Patent Publication Number: US-9854658-B2

Title: Extreme ultraviolet light generation apparatus

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of International Patent Application No. PCT/JP2013/085184 filed Dec. 27, 2013, which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an EUV (extreme ultraviolet) light generation apparatus. 
     2. Related Art 
     In recent years, as semiconductor processes become finer, transfer patterns for use in photolithographies of semiconductor processes have rapidly become finer. In the next generation, microfabrication at 70 nm to 45 nm, further, microfabrication at 32 nm or less would be demanded. In order to meet the demand for microfabrication at 32 nm or less, for example, it is expected to develop an exposure device in which a system for generating EUV light at a wavelength of approximately 13 nm is combined with a reduced projection reflective optical system. 
     Three types of EUV light generation systems have been proposed, which include an LPP (laser produced plasma) type system using plasma generated by irradiating a target material with a laser beam, a DPP (discharge produced plasma) type system using plasma generated by electric discharge, and an SR (synchrotron radiation) type system using synchrotron orbital radiation. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL1: U.S. Pat. No. 7,872,245 
         PTL2: U.S. Pat. No. 8,138,487 
         PTL3: U.S. Patent Application Publication No. 2012/0205559 
       
    
     SUMMARY 
     According to a first aspect of the present disclosure, an extreme ultraviolet light generation apparatus may include: a chamber in which extreme ultraviolet light is generated when target is irradiated with a laser beam inside the chamber; a target supply part configured to supply the target into the chamber; and a target collector configured to collect the target which is supplied by the target supply part but is not irradiated with the laser beam in a collection container, by receiving the target on a receiving surface having a contact angle of equal to or smaller than 90 degrees with the target. 
     According to a second aspect of the present disclosure, an extreme ultraviolet light generation apparatus may include: a chamber in which extreme ultraviolet light is generated when a target is irradiated with a laser beam inside the chamber; a target supply part configured to supply the target into the chamber; and a target collector including a filter configured to allow the target which is supplied by the target supply part but is not irradiated with the laser beam to pass therethrough. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter, selected embodiments of the present disclosure will be described with reference to the accompanying drawings by way of example. 
         FIG. 1  schematically shows the configuration of an exemplary LPP type EUV light generation system; 
         FIG. 2  shows the configuration of an EUV light generation apparatus including a target generation device; 
         FIG. 3  shows the configuration of a target collector; 
         FIG. 4  is a flowchart explaining a process for the target supply performed by a target generation controller; 
         FIG. 5  shows the configuration of a first example of the target collector; 
         FIG. 6  is a drawing explaining a situation in which a target collides against a receiving surface of a receiving member; 
         FIG. 7  shows contact angles of various materials with molten tin; 
         FIG. 8  shows the configuration of a second example of the target collector; 
         FIG. 9A  is a drawing explaining a state before a target passes through the filter shown in  FIG. 8 ; 
         FIG. 9B  is a drawing explaining a state when the target passes through the filter shown in  FIG. 8 ; 
         FIG. 9C  is a drawing explaining a state of the fragmented materials after the target passes through the filter shown in  FIG. 8 ; 
         FIG. 10  shows the configuration of a third example of the target collector; 
         FIG. 11  shows the configuration of a fourth example of the target collector; 
         FIG. 12  shows the configuration of a fifth example of the target collector; 
         FIG. 13A  shows the configuration of the filter of a sixth example of the target collector; 
         FIG. 13B  shows a view of  FIG. 13A  from direction A, where a via-hole is not provided in advance in the filter; 
         FIG. 13C  shows a view of  FIG. 13A  from the direction A, where the via-hole is provided in advance in the filter; 
         FIG. 14A  shows the configuration of the filter of a seventh example of the target collector; 
         FIG. 14B  shows a view of  FIG. 14A  from direction A 1 ; 
         FIG. 14C  shows a view of  FIG. 14A  from direction A 2 ; 
         FIG. 14D  shows a view of  FIG. 14A  from direction A 3 ; 
         FIG. 14E  shows a view of  FIG. 14A  from direction A 4 ; 
         FIG. 15A  is a drawing explaining a state where a target collides against and passes through the filter shown in  FIG. 14A ; 
         FIG. 15B  is a drawing explaining a state where the target passes through the filter shown in  FIG. 14A  without colliding against the filter; 
         FIG. 15C  is a drawing explaining a state of the fragmented materials after the target passes through the filter shown in  FIG. 14A ; 
         FIG. 16A  shows the configuration of the filter of an eighth example of the target collector; 
         FIG. 16B  shows a view of  FIG. 16A  from direction A; 
         FIG. 17A  shows the configuration of the filter of a ninth example of the target collector; 
         FIG. 17B  shows a view of  FIG. 17A  from direction A; 
         FIG. 18A  shows the configuration of the filter of a tenth example of the target collector; 
         FIG. 18B  shows a view of  FIG. 18A  from direction A; 
         FIG. 19A  shows another example 1 of the filter installation; 
         FIG. 19B  shows another example 2 of the filter installation; 
         FIG. 19C  shows another example 3 of the filter installation; and 
         FIG. 20  is a block diagram showing the hardware environment of each of the controllers. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     &lt;Contents&gt; 
     
         
         1. Overview 
         2. Description of terms 
         3. Overview of the EUV light generation system 
         3.1 Configuration 
         3.2 Operation 
         4. EUV light generation apparatus including a target collector 
         4.1 Configuration 
         4.2 Operation 
         4.3 Problem 
         5. Target collector of the EUV light generation apparatus acoording to Embodiment 1 
         5.1 First example of the target collector 
         6. Target collector of the EUV light generation apparatus according to Embodiment 2 
         6.1 Second example of the target collector 
         6.2 Third example of the target collector 
         6.3 Fourth example of the target collector 
         6.4 Fifth example of the target collector 
         7. Target collector of the EUV light generation apparatus according to Embodiment 3 
         7.1 Sixth example of the target collector 
         7.2 Seventh example of the target collector 
         7.3 Eighth example of the target collector 
         7.4 Ninth example of the target collector 
         7.5 Tenth example of the target collector 
         8. Other examples of filter installation 
         9. Others 
         9.1 Hardware environment of each controller 
         9.2 Modification 
       
    
     Hereinafter, selected embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments to be described below are merely illustrative in nature and do not limit the scope of the present disclosure. Further, the configuration(s) and operation(s) described in each embodiment are not all essential in implementing the present disclosure. Corresponding elements may be referenced by corresponding reference numerals and characters, and therefore duplicate descriptions will be omitted. 
     1. Overview 
     The present disclosure may at least disclose the following embodiments. 
     The EUV light generation apparatus  1  according to the present disclosure may include: a chamber  2  in which EUV light  252  is generated when a target  27  is irradiated with a pulsed laser beam  33  inside the chamber; a target supply part  26  configured to supply the target  27  into the chamber  2 ; and a target collector  28  configured to collect the target  27  which is supplied by the target supply part  26  but is not irradiated with the pulsed laser beam  33  in a collection container  281 , by receiving the target  27  on a receiving surface S having a contact angle of equal to or smaller than 90 degrees with the target. Therefore, the EUV light generation apparatus  1  according to the present disclosure can prevent the fragmented materials  274  of the target  27  from dispersing to the outside of the target collector  28 , when the target  27  not irradiated with the pulsed laser beam  33  is collected. 
     The EUV light generation apparatus  1  according to the present disclosure may include: a chamber  2  in which EUV light  252  is generated when a target  27  is irradiated with a pulsed laser beam  33  inside the chamber  2 ; a target supply part  26  configured to supply the target  27  into the chamber  2 ; and a target collector  28  including a filter  288  configured to allow the target  27  which is supplied by the target supply part  26  but is not irradiated with the pulsed laser beam  33  to pass therethrough. Therefore, the EUV light generation apparatus  1  according to the present disclosure can prevent the fragmented materials  274  of the target  27  from dispersing to the outside of the target collector  28 , when the target  27  not irradiated with the pulsed laser beam  33  is collected. 
     2. Description of Terms 
     “Target” refers to a substance which is introduced into the chamber and is irradiated with a laser beam. The target irradiated with the laser beam is turned into plasma and emits EUV light. “Droplet” refers to one form of the target introduced into the chamber. 
     3. Overview of the EUV Light Generation System 
     3.1 Configuration 
       FIG. 1  schematically shows the configuration of an exemplary LPP type EUV light generation system. The EUV light generation apparatus  1  may be used with at least one laser device  3 . In the present disclosure, the system including the EUV light generation apparatus  1  and the laser device  3  may be referred to as an EUV light generation system  11 . As shown in  FIG. 1 , and as described in detail later, the EUV light generation apparatus  1  may include the chamber  2  and the target supply part  26 . The chamber  2  may be sealed airtight. The target supply part  26  may be mounted onto the chamber  2 , for example, to penetrate a wall of the chamber  2 . A target material to be supplied from the target supply part  26  may include, but is not limited to, tin, terbium, gadolinium, lithium, xenon, or a combination of any two or more of them. 
     The chamber  2  may have at least one through-hole in its wall. A window  21  may be provided on the through-hole. A pulsed laser beam  32  outputted from the laser device  3  may transmit through the window  21 . In the chamber  2 , an EUV collector mirror  23  having a spheroidal reflective surface may be provided. The EUV collector mirror  23  may have a first focusing point and a second focusing point. The surface of the EUV collector mirror  23  may have a multi-layered reflective film in which molybdenum layers and silicon layers are alternately laminated. Preferably, the EUV collector mirror  23  may be arranged such that the first focusing point is positioned in a plasma generation region  25  and the second focusing point is positioned in an intermediate focusing (IF) point  292 . The EUV collector mirror  23  may have a through-hole  24  formed at the center thereof so that a pulsed laser beam  33  may pass through the through-hole  24 . 
     The EUV light generation apparatus  1  may further include an EUV light generation controller  5  and a target sensor  4 . The target sensor  4  may have an imaging function and detect the presence, trajectory, position and speed of the target  27 . 
     Further, the EUV light generation apparatus  1  may include a connection part  29  that allows the interior of the chamber  2  to be in communication with the interior of an exposure device  6 . In the connection part  29 , a wall  291  having an aperture  293  may be provided. The wall  291  may be positioned such that the second focusing point of the EUV collector mirror  23  lies in the aperture  293 . 
     The EUV light generation apparatus  1  may also include a laser beam direction control unit  34 , a laser beam focusing mirror  22 , and the target collector  28  for collecting the target  27 . The laser beam direction control unit  34  may include an optical element for defining the traveling direction of the laser beam and an actuator for adjusting, for example, the position and the posture of the optical element. 
     3.2 Operation 
     With reference to  FIG. 1 , a pulsed laser beam  31  outputted from the laser device  3  may pass through the laser beam direction control unit  34 , transmit through the window  21  as a pulsed laser beam  32 , and then enter the chamber  2 . The pulsed laser beam  32  may travel through the chamber  2  along at least one laser beam path, be reflected from the laser beam focusing mirror  22 , and be applied to at least one target  27  as the pulsed laser beam  33 . 
     The target supply part  26  may be configured to output the target  27  to the plasma generation region  25  in the chamber  2 . The target  27  may be irradiated with at least one pulse of the pulsed laser beam  33 . Upon being irradiated with the pulsed laser beam, the target  27  may be turned into plasma, and EUV light  251  may be emitted from the plasma together with the emission of light at different wavelengths. The EUV light  251  may be selectively reflected from the EUV collector mirror  23 . EUV light  252  reflected from the EUV collector mirror  23  may be focused onto the IF point  292 , and outputted to the exposure device  6 . Here, one target  27  may be irradiated with multiple pulses of the pulsed laser beam  33 . 
     The EUV light generation controller  5  may be configured to totally control the EUV light generation system  11 . The EUV light generation controller  5  may be configured to process the image data of the target  27  captured by the target sensor  4 . Further, the EUV light generation controller  5  may be configured to control at least one of: the timing at which the target  27  is outputted; and the direction in which the target  27  is outputted. Furthermore, the EUV light generation controller  5  may be configured to control at least one of: the timing at which the laser device  3  oscillates; the traveling direction of the pulsed laser beam  32 ; and the position on which the pulsed laser beam  33  is focused. The various controls described above are merely examples, and other controls may be added as necessary. 
     4. EUV Light Generation Apparatus Including the Target Collector 
     4.1 Configuration 
     With reference to  FIGS. 2 and 3 , the configuration of the EUV light generation apparatus  1  including a target generation device  7  and the target collector  28  will be described.  FIG. 2  shows the configuration of the EUV light generation apparatus  1  including the target generation device  7 .  FIG. 3  shows the configuration of the target collector  28 . In  FIG. 2 , the direction in which the EUV light  252  is outputted from the chamber  2  of the EUV light generation apparatus  1  to the exposure device  6  is defined as a Z-axis. An X-axis and a Y-axis are orthogonal to the Z-axis and are orthogonal to one another. The same applies to the subsequent drawings. 
     The chamber  2  of the EUV light generation apparatus  1  may be formed in, for example, a hollow spherical shape or a hollow cylindrical shape. The direction of the central axis of the cylindrical chamber  2  may be the same as the direction in which the EUV light  252  is outputted to the exposure device  6 . 
     The cylindrical chamber  2  may include a target supply hole  2   a  formed in its side portion, for supplying the target  27  into the chamber  2  from the outside of the chamber  2 . If the chamber  2  is formed in a hollow spherical shape, the target supply hole  2   a  may be formed on the wall surface of the chamber  2  at a position in which the window  21  and the connection part  29  are not provided. 
     In the chamber  2 , a laser beam focusing optical system  22   a , an EUV light focusing optical system  23   a , the target collector  28 , a plate  225  and a plate  235  may be provided. 
     The plate  235  may be fixed to the inner surface of the chamber  2 . A hole  235   a  that allows the pulsed laser beam  33  to pass therethrough may be formed at the center of the plate  235  in the thickness direction of the plate  235 . The opening direction of the hole  235   a  may be the same as the direction of the axis passing through the through-hole  24  and the plasma generation region  25  shown in  FIG. 1 . The EUV light focusing optical system  23   a  may be provided on one surface of the plate  235 . Meanwhile, on the other surface of the plate  235 , the plate  225  may be provided via a triaxial stage (not shown). 
     The EUV light focusing optical system.  23   a  provided on the one surface of the plate  235  may include the EUV collector mirror  23  and a holder  231 . The holder  231  may hold the EUV collector mirror  23 . The holder  231  holding the EUV collector mirror  23  may be fixed to the plate  235 . 
     The plate  225  provided on the other surface of the plate  235  may be changed in its position and posture by the triaxial stage. The laser beam focusing optical system  22   a  may be provided on the plate  225 . 
     The laser beam focusing optical system  22   a  may include the laser beam collector mirror  22 , a holder  223  and a holder  224 . The laser beam collector mirror  22  may include an off-axis paraboloidal mirror  221  and a plane mirror  222 . 
     The holder  223  may hold the off-axis paraboloidal mirror  221 . The holder  223  holding the off-axis paraboloidal mirror  221  may be fixed to the plate  225 . The holder  224  may hold the plane mirror  222 . The holder  224  holding the plane mirror  222  may be fixed to the plate  225 . 
     The off-axis paraboloidal mirror  221  may be placed to face each of the window  21  provided on the bottom portion of the chamber  2  and the plane mirror  222 . The plane mirror  222  may be placed to face each of the hole  235   a  and the off-axis paraboloidal mirror  221 . The positions and postures of the off-axis paraboloidal mirror  221  and the plane mirror  222  may be adjusted by changing the position and posture of the plate  225 . This adjustment may be performed such that the pulsed laser beam  33 , which is a reflected beam of the pulsed laser beam  32  having entered the off-axis paraboloidal mirror  221  and the plane mirror  222 , is focused on the plasma generation region  25 . 
     The target collector  28  may be provided on the lateral side of the chamber  2 . The target collector  28  may be disposed on the extension of a target traveling path  272  through which the target  27  outputted into the chamber  2  as a droplet  271  travels. As shown in  FIG. 3 , the target collector  28  may include a collection container  281  and a temperature adjusting mechanism  282 . Here, the configurations of the collection container  281  and the temperature adjusting mechanism  282  will be described in detail later with reference to  FIG. 3 . 
     Meanwhile, the laser beam direction control unit  34 , the EUV light generation controller  5  and the target generation device  7  may be provided outside the chamber  2 . 
     The laser beam direction control unit  34  may be provided between the window  21  formed on the bottom portion of the chamber  2  and the laser device  3 . The laser beam direction control unit  34  may include a high reflection mirror  341 , a high reflection mirror  342 , a holder  343  and a holder  344 . 
     The holder  343  may hold the high reflection mirror  341 . The holder  344  may hold the high reflection mirror  342 . The positions and postures of the holders  343  and  344  may be changed by an actuator (not shown) connected to the EUV light generation controller  5 . 
     The high reflection mirror  341  may be placed to face each of the exit aperture of the laser device  3  from which the pulsed laser beam  31  exits and the high reflection mirror  342 . The high reflection mirror  342  may be placed to face each of the window  21  of the chamber  2  and the high reflection mirror  341 . The positions and postures of the high reflection mirrors  341  and  342  may be adjusted by changing the positions and postures of the holders  343  and  344  by the EUV light generation controller  5 . This adjustment may be performed such that the pulsed laser beam  32 , which is the reflected beam of the pulsed laser beam  31  having entered the high reflection mirrors  341  and  342 , transmits through the window  21  formed in the bottom portion of the chamber  2 . 
     The EUV light generation controller  5  may send/receive control signals to/from the laser device  3  and control the operation of the laser device  3 . The EUV light generation controller  5  may send/receive control signals to/from the actuators of the laser beam direction control unit  34  and the laser beam focusing optical system  22   a . By this means, the EUV light generation controller  5  may adjust the traveling directions and the focusing positions of the pulsed laser beams  31  to  33 . The EUV light generation controller  5  may send/receive control signals to/from a target generation controller  74  (described later) of the target generation device  7  and control the operation of the target generation device  7 . Here, the hardware configuration of the EUV light generation controller  5  will be described later with reference to  FIG. 20 . 
     The target generation device  7  may be provided on the lateral side of the chamber  2 . The target generation device  7  may include the target supply part  26 , a heater  711 , a heater power source  712 , a pressure regulator  721 , a pipe  722 , a gas bomb  723 , a piezoelectric element  731 , a piezoelectric power source  732 , and the target generation controller  74 . 
     The target supply part  26  may include a tank  261  and a nozzle  262 . The tank  261  may be formed in a hollow cylindrical shape. The hollow tank  261  may accommodate the target  27 . At least the inner surface of the tank  261  accommodating the target  27  may be made of a material which is not easy to react with the target  27 . The material which is not easy to react with the target  27  may be any of, for example, silicon carbide, silicon oxide, aluminium oxide, molybdenum, tungsten and tantalum. 
     The nozzle  262  may be provided on the bottom portion of the cylindrical tank  261 . The nozzle  262  may be placed in the interior of the chamber  2  via the target supply hole  2   a  of the chamber  2 . The target supply hole  2   a  may be closed by providing the target supply part  26 . By this means, it is possible to isolate the interior of the chamber  2  from the atmosphere. The interior of the nozzle  262  may be made of a material which is not easy to react with the target  27 . 
     One end of the pipe-like nozzle  262  may be fixed to the hollow tank  261 . A nozzle hole (not shown) may be formed in the other end of the pipe-like nozzle  262 . The tank  261  provided on the one end side of the nozzle  262  may be placed outside the chamber  2 . Meanwhile, the nozzle hole provided on the other end side of the nozzle  262  may be placed inside the chamber  2 . The plasma generation region  25  and the target collector  28  placed inside the chamber  2  may be positioned on the extension of the central axis of the nozzle  262 . The interiors of the tank  261 , the nozzle  262  and the chamber  2  may communicate with each other. The nozzle hole may be formed in a shape that allows the molten target  27  to be jetted into the chamber  2 . 
     The heater  711  may be fixed to the outer side portion of the cylindrical tank  261 . The heater  711  fixed to the tank  261  may heat the tank  261 . The heater  711  may be connected to the heater power source  712 . The heater power source  712  may supply electric power to the heater  711 . The heater power source  712  that supplies electric power to the heater  711  may be connected to the target generation controller  74 . The power supply from the heater power source  712  to the heater  711  may be controlled by the target generation controller  74 . 
     A temperature sensor (not shown) may be fixed to the outer side portion of the cylindrical tank  261 . The temperature sensor fixed to the tank  261  may be connected to the target generation controller  74 . The temperature sensor may detect the temperature of the tank  261  and output a detection signal to the target generation controller  74 . The target generation controller  74  may control the electric power supplied to the heater  711  such that the temperature in the tank  261  is a target temperature, based on the detection signal outputted from the temperature sensor. By this means, it is possible to adjust the temperature in the tank  261  to the target temperature. 
     The pipe  722  may connect between the bottom portion of the cylindrical tank  261  on the opposite side of the nozzle  262  and the pressure regulator  721 . The pipe  722  allows the target supply part  26  including the tank  261  and the pressure regulator  721  to communicate with one another. The pipe  722  may be covered with a heat insulating material (not shown). A heater (not shown) may be provided on the pipe  722 . The temperature in the pipe  722  may be maintained at the same temperature as the temperature in the tank  261  of the target supply part  26 . 
     The gas bomb  723  may be filled with inert gas such as helium, argon and so forth. The gas bomb  723  may supply the inert gas into the tank  261  via the pressure regulator  721 . 
     The pressure regulator  721  may be provided on the bottom portion of the cylindrical tank  261  on the opposite side of the nozzle  262  via the pipe  722 , as described above. The pressure regulator  721  may include solenoid valves for air supply and exhaust, a pressure sensor and so forth. The pressure regulator  721  may detect the pressure in the tank  261  by using the pressure sensor. The pressure regulator  721  may be connected to the gas bomb  723 . The pressure regulator  721  may supply inert gas from the gas bomb  723  to the tank  261 . The pressure regulator  721  may be connected to an exhaust pump (not shown). The pressure regulator  721  may activate the exhaust pump to discharge the gas from the tank  261 . The pressure regulator  721  may increase or decrease the pressure in the tank  261  by supplying/discharging the gas into/out of the tank  261 . 
     The pressure regulator  721  may be connected to the target generation controller  74 . The pressure regulator  721  may output a detection signal indicating the detected pressure to the target generation controller  74 . A control signal outputted from the target generation controller  74  may be inputted to the pressure regulator  721 . The control signal outputted from the target generation controller  74  may be a signal for controlling the operation of the pressure regulator  721  to regulate the pressure in the tank  261  at a target pressure, based on the detection signal outputted from the pressure regulator  721 . The pressure regulator  721  may supply/discharge the gas into/out of the tank  261 , based on the control signal from the target generation controller  74 . By this means, it is possible to regulate the pressure in the tank  261  at the target pressure. 
     The piezoelectric element  731  may be fixed to the outer side portion of the pipe-like nozzle  262 . The piezoelectric element  731  fixed to the nozzle  262  may cause a vibration of the nozzle  262 . The piezoelectric element  731  that causes a vibration of the nozzle  262  may be connected to the piezoelectric power source  732 . The piezoelectric power source  732  may supply electric power to the piezoelectric element  731 . The piezoelectric power source  732  that supplies electric power to the piezoelectric element  731  may be connected to the target generation controller  74 . The piezoelectric power source  732  may receive the control signal outputted from the target generation controller  74 . The control signal outputted from the target generation controller  74  may be a control signal to cause the piezoelectric power source  732  to supply electric power with a predetermined waveform to the piezoelectric element  731 . The piezoelectric power source  732  may supply electric power to the piezoelectric element  731 , based on the control signal from the target generation controller  74 . The piezoelectric element  731  may cause a vibration of the nozzle  262  according to the predetermined waveform. This allows a standing wave to be given to the flow of the jetted target  27  from the nozzle  262 , and therefore it is possible to periodically divide the target  27 . The divided target  27  may forma free interface by means of its own surface tension to form a droplet  271 . 
     The target generation controller  74  may send/receive control signals to/from the EUV light generation controller  5  to totally control the entire operation of the target generation device  7 . The target generation controller  74  may output a control signal to the heater power source  712  to control the operations of the heater power source  712  and the heater  711 . The target generation controller  74  may output a control signal to the pressure regulator  721  to control the operations of the pressure regulator  721  and the gas bomb  723 . The target generation controller  74  may output a control signal to the piezoelectric power source  732  to control the operations of the piezoelectric power source  732  and the piezoelectric element  731 . The target generation controller  74  may output a control signal to a temperature controller  282   d  (described later) of the temperature adjusting mechanism  282  to control the operation of the temperature adjusting mechanism  282 . Here, the hardware configuration of the target generation controller  74  will be described later with reference to  FIG. 20 . 
     With reference to  FIG. 3 , the configuration of the target collector  28  will be described. As described above, the target collector  28  may include the collection container  281  and the temperature adjusting mechanism  282 . 
     The collection container  281  may collect the target  27  outputted into the chamber  2  as the droplet  271 . This target  27  may be one of the targets  27  supplied to the plasma generation region  25  by the target supply part  26  but not irradiated with the pulsed laser beam  33 . That is, the collection container  281  may collect one of the targets  27  which has been supplied by the target supply part  26  but not contributed to generation of the EUV light  251 . The target  27  collected in the collection container  281  may be referred to as “collected target  273 .” 
     The collection container  281  may be formed in a cylindrical shape. The central axis of the cylindrical collection container  281  may match the target traveling path  272 . An opening  281   a  of the collection container  281  may face the target supply part  26  and the plasma generation region  25 . A bottom portion  281   b  of the collection container  281  may be located on the inner surface side of a wall  2   b  of the chamber  2 . A side portion  281   c  of the collection container  281  may be provided to extend from the bottom portion  281   b  to the opening  281   a . The collection container  281  may introduce the target  27  through the opening  281   a  into the inside of the collection container  281  and store the target  27  in space formed by the bottom portion  281   b  and the side portion  281   c . The collection container  281  may collect the target  27  inside the chamber  2 . 
     The temperature adjusting mechanism  282  may adjust the temperature in the collection container  281 . The temperature adjusting mechanism  282  may include a heater  282   a , a heater power source  282   b , a temperature sensor  282   c  and the temperature controller  282   d.    
     The heater  282   a  may be provided to cover the outer surface of the collection container  281 . The heater  282   a  may be fixed to the outer surfaces of the bottom portion  281   b  and the side portion  281   c . The heater  282   a  fixed to the collection container  281  may heat the collection container  281 . The heater  282   a  may be connected to the heater power source  282   b . The heater power source  282   b  may supply electric power to the heater  282   a . The heater power source  282   b  that supplies electric power to the heater  282   a  may be connected to the temperature controller  282   d . The power supply from the heater power source  282   b  to the heater  282   a  may be controlled by the temperature controller  282   d.    
     The temperature sensor  282   c  may be fixed to the bottom portion  281   b  or the side portion  281   c  of the collection container  281 . The temperature sensor  282   c  may be embedded in and fixed to the inside of the bottom portion  281   b  or the side portion  281   c . The temperature sensor  282   c  may be fixed to the inner surface of the bottom portion  281   b  or the side portion  281   c , and directly contact the collected target  273 . The temperature sensor  282   c  may be connected to the temperature controller  282   d . The temperature sensor  282   c  may detect the temperature of the collection container  281  and output a detection signal to the temperature controller  282   d.    
     The detection signal outputted from the temperature sensor  282   c  may be inputted to the temperature controller  282   d . The temperature controller  282   d  may be connected to the target generation controller  74 . The temperature controller  282   d  may output the detection signal outputted from the temperature sensor  282   c  to the target generation controller  74 . The control signal outputted from the target generation controller  74  may be inputted to the temperature controller  282   d . The control signal outputted from the target generation controller  74  may be a signal for controlling the operation of the heater power source  282   b  to make the temperature in the collection container  281  be the target temperature, based on the detection signal outputted from the temperature sensor  282   c . The control signal may contain a temperature setting value to make the temperature in the collection container  281  be the target temperature. The temperature controller  282   d  may control the electric power supplied from the heater power source  282   b  to the heater  282   a , according to the temperature setting value contained in the control signal from the target generation controller  74 . By this means, it is possible to adjust the temperature in the collection container  281  to the target temperature. 
     The target temperature may be equal to or higher than the melting point of the target  27 . When the target  27  is tin, the target temperature may be, for example, equal to or higher than 232 degrees Celsius and lower than 270 degrees Celsius. Alternatively, the target temperature may be equal to or higher than 270 degrees Celsius. The collection container  281  having the temperature adjusted to the target temperature can melt the collected target  273 . 
     4.2 Operation 
     With reference to  FIG. 4 , the outline of the operation of the EUV light generation apparatus  1  including the target generation device  7  will be described.  FIG. 4  is a flowchart explaining a process for target supply performed by the target generation controller  74 . When a start signal to activate the target generation device  7  is inputted from the EUV light generation controller  5  to the target generation controller  74 , the target generation controller  74  may perform the following process. 
     In step S 1 , the target generation controller  74  may perform initial setting for the target generation device  7 . The target generation controller  74  may activate each component of the target generation device  7  and perform operation check on each of the components. Then, the target generation controller  74  may initialize each of the components and set an initial setting value in each of the components. 
     Particularly, the target generation controller  74  may set an initial pressure setting value of the pressure regulator  721  to make the pressure in the tank  261  have a pressure value approximate to the value of the vacuum state. The pressure value approximate to the value of the vacuum state may be, for example, 1 hPa. The gas in the tank  261 , which is easy to react with the target  27 , may be discharged before the target  27  has molten. In this case, the inert gas in the gas bomb  723  may be supplied into the tank  261  several times to purge the tank  261 . 
     Moreover, the target generation controller  74  may set an initial temperature setting value of the heater  711  to make the temperature of the target  27  have a value equal to or higher than the melting point of the target  27 . The initial temperature setting value of the heater  711  may be, for example, equal to or higher than 232 degrees Celsius and lower than 270 degrees Celsius. 
     Furthermore, the target generation controller  74  may cause the temperature controller  282   d  to set an initial temperature setting value of the heater  282   a  to make the temperature of the collected target  273  have a value equal to or higher than the melting point of the target  27  when the target  27  is collected. The initial temperature setting value of the heater  282   a  may be equal to or higher than 232 degrees Celsius and lower than 270 degrees Celsius. 
     In step S 2 , the target generation controller  74  may determine whether or not a target generation signal has been inputted from the EUV light generation controller  5 . The target generation signal may be a control signal to cause the target generation device  7  to supply the target  27  to the plasma generation region  25  in the chamber  2 . The target generation controller  74  may wait until the target generation signal is inputted. The target generation controller  74  may continuously control the heating by the heater  711  to maintain the temperature in the tank  261  within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . The target generation controller  74  may continuously control the heating by the heater  282   a  to maintain the temperature in the collection container  281  within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . When determining that the target generation signal has been inputted, the target generation controller  74  may move the step to step S 3 . 
     In the step S 3 , the target generation controller  74  may check the temperature in the tank  261 . The target generation controller  74  may appropriately correct the temperature setting value to control the heating by the heater  711 . The target  27  stored in the tank  261  may be heated to a temperature equal to or higher than its melting point. The heated target  27  may be molten. 
     In step S 4 , the target generation controller  74  may check the temperature of the collection container  281 . The target generation controller  74  may cause the temperature controller  282   d  to appropriately correct the temperature setting value to control the heating by the heater  282   a . The collected target  273  collected in the collection container  281  may be heated to a temperature equal to or higher than its melting point. The heated collected target  273  may be molten. 
     In step S 5 , the target generation controller  74  may cause the piezoelectric power source  732  to supply electric power to the piezoelectric element  731 . The piezoelectric element  731  may cause a vibration of the nozzle  262 . If the molten target  27  is jetted from the nozzle hole, the molten target  27  is divided due to the vibration of the nozzle  262  so that the droplet  271  may be formed. Here, the target generation controller  74  may control the operation of the piezoelectric power source  732  to supply electric power with a predetermined waveform to the piezoelectric element  731 . This predetermined waveform may be a waveform with which the droplet  271  is formed at a predetermined generation frequency. The predetermined generation frequency may be, for example, 50 kHz to 100 kHz. 
     In step S 6 , the target generation controller  74  may set a pressure setting value in the pressure regulator  721  so that the pressure in the tank  261  allows the target  27  to be supplied. The pressure regulator  721  may regulate the pressure in the tank  261  at the pressure setting value set as above. The pressure at which the target  27  can be supplied may be a pressure at which a constant amount of the molten target  27  jets from the nozzle hole and reaches the plasma generation region  25  at a predetermined speed. The predetermined speed may be, for example, 60 m/s to 100 m/s. The pressure may be applied to the molten target  27  in the tank  261 . The target  27  under pressure may flow from the tank  261  to the nozzle  262 , and a constant amount of the target  27  may be jetted from the nozzle hole. The constant amount of the target  27  jetted from the nozzle hole may be vibrated by the piezoelectric element  731  for a constant cycle, so that it is possible to form the uniform droplet  271  for the constant cycle. The formed droplets  271  may be outputted into the chamber  2 . The diameter of the formed droplet  271  may be, for example, 20 μm to 30 μm. 
     The EUV light generation controller  5  may control the timing at which the pulsed laser beam  31  is outputted from the laser device  3  such that the pulsed laser beam  33  is emitted to the plasma generation region  25  at the same time at which the droplet  271  reaches the plasma generation region  25 . The droplet  271  reaching the plasma generation region  25  may be irradiated with the pulsed laser beam  33  being emitted to the plasma generation region  25 . The droplet  271  irradiated with the pulsed laser beam  33  may be turned into plasma and generate the EUV light  251 . 
     Meanwhile, the droplet  271  not irradiated with the pulsed laser beam  33  may travel on the target traveling path  272  through the plasma generation region  25  and reach the target collector  28 . The droplet having reached the target collector  28  may enter the opening  281   a  of the collection container  281  and be stored in the collection container  281 . In this case, the temperature of the collection container  281  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . Therefore, the droplet  271  having entered the collection container  281  may be stored in the collection container  281 , as the molten collected target  273 . 
     In step S 7 , the target generation controller  74  may determine whether or not a target generation stop signal has been inputted from the EUV light generation controller  5 . The target generation stop signal may be a control signal to cause the target generation controller  7  to stop supplying the target  27  to the plasma generation region  25 . When determining that the target generation stop signal has not been inputted, the target generation controller  74  may move the step to the step S 3 . On the other hand, when determining that the target generation stop signal has been inputted, the target generation controller  74  may end this process. 
     4.3 Problem 
     The EUV light generation apparatus  1  can supply the target  27  as a plurality of droplets  271  to the plasma generation region  25 . The EUV light generation apparatus  1  irradiates the target  27  reaching the plasma generation region  25  with the pulsed laser beam  33  to turn the target  27  into plasma, so that the EUV light  251  can be generated. However, the EUV light generation apparatus  1  may not necessarily irradiate all the targets  27  reaching the plasma generation region  25 , with the pulsed laser beam  33 . The targets  27  not irradiated with the pulsed laser beam  33  can be collected by the target collector  28 . When the target  27  not irradiated with the pulsed laser beam  33  is collected by the target collector  28 , the target  27  may enter the collection container  281  through the opening  281   a.    
     At this time, the target  27  having entered the target collector  28  may collide against a liquid level  273   a  of the collected target  273  stored in the collection container  281  as shown in  FIG. 3 . The molten collected target  273  forming the liquid level  273   a  may be broken into splashes by the impact of the collision against the target  27  and jump out as fragmented materials  274 . Then, the fragmented materials  274  may pass through the opening  281   a  and disperse to the outside of the target collector  28 . 
     Even when the molten collected target  273  is not stored in the collection container  281 , the target  27  having entered the collection container  281  may collide against the bottom portion  281   b  or the side portion  281   c . When colliding against the bottom portion  281   b  or the side portion  281   c , the target  27  may be crushed on the surface of the bottom portion  281   b  or the side portion  281   c  and jump out as the fragmented materials  274 . Even when the surface of the bottom portion  281   b  or the side portion  281   c  is coated with a material that is not easy to be wetted by the target  27 , the crushed target  27  may jump out as the fragmented materials  274 . Then, the fragmented materials  274  may pass through the opening  281   a  and disperse to the outside of the target collector  28 . 
     Each of the fragmented materials  274  may be a fine particle having a diameter of about several μm. The fragmented materials  274  may adhere to various optical systems provided in the chamber  2  and thereby deteriorate their performance. In particular, if the fragmented materials  274  adhere to the EUV collector mirror  23  provided in the chamber  2 , the reflectivity of the EUV collector mirror  23  may be decreased. The decrease in the reflectivity of the EUV collector mirror  23  may cause power reduction of the EUV light  251 , which may cause a problem. Therefore, there is a demand for a technology that can efficiently collect the target  27  not irradiated with the pulsed laser beam  33 , while preventing the fragmented materials  274  from dispersing to the outside of the target collector  28 . 
     5. Target Collector of the EUV Light Generation Apparatus According to Embodiment 1 
     With reference to  FIGS. 5 to 7 , the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 1 will be described. When collecting the target  27 , the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 1 may change the trajectory of the target  27  having entered the target collector  28 . In addition, the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 1 may prevent the target  27  entering the target collector  28  from reflecting from the position at which the target  27  collides against the target collector  28  and jumping out. Hereinafter, a first example of the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 1 will be described. The configuration of the target collector  28 , which is the same as that of the target collector  28  shown in  FIGS. 2 and 3 , will not be described again here. 
     5.1 First Example of the Target Collector 
     With reference to  FIGS. 5 to 7 , the configuration of the first example of the target collector  28  will be described.  FIG. 5  shows the configuration of the first example of the target collector  28 .  FIG. 6  is a drawing explaining a situation in which the target collides against a receiving surface S of a receiving member  283   a .  FIG. 7  shows contact angles of various materials with molten tin. As shown in  FIG. 5 , the first example of the target collector  28  may include the collection container  281 , the temperature adjusting mechanism  282 , a receiving part  283 , and a prevention part  284 . The configuration of the first example of the target collector  28  shown in  FIG. 5 , which is the same as that of the target collector  28  shown in  FIG. 3 , will not be described again here. 
     The configuration of the collection container  281  shown in  FIG. 5  may be the same as that of the collection container  281  shown in  FIG. 3 . The configuration of the temperature adjusting mechanism  282  shown in  FIG. 5  may be the same as that of the temperature adjusting mechanism  282  shown in  FIG. 3 . 
     The receiving part  283  may receive the target  27  having entered the target collector  28 . The receiving part  283  may be provided inside the collection container  281 . The receiving part  283  may be provided inside the prevention part  284  formed integrally with the collection container  281 . The receiving part  283  may include a receiving member  283   a  and a support member  283   b.    
     The receiving member  283   a  may be detachably attached to the collection container  281  by the support member  283   b . The support member  283   b  may be formed integrally with the receiving member  283   a.    
     The temperature of the support member  283   b  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . As described above, the temperature adjusting mechanism  282  may maintain the temperature in the collection container  281  within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . The support member  283   b  fixed to the collection container  281  may be heated by, for example, the heat transfer from the collection container  281 , so that the temperature of the support member  283   b  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . Also the receiving member  283   a  fixed to the support member  283   b  may be heated by, for example, the heat transfer from the support member  283   b , so that the temperature of the receiving member  283   a  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . 
     The target  27  having entered the target collector  28  may collide against the receiving member  283   a , and therefore be received by the receiving member  283   a . The receiving member  283   a  may include the receiving surface S configured to receive the target  27  having entered the target collector  28 . 
     The receiving surface S of the receiving member  283   a  may be located on the extension of the target traveling path  272 . The receiving surface S may be disposed to face the target supply part  26  and the plasma generation region  25 . The receiving part S may be inclined with respect to the target traveling path  272  with a predetermined inclination angle. The inclination angle of the receiving surface S may be provided to prevent the fragmented materials  274  generated by the collision of the target  27  incident on the receiving surface S from dispersing to the outside of the target collector  28 . The receiving surface S is provided to incline with the predetermined inclination angle, and therefore can change the trajectory of the target  27  having entered the target collector  28 . Here, the situation where the target  27  collides against the receiving surface S of the receiving member  283   a  will be described later with reference to  FIG. 6 . 
     The receiving surface S of the receiving member  283   a  may be coated with a coating material  287   a . The coating material  287   a  may have a contact angle of equal to or smaller than 90 degrees with the liquid target  27 . The receiving surface S coated with the coating material  287   a  may be easy to be wetted by the target  27  having entered the target collector  28 . Meanwhile, the temperature of the receiving member  283   a  including the receiving surface S may be maintained within a predetermined range of temperatures at least equal to or higher than the melting point of the target  27  as describe above. Therefore, part of the target  27  incident on the receiving surface S may collide against the receiving surface S, and then its form as the droplet  271  may be broken. After that, the target  27  which is the molten target  27  may wet the receiving surface S. A liquid film  275  of the target  27  may be formed on the receiving surface Shaving been wetted by the target  27 . Here, the state after the target  27  collides against the receiving surface S will be described later with reference to  FIG. 6 . Details of the coating material  287   a  will be described later with reference to  FIG. 7 . 
     The prevention part  284  may prevent the target  27  having been received by the receiving part  283  from dispersing to the outside of the target collector  28 . The prevention part  284  shown in  FIG. 5  may prevent the fragmented materials  274  generated by the collision of the target  27  incident on the receiving surface S from dispersing to the outside of the target collector  28 . The prevention part  284  may be formed integrally with the collection container  281  as part of the collection container  281 . The prevention part  284  may be formed in a cylindrical shape. The central axis of the cylindrical prevention part  284  may match the central axis of the collection container  281 . The cylindrical prevention part  284  may be formed to extend from its base end corresponding to the periphery of the opening  281   a  of the collection container  281 , toward the target supply part  26  and the plasma generation region  25 . The cylindrical prevention part  284  may be formed such that its inside diameter is reduced toward the target supply part  26  and the plasma generation region  25 . 
     The inner periphery of the prevention part  284  may be a tapered surface  284   b  having an inside diameter that is reduced toward the target supply part  26  and the plasma generation region  25 . The tapered surface  284   b  may face the bottom portion  281   b  or the side portion  281   c  of the collection container  281 . The tapered surface  284   b  may face the receiving surface S of the receiving member  283   a . The inclination angle of the tapered surface  284   b  with respect to the target traveling path  272  may be equal to or greater than the inclination angle of the receiving surface S with respect to the target traveling path  272 . The tapered surface  284   b  may be parallel to the receiving surface S of the receiving member  283   a . The tapered surface  284   b  may reflect the fragmented materials  274  of the target  27  incident on the receiving surface S toward the bottom portion  281   b  side. By this means, it is possible to prevent the fragmented materials  274  from dispersing to the outside of the target collector  28 . 
     An opening  284   a  may be formed in the leading end of the prevention part  284  located on the target supply part  26  side. The diameter of the opening  284   a  may be sufficiently greater than that of the target  27 . The diameter of the opening  284   a  may be, for example, 30 mm. The opening  284   a  may allow the target  27  having entered the target collector  28  to be guided to the receiving member  283   a  of the receiving part  283 . 
     The heater  282   a  of the temperature adjusting mechanism  282  may be fixed to the outer periphery of the prevention part  284 . The temperature in the prevention part  284  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 , by the temperature adjusting mechanism  282 . 
     With reference to  FIG. 6 , the situation where the target  27  collides against the receiving surface S of the receiving member  283   a  will be described. The target  27  may enter the target collector  28  at an incidence angle θ with respect to the normal direction of the receiving surface S, and collide against the receiving surface S. Upon colliding against the receiving surface S, the target  27  may apply an impact force to the receiving surface S. Meanwhile, the receiving surface S may apply the reaction force of the impact force to the target  27 , and this reaction force may break the form of the target  27  as the droplet  271  having collided against the receiving surface S. The crushed target  27  may be separated into the fragmented materials  274  reflected from the receiving surface S and dispersing, and the liquid film  275  covering the receiving surface S. 
     The fragmented materials  274  reflected from the receiving surface S and dispersing may be a plurality of fine particles. The fragmented materials  274  being the plurality of fine particles may be spread out in a conical shape having the central axis corresponding to the direction of a reflection angle θ which is the same as the incidence angle θ of the target  27 . These fragmented materials  274  may be further reflected from the tapered surface  284   b  of the prevention part  284  toward the bottom portion  281   b  side as shown in  FIG. 5 . The fragmented materials  274  reflected from the tapered surface  284   b  may reach the collection container  281 . 
     The inclination angle of the receiving surface S with respect to the target traveling path  272  may be provided such that the incidence angle θ of the target  27  satisfies 0°&lt;θ&lt;90°. A normal component Rn of the reaction force acting on the target  27  colliding against the receiving surface S, which is normal to the receiving surface S (hereinafter referred to simply as “normal component Rn”), may be a driving force for which the target  27  reflected from the receiving surface S disperses as the fragmented materials  274 . That is, the normal component Rn may determine the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision of the target  27  against the receiving surface S. When the incidence angle θ of the target  27  is 0°&lt;θ&lt;90°, the normal component Rn may be smaller than when the incidence angle θ of the target  27  is θ=0°. Therefore, when the incidence angle θ of the target  27  is 0°&lt;θ&lt;90°, it is possible to reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision of the target  27  against the receiving surface S. By this means, it is possible to prevent the fragmented materials  274  of the target  27  from dispersing to the outside of the target collector  28 . 
     In addition, if the inclination angle of the receiving surface S is provided to make the incidence angle θ of the target  27  be θ=0°, the receiving surface S may be orthogonal to the target traveling path  272 . Therefore, the fragmented materials  274  generated by the collision of the target  27  against the receiving surface S may not be easy to be reflected from the tapered surface  284   b  of the prevention part  284 . Therefore, the fragmented materials  274  may pass through the opening  284   a  and disperse to the outside of the target collector  28 . 
     In addition, if the inclination angle of the receiving surface S is provided to make the incidence angle θ of the target  27  be θ=90°, the receiving surface S may be parallel to the target traveling path  272 . Therefore, the target  27  having entered the target collector  28  may not be received by the receiving surface S but collide against the liquid level  273   a  of the collected target  273 . The collected target  273  forming the liquid level  273   a  may be broken into splashes by the impact of the collision against the target  27  and jump out as the fragmented materials  274 . Then, the fragmented materials  274  may pass through the opening  284   a  and disperse to the outside of the target collector  28 . 
     As described above, it is preferred that the inclination angle of the receiving surface S with respect to the target traveling path  272  is provided to make the incidence angle θ of the target  27  satisfy 0°&lt;θ&lt;90°. 
     More preferably, the inclination angle of the receiving surface S with respect to the target traveling path  272  may be provided such that the incidence angle θ of the target  27  satisfies 45°&lt;θ&lt;90°. In this case, the normal component Rn may be further reduced. Therefore, it is possible to more effectively reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision of the target  27  against the receiving surface S. As a result, it is possible to prevent the fragmented materials  274  from dispersing to the outside of the target collector  28 . In addition, in this case, the inclination angle of the receiving surface S with respect to the target traveling path  272  may be sharper. Therefore, the fragmented materials  274  generated by the collision of the target  27  against the receiving surface S may be easy to disperse to the bottom portion  281   b  side of the collection container  281 . In addition, the fragmented materials  274  are easy to be reflected from part of the tapered surface  284   b  of the prevention part  284  on the bottom portion  281   b  side. Then, the fragmented materials  274  reflected from the part of the tapered surface  284   b  on the bottom portion  281   b  side may be easy to reach the collection container  281 . Therefore, it is possible to more effectively prevent the fragmented materials  274  from dispersing to the outside of the target collector  28 . 
     Meanwhile, the liquid film  275  covering the receiving surface S may be formed by wetting the receiving surface S with the molten target  27  crushed by the collision against the receiving surface S. The liquid film  275  may have a surface tension that allows the liquid film  275  to absorb the impact force of the subsequent target  27  incident on the receiving surface S, and catch the subsequent target  27 . By this means, the reaction force acting on the subsequent target  27  incident on the receiving surface S may be reduced. Also the normal component Rn may be reduced. Therefore, it is possible to reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision of the subsequent target  27  against the receiving surface S. By this means, it is possible to prevent the fragmented materials  274  from dispersing to the outside of the target collector  28 . In addition, even if the subsequent target  27  collides against the receiving surface S so that the fragmented materials  274  are generated, the liquid film  275  may catch the fragmented materials  274  with its own surface tension. Therefore, it is possible to reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision of the subsequent target  27  against the receiving surface S. As a result, it is possible to prevent the fragmented materials  274  from dispersing to the outside of the target collector  28 . 
     The liquid film  275  may melt the caught target  27  and accumulate the molten target  27  therein. When the volume of the liquid film  275  is increased due to the accumulation of the caught target  27 , the gravity force acting on the liquid film  275  may be increased. After that, the liquid film  275  cannot stay on the receiving surface S due to the increase in the gravity force acting on the liquid film  275 . Then, part of the liquid film  275  may fall toward the bottom portion  281   b  and reach the collection container  281 . 
     With reference to  FIG. 7 , the coating material  287   a  will be described in detail.  FIG. 7  is a table showing contact angles of various materials with molten tin. The table shown in  FIG. 7  was made based on “Wettability Technology Handbook—Fundamentals, Measurement valuation, Data” (supervisors: Toshio Ishii, Masumi Koishi, and Mitsuo Tsunoda, published by Technosystem). Generally, a state in which a contact angle α satisfies 0°&lt;α≦90° is referred to as “immersional wetting.” In this state, a solid is easy to be wetted by liquid. Under the immersional wetting state, a solid is easy to be immersed into the liquid. Meanwhile, a state in which the contact angle α satisfies 90°&lt;α≦180° is referred to as “adhesional wetting.” In this state, a solid is not easy to be wetted by liquid. Under the adhesional wetting state, the liquid in contact with the solid surface is easy to move in the direction of gravity. 
     The target  27  may be tin. The target  27  entering the target collector  28  may be molten tin formed of the droplet  271 . The coating material  287   a  applied to the receiving surface S of the receiving member  283   a  may be a material that is easy to be wetted by molten tin. The material that is easy to be wetted by molten tin may have a contact angle of equal to or smaller than 90 degrees with the target  27 . 
     As shown in  FIG. 7 , the materials having contact angles of equal to or smaller than 90 degrees with the target  27  may be, for example, aluminium, copper, stainless steel, silicon, nickel, titanium, and molybdenum which has been vacuum heat treated. When molybdenum is vacuum heat treated, the adsorption layer and the oxide layer of its surface may be removed, and therefore the molybdenum may be easy to be wetted by the molten tin. 
     Here, the materials having a contact angle of equal to or smaller than 90 degrees with the target  27  are not limited to be used as the coating material  287   a  applied to the receiving surface S of the receiving member  283   a . The materials having a contact angle of equal to or smaller than 90 degrees with the target  27  may be used to form the receiving member  283   a . In addition, means for making the contact angle of the receiving surface S with the target  27  be equal to or smaller than 90 degrees may not be limited to coating with the coating material  287   a . For example, the means for making the contact angle of the receiving surface S with the target  27  be equal to or smaller than 90 degrees may be applying of a surface treatment to the receiving surface S. 
     With the above-described configuration of the first example of the target collector  28 , the target  27  having entered the target collector  28  may collide against the receiving surface S of the receiving member  283   a . The target  27  having collided against the receiving surface S may be crushed and separated into the fragmented materials  274  reflected from the receiving surface S and dispersing, and the liquid film  275  covering the receiving surface S. The fragmented materials  274  reflected from the receiving surface S and dispersing may be further reflected from the tapered surface  284   b  of the prevention part  284  toward the bottom portion  281   b . The fragmented materials  274  reflected from the tapered surface  284   b  may reach the collection container  281 . Meanwhile, the liquid film  275  covering the receiving surface S may catch the subsequent target  27  with its surface tension and accumulate the caught target therein. If the volume of the liquid film  275  is increased, the liquid film  275  may not stay on the receiving surface S due to its own gravity. Then, part of the liquid film  275  may fall toward the bottom portion  281   b  and reach the collection container  281 . Therefore, the first example of the target collector  28  can efficiently collect the target  27  entering the target collector  28  while preventing the fragmented materials  274  from dispersing to the outside of the target collector  28 . 
     6. Target Collector of the EUV Light Generation Apparatus According to Embodiment 2 
     With reference to  FIGS. 8 to 12 , the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 2 will be described. When the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 2 collects the target  27 , it may change the trajectory of the target  27  entering the target collector  28 . In addition, the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 2 may prevent the target  27  entering the target collector  28  from being reflected from the position at which the target  27  collides against the target collector  28  and jumping out. Moreover, the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 2 may reduce the kinetic energy of the target  27  before the target  27  entering the target collector  28  is reflected from the position at which the target  27  collides against the target collector  28 . Hereinafter, the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 2 will be explained as second to fifth examples of the target collector  28 . The configuration of the target collector  28 , which is the same as that of the target collector  28  shown in  FIGS. 2 and 3 , and the first example of the target collector  28  shown in  FIGS. 5 and 6 , will not be described again here. 
     6.1 Second Example of the Target Collector 
     With reference to  FIG. 8 , the configuration of the second example of the target collector  28  will be described.  FIG. 8  shows the configuration of the second example of the target collector. As shown in  FIG. 8 , the second example of the target collector  28  may include the collection container  281 , the temperature adjusting mechanism  282 , the receiving part  283 , the prevention part  284 , a cylinder part  285 , and a filter  288 . 
     The configuration of the temperature adjusting mechanism  282  shown in  FIG. 8  may be the same as that of the temperature adjusting mechanism  282  shown in  FIG. 5 . The configuration of the receiving part  283  shown in  FIG. 8  may be the same as that of the receiving part  283  shown in  FIG. 5 . The configuration of the prevention part  284  shown in  FIG. 8  may be the same as that of the prevention part  284  shown in  FIG. 5 . 
     The collection container  281  shown in  FIG. 8  may be disposed outside the chamber  2 . The other configuration of the collection container  281  may be the same as the configuration of the collection container  281  shown in  FIG. 5 . 
     The cylinder part  285  may guide the target  27  having entered the target collector  28  to the opening  281   a  of the collection container  281  or the opening  284   a  of the prevention part  284 . The cylinder part  285  may be disposed inside the chamber  2 . The cylinder part  285  may be formed integrally with the prevention part  284  and the collection container  281 . The cylinder part  285  may be formed in a cylindrical shape. The central axis of the cylindrical cylinder part  285  may match the central axis of the collection container  281  and the target traveling path  272 . The cylindrical cylinder part  285  may be formed to extend from its base end corresponding to the periphery of the opening  284   a  of the prevention part  284 , toward the target supply part  26  and the plasma generation region  25 . 
     An opening  285   a  may be provided in the leading end of the cylinder part  285  located on the target supply part  26  side. The diameter of the opening  285   a  may be the same as the diameter of the opening  284   a  of the prevention part  284 . The opening  285   a  may introduce the target  27  having entered the target collector  28  into the opening  284   a . The target  27  introduced into the opening  284   a  may be received by the receiving member  283   a  of the receiving part  283 . 
     The heater  282   a  of the temperature adjusting mechanism  282  may be fixed on the outer periphery of the cylinder part  285 . The temperature in the cylinder part  285  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . 
     The filter  288  may allow the target  27  having entered the target collector  28  to pass therethrough. The target  27  may collide against and penetrate the filter  288 , so that the filter  288  allows the target  27  to pass therethrough. Here, a situation where the target  27  having entered the target collector  28  passes through the filter  288  will be described later with reference to  FIGS. 9A to 9C . 
     The filter  288  may be held on the inner periphery of the cylinder part  285 . The filter  288  may be located closer to the target supply part  26  and the plasma generation region  25  than the receiving surface S of the receiving member  283   a . The filter  288  may be located on the extension of the target traveling path  272 . The filter  288  may be disposed to face the target supply part  26  and the plasma generation region  25 . The filter  288  may be disposed to face the receiving surface S of the receiving member  283   a . The filter  288  may be formed as a circular plate. The central axis of the circular plate-shaped filter  288  may match the central axis of the cylinder part  285 . 
     The filter  288  may be made with a porous metallic plate or wire netting. The porous metallic plate and the wire netting may be made of a material which is easy to react with the target  27 . By this means, when the target  27  collides against the filter  288 , the filter  288  may be easy to allow the target  27  to penetrate therethrough. The porous metallic plate may be, for example, Celmet (registered trademark). The porous metallic plate may be made of a material, for example, nickel or nickel chrome alloy. The wire netting may be, for example, expanded metal. The wire netting may be made of a material, for example, aluminium, nickel, stainless steel, or copper. 
     The porous metallic plate or the wire netting constituting the filter  288  may have a large number of openings. The porous metallic plate or the wire netting may have an opening area ratio that prevents the target  27  having entered the target collector  28  from colliding against part of the porous metallic plate or the wire netting except the openings (hereinafter “non-opening portion”) many times. The opening area ratio of the porous metallic plate or the wire netting may be, for example, 90%. Here, the opening area ratio may be a ratio of the total area of the openings to the area of the surface of the filter  288  perpendicular to the incident direction of the target  27 . The filter  288  made with the porous metallic plate or the wire netting may have a thickness that allows the target  27  having entered the target collector  28  to penetrate the filter  288 . When the target  27  having a diameter of, for example, 20 μm collides against the filter  288  at a speed of 60 m/s, the thickness of the filter  288  may be about 100 μm. 
     The temperature of the filter  288  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . As described above, the temperature adjusting mechanism  282  may maintain the temperature in the cylinder part  285  within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . The filter  288  held in the cylinder part  285  may be heated by, for example, the heat transfer from the cylinder part  285 , so that the temperature of the filter  288  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . 
     As described above, the filter  288  may be made with a porous metallic plate or wire netting having a large number of openings. Therefore, when the gas in the chamber  2  is discharged, the gas in the collection container  281  may flow out into the chamber  2  via the openings of the filter  288  without problem, for example, deformation of the filter  288  due to pressure fluctuation. Then, the gas flowing out of the collection container  281  into the chamber  2  can be discharged. In this case, the fragmented materials  274  can be caught by the filter  288 . 
     Now, with reference to  FIGS. 9A to 9C , the states where the target  27  having entered the target collector  28  passes through the filter  288  will be described.  FIG. 9A  is a drawing explaining a state before the target  27  passes through the filter  288  shown in  FIG. 8 .  FIG. 9B  is a drawing explaining a state when the target  27  passes through the filter  288  shown in  FIG. 8 .  FIG. 9C  is a drawing explaining a state of the fragmented materials  274  after the target  27  passes through the filter  288  shown in  FIG. 8 . As shown in  FIG. 9A , the target  27  having entered the target collector  28  may collide against the filter  288  before colliding against the receiving surface S of the receiving member  283   a.    
     As described above, the filter  288  may have a thickness that allows the target  27  to penetrate the filter  288 . In addition, the filter  288  may have a high opening area ratio that prevents the target  27  from colliding against the non-opening portion of the filter  288  many times. Moreover, the filter  288  may be made of a material which is easy to react with the target  27 . Furthermore, the temperature of the filter  288  may be maintained within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . Therefore, as shown in  FIG. 9B , the target  27  colliding against the filter  288  may penetrate the filter  288  without being crushed on the non-opening portion so that fragmented materials  274  are generated, and without staying in the filter  288 . In this case, when the target  27  collides against and penetrates the filter  288 , its kinetic energy may be reduced. If a plurality of filters  288  are provided, it is possible to improve the effect of reducing the kinetic energy of the target  27 . 
     After that, the target  27  having penetrated filter  288  may collide against the receiving surface S of the receiving member  283   a . As described above with reference to  FIG. 6 , part of the target  27  colliding against the receiving surface S may generate the fragmented materials  274 . In this case, since the kinetic energy of the target  27  is reduced, it is possible to more effectively reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision against the receiving surface S. 
     After that, most of the fragmented materials  274  generated by the collision against the receiving surface S may be reflected from the prevention part  284  toward the bottom portion  281   b  of the collection container  281 , and the remaining part of the fragmented materials  274  may disperse to the cylinder part  285 . In this case, since the kinetic energy of the target  27  is reduced, it is possible to reduce the ratio of the fragmented materials  274  dispersing to the cylinder part  285 , to the fragmented materials  274  generated by the collision against the receiving surface S. Nevertheless, a small percentage of the fragmented materials  274  may disperse to the cylinder part  285 . However, as shown in  FIG. 9C , the fragmented materials  274  dispersing to the cylinder part  285  may be caught by the filter  288 . In this case, if a plurality of filters  288  are provided, it is possible to improve the effect of catching the fragmented materials  274 . 
     Here, the new target  27  may enter the filter  288  which the previous target  27  has already penetrated. This incoming new target  27  may pass through the filter  288  via a through-hole formed by the previous target  27 . The kinetic energy of the target  27  passing through the through-hole formed by the previous target  27  may not be reduced. Even in this case, most of the fragmented materials  274  may be reflected from the prevention part  284  and collected in the collection container  281 . Meanwhile, a small percentage of the fragmented materials  274  dispersing to the cylinder part  285  may also be caught by the filter  288 . 
     With the above-described configuration, the second example of the target collector  28  can produce the same effect as the first example of the target collector  28 . Moreover, with the second example of the target collector  28 , the target  27  having entered the target collector  28  can collide against the receiving surface S of the receiving member  283   a  via the filter  288 . Therefore, when the target  27  collides against the receiving surface S, the kinetic energy of the target  27  may have been reduced. Accordingly, it is possible to more effectively reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision against the receiving surface S. Furthermore, even though part of the fragmented materials  274  generated by the collision against the receiving surface S disperses to the cylinder part  285 , the second example of the target collector  28  can catch these fragmented materials  274  by the filter  288 . Therefore, the second example of the target collector  28  can more effectively prevent the fragmented materials  274  from dispersing to the outside of the target collector  28  than the first example of the target collector  28 . 
     6.2 Third Example of the Target Collector 
     Now, with reference to  FIG. 10 , the configuration of the third example of the target collector  28  will be described.  FIG. 10  shows the configuration of the third example of the target collector. As shown in  FIG. 10 , the third example of the target collector  28  may include the collection container  281 , the temperature adjusting mechanism  282 , the receiving part  283 , the prevention part  284 , the cylinder part  285 , and the filter  288 . The configuration of the third example of the target collector  28  shown in  FIG. 10 , which is the same as that of the second example of the target collector  28  shown in  FIG. 8 , will not be described again here. 
     The configuration of the temperature adjusting mechanism  282  shown in  FIG. 10  may be the same as that of the temperature adjusting mechanism  282  shown in  FIG. 8 . The configuration of the receiving part  283  shown in  FIG. 10  may be the same as that of the receiving part  283  shown in  FIG. 8 . The configuration of the filter  288  shown in  FIG. 10  may be the same as that of the filter  288  shown in  FIG. 8 . 
     The inner periphery of the collection container  281  shown in  FIG. 10  may be coated with the coating material  287   a . Alternatively, a surface treatment may be applied to the inner periphery of the collection container  281  to make the contact angle with the target  27  be equal to or smaller than 90 degrees. By this means, upon colliding against the inner periphery of the collection container  281 , the fragmented materials  274  may wet the inner periphery. Therefore, it is possible to reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision against the inner periphery of the collection container  281 . The other configuration of the collection container  281  may be the same as that of the collection container  281  shown in  FIG. 8 . 
     The inner periphery of the prevention part  284  shown in  FIG. 10 , which is the tapered surface  284   b , may be coated with the coating material  287   a . Alternatively, a surface treatment may be applied to the tapered surface  284   b  to make the contact angle with the target  27  be equal to or smaller than 90 degrees. By this means, upon colliding against the tapered surface  284   b , the fragmented materials  274  may wet the tapered surface  284   b . Therefore, it is possible to reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision against the tapered surface  284   b . The other configuration of the prevention part  284  may be the same as that of the prevention part  284  shown in  FIG. 8 . 
     The cylinder part  285  shown in  FIG. 10  may be formed such that its inside diameter is increased toward the target supply part  26  and the plasma generation region  25 . The inner periphery of the cylinder part  285  may be a tapered surface  285   b  having an inside diameter that is increased toward the target supply part  26  and the plasma generation region  25 . The tapered surface  285   b  may face the target supply part  26  and the plasma generation region  25 . The tapered surface  285   b  may face the receiving surface S of the receiving member  283   a . The inclination angle of the tapered surface  285   b  with respect to the target traveling path  272  may be equal to or smaller than the inclination angle of the receiving surface S with respect to the target traveling path  272 . The tapered surface  285   b  may reflect the target  27  entering the target collector  28  not through the target traveling path  272 , toward the opening  284   a  of the prevention part  284  located on the bottom portion  281   b  side. By this means, it is possible to guide the target  27  entering the target collector  28  not through the target traveling path  272 , to the opening  284   a  of the prevention part  284 . 
     The tapered surface  285   b  of the cylinder part  285  may be coated with the coating material  287   a . Alternatively, a surface treatment may be applied to the tapered surface  285   b  to make the contact angle with the target  27  be equal to or smaller than 90 degrees. By this means, when the target  27  entering the target collector  28  not through the target traveling path  272  collides against the tapered surface  285   b , the target  27  may wet the tapered surface  285   b . Therefore, it is possible to reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision against the tapered surface  285   b . The other configuration of the cylinder part  285  may be the same as that of the cylinder part  285  shown in  FIG. 8 . 
     With the above-described configuration, the third example of the target collector  28  can produce the same effect as the second example of the target collector  28 . Moreover, with the third example of the target collector  28 , the target  27  entering the target collector  28  not through the target traveling path  272  may collide against the tapered surface  285   b  of the cylinder part  285 . The target  27  colliding against the tapered surface  285   b  may be crushed. The crushed target  27  may be reflected toward the opening  284   a  of the prevention part  284  and wet the tapered surface  285   b . Therefore, it is possible to collect the target  27  entering the target collector  28  even not through the target traveling path  272  in the collection container  281 . In addition, it is possible to reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision of the target  27  against the tapered surface  285   b . Therefore, the third example of the target collector  28  can more efficiently collect the target  27  having entered the target collector  28 , while preventing the fragmented materials  274  from dispersing to the outside of the target collector  28 , than the second example of the target collector  28 . 
     6.3 Fourth Example of the Target Collector 
     Now, with reference to  FIG. 11 , the configuration of the fourth example of the target collector  28  will be described.  FIG. 11  shows the configuration of the fourth example of the target collector. As shown in  FIG. 11 , the fourth example of the target collector  28  may include the collection container  281 , the temperature adjusting mechanism  282 , the receiving part  283 , the prevention part  284 , the cylinder part  285 , and the filter  288 . The configuration of the fourth example of the target collector  28  shown in  FIG. 11 , which is the same as that of the third example of the target collector  28  shown in  FIG. 10 , will not be described again here. 
     The configuration of the collection container  281  shown in  FIG. 11  may be the same as that of the collection container  281  shown in  FIG. 10 . The configuration of the temperature adjusting mechanism  282  shown in  FIG. 11  may be the same as that of the temperature adjusting mechanism  282  shown in  FIG. 10 . The configuration of the cylinder part  285  shown in  FIG. 11  may be the same as that of the cylinder part  285  shown in  FIG. 10 . The configuration of the filter  288  shown in  FIG. 11  may be the same as that of the filter  288  shown in  FIG. 10 . 
     The receiving part  283  shown in  FIG. 11  may be different from the receiving part  283  shown in  FIG. 10  in that the receiving part  283  shown in  FIG. 11  may not be constituted by the receiving member  283   a  and the support member  283   b  which are separated from the collection container  281  and the prevention part  284 . The receiving part  283  shown in  FIG. 11  may be formed integrally with the collection container  281  and the prevention part  284 . The receiving part  283  may be formed such that its receiving surface S protrudes inward from part of the inner periphery of the side portion  281   c  of the collection container  281 . When the prevention part  284  is formed integrally with the collection container  281  as part of the collection container  281 , the receiving part  283  may be formed to protrude inward from part of the inner periphery of the prevention part  284 . 
     When the prevention part  284  shown in  FIG. 11  is formed as part of the collection container  281 , the tapered surface  284   b  of the prevention part  284  may be formed in the inner periphery of the prevention part  284  where the receiving part  283  is not formed. 
     The receiving part  283  and the prevention part  284  shown in  FIG. 11  may form a pipe line having an inner wall surface formed by at least the receiving surface S of the receiving part  283  and the tapered surface  284   b  of the prevention part  284 . This pipe line may allow the communication between the cylinder part  285  and the collection container  281 . This pipe line may allow the target  27  having entered the target collector  28  to be reflected from its inner wall surface multiple times, and then to be introduced into the collection container  281 . 
     When the target  27  and the fragmented materials  274  collide against the wall surface multiple times, the kinetic energies of the target  27  and the fragmented materials  274  may be further reduced. Therefore, it is possible to more effectively reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision. In addition, when the target  27  and the fragmented materials  274  collide against the wall surface multiple times, the target  27  and the fragmented materials  274  may be crushed into smaller pieces. When the target  27  and the fragmented materials  274  are crushed into small pieces, the impact force of the collision of the fragmented materials  274  against the liquid surface  273   a  of the collected target  273  may be weakened. Therefore, the collected target  273  may not be broken into splashes, and therefore not likely to jump up as the fragmented materials  274 . The other configurations of the receiving part  283  and the prevention part  284  may be the same as those of the receiving part  283  and the prevention part  284  shown in  FIG. 10 . 
     With the above-described configuration, the fourth example of the target collector  28  can produce the same effect as the third example of the target collector  28 . Moreover, the fourth example of the target collector  28  can introduce the target  27  into the collection container  281  after a number of collisions of the target  27  against the receiving surface S of the receiving part  283  and the tapered surface  284   b  of the prevention part  284  which constitute the inner wall surface of the pipe line. Therefore, the fourth example of the target collector  28  can more effectively prevent the fragmented materials  274  from dispersing to the outside of the target collector  28  than the third example of the target collector  28 . Moreover, the fourth example of the target collector  28  is composed of a smaller number of parts and has a simpler structure than the third example of the target collector  28 , and therefore can reduce the costs. 
     6.4 Fifth Example of the Target Collector 
     Now, with reference to  FIG. 12 , the configuration of the fifth example of the target collector  28  will be described.  FIG. 12  shows the configuration of the fifth example of the target collector. With the EUV light generation apparatus  1  including the fifth example of the target collector  28 , a Z direction in which the EUV light  252  is outputted from the chamber  2  of the EUV light generation apparatus  1  to the exposure device  6  may be inclined with respect to the horizontal direction. Therefore, the chamber  2  may be provided such that the direction of its central axis is inclined with respect to the horizontal direction. The target supply part  26  provided on the side surface of the chamber  2  may be provided such that the direction of the central axis of the nozzle  262  is inclined with respect to the direction of gravity. The target traveling path  272  may be inclined with respect to the direction of gravity. As shown in  FIG. 12 , the fifth example of the target collector  28  may include the collection container  281 , the temperature adjusting mechanism  282 , the receiving part  283 , the prevention part  284 , the cylinder part  285 , a pipe  286  and the filter  288 . The configuration of the fifth example of the target collector  28  shown in  FIG. 12 , which is the same as that of the third example of the target collector  28  shown in  FIG. 10 , will not be described again here. 
     The configuration of the temperature adjusting mechanism  282  shown in  FIG. 12  may be the same as that of the temperature adjusting mechanism  282  shown in  FIG. 10 . 
     The collection container  281  shown in  FIG. 12  may be disposed such that the direction of its central axis is parallel to the direction of gravity. The other configuration of the collection container  281  may be the same as that of the collection container  281  shown in  FIG. 10 . 
     The cylinder part  285  shown in  FIG. 12  may be disposed such that the direction of its central axis matches the target traveling path  272 . The direction of the central axis of the cylinder part  285  may be inclined with respect to the direction of gravity. The cylinder part  285  may be formed to extend from its base end corresponding to the end of the pipe  286 , toward the target supply part  26  and the plasma generation region  25 . The cylinder part  285  may guide the target  27  having entered the target collector  28  to the opening  284   a  of the prevention part  284  via the pipe  286 . The cylinder part  285  may guide the fragmented materials  274  generated by the collision of the target  27  against the tapered surface  285   b  to the opening  284   a  via the pipe  286 . The other configuration of the cylinder part  285  may be the same as that of the cylinder part  285  shown in  FIG. 10 . 
     The pipe  286  may connect between the collection container  281  and the cylinder part  285 . The pipe  286  may be disposed outside the chamber  2 . The heater  282   a  of the temperature adjusting mechanism  282  may be fixed to the outer periphery of the pipe  286 . The temperature adjusting mechanism  282  may maintain the temperature in the pipe  286  within a predetermined range of temperatures equal to or higher than the melting point of the target  27 . 
     The pipe  286  may be formed to extend from its base end corresponding to the end of the cylinder part  285  opposite to the opening  285   a , toward the prevention part  284  formed as part of the collection container  281 . The pipe  286  extending from its base end corresponding to the end of the cylinder part  285  may be bent on the extension of the target traveling path  272  and extend toward the prevention part  284 . The pipe  286  may allow the collection container  281  and the prevention part  284  to communicate with the cylinder part  285 . The bent portion of the pipe  286  may be located at the intersection of the extension of the target traveling path  272  and the extension of the central axis of the collection container  281  and the prevention part  284 . The bent portion of the pipe  286  may include a pipe receiving part  286   a.    
     The pipe receiving part  286   a  may receive the target  27  having entered the target collector  28  via the filter  288 . The pipe receiving part  286   a  may receive the target  27  by making the target  27  collide against the receiving surface S. The receiving surface S of the pipe receiving part  286   a  may be disposed to face the target supply part  26  and the plasma generation region  25 . The receiving surface S of the pipe receiving part  286   a  may be disposed to face a receiving surface P (described later) of the receiving part  283 . The receiving surface S of the pipe receiving part  286   a  may be disposed to face the opening  284   a  of the prevention part  284 . The receiving surface S of the pipe receiving part  286   a  may be located on the extension of the target traveling path  272 . The receiving surface S may be inclined with respect to the target traveling path  272  with a predetermined inclination angle. The inclination angle of the receiving surface S may be provided to prevent the fragmented materials  274  generated by the collision against the receiving surface S from dispersing to the outside of the target collector  28 . The inclination angle of the receiving surface S with respect to the target traveling path  272  may be provided such that the incidence angle θ of the target  27  satisfies 0°&lt;θ&lt;90°. More preferably, the inclination angle of the receiving surface S with respect to the target traveling path  272  may be provided such that the incidence angle θ of the target  27  satisfies 45°&lt;θ&lt;90°. Therefore, when the target  27  having entered the target collector  28  via the filter  288  collides against the receiving surface S of the pipe receiving part  286   a , the receiving surface S may reflect most of the target  27  toward the receiving surface P of the receiving part  283 . 
     The receiving surface S of the pipe receiving part  286   a  may be coated with the coating material  287   a . Alternatively, a surface treatment may be applied to the receiving surface S of the pipe receiving part  286   a  to make the contact angle with the target  27  be equal to or smaller than 90 degrees. Likewise, the inner periphery of the pipe  286  except the receiving surface S may be coated with the coating material  287   a , or subjected to the surface treatment. Therefore, when the target  27  having entered the target collector  28  via the filter  288  collides against the receiving surface S of the pipe receiving part  286   a , the receiving surface S may be wetted by part of the target  27 . Accordingly, the receiving surface S can reduce the amount and the speed of the dispersion of the fragmented materials  274  generated by the collision against the receiving surface S. 
     The receiving surface  283  shown in  FIG. 12  may receive the target  27  or the fragmented materials  274  reflected from the receiving surface S of the pipe receiving part  286   a . The receiving member  283   a  of the receiving part  283  may receive the target  27  or the fragmented materials  274  reflected from the receiving surface S of the pipe receiving part  286   a  by making the target  27  or the fragmented materials  274  collide against the receiving surface P. The other configuration of the receiving part  283  may be the same as that of the receiving part  283  shown in  FIG. 10 . 
     The prevention part  284  shown in  FIG. 12  may prevent the fragmented materials  274  generated by the collision against the receiving surface P from dispersing to the outside of the target collector  28 . The prevention part  284  may be formed to extend from its base end corresponding to the periphery of the opening  281   a  of the collection container  281 , toward the direction opposite to the direction of gravity which matches the direction of the central axis of the collection container  281 . The leading end of the prevention part  284  may be connected to the end of the pipe  286 . The other configuration of the prevention part  284  may be the same as that of the prevention part  284  shown in  FIG. 10 . 
     With the above-described configuration, the fifth example of the target collector  28  can produce the same effect as the third example of the target collector  28 . In addition, the fifth example of the target collector  28  can introduce the target  27  having entered the target collector  28  via the filter  28  into the collection container  281  after a plurality of collisions of the target  27  against the receiving surface S and the receiving surface P. Moreover, with the fifth example of the target collector  28 , it is possible to lengthen and complicate the route from the collection container  281  to the outside of the target collector  28  by providing the pipe  286  to connect between the collection container  281  and the cylinder part  285 . Therefore, the fifth example of the target collector  28  can more effectively prevent the fragmented materials  274  from dispersing to the outside of the target collector  28  than the third example of the target collector  28 . Moreover, the fifth example of the target collector  28  can collect the target  27  while preventing the target  27  from dispersing to the outside of the target collector  28 , even though the target traveling path  272  is inclined with respect to the direction of gravity, or the target  27  enters the target collector  28  not through the target traveling path  272 . 
     7. Target Collector of the EUV Light Generation Apparatus According to Embodiment 3 
     With reference to  FIGS. 13A to 19C , the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 3 will be described. The configuration of the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 3 may be the same as that of the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 2, except for the filter  288 . Hereinafter, the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 3 will be explained as sixth to tenth examples of the target collector  28 . The configuration of the target collector  28 , which is the same as that of the target collector  28  according to Embodiment 2, that is, the second to fifth examples of the target collector  28  shown in  FIGS. 8 to 12 , will not be described again here. 
     7.1 Sixth Example of the Target Collector 
     Now, with reference to  FIGS. 13A to 13C , the configuration of the filter  288  of the sixth example of the target collector  28  will be described.  FIG. 13A  shows the configuration of the filter  288  of the sixth example of the target collector  28 .  FIG. 13B  shows a view of  FIG. 13A  from direction A, where a via-hole  288   b  is not provided in advance in the filter  288 .  FIG. 13C  shows a view of  FIG. 13A  from the direction A, where the via-hole  288   b  is provided in advance in the filter  288 . Here, the direction A shown in  FIG. 13A  may be the traveling direction of the target  27  entering the target collector  28  along the target traveling path  272 . 
     The filter  288  of the sixth example of the target collector  28  may be made with metallic foil. The metallic foil may be, for example, aluminium foil. The thickness of the metallic foil may be, for example, about 20 μm to 100 μm. When the target  27  having entered the target collector  28  passes through the filter  288  made with metallic foil, the filter  288  may be penetrated by the target  27 . After the target  27  has collided against and penetrated the filter  288 , its kinetic energy may be reduced. 
     As shown in  FIG. 13B , an exhaust hole  288   a  may be formed in the filter  288  made with metallic foil. The exhaust hole  288   a  may be a through-hole that allows the gas in the collection container  281  to flow out into the chamber  2  when the gas in the chamber  2  is discharged. By this means, when the gas in the chamber  2  is discharged, it is possible to flow the gas in the collection container  281  out into the chamber  2  via the exhaust hole  288   a , without problem such as deformation of the filter  288  caused by pressure fluctuation. Then, the gas flowing out of the collection container  281  into the chamber  2  may be discharged. In this case, the fragmented materials  274  may be caught by the filter  288 . 
     As shown in  FIG. 13A , a plurality of filters  288  made with metallic foil may be provided in the cylinder part  285 . The plurality of filters  288  may include the exhaust holes  288   a , respectively. The exhaust hole  288   a  formed in each of the plurality of filters  288  may be positioned in the periphery of the filter  288  not to intersect with the extension of the target traveling path  272 . The positions of the exhaust holes  288   a  of the plurality of filters  288  may be different from each other when viewed from the traveling direction of the target  27 . As shown in  FIG. 13A , the positions of the exhaust holes  288   a  of the adjacent filters  288  may be different from each other, when viewed from the traveling direction of the target  27 . By this means, it is possible to lengthen and complicate the route from the collection container  281  to the outside of the target collector  28 . In addition, the filter  288  can easily catch the fragmented materials  274 . Moreover, the fragmented materials  274  cannot be easy to disperse to the outside of the target collector  28 . 
     As shown in  FIG. 13C , the via-hole  288   b  may be formed in advance in the filter  288  made with metallic foil. The via-hole  288   b  may be a through-hole which is formed in advance at the position at which the target  27  having entered the target collector  28  penetrates the filter  288 . By this means, the target  27  having entered the target collector  28  may not collide against but pass through the filter  288 . Therefore, there may be little possibility of generating the fragmented materials  274  caused by the collision of the target  27  against the filter  288 . 
     The plurality of filters  288  may include the via-holes  288   b , respectively. The via-holes  288   b  formed in the plurality of filters  288  respectively may be positioned to intersect with the extension of the target traveling path  272 . 
     Here, as shown in  FIG. 13B , the via-hole  288   b  may not necessarily be formed in each of the plurality of filters  288 . Even in this case, since the target  27  may pass completely through the filter  288  as described above, it is possible to significantly reduce the amount of the fragmented materials  274  generated by the collision of the target  27  against the filter  288 . Moreover, in this case, a process for alignment to place the through-hole  288   b  on the extension of the target traveling path  272  is not needed. Therefore, it is possible to prevent an increase in the number of processes. The other configuration of the filter  288  may be the same as that of the filter  288  shown in  FIGS. 8 to 12 . 
     7.2 Seventh Example of the Target Collector 
     Now, with reference to  FIGS. 14A to 14E , the configuration of the filter  288  of the seventh example of the target collector  28  will be described.  FIG. 14A  shows the configuration of the filter  288  of the seventh example of the target collector  28 .  FIG. 14B  shows a view of  FIG. 14A  from direction A 1 .  FIG. 14C  shows a view of  FIG. 14A  from direction A 2 .  FIG. 14D  shows a view of  FIG. 14A  from direction A 3 .  FIG. 14E  shows a view of  FIG. 14A  from direction A 4 . Here, the directions A 1  to A 4  shown in  FIG. 14A  may be the traveling direction of the target  27  entering the target collector  28  along the target traveling path  272 . 
     The filter  288  of the seventh example of the target collector  28  may be formed by a fiber member. When the target  27  collides against the filter  288  formed by the fiber member, the filter  288  is not penetrated by the target  27 . One fiber member forming one filter  288  may be constituted by a plurality of elastic fiber bundles. One fiber bundle may be a bundle of one or more fibers. The fiber bundle may be, for example, made with carbon fibers. The diameter of one fiber bundle may be smaller than the diameter of the target  27  having the shape of the droplet  271 . The diameter of one fiber bundle may be, for example, about 10 μm. The distance between the adjacent fiber bundles of one fiber member may be sufficiently greater than the diameter of the target  27 , when viewed from the traveling direction of the target  27 . The distance between the adjacent fiber bundles may be, for example, about 100 μm. The state in which the target  27  having entered the target collector  28  passes through the filter  288  will be described later with reference to  FIGS. 15A to 15C . 
     As shown in  FIGS. 14A to 14E , the plurality of fiber bundles constituting one fiber member may be formed to extend side by side in the same direction from their base ends corresponding to part of the inner periphery of the cylinder part  285 , when viewed from the traveling direction of the target  27 . The direction in which each of the plurality of fiber bundles extends may be the radial inward direction of the cylinder part  285  intersecting with the extension of the target traveling path  272 . The leading end of each of the plurality of fiber bundles may not be fixed to the inner periphery of the cylinder part  285 . That is, each of the plurality of fiber bundles may be fixed to the inner periphery of the cylinder part  285  with a cantilever structure having a fixed end as the base end and a free end as the leading end. As shown in  FIG. 14A , the leading end of each of the plurality of fiber bundles may be deflected in the direction of gravity. 
     In other words, one end of the fiber member constituting the filter  288  may be fixed to the inner periphery of the cylinder part  285  as a fixed end, while the other end may not be fixed to the inner periphery of the cylinder part  285  as a free end. The free end of the fiber member may be deflected in the direction of gravity. Here, space may be created between the free end of the filter  288  deflected in the direction of gravity and the inner periphery of the cylinder part  285 . The space may function as the above-described exhaust hole  288   a  as shown in  FIGS. 14B to 14E . That is, the filter  288  may include the exhaust hole  288   a.    
     As shown in  FIG. 14A , a plurality of filters  288  formed by the fiber members may be provided in the cylinder part  285 . The plurality of filters  288  may include the exhaust holes  288   a , respectively. The exhaust hole  288   a  of each of the plurality of filters  288  may be positioned in the periphery of the filter  288  not to intersect with the extension of the target traveling path  272 . The positions of the exhaust holes  288   a  of the plurality of filters  288  may be different from each other, when viewed from the traveling direction of the target  27 . As shown in  FIGS. 14B to 14E , the positions of the exhaust holes  288   a  may be shifted in the circumferential direction of the cylinder part  285  in sequence, according to the traveling direction of the target  27  having entered the target collector  28  along the target traveling path  272 . When the positions of the exhaust holes  288   a  are shifted in sequence as described above, the positions of the exhaust holes  288   a  of the adjacent filters  288  may be different from each other, when viewed from the traveling direction of the target  27 . Moreover, it is possible to lengthen and complicate the route from the collection container  281  to the outside of the target collector  28 . By this means, the filter  288  can easily catch the fragmented materials  274 . In addition, the fragmented materials  274  cannot be easy to disperse to the outside of the target collector  28 . 
     Now, with reference to  FIGS. 15A to 15C , the situation where the target  27  having entered the target collector  28  passes through the filter  288  formed by the fiber member will be described.  FIG. 15A  is a drawing explaining a state where the target  27  collides against and passes through the filter  288  shown in  FIG. 14A .  FIG. 15B  is a drawing explaining a state where the target  27  passes through the filter  288  shown in  FIG. 14A  without colliding against the filter  288 .  FIG. 15C  is a drawing explaining a state of the fragmented materials  274  after the target  27  passes through the filter  288  shown in  FIG. 14A . 
     As described above, the free end of the filter  288  formed by the fiber member, which is not fixed to the inner periphery of the cylinder part  285 , may be deflected. In addition, when viewed from the traveling direction of the target  27 , the distance between the adjacent fiber bundles may be sufficiently greater than the diameter of the target  27 . 
     Therefore, as shown in  FIG. 15A , when the target  27  collides against the filter  288  formed by the fiber member, the filter  288  may not be penetrated by the target  27  but be deflected toward the collection container  281  in the traveling direction of the target  27 . The filter  288  deflected toward the collection container  281  may not repel the target  27  colliding against the filter  288  but guide the target  27  to the collection container  281 . Therefore, the target  27  colliding against the filter  288  can pass through the filter  288  without being crushed by the filter  288  and generating the fragmented materials  274 , or staying in the filter  288 . In this case, the kinetic energy of the target  27  may be reduced due to the deflection of the filter  288  formed by the fiber member. Therefore, when a plurality of filters  288  are provided, it is possible to improve the effect of reducing the kinetic energy of the target  27 . 
     After that, as described with reference to  FIGS. 9A to 9C , the target  27  having passed through the filter  288  may collide against, for example, the receiving surface S shown in  FIG. 8 , and therefore be crushed, and a small percentage of the crushed target  27  may disperse to the cylinder part  285  as the fragmented materials  274 . However, as shown in  FIG. 15C , the fragmented materials  274  dispersing to the cylinder part  285  may be caught by the filter  288 . When a plurality of filters  288  are provided, it is possible to improve the effect of catching the fragmented materials  274 . 
     Here, as shown in  FIG. 15B , the target  27  having entered the target collector  28  may not collide against but pass through the filter  288 . The kinetic energy of this target  27  having passed through the filter  288  without colliding against the filter  288  may not be reduced. Even in this case, most of the fragmented materials  274  may be reflected from, for example, the prevention part  284  shown in  FIG. 8  and collected in the collection container  281 . A small percentage of the fragmented materials  274  dispersing to the cylinder part  285  may be caught by the filter  288 . The other configuration of the filter  288  may be the same as that of the filter  288  shown in  FIGS. 8 to 12 . 
     7.3 Eighth Example of the Target Collector 
     Now, with reference to  FIGS. 16A to 16B , the configuration of the filter  288  of the eighth example of the target collector  28  will be described.  FIG. 16A  shows the configuration of the filter  288  of the eighth example of the target collector  28 .  FIG. 16B  shows a view of  FIG. 16A  from direction A. Here, the direction A shown in  FIG. 16A  may be the traveling direction of the target  27  entering the target collector  28  along the target traveling path  272 . 
     The filter  288  of the eighth example of the target collector  28  may be formed by a fiber member in the same way as the filter  288  shown in  FIGS. 14A to 14E . Here, when viewed from the traveling direction of the target  27 , a plurality of fiber bundles constituting the fiber member may be formed to extend from their base ends corresponding to the entire inner periphery of the cylinder part  285 , toward the center of the inside diameter of the cylinder part  285  as shown in  FIG. 16B . 
     The plurality of fiber bundles constituting the fiber member may be fixed to the inner periphery of the cylinder part  285  with the cantilever structure. The base end of each of the plurality of fiber bundles may be fixed to the inner periphery of the cylinder part  285  as a fixed end. Meanwhile, the leading end of each of the plurality of fiber bundles may not be fixed to the inner periphery of the cylinder part  285  as a free end. Each of the free ends of the fiber bundles may be deflected in the direction of gravity. 
     As shown in  FIG. 16B , the base ends of the plurality of fiber bundles may be fixed to the entire inner periphery of the cylinder part  285  at intervals. By this means, when the gas in the chamber  2  is discharged, the gas in the collection container  281  may flow out into the chamber  2  via the space between the plurality of fiber bundles. Then, the gas flowing out of the collection container  281  into the chamber  2  may be discharged. In this case, the fragmented materials  274  may be caught by the fiber member constituted by the plurality of fiber bundles. In addition, as shown in  FIGS. 16A and 16B , the leading ends of the plurality of fiber bundles may contact each other at the center of the inside diameter of the cylinder part  285 , and may be deflected in the direction of gravity. By this means, the target  27  having entered the target collector  28  collides against the filter  288 , and therefore can have its kinetic energy reduced and pass through the filter  288 . 
     Moreover, as shown in  FIG. 16A , a plurality of filters  288  may be provided in the cylinder part  285 . The positions at which the distances between the plurality of fiber bundles are provided may be different for each of the plurality of filters  288 , when viewed from the traveling direction of the target  27 . The positions at which the distances between the fiber bundles of each of the plurality of filters  288  are provided may be different from the positions at which the distances between the fiber bundles of adjacent one of the filters  288  are provided, when viewed from the traveling direction of the target  27 . By this means, it is possible to lengthen and complicate the route from the collection container  281  to the outside of the target collector  28 . The other configuration of the filter  288  may be the same as that of the filter  288  shown in  FIG. 14A to 14E . 
     7.4 Ninth Example of the Target Collector 
     Now, with reference to  FIGS. 17A and 17B , the configuration of the filter  288  of the ninth example of the target collector  28  will be described.  FIG. 17A  shows the configuration of the filter  288  of the ninth example of the target collector  28 .  FIG. 17B  shows a view of  FIG. 17A  from direction A. Here, the direction A shown in  FIG. 17A  may be the traveling direction of the target  27  entering the target collector  28  along the target traveling path  272 . 
     The filter  288  of the ninth example of the target collector  28  may be formed by a curtain member. When the target  27  collides against the filter  288  formed by the curtain member, the filter  288  is not penetrated by the target  27 . The curtain member may be an elastic sheet. The curtain member forming the filter  288  may be fixed to the inner periphery of the cylinder part  285  with the cantilever structure. One end of the curtain member forming the filter  288  may be fixed to the inner periphery of the cylinder part  285  as a fixed end, while the other end may not be fixed to the inner periphery of the cylinder part  285  as a free end. As shown in  FIG. 17A , the free end of the curtain member may be deflected in the direction of gravity. By this means, the target  27  having entered the target collector  28  may collide against the filter  288 , and therefore have its kinetic energy reduced and pass through the filter  288 . Here, space may be created between the free end of the filter  288  deflected in the direction of gravity and the inner periphery of the cylinder part  285 . The space may function as the above-described exhaust hole  288   a  as shown in  FIG. 17B . That is, the filter  288  may include the exhaust hole  288   a.    
     As shown in  FIG. 17A , a plurality of filters  288  formed by the curtain members may be provided in the cylinder part  285 . The plurality of filters  288  may include the exhaust holes  288   a , respectively. The exhaust hole  288   a  of each of the plurality of filters  288  may be positioned in the periphery of the filter  288  not to intersect with the extension of the target traveling path  272 . The exhaust holes  288   a  of the adjacent filters  288  may be provided at the same position, when viewed from the traveling direction of the target  27 . Here, the curtain members of the plurality of filters  288  may be formed such that the sizes of the exhaust holes  288   a  are increased in sequence, according to the traveling direction of the target  27 . 
     The curtain member forming the filter  288  may be formed as a sheet, and therefore have a higher elasticity than, for example, the fiber member forming the filter  288  shown in  FIG. 14A . The amount of the deflection of the filter  288  formed by the curtain member when the target  27  collides against the filter  288  may be smaller than that of the filter  288  formed by the fiber member. If the amount of the deflection when the target  27  collides against the filter  288  is small, the target  27  may not be easy to fall to the collection container  281 . Therefore, the filter  288  formed by the curtain member may have a feature that the target  27  colliding against the filter  288  is not easier to fall to the collection container  281  than the filter  288  formed by the fiber member. In particular, when a plurality of filters  288  are provided, this feature may appear prominently in the filter  288  located in the downstream of the traveling direction of the target  27 . 
     Therefore, as described above, the positions of the exhaust holes  288   a  of the adjacent filters  288  are the same as each other, when viewed from the traveling direction of the target  27 . By this means, the target  27  colliding against the filter  288  can be easy to fall to the collection container  281 . The other configuration of the filter  288  may be the same as that of the filter  288  shown in  FIGS. 14A to 14E . 
     7.5 Tenth Example of the Target Collector 
     Now, with reference to  FIGS. 18A and 18B , the configuration of the filter  288  of the tenth example of the target collector  28  will be described.  FIG. 18A  shows the configuration of the filter  288  of the tenth example of the target collector  28 .  FIG. 18B  shows a view of  FIG. 18A  from direction A. Here, the direction A shown in  FIG. 18A  may be the traveling direction of the target  27  entering the target collector  28  along the target traveling path  272 . 
     The filter  288  of the tenth example of the target collector  28  may be formed by a curtain member in the same way as the filter  288  shown in  FIGS. 17A and 17B . Here, this curtain member forming the filter  288  may be fixed to the inner periphery of the cylinder part  285  via a frame  288   c . In addition, the curtain member forming the filter  288  of the tenth example of the target collector  28  may have a lower rigidity than the curtain member forming the filter  288  shown in  FIGS. 17A and 17B . 
     The frame  288   c  may be formed in a rod shape. One end of the sheet-like curtain member may be attached to the rod frame  288   c  along the longitudinal direction of the rod frame  288   c . The frame  288   c  with the curtain member may be fixed to the inner periphery of the cylinder part  285  such that the longitudinal direction of the frame  288   c  is perpendicular to the target traveling path  272 . The frame  288   c  with the curtain member may be fixed to the inner periphery of the cylinder part  285  not to intersect with the extension of the target traveling path  272 . One end of the curtain member attached to the frame  288   c  may be a fixed end. The other end of the curtain member may be a free end. 
     The curtain member fixed to the cylinder part  285  via the frame  288   c  may hang down in the direction of gravity as shown in  FIG. 18A . The curtain member has a low rigidity, and therefore its surface is curved when the curtain member hangs down. The hanging curtain member with the curved surface may intersect with the extension of the target traveling path  272  at the curved surface. By this means, the target  27  having entered the target collector  28  collides against the filter  288 , and therefore can have its kinetic energy reduced and pass through the filter  288 . 
     As shown in  FIG. 18A , a plurality of filters  288  may be provided in the cylinder part  285 . The frames  288   c  of the plurality of filters  288  may be fixed to the inner periphery of the cylinder part  285  at intervals. By this means, when the gas in the chamber  2  is discharged, the gas in the collection container  281  may flow out into the chamber  2  via the space between the plurality of frames  288   c . Then, the gas flowing out of the collection container  281  into the chamber  2  may be discharged. In this case, the fragmented materials  274  may be caught by the hanging curtain member with the curved surface. The other configuration of the filter  288  may be the same as that of the filter  288  shown in  FIGS. 17A and 17B . 
     8. Other Examples of Filter Installation 
     Now, with reference to  FIGS. 19A to 19C , other examples of the installation of the filter  288  will be described.  FIG. 19A  shows another example 1 of the filter installation.  FIG. 19B  shows another example 2 of the filter installation.  FIG. 19C  shows another example 3 of the filter installation. 
     The filter  288  shown in  FIGS. 8 to 12  made with a porous metallic plate or wire netting may be provided to incline to the target traveling path  272  as shown in  FIG. 19A . The inclination angle of the filter  288  with respect to the target traveling path  272  may be, for example, 45 degrees. 
     Among the targets  27  entering the target collector  28 , there may be the target  27  having a lower kinetic energy than usual. In particular, at the time of the start or the stop of the generation of the target  27 , the target  27  having a lower kinetic energy than usual may enter the target collector  28 . When the target  27  having a lower kinetic energy collides against the filter  288  made with, for example, a porous metallic plate, this target  27  may not penetrate the filter  288 . The target  27  that could not penetrate the filter  288  may be reflected from the surface of the filter  288 , or crushed on the surface of the filter  288  and therefore generate the fragmented materials  274 . The target  27  and the fragmented materials  274  may disperse to the outside of the target collector  28 . 
     When the filter  288  is provided to incline to the target traveling path  272 , the target  27  that could not penetrate the filter  288  may be reflected from the surface of the filter  288  toward the collection container  281 . Therefore, it is possible to prevent the target  27  that could not penetrate the filter  288  or the fragmented materials  274  from dispersing to the outside of the target collector  28 . 
     Also the filter  288  made with metallic foil shown in  FIGS. 13A to 13C  may be provided to incline to the extension of the target traveling path  272  as shown in  FIG. 19B , in the same way as the filter  288  made with a porous metallic plate or wire netting. The inclination angle of the filter  288  with respect to the target traveling path  272  may be, for example, 45 degrees. By this means, the target  27  that could not penetrate the filter  288  is reflected from the surface of the filter  288  toward the collection container  281 , and therefore it is possible to prevent the target  27  or the fragmented materials  274  from dispersing to the outside of the target collector  28 . 
     Here, when a plurality of filters  288  are provided to incline to the extension of the target traveling path  272 , the inclination directions of the filters  288  may be different from each other. For example, as shown in  FIG. 19C , the inclination directions of the adjacent filters  288  may be different from each another. Although  FIG. 19C  shows the installation state of the plurality of filters  288  made with metallic foil, the same installation state may be applied to the plurality of filters  288  made with porous metallic plates or wire netting. Moreover, the installation states shown in  FIGS. 19A to 19C  may be applied to the filter  288  formed by the fiber member shown in  FIG. 14A to 16B , and the filter  288  formed by the curtain member shown in  FIG. 17A to 18B . 
     9. Others 
     9.1 Hardware Environment of Each Controller 
     A person skilled in the art would understand that the subject matters disclosed herein can be implemented by combining a general purpose computer or a programmable controller with a program module or a software application. In general, the program module includes routines, programs, components and data structures which can execute the processes disclosed herein. 
       FIG. 20  is a block diagram showing an exemplary hardware environment in which various aspects of the subject matters disclosed herein can be implemented. An exemplary hardware environment  100  shown in  FIG. 20  may include a processing unit  1000 , a storage unit  1005 , a user interface  1010 , a parallel I/O controller  1020 , a serial I/O controller  1030 , and an A/D, D/A converter  1040 , but the configuration of the hardware environment  100  is not limited to this. 
     The processing unit  1000  may include a central processing unit (CPU)  1001 , a memory  1002 , a timer  1003 , and a graphics processing unit (GPU)  1004 . The memory  1002  may include a random access memory (RAM) and a read only memory (ROM). The CPU  1001  may be any of commercially available processors. A dual microprocessor or another multiprocessor architecture may be used as the CPU  1001 . 
     The components shown in  FIG. 20  may be interconnected with each other to perform the processes described herein. 
     During its operation, the processing unit  1000  may read and execute the program stored in the storage unit  1005 , read data together with the program from the storage unit  1005 , and write the data to the storage unit  1005 . The CPU  1001  may execute the program read from the storage unit  1005 . The memory  1002  may be a work area in which the program executed by the CPU  1001  and the data used in the operation of the CPU  1001  are temporarily stored. The timer  1003  may measure a time interval and output the result of the measurement to the CPU  1001  according to the execution of the program. The GPU  1004  may process image data according to the program read from the storage unit  1005 , and output the result of the process to the CPU  1001 . 
     The parallel I/O controller  1020  may be connected to parallel I/O devices that can communicate with the processing unit  1000 , such as the EUV light generation controller  5 , the target generation controller  74 , and the temperature controller  282   d . The parallel I/O controller  1020  may control the communication between the processing unit  1000  and those parallel I/O devices. The serial I/O controller  1030  may be connected to serial I/O devices that can communicate with the processing unit  1000 , such as the heater power source  712 , the heater power source  282   b , the piezoelectric power source  732 , and the pressure regulator  721 . The serial I/O controller  1030  may control the communication between the processing unit  1000  and those serial I/O devices. The A/D, D/A converter  1040  may be connected to analog devices such as the temperature sensor, the pressure sensor, various sensors for a vacuum gauge, the target sensor  4 , and the temperature sensor  282   c  via analog ports, may control the communication between the processing unit  1000  and those analog devices, and may perform A/D, D/A conversion of the contents of the communication. 
     The user interface  1010  may present the progress of the program executed by the processing unit  1000  to an operator, in order to allow the operator to command the processing unit  1000  to stop the program and to execute an interruption routine. 
     The exemplary hardware environment  100  may be applicable to the EUV light generation controller  5 , the target generation controller  74 , and the temperature controller  282   d  in the present disclosure. A person skilled in the art would understand that those controllers may be realized in a distributed computing environment, that is, an environment in which tasks are performed by the processing units connected to each other via a communication network. In this disclosure, the EUV light generation controller  5 , the target generation controller  74 , and the temperature controller  282   d  may be connected to each other via a communication network such as Ethernet or Internet. In the distributed computing environment, the program module may be stored in both of a local memory storage device and a remote memory storage device. 
     9.2 Modification 
     The coating material  287   a  may be a material that has a contact angle of equal to or smaller than 90 degrees with the target  27 , and that absorbs the impact of the collision against the target  27 . Alternatively, the coating material  287   a  may be replaced with a member formed by laminating a material having a contact angle of equal to or smaller than 90 degrees with the target  27  on the material absorbing the impact of the collision against the target  27 . Otherwise, the coating material  287   a  may be a material that has a contact angle of equal to or smaller than 90 degrees with the target  27  and that is not easy to react with the target  27 . 
     The inner peripheries of the prevention part  284 , the collection container  281 , the cylinder part  285  of the second example of the target collector  28  shown in  FIG. 8  may be coated with the coating material  287   a . In this case, the entire inner peripheries of the prevention part  284 , the collection container  281 , and the cylinder part  285  of the target collector  28  may not necessarily be coated with the coating material  287   a . Only the region of the target collector  28  against which the target  27  or the fragmented materials  274  collide(s) may be coated with the coating material  287   a . The same may apply to the third to fifth examples of the target collector  28  shown in  FIGS. 10 to 12 . 
     The fifth example of the target collector  28  shown in  FIG. 12  includes the receiving surface S of the pipe receiving part  286   a , and therefore may not need to include the receiving part  283 . 
     It would be obvious to a person skilled in the art that the technologies described in the above-described embodiments including the modifications may be compatible with each other. 
     For example, the filter  288  of the EUV light generation apparatus  1  according to Embodiment 3 shown in  FIGS. 13A to 19C  may be applicable to the target collector  28  of the EUV light generation apparatus  1  according to Embodiment 2 shown in  FIGS. 8 to 12 . Moreover, the exhaust hole  288   a  and the via-hole  288   b  shown in  FIGS. 13B and 13C  may be formed in the filter  288  of the EUV light generation apparatus  1  according to Embodiment 2 shown in  FIGS. 8 to 12 . 
     The descriptions above are intended to be illustrative only and the present disclosure is not limited thereto. Therefore, it will be apparent to those skilled in the art that it is possible to make modifications to the embodiments of the present disclosure within the scope of the appended claims. 
     The terms used in this specification and the appended claims should be interpreted as “non-limiting.” For example, the terms “include” or “be included” should be interpreted as “including the stated elements but not limited to the stated elements.” The term “have” should be interpreted as “having the stated elements but not limited to the stated elements.” Further, the indefinite article “a/an” should be interpreted as “at least one” or “one or more.” 
     REFERENCE SIGNS LIST 
     
         
           1  EUV light generation apparatus 
           2  chamber 
           26  target supply part 
           27  target 
           28  target collector 
           281  collection container 
           288  filter 
           5  EUV light generation controller 
         S receiving surface