High-power corona preionization excimer laser

Abstract

The invention discloses a high-power corona preionization 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] The present invention relates to a high-power corona pre-ionization excimer laser.

Background Art

[0002] Excimer lasers have the characteristics of short wavelength, high output energy, and high repetition rate, and have been widely used in the fields of optical lithography, laser annealing, atmospheric composition monitoring, and electrochemical microfabrication. Generally, the working gas of an excimer laser is a mixture of an inert gas and a halogen gas. The excimer laser excites the mixture of the inert gas and the halogen gas through high-voltage discharge to form excited-state excimers. When they dissociate back to the ground state, high-energy ultraviolet photons are released to achieve laser output.

[0003] In order to increase the output power of an excimer laser, generally, the pressure of the working gas is increased. As the pressure increases, the streamer breakdown of the working gas is likely to turn into arc discharge, and the arc discharge will cause damage to the discharge uniformity, contamination of the working gas medium, and a decrease in laser energy. In order to avoid arc discharge, an excimer laser generally needs to pre-ionize the working gas to generate an initial electron distribution with a sufficient concentration in the discharge region. These initial electrons generate uniformly overlapping electron avalanches, which can achieve a laterally uniform distribution of the electric field strength, thereby achieving the purpose of preventing arc discharge. For high-power excimer lasers, their main discharge electrode has a large width, a large discharge gap, and a large discharge region volume. Whether sufficient initial electron density can be provided in the large discharge region is a key index of the pre-ionization system of high-power excimer lasers. Since spark discharge pre-ionization can provide a very high pre-ionization electron density, for high-power excimer lasers, using spark discharge pre-ionization can provide sufficient initial electron density in their large-volume main discharge region to meet the requirements of uniform glow discharge, which is a relatively safe choice. Therefore, all high-power excimer lasers on the market currently adopt the technical solution of spark discharge pre-ionization. Although spark discharge pre-ionization can provide a very high pre-ionization electron density, for high-power excimer lasers, using spark discharge pre-ionization can relatively easily provide sufficient initial electron density in their large-volume main discharge region to meet the requirements of uniform glow discharge. However, the high-temperature electric sparks generated during the operation of spark discharge pre-ionization will corrode the metal structures of the pre-ionization strips and pre-ionization needles, generate a large amount of discharge dust to contaminate the working gas and the laser cavity plates, reduce the service life of the laser, and at the same time, the spark discharge occurs simultaneously in the gaps between multiple pre-ionization needles and pre-ionization strips, and the multiple ultraviolet light sources generated are independent of each other, and the irradiation regions overlap with each other, resulting in poor uniformity of the overall initial electron density spatial distribution generated by spark discharge pre-ionization, which hinders the improvement of the laser output stability and beam quality of high-power equipment.

[0004] Therefore, the present invention is precisely generated based on the above deficiencies.

Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and provide a high-power corona pre-ionization excimer laser. This high-power corona pre-ionization excimer laser performs corona discharge pre-ionization through a corona rod, which will not corrode the main discharge electrode, nor generate discharge dust to pollute the working gas, facilitating the improvement of the working gas life and the overall life of the laser discharge cavity. Moreover, the initial electron density generated by corona pre-ionization has better spatial uniformity, ensuring uniform glow discharge of the main discharge electrode to generate high-quality laser light.

[0006] The present invention is achieved through the following technical solutions:

[0007] A high-power corona pre-ionization excimer laser, comprising a housing. Inside the housing is a laser discharge cavity filled with a working gas. Inside the laser discharge cavity are a pair of main discharge electrodes capable of discharging and exciting the working gas to generate laser light. The main discharge electrodes include a strip-shaped main discharge cathode and a strip-shaped main discharge anode spaced from the main discharge cathode. Inside the laser discharge cavity and on one side of the main discharge cathode, a corona rod is provided at intervals and capable of discharging and pre-ionizing the working gas. The corona rod includes a pre-ionization electrode and a ceramic insulator sleeved and wrapped outside the pre-ionization electrode. There is a gap between the outer peripheral surface of the ceramic insulator and the outer side wall of the main discharge cathode and the inner side wall of the insulation cavity. The pre-ionization electrode and the main discharge anode are grounded, and the main discharge cathode is connected to a negative high-voltage pulse. When the excimer laser operates, the driving voltage pulse of the corona rod is the same as that of the main discharge electrode.

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

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

[0010] The connecting line of the centers of the longitudinal sections of the two corona rods passes through the connection point of the straight line and the arc 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 insulation cavity. The main discharge cathode is connected to the upper top surface of the insulation cavity and connected to a voltage pulse driving power supply. The main discharge anode is connected to the lower bottom surface of the insulation cavity and grounded. Transparent mirrors are provided at the centers of both ends of the insulation cavity, and the transparent mirrors on both sides and the insulation cavity form a sealed chamber.

[0014] The light-transmitting mirror described is an ultraviolet lens. On both sides outside the laser discharge cavity, a first laser resonant mirror and a second laser resonant mirror are provided at intervals from the ultraviolet lens. The first laser resonant mirror is a total reflection mirror, and the second laser resonant mirror is a partial reflection mirror.

[0015] The reflectivity of the first laser resonant mirror is 99.5%, and the reflectivity of the second laser resonant mirror is 8%.

[0016] The light 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 the present invention is wrapped by a ceramic insulator and is close to the main discharge cathode to initiate corona discharge. Corona discharge does not require an additional drive circuit. The drive voltage pulse of the corona rod is the same as that of the main discharge electrode, and it has good coordination with the discharge of the main discharge electrode, avoiding delay and interference; Corona pre-ionization generates corona discharge through displacement current, and the current is very small, which will not corrode the main discharge electrode nor generate discharge dust to pollute the working gas and optical lenses, which is beneficial to improving the service life of the working gas and the overall service life of the laser discharge cavity; The corona rod is an integral structure, and the corona discharge can be regarded as a single and uniform ultraviolet ionization light source in the length direction of the main discharge electrode. The spatial distribution uniformity of the initial electron density generated by corona pre-ionization is good, ensuring uniform glow discharge of the main discharge electrode to generate high-quality laser.

[0019] 2. The laser discharge cavity of the present invention is sealed by an insulating cavity body and ultraviolet lenses on both sides thereof. The first laser resonant mirror and the second laser resonant mirror are arranged on both sides outside the laser discharge cavity. Even if pollutants are generated during the discharge of the laser discharge cavity, they will only contaminate the inexpensive ultraviolet lenses, thereby effectively protecting the expensive first laser resonant mirror and the second laser resonant mirror. Moreover, when the ultraviolet lenses are contaminated to a certain extent, they can be wiped or replaced. Therefore, the installation positions of the first laser resonant mirror and the second laser resonant mirror do not contact the working gas in the laser discharge cavity, which can greatly reduce the maintenance cost.

[0020] 3. When the high-power corona pre-ionization excimer laser of the present invention works, the laser discharge is uniform, the output ultraviolet laser has high quality and high power, and the maintenance cost is low, which is suitable for popularization and application.

Description of the Drawings

[0021] Figure 1 is one of the schematic diagrams of the present invention;

[0022] Figure 2 is the second schematic diagram of the present invention.

Detailed Implementation Manner

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

[0024] As Figure 1 and Figure 2 shown, a high-power corona pre-ionization excimer laser includes a housing 100. Inside the housing 100, there is a laser discharge cavity 1, and a working gas formed by mixing an inert gas and a halogen gas is filled in the laser discharge cavity 1. In this embodiment, the working gas is composed of Ne, Xe, and HCl in a ratio of 99.255 / 0.67 / 0.075, the gas pressure is 0.35 Mpa, and the temperature is 323 K. Inside the laser discharge cavity 1, there is a pair of main discharge electrodes that can discharge and excite the aforementioned working gas to generate laser. The main discharge electrodes include a strip-shaped main discharge cathode 21 and a strip-shaped main discharge anode 22 spaced from the main discharge cathode 21. The main discharge cathode 21 and the main discharge anode 22 are 35 mm apart in the vertical direction. Inside the laser discharge cavity 1 and on one side of the main discharge cathode 21, there is a corona rod 3 that can perform discharge pre-ionization on the working gas. The corona rod 3 includes a pre-ionization electrode 31 made of a metal rod and a ceramic insulator 32 sleeved and wrapped outside 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 metal rod and the main discharge anode 22 are grounded, and at this time, the main discharge cathode 21 also serves as the cathode of the pre-ionization corona discharge. The main discharge cathode 21 is connected to a negative high-voltage pulse. When the excimer laser works, the drive voltage pulse of the corona rod 3 is the same as the drive voltage pulse of the main discharge electrode. During the voltage rise on the main discharge cathode 21, the pre-ionization electrode 31 discharges prior to the main discharge electrode to generate corona discharge, and the ultraviolet light generated by the corona discharge of the working gas illuminates the main discharge area 4, causing the gas in the main discharge area 4 to be ionized to generate an initial pre-ionization electron distribution. Subsequently, the glow discharge between the main discharge electrodes starts, thereby generating and outputting laser. By pre-ionizing the working gas through corona discharge, the current is very small, which will not corrode the main discharge electrodes, nor will it generate discharge dust to pollute the working gas, which is beneficial to improving the service life of the working gas and the overall service life 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 cathode 21 of the main discharge electrode to increase the corona discharge intensity and obtain a higher pre-ionization electron density.

[0025] However, in high-power excimer laser devices, due to the relatively large width of the main discharge electrode, the shielding effect of the main discharge cathode 21 is relatively serious, resulting in an obvious non-uniformity in the transverse distribution of pre-ionization in the high-power excimer laser. Therefore, in order to avoid the adverse effects of non-uniform discharge caused by the non-uniform transverse distribution of pre-ionization on the laser output quality, two corona rods 3 are provided and symmetrically arranged on both sides of the main discharge cathode 21, which can effectively offset the transverse non-uniformity of pre-ionization caused by the shielding of the main discharge cathode 21, ensure better spatial uniformity of the initial electron density generated by corona pre-ionization, and ensure the output of high-quality laser light.

[0026] As Figure 1 shown, the connecting line L of the centers of the longitudinal sections of the two corona rods 3 passes through the contact point of the straight line 21a and the arc 21b on the same longitudinal section of the main discharge cathode 21. While ensuring an appropriate distance between the corona rod 3 and the main discharge cathode 21, it reduces the shielding of the ultraviolet light generated by corona discharge by the main discharge cathode 21 itself, and ensures that the ultraviolet light generated by 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 diameter and outer diameter of the ceramic insulator 32 are set to 0.6 cm and 1.44 cm respectively, ensuring 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 sleeved on the copper rod with a gap, and the clearance fit between the two ensures that the thermal expansion of the copper rod will not cause cracking of the ceramic insulating layer.

[0028] As 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 upper surface of the insulating cavity 11 and is connected to a voltage pulse driving power supply. The main discharge anode 22 is connected to the lower bottom surface of the insulating cavity 11 and is grounded. Transparent mirrors 12 are provided at the centers of both ends of the insulating cavity 11. The transparent mirrors 12 on both sides and the insulating cavity 11 form a sealed chamber 13. The transparent mirrors 12 are ultraviolet lenses, and the light transmittance of the ultraviolet lenses is greater than or equal to 96%. On both sides outside the laser discharge cavity 1, a first laser resonant mirror 51 and a second laser resonant mirror 52 are provided at intervals from the ultraviolet lenses. 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 resonant mirror 51 and the second laser resonant mirror 52 are arranged on both sides outside the laser discharge cavity 1. Even if pollutants generated during the discharge of the laser discharge cavity 1 only contaminate the inexpensive ultraviolet lenses, thus effectively protecting the expensive first laser resonant mirror 51 and the second laser resonant mirror 52. Moreover, when the ultraviolet lenses are contaminated to a certain extent, they can be wiped or replaced. Therefore, the installation positions of the first laser resonant mirror 51 and the second laser resonant mirror 52 do not contact the working gas in the laser discharge cavity 1, which can greatly reduce the maintenance cost. The reflectivity of the first laser resonant mirror 51 is 99.5%, and the reflectivity of the second laser resonant mirror 52 is 8%. The laser emits from the second laser resonant mirror 52.

[0029] The above has described this embodiment in detail with reference to the accompanying drawings. However, the present invention is not limited to the above embodiment. Within the scope of knowledge possessed by those of ordinary skill in the art in the said technical field, various changes can also be made without departing from the gist of the present invention.

Claims

1. A high-power corona pre-ionization excimer laser, characterized in that: It includes a housing (100). Inside the housing (100), there is a laser discharge chamber (1) filled with working gas. Inside the laser discharge chamber (1), there is a pair of main discharge electrodes that can discharge and excite the working gas to generate laser. The main discharge electrodes include a strip-shaped main discharge cathode (21) and a strip-shaped main discharge anode (22) spaced from the main discharge cathode (21). Inside the laser discharge chamber (1) and on one side of the main discharge cathode (21) at an interval, there is a corona bar (3) that can pre-ionize the working gas by discharging. The corona bar (3) includes a pre-ionization electrode (31) and a ceramic insulator (32) sleeved and wrapped outside the pre-ionization electrode (31). There is a gap between the outer peripheral surface of the ceramic insulator (32), 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, and the main discharge cathode (21) is connected to a negative high-voltage pulse. When the excimer laser works, the driving voltage pulse of the corona bar (3) is the same as the driving voltage pulse of the main discharge electrode.

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

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

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

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

6. The high-power corona pre-ionization 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 high-power corona pre-ionization excimer laser according to claim 1, wherein: The laser discharge chamber (1) includes an insulating cavity (11). The main discharge cathode (21) is connected to the upper 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 lower bottom surface of the insulating cavity (11) and grounded. At the centers of both ends of the insulating cavity (11), there are light-transmitting mirrors (12). The light-transmitting mirrors (12) on both sides and the insulating cavity (11) form a sealed chamber (13).

8. The high-power corona pre-ionization excimer laser according to claim 7, characterized in that: The light-transmitting mirrors (12) are ultraviolet lenses. On both sides outside the laser discharge chamber (1), there are a first laser resonant mirror (51) and a second laser resonant mirror (52) spaced from the ultraviolet lenses. 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 high-power corona pre-ionization excimer laser according to claim 8, characterized in that: The reflectivity of the first laser resonant mirror (51) is 99.5%, and the reflectivity of the second laser resonant mirror (52) is 8%.

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

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