JP5757112B2 - Method for manufacturing plasma light source - Google Patents

Description

The present invention relates to a method of manufacturing flop plasma source for EUV radiation.

  Lithography using an extreme ultraviolet light source is expected for fine processing of next-generation semiconductors. Lithography is a technique for forming an electronic circuit by exposing a resist material to light and a beam by reducing and projecting them onto a silicon substrate through a mask on which a circuit pattern is drawn. The minimum processing dimension of a circuit formed by photolithography basically depends on the wavelength of the light source. Therefore, it is essential to shorten the wavelength of the light source for next-generation semiconductor development, and research for this light source development is underway.

  The most promising next generation lithography light source is an extreme ultra violet (EUV) light source, which means light in a wavelength region of about 1 to 100 nm. The light in this region has a high absorptance with respect to all substances, and a transmissive optical system such as a lens cannot be used. In addition, the optical system in the extreme ultraviolet region is very difficult to develop, and exhibits a reflection characteristic only at a limited wavelength.

  Currently, a Mo / Si multilayer reflector having a sensitivity of 13.5 nm has been developed, and if a lithography technique combining light of this wavelength and the reflector is developed, it is expected that a processing dimension of 30 nm or less can be realized. ing. Development of a lithography 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.

  The light source plasma generation can be broadly classified into a laser irradiation method (LPP: Laser Produced Plasma) and a gas discharge method (DPP: Discharge Produced Plasma) driven by a pulse power technique. 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.

The conversion efficiency (plasma conversion E. science: PCE) from the plasma to the radiation in the effective wavelength region (in-band) is expressed by the following equation (1).
P. C. E = (P _inband × τ) / E (1)
Here, P _inband is the EUV radiation output in the effective wavelength region, τ is the radiation duration, and E is the energy input to the plasma.

Xe, Sn, Li and the like are typical elements having a radiation spectrum in the effective wavelength region, and research has been progressed mainly on Xe in the early stages of development because of ease of experimentation and ease of handling. 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 effective wavelength 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)

JP 2000-509190 A, “Method and apparatus for generating X-ray radiation or extreme ultraviolet radiation”

  An EUV lithography light source is required to have a high average output, a small light source size, a small amount of scattered particles (debris), and the like. At present, the EUV emission amount is extremely low with respect to the required output, and increasing the output is one of the major issues. On the other hand, if the input energy is increased for increasing the output, the damage caused by the thermal load will be caused by the plasma generator and The lifetime of the optical system is reduced. 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).

  Room-temperature solid media such as Sn and Li have high spectral conversion efficiency, but the plasma generation is accompanied by phase changes such as melting and evaporation. Becomes larger. Therefore, the target supply and recovery system must be strengthened as well.

  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 (at least 1 μsec or more) in one shot. In other words, in order to develop a plasma light source having high conversion efficiency, it is necessary to restrain plasma in a temperature density state suitable for each target for 1 μsec or more to achieve stable EUV radiation.

  Here, a lithium compound (for example, LiH) is used as an interelectrode insulator as a plasma substance supply source, and the plasma substance is supplied by creeping discharge on the surface of the insulator.

However, in this case, the lithium compound is formed into a solid by sintering from the powder, but the lithium compound sintered body has poor processability and high-precision processing is difficult, and a gap is generated at the contact portion with the electrode portion. There was a case.
Further, in such a case, the gap is not always generated uniformly in the circumferential direction, and there is a problem in that variations in individual sintered parts may occur.

  Therefore, there has been a problem that the stability and reproducibility of the interelectrode discharge may not be maintained at a certain level.

The present invention has been developed to solve such problems. An object of the present invention is to provide a method of manufacturing pulp plasma source having a dielectric between not causing gap electrode in the contact portion with the electrode portion.

According to the reference example , a pair of coaxial electrodes arranged opposite to each other;
A discharge environment holding device for supplying a plasma medium into the coaxial electrode and holding the plasma medium at a temperature and pressure suitable for generating plasma;
A plasma light source comprising: a voltage applying device that applies a discharge voltage having a polarity reversed to each coaxial electrode;
Each coaxial electrode has a rod-shaped center electrode extending on a single axis, a tubular guide electrode that surrounds the center electrode with a certain interval, and is positioned between and insulates between the center electrode and the guide electrode It consists of a ring-shaped insulator,
A plasma light source is provided, wherein the insulator is pressed by a hot press and is formed by closely contacting the center electrode and the guide electrode.

  The center electrode and the guide electrode are made of tungsten or graphite.

Moreover, according to the present invention, a pair of coaxial electrodes arranged opposite to each other are prepared,
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;
Apply a discharge voltage with reversed polarity to each coaxial electrode,
A method of manufacturing a plasma light source, comprising: forming a tubular discharge between a pair of coaxial electrodes to contain plasma in an axial direction;
Each coaxial electrode has a rod-shaped center electrode extending on a single axis, a tubular guide electrode that surrounds the center electrode with a certain interval, and is positioned between and insulates between the center electrode and the guide electrode It consists of a ring-shaped insulator,
There is provided a method of manufacturing a plasma light source, characterized in that the insulator is pressed by hot pressing so that the center electrode and the guide electrode are in close contact with each other.

  According to the above invention, by using tungsten or graphite as the interelectrode insulator, no gap is generated at the contact portion with the electrode portion, so that the stability and reproducibility of the discharge characteristics can be improved.

It illustrates the principle of a flop plasma source. It is a conceptual diagram of the hot press with respect to the insulator by this invention. It is an operation explanatory view of the flop plasma source.

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

Figure 1 is a principle diagram of a flop plasma source.
In this figure, flop plasma light source 10 is provided with coaxial electrodes 11 of the pair, the discharge environment holding unit 20, and a voltage applying device 30.

The pair of coaxial electrodes 11 are arranged opposite to each other with the symmetry plane 1 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 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.

The discharge environment holding device 20 holds the coaxial electrode 11 at a temperature and pressure suitable for plasma generation in the coaxial electrode 11.
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.
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).
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 11 simultaneously.
This configuration flop plasma light source to form a tubular discharge (described later) is adapted to contain the plasma in the axial direction between the coaxial electrodes 11 of the pair.

FIG. 2 is a conceptual diagram of hot pressing on an insulator according to the present invention.
In this figure, 17 is a case for hot pressing, and 18 is a pressure applying body for hot pressing.

When the powder insulator 16 is formed into a solid, the center electrode 12 and the guide electrode 14 are housed in the hot press case 17 together with the insulator 16, and the insulator 16 and the center electrode are opposite from the coaxial electrode 11. 12 and the guide electrode 14 are integrally sintered by hot pressing under high temperature and high pressure (about 600 ° C., about 100 atm, about 1 hour) by the pressure applying body 18 for hot pressing.
By sintering the powder of the insulator 16 by such a method, the powder insulator 16 is formed into a solid without generating a gap between the insulator 16 and the center electrode 12 or the guide electrode 14. Can do.

Further, in such a case, by changing the center electrode 12 and the guide electrode 14 to a high melting point material such as graphite or tungsten, it is possible to prevent thermal deformation even when hot pressing is performed under high temperature and high pressure. .
In addition to tungsten or graphite, tantalum or the like can be used.

The hot press case 17 and the hot press pressure imparting body 18 are desirably made of a high melting point material such as graphite so as to withstand hot pressing under high temperature and pressure.
The center electrode 12 and the insulator 16 may be designed, for example, with D1 in FIG. 2 of about 10 mm, D2 of about 5 mm, and W1 of about 10 mm.

  In order to connect the center electrode 12 to the hot press case 17, a screw portion (not shown) may be provided at the tip of the center electrode 12 and connected to the hot press case 17.

Figure 3 is an operation explanatory view of the flop plasma source. In this figure, (A) shows the occurrence of a sheet discharge, (B) shows the movement of the sheet discharge, (C) shows the formation of plasma, and (D) shows the formation of the plasma confined magnetic field. .
The operation of the plasma light source of the present invention will be described below with reference to this figure.

In the plasma light source , the pair of coaxial electrodes 11 described above are arranged to face each other, the discharge environment holding device 20 holds the inside of the coaxial electrode 11 at a temperature and pressure suitable for plasma generation, and the voltage application device 30 sets each coaxial shape. A discharge voltage whose polarity is reversed is applied to the electrode 11.

  As shown in FIG. 3A, by applying this voltage, 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 respectively. The planar discharge 2 is a planar discharge current that spreads two-dimensionally.

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 (−).

  Further, in the present invention, since the insulator 16 is made of an insulating compound that is solid at room temperature and has a plasma medium as a main component, the surface of the insulating compound is vaporized by the planar discharge 2 to form the plasma medium 6 coaxially. Supplied between the electrodes.

  As shown in FIG. 3B, 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. 3C, 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. 3D, the planar discharge 2 is transformed into a tubular discharge 4 that discharges between a pair of opposed center electrodes 12 and between a 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 in the figure is formed, and the plasma 3 can be confined 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.

  In addition, this invention is not limited to embodiment mentioned above, is shown by description of a claim, and also includes all the changes within the meaning and range equivalent to description of a claim.

1 symmetry plane, 2 planar discharge, 3 plasma,
4 Tubular discharge, 5 plasma confined magnetic field,
6 plasma medium, 8 plasma light (EUV light),
10 plasma light source, 11 coaxial electrode,
12 center electrode, 12a recessed hole,
14 guide electrode, 16 insulator (insulating compound),
17 Hot press case, 18 Hot press pressure applicator,
20 discharge environment holding device, 30 voltage application device,
32 Positive voltage source, 34 Negative voltage source, 36 Trigger switch

Claims (3)

A pair of coaxial electrodes disposed opposite each other;
A discharge environment holding device for supplying a plasma medium into the coaxial electrode and holding the plasma medium at a temperature and pressure suitable for generating plasma;
A voltage application device that applies a discharge voltage with the polarity reversed to each coaxial electrode; and
Each coaxial electrodes includes a centered electrode, plasma light source has a guide electrode surrounding said central electrode spaced, the insulation body you insulation therebetween located between the center electrode and the guide electrode A manufacturing method of
The guide electrode and the center electrode are housed in a hot press case, and a powder insulator is disposed between the guide electrode and the center electrode located inside the guide electrode, and hot With the press case and the hot press pressure applicator sandwiching the powder insulator in the axial direction of the central electrode, the hot press pressure applicator pressurizes the powder insulator, A method of manufacturing a plasma light source , comprising: hot pressing an insulator, the center electrode, and the guide electrode together to sinter the powder insulator . The method for manufacturing a plasma light source according to claim 1, wherein the center electrode and the guide electrode are made of tungsten or graphite. The central electrode of each coaxial electrode is a rod extending on a single axis;
The guide electrode of each coaxial electrode is a tube that surrounds the center electrode with a constant interval,
The method of manufacturing a plasma light source according to claim 1, wherein the insulator has a ring shape .