A mask template applicable to UV-NIL technology, and its preparation method and application

Abstract

The present invention relates to the field of nanoimprinting, and particularly to a mask template applicable to ultraviolet-nanoimprinting technology (UV-NIL), a preparation method thereof, and an application thereof. The mask template includes a transparent substrate, protrusions located on the transparent substrate, and grooves located between the protrusions. The grooves correspond to a preset pattern, and a light-shielding layer covers the top and the periphery of the protrusions. The mask plate has a simple structure and can be prepared by depositing the light-shielding layer twice. Since the side surfaces of the protrusion parts of the mask template can avoid exposure, during the imprinting process, the photoresist layer on the adjacent side surfaces gradually decreases in curing degree as the thickness deepens. By controlling the development time, an undercut structure that is easy to peel off (lift-off) can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of nanoimprinting, and specifically to a mask suitable for UV-NIL technology, a preparation method thereof, and an application thereof. Background Art

[0002] Nanoimprint Lithography (NIL) is a new method for fabricating nano-scale patterns proposed by Stephen Chou in 1995. Taking the mainstream ultraviolet nanoimprinting (UV-NIL) technology as an example, it is to coat a imprinting resist on a substrate. After aligning the nanoimprint template and the substrate, the nanoimprint template is pressed into the imprinting resist and ultraviolet light is irradiated to cause the imprinting resist to undergo a polymerization reaction and harden into a shape. In the ultraviolet nanoimprinting process, since the imprinting template cannot completely penetrate the photoresist and contact the substrate during imprinting, inevitably, photoresist residues will be caused in the patterned area on the substrate, that is, there is a phenomenon of residual glue after demolding. Such residual glue needs to be removed by other processes, otherwise it will affect the subsequent processes.

[0003] In the prior art, the following several methods are generally used to solve the above-mentioned residual glue problem:

[0004] First, the resist polymer glue layer remaining on the substrate after imprinting is removed by reactive ion etching (RIE). However, RIE has varying degrees of damage to the epitaxial layer material of the III-V substrate, is not suitable for processing sensitive substrate materials, and will affect the electrical characteristics of the device; in addition, after imprinting, anisotropic etching is performed, and an undercut morphology that is easy to peel off cannot be formed in the photoresist pattern;

[0005] Second, a double-layer glue is spin-coated on the substrate. During the imprinting process, the protruding part of the mold penetrates the upper layer of glue and partially enters the lower layer of glue. Finally, the lower layer of glue is dissolved and taken away by the developer without dry etching to ensure that the substrate is minimally damaged. Although it avoids the influence of dry etching on sensitive substrate materials, it increases the process steps. And during the process of pressing into the lower layer of glue, if there is some residual glue on the surface of the lower layer of glue in the protruding part of the mold and the upper layer of glue, it will affect the subsequent development process, resulting in insufficient development and low product yield;

[0006] Thirdly, for the invention patent "A nanoimprint template, its manufacturing method and ultraviolet nanoimprint method" with the publication number CN1094074464A, by setting a light-transmitting area and a light-shielding area on a support substrate, it is ensured that the photoresist corresponding to the light-shielding area will not be cured by ultraviolet light. Finally, the uncured photoresist on the substrate is directly dissolved by a solvent to avoid the phenomenon of uneven residual glue after the substrate is demolded. However, the structure of this imprint template is relatively complex, the preparation cost is high, and it cannot form a photoresist morphology with an undercut topography, which is not easy to peel off subsequently. Summary of the Invention

[0007] Aiming at the technical problems existing in the prior art, the present invention provides a new nanoimprint mask template. By covering a light-shielding layer around the protrusion, since the side of the protrusion part can also avoid exposure, during the imprinting process, the photoresist near the adjacent side gradually decreases in curing degree as the thickness deepens. After developing the glue, an undercut structure that is easy to lift-off can be obtained.

[0008] The present invention realizes the above technical purpose through the following technical solutions: The present invention first provides a mask template applicable to the UV-NIL technology, including a transparent substrate, protrusions located on the transparent substrate, and grooves located between the protrusions. The grooves correspond to a preset pattern, and a light-shielding layer covers the top and its periphery of the protrusions.

[0009] The biggest difference between this mask template and the prior art is that light shielding is achieved by covering a light-shielding layer on the protrusion structure, and the side of the protrusion structure is also covered with a light-shielding layer. This structure is not only simple and easy to prepare, but also when manufacturing a pattern with this nanoimprint mask template, the residual glue part can be directly developed and removed without using the RIE process, which will not affect the sensitive substrate material, and the subsequent patterning process steps are simple; since the side of the protrusion part avoids exposure, during the imprinting process, the photoresist layer near the adjacent side gradually decreases in curing degree as the thickness deepens. By controlling the developing time, an undercut structure that is easy to lift-off can be obtained.

[0010] As a preferred implementation manner, the light-shielding layer is a metal light-shielding layer or an opaque inorganic material or an organic polymer material.

[0011] As a preferred implementation manner, the metal light-shielding layer is a metal chromium layer.

[0012] As a preferred implementation manner, the depth of the groove depends on the depth of the specifically designed pattern, generally in the depth range of 1 nm - 10 μm.

[0013] The second object of the present invention is to provide a preparation method for the above mask template applicable to the UV-NIL technology, including the following steps:

[0014] A photoresist layer is spin-coated on a transparent substrate, and after exposing a characteristic pattern on the photoresist layer, it is developed.

[0015] After that, a first light-shielding layer is deposited on the patterned photoresist structure. Subsequently, the photoresist and the first light-shielding layer deposited thereon are removed by lift-off, leaving the first light-shielding layer in the patterned area. Then, using the remaining first light-shielding layer as a hard mask, dry etching is carried out until the transparent substrate reaches a preset depth, and then it stops.

[0016] The second light-shielding layer is deposited again. After the deposition is completed, anisotropic etching is carried out in the vertical direction, and a nanoimprint mask template with the top and periphery of the convex part of the transparent substrate covered with the light-shielding layer is obtained.

[0017] As a preferred embodiment, the thickness of the photoresist layer is 100 nm - 10 μm.

[0018] As a preferred embodiment, the thickness of the first light-shielding layer is 1 nm - 100 nm, and / or the thickness of the second light-shielding layer is 1 nm - 100 nm.

[0019] The third object of the present invention is also to protect the application of the above-mentioned mask template applicable to the UV-NIL technology in the ultraviolet-nanoimprint lithography technology.

[0020] Specifically, the above-mentioned mask template is used to pattern-transfer the photoresist layer. After imprinting, the imprinting pressure is kept constant for a period of time, and the photoresist is irradiated with UV light to ensure that the photoresist fully fills each position of the template groove, ensuring high-fidelity pattern transfer.

[0021] After UV irradiation, demolding is carried out. The photoresist is put into an oven, and pre-baking is carried out to promote curing. Then, development and desizing are carried out, and the photoresist in the part not irradiated by UV is stripped off, leaving the UV-cured photoresist as a mask for subsequent metallization or etching processes.

[0022] As a preferred embodiment, the curing temperature is limited within the range of 20°C - 500°C, specifically depending on the curing temperature of the used photoresist, and the curing time is 1 s - 10 min, specifically depending on the properties of the photoresist.

[0023] This method is also applicable to manufacturing micro-nano structures with high aspect-ratio in a single-layer resist process.

[0024] The method provided by the present invention improves the light-transmitting and light-blocking regions on the mask, and after patterning transfer on the photoresist, the curing degree or cross-linking degree of different regions of the photoresist is different, its molecular weight and solubility in the same developer are different, which can avoid using the RIE process. The pattern on the template can be directly transferred to the photoresist through the developing process, and subsequent metallization and lift-off processes can be carried out. The patterning process steps are simple, and it will not affect the sensitive substrate material or the electrical characteristics of the device. An undercut structure can be formed during the photoresist patterning process, which is easy for subsequent metal stripping. Since dry etching is not required later, the overall thinning of the photoresist layer will not occur, and the manufacturing of micro-nano structures with an aspect ratio can be guaranteed. Brief Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the nanoimprint mask provided in Embodiment 1 of the present invention;

[0026] Figure 2 It is a schematic preparation process diagram of the nanoimprint mask provided in Embodiment 1 of the present invention;

[0027] Figure 3 It is a flow chart of the method for manufacturing micro-nano structures provided in Embodiment 2 of the present invention;

[0028] In the figure:

[0029] 01 transparent substrate, 02 photoresist layer, 03 first light-shielding layer, 04 second light-shielding layer, 05 uncured photoresist, 06 cured photoresist. Detailed Embodiments

[0030] The present invention will be further described in detail below with specific embodiments, so that those skilled in the art can understand the present invention more clearly.

[0031] In view of the problems existing in the existing technical solution that by setting light-transmitting regions and light-blocking regions on the imprint template to ensure that the photoresist corresponding to the light-blocking regions will not be cured under ultraviolet irradiation, and finally the uncured photoresist on the substrate can be directly dissolved by a solvent to avoid the phenomenon of residual glue in the patterned region after substrate demolding, such as complex imprint template structure, complex manufacturing, high cost, and inability to form a photoresist morphology with an undercut shape, which is not easy for subsequent peeling, the present invention provides a new nanoimprint mask, which includes a transparent substrate, protrusions located on the transparent substrate, and grooves located between the protrusions, wherein the grooves correspond to a preset pattern, and the top and its periphery of the protrusions are covered with a light-shielding layer, see Figure 1 .

[0032] During use, when irradiated with UV light, since the top and its periphery of the protrusion are covered with a light-shielding layer and ordinary UV light does not irradiate completely vertically, at this time, due to the presence of the light-shielding layer, not only the photoresist under the protrusion will not be cured, but also the photoresist around it will not be cured by ultraviolet light due to the presence of the light-shielding layer around the protrusion. Moreover, as the depth of the photoresist increases, the degree of curing will become lower and lower. After the uncured photoresist is dissolved, a topography with an undercut structure will be formed. After subsequent metallization is completed, when the photoresist is stripped, the photoresist can be easily stripped completely.

[0033] Among them, the light-shielding layer can be a metal light-shielding layer or an opaque inorganic material or an organic polymer material, including but not limited to a metal Cr light-shielding layer. The depth of the groove depends on the depth of the specifically designed pattern and is in the range of 1 nm - 10 μm.

[0034] The above-mentioned nanoimprint mask can be prepared by the following method:

[0035] Spin-coat a photoresist layer on a transparent substrate, expose a characteristic pattern on the photoresist layer, and then develop it;

[0036] After that, deposit a first light-shielding layer on the patterned photoresist structure, and then remove the photoresist and the first light-shielding layer deposited thereon by stripping, leaving the first light-shielding layer in the patterned area. Then, using the first light-shielding layer as a hard mask, etch dryly until the transparent substrate reaches a preset depth and stop;

[0037] Deposit a second light-shielding layer again, finish the deposition, and perform anisotropic etching in the vertical direction, then a nanoimprint mask with the top and its periphery of the protruding part of the transparent substrate covered with a light-shielding layer is obtained.

[0038] Among them, the thickness of the photoresist layer is generally 100 nm - 10 μm, the thickness of the first light-shielding layer is generally 1 nm - 100 nm, and the thickness of the second light-shielding layer is generally 1 nm - 100 nm.

[0039] To facilitate a better understanding of the technical solution of the present application, the following will be explained in detail with several specific cases. It can be understood that the following embodiments are only used to illustrate the present invention, but not to limit the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0040] Example 1

[0041] This embodiment provides a method for preparing a nanoimprint mask, taking a quartz substrate as an example, see Figure 2 , and the specific steps are as follows:

[0042] S1. First, spin - coat a photoresist layer 02 with a specific thickness on a substrate transparent substrate 01 layer (such as a quartz substrate). Expose a characteristic pattern with a designed size in the photoresist layer 02 through electron - beam lithography (EBL), and then develop it.

[0043] S2. After development, deposit a light - shielding layer 03 with a specific thickness (such as a metal Cr layer) on the patterned photoresist structure. Then, remove the photoresist and the deposited light - shielding layer on it through a stripping process. Since the etching gas of metal Cr has a high selectivity for the quartz substrate in, for example, CF4 and SF6, when the metal Cr layer is deposited, the substrate material can be dry - etched immediately. The areas covered with the metal Cr layer act as hard masks and will not be etched. By controlling the etching time, continuously etch the quartz transparent substrate layer through dry etching. When the transparent substrate reaches the desired etching depth, stop the operation.

[0044] S3. Immediately deposit a second light - shielding layer 04 made of the same material as in step S2 on the template again, and perform anisotropic etching in the vertical direction. Finally, obtain a nano - imprint mask template with the light - shielding layer covering the top and periphery of the raised part of the template as in step 7.

[0045] Example 2

[0046] An embodiment of the present invention provides a method for manufacturing micro - nano structures using the above - mentioned mask template. Refer to Figure 3 , specifically as follows:

[0047] Align the nano - imprint mask template with the substrate spin - coated with photoresist and then press it down. Transfer the pattern to the photoresist layer through the above - mentioned mask template. After imprinting, keep the imprinting force unchanged, and irradiate the photoresist with UV light. The photoresist under the transparent part of the template receives UV light and cures, while the photoresist under the raised part and its adjacent side surfaces cannot receive ultraviolet radiation and cannot cure or has a low curing degree. After UV irradiation, demold the template. Put the photoresist into an oven for pre - baking before development, cure it and then develop and remove the photoresist. The uncured photoresist 05 in the part not irradiated by UV is removed during development, leaving the UV - cured photoresist 06 as a mask for subsequent metalization stripping or etching processes.

[0048] Compared with the traditional single - layer resist technology solution, since dry etching is not used to remove the residual resist in this process, the overall thinning of the photoresist will not occur. The metalized pattern can maintain a sufficiently high aspect - ratio, and at the same time, a photoresist morphology with an undercut profile is obtained, which is easy for subsequent stripping.

[0049] It is necessary to point out here that the above embodiments are only limited to further elaborating and explaining the technical solutions of the present invention, rather than further restricting the technical solutions of the present invention. The method of the present invention is only a preferred implementation scheme and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a mask suitable for UV-NIL technology, characterized in that, The method includes the following steps: Spin-coat a photoresist layer on a transparent substrate. After exposing a characteristic pattern on the photoresist layer, develop the photoresist; Subsequently, deposit a first light-shielding layer on the photoresist structure with the characteristic pattern. Then strip the photoresist, leaving the first light-shielding layer deposited on the transparent substrate. Using the first light-shielding layer as a hard mask, etch the transparent substrate by dry etching until a preset depth is reached, and then stop; Deposit a second light-shielding layer again and perform anisotropic etching in the vertical direction to obtain a nanoimprint mask template with the top and its periphery of the raised part of the transparent substrate covered with the light-shielding layer.

2. The method for preparing a mask suitable for UV-NIL technology according to claim 1, characterized in that, The thickness of the photoresist layer is 100 nm - 10 µm.

3. The preparation method of the mask plate applicable to the UV-NIL technology according to claim 1, characterized in that, The thickness of the first light-shielding layer is 1 nm - 100 nm, and / or the thickness of the second light-shielding layer is 1 nm - 100 nm.

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