Method of manufacturing a diamond membrane for quantum systems, quantum communications and / or quantum sensors

Abstract

The present invention relates to a method of manufacturing a diamond membrane for quantum systems, quantum communications and / or quantum sensors. The method comprises - patterning a nanophotonic structure on a primary surface of a diamond membrane; - arranging a mask on a secondary surface of a diamond membrane, the secondary surface being arranged opposite of the primary surface, wherein the mask comprises a first surface and a second surface that is arranged opposite of the first surface, the mask further comprising a mask hole extending from a first opening in the first surface to a second opening in the second surface, wherein the mask hole comprises at least one mask hole wall that is arranged at an angle with respect to the secondary surface of the diamond membrane when the mask is arranged on the secondary surface, wherein the angle is in the range of 5-85 degrees; and - etching the secondary surface of the diamond membrane while the mask is arranged on the secondary surface.

Description

[0001] METHOD OF MANUFACTURING A DIAMOND MEMBRANE FOR QUANTUM SYSTEMS, QUANTUM COMMUNICATIONS AND / OR QUANTUM SENSORS

[0002] The present disclosure relates to a method of manufacturing a diamond membrane for quantum systems, quantum communications and / or quantum sensors. The method further relates to a quantum system comprising such a diamond. Furthermore, the present disclosure relates to a mask configured to be arranged on a surface of a diamond membrane during etching.

[0003] Diamond material has the highest hardness and thermal conductivity of any natural material. Therefore diamond material is of major interest in a variety of applications, for example quantum technologies. As diamond material also has the property of being chemically inert, diamond material is very hard to micromachine into structures of nanometer scale, which scale is of great interest for quantum technologies.

[0004] As a material, diamond can host a variety of optically active spin defects, which are currently promising for the realization of quantum networks. For successful fabrication of nanophotonic structures hosting color centers in diamond, certain requirements have to be met. These requirements are device layers of uniform thickness, for example around 150 nanometres to 200 nanometres, being wedge-free, having low surface roughness, being free of contamination and being free of crystal lattice damage. However, up to date, no wet based etching techniques allow for fabrication of diamond device layers in a systematic manner that would satisfy the above requirements. The state-of-the-art techniques that allow fabrication of diamond nanodevices rely on dry etching methods, such as inductively coupled plasma reactive ion etch (ICP-RIE), starting from bulk diamond substrates.

[0005] There are several known fabrication methods of nanophotonic diamond structures starting from bulk diamond material. Diamond nanofabrication processes currently lack a method for wetetch undercutting of nanophotonic structures in diamond by means of a wet etch of a sacrificial layer, as conventionally adopted strategy in the traditional silicon photonics (i.e. silicon on insulator (SOI) platform). In the past decade, various efforts have been directed towards alternative methods that would enable successful fabrication of diamond nanophotonic devices starting from bulk diamond substrates.

[0006] The main directions towards fabrication of diamond thin films of hundreds of nanometers starting from single crystal diamond (SCD) membranes of tens of micrometres can be grouped in two categories; selective etching of a sacrificial graphite layer, and thinning of the diamond membrane.

[0007] The first category is selective etching of a sacrificial graphite layer which comprises ion implantation, for example with helium ions, where the implantation energy is set such that the crystal damaged is minimized, while at the same time the dose is above the graphitization threshold such that a depth-localized graphitized layer can be formed. Such graphitized layer can be wet etched, releasing the diamond membrane, that subsequently is transferred on a carrier wafer chip.

[0008] Recent research showed a diamond thin film bonded onto a variety of substrate platforms consisting of a thin diamond membrane layer (of approximately 160 nm, area of 200 micrometers x 200 micrometers, thickness variation up to 1 nm and surface roughness 0.3 nm), bonded to substrates such as fused silica, thermal oxide silicon among others. One publication which relates to this method is “Tunable and Transferable Diamond Membranes for Integrated Quantum Technologies”, Xinghan Guo, Nazar Delegan, Jonathan C. Karsch, Zixi Li, Tianle Liu, Robert Shreiner, Amy Butcher, David D. Awschalom, F. Joseph Heremans, and Alexander A. High, Nano Letters 2021, 21 (24), 10392-10399. The fabrication of such plates is challenging, encompassing several fabrication steps, including as the main steps helium implantation to a depth predetermined by the Stopping and Range of Ions in Matter (SRIM) to damage and multistep annealling in order to graphitize a layer of diamond inside the bulk sample. This is then followed by overgrowth of a pristine non damaged layer of diamond. Subsequently, patterning of 200 micrometers x 200 micrometers membrane dimensions by means of lithography and dry etching from top down (to transfer the pattern into the diamond sample), followed by localized electrochemical etch of the graphitized diamond layer and release of such membranes from the bulk substrate. It is noted that the electrochemical etching is laborious, as it requires two electrodes to be placed in the close vicinity of each plate, to allow for a subsequent release via electrochemical etch. The diamond crystal layer that is damaged due to helium implantation is then removed on the released plates, as only the pristine overgrown diamond layer is useful for quantum applications.

[0009] The shortcomings of this fabrication process are that the required time for full release of plates from a parent diamond bulk substrate is relatively long, in particular due to electrochemical etching, the impossibility to handle membrane layers with tweezers by the operator, and the small surface area per plate.

[0010] Regarding the long release time, each 160 nm thick, 200 micrometers x 200 micrometers diamond plate is released separately from the parent chip via electrochemical etching, characterized by a relatively long release time per plate. As the electrochemical release is done individually and limited to 1 plate per round, this severely limits the overall yield of plates. Moreover, handling of each separate released plate represents a tedious process requiring several manual handling steps per full fabrication of devices per sample, with the risk of increasing organic contamination that subsequently can compromise the dry etch steps, increasing the chances of introducing micromasking on the device layer surface area, with ultimately compromising the quality of the diamond thin film.

[0011] Regarding the handling of the sample, the released thin membrane plates of 200 micrometers x 200 micrometers, each individually require a transfer printing, or pick and place process dedicated setup that would allow to place the membrane layers on a carrier chip. Furthermore, it is impossible to handle the membrane layers with tweezers by the operator. In order to overcome this sample handling challenge, a dedicated laboratory setup is required, which can be e.g. either a transfer printing setup, or a pick and place setup, resulting in additional processing time per each released plate.

[0012] Regarding the low yield, the number of released plates per each electrochemical etch step is only one plate per each round of electrochemical etching, therefore limiting the number of identical thickness devices per plate to the limited surface area.

[0013] The second category is thinning of diamond membrane that comprises starting from a commercially available diamond membrane of few micrometers thick. The diamond membrane is directly hosted by a carrier wafer chip, and is thinned down by means of reactive ion etching to a device layer compatible with nanophotonic devices fabrication (typically up to 200 nanometers thick). This is followed by dry and / or wet etching methods to undercut the host wafer chip and suspend the devices. In general the second category comprises two subcategories. The first subcategory comprises bonding of the diamond membranes to the silicon substrate and afterwards top down etching. The second subcategory comprises thinning down the diamond membrane with a quartz mask.

[0014] The shortcomings of this fabrication process are the challenges to handle membrane layers with tweezers, a non-uniform yield of the reactive ion etching, and the difficulty of obtaining uniform thickness of the bottom layer.

[0015] Regarding the handling of the sample, which mainly relates to the first subcategory, the released thin membranes require a pick and place process dedicated setup to place the membrane layers on a carrier chip, with challenging handling of the membrane layers prior to bonding stage. Bonding in general is challenging, as the surfaces need to be extremely smooth to bond effectively. Additionally, organic contamination might lead to presence of debris that can lead to imperfect bonding, or even prevent bonding.

[0016] Regarding the non-uniform yield, which mainly relates to the second subcategory, the reactive ion etching leads to round edges of the thinned down membranes. Up to this date no suitable monolithically integrated hard mask material that would allow for etching down several tens of micrometers of a large surface area of diamond in a planar uniform way is known, down to thicknesses compatible with nanophotonic integration, without compromising the surface roughness of the yielded device layer surface.

[0017] Regarding the difficulty of obtaining a uniform thickness of the bottom layer, up to date, there are no existing ICP-RIE methods to compensate the wedge of several micrometers thin diamond membranes, without employing alternative diamond fabrication processes. It is an object for the present disclosure to obviate or at least reduce the abovementioned problems. In particular, it is an object for the present disclosure to provide a method of manufacturing a diamond membrane that can effectively thin a diamond membrane from micrometer thickness order of magnitude down to a device layers thickness that is suitable for nanophotonic integrations.

[0018] This object is achieved by a method of manufacturing a diamond membrane for quantum systems, quantum communications and / or quantum sensors, wherein the method comprises: patterning a nanophotonic structure on a primary surface of a diamond membrane; arranging a mask on a secondary surface of a diamond membrane, the secondary surface being arranged opposite of the primary surface, wherein the mask comprises a first surface and a second surface that is arranged opposite of the first surface, the mask further comprising a mask hole extending from a first opening in the first surface to a second opening in the second surface, wherein the mask hole comprises at least one mask hole wall that is arranged at an angle with respect to the secondary surface of the diamond membrane when the mask is arranged on the secondary surface, wherein the angle is in the range of 5-85 degrees; and etching the secondary surface of the diamond membrane while the mask is arranged on the secondary surface.

[0019] An advantage of the angle of the at least one mask hole wall is that the secondary surface that is exposed due to being positioned under the mask hole is homogenously etched. In other words, material is removed from the etching area at substantially the same rate at all positions of the etching area. In this way, the nanophotonic structure that is positioned on the primary surface of the diamond membrane can be thinned down to a desired thickness. This is important, because the thickness of the nanophotonic structures determines at least partly the characteristics of the nanophotonic structures. With the method according to the present disclosure the thickness of the nanophotonic structure can be thinned down to e.g. 200 nanometres, or even lower if desired.

[0020] Another advantage of is that due to the mask being arranged on the secondary surface during etching a part of the diamond membrane is protected from etching during the etching of the secondary surface. In this way part of the diamond membrane, preferably the outer edges of the diamond membrane, keep the thickness they had before the etching step. A frame part is obtained that has a higher thickness than the part that is etched and that comprises the nanophotonic structure. The frame part allows for easier handling of the sample. Furthermore, it reduces the risk of breaking the thinned-down membrane upon manual tweezers handling. Alternatively, or additionally, there is no need of e.g. a pick and place setup to operate further processing steps on the sample. With the method disclosed in the present disclosure the main challenges of the prior art associated to the thinning down diamond membrane for nanophotonic fabrication of devices are solved. In order to avoid backscattering from the plasma ions, the angle of the mask is decided based on the allowed by selectivity thickness of the mask. A modular design of such mask allows for simple manual alignment of the mask around the etching region of interest, without the need of a precision alignment tool as the mask modules are manually located close to the diamond substrate walls, upon e.g. optical microscope inspection during the positioning of the mask by the operator with tweezers.

[0021] The second surface of the mask may be positioned on the secondary surface of the diamond membrane when the secondary surface of the diamond membrane is etched. The at least one hole wall being arranged at an angle with respect to the secondary surface of the diamond membrane also can be described as the at least one hole wall being positioned at an angle, or having an angle, with respect to the secondary surface of the diamond membrane. The at least one hole wall has a design such that the at least one hole wall is arranged at an angle when the mask is arranged on the secondary surface of the diamond membrane during etching.

[0022] In the context of the present disclosure, the thinned down secondary surface on which the nanophotonic devices are patterned may also be denoted as bottom layer or device layer.

[0023] In the context of the present application the diamond membrane that is manufactured can be denoted as second diamond membrane, and the diamond membrane that is initially provided and on which operation are performed to obtain the second diamond membrane can be denoted as first diamond membrane.

[0024] The steps of the method may be performed sequentially.

[0025] In an embodiment a first diameter of the first opening is smaller than a second diameter of the second opening.

[0026] An advantage of the first diameter being smaller than the second diameter is that backscattering of ions during etching due to ions hitting the at least one mask hole wall is prevented, or at least reduced. In other words, ions that enter the mask hole are not, or at least less, reflected against the at least one mask hole wall. This ensures a homogeneous etching of the secondary surface that is exposed under the mask hole.

[0027] The first diameter and the second diameter may be the effective first diameter and the effective second diameter. The first diameter and the second diameter may be a biggest distance between the edges of respectively the first opening and the second opening. For example, for a circular opening this may be the diameter, for a rectangular opening this may be the distance between opposing corners.

[0028] In an embodiment a diameter of the mask hole increases from the first opening to the second opening, wherein the diameter preferably linearly increases. An advantage of the diameter of the mask hole increasing is that ions that enter the mask hole are not, or at least less, reflected against the at least one mask hole wall. This ensures a homogeneous etching of the secondary surface that is exposed under the mask hole.

[0029] In an embodiment the etching of the secondary surface of the diamond membrane removes material from the secondary surface such that the mask protects a frame part which is configured to provide mechanical stability to the diamond membrane, including e.g. during handling of the membrane, and the etching through the mask hole reduces the thickness of a device part which comprises the nanophotonic structure.

[0030] The frame part can be defined as the part of the diamond membrane that is protected from etching. The part of the diamond membrane that is protected from etching is protected due to the mask that is arranged on top of the secondary surface of the diamond membrane. The frame part generally maintains the starting thickness, i.e. the thickness of the diamond membrane before etching.

[0031] The device part can be defined as the part of the diamond membrane that is not protected from etching. Alternatively, or additionally, the device part can be defined as the part of the diamond membrane that is thinned down during etching. The device part normally comprises the nanophotonic structure. The thickness of the device part is reduced such that the thickness of device part is suitable to give the desired properties of the nanophotonic structure.

[0032] In an embodiment a starting thickness of a frame part of the diamond membrane, before etching, is in the range of 1-100 micrometres, preferably in the range of 5-70 micrometres, most preferably in the range of 25-50 micrometres.

[0033] In an embodiment a final thickness of a device part of the diamond membrane, after etching, is in the range of 100-300 nanometres, preferably in the range of 125-250 nanometres, most preferably in the range of 150-200 nanometres.

[0034] In an embodiment the at least one mask hole wall comprises at least two mask hole walls that are oppositely arranged.

[0035] In an embodiment the angle is in the range of 40-80 degrees, preferably in the range of 60- 75 degrees.

[0036] The abovementioned ranges provide a homogeneous etching of the etching area.

[0037] In an embodiment the at least one mask hole wall comprises a planar surface.

[0038] In an embodiment a thickness of the mask is in the range of 100 nanometres-200 micrometres, preferably in the range of 50-150 micrometres, most preferably in the range of 80- 120 micrometres, for example 100 micrometres.

[0039] Experiments have shown that abovementioned thicknesses of the mask in combination with the abovementioned ranges of the at least one hole wall provide a desired etching of the etching area. Concerning the design of pre-fabricated mask, the main parameters of interest are the thickness of the mask combined with the angle of the at least one hole wall. Experiments have shown that with a pre-fabricated fused quartz mask with a starting thickness of 100 micrometers (and subsequently lower than 100 micrometers due to etching of the mask as well) and an angle of the at least one hole wall being between 60 degrees and 75 degrees, under alternated argon / chlorine (Ar / Ch) and oxygen (O2) ICP-RIE etch steps yield flat diamond device layers of thickness around 200 nm, with a typical surface roughness of 0.5 nm and a variation of the device layer of less than 65 nm over an area 600 pm x 600 pm for an aperture of the mask of 1.4 mm xl.4 mm. It is clear for the skilled person that the plasma ions used in the abovementioned experiment is not essential for the present disclosure, and that other plasma ions may also be suitable.

[0040] In an embodiment the mask comprises a quartz mask, for example a fused quartz mask, or polycrystalline diamond.

[0041] A quartz mask and a polycrystalline diamond have a lower etching rate than the diamond membrane and therefore are suitable materials for the mask. A lower etching rate in the context of the present disclosure means that material is removed at a slower rate during etching.

[0042] Alternatively, the mask comprises a silicon nitride (SixNy) mask. Alternatively, the mask comprises an aluminum oxide based ceramic material.

[0043] In an embodiment patterning the nanophotonic structure comprises electron beam lithography.

[0044] In an embodiment the method further comprises, after patterning the nanophotonic structure, applying reactive ion etching to the primary surface to transfer the pattern into a hard mask material and subsequently from the hard mask material into the diamond material. The patterning may comprise electron beam lithography.

[0045] In an embodiment the method further comprises, prior to the step of patterning the nanophotonic structure: pre-treating the primary surface and / or the secondary surface of the diamond membrane by reactive ion etching, wherein the reactive ion etching preferably comprises switching between a first cycle of applying argon and chlorine (Ar / Ch) ions and a second cycle of applying oxygen (O2) ions.

[0046] In an embodiment the method further comprises, prior to pre-treating: inorganically wet cleaning the diamond membrane.

[0047] In an embodiment the method further comprises: quasi-isotropic plane dependent reactive ion etching, preferably using oxygen ions, of the primary surface and / or secondary surface of the diamond membrane to remove a diamond wedge of the diamond membrane. By using quasi-isotropic plane dependent removal of the wedge is obtained. The quasi- isotropic plane dependent etch is characterized by an etch rate that is plane dependent. Therefore some planes, such as the <100> plane, are being etched faster than other planes, such as the < 111 > plane. This will result at the end of the process in fully exposed planes on both the primary surface and the secondary surface, thereby obtaining ideally perfectly parallel and wedge free surfaces.

[0048] Generally, the primary and / or secondary surface may be exposed to the <100> crystallographic plane or the < 111 > crystallographic plane.

[0049] In an embodiment the reactive ion etching comprises inductively coupled plasma reactive ion etching.

[0050] The reactive ion etching preferably comprises switching between a first cycle of applying argon and / or chloride ions and a second cycle of applying oxygen ions.

[0051] The present disclosure further relates to a diamond membrane obtained by the method according to any one of the foregoing embodiments.

[0052] The diamond membrane has similar effects and advantages as disclosed for the method.

[0053] The present disclosure further relates to a quantum system comprising a diamond membrane according to the abovementioned embodiment.

[0054] The present disclosure further relates to a mask configured to be arranged on a surface of a diamond membrane during etching, comprising: a first surface and a second surface that is arranged opposite of the first surface, further comprising a mask hole extending from a first opening in the first surface to a second opening in the second surface, wherein the mask hole comprises at least one mask hole wall that is arranged at an angle with respect to secondary surface, wherein the angle is in the range of 40 - 85 degrees.

[0055] The diamond membrane has similar effects and advantages as disclosed for the method and the diamond membrane.

[0056] In an embodiment a first diameter of the first opening is smaller than a second diameter of the second opening.

[0057] An advantage of the first diameter being smaller than the second diameter is that backscattering of ions during etching due to ions hitting the at least one mask hole wall is prevented, or at least reduced. In other words, ions that enter the mask hole are not, or at least less, reflected against the at least one mask hole wall. This ensures a homogeneous etching of the secondary surface that is exposed under the mask hole.

[0058] The first diameter and the second diameter may be the effective first diameter rand the effective second diameter. The first diameter and the second diameter may be a biggest distance between the edges of respectively the first opening and the second opening. For example, for a circular opening this may be the diameter, for a rectangular opening this may be the distance between opposing corners.

[0059] In an embodiment a diameter of the mask hole increases from the first opening to the second opening, wherein the diameter preferably linearly increases.

[0060] An advantage of the diameter of the mask hole increasing is that ions that enter the mask hole are not, or at least less, reflected against the at least one mask hole wall. This ensures a homogeneous etching of the secondary surface that is exposed under the mask hole.

[0061] In an embodiment the at least one mask hole wall comprises at least two mask hole walls that are oppositely arranged.

[0062] In an embodiment the angle is in the range of 50-80, preferably in the range of 60-75 degrees.

[0063] In an embodiment the at least one mask hole wall comprises a planar surface.

[0064] In an embodiment a thickness of the mask is in the range of 100 nanometres-200 micrometres, preferably in the range of 50-150 micrometres, most preferably in the range of 80- 120 micrometres, for example 100 micrometres.

[0065] Experiments have shown that abovementioned thicknesses of the mask in combination with the abovementioned ranges of the at least one hole wall provide a desired etching of the etching area.

[0066] In an embodiment the mask comprises a quartz mask, for example a fused quartz mask, or polycrystalline diamond.

[0067] A quartz mask and a polycrystalline diamond have a lower etching rate than the diamond membrane and therefore are suitable materials for the mask. A lower etching rate in the context of the present disclosure means that material is removed at a slower rate during etching.

[0068] Further advantages, features and details are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, wherein: figures 1A-1L show different stages of the manufacturing method; figures IM- IN show examples of the manufacturing method; figure 2 shows a diamond membrane upon which a mask is arranged; and figure 3 shows an example of a method according to the present disclosure.

[0069] The figures 1A-1L show different stages of the manufacturing method according to the present disclosure. The manufacturing method can generally be divided into three phases. The first phase (figures 1A) comprises surface roughness reduction and wedge removal of the diamond substrate on both the primary and the secondary surface. The second phase (figures 1B-1G) comprises patterning the nanophotonic devices on the primary surface. The third phase (figures 1H-1L) comprises thinning down of the secondary surface of the diamond substrate thickness from micrometer to approximately 200 nanometers. Diamond membrane 2 (figure 1A) comprises primary surface 4 and secondary surface 6 which is positioned opposite of primary surface 4. Diamond surface 2 has a thickness Ti, as measured from primary surface 4 to secondary surface 6, which in the illustrated embodiment is around 50 pm. Diamond membrane 2 is a single crystal diamond SCD membrane. Diamond membrane 2 may be wet cleaned. The wet cleaning may comprise inorganic cleaning with a triacid protocol, or nitric acid (HNOs), or a combination between 40% hydrofluoric acid (HF) and a Piranha mixture (sulfuric acid, H2SO4 and hydrogen peroxide, H2O2).

[0070] After the inorganic cleaning of primary surface 4 and secondary surface 6 both surfaces may undergo a further prefabrication surface treatment which comprises dry etching. The dry etching may comprise a cycled Ar / CF, and O2 anisotropic inductively coupled plasma reactive ion etching (ICP-RIE). The dry etching may comprise the removal of material from primary surface 4 and secondary surface 6 of a few micrometers. The dry etching is performed to etch the strained surface layer of the diamond crystal and to further clean the sample of organic debris. The dry etching step may remove any wedge of diamond membrane 2 that may be present. This removal of the wedge is obtained because the quasi-isotropic plane dependent ICP-RIE O2 etch is characterized by an etch rate that is plane dependent. Therefore some planes, such as the <100> plane, is being etched faster than other planes, such as the < 111 > plane. This will result at the end of the process in fully exposed planes on both primary surface 4 and secondary surface 6, thereby obtaining ideally substantially parallel and wedge free surfaces.

[0071] Next, hard mask 8 (figure IB) is positioned on top of primary surface 4 of diamond membrane 2. In this illustrated embodiment, hard mask 8 is deposited via inductively coupled plasma chemical vapor deposition (ICPCVD). Hard mask 8 may be a silicon nitride (SixNy) mask. Then, electron beam resist 10 (figure 1C) is positioned on top of hard mask 8 via spin coating. Electron beam resist 10 may be an A-RP-6200 resist.

[0072] When electron beam resist 10 (figure ID) is positioned on top of hard mask 8, a pattern may be exposed by the electron beam in electron beam resist 10. The pattern in electron beam resist 10 may be created by sequentially developing the exposed pattern in electron beam resist 10. In this illustrated embodiment, the pattern comprises first cut-out 12 and second cut-out 14 which are symmetrically positioned on opposite sides of beam 16. In beam 16 a plurality of holes 18 are created. At the end of beam 16 third cut-out 20, which is a semicircle when viewed from the top, is provided. It is noted that the pattern in this embodiment is only for illustrative purposes, and may not be in conformance with the actual design of the nanophotonic device.

[0073] Next, etching may be performed. The etching may comprise inductively coupled plasma reactive ion etching from direction E (figure 1E-F). By performing the etching hard mask 8 obtains the same pattern as electron beam resist 10, and obtains first mask cutout 22 and second mask cutout 24. Also plurality of holes 18 is transferred to mask beam 26. By etching in direction E the thickness of electron beam resist 10 is also reduced. When the etching continues the pattern, which comprises first mask cutout 22, second mask cutout 24 and plurality of holes 28, is transferred to primary surface 4 of diamond membrane 2. It is noted that the etching chemistries may be different for different layers. For example, hard mask 8 may be etched with a CHF3 / O2 plasma, while the diamond may be etched in O2 plasma. After the desired depth of first diamond cutout 30 (figure 1G) and second diamond cutout 32 is reached, the patterning step is completed. The desired depth of first diamond cutout 30 has a depth T4. Depth T4 is greater or equal to the desired thickness of the nanophotonic device (which is depicted as T2 in figure IK). Between first diamond cutout 30 and second diamond cutout 32 diamond beam 34 is positioned. Diamond membrane 2 (figure 1H) can now be flipped such that secondary surface 6 can be modified.

[0074] Quartz mask 36 (figure II) is positioned on secondary surface 6 of diamond membrane 2. Quartz mask 36 comprises first surface 38 and second surface 40 which is positioned opposite of first surface 38. Furthermore, quartz mask 36 is provided with hole 42. Hole 42 extends from first opening 44 that is arranged in first surface 38 to second opening 46 that is arranged in second surface 40. Hole 42 has two walls 48, 49 that are oppositely arranged. Mask 36 has thickness T3 that is in this illustrated embodiment around 100 micrometres. Hole 42 also comprises two other opposing walls that are oriented at a 90 degrees angle with respect to walls 48, 49. One of these walls is illustrated in figure IL, while the other opposing wall is not illustrated as figure IL depicts a cross section of the method. Further explanation of the cross section of figures 1A-1L can be found with reference to figures IM and IN. In an alternative embodiment mask 36 is made of an aluminum oxide based ceramic material or polycrystalline diamond.

[0075] After positioning quartz mask 36 on secondary surface 6 inductively coupled plasma reactive ion etching (ICP-RIE) can be performed. The etching creates recess 50 (figure 1J), as etching area 47 is etched. Mask 36 has at this stage thickness T5 which is smaller than thickness T3. Thickness T5 of mask 36 decreased with respect to thickness T3 due to the etching of mask 36 during etching of secondary surface 6. Mask 36 is etched at a lower rate than secondary surface 6. First opening 44 has a width W that in this illustrated embodiment is around 1.4 millimetres. Angle a, which is the angle of first wall 48 with respect to second surface 6, is in this illustrated embodiment 70 degrees. It is clear for the skilled person that the exact angle a depends on the thickness T3 of mask 36. Angle a-1 is in this case thus 20 degrees. Recess 50 is further cut out (figure IK), until T4 is reached in a direction perpendicular from secondary surface 6 towards primary surface 4. At this stage recess 50 is Ti - T4 such that diamond beam 24 is reached. Etching continues until desired thickness T2 (figure IK) of diamond beam 24 is obtained. In this illustrated embodiment, thickness T2 is around 200 nm. At last hard mask 8 can be removed (figure IL). Diamond membrane 2 then comprises frame part 52. Frame part 52 was protected from etching as quartz mask 36 was positioned on top of frame part 52. Frame part 52 still has thickness Ti, or at least a thickness comparable with thickness Ti. Frame part 52 comprises, in this illustrated embodiment, first frame part wall 53a, second frame part wall 53b, and third frame part wall 53c.

[0076] As explained in relation figures 1A-1L, diamond membrane 2 can be effectively obtained with the method steps disclosed therein. An advantage of diamond membrane 2 which is obtained with the above described method is that a very thin device part with thickness T2 is obtained. Furthermore, frame part keeps the original thickness of diamond membrane 2 that is in the order of thickness Ti with which diamond membrane 2 started, such as 30-50 pm. In this way, frame part 52 can be used to handle diamond membrane 2, while still retaining a device part 54 with a relatively thin thickness T2 which can be used for quantum applications. Frame part 52 allows for easier handling of the sample, reducing the risk of breaking the thinned-down membrane upon manual tweezers handling, without the need of e.g. a pick and place setup to operate further processing steps on the sample.

[0077] Diamond membrane 2 (figure IM) shows a more realistic embodiment as compared to figures 1A-1L, which were more illustrative in nature. On top of diamond membrane 2 quartz mask 36 is arranged. Quartz mask 36 comprises first surface 38 in which hole 42 is provided. First surface 38 of quartz mask 36 is rectangular, with therein a rectangular hole 42 provided.

[0078] Figure IN depicts the embodiment of figure IM which is cut through in line A - A’. In this way, figure IN shows a similar view as figures 1A-1L. Quartz mask 36 has been removed. Bottom layer 55 of diamond substrate 2 is thinned down to thickness T2 which is in this illustrated embodiment 200 nanometers. In bottom layer 55 a plurality of nanophotonic devices 57 are provided. Frame part 52 comprises, in this illustrated embodiment, first frame part wall 53a, second frame part wall 53b, and third frame part wall 53c. It is clear for the skilled person that frame 52 also comprises a frame part wall that is opposite of frame part wall 53b, but which is not shown due to the cut through line A - A’. Frame part 52 allows for easier handling of the sample. Furthermore, it is clear for the skilled person that also figures 1A-1L are for illustrative purposes also cut along a plane similar to the plane A - A’. In reality, figures 1A-1L will be embodied as depicted in figure IM.

[0079] Figure 2 depicts the embodiment of mask 136, which is positioned over diamond membrane 102. Mask 136 may be pre-fabricated e.g. in fused quartz mask or is made of polycrystalline diamond, or an aluminum oxide based ceramic material. Mask 136 comprises first surface 138 and oppositely positioned thereof second surface 140. Between first surface 138 and second surface 140 hole 142 is arranged. Hole 142 stretches out from first opening 144 in first surface 138 to second opening 146 in second surface 140. Hole 142 comprises first hole wall 148 and second hole wall 149 that are oppositely arranged. First hole wall 148 and second hole wall 149 are arranged at an angle of 60 degrees with respect to second surface 106 of diamond membrane 102, which makes angle 30 degrees. First wall 148 is connected to third wall 158. Third wall 158 stretches out in a direction that is substantially perpendicular to first surface 138 and second surface 140. Second wall 149 is connected to fourth wall 160. Fourth wall 160 stretches out in a direction that is substantially perpendicular to first surface 138 and second surface 140. First wall 148 and second wall 149 define aperture space 156. Third wall 158 and fourth wall 160 are positioned against the outer sides of diamond membrane 102. In this way, mask 138 is automatically positioned at the right position such that aperture space 156 is positioned above the desired etching location of diamond membrane 102, upon optical microscope inspection.

[0080] Furthermore, it is clear for the skilled person that also figure 2 is for illustrative purposes also cut along a plane similar to the plane A - A’ . Realistically, figure 2 will be embodied similarly to figure IM. This means that mask 136 will be rectangular, and will encapsulate all four side walls of diamond membrane 102, namely third wall 158 and fourth wall 160 and the side walls that are oriented at a 90 degrees angle thereto.

[0081] In an embodiment of the present disclosure comprises first step 270 wherein a structure, for example a nanophotonic structure, is patterned on primary surface 4 of diamond membrane 2. The patterning of the structure on primary surface 4 may be performed by electron beam lithography, as explained in figures 1A-1G. Next, mask 36 is arranged on secondary surface 6 of diamond membrane 2 in step 272. Mask 36 comprises at least one hole wall 48 that is arranged at an angle in the range of 5-85 degrees, preferably in the range of 40-80 degrees, and most preferably in the range of 60-75 degrees with respect to secondary surface 6. Then, in step 274 etching of secondary surface 6 can be performed, for example inductively coupled plasma reactive ion etching (ICP / RIE). In this way, frame part 52 is maintained as it is protected by mask 36, and device part 54 is thinned down to thickness T2 which may be around 200 nanometres. Due to the angle of wall 48 and secondary surface 6 etching area 47 is substantially homogeneously etched, meaning that material is removed from etching area 47 at substantially the same rate.

[0082] The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following clauses within the scope of which many modifications can be envisaged.

Claims

CLAIMS1. Method of manufacturing a second diamond membrane for quantum systems, quantum communications and / or quantum sensors, comprising the sequentially performed steps: patterning a nanophotonic structure on a primary surface of a first diamond membrane; arranging a mask on a secondary surface of the first diamond membrane, the secondary surface being arranged opposite of the primary surface, wherein the mask comprises a first surface and a second surface that is arranged opposite of the first surface, the mask further comprising a mask hole extending from a first opening in the first surface to a second opening in the second surface, wherein the mask hole comprises at least one mask hole wall that is arranged at an angle with respect to the secondary surface of the first diamond membrane when the mask is arranged on the secondary surface, wherein the angle is in the range of 5-85 degrees; and etching the secondary surface of the first diamond membrane while the mask is arranged on the secondary surface.

2. Method according to claim 1, wherein a first diameter of the first opening is smaller than a second diameter of the second opening.

3. Method according to claim 1 or 2, wherein a diameter of the mask hole increases from the first opening to the second opening, wherein the diameter preferably linearly increases.

4. Method according to any one of the foregoing claims, wherein the etching of the secondary surface of the first diamond membrane removes material from the secondary surface such that the mask protects a frame part which is configured to provide mechanical stability to the first diamond membrane, and the etching through the mask hole reduces the thickness of a device part which comprises the nanophotonic structure.

5. Method according to any one of the foregoing claims, wherein a starting thickness of a frame part of the first diamond membrane, before etching, is in the range of 1-100 micrometres, preferably in the range of 5-70 micrometres, most preferably in the range of 25-50 micrometres.

6. Method according to any one of the foregoing claims, wherein a final thickness of a device part of the second diamond membrane, after etching, is in the range of 100-300nanometres, preferably in the range of 125-250 nanometres, most preferably in the range of 150-200 nanometres.

7. Method according to any one of the foregoing claims, wherein the at least one mask hole wall comprises at least two mask hole walls that are oppositely arranged.

8. Method according to any one of the foregoing claims, wherein the angle is in the range of 40-80, preferably in the range of 60-75 degrees.

9. Method according to any one of the foregoing claims, wherein the at least one mask hole wall comprises a planar surface.

10. Method according to any one of the foregoing claims, wherein a thickness of the mask is in the range of 100 nanometres-200 micrometres, preferably in the range of 50-150 micrometres, most preferably in the range of 80-120 micrometres, for example 100 micrometres.

11. Method according to any one of the foregoing claims, wherein the mask comprises a quartz mask, for example a fused quartz mask, or polycrystalline diamond.

12. Method according to any one of the foregoing claims, wherein patterning the nanophotonic structure comprises electron beam lithography.

13. Method according to claim 12, wherein, after patterning the nanophotonic structure, the method further comprises applying reactive ion etching to the primary surface to transfer the pattern into a hard mask material and subsequently from the hard mask material into the diamond material.

14. Method according to any one of the foregoing claims, wherein, prior to the step of patterning the nanophotonic structure, the method further comprises: pre-treating the primary surface and / or the secondary surface of the first diamond membrane by reactive ion etching, wherein the reactive ion etching preferably comprises switching between a first cycle of applying argon and chlorine ions (Ar / Ch) and a second cycle of applying oxygen (O2) ions.

15. Method according to claim 14, wherein, prior to pre-treating, the method further comprises: inorganically wet cleaning the first diamond membrane.

16. Method according to any one of the foregoing claims, further comprising: quasi-isotropic plane dependent reactive ion etching, preferably using oxygen ions, of the primary surface and / or secondary surface of the first diamond membrane to remove a diamond wedge of the first diamond membrane.

17. Method according to any one of the foregoing claims, wherein the reactive ion etching comprises inductively coupled plasma reactive ion etching.

18. Diamond membrane obtained by the method according to any one of the foregoing claims.

19. Quantum system comprising a diamond membrane according to claim 18.

20. Mask configured to be arranged on a surface of a diamond membrane during etching, comprising: a first surface and a second surface that is arranged opposite of the first surface, further comprising a mask hole extending from a first opening in the first surface to a second opening in the second surface, wherein the mask hole comprises at least one mask hole wall that is arranged at an angle with respect to secondary surface, wherein the angle is in the range of 40 - 85 degrees, wherein the mask comprises polycrystalline diamond, silicon nitride and / or aluminum oxide based ceramic material.

21. Mask according to claim 20, wherein a first diameter of the first opening is smaller than a second diameter of the second opening.

22. Mask according to claim 20 or 21, wherein a diameter of the mask hole increases from the first opening to the second opening, wherein the diameter preferably linearly increases.

23. Mask according to claim 20, 21 or 22, wherein the at least one mask hole wall comprises at least two mask hole walls that are oppositely arranged.

24. Mask according to any one of claims 20-23, wherein the angle is in the range of 50-80, preferably in the range of 60-75 degrees.

25. Mask according to any one of claims 20-24, wherein the at least one mask hole wall comprises a planar surface.

26. Mask according to any one of claims 20-25, wherein a thickness of the mask is in the range of 100 nanometres-200 micrometres, preferably in the range of 50-150 micrometres, most preferably in the range of 80-120 micrometres, for example 100 micrometres.

27. Mask according to any one of claims 20-26, wherein the mask comprises a quartz mask, for example a fused quartz mask.

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