Through hole microneedle and preparation method thereof

Abstract

The invention provides a through hole microneedle and a preparation method thereof, and the method comprises the following steps: providing a silicon wafer, and sequentially forming a silicon nitride layer and a silicon oxide layer on the front surface and the back surface of the silicon wafer; forming a first etching mask on the front surface of the silicon wafer by utilizing photoetching and etching processes, and carrying out first deep silicon etching to form a semi-through deep hole; forming a second etching mask on the back surface of the silicon wafer by utilizing photoetching and etching processes, and carrying out secondary deep silicon etching to form a through deep hole to obtain a pinhole structure; removing the silicon oxide layers on the front surface and the back surface of the silicon wafer; forming a silicon oxide layer on the inner wall of the deep hole by adopting a thermal oxidation process; forming silicon nitride layers on the front surface and the back surface of the silicon wafer and the inner wall of the deep hole; removing all the silicon nitride layers on the front surface of the silicon wafer; etching the silicon wafer by using an anisotropic wet method to form a needle body structure; and removing the residual silicon nitride layer and the residual silicon oxide layer.

Description

Technical Field

[0001] The present application relates to the field of integrated design and manufacturing of MEMS devices, and in particular to a through-hole microneedle and a preparation method thereof. Background Art

[0002] Microelectromechanical systems (MEMS) can perform precise operations in tiny spaces that traditional instruments cannot reach, and achieve real-time monitoring. Therefore, they are widely used in biomedicine, such as precise drug injection, clinical monitoring, microsurgery, micro-implantation systems, etc. It can be said that the emergence of MEMS technology has brought new means to biomedicine, and microneedle arrays are an important application of MEMS technology in medicine. Microneedle arrays can be widely used in biomedical measurement, drug delivery, microfluid sampling and other fields. It has the characteristics of small size, high strength, and biocompatibility of materials. It can accurately control the depth of insertion, thereby reducing damage to the insertion position and achieving the purpose of painlessness, providing patients with efficient and safe medical means, which is more in line with the humanized characteristics of medical research and has injected great vitality into the biomedical field. Therefore, it has very important research significance.

[0003] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0004] The object of the present invention is to provide a through-hole microneedle and a preparation method thereof, so as to obtain a microneedle structure with a simple preparation process, suitable for mass production and good morphology.

[0005] In order to solve the above problems, in a first aspect, a method for preparing a through-hole microneedle is provided below, comprising the following steps:

[0006] S1. providing a silicon wafer, and sequentially forming a silicon nitride layer and a silicon oxide layer on the front and back sides of the silicon wafer;

[0007] S2, using photolithography and etching processes to form a first etching mask on the front side of the silicon wafer, and performing a first deep silicon etching to form a semi-penetrating deep hole;

[0008] S3, using photolithography and etching processes to form a second etching mask on the back side of the silicon wafer, and performing a second deep silicon etching to form a penetrating deep hole to obtain a pinhole structure;

[0009] S4, removing the silicon oxide layer on the front and back sides of the silicon wafer;

[0010] S5, forming a silicon oxide layer on the inner wall of the deep hole by using a thermal oxidation process;

[0011] S6, forming a silicon nitride layer on the front and back sides of the silicon wafer and the inner wall of the deep hole;

[0012] S7, removing all silicon nitride layers on the front side of the silicon wafer;

[0013] S8, etching the silicon wafer using an anisotropic wet method to form a needle structure;

[0014] S9, removing the remaining silicon nitride layer and the silicon oxide layer.

[0015] In the present application, by using a combination of silicon oxide layer + silicon nitride layer as a protective layer, it can not only play a better protective role, but also improve stress, improve the uniformity of the etching process, and ensure precise control in deep silicon etching, so as to obtain a microneedle structure with good morphology; in addition, by optimizing the process and utilizing the characteristics of the thermal oxidation process, a silicon oxide layer is formed only inside the deep hole, thereby reducing the etching of the primary oxide layer and ensuring the integrity of the internal protective layer; first, a through hole is obtained through two deep silicon etchings, and finally anisotropic corrosion is performed to obtain the needle body, avoiding the change in silicon wafer size to the wafer feeding and alignment of the machine, which is more suitable for various machines and can also reduce possible damage to the needle body structure.

[0016] The silicon wafer is a single crystal silicon wafer with a crystal orientation of (100). The silicon wafer with a crystal orientation of (100) can be etched along the crystal orientation of (54°) using an anisotropic etching solution to obtain the required microneedle structure.

[0017] In step S1, a first silicon nitride layer and a second silicon nitride layer are formed on the front and back of the silicon wafer respectively by chemical vapor deposition process; a first silicon oxide layer is formed on the surface of the first silicon nitride layer and a second silicon oxide layer is formed on the surface of the second silicon nitride layer by plasma enhanced chemical vapor deposition process. Chemical vapor deposition is a mature process for forming silicon nitride with good compatibility; PECVD is used to form oxide layers on the upper and lower surfaces of the silicon wafer in turn, considering that thermal oxidation cannot form an oxide layer on the silicon nitride surface and the depths of the two deep silicon etchings are different, and therefore oxide layers of corresponding thickness should be formed as barrier layers.

[0018] The photolithography and etching process includes: coating a photoresist on the surface of the silicon oxide layer and patterning it to form a photoresist mask; using the photoresist mask, patterning the silicon oxide layer and the silicon nitride layer through an etching process to form the first etching mask or the second etching mask. Using a three-layer structure of photoresist, silicon oxide layer and silicon nitride layer as an etching mask can ensure that the deep silicon etching process is more stable and the pattern accuracy is better.

[0019] In step S4, the silicon oxide layer is removed by using a buffered silicon oxide etching solution. BOE is a commonly used silicon oxide etching solution with a more mature process.

[0020] In step S1 and step S6, the silicon nitride layer is formed by a low stress silicon nitride process, and the silicon nitride layer is low stress silicon-rich silicon nitride. The use of low stress silicon nitride can more effectively improve stress and ensure the morphology of the microneedle.

[0021] After step S2 and step S3, a stripping process is included to remove the residual photoresist.

[0022] In step S7, the silicon nitride layer is removed by a dry etching process.

[0023] The anisotropic wet etching includes wet etching using tetramethylammonium hydroxide solution or potassium hydroxide solution; the concentration of the tetramethylammonium hydroxide solution is 2.38%. TMAH is a commonly used solution in Fab, and the obtained microneedle has a good morphology.

[0024] On the other hand, the present application further provides a through-hole microneedle, which is prepared by the method for preparing a through-hole microneedle described in any one of the first aspects, and the through-hole microneedle comprises a substrate, a needle body and a needle hole.

[0025] Compared with the prior art, the beneficial effects of the present invention mainly include the following: in the present application, a silicon oxide layer + a silicon nitride layer are used as a protective layer, wherein the silicon oxide layer is relatively soft, while the silicon nitride layer is relatively hard. Through the combination of the two, it can not only play a better protective role, but also improve stress and improve the uniformity of the etching process; in the deep silicon etching process, the silicon oxide layer + the silicon nitride layer is used as a hard mask to ensure the precise control of the pattern during the etching process, especially when the etching depth is large, it can avoid excessive etching or shape distortion. The silicon nitride mask layer can help the etching maintain a very vertical side wall, and can accelerate the internal etching reaction to make the needle body thinner; in the process of anisotropic wet etching, the role of the silicon nitride layer + silicon oxide layer on the inner wall of the deep hole is the same, which can not only ensure a good stress distribution and avoid deformation of the needle body, but also provide sufficient blocking effect to protect the needle body from being damaged during a long period of corrosion; in addition, in terms of process, we first deposited the oxide layer and then deposited the silicon nitride layer. In the subsequent process, we can use the characteristics of the thermal oxidation process to form a silicon oxide layer only inside the deep hole, and then reduce the etching of the oxide layer once in the subsequent process, which not only simplifies the process, but also ensures that the internal protective layer is as complete as possible; in the present application, firstly, a through hole is obtained by two deep silicon etchings, and finally TMAH etching is performed to obtain the needle body, which is also considered that the overall size of the silicon wafer will be greatly reduced after TMAH etching, and considering that most machines, such as dry etching machines, photolithography machines, etc., usually have higher size requirements for the processed silicon wafers. Therefore, if there are photolithography, etching and other processes after TMAH etching, the size of the silicon wafer may not be very suitable for the machine, which will cause difficulties in the wafer feeding, alignment and other processes, and may also cause damage to the needle structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is a three-dimensional schematic diagram of the through-hole microneedle structure provided by the present invention.

[0028] Figure 2 The invention provides a process flow for preparing the through-hole microneedle.

[0029] Figure 3 Schematic diagram of the through-hole microneedle preparation process provided by the present invention. DETAILED DESCRIPTION

[0030] The above and other technical contents, features and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front or back, etc., are only referenced to the directions of the attached drawings. Therefore, the directional terms used are used to illustrate and not to limit the present invention.

[0031] The following will describe the various embodiments of the present application in detail with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that in the various embodiments of the present application, many technical details are provided in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solution claimed in the present application can be implemented.

[0032] The steps in the following embodiments do not correspond one to one with the summary of the invention.

[0033] Embodiment 1

[0034] The present invention provides a through-hole microneedle and a preparation method thereof. Figure 1 As shown, the structure of the through-hole microneedle is mainly composed of three parts: substrate 9, needle body 8 and needle hole 80; wherein, the needle body 8 is a needle tip structure, which can be used to pierce the skin; the middle of the needle body 8 is a needle hole 80 structure, which runs through the needle body 8 and the substrate 9, and is used to achieve the circulation of liquid; and the substrate 9 is a platform for making and carrying the microneedle structure. It can be understood that the microneedle is usually not a single one, but a plurality of microneedles are formed on the substrate in an array, that is, a microneedle array.

[0035] Figure 2 The figure shows a process flow for preparing a through-hole microneedle provided in an embodiment of the present invention. Figure 3 A schematic diagram of the preparation process of a through-hole microneedle provided by the present invention. Figure 2 and Figure 3 As shown, a method for preparing a through-hole microneedle comprises the following steps:

[0036] Step 1: providing a silicon wafer 1, and forming a first silicon nitride layer 20 and a second silicon nitride layer 21 on the upper and lower surfaces of the silicon wafer respectively by using a low pressure chemical vapor deposition process;

[0037] refer to Figure 1 In a, the silicon wafer 1 used in this embodiment is a double-throw wafer with a thickness of 850 μm and a crystal orientation of (100). It can be understood that the silicon wafer 1 includes two opposite upper and lower surfaces. In this application, refer to Figure 1 a, with the upper surface of the silicon wafer 1 being the front side and the lower surface of the silicon wafer 1 being the back side.

[0038] The furnace tube method (i.e. chemical vapor deposition, CVD) is a common process for preparing silicon nitride film, and its principle is to react silicon-containing gas (such as trichlorosilane, SiHCl3, tetrachlorosilane, SiCl4) with ammonia (NH3) to generate silicon nitride film at a certain temperature and pressure. In the present embodiment, this step is carried out using a low-stress silicon nitride process, and the formed silicon nitride film is a low-stress silicon-rich silicon nitride film. The film layer can provide better stress distribution, which is conducive to maintaining higher uniformity and improving the microneedle morphology in the subsequent etching process. In other embodiments, other processes can also be used to prepare the silicon nitride layer.

[0039] It is understood that the preparation of the thin film in the furnace tube will form a silicon nitride layer of a certain thickness on both the upper and lower surfaces of the silicon wafer 1. In this embodiment, the thickness of the first silicon nitride layer 20 on the front side and the second silicon nitride layer 21 on the back side are both 0.2 μm. In other embodiments, the thickness of the first silicon nitride layer 20 and the second silicon nitride layer 21 can be determined by the user according to the design requirements.

[0040] Step 2: Using the PECVD process, a first silicon oxide layer 30 and a second silicon oxide layer 31 of a certain thickness are continuously deposited on the upper and lower surfaces of the silicon wafer 1 in sequence;

[0041] like Figure 1 As shown in a, in this embodiment, PECVD (plasma enhanced chemical vapor deposition) is used to sequentially form a first silicon oxide layer 30 on the surface of the first silicon nitride layer 20 and a second silicon oxide layer 31 on the surface of the second silicon nitride layer 21.

[0042] In this embodiment, the thickness of the first silicon oxide layer 30 is 0.3 μm, and the thickness of the second silicon oxide layer 31 is 0.15 μm. The oxide layer formed in this step will serve as a barrier layer in the subsequent deep silicon etching process, so the thickness of the oxide layer on different surfaces is determined according to the etching depth during the subsequent deep silicon etching. The deep silicon etching depth of the front side is larger, and the oxide layer formed on its surface should also be increased accordingly. In other embodiments, it can be determined by the structural design.

[0043] Step 3: using photolithography and etching processes to form a patterned first etching mask on the front side of the silicon wafer 1;

[0044] A photoresist is coated on the front side of the silicon wafer 1 and patterned to obtain a first photoresist mask 4 . The first photoresist mask 4 is used to pattern the first silicon nitride layer 20 and the first silicon oxide layer 30 .

[0045] Specifically, refer to Figure 1As shown in b, first, photoresist is coated on the front side of the silicon wafer 1 (i.e., the surface of the first silicon oxide layer 30) to form a photoresist layer; then, the photoresist layer is patterned using a photolithography process (including exposure, development, and other steps) to form a first photoresist mask 4 for forming a microneedle structure; using the first photoresist mask 4, the pattern of the first photoresist mask 4 is transferred to the first silicon oxide layer 30 and the first silicon nitride layer 20 in sequence through an etching process to obtain a first etching mask (the first etching mask here includes the photoresist mask 4 and the silicon oxide mask and silicon nitride mask thereunder).

[0046] In this embodiment, the first silicon oxide layer 30 and the first silicon nitride layer 20 are patterned by dry etching. In other embodiments, the etching process of the silicon oxide layer may also be wet etching.

[0047] Step 4: Perform the first deep silicon etching on the front side of the silicon wafer to form a semi-penetrating deep hole;

[0048] refer to Figure 1 As shown in b, the first etching mask formed is used as an etching barrier layer to perform the first deep silicon etching on the front side of the silicon wafer 1. As described above, in this embodiment, the first etching mask used is a three-layer structure. In other embodiments, the first photoresist mask 4 on the surface may be removed before performing the deep silicon etching.

[0049] In the prior art, some technical solutions only use a photoresist mask for deep silicon etching (i.e., no other protective layers are formed in advance). In this case, on the one hand, since the etching depth of deep silicon etching is usually deep, a large amount of photoresist will be consumed during the etching process, and the thickness of the coated photoresist layer is required to increase, which can easily lead to uneven coating and some abnormalities in the etched deep holes; on the other hand, since no other protective layers are formed in advance, the surface of the silicon wafer (especially the back side) is easily scratched, and abnormalities will occur when the silicon material is subsequently corroded to form a needle structure, affecting the final morphology of the microneedle.

[0050] In the prior art, there are also cases where only one of the silicon oxide or silicon nitride layers is used as a preformed protective layer. Considering that the silicon oxide layer is a relatively soft protective layer, while the silicon nitride layer is a relatively hard protective layer, the use of only one protective layer may be prone to scratches or high stress. Therefore, in this embodiment, a silicon oxide layer + a silicon nitride layer are used as protective layers. Through the combination of the two, a better protective effect can be achieved, stress can be improved, and uniformity during etching can be improved. In addition, during deep silicon etching, the silicon oxide layer + the silicon nitride layer are used as a hard mask to ensure precise control during etching, especially when the etching depth is large, to avoid excessive etching or shape distortion. The silicon nitride mask layer can help the etching maintain a very vertical side wall and speed up the internal etching reaction, making the needle thinner. In addition, in the process, we first deposit the oxide layer and then the silicon nitride layer. In the subsequent process, we can use the characteristics of the thermal oxidation process to form a silicon oxide layer only inside the groove, thereby reducing the etching of the oxide layer once in the subsequent process. This not only simplifies the process, but also ensures that the internal protective layer is as complete as possible.

[0051] In this embodiment, the deep silicon etching process here adopts a dry etching process, including general dry etching and deep reactive ion etching (DRIE); the etching depth is 600 μm. It can be understood that the etching depth can be flexibly determined according to the structural design of the microneedle.

[0052] Step 5: using photolithography and etching processes to form a patterned second etching mask on the back side of the silicon wafer 1;

[0053] This step 5 is similar to step 3, that is, photoresist is coated on the back side of the silicon wafer 1 and patterned to obtain a second photoresist mask 5, and the second silicon nitride layer 21 and the second silicon oxide layer 31 are patterned using the second photoresist mask 5. It can be understood that before performing this step 5, if the photoresist on the front side has not been consumed, the residual photoresist can be removed first.

[0054] Specifically, refer to Figure 1 As shown in c, first, photoresist is coated on the back side of the silicon wafer 1 (i.e., the surface of the second silicon oxide layer 31) to form a photoresist layer; then, the photoresist layer is patterned using a photolithography process (including exposure, development and other steps) to form a second photoresist mask 5; using the second photoresist mask 5, the pattern of the second photoresist mask 5 is transferred to the second silicon oxide layer 31 and the second silicon nitride layer 21 in sequence through an etching process to obtain a second etching mask (the second etching mask here includes the second photoresist mask 5 and the silicon oxide mask and silicon nitride mask thereunder).

[0055] In this embodiment, the second silicon oxide layer 31 and the second silicon nitride layer 21 are patterned by dry etching. In other embodiments, the etching process of the silicon oxide layer may also be wet etching.

[0056] Step 6: Perform a second deep silicon etching on the back of the silicon wafer to form a penetrating deep hole to obtain a pinhole 80 structure;

[0057] This step is similar to step 4. Figure 1 As shown in c, the formed second etching mask is used as an etching barrier layer to perform a second deep silicon etching. As described above, in this embodiment, the second etching mask used is a three-layer structure. In other embodiments, the second photoresist mask 5 on the surface may be removed first before performing deep silicon etching.

[0058] In this embodiment, the deep silicon etching process here adopts a dry etching process, including general dry etching and deep reactive ion etching (DRIE); the etching depth is 250μm. It can be understood that the etching in this step is based on etching through the silicon wafer 1, that is, a certain reserve amount can be retained. For example, the etching setting is set to 350μm here to ensure that a deep hole is obtained as the pinhole 80 structure of the microneedle.

[0059] It can be understood that when performing deep silicon etching, a layer of electrostatic film (not shown in the figure) must be attached to the front side of the silicon wafer 1 to avoid abnormalities during deep silicon etching; here, the "a layer of electrostatic film attached to the front side" refers to the surface of the first silicon oxide layer 30. In the actual process, the electrostatic film is placed downward on the etching machine to fix the silicon wafer 1.

[0060] Step 7: removing the first silicon oxide layer 30 and the second silicon oxide layer 31 on the surface of the silicon wafer 1;

[0061] It is understood that before performing step 7, if the photoresist on the back side has not been consumed, the residual photoresist is removed first. In this embodiment, BOE (buffered silicon oxide etching solution) is used to remove the first silicon oxide layer 30 and the second silicon oxide layer 31 on the front and back surfaces. Figure 1 As shown in d.

[0062] Step 8: forming a third silicon oxide layer 6 on the inner wall of the deep hole of the silicon wafer 1 by a thermal oxidation process;

[0063] refer to Figure 1As shown in e, first, the silicon wafer 1 is treated by a thermal oxidation process so that a third silicon oxide layer 6 of a certain thickness is formed on the inner surface of the deep hole. It can be understood that the principle of forming silicon oxide by thermal oxidation is: through the reaction of silicon and oxygen, the silicon material is sacrificed to form a silicon oxide layer. In this step, since silicon nitride layers have been formed on the upper and lower surfaces of the silicon wafer 1, during the thermal oxidation process, it can isolate the contact between oxygen and silicon, so silicon oxide will not be formed on the surface of the first silicon nitride layer 20 and the second silicon nitride layer 21, but silicon oxide is only formed on the inner wall of the deep hole. In this embodiment, the specific thermal oxidation process is as follows: the silicon wafer 1 is thermally oxidized in a high-temperature furnace, the oxidation temperature is 1150°C, and the thickness of the third silicon oxide layer 6 obtained by thermal oxidation is 0.5μm. Here, the thermal oxidation temperature of 1150°C is selected after comprehensive consideration of the density, uniformity and encapsulation of the corners of the oxide layer growth. In other embodiments, it can also be adjusted accordingly according to the growth state of the oxide layer.

[0064] Step 9: using a low pressure chemical vapor deposition process to form silicon nitride layers on the upper and lower surfaces of the silicon wafer 1 and the inner wall of the deep hole;

[0065] refer to Figure 1 e in this step is similar to step 1. In this embodiment, a low stress silicon nitride layer is deposited through a furnace tube, and the formed silicon nitride film is a low stress silicon-rich silicon nitride film, which can play a good protective role and improve the subsequent microneedle morphology. In other embodiments, other processes can also be used to prepare the silicon nitride layer.

[0066] In this embodiment, the thickness of the third silicon nitride layer 70 on the front and the fourth silicon nitride layer 71 on the back are both 0.2 μm. A silicon nitride layer is also formed on the inner wall of the deep hole (i.e., the third silicon oxide layer 6), but because it is located in the deep hole, the thickness formed may be reduced. According to experiments and production experience, its thickness is about 80%-90% of the surface thickness. In other embodiments, the thickness of the third silicon nitride layer 70 and the fourth silicon nitride layer 71 can be confirmed according to design requirements.

[0067] In this embodiment, a 0.2 μm silicon nitride layer is grown on the upper and lower surfaces of the silicon wafer 1 to ensure the stress of the silicon wafer. It can be understood that a silicon nitride layer is also formed on the inner wall of the groove, that is, a third silicon oxide layer 6 and a silicon nitride layer are formed on the inner wall of the groove.

[0068] Here, we use silicon oxide layer + silicon nitride layer as a protective layer on the inner wall of the deep hole. This is to ensure better stress distribution and avoid deformation of the needle body during the subsequent wet anisotropic etching process, and to provide sufficient blocking effect to protect the needle body from being damaged during a long corrosion process.

[0069] Step 10: removing the first silicon nitride layer 20 and the third silicon nitride layer 70 on the front side of the silicon wafer 1 by dry etching;

[0070] refer to Figure 1 In f, the silicon nitride layer on the surface is removed by dry etching process, and the protective layer on the inner wall of the deep hole and the back is retained to etch silicon to obtain the needle structure 8.

[0071] Step 11: using TMAH to etch the silicon wafer to form a needle structure 8;

[0072] In this embodiment, a low concentration of 2.38% TMAH (tetramethylammonium hydroxide) is used for wet etching. Since TMAH is anisotropic in etching silicon materials, a silicon wafer with a crystal orientation of 100 is etched along the crystal orientation (54°) in TMAH to obtain a microneedle structure that meets its morphological characteristics. The results are shown in Table 1. Figure 1 As shown in g.

[0073] In the embodiment, in order to improve the TMAH corrosion uniformity and improve the morphology of the microneedle, a small circulation supply method is adopted, that is, during the corrosion process, a small flow rate of the drug solution is provided to achieve better corrosion uniformity.

[0074] In other embodiments, other anisotropic wet etching methods may also be used, such as TMAH with different concentrations, such as TMAH with a concentration of 25%; in other embodiments, KOH solution may also be used for etching.

[0075] Step 11: Remove the remaining protective layer using wet etching.

[0076] After the microneedle structure is obtained, some protective layers will still remain in the silicon wafer 1, such as the silicon nitride layer on the back or the silicon oxide layer and / or silicon nitride layer inside the deep hole, which can be removed by wet etching process. Figure 1 For example, in this embodiment, a 49% HF solution is used to remove the remaining protective layer.

[0077] In the present application, a silicon oxide layer + a silicon nitride layer are used as a protective layer, wherein the silicon oxide layer is relatively soft, while the silicon nitride layer is relatively hard. The combination of the two can not only play a good protective role, but also improve stress and improve the uniformity of the etching process; in the deep silicon etching process, the silicon oxide layer + the silicon nitride layer are used as a hard mask to ensure precise control of the etching process, especially when the etching depth is large, to avoid excessive etching or shape distortion. The silicon nitride mask layer can help the etching maintain a very vertical side wall, and can accelerate the internal etching reaction to make the needle thinner; in the anisotropic wet etching process, the silicon nitride layer + silicon oxide layer on the inner wall of the deep hole also plays a similar role, which can ensure a good stress distribution and avoid deformation of the needle body, and can provide sufficient blocking effect to protect the needle body from being damaged during a long corrosion process; in addition, in terms of the process, we first deposited the oxide layer and then the silicon nitride layer, so in the subsequent process, we can use the characteristics of the thermal oxidation process to form only the silicon oxide layer inside the deep hole, and then in the subsequent process, the silicon oxide layer can be formed. The etching of the oxide layer is continuously reduced once, which not only simplifies the process, but also ensures that the internal protective layer is as complete as possible; in the present application, a through hole is first obtained by two deep silicon etchings, and finally TMAH etching is performed to obtain the needle body. This is also because the overall size of the silicon wafer will be greatly reduced after TMAH etching. In terms of its thickness, the base part is only 200-250μm, and the radial size will also be reduced. Considering that most machines, such as dry etching machines, photolithography machines, etc., usually have higher size requirements for the processed silicon wafers, the general wafer thickness requirement is about 400-1000μm. Therefore, if there are still processes such as photolithography and etching after TMAH etching, the size of the silicon wafer may not be very suitable for the machine at this time, which will cause difficulties in the processes such as wafer feeding and alignment, and may also cause damage to the needle body structure.

[0078] The present application also provides a through-hole microneedle, which is prepared by the above method. The structure of the through-hole microneedle mainly includes three parts: a substrate, a needle body and a needle hole.

[0079] In order to facilitate the description, some common English nouns or letters used in the present invention are only used for exemplary reference rather than restrictive interpretation or specific usage, and the protection scope of the present invention should not be limited by their possible Chinese translations or specific letters.

[0080] It should also be noted that, in this document, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

Claims

1. A method for preparing a through-hole microneedle, characterized in that: The steps include: S1. providing a silicon wafer, and sequentially forming a silicon nitride layer and a silicon oxide layer on the front and back sides of the silicon wafer; S2, using photolithography and etching processes to form a first etching mask on the front side of the silicon wafer, and performing a first deep silicon etching to form a semi-penetrating deep hole; S3, using photolithography and etching processes to form a second etching mask on the back side of the silicon wafer, and performing a second deep silicon etching to form a penetrating deep hole to obtain a pinhole structure; S4, removing the silicon oxide layer on the front and back sides of the silicon wafer; S5, forming a silicon oxide layer on the inner wall of the deep hole by using a thermal oxidation process; S6, forming a silicon nitride layer on the front and back sides of the silicon wafer and the inner wall of the deep hole; S7, removing all silicon nitride layers on the front side of the silicon wafer; S8, etching the silicon wafer using an anisotropic wet method to form a needle structure; S9, removing the remaining silicon nitride layer and the silicon oxide layer.

2. The method for preparing a through-hole microneedle according to claim 1, characterized in that: The silicon wafer is a single crystal silicon wafer with a (100) crystal orientation.

3. The method for preparing a through-hole microneedle according to claim 1, characterized in that: In step S1, a first silicon nitride layer and a second silicon nitride layer are formed on the front and back sides of the silicon wafer respectively by a chemical vapor deposition process; A first silicon oxide layer is formed on the surface of the first silicon nitride layer, and a second silicon oxide layer is formed on the surface of the second silicon nitride layer in sequence by a plasma enhanced chemical vapor deposition process.

4. The method for preparing a through-hole microneedle according to claim 1, characterized in that: The photolithography and etching process includes: Applying photoresist on the surface of the silicon oxide layer and patterning it to form a photoresist mask; The silicon oxide layer and the silicon nitride layer are patterned by an etching process using the photoresist mask to form the first etching mask or the second etching mask.

5. The method for preparing a through-hole microneedle according to claim 1, characterized in that: In step S4, the silicon oxide layer is removed using a buffered silicon oxide etching solution.

6. The method for preparing a through-hole microneedle according to claim 1, characterized in that: In step S1 and step S6, the silicon nitride layer is formed by a low stress silicon nitride process, and the silicon nitride layer is low stress silicon-rich silicon nitride.

7. The method for preparing a through-hole microneedle according to claim 4, characterized in that: After step S2 and step S3, a stripping process is included to remove the residual photoresist.

8. The method for preparing a through-hole microneedle according to claim 1, characterized in that: In step S7, the silicon nitride layer is removed by a dry etching process.

9. The method for preparing a through-hole microneedle according to claim 1, characterized in that: The anisotropic wet etching includes using a tetramethylammonium hydroxide solution or a potassium hydroxide solution for wet etching; the concentration of the tetramethylammonium hydroxide solution is 2.38%.

10. A through-hole microneedle, characterized in that: The through-hole microneedle is prepared by the method for preparing a through-hole microneedle according to any one of claims 1 to 9, wherein the through-hole microneedle comprises a substrate, a needle body and a needle hole.

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