JP5621979B2 - Plasma light source and plasma light generation method - Google Patents

Description

  The present invention relates to a plasma light source and a method for generating plasma light for EUV radiation.

  Light in the wavelength region of approximately 1 to 100 nm is called extreme ultraviolet (EUV) light, and is abbreviated as “EUV light” or “plasma light” in the present application.

  EUV light (plasma light) has a high absorptivity with respect to all substances, and a transmission optical system such as a lens cannot be used. For this reason, a reflective optical system is used for EUV light, but the light in this region has a characteristic that exhibits a reflection characteristic only at a limited wavelength.

  Currently, a Mo / Si multilayer reflector having sensitivity at 13.5 nm in the wavelength region of EUV light has been developed. Therefore, a processing dimension of 30 nm or less can be realized by a lithography technique that combines this reflecting mirror and light having a wavelength of 13.5 nm. Therefore, development of an EUV light source with a wavelength of 13.5 nm is urgently required to realize further microfabrication technology, and radiation from a high energy density plasma has attracted attention.

  Light source plasma generation can be broadly classified into laser irradiation (LPP: Laser Produced Plasma) and gas discharge (DPP: Discharge Produced Plasma) driven by pulse power technology. DPP has the advantage that the input power is directly converted into plasma energy, so that it has an advantage in conversion efficiency compared to LPP, and the apparatus is small in size and low in cost.

Typical examples of elements having a radiation spectrum in the effective wavelength region include Xe, Sn, Li, and the like. Conventionally, research has been focused on Xe. However, in recent years, Sn has been attracting attention and research is being promoted because of its high output and high efficiency. In addition, expectation for hydrogen-like Li ions (Li ²⁺ ) having just a Lyman-α resonance line in the in-band region is increasing.

The radiation spectrum from a high-temperature, high-density plasma is basically determined by the temperature and density of the target material. According to the calculation result of the atomic process of the plasma, the electron in the case of Xe, Sn is used to make the plasma in the EUV radiation region. The optimum temperature and electron density are several tens of eV and about 10 ¹⁸ cm ⁻³ , respectively, and in the case of Li, about 20 eV and 10 ¹⁸ cm ⁻³ are optimum.

  The plasma light source described above is disclosed in Non-Patent Documents 1 and 2 and Patent Document 1.

Hiroto Sato et al., “Discharge Plasma EUV Light Source for Lithography”, OQD-08-28 Jeroen Jonkers, “High power extreme-violet (EUV) light sources for future lithography”, Plasma Sources Science and Technology 16 (Science 16)

Japanese Patent Application Laid-Open No. 2004-226244, “Extreme Ultraviolet Light Source and Semiconductor Exposure Apparatus”

  An EUV light source is required to have a high average output and a small light source size. At present, the EUV emission amount is extremely low with respect to the required output, and high output is one of the major issues. However, if the input energy is increased to increase the output, the damage due to the heat load leads to a decrease in the lifetime of the plasma generator and the optical system. Therefore, high energy conversion efficiency is indispensable to satisfy both high EUV output and low heat load.

  In the initial stage of plasma formation, in addition to consuming a lot of energy for heating and ionization, high-temperature and high-density plasma that emits EUV generally expands rapidly, so the radiation duration τ is extremely short. . Therefore, in order to improve the conversion efficiency, it is important to maintain the plasma in a high temperature and high density state suitable for EUV radiation for a long time (on the order of μsec).

  The radiation time of the current general EUV plasma light source is about 100 nsec, and the output is extremely insufficient. In order to achieve both high conversion efficiency and high average output for industrial applications, it is necessary to achieve an EUV radiation time of several μsec per shot. In other words, in order to develop a plasma light source having high conversion efficiency, it is necessary to achieve stable EUV radiation by constraining plasma in a temperature density state suitable for each target for several μsec (at least 1 μsec or more).

  The present invention has been developed to solve the above-described problems. That is, an object of the present invention is to provide a plasma light source and a plasma light generation method capable of stably generating plasma light for EUV radiation for a long time (on the order of μsec).

According to the present invention, a plurality of coaxial electrode pairs having a pair of coaxial electrodes arranged opposite to each other and confining plasma in the axial direction at an intermediate position thereof,
A discharge environment holding device for supplying a plasma medium to each coaxial electrode pair and holding the inside of each coaxial electrode pair at a temperature and pressure suitable for plasma generation;
A voltage applying device that applies a discharge voltage having a polarity reversed to each coaxial electrode of each coaxial electrode pair, and
The plurality of coaxial electrode pairs are arranged to cross each other at the intermediate position,
A plasma light source is provided in which the voltage application device applies a discharge voltage having a phase shift to the coaxial electrodes of the coaxial electrode pairs.

According to an embodiment of the present invention, each of the coaxial electrodes includes a rod-shaped center electrode extending on a single axis, a tubular guide electrode surrounding the center electrode at a predetermined interval, and the center electrode and the guide. It consists of a ring-shaped insulator located between the electrodes and insulating between them,
The center electrodes of the pair of coaxial electrodes are positioned on the same axis and are symmetrically spaced from each other at a constant interval.

Further, according to the present invention, a plurality of coaxial electrode pairs having a pair of coaxial electrodes arranged opposite to each other and confining plasma in the axial direction at an intermediate position thereof are arranged so as to cross each other at the intermediate position,
Supplying a plasma medium to each of the coaxial electrode pairs and maintaining the inside of each coaxial electrode pair at a temperature and pressure suitable for plasma generation;
Applying a discharge voltage whose phase is shifted to each coaxial electrode of each coaxial electrode pair with the polarity reversed,
A planar discharge out of phase is generated in the coaxial electrodes of each coaxial electrode pair, a single plasma is formed at the intermediate position by the planar discharge, and then the planar discharge is converted into a pair of coaxial electrodes. There is provided a plasma light generation method characterized by forming an out of phase magnetic field confining the plasma at the intermediate position by switching to a tubular discharge in between.

  According to the apparatus and method of the present invention, a pair of coaxial electrodes disposed opposite to each other are provided, and a plurality of coaxial electrode pairs for confining plasma in the axial direction are provided at intermediate positions between the pair of coaxial electrodes. A planar discharge current (planar discharge) is generated, and a single plasma is formed by the planar discharge at an intermediate position opposed to each coaxial electrode, and then the planar discharge is performed between a pair of coaxial electrodes. Since a magnetic field (magnetic bin) for confining the plasma is formed by switching to the tubular discharge, plasma light for EUV radiation can be stably generated for a long time (on the order of μsec).

The plurality of coaxial electrode pairs are arranged so as to cross each other at the intermediate position, and the voltage application device applies a discharge voltage having a phase shift to the coaxial electrode of each coaxial electrode pair. A confined magnetic field out of phase can be formed in the position plasma by a plurality of coaxial electrode pairs.
Therefore, since the confined magnetic field always acts on the plasma, even with a light element such as lithium, no plasma loss occurs when the discharge current is reversed, and high EUV output and high conversion efficiency can be realized.

1 is an embodiment diagram of a plasma light source according to the present invention. FIG. It is operation | movement explanatory drawing of the plasma light source of FIG. It is explanatory drawing of the discharge current by this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

FIG. 1 is a diagram showing an embodiment of a plasma light source according to the present invention.
In this figure, the plasma light source of the present invention includes a plurality of coaxial electrode pairs 10, a discharge environment holding device 20, and a voltage application device 30.

  In this example, there are two pairs of coaxial electrodes 10. Each pair of coaxial electrodes 10 has a pair of coaxial electrodes 11 arranged to face each other, and the plasma 3 is confined in the axial direction at an intermediate position 11a. The coaxial electrode pair 10 is not limited to two pairs, and may be three or more pairs.

  In each coaxial electrode pair 10, a pair of coaxial electrodes 11 are opposed to each other with the intermediate position 11 a as the center. Each coaxial electrode 11 includes a rod-shaped center electrode 12, a tubular guide electrode 14, and a ring-shaped insulator 16.

  The rod-shaped center electrode 12 is a conductive electrode extending on a single axis ZZ. In this example, a concave hole 12a is provided on the end face of the center electrode 12 facing the symmetry plane 1 so as to stabilize the planar discharge current 2 and the tubular discharge 4 described later. This configuration is not essential, and the end face of the center electrode 12 facing the symmetry plane 1 may be arcuate or flat.

  The tubular guide electrode 14 surrounds the central electrode 12 with a certain interval, and holds a plasma medium therebetween. The plasma medium is preferably a gas such as Xe, Sn, or Li. Further, the end face of the guide electrode 14 facing the symmetry plane 1 may be arcuate or flat.

The ring-shaped insulator 16 is a hollow cylindrical electrical insulator positioned between the center electrode 12 and the guide electrode 14 and electrically insulates between the center electrode 12 and the guide electrode 14.
The shape of the insulator 16 is not limited to this example, and may be other shapes as long as the center electrode 12 and the guide electrode 14 are electrically insulated.

  In the pair of coaxial electrodes 11 described above, the center electrodes 12 are positioned on the same axis ZZ and are symmetrically spaced apart from each other.

In FIG. 1, the two pairs of coaxial electrodes 10 described above are arranged so as to cross each other at an intermediate position 11a. In this example, the intersection is an arrangement in which the axes of the two coaxial electrode pairs 10 are orthogonal to each other in the same plane (a plane parallel to the paper surface).
The present invention is not limited to this intersection, and three sets of coaxial electrode pairs 10 may be three-dimensionally arranged orthogonally. Further, the present invention is not limited to the orthogonal arrangement, and two or more pairs of coaxial electrode pairs 10 may be crossed two-dimensionally or three-dimensionally at an arbitrary angle at the intermediate position 11a.

The discharge environment holding device 20 supplies a plasma medium to each coaxial electrode pair 10 and holds the inside of each coaxial electrode pair 10 at a temperature and pressure suitable for plasma generation.
The discharge environment holding device 20 can be constituted by, for example, a vacuum chamber, a temperature controller, a vacuum device, and a plasma medium supply device. This configuration is not essential, and other configurations may be used.

  The voltage application device 30 applies a discharge voltage with the polarity reversed to each coaxial electrode 11 of each coaxial electrode pair 10. In this example, the voltage application device 30 includes a positive voltage source 32, a negative voltage source 34, and a trigger switch 36.

The positive voltage source 32 applies a positive discharge voltage higher than that of the guide electrode 14 to the center electrode 12 of the coaxial electrode 11 on one side (left side in this example).
The negative voltage source 34 applies a negative discharge voltage lower than that of the guide electrode 14 to the center electrode 12 of the other coaxial electrode 11 (right side in this example).
Each of the positive voltage source 32 and the negative voltage source 34 has a capacitor therein, and stores and reuses a discharge current at the time of discharge.

The trigger switch 36 simultaneously activates the positive voltage source 32 and the negative voltage source 34 to apply positive and negative discharge voltages to the respective coaxial electrodes 12 simultaneously.
With this configuration, the plasma light source of the present invention forms a tubular discharge (described later) between the pair of coaxial electrodes 11 to confine the plasma in the axial direction.

FIG. 2 is an operation explanatory view of the plasma light source of FIG. This figure shows the operation of each of the two coaxial electrode pairs 10 of FIG.
In this figure, (A) shows the occurrence of a planar discharge, (B) shows the movement of the planar discharge, (C) shows the formation of the plasma, and (D) shows the formation of the plasma confinement magnetic field.
Hereinafter, the plasma light generation method of the present invention will be described with reference to this drawing.

  In the plasma light generation method of the present invention, a pair of coaxial electrodes 11 constituting the above-described coaxial electrode pair 10 are arranged opposite to each other, a plasma medium is supplied into the coaxial electrode 11 by a discharge environment holding device 20, and plasma is generated. The discharge voltage with the polarity reversed is applied to each coaxial electrode 11 by the voltage application device 30.

As shown in FIG. 2A, a planar discharge current (hereinafter referred to as planar discharge 2) is generated on the surface of the insulator 16 in the pair of coaxial electrodes 11 by applying this voltage. The planar discharge 2 is a planar discharge current that spreads two-dimensionally, and is referred to as a “current sheet” in the examples described later.
At this time, the center electrode 12 of the left coaxial electrode 11 is applied with a positive voltage (+), the guide electrode 14 is applied with a negative voltage (−), and the center electrode 12 of the right coaxial electrode 11 is applied with a negative voltage (−). The guide electrode 14 is applied to a positive voltage (+).
Alternatively, both guide electrodes 14 may be grounded and held at 0 V, one center electrode 12 may be applied to a positive voltage (+), and the other center electrode 12 may be applied to a negative voltage (−).

  As shown in FIG. 2 (B), the planar discharge 2 moves in a direction (direction toward the center in the figure) discharged from the electrode by the self magnetic field.

  As shown in FIG. 2 (C), when the sheet discharge 2 reaches the tips of the pair of coaxial electrodes 11, the plasma medium 6 sandwiched between the pair of sheet discharges 2 becomes high density and high temperature. A single plasma 3 is formed at an intermediate position (symmetric surface 1 of the center electrode 12) of the coaxial electrodes 11 facing each other.

  Further, in this state, the pair of opposed center electrodes 12 are a positive voltage (+) and a negative voltage (−), and similarly, the pair of opposed guide electrodes 14 are also a positive voltage (+) and a negative voltage. Since (−), as shown in FIG. 2D, the planar discharge 2 is applied to the tubular discharge 4 that discharges between the pair of opposed center electrodes 12 and between the pair of opposed guide electrodes 14. It can be reconnected. Here, the tubular discharge 4 means a hollow cylindrical discharge current surrounding the axis ZZ.

When this tubular discharge 4 is formed, a plasma confinement magnetic field (magnetic bin) indicated by reference numeral 5 is formed in the figure, and the plasma 3 can be sealed in the radial direction and the axial direction.
That is, the central portion of the magnetic bin 5 is large due to the pressure of the plasma 3 and both sides thereof are small, and a magnetic pressure gradient in the axial direction toward the plasma 3 is formed. The plasma 3 is constrained to an intermediate position by this magnetic pressure gradient. Furthermore, the plasma 3 is compressed (Z pinch) in the center direction by the self-magnetic field of the plasma current, and the restraint by the self-magnetic field also acts in the radial direction.

  In this state, if the energy corresponding to the emission energy of the plasma 3 is continuously supplied from the voltage application device 30, the plasma light 8 (EUV) can be stably generated for a long time with high energy conversion efficiency.

  FIG. 3 is an explanatory diagram of the discharge current according to the present invention. In this figure, (A) is a change in discharge current by a single voltage application device 30, (B) is a diagram showing a phase shift of the discharge current in two pairs of coaxial electrodes 10, and (C) is three sets. 3 is a diagram showing a phase shift of a discharge current in a coaxial electrode pair 10. FIG.

  In discharging by the voltage application device 30, electricity accumulated in the capacitor is instantaneously discharged by the trigger switch 36, and excess electricity is recharged in the capacitor. Therefore, as shown in FIG. 3A, the change in the discharge current by the single voltage application device 30 is attenuated while repeating positive and negative at a constant period (2π).

  The voltage application device 30 of the present invention applies a discharge voltage whose phase is shifted to the coaxial electrode 11 of each coaxial electrode pair 10. This phase shift is preferably half of the period (π) in the case of two pairs of coaxial electrodes 10 and preferably in one third (2π / 3) of the period in the case of three pairs of coaxial electrodes 10. is there.

As a result, out-of-phase discharge currents flow through the coaxial electrodes 11 of each coaxial electrode pair 10. That is, by applying a discharge voltage that is out of phase, a discharge current that is out of phase flows through the coaxial electrode 11 as shown in FIGS.
Therefore, a phased discharge 2 is generated in the coaxial electrode 11 of each coaxial electrode pair 10, and a single plasma 3 is formed at the intermediate position 11 a by this planar discharge 2. By switching to the tubular discharge 4 between the pair of coaxial electrodes, an out-of-phase magnetic field for confining the plasma 3 in the intermediate position 11a can be formed.

  According to the apparatus and method of the present invention described above, a pair of coaxial electrodes 11 arranged opposite to each other are provided, and a pair of coaxial electrodes 11 are caused to generate planar discharge currents (planar discharge 2), respectively. A single plasma 3 is formed at the opposite intermediate position of each coaxial electrode 11 by the planar discharge 2, and then the planar discharge 2 is connected to a tubular discharge 4 between a pair of coaxial electrodes to confine the plasma 3. Since the plasma confinement magnetic field 5 (magnetic bin 5) is formed, plasma light for EUV radiation can be stably generated for a long time (on the order of μsec).

Further, the plurality of coaxial electrode pairs 10 are arranged so as to cross each other at the intermediate position 11a, and the voltage application device 30 applies a discharge voltage whose phase is shifted to the coaxial electrode 11 of each coaxial electrode pair 10, A confined magnetic field 5 whose phase is shifted by a plurality of coaxial electrode pairs 10 can be formed in the plasma 3 at the intermediate position 11a.
Therefore, since the time period in which the discharge current is reduced to zero is eliminated and the confinement magnetic field 5 always acts on the plasma 3, even with a light element such as lithium, no plasma loss occurs when the discharge current is reversed, and the EUV output is high. Output and high conversion efficiency can be realized.

  In addition, this invention is not limited to embodiment mentioned above, Of course, a various change can be added in the range which does not deviate from the summary of this invention.

1 symmetry plane, 2 sheet discharge (current sheet), 3 plasma,
4 tubular discharge, 5 plasma confinement magnetic field, 6 plasma medium,
8 Plasma light (EUV),
10 Coaxial electrode pair, 11 Coaxial electrode, 11a Intermediate position,
12 center electrode, 12a recessed hole,
14 guide electrodes, 16 insulators,
20 discharge environment holding device, 30 voltage application device,
32 positive voltage source, 34 negative voltage source, 36 trigger switch,

Claims (3)

A plurality of coaxial electrode pairs having a pair of coaxial electrodes arranged opposite to each other and confining plasma in the axial direction at an intermediate position thereof;
A discharge environment holding device for supplying a plasma medium to each coaxial electrode pair and holding the inside of each coaxial electrode pair at a temperature and pressure suitable for plasma generation;
A voltage applying device that applies a discharge voltage having a polarity reversed to each coaxial electrode of each coaxial electrode pair, and
The plurality of coaxial electrode pairs are arranged to cross each other at the intermediate position,
The plasma light source, wherein the voltage application device applies a discharge voltage having a phase shift to the coaxial electrode of each coaxial electrode pair. Each of the coaxial electrodes is a rod-shaped center electrode extending on a single axis, a tubular guide electrode that surrounds the center electrode at a predetermined interval, and is located between the center electrode and the guide electrode and insulated between them. A ring-shaped insulator that
2. The plasma light source according to claim 1, wherein the central electrodes of the pair of coaxial electrodes are located on the same axis and are symmetrically spaced apart from each other. A plurality of coaxial electrode pairs having a pair of coaxial electrodes arranged opposite to each other and confining plasma in the axial direction at an intermediate position between the coaxial electrode pairs at the intermediate position;
Supplying a plasma medium to each of the coaxial electrode pairs and maintaining the inside of each coaxial electrode pair at a temperature and pressure suitable for plasma generation;
Applying a discharge voltage whose phase is shifted to each coaxial electrode of each coaxial electrode pair with the polarity reversed,
A planar discharge out of phase is generated in the coaxial electrodes of each coaxial electrode pair, a single plasma is formed at the intermediate position by the planar discharge, and then the planar discharge is converted into a pair of coaxial electrodes. A method of generating plasma light, characterized by forming an out of phase magnetic field confining the plasma at the intermediate position by switching to a tubular discharge in between.