Projection lithography objective optical system with large field of view

Abstract

The application provides a projection lithography objective optical system with a large field of view, the objective optical system has the characteristics of a large field of view, easy production and processing, good thermal stability and the ability to meet the demand of a large exposure dose, and is provided with a first mirror group, a second mirror group, a third mirror group and a first reflector; a light beam emitted from an object plane sequentially passes through the first mirror group, the second mirror group and the third mirror group, is reflected by the first reflector, sequentially passes through the third mirror group, the second mirror group and the first mirror group and is converged and imaged to an image plane, and the objective optical system satisfies the following relationship: 0.25 < f1 / L < 1.1, 0.17 < f2 / L < 0.72 and 0.24 < -f3 / L < 0.95, wherein f1, f2 and f3 are the combined focal lengths of the first, second and third mirror groups, L is the optical distance from the object plane to the image plane of the objective optical system, and Hy is the radius of the field of view.

Description

Technical Field

[0001] This invention relates to the field of projection lithography technology, and more specifically to an optical system for projection lithography objective lenses with a large field of view. Background Technology

[0002] With the development of projection lithography technology, projection lithography lenses have been widely used in the back-end processes of semiconductors, MEMS, liquid crystals, and high-precision printed circuit boards.

[0003] With technological advancements, there is a growing demand for accommodating increasingly fine lines on larger substrates, leading to a surge in the need for high-precision projection lithography machines with micrometer-level exposure fields. To improve the production efficiency of projection lithography, the exposure field of the objective lens has gradually increased from tens of millimeters to over one hundred millimeters, placing higher demands on the design of the objective lens.

[0004] In addition, in existing technologies, lithography projection lenses generally suffer from insufficient field of view and poor thermal stability, making it difficult to meet the requirements of large exposure doses. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a projection lithography objective lens optical system with a large field of view. The objective lens optical system features a large field of view, ease of manufacturing and processing, and good thermal stability to meet the requirements of high exposure doses.

[0006] The technical solution is as follows: A projection lithography objective lens optical system with a large field of view, comprising, along the optical axis, a first mirror group, a second mirror group, a third mirror group, and a first reflecting mirror. The first and second mirror groups have positive optical power, and the third mirror group has negative optical power. A light beam emitted from the object surface passes sequentially through the first, second, and third mirror groups, is reflected by the first reflecting mirror, and then sequentially passes through the third, second, and first mirror groups before converging to form an image on the image plane. The objective lens optical system satisfies the following relationship:

[0007] 0.25 <f1 / L<1.1

[0008] 0.17 <f2 / L<0.72

[0009] 0.24 <- f3 / L < 0.95

[0010] Where f1 is the combined focal length of the first lens group, f2 is the combined focal length of the second lens group, f3 is the combined focal length of the third lens group, L is the optical distance from the object plane to the image plane of the objective lens optical system, and Hy is the radius of the field of view.

[0011] Furthermore, the first reflector is made of a material with a low coefficient of thermal expansion.

[0012] Furthermore, the reflecting surface of the first reflector is concave, and the first reflector satisfies the following relationship:

[0013] 0.25 <- R / L < 1.2

[0014] Where R is the radius of curvature of the reflecting surface of the first mirror.

[0015] Furthermore, the first lens group includes at least one positive lens, and the second lens group includes at least one positive lens, satisfying the following:

[0016] 0.7 <f1 / f2<2.9

[0017] 0.3 <d0 / d1<1.2

[0018] 0.15 < (d0 + d1) / L < 0.6

[0019] Where d0 is the optical distance between the object plane and the first lens group, and d1 is the optical distance between the first lens group and the second lens group;

[0020] The third lens group comprises at least one positive lens and one negative lens, and the third lens group satisfies the following relationship:

[0021] Vdps-Vdms>15

[0022] Wherein, Vdps is the dispersion coefficient of a positive lens in the third lens group, and Vdms is the dispersion coefficient of a negative lens in the third lens group.

[0023] Furthermore, the first lens group includes a first lens, which is a positive lens, with a first side of the first lens away from the first reflecting mirror being a convex surface, and a second side of the first lens close to the first reflecting mirror being a convex surface;

[0024] The second mirror group includes a second lens, which is a positive lens, and the first side of the second lens away from the first reflecting mirror is a convex surface;

[0025] The third lens group includes a third lens and a fourth lens. The third lens is a negative lens, and the fourth lens is a positive lens. The first side of the third lens away from the first reflector is concave, and the second side of the third lens close to the first reflector is concave. The first side of the fourth lens away from the first reflector is convex, and the second side of the fourth lens close to the first reflector is convex.

[0026] Furthermore, the objective lens optical system also includes a second reflecting mirror, which is disposed in front of the first lens group. The second reflecting mirror includes a first reflecting plane and a second reflecting plane. The straight line intersecting the first reflecting plane and the extended plane of the second reflecting plane is perpendicular to the optical axis formed by the first lens group, the second lens group, the third lens group, and the first reflecting mirror. The object plane and the image plane are parallel to each other and are both parallel to the optical axis. The light beam emitted from the object plane is reflected by the first reflecting plane and enters the first lens group. After passing through the first lens group, the second lens group, and the third lens group, it is reflected by the first reflecting mirror, and then passes through the third lens group, the second lens group, and the first lens group. The light beam emitted from the first lens group is reflected by the second reflecting plane and converges to form an image on the image plane.

[0027] Furthermore, the lenses in the first lens group, the second lens group, and the third lens group are all spherical lenses.

[0028] Furthermore, a cooling device is provided at the position of the first reflector. The cooling device is used to control the temperature of the reflective surface. The cooling device is any one or a combination of heat conduction cooling device, convection cooling device, or electric refrigeration device.

[0029] Furthermore, the optical system is capable of correcting aberrations for the i-line, h-line, and g-line in the spectrum, with wavelengths of 365 nm, 405 nm, and 436 nm, respectively.

[0030] The advantages of this invention compared to the prior art are:

[0031] This invention employs a first mirror group, a second mirror group, a third mirror group, and a reflecting mirror. The first mirror group includes a first lens arranged sequentially along the optical axis, the second mirror group includes a second lens, and the third mirror group includes a third lens and a fourth lens arranged sequentially along the optical axis. A light beam emitted from the object surface passes sequentially through the first mirror group, the second mirror group, and the third mirror group, is reflected by the first reflecting mirror, and then passes sequentially through the third mirror group, the second mirror group, and the first mirror group before converging to form an image on the image plane. By coordinating the focal lengths of each mirror group and the lenses within it, the problem of a small projection field of view of the projection objective lens can be solved. A smaller lens combination achieves better aberration correction of the optical system within a large field of view, meeting the practical application requirements of projection lithography, which is currently at a leading level both domestically and internationally. At the same time, the optical system uses commonly used optical materials and spherical lenses, making it easy to manufacture and saving on the production and assembly costs of the optical system. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the composition of a projection lithography objective lens optical system with a large field of view in one embodiment;

[0033] Figure 2This is a schematic diagram of another projection lithography objective lens optical system with a large field of view in the embodiment.

[0034] Figure 3 The MTF (Mean Transfer Function) plot of a projection lithography objective lens optical system with a large field of view is shown in the embodiment.

[0035] Figure 4 This is a schematic diagram of the field of view in the embodiment. Detailed Implementation

[0036] See Figure 1 The present invention discloses a projection lithography objective lens optical system with a large field of view, comprising, sequentially along the optical axis: a first mirror group G1, a second mirror group G2, a third mirror group G3, and a first reflecting mirror. The first mirror group G1 and the second mirror group G2 have positive optical power, and the third mirror group G3 has negative optical power. A light beam emitted from the object plane P1 passes sequentially through the first mirror group G1, the second mirror group G2, and the third mirror group G3, is reflected by the first reflecting mirror, and then sequentially passes through the third mirror group G3, the second mirror group G2, and the first mirror group G1 before converging to form an image on the image plane P2. The objective lens optical system satisfies the following relationship:

[0037] 0.25 <f1 / L<1.1

[0038] 0.17 <f2 / L<0.72

[0039] 0.24 <- f3 / L < 0.95

[0040] Where f1 is the combined focal length of the first lens group, f2 is the combined focal length of the second lens group, f3 is the combined focal length of the third lens group, and L is the optical distance from the object plane to the image plane of the objective lens optical system.

[0041] In an embodiment of the present invention, Hy = 145 mm, and the objective lens optical system also satisfies:

[0042] Hy / f1≥0.05

[0043] Where Hy is the maximum field-of-view image height, and the objective lens optical system satisfies the relationship: Hy / f1 ≥ 0.05. Figure 3 As shown, the field of view is typically a circular area, and Hy is the radius of this circle. Compared to describing the size of the field of view using the side length XX×YY, Hy more completely and accurately describes the size of the field of view. In this embodiment, by coordinating the various lens groups and the lenses within each lens group, the problem of the small field of view of the projection lens can be solved, achieving a more like wide-spectrum and large-field-of-view objective lens projection, increasing the exposure field of view of the lithography system, and improving the lithography yield of the lithography machine;

[0044] In the embodiments of the present invention, by constraining the focal length of the first lens group G1 to 0.25<f1 / L<1.1, it is possible to avoid causing excessive spherical aberration and chromatic aberration that are too difficult to be effectively compensated by other optical components; avoid damaging the overall structure of the optical system; the constraint on the focal length of the first lens group G1 also facilitates the formation of telecentric optical paths on the object side and the image side, so as to improve the imaging quality;

[0045] By constraining the focal length of the second lens group G2 to 0.17<f2 / L<0.72, it is possible to avoid causing excessive spherical aberration and chromatic aberration that are too difficult to be effectively compensated by other optical components;

[0046] By constraining the focal length of the third lens group G3 to 0.24<-f3 / L<0.95, it is possible to effectively compensate the spherical aberration, chromatic aberration and field curvature aberration of the optical system; and it can avoid damaging the overall structure of the optical system, which would lead to an excessively small working distance of the optical system.

[0047] In the embodiments of the present invention, the first reflecting mirror is made of a material with a low thermal expansion coefficient, such as the ZERODUR glass-ceramic used in this embodiment. The first reflecting mirror made of a glass material with a low thermal expansion coefficient can absorb exposure energy, and will not cause surface shape change of the reflecting curved surface even after temperature changes, so as to maintain good imaging performance. In order to enable the first reflecting mirror to perform its function, a reflecting curved surface M1 is formed by plating a reflecting film on the first reflecting mirror. The reflecting curved surface M1 is a concave surface, which may be plated with a metal-containing reflective thin film of aluminum or silver or the like, or a multilayer dielectric reflective thin film. The objective optical system in this embodiment satisfies the relational expression:

[0048] 0.25<-R / L<1.2

[0049] wherein R is the curvature radius of the reflecting curved surface of the first reflecting mirror. Therefore, the objective optical system in the embodiments can effectively compensate the spherical aberration, chromatic aberration and field curvature aberration of the optical system, especially the high-order axial chromatic aberration; at the same time, it can avoid damaging the overall structure of the optical system which would lead to a bulky structure.

[0050] Specifically in the embodiments of the present invention, the first lens group includes at least one positive lens, and the second lens group includes at least one positive lens, satisfying:

[0051] 0.7<f1 / f2<2.9

[0052] 0.3<d0 / d1<1.2

[0053] 0.15<(d0+d1) / L<0.6

[0054] Where d0 is the optical distance between the object plane and the first lens group, and d1 is the optical distance between the first lens group and the second lens group; within this range, various optical aberrations can be well balanced; otherwise, exceeding the upper or lower limit will cause excessive spherical aberration and chromatic aberration, making it difficult to effectively compensate through other optical components; it will damage the overall structure of the optical system; it will be difficult to form a telecentric optical path between the object and image sides, resulting in a decrease in image quality.

[0055] The third lens group must contain at least one positive lens and one negative lens, and the third lens group satisfies the following relationship:

[0056] Vdps-Vdms>15

[0057] Where Vdps is the dispersion coefficient of a positive lens in the third lens group, and Vdms is the dispersion coefficient of a negative lens in the third lens group; by constraining the dispersion coefficients of the lenses in the third lens group, the spherical aberration and chromatic aberration of the optical system are effectively compensated in a balanced manner; ensuring that the overall structure of the system is reasonable and stable, and can form a balanced telecentric optical path between the object and image sides.

[0058] In one specific embodiment of the present invention, the first mirror group G1 includes a first lens L1, which is a positive lens. The first side of the first lens L1 away from the first reflecting mirror is a convex surface, and the second side of the first lens L1 close to the first reflecting mirror is a convex surface.

[0059] The second lens group G2 includes a second lens L2, which is a positive lens. The first side of the second lens L2 away from the first reflecting mirror is convex, and the second side of the second lens L2 close to the first reflecting mirror is concave. The radius of curvature of the second side of the second lens L2 close to the first reflecting mirror is relatively large. In other embodiments, it can also be a convex surface.

[0060] The third lens group includes a third lens L3 and a fourth lens L4. The third lens L3 is a negative lens, and the fourth lens L4 is a positive lens. The first side of the third lens L3 away from the first reflecting mirror is concave, and the second side of the third lens L3 close to the first reflecting mirror is concave. The first side of the fourth lens L4 away from the first reflecting mirror is convex, and the second side of the fourth lens L4 close to the first reflecting mirror is convex.

[0061] In this invention, the lenses in the lens group, which includes the first to the fourth lenses, can mutually correct aberrations and improve resolution by combining positive and negative refractive forces.

[0062] Furthermore, in this invention, the lenses of the first lens group G1, the second lens group G2, and the third lens group G3 are all spherical lenses, which reduces the difficulty and cost of manufacturing and assembling the optical system, and makes the structure of the optical system balanced and stable.

[0063] In embodiments of the present invention, the optical system can correct aberrations for the i-line, h-line, and g-line spectral lines. The spectral range of the objective lens optical system is 360 nm-441 nm. The optical system can correct aberrations for the i-line, h-line, and g-line spectral lines. The wavelengths of the i-line, h-line, and g-line spectral lines are 365 nm, 405 nm, and 436 nm, respectively. The i-line, h-line, and g-line are characteristic wavelengths of the high-pressure mercury light source during exposure. The optical system can improve optical performance, increase the utilization rate of the light source, and significantly increase the exposure intensity by improving aberrations. It is suitable for photolithography exposure with large exposure doses and is applicable to photosensitive materials with different spectral lines.

[0064] See Figure 2 In another embodiment of the present invention, based on the foregoing embodiments, the objective lens optical system further includes a second reflecting mirror. The second reflecting mirror is disposed in front of the first mirror group. The second reflecting mirror includes a first reflecting plane M2 and a second reflecting plane M3. The straight line where the extended surfaces of the first reflecting plane M2 and the second reflecting plane M2 intersect is perpendicular to the optical axis formed by the first mirror group G1, the second mirror group G2, the third mirror group G3, and the first reflecting mirror. The object plane P1 and the image plane P2 are parallel to each other and are both parallel to the optical axis. The light beam emitted from the object plane P1 is reflected by the first reflecting plane and enters the first mirror group. After passing through the first mirror group, the second mirror group, the third mirror group, and the reflecting surface M1, it passes through the third mirror group, the second mirror group, and the first mirror group again. Then, the light beam emitted from the first mirror group is reflected by the second reflecting plane and converges to form an image on the image plane P2. The first reflecting plane and the second reflecting plane are respectively formed by coating a reflective film on the reflecting surface of the second reflecting mirror.

[0065] The above configuration makes the optical system compact and the projection lens has a large working distance between the object and image sides, leaving enough space for the subsequent interface design between the optical system and the illumination system, mask and silicon wafer system, and meeting the overall assembly requirements of the lithography machine.

[0066] In one embodiment of the present invention, a cooling device is provided at the position of the first reflector. The cooling device is used to control the temperature of the reflective surface. In a large field-of-view optical system, the reflective surface is relatively small. When all the exposure beam energy is concentrated at the reflective surface, the beam energy per unit area increases sharply because the reflective surface absorbs a very small portion of the beam energy and converts it into heat. As a result, the reflective surface temperature rises and causes thermal expansion. The cooling device can effectively remove the light energy absorbed by the reflective surface from the optical system, thus exhibiting good photothermal stability and being suitable for exposure processes with large exposure doses.

[0067] Specifically, the cooling device is any one or a combination of a heat conduction cooling type device, a convection cooling type device, or an electric refrigeration type device, which can effectively dissipate the light energy absorbed by the reflective curved surface out of the optical system, has good photothermal stability, and is suitable for exposure processes with large exposure doses.

[0068] In one embodiment, the first lens group G1, the second lens group G2, and the third lens group G3 satisfy:

[0069] For the first lens L1, the refractive index nd satisfies 1.4<nd<1.5, and the dispersion coefficient vd satisfies 70<vd<80;

[0070] For the second lens L2, the refractive index nd satisfies 1.5<nd<1.6, and the dispersion coefficient vd satisfies 30<vd<40;

[0071] For the third lens L3, the refractive index nd satisfies 1.5<nd<1.6, and the dispersion coefficient vd satisfies 40<vd<50;

[0072] For the fourth lens L4, the refractive index nd satisfies 1.4<nd<1.5, and the dispersion coefficient vd satisfies 70<vd<80;

[0073] Specifically, the numerical aperture of the objective optical system is NA=0.06; the object-side field of view image height: Hy=145mm; the present invention further provides specific optical parameters of the objective optical system of an embodiment, as shown in Table 1 below:

[0074]

[0075]

[0076] Table 1

[0077] In this embodiment, its characteristic parameters are shown in Table 2.

[0078] (1) f1 / L= 0.50 (2) f2 / L= 0.35 (3) -R / L= 0.56 (4) -f3 / L= 0.48

[0079] Table 2

[0080] Figure 3 is the modulation transfer function MTF diagram of the objective optical system in the specific embodiment, in Figure 3In an optical system's MTF (Modulation Transfer Function) graph, the horizontal axis represents resolution, measured in line pairs per millimeter (lp / mm). Two lines, one black and one white, constitute one line pair. The number of line pairs that can be resolved per millimeter is the resolution value. The vertical axis represents the modulation transfer function (MTF), a quantitative description of lens resolution. We use modulation to represent contrast. Let the maximum brightness be Imax and the minimum brightness be Imin. The modulation degree M is defined as: M = (Imax - Imin) / (Imax + Imin). The modulation degree ranges between 0 and 1; a larger modulation degree means greater contrast. When the maximum and minimum brightness are exactly equal, the contrast disappears completely, and the modulation degree is 0.

[0081] For a sine wave whose original modulation is M, if the modulation of the image that reaches the image plane after passing through the lens is M′, then the MTF function value is: MTF value = M′ / M.

[0082] As can be seen, the MTF value must be between 0 and 1, and the closer it is to 1, the better the lens performance. If the lens's MTF value is equal to 1, the modulation of the lens output perfectly reflects the contrast of the input sine wave; while if the modulation of the input sine wave is 1, the modulation of the output image is exactly equal to the MTF value. Therefore, the MTF function represents the contrast of the lens at a certain spatial frequency.

[0083] As can be seen from the MTF curves, the representative MTF values ​​for the Hy=15 field of view and the maximum field of view are very close to the diffraction limit. The diffraction limit refers to the limitation that, when an ideal object point is imaged by an optical system, due to the diffraction of light in physical optics, it is impossible to obtain an ideal image point. Instead, a Fraunhofer diffraction image is obtained, which is the diffraction limit of physical optics, i.e., the maximum value.

[0084] As can be seen, the present invention can approach the diffraction limit of physical optics over a wide ultraviolet spectral range and the entire field of view.

[0085] In an embodiment of the present invention, a scanning projection lithography system is also provided, characterized in that it includes the above-mentioned projection lithography objective optical system with a large field of view. The objective optical system has the characteristics of a large field of view and easy manufacturing, and at the same time, it has good thermal stability to meet the requirements of large exposure doses.

[0086] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only for the purpose of helping to understand the method and core ideas of the present invention. The above descriptions are only preferred embodiments of the present invention. It should be noted that due to the limitations of textual expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of the present invention.

Claims

1. An optical system for a projection lithography objective lens with a large field of view, characterized in that: Arranged in sequence along the optical axis are: a first lens group, a second lens group, a third lens group and a first reflecting mirror, the first lens group and the second lens group have positive optical power, the third lens group has negative optical power, the light beam emitted from the object plane sequentially passes through the first lens group, the second lens group and the third lens group, is reflected by the first reflecting mirror, then sequentially passes through the third lens group, the second lens group and the first lens group, and then converges to form an image on the image plane, and the objective optical system satisfies the relational expression: 0.25<f1 / L≤0.5; 0.17<f2 / L≤0.35; 0.24<-f3 / L≤0.48; wherein f1 is the combined focal length of the first lens group, f2 is the combined focal length of the second lens group, f3 is the combined focal length of the third lens group, and L is the optical distance from the object plane to the image plane of the objective optical system; The first reflecting mirror is made of a material with a low thermal expansion coefficient; The reflecting surface of the first reflecting mirror is a concave surface, and the first reflecting mirror satisfies the relational expression: 0.25<-R / L≤0.56; wherein R is the radius of curvature of the reflecting curved surface of the first reflecting mirror; The third lens group at least comprises one positive lens and one negative lens, and the third lens group satisfies the relational expression: Vdps-Vdms>15; wherein Vdps is the dispersion coefficient of one positive lens in the third lens group, and Vdms is the dispersion coefficient of one negative lens in the third lens group; The first lens group includes a first lens, the first lens is a positive lens, a first side surface of the first lens facing away from the first reflecting mirror is a convex surface, and a second side surface of the first lens adjacent to the first reflecting mirror is a convex surface; The second lens group includes a second lens, the second lens is a positive lens, and a first side surface of the second lens facing away from the first reflecting mirror is a convex surface; The third lens group includes a third lens and a fourth lens arranged in the direction from the image plane to the first reflecting mirror, the third lens is a negative lens, the fourth lens is a positive lens, a first side surface of the third lens facing away from the first reflecting mirror is a concave surface, and a second side surface of the third lens adjacent to the first reflecting mirror is a concave surface; a first side surface of the fourth lens facing away from the first reflecting mirror is a convex surface, and a second side surface of the fourth lens adjacent to the first reflecting mirror is a convex surface; A cooling device is arranged at the position of the first reflecting mirror, the cooling device is used for controlling the temperature of the reflecting curved surface, and the cooling device is any one or a combination of more of a heat conduction cooling type device, a convection cooling type device and an electric refrigeration type device; For the first lens, the refractive index nd satisfies 1.4<nd<1.5, and the dispersion coefficient vd satisfies 70<vd<80; For the second lens, the refractive index nd satisfies 1.5<nd<1.6, and the dispersion coefficient vd satisfies 30<vd<40; For the third lens, the refractive index nd satisfies 1.5<nd<1.6, and the dispersion coefficient vd satisfies 40<vd<50; For the fourth lens, the refractive index nd satisfies 1.4<nd<1.5, and the dispersion coefficient vd satisfies 70<vd<80; The number of lenses in the optical system is four.

2. The projection lithography objective lens optical system with a large field of view according to claim 1, characterized in that: The first lens group satisfies: 0.7<f1 / f2<2.

9.

3. The projection lithography objective lens optical system with a large field of view according to claim 1, characterized in that: The projection lithography objective optical system satisfies: 0.3 <d0 / d1<1.2 0.15 < (d0 + d1) / L < 0.6 Where d0 is the optical distance between the object plane and the first lens group, and d1 is the optical distance between the first lens group and the second lens group.

4. The projection lithography objective lens optical system with a large field of view according to claim 1, characterized in that: The lenses of the first, second, and third lens groups are all spherical lenses. The objective lens optical system also includes a second reflecting mirror, which is disposed in front of the first lens group. The second reflecting mirror includes a first reflecting plane and a second reflecting plane. The straight line where the extended surfaces of the first and second reflecting planes intersect is perpendicular to the optical axis formed by the first, second, and third lens groups and the first reflecting mirror. The object plane and the image plane are parallel to each other and are both parallel to the optical axis. The light beam emitted from the object plane is reflected by the first reflecting plane and enters the first lens group. After passing through the first, second, and third lens groups, it is reflected by the first reflecting mirror, and then passes through the third, second, and first lens groups. The light beam emitted from the first lens group is reflected by the second reflecting plane and converges to form an image on the image plane.

5. The projection lithography objective lens optical system with a large field of view according to claim 1, characterized in that: The optical system can correct aberrations for the i-line, h-line, and g-line in the spectrum, with wavelengths of 365 nm, 405 nm, and 436 nm, respectively.

Images