Thin-film blank based on Fabry-Perot interference principle and its manufacturing method

Abstract

This invention discloses a thin photomask blank based on the Fabry-Perot interference principle and its manufacturing method, relating to the field of semiconductor technology. It includes a transparent substrate, a surface anti-reflection layer, a Fabry-Perot cavity, a first metal reflective layer, and a second metal reflective layer. The thin photomask blank of this invention has a simple structure. It utilizes the first and second metal reflective layers to form a Fabry-Perot cavity, thereby achieving thinning of the light-shielding film and ensuring that the contrast and precision of the produced photomask meet production standards. The manufacturing method of the thin photomask blank of this invention is simple, with a straightforward process flow. Only simple processes are required to manufacture the thin photomask blank, making it easy to operate and widely applicable on production lines for large-scale mass production.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a thin photomask blank based on the Fabryerian interference principle and its manufacturing method. Background Technology

[0002] In recent years, with the increasing integration of large-scale integrated circuits, the miniaturization of circuit patterns and wiring patterns, and the miniaturization of contact hole patterns for interlayer wiring to form cells, the requirements for microfabrication technology have become increasingly stringent. Therefore, in the field of photomask manufacturing technology, the requirements for fabricating photomasks for chip production have also become more refined, necessitating further development of techniques for accurate circuit patterns (masking patterns).

[0003] Traditional binary intensity masks (BIMs) on chrome-plated glass substrates are too thick to support the required minimum feature size, linearity, and via spacing. Typically, when forming the photomask pattern on a traditional chrome-plated glass substrate, miniaturizing the pattern without reducing the thickness of the corresponding photoresist film results in an increased aspect ratio (the ratio of photoresist film thickness to pattern width) for the photoresist used as the etching mask. Generally, the photomask pattern becomes more prone to degradation as the aspect ratio of the photoresist pattern increases; that is, the accuracy of the photoresist pattern transferred to the etching mask decreases. In extreme cases, parts of the pattern may detach or peel off, leading to defects. Therefore, when the photomask pattern becomes finer, the thickness of the photoresist film used as the etching mask must be reduced to avoid an undesirable high aspect ratio. However, when using a photoresist pattern as a mask and etching a light-shielding film to create the pattern, a photoresist layer that is too thin will be etched and unable to protect areas of the pattern that should not be etched. One way to solve this problem is to thin the light-shielding film so that patterning is completed while the photoresist film is still half its original thickness. However, thinning the light-shielding film will prevent it from blocking sufficient exposure, resulting in poor contrast in the produced photomask. Summary of the Invention

[0004] The purpose of this invention is to provide a thin photomask blank based on the Fabry-Perot interference principle and its manufacturing method, so as to improve the above-mentioned technical problems.

[0005] To address the issue that in existing technologies, when miniaturizing photomask patterns, the thickness of the photoresist film can easily lead to deterioration of the photomask pattern as the aspect ratio of the photoresist pattern increases, resulting in reduced accuracy of the photoresist pattern transfer onto the light-shielding film, this invention provides the following technical solution:

[0006] A thin photomask blank based on the Fabry-Perot interference principle includes a substrate for producing the photomask; the substrate includes a light-shielding film and a transparent substrate; the light-shielding film includes a surface anti-reflection layer, a back anti-reflection layer, a Fabry-Perot cavity, a first metal reflective layer and a second metal reflective layer;

[0007] The back anti-reflective layer is placed on top of the transparent substrate; the first metal reflective layer is placed on top of the back anti-reflective layer; the Fabry-Perot cavity is placed on top of the first metal reflective layer; the second metal reflective layer is placed on top of the Fabry-Perot cavity; and the surface anti-reflective layer is placed on top of the second metal reflective layer.

[0008] The Fabry-Perot cavity is obtained based on the Fabry-Perot interferometer. The inner surfaces of the two mirrors of the Fabry-Perot interferometer have high reflectivity. When light undergoes multiple reflections and interferences in the Fabry-Perot cavity, only light of a specific wavelength that meets specific resonance conditions can be enhanced in the Fabry-Perot cavity, while other wavelengths of light are weakened. This can improve the monochromaticity of light and precisely control the interference effect of light, thereby improving the clarity and contrast of the photomask pattern and realizing the miniaturization of the photomask pattern.

[0009] To address the problem of partial photomask pattern detachment or misalignment due to excessively thick photoresist films, thus preventing the acquisition of complete photomask patterns, the photomask cavity is further constructed using a semi-transparent film. The semi-transparent film is made of chromium, oxygen, and nitrogen, or molybdenum, silicon, oxygen, and nitrogen. The refractive index of the semi-transparent film is greater than 2.3, and its extinction coefficient is less than 1. Using chromium, oxygen, and nitrogen, or molybdenum, silicon, oxygen, and nitrogen, to fabricate the semi-transparent film reduces the thickness of the photomask cavity and simplifies its fabrication process. Because the refractive index of the semi-transparent film is greater than 2.3 and its extinction coefficient is less than 1, light absorption and scattering during exposure are reduced, allowing most light to be reflected or transmitted. This reduces the thickness of the photomask cavity, prevents an increase in the aspect ratio of the photomask pattern, effectively reduces pattern detachment or misalignment, improves pattern integrity, accuracy, and clarity, and reduces the loss of blank areas in the thin photomask during use.

[0010] Optical density is a factor affecting the contrast and sharpness of the photomask pattern. Reducing the thickness of the light-shielding layer can, to some extent, prevent the light-shielding film from blocking sufficient exposure, resulting in poor photomask contrast. Furthermore, the first and second metal reflective layers have the same structure and materials; the first metal reflective layer is made of molybdenum and silicon or chromium; when the first metal reflective layer is made of molybdenum and silicon, the molybdenum content is greater than or equal to 60%. Because molybdenum has high reflectivity, it can improve the reflectivity of the first metal reflective layer and enhance the optical interference effect of the Fabry-Perot cavity. The combination of molybdenum and silicon can improve light transmission characteristics, making it suitable for scenarios where the refractive index of the semi-transparent film is greater than 2.3 and the extinction coefficient is less than 1, helping to reduce light loss during photomask pattern transmission and improve light transmittance. Only when the molybdenum content is greater than or equal to 60% can the stability and durability of the first metal reflective layer be effectively increased, achieving an optical density of over 2.5 or reaching 3 for the thin photomask blank.

[0011] A method for manufacturing a thin photomask blank based on the Fabry-Perot interference principle, comprising:

[0012] S1. Clean the transparent substrate;

[0013] S2. Place the cleaned transparent substrate in a sputtering apparatus for sputtering to sequentially generate a back anti-reflection layer, a first metal reflective layer, a Fabry-Perot cavity, a second metal reflective layer, and a surface anti-reflection layer, thus obtaining the original thin photomask blank.

[0014] S3. The original thin-film photomask blank is heat-treated using a hot-plate annealing device to obtain a thin-film photomask blank. This manufacturing method can realize the thin-film photomask blank based on the Fabryerian interference principle.

[0015] Further, the cleaning of the transparent substrate includes:

[0016] S1-1. Irradiate the transparent substrate with ultrasound or ultraviolet light, and perform initial cleaning of the transparent substrate with ultrapure water or functional water. Since particles on the substrate can cause unclear photomask patterns during production, initial cleaning of the transparent substrate can remove particles on the transparent substrate or on the surface of the thin film formed on the substrate, ensuring the accuracy of the photomask pattern, improving the yield, and maintaining the long-term stability and optical performance of the thin photomask blank.

[0017] S1-2. The transparent substrate is cleaned a second time using a sulfur-free cleaning method to further ensure that the production requirements of the original thin photomask blank are met. This can avoid the presence of sulfides on the substrate, which would affect the propagation and reflection characteristics in the Fabry-Perot cavity.

[0018] Further, the step of placing the cleaned transparent substrate in a sputtering apparatus for sputtering sequentially generates a back anti-reflection layer, a first metal reflective layer, a Fabry-Perot cavity, a second metal reflective layer, and a surface anti-reflection layer to obtain the original thin-film photomask blank, including:

[0019] S2-1. Place the cleaned transparent substrate in a sputtering apparatus, set a first gas pressure and a first sputtering power, input a first gas atmosphere into the sputtering apparatus, and sputter the upper surface of the cleaned transparent substrate through a chromium target to generate the back anti-reflection layer and obtain a first mask.

[0020] S2-2. Set a second gas pressure and input the second gas atmosphere into the sputtering device. Sputter the upper surface of the first mask through a chromium target to generate the first metal reflective layer and obtain the second mask.

[0021] S2-3. Set a third gas pressure and input the third gas atmosphere into the sputtering device to sputter the upper surface of the second mask through a chromium target to generate the Fabry-Perot cavity and obtain the third mask;

[0022] S2-4. Set the fourth gas pressure and the second sputtering power, input the fourth gas atmosphere into the sputtering device, and sputter the upper surface of the third mask through the chromium target to generate the second metal reflective layer and obtain the fourth mask;

[0023] S2-5. Set the fifth gas pressure and input the fifth gas atmosphere into the sputtering device. Sputter the upper surface of the fourth mask through the chromium target to generate the surface anti-reflection layer and obtain the original thin photomask blank.

[0024] Furthermore, the first gas atmosphere and the fourth gas atmosphere are both argon; the second gas atmosphere, the third gas atmosphere, and the fifth gas atmosphere are all mixed gas atmospheres of argon, nitrogen, and oxygen, which meet the thickness requirements of the thin photomask blank, reduce the thickness of the thin photomask blank to a maximum of 80% of the thickness of the traditional photomask blank.

[0025] The beneficial effects of this invention are:

[0026] The thin photomask blank structure of the present invention is simple. It utilizes a first metal reflective layer and a second metal reflective layer to form a cavity, thereby achieving thinning of the light-shielding film and ensuring that the contrast and precision of the produced photomask meet production standards.

[0027] The method for fabricating the thin photomask blank of the present invention is simple and the process is simple. Only a simple process is required to fabricate the thin photomask blank and generate a substrate photomask sheet with an optical density of 2.5 or higher. The corresponding operation is low and can be widely used on the production line to achieve large-scale mass production. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the thin photomask blank structure in Embodiment 1 of the present invention; wherein, 10, transparent substrate; 1a, first metal reflective layer; 1b, second metal reflective layer; 2, Fabry-Perot cavity; 3a, back anti-reflection layer; 3b, surface anti-reflection layer;

[0030] Figure 2 This is a graph showing the light intensity of the exposure light source in the Fabry-Perot cavity in Embodiment 1 of the present invention.

[0031] Figure 3 This is a schematic diagram of the thin photomask blank structure in Embodiment 1 of the present invention; wherein, 10, transparent substrate; 1a, first metal reflective layer; 1b, second metal reflective layer; 2, Fabry-Perot cavity; 3b, surface anti-reflection layer;

[0032] Figure 4 This is a flowchart of the method for fabricating the thin photomask blank in Embodiment 1 of the present invention;

[0033] Figure 5 This is a reflectance curve of the thinned photomask blank in Embodiment 1 of the present invention;

[0034] Figure 6 This is an optical density curve of the blank thin photomask in Embodiment 1 of the present invention;

[0035] Figure 7 This is a schematic diagram of the thin photomask blank structure in Embodiment 2 of the present invention; wherein, 10, transparent substrate; 1a, first metal reflective layer; 2, Fabry-Perot cavity; 3b, surface anti-reflection layer;

[0036] Figure 8 This is a reflectance curve of the thinned photomask blank in Embodiment 2 of the present invention;

[0037] Figure 9 This is an optical density curve of the blank thin photomask in Embodiment 2 of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] Please see Figure 1 This embodiment provides a thin photomask blank based on the Fabry-Perot interference principle, which includes a substrate for producing the photomask; the substrate includes a light-shielding film and a transparent substrate 10; the light-shielding film includes a surface anti-reflection layer 3b, a back anti-reflection layer 3a, a Fabry-Perot cavity 2, a first metal reflective layer 1a and a second metal reflective layer 1b; wherein, the thickness of the light-shielding film is less than 75nm, that is, the total thickness of the surface anti-reflection layer 3b, the back anti-reflection layer 3a, the Fabry-Perot cavity 2, the first metal reflective layer 1a and the second metal reflective layer 1b is less than 75nm.

[0041] The back anti-reflective layer 3a is placed on top of the transparent substrate 10; the first metal reflective layer 1a is placed on top of the back anti-reflective layer 3a; the Fabry-Perot cavity 2 is placed on top of the first metal reflective layer 1a; the second metal reflective layer 1b is placed on top of the Fabry-Perot cavity 2; and the surface anti-reflective layer 3b is placed on top of the second metal reflective layer 1b. The surface reflectivity of the substrate is less than 20% at exposure wavelengths of 193nm and 248nm.

[0042] In this embodiment, the thickness of the back anti-reflection layer 3a is 8 nm, the thickness of the first metal reflective layer 1a is 20 nm, the thickness of the Fabry-Perot cavity 2 is 12 nm, the thickness of the second metal reflective layer 1b is 20 nm, and the thickness of the surface anti-reflection layer 3b is 10 nm.

[0043] The Fabry-Perot cavity 2 is a semi-transparent membrane. The material of the semi-transparent membrane is chromium, oxygen, and nitrogen, or molybdenum, silicon, oxygen, and nitrogen. The refractive index of the semi-transparent membrane is greater than 2.3, and the extinction coefficient is less than 1. Based on the Fabry-Perot interference principle, its thickness can achieve the required low transmittance over a wide range, thus reducing the manufacturing difficulty of the Fabry-Perot cavity 2. When both the refractive index and extinction coefficient of the semi-transparent membrane are satisfied, light can undergo multiple reflections and transmissions within the Fabry-Perot cavity 2, thereby reducing transmission and achieving an optical density greater than or equal to 3. This effectively solves the problem of pattern detachment or positional shift, improving the integrity, accuracy, and contrast of the pattern.

[0044] The refractive index of the Fabry-Perot cavity 2 is greater than 1.5 and less than or equal to 3, and the corresponding extinction index is 0.3 or less than 1.5.

[0045] In optics, a Fabry-Perot interferometer is a multi-beam interferometer composed of two parallel mirrors, often referred to as a Fabry-Perot resonant cavity or FP cavity, specifically the Fabry-Perot cavity 2 of this invention. Both inner surfaces of the two mirrors have high reflectivity, allowing light to undergo multiple reflections and interferences within the Fabry-Perot cavity 2. The significant variation in transmittance of the Fabry-Perot cavity 2 with wavelength is due to the interference of multiple reflected light between the first metal reflective layer 1a and the second metal reflective layer 1b. When the transmitted light is in phase, the Fabry-Perot cavity 2 exhibits constructive interference, corresponding to the peak transmittance of the etalon; conversely, when the transmitted light is out of phase, it corresponds to the minimum transmittance.

[0046] Assume the reflectivities of the first metallic reflective layer 1a and the second metallic reflective layer 1b are R1 and R2, respectively, with a corresponding spacing of L, and corresponding electric field reflectivities of r1 and r2, respectively, and corresponding electric field penetration forces of t1 and t2, respectively. When light undergoes one reflection within the Fabry-Perot cavity 2, the corresponding phase difference is 2πL / λ. Using a geometric series derivation, we obtain:

[0047]

[0048] Where T represents the penetration rate of cavity 2. represents the phase difference of light, and sin represents the sine function.

[0049] As can be seen from the above penetration formula, only when When (N is a positive integer), such as Figure 2 As shown, the transmittance within the Fabry-Perot cavity 2 reaches its highest value, approaching 1. When the values ​​are other, the transmittance in the Fabry-Perot cavity 2 is less than the highest value, and the lowest value can be infinitely close to 0. Therefore, the film thickness of the Fabry-Perot cavity 2 can achieve the required low penetration within a wide range. The light intensity curve corresponding to the Fabry-Perot cavity 2 shows a highly flat feature, which further proves that the Fabry-Perot interference principle can improve the applicability of the thin photomask blank. The thin photomask blank (photomask substrate) of the present invention can be adapted to a variety of exposure light sources, increasing the application scenarios of the thin photomask blank.

[0050] Because the incident light forms a standing wave in the Fabry-Perot cavity 2, the light eventually dissipates within the Fabry-Perot cavity 2, and very little light penetrates the film layer. It is absorbed by the material with a high extinction number, thereby enabling the production of a thin photomask blank (photomask substrate) with a thickness of less than 80% of that of a conventional chromium-plated binary substrate photomask. Its optical density can be greater than 2.5 at wavelengths of 248nm or 193nm.

[0051] The anti-reflective layer of the thin photomask blank, namely the surface anti-reflective layer 3b or the back anti-reflective layer 3a, can be formed by fixing the proportion of reactant gases or gradually decreasing or gradually increasing the proportion of reactant gases.

[0052] The first metal reflective layer 1a and the second metal reflective layer 1b have the same structure and materials; the first metal reflective layer 1a is made of molybdenum and silicon or chromium; when the first metal reflective layer 1a is made of molybdenum and silicon, the molybdenum content is greater than or equal to 60%. The film thickness of both the first metal reflective layer 1a and the second metal reflective layer 1b is less than 12 nm.

[0053] When the first metal reflective layer 1a is made of molybdenum and silicon, with a molybdenum content of 60% or more, the high reflectivity of molybdenum and the excellent light transmission properties of the fused material of molybdenum and silicon make it suitable for the Fabry-Perot cavity 2 with high refractive index (>2.3) and low extinction coefficient (<1), thereby improving light transmittance. When the first metal reflective layer 1a is made of chromium, the reflectivity and optical stability of the thin photomask blank of the present invention can be improved, the light absorption performance can be enhanced, and thus the quality of the photomask pattern can be improved.

[0054] The surface anti-reflective layer 3b has a refractive index greater than 1.5 and less than or equal to 3, a corresponding extinction coefficient of 0.3 or less than 1.5, and a corresponding film thickness of less than 20 nm. The surface anti-reflective layer 3b has a surface reflectivity less than or equal to a predetermined value relative to the exposure light source, and the metal composition of the first metal reflective layer 1a and the second metal reflective layer 1b is greater than that of the surface anti-reflective layer 3b.

[0055] In addition, such as Figure 3 As shown, the thin photomask blank may not include the back anti-reflective layer 3a, and only the surface anti-reflective layer 3b is needed to achieve the same invention objective.

[0056] like Figure 4 As shown, a method for manufacturing a thin photomask blank based on the Fabry-Perot interference principle includes:

[0057] S1. Clean the transparent substrate 10; the length, width and thickness of the transparent substrate 10 are 6 inches, 6 inches and 0.25 inches respectively.

[0058] The cleaning of the transparent substrate 10 includes:

[0059] S1-1. The transparent substrate 10 is irradiated with ultrasound or ultraviolet light, and the transparent substrate 10 is initially cleaned with ultrapure water or functional water. Since there are particles on the surface of the transparent substrate 10 or the film formed on the transparent substrate 10, the particles on the transparent substrate 10 can be removed by using ultrapure water or functional water while the transparent substrate 10 is irradiated with ultrasound or ultraviolet light. Alternatively, one or two types of ultrapure water and functional water can be used for removal. The ultrapure water is ultrapure water containing surfactants, and the functional water is ultrapure water containing multiple gases such as ozone and hydrogen.

[0060] S1-2. A sulfur-free cleaning method is used to perform a secondary cleaning of the transparent substrate 10. The transparent substrate 10 also has defects caused by organic compounds, so a mixed solution of sulfuric acid and hydrogen peroxide is generally used for cleaning. Because the surface of the transparent substrate 10 is acidic after the initial cleaning, it needs to be neutralized by rinsing with alkaline ammonia (ammonia plus hydrogen peroxide or a mixed solution). However, alkaline ammonia cannot completely remove sulfate ions from the substrate surface, leaving residual sulfate ions that affect the formed light-shielding film, resulting in poor adhesion, pattern linearity, and resolution. Furthermore, when ions including sulfuric acid and ammonium salts are used to clean the photomask, if the thin photomask blank is exposed to short-wavelength ultraviolet light, such as ultraviolet light with wavelengths of 248 or 193 nm, it may generate haze pollution. Therefore, a sulfur-free cleaning method is used to perform a secondary cleaning of the transparent substrate 10.

[0061] S2. The cleaned transparent substrate 10 is placed in a sputtering device for sputtering, and the back anti-reflection layer 3a, the first metal reflective layer 1a, the Fabry-Perot cavity 2, the second metal reflective layer 1b, and the surface anti-reflection layer 3b are generated in sequence to obtain the original thin photomask blank.

[0062] The process involves placing the cleaned transparent substrate 10 into a sputtering apparatus for sputtering, sequentially generating a back anti-reflection layer 3a, a first metal reflective layer 1a, a far-field cavity 2, a second metal reflective layer 1b, and a surface anti-reflection layer 3b, to obtain the original thin photomask blank, including:

[0063] S2-1. Place the cleaned transparent substrate 10 in a sputtering apparatus, set the first gas pressure and the first sputtering power, input the first gas atmosphere into the sputtering apparatus, and sputter the upper surface of the cleaned transparent substrate 10 through a chromium target to generate a back anti-reflection layer 3a with a thickness of 8nm, thereby obtaining the first mask.

[0064] The first gas pressure is 0.05 Pa, the first sputtering power is 1.5 KW, and the first gas atmosphere is argon; wherein the flow rate of argon is 50 sccm.

[0065] S2-2. Set the second gas pressure and input the second gas atmosphere into the sputtering device. Sputter the upper surface of the first mask through the chromium target to generate a first metal reflective layer 1a with a thickness of 20nm, and obtain the second mask.

[0066] The second gas pressure is 0.05 Pa, and the second gas atmosphere is a mixture of argon, nitrogen and oxygen; wherein the flow rate of argon is 10 sccm, the flow rate of nitrogen is 31 sccm, and the flow rate of oxygen is 5 sccm.

[0067] S2-3. Set the third gas pressure and input the third gas atmosphere into the sputtering device. Sputter the upper surface of the second mask through the chromium target to generate a Fabry-Perot cavity 2 with a thickness of 12nm, and obtain the third mask.

[0068] The third gas pressure is 0.05 Pa, and the third gas atmosphere is a mixture of argon, nitrogen, and oxygen; wherein the flow rate of argon is 10 sccm, the flow rate of nitrogen is 31 sccm, and the flow rate of oxygen is 5 sccm.

[0069] S2-4. Set the fourth gas pressure and the second sputtering power, input the fourth gas atmosphere into the sputtering device, and sputter the upper surface of the third mask through the chromium target to generate a second metal reflective layer 1b with a thickness of 20nm, thus obtaining the fourth mask.

[0070] The fourth gas pressure is 0.05 Pa, the second sputtering power is 1.5 KW, and the fourth gas atmosphere is argon; wherein the flow rate of argon is 50 sccm.

[0071] S2-5. Set the fifth gas pressure and input the fifth gas atmosphere into the sputtering device. Sputter the upper surface of the fourth mask through the chromium target to generate a surface anti-reflection layer 3b with a thickness of 10nm, and obtain the original thin photomask blank.

[0072] The fifth gas pressure is 0.05 Pa, and the fifth gas atmosphere is a mixture of argon, nitrogen, and oxygen; wherein the flow rate of argon is 10 sccm, the flow rate of nitrogen is 31 sccm, and the flow rate of oxygen is 5 sccm.

[0073] S3. The original thin-film blank photomask is heat-treated at 200℃ for 10 minutes using a hot plate annealing device to obtain the thin-film blank photomask.

[0074] In the embodiment, due to the reduced film thickness of the thin photomask blank (photomask substrate), the amount of bending change within 142 mm square of the central part of the surface of the corresponding transparent substrate 10 is less than 0.2 μm in absolute value.

[0075] like Figure 5 and Figure 6 As shown, when the wavelength of the incident light is 193nm, the reflectivity of the photomask substrate in this embodiment is less than 20%, and the optical density is greater than 3, making it suitable for fabricating ArF photomask substrates. Figure 5 and Figure 6 In this context, R represents the reflectivity of the photomask substrate, and OD represents the optical density of the photomask substrate.

[0076] In summary, the thin photomask blank of the present invention has a simple structure. It utilizes a cavity 2 formed by the first metal reflective layer 1a and the second metal reflective layer 1b to achieve thinning of the light-shielding film, supporting the minimum feature size, linearity, and via spacing requirements of the substrate photomask. The fabrication method of the thin photomask blank of the present invention is simple, with a straightforward process flow. Only simple processes are required to fabricate the thin photomask blank, generating a substrate photomask with an optical density of 3 or higher. The corresponding operation difficulty is low, allowing for widespread application on production lines and enabling large-scale mass production.

[0077] Example 2

[0078] like Figure 7 As shown, this embodiment provides a thin photomask blank based on the Fabry-Perot interference principle, which includes a substrate for producing the photomask; the substrate includes a light-shielding film and a transparent substrate 10; the light-shielding film includes a surface anti-reflection layer 3b, a Fabry-Perot cavity 2, and a first metal reflective layer 1a.

[0079] The first metal reflective layer 1a is placed on top of the transparent substrate 10; the Fabry-Perot cavity 2 is placed on top of the first metal reflective layer 1a; the Fabry-Perot cavity 2 is placed on top of the first metal reflective layer 1a; and the surface anti-reflective layer 3b is placed on top of the Fabry-Perot cavity 2.

[0080] In this embodiment, the thickness of the first metal reflective layer 1a is 32 nm, the thickness of the Fabry-Perot cavity 2 is 12 nm, and the thickness of the surface anti-reflective layer 3b is 40 nm. The remaining settings of the thin photomask blank and its surface anti-reflective layer 3b, Fabry-Perot cavity 2, and first metal reflective layer 1a are the same as those in Embodiment 1.

[0081] A method for manufacturing a thin photomask blank based on the Fabry-Perot interference principle, comprising:

[0082] A1. Clean the transparent substrate 10; the length, width and thickness of the transparent substrate 10 are 6 inches, 6 inches and 0.25 inches respectively.

[0083] The cleaning of the transparent substrate 10 includes:

[0084] A1-1. The transparent substrate 10 is irradiated with ultrasound or ultraviolet light, and then initially cleaned with ultrapure water or functional water. Since particles exist on the surface of the transparent substrate 10 or the thin film formed on it, these particles can be removed using ultrapure water or functional water while the transparent substrate 10 is irradiated with ultrasound or ultraviolet light. Alternatively, one or two types of ultrapure water and functional water can be used for removal. The ultrapure water contains surfactants, and the functional water contains ozone gas, hydrogen gas, and other gases.

[0085] A1-2. A sulfur-free cleaning method is used to perform a secondary cleaning of the transparent substrate 10. The transparent substrate 10 also has defects caused by organic compounds, so a mixed solution of sulfuric acid and hydrogen peroxide is generally selected for cleaning. Because the surface of the transparent substrate 10 is acidic after the initial cleaning, it needs to be neutralized by rinsing with alkaline ammonia (ammonia plus hydrogen peroxide or a mixed solution). However, alkaline ammonia cannot completely remove sulfate ions from the substrate surface, leaving sulfate ions on the surface, which affects the formation of the light-shielding film, resulting in poor adhesion, pattern linearity, and resolution. Furthermore, when ions including sulfuric acid and ammonium salts are used to clean the photomask, if the thin photomask blank is exposed to short-wavelength ultraviolet light, such as ultraviolet light with wavelengths of 248 or 193 nm, it may generate haze pollution. Therefore, a sulfur-free cleaning method is used to perform a secondary cleaning of the transparent substrate 10.

[0086] A2. The cleaned transparent substrate 10 is placed in a sputtering device for sputtering, and the first metal reflective layer 1a, the Fabry-Perot cavity 2, and the surface anti-reflection layer 3b are generated in sequence to obtain the original thin photomask blank.

[0087] The process involves placing the cleaned transparent substrate 10 into a sputtering apparatus for sputtering, sequentially generating a first metal reflective layer 1a, a far-field cavity 2, and a surface anti-reflective layer 3b, to obtain the original thin photomask blank, including:

[0088] A2-1. Place the cleaned transparent substrate 10 in a sputtering apparatus, set the sixth gas pressure and the third sputtering power, input the sixth gas atmosphere into the sputtering apparatus, and sputter the upper surface of the cleaned transparent substrate 10 through a chromium target to generate a first metal reflective layer 1a with a thickness of 32nm, thus obtaining the fifth mask.

[0089] The sixth gas pressure is 0.05 Pa, the sixth gas atmosphere is a mixture of argon, nitrogen and oxygen, and the third sputtering power is 1.5 kW. The argon flow rate is 10 sccm, the nitrogen flow rate gradually decreases from 31 sccm to 0 sccm during film formation as the thickness of the first metal reflective layer 1a increases, and the oxygen flow rate is 5 sccm. The thin film corresponding to the first metal reflective layer 1a also has the functions of the back anti-reflection layer 3a and the first metal reflective layer 1a in Example 1 because the nitrogen flow rate gradually decreases from 31 sccm to 0 sccm during film formation as the thickness increases.

[0090] A2-2. Set the seventh gas pressure and the fourth sputtering power, input the seventh gas atmosphere into the sputtering device, and sputter the upper surface of the fifth mask through the target material made of molybdenum and silicon to generate a Fabry-Perot cavity 2 with a thickness of 12nm, thereby obtaining the sixth mask; the molar ratio of molybdenum to silicon in the target material made of molybdenum and silicon is 10:90.

[0091] The seventh gas pressure is 0.05 Pa, the seventh gas atmosphere is a mixture of argon, nitrogen and oxygen, and the fourth sputtering power is 1.5 KW; wherein the flow rate of argon is 10 sccm, the flow rate of nitrogen is 31 sccm, and the flow rate of oxygen is 5 sccm; wherein, in this embodiment, the far-field cavity 2 has a transmittance of 20% below a wavelength of 248 nm.

[0092] A2-3. Set the eighth gas pressure and the fifth sputtering power, input the eighth gas atmosphere into the sputtering device, and sputter the upper surface of the sixth mask through the chromium target to generate a surface anti-reflection layer 3b with a thickness of 40nm, thus obtaining the original thin photomask blank.

[0093] The eighth gas pressure is 0.05 Pa, the eighth gas atmosphere is a mixture of argon, nitrogen and oxygen, and the fifth sputtering power is 1.5 kW. The argon flow rate is 10 sccm, the nitrogen flow rate gradually increases from 0 sccm to 31 sccm during film formation as the thickness of the surface anti-reflection layer 3b increases, and the oxygen flow rate is 5 sccm. The thin film corresponding to the surface anti-reflection layer 3b also has the functions of the surface anti-reflection layer 3b and the second metal reflective layer 1b in Example 1 because the nitrogen flow rate gradually increases from 0 sccm to 31 sccm during film formation as the thickness increases.

[0094] A3. The original thin-film blank photomask was heat-treated at 200℃ for 10 minutes using a hot plate annealing device to obtain the thin-film blank photomask.

[0095] like Figure 8 and Figure 9 As shown, when the wavelength of the incident light is 193nm or 248nm, the reflectivity of the photomask substrate in this embodiment is less than 20%, and the optical density is greater than 3, making it suitable for fabricating ArF and KrF photomask substrates. Figure 8 and Figure 9 In this context, R represents the reflectivity of the photomask substrate, and OD represents the optical density of the photomask substrate.

[0096] In summary, the thin photomask blank of the present invention has a simple structure. By controlling the content of the gas atmosphere in the sputtering device, a surface anti-reflection layer 3b, a far-field cavity 2, and a first metal reflective layer 1a are formed, which can achieve thinning of the light-shielding film, reduce process steps, and further increase the yield of thin photomask blanks. The fabrication method of the thin photomask blank of the present invention is simple, requiring only simple processes to produce a substrate photomask sheet with an optical density of 3 or higher. The corresponding operation difficulty is low, enabling large-scale mass production.

[0097] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A thin photomask blank based on the Fabryerian interference principle, characterized in that, The invention includes a substrate for producing a photomask; the substrate includes a light-shielding film and a transparent substrate; the light-shielding film includes a surface anti-reflection layer, a back anti-reflection layer, a Fabry-Perot cavity, a first metal reflective layer and a second metal reflective layer; the total film thickness of the surface anti-reflection layer, the back anti-reflection layer, the Fabry-Perot cavity, the first metal reflective layer and the second metal reflective layer is less than 75 nm. The back anti-reflective layer is placed on top of the transparent substrate; the first metal reflective layer is placed on top of the back anti-reflective layer; the Fabry-Perot cavity is placed on top of the first metal reflective layer; the second metal reflective layer is placed on top of the Fabry-Perot cavity; and the surface anti-reflective layer is placed on top of the second metal reflective layer. The material of the first metal reflective layer is chromium; The method-paste cavity is a semi-permeable membrane; the material of the semi-permeable membrane is chromium, oxygen and nitrogen or molybdenum, silicon, oxygen and nitrogen, the refractive index of the semi-permeable membrane is greater than 2.3, and the extinction coefficient of the semi-permeable membrane is less than 1; When the wavelength of the incident light is 193nm or 248nm, the optical density of the blank of the thin photomask is greater than 2.

5.

2. The thin photomask blank based on the Fabryerian interference principle according to claim 1, characterized in that, The first metal reflective layer and the second metal reflective layer have the same structure and material.

3. A method for manufacturing a thin photomask blank based on the Fabryerian interference principle, used to realize the thin photomask blank based on the Fabryerian interference principle as described in any one of claims 1 to 2, characterized in that, include: S1. Clean the transparent substrate; S2. Place the cleaned transparent substrate in a sputtering apparatus for sputtering to sequentially generate a back anti-reflection layer, a first metal reflective layer, a Fabry-Perot cavity, a second metal reflective layer, and a surface anti-reflection layer, thus obtaining the original thin photomask blank. S3. The original thin-film blank photomask is heat-treated using a hot plate annealing device to obtain a thin-film blank photomask.

4. The method for manufacturing a thin photomask blank based on the Fabryerian interference principle according to claim 3, characterized in that, The cleaning of the transparent substrate includes: S1-1. Irradiate the transparent substrate with ultrasonic waves or ultraviolet light, and perform initial cleaning of the transparent substrate with ultrapure water or functional water. S1-2. The transparent substrate is cleaned a second time using a sulfur-free cleaning method to obtain the cleaned transparent substrate.

5. The method for manufacturing a thin photomask blank based on the Fabryerian interference principle according to claim 3, characterized in that, The process involves placing the cleaned transparent substrate in a sputtering apparatus for sputtering, sequentially generating a back anti-reflective layer, a first metal reflective layer, a Fabry-Perot cavity, a second metal reflective layer, and a surface anti-reflective layer to obtain the original thin photomask blank, including: S2-1. Place the cleaned transparent substrate in a sputtering apparatus, set a first gas pressure and a first sputtering power, input a first gas atmosphere into the sputtering apparatus, and sputter the upper surface of the cleaned transparent substrate through a chromium target to generate the back anti-reflection layer and obtain a first mask. S2-2. Set a second gas pressure and input the second gas atmosphere into the sputtering device. Sputter the upper surface of the first mask through a chromium target to generate the first metal reflective layer and obtain the second mask. S2-3. Set a third gas pressure and input the third gas atmosphere into the sputtering device to sputter the upper surface of the second mask through a chromium target to generate the Fabry-Perot cavity and obtain the third mask; S2-4. Set the fourth gas pressure and the second sputtering power, input the fourth gas atmosphere into the sputtering device, and sputter the upper surface of the third mask through the chromium target to generate the second metal reflective layer and obtain the fourth mask; S2-5. Set the fifth gas pressure and input the fifth gas atmosphere into the sputtering device. Sputter the upper surface of the fourth mask through the chromium target to generate the surface anti-reflection layer and obtain the original thin photomask blank.

6. The method for manufacturing a thin photomask blank based on the Fabryerian interference principle according to claim 5, characterized in that, The first gas atmosphere and the fourth gas atmosphere are both argon; the second gas atmosphere, the third gas atmosphere, and the fifth gas atmosphere are all mixed gas atmospheres of argon, nitrogen, and oxygen.

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