Superconducting nanowire single-photon detector film thickness testing structure and method and preparation method

Abstract

The invention provides a superconducting nanowire single-photon detector film thickness testing structure and method and a preparation method. The film thickness testing structure comprises a substrate, a bottom reflecting layer, a superconducting film layer, a dielectric material layer and a top reflecting layer which are sequentially stacked from bottom to top. Wherein the bottom reflecting layer, the superconducting film layer, the dielectric material layer and the top reflecting layer form an optical microcavity structure; the bottom reflecting layer and the top reflecting layer are used as two reflecting surfaces of the optical microcavity structure; the superconducting film layer and the dielectric material layer are used as spacing layers of the optical microcavity structure. According to the superconducting nanowire single-photon detector film thickness testing structure and method and the preparation method provided by the invention, the problem that the film thickness of the superconducting film layer of the superconducting nanowire single-photon detector cannot be accurately tested by the existing film thickness testing means can be solved.

Description

Technical Field

[0001] The present invention relates to the field of laser radar, and in particular to a film thickness testing structure, method and preparation method of a superconducting nanowire single-photon detector. Background Art

[0002] As a high-performance single-photon detector, superconducting nanowire single-photon detector (SNSPD) has been widely used in quantum information, lidar, deep space communication and other fields, and has effectively promoted scientific and technological progress in related fields. In order to increase the detection efficiency of SNSPD, it is necessary to add a high-reflectivity dielectric film under the original device. However, while the addition of a high-reflectivity film improves the detection performance of the device, it also increases the unevenness of the thickness of the superconducting film layer in the device layer.

[0003] The thickness non-uniformity of the superconducting film layer in the device layer directly affects the yield of the detector, especially for devices with large or even ultra-large photosensitive surfaces. Therefore, timely obtaining the thickness and uniformity of the superconducting film layer in the device layer is crucial for the research and development of SNSPD.

[0004] Normally, an ellipsometer (spectroscopic ellipsometry) is used to measure parameters such as the thickness and refractive index of a film. However, the ellipsometer cannot directly obtain these parameters, but can only obtain these parameters through data fitting. When fitting the data, the model used is very important, and the choice of model directly affects the accuracy of the test results. However, after the superconducting nanowire single-photon detector introduces a high-reflectivity dielectric film (optical reflective film is usually formed by stacking several or even dozens of dielectric films), if it is a multi-layer film, or the film surface is not smooth, or the lattice structure of the film needs to be considered, the model will be more complicated, resulting in low test accuracy.

[0005] Therefore, a simpler and more effective method for testing the thickness of a superconducting film layer on a surface of a high reflectivity substrate is needed. Summary of the invention

[0006] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide a film thickness testing structure, method and preparation method of a superconducting nanowire single-photon detector, so as to solve the problem that the existing film thickness testing means cannot accurately test the film thickness of the superconducting film layer of the superconducting nanowire single-photon detector.

[0007] To achieve the above-mentioned purpose and other related purposes, the present invention provides a film thickness test structure of a superconducting nanowire single-photon detector, wherein the film thickness test structure comprises a substrate, a bottom reflection layer, a superconducting film layer, a dielectric material layer and a top reflection layer stacked in sequence from bottom to top; wherein:

[0008] The bottom reflection layer, the superconducting film layer, the dielectric material layer and the top reflection layer form an optical microcavity structure;

[0009] The bottom reflection layer and the top reflection layer serve as two reflection surfaces of the optical microcavity structure;

[0010] The superconducting film layer and the dielectric material layer serve as spacer layers of the optical microcavity structure.

[0011] Optionally, the bottom reflection layer includes a silicon dioxide layer and a tantalum pentoxide layer stacked together.

[0012] Optionally, the bottom reflection layer and the top reflection layer have the same film structure.

[0013] Optionally, the dielectric material layer is made of silicon dioxide and has a thickness of 530 nm.

[0014] Optionally, the thickness of the superconducting film layer is between 1 and 15 nm.

[0015] The present invention also provides a film thickness testing method for a superconducting nanowire single-photon detector, the film thickness testing method comprising:

[0016] Prepare a film thickness test structure as described in any of the preceding items;

[0017] measuring a transmission spectrum of the film thickness test structure;

[0018] The film thickness of the superconducting film layer is obtained based on the transmission spectrum.

[0019] Optionally, the film thickness of the superconducting film layer is obtained based on the transmitted light intensity of the transmission spectrum.

[0020] Optionally, the film thickness of the superconducting film layer is obtained based on the peak wavelength of the transmission peak of the transmission spectrum.

[0021] The present invention also provides a method for preparing a film thickness test structure as described in any of the preceding items, the method comprising:

[0022] Providing a substrate, and forming a bottom reflection layer on the surface of the substrate;

[0023] Forming a superconducting film layer on the upper surface of the bottom reflection layer;

[0024] Forming a dielectric material layer on the upper surface of the superconducting film layer;

[0025] A top reflection layer is formed on the upper surface of the dielectric material layer.

[0026] As described above, the film thickness test structure, method and preparation method of the superconducting nanowire single-photon detector of the present invention form a dielectric material layer and a top reflection layer on the superconducting film layer of the test sample piece of the superconducting nanowire single-photon detector. The dielectric material layer, the top reflection layer, the bottom reflection layer and the superconducting film layer together constitute an optical microcavity structure. The bottom reflection layer and the top reflection layer serve as two reflection surfaces of the optical microcavity structure, and the superconducting film layer and the dielectric material layer serve as spacer layers of the optical microcavity structure. Since the film thickness of the superconducting film layer is much smaller than the test wavelength, according to the multi-beam interference theory, its thickness change will cause the transmission spectrum to change. According to the change in the transmission spectrum, the film thickness distribution and uniformity of the superconducting film layer of the test sample piece can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Shown is a schematic structural diagram of the film thickness test structure of the superconducting nanowire single-photon detector described in the present invention.

[0028] Figure 2 Shown are transmission spectra of superconducting film layers of different thicknesses according to the present invention.

[0029] Figure 3 Shown are local transmission spectra of superconducting film layers of different thicknesses according to the present invention.

[0030] Component number description

[0031] 10 Film thickness test structure of superconducting nanowire single photon detector

[0032] 110 Substrate

[0033] 120 bottom reflection layer

[0034] 130 Superconducting film layer

[0035] 240 dielectric material layer

[0036] 250 Top reflective layer DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] See also Figures 1 to 3It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0039] Embodiment 1

[0040] This embodiment provides a film thickness testing structure 10 for a superconducting nanowire single-photon detector.

[0041] like Figure 1 As shown, the superconducting nanowire single-photon detector in this embodiment includes:

[0042] The substrate 110 may be made of silicon, silicon dioxide, sapphire, magnesium oxide or magnesium fluoride.

[0043] The bottom reflection layer 120 is formed on the upper surface of the substrate 110. It is a high reflection efficiency film. The material and number of layers of the film are designed according to the reflection efficiency and the wavelength range of the reflected light. Taking 1540nm as the peak wavelength of the reflection film as an example, the bottom reflection layer 120 can be composed of periodically stacked silicon dioxide layers and tantalum pentoxide layers (for example, periodically stacked 3 to 15 times). Figure 1 The bottom reflection layer 120 is shown to have a film thickness test structure 10 in which four groups of silicon dioxide layers and tantalum pentoxide layers are periodically stacked.

[0044] The superconducting film layer 130 is formed on the upper surface of the bottom reflection layer and is used to form a superconducting nanowire structure in the superconducting nanowire single-photon detector. The superconducting film layer 130 is made of materials such as NbN, MoSi, and WSi.

[0045] like Figure 1 As shown, the film thickness test structure 10 in this embodiment includes:

[0046] Superconducting nanowire single-photon detector. It should be noted that the superconducting film layer 130 in the superconducting nanowire single-photon detector needs to adopt etching and other processes to form superconducting nanowires, and after the superconducting nanowires are formed, a protective layer and other structures need to be formed to prepare the superconducting nanowire single-photon detector; and in the present embodiment, since the film thickness test structure 10 is formed as a test sample for detecting the film thickness of the superconducting film layer 130, the structure referred to by the nanowire single-photon detector in the present embodiment includes the substrate 110, the bottom reflection layer 120 and the superconducting film layer 130, and the superconducting film layer 130 does not need to be etched to form a pattern.

[0047] The dielectric material layer 240 is formed on the upper surface of the superconducting film layer 130 and is made of, for example, silicon dioxide, silicon nitride or the like.

[0048] The top reflection layer 250 is formed on the upper surface of the dielectric material layer 240 and is also a high reflectivity film. The film material and film stacking period used can be the same as or different from those of the bottom reflection layer 120, but the wavelength range of the reflected light of the two should be the same.

[0049] In this embodiment, the bottom reflection layer 120, the superconducting film layer 130, the dielectric material layer 240 and the top reflection layer 250 form an optical microcavity structure, and the bottom reflection layer 120 and the top reflection layer 250 serve as two reflection surfaces of the optical microcavity structure; the superconducting film layer 130 and the dielectric material layer 240 serve as spacer layers of the optical microcavity structure.

[0050] For an optical microcavity, after a light wave of the target wavelength (a light wave within the reflection range of the reflection surface) is injected into the optical microcavity, due to the destructive interference and the attenuation of the light wave, the spectrum of the transmitted light will show a transmission peak. The peak wavelength λ of the transmission peak is related to the thickness d and refractive index n of the spacer layer of the optical microcavity structure, where: m is the interference order.

[0051] When the spacer layer between the two reflective surfaces is only a dielectric material layer, equation [1] can be expressed as n 1 Expressed as the refractive index of the dielectric material layer, d 1 It is expressed as the thickness of the dielectric material layer. Taking the dielectric material layer as an example, the thickness of silicon dioxide is 530nm. The optical refractive index of silicon dioxide is 1.4 (the refractive index of silicon dioxide under different film forming conditions is different, usually between 1.3 and 1.45). Substituting it into formula 2, the peak wavelength of the transmission peak is Taking the value of m as 1 as an example, the peak transmission wavelength λ=1484 nm.

[0052] When the spacer layer between the two reflective surfaces includes not only the dielectric material layer 240 but also the superconducting film layer 130, the thickness variation of the superconducting film layer 130 will result in the optical thickness of the entire spacer layer being The change in the transmission peak position of the optical microcavity causes a shift. By using this corresponding relationship, we can obtain the change in the thickness of the superconducting film layer 130 and its uniformity through the change in the transmission peak.

[0053] As an example, Figure 2 and Figure 3 As shown:

[0054] Curve A shows the transmission spectrum of the test sample with a dielectric material layer (silicon dioxide) thickness of 530 nm and a superconducting film layer 130 (niobium nitride) thickness of 6 nm. The peak wavelength of the transmission peak is 1537.5 nm and the transmittance is 46.5%.

[0055] Curve B shows the transmission spectrum of the test sample with a dielectric material layer (silicon dioxide) thickness of 530 nm and a superconducting film layer 130 (niobium nitride) thickness of 7 nm. The peak wavelength of the transmission peak is 1538.4 nm and the transmittance is 45.1%.

[0056] Curve C shows the transmission spectrum of the test sample with a dielectric material layer (silicon dioxide) thickness of 530 nm and a superconducting film layer 130 (niobium nitride) thickness of 8 nm. The peak wavelength of the transmission peak is 1539.5 nm and the transmittance is 41.3%.

[0057] It can be seen from the above examples that as the thickness of the superconducting film layer 130 increases, the peak wavelength and transmittance of the transmission peak in the transmission spectrum of the test sample also change accordingly, and have a corresponding relationship with the change in film thickness. Therefore, the change in the thickness of the superconducting film layer 130 can be judged by the change in the peak wavelength; the change in the thickness of the superconducting film layer 130 can also be judged by the transmittance of the transmission spectrum (the ratio of the optical power of the outgoing light to the optical power of the incident light). After comprehensive testing is performed on different positions of the entire test sample (wafer), the thickness distribution and uniformity of the superconducting film layer 130 in the entire test sample can be obtained after obtaining the transmission spectra at different positions.

[0058] Embodiment 2

[0059] This embodiment provides a method for preparing the film thickness test structure 10 as described in the first embodiment, and the preparation method includes steps S1) to S3).

[0060] In step S1 , a substrate 110 is provided, and a bottom reflection layer 120 is formed on a surface of the substrate 110 .

[0061] In this embodiment, the substrate 110 may include a SOI wafer of a size of 2 inches, 6 inches, 8 inches, 12 inches, etc., but is not limited thereto; the SOI wafer may also be cut into a square substrate of a size of 2 cm×2 cm by a dicing machine. The bottom reflection layer 120 may be prepared by ion beam assisted sputtering deposition technology, electron beam evaporation, plasma enhanced chemical vapor deposition, etc., and the materials used in the bottom reflection layer are periodically alternately stacked.

[0062] Step S2), forming a superconducting film layer 130 on the upper surface of the bottom reflection layer 120 .

[0063] In this embodiment, the superconducting film layer 130 may be prepared by molecular beam epitaxy or magnetron sputtering. The thickness of the superconducting film layer 130 may be 1 nm to 15 nm, such as 1 nm, 4 nm, 5 nm, 8 nm, 10 nm, 15 nm, etc.

[0064] It should be noted that in the actual production process of preparing the film thickness test structure 10, the process steps before preparing the superconducting film layer 130 are no different from the preparation process of preparing the superconducting nanowire single-photon detector. It is just necessary to mark one of the wafers as a test sample in batch production, for example, in each clamped wafer. After executing steps S1) and S2), the test sample is no longer prepared according to the process route of the superconducting nanowire single-photon detector, but executes the subsequent steps S3) to S4) to form the film thickness test structure 10.

[0065] Steps S3) to S4) are to form a dielectric material layer 240 on the upper surface of the superconducting film layer 130 , and to form a top reflection layer 250 on the upper surface of the dielectric material layer 240 .

[0066] In this embodiment, the dielectric material layer 240 is prepared by, for example, electron beam evaporation, and the preparation process of the top reflection layer 250 is the same as that of the bottom reflection layer 120. After the top reflection layer 250 is prepared, the top reflection layer 250 and the bottom reflection layer 120 serve as two reflection surfaces of the optical microcavity to form an FP type optical microcavity, and the superconducting film layer 130 and the dielectric material layer 240 located between the top reflection layer 250 and the bottom reflection layer 120 serve as the spacing layer of the optical microcavity. The thickness change of the spacing layer (the superconducting film layer 130 to be measured) will cause the transmission peak and transmittance of the optical microcavity to shift, thereby obtaining the change of the thickness of the superconducting film layer 130 and its uniformity.

[0067] Embodiment 3

[0068] This embodiment provides a method for testing the film thickness of a superconducting nanowire single-photon detector, comprising:

[0069] Step K1), using the preparation method described in Example 2 to prepare the film thickness test structure described in Example 1.

[0070] Step K2), measuring the transmission spectrum of the film thickness test structure.

[0071] Step K3), obtaining the film thickness of the superconducting film layer based on the transmission spectrum.

[0072] In this embodiment, a single point light source can be used for measurement to measure the transmittance of monochromatic light, and the intensity of the transmitted light is used as a basis for judgment to obtain the film thickness of the superconducting film layer. Figure 3 Taking the monochromatic light of 1537nm as an example, when the optical microcavity has superconducting film layers of different thicknesses, the transmittance of the 1537nm light is different; a multi-spectral light source can also be used to perform spectral scanning, measure the transmission peak of the transmission spectrum, and use the peak wavelength of the transmission peak as the basis for judgment to obtain the film thickness of the superconducting film layer. Figure 3Taking the transmission spectrum in as an example, when the optical microcavity has superconducting film layers of different thicknesses, the peak wavelength of the transmission peak of the transmission spectrum is different.

[0073] In summary, the film thickness test structure, method and preparation method of the superconducting nanowire single-photon detector of the present invention form a dielectric material layer and a top reflection layer on the superconducting film layer of the test sample piece of the superconducting nanowire single-photon detector. The dielectric material layer, the top reflection layer, the bottom reflection layer and the superconducting film layer together constitute an optical microcavity structure. The bottom reflection layer and the top reflection layer serve as two reflection surfaces of the optical microcavity structure, and the superconducting film layer and the dielectric material layer serve as spacer layers of the optical microcavity structure. Since the film thickness of the superconducting film layer is much smaller than the test wavelength, according to the multi-beam interference theory, its thickness change will cause a change in the transmission spectrum. The film thickness distribution and uniformity of the superconducting film layer of the test sample piece can be obtained based on the change in the transmission spectrum.

[0074] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A film thickness test structure for a superconducting nanowire single-photon detector, characterized in that: The film thickness test structure comprises a substrate, a bottom reflection layer, a superconducting film layer, a dielectric material layer and a top reflection layer stacked in sequence from bottom to top; wherein the bottom reflection layer, the superconducting film layer, the dielectric material layer and the top reflection layer form an optical microcavity structure; The bottom reflection layer and the top reflection layer serve as two reflection surfaces of the optical microcavity structure; The superconducting film layer and the dielectric material layer serve as spacer layers of the optical microcavity structure.

2. The film thickness test structure of the superconducting nanowire single-photon detector according to claim 1, characterized in that: The bottom reflection layer includes a silicon dioxide layer and a tantalum pentoxide layer which are stacked.

3. The film thickness test structure of the superconducting nanowire single-photon detector according to claim 1, characterized in that: The bottom reflection layer and the top reflection layer have the same film structure.

4. The film thickness test structure of the superconducting nanowire single-photon detector according to claim 1, characterized in that: The dielectric material layer is made of silicon dioxide and has a thickness of 530 nm.

5. The film thickness test structure of the superconducting nanowire single-photon detector according to claim 1, characterized in that: The thickness of the superconducting film layer is between 1 and 15 nm.

6. A method for testing the film thickness of a superconducting nanowire single-photon detector, characterized in that: The film thickness testing method includes: Prepare a film thickness test structure as described in any one of claims 1 to 5; measuring a transmission spectrum of the film thickness test structure; The film thickness of the superconducting film layer is obtained based on the transmission spectrum.

7. The film thickness testing method of the superconducting nanowire single-photon detector according to claim 6, characterized in that: The film thickness of the superconducting film layer is obtained based on the transmitted light intensity of the transmission spectrum.

8. The film thickness testing method of the superconducting nanowire single-photon detector according to claim 6, characterized in that: The film thickness of the superconducting film layer is obtained based on the peak wavelength of the transmission peak of the transmission spectrum.

9. A method for preparing a film thickness test structure according to any one of claims 1 to 5, characterized in that: The preparation method comprises: Providing a substrate, and forming a bottom reflection layer on the surface of the substrate; Forming a superconducting film layer on the upper surface of the bottom reflection layer; Forming a dielectric material layer on the upper surface of the superconducting film layer; A top reflection layer is formed on the upper surface of the dielectric material layer.

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