Abstract:
A Plasma processing method and apparatus exhibit excellent characteristics of reducing the amount of electric charge on a plasma-processed processing-object substrate and of preventing plasma damage and dielectric breakdown. Before the processing-object substrate is plasma-processed, top-and-bottom surfaces of the processing-object substrate are simultaneously subjected to a weak plasma in gas composed mainly of inert gas, which makes it possible to neutralize the charges on the processing-object substrate. The inert gas is any one of Ar, He, N 2 , H 2 , and vaporized H 2 O gas or a mixed gas of these gases.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a plasma processing method and apparatus which can be used for thin-film circuit formation methods in semiconductor and thin-film display industries thin-film circuit formation and, in particular, which allow transistor devices to be formed on such highly insulative substrates as glass, quartz, and compound semiconductors. The present invention also relates to a plasma processing method and apparatus capable of efficiently reducing occurrence of device damage and device breakage that otherwise might occur when a processing-object substrate, which has already been in a charge-stored state since before plasma processing, is subjected to plasma processing in such a charge-stored state. 
   In recent years, in thin-film device manufacturing fields, there has been a growing demand for process simplification and manufacturing-method modifications toward those which involve less environmental loads, from the viewpoints of manufacturing cost and environmental protection. Thus, there are desires for advancement from conventional engineering methods using chemicals toward engineering methods, as well as apparatuses, in which thin-film processing is performed by applying plasma. 
   However, such thin-film devices as shown above are manufactured through a wide variety of manufacturing steps, including, for example, a step of heat treatment, a step of water washing treatment, and a step using the plasma application. As a result of this, there are possibilities, at all times, of occurrence of electric charge storage on the top and bottom of the processing-object substrate from various factors. 
   Thin-film processing and apparatuses using the application of plasma, which include the steps of generating plasma in a vacuum, alienating process gas, and performing processing in combination of physical and chemical reactions by ions and radicals, would involve generation of much larger amounts of charges on the processing-object substrate. 
   With regard to the charges generated in large amounts, although a dielectric film for insulating metal films is formed as a thin film, involving a threshold value for withstanding voltage in terms of the structure of thin-film circuits, there are cases where if the processing-object substrate is charged and electrified with such charges at which the threshold value would be exceeded, a breakdown of the dielectric film would occur, making it impossible to make up a thin-film circuit. For this reason, it has conventionally been discussed and practiced to use a plasma that would be charged on the processing-object substrate as little as possible, or to reduce the given charges by devising plasma process measures. 
   Hereinbelow, a typical form of dry etching apparatus is explained with reference to  FIG. 3 . 
   Reference numeral  101  denotes a plasma processing vessel for performing a dry etching process,  101   a  denotes a process gas and inert-gas introducer,  102  denotes an electrode having functions of generating a plasma and serving for placing thereon a processing-object substrate (i.e., a substrate to be processed)  112 ,  103  denotes an evacuator,  104  denotes a vacuum transfer vessel for putting the processing-object substrate  112  into and out of the plasma processing vessel in a state of vacuum pressure,  104   a  denotes an evacuator,  104   b  denotes an inert-gas introducer,  105  denotes a gate door which serves as a partition wall between the plasma processing vessel  101  and the vacuum transfer vessel  104  and which has an opening/closing mechanism,  106  denotes a vacuum conveyance mechanism,  106   a  denotes a lift pin which is interlocked with the vacuum conveyance mechanism  106  and which operates for placing the processing-object substrate  112  onto the electrode  102 ,  107  denotes a load lock vessel capable of performing an operation of reducing the internal pressure of the vessel from atmospheric to vacuum state and, conversely, an operation of pressurizing the vessel from vacuum to atmospheric state,  107   a  denotes an evacuator,  107   b  denotes an inert-gas introducer,  108  denotes a gate door which serves as a partition wall between the vacuum transfer vessel  104  and the load lock vessel  107  in a vacuum state and which has an opening/closing mechanism,  109  denotes a gate door for holding the load lock vessel  107  in a vacuum state,  110  denotes a substrate storage device in which processing-object substrates  112  are stored, and  111  denotes an atmospheric conveyance mechanism for taking a processing-object substrate  112  out of the substrate storage device  110  and transferring the substrate  112  to the load lock vessel  107 . 
   With respect to the dry etching apparatus constructed as shown above, its operation is explained below. 
   First, the processing-object substrate  112  (i.e., the substrate to be processed) is taken out of the substrate storage device  110  by the atmospheric conveyance mechanism  111 , inert gas is purged from the inert-gas introducer  107   b  to the load lock vessel  107  to obtain an atmospheric state, the gate door  109  is opened, and the processing-object substrate  112  is transferred to the load lock vessel  107  by the atmospheric conveyance mechanism  111 . 
   Subsequently, the gate door  109  is closed, and in the load lock vessel  107 , the operation of the inert-gas introducer  107   b  is halted and the load lock vessel  107  is evacuated from the evacuator  107   a . After the evacuation to a specified pressure is completed, the gate door  108  is opened. The vacuum transfer vessel  104  is normally held in a vacuum state by the evacuator  104   a  operating for evacuation at all times. The processing-object substrate  112  placed on the load lock vessel  107  is taken out by the vacuum conveyance mechanism  106  and transferred to the vacuum transfer vessel  104 , and the gate door  108  is closed. 
   The evacuator  103  provided at the plasma processing vessel  101  normally performs the evacuation operation, so that the vessel  101  is normally held in the vacuum state. The gate door  105  is opened, and the processing-object substrate  112  present on the vacuum conveyance mechanism  106  within the vacuum transfer vessel  104  is transferred to the electrode  102  of the plasma processing vessel  101 . After the processing-object substrate  112  is placed onto the lift pins  106   a , the gate door  105  is closed, and the lift pins  106   a  move down so that the processing-object substrate is placed onto the electrode  102 . After that, plasma processing is carried out. 
   Subsequent to completion of the plasma processing, after performing a process which is a so called charge-neutralizing process by such gas as N 2  or O 2  and which neutralizes or removes charges electrified on the processing-object substrate  112  by changing the plasma generation area by pressure or power, or during this process, the lift pins  106   a  move up, so that the processing-object substrate  112  is lifted. 
   Thereafter, the gate door  105  is opened, and the processing-object substrate  112  present on the lift pins  106   a  within the plasma processing vessel  101  is taken out of the plasma processing vessel  101  and transferred into the vacuum transfer vessel  104  by the vacuum conveyance mechanism  106 . 
   In this case, the evacuator  103  of the plasma processing vessel  101  performs an evacuation operation so that the reaction product after the plasma processing does not flow into the vacuum transfer vessel  104 . The gate door  105  is closed, then the gate door  108  is opened, the processing-object substrate  112  is transferred to the load lock vessel  107  by the vacuum conveyance mechanism  106 , and the gate door  108  is closed. The evacuator  107   a  within the load lock vessel  107  is halted, and the inert gas is purged from the inert-gas introducer  107   b , where the interior of the load lock vessel  107  is changed from vacuum pressure to an atmospheric pressure state. Then, the gate door  109  is opened, and the processing-object substrate  112  present in the load lock vessel  107  is taken out and stored into the substrate storage device  110  by the atmospheric conveyance mechanism  111  (see Japanese Unexamined Patent Publication No. 07-106314, and Japanese Patent Nos. 3227812, and 3170849). 
   However, the processes subsequent to the completion of the plasma processing of the processing-object substrate  112  in the plasma processing vessel  101  include the steps of, after completion of the charge-neutralizing process, opening the gate door  105 , taking out the processing-object substrate  112  present on the electrode  102  within the plasma processing vessel  101  from within the plasma processing vessel  101 , and then transferring the processing-object substrate  112  into the vacuum transfer vessel  104  by the vacuum conveyance mechanism  106 . Thus, potential values of the residual charges remaining on the surface of the processing-object substrate  112  exhibit such behavior as shown in  FIG. 4B . 
   The charges electrified on the surface of the processing-object substrate  112  after the plasma processing show the maximum potential value at the passage through the gate door  105 . While still keeping a high voltage state thereafter, the processing-object substrate  112  is placed onto the vacuum transfer vessel  104 . There is an issue, in this case, that dielectric breakdown may occur when the charging potential that varies during the transfer of the processing-object substrate  112  in the vacuum has exceeded a withstand voltage threshold  102   a  of the dielectric film formed on the processing-object substrate  112 . 
   This breakdown is limited to cases where, as shown in  FIG. 5 , there exists a distance d that satisfies the following formula (Eq. 1) during the transfer of the processing-object substrate  112  in transitions from the charges of +Q at the surface of the electrode  102 , as opposed to and polarized from the charges of −Q electrified on the surface of the processing-object substrate  112  (at this time point, the distance d between the rear face of the processing-object substrate  112  and the top surface of the electrode  102  is infinitely large so that the formula (Eq. 1) is not applicable), to the bottom face of the plasma processing vessel, to the bottom face of the gate door  105 , and to the bottom face of the vacuum transfer vessel  104 :
 
− Q=C   g   ×V   g =ε×( S/d )× V   g 1  (Eq. 1): Basic formula for capacitors,
 
   wherein C g : capacitor capacity at the gap of distance d, V g : potential difference at the gap of distance d, S: area, d: distance, ε: dielectric constant. In  FIG. 5 , V gmax  is a potential at the maximum gap at the distance d. 
   As can be understood from the above equation (Eq. 1), the reason (for the breakdown) could be attributed to the possibility that V g  may increase upon arrival at a region (dmin) which is affected by d (distance). 
   Of course, it can easily be presumed that the surface potential of the processing-object substrate  112  increases to its largest level at the moment when the processing-object substrate  112  separates from the electrode  102 . At this time point, a portion of the processing-object substrate  112  has passed through the gate door  105 , so that even if occurrence of the dielectric breakdown is avoided, the surface potential can abnormally increase only at a portion of the processing-object substrate  112 . On this basis, it is inferred that the dielectric breakdown can occur at that portion. 
   Also, without occurrence of the dielectric breakdown, a thin film bearing an active state, which is generally called damage, formed on the processing-object substrate  112 , would cause the composition of the thin film interior to be changed along with local increases in the charges, thus creating a factor for deterioration in characteristics and performance of the thin film. 
   In common vacuum mass-production equipment, the gate door is manufactured as small as possible in order to reduce the pressure loss upon opening and closing of the gate door. At the point where the processing-object substrate  112  passes through the gate door  105 , the distance between the processing-object substrate  112  and the gate door  105  becomes an extremely small one. In other words, the processing-object substrate  112  and the gate door  105  become infinitely close to each other at this point, and the distance d falls within a range subject to influences of the basic formula for electrostatic capacity. The potential V g  in a portion of the processing-object substrate  112  shows a value higher than that on the electrode  102 . 
   In conjunction with the above description, since there are no places where the accumulated charges are discharged as far as the processing-object substrate  112  is transferred in the vacuum, which makes the processing-object substrate  112  keep bearing charges at a very high level until coming to an atmospheric state, portions other than the gate door  105  can become more influenced by the equation (Eq. 1), depending on the configuration of mass-production equipment. 
   In view of these and other issues of the prior art, an object of the present invention is to provide a plasma processing method and apparatus capable of reducing the amount of charge on a processing-object substrate, which varies during transfer of the processing-object substrate subsequent to its plasma processing. 
   SUMMARY OF THE INVENTION 
   In order to achieve the above object, according to a first aspect of the present invention, there is provided a plasma processing method for forming, under a reduced pressure, a thin-film circuit on a processing-object substrate (i.e., a substrate to be processed) which is to be subjected to plasma processing, the method comprising: 
   before performing plasma processing on the processing-object substrate, subjecting the processing-object substrate to a charge-neutralization-use plasma in gas composed mainly of inert gas so that charges electrified on the processing-object substrate are neutralized. 
   According to a second aspect of the present invention, there is provided the plasma processing method as defined in the first aspect, wherein the inert gas is at least one gas selected from among Ar, He, N 2 , H 2 , and vaporized H 2 O gas. 
   According to a third aspect of the present invention, there is provided the plasma processing method as defined in the first or second aspect, wherein top and bottom surfaces of the processing-object substrate are simultaneously subjected to the plasma in the inert gas. 
   According to a fourth aspect of the present invention, there is provided a plasma processing apparatus comprising: 
   a vacuum vessel; 
   a first electrode for placing thereon a processing-object substrate (i.e., a substrate to be processed) which is to be subjected to plasma processing; 
   a lift pin for holding thereon the processing-object substrate and placing the substrate onto the first electrode; 
   a conveyance system for transferring the processing-object substrate to the lift pin; 
   a second electrode disposed so as to confront the first electrode; 
   an evacuator for evacuating the interior of the vacuum vessel; 
   a process-gas introducer for introducing process gas into the vacuum vessel; 
   a high-frequency power supply for, in a state in which the process gas is introduced into the vacuum vessel by the process-gas introducer while the interior of the vacuum vessel is evacuated by the evacuator, applying a high-frequency power to the first electrode so that a plasma is generated in the vacuum vessel; 
   an inert-gas introducer for introducing inert gas into the vacuum vessel before the processing-object substrate is subjected to plasma processing with the process gas introduced into the vacuum vessel by the process-gas introducer; and 
   a control unit for, before execution of the plasma processing on the processing-object substrate, controlling the high-frequency power supply to generate an electrified charge-neutralization-use plasma in the inert gas. 
   According to a fifth aspect of the present invention, there is provided the plasma processing apparatus as defined in the fourth aspect, wherein the control unit controls operation of the lift pin so that before the placement of the processing-object substrate onto the first electrode, top-and-bottom surfaces of the processing-object substrate are simultaneously subjected to the electrified charge-neutralization-use plasma by the inert gas. 
   According to the present invention, there can be provided a plasma processing method and apparatus in which, before execution of the plasma processing on the processing-object substrate, the processing-object substrate is subjected to the charge-neutralization-use plasma composed mainly of inert gas so that initial charges electrified on the processing-object substrate are neutralized immediately before the plasma processing. As a result, the top-and-bottom surfaces of the processing-object substrate, as well as the top surface of the electrode, are made equal in potential to each other, thus making it possible to prevent plasma damage that otherwise could occur after the plasma processing. 
   Generally, it has never been conceived hitherto to perform plasma discharge before the plasma processing because of a possibility that reaction products or the like deposited on the wall surfaces of the plasma processing chamber might fly around to stick to the processing-object substrate, resulting in particle failures. However, in recent years, there has been a tendency that the rate of the particle failures is exceeded by the rate of failures that occur when the processing-object substrate, which has been charged during its transfer, is placed onto an electrode that has been charged at a different potential. Therefore, in the present invention, while reaction products or the like deposited on the wall surfaces of the plasma processing chamber are prevented from flying around as much as possible with a view to avoiding particle failures, a minimum necessary plasma is generated so that the top-and-bottom two surfaces of the processing-object substrate and the top surface of the electrode are made equal in potential to each other. In other words, by generating the minimum necessary plasma, i.e. a charge-neutralization-use plasma, that allows the top-and-bottom two surfaces of the processing-object substrate and the top surface of the electrode to be made equal in potential to each other, it becomes possible to more effectively prevent plasma damage that otherwise could occur after the plasma processing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: 
       FIG. 1A  is a plan view of an outlined configuration of a plasma processing apparatus according to a first embodiment of the present invention; 
       FIG. 1B  is a side view of the outlined configuration of a plasma processing vessel of the plasma processing apparatus according to the first embodiment of the present invention; 
       FIG. 2  is a side view of the outlined configuration of the plasma processing apparatus according to the first embodiment; 
       FIG. 3  is an outlined structural view of a conventional plasma processing apparatus; 
       FIGS. 4A and 4B  are, respectively, an outlined structural view of the conventional plasma processing apparatus and a graph showing the relationship between the position of the processing-object substrate and the surface charging value in the outlined structure of the conventional plasma processing apparatus; and 
       FIG. 5  is an outlined view of the mechanism indicating the increase of the surface potential (voltage) of the processing-object substrate. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. 
   Hereinbelow, embodiments of the present invention are described in detail with reference to the accompanying drawings. 
   A plasma processing method and apparatus according to a first embodiment of the present invention are explained with reference to the drawings. 
   Here are described a typical dry etching apparatus and method corresponding to the plasma processing method and apparatus of the first embodiment, which are explained with reference to  FIGS. 1A and 1B  and  FIG. 2 . Reference numeral  1  denotes a plasma processing vessel (one example of a plasma processing chamber) for dry etching,  1   a  denotes an inert-gas introducer (introducing device) for introducing inert gas into the plasma processing vessel  1  at the time of neutralization of electrified charges before plasma processing, and  1   b  denotes a process-gas introducer (introducing device) for introducing process gas into the plasma processing vessel  1  at the time of plasma processing. Also, numeral  2  denotes an electrode having a function of generating a plasma and supporting thereon a processing-object substrate (a substrate to be processed)  12  that is to be subjected to plasma processing,  2   a  denotes a high-frequency power supply,  2   b  denotes a grounded counter electrode, and  2   c  denotes a matching box which is an impedance matching circuit interposed between the high-frequency power supply  2   a  and the electrode  2 . Further, numeral  3  denotes an evacuator (evacuating device) such as a pump for reducing the internal pressure of the plasma processing vessel  1 ,  4  denotes a vacuum transfer vessel (one example of a vacuum transfer chamber) provided adjacent to the plasma processing vessel  1  so as to allow the processing-object substrate  12  to be put into and taken out of the plasma processing vessel  1  in a vacuum pressure state,  4   a  denotes an evacuator (evacuating device) such as a pump for reducing the internal pressure of the vacuum transfer vessel  4  as with the plasma processing vessel  1 ,  4   b  denotes an N 2  gas introducer (introducing device) for introducing N 2  gas into the vacuum transfer vessel  4 ,  5  denotes a gate door which serves as a partition wall between the plasma processing vessel  1  and the vacuum transfer vessel  4 , and which has an opening/closing mechanism for opening and closing the door  5 , and  6  denotes a vacuum conveyance mechanism for conveying the processing-object substrate  12  between the plasma processing vessel  1  and the vacuum transfer vessel  4  which are both in a vacuum state. Also,  6   a  denotes lift pins which are used to separate the processing-object substrate  12  and the electrode  2  from each other in the plasma processing vessel  1 ,  6   b  denotes a lift pin up/down device such as a motor or an air cylinder for lifting and lowering all of the lift pins  6   a ,  7  denotes a load lock vessel (one example of load lock chamber) capable of performing an operation of reducing the internal pressure of the vessel from atmospheric to a vacuum state and, conversely, an operation of pressurizing the vessel from vacuum to atmospheric state,  7   a  denotes an evacuator (evacuating device) such as a pump for performing the above-mentioned pressure-reducing operation, and  7   b  denotes an N 2  gas introducer (introducing device). Further,  8  denotes a gate door which serves as a partition wall between the vacuum transfer vessel  4  and the load lock vessel  7 , and which has an opening/closing mechanism for opening and closing the door  8 ,  9  denotes a gate door for maintaining the load lock vessel  7  in a vacuum state, and  10  denotes a substrate storage device in which processing-object substrates  12  are stored. Numeral  11  denotes an atmospheric conveyance mechanism such as a robot arm for taking a processing-object substrate  12  out of the substrate storage device  10  and transferring the substrate  12  to the load lock vessel  7 . Also, numeral  1000  denotes a control unit for controlling operations of the inert-gas introducer  1   a , the process-gas introducer  1   b , the high-frequency power supply  2   a , the matching box  2   c , the evacuator  3 , the evacuator  4   a , the N 2  gas introducer  4   b , the gate door  5 , the vacuum conveyance mechanism  6 , the lift pin up/down device  6   b , the evacuator  7   a , the N 2  gas introducer  7   b , the gate door  8 , the gate door  9 , the substrate storage device  10 , and the atmospheric conveyance mechanism  11 , respectively. 
   With respect to the dry etching apparatus constructed as described above, its operation is explained below. The following operation is controlled by the control unit  1000 . 
   First, the processing-object substrate  12  is taken out of the substrate storage device  10  by the atmospheric conveyance mechanism  11 , N 2  gas is introduced from the inert-gas introducer  7   b  to the load lock vessel  7  to obtain an atmospheric state, the gate door  9  is opened, and the processing-object substrate  12  is conveyed to the load lock vessel  7  by the atmospheric conveyance mechanism  11 . Subsequently, the gate door  9  is closed, and in the load lock vessel  7 , the operation of the inert-gas introducer  7   b  is halted and the load lock vessel  7  is evacuated by the evacuator  7   a . After the evacuation to a specified pressure is completed, the gate door  8  is opened. 
   The vacuum transfer vessel  4  is normally held in a vacuum state by the evacuator  4   a  operating for evacuation of vessel  4  at all times. The processing-object substrate  12  placed in the load lock vessel  7  is taken out by the vacuum conveyance mechanism  6  and is transferred to the vacuum transfer vessel  4 , and the gate door  8  is closed. The evacuator  3  provided at the plasma processing vessel  1  is normally performing the evacuation operation, so that the interior of the plasma processing vessel  1  is normally held in the vacuum state. The gate door  5  is opened, the processing-object substrate  12  present on the vacuum conveyance mechanism  6  within the vacuum transfer vessel  4  is transferred onto the lift pins  6   a  of the plasma processing vessel  1 , and the gate door  5  is then closed. 
   In the state in which the processing-object substrate  12  is held on the lift pins  6   a , the inert gas is introduced from the inert-gas introducer  1   a  into the plasma processing vessel  1 , and with a high-frequency power applied from the high-frequency power supply  2   a  to the electrode  2 , there is generated an electrified charge-neutralization-use weak (faint) plasma which is generated in gas composed mainly of inert gas and which is of such a level that the processing-object substrate  12  will not be etched and that a thin film will not be formed thereon. That is, in this case where, with an inert gas such as N 2  gas introduced from the inert-gas introducer  1   a , the interior of the plasma processing vessel  1  is adjusted to about 40 Pa by the evacuator  3 , and with the application of a high-frequency power of 0.1 W/cm 2  from the high-frequency power supply  2   a  to the electrode  2 , the electrified-charge-neutralization-use weak plasma is generated for five seconds. As a result, preprocessing charge neutralization on the top-and-bottom two surfaces of the processing-object substrate  12  and the top surface of the electrode  2  is performed so that the top-and-bottom two surfaces of the processing-object substrate  12  and the top surface of the electrode  2  are made equal in potential to each other. Thereafter, the lift pins  6   a  are lowered by driving the lift pin up/down device  6   b , and the processing-object substrate  12  is placed onto the electrode  2 . Then, the introduction of the inert gas from the inert-gas introducer  1   a  is halted, and meanwhile the process gas is introduced from the process-gas introducer  1   b . Then a desired plasma processing is performed on a wafer of 8 inches as an example of the processing-object substrate  12  with a high-frequency power of, for example, 100 to 150 W/cm 2  applied from the high-frequency power supply  2   a  to the electrode  2 . For the desired plasma processing, a chlorine-based gas is introduced as the process gas for metal-based thin films of the processing-object substrates  12 , a fluorine-based gas is introduced as the process gas for the processing-object substrate  12  of silicon, and an oxygen-based gas is introduced as the process gas for plasma processing of a resist or similar portion of the processing-object substrate  12 , where the desired plasma processing, such as etching, thin film formation, or resist removal, is performed. 
   It is noted here that the high-frequency power to be used for the generation of the weak plasma, which is generated in the gas composed mainly of inert gas and which is of such a level that the processing-object substrate  12  will not be etched and that a thin film will not be formed thereon, is preferably not more than ⅓ of the high-frequency power for the plasma processing, or 0.1 to 1.0 W/cm 2 . The time duration of the high-frequency power is preferably not more than 10 seconds. 
   The inert gas is at least one selected from among Ar, He, N 2 , H 2 , and vaporized H 2 O. 
   Without a limitation to the construction in which the lift pins  6   a  are lowered after execution of the pre-process charge neutralization of the processing-object substrate  12  and the electrode  2 , the invention may also be constructed so that the lift pins  6   a  are lowered while the pre-process charge neutralization of the processing-object substrate  12  and the electrode  2  is being executed. 
   In cases where the above-described preprocessing by weak plasma was executed and not executed, charging potential values on the processing-object substrates  12  were measured in the plasma processing vessel  1  under a vacuum with a noncontact type surface potential electrometer. As a result, charges accumulated on the surface of the processing-object substrate  12  are as shown in Table 1. 
   
     
       
             
             
             
           
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Before desired 
               After desired 
             
             
                 
               plasma processing 
               plasma processing 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Prior art 
               Large variations 
               −tens of volts 
             
             
                 
               (without pre- 
               (−tens of volts 
               through hundreds of 
             
             
                 
               process charge 
               through +tens of 
               volts 
             
             
                 
               neutralization 
               volts) 
               (reducible to about 
             
             
                 
               by plasma) 
                 
               −tens of volts by 
             
             
                 
                 
                 
               charge-neutralizing 
             
             
                 
                 
                 
               removing process, but 
             
             
                 
                 
                 
               damage involved) 
             
             
                 
               Present 
               Small variations 
               −tens of volts 
             
             
                 
               invention 
               (−a few volts 
             
             
                 
               (with pre- 
               through +a few 
             
             
                 
               process charge 
               volts) 
             
             
                 
               neutralization 
             
             
                 
               by plasma) 
             
             
                 
                 
             
           
        
       
     
   
   Hitherto, it has been considered that plasma damage or dielectric breakdown would occur due to charges generated and given from the plasma during a desired plasma processing. 
   However, from the evaluation results on which the present invention is based, it can be considered that, due to the fact that charges electrified only on the top side of the processing-object substrate  12  are added as a result of the desired plasma processing to the charges that had been accumulated before the processing and that are present on top and bottom of the processing-object substrate  12 , the balance of charges between the top and bottom of the processing-object substrate  12  is disturbed. This occurrence would adversely affect the devices on the thin-film circuit, thus causing the generation of plasma damage or dielectric breakdown. 
   The charges that the processing-object substrate  12  has had since early stages (i.e., prior to plasma processing) can be presumed to be charges due to heat treatment or water washing treatment during the preprocessing, or to frictional electrification during the transfer of the processing-object substrate  12  in the atmospheric air, as well as charges due to frictional electrification during the transfer from the substrate storage device  10  to the load lock vessel  7  and exhaustion from the atmospheric pressure to the vacuum state. 
   Accordingly, by performing the charge-neutralizing process as a pre-process on the top and bottom surfaces of the processing-object substrate  12  and the top surface of the electrode  2  at the same time with a weak plasma immediately before the desired plasma processing is performed, the charges on the top and bottom of the processing-object substrate  12  and the top surface of the electrode  2  are electrically eliminated so that the top-and-bottom two surfaces of the processing-object substrate  12  and the top surface of the electrode  2  are made equal in potential to each other. Thus, plasma damage that could occur after the plasma processing, such as occurrence of plasma damage or dielectric breakdown on the devices on the thin-film circuit, can effectively be prevented. 
   After the plasma processing, the lift pins  6   a  are lifted by the drive of the lift pin up/down device  6   b , and the processing-object substrate  12  is separated from the electrode  2 . Then, the gate door  5  is opened, and the processing-object substrate  12  present on the lift pins  6   a  in the plasma processing vessel  1  is taken out of the plasma processing vessel  1  and transferred into the vacuum transfer vessel  4  by the vacuum conveyance mechanism  6 . 
   Further, the damage suppression effect is fulfilled to a greater extent by performing, after completion of the plasma processing, a process step of eliminating the charges electrified on the top-and-bottom two surfaces of the processing-object substrate  12  and the top surface of the electrode  2  in the charge-neutralizing process by such gas as N 2  or O 2 . 
   Thereafter, the N 2  gas introducer  4   b  is halted, the gate door  5  is closed, the evacuator  4   a  is operated, the interior of the vacuum transfer vessel  4  is evacuated to a specified pressure or lower, and the interior of the plasma processing vessel  1  as well is evacuated to a specified pressure or lower by the evacuator  3 . Subsequently, the gate door  8  is opened, the processing-object substrate  12  is transferred to the load lock vessel  7  by the vacuum conveyance mechanism  6 , and the gate door  8  is closed. The evacuator  7   a  in the load lock vessel  7  is halted, the inert gas is introduced from the inert-gas introducer  7   b , and the interior of the load lock vessel  7  is changed from vacuum pressure to atmospheric pressure state. Then, the gate door  9  is opened, and the processing-object substrate  12  present in the load lock vessel  7  is taken out and stored in the substrate storage  10  device by the atmospheric conveyance mechanism  11 . 
   The embodiment of the present invention has been described with respect to a parallel-plate RIE plasma processing system. However, even if this system is replaced by such a plasma processing system as an ICP, an ECR, and a PE system, the same effects can be obtained. 
   Also when a processing vessel for exclusive use of preprocessing for generating the electrified charge-neutralization-use plasma is disposed independently with respect to the plasma processing vessel  1 , or when the preprocessing is performed with such a vessel as the vacuum transfer vessel  4 , the same effects can be obtained. 
   By properly combining arbitrary embodiments of the aforementioned various embodiments, the features provided by each of them can be made effectual. 
   Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.