JP3817634B2 - Target for generating light of very short wavelength, method for manufacturing the target, light generation method using the target, and apparatus therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to a method and apparatus for generating light having a wavelength shorter than ultraviolet light, particularly extreme ultraviolet light, and can be suitably used for photolithography.
[0002]
[Prior art]
The degree of integration of semiconductors has been increasing rapidly according to Moore's Law so far, and there is a demand for increasing the same trend in the future. The integrated circuit is formed by photolithography. Therefore, in order to meet the demand for increasing the degree of integration, it is desirable to use light having an exposure wavelength shorter than conventional ultraviolet light (hereinafter referred to as ultrashort wavelength light) as a lithography light source. The most promising light source candidate is extreme ultraviolet light (hereinafter referred to as EUV) having a wavelength of 10 nm to 100 nm.
In general, xenon, which is a gaseous substance at room temperature, remains in a gaseous state, or is cooled, solidified, and liquefied to obtain a high-density target. Is known to radiate.
[0003]
[Problems to be solved by the invention]
However, in the conventional target, since the critical density of the target capable of absorbing laser light energy is lower than the density in the temperature region that emits light of a predetermined wavelength, the conversion efficiency is too low and the cost is high. That is, for example, when a substance gasified from a solid is used as a target, as it is closer to the solid surface as shown in FIG. Therefore, when this is irradiated with laser light, it emits light of a specific wavelength such as EUV in the low temperature region (EUV emission region in the figure) close to the solid surface, but the critical density is Since it is lower than the density of the region, most of the laser light energy is absorbed in a low density region (laser light absorption region in the figure) farther from the solid surface than the EUV light emitting region.
[0004]
In addition, since the high density region is constantly in heat exchange with the solid and is at a low temperature, heat loss occurs due to heat conduction from the low density region where the laser beam energy is absorbed to a high temperature to a high density region. Therefore, this helps to reduce the conversion efficiency.
Furthermore, in solid targets and liquid targets, debris of the target scatters due to shock waves generated after laser irradiation, etc., causing damage to the optical system etc. that handles the emitted light, and causing deterioration of its optical characteristics. It was.
Therefore, an object of the present invention is to provide a target with high radiation conversion efficiency, a target with high cleanness, an ultrashort wavelength light generation method using the target, and an apparatus therefor, without wasting input laser light energy very much. It is to provide.
[0005]
[Means for Solving the Problems]
In order to solve the problem, the laser irradiation target of the present invention is
It consists of frost which has a density of 1/100 to 1/2 of the solid density. Since the frost is composed of particles generated by quenching the gas, its density and temperature can be made substantially uniform over the entire target. The element constituting the frost is not particularly limited, and the critical density varies depending on the element because the number of electrons emitted from one ion varies depending on the element. However, it may be within the range of 1/100 to 1/2 of the solid density. For example, it is below the critical density of most elements. Therefore, as shown in FIG. 1, the above-described frost emits ultrashort wavelength light with high efficiency because the absorption region and the light emission region overlap deeply with respect to the laser light and the volume of the region contributing to light emission increases. Moreover, since it is low density, generation | occurrence | production of debris can be suppressed and the usage-amount of luminescent gas can also be suppressed.
[0006]
For this reason, the ultrashort wavelength light generation method of the present invention that solves the above problems is
A laser is irradiated to a frost having a density of 1/100 to 1/2 of the solid density.
In order to generate EUV, xenon is usually used as an element constituting frost. However, any substance that can become frost, such as hydrogen, oxygen, nitrogen, argon, and krypton, may be used, and a spectrum that emits light by changing the substance. Have different wavelengths.
[0007]
A generator suitable for the ultrashort wavelength light generation method of the present invention is:
A hopper having a discharge port capable of discharging frost on one side;
A refrigerator to make the hopper extremely cold,
A heater capable of intermittently heating the hopper wall;
A vacuum chamber provided with a first window for maintaining a vacuum around the hopper and guiding external laser light to the vicinity of the discharge port on one side, and a second window for extracting extreme ultraviolet light on the other side; It is characterized by providing.
[0008]
According to this apparatus, when a predetermined gas is injected into the hopper while the refrigerant is kept at a very low temperature in the refrigerator, the gas is solidified and a solidified layer is formed on the inner wall surface of the hopper. When the wall surface of the hopper is heated with a heater in this state, the solidified layer is sublimated to become a high-density gas, immediately cooled by turning off the heater, becomes a snow state, and descends to become frost. At the same time, a new solidified layer is formed on the wall surface. Therefore, frost is deposited in the hopper by intermittently heating the heater. Extremely short wavelength light can be generated by discharging the accumulated frost out of the hopper through the discharge port, allowing laser light to enter the vacuum chamber from the first window and irradiating the frost. Note that the first window may be configured by a lens and also serving as a condenser.
[0009]
When the heater is based on the principle of high-frequency discharge, the inside of the hopper becomes high pressure due to the discharge and is rapidly cooled when the discharge is stopped. In this case, if a plurality of pairs of heater discharge electrodes are provided on the outer periphery of the hopper, the discharge electrode of one set is stopped during the discharge by one set of discharge electrodes to form a solidified layer. Can do. Therefore, it is preferable because frost can be continuously deposited.
The apparatus further comprises an impeller having a plurality of blades that are rotatably fixed immediately before the hopper outlet and project radially in the radial direction,
It is preferable that the hopper is formed in a substantially cylindrical shape concentric with the impeller so as to surround the impeller immediately before the discharge opening. By doing so, the frost accumulated between the adjacent blades is sequentially discharged by an appropriate amount as the impeller rotates. In addition, it is preferable to make the rotating shaft of the impeller hollow and to let a refrigerant pass through it, since sublimation of frost is suppressed.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
A first embodiment of the present invention will be described with reference to FIG. FIG. 3 is a longitudinal sectional view of an ultrashort wavelength generator (hereinafter referred to as the present apparatus 100) according to the first embodiment.
The apparatus 100 includes a refrigerator 1, a gas injection pipe 2, a heater 3, a hopper 4, an extrusion bar 5, a monitor 6, a vacuum chamber 7, a high-power pulse laser light generator 8, and a wavelength converter 9.
[0011]
The hopper 4 is fixed in the vacuum chamber 7 and has an upper cylindrical portion 4a and a lower conical guide portion 4b, both of which are made of an insulating material such as glass or ceramics, and the upper surface is closed. It has a discharge port 41 that can discharge frost at the lower end. Around the hopper 4, a pipe 42 through which a refrigerant (not shown) such as liquid helium circulates is provided along the wall surface. The pipe 42 passes through the vacuum chamber 7 in an airtight manner and is connected to the refrigerator 1. The heater 3 is based on the principle of high frequency discharge, and its discharge electrodes 31a and 31b are provided on the inner surface of the wall of the body 4a. Depending on the thickness and material of the wall, the discharge electrode may be provided on the outer surface of the wall. The push bar 5 is set up vertically in the hopper 4 and is set to be movable up and down by remote control from outside the vacuum chamber 7.
[0012]
On one side of the vacuum chamber 7, a first window 10 made of a lens is provided at the same height as the discharge port 41, and on the other side, a second window 11 is opposed to the first window 10. Is provided. A wavelength converter 9 and a laser light generator 8 are sequentially connected to the window 10 outside the vacuum chamber 7. The gas injection tube 2 airtightly penetrates one side surface of the vacuum chamber 7 and the body portion 4a so that gas can be injected into the hopper 4 from the outside. The vacuum chamber 7 also penetrates the monitoring device 6, and the tip of the monitoring device 6 is close to the discharge port 41.
The lens constituting the window 10 is adjusted so that its focal point is located directly below the discharge port 41, and also serves as a condenser. Therefore, the pulsed laser light emitted from the laser light generator 8 is converted into a harmonic having a high absorption rate with respect to the frost by the wavelength converter 9, refracted by the window 10, and condensed immediately below the discharge port 41.
[0013]
The operation of the apparatus 100 will be described below with an example in which xenon Xe is targeted. First, the refrigerator 1 is started up and the hopper 4 is cooled to 161 K at which the xenon is solidified at normal pressure. When xenon gas is injected from the gas injection pipe 2, a solidified layer of xenon is formed on the inner wall surface of the hopper 4. Therefore, the heater 3 is energized to cause high-frequency discharge between the discharge electrodes 31a and 31b, and the surface of the solid layer once formed on the inner wall surface of the hopper 4 is locally heated to generate steam. As soon as the energization of the heater 3 is stopped, the vaporized gas is rapidly cooled and becomes a “snow” state, which falls and becomes frost ((reference numeral F in FIG. 3) and accumulates on the guide portion 4b of the hopper 4. A bar-like target is formed by extruding this from the outlet 41 with the extruding bar 5.
[0014]
The obtained target is lower than the temperature of the “triple point” where a solid phase, a liquid phase, and a gas phase exist at the same time, and is approximately 2 × 10 ²⁰ to 8 under temperature density conditions where the solid phase and the gas phase can exist simultaneously. X10 Particle density around ²¹ / cc. This is a mass density of xenon of 3.5 g / cc, an atomic weight of xenon of 131.3 and an Avogadro number of 6.02 × 10 ²³ and a number density of 1.6 × 10 ²² /cc=(3.5/131.3)×6.02× This corresponds to approximately 1/100 to 1/2 of 10 ²³ . Therefore, when this target is irradiated with, for example, YAG laser light, it is heated and ionized to have an ion density of 2 × 10 ²⁰ to 8 × 10 ²¹ ions / cc and an electron density of 10 ²⁰ to 10 ²³ ions / cc. Plasma is generated. The upper limit of the electron density is almost 10 times the ion density because one ion emits 10 to 15 electrons, and the lower limit is not 10 times that the heated plasma expands rapidly. Because. The generated plasma generates EUV having a wavelength of 13-14 nm. In addition, the target as a whole is composed of frost with a density slightly lower than the critical density for the fundamental wavelength light of the YAG laser, for example, at the above EUV emission temperature, and thus emits light with high efficiency close to black body radiation, which is the emission limit. Further, according to the present apparatus 100, a portion that does not contribute to light emission is not wastedly heated with laser light, so that energy loss can be minimized and occurrence of debris can also be suppressed.
[0015]
Embodiment 2
A second embodiment of the present invention will be described with reference to FIGS. 4 is a longitudinal sectional view showing an ultrashort wavelength light generating apparatus (hereinafter referred to as the present apparatus 200) of the second embodiment, and FIG. 5 is a sectional view taken along the line AA in FIG.
The apparatus 200 also includes a refrigerator 1, a gas injection pipe 2, a heater 3, a hopper 4, an extrusion bar 5, a monitor 6, a vacuum chamber 7, a high-power pulse laser light generator 8, and a wavelength converter 9. Constituent elements other than the hopper 4 are basically the same shape and the same, and the arrangement relationship is the same. In addition, the impeller 12 is provided. Therefore, only the impeller 12, the heater 3, and the hopper 4 will be described in detail.
[0016]
The heater 3 has three pairs of discharge electrodes 32a, 32b, 33a, 33b, 34a, 34b, and the body of the hopper 4 so that the discharge electrodes 32a, 33a, 34a and the discharge electrodes 32b, 33b, 34b face each other. It is fixed to the wall surface of the portion 4a.
The hopper 4 integrally has a cylindrical housing 4c perpendicular to the body 4a below the guide portion 4b, and a discharge port 41 is provided at the lower end of the housing 4c. The impeller 12 has a plurality of (eight in the drawing) blades 12a that are concentric with the housing 4c and are rotatably fixed in the housing 4c and project radially in the radial direction. The tip of the blade 12a is opposed to the inner peripheral surface of the housing 4c via a minute gap. Further, the same refrigerant as the refrigerant around the trunk portion 4 a is also stored in the center of the impeller 12, and illustration of piping is omitted, but this refrigerant also circulates between the impeller 12 and the refrigerator 1.
[0017]
According to this apparatus 200, while energizing a pair of discharge electrodes (for example, 32a and 32b) to peel off the solidified layer, the discharge of the remaining discharge electrodes is stopped and the injected gas is cooled and solidified. A solidified layer can be formed. Therefore, frost can be continuously deposited. Further, the peeled frost (symbol F in FIG. 3) is accumulated between the adjacent blades 12a, and only an appropriate amount of accumulated frost facing the discharge port 41 as the impeller 12 rotates is sequentially discharged. The discharged frost generates EUV when irradiated with laser light as in the first embodiment.
[0018]
【The invention's effect】
According to the present invention, the light emitting region of the target can be matched with the laser light absorbing region, and therefore, it is possible to generate ultrashort wavelength light with high efficiency. Therefore, it can be expected to be used not only in the field of material processing such as photolithography but also in a wide range of fields such as material inspection and material diagnosis.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the distance of a target of the present invention, temperature and density.
FIG. 2 is a graph showing the relationship between the distance of a conventional target and the temperature and density.
FIG. 3 is a longitudinal sectional view showing an apparatus according to the first embodiment of the present invention.
FIG. 4 is a longitudinal sectional view showing an apparatus according to a second embodiment of the present invention.
5 is a cross-sectional view taken along the line AA in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Refrigerator 2 Gas injection pipe 3 Heater 4 Hopper 5 Extrusion stick 6 Monitor 7 Vacuum chamber 8 Laser light generator 9 Wavelength converter 10 First window 11 Second window 12 Impeller 100, 200 Generation of ultrashort wavelength light apparatus

Claims (7)

A target for laser irradiation , which is a group of particles produced by cooling a gas and comprising frost having a density of 1/100 to 1/2 of the solid density. Gas to a particle group generated by cooling, have a 1 / 100-1 / 2 in the density of the solid density, the frost present alone in a vacuum, characterized in that to irradiate the laser, ultrashort A method of generating light of a wavelength. A hopper having a discharge port capable of discharging frost which is a particle group generated by cooling the gas on one side;
A refrigerator to make the hopper extremely cold,
A heater capable of intermittently heating the hopper wall;
A vacuum chamber provided with a first window for maintaining a vacuum around the hopper and guiding external laser light to the vicinity of the discharge port on one side, and a second window for extracting extreme ultraviolet light on the other side; An ultrashort wavelength light generator characterized by comprising:   The apparatus according to claim 3, wherein the heater is based on a high frequency discharge.   The apparatus according to claim 4, wherein a plurality of pairs of discharge electrodes of the heater are provided on an outer periphery of the hopper. Furthermore, an impeller having a plurality of blades that are rotatably fixed immediately before the discharge port of the hopper and project radially in the radial direction,
The apparatus according to claim 3, wherein the hopper is formed in a substantially cylindrical shape concentric with the impeller so as to surround the impeller immediately before the discharge opening. 2. A solidified layer is formed by injecting a predetermined gas into a cryogenic hopper, the solidified layer is vaporized by heating the hopper while it is cooled, and heating is stopped immediately thereafter. The manufacturing method of the target for laser irradiation as described in 2.

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