Reflection type grating blank, manufacturing method and detection system thereof

Abstract

The invention relates to the field of optical diffraction, and provides a reflective grating blank, a manufacturing method and a detection system thereof, the reflective grating blank comprises a semi-transparent layer and a reflective layer, the semi-transparent layer is parallel to the reflective layer, the semi-transparent layer comprises a plurality of parallel lines which are arranged at equal intervals, and when a light beam irradiates the surface of the semi-transparent layer, the parallel lines are parallel to the semi-transparent layer. The lines transmit part of light beams and reflect other light beams, the light beams transmitting the semi-transparent layer irradiate the reflecting layer, and the reflecting layer reflects all the light beams. By adopting the reflective grating blank, the resolution ratio of grating pitch measurement can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of optical diffraction, and in particular to a reflective grating blank. Background Art

[0002] Reflective grating blanks are one of the most important optical components in grating scale displacement sensors. Due to their stable and reliable performance and simple structure, reflective grating blanks are often used in precision linear measurement equipment such as machine tools. Reflective grating blanks are usually made of transparent or translucent materials. The amplitude of the incident light is spatially modulated through a periodic structure. After photoelectric scanning, fine lines several microns wide can be detected and an output signal with a very small signal period can be generated, thereby achieving the detection of fine spacing. Scanning methods for reflective grating blanks include imaging scanning and interferometric scanning. The interferometric scanning principle uses the diffraction and interference of fine gratings to form a displacement measurement signal, which can be applied to gratings with a 4μm pitch.

[0003] See also Figure 1 The existing reflective grating blank includes a reflective layer, the surface of which has a plurality of spaced protrusions, the width of the protrusions are the same, the spacing between two adjacent protrusions is the same, and the plurality of protrusions together form a diffraction grating. Film, has high reflectivity in the ultraviolet to infrared band, and added or The film is used as a protective layer to prevent metal Oxidation occurs, resulting in a decrease in reflectivity.

[0004] By placing a scanning mask in front of a reflective grating blank, the grating pitch of the scanning mask can be detected. The scanning mask includes multiple parallel and spaced lines, each with a width of b and a spacing of c between two adjacent lines. The multiple lines together form a transmission grating; when the light beam passes through the scanning mask, diffraction occurs to form initial diffracted beams of similar light intensities -1, 0, and +1.

[0005] When the initial diffracted beam passes through the reflective layer of the reflective grating blank, it is diffracted and reflected to form a modulated diffracted beam. The strongest diffracted light in the modulated diffracted beam is the -1st and +1st order beams. When these -1st and +1st order beams exit the scanning mask, they interfere with each other, forming a scale interference beam consisting of multiple beams, which exit the scanning mask at different angles. When the reflective grating blank and the scanning mask undergo relative displacement, the intensity of the scale interference beam changes. A sensor converts these alternating light intensity signals into electrical signals to detect the grating pitch of the scanning mask.

[0006] However, existing reflective grating blanks can only accurately detect scanning masks with a grating pitch greater than 4 μm, but have poor detection effects on scanning masks with a grating pitch less than 4 μm, and the detection resolution of fine pitches is low. Summary of the Invention

[0007] Based on this, the purpose of the present invention is to provide a reflective grating blank, which forms a phase difference by separating the optical paths of the double grating diffraction beams, increases the light intensity change after multi-level beam interference, and greatly improves the resolution of grating pitch measurement.

[0008] A reflective grating blank comprises a semi-transparent layer and a reflective layer. The semi-transparent layer is parallel to the reflective layer and comprises a plurality of parallel lines arranged at equal intervals. When a light beam is irradiated on the surface of the semi-transparent layer, the lines transmit part of the light beam and reflect the rest. When the light beam that has passed through the semi-transparent layer is irradiated on the reflective layer, the reflective layer reflects the entire light beam.

[0009] Compared with the prior art, the reflective grating blank of the present application forms two beams with a 180° optical path difference by providing a semi-transparent layer, thereby increasing the light intensity change after multi-level beam interference and greatly improving the resolution of grating measurement.

[0010] Furthermore, a phase shift layer is included, which is arranged between the semi-transparent layer and the reflective layer to generate an optical path difference between the light beam passing through the semi-transparent layer and the light beam reflected by the semi-transparent layer.

[0011] Furthermore, the thickness of the reflective layer is 80-100 nm; the thickness of the phase-shift layer is 300-350 nm; and the thickness of the semi-transparent layer is 10-20 nm.

[0012] Furthermore, the width of each line is x, the distance between two adjacent lines is L, and the grid pitch is s=x+L, where x=L.

[0013] Furthermore, the main component of the reflective layer is The main components of the phase shift layer are or The main component of the semipermeable layer is .

[0014] Furthermore, the thickness of the phase shift layer and the wavelength of the corresponding light beam satisfy the relationship: phase difference And the optical path difference satisfies: ; The optical path difference , is the incident wavelength, n is the refractive index determined by the phase shift layer, and d is the thickness of the phase shift layer. In order to maximize the intensity interference contrast of adjacent regions, ,get ; Right now .

[0015] Furthermore, a substrate is included, and the reflective layer is arranged on the surface of the substrate to provide support for the reflective layer.

[0016] The present invention also provides a method for manufacturing the reflective grating blank as described above, comprising: Polishing the substrate surface to a flatness of less than 5 μm and a roughness of less than 1 nm; The first coating process, using Sputtering as a target material on the surface of the substrate to form a reflective layer; Second coating treatment, use sputtering as a target material on the surface of the reflective layer to form a phase shift layer; The third coating treatment, using sputtering as a target material on the surface of the phase shift layer to form a film to be determined; Glue coating: spin-coating a layer of positive photoresist on the surface of the film to be determined; Pattern exposure processing, forming an exposure pattern of a grating structure on the surface of the positive photoresist under light of a certain wavelength; Etching treatment: dry etching the exposed positive photoresist to remove the positive photoresist and the film to be determined in the exposed area to form a semi-transparent layer; Degumming treatment: using degumming liquid to remove the residual photoresist.

[0017] The present invention also provides a reflective grating blank detection system, comprising a light source, a focusing lens, a scanning mask, the reflective grating blank as described above, and a sensor; the light source continuously emits a starting light beam; the focusing lens is arranged in the direction of the starting light beam to focus the transmitted light beam; the scanning mask is arranged on one side of the focusing lens and on a different side from the light source, causing the transmitted light beam to diffract; the reflective grating blank is arranged on one side of the scanning mask and on a different side from the focusing lens, reflecting the light beam and causing it to diffract; the sensor is arranged on one side of the focusing lens and on the same side as the light source, and is used to receive the light signal and convert it into an electrical signal to detect the intensity change of the light wave.

[0018] Furthermore, it also includes a mechanical unit, which is arranged at the scanning mask or the reflective grating blank to control the scanning mask or the reflective grating blank to undergo spatial displacement, and the displacement direction is perpendicular to the initial light beam direction and the line direction of the scanning mask, so that the scanning mask and the reflective grating blank produce relative displacement.

[0019] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a reflective grating blank in the prior art.

[0021] Figure 2 It is a structural schematic diagram of the reflective grating blank detection system of the present invention.

[0022] Figure 3 It is a structural schematic diagram of a reflective grating blank displacement of half a period in the reflective grating blank detection system of the present invention.

[0023] Figure 4 This is a schematic diagram of the structure of the reflective grating blank after the gluing process during the production process of the present invention.

[0024] Figure 5 It is a schematic structural diagram of the reflective grating blank after pattern exposure treatment during the production process of the present invention.

[0025] Figure 6 This is a schematic diagram of the structure of the reflective grating blank after etching during the production process of the present invention.

[0026] Figure 7 This is a schematic diagram of the structure of the reflective grating blank after debonding during the production process of the present invention. DETAILED DESCRIPTION

[0027] The applicant carefully analyzed existing reflective grating blanks and discovered that their low resolution is due to the fact that each grating pitch shift corresponds to only one cycle of the final output electrical signal, making it only possible to detect the pitch corresponding to a single signal cycle. Therefore, the present invention attempts to modify the structure of the reflective grating blank by adding a semi-transparent layer before the reflective layer, with a phase shift layer of a certain thickness placed between the reflective and semi-transparent layers. This causes the phase shift of a portion of the initial diffracted light beam to increase by 180° after reflection from the reflective grating blank. When the reflective grating blank and the scanning mask undergo a relative displacement of one cycle, the ratio of the final output signal period to the grating pitch increases, thereby improving the resolution relative to the grating pitch.

[0028] Based on this, see Figure 2 The present invention designs a reflective grating blank detection system, which includes a light source 10, a focusing lens 20, a reflective grating blank 40, a sensor 50, a mechanical unit (not shown) and a processor (not shown) to detect the grating pitch of a scanning mask 30.

[0029] The light source 10 continuously emits an initial light beam having a wavelength of 436 nm.

[0030] The focusing lens 20 is arranged in the direction of the initial light beam to focus the transmitted light beam.

[0031] The scanning mask 30 is positioned on one side of the focusing lens 20, on a different side from the light source 10, causing the transmitted light beam to diffract. The scanning mask 30 comprises a plurality of parallel, spaced lines, each with a width b and a spacing c between adjacent lines. Together, these lines form a transmission grating. Specifically, using specific values ​​as a detection reference, the width of each line is b = 1 μm, and the spacing between adjacent lines is c = 1 μm, resulting in a grating pitch of w = b + c = 2 μm.

[0032] The reflective grating blank 40 is disposed on one side of the scanning mask 30 and on a different side from the focusing lens 20, reflecting the light beam and causing it to diffract. The reflective grating blank 40 includes a substrate 41, a reflective layer 42, a phase shift layer 43, and a semi-transparent layer 44 stacked together in sequence.

[0033] The substrate 41 is used to support the reflective layer 42 . The substrate 41 is a square quartz plate with a side length of 153 mm, a thickness of 6.35 mm, a surface flatness of 1 μm-5 μm, and a roughness of 0.5-1 nm.

[0034] The reflective layer 42 is provided on the surface of the substrate 41. The reflective layer 42 is a smooth and continuous film layer. The main components of the film layer are , with a thickness of 80-100 nm, preferably 100 nm. Compared with the reflective layer 42 of the existing reflective grating blank 40 with a protective layer As a film layer, its production process is tedious and complicated, and its production cost is much higher than that of the reflective layer 42 of the present invention.

[0035] The phase shift layer 43 is superimposed on the surface of the reflective layer 42. The phase shift layer 43 is a smooth and continuous film layer, and its main components are or , the film thickness is 300-350nm, preferably 320nm. In particular, the phase difference Determined by the optical path difference (OPD): ; The optical path difference , is the incident wavelength, n is the known refractive index of the phase shift layer 43 material, and d is the thickness of the phase shift layer 43. To maximize the light intensity interference contrast of adjacent regions, , Therefore, we get ; Right now ; For light beams of different wavelengths, such as the commonly used 436nm, 356nm, 248nm, 193nm, etc., the corresponding thickness of the phase shift layer 43 should also be different. In this embodiment, the film thickness of the phase shift layer 43 is 300-350nm, corresponding to the wavelength of 436nm.

[0036] The semi-transparent layer 44 includes a plurality of parallel and spaced lines, each of which has a width of x=1μm, and a spacing of L=μm between two adjacent lines. The plurality of lines together form a transmission grating with a grating pitch of s=x+L=2μm. It is understood that the length of the line does not affect the formation of the transmission grating, and therefore is not limited. The smaller the grating pitch, the higher the resolution that can be detected, and it is not limited to 2μm. It is understood that when the duty cycle is 50%, that is, x=s / 2, the even-order diffraction of the transmission grating is suppressed, and the intensity of the first-order diffraction is the largest. At this time, the energy utilization rate is the highest, which helps to improve the signal contrast and signal-to-noise ratio. Specifically, the main components of the film layer of the semi-transparent layer 44 are or , the film thickness is 10-20 nm, preferably 10 nm; the lines of the semi-transparent layer 44 can transmit part of the light beam and reflect the rest of the light beam.

[0037] The sensor 50 is disposed on one side of the focusing lens 20 and on the same side as the light source 10 . The sensor 50 receives the light signal and converts it into an electrical signal to detect changes in the intensity of the light wave.

[0038] The mechanical unit is used to cause relative displacement between the scanning mask 30 and the reflective grating blank 40. Specifically, the mechanical unit can be set at the scanning mask 30 or the reflective grating blank 40 to cause one of the structures to undergo spatial displacement, and the displacement direction is perpendicular to the initial light beam direction and the line direction of the scanning mask 30. Figure 3 The mechanical unit is set at the reflective grating blank 40. When the mechanical unit is working, the reflective grating blank 40 translates half a cycle, and the position of the light beam irradiated on the reflective grating blank 40 changes, from the initial light beam directly irradiating the semi-transparent layer 44 to directly irradiating the reflective layer 42, so that the initial diffracted light beams of -1 order and +1 order are irradiated on the semi-transparent layer 44, and after reflection and transmission through the semi-transparent layer 44, two beams of light with a phase difference of 180° are formed.

[0039] The processor is connected to the sensor 50 , and continuously receives light wave intensity variation data from the sensor 50 , and analyzes the data to obtain the grating pitch of the scanning mask.

[0040] The following describes in detail the operating process of the reflective grating blank detection system of the present invention: The light source 10 continuously emits an initial light beam, which is focused by the focusing lens 20 and then passes through the scanning mask 30 . When passing through the scanning mask 30 , the initial light beam is diffracted to form initial diffracted light beams of −1 order, 0 order, and +1 order.

[0041] When the mechanical unit is not working, the initial diffraction beam of order 0 is transmitted through the semi-transparent layer 44 and the phase shift layer 43 and then irradiated on the reflective layer 42, and is reflected to form a modulated beam of order 0; the initial diffraction beams of order -1 and order +1 are transmitted through the phase shift layer 43 and then directly irradiated on the reflective layer 42, and are reflected to form modulated beams of order -1 and order +1; the modulated beams of order -1, order 0 and order +1 interfere on the scanning mask 30 to form a stripe beam.

[0042] When the mechanical unit is working, the reflective grating blank 40 translates in the x direction, and the initial diffraction beam of order 0 passes through the phase shift layer 43 and irradiates the reflective layer 42. After reflection, it passes through the phase shift layer 43 again and diffracts to form modulated diffraction beams of order -1 and +1; the initial diffraction beams of order -1 and +1 irradiate the semi-transparent layer 44, and part of the beams are reflected by the semi-transparent layer 44 to form a first modulated beam; the remaining beams pass through the semi-transparent layer 44 and the phase shift layer 43 to irradiate the reflective layer 42, and are reflected by the reflective layer 42 to form a second modulated beam, and the phase difference between the second modulated beam and the first modulated beam is 180°; the modulated diffraction beam, the first modulated beam, and the second modulated beam pass through the scanning mask 30 together and interfere with each other to form a stripe beam.

[0043] The stripe light beam is focused by the focusing lens 20 and then irradiated onto the sensor 50 . The sensor 50 receives the light intensity of the stripe light beam. The processor obtains the grating pitch of the scanning mask 30 by analyzing the change of the light intensity received by the sensor 50 .

[0044] The reflective grating blank 40 of the present invention is manufactured by the following method: A layer of sputtering is deposited on the smooth surface of the substrate 41. As the main component, Elements and The reflective layer 42 is doped with an element, and then 、 or Sputtering a layer of 、 Elements as main components, and The phase shift layer 43 is doped with at least one of the elements, and finally deposited on the surface with 、 Elements as main components, and The semi-transparent layer 44 , in which at least one of the elements is a doping component, forms a reflective grating blank 40 having a phase difference of about 180° when reflecting light having a wavelength of 436 nm.

[0045] The specific steps include: Polishing of the substrate 41 surface: The surface of the substrate 41 is ground and polished to a flatness of less than 5 μm and a roughness of less than 1 nm. A square quartz plate with a side length of 153 mm and a thickness of 6.35 mm is used as the substrate 41 .

[0046] Cleaning the surface of the substrate 41: The polished surface of the substrate 41 is cleaned to remove impurities and debris generated during polishing. The substrate 41 is placed in a clean room and wet-cleaned with clean water to remove contaminants such as particles and marks.

[0047] First coating process: sputtering is performed on the surface of the substrate 41 to form a reflective layer 42. Specifically, the DC magnetron sputtering method is used for coating. The substrate 41 is placed in a sputtering chamber and a liquid is introduced into the sputtering chamber. and Mixed gas, pressure is 0.2-0.5Pa, and The flow ratio is (100-200): (2-5), the DC sputtering power of the sputtering chamber is set to 4.2kW, and high-purity The target material is sputtered onto the surface of the substrate 41 to obtain a main component of The reflective layer 42 has a thickness of 80-100 nm.

[0048] First surface cleaning: Clean the surface of the reflective layer 42 to remove impurities remaining during the coating process. Take out the substrate 41 coated with the reflective layer 42 and place it in a clean room and clean it with clean water.

[0049] Second coating process: sputtering is performed on the surface of the reflective layer 42 to form a phase shift layer 43. Specifically, the substrate 41 with the reflective layer 42 on its surface is placed in the sputtering chamber again, and a liquid is introduced into the sputtering chamber. and The mixed gas has a flow ratio of (100-200): (120-200), a pressure of 0.2-0.5 Pa, and a DC sputtering power of 1.25 kW in the sputtering chamber. The target material is sputtered onto the surface of the reflective layer 42. The atomic ratio is , and the principal components are The phase shift layer 43 has a thickness of 300-350 nm, preferably 320 nm. and The mixed gas has a flow ratio of (100-200): (20-50), a pressure of 0.2-0.5 Pa, and a DC sputtering power of 1.25 kW in the sputtering chamber. The target material is sputtered onto the surface of the reflective layer 42. The atomic ratio is , and the principal components are The phase shift layer 43 has a film thickness of 300-350 nm, preferably 320 nm.

[0050] Second surface cleaning: Clean the surface of the phase shift layer 43 to remove dust and impurities left during coating. Take out the substrate 41 coated with the reflective layer 42 and the phase shift layer 43 and place it in a clean room and clean it with clean water.

[0051] The third coating process: sputtering is performed on the surface of the phase shift layer 43 to form a film to be determined. The substrate 41 coated with the reflective layer 42 and the phase shift layer 43 is placed in the sputtering chamber, and a flow of and The mixed gas has a flow ratio of (100-200): (10-30), a pressure of 0.2-0.5 Pa, and a DC sputtering power of 3.5 kW in the sputtering chamber. High purity The surface of the targeted phase shift layer 43 is sputtered to obtain a main component of The film to be determined has a thickness of 10-20 nm.

[0052] Third surface cleaning: The surface of the film to be coated is cleaned to remove any impurities remaining from the coating. The substrate 41, which has undergone three coatings, is removed and placed in a clean room. It is then ultrasonically cleaned with isopropyl alcohol (IPA) to remove surface contaminants and dried. Isopropyl alcohol evaporates and dries easily.

[0053] Gluing: Please refer to Figure 4 A layer of positive photoresist 45 is spin-coated on the surface of the film to be determined. Spin coating is performed to a thickness of 500 nm. After the photoresist 45 is applied, the substrate 41 is baked in a 120°C oven for 20 minutes to fully evaporate the solvent. AZ1500 manufactured by Tokyo Ohka Co., Ltd. can be used as the photoresist 45.

[0054] Pattern exposure processing: please refer to Figure 5 A grating master is used to form an exposure pattern of a grating structure on the surface of the positive photoresist 45 under 436nm wavelength light. Specifically, the substrate 41 after the resin coating is exposed to 436nm wavelength light, and a developer is used to produce a grating pattern on the photoresist 45 with a grid pitch of 2μm.

[0055] Etching: See Figure 6 ,use and The mixed gas etches the positive photoresist at the exposed part, and the exposed film to be determined can be etched to form a semi-transparent layer 44, wherein and The gas flow ratio is 4:1.

[0056] Glue removal: Please refer to Figure 7 , use a stripping solution to remove the residual photoresist 45 to obtain the reflective grating blank of the present invention. As a stripping solution, the photoresist 45 in the non-exposed area is completely stripped off and removed, thereby obtaining the desired reflective grating blank 40.

[0057] The reflective phase scale grating of the present invention produces a 180° phase difference in the light beam after diffraction by the double grating by providing a semi-transparent layer, thereby increasing the ratio of the variation period of the diffracted light signal to the movement period of the reflective grating blank, thereby improving the resolution of the grating pitch measurement for the scanning mask.

[0058] The above-described embodiments merely represent the best modes of carrying out the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that variations and modifications are possible, as would be apparent to those skilled in the art, without departing from the spirit of the present invention, and the present invention is intended to encompass such variations and modifications.

Claims

1. A reflective grating blank, characterized in that: The invention comprises a semi-transparent layer and a reflective layer, wherein the semi-transparent layer is parallel to the reflective layer and comprises a plurality of parallel lines arranged at equal intervals. When a light beam is irradiated on the surface of the semi-transparent layer, the lines transmit part of the light beam and reflect the rest. When the light beam passing through the semi-transparent layer is irradiated on the reflective layer, the reflective layer reflects the entire light beam.

2. The reflective grating blank according to claim 1, wherein: The invention also includes a phase shift layer, which is arranged between the semi-transmissive layer and the reflective layer to generate an optical path difference between the light beam passing through the semi-transmissive layer and the light beam reflected by the semi-transmissive layer.

3. The reflective grating blank according to claim 2, wherein: The thickness of the reflective layer is 80-100 nm; the thickness of the phase-shift layer is 300-350 nm; and the thickness of the semi-transparent layer is 10-20 nm.

4. The reflective grating blank according to claim 3, wherein: The width of each line is x, the distance between two adjacent lines is L, and the grid pitch is s=x+L, where x=L.

5. The reflective grating blank according to claim 4, wherein: The main components of the reflective layer are The main components of the phase shift layer are or The main component of the semipermeable layer is .

6. The reflective grating blank according to claim 5, wherein: The thickness of the phase shift layer and the wavelength of the corresponding light beam satisfy the relationship: Phase difference And the optical path difference satisfies: ； The optical path difference , is the incident wavelength, n is the refractive index determined by the phase shift layer, and d is the thickness of the phase shift layer. In order to maximize the intensity interference contrast of adjacent regions, ,get ； Right now .

7. The reflective grating blank according to claim 6, wherein: A substrate is also included, and the reflective layer is disposed on a surface of the substrate to provide support for the reflective layer.

8. A method for manufacturing a reflective grating blank according to any one of claims 1 to 7, characterized in that: include: Polishing the substrate surface to a flatness of less than 5 μm and a roughness of less than 1 nm; The first coating process, using Sputtering as a target material on the surface of the substrate to form a reflective layer; Second coating treatment, use sputtering as a target material on the surface of the reflective layer to form a phase shift layer; The third coating treatment, using sputtering as a target material on the surface of the phase shift layer to form a film to be determined; Glue coating: spin-coating a layer of positive photoresist on the surface of the film to be determined; Pattern exposure processing, forming an exposure pattern of a grating structure on the surface of the positive photoresist under light of a certain wavelength; Etching treatment: dry etching the exposed positive photoresist to remove the positive photoresist and the film to be determined in the exposed area to form a semi-transparent layer; Degumming treatment: using degumming liquid to remove the residual photoresist.

9. A reflective grating blank detection system, characterized by: The invention comprises a light source, a focusing lens, a scanning mask, a reflective grating blank according to any one of claims 1 to 7, and a sensor; the light source continuously emits a starting light beam; the focusing lens is arranged in the direction of the starting light beam to focus the transmitted light beam; the scanning mask is arranged on one side of the focusing lens and on a different side from the light source, causing the transmitted light beam to diffract; the reflective grating blank is arranged on one side of the scanning mask and on a different side from the focusing lens, reflecting the light beam and causing it to diffract; the sensor is arranged on one side of the focusing lens and on the same side as the light source, and is used to receive the light signal and convert it into an electrical signal to detect the intensity change of the light wave.

10. The reflective grating blank detection system according to claim 9, characterized in that: It also includes a mechanical unit, which is arranged at the scanning mask or the reflective grating blank to control the scanning mask or the reflective grating blank to undergo spatial displacement. The displacement direction is perpendicular to the direction of the initial light beam and the line direction of the scanning mask, so that the scanning mask and the reflective grating blank produce relative displacement.

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