Uniform illumination system based on free-form surface and its design method

Abstract

The embodiment of the present invention provides a uniform illumination system based on a free-form surface and a design method thereof, and relates to the field of illumination technology. The uniform illumination system based on a free-form surface includes a collimation module, an optical integrator, and a collimation and beam expansion system. The collimation module includes a double free-form surface collimation lens array. The collimation module is used to receive light from a light source and form collimated light; the optical integrator is used to receive the collimated light and form a plurality of light beams for remixing, and the slight unevenness within the range of each light beam is compensated due to the superposition of light beams in symmetrical positions, so that the light energy within the entire aperture is effectively and evenly utilized; the collimation and beam expansion system is used to receive the mixed light beams and form a uniform illumination spot. The collimation module, the optical integrator, and the collimation and beam expansion system are arranged in sequence, which can not only form a uniform illumination spot, but also achieve a compact optical path and satisfy the lighting effect.

Description

Technical Field

[0001] The present invention relates to the field of lighting technology, and in particular to a uniform lighting system based on a free-form surface and a design method thereof. Background Art

[0002] In the illumination system of a lithography machine, an illumination light field with very good light intensity distribution uniformity is usually required to enhance the resolution of the lithography system, increase the depth of focus, and improve the lithography contrast, thereby improving the lithography quality.

[0003] Early photolithography systems used an integrating rod to achieve uniform illumination. The principle of the integrating rod to achieve uniform illumination is to allow multiple sub-beams to undergo multiple total reflections on the inner wall of the integrating rod, and then superimpose them at the outlet of the integrating rod to form a uniform light field. Then, an imaging lens group is used to image the uniform light field at the outlet of the integrating rod onto the mask surface, thereby achieving uniform illumination. Due to the multiple reflections of the light beam, there is a large energy loss, so the energy utilization rate of this homogenization method is low; in addition, in order to improve the uniformity of the output light field, it is necessary to increase the number of reflections and the length of the integrating rod, which is not conducive to reducing the size of the system.

[0004] In order to improve the energy utilization rate of the uniform illumination light field and shorten the size of the uniform light device, a micro lens array is needed to achieve uniform illumination. The micro lens array is placed perpendicular to the optical axis, and its working principle is: each micro lens cuts the incident light beam into sub-beams of the same size, and then passes through the converging effect of the condenser and is superimposed on the focal plane of the condenser. Since there are only reflection and absorption losses when the light beam passes through the micro lens array, and it can be made by coating an anti-reflection film and selecting materials with a small absorption coefficient at the working wavelength, a higher energy utilization rate can be obtained. In addition, the thickness of the micro lens array is generally on the order of several millimeters, which is much smaller than the usual length of several hundred millimeters of the integrating rod, which is conducive to reducing the axial size of the device.

[0005] The photolithography illumination system usually has high requirements for the uniformity of the illumination light field, which should be no less than 94%. If the surface shape of the joint is not designed, the performance of the microlens array will not meet the index requirements of the photolithography illumination system. Secondly, the light of the photolithography illumination system should have a good exposure effect after passing through the photolithography mask, so the light output angle of the photolithography illumination system is required to be no more than 3 degrees. Summary of the invention

[0006] The purpose of the present invention includes providing a uniform lighting system based on a free-form surface and a design method thereof, which can achieve a compact optical path and satisfy the lighting effect.

[0007] The embodiments of the present invention can be implemented as follows:

[0008] In a first aspect, the present invention provides a uniform illumination system based on a free-form surface, and the uniform illumination system based on a free-form surface comprises:

[0009] A collimation module, comprising a double free-form surface collimation lens array, the collimation module is used to receive light from a light source and form collimated light;

[0010] An optical integrator, used for receiving collimated light and forming a plurality of thin light beams for re-mixing;

[0011] The collimating and beam expanding system is used to receive the mixed fine light beams and form a uniform illumination spot.

[0012] In an alternative embodiment, the optical integrator comprises a plurality of microlens arrays.

[0013] In an optional embodiment, the collimating and beam expanding system includes a negative lens group, a convex lens, and a light exit aperture, which are arranged in sequence.

[0014] In a second aspect, the present invention provides a design method for a uniform illumination system based on a free-form surface, and the design method for a uniform illumination system based on a free-form surface comprises:

[0015] Designing a collimation module, the collimation module includes a double free-form surface collimation lens array, and the collimation module is used to receive light from a light source and form collimated light;

[0016] Design an optical integrator, which is used to receive collimated light and form multiple thin light beams for re-mixing;

[0017] A collimating beam expansion system is designed to receive the mixed fine light beams and form a uniform illumination spot.

[0018] In an optional implementation, the lens structure of the collimating module is formed by rotating a double free curve around a central axis.

[0019] In an optional embodiment, the step of designing a collimation module comprises:

[0020] Define the refractive index of the lens material of the collimating module as n, and the refractive index of air as n0=1;

[0021] The selected simulated light source intensity distribution is Lambertian distribution: I=I0cosθ, θ is the limit value of the light output angle, and only the light within the light source angle range: 0°~θ is collimated.

[0022] In an alternative embodiment, the optical integrator comprises a plurality of microlens arrays.

[0023] In an optional embodiment, the relationship between the focal length of the optical integrator and the lens radius is designed to be:

[0024]

[0025] In the formula, f e is the focal length, r is the lens radius, and n is the lens refractive index.

[0026] In an optional embodiment, the collimating and beam expanding system includes a negative lens group, a convex lens, and a light exit aperture, which are arranged in sequence.

[0027] In an optional embodiment, the collimation and beam expansion system satisfies the following relationship:

[0028]

[0029] Where Y i is the half height of the light spot before beam expansion, Y o is the half height of the spot after beam expansion, d1 is the distance from the concave lens to the virtual image position, d2 is the distance between the concave lens and the convex lens, f1 is the focal length of the concave lens, f2 is the focus of the convex lens, and n b is the magnification of the beam expansion system.

[0030] The free-form surface-based uniform illumination system and design method thereof provided by the embodiments of the present invention have the following beneficial effects:

[0031] 1. The collimated light passes through the incident surface of the optical integrator to form multiple light beams, which are then remixed by the optical integrator. The slight inhomogeneity within each light beam is compensated by the superposition of light beams in symmetrical positions, so that the light energy within the entire aperture is effectively and evenly utilized;

[0032] 2. The collimation module, optical integrator and collimation beam expansion system are set up in sequence, which can not only form a uniform illumination spot, but also achieve a compact optical path and satisfy the lighting effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 A schematic diagram of the structure of a uniform illumination system based on a free-form surface provided in an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of the full cross-section structure of a uniform illumination system based on a free-form surface provided in an embodiment of the present invention;

[0036] Figure 3 A flow chart of a design method for a uniform lighting system based on a free-form surface provided in an embodiment of the present invention;

[0037] Figure 4 is a schematic diagram of the lens structure of the collimating module;

[0038] Figure 5 It is a schematic diagram of the algorithm design principle of the lens structure of the collimating module;

[0039] Figure 6 A schematic diagram of the derivation of the algorithm iteration relationship of the lens structure of the collimating module;

[0040] Figure 7 Schematic diagram of the design principle of the optical integrator;

[0041] Figure 8 Schematic diagram of the design principle of the collimation and beam expansion system;

[0042] Fig. 9 is a schematic diagram of the structure of an optical integrator;

[0043] Fig.10 It is a structural schematic diagram of the collimation and beam expansion system;

[0044] Fig.11 Schematic diagram of the light spot effect in the simulation.

[0045] Icons: 100 - uniform illumination system based on free-form surface; 110 - light source; 120 - collimation module; 130 - optical integrator; 140 - collimation beam expansion system; 141 - negative lens group; 142 - first negative lens; 143 - second negative lens; 144 - convex lens; 145 - light exit aperture. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0049] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear to indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the invention is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0050] In addition, the terms “first”, “second”, etc., if used, are merely used to distinguish between the descriptions and should not be understood as indicating or implying relative importance.

[0051] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0052] Please refer to Figure 1 and Figure 2 The present embodiment provides a free-form surface-based uniform illumination system 100. The free-form surface-based uniform illumination system 100 includes a light source 110, a collimation module 120, an optical integrator 130, and a collimation beam expansion system 140 arranged in sequence, which can not only form a uniform illumination spot, but also realize a compact optical path and satisfy the lighting effect.

[0053] Specifically, the light source 110 is preferably an LED.

[0054] The collimation module 120 includes a double free-form surface collimation lens array, and the collimation module 120 is used to receive light from the light source 110 and form collimated light. In the case of low power requirements, the collimation module 120 can be a single lens, and in the case of high power requirements, the collimation module 120 can be a combination of multiple single-piece lenses, fixed together by structural parts, or directly made into an all-in-one lens element.

[0055] The optical integrator 130 includes a plurality of microlens arrays. The collimated light passes through the light incident surface of the optical integrator 130 to form a plurality of light beams, which are then remixed through the optical integrator 130, and the slight inhomogeneity within the range of each light beam is compensated due to the superposition of light beams in symmetrical positions, so that the light energy within the entire aperture is effectively and evenly utilized.

[0056] The collimating and beam expanding system 140 includes a negative lens group 141, a convex lens 144 and a light exit aperture 145 arranged in sequence. The mixed light passes through the collimating and beam expanding system 140 to form a uniform illumination spot, wherein the negative lens group 141 includes a first negative lens 142 and a second negative lens 143.

[0057] See also Figure 3 This embodiment also provides a design method for the above-mentioned free-form surface-based uniform illumination system 100, comprising the following steps:

[0058] S1: Determine the optical requirements of the lighting system.

[0059] Specifically, the light output angle of the free-form surface-based uniform illumination system 100 provided in this embodiment is less than the limit value θ, the illumination distance is L, the spot size is H*W, and the maximum irradiance is E max .

[0060] Calculation of irradiance: E max =L·π·sin 2 θ max (1-1)

[0061] System caliber calculation:

[0062] In the formula, θ max is the half-angle of the beam angle of the LED light source, r1 is the effective radius of the previous optical window, r2 is the effective radius of the next optical window, θ1 is the half-angle of the beam angle of the light passing through the previous optical window, and θ2 is the half-angle of the beam angle of the light passing through the next optical window.

[0063] S2: Design the optical solution of the lighting system.

[0064] S21: Design the collimation module 120 .

[0065] The collimating module 120 includes a double free-form surface collimating lens array. The collimating module 120 is used to receive light from the light source 110 and form collimated light.

[0066] See also Figure 4 The lens structure of the collimation module 120 is formed by rotating a double free curve around the central axis. The refractive index of the lens material of the collimation module 120 is defined as n, and the refractive index of air is n0=1. Since the LED selected by the light source 110 is similar to a Lambertian light source, the energy is concentrated in a small angle range. In view of this, in the design process, the selected simulated light source intensity distribution is a Lambertian distribution: I=I0cosθ, θ is the limit value of the light output angle, and only the light within the light source angle range: 0°~θ is collimated.

[0067] The specific algorithm design of the collimation module 120 is as follows:

[0068] See also Figure 5 , establish a rectangular coordinate system, the light source 110 is located at point O, and the light emitted by the light source 110 is refracted by the inner surface point A and the outer surface point B of the lens of the collimating module 120 and then vertically enters the receiving surface. After refraction from the inner surface, the outgoing light is formed The normal vector is The tangent vector is Then the emitted light As the incident light on the outer surface, it is refracted again to form the outgoing light The normal vector is The tangent vector is

[0069] According to Fresnel's law, we can conclude that:

[0070]

[0071]

[0072] After simplifying equations (2-1) and (2-2), we can obtain the following equation:

[0073]

[0074]

[0075] In order to solve equations (2-3) and (2-4), define the coordinates of A and B as (xa, ya) and (xb, yb) respectively, then:

[0076]

[0077] Combining equations (2-3), (2-4), and (2-5), we have:

[0078]

[0079] in:

[0080]

[0081]

[0082] in:

[0083]

[0084] According to equations (2-6) and (2-8), the tangent vector slopes ka and kb of the inner and outer surfaces can be obtained respectively:

[0085]

[0086]

[0087] See also Figure 6 In order to further find the discrete trajectory coordinate points of the inner and outer surfaces, we select any two adjacent points on the inner and outer surfaces as A n , A n+1 , B n , B n+1 , whose coordinates are (xa n ,ya n )、(xa n+1 ,ya n+1 ), (xb n ,yb n )、(xb n+1 ,yb n+1 ), and the incident point coordinates of the receiving surface are R n , R n+1 The corresponding coordinates are (xr n ,yr n )、(xr n+1 ,yr n+1 ) and define and The angle is Δθ, The angle with the x-axis is θ n .

[0088] When Δθ is very small, Euler's formula can be used to calculate the n , B n Find the coordinates of two points A n+1 , B n+1 The coordinates of are derived as follows:

[0089] First, according to equations (2-10) and (2-11), we can find n With B n The equation of the tangent line is:

[0090] y=ka n ·(x-xa n )+ya n (2-12)

[0091] y=kb n ·(x-xb n )+yb n (2-13)

[0092] Among them, ka n , kb n A n and B n The slope of the tangent line.

[0093] In addition, it is easy to write OA nThe equation of the straight line is as follows:

[0094] y = tan(Δθ + θ n )·x (2-14)

[0095] Using Euler's formula, when Δθ is very small, A n+1 Coordinates and Line OA n+1 and over A n The intersection of the tangent lines is approximately coincident, so by combining equations (2-12) and (2-14), we can find A n+1 Coordinates:

[0096]

[0097]

[0098] And B n+1 The coordinates can be obtained by the law of conservation of energy, ignoring Fresnel loss and uniform distribution of illumination on the receiving surface:

[0099]

[0100] Simplifying formula (2-17) we have:

[0101]

[0102] By B n+1 R n+1 , B n R n are parallel to the x-axis, and when Δθ is small, B n+1 Coordinates and Line A n+1 R n+1 and over B n The intersection of the tangent lines is approximately coincident, so by combining equations (2-13) and (2-18), we can find B n+1 coordinate:

[0103]

[0104]

[0105] At this point, the algorithm derivation of the lens structure of the collimating module 120 is completed.

[0106] S22: Design the optical integrator 130.

[0107] The optical integrator 130 is used to receive the collimated light and form a plurality of light beams for re-combination.

[0108] See also Figure 7 , the design of the optical integrator 130 satisfies the following formula:

[0109]

[0110] The relationship between the focal length of the optical integrator 130 and the lens radius is:

[0111]

[0112] In the formula, f e is the focal length, r is the lens radius, and n is the lens refractive index.

[0113] S23: Design a collimating and beam expanding system 140.

[0114] The collimating and beam expanding system 140 is used to receive the mixed fine light beams and form a uniform illumination spot.

[0115] See also Figure 8 , the collimation and beam expansion system 140 satisfies the following relationship:

[0116]

[0117] Where Y i is the half height of the light spot before beam expansion, Y o is the half height of the spot after beam expansion, d1 is the distance from the concave lens to the virtual image position, d2 is the distance between the concave lens and the convex lens, f1 is the focal length of the concave lens, f2 is the focus of the convex lens, and n b is the magnification of the beam expansion system.

[0118] The following is a specific design example of a lighting system. The optical requirements are that the light angle is less than 3°, the lighting distance is 400mm, the spot size is 200mm*200mm, and the irradiance is 1mW / cm 2 .

[0119] Irradiance Select a light source 110, the brightness of which is not less than L, i.e. 464.5 mW / (cm 2 *Sr), where the light source 110 is a Seoul 385nm 3535LED light source with a lens, one can meet the requirements, and the lamp bead light chip is about 1mm. According to formula (1-2), the minimum size of the collimating lens of the collimating module 120 is 28.7mm.

[0120] The material refractive index of the lens is n=1.46. The initial values ​​A1(12,0.012), B1(25,0.08) and the initial angle ∠A1OX=0.001 are introduced. The step size Δθ=0.001 is defined. Then, the trajectory curve of each discrete coordinate point is calculated by substituting it into the iterative relationship of the derived algorithm. The calculated discrete coordinate data is then imported into the 3D modeling software to establish a solid lens model.

[0121] See also Fig. 9The optical integrator 130 is made of quartz with a refractive index of 1.46. According to the current lens processing capability, h is set to 1.25 mm and f e The thickness of the optical integrator 130 is set to 7.5 mm, that is, the thickness of the optical integrator 130 is also 7.5 mm. The curvature radius of the microlens of the optical integrator 130 is obtained by equation (3-1) as r = 2.4 mm. The optical integrator 130 model is constructed by 3D structure software. The model has a width and height of 32, which is slightly larger than the minimum size of the collimating lens in front.

[0122] System effective light aperture Including the mounting edge, the diameter of the light-emitting lens needs to be greater than 282.8 mm. In this embodiment, the light-emitting lens is a convex lens with a diameter of 326 mm, a center thickness of 75 mm, and a curvature radius of the front and back surfaces of the lens of 460 mm.

[0123] The initial structure of the collimation and beam expansion module is as follows Fig.10 As shown, the front section defines the largest lens for emitting light, and is designed according to LightTools to obtain a negative lens group 141, wherein the diameter of the first negative lens 142 is 40 mm, the center thickness is 3 mm, and the radius of curvature of the front and back surfaces of the lens is 60 mm, and the diameter of the second negative lens 143 is 40 mm, the center thickness is 3 mm, and the radius of curvature of the front and back surfaces of the lens is 90 mm.

[0124] S3: Perform simulation.

[0125] If the simulation is qualified, the design of the lighting system is completed. If the simulation is unqualified, the process returns to S1.

[0126] Specifically, the optimization takes the axial position of the light source 110 and each module as variables, sets the collimation evaluation function, and obtains the final light path arrangement position. The optimized spot effect is as follows: Fig.11 The beam angle of the entire lighting system is 1.43°, which is approximately collimated, and the spot uniformity U on the target surface reaches 96.1%.

[0127] The free-form surface-based uniform illumination system 100 and the design method thereof provided in this embodiment have the following beneficial effects:

[0128] 1. The collimated light passes through the light incident surface of the optical integrator 130 to form a plurality of light beams, which are then remixed by the optical integrator 130. The slight inhomogeneity within the range of each light beam is compensated by the superposition of light beams in symmetrical positions, so that the light energy within the entire aperture is effectively and evenly utilized;

[0129] 2. The collimation module 120, the optical integrator 130 and the collimation beam expansion system 140 are arranged in sequence, which can not only form a uniform illumination spot, but also achieve a compact optical path and satisfactory lighting effect.

[0130] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A uniform illumination system based on a free-form surface, characterized in that: The free-form surface-based uniform illumination system comprises: A collimating module (120), comprising a double free-form surface collimating lens array, the collimating module (120) being used to receive light from the light source (110) and form collimated light; An optical integrator (130) is used to receive the collimated light and form a plurality of fine light beams for re-mixing, wherein the optical integrator (130) comprises a plurality of microlens arrays; the design of the optical integrator (130) satisfies the following formula: A collimating beam expansion system (140) is used to receive the mixed fine light beams and form a uniform illumination spot, wherein the collimating beam expansion system (140) comprises a negative lens group (141), a convex lens (144), and a light exit aperture (145) which are arranged in sequence, and the collimating beam expansion system (140) satisfies the following relationship: Where Y ｉ is the half height of the light spot before beam expansion, Y o is the half height of the light spot after beam expansion, d1 is the distance from the concave lens to the virtual image position, d ２ is the distance between the concave lens and the convex lens, f1 is the focal length of the concave lens, and f ２ is the focus of the convex lens, n b is the magnification of the beam expansion system.

2. A design method for a uniform illumination system based on a free-form surface, characterized in that: The design method of the uniform illumination system based on free-form surfaces includes: Designing a collimating module (120), the collimating module (120) comprising a double free-form surface collimating lens array, the collimating module (120) being used to receive light from a light source (110) and form collimated light; An optical integrator (130) is designed, wherein the optical integrator (130) is used to receive the collimated light and form a plurality of fine light beams for re-mixing, and the optical integrator (130) comprises a plurality of microlens arrays; the design of the optical integrator (130) satisfies the following formula: A collimating beam expansion system (140) is designed, the collimating beam expansion system (140) being used to receive the mixed fine light beams and form a uniform illumination light spot, the collimating beam expansion system (140) comprising a negative lens group (141), a convex lens (144) and a light exit aperture (145) arranged in sequence, and the collimating beam expansion system (140) satisfies the following relationship: Where Y ｉ is the half height of the light spot before beam expansion, Y o is the half height of the light spot after beam expansion, d1 is the distance from the concave lens to the virtual image position, d ２ is the distance between the concave lens and the convex lens, f1 is the focal length of the concave lens, and f ２ is the focus of the convex lens, n b is the magnification of the beam expansion system.

3. The design method of a uniform illumination system based on a free-form surface according to claim 2, characterized in that: The lens structure of the collimating module (120) is formed by rotating a double free curve around a central axis.

4. The design method of a uniform illumination system based on a free-form surface according to claim 3, characterized in that: The step of designing the collimation module (120) comprises: The refractive index of the lens material of the collimating module (120) is defined as n, and the refractive index of air is defined as n0=1; The selected simulated light source (110) has a light intensity distribution of Lambertian distribution: I=I0cosθ, where θ is a limit value of the light output angle, and only light within the angle range of the light source (110): 0°~θ is collimated.

5. The design method of a uniform illumination system based on a free-form surface according to claim 3, characterized in that: The relationship between the focal length and lens radius of the designed optical integrator (130) is: In the formula, f ｅ is the focal length, r is the lens radius, and n is the lens refractive index.

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