A stepped-diameter capillary device and method for generating extreme ultraviolet laser.

Abstract

This application discloses a stepped-diameter capillary device and method for generating extreme ultraviolet (EUV) lasers. The device includes multiple capillary segments coaxially arranged to form a continuous inner hole for containing a working gas. Each capillary segment includes at least a first capillary segment with a first inner diameter and a second capillary segment with a second inner diameter, the first inner diameter being smaller than the second inner diameter. The first and second inner diameters are configured such that, in response to a pulsed discharge current applied across the stepped-diameter capillary device, the plasma column of the first capillary segment reaches its maximum gain state for the target wavelength EUV laser earlier than the plasma column of the second capillary segment, and generates laser light first. This application enables cascaded amplification of EUV lasers, breaking through the single-pass amplification energy limitation and significantly improving the single-pass output pulse energy extraction efficiency.

Description

Technical Field

[0001] This invention relates to the field of extreme ultraviolet laser generation, and more specifically to a stepped inner diameter capillary device and method for generating extreme ultraviolet lasers. Background Technology

[0002] Capillary discharge technology typically involves filling a capillary tube, which is several centimeters to tens of centimeters long, with a suitable amount of gas, and then applying a pulsed current (with an amplitude typically in the range of 10-40 kV and a pulse half-cycle of about 100 ns) to both ends of the capillary tube to ionize the gas inside the capillary tube and form a plasma column; in this process, the applied pulsed current is usually referred to as the main pulse current.

[0003] A main pulse current flowing through a plasma column generates an angular magnetic field. The plasma moving within this field produces a Lorentz force pointing towards the axis. Under the influence of this Lorentz force, the plasma is pinched towards the axis, shrinking the diameter of the plasma column from an initial few millimeters to several hundred micrometers. This phenomenon is generally called the Z-pinch effect. Under the influence of the Z-pinch effect, the plasma column shrinks inward, and the electron density and electron temperature within the column gradually increase. When it shrinks to near the point of minimum plasma column radius, a gain medium that enhances extreme ultraviolet (EUV) light is formed, thus generating EUV laser light.

[0004] The 46.9nm laser, a type of extreme ultraviolet (EUV) laser, is currently the shortest wavelength, highest intensity, and most well-researched EUV laser that uses capillary discharge-generated plasma as the gain medium. In the process of generating a 46.9nm laser through capillary discharge, an energy of around 1 mJ and a pulse half-width of 1-2 ns are typically produced. To broaden the applications of the 46.9nm laser, its energy needs to be further increased. Unlike lasers with wavelengths above 100nm, finding suitable back-reflecting and output mirrors for the 46.9nm laser is difficult. Currently, internationally, EUV lasers using plasma as the gain medium generally employ a cavity-less operating mode, known as single-pass amplification lasers. Therefore, increasing the output energy of EUV lasers in the 46.9nm wavelength range is more challenging than for longer wavelength lasers. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a stepped inner diameter capillary device and method for generating extreme ultraviolet laser, so as to solve the above-mentioned problems existing in the prior art.

[0006] According to one aspect of the present invention, a stepped-diameter capillary device for generating extreme ultraviolet (EUV) laser is provided, comprising a plurality of capillary segments coaxially arranged to form a continuous inner hole for containing a working gas; wherein the plurality of capillary segments include at least a first capillary segment having a first inner diameter and a second capillary segment having a second inner diameter, the first inner diameter being smaller than the second inner diameter; the first inner diameter and the second inner diameter are configured such that, in response to a pulsed discharge current applied to both ends of the stepped-diameter capillary device, the plasma column of the first capillary segment reaches the maximum gain state for the target wavelength EUV laser earlier than the plasma column of the second capillary segment, and generates laser light first; wherein, within a preset time period after the first capillary segment generates laser light, the second capillary segment reaches the maximum gain state and generates a first seed light, the first seed light being injected into the first capillary segment and amplified and output by the plasma column in the first capillary segment that is in the gain state.

[0007] Furthermore, the preset time period is less than or equal to the pulse duration of the laser spontaneously generated by the first capillary segment.

[0008] Furthermore, the dimensions of the first inner diameter and the second inner diameter are set such that when the second capillary segment generates the first seed light of extreme ultraviolet laser, the plasma column in the first capillary segment is still in a state of gain for the target wavelength, so as to amplify the first seed light.

[0009] Furthermore, the plurality of capillary segments include N-stage segments connected end to end along the axial direction, where N is an integer greater than 2; and the inner diameters of the first stage to the Nth stage increase sequentially, so that the plasma columns corresponding to each stage of the capillary segment reach the maximum gain state sequentially in order of increasing inner diameter.

[0010] Furthermore, the difference in inner diameter between the first capillary segment and the second capillary segment is between 0.1 mm and 0.5 mm.

[0011] Furthermore, the target wavelength is 46.9 nm, and the inner diameter of each capillary segment is in the range of 2 mm to 4 mm.

[0012] Furthermore, the first inner diameter is 2.5 mm, and the second inner diameter is 2.6 mm.

[0013] Furthermore, with N=3, the third inner diameter corresponding to the third stage capillary segment is 2.7 mm.

[0014] According to another aspect of the present invention, a method for generating extreme ultraviolet laser is also provided, which employs a stepped inner diameter capillary as described above. The method includes: filling the stepped inner diameter capillary with a working gas; applying a pulsed discharge current to both ends of the stepped inner diameter capillary to generate a plasma column exhibiting a Z-pinch effect; utilizing the time difference in reaching maximum gain state among different inner diameter segments, using the extreme ultraviolet laser generated by one or more segments as seed light, injecting it into a segment still in the gain state for amplification; wherein the segment with a smaller inner diameter reaches maximum gain state earlier than the segment with a larger inner diameter.

[0015] Furthermore, the step of using the time difference between the different inner diameter pipe segments reaching the maximum gain state to inject the extreme ultraviolet laser generated by one or more pipe segments as seed light into the pipe segment still in the gain state for amplification includes: causing the first capillary segment with the first inner diameter to reach the maximum gain state earlier and generate laser light first than the second capillary segment with the second inner diameter; within a preset time period after the first capillary segment generates laser light, injecting the extreme ultraviolet laser generated by another one or more pipe segments as seed light into the first capillary segment still in the gain state for amplification.

[0016] This invention discloses a stepped-diameter capillary device and method for generating extreme ultraviolet (EUV) lasers. It utilizes the time difference between the different inner diameter segments reaching maximum gain under Z-pinch compression during main pulse current excitation, allowing the first segment with a smaller inner diameter to generate laser light first. This first segment then acts as a gain medium to inject and amplify the seed light generated by the second segment with a larger inner diameter. Furthermore, in some embodiments, in addition to the first and second segments, the stepped-diameter capillary may include one or more additional capillary segments with even larger inner diameters to achieve cascaded amplification of higher energy levels through continuous injection of multi-stage seeds. Thus, this invention, utilizing a stepped-diameter-controlled seed light injection mechanism, enables cascaded amplification of EUV lasers without the need for a physical resonant cavity, breaking through the single-pass amplification energy limitation and significantly improving the energy extraction efficiency of the single-pass output pulse.

[0017] This invention achieves precise time difference between pipe segments (e.g., 1.5 ns) by configuring the inner diameter difference, thereby enabling multiple stimulated emission segments to superimpose in part of the time domain. This enhances peak power while effectively widening the pulse duration of the extreme ultraviolet laser, thus enabling simultaneous widening of pulse width and energy.

[0018] Furthermore, in existing technologies, due to the extreme sensitivity of optical path alignment and the extremely short wavelength of extreme ultraviolet light, relying on external mirrors to manually adjust the nanosecond-level delay means that even minor mechanical vibrations or thermal deformations can cause the seed light to deviate from the gain center. Moreover, because the 46.9nm wavelength is easily absorbed by matter, the seed light loses a significant amount of energy each time it passes through an external mirror, resulting in extremely low final injection amplification efficiency, severe energy loss, and high system complexity, making it difficult to maintain stability. In contrast, this invention can directly control the time difference generated by the laser using only the preset inner diameter difference of each segment of the capillary (e.g., 0.1mm-0.5mm), achieving precise matching of the seed light and the gain medium on the nanosecond scale. This invention eliminates the need for a complex external optical delay system, greatly simplifying the system structure and enhancing the reliability and stability of the extreme ultraviolet laser output. Attached Figure Description

[0019] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example and not limitation, wherein: Figure 1 This is a cross-sectional view of an example of a stepped inner diameter capillary device for generating extreme ultraviolet laser according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of two capillary segments of a stepped inner diameter capillary device for generating extreme ultraviolet laser according to an embodiment of the present invention. Figure 3 This is a schematic diagram showing the relationship between the plasma column radius and time under the action of Z-pinch, generated by 2.5mm and 2.6mm capillary segments; Figure 4 This is a schematic diagram showing the relationship between the gain coefficient of the plasma column corresponding to the 46.9nm laser and time, calculated based on experimental results; Figure 5 This is a schematic diagram of the structure of three capillary segments of a stepped inner diameter capillary device for generating extreme ultraviolet laser according to another embodiment of the present invention. Detailed Implementation

[0020] The principles and spirit of the invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are given merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0021] An embodiment of the present invention provides a stepped-diameter capillary device for generating extreme ultraviolet (EUV) laser, comprising a plurality of capillary segments coaxially arranged to form a continuous inner hole for accommodating a working gas; wherein the plurality of capillary segments include at least a first capillary segment having a first inner diameter and a second capillary segment having a second inner diameter, the first inner diameter being smaller than the second inner diameter; the first inner diameter and the second inner diameter are configured such that, in response to a pulsed discharge current applied to both ends of the stepped-diameter capillary device, the plasma column of the first capillary segment reaches the maximum gain state for the target wavelength EUV laser earlier than the plasma column of the second capillary segment, and generates laser light first; wherein, within a preset time period after the first capillary segment generates laser light, the second capillary segment reaches the maximum gain state and generates a first seed light, the first seed light being injected into the first capillary segment and amplified and output by the plasma column in the first capillary segment that is in the gain state.

[0022] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0023] As mentioned above, a stepped inner diameter capillary device for generating extreme ultraviolet lasers according to the present invention includes multiple capillary segments, which are coaxially arranged.

[0024] The inner holes in each capillary segment are interconnected, thus forming a continuous series of inner holes within multiple capillary segments to contain the working gas.

[0025] The multiple capillary segments include at least two capillary segments, namely a first capillary segment and a second capillary segment. The first capillary segment has a first inner diameter, the second capillary segment has a second inner diameter, and the first inner diameter is smaller than the second inner diameter.

[0026] In an embodiment of the invention, the first inner diameter and the second inner diameter are configured such that, in response to a pulsed discharge current applied to both ends of the stepped inner diameter capillary device, the plasma column of the first capillary segment reaches the maximum gain state for the target wavelength extreme ultraviolet laser earlier than the plasma column of the second capillary segment, and generates laser light first. The target wavelength is, for example, 46.9 nm.

[0027] By setting the difference between the second inner diameter and the first inner diameter, the second capillary segment can reach the maximum gain state within a preset time period after the first capillary segment starts generating laser light, and generate a corresponding seed light, which is injected into the first capillary segment as the first seed light of extreme ultraviolet laser (hereinafter also referred to as the first seed light), and amplified and output by the plasma column in the first capillary segment that is in the gain state.

[0028] For example, the dimensions of the first inner diameter and the second inner diameter can be set such that when the second capillary segment starts to generate extreme ultraviolet laser, the plasma column in the first capillary segment is still in a state of gain for the target wavelength, and the extreme ultraviolet laser generated by the second capillary segment is injected into the first capillary segment as the first seed light and amplified by its plasma column.

[0029] As an example, the difference in inner diameter between the first capillary segment and the second capillary segment can be between 0.1 mm and 0.5 mm (including the end value).

[0030] Furthermore, as an example, the preset time period can be less than or equal to the pulse duration of the spontaneously generated laser in the first capillary segment. For example, the preset time period is set to 1.5 ns.

[0031] According to an embodiment of the present invention, the multiple capillary segments include, for example, N stages of segments connected end-to-end along the axial direction, where N is an integer. Thus, the inner diameters corresponding to the first to Nth stages of the capillary segments can be set to increase sequentially, thereby enabling the plasma columns corresponding to each stage of the capillary segments to reach maximum gain in order of increasing inner diameter.

[0032] When N equals 2, the multiple capillary segments consist only of the first and second capillary segments. In this way, the first capillary segment reaches the maximum gain state for the target wavelength first, followed by the second capillary segment reaching the corresponding maximum gain state.

[0033] For example, in an example where N equals 2, the first inner diameter can be set to 2.5 mm and the second inner diameter to 2.6 mm. Thus, approximately 1.5 ns after the plasma column in the first capillary segment reaches its maximum gain for the target wavelength, the corresponding plasma column in the second capillary segment also reaches its maximum gain. In this example, the 2.6 mm capillary can serve as the input side of the main pulse current, and the 2.5 mm capillary serves as the ground terminal and the output side of the extreme ultraviolet laser.

[0034] When N is greater than 2, that is, multiple capillary segments include three or more capillary segments. In other words, when N is greater than 2, the stepped inner diameter capillary device may include one or more capillary segments as the third, fourth, ..., Nth capillary segments in addition to the first and second capillary segments mentioned above.

[0035] For example, in an example where N equals 3, the first inner diameter can be set to 2.5 mm, the second inner diameter to 2.6 mm, and the third inner diameter to 2.7 mm. Thus, approximately 1.5 ns after the plasma column in the first capillary segment reaches its maximum gain for the target wavelength, the corresponding plasma column in the second capillary segment reaches its corresponding maximum gain; and approximately 3 ns after the plasma column in the first capillary segment reaches its maximum gain for the target wavelength, the corresponding plasma column in the third capillary segment reaches its corresponding maximum gain.

[0036] As an example, the inner diameter of each capillary segment in a plurality of capillary segments is, for example, in the range of 2 mm to 4 mm (including the end value).

[0037] Embodiments of the present invention also provide a method for generating extreme ultraviolet (EUV) laser light, which is implemented using a stepped-diameter capillary device as described above. The method includes: filling the stepped-diameter capillary with a working gas; applying a pulsed discharge current to both ends of the stepped-diameter capillary to generate a plasma column exhibiting a Z-pinch effect; utilizing the time difference between different inner diameter segments reaching their maximum gain state, using the EUV laser light generated by one or more segments as seed light, and injecting it into the segments still in the gain state for amplification; wherein the segment with the smaller inner diameter reaches its maximum gain state earlier than the segment with the larger inner diameter.

[0038] In this method, working gas is pre-filled into the aforementioned stepped inner diameter capillary tube.

[0039] In this way, during operation, a pulsed discharge current is applied to both ends of the aforementioned stepped inner diameter capillary so that each capillary segment generates a plasma column capable of exhibiting the Z-pinch effect.

[0040] In this way, by utilizing the time difference between the different inner diameter pipe sections reaching the maximum gain state, the extreme ultraviolet laser generated by one or more pipe sections is used as seed light and injected into the pipe section that is still in the gain state for amplification; among them, the pipe section with a smaller inner diameter reaches the maximum gain state earlier than the pipe section with a larger inner diameter.

[0041] For example, the first capillary segment with the first inner diameter reaches the maximum gain state and generates laser light earlier than the second capillary segment with the second inner diameter; within a preset time period after the first capillary segment generates laser light, extreme ultraviolet laser light generated by one or more other segments is injected into the first capillary segment, which is still in the gain state, for amplification.

[0042] In an embodiment of the present invention, the seed light is generated by a pipe segment with a larger inner diameter and injected into a pipe segment with a smaller inner diameter for single-pass amplification.

[0043] For example, when N=2, the second capillary segment generates the first seed light, which is injected into the first capillary segment for amplification, and the resulting amplified light is used as the first amplified light. In this way, the extreme ultraviolet laser generated first by the first capillary segment and the first amplified light are output through the output end of the stepped inner diameter capillary device.

[0044] For example, when N=3, the first seed light generated by the second capillary segment is injected into the first capillary segment for amplification (resulting in the first amplified light), and the second seed light of the extreme ultraviolet laser generated by the third capillary segment (referred to as the second seed light) is also injected into the first capillary segment after passing through the second capillary segment for amplification (resulting in the second amplified light). In this way, the extreme ultraviolet laser, the first amplified light, and the second amplified light generated first by the first capillary segment are output through the output end of the stepped inner diameter capillary device.

[0045] Preferred embodiment 1 In a preferred embodiment of the invention, a gas pressure in the range of 34-36 Pa is first introduced into the capillary. Preferably, for example, a gas pressure of 35 Pa can be introduced, at which the effect of generating 46.9 nm laser corresponding to a 2.5 mm tube section is optimal. Since the generation of extreme ultraviolet laser during capillary discharge occurs near the point when the plasma column is constricted to its minimum radius, the time for laser generation during capillary discharge is related to the inner diameter of the capillary. Figure 3 As shown, when the capillary inner diameter is larger, the time required to constrict to the minimum radius of the plasma column is longer. Therefore, the plasma column generated on the 2.5mm capillary side will reach the moment of maximum gain for the 46.9nm laser first, generating a 46.9nm laser with a pulse width of 1-2ns. Figure 4 As shown, previous experiments revealed that although the plasma column generated by the 2.5mm side capillary no longer spontaneously produces 46.9nm laser light, the plasma column still provides a gain for the 46.9nm laser. Figure 3 As shown, the time difference between the plasma columns generated by the 2.5mm and 2.6mm capillaries reaching their minimum radius is 1.5ns. 1.5ns after the laser generation on the 2.5mm capillary side, a 46.9nm laser is generated on the 2.6mm capillary side, injecting seed light into the plasma column generated on the 2.5mm capillary side. This seed light is then amplified by the plasma column on the 2.5mm capillary side, resulting in a higher-intensity 46.9nm laser. The lasers generated by the two capillary segments are superimposed, resulting in a 46.9nm laser output with higher intensity and wider pulse width.

[0046] Preferred embodiment 2 In another preferred embodiment of the invention, it is possible to Figure 2 On top of that, a 2.7mm capillary segment is further added, such as... Figure 5 As shown. According to Figure 3Calculations show that the time when the 2.7 mm capillary is constricted to the minimum plasma column radius differs from the time when the 2.5 mm capillary is constricted to the minimum plasma column radius by 3 ns. Figure 4 It can be seen that the plasma column corresponding to the 2.5mm capillary still has a gain for the 46.9nm laser. By adding a 2.7mm capillary, it is expected to obtain a 46.9nm laser output with a wider pulse width and higher energy.

[0047] It should be noted that although several units, modules, or sub-modules are mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of the present invention, the features and functions of two or more modules described above can be embodied in one module. Conversely, the features and functions of one module described above can be further divided and embodied by multiple modules.

[0048] Furthermore, although the operations of the method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0049] While the spirit and principles of the invention have been described with reference to several specific embodiments, it should be understood that the invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A stepped-diameter capillary device for generating extreme ultraviolet laser, characterized in that, It includes multiple capillary segments, which are coaxially arranged to form a continuous inner hole for containing working gas; wherein the multiple capillary segments include at least a first capillary segment having a first inner diameter and a second capillary segment having a second inner diameter, the first inner diameter being smaller than the second inner diameter; The first inner diameter and the second inner diameter are configured as follows: In response to the pulsed discharge current applied to both ends of the stepped inner diameter capillary device, the plasma column of the first capillary segment reaches the maximum gain state for the target wavelength extreme ultraviolet laser earlier than the plasma column of the second capillary segment, and generates laser first. Within a preset time period after the first capillary segment generates laser light, the second capillary segment reaches its maximum gain state and generates a first seed light. The first seed light is injected into the first capillary segment and amplified and output by the plasma column in the first capillary segment that is in a gain state.

2. The stepped inner diameter capillary device according to claim 1, characterized in that: The preset time period is less than or equal to the pulse duration of the laser spontaneously generated by the first capillary segment.

3. The stepped inner diameter capillary device according to claim 2, characterized in that: The dimensions of the first inner diameter and the second inner diameter are set such that when the second capillary segment generates the first seed light of extreme ultraviolet laser, the plasma column in the first capillary segment is still in a state of gain for the target wavelength, so as to amplify the first seed light.

4. The stepped inner diameter capillary device according to claim 1, characterized in that: The plurality of capillary segments include N stages of segments connected end to end along the axial direction, where N is an integer greater than 2; and the inner diameters of the first stage to the Nth stage increase sequentially, so that the plasma columns corresponding to each stage of the capillary segment reach the maximum gain state in order of increasing inner diameter.

5. The stepped inner diameter capillary device according to claim 1, characterized in that: The difference in inner diameter between the first capillary segment and the second capillary segment is between 0.1 mm and 0.5 mm.

6. The stepped inner diameter capillary device according to claim 1, characterized in that: The target wavelength is 46.9 nm, and the inner diameter of each capillary segment is in the range of 2 mm to 4 mm.

7. The stepped inner diameter capillary device according to any one of claims 1-6, characterized in that: The first inner diameter is 2.5 mm, and the second inner diameter is 2.6 mm.

8. The stepped inner diameter capillary device according to claim 7, characterized in that, N=3, the third inner diameter of the third stage capillary segment is 2.7mm.

9. A method for generating extreme ultraviolet laser, implemented using a stepped inner diameter capillary device as described in any one of claims 1-8, characterized in that, The method includes: A working gas is introduced into the stepped inner diameter capillary device; A pulsed discharge current is applied to both ends of the stepped inner diameter capillary device to generate a plasma column that exhibits the Z-pinch effect. By utilizing the time difference in the time it takes for pipe segments with different inner diameters to reach the maximum gain state, extreme ultraviolet laser light generated by one or more pipe segments is used as seed light and injected into the pipe segment that is still in the gain state for amplification; among them, the pipe segment with a smaller inner diameter reaches the maximum gain state earlier than the pipe segment with a larger inner diameter.

10. The method according to claim 9, characterized in that, The method of utilizing the time difference between different inner diameter pipe sections reaching the maximum gain state, and using the extreme ultraviolet laser generated by one or more pipe sections as seed light, to inject into the pipe section still in the gain state for amplification includes: The first capillary segment with the first inner diameter reaches the maximum gain state earlier and generates laser light first than the second capillary segment with the second inner diameter. Within a preset time period after the laser is generated in the first capillary segment, extreme ultraviolet lasers generated by one or more other segments are injected as seed light into the first capillary segment, which is still in a gain state, for amplification.

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