JP4873443B2 - Fine particle generation method and apparatus - Google Patents

Description

  The present invention relates to a method for generating fine particles and a radiation light source using the same.

  There is a method for generating fine particles by irradiating a solid target with a pulse laser (see Non-Patent Document 1 below). This can be explained by the fact that the heated and melted solid surface is shaken by the pressure of the plasma generated by the pulse laser and is generated as droplets. The size of the fine particles generated by this mechanism has a wide distribution from several tens of nanometers to several tens of micrometers centering on several micrometers.

There is also a known method of forming ultrafine particles of several nm to several tens of nm by agglomerating in a vapor aggregating gas vaporized from a solid target heated to an ultrahigh temperature of several thousand to several tens of thousands of degrees by laser irradiation. (See Non-Patent Document 2 below).
Z. Toth et al. Appl. Surface Science, 138-139, 130-134, (1999) H. Kroto, et.al. Nature, 318, p162, (1985)

  There are several applications that require fine particles with particle sizes from sub-μm to several μm. For example, when extreme ultraviolet light with a wavelength of sub-nm to several tens of nm is generated in a plasma light source, the ultimate conversion efficiency is obtained with a target with a diameter of several hundred μm, a uniform distribution, and a solid density of about 1/10000 It is done. This can be realized by supplying sub-μm fine particle groups.

  However, the fine particles generated by the above-described plasma bombardment have a wide particle size distribution from several tens of nm to several μm, and the required proportion of fine particles of sub-μm cannot be increased. Further, the solid surface heated and melted by the laser is strongly shaken by a reaction when the plasma generated on the surface is scattered. As a result, a very small part of the melted solid surface is broken and fine particles are released, so that the size of the fine particles cannot be controlled. In addition, since only a part of the melted material is scattered as fine particles, there is a problem that the amount of fine particles generated by one shot of the pulse laser is not sufficient. Further, the method of aggregating the vaporized substance in the air has a problem that it is not easy to make the fine particle diameter several tens nm or more.

  In order to solve the above problems of the prior art, first, a material to be finely divided is deposited on a transparent substrate by vapor deposition, plating, adhesion, or other methods, and a laser having a wavelength transparent to the substrate is formed on the substrate. There is provided a method for generating fine particles, characterized in that the adhered substance is released as fine particles by irradiation from the side.

  Second, the present invention provides a fine particle generation method characterized in that a material adhered on a substrate is subdivided into a lattice shape or other shapes.

  Thirdly, the present invention provides a fine particle generation method characterized by irradiating a substrate with a subdivided pattern obtained by shaping a beam pattern of a laser to be irradiated by means of interference, diffraction, or image transfer.

  Fourth, the present invention provides a method for generating fine particles, characterized in that a transparent substrate on which a substance to be made fine is attached is continuously moved and supplied in a tape shape or a plate shape.

  When a substance attached to the transparent substrate is heated with a pulse laser from the substrate side, the substance becomes high-temperature plasma at the interface with the substrate, and high pressure is generated. By this pressure, the adhered substance can be peeled off from the substrate. By controlling the film thickness of the substance attached to the substrate, the amount of the substance generated can be controlled.

  The thin film peeled off from the substrate cannot move as a large-area thin film, and is pulverized with a high pressure for peeling, and then becomes spherical with surface tension.

  By controlling the thickness of the thin film, the pressure at the time of peeling, etc., the size to be crushed can be controlled to some extent, and the particle size can be controlled. If the film to be peeled is cut in advance, the particle size can be controlled with higher accuracy.

  The particle diameter can be controlled by forming a laser beam pattern by interference, diffraction, or image transfer, instead of making a cut in the film.

  If a long tape is used as a substrate, it can be supplied with high repetition. Highly repetitive supply is possible by using a rigid rotating disk as a substrate.

  In the present invention, fine particles are generated by irradiating a deposited material such as a deposited film with a laser beam from the back side of the transparent side. Since the deposited material is peeled off at the interface, a larger total amount of fine particles can be obtained as compared with the case where laser ablation is performed on the solid from the surface. In the method of subdividing the vapor deposition film and the method of subdividing the laser pattern and irradiating the vapor deposition film to release the fine particles, the desired uniform particle diameter can be obtained. Therefore, it is possible to supply a supply amount necessary for an application requiring a narrow-band particle size distribution with a small total amount of fine particles.

  In addition, since the tape-shaped and plate-shaped vapor deposition targets can be moved and rotated easily, highly repetitive operations are possible. In view of the above, when the target particle size is limited, it is possible to generate particles having a uniform particle size with a small irradiation area. For this reason, the speed of the tape or the like to be supplied can be reduced and the structure can be adapted to continuous supply for a long time. Further, since the output of the ablation laser can be suppressed, a small laser can be used, and the apparatus can be miniaturized.

  The best mode for carrying out the present invention will be described below.

  As shown in FIG. 1, a highly repeatable pulse laser is irradiated from the direction of the transparent medium 1, and laser energy is absorbed at the interface between the transparent medium 1 and the vapor deposition film 2, thereby generating high-pressure plasma at the interface. . The deposited film 2 is peeled off by the high pressure plasma. At this time, the vapor deposition material liquefied by heating is separated as fine particles by the thickness of the vapor deposition film, the viscosity, and the pressure from the plasma and simultaneously released.

In the case of YAG laser irradiation with an irradiation intensity of ² J / cm ^{2 at} the laser ablation threshold level on a 100 nm vapor-deposited film, when the laser was irradiated from the back transparent substrate side, the vapor-deposited film was completely released as fine particles. When irradiated from the front deposition surface side, the deposited film was not completely released.

  Most of the fine particles released by laser irradiation from the back surface had a diameter of 1 μm or less, and about 2 μm at the maximum. When laser ablation is performed on a lump solid target under similar conditions, a large number of fine particles of several tens of μm or more are released. These have a volume several thousand times that of sub-μm fine particles. In the case of an extreme ultraviolet plasma light source in which the particle size is limited to sub-μm, the amount of usable particles is greatly reduced.

In the case of a vapor deposition target, depending on the irradiation intensity and pulse width, the ablation depth at which liquefaction is performed at a irradiation intensity of ² J / cm ² of a YAG laser with a pulse width of 10 ns is several hundred nm. A 100 nm target can be miniaturized.

  For a target having a film thickness of more than 1 μm, it is not liquefied to the surface by heating with a laser, leaving a sufficient strength in the plane direction and not being a fine particle, but being released in a planar shape. Therefore, the maximum value of the thickness of the deposited film for the purpose of atomization is about 1 μm.

  However, since the fine-structure film shown in FIG. 2 is separated in the plane direction, the maximum value of the film thickness is not limited to this.

  The minimum film thickness is a thickness that can absorb the energy of the irradiated laser. As a typical example, when a YAG laser (wavelength: 1.06 μm) is irradiated onto an Sn vapor deposition film, the attenuation coefficient k is 8.05, and therefore, approximately 60% of laser light is absorbed at 10 nm. For this reason, the minimum film thickness is 10 nm or more that can absorb most of the laser light. Therefore, the target film thickness range is considered to be 10 nm to 1 μm.

  The ablation material to be released must be a film-like material having a high absorption rate at the oscillation wavelength of the laser, such as a metal. In the case where both the substance and the amount of the fine particle impurities do not matter, the vapor deposition film may be provided with a thin layer of another material having high adhesion on the intermediate layers 1 and 2 for improving the absorption rate.

  For the production of the deposited film, methods such as vacuum deposition, ion gun, and RF plasma sputter deposition are conceivable. Moreover, the film thickness may be controlled by plating the deposited film on one side. It is possible to use a transparent adhesive with a film attached on one side, or an insulating substance with fine particles attached on one side by charging or the like.

  The material to be adhered, which is a transparent substrate, may be a polymer material such as polyethylene or vinyl chloride that can form a film shape or a plate shape, or a material such as glass or quartz.

  As the thickness of the transparent substrate, a thickness of about several μm to 100 μm that can be handled as a film is suitable. Also, when rotating and moving as a plate, a thickness of about 1 mm to 10 mm that can be handled as a rigid body is appropriate.

  A pulse laser is used as a laser for ablation. As a typical example, a visible and near infrared YAG laser (wavelengths 1.06 μm, 0.53 μm), which can easily obtain the above transparent material at the oscillation wavelength, can be considered.

  The laser irradiation area is not limited, but in the method of capturing and transporting fine particles using the working exhaust of the transfer pipe, the trapping efficiency of the fine particles generated by laser ablation is 100 Torr air pressure at the working exhaust inlet Fine particles generated at a diameter of 3 mm can be collected up to 30%, but at a diameter of 20 mm, they fall to about 1-2%. Therefore, the amount of fine particles cannot be increased by increasing the laser irradiation area. The realistic laser irradiation area is considered to be about 1 cm in diameter.

  As shown in FIG. 2, there is also a method in which the deposited film is separated into a desired fixed size by separating in advance by a lattice shape or a similar method. In this method, since the film itself is subdivided, it is not affected at all by the film thickness.

Similarly, as shown in FIG. 3, the particle size can be controlled by making the laser pattern into a lattice pattern or the like. In this case, since the film itself is not subdivided in order to take out uniform particles, the thickness is as shown in FIG. Further, since the irradiation pattern is not affected by the heat conduction corresponding to the ablation depth of the irradiation bright portion in the irradiation dark portion, an interval of 1 μm or more is necessary. In the case of a YAG laser having a pulse width of 10 ns in the dark area, the laser ablation threshold needs to be about 1 J / cm ² or less, and the bright area needs to be more than that.

  When the fine particle group target is an extreme ultraviolet plasma light source using a YAG laser with a pulse width of 10 ns, the diameter that can be converted to plasma is about 1 μm. It is possible to reduce the influence of the contamination of the scattered matter by converting the plasma to the center of the fine particles. For this reason, the fine particle diameter needs to be set to 1 μm or less.

  As for the laser pulse width, energy can be injected into the interface, and a pulse width that is sufficiently short is required to peel off the film with a high-pressure gas generated by ablation and make it finer. As described above, as the maximum value of the film thickness by a 10 ns pulse laser is about 1 μm, the film thickness decreases as the pulse becomes shorter. Therefore, the supply amount as fine particles is also reduced. On the other hand, with a long pulse laser, the optimum film thickness is large, but the maximum diameter of the generated fine particles increases. In the case of an extreme ultraviolet light source whose target fine particle diameter is a sub-μm diameter, a diameter that cannot be converted to plasma is generated to the center. Therefore, when considering the generation of fine particles with an optimum diameter to the plasma light source, the laser pulse width is considered to be optimal at 10 ns.

  In the arrangement of FIG. 1, a minute particle group is transiently generated by irradiating with a YAG laser. By capturing and transporting the emitted fine particles, it can be used as an application of a plasma light source or the like. It is also possible to generate a plasma light source by further irradiating the emitted fine particle group with a laser. At this time, a deposited film of 1 μm or more is too thick and cannot be applied to such a strength that it cannot be subdivided by the pressure at the time of ablation discharge.

  As shown in FIG. 2, the vapor deposition surface is subdivided into a lattice shape or a similar shape, and the laser beam is absorbed by irradiating the subdivided vapor deposition surface from the back side of the transparent side to the interface. Can be released as finely divided fine particles. The same fine particle target as in Example 1 can be used for drawing, a plasma source, and the like. Even when the vapor deposition film is thick, since there is no connection in the lateral direction of the vapor deposition film in advance, fine particles can be released regardless of the thickness.

  As shown in FIG. 3, by subdividing the laser light for ablating the interface, when the interface is irradiated, the laser beam is subdivided into a place not to be irradiated with the laser, and the same effect as in Example 2 can be produced. it can. In the same manner as in Example 1, when it is too thick to be subdivided by ablation pressure, it may not be suitable. At the same time, the width of the dark part needs an interval of about 1 μm so that the laser energy applied to the bright part is not transmitted by heat conduction.

The figure explaining the fine particle generation method by the most basic laser irradiation based on this invention The figure explaining the fine particle generation method by the improved laser irradiation based on this invention The figure explaining the fine particle generation method by another improved laser irradiation based on this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent medium 2 Deposition film 3 Ablation area | region 4 Emitted particle

Claims (10)

A method for generating fine particles having a particle size of sub-μm used for a plasma light source, in which a vapor deposition film having a thickness of 1 μm or less is deposited on a transparent substrate by vapor deposition on a transparent substrate, and a laser having a wavelength transparent to the substrate A method for generating fine particles, wherein the substance is released as a group of fine particles by irradiating from the substrate side.   The fine particle generation method according to claim 1, wherein the laser is a pulse laser.   The method for generating fine particles according to claim 1 or 2, wherein the substance is subdivided.   4. The fine particle generating method according to claim 1, wherein the laser beam pattern is subdivided by means of interference, diffraction or image transfer and irradiated onto the substrate.   The method for generating fine particles according to any one of claims 1 to 4, wherein the substrate is formed in a tape shape or a plate shape and continuously supplied.   6. The method for generating fine particles according to claim 1, wherein a metal is used as the substance.   The substance is Al, Ti, Cr, Fe, Ni, Cu, Zn, Zr, Mo, Ag, In, Sn, Ta, W, Ta, Pt, Au, or Pb or an oxide thereof. The method for generating fine particles according to any one of claims 1 to 6.   A plasma radiation light source, wherein the fine particle group generated by the fine particle generation method according to claim 1 is irradiated with another pulse laser, and the generated plasma is used as a light source. A fine particle generator for generating fine particles having a particle diameter of sub-μm used for a plasma light source, a transparent substrate having a deposited film of 1 μm or less made of a material to be atomized, and the substrate for peeling the adhered material A fine particle generator characterized by having a laser having a transparent wavelength and means for irradiating the laser from the substrate side and emitting the substance as a group of fine particles.   A radiation light source device, comprising: a pulse laser; an apparatus for generating fine particles by the method for generating fine particles according to any one of claims 1 to 7; a means for irradiating the generated fine particle group with another pulse laser; Radiation light source device characterized in that the plasma is used as a light source.

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