Ultraviolet laser adjustable beam expanding optical system and beam expanding lens

Abstract

The embodiment of the invention discloses an ultraviolet laser adjustable beam expanding optical system and a beam expanding lens, and relates to the field of optics. The system sequentially comprises a first lens group with positive diopter, a second lens group with negative diopter, a third lens group with negative diopter and a fourth lens group with positive diopter which are arranged along the same optical axis along the incident direction of a laser beam, wherein the positions of the first lens group and the fourth lens group are fixed in the system, the second lens group can move along an optical axis so as to adjust the beam expanding magnification of a light beam, and the third lens group can move along the optical axis so as to perform collimation compensation of a laser beam. By arranging the movable second lens group and the third lens with the compensation function, the beam expanding multiple of the optical system is variable, and the output light beam meets the requirements of high collimation and high image quality.

Description

Technical Field

[0001] The present application relates to the field of optical technology, and in particular to an ultraviolet laser adjustable beam expanding optical system and a beam expanding mirror. Background Art

[0002] Ultraviolet lasers have important applications in chip manufacturing-related equipment such as lithography machines and wafer inspection. Generally speaking, the laser output by the laser must undergo adjustments such as beam expansion and shaping before it can output a laser beam that meets the requirements of the equipment. Therefore, beam expansion is very important as the first step in laser shaping.

[0003] Due to the differences in manufacturing tolerances, beam waists, divergence angles, M2 and other parameters between different UV lasers, the laser parameters output by different lasers are different. At the same time, there will be beam differences between different units of the same laser. Therefore, when the laser is applied to a certain device, a fixed-magnification beam expander often cannot meet the requirements, causing the size of the output beam to change, thereby indirectly or directly affecting the performance of the device. Summary of the invention

[0004] The present application provides an ultraviolet laser adjustable beam expansion optical system and a beam expander, which can meet the requirements of beam expansion with variable magnification.

[0005] This application provides the following solutions:

[0006] In the first aspect, a UV laser adjustable beam expansion optical system is provided, which includes, along the incident direction of the laser beam, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with negative refractive power, and a fourth lens group with positive refractive power in sequence; the first lens group, the second lens group, the third lens group, and the fourth lens group are arranged along the same optical axis. The first lens group and the fourth lens group are fixed in position in the system, the second lens group can be moved along the optical axis to adjust the beam expansion magnification, and the third lens group can be moved along the optical axis to perform collimation compensation for the laser beam.

[0007] According to an achievable manner in the embodiment of the present application, the first lens group includes, in order from the laser incident direction along the optical axis: a first lens with negative optical power and a second lens with positive optical power; and / or,

[0008] The second lens group includes, along the optical axis from the laser incident direction: a third lens having negative optical power; and / or,

[0009] The third lens group includes, in order from the laser incident direction along the optical axis: a fourth lens having negative optical power and a fifth lens having negative optical power; and / or,

[0010] The fourth lens group includes, in order from the laser incident direction along the optical axis, a sixth lens with positive optical power and a seventh lens with negative optical power.

[0011] According to an implementable manner in the embodiment of the present application, the first lens, the fourth lens, the fifth lens and the seventh lens are negative meniscus lenses; the second lens is a biconvex lens; the third lens is a biconcave lens; and the sixth lens is a positive meniscus lens.

[0012] According to an achievable manner in the embodiment of the present application, the moving directions of the fourth lens and the fifth lens are consistent with that of the second lens group.

[0013] According to an implementable manner in the embodiment of the present application, the first lens, the second lens, the third lens, the fourth lens and the fifth lens are made of calcium fluoride; and the sixth lens and the seventh lens are made of fused quartz glass.

[0014] According to an achievable manner in an embodiment of the present application, the refractive index of the calcium fluoride is ≥1.43, and the dispersion coefficient is ≥95; the refractive index of the fused quartz glass is ≥1.45, and the dispersion coefficient is ≥67.8.

[0015] According to an achievable method in an embodiment of the present application, the overall length of the optical system is less than 90 mm, the movable range of the second lens group is greater than 5.5 mm, and the movable range of the third lens group is greater than 4.5 mm.

[0016] According to an achievable method in an embodiment of the present application, the maximum aperture of each lens in the system is 22 mm.

[0017] According to an achievable method in an embodiment of the present application, the wavelength of the incident laser is 266 nm and the bandwidth is 1 nm.

[0018] In a second aspect, a beam expander is provided, wherein the beam expander comprises the optical system as described in the first aspect above.

[0019] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0020] In the adjustable beam expansion optical system of the present application, the beam expansion ratio is adjusted by setting a movable second lens group, and the laser light beam after variable beam expansion is collimated and adjusted by a third lens group with a compensation function, so that the beam expansion ratio of the optical system is variable, and the output light beam can meet the requirements of high collimation and high image quality.

[0021] The present application can achieve an ultra-large zoom range of 4 to 20 times by arranging one or more lenses with positive or negative optical focal power in each lens group, and by coordinating and moving the third lens, the fourth lens and the fifth lens.

[0022] All lenses in the optical system of the present application adopt a spherical design to avoid the problem of manufacturing difficulties caused by introducing aspherical or free-form surface lenses.

[0023] In the optical system of the present application, the first five lenses are all made of calcium fluoride material, which has ultra-high transmittance and extremely high damage threshold in the deep ultraviolet spectrum, and can meet the requirements of beam expansion applications in watt-level deep ultraviolet lasers.

[0024] In the optical system of the present application, when the wavelength of the input light beam is 266 nm, the input light beam size can range from 0.4 mm to 2 mm, and the output light beam size can be kept constant, and the emission angle is less than 0.01 mrad.

[0025] Of course, any product implementing the present application does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, 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.

[0027] Figure 1 A schematic diagram of the structure of an optical system applicable to an embodiment of the present application;

[0028] Figure 2 A schematic diagram of an optical system structure applicable to another embodiment of the present application;

[0029] Figure 3 A schematic diagram of the optical path of an optical system applicable to an embodiment of the present application;

[0030] Figure 4a This is an output wavefront diagram of the optical system under 20x beam expansion applicable to the embodiment of the present application;

[0031] Figure 4b This is an output wavefront diagram of the optical system under 10x beam expansion applicable to the embodiment of the present application;

[0032] Figure 4c This is an output wavefront diagram of the optical system under 4x beam expansion applicable to the embodiment of the present application;

[0033] Figure 5A diagram showing light emission angles of an optical system applicable to an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0035] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0036] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0037] The directions or positional relationships such as "upper", "lower", "front", "back", "left", and "right" involved in the embodiments of the present application are only for the convenience of describing the present application, and are not intended to limit the devices or components of the present disclosure to have specific directions or positions. It should be understood that the expressions of these directions or positional relationships are all relative. Any modifications, equivalent substitutions, improvements, etc. made within the scope of the present disclosure shall be included in the protection scope of the present disclosure.

[0038] At present, there is a UV laser beam expansion technology, which mainly uses a combination of three lenses to achieve beam expansion. The range of the zoom ratio of this method is small, and it can only achieve 2-8 times of beam expansion, which cannot meet the requirements of a larger zoom range. In addition, most of the existing UV zoom beam expanders operate at wavelengths of 355nm and above. However, the wavelength of UV lasers is usually between 200 nanometers and 400 nanometers, especially in deep UV lasers that are widely used in lithography machines, whose wavelengths are usually between 200-300 nanometers. Therefore, traditional UV zoom beam expanders cannot meet the beam expansion requirements for UV lasers in the low wavelength range.

[0039] In view of this, in order to achieve the requirement of wide-range variable magnification beam expansion for ultraviolet lasers in the low wavelength range, the present application provides an ultraviolet laser adjustable beam expansion optical system. In order to facilitate the understanding of the present application, the optical system structure based on the present application is first described. Figure 1This is a schematic diagram of the optical system structure applicable to the embodiment of the present application, such as Figure 1 As shown, the left side is the input direction of the laser, and the laser enters the optical system from the left side along the optical axis. In the optical system, along the incident direction of the laser, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with negative refractive power, and a fourth lens group with positive refractive power are sequentially included along the optical axis, wherein each lens group is arranged along the same optical axis.

[0040] The first lens group and the fourth lens group are fixed in position in the system to correct the aberration of the laser. At the same time, the first lens group and the fourth lens group are fixed to reduce the number of moving components and the manufacturing difficulty.

[0041] The second lens group can move along the optical axis, and the beam expansion ratio of the light beam can be adjusted by moving the second lens group. During the movement of the second lens group from left to right, the beam expansion ratio gradually decreases. The beam expansion range that can be achieved by the optical system of the present application is related to the movement range of the second lens group.

[0042] After the laser beam is expanded by the second lens group, in order to achieve collimated emission, the present application sets a third lens group for collimation compensation. The third lens group can also move along the optical axis, and the collimation compensation of the laser beam can be achieved by moving the third lens group. The third lens group works in conjunction with the second lens group, and for different settings, the third lens group and the second lens group can move within their respective movable ranges.

[0043] In the optical system of the present application, the four lens groups can be directly implemented by a single lens that meets the refractive power requirements, or by a combination of multiple lenses. For example, the first lens group can be implemented by only one lens with positive optical power, or by a combination of multiple lenses, as long as the refractive power of the multiple lenses combined is positive.

[0044] As a preferred embodiment, along the optical axis from the laser incident direction, the first lens group includes: a first lens with negative optical power, and a second lens with positive optical power. The second lens group includes: a third lens with negative optical power. The third lens group includes: a fourth lens with negative optical power, and a fifth lens with negative optical power. The fourth lens group includes: a sixth lens with positive optical power, and a seventh lens with negative optical power. During the operation of the optical system, the movement direction of the fourth lens and the fifth lens is consistent with that of the second lens group.

[0045] The first lens to the seventh lens can be implemented by various types of lenses that meet the focal power requirements. For example, a lens with positive focal power can be set as a biconvex type lens, or can be set as a positive meniscus type lens.

[0046] As a preferred embodiment, the first lens, the fourth lens, the fifth lens and the seventh lens can be set as negative meniscus lenses; the second lens is a double convex lens; the third lens is a double concave lens; and the sixth lens is a positive meniscus lens. In this embodiment, all lenses adopt a spherical design, which can avoid the problem of manufacturing difficulties caused by introducing aspherical or free-form lenses.

[0047] The present application is used for beam expansion of ultraviolet lasers. The power of ultraviolet lasers is relatively high. To ensure that the lens is not damaged by the laser, materials with strong radiation resistance can be selected, such as magnesium fluoride (MgF2), calcium fluoride (CaF2), etc. In particular, along the direction of laser incidence, the spot size formed by the front lens is smaller, the laser power density is larger, and it is more easily damaged by the laser. Therefore, as a preferred embodiment, the first lens to the fifth lens of the present application adopt calcium fluoride (CaF2) glass; the sixth lens and the seventh lens adopt fused quartz glass. Because there are certain differences in refractive index and dispersion between fused quartz glass and calcium fluoride glass, setting the sixth lens and the seventh lens as fused quartz glass lenses can correct certain chromatic aberrations. Among them, when the first lens to the fifth lens adopt calcium fluoride (CaF2) glass, the refractive index Nd≥1.43, the dispersion coefficient Vd≥95.0, and when the sixth lens and the seventh lens adopt fused quartz glass, the refractive index Nd≥1.45, the dispersion coefficient Vd≥67.8.

[0048] More specifically, the first to fifth lenses of the present application may use calcium fluoride (CaF2) glass with a refractive index Nd of 1.43 and an dispersion coefficient Vd of 95.0; the sixth and seventh lenses may use fused quartz glass with a refractive index Nd of 1.45 and an dispersion coefficient Vd of 67.8.

[0049] The optical system of the present application can work in the entire ultraviolet wavelength range, and is particularly suitable for beam expansion of lasers with an operating wavelength of 266nm and a bandwidth of 1nm. In the embodiment of the present application, the required beam expansion requirements can be achieved by determining parameters such as the lens spacing according to the operating wavelength of the laser and the beam expansion requirements.

[0050] In order to ensure the working quality of the system, an optimal parameter setting method is given: the overall length of the optical system of the present application is less than 90 mm, the maximum aperture of the lens is 22 mm; the moving range of the second lens group is greater than 5.5 mm, and the moving range of the third lens group is set to be greater than 4.5 mm.

[0051] Applying this parameter setting method to the optical system of the present application can achieve a beam expansion effect of 4-20 times for ultraviolet lasers, especially deep ultraviolet lasers. In particular, when the working wavelength is 266nm and the bandwidth is 1nm, the incident laser beam size range of the optical system is 0.4mm~2mm, and the incident laser beam divergence range is 0.35mrad~1.05mrad; the optical system emits parallel light, the maximum beam diameter of the emittance light is 18mm, and the emission angle is less than 0.01mrad.

[0052] A specific embodiment of the present application is given below:

[0053] Figure 2 A schematic diagram of the optical path of an optical system applicable to another embodiment of the present application is shown in FIG. Figure 2 As shown in the figure, the optical system is an ultraviolet laser beam expander, which defines that the laser input direction is on the left and the laser output direction after beam expansion is on the right. The beam expander includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power along its optical axis.

[0054] Among them, the first lens group G1 and the fourth lens group G4 are fixed groups, the second lens group G2 is a movable group to adjust the beam expansion ratio, and the third lens group G3 is a compensation group to collimate the laser beam after the variable magnification beam expansion. The focal length of the first lens group G1 is 17.54mm, the focal length of the second lens group G2 is -13.28mm, the focal length of the third lens group G3 is -44.23mm, and the focal length of the fourth lens group is 158.90mm.

[0055] The first lens group G1 includes, from the object side to the image side along the optical axis, a first lens 1 with negative optical power and a second lens 2 with positive optical power. The first lens 1 is a negative meniscus lens, and the second lens 2 is a biconvex lens.

[0056] The second lens group G2 includes a third lens 3 with negative optical power, and the third lens 3 is a biconcave lens. In the process of moving from left to right, the beam expansion ratio gradually decreases. The moving range of the second lens group G2 is 4.1mm to 9.6mm.

[0057] The third lens group G3 includes, from the object side to the image side, along the optical axis direction: a fourth lens 4 and a fifth lens 5 having negative optical power. The fourth lens 4 and the fifth lens 5 are both negative meniscus lenses, and the movement directions of the fourth lens 4 and the fifth lens 5 are consistent with those of the second lens group to achieve collimation compensation. The movement range of the third lens group G3 is 1.4mm to 5.9mm.

[0058] The fourth lens group G4 includes, from the object side to the image side along the optical axis direction, a sixth lens 6 with positive power and a seventh lens 7 with negative power. The sixth lens 6 is a positive meniscus lens, and the seventh lens 7 is a negative meniscus lens. The specific parameters of each lens in this embodiment are shown in Table 1 below:

[0059] Table 1

[0060]

[0061] In the above table, the two curvature radii corresponding to each lens are the radii of the left and right curved surfaces of the lens; the thickness is the center thickness of the lens on the optical axis; the air gap is the distance between the lens and the lens on the right. For the seventh lens, the air gap refers to the working distance of the lens. The specific parameters of the above lenses can be fine-tuned in actual operation to meet the parameter requirements of different systems.

[0062] Among them, the materials of the first lens 1 to the fifth lens 5 are all high-transmittance fused quartz lenses in the deep ultraviolet spectrum, with a refractive index Nd of 1.45 and a dispersion coefficient Vd of 67.8; the materials of the sixth lens and the seventh lens are calcium fluoride glass, with a refractive index Nd of 1.43 and a dispersion coefficient Vd of 95.0; the selected materials are all deep ultraviolet grade materials, with a transmittance greater than 99.9% in the deep ultraviolet 266nm band and no fluorescence effect.

[0063] The present application conducted an effect test for this embodiment. The test used a deep ultraviolet laser with a wavelength of 266nm as the working wavelength, and the beam expander provided by this embodiment expanded the deep ultraviolet laser by 20, 10, and 4 times respectively. The test optical path diagram is shown in FIG. Figure 3 This application evaluates the quality of the output beam after beam expansion, and the specific evaluation indicators are as follows:

[0064] 1. Wavefront aberration

[0065] Wavefront aberration is an important parameter in optical systems, which is used to describe the optical path difference between the actual wavefront and the ideal wavefront when they are tangent at the exit pupil. Wavefront aberration is usually used to evaluate the imaging quality and performance of optical systems, and is more suitable for systems with high collimation and high image quality requirements such as lasers.

[0066] The present application measures the wavefront aberration of this embodiment at different beam expansion ratios, such as Figures 4a to 4cThey are respectively the output wavefront diagrams of the optical system applicable to the embodiments of the present application under 20x, 10x, and 4x beam expansion. The function distribution diagram in the figure reflects the distribution of the wavefront function. The horizontal and vertical axes are the X aperture and Y aperture, respectively, indicating the width of the wavefront in the X and Y directions. The wavefront aberration RMS (Root Mean Square) is an indicator that describes the aberration in an optical system. In an optical system, aberration refers to the deviation caused by the light beam not being focused on the ideal focus when the light passes through a lens or a reflective device. The wavefront aberration RMS is a quantitative description of these deviations. It represents the square root of the average value of the square of the aberration within a given wavelength range, and is used to measure the overall aberration level of the optical system. The smaller the wavefront aberration RMS, the higher the imaging quality of the optical system and the smaller the aberration. Figures 4a to 4c As shown in the figure, under 20 times beam expansion, the wavefront aberration RMS is 0.0375λ; under 10 times beam expansion, the wavefront aberration RMS is 0.0269λ; under 4 times beam expansion, the wavefront aberration RMS is 0.0425λ. That is, within the zoom range of 4 times to 20 times, the wavefront aberration RMS of this embodiment is less than 0.05λ, indicating that the imaging quality of the laser after the beam expander is extremely good.

[0067] 2. Outgoing beam angle

[0068] The exit beam angle is an important indicator for evaluating the effect of laser beam expansion. The exit beam angle refers to the direction or tilt angle of the beam when it exits the optical system. A smaller exit beam angle can ensure that the laser exit spot remains a fixed size within the Rayleigh length.

[0069] The present application measured the angle of the emitted light beam of this embodiment at different magnifications, and the results are as follows: Figure 5 shown. Figure 5 In the figure, the three straight lines in red, green, and blue from bottom to top represent the angle values ​​of the outgoing beam under 20x, 10x, and 4x beam expansion respectively. Figure 5 It can be seen that as the beam expansion ratio decreases, the angle of the exiting beam increases successively. The angle of the exiting beam under 4-fold beam expansion is larger, but the angles of the exiting beam under the three beam expansion ratios are all less than 0.0006°, i.e., 0.01 mrad, which proves that the image formed by the laser after the present embodiment meets the quality requirements.

[0070] It should be noted that the definitions such as “first” and “second” in the present disclosure do not have limitations in terms of size, order, and quantity, and are only used to distinguish them in name. For example, “first lens group” and “second lens group” are used to distinguish two groups of lenses.

[0071] The above system provided in the embodiment of the present application can be applied to a variety of application scenarios, including but not limited to: it can be used in micro-processing fields such as semiconductor manufacturing, photolithography, and microelectronics processing. The system of the present application is used to control and adjust the size and shape of the laser beam to achieve precise processing effects. For example, it can be applied to a particle detection equipment machine (PCG) as a component of the optical path of the equipment. The system of the present application can also be used in an optical communication system to adjust the transmission performance of the laser beam, such as focusing and divergence, to ensure the stability and accuracy of signal transmission.

[0072] The technical solution provided by the present application is described in detail above. The principle and implementation method of the present application are described in detail using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. An ultraviolet laser adjustable beam expansion optical system, characterized in that: Along the incident direction of the laser beam, it includes in sequence a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with negative refractive power and a fourth lens group with positive refractive power; The first lens group, the second lens group, the third lens group and the fourth lens group are arranged along the same optical axis; wherein, the first lens group and the fourth lens group are fixed in position in the system, the second lens group can be moved along the optical axis to adjust the beam expansion ratio of the light beam, and the third lens group can be moved along the optical axis to perform collimation compensation for the laser beam.

2. The optical system according to claim 1, characterized in that The first lens group includes, in order from the laser incident direction along the optical axis: a first lens with negative optical power and a second lens with positive optical power; and / or, The second lens group includes, along the optical axis from the laser incident direction: a third lens having negative optical power; and / or, The third lens group includes, in order from the laser incident direction along the optical axis: a fourth lens having negative optical power and a fifth lens having negative optical power; and / or, The fourth lens group includes, in order from the laser incident direction along the optical axis, a sixth lens with positive optical power and a seventh lens with negative optical power.

3. The optical system according to claim 2, characterized in that The first lens, the fourth lens, the fifth lens and the seventh lens are negative meniscus lenses; the second lens is a biconvex lens; the third lens is a biconcave lens; and the sixth lens is a positive meniscus lens.

4. The optical system according to claim 2, characterized in that The moving directions of the fourth lens and the fifth lens are consistent with that of the second lens group.

5. The optical system according to claim 2, characterized in that The first lens, the second lens, the third lens, the fourth lens and the fifth lens are made of calcium fluoride; the sixth lens and the seventh lens are made of fused quartz glass.

6. The optical system according to claim 5, characterized in that The refractive index of the calcium fluoride is ≥1.43, and the dispersion coefficient is ≥95; the refractive index of the fused quartz glass is ≥1.45, and the dispersion coefficient is ≥67.

8.

7. The optical system according to claim 1, characterized in that The overall length of the optical system is less than 90 mm, the movable range of the second lens group is greater than 5.5 mm, and the movable range of the third lens group is greater than 4.5 mm.

8. The optical system according to claim 7, characterized in that The maximum aperture of each lens in the system is 22 mm.

9. The optical system according to claim 8, characterized in that The incident laser wavelength is 266 nm and the bandwidth is 1 nm.

10. A beam expander, characterized in that: The beam expander comprises an optical system as described in any one of claims 1-9.

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