JP2009105006A - Method for radiating euv light and exposure method of sensitive substrate using euv light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for radiating EUV light at a low cost, which can obtain higher conversion efficiency to the EUV light than that of the conventional method by using laser beams and can generate less debris than the conventional method. <P>SOLUTION: The method for radiating the EUV light is a double pulse radiation method, which emits the EUV light by radiating a main pulse laser after plasma is generated by radiating pre-pulse laser beams to a target material, the target material is composed of at least one of tin and a tin compound, the ion density of the plasma generated by the radiation of the pre-pulse laser beams is 1×10<SP>16</SP>to 1×10<SP>19</SP>cm<SP>-3</SP>, and the main pulse laser beams are infrared region laser beams. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for emitting EUV light. More specifically, the present invention relates to a method of emitting EUV light with high conversion efficiency by a double pulse irradiation method in which a main pulse is an infrared laser beam.

Extreme ultraviolet (EUV) light has attracted attention as light used in next-generation semiconductor lithography. Currently, the conversion efficiency to EUV light by a laser beam is about 3%, but it is necessary to radiate EUV light with a higher conversion efficiency to make it a practical light source, and many studies have been made to improve the conversion efficiency. .
As a technique for increasing the conversion efficiency into EUV light, for example, there is a double pulse method, and a high-power laser beam from an Nd: YAG laser is irradiated as a preceding pulse to a target material such as xenon to generate weakly ionized plasma, and then An EUV light radiation source that emits EUV light by irradiating the plasma with a main pulse laser beam has been proposed (for example, Patent Document 1).
JP 2005-17274 A

  However, in the method of Patent Document 1, since a high-power laser beam is used, debris (particles scattered from the target) is often generated, the cost is high, and the conversion efficiency into EUV light is not sufficiently high. There is a problem.

  An object of the present invention is to provide a method of emitting EUV light at a low cost by using a laser beam to obtain a higher conversion efficiency to EUV light than before, to reduce the amount of debris generated compared to the prior art. Is to provide.

As a result of intensive studies, the present inventor has created a low ion density state of plasma by irradiating a prepulse laser beam with at least one of tin and a tin compound as a target material, and the main material in the infrared region. It has been found that EUV light is emitted with high conversion efficiency by a method of irradiating a pulsed laser beam, and the present invention has been completed.
Hereinafter, the invention of each claim will be described.

The invention described in claim 1
A method of emitting EUV light by a double pulse irradiation method in which a target material is irradiated with a pre-pulse laser beam to generate plasma and then irradiated with a main pulse laser beam to emit EUV light,
The target material comprises at least one of tin and a tin compound;
The ion density of the plasma generated by the irradiation with the prepulse laser beam is 1 × 10 ¹⁶ to 1 × 10 ¹⁹ cm ⁻³ ,
In addition, the EUV light emission method is characterized in that the main pulse laser beam is an infrared laser beam.

  According to the first aspect of the present invention, a main pulse laser beam in the infrared region is applied to plasma having a specific ion density generated by irradiating a target material made of at least one of tin and a tin compound with a prepulse laser beam. EUV light can be radiated with higher conversion efficiency than before by double pulse irradiation of irradiation. The conversion efficiency to EUV light is conventionally about 3%, but high conversion efficiency of 6 to 8% or more can be achieved. In addition, debris generated when obtaining the same amount of EUV light can be reduced as compared with the conventional case. Furthermore, EUV light can be emitted at low cost.

  In the present invention, EUV light means light having a 2% bandwidth (± 1% bandwidth) centering on a wavelength of 13.5 nm, and the conversion efficiency is the total energy of the prepulse laser beam and the main pulse laser beam. Is a percentage of the radiant energy of EUV light within a solid angle 2π with the laser irradiation direction as a central axis. The solid angle 2π is half of the total sphere of 4π and corresponds to a hemisphere. The amount of EUV radiation is measured with a photodiode.

In the present invention, the ion density of plasma generated by the irradiation with the prepulse laser beam is set to 1 × 10 ¹⁶ to 1 × 10 ¹⁹ cm ⁻³ in order to achieve the high conversion efficiency to EUV light. Is necessary for the following reason.
Although the plasma generation technology using the preceding prepulse laser increases the absorption of the laser and the generated plasma size, it is known that both of them contribute to increase the radiation efficiency of EUV light. In addition to this, the present invention has also focused on how efficiently EUV light radiates compared to the emission of all wavelengths.

The conversion efficiency of EUV light is expressed by the following equation (1).
EUV light conversion efficiency = EUV light emission energy (or power) / Laser energy (or power) input (1)

As a result of intensive studies, the present inventors paid attention to the third term of the following formula (1 ′) in which the formula (1) is rewritten into another form.
EUV light conversion efficiency = laser absorption rate x total wavelength integrated light conversion rate x (radiation power of EUV light / total wavelength integrated emission power) (1 ')
That is, in the above formula (1 ′), when the laser absorption rate of the first term generates plasma, the laser absorption rate increases as the ionization degree increases and the scale length increases as compared with the neutral state. It is known that the conversion rate of light obtained by integrating all the wavelengths of the terms generally increases as the plasma size increases, and that both terms increase by generating plasma with the preceding prepulse.
However, the present inventors can convert to EUV light if the value of the third item indicating the ratio of the emission of EUV light in the total amount of light emitted at all wavelengths, which has not been noticed in the past, can be increased. We thought that efficiency could be improved.

In order to increase the value of the third term, the ion density of the plasma generated by the prepulse laser beam is set to a low ion density state of 1 × 10 ¹⁶ to 1 × 10 ¹⁹ cm ⁻³ , and this low ion In the density state, it has been found that it is effective to irradiate a laser beam having a wavelength in the infrared region with a lower critical density, which is the highest density at which the laser can propagate in the plasma.
That is, when a laser beam having a wavelength in the infrared region is irradiated in this low ion density state, the ratio of EUV light emission in the total amount of light emitted at all wavelengths is improved, so that the conversion efficiency into EUV light as a whole is improved. Will be significantly improved. If the ion density is less than 1 × 10 ¹⁶ cm ⁻³ or exceeds 1 × 10 ¹⁹ cm ⁻³ , the ratio of EUV light emission in the total amount of light emitted at all wavelengths does not improve, and conversion to EUV light The efficiency was found to be insufficient. On the other hand, even within the above range, in particular, when the ion density is 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ , the ratio of EUV light emission in the total amount of light emitted at all wavelengths further improves, and EUV light It has been found that the conversion efficiency is further increased.

And xenon, which has been used as a target material for EUV generation, has high conversion efficiency to EUV light unless it is irradiated with a main pulse laser beam with a plasma ion density as high as about 1 × 10 ²⁰ cm ^−3. However, while the conversion efficiency is limited, tin can emit EUV light by irradiating it with a main pulse laser beam even if the plasma has a low ion density. It has been found that when a plasma having a low density is applied, a high conversion efficiency that has not been obtained in the past can be achieved.

Among tin and tin compounds, tin is particularly preferable because higher EUV light conversion efficiency can be obtained. Tin is a metal, and the higher the pure content of tin, the higher the efficiency of conversion to EUV light. Therefore, tin metal with a high pure content is most preferable. Moreover, as a shape, a solid form can be used in addition to a molten liquid form or a gaseous form. It is also possible to target a solid flat plate itself.
Examples of the tin compound include tin oxide (SnO, SnO ₂ , SnO ₃ etc.), tin sulfide (SnS, SnS ₂ etc.), tin chloride (SnCl ₂ , SnCl ₄ etc.), stannane (SnH ₄ ), tin bromide ( SnBr ₂ etc.) are preferred. Among the tin compounds, tin oxides such as SnO that are easy to handle chemically and can reduce the initial ion density are more preferable.

Furthermore, if the laser beam having a wavelength in the infrared region is used as the main pulse laser beam irradiated to the low ion density plasma generated by the prepulse laser beam, the absorption in the low ion density state is good, and the EUV light is emitted. It turned out that the conversion efficiency of becomes high. There is no particular limitation as long as it is a laser beam in the infrared region, but an inexpensive carbon dioxide gas laser beam that is generally used is preferable.
The pulse duration of the main pulse laser beam is preferably 2 to 20 ns. A higher conversion efficiency is obtained when the pulse duration is 2 to 20 ns. The pulse intensity is preferably 5 × 10 ⁸ to 1 × 10 ¹⁰ W / cm ² . A pulse intensity of 5 × 10 ⁸ to 1 × 10 ¹⁰ W / cm ² is preferable because the plasma is heated to an optimum temperature (30-50 eV).

Moreover, in order to absorb the laser efficiently, a plasma size of a certain size is required. However, if the plasma is made too large and the size is increased, the EUV light that is radiated is absorbed by the plasma and the conversion efficiency is increased. It leads to lowering. For this reason, the specific width of the plasma scale length is also effective, preferably 100 to 500 μm, and more preferably 100 to 200 μm. When the plasma scale length is 100 μm or more, the conversion efficiency into EUV light is improved, and when it is 500 μm or less, the conversion efficiency into EUV light is improved and the emitted EUV light can be efficiently collected. When it is 200 μm or less, the conversion efficiency into EUV light is further increased, and the collected EUV light is more efficiently collected. Here, the scale length of the plasma refers to the distance at which the ion density decreases to 1 / e.
That is, the optimum plasma state for EUV light emission in the present invention has an ion density of 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ and preferably a scale length of 100 to 200 μm.

The low ion density state and scale length of the plasma can be controlled by the pulse intensity and pulse duration of the prepulse laser beam, the time from the prepulse laser beam irradiation to the main pulse laser beam irradiation, and the wavelength of the prepulse laser beam. . Here, the wavelength of the pre-pulse laser beam is not particularly limited.
The pulse duration of the prepulse for generating the low ion density plasma is preferably 1 to 50 ns, more preferably 2 to 40 ns. A particularly high conversion efficiency is obtained when the pulse duration is 2 to 40 ns. The pulse intensity is preferably 5 × 10 ^{7 to} 5 × 10 ¹¹ W / cm ² , and more preferably 1 × 10 ⁸ to 1 × 10 ¹⁰ W / cm ² . Particularly high conversion efficiency is obtained when the pulse intensity is 1 × 10 ⁸ to 1 × 10 ¹⁰ W / cm ² .

  The time from when the pre-pulse laser beam reaches the target area until the main pulse laser beam reaches the target area is preferably 20 to 500 ns, and more preferably 20 to 300 ns. When it is 20 to 500 ns, the main pulse laser beam can be irradiated in the low ion density state of the plasma, and high conversion efficiency to EUV light can be obtained.

  In the invention of claim 1, since high conversion efficiency to EUV light can be achieved, the required input laser energy is small, the generation amount of debris can be reduced, and the wavelength is in the infrared region where the laser power is low. Since a laser is used, EUV light can be emitted at a low cost.

From the above, as claim 2,
The method of emitting EUV light according to claim 1, wherein the tin compound is a tin oxide.

  According to the invention described in claim 2, since a tin oxide that can be easily handled chemically and can reduce the initial ion density among the tin compounds is used as a target, EUV light can be converted with higher conversion efficiency. Can be radiated. Further, it is possible to reduce debris generated when obtaining the same amount of EUV light.

From the above, as claim 3,
3. The EUV light emission method according to claim 1, wherein an ion density of plasma generated by the irradiation with the prepulse laser beam is 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ^−3. To do.

  According to the invention described in claim 3, since the ion density of the plasma generated by the pre-pulse is optimal, it is possible to emit EUV light with higher conversion efficiency, and when obtaining the same amount of EUV light. The generated debris can be further reduced.

Furthermore, as claim 4,
4. The EUV light emission method according to claim 1, wherein the scale length of the plasma generated by the irradiation with the prepulse laser beam is 100 to 500 μm. 5.

  According to the fourth aspect of the present invention, since the scale length of the plasma generated by the prepulse is an optimal size, EUV light can be generated with higher conversion efficiency, and the emitted EUV light can be collected. Can also be efficient.

Further, as claim 5,
5. The EUV light emission method according to claim 1, wherein the infrared laser beam is a carbon dioxide laser beam.

  According to the invention described in claim 5, since the main pulse laser beam uses a general-purpose and inexpensive laser, the cost of EUV light radiation is reduced. Further, the debris can be reduced as compared with the prior art.

The invention described in claim 6
An EUV light emitted by the EUV light emission method according to any one of claims 1 to 5 is collected and applied to a mask, and an illumination optical system that reflects the mask onto the sensitive substrate. A method for exposing a sensitive substrate, comprising: exposing a sensitive substrate through a projection optical system that performs projection imaging.

  In the method for exposing a sensitive substrate of the present invention, a target material composed of at least one of tin and a tin compound is supplied to a target area, and a prepulse laser beam is irradiated to the target material to generate plasma in the low ion density state. In this exposure method, the sensitive substrate is exposed by irradiating the main pulse laser beam to emit EUV light. The emitted EUV light is condensed and emitted and used.

  According to the invention described in claim 6, since EUV light is radiated with high efficiency, the laser output required for exposure can be smaller than the conventional one.

  The EUV light emission method of the present invention can achieve higher conversion efficiency to EUV light than before by using a laser beam, can generate less debris than the conventional method, and can emit EUV light at low cost. . Therefore, the EUV light emission method of the present invention makes it possible to produce an exposure light source with higher efficiency, lower debris, and lower cost than before, and has a great economic effect on related industries of semiconductor manufacturing.

The method of the present invention can be performed using a known EUV light source capable of double pulse irradiation.
As a device for supplying the target material to the target area, a conventionally known supply device can be applied. Tin or a tin compound is usually solid at room temperature, and is preferable because it can be easily adjusted by supplying it as a liquid or gas by heating, but a solid material may also be used. A target material in a liquid or gaseous state is usually guided to a target area by a nozzle and ejected from the nozzle to become a target. A known nozzle is applied, but a supersonic nozzle may be preferably used. Therefore, the supply device includes a heating device and a tank, and the supply amount of the target material can be controlled by the heating temperature of the heating device. If EUV light is generated in a reduced pressure or vacuum chamber, the heating temperature of the tin or tin compound does not have to be heated to the boiling point of atmospheric pressure.

  Next, this target is irradiated with a laser beam. The laser beam is generated by a laser generator and focused on the target by a condenser lens. In the present invention, since the laser in the infrared region becomes the main pulse laser beam, it is not necessary to be a laser different from this, and both the prepulse and the main pulse are preferably laser beams in the infrared region. The pre-pulse laser beam is irradiated in advance, and the main pulse laser beam is irradiated after the plasma in the low ion density state is generated. The time from when the pre-pulse reaches the target area until the main pulse reaches the target area is preferably 20 to 500 ns, more preferably 20 to 300 ns. This time is usually controlled by connecting the laser generator to the controller. The control device is, for example, a central processing unit (CPU) including a memory storing a predetermined program and a clock. With this device, control is performed so that the main pulse reaches the target area after a predetermined time after the pre-pulse reaches the target area.

The main pulse and prepulse target paths are, for example, generated by the same laser generator and reach the target area via the same path. There are a route to reach the target area at a certain angle, a route in which the main pulse and the prepulse are generated by different laser generators and reach the target area via different routes, but there is no particular limitation.
In order for the prepulse to provide sufficient energy to excite the target material and generate a plasma, a certain intensity in the target area must be irradiated for a certain time. The pulse duration of the prepulse is preferably 1 to 50 ns, more preferably 2 to 40 ns. The pulse intensity is preferably 5 × 10 ^{7 to} 5 × 10 ¹¹ W / cm ² , more preferably 1 × 10 ⁸ to 1 × 10 ¹⁰ W / cm ² . The pulse duration of the main pulse is preferably 10-20 ns. The pulse intensity is preferably 5 × 10 ⁹ to 1 × 10 ¹⁰ W / cm ² .

In addition, the debris adheres to the tip of the nozzle and prevents the target from being normally ejected, or adheres to and accumulates on an optical element such as a condensing mirror or a filter. Or reduce the performance. In particular, the condensing mirror for condensing EUV light radiated from plasma is extremely contaminated, and it is necessary to frequently replace the mirror, which requires a lot of labor and cost.
In the present invention, the use of a laser having a low laser power and a wavelength in the infrared region and high conversion efficiency to EUV light reduce the amount of debris generated when obtaining the same amount of EUV light. There is also an advantage of being able to.

  When the main pulse laser beam in the infrared region is irradiated to the low ion density plasma generated by the pre-pulse laser beam irradiation under the above pulse conditions, EUV light is emitted. The emitted EUV light is emitted toward the outside and used. For example, it is directed to circuits that are collected and patterned by collector optics (eg, a collector mirror) and other systems that use EUV light irradiation. For example, the exposure apparatus includes an illumination optical system that strikes the mask and a projection optical system that projects and images light reflected from the mask onto the sensitive substrate.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.
Note that each of the following embodiments and comparison modes are simulation-based embodiments or comparison modes unless otherwise specified.

(Embodiment 1)
FIG. 1 is a schematic diagram of an EUV light source for explaining a method of emitting EUV light in the present embodiment.
As shown in FIG. 1, an EUV light source 1 includes a target area 2, a target material supply device 5, a nozzle 6 connected to the target material supply device 5 and extending toward the target area 2, a prepulse laser beam 3, and a main pulse laser beam. 4 by means of an infrared laser generator 7, a control device 7 a for controlling the pulse intensities, durations, and irradiation intervals of both beams of the pre-pulse laser beam 3 and main pulse laser beam 4, lenses 8 and 9, and mirror 10. It is configured.

  First, the target material (tin) is heated by the target material supply device 5 to become a droplet, and is discharged to the target area 2 through the nozzle 6.

On the other hand, the prepulse laser beam 3 generated by the infrared laser generator 7 is focused on the target area 2 by the lens 8.
In the present embodiment, the pulse intensity of the prepulse laser beam 3 is set to 5 × 10 ⁸ W / cm ² and the pulse duration is set to 10 ns.
The focused prepulse laser beam 3 generates tin plasma in a low ion density state.
As a result of simulation, the ion concentration of the plasma generated at this time was 5 × 10 ¹⁷ cm ⁻³ and the plasma scale length was 150 μm.

Next, 150 ns after the pre-pulse laser beam 3 reaches the target area 2, the main pulse laser beam 4 similarly generated by the infrared laser generator 7 is irradiated onto the target area 2 to emit EUV light.
At this time, the main pulse laser beam 4 travels on a different path from the prepulse laser beam 3. Specifically, after being focused by the lens 9, the main pulse laser beam 4 is 45 with respect to the prepulse laser beam 3 using the mirror 10. The target area 2 is irradiated at an angle of °.
In the present embodiment, the pulse intensity of the main pulse laser beam 4 irradiated at this time is set to 2 × 10 ⁹ W / cm ² and the pulse duration is set to 20 ns.
As a result of the simulation, the conversion efficiency into EUV light in the present embodiment was 7.2%.

(Embodiments 2-4, Comparative Embodiments 1-3)
Next, settings of the pulse intensity, duration, and pre-pulse and main pulse irradiation interval of the pre-pulse laser beam 3 in the first embodiment are shown in Embodiments 2 to 4 and Comparative Embodiments 1 and 2 in Table 1. Thus, EUV radiation was simulated, and the ion density, plasma scale length, and conversion efficiency of the generated plasma were determined.
The results are also shown in Table 1.

Further, EUV light emission by a single pulse method in which only the main pulse laser beam 4 is irradiated was performed in an experiment (Comparative embodiment 3), and the plasma scale length and the conversion efficiency were obtained. In addition, the plasma scale length in Comparative Example 3 was obtained by a calculated value instead of an experimental value.
The results are also shown in Table 1.

As is clear from Table 1, when the ion density of the generated plasma is 1 × 10 ¹⁶ to 1 × 10 ¹⁹ cm ⁻³ (Embodiments 1 to 4), high conversion efficiency is obtained. EUV light is obtained. On the other hand, even if it is a double pulse method, the case where the ion density of the generated plasma is outside the range of 1 × 10 ¹⁶ to 1 × 10 ¹⁹ cm ⁻³ (comparative embodiments 1 and 2), or the single pulse method In the case of (Comparative Form 3), high conversion efficiency cannot be obtained.

(Embodiment 5)
FIG. 2 is a schematic diagram of an EUV light source for explaining a method of emitting EUV light in the present embodiment.
As shown in FIG. 2, the EUV light source 11 includes a target area 12, a target material supply device 15, a nozzle 16 connected to the target material supply device 15 and extending toward the target area 12, a prepulse laser beam 13, and a main pulse laser beam. 14 for generating an infrared laser, a control device 17a for controlling the pulse intensity and duration of the pre-pulse laser beam 13 and the main pulse laser beam 14, and the time between irradiation of both beams, a wavelength conversion element 18, and a wavelength selection type. A mirror 19, lenses 20 and 21, and a mirror 22 are included.

  First, the target material (tin) is heated by the target material supply device 15 to become a droplet, and is discharged to the target area 12 through the nozzle 16.

On the other hand, the prepulse laser beam 13 generated by the infrared laser generator 17 is wavelength-converted through the wavelength conversion element 18, then reflected by the wavelength selective mirror 19, and the target area 12 by the mirror 22 and the lens 21. Focused on top.
In the present embodiment, the pulse intensity of the prepulse laser beam 13 is set to 5 × 10 ⁸ W / cm ² and the pulse duration is set to 10 ns.
The focused prepulse laser beam 13 generates tin plasma in a low ion density state.
As a result of simulation, the ion concentration of the plasma generated at this time was 5 × 10 ¹⁷ cm ⁻³ and the scale length was 150 μm.

Next, 150 ns after the pre-pulse laser beam 13 reaches the target area 12, the main pulse laser beam 14 generated by the infrared laser generator 17 is irradiated onto the target area 12 to emit EUV light.
At this time, the main pulse laser beam 14 passes through the wavelength conversion element 18 in the same manner as the pre-pulse laser beam 13 (coaxially, while passing through the same element, the wavelength is spatially different). Take another route. That is, when passing through the wavelength conversion element 18, the main pulse laser beam 14 is wavelength-converted to a wavelength different from that of the pre-pulse laser beam 13, or is not wavelength-converted. The wavelength selective mirror 19 is not reflected and travels in a spatially different path. The main pulse laser beam 14 that has passed through the wavelength selective mirror 19 is focused by the lens 20 and then irradiated to the target area 12 at an angle of 45 ° with respect to the prepulse laser beam 13.
In the present embodiment, the pulse intensity of the main pulse laser beam 14 irradiated at this time is set to 2 × 10 ⁹ W / cm ² and the pulse duration is set to 20 ns.
As a result of the simulation, the conversion efficiency into EUV light in the present embodiment was 7.2%.
Thus, also in this embodiment, EUV light can be obtained with high conversion efficiency.

(Supplement to Embodiments 1 to 5)
In the first to fifth embodiments, the two laser beams are irradiated at different angles, but the main pulse, the pre-pulse, and the two laser beams are coaxial, but the central part of the shaft and the periphery. It is also possible to irradiate the target area with two laser beams at the same angle by proceeding separately in each space of the part.

(Embodiment 6)
FIG. 3 is a perspective view conceptually showing a method of emitting EUV light in the present embodiment.
In FIG. 3, a prepulse laser beam 31 having a wavelength of 1 μm is reflected by a mirror 33 and applied to a disk 34 coated with tin. Then, the main pulse laser beam 32 generated by an infrared laser emitting device (not shown) is irradiated onto the tin plasma 35 in a low ion density state ejected by the irradiation with the prepulse laser beam 31, thereby EUV light. 36 is emitted. The emitted EUV light 36 is reflected by the concave mirror 37 and collected.
As described above, it is possible to irradiate the target area with the main pulse laser beam 32 at an angle of 90 degrees with respect to the pre-pulse laser beam 31.

It is a schematic diagram explaining the radiation | emission method of EUV light in one embodiment of this invention. It is a schematic diagram explaining the radiation | emission method of EUV light in another embodiment of this invention. It is a perspective view which shows notionally the radiation | emission method of EUV light in another embodiment of this invention.

Explanation of symbols

1, 11 EUV light source 2, 12 Target area 3, 13, 31 Pre-pulse laser beam 4, 14, 32 Main pulse laser beam 5, 15 Target material supply device 6, 16 Nozzle 7, 17 Infrared laser generator 7a, 17a Control Apparatus 8, 9, 20, 21 Lens 10, 22, 33 Mirror 18 Wavelength conversion element 19 Wavelength selection type mirror 34 Disk 35 Plasma 36 EUV light 37 Concave mirror

Claims (6)

A method of emitting EUV light by a double pulse irradiation method in which a target material is irradiated with a pre-pulse laser beam to generate plasma and then irradiated with a main pulse laser beam to emit EUV light,
The target material comprises at least one of tin and a tin compound;
The ion density of the plasma generated by the irradiation with the prepulse laser beam is 1 × 10 ¹⁶ to 1 × 10 ¹⁹ cm ⁻³ ,
The method of emitting EUV light, wherein the main pulse laser beam is an infrared laser beam.   2. The EUV light emission method according to claim 1, wherein the tin compound is a tin oxide. 3. The EUV light emission method according to claim 1, wherein an ion density of plasma generated by the irradiation with the prepulse laser beam is 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ .   The EUV light emission method according to any one of claims 1 to 3, wherein the scale length of the plasma generated by the irradiation with the prepulse laser beam is 100 to 500 µm.   5. The EUV light emission method according to claim 1, wherein the infrared laser beam is a carbon dioxide laser beam.   An EUV light emitted by the EUV light emission method according to any one of claims 1 to 5 is collected and applied to a mask, and an illumination optical system that reflects the mask onto the sensitive substrate. A method for exposing a sensitive substrate, comprising: exposing a sensitive substrate through a projection optical system for projecting and forming an image.

Images