Solid-gas mixed deep ultraviolet laser and imaging method

Abstract

The invention discloses a solid-gas mixed deep ultraviolet laser. The solid-gas mixed deep ultraviolet laser comprises an all-solid-state seed laser, an ArF excimer laser and a laser controller, the all-solid-state seed laser comprises an all-solid-state laser and a nonlinear optical crystal frequency converter, the all-solid-state laser is used for generating fundamental frequency laser, and the nonlinear optical crystal frequency converter is used for receiving the fundamental frequency laser and converting the fundamental frequency laser into a target wavelength; the all-solid-state seed laser injects the seed laser into the ArF excimer laser; the ArF excimer laser receives and amplifies the seed laser; and the laser controller controls the seed laser output by the ArF excimer laser in a target state. The light source has the advantages of high output power of an excimer laser and high beam quality of a solid laser, has the advantages of short wavelength and narrow linewidth, and is used as a novel exposure light source, so that the application scene and the adaptive capacity are greatly improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor integrated circuit manufacturing technology, and more specifically, to a solid-gas hybrid deep ultraviolet laser and an imaging method. Background Art

[0002] With the miniaturization and high integration of semiconductor integrated circuits, the resolution of semiconductor exposure devices is required to be improved, so deep ultraviolet lasers have been developed, such as excimer lasers used in exposure light sources. Currently, as an excimer laser device for exposure, KrF excimer lasers with an output wavelength of 248nm are one of the main light sources. In addition, due to the advantages of short wavelength, high resolution, and concentrated energy of lasers in this band, deep ultraviolet lasers have become increasingly important in many application fields such as ultra-precision processing, surface modification of materials, biomedicine, and spectral detection.

[0003] The natural oscillation line width of the KrF excimer laser device is relatively wide, about 350 to 400pm. A line width narrowing module can be set in the laser resonator of the excimer laser device to achieve narrowband spectral width and achieve good temporal coherence. However, the output laser beam quality of this method is poor, so the spatial coherence is poor, and it cannot meet the application scenarios that require coherence in this field. All-solid-state deep ultraviolet lasers have the advantages of compact structure, easy maintenance, high beam quality, and narrow line width, but they are limited by the research of basic materials and cannot currently achieve high-power 248nm deep ultraviolet laser output. Summary of the invention

[0004] In response to at least one defect or improvement need in the prior art, the present invention provides a solid-gas hybrid deep ultraviolet laser and an imaging method, which can take into account the advantages of high output power of excimer lasers and high beam quality of solid lasers, and at the same time has the advantages of short wavelength and narrow linewidth. As a new type of exposure light source, its application scenarios and adaptability are greatly improved.

[0005] To achieve the above-mentioned purpose, according to the first aspect of the present invention, a solid-gas hybrid deep ultraviolet laser is provided, comprising: an all-solid-state seed laser, an ArF excimer laser and a laser controller; the all-solid-state seed laser comprises an all-solid-state laser and a nonlinear optical crystal frequency converter, the all-solid-state laser is used to generate a fundamental frequency laser, the nonlinear optical crystal frequency converter is used to receive the fundamental frequency laser and convert it to a target wavelength, the all-solid-state seed laser injects the seed laser into the ArF excimer laser; the ArF excimer laser receives and amplifies the seed laser; the laser controller controls the seed laser output by the ArF excimer laser to be in a target state.

[0006] In one embodiment of the present invention, the laser controller also includes: an injection locking part, which includes a beam splitter, a detector and a frequency controller. The beam splitter splits a part of the laser output by the ArF excimer laser to the detector, and the detector converts the received laser signal into an electrical signal and outputs it to the frequency controller. The frequency controller controls the all-solid-state seed laser or the ArF excimer laser according to the received electrical signal to achieve frequency matching between the two.

[0007] In one embodiment of the present invention, the laser controller further comprises: a timing controller, which controls the all-solid-state laser driving source and the excimer laser driving source to achieve temporal synchronization of laser pulse outputs of the all-solid-state seed laser and the ArF excimer laser.

[0008] In one embodiment of the present invention, the frequency controller uses a DBR / DFB laser, which causes a change in the free carrier concentration in the semiconductor material by changing the injected current on each electrode. The effective refractive index of the material changes due to the plasma dispersion effect, thereby causing a change in the central wavelength of the Bragg grating, thereby changing the laser output lasing mode to tune the wavelength.

[0009] In one embodiment of the present invention, the all-solid-state seed laser further includes: a laser power amplifier, which uses a MOPA structure or an Innoslab slab or a Zig-Zag slab structure to amplify the fundamental frequency laser to obtain a laser with target power, target line width, and tunable wavelength as a solid laser source.

[0010] In one embodiment of the present invention, the nonlinear optical crystal frequency converter converts one path of the fundamental frequency laser into a 355nm laser and another path into an 822.5nm laser. Finally, the two paths of laser are combined to generate a 248nm laser with a target line width.

[0011] In one embodiment of the present invention, the solid-gas hybrid deep ultraviolet laser also includes: an optical shaper, which uses a combination of a cylindrical lens group and a spherical mirror to shape the horizontal and vertical axis directions of the solid laser output spot respectively, and shapes the original spot into a target spot size, thereby achieving spatial matching between the seed light and the subsequent excimer PA part.

[0012] In one embodiment of the present invention, the original spot size of the laser output by the all-solid-state seed laser is a circular spot with a diameter of 0.5 mm and a beam quality of M 2 <1.2, divergence angle <1mrad, the circular spot is collimated and shaped on the horizontal and vertical axes by the cylindrical lens group, and the spot size after shaping is 4*3mm 2 .

[0013] According to the second aspect of the present invention, there is also provided an imaging method for the solid-gas hybrid deep ultraviolet laser described in any one of the above embodiments, characterized in that imaging is performed after the light passes through the all-solid-state seed laser, the ArF excimer laser and the laser controller in sequence from the incident direction.

[0014] In general, the above technical solutions conceived by the present invention can achieve at least the following beneficial effects compared with the prior art:

[0015] 1) By adopting the MOPA-PA laser structure combining fiber-solid laser and excimer laser, compared with the all-solid-state laser system, it can achieve high-power stable output of deep ultraviolet laser and has long-term reliability. Compared with the excimer laser, it can achieve high beam quality output of laser in this band, that is, it can achieve the high requirements of spatial coherence of the output laser, and can greatly reduce the pressure of the subsequent objective shaping system;

[0016] 2) Use DBR or DFB laser as the solid laser seed source, and then amplify it through MOPA structure or Innoslab slab or Zig-Zag slab structure. This mode selects DBR or DFB lasers with wavelengths of 1064nm & 1635nm as seed sources to obtain high-power, ultra-narrow linewidth, wavelength-tunable high-quality 1064nm & 1635nm lasers as solid laser sources, and then converts one path into 355nm laser through non-linear conversion, and the other path into 822.5nm laser. Finally, the two lasers are frequency-converted to generate high-quality, ultra-narrow linewidth 248nm lasers;

[0017] 3) Use DBR / DFB laser, whose wavelength tuning is electrical tuning. The mechanism is to change the free carrier concentration in the semiconductor material by changing the injected current on each electrode. The effective refractive index of the material changes due to the plasma dispersion effect, which causes the change of the central wavelength of the Bragg grating, and then changes the laser output lasing mode to tune the wavelength. This tuning method is easy to implement and the speed of the plasma dispersion effect generated by the injected current can be in the nanosecond level, so it has obvious advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A schematic diagram of the structure of a solid-gas hybrid deep ultraviolet laser provided in an embodiment of the present application;

[0020] Figure 2 A schematic diagram of the optical path structure of the amplifying cavity provided in an embodiment of the present application;

[0021] Figure 3 A schematic diagram of the structure of a laser control system provided in an embodiment of the present application;

[0022] Figure 4 A schematic diagram of the structure of an optical shaping system provided in an embodiment of the present application; DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0024] The terms "first", "second", "third", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0025] like Figure 1As shown, the solid-gas hybrid deep ultraviolet laser proposed in the first embodiment of the present application adopts a MOPA-PA laser structure combining an optical fiber-solid laser and an excimer laser, wherein the first part adopts an all-solid-state structure, including a set of independent MOPA structures, the main oscillation part is a seed source that meets the requirements of other indicators except wavelength, including but not limited to an optical fiber seed source, a semiconductor laser seed source, etc.; including a PA structure of a fundamental frequency laser, including but not limited to a single-pass / multi-pass traveling wave amplification method, a slab (Zig-Zag / Innoslab) amplification method, and a wavelength conversion structure, wherein the main function is to convert the amplified fundamental frequency laser into a target value wavelength laser 248nm commonly used wavelength laser in the lithography field; including a laser control system part, the main function is to realize the control of the output laser of the all-solid-state laser here so as to match the frequency domain and time domain of the subsequent excimer PA structure; including an optical shaping system, this part mainly performs optical shaping on the solid output laser to achieve the spatial matching of the seed light and the subsequent excimer part. The second part is mainly an excimer PA structure, including but not limited to a single-amplifier single-pass / multi-layer mode or a double-amplifier single-pass / multi-pass mode. Through this combination, we can eventually achieve high power, high beam quality, narrow linewidth, short wavelength in the deep ultraviolet band for lithography, and other optical indicators can be flexibly adjusted with long-term stability and reliability laser output to meet the needs of light sources in this field.

[0026] Specifically, an electrically modulated DBR / DFB butterfly fiber laser with ultra-narrow linewidth is used as a fundamental frequency seed source, and other optical fiber / solid lasers with structures that meet the index requirements are all acceptable. The fundamental frequency laser that meets the index requirements is amplified by traveling wave amplification, such as free space single-pass / multi-pass amplification or optical fiber structure amplification or slab amplification, including but not limited to Zig-Zag structure or Innoslab structure, and the power is amplified to meet the use requirements.

[0027] Then, the wavelength is converted through the wavelength conversion structure, and the fundamental wavelength is converted to the target wavelength of 248nm through multiple frequency doubling by nonlinear crystals, including but not limited to triple frequency doubling and quadruple frequency doubling. The laser control system can control the indicators of the solid laser output laser, such as repetition frequency, wavelength tuning, and synchronous matching and closed-loop feedback adjustment of the frequency domain and time domain of the subsequent amplification cavity. In addition, considering that the matching of the airspace involved in solid-gas mixing will have a great impact on the efficiency and beam quality of the final output laser, it is also necessary to establish a connection between this system and the subsequent optical shaping system to achieve closed-loop feedback.

[0028] The control system has an active feedback adjustment function, which can control the output laser of the entire solid-gas combined laser to the target state (such as repetition rate, wavelength, output power, etc.). For example, when the feedback signal detects that the laser output repetition frequency and central wavelength are out of the target range, the control system can modulate the ultra-narrow linewidth electrically modulated DBR / DFB butterfly fiber laser to achieve control of the output laser repetition frequency and fine-tune the central wavelength, so that it is in the target state for a long period. In addition, because the output laser of the solid laser is a pulsed laser, the electrical pumping method of the excimer amplifier cavity is also pulsed pumping, and the duty cycle is not high, the time domain matching between the two becomes particularly important for the amplification result. To address this problem, the control system can also be used to achieve clock synchronization in the time domain, so that when the solid laser output laser passes through the excimer amplifier cavity, it is in the excimer amplifier cavity discharge state, thereby maximizing the amplification efficiency.

[0029] In one embodiment, the laser controller also includes: an injection locking part, which includes a beam splitter, a detector and a frequency controller, wherein the beam splitter splits a part of the laser output by the ArF excimer laser to the detector, and the detector converts the received laser signal into an electrical signal and outputs it to the frequency controller, and the frequency controller controls the all-solid-state seed laser or the ArF excimer laser according to the received electrical signal to achieve frequency matching between the two.

[0030] In one embodiment, the laser controller further comprises: a timing controller, which controls the all-solid-state laser driving source and the excimer laser driving source to achieve temporal synchronization of laser pulse outputs of the all-solid-state seed laser and the ArF excimer laser.

[0031] The laser output from the solid laser part will pass through a designed optical shaping system, which can realize optical shaping of the solid laser output, so as to achieve spatial matching between the seed light and the subsequent excimer PA part. The output laser that meets the index requirements after shaping will be introduced into the amplifying cavity of the excimer laser. At the same time, in order to ensure the real-time and stable matching between the solid laser output seed and the amplifying cavity, the shaping system needs to be adjusted by real-time feedback through the laser control system.

[0032] like Figure 2 The solid laser laser light after shaping as shown is introduced into the gas amplifier cavity, and its power can be amplified by single-pass or multi-pass amplification. The light reflection of the solid laser output laser in the excimer amplifier cavity can be achieved by using a prism, such as a Dove prism, or a reflector coated with a film layer.

[0033] The following is an example of multi-pass amplification: Since the solid laser output laser has high beam quality, the spot can be shaped to the target state as needed and the laser divergence angle can be compressed to a very small value, and the spot size remains basically unchanged in a long optical path. For example, assuming that the excimer discharge cavity discharge energy accumulation area is 1500*16*3mm in length, width and height 3 In order to realize multi-pass amplification of the output laser of the solid laser, the output laser of the solid laser can be shaped into a rectangular laser spot by combining cylindrical lenses. For example, the original spot size of the output laser of the solid laser is a circular spot with a diameter of 0.5 mm, and the beam quality M 2 <1.2, divergence angle <1mrad, for this, the circular spot can be collimated and shaped by the cylindrical lens group on the horizontal and vertical axes respectively, and the spot size after shaping is 4*3mm 2 , under this size, the laser can pass through the gain range of the excimer laser amplifier cavity three times, such as Figure 2 As shown, achieving triple amplification can effectively improve the energy extraction efficiency.

[0034] like Figure 3 As shown, a cylindrical lens group and a spherical mirror are combined to shape the horizontal and vertical axes of the solid laser output spot. A reasonable lens focal length combination is designed to shape the original spot (e.g., a circular spot) into a target spot size (e.g., 4*3mm size).

[0035] At present, the existing technology uses all-solid-state Ti:sapphire laser to output 772nm wavelength laser, and then LBO double frequency and KBBF quadruple frequency to produce 193nm laser. However, the KBBF crystal used in the frequency doubler is not very mature, and its output power and reliability are insufficient.

[0036] like Figure 4 As shown, this embodiment uses DBR or DFB laser as the seed source of solid laser. This seed source belongs to semiconductor laser, with tunable wavelength and ultra-narrow line width. In addition, the repetition rate and pulse width can be adjusted electrically, and then amplified through MOPA structure or Innoslab slab or Zig-Zag slab structure. In this mode, DBR or DFB laser with wavelengths of 1064nm & 1635nm is selected as the seed source to obtain high-power, ultra-narrow line width, high-quality 1064nm & 1635nm laser with tunable wavelength as the solid laser source. Then through non-linear conversion, one way is converted to 355nm laser, and the other way is converted to 822.5nm laser. Finally, the two lasers are frequency-converted to generate high-quality, ultra-narrow line width 248nm laser.

[0037] In the actual product process, the laser line width is a very important indicator of the laser indicators of this band finally output by the excimer laser, and a complex line width narrowing system is often required later. This solution uses DBR / DFB laser output with ultra-narrow line width based on this requirement at the beginning of the design, which reduces the pressure on subsequent work.

[0038] In the frequency domain, that is, wavelength matching, the prior art uses a method of adjusting the length of the resonant cavity for matching adjustment. This method is a mechanical adjustment, which is complex to operate, has low reliability, and is highly dependent on ambient temperature. In one embodiment of the present application, a DBR / DFB laser is selected, and its wavelength tuning is an electrical adjustment. The electrical tuning mechanism is to change the free carrier concentration in the semiconductor material by changing the injected current on each electrode. The effective refractive index of the material changes due to the plasma dispersion effect, thereby causing the change in the central wavelength of the Bragg grating, and then changing the laser output lasing mode, and thus tuning the wavelength. This tuning method is relatively easy to implement, and the speed of the plasma dispersion effect generated by the injected current is very fast, generally in the nanosecond order, so the advantage is very obvious.

[0039] In the time domain, the existing technologies for solid-state lasers all use a resonant cavity to directly output lasers, and achieve timing matching with the excimer amplifier cavity by controlling the pump frequency of the pump source. In one embodiment of the present application, a solid seed source + traveling wave amplification structure is used, that is, there are actually two amplification structures. One is that the solid laser itself is a seed source + traveling wave amplification structure, that is, infrared wavelength amplification, and the other is the structure of the solid laser through the excimer amplifier cavity, that is, 248nm amplification. The timing is matched by electrically adjusting the solid seed source, that is, the DBR laser, while the stable pump power is maintained unchanged in the traveling wave amplification part. The advantage of this method is that the thermal impact is relatively small, the output is stable, and it has practical significance.

[0040] In addition, in terms of spatial adjustment, that is, full utilization of the gain range in the excimer amplifier cavity, the solid laser can pass through the excimer amplifier cavity multiple times through the shaping of the cylindrical lens group, so that the energy accumulated in the excimer amplifier cavity can be fully extracted.

[0041] In summary, the solid-gas hybrid deep ultraviolet laser proposed in the first embodiment of the present application adopts a MOPA-PA laser structure combining an optical fiber-solid laser and an excimer laser. Compared with an all-solid-state laser system, it can achieve high-power stable output of lasers in the deep ultraviolet band and has long-term reliability. Compared with an excimer laser, it can achieve high beam quality output of lasers in this band, that is, it can meet the high requirements of spatial coherence of the output laser, and can greatly reduce the pressure of the subsequent objective lens shaping system; a DBR or DFB laser is used as a solid laser seed source, and then amplified by a MOPA structure or an Innoslab slab or a Zig-Zag slab structure. This mode is used to select DBR or DFB lasers with wavelengths of 1064nm & 1635nm as seed sources. High-power, ultra-narrow linewidth, wavelength-tunable high-quality 1064nm & 1635nm lasers can be used as solid laser sources, and then one channel is converted into 355nm laser through non-linear conversion, and the other channel is converted into 822.5nm laser. Finally, the two lasers are frequency-generated to generate high-quality, ultra-narrow linewidth 248nm lasers; DBR / DFB lasers are selected, and their wavelength tuning is electrical tuning. The mechanism is to change the free carrier concentration in the semiconductor material by changing the injected current on each electrode, and the effective refractive index of the material changes due to the plasma dispersion effect, thereby causing the change of the central wavelength of the Bragg grating, and then changing the laser output lasing mode to tune the wavelength. This tuning method is easy to implement and the speed of the plasma dispersion effect generated by the injected current can be in the nanosecond level, so it has obvious advantages.

[0042] In addition, the second embodiment of the present invention proposes an imaging method applied to the solid-gas hybrid deep ultraviolet laser described in the first embodiment above, and imaging is performed after the light passes through the all-solid-state seed laser, the ArF excimer laser and the laser controller in sequence from the incident direction.

[0043] It is worth mentioning that the specific functions realized by the solid-gas hybrid deep ultraviolet laser can refer to the contents described in the first embodiment, which will not be described in detail here. The beneficial effects of this embodiment are the same as those of the aforementioned first embodiment, and will not be repeated here for the sake of brevity.

[0044] The above is only an exemplary embodiment of the present disclosure, and the scope of the present disclosure cannot be limited thereto. That is, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. After considering the specification and practicing the disclosure here, those skilled in the art will easily think of the implementation scheme of the present disclosure. This application is intended to cover any modification, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the technical field not recorded in the present disclosure. The description and examples are regarded as exemplary only, and the scope and spirit of the present disclosure are defined by the claims.

[0045] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0046] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A solid-gas hybrid deep ultraviolet laser, characterized in that: include: Solid laser seed source, laser amplification system, wavelength conversion system, KrF excimer laser system and laser control system; The all-solid-state seed laser comprises an all-solid-state laser and a nonlinear optical crystal frequency converter. The all-solid-state laser is used to generate a fundamental frequency laser. The nonlinear optical crystal frequency converter is used to receive the fundamental frequency laser and convert the fundamental frequency laser to a target wavelength. The all-solid-state seed laser injects the seed laser into the KrF excimer laser. The KrF excimer laser receives and amplifies the seed laser; The laser controller controls the seed laser output by the KrF excimer laser to be in a target state.

2. The solid-gas hybrid deep ultraviolet laser according to claim 1, characterized in that: The laser controller also includes: The injection locking part includes a beam splitter, a detector and a frequency controller. The beam splitter splits a part of the laser light output by the ArF excimer laser to the detector. The detector converts the received laser signal into an electrical signal and outputs it to the frequency controller. The frequency controller controls the all-solid-state seed laser or the ArF excimer laser according to the received electrical signal to achieve frequency matching between the two.

3. The solid-gas hybrid deep ultraviolet laser according to claim 1, characterized in that: The laser controller also includes: A timing controller controls the all-solid-state laser driving source and the excimer laser driving source to achieve time synchronization of laser pulse outputs of the all-solid-state seed laser and the ArF excimer laser.

4. The solid-gas hybrid deep ultraviolet laser according to claim 2, characterized in that: The frequency controller uses DBR / DFB laser, which changes the injected current on each electrode to cause a change in the free carrier concentration in the semiconductor material. The plasma dispersion effect causes the effective refractive index of the material to change, thereby causing the center wavelength of the Bragg grating to change, thereby changing the laser output lasing mode to tune the wavelength.

5. The solid-gas hybrid deep ultraviolet laser according to claim 1, characterized in that: The all-solid-state seed laser also includes: The laser power amplifier adopts a MOPA structure or an Innoslab slab or a Zig-Zag slab structure to amplify the fundamental frequency laser to obtain a laser with target power and target line width and tunable wavelength as a solid laser source.

6. The solid-gas hybrid deep ultraviolet laser according to claim 1, characterized in that: The nonlinear optical crystal frequency converter converts one path of the fundamental frequency laser into a 355nm laser and another path into an 822.5nm laser. Finally, the two paths of laser are combined to generate a 248nm laser with a target line width.

7. The solid-gas hybrid deep ultraviolet laser according to claim 1, characterized in that: Also includes: The optical shaper uses a combination of a cylindrical lens group and a spherical mirror to shape the horizontal and vertical axes of the solid laser output spot respectively, and shapes the original spot into a target spot size, thereby achieving spatial matching between the seed light and the subsequent excimer PA part.

8. The solid-gas hybrid deep ultraviolet laser according to claim 1, characterized in that: The original spot size of the all-solid-state seed laser output laser is a circular spot with a diameter of 0.5 mm and a beam quality of M 2 <1.2, divergence angle <1mrad, the circular spot is collimated and shaped on the horizontal and vertical axes by the cylindrical lens group, and the spot size after shaping is 4*3mm 2 .

9. An imaging method applied to the solid-gas hybrid deep ultraviolet laser according to any one of claims 1 to 8, characterized in that: The light is imaged after passing through the all-solid-state seed laser, the ArF excimer laser and the laser controller in sequence from the incident direction.

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