Off-axis illumination grating and preparation method therefor, and separable off-axis illumination lithography mask

Abstract

An off-axis illumination grating and a preparation method therefor, and a separable off-axis illumination lithography mask. The preparation method comprises: by means of electron beam lithography and reactive ion etching, preparing a grating master template (1) having a grating pattern (S1); copying the grating pattern on the grating master template (1) to the surface of a working template (2) by means of first nanoimprint, so as to form a working template having the grating pattern (S2); sequentially preparing a grating material layer (4), a transfer layer (5) and an imprint resist layer (6) on a substrate (3), copying, by means of second nanoimprint, the grating pattern of the working template (2) obtained in step (S2) to the imprint resist layer (6), and performing curing (S3); and performing etching transfer on the grating pattern on the imprint resist layer (6) to the transfer layer (5) and the grating material layer (4) in sequence, and removing the residual transfer layer (5), so as to obtain an off-axis illumination grating (S4). The off-axis illumination grating can be separated from a mask, and can be reused.

Description

Off-axis illumination grating and preparation method thereof, and detachable off-axis illumination photolithography mask

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 202311559466.0 filed with the State Intellectual Property Office of China on November 21, 2023, entitled “Off-axis illumination grating and its preparation method, detachable off-axis illumination photolithography mask,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present disclosure relates to the technical field of semiconductor device manufacturing, and in particular to an off-axis illumination grating and a preparation method thereof, and a detachable off-axis illumination photolithography mask. Background Art

[0004] The semiconductor manufacturing industry is continuously developing towards high integration and high precision. Lithography is a core technology for large-scale integrated circuit manufacturing. Improving the resolution of lithography machines to meet the demands of shrinking technology nodes is a key area of ​​modern lithography research. Off-axis illumination (OAI), a commonly used lithography illumination technique, can improve lithography resolution, increase depth of focus, and enhance contrast in lithography images. It is widely used in DUV and EUV lithography. There are two ways to achieve off-axis illumination: one is to block the vertical component of light in the exposure apparatus, allowing only oblique light to reach the mask; the other is to fabricate a grating with a fixed period on the back of the mask. Light refracts as it passes through the grating. By controlling the grating period and the refractive index of the material, the incident light is deflected onto the mask pattern for exposure. This is a commonly used off-axis illumination technique.

[0005] The processing method of off-axis illumination grating is usually to coat a layer of material with a certain refractive index on the back of the mask, apply photoresist on the surface of the material, and use electron beam lithography or other photolithography technology to expose to form a grating pattern. Then, the grating pattern is etched into the material with a certain refractive index using etching technology to form an off-axis illumination grating. In this way, the processed grating and mask are integrated.

[0006] Integrated off-axis illumination photolithography masks have several drawbacks. First, they present significant processing difficulties. The processing of integrated off-axis illumination photolithography masks typically requires fabricating an illumination grating on one side (the back surface). After the grating is fabricated, the metal Cr mask pattern is fabricated on the other side (the front surface). Since the grating period is typically 200-300 nm, the fine grating on the back surface can be easily damaged during the process of fabricating the Cr mask pattern on the front surface. Second, after a certain number of exposures, the photomask inevitably becomes contaminated on the Cr mask pattern surface. To achieve better pattern quality, the contamination on the mask surface must be cleaned. The acid or alkaline solutions used in this cleaning process are very likely to corrode the grating material on the back surface, thereby damaging the grating structure and affecting the illumination effect. Third, due to the small grating period and strict requirements for period and line edge roughness, electron beam lithography is typically used for grating fabrication. The edge length of a grating area is typically tens of millimeters, and illumination requires at least four directions, meaning four identical gratings. Electron beam lithography exposure of such a large grating area takes an extremely long time (hundreds of hours), resulting in low efficiency and high cost. Electron beam lithography is also commonly used for processing high-resolution mask patterns. Damage to the mask pattern or gratings requires reprocessing the entire mask.

[0007] Therefore, there is an urgent need in the art for an off-axis illumination grating that can be processed separately and can combine or separate the grating and the mask according to needs to overcome the above problems.

[0008] Summary of the Invention

[0009] (1) Technical issues to be resolved

[0010] In response to the above problems, the present disclosure provides an off-axis illumination grating and a preparation method thereof, and a detachable off-axis illumination photolithography mask, which are used to solve the technical problems of traditional integrated off-axis illumination photolithography masks, such as easy damage to the grating during the processing process, low preparation efficiency, and high cost.

[0011] (2) Technical solution

[0012] A first aspect of the present disclosure provides a method for preparing an off-axis illumination grating, comprising: S1, preparing a grating master having a grating pattern by electron beam lithography and reactive ion beam etching; S2, copying the grating pattern on the grating master to the surface of a working template by a first nanoimprint, to form a working template having a grating pattern; S3, sequentially preparing a grating material layer, a transfer layer, and an imprinting adhesive layer on a substrate, copying the grating pattern of the working template obtained in S2 to the imprinting adhesive layer by a second nanoimprint, and curing the resultant grating; S4, sequentially etching and transferring the grating pattern on the imprinting adhesive layer to the transfer layer and the grating material layer, removing the remaining transfer layer, to obtain an off-axis illumination grating.

[0013] According to the embodiments of the present disclosure, the acceleration voltage of the electron beam lithography in S1 is 50 to 125 kV, and the current is 3 to 6 nA; the inductively coupled plasma (ICP) power of the reactive ion beam etching is 800 to 1500 W, the radio frequency power is 8 to 15 W, and the reaction gases are SF6 and CHF3; the grating etching depth of the grating master is 80 to 100 nm, and the grating period is 200 to 250 nm.

[0014] According to an embodiment of the present disclosure, the working template in S2 is made of a flexible material that is transparent to ultraviolet light; before the first nanoimprinting, a layer of anti-sticking material is evaporated on the surface of the grating master, and the thickness of the anti-sticking material is a monomolecular layer.

[0015] According to the embodiments of the present disclosure, the material of the substrate in S3 is quartz or sapphire; the material of the grating material layer is TiO2, with a thickness of 100 to 150 nm; the material of the transfer layer is an anti-etching material such as chromium, molybdenum or aluminum, with a thickness of 15 to 20 nm; the material of the imprinted adhesive layer is a UV-curing adhesive with a thickness of 80 to 100 nm.

[0016] According to an embodiment of the present disclosure, S3 further includes: replicating the grating pattern of the working template obtained in S2 multiple times by a second nanoimprint to obtain multiple grating patterns on the imprinted adhesive layer; and after S3, further includes: removing the residual imprinted adhesive by oxygen plasma etching.

[0017] According to an embodiment of the present disclosure, S4 includes: using ion beam etching to etch and transfer the grating pattern on the imprinted adhesive layer to the transfer layer; using reactive ion beam etching to etch and transfer the grating pattern on the transfer layer to the grating material layer; using chemical liquid to remove the remaining transfer layer to obtain an off-axis illumination grating.

[0018] A second aspect of the present disclosure provides an off-axis illumination grating, which is prepared according to the above-mentioned off-axis illumination grating preparation method.

[0019] A third aspect of the present disclosure provides a detachable off-axis illumination photolithography mask, comprising: a mask body, including a substrate and a mask absorption layer; an off-axis illumination grating, prepared according to the above-mentioned off-axis illumination grating preparation method, and detachably arranged on the other side of the mask body opposite to the mask absorption layer; wherein the substrate material of the off-axis illumination grating is the same as the substrate material of the mask body, and the substrate of the off-axis illumination grating is adhered to the substrate of the mask body by a refractive index matching liquid and fixed by a UV curing adhesive to achieve off-axis illumination.

[0020] A fourth aspect of the present disclosure provides a method for using the above-mentioned detachable off-axis illumination lithography mask, comprising: dripping a refractive index matching liquid onto the back surface of the off-axis illumination grating, fixing the off-axis illumination grating to the other side of the mask body opposite to the mask absorption layer via a grating position fixing mold; pressing the off-axis illumination grating to form a uniform film layer of the refractive index matching liquid, and applying ultraviolet curing glue along the four sides of the grating strips; curing the ultraviolet curing glue, removing the grating position fixing mold, and fixing the off-axis illumination grating to the mask body.

[0021] According to an embodiment of the present disclosure, the method further includes: applying a de-curing agent on the UV curing adhesive to release the off-axis illumination grating from the mask body. (3) Beneficial effects

[0022] The disclosed off-axis illumination grating, its fabrication method, and detachable off-axis illumination photolithography mask utilize nanoimprint technology to replicate the grating pattern, enabling the independent fabrication of the off-axis illumination grating, improving processing efficiency and reducing processing costs. Furthermore, by using a refractive index matching fluid to adhere the off-axis illumination grating to the side of the mask body opposite the mask absorption layer, the off-axis illumination grating achieves the same lighting effect as a conventional integrated off-axis illumination photomask. Furthermore, the mask body and off-axis illumination grating can be separated, preventing damage to the off-axis illumination grating during mask pattern fabrication and cleaning. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 schematically shows a flow chart of a method for preparing an off-axis illumination grating according to an embodiment of the present disclosure;

[0024] FIG2 schematically shows a flow chart of a method for preparing an off-axis illumination grating according to an embodiment of the present disclosure;

[0025] FIG3 schematically shows a structural diagram of a detachable off-axis illumination photolithography mask according to an embodiment of the present disclosure;

[0026] FIG4 schematically shows a schematic structural diagram of an off-axis illumination grating arranged on the back side of a mask body according to an embodiment of the present disclosure;

[0027] FIG5 schematically shows a structural diagram of a grating position fixing mold according to an embodiment of the present disclosure;

[0028] FIG6 schematically shows a picture of grating strips after cutting according to an embodiment of the present disclosure;

[0029] FIG7 schematically shows a scanning electron microscope image of the upper surface of a grating master according to an embodiment of the present disclosure;

[0030] FIG8 schematically shows a scanning electron microscope image of a cross section of a grating master according to an embodiment of the present disclosure;

[0031] FIG9 schematically shows a distribution diagram of a grating pattern imprinted on a substrate according to an embodiment of the present disclosure;

[0032] FIG10 schematically shows a raster scanning electron microscope image of TiO2 after etching according to an embodiment of the present disclosure;

[0033] FIG11 schematically shows a schematic diagram of transmittance calculation of a detachable off-axis illumination photolithography mask according to an embodiment of the present disclosure;

[0034] FIG12 schematically shows a schematic diagram of transmittance calculation of an integrated off-axis illumination photolithography mask according to an embodiment of the present disclosure;

[0035] Explanation of the accompanying reference numerals: 1, grating master; 2, working template; 3, substrate; 4, grating material layer; 5, transfer layer; 6, embossing adhesive layer. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0037] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0038] It should be noted that if directional indications are involved in the embodiments of the present disclosure, the directional indications are only used to explain the relative positional relationship, movement status, etc. between the components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0039] To address the problems of existing technologies, if the off-axis illumination grating and the mask pattern can be processed separately, the off-axis illumination grating can be removed and separated during mask pattern processing or mask cleaning. This can avoid damage to the off-axis illumination grating and allow the grating to be reused. Nanoimprint technology can replicate nanopatterns with a resolution of less than 10nm. If nanoimprint technology is applied to the processing of off-axis illumination gratings, it can improve processing efficiency and reduce processing costs.

[0040] Based on this, the present disclosure provides, on the one hand, a method for preparing an off-axis illumination grating, as shown in Figures 1 and 2, comprising: S1, preparing a grating master 1 having a grating pattern by electron beam lithography and reactive ion beam etching; S2, copying the grating pattern on the grating master 1 to the surface of a working template 2 by a first nanoimprint, to form a working template 2 having a grating pattern; S3, sequentially preparing a grating material layer 4, a transfer layer 5 and an imprinting adhesive layer 6 on a substrate 3, copying the grating pattern of the working template 2 obtained in S2 to the imprinting adhesive layer 6 by a second nanoimprint, and curing the resultant; S4, etching the grating pattern on the imprinting adhesive layer 6 and transferring it to the transfer layer 5 and the grating material layer 4 in sequence, removing the remaining transfer layer 5, and obtaining an off-axis illumination grating.

[0041] This method first prepares a grating master 1, then uses nanoimprint technology to copy the grating pattern onto the surface of a working template 2. A second nanoimprint technique is then used to copy the grating pattern onto an imprint adhesive layer 6. Finally, the grating pattern is transferred to a grating material layer 4 via etching, resulting in an off-axis illumination grating. This method enables the independent processing of off-axis illumination gratings, improving processing efficiency and reducing processing costs.

[0042] Based on the above embodiment, the acceleration voltage of the electron beam lithography in S1 is 50-125 kV, and the current is 3-6 nA; the inductively coupled plasma (ICP) power of the reactive ion beam etching is 800-1500 W, the radio frequency power is 8-15 W, and the reaction gases are SF6 and CHF3; the grating etching depth of the grating master 1 is 80-100 nm, and the grating period is 200-250 nm.

[0043] Electron beam lithography involves electron beam exposure and development. Reactive ion beam etching involves the directional bombardment of the ion beam and the reaction between the gas and the substrate. Etching the grating master 1 within the above range facilitates achieving the desired depth of the imprinted pattern in the subsequent imprint process.

[0044] Based on the above embodiment, the working template 2 in S2 is made of a flexible material that is transparent to ultraviolet light; before the first nanoimprinting, a layer of anti-sticking material is evaporated on the surface of the grating master 1, and the thickness of the anti-sticking material is a monomolecular layer.

[0045] The use of flexible material for the working template 2 is conducive to uniformly imprinting the pattern onto the substrate material. The thickness of the anti-stick material should not be too thick, otherwise it will reduce the accuracy of pattern transfer on the nanoscale.

[0046] Based on the above embodiments, the material of the substrate 3 in S3 is quartz or sapphire; the material of the grating material layer 4 is TiO2, with a thickness of 100 to 150 nm; the material of the transfer layer 5 is any one of chromium, molybdenum, and aluminum, with a thickness of 15 to 20 nm; the material of the imprinted adhesive layer 6 is UV-curing adhesive, with a thickness of 80 to 100 nm.

[0047] The transfer layer 5 plays a role in enhancing the etching barrier. The thickness of the embossing adhesive layer 6 within the above range is beneficial to resisting the consumption of the embossing adhesive thickness during the etching process and transferring the embossing adhesive pattern to the transfer layer.

[0048] Based on the above embodiment, S3 further includes: replicating the grating pattern of the working template 2 obtained in S2 multiple times by a second nanoimprint to obtain multiple grating patterns on the imprint adhesive layer 6; and after S3, further includes: removing the residual imprint adhesive by oxygen plasma etching.

[0049] The working template 2 can be reused, and multiple grating patterns can be obtained by multiple imprinting on the substrate 3 using a step-by-step method, which greatly saves preparation time and improves processing efficiency. After curing, oxygen plasma etching is required to remove the remaining uncured imprint adhesive.

[0050] Based on the above embodiment, S4 includes: using ion beam etching to etch and transfer the grating pattern on the imprinted adhesive layer 6 to the transfer layer 5; using reactive ion beam etching to etch and transfer the grating pattern on the transfer layer 5 to the grating material layer 4; using chemical liquid to remove the remaining transfer layer 5 to obtain an off-axis illumination grating.

[0051] Ion beam etching is beneficial for etching the transfer layer material Cr; reactive ion beam etching is beneficial for selectively etching the TiO2 layer; when the transfer layer 5 is Cr, a chromium etchant composed of ammonium cerium nitrate and perchloric acid is used to remove residual Cr.

[0052] The present disclosure also provides an off-axis illumination grating, which is prepared according to the above-mentioned off-axis illumination grating preparation method.

[0053] The present invention adopts nanoimprint technology to replicate grating patterns, and combines it with reactive ion beam etching to produce off-axis illumination gratings. It has a comparable illumination effect on mask patterns as conventional integrated off-axis illumination gratings, and can replace existing integrated off-axis illumination photomasks.

[0054] The present disclosure also provides a detachable off-axis illumination photolithography mask, comprising: a mask body, including a substrate and a mask absorption layer; an off-axis illumination grating, which is prepared according to the above-mentioned off-axis illumination grating preparation method and is detachably arranged on the other side of the mask absorption layer; wherein the substrate 3 of the off-axis illumination grating is made of the same material as the substrate of the mask body, and the substrate 3 of the off-axis illumination grating is adhered to the substrate of the mask body by a refractive index matching liquid and fixed by a UV curing adhesive to achieve off-axis illumination.

[0055] The detachable off-axis illumination photolithography mask disclosed in the present invention includes a mask body and an off-axis illumination grating. The mask body includes a substrate and a mask absorption layer located on the front side of the mask. The mask absorption layer is processed with a mask pattern having light-transmitting areas and non-light-transmitting areas, as shown in Figure 3; the off-axis illumination grating can be detachably arranged at a predetermined position on the back side of the mask body (the other side opposite to the mask absorption layer) and is arranged in a pasting manner.

[0056] The mask body substrate can be sapphire or quartz, with a thickness of, for example, 6.35 mm. The mask absorption layer can be made of Cr or MoSi, with a thickness of, for example, 40 nm or other thicknesses. The critical dimension of the mask pattern is 14 to 130 nm.

[0057] The off-axis illumination grating substrate 3 is made of the same material as the mask body substrate, which can be sapphire or quartz. The period p, duty cycle f, and thickness t of the off-axis illumination grating are determined by the wavelength of the lithography illumination light source, the illumination angle, and the grating material. Preferably, the thickness t of the off-axis illumination grating is 100-150 nm, the period p is 200-260 nm, and the duty cycle f is 0.3-0.6. TiO2 can be used. Specifically, it is manufactured using nanoimprinting technology combined with reactive ion beam etching.

[0058] The off-axis illumination grating is affixed to the back of the mask body, symmetrically in the X and Y directions, with the front mask absorption layer pattern area as the center, forming a cross-shaped arrangement, as shown in Figure 4. The distance between the center of the off-axis illumination grating and the center of the mask pattern area is determined based on the grating's diffraction angle β, so that the incident light diffracted by the off-axis illumination grating will directly illuminate the mask pattern area.

[0059] Among them, it is preferred to use a refractive index matching liquid for pasting, and the refractive index of the refractive index matching liquid is determined according to the base material of the mask body. Specifically, drop the refractive index matching liquid to the center of the grating strip substrate 3, then place the grating strip on the set position on the back of the mask body, and gently press the grating strip to allow the refractive index matching liquid to diffuse and evenly distribute to the contact area between the grating strip substrate 3 and the mask body, and expel any bubbles that may exist. After pasting, apply UV curing glue around the grating strip to fix the grating strip and prevent the refractive index matching liquid between the grating strip and the mask body from volatilizing. The refractive index of the refractive index matching liquid for a wavelength of 365nm needs to be selected as n2±0.005, where n2 is the refractive index of sapphire or quartz, the base material of the mask body, at a wavelength of 365nm. The refractive index matching liquid has no special requirements for materials.

[0060] The present disclosure also provides a method for using the above-mentioned detachable off-axis illumination photolithography mask, comprising: dripping a refractive index matching liquid onto the back surface of the off-axis illumination grating, fixing the grating strips to the other side of the mask body opposite to the mask absorption layer through a grating position fixing mold; pressing the off-axis illumination grating to form a uniform film layer of the refractive index matching liquid, and applying ultraviolet curing glue along the four sides of the off-axis illumination grating; curing the ultraviolet curing glue, removing the grating position fixing mold, and fixing the off-axis illumination grating to the mask body.

[0061] First, the grating position fixing mold is processed. It should be noted that before pasting, the off-axis illumination grating can also be cut to obtain grating strips of the target size. In order to paste the grating strips to the correct position on the back of the mask body (the other side relative to the mask absorption layer), Teflon material is used to process the grating position fixing mold. The holes for placing the grating strip positions in the grating position fixing mold are set according to the size of the grating strips and the relative distance between the grating strips and the front absorption area of ​​the mask. Figure 5 is a structural diagram of the grating position fixing mold used for pasting the off-axis illumination grating.

[0062] Next, laser cutting of the grating strips is performed. The off-axis illumination grating is cut from the substrate using a laser to form the grating strips. The cutting dimensions are, for example, (L+2) mm x (W+2) mm, where L and W are the length and width of the off-axis illumination grating region, respectively. Before cutting, a 3-5 μm thick layer of photoresist is spin-coated on the surface of the off-axis illumination grating as a protective layer. After cutting, the photoresist is removed with acetone. Figure 6 shows a picture of the resulting grating strips (with the protective layer on the grating surface not removed).

[0063] Next, the grating strips are attached. The grating position fixing mold is fixed to the back of the mask body. A refractive index matching liquid is dripped onto the grating strip substrate 3. The grating strips are then placed onto the grating positions set in the grating position fixing mold, adhering the grating strip substrate 3 to the back of the mask body. Gently press the grating strips to evenly distribute the refractive index matching liquid and remove any bubbles.

[0064] Finally, the grating strips are fixed. After the refractive index matching liquid forms a uniform film between the back of the mask body and the grating strip substrate 3, UV-curable adhesive is evenly applied around the grating strips. UV light is then applied to the adhesive, securing the grating strips to the back of the mask body while preventing the evaporation of the refractive index matching liquid. After the UV adhesive cures, the grating position fixing mold is removed, resulting in a detachable off-axis illumination photolithography mask.

[0065] Based on the above embodiment, the method further includes: applying a de-curing agent on the UV curing adhesive, and releasing the off-axis illumination grating from the mask body.

[0066] Grating strip separation involves applying a UV-curing de-curing agent to the UV-curing adhesive to de-cure and remove the grating strips. Once the grating strips are removed, the mask body can be cleaned and other processes can be performed, preventing damage to the off-axis illumination grating during mask pattern processing and cleaning.

[0067] The working principle of the detachable off-axis illumination photolithography mask prepared by the present invention is described in detail below:

[0068] Figure 3 is a schematic diagram of the working principle of a detachable off-axis illumination lithography mask. After the incident light passes through the off-axis illumination grating, it is deflected due to light diffraction. The angle of deflection is determined by the diffraction formula of light, namely: p(n2sinβ m -n1sinα)=mλ; m=0, ±1, ±2,…

[0069] Where α and β are the incident and diffraction angles of light, respectively; m is the diffraction order; p is the grating period; n1 is the refractive index of air; and n2 is the refractive index of the mask substrate. In practice, first-order diffraction is used as the illumination light for the mask pattern. By selecting the period of the off-axis illumination grating, the desired light deflection angle can be achieved. The transmission efficiency of the off-axis illumination grating is optimized by optimizing the duty cycle and the refractive index of the off-axis illumination grating material.

[0070] By arranging off-axis illumination gratings in an orthogonal pattern on the back of the mask, the mask pattern can be illuminated from four directions. Figure 4 shows a schematic diagram of the distribution of off-axis illumination gratings for quadrupole illumination on the back of the mask body. Of course, other distribution patterns of off-axis illumination gratings can be used as required.

[0071] The present disclosure provides an off-axis illumination grating and a preparation method thereof, and a detachable off-axis illumination photolithography mask, which solve the problems of grating damage easily caused by the processing and cleaning process of conventional integrated off-axis illumination photolithography masks, as well as high processing costs and low processing efficiency, and realizes the rapid and low-cost processing and reuse of off-axis illumination gratings and the overall mask.

[0072] The present disclosure is further described below through specific embodiments. The off-axis illumination grating, its preparation method, and the detachable off-axis illumination photolithography mask are specifically described in the following examples. However, the following examples are merely illustrative of the present disclosure and are not intended to limit the scope of the present disclosure.

[0073] The basic technical solution of this embodiment includes: 1) using a thin sheet made of the same material as the substrate of the mask body, and using nanoimprint technology combined with reactive ion beam etching to design an off-axis illumination grating; 2) then sticking the processed off-axis illumination grating to the back of the mask body according to a specific position using a refractive index matching liquid. After passing through the off-axis illumination grating, light is refracted at a certain angle onto the mask pattern on the front of the mask body to achieve photolithography exposure; 3) during the process of processing the mask pattern and cleaning the mask body, the off-axis illumination grating on the back of the mask body is removed to prevent damage.

[0074] This embodiment uses nanoimprint technology to prepare off-axis illumination gratings and detachable off-axis illumination photolithography masks, as shown in Figures 1 and 2, including the following steps:

[0075] Step 1: Use electron beam lithography combined with conventional reactive ion beam etching to process a grating master 1 having a grating pattern. The etching depth of the grating master 1 is 80-100 nm. This is equivalent to the above step S1.

[0076] Step 2: Use the grating master 1 to create a UV-transparent flexible working template 2. Prior to embossing, a layer of monomolecular anti-sticking material is deposited on the patterned surface of the working template 2 to facilitate separation of the working template 2 from the grating master 1 after embossing. This is equivalent to step S2 above.

[0077] Step 3: Prepare a transparent substrate 3 as a carrier substrate for off-axis illumination grating processing, such as a quartz plate or a sapphire plate. Clean the substrate 3 using conventional semiconductor cleaning methods to remove surface contaminants. Coat a grating material layer 4 on the surface of the substrate 3, and then coat a transfer layer 5 with a thickness of 15 to 20 nm. Use a glue spreader to spin-coat a layer of embossed adhesive layer 6 with a thickness of 80 to 100 nm on the surface of the transfer layer 5; use the prepared working template 2 to emboss the grating pattern onto the embossed adhesive layer 6, and cure the embossed adhesive layer 6 with ultraviolet light; and use a stepping method to emboss multiple gratings on the substrate. This is equivalent to the above-mentioned step S3.

[0078] Step 4: Separate the working template 2 from the substrate 3 to obtain a solidified embossed resin grating, which serves as a barrier layer for subsequent etching.

[0079] Step 5: Oxygen plasma is used to etch the remaining imprinted adhesive layer 6 after imprinting. Ion beam etching is then used to transfer the grating pattern on the imprinted adhesive layer 6 to the transfer layer 5. Reactive ion beam etching is then used to further transfer the grating pattern to the grating material layer 4, resulting in an off-axis illumination grating. Finally, a chemical solution is used to remove the remaining transfer layer 5 from the surface of the off-axis illumination grating. This is equivalent to step S4 described above.

[0080] Step 6: Grating pasting: Cut the off-axis illumination grating on the substrate 3 to obtain grating strips of the target size; drip refractive index matching liquid on the substrate 3 of the grating strip, and fix the grating strip to the other side of the mask body opposite to the mask absorption layer through the grating position fixing mold; press the grating strip to form a uniform film layer of the refractive index matching liquid, and apply UV curing glue along the four sides of the grating strip; cure the UV curing glue, remove the grating position fixing mold, and fix the off-axis illumination grating to the mask body.

[0081] Step 7: Grating separation: Apply de-curing agent to the UV curing adhesive and release the off-axis illumination grating from the mask body.

[0082] According to the above steps 1 to 7, a specific embodiment is provided below.

[0083] Example 1:

[0084] This embodiment uses nanoimprint technology to prepare an off-axis illumination photomask for 365nm near-field super-resolution lithography. The implementation steps are as follows:

[0085] Step 1-1: A grating master 1 was fabricated on a 1 mm thick, 50 mm diameter silicon wafer using electron beam lithography combined with reactive ion etching (RIE). The period p of the grating master 1 was 240 nm, and the etching depth was 90 nm. The electron beam lithography was performed at an accelerating voltage of 125 kV and a current of 5 nA. During the RIE process, the ICP power used was 1000 W, the RF power was 10 W, and the reaction gases used were SF6 and CHF3. Figures 7 and 8 show scanning electron microscope images of the top surface and cross section of the grating master produced according to this embodiment.

[0086] Step 1-2: Using the grating master 1, a UV-transparent working template 2 is embossed. The working template 2 is made of PET. Before embossing, a layer of monomolecular anti-sticking material is grown on the patterned surface of the grating master 1 by evaporation.

[0087] Steps 1-3: Prepare a circular transparent sapphire substrate 3. The thickness of the sapphire substrate 3 is 0.5 mm and the diameter is 100 mm. Clean the sapphire substrate 3 using conventional semiconductor cleaning methods to remove surface contaminants. Plate a 130 nm layer of TiO2 on the surface of the sapphire substrate 3, and then plate a 20 nm thick chromium layer. Use a glue spreader to spin-coat a layer of UV imprint glue on the surface of the chromium layer with a thickness of 90 nm; use the prepared working template 2 to imprint the grating pattern onto the imprint glue, and cure the imprint glue with UV light; use a stepping method to imprint multiple grating patterns on the sapphire substrate 3.

[0088] Step 1-4: Separate the working mold 2 and substrate 3 to obtain a solidified imprinted grating. The grating pattern distribution is shown in Figure 9.

[0089] Steps 1-5: Oxygen plasma is used to etch away any remaining imprint glue. Ion beam etching and reactive ion beam etching are then used to transfer the grating pattern to the chromium and TiO2 layers, respectively. Finally, a chemical solution is used to remove any remaining Cr from the surface, forming the TiO2 grating. Figure 10 shows a scanning electron microscope image of the etched TiO2 grating.

[0090] Steps 1-6: TiO2 grating attachment process: The TiO2 grating is laser-cut from the sapphire sheet, forming TiO2 grating strips on the sapphire substrate. Figure 6 shows a picture of the resulting TiO2 grating strips. After cutting, the resulting TiO2 grating strips are attached to the back of the sapphire-based mask body using a refractive index matching solution. UV-curable adhesive is then used to secure the TiO2 grating strips from all sides. The position-fixing fixture is then removed, forming the TiO2 off-axis illumination grating on the back of the mask body. Figure 5 shows the grating position-fixing mold used to attach the TiO2 grating strips.

[0091] In order to verify the illumination effect of the off-axis mask grating, the light transmission efficiency of the detachable off-axis illumination photolithography mask of this embodiment and the conventional integrated off-axis illumination photolithography mask were calculated.

[0092] In the calculation, the period of the TiO2 off-axis illumination grating is 240nm, the width is 128nm, and the height is 130nm; the refractive index of the refractive index matching liquid is 1.791@365nm, and the thickness is 200nm; the base thickness of the mask body is 6.35mm, the thickness of the sapphire substrate used for the TiO2 off-axis illumination grating is 0.5mm, the wavelength of the incident light is 365nm, and the incident angle is 10°.

[0093] Calculations using a rigorous coupled-wave algorithm show that the light transmittance efficiency of the separable off-axis illumination lithography mask of this embodiment is 0.5224, while the light transmittance of a conventional integrated off-axis illumination lithography mask is 0.5246. Figures 11 and 12 are schematic diagrams showing the transmittance calculations for the separable off-axis illumination lithography mask of this embodiment and a conventional integrated off-axis illumination lithography mask, respectively. This indicates that the light transmittance of the separable off-axis illumination lithography mask of this embodiment and a conventional integrated off-axis illumination lithography mask are comparable.

[0094] The off-axis illumination grating disclosed herein can be separated from the mask body. When photolithography exposure is required, the off-axis illumination grating is attached to the back of the mask body, achieving the same lighting effect as a conventional integrated off-axis illumination lithography mask. During mask body processing and cleaning, the off-axis illumination grating can be separated from the mask body to prevent damage to the off-axis illumination grating during the mask body processing and cleaning processes. The application of nanoimprint technology to off-axis illumination grating processing improves processing efficiency and reduces processing costs compared to conventional electron beam lithography processing. In terms of light transmission, the detachable off-axis illumination lithography mask disclosed herein has a comparable lighting effect on the mask pattern as a conventional integrated off-axis illumination lithography mask, and can replace existing integrated off-axis illumination lithography masks.

[0095] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the scope of protection of the present disclosure. Industrial Applicability

[0096] The present invention provides an off-axis illumination grating and a preparation method thereof, and a detachable off-axis illumination photolithography mask. The preparation method comprises: S1, preparing a grating master (1) having a grating pattern by electron beam lithography and reactive ion beam etching; S2, copying the grating pattern on the grating master (1) to the surface of a working template (2) by a first nanoimprinting to form a working template having a grating pattern; S3, sequentially preparing a grating material layer (4), a transfer layer (5), and an imprinting adhesive layer (6) on a substrate (3), copying the grating pattern of the working template (2) obtained in S2 to the imprinting adhesive layer (6) by a second nanoimprinting, and curing the grating pattern; S4, sequentially etching and transferring the grating pattern on the imprinting adhesive layer (6) to the transfer layer (5) and the grating material layer (4), removing the remaining transfer layer (5), and obtaining the off-axis illumination grating. The off-axis illumination grating disclosed in the present invention is detachable from the mask and can be reused.

[0097] Furthermore, it will be appreciated that the off-axis illumination grating, its fabrication method, and the detachable off-axis illumination photolithography mask and its use method disclosed herein are reproducible and can be used in a variety of applications. For example, the off-axis illumination grating, its fabrication method, and the detachable off-axis illumination photolithography mask and its use method disclosed herein can be used in the field of semiconductor device manufacturing technology.

Claims

1. A method for preparing an off-axis illumination grating, characterized in that, it includes: S1. Prepare a grating master (1) with a grating pattern by electron beam lithography and reactive ion beam etching; S2. Copy the grating pattern on the grating master (1) to the surface of a working template (2) through first nanoimprinting to form a working template (2) with a grating pattern; S3. Sequentially prepare a grating material layer (4), a transfer layer (5) and an imprinting glue layer (6) on a substrate (3). Copy the grating pattern of the working template (2) obtained in S2 to the imprinting glue layer (6) through second nanoimprinting and cure it; S4. Transfer the grating pattern on the imprinting glue layer (6) to the transfer layer (5) and the grating material layer (4) by etching in sequence, and remove the residual transfer layer (5) to obtain an off-axis illumination grating.

2. The method for preparing an off-axis illumination grating according to claim 1, characterized in that, in S1, the acceleration voltage of the electron beam lithography is 50 - 125 kV and the current is 3 - 6 nA; The inductively coupled plasma power of the reactive ion beam etching is 800 - 1500 W, the radio frequency power is 8 - 15 W, and the reactive gas is SF 6 and CHF 3 ; the grating etching depth of the grating master (1) is 80 - 100 nm and the grating period is 200 - 250 nm.

3. The method for preparing an off-axis illumination grating according to claim 1, characterized in that, in S2, the working template (2) is made of a flexible material transparent to ultraviolet light; before the first nanoimprinting, deposit a layer of anti-sticking material on the surface of the grating master (1), and the thickness of the anti-sticking material is the thickness of a single molecular layer.

4. The method for preparing an off-axis illumination grating according to claim 1, characterized in that, in S3, the material of the substrate (3) is quartz or sapphire; The material of the grating material layer (4) is TiO 2 , and the thickness is 100 - 150 nm; the material of the transfer layer (5) is any one of chromium, molybdenum, and aluminum, and the thickness is 15 - 20 nm; the material of the imprinting glue layer (6) is an ultraviolet curable glue, and the thickness is 80 - 100 nm.

5. The method for preparing an off-axis illumination grating according to claim 1, characterized in that, S3 further includes: Copy the grating pattern of the working template (2) obtained in S2 multiple times through second nanoimprinting to obtain multiple grating patterns on the imprinting glue layer (6); After S3, it further includes: removing the residual imprinting glue by oxygen plasma etching.

6. The method for preparing an off-axis illumination grating according to claim 1, characterized in that, S4 includes: Transfer the grating pattern on the imprinting glue layer (6) to the transfer layer (5) by ion beam etching; Transfer the grating pattern on the transfer layer (5) to the grating material layer (4) by reactive ion beam etching; Remove the residual transfer layer (5) by chemical liquid to obtain an off-axis illumination grating.

7. An off-axis illumination grating, characterized in that, the off-axis illumination grating is prepared by the method for preparing an off-axis illumination grating according to any one of claims 1 - 6.

8. A separable off-axis illumination lithography mask, characterized in that, it includes: A mask body, including a substrate and a mask absorption layer; The off-axis illumination grating is prepared by the method for preparing an off-axis illumination grating according to any one of claims 1 to 6, and is separably disposed on the other side of the mask body opposite to the mask absorption layer; wherein, the substrate (3) material of the off-axis illumination grating is the same as the substrate material of the mask body, and the substrate (3) of the off-axis illumination grating is pasted by a refractive index matching liquid and fixed on the substrate of the mask body by an ultraviolet curable adhesive to achieve off-axis illumination.

9. A method for using a separable off-axis illumination photolithography mask according to claim 8, characterized in that, comprising: dropping a refractive index matching liquid on the back of the off-axis illumination grating, and fixing the grating bars on a predetermined position on the other side of the mask body opposite to the mask absorption layer through a grating position fixing mold; pressing the off-axis illumination grating to form a uniform film layer of the refractive index matching liquid, and coating an ultraviolet curable adhesive along the periphery of the off-axis illumination grating; curing the ultraviolet curable adhesive, removing the grating position fixing mold, and fixing the off-axis illumination grating to the mask body.

10. The method for using a separable off-axis illumination photolithography mask according to claim 9, characterized in that, further comprising: coating a decuring agent on the ultraviolet curable adhesive to release the fixation between the off-axis illumination grating and the mask body.

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