Abstract:
A plasma processing apparatus includes an upper electrode which allows a source gas to flow into a vacuum chamber via a shower plate, a lower electrode facing the upper electrode, on which a sample to be processed is placed, and a detector which detects light from the surface of the sample to be processed via the shower plate. The detector includes at least one light introducing section made up of a transparent body to which the light is input and a spectroscope which analyzes the light obtained at the light introducing section. A plurality of the light-introducing through holes are provided in the shower plate for the at least one light introducing section, and the at least one light introducing section is made up of two members.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a division of U.S. application Ser. No. 11/353,165, filed Feb. 14, 2006, the contents of which are incorporated herein by reference. 
         [0002]    The present application is based on and claims priority of Japanese patent application No. 2005-358679 filed on Dec. 13, 2005, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a semiconductor manufacturing apparatus for manufacturing a semiconductor device, and more particularly, to a dry etching technique for etching a semiconductor material such as a silicon and silicon oxide film according to the shape of a mask pattern made of a resist material or the like using plasma. 
         [0005]    2. Description of the Related Art 
         [0006]    Dry etching introduces a source gas into a vacuum chamber having evacuation means, converts the source gas to plasma through electromagnetic radiation, exposes a sample to be processed to the plasma, applies etching to the surface of the sample to be processed except a masked area and thereby obtains a desired shape. A high-frequency voltage which is different from that used for plasma generation is applied to the sample to be processed, ions are accelerated from plasma at the high-frequency voltage, and input to the surface of the sample to be processed, and it is possible to thereby improve etching efficiency and achieve verticality of the processed shape. 
         [0007]    Dry etching judges an end point for judging whether a predetermined amount of etching processing has been completed or not normally through an observation of plasma emission. More specifically, this is done by monitoring an amount of light emission from the material to be etched in plasma or a reaction product of a base material which is exposed when etching is completed. However, with improvement in etching accuracy in recent years and from the standpoint of a cost reduction through simplification of steps, there is a demand for stopping etching processing at some midpoint of a single material or just before finishing the etching instead of finishing the etching with the base material. 
         [0008]    It is not possible to judge an end point of etching to meet this demand using the above described method of monitoring light emission from plasma and it is necessary to directly monitor the amount of etching of the material to be etched or the amount of the remaining film. Monitoring of the amount of etching of the material to be etched or the amount of the remaining film is performed by letting in light from plasma reflected on the surface of the sample to be processed or light from an independently provided light source and analyzing an interference pattern of light due to a decrease of the material to be etched on the surface of the sample to be processed (see, for example, Japanese Patent No. 3643540 (Patent Document 1)). 
         [0009]    An etching apparatus which etches an insulating film material such as a silicon oxide film is provided with a shower plate made of a conductor such as silicon facing the surface of a sample to be processed and applies high-frequency power to the entire conductor including the shower plate to generate plasma. Therefore, it is necessary to place a light introducing section in a conductor electrode section facing the surface of the sample to be processed when the above described amount of etching is calculated through an analysis of an interference pattern of light produced by a decrease of the material to be etched. The light introducing section generally has a structure guiding light to the outside of a vacuum chamber through a transparent body rod of quartz or sapphire or the like and then guiding the light to a light interference pattern analysis section made up of a spectroscope or the like via an optical fibre. 
         [0010]    When the above described transparent body of quartz or sapphire which is the light introducing section is directly exposed to the surface of the shower plate made of silicon or the like, wearing and deposition due to accelerated ions from plasma occur on the transparent body rod end face, preventing light from being let in for an extremely short time. A publicly known example shown in Japanese Patent No. 3643540 (Patent Document 1) adopts a structure to solve the problem, forming a plurality of micro pores into which plasma cannot enter in part of the silicon shower plate and placing a transparent body rod on the back thereof. Adopting this structure can extend the light collection life drastically compared to the case where the transparent body rod is directly exposed to plasma. However, even when the structure shown in Japanese Patent No. 3643540 (Patent Document 1) is used, it becomes difficult to let in light after a discharge time of 100 to 200 hours and it is not possible to achieve a sufficient life depending on the degree of volume production of a semiconductor device. Furthermore, it is possible to extend the life of the light introducing section to a certain degree through improvements such as reducing the diameter of micro pores formed in the shower plate and gaining the aspect ratio or the like, but there is a problem that the light quantity decreases and necessary accuracy cannot be secured. 
         [0011]    It is an object of the present invention to provide a plasma processing apparatus which judges etching end points by measuring an amount of processing using the above described light interference, provided with means capable of making an extension of life of a light introducing section compatible with securing of an amount of light collection and allowing a long-term stable operation and improvement of processing accuracy through accurate detection of an amount of etching. 
         [0012]    The present invention provides a plasma processing apparatus which judges etching end points by measuring an amount of etching of a sample to be processed using light interference on the surface of a sample to be processed, provided with means capable of making an extension of life of a light introducing section compatible with securing of an amount of light collection and allowing a long-term operation and improvement of processing accuracy through accurate detection of an amount of etching. 
       SUMMARY OF THE INVENTION 
       [0013]    An end face of the light introducing section which lets in interference light from the sample to be processed is placed at a distance from a boundary with plasma equal to or greater than 5 times a mean free path of a gas in a vacuum chamber. 
         [0014]    Positioning the end face of the photo-detection section at a distance equal to or greater than 5 times a mean free path of a gas in a vacuum chamber from the boundary with plasma reduces the probability that ions accelerated from plasma may directly arrive at the light introducing section without collision to 1/100 or less. This can drastically reduce wearing of the end face of the light introducing section and extend the life of the light introducing section to a discharge time of 1000 hours or more. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a basic block diagram of a plasma processing apparatus according to a first embodiment of the present invention; 
           [0016]      FIG. 2  illustrates details of the structure of a photo-detection section according to the first embodiment of the present invention; 
           [0017]      FIG. 3  illustrates details of the structure of a photo-detection section according to a conventional system; 
           [0018]      FIG. 4  illustrates multiples of a mean free path and a proportion of atoms/molecules traveling that distance without collision; 
           [0019]      FIG. 5A  illustrates details of the structure of a photo-detection section according to a second embodiment of the present invention; 
           [0020]      FIG. 5B  illustrates details of a modification example of the structure of the photo-detection section according to the second embodiment of the present invention; 
           [0021]      FIG. 5C  illustrates details of another modification example of the structure of the photo-detection section according to the second embodiment of the present invention; and 
           [0022]      FIG. 6  illustrates details of the structure of a photo-detection section according to a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The construction of a first embodiment of a plasma processing apparatus according to the present invention will be explained using  FIG. 1 . 
       Embodiment 1 
       [0024]    In the plasma processing apparatus according to the first embodiment, a discharge electrode  2  is placed in a vacuum chamber  1  at a position facing a sample to be processed  3 . The discharge electrode  2  is made of a metal such as aluminum. A shower plate  4  made of silicon is placed on the surface of the discharge electrode  2 , constituting a structure where a source gas for plasma generation is discharged through micro pores  5  formed over the shower plate  4  into the vacuum chamber  1 . A discharge high-frequency power supply  6  is connected to the discharge electrode  2  via a matching circuit  7 . A 200 MHz high frequency is used for the discharge high-frequency power supply in this embodiment. 
         [0025]    Furthermore, the sample to be processed  3  is placed on a sample setting electrode  8  having an electrostatic adsorption function and held by means of electrostatic adsorption. A high-frequency power supply  9  having a frequency different from the discharge high frequency is connected to the sample setting electrode  8  via a matching circuit  10  so as to apply a high-frequency voltage to the sample to be processed  3 . In this embodiment, 4 MHz is used as the frequency of the high-frequency power applied to the sample to be processed. Furthermore, high-frequency power having the same frequency (4 MHz) as the high frequency applied to the sample to be processed  3  with the phase controlled by phase control means  11  is applied to the discharge electrode  2  via a matching circuit  12 , superimposed on the discharge high-frequency power. 
         [0026]    The high-frequency power applied to the sample to be processed  3  from the high-frequency power supply  9  has the role of accelerating and drawing ions from plasma, can be controlled independently of the discharge high-frequency power supply  6 , and can thereby control energy of ions entering the sample to be processed  3  independently of plasma generation. By applying a phase-controlled high-frequency voltage having the same frequency as the frequency applied to the sample to be processed  3  to the discharge electrode  2  from the high-frequency power supply  9 , it is possible to suppress increases in the plasma potential and reduce unnecessary wearing due to plasma upon the inner wall of the vacuum chamber  1 . Especially, by applying the same frequency yet with a phase 180 degrees different from the high frequency applied to the sample to be processed  3  to the discharge electrode  2 , it is possible to suppress energy of ions incident upon the inner wall of the vacuum chamber  1  while controlling energy of ions incident upon the surface of the sample to be processed  3  and the surface of the discharge electrode  2  (surface of the shower plate  4 ). The application of a phase-controlled high-frequency voltage to the sample to be processed  3  and discharge electrode  2  at a plasma processing apparatus is described, for example, in Japanese Patent Publication No. 2002-184766 (Patent Document 2) or 2003 Proceedings of International Symposium on Dry Process, P43-48 (Non Patent Document 1). 
         [0027]    In the plasma processing apparatus of  FIG. 1 , the discharge electrode  2  is provided with detecting means for detecting reflected light from the surface of the sample to be processed  3  and this detecting means includes a space  13 , a light-introducing rod  14  made up of a transparent body of quartz or the like and spectroscopes  16 , the shower plate  4  is provided with light-collecting micro pores  15 , and the light-introducing rod  14  and spectroscope  16  are connected via an optical fibre  26 . The detecting means is means for detecting a wavelength of reflected light from the surface of the sample to be processed  3  and a variation of light intensity of each wavelength. The above described light-introducing rod  14  according to this embodiment may use any one of quartz, sapphire, YAG (yttrium-aluminum-garnet) and yttria crystal (Y 2 O 3 ), and more preferably, any one of sapphire, YAG (yttrium-aluminum-garnet) and yttria crystal (Y 2 O 3 ). Sapphire, YAG or yttria crystal is expensive, yet generally tends to be less sputtered than quartz and expected to have a longer life than quartz. 
         [0028]    A thermal medium is supplied to the discharge electrode  2  from a temperature control function  24  and a thermal medium is supplied to the sample setting electrode  8  from a temperature control function  25 . Plasma  17  is generated between the shower plate  4  of the discharge electrode and the sample to be processed  3 . An insulator  27  is provided between the vacuum chamber  1  and discharge electrode  2  and a seal  18  is provided around the light-collecting micro pores  15  of the shower plate  4 . 
         [0029]    The structure of a conventional light collection section will be explained using  FIG. 3 . The discharge electrode section is constructed of the discharge electrode  2 , a gas diffusion section  22 , a gas diffusion passage section  23  and the shower plate  4  stacked one atop another and a gas supplied from a gas supply source which is not shown is diffused by the gas diffusion section  22 , passed through the gas diffusion passage section  23  and supplied into the processing chamber through the micro pores  5  provided in the shower plate  4 . A space is provided which penetrates the discharge electrode  2 , gas diffusion section  22  and gas diffusion passage section  23  and reaches the light-collecting micro pores  15  provided in the shower plate  4 , and the light-introducing rod  14  is inserted into this space. An end face  21  of the light-introducing rod  14  is placed in contact with the back of the shower plate  4 . In order to prevent the gas from reaching the space through the gas diffusion pores of the gas diffusion section  22  and gas diffusion section  23 , seals  18  are provided around the space. 
         [0030]    If the light-collecting micro pores  15  formed in the shower plate  4  are formed with a diameter smaller than the thickness of a plasma sheath, they have a plasma shielding function, and therefore plasma cannot enter the space. However, ions accelerated by plasma through the light-collecting micro pores  15  can reach the space. Therefore, if the light-introducing rod end face  21  for light collection is placed right behind the light-collecting micro pores  15  formed in the shower plate  4 , there is a problem that the light-introducing rod end face  21  is etched through ion bombardment and the light collection efficiency decreases in a short time. Since the shower plate  4  normally has a thickness on the order of only 6 to 10 mm, the distance from plasma that can be secured is only 6 to 10 mm right behind the shower plate  4 . For example, when processing is performed under a pressure of 2 Pa, there is only a distance approximately 2 to 3 times the mean free path of gas molecules of a plasma generation gas (the mean free path of a gas molecule of the plasma generation gas at 2 Pa is 3 to 4 mm), and therefore a considerable amount of accelerated ions directly reach the light-introducing rod end face  21 , which results in a problem that the light-introducing rod end face  21  is worn. 
         [0031]    Using  FIG. 2 , details of the structure in the vicinity of the photo-detection section according to the first embodiment of the present invention will be explained. The light-introducing rod  14  which is the photo-detection section is placed on the back of the shower plate  4  of the discharge electrode  2  via the space  13 . This embodiment assumes that the thickness of the shower plate  4  is 10 mm and the length of the space  13  (distance from the back of the shower plate  4  to the light-introducing rod end face  21 ) is 15 mm. A plurality of light-collecting micro pores  15  having a diameter of 0.5 mm are formed within an area of 10 mm in diameter in the space  13  of the shower plate  4 . Reflected light from the sample to be processed  3  is collected by the light-introducing rod  14  via the light-collecting micro pores  15 , a variation of interference light caused by a variation of the film thickness on the surface of the sample to be processed  3  is analyzed using the spectroscope  16  and an amount of processing by plasma is detected in real time. The method of detecting the amount of processing with the variation of interference light caused by the variation of the film thickness on the surface of the sample to be processed  3  is described in aforementioned Japanese Patent No. 3643540 (Patent Document 1). 
         [0032]    This embodiment places the light-introducing rod end face  21  which collects reflected light from the sample to be processed  3  through the light-collecting micropores  15  formed in the shower plate  4  and space  13 . Furthermore, the length of the space  13  is set so that the distance from the shower plate  4  on the plasma side to the light-introducing rod end face  21  is a distance equal to or greater than 5 times the mean free path of gas molecules under a gas pressure condition in a plasma generation atmosphere inside the vacuum chamber  1 . The light-collecting micro pores  15  formed in the shower plate  4  has a plasma shielding function. In this embodiment, the diameter of each of the light-collecting micro pores  15  is 0.4 to 0.5 mm. This prevents plasma from entering the space  13 . According to this embodiment, the end face  21  of the light-introducing rod  14  placed at the back of the space  13  formed on the back of the shower plate from the processing chamber is located at a sufficient distance from the plasma  17 . That is, in this embodiment, the light-introducing rod end face  21  is placed via the space  13  having a length of 15 mm. Therefore, the distance from the plasma  17  to the light-introducing rod end face  21  is 25 mm, gaining a distance 7 to 8 times the mean free path of gas molecules in an atmosphere of 2 Pa. Thus, the light-introducing rod end face  21  involves almost no ion irradiation, has fewer occasions when the end face is worn, and can thereby obtain a long life. 
         [0033]    The proportion of molecules/atoms that travel without collision to a multiple of a mean free path is shown using  FIG. 4 . The proportion of molecules/atoms that travel without collision decreases exponentially with respect to multiples of the mean free path. From  FIG. 4 , the probability that molecules/atoms can travel a distance approximately 5 times the mean free path falls to or below 1% and most molecules/atoms collide with one another in the vapor phase and lose initial kinetic energy. In distances approximately 7 to 8 times the mean free path, the probability that molecules/atoms can travel without collision falls to or below 0.1%. 
         [0034]    Thus, with the construction shown in this embodiment, ions accelerated from the plasma  17  that can reach the light-introducing rod end face  21  without collision falls to or below 0.1%. When the light-introducing rod end face  21  is placed right behind the shower plate  4  which is the conventional method shown in  FIG. 3 , the mean free path is 2 to 3 times, and therefore according to  FIG. 4 , the proportion of ions that reach the light-introducing rod end face  21  without collision is approximately 5% to 15%. Therefore, according to the construction of this embodiment, the proportion of ions that reach the light-introducing rod end face  21  without collision is 1/50 to 1/150 compared to the conventional construction and it is possible to drastically extend the life of the light-introducing rod end face  21 . The result of an actual evaluation shows that this embodiment secures an enough amount of light collection for a discharge time of 1000 hours, equal to or greater than 5 times that of the conventional system. 
         [0035]    Also in the conventional structure of  FIG. 3 , by letting the source gas of plasma discharged from the shower plate  4  discharge from the light-collecting micro pores  15 , it is possible to drastically increase the pressure in the light-collecting micro pores  15  compared to that in the vacuum chamber  1  and even a thickness of the light-collecting micro pores  15  of only approximately 10 mm can have a distance equal to or greater than 5 times the mean free path. However, in this case, since the light-collecting micro pores  15  provided for light collection are formed concentrated on one location, the density of pores is much higher than that of the micro pores  5  for gas discharging, and a large amount of the plasma generation gas is discharged from the light-collecting micro pores  15 , deteriorating the uniformity of gas supply by the shower plate  4 . Furthermore, depending on the conditions, discharging a large amount of gas from the light-collecting micro pores  15  provokes discharge in the micro pores, which disables detection of reflected light from the wafer. Therefore, the first embodiment provides the seals  18  to prevent the source gas for plasma formation from being discharged from the light-collecting micro pores  15  formed in the shower plate  4 . These seals  18  keep the gas pressure inside the light-collecting micro pores  15  and the space  13  to substantially the same level as that in the vacuum chamber  1 . 
       Embodiment 2 
       [0036]    A second embodiment of the present invention will be explained using  FIG. 5A . As in the case of  FIG. 2  of the first embodiment,  FIG. 5A  illustrates details of the structure of a photo-detection section formed in a discharge electrode  2 . A gas diffusion passage section  23  is provided with a conductor section  19  in  FIG. 5A . The conductor section  19  includes similar micro pores aligned with light-collecting micro pores  15  of a shower plate  4  right behind the shower plate  4 . 
         [0037]    In the structure of  FIG. 2  according to the first embodiment shown above, the space  13  is placed right behind the shower plate  4 . In the structure of  FIG. 2 , a discharge high frequency may enter the space  13  and produce discharge inside the space  13  depending on the resistance value of the shower plate  4 . Therefore, the second embodiment in  FIG. 5A  provides the conductor section  19  having a length of several mm (assumed to be 3 mm in this Embodiment 2) right behind the shower plate  4  provided with micro pores similar to those in the shower plate  4  and places a light-introducing rod end face  21  after this via a space  13 . This Embodiment 2 produces a loss of light quantity at the conductor section  19  compared to the foregoing Embodiment 1, but setting the length of the conductor section  19  to 1 to 5 mm makes it possible to minimize the amount of loss. The provision of the conductor section  19  completely shuts off the high-frequency power entering the space  13 , thus preventing discharge from occurring in the space  13 . 
         [0038]      FIG. 5B  shows a modification example of the second embodiment in the case where the area of the space  13  in the embodiment of  FIG. 5A  is filled with the light-introducing rod  14  and the light-introducing rod end face  21  is extended up to the top of the gas diffusion passage section  23 . 
         [0039]    In the embodiment of  FIG. 5A , the light-introducing rod end face  21  is placed at a sufficient distance from the plasma boundary, but the space  13  causes the light quantity at the light-introducing rod end face  21  to be decreased. Therefore, in  FIG. 5B , the light-introducing rod  14  is placed up to the top of the gas diffusion passage section  23  so as to collect most of light which has passed through the micro pores of the light-collecting micro pores  15  and conductor section  19  of the shower plate  4  and allow the light to transmit up to the top surface of the light-introducing rod  14 . If a distance equal to or greater than 5 times the mean free path is secured for the distance from the plasma boundary to the light-introducing rod end face  21  by means of the thickness of the shower plate  4  and the thickness of the conductor of the gas diffusion passage section  23 , it is possible to secure a sufficient life of the end face of the light-introducing rod  14 . 
         [0040]      FIG. 5C  shows another modification example of the second embodiment. In the embodiment of  FIG. 5B , the single light-introducing rod  14  is extended up to the top of the gas diffusion passage section  23 . In contrast, in  FIG. 5C , the light-introducing rod  14  consists of two pieces. More specifically, a fore-end section  30  is provided between the light-introducing rod  14  and gas diffusion passage section  23 . The material of the fore-end section  30  is basically the same as that of the light-introducing rod  14 , yet preferably anyone of sapphire, YAG (yttrium-aluminum-garnet) and yttria crystal (Y 2 O 3 ) is used. Though sapphire, YAG or yttria crystal is expensive, it is generally less likely to be sputtered compared to quartz and a longer life is expected than the case where quartz is used. 
         [0041]    It is also possible to extend the life of the light-introducing rod  14  even with the construction in  FIG. 5B , but there is no change in the fact that the light-introducing rod  14  is a consumable. In the construction in  FIG. 5C , the fore-end section  30  is provided as another piece, and therefore in the case of replacement, only the fore-end section  30  needs to be replaced, which improves the easiness of replacement operation and reduces the replacement cost. Therefore, if the light-introducing rod  14  is made of, for example, quartz and the fore-end section  30  is made of any one of sapphire, YAG, yttria crystal, it is possible to realize both cost reduction and extension of life in a well-balanced manner. 
       Embodiment 3 
       [0042]    A third embodiment of the present invention will be explained using  FIG. 6 .  FIG. 6  shows details of the structure of a photo-detection section formed in a discharge electrode  2  as in the case of  FIG. 2  of the first embodiment. In the embodiment of  FIG. 6 , a light-introducing rod end face  21  for light collection is placed right behind a shower plate  4 , but it is structured in such a way that a gas whose flow rate is controlled independently of the discharge source gas is discharged by gas introducing means  20  from light-collecting micro pores  15  formed in the shower plate  4  into a vacuum chamber  1  via the periphery of a light-introducing rod  14 . 
         [0043]    By flowing the gas from the gas introducing means  20  into the light-collecting micro pores  15 , it is possible to increase the gas pressure in the light-collecting micro pores  15  a great deal and secure a distance equal to or greater than 5 times the mean free path of plasma gas molecules sufficiently with only the thickness of the shower plate  4 . In this way, even when the light-introducing rod end face  21  is placed right behind the shower plate  4 , the probability that directly accelerated ions constituting plasma may reach is reduced considerably, making it possible to suppress damage to the light-introducing rod end face  21 . 
         [0044]    By flowing a gas whose flow rate is controlled independently of a source gas for discharge formation through the sealed light-collecting micro pores  15 , it is possible to prevent disturbance in the uniformity of supplies of the source gas from the shower plate  4  explained in the foregoing Embodiment 1. Furthermore, using an inert gas such as helium, argon, krypton, xenon or nitrogen as the gas flowing into the light-collecting micro pores  15  by the gas-introducing means  20  eliminates almost all influences on the original plasma processing. The inert gas discharged may be of one kind or may be a mixture of a plurality of kinds of inert gases. 
         [0045]    In the above described first embodiment, second embodiment and third embodiment, a coolant for cooling is flown through the discharge electrode  2  and sample setting means  8  and their temperatures are controlled by temperature control functions  24 ,  25  respectively. 
         [0046]    In the above described first embodiment, second embodiment and third embodiment 3, high-frequency power to be applied to the sample to be processed  3  is phase-controlled and applied to the discharge electrode  2 , superimposing on the discharge high-frequency power, but equivalent effects of the present invention can also be obtained by applying only discharge high-frequency power to the discharge electrode  2  or applying high-frequency power having a frequency which is different from that applied to the sample to be processed  3 , superimposed on the discharge high-frequency power.