Debris mitigation method for electrodeless soft x-ray light source and light source system

Abstract

The present application relates to a method for debris mitigation for electrodeless soft X-ray light source and a light source system, comprising: a mounting flange interface; an insulating isolation component arranged inside the mounting flange interface; a bias voltage electrode mounted on the insulating isolation component and coaxially arranged with an exit port, the bias voltage electrode being a hollow conductive body with an inner diameter greater than the diameter of a soft X-ray beam; a high-voltage introduction component for applying a bias voltage to the bias voltage electrode; the bias voltage electrode is configured to apply a negative high voltage relative to the plasma potential during operation of the light source, thereby forming an electric field to directly adsorb the positively charged high-energy cations ejected by the plasma itself to the surface of the bias voltage electrode. The beneficial effects of the present application are: the present application only needs a bias voltage electrode to cooperate with an insulating component and a high-voltage introduction component to realize the debris mitigation function, and is easy to integrate into the existing light source cavity.

Description

Technical Field

[0001] This invention belongs to the field of plasma debris control technology, and particularly relates to a debris mitigation method and a light source system for electrodeless soft X-ray sources. Background Technology

[0002] Electrodeless Z-pinch extreme ultraviolet (EUV) light sources have become a highly promising EUV light source solution for next-generation lithography and mask inspection due to their compact structure, long electrode life, and high-frequency operation capabilities. However, during the process of forming high-temperature, high-density plasma through pulsed discharge, these light sources simultaneously eject a large number of high-energy cations (mainly from the target material, such as Cu, Li, and Sn) in all directions. Once these high-energy cations bombard the surfaces of the back-end EUV collector mirror, thin-film filter, or other optical components, they can cause sputtering corrosion, decreased reflectivity, and deterioration of transmittance, ultimately leading to a rapid decline in the light source's output power and a severe reduction in the lifespan of optical components. Therefore, effectively mitigating the damage to optical components caused by high-energy cation debris is one of the key issues that urgently needs to be addressed for these light sources to achieve engineering applications.

[0003] Currently known debris mitigation techniques mainly fall into the following categories: electric field deflection method, magnetic field deflection method, and pure gas dynamics method.

[0004] The basic idea of ​​the electric field deflection method is to apply a transverse electric field along the debris flight path, causing charged debris to be deflected to a collection plate that is off the light path. In order to process neutral debris at the same time, existing schemes usually require additional active ionization devices such as corona discharge needles and electron guns in the system so that neutral particles can be deflected by the electric field after being charged. This type of scheme has the following shortcomings: (1) The device structure is complex, requiring multiple electrodes to cooperate with active ionization devices and independent collectors, making system integration difficult; (2) The active ionization process may introduce secondary pollution or interfere with the discharge plasma; (3) The transverse deflection electric field requires a sufficient deflection stroke, resulting in a large axial or radial dimension of the device, which is not conducive to the miniaturization of the light source system.

[0005] The magnetic field deflection method utilizes the Lorentz force of a magnetic field on charged particles to deflect them. However, this method usually requires the introduction of a strong magnetic field source (such as a permanent magnet or an electromagnetic coil), which not only increases the complexity and cost of the system, but may also have an adverse effect on the discharge process of the light source. Furthermore, the deflection efficiency for high-energy cations is limited by the strength and gradient of the magnetic field.

[0006] The pure gas dynamics method introduces a buffer gas near the optical path, using the collision of gas molecules with debris to slow it down or change its direction. However, this method introduces an additional gas load, increasing the burden on the vacuum system. At the same time, the gas itself absorbs EUV radiation, directly reducing the output efficiency of EUV.

[0007] Therefore, existing debris mitigation technologies generally suffer from problems such as complex structure, need to introduce additional gas or magnetic field, negative impact on EUV transmittance, or inability to efficiently capture high-energy cations. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a debris mitigation method and a light source system for electrodeless soft X-ray sources.

[0009] In a first aspect, a debris mitigation device for an electrodeless soft X-ray source is provided, the electrodeless soft X-ray source generating plasma through pulsed discharge, the device comprising:

[0010] A mounting flange interface is used to fix the device to the soft X-ray emission port of the plasma chamber of the electrodeless soft X-ray source;

[0011] An insulating isolation component is disposed inside the mounting flange interface to achieve electrical isolation between the bias voltage electrode and the chamber wall;

[0012] The bias voltage electrode is mounted on the insulating isolation component and arranged coaxially with the emission port. The bias voltage electrode is a hollow conductor with an inner diameter larger than the diameter of the soft X-ray beam.

[0013] A high-voltage introduction component is used to apply a bias voltage to the bias voltage electrode;

[0014] The bias voltage electrode is configured to apply a negative high voltage relative to the plasma potential when the light source is working, thereby forming an electric field that directly adsorbs the positively charged high-energy cations ejected by the plasma onto the surface of the bias voltage electrode.

[0015] Preferably, the surface of the bias voltage electrode is provided with an anti-sputtering coating, and the material of the anti-sputtering coating is platinum, rhodium or titanium nitride.

[0016] Preferably, the bias voltage electrode is made of copper T2 or oxygen-free copper.

[0017] Preferably, the high-voltage introduction assembly includes an electric shock rod isolation post and a spring electric shock rod, one end of which elastically contacts the bias voltage electrode, and the other end is connected to an external high-voltage feed terminal.

[0018] Preferably, the mounting flange interface is a T-type three-way flange metal seal, or the device is directly installed inside the plasma chamber.

[0019] Preferably, the inner diameter of the bias voltage electrode is larger than the diameter of the soft X-ray beam, and the bias voltage electrode is disposed between the plasma luminescence region and the rear optical element.

[0020] In a second aspect, a debris mitigation method for an electrodeless soft X-ray source is provided, performed by any of the apparatuses described in the first aspect, comprising:

[0021] S1. The bias voltage electrode is set at the soft X-ray emission port of the plasma chamber of the electrodeless soft X-ray source, and the bias voltage electrode is arranged coaxially with the emission port.

[0022] S2. Apply a negative bias voltage relative to the plasma potential to the bias voltage electrode;

[0023] S3. Activate the electrodeless soft X-ray source to generate plasma;

[0024] S4. The positively charged high-energy cations ejected by the plasma are directly adsorbed onto the surface of the bias voltage electrode under the action of the electrostatic field formed by the negative bias voltage, and cannot reach the back-end optical components.

[0025] Preferably, the negative bias voltage in S2 is a DC negative bias voltage with a voltage range of -500V to -5kV.

[0026] Preferably, the negative bias voltage in S2 is a pulsed negative bias voltage synchronized with the discharge pulse of the light source, and the pulse width covers the ion flight time window.

[0027] Thirdly, an electrodeless soft X-ray source system is provided, including an electrodeless soft X-ray plasma chamber and a pulsed power drive system, and further including a debris mitigation device as described in any one of the first aspects, wherein the debris mitigation device is disposed between the soft X-ray exit port of the plasma chamber and the rear optical element.

[0028] The beneficial effects of this invention are:

[0029] 1. Extremely simple structure and high integration: This invention only requires a bias voltage electrode, an insulating component and a high voltage inlet to achieve the debris mitigation function. There are no moving parts, no need for gas pipelines or magnets. The overall structure is extremely simple, highly reliable and easy to integrate into existing light source cavities.

[0030] 2. Excellent capture efficiency and significant protection for optical components: This invention directly utilizes electrostatic force to adsorb positively charged high-energy cations ejected from the plasma itself, exhibiting natural selectivity for charged debris without any active ionization step. For cations generated by an electrodeless Z-pinch source, the capture efficiency can reach over 92%, and the contamination rate on the surface of the downstream collection mirror is reduced by more than 90%, significantly extending the service life of optical components.

[0031] 3. Does not interfere with light source output and is easy to maintain: The bias voltage electrode adopts a hollow structure with an inner diameter larger than the beam diameter, so it does not obstruct the soft X-ray output; at the same time, no gas is introduced into the chamber during the entire operation, maintaining a high vacuum environment with no additional radiation absorption. In addition, the bias can be designed as a quick-change part, with low replacement cost, and can also integrate a self-cleaning pulse mode (by periodically changing the bias polarity or applying a positive high-voltage pulse to bombard deposits), further extending the maintenance cycle. Attached Figure Description

[0032] Figure 1 This is a cross-sectional schematic diagram of the device of the present invention installed on the electrodeless Z-pinch light source chamber.

[0033] Figure 2 This is a partial enlarged view of the bias voltage electrode and the insulation isolation components.

[0034] Figure 3 This is a schematic diagram showing the relative positions of the device of the present invention and the EUV collection mirror at the back end.

[0035] Figure 4 This is a diagram showing the synchronization relationship between the pulse bias voltage timing and the light source discharge pulse.

[0036] Figure 5 This is a schematic diagram of cation transport.

[0037] Figure 6 Schematic diagram of a cation trapping electrode;

[0038] Explanation of reference numerals in the attached diagram: 1. Mounting flange interface; 2. Insulation isolation assembly; 3. Bias voltage electrode; 4. High voltage introduction assembly; 5. External insulation shell; 6. Plasma chamber wall; 7. Plasma luminescence area. Detailed Implementation

[0039] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0040] Example 1:

[0041] To address the problems of existing technologies, Embodiment 1 of this invention provides a debris mitigation device for an electrodeless soft X-ray source. The electrodeless soft X-ray source generates plasma through pulsed discharge. For example, an electrodeless Z-pinch source is used, with the following operating parameters: repetition frequency 2 kHz, plasma emission region diameter 0.5 mm, and EUV emission spot diameter approximately 8 mm. The debris mitigation device is as follows: Figure 1As shown in the diagram, the bias electrode 3 is made of oxygen-free copper, with an inner diameter of 20 mm, a thickness of 5 mm, and a platinum coating of 1 µm. The bias electrode is axially 35 mm from the plasma center. A -2.5 kV DC negative voltage is applied via a high-voltage power supply. The cation flux reaching the downstream collection mirror is measured using a Faraday cup and a quadrupole mass spectrometer, with a capture efficiency of 92%.

[0042] Specifically, such as Figure 1 and Figure 2 As shown, the apparatus provided in this embodiment of the invention includes:

[0043] Mounting flange interface 1 is used to fix the device to the soft X-ray emission port of the plasma chamber wall 6 of the electrodeless soft X-ray source. The mounting flange interface 1 is a T-type three-way flange metal seal with a central channel for the light source radiation and debris to pass through, or the device can be directly installed inside the plasma chamber.

[0044] An insulating isolation component 2 is disposed inside the mounting flange interface 1 to achieve electrical isolation between the bias voltage electrode 3 and the chamber wall. For example, the insulating isolation component 2 is made of a high-temperature resistant material such as ceramic to achieve electrical isolation between the bias voltage electrode 3 and the grounded chamber wall.

[0045] The bias voltage electrode 3 is mounted on the insulating isolation component 2 and is arranged coaxially with the emission port. The bias voltage electrode 3 is a hollow conductor with an inner diameter larger than the diameter of the soft X-ray beam, and its side facing the plasma is the adsorption working surface.

[0046] The bias voltage electrode 3 is configured to apply a negative high voltage relative to the plasma potential when the light source is working, thereby forming an electric field. This electric field exerts a pulling force on the high-energy cations ejected by the plasma itself, causing the high-energy cations to be directly deflected and impacted onto the surface of the bias voltage electrode 3 or its adjacent collection surface, thus preventing them from reaching the back-end optical elements.

[0047] It should be noted that when the bias voltage electrode 3 does not block the beam, cations near the central axis will inevitably collide with the electrode surface. This is because the space charge effect causes the ion trajectory to expand and diverge. Even ions initially emitted in the axial direction will acquire a certain radial divergence angle under the influence of space charge. For example, for a cation with a small radial offset r0 (charge q = +e, mass m), the radial motion equation can be written as:

[0048]

[0049] Therefore, cations near the central axis will eventually collide with the electrode surface under the influence of the electric field.

[0050] Specifically, the surface of the bias voltage electrode 3 is provided with an anti-sponge coating, the material of which is platinum, rhodium, titanium nitride, or a replaceable sacrificial liner to extend the maintenance cycle. The bias voltage electrode 3 is made of copper (such as copper T2) or oxygen-free copper. Figure 6 Ultimately, the cations will strike the electrode. It should be noted that this invention does not limit the shape of the bias voltage electrode 3. Figure 3 Taking the bias voltage electrode 3 as an example, the bias voltage electrode 3 can also be other shapes such as blade-shaped, plate-shaped, arc-shaped, etc.

[0051] The inner diameter of the bias voltage electrode 3 is larger than the diameter of the soft X-ray beam, and the bias voltage electrode 3 is disposed between the plasma luminescent region 7 and the rear optical element.

[0052] A high-voltage input component 4 is used to apply a bias voltage to the bias voltage electrode 3. The high-voltage input component 4 includes an electric shock rod isolation post and a spring electric shock rod, one end of which elastically contacts the bias voltage electrode 3, and the other end is connected to an external high-voltage feed terminal.

[0053] Furthermore, the device also includes an external insulating shell 5, which covers the high-voltage components exposed to the atmosphere and provides electrical safety protection.

[0054] It should be noted that this invention does not include any charging device (such as a corona discharge needle, electron gun, etc.) for charging neutral debris, does not introduce any buffer gas or gas flow, and does not use mechanical moving parts, metal foils, or permanent magnets. The electric field of this invention is not intended to deflect charged debris to a specific collector, but rather to directly apply it along the path that high-energy cations must take to reach the optical element. Figure 5 This creates a "trap," deflecting cations so that they are directly adsorbed onto the bias electrode itself. The "necessary path" refers to a portion of the transmission path from the soft X-ray source to the downstream thin film or mirror.

[0055] Example 2:

[0056] Based on Example 1, Example 2 of the present invention provides a debris mitigation method for an electrodeless soft X-ray source, comprising:

[0057] S1. The bias voltage electrode 3 is placed at the soft X-ray emission port of the plasma chamber wall 6 of the electrodeless soft X-ray source, and the bias voltage electrode 3 is arranged coaxially with the emission port.

[0058] S2. Apply a negative high voltage relative to the plasma potential to the bias voltage electrode 3.

[0059] The negative high voltage mentioned in S2 is a DC negative high voltage with a voltage range of -500V to -5kV.

[0060] For example, to reduce the average power of the high-voltage power supply and decrease the thermal load of ion bombardment on the bias electrodes, a pulsed negative high voltage synchronized with the discharge pulse is used, with the pulse width covering the ion flight time window to reduce average power consumption. A -3 kV negative high-voltage pulse with a pulse width of 3 µs is generated 1.5 µs before each discharge trigger. Figure 4 There is a time delay between the two. A short period after the main pulse begins, the bias electrode becomes negatively charged, ensuring that the generated cations are delivered to the bias electrode position. The timing can be adjusted under different operating conditions. After the pulse ends, the bias electrode potential either floats or is grounded. In this mode, the surface temperature rise of the bias electrode is reduced by 70%. It is suitable for high duty cycle operation with a repetition frequency above 5kHz.

[0061] S3. Start the electrodeless soft X-ray source to generate plasma.

[0062] S4. The positively charged high-energy cations ejected by the plasma are directly adsorbed onto the surface of the bias voltage electrode 3 under the action of the electrostatic field formed by the negative high voltage, and cannot reach the back-end optical components.

[0063] In addition, the bias voltage electrode should be replaced or deposits should be cleaned during regular maintenance.

[0064] It should be noted that the method provided in this embodiment is the method corresponding to the device provided in embodiment 1. Therefore, the parts in this embodiment that are the same as or similar to those in embodiment 1 can be referred to each other, and will not be repeated in this application.

[0065] Example 3:

[0066] Based on Embodiment 1, Embodiment 3 of the present invention provides an electrodeless soft X-ray source system, including an electrodeless soft X-ray plasma chamber and a pulsed power drive system, and further including a debris mitigation device, such as... Figure 3 As shown, the debris mitigation device is disposed between the soft X-ray exit port of the plasma chamber and the rear optical element.

[0067] It should be noted that the system provided in this embodiment is the same as the system of the device provided in embodiment 1. Therefore, the parts that are the same as or similar to those in embodiment 1 in this embodiment can be referred to each other, and will not be described again in this application.

Claims

1. A debris mitigation device for an electrodeless soft X-ray source, wherein the electrodeless soft X-ray source generates plasma through pulsed discharge, characterized in that, The device includes: A mounting flange interface is used to fix the device to the soft X-ray emission port of the plasma chamber of the electrodeless soft X-ray source; An insulating isolation component is disposed inside the mounting flange interface to achieve electrical isolation between the bias voltage electrode and the chamber wall; The bias voltage electrode is mounted on the insulating isolation component and arranged coaxially with the emission port. The bias voltage electrode is a hollow conductor with an inner diameter larger than the diameter of the soft X-ray beam. A high-voltage introduction component is used to apply a bias voltage to the bias voltage electrode; The bias voltage electrode is configured to apply a negative high voltage relative to the plasma potential when the light source is working, thereby forming an electric field that directly adsorbs the positively charged high-energy cations ejected by the plasma onto the surface of the bias voltage electrode.

2. The debris mitigation device for an electrodeless soft X-ray source according to claim 1, characterized in that, The surface of the bias voltage electrode is provided with an anti-sputtering coating, and the material of the anti-sputtering coating is platinum, rhodium or titanium nitride.

3. The debris mitigation device for an electrodeless soft X-ray source according to claim 2, characterized in that, The bias voltage electrode is made of copper or oxygen-free copper.

4. The debris mitigation device for an electrodeless soft X-ray source according to claim 3, characterized in that, The high-voltage introduction component includes an electric shock rod isolation column and a spring electric shock rod. One end of the spring electric shock rod elastically contacts the bias voltage electrode, and the other end is connected to an external high-voltage feed terminal.

5. The debris mitigation device for an electrodeless soft X-ray source according to claim 4, characterized in that, The mounting flange interface is a T-type three-way flange metal seal, or the device is directly installed inside the plasma chamber.

6. The debris mitigation device for an electrodeless soft X-ray source according to claim 5, characterized in that, The inner diameter of the bias voltage electrode is larger than the diameter of the soft X-ray beam, and the bias voltage electrode is disposed between the plasma luminescence region and the rear optical element.

7. A method for debris mitigation in an electrodeless soft X-ray source, characterized in that, Performed by the apparatus according to any one of claims 1 to 6, comprising: S1. The bias voltage electrode is set at the soft X-ray emission port of the plasma chamber of the electrodeless soft X-ray source, and the bias voltage electrode is arranged coaxially with the emission port. S2. Apply a negative high voltage relative to the plasma potential to the bias voltage electrode; S3. Activate the electrodeless soft X-ray source to generate plasma; S4. The positively charged high-energy cations ejected by the plasma are directly adsorbed onto the surface of the bias voltage electrode under the action of the electrostatic field formed by the negative high voltage, and cannot reach the back-end optical components.

8. The debris mitigation method for an electrodeless soft X-ray source according to claim 7, characterized in that, The negative high voltage mentioned in S2 is a DC negative high voltage with a voltage range of -500V to -5kV.

9. The debris mitigation method for an electrodeless soft X-ray source according to claim 8, characterized in that, The negative high voltage mentioned in S2 is a pulsed negative high voltage synchronized with the discharge pulse of the light source, and the pulse width covers the ion flight time window.

10. An electrodeless soft X-ray source system, comprising an electrodeless soft X-ray plasma chamber and a pulsed power drive system, characterized in that, It also includes a debris mitigation device as described in any one of claims 1 to 6, the debris mitigation device being disposed between the soft X-ray exit port of the plasma chamber and the rear optical element.

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