CN104166316A - Online projection objective wave aberration detection device and method - Google Patents

Abstract

An on-line detection device and method for wave aberration of a projection objective lens, the structure of the detection device includes a light source, a rotating scatterer, a first focusing lens, an optical fiber array, a second focusing lens, a scattering optical element, an object plane grating plate, and an image plane grating plate, two-dimensional photoelectric sensor, phase shift control module and computer; the rotating scatterer is composed of a bracket, a motor and a circular diffuse scattering optical element, and is used together with a multimode fiber array to convert the light source of coherent light or partially coherent light into incoherent light. By collecting the phase shift amount is 0, π, The 10 interference fringe patterns are used to calculate the phase, eliminating the influence of grating multi-level diffracted light interference on the phase extraction accuracy. The invention improves the modulation effect of the object plane grating on the spatial coherence of the light field, realizes a high-precision alignment effect, reduces the systematic error of phase extraction in wave aberration detection, and thus improves the wave aberration detection accuracy of the optical system.

Description

Projection objective lens wave aberration online detection device and detection method

technical field

The invention relates to a wave aberration detection device of an optical system, in particular to an online wave aberration detection device and method of a projection objective lens of a lithography machine illuminated by an expanded light source.

Background technique

Photolithography technology is one of the core technologies in the manufacture of very large-scale integrated circuits. The pattern on the mask is transferred to the photoresist coated on the surface of the silicon wafer by exposure method, and then the pattern is transferred by developing, etching and other processes. transferred to silicon wafers. The projection objective lens is the core component of the imaging system of the lithography machine. The wave aberration of the projection objective lens is the main factor leading to the deterioration of the lithography imaging quality, and ultimately leads to the decrease of the imaging contrast of the lithography machine, the narrowing of the process window and the reduction of the product yield. In the actual exposure process, factors such as system microvibration and continuous uneven heating of the lens by the excimer laser will cause drastic changes in the wave aberration of the projection objective lens. Therefore, it is necessary to integrate the wave aberration of the projection objective lens in the lithography machine into an online The measuring device realizes the online detection of the wave aberration of the projection objective lens quickly and with high precision.

The wave aberration detection technology of the projection objective lens of lithography machine can be divided into three categories according to the measurement object: wave aberration detection technology based on photoresist exposure, wave aberration detection technology based on aerial image measurement, and wave aberration detection technology based on pupil plane measurement Detection technology (PMI). Ronchi shearing interferometry is a wave aberration detection technology based on pupil plane measurement. The illumination beam passes through the mask mark made by the diffuser to form a uniform diffracted light and enters the pupil of the projection objective lens. The beam is sheared by the projection object mirror surface. A tangential grating splits into two identical wavefronts that are offset from each other by a certain distance and coherently produce a diffraction pattern in the far field. By measuring the interference pattern and using the phase recovery algorithm, the wave aberration of the projection objective can be extracted. It has the advantages of no spatial optical path error, high detection accuracy, and high sensitivity, and can be well applied to the online detection of wave aberration of the projection objective. . However, Ronchi shearing interference requires the light source to be incoherent, and the mutual interference of grating multi-level diffracted light will seriously affect the phase extraction accuracy. At the same time, the parallelism and collimation of the diffraction grating on the object plane and image plane are high. . Therefore, reducing the spatial coherence of the light source, eliminating the multi-level diffraction error of the grating, and improving the alignment and parallel effect of the grating are the prerequisites for the application of Ronchi shearing interference to the detection of wave aberration of high-precision projection objectives.

Van De Kerkhof et al. proposed a wave aberration detection device based on the Ronchi shear interference principle integrated on the mask platform and silicon wafer platform of the lithography machine (refer to the prior art [1], Van de Kerkhof, M., et al.,Fulloptical column characterization of DUV lithographic projection tools.Optical Microlithography Xvii,Pts 1-3,2004.5377:p.1960-1970), to realize online detection of wave aberration of projection objective lens of lithography machine. However, the problem with this device is that the light source is partially coherent light, which directly affects the modulation effect of the spatial coherence of the light field, thereby affecting the measurement accuracy and the like. U.S. Patent No. 7,333,216 discloses a wave aberration detection device that adopts a multimode fiber array to reduce the spatial coherence of the light source (refer to prior art [2], U.Wegmann, H.Haidner, M.Schriever.Apparatus for wavefront detection, United Statespatent US7333216B2,2008.), but the problem of this device is: lack of effective alignment and parallel adjustment functions between the object plane grating and the image plane grating, and it is easy to introduce system errors. Matthieu Visser et al. proposed an extended light source interferometer for EUV lithography objective lens wave aberration detection (refer to prior art [3], Matthieu Visser, Martign K.Dekker, Petra Hegeman, et al., "Extended source interferometry forat-wavelength test of EUV-optics”, Emerging Lithographic Technologies Iii, Pts 1 and 2, 1999.3676: p.253-263), but there is a problem that the interference between higher order diffraction items and 0th order is not eliminated.

Contents of the invention

The object of the present invention is to overcome above-mentioned deficiencies in the prior art, provide a kind of wave aberration on-line detection device of projection objective lens based on Ronci's shearing interference principle, utilize this device to measure wave aberration of projection objective lens, have speed, precision high merit.

Technical solution of the present invention is as follows:

An on-line detection device for wave aberration of a projected objective lens is characterized in that: along the output beam direction of a light source, there are a rotating diffuser, a first focusing lens, an optical fiber array, a second focusing lens, a scattering optical element, an object plane grating plate, and an image plane. grating plate, two-dimensional photoelectric sensor; the object plane grating plate is placed on the object plane grating translation platform, the image plane grating plate is placed on the image plane grating translation platform, and the image plane grating translation platform is connected with the corresponding The mobile control module is connected, and the two-dimensional photoelectric sensor is connected with the computer.

The rotating diffuser is composed of a bracket, a motor and a circular diffuse scattering optical element, and is used to convert coherent light or partially coherent light into incoherent light; the circular diffuse scattering optical element is installed on the motor, Driven by the motor, it rotates along the central axis;

The scattering optical element is an optical element such as frosted glass, a microlens array, etc. that uniformly illuminates the illumination beam within the numerical aperture of the measured optical system;

The optical fiber array is an optical fiber bundle arranged in a honeycomb shape by multimode optical fibers, which can further destroy the spatial coherence of the light field;

The object plane grating plate is composed of two object plane gratings with a period of P _o and a duty ratio of 50% and an object plane grating alignment mark, and the two object plane gratings are respectively the first grating of the grating line along the y direction and a second grating with grating lines along the x-direction.

The first grating and the second grating are phase gratings or amplitude gratings or other types of diffraction gratings.

The period P _o of the object plane grating and the period P _i of the image plane grating satisfy the following relationship,

P _o =P _i ·M

Among them, M is the imaging magnification of the optical system under test;

The object plane grating alignment mark is composed of a third grating at the top and a fourth grating at the bottom; the third grating and the fourth grating are both line gratings, and the periods are P ₁ and P ₂ , respectively, and The difference is 5%;

The numerical aperture of the measured optical system is NA, and the imaging magnification is M:1;

The image plane grating plate is composed of an image plane grating and an image plane grating alignment mark;

The image plane grating has a checkerboard layout, the light-transmitting unit and the light-shielding unit are squares of the same size, and each light-transmitting unit is surrounded by 4 light-shielding units, and each light-shielding unit is surrounded by 4 light-transmitting units; The cycle _Pi of described image plane grating is equal to the diagonal length of square; The diagonal direction of described image plane grating light transmission unit and shading unit is parallel to x-axis and y-axis direction;

The image plane grating alignment mark is composed of the fifth grating at the top and the sixth grating at the bottom, the period of the fifth grating is equal to the period of the fourth grating of the object plane grating alignment mark and the measured optical system The product of the imaging magnification, the period of the sixth grating is equal to the product of the period of the third grating of the object plane grating alignment mark and the imaging magnification of the optical system under test;

The object-plane grating displacement stage is a displacement stage that moves the first grating and the second grating into the object-side optical path of the optical system under test;

The image plane grating displacement platform is a displacement platform that moves the image plane grating into the image square optical path of the optical system under test, and drives the image plane image plane grating to move along the x direction and along the y direction;

The two-dimensional photoelectric sensor is a camera, a CCD, a CMOS image sensor, a PEEM, or a two-dimensional photodetector array, and its detection surface receives the shearing interference fringes generated by the image plane grating;

The computer is used to control the wave aberration detection process, store measurement data, and process and analyze the interferogram.

An online detection method for wave aberration of a projection objective lens, the implementation steps are as follows:

(1) Adjust the height of the rotating diffuser so that the light beam emitted by the light source passes through the upper half of the circular diffuse scattering optical element; adjust the first focusing lens and the input end of the fiber array to make the transmitted light of the rotating diffuser better coupled into an optical fiber array;

(2) The object plane grating plate is placed on the object plane grating displacement stage, and adjusted to the object surface of the optical system under test, and the object plane grating displacement stage is moved to move the first grating on the object plane grating plate into the measured optical system The position of the object view point of ;

(3) Place the scattering optical element close to the object plane grating plate, adjust the second focusing lens and the output end of the fiber array so that the object plane grating plate is evenly illuminated;

(4) The image plane grating plate is placed on the image plane grating displacement table, and adjusted to the image plane of the optical system under test, the image plane grating displacement table is moved, and the image plane grating is moved into the image square of the optical system under test. The dimensional photoelectric sensor is placed behind the image plane grating plate to detect the interference fringes formed by the image plane grating;

(5) Adjust the object plane grating translation stage, according to the differential alignment grating formed by the object plane grating alignment mark on the object plane grating plate and the image plane grating alignment mark on the image plane grating plate on the two-dimensional photoelectric sensor Align the formed Moiré fringes, and when the two groups of fringes completely overlap, it means that the alignment and parallel adjustment of the first grating and the image plane grating are completed (see prior art [4], Moon, E.E. and H.I.Smith, Nanometer -precision patternregistration for scanning-probe lithographies using interferometric-spatial-phase imaging. Journal of Vacuum Science&Technology B: Microelectronics and Nanometer Structures,2006.24(6):p.3083-3087.);

(6) The image plane grating translation stage moves the image plane grating along the x direction, moves 12 times, each time moves 1/12 grating period, after each movement, the two-dimensional photoelectric sensor collects a shearing interferogram I _xk , where k= 1, 2, 3..., 12; select the 10 interference fringe patterns except the 8th and 9th, and calculate the phase according to the following formula:

in, is the phase of the measured wave front in the x direction, representing the gradient information of the measured wave front in the x direction;

(7) Move the object-plane grating translation stage, and move the second grating on the object-plane grating plate into the position of the object field of view of the optical system under test; adjust the object-plane grating translation stage, according to the object-plane grating on the object-plane grating plate Align the moiré fringes formed by the differential alignment grating formed by the alignment marks on the image plane grating plate and the image plane grating alignment marks on the two-dimensional photoelectric sensor. Alignment and parallel adjustment of the second grating and the image plane grating;

(8) The image plane grating translation stage moves the image plane grating along the y direction, moves 12 times, and moves 1/12 of the grating period each time. After each movement, the two-dimensional photoelectric sensor collects a shearing interferogram I _yk , where k= 1, 2, 3..., 12; select the 10 interference fringe patterns except the 8th and 9th, and calculate the phase according to the following formula:

in, is the phase of the measured wave front in the y direction, representing the gradient information of the measured wave front in the y direction;

(9) Unpack the above phase extraction results to obtain the differential wavefronts ΔW _x and ΔW _y in the x-direction and y-direction respectively, and perform shear interference wavefront reconstruction to obtain the wavefront of the optical system under test.

Compared with the prior art, the present invention has the following advantages:

1. The use of rotating diffusers and fiber arrays further destroys the spatial coherence of the light source, improves the modulation effect of the object plane grating on the spatial coherence of the light field, and improves the measurement accuracy of the wave aberration of the optical system.

2. Differential gratings are used as alignment marks to generate amplified Moiré fringes with high sensitivity to displacement, thereby achieving high-precision alignment effects and reducing system errors.

3. It can well eliminate the higher-order diffraction items other than the 0th order and ±1st order, and can well eliminate the influence on the phase extraction accuracy caused by the multi-level diffracted light interference in the Ronchi shearing interference.

4. The modulation effect of the object plane grating on the spatial coherence of the light field is improved, a high-precision alignment effect is achieved, and the systematic error of phase extraction in wave aberration detection is reduced, thereby improving the wave aberration detection accuracy of the optical system.

Description of drawings

Fig. 1 is the schematic diagram of projection objective lens wave aberration online detection device of the present invention;

Figure 2 is a schematic diagram of a rotating diffuser;

Fig. 3 is a cross-sectional view of an optical fiber array;

Fig. 4 is a schematic diagram of the object plane grating plate;

Fig. 5 is a schematic diagram of an image plane grating plate;

FIG. 6 shows Moiré fringes generated under different relative displacements of the grating alignment marks.

Detailed ways

In order to make the content, implementation process and advantages of the present invention clearer, the present invention will be further described below in conjunction with the examples and drawings, but the examples should not limit the protection scope of the present invention.

Fig. 1 is the schematic diagram of projection object lens wave aberration on-line detection device of the present invention, as can be seen from the figure, this device structure comprises: along light source 1 output light beam direction successively be rotating scatterer 2, the first focusing lens 3, fiber array 4, the first Two focusing lens 5, scattering optical element 6, object plane grating plate 7, image plane grating plate 10, two-dimensional photoelectric sensor 13; Described object plane grating plate 7 is placed on object plane grating displacement platform 8, and described image The surface grating plate 10 is placed on the image surface grating displacement stage 11, the image surface grating displacement stage 11 is connected to the phase shift control module 12, and the described two-dimensional photoelectric sensor 11 is connected to the computer 14;

Described rotating scatterer 2 (referring to Fig. 2) is made up of bracket 203, motor 202 and circular diffuse scattering optical element 201, is used to convert coherent light or partially coherent light into incoherent light; The scattering optical element 201 is installed on the motor 202 and rotates along the central axis under the drive of the motor 202;

The scattering optical element 6 is an optical element such as frosted glass, a microlens array, etc. that enable the illumination beam to be uniformly illuminated within the numerical aperture of the measured optical system 9;

Described optical fiber array 4 (referring to Fig. 3) is by the optical fiber bundle of honeycomb arrangement by multimode optical fiber, is used for further destroying the spatial coherence of light field;

The object plane grating plate 7 (see FIG. 4 ) is composed of two object plane gratings and an object plane grating alignment mark 703 whose period is _Po and whose duty cycle is 50%. The two object plane gratings are grating lines respectively. A first grating 701 along the y-direction and a second grating 702 with grating lines along the x-direction.

The first grating 701 and the second grating 702 are phase-type or amplitude-type or other types of one-dimensional diffraction gratings.

The object plane grating alignment mark 703 is composed of a third grating 704 at the top and a fourth grating 705 at the bottom; the third grating 704 and the fourth grating 705 are both line gratings, and the periods are P ₁ and P ₂ , and the difference is 5%;

The image plane grating plate 10 (see FIG. 5 ) is composed of an image plane grating 1001 and an image plane grating alignment mark 1002;

The image plane grating 1001 is a checkerboard grating with a checkerboard layout. The light-transmitting units and the light-shielding units are squares of the same size. There are four light-shielding units around each light-shielding unit, and four light-shielding units around each light-shielding unit. Light unit; the period P _i of the image plane grating 1001 is equal to the diagonal length of the square; the diagonal direction of the image plane grating 1001 light-transmitting unit and the light-shielding unit is parallel to the x-axis and the y-axis direction;

Ideally, the image plane grating 1001 has only the 0th order and other odd-numbered items in the diffraction, and the even-numbered items lack orders, and the light energy is mainly concentrated on the 0th order and ±1 order, and each odd-numbered diffraction order interferes with the 0th order in the far field. The period of the equivalent grating in the shearing direction is the side length of each unit structure of the checkerboard grating times.

The image plane grating 1001 is placed in such a state that the diagonal direction of the light-transmitting unit and the light-shielding unit is parallel to the x-axis and y-axis directions, and it is a Ronchi grating viewed along the x-direction and y-direction, with a duty cycle of 50%. .

The image plane grating alignment mark 1002 is composed of a fifth grating 1003 at the top and a sixth grating 1004 at the bottom, and the period of the fifth grating 1003 is equal to that of the object plane grating alignment mark 703 and the fourth grating 705 The product of the period and the imaging magnification of the optical system 9 under test, the period of the sixth grating 1004 is equal to the product of the period of the object plane grating alignment mark 703 and the third grating 704 and the imaging magnification of the optical system 9 under test;

Example:

In the DUV exposure optical system, the light source 1 is generally ArF and KrF excimer lasers, that is, the wavelengths of the output light are 193nm and 248nm respectively. With an ArF excimer laser with a wavelength of 193nm as the light source 1, the numerical aperture of the measured optical system 9 is 0.75, the imaging magnification is 4×, the shear rate is set to 1/20, and the period _Pi of the image plane grating 801 is selected as 2.6μm, the object plane grating period is P _o is 10.4μm; the period of the fifth grating and the sixth grating of the image plane grating alignment mark are 25μm and 26μm respectively; the period of the third grating and the fourth grating of the object plane grating mark They are 104 μm and 100 μm, respectively.

The object-plane grating displacement stage 8 is a displacement stage that moves the first grating 701 and the second grating 702 into the object-side optical path of the measured optical system 9 respectively;

The image plane grating displacement stage 11 is a displacement stage that moves the object plane grating 1001 into the image side optical path of the measured optical system 9, and drives the object plane grating 1001 to move along the x direction and along the y direction;

The object plane grating alignment mark 703 and the image plane grating alignment mark 802 constitute a differential mode grating mark, which is used to realize nanoscale high-precision alignment of the object plane grating plate 7 and the image plane grating plate 10;

The two-dimensional photoelectric sensor 13 is a camera, a CCD, a CMOS image sensor, a PEEM, or a two-dimensional photodetector array, and its detection surface receives the shearing interference fringes generated by the image plane grating 10;

The computer 14 is used to control the wave aberration detection process, store measurement data, and process and analyze the interferogram.

The above-mentioned device and technology can be used to detect the wave aberration of the projection objective lens, and the detection method includes the following steps:

(1) Adjust the height of the rotating diffuser 2 so that the light beam sent by the light source 1 passes through the upper half of the circular diffuse scattering optical element 201; adjust the first focusing lens 3 and the input end of the optical fiber array 4 to make the rotating diffuser 2 The transmitted light is well coupled into the fiber array4;

(2) The object plane grating plate 7 is placed on the object plane grating displacement table 8, and adjusted to the object plane of the measured optical system 9, the object plane grating displacement table 8 is moved, and the first grating on the object plane grating plate 7 701 moves into the position of the object field of view of the measured optical system 9;

(3) Place the scattering optical element 6 near the object plane grating plate 7, adjust the second focusing lens 5 and the output end of the fiber array 4 so that the object plane grating plate 7 is evenly illuminated, and ensure that the first grating 701 and the object plane grating Alignment marks 703 are all illuminated;

(4) The image plane grating plate 10 is placed on the image plane grating displacement table 11, and adjusted to the image plane of the measured optical system 9, the image plane grating displacement table 11 is moved, and the image plane grating 1001 is moved into the measured optical system 9 Fang Guanglu’s image, the two-dimensional photoelectric sensor 13 is placed behind the image plane grating plate 10 to detect the interference fringes of the image plane grating 1001;

(5) Adjust the object plane grating displacement table 8, and the differential alignment grating formed by the object plane grating alignment mark 703 on the object plane grating plate 7 and the image plane grating alignment mark 1002 on the image plane grating plate 10 is in two phases. The moiré fringes formed on the three-dimensional photoelectric sensor 13 are aligned; see accompanying drawing 6, (a)～(d) are the corresponding moiré fringe patterns in the process of the relative displacement of the two groups of marking gratings gradually decreasing respectively, (e) The two groups of gratings are completely overlapped to realize the fringe pattern when the object plane grating and the image plane grating are aligned; when the object plane grating displacement table 11 is adjusted to make the two groups of fringes completely overlap, it means that the first grating 701 and the image plane grating 1001 have been aligned. Alignment and parallel adjustment;

(6) The image plane grating displacement stage 11 moves the image plane grating 1001 along the x direction, moves 12 times, and moves 1/12 grating period each time, after each movement, the two-dimensional photoelectric sensor 13 collects a shearing interferogram I _xk , Where k=1,2,3...,12; select I _x1 , I _x2 , I _x3 , I _x4 , I _x5 , I _x6 , I _x7 , I _x10 , I _x11 , and I _x12 , which correspond to x The phase shift in the direction is 0, π, The 10 interference fringe diagrams, the phase is calculated according to the following formula:

in, is the phase of the measured wave front in the x direction, representing the gradient information of the measured wave front in the x direction;

(7) Move the object plane grating displacement stage 8, move the second grating 702 on the object plane grating plate 7 into the object side field of view point position of the measured optical system 9; adjust the object plane grating displacement stage 8, according to the object plane grating plate The moiré fringes formed by the differential alignment grating formed by the object plane grating alignment mark 703 on the image plane grating plate 10 and the image plane grating alignment mark 1002 on the image plane grating plate 10 on the two-dimensional photoelectric sensor are aligned. When the group fringes are completely overlapped, it means that the alignment and parallel adjustment of the second grating 702 and the image plane grating 1001 are completed;

(8) The image plane grating displacement stage 11 moves the image plane grating 1001 along the y direction, and moves 12 times, each time moving 1/12 of the grating period, after each movement, the two-dimensional photoelectric sensor 13 collects a shearing interferogram I _yk , Where k=1,2,3...,12; I _y1 , I _y2 , I _y3 , I _y4 , I _y5 , I _y6 , I _y7 , I _y10 , I _y11 , I _y12 are selected, corresponding to y The phase shift in the direction is 0, π, 10 interference fringe images, the phase is calculated according to the following formula:

in, is the phase of the measured wave front in the y direction, representing the gradient information of the measured wave front in the y direction;

(9) Unpack the above phase extraction results to obtain the differential wavefronts ΔW _x and ΔW _y in the x-direction and y-direction respectively, and perform shearing interference wavefront reconstruction to obtain 9 wavefronts of the optical system under test.

The specific theoretical discussion of the above wave aberration detection method to eliminate the multi-level diffraction error of the image plane grating is as follows:

According to the Ronchi shearing interference principle, the light intensity on the detection plane is

Among them, a ₀ is the background light intensity, k is a positive integer, a _m is the contrast ratio of the mth order diffraction of the grating in the x direction and the 0th order interference fringe, is the phase difference between the mth order diffraction and the 0th order of the grating in the x direction. When considering the phase shift, the light intensity expression can be rewritten as

in, is the phase difference between the mth order diffraction and the 0th order in the x direction, δ is the phase shift of the image plane grating 1001 along the shearing direction, then mδ represents the phase shift of the mth order diffraction when the grating moves along the shearing direction quantity.

If considering the first 9 orders of diffraction of the image plane grating, it is assumed that is the phase difference between the mth order diffraction and the 0th order in the shearing direction, m=±1,±3,…,±9. In order to suppress the influence of grating multi-level diffracted light on the phase extraction accuracy, the acquisition phase shift is 0, π, 10 interferograms of , the light intensity of each step is

According to formulas (3)~(12), it can be obtained:

Since when the phase shift is not considered, the condition of small shear amount satisfies

but The phase of the measured optical system 9 along the shear direction for:

In order to restore the two-dimensional original wavefront of the measured optical system 9, two shearing interferences need to be performed using two orthogonal shearing directions to obtain gradient information representing the measured wavefront in the x direction and the y direction respectively. and Unpack the above phase extraction results to obtain the differential wavefronts ΔW _x and ΔW _y in the x-direction and y-direction respectively, and perform shear interference wavefront reconstruction to obtain 9 wavefronts of the optical system under test.

Those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the present invention, rather than as a limitation of the present invention, as long as within the scope of the spirit of the present invention, the changes and The deformations all belong to the scope of the claims of the present invention.

Claims (3)

1. An on-line detection device for wave aberration of projection objective is characterized by comprising: the optical fiber grating comprises a rotary diffuser (2), a first focusing lens (3), an optical fiber array (4), a second focusing lens (5), a scattering optical element (6), an object plane grating plate (7), an image plane grating plate (10) and a two-dimensional photoelectric sensor (13) which are sequentially arranged along the direction of a light beam output by a light source (1);

the object plane grating plate (7) is arranged on the object plane grating displacement table (8), the image plane grating plate (10) is arranged on the image plane grating displacement table (11), the image plane grating displacement table (11) is connected with the phase shift control module (12), and the two-dimensional photoelectric sensor (13) is connected with the computer (14);

the object plane grating plate (7) is positioned on the object plane of the measured optical system (9), and the image plane grating plate (10) is positioned on the image plane of the measured optical system (9);

the object plane grating plate (7) comprises two periods P_oThe two object plane gratings are respectively a first grating (701) with grating lines along the y direction and a second grating (702) with grating lines along the x direction;

the image surface grating plate consists of an image surface grating and an image surface grating alignment mark;

the period P of the object plane grating_oAnd the period P of the image surface grating_iThe following relationship is satisfied,

P_o＝P_i·M

wherein M is the imaging magnification of the optical system (9) to be detected.

2. The projection objective wavefront aberration online detection apparatus of claim 1, characterized in that the rotating diffuser (2) is composed of a holder (203), a motor (202) and a circular diffuse scattering optical element (201) for converting coherent light or partially coherent light into incoherent light; the circular diffuse scattering optical element (201) is arranged on a motor (202) and rotates along a central shaft under the driving of the motor (202).

3. An on-line detection method for the wave aberration of a projection objective is characterized by comprising the following steps:

firstly, adjusting the height of a rotary diffuser (2) to enable a light beam emitted by a light source (1) to transmit from the upper half part of a circular diffuse scattering optical element (201);

adjusting the first focusing lens (3) and the input end of the optical fiber array (4) to enable the transmitted light of the rotating diffuser (2) to be coupled into the optical fiber array (4);

secondly, the object plane grating plate (7) is arranged on the object plane grating displacement table (8), the object plane grating plate (7) is positioned on the object plane of the measured optical system (9) by adjusting the object plane grating displacement table (8), and the first grating (701) on the object plane grating plate (7) is moved into the position of the object space view field of the measured optical system (9);

thirdly, the scattering optical element (6) is arranged at a position close to the object plane grating plate (7), and the second focusing lens (5) and the output end of the optical fiber array (4) are adjusted to enable the object plane grating plate (7) to be uniformly illuminated;

placing the image plane grating plate (10) on the image plane grating displacement table (11), moving the image plane grating displacement table (11) to enable the image plane grating plate (10) to be located on an image plane of the measured optical system (9), and moving the image plane grating (1001) into an image space optical path of the measured optical system (9);

after the two-dimensional photoelectric sensor (13) is arranged on the image plane grating plate (10), the two-dimensional photoelectric sensor is used for detecting interference fringes formed by the image plane grating (1001);

adjusting an object plane grating displacement table (8), aligning according to Moire fringes formed by a differential alignment grating on a two-dimensional photoelectric sensor (13) by an object plane grating alignment mark (703) on an object plane grating plate (7) and an image plane grating alignment mark (1002) on an image plane grating plate (10), when the two groups of fringes are completely overlapped, indicating that the alignment and parallel adjustment of a first grating (701) and the image plane grating (1001) are completed, and entering the step (c);

sixthly, moving the image plane grating (1001) of the image plane grating displacement platform (11) along the x direction for 12 times, moving for 1/12 grating periods each time, and collecting a shearing interference pattern I by a two-dimensional photoelectric sensor (13) after each movement_xkWherein k is 1,2,3 …, 12;

selecting I in_x1、I_x2、I_x3、I_x4、I_x5、I_x6、I_x7、I_x10、I_x11、I_x12The phase is calculated according to the following formula:

wherein,to be measuredThe phase position of the wave front in the x direction represents the gradient information of the measured wave front in the x direction;

seventhly, moving the object surface grating displacement table (8) to move a second grating (702) on the object surface grating plate (7) into the position of an object space view field of the measured optical system (9); adjusting an object plane grating displacement table (8), aligning according to Moire fringes formed by a differential alignment grating on a two-dimensional photoelectric sensor (13) by an object plane grating alignment mark (703) on an object plane grating plate (7) and an image plane grating alignment mark (1002) on an image plane grating plate (10), and when the two groups of fringes are completely overlapped, finishing the alignment and parallel adjustment of a second grating (702) and the image plane grating (1001), and entering the step (V);

moving an image plane grating displacement table (11) along the y direction to move an image plane grating (1001) for 12 times, moving the grating for 1/12 grating periods each time, and collecting a shearing interference pattern I by a two-dimensional photoelectric sensor (13) after each movement_ykWherein k is 1,2,3 …, 12;

selecting I in_x1、I_x2、I_x3、I_x4、I_x5、I_x6、I_x7、I_x10、I_x11、I_x12The phase is calculated according to the following formula:

wherein,representing gradient information of the measured wave front in the y direction as the phase of the measured wave front in the y direction;

ninthly, unwrapping the phase extraction result obtained in the step (c) and the step (c), and obtaining the difference wave front delta W in the x direction and the y direction respectively_xAnd Δ W_yAnd performing shearing interference wavefront reconstruction to obtain the wavefront of the detected optical system (9).