurality of semiconductor devices  2  are arranged in a matrix in place on a surface of the semiconductor substrate  1 . 
         [0017]    Further, a plurality of pipes for the circulation of the chemical solution is connected to the processing tank  12 . The chemical solution overflows from an upper portion of the processing tank  12 , and passes through a first switching valve  112 , a second switching valve  113 , and a third switching valve  114 , a first filter  141  and a second filter  142 , and a first circulation pump  131  and a second circulation pump  132 , to return into the processing tank  12 . The first circulation pump  131  and the first filter  141  are connected to each other in series, and the second circulation pump  132  and the second filter  142  are also connected to each other in series. Further, the first circulation pump  131  and the first filter  141 , which are connected to each other in series, are connected in parallel to the second circulation pump  132  and the second filter  142 , which are connected to each other in series. 
         [0018]    The first switching valve  112  is arranged between the first circulation pump  131  and the second circulation pump  132 , and the second switching valve is arranged between the first filter  141  and the second filter  142 . Further, an ozone gas generating device  30  configured to inject ozone gas into the processing tank  12  is connected to the processing tank  12  via a first ozone gas injecting valve  321  and a pipe. The ozone gas generating device  30  is also connected to a chemical solution circulating system at a gas introducing jig  34  via a second ozone gas injecting valve  322  and a pipe. The chemical solution injecting valves, the heater, the switching valves, the circulation pumps, the ozone gas injecting valves, and other devices described above are controlled by a control unit  50 . 
         [0019]    Next, referring to  FIG. 1 , processing performed on the semiconductor substrate according to the present invention is described as an example. 
         [0020]    The semiconductor substrate  1  is accommodated in the wafer-holding jig  16 , e.g., a cassette, to thereby be introduced into the processing tank  12 . The duckboard-shaped jig  15  for placing the wafer-holding jig  16  is accommodated in the processing tank  12 . The wafer holding jig  16  is placed on the duckboard-shaped jig  15 , to thereby hold the semiconductor substrate. First, the wafer holding jig  16  is conveyed into the processing tank  12  by a conveying robot (not shown). 
         [0021]    The chemical solution is supplied into the processing tank  12  from the chemical solution injecting device  10  through the opening and closing of the chemical solution injecting valve  111 . Sulfuric acid is mainly used for the chemical solution. The chemical solution is accumulated in the processing tank  12  before the semiconductor substrate  1  is conveyed into the processing tank  12 . The accumulated chemical solution is circulated by the first circulation pump  131 , and the circulating chemical solution is filtered through the first filter  141 . At this time, the opening and closing states of the valves are as follows, that is, the first switching valve  112 : open, the second switching valve  113 : open, the third switching valve  114 : closed. 
         [0022]    The heater  40  configured to heat the chemical solution is arranged inside the processing tank  12 . The heater  40  is configured to heat the chemical solution that is accumulated in the processing tank  12  up to a predetermined temperature. Further, the ozone gas diffusing jig  31  configured to diffuse the ozone gas into the processing tank  12  is mounted to a lower portion of the duckboard-shaped jig  15  in the processing tank  12 . By opening the first ozone gas injecting valve  321 , gas generated in the ozone gas generating device  30  is diffused through the ozone gas diffusing jig  31  into the chemical solution that is accumulated in the processing tank  12 . The entire processing sequence described above is unitarily controlled by the control unit  50 . This control is defined by a so-called recipe, and the control unit is configured to perform control based on instructions set in this recipe. An example of a processing sequence is described below. 
       Step 1 
       [0023]    The sulfuric acid is injected into the processing tank  12  up to a fixed quantity. It is desired that the concentration of the sulfuric acid used at this time have the highest concentration value (96% or more) among sulfuric acid that is available for use in semiconductor. 
       Step 2 
       [0024]    The sulfuric acid that is injected into the processing tank  12  is heated by the heater  40  up to a preset temperature. It is desired that a temperature of the sulfuric acid at this time be 140 degrees Celsius or more. 
       Step 3 
       [0025]    The semiconductor substrate  1  that has the photoresist adhered thereto is immersed into the processing tank  12  filled with the sulfuric acid. 
       Step 4 
       [0026]    The ozone gas is introduced into the processing tank  12  through the ozone gas diffusing jig  31 . It is desired that a flow rate of the ozone gas be from 10 L to 15 L. When gas having a flow rate exceeding that flow rate is introduced, there is a fear in that, due to gas current of the gas in the liquid, the semiconductor substrate  1  may vibrate in the chemical solution, leading to a breakage of the substrate. 
         [0027]    A circulation path of the chemical solution at this time is illustrated in  FIG. 2 . The arrows of  FIG. 2  are for indicating the direction the chemical solution flows. This circulation path is referred to as a first circulation path. At this time, the opening and closing of the valves are set to be as follows: the first switching valve  112  is open; the second switching valve  113  is open; and the third switching valve  114  is closed. 
       Step 5 
       [0028]    The semiconductor substrate  1  is immersed into the processing tank  12  until a preset time. It is desired that immersing time be from about 5 minutes to about 10 minutes. When the immersing time is too short, a large amount of resist remains on the surface. Meanwhile, when the immersing time is too long, productivity is lowered. At this time, the resist is beginning to be stripped in the processing tank  12 . When the processing is continued for about 10 minutes, the color of the chemical solution becomes nearly colorless, and the color of the filter changes into dark brown due to stripped pieces of the resist. 
       Step 6 
       [0029]    When the preset time has come, the setting of the valves is changed as follows: the first switching valve  112  is closed; the second switching valve  113  is closed; and the third switching valve  114  is open. Then, the circulation path of the chemical solution is changed as illustrated in  FIG. 3 . The chemical solution from the processing tank  12  passes through the second filter  142 , which is not contaminated by the resist, and then circulates to the processing tank  12 . Therefore, there is hardly any contamination of the semiconductor substrate  1  due to the resist. This path is referred to as a second circulation path. At this point of time, the remaining resist is diminished to an admissible level of amount, and thus there is no fear of the filter being contaminated by the resist. 
         [0030]    Further, the fine particles of the resist that are collected by the first filter  141  are also dissolved into a reaction solution formed of the sulfuric acid and the ozone. Here, the path that the chemical solution circulates to the first filter  141  is referred to as a third circulation path. It is desired that the processing time be from about 0 minutes to about 5 minutes. The second ozone gas injecting valve  322  is opened at the same time as the opening and closing of the switching valves  112 ,  113 , and  114  are changed. As a result, the ozone gas is interfused with the chemical solution through the gas introducing jig  34 . At this time, it is desired that the flow rate of the ozone gas be from about 1 L to about 5 L. Then, through use of the chemical solution in which the sulfuric acid and the ozone gas are reacted, circulation cleaning is performed on the first filter  141  on which the resist is adhered. Therefore, the first filter  141  is able to be in a clean state at the initiation of the next batch processing. 
       Step 7 
       [0031]    When the preset time is over, the semiconductor substrate  1  is placed out of the processing tank  12  into a pure water tank filled with pure water, and the chemical solution components that are remaining on the surface of the semiconductor substrate  1  are removed. At this time, the settings of the valves are switched to have the following states: the first switching valve  112  is open; the second switching valve  113  is open; and the third switching valve  114  is closed. The supply of the ozone gas is to be stopped at this point of time, and therefore the second ozone gas injecting valve  322  is closed. 
       Step 8 
       [0032]    The semiconductor substrate  1  is moved out of the pure water tank and is placed into a drying device to be dried therein. 
         [0033]    The example of the sequence ends with this step. 
         [0034]    As described above, in general, one processing cycle is as follows. The chemical solution having the ozone gas introduced therein is circulated through a first circulation line that passes through the first circulation pump  131  and the first filter  141 . Then, when the resist is dissolved in the processing tank  12  through resist stripping, there is performed circulation in which the chemical solution having the ozone gas introduced therein is circulated through a second circulation line that passes through the second circulation pump  132  and the second filter  142 , to thereby be returned into the processing tank  12 . At the same time, the ozone gas is introduced into a third circulation line that passes through the first circulation pump  131 , the first filter  141 , and the gas introducing jig  34 , to clean the first filter  141 . 
         [0035]      FIG. 4  is a diagram for showing the number of remaining fine particles when processing is performed using the semiconductor-substrate processing apparatus according to the present invention. The number of fine particles remaining on the semiconductor substrate surface after the processing is compared between a case where the related art is used and a case where the present invention is used. According to this diafram, it is apparent that the number of fine particles remaining on the semiconductor substrate surface decreases through use of the present invention.