Abstract:
A method of cleaning a substrate is provided which can remove contamination after working a surface of a substrate by use of chemicals etc. or treat the surface of a substrate by use of the chemicals, etc. prior to film formation. The method of cleaning the substrate can clean the surface of the substrate  30  by use of a vapor of chlorosulfonic acid (SO 2 Cl(OH)).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of cleaning a substrate and a method of manufacturing a semiconductor device and, more particularly, a method of cleaning a substrate and a method of manufacturing a semiconductor device removing contaminants after working a surface of a substrate by chemicals etc. or treating the surface of the substrate by the chemicals, etc. prior to film formation.  
           [0003]    2. Description of the Prior Art  
           [0004]    In recent years, mainly a mixed solution consisting of sulfuric acid, hydrochloric acid, ammonium, hydrogen peroxide, etc. has been employed to clean the silicon wafer in the prior art. Since these are effective to remove metals and organic matters, this cleaning method is effective.  
           [0005]    A cleaning method used in various steps to manufacture semiconductors in the prior art will be explained hereunder.  
           [0006]    First, FIGS. 1A and 1B are sectional views showing steps of cleaning a surface of a semiconductor substrate  1  after trench grooves  3  have been formed on the semiconductor substrate  1 .  
           [0007]    At first, as shown in FIG. 1A, the trench grooves  3  are formed on the semiconductor substrate  1  using a resist film  2  as a mask. Then, the resist film  2  is removed by resist removing liquid and, as shown in FIG. 1B, the semiconductor substrate  1  on which the trench grooves  3  are formed is exposed to a liquid such as the sulfuric acid to remove contaminants such as the resist removing liquid.  
           [0008]    Second, FIGS. 2A to  2 C are sectional views showing steps of forming a wiring  13  and then covering the wiring  13  with an insulating film  15 .  
           [0009]    At first, as shown in FIG. 2A, wirings  13  are formed on an underlying insulating film  12  formed on a semiconductor substrate  11  by patterning using the resist film  14  as a mask. Then, as shown in FIG. 2B, the resist film  14  is removed by the resist removing liquid. Then, as shown in FIG. 2C, an insulating film  15  is formed by the CVD method to cover the wirings  13  formed on the underlying insulating film  12 .  
           [0010]    Third, FIGS. 3A and 3B are sectional views showing steps of forming a silicon containing insulating film  23  on an underlying insulating film  22 .  
           [0011]    At first, as shown in FIG. 3A, a surface of the underlying insulating film  22  on a semiconductor substrate  21  is cleaned by a liquid of the sulfuric acid, etc. Then, as shown in FIG. 3B, a silicon containing insulating film  23  is deposited on the underlying insulating film  22  by the thermal CVD method with using a reaction gas including TEOS (for exanple, N 2  is employed as the carrier gas) and ozone (which is included in O 2  at a predetermined concentration).  
           [0012]    In the meanwhile, in the case of FIG. 1, in recent years, with the progress of miniaturized working of the semiconductor, an opening portion has become narrower and thus a ratio of a depth to an opening portion of the trench groove  3  (this ratio is called an aspect ratio) has become higher. Such aspect ratio, if being highest, comes up to five to eight. In the case of the groove which has a narrow opening width but a deep depth, according to the chemicals process shown in FIG. 1B, the chemicals has been difficult to enter into a bottom of the trench groove  3  completely and then the chemicals has become difficult to be replaced next with a pure water, etc. once the chemicals has entered into such groove. In the end, such a problem has existed that it becomes extremely hard to clean the bottom or the side surface of the trench groove  3  completely.  
           [0013]    In the case of FIG. 2, when the insulating film  15  is formed by the CVD method to cover the wirings  13  after surface treatment, the insulating film  15  is difficult to be deposited on the portions. As a result, as shown in FIG. 2B, sometimes deep hollows have been produced in the middle portions between the concave portions between the wirings  13 . If a conductive film used as the wirings is formed on such insulating film  15 , such a problem has arisen that the conductive film cannot be deposited satisfactorily on such concave portions or the conductive film entering into the concave portions cannot be removed. If the chemicals such as EKC (made by the EKC Company, product name) as the particular example is employed as the resist removing liquid, the growth rate of the SiO 2  film  15  is extremely slow on the concave portion when the film is formed by the CVD method after the pre-treatment prior to film formation has been carried out, so that the concave portions cannot be buried evenly. The reason for this event may be supposed, though not clearly analyzed, such that perhaps the EKC cannot be removed from the surface of the underlying insulating film  12  and thus left thereon, which has a vicious influence upon the growth rate of the SiO 2  film  15 .  
           [0014]    In the case of FIG. 3, there has been such a problem that, when the film is formed on the insulating film  22 , for example, the silicon thermal oxide film formed on the semiconductor substrate  21  made of semiconductor by the thermal CVD method using the reaction gas including TEOS, the film forming rate becomes extremely slow on the insulating film  22  rather than the case where the film is formed directly on the silicon substrate.  
           [0015]    As a diameter of the wafer is enlarged from 200 mm to 300 mm, consumption of the chemicals is increased more and more. As a consequence, not only the cost is brought up but also drainage process takes extremely much time, which will create problems for the environmental protection.  
         SUMMARY OF THE INVENTION  
         [0016]    It is an object of the present invention to provide a substrate cleaning method capable of cleaning insides of grooves each having a narrow opening width and a deep depth clearly while reducing consumption of chemicals, and removing contaminants such as a resist removing liquid clearly, and forming a film on an insulating film while keeping a film forming rate.  
           [0017]    In the present invention, a surface of a substrate is cleaned by use of either a vapor including at least any one of a vapor of sulfuric acid, a vapor of hydrochloric acid, and a vapor of nitric acid or a vapor of chlorosulfonic acid (SO 2 Cl(OH)).  
           [0018]    Since the vapor of the chemicals is employed, consumption of the chemicals can be extremely reduced rather than the case where a liquid is employed.  
           [0019]    In addition, since the vapor of the chemicals is employed, the chemicals can be supplied as moleculars so that it can enter into the groove which has a narrow opening width and a deep depth. Accordingly, bottoms and side walls of trench grooves each having the opening width of less than 0.3 μm and the deep depth can be cleaned clearly.  
           [0020]    Further, according to the experiment, contaminants which is hard to remove, for example, the resist removing liquid on the insulating film have been able to be removed clearly by using the liquid or vapor of the chlorosulfonic acid.  
           [0021]    Furthermore, according to the experiment, when the insulating film is formed on the underlying insulating film by the thermal CVD method, the substantially same growth rate as the case where the film is formed directly on the semiconductor substrate, especially the silicon substrate has been able to be maintained by using the liquid or vapor of the chlorosulfonic acid. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIGS. 1A and 1B are sectional views showing steps of a substrate cleaning method according to a first example in the prior art respectively;  
         [0023]    [0023]FIGS. 2A to  2 C are sectional views showing steps of a substrate cleaning method according to a second example in the prior art respectively;  
         [0024]    [0024]FIGS. 3A and 3B are sectional views showing steps of a substrate cleaning method according to a third example in the prior art respectively;  
         [0025]    [0025]FIGS. 4A to  4 D are sectional views showing steps of a substrate cleaning method according to a first embodiment of the present invention respectively;  
         [0026]    [0026]FIGS. 5A to  5 C are sectional views showing steps of a substrate cleaning method according to a second embodiment of the present invention respectively;  
         [0027]    [0027]FIGS. 6A to  6 D are sectional views showing steps of a substrate cleaning method according to a third embodiment of the present invention respectively; and  
         [0028]    [0028]FIG. 7 is a side view showing a cleaning chemicals vapor supplying equipment and a substrate processing equipment according to the present invention respectively.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Embodiments of the present invention will be explained with reference to the accompanying drawings hereinbelow.  
         [0030]    (1) First Embodiment  
         [0031]    [0031]FIGS. 4A to  4 D are sectional views showing steps of a substrate cleaning method according to a first embodiment of the present invention respectively. For samples processed by four types of the chemicals or liquids of the chemicals and unprocessed samples, growth rates of insulating films on an underlying insulating film are compared to each other.  
         [0032]    First, as shown in FIG. 4A, a p-type silicon substrate (semiconductor substrate)  31  having a resistivity of 5 Ωcm is prepared.  
         [0033]    Then, as shown in FIG. 4B, the silicon substrate  31  is thermally oxidized at a temperature of 1100° C. in oxygen atmosphere to form a silicon oxide film (underlying insulating film)  32  of about 100 nm thickness on a surface of the silicon substrate  31 . With the above, a substrate  30  can be formed.  
         [0034]    Then, as shown in FIG. 4C, the substrate  30  is cleaned by using cleaning chemicals or vapor of the chemicals. In the experiments, four types of the chemicals or vapors of the chemicals described in the following have been employed.  
         [0035]    More particularly, a first sample has been prepared as follows. In other words, as shown in FIG. 7, a liquid  102  of chlorosulfonic acid (SO 2 Cl(OH)) has been filled in a flask  101  and then a liquid temperature has been held at a room temperature without heating. A nitrogen (N 2 ) gas as a carrier gas has been passed through the liquid  102  of the chiorosulfonic acid (SO 2 Cl (OH)) via a pipe  103  and then introduced via a pipe  105  into a chamber  106  into which the substrate  30  has been loaded. Then, the nitrogen gas including the chiorosulfonic acid has been sprayed onto a surface of the substrate  30  for thirty minutes. A temperature of the liquid  102  of chlorosulfonic acid (SO 2 Cl(OH)), as the case may be, may be increased by heating by means of a heater  104 .  
         [0036]    Then, a second sample has been prepared by supplying vapor of sulfuric acid directly from a sulfuric acid bomb and then spraying it onto a surface of the to-be-processed substrate  30  for thirty minutes.  
         [0037]    Then, third and fourth samples have been prepared as follows. The liquid of the chlorosulfonic acid of 30 cc has been filled in two beakers. The liquid temperature in one beaker is held at a room temperature, while the other beaker has been heated to hold the liquid temperature at 58° C. Then, the substrates  30  have been immersed in respective chemicals for thirty minutes.  
         [0038]    For the sake of comparison, a fifth sample which is not treated by the cleaning chemicals or vapor of the chemicals has also been prepared.  
         [0039]    In all cases, the substrates  30  have been cleaned by the flowing pure water after the process has been completed and in turn dried by blowing the nitrogen gas respectively.  
         [0040]    Next, under the conditions set forth in the following, as shown in FIG. 4D, another silicon oxide film (insulating film)  33  has been formed on the silicon oxide film  32  formed by thermal oxidation by virtue of the thermal CVD method using the following reaction gas given in a Table 1.  
                       TABLE 1                                   Reaction gas condition:                           TEOS: 1 sccm           O 3  in O 2 : 120 g (mass of O 3  in 1 m 3  of O 3  + O 2 ),           Flow rate of O 3  + O 2 : 7.5 sccm           Flow rate of N 2  (carrier gas): 18 sccm           Film forming temperature: 450° C.                      
 
         [0041]    The results are given in a Table 2. In Table 2, a notation “growth rate” signifies a growth rate of the silicon oxide film  33 , and a notation “ratio to Si” signifies a ratio of the growth rate of respective samples to the growth rate obtained when the film is formed directly on the silicon substrate, shown in percentages.  
                                                     TABLE 2                       Processing   Temp.   Process   Growth rate   Ratio to       Chemicals   (° C.)   Time (min.)   (Å/min.)   Si (%)                                chlorosulfonic acid   room   30   470   104       vapor   temp.       hydrochloric acid   room   30   398   87       vapor   temp.       chlorosulfonic acid   room   30   491   103       liquid   temp.       chlorosulfonic acid   58   30   493   104       liquid       none   —   —   355   75                  
 
         [0042]    According to the results shown in Table 2, if surface treatment has been made by both the liquid or vapor of the chlorosulfonic acid, the growth rate has been equal to or higher than the growth rate obtained when the film is formed directly on the silicon substrate.  
         [0043]    As a result, the growth rate on the surface of the insulating film can be improved and therefore a throughput can also be improved.  
         [0044]    In addition, consumption of the chemicals a large amount of which is needed as the liquid can be reduced significantly by employing the vapor of the chemicals.  
         [0045]    In the above first embodiment, either the vapor or liquid of the chlorosulfonic acid or the vapor of the hydrochloric acid has been employed as the cleaning chemicals. However, in addition to only the vapor of sulfuric acid, only the vapor of nitric acid, or the mixed vapor of the vapor of sulfuric acid and the vapor of nitric acid, such vapor including at least any one of the vapor of sulfuric acid, the vapor of hydrochloric acid, and the vapor of nitric acid may be employed.  
         [0046]    (2) Second Embodiment  
         [0047]    [0047]FIGS. 5A to  5 C are sectional views showing steps of a substrate cleaning method according to a second embodiment of the present invention respectively.  
         [0048]    First, as shown in FIG. 5A, a resist film  42  is formed on a silicon substrate (semiconductor substrate)  41  and then opening portions  43  are formed in the resist film  42 .  
         [0049]    Then, the silicon substrate  41  is etched via the opening portions  43  by the dry etching using chlorine (Cl 2 ) to form grooves  44  each having a diameter of about 0.25 μm and a depth of 1.5 μm.  
         [0050]    Next, as shown in FIG. 5B, the resultant structure is immersed in the EKC as the resist removing liquid to remove the resist. With the above steps, a substrate  40  can be prepared. At this time, the EKC liquid would remain in the grooves  44 .  
         [0051]    Then, as shown in FIG. 7, the liquid  102  of the chlorosulfonic acid (SO 2 Cl(OH)) has been filled in the flask  101  and then the liquid temperature has been held at a room temperature or the liquid temperature has been increased by being heated by the heater  104 . The nitrogen gas as the carrier gas has been passed through the liquid  102  of chlorosulfonic acid (SO 2 Cl(OH)) to thus form the nitrogen gas including the chlorosulfonic acid. Then, such nitrogen gas has been introduced into the chamber  106  via the pipe  105 . Then, the nitrogen gas including the chlorosulfonic acid has been sprayed onto a surface of the substrate  40  (FIG. 5C) in the chamber  106 .  
         [0052]    At that time, since the molecular chlorosulfonic acid can enter easily into the grooves  44  each having a narrow opening portion and a deep depth, it can react with the EKC attached onto the bottoms and sidewalls of the grooves  44 . Hence, all EKC remaining on the bottoms and sidewalls of the grooves  44  can be removed easily.  
         [0053]    In the above second embodiment, the vapor of the chlorosulfonic acid has been employed as the cleaning chemicals. However, in addition to only the vapor of sulfuric acid, only the vapor of nitric acid, or the mixed vapor of the vapor of sulfuric acid and the vapor of nitric acid, the vapor including at least any one of the vapor of sulfuric acid, the vapor of hydrochloric acid, and the vapor of nitric acid may be employed.  
         [0054]    (3) Third Embodiment  
         [0055]    [0055]FIGS. 6A to  6 D are sectional views showing steps of a substrate cleaning method according to a third embodiment of the present invention respectively.  
         [0056]    [0056]FIG. 6A is a sectional view showing a structure before wirings are formed on the substrate. In FIG. 6A, a reference  51  denotes a silicon substrate (semiconductor substrate);  52 , a silicon oxide film (underlying insulating film) formed by thermal oxidation;  53 , a conductive film made of aluminum which is formed on the silicon oxide film  52  to have a thickness of 800 nm; and  54 , a resist film formed on the conductive film to remain on wiring forming regions.  
         [0057]    First, as shown in FIG. 6B, the conductive film  53  is etched by using the resist film  54  as a mask to form a plurality of wirings  53   a  each having a width of 0.5 μm at a distance 1 μm between adjacent wirings  53   a.    
         [0058]    Then, as shown in FIG. 6C, a surface of the substrate  50  is cleaned by the vapor of the cleaning chemicals. In other words, as shown in FIG. 7, the liquid  102  of the chlorosulfonic acid (SO 2 Cl(OH)) has been filled in the flask  101 , and then held at a room temperature or heated by the heater  104 . The nitrogen gas as the carrier gas has been passed through the liquid  102  of chlorosulfonic acid (SO 2 Cl(OH)) to thus form the nitrogen gas including the chlorosulfonic acid. Then, the nitrogen gas including the chlorosulfonic acid has been sprayed onto a surface of the substrate  50  for two minutes.  
         [0059]    For the sake of comparison, a sample which is not treated by the cleaning. chemicals or the vapor of the chemicals has also been prepared.  
         [0060]    In all cases, the substrates  50  have been has been cleaned by the flowing pure water after the process and then dried by blowing the nitrogen gas.  
         [0061]    Next, under the conditions set forth in the following, as shown in FIG. 6D, according to thermal oxidation by virtue of the thermal CVD method using the following reaction gas given in a Table 3, another silicon oxide film (insulating film)  55  has been formed to cover the wirings  53   a .  
                       TABLE 3                                   Reaction gas condition:                           TEOS: 1 sccm           O 3  in O 2 : 120 g (mass of O 3  in 1 m 3  of O 3  + O 2 ),           Flow rate of O 3  + O 2 : 7.5 sccm           Flow rate of N 2  (carrier gas): 18 sccm           Film forming temperature: 450° C.                      
 
         [0062]    Sectional shapes of the insulating films obtained as above to cover the wirings have been compared to each other with reference to FIGS. 6D and 2C. FIG. 6D is a sectional view showing the sample which has been formed and cleaned by the cleaning method according to the present invention, and FIG. 2C is a sectional view showing the sample which has been formed without treatment.  
         [0063]    According to the results, in the case where surface treatment has been carried out by the vapor of chlorosulfonic acid as shown in FIG. 6D, hollows of the concave portions between the wirings  53   a  have been able to be made shallower in the sectional shape of the insulating film  55  to cover the wirings than the case where no treatment has been applied as shown in FIG. 2C.  
         [0064]    Consequently, the conductive film serving as the upper wirings can be formed normally on the hollow portions on the surface of the insulating film  55 . Also, since the depths of the hollow portions are shallow, the conductive film on the bottoms of the hollow portions can be removed clearly at the time when the conductive film once formed is to be patterned by etching.  
         [0065]    In the above third embodiment, the vapor of chlorosulfonic acid has been employed as the cleaning chemicals. However, in addition to only the liquid of chlorosulfonic acid, only the vapor of sulfuric acid, only the vapor of nitric acid, or the mixed vapor of the vapor of sulfuric acid and the vapor of nitric acid, the vapor including at least any one of the vapor of sulfuric acid, the vapor of hydrochloric acid, and the vapor of nitric acid may be employed.  
         [0066]    The silicon substrate has been employed as the semiconductor substrates  31 ,  41 ,  51  in the above first to third embodiments, but these substrates are not limited to the silicon substrate.  
         [0067]    In addition, the silicon oxide film formed by the thermal oxidation has been employed as the underlying insulating films  32 ,  52 , but these underlying insulating films are not limited to the thermal silicon oxide film. SiO 2  film, PSG film, BSG film, BPSG film, and others formed by thermal CVD method, and other CVD method may be employed.  
         [0068]    The silicon oxide film has been employed as the insulating films  33 ,  55 , but these insulating films are not limited to the silicon oxide film. Moreover, the thermal CVD method using TEOS/O 3  has been employed as the method of forming the insulating films  33 ,  55 , but the thermal CVD method using other reaction gas or other CVD method may be employed. For instance, the low pressure OVD method (LPCVD method) using an SiH 4 —N 2 O reaction gas, the LPCVD method using a TEOS-O 2  reaction gas, the plasma-CVD method using the TEOS-O 2  reaction gas, or the plasma CVD method using an SiH 4 —O 2  reaction gas may be applied. Hence, the SiO 2  film, the PSG film, the BSG film, the BPSG film, or the like formed by these CVD methods may be employed.  
         [0069]    As discussed above, in the present invention, the surface of the substrate is exposed to either the vapor including at least any one of the vapor of sulfuric acid, the vapor of hydrochloric acid, and the vapor of nitric acid or the vapor of chlorosulfonic acid (SO 2 Cl(OH)).  
         [0070]    Since the vapor is employed, molecular chemicals are ready to enter into the insides of the grooves each having the narrow width and the deep depth, so that they can achieve a noticeable effect of removing the contaminants.  
         [0071]    Since the vapor is employed, consumption of the chemicals, a large quantity of which is needed as the liquid, can be extremely reduced.  
         [0072]    Since the surface of the insulating film is treated by the liquid or vapor of the chlorosulfonic acid (SO 2 Cl(OH)) prior to film formation, the growth rate on the surface of the insulating film can be improved and also a throughput can be improved.  
         [0073]    Since the surface of the substrate is treated by the liquid or vapor of the chlorosulfonic acid (SO 2 Cl(OH)) before the insulating film to cover the wirings is formed, contaminants on the underlying insulating film can be removed, otherwise the growth rate of the insulating film to the surface of the underlying insulating film can be put close to the growth rate of the insulating film to the surface of the silicon substrate.  
         [0074]    As a result, since the growth rate of the insulating film to the underlying insulating film in the concave portions between the wirings can be improved and thus hollows of the insulating film on the concave portions can be reduced as small as possible, the upper wirings can be formed regularly on the insulating film.