Laser plasma discharge chamber device and plasma generation and maintenance method

Abstract

The application relates to the technical field of plasma light sources, in particular to a laser plasma discharge cavity device and a plasma generation and maintenance method. The device comprises a discharge cavity body provided with an electrode mounting through hole and internally used for accommodating working gas, and a movable electrode device arranged in the discharge cavity body through the electrode mounting through hole, wherein the movable electrode device comprises an electrode, an insulating guide sleeve, a limiting mechanism and a sealing assembly; the electrode can move between an insertion position and a withdrawal position; in the insertion position, the electrode at least partially extends into the interior of the discharge cavity body and is used for discharging and breaking the working gas to generate initial plasma; in the withdrawal position, the electrode completely exits the discharge cavity body; the insulating guide sleeve is arranged at the electrode mounting through hole and is sleeved outside the electrode, and is used for radially positioning, movement guiding and high-voltage insulation of the electrode; the limiting mechanism is used for limiting the ignition position of the electrode; and the sealing assembly is used for sealing the electrode mounting through hole after the electrode is in the withdrawal position.

Description

Technical Field

[0001] This invention relates to the field of plasma light source technology, and in particular to a laser plasma discharge cavity device and a method for generating and maintaining plasma. Background Technology

[0002] Laser plasma sources, especially those operating in the vacuum ultraviolet band, possess high brightness, a wide spectrum, and good spatial stability, making them widely used in high-precision optical inspection fields such as bright-field defect detection in semiconductor wafers and photolithography mask inspection. In typical bright-field inspection applications, laser plasma sources are usually generated and maintained within a sealed cavity, typically filled with an inert gas at tens of atmospheres as the working medium to improve plasma density and radiation efficiency. In the traditional startup process of a laser plasma source, an initial plasma is typically generated inside the cavity using discharge electrodes, which is then maintained by a laser. This involves placing one or more pairs of high-voltage discharge electrodes within the cavity; an instantaneous high-voltage discharge breaks down the working gas to generate initial ionized seed electrons, and then the laser beam injects energy along the plasma channel to maintain the plasma.

[0003] However, due to the extremely high temperature in the plasma region, the electrodes are exposed to high-temperature, high-energy particle bombardment for extended periods during ignition and operation. This leads to evaporation or sputtering of the electrode material, causing vapor to migrate and deposit on the cooler laser incident window surface. This results in a sharp decrease in window transmittance, reduced laser energy conversion efficiency, unstable plasma maintenance, and deterioration of the light source's output performance and lifespan. To mitigate these problems, existing technologies typically employ optimized electrode materials or electrodeless plasma excitation methods. However, these methods suffer from difficulties in obtaining triggering conditions and high implementation costs. Therefore, it is necessary to take measures to design removable electrode devices that, while ensuring reliable plasma ignition, prevent electrode contamination of the cavity's internal environment and optical window during high-temperature operation. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a laser plasma discharge cavity device and a method for plasma generation and maintenance. By introducing a movable electrode device, the electrodes can be actively removed after the plasma stabilizes, avoiding evaporation or sputtering of the electrodes due to prolonged exposure to a high-temperature plasma environment. This fundamentally solves the problem of electrode evaporation contaminating the discharge cavity and optical components, extends the overall lifespan of the light source device, and improves the purity of the output spectrum.

[0005] A first aspect of the present invention provides a laser plasma discharge cavity device, comprising:

[0006] A discharge cavity, which is a sealed structure, is provided with a laser incident window, a light source exit window, and an electrode mounting through-hole, and its interior is used to contain the working gas; and

[0007] A movable electrode device is disposed in the discharge cavity via the electrode mounting through-hole. The movable electrode device includes an electrode, an insulating guide sleeve, a limiting mechanism, and a sealing assembly.

[0008] The electrode is movable between an insertion position and a withdrawal position; in the insertion position, the electrode is at least partially inserted into the discharge cavity and used to discharge and break down the working gas to generate initial plasma; in the withdrawal position, the electrode is completely withdrawn from the discharge cavity.

[0009] The insulating guide sleeve is disposed at the electrode mounting through hole and sleeved on the outside of the electrode, and is used for radial positioning, motion guidance and high voltage insulation of the electrode;

[0010] The limiting mechanism is used to limit the ignition position of the electrode;

[0011] The sealing assembly is used to seal the electrode mounting through hole after the electrode is in the withdrawn position.

[0012] According to the laser plasma discharge cavity device of the first aspect of the present invention, the movable electrode device further includes a driving mechanism, the driving mechanism being drivenly connected to the electrode and used to drive the electrode to move between the insertion position and the withdrawal position;

[0013] According to the laser plasma discharge cavity device of the first aspect of the present invention, the driving mechanism is a manual operation mechanism, an electric drive mechanism, or a pneumatic drive mechanism.

[0014] According to the laser plasma discharge cavity device of the first aspect of the present invention, a motion conversion mechanism is provided between the driving mechanism and the electrode, the motion conversion mechanism being used to convert rotational motion into linear motion of the electrode.

[0015] According to the laser plasma discharge cavity device of the first aspect of the present invention, the electrode includes an electrode portion and a rack drive section connected to the electrode portion, the rack drive section being drively connected to the drive mechanism, the electrode portion being made of a high-temperature resistant metal material, and the rack drive section being an insulated rack drive section.

[0016] According to the laser plasma discharge cavity device of the first aspect of the present invention, the movable electrode device is a pair, the pair of movable electrode devices are disposed opposite to each other in the discharge cavity, one of the electrodes is connected to a high-voltage ignition power supply, and the other electrode is grounded.

[0017] According to the laser plasma discharge cavity device of the first aspect of the present invention, a static sealing element is provided between the outer wall of the insulating guide sleeve and the electrode mounting through hole; a boss is provided in the portion of the insulating guide sleeve extending into the discharge cavity, the discharge cavity is provided with a step that mates with the boss, and a sealing element is provided between the boss and the step.

[0018] According to a laser plasma discharge cavity device of a first aspect of the present invention, the limiting mechanism includes a first limiting mechanism portion disposed on the electrode and a second limiting mechanism portion disposed on the insulating guide sleeve, wherein the first limiting mechanism portion and the second limiting mechanism portion cooperate to define the ignition position.

[0019] According to a laser plasma discharge cavity device of the first aspect of the present invention, the sealing assembly includes a sealing cover and a sealing element, the sealing cover being pressed against the outside of the discharge cavity body, and the sealing element being disposed between the sealing cover and the discharge cavity body.

[0020] A second aspect of the present invention provides a method for generating and maintaining plasma, employing a laser plasma discharge cavity device according to a first aspect of the present invention, the method comprising:

[0021] The discharge cavity is kept at a starting pressure lower than the target working pressure.

[0022] The electrode is extended to the ignition position and discharged to break down the working gas, thereby generating initial plasma;

[0023] The external laser is turned on, allowing the laser to enter the discharge cavity through the laser incident window and act on the initial plasma;

[0024] After the plasma is maintained by the laser, the electrode is withdrawn to the retraction position;

[0025] The electrode mounting through hole is sealed by the sealing assembly;

[0026] The gas pressure inside the discharge cavity is increased to the target working gas pressure, and the output power of the external laser is increased to the sustaining power to maintain the plasma.

[0027] According to the plasma generation and maintenance method of the second aspect of the present invention, during the process of raising the gas pressure in the discharge cavity to a target working gas pressure, the output power of the external laser is adjusted according to the gas pressure value in the discharge cavity.

[0028] According to the plasma generation and maintenance method of the second aspect of the present invention, the output power of the external laser is adjusted by increasing the power of a single laser beam, increasing the number of radially incident laser beams, or simultaneously increasing the power of a single laser beam and increasing the number of radially incident laser beams.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0030] The laser plasma discharge cavity device with removable electrodes proposed in this application employs a movable electrode design, limiting the electrode function to the initial ignition stage. Once the plasma is established and stabilized, the electrodes are removed from the high-temperature radiation region. This approach effectively avoids the electrode materials being exposed to a high-temperature plasma environment for extended periods. Furthermore, the segmented operation process enables coordinated control of electrode removal, gas pressure, and laser power, fulfilling the requirements for ignition and high-power, high-pressure operation of the laser plasma source device. Attached Figure Description

[0031] Figure 1 This is an overall schematic diagram of the first embodiment of the laser plasma discharge cavity device with removable electrodes provided in this application, wherein the movable electrode device is in the extended ignition position;

[0032] Figure 2 This is a partially enlarged structural schematic diagram of the movable electrode device according to the first embodiment of this application, highlighting the assembly relationship of the electrode, driving mechanism, insulating guide sleeve and sealing assembly;

[0033] Figure 3 This is a cross-sectional view of the discharge cavity after the electrode has been removed according to the first embodiment of this application, wherein the electrode has been withdrawn to the standby position and the sealing assembly has closed the cavity opening.

[0034] Figure 4 This is a partially enlarged structural schematic diagram of the movable electrode device according to the second embodiment of this application.

[0035] The text labels in the image represent:

[0036] 100. Discharge chamber; 101. Working gas; 102. Plasma; 210. Movable electrode; 211. Electrode section; 212. Rack and pinion drive section; 220. Drive mechanism; 230. Insulating guide sleeve; 231. Static sealing element; 232. Boss; 233. Step; 240. Limiting mechanism; 241. First part of limiting mechanism; 242. Second part of limiting mechanism; 251. Sealing cover; 252. Sealing element; 301. Laser entrance window; 302. Light source exit window. Detailed Implementation

[0037] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] As mentioned in the background section, to address the problem of electrodes being exposed to a high-temperature plasma environment for extended periods in existing technologies, this application proposes a laser plasma discharge cavity device with removable electrodes. The invention will now be described in detail with reference to the accompanying drawings.

[0040] like Figure 1 The diagram shown is a schematic representation of a first embodiment of a laser plasma discharge cavity device with removable electrodes provided by this invention. The structure includes a discharge cavity 100 made of metal, which can accommodate a working gas 101. The discharge cavity 100 includes a laser incident window 301 for transmitting an external laser used to generate and maintain plasma, and a light source exit window 302 for emitting laser plasma 102. A movable electrode device is installed in a through-hole in the wall of the discharge cavity 100, configured to generate initial plasma 102 during the startup phase and to be removed from the high-temperature region after the plasma 102 stabilizes. For details, please refer to... Figure 2 As shown, the movable electrode device has multiple components, including a metal electrode part 211, an insulated rack and pinion drive section 212, a limiting mechanism 240, a drive mechanism 220, an insulated guide sleeve 230, a sealing cover 251, and a sealing element 252. All of these parts are arranged in a straight line along the axial direction.

[0041] Specifically, the electrode section 211 has an electrode tip at one end, with an included angle between 30° and 120°. From its middle to its tail, it is fitted with an insulated rack as a transmission section, which is connected to the drive mechanism. A pair of movable electrodes 210 are fixed symmetrically within the discharge chamber 100. One electrode's tail is connected to an external high-voltage ignition power supply via a high-voltage cable, while the other electrode is connected to the power supply's ground terminal. The two movable electrodes 210 form a discharge circuit. The electrode section 211 is configured to generate an electric arc at a designated location within the discharge chamber 100, exciting the working gas 101 to form an initial plasma 102.

[0042] Specifically, the drive mechanism 220 is fixed at a designated position outside the cavity and directly connected to the rack and pinion drive section of the movable electrode 210. In this embodiment, the drive mechanism 220 can be a linear stepper motor, configured to drive the electrode part 211 to perform precise linear translational movement along its axial direction, realizing the action of extending into the discharge cavity 100 or retracting to an external standby position. Alternatively, the drive mechanism 220 can be fixed at a designated position outside the discharge cavity 100. The drive mechanism 220 may include a rotary stepper motor and a gear connected to the output shaft of the rotary stepper motor. The gear meshes with the rack and pinion drive section 212, thereby forming a motion conversion mechanism that converts the rotary motion output by the rotary stepper motor into the linear reciprocating motion of the electrode. Through the above-mentioned gear and rack drive structure, the drive mechanism 220 can drive the electrode to extend into the discharge cavity 100 or retract to a withdrawn position along its axial direction. The stroke range of the drive mechanism 220 is set according to the required movement distance of the electrode, with a typical value of 20mm to 180mm.

[0043] In other embodiments, the drive mechanism 220 can be a manual operating mechanism, an electric drive mechanism, or a pneumatic drive mechanism. The manual operating mechanism may include a handwheel, knob, push rod, or screw structure; the electric drive mechanism may include a stepper motor, servo motor, electric push rod, or linear motor; the pneumatic drive mechanism may include a cylinder and a transmission component connected to the cylinder. All of the above drive mechanisms can directly or indirectly drive the electrode to move between the insertion position and the withdrawal position.

[0044] Specifically, the insulating guide sleeve 230 is sleeved on the outside of the movable electrode 210 and fixed to the opening in the side wall of the discharge cavity 100. The insulating guide sleeve 230 is made of high-purity alumina ceramic through precision machining. Its inner wall is in clearance fit with the outer wall of the movable electrode 210, with a single-sided clearance distance of 0.1mm to 0.3mm. The static sealing element 231 between the outer wall of the insulating guide sleeve and the opening of the discharge cavity 100 is an O-ring. The portion of the insulating guide sleeve near the inner side of the discharge cavity 100 has an annular boss 232. The end face of the boss faces the metal wall of the discharge cavity 100 and forms a mating relationship with the step 233 provided on the inner side of the discharge cavity 100. An O-ring is installed between the boss and the step to prevent high-pressure gas leakage. The insulating guide sleeve 230 simultaneously performs the triple functions of radial positioning, motion guidance, and high-pressure insulation of the movable electrode 210. The limiting mechanism 240 is arranged in pairs. The first part 241 of the limiting mechanism is sleeved on a specific part of the movable electrode 210 and forms a matching relationship with the limiting protrusion of the second part 242 of the limiting mechanism on the inner surface of the insulating guide sleeve, thereby accurately fixing the ignition position of the electrode part 211.

[0045] Specifically, the sealing assembly is located at the electrode opening on the outside of the discharge chamber 100. The sealing assembly includes a stainless steel sealing cap 251 and an O-ring sealing element 252. The sealing cap 251 is pressed against the housing of the discharge chamber 100 from the outside by eight evenly distributed screws, and the O-ring is positioned between the sealing cap 251 and the discharge chamber 100. After the movable electrode 210 is completely withdrawn from the discharge chamber 100 by the drive mechanism 220, the operator manually tightens the screws on the sealing cap 251, causing the O-ring to deform under pressure, thus achieving a reliable seal of the opening and maintaining the high-pressure airtightness within the discharge chamber 100.

[0046] like Figure 4 The diagram shown is a schematic representation of a second embodiment of a laser plasma discharge cavity device with removable electrodes provided by this invention. Compared to the first embodiment, the electrode portion does not have an insulating rack and pinion drive section on its outer side, and no drive mechanism is provided. The movable electrode 210 is placed and removed manually by insertion and removal. The first part 241 of its limiting mechanism and the second part 242 of the limiting mechanism on the inner surface of the insulating guide sleeve form a matching relationship, thereby accurately fixing the ignition position of the electrode portion 211. This embodiment is suitable for cost-sensitive or low-frequency applications.

[0047] A method for generating and maintaining laser plasma with a movable electrode device, the movable electrode device being configured to perform the following segmented operation process:

[0048] Step 1: The discharge chamber 100 is first evacuated and then filled with one atmosphere of high-purity xenon gas selected in this embodiment. The drive mechanism 220 drives the movable electrode 210 to extend axially into the discharge chamber 100 until the tip of the electrode 211 reaches the preset ignition position. The high-voltage ignition power supply applies a high-voltage pulse to the movable electrode 210, generating an electric arc between the tip of the electrode 211 and the counter electrode, which instantly breaks down the working gas 101 and generates the initial plasma 102.

[0049] Step 2: The external axial laser is turned on in low-power mode. After being focused, the laser beam acts on the initial plasma 102 region. After absorbing the laser energy, the plasma 102 enters a maintenance state. After the plasma 102 stabilizes for 1-2 seconds, the drive mechanism 220 reverses its movement, causing the movable electrode 210 to rapidly exit the discharge cavity 100 axially until it reaches the standby position.

[0050] Step 3: The operator or automatic mechanism presses the sealing cover 251 of the sealing assembly to seal the original electrode opening. At this time, the discharge chamber 100 is completely sealed, the plasma 102 is maintained only by low-power laser, and the movable electrode 210 has been completely removed from the high-temperature radiation area.

[0051] Step 4: Gradually increase the intracavity pressure to the target high pressure. During the pressurization process, simultaneously increase the output power of the external laser to the corresponding maintenance level. In this embodiment, by real-time acquisition of the intracavity pressure value and outputting a laser power control signal according to a pre-calibrated functional relationship, closed-loop coordinated regulation of pressure and laser power is achieved. When the pressure reaches the target value and the laser power is simultaneously increased to the corresponding maintenance level, the plasma 102 stably radiates high-brightness, wide-spectrum light output under high pressure and high laser power conditions. Since the movable electrode 210 has been completely removed, there is no evaporation source of electrode material in the discharge cavity 100, and no electrode evaporation contaminants will be generated during long-term operation.

[0052] In some implementations, the output power of the external laser can be increased by increasing the power of a single laser beam, by increasing the number of incident laser beams, or by simultaneously increasing both the power of a single laser beam and the number of incident laser beams. Specifically, multiple laser incident windows 301 can be provided on the discharge cavity 100, allowing multiple laser beams to be incident on the region where the plasma 102 is located along different radial directions, thereby increasing the total laser power acting on the plasma 102.

[0053] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "middle," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the shape of the electrode, the type of the driving mechanism, the specific form and installation method of the sealing assembly, and the selection of the limiting mechanism can all be replaced or combined according to actual application requirements. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser plasma discharge cavity device, characterized in that, include: A discharge cavity, which is a sealed structure, is provided with a laser incident window, a light source exit window, and an electrode mounting through-hole, and its interior is used to contain the working gas; and A movable electrode device is disposed in the discharge cavity via the electrode mounting through-hole. The movable electrode device includes an electrode, an insulating guide sleeve, a limiting mechanism, and a sealing assembly. The electrode is movable between an insertion position and a withdrawal position; in the insertion position, the electrode extends at least partially into the discharge cavity and is used to discharge and break down the working gas to generate an initial plasma; In the withdrawn position, the electrode is completely withdrawn from the discharge cavity; The insulating guide sleeve is disposed at the electrode mounting through hole and sleeved on the outside of the electrode, and is used for radial positioning, motion guidance and high voltage insulation of the electrode; The limiting mechanism is used to limit the ignition position of the electrode; The sealing assembly is used to seal the electrode mounting through hole after the electrode is in the withdrawn position.

2. The laser plasma discharge cavity device according to claim 1, characterized in that, The movable electrode device further includes a drive mechanism, which is connected to the electrode for driving the electrode to move between the insertion position and the withdrawal position.

3. The laser plasma discharge cavity device according to claim 2, characterized in that, The drive mechanism can be a manual operating mechanism, an electric drive mechanism, or a pneumatic drive mechanism.

4. The laser plasma discharge cavity device according to claim 2, characterized in that, A motion conversion mechanism is provided between the driving mechanism and the electrode, which is used to convert rotational motion into linear motion of the electrode.

5. The laser plasma discharge cavity device according to claim 2, characterized in that, The electrode includes an electrode portion and a rack drive section connected to the electrode portion. The rack drive section is drively connected to the drive mechanism. The electrode portion is made of high-temperature resistant metal, and the rack drive section is an insulated rack drive section.

6. The laser plasma discharge cavity device according to claim 1, characterized in that, The movable electrode devices are a pair, and the pair of movable electrode devices are arranged opposite to each other in the discharge cavity. One of the electrodes is connected to a high-voltage ignition power supply, and the other electrode is grounded.

7. The laser plasma discharge cavity device according to claim 1, characterized in that, A static sealing element is provided between the outer wall of the insulating guide sleeve and the electrode mounting through hole; a boss is provided on the part of the insulating guide sleeve that extends into the discharge cavity, and a step that mates with the boss is provided in the discharge cavity, and a sealing element is provided between the boss and the step.

8. The laser plasma discharge cavity device according to claim 1, characterized in that, The limiting mechanism includes a first limiting mechanism part disposed on the electrode and a second limiting mechanism part disposed on the insulating guide sleeve. The first limiting mechanism part and the second limiting mechanism part cooperate to limit the ignition position.

9. The laser plasma discharge cavity device according to claim 1, characterized in that, The sealing assembly includes a sealing cap and a sealing element. The sealing cap is pressed against the outside of the discharge cavity, and the sealing element is disposed between the sealing cap and the discharge cavity.

10. A method for generating and maintaining plasma, characterized in that, The method using the laser plasma discharge cavity device according to any one of claims 1 to 9 comprises: The discharge cavity is kept at a starting pressure lower than the target working pressure. The electrode is extended to the ignition position and discharged to break down the working gas, thereby generating initial plasma; The external laser is turned on, allowing the laser to enter the discharge cavity through the laser incident window and act on the initial plasma; After the plasma is maintained by the laser, the electrode is withdrawn to the retraction position; The electrode mounting through hole is sealed by the sealing assembly; The gas pressure inside the discharge cavity is increased to the target working gas pressure, and the output power of the external laser is increased to the sustaining power to maintain the plasma.

11. The plasma generation and maintenance method according to claim 10, characterized in that, During the process of raising the gas pressure inside the discharge cavity to the target working gas pressure, the output power of the external laser is adjusted according to the gas pressure value inside the discharge cavity.

12. The plasma generation and maintenance method according to claim 11, characterized in that, The output power of the external laser is adjusted by increasing the power of a single laser beam, increasing the number of radially incident laser beams, or simultaneously increasing the power of a single laser beam and increasing the number of radially incident laser beams.

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