CN104993364A - Excimer laser system with ring chamber structure - Google Patents

Abstract

The invention discloses an excimer laser system. The main oscillation cavity generates a small-energy narrow-linewidth laser light pulse as a seed light by means of a line width narrowing module. After the seed light is refracted by the wave front engineering box of the main oscillation cavity, it passes through the The beam splitting system enters the power amplification cavity, the beam splitting system, the first high reflection mirror, the second high reflection mirror and the third high reflection mirror form a quadrilateral annular optical path, and the power amplification cavity has a pair of first Brewster windows and The second pair of Brewster windows, the first pair of Brewster windows and the discharge electrode of the power amplification cavity are in the first optical path of the annular optical path, and the second pair of Brewster windows are in parallel to the first optical path of the annular optical path. A second optical path of said annular optical path that amplifies the optical path. The invention shortens the ring cavity length of the excimer laser system with the ring cavity structure, increases the amplification times, realizes deeper gain saturation amplification than the traditional structure, and improves the output characteristics of the excimer laser system.

Description

An Excimer Laser System with Ring Cavity Structure

technical field

The invention belongs to the technical field of gas lasers, in particular to excimer laser technology and its application, in particular to an excimer laser system with a ring cavity structure.

Background technique

With the continuous improvement of the lithography industry's requirements for light source output power and line width, limited by structural characteristics, single-cavity excimer devices cannot meet the characteristics of simultaneous output of high-level output power and line width. The main oscillation-amplification technology of dual-cavity structure is introduced to solve the contradiction between output power and line width. The basic idea is to use the seed cavity to generate small-energy narrow-linewidth seed light, inject it into the amplifier cavity to output high-energy pulses, and thus obtain high-quality laser output with narrow linewidth and high power.

At present, related amplification mechanisms mainly include: MOPA, MOPO (Gigaphoton), MOPRA (Cymer), MORRA (Lambda Physik), etc. Cymer's XLA100 series (entered the market in 2002) was the first to introduce the MOPA mechanism into the photolithography light source, and obtained higher operating efficiency and index output than the previous single cavity. However, the output of the power amplifier cavity (power amplifier cavity PA) in the MOPA structure is easily affected by the synchronous jitter of the main oscillator cavity (MO cavity) and the power amplifier cavity PA, resulting in unstable laser output energy. At this time, the ring cavity technology is introduced into the dual-cavity structure. Compared with the MOPA technology, in the ring cavity structure, the seed light injected into the amplifier cavity is multi-pass amplified in a deeper saturation gain state, so the output energy stability is better, and the output beam The mass is modulated by the amplifying cavity, increasing the controllability of the output beam.

However, for a certain pulse width of seed light injected into the amplification cavity, the number of amplifications is limited by the length of the amplification cavity, and the number of amplifications is N=c·Δt/L, where L represents the length of the ring cavity, c is the speed of light, and Δt is the pulse width , the larger L is, the smaller the number of amplifications is, therefore, reducing the length of the ring cavity can increase the number of amplifications, thereby obtaining a more stable laser output.

A typical MORRA ring cavity structure is shown in Figure 1. The laser system includes a main oscillator MO (Master Oscillator Chamber), a power amplifier PA (Power Amplifier Chamber), a linear narrowing module LNM (Linewidth Narrowing Module), and a line width analysis module LAM (Linewidth Analysis Module), MO WEB (Master Oscillator Wavefront Engineering Box), Optical Pulse Stretcher OPS (Optical Pulse Stretcher), Auto Shutter, Partial Reflector PR (Partial Reflector), beam system (Splitter), the first high reflection mirror HR1, the second high reflection mirror HR2, and the third high reflection mirror HR3. The main oscillation cavity MO generates small-energy narrow-linewidth laser light pulses (seed light) with the help of the line width narrowing module LNM. After the seed light is refracted by the main oscillation cavity wavefront engineering box MO WEB, it enters the power amplification cavity through a beam splitting system. PA, three 45° incident high-reflectivity mirrors HR1, HR2, HR3 and the splitter system (Splitter) are used as the ring-shaped amplifier cavity mirror of the power amplifier PA to form a ring-shaped multi-pass amplifier system for the seed light. The ring-shaped amplification optical path structure of the system can be regarded as a quadrilateral, in which only one side passing through the discharge cavity has the effect of amplifying the optical power of the seed, and the other three sides are arranged outside the discharge cavity. Due to the size limitation of the discharge cavity, the length of the ring cavity cannot be further improved. Reduced, resulting in fewer amplification times, the superiority of the multi-pass amplification of the annular cavity cannot be well applied.

Contents of the invention

(1) Technical problems to be solved

The purpose of this patent is to solve the problem that the excimer laser ring cavity structure is limited by the physical size and cannot continue to shorten the ring cavity length, and the advantages of the ring cavity structure multi-pass amplification to achieve the deep gain saturation effect cannot be fully utilized.

(2) Technical solutions

In order to solve the above technical problems, the present invention proposes an excimer laser system, including a main oscillator cavity, a power amplification cavity, a linear compression module, a line width analysis module, a main oscillator cavity wavefront engineering box, an optical pulse stretcher, and an automatic shutter , a partial reflector, a beam splitting system, a first highly reflective mirror, a second highly reflective mirror and a third highly reflective mirror,

The main oscillating cavity generates a small-energy narrow-linewidth laser light pulse as a seed light by means of a linewidth narrowing module, and the seed light enters the power amplification cavity through the beam splitting system after being refracted by the wavefront engineering box of the main oscillating cavity ,

The beam splitting system, the first high reflection mirror, the second high reflection mirror and the third high reflection mirror form a quadrilateral annular optical path,

The power amplifying cavity has a first pair of Brewster windows and a second pair of Brewster windows, and the first pair of Brewster windows and the discharge electrode of the power amplifying cavity are in the first position of the annular light path. An optical path, the second pair of Brewster windows is in a second optical path of the annular optical path parallel to the first amplification optical path.

According to a specific embodiment of the present invention, the power amplification cavity has two parallel discharge electrodes, and the first light path and the second light path in the annular light path respectively pass through the two discharge electrodes.

According to a specific embodiment of the present invention, the first high reflection mirror, the second high reflection mirror and the third high reflection mirror are 45° angle reflection mirrors.

(3) Beneficial effects

The invention shortens the ring cavity length of the excimer laser system with the ring cavity structure, increases the amplification times, realizes deeper gain saturation amplification than the traditional structure, and improves the output characteristics of the excimer laser system.

Description of drawings

Fig. 1 is the structure schematic diagram of the excimer laser system with dual-cavity MORRA structure of prior art;

Fig. 2 is a schematic structural view of an excimer laser system with a single-electrode dual-cavity MORRA structure according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of an excimer laser system with a dual-electrode dual-cavity MORRA structure according to another embodiment of the present invention.

Detailed ways

Aiming at the problem that the existing ring cavity structure of excimer laser cannot continue to reduce the length of the ring cavity due to the limitation of physical size, the present invention proposes to change the traditional design of the ring cavity partially exposed outside the cavity, and place the entire loop structure in Amplify the inside of the cavity, thereby reducing the length of the annular cavity, increasing the number of amplifications, and improving output stability.

In this patent, part of the loop outside the traditional annular cavity is placed in the amplifying cavity to realize the obvious shortening of the length of the annular cavity. Since the number of amplifications N=c·Δt/L, where L represents the length of the annular cavity, c is the speed of light, Δt is the pulse width, the reduction of L can realize the increase of the number of amplification N, therefore, the reduction of the length of the ring cavity can increase the number of amplification, so as to obtain a more stable laser output. At the same time, placing the annular optical path in the amplifying cavity can reduce the adverse influence of external unstable factors on beam propagation.

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

FIG. 2 is a schematic structural diagram of an excimer laser system with a single-electrode dual-cavity MORRA structure according to an embodiment of the present invention. As shown in Figure 2, the laser system includes the main oscillator MO, the power amplifier PA, the linear narrowing module LNM, the line width analysis module LAM, the main oscillator wavefront engineering box MO WEB, the optical pulse stretcher OPS and the automatic shutter Auto Shutter, beam splitter system Splitter.

The main oscillator MO uses the linewidth narrowing module LNM to generate small-energy narrow-linewidth laser light pulses as seed light. After the seed light is refracted by the main oscillator wavefront engineering box MO WEB, it enters the power amplification cavity through a beam splitter system Splitter PA, three 45° incident high-reflectivity mirrors HR1, HR2, HR3 and the beam splitter system Splitter are used as the ring-shaped amplifier cavity mirror of the power amplifier cavity PA to form a ring-shaped multi-pass amplification system for the seed light. The beam splitter system (Splitter), the first high reflection mirror (HR1), the second high reflection mirror (HR2) and the third high reflection mirror (HR3) form a quadrilateral annular optical path, that is, the annular amplification optical path structure of the system can be It is regarded as a quadrilateral, in which the light path passing through the discharge chamber discharge electrodes has the effect of amplifying the seed light power.

The difference from the structure shown in Figure 1 is that the power amplification chamber PA of this embodiment has two pairs of Brewster windows up and down. A pair of Brewster windows (shown as B1 and B1' in the drawings), two Brewster windows placed on another optical path in the discharge chamber parallel to the amplification optical path are called the second Brewster windows A pair of windows (shown as B2, B2' in the drawings).

The first pair of Brewster windows (B1, B1') and the discharge electrode of the power amplification cavity (PA) are in the first optical path of the annular optical path, and the second pair of Brewster windows (B2 , B2') is in the second optical path of the annular optical path parallel to the first amplification optical path.

As shown in Figure 2, the laser light emitted by one of the Brewster window B1' in the first Brewster window pair B1, B1' is incident on the second cloth mirror HR3 and HR2 through a 45° incident high reflectivity mirror. The Brewster window B2' of the Brewster window pair B2 and B2' is located on the same side of the power amplification cavity PA as the Brewster window B1', so as to be incident into the power amplification cavity PA, and from the second Brewster window B1' The Brewster window emits to another Brewster window B2 in B2, B2'. In addition, compared with the traditional structure, the power amplification cavity PA with two pairs of Brewster windows shown in Figure 2 can increase the polarization degree of P light passing through the laser, and obtain more superior laser polarization characteristics. Since the optical path parallel to the discharge optical path is placed in the discharge cavity, the remaining two optical paths perpendicular to the discharge optical path are no longer limited by the size of the discharge cavity, effectively shortening the cavity length of the ring-shaped amplifying cavity.

In the structure of this embodiment, the amplifying cavity is a single-electrode structure. Compared with the traditional double-cavity MORRA structure, the length of the annular cavity is effectively shortened, which is conducive to multi-pass amplification to achieve deep gain saturation amplification, thereby obtaining a more stable index than the traditional structure. output.

FIG. 3 is a structural schematic diagram of an excimer laser system with a dual-electrode dual-cavity MORRA structure according to another embodiment of the present invention. The structure of the amplifying cavity is a dual-electrode structure.

The difference from the embodiment shown in Fig. 2 is that the power amplification chamber PA has two parallel discharge electrodes, and the first light path and the second light path in the annular light path pass through the two discharge electrodes respectively, and both have a pair of seed light It can be seen that in this embodiment, not only the length of the annular cavity is effectively shortened, but also the magnification is doubled compared with the single electrode structure, that is to say, the same seed light is injected into the amplifying cavity, and this structure can be obtained Higher output energy; and the increase of the magnification makes the amplification occur in a deeper gain saturation state, therefore, the output beam stability obtained by this structure is better.

To sum up, the present invention improves the structure and performance of the ring cavity energy amplification structure in the excimer laser system. Through the design of single (double) electrode structure, the problem of low amplification times caused by the cavity length is improved, the gain utilization efficiency in the cavity is effectively improved, and the effective output of system energy is guaranteed. The essence of the present invention is to realize the improvement of energy amplification characteristics by means of multi-pass cavity transition. At the same time, the annular cavity structure in the cavity can also reduce the influence of external unfavorable factors caused by the light path passing through the atmosphere.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (3)

1. an excimer laser system, comprise main oscillations chamber (MO), power amplification chamber (PA), linearly narrow module (LNM), Analysis of Linewidth module (LAM), main oscillations chamber wavefront engineering case (MOWEB), optical pulse stretcher (OPS), automatic gate (Auto Shutter), partially reflecting mirror (PR), divided beam system (Splitter), the first high reflective mirror (HR1), the second high reflective mirror (HR2) and the anti-mirror of third high (HR3)

Described main oscillations chamber (MO) produces the light pulse of little energy narrow-linewidth laser as seed light by linewidth narrowing module (LNM), this seed light is after main oscillations chamber wavefront engineering case (MO WEB) refraction, described power amplification chamber (PA) is entered by described divided beam system (Splitter)

Described divided beam system (Splitter), the first high reflective mirror (HR1), the second high reflective mirror (HR2) and the anti-mirror of third high (HR3) form the annular light path of quadrangle,

It is characterized in that:

Described power amplification chamber (PA) has the first Brewster window to (B1, B1 ') and the second Brewster window to (B2, B2 '), described first Brewster window is in the first light path of described annular light path together to (B1, B1 ') and the sparking electrode in this power amplification chamber (PA), and described second Brewster window is in (B2, B2 ') and is parallel to the second light path that described first amplifies the described annular light path of light path.

2. excimer laser system as claimed in claim 1, it is characterized in that, described power amplification chamber (PA) has two parallel sparking electrodes, and the first light path in annular light path and the second light path are respectively by described two sparking electrodes.

3. excimer laser system as claimed in claim 1 or 2, it is characterized in that, described first high reflective mirror (HR1), the second high reflective mirror (HR2) and the anti-mirror of third high (HR3) are 45° angle speculum.