Extreme ultraviolet light generation apparatus and electronic device manufacturing method

An extreme ultraviolet light generation apparatus includes a target supply unit configured to output a droplet target into a chamber device, a prepulse laser light irradiation system configured to irradiate the droplet target with prepulse laser light having linear polarization to generate a diffusion target, and a main pulse laser light irradiation system configured to irradiate the diffusion target with main pulse laser light to generate extreme ultraviolet light. Here, a cross section perpendicular to an optical axis of the main pulse laser light when being radiated to the diffusion target having a shape longer in a polarization direction of the prepulse laser light when being radiated to the droplet target than in directions other than the polarization direction.

The present application claims the benefit of Japanese Patent Application No. 2021-213007, filed on Dec. 27, 2021, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to an extreme ultraviolet light generation apparatus and an electronic device manufacturing method.

2. Related Art

Recently, miniaturization of a transfer pattern in optical lithography of a semiconductor process has been rapidly proceeding along with miniaturization of the semiconductor process. In the next generation, microfabrication at 10 nm or less will be required. Therefore, it is expected to develop a semiconductor exposure apparatus that combines an apparatus for generating extreme ultraviolet (EUV) light having a wavelength of about 13 nm with a reduced projection reflection optical system.

As the EUV light generation apparatus, a laser produced plasma (LPP) type apparatus using plasma generated by irradiating a target substance with laser light has been developed.

PATENT DOCUMENTS

List of Documents

Patent Document 2: US Patent Application Publication No. 2013/0105712

SUMMARY

An extreme ultraviolet light generation apparatus according to an aspect of the present disclosure includes a target supply unit configured to output a droplet target into a chamber device, a prepulse laser light irradiation system configured to irradiate the droplet target with prepulse laser light having linear polarization to generate a diffusion target, and a main pulse laser light irradiation system configured to irradiate the diffusion target with main pulse laser light to generate extreme ultraviolet light. Here, a cross section perpendicular to an optical axis of the main pulse laser light when being radiated to the diffusion target has a shape longer in a polarization direction of the prepulse laser light when being radiated to the droplet target than in directions other than the polarization direction.

Further, an electronic device manufacturing method according to an aspect of the present disclosure includes outputting extreme ultraviolet light generated with an extreme ultraviolet light generation apparatus to an exposure apparatus, and exposing a photosensitive substrate to the extreme ultraviolet light in the exposure apparatus to manufacture an electronic device. Here, the extreme ultraviolet light generation apparatus includes a target supply unit configured to output a droplet target into a chamber device, a prepulse laser light irradiation system configured to irradiate the droplet target with prepulse laser light having linear polarization to generate a diffusion target, and a main pulse laser light irradiation system configured to irradiate the diffusion target with main pulse laser light to generate extreme ultraviolet light. Further, a cross section perpendicular to an optical axis of the main pulse laser light when being radiated to the diffusion target has a shape longer in a polarization direction of the prepulse laser light when being radiated to the droplet target than in directions other than the polarization direction.

Further, an electronic device manufacturing method according to another aspect of the present disclosure includes inspecting a defect of a mask by irradiating the mask with extreme ultraviolet light generated with an extreme ultraviolet light generation apparatus, selecting a mask using a result of the inspection, and exposing and transferring a pattern formed on the selected mask onto a photosensitive substrate. Here, the extreme ultraviolet light generation apparatus includes a target supply unit configured to output a droplet target into a chamber device, a prepulse laser light irradiation system configured to irradiate the droplet target with prepulse laser light having linear polarization to generate a diffusion target, and a main pulse laser light irradiation system configured to irradiate the diffusion target with main pulse laser light to generate extreme ultraviolet light. Further, a cross section perpendicular to an optical axis of the main pulse laser light when being radiated to the diffusion target has a shape longer in a polarization direction of the prepulse laser light when being radiated to the droplet target than in directions other than the polarization direction.

DESCRIPTION OF EMBODIMENTS

1. Overview2. Description of electronic device manufacturing apparatus3. Description of extreme ultraviolet light generation apparatus of comparative example3.1 Configuration3.2 Operation3.3 Problem4. Description of extreme ultraviolet light generation apparatus of first embodiment4.1 Configuration4.2 Operation4.3 Effect5. Description of extreme ultraviolet light generation apparatus of second embodiment5.1 Configuration5.2 Effect6. Description of extreme ultraviolet light generation apparatus of third embodiment6.1 Configuration6.2 Effect

The embodiments described below show some examples of the present disclosure and do not limit the contents of the present disclosure. Also, all configurations and operation described in the embodiments are not necessarily essential as configurations and operation of the present disclosure. Here, the same components are denoted by the same reference numerals, and duplicate description thereof is omitted.

Embodiments of the present disclosure relate to an extreme ultraviolet light generation apparatus generating light having a wavelength of extreme ultraviolet (EUV) and an electronic device manufacturing apparatus. In the following, extreme ultraviolet light is referred to as EUV light in some cases.

2. Description of Electronic Device Manufacturing Apparatus

FIG.1is a schematic view showing a schematic configuration example of an entire electronic device manufacturing apparatus. The electronic device manufacturing apparatus shown inFIG.1includes an EUV light generation apparatus100and an exposure apparatus200. The exposure apparatus200includes a mask irradiation unit210including a plurality of mirrors211,212that constitute a reflection optical system, and a workpiece irradiation unit220including a plurality of mirrors221,222that constitute a reflection optical system different from the reflection optical system of the mask irradiation unit210. The mask irradiation unit210illuminates, via the mirrors211,212, a mask pattern of the mask table MT with EUV light101incident from the EUV light generation apparatus100. The workpiece irradiation unit220images the EUV light101reflected by the mask table MT onto a workpiece (not shown) arranged on a workpiece table WT via the mirrors211,212. The workpiece is a photosensitive substrate such as a semiconductor wafer on which photoresist is applied. The exposure apparatus200synchronously translates the mask table MT and the workpiece table WT to expose the workpiece to the EUV light101reflecting the mask pattern. Through the exposure process as described above, a device pattern is transferred onto the semiconductor wafer, thereby a semiconductor device can be manufactured.

FIG.2is a schematic view showing a schematic configuration example of an entire electronic device manufacturing apparatus different from the electronic device manufacturing apparatus shown inFIG.1. The electronic device manufacturing apparatus shown inFIG.2includes the EUV light generation apparatus100and an inspection apparatus300. The inspection apparatus300includes an illumination optical system310including a plurality of mirrors311,313,315that constitute a reflection optical system, and a detection optical system320including a plurality of mirrors321,322that constitute a reflection optical system different from the reflection optical system of the illumination optical system310and a detector325. The illumination optical system310reflects, with the mirrors311,313,315, the EUV light101incident from the EUV light generation apparatus100to illuminate a mask333placed on a mask stage331. The mask333includes a mask blanks before a pattern is formed. The detection optical system320reflects, with the mirrors321,323, the EUV light101reflecting the pattern from the mask333and forms an image on a light receiving surface of the detector325. The detector325having received the EUV light101obtains an image of the mask333. The detector325is, for example, a time delay integration (TDI) camera. A defect of the mask333is inspected based on the image of the mask333obtained by the above-described process, and a mask suitable for manufacturing an electronic device is selected using the inspection result. Then, the electronic device can be manufactured by exposing and transferring the pattern formed on the selected mask onto the photosensitive substrate using the exposure apparatus200.

3. Description of Extreme Ultraviolet Light Generation Apparatus of Comparative Example

The EUV light generation apparatus100of a comparative example will be described. The comparative example of the present disclosure is an example recognized by the applicant as known only by the applicant, and is not a publicly known example admitted by the applicant. Further, the following description will be given with reference to the EUV light generation apparatus100that outputs the EUV light101to the exposure apparatus200as an external apparatus as shown inFIG.1. Here, the EUV light generation apparatus100that outputs the EUV light101to the inspection apparatus300as an external apparatus as shown inFIG.2can obtain the same operation and effect.

FIG.3is a schematic view showing a schematic configuration example of the entire EUV light generation apparatus100of the present example. As shown inFIG.3, the EUV light generation apparatus100mainly includes a chamber device10, a main pulse laser light irradiation system MPS including a main pulse laser device130, a prepulse laser light irradiation system PPS including a prepulse laser device140, and a control system120.

The chamber device10is a sealable container. The chamber device10includes an inner wall10bsurrounding the internal space having a low pressure atmosphere. The chamber device10also includes a sub-chamber15. A target supply unit40is attached to the sub-chamber15to penetrate a wall of the sub-chamber15. The target supply unit40includes a tank41, a nozzle42, and a pressure regulator43to supply a droplet target DL to the internal space of the chamber device10. A droplet target DL is sometimes abbreviated as a droplet or a target.

The tank41stores therein a target substance which becomes the droplet target DL. The target substance contains tin. The inside of the tank41is in communication with the pressure regulator43which regulates the pressure in the tank41. A heater44and a temperature sensor45are attached to the tank41. The heater44heats the tank41with current applied from a heater power source46. Through the heating, the target substance in the tank41melts. The temperature sensor45measures, via the tank41, the temperature of the target substance in the tank41. The pressure regulator43, the temperature sensor45, and the heater power source46are electrically connected to a processor121included in the control system120.

The nozzle42is attached to the tank41and outputs the target substance. A piezoelectric element47is attached to the nozzle42. The piezoelectric element47is electrically connected to a piezoelectric power source48and is driven by voltage applied from the piezoelectric power source48. The piezoelectric power source48is electrically connected to the processor121. The target substance output from the nozzle42is formed into the droplet target DL through operation of the piezoelectric element47.

The chamber device10includes a target collection unit14. The target collection unit14is a box body attached to an inner wall10bof the chamber device10and communicates with the internal space of the chamber device10via an opening10aformed at the inner wall10bof the chamber device10. The opening10ais arranged directly below the nozzle42. The target collection unit14is a drain tank to collect any unnecessary droplet target DL having passed through the opening10aand reaching the target collection unit14.

At least one through hole is formed in the inner wall10bof the chamber device10. The through hole is blocked by a window12through which pulse laser light output from the main pulse laser device130and the prepulse laser device140passes.

Further, a laser light concentrating optical system13is arranged at the internal space of the chamber device10. The laser light concentrating optical system13includes a laser light concentrating mirror13A and a high reflection mirror13B. The laser light concentrating mirror13A reflects and concentrates the laser light having passed through the window12. The high reflection mirror13B reflects light concentrated by the laser light concentrating mirror13A. Positions of the laser light concentrating mirror13A and the high reflection mirror13B are adjusted by a laser light manipulator13C so that a light concentration position of the laser light at the internal space of the chamber device10coincides with a position specified by the processor121. The light concentration position is adjusted to be a position directly below the nozzle42, and when the target substance is irradiated with the laser light at the light concentration position, plasma is generated by the irradiation, and the EUV light101is radiated from the plasma. The region in which plasma is generated is sometimes referred to as a plasma generation region AR.

For example, an EUV light concentrating mirror75having a spheroidal reflection surface75ais arranged at the internal space of the chamber device10. The reflection surface75areflects the EUV light101radiated from the plasma in the plasma generation region AR. The reflection surface75ahas a first focal point and a second focal point. The reflection surface75amay be arranged such that, for example, the first focal point is located in the plasma generation region AR and the second focal point is located at an intermediate focal point IF. InFIG.3, a straight line passing through the first focal point and the second focal point is shown as a focal line L0. In the following, the direction in which the focal line L0extends may be referred to as the Z direction, the direction which is the discharge direction of the droplet target DL and is orthogonal to the Z direction may be referred to as the Y direction, and the direction orthogonal to the Z direction and the Y direction may be referred to as the X direction.

Further, the EUV light generation apparatus100includes a connection portion19providing communication between the internal space of the chamber device10and the internal space of the exposure apparatus200. A wall in which an aperture is formed is arranged inside the connection portion19. The wall is preferably arranged such that the aperture is located at the second focal point. The connection portion19is an outlet port of the EUV light101in the EUV light generation apparatus100, and the EUV light101is output from the connection portion19and enters the exposure apparatus200.

Further, the EUV light generation apparatus100includes a pressure sensor26and a target sensor27. The pressure sensor26and the target sensor27are attached to the chamber device10and are electrically connected to the processor121. The pressure sensor26measures the pressure at the internal space of the chamber device10and outputs a signal indicating the pressure to the processor121. The target sensor27has, for example, an imaging function, and detects the presence, trajectory, position, velocity, and the like of the droplet target DL output from the nozzle hole of the nozzle42in accordance with an instruction from the processor121. The target sensor27may be arranged inside the chamber device10, or may be arranged outside the chamber device10and detect the droplet target DL through a window (not shown) arranged on a wall of the chamber device10. The target sensor27includes a light receiving optical system (not shown) and an imaging unit (not shown) such as a charge-coupled device (CCD) or a photodiode. In order to improve the detection accuracy of the droplet target DL, the light receiving optical system forms an image of the trajectory of the droplet target DL and the periphery thereof on a light receiving surface of the imaging unit. When the droplet target DL passes through a light concentration region of a light source unit (not shown) arranged to improve contrast in the field of view of the target sensor27, the imaging unit detects a change of the light passing through the trajectory of the droplet target DL and the periphery thereof. The imaging unit converts the detected light change into an electric signal as a signal related to the image data of the droplet target DL. The imaging unit outputs the electric signal to the processor121.

The main pulse laser device130is configured by, for example, a YAG laser device or a CO2laser device, includes a master oscillator that performs burst operation, and outputs main pulse laser light MPL. In the burst operation, the main pulse laser light MPL is continuously output at a predetermined repetition frequency in a burst-on duration and the output of the main pulse laser light MPL is stopped in a burst-off duration.

The prepulse laser device140outputs prepulse laser light PPL linearly polarized in a predetermined direction. In the example ofFIG.3, the wavelength of the prepulse laser light PPL is different from the wavelength of the main pulse laser light MPL. Therefore, for example, when the main pulse laser device130is a YAG laser device, the prepulse laser device140is, for example, a CO2laser device. Here, the prepulse laser light PPL and the main pulse laser light MPL may have the same wavelength. In this case, the main pulse laser device130and the prepulse laser device140are, for example, both YAG laser devices or both CO2laser devices. The prepulse laser device140is configured to output the prepulse laser light PPL at the timing different from the timing at which the main pulse laser light MPL is output from the main pulse laser device130. This control is performed by the control system120described below.

Travel directions of the main pulse laser light MPL and the prepulse laser light PPL are adjusted by a laser light delivery optical system including a plurality of mirrors. The laser light delivery optical system for adjusting the travel direction of the main pulse laser light MPL includes mirrors31,32. The laser light delivery optical system for adjusting the travel direction of the prepulse laser light PPL includes a mirror33and an optical path combining member34. The optical path combining member34is arranged at a position where the optical path of the prepulse laser light PPL intersects with the optical path of the main pulse laser light MPL. In the present example, the optical path combining member34arranged as described above is a dichroic mirror that reflects the prepulse laser light PPL and transmits the main pulse laser light MPL to substantially overlap the optical path of the main pulse laser light MPL with the optical path of the prepulse laser light PPL. The orientation of at least one of the mirrors31,32,33and the optical path combining member34is adjusted by an actuator (not shown), and according to this adjustment, the main pulse laser light MPL and the prepulse laser light PPL can be appropriately propagated through the window12to the internal space of the chamber device10. Here, when the prepulse laser light PPL and the main pulse laser light MPL have the same wavelength and have polarization directions different from each other by 90°, the optical path combining member34may be a polarizer.

The main pulse laser light irradiation system MPS is a system for irradiating a target substance with the main pulse laser light MPL. Therefore, in the present example, the main pulse laser light irradiation system MPS includes the mirrors31,32, the optical path combining member34, and the laser light concentrating optical system13, in addition to the main pulse laser device130. Further, the prepulse laser light irradiation system PPS is a system for irradiating a target substance with the prepulse laser light PPL. Therefore, in the present example, the prepulse laser light irradiation system PPS includes the mirror33, the optical path combining member34, and the laser light concentrating optical system13in addition to the prepulse laser device140.

The processor121of the control system120of the present disclosure is a processing device including a storage device in which a control program is stored and a central processing unit (CPU) that executes the control program. The processor121is specifically configured or programmed to perform various processes included in the present disclosure and controls the entire EUV light generation apparatus100. The processor121receives a signal related to the pressure at the internal space of the chamber device10, which is measured by the pressure sensor26, a signal related to image data of the droplet target DL captured by the target sensor27, a burst signal instructing the burst operation from the exposure apparatus200, and the like. The processor121processes the various signals, and may control, for example, the timing at which the droplet target DL is output, the output direction of the droplet target DL, and the like. Further, the processor121may control output timings of the main pulse laser device130and the prepulse laser device140, the travel directions and the light concentration positions of the main pulse laser light MPL and the prepulse laser light PPL, and the like. Such various kinds of control described above are merely exemplary, and other control may be added as necessary, as described later.

The processor121of the present example is electrically connected to the main pulse laser device130and the prepulse laser device140via a delay circuit122of the control system120. The delay circuit122slightly changes the trigger signals for the main pulse laser device130and the prepulse laser device140output from the processor121. Specifically, the trigger signals input to the main pulse laser device130and the prepulse laser device140are shifted so that the irradiation timing of the main pulse laser device130is set later than the irradiation timing of the prepulse laser device140.

A central gas supply unit81for supplying etching gas to the internal space of the chamber device10is arranged at the chamber device10. As described above, since the target substance contains tin, the etching gas is, for example, hydrogen-containing gas having hydrogen gas concentration of 100% in effect. Alternatively, the etching gas may be, for example, balance gas having hydrogen gas concentration of approximately 3%. The balance gas contains nitrogen (N2) gas and argon (Ar) gas. Tin fine particles and tin charged particles are generated when the target substance constituting the droplet target DL is turned into plasma in the plasma generation region AR by being irradiated with the main pulse laser light MPL. Tin constituting these fine particles and charged particles reacts with hydrogen contained in the etching gas supplied to the internal space of the chamber device10. Through the reaction with hydrogen, tin becomes stannane (SnH4) gas at room temperature.

The central gas supply unit81has a side surface shape of a circular truncated cone, and is inserted through a through hole75cformed in the center of the EUV light concentrating mirror75. The central gas supply unit81is called a cone in some cases. Further, the central gas supply unit81has a central gas supply port81abeing a nozzle. The central gas supply port81ais provided on the focal line L0passing through the first focal point and the second focal point of the reflection surface75a. The focal line L0is extended along the center axis direction of the reflection surface75a. The central gas supply port81asupplies the etching gas from the center side of the reflection surface75atoward the plasma generation region AR. Here, it is preferable that the etching gas is supplied from the central gas supply port81aalong the focal line L0in the direction away from the reflection surface75afrom the center side of the reflection surface75a. The central gas supply port81ais connected to a gas supply device (not shown) being a tank through a pipe (not shown) of the central gas supply unit81and the etching gas is supplied therefrom. The gas supply device is driven and controlled by the processor121. A supply gas flow rate adjusting unit being a valve (not shown) may be arranged in the pipe (not shown).

The central gas supply port81ais a gas supply port for supplying the etching gas to the internal space of the chamber device10as well as an outlet port through which the prepulse laser light PPL and the main pulse laser light MPL are output to the internal space of the chamber device10. The prepulse laser light PPL and the main pulse laser light MPL travel toward the internal space of the chamber device10through the window12and the central gas supply port81a.

An exhaust port10E is arranged at the inner wall10bof the chamber device10. Since the exposure apparatus200is arranged on the focal line L0, the exhaust port10E is arranged at the inner wall10bon the side lateral to the focal line L0. The direction along the center axis of the exhaust port10E is, for example, perpendicular to the focal line L0. The exhaust port10E is arranged on the side opposite to the reflection surface75awith respect to the plasma generation region AR when viewed from the direction perpendicular to the focal line L0. The exhaust port10E exhausts gas at the internal space of the chamber device10. The exhaust port10E is connected to an exhaust pipe10P, and the exhaust pipe10P is connected to an exhaust pump60.

As described above, when the target substance is turned into plasma in the plasma generation region AR, the residual gas as exhaust gas is generated at the internal space of the chamber device10. The residual gas contains tin fine particles and tin charged particles generated through the plasma generation from the target substance, stannane generated through the reaction of the tin fine particles and tin charged particles with the etching gas, and unreacted etching gas. Some of the charged particles are neutralized at the internal space of the chamber device10, and the residual gas contains the neutralized charged particles as well. The residual gas is suctioned to the exhaust pump60through the exhaust port10E and the exhaust pipe10P.

Next, operation of the EUV light generation apparatus100of the comparative example will be described.

In the EUV light generation apparatus100, for example, at the time of new installation or maintenance or the like, atmospheric air at the internal space of the chamber device10is exhausted. At this time, purging and exhausting of the internal space of the chamber device10may be repeated for exhausting atmospheric components. For example, inert gas such as nitrogen or argon is preferably used for the purge gas. Thereafter, when the pressure at the internal space of the chamber device10becomes equal to or lower than a predetermined pressure, the processor121starts introduction of the etching gas from the gas supply device to the internal space of the chamber device10through the central gas supply unit81. At this time, the processor121may control the supply gas flow rate adjusting unit (not shown) and the exhaust pump60so that the pressure at the internal space of the chamber device10is maintained at a predetermined pressure. Thereafter, the processor121waits until a predetermined time elapses from the start of introduction of the etching gas.

Further, the processor121causes the gas at the internal space of the chamber device10to be exhausted from the exhaust port10E by the exhaust pump60, and keeps the pressure at the internal space of the chamber device10substantially constant based on the signal of the pressure at the internal space of the chamber device10measured by the pressure sensor26.

In order to heat and maintain the target substance in the tank41to and at a predetermined temperature equal to or higher than the melting point, the processor121causes the heater power source46to supply current to the heater44to increase temperature of the heater44. In this case, the processor121controls the temperature of the target substance to the predetermined temperature by adjusting a value of the current supplied from the heater power source46to the heater44based on an output from the temperature sensor45. When the target substance is tin, the predetermined temperature is equal to or higher than 231.93° C. being the melting point of tin and, for example, is 240° C. or higher and 290° C. or lower. Thus, the preparation for outputting the droplet target DL is completed.

When the preparation is completed, the processor121causes the pressure regulator43to supply the inert gas from the gas supply source to the tank41and to adjust the pressure in the tank41so that the melted target substance is output through the nozzle hole of the nozzle42at a predetermined velocity. Under this pressure, the target substance is output into the chamber device10through the nozzle hole of the nozzle42. The target substance output through the nozzle hole may be in the form of a jet. At this time, the processor121causes the piezoelectric power source48to apply voltage having a predetermined waveform to the piezoelectric element47to generate the droplet target DL. The piezoelectric power source48applies voltage so that the waveform of the voltage value becomes, for example, a sine wave, a rectangular wave, or a sawtooth wave. Vibration of the piezoelectric element47can propagate through the nozzle42to the target substance to be output through the nozzle hole of the nozzle42. The target substance is divided at a predetermined cycle by the vibration into liquid droplet targets DL. The diameter of the droplet target DL is approximately 20 μm or less.

When the droplet target DL is output, the target sensor27detects the passage timing of the droplet target DL passing through a predetermined position at the internal space of the chamber device10. The processor121outputs the trigger signal to control the timing of outputting the prepulse laser light PPL from the prepulse laser device140based on the signal from the target sensor27so that the droplet target DL is irradiated with the prepulse laser light PPL. The trigger signal output from the processor121is input to the prepulse laser device140and the main pulse laser device130via the delay circuit122. Here, the delay circuit122outputs the trigger signal to the prepulse laser device140prior to the main pulse laser device130. The prepulse laser device140outputs the prepulse laser light PPL when the trigger signal is input. At the timing when the prepulse laser light PPL is output, the main pulse laser light MPL is not output.

The prepulse laser light PPL is a picosecond pulse laser light having a temporal pulse width of, for example, 10 ps or more and 100 ps or less, or a nanosecond pulse laser light having a pulse width of, for example, 10 ns or more and 300 ns or less. Here, the above pulse width is an interval between times when the intensity of the laser light becomes a half value of the maximum value before and after the intensity becomes the maximum value. The picosecond pulse laser light and the nanosecond pulse laser light have substantially the same energy per pulse. Therefore, the picosecond pulse laser light has a higher energy density than the nanosecond pulse laser light. Here, the fluence of the prepulse laser light PPL is, for example, 0.1 J/cm2or more and 100 J/cm2or less. Preferably, the fluence is equal to or larger than to 1 J/cm2and equal to or smaller than 20 J/cm2for picosecond pulse laser light and equal to or larger than 1 J/cm2and equal to or smaller than 3 J/cm2for nanosecond pulse laser light. The prepulse laser light PPL having linear polarization and output from the prepulse laser device140is reflected by the mirror33and the optical path combining member34, and is radiated to the droplet target DL via the laser light concentrating optical system13. At this time, the processor121controls the laser light manipulator13C of the laser light concentrating optical system13so that the prepulse laser light PPL is concentrated in the vicinity of the plasma generation region AR. The droplet target DL irradiated with the prepulse laser light PPL is diffused by laser ablation due to the energy of the laser light, and becomes a diffusion target. Therefore, the prepulse laser light irradiation system PPS is a system for generating a diffusion target by irradiating the droplet target DL with the prepulse laser light PPL.

Since the diffusion target is a target in which the droplet target DL is diffused, the diameter thereof is larger than that of the droplet target DL, and the density thereof is lower than that of the droplet target DL.

When the trigger signal is input to the main pulse laser device130with a delay from the timing at which the trigger signal is input to the prepulse laser device140, the main pulse laser device130outputs the main pulse laser light MPL. The time difference between the output timing of the prepulse laser light PPL and the output timing of the main pulse laser light MPL is, for example, 50 ns or more and 500 ns or less in the case of the picosecond pulse laser light, and 50 ns or more and 150 ns or less in the case of the nanosecond pulse laser light. The processor121and the delay circuit122output the light emission trigger signal to control the timing at which the main pulse laser light MPL is output from the main pulse laser device130so that the diffusion target is irradiated with the main pulse laser light MPL.

The main pulse laser light MPL is laser light having a pulse width of, for example, 1 ns or more and 50 ns or less, more preferably of 15 ns or more and 20 ns or less. The main pulse laser light MPL output from the main pulse laser device130is reflected by the mirrors31,32, transmitted through the optical path combining member34, and radiated to the diffusion target in the plasma generation region AR via the laser light concentrating optical system13. At this time, the processor121controls the laser light manipulator13C of the laser light concentrating optical system13so that the main pulse laser light MPL is concentrated in the plasma generation region AR. The diffusion target irradiated with the main pulse laser light MPL is turned into plasma due to the energy of the laser light, and light including EUV light is radiated from the plasma. Thus, the main pulse laser light irradiation system MPS is a system for generating EUV light by irradiating the diffusion target with the main pulse laser light MPL.

When the diffusion target in which the density of the target substance is lowered is irradiated with the main pulse laser light MPL as described above, a larger amount of the target substance may be turned into plasma and EUV light may be efficiently radiated, compared to a case in which the droplet target DL is directly irradiated with the main pulse laser light MPL.

Among the light including the EUV light generated in the plasma generation region AR, the EUV light101is concentrated at the intermediate focal point IF by the EUV light concentrating mirror75, and then, is incident on the exposure apparatus200from the connection portion19.

Here, when the target substance is turned into plasma, tin fine particles are generated as described above. The fine particles diffuse to the internal space of the chamber device10. The fine particles diffusing to the internal space of the chamber device10react with the hydrogen-containing etching gas supplied from the central gas supply unit81to become stannane. Most of the stannane obtained through the reaction with the etching gas flows into the exhaust port10E along with the flow of the unreacted etching gas. At least some of the unreacted charged particles, fine particles, and etching gas flow into the exhaust port10E.

The unreacted etching gas, fine particles, charged particles, stannane, and the like having flowed into the exhaust port10E flow as residual gas through the exhaust pipe10P into the exhaust pump60and are subjected to predetermined exhaust treatment such as detoxification.

In the EUV light generation apparatus100of the comparative example, the prepulse laser device140outputs the prepulse laser light PPL having linear polarization. When the droplet target DL is irradiated with the prepulse laser light PPL having linear polarization, the diffusion target tends to spread in a shape longer in the polarization direction of the prepulse laser light PPL than in directions other than the polarization direction. In general, the cross section of the main pulse laser light MPL perpendicular to the optical axis thereof has a circular shape.FIG.4is a diagram showing an example of the relationship between cross sections of the diffusion target DT and the main pulse laser light MPL when being radiated to the diffusion target DT.FIG.5is a diagram showing another example of the relationship between cross sections of the diffusion target DT and the main pulse laser light MPL when being radiated to the diffusion target DT. InFIGS.4and5, the diffusion target DT is shown by a broken line for ease of viewing. As shown inFIG.4, when the diameter of the cross section of the main pulse laser light MPL is smaller than the length of the cross section of the diffusion target DT in the longitudinal direction, a part of the diffusion target DT is not irradiated with the main pulse laser light MPL. Therefore, it becomes difficult for a part of the target substance to turn into plasma, and the unreacted target substance which is not turned into plasma is discharged from the exhaust pipe10P or becomes debris and adheres to the inner wall10bof the chamber device10or the reflection surface75aof the EUV light concentrating mirror75. On the other hand, as shown inFIG.5, when the diameter of the cross section of the main pulse laser light MPL is larger than the length of the cross section of the diffusion target DT in the longitudinal direction, the cross section of the main pulse laser light MPL is larger than that of the diffusion target DT. Therefore, a part of the main pulse laser light MPL is not radiated to the diffusion target DT, so that loss occurs in the main pulse laser light MPL. Therefore, there is a demand for efficient generation of EUV light.

Therefore, in the following embodiments, an EUV light generation apparatus capable of efficiently generating EUV light will be exemplified.

4. Description of Extreme Ultraviolet Light Generation Apparatus of First Embodiment

Next, the configuration of the EUV light generation apparatus100of a first embodiment will be described. Any component same as that described above is denoted by an identical reference sign, and duplicate description thereof is omitted unless specific description is needed.

FIG.6is a schematic view showing a schematic configuration example of the entire EUV light generation apparatus100of the present embodiment. In the EUV light generation apparatus100of the present embodiment, the main pulse laser light irradiation system MPS differs from that of the comparative example in that a shaping unit150is included.

The shaping unit150is arranged on the upstream side of the optical path combining member34in the travel direction of the main pulse laser light MPL.FIG.6shows an example in which the shaping unit150is arranged between the mirror31and the mirror32.

FIG.7is a partial sectional view showing a schematic configuration example of the shaping unit150. Specifically,FIG.7is a partial sectional view of the shaping unit150taken along a plane including the optical axis of the main pulse laser light MPL. The shaping unit150includes a pedestal151, a rotation stage153, actuators155a,155b, a housing157, a cylindrical concave lens159a, a cylindrical convex lens159b, holders161a,161b, a base member163, and a stage165. InFIG.7, the rotation stage153and the housing157are shown in cross section.

An opening157aserving as an entrance port of the main pulse laser light MPL and an opening157bserving as an outlet port of the main pulse laser light MPL are provided at the sidewall of the housing157. The base member163is arranged on the bottom wall of the housing157, and the holder161afor holding the cylindrical concave lens159aand the stage165are arranged on the base member163. The holder161bfor holding the cylindrical convex lens159bis arranged on the stage165.

The concave surface of the cylindrical concave lens159afaces the opening157a, and the cylindrical convex lens159bis positioned between the cylindrical concave lens159aand the opening157b. Further, the convex surface of the cylindrical convex lens159bfaces the opening157b, and the flat surface on the side opposite to the convex surface of the cylindrical convex lens159bfaces the flat surface on the side opposite to the concave surface of the cylindrical concave lens159a. When the main pulse laser light MPL passes through the cylindrical concave lens159a, the cross section of the main pulse laser light MPL perpendicular to the optical axis thereof expands in a predetermined direction. When the main pulse laser light MPL passes through the cylindrical convex lens159b, the main pulse laser light MPL expanded in the predetermined direction is collimated.

The actuator155bis attached to the outer wall of the housing157, the shaft of the actuator155bextends along the optical axis of the main pulse laser light MPL, and the tip of the shaft of the actuator155bis connected to the side surface of the stage165. The actuator155bis electrically connected to the processor121and moves the shaft thereof along the optical axis of the main pulse laser light MPL in accordance with a control signal from the processor121to push and pull the stage165. As a result, the cylindrical convex lens159bis moved, and the distance between the cylindrical concave lens159aand the cylindrical convex lens159bis adjusted.

By adjusting the above distance, the shaping unit150shapes the cross section of the main pulse laser light MPL perpendicular to the optical axis thereof when being radiated to the diffusion target DT into a shape longer in the polarization direction of the prepulse laser light PPL than in directions other than the polarization direction, thereby adjusting the length of the cross section in the polarization direction. The cross section of such main pulse laser light MPL is an elliptical shape long in the polarization direction. The cross section refers to a cross section in a region where the intensity of the main pulse laser light MPL is equal to or larger than a half value of the maximum value of the intensity in the intensity distribution in the cross section of the main pulse laser light MPL.

The rotation stage153and the actuator155aare arranged on the pedestal151. The rotation stage153is cylindrical, and the housing157is supported at the inside of the rotation stage153. The actuator155ais connected to the rotation stage153and electrically connected to the processor121, and rotates the rotation stage153about the optical axis of the main pulse laser light MPL passing through the housing157in accordance with a control signal from the processor121. As a result, the cylindrical concave lens159aand the cylindrical convex lens159binside the housing157rotate, and the cross section perpendicular to the optical axis of the main pulse laser light MPL when being radiated to the diffusion target DT also rotates about the optical axis.

The holder161amay be arranged on the stage165instead of the holder161b. Alternatively, the holders161a,161bmay be individually arranged on different stages165, and each stage165may be individually connected to the actuator155b. The actuator155bmay move at least one of the cylindrical concave lens159aand the cylindrical convex lens159balong the optical axis of the main pulse laser light MPL to adjust the distance between the cylindrical concave lens159aand the cylindrical convex lens159b.

Next, operation of the EUV light generation apparatus100of the present embodiment will be described.

Similarly to the comparative example, when the droplet target DL is output from the target supply unit40, the prepulse laser device140outputs the prepulse laser light PPL having linear polarization. When the droplet target DL is irradiated with the prepulse laser light PPL, the diffusion target DT is generated. The diffusion target DT tends to spread in a shape longer in the polarization direction of the prepulse laser light PPL than in directions other than the polarization direction owing to the prepulse laser light PPL having linear polarization when being radiated to the droplet target DL. In the arrangement ofFIG.8described below, for example, the XZ plane will be described as the incidence surface of the prepulse laser light PPL having linear polarization. Further, in the case that the prepulse laser light PPL at the time of being radiated to the droplet target DL has S polarization, the polarization direction of the prepulse laser light PPL is the Y direction. Further, in the case that the prepulse laser light PPL at the time of being radiated to the droplet target DL has P polarization, the polarization direction of the prepulse laser light PPL is the X direction.

FIG.8is a diagram showing an example of the relationship between cross sections of the diffusion target DT and the main pulse laser light MPL when being radiated to the diffusion target DT in the present embodiment. When the prepulse laser light PPL having S polarization is radiated to the droplet target DL, the diffusion target DT tends to spread in an elliptical shape long in the Y direction as shown by a broken line inFIG.8. The cross section of the main pulse laser light MPL shown by a solid line inFIG.8will be described later. Here, when the prepulse laser light PPL having P polarization is radiated to the droplet target DL, the diffusion target DT tends to spread in an elliptical shape long in the X direction.

Next, the processor121of the present embodiment measures the length of the diffusion target DT in the longitudinal direction and the length of the diffusion target DT in a direction perpendicular to the longitudinal direction from the signal related to the shape of the diffusion target DT imaged by the target sensor27. Then, the processor121controls the actuator155bbased on the measurement result to adjust the distance between the cylindrical concave lens159aand the cylindrical convex lens159b. Further, the processor121controls the actuator155abased on the measurement result to rotate the housing157about the optical axis of the main pulse laser light MPL.

Next, similarly to the comparative example, the main pulse laser device130outputs the main pulse laser light MPL, and the main pulse laser light MPL passes through the cylindrical concave lens159aand the cylindrical convex lens159bof the shaping unit150. Then, the main pulse laser light MPL is reflected by the mirror32, passes through the optical path combining member34and the window12, is reflected by the mirrors13A,13B, and is radiated to the diffusion target DT. The shaping unit150shapes the cross section of the main pulse laser light MPL perpendicular to the optical axis thereof when being radiated to the diffusion target DT into an elliptical shape longer in the polarization direction of the prepulse laser light PPL than in directions other than the polarization direction. By adjusting the distance described above, the length of the cross section of the main pulse laser light MPL in the longitudinal direction becomes close to the length of the diffusion target DT in the longitudinal direction. InFIG.8, the length of the main pulse laser light MPL shown by a solid line is indicated by L1, and the main pulse laser light MPL is shown slightly larger than the diffusion target DT for ease of viewing. The length L1is shortened when the distance is shortened, and is lengthened when the distance is lengthened. The processor121adjusts the distance so that the length L1is 20 μm or more and 100 μm or less. Further, the cylindrical concave lens159aand the cylindrical convex lens159bare rotated by the rotation of the housing157, so that the inclination of the major axis of the cross section of the main pulse laser light MPL with respect to the X direction when being radiated to the diffusion target DT is adjusted. With respect to the prepulse laser light PPL having S polarization when being radiated to the droplet target DL, the processor121causes the elliptical cross section of the main pulse laser light MPL to be elongated in the Y direction as shown inFIG.8by the rotation. Further, with respect to the prepulse laser light PPL having P polarization when being radiated to the droplet target DL, the processor121causes the elliptical cross section of the main pulse laser light MPL to be elongated in the X direction. By adjusting the distance and the inclination of the major axis, the deviation of the irradiation of the diffusion target DT with the main pulse laser light MPL is suppressed.

The diffusion target DT is irradiated with the main pulse laser light MPL in which the length L1and the inclination of the major axis are adjusted, and the EUV light101is emitted from the diffusion target DT.

As described above, the cross section perpendicular to the optical axis of the main pulse laser light MPL when being radiated to the diffusion target DT in the present embodiment has a shape longer in the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL than in directions other than the polarization direction.

The prepulse laser light irradiation system PPS generates the diffusion target DT by irradiating the droplet target DL output from the target supply unit40into the chamber device10with the prepulse laser light PPL. The generated diffusion target DT tends to spread in a shape longer in the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL than in directions other than the polarization direction. In the above configuration, the cross section of the main pulse laser light MPL perpendicular to the optical axis thereof when being radiated to the diffusion target DT has a shape longer in the polarization direction of the prepulse laser light PPL than in directions other than the polarization direction. Therefore, compared to a case in which the cross section of the main pulse laser light MPL is circular and the diameter of the circle is smaller than the length of the diffusion target DT in the polarization direction of the prepulse laser light PPL, it can be suppressed that a part of the diffusion target DT is not irradiated with the main pulse laser light MPL. Therefore, the droplet target DL can be easily turned into plasma. Further, on the other hand, compared to a case in which the diameter of the circle is longer than the length of the diffusion target DT in the polarization direction of the prepulse laser light PPL, the loss of the main pulse laser light MPL can be suppressed. Therefore, according to the EUV light generation apparatus100of the present embodiment, the EUV light101can be efficiently generated.

The shaping unit150of the present embodiment includes the cylindrical concave lens159a, the cylindrical convex lens159b, and the actuator155bwhich adjusts the distance between the cylindrical concave lens159aand the cylindrical convex lens159b. In the above configuration, by adjusting the distance between the cylindrical concave lens159aand the cylindrical convex lens159bby the actuator155b, the length of the cross section of the main pulse laser light MPL in the longitudinal direction when being radiated to the diffusion target DT can be adjusted. Therefore, the main pulse laser light MPL having an appropriate cross section can be radiated to the diffusion target DT.

The processor121controls the adjustment of the distance between the cylindrical concave lens159aand the cylindrical convex lens159bby the actuator155b. Therefore, compared to a case in which an operator of the EUV light generation apparatus100manually adjusts the distance between the cylindrical concave lens159aand the cylindrical convex lens159b, the burden on the operator for the adjustment can be reduced.

Further, the shaping unit150is arranged on the upstream side of the optical path combining member34with respect to the travel direction of the main pulse laser light MPL. According to the above configuration, only the main pulse laser light MPL travels to the shaping unit150. Therefore, the shaping unit150can shape only the cross section of the main pulse laser light MPL when being radiated to the diffusion target DT to a shape longer in the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL than in directions other than the polarization direction.

In the EUV light generation apparatus100of the present embodiment, the main pulse laser light MPL and the prepulse laser light PPL have different wavelengths but the polarization directions thereof may be the same or different. In this case, the optical path combining member34is a dichroic mirror. Further, the main pulse laser light MPL and the prepulse laser light PPL may have the same wavelength and polarization directions different from each other by 90°. In this case, the optical path combining member34is a polarizer. Further, in this case, the main pulse laser device130and the prepulse laser device140are, for example, both YAG laser devices or both CO2laser devices. By matching the polarization direction of the polarizer to the polarization direction of the main pulse laser light MPL, the main pulse laser light MPL passes through the polarizer. Further, by setting the polarization direction of the polarizer different from the polarization direction of the prepulse laser light PPL, the polarizer reflects the prepulse laser light PPL.

5. Description of Extreme Ultraviolet Light Generation Apparatus of Second Embodiment

Next, the configuration of the EUV light generation apparatus100of a second embodiment will be described. Any component same as that described above is denoted by an identical reference sign, and duplicate description thereof is omitted unless specific description is needed.

FIG.9is a schematic view showing a schematic configuration example of the entire EUV light generation apparatus100of the present embodiment. The EUV light generation apparatus100of the present embodiment is the EUV light generation apparatus100that outputs the EUV light101toward the inspection apparatus300instead of the exposure apparatus200. In this case, in the EUV light generation apparatus100of the present embodiment, a collection solid angle of the EUV light concentrating mirror75for the EUV light101may be limited as compared with the EUV light generation apparatus100that outputs the EUV light101toward the exposure apparatus200. Due to the limitation of the collection solid angle, the EUV light concentrating mirror75can be made smaller than that when used in the EUV light generation apparatus100that outputs the EUV light101toward the exposure apparatus200. Therefore, in the EUV light generation apparatus100of the present embodiment, the EUV light concentrating mirror75is different from the EUV light concentrating mirror of the first embodiment in that the EUV light concentrating mirror75is arranged in a part of the circumference of the optical axis in the circumferential direction of the optical axis of the prepulse laser light PPL when being radiated on the droplet target DL rather than over the entire circumference of the optical axis. That is, the EUV light concentrating mirror75is arranged at a position laterally offset from the optical axis of the prepulse laser light PPL when being radiated to the droplet target DL. Further, the EUV light concentrating mirror75is different from the EUV light concentrating mirror75of the first embodiment in that the EUV light concentrating mirror75is arranged within a predetermined range on the lateral side of the optical axis.FIG.10is a view of the arrangement position of the EUV light concentrating mirror75with respect to the optical axis of the prepulse laser light PPL when the diffusion target DT is generated viewed from the Y direction. The predetermined range for the EUV light concentrating mirror75is a range within, for example, 33° or larger and 105° or smaller with respect to the optical axis of the prepulse laser light PPL when being radiated to the droplet target DL.

In the EUV light generation apparatus100of the present embodiment, the main pulse laser device130outputs the main pulse laser light MPL having polarization in the X direction, and the prepulse laser device140outputs prepulse laser light PPL having polarization in the X direction. Further, in the EUV light generation apparatus100of the present embodiment, the main pulse laser light MPL and the prepulse laser light PPL have the same wavelength. Therefore, the optical path combining member34is a polarizer.

Here, unlike the present embodiment, a case in which the diffusion target DT is generated by the prepulse laser light PPL having polarization in the X direction will be described. In this case, as shown inFIG.10, the diffusion target DT tends to spread in the X direction which is the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL, and debris171generated from the diffusion target DT tends to scatter in the X direction. When the EUV light concentrating mirror75is arranged in the predetermined range, since the EUV light concentrating mirror75is located at the scattering destination of the debris171, the debris171may scatter and adhere to the EUV light concentrating mirror75.

Therefore, in the EUV light generation apparatus100of the present embodiment, the prepulse laser light irradiation system PPS is different from that of the first embodiment in that a λ/2 wavelength plate141is included as shown inFIG.9. The λ/2 wavelength plate141is arranged on the upstream side of the optical path combining member34in the travel direction of the prepulse laser light PPL.FIG.9shows an example in which the λ/2 wavelength plate141is arranged between the mirror33and the optical path combining member34.

FIG.11is a view of the diffusion target DT generated by the prepulse laser light PPL viewed from the Y direction. The λ/2 wavelength plate141changes the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL from the optical axis of the prepulse laser light PPL when being radiated to the droplet target DL to a direction different from the direction toward the EUV light concentrating mirror75. The λ/2 wavelength plate141rotates the polarization direction of the prepulse laser light PPL having polarization in the X direction to change the polarization direction of the prepulse laser light PPL into the Y direction. That is, the λ/2 wavelength plate141changes the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL to the Y direction which is perpendicular to the XZ plane including the center axis C1of the EUV light101traveling from the plasma generation region AR to the EUV light concentrating mirror75and the center axis C2of the EUV light101reflected by the EUV light concentrating mirror75.

FIG.12is a view of the diffusion target DT shown inFIG.11viewed from the Z direction. As shown inFIGS.11and12, the EUV light concentrating mirror75of the present embodiment is arranged at a position laterally offset from the optical axis of the prepulse laser light PPL when being radiated to the droplet target DL so as not to cross a straight line passing through the plasma generation region AR and extending in the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL. The diffusion target DT generated by the prepulse laser light PPL having polarization in the Y direction tends to spread in the Y direction which is the polarization direction of the prepulse laser light PPL when being radiated to the droplet target DL. The debris171generated from the diffusion target DT tends to scatter in the Y direction. Therefore, scattering of the debris171to the EUV light concentrating mirror75can be suppressed. Further, since the adhesion of the debris171to the EUV light concentrating mirror75is suppressed, failure of the EUV light generation apparatus100can be suppressed.

6. Description of Extreme Ultraviolet Light Generation Apparatus of Third Embodiment

Next, the configuration of the EUV light generation apparatus100of a third embodiment will be described. Any component same as that described above is denoted by an identical reference sign, and duplicate description thereof is omitted unless specific description is needed.

FIG.13is a schematic view showing a schematic configuration example of the entire EUV light generation apparatus100of the present embodiment. In the EUV light generation apparatus100of the present embodiment, the configurations of the main pulse laser light irradiation system MPS and the prepulse laser light irradiation system PPS are different from those of the second embodiment.

The main pulse laser light irradiation system MPS of the present embodiment includes the main pulse laser device130, the mirrors31,32, the shaping unit150, a λ/2 wavelength plate131, a laser light concentrating mirror13D, and a high reflection mirror13E.

The λ/2 wavelength plate131is arranged on the downstream side of the shaping unit150in the travel direction of the main pulse laser light MPL.FIG.13shows an example in which the λ/2 wavelength plate131is arranged on the upstream side of the mirror32.FIG.14is a view of the diffusion target DT irradiated with the main pulse laser light MPL having polarization in the Y direction viewed from the Y direction. The λ/2 wavelength plate131changes the polarization direction of the main pulse laser light MPL when being radiated to the diffusion target DT from the optical axis of the main pulse laser light MPL when being radiated to the diffusion target DT to a direction different from the direction toward the EUV light concentrating mirror75. The λ/2 wavelength plate131rotates the polarization direction of the main pulse laser light MPL having polarization in the X direction to change the polarization direction of the main pulse laser light MPL into the Y direction. That is, the λ/2 wavelength plate131changes the polarization direction of the main pulse laser light MPL when being radiated to the diffusion target DT to the Y direction which is perpendicular to the XZ plane including the center axis C1and the center axis C2. As shown inFIG.13, the main pulse laser light MPL is reflected by the mirror32, passes through a window12aprovided on the inner wall10bof the chamber device10, and travels to the laser light concentrating mirror13D.

The laser light concentrating mirror13D and the high reflection mirror13E are included in the laser light concentrating optical system13, and are arranged at the internal space of the chamber device10. The laser light concentrating mirror13D reflects and concentrates the main pulse laser light MPL having passed through the window12a. The high reflection mirror13E reflects the light concentrated by the laser light concentrating mirror13D toward the plasma generation region AR. Positions of the laser light concentrating mirror13D and the high reflection mirror13E are adjusted by the laser light manipulator13C so that the light concentration position of the main pulse laser light MPL at the internal space of the chamber device10coincides with a position specified by the processor121. The light concentration position is adjusted so as to be positioned directly below the nozzle42.

The prepulse laser light irradiation system PPS of the present embodiment includes the prepulse laser device140, the mirror33, the λ/2 wavelength plate141, a mirror35, the laser light concentrating mirror13A, and the high reflection mirror13B.

The mirror35is arranged between the λ/2 wavelength plate141and the laser light concentrating mirror13A, and reflects the prepulse laser light from the λ/2 wavelength plate141toward the laser light concentrating mirror13A.

In the present embodiment, since the main pulse laser light MPL and the prepulse laser light PPL has the same polarization, that is, polarization in the X direction, a polarizer is not used. Further, since the main pulse laser light MPL and the prepulse laser light PPL of the present embodiment have the same wavelength, a dichroic mirror is not used. Since the polarizer and the dichroic mirror are not used, the optical path of the main pulse laser light MPL and the optical path of the prepulse laser light PPL of the present embodiment are divided and do not overlap at the upstream of the plasma generation region AR. Here, in the case that the main pulse laser light MPL and the prepulse laser light PPL have different wavelengths, the dichroic mirror may be used and the optical path of the main pulse laser light MPL and the optical path of the prepulse laser light PPL may overlap at the downstream side of the λ/2 wavelength plates131,141due to the dichroic mirror.

FIG.15is a view of the diffusion target DT shown inFIG.14viewed from the Z direction. As shown inFIGS.14and15, the EUV light concentrating mirror75of the present embodiment is arranged at a position laterally offset from the optical axis of the main pulse laser light MPL when being radiated to the diffusion target DT so as not to cross a straight line passing through the plasma generation region AR and extending in the polarization direction of the main pulse laser light MPL when being radiated to the diffusion target DT. When the diffusion target DT is irradiated with the main pulse laser light MPL having polarization in the Y direction, the diffusion target DT tends to spread in the Y direction which is the polarization direction of the main pulse laser light MPL when being radiated to the diffusion target DT. The debris171generated from the diffusion target DT tends to scatter in the Y direction. Therefore, scattering of the debris171to the EUV light concentrating mirror75can be suppressed. Further, since the adhesion of the debris171to the EUV light concentrating mirror75is suppressed, failure of the EUV light generation apparatus100can be suppressed.

The description above is intended to be illustrative and the present disclosure is not limited thereto. Therefore, it would be obvious to those skilled in the art that various modifications to the embodiments of the present disclosure would be possible without departing from the spirit and the scope of the appended claims.

Further, it would be also obvious to those skilled in the art that embodiments of the present disclosure would be appropriately combined. The terms used throughout the present specification and the appended claims should be interpreted as non-limiting terms unless clearly described. For example, terms such as “comprise”, “include”, “have”, and “contain” should not be interpreted to be exclusive of other structural elements. Further, indefinite articles “a/an” described in the present specification and the appended claims should be interpreted to mean “at least one” or “one or more.” Further, “at least one of A, B, and C” should be interpreted to mean any of A, B, C, A+B, A+C, B+C, and A+B+C as well as to include combinations of the any thereof and any other than A, B, and C.