Abstract:
A semiconductor processing system includes a casing forming a handling area. The handling area includes a main-process area and a pre-process area divided from each other and connected through an openable port. The main-process area and the pre-process area are connected to their own lines for vacuum-exhausting gas therefrom and their own lines for supplying an inactive gas thereinto and adjust pressure independently. A transfer port unit is disposed on the casing to place a transfer container that stores target objects. The transfer port unit allows the transfer container to open to the main-process area while maintaining an airtightness of the main-process area. The system includes a vertical batch main-processing apparatus. The system also includes a vertical batch pre-processing apparatus connected to the pre-process area and that performs a pre-process on the target objects and transforms a semiconductor oxide film on the target objects into an intermediate film.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-043245, filed Feb. 18, 2005, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vertical batch processing apparatus used for removing a semiconductor oxide film present on target objects, such as semiconductor wafers, and a semiconductor processing system including the apparatus. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target object, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target object. 
     2. Description of the Related Art 
     In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target object, such as a semiconductor wafer, is subjected to various processes, such as film formation, oxidation, diffusion, reformation, annealing, and etching. A process of this kind may be performed in a vertical processing apparatus (of the so-called batch type). In this case, semiconductor wafers are first transferred from a wafer cassette onto a vertical wafer boat and supported thereon at intervals in the vertical direction. For example, the wafer cassette can store 25 wafers, while the wafer boat can support 30 to 150 wafers. Then, the wafer boat is loaded into a process container from below, and the process container is airtightly closed. Then, a predetermined process is performed, while the process conditions, such as process gas flow rate, process pressure, and process temperature, are controlled. 
     In recent years, semiconductor integrated circuits are required to have higher operation speed, increased integration and miniaturization, and smaller film thickness. However, for example, in the case of a film formation process for a thin film, such as a gate insulating film, a semiconductor wafer may have a natural oxide film (consisting of SiO 2  if the wafer is Si) formed on the surface before the process. The natural oxide film can cause semiconductor devices to have lower electrical characteristics or to be defective. Accordingly, it is preferable to remove the natural oxide film on the surface of the semiconductor wafer to set the wafer surface in an activated state immediately before the process, and then form a film on the wafer surface in this activated state. 
     As a method for removing a natural oxide film, there is known a method of the wet process type using HF vapor or diluted HF solution to directly remove a natural oxide film. In this case, the wafer surface unfavorably suffers fluorine left thereon. On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 2003-133284 (Patent document 1) discloses a technique of the dry process type to remove a natural oxide film. According to this technique, a fluorine family etching gas, such as NF 3 , is caused to react with active species (radicals) generated by plasma to produce an intermediate substance (NH x F y : x and y are positive numbers). Then, the intermediate substance is caused to react with a natural oxide film to form an intermediate film of ammonium silicofluoride [(NH 4 ) 2 SiF 6 ]. Then, the intermediate film is decomposed or sublimated by heating, and is thereby removed as gas. 
     In the technique disclosed in Patent document 1, a process chamber and a heating chamber are stacked one on the other and configured to selectively communicate with each other. However, the structure and material of an apparatus for forming ammonium silicofluoride are not clarified. Further, the transfer route of a wafer from carry-in through processing to carry-out is not clarified in relation to a system. 
     Jpn. Pat. Appln. KOKAI Publication No. 2001-284307 (Patent document 2) discloses another related technique. According to the technique disclosed in Patent document 2, a vertical auxiliary chamber is disposed on one side of a vertical reaction chamber to communicate therewith. H 2  gas and N 2  gas are supplied into the auxiliary chamber and irradiated with microwaves from above to generate plasma. In this case, however, the gases may be insufficiently activated. 
     Jpn. Pat. Appln. KOKAI Publication No. 2002-100574 (Patent document 3) discloses another related technique. According to the technique disclosed in Patent document 3, active species and an etching gas are supplied into a vertical process chamber through a lateral side. In this case, the interior of the process chamber is exhausted from the bottom, and the gases may less uniformly flow in the process chamber. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a vertical batch processing apparatus and semiconductor processing system including the same, which can be used with high reliability to remove a semiconductor oxide film present on target objects, such as semiconductor wafers. 
     According to a first aspect of the present invention, there is provided a vertical batch processing apparatus configured to transform a semiconductor oxide film on a plurality of target objects into an intermediate film, which is decomposed or sublimated more easily than the semiconductor oxide film, so as to remove the semiconductor oxide film, the apparatus comprising: 
     a process container configured to form an airtight process field for accommodating the target objects; 
     a holder configured to support the target objects at intervals in a vertical direction within the process field; 
     a first process gas supply circuit comprising a first supply port disposed outside the process field, and configured to supply a first process gas to the process field through the first supply port; 
     a second process gas supply circuit comprising a second supply port disposed between the first supply port and the process field, and configured to supply a second process gas to the process field through the second supply port; 
     a plasma generation field disposed between the first supply port and the second supply port, and configured to activate the first process gas to produce first active species, wherein the first active species react with the second process gas and thereby produce a reactant to react with the semiconductor oxide film to form the intermediate film; and 
     an exhaust system comprising an exhaust port disposed opposite the second supply port with the process field interposed therebetween, and configured to vacuum-exhaust gas from the process field through the exhaust port. 
     According to a second aspect of the present invention, there is provided a semiconductor processing system comprising: 
     a casing configured to form a handling area in an airtight state; 
     a transfer port unit disposed on the casing to place thereon a transfer container for storing a plurality of target objects, the transfer port unit being configured to allow the transfer container to be opened to the handling area while maintaining an airtight state of the handling area; 
     a vertical batch main-processing apparatus connected to the casing to perform a semiconductor process on the target objects; 
     a vertical batch pre-processing apparatus connected to the casing to perform a pre-process on the target objects, the vertical batch pre-processing apparatus being configured to transform a semiconductor oxide film on the target objects into an intermediate film, which is decomposed or sublimated more easily than the semiconductor oxide film, so as to remove the semiconductor oxide film; and 
     a transfer mechanism disposed inside the handling area to directly or indirectly transfer the target objects between the transfer container, the vertical batch main-processing apparatus, and the vertical batch pre-processing apparatus, 
     wherein the vertical batch pre-processing apparatus comprises 
     a process container configured to form an airtight process field for accommodating the target objects, 
     a holder configured to support the target objects at intervals in a vertical direction within the process field, 
     a first process gas supply circuit comprising a first supply port disposed outside the process field, and configured to supply a first process gas to the process field through the first supply port, 
     a second process gas supply circuit comprising a second supply port disposed between the first supply port and the process field, and configured to supply a second process gas to the process field through the second supply port, 
     a plasma generation field disposed between the first supply port and the second supply port, and configured to activate the first process gas to produce first active species, wherein the first active species react with the second process gas and thereby produce a reactant to react with the semiconductor oxide film to form the intermediate film, and 
     an exhaust system comprising an exhaust port disposed opposite the second supply port with the process field interposed therebetween, and configured to vacuum-exhaust gas from the process field through the exhaust port. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a perspective view schematically showing a semiconductor processing system according to a first embodiment of the present invention; 
         FIG. 2  is a sectional plan view schematically showing the processing system shown in  FIG. 1 ; 
         FIG. 3  is a sectional side view schematically showing a vertical batch main-processing apparatus disposed in the processing system shown in  FIG. 1 ; 
         FIG. 4  is a sectional side view of the processing system shown in  FIG. 1  viewing from the pre-process area thereof; 
         FIG. 5  is a sectional side view showing a film transformation apparatus (vertical batch pre-processing apparatus) disposed in the processing system shown in  FIG. 1 ; 
         FIG. 6  is a sectional plan view of the film transformation apparatus shown in  FIG. 5 ; 
         FIG. 7  is a plan view showing a rectifier plate used in the film transformation apparatus shown in  FIG. 5 ; 
         FIG. 8  is a sectional side view showing a heat-processing apparatus disposed in the processing system shown in  FIG. 1 ; 
         FIG. 9  is a graph showing the temperature dependency of etching amount for a silicon oxide film and a silicon film; 
         FIG. 10  is a graph showing the vapor pressure curve of ammonium silicofluoride; 
         FIG. 11  is a sectional side view showing a film transformation apparatus (vertical batch pre-processing apparatus) according to a modification of the first embodiment, which may be used in the processing system shown in  FIG. 1 ; 
         FIGS. 12A and 12B  are sectional plan views respectively showing two different structures of a plasma generation field used in the film transformation apparatus shown in  FIG. 11 ; 
         FIG. 13  is a perspective view schematically showing a semiconductor processing system according to a second embodiment of the present invention; 
         FIG. 14  is a sectional plan view schematically showing the processing system shown in  FIG. 13 ; 
         FIG. 15  is a sectional side view showing a vertical batch pre-processing apparatus disposed in the processing system shown in  FIG. 13 ; 
         FIG. 16  is a sectional side view showing a vertical batch pre-processing apparatus according to a modification of the second embodiment, which may be used in the processing system shown in  FIG. 13 ; 
         FIG. 17  is a perspective view schematically showing a semiconductor processing system according to a third embodiment of the present invention; 
         FIG. 18  is a sectional plan view schematically showing the processing system shown in  FIG. 17 ; 
         FIG. 19  is a sectional side view showing a vertical batch pre-processing apparatus disposed in the processing system shown in  FIG. 17 ; and 
         FIG. 20  is a sectional side view showing a vertical batch pre-processing apparatus according to a modification of the third embodiment, which may be used in the processing system shown in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will now be described with reference to the accompanying drawings. In the following description, the constituent elements having substantially the same function and arrangement are denoted by the same reference numerals, and a repetitive description will be made only when necessary. 
     First Embodiment 
     [Semiconductor Processing System] 
       FIG. 1  is a perspective view schematically showing a semiconductor processing system according to a first embodiment of the present invention.  FIG. 2  is a sectional plan view schematically showing the processing system shown in  FIG. 1 . As shown in  FIGS. 1 and 2 , this processing system  2  includes an airtight casing  4  formed of a cubic or rectangular box as a whole. The casing  4  defines therein an airtight handling area  5  for handling semiconductor wafers (typically made of silicon) as target objects. The casing  4  is made of a metal material, such as aluminum, with the inner surface covered with a corrosion resistant coating, such as an alumite coating (aluminum oxide). The casing  4  may be made of another metal, such as stainless steel. 
     As shown in  FIG. 2 , the handling area  5  is airtightly divided by a partition wall  6  into two rooms, i.e., a main-process area  8  and a pre-process area  10 . The partition wall  6  is made of a metal material, such as aluminum, with the surface covered with a corrosion resistant coating, such as an alumite coating. The partition wall  6  has an opening  12  with a width to allow the target object or semiconductor wafer to pass therethrough. The opening  12  is arranged to be opened and closed by a slide door  14  connected to a drive portion (not shown). A sealing member  14 A, such as an O-ring, is disposed on the periphery of the slide door  14  to keep this portion airtight when the slide door  14  is closed. 
     An I/O table or shelf board  16  is disposed outside the casing  4 , specifically on the front side of the wall defining the main-process area  8 . The I/O table  16  is configured to place thereon a cassette or transfer container  18 , which can store a plurality of, e.g., 10 to 25, target objects or semiconductor wafers W. In  FIGS. 1 and 2 , two transfer containers  18  are placed on the I/O table  16 . 
     A transfer port unit  20  is disposed at the wall of the casing  4  between the I/O table  16  and main-process area  8 . The transfer port unit  20  is configured to allow the transfer container  18  to be opened to the handling area  5  while keeping the handling area  5  airtight. Specifically, the transfer port unit  20  comprises a load-lock box  22  penetrating the wall of the casing  4 . The load-lock box  22  has openings respectively on the opposite sides, which are airtightly closed by gate valves  24  and  26 . The size of the interior of load-lock box  22  is set such that it can accommodate the transfer container  18 . The gate valve  24  on the atmospheric side is opened when the transfer container  18  is transferred between the I/O table  16  and load-lock box  22 . The other gate valve  26  on the main-process area  8  side is opened when wafers W are transferred between the transfer container  18  placed in the load-lock box  22  and the main-process area  8 . 
     The load-lock box  22  is connected to an inactive gas line  28  for supplying therein an inactive gas, such as N 2  gas, and is also connected to a vacuum exhaust line  30  for vacuum-exhausting the interior thereof. The main-process area  8  is connected to an inactive gas line  32  for supplying therein an inactive gas, such as N 2  gas, and is also connected to a vacuum exhaust line  36  for vacuum-exhausting the interior thereof. The pre-process area  10  is connected to an inactive gas line  34  for supplying therein an inactive gas, such as N 2  gas, and is also connected to a vacuum exhaust line  38  for vacuum-exhausting the interior thereof. 
     A main-processing apparatus (vertical batch main-processing apparatus)  40  for performing a main semiconductor process on wafers W is connected to the ceiling portion of the main-process area  8  on the rear side. For example, the main semiconductor process is a film formation process to form a silicon oxide film used as a gate insulating film, a poly-crystalline silicon film used as an electrode, or a selective epitaxial layer, on the surface of the wafers W. 
     On the other hand, a film transformation apparatus (vertical batch pre-processing apparatus)  42  and a heat-processing apparatus (vertical batch heat-processing apparatus)  44  are disposed side by side, each being connected to the ceiling portion of the pre-process area  10 . In this embodiment, the film transformation apparatus  42  is disposed on the front side, and the heat-processing apparatus  44  is disposed on the rear side. The film transformation apparatus  42  is configured to perform a process (intermediate film formation step) for transforming a natural oxide film (SiO 2 ) present on the wafer surface into an intermediate film that can be more easily decomposed or sublimated. The heat-processing apparatus  44  is configured to perform a process (intermediate film removal step) for decomposing or sublimating the intermediate film by heating to remove it. The film transformation apparatus  42  and heat-processing apparatus  44  may be implemented in various manners, which will be described later in detail. 
     The intermediate film formation step and intermediate film removal step are combined to realize a so-called pre-process. With this pre-process, the natural oxide film present on the wafer surface is completely removed, so that the wafer surface comes into an activated state. For example, on this activated wafer surface, a predetermined thin film, such as a gate insulating film, is deposited by the main-processing apparatus  40 . 
     The main-process area  8  is provided with a transfer arm unit  46  therein at a position facing the load-lock box  22  to transfer wafers W between the transfer container  18 , main-process area  8 , and pre-process area  10 . For example, the transfer arm unit  46  comprises an articulated arm that can extend/retract and rotate (pivot). The articulated arm is connected to a vertical drive portion  48 , such as a ball screw, and is moved up and down by the drive portion  48 . The transfer arm unit  46  has a pick  46 A at the distal end to support a wafer W, so as to transfer the wafer W to a wafer boat for the main-processing apparatus  40  or a wafer boat for the film transformation apparatus  42 , as described later. 
       FIG. 4  is a sectional side view of the processing system  2  shown in  FIG. 1  viewing from the pre-process area  10  thereof. The film transformation apparatus  42  and heat-processing apparatus  44  shares a lid  92  for closing the bottom load port of a process container, and a wafer boat (holder)  90 . The wafer boat  90  is configured to support a plurality of, e.g., 20 to 100, wafers W at intervals in the vertical direction, so as to simultaneously subject all the wafers to a certain process. The pre-process area  10  is provided with a boat shifter  50  (see  FIG. 2 ) on the bottom to transfer the lid  92  and wafer boat  90 . Specifically, the boat shifter  50  includes a vertical drive portion  50 A formed of, e.g., a vertical ball screw for moving the wafer boat  90  and so forth up and down, and a horizontal drive portion  50 B formed of, e.g., a horizontal ball screw for moving the vertical drive portion  50 A as a whole in a horizontal direction. Accordingly, the boat shifter  50  can move the wafer boat  90  and so forth between the film transformation apparatus  42  and heat-processing apparatus  44 , and further load and unload the wafer boat  90  into and from each of the apparatuses  42  and  44 . 
     The processing system  2  further includes a system control section  52  (see  FIG. 2 ) formed of, e.g., a computer, to control the entire system. The system control section  52  has a storage section  54  including a storage medium that stores a program to control the entire operation of the processing system  2 . Examples of the storage medium or media are a magnetic disk (flexible disk, hard disk (a representative of which is a hard disk included in the storage section  54 ), etc.), an optical disk (CD, DVD, etc.), a magneto-optical disk (MO, etc.), and a semiconductor memory. A computer for controlling the operation of the processing system  2  reads program instructions stored in the storage medium or media, and executes them on a processor, thereby performing various processes. 
     [Main-processing Apparatus] 
       FIG. 3  is a sectional side view schematically showing the main-processing apparatus (vertical batch main-processing apparatus)  40  of the processing system  2  shown in  FIG. 1 . The main-processing apparatus  40  is supported by the ceiling board  4 A (see  FIG. 1 ) of the main-process area  8  as a whole. In order to form an airtight process field for accommodating wafers W, the main-processing apparatus  40  includes a vertical process container  60  made of quartz, which is cylindrical and opened at the bottom. An exhaust port is formed at the top of the process container  60 , and is connected to, e.g., an exhaust line  86  laterally bent at right angles. The exhaust line  86  is connected to a vacuum exhaust system (not shown) including a pressure control valve, a vacuum pump, and so forth provided thereon. The atmosphere within the process container  60  is vacuum-exhausted by this exhaust system. 
     The bottom of the process container  60  is supported by a cylindrical manifold  62  made of, e.g., stainless steel. A sealing member  82 , such as an O-ring, is interposed between the bottom of the process container  60  and the top of the manifold  62  to keep this portion airtight. The manifold  62  has a load port at the bottom to be opened and closed by a lid  72 , through which a wafer boat (holder)  66  is loaded and unloaded. The wafer boat  66  is made of quartz, and configured to support a plurality of, e.g., 20 to 100, wafers W at almost regular intervals in the vertical direction. 
     The wafer boat  66  is placed on a turntable  68  through a heat-insulating cylinder  70  made of quartz. The turntable  68  is supported on the top of a rotary shaft  74 , which penetrates the lid  72  used for opening/closing the bottom load port of the manifold  62 . The portion of the lid  72  where the rotary shaft  74  penetrates is provided with, e.g., a magnetic-fluid seal  76 , so that the rotary shaft  74  is rotatably supported in an airtightly sealed state. A sealing member  80 , such as an O-ring, is interposed between the periphery of the lid  72  and the bottom of the manifold  62 , so that the interior of the process container  60  can be kept sealed. For example, the rotary shaft  74  is attached to a rotary drive  77  at the distal end of an arm  78 A supported by an elevating mechanism  78 , such as a boat elevator. The elevating mechanism  78  moves the wafer boat  66  and lid  72  up and down integratedly. 
     A cylindrical heater  64  is disposed to surround the process container  60 . The heater  64  is arranged to heat the atmosphere of the process field within the process container  60 , thereby heating up the semiconductor wafers W in the process field. The heater  64  is surrounded by a thermal insulator to ensure thermal stability. The manifold  62  is connected to several gas supply circuits  84  to supply various gases (process gases for film formation and an inactive gas, such as N 2  gas) into the process container  60 . 
     The main-processing apparatus  40  further includes a control section  88  formed of, e.g., a computer, to control the entire apparatus. The control section  88  is operated under the control of the system control section  52 , and thereby controls the main-processing apparatus  40  to perform a predetermined film formation process on the wafers from which natural oxide films have been removed. The control section  88  can perform a film formation process in accordance with the process recipe of the film formation processes concerning, e.g., the film thickness and composition of a film to be formed, stored in a storage section  90  thereof in advance. In the storage section  90 , the relationship between the process gas flow rates and the thickness and composition of the film and so forth are also stored as control data in advance. Accordingly, the control section  88  can control the gas supply circuits, exhaust system, elevating mechanism, heater, and so forth, based on the stored process recipe and control data. 
     [Film Transformation Apparatus] 
       FIG. 5  is a sectional side view showing the film transformation apparatus (vertical batch pre-processing apparatus)  42  disposed in the processing system  2  shown in  FIG. 1 .  FIG. 6  is a sectional plan view of the film transformation apparatus  42  shown in  FIG. 5 . The film transformation apparatus  42  is supported by the ceiling board  4 B (see  FIG. 1 ) of the pre-process area  10  as a whole. In order to form an airtight process field  95  for accommodating wafers W, the film transformation apparatus  42  includes a vertical process container  94 , which is cylindrical and opened at the bottom. The process container  94  has a load port  94 A (see  FIG. 4 ) at the bottom to be opened and closed by a lid  92 , through which a wafer boat (holder)  90  is loaded and unloaded. 
     Each of the process container  94  and lid  92  is made of a metal material, such as aluminum, with the inner surface covered with a corrosion resistant coating, such as an alumite coating (Al 2 O 3 ), which is resistant to a second process gas (a gas containing a halogen element) described later. The process container  94  is grounded. The wafer boat  90  is made of a metal material, such as aluminum, with the surface covered with a corrosion resistant coating, such as an alumite coating, which is resistant to the second process gas. The wafer boat  90  is configured to support a plurality of, e.g., 20 to 100, wafers W at almost regular intervals in the vertical direction. 
     The wafer boat  90  is placed on a turntable  102  supported on the top of a rotary shaft  100 , which penetrates the lid  92 . The portion of the lid  92  where the rotary shaft  100  penetrates is provided with, e.g., a magnetic-fluid seal  98 , so that the rotary shaft  100  is rotatably supported in an airtightly sealed state. A sealing member  96 , such as an O-ring, is interposed between the periphery of the lid  92  and the bottom of the process container  94 , so that the interior of the process container  94  can be kept sealed. For example, the rotary shaft  100  is attached to a rotary drive  99  at the distal end of an arm  104  supported by the vertical drive portion  50 A of the boat shifter  50 . The vertical drive portion  50 A moves the wafer boat  90  and lid  92  up and down integratedly. 
     On one side of the process container  94 , a wall portion is integrally attached to and projected outward from the process container  94  to form a vertically long supply head region  106 . The supply head region  106  has a length to cover almost the entire length of the wafer boat  90  in the vertical direction. The supply head region  106  is connected to a first gas supply circuit  122  for supplying a first process gas (a gas containing nitrogen atoms and hydrogen atoms) into the process container  94 , and is also connected to a second gas supply circuit  108  for supplying a second process gas (a gas containing a halogen element) into the process container  94 . The first process gas is supplied in an activated state obtained by plasma into the supply head region  106 , while the second process gas is supplied into the supply head region  106  without having been turned into plasma. 
     The second gas supply circuit  108  is arranged to supply a fluoride gas, such as NF 3 , at a controlled flow rate, as the second process gas not activated by plasma. Specifically, the second gas supply circuit  108  includes a distribution nozzle  110  extending in the longitudinal direction of the supply head region  106 . The distribution nozzle  110  has a plurality of gas holes  100 A arrayed in the vertical direction essentially over all the wafers W supported on the boat. The gas holes  110 A deliver the second process gas in the horizontal direction, so as to supply the gas toward the center of the process container  94 . The distribution nozzle  110  is made of a material resistant to corrosion caused by the first and second process gases, such as aluminum with the surface covered with an alumite coating. 
     On the other hand, the first gas supply circuit  122  is combined with an active species supply portion  112  to supply active species into the supply head region  106 . Specifically, the active species supply portion  112  includes a supply pipe  116  connected to an opening  114  formed at the essential center of the supply head region  106  in the longitudinal direction. The supply pipe  116  has a plasma generation field  121  at the midpoint, which is connected to a microwave generator  120  through a wave guide tube  118 . The first gas supply circuit  122  is connected at the end of the supply pipe  114  to supply the first process gas at a controlled flow rate. In the plasma generation field  121 , the first process gas is turned into plasma and thereby activated to produce active species by microwaves applied from the microwave generator  120 . Active species thus generated are supplied through the opening  114  into the supply head region  106  and diffused in the vertical direction within the region  106 . 
     The microwaves applied from the microwave generator  120  have a frequency of, e.g., 2.45 GHz. Alternatively, the microwaves may have another frequency of, e.g., 400 MHz. For example, the process gas to be turned into plasma (first process gas) is a combination of N 2  gas, H 2  gas, and NH 3  gas. Alternatively, the first process gas may be a combination of N 2  gas and H 2  gas, or a single gas of NH 3  gas. 
     Active species of N 2 , H 2 , and NH 3  gases thus generated from the first process gas meet the second process gas or NF 3  gas in the supply head region  106 . Consequently, a gas reaction takes place to produce an intermediate substance (etchant: NH x F y : x and y are positive numbers). Then, the intermediate substance reacts with a natural oxide film (SiO 2 ) on the wafers W, thereby forming an intermediate film of ammonium silicofluoride [(NH 4 ) 2 SiF 6 ], which can be decomposed or sublimated more easily than the natural oxide film. 
     The vertically long opening portion of the supply head region  106  is provided with a rectifier plate  124  to rectify the flow of the active species and second process gas into a laminar flow state.  FIG. 7  is a plan view showing the rectifier plate  124  used in the film transformation apparatus  42  shown in  FIG. 5 . Specifically, the rectifier plate  124  consists of an aluminum plate having a thickness of, e.g., about 10 mm with a number of gas distribution holes (slit)  126  formed therein at predetermined intervals. The rectifier plate  124  is fitted in and attached to the vertically long opening portion of the supply head region  106 . The surface of the rectifier plate  124  is totally covered with, e.g., an alumite coating to increase the corrosion resistant. The entirety of the rectifier plate  124  is grounded. The distribution nozzle  110  may be disposed inside the process container  94  on the inner side of the rectifier plate  124 , instead of inside the supply head region  106 . 
     On the opposite side of the process container  94  facing the supply head region  106 , a wall portion is integrally attached to and projected outward from the process container  94  to form a vertically long exhaust buffer region  128 . The exhaust buffer region  128  has a length to sufficiently cover the entire length of the wafer boat  90  in the vertical direction. The exhaust buffer region  128  is connected through an exhaust port  129  formed at the center to a vacuum exhaust system  130  including a pressure control valve  132 , a vacuum pump (not shown), and so forth provided thereon. The vacuum exhaust system  130  is configured to vacuum-exhaust the interior of the process container  94  through the exhaust buffer region  128 , and to maintain the interior of the process container at a predetermined vacuum pressure. A pressure gauge  134  is disposed at the ceiling portion of the process container  94 , so that the pressure control valve  132  is controlled on the basis of measurement performed by the pressure gauge  134 . 
     The process container  94  is provided with a cooling mechanism  136  to cool the container wall. Specifically, the cooling mechanism  136  includes a thermal medium passage  138  formed in the wall of the process container  94 . A cooling medium is supplied from the cooling medium source  140  into the thermal medium passage  138  to cool the process container  94  and maintain it at a predetermined temperature. A shutter member  142  (see  FIG. 4 ) is disposed near the load port  94 A at the bottom of the process container  94 , and is driven by a slide mechanism (not shown). The shutter member  142  is used to cover the load port  94 A, when the lid  92  is positioned down after the wafer boat  90  is unloaded. 
     The film transformation apparatus  42  further includes a control section  144  formed of, e.g., a computer, to control the entire apparatus. The control section  144  is operated under the control of the system control section  52 , and thereby controls the film transformation apparatus  42  to perform a process of transforming a natural oxide film on the wafer surfaces into an intermediate film. The control section  144  can perform a predetermined transformation process in accordance with the process recipe stored in a storage section  140  thereof in advance. In the storage section  140 , the relationship between the process gas flow rates and process progress and so forth are also stored as control data in advance. Accordingly, the control section  144  can control the gas supply circuits, exhaust system, plasma generation system, elevating mechanism, and so forth, based on the stored process recipe and control data. 
     [Heat-processing Apparatus] 
       FIG. 8  is a sectional side view showing the heat-processing apparatus (vertical batch heat-processing apparatus)  44  disposed in the processing system  2  shown in  FIG. 1 . The heat-processing apparatus  44  is supported by the ceiling board  4 B (see  FIG. 1 ) of the pre-process area  10  as a whole. In order to form an airtight heat-process field  151  for accommodating wafers W, the heat-processing apparatus  44  includes a vertical process container  150 , which is cylindrical and opened at the bottom. The process container  150  has a load port  150 A (see  FIG. 4 ) at the bottom to be opened and closed by a lid  92 , through which a wafer boat (holder)  90  is loaded and unloaded. 
     The process container  150  is made of a metal material, such as aluminum, with the inner surface covered with a corrosion resistant coating, such as an alumite coating (Al 2 O 3 ). However, since this apparatus does not use the second process gas, which can etch quartz, the process container  150  may be made of quartz (SiO 2 ) or another metal material, such as stainless steel. The process container  150  shares the lid  92 , turntable  102 , wafer boat  90 , and so forth with the film transformation apparatus  42 , as described above. The sealing member  96 , such as an O-ring, is interposed between the periphery of the lid  92  and the bottom of the process container  150 , so that the interior of the process container  150  can be kept sealed. 
     A cylindrical outer heater  152  is disposed around the process container  150  and extended along the heat-process field  151 . The outer heater  152  is mainly used for directly heating the process container  150  from outside. An inner heater  154  is disposed inside the process container  150  and extended along the heat-process field  151 , i.e., to surround the wafer boat  90  loaded therein. The inner heater  154  is used for directly heating the wafers W supported on the wafer boat  90 . For example, the inner heater  154  comprises carbon wire heaters  154 A, which are heat-resistant and less contaminative to the wafers W. Each of the carbon wire heaters  154 A is bent in a U-shape to extend along the process container  150  in the vertical direction, and is supported by the ceiling portion. The process container  150  is provided with a plurality of, e.g., four, carbon wire heaters  154 A equidistantly disposed to surround the wafer boat  90 .  FIG. 4  shows only two of the carbon wire heaters  154 A. Since the wafers W are directly heated, as described above, their temperature can be quickly increased to decompose or sublimate and thereby remove the intermediate film of ammonium silicofluoride on the wafer surface. 
     An exhaust port  156  is formed at the top of the process container  150 , and connected to, e.g., an exhaust line  157  laterally bent at right angles. The exhaust line  157  is connected to a vacuum exhaust system  160  including a pressure control valve  158 , a vacuum pump (not shown), and so forth provided thereon. The vacuum exhaust system  160  is configured to vacuum-exhaust the interior of the process container  150 , and to maintain the interior of the process container at a predetermined vacuum pressure. A pressure gauge  162  is disposed at the sidewall of the process container  150 , so that the pressure control valve  158  is controlled on the basis of measurement performed by the pressure gauge  162 . 
     The process container  150  is provided with an inactive gas supply circuit  164  for supplying an inactive gas thereinto. In this embodiment, the inactive gas supply circuit  164  includes a gas nozzle  164 A, which penetrates the ceiling portion of the process container  150  and extends toward the container bottom. The gas nozzle  164 A is made of, e.g., aluminum with the surface covered with an alumite coating. The inactive gas supply circuit  164  is arranged to supply an inactive gas, such as N 2  gas, at a controlled flow rate, toward the bottom of the process container  150 . 
     A quartz tube  166  is inserted from the ceiling portion of the process container  150 , and has a plurality of temperature measuring elements  168 , such as thermo-couples, built therein at predetermined intervals. The temperature measuring elements  168  are arranged to detect the temperature of the wafers W in respective zones arrayed in the vertical direction. The detective values are input to a control section  170  formed of, e.g., a microcomputer, to control the wafer temperature. 
     A shutter member  172  (see  FIG. 4 ) is disposed near the load port  150 A at the bottom of the process container  150 , and is driven by a slide mechanism (not shown). The shutter member  172  is used to cover the load port  150 A, when the lid  92  is positioned down after the wafer boat  90  is unloaded. 
     The heat-processing apparatus  44  further includes a control section  170  formed of, e.g., a computer, to control the entire apparatus. The control section  170  is operated under the control of the system control section  52 , and thereby controls the heat-processing apparatus  44  to perform a heat-process for heating and thereby removing the intermediate film on the wafer surface. The control section  170  can perform a predetermined process in accordance with the process recipe stored in a storage section  173  thereof in advance. In the storage section  173 , the relationship between the temperature, process gas flow rate, and process progress and so forth are also stored as control data in advance. Accordingly, the control section  170  can control the gas supply circuit, exhaust system, heater, elevating mechanism, and so forth, based on the stored process recipe and control data. 
     [Operation of Semiconductor Processing System] 
     At first, explanation will be given of the whole process flow for semiconductor wafers W. In the following explanation, it is assumed that the wafers W are silicon substrate wafers. Further, the interior of the casing  4  is set to have an inactive gas atmosphere, such as an N 2  atmosphere, as a whole. 
     As shown in  FIGS. 1 and 2 , transfer containers  18  that stores wafers W are placed on the I/O table  16  of the processing system  2 . Then, one of the transfer containers  18  is carried into the load-lock box  22  through the opened gate valve  24 . Then, the gate valve  24  is closed, and the atmosphere inside the load-lock box  22  is replaced with N 2  gas. Then, the gate valve  26  on the inner side is opened. 
     Thereafter, the slide door  14  on the partition wall  6  is opened between the main-process area  8  and pre-process area  10 . Then, the transfer arm unit  46  disposed in the main-process area  8  is driven to extend/retract, pivot, and move up and down, so as to transfer the wafers W in the transfer container  18  to the wafer boat  90  (see  FIG. 4  as well) positioned below the film transformation apparatus  42 . This transfer operation is continued until, e.g., the wafer boat  90  comes into a full load state with wafers W. At this time, a natural oxide film (SiO 2 ) is present on the surface of the wafers W, because they were exposed to clean air during standby. 
     After the transfer of the wafers W is finished, the slide door  14  is closed. Then, the wafer boat  90  is loaded into the process container  94  of the film transformation apparatus  42  (see  FIG. 5 ) by the vertical drive portion  50 A of the boat shifter  50  (see  FIG. 2 ). Then, the transformation process is performed in the process container  94  to transform the natural oxide film on the wafer surface into an intermediate film of ammonium silicofluoride. This transformation process, i.e., the process of forming the intermediate film, will be described later. 
     After the intermediate film formation step is finished, the wafer boat  90  is moved down by the boat shifter  50  along with the wafers W supported thereon, and is thereby unloaded from process container  94 . Then, the wafer boat  90  is horizontally moved to a position below the heat-processing apparatus  44  by the boat shifter  50 . Then, the wafer boat  90  is moved up and loaded into the process container  150  of the heat-processing apparatus  44  from below by the boat shifter  50 . Then, the wafers W are heated up and maintained at a predetermined temperature within the process container  150  by the outer heater  152  and inner heater  154 . Thus, a heat-process is performed to decompose or sublimate and thereby remove the intermediate film on the wafer surface. The gas generated at this time is vacuum-exhausted solely or along with N 2  gas supplied into the container. Consequently, the wafer surface comes into an activated state without any natural oxide film attached thereon. 
     After the intermediate film removal step is finished, the wafer boat  90  is moved down by the boat shifter  50  along with the wafers W supported thereon, and is thereby unloaded from process container  150 . Then, the wafer boat  90  is horizontally moved to the home position below the film transformation apparatus  42  by the boat shifter  50 , as shown in  FIG. 4 . 
     During these serial operations, the slide door  14  on the partition wall  6  is closed to prevent particles or the like generated from the intermediate film and poisonous to wafers W from flowing into the main-process area  8 . Further, when the wafer boat  90  is positioned down, the load ports  94 A and  150 A at the bottom of the process containers  94  and  150  of the film transformation apparatus  42  and heat-processing apparatus  44  are covered with the shutter members  142  and  172 , respectively. 
     Then, the slide door  14  on the partition wall  6  is opened for the main-process area  8  and pre-process area  10  to communicate with each other. Then, the transfer arm unit  46  disposed in the main-process area  8  is driven to transfer all the wafers W on the wafer boat  90  to the wafer boat  66  (see  FIG. 3 ) positioned below the main-processing apparatus  40 . After the transfer of the wafers W is finished, the wafer boat  66  is loaded into the process container  60  of the main-processing apparatus  40  to perform the main process on the surface of the wafers W in an activated state, such as a film formation process of, e.g., forming a gate insulating film thereon. For example, the gate insulating film may consist of SiO 2  or a high-k (high specific dielectric constant) material, such as HfSiO or HfO 2 . 
     After the main process is finished, the wafer boat  66  is moved down and unloaded from process container  60 . Then, the wafers W thus processed are transferred by the transfer arm unit  46  into the empty transfer container  18  within the load-lock box  22 . After the transfer is finished, the transfer container  18  is carried out onto the outside I/O table  16 , thereby completing the operation sequence. As described above, according to the processing system  2 , the removal process (pre-process) for removing an oxide film on the target object surface and the main process, such as film formation, can be continuously and efficiently performed. After the surface of the wafers W is set in an activated state by the pre-process, they are immediately transferred through an inactive gas or N 2  gas atmosphere within the casing  4  and loaded into the main-processing apparatus  40 . Accordingly, the wafer surface never suffers a natural oxide film formed thereon again. 
     [Operation of Film Transformation Apparatus] 
     As shown in  FIG. 5 , the wafer boat  90  is rotated while the interior of the process container  94  is airtightly closed by the lid  92 . Further, while the interior of the process container  94  is vacuum-exhausted, NF 3  gas used as the second process gas is supplied from the second gas supply circuit  108  into the process container  94 . Furthermore, N 2  gas, H 2  gas, and NH 3  gas used as the first process gas are supplied from the first gas supply circuit  122 . NF 3  gas may be supplied along with an inactive gas, such as N 2  gas, used as a carrier gas. The first process gas is turned into plasma within the plasma generation field  121  by microwaves of, e.g., 2.45 GHz transmitted from the microwave generator  120  of the active species supply portion  112 . Consequently, the first process gas is activated and active species are thereby generated. 
     The active species are supplied through the opening  114  into a vertically long supply head region  106  and diffused in the vertical direction within the region  106 . Then, the active species are mixed with NF 3  gas spouted from the gas holes  110 A of the distribution nozzle  110 . This mixture gas is rectified by the rectifier plate  124  to be in a laminar flow state and flows in the horizontal direction into the gaps between the wafers W supported on the wafer boat  90 . At this time, the mixture gas reacts with a natural oxide film on the surface of the wafers W, and an intermediate film of ammonium silicofluoride is thereby formed, as described later. The residual gas having passed through the gaps between the wafers W enters the vertically long exhaust buffer region  128  on the side opposite to the supply head region  106 , and is exhausted out of the apparatus by the vacuum exhaust system  130 . 
     The reaction mechanism at this time proceeds, as follows. Specifically, when active species of the first process gas, such as N*, H*, NH*, NH 2 *, and NH 3 * (hereinafter, the symbol “*” denotes active species), react with NF 3 , an intermediate substance (etchant: NH x F y : x and y are positive numbers) is produced. Then, the intermediate substance reacts with a natural oxide film (SiO 2 ) to generate an intermediate film of ammonium silicofluoride [(NH 4 ) 2 SiF 6 ] and water (H 2 O). The ammonium silicofluoride can be decomposed or sublimated more easily than the natural oxide film. 
     The pressure inside the process container  94  in the film transformation process is set to be within a range of, e.g., abut 100 to 400 Pa. During the film transformation process, the mixture gas tends to have a high temperature, and thus the wafers W are likely heated by the mixture gas. However, a cooling medium, such as cooling water, is supplied into the thermal medium passage  138  of the cooling mechanism  136  arranged on the process container  94 . Consequently, the wafer temperature can be cooled and maintained around room temperature, such as 20 to 30° C., so that the intermediate film is efficiently formed with high selectivity. 
     An explanation will be given of the reason as to why the temperature of the wafer W is maintained around room temperature in the film transformation process.  FIG. 9  is a graph showing the temperature dependency of etching amount for a silicon oxide film (natural oxide film) and a silicon film (poly-crystalline silicon). It should be noted that the term “etching amount” used here means the film thickness of the intermediate film formed by reaction with the etchant described above. In  FIG. 9 , a line L 1  represents the natural oxide film, and a line L 2  represents the silicon film. 
     As shown in  FIG. 9 , the etching amount for the silicon film is almost constant, regardless of temperature, while the etching amount for the natural oxide film is increased with decrease in the temperature. Accordingly, the selectivity for the silicon film is increased with decrease in the temperature. However, if the wafers W are excessively cooled, the process container  94  of the film transformation apparatus  42  unfavorably suffers dew condensation generated on the outer wall due to moisture in atmosphere. Accordingly, in order to etch the natural oxide film with high selectivity relative to the silicon film (i.e., without damaging the underlying silicon film), the wafer temperature is preferably set to be within a range of about 20 to 30° C. 
     As described above, according to the film transformation apparatus  42 , the natural oxide film on the surface of the wafers W can be efficiently transformed into the intermediate film. The mixture gas of the second process gas with the active species is rectified by the rectifier plate  124  to be in a laminar flow state when it flows from the supply head region  106  toward the center of the process container  94 . Consequently, the gas is prevented from forming a turbulent flow, thereby coming into uniform contact with the wafer surface. The members exposed to the atmosphere inside the container, such as the process container  94 , lid  92 , wafer boat  90 , and rectifier plate  124 , are made of a metal material, such as aluminum, covered with a corrosion resistant coating, such as an alumite coating, so that they are not corroded. After the processed wafers W are unloaded downward, the load port  94 A at the bottom of the process container  94  is covered with the shutter member  142  (see  FIG. 4 ) to prevent particles or the like generated from the intermediate film from scattering. 
     [Operation of Heat-processing Apparatus] 
     As shown in  FIG. 8 , the wafer boat  90  is rotated while the interior of the process container  150  is airtightly closed by the lid  92 . Further, while the interior of the process container  150  is vacuum-exhausted, the wafers W are heated up and maintained at a predetermined temperature. In this respect, even when the heat-processing apparatus  44  is in an idling state, the outer heater  152  is maintained in the ON-state, to heat the process container  150  at a certain temperature. Then, when the wafers W are loaded into the process container  150  after they are processed in the film transformation apparatus  42 , the inner heater  154  is also turned on to heat up the wafers W. In this case, since the container itself is pre-heated, the temperature of the wafers W can be swiftly increased to a predetermined temperature. 
     When the wafers W are heated to a high temperature, as described above, the intermediate film of ammonium silicofluoride [(NH 4 ) 2 SiF 6 ] formed on the wafer surface is decomposed to gases, such as SiF4, NH 3 , HF, and H 2 O, or directly sublimated to gas, and thereby removed. As a result, the wafer surface is turned into a state where a clean and active silicon surface with hydrogen termination is exposed thereon. During this heat-process, in order to promote exhaust of the decomposition gases or sublimation gas, an inactive gas, such as N 2  gas, may be supplied from the inactive gas supply circuit  164  at a controlled flow rate. 
     The process pressure within this process container  150  during this heat-process is preferably set to be as low as possible, such as about 1 to 1,000 Pa. Further, the wafer temperature is preferably set to be within a range of 150 to 250° C.  FIG. 10  is a graph showing the vapor pressure curve of ammonium silicofluoride. As shown in  FIG. 10 , the higher the temperature is, the larger the decomposition or sublimation rate of ammonium silicofluoride becomes. If the wafer temperature is higher than 250° C., thermal damage is unfavorably caused to various films formed on the wafers in advance. Further, if the wafer temperature is lower than 150° C., the decomposition or sublimation rate is decreased to an unfavorably low level. 
     The process container  150  is provided with the inner heater  154  comprising the carbon wire heaters  154 A. This heater can not only quickly heat up the wafers W to efficiently remove the intermediate film, but also prevent contamination of the wafers W. The process container  150  is made of a metal material, such as aluminum, with the inner surface covered with a corrosion resistant coating, such as an alumite coating, as in the process container  94  of the film transformation apparatus  42 . The process container  150  can be thus durable against corrosive gases generated by decomposition or sublimation of the intermediate film. After the processed wafers W are unloaded downward, the load port  150 A at the bottom of the process container  150  is covered with the shutter member  172  (see  FIG. 4 ) to prevent heat radiation and particle scattering into the re-process area  10 . 
     Film Transformation Apparatus According to Modification of First Embodiment 
       FIG. 11  is a sectional side view showing a film transformation apparatus (vertical batch pre-processing apparatus)  200  according to a modification of the first embodiment, which may be used in the processing system  2  shown in  FIG. 1 .  FIGS. 12A and 12B  are sectional plan views respectively showing two different structures of the plasma generation field used in the film transformation apparatus  200  shown in  FIG. 11 . This modified apparatus  200  has essentially the same structure as the apparatus  42  shown in  FIG. 5 , except for the process gas supply circuits and plasma generation mechanism. The apparatus  42  shown in  FIG. 5  uses microwaves of, e.g., 2.45 GHz to generate plasma, while the apparatus  200  shown in  FIG. 11  uses an RF (radio frequency) power of, e.g., 13.56 MHz. 
     Specifically, in the film transformation apparatus  200 , a first process gas comprising N 2 , H 2 , and NH 3  gases is directly supplied through an opening  114  into a vertically long supply head region  106 . Further, the supply head region  106  is also arranged to serve as a plasma generation field  202  for generating plasma and thereby producing active species. Specifically, the plasma generation field  202  includes an electrode  204 , which is made of aluminum covered with an alumite-processed surface, and extends in the longitudinal direction of the supply head region  106 . The electrode  204  is connected to an RF power supply  206  for applying an RF power of, e.g., 13.56 MHz through a feeder line  208 . The feeder line  208  is provided with a matching circuit  210  for impedance alignment to increase the RF plasma generation efficiency. 
     In one manner, as shown in  FIG. 12A , a pair of electrodes  204  are disposed to face each other on the opposite walls forming the supply head region  106 . In order to electrically isolate each of the electrodes  204  from the wall of the supply head region  106 , an insulating  212  made of, e.g., alumina is interposed between the electrode and wall. Further, a sealing member  214 , such as an O-ring, is disposed on either side of each insulating  212  to keep this portion sealed. Each electrode  204  has a cooling water passage  216  formed therein to cool the electrode  204  in operation, thereby preventing the electrode  204  from being overheated by the RF power. An RF power supply  206  is connected to the pair of electrodes  204  through a feeder line  208 . Accordingly, as indicated by an arrow  218  in  FIG. 12A , an electric field can be formed between the electrodes  204 . 
     In another manner, as shown in  FIG. 12B , only one of the electrodes  204  shown in  FIG. 12A , e.g., a lower side electrode  204  in this example, is disposed. An RF power supply  206  is connected between the electrode  204  and the grounded process container  94  through a feeder line  208 . Accordingly, as indicated by an arrow  220  in  FIG. 12B , an electric field can be formed between the electrode  204  and the grounded portion of the process container  94  (including the wall of the supply head region  106  and the rectifier plate (ion shield plate)  124 ). 
     The vertically long opening portion of the supply head region  106  is provided with an ion shield plate  224  that is grounded. The ion shield plate  224  prevents plasma generated in the supply head region  106  from leaking into the process container  94 . Specifically, the ion shield plate  224  is structured as in the rectifier plate  124  according to the first embodiment. As shown in  FIG. 7 , the ion shield plate  224  consists of an aluminum plate having a thickness of, e.g., about 10 mm with a number of gas distribution holes  126  formed therein at predetermined intervals. The ion shield plate  224  is fit in and attached to the vertically long opening portion of the supply head region  106 . The surface of the ion shield plate  224  is totally covered with, e.g., an alumite coating to increase the corrosion resistance. The entirety of the ion shield plate  224  is grounded. 
     Since plasma is prevented from leaking from the supply head region  106  by the ion shield plate  224 , the wafers W placed in the process container  94  are protected from plasma damage. Further, the gas containing active species is rectified by the ion shield plate  224  into a laminar flow state. The distribution nozzle  110  of the second gas supply circuit  108  is disposed inside the process container  150  on the inner side of the ion shield plate  224 , instead of inside the supply head region  106 . Accordingly, the second process gas or NF 3  gas is not turned into plasma. 
     The apparatus  200  shown in  FIG. 11  provides the same effects as in the apparatus  42  shown in  FIG. 5 . Specifically, N 2  gas, H 2  gas, and NH 3  gas used as the first process gas are supplied from the first gas supply circuit  122  through the supply pipe  110  into the supply head region  106 , and diffused in the vertical direction within the region  106 . The first process gas is turned into plasma and thereby activated to produce active species by an RF power applied from the RF power supply  206  to the electrode  204 . The active species flow in the horizontal direction while being rectified by the rectifying function of the ion shield plate  224  to be in a laminar flow state. The active species are mixed with NF 3  gas delivered from the gas holes  110 A of the distribution nozzle  110 , and flow in a laminar flow state into the gaps between the wafers W supported on the wafer boat  90 . At this time, the mixture gas reacts with a natural oxide film on the surface of the wafers W, and an intermediate film of ammonium silicofluoride is thereby formed, as described previously. The residual gas having passed through the gaps between the wafers W enters the vertically long exhaust buffer region  128  on the side opposite to the supply head region  106 , and is exhausted out of the apparatus by the vacuum exhaust system  130 . 
     According to the apparatus  200  shown in  FIG. 11 , the ion shield plate  224  is disposed on the opening of the supply head region  106  to prevent plasma from leaking from the supply head region  106 . With this arrangement, the wafers W placed in the process container  94  are protected from plasma damage. The frequency of the RF power is not limited to 13.56 MHz, and it may be another frequency, such as 27 MHz or 40 MHz. 
     Second Embodiment 
     [Semiconductor Processing System] 
       FIG. 13  is a perspective view schematically showing a semiconductor processing system according to a second embodiment of the present invention.  FIG. 14  is a sectional plan view schematically showing the processing system shown in  FIG. 13 . The processing system  230  according to the second embodiment includes a pre-processing apparatus (vertical batch pre-processing apparatus)  232 , which is a combination of a film transformation apparatus  42  according to the first embodiment with a heat-processing function. 
     Specifically, the processing system  230  includes an airtight casing  4 X having a shape formed such that the portion corresponding to the heat-processing apparatus  44  (see  FIG. 1 ) is removed from the casing  4  shown in  FIG. 1 . As shown in  FIG. 14 , the casing  4 X defines therein an airtight handling area  5 X for handling semiconductor wafers (typically made of silicon) as target objects. The handling area  5 X is formed of a main-process area  8  the same as that shown in  FIG. 2 , and a pre-process area  10 X having a floorage about half of the floorage of the pre-process area  10  shown in  FIG. 2 . The pre-processing apparatus  232  is connected to the ceiling portion of the pre-process area  10 X at a position corresponding to the film transformation apparatus  42  (see  FIG. 1 ). Since the pre-process area  10 X is not required to shift a wafer boat  90  in the horizontal direction, it is provided with a boat shifter  50  that has no horizontal drive portion  50 B (see  FIG. 2 ) but consists of a vertical drive portion  50 A. 
     In other respects, the processing system  230  is structured almost the same as the processing system  2  according to the first embodiment. Accordingly, the processing system  230  can reduce the equipment cost and occupied area, in addition to providing the same effects as in the processing system  2  according to the first embodiment. 
     [Pre-processing Apparatus] 
       FIG. 15  is a sectional side view showing the vertical batch pre-processing apparatus  232  disposed in the processing system  230  shown in  FIG. 13 . The pre-processing apparatus  232  has essentially the same structure as the film transformation apparatus  42  shown in  FIG. 5 , and further includes a heated inactive gas supply circuit  233 . In other words, the pre-processing apparatus  232  is structured by adding the heated inactive gas supply circuit  233  to the film transformation apparatus  42  shown in  FIG. 5 . 
     The heated inactive gas supply circuit  233  includes a distribution nozzle  234  inside the process container  94  on the inner side of the rectifier plate  124 . The distribution nozzle  234  has a plurality of gas holes  234 A arrayed in the vertical direction essentially over all the wafers W supported on the boat. The gas holes  234 A deliver the heated inactive gas in the horizontal direction, so as to supply the gas toward the center of the process container  94 . The distribution nozzle  234  is made of a material resistant to corrosion caused by the first and second process gases, such as aluminum with the surface covered with an alumite coating. 
     The distribution nozzle  234  is connected to a gas line  238  provided with a gas heating unit  236  for heating an inactive gas, such as N 2  gas. The gas heating unit  236  is capable of heating N 2  gas to a temperature within a range of, e.g., about 800 to 1,000° C. 
     The process container  94  is provided with a temperature control mechanism  242  to selectively cool and heat the container wall. Specifically, the temperature control mechanism  242  includes a thermal medium passage  138  formed in the wall of the process container  94 . A cooling medium and a heating medium are alternatively supplied from the thermal medium source  240  into the thermal medium passage  138  to maintain the process container  94  at a predetermined temperature. For example, the temperature control mechanism  242  supplies the cooling medium while the intermediate film is being formed, and supplies the heating medium while the intermediate film is being removed. The cooling medium may be a chiller. 
     When the intermediate film formation step is performed, the pre-processing apparatus  232  is operated as in the film transformation apparatus  42  shown  FIG. 5 , while the heated inactive gas supply circuit  233  is set in the OFF-state. Specifically, the first process gas is supplied from the first gas supply circuit  122 , and is activated to produce active species, utilizing plasma generated by microwaves applied from the microwave generator  120 . The active species are mixed with the second process gas or NF 3  gas supplied from the second gas supply circuit  108 , and the mixture gas is delivered from the supply head region  106  and spread over the wafers W. The mixed gas reacts with a natural oxide film (SiO 2 ) on the wafer surfaces to form an intermediate film of ammonium silicofluoride. During this process, the thermal medium source  240  of the temperature control mechanism  242  supplies the cooling medium into the thermal medium passage  138  to cool the process container  94 . Consequently, the wafers W are maintained at, e.g., room temperature or a temperature within a range of about 10 to 20° C. 
     After the intermediate film formation step is performed for a predetermined time, the intermediate film removal step is performed. Specifically, the first and second process gases are stopped, and the microwaves are also stopped. Then, operation of the heated inactive gas supply circuit  233  is started to deliver N 2  gas heated at the gas heating unit  236  from the gas holes  234 A of the distribution nozzle  234 . Consequently, the wafers W are heated to decompose or sublimate and thereby remove the intermediate film. 
     At this time, for example, N 2  gas is heated to about 800 to 1,000 by the gas heating unit  236 , so that the wafers W are heated to about 150 to 250° C. Further, the process pressure inside the process container  94  is set at a value within a range of about 100 to 80 kPa, so that the decomposition rate or sublimation rate of the intermediate film is sufficiently large. At this time, the thermal medium source  240  supplies the heating medium in place of the cooling medium into the thermal medium passage  138  to heat the process container  94  to a temperature within a range of, e.g., about 60 to 80° C. Consequently, the decomposition or sublimation of the intermediate film is promoted. After the intermediate film removal step is performed for a predetermined time, the pre-process is completed. Thereafter, the wafers W are processed in the main-processing apparatus  40 . 
     As described above, according to the pre-processing apparatus  232 , the intermediate film formation step and intermediate film removal step are serially performed within a single apparatus. Accordingly, the equipment cost is reduced, the throughput is improved, and the occupied area of the processing system  230  is reduced. 
     Pre-processing Apparatus According to Modification of Second Embodiment 
       FIG. 16  is a sectional side view showing a vertical batch pre-processing apparatus  250  according to a modification of the second embodiment, which may be used in the processing system  230  shown in  FIG. 13 . This modified pre-processing apparatus  250  is structured by adding the heated inactive gas supply circuit  233  and temperature control mechanism  242  described with reference to  FIG. 15  to the film transformation apparatus  200  shown in  FIG. 11 . 
     The heated inactive gas supply circuit  233  includes a distribution nozzle  234  inside the process container  94  on the inner side of the ion shield plate  224  and next to the second gas supply circuit  108 . As described above, the distribution nozzle  234  has a plurality of gas holes  234 A to deliver a heated inactive gas, such as N 2  gas, during the intermediate film removal step. 
     When the intermediate film formation step is performed, the pre-processing apparatus  250  is operated as in the film transformation apparatus  200  shown  FIG. 11 , while the heated inactive gas supply circuit  233  is set in the OFF-state. Specifically, the first process gas is supplied from the first gas supply circuit  122  into the supply head region  106 , and is activated to produce active species, utilizing plasma generated by an RF power applied from the RF power supply  206 . The active species are delivered through the ion shield plate  224  into the process container  94 , and mixed with NF 3  gas supplied from the second gas supply circuit  108 , so that the mixture gas is spread over the wafers W. The mixed gas reacts with a natural oxide film (SiO 2 ) on the wafer surfaces to form an intermediate film of ammonium silicofluoride. During this process, the thermal medium source  240  of the temperature control mechanism  242  supplies the cooling medium into the thermal medium passage  138  to cool the process container  94 . Consequently, the wafers W are maintained at, e.g., room temperature or a temperature within a range of about 10 to 20° C. 
     After the intermediate film formation step is performed for a predetermined time, the intermediate film removal step is performed. Specifically, the first and second process gases are stopped, and the RF power is also stopped. Then, operation of the heated inactive gas supply circuit  233  is started to deliver N 2  gas heated at the gas heating unit  236  from the gas holes  234 A of the distribution nozzle  234 . Consequently, the wafers W are heated to decompose or sublimate and thereby remove the intermediate film. 
     At this time, for example, N 2  gas is heated to about 800 to 1,000 by the gas heating unit  236 , so that the wafers W are heated to about 150 to 25° C. Further, the process pressure inside the process container  94  is set at a value within a range of about 100 to 80 kPa, so that the decomposition rate or sublimation rate of the intermediate film is sufficiently large. At this time, the thermal medium source  240  supplies the heating medium in place of the cooling medium into the thermal medium passage  138  to heat the process container  94  to a temperature within a range of, e.g., about 60 to 80° C. Consequently, the decomposition or sublimation of the intermediate film is promoted. After the intermediate film removal step is performed for a predetermined time, the pre-process is completed. Thereafter, the wafers W are processed in the main-processing apparatus  40 . 
     As described above, according to the pre-processing apparatus  250 , the intermediate film formation step and intermediate film removal step are serially performed within a single apparatus. Accordingly, the equipment cost is reduced, the throughput is improved, and the occupied area of the processing system  230  is reduced. 
     Third Embodiment 
     [Semiconductor Processing System] 
       FIG. 17  is a perspective view schematically showing a semiconductor processing system according to a third embodiment of the present invention.  FIG. 18  is a sectional plan view schematically showing the processing system shown in  FIG. 17 . The processing system  260  according to the third embodiment includes a pre-processing apparatus  262 , which has the same function as the pre-processing apparatus  232  according to the second embodiment, but is disposed on one side of a casing  4 Y. 
     Specifically, the processing system  260  includes an airtight casing  4 Y having a shape formed such that the portion corresponding to the pre-process area  10  is removed from the casing  4  shown in  FIG. 1 . As shown in  FIG. 18 , the casing  4 Y defines therein an airtight handling area  5 Y for handling semiconductor wafers (typically made of silicon) as target objects, which is formed only of the same main-process area  8  as that shown in  FIG. 2 . The pre-processing apparatus  262  is connected to one side of the casing  4 Y at a position corresponding to the outside of the slide door  14  of the pre-process area  10  shown in  FIG. 2 . Since the pre-processing apparatus  262  does not require shifting a wafer boat  90  in either the vertical or horizontal direction, the boat shifter  50  is not disposed. 
     In other respects, the processing system  260  is structured almost the same as the processing system  2  according to the first embodiment. Accordingly, the processing system  260  can reduce the equipment cost and occupied area, in addition to providing the same effects as in the processing system  2  according to the first embodiment. 
     [Pre-processing Apparatus] 
       FIG. 19  is a sectional side view showing the vertical batch pre-processing apparatus  262  disposed in the processing system  260  shown in  FIG. 17 . The pre-processing apparatus  262  includes a process container  94  having an essentially semi-elliptic shape in the cross section. The process container  94  has a vertically long load port  264  (see  FIG. 18 ) formed in the side wall, through which the wafers W are loaded and unloaded. The process container  94  is directly attached and fixed to one side of the casing  4 Y, so that the load port  264  faces the slide door  14 . The slide door  14  is arranged to airtightly close the load port  264  of the process container  94 . Since the slide door  14  is a member that partly defines the process container  94 , the surface of the slide door  14  to be exposed to the process gases is covered with a corrosion resistant coating, such as an alumite coating. 
     The wafers W are transferred to and from the wafer boat  90  placed in the process container  94  through the load port  264 , which has been opened by moving the slide door  14  in the horizontal direction. The pre-processing apparatus  262  does not require loading or unloading the wafer boat  90  to and from the process container  94 . Accordingly, the bottom of process container  94  is closed and provided with a rotary shaft  100  rotatably connected by the magnetic-fluid seal  98 . The pre-processing apparatus  262  thus does not need the boat shifter  50  (including the vertical drive portion  50 A and horizontal drive portion  50 B shown in  FIG. 2 ) necessitated in each of the embodiments described above. Since the whole operation of the pre-processing apparatus  262  is the same as that of the pre-processing apparatus  232  shown in  FIG. 15 , the description thereon will be omitted. 
     Pre-processing Apparatus According to Modification of Third Embodiment 
       FIG. 20  is a sectional side view showing a vertical batch pre-processing apparatus  270  according to a modification of the third embodiment, which may be used in the processing system  260  shown in  FIG. 17 . This modified pre-processing apparatus  270  is structured by adding the changes described with reference to  FIG. 19  to the film transformation apparatus  250  shown in  FIG. 16 . 
     The pre-processing apparatus  270  includes a process container  94  having an essentially semi-elliptic shape in the cross section. The process container  94  has a vertically long load port  264  (see  FIG. 18 ) formed in the side wall, through which the wafers W are loaded and unloaded. The process container  94  is directly attached and fixed to one side of the casing  4 Y, so that the load port  264  faces the slide door  14 . The slide door  14  is arranged to airtightly close the load port  264  of the process container  94 . Since the slide door  14  is a member that partly defines the process container  94 , the surface of the slide door  14  to be exposed to the process gases is covered with a corrosion resistant coating, such as an alumite coating. 
     The wafers W are transferred to and from the wafer boat  90  placed in the process container  94  through the load port  264 , which has been opened by moving the slide door  14  in the horizontal direction. The pre-processing apparatus  270  does not require loading or unloading the wafer boat  90  to and from the process container  94 . Accordingly, the bottom of process container  94  is closed and provided with a rotary shaft  100  rotatably connected by the magnetic-fluid seal  98 . Since the whole operation of the pre-processing apparatus  270  is the same as that of the pre-processing apparatus  250  shown in  FIG. 16 , the description thereon will be omitted. 
     In the third embodiment, the sectional shape of the process container  94  is not limited to a semi-elliptic shape (see  FIGS. 17 and 18 ), and it may be another shape, such as a square shape in the cross section. 
     Matters Common to First to Third Embodiments 
     In the embodiments described above, the transfer port unit  20  is exemplified by a structure using the load-lock box  22 . However, for example, there is a case where used as a transfer container  18  is an airtight container filled with N 2  gas, such as a SMIFBOX™ or FOOP™. In this case, the transfer port unit  20  may have a structure directed to such a special container. Typically, the door for airtightly closing a transfer port is provided with a drive portion for opening and closing the lid of a SMIFBOX or the like. The SMIFBOX or the like is pressed airtightly against the transfer port, and the lid is detached by the drive portion disposed on the door. Then, the door is moved along with the lid from the transfer port, so that the SMIFBOX or the like is opened in an airtight state to the handling area. 
     In the embodiments described above, the handling area is entirely filled with an inactive gas (N 2 ). Alternatively, the handling area may be maintained in a vacuum state hardly containing O 2  gas components. The present invention may be applied to removal of an SiO 2  film formed by a thermal CVD or plasma CVD process, in place of removal of a natural oxide film. The second process gas is not limited to NF 3  gas, and it may be another gas containing a halogen element, such as N 2 F 4  (tetrafluorohydrazine). Further, the inactive gas used here is not limited to N 2  gas, and it may be another inactive gas, such as Ar gas or He gas. The main process performed by the main-processing apparatus  40  is not limited to a film formation process, and the present invention may be applied to various processes which require performing a process on an activated wafer surface. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.