Abstract:
A photolithographic apparatus in which a light source exposes a substrate for patterning includes an enclosure having a controllable internal ambient for transferring the substrate in and out of the apparatus, a gate valve through which the substrate is transferred into or out of the enclosure, and a gas ejection unit for ejecting a gas into a region in close proximity to the gate valve, and in a direction substantially perpendicular to the direction of movement of the substrate as it is transferred into or out of the enclosure. A gas curtain is formed by the gas ejected by the gas ejection unit, such that an opening of the gate valve is shielded by the gas curtain, thereby suppressing intrusion or leakage of an ambient gas which can occur when the substrate is transferred in or out of the apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exposure apparatus for exposing a wafer so as to transfer a reticle pattern onto the wafer, a coating/developing apparatus for coating a resist on a wafer and developing the resist-coated wafer, a method of transferring a substrate (e.g., a reticle, a wafer), a method of producing a device, a semiconductor production factory, and a method of maintaining an exposure apparatus. 
     2. Description of the Related Art 
     A recent trend in the exposure apparatus industry has been to reduce the wavelength of exposure light to enhance resolution, thereby allowing exposure of an even finer pattern. A fluorine (F 2 ) excimer laser is an example of a light source capable of emitting light with a short wavelength. If an exposure apparatus employs a fluorine excimer laser, however, it is necessary to purge oxygen (O 2 ) from the optical path of the exposure light to prevent a reduction in transmission of the exposure light. More specifically, it is desirable that the oxygen concentration in the path of the exposure light be less than about 1 ppm. 
     When a substrate such as a wafer or a reticle is transferred from a coating/developing apparatus (CD apparatus), having an ambient of atmospheric air, into an exposure apparatus, having a low-oxygen-concentration ambient such as an inert gas, the transfer is effected through a load lock chamber (LL chamber) to prevent intrusion of oxygen from the atmospheric air into the exposure apparatus. More specifically, the wafer or the reticle first is transferred from the CD apparatus into the LL chamber, which initially is filled with atmospheric air. The atmospheric air in the LL chamber then is replaced with an inert gas. After that, the wafer or the reticle is transferred into the exposure apparatus having an ambient of the inert gas. 
     A problem with the foregoing process is that it takes a long time to replace the atmospheric air in the LL chamber with the inert gas. Thus, the wafer or the reticle must remain in the LL chamber until the atmospheric air has been replaced. This limits throughput. 
     SUMMARY OF THE INVENTION 
     The present invention provides a technique for suppressing intrusion or leakage of an ambient gas which can occur when a substrate is carried between apparatuses such as an exposure apparatus, a coating/developing apparatus, and a load lock chamber, thereby achieving an improvement in throughput and a reduction in operating cost. 
     According to one aspect of the present invention, there is provided an exposure apparatus comprising an enclosure having a controllable internal ambient; a gate valve through which a substrate is transferred into or out of the enclosure; and gas ejection means for ejecting a gas into a region in close proximity to the gate valve, and in a direction substantially perpendicular to the direction of movement of the substrate as it is transferred into or out of the enclosure, wherein a gas curtain is formed by the gas ejected by the gas ejection means, such that an opening of the gate valve is shielded by the gas curtain. A stage on which a substrate such as a wafer or a reticle is placed during an exposure process may be provided within the enclosure. 
     According to another aspect of the present invention, there is provided a coating/developing apparatus comprising a resist coating unit for coating a resist on a wafer and a developing unit for developing the wafer. The coating/developing apparatus further comprises an enclosure in which the resist coating unit and the developing unit are disposed, the enclosure having a controllable internal environment; a gate valve through which a substrate is transferred into or out of the enclosure; and gas ejection means for ejecting a gas into a region in close proximity to the gate valve, and in a direction substantially perpendicular to the direction of movement of the substrate as it is transferred into or out of the enclosure, wherein a gas curtain is formed by the gas ejected by the gas ejection means, such that an opening of the gate valve is shielded by the gas curtain. 
     Preferably, the gas is ejected in a direction substantially parallel to a face of the substrate so that the substrate does not disturb the flow of the gas curtain as it passes therethrough. 
     Although the ejected gas may have the same composition as that of the atmospheric air, it is desirable to employ a gas having the same composition as that of the ambient gas in each chamber. More specifically, a gas having the same composition as that of a purge gas used to purge oxygen or moisture may be employed. An example is a pure inert gas such as pure nitrogen gas or pure helium gas. Use of such a gas makes it possible to create a gas curtain without causing an increase in the oxygen concentration of the ambient of the apparatus in which the gas curtain is created. 
     A guide may be disposed near a gas ejection unit for the gas curtain and also at the opposite end of the gas curtain to regulate the flow of the gas. This prevents mixing between the gas of the gas curtain and the ambient gas. Thus it is possible to form the gas curtain using a low-cost gas such as atmospheric air (or a gas having a higher oxygen content than the ambient gas). Even when an inert gas is used for the gas curtain, use of the guide prevents turbulent flow from occurring in the gas curtain, further enhancing the sealing capability. 
     In the present invention, although the gas of the gas curtain may be ejected at a constant flow rate throughout the process, it is preferable that, in order to reduce operating costs, the gas curtain be created only when necessary or that the flow rate of the gas curtain be changed as required. 
     In a specific example, a concentration detection means (such as a sensor, or a F 2  light transmission meter) is disposed to detect the concentration of oxygen or moisture in the internal ambient of an enclosure enclosing an exposure apparatus, a coating/developing apparatus, or a load lock chamber disposed between the exposure apparatus and the coating/developing apparatus. A means is disposed for turning on or off the gas curtain or continuously varying the flow rate of the gas curtain in accordance with the concentration detected by the concentration detection means. 
     In another specific example, a substrate detection means (such as a sensor, or means for detection by means of a sequence) is disposed to detect the presence or absence of a substrate in a region close to the gate valve, and a means is disposed for turning on or off the gas curtain or continuously varying the flow rate of the gas curtain, in response to the detection of the presence or absence of the substrate. 
     In the system according to the present invention, when the gate valve is opened to transfer a substrate, if a sensor detects that the substrate is being passed through the gate valve, a control signal is sent to the flow rate control means to increase the flow rate of the gas curtain, thereby preventing the intrusion of oxygen. When wafers are continuously transferred, the opening in the gate valve is sealed with the gas curtain. Otherwise, the gate valve closes when transferring is not performed for a while. This allows the gas of the gas curtain to be saved. 
     In the system according to the present invention described above, it is possible to transfer a wafer or a reticle into the exposure apparatus even when the environment outside the exposure apparatus includes a relatively high oxygen concentration. This reduces the time needed to replace the gas in the load lock chamber with an inert gas. 
     According to still another aspect of the present invention, there is provided a method of transferring a reticle or a wafer into or out of an exposure apparatus, the method comprising the steps of controlling an ambient in an enclosure; opening and closing a gate valve disposed in the enclosure; transferring the reticle or the wafer into or out of the enclosure through the gate valve; and ejecting a gas into a region in close proximity to the gate valve and in a direction substantially perpendicular to the direction of movement of the reticle or the wafer as it is transferred into or out of the enclosure, wherein a gas curtain is formed by the ejected gas, such that an opening of the gate valve is shielded by the gas curtain. 
     Preferably, the exposure apparatus according to the present invention further includes a display, a network interface, and a computer for executing a network software program, thereby allowing maintenance information for the exposure apparatus to be transmitted by means of data communication via a computer network. The network software program provides a user interface displayed on the display to access, via an external network, a maintenance database provided by a vendor of the exposure apparatus or by a user thereof, thereby obtaining information from the maintenance database. 
     According to another aspect of the present invention, there is provided a method of producing a semiconductor device, including the steps of installing, in a semiconductor production factory, a plurality of production apparatuses for performing various processes including an exposure; and producing a semiconductor device by means of a plurality of processes using the production apparatuses. The method may further include the steps of connecting the production apparatuses to each other via a local area network; and transmitting, by means of data communication, information about at least one of the production apparatuses between the local area network and an external network outside the semiconductor production factory. The method may further include the step of accessing a database provided by a vendor of the exposure apparatus or provided by a user via an external network to obtain maintenance information for the exposure apparatus or the step of performing data communication with another semiconductor production factory, thereby managing production. 
     According to another aspect of the present invention, there is provided a semiconductor production factory, including a plurality of production apparatuses for performing various processes, including the exposure apparatus of the present invention; a local area network for connecting the plurality of production apparatuses; and a gateway for connecting the local area network to an external network outside the factory, thereby making it possible to transmit information about at least one of the production apparatuses by means of data communication. 
     According to still another aspect of the present invention, there is provided a method of maintaining an exposure apparatus, including the steps of providing, by a vendor of or a user of the exposure apparatus, a maintenance database connected to an external network outside a semiconductor production factory; giving permission to access the maintenance database from the semiconductor production factory via the external network; and transmitting maintenance information stored in the maintenance database to the semiconductor production factory via the external network. 
     Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view illustrating an example of a semiconductor exposure apparatus including a fluorine (F 2 ) excimer laser as a light source, according to the present invention; 
     FIG. 2 is a schematic diagram illustrating an exposure apparatus and associated apparatuses according to a first embodiment of the present invention; 
     FIG. 3 is a flow chart illustrating a process of carrying a wafer into the exposure apparatus through a load lock chamber, in the system shown in FIG. 2; 
     FIG. 4 is a schematic diagram illustrating an exposure apparatus and associated apparatuses according to a second embodiment of the present invention; 
     FIG. 5 is a flow chart illustrating an example of a process of carrying a wafer into the exposure apparatus through a load lock chamber, in the system shown in FIG. 4; 
     FIG. 6 is a flow chart illustrating another example of a process of carrying a wafer into the exposure apparatus through the load lock chamber, in the system shown in FIG. 4; 
     FIG. 7 is a schematic diagram illustrating an exposure apparatus and associated apparatuses according to a fourth embodiment of the present invention; 
     FIG. 8 is a flow chart illustrating a process of carrying a wafer into the exposure apparatus through a load lock chamber, in the system shown in FIG. 7; 
     FIG. 9 is a conceptual diagram of a production system for producing a semiconductor device, seen from a certain perspective; 
     FIG. 10 is a conceptual diagram of a production system for producing a semiconductor device, seen from another perspective; 
     FIG. 11 is a diagram illustrating a specific example of a user interface; 
     FIG. 12 is a flow chart of a device production process; and 
     FIG. 13 is a flow chart of a wafer process. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     FIG. 1 is a cross-sectional view illustrating an example of a semiconductor exposure apparatus including a fluorine (F 2 ) excimer laser as a light source, according to the present invention. 
     In FIG. 1, reference numeral  1  denotes a reticle stage on which a reticle having a pattern formed thereon is placed. Reference numeral  2  denotes a projection optical system (lens barrel) for projecting the pattern formed on the reticle onto a wafer. Reference numeral  3  denotes a wafer stage for carrying a wafer placed thereon in X, Y, Z, θ, and tilt directions. Reference numeral  4  denotes an illumination light system for illuminating the reticle with illumination light. Reference numeral  5  denotes an optical system for transmitting the light emitted from the light source to the illumination light system  4 . Reference numeral  6  denotes the F 2  laser which serves as the light source. Reference numeral  7  denotes a masking blade for blocking exposure light so that areas on the reticle other than the pattern area are not illuminated with the exposure light. Reference numerals  8  and  9  denote enclosures for enclosing the reticle stage  1  and the wafer stage  3  and the optical path of the exposure light. Reference numeral  10  denotes a helium-conditioning apparatus for conditioning a helium (He) ambient in the lens barrel  2  and the illumination light system  4 . Reference numerals  11  and  12  denote nitrogen-conditioning apparatuses for conditioning a nitrogen (N 2 ) ambient in the enclosures  8  and  9 . Reference numerals  13  and  14  denote load lock (LL) chambers which are used when a reticle and a wafer are carried into the enclosures  8  and  9 . Reference numerals  15  and  16  denote a reticle hand and a wafer hand, respectively, for carrying a reticle and a wafer. Reference numeral  17  denotes a reticle alignment detection system used in adjusting the position of the reticle. Reference numeral  18  denotes a reticle storage case for storing reticles in the enclosure  8 . Reference numeral  19  denotes a prealignment unit for prealigning a wafer. 
     FIG. 2 is a schematic diagram illustrating an exposure apparatus and associated apparatuses according to one embodiment of the present invention. In FIG. 2, reference numeral  21  denotes a coating and developing (CD) apparatus including a coating apparatus for coating a resist on a wafer  26  and a developing apparatus for developing an exposed wafer. Reference numeral  22  denotes an exposure apparatus. Reference numeral  14  denotes a LL chamber used when a wafer  26  is carried between the CD apparatus  21  and the exposure apparatus  22 . Reference numeral  23   a  denotes a gas curtain disposed between the CD apparatus  21  and the LL chamber  14 . Reference numeral  23   b  denotes a gas curtain disposed between the LL chamber  14  and the exposure apparatus  22 . Reference numeral  24   a  denotes a gate valve disposed between the CD apparatus  21  and the LL chamber  14 . Reference numeral  24   b  denotes a gate valve disposed between the LL chamber  14  and the exposure apparatus  22 . Reference numeral  25  denotes a guide for the gas curtain  23   a.    
     In the present embodiment, oxygen (O 2 ) in the CD apparatus  21  is purged with an inert gas such as N 2  so that the concentration of oxygen in the CD apparatus is about 1%. Similarly, O 2  in the LL chamber  14  and O 2  in the exposure apparatus  22  are purged and the O 2  concentrations in the LL chamber  14  and the exposure apparatus  22  are controlled at about 10 ppm and 1 ppm, respectively. Although in the present embodiment, the O 2  concentrations in the CD apparatus  21 , the LL chamber, and the exposure apparatus are controlled at about 1%, 10 ppm, and 1 ppm, respectively, the O 2  concentrations are not limited to those values. The allowable ranges of the O 2  concentrations in the respective apparatuses may be determined depending upon the effectiveness of the gas curtain in preventing disturbance of the ambient in the exposure apparatus. However, it is desirable that the O 2  concentration in the LL chamber be higher than that in the exposure apparatus, and the O 2  concentration in the CD apparatus be higher than that in the LL chamber. The flowing gas of the gas curtain  23   a  has the same composition of that of the atmospheric air. The flow of the gas curtain  23   a  is passed through a path provided by the guide  25  and circulated through a circulating system (not shown) such that the flow of the gas curtain  23   a  does not intrude into the CD apparatus  21 . On the other hand, the main ingredient of the flowing gas of the gas curtain  23   b  is N 2 , so that the flowing gas of the gas curtain  23   b  does not cause an increase in the concentration of O 2  or hydrogen (H 2 ) of the ambient in the exposure apparatus  22 . The LL chamber  1  is capable of replacing the ambient such that when the wafer  26  is in the LL chamber  14  during transfer of the wafer  26  from the CD apparatus  21  into the exposure apparatus  22 , the gate valves  24   a  and  24   b  at respective ends of the LL chamber  14  are closed and the internal ambient of the LL chamber  14  is replaced so as to reduce the oxygen concentration to a level that is lower than the maximum allowable value. 
     In the present embodiment, the gas of the gas curtain  23   a  or  23   b  is ejected through a gas ejection nozzle  27   a  or  27   b . Although the gas of the gas curtain may be ejected at a constant flow rate throughout the operation of the apparatus, it is preferable that control means be employed to turn the gas curtain on and off or to change the flow rate thereof, in synchronization with the operation of wafer carrying means (not shown) and/or the operation of the gate valves  24   a  and  24   b  disposed between the LL chamber  14  and the respective apparatuses. A method of turning the gas curtain on and off or changing the flow rate thereof using the control means is described below with reference to FIG.  3 . 
     FIG. 3 is a flow chart illustrating the process of carrying a wafer  26  into the exposure apparatus  22  through the LL chamber  14 . 
     First, in the CD apparatus  21 , a resist is coated on the wafer  26 . The resist-coated wafer  26  then is transferred into the LL chamber  14  through the gate valve  24   a . At this stage, the gate valve  24   b  on the side of the exposure apparatus  22  is in a closed state, and the gas curtain  23   b  is in an initial state in which no gas is ejected from the nozzle  27   b  (or a small amount of gas is ejected) (step S 101 ). The gate valve  24   a  on the side of the CD apparatus  21  then is closed and transfer of the wafer  26  is started (step S 102 ). When transfer of the wafer  26  is started in step S 102 , a gas curtain  23   b  is created. That is, gas is ejected from the nozzle  27   b  (or the flow rate is increased) synchronously with the start of transferring the wafer  26  (step S 103 ). Thereafter, the gate valve  24   b  located between the LL chamber  14  and the exposure apparatus  22  is opened (step S 104 ), and the wafer  26  is moved from the LL chamber  14  into the exposure apparatus  22  (step S 105 ). In the above process, the gas of the gas curtain  23   b  is ejected such that the flow of gas passes by a side of the wafer  26  without striking the broad surface of the wafer  26 , thereby preventing turbulent flow from occurring. After the wafer  26  has been transferred into the exposure apparatus  22  (step S 106 ), the gate valve  24   b  is closed (step S 107 ), and the ejection of the gas of the gas curtain  23   b  is stopped (step S 108 ). 
     By turning on and off the flow of gas of the gas curtain  23   b  or by changing the flow rate thereof in the above-described manner, it is possible to save the inert gas and thus reduce operating costs. 
     Similarly, the flow of gas of the gas curtain  23   a  disposed in the CD apparatus  21  may be turned on and off or the flow rate thereof may be changed. In the present embodiment, because air is used as the flowing gas of the gas curtain  23   a , turning the flow of the air on/off or the controlling the flow rate of the air minimizes degradation of the ambient in the CD apparatus  21 . 
     Although, in the present embodiment, the gas curtain  23   a  is disposed in the CD apparatus  21  and the gas curtain  23   b  is disposed in the exposure apparatus  22 , gas curtains may be disposed at other locations. For example, as shown by dashed lines in FIG. 2, a gas curtain  23   a ′ may be disposed in the LL chamber  14 , at a location on the side of the CD apparatus, instead of the gas curtain  23   a  in the CD apparatus  21 . Likewise, a gas curtain  23   b ′ may be disposed in the LL chamber  14 , at a location on the side of the exposure apparatus, instead of the gas curtain  23   b  in the exposure apparatus  22 . Furthermore, various other combinations of gas curtains are possible. For example, a combination of gas curtains  23   a  and  23   b , a combination of gas curtains  23   a  and  23   b ′, a combination of gas curtains  23   a ′ and  23   b , and a combination of gas curtains  23   a ′ and  23   b ′ are all possible. 
     Second Embodiment 
     FIG. 4 illustrates an exposure apparatus and associated apparatuses according to a second embodiment of the present invention. 
     In the present embodiment, an oxygen concentration meter  28   a  for measuring oxygen concentration is disposed in a LL chamber  14 . The flow rate of gas ejected from an ejection nozzle  27   a  is controlled by a flow rate controller  29   a  in accordance with the oxygen concentration in the LL chamber  14  measured by the oxygen concentration meter  28   a . Similarly, an oxygen concentration meter  28   b  is disposed in an exposure apparatus  22 , and the flow rate of gas ejected from an ejection nozzle  27   b ′ is controlled by a flow rate controller  29   b  in accordance with the oxygen concentration measured in the exposure apparatus  22  by the oxygen concentration meter  28   b . The flow rate controllers  29   a  and  29   b  are capable of continuously varying the flow rate of ejected gas and also are capable of turning on/off the flow of gas. 
     In the present embodiment, N 2  is employed as the flowing gas for both a gas curtain  23   a  and a gas curtain  23   b ′. The other components are similar to those in the first embodiment. 
     The process of transferring a wafer  26  into the exposure apparatus  22  through the LL chamber  14  in the system according to the present embodiment is described below with reference to FIG.  5 . 
     First, in a CD apparatus  21 , a resist is coated on the wafer  26 . The resist-coated wafer  26  then is transferred into the LL chamber  14  through a gate valve  24   a . At this stage, a gate valve  24   b  on the side of the exposure apparatus  22  is in a closed state, and the gas curtain  23   b ′ is in an initial state in which no gas is ejected from the nozzle  27   b ′ (or a small amount of gas is ejected) (step S 201 ). The gate valve  24   a  on the side of the CD apparatus  21  then is closed and transfer of the wafer  26  is started (step S 202 ). 
     Thereafter, the following processes are performed in a parallel fashion under the control of a control means (not shown). 
     In one processing flow, a gate valve  24   b  located between the LL chamber  14  and the exposure apparatus  22  is opened (step S 203 ), and the wafer  26  is moved from the LL chamber  14  into the exposure apparatus  22  (step S 204 ). After the wafer  26  has been transferred into the exposure apparatus  22  (step S 205 ), the gate valve  24   b  is closed (step S 206 ) and this processing flow is completed. 
     In another processing flow performed in parallel with steps  202 - 206  of the above-described processing flow, the flow rate of the gas curtain  23   b ′ is controlled as described below. 
     First, the control means (not shown) reads the oxygen concentration in the exposure apparatus  22  measured by the oxygen concentration meter  28   b  and determines whether the oxygen concentration in the exposure apparatus  22  is equal to or greater than a predetermined target value (step S 207 ). If the measured oxygen concentration is equal to or greater than the target value, the process proceeds to step S 208 . In step S 208 , the control means sends a control signal to the flow rate controller  29   b  to eject a purge gas to reduce the oxygen concentration whose current value is too high (or to increase the flow rate of the purge gas in the case where a small amount of purge gas is ejected in the initial state in step S 201 ). In accordance with the control signal from the control means, the flow rate controller  29   b  adjusts the flow rate of the gas curtain  23   b ′ (step S 209 ). Then the process proceeds to step S 210 . In the case where it has been determined in step S 207  that the measured oxygen concentration is lower than the predetermined target value, the process proceeds to step S 211 . In step S 211 , the control means sends a control signal to the flow rate controller  29   b  to stop ejection of the purge gas (or to reduce the flow rate of the purge gas in the case where a small amount of purge gas is ejected in the initial state in step S 201 ), because the oxygen concentration is low enough. In accordance with the control signal from the control means, the flow rate controller  29   b  adjusts the flow rate of the gas curtain  23   b ′ (step S 212 ). The process then proceeds to step S 210 . 
     In step S 210 , it is determined whether the gate valve  20   24   b  is in a closed state. If the gate valve  24   b  is not closed, the process returns to step S 207 . However, if the gate valve  24   b  is closed, the process flow is completed. 
     In the present embodiment, as described above, the flow rate of the gas curtain  23   b ′ is controlled such that the oxygen concentration in the exposure apparatus  22  is maintained lower than about 1 ppm. 
     Furthermore, in the present embodiment, the flow rate of the gas curtain  23   a  can be controlled in a similar manner when the wafer  26  is moved from the CD apparatus  21  into the LL chamber  14 . In this case, the flow rate controller  29   a  increases the flow rate of the gas curtain  23   a  when the oxygen concentration in the LL chamber  14  measured by the oxygen concentration meter  28   a  exceeds about 10 ppm, thereby suppressing intrusion of oxygen into the LL chamber  14 . 
     Third Embodiment 
     The system employed in this third embodiment is similar to that employed in the second embodiment (FIG.  4 ). 
     The process of carrying a wafer  26  into the exposure apparatus  22  through the LL chamber  14  in the system according to the present embodiment is described below with reference to FIG.  6 . 
     First, in the CD apparatus  21 , a resist is coated on the wafer  26 . The resist-coated wafer  26  then is transferred into the LL chamber  14  through the gate valve  24   a . At this stage, the gate valve  24   b  on the side of the exposure apparatus  22  is in a closed state, and the gas curtain  23   b ′ is in an initial state in which no gas is ejected from the nozzle  27   b ′ (step S 301 ). The gate valve  24   a  on the side of the CD apparatus  21  then is closed and transfer of the wafer  26  is started (step S 302 ). When transfer of the wafer  26  is started in step S 302 , the gas curtain  23   b ′ is created. That is, gas is ejected from the nozzle  27   b ′ synchronously with the start of transferring the wafer  26  (step S 303 ). Thereafter, the gate valve  24   b  located between the LL chamber  14  and the exposure apparatus  22  is opened (step S 304 ), and the wafer  26  is moved from the LL chamber  14  into the exposure apparatus  22  (step S 305 ). After the wafer  26  has been transferred into the exposure apparatus  22  (step S 306 ), the gate valve  24   b  is closed (step S 307 ) and the ejection of the gas of the gas curtain  23   b ′ is stopped (step S 308 ). Thus, the process is completed. 
     At substantially the same time as the creation of the gas curtain  23   b ′, the control means (not shown) starts to monitor the oxygen concentration in the exposure apparatus  22  measured by the oxygen concentration meter  28   b  (step S 309 ). Thereafter, the control means controls the flow rate of the gas curtain  23   b ′ using the flow rate controller  29   b  depending upon the oxygen concentration measured by the oxygen concentration meter  28   b  (step S 310 ) in parallel with steps S 303 -S 307 . More specifically, in the present embodiment, the flow rate of the gas curtain  23   b ′ is increased when the oxygen concentration measured by the oxygen concentration meter  28   b  exceeds about 1 ppm, thereby suppressing intrusion of oxygen into the exposure apparatus  22 . The flow rate controller  29   b  determines whether the gate valve  24   b  is closed on the basis of a control signal from the control means (not shown) (step S 311 ). If the gate valve  24   b  is closed, the flow rate controller  29   b  stops the operation. 
     In the present embodiment described above, the flow rate of the gas curtain  23   b ′ is controlled such that the oxygen concentration in the exposure apparatus  22  is maintained at less than about 1 ppm. 
     Furthermore, in the present embodiment, the flow rate of the gas curtain  23   a  can be controlled in a similar manner when the wafer  26  is moved from the CD apparatus  21  into the LL chamber  14 . In this case, the flow rate controller  29   a  increases the flow rate of the gas curtain  23   a  when the oxygen concentration in the LL chamber measured by the oxygen concentration meter  28   a  exceeds about 10 ppm, thereby suppressing intrusion of oxygen into the LL chamber  14 . 
     Fourth Embodiment 
     FIG. 7 illustrates an exposure apparatus and associated apparatuses according to a fourth embodiment of the present invention. 
     In the present embodiment, a wafer detection means  30   a  for detecting a wafer  26  is disposed between a CD apparatus  21  and a LL chamber  14 . The flow rate of gas ejected from an ejection nozzle  27   a  is controlled by a flow rate controller  29   a  in response to the detection of the wafer  26  by the wafer detection means  30   a . Similarly, a wafer detection means  30   b  is disposed between the LL chamber  14  and an exposure apparatus  22 , and the flow rate of gas ejected from an ejection nozzle  27   b ′ is controlled by a flow rate controller  29   b  in response to the detection of the wafer  26  by the wafer detection means  30   b . The flow rate controllers  29   a  and  29   b  are capable of continuously varying the flow rate of ejected gas and also are capable of turning on/off the flow of gas. 
     In the present embodiment, N 2  is employed as the flowing gas for both a gas curtain  23   a  and a gas curtain  23   b ′. The other components are similar to those in the preceding embodiments. 
     The process of transferring a wafer  26  into the exposure apparatus  22  through the LL chamber  14  in the system according to the present embodiment is described below with reference to FIG.  8 . When the wafer  26  is moved from the CD apparatus  21  into the LL chamber  14 , a similar process is performed. 
     First, in the CD apparatus  21 , a resist is coated on the wafer  26 . The resist-coated wafer  26  then is transferred into the LL chamber  14  through a gate valve  24   a . The gate valve  24   a  on the side of the CD apparatus  21  then is closed and transfer of the wafer  26  is started (step S 401 ). After starting transfer of the wafer  26 , a gate valve  24   b  on the side of the exposure apparatus  22  is maintained in the closed state, and the gas curtain  23   b ′ is maintained in an initial state in which no gas is ejected from the nozzle  27   b ′ (or a small amount of gas is ejected) (step S 402 ). The gas curtain  23   b ′ is maintained in the initial state until the wafer detection means  30   b  detects the wafer  26 . If the wafer  26  is detected in step S 403 , a processing flow including steps S 404 -S 407  and a processing flow including steps S 408 -S 412  are performed in parallel. 
     In steps S 404 -S 407 , the gate valve  24   b  located between the LL chamber  14  and the exposure apparatus  22  is opened (step S 404 ), and the wafer  26  is moved from the LL chamber  14  into the exposure apparatus  22  (step S 405 ). After the wafer  26  has been transferred into the exposure apparatus  22  (step S 406 ), the gate valve  24   b  is closed (step S 407 ) and this processing flow is completed. 
     On the other hand, in steps S 408 -S 412 , a control means (not shown) sends a control signal to the flow rate controller  29   b  to eject a purge gas (or to increase the flow rate of the purge gas in the case where a small amount of purge gas is ejected in the initial state in step S 402 ) in step S 408 . In accordance with the control signal from the control means, the flow rate controller  29   b  signals the nozzle  277  to eject the purge gas at a predetermined flow rate, thereby creating the gas curtain  23   b ′ (step S 409 ). This state is maintained until the gate valve  24   b  is closed (step S 410 ). If it is determined in step S 410  that the gate valve  24   b  is closed, the process proceeds to step S 411 . In step S 411 , the control means sends a control signal to the flow rate controller  29   b  to stop the purge gas (or to reduce the flow rate of the purge gas in the case where a small amount of purge gas is ejected in the initial state in step S 402 ). In accordance with the control signal from the control means, the flow rate controller  29   b  stops or reduces the flow of the gas curtain  23   b ′ (step S 412 ), and the process is completed. 
     In the present embodiment, as described above, when the wafer detection means  30   a  or  30   b  detects the passage of the wafer  26 , the flow rate of the gas curtain  23   a  or  23   b ′ is increased to prevent intrusion of oxygen. 
     In the first through fourth embodiments described above, the system configuration and its operation are described primarily for the case where a wafer is transferred into the exposure apparatus. A similar configuration and a similar operation can be applied when a wafer is transferred from the CD apparatus into the LL chamber or when a reticle is transferred into the exposure apparatus. 
     In the system according to any one of the first through fourth embodiments, the ambient in the load lock chamber can be maintained substantially unchanged, and thus it is unnecessary to replace the ambient in the load lock chamber. That is, it is possible to transfer a wafer or a reticle without causing a reduction in throughput. 
     Semiconductor Production System Embodiment 
     An embodiment of a system for producing a semiconductor device (e.g., a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin film magnetic head, a micromachine) is described below. This semiconductor device production system has the capability of providing, for example, a maintenance service for handling a malfunction of a production apparatus installed in a semiconductor production factory, scheduling maintenance thereof, and providing software, via a computer network outside the factory. 
     FIG. 9 illustrates a complete production system for producing a semiconductor device, as seen from one perspective. In FIG. 9, reference numeral  101  denotes an office of a vendor (manufacturer) of semiconductor device production apparatuses. Specific examples of production apparatuses include various types of semiconductor processing apparatuses used in semiconductor production factories such as wafer processing apparatuses (e.g., lithography apparatus such as an exposure apparatus, a resist processing apparatus, and an etching apparatus, a heat treatment apparatus, a film deposition apparatus, a planarization apparatus), assembling apparatuses, and testing apparatuses. In the office  101 , there are a host management system  108  for providing a production apparatus maintenance database, a plurality of control terminals  110 , and a local area network (LAN)  109  for connecting them to provide an intranet. The host management system  108  includes a gateway for connecting the LAN  109  to an external network, such as the Internet  105 , and has a security capability for limiting external access to the LAN  109 . 
     Reference numerals  102  to  104  denote factories of semiconductor manufacturers, that is, users of production apparatuses. These factories may be of different manufacturers or of the same manufacturer (for example, a wafer processing factory and an assembling factory of the same manufacturer). In each factory  102  to  104 , there are production apparatuses  106 , an intranet or a local area network (LAN)  111  for connecting the apparatuses  106  to one another, and a host management system  107  for managing and controlling the operations of the respective production apparatuses  106 . Each of the host management systems  107  in the respective factories  102  to  104  has a gateway for connecting the LAN  111  of the factory with an external network, such as the Internet  105 . The gateway makes it possible to access, via the Internet  105 , the host management system  108  located in the vendor  101  from the LAN  111  in each factory. The security capability of the host management system  108  permits only authorized users to access the host management system  108 . More specifically, it is possible to transmit status information indicating the status of the operation (for example, information representing a symptom of a problem or malfunction) of each production apparatus  106  from a factory to the vendor via the Internet  105 . In response to the status information, the vendor may transmit to the factory response information (information indicating how to handle a problem or malfunction, including any necessary software or data) or maintenance information such as updated software or help information. Data communication between each factory  102  to  104  and the vendor  101  and also data communication within each factory via the LAN  111  may be performed using a communication protocol known as TCP/IP which is widely used in Internet communications. Instead of using the Internet for the external network, a dedicated network (such as an IDSN) may be used to achieve higher security to prevent access by unauthorized users. The host management system is not limited to that which is provided by the vendor. For example, a user may provide a host management system including a database accessible via an external network from a plurality of factories. 
     FIG. 10 is a conceptual diagram illustrating a complete production system according to the present embodiment, seen from a different perspective than that of FIG.  9 . In the previous example, the system includes a plurality of user factories each including production apparatuses, and a vendor having a management system connected to each factory via an external network to manage production in each factory or transmit information about at least one production apparatus by means of data communication via the external network. In contrast, in the present example, the system includes a factory in which a plurality of production apparatuses provided by different vendors are installed, and the vendors of the production apparatuses have their own management systems connected to the factory via an external network so that maintenance information for the respective production apparatuses may be transmitted by means of data communication. In FIG. 10, reference numeral  201  denotes a factory (e.g., semiconductor device manufacturer), that is, a user of production apparatuses. The factory  201  has a production line in which there are various processing apparatuses for production. In this specific example, the production apparatuses in the factory include exposure apparatuses  202 , a resist processing apparatus  203 , and a film deposition apparatus  204 . Although only one factory  201  is shown in FIG. 10, there can be a plurality of networked factories. The respective apparatuses within the factory are connected to each other via a LAN  206  so as to form an intranet. A host management system  205  manages the operation of the production line. On the other hand, host management systems  211 ,  221 , and  231 , for performing remote maintenance upon the factory apparatuses, are disposed in respective vendors (e.g., apparatus manufacturers) such as an exposure apparatus manufacturer  210 , a resist processing apparatus manufacturer  220 , and a film deposition apparatus manufacturer  230 . Each host management system has a maintenance database and a gateway for connection with the external network. The host management system  205  for managing the respective apparatuses in the production factory of the user is connected to the respective management systems  211 ,  221 , and  231  of the vendors of the apparatuses via the external network  200 , which can be the Internet or a dedicated external network, for example. In this system, if a problem or malfunction occurs in one of the production apparatuses in the production line, the operation of the production line stops. The production line can recover very quickly from the problem or malfunction by receiving remote maintenance from the vendor of the apparatus having the problem or malfunction via the external network  200 . Thus, it is possible to minimize the offline period of the production line. 
     Each production apparatus installed in the semiconductor factory has a display, a network interface, and a computer for executing network access software and apparatus control software stored in a storage device. Specific examples of storage devices include a built-in memory, a hard disk, and a network file server. The network accessing software includes a dedicated or general-purpose web browser which provides a user interface, such as that shown in FIG. 11, displayed on the display. A human operator who is responsible for managing an apparatus in the factory may input, via the user interface screen, information as to the type of the production apparatus ( 401 ), the serial number of the production apparatus ( 402 ), the title of the problem or malfunction report ( 403 ), the date of occurrence ( 404 ), the degree of urgency ( 405 ), the symptom ( 406 ), the way to avoid the problem ( 407 ), and the action done ( 408 ). The input information is transmitted to the maintenance database via the Internet. In response, maintenance information is returned from the maintenance database and displayed on the display. The web browser user interface may include hyperlinks ( 410  to  412 ), as shown in FIG. 11, for allowing the operator to obtain further detailed information of a particular item from the maintenance database, download the latest version of software to a production apparatus from a software library provided by a vendor, and read an operation guide (e.g., help information) for an apparatus. 
     A process of producing a semiconductor device using the above-described production system is described below. FIG. 12 is a flow chart of an overall device production process. In step  1  (circuit design), a semiconductor device circuit is designed. In step  2  (mask production), masks having patterns designed in step  1  are produced. In step  3  (wafer production), a wafer is produced using silicon or the like. 
     In step  4  (wafer process, or often called a “first half” process), an actual circuit is formed on the wafer by means of a lithography technique using the masks and the wafer produced in the previous steps. In step  5  (assembly or often called a “second half” process), the wafer produced in step  4  is divided into chips. This step includes substeps of assembly (dicing and bonding) and packaging (chip encapsulation). In step  6  (test), the semiconductor devices produced in the previous steps are tested to conform that they operate correctly. The reliability of the devices is also evaluated in step  6 . The satisfactory semiconductor devices then are shipped in step  7 . Typically, the wafer process and the assembling process are performed in different factories, and the production apparatuses in each factory are maintained by the remote maintenance system described above. Furthermore, information necessary for production management and maintenance of apparatuses is transmitted by means of data communication between the wafer process factory and the assembling factory via the Internet or a dedicated network. 
     FIG. 13 is a flowchart illustrating the details of the wafer process. In step  11  (oxidation), the surface of the wafer is oxidized. In step  12  (CVD), an insulating film is formed on the surface of the wafer. In step  13  (metalization), electrodes are formed on the surface of the wafer by means of evaporation. In step  14  (ion implantation), ions are implanted into the wafer. In step  15  (resist processing), a photosensitive material is coated on the wafer. In step  16  (exposure), a latent image of a circuit pattern formed on a mask is formed in the resist using the semiconductor exposure apparatus described above. In step  17  (development), the wafer is developed. In step  18  (etching), the surface of the wafer is partially removed except for the portions covered by the resist pattern developed in the previous step. In step  19  (resist removal), the resist, which has become no longer necessary after the etching process, is removed. The above process is performed repeatedly, thereby forming a multilevel circuit pattern on the wafer. Because the production apparatuses in each factory are maintained by the remote maintenance system described above, problems with the production apparatuses can be prevented. Even if a problem occurs in an apparatus, it is possible to quickly recover from the problem. Thus, it is possible to improve the productivity of the semiconductor device production process. 
     Furthermore, when a substrate is transferred into or out of the exposure apparatus or the coating/developing apparatus, transfer of the substrate is performed via the gate valves and the gas curtains formed near the gate valves so that intrusion or leakage of the ambient gas is minimized thereby allowing an improvement in throughput and a reduction in operating costs. 
     Except as otherwise disclosed herein, the various components shown in outline or block form in the figures are individually well known and their internal construction and operation is not critical either to the making or using of this invention or to a description of the best mode of the invention. 
     While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.