WO2025154102A1 - Nanopore device structure and fabrication method thereof - Google Patents

Abstract

Present subject matter relates to nanopore device structure (100) and fabrication method of the nanopore device structure. Nanopore device structure comprises substrate (1), first silicon nitride (SN) layer (2), second SN layer (3), and third SN layer (6). First SN layer is deposited on first side of substrate and second SN layer is deposited on second side of substrate. First SN layer and first side of substrate are etched to form first feature, and second SN layer (3) and second side of substrate are etched to form second feature such that first feature has feature size different from second feature. First feature on first side of substrate is deposited with third SN layer (6) such that third SN layer forms suspended SN membrane (8) on etching second feature on second side of substrate. Suspended SN membrane is drilled using electron beam to form a nanopore (9) in suspended SN membrane.

Description

NANOPORE DEVICE STRUCTURE AND FABRICATION METHOD THEREOF

CROSS -REFERENCE TO REEATED APPLICATIONS

This application claims the benefit of Indian Patent Application No. 202441004079, filed on January 19, 2024, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[1] The present subject matter generally relates to nanopore technology. Particularly, the present subject matter relates to a nanopore device structure and fabrication method of the nanopore device structure.

BACKGROUND

[2] Nanopores serve as electrophoretic sensors for single molecules. These sensors consist of a nanoscale pore situated on an ultra-thin insulating layer that separates two liquid-filled chambers. The core mechanism underlying nanopore sensing revolves around observing the ion current through the pore. This provides valuable information regarding the presence and movement of charged biomolecules such as nanoparticles, Deoxyribonucleic acid (DNA), Ribonucleic acid (RNA), and proteins. When an analyte enters the nanopore, it disrupts the ion flow, resulting in noticeable variations in the current.

[3] Traditional nanopore membranes made from silicon nitride typically have a thickness ranging from 12-30 nm and lateral dimensions spanning 10-40pm. However, these large lateral dimensions pose challenges. Firstly, these membranes inherently have a larger surface area exposed to mechanical stresses and thermal fluctuations, increasing the risk of rupture. Secondly, the longer perimeter of larger membranes increases the chances of breakage. Moreover, ensuring uniform thickness over a larger area becomes challenging, leading to regions that are potentially more prone to breakage.

[4] Additionally, the conventional Potassium Hydroxide (KOH) etching method used to produce these membranes present difficulties in achieving consistent, small lateral dimensions, especially when scaling from wafer to wafer. Not only does the large surface area of membranes increase the membrane fragility, but it also makes membranes more susceptible to damage during fabrication and handling, especially when placed on uneven surfaces.

[5] The information disclosed in this background of the disclosure section is for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY

[6] Embodiments of the present disclosure address the problems associated with the existing nanopore technology.

[7] In an embodiment, the present invention provides a nanopore device structure. The nanopore device structure comprising a substrate, a first silicon nitride layer, a second silicon nitride layer, and a third silicon nitride layer. The first silicon nitride layer is deposited on a first side of the substrate and the second silicon nitride layer is deposited on a second side of the substrate. The first silicon nitride layer and the first side of the substrate are etched to form a first feature, and the second silicon nitride layer and the second side of the substrate are etched to form a second feature such that the first feature has a feature size different from the second feature. The first feature on the first side of the substrate is deposited with the third silicon nitride layer such that the third silicon nitride layer forms a suspended silicon nitride membrane on etching the second feature on the second side of the substrate. The suspended silicon nitride membrane is drilled using an electron beam to form a nanopore in the suspended silicon nitride membrane.

[8] In an embodiment the present invention provides a method of forming a nanopore device structure. The method comprising etching a first feature on a first side and a second feature on a second side of the structure using a wet chemical technique. The structure comprises the first feature etched on a first silicon nitride layer and the first side of the substrate, and the second feature etched on a second silicon nitride layer and the second side of the substrate. The first silicon nitride layer is deposited on the first side of the substrate and the second silicon nitride layer is deposited on the second side of the substrate. The first feature has a feature size different from the second feature. Thereafter, the method comprising depositing a third silicon nitride layer on the first side of the structure and a fourth silicon nitride layer on the second side of the structure using a low-pressure chemical vapor deposition technique. Subsequently, the method comprising etching the second feature on the second side of the structure to remove the fourth silicon nitride layer using a dry etching technique and etching the second feature on the second side of the structure using a time-controlled wet chemical technique to obtain the third silicon nitride layer as a suspended silicon nitride membrane. Lastly, the method comprising drilling the suspended silicon nitride membrane using an electron beam to form a nanopore in the suspended silicon nitride membrane.

[9] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[10] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and together with the description, serve to explain the disclosed principles. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described below, by way of example only, and with reference to the accompanying figures.

[11] FIG. 1 illustrates fabrication steps of a nanopore device structure in accordance with some embodiments of the present disclosure.

[12] FIG. 2 illustrate flowcharts showing a method of forming a nanopore device structure in accordance with some embodiments of the present disclosure.

[13] FIGS. 3a to 3c illustrates possibilities of nanopore device structures after a first run of KOH etching depending on feature sizes patterned on a substrate in accordance with some embodiments of the present disclosure. [14] FIGS. 4a to 4c illustrates a transmission electron microscope images of a suspended silicon nitride membrane in accordance with some embodiments of the present disclosure.

[15] FIG. 5 illustrates current blockade obtained with a nanopore in a nanopore device structure during translocation of 6-Helix bundle DNA origami structures in accordance with some embodiments of the present disclosure. Inset shows a magnified view of a single translocation event.

[16] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flowcharts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION

[17] In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[18] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[19] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises. . . a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.

[20] In the following detailed description of embodiments of the disclosure, reference is made to the accompanying drawings which illustrates specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

[21] In the present disclosure, a feature may, also, be referred to as a pattern and a substrate may, also, be referred to as a wafer. Further, a first side of a substrate may, also, be referred to as a top side of the substrate and a second side of the substrate may, also, be referred to as a bottom side of the substrate.

[22] The fabrication of the nanopore device structure 100 is explained with reference to FIG. 1 and FIG. 2.

[23] FIG. 1 illustrates fabrication steps of the nanopore device structure 100 in accordance with some embodiments of the present disclosure. FIG. 2 illustrate flowcharts showing a method of forming the nanopore device structure 100 in accordance with some embodiments of the present disclosure.

[24] In an embodiment, a substrate 1 is a Silicon (Si) substrate (refer FIG. la). The Si substrate may have a (100) crystal orientation. In an embodiment, the Si substrate may be doped with n-type or p-type doping impurities. The Si substrate may have, but not limited to, a thickness in a range of 200pm to 525pm. The substrate 1 comprises a first side and a second side. The first side and the second side of the substrate 1 are polished.

[25] At step 201, the first side and the second side of the substrate 1 are cleaned using Radio Corporation of America (RCA) process and thereafter, Si oxide layer from the first side and the second side of the substrate 1 is stripped using chemical stripping process. For instance, the first side and the second side of the substrate 1 are first cleaned using RCA-1 process involving Ammonium Hydroxide (NH4OH): Hydrogen peroxide (H2O2): Deionized (DI) water in the ratio of vol.% 1:1:5 at 80°C for 10 minutes. Subsequently, the first side and the second side of the substrate 1 are cleaned using RCA-2 process involving Hydrochloric acid (HCL):H2O2:DI water in the ratio of vol.% 1:1:6 at 80°C for 10 minutes. Once the first side and the second side of the substrate 1 are cleaned using RCA-1 and RCA-2 processes, the Si oxide layer from the first side and the second side of the substrate 1 is stripped using the chemical stripping process involving Hydrofluoric acid (HF):DI water in the ratio of vol.% 1:50 at 25°C for 20 seconds.

[26] At step 202, a first silicon nitride layer 2 is deposited on the first side of the substrate 1 and a second silicon nitride layer 3 is deposited on the second side of the substrate 1 (refer FIG. lb). The thickness of the first silicon nitride layer 2 and the second silicon nitride layer 3 are in the range of, but not limited to, 50nm to 150nm. The first silicon nitride layer 2 is deposited on the first side of the substrate 1 and the second silicon nitride layer 3 is deposited on the second side of the substrate 1 using a first run (also, referred as first round) of Low Pressure Chemical Vapor Deposition (LPCVD) technique. The recipe used for LPCVD technique is temperature 750°C and pressure 200mTorr using a precursor Dichloro silane (DCS):Ammonia (NH3) in the ratio of flow rate 10:70 seem.

[27] At step 203, the first silicon nitride layer 2 deposited on the first side of the substrate 1 is cleaned using acetone, IPA, and DI water for 2 minutes each and thereafter, baked at 110°C for 10 minutes to remove any traces of solvent. Subsequently, the first silicon nitride layer 2 deposited on the first side of the substrate 1 is spin coated using a positive photoresist at 4000 rpm for a duration of 40 seconds using a spin coater. In one embodiment, the positive photoresist may be AZ4562 and the spin coater may be Laurell H6-23 spin coater. Spin coating of the positive photoresist on the first silicon nitride layer 2 deposited on the first side of the substrate 1 is followed by a soft bake at 110°C for 1 minute. The positive photoresist is exposed using an optical lithography technique for direct writing of first feature on the positive photoresist. The first feature may have a square or a circular pattern of diameter 110 pm. In one embodiment, the optical lithography technique is carried out using Heidelberg UPG 501 having a focused laser beam of excitation wavelength of 390nm. Thereafter, the first feature is developed using a developer for nearly 2 minutes at 20°C and relative humidity of 45 in a class 100 cleanroom. In one embodiment, the developer may be MIF726. Once the first feature is developed, the remaining photoresist on the first silicon nitride layer 2 deposited on the first side of the substrate 1 is hard baked at 110°C for 3 minutes (refer FIG. 1c). [28] At step 204, to transfer the first feature from the remaining photoresist to the first silicon nitride layer 2, a Reactive Ion Etching (RIE) technique (also, referred as isotropic etching technique) is used. Using the RIE, the first silicon nitride layer 2 is etched or removed to form the first feature in the first silicon nitride layer 2 deposited on the first side of the substrate 1 (refer FIG. Id). The dry etching recipe used for RIE technique is Trifluoromethane (CHF3) and O2 in a 1:10 gas ratio at 20°C and 55mT. In one embodiment, the RIE technique is carried out using Plasma lab systems 100 from Oxford Instruments.

[29] At step 205, the second silicon nitride layer 3 deposited on the second side of the substrate 1 is cleaned using acetone, IPA, and DI water for 2 minutes each and thereafter, baked at 110°C for 10 minutes to remove any traces of solvent. Subsequently, the second silicon nitride layer 3 deposited on the second side of the substrate 1 is spin coated using a positive photoresist at 4000rpm for a duration of 40 seconds using a spin coater. In one embodiment, the positive photoresist may be AZ4562 and the spin coater may be Laurell H6-23 spin coater. Spin coating of the positive photoresist on the second silicon nitride layer 3 deposited on the second side of the substrate 1 is followed by a soft bake at 110°C for 1 minute. The positive photoresist is exposed using an optical lithography technique for direct writing of second feature on the positive photoresist. The second feature may have a square or a circular pattern of diameter in a range of 330pm to 360pm. In one embodiment, the optical lithography technique is carried out using Heidelberg UPG 501 having a focused laser beam of excitation wavelength of 390nm. Thereafter, the second feature is developed using the developer for nearly 2 minutes at 20°C and relative humidity of 45 in a class 100 cleanroom. In one embodiment, the developer may be MIF726. Once the second feature is developed, the remaining photoresist on the second silicon nitride layer 3 deposited on the second side of the substrate 1 is hard baked at 110°C for 3 minutes (refer FIG. le).

[30] At step 206, to transfer the second feature from the remaining photoresist to the second silicon nitride layer 3, the RIE technique is used. Using the RIE, the second silicon nitride layer 3 is etched or removed to form the second feature in the second silicon nitride layer 3 deposited on the second side of the substrate 1 (refer FIG. If). The dry etching recipe used for RIE technique is CHF3 and O2 in a 1:10 gas ratio at 20°C and 55mT. In one embodiment, the RIE technique is carried out using Plasma lab systems 100 from Oxford Instruments. The first feature has a feature size different from the second feature. In one embodiment, the first feature has a feature size smaller than the second feature. In another embodiment, the first feature has a feature size larger than the second feature.

[31] At step 207, to transfer the first feature from the first silicon nitride layer 2 onto the first side of the substrate 1 and the second feature from the second silicon nitride layer 3 onto the second side of the substrate 1 , a first run of wet chemical technique (also, referred as anisotropic etching technique) is used. Using the wet chemical technique, the substrate 1 with the first feature on the first silicon nitride layer 2 and the second feature on the second silicon nitride layer 3 is etched using a 30wt.% KOH solution by weight at 90°C for 1 hour using a standard hotplate. In one embodiment, the standard hotplate may be IKA C MAG H7 hotplate. Additionally, due to the (100) crystal orientation of Si substrate, pyramidal structures of the first feature and the second feature will be formed after first run of wet chemical technique. These pyramidal structures will be bounded by (111) crystal orientation, which etch slower compared to the (100) crystal orientation of Si substrate. The first run of wet chemical technique results in an etch stop with the first feature on the first side of the substrate 1 being smaller than the second feature on the second side of the substrate 1 (refer FIG. 1g). In detail, the etching is stopped once the etch- stop is formed in the first feature such that the first feature on the first side of the substrate 1 and the second feature on the second side of the substrate 1 do not merge. At this stage, the first feature etched on the first silicon nitride layer 2 and the first side of the substrate 1 and the second feature etched on a second silicon nitride layer 3 and the second side of the substrate 1 may be referred as a structure.

[32] FIGS. 3a to 3c illustrates possibilities of nanopore device structures after a first run of KOH etching depending on feature sizes patterned on a substrate in accordance with some embodiments of the present disclosure. The feature size of the second feature on the second side of the structure 1 is chosen such that the feature size of the second feature does not become an etch stop before the feature size of the first feature on the first side of the structure 1 reaches the etch stop as shown in FIG. 3a. Further, the difference in the dimensions of the first feature and the second feature is large enough such that after the first run of wet chemical technique, the first feature and the second feature do not meet otherwise the first feature and the second feature meet as shown in FIG. 3b. The present disclosure overcomes the above-mentioned problems as shown in FIG. 3a and FIG. 3b with the first feature having a feature size different from the second feature as shown in FIG. 3c (also, refer FIG. 1g). The dotted line shown in FIG. 3c indicates probable etching profile of the second feature (which is a larger feature compared to the first feature in this example) during the first run of wet chemical technique.

[33] Prior to depositing a third silicon nitride layer 6 on the first side of the substrate 1 (or structure) and a fourth silicon nitride layer 7 on the second side of the structure 1 (or structure), the first side and the second side of the substrate 1 are cleaned using the RCA process and thereafter, Si oxide layer on the first feature on the first side and Si oxide layer on the second feature on the second side of the substrate 1 is stripped using chemical stripping process. For instance, the first side and the second side of the substrate 1 are first cleaned using RCA-1 process involving NEUOELEbC iDI water in the ratio of vol.% 1:1:5 at 80°C for 10 minutes. Subsequently, the first side and the second side of the substrate 1 are cleaned using RCA-2 process involving HCL:H2O2:DI water in the ratio of vol.% 1:1:6 at 80°C for 10 minutes. Once the first side and the second side of the substrate 1 are cleaned using RCA-1 and RCA-2 processes, the Si oxide layer on the first feature on the first side and Si oxide layer on the second feature on the second side of the substrate 1 is stripped using the chemical stripping process involving HF:DI water in the ratio of vol.% 1:50 at 25°C for 20 seconds.

[34] At step 208, a third silicon nitride layer 6 on the first side of the substrate 1 (or structure) and a fourth silicon nitride layer 7 on the second side of the substrate 1 (or structure) are deposited (refer FIG. Ih). The thickness of the third silicon nitride layer 6 and the fourth silicon nitride layer 7 are in the range of, but not limited to, 2nm to 300nm. The third silicon nitride layer 6 is deposited on the first side of the substrate 1 and the fourth silicon nitride layer 7 is deposited on the second side of the substrate 1 using a second run (also, referred as second round) of LPCVD technique. The recipe used for LPCVD technique is temperature 500°C to 800°C and pressure 50 mT to 200 mT using a precursor DCS:NH3 in the ratio of flow rate 10:70 seem. In an embodiment, the third silicon nitride layer 6 has a tetrahedral shape or structure.

[35] At step 209, to remove the fourth silicon nitride layer 7 from the second feature on the second side of the substrate 1 (or structure), the RIE technique is used. Using the RIE, the fourth silicon nitride layer 7 is etched or removed from the second feature in the second side of the substrate 1 (refer FIG. li). The dry etching recipe used for RIE technique is CHF3 and O2 in a 1:10 gas ratio at 20°C and 55mT. In one embodiment, the RIE technique is carried out using Plasma lab systems 100 from Oxford Instruments. [36] At step 210, to obtain the third silicon nitride layer 6 as a suspended silicon nitride membrane 8, the second feature on the second side of the substrate 1 (or structure) is etched using a second run of wet chemical technique. Using the wet chemical technique, the second feature on the second side of the substrate 1 (or structure) is etched using 10wt.% to 30wt.% KOH solution by weight at 90°C using a standard hotplate for 5 minutes - 120 minutes depending on the required membrane size. In one embodiment, the standard hotplate may be IKA C MAG H7 hotplate. This second run of wet chemical technique selectively etches the Si and/or Si oxide from the second feature on the second side of the substrate 1 (or structure) and remains non-reactive to the third silicon nitride layer 6 on the first side of the substrate 1 resulting in the third silicon nitride layer 6 forming as a suspended silicon nitride membrane 8 (refer FIG. Ij). This second run of wet chemical technique is a time-controlled wet chemical technique. The time required for the second run of wet chemical technique is correlated to the thickness of the remaining Si and/or Si oxide on the second side of the substrate 1 (or structure) after the first run of wet etching. The size of the suspended silicon nitride membrane 8 is controlled by etch-time and not by pattern (or design) of the silicon nitride membrane 8. The thickness of the Si and/or Si oxide on the second side of the substrate 1 (or structure) is measured using Dektak Surface profilometer-from Bruker.

[37] FIGS. 4a to 4c illustrates a transmission electron microscope images of a suspended silicon nitride membrane in accordance with some embodiments of the present disclosure. The transmission electron microscope images of the suspended silicon nitride membrane 8 of sizes 100 nm, 7 m, and 35 f m are shown in FIG. 4a, FIG. 4b, and FIG. 4c, respectively that are formed by doing the second run of etching.

[38] At step 211, to form a nanopore 9 in the suspended silicon nitride membrane 8, (the third silicon nitride layer 6 acting as) the suspended silicon nitride membrane 8 on the first side of the substrate 1 is drilled using an electron beam (refer FIG. Ik). The structure 100 with the nanopore 9 shown in FIG. Ik may be referred as nanopore device structure 100. The size of the nanopore 9 is 1 nm to 1 micron. In one embodiment, the size of the nanopore 9 is 3 to 6 nm. The electron beam is the electron beam of a transmission electron microscope. In one embodiment, the transmission electron microscope used is a Titan Themis 300kV from Thermofisher Scientific. The parameters of the transmission electron microscope technique are an accelerating voltage of 300kV, an electron beam with an intensity of 10⁸ -10⁹ e/nm²s with full- width half maxima of 2-10nm. The size of the nanopore 9 can be varied as per experimental requirement, for example for translocation experiment, by defocusing the electron beam.

[39] FIG. 5 illustrates current blockade obtained with a nanopore in a nanopore device structure during translocation of 6-Helix bundle DNA origami structures in accordance with some embodiments of the present disclosure. Inset shows a magnified view of a single translocation event.

[40] As a proof of concept to validate the functionality of the nanopore 9 in the suspended silicon nitride membrane 8, an experiment result of a translocated 6-helix bundle DNA origami nanostructures through the nanopore 9 at a bias voltage of 200mV and a sampling frequency of 200kHz is shown in FIG. 5.

[41] Some of the technical advantages of the present disclosure are listed below.

[42] The nanopore device structure of the present disclosure owing to its inherent device structure offers an enhanced mechanical stability, making nanopore device structure more robust than device structures with flat membranes currently employed in nanopore technologies.

[43] The reduced membrane size in the nanopore device structure of the present disclosure allows increased stability and robustness of the suspended silicon nitride membrane, which is vital for long-duration experiments and its usage in harsh environments. This suspended silicon nitride membrane has shown to be stable for nanopore sensing experiments lasting without damage for few months.

[44] Given the robustness and versatility of the nanopore device structure of the present disclosure, the suspended silicon nitride membrane with TEM-created nanopores represents a significant advancement, paving the way for their adoption in diverse applications ranging from rapid DNA sensing to advanced nanoscale sensors.

[45] The suspended silicon nitride membrane in the nanopore device structure of the present disclosure is formed ‘buried’ within this device structure such that the suspended silicon nitride membrane formed does not come in contact with external surfaces during handling and storage. Consequently, this increases reuse of these devices over a longer period of time without any damage to the nanopore and/or the suspended silicon nitride membrane.

[46] The fabrication method of the present disclosure allows a higher flexibility in choosing the bottom side feature dimensions in the nanopore device structure as the suspended silicon nitride membrane dimensions are independent of the bottom side feature dimensions.

[47] Some of the clauses are mentioned below.

[48] [1]: A nanopore device structure (100), comprising: a substrate (1); a first silicon nitride layer (2); a second silicon nitride layer (3); and a third silicon nitride layer (6), wherein the first silicon nitride layer (2) is deposited on a first side of the substrate (1) and the second silicon nitride layer (3) is deposited on a second side of the substrate (1), wherein the first silicon nitride layer (2) and the first side of the substrate (1) are etched to form a first feature, and the second silicon nitride layer (3) and the second side of the substrate (1) are etched to form a second feature such that the first feature has a feature size different from the second feature, wherein the first feature on the first side of the substrate (1) is deposited with the third silicon nitride layer (6) such that the third silicon nitride layer (6) forms a suspended silicon nitride membrane (8) on etching the second feature on the second side of the substrate (1), and wherein the suspended silicon nitride membrane (8) is drilled using an electron beam to form a nanopore (9) in the suspended silicon nitride membrane (8).

[49] [2]: A method of forming a nanopore device structure (100), comprising: a) etching (107) a first feature on a first side and a second feature on a second side of a structure using a wet chemical technique; wherein the structure comprises the first feature etched on a first silicon nitride layer (2) and the first side of the substrate (1) and the second feature etched on a second silicon nitride layer (3) and the second side of the substrate (1), wherein the first silicon nitride layer (2) is deposited on the first side of the substrate (1) and the second silicon nitride layer (3) is deposited on the second side of the substrate (1), wherein the first feature has a feature size different from the second feature; b) depositing (108) a third silicon nitride layer (6) on the first side of the structure and a fourth silicon nitride layer (7) on the second side of the structure using a low-pressure chemical vapor deposition technique; c) etching (109) the second feature on the second side of the structure to remove the fourth silicon nitride layer (7) using a dry etching technique; d) etching (110) the second feature on the second side of the structure using a time-controlled wet chemical technique to obtain the third silicon nitride layer (6) as a suspended silicon nitride membrane (8); and e) drilling (111) the suspended silicon nitride membrane (8) using an electron beam to form a nanopore (9) in the suspended silicon nitride membrane (8).

[50] [3]: The method described in [2], wherein etching in step a) is stopped once the etchstop is formed in the first feature such that the first feature on the first side of the structure (1) and the second feature on the second side of the structure (1) do not merge.

[51] [4]: The method described in any of [2] to [3], wherein the first feature has a feature size smaller than the second feature, or wherein the first feature has a feature size larger than the second feature.

[52] [5]: The nanopore device structure (100) described in [1], wherein the third silicon nitride layer (6) has a tetrahedral shape.

[53] [6]: The nanopore device structure (100) described in [1], wherein the electron beam is the electron beam of a transmission electron microscope. [54] [7]: The nanopore device structure (100) described in [1], wherein the first feature has a feature size smaller than the second feature, or wherein the first feature has a feature size larger than the second feature.

[55] [8]: The nanopore device structure (100) described in [1], wherein the thickness of the third silicon nitride layer (6) is in the range of 2nm to 300nm.

[56] [9]: The nanopore device structure (100) described in [1], wherein the size of the nanopore (9) is Inm to Imicron.

[57] [10]: The method described in [2], wherein the wet chemical technique uses 10wt.% to 30wt.% potassium hydroxide solution.

[58] [11]: The method described in [2], wherein the dry etching technique is a reactive ion etching technique.

[59] [12]: The method described in [2], wherein the low-pressure chemical vapor deposition is carried out at temperature of 500°C to 800°C and pressure of 50mT to 200mT.

[60] [13]: The method described in [2], wherein the electron beam is the electron beam of a transmission electron microscope.

[61] [14]: The method described in [2], wherein the substrate (1) is silicon substrate.

[62] [15]: The method described in [2], wherein the thickness of the substrate (1) is in the range of 200pm to 525pm.

[63] [16]: The method described in [2], wherein the thickness of the first silicon nitride layer (2) and the second silicon nitride layer (3) is in the range of 50nm to 150nm.

[64] [17]: The method described in [2], wherein the thickness of the third silicon nitride layer (6) and fourth silicon nitride layer (7) is in the range of 2nm to 300nm. [65] [18]: The method described in [2], wherein the thickness of the suspended silicon nitride membrane (8) is in the range of 5nm to 150nm.

[66] [19]: The method described in [2], wherein the size of the nanopore (9) is in the range of Inm to 1 micron.

[67] [20]: The method described in [2], wherein the formation of the structure in the step a) comprising: depositing (102) the first silicon nitride layer (2) on the first side of the substrate

(1) and the second silicon nitride layer (3) on the second side of the substrate (1); and forming (103, 104, 105, 106) the first feature on the first silicon nitride layer (2) and the first side of the substrate (1) and the second feature on the second silicon nitride layer (3) and the second side of the substrate (1) using an optical lithography technique and one or more etching techniques.

[68] [21]: The method described in [2], wherein the suspended silicon nitride membrane (8) size is controlled by etch-time.

[69] The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment” mean “one or more (but not all) embodiments of the invention(s)” unless expressly specified otherwise.

[70] The terms “including”, “comprising”, “having” and variations thereof mean “including but not limited to”, unless expressly specified otherwise.

[71] The enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise.

[72] The terms “a”, “an” and “the” mean “one or more”, unless expressly specified otherwise.

[73] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention.

[74] When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article, or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself.

[75] Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

[76] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the scope being indicated by the following claims.

Claims

WE CLAIM:

1. A nanopore device structure (100), comprising: a substrate (1); a first silicon nitride layer (2); a second silicon nitride layer (3); and a third silicon nitride layer (6), wherein the first silicon nitride layer (2) is deposited on a first side of the substrate (1) and the second silicon nitride layer (3) is deposited on a second side of the substrate (1), wherein the first silicon nitride layer (2) and the first side of the substrate (1) are etched to form a first feature, and the second silicon nitride layer (3) and the second side of the substrate (1) are etched to form a second feature such that the first feature has a feature size different from the second feature, wherein the first feature on the first side of the substrate (1) is deposited with the third silicon nitride layer (6) such that the third silicon nitride layer (6) forms a suspended silicon nitride membrane (8) on etching the second feature on the second side of the substrate (1), and wherein the suspended silicon nitride membrane (8) is drilled using an electron beam to form a nanopore (9) in the suspended silicon nitride membrane (8).

2. A method of forming a nanopore device structure (100), comprising: a) etching (107) a first feature on a first side and a second feature on a second side of a structure using a wet chemical technique; wherein the structure comprises the first feature etched on a first silicon nitride layer (2) and the first side of the substrate (1) and the second feature etched on a second silicon nitride layer (3) and the second side of the substrate (1), wherein the first silicon nitride layer (2) is deposited on the first side of the substrate (1) and the second silicon nitride layer (3) is deposited on the second side of the substrate (1), wherein the first feature has a feature size different from the second feature; b) depositing (108) a third silicon nitride layer (6) on the first side of the structure and a fourth silicon nitride layer (7) on the second side of the structure using a low-pressure chemical vapor deposition technique; c) etching (109) the second feature on the second side of the structure to remove the fourth silicon nitride layer (7) using a dry etching technique; d) etching (110) the second feature on the second side of the structure using a time- controlled wet chemical technique to obtain the third silicon nitride layer (6) as a suspended silicon nitride membrane (8); and e) drilling (111) the suspended silicon nitride membrane (8) using an electron beam to form a nanopore (9) in the suspended silicon nitride membrane (8).

3. The method as claimed in claim 2, wherein etching in step a) is stopped once the etchstop is formed in the first feature such that the first feature on the first side of the structure (1) and the second feature on the second side of the structure (1) do not merge.

4. The method as claimed in claim 2, wherein the first feature has a feature size smaller than the second feature, or wherein the first feature has a feature size larger than the second feature.

5. The nanopore device structure (100) as claimed in claim 1, wherein the third silicon nitride layer (6) has a tetrahedral shape.

6. The nanopore device structure (100) as claimed in claim 1, wherein the electron beam is the electron beam of a transmission electron microscope.

7. The nanopore device structure (100) as claimed in claim 1, wherein the first feature has a feature size smaller than the second feature, or wherein the first feature has a feature size larger than the second feature.

8. The nanopore device structure (100) as claimed in claim 1, wherein the thickness of the third silicon nitride layer (6) is in the range of 2 nm to 300 nm.

9. The nanopore device structure (100) as claimed in claim 1, wherein the size of the nanopore (9) is 1 nm to 1 micron.

10. The method as claimed in claim 2, wherein the wet chemical technique uses 10 wt.% to 30 wt.% potassium hydroxide solution.

11. The method as claimed in claim 2, wherein the dry etching technique is a reactive ion etching technique.

12. The method as claimed in claim 2, wherein the low-pressure chemical vapor deposition is carried out at temperature of 500 °C to 800 °C and pressure of 50 mT to 200 mT.

13. The method as claimed in claim 2, wherein the electron beam is the electron beam of a transmission electron microscope or of an electron beam lithography.

14. The method as claimed in claim 2, wherein the substrate (1) is silicon substrate.

15. The method as claimed in claim 2, wherein the thickness of the substrate (1) is in the range of 200 pm to 525 pm.

16. The method as claimed in claim 2, wherein the thickness of the first silicon nitride layer

(2) and the second silicon nitride layer (3) is in the range of 50 nm to 150 nm.

17. The method as claimed in claim 2, wherein the thickness of the third silicon nitride layer (6) and fourth silicon nitride layer (7) is in the range of 5 nm to 150 nm.

18. The method as claimed in claim 2, wherein the thickness of the suspended silicon nitride membrane (8) is in the range of 5 nm to 150 nm.

19. The method as claimed in claim 2, wherein the size of the nanopore (9) is in the range of 1 nm to 1 micron.

20. The method as claimed in claim 2, wherein the formation of the structure in the step a) comprising: depositing (102) the first silicon nitride layer (2) on the first side of the substrate (1) and the second silicon nitride layer (3) on the second side of the substrate (1); and forming (103, 104, 105, 106) the first feature on the first silicon nitride layer (2) and the first side of the substrate (1) and the second feature on the second silicon nitride layer (3) and the second side of the substrate (1) using an optical lithography technique and one or more etching techniques.

21. The method as claimed in claim 2, wherein the suspended silicon nitride membrane (8) size is controlled by etch-time.