CN114967365A - Measuring device and measuring method for absolute detection of wave aberration of projection objective - Google Patents
Measuring device and measuring method for absolute detection of wave aberration of projection objective Download PDFInfo
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- CN114967365A CN114967365A CN202210538787.1A CN202210538787A CN114967365A CN 114967365 A CN114967365 A CN 114967365A CN 202210538787 A CN202210538787 A CN 202210538787A CN 114967365 A CN114967365 A CN 114967365A
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
- G03F7/70591—Testing optical components
- G03F7/706—Aberration measurement
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
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- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70425—Imaging strategies, e.g. for increasing throughput or resolution, printing product fields larger than the image field or compensating lithography- or non-lithography errors, e.g. proximity correction, mix-and-match, stitching or double patterning
- G03F7/70433—Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors
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Abstract
The invention discloses a measuring device and a measuring method for the wave aberration absolute detection of a projection objective, wherein the measuring device comprises a light source, an illumination system, a filtering system, a projection objective to be measured, a ball lens, a collimation system and a wavefront sensor, the filtering system, the projection objective to be measured, the ball lens, the collimation system and the wavefront sensor are sequentially arranged along the direction of incoherent light output by the light source and the illumination system, the projection objective to be measured, the ball lens, the collimation system and the wavefront sensor are arranged along the direction of incoherent light of the output space of the light source and the illumination system, the filtering system is arranged at the position of the diffraction limit of the light source and the illumination system to form ideal spherical waves, the projection objective to be measured, the light source and the diffraction limit of the illumination system are at confocal positions, the ball lens is arranged at the position of the projection objective to be measured, and the collimation system and the ball lens are also at the confocal state; and calibrating the system error of the projection objective wave aberration detection device by combining a random average method, and removing the system error from the relative measurement result, thereby improving the wavefront measurement precision.
Description
Technical Field
The invention belongs to the technical field of optical measurement and lithography machines, and particularly relates to a measuring device and a measuring method for absolute detection of wave aberration of a projection objective.
Background
The integrated circuit integrates electronic elements such as a resistor, a capacitor, and an inductor in a microstructure, and thus has various circuit functions. Integrated circuits can be developed from small to very large scale in decades and the technological support is a continuing development of lithography. The principle of lithography is to etch the circuit information of a mask plate onto a wafer by an optical exposure projection method, and in the process, a lithography projection imaging system plays a critical role. The precision of the projection imaging system determines the critical feature line width, so that the improvement of the precision of the photoetching objective system plays a crucial role in reducing the critical feature line width.
The current measuring methods for detecting the wave aberration of the projection objective mainly comprise a traditional interference detection method, a shack-Hartmann detection method, a point diffraction detection method and a shearing interference detection method. The traditional interferometer mainly comprises two categories of a Taeman-Green type interferometer and a Fizeau type interferometer, a quasi monochromatic light source forms a plane wave after passing through a collimating lens, the plane wave is divided into reference light and measuring light by a beam splitter, the two beams of light respectively carry information of a reference surface and a test surface to form a final interference pattern on an observation plane, and wavefront information to be detected or surface shape information to be detected is obtained through data analysis. Both interferometers require a reference wavefront generated by a high-precision standard optical surface to interfere with a wavefront to be measured, so that the detection precision is directly influenced by the precision of the reference surface.
The shack-Hartmann detection method is an improvement on the Hartmann detection method in 1971, a lens array is used for replacing an aperture array grating (Hartman grating) to be placed at the exit pupil position of a system to be detected, and the wavefront to be detected reaches a detector plane after being divided by the lens array. And collecting the divided light beam arrays by using a detector, measuring deviation delta x and delta y of the positions of the sub light beam arrays relative to a reference position from the horizontal direction and the vertical direction so as to calculate the slope of the wavefront to be measured relative to the horizontal direction and the vertical direction, and reconstructing the wavefront to be measured by using slope information.
In 1996, Medecki et al proposed a phase-shifted point diffraction interferometer (PS/PDI) whose measurement accuracy can be significantly improved by phase shifting. The incident light beam is filtered by the pinhole to generate spherical wave without aberration, and is divided into 0-level and 1-level diffraction light after passing through the binary grating, and the light waves carry the aberration of the photoetching objective lens after passing through the objective lens to be detected and reach a second mask. The second mask consists of a pinhole and a window, 0-level light is diffracted into spherical reference wave after passing through the pinhole on the diffraction plate, 1-level light serving as test wave still carries objective wave aberration information after passing through the window on the diffraction plate, and interference fringes are formed on a detector plane by the two and are detected by a CCD camera. The grating is moved along the direction vertical to the grating lines of the grating, so that the 1-level light can generate periodic phase shift, and the wave aberration of the objective lens to be measured can be calculated by utilizing the interference patterns after phase shift in two orthogonal directions. The point diffraction method is limited in that the size of a pinhole for detection needs to be reduced as the operating wavelength is reduced, and the contrast of fringes is reduced due to a reduced light flux passing through the pinhole, which affects the final detection accuracy.
In contrast to conventional interferometers, shearing interferometers do not require a reference surface, but rather achieve interference by splitting a wavefront into two wavefronts with the same slight offset by optical elements. The shearing interference method can be divided into a radial shearing interference method, a rotary shearing interference method, a reversal shearing interference method and a transverse shearing interference method according to the working principle, and the transverse shearing interference method is the most commonly used method in wave aberration detection. According to the transverse shearing interference method, a transverse displacement is generated on a measured wavefront relative to an original wavefront through optical elements such as a mask and a grating, interference is generated on a part where the two wavefronts are overlapped, interference images of the two wavefronts are detected by using a CCD, and original wavefront reconstruction is realized through an algorithm. However, the existing detection method for the projection objective reaches the practical accuracy detection limit, and obtains a relative measurement result containing a system error, so that the absolute detection accuracy of the wave aberration of the projection objective cannot be obtained.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a measuring device and a measuring method for absolute detection of the wave aberration of a projection objective.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a measuring device for absolute detection of wave aberration of a projection objective comprises a light source and illumination system 1, a filter system 2, a projection objective 3 to be detected, a ball lens 4, a collimation system 5 and a wavefront sensor 6; the system comprises a light source, a collimating system, a wavefront sensor, a filter system, a measured projection objective, a ball lens, a collimating system and a wavefront sensor, wherein the filter system is positioned in an object space view field of the measured projection objective along the filter system, and the numerical aperture of illumination is full of the object space numerical aperture range of the measured projection objective; the ball lens is arranged at the position which is confocal with the projection objective to be measured, and the collimating system and the ball lens are also in a confocal state;
the filtering system is a pinhole with high resolution, and the pinhole is placed at the diffraction limit, so that the spatial incoherent light generated by the light source is changed into ideal spherical waves, and the errors of the illumination and light source systems are eliminated;
the ball lens is used for a random averaging method to eliminate the measurement error of the whole system;
the collimation system is used for collimating and expanding beams or collimating and contracting beams, and the generated parallel light is more accurate through data measured by the wavefront sensor;
the wavefront sensor 6 may be a hartmann sensor, which divides a light beam by a microlens array to obtain shearing amounts in an X direction and a Y direction, respectively, and finally obtains wavefront information, or an SID4 camera, i.e., a four-wave shearing interferometer, which interferes with four beams of ± 1-order light to obtain wavefront information;
the method for detecting the wave aberration of the projection objective by adopting the projection objective wave aberration detection device comprises the following steps:
the method comprises the following steps: the light source and the illumination system 1 are used for generating a spatial incoherent light source, an ideal spherical wave is formed by the filtering system 2, the spherical wave passes through the collimation system 5 and then is received by the wavefront sensor 6, so that system errors generated by the collimation system 5 and the wavefront sensor 6 are obtained, and the data are stored, so that the system errors generated by the collimation system 5 and the wavefront sensor 6 can be removed and measured at a later period;
step two: the method comprises the steps that a light source and an illumination system 1 are used for generating a spatial incoherent light source, ideal spherical waves are obtained through a filtering system 2, after a wave surface passes through a projection objective 3 to be measured, the spherical waves carry wave aberration information of the projection objective and reach a wavefront sensor 6 through a ball lens 4 and a collimation system 5, and information containing the wave aberration information and system errors of the projection objective is obtained;
step three: randomly rotating the ball lens 4 for N times to obtain N pieces of information containing wave aberration information and system errors of the projection objective, averaging the information, and eliminating random errors of the whole system and non-uniform surface shape errors of the ball lens;
step four: calculating the inherent spherical aberration of the ball lens according to the aperture, the curvature radius and the focal length parameters of the ball lens;
step five: the real wave aberration information of the projection objective is obtained by eliminating random errors, system errors generated by the light source and illumination system 1, the filtering system 2 and the wavefront sensor 6 and the inherent spherical aberration of the spherical lens from signals containing the wave aberration information and the system errors of the projection objective to be measured.
The principle of the invention is as follows: the invention generates incoherent light through a light source and an illumination system, forms ideal spherical waves after passing through a filtering system, carries wave aberration information of a projection objective through an objective system, obtains shearing slopes in the X direction and the Y direction respectively after light waves containing the wave aberration information pass through a ball lens and a collimation system and reach a wavefront sensor, finally reconstructs wavefront according to the slope information, and calibrates the error of the whole detection system by using a random average method, thereby obtaining the absolute detection precision of the projection objective without system errors.
Compared with the prior art, the invention has the advantages that: the device is simple, the experimental operation is convenient, and the purpose of high-precision detection by using the low-precision reference body is realized by combining the random average method in the absolute detection method. The method comprises the steps of calibrating a measurement system error by using a random average method, separating the measurement system error from a relative measurement result to obtain the absolute detection precision of the wave aberration of the projection objective system, and breaking through the practical limit of the existing projection objective wave aberration detection technology. In addition, the invention has strong universality, not only can be used for detecting the wave aberration of the projection objective, but also is suitable for detecting the wave aberration of other high-precision objectives.
Drawings
FIG. 1 is a schematic diagram of a measuring device for absolute detection of wave aberration of a projection objective according to the present invention;
FIG. 2 is a flow chart of a measurement method for absolute detection of wave aberration of a projection objective according to the present invention;
FIG. 3 is a schematic diagram of the calibration of the alignment system and wavefront sensor system error of the present invention;
FIG. 4 is a schematic diagram of the random averaging method of the present invention.
In the figure: the system comprises a light source and an illumination system 1, a filtering system 2, a measured projection objective lens 3, a ball lens 4, a collimation system 5 and a wavefront sensor 6.
Detailed Description
To better illustrate the objects, technical solutions and advantages of the present invention, the following detailed description is given with reference to the accompanying drawings, but should not be construed to limit the scope of the present invention.
As shown in fig. 1, a measuring device for absolute detection of wave aberration of a projection objective according to the present invention comprises a light source and illumination system 1, a filter system 2, a projection objective 3 to be detected, a ball lens 4, a collimation system 5 and a wavefront sensor 6; the system comprises a light source and an illumination system 1, wherein a filtering system 2, a projection objective lens 3 to be measured, a ball lens 4, a collimation system 5 and a wavefront sensor 6 are sequentially arranged along the direction of spatial incoherent light output by the light source and the illumination system 1, the filtering system 2 is positioned in an object space view field of the projection objective lens 3 to be measured, and the numerical aperture of illumination is full of the range of the object space numerical aperture of the projection objective lens 3 to be measured; the light source and illumination system 1 provides uniform illumination for the whole measuring device, the filter system 2 is arranged at the diffraction limit of the light source and illumination system 1 to form ideal spherical waves, the projection objective 3 to be measured and the diffraction limit of the light source and illumination system 1 are in confocal positions, the ball lens 4 is arranged at the confocal position of the projection objective 3 to be measured, and the collimation system 5 and the ball lens 4 are also in confocal states;
the filtering system 2 is a pinhole with high resolution, and the pinhole is placed at the diffraction limit, so that the spatial incoherent light generated by the light source of the light source and the light source of the illumination system 1 is changed into ideal spherical waves, and the errors of the light source and the illumination system are eliminated;
the ball lens 4 is used for a random averaging method to eliminate the measurement error of the whole system;
the collimation system 5 is used for collimating and expanding beams or collimating and contracting beams, and the generated parallel light is more accurate through data measured by the wavefront sensor 6;
the wavefront sensor 6 may be a hartmann sensor, which divides a light beam by a microlens array to obtain shearing amounts in an X direction and a Y direction, respectively, and finally obtains wavefront information, or an SID4 camera, i.e., a four-wave shearing interferometer, which interferes with four beams of ± 1-order light to obtain wavefront information;
as shown in fig. 2, a method for measuring absolute detection of wave aberration of a projection objective specifically includes the following steps:
the method comprises the following steps: the light source and the illumination system 1 are used for generating a spatial incoherent light source, an ideal spherical wave is formed by the filtering system 2, the spherical wave passes through the collimation system 5 and then is received by the wavefront sensor 6, so that system errors generated by the collimation system 5 and the wavefront sensor 6 are obtained, and the data are stored so as to eliminate and measure the system errors W generated by the collimation system 5 and the wavefront sensor 6 at a later period 1 ；
Step two: the light source and the illumination system 1 are used for generating a spatial incoherent light source, an ideal spherical wave is obtained through the filtering system 2, after a wave surface passes through the projection objective 3 to be measured, the spherical wave can carry wave aberration information of the projection objective and reaches the wavefront sensor 6 through the spherical lens 4 and the collimating system 5, and information W containing the wave aberration information and system errors of the projection objective is obtained i ；
Step three: randomly rotating the ball lens 4N times to obtain N pieces of information containing wave aberration information and system error of the projection objective, and averaging the information
Eliminating whole system random error W i,N Error W of non-uniform spherical lens surface shape i,S ；
Step four: calculating the inherent spherical aberration W of the ball lens according to the aperture, curvature radius and focal length parameters of the ball lens SP ；
Step five: from information containing wave aberration information and systematic errors of the projection objective
Rejecting systematic errors W produced by a collimation system and a wavefront sensor 1 And the inherent spherical aberration W of the spherical lens SP Obtaining the true wave aberration information W of the projection objective T 。
As shown in FIG. 3, the light source is filtered to generate an ideal spherical wave, and then the system error of the collimation system and the wavefront sensor can be measured through the collimation system and the wavefront sensor, and is represented as W 1 ；
Principle of random averaging when measuring a wavefront transmitted through a ball lens using a wavefront sensor, as shown in fig. 4, each measurement will be a combination of the projection objective true wave aberration, system aberrations, ball lens induced wavefront aberrations and random errors. If the ball lens is spherical, uniform, and centered on the optical axis, it will only produce spherical aberration to the measured wavefront. All other measured aberrations can be attributed to systematic deviations and random errors.
The amount of intrinsic spherical aberration of a spherical lens is a function of aperture, spherical radius and refractive index. A real spherical lens has shape errors and refractive index non-uniformities, which introduce additional aberrations, requiring separation of the inherent spherical aberration from the additional aberrations caused by other factors. So that each measurement W of the transmitted wavefront i Can be expressed as:
W i ＝W 1 +W T +W i,S +W SP +W i,N (1)
wherein, W 1 Is the systematic error, W, produced by the collimation system and wavefront sensor T Is the true wave aberration of the projection objective，W i,S Wave aberration of the i-th measurement due to surface shape error of the ball lens, W SP Is the inherent spherical aberration, W, of the ball lens i,N Is the random error generated by the system at the ith measurement;
if the ball lens is oriented in a random direction and a sufficient number of wavefronts are averaged, the effect will be to eliminate the randomly varying component, expressed as:
(W i,S +W i,N )→0 (2)
the average wavefront can be expressed as:
the inherent spherical aberration W of the ball lens can be calculated or simulated according to the aperture, curvature radius and focal length parameters of the ball lens sp Systematic error W produced by collimation system and wavefront sensor 1 Which can be calibrated separately, the true wave aberration of the projection objective can be expressed as:
Claims (4)
1. a measuring device for absolute detection of the wave aberration of a projection objective, characterized by: the device comprises a light source and illumination system (1), a filtering system (2), a projection objective lens (3) to be measured, a ball lens (4), a collimation system (5) and a wavefront sensor (6); a filtering system (2), a projection objective (3) to be measured, a ball lens (4), a collimation system (5) and a wavefront sensor (6) are sequentially arranged along the direction of the spatial incoherent light output by the light source and illumination system (1), the filtering system (2) is positioned in an object space view field of the projection objective (3) to be measured, and the numerical aperture of illumination is full of the range of the numerical aperture of the object space of the projection objective (3) to be measured; the spherical lens (4) is placed at a position which is confocal with the projection objective (3) to be measured, and the collimating system (5) and the spherical lens (4) are also in a confocal state;
the filtering system (2) is a pinhole with high resolution, and is placed at the diffraction limit, so that the spatial incoherent light generated by the light source of the light source and the light source of the lighting system (1) becomes ideal spherical waves, and the errors of the light source and the lighting system (1) are eliminated;
the ball lens (4) is used for a random averaging method to eliminate the measurement error of the whole measuring device;
the collimation system (5) is used for collimating and expanding beams or collimating and contracting beams, and the generated parallel light is more accurate through data measured by the wavefront sensor (6).
2. The apparatus for measuring absolute detection of wave aberration of a projection objective of claim 1, wherein: the wavefront sensor (6) can be a Hartmann sensor, and light beams are divided through a micro-lens array to respectively obtain shearing quantities in the X direction and the Y direction so as to finally obtain wavefront information; the optical system can also be a SID4 camera, namely a four-wave shearing interferometer, and the wavefront information is obtained by interference of four beams of +/-1 order light.
3. A wavefront measurement method using the measurement apparatus for absolute detection of wave aberration of a projection objective of claim 1, characterized in that: the method comprises the following steps:
the method comprises the following steps: a light source and an illumination system (1) are used for generating a spatial incoherent light source, ideal spherical waves are formed through a filtering system (2), the spherical waves pass through a collimation system (5), a wavefront sensor (6) receives signals, system errors generated by the collimation system (5) and the wavefront sensor (6) are obtained, and the data are stored so as to be convenient for later-period elimination and measurement of the system errors generated by the collimation system (5) and the wavefront sensor (6);
step two: a light source and an illumination system (1) are used for generating a spatial incoherent light source, ideal spherical waves are obtained through a filtering system (2), after a wave surface passes through a projection objective (3) to be measured, the spherical waves can carry wave aberration information of the projection objective and reach a wavefront sensor (6) through a ball lens (4) and a collimation system (5), and information containing the wave aberration information of the projection objective to be measured and system errors is obtained;
step three: randomly rotating the ball lens (4) for N times to obtain N pieces of information containing wave aberration information and system errors of the projection objective, taking the average value of the information, and eliminating random errors of the whole system and errors of uneven surface shapes of the ball lens (4);
step four: calculating the inherent spherical aberration of the ball lens (4) according to the aperture, the curvature radius and the focal length parameter of the ball lens (4);
step five: the real wave aberration information of the projection objective is obtained by eliminating random errors, system errors generated by a light source and illumination system (1), a filtering system (2) and a wavefront sensor (6) and the inherent spherical aberration of a ball lens (4) from signals containing the wave aberration information and the system errors of the projection objective to be measured.
4. The method for measuring the absolute detection of the wave aberration of the projection objective according to claim 3, wherein: the device has simple structure and simple absolute detection measurement principle, eliminates the influence of system errors on the measurement result compared with the traditional measurement method, and achieves the effect of detecting the wave aberration of the projection objective with high precision.
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