Reflection-type all-medium two-dimensional plane metering grating

Abstract

A reflective all-dielectric two-dimensional plane metering grating is characterized in that the grating sequentially comprises a grating substrate, a periodic film system, a phase matching layer and a top two-dimensional grating layer from bottom to top, and adjacent film layers are alternately stacked with high and low refractive indexes. The all-medium two-dimensional plane metering grating has the characteristics of polarization insensitivity, high chemical stability, long service life and the like, and is suitable for a plane grating measuring system under an immersed exposure condition.

Description

Technical Field

[0001] The invention relates to a two-dimensional plane grating used in the field of displacement measurement and positioning based on a plane grating ruler, in particular to a reflective all-dielectric two-dimensional plane grating. Background Art

[0002] As an important tool for micro-nano precision displacement measurement, the plane grating ruler not only has sub-micron or even nanometer resolution and accuracy, but also can perform long-range measurements of hundreds of millimeters or even meters. Compared with laser interferometers, plane grating rulers have the advantages of compact structure, high measurement repeatability, insensitivity to environmental changes, and low cost. They have been widely used in high-end lithography workpiece position measurement, precision machine tool CNC machining, robot machine vision and other fields. The two-dimensional grating is the core component of the plane grating ruler. Its diffraction efficiency, polarization characteristics, grating pattern positioning accuracy, etc. are the core factors that determine the measurement accuracy of the grating ruler. Therefore, the study of high-precision two-dimensional grating technology is of great significance to promoting the advancement of lithography technology.

[0003] In 1987, Heidenhain of Germany first launched an interference scanning linear grating ruler LS101 based on the interference measurement principle, with a measurement resolution of 0.02μm. 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 allow for relatively loose installation. In 1995, Heidenhain manufactured a two-dimensional plane grating with a period of 8μm on a glass substrate, which made it possible to measure two-dimensional displacement using a grating reading head and a grating. At the same time, the company developed the PP281 two-dimensional grating ruler based on this period two-dimensional plane grating. The measurement range of the PP281 two-dimensional grating ruler is 68mm×68mm, the measurement resolution can reach 1nm, and the measurement accuracy is ±2μm. In 1999, Optra of the United States launched the NanoGrid plane grating encoder, which uses a two-dimensional plane grating with a grating pitch of 10μm. The current maximum measurement range can reach 400mm×400mm, the highest measurement resolution can reach 0.305nm, the repeatability measurement accuracy is less than 5nm, and the measurement accuracy is less than 1um. In 2009, Heidenhain of Germany developed a large-scale two-dimensional plane grating of 400mmx400mm. The grating displacement measurement system developed based on this was first applied to the NXT:1950i lithography machine of ASML of the Netherlands, achieving large-scale measurement and 2.5nm single-machine overlay accuracy; and the plane grating measurement technology was used in the subsequent NXT:1970Ci and NXT:1980Di lithography machines to achieve 2.0nm and 1.6nm overlay accuracy. Starting from the 4th generation DUV lithography machine, subsequent high-end EUV lithography machines all use immersion lithography technology. Under the same wavelength and projection numerical aperture conditions, the immersion exposure system can obtain smaller line width and higher lithography accuracy. In the immersion lithography machine, the plane grating ruler is required to maintain the corresponding performance stability and service life in a high humidity environment. At present, the plane grating rulers used by international high-end lithography machine manufacturers mainly use two-dimensional gold-plated gratings with metal film on the surface. This type of grating is easily oxidized during long-term use and the gold film is soft, which affects its performance and life. In contrast, the all-dielectric two-dimensional plane metrology grating uses highly stable all-dielectric oxide thin film materials such as silicon oxide and tantalum oxide. Its material properties are more stable and not easy to hydrolyze. It can maintain a long service life in a high humidity environment. At the same time, its polarization insensitivity is suitable for the use of metrology gratings with multiple diffraction orders. Summary of the invention

[0004] The present invention proposes a reflective all-dielectric two-dimensional plane metrology grating, which has the characteristics of polarization insensitivity, high chemical stability and long service life, and is suitable for a plane grating measurement system under immersion exposure conditions.

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

[0006] A reflective all-dielectric two-dimensional planar metrology grating, which comprises a grating substrate, a periodic film system, a phase matching layer and a top two-dimensional grating layer from bottom to top, and adjacent film layers are alternately stacked with high and low refractive indices; the periodic film system is composed of a periodic film system high refractive index material layer and a periodic film system low refractive index material layer alternately stacked; the grating substrate and the periodic film system constitute a bottom high reflective layer, and the film system of the bottom high reflective layer is: S|(HnL) ^m |H, where S is the grating substrate material, H and L represent the optical thickness λ r / 4 periodic film system high refractive index material layer and periodic film system low refractive index material layer, λ r is the reference wavelength, m represents the number of film periods, m is a positive integer, n represents the thickness coefficient of the periodic film system low refractive index material layer, n>0; the phase matching layer is composed of high refractive index material and / or low refractive index material; the top two-dimensional grating layer is composed of high refractive index material or low refractive index material, and the period P of the grating layer in the x and y directions is x and P y The x-direction grating vector and the y-direction grating vector are orthogonal to form an angle of 90° or 45°. The width ratio of the grating top in the x-direction and y-direction is f x and f y 0.4-0.7 respectively, preferably f x and f y The periodic film system high refractive index material layer is composed of a high refractive index material, and the periodic film system low refractive index material layer is composed of a low refractive index material. Preferably, the low refractive index material used in the top grating layer, phase matching layer, and periodic film system is SiO2; the high refractive index material is HfO2 or Ta2O5.

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

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

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

[0010] 1. The grating is made of all-dielectric materials, with stable mechanical / chemical properties, long service life, minimal absorption, and high damage threshold.

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

[0012] 3. It has high polarization insensitivity, and the difference in diffraction efficiency between s- and p-polarized light is ≤2%. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0014] Figure 2 It is a schematic diagram of a cylindrical and rectangular structure in which the horizontal cross-sections of the top two-dimensional grating layer in the grating structure of the present invention are respectively.

[0015] Figure 3 It 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 cylindrical two-dimensional plane grating of Example 1 is incident at 0°.

[0016] Figure 4 These are the diffraction efficiency curves of the four diffraction orders [+1, 0], [-1, 0], [0, +1], and [0, -1] at different polarization angles at a wavelength of 633 nm when the cylindrical two-dimensional plane grating in Example 1 is incident at 0°.

[0017] Figure 5 It 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 plane grating of Example 2 is incident at 0°.

[0018] Figure 6 These are the diffraction efficiency curves of the four diffraction orders [+1, 0], [-1, 0], [0, +1], and [0, -1] at different polarization angles at a wavelength of 633 nm when the rectangular two-dimensional plane grating of Example 2 is incident at 0°.

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

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

[0021] Fig. 9 It 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 cylindrical two-dimensional plane grating with a period of 0.8um in Example 4 is incident at 0°.

[0022] Fig.10 It is the diffraction efficiency of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] at different polarization angles of the 633nm wavelength when the cylindrical two-dimensional plane grating with a period of 0.8um in Example 4 is incident at 0°.

[0023] Fig.11 It is the diffraction efficiency of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] near the 976nm band when the cylindrical two-dimensional plane grating with a period of 2.1um in Example 5 is incident at 0°.

[0024] Fig.12 It is the diffraction efficiency of the four diffraction orders [+1,0], [-1,0], [0,+1], and [0,-1] at different polarization angles of the 976nm wavelength when the cylindrical two-dimensional plane grating with a period of 2.1um in Example 5 is incident at 0°.

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

[0026] The following is a further description of the embodiments of the present invention in conjunction with the examples and drawings, but this should not limit the scope of protection of the present invention.

[0027] See also Figure 1 , Figure 1 The present invention is a schematic diagram of a reflective all-dielectric two-dimensional planar metrology grating structure. As can be seen from the figure, a reflective all-dielectric two-dimensional planar grating is characterized in that the grating includes a grating substrate 1, a periodic film system 4, a phase matching layer 5 and a top two-dimensional grating layer 6 arranged in sequence from bottom to top, and adjacent film layers with high and low refractive indices are alternately stacked; the periodic film system 4 is composed of a periodic film system high refractive index material layer 2 and a periodic film system low refractive index material layer 3 alternately stacked; the grating substrate 1 and the periodic film system 4 constitute a bottom high reflection layer, and the film system of the bottom high reflection layer is: S|(HnL) ^m |H, where S is the grating substrate 1, H and L represent the optical thickness λ r / 4 periodic film system high refractive index material layer 2 and periodic film system low refractive index material layer 3, λr is the reference wavelength, m represents the number of film periods (m=1, 2, 3…), n represents the thickness coefficient of the periodic film low refractive index material layer (n>0); the phase 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 of the grating layer in the x and y directions is x and P y The x-direction grating vector and the y-direction grating vector intersect at an angle of 90° or 45°. The x-direction grating structure has a width ratio of f x is 0.4-0.7, and the y-direction grating structure width ratio f y is 0.4-0.7. To ensure the efficiency, the symmetry requirement is |f x -f y |≤0.1. The periodic film high refractive index material layer 2 is composed of a high refractive index material, and the periodic film high refractive index material layer 3 is composed of a low refractive index material. Specifically, the horizontal cross-section of the grating ridge of the top two-dimensional grating layer 6 in the grating structure (i.e. Figure 1 The XY plane) can be a cylindrical or rectangular structure, and the grating grooves are filled with air. The typical structure is as follows Figure 2 shown.

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

[0029] The present invention adopts rigorous coupled wave theory [prior art 1: MG Moharam, et.al., J. Opt. Soc. Am. A12, 1077-1086 (1995] to calculate the spectrum curve of two-dimensional plane grating.

[0030] Embodiment 1:

[0031] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high reflection layer, and the film system of the bottom high reflection layer is: S|(HnL) ^15 |H, n = 2, S is the quartz substrate, H and L represent the optical thickness λ r / 4(λ r=430nm) of a periodic film system high refractive index material layer 2 and a periodic film system low refractive index material layer 3; the periodic film system high refractive index material layer 2 uses Ta2O5 material with a refractive index of 2.14; the periodic film system low refractive index material layer 3 is SiO2 material with a refractive index of 1.47; the grating period is 2μm, and the grating vector in the x direction and the grating vector in the y direction intersect at an angle of 90°; the phase matching layer 5 includes a 227nm physical thickness SiO2 material layer, a 81.85nm physical thickness Ta2O5 material layer and a 50nm physical thickness SiO2 material layer arranged from bottom to top; the top two-dimensional grating layer 6 is a 441nm physical thickness SiO2 material; the grating structure has a width ratio of f x and f y is 0.5, the groove structure is a cylindrical morphology with a side wall angle of 80°; the grating uses a wavelength of 633nm, and uses four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. Figure 3 The figure shows the four diffraction order efficiencies of the incident light wavelength in the band around 633nm when the polarization angle is 0° and the incident angle is 0°. The diffraction efficiency of the wavelength of 633nm 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 polarization angle is 0° for p-polarized light, and the polarization angle is 90° for s-polarized light. It can be seen from the figure that the efficiency change value of the two-dimensional plane grating is ≤0.02% when the incident polarization of the four diffraction orders changes, and the grating has excellent polarization insensitivity.

[0032] Embodiment 2:

[0033] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high reflection layer, and the film system of the bottom high reflection layer is: S|(HnL) ^15 |H, n = 2, S is the quartz substrate, H and L represent the optical thickness λ r / 4(λ r =450nm) of a periodic film system high refractive index material layer 2 and a periodic film system low refractive index material layer 3; the periodic film system high refractive index material layer 2 uses Ta2O5 material with a refractive index of 2.14; the periodic film system low refractive index material layer 3 is SiO2 material with a refractive index of 1.47; the grating period is 2μm, and the grating vector in the x direction and the grating vector in the y direction intersect at an angle of 90°; the phase matching layer 5 includes a 241nm physical thickness SiO2 material layer and a 84.9nm physical thickness Ta2O5 material layer arranged from bottom to top; the top two-dimensional grating layer 6 is a 461nm physical thickness SiO2 material; the grating structure has a width ratio of f x and f yis 0.5, the groove structure is a rectangular shape with a side wall angle of 80°; the grating uses a wavelength of 633nm, and uses four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. Figure 5 The figure shows the four diffraction order efficiencies of the incident light wavelength in the band around 633nm when the polarization angle is 90° and the incident angle is 0°. The diffraction efficiency of the wavelength of 633nm 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 polarization angle is 0° for p-polarized light, and the polarization angle is 90° for s-polarized light. It can be seen from the figure that the efficiency change value of the two-dimensional plane grating is ≤0.4% when the incident polarization of the four diffraction orders changes, and the grating has excellent polarization insensitivity.

[0034] Embodiment 3:

[0035] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high reflection layer, and the film system of the bottom high reflection layer is: S|(HnL) ^10 |H, n = 2, S is the quartz substrate, H and L represent the optical thickness λ r / 4(λ r =737nm) of a periodic film system high refractive index material layer 2 and a periodic film system low refractive index material layer 3; the periodic film system high refractive index material layer uses Ta2O5 material with a refractive index of 2.05; the periodic film system low refractive index material layer is SiO2 material with a refractive index of 1.45; the grating period is 2.048μm, and the x-direction grating vector and the y-direction grating vector intersect at an angle of 90°; the phase matching layer 5 includes a 327nm physical thickness SiO2 material layer, a 63.84nm physical thickness Ta2O5 material layer and a 30nm physical thickness SiO2 material arranged from bottom to top; the top two-dimensional grating layer 6 is a 570nm physical thickness SiO2 material; the grating structure width ratio f x and f y is 0.5, the groove structure is a cylindrical morphology with a side wall angle of 80°; the grating uses a wavelength of 976nm, and uses four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. Figure 7 The figure shows the diffraction efficiency of the four orders of the grating at the 976nm wavelength when the polarization angle is 90 degrees and the incident angle is 0 degrees. The diffraction efficiency of the 976nm wavelength band is ≥18%. Figure 8The figure shows the diffraction efficiency distribution of the grating at 976nm wavelength under different polarization angles when the incident angle is 0°. The polarization angle of 0° is p-polarized incident light, and 90° is s-polarized incident light. It can be seen from the figure that the efficiency change value of the two-dimensional plane grating is ≤0.05% when the incident polarization of the four diffraction orders changes, and the grating has excellent polarization insensitivity.

[0036] Embodiment 4:

[0037] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high reflection layer, and the film system of the bottom high reflection layer is: S|(HnL) ^10 |H, n = 1.67, S is the quartz substrate, H and L represent the optical thickness λ r / 4(λ r =520.7nm) of a periodic film system high refractive index material layer 2 and a periodic film system low refractive index material layer 3; the periodic film system high refractive index material layer uses Ta2O5 material with a refractive index of 2.05; the periodic film system low refractive index material layer is SiO2 material with a refractive index of 1.45; the grating period is 0.8μm, and the grating vector in the x direction and the grating vector in the y direction intersect at an angle of 90°; the phase matching layer 5 includes a SiO2 material layer with a physical thickness of 318nm and a Ta2O5 material layer with a physical thickness of 556nm arranged from bottom to top; the top two-dimensional grating layer 6 is a SiO2 material with a physical thickness of 639nm; the grating structure has a width ratio of f x and f y is 0.4, the groove structure is a cylindrical morphology with a side wall angle of 85°; the grating uses a wavelength of 633nm, and uses four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. Fig. 9 The figure shows the diffraction efficiency of the four orders of the grating at the 633nm wavelength when the polarization angle is 90 degrees and the incident angle is 0 degrees. The diffraction efficiency of the 633nm wavelength band is ≥24%. Fig.10 The figure shows the diffraction efficiency distribution of the grating at 633nm wavelength under different polarization angles when the incident angle is 0°. The polarization angle of 0° is p-polarized incident light, and the polarization angle of 90° is s-polarized incident light. It can be seen from the figure that the efficiency change value of the two-dimensional plane grating is ≤2% when the incident polarization of the four diffraction orders changes, and the grating has good polarization insensitivity.

[0038] Embodiment 5:

[0039] Combination Figure 1 The grating substrate 1 and the periodic film system 4 constitute a bottom high reflection layer, and the film system of the bottom high reflection layer is: S|(HnL) ^10 |H, n = 1.3, S is the quartz substrate, H and L represent the optical thickness λ r / 4(λr =920.86nm) of a periodic film system high refractive index material layer 2 and a periodic film system low refractive index material layer 3; the periodic film system high refractive index material layer uses Ta2O5 material with a refractive index of 2.05; the periodic film system low refractive index material layer is SiO2 material with a refractive index of 1.45; the grating period is 2.1μm, and the grating vector in the x direction and the grating vector in the y direction intersect at an angle of 90°; the phase matching layer 5 includes a 25nm physical thickness SiO2 material layer, a 215nm physical thickness Ta2O5 material layer, and a 70nm physical thickness SiO2 material layer arranged from bottom to top; the top two-dimensional grating layer 6 is a 545nm physical thickness SiO2 material; the grating structure width ratio f x and f y is 0.59, the groove structure is a cylindrical morphology with a side wall angle of 85°; the grating uses a wavelength of 976nm, and uses four diffraction orders: [+1,0], [-1,0], [0,+1], and [0,-1]. Fig.11 The figure shows the diffraction efficiency of the four orders of the grating at the 976nm wavelength when the polarization angle is 90 degrees and the incident angle is 0 degrees. The diffraction efficiency of the 976nm wavelength band is ≥19%. Fig.12 The figure shows the diffraction efficiency distribution of the grating at 976nm wavelength under different polarization angles when the incident angle is 0°. The polarization angle of 0° is p-polarized incident light, and 90° is s-polarized incident light. It can be seen from the figure that the efficiency change value of the two-dimensional plane grating is ≤1.5% when the incident polarization of the four diffraction orders changes, and the grating has good polarization insensitivity.

Claims

1. A reflective all-dielectric two-dimensional planar metrology grating, It is characterized in that The grating is composed of a grating substrate, a periodic film system, a phase matching layer and a top two-dimensional grating layer from bottom to top, and adjacent film layers are alternately stacked with high and low refractive indices; the periodic film system is composed of a periodic film system high refractive index material layer and a periodic film system low refractive index material layer alternately stacked; the grating substrate and the periodic film system constitute a bottom high reflective layer, and the film system of the bottom high reflective layer is: S|(HnL) ^m |H, where S is the grating substrate; H and L represent the optical thickness λ r / 4 periodic film system high refractive index material layer and periodic film system low refractive index material layer, λ r is the reference wavelength, m represents the number of film periods, m is a positive integer, n represents the thickness coefficient of the periodic film system low refractive index material layer, n>0; the phase matching layer is composed of high refractive index material and / or low refractive index material; the top two-dimensional grating is composed of high refractive index material or low refractive index material, and the period P of the grating layer in the x and y directions is x and P y The x-direction grating vector and the y-direction grating vector are orthogonal to form an angle of 90° or 45°. The width ratio of the grating top in the x-direction and y-direction is f x and f y 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.

2. The reflective all-dielectric two-dimensional planar metrology grating according to claim 1, It is characterized in that The low refractive index material used in the top grating layer, phase matching layer and periodic film system is SiO 2 ; High refractive index material is HfO 2 or 2 O 5 .

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

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

5. The reflective all-dielectric two-dimensional planar metrology grating according to claim 1, It is characterized in that |f x -f y |≤0.1。 6. The reflective all-dielectric two-dimensional planar metrology grating according to claim 1, It is characterized in that f x and f y They are 0.4-0.59 respectively.

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