Abstract:
A predetermined gas, which differs from a cleaning gas and is not required to be decomposed for evacuation, is introduced into a film deposition chamber provided upstream of a main process, wherein a cleaning gas for cleaning the film deposition chamber is introduced into the film deposition chamber, and plasma is developed to decompose the cleaning gas, thereby cleaning up the film deposition chamber. Plasma is developed before introduction of the cleaning gas. Alternatively, subsequent to the main process, a predetermined gas, which differs from the cleaning gas and is not required to be decomposed for evacuation, is introduced into the film deposition chamber, and plasma development is continued from the main process. A cleaning gas may be evacuated after substantially totally decomposed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of decomposing cleaning gas used for cleaning a film deposition chamber, in which a film for forming an electronic circuit device is deposited on a wafer. More particularly, the present invention relates to a method of decomposing cleaning gas used in a thin film deposition process for forming a functional component typified by a semiconductor device or a liquid crystal display device. 
     2. Background Art 
     A process for fabricating an electronic device, such as a semiconductor device or a liquid crystal element, has inevitably includes a process of depositing a thin film within a thin film deposition chamber. Such film may be a silicon oxide (SiO) film, a silicon nitride (SiN) film, a silicon (Si) film, a tungsten (W) film, or a tungsten silicide (WSi) film. 
     In the thin film deposition chamber, when a thin film is deposited on an element which is under manufacture, same film is gradually accumulated and stored within the thin film deposition chamber. Such accumulated film may be exfoliated from the chamber and become the source of dust, thereby involving a risk of increasing the amount of defects in the film used for forming an element. In order to prevent generation of the dust, the interior of the thin film deposition chamber must be periodically cleaned. 
     The cleaning gas is eventually emitted to the atmosphere. For example, in the case of nitrogen trifluoride (NF 3 ), in a final emission phase the concentration of NF 3  must be controlled to an allowable level of the order of ppm. 
     FIG. 8 is a descriptive view for describing the concept of conventional plant-wide gas exhaust facilities. 
     In FIG. 8, reference numeral  10  designates a thermal CVD system for depositing a tungsten film;  21  designates a pump;  22  designates an NF 3  gas decomposer;  23  designates a plant-wide decomposer; and  24  and  25  designate other thin film deposition apparatus. 
     As shown in FIG. 8, an actual plant is equipped with a number of thin film deposition systems  10 ,  24 , and  25 , and the respective thin film deposition systems  10 ,  24 , and  25  emit gases. The thus-emitted gases are collected in the plant-wide decomposer  23  connected to the thin film deposition systems  10 ,  24 , and  25 , where the gases are subjected to decomposing until they are brought to a safe exhaust level and are discharged to the atmosphere. 
     In this case, for example, the gas emitted from the CVD system  10  is decomposed by means of the stand-alone NF 3  gas decomposer  22  which is specifically designed for removing NF 3  and is disposed between the CVD system  10  and the plant-wide decomposer  23 . After having been decomposed to a safe exhaust level at which it can be mixed with other gases, the gas is emitted to the plant-wide decomposer  23 . 
     If no plasma is developed in the CVD system  10 , the film deposition room cleaning gas is not decomposed, and the NF 3  gas decomposer  22  is required to decompose the cleaning gas. 
     For example, in the case of a thin film deposition apparatus, such as the CVD system  10 , at the time of purchase of the thin film deposition apparatus, the user must purchase a standalone gas decomposer specifically designated for use with the thin film deposition apparatus. Further, the user must bear costs for operating the gas decomposer. 
     SUMMARY OF THE INVENTION 
     The present invention has been conceived to solve these problems, and the object of the present invention is to provide a processing method which prevents emission of gas to be filtered at the time of cleaning of a processing system, reduces the toxicity of exhaust gas from a plant, and diminishes the necessity for an apparatus designated for filtering purpose. 
     According to one aspect of the present invention, in a method of decomposing a cleaning gas introduced into a film deposition chamber, a predetermined gas is introduced into the film deposition chamber and a plasma is developed before introduction of a cleaning gas in a preliminary process. The predetermined gas is different from the cleaning gas and is not required to be decomposed for evacuation. In a main process subsequent to the preliminary process, the cleaning gas is introduced into the the film deposition chamber, and plasma is developed to decompose the cleaning gas for cleaning a deposited film in the film deposition chamber, whereby the cleaning gas is evacuated while being substantially totally decomposed. 
     According to another aspect of the present invention, in a method of decomposing a cleaning gas introduced into a film deposition chamber, the cleaning gas is introduced into the the film deposition chamber, and plasma is developed to decompose the cleaning gas for cleaning a deposited film in the film deposition chamber in a main process. In a subsequent process, a predetermined gas is introduced into the film deposition chamber and development of plasma is continued subsequent to the main process. The predetermined gas is different from the cleaning gas and is not required to be decomposed for evacuation, whereby the cleaning gas is evacuated while being substantially totally decomposed. 
     In another aspect, the preliminary process, the main process and the subsequent process as described above may be combined in series. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS.  1 ( a ) through ( d ) shows descriptive views for describing a conventional method for cleaning a film deposition chamber, for comparison with a first embodiment of the present invention. 
     FIGS.  2 ( a ) through ( d ) show views for describing a method of decomposing a cleaning gas introduced into a film deposition chamber for cleaning the film deposition chamber according to a first embodiment of the present invention. 
     FIGS.  3 ( a ) through ( c ) show descriptive views for describing a conventional method for cleaning a film deposition chamber, for comparison with a second embodiment of the present invention. 
     FIGS.  4 ( a ) through ( c ) show views for describing a method of decomposing a cleaning gas introduced into a film deposition chamber for cleaning the film deposition chamber according to the second embodiment. 
     FIGS.  5 ( a ) through ( c ) show descriptive views for describing a conventional method for cleaning a film deposition chamber, for comparison with a third embodiment of the present invention. 
     FIGS.  6 ( a ) through ( c ) show views for describing a method of decomposing a cleaning gas introduced into a film deposition chamber for cleaning the film deposition chamber according to the third embodiment. 
     FIG. 7 is a conceptual view showing an outline of structure of a plant decomposing system according to the present invention. 
     FIG. 8 is a descriptive view for describing the concept of conventional plant-wide gas exhaust facilities. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described hereinbelow by reference to the accompanying drawings. Throughout the drawings, like reference numerals are assigned to like or corresponding elements, and repetition of their explanations may be simplified or omitted for brevity. 
     First Embodiment 
     A first embodiment of the present invention will be described in comparison with a conventional example, in which an application of the present invention to a thermal CVD system for depositing a tungsten (W) film is taken as an example. 
     FIG. 1 shows descriptive views for describing a conventional method for comparison. Processing is performed in sequence of ( a ), ( b ) and ( c ) in FIG.  1 . ( d ) in FIG. 1 is a table showing comparison of the respective processing steps in terms of development of plasma and inflow of NF 3  gas. 
     An explanation will first be given of a conventional cleaning method. In a process prior to a cleaning process, a tungsten film is deposited on a wafer within a CVD system  10  for depositing a tungsten (W) film (hereinafter referred to simply as a “CVD system  10 ”), and then the wafer having the tungsten film deposited thereon is withdrawn from the CVD system  10 . 
     When the CVD system  10  is cleaned, NF 3  gas is introduced into a film deposition chamber  11  in step  1  shown in ( a ) in FIG.  1 . In step  1 , NF 3  gas is emitted from the CVD system  10  by way of an exhaust port  15  without being decomposed. Reference numeral  12  designates a heater for heating a wafer;  13  designates a tungsten film deposited on the heater  12 ; and  14  designates a gas head for introducing cleaning gas (NF 3  gas is employed in this embodiment). 
     In step  2  shown in ( b ) of FIG. 1, plasma  16  is developed in NF 3  gas, whereby NF 3  gas is decomposed into N 2  and F 2  ions. The thus-decomposed elements react with tungsten to form WF 6 , with the result that the tungsten film  13  deposited on the heater  12  is decomposed, removed, and cleaned. 
     In step  3  shown in ( c ) of FIG. 1, development of plasma is stopped, and then the supply of NF 3  gas is stopped. 
     ( d ) of FIG. 1 shows the state of development of plasma and the state of introduction of NF 3  gas in the three respective processing steps. As shown in ( d ) of FIG. 1, under the conventional method, there is a case where NF 3  gas is introduced into the CVD system  10  while no plasma is being developed. In this case, NF 3  gas is emitted from the film deposition chamber  11  by way of the exhaust port  15  without being decomposed. 
     Therefore, as shown in FIG. 8, a designated NF 3  gas decomposer  22  is needed to follow the pump  21  which evacuates NF 3  gas by means of suction. 
     In order to eliminate the necessity for the NF 3  gas decomposer  22 , the present embodiment is directed toward preventing emission of cleaning gas, such as NF 3  gas, that is not decomposed. 
     FIG. 2 shows views for describing a method of eliminating cleaning gas according to a first embodiment of the present invention. 
     In the present embodiment, in a process prior to the cleaning process, a tungsten film has been deposited on a wafer within the CVD system  10 , and then the wafer having the tungsten film deposited thereon is withdrawn from the CVD system  10 . 
     In the cleaning process where the CVD system  10  is cleaned, gas other than the cleaning gas; that is, H 2  gas for example, which is less likely to damage the interior of the film deposition chamber  11  as a result of plasma development, is introduced into the CVD system  10  in step  1  (a preceding process) shown in ( a ) of FIG.  2 . Plasma is developed substantially simultaneously with introduction of the H 2  gas. Reference numeral  12  designates a heater for heating a wafer;  13  designates a tungsten film deposited on the heater  12 ;  14  designates a gas head for introducing a cleaning gas (H 2  gas is employed in this embodiment) or another gas; and  15  designates an exhaust port. 
     The thus-introduced H 2  gas is decomposed into H +  ions by means of plasma development, and the H +  ions are emitted by way of the exhaust port  15 . 
     In step  2  (main process) shown in ( b ) of FIG. 2, NF 3  gas is introduced into the CVD system  10  in lieu of H 2  gas. Plasma  16  is developed in the NF 3  gas, whereby the gas is decomposed into N 2  and F 2  ions. The ions react with tungsten to form WF 6 . In this way, the tungsten film  13  deposited on the heater  12  is decomposed and removed, thereby cleaning the film deposition chamber  11 . 
     When the cleaning operation is terminated, in step  3  (subsequent process) shown in ( c ) of FIG. 2, the introduction of NF 3  gas is stopped, and H 2  gas is introduced into the CVD system  10  in lieu of NF 3  gas. The thus-introduced H 2  gas is decomposed into H +  ions by means of plasma development, and the H +  ions are emitted. Subsequently, development of plasma is stopped after the residual NF 3  gas has been evacuated from the inside of the film deposition chamber  11 . During steps  1  through  3 , plasma is developed continuously. 
     ( d ) of FIG. 2 shows the state of plasma development and the state of introduction of NF 3  gas in the three processing steps. As shown in ( d ) of FIG. 2, in the present embodiment, plasma is developed before introduction of NF 3  gas and is continued for a while after introduction of NF 3  gas has been stopped. Accordingly, the NF 3  gas is completely decomposed. 
     As mentioned above, in the present embodiment, the cleaning gas can be decomposed by utilization of the film deposition chamber  11 . More specifically, the cleaning gas is introduced into the film deposition chamber  11  only while plasma is being developed in the CVD system  10 . 
     In the present embodiment, in order to prevent NF 3  gas from being evacuated without being decomposed, gas other than the cleaning gas; for example, H 2  gas, which is less likely to damage the interior of the film deposition chamber  11  as a result of plasma development is introduced, and plasma is developed substantially simultaneously with introduction of H 2  gas. 
     During a period in which NF 3  gas is introduced into the film deposition chamber  11 , plasma is inevitably developed, to thereby prevent evacuation of NF 3  gas that has not been decomposed. 
     Therefore, there is eliminated a necessity for providing the dedicated NF 3  gas decomposer downstream of the CVD system  10  in the plant decomposing system. 
     FIG. 7 is a conceptual view showing the outline of structure of the plant decomposing system according to the first embodiment. As shown in FIG. 7, gas is evacuated from the CVD system  10  through use of the pump  21 , and the thus-evacuated gas can be sent directly to the plant-wide decomposer  23 . Reference numerals  24  and  25  designate other thin film deposition systems, which do not originally require a designated gas decomposer respectively and connected to the common plant-wide decomposer  23 . 
     According to the first embodiment, there can be prevented evacuation of the cleaning gas that is required to be decomposed during the cleaning of the film deposition chamber, thus reducing the toxicity of exhaust gas. 
     Further, there can be eliminated a necessity for a dedicated gas decomposer specifically designated for the type of cleaning gas and provided downstream of the CVD system. 
     Thus, the plant decomposing system does not require a dedicated gas decomposer or composers for individual film deposition systems, thus contributing to a reduction in facility costs. 
     Second Embodiment 
     A second embodiment of the present invention will be described in comparison with a conventional example, in which an application of the present invention to a thermal CVD system for depositing a tungsten (W) film is taken as an example. 
     FIG. 3 show descriptive views for describing a conventional method for comparison. Processing is performed in sequence from ( a ) to ( b ) of FIG.  3 . ( c ) in FIG. 3 is a table showing comparison in respective two processing steps in terms of development of plasma and inflow of NF 3  gas. 
     According to the conventional method, a tungsten film has been deposited on a wafer within the CVD system  10 , and thereafter the wafer having the tungsten film deposited thereon is withdrawn from the CVD system  10 . 
     In order to clean the CVD system  10 , NF 3  gas is introduced into the film deposition chamber  11  in step  1  shown in ( a ) of  3 . In step  1 , NF 3  gas is evacuated from the CVD system  10  by way of the exhaust port  15  without being decomposed. 
     Plasma  16  is developed in NF 3  gas in step  2  shown in ( b ) of FIG. 3, so that NF 3  gas is decomposed into N 2  and F 2  ions. The thus-decomposed ions react with tungsten to form WF 6  or like compounds. Accordingly, the tungsten film  13  deposited on the heater  12  is eliminated. Subsequently, development of plasma and introduction of NF 3  gas are stopped. 
     ( c ) of FIG. 3 is a table showing the state of development of plasma and the state of introduction of NF 3  gas in the two respective processing steps. As shown in ( c ) of FIG. 3, under the conventional method, there is a case where NF 3  gas is introduced into the film deposition chamber  11  while no plasma is being developed. In this case, NF 3  gas is evacuated from the film deposition chamber  11  by way of the exhaust port  15  without being decomposed. 
     Therefore, as shown in FIG. 8, the designated NF 3  gas decomposer  22  must follow the pump  21  which excavates NF 3  gas by means of suction. 
     In order to eliminate the necessity for the NF 3  gas decomposer  22 , the second embodiment of the present invention is directed toward preventing the cleaning gas, such as NF 3  gas, from being evacuated without being decomposed. 
     FIG. 4 show views for describing a method of eliminating cleaning gas according to the second embodiment. 
     In the present embodiment, after a tungsten film has been deposited on a wafer within the CVD system  10  prior to a cleaning process, the wafer having the tungsten film deposited thereon is withdrawn from the CVD system  10 . 
     When the CVD system  10  is cleaned in the cleaning process, gas other than the cleaning gas; for example, H 2  gas, which is less likely to damage the interior of the film deposition chamber  11  as a result of plasma development, is introduced into the CVD system  10  in step  1  (a preceding process) shown in ( a ) of FIG.  4 . Plasma is developed substantially simultaneously with introduction of the H 2  gas. The thus-introduced H 2  gas is decomposed into H +  ions by means of plasma development, and the H +  ions are emitted by way of the exhaust port  15 . 
     In step  2  (main process) shown in ( b ) FIG. 4, NF 3  gas is introduced into the film deposition chamber  11  in lieu of H 2  gas. Plasma  16  is developed in NF 3  gas, whereby the gas is decomposed into N 2  and F 2  ions. The ions react with tungsten to form WF 6 . In this way, the tungsten film  13  deposited on the heater  12  is decomposed and removed, thus cleaning the film deposition chamber  11 . 
     In order to terminate the cleaning operation, introduction of NF 3  gas is stopped, and plasma development is stopped when residual NF 3  gas that has not reacted is found to have been eliminated. 
     ( c ) in FIG. 4C shows the state of development of plasma and the state of introduction of NF 3  gas in the two respective processing steps. As shown in ( c ) of FIG. 4, in the present embodiment, plasma is developed before introduction of NF 3  gas and is continued for a while after introduction of NF 3  gas has been stopped. 
     As described above, in the present embodiment, in order to prevent NF 3  gas from being evacuated without being decomposed, gas other than the cleaning gas; for example, H 2  gas, which is less likely to damage the interior of the film deposition chamber  11  as a result of plasma development is introduced, and plasma is developed substantially simultaneously with introduction of H 2  gas. 
     During a period in which NF 3  gas is introduced into the film deposition chamber  11 , plasma is inevitably developed, to thereby prevent evacuation of NF 3  gas that has not been decomposed. 
     Therefore, there is eliminated a necessity for providing the dedicated NF 3  gas decomposer downstream of the CVD system  10  in the plant decomposing system. 
     FIG. 7 is a conceptual view showing the outline of the structure of the plant decomposing system utilizing the second embodiment. As shown in FIG. 7, gas is evacuated from the CVD system  10  through use of the pump  21 , and the thus-evacuated gas can be sent directly to the plant-wide decomposer  23 . 
     According to the second embodiment, evacuation of the cleaning gas that is required to be decomposed can be prevented during the cleaning of the film deposition chamber, thus reducing the toxicity of exhaust gas. 
     Further, there can be eliminated a necessity for a dedicated gas decomposer specifically designed for the type of cleaning gas and provided downstream the CVD system. 
     The plant decomposing system does not require a dedicated gas decomposer of composers for individual film deposition system, thus contributing to a reduction facility costs. 
     Third Embodiment 
     A third embodiment of the present invention will be described in comparison with a conventional example, in which an application of the present invention to a thermal CVD system for depositing a tungsten (W) film is taken as an example. 
     FIG. 5 show descriptive views for describing a conventional method for comparison. Processing is performed in sequence from ( a ) to ( b ) in FIG.  5 . ( c ) in FIG. 5 is a table showing comparison of the two respective processing steps in terms of development of plasma and inflow of NF 3  gas. 
     According to the conventional method, after a tungsten film has been deposited on a wafer within the CVD system  10 , the wafer having the tungsten film deposited thereon is withdrawn from the CVD system  10 . 
     When the CVD system  10  is cleaned, in step  1  shown in ( a ) of FIG. 5, NF 3  gas is introduced into the film deposition chamber  11  simultaneously with development of plasma  16 , so that NF 3  gas is decomposed into N 2  and F 2  ions. The thus-decomposed ions react with tungsten to form WF 6  or like compounds. Accordingly, the tungsten film  13  deposited on the heater  12  is decomposed and eliminated, thereby cleaning the film deposition chamber  11 . 
     Subsequently, in step  3  shown in ( b ) of FIG. 5, development of plasma and introduction of NF 3  gas are stopped. 
     ( c ) of FIG. 5 is a table showing the state of development of plasma and the state of introduction of NF 3  gas in the two respective processing steps. As shown in ( c ) of FIG. 5, under the conventional method, there is a case where NF 3  gas is introduced into the film deposition chamber  11  while no plasma is being developed. In this case, NF 3  gas is evacuated from the film deposition chamber  11  by way of the exhaust port  15  without being decomposed. 
     Therefore, as shown in FIG. 8, the designated NF 3  gas decomposer  22  must be provided downstream of the pump  21  which evacuates NF 3  gas by means of suction. 
     In order to eliminate the necessity for the NF 3  gas decomposer  22 , the present embodiment is directed toward preventing the cleaning gas, such as NF 3  gas, from being evacuated without being decomposed. 
     FIG. 6 show views for describing a method of eliminating cleaning gas according to the third embodiment. 
     In the present embodiment, after a tungsten film has been deposited on a wafer within the CVD system  10  prior to a cleaning process, the wafer having the tungsten film deposited thereon is withdrawn from the CVD system  10 . 
     When the CVD system  10  is cleaned in the cleaning process, plasma  16  is developed in step  1  (a preceding process) shown in ( a ) of FIG.  6 . NF 3  gas is introduced substantially simultaneously with or immediately after development of plasma  16 . As a result of development of plasma  16  in NF 3  gas, NF 3  gas is decomposed by plasma into N 2  and F 2  ions. The thus-decomposed ions react with tungsten to form WF 6  or like compounds. Accordingly, the tungsten film  13  deposited on the heater  12  is decomposed and eliminated, thereby cleaning the film deposition chamber  11 . 
     Subsequently, in order to terminate the cleaning operation, introduction of NF 3  gas is stopped in step  2  (subsequent process) shown in ( b ) of FIG. 6. H 2  gas is introduced into the film deposition chamber  11  in lieu of NF 3  gas. The thus-introduced H 2  gas is decomposed into H +  ions by means of plasma, and the ions are evacuated. Subsequently, plasma development is stopped when residual NF 3  gas that has not reacted is found to have been eliminated. 
     ( c ) in FIG. 6 shows the state of development of plasma and the state of introduction of NF 3  gas in the two respective processing steps. As shown in ( c ) of FIG. 6, in the present embodiment, development of plasma is continued even after introduction of NF 3  gas has been stopped, whereby NF 3  gas is completely decomposed. 
     As described above, in the present embodiment, in order to prevent NF 3  gas from being evacuated without being decomposed, NF 3  gas is introduced substantially simultaneously with development of plasma. After introduction of NF 3  gas has been stopped subsequent to completion of the cleaning operation, there is introduced gas other than the cleaning gas; for example, H 2  gas, which is less likely to damage the interior of the film deposition chamber  11  as a result of plasma. 
     During a period in which NF 3  gas is introduced into the film deposition chamber  11 , plasma is inevitably developed, to thereby prevent evacuation of NF 3  gas that has not been decomposed. 
     Therefore, there is eliminated a necessity for providing the respective dedicated NF 3  gas decomposer downstream of the CVD system  10  in the plant decomposing system. 
     FIG. 7 is a conceptual view showing the outline of the structure of the plant decomposing system utilizing the third embodiment. As shown in FIG. 7, gas is evacuated from the CVD system  10  through use of the pump  21 , and the thus-evacuated gas can be sent directly to the plant-wide decomposer  23 . 
     Thus, according to the third embodiment, there can be prevented evacuation of the cleaning gas that is required to be decomposed during the cleaning of the film deposition chamber, thus reducing the toxicity of exhaust gas. 
     Further, there can be eliminated a necessity for a dedicated gas decomposer specifically designed for the type of cleaning gas and provided downstream of the CVD system respectively. 
     Thus, the plant decomposing system does not require a dedicated gas decomposer respectively, thus contributing to a reduction in facility costs. 
     In summary, the present invention embodied in the manner as mentioned above yields the following advantages results. 
     According to the present invention, there can be prevented evacuation of cleaning gas which is required to be decomposed during the cleaning of the film deposition chamber, thus reducing the toxicity of exhaust gas. 
     Further, there can be eliminated a necessity for a dedicated gas decomposer specifically designed for the type of cleaning gas and provided downstream of the CVD system respectively. 
     The plant decomposing system does not require a dedicated gas decomposer respectively, thus contributing to a reduction in facility costs. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may by practiced otherwise than as specifically described. 
     The entire disclosure of a Japanese Patent Application No. 11-167343, filed on Jun. 14, 1999 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.