Method for producing a relief-like diffraction grating

Abstract

A method for producing a relief-like diffraction grating (1) includes forming a first silicon nitride film (10) on a silicon element (2), oxidizing the silicon element (2) using the first silicon nitride film (10) as a mask to change part of the silicon element (2) into a first silicon oxide film (15), removing the first silicon nitride film (10) and selectively removing the first silicon oxide film (15) to form a first step section (4a) in the silicon element (2).

Description

TECHNICAL AREA

[0001] The present disclosure relates to a method for producing a relief-like diffraction grating. STATE OF THE ART

[0002] Japanese Patent Application No. 2000-105307 (PTL 1) discloses a method for producing a stepped, relief-like diffraction grating by etching a glass substrate using a photoresist as a mask. Japanese Patent Application No. 2000-155207 (PTL 2) discloses a method for producing a stepped, relief-like diffraction grating by etching a stack of a SiO2 film and an Al2O3 film using a photoresist as a mask. LIST OF CAPLETS PATENT LITERATURE PTL 1: Japanese Disclosure Document No. 2000-105307 PTL 2: Japanese Disclosure Document No. 2000-155207 BRIEF DESCRIPTION OF THE INVENTIONAL PROBLEM

[0003] However, when etching with a photoresist, the dimensional accuracy of a diffraction grating decreases with increasing protrusion of a periodic uneven structure of the diffraction grating. The present disclosure was prepared with regard to the problem described above. One objective of the present disclosure is to provide a method for producing a relief-like diffraction grating with higher dimensional accuracy. SOLUTION TO THE PROBLEM

[0004] A method for producing a relief-like diffraction grating of the present disclosure includes forming a first silicon nitride film on a silicon element, oxidizing the silicon element using the first silicon nitride film as a mask to change part of the silicon element into a first silicon oxide film, removing the first silicon nitride film, and selectively removing the first silicon oxide film to form a first step section in the silicon element. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0005] By oxidizing the silicon element using the first silicon nitride film as a mask, a first silicon oxide film with higher dimensional accuracy can be formed. Then, a relief-like diffraction grating is produced by selectively removing the first silicon oxide film. The method for producing a relief-like diffraction grating according to the present embodiment can produce a relief-like diffraction grating with higher dimensional accuracy. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic partial sectional view of a relief-like diffraction grating of embodiment 1. Fig. Figure 2 is an enlarged schematic partial sectional view of the relief-like diffraction grating of embodiment 1. Fig. Figure 3 is an enlarged schematic partial sectional view showing one step of a method for producing a relief-like diffraction grating of embodiment 1. Fig. 4 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 3 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. 5 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 4 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 6 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 5 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 7 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 6 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 8 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 7 illustrates the process for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 9 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 8 illustrates the process for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 10 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 9 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 11 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 10 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 12 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 11 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 13 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 12 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 14 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 13 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. 15 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 14 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 16 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 15 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. 17 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 16 illustrates the method for producing a relief-like diffraction grating of embodiment 1. Fig. Figure 18 is a schematic partial sectional view of a relief-like diffraction grating of embodiment 2. Fig. Figure 19 is an enlarged schematic partial sectional view of the relief-like diffraction grating of embodiment 2. Fig. Figure 20 is an enlarged schematic partial sectional view showing one step of a method for producing a relief-like diffraction grating of embodiment 2. Fig. 21 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 20 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. 22 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 21 is illustrated in the method for producing a relief-like diffraction grating of embodiment 2. Fig. Figure 23 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 22 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. 24 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 23 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. 25 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 24 illustrates the method for producing a relief-like diffraction grating of embodiment 2. Fig. Figure 26 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 25 illustrates the method for producing a relief-like diffraction grating of embodiment 2. Fig. 27 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 26 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. 28 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 27 is illustrated in the method for producing a relief-like diffraction grating of embodiment 2. Fig. 29 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 28 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. 30 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 29 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. Figure 31 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 30 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. 32 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 31 is illustrated in the method for producing a relief-like diffraction grating of embodiment 2. Fig. Figure 33 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 32 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. Figure 34 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 33 illustrates the process for producing a relief-like diffraction grating of embodiment 2. Fig. Figure 35 is a schematic partial sectional view of a relief-like diffraction grating of embodiment 3. Fig. Figure 36 is an enlarged schematic partial sectional view of the relief-like diffraction grating of embodiment 3. Fig. Figure 37 is an enlarged schematic partial sectional view showing a step in the production of a relief-like diffraction grating of embodiment 3. Fig. Figure 38 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 37 is illustrated in the method for producing a relief-like diffraction grating of embodiment 3. Fig. Figure 39 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 38 is illustrated in the method for producing a relief-like diffraction grating of embodiment 3. Fig. 40 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 39 illustrates the process for producing a relief-like diffraction grating of embodiment 3. Fig. 41 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 40 illustrates the process for producing a relief-like diffraction grating of embodiment 3. Fig. 42 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 41 is illustrated in the method for producing a relief-like diffraction grating of embodiment 3. Fig. 43 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 42 illustrates the method for producing a relief-like diffraction grating of embodiment 3. Fig. 44 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 43 illustrates the process for producing a relief-like diffraction grating of embodiment 3. Fig. 45 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 44 illustrates the method for producing a relief-like diffraction grating of embodiment 3. Fig. 46 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 45 illustrates the method for producing a relief-like diffraction grating of embodiment 3. Fig. 47 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 46 illustrates the method for producing a relief-like diffraction grating of embodiment 3. Fig. 48 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 47 is illustrated in the method for producing a relief-like diffraction grating of embodiment 3. Fig. 49 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 48 illustrates the process for producing a relief-like diffraction grating of embodiment 3. Fig. Figure 50 is a schematic partial sectional view of a relief-like diffraction grating of embodiment 4. Fig. Figure 51 is an enlarged schematic partial sectional view of the relief-like diffraction grating of embodiment 4. Fig. Figure 52 is an enlarged schematic partial sectional view showing one step of a method for producing a relief-like diffraction grating of embodiment 4. Fig. 53 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 52 is illustrated in the method for producing a relief-like diffraction grating of embodiment 4. Fig. 54 is an enlarged schematic partial sectional view, showing a step following the one in Fig. The step shown in Figure 53 illustrates the method for producing a relief-like diffraction grating of embodiment 4. Fig. Figure 55 is a schematic top view of an optical scanning device of embodiment 5. DESCRIPTION OF EXECUTION FORMS

[0006] Embodiments of the present disclosure are described below. Identical components are assigned the same reference numerals and their descriptions are not repeated. Design 1.

[0007] A relief-like diffraction grating 1 of embodiment 1 is described with reference to the Fig. 1 and Fig. 2 described. One diffraction wavelength of the relief-like diffraction grating 1 lies, for example, in the wavelength range from infrared rays to far-infrared rays.

[0008] The relief-like diffraction grating 1 comprises a silicon element 2 and a periodic uneven structure 9 formed within the silicon element 2. The relief-like diffraction grating 1 may further include a reflective film (not shown) provided on the surface of the periodic uneven structure 9. The reflective film is, for example, made of a metal.

[0009] The relief-like diffraction grating 1 is formed in the silicon element 2. In the present embodiment, the silicon element 2 is a silicon substrate 2a.

[0010] The periodic uneven structure 9 includes a plurality of projections 3, which are arranged periodically. Each projection 3 includes a side surface 3a, a side surface 3b facing side surface 3a, and a top surface 4t. The top surface 4t is located between side surface 3a and side surface 3b and is connected to both side surface 3a and side surface 3b.

[0011] In the present embodiment, the projections 3 each have a plurality of height levels. The relief-like diffraction grating 1 is a stepped diffraction grating that has a plurality of height levels. In particular, the projections 3 each have, for example, four height levels. The projections 3 each include step sections 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b.

[0012] Step sections 4a, 5a, 6a, and 7a are provided in side surface 3a. Step section 4a is the topmost step section of steps 4a, 5a, 6a, and 7a. Step section 5a is the second-topmost step section of steps 4a, 5a, 6a, and 7a. Step section 6a is the second-bottom step section of steps 4a, 5a, 6a, and 7a. Step section 7a is the bottommost step section of steps 4a, 5a, 6a, and 7a.

[0013] Step sections 4b, 5b, 6b, and 7b are provided in side surface 3b. Step section 4b is the topmost step section of steps 4b, 5b, 6b, and 7b. Step section 5b is the second-topmost step section of steps 4b, 5b, 6b, and 7b. Step section 6b is the second-bottom step section of steps 4b, 5b, 6b, and 7b. Step section 7b is the bottommost step section of steps 4b, 5b, 6b, and 7b.

[0014] Step section 4b is the same as step section 4a in the direction in the plane (right-left direction in the plane). Fig. 2) facing, perpendicular to the vertical direction (the upward-downward direction in Fig. 2) Each of the projections 3 extends. Step section 5b faces step section 5a in the plane direction. Step section 6b faces step section 6a in the plane direction. Step section 7b faces step section 7a in the plane direction. The upper surface 4t is located between step section 4a and step section 4b and is connected to step section 4a and step section 4b.

[0015] Step section 4a has a smooth edge section 4c. Step section 4b has a smooth edge section 4d. Step section 5a has a smooth edge section 5c. Step section 5b has a smooth edge section 5d. Step section 6a has a smooth edge section 6c. Step section 6b has a smooth edge section 6d. Step section 7a has a smooth edge section 7c. Step section 7b has a smooth edge section 7d. In this description, a smooth edge section means that the minimum radius of curvature of the edge section is at least greater than or equal to one-tenth of the diffraction wavelength of the relief-like diffraction grating 1.

[0016] A method for producing the relief-like diffraction grating 1 of the present embodiment is described with reference to the Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15, Fig. 16, Fig. 17 to Fig. 18 described.

[0017] Regarding Fig. 3. A silicon nitride film 10 is formed on a main surface 2s of the silicon element 2. Part of the main surface 2s of the silicon element 2 is covered with the silicon nitride film 10. The remaining part of the main surface 2s of the silicon element 2 is exposed by the silicon nitride film 10.

[0018] For example, a silicon nitride film is formed over the entire main surface 2s of the silicon element 2 by low-pressure chemical vapor deposition (LPCVD). A photoresist (not shown) is applied to the silicon nitride film. The photoresist is exposed and developed to pattern it. A portion of the silicon nitride film exposed by the photoresist is removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like. The photoresist is removed from the silicon element 2 using oxygen plasma or an organic solvent, such as acetone. In this way, the silicon nitride film 10 is formed over a portion of the main surface 2s of the silicon element 2. The silicon nitride film formed by LPCVD can withstand the step of oxidizing the silicon element 2 (see Fig. 4) The thickness of the silicon nitride film 10 is in the range of, for example, 0.1 µm to 0.3 µm, which is smaller than the thickness of the photoresist (1 µm or more).

[0019] Regarding Fig. 4. The silicon element 2 is placed in a thermal oxidation oven (not shown). Using the silicon nitride film 10 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to transform it into a silicon oxide film 15. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 10 and a section of the silicon element 2 located beneath the circumferential edge section of the silicon nitride film 10 are transformed into the silicon oxide film 15. The silicon oxide film 15 is formed such that it coils up beneath the circumferential edge section of the silicon nitride film 10, lifting the circumferential edge section. This coiling beneath the circumferential edge section of the silicon nitride film 10 by the silicon oxide film 15 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0020] Regarding Fig. 5 The silicon nitride film 10 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0021] Regarding Fig. 6. The silicon oxide film 15 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor, or the like to form the step sections 4a, 4b in the silicon element 2. The step section 4a has a smooth edge section 4c. The step section 4b has a smooth edge section 4d. The edge sections 4c, 4d of the step sections 4a, 4b are treated by a local oxidation step (see Fig. 4) and a step of selectively removing a silicon oxide film (see Fig. 6) smoothed. The upper surface 4t is part of the main surface 2s (see Fig. 3) of the silicon element 2 and is similarly flat to the main surface 2s.

[0022] Regarding Fig. 7 A silicon nitride film 11 is formed on the upper surface 4t of the silicon element 2 and on the step section 4a. The step section 4b and a section of the silicon element 2 which faces the upper surface 4t relative to the step section 4a in the plane direction (right-left direction) Fig. 7) opposite, are exposed by the silicon nitride film 11. The silicon nitride film 11 is formed in the same way as the silicon nitride film 10. The thickness of the silicon nitride film 11 is, for example, in the range of 0.1 µm to 0.3 µm.

[0023] Regarding Fig. In step 8, the silicon element 2 is placed in the oven for thermal oxidation (not shown). Using the silicon nitride film 11 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to transform it into a silicon oxide film 16. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 11 and a section of the silicon element 2 located beneath the circumferential edge portion of the silicon nitride film 11 are transformed into the silicon oxide film 16. The silicon oxide film 16 is formed such that it coils up beneath the circumferential edge portion of the silicon nitride film 11, lifting the circumferential edge portion. This coiling beneath the circumferential edge portion of the silicon nitride film 11 by the silicon oxide film 16 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0024] Regarding Fig. 9 the silicon nitride film 11 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0025] Regarding Fig. 10. The silicon oxide film 16 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor, or the like to form the step sections 5a, 5b in the silicon element 2. The step section 5a has a smooth edge section 5c. The step section 5b has a smooth edge section 5d. The edge sections 5c, 5d of the step sections 5a, 5b are treated by a local oxidation step (see Fig. 8) and a step of selectively removing a silicon oxide film (see Fig. 10) smoothed.

[0026] Regarding Fig. 11 A silicon nitride film 12 is formed on the upper surface 4t of the silicon element 2 and on the step sections 4a, 5a. The step sections 4b, 5b and a section of the silicon element 2 which faces the upper surface 4t in relation to the step section 5a in the direction in the plane (right-left direction in Fig. 11) opposite, are exposed by the silicon nitride film 12. The silicon nitride film 12 is formed in the same way as the silicon nitride film 10. The thickness of the silicon nitride film 12 is, for example, in the range of 0.1 µm to 0.3 µm.

[0027] Regarding Fig. In step 12, the silicon element 2 is placed in the oven for thermal oxidation (not shown). Using the silicon nitride film 12 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to transform it into a silicon oxide film 17. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 12 and a section of the silicon element 2 located beneath the circumferential edge section of the silicon nitride film 12 are transformed into the silicon oxide film 17. The silicon oxide film 17 is formed such that it coils up beneath the circumferential edge section of the silicon nitride film 12, lifting the circumferential edge section. This coiling beneath the circumferential edge section of the silicon nitride film 12 by the silicon oxide film 17 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0028] Regarding Fig. 13 the silicon nitride film 12 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0029] Regarding Fig. 14 The silicon oxide film 17 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor, or the like to form the step sections 6a, 6b in the silicon element 2. The step section 6a has a smooth edge section 6c. The step section 6b has a smooth edge section 6d. The edge sections 6c, 6d of the step sections 6a, 6b are treated by a local oxidation step (see Fig. 12) and a step of selective removal of a silicon oxide film (see Fig. 14) smoothed.

[0030] Regarding Fig. 15 A silicon nitride film 13 is formed on the upper surface 4t of the silicon element 2 and on the step sections 4a, 5a, 6a. The step sections 4b, 5b, 6b and a section of the silicon element 2 which faces the upper surface 4t relative to the step section 6a in the plane direction (right-left direction) Fig. 15) opposite, are exposed by the silicon nitride film 13. The silicon nitride film 13 is formed in the same way as the silicon nitride film 10. The thickness of the silicon nitride film 13 is, for example, in the range of 0.1 µm to 0.3 µm.

[0031] Regarding Fig. In step 16, the silicon element 2 is placed in the thermal oxidation oven (not shown). Using the silicon nitride film 13 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to transform that portion into a silicon oxide film 18. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 13 and a section of the silicon element 2 located beneath the circumferential edge portion of the silicon nitride film 13 are transformed into the silicon oxide film 18. The silicon oxide film 18 is formed such that it coils up beneath the circumferential edge portion of the silicon nitride film 13, lifting the circumferential edge portion. This coiling beneath the circumferential edge portion of the silicon nitride film 13 by the silicon oxide film 18 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0032] Regarding Fig. 17 the silicon nitride film 13 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0033] The silicon oxide film 18 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor or the like to expose the step sections 7a, 7b (see Fig. 2) to form in the silicon element 2. Step section 7a has a smooth edge section 7c. Step section 7b has a smooth edge section 7d. The edge sections 7c, 7d of step sections 7a, 7b are formed by a local oxidation step (see Fig. 16) and a step of selective removal of a silicon oxide film smoothed. Thus, the in the Fig. 1 and Fig. 2 relief-like diffraction gratings 1 are obtained.

[0034] In the present embodiment, the local oxidation step and the step of selectively removing a silicon oxide film are each performed four times to form four step sections 4a, 5a, 6a, 7a and four step sections 4b, 5b, 6b, 7b, however, the local oxidation step and the step of selectively removing a silicon oxide film can each be performed n times (where n is a natural number) to form a number n of step sections.

[0035] The advantageous effects of the method for producing the relief-like diffraction grating 1 of the present embodiment are described.

[0036] The method for producing the relief-like diffraction grating 1 of the present embodiment comprises the following steps: forming a first silicon nitride film (e.g., the silicon nitride film 10) on the silicon element 2; oxidizing the silicon element 2 using the first silicon nitride film as a mask to change a portion of the silicon element 2 into a first silicon oxide film (e.g., the silicon oxide film 15); removing the first silicon nitride film; and selectively removing the first silicon oxide film to form a first step section (e.g., the step section 4a) in the silicon element 2.

[0037] By oxidizing (local oxidation) the silicon element 2 using the first silicon nitride film as a mask, the first silicon oxide film (e.g., the silicon oxide film 15) can be formed with higher dimensional accuracy. Then, by selectively removing the first silicon oxide film, the relief-like diffraction grating 1 is produced. As a result, the dimensional accuracy of the diffraction grating in the vertical direction and in the direction in the plane of the diffraction grating perpendicular to the vertical direction are improved. The method for producing the relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with higher dimensional accuracy.

[0038] When the surface of the diffraction grating is formed by etching or deposition, the surface becomes rough. Light scattering occurs at the grating surface, reducing its diffraction efficiency. In contrast, the surface of the silicon element 2, formed by selectively removing the first silicon oxide film (e.g., silicon oxide film 15), as in the present embodiment, exhibits greater smoothness. Light scattering at the grating surface is suppressed. The method for producing the relief-like diffraction grating 1 according to the present embodiment can produce a relief-like diffraction grating 1 with higher diffraction efficiency.

[0039] The relief-like diffraction grating 1 of the present embodiment is formed in the silicon element 2, which is made of a single material, namely silicon. Thus, the method for producing the relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with excellent temperature stability of the diffraction efficiency compared to a relief-like diffraction grating of a comparable example, which is made of a variety of materials with different linear expansion coefficients.

[0040] In the method for producing the relief-like diffraction grating 1 of the present embodiment, the first step section (e.g., step section 4a) has a smooth edge section (e.g., edge section 4c).

[0041] Thus, light scattering at the edge section (e.g., edge section 4c) is suppressed. The method for producing the relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with higher diffraction efficiency.

[0042] The method for producing the relief-like diffraction grating 1 of the present embodiment further comprises the following steps: forming a second silicon nitride film (e.g., silicon nitride film 11) on the upper surface 4 of the silicon element 2, which is connected to the first step section (e.g., step section 4a), and on the first step section itself; oxidizing the silicon element 2 using the second silicon nitride film as a mask to change a portion of the silicon element 2 into a second silicon oxide film (e.g., silicon oxide film 16); removing the second silicon nitride film; and selectively removing the second silicon oxide film to form a second step section (e.g., step section 5a) connected to the first step section in the silicon element 2. The projections 3 of the relief-like diffraction grating 1 each have a plurality of height levels.

[0043] To form the projection 3, which has a multitude of height levels, by etching using a photoresist as a mask, a thick photoresist structure is required. When a thick photoresist is structured by exposure and development, the structure cannot be achieved with high accuracy due to the defocusing of the light used for exposure. In contrast, the method for producing the relief-like diffraction grating 1 of the present embodiment uses a silicon nitride film, which is thinner than the photoresist, to form the projection 3 with a multitude of height levels. Then, by oxidation (local oxidation) of the silicon element 2, using the silicon nitride film as a mask, a silicon oxide film with higher dimensional accuracy can be formed. Selective removal of the silicon oxide film produces the relief-like diffraction grating 1.Thus, even if the projections 3 of the relief-like diffraction grating 1 each have a multitude of height levels, a relief-like diffraction grating 1 with higher dimensional accuracy can be produced.

[0044] In the method for producing the relief-like diffraction grating 1 of the present embodiment, the silicon element 2 is the silicon substrate 2a.

[0045] The relief-like diffraction grating 1 of the present embodiment is formed in the silicon substrate 2a, which is made of a single material, namely silicon. Thus, the method for producing the relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with excellent temperature stability of the diffraction efficiency compared to the relief-like diffraction grating of the comparative example, which is made of a variety of materials with different linear expansion coefficients. Design 2.

[0046] The relief-like diffraction grating 1 of embodiment 2 is described with reference to the Fig. 18 and Fig. 19 described. The relief-like diffraction grating 1 of the present embodiment includes a similar configuration to the relief-like diffraction grating 1 of embodiment 1, but differs from the relief-like diffraction grating 1 of embodiment 1 in the following points.

[0047] In the relief-like diffraction grating 1 of the present embodiment, the projections 3 each have a single height level. The relief-like diffraction grating 1 is a diffraction grating with a single height level. The projections 3 each have smooth side surfaces 3a, 3b. In this description, a smooth side surface means that the arithmetic mean roughness Ra of the side surface is less than or equal to one-tenth of the diffraction wavelength of the relief-like diffraction grating 1. The side surfaces 3a, 3b have no edge segments.

[0048] Regarding the Fig. 20, Fig. 21, Fig. 22, Fig. 23, Fig. 24, Fig. 25, Fig. 26, Fig. 27, Fig. 28, Fig. 29, Fig. 30, Fig. 31, Fig. 32, Fig. 33 to Fig. 34 describes a method for producing the relief-like diffraction grating 1 of the present embodiment.

[0049] Regarding Fig. In step 20, the silicon nitride film 10 is formed on the main surface 2s of the silicon element 2. Part of the main surface 2s of the silicon element 2 is covered with the silicon nitride film 10. The remaining part of the main surface 2s of the silicon element 2 is exposed by the silicon nitride film 10. The step of forming the Fig. The silicon nitride film 10 shown in 20 is the same as the step of forming the in Fig. 3 silicon nitride film shown 10.

[0050] Regarding Fig. 21, using the silicon nitride film 10 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to change that portion of the silicon element 2 into the silicon oxide film 15. The in Fig. The local oxidation step shown in Figure 21 is the same as the one in Figure 21. Fig. 4 local oxidation steps shown.

[0051] Regarding Fig. 22 The silicon nitride film 10 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like. The step of removing the in Fig. The silicon nitride film 10 shown in 22 is the same as the step of removing the in Fig. 5 silicon nitride film shown 10.

[0052] Regarding Fig. 23 The silicon oxide film 15 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor, or the like to form the step sections 4a, 4b in the silicon element 2. The upper surface 4t is part of the main surface 2s (see Fig. 20) of the silicon element 2 and is similarly flat to the main surface 2s. The upper surface 4t is located between the step section 4a and the step section 4b and is connected to the step section 4a and the step section 4b. The step of removing the in Fig. The silicon oxide film 15 shown in 23 is the same as the step of removing the in Fig. 6 depicted silicon dioxide film 15.

[0053] Regarding Fig. In step 24, the silicon nitride film 11 is formed on the upper surface 4t of the silicon element 2. The step sections 4a, 4b are exposed by the silicon nitride film 11. The silicon nitride film 11 is formed by the same process as the silicon nitride film 10.

[0054] Regarding Fig. In step 25, the silicon element 2 is placed in the thermal oxidation oven (not shown). Using the silicon nitride film 11 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to modify the silicon oxide film 16. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 11 and a section of the silicon element 2 located beneath the circumferential edge section of the silicon nitride film 11 are modified by the silicon oxide film 16. The silicon oxide film 16 is formed to coil beneath the circumferential edge section of the silicon nitride film 11, thereby lifting the circumferential edge section. This coiling beneath the circumferential edge section of the silicon nitride film 11 by the silicon oxide film 16 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0055] Regarding Fig. 26 The silicon nitride film 11 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0056] Regarding Fig. 27 The silicon oxide film 16 is selectively removed by a hydrofluoric acid solution, a hydrofluoric acid vapor or the like to form the step sections 5a, 5b in the silicon element 2.

[0057] Through the in the Fig. 24, Fig. 25, Fig. 26 to Fig. The 27 steps shown represent stage section 4a (see Fig. 23) to stage section 5a and stage section 4b (see Fig. 23) to step section 5b. Step section 5a is higher or lower than step section 4a. Step section 5b is higher or lower than step section 4b. Step section 5b is closer to step section 5a in the direction in the plane (right-left direction in) Fig. 27) facing. The upper surface 4t is arranged between the step section 5a and the step section 5b and is connected to the step section 5a and the step section 5b.

[0058] Regarding Fig. 28 The silicon nitride film 12 is formed on the upper surface 4t of the silicon element 2. The step sections 5a, 5b are exposed by the silicon nitride film 12. The silicon nitride film 12 is formed in the same way as the silicon nitride film 10.

[0059] Regarding Fig. 29 The silicon element 2 is placed in the oven for thermal oxidation (not shown). Using the silicon nitride film 12 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to modify the portion of the silicon element 2 within the silicon oxide film 17. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 12 and a section of the silicon element 2 located beneath the circumferential edge section of the silicon nitride film 12 are modified within the silicon oxide film 17. The silicon oxide film 17 is formed such that it coils up beneath the circumferential edge section of the silicon nitride film 12, lifting the circumferential edge section of the silicon nitride film 12. This coiling beneath the circumferential edge section of the silicon nitride film 12 by the silicon oxide film 17 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0060] Regarding Fig. 30 The silicon nitride film 12 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using phosphoric acid or the like.

[0061] Regarding Fig. 31 The silicon oxide film 17 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor, or the like to form the step sections 6a, 6b in the silicon cell 2. Through the Fig. 28, Fig. 29, Fig. 30 to Fig. The 31 steps shown represent stage section 5a (see Fig. 27) to stage section 6a and stage section 5b (see Fig. 27) to step section 6b. Step section 6a is higher or lower than step section 5a. Step section 6b is higher or lower than step section 5b. Step section 6b is closer to step section 6a in the direction in the plane (right-left direction in) Fig. 31) facing. The upper surface 4t is arranged between the step section 6a and the step section 6b and is connected to the step section 6a and the step section 6b.

[0062] Regarding Fig. 32 The silicon nitride film 13 is formed on the upper surface 4t of the silicon element 2. The step sections 6a, 6b are exposed by the silicon nitride film 13. The silicon nitride film 13 is formed in the same way as the silicon nitride film 10.

[0063] Regarding Fig. In step 33, the silicon element 2 is placed in the oven for thermal oxidation (not shown). Using the silicon nitride film 13 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to modify the silicon oxide film 18. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 13 and a section of the silicon element 2 located beneath the circumferential edge portion of the silicon nitride film 13 are modified by the silicon oxide film 18. The silicon oxide film 18 is formed to coil beneath the circumferential edge portion of the silicon nitride film 13 and to raise the circumferential edge portion of the silicon nitride film 13. This coiling beneath the circumferential edge portion of the silicon nitride film 13 by the silicon oxide film 18 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0064] Regarding Fig. 34 The silicon nitride film 13 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0065] The silicon oxide film 18 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor or the like to expose the smooth side surfaces 3a, 3b (see Fig. 19) to form in the silicon element 2. The step section 6a (see Fig. 31) becomes the smooth side surface 3a and the step section 6b (see Fig. 31) becomes the smooth side surface 3b. The smooth side surface 3a is higher or lower than the step section 6a. The smooth side surface 3b is higher or lower than the step section 6b. The smooth side surface 3b is the same as the smooth side surface 3a in the direction in the plane (right-left direction in). Fig. 19) facing. The upper surface 4t is arranged between the side surface 3a and the side surface 3b and is connected to the side surface 3a and the side surface 3b. Thus, the in the Fig. 1 and Fig. 19 relief-like diffraction gratings 18 were obtained.

[0066] In the present embodiment, the local oxidation step and the step of selective removal of a silicon oxide film are each performed four times; however, depending on the height of the projection 3, the local oxidation step and the step of selective removal of a silicon oxide film can each be performed n times (where n is a natural number), or the thickness of the silicon oxide film produced in the local oxidation step can be adjusted.

[0067] In addition to the advantageous effects of the method for producing the relief-like diffraction grating 1 of the present embodiment, the method for producing the relief-like diffraction grating 1 of embodiment 1 achieves the following advantageous effects.

[0068] The method for producing the relief-like diffraction grating 1 of the present embodiment further comprises the following steps: forming a second silicon nitride film (e.g., silicon nitride film 11) on the upper surface 4t of the silicon element 2; oxidizing the silicon element 2 using the second silicon nitride film as a mask to change a portion of the silicon element 2 into a second silicon oxide film (e.g., silicon oxide film 16); removing the second silicon nitride film; and selectively removing the second silicon oxide film. During the selective removal of the first silicon oxide film (e.g., silicon oxide film 15), a second step section (e.g., step section 4b) is formed, which faces the first step section (e.g., step section 4a). The upper surface 4t of the silicon element 2 is connected to the first step section and the second step section.When silicon element 2 is oxidized using the second silicon nitride film as a mask, the first and second step sections are exposed by the second silicon nitride film. The projections 3 of the relief-like diffraction grating 1 each have a smooth side surface (side surfaces 3a, 3b).

[0069] By oxidizing (local oxidation) the silicon element 2 using the silicon nitride film as a mask, a silicon oxide film with higher dimensional accuracy can be formed. Then, by selectively removing the silicon oxide film, the relief-like diffraction grating 1 is produced. Consequently, even if the height of each of the protrusions 3 is increased, the relief-like diffraction grating 1 can be produced with higher dimensional accuracy.

[0070] Furthermore, the relief-like diffraction grating 1 of the present embodiment has no edge sections on any of the side faces 3a, 3b of the projection 3, and no light scattering occurs at the edge section. The method for producing the relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with higher diffraction efficiency. Design 3.

[0071] The relief-like diffraction grating 1 of embodiment 3 is described with reference to the Fig. 35 and Fig. 36 described. The relief-like diffraction grating 1 of the present embodiment includes a similar configuration to the relief-like diffraction grating 1 of embodiment 1, but differs from the relief-like diffraction grating 1 of embodiment 1 in the following points.

[0072] In the relief-like diffraction grating 1 of the present embodiment, the step section 4a has an angled edge section 4c. The step section 5a has an angled edge section 5c. In this description, the angled edge section means that the minimum radius of curvature of the edge section is less than one-tenth of the diffraction wavelength of the relief-like diffraction grating 1. The step section 4a has a flat side surface 8a. The step section 5a has a flat side surface 8c. The side surface 3b is a smooth side surface.

[0073] Regarding the Fig. 37, Fig. 38, Fig. 39, Fig. 40, Fig. 41, Fig. 42, Fig. 43, Fig. 44, Fig. 45, Fig. 46, Fig. 47, Fig. 48 to Fig. 49 describes the method for producing the relief-like diffraction grating 1 of embodiment 3.

[0074] Regarding Fig. 37. A photoresist 20 is formed on the main surface 2s of the silicon element 2. Part of the main surface 2s of the silicon element 2 is covered with the photoresist 20. The remaining part of the main surface 2s of the silicon element 2 is exposed by the photoresist 20. The thickness of the photoresist 20 is 1 µm or more. The photoresist 20 is formed by applying the photoresist to the entire main surface 2s of the silicon element 2, exposing the photoresist, and developing it.

[0075] Regarding Fig. 38 Using the photoresist 20 as an etching mask, a section of the silicon element 2 exposed by the photoresist 20 is removed by dry etching, such as deep reactive ion etching (DRIE). The step sections 4a and 4b are formed in the silicon element 2. Step section 4a has the flat side face 8a and the angled edge section 4c. Step section 4b is opposite step section 4a in the in-plane direction (right-left direction). Fig. 38) facing. The step section 4b has a flat side surface 8b and the angled edge section 4d. The flat side surfaces 8a, 8b can be perpendicular to the upper surface 4t. The upper surface 4t is arranged between the step section 4a and the step section 4b and is connected to the step section 4a and the step section 4b.

[0076] Regarding Fig. 39 the photoresist 20 is removed from the silicon element 2 using oxygen plasma or an organic solvent, such as acetone.

[0077] Regarding Fig. 40 A photoresist 21 is formed on the upper surface 4t of the silicon element 2 and on the step section 4a. The step section 4b and a section of the silicon element 2 which faces the upper surface 4t relative to the step section 4a in the direction in the plane (right-left direction) Fig. 40) opposite are exposed by the photoresist 21. The photoresist 21 is thicker than the photoresist 20. The photoresist 21 is formed in the same way as the photoresist 20.

[0078] Regarding Fig. 41, using the photoresist 21 as an etching mask, a section of the silicon element 2 exposed by the photoresist 21 is removed by dry etching, such as deep reactive ion etching (DRIE). The step sections 5a, 5b are formed in the silicon element 2. The step section 5a has the flat side surface 8c and the angled edge section 5c. By means of the in the Fig. 40, Fig. 41 to Fig. The 42 steps shown represent stage section 4b (see Fig. 39) to step section 5b. Step section 5b is higher or lower than step section 4b. Step section 5b is similar to step sections 4a and 5a in the direction in the plane (right-left direction). Fig. 41) facing. The step section 5b has a flat side surface 8d and an angled edge section 4d. The flat side surfaces 8c, 8d can be perpendicular to the upper surface 4t. The upper surface 4t is located between the step section 4a and the step section 5b and is connected to the step section 4a and the step section 5b.

[0079] Regarding Fig. 42 The photoresist 21 is removed from the silicon element 2 using oxygen plasma or an organic solvent, such as acetone.

[0080] Regarding Fig. 43 The silicon nitride film 10 is formed on the upper surface 4t of the silicon element 2 and on the step sections 4a, 5a. The step section 5b and a section of the silicon element 2 which faces the upper surface 4t in relation to the step section 5a in the direction in the plane (right-left direction in Fig. 43) opposite, are exposed by the silicon nitride film 10. The silicon nitride film 10 of the present embodiment is formed in the same way as the silicon nitride film 10 of embodiment 1. The silicon nitride film 10 is thinner than any of the photoresists 20, 21. The thickness of the silicon nitride film 10 is, for example, in the range of 0.1 µm to 0.3 µm.

[0081] Regarding Fig. 44. The silicon element 2 is placed in the oven for thermal oxidation (not shown). Using the silicon nitride film 10 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to modify the silicon oxide film 15. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 10 and a section of the silicon element 2 located beneath the circumferential edge section of the silicon nitride film 10 are modified by the silicon oxide film 15. The silicon oxide film 15 is formed to coil beneath the circumferential edge section of the silicon nitride film 10 and to raise the circumferential edge section of the silicon nitride film 10. This coiling beneath the circumferential edge section of the silicon nitride film 10 by the silicon oxide film 15 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0082] Regarding Fig. 45 The silicon nitride film 10 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0083] Regarding Fig. 46 The silicon oxide film 15 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor, or the like to form the step sections 6a, 6b in the silicon element 2. The step section 6a has a smooth edge section 6c. The edge section 6c of the step section 6a is treated by a local oxidation step (see Fig. 44) and a step of selective removal of a silicon oxide film (see Fig. 46) smoothed. The step section 5b (see Fig. 42) is through the in the Fig. 43, Fig. 44, Fig. 45 to Fig. The 46 steps shown lead to step section 6b. Step section 6b is higher or lower than step section 5b. Step section 6b is related to step sections 4a, 5a, and 6a in the direction in the plane (right-left direction). Fig. 46) facing. Step section 6b has a flat side surface. The side surface of step section 6b is steeper than that of step section 6a. The upper surface 4t is located between step section 4a and step section 6b and is connected to both step section 4a and step section 6b.

[0084] Regarding Fig. 47 The silicon nitride film 11 is formed on the upper surface 4t of the silicon element 2 and on the step sections 4a, 5a, 6a. The step section 6b and a section of the silicon element 2 which faces the upper surface 4t in relation to the step section 6a in the direction in the plane (right-left direction in Fig. 47) opposite, are exposed by the silicon nitride film 11. The silicon nitride film 11 of the present embodiment is formed in the same way as the silicon nitride film 10 of the present embodiment. The silicon nitride film 11 is thinner than either of the photoresists 20, 21. The thickness of the silicon nitride film 11 is, for example, in the range of 0.1 µm to 0.3 µm.

[0085] Regarding Fig. 48. The silicon element 2 is placed in the oven for thermal oxidation (not shown). Using the silicon nitride film 11 as a mask, a portion of the silicon element 2 is oxidized (locally oxidized) to modify the silicon oxide film 16. Specifically, a section of the silicon element 2 exposed by the silicon nitride film 11 and a section of the silicon element 2 located beneath the circumferential edge portion of the silicon nitride film 11 are modified by the silicon oxide film 16. The silicon oxide film 16 is formed to wrap around beneath the circumferential edge portion of the silicon nitride film 11, lifting the circumferential edge portion. This wrapping around beneath the circumferential edge portion of the silicon nitride film 11 by the silicon oxide film 16 can be achieved with high reproducibility and dimensional accuracy.Silicon element 2 is removed from the oven for thermal oxidation.

[0086] Regarding Fig. 49 The silicon nitride film 11 is selectively removed by dry etching using CF-based plasma or the like, or by wet etching using warm phosphoric acid or the like.

[0087] The silicon oxide film 16 is selectively removed by a hydrofluoric acid solution, hydrofluoric acid vapor or the like to expose the step section 7a (see Fig. 36) to form in the silicon element 2. The step section 7a has the smooth edge section 7c (see Fig. 36). The edge section 7c of the step section 7a is oxidized by a local oxidation step (see Fig. 48) and a step of selective removal of a silicon oxide film smoothed. Step section 6b (see Fig. 46) becomes the smooth side surface 3b (see Fig. 36). The side surface 3b is higher or lower than the side surface of the step section 6b. The side surface 3b is adjacent to the step sections 4a, 5a, 6a, 7a in the direction in the plane (right-left direction in Fig. 36) facing. The side surface 3b is steeper than the step sections 6a, 7a. The side surface 3b is gentler than the side surface of step section 4a and the side surface of step section 5a. Thus, the in the Fig. 35 and Fig. 36 relief-like diffraction gratings 1 were obtained.

[0088] In the present embodiment, the step of removing the silicon element 2 using a photoresist is performed twice to form two step sections 4a, 5a, and then the local oxidation step and the step of selectively removing a silicon oxide film are each performed twice to form the two step sections 6a, 7a. However, the step of removing the silicon element 2 using a photoresist can be performed m times (where m is a natural number) to form a number m of step sections, and then the local oxidation step and the step of selectively removing a silicon oxide film can each be performed n times (where n is a natural number) to form a number n of step sections.

[0089] In addition to the advantageous effects of the method for producing the relief-like diffraction grating 1 of the present embodiment, the method for producing the relief-like diffraction grating 1 of embodiment 1 achieves the following advantageous effects.

[0090] The method for producing the relief-like diffraction grating 1 of the present embodiment further comprises the following steps: forming a photoresist (e.g., photoresist 20) on the silicon element 2; dry-etching a portion of the silicon element 2 using the photoresist as an etching mask to form a second step section (e.g., step section 4a) in the silicon element 2; and removing the photoresist. The first silicon nitride film (e.g., silicon nitride film 10) is formed on the second step section and on the upper surface 4t of the silicon element 2 that is connected to the second step section. The first step section (e.g., step section 6a) is located below the second step section. The projections 3 of the relief-like diffraction grating 1 each have a plurality of height levels.

[0091] If an upper stage section (e.g., stage section 4a, 5a) is formed by etching using a photoresist as a mask, the photoresist can be relatively thin. Thus, etching using a photoresist as a mask also allows the upper stage section to be formed with relatively high dimensional accuracy. However, if a lower stage section (e.g., stage section 6a, 7a) is formed by etching using a photoresist as a mask, a thick photoresist structure is required. If the thick photoresist is structured by exposure and development, it cannot be structured with high accuracy due to the defocusing of the light used for exposure. Therefore, if the lower stage section (e.g., stage section 6a, 7a) is formed by etching using a photoresist as a mask, the dimensional accuracy of the lower stage section (e.g.,of stage section 6a, 7a).

[0092] In contrast, the present embodiment employs oxidation (local oxidation) of the silicon element 2 using a silicon nitride mask thinner than the photoresist, and selective removal of the silicon oxide film to form the lower step section (e.g., step sections 6a, 7a). Oxidation (local oxidation) of the silicon element 2 using the silicon nitride film as a mask allows for the formation of a silicon oxide film with higher dimensional accuracy. The relief-like diffraction grating 1 is produced by selective removal of the silicon oxide film. Consequently, the dimensional accuracy of the lower step section (e.g., step sections 6a, 7a) is improved. The method for producing a relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with higher dimensional accuracy.

[0093] Furthermore, the dimensions of the projections 3 in the plane can be adjusted by etching using a photoresist as a mask to form the upper step section (e.g., step section 4a, 5a). This allows for adjustment of the diffraction wavelength of the relief-like diffraction grating 1.

[0094] In the process for producing the relief-like diffraction grating 1 of the present embodiment, a flat side surface (e.g., the flat side surface 8b) facing the second stage section (e.g., the stage section 4a) is formed in the silicon element 2 when a portion of the silicon element 2 is removed. During oxidation of the silicon element 2, the flat side surface is exposed from the first silicon nitride film (e.g., the silicon nitride film 10). Upon selective removal of the first silicon oxide film (e.g., the silicon oxide film), a side surface (e.g., the side surface 6b) facing a first stage section (e.g., the stage section 6a) and a second stage section, and which is smoother than the first and second stage sections, is formed in the silicon element 2.

[0095] Therefore, the dimension of the projection 3 can be adjusted in the plane direction. This allows for adjustment of the diffraction wavelength of the relief-like diffraction grating 1. Design 4.

[0096] The relief-like diffraction grating 1 of embodiment 4 is described with reference to the Fig. 50 and Fig. 51 described. The relief-like diffraction grating 1 of the present embodiment includes a similar configuration to the relief-like diffraction grating 1 of embodiment 1, but differs from the relief-like diffraction grating 1 of embodiment 1 in the following points.

[0097] In the present embodiment, the silicon element 2 is a silicon layer 33 of a silicon-on-insulator (SOI) substrate 30. The SOI substrate 30 comprises a silicon substrate 31, a SiO2 insulating layer 32, and a silicon layer 33. The SiO2 insulating layer 32 is located between the silicon substrate 31 and the silicon layer 33. The relief-like diffraction grating 1 is formed in the silicon layer 33.

[0098] The side surface 3b of each of the projections 3 is a flat side surface 8e facing the step sections 4a, 5a, 6a, 7a. The side surface 3b can be perpendicular to the upper surface 4t. The side surface 3b can extend to the SiO2 insulating layer 32.

[0099] Regarding the Fig. 52, Fig. 53 to Fig. 54 describes the method for producing the relief-like diffraction grating 1 of embodiment 4.

[0100] Regarding Fig. Step 52 prepares the SOI substrate 30. The SOI substrate 30 comprises the silicon substrate 31, the SiO2 insulating layer 32, and the silicon layer 33. The SiO2 insulating layer 32 is located between the silicon substrate 31 and the silicon layer 33. The silicon layer 33 has its main area 2s facing the SiO2 insulating layer 32.

[0101] Regarding Fig. 53 The relief-like diffraction grating 1 is formed in the silicon layer 33 by a manufacturing process similar to the process for manufacturing the relief-like diffraction grating 1 of embodiment 1. The relief-like diffraction grating 1 comprises a periodic uneven structure 9. The periodic uneven structure 9 of the relief-like diffraction grating 1 comprises a plurality of projections 3, which are arranged periodically. The projections 3 each comprise the side surface 3a, the side surface 3b facing side surface 3a, and the upper surface 4t. The step sections 4a, 5a, 6a, 7a are formed in side surface 3a. The step sections 4b, 5b, 6b, 7b are formed in side surface 3b.

[0102] Regarding Fig. In step 54, a photoresist 35 is formed on the upper surface 4t of the silicon layer 33 and on the step sections 4a, 5a, 6a, 7a. The step sections 4b, 5b, 6b, 7b are exposed by the photoresist 35. The photoresist 35 is thicker than the silicon nitride films 10, 11, 12, 13 of embodiment 1. The photoresist 35 is formed in the same way as the photoresist 20 of embodiment 3.

[0103] Using the photoresist 35 as an etching mask, a section of the silicon layer 33 exposed by the photoresist 35 is removed by dry etching, such as deep reactive ion etching (DRIE). The side surface 3b (see Fig. 51), which is the flat side surface 8e, is formed. In the step of etching the silicon layer 33, the SiO2 insulating layer 32 acts as an etch stop layer. Then the photoresist 21 is removed using oxygen plasma or an organic solvent, such as acetone. In this way, the in the Fig. 50 and Fig. 51 relief-like diffraction gratings 1 were obtained.

[0104] In addition to the advantageous effects of the method for producing the relief-like diffraction grating 1 of the present embodiment, the method for producing the relief-like diffraction grating 1 of embodiment 1 achieves the following advantageous effects.

[0105] The method for producing the relief-like diffraction grating 1 of the present embodiment further includes the step of etching the silicon element 2 (e.g. the silicon layer 33) to form the flat side surface 8e which faces the first step section (e.g. the step section 4a).

[0106] Thus, the dimension of the projection 3 can be adjusted in the plane direction. This allows for an adjustment of the diffraction wavelength of the relief-like diffraction grating 1.

[0107] In the method for producing the relief-like diffraction grating 1 of the present embodiment, the silicon element 2 is the silicon layer 33 of the silicon-on-insulator substrate 30.

[0108] The relief-like diffraction grating 1 of the present embodiment is formed in the silicon layer 33, which is made of a single material, namely silicon. Thus, the method for producing the relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with excellent temperature stability of the diffraction efficiency compared to the relief-like diffraction grating of the comparative example, which is made of a variety of materials with different linear expansion coefficients.

[0109] In the step of etching the silicon layer 33, the SiO2 insulating layer 32 of the silicon-on-insulator substrate acts as an etch stop layer. Thus, the height dimension of the projection 3 is precisely determined. The method for producing the relief-like diffraction grating 1 according to the present embodiment can produce the relief-like diffraction grating 1 with higher dimensional accuracy. Design 5.

[0110] With reference to 55, an optical scanning device 40 of embodiment 5 is described. The optical scanning device 40 is an example in which the relief-like diffraction grating 1 of each of embodiments 1 to 4 is used.

[0111] The optical scanning device 40 includes the relief-like diffraction grating 1, a frame 41, struts 42, 44, armature 43, a coil 45 and a magnetic field generator 46.

[0112] The relief-like diffraction grating 1 is coupled to the frame 41 via the webs 42. The frame 41 is coupled to the armature 43 via the web 44. The coil 45 is provided on the frame 41. The coil 45 is wound around the relief-like diffraction grating 1. The magnetic field generator 46 generates a magnetic field 47. The magnetic field generator 46 is, for example, a permanent magnet.

[0113] When an alternating current is applied to the coil 45, the alternating current flowing through the coil and the magnetic field 47 from the magnetic field generator 46 exerts an electromagnetic force on the frame 41. Due to this electromagnetic force, the frame 41 oscillates around the struts 44. The relief diffraction grating 1 oscillates together with the frame 41 and scans the light incident on the relief diffraction grating 1.

[0114] The advantageous effects of the optical scanning device 40 of the present embodiment are achieved.

[0115] The optical scanning device 40 includes the relief-like diffraction grating 1. The relief-like diffraction grating 1 exhibits higher dimensional accuracy. Thus, the relief-like diffraction grating 1 exhibits high diffraction efficiency. The optical scanning device 40 according to the present embodiment can scan the light incident on the relief-like diffraction grating 1 with low optical loss.

[0116] It is understood that the embodiments 1 to 5 disclosed herein are in every respect illustrative and not limiting. At least two of the embodiments 1 to 5 disclosed herein may be combined, provided that this does not result in a contradiction. For example, the relief-like diffraction grating of each of the embodiments 1 to 3 may be formed in the silicon layer 33 of the SOI substrate 30 as in embodiment 4. Therefore, it is intended that the scope of this disclosure is defined by the claims and not by the preceding description and includes all modifications and variations that are equivalent to the claims in meaning and scope. REFERENCE MARK LIST

[0117] 1 Relief diffraction grating; 2 Silicon element; 2a Silicon substrate; 2s Main surface; 3 Projection; 3a, 3b, 6b Side surface; 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b Step section; 4c, 4d, 5c, 5d, 6c, 6d, 7c, 7d Edge section; 4t Top surface; 8a, 8b, 8c, 8d, 8e Flat side surface; 9 Periodic uneven structure; 10, 11, 12, 13 Silicon nitride film; 15, 16, 17, 18 Silicon oxide film; 20, 21, 35 Photoresist; 30 Silicon-on-insulator substrate; 31 Silicon substrate; 33 Silicon layer; 32 Insulating layer; 40 Optical scanning device; 41 Frame; 42, 44 Bridge; 43 Armature; 45 Coil; 46 Magnetic field generator; 47 Magnetic field. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2000-105307

[0002] JP 2000-155207

[0002]

Claims

[1] Method for producing a relief-like diffraction grating, the method comprising: Formation of a first silicon nitride film on a silicon element; Oxidation of the silicon element using the first silicon nitride film as a mask to change part of the silicon element into a first silicon oxide film; Removal of the first silicon nitride film; and selective removal of the first silicon oxide film to form a first step section in the silicon element. [2] Method for producing a relief-like diffraction grating according to claim 1, wherein the first step section has a smooth edge section. [3] Method for producing a relief-like diffraction grating according to claim 1 or 2, wherein the method further comprises: Forming a second silicon nitride film on an upper surface of the silicon element that is connected to the first step section, and on the first step section; Oxidation of the silicon element using the second silicon nitride film as a mask to change part of the silicon element into a second silicon oxide film; Removal of the second silicon nitride film; and selective removal of the second silicon oxide film to form a second step section in the silicon element, which is connected to the first step section, the projections of the relief-like diffraction grating each exhibit a multitude of height levels. [4] Method for producing a relief-like diffraction grating according to claim 1 or 2, wherein the method further comprises: Formation of a second silicon nitride film on an upper surface of the silicon element; Oxidation of the silicon element using the second silicon nitride film as a mask to change part of the silicon element into a second silicon oxide film; Removal of the second silicon nitride film; and selective removal of the second silicon oxide film, wherein During the selective removal of the first silicon oxide film, a second stage section is formed, which faces the first stage section. the upper surface of the silicon element is connected to the first step section and the second step section, When oxidizing the silicon element using the second silicon nitride film as a mask, the first step section and the second step section are exposed by the second silicon nitride film and The projections of the relief-like diffraction grating each have a smooth side surface. [5] Method for producing a relief-like diffraction grating according to claim 1 or 2, wherein the method further comprises: Formation of a photoresist on the silicon element; Dry etching of a portion of the silicon element using the photoresist as an etching mask to form a second stage section in the silicon element; and Removal of the photoresist, whereby the first silicon nitride film is formed on the second step section and on an upper surface of the silicon element that is connected to the second step section, the first step section is located below the second step section and The projections of the relief-like diffraction grating each exhibit a multitude of height levels. [6] Method for producing a relief-like diffraction grating according to claim 5, wherein When removing part of the silicon element, a flat side surface facing the second stage section in which the silicon element is formed, During the oxidation of the silicon element, the flat side surface of the first silicon nitride film is exposed and During the selective removal of the first silicon oxide film, a side surface is formed in the silicon element, wherein the side surface faces the first step section and the second step section and is smoother than the first step section and the second step section. [7] Method for producing a relief-like diffraction grating according to any one of claims 1 to 5, further comprising etching the silicon element to form a flat side surface facing the first step section. [8] Method for producing a relief-like diffraction grating according to any one of claims 1 to 7, wherein the silicon element is a silicon substrate. [9] Method for producing a relief-like diffraction grating according to any one of claims 1 to 7, wherein the silicon element is a silicon layer of a silicon-on-insulator substrate.

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