Reflective all-dielectric two-dimensional planar metrology grating

Abstract

The application discloses a reflective full-dielectric two-dimensional planar metrology grating, characterized in that the grating is sequentially provided with a grating base, a periodical film system, a phase matching layer and a top two-dimensional grating layer from bottom to top, and high and low refractive indexes of adjacent film layers are alternately stacked. The full-dielectric two-dimensional planar metrology grating has the characteristics of polarization insensitivity, high chemical stability and long service life, and is suitable for a planar grating measurement system under an immersion exposure condition.

Description

TECHNICAL FIELD

[0001] The present application relates to a two-dimensional planar grating used in the field of displacement measurement positioning based on planar grating ruler, in particular to a reflective all-dielectric two-dimensional planar grating. BACKGROUND

[0002] As an important tool for micro-nano precision displacement measurement, planar grating ruler not only has sub-micron or even nanometer resolution and accuracy, but also can perform long-range measurement of hundreds of millimeters or even meters. Compared with laser interferometer, planar grating ruler has the advantages of compact structure, high measurement repeatability, low sensitivity to environmental changes, low cost, and has been widely used in high-end lithography machine worktable position measurement, precision machine tool numerical control machining, robot machine vision and other fields. Two-dimensional grating is the core component of planar grating ruler, and its diffraction efficiency, polarization characteristics, grating pattern positioning accuracy, etc. are the core to determine the measurement accuracy of the grating ruler. Therefore, the research on high-precision two-dimensional grating technology has great significance for promoting the progress of lithography machine technology.

[0003] In 1987, the German Heidenhain company first introduced an interference scanning linear grating ruler LS101 based on the interference measurement principle, with a measurement resolution of 0.02 μm. Unlike the early geometric measurement principle based on Moiré fringes, the interference measurement principle uses a phase-type diffraction grating with a smaller period, which can achieve nanometer-level measurement and allows for more relaxed installation. In 1995, the Heidenhain company manufactured an 8 μm period two-dimensional planar grating on a glass substrate, which made it possible to realize two-dimensional displacement measurement using one grating reading head and one grating. At the same time, the company developed a PP281 type two-dimensional grating ruler based on this period two-dimensional planar grating. The measurement range of the PP281 type two-dimensional grating ruler is 68 mm x 68 mm, and the measurement resolution can reach 1 nm, with a measurement accuracy of ±2 μm. In 1999, the American Optra company introduced the NanoGrid planar grating encoder, which uses a two-dimensional planar grating with a grating pitch of 10 μm. The current maximum measurement range can reach 400 mm x 400 mm, the highest measurement resolution can reach 0.305 nm, the repeatability measurement accuracy is less than 5 nm, and the measurement accuracy is less than 1 um. In 2009, the German Heidenhain company developed a large two-dimensional planar grating of 400 mm x 400 mm, and based on this, a grating displacement measurement system was developed, which was first applied to the NXT:1950i type lithography machine of the Dutch ASML company, realizing large range measurement and 2.5 nm single machine overlay accuracy; and in the subsequent NXT:1970Ci, NXT:1980Di type lithography machines, the planar grating measurement technology was used to realize 2.0 nm, 1.6 nm overlay accuracy. From the 4th generation DUV lithography machine to the subsequent high-end EUV lithography machine, immersion lithography technology is used. Under the same wavelength and projection numerical aperture conditions, the immersion exposure system can obtain smaller line width and higher lithography precision. In the immersion lithography machine, the planar grating ruler is required to maintain corresponding performance stability and service life in a high humidity environment. At present, the planar grating ruler used by international high-end lithography machine manufacturers is mainly a two-dimensional gold-coated grating with a metal thin film coated on the surface. This type of grating is easily oxidized on the surface during long-term use, and the gold thin film is relatively soft, which affects its performance and service life. In contrast, the all-dielectric two-dimensional planar measurement grating uses high-stability all-dielectric oxide thin film materials such as silicon oxide and tantalum oxide, which have more stable material properties and are not easily hydrolyzed. They can maintain a long service life in a high humidity environment, and are not sensitive to polarization and suitable for the use requirements of multiple diffraction orders of measurement gratings. SUMMARY

[0004] This invention proposes a reflective all-dielectric two-dimensional planar metrological grating, which features polarization insensitivity, high chemical stability, and long service life, and is suitable for planar grating measurement systems under immersion exposure conditions.

[0005] The technical solution of the present invention is as follows:

[0006] A reflective all-dielectric two-dimensional planar metrological grating is disclosed. From bottom to top, the grating comprises a grating substrate, a periodic film system, a matching layer, and a top two-dimensional grating layer, with adjacent layers of alternating high and low refractive indices. The periodic film system is composed of alternating layers of high-refractive-index and low-refractive-index materials. The grating substrate and the periodic film system form a bottom high-reflectivity layer, the film system of which is: S|(HnL). ^m |H, where S is the grating substrate material, and H and L represent optical thicknesses of λ, respectively. r / 4 periodic film system high refractive index material layer and periodic film system low refractive index material layer, λ r The reference wavelength is denoted by m, which represents the number of film periods and is a positive integer. n represents the thickness coefficient of the low-refractive-index material layer in the periodic film system, where n > 0. The matching layer is composed of high-refractive-index and / or low-refractive-index materials. The top two-dimensional grating layer is composed of high-refractive-index or low-refractive-index materials, and the period P in the x and y directions of this grating layer is... x and P y Equal, both ranging from 800 to 2100 nanometers, with the x-direction grating vector and y-direction grating vector orthogonal at an angle of 90° or 45°, and the area ratio f at the top of the grating in the x and y directions. x and f y The values ​​are 0.4-0.7, with f being preferred. x and f y The values ​​are 0.4-0.59 respectively. The high-refractive-index material layer of the periodic film system is composed of a high-refractive-index material, and the low-refractive-index material layer of the periodic film system is composed of a low-refractive-index material. Preferably, the low-refractive-index material used in the top grating layer, the matching layer, and the periodic film system is SiO2; the high-refractive-index material is HfO2 or Ta2O5.

[0007] Optionally, the horizontal cross-section of the grating ridge of the top two-dimensional grating layer is circular or rectangular.

[0008] Optionally, the grating substrate is a low-expansion microcrystalline or quartz glass.

[0009] Preferably, |f x -f y |≤0.1. This invention has the following beneficial technical effects:

[0010] 1. The grating uses all-dielectric materials, which have stable mechanical / chemical properties, long service life, minimal absorption, and high damage resistance threshold.

[0011] 2. The grating has high diffraction efficiency in the operating band (efficiency of each order ≥ 17%), and the efficiency of each order is uniform.

[0012] 3. It has high polarization insensitivity, with a diffraction efficiency difference of ≤2% between s and p polarized light. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the reflective all-dielectric two-dimensional planar metrological grating structure of the present invention.

[0014] Figure 2 This is a schematic diagram of the top two-dimensional grating layer in the grating structure of the present invention, with horizontal cross-sections of a cylinder and a rectangle, respectively.

[0015] Figure 3 The diffraction efficiency curves of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] near the 633nm wavelength band when the cylindrical two-dimensional planar grating of Example 1 is incident at 0°.

[0016] Figure 4 The diffraction efficiency curves of four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] are shown for a cylindrical two-dimensional planar grating at 0° incident wavelength with different polarization angles at a wavelength of 633nm in Example 1.

[0017] Figure 5 This is the diffraction efficiency curve of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] near the 633nm band when the rectangular two-dimensional planar grating is incident at 0°.

[0018] Figure 6 The diffraction efficiency curves for four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] are shown for a rectangular two-dimensional planar grating at 0° incident light and a wavelength of 633nm under different polarization angles.

[0019] Figure 7 The diffraction efficiency curves of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] near the 976nm band when the cylindrical two-dimensional planar grating of Example 3 is incident at 0°.

[0020] Figure 8 This refers to the diffraction efficiency of four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] at different polarization angles when the cylindrical two-dimensional planar grating is incident at 0° with a wavelength of 976nm in Example 3.

[0021] Figure 9 This is the diffraction efficiency curve of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] near the 633nm wavelength when the 0.8µm periodic cylindrical two-dimensional planar grating is incident at 0°.

[0022] Figure 10 This refers to the diffraction efficiency of four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] at different polarization angles when a 0° incident 0.8µm cylindrical two-dimensional planar grating with a wavelength of 633nm is used in Example 4.

[0023] Figure 11 The diffraction efficiency of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] near the 976nm band when the 2.1µm periodic cylindrical two-dimensional planar grating is incident at 0°. This is the diffraction efficiency of Example 5.

[0024] Figure 12 The diffraction efficiency of four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] is obtained for a 2.1µm cylindrical two-dimensional planar grating with a 0° incident wavelength of 976nm under different polarization angles.

[0025] In the figure: 1-grating substrate, 2-periodic high-refractive-index material layer, 3-periodic low-refractive-index material layer, 4-periodic film system, 5-material site matching layer, 6-low-refractive-index top grating layer, Px and Py are the grating periods in the x and y directions, respectively, and fx and fy are the grating structure aspect ratios in the x and y directions, respectively (the ratio of the width of the grating strips to the grating period). Detailed Implementation

[0026] The embodiments of the present invention will be further described below with reference to the examples and accompanying drawings, but these should not be construed as limiting the scope of protection of the present invention.

[0027] Please see Figure 1 , Figure 1 This is a schematic diagram of the reflective all-dielectric two-dimensional planar metrological grating structure of the present invention. As shown in the figure, a reflective all-dielectric two-dimensional planar grating is characterized in that the grating includes, from bottom to top, a grating substrate 1, a periodic film system 4, a matching layer 5, and a top two-dimensional grating layer 6, with adjacent film layers alternately stacked with high and low refractive indices; the periodic film system 4 is composed of alternating layers of periodic film system high refractive index material 2 and periodic film system low refractive index material 3; the grating substrate 1 and the periodic film system 4 constitute a bottom high-reflectivity layer, the film system of which is: S|(HnL). ^m |H, where S is the grating substrate 1, and H and L represent optical thicknesses of λ, respectively. r / 4 periodic film system high refractive index material layer 2 and periodic film system low refractive index material layer 3, λr For the reference wavelength, m represents the number of film layers (m = 1, 2, 3…), and n represents the thickness coefficient of the low-refractive-index material layer of the periodic film system (n > 0); the matching layer 5 is composed of high-refractive-index material and / or low-refractive-index material; the top two-dimensional grating layer 6 is composed of high-refractive-index material or low-refractive-index material, and the grating period P in the x and y directions of this grating layer is… x and P y Equal in size, both ranging from 800 to 2100 nanometers, with the x-direction grating vector and y-direction grating vector intersecting at an angle of 90° or 45°, and the x-direction grating structure having an aspect ratio f. x The y-direction grating structure has a coverage ratio of 0.4-0.7. y The value is 0.4-0.7, to ensure efficiency symmetry requirements |f x -f y |≤0.1. The periodic film system high refractive index material layer 2 is composed of a high refractive index material, and the periodic film system high refractive index material layer 3 is composed of a low refractive index material. Specifically, the cross-section of the grating ridge in the top two-dimensional grating layer 6 of the grating structure in the horizontal direction (i.e., Figure 1 The XY plane can be a cylindrical or rectangular structure, with air filling the grating grooves. A typical structure is shown below. Figure 2 As shown.

[0028] The low-refractive-index material is SiO2; the high-refractive-index material is HfO2 or Ta2O5.

[0029] This invention uses rigorous coupled-wave theory [Prior Art 1: MG Moharam, et al., J. Opt. Soc. Am. A12, 1077-1086 (1995)] to calculate the spectral curve of a two-dimensional planar grating.

[0030] Example 1:

[0031] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high-reflectivity layer, and the film system of the bottom high-reflectivity layer is: S|(HnL). ^15 |H, n=2, S is a quartz substrate, H and L represent optical thicknesses of λ respectively. r / 4(λ rThe grating consists of a periodic high-refractive-index material layer 2 (430 nm thick) and a periodic low-refractive-index material layer 3; the periodic high-refractive-index material layer 2 uses Ta2O5 material with a refractive index of 2.14; the periodic low-refractive-index material layer 3 is SiO2 material with a refractive index of 1.47; the grating period is 2 μm, and the grating vectors in the x and y directions intersect at a 90° angle; the matching layer 5 includes a 227 nm thick SiO2 material layer, an 81.85 nm thick Ta2O5 material layer, and a 50 nm thick SiO2 material layer arranged from bottom to top; the top two-dimensional grating layer 6 is made of 441 nm thick SiO2 material; the grating structure has a fill factor f. x and f y The value is 0.5, and the groove structure is a cylindrical shape with 80° sidewall angles; the grating uses a wavelength of 633nm and four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. For example... Figure 3 The figure shows the diffraction efficiency of four diffraction orders in the wavelength band near 633nm when the polarization angle is 0° and the incident angle is 0°. The diffraction efficiency for the 633nm wavelength shown in the figure is ≥18%. Figure 4 The figure shows the efficiency distribution of four diffraction orders with an incident angle of 0°, an incident wavelength of 633nm, and a polarization angle ranging from 0° to 90°. Here, the light at 0° polarization is p-polarized, and the light at 90° polarization is s-polarized. The figure shows that the efficiency change of the two-dimensional planar grating is ≤0.02% when the incident polarization changes in the four diffraction orders, indicating that the grating has excellent polarization insensitivity.

[0032] Example 2:

[0033] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high-reflectivity layer, and the film system of the bottom high-reflectivity layer is: S|(HnL). ^15 |H, n=2, S is a quartz substrate, H and L represent optical thicknesses of λ respectively. r / 4(λ r The grating consists of a periodic high-refractive-index material layer 2 (approximately 450 nm thick) and a periodic low-refractive-index material layer 3. The high-refractive-index material layer 2 is made of Ta₂O₅ with a refractive index of 2.14; the low-refractive-index material layer 3 is made of SiO₂ with a refractive index of 1.47. The grating period is 2 μm, and the grating vectors in the x and y directions intersect at a 90° angle. The matching layer 5 includes a 241 nm thick SiO₂ material layer and an 84.9 nm thick Ta₂O₅ material layer arranged from bottom to top. The top two-dimensional grating layer 6 is made of 461 nm thick SiO₂ material. The grating structure has a fill factor of f. x and f yThe value is 0.5, and the groove structure is a rectangular shape with 80° sidewall corners; the grating uses a wavelength of 633nm and four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. Figure 5 The diagram shows the diffraction efficiency of four diffraction orders in the wavelength band near 633nm when the polarization angle is 90° and the incident angle is 0°. The diffraction efficiency for the 633nm wavelength shown in the figure is ≥19%. Figure 6 The figure shows the efficiency distribution of four diffraction orders with an incident angle of 0°, an incident wavelength of 633nm, and a polarization angle ranging from 0° to 90°. Here, the light at 0° polarization is p-polarized, and the light at 90° polarization is s-polarized. The figure shows that the efficiency change of the two-dimensional planar grating is ≤0.4% when the incident polarization changes across the four diffraction orders, indicating that the grating exhibits excellent polarization insensitivity.

[0034] Example 3:

[0035] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high-reflectivity layer, and the film system of the bottom high-reflectivity layer is: S|(HnL). ^10 |H, n=2, S is a quartz substrate, H and L represent optical thicknesses of λ respectively. r / 4(λ r The grating consists of a periodic high-refractive-index material layer 2 (737 nm thick) and a periodic low-refractive-index material layer 3; the periodic high-refractive-index material layer uses Ta2O5 material with a refractive index of 2.05; the periodic low-refractive-index material layer is SiO2 material with a refractive index of 1.45; the grating period is 2.048 μm, and the grating vectors in the x and y directions intersect at a 90° angle; the matching layer 5 includes a 327 nm thick SiO2 material layer, a 63.84 nm thick Ta2O5 material layer, and a 30 nm thick SiO2 material layer arranged from bottom to top; the top two-dimensional grating layer 6 is a 570 nm thick SiO2 material; the grating structure has an aspect ratio f. x and f y The value is 0.5, and the groove structure is a cylindrical shape with 80° sidewall angles; the grating uses a wavelength of 976nm and four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. For example... Figure 7 The figure shows the diffraction efficiency of the four orders of a wavelength grating near 976nm when the polarization angle is 90 degrees and the incident angle is 0°. The diffraction efficiency at 976nm is ≥18%. Figure 8The figure shows the diffraction efficiency distribution of the grating at a wavelength of 976 nm under different polarization angles, with an incident angle of 0°. The polarization angle of 0° represents p-polarized incident light, and 90° represents s-polarized incident light. The figure shows that the efficiency change of the two-dimensional planar grating is ≤0.05% when the incident polarization changes in the four diffraction orders, indicating that the grating has excellent polarization insensitivity.

[0036] Example 4:

[0037] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high-reflectivity layer, and the film system of the bottom high-reflectivity layer is: S|(HnL). ^10 |H, n=1.67, S is a quartz substrate, H and L represent optical thicknesses of λ respectively. r / 4(λ r The grating consists of a periodic high-refractive-index material layer 2 (520.7 nm thick) and a periodic low-refractive-index material layer 3; the periodic high-refractive-index material layer uses Ta2O5 material with a refractive index of 2.05; the periodic low-refractive-index material layer is SiO2 material with a refractive index of 1.45; the grating period is 0.8 μm, and the grating vectors in the x and y directions intersect at a 90° angle; the matching layer 5 includes a 318 nm thick SiO2 material layer and a 556 nm thick Ta2O5 material layer arranged from bottom to top; the top two-dimensional grating layer 6 is made of 639 nm thick SiO2 material; the grating structure has an aspect ratio f. x and f y The value is 0.4, and the groove structure is a cylindrical morphology with a sidewall angle of 85°; the grating uses a wavelength of 633nm and four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. For example... Figure 9 The figure shows the diffraction efficiency of the four orders of a wavelength grating near 633nm when the polarization angle is 90 degrees and the incident angle is 0°. The diffraction efficiency at 633nm is shown to be ≥24%. Figure 10 The figure shows the diffraction efficiency distribution of the grating at a wavelength of 633 nm under different polarization angles, with an incident angle of 0°. The polarization angle of 0° represents p-polarized incident light, and 90° represents s-polarized incident light. The figure shows that the efficiency change of the two-dimensional planar grating is ≤2% when the incident polarization changes in the four diffraction orders, indicating that the grating has good polarization insensitivity.

[0038] Example 5:

[0039] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high-reflectivity layer, and the film system of the bottom high-reflectivity layer is: S|(HnL). ^10 |H, n=1.3, S is a quartz substrate, H and L represent optical thicknesses of λ. r / 4(λr The grating consists of a periodic high-refractive-index material layer 2 (920.86 nm) and a periodic low-refractive-index material layer 3; the periodic high-refractive-index material layer uses Ta2O5 material with a refractive index of 2.05; the periodic low-refractive-index material layer is SiO2 material with a refractive index of 1.45; the grating period is 2.1 μm, and the grating vectors in the x and y directions intersect at a 90° angle; the matching layer 5 includes a 25 nm physically thick SiO2 material layer, a 215 nm physically thick Ta2O5 material layer, and a 70 nm physically thick SiO2 material layer arranged from bottom to top; the top two-dimensional grating layer 6 is made of 545 nm physically thick SiO2 material; the grating structure has an aspect ratio f. x and f y The value is 0.59, and the groove structure is a cylindrical shape with a sidewall angle of 85°; the grating uses a wavelength of 976nm and four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. Figure 11 The figure shows the diffraction efficiency of the four orders of a wavelength grating near 976nm when the polarization angle is 90 degrees and the incident angle is 0°. The diffraction efficiency at 976nm is ≥19%. Figure 12 The figure shows the diffraction efficiency distribution of the grating at a wavelength of 976 nm under different polarization angles, with an incident angle of 0°. The polarization angle of 0° represents p-polarized incident light, and 90° represents s-polarized incident light. The figure shows that the efficiency change of the two-dimensional planar grating is ≤1.5% when the incident polarization changes across the four diffraction orders, indicating that the grating exhibits good polarization insensitivity.

Claims

1. A reflective all-dielectric two-dimensional planar metrological grating, characterized in that, The grating consists of, from bottom to top, a grating substrate, a periodic film system, a matching layer, and a top two-dimensional grating layer, with adjacent layers of high and low refractive indices stacked alternately. The periodic film system is composed of alternating layers of high-refractive-index material and low-refractive-index material. The grating substrate and the periodic film system form a bottom high-reflectivity layer, the film system of which is: S|(HnL). ^m |H, where S is the grating substrate; H and L represent optical thicknesses of λ, respectively. r / 4 periodic film system high refractive index material layer and periodic film system low refractive index material layer, λ r The reference wavelength is denoted by m, which represents the number of film periods and is a positive integer. n represents the thickness coefficient of the low-refractive-index material layer in the periodic film system, where n > 0. The matching layer is composed of high-refractive-index and / or low-refractive-index materials. The top two-dimensional grating is composed of high-refractive-index or low-refractive-index materials, and the period P of this grating layer in both the x and y directions is... x and P y Equal, both ranging from 800 to 2100 nanometers, with the x-direction grating vector and y-direction grating vector orthogonal at an angle of 90° or 45°, and the area ratio f at the top of the grating in the x and y directions. x and f y The values ​​are 0.4-0.7 respectively; the periodic film system high refractive index material layer is composed of high refractive index material, and the periodic film system low refractive index material layer is composed of low refractive index material; The low-refractive-index material used in the top grating layer, the matching layer, and the periodic film system is SiO2; the high-refractive-index material is HfO2 or Ta2O5.

2. The reflective all-dielectric two-dimensional planar metrological grating according to claim 1, characterized in that, The horizontal cross-section of the grating ridge of the top two-dimensional grating layer is circular or rectangular.

3. The reflective all-dielectric two-dimensional planar metrological grating according to claim 1, characterized in that, The grating substrate is a low-expansion microcrystalline or quartz glass.

4. The reflective all-dielectric two-dimensional planar metrological grating according to claim 1, characterized in that, |f x -f y |≤0.1。 5. The reflective all-dielectric two-dimensional planar metrological grating according to claim 1, characterized in that, f x and f y The values ​​are 0.4 and 0.59 respectively.

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