Master mold for nanoimprint, method for manufacturing master mold for nanoimprint, and method for manufacturing photonic crystal surface emitting laser

Abstract

On a substrate (12), a thin film (13) made of a material different from that of the substrate (12) is provided. The thin film (13) has a first opening (13a) and a second opening (13b) that reach the substrate (12). The first opening (13a) and the second opening (13b) have different widths and the same depth.

Description

Master mold for nanoimprint, method for manufacturing a master mold for nanoimprint, and method for manufacturing a photonic crystal surface-emitting laser

[0001] This disclosure relates to a master mold for nanoimprinting, a method for manufacturing a master mold for nanoimprinting, and a method for manufacturing a photonic crystal surface-emitting laser.

[0002] Distributed Feedback (DFB) lasers have diffraction gratings, and Photonic Crystal Surface-Emitting (PCSEL) lasers have photonic crystals (see, for example, Non-Patent Document 1). Nanoimprint lithography (NIL) is used for patterning microstructures such as diffraction gratings and photonic crystals.

[0003] Applied Physics Express 17, 042004 (2024)

[0004] Master molds used in nanoimprint lithography are formed, for example, by dry etching a silicon substrate using a mask. The smaller the opening width of the mask, the slower the etching speed due to the microloading effect. Therefore, if the mask has openings of different widths, there will be a difference in the depth of the corresponding recesses in the master mold. This will also result in a difference in the remaining thickness of the resist patterned using this master mold. When dry etching is performed using this resist as a mask, a CD (Critical Dimension) shift occurs, in which the pattern dimensions after etching change from the mask dimensions before etching.

[0005] This disclosure was made to solve the problems described above, and its purpose is to obtain a master mold for nanoimprinting that can reduce the amount of CD shift, a method for manufacturing a master mold for nanoimprinting, and a method for manufacturing a photonic crystal surface-emitting laser.

[0006] The nanoimprint master mold according to this disclosure comprises a substrate and a thin film provided on the substrate and made of a material different from the substrate, wherein the thin film has a first opening and a second opening that reach the substrate, and the first opening and the second opening have different widths but the same depth.

[0007] In this disclosure, since the depths of the first and second openings, which have different widths in the master mold, are the same, the remaining thickness of the resist after nanoimprint lithography can be made uniform. Therefore, the amount of CD shift can be reduced in dry etching using the resist as a mask.

[0008] This is a cross-sectional view showing a photonic crystal surface-emitting laser. This is a plan view showing an enlarged portion of a photonic crystal. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 1. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 1. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 1. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 1. This is a diagram showing a method for manufacturing a photonic crystal. This is a diagram showing a method for manufacturing a photonic crystal. This is a diagram showing a method for manufacturing a photonic crystal. This is a diagram showing a method for manufacturing a photonic crystal. This is a diagram showing a method for manufacturing a photonic crystal. This is a diagram showing a method for manufacturing a photonic crystal. This is a diagram showing a method for manufacturing a photonic crystal. This is a cross-sectional view showing nanoimprint lithography according to a comparative example. This is a cross-sectional view showing nanoimprint lithography according to a comparative example. This is a cross-sectional view showing nanoimprint lithography according to a comparative example. This is a cross-sectional view showing nanoimprint lithography according to a comparative example. This is a cross-sectional view showing a master mold according to a comparative example. This is a perspective view showing a master mold according to Embodiment 1. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 2. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 2. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 2. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 2. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 3. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 3. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 3. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 4. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 4. This is a cross-sectional view showing a method for manufacturing a master mold for nanoimprint according to Embodiment 4.

[0009] A nanoimprint master mold, a method for manufacturing a nanoimprint master mold, and a method for manufacturing a photonic crystal surface-emitting laser according to the embodiment will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repetition of the description may be omitted.

[0010] Embodiment 1 Figure 1 is a cross-sectional view showing a photonic crystal surface-emitting laser. An n-InP cladding layer 2, a photonic crystal 3, an MQW (Multi Quantum Wells) structured active layer 4, a p-InP cladding layer 5, and a p-InGaAs contact layer 6 are sequentially stacked on an n-InP substrate 1. A highly reflective p-electrode 7 is formed on the p-InGaAs contact layer 6. An n-electrode 8 is formed on the lower surface of the n-InP substrate 1. An opening is formed in the n-electrode 8. A low-reflectivity film 9 is formed on the lower surface of the n-InP substrate 1 at this opening.

[0011] Figure 2 is a magnified plan view of a portion of the photonic crystal. The photonic crystal 3 is a double-lattice photonic crystal in which pairs of first grooves 3a and second grooves 3b, each with different widths, are periodically formed. High-power single-mode operation at a wavelength of 1550 nm is possible by using such a double-lattice photonic crystal.

[0012] When attempting to pattern the fine structure of photonic crystal 3 using electron beam lithography, it takes more than a week to pattern the entire surface of a 3-inch wafer. In contrast, nanoimprint lithography can form relatively high-resolution patterns on a single wafer in less than 10 minutes. Therefore, nanoimprint lithography has high throughput. A master mold is used in nanoimprint lithography. Hereinafter, a method for manufacturing a master mold according to Embodiment 1 will be described. Figures 3 to 6 are cross-sectional views showing a method for manufacturing a master mold for nanoimprint according to Embodiment 1.

[0013] First, as shown in Figure 3, a thin film 13 made of a material different from that of the substrate 12 is formed on the substrate 12. A resist 14 is then applied to the thin film 13. Next, as shown in Figure 4, the resist 14 is patterned using electron beam lithography to form a resist pattern. This creates a repeating pattern of two types of apertures with different widths on the resist 14.

[0014] Next, as shown in Figure 5, the patterned resist 14 is used as a mask to selectively dry etch the thin film 13 onto the substrate 12. This creates a first opening 13a and a second opening 13b that penetrate the thin film 13 and reach the substrate 12. After removing the resist 14, the master mold 15 is manufactured as shown in Figure 6. The first opening 13a and the second opening 13b have different widths but the same depth.

[0015] The substrate 12 is, for example, Si, GaAs, or InP, and the thin film 13 is made of a material with a high dry processing selectivity ratio relative to the substrate 12. During dry etching, an etchant with a high dry processing selectivity ratio for the thin film 13 relative to the substrate 12 is used. As a result, etching does not proceed on the substrate 12, so even if the widths of the first opening 13a and the second opening 13b of the master mold 15 are different, the depths of the first opening 13a and the second opening 13b can be made the same.

[0016] For example, if the substrate 12 is made of GaAs and the thin film 13 is made of SiN, then SF is used as the etchant for dry etching the thin film 13. ６ and CHF ３ This is used. This allows for selective dry processing of SiN with respect to GaAs. The insulating film 13 may be SiO, but SiN is preferred. SiN can form a denser film, has strong resistance to mechanical damage during demolding of the replica mold 17, and improves process stability. Furthermore, if the substrate 12 is made of GaAs and the thin film 13 is made of InGaAs, CH is used as the etchant for dry etching the thin film 13. ４ and H ２ Use this.

[0017] Next, a method for manufacturing photonic crystals 3 by nanoimprint lithography using a master mold 15 will be described. Figures 7 to 13 show the method for manufacturing photonic crystals.

[0018] First, as shown in Figure 7, a photocurable resin 16 is applied to the surface of the master mold 15, which has a first opening 13a and a second opening 13b formed thereon, and the photocurable resin 16 is cured by irradiating it with ultraviolet light. Next, as shown in Figure 8, a replica mold 17 is obtained by separating the cured photocurable resin 16 from the master mold 15. The pattern of the replica mold 17 is an inverted version of the pattern of the master mold 15.

[0019] Next, as shown in Figure 9, an insulating film 19 made of SiO is formed on the semiconductor layer 18, and a resist 20 is applied on the insulating film 19. Next, as shown in Figure 10, a replica mold 17 is pressed onto the resist 20 and patterned. In this state, ultraviolet light is irradiated to cure the resist 20. Next, as shown in Figure 11, the replica mold 17 is separated from the resist 20. In this way, the resist 20 patterned by nanoimprint lithography has a characteristic residual thickness at the bottom of the recesses. As described above, since the depths of the first opening 13a and the second opening 13b of the master mold 15 are the same, the residual thickness of each recess in the resist 20 is uniform.

[0020] Next, as shown in Figure 12, the insulating film 19 is dry-etched using the patterned resist 20 as a mask. Then, the resist 20 is removed. Next, as shown in Figure 13, the semiconductor layer 18 is dry-etched using the insulating film 19 as a mask to form a first groove 3a and a second groove 3b with different widths. Then, the insulating film 19 is removed with an HF-based solution. This produces a photonic crystal 3, which is a semiconductor layer 18 with the first groove 3a and the second groove 3b formed thereon.

[0021] Next, the manufacturing method for a photonic crystal surface-emitting laser will be described. First, an n-InP cladding layer 2 and a semiconductor layer 18 are epitaxially grown on an n-InP substrate 1 in sequence using MOCVD. Next, a first groove 3a and a second groove 3b are formed in the semiconductor layer 18 by nanoimprint lithography to obtain a photonic crystal 3. Next, an active layer 4, a p-InP cladding layer 5, and a p-InGaAs contact layer 6 are epitaxially grown on the photonic crystal 3 in sequence using MOCVD. The first groove 3a and the second groove 3b of the photonic crystal 3 become voids. After that, a p electrode 7, an n electrode 8, and a low-reflection film 9 are formed. A photonic crystal surface-emitting laser is manufactured through the above steps.

[0022] Next, the effects of this embodiment will be explained in comparison with the comparative example. Figures 14 to 17 are cross-sectional views showing nanoimprint lithography according to the comparative example. In the comparative example, a master mold is formed by dry etching the silicon substrate 23. When the opening width of the mask is small relative to the etching depth, the etching speed slows down due to the microloading effect. Therefore, if the resist 14 has openings of different widths, a difference in the depth of the corresponding recesses in the master mold occurs. When nanoimprint lithography is performed using such a master mold, as shown in Figure 15, a difference in the remaining thickness of the recesses of the resist 20 with different widths occurs. As shown in Figure 16, the insulating film 19 is dry etched using the resist 20 as a mask. However, since the difference in processing rates between the insulating film 19 and the resist 20 is not large, CD shift is likely to occur in the insulating film 19, as shown in Figure 17. Note that only the remaining thickness of the resist 20 is O ２ There is also a method of etch-back using plasma, but CD shift occurs in that case as well.

[0023] In contrast, in this embodiment, since the depths of the first opening 13a and the second opening 13b of the master mold 15, which have different widths, are the same, the remaining thickness of the resist 14 after nanoimprint lithography can be made uniform. Therefore, the amount of CD shift can be reduced in dry etching using the resist 14 as a mask.

[0024] Figure 18 is a perspective view showing a master mold according to a comparative example. The depth of the large holes is 120 nm, while the depth of the small holes is 95 nm. Figure 19 is a perspective view showing a master mold according to Embodiment 1. It can be seen that both the large and small holes have a depth of 100 nm.

[0025] The thin film 13 is a single crystal or polycrystalline material grown on the substrate. This increases the adhesion between the thin film 13 and the substrate 12, making it less likely for the thin film to peel off when the replica mold 17 is released, thus stabilizing the process.

[0026] Alternatively, the semiconductor layer 18 may be processed using the resist 14 as a mask instead of the insulating film 19 as a hard mask. However, in the manufacturing of compound semiconductor substrates for optical devices, it is common practice to perform epitaxial growth again after dry processing of the substrate to embed the film. In this case, an insulating film is required as a selective growth mask, and it is common practice to use the insulating film 19 used during semiconductor processing. Since using a hard mask of the insulating film 19 adds an extra step that causes CD shift, this embodiment is particularly effective when using a hard mask of the insulating film 19. Furthermore, the lifespan of the master mold 15 can be increased by transferring the pattern of the master mold 15 to the replica mold 17 and using the replica mold 17 in nanoimprint lithography.

[0027] Embodiment 2 Figures 20-23 are cross-sectional views showing a method for manufacturing a nanoimprint master mold according to Embodiment 2. First, as shown in Figure 20, an etching stop film 24 is formed on a substrate 12. A thin film 13 made of a different material from the etching stop film 24 is formed on the etching stop film 24. A resist 14 is applied on the thin film 13. Next, as shown in Figure 21, the resist 14 is patterned by electron beam lithography. This forms a repeating pattern of two types of openings with different widths on the resist 14.

[0028] Next, as shown in FIG. 22, using the patterned resist 14 as a mask, the thin film 13 is selectively dry-etched with respect to the etching stop film 24. As a result, a first opening 13a and a second opening 13b that penetrate the thin film 13 and reach the etching stop film 24 are formed. Then, when the resist 14 is removed, as shown in FIG. 23, a master mold 15 is obtained. The first opening 13a and the second opening 13b have different widths from each other and the same depth.

[0029] The thin film 13 is made of a material with a high dry processing selection ratio with respect to the etching stop film 24. Then, during dry etching, an etchant with a high dry processing selection ratio of the thin film 13 with respect to the etching stop film 24 is used. As a result, since etching does not proceed in the etching stop film 24, even when the widths of the first opening 13a and the second opening 13b of the master mold 15 are different, the depths of the first opening 13a and the second opening 13b can be made the same.

[0030] For example, when the substrate 12 is made of InP, the etching stop film 24 is made of AlInAs, and the thin film 13 is made of InP, CH ４ and H ２ are used as the etchant for dry-etching the thin film 13. Or, when the substrate 12 is made of GaAs, the etching stop film 24 is made of AlInGaAs, and the thin film 13 is made of InP, CH <{0000008}>and H ２ are used.

[0031] Thereafter, similarly to Embodiment 1, a replica mold 17 is formed using the master mold 15 according to this embodiment. Further, a fine structure of the photonic crystal 3 of the photonic crystal surface-emitting laser is formed by nanoimprint lithography using the replica mold 17. Other configurations and processes are the same as those in Embodiment 1.

[0032] In this embodiment, since the depths of the first opening 13a and the second opening 13b of the master mold 15, which have different widths, are the same, the remaining thickness of the resist 14 after nanoimprint lithography can be made uniform. Therefore, the amount of CD shift can be reduced in dry etching of the insulating film 19 using the resist 14 as a mask.

[0033] The etching stop film 24 and the thin film 13 are single crystals or polycrystalline materials grown on the substrate. This increases the adhesion between the etching stop film 24 and the thin film 13 and the substrate 12, making it difficult for the thin film to peel off when the replica mold 17 is demolded, thus stabilizing the process.

[0034] Embodiment 3 Figures 24 to 26 are cross-sectional views showing a method for manufacturing a master mold for nanoimprint according to Embodiment 3. First, as shown in Figure 24, a first mask 25a and a second mask 25b with different widths are formed on a substrate 12. In practice, a repeating pattern of the first mask 25a and the second mask 25b is formed on the substrate 12. The first mask 25a and the second mask 25b are formed by dry etching an insulating film such as SiO using an EB exposure process.

[0035] Next, as shown in Figure 25, a thin film 13 is selectively epitaxially grown on the substrate 12 that is not covered by the first mask 25a and the second mask 25b. Then, when the first mask 25a and the second mask 25b are removed, a master mold 15 is obtained in which the thin film 13 has a first opening 13a and a second opening 13b formed thereon, as shown in Figure 26. The first opening 13a and the second opening 13b have different widths but the same depth.

[0036] Subsequently, a replica mold 17 is formed using the master mold 15 according to this embodiment, similar to the first embodiment. Furthermore, the microstructure of the photonic crystal 3 of the photonic crystal surface-emitting laser is formed by nanoimprint lithography using the replica mold 17. The other configurations and processes are the same as in the first embodiment.

[0037] In this embodiment, since the depths of the first opening 13a and the second opening 13b with different widths of the master mold 15 are the same, the remaining thickness of the resist 14 after nanoimprint lithography can be made uniform. Therefore, the CD shift amount can be reduced in dry etching using the resist 14 as a mask.

[0038] In addition, since the adhesion between the crystallized thin film 13 and the substrate 12 is increased, the thin film 13 is difficult to peel off when the replica mold 17 is peeled off, and the process is stabilized. Further, the cross-sections of the first opening 13a and the second opening 13b formed in the thin film 13 are tapered. Thereby, the burden when peeling off the replica mold 17 is reduced.

[0039] Embodiment 4 Figs. 27 to 29 are cross-sectional views showing a method for manufacturing a master mold for nanoimprinting according to Embodiment 4. First, as shown in Fig. 27, on the substrate 12, a first mask 25a and a second mask 25b having an inverted tapered cross-section and different widths from each other are formed by an image reversal resist.

[0040] Next, as shown in Fig. 28, a thin film 13 is selectively formed by electroless plating on the substrate 12 not covered by the first mask 25a and the second mask 25b. For example, palladium is added on a GaAs substrate, and a Ni film is formed by electroless plating. A reaction layer is formed at the Ni and GaAs interface, and the adhesion between the substrate 12 and the thin film 13 is improved. Not limited to this, the substrate 12 is made of Si or GaAs, and the thin film 13 is made of Ni, Co, Pd, Pt, or At.

[0041] Next, when the first mask 25a and the second mask 25b are removed, as shown in Fig. 29, a master mold 15 in which a first opening 13a and a second opening 13b are formed in the thin film 13 is obtained. The first opening 13a and the second opening 13b have different widths from each other and the same depth.

[0042] After that, similar to Embodiment 1, a replica mold 17 is formed using the master mold 15 according to this embodiment. Further, a fine structure of the photonic crystal 3 of the photonic crystal surface-emitting laser is formed by nanoimprint lithography using the replica mold 17. Other configurations and processes are the same as those in Embodiment 1.

[0043] In this embodiment, since the depths of the first opening 13a and the second opening 13b with different widths of the master mold 15 are the same, the remaining thickness of the resist 14 after nanoimprint lithography can be made uniform. Therefore, the CD shift amount can be reduced in dry etching using the resist 14 as a mask.

[0044] Also, since the thin film 13 is a metal film formed by plating, it has high mechanical strength. Since it can be formed without an underlying metal, the surface roughness is suppressed. Further, the cross-sections of the first opening 13a and the second opening 13b formed in the thin film 13 are tapered. For this reason, the burden when detaching the replica mold 17 is reduced.

[0045] 1 n-InP substrate, 2 n-InP cladding layer, 3 photonic crystal, 3a first groove, 3b second groove, 4 active layer, 5 p-InP cladding layer, 12 substrate, 13 thin film, 13a first opening, 13b second opening, 14, 20 resist, 15 master mold, 18 semiconductor layer, 24 etching stop film, 25a first mask, 25b second mask

Claims

1. A master mold for nanoimprint, comprising a substrate and a thin film provided on the substrate and made of a material different from the substrate, wherein a first opening and a second opening are formed that penetrate the thin film and reach the substrate, and the first opening and the second opening have different widths but the same depth.

2. A master mold for nanoimprint, comprising a substrate, an etching stop film provided on the substrate, and a thin film provided on the etching stop film and made of a different material from the etching stop film, wherein a first opening and a second opening are formed that penetrate the thin film and reach the etching stop film, and the first opening and the second opening have different widths and the same depth.

3. A method for manufacturing a master mold for nanoimprint, comprising the steps of: forming a thin film made of a material different from the substrate on a substrate; forming a resist pattern having apertures of different widths on the thin film by an electron beam exposure process; and using the resist pattern as a mask, selectively dry etching the thin film onto the substrate to form a first aperture and a second aperture reaching the substrate, wherein the first aperture and the second aperture have different widths.

4. The substrate is made of GaAs, the thin film is made of SiN, and SF is used as the etchant for dry etching the thin film. ６ and CHF ３ A method for manufacturing a master mold for nanoimprint according to claim 3, characterized by using 5. The substrate is made of GaAs, the thin film is made of InGaAs, and CH is used as the etchant for dry etching the thin film. ４ and H ２ A method for manufacturing a master mold for nanoimprint according to claim 3, characterized by using 6. The method for manufacturing a master mold for nanoimprint according to any one of claims 3 to 5, characterized in that the thin film is a single crystal or polycrystalline material grown on the substrate.

7. A method for manufacturing a master mold for nanoimprint, comprising the steps of: forming an etching stop film on a substrate; forming a thin film made of a material different from the etching stop film on the etching stop film; forming a resist pattern having apertures of different widths on the thin film by an electron beam exposure process; and using the resist pattern as a mask, selectively dry etching the thin film with respect to the etching stop film to form a first aperture and a second aperture reaching the etching stop film, wherein the first aperture and the second aperture have different widths.

8. The etching stop film is made of AlInAs or AlInGaAs, the thin film is made of InP, and CH is used as the etchant for dry etching the thin film. ４ and H ２ A method for manufacturing a master mold for nanoimprint according to claim 7, characterized by using 9. The method for manufacturing a master mold for nanoimprint according to claim 7 or 8, characterized in that the etching stop film and the thin film are single crystals or polycrystalline grown on the substrate.

10. A method for manufacturing a master mold for nanoimprint, comprising the steps of: forming a first mask and a second mask having different widths on a substrate; selectively epitaxially growing a thin film on the substrate not covered by the first mask and the second mask; and removing the first mask and the second mask to form a first opening and a second opening in the thin film, respectively.

11. The method for manufacturing a master mold for nanoimprint according to claim 10, characterized in that the cross-sections of the first opening and the second opening are tapered.

12. A method for manufacturing a master mold for nanoimprint, comprising the steps of: forming a first mask and a second mask having different widths and inversely tapered cross-sections on a substrate using an image reversal resist; selectively forming a thin film on the substrate not covered by the first mask and the second mask by electroless plating; and removing the first mask and the second mask to form a first opening and a second opening in the thin film, respectively, wherein the cross-sections of the first opening and the second opening are tapered.

13. A method for manufacturing a photonic crystal surface-emitting laser, comprising the steps of: manufacturing a master mold for nanoimprint by the method of any one of claims 3 to 12; sequentially forming a cladding layer of a first conductivity type and a semiconductor layer on a semiconductor substrate; coating a resist on the semiconductor layer; patterning the resist by nanoimprint lithography using the master mold for nanoimprint; dry etching the semiconductor layer using the patterned resist as a mask to form a first groove and a second groove of different widths to obtain a photonic crystal; and sequentially forming an active layer and a cladding layer of a second conductivity type on the photonic crystal.

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