A single-frequency phase-locked laser amplifier

Abstract

The invention discloses a single-frequency phase-locked laser amplifier for further improving the power of a deep ultraviolet laser light source, which includes an optical fiber beam splitter, an optical fiber amplitude modulator, a primary power amplifier, a phase modulator, a secondary power amplifier, a tertiary power amplifier, a pulse train output switch module and a closed-loop control module; the optical fiber beam splitter, the optical fiber amplitude modulator, the primary power amplifier, the phase modulator, the secondary power amplifier, the tertiary power amplifier and the pulse train output switch module are connected in sequence; the closed-loop control module is respectively connected to the optical fiber amplitude modulator, the primary power amplifier, the phase modulator, the secondary power amplifier, the tertiary power amplifier and the pulse train output switch module by signal. The invention has a relatively simple technical route, higher stability, and can achieve the beneficial effect of batch commercial use.

Description

Technical Field

[0001] The invention relates to the field of semiconductor photolithography light sources in the field of laser technology, and in particular to a single-frequency phase-locked laser amplifier. Background Art

[0002] The photolithography process is one of the most important process steps in semiconductor manufacturing, and the laser, or light source, is one of the core equipment of the photolithography machine. Take the deep ultraviolet laser light source that was widely used before as an example. It uses an excimer laser with a wavelength of up to 193nm. At the same time, studies have shown that in the future semiconductor process upgrade process, high-power ultra-deep ultraviolet light sources are the most important light sources used in the field of semiconductor lithography. Therefore, further increasing the power of the light source through laser amplifiers on the basis of existing laser light sources is also a technical difficulty that needs to be overcome at present.

[0003] In the prior art, generally, an excimer laser is used to bombard a metal tin target to further generate a 13.5nm ultra-deep ultraviolet light source to increase the power of the light source. However, the inventor of this patent application has found through research that the technical route involved in this method is very complicated, and the technical difficulty of further narrowing the wavelength and further increasing the power is very high. The method proposed in recent years of multiple interactions between electron micro-bunching and single-frequency laser to obtain high-order harmonic laser output is expected to provide a more efficient and high-power ultra-deep ultraviolet light source technology path, in which the laser acting on the electron beam needs to use the laser amplifier described in this article.

[0004] In summary, there is currently a lack of an amplifier that has a relatively simple technical route, higher stability, and can be commercialized in large quantities to further increase the power of deep ultraviolet laser light sources. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a single-frequency phase-locked laser amplifier which has a relatively simple technical route, higher stability and can be commercialized in batches to further increase the power of a deep ultraviolet laser light source.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is: a single-frequency phase-locked laser amplifier, which includes an optical fiber beam splitter, an optical fiber amplitude modulator, a primary power amplifier, a phase modulator, a secondary power amplifier, a tertiary power amplifier, a pulse train output switch module and a closed-loop control module; the optical fiber beam splitter, the optical fiber amplitude modulator, the primary power amplifier, the phase modulator, the secondary power amplifier, the tertiary power amplifier and the pulse train output switch module are connected in sequence; the closed-loop control module is respectively connected to the optical fiber amplitude modulator, the primary power amplifier, the phase modulator, the secondary power amplifier, the tertiary power amplifier and the pulse train output switch module by signal; the optical fiber beam splitter is used to divide the input seed source laser into two parts, A part is injected into the subsequent optical path for laser amplification, and the other part is used as reference light to interfere with the amplified main laser in the pulse train output switch module at the end, so that the phase of the main laser is locked to the reference light; the fiber amplitude modulator is used to chop the continuous single-frequency seed laser into a pulse laser with a specific repetition frequency and pulse width; the phase modulator is used to modulate the phase of the main laser optical path, and the control circuit controls the signal of the phase modulator by extracting the interference measurement signal in the final pulse train output module to achieve the purpose of phase locking; the pulse train output switch module is used to enable the main laser to achieve pulse train output while generating a power control signal and a phase control signal; the closed-loop control module is used to generate a closed-loop control signal to control the fiber phase modulator to achieve phase closure.

[0007] Preferably, the chopping pulse width of the fiber amplitude modulator is within 3ns.

[0008] Preferably, the first-stage power amplifier adopts a single-mode fiber amplifier to increase the average power of the pulsed laser to the level of 100 mW.

[0009] Preferably, the secondary power amplifier adopts a large mode field fiber amplifier to increase the average power of the pulsed laser to the order of several watts.

[0010] Preferably, the three-stage power amplifier adopts an ultra-large mode field fiber amplifier to further increase the average power of the pulsed laser to the order of hundreds of watts, while the peak power reaches the order of tens of kilowatts.

[0011] As a further preference, the pump source in the three-stage power amplifier includes a high-power multi-mode diode laser and a plurality of butterfly diode lasers.

[0012] Preferably, the pulse train output switch module includes a main laser output collimator, a reference light output collimator, a first polarization beam splitter, a second polarization beam splitter, a third polarization beam splitter, a fourth polarization beam splitter, an electro-optical switch, a waste light bucket, a first half glass slide, a second half glass slide, a first photodetector and a second photodetector; the main laser output collimator is connected to the electro-optical switch, the second polarization beam splitter and the waste light bucket in sequence through the first polarization beam splitter; the first polarization beam splitter is also connected to the first half glass slide, the third polarization beam splitter, the second half glass slide and the fourth polarization beam splitter in sequence; the first photodetector is connected to the third polarization beam splitter; the reference light output collimator and the second photodetector are both connected to the fourth polarization beam splitter.

[0013] Preferably, it adopts forced water cooling for heat dissipation, and the water cooling temperature control accuracy is better than 0.1 degrees Celsius.

[0014] Preferably, the splitting ratio of the optical fiber beam splitter is 90:10.

[0015] After adopting the above structure, the present invention has the following beneficial effects: creatively utilizing the interaction between a single-frequency laser and an electron microbunch in an electron ring accelerator to obtain extreme deep ultraviolet laser output through multiple modulations, and controlling the laser to be strictly single-frequency and phase-locked during the process, so as to ensure that the phase remains consistent when the electrons interact with the laser multiple times. Compared with the methods in the prior art such as bombarding a metal tin target with an excimer laser, the technical route of this patent application is relatively simple, the stability is higher, and it can be commercialized in batches; various preferred options can further improve the amplification efficiency and stability of the amplifier.

[0016] In summary, the present invention provides a single-frequency phase-locked laser amplifier that has a relatively simple technical route, higher stability, and can be commercialized in batches to further increase the power of deep ultraviolet laser light sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the single-frequency phase-locked laser amplifier in the present invention.

[0018] Figure 2 It is a structural schematic diagram of a pulse train output switch module in a single-frequency phase-locked laser amplifier in the present invention.

[0019] As shown in the figure: a single-frequency continuous laser seed source 101, an optical fiber beam splitter 102, an optical fiber amplitude modulator 103, a first-stage power amplifier 104, a phase modulator 105, a second-stage power amplifier 106, a third-stage power amplifier 107, a pulse train output switch module 108 and a closed-loop control module 109, a main laser output collimator 201, a reference light output collimator 210, a first polarization beam splitter 202, a second polarization beam splitter 204, a third polarization beam splitter 207, a fourth polarization beam splitter 211, an electro-optical switch 203, a waste light bucket 205, a first half glass slide 206, a second half glass slide 209, a first photodetector 208, and a second photodetector 212. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0021] The present invention discloses a single-frequency phase-locked laser amplifier, which comprises an optical fiber beam splitter 102, an optical fiber amplitude modulator 103, a primary power amplifier 104, a phase modulator 105, a secondary power amplifier 106, a tertiary power amplifier 107, a pulse train output switch module 108 and a closed-loop control module 109; the optical fiber beam splitter 102, the optical fiber amplitude modulator 103, the primary power amplifier 104, the phase modulator 105, the secondary power amplifier 106, the tertiary power amplifier 107 and the pulse train output switch module 108 are connected in sequence; the closed-loop control module 109 is respectively connected to the optical fiber amplitude modulator 103, the primary power amplifier 104, the phase modulator 105, the secondary power amplifier 106, the tertiary power amplifier 107 and the pulse train output switch module 108 by signals; the optical fiber beam splitter 102 It is used to divide the input seed source laser into two parts, one part is injected into the subsequent optical path for laser amplification, and the other part is used as reference light to interfere with the amplified main laser in the pulse train output switch module 108 at the end, so that the phase of the main laser is locked to the reference light; the fiber amplitude modulator 103 is used to chop the continuous single-frequency seed laser into a pulse laser with a specific repetition frequency and pulse width; the phase modulator 105 is used to modulate the phase of the main laser optical path, and the control circuit controls the signal of the phase modulator by extracting the interference measurement signal in the final pulse train output module to achieve the purpose of phase locking; the pulse train output switch module 108 is used to enable the main laser to achieve pulse train output while generating a power control signal and a phase control signal; the closed-loop control module 109 is used to generate a closed-loop control signal to control the fiber phase modulator 105 to achieve phase closure. The pulse train output switch module 108 includes a main laser output collimator 201, a reference light output collimator 210, a first polarization beam splitter 202, a second polarization beam splitter 204, a third polarization beam splitter 207, a fourth polarization beam splitter 211, an electro-optical switch 203, a waste light bucket 205, a first half glass slide 206, a second half glass slide 209, a first photodetector 208 and a second photodetector 212; the main laser output collimator 201 is connected to the electro-optical switch 203, the second polarization beam splitter 204 and the waste light bucket 205 in sequence through the first polarization beam splitter 202; the first polarization beam splitter 202 is also connected to the first half glass slide 206, the third polarization beam splitter 207, the second half glass slide 209 and the fourth polarization beam splitter 211 in sequence; the first photodetector 208 is connected to the third polarization beam splitter 207; the reference light output collimator 210 and the second photodetector 212 are both connected to the fourth polarization beam splitter 211.

[0022] Further combined with Figure 1 and attached Figure 2In the specific implementation of this patent application, the single-frequency continuous laser seed source 101 is used as the injection light source of the amplifier, and the line width is required to be less than 10kHz to ensure a sufficiently long coherence length. At the same time, in order to ensure long-term stability, the seed source is required to lock the frequency internally to ensure that the frequency stability is at least higher than 10 -12 Order of magnitude. The splitting ratio of the optical fiber beam splitter 102 is preferably 90:10, that is, the main laser power enters the post-amplification optical path, and a small amount enters the closed-loop control module 109 as a reference light. The pump source used by the first-stage power amplifier 104, the second-stage power amplifier 106 and the third-stage power amplifier 107, its circuit drive should ensure sufficiently high stability, so that the open-loop power stability is better than 1%. In addition to completing the power amplification of the final stage, the third-stage power amplifier 107 also reserves a pump path, using a butterfly single-mode pump, and user power closed-loop feedback. In the pulse train output switch module 108, in addition to ensuring that the high-repetition-rate pulse laser forms a pulse train output, the main laser is also sampled, and part of the sampled laser is interfered with the reference laser. The sampling laser and the interfering laser signal are detected by a low-noise photodetector, and the signal enters the closed-loop control module 109. Preferably, the laser amplifier in this patent application uses forced water cooling to dissipate heat, and the water cooling temperature control accuracy is better than 0.1 degrees Celsius.

[0023] The main laser enters the pulse train output switch module 108 through the main laser output collimator 201, and is polarized by the first polarization beam splitter 202. Part of the vertical polarization component is reflected for monitoring. After the main laser is polarized, it passes through the electro-optical switch 203, and the electro-optical switch 203 is controlled by the timing of the control circuit. When the polarization state is consistent with the polarization direction of the second polarization beam splitter 204 at the output end, the laser is output, otherwise it enters the waste light bucket 205.

[0024] The monitoring light rotates the polarization state through the first half-wave plate 206 to control the third polarization beam splitter 207 before entering the first photodetector 208. The first photodetector 208 is used to monitor the power of the main laser and control a group of pumps of the three-stage power amplifier 107 through the closed-loop control module 109 to achieve power closed-loop control. The laser power passing through the third polarization beam splitter 207 passes through the second half-wave plate 209, and is polarized and synthesized with the reference light passing through the reference light output collimator 210 before entering the second photodetector 212. The detected signal enters the closed-loop control module 109 and generates a closed-loop control signal to control the fiber phase modulator 105 to achieve phase closed-loop.

[0025] The power closed loop can use the PID algorithm to lock the output power at a certain absolute value. The phase closed loop uses the SPGD algorithm to lock the phase of the output main laser to the reference light source. The closed loop locking bandwidth is within 1MHz, which is mainly used to compensate for the amplifier noise introduced by the amplification process and the noise caused by environmental vibration and thermal fluctuations.

[0026] The seed source of the single-frequency phase-locked laser amplifier uses a line width less than 10kHz and a frequency stability better than 10 -12 Highly stable single-frequency continuous laser. Single-frequency continuous laser can be made of fiber single-frequency laser or non-planar ring cavity (NPRO). In order to further improve the long-term stability of the system, a variety of closed-loop frequency stabilization measures can be used to control the long-term stability of the output laser within 10 -12 above.

[0027] The working principle of this patent application is briefly described as follows: the fiber beam splitter divides the input single-frequency continuous laser seed source 101 into two parts, one part is injected into the subsequent optical path for laser amplification, and the other part is used as a reference light to interfere with the amplified main laser in the pulse train output switch module at the end, so that the phase of the main laser is locked to the reference light. The fiber amplitude modulator is used to chop the continuous single-frequency seed laser into a pulse laser with a specific repetition frequency and pulse width. If the laser needs to interact with the electron beam, the repetition frequency of the laser should be strictly consistent with the cycle period of the electron micro-bunch in the storage ring. In order to suppress the stimulated Brillouin scattering (SBS) effect that may occur in the subsequent fiber laser amplification process of the single-frequency laser pulse, the chopping pulse width needs to be controlled within 3ns. The average power of the single-frequency continuous seed laser is generally about 100mW. Taking the chopping pulse width of 3ns and the repetition frequency of 6MHz as an example, without considering the loss, the average power of the pulse is 1.8mW. In order to achieve a strong interaction between the laser and the electron beam, the laser is required to have a peak power of more than 10kW, so it is necessary to use a multi-stage power amplifier for power boosting. The first-stage power amplifier uses a single-mode fiber amplifier to increase the average power of the pulsed laser to about 100mW. The output laser of the first-stage power amplifier enters the fiber phase modulator. The phase modulator is used to modulate the phase of the main laser optical path. The control circuit controls the signal of the phase modulator by extracting the interference measurement signal in the final pulse train output module to achieve the purpose of phase locking. The second-stage power amplifier uses a large mode field fiber amplifier to increase the average power of the pulsed laser to the order of several watts. The third-stage power amplifier uses an ultra-large mode field fiber amplifier to further increase the average power of the pulsed laser to the order of hundreds of watts, while the peak power reaches tens of kilowatts. In addition to using a high-power multi-mode diode laser (LD) as a pump source, the third-stage power amplifier also uses multiple butterfly diode lasers as pump sources for power closed loops. The three-stage power amplifier outputs a laser signal that enters the pulse train output switch module. The functions of this module include three parts: 1) The main laser achieves pulse train output through the electro-optical switch in the module; 2) The main laser is sampled and photoelectrically detected. The control module extracts power fluctuation information through the detection signal, and generates a power control signal after algorithm processing to control the output power of the pump source in the three-stage power amplifier, thereby maintaining the stability of the laser power; 3) A portion of the sampled main laser is interfered with the reference light split from the seed source, and the photoelectric detector is used to measure the beat signal. After the control circuit extracts the signal and processes the algorithm, it generates a phase control signal for controlling the phase modulator, thereby achieving phase stability. Considering the stability of the system, this laser amplifier adopts forced water cooling.In specific implementation, in addition to the seed source, the amplifier itself is affected by ambient temperature, vibration, and amplifier pump noise, which can also cause fluctuations in laser power and phase. The frequencies of these noise signals are basically within 1 MHz, so the control speed of the power closed loop and phase closed loop can be achieved at around 1 MHz.

[0028] The present invention and its implementation methods are described above, which is not restrictive. The drawings show only one implementation method of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the purpose of the invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A single-frequency phase-locked laser amplifier, characterized in that: It comprises an optical fiber beam splitter (102), an optical fiber amplitude modulator (103), a primary power amplifier (104), a phase modulator (105), a secondary power amplifier (106), a tertiary power amplifier (107), a pulse train output switch module (108) and a closed-loop control module (109); the optical fiber beam splitter (102), the optical fiber amplitude modulator (103), the primary power amplifier (104), the phase modulator (105), the secondary power amplifier (106), the tertiary power amplifier (107) and the pulse train output switch module (108) are connected in sequence; the closed-loop control module (109) is respectively connected to the optical fiber amplitude modulator (103), the primary power amplifier (104), the phase modulator (105), the secondary power amplifier (106), the tertiary power amplifier (107) and the pulse train output switch module (108) by signals; the optical fiber The beam splitter (102) is used to split the input seed source laser into two parts, one part is injected into the subsequent optical path for laser amplification, and the other part is used as reference light to interfere with the amplified main laser in the pulse train output switch module (108) at the end, so that the phase of the main laser is locked to the reference light; the fiber amplitude modulator (103) is used to chop the continuous single-frequency seed laser into a pulse laser with a specific repetition frequency and pulse width; the phase modulator (105) is used to modulate the phase of the main laser optical path, and the control circuit controls the signal of the phase modulator by extracting the interference measurement signal in the final pulse train output module to achieve the purpose of phase locking; the pulse train output switch module (108) is used to enable the main laser to achieve pulse train output while generating a power control signal and a phase control signal; the closed-loop control module (109) is used to generate a closed-loop control signal to control the fiber phase modulator (105) to achieve phase closure.

2. The single-frequency phase-locked laser amplifier according to claim 1, characterized in that: The chopping pulse width of the optical fiber amplitude modulator (103) is within 3ns.

3. The single-frequency phase-locked laser amplifier according to claim 1, characterized in that: The first-stage power amplifier (104) adopts a single-mode optical fiber amplifier and is used to increase the average power of the pulsed laser to the 100mW level.

4. The single-frequency phase-locked laser amplifier according to claim 1, characterized in that: The secondary power amplifier (106) adopts a large mode field optical fiber amplifier to increase the average power of the pulse laser to the order of several watts.

5. The single-frequency phase-locked laser amplifier according to claim 1, characterized in that: The three-stage power amplifier (107) uses an ultra-large mode field optical fiber amplifier to further increase the average power of the pulsed laser to the order of hundreds of watts, while the peak power reaches the order of tens of kilowatts.

6. The single-frequency phase-locked laser amplifier according to claim 5, characterized in that: The pump source in the three-stage power amplifier (107) includes a high-power multi-mode diode laser and a plurality of butterfly diode lasers.

7. The single-frequency phase-locked laser amplifier according to claim 1, characterized in that: The pulse train output switch module (108) comprises a main laser output collimator (201), a reference light output collimator (210), a first polarization beam splitter (202), a second polarization beam splitter (204), a third polarization beam splitter (207), a fourth polarization beam splitter (211), an electro-optical switch (203), a waste light bucket (205), a first half glass slide (206), a second half glass slide (209), a first photodetector (208) and a second photodetector (212); the main laser output collimator (201) outputs a reference light through the first polarization beam splitter (204), a third polarization beam splitter (207), a fourth polarization beam splitter (211), an electro-optical switch (203), a waste light bucket (205), a first half glass slide (206), a second half glass slide (209), a first photodetector (208) and a second photodetector (212); The polarization beam splitter (202) is connected to the electro-optical switch (203), the second polarization beam splitter (204) and the waste light bucket (205) in sequence; the first polarization beam splitter (202) is also connected to the first half glass plate (206), the third polarization beam splitter (207), the second half glass plate (209) and the fourth polarization beam splitter (211) in sequence; the first photodetector (208) is connected to the third polarization beam splitter (207); the reference light output collimation head (210) and the second photodetector (212) are both connected to the fourth polarization beam splitter (211).

8. The single-frequency phase-locked laser amplifier according to claim 1, characterized in that: It uses forced water cooling to dissipate heat, and the water cooling temperature control accuracy is better than 0.1 degrees Celsius.

9. The single-frequency phase-locked laser amplifier according to claim 1, characterized in that: The optical fiber beam splitter (102) has a beam splitting ratio of 90:10.

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