RU2496282C1 - Device and method for emission generation from discharge plasma - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in device and method for generation of emission from discharge plasma there performed is laser-induced discharge between the first and the second electrodes with energy input of pulse power source to discharge plasma and generation from discharge plasma of emission together with by-product in the form of neutral and charged debris. Based on selection of irradiation point of electrode with laser beam, geometry of electrodes and discharge outline, there formed is asymmetric discharge of mainly bent/banana shape, the own magnetic field of which has gradient immediately near discharge, which determines direction of predominant movement of discharge plasma flow from electrodes to area of less strong magnetic field.

EFFECT: increasing optic emission beam power.

8 cl, 4 dwg

Description

FIELD OF THE INVENTION

The invention relates to a device and method for generating high-power optical radiation, in particular in the field of extreme UV (EUV) or soft x-ray radiation (MRI) in the wavelength range from about 1 nm to 30 nm. The radiation source is a discharge plasma with a high pulse repetition rate. In addition to the radiation used, undesirable contaminant particles are generated in the discharge that can be deposited on the surfaces of the optical system located in the path of the used radiation, which requires suppressing the flow of polluting particles in the direction of radiation output to the optical collector and / or protecting the optical collector from the flow of polluting particles. The scope includes EUV lithography in the manufacture of integrated circuits or metrology.

BACKGROUND

The development of sources of short-wave radiation, in particular extreme UV (EUV) radiation corresponding to the effective reflection range of mirror optics, is stimulated by the creation of a technology for the production of integrated circuits with dimensions of structures having dimensions of only a few nm. Dense high-temperature plasma of a number of elements, in particular Sn, can be used to generate EUV radiation.

Plasma efficiently emitting EUV and / or MRI radiation can be obtained both by focusing the radiation of high-power lasers on a target and in a discharge. Discharge radiation sources are more efficient because the electrical energy stored in the capacitor bank is directly converted to the energy of the emitting plasma. Along with the emission of short-wave radiation, a stream of unwanted charged and neutral particles (debris) is generated from the plasma as a by-product, polluting the optical system for collecting short-wave radiation, which includes collector optics, which can consist of one or several mirrors located near the radiation source. If the particles have a high speed, they can damage the collector optics and, possibly, other parts of the lighting system, located after the radiation collection system.

In the most effective sources of EUV and MRI radiation, a vacuum spark type discharge is used. They also use laser radiation, but of low energy - only to initiate a discharge, and plasma is heated to the required ionization state by introducing the main energy into the discharge from a pulsed power source and magnetic compression of the plasma. A small region of the discharge channel in the region of its constriction is a pinch formed as a result of magnetic compression and is an effective source of short-wave radiation used by the optical system. To obtain a high radiation power, the discharge is carried out with a high repetition rate.

An optical collector, as a rule, is designed to use an axisymmetric diverging optical beam with a center (apex) in the region of the discharge pinch. The collector angle can reach to steradian. The part of the beam adjacent to the axis is not used. An optical radiation collection system may include a system for protecting it from polluting particles placed between the radiation source and the optical collector.

A device and method are known for generating radiation from a discharge plasma with an optical collector protection system including rotating and stationary foil traps separated by an intermediate space into which buffer gas is supplied, US Patent Application 20110002569. Due to this design, the plasma generation volume and volume, containing the collector can be maintained at low pressure, while the buffer gas in the intermediate space can be supplied at a higher pressure, which allows you to effectively slow down contaminating particles. Foil traps include structures with passages through which radiation passes directly into the optical collector, while contaminants predominantly condense on the walls of this structure without reaching the collector. In the presence of a rotating trap, slowly moving, but relatively large and heavy droplets, which are almost not deflected in collisions with atoms of the buffer gas and, therefore, passing through the foil trap, collide with the foils of the rotating foil trap and are mainly deposited on the surface of these foils.

The use of an optical radiation collection system provides for the use of other methods for reducing corpuscular radiation in its direction.

In some of the most powerful and efficient sources of EUV radiation, a discharge is carried out between two disk electrodes, each of which has a shaft with a rotation drive. As a rule, disk electrodes rotating around horizontal axes are partially immersed in molten metal baths used to cool electrodes subjected to extremely high thermal loads in the discharge zone with a high pulse repetition rate. At the same time, baths with liquid metal serve as sliding contacts for connecting a power source to rotating disk electrodes, as well as for supplying a liquid metal, in particular Sn, serving as a plasma-forming substance to the discharge zone. In such sources, the movement of polluting particles from the discharge zone occurs in directions that substantially coincide with the direction of the output of optical radiation. Effective suppression of the flow of polluting particles in the direction of the radiation collection system is possible due to the use of screens located near the electrode regions of the discharge and providing direct visibility of the optical collector from a small part of the discharge region in the pinch region. In high-power radiation sources, such screens should be subjected to approximately the same high thermal loads as the electrodes.

In a known device and method for generating radiation from a discharge plasma, US Pat. into a spherical angle, determined by the location and configuration of the electrodes, which at the same time serve as protective shields that impede movement in the direction of radiation emission of polluting particles produced in the electrode regions tyah discharge. In the aforementioned method and device, an effective reduction of the particle flow in the direction of the optical collector is achieved, since a significant part of the discharge, with the exception of the region in the pinch region, is located in the zone enclosed by electrodes that is not optically connected to the collector. However, these devices and methods do not suppress the flow of polluting particles, in particular plasma, from the discharge region in the pinch region, which is an effective radiation source and is in direct line of sight of the optical collector.

Also known is a device and method for generating radiation from a discharge plasma, in particular extreme ultraviolet or soft X-ray radiation, in which the first and second electrodes are jets of liquid metal, formed, respectively, by the first and second nozzles to which a switching power supply is connected, and one of the electrodes is irradiated with a focused laser beam, initiating a discharge between the first and second electrodes, in which, along with radiation, ytralnye and charged dust particles (debris), US Patent 7,557,366.

These device and method can highly efficiently obtain powerful EUV / MRI radiation in a large spatial angle. In this case, the velocity of the liquid metal in the jets serving as electrodes determines the component of the flow rate of polluting particles, in particular micro particles and droplets, in the direction of the jets, which avoids their contact with the optical collector.

However, this device and method also do not provide for suppressing the flow of polluting particles from the discharge region, which is an effective source of radiation.

SUMMARY OF THE INVENTION

The objective of the invention is to provide a device and method for generating EUV / MRI radiation from a discharge plasma, which effectively suppresses a plasma stream from a most efficiently emitting discharge region in a radiation beam, typically used by a radiation collection system and in direct line of sight of an optical collector.

The task can be achieved using the proposed device for generating radiation from a discharge plasma, in particular extreme ultraviolet or soft x-ray radiation containing

a pulsed power source, a first electrode, a second electrode irradiated by a focused laser beam, initiating a discharge between the first and second electrodes, producing, along with radiation, a neutral and charged contaminating particles (debris), as a by-product,

in which, due to the choice of the location of the electrode irradiation with the laser beam, the geometry of the electrodes and the discharge circuit, the laser-initiated discharge is asymmetric, having a predominantly curved / banana shape, while the gradient of the intrinsic magnetic field of the current of the asymmetric discharge directly in the vicinity of the discharge region determines the direction of the preferred the motion of the discharge plasma flow from the electrodes into the region of a less strong magnetic field, and the direction of the discharge from the discharge plasma is optical of radiation in a divergent beam, characterized by an optical axis essentially differs from the direction of preferential movement of the plasma discharge region.

It is preferable that at the site of irradiation with a laser beam, the normal to the surface of the second electrode, which determines the direction of the predominant propagation of the laser-induced plasma, differs significantly from the direction to the nearest point of the first electrode.

In an embodiment of the device, the first and second electrodes are made in the form of rotating disks coated with a liquid plasma-forming metal.

In another embodiment of the device, the first and second electrodes are jets of liquid metal, formed, respectively, by the first and second nozzles, to which a switching power supply is connected.

A method for generating radiation from a discharge plasma is to carry out a laser-initiated discharge between the first and second electrodes with the introduction of the energy of a pulsed power source into the discharge plasma and generation of radiation from the discharge plasma along with a by-product in the form of neutral and charged polluting particles, in which, by choosing the places where the electrode is irradiated with a laser beam, the geometry of the electrodes and the discharge circuit form an asymmetric discharge of a predominantly curved / banana shape, its own magnetically field is directly near the discharge has a gradient, which determines the direction of the preferential discharge plasma flow from the electrodes to less strong magnetic field

and carry out the output of radiation in the form of a diverging beam, characterized by an optical axis, in a direction substantially different from the direction of the predominant motion of the plasma from the discharge region.

In an embodiment of the method, the first and second electrodes are made in the form of disks with a rotation drive, and a plasma-forming liquid metal is supplied to the working surface of the electrodes.

In another embodiment of the method, the first and second electrodes are formed in the form of two jets of liquid metal.

The proposed device and method for generating radiation from a discharge plasma by choosing the location of the laser beam on the electrode, the geometry of the electrodes and the discharge circuit provide the creation of the own magnetic field of the discharge, which has the selected direction of the magnetic field gradient near the discharge. In turn, this determines the directional motion of the discharge plasma, including the most efficiently emitting region of the discharge plasma, intended for use by the radiation collection system and located in the line of sight of the optical collector.

As a result, when optical radiation is extracted from a discharge plasma in the form of a diverging beam characterized by an optical axis in a direction substantially different from the preferred direction of plasma motion, effective suppression of the plasma flow in the radiation beam from the most efficiently emitting region of the discharge is achieved. This is a highly effective solution to one of the most complex problems of suppressing the flow of polluting particles during the generation of radiation from a discharge plasma.

The creation of a plasma stream and neutral polluting particles carried away by it from the discharge region in the direction from the electrodes contributes to the rapid restoration of the electric strength of the discharge gap, which makes it possible to increase the repetition rate of discharge pulses and increase the radiation power from the discharge plasma.

The choice of the place of irradiation of the second electrode with the laser beam in this way, in which the normal to the surface of the second electrode, which determines the direction of the predominant propagation of the laser-induced plasma, differs significantly from the direction to the nearest point of the first electrode, contributes to the formation of an asymmetric discharge having a predominantly curved / banana shape.

The use in combination with the proposed method for generating radiation from a discharge plasma of known methods for protecting the optical collector from contaminating particles, such as screening the electrode regions of the discharge, the use of stationary and rotating foil traps partially filled with gas, allows the most complete solution to the problem of suppressing the flow of polluting particles in the beam radiation from a discharge plasma.

The embodiment of the proposed method and device of the first and second electrodes in the form of rotating disks coated with a liquid plasma-forming metal allows, along with highly effective suppression of the plasma flow in the radiation beam, to obtain high-power EUV / MRI radiation.

The implementation of the first and second electrodes in the form of two jets of liquid metal is another embodiment of the invention, in which, along with highly efficient suppression of the plasma stream and the neutral particles carried away by it, it is possible to achieve high-power EUV / MRI radiation.

All this allows, along with the receipt of powerful EUV / MRI radiation in large, up to π cf solid angle, to provide the selected direction of motion of the polluting particles generated in the discharge plasma as a by-product, and to realize the radiation output in a direction significantly different from the direction of the predominant distribution of the polluting particles.

Thus, along with the possibility of generating high-power EUV / MRI radiation, a highly efficient suppression of the plasma stream and neutral particles carried away by it from the discharge, including from its most efficiently emitting region, is ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings in the application are presented in a form sufficient to understand the principles of the invention, and in no way limit the scope of the present invention.

In the drawings, matching device elements have the same item numbers.

Figure 1 schematically shows a device for generating radiation from a discharge plasma between rotating electrodes.

On figa schematically shows a cross section in the discharge region of a device for generating radiation from a discharge plasma between electrodes in the form of jets of liquid metal.

On fig.2b presents a diagram of a device with an annular collector for visualizing plasma flows from the discharge.

Figure 2c shows an expanded collector for visualizing plasma flows after exposure to a radiation source with electrodes in the form of jets of liquid metal.

MODE FOR CARRYING OUT THE INVENTION

This description serves to illustrate the implementation of the invention, but not the scope of the present invention.

A device for generating radiation from a discharge plasma, in particular extreme ultraviolet or soft X-ray radiation, comprises a switching power supply 1, a first electrode 2, a second electrode 3, irradiated by a focused laser beam 4, initiating a discharge 5 between the first and second electrodes 2, 3, producing along with radiation as a by-product, neutral and charged pollutants (debris). In the device for receiving radiation from the discharge plasma by choosing the geometry of the electrodes and the location of the laser beam 4 of the electrode 3, the laser-initiated discharge 5 is asymmetric, having a predominantly curved / banana shape. In the immediate vicinity of discharge 5, the skin layers 2a, 3a of the electrodes 2, 3, located mainly on the concave side of the discharge, serve as current-carrying parts of the discharge circuit. Defined by the geometry of the discharge and the discharge circuit, the gradient of the intrinsic magnetic field 6 of the discharge current 5 near it has a distinguished direction: the region of a strong magnetic field is located on the concave side of the discharge. The gradient of the intrinsic magnetic field 6 of the discharge current determines the direction 7 of the predominant motion of the stream 8 of the discharge plasma and the neutral polluting particles carried away by it from the electrodes 2, 3 to the region of a weak magnetic field located on the curved side of the discharge. In this case, the direction of the output from the plasma of the discharge 5 of optical radiation in the form of a diverging beam 9 with a peak in the pinch region 5a and the optical axis 10 differs significantly from the direction 6 of the predominant motion of the plasma flow 7 from the discharge region.

According to the invention, it is preferable that at the site of irradiation with the laser beam 4, the normal to the surface of the second electrode 3, which determines the direction of the predominant propagation of the laser-induced plasma, differs significantly from the direction 12 to the nearest point of the first electrode 2.

In an embodiment of the device (Fig. 1), the first and second electrodes 2, 3 are made in the form of rotating disks coated with a thin layer of liquid plasma-forming metal. In this case, the current supply to the electrodes 2, 3 is carried out using the sliding contacts 13a, 13b. The electrodes are coated with a thin layer of liquid plasma-forming metal and supplied to the discharge region during the rotation of the electrodes, for example, by partially immersing the electrodes in baths with liquid metal, which are not shown in FIG. 1 for simplicity. Baths with liquid metal when connected to them, the power source 1 also serve as sliding contacts 13A, 13b.

In another embodiment of the device (Fig. 2a, 2b), the first and second electrodes 2, 3 are jets of molten metal formed, respectively, by the first and second nozzles 14, 15, to which a switching power supply is connected (Fig. 2b). For experimental determination of the nature of the distribution of the plasma flow from the discharge region 5, the device comprises an annular collector 16 for visualizing plasma flows, made in the form of a strip of metal foil surrounding the discharge (Fig.2b).

A method for generating radiation, in particular extreme ultraviolet or soft X-ray radiation from a discharge plasma, is implemented as follows.

In an embodiment of the method (Fig. 1), the first and second electrodes 2, 3 are made in the form of disks with a rotation drive, and a plasma-forming liquid metal is supplied to the working surface of the electrodes. Turn on the switching power supply 1, connected at the terminals A, B to the first and second electrodes 2, 3, as a result, the voltage rises on the electrodes 2, 3 and on the vacuum discharge gap between them. The focused beam 4 of the pulsed laser irradiates the electrode 3, evaporating and ionizing a small portion of the material on the surface of the electrode 3. It is preferable that at the site of the laser beam 4 normal 11 to the surface of the second electrode, which determines the direction of the predominant propagation of the laser-induced plasma, differs significantly from direction 12 to the nearest point of the first electrode 2. Close the discharge gap between the electrodes 2, 3 of the expanding laser-induced plasma. By choosing the geometry of the electrodes 2, 3 and the place where the laser beam 4 acts on the electrode 3, an asymmetric discharge 5 of predominantly curved / banana shape is formed, the intrinsic magnetic field 6 of which has a gradient directly near the discharge region 5, which determines the preferred direction 7 of the flow of the 8 discharge plasma from electrodes 2, 3 to the region of a less strong magnetic field 6. The directed action of electromagnetic forces on the discharge plasma 5 is due to the shape of the discharge, in which the magnitude of the magnetic field is higher than c in the bent side of the discharge channel. In addition, due to the choice of the geometry of the discharge circuit, the current leads to the discharge, which are the skin layers 2a, 3a of the electrodes 2, 3, are located mainly on the concave side of the discharge channel. All this increases the difference in the magnitude of the magnetic field 6 on opposite sides of the discharge channel, which increases the strength of the action of electromagnetic forces on the discharge plasma in the selected direction 7. During the discharge, the energy of the switching power supply 1 is introduced into the discharge plasma 5. By choosing the plasma-forming material of the electrode 2, in particular, tin, whose ion emission lines are in the desired region of the short-wavelength range of the spectrum, produce highly efficient EUV and / or MRI radiation from a small region of the discharge channel in Iona its necking - pinch 5a formed as a result of magnetic compression of the plasma. The output of radiation in the form of a diverging beam 9, having a vertex in the pinch region 5a and characterized by an optical axis 10, is carried out in the direction 9, 10, which differs significantly from the direction 7 of the predominant plasma motion from the discharge region 5. To obtain a high average radiation power, the discharge is carried out with a high pulse repetition rate.

It should also be noted that, in contrast to known analogues, for example, US Patent Application 20090168967, in the proposed device and method, the contaminating particles do not stay in the electrode region, but freely leave the discharge region in the selected direction, which provides highly efficient cleaning of the discharge region from plasma and neutral particles from the previous discharge pulse and provides the opportunity to increase the frequency of the discharge pulses. This makes it possible to increase the power of the EUV / MRI beam with highly efficient suppression of the plasma flow in the direction of output of the radiation beam.

In another embodiment of the method for generating radiation from a discharge plasma using the first and second nozzles 14, 15, to which a switching power supply 1 is connected, the first and second electrodes 2, 3 are formed in the form of two jets of liquid metal (Figs. 2a, 2b). Otherwise, this embodiment of the method for generating radiation from a discharge plasma does not differ from the above.

Figure 2b shows a diagram of a device with an annular collector 16 for visualizing plasma flows from a discharge, and Fig. 2c shows an annular collector 16 in expanded form after a long exposure to plasma flows and polluting particles generated in the discharge along with radiation. The image in FIG. 2c illustrates the positive result achieved by applying the proposed device and method in which the plasma exit from the discharge region is concentrated in a relatively narrow solid angle, about 2 sr.

Thus, the proposed device and method provide the generation of powerful radiation from a discharge plasma with highly efficient suppression of plasma flows from a discharge in a radiation beam, including from its most efficiently emitting region.

Designation List

1. switching power supply with terminals A, B connected to the electrodes

2. first electrode

2a. skin region of the first electrode

3. second electrode

3a. skin region of the second electrode

4. focused laser beam

5. discharge between the first and second electrodes 5a bit pinch

6. direction of the predominant motion of the plasma stream from the discharge region

7. plasma flow propagating from the discharge region

8. magnetic field lines

9. a divergent beam of radiation with a peak in the pinch region

10. optical axis of the radiation beam

11a, b sliding contacts of rotating electrodes

12. normal to the surface of the electrode at the site of irradiation with a laser beam

13. direction to the nearest point of the first electrode in the place of irradiation of the second electrode with a laser beam

14. first nozzle

15. second nozzle

16. An annular collector for visualizing plasma flows.

Claims (8)

1. Device for generating radiation from a discharge plasma, in particular extreme ultraviolet or soft x-ray radiation,
containing a pulsed power source, a first electrode, a second electrode irradiated by a focused laser beam, initiating a discharge between the first and second electrodes, which produces, along with radiation, a neutral and charged contaminating particles (debris) as a by-product,
in which due to the choice of the location of the electrode irradiation with a laser beam, the geometry of the electrodes and the discharge circuit
the laser-initiated discharge is asymmetric, having a predominantly curved / banana-like shape, while the gradient of the intrinsic magnetic field of the asymmetric discharge current directly in the vicinity of the discharge region has a distinguished direction, which determines the direction of the predominant movement of the discharge plasma flow from the electrodes to the region of a less strong magnetic field,
and the direction of the discharge from the plasma of the discharge of optical radiation in the form of a diverging beam, characterized by the magnitude of the spatial angle and the optical axis, differs significantly from the direction of the predominant motion of the plasma from the region of the discharge. 2. The device for generating radiation from a discharge plasma according to claim 1, wherein in the place of irradiation with a laser beam, the normal to the propagation surface of the laser-induced plasma differs significantly from the direction to the nearest point of the first electrode. 3. The device for generating radiation from a discharge plasma according to claim 1, in which the current-carrying parts of the discharge circuit adjacent to the discharge region, in particular the skin layers of the electrodes, are located mainly on the concave side of the discharge. 4. A device for generating radiation from a discharge plasma according to one of claims 1 to 3, in which the first and second electrodes are made in the form of rotating disks coated with a liquid plasma-forming metal. 5. A device for generating radiation from a discharge plasma according to one of claims 1 to 3, in which the first and second electrodes are jets of liquid metal, formed, respectively, by the first and second nozzles, to which a switching power supply is connected. 6. A method for generating radiation from a discharge plasma, in particular extreme ultraviolet or soft X-ray radiation, which consists in carrying out a laser-initiated discharge between the first and second electrodes by introducing the energy of a pulsed power source into the discharge plasma and generating radiation from the discharge plasma along with the by-product in the form of neutral and charged contaminating particles, in which as mmetrichny discharge preferably curved / shape of banana, its own magnetic field which is immediately adjacent the discharge has a gradient that defines a preferred direction preferential discharge plasma flow from the electrodes disposed in the convex part of the discharge region less strong magnetic field,
and using their own electromagnetic forces of the discharge, they pulsely act on the discharge plasma mainly in the selected direction,
and the output of radiation in the form of a diverging beam is carried out in a direction substantially different from the direction of the predominant motion of the plasma from the discharge region. 7. The method of generating radiation from a discharge plasma according to claim 6, wherein the first and second electrodes are made in the form of disks with a rotation drive, and a plasma-forming liquid metal is supplied to the working surface of the electrodes. 8. The method of generating radiation from a discharge plasma according to claim 6, wherein the first and second electrodes are formed in the form of two jets of liquid metal.

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