CN114899302A - Preparation method of turn region thickened SNSPD device - Google Patents
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Abstract
The invention provides a preparation method of a curve region thickened SNSPD device, which is characterized in that an electron beam corrosion-resistant mask with a height difference is formed on the basis of electron beam gray level exposure to be used as a pattern mask of a superconducting thin film, then pattern transfer is carried out through an etching process with an obvious etching selection ratio to form superconducting nanowires comprising a straight line region and a curve region, and the thickness of the superconducting nanowires corresponding to the curve region is larger than that of the superconducting nanowires corresponding to the straight line region, so that the curve region thickened SNSPD device is prepared, the current crowding effect is inhibited to a greater extent, the advantages of higher critical current, low dark counting rate and the like are achieved, and the performance of the SNSPD device is obviously improved. According to the invention, the preparation of the superconducting nanowire with the thickened corner region can be realized only by one-step electron beam exposure and one-step pattern transfer, the preparation process flow is simplified, and the performance and the preparation yield of the thickened SNSPD device in the corner region can be improved.
Description
Technical Field
The invention relates to the technical field of optical detection, in particular to a preparation method of a turn region thickened SNSPD device.
Background
Superconducting Nanowire Single Photon Detectors (SNSPDs) are a quantum-limited sensitivity photodetector, first reported by Gol' tsman et al in 2001. The basic principle of the work is to realize the disconnection of an electron Cooper pair (Cooper pair) in the superconducting nanowire by utilizing photon energy, so that superconducting-non-superconducting phase change occurs in the superconducting nanowire area. Compared with the traditional semiconductor single-photon detector, the SNSPD has the characteristics of high speed, wide response bandwidth, low dark counting rate, small time jitter and the like, is widely applied to the fields of quantum information, laser radar, deep space communication and the like, and powerfully promotes the technological development of the related fields.
The core of the SNSPD device is a zigzag nanowire made of an ultrathin superconducting thin film, and the zigzag nanowire comprises an active straight line region used for photon detection, and two ends of the straight line region also comprise a turning region used for electrical interconnection. Although the turn region of the superconducting nanowire does not directly participate in photon detection, the switching current I in the superconducting nanowire C Will be reduced by the "current crowding effect" of the corner region, resulting in an applicable bias current I B Which can lead to poor detector sensitivity. In addition, the dark count rate is also increased by the "current crowding effect", which results in a decrease in the detection performance of the detector.
In order to solve the "current crowding effect" of the turn region of the superconducting nanowire in the SNSPD device, various schemes have been proposed, including optimizing the turn radian (reducing the current crowding effect is limited), reducing the duty cycle to reduce the number of turns in the SNSPD device structure (not suitable for a high-efficiency detection device), and the like. One very attractive solution proposed by Reza Baghdadi et al, the american academy of labor for hemp, to reduce the current crowding effect by using a change in nanowire thickness. In the SNSPD device structure with the variable thickness of the superconducting thin film, the nanometer zigzag line is composed of two areas with different film thicknesses, namely a thin straight nanowire (an active straight line area) and a thick bent nanowire (a turning area). Compared with a straight line region nanowire part, the bent nanowire in the turning region reduces the current density of the turning region due to the fact that the thickness of a film is relatively thick, so that the influence of current crowding effect on critical current is restrained.
At present, two methods are mainly used for constructing areas with different film thicknesses on a nanometer zigzag line, and the key preparation technology is based on two-step electron beam lithography. The first method is partitioned photoetching thinning: the thickness of the nanowire is reduced by adopting an etching means after the electron beam exposure, for example, the whole nano zigzag line structure area can be firstly processed by photoetching, and then the thickness of the nanowire in the active area is reduced by alignment; or the thickness of the nano line of the active region can be reduced by photoetching, and then the whole nano zigzag line structure region can be processed by alignment. The second method is the divisional lithographic thickening: the method comprises the steps of photoetching a turning area, depositing a superconducting film with a certain thickness, increasing the thickness of the film in the turning area in a deposition-stripping mode, and photoetching the whole nano zigzag line structure area. The two methods mainly face the following common problems that firstly, two-step electron beam lithography is involved, and the process steps increase the complexity of the device processing technology; and secondly, the sectional photoetching of a straight line region and a turning region is involved, and the requirement on an electron beam exposure alignment process is high. In addition, for the second method (the sectional lithography thickening) mentioned above, consideration is also needed to overcome the problem of interface oxidation during the film deposition during the thickening of the turning region, and a common solution is to require that the superconducting film deposition equipment is provided with an in-situ ion cleaning device to remove the surface oxide layer before deposition, which not only puts higher requirements on the equipment, but also further increases the process steps and complexity of device processing.
In summary, the conventional manufacturing process for realizing the thickened SNSPD device in the turning region has more steps and involves complex processes such as electron beam alignment, so that the manufacturing repeatability and yield of the SNSPD device are not high.
Therefore, how to realize a simple, efficient and stable processing technology of the core structure nano meander line of the thickened SNSPD device with the turning region becomes an important technical problem to be solved urgently at present.
Disclosure of Invention
In view of the above disadvantages of the prior art, the present invention aims to provide a method for manufacturing a turn region-thickened SNSPD device, which is used to solve the above series of manufacturing problems of the turn region-thickened SNSPD device in the prior art.
In order to achieve the above objects and other related objects, the present invention provides a method for manufacturing a corner region thickened SNSPD device, comprising the steps of:
providing a substrate;
forming a superconducting thin film on the substrate;
forming an electron beam resist layer on the superconducting thin film;
carrying out photoetching, adopting electron beam gray level exposure and development, and patterning the electron beam resist layer to form an electron beam resist mask with a height difference;
and etching the superconducting film based on the electron beam anti-corrosion mask to form a superconducting nanowire, wherein the superconducting nanowire comprises a straight line area and a turning area, and the thickness of the superconducting nanowire corresponding to the turning area is greater than that of the superconducting nanowire corresponding to the straight line area.
Optionally, the etching step includes the following steps:
etching at a first stage to remove the superconducting film which is not covered by the electron beam corrosion-resistant mask, and completely removing the electron beam corrosion-resistant mask corresponding to the linear area to expose the linear area;
and etching at the second stage, and thinning the exposed linear region.
Optionally, the step of patterning the electron beam resist layer using electron beam gray scale exposure and development to form the electron beam resist mask having a height difference comprises:
defining the thickness of the electron beam resist layer as t 1 The thickness of the superconducting nanowire corresponding to the turning region is t 2 After the photoetching step is carried out, the thickness of the electron beam corrosion-resistant mask corresponding to the straight line area is t 3 After the etching step is carried out, the turning area corresponds to the turning areaThe thickness of the electron beam resist mask is t 5 The thickness of the corresponding superconducting nanowire on the linear region is t 6 ，V r Representing the etch rate, V, of the electron beam resist layer m Represents the etching rate of the superconducting thin film, and S represents the etching selection ratio of the electron beam resist layer to the superconducting thin film, i.e. S ═ V r /V m ；
Wherein, t 3 ＝t 2 ·S，t 5 ＝t 1 -(t 2 -t 6 )·S-t 2 S, and t 5 Is greater than or equal to 0, then t 1 ≥(2t 2 –t 6 ) S to determine t 1 And t 3 Taking the value of (A);
determining the electron beam Dose corresponding to the formation of the whole superconducting nanowire in the electron beam resist layer by combining the contrast curve of the electron beam resist layer 1 And Dose 1 Exposing the electron beam Dose corresponding to the linear region on the basis of 2 And after the electron beam gray level exposure and the development, obtaining the electron beam corrosion-resistant mask with a three-dimensional glue type structure and height difference.
Optionally, etching in the first stage for a time T 1 ＝t 2 /V m Etching in the second stage for a period of time T 2 ＝(t 2 –t 6 )/V m And the total etching time T is equal to (2T) 2 –t 6 )/V m 。
Optionally, the electron beam resist layer comprises one of HSQ series, PMMA series, AR-P6200 series, and ZEP series.
Optionally, the method for etching the superconducting thin film based on the electron beam resist mask includes a reactive ion etching method or an inductively coupled plasma etching method.
Optionally, the superconducting film includes one or a combination of a NbN superconducting film, a WSi superconducting film, a NbSi superconducting film, a MoSi superconducting film, and a Nb superconducting film.
Optionally, the profile of the superconducting nanowire formed comprises one or a combination of a circle, an ellipse, and a polygon.
Optionally, the superconducting nanowire is formed in a zigzag shape, and the linear regions are arranged in parallel.
Optionally, the superconducting nanowire corresponding to the turning region includes a right-angle turning superconducting nanowire or a U-shaped turning superconducting nanowire.
As described above, the method for manufacturing the turn-region thickened SNSPD device according to the present invention forms an electron beam resist mask having a height difference by using different dissolution rates of an electron beam resist layer in a developer under different irradiation intensities based on electron beam gray scale exposure, realizes a colloid morphology having a three-dimensional structure to serve as a pattern mask of a superconducting thin film, and then performs pattern transfer by an etching process having an obvious etching selection ratio to form a superconducting nanowire including a straight line region and a turn region, wherein the thickness of the superconducting nanowire corresponding to the turn region is greater than that of the superconducting nanowire corresponding to the straight line region, thereby manufacturing the turn-region thickened SNSPD device, suppressing a current crowding effect to a greater extent, having advantages of a higher critical current Ic and a low dark count rate, and significantly improving the performance of the SNSPD device.
The preparation method of the thickened SNSPD device in the turning region can realize the preparation of the thickened superconducting nanowire in the turning region only by one-step electron beam exposure and one-step pattern transfer based on electron beam gray level exposure, simplifies the preparation process flow of the superconducting nanowire with variable thickness, not only can greatly shorten the processing cost and preparation period of the device, but also can avoid the problems of poor process stability and reliability caused by secondary photoetching alignment deviation, twice-patterned thin film interface oxidation and the like, thereby improving the performance and preparation yield of the thickened SNSPD device in the turning region.
Drawings
Fig. 1 shows a process flow diagram for preparing a corner region thickened SNSPD device in the practice of the present invention.
Fig. 2a shows a perspective view of a turn region thickened SNSPD device in the practice of the present invention.
Fig. 2b shows a front view of the turn region thickened SNSPD device of fig. 2 a.
Fig. 2c shows a top view of the turn region thickened SNSPD device of fig. 2 a.
FIG. 3a is a front view of an electron beam resist layer after formation in accordance with an embodiment of the present invention.
Fig. 3b shows a top view of fig. 3 a.
Fig. 4a is a front view of an electron beam gray scale exposure and development in accordance with an embodiment of the present invention.
Fig. 4b shows a top view of fig. 4 a.
Fig. 5a is a front view of the present invention after a first stage etch.
Fig. 5b shows a top view of fig. 5 a.
Fig. 6a is a front view of the second stage of etching in accordance with the practice of the present invention.
Fig. 6b shows a top view of fig. 6 a.
FIG. 7 is a graph showing the contrast of the ZEP520A electron beam resist layer in the practice of the present invention.
Description of the element reference numerals
100 substrate
200 insulating layer
300 superconducting thin film
301 straight line region
302 region of turning
400E-beam resist layer
t 1 ～t 6 Thickness of
S1-S5
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
As in the detailed description of the embodiments of the present invention, the cross-sectional views illustrating the device structures are not partially enlarged in general scale for convenience of illustration, and the schematic views are only examples, which should not limit the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
For convenience in description, spatial relational terms such as "below," "beneath," "below," "under," "over," "upper," and the like may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that these terms of spatial relationship are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the figures. Further, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. As used herein, "between … …" is meant to include both endpoints.
In the context of this application, a structure described as having a first feature "on" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed in between the first and second features, such that the first and second features may not be in direct contact.
It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed freely, and the layout of the components may be more complicated.
As shown in fig. 1, this embodiment provides a method for manufacturing an SNSPD device with a thickened corner region, including the following steps:
s1: providing a substrate;
s2: forming a superconducting thin film on the substrate;
s3: forming an electron beam resist layer on the superconducting thin film;
s4: carrying out photoetching, adopting electron beam gray level exposure and development, and patterning the electron beam resist layer to form an electron beam resist mask with a height difference;
s5: and etching the superconducting film based on the electron beam corrosion-resistant mask to form a superconducting nanowire, wherein the superconducting nanowire comprises a linear area and a turning area, and the thickness of the superconducting nanowire corresponding to the turning area is greater than that of the superconducting nanowire corresponding to the linear area.
As shown in fig. 2a to 2c, in this embodiment, based on the electron beam gray scale exposure, the preparation of the turn-region thickened SNSPD device can be achieved only by one-step electron beam exposure and one-step pattern transfer, where the turn-region thickened SNSPD device includes a substrate 100 and a superconducting thin film 300 having a straight line region 301 and a turn region 302, that is, a superconducting nanowire, and the thickness of the superconducting nanowire corresponding to the turn region 302 is greater than the thickness of the superconducting nanowire corresponding to the straight line region 301, so that the current crowding effect can be greatly suppressed, and the critical current I is higher C And low dark counting rate, and the like, and can obviously improve the performance of the SNSPD device.
Referring to fig. 3 a-6 b, the following describes a method for manufacturing the turn region thickened SNSPD device with reference to the accompanying drawings.
First, referring to fig. 3a and 3b, step S1 is performed to provide the substrate 100.
Specifically, the substrate 100 may be a silicon substrate, an MgO substrate, a sapphire substrate, or the like, and in this embodiment, the substrate 100 is a silicon substrate, but is not limited thereto. Wherein the surface of the substrate 100 is preferably formed with an insulating layer 200, such as SiO, before the superconducting thin film 300 is formed 2 Insulating layer to provide SiO, e.g. 200nm thick 2 a/Si composite substrate, and the SiO 2 the/Si composite substrate was sequentially sonicated in acetone and isopropanol for 5min and blown dry with dry nitrogen to clean. The structure of the substrate for preparing the superconducting thin film 300 is not excessively limited herein.
Next, step S2 is performed to form the superconducting thin film 300 on the insulating layer 200.
Specifically, the superconducting thin film 300 may be deposited with a certain thickness by using a high vacuum magnetron sputtering apparatus, wherein the superconducting thin film 300 may include one or a combination of a NbN superconducting thin film, a WSi superconducting thin film, a NbSi superconducting thin film, a MoSi superconducting thin film, and a Nb superconducting thin film, and the preparation and material of the superconducting thin film 300 are not limited herein.
Next, step S3 is performed to form an electron beam resist layer 400 on the superconducting thin film 300.
By way of example, the e-beam resist layer 400 may include one of HSQ series, PMMA series, AR-P6200 series, and ZEP series.
Specifically, electron beam exposure is to change the molecular cross-linking in an electron resist by electron irradiation, wherein for positive photoresist, the irradiation destroys the cross-linking, the resist is dissolved in a developer, and for negative photoresist, the irradiation causes the molecular cross-linking and is not easily dissolved by the developer. In the present embodiment, the electron beam resist layer 400 is made of an electropositive electron beam resist, and the kind of the electropositive electron beam resist is not limited herein, and the electropositive electron beam resist may include one of PMMA series, AR-P6200 series, and ZEP series. When the electron beam resist layer 400 is formed, the sample on which the superconducting thin film 300 is deposited in step S2 may be placed in a spin coater, and after the sample is fixed, the thickness of the electron beam resist layer 400 may be set by selecting a suitable rotation speed and acceleration through a spin coating method. The gummed sample is placed on a hot plate with a proper temperature for baking for a certain time, and after the baking is finished, the sample is taken down and cooled to room temperature, so that the electron beam resist layer 400 is formed on the superconducting thin film 300.
Next, referring to fig. 4a and 4b, step S4 is performed to perform photolithography, and the electron beam resist layer 400 is patterned by electron beam gray scale exposure and development to form the electron beam resist mask having a height difference.
As an example, the step of forming the electron beam resist mask having a height difference may include:
defining the thickness of the electron beam resist layer as t as shown in FIGS. 3a to 6b 1 SaidThe thickness of the superconducting nanowire corresponding to the turning region is t 2 After the photoetching step is carried out, the thickness of the electron beam corrosion-resistant mask corresponding to the straight line area is t 3 After the etching step is carried out, the thickness of the electron beam anti-corrosion mask corresponding to the turning area is t 5 The thickness of the corresponding superconducting nanowire on the linear region is t 6 ，V r Representing the etch Rate, V, of the Electron Beam resist layer m Represents the etching rate of the superconducting thin film, and S represents the etching selection ratio of the electron beam resist layer to the superconducting thin film, i.e. S ═ V r /V m ；
Wherein, t 3 ＝t 2 ·S，t 5 ＝t 1 -(t 2 -t 6 )·S-t 2 S, and t 5 Is greater than or equal to 0, then t 1 ≥(2t 2 –t 6 ) S to determine t 1 And t 3 Taking the value of (A);
in combination with the contrast curve of the electron beam resist layer, as shown in FIG. 7, the Dose of the electron beam in the electron beam resist layer 400 corresponding to the formation of the entire superconducting nanowire is determined 1 And Dose 1 Exposing the electron beam Dose corresponding to the linear region 301 on the basis of 2 And after the electron beam gray level exposure and the development, the electron beam corrosion-resistant mask with a three-dimensional glue type structure and height difference is obtained.
In this embodiment, when step S4 is executed, the sample is placed in an electron beam exposure apparatus, and appropriate exposure parameters are selected, including acceleration voltage, aperture size, beam current, exposure Dose, and the like, for example, the acceleration voltage is 100kV, the aperture size is 25 μm, the beam current is 100pA, and the exposure Dose of the straight nanowire region is Dose 1 The nanowire exposure Dose of the turning region is Dose 2 To perform the electron beam gray scale exposure. The setting of the electron beam exposure dose needs to be comprehensively considered according to the etching selection ratio of the electron beam resist layer 400 and the superconducting thin film 300, the thickness of the nanowire in the turning area 302 and the contrast curve of the electron beam resist layer under the selected exposure and development conditions.
After the exposure is finished and the development is carried out for a certain time at normal temperature or low temperature, the adopted developer can comprise TMAH, MIBK IPA, O-xylene, pental-acetate and the like, and the specific selection of the adopted developer needs to correspond to the setting of the exposure dose. And after the development is finished, fixing by using Isopropanol (IPA), and finally drying by using dry nitrogen.
Next, referring to fig. 5a to 6b, step S5 is executed to etch the superconducting thin film 300 based on the electron beam resist mask to form a superconducting nanowire, where the superconducting nanowire includes the straight line region 301 and the corner region 302, and a thickness of the superconducting nanowire corresponding to the corner region 302 is greater than a thickness of the superconducting nanowire corresponding to the straight line region 301.
In this embodiment, when step S5 is executed, the colloid mask samples with different thicknesses obtained in step S4 are placed in an etching apparatus, such as a reactive ion etching machine (RIE), etching parameters such as etching power, gas flow, working pressure, etching time, and the like are set, the colloid mask pattern structure is transferred by etching, and then the top-layer residual glue is removed, so as to obtain the superconducting nanowire with thickened turning region.
As an example, the etching step is performed by the following stages:
as shown in fig. 5a and 5b, a first stage etching is performed to remove the superconducting thin film 300 not covered by the electron beam resist mask, and the electron beam resist mask corresponding to the linear region 301 is completely removed to expose the linear region 301;
as shown in fig. 6a and fig. 6b, a second stage etching is performed to thin the exposed linear region 301.
Specifically, the electron beam gray scale exposure is to realize a colloid morphology with a three-dimensional structure by utilizing different dissolution speeds of an electronic resist in a developer under different irradiation intensities (different doses), so that the electron beam gray scale exposure is used for a graphic mask for processing a micro-nano structure. Masks with different thicknesses of the straight line area 301 and the turning area 302 can be defined by means of dose size modulation in one-time electron beam lithography by using an electron beam gray scale exposure technology, and then a pattern transfer means, such as a reactive ion etching technology (RIE) or inductively coupled plasma etching (ICP) is carried out through an etching process with a significant etching selection ratio, so that colloid morphology with height difference can be transferred to the underlying superconducting thin film 300.
The thickness of the superconducting nanowire corresponding to the requirement for preparing the linear region 301 is t 6 The thickness of the superconducting nanowire corresponding to the turning region 302 is t 2 The SNSPD device of fig. 3a to 6b are taken as an example to explain the embodiments of the present invention in detail.
As shown in FIG. 3a and FIG. 3b, the thickness t of the electron beam resist layer 400 is uniform 1 And the dose (different in different regions) during electron beam exposure are key parameters for building a three-dimensional glue-type structure. As shown in fig. 4a to 4b and fig. 5a to 5b, since the thickness of the superconducting thin film 300 to realize the non-mask region is t in the first stage of the etching 2 The removal is completed, and the thickness of the electron beam resist layer 400 in the active region, i.e., the straight line region 301, is just t 3 After the removal, the superconducting thin film 300 corresponding to the linear region 301 is exposed, so that the thickness t of the electron beam resist layer 400 corresponding to the active linear region 301 is increased 3 It should satisfy: t is t 3 ＝t 2 S, wherein S is an etching selection ratio V of the electron beam resist layer 400 to the superconducting thin film 300 r /V m At this time, the thickness of the electron beam resist layer 400 corresponding to the turning region 302 is t 4 . As shown in FIGS. 6a to 6b, for the thickness of the electron beam resist layer 400 in the corner region 302, since the mask effect on the underlying superconducting thin film 300 is maintained in this region during the whole etching process, i.e. a certain thickness of the electron beam resist layer 400 still exists in the corner region 302 after the etching process is completed, i.e. t 5 Is more than or equal to 0 due to t 5 ＝t 1 -(t 2 -t 6 )·S-t 2 S, from which the spin thickness t of the electron beam resist layer 400 can be determined 1 To satisfy t 1 ≥(2t 2 –t 6 )·S。
Determining a thickness t of the electron beam resist layer 400 1 Then, the spin coating technological parameters can be determined; determining the electricityBeamlet resist layer 400 thickness t 1 And t 3 Thereafter, the electron beam Dose for forming the entire superconducting nanowire in the electron beam resist layer 400 can be determined from the contrast curve of the electron beam resist layer 400, as shown in FIG. 7, which is a conventional 1:1ZEP520A positive electron beam resist contrast curve 1 And Dose 1 Exposing the electron beam Dose corresponding to the linear region 301 on the basis of 2 . After electron beam gray level exposure, developing is carried out, and the graphic mask with the three-dimensional glue type structure can be obtained.
In the first stage, the thickness of the superconducting thin film 300 is t since the non-mask region is completed 2 Is removed, thereby etching time T 1 ＝t 2 /V m In the second stage of etching, the thinning of the active linear region is completed, and the etching time T is 2 ＝(t 2 –t 6 )/V m Then, the total etching time T is (2T) 2 –t 6 )/V m . And after the etching is finished, the preparation of the thickened superconducting nanowire in the turning region can be realized.
By way of example, the profile of the superconducting nanowire formed may include one or a combination of a circle, an ellipse and a polygon, and the specific shape of the superconducting nanowire may be selected according to the needs, and is not limited herein.
As an example, the superconducting nanowire is formed in a zigzag serpentine shape, and the linear regions 301 are arranged in parallel. The spacing distance between adjacent parallel linear regions 301 may be set based on actual needs, and is not limited herein, and the formed superconducting nanowire is preferably in a zigzag serpentine shape, so as to improve the performance of the manufactured SNSPD device.
As an example, the superconducting nanowire corresponding to the turn region 302 includes a right-angle turn superconducting nanowire or a U-shaped turn superconducting nanowire. The specific shape of the superconducting nanowire corresponding to the turning region 302 can be selected according to the requirement, and is not limited herein.
In summary, the method for preparing the turn-region thickened SNSPD device of the present invention forms an electron beam resist mask with a height difference by using different dissolution speeds of an electron beam resist layer in a developer under different irradiation intensities based on electron beam gray scale exposure, realizes a colloid morphology with a three-dimensional structure to serve as a pattern mask of a superconducting thin film, and then performs pattern transfer by an etching process with an obvious etching selection ratio to form a superconducting nanowire including a straight line region and a turn region, wherein the thickness of the superconducting nanowire corresponding to the turn region is greater than that of the superconducting nanowire corresponding to the straight line region, thereby preparing the turn-region thickened SNSPD device, suppressing a current crowding effect to a greater extent, having advantages of higher critical current, low dark count rate, and the like, and significantly improving the performance of the SNSPD device.
The preparation method of the thickened SNSPD device in the turning region can realize the preparation of the thickened superconducting nanowire in the turning region only by one-step electron beam exposure and one-step pattern transfer based on electron beam gray level exposure, simplifies the preparation process flow of the superconducting nanowire with variable thickness, not only can greatly shorten the processing cost and preparation period of the device, but also can avoid the problems of poor process stability and reliability caused by secondary photoetching alignment deviation, twice-patterned thin film interface oxidation and the like, thereby improving the performance and preparation yield of the thickened SNSPD device in the turning region.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. A preparation method of a corner region thickened SNSPD device is characterized by comprising the following steps:
providing a substrate;
forming a superconducting thin film on the substrate;
forming an electron beam resist layer on the superconducting thin film;
carrying out photoetching, adopting electron beam gray level exposure and development, and patterning the electron beam resist layer to form an electron beam resist mask with a height difference;
and etching the superconducting film based on the electron beam anti-corrosion mask to form a superconducting nanowire, wherein the superconducting nanowire comprises a straight line area and a turning area, and the thickness of the superconducting nanowire corresponding to the turning area is greater than that of the superconducting nanowire corresponding to the straight line area.
2. The method for preparing the turn region thickened SNSPD device according to claim 1, wherein the etching step comprises the following stages:
etching at a first stage to remove the superconducting film which is not covered by the electron beam corrosion-resistant mask, and completely removing the electron beam corrosion-resistant mask corresponding to the linear area to expose the linear area;
and etching at the second stage, and thinning the exposed linear region.
3. The method for preparing a SNSPD device with a thickened turning area according to claim 2, wherein the step of patterning the electron beam resist layer by electron beam gray scale exposure and development to form the electron beam resist mask with a height difference comprises:
defining the thickness of the electron beam resist layer as t 1 The thickness of the superconducting nanowire corresponding to the turning region is t 2 After the photoetching step is carried out, the thickness of the electron beam corrosion-resistant mask corresponding to the straight line area is t 3 After the etching step is carried out, the thickness of the electron beam anti-corrosion mask corresponding to the turning area is t 5 The thickness of the corresponding superconducting nanowire on the linear region is t 6 ，V r Representing the etch rate, V, of the electron beam resist layer m Representing the etching rate of the superconducting film, and S representing the etching selection of the electron beam resist layer and the superconducting filmSelective ratio, i.e. S ═ V r /V m ；
Wherein, t 3 ＝t 2 ·S，t 5 ＝t 1 -(t 2 -t 6 )·S-t 2 S, and t 5 Is greater than or equal to 0, then t 1 ≥(2t 2 –t 6 ) S to determine t 1 And t 3 Taking the value of (A);
determining the electron beam Dose corresponding to the formation of the whole superconducting nanowire in the electron beam resist layer by combining the contrast curve of the electron beam resist layer 1 And Dose 1 Exposing the electron beam Dose corresponding to the linear region on the basis of 2 And after the electron beam gray level exposure and the development, the electron beam corrosion-resistant mask with a three-dimensional glue type structure and height difference is obtained.
4. The method for preparing the turn region thickened SNSPD device according to claim 3, which is characterized in that:
etching in the first stage for a time T 1 ＝t 2 /V m Etching in the second stage for a period of time T 2 ＝(t 2 –t 6 )/V m And the total etching time T is equal to (2T) 2 –t 6 )/V m 。
5. The method for preparing the turn region thickened SNSPD device according to claim 1, which is characterized in that: the electron beam resist layer includes one of HSQ series, PMMA series, AR-P6200 series, and ZEP series.
6. The method for preparing the turn region thickened SNSPD device according to claim 1, which is characterized in that: the method for etching the superconducting film based on the electron beam corrosion-resistant mask comprises a reactive ion etching method or an inductive coupling plasma etching method.
7. The method for preparing the turn region thickened SNSPD device according to claim 1, which is characterized in that: the superconducting film comprises one or a combination of a NbN superconducting film, a WSi superconducting film, a NbSi superconducting film, a MoSi superconducting film and a Nb superconducting film.
8. The method for preparing the turn region thickened SNSPD device according to claim 1, which is characterized in that: the outline of the superconducting nanowire formed comprises one or a combination of a circle, an ellipse and a polygon.
9. The method for preparing the turn region thickened SNSPD device according to claim 1, which is characterized in that: the formed superconducting nanowire is in a zigzag serpentine shape, and the linear regions are arranged in parallel.
10. The method for preparing the turn region thickened SNSPD device according to claim 1, which is characterized in that: the superconducting nanowires corresponding to the turning region comprise right-angle turning superconducting nanowires or U-shaped turning superconducting nanowires.
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