Thin film absorber for extreme ultraviolet light and preparation method thereof

Abstract

The invention discloses a thin film absorber for extreme ultraviolet light and a preparation method of the thin film absorber, and belongs to the technical field of extreme ultraviolet optical absorption elements. The thin film absorber comprises an absorption layer, a phase shift layer and an anti-reflection layer which are sequentially arranged on the extreme ultraviolet reflector or a protective layer of the extreme ultraviolet reflector; wherein the absorption layer is made of AgAl alloy, the thickness of the absorption layer is 18-22 nm, and the atomic percentage of Ag is 90%-98%; the phase shift layer is made of AlAg alloy, the thickness of the phase shift layer is 2-4 nm, and the atomic percent of Al is 95%-99%; the anti-reflection layer is Al2O3, and the thickness of the anti-reflection layer is 1-2 nm. The thickness of the whole film absorber can be controlled within 21-28 nm, the extreme ultraviolet reflectivity is lower than 1%, and the film absorber has remarkable advantages in the aspects of inhibiting the shadow effect, reducing light focusing offset and improving the imaging contrast ratio in a photoetching mask system. Meanwhile, the preparation method disclosed by the invention is simple, easy to regulate and control, low in cost and suitable for actual production and preparation.

Description

Technical Field

[0001] The invention belongs to the technical field of extreme ultraviolet optical absorption elements, and in particular relates to a thin film absorber for extreme ultraviolet light and a preparation method thereof. Background Art

[0002] With the acceleration of industrialization, extreme ultraviolet lithography technology has become the key to the next generation of mass printing of micro-integrated circuits. In the extreme ultraviolet lithography mask system, the extreme ultraviolet absorber is the core component of the imaging dark area, and its performance and structure directly determine the quality of the lithography image. The extreme ultraviolet absorber is usually superimposed on the reflector in the form of a unit, and by selectively absorbing the extreme ultraviolet light in the plane, a strong contrast in the intensity of the reflected light between the units is formed, thereby achieving the light and dark contrast of the projection. However, in this process, when the obliquely incident extreme ultraviolet light passes through the absorber, it will be affected by multiple factors such as the thickness of the absorber and the sudden change of the wavefront phase, resulting in the generation of photomask imaging aberrations. Therefore, the performance requirements of both high imaging contrast and low shadow effect are put forward for the extreme ultraviolet absorber. How to achieve high-efficiency absorption at a thin thickness has become a key technical problem that needs to be solved urgently.

[0003] In the extreme ultraviolet band, especially at 13.5nm, the properties of most materials are very similar. Their refractive index is limited to a narrow range of 0.86-1.02, and the extinction coefficient d is mostly below 0.08. Therefore, researchers currently generally use materials with a refractive index close to 1 so that as much extreme ultraviolet light as possible can enter the absorption layer from the vacuum. At the same time, the extinction coefficient should be as large as possible so that the extreme ultraviolet light can be perfectly absorbed in a shorter optical path. However, in practical applications, it is found that even if a material with a refractive index close to 1 and a high extinction coefficient is used, it is still difficult to avoid a part of the light waves being reflected by the top layer of the absorber. These reflected light waves will interfere with the light reflected from the absorber / reflector interface, thereby affecting the quality of the lithographic image. In order to eliminate this interference effect, it is necessary to ensure that the phase accumulation of light traveling in the absorber reaches π to achieve interference destructiveness.

[0004] At present, the most representative Ta-based extreme ultraviolet absorbers, such as TaN and TaBN, usually require a thickness of 50-80nm to obtain a reflectivity of less than 1%. In addition, researchers have further explored other materials with higher extinction coefficients such as Ni and Co, and have comprehensively improved the extreme ultraviolet light capture and absorption capabilities by superimposing oxide anti-reflection layers, but the overall thickness of the absorber is still relatively large. In addition, in order to obtain an ideal absorber material with both extreme ultraviolet high refractive index (usually less than 1) and high extinction coefficient, researchers also use alloying to modify the material, such as compounding a certain proportion of high extinction coefficient material Ni with high refractive index material Al to obtain a nearly 40nm thick high absorption film. However, conventional material combination ideas still cannot achieve further compression of the absorber thickness. This means that new absorber thinning strategies must be found while ensuring high-quality growth of the film and its good compatibility with existing lithography processes. Therefore, designing and developing a new extreme ultraviolet thin film absorber to support lithography masks to obtain high image contrast, low shadow effect, and low aberration is one of the keys to the development of extreme ultraviolet lithography technology. Summary of the invention

[0005] In view of the above, the purpose of the present invention is to provide a thin film absorber for extreme ultraviolet light and a preparation method thereof, and to prepare a thin film absorber including an AgAl alloy absorption layer, an AlAg alloy phase shift layer and an Al2O3 anti-reflection layer, which effectively reduces the overall thickness and extreme ultraviolet reflectivity of the thin film absorber to support the photolithography mask to obtain high image contrast, low shadow effect and low aberration performance, provide strong support for the further development of extreme ultraviolet lithography technology, and promote the continuous upgrading of the semiconductor industry.

[0006] In order to achieve the above-mentioned invention object, the technical solution provided by the present invention is as follows:

[0007] A thin film absorber for extreme ultraviolet light provided in an embodiment of the present invention comprises: an absorption layer, a phase shift layer and a transmittance-enhancing layer which are sequentially arranged on an extreme ultraviolet reflector or a protective layer thereof.

[0008] Preferably, the absorption layer is an AgAl alloy, which is composed of Ag doped with a small amount of Al. Ag with a high extinction coefficient can improve the extreme ultraviolet light absorption efficiency, and the problem of large surface roughness and poor thermal stability of the Ag film is solved by doping a small amount of Al in Ag. Specifically, during the co-sputtering process of Ag and Al, the diffusely distributed Al provides additional nucleation sites for the growth of Ag grains, thereby inhibiting the island growth and thermal diffusion of Ag, reducing the roughness of the Ag film and improving the thermal stability of the film layer.

[0009] Preferably, the phase shift layer is an AlAg alloy, which is composed of Al doped with a small amount of Ag. Al materials with an extreme ultraviolet refractive index greater than that of vacuum (>1) can cause a phase shift of nearly π in the reflected light, compensate for the cumulative phase of the light wave in the absorption layer, and further reduce the required thickness of the AgAl alloy absorption layer. At the same time, the addition of a very small amount of Ag is conducive to the continuous film formation of Al. Specifically, under the co-sputtering of Al and Ag, the diffusely distributed Ag provides nucleation sites for Al, reduces the permeation threshold of Al film formation, forms a continuous Al-rich nanofilm, and obtains a phase shift layer.

[0010] Preferably, the anti-reflection layer is Al2O3. The oxide anti-reflection layer uses its own refractive index of nearly 1 to improve optical matching and reduce the reflectivity of extreme ultraviolet light. It can also prevent external oxygen and other molecules from further penetrating into the absorber, thereby improving its environmental stability. Specifically, since the formation energy of Al2O3 is much negative than that of Ag2O, Al is very easy to form a bond with oxygen in the external environment. When the sample is placed in the air, the surface of the AlAg alloy phase-shift layer will naturally oxidize to form a nanometer-scale Al2O3 film as an anti-reflection layer. The dense Al2O3 film covers the phase-shift layer, effectively maintaining the stability of the film layer.

[0011] Preferably, the absorption layer has a thickness of 18-22 nm, wherein the atomic percentage of Ag is 90%-98%, which can ensure that the extinction coefficient of the absorption layer is high enough to support high absorption of extreme ultraviolet light in a shorter optical path.

[0012] Preferably, the thickness of the phase shift layer is 2-4 nm, wherein the atomic percentage of Al is 95%-99%, which can ensure that the film is smooth and continuous, and maintains a high and low refractive index difference with the vacuum interface, so that the interface reflected light produces a reflection phase shift of nearly π.

[0013] Preferably, the thickness of the anti-reflection layer is 1-2 nm, and the nano-scale dense natural oxide layer has an anti-reflection effect on extreme ultraviolet light, which can improve the absorption performance of the entire absorber.

[0014] In summary, a thin film absorber for extreme ultraviolet light provided in an embodiment of the present invention can be deposited on any extreme ultraviolet reflector and protective layer. The absorber includes an AgAl alloy absorption layer, an AlAg alloy phase shift layer, and an Al2O3 anti-reflection layer. The thickness of the entire absorber can be controlled within the range of 21-28nm, and the extreme ultraviolet reflectivity is less than 1%, which is beneficial to improving the actual extreme ultraviolet lithography process effect.

[0015] To achieve the above-mentioned object of the invention, an embodiment of the present invention further provides a method for preparing a thin film absorber for extreme ultraviolet light, comprising the following steps:

[0016] S1, placing a substrate coated with an extreme ultraviolet reflector or a substrate coated with an extreme ultraviolet reflector and a protective layer thereof into a magnetron sputtering vacuum chamber;

[0017] S2, introducing high-purity argon gas, using DC sputtering to clean the Ag target and the Al target. After the cleaning is completed, the argon gas flow is adjusted to control the gas pressure in the deposition chamber;

[0018] S3, selecting Ag and Al as target materials, setting the working power of the Ag target and the Al target, controlling the Ag and Al targets to perform co-sputtering deposition, and obtaining an AgAl alloy absorption layer;

[0019] S4, adjusting the working power of the Al target and the Ag target, controlling the Al target and the Ag target to perform co-sputtering deposition, and obtaining an AlAg alloy phase-shift layer;

[0020] S5, turning off the driving power of the Al target and the Ag target, taking the sample including the AgAl alloy absorption layer and the AlAg alloy phase-shift layer out of the vacuum chamber, and spontaneously oxidizing the Al on the upper surface of the AlAg alloy phase-shift layer to form an Al2O3 anti-reflection layer, and finally obtaining a thin film absorber for extreme ultraviolet light.

[0021] Preferably, the vacuum chamber is pre-evacuated to 9×10 -5 Pa, adjust the argon gas flow to make the pressure in the deposition chamber reach 0.1-0.3Pa.

[0022] Preferably, when magnetron sputtering is used to deposit the AgAl alloy absorption layer, the Ag target power density is set to 3-10 W / cm 2 , the Al target power density is set to 0.5-2W / cm 2 .

[0023] Preferably, when magnetron co-sputtering is used to deposit the AlAg alloy phase-shift layer, the Al target power density is set to 3-10 W / cm 2 , the Ag target power density is set to 0.3-1W / cm 2 By controlling the power density and other parameters of magnetron sputtering within the preferred range, the sputtering efficiency can be further improved, and the atomic stacking and diffusion state can be optimized to improve the film quality.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The AgAl alloy absorption layer of the present invention uses Ag with a high extinction coefficient as the main absorption material. Its strong extreme ultraviolet light absorption ability can achieve a significant reduction in extreme ultraviolet reflectivity at a relatively thin thickness. At the same time, by doping Al, the film is flattened and its thermal stability is improved, thereby obtaining a more excellent extreme ultraviolet performance.

[0026] (2) The AlAg alloy phase shift layer of the present invention introduces Al with a refractive index greater than 1 to stimulate the surface reflection phase shift, compensate for the propagation phase accumulation of light waves in the absorber, and further reduce the required thickness of the absorption layer, which has a positive effect on reducing the shadow effect and light focusing offset in the mask system. At the same time, by doping a very small amount of Ag, the film layer is ensured to be continuous at the nanometer level.

[0027] (3) The Al2O3 anti-reflection layer in the present invention is formed by natural oxidation on the upper surface of the AlAg alloy phase-shift layer, which is beneficial to the capture of extreme ultraviolet light by the absorber, reduces the reflectivity, and promotes the improvement of the intensity contrast in the imaging system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 It is a schematic diagram of the structure of a thin film absorber for extreme ultraviolet light provided in an embodiment of the present invention.

[0030] Figure 2 It is a schematic flow chart of a method for preparing a thin film absorber for extreme ultraviolet light provided in an embodiment of the present invention.

[0031] Figure 3 It is a schematic diagram comparing the theoretical reflectivity spectra of the thin film absorbers for extreme ultraviolet light prepared in the embodiments of the present invention and the comparative examples.

[0032] The specific symbols in the accompanying drawings are:

[0033] 100. substrate; 101. extreme ultraviolet reflector; 102. protective layer; 103. thin film absorber; 104. Mo low refractive index layer; 105. Si high refractive index layer; 106. AgAl alloy absorption layer; 107. AlAg alloy phase shift layer; 108. Al2O3 anti-reflection layer. DETAILED DESCRIPTION

[0034] To make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation methods described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0035] Example

[0036] According to Figure 2The preparation method shown is used to prepare a thin film absorber for extreme ultraviolet light. In the embodiment, the method specifically includes the following steps:

[0037] (1) Place the substrate 100 coated with the extreme ultraviolet reflector 101 and the protective layer 102 in a magnetron sputtering vacuum chamber, and pre-evacuate the vacuum chamber to 9×10 -5 Below Pa.

[0038] (2) High-purity argon gas is introduced and the Ag target and Al target are cleaned by DC sputtering. After cleaning, the argon gas flow is adjusted to make the pressure in the deposition chamber reach 0.1-0.3 Pa.

[0039] (3) Select Ag and Al as target materials, control the operation of Ag and Al targets, and set the power density of Ag target to 3-10 W / cm 2 , the Al target power density is set to 0.5-2W / cm 2 The Ag target and the Al target are co-sputtered and deposited at a certain angle toward each other to obtain the AgAl alloy absorption layer 106 .

[0040] (4) Adjust the working power of Al target and Ag target, and set the power density of Al target to 3-10W / cm 2 , the Ag target power density is set to 0.3-1W / cm 2 , controlling the Al target and the Ag target to perform co-sputtering deposition to obtain the AlAg alloy phase-shift layer 107 .

[0041] (5) Turn off the driving power of the Al target and the Ag target, take the sample including the AgAl alloy absorption layer 106 and the AlAg alloy phase-shift layer 107 out of the vacuum chamber, and the Al on the upper surface of the AlAg alloy phase-shift layer is spontaneously oxidized in the air at room temperature to form an Al2O3 anti-reflection layer 108, and finally obtain a thin film absorber 103 for extreme ultraviolet light.

[0042] like Figure 1 As shown, the substrate 100 is a silicon wafer, the extreme ultraviolet reflector 101 is a 2.7nm thick Mo low refractive index layer 104 and a 4.2nm thick Si high refractive index layer alternately plated with 41 cycles, and the protective layer 102 is a 3nm thick Ru. In the above-mentioned thin film absorber 103 for extreme ultraviolet light, the thickness of the AgAl alloy absorption layer 106 is 20nm, and the Ag atomic percentage is 97%; the thickness of the AlAg alloy phase shift layer 107 is 3nm, and the Al atomic percentage is 99%; the thickness of the Al2O3 anti-reflection layer 108 is 1.5nm; that is, the overall thickness of the absorber 103 is 24.5nm. The thin film absorber 103 for extreme ultraviolet light prepared in the embodiment has a theoretical reflectivity as low as 0.7% under 13.5nm extreme ultraviolet light, as shown in FIG. Figure 3 shown.

[0043] Comparative Example 1

[0044] As a comparison, an EUV reflector 101 and a protective layer 102 with the same parameters as those in the embodiment, and a Ta material with the same thickness (24.5 nm) as the absorber in the embodiment are deposited on a silicon wafer substrate 100. As the absorber, the theoretical reflectivity of the absorber for 13.5 nm EUV light is 8.8%. Figure 3 shown.

[0045] Comparative Example 2

[0046] As a comparison, an EUV reflector 101 and a protective layer 102 with the same parameters as those in the embodiment, and a TaN material with the same thickness (24.5 nm) as the absorber in the embodiment are deposited on a silicon wafer substrate 100 as an absorber, and its theoretical reflectivity for 13.5 nm EUV light is 8.2%. Figure 3 shown.

[0047] comprehensive Figure 3 The results of the theoretical reflectivity curve shown in the figure show that compared with the conventional extreme ultraviolet absorbers currently available, the thin film absorber for extreme ultraviolet light prepared in the embodiment of the present invention has a theoretical reflectivity of less than 1%, and has strong extreme ultraviolet absorption ability. At the same time, the thickness of the entire absorber prepared in the embodiment is less than 25nm, which has significant advantages in reducing the shadow effect and light wave phase shift in the mask system. In addition, the preparation method provided in the embodiment of the present invention has a simple preparation process, low cost, and is suitable for practical application preparation.

[0048] The specific implementation methods described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A thin film absorber for extreme ultraviolet light, characterized in that: include: An absorption layer, a phase shift layer and an anti-reflection layer are sequentially arranged on an extreme ultraviolet reflector or a protective layer thereof, wherein the absorption layer is made of AgAl alloy, the phase shift layer is made of AlAg alloy, and the anti-reflection layer is made of Al2O3.

2. The thin film absorber for extreme ultraviolet light according to claim 1, characterized in that: In the absorption layer, the atomic percentage of Ag is 90%-98%.

3. The thin film absorber for extreme ultraviolet light according to claim 1, characterized in that: In the phase-shift layer, the atomic percentage of Al is 95%-99%.

4. The thin film absorber for extreme ultraviolet light according to claim 1, characterized in that: The thickness of the absorption layer is 18-22 nm.

5. The thin film absorber for extreme ultraviolet light according to claim 1, characterized in that: The thickness of the phase shift layer is 2-4 nm.

6. The thin film absorber for extreme ultraviolet light according to claim 1, characterized in that: The thickness of the anti-reflection layer is 1-2 nm.

7. A method for preparing a thin film absorber for extreme ultraviolet light according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, placing a substrate coated with an extreme ultraviolet reflector or a substrate coated with an extreme ultraviolet reflector and a protective layer thereof into a magnetron sputtering vacuum chamber; S2, introducing high-purity argon gas, using DC sputtering to clean the Ag target and the Al target. After the cleaning is completed, the argon gas flow is adjusted to control the gas pressure in the deposition chamber; S3, selecting Ag and Al as target materials, setting the working power of the Ag target and the Al target, controlling the Ag and Al targets to perform co-sputtering deposition, and obtaining an AgAl alloy absorption layer; S4, adjusting the working power of the Al target and the Ag target, controlling the Al target and the Ag target to perform co-sputtering deposition, and obtaining an AlAg alloy phase-shift layer; S5, turning off the driving power of the Al target and the Ag target, taking the sample including the AgAl alloy absorption layer and the AlAg alloy phase-shift layer out of the vacuum chamber, and spontaneously oxidizing the Al on the upper surface of the AlAg alloy phase-shift layer to form an Al2O3 anti-reflection layer, and finally obtaining a thin film absorber for extreme ultraviolet light.

8. The method for preparing a thin film absorber for extreme ultraviolet light according to claim 7, characterized in that: Pre-evacuate the vacuum chamber to 9×10 -5 Pa, adjust the argon gas flow to make the pressure in the deposition chamber reach 0.1-0.3Pa.

9. The method for preparing a thin film absorber for extreme ultraviolet light according to claim 7, characterized in that: When magnetron sputtering is used to deposit the AgAl alloy absorption layer, the Ag target power density is set to 3-10 W / cm 2 , the Al target power density is set to 0.5-2W / cm 2 .

10. The method for preparing a thin film absorber for extreme ultraviolet light according to claim 7, characterized in that: When magnetron co-sputtering is used to deposit the AlAg alloy phase-shift layer, the Al target power density is set to 3-10 W / cm 2 , the Ag target power density is set to 0.3-1W / cm 2 .

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