EXTREME ULTRAVIOLET LIGHT SOURCE DEVICE AND METHOD OF GENERATING EXTREME ULTRAVIOLET RADIATION

Abstract

Extreme ultraviolet light source device in which an EUV radiation fuel is introduced into a chamber, and high-voltage pulsed voltage from a high-voltage generator is applied between first and second main discharge electrodes, thereby producing a high-temperature plasma from discharge gas between the main discharge electrodes; EVU radiation with a wavelength of 13.5 nm is emitted. Of the EVU radiation emitted, the EUV radiation on the optical axis of the EUV collector mirror passes through a through-hole in the foil trap and through a through hole in the central support of the collector mirror, is reflected away from the optical axis by a reflector, and enters an EUV monitor. On the basis of EUV intensity signals input to the EUV monitor, a controller adjusts the power supplied from the high-voltage generator so that the EUV intensity is steady.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a first embodiment of this invention.

FIG. 2 is a diagram showing the foil trap used in this invention.

FIG. 3 is a diagram showing an outline of the constitution of the EUV collector mirror of this invention.

FIG. 4 is a diagram showing an alternate form of the first embodiment.

FIG. 5 is a diagram showing a second embodiment of this invention.

FIG. 6 is a diagram showing a third embodiment of this invention.

FIG. 7 is a diagram showing an example of the constitution of conventional DPP-type EUV light source device.

FIG. 8 is a diagram showing an example of embodiment of the conventional foil trap.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagram showing the first embodiment of this invention's EUV light source device having an EUV monitor.

Now, the following explanation of this embodiment refers to EUV radiation on the optical axis that connects the high-temperature plasma and the focal point as light that enters the collector mirror but that enters the EUV monitor without being reflected by the reflective surface of the collector mirror. However, that does not mean the EUV radiation has to be strictly on the optical axis. As long as EUV radiation enters the collector mirror but is not reflected by the reflective surface, it can be used as EUV radiation made to enter the EUV monitor, even if it is not EUV radiation on the optical axis.

Like FIG. 7 described above, FIG. 1 shows a DPP-type EUV light source device; and parts in FIG. 1 that are the same as in FIG. 7 are labeled with the same reference characters.

As with the equipment shown in FIG. 7, discharge gas that includes an EUV discharge fuel enters the chamber 1, which is a discharge vessel, from a discharge gas supply unit 7, by way of a gas introduction port 2 on the first main discharge electrode 3a side. The discharge gas is, for example, stannane (SnH₄), and the SnH₄ that is introduced flows in the chamber 1 side through the passage formed by the first main discharge electrode 3a, the second main discharge electrode 3b, and the insulator 3c of the discharge portion 9; it reaches the gas exhaust port 4 and is exhausted from the gas exhaust unit 8.

With the discharge gas flowing through the passage formed by the ring-shaped first main discharge electrode 3a, second main discharge electrode 3b, and insulator 3c, a pulsed high-voltage from the high-voltage generator 13 is applied between the second main discharge electrode 3b and the first main discharge electrode 3a, and a large, pulsed current flows between the first main discharge electrode 3a and the second main discharge electrode 3b. Then, because of Joule heating from the pinch effect, a high-temperature plasma P is generated from the discharge gas between the first and second main discharge electrodes 3a, 3b, and EVU radiation with a wavelength of 13.5 nm is emitted from the plasma.

A foil trap 5 is located between the discharge portion 9 and the EUV collector mirror 6; it acts to prevent debris arising from Sn or other radiation fuel or from metal (perhaps from an electrode) spattered by the high-temperature plasma from moving toward the EUV collector mirror 6.

The radiated EVU radiation is reflected by the EUV collector mirror 6, and emitted from an extractor 10 to the illumination portion, which is a lithography optical system (not shown).

A reflector 11a that reflects EVU radiation on the optical axis away from the optical axis is located on the output side of the EUV collector mirror 6; of the EVU radiation emitted from the high-temperature plasma P, the EUV radiation on the optical axis of the EUV collector mirror 6 is reflected and enters an EUV monitor 11.

The EUV monitor 11 monitors the incident EVU radiation, and EUV intensity signals are output from an EUV monitor equipment 12 to a controller 14. On the basis of the EUV intensity signals that are input, the controller 14 adjusts the power supplied to the discharge portion 9 from the high-voltage generator 13 so that the EUV intensity remains steady.

In the past, structures, such as supports that support the inner ring 5b of the foil trap 5 or the mirrors of the EUV collector mirror 6, have been located on the optical axis between the discharge portion 9 and the reflector 11a, and the EUV radiation on the optical axis that is not reflected by the EUV collector mirror 6 has been prevented from reaching the focal point.

However, in this invention, the EUV radiation on the optical axis that enters within the EUV collector mirror 6 but is not reflected by the reflective surfaces is used to measure the intensity of the EVU radiation. Therefore, a through hole 5d that allows passage of EVU radiation is formed in the support or other structure located on the optical axis, as shown in FIG. 1.

For example, the foil trap 5 used in this invention is shown in FIG. 2. As shown in that figure, there is a through hole 5d in the inner ring 5b of the foil trap 5, which is on the optical axis.

The diameter of the through hole 5d should be set appropriately so that EUV radiation can be obtained for the EUV monitor 11 to measure the intensity. Because the intensity of radiation on the optical axis is strong, however, the diameter of the through hole 5d can be as small as several hundred μm to several mm.

It is possible that, when there is a through hole 5d in the inner ring 5b of the foil trap 5, debris from the electrodes could pass through the through hole 5d and reach the collector mirror 6, but because the diameter of the through hole 5d is small, as stated above, it is thought that conductance within the through hole 5d will be high, the internal pressure will be high, the kinetic energy of the debris passing through will be reduced, and debris will have almost no effect on the reflecting mirrors of the collector mirror 6.

Further, an outline of the constitution of the EUV collector mirror of this invention is shown in FIG. 3. This Figure is an oblique view with a part of the EUV collector mirror 6 cut away, and is a diagram as seen from the EUV output side.

As shown in this figure, the EUV collector mirror 6 has multiple mirrors 6a (there are two in this example, but there may be five to seven) in the form of ellipsoids of revolution or paraboloids of revolution of which a cross section taken in a plain that includes the central axis is an ellipse or parabola (this central axis is called the “central axis of revolution” hereafter).

These mirrors 6a are nested with their axes of revolution on the same axis so that their focal point positions are approximately the same; the central support 6b is placed in position on the central axis of revolution, with radial hub-shaped supports 6c attached to the central support 6b. Each mirror 6a (the inner surface of which is a mirrored surface of an ellipsoid of revolution or a paraboloid of revolution) is supported by these hub-shaped supports 6c.

The central support 6b and hub-shaped supports 6c are positioned so as to obstruct the EVU radiation entering the collector mirror 6 as little as possible.

As shown in this figure, there is a through hole 6d in the central support 6b on the optical axis, the same as the foil trap 5 of FIG. 2.

Next, a reflector 11a that reflects (turns back) the EVU radiation on the optical axis away from the optical axis is located on the optical axis that connects the high-temperature plasma P generated in the discharge portion 9 and the focal point of the EUV collector mirror 6, and on the output side of the EUV collector mirror 6. Specifically, the reflector 11a is attached to the central support 6b, as shown in FIG. 3.

Of the EVU radiation emitted from the high-temperature plasma P, the light on the optical axis of the EUV collector mirror 6 passes through the through hole 5d of the inner ring 5b of the foil trap 5 and continues to enter the through hole 6d of the central support 6b.

When the EVU radiation that enters the through hole 6d of the central support 6b passes through the through hole 6d, it is reflected away from the optical axis by the reflector 11a mounted on the output side of the central support, and enters the EUV monitor 11.

The reflector 11a is a reflecting mirror formed by vapor deposition of many layers of molybdenum (Mo) and silicon (Si) on its surface. The multiple layers are designed, with consideration to the angle of reflection, so that the central wavelength of the reflected EUV radiation will be 13.5 nm.

The reflector 11a also fills the role of an obstruction that prevents EUV radiation on the optical axis from entering the focal point, and so no unnecessary EUV radiation on the optical axis, which has entered the collector mirror 6 but has not been reflected by the reflective surfaces, enters the focal point. Now, the angle at which the EVU radiation is turned back by the reflector 11a need not be a right angle as shown in the figure.

Further, there is no need to use EVU radiation that has passed outside the EUV collector mirror 6, and so the opening in the foil trap 5 can be the same size as the inputrange of the EUV collector mirror 6.

FIG. 4 shows an alternate form of the first embodiment.

In the first embodiment, the EVU radiation is turned back by the reflector 11a and enters the EUV monitor 11, but this example is one in which the EUV monitor is directly positioned in the place of the reflector 11a; otherwise the constitution is the same as that of the first embodiment.

In this case, there is a through hole through which EVU radiation passes on a structure on the optical axis between the discharge portion 9 and the EUV monitor 11, the same as described above.

With such a constitution, it is possible to monitor the EVU radiation in the same way as described above, and the EUV monitor 11 fills the role of an obstruction that prevents light on the optical axis from entering the focal point.

Now, in this embodiment, the support member 11b that supports the EUV monitor 11 located on the optical axis and the wiring connected to the EUV monitor 11 cut across the output side of the EUV collector mirror 6. For that reason, the support member and wiring can be positioned along the hub-shaped support 6c that supports the mirrors of the EUV collector mirror 6 shown in FIG. 3, so that the light emitted from the EUV collector mirror 6 is not obstructed.

The second embodiment of this invention is shown in FIG. 5.

The difference from the first embodiment is that a film thickness monitor 15 is located in the chamber 1 so as to correct the EUV intensity data from the EUV monitor by means of the measurement results from the film thickness monitor 15; otherwise its constitution and operation are the same as those of the first embodiment described above.

The film thickness monitor 15 measures the thickness of attached debris on the basis of changes in the frequency of a crystal oscillator that are caused by the depositions.

For example, if stannane (SnH₄) is used as the discharge gas in order to use Sn as the EUV generation fuel, tin and tin compounds will be generated by the discharge. Almost all of this is caught by the foil trap 5 or exhausted, but it is possible for a part of it to accumulate on and adhere to the detector (the incidence surface) of the EUV monitor 11 or the surface of the reflector 11a mirror if one is used.

When debris adheres to the reflector 11a or the detector of the EUV monitor 11, the volume of light received by the EUV monitor is reduced to that extent, and so even though EVU radiation of the same intensity is radiated from the high-temperature plasma P, the EUV intensity signals output from the EUV monitor 11 grow smaller. For that reason, the controller 14 raises the voltage supplied to the discharge portion.

To prevent this, in this embodiment, a film thickness monitor is placed in the chamber to measure the film thickness of the accumulated debris adhered to the EUV monitor 11 or the reflector 11a and to output the data signals to the controller 14.

Further, the reflectance (transmittance) of EVU radiation relative to the thickness of the deposition is measured experimentally in advance, and the data is stored in the controller 14.

The controller 14 determines the reflectance (transmittance) relative to the EVU radiation of the EUV monitor 11 or the reflector 11a, on the basis of the reflectance (transmittance) of EVU radiation relative to the thickness of contaminated debris stored as stated above and the input film thickness data of deposition in the chamber 1, such as on the reflector 11a or the EUV monitor 11, and then corrects the EUV intensity data from the EUV monitor 11.

For example, in the event that the transmittance based on the film thickness is 50% and there are depositions of the same thickness on both the reflector 11a and the EUV monitor 11, the actual EUV intensity would be four times the value of EUV intensity from the EUV monitor 11.

In this way, even in the event that a discharge gas that is made solid (produces depositions) by discharge, it is possible to measure the intensity of the EVU radiation by installing a film thickness monitor 15 in the chamber 1.

In the event that correction becomes difficult because the film continues to accumulate and the film thickness that accumulates on the film thickness monitor 15 exceeds the thickness that was determined in advance, the EUV monitor 11 and the reflector 11a are replaced. Further, when the EUV monitor 11 and the reflector 11a are replaced, there is a strong possibility that there will be a similar thick deposition of debris on the EUV collector mirror 6, and so it is best to replace the entire EUV collector mirror 6.

FIG. 6 is the third embodiment of this invention, which is an example of the constitution in the event that electrode disks that rotate are used in the discharge portion 9.

Now, in this figure, as in the embodiments described above, there is a optical axis that connects the high-temperature plasma P and the focal point of the EUV collector mirror 6, and an EUV monitor 11 is mounted on the output side of the EUV collector mirror 6, but a reflector 11a can be located as shown in FIG. 1 so that the EUV monitor 11 receives EUV radiation reflected by the reflector 11a.

The constitution of the EUV light source device of this embodiment is basically the same as that of the first embodiment described above, with the exception of the structure of the electrodes etc. in the discharge portion 9. As stated hereafter, however, the Sn or Li raw material that is the EUV generation fuel is liquefied by heating and supplied in that form. For that reason, there is no gas supply unit 7 or gas introduction port 2 as shown in the first embodiment described above; rather, there are first and second gas exhaust ports 4a, 4b and first and second gas exhaust units 8a, 8b. Further, there is a laser 24 to gasify the Sn or Li raw material.

The structure of the discharge portion 9 in the third embodiment shown in FIG. 6 is explained next.

The structure of the discharge portion 9 has a first main discharge electrode 23a made of a disk-shaped metal and a second main discharge electrode 23b similarly made of a disk-shaped metal placed to sandwich an insulator 23c. The center of the first main discharge electrode 23a and the center of the second main discharge electrode 23b are located on approximately the same axis, and the first main discharge electrode 23a and the second main discharge electrode 23b are fixed in positions separated by a gap the thickness of the insulator 23c. Here, the diameter of the second main discharge electrode 23b is larger than the diameter of the first main discharge electrode 23a. Further, the thickness of the insulator 23c, which is the gap separating the first main discharge electrode 23a and the second main discharge electrode 23b, is from about 1 mm to about 10 mm.

A rotary shaft 23d of a motor 21 is attached to the second main discharge electrode 23b. The rotary shaft 23d is attached to approximately the center of the second main discharge electrode 23b so that the center of the first main discharge electrode 23a and the center of the second main discharge electrode 23b are positioned approximately on the axis of the rotary shaft 23d.

The rotary shaft 23d is introduced into the chamber 1 by way of, for example, a mechanical seal. The mechanical seal allows the rotary shaft 23d to rotate while maintaining the reduced-pressure atmosphere of the chamber 1.

A first wiper 23e, comprising a carbon brush, for example, and a second wiper 23f are installed on one face of the second main discharge electrode 23b. The second wiper 23f is electrically connected to the second main discharge electrode 23b.

The first wiper 23e, on the other hand, is electrically connected to the first main discharge electrode 23a, through a through hole that penetrates the second main discharge electrode 23b, for example. Now, an insulation mechanism (not shown) is constituted so that there is no electrical breakdown between the second main discharge electrode 23b and the first wiper 23e that is electrically connected to the first main discharge electrode 23a.

The first wiper 23e and the second wiper 23f are electrical contacts that maintain an electrical connection while wiping; they are connected to the high-voltage generator 13. The high-voltage generator 13 supplies pulsed power between the first main discharge electrode 23a and the second main discharge electrode 23b by way of the first wiper 23e and the second wiper 23f.

In other words, even though the motor 21 rotates and the first main discharge electrode 23a and the second main discharge electrode 23b are rotated, pulsed power from the high-voltage generator 13 is applied between the first main discharge electrode 23a and the second main discharge electrode 23b by way of the first wiper 23e and the second wiper 23f.

Now, another structure can be used as long as it enables electrical connection between the first main discharge electrode 23a, the second main discharge electrode, and the high-voltage generator 13.

The high-voltage generator 13 applies pulsed power with a short pulse width between the first main discharge electrode 23a and the second main discharge electrode 23b, which constitute the load, by way of a magnetic pulse compression circuit that comprises a capacitor and a magnetic switch. The wiring from the high-voltage generator 13 to the first wiper 23e and the second wiper 23f is by way of insulated current introduction terminals, illustration of which has been omitted.

The current introduction terminals are mounted in the chamber 1, and allow an electrical connection from the high-voltage generator 13 to the first wiper 23e and the second wiper 23f while maintaining the reduced-pressure atmosphere of the chamber 1.

The peripheries of the first main discharge electrode 23a and the second main discharge electrode 23b, which are disk-shaped metal pieces, are constituted in an edge shape. As described hereafter, when power from the high-voltage generator 13 is applied between the first main discharge electrode 23a and the second main discharge electrode 23b, a discharge is generated between the edge-shaped portions of the two electrodes.

The electrodes reach a high temperature because of the high-temperature plasma, and so the first main discharge electrode 23a and the second main discharge electrode 23b are made of a metal with a high melting point, such as tungsten, molybdenum, or tantalum. Further, the insulator 23c is made of silicon nitride, aluminum nitride, or diamond, for example.

A groove 23g is made in the periphery of the second main discharge electrode 23b, and solid Sn or solid Li, which is the EUV generation fuel, is supplied to this groove 23g. For example, the raw material supply portion 22 liquidizes the raw material Sn or Li, which is the EUV generation fuel, by heating, and supplies it to the groove 23g of the second main discharge electrode 23b.

In the event that a liquefied raw material Sn or Li is supplied by the raw material supply portion 22, the liquefied raw material Sn or Li can be supplied by the raw material supply portion 22 in the form of droplets, for example, by rotating the EUV light source device as shown in FIG. 6 90° counter-clockwise, so that the raw material supply portion is on the left and the EVU radiation extraction portion is on the right.

Alternatively, the raw material supply unit can be constituted to supply solid Sn or Li to the groove 23g of the second main discharge electrode 23b periodically.

The motor 21 rotates in only one direction, and by means of operation of the motor 21, the rotary shaft 23d rotates and the second main discharge electrode 23b and the first main discharge electrode 23a attached to the rotary shaft 23d rotate in that direction. The Sn or Li placed in or supplied to the groove 23g of the second main discharge electrode 23b moves.

In the chamber 1, on the other hand, there is a laser 24 that generates a laser beam irradiating the Sn or Li moving to the EUV collector mirror 6 side. By way of an unillustrated laser beam aperture and a laser beam condensing means installed in the chamber 1, the laser beam from the laser 24 is condensed and irradiates the Sn or Li moving to the EUV collector mirror 6 side.

As stated above, the diameter of the second main discharge electrode 23b is larger than the diameter of the first main discharge electrode 23a. Therefore the laser beam can easily be aligned to pass by the side of the first main discharge electrode 23a and irradiate the groove 23b of the second main discharge electrode 23b.

The emission of EVU radiation from the electrodes happens as follows.

The laser beam from the laser 24 irradiates the Sn or Li. The Sn or Li irradiated by the laser beam is gasified between the first main discharge electrode 23a and the second main discharge electrode 23b, and a portion is ionized. Under these conditions, pulsed power from the high-voltage generator 13 with a voltage of about +20 kV to −20 kV is applied between the first and second main discharge electrodes 23a, 23b, at which time a discharge is generated between the edge-shaped portions on the periphery of the first main discharge electrode 23a and the second main discharge electrode 23b.

At that time, a large, pulsed current flows through the ionized portion of the gasified Sn or Li between the first main discharge electrode 23a and the second main discharge electrode 23b. Then, by means of Joule heating, a high-temperature plasma P is formed from the gasified Sn or Li in the vicinity between the two electrodes, and EVU radiation with a wavelength of 13.5 nm is emitted from the high-temperature plasma P.

The radiation passes through the foil trap 5, enters the EUV collector mirror 6, and is collected on the EUV extractor 10 that is the focal point; from the EVU extractor 10 it is emitted outside the EUV light source device.

An EUV monitor 11 is located on the optical axis on the radiation side of the EUV collector mirror 6, and as in the embodiments described above, there is a through hole through which EVU radiation passes on a structure on the optical axis between the discharge portion and EUV monitor 11. Of the EVU radiation emitted from the high-temperature plasma P, light on the optical axis of the EUV collector mirror 6 enters the EUV monitor 11.

The EUV monitor 11 monitors the incident EVU radiation, and an EUV intensity signal is output from the EUV monitor equipment 12 to the controller 14. On the basis of the input EUV light intensity signal, the controller 14 regulates the power supplied by the high-voltage generator 13 so that the EUV intensity is steady.

Claims

1. Extreme ultraviolet light source device having a vessel,an extreme ultraviolet radiation fuel supply means for supplying an extreme ultraviolet radiation fuel to the vessel,a heating and excitation means for heating and exciting the extreme ultraviolet radiation fuel and generating a high-temperature plasma,a collector mirror having a reflective surface that reflects and collects the extreme ultraviolet radiation emitted from the high-temperature plasma,an extreme ultraviolet radiation extractor formed in the vessel that extracts the collected light, and an exhaust means that exhausts the vessel, andan optical monitor that measures the intensity of the extreme ultraviolet radiation positioned for receiving a portion of the extreme ultraviolet radiation that enters the collector mirror from the high-temperature plasma that is not reflected by the reflective surface of the collector mirror.

2. Extreme ultraviolet light source device as claimed in claim 1, further comprising a reflector that reflects the radiation that is not reflected by the reflective surface of the collector mirror to the optical monitor that measures the intensity of the extreme ultraviolet radiation.

3. Extreme ultraviolet light source device as claimed in claim 2, wherein a film thickness monitor is mounted in the vessel to correct the output of the optical monitor.

4. Extreme ultraviolet light source device as claimed in claim 1, wherein a film thickness monitor is mounted in the vessel to correct the output of the optical monitor.

5. Method of generating extreme ultra violet radiation, comprising the steps of: introducing an extreme ultraviolet radiation fuel into a chamber,pulsing a high voltage from a high-voltage generator and applying the pulsed high-voltage between first and second main discharge electrodes, thereby producing a high-temperature plasma from discharge gas between the main discharge electrodes so as to emit extreme ultraviolet radiation,causing the extreme ultraviolet radiation emitted on a optical axis of an extreme ultraviolet radiation collector mirror to pass through a through-hole in a foil trap and through a through hole in a central support of the collector mirror, and reflecting it away from the optical axis by a reflector,directing the light reflected by the reflector into an extreme ultraviolet monitor, andusing a controller to adjust the power supplied from the high-voltage generator so that the extreme ultraviolet intensity is steady on the basis of the extreme ultraviolet intensity detected by the extreme ultraviolet monitor.