Abstract:
To provide a plasma CVD apparatus for forming a silicon nitride film and a fluorine-containing silicon oxide film in one and the same chamber, in which a NH 3  gas pipeline for introducing NH 3  gas as a part of raw material gases of the silicon nitride film and a SiF 4  gas pipeline for introducing SiF 4  gas as a part of the raw material gases of the fluorine-containing silicon oxide film are separately connected to an upper electrode also functioning as a shower head.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a plasma CVD apparatus, and especially relates to a CVD apparatus for continuously forming a silicon nitride film (SiN film) and a fluorine-containing silicon oxide film (SiOF film) in one and the same chamber.  
           [0003]    2. Description of the Prior Art  
           [0004]    Following the tendency of making a semiconductor device ultra fine, fine multilayered wiring is inevitably required for a semiconductor device. In order to prevent operation speed retardation of the semiconductor device, it is desirable to use Cu wiring for the wiring, and it is necessary to use a film with a low dielectric constant for an interlayer insulating film.  
           [0005]    The film with a low dielectric constant is supposed to be made available in relatively near future by using a SiOF film possible to be easily integrated in the same production process as a conventionally employed silicon oxide film (SiO 2  film).  
           [0006]    A method for forming a SiO 2  film after formation of a SiN film is commonly employed for forming the interlayer insulating film on the conventional Cu wiring in order to prevent oxidation of the Cu wiring, and it is desirable to carry out these processes to successively form the SiN film and the SiO 2  film in one and the same chamber in order to reduce the cost. In the case of changing the SiO 2  film to a SiOF film to lower the dielectric constant, it is also desirable to successively carry out film formation processes in one and the same chamber in the same manner.  
           [0007]    Next, referring to FIG. 5, a conventional example that a SiN film and a SiOF film are practically formed in one and the same chamber will be described.  
           [0008]    With reference to cross-sectional view in FIG. 5, this example shows a parallel plate type plasma CVD apparatus. With regard to the configuration of the apparatus, there exist a chamber  11 , a N 2  gas pipeline  1  equipped with a final valve  12 , and a SiF 4  gas pipeline  2 , a NH 3  gas pipeline  3 , and a SiH 4  gas pipeline  4  joined to a single line and then equipped with a final valve  23 , and these pipelines are connected to a chamber  11 . An upper electrode  7  which also functions as a shower head and a high frequency power source  5  are installed in the upper part of the chamber  11  and a lower electrode  9  which functions as a heater and which is connected with a low frequency power source  6  is installed in the lower part of the chamber. A wafer  8  is mounted on the lower electrode  9 . An exhaust part  10  is formed in a sidewall of the chamber.  
           [0009]    Next, the steps for film formation will be described. At first, in a first step, a NH 3  gas valve  15 , a SiH 4  gas valve  16  and the final valve  23  were opened, and NH 3  gas and SiH 4  gas were introduced into the chamber  11  to form a SiN film. The substrate temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiN film with about 100 nm thickness on the wafer  8  in this step.  
           [0010]    Next, in a second step, after the film formation of the SiN film, the high frequency power source  5  and the low frequency power source  6  were turned off and the NH 3  gas valve  15  and the SiH 4  gas valve  16  were closed to stop introduction of NH 3  gas and SiH 4  gas and then the gases remaining in the pipelines from a SiF 4  gas valve  13 A, the NH 3  gas valve  15 , and the SiH 4  gas valve  16  to the chamber  11  were evacuated.  
           [0011]    Then, the N 2  gas valve, which is the final valve  12 , the SiF 4  gas valve  13 A, the SiH 4  gas valve  16 , and the final valve  23  were opened to introduce N 2  gas, SiF 4  gas and SiH 4  gas into the chamber  11  to try to form a SiOF film. The substrate temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively.  
           [0012]    Though a SiOF film was expected to be formed on the wafer  8  in this step by applying each 500 W power of the high frequency power source  5  and the low frequency power source  6  to those electrodes, only particles of reaction products were found adhering to the wafer. Additionally, the pipelines were clogged in this step and gas flow was inhibited. According to the analysis of the disassembled pipeline near the final valve  23 , a reaction product supposed to be [(NH 4 )  2 SiF 6 ] was observed. Consequently, it was confirmed that reaction of SiF 4  and NH 3  was caused at a normal temperature in vacuum.  
           [0013]    Next, since reaction of SiF 4  and NH 3  is caused at a normal temperature, continuous film formation in one and the same chamber is given up and hence, a method for respectively forming a SiN film and a SiOF film in independent chambers will be described with reference to FIG. 6 and FIG. 7.  
           [0014]    [0014]FIG. 6 shows a chamber  11  for formation of a SiN film. NH 3  gas and SiH 4  gas were introduced into the chamber  11  by opening a final valve  14  to form a SiN film. The substrate temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively.  
           [0015]    Respective gases were introduced into the chamber  11  through a NH 3  gas pipeline  3  and a SiH 4  gas pipeline  4 . About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiN film with about 100 nm thickness on the wafer  8  in this step.  
           [0016]    Further, after evacuation, the pressure in the chamber was increased to atmospheric pressure by N 2  gas and after being transferred to another chamber, the resultant wafer  8  was transferred to the chamber  11  for formation of SiOF film shown in FIG. 7.  
           [0017]    [0017]FIG. 7 shows the chamber  11  for formation of SiOF film. By opening the final valves  12 ,  14 B, N 2 O gas and SiF 4  gas were introduced into the chamber  11  to form a SiOF film. The substrate temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiOF film on the wafer  8  in this step.  
           [0018]    In this method, there were problems that since two chambers were employed, throughput was delayed in consideration of the time for the transportation between the chambers, and that the apparatus became expensive due to use of two chambers.  
           [0019]    Regarding the conventional gas pipelines shown in FIG. 5, there existed problems as follows: the apparatus was so composed as to introduce NH 3  gas and SiF 4  gas through a single gas pipeline into the chamber and only a common final valve was installed, so that NH 3  gas evacuation is made incomplete and NH 3  gas and SiF 4  gas were mixed with each other in the gas pipeline before the chamber and consequently, reaction took place at a normal temperature and a reaction product [(NH 4 ) 2 SiF 6 ) of NH 3  and SiF 4  was produced in the gas pipeline to clog the pipeline or to increase the quantity of particles on a wafer by the reaction product in the pipeline.  
           [0020]    On the other hand, in the method for forming the SiN film and the SiOF film in separate chambers as shown in FIG. 6 and FIG. 7, there existed problems that the throughput was delayed and the cost of the apparatus was increased.  
         BRIEF SUMMARY OF THE INVENTION  
         [0021]    Object of the Invention  
           [0022]    An object of the present invention is to provide a plasma CVD apparatus capable of preventing clogging of pipelines and forming a SiN film and a SiOF film in one and the same chamber.  
           [0023]    Summary of the Invention  
           [0024]    A plasma CVD apparatus for forming a silicon nitride film and a fluorine-containing silicon oxide film in a same single chamber according to the present invention comprises a NH 3  gas pipeline for introducing NH 3  gas as a part of raw material gases of the silicon nitride film and a SiF 4  gas pipeline for introducing SiF 4  gas as a part of raw material gases of the fluorine-containing silicon oxide film, in which these pipelines are separately connected to an upper electrode which also functions as a shower head. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The above-mentioned and other objects, features and a advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0026]    [0026]FIG. 1 is a cross-section figure of a CVD apparatus showing a first embodiment of the present invention;  
         [0027]    [0027]FIG. 2 is a cross-section figure of a CVD apparatus showing a second embodiment of the present invention;  
         [0028]    [0028]FIG. 3 is a cross-section figure of a CVD apparatus showing a third embodiment of the present invention;  
         [0029]    [0029]FIG. 4 is across-section figure of a CVD apparatus showing a fourth embodiment of the present invention;  
         [0030]    [0030]FIG. 5 is a cross-section figure of a conventional CVD apparatus;  
         [0031]    [0031]FIG. 6 is a cross-section figure of another conventional CVD apparatus; and  
         [0032]    [0032]FIG. 7 is across-section figure of the other conventional CVD apparatus.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-section figure of a parallel plate type plasma CVD apparatus for illustrating a first embodiment of the present invention.  
         [0034]    By reference to FIG. 1, in the parallel plate type plasma CVD apparatus of the present invention, a N 2  gas pipeline  1  equipped with a final valve  12  is connected with the outer circumferential part  7 A of an upper electrode functioning also as a shower head. A NH 3  gas pipeline  3  and a SiH 4  gas pipeline  4  are joined to a single pipeline and also connected via a final valve  14  to the outer circumferential part  7 A of the upper electrode functioning also as the shower head. Further a SiF 4  gas pipeline  2  equipped with a final valve  13  is connected to the center part  7 B of the upper electrode functioning also as the shower head. The outer circumferential part and the center part  7 A,  7 B of the upper electrode functioning also as the shower head and a high frequency power source  5  are installed in the upper part of the chamber  11  and a lower electrode  9  also functioning as a heater to mount a wafer  8  thereon and a low frequency power source  6  are installed in the lower part of the chamber and an exhaust part  10  is formed in a side wall of the chamber.  
         [0035]    [0035]FIG. 2 is a cross-section figure of a parallel plate type plasma CVD apparatus for illustrating a second embodiment of the present invention and the parallel plate type plasma CVD apparatus has a configuration wherein: a N 2 O gas pipeline  1  equipped with a final valve  12  is connected with an upper electrode  7  functioning also as a shower head; a NH 3  gas pipeline  3  equipped with a valve  15  and a SiH 4  gas pipeline  4  equipped with a valve  16  are joined to a single pipeline and via a final valve  14 , joined in the downstream side to a SiF 4  gas pipeline  2  equipped with a valve  13  and further connected to the upper electrode  7  functioning also as the shower head; and the upper electrode  7  functioning also as the shower head and a high frequency power source  5  are installed in the upper part of the chamber  11  and a lower electrode  9  also functioning as a heater to mount a wafer  8  thereon and a low frequency power source  6  are installed in the lower part of the chamber and an exhaust part  10  is formed in a side wall of the chamber.  
         [0036]    [0036]FIG. 3 is a cross-section figure of a high density plasma CVD apparatus for illustrating a third embodiment of the present invention and the high density plasma CVD apparatus has a configuration wherein: a N 2 O gas pipeline  1  equipped with a final valve  12  and a SiF 4  gas pipeline  2  equipped with a final valve  13  are connected with a chamber  11 A and a NH 3  gas pipeline  3  and a SiH 4  gas pipeline  4  are joined to a single pipeline and via a final valve  14  further connected to the chamber  11 A as to introduce respective gases into the chamber through gas nozzles  1 A,  2 A, and  3 A; and a coil  17  and a high frequency power source  5 A are installed in a dome part of the upper part of the chamber  11 A, a lower electrode  9  also functioning as a heater to mount a wafer  8  thereon and a high frequency power source  5 B are installed in the lower part of the chamber, and an exhaust part  10 A is formed in a side wall of the chamber.  
         [0037]    [0037]FIG. 4 is a parallel plate type plasma CVD apparatus for illustrating a fourth embodiment of the present invention and the parallel plate type plasma CVD apparatus has a configuration wherein: a N 2 O gas pipeline  1  equipped with a final valve  12  is connected with an upper electrode  7  functioning also as a shower head; a NH 3  gas pipeline  3  equipped with a NH 3  gas valve  15  and a SiH 4  gas pipeline  4  equipped with a SiH 4  gas valve  16  are joined to a single pipeline which is further equipped with a NH 3 /SiH 4  valve  14 A in the downstream side; the single pipeline, N 2  gas pipeline  18  equipped with a N 2  gas valve  19 , and a SiF 4  gas pipeline  2  equipped with a SiF 4  gas valve  13 A are joined to a single line extending in two directions, which is connected to a gas exhaust part  21  via an exhaust valve  22  in one direction and to an upper electrode  7  functioning also as the shower head via a final valve  20  in the other direction; and the upper electrode  7  functioning also as the shower head and a high frequency power source  5  are installed in the upper part of the chamber  11 , a lower electrode  9  also functioning as a heater to mount a wafer  8  thereon and a low frequency power source  6  are installed in the lower part of the chamber, and an exhaust part  10  is formed in a side wall of the chamber. Additionally, a N 2  gas pipeline  18  may be installed based on the necessity.  
         [0038]    The CVD film formation will be described below based on respective embodiments of the present invention.  
         [0039]    At first, the CVD film formation will be described with reference to the CVD apparatus of the first embodiment shown in FIG. 1. At first, in a first step, a NH 3  gas valve  15 , a SiH 4  gas valve  16  and the final valve  14  were opened and NH 3  gas and SiH 4  gas were introduced into the chamber  11  through the outer circumferential part  7 A of the upper electrode also functioning as a shower head to form a SiN film. The film formation temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiN film with about 100 nm thickness on the wafer  8  in this step.  
         [0040]    Secondarily, in a second step, after the film formation of the SiN film, the high frequency power source  5  and the low frequency power source  6  were turned off and then the gases remaining in the pipelines from the NH 3  gas valve  15  and the SiH 4  gas valve  16  to the chamber  11  were evacuated.  
         [0041]    Thirdly, in a third step, the final valve  12  was opened to introduce N 2  gas into the chamber  11  through the outer circumferential part  7 A of the upper electrode also functioning as the shower head and the final valve  13  was opened to introduce SiF 4  into the chamber  11  through the center part  7 B of the upper electrode also functioning as the shower head. Further, the SiH 4  gas valve  16  and the final valve  14  were opened to introduce SiH 4  gas into the chamber  11  to form a SiOF film. The substrate temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiOF film with about 800 nm thickness on the wafer  8  in this step.  
         [0042]    Next, in a fourth step, after the film formation of the SiOF film, the high frequency power source  5  and the low frequency power source  6  were turned off and the final valves  12 ,  13  were closed to stop introduction of N 2 O gas and SiF 4  gas, the SiH 4  gas valve  16  was closed to stop introduction of SiH 4  gas and then the gases remaining in the pipelines from the final valves  12 ,  13 , the NH 3  gas valve  15 , and the SiH 4  gas valve  16  to the chamber  11  were evacuated. Hereafter, it was succeeded by the next film formation step.  
         [0043]    In the case of employing this CVD apparatus, since the SiF 4  gas line and the NH 3  gas line were separated, SiF 4  gas and NH 3  gas were inhibited to be mixed with each other in any step in the pipelines and therefore a SiN film and SiOF film were made possible to be successively formed without causing clogging of the pipelines with a production product.  
         [0044]    Next, the CVD film formation will be described with reference to the CVD apparatus of the second embodiment shown in FIG. 2. At first, in a first step, a NH 3  gas valve  15 , a SiH 4  gas valve  16  and the final valve  14  were opened and NH 3  gas and SiH 4  gas were introduced into the chamber  11  through the upper electrode  7  also functioning as a shower head to form a SiN film. At that time, the final valve  13  interlockingly operated with the NH 3  gas valve  15  was closed. The film formation temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiN film with about 100 nm thickness on the wafer  8  in this step.  
         [0045]    Secondarily, in a second step, after the film formation of the SiN film, the high frequency power source  5  and the low frequency power source  6  were turned off, the NH 3  gas valve  15  and the SiH 4  gas valve  16  were closed to stop introduction of NH 3  gas and SiH 4  gas, and the gases remaining in the pipelines from the final valves  12  and  13 , the NH 3  gas valve  15  and the SiH 4  gas valve  16  to the chamber  11  were evacuated.  
         [0046]    Thirdly, in a third step, the final valve  14  was closed and gases remaining in the pipelines from the final valves  12 ,  13 ,  14  to the chamber  11  were evacuated.  
         [0047]    Next, in a fourth step, the final valve  12  was opened to introduce N 2 O gas into the chamber  11  through the outer circumferential part  7 A of the upper electrode also functioning as the shower head and the final valve  13  was opened and further the SiH 4  gas valve  16  and the final valve  14  were opened to introduce SiF 4  and SiH 4  gas respectively into the chamber  11  through the upper electrode  7  also functioning as the shower head to form a SiOF film. At this time, the NH 3  gas valve  15  interlockingly operated with the final valve  13  was closed. The film formation temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiOF film with about 800 nm thickness on the wafer  8  in this step.  
         [0048]    Next, in a fifth step, after the film formation of the SiOF film, the high frequency power source  5  and the low frequency power source  6  were turned off and the final valves  12  and  13  were closed to stop introduction of N 2 O gas and SiF 4  gas, the SiH 4  gas valve  16  was closed to stop introduction of SiH 4  gas and then the gases remaining in the pipelines from the final valves  12  and  13 , the NH 3  gas valve  15 , and the SiH 4  gas valve  16  to the chamber  11  were evacuated.  
         [0049]    Finally, in a sixth step, the final valve  14  was closed and gases remaining in pipelines from the final valves  12 ,  13  and  14  to the chamber  11  were evacuated.  
         [0050]    In the case of employing this CVD apparatus, since SiF 4  gas and NH 3  gas were kept from each other in pipelines in any step and therefore successive film formation was made possible without causing clogging of the pipelines. Further, the configuration of this apparatus, being compared with that of the first embodiment, was so constituted as to utilize the upper electrode  7  also functioning as the shower head in common for respective gases to introduce the gases into the chamber  11  and the apparatus had an advantage that the apparatus could be obtained at a low cost only by reconstructing a conventional CVD apparatus shown in FIG. 5 by replacing only pipelines.  
         [0051]    Next, the CVD film formation will be described with reference to the CVD apparatus of the third embodiment shown in FIG. 3. At first, in a first step, a NH 3  gas valve  15 , a SiH 4  gas valve  16  and the final valve  14  were opened and NH 3  gas and SiH 4  gas were introduced through a NH 3  and SiH 4  gas nozzle  3 A into the chamber  11 A to form a SiN film. The film formation temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About 1,000 to 4,000 W power and about 3,000 to 4,000 W power of the high frequency power sources  5 A and  5 B, receptively, were applied to form a SiN film with about 100 nm thickness on the wafer  8  in this step.  
         [0052]    Secondarily, in a second step, after the film formation of the SiN film, the high frequency power sources  5 A,  5 B were turned off and then the NH 3  gas valve  15  and the SiH 4  gas valve  16  were closed to stop introduction of NH 3  gas and SiH 4  gas and the gases remaining in the pipelines from the final valves  12 ,  13 , the NH 3  gas valve  15  and the SiH 4  gas valve  16  to the chamber  11  were evacuated.  
         [0053]    Thirdly, in a third step, the final valves  12 ,  13  and the SiH 4  gas valve  16  were opened to introduce N 2 O gas, SiF 4  gas and SiH 4  gas into the chamber  11  through a N 2 O gas nozzle  1 A, a SiF 4  gas nozzle  2 A, and a NH 3  and SiH 4  gas nozzle  3 A, respectively, to form a SiOF film. The film formation temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About 1,000 to 4,000 W power and about 3,000 to 4,000 W power of the high frequency power sources  5 A,  5 B were applied to form a SiOF film with about 800 nm thickness on the wafer  8  in this step.  
         [0054]    Next, in a fourth step, after the film formation of the SiOF film, the high frequency power sources  5 A,  5 B were turned off and the final valves  12 ,  13  and the SiH 4  gas valve  16  were closed to stop introduction of N 2 O gas, SiF 4  gas, and SiH 4  gas and then the gases remaining in the pipelines from the final valves  12 ,  13  and the SiH 4  gas valve  16  to the chamber  11  were evacuated.  
         [0055]    In the case of employing this CVD apparatus, since SiF 4  gas and NH 3  gas were kept from each other in pipelines in any step and therefore successive film formation was made possible without causing clogging of the pipelines. Further, compared with that of the first and the second embodiments, the apparatus had an advantage that the apparatus is capable of forming high quality films owing to utilization of high density plasma.  
         [0056]    Next, the CVD film formation will be described with reference to the CVD apparatus of the fourth embodiment shown in FIG. 4. At first, in the first step, a NH 3  gas valve  15 , a SiH 4  gas valve  16 , a NH 3 —SiH 4  gas valve  14 A, and the final valve  20  were opened and NH 3  gas and SiH 4  gas were introduced into the chamber  11  through the upper electrode also functioning as a shower head to form a SiN film. At that time, the SiF 4  gas valve  13 A interlockingly operated with the NH 3  gas valve  15  was closed. The film formation temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiN film with about 100 nm thickness on the wafer  8  in this step.  
         [0057]    Secondarily, in a second step, after the film formation of the SiN film, the high frequency power source  5  and the low frequency power source  6  were turned off and then the NH 3  gas valve  15  and the SiH 4  gas valve  16  were closed to stop introduction of NH 3  gas and SiH 4  gas and the gases remaining in the pipelines from the N 2  gas valve  19 , the SiH 4  gas valve  13 A, the NH 3  gas valve  15 , the SiH 4  gas valve  16 , and the exhaust valve  22  to the chamber  11  were evacuated.  
         [0058]    Thirdly, in a third step, the NH 3 —SiH 4  gas valve  14 A was closed and the N 2  gas valve  19  was opened to fill N 2  gas in pipelines from the SiF 4  gas valve  13 A and the NH 3 —SiH 4  valve  14 A to the exhaust valve  22  and the final valve  20 .  
         [0059]    Next, in a fourth step, the exhaust valve  22  was opened to evacuate the pipelines to vacuum from the N 2  gas valve  19 , the SiF 4  gas valve  13 A and the NH 3 —SiH 4  valve  14 A to the final valve  20 .  
         [0060]    Next, in a fifth step, the N 2 O gas valve  12  was opened to introduce N 2 O gas into the chamber  11  through the upper electrode  7  also functioning as the shower head and the exhaust valve  22  was closed and further the SiF 4  gas valve  13 A and the NH 3 —SiH 4  valve  14 A, the SiH 4  gas valve  16 , and the final valve  20  were opened to introduce SiF 4  and SiH 4  gas respectively into the chamber  11  through the upper electrode  7  also functioning as the shower head to form a SiOF film. At that time, the NH 3  gas valve  15  interlockingly operated with the SiF 4  gas valve  13 A was closed. The substrate temperature and the pressure in the chamber were controlled to be 400° C. and 4 to 5 Torr, respectively. About each 500 W power of the high frequency power source  5  and the low frequency power source  6  was applied to form a SiOF film with about 800 nm thickness on the wafer  8  in this step.  
         [0061]    Next, in a sixth step, after the film formation of the SiOF film, the high frequency power source  5  and the low frequency power source  6  were turned off and the N 2 O gas valve  12  was closed to stop introduction of N 2 O gas and the SiF 4  gas valve  13 A and the SiH 4  gas valve  16  were closed to stop introduction of SiF 4  gas and SiH 4  gas and then the gases remaining in the pipelines from the N 2  gas valve  19 , the SiF 4  gas valve  13 A, the NH 3  gas valve  15 , the SiH 4  gas valve  16  and the exhaust valve  22  to the chamber  11  were evacuated.  
         [0062]    Next, in a seventh step, the NH 3 —SiH 4  gas valve  14 A was closed and the N 2  gas valve  19  was opened to fill N 2  gas in pipelines from the SiF 4  gas valve  13 A, the NH 3 —SiH 4  gas valve  14 A, and the exhaust valve  22  to the final valve  20 .  
         [0063]    Finally, in an eighth step, as same in the fourth step, the exhaust valve  22  was opened to evacuate the pipelines to vacuum from the N 2  gas valve  19 , the SiF 4  gas valve  13 A and the NH 3 —SiH 4  valve  14 A to the final valve  20 .  
         [0064]    In the case of employing this CVD apparatus, since the pipelines were evacuated to vacuum after film formation of the SiN film or the SiOF film, and then N 2  gas was enclosed, and the pipelines were evacuated to vacuum, as compared with the second embodiment, the remaining gases could be evacuated at a high efficiency. As a result, SiF 4  and NH 3  were kept from each other in pipelines in any step and therefore successive film formation was made possible without causing clogging of the pipelines.  
         [0065]    Although in the method for forming a film utilizing the fourth embodiment, the evacuation and N 2  pressurization are repeatedly carried out between the final valve  20  and the exhaust valve  22 , the N 2  filling may be omitted by sufficiently carrying out the evacuation.  
         [0066]    Incidentally, although the foregoing embodiments have been described with reference to the cases of applying the present invention to the parallel plate type plasma CVD apparatus and the high density plasma CVD apparatus, needless to say, the present invention may be applied to a remote plasma CVD apparatus having a configuration in which plasma generated in another site is introduced into the chamber.  
         [0067]    As described above, a plasma CVD apparatus of the present invention for successive formation of a SiN film and SiOF film in one and the same chamber is effective to prevent reaction of SiF 4  gas and NH 3  gas in pipelines in a normal temperature since the NH 3  gas and SiF 4  gas are introduced into the chamber through separate gas lines or through gas lines equipped with separate valves independently interlockingly operated with the NH 3  gas pipeline and the SiF 4  gas pipeline and is, therefore, effective to prevent production of a reaction product [(NH 4 )  2 SiF 6 ] of NH 3  and SiF 4 , and avoid clogging of the pipelines and production of reaction products in the pipelines. Further, since the SiN film and the SiOF film can successively be formed in one and the same chamber, the production cost can be lowered and the throughput can be heightened.  
         [0068]    Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any modifications or embodiments as fall within the true scope of the invention.