Method for integrating diamond structure

Abstract

To provide a method for surely integrating a fine diamond structure on a substrate formed of a desired material.SOLUTION: A method for integrating a diamond structure comprises steps of: printing a mask on the surface of a diamond substrate; transferring a mask pattern to the surface of the diamond substrate having the printed mask by anisotropic etching; obliquely removing the bottom of a transfer area by anisotropically etching the transfer area in an oblique direction; sticking a first adhesive film having a first adhesive force on the surface side of a diamond structure to pick up the diamond structure; reversing the adhesive state of the diamond structure by sticking a second adhesive film having a second adhesive force served as an adhesive force larger than the first adhesive force on the bottom side of the diamond structure and peeling the first adhesive film; and sticking the surface side of the diamond structure on a predetermined substrate to peel the second film from the bottom side of the diamond structure.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for integrating diamond structures of desired shapes formed by diamond crystals containing color centers on a desired substrate, and in particular to a processing method for integrating fine diamond structures. [Background technology]

[0002] Diamond crystals containing point defects (color centers) in which carbon atoms in single crystal diamond are replaced by other atoms and vacancies where no carbon atoms exist are formed have been studied for application to various quantum technologies such as quantum sensing, quantum communication, and quantum computing (see Non-Patent Documents 1-3). In particular, a complex (NV center) of nitrogen (N) replacing a carbon atom and an adjacent vacancy (V) has excellent properties in electron spin with a long coherence time at room temperature, and can be made to act as a quantum bit. When used as a quantum sensor, it is used to detect various environmental parameters such as magnetic field, electric field, strain, or temperature (Non-Patent Documents 4-8).

[0003] On the other hand, the NV center in a diamond single crystal acts as one quantum bit, but recently, diamond single crystals having an NV center that acts as three quantum bits have also been manufactured (see Patent Document 1). In addition, the method of manufacturing a diamond layer having an NV center has also been improved, and a method of manufacturing NV centers at a high density has been proposed (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-029386 A [Patent Document 2] JP 2020-183332 A [Non-patent literature]

[0005] [Non-licensed document 1] JM Taylor, P. Cappellaro, L. Childress, L. Jiang, D. Budker, PR Hemmer, A. Yacoby, R. Walsworth, and MD Lukin, Nat. Phys. 4, 810 (2008) [Non-licensed document 2] JF Barry, JM Schloss, E. Bauch, MJ Turner, CA Hart, LM Pham, and RL Walsworth, Rev. Mod. Phys. 92, 015004 (2020) [Non-licensed document 3] M. Ruf, NH Wan, H. Choi, D. Englund, and R. Hanson, J. Appl. Phys. 130, 070901 (2021)

Non-licensed Document 4

Non-licensed Document 5

Non-licensed Document 6

Non-licensed Document 7

[0006] In order to accelerate the progress of quantum technology using diamond, it is important to implement micro- or nano-level fine structures in diamond, and various processing methods are currently being proposed. In particular, applications to scalable quantum photonics require the integration of diamond color centers (NV centers) on desired chips, and it is particularly important to be able to integrate them on substrates such as Si, SiN, LiNbO3, and AlN.

[0007] However, it is difficult to form a high-quality single-crystal diamond thin film on a dissimilar material by heterogeneous epitaxial growth, and as a result, hybrid integration using a technique in which a separately formed single-crystal diamond structure is attached to the dissimilar material (pick-and-place technology) is considered to be the most realistic approach.

[0008] By the way, in order to attach a diamond structure to a substrate using a pick-and-place technique, it is possible to use, for example, a micromanipulator to integrate a color center of a single crystal diamond on the substrate. However, the nanofabrication technique in the field of diamond photonics cannot immediately convert the hybrid integration method in the existing technique. For example, a diamond structure formed by angle etching has a triangular bottom surface, and is therefore not suitable for hybrid integration. Recently, a technique for hybrid integration has been reported in which a diamond waveguide array including a GeV center and a SiV center, which are fabricated by quasi-isotropic etching, is integrated on an AlN photonic chip (see Non-Patent Document 9). However, even when quasi-isotropic etching is used, the bottom of the diamond structure is not flat, and it has not yet been put to practical use.

[0009] The present invention has been made in view of the above points, and an object of the present invention is to provide a method capable of reliably integrating fine diamond structures on a substrate made of a desired material. [Means for solving the problem]

[0010] Therefore, the present invention provides a method for forming a diamond structure by forming a diamond substrate having a diamond crystal including a color center, the method comprising the steps of: a mask printing step of printing a mask formed in a desired shape from a material that is resistant to diamond etching on the surface of the diamond substrate on which the mask is printed, a transfer step of transferring a mask pattern by anisotropic etching in a direction perpendicular to the surface of the diamond substrate on which the mask is printed, and an undercut step of obliquely removing the bottom of the transfer region transferred by the transfer step by quasi-isotropic etching, which performs anisotropic etching in an oblique direction, and separating the transfer region into a substantially triangular cross section to form a diamond structure. The method includes a pick-up process in which a first adhesive film having a first adhesive strength is adhered to the surface side of the diamond structure and the diamond structure is picked up; an inversion process in which a second adhesive film having a second adhesive strength greater than the first adhesive strength is adhered to the bottom side of the diamond structure and the first adhesive film is peeled off from the surface side of the diamond structure to invert the adhesion state of the diamond structure; and a placing process in which the surface side of the diamond structure is adhered to a specified substrate and the second film is peeled off from the bottom side of the diamond structure.

[0011] According to the above-mentioned configuration, basically, a diamond structure having a surface shape that matches the mask shape printed on the diamond substrate and an undercut bottom surface with a substantially triangular cross section is formed, and then the flat surface portion of the diamond structure can be attached to the substrate surface in a reversed state. At this time, the surface portion of the diamond structure is protected from etching by the mask, and is on a smooth flat surface, so that the diamond structure can be stably integrated when attached to the substrate.

[0012] In the invention having the above configuration, the shape of the mask may include a linear portion and an annular portion continuous with this linear portion, and the annular portion may be formed with an outer diameter larger than the width dimension of the linear portion.

[0013] According to the above configuration, a diamond beam (nanobeam) can be formed by transferring the linear mask shape portion, and a large diameter region integral with the diamond beam can be formed by transferring the annular mask shape portion, and can function as an adhesion assistant in the pick-up process and the inversion process. That is, the first and second adhesive films can apply an adhesive force to the large diameter region, and the pick-up process or the inversion process can be reliably performed. In particular, the second adhesive force can be sufficiently applied even to the non-flat bottom portion of the second adhesive film.

[0014] Furthermore, in the invention having the above configuration, the undercut process involves etching to a state in which the area to which the linear portion has been transferred is raised, and a portion of the area to which the annular portion has been transferred remains as a tether, so that the entire diamond structure formed by the undercut process can be in an air-bridged state via the tether.

[0015] According to the above-mentioned configuration, the area where the linear part is transferred is a diamond beam (nano beam), while the area where the annular part is transferred functions as an adhesion assistant, so that the pick-up process can be easily performed by forming a tether in this adhesion assistant to air-bridge the diamond structure. In particular, since the adhesion assistant is for effectively exerting the adhesion force of the adhesive film, forming a tether at this position makes the separation operation easy.

[0016] The invention having the above configuration may further include a step of removing the mask remaining on the surface of the diamond structure after the undercutting step.

[0017] According to the above-mentioned configuration, the mask that is printed on the diamond substrate for transfer remains on the surface of the diamond substrate as it is, so this mask can be removed before being integrated on the heterogeneous material substrate, and the surface of the diamond structure can be directly integrated on the substrate.Even if the mask remains, the mask itself is made of a material that is robust against diamond etching, so the surface is smooth, so there is no need to remove it, but depending on the smoothness of both, the smoother surface can be selectively used.

[0018] Furthermore, in the invention of each of the above configurations, a preliminary step for producing the mask of the desired shape may be included, which may include a step of appropriately laminating a sacrificial layer on a substrate, a step of laminating a mask material on the surface of the sacrificial layer, a step of patterning a resist of a shape matching the shape of the mask on the surface of the laminated mask material, a step of etching the mask material to form the mask of the desired shape, a step of removing the resist, and a step of removing the sacrificial layer by etching.

[0019] According to the above-mentioned configuration, a series of steps related to the diamond structure integration method includes a pre-step, and a mask of a desired shape can be formed by lithography technology and an etching process. Incidentally, in the mask fabrication, a portion where a tether is to be formed during patterning can be provided in advance in order to release the mask by an air bridge after removing the sacrificial layer. This tether portion is also reflected in the mask, and can also form the tether of the diamond structure after being transferred to the diamond substrate. When forming the mask, the pattern shape can be provided with a linear portion and a ring portion, and the tether can be provided in the ring portion to facilitate picking up when printing the mask.

[0020] In the invention having each of the configurations, it is preferable that the second adhesive strength of the second adhesive film is at least twice as large as the second adhesive strength of the first adhesive film.

[0021] According to the above configuration, in the inversion process, the diamond structure is picked up using the first adhesive film, and then the bottom of the diamond structure is adhered to the second adhesive film and the first adhesive film is peeled off. However, by setting a difference of three times or more between the adhesive strengths of the two, it becomes easy to peel off only the first adhesive film.

[0022] The color center in each of the inventions may be a complex (NV center) of nitrogen (N) substituting a carbon atom and a vacancy (V) adjacent to the nitrogen. Effect of the Invention

[0023] According to the present invention, the fine diamond structure is formed by obliquely removing the bottom of the transfer region by quasi-isotropic etching, which is anisotropic etching in an oblique direction, and has a substantially triangular cross-sectional shape, while the surface side of the diamond substrate, which is not affected by etching, can be attached to a substrate made of a different material, so that the fine diamond structure can be accumulated on the substrate with a smooth surface. Therefore, the fine diamond structure can be reliably accumulated on the substrate. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is an explanatory diagram showing a mask printing process. [Diagram 2] 1A to 1C are explanatory diagrams showing a transfer step, an undercut step, and a pick-up step. [Diagram 3] FIG. 13 is an explanatory diagram showing a reversing process and a placing process. [Figure 4] FIG. 2 is an explanatory diagram showing details of a diamond structure. [Diagram 5] FIG. 13 is an explanatory diagram showing the first half of the preliminary process. [Figure 6] FIG. 13 is an explanatory diagram showing the latter half of the preliminary process. [Figure 7](a) is an optical microscope image of the prepared mask, (b) is an optical microscope image of the mask printed on the surface of a diamond plate, (c) is an optical microscope image of the transferred state, (d) is a photograph illustrating a conical Faraday cage, and (e) and (f) are optical microscope images of the undercut state. [Figure 8] 1A is an optical microscope image showing the state of the diamond structure, and FIG. 1B is an optical microscope image of the diamond structure observed from the bottom side. [Figure 9] (a) is a graph showing the PL spectrum, (b) is a graph showing the photon count versus the output from the input laser, and (c) is a graph showing the ODMR spectrum. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, the embodiment of the present invention will be described with reference to the drawings. The present invention relates to a method for integrating fine diamond structures on a desired substrate made of a different material, and the outline of this embodiment is to print a mask made of a material that is resistant to diamond etching and formed into a desired shape on the surface of the diamond substrate, transfer the mask shape by etching, and then separate the diamond structure and attach it onto the substrate made of the different material.

[0026] <Specific Methods in the Embodiments> The procedure based on the above-mentioned integration method will be described with reference to Figs. 1 to 3. A mask 10 is used that has been formed in advance into a desired shape on a predetermined substrate 11 by lithography technology and an etching process. The method for producing this mask 10 will be described later. There are no particular limitations on the mask material as long as it is a material that is robust against diamond etching, and aluminum oxide (AlOx), silicon nitride (SiN), etc. can be used.

[0027] As shown in Fig. 1, the mask 10 is suspended (air-bridged using a tether) on the surface of the fabrication substrate 11, and can be removed using an appropriate adhesive film 20 (see Fig. 1(a)). The removed mask 10 is printed on the surface of a diamond plate 30 while attached to the adhesive film 20 (mask printing process).

[0028] The mask 10 is attached by van der Waals forces to the surface of the diamond plate 30. The state of adhesion between the mask 10 and the adhesive film 20 can be manipulated according to the peeling speed, and after being attached to the surface of the diamond plate 30, the mask 10 and the adhesive film 20 can be peeled off by gently pulling up the adhesive film 20 (see FIG. 1(b)), so that only the mask 10 is attached to the surface of the diamond plate 30 (see FIG. 1(c)).

[0029] Next, as shown in Fig. 2, a diamond structure 50 of a desired shape is formed from the diamond plate 30. First, the mask shape is transferred to the diamond plate 30 by anisotropic etching (transfer process, see Fig. 2(a)). By this transfer, a transfer region 40 is formed in the area where the mask 10 is printed, and the area where the mask 10 is not printed is removed by etching. The etching at this time can be performed by O2 / Ar plasma etching using a mixed gas of argon and oxygen.

[0030] Next, the transfer region 40 to which the mask shape has been transferred is anisotropically etched in an oblique direction (quasi-isotropic etching) to obliquely remove the bottom of the transfer region 40 (undercut process, see FIG. 2(b)). This etching can also be performed by O2 / Ar plasma etching. Note that the oblique anisotropic etching of the transfer region 40 involves irradiating the transfer region 40 with a plasma flow from an oblique direction, and by processing in a pyramidal Faraday cage, the direction of the plasma flow passing through the pyramidal surface can be changed to an oblique direction.

[0031] In this manner, by performing anisotropic etching (quasi-isotropic etching) in the oblique direction, the bottom of the transfer region 40 (the portion not protected by the mask 10) is obliquely etched, thereby forming a diamond structure 50 separated into an approximately triangular cross section.

[0032] Here, the diamond structure 50 can be picked up by attaching a first adhesive film to the front side (the side to which the mask 10 is attached) of the diamond structure 50 (pick-up step, see FIG. 2(c)). Note that it is preferable to configure a tether in order to suspend the diamond structure 50, but the explanation is omitted here.

[0033] As shown in FIG. 3, the diamond structure 50 formed as described above is finally integrated on the surface of a desired substrate 80. First, the diamond structure 50 picked up by the first adhesive film 60 is placed on the upper side of the first adhesive film 60 with the first adhesive film 60 facing down (see FIG. 3(a)). A second adhesive film 70 is attached from above to the bottom side of the diamond structure 50 (the side opposite to the surface side to which the first adhesive film 60 is attached) (see FIG. 3(b)). In this state, the surface side and the bottom side of the diamond structure 50 are individually attached by different adhesive films 60, 70. Then, by peeling off only the first adhesive film 60, the attachment state to the diamond structure 50 can be reversed (reversal process, see FIG. 3(b) to (d)). In order to facilitate this reversal process, the adhesive strength of the second film 70 (second adhesive strength) is stronger than the adhesive strength of the first adhesive film 60 (first adhesive strength). Also, the first adhesive film 60 can be easily peeled off by gently pulling it away.

[0034] In this way, the adhesion state is reversed, and the second adhesive film 70 is in a state where the bottom side (the apex side of the triangular cross section by oblique etching) of the diamond structure 50 is adhered, so that the surface side of the diamond structure 50 can be closely attached to the surface of the desired substrate 80 to be integrated (see FIG. 3(e)). Then, after the surface side of this diamond structure 50 is adhered to the surface of the substrate 80 by van der Waals force, the second adhesive film 70 is peeled off (placement process), and the diamond structure 50 can be integrated on the substrate 80 (see FIG. 3(f)). Even when peeling off the second adhesive film 70, the film 70 can be peeled off while maintaining the adhesion force by van der Waals force by slowing down the peeling speed.

[0035] Incidentally, the diamond structure 50 formed as described above is formed by dividing it into a linear portion 51 having a linear shape (a straight line in the figure) and an annular portion 52 having an annular shape (annular in the figure), as shown in Fig. 4(a). To form the diamond structure 50 having such a shape, the linear portion 51 and the annular portion 52 are initially divided when the mask 10 is formed, but by forming the diamond structure 50 while dividing it into the two portions 51 and 52, each of the steps of the pick-up step (see Fig. 2(c)) and the inversion step (see Figs. 3(b) to (d)) can be facilitated.

[0036] That is, although the surface of the linear portion 51 has some area, it is almost linear and often does not have an area where the adhesive film 60, 70 can be sufficiently attached. On the other hand, the annular portion 52 is formed with a larger outer diameter, and the adhesive film 60, 70 can be attached to the periphery of the annular portion 52, so that the adhesive film 60, 70 can be sufficiently attached. In particular, when the diamond structure 50 in the present invention has a fine structure (micro-level or nano-level), the difficulty of attachment by the linear portion 51 becomes significant, so that the pick-up process (see FIG. 2(c)) and the inversion process (see FIG. 3(b) to (d)) can be realized by exclusively using the annular portion 52. In this way, the annular portion 52 can function as an attachment auxiliary part. In this embodiment, the entire diamond structure 50 is formed as a two-layer structure composed of the remaining part of the transfer region 40 and the mask 10. The diamond structure 50 may have such a two-layer structure, but may also be composed of only the area where the mask 10 is removed and the transfer region 40 is undercut.

[0037] Also, as shown in Fig. 4(b), in the inversion process (see Figs. 3(b) to (d)), the bottom side of the diamond structure 50 is etched obliquely to form the apex corner portion 50a of a triangle by the undercut process (see Fig. 2(b)). Therefore, it is necessary to consider the difficulty of attaching the bottom side of the diamond structure 50 by the second adhesive film 70 in the inversion process (see Figs. 3(b) to (d)).

[0038] Therefore, as shown in Fig. 4(c), by using a material having suitable flexibility as the base material for the second adhesive filler 70, the adhesive surface of the second adhesive filler 70 can be made to be able to adhere to the oblique side portions 50b, 50c located on both sides of the apex angle portion 50a on the bottom side of the diamond structure 50. In this way, by adhering the second adhesive filler 70 to the bottom side oblique side portions 50b, 50c of the diamond structure 50, it is possible to make it possible to adhere to a range exceeding the area of ​​the flat portion 50d on the surface side of the diamond structure 50. Note that the material as the base material may be elastic instead of flexible.

[0039] Thus, even when the bottom side of the diamond structure 50 is attached by the second adhesive film 70, it is necessary to provide a difference in adhesive strength between the first adhesive film 60 and the second adhesive film 70. Even if it is assumed that both films 60, 70 are attached to a moderate area on both sides (especially centered on the annular portion 52), the first adhesive film 60 can be peeled off suitably if the adhesive strength of the second adhesive film 70 is about twice or more that of the first adhesive film 60. Incidentally, it was confirmed that when the adhesive strength (peel strength in 180-degree direction peel strength test) of the first adhesive film 60 is 4.5 to 6.5 (g / 0.75"), by setting the adhesive strength (same peel strength) of the second adhesive film 70 to 14.0 to 20.0 (g / 0.72"), it is possible to peel off only the first adhesive film 60 while maintaining the adhesion state by the second adhesive film 70.

[0040] Since this embodiment uses the above-mentioned method, it is possible to integrate the smooth surface side of the undercut diamond structure 50 on the substrate 80. In the above-mentioned embodiment, the mask 10 printed on the surface side of the diamond structure 50 is left in a state of being laminated on the surface side of the diamond structure 50 as it is, but this mask 10 may be removed at an intermediate stage. The mask 10 can be removed by etching using a specified etching agent, or the like.

[0041] <Example of preliminary process> As described above, diamond etching requires that the mask 10 made of a material that is robust against diamond etching be printed on the diamond plate 30. A specific example of a process (preliminary process) for producing this mask 10 will now be described.

[0042] 5 to 6 are diagrams illustrating the preliminary steps. When making the mask 10, first, an arbitrary substrate (preferably a Si substrate because lithography and etching processes are used) 91 is used, and a sacrificial layer 92 is laminated on the surface of the substrate 91 (see FIG. 5(a)). The sacrificial layer can be formed by oxidizing a silicon substrate to form a silicon oxide film (SiO2). The sacrificial layer means a layered region on the surface of which other materials can be laminated, on the premise that it will be removed later by etching. A mask material layer 93 made of a mask material (material that will later become the mask 10) is laminated on the surface of the sacrificial layer 91 (see FIG. 5(b)). Furthermore, a resist 94 of a desired shape that is to be left as a mask shape is patterned on the surface of the mask material layer 93 (see FIG. 5(c)).

[0043] Then, a mask of the desired shape is formed by transferring the mask material layer 93 by anisotropic etching (see FIG. 6(a)), and after removing the resist 94 (see FIG. 6(b)), the sacrificial layer is finally removed by etching, so that only the mask 10 portion can be obtained as an independent entity.

[0044] Although not shown in the figure, the mask portion 10 that will eventually be separated from the surrounding mask materials 95, 96 is not completely separated, but is configured to be connected by a part (fine part) as a tether. By providing this tether, the mask portion 10 is in an air-bridged state, and it becomes possible to pick up only the mask portion 10 from the front side by the adhesive film. EXAMPLES

[0045] <Experimental Example 1> 1.Preliminary process As a preliminary step, a mask was made of silicon nitride (SiN). First, the surface of the Si substrate was oxidized to form a silicon oxide (SiO2) film with a thickness of 100 nm, and a sacrificial layer was constructed. Silicon nitride (SiN) was deposited on the surface to form a slab with a thickness of 200 nm. Next, a polymer resist (Zeon Corporation, main chain break type positive electron beam resist ZEP520A) was patterned by electron beam lithography, laminated as a mask for the pre-process, and unnecessary parts were removed by dry etching (anisotropic etching). After that, the resist was removed by an ashing process, and finally, the sacrificial layer (silicon oxide) was removed by wet etching with a hydrogen fluoride (HF) solution, and the part to be the mask was made in a floating state by an air bridge (using a tether). An optical microscope image of the fabricated mask is shown in Figure 7(a).

[0046] The mask shape was made so that the ring-shaped parts were circular and the linear parts were straight. The dimensions of each part were: outer diameter 2.0 μm, inner diameter 1.4 μm for the ring-shaped parts, width 0.4 μm, total length 3.0 μm for the linear parts, and the overall structure was micro-level fine.

[0047] 2. Diamond Etching A diamond plate was prepared to fabricate the diamond structure. The diamond plate prepared for the experiment was a 3 mm thick plate (30 mm x 30 mm) made of single crystal type II-a diamond manufactured by ElementSix, which was mechanically polished and then cleaned with acetone. Since it was not necessary to measure the quantum properties here, we decided to use one that did not contain a color center (NV center).

[0048] The adhesive film for printing was made of PDMS (polydimethylsiloxane), specifically Sylgard184 manufactured by Dow Corning. The mask was quickly lifted using this adhesive film, and the floating mask was removed and printed on the surface of the diamond plate. The van der Waals forces were used between the diamond plate surface and the mask during printing, and the mask could be fixed without using any special adhesive material. The optical microscope image at this time is shown in Figure 7(b).

[0049] Next, the mask pattern was transferred to the diamond plate. The transfer was performed by anisotropic etching using O2 / Ar plasma dry etching using a mixed gas of argon and oxygen, except for the area protected by the mask. Using an inductively coupled plasma dry etching device (ICP-RIE device) manufactured by ULVAC, Inc., the etching was performed with a volumetric flow rate of oxygen (O2) gas of 40 sccm, a volumetric flow rate of argon (Ar) gas of 2 sccm, a pressure of 1 Pa, a bias high frequency power of 1000 W, and an etching time of 8 minutes, completing the transfer. The optical microscope image at this time is shown in Figure 7(c).

[0050] The bottom of the transferred diamond was then undercut by anisotropic etching (quasi-isotropic etching) in the oblique direction. The etching was performed using an inductively coupled plasma dry etching apparatus (ICP-RIE apparatus) manufactured by ULVAC, Inc., in the same manner as in the transfer process, with the same volumetric flow rates of oxygen (O2) gas and argon (Ar) gas, a pressure of 1 Pa, a bias high-frequency power of 1000 W, and an etching time of 10 minutes. In this undercut process, the transfer area was covered with a pyramidal Faraday cage as shown in Figure 7(d), which enabled oblique etching by guiding the plasma flow obliquely. The size of the pyramidal Faraday cage was about 5 mm in bottom diameter, about 2 mm in top diameter, and 60 degrees inclination angle of the oblique side, so that multiple transfer areas could be covered at once. Optical microscope images after the undercut process are shown in Figures 7(e) and (f). In addition, the undercut transfer region is clearly separated in the linear portion, and only a small continuous portion remains in the annular portion, and the continuous portion can be finished as a tether and in an air-bridged state.

[0051] 3. Evaluation As described above, in the experiment using single crystal type II-a diamond, it was found that a diamond structure can be fabricated. Also, by separately constructing the ring part and the linear part, it is possible to obtain a diamond structure in an air bridge state supported by the tether of the ring part.

[0052] The linear part (straight part) can be used as a waveguide, and the diamond waveguide containing the NV center is generally placed on a silicon substrate (silicon oxide film surface), which is an integrated optics and low refractive index material, and this allows efficient light confinement within the waveguide. On the other hand, the NV center has two even-pole directions, and efficient wave coupling of the NV emission requires support for both transverse electric (TE) polarization and transverse magnetic (TM) polarization. Therefore, the refractive index dispersion of the waveguide mode was simulated using the finite element method, and it was found that when the width of the waveguide was about 400 nm, an efficient refractive index of "2.0" for both polarizations was obtained, but when the width was less than 300 nm, the refractive index was "1.5", which resulted in weak light confinement and low even-pole-wave coupling. In addition, when the width was 450 nm or more, the dispersion of the higher-order mode was expressed, and the phenomenon of waveguide coupling was predicted. Therefore, we further simulated the dipole-waveguide coupling efficiency by the finite difference time domain method, and confirmed that the waveguide width is maximized at about 400 nm in both even pole directions. Since this is very similar to the dispersion calculation result, it is considered that the waveguide width should be set at 400 nm. Therefore, the width dimension of the linear part in the above-mentioned diamond structure is based on 400 nm.

[0053] <Experimental Example 2> 1. Diamond structure assembly Next, as Experimental Example 2, a diamond structure was produced using a diamond plate containing an NV center, and was integrated on a silicon substrate (silicon oxide film). The pre-processing to the undercutting process were the same as in Experimental Example 1. However, the diamond plate used was a 5 mm thick plate (30 mm x 30 mm) made of a diamond NV substrate (DNV-B1) manufactured by ElementSix. The substrate to be integrated was a silicon substrate whose surface was oxidized to produce a silicon oxide film having a thickness of 1 μm. FIG. 8(a) is an optical microscope image showing the state of a diamond structure containing an undercut NV center, and FIG. 8(b) is an optical microscope image of the diamond structure observed from the bottom side (undercut side).

[0054] As described above (Example 1), a homemade adhesive film with adhesive strength equivalent to that of a commercial PDMS film (Gel-Pak (registered trademark) X4 manufactured by Delphon Industries LLC (peel strength 4.5 to 6.5 (g / 0.75") in a 180-degree peel strength test) was fabricated for the diamond structure in an air-bridged state via a tether, and the diamond structure was picked up.

[0055] Then, the homemade film was turned over, and a commercial PDMS film ("Gel-Pak (registered trademark)" X8 (peel strength in 180 degree peel strength test: 14.0 to 20.0 (g / 0.72"), manufactured by Delphon Industries LLC) was attached to the diamond structure from the other side, and the homemade film was peeled off to invert the diamond structure onto the commercial film.

[0056] The inverted diamond structure was placed on a silicon substrate with the front side in close contact with the surface of a silicon oxide film formed on the silicon substrate, and the commercial film was gently pulled up to separate it. The diamond structure and the silicon oxide film were fixed together by van der Waals forces.

[0057] As described above, the surface side of the diamond structure protected by the mask (or the printed mask surface) is fixed in intimate contact with the silicon substrate (silicon oxide film surface), thereby enabling the diamond structure to be integrated on the silicon substrate.

[0058] 2. Evaluation The diamond structure integrated on the silicon substrate in the above manner can function as a waveguide using its linear portion. Therefore, the optical characteristics of the diamond structure integrated on the silicon substrate (hereinafter referred to as the fabricated device) were measured.

[0059] First, photoluminescence (PL) characterization was performed. The fabricated device was irradiated with an optically excited laser beam using a continuous wave laser (Gem532, Laser Quantum) oscillating at a wavelength of 532 nm, and the PL signal was collected. A 1.25×100 numerical aperture objective lens was used to collect the PL signal. In addition, to suppress the background light of the input laser, the PL signal from the NV center was filtered with a notch filter (533 nm) and a long pass filter (>600 nm), and the background emission from the silicon substrate was processed with a short pass filter (<800 nm). The collected PL signal was analyzed using a grating spectrometer (Acton SP2500, Princeton Instruments) and a silicon charge-coupled device camera (CCD camera, PIXIS256E, Princeton Instruments).

[0060] The results are shown in Figure 9(a) and (b). Figure 9(a) shows the PL spectrum measured for the fabricated device, which shows a strong peak of phonon sideband emission (~700 nm) with the zero phonon line (637 nm) and the input laser peak (532 nm), confirming the PL signal originating from the emission from the integrated NV centers. Figure 9(b) shows the photon count versus the input laser power.

[0061] Next, to confirm the applicability of the fabricated device as a quantum sensor, we performed optically detected magnetic resonance (ODMR) measurements on the fabricated device. The diamond structure containing the NV center was excited with microwaves using a copper thin film placed near the fabricated device. The results are shown in Figure 9(c). Figure 9(c) shows the ODMR spectrum of the fabricated device in the absence of an external magnetic field, and the ODMR spectrum of a diamond containing a typical NV center is overlaid on it.

[0062] The results showed that the ODMR dip with a contrast of about 0.006 was observed at a microwave frequency of 2.88 GHz, which was almost consistent with a typical ODMR spectrum, indicating that the fabricated device has potential for use as a quantum sensor.

[0063] <Summary> As described above, according to the method for integrating diamond structures shown in the above embodiment, fine diamond structures can be easily integrated on any substrate surface of different materials. In particular, by undercutting the bottom of the area where the mask pattern is transferred by anisotropic etching (quasi-isotropic etching) in an oblique direction, a diamond structure with a cross section of approximately triangular shape is formed, and then the smooth surface side that is not affected by etching is attached to a substrate of a different material, so that the diamond structure can be integrated on the substrate. Naturally, this enables the scalable integration of the technology disclosed above with other advanced photonics technologies.

[0064] It should be noted that the above-described embodiment is merely an example of the present invention, and the present invention is not limited to these embodiments. Therefore, each element of the above-described embodiment may be changed, or other elements may be added.

[0065] For example, in the above embodiment, PDMS film is used as the base material of the first and second adhesive films 60, 70, but other base materials may be used, such as films having appropriate flexibility. Also, the difference in adhesion between these is preferably 2 times or more, but it is not necessary to have a very large difference, and a difference of up to 10 times can achieve the purpose.

[0066] In addition, the length of the linear portion of the diamond structure is 4 μm as an experimental level, and a mask pattern is formed to form the linear portion of the length by transferring the mask pattern, but the diamond structure can be made to an appropriate length depending on the purpose. On the other hand, the ring-shaped portion is made circular as an example, but it is not limited to a ring, and can be formed as a polygonal ring as long as the adhesion area by the adhesive film can be secured. The difference between the outer diameter and the inner diameter (the width dimension of the ring-shaped portion) at this time is appropriately selected according to the width dimension of the linear portion, and if the width dimension of the ring-shaped portion is much larger than the width dimension of the linear portion, the etching time for undercutting the ring-shaped portion will be long, and the approximately triangular cross section will be enlarged, so it is preferable to make the width dimension appropriate to the extent that a tether is formed. [Explanation of symbols]

[0067] 10. Mask 11 Substrate for mask production 20 Adhesive film (for mask printing) 30 Diamond Plate 40 Transcription Region 50 Diamond Structure 50a Apex corner (bottom side of diamond structure) 50b, 50c Bottom side hypotenuse portion (bottom side of diamond structure) 50d Flat surface (surface side of diamond structure) 51 Linear part (straight line part) 52 Ring section (ring section) 60 First adhesive film 70 Second adhesive filter 80 Desired substrate 91 Any substrate (silicon substrate) 92 Sacrificial layer (silicon oxide film) 93 Mask material layer 94 Resist 95,96 Mask materials (materials around the mask)

Claims

1. A mask printing process for printing a mask formed in a desired shape and made of a material that is resistant to diamond etching on a surface of a diamond substrate formed of a diamond crystal including a color center; a transfer step of transferring a mask pattern by anisotropic etching in a direction perpendicular to the surface of the diamond substrate on which the mask is printed; an undercut process in which a bottom portion of the transfer region transferred in the transfer process is obliquely removed by quasi-isotropic etching, which is anisotropic etching in an oblique direction, to separate the transfer region into a substantially triangular cross section to form a diamond structure; a pick-up step of sticking a first adhesive film having a first adhesive strength to a surface side of the diamond structure and picking up the diamond structure; a reversal step of adhering a second adhesive film having a second adhesive strength greater than the first adhesive strength to a bottom side of the diamond structure, and peeling off the first adhesive film from the surface side of the diamond structure to reverse the adhesion state of the diamond structure; a placing step of adhering the surface side of the diamond structure to a predetermined substrate and peeling off the second film from the bottom side of the diamond structure; 2. A method for integrating diamond structures comprising:

2. 2. The method for integrating diamond structures as described in claim 1, wherein the shape of the mask includes a linear portion and an annular portion continuous with the linear portion, and the annular portion is formed with an outer diameter larger than the width dimension of the linear portion.

3. 3. The method for integrating diamond structures as described in claim 2, wherein the undercutting process involves etching to a state in which the area to which the linear portion has been transferred is raised, and a portion of the area to which the annular portion has been transferred remains as a tether, and the entire diamond structure formed by the undercutting process is in an air-bridged state via the tether.

4. 4. The method for assembling diamond structures according to claim 3, further comprising the step of removing the mask remaining on the surface of the diamond structure after the undercutting step.

5. A preliminary step for producing the mask in a desired shape, the preliminary step comprising: depositing a sacrificial layer onto the substrate as appropriate; depositing a mask material on a surface of the sacrificial layer; A step of patterning a resist having a shape that matches the shape of the mask on a surface of the deposited mask material; forming the mask in a desired shape by etching the mask material; removing the resist; removing the sacrificial layer by etching; The method for assembling diamond structures according to any one of claims 1 to 4, comprising:

6. A method for accumulating diamond structures as described in any one of claims 1 to 4, wherein the second adhesive strength of the second adhesive film is at least twice as large as the second adhesive strength of the first adhesive film.

7. 5. The method for assembling a diamond structure according to claim 1, wherein the color center is a complex (NV center) of nitrogen (N) substituting a carbon atom and a vacancy (V) adjacent to the nitrogen.

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