Abstract:
An exposure apparatus for projecting a pattern of an original onto a substrate includes a chamber comprising at least a part of an optical element, and a circulating system for circulating a gas which is temperature-controlled through the chamber. The circulating system includes a unit for effecting at least one of heating and cooling of the gas, and a control system for changing an operation state of the unit so as to limit a timewise changing rate of a temperature in the chamber.

Description:
FIELD OF THE INVENTION AND RELATED ART  
       [0001]     The present invention relates to an exposure apparatus and a device manufacturing method.  
         [0002]     A shorter wavelength of exposure light from a light source of an exposure apparatus for use in semiconductor manufacturing or the like has progressed as a finer exposure pattern is used. More specifically, the light source has been shifted from that for i-ray to excimer laser, and its laser light source has been shifted from KrF laser to ArF laser. At present, the use of F2 laser is studied in order to satisfy the requirement for further fine patterning.  
         [0003]     In order to construct an exposure system using the F2 laser as the light source, it is necessary to take a countermeasure against energy attenuation of exposure light. Energy of F2 laser light is absorbed by moisture, oxygen, organic gas and so on in atmospheric air, so that a conventional exposure apparatus cannot be applied at it is.  
         [0004]     For this reason, as a means for bringing the exposure apparatus into correspondence with the F2 laser, it is possible to apply such a method that the entire space through which exposure light passes is hermetically sealed by a partition wall and is filled with inert gas such a nitrogen etc. Further, there is a large amount of heat, generated by a linear motor or the like for a stage, in a space in which a wafer and a reticle are disposed, so that the space requires a temperature-control circulating system of inert gas for the purpose of preventing a change in temperature in the space in order to retain a positional accuracy.  
         [0005]      FIG. 5  is a schematic view showing a conventional inert gas circulating system.  
         [0006]     As shown in  FIG. 5 , a wafer space  1  and a reticle space  2  are surrounded by a chamber  3 W and a chamber  3 R, respectively. The inside of the chamber  3  ( 3 R,  3 W) is a closed space. Each of the spaces  1  and  2  is provided with a temperature-control gas blowoff portion  4  and a temperature-control gas recovery portion  5 .  
         [0007]     In order to circulate inert gas which is subjected to temperature control and contaminant removal in the chamber  3 , the inert gas circulating system is provided with a circulating apparatus  6  which is connected with the gas blowoff portion  4  through a supply duct  7  and the gas recovery portion  5  through a return duct  8 , respectively. The circulating apparatus  6  includes a cooling device  9 , a blower  10 , a filter  11 , and a heating device  12  in this order in an inert gas flowing direction.  
         [0008]     The inert gas recovered through the return duct  8  from the inside of the wafer space  1  and the reticle space  2  has absorbed heat generated in the wafer space  1  and the reticle space  2 , so that it is subjected to heat exchange with a cooling medium by the cooling device  9 . The cooled inert gas is sent to the filter to be subjected to removal of contaminant. The filter  11  may include a chemical filter for removing ammonia rich in resist reactivity, an activated carbon filter for removing, e.g., siloxane or other organic gases, ULPA filter for removing particles. etc. The inert gas which has been subjected to cooling and contaminant removal in further subjected to temperature control (heating) by heating with the heating device  12  and is circulated to the gas blowoff portion  4 . A power source for fluid transfer by the circulation is the blower  10 .  
         [0009]     During the circulation, high-purity inert gas is supplied into the wafer space  1  and the reticle space  2  to maintain a concentration of the inert gas in the wafer space  1  and the reticle space  2 . Further, a predetermined amount of gas is exhausted from an exhaust valve  14  through a throttle valve, whereby an internal pressure of the wafer space  1  and the reticle space  2  is set to be higher than an outside atmospheric pressure to prevent entrance of outside air.  
         [0010]     The temperature control of the inert gas is performed by detecting the inert gas temperature by a temperature sensor  16 , inputting a resultant signal into a temperature controller  17 , and adjusting an output of the heating device  12  through PID feedback control.  
         [0011]     Japanese Laid-Open Patent Application (JP-A) No. 2003-14239 filed by the assignee of the present application discloses a temperature-controlled fluid supplying apparatus having such a structure that a fluid supplying pipe for supplying a temperature-controlled fluid to an object to be temperature-controlled and a heat-exchange fluid pipe for supplying a heat-exchange fluid which is heat-exchanged with the temperature-controlled fluid are partially contacted closely to each other.  
         [0012]     Further, JP-A No. 2000-315640 filed by the assignee of the present application discloses an exposure apparatus including: an air state quantity detecting means comprising a means for detecting at least a temperature as a state quantity of an air to be supplied to a main body of the exposure apparatus; a thermal capacity calculation means for calculating a thermal capacity of the air from the state quantity of the air detected by the air state quantity detecting means; a temperature control parameter calculation means for calculating a temperature control parameter on the basis of the thermal capacity value of the air calculated by the thermal capacity calculation means, the air temperature detected by the air state quantity detecting means, and a target temperature; and a temperature control device for temperature-controlling the temperature of the air on the basis of the temperature control parameter calculated by the parameter calculation means.  
         [0013]     During start of an operation of an inert gas circulation system, when a temperature control heater is actuated after a circulation blower is actuated, it was confirmed that an internal pressure of a purge jumper fluctuates largely. This internal pressure fluctuation was also confirmed similarly during operation termination. Further, it was clarified that the internal pressure fluctuation was caused to occur in the case where a circulation gas was abruptly increased in temperature by a heater or where the circulation gas was rapidly cooled by a cooling device at power-off of the temperature control heater. In addition, a unit such as a projection lens or the like in a chamber has a pressure-resistant range, so that an upper-limit pressure and a lower-limit pressure are determined. Accordingly, there is a possibility that an equipment, such as a lens, which is sensitive to pressure is damaged by the above-described pressure fluctuation.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention has been accomplished in view of the above described problem.  
         [0015]     An exemplary object of the present invention is to provide an exposure apparatus with high reliability.  
         [0016]     According to an aspect of the present invention, there is provided an exposure apparatus for projecting a pattern of an original onto a substrate, comprising: 
        a chamber comprising at least a part of an optical element, and     a circulating system for circulating a gas which is temperature-controlled through the chamber,     wherein the circulating system comprises:     i) a unit for effecting at least one of heating and cooling of the gas, and     ii) a control system for changing an operation state of the unit so as to limit a timewise changing rate of a temperature in the chamber.        
 
         [0022]     Based on the exposure apparatus described above, the present invention provides a high-reliability exposure apparatus.  
         [0023]     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a schematic view of an embodiment of the exposure apparatus according to the present invention.  
         [0025]      FIG. 2  is a schematic view of another embodiment of the exposure apparatus of the present invention.  
         [0026]      FIG. 3  is a flow chart showing a procedure of device manufacture.  
         [0027]      FIG. 4  is a flow chart showing a detailed procedure of wafer process shown in  FIG. 3 .  
         [0028]      FIG. 5  is a schematic view of a conventional inert gas circulating system.  
         [0029]      FIG. 6  is a graph showing a relationship between a change in internal pressure and a time required to suppress the internal pressure change. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     An exposure apparatus according to a first preferred embodiment of the present invention includes a gastight chamber, and an air conditioning means for effecting temperature control and cleanup in the gastight chamber by use of a blower for circulating inert gas to the gastight chamber, a cooling device for cooling the inert gas, a heating device for heating the inert gas, a filter for removing a contaminant from the inert gas, and a sensor disposed at a predetermined position of an inert gas circulating system comprising the gastight chamber, the blower, the cooling device, the heating device, and the filter. The exposure apparatus is characterised in that it is provided with a gradient control mechanism capable of controlling a rate of temperature rise of the heating device up to a target set temperature in order to prevent a lens breakage due to a change (fluctuation) in internal pressure of the gastight chamber.  
         [0031]     The control mechanism is characterized in that it has a temperature sensor at an upstream portion of the heating device in the circulating system and can detect a difference between a circulation temperature and a target set temperature to determine a temperature rising rate gradient on the basis of a rise temperature per unit time determined by volume and flow rate in order to prevent the lens breakage due to the change in internal pressure of the gastight chamber.  
         [0032]     An exposure apparatus according to a second preferred embodiment of the present invention includes a gastight chamber, and an air conditioning means for effecting temperature control and cleanup in the gastight chamber by use of a blower for circulating inert gas to the gastight chamber, a cooling device for cooling the inert gas, a heating device for heating the inert gas, a filter for removing a contaminant from the inert gas, and a sensor disposed at a predetermined position of an inert gas circulating system comprising the gastight chamber, the blower, the cooling device, the heating device, and the filter. The exposure apparatus is characterized in that it is provided with a gradient control mechanism provided with a chiller comprising a heater for a coolant and a temperature control device, capable of controlling a cooling rate of the cooling device down to a target set temperature in order to prevent a lens breakage due to a change (fluctuation) in internal pressure of the gastight chamber.  
         [0033]     The control mechanism in this (second) embodiment is characterized in that it has temperature sensors at an upstream and downstream portions of the cooling device in the circulating system and can detect a difference between a circulation temperature and a target set temperature to determine a cooling rate gradient in order to prevent the lens breakage due to the change in internal pressure of the gastight chamber.  
         [0034]     Further, as a cooling rate control mechanism, the gradient control mechanism is provided with a control mechanism of the number of revolutions of pump in the chiller, whereby flow rate control of the coolant is effected to control the cooling rate of the cooling device in order to prevent the lens breakage due to the internal pressure change of the gastight chamber.  
         [0035]     An exposure apparatus according to a third preferred embodiment of the present invention includes a gastight chamber, and an air conditioning means for effecting temperature control and cleanup in the gastight chamber by use of a blower for circulating inert gas to the gastight chamber, a cooling device for cooling the inert gas, a temperature control heater for heating the inert gas, a filter for removing a contaminant from the inert gas, and a sensor disposed at a predetermined position of an inert gas circulating system comprising the gastight chamber, the blower, the cooling device, the temperature control heater, and the filter. The exposure apparatus is characterized in that it is provided with a gradient control mechanism capable of controlling a rate of temperature rise of the temperature control heater up to a target set temperature and a cooling rate of the cooling device down to a target set temperature, in order to prevent a lens breakage due to a change (fluctuation) in internal pressure of the gastight chamber.  
         [0036]     The control mechanism in this (third) embodiment is characterized in that it has a temperature sensor at an upstream portion of the temperature control heater in the gas circulating system. Further, a heater for a coolant (cooling medium), a temperature control device, and a gradient control mechanism are provided in the chiller as a mechanism capable of controlling a cooling rate of the cooling device, and temperature sensors are disposed at upstream and downstream portions of the cooling device, whereby gradient control is effected by detecting a difference between a circulation internal temperature and a set temperature to permit suppression of an internal pressure change of a purge chamber occurring during start and stop of circulation operation within a pressure-resistant range of the lens.  
         [0037]     Further, as a control mechanism of the cooling rate, a control mechanism of the number of revolutions of a pump is provided in the chiller, whereby flow rate control of the coolant is effected to control a cooling rate gradient of the cooling device in order to prevent the breakage of lens due to the internal pressure change of the gastight chamber.  
         [0038]     According to the first to third preferred embodiments described above, the internal pressure change of the purge chamber which can occur by rapid increase and/or decrease in temperature of the circulation gas during circulating operation start and/or stop is suppressed to effect gradient control of temperature rise rate and cooling rate while monitoring the circulation temperature in the purge chamber. As a result, it becomes possible to realize ensuring of the internal pressure change within a pressure-resistant range of the lens.  
         [0039]     Hereinbelow, the present invention will be described in detail based on same specific embodiments.  
       Embodiment 1  
       [0040]      FIG. 1  is a schematic view of an exposure apparatus in this embodiment according to the present invention.  
         [0041]     The exposure apparatus shown in  FIG. 1  has the same structure as that (of conventional inert gas circulating system) shown in  FIG. 5  except that it further includes temperature sensors  18 ,  19  and  24 , a heater gradient control portion  20 , a heater  22  for a coolant, and a gradient control mechanism  23 . In  FIG. 1 , members and means are indicated by reference numerals identical to those shown in  FIG. 5  and detailed explanation thereof will be omitted. Incidentally, a chiller  21 , a pump  25  and a heat exchanger  26  are not shown in  FIG. 5  but are used in common with the conventional inert gas circulating system.  
         [0042]     In the exposure apparatus shown in  FIG. 1 , temperature control of inert gas is performed by detecting the temperature of inert gas through the temperature sensors  18  and  16 , inputting their signals into the heater gradient control portion  20 , performing gradient control on the basis of a difference between an internal circulation temperature and a target set temperature, and outputting a resultant signal to the temperature control device  17  to effect control of the heating device (temperature control heater)  12 .  
         [0043]     Further, also with respect to the cooling of the inert gas, the gradient control is performed by detecting the inert gas temperature by use of the temperature sensors  19  and  24 , and inputting their signals into the gradient control mechanism  23  in the chiller  21 , on the basis of a difference between a circulation temperature and a target set temperature. A resultant signal is outputted to the temperature control device  17  to control the heater  22  for the coolant. The cooling rate of the inert gas is controlled by effecting gradient control of the coolant.  
         [0044]     Here, mechanisms of occurrence and suppression of the internal pressure change will be described by taking the case where the inert gas temperature is increased as an example.  
         [0045]     In this case, a circulating system is not a complete closed circulating system, thus permitting supply and exhaust of gas. Accordingly, a predetermined change in internal pressure can be suppressed by a certain period of time. Such a relationship therebetween is shown in  FIG. 6 . Referring to  FIG. 6 , a time required to suppress a certain internal pressure change ΔP when the internal pressure change ΔP occurs is taken as t. A relationship (time constant) therebetween is determined by a volume of the circulating system, an exhaust flow rate, and a resistance at an exhaust port.  
         [0046]     On the basis of this relationship, a time t required to suppress the predetermined internal pressure change ΔP is determined.  
         [0047]     Further, from equation of state of gas, ΔP which is increased by a temperature rise ΔT is determined. When a time required for the temperature rise is equal to or longer than the time t required to suppress the internal pressure change described above, it is possible to suppress the internal pressure change in an acceptable range. As described above, it becomes possible to determine such a temperature gradient (temperature changing rate or timewise changing rate) that the internal pressure change does not occur. Accordingly, when the gradient control mechanism  20  generates a target temperature value varying depending on the temperature gradient determined as described above on the basis of a difference between a target temperature set value of gas and a measured temperature value (a measured value by the temperature sensor  16 ) and (on the basis of) a measured temperature value (a measured value by the temperature sensor  18 ) disposed upstream of the heating device  12 , and provides the generated target temperature value to the temperature control device  17 , it is possible to suppress the internal pressure change of the chamber in an acceptable range thereof.  
         [0048]     According to this embodiment, by controlling the temperature rise (heating) or cooling rate gradient while monitoring the circulation temperature in the purge chamber, it becomes possible to suppress the change in internal pressure of the purge chamber while avoiding abrupt temperature rise state or radial cooling state of the circulation gas to ensure a withstanding pressure of the lens.  
         [0049]     In this embodiment, the gradient control portion and the temperature control device are independently disposed but they may be constituted as an integrated control mechanism.  
       Embodiment 2  
       [0050]      FIG. 2  is a schematic view of an exposure apparatus in this embodiment according to the present invention.  
         [0051]     The exposure apparatus shown in  FIG. 2  has the same structure as that (of conventional inert gas circulating system) shown in  FIG. 5  except that it further includes temperature sensors  18 ,  19  and  24 , an inverter  27 , and a gradient control mechanism  28 . In  FIG. 2 , members and means are indicated by reference numerals identical to those shown in  FIG. 5  and  FIG. 1  and detailed explanation thereof will be omitted.  
         [0052]     The exposure apparatus of this embodiment has the same function as that of Embodiment 1 except that cooling rate control at a cooling portion is performed by controlling the inverter  27  in a chiller  21  to regulate the number of revolutions of a pump  25 , thereby to effect flow rate control of a coolant to control a gradient of the cooling rate.  
         [0053]     In the exposure apparatus shown in  FIG. 2 , temperature control of inert gas is performed by detecting the temperature of inert gas through the temperature sensors  18  and  16 , inputting their signals into the heater control portion  20 , performing gradient control on the basis of a difference between an internal circulation temperature and a target set temperature, and outputting a resultant signal to the temperature control device  17  to effect control of the heating device  12 .  
         [0054]     Further, also with respect to the cooling of the inert gas, the gradient control is performed by detecting the inert gas temperature by use of the temperature sensors  19  and  24 , and inputting their signals into the gradient control mechanism  28  on the basis of a difference between a circulation temperature and a target set temperature. As a gradient control method in this embodiment, the number of revolution of the pump is controlled by the inverter  27  for the pump  25  in the chiller  21 , whereby gradient control of a cooling rate is performed through flow rate control of the coolant.  
         [0055]     As described above, this embodiment is identical to Embodiment 1 except that the gradient control of the cooling device is performed by the flow rate of the coolant. As a result, according to this embodiment, by controlling the temperature rise rate and/or the cooling rate, the internal pressure change in the purge chamber is suppressed to ensure a withstanding pressure of the lens.  
         [0056]     In this embodiment, the inverter and the temperature control device are independently disposed but they may be constituted as an integrated control mechanism.  
         [0057]     According to this embodiment, by suppressing a possible change in internal pressure of the purge chamber due to abrupt temperature rise state or radial cooling state of the circulation gas during start and stop of the circulation operation and controlling the temperature rise (heating) or cooling rate gradient while monitoring the circulation temperature in the purge chamber, it becomes possible to ensure a withstanding pressure of the lens.  
       Embodiment 3  
       [0058]     A device manufacturing method, utilizing the exposure apparatus described above, according to this embodiment of the present invention will be described.  
         [0059]      FIG. 3  shows a flow chart of manufacture of microdevices (such as semiconductor chips (IC, LSI, etc.), a liquid crystal panel, CDD, a thin film magnetic head, and a micromachine).  
         [0060]     In Step  1  (circuit design), pattern designing of a device is performed. In Step  2  (mask manufacture), a mask provided with the designed pattern is manufactured. On the other hand, in Step  3  (wafer manufacture), a wafer is manufactured by use of a material such as silicon or glass. Step  4  (wafer process) is referred to as a pre-step in which the above prepared mask and wafer are used to form an actual circuit on the wafer through lithography. A subsequent Step  5  (fabrication) is referred to as a post-step in which the circuit-formed wafer is fabricated in a semiconductor chip, and includes an assembly step (dicing and bonding), a packaging step (chip sealing), etc. In Step  6  (inspection), the semiconductor device fabricated in Step  5  is subjected to inspection such as operation check, durability test, etc. Through the steps described above, the semiconductor device is finished and then is shipped (Step  7 ).  
         [0061]      FIG. 4  shows a flow chart of a detailed wafer step (Step  3  in  FIG. 3 ).  
         [0062]     In Step  11  (oxidation), the surface of wafer is oxidized. In Step  12  (CVD), an insulating film is formed on the wafer surface through CVD. In Step  13  (electrode formation), an electrode is formed on the wafer by (vacuum) vapor deposition. In Step  14  (ion implantation), ion is implanted in the wafer. In Step  15  (resist treatment), a photosensitive agent is applied onto the wafer. In Step  16  (exposure), the circuit pattern of the mask is transferred onto the wafer by exposure through the above described exposure apparatus. In Step  17  (development), the exposed wafer is subjected to development. In Step  18  (etching) a portion other than the developed resist image is removed. In Step  19  (resist removal), the unnecessary resist after completion of the etching is removed. These steps are repetitively performed to form a multiply circuit pattern. By using the device manufacturing method of the present invention, it is possible to inexpensively manufacture a high-integrated device which has not been manufactured readily by a conventional device manufacturing method.  
         [0063]     As described hereinabove, according to the above described embodiments of the present invention, by providing the temperature gradient control means for controlling the temperature gradient during a period in which the temperature in the chamber is changed, particularly during start and/or step of operation of an air conditioning system, it is possible to prevent an abrupt pressure change in the chamber. As a result, it becomes possible to prevent deterioration or damage of an apparatus constitutional element such as a lens, thereby to improve a reliability of the exposure apparatus.  
         [0064]     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.  
         [0065]     This application claims priority from Japanese Patent Application No. 377657/2003 filed Nov. 7, 2003, which is hereby incorporated by reference.