CN104483816B - A kind of class critical illumination system for extreme ultraviolet photolithographic - Google Patents

Abstract

The quasi-critical illumination system for extreme ultraviolet lithography belongs to the field of critical illumination systems in extreme ultraviolet lithography systems. , condensing main mirror, condensing system secondary mirror, dandruff removal system and condensing system vacuum box, the dandruff removal system is arranged on the symmetry axis of the light source exit fan along the optical path; the condensing system secondary mirror and condensing primary mirror It is located behind the anti-dandruff system in sequence. The light source, the secondary mirror of the condenser system and the primary mirror of the condenser constitute the Schwarz-Child system; the secondary mirror of the condenser system and the primary mirror of the condenser are both located in the vacuum box of the condenser system; The front end of the dandruff removal system is close to the light source, and its rear end is fixedly connected with the rear end of the secondary mirror of the condenser system. The invention has a solid angle of 0.48Sr for light source collection and less than 25% of central area blocking, which greatly improves the efficiency of light energy collection; increases the effective distance of the dandruff removal system, so that the dandruff removal effect can be better exerted.

Description

A critical-like illumination system for extreme ultraviolet lithography

technical field

The invention belongs to the field of critical illumination systems in extreme ultraviolet lithography systems, and in particular relates to a quasi-critical illumination system for extreme ultraviolet lithography.

Background technique

The main optical structure of a lithography system usually includes two parts, an illumination system and an objective lens system. As shown in FIG. pupil), the secondary mirror 32 of the objective lens system 3, and the wafer surface 33, the illuminating light emitted by the illumination system is reflected by the mask surface 30, the primary mirror 31 of the objective lens system 3, and the secondary mirror 32 of the objective lens system in sequence, and finally the mask The pattern on the mold surface 30 is projected on the wafer surface 33 and has an etching effect on it.

The lighting system can be divided into critical lighting and Kohler lighting due to different lighting principles. The patent US5737137 published on April 7, 1998 introduces a lighting system using critical lighting. The system includes three reflectors: the first two The first optical mirror group using the Schwarz-Child system collects light energy, and the third mirror is used to match the light source with the mask, the exit pupil and the entrance pupil, and achieve a specific illumination coherence factor. The critical illumination system can also realize scanning exposure in the arc-shaped field of view by moving the light source or deflecting the primary mirror.

The 22nm etching pitch is usually a bottleneck that is difficult for existing lithography manufacturing technologies to break through, and extreme ultraviolet lithography (EUVL: Extreme Ultraviolet Lithography) is considered to be the most potential next-generation lithography technology that may break through the bottleneck of this technology. Theoretically, compared with the lithography system using the Koehler illumination system, if the extreme ultraviolet lithography system can adopt the critical illumination system, it will be able to obtain higher energy utilization efficiency and reduce the layout difficulty of internal components.

As a more sophisticated lithography system, the extreme ultraviolet lithography system to be developed puts forward many stricter requirements on the manufacture, layout and use environment of core components.

For example, the extreme ultraviolet lithography system needs to use the extreme ultraviolet light filter transmission film to filter out the stray light spectrum harmful to the exposure system, and only transmit and retain the extreme ultraviolet spectrum. However, since all substances are opaque to extreme ultraviolet light, even the extreme ultraviolet light filter transmission film, its thickness should be strictly controlled on the order of tens to hundreds of nanometers to reduce its absorption of the working spectrum in the extreme ultraviolet spectrum effect. Therefore, the extreme ultraviolet light filter film element whose thickness is only on the order of tens to hundreds of nanometers must have a very small diameter, and its external dimensions cannot be made too large, which not only makes the exposure projection system a small field of view exposure projection system , which also limits the maximum size and spacing of other optical components in the entire EUV lithography system.

Another example is that the light source used in the extreme ultraviolet lithography system is a gas discharge plasma light source, and its gas electrode will generate a large amount of high-temperature particle debris during the light-emitting process. When these debris are adsorbed on the surface of the reflector of the lighting system, they will cause pollution. And ablate the optical reflective coating on the mirror surface, thereby reducing the reflectivity of the mirror surface. In order to remove the particle debris, a chip removal system 13 can be used, which uses a strong electromagnetic field to suck out the charged particle debris from a direction perpendicular to the optical path, and simultaneously uses a reverse blowing wind The neutral particles advancing along the light path are blown out of the light path.

For another example, in order to reduce the absorption effect of air on the working spectrum in the extreme ultraviolet spectrum, the objective lens system of the extreme ultraviolet lithography system should be placed in a vacuum environment isolated from air in theory. However, the electric plasma of the extreme ultraviolet lithography system The gas electrode light source must be in an environment that is not too low in order to be effectively excited. Therefore, the objective lens system and the illumination system in the entire extreme ultraviolet lithography system should be in two environments that are isolated from each other, so that the two The environment is close to a vacuum, while the latter environment is at a pressure level that is higher than the lower limit of the excitation pressure of the light source and has a certain degree of vacuum, so as to minimize the absorption of the air on the extreme ultraviolet spectrum. The above-mentioned two isolated vacuum environments need not block or affect the optical path, and the distance between the two can be adjusted according to the focusing requirements of the lighting system.

However, the classic critical illumination system of the patented technology cited above does not use any filter transmission film to filter out the stray light spectrum harmful to the lithography system, so it is only suitable for laser plasma light sources with relatively pure spectra; at the same time, the previous The theoretical limit of the distance between the light source and the sub-reflector designed by the cited patent technology is small, and cannot be made larger, which leads to insufficient clearance between the two, and the anti-dandruff system cannot be added to the critical lighting system, or the The anti-dandruff system cannot play its due role because the action distance is too short. Moreover, in addition to the lack of a vacuum isolation design between the objective lens system and the illumination system, the patented technology adopts an overly compact and irregular layout of the illumination system and the objective lens system, which will make the processing of the entire EUV lithography system difficult. The difficulty of adjustment and calibration in the later stage has increased.

On the other hand, it is a relatively common and effective method to improve the uniformity of illumination by adding fixed occlusion devices. However, the occlusion devices used in this method are usually kept fixed. After that, its position, angle, and effective shading area in the optical path will not change, and it does not have the function of continuously adjusting the uniformity of illumination in the optical path.

Contents of the invention

In order to solve the problem that the existing classical critical lighting system is only suitable for pure-spectrum light sources, it lacks a secondary vacuum isolation system that allows the light path to pass through, an extreme ultraviolet light filter and transmission film, and an effective space for the dandruff removal system, so it cannot be directly used to construct an extreme lighting system. At the same time, the layout of the illumination system and objective lens system used in the ultraviolet lithography system is too compact and irregular, which increases the difficulty of processing various components and the difficulty of later assembly and calibration. On the other hand, the existing conventional blocking devices cannot change the position, angle and effective blocking area in the light path, and do not have the technical problem of continuously adjusting the uniformity of illumination in the light path. The present invention provides an extreme ultraviolet Critical-like illumination systems for lithography.

The technical solution adopted by the present invention to solve the technical problems is as follows:

A critical-like illumination system for extreme ultraviolet lithography, which includes a concentrating system, a relay system, a vacuum box for an exposure system, a bellows, and a conical cylinder. The concentrating system includes a light source, a concentrating primary mirror, a concentrating The secondary mirror of the system, the dust removal system and the vacuum box of the condenser system, the dust removal system is arranged on the rotational symmetry axis of the light source exit light cone along the optical path; the secondary mirror of the condenser system and the primary mirror of the condenser are located in the At the rear, the secondary mirror of the condenser system and the primary mirror of the condenser together constitute a Schwarz-Child system; both the secondary mirror of the condenser system and the primary mirror of the condenser are located in the vacuum box of the condenser system; the front end of the dandruff removal system is close to the light source , the rear end of which is fixedly connected to the front end of the secondary mirror of the concentrating system, and the rear end of the secondary mirror of the concentrating system is a reflective surface for receiving light; the relay system includes optical filters, optical blocking devices, Spherical reflector, field mirror and reflective torus; wherein, the optical blocking device comprises a baffle plate with a circular hole in the center and a central occlusion, the central occlusion is located in the circular hole of the baffle plate, and the rotation axis of the central occlusion is in contact with the baffle The Y-axis of the plate coordinate system coincides, and the rotation axis can be displaced along the X-axis or the Z-axis at a small distance; the filter is an extreme ultraviolet light filter and transmission film added with a zirconium film for preventing oxidation.

The above-mentioned relay system can make the light source and the mask plane of the objective lens system conjugate, and the relay system can also make the main mirror of the light-condensing lens conjugate with the main mirror of the objective lens system at the same time.

The above-mentioned relay system and objective lens system are all sealed inside the vacuum box of the exposure system, the outlet of the vacuum box of the focusing system and the entrance of the vacuum box of the exposure system are located on the same optical axis, the vacuum box of the focusing system and the vacuum box of the exposure system The body is connected by a bellows; the larger end of the tapered tube is connected to the end of the bellows, the other end of the tapered tube extends into the vacuum box of the lithography system, and the filter is set at the opening at the top of the cone of the tapered tube .

The beneficial effects of the present invention are as follows:

1) The present invention innovates a quasi-critical illumination system suitable for extreme ultraviolet lithography with a small field of view and wide-spectrum light source by making necessary improvements to the old classic critical illumination system.

2) The concentrating system based on the Schwarz-Child system greatly improves the efficiency of light energy collection, and the relay system simultaneously realizes the conjugation of the light source and the mask surface of the objective lens system, the aperture diaphragm of the illumination system and the objective lens system The two conjugate relations of the entrance pupil conjugate.

3) The introduction of the field mirror in the relay system effectively controls the system aperture and reduces the size of the optical components, thereby realizing the compatibility of the relay system with the small field of view objective lens system; the field mirror expands the light propagation space and increases the length of the optical path. It makes it easier to realize the object plane and pupil plane flipping in an extremely limited space, and realize the pupil matching of the illumination system and the objective lens system. On these basis, the approximation between the mask surface and the light source can be realized by adjusting the radius of curvature of the field lens Conjugate imaging, forming a critical-like illumination system.

4) Both the vacuum box of the concentrating system and the vacuum box of the exposure system can greatly reduce the absorption of the air on the working spectrum in the extreme ultraviolet spectrum. At the top of the cone, that is, at the middle image plane of the lighting system, the light beams of the lighting system converge to the thinnest, so it can greatly reduce the difficulty of making the zirconium film on the filter, and at the same time, the filter can filter out the light Harmful stray light spectrum of the engraving system, and can also play the role of vacuum isolation. The critical lighting system uses a larger back intercept, which provides enough layout space for the vacuum box of the lithography system and the vacuum box of the concentrating system, and also increases the effective distance of the chip removal system and improves its use effect .

5) The toroidal surface introduced in the relay system can correct the astigmatism of the system, realize the matching of the magnification in the X-axis and Y-axis directions, and adjust its effective position in the optical path by changing the position or angle of the optical blocking device. The occlusion area is equivalent to the adjustment of the size and aspect ratio of the occlusion, which can make it have the function of continuously adjusting the uniformity of illumination in the optical path.

Description of drawings

Fig. 1 is the three-dimensional layout diagram of the optical elements in the critical illumination system for extreme ultraviolet lithography of the present invention;

Fig. 2 is a schematic diagram of the optical path of the critical-like illumination system used in extreme ultraviolet lithography according to the present invention;

Fig. 3 is the schematic diagram of the optical path of the relay system of the present invention;

Fig. 4 is a schematic structural view of the optical blocking device of the present invention;

Fig. 5 is a three-dimensional schematic view of the central barrier of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Figures 1 to 5, a critical-like illumination system for extreme ultraviolet lithography, the illumination system includes a concentrating system 1, a relay system 2, an exposure system vacuum box 4, a bellows 5 and a conical Tube 6, concentrating system 1 includes light source 10, concentrating main mirror 11, concentrating system secondary mirror 12, dandruff removal system 13 and concentrating system vacuum box 14, dandruff removal system 13 is arranged on the exit light cone of light source 10 along the optical path on the axis of rotational symmetry; the secondary mirror 12 of the condenser system and the primary mirror 11 of the condenser are positioned at the rear of the dandruff removal system 13 in turn, the light source 10 is a wide-spectrum DPP light source, and the secondary mirror 12 of the condenser system and the primary mirror 11 of the condenser are common A Schwartz-Child system is constituted, the central area obscuration ratio of the Schwarz-Child system is lower than 25%, and the linear obscuration ratio is lower than 50%. The secondary mirror 12 of the condenser system and the primary mirror 11 of the condenser are all located in the vacuum box 14 of the condenser system; The rear end of the optical system secondary mirror 12 is a reflective surface for receiving light.

The relay system 2 includes an optical filter 20, an optical blocking device 21, a spherical mirror 22, a field lens 23, and a reflective torus 24 sequentially connected along the optical path; wherein, the optical blocking device 21 includes a circle with a center The baffle plate 21-1 of the hole and the center block 21-2, the center block 21-2 is located in the circular hole of the baffle plate 21-1, the rotation axis of the center block 21-2 and the Y of the baffle plate 21-1 coordinate system The axes are coincident, and the rotation axis can also be displaced along the X-axis or the Z-axis by a small distance. The filter 20 is an extreme ultraviolet light filter and transmission film added with a zirconium (Zr) film to prevent oxidation. By changing the position or angle of the optical blocking device 21 to adjust its effective blocking area in the optical path, it can have the function of continuously adjusting the uniformity of illumination in the optical path.

The filter 20 is an extreme ultraviolet light filter and transmission film to filter out the stray light spectrum that is harmful to the photolithography system.

The relay system 2 can make the light source 10 conjugate to the mask surface 30 of the objective lens system 3 , and the relay system 2 can also make the converging main mirror 11 conjugate to the main mirror 31 of the objective lens system 3 at the same time.

The relay system 2 and the objective lens system 3 are all sealed inside the exposure system vacuum box 4, the outlet of the concentrating system vacuum box 14 is located on the same optical axis as the entrance of the exposure system vacuum box 4, and the concentrating system vacuum box Both the body 14 and the vacuum box 4 of the exposure system can greatly reduce the absorption of the air on the working spectrum in the extreme ultraviolet spectrum. position to achieve alignment and focus adjustment of the optical path.

According to the definition of classical critical illumination, it needs to satisfy a strict conjugate relationship, that is, the light source is imaged on the object plane of the objective lens system 3 through the critical illumination system, that is, on the mask surface 30. At the same time, the exit pupil of the critical illumination and the objective lens The entrance pupils of system 3 coincide. In the quasi-critical lighting system of the present invention, since the condenser primary mirror 11 is also the aperture stop of the lighting system, and the primary mirror 31 of the objective lens system 3 is also the entrance pupil of the objective lens system 3, therefore, the relay system 2 simultaneously realizes The two conjugate relations of the conjugate of the light source 10 and the mask surface 30 of the objective lens system 3 and the conjugate of the aperture stop of the illumination system and the entrance pupil of the objective lens system 3 are established, which conforms to the definition of classical critical illumination.

But on the other hand, if the strict critical illumination relationship is satisfied, the inherent inhomogeneity of the light source 10 will be directly reflected on the object plane of the objective lens system 3, that is, on the mask surface 30, resulting in uneven illumination of the object plane of the objective lens system 3 . Therefore, the present invention makes the object plane of the objective lens system 3, that is, the mask surface 30, be located at a certain defocus plane of the illumination system. A derivative, so it can be called a quasi-critical lighting system.

Condensing main mirror 11 is also the aperture stop of illumination system, and after this aperture stop passes through light-condensing system sub-mirror 12, relay system 2 and mask surface 30 successively, it is imaged on the entrance pupil surface of objective lens system 3, also Be the main mirror 31 of objective lens system 3, the linear dimension ratio of its illumination region in the plane where main mirror 31 is located and the entrance pupil of objective lens system 3 is the partially coherent illumination factor of the illumination system, and this parameter will affect the photolithography system Aerial image quality and depth of focus.

Since the object-space mask adjustment mechanism and alignment monitoring mechanism and other auxiliary devices on the mask surface 30 strictly limit the object-space space, the size and arrangement of optical elements are greatly restricted. At the same time, it is necessary to consider the realizable Therefore, a field lens 23 is introduced into the relay system 2 to expand the light propagation space, increase the length of the optical path, and facilitate the layout of optical components. At the same time, the introduction of the field lens 23 greatly simplifies the matching relationship between the illumination system and the pupil of the objective lens system, so that the easy imaging relationship of the object image required by the relay system 2 can be realized in a limited geometric space, and the field lens 23 also The burden of the rotation angle of each optical element in the relay system 2 is shared.

Since the optical axes perpendicular to each other of the condenser system 1 and the objective lens system 3 need to coincide with each other after passing through the relay system 2, the magnifications of the relay system 2 in the X and Y directions will have large deviations, resulting in X and Y directions. The pupil is asymmetrical and makes the resolution in the X and Y directions inconsistent. In order to make up for this deficiency, a toroid 23 with the function of correcting astigmatism is introduced into the relay system 2 .

The optical obscuring device 21 of the present invention is a uniformity correction device matched with the critical lighting system. Since the critical lighting system requires the mask surface 30 to be conjugate to the optical filter 20, by adjusting the illumination distribution of the optical filter 20 The illumination uniformity of the mask surface 30 can be modulated. By adding an optical blocking device 21 near the optical filter 20 as an intermediate phase plane, the central blocking 20-2 that can be translated and rotated can block different parts of the light energy, which is equivalent to adjusting the blocking size and aspect ratio. The illumination uniformity is thus continuously optimized. After the optical blocking device 21 is adopted, the illumination non-uniformity of the mask surface 30 is reduced from ±9% to ±4%, and the uniformity is doubled, while the edge illumination does not decrease.

The present invention divides the quasi-critical lighting system into two parts, the concentrating system 1 and the relay system 2, and designs them separately to complete different functional divisions, reduce the difficulty of design, and also provide convenience for the structural layout of the quasi-critical lighting system. This type of critical illumination system has a larger back intercept, and provides sufficient layout space for the vacuum box 4 of the lithography system and the vacuum box 14 of the focusing system.

Arrange the optical filter 20 at the intermediate image plane of the light concentrating system 1, because the optical filter 20 is the conjugate point position of the light source 10, so the beam aperture at this place is the smallest, so the optical filter 20 is arranged here, which can make Its aperture is minimized, thereby ensuring that the filtered light 20 has sufficient strength even when the thickness is small and will not be damaged; at the same time, the optical filter 20 also plays the role of slowing down the movement of air, thus playing the role of vacuum isolation. Since the caliber of the optical filter 20 is only on the order of a few millimeters, it is necessary to introduce a conical cylinder 6, the end of the conical cylinder 6 with a larger diameter is connected to the end of the bellows 5, and the other end of the conical cylinder 6 extends into the photolithography system Inside the vacuum box 4 , the optical filter 20 is arranged at the opening at the top of the conical cylinder 6 . The filter 20 is an extreme ultraviolet light filter and transmission film to filter out stray light spectrum harmful to the photolithography system.

The introduction of the field lens 23 in the relay system 2 mainly has three advantages: first, the system aperture is effectively controlled, and the size of the optical element is reduced, thereby realizing the compatibility of the relay system 2 and the objective lens system 3; secondly, the field lens The introduction of 23 increases the optical path, and it is easier to realize the object plane and pupil plane inversion in an extremely limited space; moreover, due to the introduction of the field lens 23, the pupil matching between the illumination system and the objective lens system 3 can be preferentially realized. , the approximate conjugate imaging between the mask surface 30 and the light source 10 is realized by adjusting the radius of curvature of the field lens 23 .

In addition, the light concentrating system 1 of the present invention can realize the collection of all the outgoing light of the light source 10 under the existing processing conditions, its collection solid angle reaches 0.48Sr, and the center area intercepts less than 25%, which greatly improves the light energy collection efficiency; The concentrating system 1, which matches the larger back intercept in the quasi-critical lighting system, also provides a longer layout space for the chip removal system, which increases the effective distance of the chip removal system, so that it can better play chip removal effect.

Restricted by the manufacturing level and cost considerations, the diameter of the main condenser mirror 11 is strictly limited to 300 mm, and it is necessary to collect light energy as much as possible, so the distance between the light source 10 and the main condenser mirror 11 must not be greater than 400 mm; The pollution of the light source 10 to the chip removal system 13 prolongs the working cycle, and the chip removal system 13 needs to be at least 25 mm away from the light source 10; and in order to ensure the quality of chip removal and reduce the pollution of debris to subsequent optical components, the length of the chip removal system 13 needs to be at least 220mm; taking into account the thickness of the condenser system secondary mirror 12 and the system adjustment margin, and reducing the incident angle of light on the condenser primary mirror 11 and the condenser system secondary mirror 12 as much as possible, the condenser system secondary mirror 12 and the distance between the condenser main mirror 11 is set to 150mm; because the air has a strong absorption of extreme ultraviolet light, so the exposure system needs to be placed in a vacuum box, and needs to be compatible with another device, so the condenser system 1 needs to have With a sufficiently long back working intercept, it is finally determined that the distance between the rear surface of the main condenser mirror 11 and the intermediate image plane, that is, the plane where the optical filter 20 is located, is at least 1450 mm, and the thickness of the main condenser mirror 11 is taken as 45 mm. At the optical filter 20 , that is, the intermediate image plane 20 , the light beam of the illumination system converges to be the thinnest, so the optical filter 20 is arranged there to reduce the difficulty of manufacturing the zirconium film on the optical filter 20 .

The light source 10 is a wide-spectrum light source DPP, and the light emitted by it passes through the light-concentrating system 1 and the above-mentioned filter 20 and then the spectrum is narrowed, and then enters the relay system 2 . Since the relay system 2 as a whole has been extended into the objective lens system 3, the size and spatial layout of its optical elements need to be strictly limited. First of all, the diameter of the spherical mirror 22 is limited by the support of the objective lens system 3, and cannot be higher than 25mm, thus determining the upper limit of the distance between the spherical mirror 22 and the intermediate image plane 20, and at the same time, a filter needs to be placed at the intermediate image plane 20 20 is compatible with the size of the detector used for assembly and the vacuum box 4 of the objective lens system 3, and the distance between the intermediate image plane 20 and the spherical mirror 22 must be greater than a lower limit. After analysis, in the initial structure, the spherical mirror 22 and The distance of the intermediate image plane 20 is taken as 200 mm, and it will be used as an optimization variable in the subsequent optimization design. The reflective toroid 24 needs to be supported on the back of the secondary mirror 32 of the objective lens system 3. Considering the arrangement of the supporting structure and the adjustment margin, the distance between the reflective toroid 24 and the mask surface 30 should not be greater than 80mm; The angle of incidence on the mask plane 30 is 4 degrees, so the position of the reflective toroid 24 is constant throughout the system.

According to the principle of critical illumination, two conjugate relations need to be satisfied, that is, the aperture stop of the illumination system, that is, the primary condenser mirror 11 forms an image on the objective lens system 3 after passing through the secondary mirror 12 of the condenser system, the relay system 2 and the mask surface 30 The entrance pupil is the main mirror 31 of the objective lens system, and the light source 10 is imaged on the mask surface 30 through the condenser system 1 and the relay system 2 . It is known that the light source 10 is imaged at the intermediate image plane 20 after passing through the condenser system 1, and the main condenser mirror 11 forms a virtual image near the secondary mirror 12 of the condenser system after passing through the secondary mirror 12 of the condenser system, that is, the light source 10 and the main mirror of the condenser system Mirror 1 realizes the imaging relationship of AB'BA' along the positive z direction after passing through the condenser system 1, then the relay system 2 needs to satisfy the imaging relationship of B'A'→A"B" to realize the conjugate imaging relationship of critical illumination , and both A″ and B″ are real images, so an intermediate real image of B must be added between A′A″, that is, B′A′B″′A″B″ to realize the pupil matching relationship between the illumination system and the objective lens system . In view of the limited space between the mask surface 30 and the secondary mirror 32 of the objective lens system 3, to form a pupil real image B "' in the relay system 2, a field mirror 23 needs to be added to increase the optical path. For the convenience of the initial structure Assuming that the aperture stop of the illumination system, that is, the intermediate image of the condenser main mirror 11 is located on the field mirror 23, the radii of curvature of the spherical mirror 22 and the reflective toroid 24 are obtained respectively according to the pupil matching relationship, and then according to The conjugate relationship between the intermediate image surface 20 and the mask surface 30 obtains the radius of curvature of the field lens 23.Because the illumination system aperture stop, that is, the intermediate image of the main mirror 11 of the condenser system 1 is on the field lens 23, so the field lens 23 The change of the radius of curvature will not destroy the pupil matching relationship.

The inclination of the three reflectors should realize the deflection of the light at about 90°, the average incident angle of the light on each mirror should not exceed 20°, and it is also necessary to fully consider that the light cannot contact the supporting structure of the mask surface 30 during the propagation process, and If there is interference with the quasi-mechanism, etc., it is necessary to prioritize the layout of the deflection angle and spacing of the spherical mirror 22 and the field mirror 23 from a mechanical point of view, and then fine-tune it to optimize the system.

The above-mentioned relay system 2 needs to realize the deflection of the optical path by 90°, and all of them need to use reflectors with a radius of curvature, so it will bring large astigmatism, so that the magnification of the relay system 2 in the X and Y directions is inconsistent, and the The aperture diaphragm of the lighting system, that is, the primary condenser mirror 11 forms an elliptical image after passing through the relay system 2, which causes the partial coherence factors of the lighting system in the X and Y directions to be inconsistent, resulting in a deviation in the exposure resolution in the two directions , which is extremely unfavorable for the photolithography system. Therefore, the reflective toroid 24 is set as a toroid to compensate the astigmatism generated by the spherical mirror 22 and the field lens 23 .

In summary, the following table lists the parameter settings of a lighting system according to the present invention:

As mentioned above, because the system adopts the critical lighting method, the luminous characteristics of the light source 10 will be reflected on the axial direction of the mask surface 30, and the light source 10 is a gas discharge plasma light source, which is an integrated light source, so the light source 10 has a certain length, and then Not all the light can be focused at the intermediate image plane 20, some of the light will be defocused and become stray light of the system, so it is necessary to add a baffle 21 with a circular hole 21-1 at or near the intermediate image plane 20 , to prevent stray light from entering the objective lens system 3; in the radial direction, the light intensity of the light source is Gaussian distributed. Due to the critical lighting method, the uniformity that meets the requirements cannot be achieved only by the condenser system 1 and the relay system 2, and uniformity is required. means of correction. One of the most direct means of uniformity correction is shown in FIG. 4 . Adding a blocking 21 - 2 to the circular hole 21 - 1 blocks the light energy entering the central area of the mask surface 30 without significantly weakening the light energy entering the edge area. Thereby reducing the illuminance difference in the entire exposure area and improving the uniformity. Since the system is symmetrical about the YOZ plane, it only needs to perform translation and rotation around the OY axis on the obscuration 21-2 in the YOZ plane to optimize the uniformity modulation. These two operations mainly realize three functions:

First, the translation of the obscuration 21-2 in the OY direction adjusts the relative position between the obscuration 21-2 and the optical axis, and modulates the uniformity of the mask surface 30 in the Y direction;

Second, the translation of the barrier 21-2 in the OZ direction is equivalent to the change of the size of the barrier 21-2;

Thirdly, the rotation of the obscuration 21-2 around the OY axis can adjust the size ratio of the obscuration 21-2 in the X and Y directions. After adopting the correction device, the non-uniformity of illumination on the mask surface is reduced from ±9% to ±4%, and the uniformity is doubled, while the edge illumination does not decrease.

Claims (3)

1. A class critical lighting system for extreme ultraviolet lithography, characterized in that: the lighting system comprises a light concentrating system (1), a relay system (2), an exposure system vacuum box (4), a bellows ( 5) and the conical barrel (6), the focusing system (1) includes a light source (10), a focusing primary mirror (11), a focusing system secondary mirror (12), a dandruff removal system (13) and a focusing system vacuum The box body (14), the anti-dandruff system (13) are arranged on the rotational symmetry axis of the light source (10) exit light cone along the optical path; Behind the anti-dandruff system (13), the secondary mirror (12) and the primary mirror (11) of the condenser system together constitute the Schwarz-Child system; the secondary mirror (12) and the primary mirror (11) of the condenser system ) are all located in the vacuum box (14) of the concentrating system; The rear end of the mirror (12) is a reflective surface for receiving light; the relay system (2) includes an optical filter (20), an optical blocking device (21), a spherical reflector (22), Field lens (23) and reflective toroid (24); Wherein, optical blocking device (21) comprises the baffle plate (21-1) that the center has circular hole and center blocks (21-2), and described center blocks (21-2) is located in the circular hole of the baffle (21-1), and the rotation axis of the center block (21-2) coincides with the Y axis of the baffle (21-1) coordinate system, and the rotation axis can be along the X Axis or Z-axis micro-displacement; the filter (20) is an extreme ultraviolet light filter transmissive film added with a zirconium film of an oxidation prevention cap layer. 2. The critical illumination system for extreme ultraviolet lithography according to claim 1, characterized in that: the relay system (2) can make the light source (10) and the mask surface (3) of the objective lens system (3) 30) Conjugation, and the relay system (2) also conjugates the condenser main mirror (11) and the objective lens system main mirror (31) at the same time. 3. The critical-like illumination system for extreme ultraviolet lithography according to claim 1, characterized in that: the relay system (2) and the objective lens system (3) are both sealed in the exposure system vacuum box (4) Inside, the outlet of the vacuum box of the focusing system (14) and the entrance of the vacuum box of the exposure system (4) are located on the same optical axis, and the vacuum box of the focusing system (14) and the vacuum box of the exposure system (4) pass through the corrugated The pipe (5) is connected; the end of the conical cylinder (6) with a larger diameter is connected to the end of the bellows (5), and the other end of the conical cylinder (6) extends into the vacuum box (4) of the photolithography system to filter light The sheet (20) is arranged at the opening at the top of the cone of the cone (6).