Imaging contrast enhancement mask and method of making the same

Abstract

The present disclosure provides an imaging contrast enhancement mask and a preparation method thereof. The imaging contrast enhancement mask comprises a mask substrate and an absorption layer formed on the mask substrate, wherein a tip mask pattern structure is formed in a pattern area of the absorption layer, and a material of the absorption layer is a noble metal material. The imaging contrast enhancement mask uses the noble metal and the tip shape to double enhance the excitation of surface plasmons, thereby improving the imaging contrast of the pattern and realizing the processing of high-resolution patterns.

Description

Technical Field

[0001] This disclosure relates to the field of photolithography mask technology, and in particular to an imaging contrast enhancement mask and its fabrication method. Background Technology

[0002] Surface plasmons (SPs) originate from the coherent resonance of electrons on a metal surface driven by external electromagnetic waves, enhancing electromagnetic fields at subwavelength scales. Compared to free-space light waves, SPs have shorter propagation wavelengths at the same frequency, effectively resonantly coupling evanescent waves on the surface of an object to achieve evanescent wave amplification, resonant interference, and local enhancement, thereby obtaining patterns that surpass the traditional optical diffraction limit. Surface plasmons offer advantages such as high resolution and low cost, and are widely used in the fabrication of various nanodevices.

[0003] To fabricate various nanodevices or patterned structures, it is necessary to design various device patterned structures and fabricate them into the required mask templates. In the ultraviolet band, almost all mask patterns are fabricated using metallic chromium (Cr) as the light-blocking layer. Cr has advantages such as good light-blocking properties and high film hardness, and is widely used in the fabrication of mask patterns with feature sizes greater than 100 nm. When the feature size of the nanodevice patterned structure is less than 50 nm, the pattern contrast produced by traditional Cr masks can no longer meet the imaging contrast requirements (>0.4) of SP lithography patterns, making it difficult to achieve high-resolution pattern fabrication. Summary of the Invention

[0004] To address the aforementioned technical problems, this disclosure provides an imaging contrast enhancement mask and its fabrication method, which at least partially solves the technical problem of low imaging contrast produced by current Cr masks in high-resolution images in the prior art.

[0005] Based on this, the first aspect of this disclosure provides an imaging contrast enhancement mask, comprising: a mask substrate; an absorption layer formed on the mask substrate, wherein a pointed mask pattern structure is formed in the pattern area of ​​the absorption layer, and the material of the absorption layer is a noble metal material.

[0006] According to an embodiment of this disclosure, the width of the tip mask pattern structure at the end near the mask substrate is greater than the width at the end away from the mask substrate.

[0007] According to an embodiment of this disclosure, the angle between the tip mask pattern structure and the mask substrate is 30° to 70°.

[0008] According to embodiments of this disclosure, the feature size of the tip mask pattern structure is 10nm to 45nm.

[0009] According to embodiments of this disclosure, the precious metal material includes one of Ag, Au, and Cu.

[0010] According to embodiments of this disclosure, the thickness of the absorption layer ranges from 20 nm to 500 nm.

[0011] According to embodiments of this disclosure, the mask substrate includes one of a quartz mask substrate, a glass mask substrate, and a sapphire mask substrate, and the mask substrate has adhesion to the absorption layer.

[0012] The second aspect of this disclosure provides a method for fabricating an imaging contrast enhancement mask as described above. The method includes: depositing an absorption layer on a mask substrate, wherein the material of the absorption layer is a noble metal; spin-coating photoresist on the absorption layer and forming a mask pattern structure on the photoresist; and using a lateral etching transfer process to transfer the mask pattern structure on the photoresist to the absorption layer to form a pointed mask pattern structure in the patterned area of ​​the absorption layer.

[0013] According to an embodiment of this disclosure, spin-coating photoresist onto an absorption layer and forming a mask pattern structure on the photoresist specifically includes: spin-coating electron beam photoresist onto the absorption layer and performing electron beam direct writing to form a mask pattern structure on the electron beam photoresist, wherein the thickness of the electron beam photoresist ranges from 20 nm to 200 nm.

[0014] According to embodiments of this disclosure, the etching method of the lateral etching transfer process includes one of ion beam etching, reactive ion etching, inductively coupled plasma etching, and capacitively coupled plasma etching; the etching gas includes at least one of O2, N2, Ar, SF6, Cl2, and HBr; and the etching angle range is 30° to 70°.

[0015] The imaging contrast enhancement mask and its preparation method provided according to the embodiments of this disclosure have at least the following beneficial effects:

[0016] The absorption layer of the imaging contrast enhancement mask is made of noble metal material, and the absorption layer is a pointed mask pattern structure. By utilizing the dual enhancement of noble metal and pointed shape to enhance the excitation of surface plasma, the coupling transmission strength is further enhanced, thereby improving the imaging contrast of the pattern and realizing the processing of high-resolution patterns.

[0017] Furthermore, the width of the tip mask pattern structure near the mask substrate is greater than the width of the end away from the mask substrate, and the angle between the tip mask pattern structure and the mask substrate is 30° to 70°, which can further facilitate the excitation of surface plasma, thereby further improving the imaging contrast of the pattern.

[0018] Furthermore, imaging contrast enhancement masks based on this structure can be fabricated using only conventional coating, photolithography, and etching processes. The fabrication method is simple, low-cost, and conducive to widespread application. Attached Figure Description

[0019] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0020] Figure 1 A schematic diagram illustrating the structure of an imaging contrast enhancement mask provided in an embodiment of this disclosure is shown.

[0021] Figure 2 The illustration schematically shows a method for preparing an imaging contrast enhancement mask provided in an embodiment of the present disclosure.

[0022] Figure 3A This illustration schematically shows the embodiments provided by the present disclosure. Figure 2 The structural diagram corresponding to operation S201.

[0023] Figure 3B This illustration schematically shows the embodiments provided by the present disclosure. Figure 2 The structural diagram corresponding to operation S202.

[0024] Figure 3C This illustration schematically shows the embodiments provided by the present disclosure. Figure 2 The structural diagram corresponding to operation S203.

[0025] Figure 3D This illustration schematically shows the embodiments provided by the present disclosure. Figure 2 The structural diagram corresponding to operation S204.

[0026] Figure 3E This illustration schematically shows the embodiments provided by the present disclosure. Figure 2 The structural diagram corresponding to operation S205.

[0027] Figure 4 The illustration schematically shows the curves of the imaging contrast calculated in different metal masks as a function of air gap for a 32nm resolution mask pattern provided in an embodiment of the present disclosure.

[0028] [Attached image labels]

[0029] 1-Mask substrate, 2-Absorbing layer, 3-Photoresist. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0032] In this disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0033] In the description of this disclosure, it should be understood that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the subsystem or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure.

[0034] Throughout the accompanying drawings, identical elements are represented by the same or similar reference numerals. Conventional structures or constructions have been omitted where they may cause confusion in understanding this disclosure. Furthermore, the shapes, dimensions, and positional relationships of the components in the drawings do not reflect actual size, scale, or actual positional relationships. Additionally, any reference numerals placed between parentheses in the claims should not be construed as limiting the claims.

[0035] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0037] Figure 1 A schematic diagram illustrating the structure of an imaging contrast enhancement mask provided in an embodiment of this disclosure is shown.

[0038] like Figure 1 As shown, the imaging contrast enhancement mask may include, for example, a mask substrate 1 and an absorption layer 2.

[0039] An absorption layer 2 is formed on a mask substrate 1. A pointed mask pattern structure is formed in the patterned area of ​​the absorption layer 2, which is beneficial for the excitation of surface plasmons. The absorption layer 2 is a metal layer, and its material is a noble metal. Noble metal materials are also beneficial for the excitation of surface plasmons. The combination of noble metal and pointed shape can further enhance the coupling transmission strength of SP, thereby improving the imaging contrast of the pattern.

[0040] In this embodiment of the disclosure, the width of the tip mask pattern structure near the mask substrate 1 is greater than the width away from the mask substrate 1. Figure 1 Viewed from the indicated direction, the patterned area of ​​the absorption layer 2 contains a pointed mask pattern structure that is wide at the bottom and narrow at the top.

[0041] Furthermore, the angle between the tip mask pattern structure and the mask substrate is 30° to 70°, that is... Figure 1 The included angle θ is 30° to 70°.

[0042] Designing the shape of the tip mask pattern structure can help to further enhance the excitation of surface plasma.

[0043] In the embodiments of this disclosure, the noble metal material includes one of Ag, Au, and Cu. The specific type of noble metal material can be selected according to actual application requirements, and this disclosure does not impose any limitations. The thickness of the absorption layer 2 ranges from 20 nm to 500 nm, and an absorption layer of appropriate thickness can be etched according to actual application requirements.

[0044] Furthermore, the feature size of the tip mask pattern structure can be designed to be 10nm to 45nm.

[0045] In this embodiment of the disclosure, the mask substrate 1 includes one of a quartz mask substrate, a glass mask substrate, and a sapphire mask substrate. The mask substrate 1 has adhesion to the absorption layer, that is, the selected mask substrate 1 has good adhesion performance to the noble metal of the absorption layer 2.

[0046] Based on the same inventive concept, this disclosure also provides a method for preparing an imaging contrast enhancement mask.

[0047] Figure 2 The illustration schematically shows a method for preparing an imaging contrast enhancement mask provided in an embodiment of the present disclosure.

[0048] like Figure 2 As shown, the preparation method may include, for example, operations S201 to S205.

[0049] In operation S201, an absorption layer is deposited on the mask substrate, wherein the material of the absorption layer is a noble metal material.

[0050] In operation S202, photoresist is spin-coated onto the absorption layer.

[0051] In operation S203, a mask pattern structure is formed on the photoresist.

[0052] In operation S204, a lateral etching transfer process is used to transfer the mask pattern structure on the photoresist to the absorption layer, so as to form a tip mask pattern structure in the pattern area of ​​the absorption layer.

[0053] In operation S205, the etched absorption layer is cleaned to obtain an imaging contrast enhancement mask.

[0054] Figures 3A-3E This illustration schematically shows the embodiments provided by the present disclosure. Figure 2 The structural diagrams corresponding to each operation of the preparation method shown are illustrated.

[0055] like Figure 3A As shown, a dense noble metal layer is deposited on the mask substrate 1 as the absorption layer 2.

[0056] like Figure 3BAs shown, electron beam photoresist is spin-coated onto the absorption layer 2. The electron beam photoresist may include, for example, polymethyl methacrylate (PMMA), SU-8, HSQ, etc. The thickness of the electron beam photoresist ranges from 20 nm to 200 nm.

[0057] like Figure 3C As shown, electron beam photoresist is directly written with an electron beam to form a mask pattern structure on the electron beam photoresist.

[0058] like Figure 3D As shown, ion beam etching (IBE), reactive ion etching, inductively coupled plasma (ICP), or capacitively coupled plasma (CCP) etching can be used, with an etching angle range of 30°–70°. The etching gas is one or more of O2, N2, Ar, SF6, Cl2, and HBr. During the etching process, lateral etching and protective processes are used to control the etching, resulting in less lateral etching at the bottom of the mask and more lateral etching at the top, thus forming a pointed mask pattern structure with a wide bottom and a narrow top in the patterned area.

[0059] like Figure 3E As shown, residual electron beam photoresist can be removed using either dry or wet cleaning methods. Dry cleaning methods include reactive ion etching and inductively coupled plasma etching, while wet cleaning methods include photoresist remover solutions and acetone.

[0060] To further verify the advantages of the imaging contrast enhancement mask and its preparation method provided in the embodiments of this disclosure, several specific examples are given below.

[0061] Example 1

[0062] First, a 40 nm thick Ag film was deposited on a quartz substrate using magnetron sputtering deposition. The deposition power was 400 W, the cavity pressure was 1 Torr, and the deposition temperature was 50 °C. Specifically, 10 nm was deposited, paused for 1 min, and then another 10 nm was deposited. This was mainly to prevent the Ag particles from growing too quickly and becoming too large, which would increase the roughness of the film.

[0063] Then, a 50nm thick PMMA electron beam resist is coated onto the surface of the Ag film. Electron beam exposure is then performed, and after development, a photolithographic structure composed of electron beam photoresist is obtained. The photolithographic structure is a dense grating pattern with a half-period of 32nm.

[0064] Next, using electron beam photoresist as a masking layer, ICP is used to etch the metal Ag film. By controlling the pressure of the etching chamber and the ratio of the lateral protective gas, the electron beam photoresist pattern is transferred to the metal Ag layer to form a pointed metal Ag mask pattern that is wide at the bottom and narrow at the top, with an included angle of 40°.

[0065] Finally, the processed mask is cleaned with a resist remover to remove residual electron beam photoresist, completing the processing of the Ag mask with a half-cycle of 32nm.

[0066] Example 2

[0067] First, a 50 nm thick Au film was deposited on the glass substrate using magnetron sputtering deposition. The deposition power was 600 W, the cavity pressure was 0.5 Torr, and the deposition temperature was 100 °C. Specifically, 10 nm was deposited, paused for 2 minutes, and then another 10 nm was deposited. This was mainly to prevent the Au particles from growing too quickly and becoming too large, which would increase the roughness of the film.

[0068] Then, a 100nm thick layer of SU-8 electron beam photoresist is coated onto the surface of the Au film. Electron beam exposure is then performed, and after development, a photolithographic structure composed of electron beam photoresist is obtained. The photolithographic structure is a dense grating pattern with a half-period of 22nm.

[0069] Next, using electron beam photoresist as a masking layer, the metal Au film is etched using RIE. The proportion of lateral protective gas is gradually reduced from top to bottom to transfer the electron beam photoresist pattern to the metal Au layer, thereby obtaining the metal Au tip mask pattern. The included angle of the tip Au mask is 30°.

[0070] Finally, the processed mask is cleaned with acetone to remove residual electron beam photoresist, completing the processing of the Au tip mask with a half-cycle of 22nm.

[0071] Example 3

[0072] First, an 80 nm thick Cu film was deposited on the sapphire substrate using electron beam evaporation deposition (EBD). The deposition current was 5 mA, and the deposition rate was 0.5 A. Specifically, a 20 nm deposition was performed, followed by a 5-minute pause, and then another 20 nm deposition was performed. This was primarily to prevent the Cu particles from growing too quickly and becoming too large, which would increase the film roughness.

[0073] Then, a 30nm thick SU-8 electron beam resist is coated onto the Cu film surface. Electron beam exposure is then performed, and after development, a photolithographic structure composed of electron beam photoresist is obtained. The photolithographic structure is a dense grating pattern with a half-period of 16nm.

[0074] Next, using electron beam photoresist as a masking layer, the metal Cu film is etched using IBE at an etching angle of 15° and a rotation speed of 20 rpm to transfer the electron beam photoresist pattern to the metal Cu layer, thus obtaining the metal Cu mask pattern. The included angle of the Cu mask at the tip is 60°.

[0075] Finally, the processed mask was cleaned using RIE dry oxygen plasma to remove residual electron beam photoresist, completing the processing of the Cu mask with a half-cycle of 16nm.

[0076] Figure 4 The illustration schematically shows the curves of the imaging contrast calculated in different metal masks as a function of air gap for a 32nm resolution mask pattern provided in an embodiment of the present disclosure.

[0077] like Figure 4 As shown, the solid line represents the curve of the imaging contrast calculated in the Ag mask with respect to the air gap for a 32nm resolution tip mask pattern, while the dashed line represents the curve of the imaging contrast calculated in the Cr mask with respect to the air gap for a 32nm resolution conventional mask pattern. Comparing the solid and dashed lines, it can be seen that by using a dense grating mask structure with a half-period 32nm feature size, the processed Ag tip mask pattern achieves a significant improvement in imaging contrast compared to the conventional Cr mask pattern within a 40nm air gap, verifying the feasibility of the method.

[0078] Furthermore, the imaging contrast of the 22nm resolution pattern calculated using an Au-tipped mask is 0.8, while the imaging contrast calculated using a Cr conventional mask is 0.3. Figure 4 The image is not shown in the diagram, which indicates that the imaging contrast of the processed Au-tipped mask is also significantly improved. The processed Cu-tipped mask is similar to that of the Ag and Au-tipped masks, and will not be described in detail here.

[0079] In summary, the imaging contrast enhancement mask provided in this embodiment uses a noble metal material capable of exciting surface plasmons, and the mask pattern structure is designed with a pointed shape to form a noble metal pointed mask pattern structure. This utilizes the enhanced coupling and transmission strength of the noble metal and the pointed shape to the surface plasmon lithography (SP), thereby improving the imaging contrast of the pattern. This method can fabricate high-contrast new material masks through conventional deposition and etching processes, while simultaneously improving the lithographic quality of surface plasmon lithography and expanding its application range.

[0080] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. An imaging contrast enhancement mask, characterized in that, include: Mask substrate, including one of quartz mask substrate, glass mask substrate and sapphire mask substrate; An absorption layer is formed on the mask substrate, and the mask substrate and the absorption layer have adhesion. A pointed mask pattern structure is formed in the pattern area of ​​the absorption layer. The material of the absorption layer is a noble metal material. The surface plasma excitation is enhanced by the noble metal material and the pointed mask pattern structure to improve the imaging contrast of the pattern. The angle between the tip mask pattern structure and the mask substrate is 30°~70°; the feature size of the tip mask pattern structure is 10 nm~45 nm.

2. The imaging contrast enhancement mask according to claim 1, characterized in that, The width of the tip mask pattern structure near the mask base is greater than the width away from the mask base.

3. The imaging contrast enhancement mask according to claim 1, characterized in that, The precious metal material includes one of Ag, Au, and Cu.

4. The imaging contrast enhancement mask according to claim 1, characterized in that, The thickness of the absorption layer ranges from 20 nm to 500 nm.

5. A method for preparing an imaging contrast enhancement mask, characterized in that, The method for preparing the imaging contrast enhancement mask as described in any one of claims 1 to 4 includes: An absorption layer is deposited on a mask substrate, wherein the material of the absorption layer is a noble metal. Photoresist is spin-coated onto the absorption layer, and a mask pattern structure is formed on the photoresist; A lateral etching transfer process is used to transfer the mask pattern structure on the photoresist to the absorption layer, so as to form a tip mask pattern structure in the pattern area of ​​the absorption layer.

6. The method for preparing the imaging contrast enhancement mask according to claim 5, characterized in that, The step of spin-coating photoresist onto the absorption layer and forming a mask pattern structure on the photoresist specifically includes: Electron beam photoresist is spin-coated onto the absorption layer and electron beam direct writing is performed to form the mask pattern structure on the electron beam photoresist, wherein the thickness of the electron beam photoresist ranges from 20 nm to 200 nm.

7. The method for preparing the imaging contrast enhancement mask according to claim 5, characterized in that, The etching method of the lateral etching transfer process includes one of ion beam etching, reactive ion etching, inductively coupled plasma etching, and capacitively coupled plasma etching. The etching gas used includes at least one of O2, N2, Ar, SF6, Cl2, and HBr; The etching angle range is 30° to 70°.

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