Plane wave based illumination system and exposure apparatus

Abstract

The application discloses a kind of illumination system and exposure equipment based on plane wave, comprising: first mirror, wavefront aberration detection module is inclined relative to light incidence direction, first mirror is used to receive light from light source and reflect light;Second mirror, for receiving the light reflected by first mirror and expanding the beam of light;Third mirror, for receiving the light reflected by second mirror and collimating the light back to the target object and reflecting light.The application realizes light path folding through the reflection path of first mirror, second mirror and third mirror, significantly shortens the axial length of illumination system, and significantly saves space.The number of structures of the three mirrors is much less than that of the conventional multi-lens group, and the positioning accuracy requirement of the mirrors is lower than the coaxiality requirement of the multi-lens, which simplifies the overall structure design and assembly process of the illumination system, and reduces the system complexity and use cost.

Description

Technical Field

[0001] This invention relates to the field of holographic lithography, and more specifically, to an illumination system and exposure apparatus based on plane waves. Background Technology

[0002] Photolithography is a crucial piece of equipment in the manufacturing process of large-scale integrated circuits. It is a technology that uses lasers to image mask patterns onto silicon wafers.

[0003] In the field of traditional projection lithography, projection lithography objectives are the core components of projection lithography devices used to fabricate ultra-fine patterns. However, these objectives have complex structures, and most possess advanced aspherical surfaces, resulting in large system volumes and high requirements for manufacturing integration and assembly processes. For example, patent US20030030916A1 describes a projection lithography objective with a maximum numerical aperture of 0.89, comprising at least four lens groups, totaling 29 lenses. Each lens group has either positive or negative optical power, requiring multiple lens groups to expand and focus the beam multiple times. Therefore, low-cost, highly integrated new lithography technologies will promote the development of the lithography and semiconductor fields.

[0004] Holographic lithography systems, used in integrated circuit manufacturing, employ lasers to image holographic mask patterns onto substrates such as silicon wafers. Compared to projection lithography, holographic lithography has lower requirements for the illumination system, and since there is no object-image relationship between the mask and the silicon wafer, it avoids the dependence on projection lenses found in conventional projection lithography. However, the illumination system in holographic lithography systems still uses multiple lenses arranged along the optical axis, resulting in a complex structure and significant space requirements. Summary of the Invention

[0005] The main objective of this invention is to provide a plane wave-based lighting system to solve the problems of complex structure and large space occupation in related lighting systems.

[0006] To achieve the above objectives, the present invention provides a plane wave-based illumination system, comprising:

[0007] The first reflecting mirror has its reflective surface facing the light source and is tilted relative to the direction of light incidence. The first reflecting mirror is used to receive light from the light source and reflect it.

[0008] The second reflecting mirror is used to receive the light reflected by the first reflecting mirror and expand the light beam;

[0009] The third reflecting mirror is used to receive the light reflected by the second reflecting mirror, collimate the light, and then output a plane wave laser for exposure to the target object.

[0010] With the above configuration, on the one hand, the light emitted from the light source is reflected by the first reflecting mirror to the second reflecting mirror. Under the action of the second reflecting mirror, the light beam is expanded and reflected towards the third reflecting mirror. The third reflecting mirror collimates the light beam into parallel light before reflecting it towards the target object. In this invention, the light path is folded through the reflection paths of the first, second, and third reflecting mirrors, which significantly shortens the axial length of the lighting system and saves considerable space. The number of three reflecting mirrors is far less than that of traditional multi-lens groups, and the positioning accuracy requirement of the reflecting mirrors is lower than the coaxiality requirement of multi-lens systems. This simplifies the overall structural design and assembly process of the lighting system, and reduces system complexity and operating costs.

[0011] On the other hand, when applied to holographic lithography, the mirrors alter the optical path through light reflection, avoiding higher-order aberrations caused by insufficient refractive index or multi-surface refraction in lenses. The collimation effect of the third mirror is based on the law of reflection, resulting in a stable optical path and higher wavefront uniformity in the output plane wave. Furthermore, in holographic lithography, the uniformity of the plane wave primarily depends on the light source itself, eliminating the need for additional homogenizing elements. The optical path design of the reflection system does not introduce refractive losses that affect the light intensity distribution, avoiding uneven light intensity caused by absorption and scattering by lenses. This further simplifies the system while ensuring lithographic precision.

[0012] Optionally, the first reflector is configured to both reflect and transmit light;

[0013] The lighting system also includes a wavefront aberration detection module for receiving light transmitted by the first mirror in a first direction, which is parallel to the optical path direction between the first mirror and the second mirror.

[0014] The side of the target object facing the third reflecting mirror is a planar reflecting surface.

[0015] Through the above setup, on the one hand, the planar reflective surface of the target object, together with the third, second, and first reflecting mirrors, forms a round-trip optical path. That is, light is reflected by the first reflecting mirror, expanded by the second reflecting mirror, and collimated by the third reflecting mirror before illuminating the target object. It then returns along the original optical path via the planar reflective surface of the target object (reflected sequentially by the third and second reflecting mirrors back to the first reflecting mirror). At this point, the returning light carries the wavefront information resulting from the target object's interaction. The first reflecting mirror, through its dual-function design of reflection and transmission, transmits a portion of the returning light along a first direction (parallel to the optical path direction from the first to the second reflecting mirrors) to the wavefront aberration detection module, which then detects the wavefront aberration. Since the wavefront aberration detection module receives the complete wavefront after the target object's interaction and its return along the original optical path, it avoids aberration interference caused by additional optical path deflections, ensuring that the detected wavefront information is highly consistent with the actual wavefront state after the target object's interaction, thus providing reliable raw data for wavefront aberration analysis.

[0016] On the other hand, the first reflector simultaneously serves as the main optical path reflector and the detection optical path transmitter. It does not require additional beam splitters and directly utilizes its inherent reflection-transmission characteristics to complete the optical path allocation, which significantly simplifies the system structure, reduces the aberrations introduced by multi-component assembly errors, and improves system stability.

[0017] On the other hand, by using a total reflection mirror group (first, second, and third reflection mirrors), the propagation of light depends on the law of reflection, which eliminates chromatic aberration in principle and ensures that wavefront aberrations of different wavelengths of light can be detected uniformly and accurately.

[0018] Optionally, the illumination system also includes a collimating lens group, which is located between the first reflecting mirror and the wavefront aberration detection module. The collimating lens group is used to receive and collimate the light transmitted through the first reflecting mirror along the first direction.

[0019] The above settings optimize input adjustment for wavefront aberration detection, improving detection accuracy and stability. Specifically, the light transmitted through the first reflecting mirror is precisely converted into parallel light after passing through the collimating lens group, eliminating additional angular deviations introduced during light propagation. This ensures that the light entering the wavefront aberration detection module is strictly parallel, guaranteeing the consistency of the detection reference. Furthermore, the collimating lens group precisely matches the operating conditions of the wavefront aberration detection module, significantly improving the quantitative accuracy of aberration detection.

[0020] Furthermore, although the collimating lens group is a lens element, it only acts on the detection branch, not the main illumination path, which can minimize the aberrations it introduces. At the same time, the reflective design of the main optical path has eliminated chromatic aberration. The addition of the collimating lens group will not destroy the overall low aberration advantage of the system. On the contrary, by optimizing the input light quality of the detection optical path, the chromatic aberration-free and low aberration characteristics of the reflective system can better serve the wavefront aberration detection, forming a synergistic advantage of low aberration in the main optical path and collimation correction in the detection optical path.

[0021] Optionally, the collimating lens group includes a first biconvex lens and a first plano-convex lens arranged sequentially along the light transmission direction, wherein the radius of curvature of the first biconvex lens is smaller than the radius of curvature of the first plano-convex lens.

[0022] With the above configuration, the first biconvex lens has a small radius of curvature, enabling it to initially deflect the incident non-parallel light, quickly compressing the divergence angle of the light rays and undertaking the main coarse collimation adjustment function. The first plano-convex lens has a large radius of curvature, enabling it to finely adjust the light rays after initial collimation, further calibrating the light rays into strictly parallel light. By deflecting the incident light rays in stages, spherical aberration caused by a single high-curvature lens deflecting at a large angle is avoided, thus improving the wavefront consistency of the collimated parallel light.

[0023] Optionally, both the light-incoming surface and the light-outcoming surface of the first reflecting mirror are planar.

[0024] With the above settings, on the one hand, for the reflected light path of illumination, planar reflection ensures that the reflection direction is stable and will not introduce additional convergence or divergence tendencies due to the curvature of the mirror, thus avoiding damage to the stability of the subsequent beam expansion and collimation light path; on the other hand, for the transmitted light path of detection, planar transmission makes the optical path of the light uniform in the mirror body, and the transmission direction is determined only by the tilt angle of the mirror, and will not cause local deflection due to the surface curvature, thus ensuring that the wavefront information carried by the transmitted light truly reflects the aberration state of the target object.

[0025] On the other hand, compared to curved mirrors, flat mirrors are easier to manufacture, improving surface accuracy and reducing inherent aberrations. Furthermore, the direction of the light path is determined by a single parameter—the mirror's tilt angle—eliminating the need for complex optical path calculations due to curvature.

[0026] Optionally, the target object is a fourth reflector or a silicon wafer to be exposed.

[0027] With the above settings, when the target object is the fourth reflecting mirror, the light returns along the original optical path after reflection. The wavefront aberration carried is mainly due to the system itself. The wavefront aberration detection module can quantify the inherent aberrations of the system by analyzing this reference wavefront, providing an error compensation benchmark for subsequent actual inspection. When the target object is a silicon wafer to be exposed, the wavefront aberration carries information including the microstructure of the semiconductor wafer surface and wavefront distortion during the photolithography process. The wavefront aberration detection module can capture this information in real time, providing feedback to the photolithography system, realizing closed-loop control from processing to inspection, and reducing photolithography pattern deviations caused by defects in the semiconductor wafer itself or process fluctuations.

[0028] Optionally, the radius of curvature of the reflecting surface of the second reflecting mirror is smaller than that of the reflecting surface of the third reflecting mirror.

[0029] With the above configuration, the second mirror, with a larger radius of curvature, can quickly expand the beam aperture to the target size. The third mirror, with a smaller radius of curvature, has a longer focal length, making it easier for its focal point to align with the backward extension of the light reflected by the second mirror. This ensures that the divergent light after beam expansion is completely converted into parallel light after reflection by the third mirror. Furthermore, the smaller radius of curvature of the third mirror reduces the angle of incidence between light rays from different directions, fundamentally reducing spherical aberration. The resulting parallel light has higher wavefront uniformity, providing a superior illumination foundation for holographic lithography. Moreover, the smaller radius of curvature of the second mirror spreads the energy of the incident light, preventing excessive energy concentration at the beam center, while the larger radius of curvature of the third mirror allows for a more uniform energy distribution of the reflected parallel light through its gentler curvature.

[0030] Optionally, the lighting system also includes a focusing lens assembly, which is located between the first reflecting mirror and the light source, and is used to receive and converge the light emitted from the light source.

[0031] By employing the above configuration, the divergent light emitted by the light source can be compressed into a converging light, allowing more light to be concentrated within the effective working area of ​​the first reflecting mirror, significantly improving the utilization rate of light energy. Furthermore, the focusing lens assembly, through precise design of its focal length and aperture, can standardize the outgoing light from different light sources into a converging beam with preset parameters, ensuring stable light parameters incident on the first reflecting mirror and improving the overall system stability. Additionally, by setting up the focusing lens assembly, the aperture of the beam incident on the first reflecting mirror can be compressed to a reasonable range, allowing for the use of a smaller first reflecting mirror, thus reducing the manufacturing and assembly costs of the reflecting mirror while maintaining high light energy utilization.

[0032] Optionally, the second reflecting mirror is a convex reflecting mirror, and the third reflecting mirror is a concave reflecting mirror, with the focal point of the third reflecting mirror being conjugate with that of the focusing lens group.

[0033] With the above setup, the beam aperture is enlarged after the light is reflected by the second mirror. After the third mirror and the focusing lens group are conjugate at their focal points, the third mirror collimates the incident light before it exits, achieving a seamless connection between beam expansion and collimation. In addition, compared to beam expansion and collimation systems with multiple lenses, the reflective combination of convex and concave mirrors achieves efficient space utilization through optical path folding.

[0034] Optionally, the focusing lens group includes a second plano-convex lens and a second biconvex lens arranged sequentially along the light transmission direction, wherein the radius of curvature of the second plano-convex lens is greater than the radius of curvature of the second biconvex lens.

[0035] With the above settings, the second plano-convex lens with a larger radius of curvature is more adaptable to high-divergence light sources. Its gentle deflection capability can gradually converge large-angle light rays, avoiding edge reflection loss caused by excessive light incident angle. The second biconvex lens with a smaller radius of curvature has higher focusing accuracy for low-divergence light sources: it can precisely control the beam convergence angle through strong deflection capability, ensuring that even if the light source has a small divergence angle.

[0036] According to another aspect of the present invention, an exposure apparatus is provided for use in a chip fabrication process, including the above-described illumination system. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention, making other features, objects, and advantages of the invention more apparent. The illustrative embodiments of the invention illustrated in the drawings and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 This is a schematic diagram of a lighting system according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of a wavefront aberration detection module according to an embodiment of the present invention.

[0040] Among them, 1. First reflecting mirror; 2. Second reflecting mirror; 3. Third reflecting mirror; 4. Target object; 5. Collimating lens group; 50. First biconvex lens; 51. First plano-convex lens; 6. Wavefront aberration detection module; 7. Focusing lens group; 70. Second plano-convex lens; 71. Second biconvex lens; 8. Light source. Detailed Implementation

[0041] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein.

[0043] In this invention, the terms "upper," "lower," "inner," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0044] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0045] Furthermore, the terms "set up," "equipped with," "connected," and "fixed" should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0046] In addition, the term "multiple" should mean two or more.

[0047] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] Holographic lithography is a technology that uses lasers to image patterns from a holographic mask onto a substrate such as a silicon wafer, and can be used in the manufacture of integrated circuits. Compared to projection lithography, holographic lithography has lower requirements for the illumination system process, and there is no object-image relationship between the mask and the silicon wafer, avoiding the dependence on projection lenses in conventional projection lithography. In a holographic lithography system, the performance of the illumination system is crucial, directly determining the pattern transfer capability of the entire exposure apparatus. While holographic lithography has lower requirements for the illumination system process and there is no object-image relationship between the mask and the silicon wafer, avoiding the dependence on projection lenses in conventional projection lithography, the illumination system in related technologies still uses multiple lenses arranged along the optical axis, resulting in a complex structure and a large footprint.

[0049] Therefore, this embodiment provides a plane wave-based illumination system for use in holographic lithography. Please refer to [link to relevant documentation]. Figure 1 , Figure 1 The main structure of the lighting system is shown. The lighting system includes a first reflector 1, a second reflector 2, and a third reflector 3, forming a reflective combination. The reflective surface of the first reflector 1 faces the light source 8 and is tilted relative to the direction of light incidence, allowing incident light from the light source 8 to be reflected in another direction by the first reflector 1. For example, if light from the light source 8 is incident horizontally onto the reflective surface of the first reflector 1, the light will be reflected downwards or upwards. Figure 1 In this process, light rays are reflected downwards after passing through the first reflecting mirror 1. The specific reflection angle and direction can be determined by adjusting the tilt direction and tilt angle of the first reflecting mirror 1 relative to the incident direction of the light rays.

[0050] The second reflecting mirror 2 is positioned in the light reflection direction of the first reflecting mirror 1. Taking the downward reflection of light by the first reflecting mirror 1 as an example, the second reflecting mirror 2 is arranged below the first reflecting mirror 1. The second reflecting mirror 2 can receive the light reflected by the first reflecting mirror 1 and expand the light beam. For example, if the second reflecting mirror 2 is set as a convex reflecting mirror, the incident light beam can be expanded under the action of the convex reflecting mirror. The distance between the second reflecting mirror 2 and the first reflecting mirror 1 can be designed according to requirements, and is not limited in this embodiment. When the second reflecting mirror 2 is a convex reflecting mirror, the radius of curvature of its reflecting surface can also be designed according to actual requirements. Obviously, different radii of curvature will affect the beam expansion effect of the second reflecting mirror 2.

[0051] The third reflecting mirror 3 is positioned in the light reflection direction of the second reflecting mirror 2. Taking the second reflecting mirror 2 as an example where it is located below the first reflecting mirror 1 and can reflect light upwards, the third reflecting mirror 3 can be positioned diagonally above the second reflecting mirror 2. For example, as... Figure 1 As shown, the third reflecting mirror 3 is located to the upper left front of the second reflecting mirror 2. The third reflecting mirror 3 is used to receive the light reflected by the second reflecting mirror 2 and to collimate the light. The target object 4 is arranged in the direction of light reflection from the third reflecting mirror 3, for example, as shown in the image. Figure 1 As shown, the target object 4 is positioned directly below the third reflecting mirror 3. With this arrangement, the light collimated by the third reflecting mirror 3 can be directed downwards towards the target object 4, outputting a plane-wave laser beam for exposure. In this embodiment, the third reflecting mirror 3 can collimate the light, therefore a concave reflecting mirror can be used. The distance between the third reflecting mirror 3 and the second reflecting mirror 2 can be designed according to requirements. With other parameters remaining constant, the greater the vertical distance between the third reflecting mirror 3 and the second reflecting mirror 2, the larger the beam expanded from the second reflecting mirror 2 to the third reflecting mirror 3. The radius of curvature of the reflecting surface of the third reflecting mirror 3 can also be designed according to actual needs; this embodiment does not impose any limitations. The third reflecting mirror 3 and the second reflecting mirror 2 only need to meet sufficient beam aperture and light collimation effect in terms of position and radius of curvature.

[0052] The first reflecting mirror 1, the second reflecting mirror 2, and the third reflecting mirror 3 can all be made of fused silica. The second reflecting mirror 2 and the third reflecting mirror 3 are aspherical reflecting mirrors, which can maximize the improvement of beam quality or imaging accuracy and avoid aberrations from affecting core performance.

[0053] In this embodiment, the light emitted from the light source 8 is reflected by the first reflecting mirror 1 to the second reflecting mirror 2. The second reflecting mirror 2 expands the light beam and reflects it towards the third reflecting mirror 3. The third reflecting mirror 3 collimates the light beam into parallel light before reflecting it towards the target object 4. This embodiment achieves light path folding through the reflection paths of the first reflecting mirror 1, the second reflecting mirror 2, and the third reflecting mirror 3. The three reflecting mirrors can also be arranged vertically, and the entire system can be housed in a square component (e.g., a square fixed housing), significantly shortening the axial length of the lighting system and saving considerable space. The number of reflecting mirrors is far less than that of traditional multi-lens systems, and the positioning accuracy requirement of the reflecting mirrors is lower than the coaxiality requirement of multi-lens systems, simplifying the overall structural design and assembly process of the lighting system and reducing system complexity and operating costs. Furthermore, after the light from the light source 8 is reflected by the first reflecting mirror 1, the reflecting surface of the first reflecting mirror 1 can change the angle of the light. Therefore, within a certain range, the light source 8 can be selected to be placed in one of multiple locations (as an example, in...). Figure 1Based on this, the light source 8 can be arranged further below or above, making the arrangement more flexible. Furthermore, the position and reflection angle of the first reflecting mirror 1 can be flexibly adjusted based on the position of the light source 8 to form the desired light path.

[0054] When applied to holographic lithography, the reflector alters the optical path through light reflection, avoiding higher-order aberrations caused by the lens's material refractive index differences and multi-surface refraction. The collimation effect of the third reflector 3 is based on the law of reflection, resulting in a stable optical path and higher wavefront uniformity in the output plane wave. Furthermore, in holographic lithography, the uniformity of the plane wave primarily depends on the light source 8 itself, eliminating the need for additional homogenizing elements. The optical path design of the reflection system does not introduce refractive losses that affect the light intensity distribution, avoiding uneven light intensity caused by lens absorption and scattering, further simplifying the system while ensuring lithographic precision.

[0055] In some embodiments, based on the above-described reflective optical path system, such as Figure 2 As shown, the first reflecting mirror 1 is configured to both reflect and transmit light; that is, the first reflecting mirror 1 has a certain reflectivity and transmittance, so that incident light can both be reflected and transmitted through the first reflecting mirror 1. As an example, the reflectivity of the first reflecting mirror 1 can be 70%-90%, and the transmittance can be 30%-10%. As an example, the reflectivity of the first reflecting mirror 1 can be 90%, and the transmittance can be 10%.

[0056] To detect wavefront aberrations, the illumination system also includes a wavefront aberration detection module 6, which receives light transmitted from the first reflecting mirror 1 in a first direction. The first direction is parallel to the optical path between the first reflecting mirror 1 and the second reflecting mirror 2, and the side of the target object 4 facing the third reflecting mirror 3 is a planar reflective surface. The wavefront aberration detection module 6 can employ a Hardmann wavefront sensor.

[0057] Specifically, in this embodiment, such as Figure 2 As shown, the wavefront aberration detection module 6 is positioned above the first reflecting mirror 1. When the target object 4 located below the third reflecting mirror 3 has a planar reflective surface facing the third reflecting mirror 3, the planar reflective surface of the target object 4, together with the third reflecting mirror 3, the second reflecting mirror 2, and the first reflecting mirror 1, forms a round-trip optical path. That is, the light is reflected by the first reflecting mirror 1, expanded by the second reflecting mirror 2, and collimated by the third reflecting mirror 3 before illuminating the target object 4. Then, it returns along the original optical path via the planar reflective surface of the target object 4 (reflected sequentially by the third and second reflecting mirrors 2 to the first reflecting mirror 1). At this time, the returning light carries the wavefront information after the target object 4 has acted upon it. The first reflecting mirror 1, through its dual-function design of reflection and transmission, transmits part of the returning light along the first direction (parallel to the optical path direction from the first to the second reflecting mirror 2) to the wavefront aberration detection module 6. Figure 2The wavefront aberration is detected by the wavefront aberration detection module 6 (shown as dashed line portion). Since the light received by the wavefront aberration detection module 6 is the complete wavefront after being acted upon by the target object 4 and returning along the original optical path, aberration interference caused by additional optical path deflection is avoided. This ensures that the detected wavefront information is highly consistent with the actual wavefront state after the target object 4 is acted upon, providing true and reliable raw data for wavefront aberration analysis.

[0058] In this embodiment, the first reflector 1 simultaneously undertakes the functions of main optical path reflection and detection optical path transmission. No additional beam splitting element is required. It directly utilizes its inherent reflection-transmission characteristics to complete the optical path allocation, which significantly simplifies the system structure, reduces the aberrations introduced by multi-component assembly errors, and improves system stability.

[0059] Furthermore, since this embodiment employs a total internal reflection mirror group (first reflecting mirror 1, second reflecting mirror 2, and third reflecting mirror 3), light propagation relies on the law of reflection, fundamentally eliminating chromatic aberration and ensuring that wavefront aberrations of different wavelengths of light can be detected uniformly and accurately. Simultaneously, the first direction of the light received by the wavefront aberration detection module 6 is defined as parallel to the optical path direction from the first reflecting mirror 1 to the second reflecting mirror 2. After the returning light is transmitted through the first reflecting mirror 1, its propagation direction is parallel to the light direction from the first reflecting mirror 1 to the second reflecting mirror 2 in the main optical path, avoiding wavefront distortion caused by optical path direction deviation and further ensuring the accuracy of the detection results.

[0060] Furthermore, in this embodiment, by using a high-reflectivity, low-transmittance lens for the first reflector 1, its high reflectivity allows more energy from the light source 8 to be transferred to the target object 4 along the reflected light path, while its low transmittance reduces energy loss. Moreover, the light source 8 used for photolithography is a high-precision, controllable, high-intensity light source. After being reflected by the target object 4 (e.g., the fourth reflector or the silicon wafer to be exposed), it still carries a certain amount of energy. The returned light carrying this energy is affected by the low transmittance of the first reflector 1, resulting in lower energy transmitted along the first direction. This means the wavefront aberration detection module 6 receives lower energy light, preventing damage to the high-precision wavefront aberration detection module 6. In the field of photolithography, the high-precision wavefront aberration detection module 6 can still detect wavefront aberrations even when receiving lower-energy light.

[0061] In some embodiments, such as Figure 2 As shown, the lighting system also includes a collimating lens group 5, which is located between the first reflecting mirror 1 and the wavefront aberration detection module 6. The collimating lens group 5 is used to receive and collimate the light transmitted through the first reflecting mirror 1 along the first direction.

[0062] This embodiment optimizes the input adjustment for wavefront aberration detection, improving detection accuracy and stability. Specifically, the light transmitted through the first reflecting mirror 1 is precisely converted into parallel light after passing through the collimating lens group 5, eliminating additional angular deviations introduced during light path propagation. This ensures that the light entering the wavefront aberration detection module 6 is strictly based on parallel light, guaranteeing the consistency of the detection reference. Furthermore, the collimating lens group 5 precisely matches the operating conditions of the wavefront aberration detection module 6, significantly improving the quantitative accuracy of aberration detection.

[0063] Furthermore, although the collimating lens group 5 is a lens element, it only acts on the detection branch, not the main illumination optical path, which can minimize the aberrations it introduces. At the same time, the reflective design of the main optical path has eliminated chromatic aberration. The addition of the collimating lens group 5 will not destroy the overall low aberration advantage of the system. On the contrary, by optimizing the input light quality of the detection optical path, the chromatic aberration-free and low aberration characteristics of the reflective system can better serve the wavefront aberration detection, forming a synergistic advantage of low aberration in the main optical path and collimation correction in the detection optical path.

[0064] In one embodiment of the collimating lens group 5, such as Figure 2 As shown, the collimating lens group 5 includes a first biconvex lens 50 and a first plano-convex lens 51 arranged sequentially along the light transmission direction. The first biconvex lens 50 and the first plano-convex lens 51 may have a gap in the light transmission direction; for example, this gap may be 2 mm. The radius of curvature of the first biconvex lens 50 is smaller than that of the first plano-convex lens 51; for example, the radius of curvature of the first biconvex lens 50 may be 81 mm, and the radius of curvature of the first plano-convex lens 51 may be 91 mm.

[0065] Specifically, the first biconvex lens 50 has a small radius of curvature, enabling it to initially deflect the incident non-parallel light, quickly compressing the divergence angle of the light and undertaking the main coarse collimation adjustment function. The first plano-convex lens 51 has a large radius of curvature, enabling it to finely adjust the light after initial collimation, further calibrating the light into strictly parallel light. By deflecting the incident light in stages, spherical aberration caused by a single high-curvature lens deflecting at a large angle is avoided, thus improving the wavefront consistency of the collimated parallel light.

[0066] In one embodiment of the first reflector 1, both the light-incoming surface and the light-outgoing surface of the first reflector 1 are planar.

[0067] Specifically, for the reflected light path of illumination, planar reflection ensures a stable reflection direction and does not introduce additional convergence or divergence tendencies due to the curvature of the mirror, thus avoiding disruption of the stability of the subsequent beam expansion and collimation light paths; for the transmitted light path of detection, planar transmission makes the optical path of the light uniform within the mirror body, and the transmission direction is determined only by the tilt angle of the mirror, without causing local deflection due to the surface curvature, ensuring that the wavefront information carried by the transmitted light truly reflects the aberration state of the target object 4.

[0068] Furthermore, compared to curved mirrors, flat mirrors are easier to manufacture, improving surface accuracy and reducing inherent aberrations. Also, the optical path direction is determined by a single parameter—the mirror's tilt angle—eliminating the need for complex optical path calculations due to curvature.

[0069] In this invention, the target object 4 can be a fourth reflecting mirror or a semiconductor wafer, such as a silicon wafer. When the target object 4 is a fourth reflecting mirror, the light returns along the original optical path after being reflected by it. The wavefront aberration carried is mainly due to the system itself. The wavefront aberration detection module 6 can quantify the inherent aberration of the system by analyzing the reference wavefront, and provide an error compensation benchmark for subsequent actual detection.

[0070] When the target object 4 is a silicon wafer to be exposed, the wavefront aberration it carries includes microscopic morphological information of the semiconductor wafer surface and wavefront distortion during the photolithography process. The wavefront aberration detection module 6 can capture this information in real time, providing feedback to the photolithography system, realizing closed-loop control from processing to inspection, and reducing photolithography pattern deviations caused by defects in the semiconductor wafer itself or process fluctuations.

[0071] Understandably, during the commissioning of the lighting system, target object 4 can employ a fourth reflecting mirror, which enables precise detection of wavefront aberrations in the lighting system. In the actual photolithography process, target object 4 can utilize a fabricated semiconductor wafer, such as a silicon wafer, allowing for wavefront aberration detection of the lighting system during photolithography as well. Furthermore, it enables real-time observation of wavefront aberrations, offering extremely flexible application environments and low operating costs.

[0072] In some embodiments, the radius of curvature of the reflecting surface of the second reflecting mirror 2 is smaller than the radius of curvature of the reflecting surface of the third reflecting mirror 3.

[0073] With the above configuration, the second reflecting mirror 2, with its larger radius of curvature, can quickly expand the beam aperture to the target size. The third reflecting mirror 3, with its smaller radius of curvature, has a longer focal length, making it easier for its focal point to align with the backward extension of the light reflected by the second reflecting mirror 2. This ensures that the divergent light after beam expansion is completely converted into parallel light after reflection by the third reflecting mirror 3. Furthermore, the smaller radius of curvature of the third reflecting mirror 3 reduces the angle difference of incidence between light rays from different directions, fundamentally reducing spherical aberration. The resulting parallel light has higher wavefront uniformity, providing a superior illumination foundation for holographic lithography. Moreover, the smaller radius of curvature of the second reflecting mirror 2 spreads the energy of the incident light, preventing excessive energy concentration at the beam center, while the larger radius of curvature of the third reflecting mirror 3, with its gentler curvature, makes the energy distribution of the reflected parallel light more uniform.

[0074] In some embodiments, such as Figure 1 and Figure 2 As shown, the lighting system also includes a focusing lens group 7, which is located between the first reflecting mirror 1 and the light source 8. The focusing lens group 7 is used to receive and converge the light emitted from the light source 8.

[0075] Through the above configuration, the divergent light emitted by the light source 8 can be compressed into a converging light, allowing more light to be concentrated within the effective working area of ​​the first reflecting mirror 1, significantly improving the utilization rate of light energy. Furthermore, the focusing lens group 7, through precise design of its focal length and aperture, can standardize the emitted light from different light sources 8 into a converged beam with preset parameters, ensuring stable light parameters incident on the first reflecting mirror 1 and improving the overall system stability. Additionally, by setting the focusing lens group 7, the aperture of the beam incident on the first reflecting mirror 1 can be compressed to a reasonable range, allowing for the use of a smaller first reflecting mirror 1, thus reducing the processing and assembly costs of the reflecting mirror while maintaining high light energy utilization.

[0076] In some embodiments, the second reflecting mirror 2 is a convex reflecting mirror, and the third reflecting mirror 3 is a concave reflecting mirror, with the focal point of the third reflecting mirror 3 conjugate with that of the focusing lens group 7. With this configuration, after the light is reflected by the second reflecting mirror 2, the beam aperture is enlarged. After the focal point of the third reflecting mirror 3 is conjugate with that of the focusing lens group 7, the third reflecting mirror 3 collimates the incident light before it exits, achieving a seamless connection between beam expansion and collimation. Furthermore, compared to beam expansion and collimation systems using multiple lenses, the reflective combination of convex and concave reflecting mirrors achieves efficient space utilization through optical path folding.

[0077] In some embodiments, such as Figure 1 and Figure 2 As shown, the focusing lens group 7 includes a second plano-convex lens 70 and a second biconvex lens 71 arranged sequentially along the light transmission direction. The radius of curvature of the second plano-convex lens 70 is greater than the radius of curvature of the second biconvex lens 71.

[0078] With the above settings, the second plano-convex lens 70, with a larger radius of curvature, is more adaptable to the high-divergence light source 8. Its gentle deflection capability can gradually converge large-angle light rays, avoiding lens edge reflection loss caused by excessive light incident angle. The second biconvex lens 71, with a smaller radius of curvature, has higher focusing accuracy for the low-divergence light source 8: it can accurately control the beam convergence angle through strong deflection capability, ensuring that even if the divergence angle of the light source 8 is small.

[0079] In some embodiments, the illumination system uses a 355nm ultraviolet laser as the illumination source 8, with an output beam of 200mm in diameter and a root mean square error of less than 35nm (0.1λ). In this embodiment, the second plano-convex lens 70 has a radius of curvature of 90.362mm and a thickness of 3mm, the second biconvex lens 71 has a radius of curvature of 89.625mm and a thickness of 3mm, and the distance between the second biconvex lens 71 and the second plano-convex lens 70 is 2mm. The distance between the first reflecting mirror 1 and the second biconvex lens 71 is 120mm.

[0080] The second reflecting mirror 2 is a convex reflecting mirror with a radius of curvature of 90.155 mm, and the distance between the second reflecting mirror 2 and the first reflecting mirror 1 is 300 mm.

[0081] The third reflecting mirror 3 is a concave reflecting mirror with a radius of curvature of 935.455 mm. The distance between the third reflecting mirror 3 and the second reflecting mirror 2 is 350.225 mm. The distance between the third reflecting mirror 3 and the target object 4 is 500 mm.

[0082] The first biconvex lens 50 has an incident surface radius of curvature of 81.565 mm, an exit surface radius of curvature of 89.925 mm, and a thickness of 3 mm. The first plano-convex lens 51 has a radius of curvature of 91.065 mm and a thickness of 3 mm. The distance between the first biconvex lens 50 and the first plano-convex lens 51 is 2 mm.

[0083] It should be noted that the above descriptions of the radius of curvature and distance are not restrictive. Those skilled in the art can adaptively adjust the distance between the components and the radius of curvature according to the actual output beam requirements to meet different coefficient parameter requirements.

[0084] According to another aspect of the present invention, an exposure apparatus is provided for use in a chip fabrication process, including the above-described illumination system.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A plane wave based illumination system, characterized in that, The illumination system comprises: a first reflector (1) having a reflecting surface facing a light source (8) and being inclined relative to the direction of incidence of the light rays, the first reflector (1) being configured to receive the light rays from the light source (8) and reflect the light rays; a second reflector (2) configured to receive the light rays reflected by the first reflector (1) and expand the light rays; a third reflector (3) configured to receive the light rays reflected by the second reflector (2) and collimate the light rays to output planar wave laser for exposure to a target object (4); the first reflector (1) is configured to reflect and transmit the light rays; the illumination system further comprises a wavefront aberration detection module (6) configured to receive the light rays transmitted by the first reflector (1) in a first direction, the first direction being parallel to the direction of the optical path between the first reflector (1) and the second reflector (2); a surface of the target object (4) facing the third reflector (3) is a planar reflecting surface.

2. The plane wave based illumination system of claim 1, wherein, The illumination system further comprises a collimating lens group (5) disposed between the first reflector (1) and the wavefront aberration detection module (6), the collimating lens group (5) being configured to receive the light rays transmitted by the first reflector (1) in the first direction and collimate the light rays.

3. The plane wave based illumination system of claim 2, wherein, The collimating lens group (5) comprises a first lenticular lens (50) and a first plano-convex lens (51) disposed in sequence along the direction of light transmission, the first lenticular lens (50) having a smaller curvature radius than the first plano-convex lens (51).

4. The plane wave based illumination system of claim 1, wherein, The light entrance surface and the light exit surface of the first reflector (1) are both planar.

5. The plane wave based illumination system of claim 1, wherein, The reflectivity of the first reflector (1) is 70%-90%, and the transmissivity is 30%-10%.

6. The plane wave based illumination system of claim 1, wherein, The target object (4) is a fourth reflector or a silicon wafer to be exposed.

7. The plane wave based illumination system of claim 1, wherein, The second reflector (2) has a reflecting surface with a smaller curvature radius than the reflecting surface of the third reflector (3).

8. The plane wave based illumination system of claim 1, wherein, The illumination system further comprises a focusing lens group (7) disposed between the first reflector (1) and the light source (8), the focusing lens group (7) being configured to receive the light rays emitted by the light source (8) and converge the light rays.

9. The plane wave based illumination system of claim 8, wherein, The second reflector (2) is a convex reflector, and the third reflector (3) is a concave reflector, the third reflector (3) being conjugate with the focal point of the focusing lens group (7).

10. The plane wave based illumination system of claim 8, wherein, The focusing lens group (7) comprises a second plano-convex lens (70) and a second lenticular lens (71) disposed in sequence along the direction of light transmission, the second plano-convex lens (70) having a larger curvature radius than the second lenticular lens (71).

11. An exposure apparatus applied to a chip manufacturing process, characterized by comprising: The illumination system comprises any one of claims 1-10. The illumination system comprises any one of claims 1-10.

Images