A T-type grid template and its preparation method and application

Abstract

The present invention provides a T-type gate template, a preparation method, and an application thereof, belonging to the field of semiconductor device technology. The T-type gate template is made of a transparent material, including a substrate, a first raised structure located on the substrate, and a second raised structure located on the first raised structure; the side of the first raised structure is covered with a light-shielding layer; and the side of the second raised structure is covered with a light-shielding layer. When the T-type gate template is used to prepare a T-type gate in ultraviolet-nanoimprint lithography technology, an undercut structure can be formed without spin-coating multiple layers of photoresist, making the photoresist easy to peel off and without affecting the mechanical stability of the T-type gate. The template can be used for mass replication of T-gate structure devices with extremely high production efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and in particular relates to a T-shaped gate template and a preparation method and application thereof. Background Art

[0002] To achieve higher application frequencies in semiconductor devices, one of the most direct methods is to reduce the gate length of the high electron mobility transistor (HEMT), reducing the carrier transit time under the gate, thereby improving the device's frequency characteristics. However, the device's high-frequency gain is affected not only by the gate length but also by the gate resistance (Rg) and gate capacitance (Cgs). To ensure that the gate capacitance is reduced while the gate resistance is not reduced, the most commonly used process is the "T" gate technology.

[0003] Nanoimprint lithography (NIL), invented in 1995, is a novel method for fabricating nanoscale patterns. Currently, the most widely used method is ultraviolet nanoimprint lithography (UV-NIL), based on ultraviolet exposure. The advantages of nanoimprint lithography lie in its simplicity and straightforwardness, enabling small feature sizes, large-area patterning, and high throughput without requiring complex equipment systems and processes. The nanoimprint process primarily involves three elements: the fabrication of a mold or stamp, a resist material (typically a polymer), and a substrate. The stamp surface contains certain micro-nanographic structures created using electron beam lithography (EBL). These structures are then inversely replicated into the resist material atop the substrate in the next step. Key challenges in nanoimprint lithography include ensuring conformal contact between the mold and substrate, replicating the template surface pattern into the resist without distortion, ensuring the overall integrity of the replicated structure after demolding, and achieving a uniform and minimized residual resist layer thickness in the imprinted micro-nanostructures. Compared to the inefficiency of electron beam lithography, nanoimprint lithography allows for rapid mass production using the same template. However, during the development of T-gates, nanoimprint lithography struggles to achieve high-precision alignment. Furthermore, due to the inherent properties of the nanoimprint lithography demolding process, it is impossible to create an undercut profile that is easily lift-offable. These factors have limited the further development of nanoimprint lithography for the fabrication of T-gates.

[0004] like Figure 1As shown, the scheme of the T-shaped gate manufactured by ultraviolet nanoimprinting technology in prior art 1 (Zhu M, et al. Nanofabrications of T shape gates for high electron mobility transistors in microwaves and THz waves, areview [J]. Micro and Nano Engineering, 2021 (2): 100091.) is to first spin-coat a UV-curable first photoresist layer 02 on the substrate 01, and use the prepared fully transparent T-shaped template 04 for subsequent molding and UV light curing process, so that the first photoresist layer 02 can still retain the inverted T-shaped pattern on the template after demolding, thereby realizing the transfer of the T-shaped pattern to the photoresist. After the transfer is completed, a very thin layer of photoresist will remain on the substrate 01, and the residual glue needs to be removed by dry etching (such as reactive ion etching process), and then the metal layer 07 is deposited by electron beam evaporation and the photoresist is stripped to obtain the final T-shaped gate. Due to the structure of the T-shaped template, it is impossible to form an undercut structure in this process, and therefore it is not conducive to subsequent stripping.

[0005] As an improvement to the prior art 1, the prior art 2 (Iwamoto T, et al. Passivation-layer thickness and field-plate optimization to obtain high breakdown voltage in AlGaN / GaN HEMTs with short gate-to-drain distance [J]. Microelectronics Reliability, 2021, 121: 114153) discloses the following Figure 2 The process shown forms an undercut structure. This method involves spin-coating a first photoresist layer 02 and a second photoresist layer 03 onto a substrate 01. During molding, the T-shaped structure on a fully transparent T-shaped template 04 is pressed into the second photoresist layer 03, thereby opening the process window for the first photoresist layer 02. After demolding, the first photoresist layer 02 corresponding to the protrusions of the T-shaped structure on the template is removed using a developer. The second photoresist layer 03 is not affected during the development process, so that when a metal layer 07 is subsequently deposited via electron beam evaporation to form a T-shaped grid, a clear undercut structure can be formed at the foot of the T-shaped grid. Finally, the first photoresist layer 02 and the second photoresist layer 03 are peeled off to obtain the T-shaped grid. Although this method forms an undercut structure at the foot of the T-shaped grid, making the foot easy to peel off, the metal at the grid cap remains difficult to peel off. Furthermore, this method requires the use of a double layer of photoresist, making the process more complex. Summary of the Invention

[0006] To address the problems existing in the prior art, the first objective of the present invention is to provide a T-shaped grid template. This template is fully transparent and has a raised structure, and the sides of the raised structure are covered with a light-shielding layer. This ensures that after the template is pressed into the photoresist and during the exposure and curing process, the upper layer of the photoresist receives a high intensity of ultraviolet radiation, while the adjacent side portions of the raised structure are shielded from ultraviolet radiation. Therefore, as the thickness of the photoresist increases, the degree of curing of the photoresist in the deeper layers that contact the side portions of the raised structure becomes increasingly lower. Subsequently, the contour formed by the stamping is modified again with a specific developer, forming an undercut structure in the stamped pattern that is easy to peel off.

[0007] Specifically, the present invention adopts the following technical solutions to achieve the above objectives:

[0008] A T-shaped grid template is made of a transparent material; the T-shaped grid template includes a substrate, a first raised structure located on the substrate, and a second raised structure located on the first raised structure; the side of the first raised structure is covered with a light-shielding layer; the side of the second raised structure is covered with a light-shielding layer.

[0009] In a preferred embodiment, a side surface of the first protrusion structure forms a right angle or an obtuse angle with the surface of the substrate.

[0010] In a preferred embodiment, the side surface of the first protruding structure is perpendicular to the bottom surface of the substrate, and the side surface of the second protruding structure is perpendicular to the bottom surface of the substrate.

[0011] In a preferred embodiment, the first protruding structure, the second protruding structure, and the substrate are all symmetrical about the central axis of the substrate.

[0012] In a preferred embodiment, the light shielding layer is made of a light-impermeable metal (such as metal Cr or Ni), an inorganic material, or an organic polymer material.

[0013] A second object of the present invention is to provide a method for preparing the T-shaped grid template described in any one of the above items, the method comprising the following steps:

[0014] S1. Prepare a fully transparent T-shaped template, the fully transparent T-shaped template comprising a substrate, a first protruding structure located on the substrate, and a second protruding structure located on the first protruding structure; the first protruding structure has a plane parallel to the bottom surface of the substrate, and the second protruding structure has a plane parallel to the bottom surface of the substrate;

[0015] S2, depositing a light-shielding layer on the fully transparent T-shaped template;

[0016] S3. Etch away the light-shielding layer on the plane of the first protruding structure, the light-shielding layer on the plane of the second protruding structure, and the light-shielding layer on the surface of the substrate, and retain the light-shielding layer on the side of the first protruding structure and the light-shielding layer on the side of the second protruding structure to obtain the T-type gate template.

[0017] A third object of the present invention is to provide a method for preparing a T-gate using the T-gate template described in any one of the above items, the method comprising the following steps:

[0018] (1) spin coating a photoresist layer on a substrate, and aligning the T-shaped gate template with the photoresist layer;

[0019] (2) pressing the T-shaped gate template into the photoresist layer for pattern transfer, maintaining the T-shaped gate template under a constant imprint pressure, and irradiating the photoresist layer with ultraviolet light;

[0020] (3) After the ultraviolet irradiation is completed, the mold is demolded, and the demolded device is pre-baked to solidify the photoresist;

[0021] (4) After the curing is completed, the device is developed and modified to dissolve the insufficiently cured photoresist, and then post-baked; the residual photoresist on the substrate is then removed by dry etching to form an undercut structure;

[0022] After the curing is completed, the residual photoresist on the substrate is removed by dry etching; the device is then developed and modified to remove the insufficiently cured photoresist, and then post-baked;

[0023] (5) depositing a metal layer on the device;

[0024] (6) Peeling off the photoresist layer to obtain a T-type gate.

[0025] The T-shaped grating template provided by the present invention is suitable for preparing T-shaped gratings using ultraviolet-nanoimprint lithography technology. When the T-shaped grating template is aligned with the photoresist layer, ultraviolet light is incident from the bottom surface of the T-shaped grating template. On the one hand, the intensity of ultraviolet light decreases as the thickness of the photoresist layer increases, that is, the photoresist closer to the substrate receives less light intensity. Therefore, the photoresist closer to the template has a higher degree of curing, and the photoresist closer to the substrate has a lower degree of curing. In the subsequent development process, the photoresist with a lower degree of curing is more easily dissolved, and the development is isotropic, thus forming an undercut structure that is easy to peel. On the other hand, after the ultraviolet light enters the fully transparent template, it will also be scattered, reflected, and refracted at the interface contact. The light-shielding layer covering the side of the template protrusion structure can prevent the photoresist in contact with the side of the template protrusion structure from receiving ultraviolet light radiation, so that the solubility of this part of the photoresist will not increase due to ultraviolet light radiation in the subsequent development process, promoting the formation of undercut structures on the side of the pattern.

[0026] In an optional embodiment, the dry etching is an anisotropic reactive ion etching method.

[0027] In an optional embodiment, the photoresist layer is stripped in step (6) by immersion stripping in an organic solution, preferably acetone or N-methylpyrrolidone (NMP).

[0028] In a preferred embodiment, the pre-baking conditions in step (3) are: baking at 25°C to 500°C for 5s to 5min.

[0029] In a preferred embodiment, the post-baking conditions in step (3) are: baking at 25°C to 500°C for 5s to 5min.

[0030] In a preferred embodiment, when developing and modifying the device in step (4), the device is placed in a developer for 10 seconds to 5 minutes.

[0031] The present invention has the following beneficial effects: A light-shielding layer is applied to the sides of the raised structure of the fully transparent T-shaped template, enabling the formation of an easily peelable undercut structure when the template is used to prepare a T-shaped gate in ultraviolet-nanoimprint lithography, while simultaneously not adversely affecting the mechanical stability of the T-shaped gate. The present invention can address the difficulties and low yield rates of T-shaped gates produced using nanoimprint lithography in the industry. The provided T-shaped gate template is suitable for high-efficiency, large-scale replication of T-shaped gates, particularly when used to produce T-shaped gates with a gate foot width of no more than 100 nm, significantly improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the process of manufacturing a T-gate in prior art 1;

[0033] Figure 2 Schematic diagram of the process of manufacturing a T-type gate in prior art 2;

[0034] Figure 3 A schematic structural diagram of a T-type gate template suitable for UV-nanoimprint lithography technology prepared in Example 1 of the present invention;

[0035] Figure 4 This is a schematic diagram of the process of preparing a T-type gate template suitable for UV-nanoimprint lithography technology according to Example 1 of the present invention;

[0036] Figure 5 A schematic structural diagram of a T-type gate template suitable for UV-nanoimprint lithography technology prepared in Example 2 of the present invention;

[0037] Figure 6 A schematic structural diagram of a T-type gate template suitable for UV-nanoimprint lithography technology prepared in Example 3 of the present invention;

[0038] Figure 7 Schematic diagram of the process of preparing a T-gate by ultraviolet-nanoimprint lithography technology according to Example 4 of the present invention.

[0039] In the figure: 01, substrate; 02, first photoresist layer; 021, insufficiently cured photoresist; 022, fully cured photoresist; 03, second photoresist layer; 04, fully transparent T-shaped template; 041, base plate; 0411, bottom surface of base plate; 042, first protruding structure; 043, second protruding structure; 05, light-shielding layer; 06, T-shaped gate template; 07, metal layer; 08, T-shaped gate. DETAILED DESCRIPTION

[0040] The following is a clear and complete description of the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, any equivalent transformation or substitution made by ordinary technicians in this field based on the following implementation methods without making any creative work shall fall within the scope of protection of the present invention.

[0041] The methods not described in detail in the following examples are conventional techniques known to those skilled in the art.

[0042] Example 1

[0043] Reference Figure 4 This embodiment provides a method for preparing a T-type gate template suitable for ultraviolet-nanoimprint lithography technology. The method comprises the following steps:

[0044] S1. Prepare a fully transparent T-shaped template 04 (for example, a fully transparent T-shaped template made of quartz glass). The fully transparent T-shaped template 04 includes a substrate 041, a first protruding structure 042 located on the substrate 041, and a second protruding structure 043 located on the first protruding structure 042. The substrate 041 includes a substrate bottom surface 0411 and a substrate surface parallel to the substrate bottom surface. The first protruding structure 042 has a side surface and a plane parallel to the substrate bottom surface 0411; the second protruding structure 043 has a side surface and a plane parallel to the substrate bottom surface 0411. The first protruding structure 042, the second protruding structure 043, and the substrate 041 are all symmetrically arranged about the central axis of the substrate 041; both side surfaces of the first protruding structure 042 are perpendicular to the substrate bottom surface 0411; and both side surfaces of the second protruding structure 043 are perpendicular to the substrate bottom surface 0411.

[0045] S2 . Depositing a light shielding layer 05 (eg, depositing chromium metal) on the fully transparent T-shaped template 04 .

[0046] S3, etching away the light shielding layer 05 on the plane of the first protruding structure 042, the plane of the second protruding structure 043, and the surface of the substrate by an anisotropic etching process (such as reactive ion etching process, RIE), and retaining the light shielding layer 05 on the side surface of the first protruding structure 042 and the side surface of the second protruding structure 043, to obtain the following Figure 3 The T-shaped grid template 06 is shown.

[0047] Example 2

[0048] This embodiment provides a method for preparing a T-type gate template suitable for ultraviolet-nanoimprint lithography technology, comprising the following steps:

[0049] S1. Prepare a fully transparent T-shaped template 04 (e.g., a fully transparent T-shaped template made of indium tin oxide). The fully transparent T-shaped template 04 includes a substrate 041, a first protruding structure 042 located on the substrate 041, and a second protruding structure 043 located on the first protruding structure 042. The substrate 041 includes a substrate bottom surface 0411 and a substrate surface parallel to the substrate bottom surface. The first protruding structure 042 has a side surface and a plane parallel to the substrate bottom surface 0411; the second protruding structure 043 has a side surface and a plane parallel to the substrate bottom surface 0411. The first protruding structure 042, the second protruding structure 043, and the substrate 041 are all symmetrically arranged about the central axis of the substrate 041. Both side surfaces of the first protruding structure 042 form the same obtuse angle with the substrate surface, so that the cross-section of the first protruding structure 042 is an isosceles trapezoidal structure, and the longer base of the isosceles trapezoid is located on the surface of the substrate 041; both side surfaces of the second protruding structure 043 are perpendicular to the bottom surface 0411 of the substrate.

[0050] S2. Depositing a light shielding layer 05 (for example, depositing nickel metal) on the fully transparent T-shaped template.

[0051] S3, using an anisotropic etching process (such as a reactive ion etching process) to remove the light shielding layer 05 on the plane of the first protruding structure 042, the plane of the second protruding structure 043 and the surface of the substrate, and retaining the light shielding layer 05 on the side of the first protruding structure 042 and the side of the second protruding structure 043, to obtain Figure 5 The T-shaped grid template 06 is shown.

[0052] Example 3

[0053] This embodiment provides a method for preparing a T-type gate template suitable for ultraviolet-nanoimprint lithography technology. The method is basically the same as that of Example 1, except that the first protruding structure 042 and the substrate 041 are symmetrical with respect to the central axis of the substrate 041, while the second protruding structure 043 is asymmetrical with respect to the central axis of the substrate 041. The structure of the T-type gate prepared in this embodiment is as follows: Figure 6 shown.

[0054] Example 4

[0055] Reference Figure 7 This embodiment provides a method for preparing a T-type gate using the T-type gate template prepared in Example 1, comprising the following steps:

[0056] P1. Spin-coat a first photoresist layer 02 on the substrate 01 ; align the T-shaped gate template 06 prepared in Example 1 with the first photoresist layer 02 .

[0057] P2. Press the T-shaped grid template 06 into the first photoresist layer 02 for pattern transfer. After imprinting, keep the imprinting force unchanged and irradiate the first photoresist layer 02 with ultraviolet light. The first photoresist layer 02 is continuously solidified under ultraviolet light irradiation. Since the sides of the first protruding structure 042 and the second protruding structure 043 of the T-shaped grid template 06 are covered with a light-shielding layer 05 and are not transparent, the first photoresist layer 02 in contact with the side cannot receive ultraviolet light from the side and can only receive vertically incident ultraviolet light. As the thickness of the first photoresist layer 02 increases, the intensity of ultraviolet light it receives decreases, and its degree of solidification also decreases; as the degree of solidification decreases, its solubility in the developer becomes greater.

[0058] P3. After the UV irradiation is completed, demould the device and place it in an oven for baking before development and modification, and cure it at 150°C for 3 minutes.

[0059] P4. After curing, place the device in the developer for 3 minutes for modification, wash away the uncured photoresist 021 that is in contact with the side of the raised structure on the T-type gate template, and leave the photoresist 022 that is fully cured by ultraviolet light. After modification, bake and cure at 150°C for 3 minutes.

[0060] P5. Remove the residual photoresist on the substrate by dry etching (such as reactive ion etching process) to form an undercut structure.

[0061] P6. Deposit a metal layer 07 on the device.

[0062] P7. Strip the first photoresist layer 02 by electron beam evaporation to obtain a T-type gate 08.

[0063] Example 5

[0064] In this embodiment, the method for preparing a T-type gate using the T-type template prepared in Example 2 is basically the same as that in Example 4, except that: in step P3, the pre-bake is cured at 25°C for 5 minutes, in step P4, the device is placed in the developer and maintained for 10 seconds, and the post-bake is cured at 25°C for 5 minutes, and the order of steps P4 and P5 is reversed.

[0065] Example 6

[0066] In this embodiment, the method for preparing a T-type gate using the T-type template prepared in Example 3 is basically the same as that in Example 4, except that: in step P3, the pre-bake is cured at 500°C for 5 seconds, in step P4, the device is placed in the developer for 5 minutes, and the post-bake is cured at 500°C for 5 seconds.

[0067] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It will be apparent to anyone skilled in the art that various modifications and variations of the present invention are possible. Any simple equivalent variations and modifications made in accordance with the scope of protection of the present invention and the contents of the specification are intended to be included within the scope of protection of the present invention.

Claims

1. A T-type grid template, characterized in that: The T-shaped grid template is made of a transparent material; the T-shaped grid template includes a substrate, a first protruding structure located on the substrate, and a second protruding structure located on the first protruding structure; The side of the first protruding structure is covered with a light shielding layer; the side of the second protruding structure is covered with a light shielding layer; the method for preparing the T-shaped grid template comprises the following steps: S1, preparing a fully transparent T-shaped template, the fully transparent T-shaped template comprising a substrate, a first protruding structure located on the substrate, and a second protruding structure located on the first protruding structure; the first protruding structure has a plane parallel to the bottom surface of the substrate, and the second protruding structure has a plane parallel to the bottom surface of the substrate; S2, depositing a light-shielding layer on the fully transparent T-shaped template; S3. Etch away the light-shielding layer on the plane of the first protruding structure, the light-shielding layer on the plane of the second protruding structure, and the light-shielding layer on the surface of the substrate, and retain the light-shielding layer on the side of the first protruding structure and the light-shielding layer on the side of the second protruding structure to obtain the T-type gate template.

2. The T-shaped grid template according to claim 1, characterized in that: The side surface of the first protruding structure is perpendicular to the bottom surface of the substrate, and the side surface of the second protruding structure is perpendicular to the bottom surface of the substrate.

3. The T-shaped grid template according to claim 1, wherein: The first protruding structure, the second protruding structure and the substrate are all symmetrical about the central axis of the substrate.

4. The T-shaped grid template according to claim 1, characterized in that: The material of the light-shielding layer is opaque metal.

5. A method for preparing a T-gate using the T-gate template according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Spin-coating a photoresist layer on a substrate and aligning the T-shaped gate template with the photoresist layer; (2) pressing the T-shaped gate template into the photoresist layer for pattern transfer, maintaining the T-shaped gate template under a constant imprint pressure, and irradiating the photoresist layer with ultraviolet light; (3) After the ultraviolet irradiation is completed, the mold is demolded, and the demolded device is pre-baked to solidify the photoresist; (4) After curing, the device is developed and modified to dissolve the insufficiently cured photoresist, and then post-baked; Then, removing the residual photoresist on the substrate by dry etching to form an undercut structure; or after curing, removing the residual photoresist on the substrate by dry etching; Then, the device is developed and modified to remove the insufficiently cured photoresist, and then post-baked; (5) depositing a metal layer on the device; (6) Peeling off the photoresist layer to obtain a T-type gate.

6. The method for preparing a T-gate according to claim 5, wherein: The pre-baking conditions in step (3) are: baking at 25°C~500°C for 5s~5min.

7. The method for preparing a T-gate according to claim 5, wherein: The post-baking conditions in step (3) are: baking at 25°C~500°C for 5s~5min.

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