Glass diffraction grating and method of manufacturing the same

Abstract

Provided is a method for producing a glass diffraction grating having a groove aspect ratio of 2 or more and a period of 10 micrometers or less. The method is a method for producing a borosilicate glass or barium borosilicate glass diffraction grating having a period of 0.2 micrometers to 10 micrometers and a groove aspect ratio of 2 or more, wherein the method for producing the glass diffraction grating comprises the following steps: a step of forming a grating on the surface of a silicon substrate; a step of heating to about 1,000°C and exposing to water vapor to thereby form an oxide film on the surface of the grating; a step of removing the oxide film; a step of anodically bonding the face of the silicon substrate having the grating to one face of a glass plate; a step of heating the silicon substrate and the glass plate after bonding in a manner such that the glass melts and fills in the valleys of the grating composed of silicon; a step of polishing the opposite faces of the respective bonded faces of the silicon substrate and the glass plate; and a step of removing silicon from the glass plate by selective etching.

Description

Technical Field

[0001] This invention relates to glass diffraction gratings and their manufacturing methods. Background Technology

[0002] For example, there is a demand for transmission-type diffractive optical elements with large angular dispersion used in spectrometers for astronomical observations in artificial satellite orbits and for lunar and planetary probes. To manufacture such transmission-type diffractive optical elements with large angular dispersion and high efficiency, it is necessary to use rectangular (volume binary) or trapezoidal diffraction gratings made of glass with high radiation resistance, having a groove aspect ratio of 2 or higher and a period of 0.2 micrometers to 10 micrometers.

[0003] In the prior art, there is a known method for fabricating deep-groove diffraction gratings on quartz glass by plasma etching using a metal film such as chromium (Cr) as a mask. However, the above method has the following problems.

[0004] First, plasma etching of quartz glass primarily utilizes ion bombardment; therefore, when processing deep-groove diffraction gratings, the quartz glass is damaged. Consequently, it is difficult to optically smooth the grating surface. Furthermore, the quartz glass removed by plasma etching re-adheres onto the grating walls, further deteriorating the surface roughness.

[0005] Secondly, if the groove becomes deeper, the mask material needs to have higher toughness. If the mask's toughness is insufficient, the cross-sectional shape of the groove will easily become conical as the mask pattern becomes thinner. If the thickness of the chromium (Cr) film is increased to improve the mask's toughness, the film itself will crack or peel off.

[0006] Third, as the groove becomes deeper, fewer ions reach the bottom surface, which serves as the machining surface. Ions that do not reach the bottom surface cut the side surfaces, causing the side surfaces of the ridge section to become concave (bowing) in shape. Conical or bow-shaped designs that deviate from the intended design worsen optical properties.

[0007] Due to the aforementioned problems, it is difficult to manufacture diffraction gratings with an aspect ratio of 2 or higher using the methods described above.

[0008] As another method for manufacturing high aspect ratio glass diffraction gratings, a method using SOQ (Silicon on Quartz) substrates has been developed (e.g., Patent Document 1). However, in the method of Patent Document 1, it is difficult to completely oxidize silicon to produce silicon dioxide (quartz glass: SiO2). The refractive index of the incompletely oxidized silicon (silicon monoxide: SiO, silicon trioxide: Si2O3, etc.) is higher than that of quartz glass (nd = 1.46) (SiO: nd = 1.97), resulting in significantly different design values ​​and properties. Furthermore, during the cooling process from the oxidation temperature (around 1000°C) to room temperature, the diffraction grating warps due to the difference in the coefficients of linear expansion between silicon, silicon monoxide, and silicon dioxide. According to the method of Patent Document 1, extremely high-precision process adjustments are required to achieve a glass diffraction grating with adequate shape, material, and properties.

[0009] As another method, a method for fabricating glass grating structures by filling borosilicate glass into a silicon mold has been developed (e.g., Non-Patent Document 1). However, the period of the grating structure fabricated by the above method is tens of micrometers, which is about 10 times the period of a diffraction grating suitable for the above purpose. Therefore, it is impossible to fabricate a glass diffraction grating with a period of less than 10 micrometers suitable for the above purpose using the above method.

[0010] Thus, no glass diffraction grating with an aspect ratio of 2 or higher and a period of less than 10 micrometers, nor its manufacturing method, has been developed. Therefore, there is a demand for glass diffraction gratings with an aspect ratio of 2 or higher and a period of less than 10 micrometers, and their manufacturing method.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2020-56973

[0014] Non-patent literature

[0015] Non-patent document 1: A. Amnache and LG Frechette, "High-aspect ratiomicrostructures in borosilicate glass by molding and sacrificial siliconetching: capabilities and limits", Solid-State Sensors, Actuators and Microsystems Workshop Hilton Head Island, South Carolina, June 5-9, 2016 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] The objective of this invention is to provide a glass diffraction grating with an aspect ratio of 2 or higher and a period of 0.2 micrometers to 10 micrometers, and a method for manufacturing the same.

[0018] Methods for solving problems

[0019] The manufacturing method of the glass diffraction grating according to the first aspect of the present invention is a method for manufacturing a diffraction grating of borosilicate glass or barium borosilicate glass with a period of 0.2 micrometers to 10 micrometers and a groove aspect ratio of 2 or more. This manufacturing method includes the following steps: forming a grating on the surface of a silicon substrate using a Bosch process (cyclic etching); heating to approximately 1,000°C and forming an oxide film on the surface of the grating by exposure to water vapor; removing the oxide film using hydrofluoric acid; anodicly bonding the surface of the silicon substrate having the grating to one surface of a glass plate in a container with a pressure of 0.01 Pa to 0.1 Pa; heating the bonded silicon substrate and the glass plate to melt the glass and fill the spaces between the grooves of the silicon-based grating; grinding the opposite sides of the bonded surfaces of the silicon substrate and the glass plate; and removing silicon from the glass plate by selective etching based on xenon difluoride gas.

[0020] This manufacturing method includes the following steps: after the Bosch process, heating to approximately 1,000°C to form an oxide film on the grating surface by exposure to water vapor; and removing the oxide film with hydrofluoric acid. This smooths the small undulations (fan-shaped irregularities) on the sides of the grating produced by the Bosch process, resulting in a roughness of less than 10 nanometers. Therefore, the optical performance of the glass diffraction grating can be improved. Furthermore, this manufacturing method includes a step of selectively etching the silicon from the glass plate using xenon difluoride gas, thereby improving the material purity of the glass diffraction grating. Therefore, the optical performance of the glass diffraction grating can be improved.

[0021] The method for manufacturing a glass diffraction grating according to the first embodiment of the first aspect of the present invention further includes a step of etching the surface of the glass plate with hydrofluoric acid before the anode bonding step.

[0022] According to this embodiment, by treating with hydrofluoric acid, the precipitation of additives contained in the glass on the glass surface generated when the glass melts at high temperature is reduced, thereby improving the optical performance of the glass diffraction grating.

[0023] The method for manufacturing a glass diffraction grating according to the second embodiment of the first aspect of the present invention includes, after the step of selectively removing silicon from the glass plate by etching, the step of heating the glass plate to about 1,000°C and exposing it to water vapor.

[0024] According to this embodiment, silicon (Si) oxides such as silicon monoxide (SiO) that remain after etching can be further oxidized to form silicon dioxide, making it homogeneous with glass.

[0025] The glass diffraction grating of the second aspect of the present invention is a diffraction grating of borosilicate glass or barium borosilicate glass with a period of 0.2 micrometers to 10 micrometers and a groove aspect ratio of 2 or more.

[0026] In the glass diffraction grating of the first embodiment of the second aspect of the present invention, in a cross section in the direction including the period and the height of the diffraction grating, the radius of curvature of the side corresponding to the side of the rectangular ridge is greater than 10 times the period of the diffraction grating.

[0027] The shape of this embodiment allows for even better optical performance of the diffraction grating.

[0028] In the glass diffraction grating of the second embodiment of the second aspect of the present invention, the width of the ridge portion of the grating is in the range of 0.1 to 0.9 relative to the period of the grating.

[0029] In the glass diffraction grating of the third embodiment of the second aspect of the present invention, the roughness of the side surface of the ridge portion of the grating is less than 10 nanometers.

[0030] The shape of this embodiment allows for even better optical performance of the diffraction grating.

[0031] In the glass diffraction grating of the fourth embodiment of the second aspect of the present invention, in the cross section formed by the periodic direction and the height direction of the diffraction grating, the angle between the side of the periodic direction of the rectangular or trapezoidal grating and the side of the approximately height direction is in the range of 70 degrees or more and less than 90 degrees.

[0032] The reasons for prioritizing a temperature range of 70 degrees or higher but less than 90 degrees are as follows.

[0033] First, by changing the angle from a right angle to an acute angle, the diffraction efficiency characteristics of P-polarized waves, whose electric field vibrates within the incident plane containing both incident and reflected light, and S-polarized waves, whose electric field vibrates perpendicularly to the incident plane, can be made closer together, thereby improving the overall diffraction efficiency.

[0034] Secondly, by changing the aforementioned angle from a right angle to an acute angle, in Figure 2 In step S1050, the glass more easily fills the space formed by the silicon grating between the silicon substrate 10 and the glass plate 50. Attached Figure Description

[0035] Figure 1 This is a diagram illustrating the glass grating of the present invention.

[0036] Figure 2 This is a flowchart illustrating the manufacturing method of the glass grating of the present invention.

[0037] Figure 3A This is a diagram showing the silicon grating after Bosch's process.

[0038] Figure 3B Corresponding to Figure 3A , is a diagram showing a grating with an inverted conical shape on the ridge of the silicon substrate 10.

[0039] Figure 4 This is a diagram showing a silicon grating after heating.

[0040] Figure 5A This is a diagram showing a silicon grating after hydrofluoric acid treatment.

[0041] Figure 5B Corresponding to Figure 5A This is a diagram showing the tapered grating of the silicon substrate 10 after hydrofluoric acid treatment.

[0042] Figure 6 This is a diagram showing the silicon substrate and glass plate after anodizing.

[0043] Figure 7 This is a diagram showing the state in which glass is being filled in the space formed by the silicon grating between the silicon substrate and the glass plate.

[0044] Figure 8 This diagram shows the state in which the space formed by the silicon grating between the silicon substrate and the glass plate is filled with glass.

[0045] Figure 9 This is a diagram showing the glass plate after grinding.

[0046] Figure 10 The glass plate with a grating is shown after step S1070.

[0047] Figure 11 This is a SEM (scanning electron microscope) image of a silicon substrate with a grating after Bosch processing.

[0048] Figure 12 This is an SEM image of a heated silicon grating.

[0049] Figure 13 This is a SEM image of a silicon grating after hydrofluoric acid treatment.

[0050] Figure 14 This is a SEM image of a silicon grating after hydrofluoric acid treatment.

[0051] Figure 15 These are SEM images of the silicon substrate and glass plate after anodizing.

[0052] Figure 16 This is a SEM image of a space formed by a silicon grating between a silicon substrate and a glass plate, where the glass is filled with glass.

[0053] Figure 17 This shows the surface of the glass plate in step S1050 without hydrofluoric acid treatment. Figure 8 The diagram of face A).

[0054] Figure 18 This shows the surface of the glass plate in step S1050 during hydrofluoric acid treatment. Figure 8 The diagram of face A).

[0055] Figure 19A It is an SEM image of the cross-section of the glass plate with a grating after step S1070.

[0056] Figure 19B This is a SEM image of the cross-section of a diffraction grating, produced by a conventional method of plasma etching of quartz glass.

[0057] Figure 20 This is a diagram showing an electric furnace used to heat a silicon substrate (silicon wafer).

[0058] Figure 21 This is a diagram showing the chamber in which the anode bonding is performed.

[0059] Figure 22 This is a diagram showing the chamber in which the anode bonding is performed.

[0060] Figure 23 This is a diagram showing the chamber in which the anode bonding is performed.

[0061] Figure 24 This diagram illustrates the principle of anodic bonding.

[0062] Figure 25AThis is a diagram showing a hot isostatic pressing apparatus.

[0063] Figure 25B This is a diagram showing a hot pressing device.

[0064] Figure 26 This refers to the side of the glass plate and the silicon substrate opposite to the bonding surface, respectively. Figure 8 The diagram shows the grinding of surfaces A and B.

[0065] Figure 27 This is a diagram illustrating an apparatus for removing silicon from a glass plate by etching based on xenon difluoride gas (XeF2).

[0066] Figure 28 This diagram illustrates how to determine the duty cycle when the angle θ is an acute angle. Detailed Implementation

[0067] Figure 1 This is a diagram illustrating the glass grating of the present invention. The glass diffraction grating of the present invention has a grating period P of 0.2 micrometers to 10 micrometers, a grating height h of 0.4 micrometers to 200 micrometers, and a groove aspect ratio h / w of 2 or more. Here, w represents the spacing between ridges r of the grating. The duty cycle (Pw) / P is 0.1 to 0.9. The grating material is borosilicate glass or barium borosilicate glass.

[0068] Figure 2 This is a flowchart illustrating the manufacturing method of the glass grating of the present invention.

[0069] exist Figure 2 In step S1010, a photoresist is coated on the surface of the silicon substrate (silicon wafer) 10. After a grating pattern is formed on the photoresist by means of a mask exposure device, a laser drawing device, an electron beam drawing device, a stepper, or a laser interference exposure, the silicon is etched by Bosch process to form a grating on the surface of the silicon substrate 10.

[0070] Figure 3A This is a diagram showing the grating of silicon 10 after Bosch processing. Photoresist 20 is retained on the ridges of the silicon grating.

[0071] Figure 11 This is a SEM (scanning electron microscope) image of a silicon substrate 10 with a grating after Bosch processing. Figure 11 The image corresponds to Figure 3A . Figure 11 The scales recorded in the images and other images are marked in 0.5-micrometer increments. Therefore, the period of the grating is approximately 2 micrometers.

[0072] exist Figure 2In step S1020, after removing the resist, the silicon substrate 10 with the grating is heated in a furnace, thereby forming an oxide film on the surface of the grating.

[0073] Figure 20 This diagram shows an electric furnace 200 used for heating the silicon substrate (silicon wafer) 10. The silicon substrate 10, indicated by W, is placed on a boat 240 inside a quartz tube 220 and heated from the outside by a heater 230. As an example, the heating temperature is 1000 degrees Celsius (°C), and the heating time is 20 minutes. Oxygen and hydrogen are introduced into the quartz tube 220 through a gas inlet 210, and an oxide film is formed on the surface of the silicon grating by H2O (water vapor) generated by combustion. The thickness of the oxide film is, as an example, 350 nanometers.

[0074] Figure 4 This is a diagram showing a grating of silicon 10 after heating. An oxide film 30 is formed on the surface of the grating.

[0075] Figure 12 This is an SEM image of a silicon 10 grating after heating. Figure 12 The image corresponds to Figure 4 .

[0076] exist Figure 2 In step S1030, the oxide film on the grating surface is removed by hydrofluoric acid. Specifically, the oxide film is removed by immersing the silicon substrate 10 in hydrofluoric acid in a container within a ventilated chamber.

[0077] Figure 5A This is a diagram showing the grating of the silicon substrate 10 after hydrofluoric acid treatment.

[0078] Figure 13 and Figure 14 This is an SEM image of a silicon-10 grating after hydrofluoric acid treatment. Figure 13 The image is the image of the grating viewed from the side. Figure 14 The image is an image of the grating viewed from an oblique angle above. Figure 13 and Figure 14 The image corresponds to Figure 5A .

[0079] pass Figure 2 Steps S1020 and S1030, after forming an oxide film on the surface of the grating, remove it to reduce the roughness of the side surfaces of the grating's ridges. Figure 11The side surface of the grating of the silicon substrate 10 after the Bosch process is shown to have multiple small undulations (fan-shaped bumps) in a direction perpendicular to the height direction. The height of these small undulations ranges from several nanometers to tens of nanometers. By forming an oxide film on the surface of the grating and then removing it, these multiple small undulations are removed, thereby reducing the surface roughness. The arithmetic mean roughness Ra of the surface after step S1030 is less than 10 nanometers. In step S1020, the ratio of the thickness of the oxide film formed on the outer side to the thickness of the oxide film formed on the inner side is approximately 3 to 2, based on the initial silicon surface. Since the oxide film is removed in step S1030, the size of the silicon grating in step S1010 and the thickness of the oxide film in step S1020 are determined by taking into account the above ratio.

[0080] exist Figure 2 In step S1040, the grating-featured surface of the silicon substrate 10 is anodicly bonded to one surface of the glass plate in a vacuum.

[0081] Figures 21-23 This is a diagram showing the chamber 300 in which the anode connection is performed.

[0082] like Figure 21 As shown, a silicon substrate 10 with a grating and a glass plate 50 are arranged on a base 330 within a chamber 300, with the grating-covered surface of the silicon substrate 10 facing the surface of the glass plate 50, spaced apart by rod-shaped spacers 320. The vacuum level within the chamber 300 is set to 0.01 to 0.1 Pascals, and the chamber is heated to 400°C. Due to the presence of the spacers, the space between the ridges of the silicon grating also has the aforementioned vacuum level.

[0083] Next, as Figure 22 As shown, the spacer 320 is pulled out so that the surface of the silicon substrate 10 with the grating comes into contact with the surface of the glass plate 50.

[0084] Next, as Figure 23 As shown, while applying a pressure of about 10 kPa to the silicon substrate 10 and the glass plate 50 using the pressure plate 310, a negative voltage of -500 volts to -1000 volts is applied to the glass plate through the pressure plate 310 and the base 330.

[0085] Figure 24 This diagram illustrates the principle of anodic bonding. By heating the glass plate 50, sodium ions (Na₂O₃) in the borosilicate glass or barium borosilicate glass... +It is easily movable. After the silicon substrate 10 and the glass plate 50 are brought into contact, if the silicon substrate 10 and the glass plate 50 are respectively connected to the positive and negative electrodes of a voltage source, sodium ions move to the negative electrode side. As a result, a layer lacking sodium ions is generated near the boundary between the glass plate 50 and the silicon substrate 10. This layer carries a negative charge due to an excess of anions. Near the boundary between the silicon substrate 10 and the glass plate 50, a positive charge corresponding to the negative charge is generated, and the surfaces of the two attract each other and are firmly bonded together due to the Coulomb force acting between the positive and negative charges.

[0086] Figure 6 This is a diagram showing the silicon substrate 10 and the glass plate 50 after anodic bonding. The vacuum level of the space formed by the silicon grating between the silicon substrate 10 and the glass plate 50 is 0.01 to 0.1 Pascals, as described above.

[0087] Figure 15 These are SEM images of the silicon substrate 10 and the glass plate 50 after anodic bonding. Figure 15 The image corresponds to Figure 6 .

[0088] exist Figure 2 In step S1050, the bonded silicon substrate 10 and glass plate 50 are heated in an electric furnace. The electric furnace can be as follows: Figure 20 As shown. The heating temperature is 1100℃, the heating time is 30 minutes, and the supplied gas is nitrogen. The pressure inside the furnace is atmospheric pressure. The glass is melted by heating, and the low-pressure space formed by the silicon grating between the silicon substrate 10 and the glass plate 50 is filled under atmospheric pressure.

[0089] A hot isostatic pressing device or a hot pressing device can also be used instead of an electric furnace.

[0090] Figure 25A This diagram illustrates a hot isostatic pressing (HIP) apparatus 400. A bonded silicon substrate 10 (denoted by W) and a glass plate 50 are placed inside a pressure vessel 420. An inert gas, such as argon or nitrogen, is introduced into the pressure vessel 420 through a gas inlet 410. While maintaining a pressure of 0.1 to 200 MPa inside the pressure vessel 420, heating is performed using a heater 430, thereby promoting the filling of the space between the silicon substrate 10 and the glass plate 50 by the glass into the space formed by the silicon grating. 425 indicates a heat insulation layer.

[0091] Figure 25BThis diagram shows the hot pressing apparatus 400'. The bonded silicon substrate 10 and glass plate 50 shown in W are placed in the heating chamber 425' within the chamber 420'. Inert gases such as argon and nitrogen are introduced into the chamber 420' through the gas inlet 410'. While applying pressure to the workpiece using the cylinder 405', the workpiece is heated using the heater 430', thereby promoting the filling of the space formed by the silicon grating between the silicon substrate 10 and the glass plate 50 by the glass.

[0092] Figure 7 This diagram shows the state in which glass is being filled in the space formed by the silicon grating between the silicon substrate 10 and the glass plate 50.

[0093] Figure 8 This diagram shows a state where the space formed by the silicon grating between the silicon substrate 10 and the glass plate 50 is filled with glass. The glass filling the spaces between the ridges of the silicon grating forms a glass grating.

[0094] Figure 16 This is a SEM image of a space formed by a silicon grating between a silicon substrate 10 and a glass plate 50, where the glass is filled. Figure 16 The image corresponds to Figure 8 .

[0095] In steps S1040 and S1050, if the borosilicate glass or barium borosilicate glass is heated, additives such as sodium and aluminum contained in the glass may precipitate on the surface of the glass plate 50, thereby degrading the optical properties of the diffraction grating. Therefore, it is preferable to etch the surface of the glass plate 50 with hydrofluoric acid for about 500 nanometers before step S1040 or before step S1050 to remove the additives near the surface.

[0096] Figure 17 This shows the surface of the glass plate 50 in step S1050 before hydrofluoric acid treatment. Figure 8 The diagram of face A).

[0097] Figure 18 This shows the surface of the glass plate 50 during step S1050 of the hydrofluoric acid treatment process. Figure 8 The diagram of face A).

[0098] If Figure 17 Images and Figure 18 By comparing the images, it can be understood that the precipitation of additives on the surface of glass plate 50 is reduced due to hydrofluoric acid treatment.

[0099] exist Figure 2 In step S1060, the surfaces of the glass plate 50 and the silicon substrate 10 on opposite sides of the surfaces to be joined are... Figure 8 Grind surfaces A and B.

[0100] Figure 26 These are the surfaces opposite to the bonding surfaces of the glass plate 50 and the silicon substrate 10, respectively. Figure 8 The image shows the polishing of surfaces A and B. The silicon substrate, except for the grating portion surrounded by glass, is removed by polishing. Polishing is performed using CMP (Chemical Mechanical Polishing). The roughness of each surface after polishing is less than 1 nanometer. The thickness of the glass plate 50 and the silicon substrate 10 before polishing is 500 micrometers. The thickness of the glass plate after polishing is 400 micrometers, and the height (depth) of the grating is 6.5 micrometers.

[0101] Figure 9 This is a diagram showing the ground glass plate 50. Silicon 10' remains between the ridges of the glass grating.

[0102] exist Figure 2 In step S1070, silicon between the ridges of the glass grating is removed by selective etching based on xenon difluoride gas (XeF2).

[0103] Figure 27 This diagram illustrates an apparatus 500 for removing silicon from a glass plate 50 by etching using xenon difluoride gas (XeF2). A glass plate 50 (denoted by W) is placed inside a vacuum chamber 520, and xenon difluoride gas (XeF2) is introduced into the vacuum chamber 520 through a gas inlet 510 using a rotary pump 530. Since the bond between xenon (Xe) and fluorine (F) is weak, silicon (Si) reacts with fluorine (F) to form silicon tetrafluoride (SiF4), which then volatilizes, selectively etching silicon (Si) relative to the oxide (glass). If silicon (Si) oxides such as silicon monoxide (SiO) remain unetched, a thermal oxidation process can be added to produce silicon dioxide (SiO2), thereby changing its refractive index to that of the glass. Thermal oxidation is preferably a wet oxidation process with a fast oxidation rate.

[0104] Figure 10 The glass plate 50 with a grating is shown after step S1070.

[0105] Figure 19A It is an SEM image of the cross-section of the glass plate 50 with a grating after step S1070. Figure 19A The image corresponds to Figure 10 .

[0106] according to Figure 19A The image shows a grating with a period of 2 micrometers, a depth (height) of 6 micrometers, an aspect ratio of 14, and a duty cycle of 0.785. Additionally, in the direction of the period of the diffraction grating ( Figure 19A(horizontal direction) and height direction ( Figure 19A In the cross section formed by the vertical direction, the angle (acute angle) θ between the side of the periodic direction of the rectangular ridge and the side of the approximate height direction is 88 degrees.

[0107] Figure 28 This diagram illustrates the method for determining the duty cycle when the angle θ is acute. The spacing w between the ridges r of the grating is determined by the position of half the height h of the ridge.

[0108] Generally speaking, the aforementioned angle (acute angle) θ is preferably in the range of 70 degrees or more and less than 90 degrees. The reasons are as follows.

[0109] First, by changing the angle from a right angle to an acute angle, the diffraction efficiency characteristics of P-polarized waves, whose electric field vibrates within the incident plane containing both incident and reflected light, and S-polarized waves, whose electric field vibrates perpendicularly to the incident plane, can be made closer together, thereby improving the overall diffraction efficiency.

[0110] Second, by changing the angle from a right angle to an acute angle, in step S1050, the glass can more easily fill the space formed by the silicon grating between the silicon substrate 10 and the glass plate 50.

[0111] The method for adjusting the above angles will be explained.

[0112] exist Figure 2 When forming the oxide film in step S1020, Figure 4 The oxide film 30 shown is actually thicker closer to the upper surface of the grating. Therefore, when the oxide film 30 is removed in step S1030, the cross-sectional shape of the grating becomes a cone shape that narrows closer to the upper surface of the grating.

[0113] Figure 5B Corresponding to Figure 5A This is a diagram showing the tapered grating of the silicon substrate 10 after hydrofluoric acid treatment.

[0114] When using the aforementioned conical silicon grating to manufacture a glass grating, the cross-sectional shape of the ridge of the glass grating also becomes a cone shape that narrows as it approaches the upper surface of the grating. That is, the angle θ formed by the periodic side and the approximately height side of the rectangular cross-section is an acute angle.

[0115] exist Figure 2 In step S1010, when manufacturing a silicon grating using the Bosch process, by adjusting the silicon etching process based on sulfur hexafluoride (SF6) plasma and the deposition process of the sidewall protective film based on octafluorocyclobutane (C4F8) plasma, the cross-sectional shape of the grating ridge can be made into an inverted cone shape that is wider closer to the upper surface of the grating.

[0116] Figure 3B and Figure 3A The corresponding diagram shows a grating with an inverted conical shape on the ridge of the silicon substrate 10.

[0117] By adjusting the shape of the silicon grating before oxide film formation, the shape of the silicon grating after oxide film formation and removal can be adjusted, thereby adjusting the grating shape of the glass substrate.

[0118] In short, Figure 2 In step S1010, when manufacturing the silicon grating using the Bosch process, the shape of the ridges in the silicon grating can be adjusted to be aligned with the direction of the period of the glass diffraction grating. Figure 19A (horizontal direction) and height direction ( Figure 19A The angle formed by the periodic side of the rectangular ridge in the cross-section (in the vertical direction) and the side in the approximate height direction. Figure 19A (θ).

[0119] according to Figure 19A The image is a rectangular cross-section formed by the period and height directions of the diffraction grating, with the radius of curvature of the side along the height direction approximately 10 times the period of the diffraction grating.

[0120] Figure 19B This is a SEM image of a cross-section of a diffraction grating manufactured using an existing method of plasma etching of quartz glass.

[0121] according to Figure 19B The image is a rectangular cross-section formed by the period and height directions of the diffraction grating, with the radius of curvature of the side in the height direction being approximately 3 times the period of the diffraction grating.

[0122] In this embodiment, by using a large radius of curvature, the optical properties of the diffraction grating can be significantly improved compared to the prior art.

Claims

1. A method for manufacturing a glass diffraction grating, wherein the method comprises a diffraction grating of borosilicate glass or barium borosilicate glass with a period of 0.2 micrometers to 10 micrometers and a groove aspect ratio of 2 or higher, wherein... The manufacturing method of this glass diffraction grating includes the following steps: A grating is formed on the surface of a silicon substrate using Bosch technology; The silicon substrate is heated, and an oxide film is formed on the surface of the grating by exposing it to water vapor. The oxide film was removed using hydrofluoric acid. The silicon substrate with the grating is anodicly bonded to one side of a glass plate in a container with a vacuum of 0.01 Pa to 0.1 Pa. The bonded silicon substrate and glass plate are heated to melt the glass and fill the spaces between the ridges of the silicon grating. The surfaces opposite to the bonded surfaces of the silicon substrate and the glass plate are ground. as well as Silicon is removed from the glass plate by selective etching based on xenon difluoride gas.

2. The method for manufacturing a glass diffraction grating according to claim 1, wherein, The process includes a thermal oxidation step of heating the glass plate and exposing it to water vapor after the step of selectively etching away silicon from the glass plate.

3. The method for manufacturing a glass diffraction grating according to claim 1, wherein, The step of heating the bonded silicon substrate and glass plate is carried out by a hot isostatic pressing heating device.

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