Corona pre-ionization high-power excimer laser

Abstract

The utility model discloses a corona preionization high-power excimer laser, which is characterized in that a laser discharge cavity is arranged in a shell, a main discharge electrode is arranged in the laser discharge cavity, and the main discharge electrode comprises a main discharge cathode and a main discharge anode; corona rods capable of conducting discharge preionization on working gas are arranged in the laser discharge cavity and located on one side of the main discharge cathode at intervals, each corona rod comprises a preionization electrode and a ceramic insulator, gaps are formed between the peripheral face of each ceramic insulator and the outer side wall of the main discharge cathode and the inner side wall of the insulation cavity, and the preionization electrodes and the main discharge anode are grounded. The main discharge cathode is connected with a negative high-voltage pulse, and when the excimer laser works, the driving voltage pulse of the corona rod is the same as the driving voltage pulse of the main discharge electrode. Corona discharge preionization is carried out through the corona rod, the main discharge electrode cannot be corroded, discharge dust cannot be generated, and it is ensured that the main discharge electrode carries out uniform glow discharge to generate high-quality laser.

Description

[Technical Field]

[0001] This utility model relates to a high-power excimer laser with corona pre-ionization. [Background Technology]

[0002] Excimer lasers, characterized by short wavelengths, high output energy, and high repetition rates, have been widely applied in optical lithography, laser annealing, atmospheric composition monitoring, and electrochemical micromachining. Typically, the working gas of an excimer laser is a mixture of inert and halogen gases. The excimer laser excites this mixture with high-voltage discharge to form excited-state excimer molecules. When these excimer molecules dissociate back to their ground state, they release high-energy ultraviolet photons, thus achieving laser output.

[0003] To increase the output power of excimer lasers, the pressure of the working gas is typically increased. However, with increased pressure, the streamer breakdown of the working gas is more prone to transforming into arc discharge. Arc discharge leads to the destruction of discharge uniformity, contamination of the working gas medium, and a decrease in laser energy. To avoid arc discharge, excimer lasers generally require pre-ionization of the working gas to generate a sufficiently high initial electron distribution in the discharge region. These initial electrons then generate a uniformly overlapping electron avalanche. ， This allows for a lateral uniform distribution of the electric field intensity, thereby preventing arc discharge. For high-power excimer lasers, with their large main discharge electrode width, large discharge spacing, and large discharge region volume, providing sufficient initial electron density in this large discharge region is a key indicator of the pre-ionization system. Since spark discharge pre-ionization can provide a very high pre-ionization electron density, it is a relatively reliable choice for high-power excimer lasers, as it can provide sufficient initial electron density in the large main discharge region to meet the requirements of uniform glow discharge. Therefore, all high-power excimer lasers currently on the market employ spark discharge pre-ionization technology. Although spark discharge pre-ionization can provide a very high pre-ionization electron density, for high-power excimer lasers, it can relatively easily provide sufficient initial electron density in the large main discharge region to meet the requirements of uniform glow discharge. However, the high-temperature electric sparks generated during spark discharge pre-ionization can corrode the metal structure of the pre-ionization bar and pre-ionization needle, producing a large amount of discharge dust that contaminates the working gas and laser cavity, reducing the lifespan of the laser. At the same time, spark discharge occurs simultaneously in the gaps between multiple pre-ionization needles and pre-ionization bars, and the multiple ultraviolet light sources generated are independent of each other, with the irradiation areas overlapping each other. This results in poor spatial uniformity of the overall initial electron density generated by spark discharge pre-ionization, hindering the improvement of laser output stability and beam quality of high-power equipment.

[0004] Therefore, this utility model was created based on the above-mentioned shortcomings. [Utility Model Content]

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-power excimer laser with corona pre-ionization. This high-power excimer laser uses a corona rod for corona discharge pre-ionization, which avoids corrosion of the main discharge electrode and the generation of discharge dust that contaminates the working gas. This improves the lifespan of the working gas and the overall lifespan of the laser discharge cavity. Furthermore, the initial electron density generated by corona pre-ionization has better spatial uniformity, ensuring uniform glow discharge of the main discharge electrode to produce high-quality laser light.

[0006] This utility model is achieved through the following technical solution:

[0007] A high-power excimer laser with corona pre-ionization includes a housing. Inside the housing is a laser discharge cavity filled with working gas. Within the laser discharge cavity are a pair of main discharge electrodes capable of exciting the working gas to generate laser light. Each main discharge electrode includes an elongated main discharge cathode and an elongated main discharge anode spaced apart from the main discharge cathode. A corona rod capable of pre-ionizing the working gas is spaced apart within the laser discharge cavity and located on one side of the main discharge cathode. The corona rod includes a pre-ionization electrode and a ceramic insulator surrounding the pre-ionization electrode. A gap exists between the outer circumferential surface of the ceramic insulator and the outer wall of the main discharge cathode and the inner wall of the insulating cavity. The pre-ionization electrode and the main discharge anode are grounded. The main discharge cathode is connected to a negative high-voltage pulse. When the excimer laser is operating, the driving voltage pulse of the corona rod is the same as the driving voltage pulse of the main discharge electrode.

[0008] The working gas is a mixture of Ne, Xe, and HCl, with a gas pressure of 0.35 MPa.

[0009] The corona rods are two in number and are symmetrically arranged on both sides of the main discharge cathode, parallel to the main discharge cathode.

[0010] The line connecting the centers of the two corona rods in their longitudinal sections passes through the point where the straight line and the arc meet on the same longitudinal section of the main discharge cathode.

[0011] The pre-ionization electrode is a metal rod, and the ceramic insulator is alumina ceramic.

[0012] The metal rod is a copper rod, and the ceramic insulator is sleeved on the copper rod with a gap between them.

[0013] The laser discharge cavity includes an insulating cavity. The main discharge cathode is connected to the top surface of the insulating cavity and connected to a voltage pulse drive power supply. The main discharge anode is connected to the bottom surface of the insulating cavity and grounded. A light-transmitting mirror is provided at the center of both ends of the insulating cavity. The light-transmitting mirrors on both sides and the insulating cavity form a sealed chamber.

[0014] The light-transmitting mirror is an ultraviolet mirror. The laser discharge cavity is provided with a first laser resonant mirror and a second laser resonant mirror on both sides of the outside, which are spaced apart from the ultraviolet mirror. The first laser resonant mirror is a total reflection mirror, and the second laser resonant mirror is a partial reflection mirror.

[0015] The first laser resonant lens has a reflectivity of 99.5%, and the second laser resonant lens has a reflectivity of 8%.

[0016] The transmittance of the ultraviolet lens is greater than or equal to 96%.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. The pre-ionization electrode of the corona rod of this invention is wrapped in a ceramic insulator and placed close to the main discharge cathode to induce corona discharge. Corona discharge does not require an additional driving circuit. The driving voltage pulse of the corona rod is the same as the driving voltage pulse of the main discharge electrode, which has good synergy with the discharge of the main discharge electrode and avoids delay and interference. Corona pre-ionization generates corona discharge through displacement current. The current is very small and will not corrode the main discharge electrode or generate discharge dust to contaminate the working gas and optical lenses. This is beneficial to improving the life of the working gas and the overall life of the laser discharge cavity. The corona rod is an integral structure. The corona discharge can be regarded as a single and uniform ultraviolet ionization source along the length of the main discharge electrode. The initial electron density generated by the corona pre-ionization has good spatial uniformity, ensuring that the main discharge electrode generates high-quality laser through uniform glow discharge.

[0019] 2. The laser discharge cavity of this invention is composed of an insulating cavity and sealed with ultraviolet (UV) mirrors on both sides. The first and second laser resonant mirrors are located on the outer sides of the laser discharge cavity. Even if contaminants are generated during the discharge of the laser discharge cavity, they will only contaminate the inexpensive UV mirrors, thus effectively protecting the expensive first and second laser resonant mirrors. Moreover, when the UV mirrors become contaminated to a certain extent, they can be wiped or replaced. Therefore, the placement of the first and second laser resonant mirrors prevents them from contacting the working gas inside the laser discharge cavity, greatly reducing maintenance costs.

[0020] 3. When the corona pre-ionization high-power excimer laser of this invention is working, the laser discharge is uniform, the output ultraviolet laser has high quality and high power, and the maintenance cost is low, making it suitable for widespread application. [Attached Image Description]

[0021] Figure 1 This is one of the schematic diagrams of this utility model;

[0022] Figure 2 This is the second schematic diagram of this utility model.

Detailed Implementation Methods

[0023] The present invention will be further described below with reference to the accompanying drawings:

[0024] like Figure 1 and Figure 2 As shown, a corona pre-ionization high-power excimer laser includes a housing 100, within which a laser discharge cavity 1 is provided. The laser discharge cavity 1 is filled with a working gas composed of a mixture of inert gas and halogen gas. In this embodiment, the working gas is composed of Ne, Xe, and HCl in a ratio of 99.255 / 0.67 / 0.075, with a gas pressure of 0.35 MPa and a temperature of 323 K. The laser discharge cavity 1 is provided with a pair of main discharge electrodes that can discharge and excite the aforementioned working gas to generate laser. The main discharge electrodes include a long strip-shaped main discharge cathode 21 and a long strip-shaped main discharge anode 22 spaced apart from the main discharge cathode 21. The main discharge cathode 21 and the main discharge anode 22 are 35mm apart in the vertical direction. The laser discharge cavity 1 is provided with a corona rod 3 that can discharge and pre-ionize the working gas, located on one side of the main discharge cathode 21. The corona rod 3 includes a pre-ionization electrode 31 made of a metal rod and a ceramic insulator 32 wrapped around the pre-ionization electrode 31. There is a gap between the outer peripheral surface of the ceramic insulator 32 and the outer wall of the main discharge cathode 21 and the inner wall of the insulating cavity 11. The metal rod and the main discharge anode 22 are grounded. The main discharge cathode 21 also serves as the cathode for the pre-ionization corona discharge. The main discharge cathode 21 is connected to a negative high voltage pulse. When the excimer laser is operating, the driving voltage pulse of the corona rod 3 is the same as the driving voltage pulse of the main discharge electrode. During the voltage rise on the main discharge cathode 21, the pre-ionization electrode 31 discharges before the main discharge electrode, resulting in corona discharge. The ultraviolet light generated by the corona discharge on the working gas illuminates the main discharge region 4, causing the gas in the main discharge region 4 to ionize and generate an initial pre-ionized electron distribution. Subsequently, glow discharge between the main discharge electrodes begins, thereby generating and outputting laser light. By pre-ionizing the working gas through corona discharge, the current is very small, which does not corrode the main discharge electrode or generate discharge dust that contaminates the working gas, thus improving the lifespan of the working gas and the overall lifespan of the laser discharge cavity. In this embodiment, the corona rod 3 is placed parallel to the main discharge cathode 21 and close to the main discharge cathode 21 to increase the corona discharge intensity and obtain a higher pre-ionized electron density.

[0025] However, in high-power excimer laser equipment, due to the large width of the main discharge electrode, the shielding effect of the main discharge cathode 21 is quite severe, resulting in a significantly uneven lateral distribution of pre-ionization in the high-power excimer laser. Therefore, to avoid the adverse effects of non-uniform discharge caused by the uneven lateral distribution of pre-ionization on the laser output quality, two corona rods 3 are symmetrically arranged on both sides of the main discharge cathode 21. This can effectively counteract the lateral non-uniformity of pre-ionization caused by the shielding of the main discharge cathode 21, ensuring better spatial uniformity of the initial electron density generated by corona pre-ionization and ensuring high-quality laser output.

[0026] like Figure 1 As shown, the line L connecting the centers of the two corona rods 3 in their longitudinal sections passes through the intersection of the straight line 21a and the arc 21b on the same longitudinal section of the main discharge cathode 21. This ensures a suitable distance between the corona rods 3 and the main discharge cathode 21, while reducing the shielding of the ultraviolet light generated by the corona discharge by the main discharge cathode 21 itself. This ensures that the ultraviolet light generated by the corona discharge has a sufficient viewing angle for the main discharge region 4, so as to efficiently trigger the main discharge of the discharge electrode.

[0027] The ceramic insulator 32 is made of alumina ceramic, and the pre-ionization electrode 31 is a copper rod, ensuring that no arc discharge occurs between the main discharge cathode 21 and the pre-ionization electrode 31. The inner and outer diameters of the ceramic insulator 32 are set to 0.6 cm and 1.44 cm, respectively, to ensure that the ceramic insulator 32 will not be broken down by the high voltage between the pre-ionization electrode 31 and the main discharge cathode 21. The ceramic insulator 32 is fitted onto the copper rod with a gap, and the gap fit between the two prevents the ceramic insulation layer from cracking due to thermal expansion of the copper rod.

[0028] like Figure 1 and Figure 2As shown, the laser discharge cavity 1 includes an insulating cavity 11. The main discharge cathode 21 is connected to the top surface of the insulating cavity 11 and connected to a voltage pulse driving power supply. The main discharge anode 22 is connected to the bottom surface of the insulating cavity 11 and grounded. A light-transmitting mirror 12 is provided at the center of both ends of the insulating cavity 11. The light-transmitting mirrors 12 on both sides and the insulating cavity 11 form a sealed chamber 13. The light-transmitting mirror 12 is an ultraviolet mirror with a transmittance greater than or equal to 96%. A first laser resonant mirror 51 and a second laser resonant mirror 52 are provided on both sides of the outside of the laser discharge cavity 1, spaced apart from the ultraviolet mirror. The first laser resonant mirror 51 is a total reflection mirror, and the second laser resonant mirror 52 is a partial reflection mirror. The first laser resonator lens 51 and the second laser resonator lens 52 are disposed on opposite sides of the outside of the laser discharge cavity 1. Even if contaminants are generated during the discharge of the laser discharge cavity 1, they will only contaminate the inexpensive ultraviolet lens, thus effectively protecting the expensive first laser resonator and the second laser resonator 52. Furthermore, the ultraviolet lens can be wiped or replaced when it becomes sufficiently contaminated. Therefore, the placement of the first laser resonator lens 51 and the second laser resonator lens 52 prevents them from contacting the working gas inside the laser discharge cavity 1, significantly reducing maintenance costs. The first laser resonator lens 51 has a reflectivity of 99.5%, and the second laser resonator lens 52 has a reflectivity of 8%. The laser beam is emitted from the second laser resonator lens 52.

[0029] The present invention has been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the invention.

Claims

1. A high-power excimer laser with corona pre-ionization, characterized in that: The device includes a housing (100), within which a laser discharge cavity (1) filled with working gas is provided. The laser discharge cavity (1) contains a pair of main discharge electrodes capable of exciting the working gas to generate laser light. Each main discharge electrode includes a long strip-shaped main discharge cathode (21) and a long strip-shaped main discharge anode (22) spaced apart from the main discharge cathode (21). Corona rods (3) capable of pre-ionizing the working gas are spaced apart within the laser discharge cavity (1) and located on one side of the main discharge cathode (21). The corona rod (3) includes a pre-ionization electrode (31) and a ceramic insulator (32) wrapped around the pre-ionization electrode (31). There is a gap between the outer peripheral surface of the ceramic insulator (32) and the outer side wall of the main discharge cathode (21) and the inner side wall of the insulating cavity (11). The pre-ionization electrode (31) and the main discharge anode (22) are grounded. The main discharge cathode (21) is connected to a negative high voltage pulse. When the excimer laser is working, the driving voltage pulse of the corona rod (3) is the same as the driving voltage pulse of the main discharge electrode.

2. The corona pre-ionization high-power excimer laser according to claim 1, characterized in that: The working gas is a mixture of Ne, Xe, and HCl, with a gas pressure of 0.35 MPa.

3. The corona pre-ionization high-power excimer laser according to claim 1 or 2, characterized in that: The corona rod (3) has two rods and is symmetrically arranged on both sides of the main discharge cathode (21) and parallel to the main discharge cathode (21).

4. The high-power excimer laser with corona pre-ionization according to claim 3, characterized in that: The line (L) connecting the centers of the two corona rods (3) in the longitudinal section passes through the point where the straight line (21a) and the arc (21b) on the same longitudinal section of the main discharge cathode (21) meet.

5. The corona pre-ionization high-power excimer laser according to claim 1, characterized in that: The pre-ionization electrode (31) is a metal rod, and the ceramic insulator (32) is alumina ceramic.

6. The corona pre-ionization high-power excimer laser according to claim 5, characterized in that: The metal rod is a copper rod, and the ceramic insulator (32) is sleeved on the copper rod with a gap between them.

7. The corona pre-ionization high-power excimer laser according to claim 1, characterized in that: The laser discharge cavity (1) includes an insulating cavity (11), the main discharge cathode (21) is connected to the top surface of the insulating cavity (11) and connected to a voltage pulse driving power supply, the main discharge anode (22) is connected to the bottom surface of the insulating cavity (11) and grounded, and a light-transmitting mirror (12) is provided at the center of both ends of the insulating cavity (11), and the light-transmitting mirrors (12) on both sides and the insulating cavity (11) form a sealed chamber (13).

8. The corona pre-ionization high-power excimer laser according to claim 7, characterized in that: The light-transmitting mirror (12) is an ultraviolet mirror. The laser discharge cavity (1) is provided with a first laser resonant mirror (51) and a second laser resonant mirror (52) on both sides of the outside, which are spaced apart from the ultraviolet mirror. The first laser resonant mirror (51) is a total reflection mirror, and the second laser resonant mirror (52) is a partial reflection mirror.

9. The corona pre-ionization high-power excimer laser according to claim 8, characterized in that: The first laser resonant lens (51) has a reflectivity of 99.5%, and the second laser resonant lens (52) has a reflectivity of 8%.

10. The corona pre-ionization high-power excimer laser according to claim 9, characterized in that: The transmittance of the ultraviolet lens is greater than or equal to 96%.

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