Diffraction grating manufacturing method and diffraction grating

Abstract

The present invention improves the performance of a diffraction grating. The present invention uses, as a means therefor, a diffraction grating manufacturing method which comprises (a) a step for preparing a substrate provided with a first surface and a second surface on the opposite side of the first surface, (b) a step for forming, on the first surface of the substrate, a photoresist film provided with a first groove having a sinusoidal shape on a third surface on the opposite side to the substrate side, and (c) a step for forming a reflective metal film that fills the first groove having a sinusoidal shape on the third surface of the photoresist film by an electroless plating method, and which is for forming a diffraction grating provided with the reflective metal film.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a diffraction grating and a diffraction grating, and more particularly to a method for manufacturing a diffraction grating that is suitable for faithfully reproducing the groove shape of a diffraction grating formed on a photoresist applied to a silicon wafer, in a manufacturing method in which the groove shape of the diffraction grating is transferred to a metal film. [Background technology]

[0002] A diffraction grating is an optical element used in spectroscopes in analytical equipment to separate light containing a mixture of various wavelengths (such as white light) into narrow bands of wavelengths. It consists of fine grooves engraved on the surface of an optical material with a reflective film deposited on it.

[0003] Diffraction gratings include, for example, blazed (sawtooth) diffraction gratings, sinusoidal diffraction gratings, and laminar diffraction gratings. Blazed diffraction gratings are manufactured by creating a master diffraction grating by rubbing grooves one by one on a glass substrate coated with a metal film using a processing machine such as a ruling engine, and then transferring the rubbing groove shape to a resin or metal. As for a method for manufacturing a sinusoidal diffraction grating, a method using photolithography technology is disclosed, for example, in Patent Document 1 (JP 2003-172639 A).

[0004] The wavelength resolution performance of a sinusoidal diffraction grating is determined by the number of grooves engraved on the diffraction grating (number of grooves per mm), so a diffraction grating with a large number of grooves is required to increase the wavelength resolution of the device.

[0005] Furthermore, laminar diffraction gratings have lower diffraction efficiency than blazed and sinusoidal diffraction gratings, so diffraction gratings used in the soft X-ray and vacuum ultraviolet regions are required to have high efficiency. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-172639 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional methods using machining, such as a ruling engine, grooves are scribed one by one using a tool. This makes manufacturing time consuming, which has been an issue. Because the groove shape that can be scribed is determined by the tool, it is difficult to produce a sinusoidal diffraction grating with a large number of grooves. Furthermore, when attempting to transfer the shape to a metal film using conventional replica technology, the metal does not reach the bottom of sinusoidal grooves with a high aspect ratio, making groove transfer difficult. When metal does not reach the bottom of the sinusoidal grooves, the shape of the grooves on the surface of the reflective metal film is not sinusoidal but is deformed, resulting in reduced diffraction efficiency.

[0008] The present invention has been conceived to solve such problems, and an object of the present invention is to improve the performance of diffraction gratings. [Means for solving the problem]

[0009] A brief summary of a representative embodiment of the present invention will be given below.

[0010] One embodiment of a method for manufacturing a diffraction grating includes the steps of: (a) preparing a substrate having a first surface and a second surface opposite the first surface; (b) forming a photoresist film on the first surface of the substrate, the photoresist film having a sinusoidal first groove on a third surface opposite the substrate; and (c) using an electroless plating method, forming a first metal film on the third surface of the photoresist film that fills the sinusoidal first groove, thereby forming a diffraction grating having the first metal film.

[0011] In addition, one embodiment of the diffraction grating comprises a substrate and a first metal film formed on the substrate and having sinusoidal grooves on the surface opposite the substrate, and the groove width of the sinusoidal grooves in the first metal film is 100 nm or less. [Effects of the Invention]

[0012] According to the present invention, the performance of the diffraction grating can be improved. [Brief explanation of the drawings]

[0013] [Figure 1] 4 is a flowchart showing a method for manufacturing a diffraction grating according to the first embodiment. [Figure 2] 3 is a flowchart showing a manufacturing method for forming a groove in a photoresist film according to the first embodiment. [Figure 3] 3A to 3C are cross-sectional views showing a manufacturing method for forming grooves in a photoresist film according to the first embodiment. [Figure 4] 4 is a cross-sectional view showing the manufacturing method following FIG. 3. [Figure 5] 5 is a cross-sectional view showing the manufacturing method following FIG. 4. [Figure 6] 6 is a cross-sectional view showing the manufacturing method following FIG. 5. [Figure 7] 5A to 5C are cross-sectional views illustrating a method for manufacturing a diffraction grating according to the first embodiment. [Figure 8] 8 is a cross-sectional view showing the manufacturing method following FIG. 7. [Figure 9] 9 is a cross-sectional view showing the manufacturing method following FIG. 8. [Figure 10] 10A to 10C are cross-sectional views showing the manufacturing method following FIG. 9. [Figure 11] 11A to 11C are cross-sectional views showing the manufacturing method following FIG. 10. [Figure 12] 12 is a cross-sectional view showing the manufacturing method following FIG. 11. [Figure 13] 13 is a cross-sectional view showing the manufacturing method following FIG. 12. [Figure 14] 3A to 3C are diagrams showing a manufacturing method in which heat is applied to a photoresist to deform the photoresist according to the first embodiment. [Figure 15] 15 is a cross-sectional view showing the manufacturing method following FIG. 14. [Figure 16] 10 is a flowchart showing a method for manufacturing a diffraction grating according to the second embodiment. [Figure 17]5A to 5C are cross-sectional views showing a method for manufacturing a diffraction grating according to the second embodiment. [Figure 18] 18 is a cross-sectional view showing the manufacturing method subsequent to FIG. 17. [Figure 19] FIG. 2 is a schematic diagram of a cross-sectional shape of a groove of a blazed diffraction grating. [Figure 20] FIG. 2 is a schematic diagram of a cross-sectional shape of a groove of a sinusoidal diffraction grating. [Figure 21] FIG. 1 is a schematic diagram of a cross-sectional shape of a groove of a laminar diffraction grating. [Figure 22] FIG. 10 is a diagram showing a state in which a reflective metal film is uniformly formed on a sinusoidal groove made of photoresist. [Figure 23] FIG. 10 is a diagram showing a state in which a reflective metal film is formed in a tip-concentrated manner in a sinusoidal groove made of photoresist. [Figure 24] 10 is a graph showing the diffraction efficiency when a reflective metal film is uniformly formed on a sinusoidal groove made of photoresist, and when a reflective metal film is uniformly formed on a sinusoidal groove made of photoresist. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. In addition, in the embodiments, explanations of the same or similar parts will not be repeated unless particularly necessary.

[0015] <Room for improvement> The room for improvement will be described in detail below with reference to FIGS.

[0016] Diffraction gratings are classified into several types depending on the shape of the grooves engraved into them. First, we will explain blazed (sawtooth) diffraction gratings. Figure 19 shows a schematic diagram of the cross-sectional groove shape of a blazed diffraction grating 201. Spectrophotometers and other spectroscopic analysis devices are required to make measurements with a high S / N ratio by efficiently utilizing the energy of the light source, so reflective blazed diffraction gratings are preferred because they can efficiently extract only diffracted light of specific diffraction orders. One method for manufacturing blazed diffraction gratings is to create a master diffraction grating by rubbing grooves one by one into a glass substrate coated with a metal film using a processing machine such as a ruling engine, and then transfer the rubbing groove shape to a resin or metal.

[0017] Next, we will explain sinusoidal diffraction gratings. Figure 20 shows the cross-sectional groove shape of a sinusoidal diffraction grating 202. Sinusoidal diffraction gratings have different optical properties from blazed diffraction gratings, such as broad diffraction efficiency over a wide wavelength range and the peak wavelength of diffraction efficiency being determined by the groove depth and groove width. Sinusoidal diffraction gratings are used in devices such as inductively coupled plasma (abbreviated as ICP in the following text) optical emission spectroscopy. The wavelength resolution of an ICP optical emission spectroscopy device is determined by the number of grooves engraved on the diffraction grating (number of grooves per mm), so a diffraction grating with a large number of grooves is required to increase the wavelength resolution of the device.

[0018] Next, we will explain laminar diffraction gratings. Figure 21 shows a schematic diagram of the groove cross-section of a laminar diffraction grating 203. Laminar diffraction gratings have high reflectivity in the soft X-ray and vacuum ultraviolet (VUV) wavelength ranges of 0.1 nm to 200 nm. Therefore, they are used in spectrometers for soft X-rays and VUV, or in research applications such as material analysis in this wavelength range. Because laminar diffraction gratings have lower diffraction efficiency than blazed diffraction gratings and sinusoidal diffraction gratings, diffraction gratings used in the soft X-ray and VUV regions must be highly efficient. In other words, the first area of ​​improvement is the challenge of creating a diffraction grating with high diffraction efficiency.

[0019] Furthermore, methods using mechanical processing, such as a ruling engine, require the use of a tool to scribe each groove one by one. This results in a time-consuming manufacturing process. Furthermore, diffraction gratings used in the soft X-ray and vacuum ultraviolet regions must have a large number of ruling lines (e.g., 10,000 lines / mm or more). In this case, since the grooves to be scribed are very fine, it is possible to manufacture a sinusoidal diffraction grating. However, with methods using mechanical processing, the groove shape that can be scribed is determined by the tool, making it difficult to manufacture a sinusoidal diffraction grating with a large number of ruling lines. Furthermore, when attempting to transfer a shape to a metal film using well-known replica techniques, metal does not penetrate the bottom of sinusoidal grooves with a high aspect ratio, making it difficult to transfer the grooves.

[0020] That is, in order to use sinusoidal grooves with a high aspect ratio as a diffraction grating, it is necessary to form a reflective metal film 501 uniformly in the sinusoidal grooves made in the photoresist film 101, as shown in Fig. 22. In other words, it is necessary to embed the reflective metal film 501 along the sinusoidal grooves on the upper surface of the photoresist film 101 without any gaps.

[0021] In contrast, the method disclosed in Patent Document 1 uses a vacuum deposition method to form the metal film. With this method, when manufacturing a diffraction grating with, for example, 10,000 or more rulings per mm and a groove width (pitch) of 100 nm or less, the reflective metal film 501 concentrates at the tips of the grooves, forming a mushroom shape, as shown in Fig. 23. That is, the reflective metal film 501 is not embedded in the bottoms of the sinusoidal grooves on the top surface of the photoresist film 101, but is instead formed in a concentrated manner at the tips of the irregularities on the top surface of the photoresist film 101.

[0022] FIG. 24 is a graph showing the relationship between wavelength and diffraction efficiency. The horizontal axis of FIG. 24 represents wavelength, and the vertical axis represents diffraction efficiency. In FIG. 24, the solid line represents the diffraction efficiency when the reflective metal film 501 is uniformly applied to sinusoidal grooves (see FIG. 22), and the dashed line represents the diffraction efficiency when the reflective metal film 501 is concentrated at the tips of the grooves to form a mushroom shape (see FIG. 23). As shown in FIG. 23, when the reflective metal film 501 is concentrated at the tips of the grooves to form a mushroom shape, the diffraction efficiency decreases compared to when the reflective metal film 501 is uniformly applied to the grooves in FIG. 23 because the surface shape of the reflective metal film 501 is deformed rather than sinusoidal.

[0023] Thus, as a second area for improvement, when attempting to manufacture a diffraction grating with a number of rulings of 10,000 or more per mm and a groove width of 100 nm or less, it is difficult to form the surface of the reflective metal film 501 into a sinusoidal wave shape, which poses a problem of reduced diffraction efficiency.

[0024] Therefore, in each embodiment of the present application, some measures are taken to solve the above-mentioned room for improvement. The technical concept of the embodiments in which these measures are taken will be described below.

[0025] (Embodiment 1) The present embodiment will be described below with reference to Figures 1 to 15. In the following embodiments, the groove width (pitch) of a diffraction grating refers to the period of the repeated irregularities in a direction when a plurality of grooves aligned in one direction are formed on the surface of the diffraction grating. For example, in the case of a sinusoidal diffraction grating, the groove width of the diffraction grating refers to the distance between the centers (vertices) of adjacent convex portions in that direction.

[0026] A manufacturing flow of the diffraction grating according to this embodiment is shown in Figure 1. The manufacturing method of the diffraction grating according to this embodiment is composed of steps S11 to S17 shown below.

[0027] That is, first, as shown in FIG. 7, grooves are formed on a substrate (silicon substrate) 102 using a photoresist film 101 (step S11). Next, as shown in FIG. 8, a reflective metal film (electroless plated film) 103 is formed on the photoresist film 101 using electroless plating (step S12). Next, as shown in FIG. 9, an adhesive 104 is applied to the reflective metal film 103 (step S13). Next, as shown in FIG. 10, the reflective metal film 103 is bonded to a glass substrate 105 (step S14). Next, as shown in FIG. 11, the substrate 102 is peeled off from the photoresist film 101 (step S15). Next, as shown in FIG. 12, the photoresist film 101 remaining on the reflective metal film 103 is removed (step S16). Next, as shown in FIG. 13, a protective film 106 is formed on the surface of the reflective metal film 103 on which the grooves are formed (step S17). With the above steps, the diffraction grating of this embodiment is almost completed.

[0028] Here, the process of step S11, that is, the process of forming the photoresist film 101 having sinusoidal grooves on the surface, will be described with reference to Figures 2 to 6. Figure 2 shows the manufacturing flow of the photoresist film 101.

[0029] First, as shown in FIG. 3, a photoresist film 101 is applied to a substrate 102 (step S1). Next, as shown in FIG. 4, rectangular diffraction grating grooves are formed using photolithography (step S2). Next, as shown in FIG. 5, the photoresist film 101 is heated to deform the grooves (step S3). Next, as shown in FIG. 6, a water immersion treatment is performed on the outermost surface of the photoresist film 101 (step S4). As a result, a photoresist film 101 having sinusoidal grooves on its surface is formed. Next, each step will be described in detail.

[0030] In step S1, the substrate 102 is a silicon substrate having a first surface and a second surface opposite to the first surface. Photoresists are broadly divided into negative and positive types based on how they react with light or electron beams. When negative types are exposed to light, their solubility in a developer decreases, and the exposed portions remain after development. In contrast, when positive types are exposed to light, their solubility in a developer increases, and the exposed portions are removed during development. Either negative or positive types may be used for the photoresist film 101 used in step S1.

[0031] In step S2, the groove shape is formed using photolithography technology used in semiconductor manufacturing. In photolithography technology, a photoresist (photosensitive organic material) film 101 is applied onto a substrate 102 (step S1), and a mask pattern drawn on a photomask is exposed to the photoresist film 101, which is then developed to transfer the mask pattern to the photoresist film 101 (step S2).

[0032] The wavelength of the exposure device used to expose the mask pattern includes 248 nm (KrF excimer laser) and 193 nm (ArF excimer laser), but any wavelength of the exposure device can be used here, and there is no limitation on the wavelength of the exposure device used. Here, the film thickness of the photoresist film 101 and the exposure amount of the exposure device are adjusted, and exposure is performed so that the photoresist film 101 on the bottom of the groove remains. The shape of the exposed film is, for example, a rectangular shape as shown in FIG. 14. Although a rectangular shape is shown as an example in FIG. 14, other examples of shapes include a trapezoidal shape. The same effect as the rectangular shape can be obtained with a trapezoidal shape. That is, here, multiple rectangular or trapezoidal grooves are formed on the surface of the photoresist film 101.

[0033] In step S3, the diffraction grating of the developed photoresist film 101 is heated to melt the resist and cause it to flow in the direction indicated by the arrow in Fig. 14, thereby deforming the photoresist film 101 into a sinusoidal shape as shown in Fig. 15. That is, the rectangular or trapezoidal grooves arranged on the surface of the photoresist film 101 are deformed by heat treatment to form sinusoidal grooves. The photoresist film 101 is heated, for example, until the glass transition temperature of the photoresist is reached.

[0034] The heating device in step S3 may be, for example, a hot plate that generates heat by passing an electric current through a heating wire to heat a plate, or an oven that heats the air in a heating chamber with a gas or heater. However, any device having a heating mechanism that can heat and fluidize the photoresist film 101 is sufficient, and is not limited to a hot plate or an oven. As a result, the distance between the apex and the bottom surface of the sinusoidal grooves formed in the photoresist film 101, i.e., the depth of the sinusoidal grooves, is, for example, about 100 nm.

[0035] The hydrophilic treatment in step S4 involves ashing using oxygen plasma. By performing the ashing, a hydrophilic surface 107 having functional groups (OH groups) such as carbonyl groups and carboxyl groups can be formed, thereby chemically improving the hydrophilicity of the photoresist film 101.

[0036] Step S12 uses an autocatalytic electroless plating method. In electroless plating, a metal film is formed in a solution, so the metal film does not concentrate on the tips of the convex portions, as occurs in the comparative example described with reference to FIG. 23, where a vacuum deposition method is used. In other words, in electroless plating, the reflective metal film 103 can be formed uniformly along the irregularities on the surface of the photoresist film 101, so the sinusoidal groove shape formed on the surface of the photoresist film 101 can be faithfully reproduced. The material used for the reflective metal film 103 to be formed is, for example, gold (Au), copper (Cu), or silver (Ag).

[0037] The adhesive 104 used in step S13 is, for example, an epoxy resin.

[0038] The material of the glass substrate 105 used in step S14 is, for example, synthetic silica glass or borosilicate glass (BK7).

[0039] In steps S15 and S16, the substrate 102 and the photoresist film 101 are removed to expose the sinusoidal surface of the reflective metal film 103.

[0040] For example, magnesium fluoride, which has a wide transmission wavelength band and is resistant to thermal and mechanical shocks, is used for the protective film 106 in step S17. The protective film 106 can be formed by, for example, a vapor deposition method. For example, when magnesium fluoride is used as the protective film for a diffraction grating for vacuum ultraviolet (wavelengths of 110 nm to 200 nm), it is possible to prevent a decrease in diffraction efficiency due to the influence of oxidation of the metal film. The effect of magnesium fluoride in preventing a decrease in diffraction efficiency can be obtained in any wavelength band, including ultraviolet, visible, and infrared, as long as it is within the transmission wavelength band (wavelengths of approximately 110 nm to 7500 nm). The protective film 106 is transparent to such light.

[0041] The diffraction grating of this embodiment formed by the above steps has a glass substrate 105 with a first surface and a second main surface opposite the first main surface, as shown in FIG. 13 . A reflective metal film 103 is formed on the first surface of the glass substrate 105 via an adhesive 104. A plurality of irregularities are formed on the surface of the reflective metal film 103 opposite the adhesive 104 side, aligned in a predetermined direction along the first main surface of the glass substrate 105, and the irregularities are formed by alternately arranging convex portions and concave portions to form sinusoidal grooves. The surface of the reflective metal film 103 on which the sinusoidal grooves are formed is covered with a protective film 106.

[0042] The diffraction grating of this embodiment can have a ruling number of 10,000 lines / mm or more. That is, the groove width (pitch) W is 100 nm or less. Furthermore, the distance between the apex and the bottom surface of the sinusoidal groove in the direction perpendicular to the first main surface of the glass substrate 105 (vertical direction, longitudinal direction), i.e., the depth D of the sinusoidal groove, is, for example, about 100 nm.

[0043] (Effects of the embodiment) In this embodiment, after forming a photoresist film 101 with sinusoidal grooves as shown in FIG. 7, a reflective metal film 103 is formed by electroless plating as shown in FIG. 12. In this case, since the reflective metal film 103 can be formed along the sinusoidal surface of the grooves, a diffraction grating with fine sinusoidal grooves with a ruling count of 10,000 lines / mm or more and a groove width of 100 nm or less can be realized. Therefore, a diffraction grating with high diffraction efficiency can be realized, and the first and second room for improvement described above can be resolved. Therefore, in this embodiment, the performance of the diffraction grating can be improved.

[0044] (Embodiment 2) The second embodiment will be described below with reference to Figures 16 to 18. Figure 16 shows a manufacturing flow of the diffraction grating according to this embodiment.

[0045] First, as shown in FIG. 7, a groove is formed on a substrate 102 using a photoresist film 101 (step S21). Next, as shown in FIG. 8, a reflective metal film (electroless plated film) 103 is formed on the photoresist film 101 using electroless plating (step S22). Next, as shown in FIG. 17, a reflective metal film (electrolytic plated film) 204 is formed on the reflective metal film 103 using electrolytic plating (step S22). The subsequent steps are the same as steps S13 to S17 shown in FIG. 1. That is, next, an adhesive 104 is applied to the reflective metal film 204 (step S24). Next, the reflective metal film 204 is bonded to a glass substrate 105 (step S25). Next, the substrate 102 is peeled off from the photoresist film 101 (step S26). Next, the photoresist film 101 remaining on the reflective metal film 103 is removed (step S27). 18, a protective film 106 is formed on the surface of the reflective metal film 103 on which the grooves are formed (step S28). Through the above steps, the diffraction grating of this embodiment is almost completed.

[0046] This embodiment differs from the first embodiment in that, after a reflective metal film 103 is formed on a photoresist film 101 by electroless plating in step S22, a reflective metal film 204 is formed on the reflective metal film 103 in step S23. The reflective metal film 204 is made of, for example, gold (Au). By forming the reflective metal film 204 by electrolytic plating, it is possible to form a thicker metal film than in the first embodiment.

[0047] By forming a thick metal film, for example, in a diffraction grating for soft X-rays, the amount of soft X-rays that pass through the metal film can be reduced, making it possible to improve optical performance such as diffraction efficiency and stray light.

[0048] The invention made by the present inventors has been specifically described above based on the embodiments thereof, but the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the invention. [Industrial Applicability]

[0049] The present invention can be widely applied to diffraction grating manufacturing methods and diffraction gratings. [Explanation of symbols]

[0050] 101 Photoresist film 102 Circuit Board 103, 204, 501 Reflective metal film 104 Adhesive 105 Glass substrate 106 Protective film 107 Hydrophilic surface 201 Blazed Diffraction Grating 202 Sinusoidal diffraction grating 203 Laminar Diffraction Grating

Claims

1. (a) providing a substrate having a first surface and a second surface opposite the first surface; (b) forming a photoresist film on the first surface of the substrate, the photoresist film having a sinusoidal first groove on a third surface opposite to the substrate side; (c) forming a first metal film on the third surface of the photoresist film by an autocatalytic electroless plating method, the first metal film filling the sinusoidal first groove; (d) after the step (c), removing the substrate and the photoresist film to expose a fourth surface of the first metal film; (e) forming a protective film covering the fourth surface of the first metal film by a vapor deposition method; and The step (b) comprises: (b1) forming the photoresist film on the first surface of the substrate, the photoresist film having a plurality of rectangular or trapezoidal third grooves aligned on the third surface; (b2) heating the photoresist film to deform the third grooves, thereby forming the first grooves in a sinusoidal shape on the third surface; and the first metal film includes copper or silver; the protective film contains magnesium fluoride; A method for manufacturing a diffraction grating, which includes forming a diffraction grating including the first metal film.

2. 2. The method for manufacturing a diffraction grating according to claim 1, a fourth surface of the first metal film in contact with the third surface of the photoresist film has a second groove having a sine wave shape; The method for manufacturing a diffraction grating, wherein the groove width of the sinusoidal second grooves is 100 nm or less.

3. (delete)

4. 2. The method for manufacturing a diffraction grating according to claim 1, (f) after the step (c), forming a second metal film on the first metal film by electroplating; The method for manufacturing a diffraction grating further comprises:

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