Abstract:
A method for forming an interlayer insulating film is disclosed. This method comprises the steps of: forming an Si—C film or an Si—C—H film on an underlying insulating film by performing plasma polymerization for an Si and C containing compound; forming a porous SiO 2  film by performing O (oxygen) plasma oxidation for the Si—C film or the Si—C—H film; and forming a cover insulating film on the porous SiO 2  film by performing H (hydrogen) plasma treatment for the porous SiO 2  film.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for forming an interlayer insulating film and, more particularly, to a method for forming an interlayer insulating film having a low dielectric constant, which is necessary for a highly-integrated semiconductor device. A progress in high integration regarding the semiconductor device in recent years has resulted in a narrower interval between wiring lines. As the narrowed interval between the wiring lines causes an increase in capacitance between the wiring lines, a request has been made for formation of an interlayer insulating film, which has a low dielectric constant. 
     With recent progresses in high integration of an LSI device, the wiring line has been micronized and multilayered. There has also been an increase in capacitance between the wiring lines. Such an increase in capacitance has caused a great reduction in an operating speed. Thus, improvement in this regard has been strongly demanded. As one of improvement measures, a method for reducing capacitance between the wiring lines has been studied. This method uses an interlayer insulating film, which has a dielectric constant lower than that of SiO 2  currently used for an interlayer insulating film. 
     Typical interlayer insulating films of low dielectric constants currently under study are {circle around (1)} an SiOF film, and {circle around (2)} an organic insulating film of a low dielectric constant. Description will now be made of these films. 
     {circle around (1)} SiOF Film 
     An SiOF film is formed by using source gas containing F and substituting Si—F bond for a portion of Si—O bond in SiO 2 . This SiOF film has a relative dielectric constant, which is monotonically reduced as concentration of F in the film increases. 
     For forming such SiOF films, several methods have been reported (see p.82 of monthly periodical “Semiconductor World”, February issue of 1996). Most promising among these methods is one for forming an SiOF film by using SiH 4 , O 2 , Ar and SiF 4  as source gases, and by a high-density plasma enhanced CVD method (HDPCVD method). A relative dielectric constant of an SiOF film formed by this method is in a range of 3.1 to 4.0 (varies depending on F concentration in the film). This value is lower than a relative dielectric constant 4.0 of SiO 2 , which has conventionally been used for the interlayer insulating film. 
     {circle around (2)} Organic Insulating Film of Low Dielectric Constant 
     As an insulating film which has a lower dielectric constant (3.0 or lower) compared with the SiOF film, an organic insulating film of a low dielectric constant is now a focus of attention. Table 1 shows a few organic insulating films of low dielectric constants, which have been reported, and respective relative dielectric constants and thermal decomposition temperatures thereof. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Thermal 
                   
               
               
                 Organic 
                 Relative 
                 Decomposition 
               
               
                 Insulating 
                 Dielectric 
                 Temperature 
               
               
                 Film 
                 Constant 
                 (° C.) 
                 Note 
               
               
                   
               
             
             
               
                 Fluorine- 
                 2.4 
                 420 
                 p. 82 of monthly periodical 
               
               
                 containing 
                   
                   
                 “Semiconductor World”, 
               
               
                 resin 
                   
                   
                 February issue of 1997 
               
               
                 Cytop 
                 2.1 
                 400 
                 p. 90 of monthly periodical 
               
               
                   
                   
                   
                 “Semiconductor World”, 
               
               
                   
                   
                   
                 February issue of 1996 
               
               
                 Amorphous 
                 1.9 
                 400 
                 p. 91 of monthly periodical 
               
               
                 telon 
                   
                   
                 “Semiconductor World”, 
               
               
                   
                   
                   
                 February issue of 1996 
               
               
                   
               
             
          
         
       
     
     However, the SiOF film is disadvantageous in that an increase in concentration of F in the film leads to a reduction in moisture absorption resistance. The reduced moisture absorption resistance poses a serious problem, because a transistor characteristic and adhesion of an upper barrier metal layer are affected. 
     Peeling-off easily occurs in the organic insulating film of a low dielectric constant, because of bad adhesion with a silicon wafer or the SiO 2  film. Furthermore, the organic insulating film is disadvantageous in that heat resistivity is low since a thermal decomposition temperature is around 400° C. The disadvantage of low heat resistivity poses a problem for annealing a wafer at a high temperature. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for forming an interlayer insulating film of a low dielectric constant, which has good moisture absorption resistance and heat resistivity. It is another object of the invention to provide a semiconductor device, which employs the above method. 
     Description will now be made of an interlayer insulating film of the present invention by referring to Table 2. 
     
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Porous Film 
                 Source Gas 
                 Film by Plasma Polymerization 
               
               
                   
               
             
             
               
                 SiO 2  film 
                 TEOS 
                 Si—C film 
               
               
                   
                   
                 Si—C—H film 
               
               
                   
                 TEOS + O 2   
                 Si—C—O film 
               
               
                   
                   
                 Si—C—O—H film 
               
               
                   
                 TEOS + H 2 O 
                 Si—C—O—H film 
               
               
                 B-containing 
                 TEOS + B 2 H 6   
                 Si—C—B film 
               
               
                 SiO 2  film 
                   
                 Si—C—B—H film 
               
               
                   
                 TEOS + B 2 H 6  + O 2   
                 Si—C—B—O film 
               
               
                   
                   
                 Si—C—B—O—H film 
               
               
                   
                 TEOS + B 2 H 6  + H 2 O 
                 Si—C—B—O—H film 
               
               
                 F-containing 
                 TEOS + C 2 F 6   
                 Si—C—F film 
               
               
                 SiO 2  film 
                   
                 Si—C—F—H film 
               
               
                   
                 TEOS + C 2 F 6  + O 2   
                 Si—C—F—O film 
               
               
                   
                   
                 Si—C—F—O—H film 
               
               
                   
                 TEOS + C 2 F 6  + H 2 O 
                 Si—C—F—O—H film 
               
               
                   
               
             
          
         
       
     
     For formation of a porous SiO 2  film of the present invention, TEOS, TEOS+O 2  or TEOS+H 2 O is used as source gas. By performing plasma polymerization for such source gas, an Si—C film, an Si—C—H film, an Si—C—O film or an Si—C—O—H film is formed on a formed body. Then, by performing O (oxygen) plasma treatment for these films, C or H is oxidized in the film. C or H is oxidized in the film, and voids are formed in portions from which C or H has been discharged. Accordingly, a porous SiO 2  film is formed. A porous SiO 2  film can also be formed by using methylsilane (Si(CH 3 )H 3 ), instead of TEOS. 
     For formation of a porous B(boron)-containing SiO 2  film of the present invention, TEOS+B 2 H 6 , TEOS+B 2 H 6 +O 2  or TEOS+B 2 H 6 +H 2 O is used as source gas. By performing plasma polymerization for such source gas, an Si—C—B film, an Si—C—B—H film, an Si—C—B—O film or an Si—C—B—O—H film is formed on a formed body. Then, by performing O (oxygen) plasma treatment for these films, C or H is oxidized in the film. C or H is oxidized in the film, and voids are formed in portions from which C or H has been discharged. Accordingly, a porous B-containing SiO 2  film is formed. A porous B-containing SiO 2  film can also be formed by using methylsilane (Si(CH 3 )H 3 ) or trimethyl-siliruborate ({(CH 3 ) 3 SiO} 3 B), instead of TEOS in source gas. Instead of B 2 H 6  in source gas, TMB(B(OCH 3 )) or TEB(B(OC 2 H 5 ) 3 ) can be used to form a porous B-containing SiO 2  film. 
     For formation of a porous F-containing SiO 2  film of the present invention, TEOS+C 2 F 6 , TEOS+C 2 F 6 +O 2  or TEOS+C 2 F 6 +H 2 O is used as source gas. By performing plasma polymerization for such source gas, an Si—C—F film, an Si—C—F—H film, an Si—C—F—O film or an Si—C—F—O—H film is formed on an object to be formed. Then, by performing O (oxygen) plasma treatment for there films, C or H is oxidized in the film. C or H is oxidized in the film, voids are formed in portions from which C or H has been discharged. Accordingly, a porous F-containing SiO 2  film is formed. A porous F-containing SiO 2  film can also be formed by using methylsilane (Si(CH 3 )H 3 ), instead of TEOS. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A to  1 H are cross-sectional views respectively showing methods for forming interlayer insulating films according to 1st, 3rd, 5th, 7th, 9th, 11th and 13th embodiments of the preset invention; and 
     FIGS. 2A to  2 M are cross-sectional view respectively showing methods for forming interlayer insulating films according to 2nd, 4th, 6th, 8th, 10th, 12th and 14th embodiments of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Next, description will be made of the preferred embodiments of the present invention with reference to the accompanying drawings. 
     First Embodiment 
     FIGS. 1A to  1 H are cross-sectional views illustrating a first embodiment of the present invention. 
     First, as shown in FIG. 1A, a BPSG (borophosphosilicate glass) film  102  is formed on a silicon substrate  101 . Then, after an aluminum film is formed on the BPSG film  102 , an aluminum wiring layer  103  is formed by patterning the aluminum film. The silicon substrate  101 , the BPSG film  102  and the aluminum wiring layer  103  formed in this manner constitute an object  104  to be formed. 
     Then, as shown in FIG. 1B, an SiO 2  film  105  (underlying insulating film) is formed on the object  104  to be formed. This SiO 2  film  105  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. A film thickness of this SiO 2  film  105  is 100 nm. This SiO 2  film  105  can prevent H 2 O from being dispersed in the aluminum wiring layer  103 , which may cause corrosion. 
     Subsequently, as shown in FIG. 1C, a carbon or carbon and hydrogen containing (referred to as Si—C (—H), hereinafter) film  106  is formed on the SiO 2  film  105  (underlying insulating film). This Si—C (—H) film  106  is formed by using 50 sccm TEOS (Tetra-Ethyl-Ortho-Silicate) as source gas, applying an RF power having a frequency of 13.56 MHz and a power of 100 W while keeping the silicon substrate  101  at 100° C., and performing plasma polymerization for TEOS at pressure of 1 Torr. A film thickness of this Si—C (—H) film  106  is 500 nm. It should be noted that, in forming the Si—C (—H) film  106 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 50 sccm and other process conditions are the same as in the case using the TEOS. Using the trimethysililbotrate, the Si—C (—H) film  106  further contains B (boron). 
     Then, as shown in FIG. 1D, O (oxygen) plasma treatment is performed for the Si—C (—H) film  106 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  101  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C (—H) film  106  is oxidized, and discharged to the outside of the film. Voids are formed in portions from which C or H has been discharged, and Si—O bond is formed in the portions. Thus, the Si—C (—H) film  106  becomes a porous SiO 2  film  107 . 
     Subsequently, as shown in FIG. 1E, H (hydrogen) plasma treatment is performed for the porous SiO 2  film  107 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 1F, an SiO 2  film  108  is formed on the porous SiO 2  film  107 . This SiO 2  film  108  is formed by a CVD method, which contains TEOS and O 3  as source gases. O 3  contained as source gas has concentration enough for oxidation of TEOS. Accordingly, the SiO 2  film  108  shows flowability, and can be planarized to a considerable extent. 
     Then, as shown in FIG. 1G, the SiO 2  film  108  is polished by a CMP method (chemical mechanical polishing method) to planarize its surface. At this time, some portions of the previously formed SiO 2  films  105  and  107  are eliminated by polishing. The planarization by the CMP method should be carried out to prevent complete elimination of the SiO 2  film  105  formed on a convexity  103   a  of the aluminum wiring layer. 
     Subsequently, as shown in FIG. 1H, an SiO 2  film  109  (cover insulating layer) is formed on the planarized surface. This SiO 2  film  109  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. A film thickness of this SiO 2  film  109  is 100 nm. 
     The foregoing process of forming the SiO 2  film  105  (underlying insulating film),  107  and  109  (cover insulating film) results in formation, on the object  104  to be formed, of an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the SiO 2  film  107  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  109  is formed on the porous SiO 2  film  107 , incursion of water into the SiO 2  film  107  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  105 ,  107  and  109  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Second Embodiment 
     A second embodiment is a case of applying the first embodiment to a damascene process. 
     FIGS. 2A to  2 M are cross-sectional views illustrating the second embodiment. 
     First, as shown in FIG. 2A, a BPSG (borophosphosilicate glass) film  202  is formed on a silicon substrate  201 . After an aluminum layer is formed on the BPSG film  202  an aluminum wiring layer  203  is formed by patterning the aluminum layer. It should be noted that the aluminum wiring layer  203  in figures is not patterned for convenience. Then, the silicon substrate  201 , the BPSG film  202  and the aluminum wiring layer  203  constitute an object  204  to be formed. 
     Then, as shown in FIG. 2B, an SiO 2  film  205  (underlying insulating film) having a film thickness of 100 mn is formed on the aluminum wiring layer  203 . This SiO 2  film  205  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. 
     Subsequently, as shown in FIG. 2C, an Si—C (—H) film  206  is formed on the SiO 2  film  205  (underlying insulating film). This Si—C (—H) film  206  is formed by using 50 sccm TEOS (Tetra-Ethyl-Ortho-Silicate) as source gas, applying an RF power having a frequency of 13.56 MHz and a power of 100 W while keeping the silicon substrate  201  at 100° C., and performing plasma polymerization for TEOS at pressure of 1 Torr. A film thickness of the Si—C (—H) film  206  is 500 nm. It should be noted that, in forming the Si—C (—H) film  206 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 50 sccm and other process conditions are the same as in the case using the TEOS. Using the trimethysililbotrate, the Si—C (—H) film  206  further contains B (boron). 
     Then, as shown in FIG. 2D, O (oxygen) plasma treatment is performed for the Si—C (—H) film  206 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  201  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment.. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C (—H) film  206  is then oxidized, and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portions. Accordingly, the Si—C (—H) film  206  becomes a porous SiO 2  film  207 . 
     Subsequently, as shown in FIG. 2E, H (hydrogen) plasma treatment is performed for the porous SiO 2  film  207 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  201  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 2F, a damascene trench  208  is formed by patterning the SiO 2  film  207 . This damascene trench  208  reaches the SiO 2  film  205 , which has been formed below the SiO 2  film  207 . 
     Then, as shown in FIG. 2G, an SiO 2  film  209  (first insulating film) is formed on the SiO 2  film  207  and on the side and bottom portions of the damascene trench  208 . This SiO 2  film  209  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. By the SiO 2  film  209  formed in the side portion of the damascene trench  208 , Cu buried later in the damascene trench  208  can be prevented from being dispersed inside the porous SiO 2  film  207 . 
     Then, as shown in FIG. 2H, anisotropic etching is performed for the SiO 2  film  209  (first insulating film) and the SiO 2  film  205  (underlying insulating film) formed on the bottom portion of the damascene trench  208 . Accordingly, the SiO 2  film  209  is eliminated except for a portion formed on the side portion of the damascene trench  208 . Also, since the SiO 2  film  205  formed below the damascene trench  208  is eliminated, a contact hole that reaches the aluminum wiring layer  203 is formed below the damascene trench  208 . 
     Subsequently, as shown in FIG. 2I, a Cu-plated film  210  is formed in the damascene trench  208  and on the SiO 2  film  207 . The Cu-plated film  210  formed in the damascene trench  208  is used as a Cu wiring line. 
     Then, as shown in FIG. 2J, the Cu-plated film  210  formed on the SiO 2  film  207  is polished by a CMP method to be eliminated. Accordingly, the Cu-plated film remains only in the damascene trench  208 . 
     Subsequently, as shown in FIG. 2K, a barrier metal TiN film  211  is formed above the damascene trench  208 . Accordingly, Cu in the damascene trench  208  can be prevented from being dispersed in an SiO 2  film formed later above the damascene trench  208 . 
     Then, as shown in FIG. 2L, patterning is performed for the TiN film  211  to leave a TiN film  211   a  formed above the damascene trench  208 , and the TiN film  211  formed in the other portions is etched to be eliminated. 
     Subsequently, as shown in FIG. 2M, an SiO 2  film  212  (cover insulating film) is formed on the SiO 2  film  207  and the TiN film  211   a.  This SiO 2  film  212  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. 
     The foregoing process results in formation, on the object  204  to be formed, of an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the SiO 2  film  207  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  212  (cover insulating film) is formed on the porous SiO 2  film  207 , incursion of water into the SiO 2  film  207  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  207  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  207  and  212  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Third Embodiment 
     FIGS. 1A to  1 H are cross-sectional views illustrating a third embodiment. 
     First, as shown in FIG. 1A, a BPSG (borophosphosilicate glass) film  107  is formed on a silicon substrate  101 . Then, after an aluminum film is formed on the BPSG film  102 , patterning is performed for the same to form an aluminum wiring layer  103 . The silicon substrate  101 , the BPSG film  102  and the aluminum wiring layer  103  formed in this manner constitute an object  104  to be formed. 
     Then, as shown in FIG. 1B, an SiO 2  film  105  (underlying insulating film) is formed on the object  104  to be formed. This SiO 2  film  105  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  105  is 100 nm. The SiO 2  film  105  can prevent H 2 O from being dispersed in the aluminum wiring layer  103 , which may cause corrosion. 
     Subsequently, as shown in FIG. 1C, a carbon or a carbon and hydrogen containing (referred to as Si—C (—H), hereinafter) film  106  is formed on the SiO 2  film  105  (underlying insulating film). This Si—C (—H) film  106  is formed by using SiH 4  and H 2 O as source gases, applying an RF power having a frequency of 13.56 MHz and power of 300 W while keeping the silicon substrate  101  at 100° C., and performing plasma polymerization for SiH 4  and H 2 O at pressure of 1 Torr. At this time, flow rates of the source gases are 30 sccm and 60 sccm for SiH 4  and H 2 O respectively. A film thickness of the Si—C (—H) film  106  is 500 nm. 
     It should be noted that in forming Si—C (—H) film  106  the metylsilane (Si(CH 3 )H 3 ) can also be used instead of the SiH 4 . When using the metylsilane (Si(CH 3 )H 3 ) its flow rate is 30 sccn and the power of the RF power is 100 W, and the other process conditions are the same as in the case using the SiH 4 . 
     Then, as shown in FIG. 1D, O (oxygen) plasma treatment is performed for the Si—C (—H) film  106 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  101  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C (—H) film  106  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C (—H) film  106  becomes a porous SiO 2  film  107 . 
     Subsequently, as shown in FIG. 1E, H (hydrogen) plasma treatment is performed for the porous SiO 2  film  107 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 1F, an SiO 2  film  108  is formed on the porous SiO 2  film  107 . This SiO 2  film  108  is formed by a CVD method, which employs source gas containing TEOS and O 3 . In this case, since O 3  in source gas has concentration enough for oxidation of TEOS, the SiO 2  film  108  shows flowability, and can be planarized to a considerable extent. 
     Then, as shown in FIG. 1G, the SiO 2  film  108  is polished by a CMP method (chemical mechanical polishing method) so as to planarize its surface. At this time, some portions of the previously formed SiO 2  films  105  and the SiO 2  film  107  are eliminated by polishing. The planarizing by the CMP method should be carried out not to eliminate the whole SiO 2  film  105  formed on a convexity  103   a  of the aluminum wiring layer. 
     Subsequently, as shown in FIG. 1H, an SiO 2  film  109  (cover insulating film) is formed on the planarized surface. This SiO 2  film  109  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  109  is 100 nm. 
     The foregoing process of forming the SiO 2  films  105  (underlying insulating film),  107  and  109  (cover insulating film) results in formation, on the object  104  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the SiO 2  film  107  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  109  is formed on the porous SiO 2  film  107 , incursion of water into the SiO 2  film  107  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  105 ,  107  and  109  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Fourth Embodiment 
     A fourth embodiment is a case of applying the third embodiment to a damascene process. 
     FIGS. 2A to  2 M are cross-sectional views illustrating the fourth embodiment. 
     First, as shown in FIG. 2A, a BPSG (borophosphosilicate glass) film  202  is formed on a silicon substrate  201 . Then, after an aluminum layer is formed thereon, patterning is performed for the same to form an aluminum wiring layer  203 . It should be noted that the aluminum wiring layer  203  in figures is not patterned for convenience. The silicon substrate  201 , the BPSG film  202  and the aluminum wiring layer  203  constitute an object  204  to be formed. 
     As shown in FIG. 2B, an SiO 2  film  205  (underlying insulating film) having a film thickness of 100 nm is formed on the aluminum wiring layer  203 . This SiO 2  film  205  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. 
     Subsequently, as shown in FIG. 2C, an Si—C (—H) film  206  is formed on the SiO 2  film  205  (underlying insulating film). This Si—C (—H) film  206  is formed by using SiH 4  and H 2 O as source gases, applying an RF power having a frequency of 13.56 MHz and power of 300 W while keeping the silicon substrate  201  at 100° C., and performing plasma polymerization for SiH 4  and H 2 O at pressure of 1 Torr. At this time, flow rates of source gases are 30 sccm and 60 sccm for SiH 4  and H 2 O respectively. A film thickness of the Si—C (—H) film  206  is 500 nm. 
     It should be noted that in forming Si—C (—H) film  206  the metylsilane (Si(CH 3 )H 3 ) can also be used instead of the SiH 4 . When using the metylsilane (Si(CH 3 )H 3 ) its flow rate is 30 sccm and the power of the RF power is 100 W, and the other process conditions are the same as in the case using the SiH 4 . 
     Then, as shown in FIG. 2D, O (oxygen) plasma treatment is performed for the Si—C (—H) film  206 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  201  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C (—H) film  206  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C (—H) film  206  becomes a porous SiO 2  film  207 . 
     Subsequently, as shown in FIG. 2E, H (hydrogen) plasma treatment is performed for the porous SiO 2  film  207 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  201  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 2F, patterning is performed for the porous SiO 2  film  207  to form a damascene trench  208 . This damascene trench  208  reaches the SiO 2  film  205  formed below the SiO 2  film  207 . 
     Then, as shown in FIG. 2G, an SiO 2  film  209  (first insulating film) is formed on the SiO 2  film  207  and on the side and bottom portions of the damascene trench  208 . This SiO 2  film  209  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. By the SiO 2  film  209  formed on the side portion of the damascene trench  208 , Cu buried later in the damascene trench  208  can be prevented from being dispersed in the porous SiO 2  film  207 . 
     Then, as shown in FIG. 2H, anisotropic etching is performed for the SiO 2  film  209  (first insulating film) and the SiO 2  film  205  (underlying insulating film) formed below the damascene trench  208 . Accordingly, the SiO 2  film  209  is eliminated except for a portion formed on the side portion of the damascene trench  208 . The SiO 2  film  205  formed below the damascene trench  208  is also eliminated. Thus, a contact hole that reaches the aluminum wiring layer  203  is formed below the damascene trench  208 . 
     Subsequently, as shown in FIG. 2I, a Cu-plated film  210  is formed in the damascene trench  208  and on the SiO 2  film  207 . The Cu-plated film  210  formed in the damascene trench  208  is used as a Cu wiring line. 
     Then, as shown in FIG. 2J, the Cu-plated film  210  formed on the SiO 2  film  207  is polished by a CMP method to be eliminated. Accordingly, the Cu-plated film remains only in the damascene trench  208 . 
     Subsequently, as shown in FIG. 2K, a barrier metal TiN film  211  is formed above the damascene trench  208 . Accordingly, Cu in the damascene trench  208  can be prevented from being dispersed in an SiO 2  film later formed above the same. 
     Then, as shown in FIG. 2L, patterning is performed to leave a TiN film  211   a  formed above the damascene trench  208 , and the TiN film  211  formed on the other portions is etched to be eliminated. 
     Subsequently, as shown in FIG. 2M, an SiO 2  film  212  (cover insulating film) is formed on the SiO 2  film  207  and the TiN film  211   a.  This SiO 2  film  212  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. 
     The foregoing process results in formation, on the object  204  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the SiO 2  film  207  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  212  (cover insulating film) is formed on the porous SiO 2  film  207 , incursion of water into the SiO 2  film  207  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  207  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  207  and  212  have better heat resistivity compared with the organic insulating film film since these films consist mainly of Si and O. 
     Fifth Embodiment 
     A fifth embodiment is different from the first to fourth embodiments in that a carbon and oxygen containing, or carbon, oxygen and hydrogen containing (referred to as Si—C—O (—H), hereinafter) film is formed by performing plasma polymerization for TEOS and O 2 . 
     FIGS. 1A to  1 H are cross-sectional views illustrating the fifth embodiment. 
     First, as shown in FIG. 1A, a BPSG (borophosphosilicate glass) film  102  is formed on a silicon substrate  101 . Then, after an aluminum film is formed on the BPSG film  102 , patterning is performed for the same to form an aluminum wiring layer  103 . The silicon substrate  101 , the BPSG film  102  and the aluminum wiring layer  103  formed in this manner constitute an object  104  to be formed. 
     Then, as shown in FIG. 1B, an SiO 2  film  105  (underlying insulating film) is formed on the object  104  to be formed. This SiO 2  film  105  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH4 and N 2 O are used as source gases. A film thickness of this SiO 2  film  105  is 100 nm. The SiO 2  film  105  can prevent H 2 O from being dispersed in the aluminum wiring layer  103 , which may cause corrosion. 
     Subsequently, as shown in FIG. 1C, an Si—C—O (—H) film  106  is formed on the SiO 2  film  105  (underlying insulating film). This Si—C—O (—H) film  106  is formed by performing plasma polymerization for TEOS and O 2 . This plasma polymerization is performed by applying an RF power having a frequency of 13.56 MHz and power of 100 W to the TEOS and O 2 . Flow rates of the source gases at this time are 30 sccm for TEOS and 240 sccm for O 2 , respectively. In forming the Si—C—O (—H) film  106  the temperature of the silicon substrate  101  is maintained at 400° C. and the pressure is held at 1 Torr. A film thickness of the Si—C—O (—H) 106 is 500 nm. 
     It should be noted that, in forming the Si—C—O (—H)  106 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 30 sccm and other process conditions are the same as in the case using the TEOS. Using the trimethysililbotrate, the Si—C—O (—H) film  106  further contains B (boron). 
     Then, as shown in FIG. 1D, O (oxygen) plasma treatment is performed for the Si—C—O (—H) film  106 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  101  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—O (—H) film  106  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—O (—H) film  106  becomes a porous SiO 2  film  107 . 
     Subsequently, as shown in FIG. 1E, H (hydrogen) plasma treatment is performed for the porous SiO 2  film  107 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 1F, an SiO 2  film  108  is formed on the porous SiO 2  film  107 . This SiO 2  film  108  is formed by a CVD method, which employs source gas containing TEOS and O 3 . In this case, since O 3  contained in source gas has concentration enough for oxidation of TEOS, the SiO 2  film  108  exhibits flowability, and can be planarized to a considerable extent. 
     Then, as shown in FIG. 1G, the SiO 2  film  108  is polished by a CMP method (chemical mechanical polishing method) so as to planarize its surface. At this time, some portions of the previously formed SiO 2  films  105  and  107  are eliminated by polishing. The planarizing by the CMP method should be carried out not to eliminate the whole SiO 2  film  105  formed on a convexity  103   a  of the aluminum wiring layer. 
     Subsequently, as shown in FIG. 1H, an SiO 2  film  109  (cover insulating film) is formed on the smoothed surface. This SiO 2  film  109  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  109  is 100 nm. 
     The foregoing process of forming the SiO 2  films  105  (underlying insulating film),  107  and  109  (cover insulating film) results in formation, on the object  104  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the SiO 2  film  107  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  109  is formed on the porous SiO 2  film  107 , incursion of water into the SiO 2  film  107  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  105 ,  107  and  109  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Sixth Embodiment 
     A sixth embodiment is a case of applying the fifth embodiment to a damascene process. 
     FIGS. 2A to  2 M are cross-sectional views illustrating the sixth embodiment. 
     First, as shown in FIG. 2A, a BPSG (borophosphosilicate glass) film  202  is formed on a silicon substrate  201 . Then, after an aluminum layer is formed thereon, patterning is performed for the same to form an aluminum wiring layer  203 . It should be noted that the aluminum wiring layer  203  in figures is not patterned for convenience. The silicon substrate  201 , the BPSG film  202  and the aluminum wiring layer  203  constituted an object  204  to be formed. 
     As shown in FIG. 2B, an SiO 2  film  205  (underlying insulating film) having a film thickness of 100 nm is formed on the aluminum wiring layer  203 . This SiO 2  film  205  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. 
     Subsequently, as shown in FIG. 2C, an Si—C—O (—H) film  206  is formed on the SiO 2  film  205  (underlying insulating film). This Si—C—O (—H) film  206  is formed by performing plasma polymerization for TEOS and O 2 . This plasma polymerization is performed by applying an RF power having a frequency of 13.56 MHz and power of 100 W to the TEOS and O 2 . Flow rates of source gases at this time are 30 sccm and 240 sccm for TEOS and O 2  respectively. In forming the Si—C—O (—H) film  106  the temperature of the silicon substrate  201  is maintained at 400° C. and the pressure is held at 1 Torr. A film thickness of the Si—C—O (—H) film  206  is 500 nm. 
     It should be noted that, in forming the Si—C—O (—H)  206 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 30 sccm and other process conditions are the same as in the case using the TEOS. Using the trimethysililbotrate, the Si—C—O (—H) film  206  further contains B (boron). 
     Then, as shown in FIG. 2D, O (oxygen) plasma treatment is performed for the Si—C—O (—H) film  206 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  201  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—O (—H) film  206  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—O (—H) film  206  becomes a porous SiO 2  film  207 . 
     Subsequently, as shown in FIG. 2E, H (hydrogen) plasma treatment is performed for the porous SiO 2  film  207 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  201  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 2F, patterning is performed for the SiO 2  film  207  to damascene trench  208 . This damascene trench  208  reaches the SiO 2  film  205  formed below the SiO 2  film  207 . 
     Then, as shown in FIG. 2G, an SiO 2  film  209  (first insulating film) is formed on the SiO 2  film  207  and on the side and bottom portions of the damascene trench  208 . This SiO 2  film  209  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. By the SiO 2  film  209  formed on the side portion of the damascene trench  208 , Cu buried later in the damascene trench  208  can be prevented from being dispersed in the porous SiO 2  film  207 . 
     Then, as shown in FIG. 2H, anisotropic etching is performed for the SiO 2  film  209  (first insulating film) and the SiO 2  film  205  (underlying insulating film) formed below the damascene trench  208 . Accordingly, the SiO 2  film  209  is eliminated except for a portion formed on the side portion of the damascene trench  208 . Also, since the SiO 2  film  205  formed below the damascene trench  208  is eliminated, a contact hole that reaches the aluminum wiring layer  203  is formed below the damascene trench  208 . 
     Subsequently, as shown in FIG. 2I, a Cu-plated film  210  is formed in the damascene trench  208  and on the SiO 2  film  207 . The Cu-plated film  210  formed in the damascene trench  208  is used as a Cu wiring line. 
     Then, as shown in FIG. 2J, the Cu-plated film  210  formed on the SiO 2  film  207  is polished by a CPM method to be eliminated. Accordingly, the Cu-plated film remains only in the damascene trench  208 . 
     Subsequently, as shown in FIG. 2K, a barrier metal TiN film  211  is formed above the damascene trench  208 . Accordingly, Cu in the damascene trench  208  can be prevented from being dispersed in an SiO 2  film later formed above the damascene trench  208 . 
     Then, as shown in FIG. 2L, patterning is performed to leave a TiN film  211   a  formed above the damascene trench  208 , and the TiN film  211  formed in the other portions is etched to be eliminated. 
     Subsequently, as shown in FIG. 2M, an SiO 2  film  212  (cover insulating film) is formed on the SiO 2  film  207  and the TiN film  211   a.  This SiO 2  film  212  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. 
     The foregoing process results in formation, on the object  204  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the SiO 2  film  207  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  212  (cover insulating film) is formed on the porous SiO 2  film  207 , incursion of water into the SiO 2  film  207  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  207  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  207  and  212  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Seventh Embodiment 
     A seventh embodiment is different from the first to sixth embodiments in that, instead of forming a porous SiO 2  film, a porous B-containing SiO 2  film is formed. 
     FIGS. 1A to  1 H are cross-sectional views illustrating the seventh embodiment. 
     First, as shown in FIG. 1A, a BPSG (borophosphosilicate glass) film  102  is formed on a silicon substrate  101 . Then, after an aluminum film is formed on the BPSG film  102 , patterning is performed for the same to form an aluminum wiring layer  103 . The silicon substrate  101 , the BPSG film  102  and the aluminum wiring layer  103  formed in this manner constitute an object  104  to be formed. 
     Then, as shown in FIG. 1B, an SiO 2  film  105  (underlying insulating film) is formed on the object  104  to be formed. This SiO 2  film  105  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  105  is 100 nm. The SiO 2  film  105  can prevent H 2 O from being dispersed in the aluminum wiring layer  103 , which may cause corrosion. 
     Subsequently, as shown in FIG. 1C, a carbon and boron, or carbon, boron and hydrogen containing (referred to as Si—C—B (—H), hereinafter) film  106  is formed on the SiO 2  film  105  (underlying insulating film). This Si—C—B (—H) film  106  is formed by using TEOS and B 2 H 6  as source gases, applying an RF power having a frequency of 13.56 MHz and a power of 100 W while keeping the silicon substrate  101  at 100° C., and performing plasma polymerization for TEOS and B 2 H 6  at pressure of 1 Torr. Flow rates of source gases at this time are 30 sccm and 24 sccm for TEOS and B 2 H 6  respectively. A film thickness of this Si—C—B (—H) film  106  is 500 nm. 
     It should be noted that, in forming the Si—C—B (—H) film  106 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Furthermore, one of TMB (B(OCH 3 ) 3 ) and TEB (B(OC 2 H 5 ) 3 ) can also be used instead of the B 2 H 6 . When using one of these gases, the flow rate of the gas is 48 sccm and the other process condition is the same as in the above. 
     Then, as shown in FIG. 1D, O (oxygen) plasma treatment is performed for the Si—C—B (—H) film  106 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  101  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—B (—H) film  106  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—B (—H) film  106  becomes a porous B-containing SiO 2  film  107 . 
     Subsequently, as shown in FIG. 1E, H (hydrogen) plasma treatment is performed for the porous B-containing SiO 2  film  107 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 1F, an SiO 2  film  108  is formed on the porous B-containing SiO 2  film  107 . This SiO 2  film  108  is formed by a CVD method, which contains TEOS and O 3  as source gases. In this case, since O 3  in source gas has concentration enough for oxidation of TEOS, the SiO 2  film  108  exhibits flowability, and can be planarized to a considerable extent. 
     Then, as shown in FIG. 1G, the SiO 2  film  108  is polished by a CMP method (chemical mechanical polishing method) to planarize its surface. At this time, some portions of the SiO 2  film  105  and the B-containing SiO 2  film  107  which have been formed before are eliminated by polishing. The planarizing by the CMP method should be carried out not to eliminate the whole SiO 2  film  105  formed on a convexity  103   a  of the aluminum wiring layer. 
     Subsequently, as shown in FIG. 1H, an SiO 2  film  109  (cover insulating film) is formed on the planarized surface. This SiO 2  film  109  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  109  is 100 nm. 
     The foregoing process of forming the SiO 2  films  105  (underlying insulating film),  109  (cover insulating film) and the B-containing SiO 2  film  107  results in formation, on the object  104  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the B-containing SiO 2  film  107  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  109  is formed on the porous B-containing SiO 2  film  107 , incursion of water into the B-containing SiO 2  film  107  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  105  and  109  and the B-containing SiO 2  film  107  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Eighth Embodiment 
     An eight embodiment is a case of applying the seventh embodiment to a damascene process. 
     FIGS. 2A to  2 M are cross-sectional views illustrating the eighth embodiment. 
     First, as shown in FIG. 2A, a BPSG (borophosphosilicate glass) film  202  is formed on a silicon substrate  201 . Then, after an aluminum layer is formed thereon, patterning is performed for the same to form an aluminum wiring layer  203 . It should be noted that the aluminum wiring layer  203  in figures is not patterned for convenience. The silicon substrate  201 , the BPSG film  202  and the aluminum wiring layer  203  constitute an object  204  to be formed. 
     As shown in FIG. 2B, an SiO 2  film  205  (underlying insulating film) having a film thickness of 100 nm is formed on the aluminum wiring layer  203 . This SiO 2  film  205  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. 
     Subsequently, as shown in FIG. 2C, an Si—C—B (—H) film  206  is formed on the SiO 2  film  205  (underlying insulating film). This Si—C—B (—H) film  206  is formed by using TEOS (Tetra-Ethyl-Ortho-Silicate) and B 2 H 6  as source gases, applying an RF power having a frequency of 13.56 MHz and a power of 100 W while keeping the silicon substrate  201  at 100° C., and performing plasma polymerization for TEOS and B 2 H 6  at pressure of 1 Torr. At this time, flow rates of source gases are 30 sccm and 24 sccm for TEOS and B 2 H 6  respectively. A film thickness of the Si—C—B (—H) film  206  is 500 nm. 
     It should be noted that, in forming the Si—C—B (—H) film  206 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Furthermore, one of TMB (B(OCH 3 ) 3 ) and TEB (B(OC 2 H 5 ) 3 ) can also be used instead of the B 2 H 6 . When using one of these gases, the flow rate of the gas is 48 sccm and the other process condition is the same as in the above. 
     Then, as shown in FIG. 2D, O (oxygen) plasma treatment is performed for the Si—C—B (—H) film  206 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  201  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—B (—H) film  206  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed. Accordingly, the Si—C—B (—H) film  206  becomes a porous B-containing SiO 2  film  207 . 
     Subsequently, as shown in FIG. 2E, H (hydrogen) plasma treatment is performed for the porous B-containing SiO 2  film  207 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  201  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 2F, patterning is performed for the B-containing SiO 2  film  207  to form a damascene trench  208 . This damascene trench  208  reaches the SiO 2  film  205  formed below the B-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2G, an SiO 2  film  209  (first insulating film) is formed on the B-containing SiO 2  film  207  and on the side and bottom portions of the damascene trench  208 . This SiO 2  film  209  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. By the SiO 2  film  209  formed on the side portion of the damascene trench  208 , Cu later buried in the damascene trench  208  can be prevented from being dispersed in the porous B-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2H, anisotropic etching is performed for the SiO 2  film  209  (first insulating film) and the SiO 2  film  205  (underlying insulating film) formed below the damascene trench  208 . Accordingly, the SiO 2  film  209  is eliminated except for a portion formed on the side portion of the damascene trench  208 . Also, since the SiO 2  film  205  formed below the damascene trench  208  is eliminated, a contact hole that reaches the aluminum wiring layer  203  is formed below the damascene trench  208 . 
     Subsequently, as shown in FIG. 2I, a Cu-plated film  210  is formed in the damascene trench  208  and on the B-containing SiO 2  film  207 . The Cu-plated film  210  formed in the damascene trench  208  is used as a Cu wiring line. 
     Then, as shown in FIG. 2J, the Cu-plated film  210  formed on the B-containing SiO 2  film  207  is polished by a CMP method to be eliminated. Accordingly, the Cu-plated film  210  remains only in the damascene trench  208 . 
     Subsequently, as shown in FIG. 2K, a barrier metal TiN film  211  is formed above the damascene trench  208 . Accordingly, Cu in the damascene trench  208  can be prevented from being dispersed in an SiO 2  film formed later above the damascene trench  208 . 
     Then, as shown in FIG. 2L, patterning is performed to leave a TiN film  211   a  formed above the damascene trench  208 , and the TiN film  211  formed on the other portions are etched to be eliminated. 
     Subsequently, as shown in FIG. 2M, an SiO 2  film  212  (cover insulating film) is formed on the B-containing SiO 2  film  207  and the TiN film  211   a.  This SiO 2  film  212  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. 
     The foregoing process results in formation, on the object  204  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the B-containing SiO 2  film  207  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  212  (cover insulating film) is formed on the porous B-containing SiO 2  film  207 , incursion of water into the B-containing SiO 2  film  207  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  207  can improve the moisture absorption resistance of the film. Moreover, the B-containing SiO 2  film  207  and the SiO 2  film  212  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Ninth Embodiment 
     In a ninth embodiment, a film containing carbon, boron and oxygen, or a film containing carbon, boron, oxygen and hydrogen (referred to as Si—C—B—O (—H) film, hereinafter) is formed in order to form a porous B-containing SiO 2  film. 
     FIGS. 1A to  1 H are cross-sectional views illustrating the ninth embodiment. 
     First, as shown in FIG. 1A, a BPSG (borophosphosilicate glass) film  102  is formed on a silicon substrate  101 . Then, after an aluminum film is formed on the BPSG film  102 , patterning is performed for the same to form an aluminum wiring layer  103 . The silicon substrate  101 , the BPSG film  102  and the aluminum wiring layer  103  formed in this manner constitute an object  104  to be formed. 
     Then, as shown in FIG. 1B, an SiO 2  film  105  (underlying insulating film) is formed on the object  104  to be formed. This SiO 2  film  105  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  105  is 100 nm. The SiO 2  film  105  can prevent H 2 O from being dispersed in the aluminum wiring layer  103 , which may cause corrosion. 
     Subsequently, as shown in FIG. 1C, an Si—C—B—O (—H) film  106  is formed on the SiO 2  film  105  (underlying insulating film). This Si—C—B—O (—H) film  106  is formed by performing plasma polymerization for TEOS, B 2 H 6 , and O 2 . This plasma polymerization is performed by applying an RF power having frequency of 13.56 MHz and power of 100 W to the TEOS, B 2 H 6 , and O 2 . And the flow rates of source gases at this time are 30 sccn, 24 sccm and 260 sccm for TEOS, B 2 H 6  and O 2  respectively. In forming the Si—C—B—O (—H) film  106  the temperature of the silicon substrate  101  is maintained at 400° C. and the pressure is held at 1 Torr. A film thickness of the Si—C—B—O (—H) film  106  is 500 nm. 
     It should be noted that, in forming the Si—C—B—O (—H) film  106 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Furthermore, one of TMB (B(OCH 3 ) 3 ) and TEB (B(OC 2 H 5 ) 3 ) can also be used instead of the B 2 H 6 . When using one of these gases, the flow rate of the gas is 48 sccm and the other process conditions are the same as in the above. 
     Then, as shown in FIG. 1D, O (oxygen) plasma treatment is performed for the Si—C—B—O (—H) film  106 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  101  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—B—O (—H) film  106  is oxidized, and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—B—O (—H) film  106  becomes a porous B-containing SiO 2  film  107 . 
     Subsequently, as shown in FIG. 1E, H (hydrogen) plasma treatment is performed for the porous B-containing SiO 2  film  107 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 1F, an SiO 2  film  108  is formed on the porous B-containing SiO 2  film  107 . This SiO 2  film  108  is formed by a CVD method, which contains TEOS and O 3  as source gases. In this case, since O 3  in source gas has concentration enough for oxidation of TEOS, the SiO 2  film  108  exhibits flowability, and can be planarized to a considerable extent. 
     Then, as shown in FIG. 1G, the SiO 2  film  108  is polished by a CMP method (chemical mechanical polishing method) to planarize its surface. At this time, some portions of the SiO 2  film  105  and the B-containing SiO 2  film  107  which have been formed before are eliminated by polishing. The planarizing by the CMP method should be carried out not to eliminate the whole SiO 2  film  105  formed on a convexity  103   a  of the aluminum wiring layer. 
     Subsequently, as shown in FIG. 1H, an SiO 2  film  109  (cover insulating film) is formed on the planarized surface. This SiO 2  film  109  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  109  is 100 nm. 
     The foregoing process of forming the SiO 2  films  105  (underlying insulating film) and  109  (cover insulating film), and the B-containing SiO 2  film  107  results in formation, on the object  104  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the B-containing SiO 2  film  107  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  109  is formed on the porous B-containing SiO 2  film  107 , incursion of water into the B-containing SiO 2  film  107  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  105  and  109  and the B-containing SiO 2  film  107  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Tenth Embodiment 
     A tenth embodiment is a case of applying the ninth embodiment to a damascene process. 
     FIGS. 2A to  2 M are cross-sectional views illustrating the tenth embodiment. 
     First, as shown in FIG. 2A, a BPSG (borophosphosilicate glass) film  202  is formed on a silicon substrate  201 . After an aluminum layer is formed thereon, patterning is performed for the same to form an aluminum wiring layer  203 . It should ne noted that the aluminum wiring layer  203  in figures is not patterned for convenience. The silicon substrate  201 , the BPSG film  202  and the aluminum wiring layer  203  constitute an object  204  to be formed. 
     Then, as shown in FIG. 2B, an SiO 2  film  205  (underlying insulating film) having a film thickness of 100 nm is formed on the aluminum wiring layer  203 . This SiO 2  film  205  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. 
     Subsequently, as shown in FIG. 2C, an Si—C—B—O (—H) film  206  is formed on the SiO 2  film  205  (underlying insulating film). This Si—C—B—O (—H) film  206  is formed by using TEOS (Tetra-Ethyl-Ortho-Silicate), B 2 H 6  and O 2  as source gases, and performing plasma polymerization for these source gases. This plasma polymerization is performed by applying an RF power having frequency of 13.56 MHz and power of 100 W to the TEOS, B 2 H 6 , and O 2 . And the flow rates of source gases at this time are 30 sccm, 24 sccm and 260 sccm for TEOS, B 2 H 6  and O 2  respectively. In forming the Si—C—B—O (—H) film  206  the temperature of the silicon substrate  201  is maintained at 400° C. and the pressure is held at 1 Torr. A film thickness of the Si—C—B—O (—H) film  206  is 500 nm. 
     It should be noted that, in forming the Si—C—B—O (—H) film  206 , one of metylsilane (Si(CH 3 )H 3 ) and trimethysililbotrate ({(CH 3 ) 3 SiO} 3 B) can also be used instead of the TEOS. When using one of these gases, the flow rate of the gas is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Furthermore, one of TMB (B(OCH 3 ) 3 ) and TEB (B(OC 2 H 5 ) 3 ) can also be used instead of the B 2 H 6 . When using one of these gases, the flow rate of the gas is 48 sccm and the other process conditions are the same as in the above. 
     Then, as shown in FIG. 2D, O (oxygen) plasma treatment is performed for the Si—C—B—O (—H) film  206 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  201  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—B—O (—H) film  206  is oxidized, and discharged to the outside. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—B—O (—H) film  206  becomes a porous B-containing SiO 2  film  207 . 
     Subsequently, as shown in FIG. 2E, H (hydrogen) plasma treatment is performed for the porous B-containing SiO 2  film  207 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  201  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 2F, patterning is performed for the B-containing SiO 2  film  207  to form a damascene trench  208 . This damascene trench  208  reaches the SiO 2  film  205  formed below the B-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2G, an SiO 2  film  209  (first insulating film) is formed on the B-containing SiO 2  film  207  and on the side and bottom portions of the damascene trench  208 . This SiO 2  film  209  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. By the SiO 2  film  209  formed on the side portion of the damascene trench  208 , Cu buried later in the damascene trench  208  can be prevented from being dispersed in the porous B-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2H, anisotropic etching is performed for the SiO 2  film  209  (first insulating film) and the SiO 2  film  205  (underlying insulating film) formed below the damascene trench  208 . Accordingly, the SiO 2  film  209  is eliminated except for a portion formed on the side portion of the damascene trench  208 . Also, since the SiO 2  film  205  formed below the damascene trench  208  is eliminated, a contact hole that reaches the aluminum wiring layer  203  is formed below the damascene trench  208 . 
     Subsequently, as shown in FIG. 2I, a Cu-plated film  210  is formed in the damascene trench  208  and on the B-containing SiO 2  film  207 . The Cu-plated film  210  formed in the damascene trench  208  is used as a Cu wiring line. 
     Then, as shown in FIG. 2J, The Cu-plated film  210  formed on the B-containing SiO 2  film  207  is polished by a CMP method to be eliminated. Accordingly, the Cu-plated film remains only in the damascene trench  208 . 
     Subsequently, as shown in FIG. 2K, a barrier metal TiN film  211  is formed above the damascene trench  208 . Accordingly, Cu in the damascene trench  208  can be prevented from being dispersed in an SiO 2  film formed later above the damascene trench  208 . 
     Then, as shown in FIG. 2L, patterning is performed to leave a TiN film  211   a  formed above the damascene trench  208 , and the TiN film  211  formed on the other portions are etched to be eliminated. 
     Subsequently, as shown in FIG. 2M, an SiO 2  film  212  (cover insulating film) is formed on the B-containing SiO 2  film  207  and the TIN film  211   a.  This SiO 2  film  212  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. 
     The foregoing process results in formation, on the object  204  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the B-containing SiO 2  film  207  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  212  (cover insulating film) is formed on the porous B-containing SiO 2  film  207 , incursion of water into the B-containing SiO 2  film  207  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  207  can improve the moisture absorption resistance of the film. Moreover, the B-containing SiO 2  film  207  and the SiO 2  film  212  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Eleventh Embodiment 
     An eleventh embodiment is different from the first to tenth embodiments in that porous F-containing SiO 2  film is formed instead of forming a porous SiO 2  film or a porous B-containing SiO 2  film. 
     FIGS. 1A to  1 H are cross-sectional views illustrating the eleventh embodiment. 
     First, as shown in FIG. 1A, a BPSG (borophosphosilicate glass) film  102  is for on a silicon substrate  101 . Then, after an aluminum film is formed on the BPSG film  102 , patterning is performed for the same to form an aluminum wiring layer  103 . The silicon substrate  101 , the BPSG film  102  and the aluminum wiring layer  103  constitute an object  104  to be formed. 
     Then, as shown in FIG. 1B, an SiO 2  film  105  (underlying insulating film) is formed on the object  104  to be formed. This SiO 2  film  105  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  105  is 100 mn. The SiO 2  film  105  can prevent H 2 O from being dispersed in the aluminum wiring layer  103 , which may cause corrosion. 
     Subsequently, as shown in FIG. 1C, a film  106  containing carbon and fluorine or carbon, fluorine and hydrogen (referred to as Si—C—F (—H) film, hereinafter) is formed on the SiO 2  film  105  (underlying insulating film). This Si—C—F (—H) film  106  is formed by using TEOS and C 2 F 6  as source gases, applying an RF power having a frequency of 13.56 MHz and a power of 100 W while keeping the silicon substrate  101  at 100° C., and performing plasma polymerization for TEOS and C 2 F 6  at pressure of 1 Torr. Flow rates of source gases at this time are 30 sccm and 5 sccm for TEOS and C 2 F 6  respectively. A film thickness of the Si—C—F (—H) film  106  is 500 nm. 
     It should be noted that in forming the Si—C—F (—H) film  106 , metylsilane (Si(CH 3 )H 3 ) can also be used instead of the TEOS. When using the metylsilane, its flow rate is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Then, as shown in FIG. 1D, O (oxygen) plasma treatment is performed for the Si—C—F (—H) film  106 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  101  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—F (—H) film  106  is oxidized, and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—F (—H) film  106  becomes a porous F-containing SiO 2  film  107 . 
     Subsequently, as shown in FIG. 1E, H (hydrogen) plasma treatment is performed for the porous F-containing SiO 2  film  107 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 1F, an SiO 2  film  108  is formed on the porous F-containing SiO 2  film  107 . This SiO 2  film  108  is formed by a CVD method, which contains TEOS and O 3  as source gases. In this case, since O 3  in source gas had concentration enough for oxidation of TEOS, the SiO 2  film  108  exhibits flowability, and can be planarized to a considerable extent. 
     Then, as shown in FIG. 1G, the SiO 2  film  108  is polished by a CMP method (chemical mechanical polishing method) to planarize its surface. At this time, same portions of the SiO 2  film  105  and the F-containing SiO 2  film  107  which have been formed before are eliminated by polishing. The planarizing by the CMP method should be carried out not to eliminate the whole SiO 2  film  105  formed in a convexity  103   a  of the aluminum wiring layer. 
     Subsequently, as shown in FIG. 1H, an SiO 2  film  109  (cover insulating film) is formed on the planarized surface. This SiO 2  film  109  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  109  is 100 nm. 
     The foregoing process of forming the SiO 2  films  105  (underlying insulating film) and  109  (cover insulating film), and the F-containing SiO 2  film  107  results in formation, on the object  104  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the F-containing SiO 2  film  107  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  109  is formed on the porous F-containing SiO 2  film  107 , incursion of water into the F-containing SiO 2  film  107  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  105  and  109 , and the F-containing SiO 2  film  107  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Twelfth Embodiment 
     A twelfth embodiment is case of applying the eleventh embodiment to a damascene process. 
     FIGS. 2A to  2 M are cross-sectional views illustrating the twelfth embodiment. 
     First, as shown in FIG. 2A, a BPSG (borophosphosilicate glass) film  202  is formed on a silicon substrate  201 . Then, after an aluminum layer is formed thereon, patterning is performed for the same to form an aluminum wiring layer  203 . It should be noted that the aluminum wiring layer  203  in figures is not patterned for convenience. The silicon substrate  201 , the BPSG film  202  and the aluminum wiring layer  203  constituted an object  204  to be formed. 
     As shown in FIG. 2B, an SiO 2  film  205  (underlying insulating film) having a film thickness of 100 nm is formed on the aluminum wiring layer  203 . This SiO 2  film  205  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. 
     Subsequently, as shown in FIG. 2C, an Si—C—F (—H) film  206  is formed on the SiO 2  film  205  (underlying insulating film). This Si—C—F (—H) film  206  is formed by using TEOS (Tetra-Ethyl-Ortho-Silicate) and C 2 F 6  as source gases, applying an RF power having a frequency of 13.56 MHz and a power of 100 W while keeping the silicon substrate  201  at 100°, and performing plasma polymerization for TEOS and C 2 F 6  at pressure of 1 Torr. Flow rates of source gases at this time are 30 sccm and 5 sccm for TEOS and C 2 F 6  respectively. A film thickness of the Si—C—F (—H) film  206  is 500 nm. 
     It should be noted that in forming the Si—C—F (—H) film  206 , metylsilane (Si(CH 3 )H 3 ) can also be used instead of the TEOS. When using the metylsilane, its flow rate is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Then, as shown in FIG. 2D, O (oxygen) plasma treatment is performed for the Si—C—F (—H) film  206 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  201  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—F (—H) film  206  is oxidized, and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—F (—H) film  206  becomes a porous F-containing SiO 2  film  207 . 
     Subsequently, as shown in FIG. 2E, H (hydrogen) plasma treatment is performed for the porous F-containing SiO 2  film  207 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  201  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 2F, patterning is performed for the F-containing SiO 2  film  207  to form a damascene trench  208 . This damascene trench  208  reaches the SiO 2  film  205  formed below the F-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2G, an SiO 2  film  209  (first insulating film) is formed on the F-containing SiO 2  film  207  and on the side and bottom portions of the damascene trench  208 . This SiO 2  film  209  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. By the SiO 2  film  209  formed on the side portion of the damascene trench  208 , Cu buried later in the damascene trench  208  can be prevented from being dispersed in the porous B-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2H, anisotropic etching is performed for the SiO 2  film  209  (first insulating film) and the SiO 2  film  205  (underlying insulating film) formed below the damascene trench  208 . Accordingly, the SiO 2  film  209  is eliminated except for a portion formed on the side portion of the damascene trench  208 . Also, since the SiO 2  film  205  formed below the damascene trench  208  is eliminated, a contact hole that reaches the aluminum wiring layer  203  is formed below the damascene trench  208 . 
     Subsequently, as shown in FIG. 2I, a Cu-plated film  210  is formed in the damascene trench  208  and on the F-containing SiO 2  film  207 . The Cu-plated film  210  formed in the damascene trench  208  is used as a Cu wiring line. 
     Then, as shown in FIG. 2J, the Cu-plated film  210  formed on the F-containing SiO 2  film  207  is polished by a CMP method to be eliminated. Accordingly, the Cu-plated film remains only in the damascene trench  208 . 
     Subsequently, as shown in FIG. 2K, a barrier TiN film  211  is formed above the damascene trench  208 . Accordingly, Cu in the damascene trench  208  can be prevented from being dispersed in an SiO 2  film formed later above the damascene trench  208 . 
     Then, as shown in FIG. 2L, patterning is performed to leave a TiN film  211   a  formed above the damascene trench  208 , and the TiN film  211  formed in the other portions is etched to be eliminated. 
     Subsequently, as shown in FIG. 2M, an SiO 2  film  212  (cover insulating film) is formed on the F-containing SiO 2  film  207  and the TiN film  211   a.  This SiO 2  film  212  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. 
     The foregoing process results in formation, on the object  204  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the F-containing SiO 2  film  207  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  212  (cover insulating film) is formed on the porous F-containing SiO 2  film  207 , incursion of water into the F-containing SiO 2  film  207  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  207  can improve the moisture absorption resistance of the film. Moreover,the F-containing SiO 2  film  207  and the SiO 2  film  212  have better heat resistivity compared with the organic insulating film since these films consist many of Si and O. 
     Thirteenth Embodiment 
     In a thirteenth diet, a film containing carbon, fluorine and oxygen, or a film containing carbon, fluorine, oxygen and hydrogen (referred to as Si—C—F—O (—H) film, hereinafter) is formed in order to form a porous F-containing SiO 2  film. 
     FIGS. 1A to  1 H are cross-sectional views illustrating the thirteenth embodiment. 
     First, as shown in FIG. 1A, a BPSG (borophosphosilicate glass) film  102  is formed on a silicon substrate  101 . Then, after an aluminum film is formed on the BPSG film  102 , patterning is performed for the same to form an aluminum wiring layer  103 . The silicon substrate  101 , the BPSG film  102  and the aluminum wiring layer  103  formed in this manner constitute an object  104  to be formed. 
     Then, as shown in FIG. 1B, an SiO 2  film  105  (underlying insulating film) is formed on the object  104  to be formed. This SiO 2  film  105  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  105  is 100 nm. The SiO 2  film  105  can prevent H 2 O from being dispersed in the aluminum wiring layer  103 , which may cause corrosion. 
     Subsequently, as shown in FIG. 1C, an Si—C—F—O (—H) film  106  is formed on the SiO 2  film  105  (underlying insulating film). This Si—C—F—O (—H) film  106  is formed by performing plasma polymerization for TEOS, C 2 F 6  and O 2 . This plasma polymerization is performed by applying an RF power having frequency of 13.56 MHz and power of 100 W to the TEOS, C 2 F 6  and O 2 . And the flow rates of source gases at this time are 30 sccm, 5 sccm and 260 sccm for TEOS, C 2 F 6  and O 2  respectively. 
     In forming the Si—C—F—O (—H) film  106  the temperature of the silicon substrate  101  is maintained at 400° C. and the pressure is held at 1 Torr. A film thickness of the Si—C—F—O (—H) film  106  is 500 nm. 
     It should be noted that in forming the Si—C—F—O (—H) film  106 , metylsilane (Si(CH 3 )H 3 ) can also be used instead of the TEOS. When using the metylsilane, its flow rate is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Then, as shown in FIG. 1D, O (oxygen) plasma treatment is performed for the Si—C—F—O (—H) film  106 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  101  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—F—O (—H) film  106  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—F—O (—H) film  106  becomes a porous F-containing SiO 2  film  107 . 
     Subsequently, as shown in FIG. 1E, H (hydrogen) plasma treatment is performed for the porous F-containing SiO 2  film  107 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Accordingly, Si—H bond is substituted for Si dangling bond in the Si—O bond on the surface of the void, and moisture absorption resistance of the film can be increased. 
     Subsequently, as shown in FIG. 1F, an SiO 2  film  108  is formed on the porous F-containing SiO 2  film  107 . This SiO 2  film  108  is formed by a CVD method, which contains TEOS and O 3  as source gases. In this case, since O 3  in source gas has concentration enough for oxidation of TEOS, the SiO 2  film  108  exhibits flowability, and can be planarized to a considerable extent. 
     Then, as shown in FIG. 1G, the SiO 2  film  108  is polished by a CMP method (chemical mechanical polishing method) to planarize its surface. At this time, some portions of the SiO 2  film  105  and the F-containing SiO 2  film  107  which have been formed before are eliminated by polishing. The planarizing by the CMP method should be carried out not to eliminate the whole SiO 2  film  105  formed on a convexity  103   a  of the aluminum wiring layer. 
     Subsequently, as shown in FIG. 1H, an SiO 2  film (cover insulating film) is formed on the planarized surface. This SiO 2  film  109  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. A film thickness of the SiO 2  film  109  is 100 nm. 
     The foregoing process of forming the SiO 2  films  105  (underlying insulating film) and  109  (cover insulating film), and the F-containing SiO 2  film  107  results in formation, on the object  104  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the F-containing SiO 2  film  107  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  109  is formed on the porous F-containing SiO 2  film  107 , incursion of water into the F-containing SiO 2  film  107  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the SiO 2  films  105  and  109  and the F-containing SiO 2  film  107  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O. 
     Fourteenth Embodiment 
     A fourteenth embodiment is a case of applying the thirteenth embodiment to a damascene process. 
     FIGS. 2A to  2 M are cross-sectional views illustrating the fourteenth embodiment. 
     First, as shown in FIG. 2A, a BPSG (borophosphosilicate glass) film  202  is formed on a silicon substrate  201 . Then, after an aluminum layer is formed thereon, patterning is performed for the same to form an aluminum wiring layer  203 . It should be noted that the aluminum wiring layer  203  in figures is not patterned for convenience. The silicon substrate  201 , the BPSG film  202  and the aluminum wiring layer  203  constitute an object  204  to be formed. 
     As shown in FIG. 2B, an SiO 2  film  205  (underlying insulating film) having a film thickness of 100 nm is formed on the aluminum wiring layer  203 . This SiO 2  film  205  is formed by a plasma enhanced CVD method (plasma enhanced chemical vapor deposition method), and SiH 4  and N 2 O are used as source gases. 
     Subsequently, as shown in FIG. 2C, an Si—C—F—O (—H) film  206  is formed on the SiO 2  film  205  (underlying insulating film). This Si—C—F—O (—H) film  206  is formed by using TEOS (Tetra-Ethyl-Ortho-Silicate), C 2 F 6  and O 2  as source gases, and performing plasma polymerization for these source gases. This plasma polymerization is performed by applying an RF power having frequency of 13.56 MHz and power of 100 W to the TEOS, C 2 F 6  and O 2 . And the flow rates of source gases at this time are 30 sccm, 5 sccm and 260 sccm for TEOS, C 2 F 6  and O 2  respectively. 
     In forming the Si—C—F—O (—H) film  206  the temperature of the silicon substrate  201  is maintained at 400° C. and the pressure is held at 1 Torr. A film thickness of the Si—C—F—O (—H) film  206  is 500 nm. 
     It should be noted that in forming the Si—C—F—O (—H) film  206 , metylsilane (Si(CH 3 )H 3 ) can also be used instead of the TEOS. When using the metylsilane, its flow rate is 30 sccm and the other process conditions are the same as in the case using the TEOS. 
     Then, as shown in FIG. 2D, O (oxygen) plasma treatment is performed for the Si—C—F—O (—H) film  206 . This O (oxygen) plasma treatment is performed supplying 600 sccm O 2  to a chamber (not shown) and applying RF power having frequency of 400 kHz and power of 300 W to the O 2 . The time for the O (oxygen) plasma treatment is 360 sec, and the temperature of the silicon substrate  201  is maintained at 350° C. during undergoing the O (oxygen) plasma treatment. 
     In this O (oxygen) plasma treatment C or H contained in the Si—C—F—O (—H) film  206  is oxidized and discharged to the outside of the film. Voids are formed in portions, from which C or H has been discharged, and Si—O bond is formed on the portion. Accordingly, the Si—C—F—O (—H) film  206  becomes a porous F-containing SiO 2  film  207 . 
     Subsequently, as shown in FIG. 2E, H (hydrogen) plasma treatment is performed for the porous F-containing SiO 2  film  207 . 
     This H plasma treatment is performed by supplying H 2  of 600 sccm to a chamber (not shown) and applying RF power to upper and lower electrodes (not shown) that is opposing each other in the chamber. And the RF power applied to the upper electrode has frequency of 13.56 MHz and power of 50 W. On the other hand, the RF power applied to the lower electrode has frequency of 400 kHz and power of 400 W. Further, during undergoing the H plasma treatment, the pressure in the chamber is 0.1˜0.2 Torr and the temperature of the silicon substrate  101  is maintained at 400° C. Still further, the time for the H plasma treatment is 60 sec. 
     The H plasma treatment substitutes Si—H bonds for dangling bonds of Si in an Si—O bond in the surface of the void. Therefore, OH radicals and water are made to be hard to bond to the dangling bonds of Si, which improves the moisture absorption resistance of the film. 
     Subsequently, as shown in FIG. 2F, patterning is performed for the B-containing SiO 2  film  207  to form a damascene trench  208 . This damascene trench  208  reaches the SiO 2  film  205  formed below the F-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2G, an SiO 2  film  209  (first insulating film) is formed on the F-containing SiO 2  film  207  and on the side and bottom portions of the damascene trench  208 . This SiO 2  film  209  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. By the SiO 2  film  209  formed on the side portion of the damascene trench  208 , Cu buried later in the damascene trench  208  can be prevented from being dispersed in the porous B-containing SiO 2  film  207 . 
     Then, as shown in FIG. 2H, anisotropic etching is performed for the SiO 2  film  209  and the SiO 2  film  205  (underlying insulating film) formed below the damascene trench  208 . Accordingly, the SiO 2  film  209  is eliminated except for a portion formed on the side portion of the damascene trench  208 . Also, since the SiO 2  film  205  formed below the damascene trench  208  is eliminated, a contact hole that reaches the aluminum wiring layer  203  is formed below the damascene trench  208 . 
     Subsequently, as shown in FIG. 2I, a Cu-plated film  210  is formed in the damascene trench  208  and on the B-containing SiO 2  film  207 . The Cu-plated film  210  formed in the damascene trench  208  is used as a Cu wiring line. 
     Then, as shown in FIG. 2J, the Cu-plated film  210  formed on the F-containing SiO 2  film  207  is polished by a CMP method to be eliminated. Accordingly, the Cu-plated film remains only in the damascene trench  208 . 
     Subsequently, as shown in FIG. 2K, a barrier metal TiN film  211  is formed above the damascene trench  208 . Accordingly, Cu in the damascene trench  208  can be prevented from being dispersed in an SiO 2  film formed later above the same. 
     Then, as shown in FIG. 2L, patterning is performed to leave a TiN film  211   a  formed above the damascene trench  208 , and the TiN film  211  formed on the other portions is etched to be eliminated. 
     Subsequently, as shown in FIG. 2M, an SiO 2  film  212  (cover insulating film) is formed on the F-containing SiO 2  film  207  and the TiN film  211   a.  This SiO 2  film  212  is formed by a plasma enhanced CVD method, and SiH 4  and N 2 O are used as source gases. 
     The foregoing process results in formation, on the object  204  to be formed, an interlayer insulating film of a low dielectric constant, which has good heat resistivity and moisture absorption resistance. That is, since the F-containing SiO 2  film  207  has porosity, a relative dielectric constant thereof is smaller than that of a usual SiO 2  film. Also, since the usual SiO 2  film  212  (cover insulating film) is formed on the porous F-containing SiO 2  film  207 , incursion of water into the SiO 2  film  207  can be prevented. Furthermore, performing the H plasma treatment for the SiO 2  film  107  can improve the moisture absorption resistance of the film. Moreover, the F-containing SiO 2  film  207  and the SiO 2  film  212  have better heat resistivity compared with the organic insulating film since these films consist mainly of Si and O.