Abstract:
Disclosed is an exposure apparatus for illuminating a reticle with exposing light from an exposing light source via a light-source lens system constituting illumination optics, and projecting a pattern, which has been formed on the reticle, onto a wafer via a projection lens system constituting projection optics, thereby exposing the wafer to the patter. The apparatus includes vessels for hermetically sealing the light-source lens system and the projection lens system disposed on the optical path of the exposing light from the exposing light source to the reticle, means for supplying the vessels with a specific gas, a vacuum source for evacuating the interior of the vessels, a vacuum-pressure controller for exercising control to hold the internal pressure of the vessels constant, and an escape valve for reducing the differential pressure between the internal pressure of the vessels and atmospheric pressure to a value below a predetermined pressure.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to an exposure apparatus in which the illuminating light is ultraviolet radiation or excimer laser light that has a particularly strong luminous flux and readily activates an atmospheric gas.  
         BACKGROUND OF THE INVENTION  
         [0002]    An exposure apparatus used in the manufacture of semiconductors and the like is required to have higher throughput and resolution owing to much smaller pattern line width. This has been accompanied by the need for exposing light having ever higher illuminance. At the same time, the wavelength of the exposing light is becoming increasingly short.  
           [0003]    However, it is known that exposing light causes impurities in the air to react photochemically with oxygen in an exposure apparatus that uses i lines (wavelength λ=365 [nm]) as the exposing light and in an exposure apparatus that uses exposing light the wavelength whereof is shorter than that of i lines. Such reaction products (fogging substances) attach themselves to glass members and produce an opaque fog on the glass members. A typical example of such a fogging substance is ammonium sulfate (NH 4 ) 2 SO 4 , which is produced by a reaction (oxidation) with oxygen in the air, if sulfur dioxide (SO 2 ) absorbs the energy of the exposing light and attains the excited state. The ammonium sulfate is white in color and results in fogging when it attaches itself to the surfaces of optical members such as lenses and mirrors. The exposing light is scattered and absorbed by the ammonium sulfate, as a consequence of which there is a decline in the transmittance of the optical system.  
           [0004]    In the region of short wavelengths in which the exposing light has a wavelength of less than 248 [nm], which is shorter than that of i lines, as in the case of a KrF excimer laser, the exposing light causes an even stronger photochemical reaction. As a result, not only does the above-mentioned fogging occur but so does a phenomenon in which the exposing light reacts with oxygen in the air to produce ozone, with both residual oxygen and the generated ozone absorbing the exposing light.  
           [0005]    Accordingly, a method of preventing the contamination of optical members has been developed. The method involves placing the optical system, such as the lens of the light source or the projecting lens system, within a vessel and then replacing the air in the vessel with an inert gas such as nitrogen gas or with another gas from which impurities have been removed, whereby the aforementioned contamination is avoided.  
           [0006]    In recent years, however, the illuminating systems of exposure apparatus have been increasingly complex in order to achieve diverse illuminating conditions and deformed illumination. As a consequence, maintenance is essential and the spaces filled with the inert gas frequently are exposed to the outside atmosphere whenever such maintenance is carried out. In addition, the inert gas used, such as nitrogen or helium, may have an influence upon the human body. This means that while maintenance is being performed, the supply of the inert gas must be stopped in order to assure safety. A consequence of this is that the interior of the vessel becomes filled with atmospheric air during maintenance work. After maintenance the atmospheric air within the vessel must be replaced with inert gas again. Furthermore, if the exposure apparatus is out of action for a long period of time, it is likewise necessary for the inert gas to be substituted.  
           [0007]    However, the areas filled with the inert gas inside the illuminating system and projecting lens system have become increasingly complex in structure and it is difficult for the inert gas to flow when the substitution is made from atmospheric air to the inert gas. Many points of stagnation result. Air accumulates at the stagnation points and the air accumulated at such points flows out only in small increments. As a consequence, the time needed for air within the vessel to be fully replaced with the inert gas is prolonged. The structure internally of the projecting lens system is particularly complicated and does not lend itself to the incorporation of a mechanism that prevents the accumulation of air within the vessel.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, an object of the present invention is to provide an exposure apparatus in which the air within the vessel of an illuminating system and within the vessel of projection lenses can be replaced with an inert gas highly efficiently, thereby minimizing the time needed to make the substitution from atmospheric air to the inert gas.  
           [0009]    According to the present invention, the foregoing object is attained by providing an exposure apparatus for illuminating a reticle with exposing light from an exposing light source via an illuminating optical system and projecting a pattern, which has been formed on the reticle, onto a substrate via a projection optical system, comprising: a first vessel within which the illuminating optical system is placed; a second vessel within which the projection optical system is placed; the first vessel having an inlet and an outlet for a first gas and the second vessel having an inlet and an outlet for a second gas; substitution means for substituting the first gas and/or the second gas for a gas in the interior of the first vessel and/or the second vessel; and exhaust means for evacuating the first vessel and/or the second vessel in order to establish negative pressure in the interior thereof when the first gas and/or the second gas is substituted for the gas in the interior of the first vessel and/or the second vessel.  
           [0010]    Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a schematic view illustrating the overall structure of an exposure apparatus according to an embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a conceptual view showing a semiconductor device production system, which includes the exposure apparatus of this embodiment, as seen from a certain angle;  
         [0013]    [0013]FIG. 3 is a conceptual view showing the semiconductor device production system, which includes the exposure apparatus of this embodiment, as seen from another angle;  
         [0014]    [0014]FIG. 4 shows a specific example of a user interface in the semiconductor device production system that includes the exposure apparatus of this embodiment;  
         [0015]    [0015]FIG. 5 is a diagram useful in describing the flow of a device manufacturing process that uses the exposure apparatus according to this embodiment; and  
         [0016]    [0016]FIG. 6 is a diagram useful in describing a wafer process that uses the exposure apparatus according to this embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    A preferred embodiment of the present invention will now be described in detail with reference to the drawings.  
         [0018]    [Embodiment of Exposure Apparatus] 
         [0019]    [0019]FIG. 1 is a schematic view illustrating the overall structure of an exposure apparatus E 1  according to an embodiment of the present invention.  
         [0020]    The exposure apparatus E 1  of this embodiment generally includes an exposing light source  1  comprising an excimer laser, a light source lens system  2  constituting illuminating optics for forming laser light L 1 , which is the illuminating light emitted from the exposing light source  1 , into a luminous flux of a prescribed shape, and a projection lens system  6  constituting projection optics for forming the image of laser light L 1 , which has been formed into the prescribed shape by the light source lens system  2 , onto a wafer (substrate) W 1  via a reticle R 1  serving as a mask.  
         [0021]    The light source lens system  2  includes optical elements such as a number of lenses and mirrors  4   a,    4   b  and illuminates, at a uniform illuminance, an illumination area on the reticle R 1  with the laser light L 1  from the exposing light source  1 . The light source lens system  2  is constituted by collimator lenses  5   a,    5   b,  a fly-eye lens  8  serving as an optical integrator, condenser lenses  7   a,    7   b,    7   c,  and a subunit such as a blind  9  for regulating the shape of the illumination area on the reticle R 1 .  
         [0022]    The light source lens system  2  is placed inside a first vessel  3 . The interior of the vessel  3  is connected to a gas supply unit  11 , which supplies nitrogen gas serving as an inert gas (a first gas) from a gas inlet, via a gas supply line (piping)  12  and a solenoid valve  13  serving as a switch valve provided in the gas supply line  12 .  
         [0023]    A gas exhaust line (piping)  15  is connected to a gas outlet of the vessel  3 . Connected to the gas exhaust line  15  is a gas-exhaust changeover unit  16  capable of switching between an evacuating mechanism, which comprises a vacuum source  18  for evacuating the vessel, a vacuum-pressure controller  19  and an oxygen densitometer  21 , and an atmosphere-release mechanism comprising a gas exhaust (ventilation) unit  14 . The gas-exhaust changeover unit  16  is capable of switching between the evacuating mechanism and the atmosphere-release mechanism automatically when the concentration of the gas in vessel  3  attains a predetermined concentration.  
         [0024]    The timings at which the gas supply unit  11 , gas-exhaust changeover unit  16  and gas exhaust unit  14  operate are decided by a program that has been stored in a controller  10 .  
         [0025]    During usual operation of the exposure apparatus, nitrogen gas is supplied while the pressure thereof is held constant in precise fashion by the gas supply line  12  and a flow-rate controller within the gas supply unit  11 . Here the gas-exhaust changeover unit  16  switches over to the gas exhaust unit  14 , which is on the atmosphere-release side, to thereby supply the nitrogen gas continuously or intermittently so that the air in the vessel  3  is constantly being replaced with the nitrogen gas.  
         [0026]    An escape valve  20  capable effecting release to the atmosphere is provided in the gas exhaust line  15 . If optical components have been installed, the escape valve  20  prevents any further rise in pressure when the differential pressure between the internal pressure at locations  17   a,    17   b,    17   c,    17   d  and  17   e,  at which the nitrogen gas encounters difficulty in flowing, an atmospheric pressure exceeds a predetermined value. The vacuum source  18 , which is connected to the vacuumpressure controller  19 , controls the internal pressure of the vessel  3  to hold the interior at a constant negative pressure (i.e., the internal pressure is capable of being regulated to a constant value). Further, the internal pressure may be varied at a suitable frequency by the vacuum-pressure controller  19  to generate pulsation.  
         [0027]    Atmospheric air flows into the vessel  3  if the vessel is opened for maintenance or for some other reason. Further, when the exposure apparatus E 1  is placed in operation again after having been opened, it is necessary to replace the atmospheric air in vessel  3  with inert gas again. In such case a changeover is made to the evacuation side by the gas-exhaust changeover unit  16  on the exhaust side to thereby evacuate the interior of the vessel  3 . The internal pressure of the first vessel  3  is made a suitable negative pressure or is caused to pulsate at a negative pressure and is supplied with the gas from the gas supply unit  11 .  
         [0028]    The described rendered above deals with the components of the illumination system. However, similar effects can be obtained by a similar method applied to substitution (not shown) of gas such as inert gas within the lens vessel (a second vessel) in the projection lens system  6 .  
         [0029]    Further, similar effects can be obtained by a similar method applied to substitution (not shown) of gas such as inert gas within a wafer-stage space and reticle-stage space, etc., constructed as air-tight vessels (third and fourth vessels).  
         [0030]    Thus, as described above, a forced flow of nitrogen gas is produced at the points  17   a  to  17   e  where the nitrogen does not readily flow and at points (not shown) where air accumulates within the projection lens system  6 , thereby making it possible to rapidly eliminate accumulated atmospheric air.  
         [0031]    It should be noted that the inert gas is not limited to nitrogen, and a gas such as helium may be used. Further, the gas is not limited to inert gas. It is permissible to use clean, dry air or a specific active gas (second gas) such as ozone for cleaning the optical members.  
         [0032]    [Embodiment of Semiconductor Production System] 
         [0033]    Described next will be an example of a system for producing semiconductor devices (semiconductor chips such as IC and LSI chips, liquid crystal panels, CCDs, thin-film magnetic heads and micromachines, etc.) utilizing the exposure apparatus described above. This system utilizes a computer network outside the semiconductor manufacturing plant to provide troubleshooting and regular maintenance of manufacturing equipment installed at the manufacturing plant and to furnish maintenance service such as the provision of software.  
         [0034]    [0034]FIG. 2 illustrates the overall system as seen from a certain angle. The system includes the business office  101  of the vendor (equipment supplier) that provides the equipment for manufacturing semiconductor devices. Semiconductor manufacturing equipment for various processes used in a semiconductor manufacturing plant is assumed to be the manufacturing equipment. Examples of the equipment are pre-treatment equipment (lithographic equipment such as exposure equipment, resist treatment equipment and etching equipment, heat treatment equipment, thin-film equipment and smoothing equipment, etc.) and post-treatment equipment (assembly equipment and inspection equipment, etc.). The business office  101  includes a host management system  108  for providing a manufacturing-equipment maintenance database, a plurality of control terminal computers  110 , and a local-area network (LAN)  109  for connecting these components into an intranet. The host management system  108  has a gateway for connecting the LAN  109  to the Internet  105 , which is a network external to the business office  101 , and a security function for limiting access from the outside.  
         [0035]    Numerals  102  to  104  denote manufacturing plants of semiconductor makers which are the users of the manufacturing equipment. The manufacturing plants  102  to  104  may be plants belonging to makers that differ from one another or plants belonging to the same maker (e.g., pre-treatment plants and post-treatment plants, etc.). Each of the plants  102  to  104  is provided with a plurality of pieces of manufacturing equipment  106 , a local-area network (LAN)  111  which connects these pieces of equipment to construct an intranet, and a host management system  107  serving as a monitoring unit for monitoring the status of operation of each piece of manufacturing equipment  106 . The host management system  107  provided at each of the plants  102  to  104  has a gateway for connecting the LAN  111  in each plant to the Internet  105  serving as the external network of the plants.  
         [0036]    As a result, it is possible for the LAN of each plant to access the host management system  108  on the side of the vendor  101  via the Internet  105 . By virtue of the security function of the host management system  108 , users allowed to access the host management system  108  are limited. More specifically, status information (e.g., the condition of manufacturing equipment that has malfunctioned), which indicates the status of operation of each piece of manufacturing equipment  106 , can be reported from the plant side to the vendor side. In addition, information in response to such notification (e.g., information specifying how to troubleshoot the problem, troubleshooting software and data, etc.), as well as the latest software and maintenance information such as help information, can be acquired from the vendor side.  
         [0037]    A communication protocol (TCP/IP), which is used generally over the Internet, is employed for data communication between the plants  102 ˜ 104  and the vendor  101  and for data communication over the LAN  111  within each plant. Instead of utilizing the Internet as the external network of a plant, it is also possible to utilize a highly secure leased-line network (ISDN, etc.) that cannot be accessed by a third party. Further, the host management system is not limited to that provided by a vendor, for an arrangement may be adopted in which the user constructs a database, places it on an external network and allows the database to be accessed from a number of plants that belong to the user.  
         [0038]    [0038]FIG. 3 is a conceptual view illustrating the overall system of this embodiment as seen from an angle different from that depicted in FIG. 2. In the earlier example, a plurality of user plants each having manufacturing equipment are connected by an external network to the management system of the vendor that provided the manufacturing equipment, and information concerning the production management of each plant and information concerning at least one piece of manufacturing equipment is communicated by data communication via the external network.  
         [0039]    In the example of FIG. 3, on the other hand, a plant having manufacturing equipment provided by a plurality of vendors is connected by an outside network to management systems of respective ones of the vendors of these plurality of pieces of manufacturing equipment, and maintenance information for each piece of manufacturing equipment is communicated by data communication. As shown in the drawing, the system includes a manufacturing plant  201  of the user of manufacturing equipment (the maker of semiconductor devices). The manufacturing line of this plant includes manufacturing equipment for implementing a variety of processes. Examples of such equipment are exposure equipment  202 , resist treatment equipment  203  and thin-film treatment equipment  204 .  
         [0040]    Though only one manufacturing plant  201  is shown in FIG. 3, in actuality a plurality of these plants are networked in the same manner. The pieces of equipment in the plant are interconnected by a LAN  206  to construct an intranet and the operation of the manufacturing line is managed by a host management system  205 . The business offices of vendors (equipment suppliers) such as an exposure equipment maker  210 , resist treatment equipment maker  220  and thin-film treatment equipment maker  230  have host management systems  211 ,  221 ,  231 , respectively, for remote maintenance of the equipment they have supplied. These have maintenance databases and gateways to the outside network, as described earlier.  
         [0041]    The host management system  205  for managing each piece of equipment in the manufacturing plant of the user is connected to the management systems  211 ,  221 ,  231  of the vendors of these pieces of equipment by the Internet or leased-line network serving as an external network  200 . If any of the series of equipment in the manufacturing line malfunctions, the line ceases operating. However, this can be dealt with rapidly by receiving remote maintenance from the vendor of the faulty equipment via the Internet  200 , thereby making it possible to minimize line downtime.  
         [0042]    Each piece of manufacturing equipment installed in the semiconductor manufacturing plant has a display, a network interface and a computer for executing network-access software and equipment operating software stored in a storage device. The storage device can be an internal memory or hard disk or a network file server.  
         [0043]    The software for network access includes a special-purpose or general-purpose Web browser and presents a user interface, which has a screen of the kind shown by way of example in FIG. 4, on the display. The operator managing the manufacturing equipment at each plant enters information at the input items on the screen while observing the screen. The information includes model  401  of the manufacturing equipment, its serial number  402 , subject matter  403  of the problem, its date of occurrence  404 , degree of urgency  405 , the particular condition  406 , countermeasure method  407  and progress report  408 .  
         [0044]    The entered information is transmitted to the maintenance database via the Internet. The resulting appropriate maintenance information is sent back from the maintenance database and is presented on the display screen. The user interface provided by the Web browser implements hyperlink functions  410 ,  411 ,  412  as illustrated and enables the operator to access more detailed information for each item, to extract the latest version of software, which is used for the manufacturing equipment, from a software library provided by the vender, and to acquire an operating guide (help information) for reference by the plant operator.  
         [0045]    Here the maintenance information provided by the maintenance database also includes the above-described information relating to the present invention, and the software library also provides the latest software for implementing the present invention.  
         [0046]    A process for manufacturing a semiconductor device utilizing the production system set forth above will now be described. FIG. 5 illustrates the overall flow of a process for manufacturing semiconductor devices. The circuit for the device is designed at step  1  (circuit design). A mask on which the designed circuit pattern has been formed is fabricated at step  2  (mask fabrication). Meanwhile, a wafer is manufactured using a material such as silicon or glass at step  3  (wafer manufacture). The actual circuit is formed on the wafer by lithography, using the mask and wafer that have been prepared, at step  4  (wafer process), which is also referred to as “pre-treatment”.  
         [0047]    A semiconductor chip is obtained, using the wafer fabricated at step  4 , at step  5  (assembly), which is also referred to as “post-treatment”. This step includes steps such as actual assembly (dicing and bonding) and packaging (chip encapsulation). The semiconductor device fabricated at step  5  is subjected to inspections such as an operation verification test and durability test at step  6  (inspection). The semiconductor device is completed through these steps and then is shipped (step  7 ). The pre- and post-treatments are performed at separate special-purpose plants. Maintenance is carried out on a per-plant basis by the above-described remote maintenance system. Further, information for production management and equipment maintenance is communicated by data communication between the pre- and post-treatment plants via the Internet or leased-line network.  
         [0048]    [0048]FIG. 6 is a flowchart illustrating the detailed flow of the wafer process mentioned above. The surface of the wafer is oxidized at step  11  (oxidation). An insulating film is formed on the wafer surface at step  12  (CVD), electrodes are formed on the wafer by vapor deposition at step  13  (electrode formation), and ions are implanted in the wafer at step  14  (ion implantation). The wafer is coated with a photoresist at step  15  (resist treatment), the wafer is exposed to the circuit pattern of the mask to print the pattern onto the wafer by the above-described exposure apparatus at step  16  (exposure), and the exposed wafer is developed at step  17  (development). Portions other than the developed photoresist are etched away at step  18  (etching), and unnecessary resist left after etching is performed is removed at step  19  (resist removal). Multiple circuit patterns are formed on the wafer by implementing these steps repeatedly. Since the manufacturing equipment used at each step is maintained by the remote maintenance system described above, malfunctions can be prevented and quick recovery is possible if a malfunction should happen to occur. As a result, the productivity of semiconductor device manufacture can be improved over the prior art.  
         [0049]    Thus, as described above, the present invention is such that when the atmospheric air in a vessel to be filled with an inert gas is replaced with the inert gas, the internal pressure of the vessel is held at negative pressure and the vessel is supplied with the inert gas, whereby the gases within the entire space internally of the vessel are mixed uniformly and discharged. As a result, reliable replacement with inert gas can be discharged in a short period of time without leaving any accumulated air. After the vessel filled with inert gas is exposed to the atmosphere for maintenance or the like, therefore, the replacement of the air inside the vessel with inert gas can be performed more rapidly (with higher efficiency), enabling the exposure apparatus to be restored to operation quickly. This makes it possible to minimize a decline in production.  
         [0050]    As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.