CN101556431B - Translational symmetric mark and photoetching machine projection objective wave aberration in-situ detection method - Google Patents
Translational symmetric mark and photoetching machine projection objective wave aberration in-situ detection method Download PDFInfo
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Abstract
A translational symmetry mark and a method for detecting wave aberration of a projection objective of a photoetching machine in situ are provided, wherein the translational symmetry mark is composed of an X-direction translational symmetry grating mark and a Y-direction translational symmetry grating mark, and the structure of one period of the translational symmetry grating mark is as follows: each period is composed of 10 line regions with certain width which are arranged in parallel and orderly without intervals, the 1 st and the 6 th are light-tight regions, the 2 nd, the 4 th, the 8 th and the 10 th are 180-degree phase shift light-transmitting regions, and the 3 rd, the 5 th, the 7 th and the 9 th are 0-degree phase shift light-transmitting regions. The wave aberration sensitivity of the projection objective of the photoetching machine can be greatly improved by utilizing the translational symmetric phase shift mask grating mark to carry out in-situ detection on the wave aberration of the projection objective of the photoetching machine.
Description
Technical Field
The invention relates to a wave aberration in-situ detection technology for a projection objective of a lithography machine, in particular to a translational symmetric mark and a wave aberration in-situ detection method for the projection objective of the lithography machine.
Background
The lithography machine is a core device in the process of manufacturing very large scale integrated circuits. Projection objective systems are one of the most important subsystems of a lithography machine. The wave aberration of the projection objective can reduce the lithography imaging quality and reduce the lithography process window. In the imaging process of the projection objective, coma causes the space image to generate transverse position offset, and the alignment error of the photoetching machine is increased; coma can also cause line widths of the imaged pattern to be asymmetric, increasing CD non-uniformity within the exposure field of view. The spherical aberration causes the optimal focal plane of the exposed pattern to shift, which reduces the depth of focus of the lithography machine. With the continuous reduction of lithographic feature sizes, especially the use of various resolution enhancement techniques, the impact of projection objective wave aberration on lithographic imaging quality is more and more prominent. The high-precision projection objective wave aberration in-situ detection technology can provide timely and reliable data for wave aberration correction, and is an important photoetching machine technology.
TAMIS (TIS At Multiple Illumination settings) technology is one of the major technologies currently used internationally for detecting wave aberration of projection lenses of lithography machines. (see Prior Art 1, Hans van der Laan, Marcel Diriches, Henk van GreevenBroek, Elaine McCoo, free Stoffels, RichardPongers, Rob Willeberers. "Material image measurement methods for robust set-up and attenuation pulse verification." Proc. SPIE 2001, 4346, 394-407.) TAMIS technique calculates spherical aberration and coma of a projection objective by measuring the axial optimal focal plane offset and lateral position offset when the test marks are imaged, using a test mark based on a binary mask pattern. The detection precision of the technology on spherical aberration and coma aberration can reach 3nm and 2nm respectively under the condition of 3 sigma. The wave aberration detection accuracy of this technique is determined by the aberration sensitivity of the test mark. The greater the aberration sensitivity, the higher the detection accuracy thereof. The TAMIS technique selects a grating composed of a common binary mask pattern as a test mark (as shown in fig. 1), ignores the difference between the aberration sensitivities of test marks composed of different types of mask patterns, and limits further improvement of the wave aberration detection accuracy.
Based on TAMIS technology, FAN WANG et al propose an in-situ detection technology for wave aberration of a projection objective of a lithography machine based on a phase shift mask test mark. (see Prior Art 2, Fan Wang, Xiangzhao Wang, Mingying Ma, Dongqing Zhang, Weijie Shi and Jianming Hu, "Absolute measurement of project optics in a litigraphic tools by use of an alternative phase-shifting mask," application. Opt.45, 281-. According to the technology, a symmetrical phase shift mask grating with the line width of 250nm and the line space ratio of 1: 1 is used as a test mark, and the spherical aberration and the coma aberration of the imaging optical system to be tested are calculated according to an existing wave aberration calculation model. The prior art 2 improves the detection accuracy of the spherical aberration and the coma aberration of the projection objective by 20% and 30%, respectively, compared with the prior art 1, by replacing the mask patterns constituting the detection marks.
Since the prior art 2 ignores the influence of the grating structure of the phase shift mask on the wave aberration sensitivity, and does not further improve the detection precision by optimizing the grating structure, based on the prior art 2, Zicheng Qiu et al propose an asymmetric phase shift mask grating mark (as shown in fig. 3) for in-situ detection of the wave aberration of the projection objective. (see Prior Art 3, Zicheng Qiu, Xiangzhao Wang, Qiangyan Yuan, and Fan Wang, "Coma measurement by use of an alternating phase-shifting mask with a specific phase width", APPLID OPTICS, Vol.48, No.2261-269 (2009)). Ziheng Qiud et al optimize the structure of the phase shift mask grating to make the width of the phase region two thirds of the period, thereby realizing the defect of marking + -3-order diffraction light, improving the wave aberration sensitivity of the mark, and further improving the detection precision. However, the prior art 3 does not consider the situation that the higher-order diffracted light is defective, and the improvement of the detection precision by optimizing the original phase shift mask grating structure is limited, so that the principle of beam interference imaging is utilized to redesign a new grating mark, so that the higher-order diffracted light is defective, and the wave aberration sensitivity of the test mark is continuously improved, which is an effective way to improve the wave aberration in-situ detection precision.
Disclosure of Invention
The invention aims to provide a translational symmetric mark and a photoetching machine projection objective wave aberration in-situ detection method, which can improve the detection precision of the projection objective wave aberration.
The technical solution of the invention is as follows:
the utility model provides a translational symmetry grating mark, its characterized in that comprises X direction translational symmetry grating mark and Y direction translational symmetry grating mark, X direction translational symmetry grating mark's grating lines arrange along the X direction, Y direction translational symmetry grating mark's grating lines arrange along the Y direction, this translational symmetry type grating mark's a periodic structure is:
each period is composed of 10 parallel and sequential line regions without interval arrangement and with certain width, the 6 th, 7 th, 8 th, 9 th and 10 th line regions are respectively equal to the widths of the 1 st, 2 nd, 3 rd, 4 th and 5 th line regions, and the ratio of the widths of the 1 st, 2 nd, 3 rd, 4 th and 5 th line regions is as follows: 90: 481: 43: 102: 83;
the 1 st and 6 th are opaque regions, the 2 nd, 4 th, 8 th and 10 th are 180 DEG phase shift transparent regions, and the 3 rd, 5 th, 7 th and 9 th are 0 DEG phase shift transparent regions;
the value range of the period is as follows: (5.3846-0.6, 5.3846+0.6) lambda/NA, wherein lambda is the wavelength of an illumination light source of the photoetching machine, and NA is the average value of the maximum value and the minimum value in the numerical aperture variable range of a projection objective of the photoetching machine;
the transmittance of the light-transmitting area ranges from 95% to 100%.
The deviation of the phase shift amount of the light-transmitting region is ± 10%.
The optimal value of the grating period is 5.3846 lambda/NA, and the optimal values of the widths of the 1 st, 2 nd, 3 rd, 4 th and 5 th line regions are respectively as follows: 0.3033 λ/NA, 1.6208 λ/NA, 0.1449 λ/NA, 0.3437 λ/NA and 0.2797 λ/NA.
The method for detecting the wave aberration of the projection objective of the photoetching machine in situ by utilizing the translational symmetric grating mark comprises the following steps:
(1) calibrating spherical aberration, coma aberration and astigmatism sensitivity coefficients of the projection objective: calibrating wave aberration sensitivity coefficient by using photoetching simulation software PROLITH: the sensitivity coefficient changes along with the change of the numerical aperture of the projection objective and the partial coherence factor of the illumination system, the change of the illumination condition is realized by setting in PROLITH software, the change range of the partial coherence factor is 0.3-0.8, and the step length is 0.1; the numerical aperture change range is 0.5-0.8, the step length is 0.1, and 24 groups of different illumination conditions can be obtained:
{(NAi，σi)|i＝1，2......24}＝{(0.5，0.3)，(0.5，0.4)......(0.8，0.8)}。
in calibration of third-order coma Z7Sensitivity coefficient S of2(NAi，σi) When a certain Z is set7Taking the other Zernike coefficients as zero values, calculating by using photoetching simulation software to obtain the value of Z7Induced imaging position offset Δ X (NA)i，σi) Then the sensitivity coefficient S at this time2(NAi，σi) Is delta X (NA)i，σi) And Z7The ratio of (A) to (B);
calibrating S by the same method1(NAi，σi)、S3(NAi，σi)、S4(NAi，σi)、S5(NAi，σi)、S6(NAi，σi)、S7(NAi，σi)、S8(NAi，σi)、S9(NAi，σi)、S10(NAi，σi)、S11(NAi，σi)、S12(NAi，σi) (ii) a And finally, obtaining the following four sensitivity coefficient matrixes:
(2) placing and accurately positioning the translational symmetric grating mark on a mask stage, and projecting objective lens on different numerical apertures NAiAnd a partial coherence factor sigmaiImaging under the conditions: adjusting a partial coherence factor through an illumination system, wherein the variation range of the partial coherence factor is 0.3-0.8, and the step length is 0.1; the numerical aperture is adjusted through the projection objective, the variation range is 0.5-0.8, the step length is 0.1, and under 24 groups of different illumination conditions ({ (NA)i，σi) 1, 2.. 24 { (0.5, 0.3), (0.5, 0.4) · and 0.8, 0.8) } using a spatial image sensor on the workpiece stage to measure a lateral position offset Δ X in the X direction when the X-direction translational symmetry type grating mark is imaged41(NAi，σi) And the optimum focal plane offset Δ Z41(NAi，σi) Measuring the transverse position offset delta Y in the Y direction during the imaging of the Y-direction translation symmetric grating mark42(NAi，σi) And the optimum focal plane offset Δ Z42(NAi，σi)；
(3) Calculating spherical aberration and coma aberration of the projection objective according to the sensitivity matrix obtained by calibration and the offset obtained by measurement:
firstly, the imaging position deviation Delta X (NA) of the space image of the X-direction translation symmetric grating mark in the X direction is calculated by the following formulai，σi) And the imaging position deviation delta Y (NA) of the space image of the Y-direction translation symmetrical type grating mark in the Y directioni，σi) And the optimum focal plane offset Δ Zs(NAi，σi) And Δ Zhv(NAi，σi)：
ΔX(NAi，σi) To be different in
Andmeasuring the imaging position deviation Delta X of the space image of the test mark in the X direction under the condition41(NAi，σi) I.e. by
ΔX(NAi，σi)＝ΔX41(NAi，σi)；
ΔY(NAi，σi) To be different inAnd
measuring the imaging position deviation delta Y of the space image of the Y-direction translation symmetric grating mark in the Y direction under the condition42(NAi，σi) I.e. by
ΔY(NAi，σi)＝ΔY42(NAi，σi)
ΔZs(NAi，σi) To be different in
And
measured under the conditions of Δ Z41(NAi，σi) And Δ Z42(NAi，σi) Average value of (i), i.e.
ΔZs(NAi，σi)＝[ΔZ41(NAi，σi)+ΔZ42(NAi，σi)]/2；
ΔZhv(NAi，σi) To be different in
And
measured under the conditions of Δ Z41(NAi，σi) And Δ Z42(NAi，σi) Difference of difference, i.e.
ΔZhv(NAi，σi)＝ΔZ41(NAi，σi)-ΔZ42(NAi，σi)；
Then, according to the measured position offset and the calibrated sensitivity coefficient matrix, solving the following equation sets by using a least square method to obtain zernike coefficients Z2, Z7, Z14, Z3, Z8, Z15, Z4, Z9, Z16, Z5, Z12 and Z21 which represent coma, spherical aberration and astigmatism of the projection objective:
due to the adoption of the technical scheme, compared with the prior art (prior art 1 and prior art 2), the invention has the following advantages:
the even order, 3, and 5 orders diffracted light of the translationally symmetric phase shift mask grating marks are all off-order, and thus the wave aberration sensitivity of the marks is higher than that of the test marks of prior art 1 and prior art 2. As shown in fig. 10, it is understood that the linear coma aberration models of the three marks have the maximum slope of the straight line of the shift-symmetric phase shift mask grating mark, that is, the maximum coma aberration sensitivity, and the accuracy is the highest when coma aberration is detected using the mark. Through simulation calculation of the sensitivity of the mark to coma aberration, spherical aberration and astigmatism, the translational symmetric phase shift mask grating mark can be ensured to have relatively high wave aberration sensitivity, and the in-situ detection precision of the wave aberration can be improved by using the translational symmetric phase shift mask grating mark as a test mark.
Drawings
FIG. 1: schematic diagram of the test mark structure used in prior art 1.
FIG. 2: schematic diagram of test mark structure used in prior art 2.
FIG. 3: schematic diagram of test mark structure used in prior art 3.
FIG. 4: the invention is a schematic diagram of a translational symmetric grating mark.
FIG. 5: the invention relates to a structural schematic diagram of a translational symmetric grating mark in one period.
FIG. 6: curve of linear relationship of coma.
FIG. 7 is a linear relationship of spherical aberration
FIG. 8 is a linear plot of astigmatism
FIG. 9: the invention adopts a wave aberration detection system structure schematic diagram.
FIG. 10: the binary mask mark, the phase shift mask mark, and the translational symmetric phase shift mask mark have a Coma-IPE linear relationship.
FIG. 11: translational symmetry type phase shift mask grating mark pair third-order coma Z7With the range of variation of the numerical aperture and the partial coherence factor.
FIG. 12: translational symmetry type phase shift mask grating mark pair five-order coma Z14With the range of variation of the numerical aperture and the partial coherence factor.
FIG. 13: translational symmetry type phase shift mask grating mark pair third-order spherical aberration Z9With the range of variation of the numerical aperture and the partial coherence factor.
FIG. 14: translational symmetric phase shift mask grating mark pair five-order spherical aberration Z16With the range of variation of the numerical aperture and the partial coherence factor.
FIG. 15: translational symmetry type phase shift mask grating mark pair fifth-order astigmatism Z12With the range of variation of the numerical aperture and the partial coherence factor.
Detailed Description
The invention is further illustrated by the following examples and figures, without restricting the scope of the invention to these examples.
Referring first to fig. 4, fig. 4: the invention is a schematic diagram of a translational symmetric grating mark. As can be seen from the figure, the translational symmetric grating mark of the present invention is composed of an X-direction translational symmetric grating mark 41 and a Y-direction translational symmetric grating mark 42, grating lines of the X-direction translational symmetric grating mark 41 are arranged along the X-direction, grating lines of the Y-direction translational symmetric grating mark 42 are arranged along the Y-direction, and a structure of one period of the translational symmetric grating marks 41 and 42 (see fig. 5) is:
each period is composed of 10 line regions with certain width which are arranged in parallel and without intervals, the widths of the line regions of the No. 6(56), the No. 7(57), the No. 8(58), the No. 9(59) and the No. 10(510) are respectively equal to the widths of the line regions of the No. 1(51), the No. 2(52), the No. 3(53), the No. 4(54) and the No. 5(55), and the ratios of the widths of the line regions of the No. 1(51), the No. 2(52), the No. 3(53), the No. 4(54) and the No. 5(55) are as follows: 90: 481: 43: 102: 83;
the 1 st (51) th (56) th (2 st), (52 th), (4 th), (54 th), (8 th), (58) th (10 th), (510) th (3 st), (53 th), (5 th), (55 th), (7 th), (57) th (9 th), (59) th (0 th) phase shift transmission region;
the value range of the period is as follows: (5.3846-0.6, 5.3846+0.6) lambda/NA, wherein lambda is the wavelength of an illumination light source of the photoetching machine, and NA is the average value of the maximum value and the minimum value in the numerical aperture variable range of a projection objective of the photoetching machine;
the transmittance of the light transmission area ranges from 95% to 100%.
The optimal value of the width of each part in one period of the translational symmetry type phase shift mask grating is as follows: marker 51 was 0.3033 λ/NA wide, marker 52 was 1.6208 λ/NA wide, marker 53 was 0.1449 λ/NA wide, marker 54 was 0.3437 λ/NA wide, and marker 55 was 0.2797 λ/NA wide. NA is the average of the maximum and minimum values of the numerical aperture of the projection objective of the photoetching machine in the variable range.
The width of each part in one period of the grating allows deviation within +/-11.14% around the optimal value, namely all grating marks within the deviation range are regarded as the grating marks of the translational symmetry type phase shift mask.
Wave aberration in-situ detection method based on wave aberration linear model of projection objective of photoetching machine
First, based on a linear relationship model between Coma aberration and Image position offset (IPE), a linear relationship model between Spherical aberration and optimal focal plane offset (BFS), a Spherical-BFS linear model, and a linear relationship model between Astigmatism and vertical/horizontal line grating with respect to optimal focal plane offset (asm-BFS)hvLinear model) to establish a projection objective wave aberration in-situ detection linear relation model.
An optical lithography imaging system is a partially coherent imaging system for imaging an aerial or photoresist image through a projection objective under kohler illumination. In order to facilitate the discussion of imaging performance, the space domain and frequency domain Cartesian coordinates are normalized, and the system is modeled by using a Hopkins partial coherent imaging theory based on a cross transfer function. The normalized cartesian coordinate system is shown in equation (1).
Where λ is the wavelength of the monochromatic light source and NA is the image-side numerical aperture of the projection objective. Object plane coordinates
And image plane coordinatesAre respectively normalized to (x) by diffraction unit lambda/NAo，yo) And (x)i，yi). Coordinates in pupil plane
Then normalized to (f, g) by the frequency unit NA/λ. And the coordinate of each point in the object plane is zoomed according to the transverse magnification factor M, so that the coordinate value which is the same as the corresponding geometric image point on the image plane is obtained. The scalar form of the Hopkins partial coherence imaging formula is as follows:
wherein TCC (f ', g'; f ', g') is a cross-transfer function:
in the above formula, O (f ', g') is the diffraction spectrum of the mask. J (f, g) is the intensity distribution of the effective light source under kohler illumination, when using conventional partially coherent illumination:
h (f, g) is the pupil function of the projection objective, expressed as follows:
where Φ (f, g) is the projection objective wave aberration function, expressed as an orthogonal fringe zernike polynomial:
equation (6) lists the coma (Z) to be discussed7，Z14) Spherical aberration (Z)9，Z16) And astigmatism (Z)12) A zernike polynomial of (a). Wherein, coma is odd aberration, which causes the lateral position shift of the test mark space image; spherical and astigmatic differences are even aberrations that cause the best focus plane offset of the aerial image of the test mark. Δ z represents defocus of the image plane by Rayleigh length λ/NA2Is a unit. Equation (5) takes into account the effect of a high numerical aperture when calculating the aerial image on the out-of-focus plane.
When the phase shift mask grating marks are imaged through the projection objective, their transmittance function is:
the diffraction spectrum of the mark is a transmittance function t (x)0) Fourier transform of (d):
where p represents the geometric period of the phase shift mask grating, i.e., the sum of the line width and the phase field width. pw represents the width of the phase region. The conditions that the common phase shift mask grating mark and the optimized phase shift mask grating mark meet +/-1-order diffraction light double-beam interference imaging are respectively as follows:
lambda/2 (1-sigma) NA < p is less than or equal to 3 lambda/2 (sigma +1) NA and lambda/2 (1-sigma) NA < p is less than or equal to 5 lambda/2 (sigma +1) NA. Namely, it is
O(f)＝Co[δ(f-f0)-δ(f+f0)]， (9)
Wherein f is0＝1/2pand Co0.5 · i · sinc (0.25). According to the formulae (2) to (6) and (9), the intensity distribution of the label aerial image is:
I(xi，Δz)＝TCC(f0，0；f0，0)+TCC(-f0，0；f0，0)+
+exp(-i4f0xi)∫∫J(f，g)exp(-iα)exp(iβ)dfdg+， (10)
+exp(i4f0xi)∫∫J(f，g)exp(iα)exp(-iβ)dfdg
wherein,
α＝2πΦ(f+f0，g)/λ+πΔz[(f+f0)2+g2]， (11)
β＝2πΦ(f-f0，g)/λ+πΔz[(f-f0)2+g2]
approximation to the defocus term in the pupil function H (f, g): <math><mrow><msqrt><msup><mi>NA</mi><mn>2</mn></msup><mrow><mo>(</mo><msup><mi>f</mi><mn>2</mn></msup><mo>+</mo><msup><mi>g</mi><mn>2</mn></msup><mo>)</mo></mrow></msqrt><mo>≈</mo><mn>1</mn><mo>-</mo><msup><mi>NA</mi><mn>2</mn></msup><mrow><mo>(</mo><msup><mi>f</mi><mn>2</mn></msup><mo>+</mo><msup><mi>g</mi><mn>2</mn></msup><mo>)</mo></mrow><mo>/</mo><mn>2</mn><mo>.</mo></mrow></math> simplifying to obtain:
I(xi，Δz)＝2C0 2[∫∫J(f，g)cos(α-β-4πf0x)dfdg+1] (12)
separately solve the equation <math><mrow><mo>∂</mo><mi>I</mi><mrow><mo>(</mo><msub><mi>x</mi><mi>i</mi></msub><mo>,</mo><mi>Δz</mi><mo>=</mo><mn>0</mn><mo>)</mo></mrow><mo>/</mo><mo>∂</mo><msub><mi>x</mi><mi>i</mi></msub><mo>=</mo><mn>0</mn></mrow></math> And <math><mrow><mo>∂</mo><mi>I</mi><mrow><mo>(</mo><msub><mi>x</mi><mi>i</mi></msub><mo>=</mo><mn>0</mn><mo>,</mo><mi>Δz</mi><mo>)</mo></mrow><mo>/</mo><mo>∂</mo><mi>Δz</mi><mo>=</mo><mn>0</mn></mrow></math> obtaining a solution of imaging position offset IPE and optimal focal plane offset BFS:
wherein S isIPE-nAnd SBFS-nSensitivity coefficients representing an imaging position offset and an optimum focal plane offset, respectively. From the equations (13) and (14), S is an even aberrationIPE-n0 [ identical to ] or; for odd aberration, SBFS-nIs equal to 0. When the partial coherence factor sigma, the mark structure and the numerical aperture NA are fixed, the imaging position offset and the odd image difference Zernike coefficient are in a linear relation, and the optimal focal plane offset and the even image difference Zernike coefficient are in a linear relation. When p is increased to break through the limitation condition of double-beam interference imaging, the marked space image is formed by multi-beam interference, at the moment, analytical expressions of IPE and BFS cannot be obtained, and a linear relation model of the marked space image can be analyzed only through numerical calculation. Fig. 6, 7 and 8 show numerical solutions of linear relations of coma, spherical aberration and astigmatism, respectively. The tangent values of the straight line inclination angles in the graph correspond to the sensitivity coefficients of the test marks to the wave aberration respectively. In this context, the sensitivity of one wave aberration means an imaging position offset or an optimum focal plane offset per 1nm wave aberration when the other wave aberrations are zero.
It should be noted that the peak of the aerial image intensity in the two-beam interference imaging is not modulated by the higher order diffracted light, so that the IPE and BFS can be determined by the extremum method. In the actual detectionThe IPE and CD need to be determined by measuring a threshold of aerial image intensity. When BFS is determined, CD values in different defocusing planes need to be scanned, and the position of the optimal focal plane is determined according to CD deviation. Astigmatism (Z) unlike the best focal plane offset due to spherical aberration12And Z21) The resulting optimal focal plane offset includes components in both the horizontal and vertical directions, typically BFS, from the difference between the focal plane offsets of the horizontally disposed grating marks and the vertically disposed grating markshvTo decide.
Secondly, according to the analysis results of the theoretical derivation and the numerical calculation, establishing a projection objective wave aberration in-situ detection linear model as follows:
ΔX(NAi，σi)＝S1(NAi，σi)Z2+S2(NAi，σi)Z7+S3(NAi，σi)Z14，(i＝1，1，3……n)，
(15)
ΔY(NAi，σi)＝S4(NAi，σi)Z3+S5(NAi，σi)Z8+S6(NAi，σi)Z15，(i＝1，2，3……n)， (16)
ΔZs(NAi，σi)＝S7(NAi，σi)Z4+S8(NAi，σi)Z9+S9(NAi，σi)Z16，(i＝1，2，3……n)，
(17)
ΔZhv(NAi，σi)＝S10(NAi，σi)Z5+S11(NAi，σi)Z12+S12(NAi，σi)Z21，(i＝1，2，3……n)，(18)
the above equation can be represented by the following matrix equation:
wherein, Δ X (NA)i，σi) Displacement of imaging position in X direction for measuring space image of test mark under different NA and sigma conditions41(NAi，σi) I.e. by
ΔX(NAi，σi)＝ΔX41(NAi，σi)。 (23)
ΔY(NAi，σi) Displacement of imaging position in Y direction for measuring aerial image of test mark under different NA and sigma conditions42(NAi，σi) I.e. by
ΔY(NAi，σi)＝ΔY42(NAi，σi)。 (24)
ΔZs(NAi，σi) For measuring Δ Z under different NA and σ conditions41(NAi，σi) And Δ Z42(NAi，σi) Average value of (i), i.e.
ΔZs(NAi，σi)＝[ΔZ41(NAi，σi)+ΔZ42(NAi，σi)]/2。 (25)
ΔZhv(NAi，σi) For measuring Δ Z under different NA and σ conditions41(NAi，σi) And Δ Z42(NAi，σi) Difference of difference, i.e.
ΔZhv(NAi，σi)＝ΔZ41(NAi，σi)-ΔZ42(NAi，σi)。 (26)
S1(NAi，σi)、S2(NAi，σi)、S3(NAi，σi)、S4(NAi，σi)、S5(NAi，σi)、S6(NAi，σi)、S7(NAi，σi)、S8(NAi，σi)、S9(NAi，σi)、S10(NAi，σi)、S11(NAi，σi)、S12(NAi，σi) Are respectively and Z2、Z7、Z14、Z3、Z8、Z15、Z4、Z9、Z16、Z5、Z12And Z21The corresponding aberration sensitivity coefficient is defined by the following formula:
finally, according to the linear model, a photoetching machine projection objective wave aberration in-situ detection method based on the translational symmetry type phase shift mask grating mark is provided.
The method uses a detection system as shown in fig. 9. The system comprises a light source 1 for generating an illumination beam; an illumination system 2 for adjusting the beam waist size, the light intensity distribution, the partial coherence factor and the illumination mode of the light beam emitted by the light source; a mask stage 5 capable of carrying the test mask 3 and accurately positioning; a projection objective 6 which can image the test mark 4 on the test mask 3 and has an adjustable numerical aperture; the device comprises a workpiece table 7 capable of bearing a silicon wafer and having three-dimensional scanning capability and accurate positioning capability, and a spatial image sensor 8 which is arranged on the workpiece table 7 and is used for measuring the spatial image position of a test mark 4 on a test mask 3.
The light source 1 may be a uv and deep uv light source such as a mercury lamp, an excimer laser, a laser plasma light source, and a discharge plasma light source.
The illumination system 2 comprises a beam expanding lens group, a beam shaper and a beam homogenizer.
The lighting modes comprise traditional lighting, annular lighting, secondary lighting, four-level lighting and the like.
The test mark 4 is a translational symmetric phase shift mask grating mark in one aspect of the present disclosure.
The image sensor may be a CCD, photodiode array or other detector with photoelectric signal conversion capability. When measuring the offset of the space image of the test mark 4, firstly, the workpiece table 7 is focused and leveled, then, the space image formed by the test mark 4 through the projection objective is scanned in three dimensions, and the optimal focal plane offset and the imaging position offset in the focal plane of the space image are measured.
The projection objective wave aberration in-situ detection method specifically comprises the following operation steps:
(1) and calibrating the spherical coma aberration and astigmatism sensitivity coefficients of the projection objective 6. Using lithography simulation softwarePROLITH calibrates the wave aberration sensitivity coefficient. The sensitivity coefficient varies with the numerical aperture of the projection objective and the partial coherence factor of the illumination system in order to be able to utilize different illumination conditions (NA)i，σi) Measured imaging position offset (Δ X (NA))i，σi)、ΔY(NAi，σi)、ΔZs(NAi，σi) And Δ Zhv(NAi，σi) Calculating Zernike coefficient representing wave aberration of projection objective, and calibrating wave aberration sensitivity coefficient S (NA) under corresponding illumination conditioni，σi). The change of the illumination condition is realized by setting in PROLITH software, the change range of the partial coherence factor is 0.3-0.8, and the step length is 0.1; the numerical aperture change range is 0.5-0.8, the step length is 0.1, and 24 groups of different illumination conditions can be obtained: { (NA)i，σi) 1, 2.. 20 { (0.5, 0.3), (0.5, 0.4) }. The calibration method for sensitivity coefficients is illustrated as follows: in calibration of third-order coma Z7Sensitivity coefficient S of2(NAi，σi) In this case, a certain Z value can be set7Taking the other Zernike coefficients as zero values, calculating by using photoetching simulation software to obtain the value of Z7Induced imaging position offset Δ X (NA)i，σi) Then the sensitivity coefficient S at this time2(NAi，σi) Is delta X (NA)i，σi) And Z7The ratio of. S1(NAi，σi)、S3(NAi，σi)、S4(NAi，σi)、S5(NAi，σi)、S6(NAi，σi)、S7(NAi，σi)、S8(NAi，σi)、S9(NAi，σi)、S10(NAi，σi)、S11(NAi，σi)、S12(NAi，σi) Is calibrated and2(NAi，σi) Similarly. Four sensitivity systems of 20X 3 in the formulae (19) to (22) were obtainedA matrix of numbers.
(2) The test marks 4 pass through the projection objective 6 at different numerical apertures NAiAnd a partial coherence factor sigmaiImaging under the conditions. Adjusting a partial coherence factor through an illumination system 2, wherein the variation range of the partial coherence factor is 0.3-0.8, and the step length is 0.1; the numerical aperture is adjusted through the projection objective 6, the change range is 0.5-0.8, and the step length is 0.1. Under 24 different sets of lighting conditions ({ (NA)i，σi) 1, 2.. 20 { (0.5, 0.3), (0.5, 0.4) · 0.8, 0.8) } the lateral position offset Δ X in the X direction when the test mark 51 is imaged is measured by the aerial image sensor 8 on the workpiece stage 741(NAi，σi) And the optimum focal plane offset Δ Z41(NAi，σi) Measuring the amount of lateral position shift DeltaY in the Y direction when the test mark 52 is imaged42(NAi，σi) And the optimum focal plane offset Δ Z42(NAi，σi)。
(3) And calculating spherical aberration and coma aberration of the projection objective according to the sensitivity matrix obtained by calibration and the offset obtained by measurement. Firstly, the imaging position deviation Delta X (NA) of the space image of the test mark in the X direction is calculated by using the formulas (23) to (26)i，σi) And the image forming position deviation delta Y (NA) of the aerial image of the test mark in the Y directioni，σi) And the optimum focal plane offset Δ Zs(NAi，σi) And Δ Zhv(NAi，σi). Then, according to the position offset obtained by measurement and the sensitivity coefficient matrix obtained by calibration, solving equations (19) - (22) by using a least square method to obtain Zernike coefficients Z representing coma aberration, spherical aberration and astigmatism of the projection objective2、Z7、Z14、Z3、Z8、Z15、Z4、Z9、Z16、Z5、Z12And Z21。
The structure of the photoetching machine system adopted in the embodiment of the invention is shown in fig. 7, the light source 1 adopts an ArF excimer laser with the wavelength of 193nm, the illumination mode provided by the illumination system 2 is the traditional illumination, the variation range of partial coherence factors is 0.3-0.8, and the step length is 0.1. The numerical aperture of the projection objective 6 is varied within a range of 0.5-0.8, and the step length is 0.1. The test marks 4 on the test mask 3 are shift symmetric type phase shift mask grating marks, and as shown in fig. 5, the period (p) of the test marks 4 is 799nm, and the widths of 51, 53, 54, and 55 are 90nm, 481nm, 43nm, 102nm, and 83nm, respectively.
In this embodiment, the asymmetric grating of one aspect of the present invention is used to detect spherical aberration and coma aberration of a projection objective of a lithography machine, and the steps are as follows.
(1) The wave aberration sensitivity coefficient matrix of the projection objective is calibrated by utilizing lithography simulation software PROLITH, and the sensitivity coefficient matrix is obtained by the calibration method as follows:
(2) at different numerical apertures NAiAnd a partial coherence factor sigmaiMeasuring the X-direction lateral imaging position deviation amount DeltaX of the test mark 41 under the condition41(NAi，σi) And the optimum focal plane offset Δ Z41(NAi，σi) Measuring the Y-direction lateral imaging position shift amount DeltaY of the test mark 4242(NAi，σi) And the optimum focal plane offset Δ Z42(NAi，σi). Under different lighting conditions, 24 sets of data were obtained for each offset measurement.
(3) And solving equations (19) - (22) by using a least square method according to the luminance coefficient matrix obtained by calibration and the offset obtained by measurement, and calculating spherical aberration, coma aberration and astigmatism of the projection objective. The calculation method is as described in the description.
When the wave aberration of the projection objective is measured, the sensitivity matrix of the calibration test mark 4 is the key in the measurement, and the variation range of the sensitivity coefficient in the sensitivity matrix directly determines the wave aberration measurement precision, and the larger the variation range is, the higher the wave aberration measurement precision is. FIG. 11 shows 4 pairs of third-order coma Z marks of the translational symmetric phase shift mask grating used in the present invention7Sensitivity coefficient ofAperture and range of partial coherence factors. FIG. 12 shows 4 pairs of five-step coma Z marks for the translational symmetric phase shift mask grating used in the present invention14With the range of variation of the numerical aperture and the partial coherence factor. FIG. 13 shows a diagram of a translational symmetric phase shift mask grating with 4 pairs of third-order spherical aberration Z9With the range of variation of the numerical aperture and the partial coherence factor. FIG. 14 shows a diagram of 4 pairs of fifth-order spherical aberration Z of the translational symmetric phase shift mask grating used in the present invention16With the range of variation of the numerical aperture and the partial coherence factor. FIG. 15 shows a diagram of 4 pairs of fifth-order astigmatism Z of a translational symmetric phase shift mask grating mark adopted in the present invention12With the range of variation of the numerical aperture and the partial coherence factor. The detection accuracy of the wave aberration is evaluated according to the sensitivity coefficient variation range, and the detection accuracy of the spherical aberration and the coma aberration of the projection objective lens in the embodiment is obviously improved compared with the prior art 1, the prior art 2 and the prior art 3.
Claims (4)
1. The utility model provides a translational symmetry grating mark, its characterized in that comprises X direction translational symmetry grating mark (41) and Y direction translational symmetry grating mark (42), the grating lines of X direction translational symmetry grating mark (41) arrange along the X direction, the grating lines of Y direction translational symmetry grating mark (42) arrange along the Y direction, the structure of a period of this translational symmetry type grating mark (41, 42) is:
each period is composed of 10 line regions with certain width which are arranged in parallel and without intervals, the widths of the line regions of the No. 6(56), the No. 7(57), the No. 8(58), the No. 9(59) and the No. 10(510) are respectively equal to the widths of the line regions of the No. 1(51), the No. 2(52), the No. 3(53), the No. 4(54) and the No. 5(55), and the ratios of the widths of the line regions of the No. 1(51), the No. 2(52), the No. 3(53), the No. 4(54) and the No. 5(55) are as follows: 90: 481: 43: 102: 83;
the 1 st (51) th (6 th) (56) line regions are opaque regions, the 2 nd (52) th (4 th) (54) th (8 th) (58) th (10 th) (510) th line regions are 180 DEG phase-shift light-transmitting regions, and the 3 rd (53) th (5 th) (55) th (7 th) (57) th (9 th) (59) th line regions are 0 DEG phase-shift light-transmitting regions;
the value range of the period is as follows: (5.3846-0.6, 5.3846+0.6) lambda/NA, wherein lambda is the wavelength of an illumination light source of the photoetching machine, and NA is the average value of the maximum value and the minimum value in the numerical aperture variable range of a projection objective of the photoetching machine;
the transmittance of the light-transmitting area ranges from 95% to 100%.
2. The translationally symmetric grating marker of claim 1, wherein the amount of phase shift of said light transmissive region varies by ± 10%.
3. The translational symmetric grating marker of claim 1, wherein the optimal value of the grating period is 5.3846 λ/NA, and the optimal values of the widths of the line regions 1(51), 2(52), 3(53), 4(54), and 5(55) are: 0.3033 λ/NA, 1.6208 λ/NA, 0.1449 λ/NA, 0.3437 λ/NA and 0.2797 λ/NA.
4. The method for in-situ detection of the wave aberration of a projection objective of a lithography machine by using the translational symmetric grating mark as claimed in claim 1, is characterized by comprising the following steps:
(1) calibrating spherical aberration, coma aberration and astigmatism sensitivity coefficients of the projection objective: calibrating wave aberration sensitivity coefficient by using photoetching simulation software PROLITH: the sensitivity coefficient changes along with the change of the numerical aperture of the projection objective and the partial coherence factor of the illumination system, the change of the illumination condition is realized by setting in PROLITH software, the change range of the partial coherence factor is 0.3-0.8, and the step length is 0.1; the numerical aperture range of variation is 0.5-0.8, the step length is 0.1, and 24 groups of different illumination conditions can be obtained:
{(NAi，σi)|i＝1，2......24}＝{(0.5，0.3)，(0.5，0.4)......(0.8，0.8)}，
in calibration of third-order coma Z7Sensitivity coefficient S of2(NAi，σi) When a certain Z is set7Taking the other Zernike coefficients as zero values, calculating by using photoetching simulation software to obtain the value of Z7Induced imaging position offset Δ X (NA)i，σi) Then the sensitivity coefficient S at this time2(NAi，σi) Is delta X (NA)i，σi) And Z7The ratio of (A) to (B);
calibrating S by the same method1(NAi，σi)、S3(NAi，σi)、S4(NAi，σi)、S5(NAi，σi)、S6(NAi，σi)、S7(NAi，σi)、S8(NAi，σi)、S9(NAi，σi)、S10(NAi，σi)、S11(NAi，σi)、S12(NAi，σi) (ii) a And finally, obtaining the following four sensitivity coefficient matrixes:
(2) the translational symmetrical grating mark (4) is arranged and accurately positioned on a mask table (5) and is projected by an objective lens (6) at different numerical apertures NAiAnd a partial coherence factor sigmaiImaging under the conditions: adjusting a partial coherence factor through an illumination system (2), wherein the variation range of the partial coherence factor is 0.3-0.8, and the step length is 0.1; the numerical aperture is adjusted through the projection objective (6), the variation range is 0.5-0.8, the step length is 0.1, and under 24 groups of different illumination conditions ({ (NA)i，σi) 1, 2.. 24 { (0.5, 0.3), (0.5, 0.4). once. (0.8 ) } and a spatial image sensor (8) on a workpiece table (7) is used for measuring a transverse position offset quantity delta X in the X direction when the X-direction translational symmetry type grating mark (41) is imaged41(NAi，σi) And the optimum focal plane offset Δ Z41(NAi，σi) Measuring the transverse position offset delta Y in the Y direction when the Y direction translation symmetrical type grating mark (42) is imaged42(NAi，σi) And the optimum focal plane offset Δ Z42(NAi，σi)；
(3) Calculating spherical aberration and coma aberration of the projection objective according to the sensitivity matrix obtained by calibration and the offset obtained by measurement:
first, the imaging position deviation DeltaX (NA) of the aerial image of the X-direction translational symmetry type grating mark (41) in the X direction is calculated by the following formulai，σi) And the imaging position deviation delta Y (NA) of the space image of the Y-direction translation symmetrical type grating mark (42) in the Y directioni，σi) And the optimum focal plane offset Δ Zs(NAi，σi) And Δ Zhv(NAi，σi)：ΔX(NAi，σi) Displacement of imaging position in X direction of aerial image of test mark 41 measured under different NA and sigma conditions41(NAi，σi) I.e. by
ΔX(NAi，σi)＝ΔX41(NAi，σi)；
ΔY(NAi，σi) For measuring Y-direction translational symmetry type grating marks obtained under different NA and sigma conditions
(42) The image forming position deviation DeltaY of the aerial image in the Y direction42(NAi，σi) I.e. by
ΔY(NAi，σi)＝ΔY42(NAi，σi)
ΔZs(NAi，σi) For measuring Δ Z under different NA and σ conditions41(NAi，σi) And Δ Z42(NAi，σi) Average value of (i), i.e.
ΔZs(NAi，σi)＝[ΔZ41(NAi，σi)+ΔZ42(NAi，σi)]/2；
ΔZhv(NAi，σi) For measuring Δ Z under different NA and σ conditions41(NAi，σi) And Δ Z42(NAi，σi) Difference of difference, i.e.
ΔZhv(NAi，σi)＝ΔZ41(NAi，σi)-ΔZ42(NAi，σi)；
Then, according to the measured position offset and the calibrated sensitivity coefficient matrix, solving the following equation sets by using minimum two multiplication to obtain Zernike coefficients Z2, Z7, Z14, Z3, Z8, Z15, Z4, Z9, Z16, Z5, Z12 and Z21 which represent coma, spherical aberration and astigmatism of the projection objective:
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