EUV mask blank with controllable roughness and method of manufacturing the same

Abstract

The application provides an EUV mask with controllable roughness and a preparation method thereof, and relates to the technical field of extreme ultraviolet elements.The application provides a preparation method of an EUV mask with controllable roughness, which comprises the following steps: alternately performing chromium layer deposition and ion source bombardment thinning on a substrate x times to form a period structure, so that a roughness control layer is obtained; the x is not less than 1; and a multilayer film is deposited on the roughness control layer, so that the EUV mask is obtained.The chromium layer is first deposited, and then thinned by using ion source bombardment, the period structure of 'deposition-bombardment' is used to realize accurate control of the roughness, and the process repeatability and roughness controllability of the EUV mask manufacturing are significantly improved.The results of the embodiments show that the roughness uniformity (9.5%) of the method provided by the application is significantly better than that of a pure Cr process (27.5%), and accurate and stable control of the roughness is realized.

Description

Technical Field

[0001] This invention relates to the field of extreme ultraviolet (EUV) element technology, specifically to an EUV mask with adjustable roughness and its preparation method. Background Technology

[0002] With the development of integrated circuits, extreme ultraviolet lithography has become the most effective means of manufacturing very large-scale integrated circuits.

[0003] Since the extreme ultraviolet (EUV) optical path is in a vacuum environment and employs a total internal reflection design, and the mask used for patterning does not have the function of diffusing the beam, a mask with controllable scattering or controllable roughness is needed to achieve in-situ wavefront measurement in a vacuum environment, meeting the aberration control requirements of high numerical aperture and next-generation EUV lithography systems.

[0004] The traditional method for fabricating controllable roughness masks is to directly apply a chromium layer to the substrate. Roughness is controlled by fabricating a chromium layer of 200~500nm. However, severe crystallization of the chromium layer can cause instability in the roughness, resulting in unstable process repeatability and roughness controllability. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide an EUV mask with adjustable roughness and its preparation method. This invention first deposits a chromium layer, then thins it by bombardment with an ion source. Utilizing a "deposition-bombardment" periodic structure, precise control of roughness is achieved, significantly improving the process repeatability and roughness controllability of EUV mask manufacturing.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for fabricating an EUV mask with adjustable roughness, comprising the following steps: Chromium layer deposition and ion source bombardment thinning are performed alternately on the substrate, with the alternation occurring x times to form a periodic structure, resulting in a roughness control layer; where x is not less than 1. A multilayer film is deposited on the roughness control layer to obtain the EUV mask.

[0007] Preferably, x is a positive integer from 1 to 50.

[0008] Preferably, the thickness of the chromium layer deposition is 10~14 nm.

[0009] Preferably, the single-pass thinning thickness of the ion source bombardment is 2~3 nm.

[0010] Preferably, the chromium layer deposition is performed using DC magnetron sputtering, and the background vacuum level before DC magnetron sputtering is <9×10⁻⁶. -5 Pa.

[0011] Preferably, the DC magnetron sputtering method is target grazing, and the sputtering power of the DC magnetron sputtering is 1000~2500W.

[0012] Preferably, the working gas for the DC magnetron sputtering is argon, the working pressure is 0.1~0.2 Pa, and the volumetric flow rate of the working gas is 50~70 sccm.

[0013] Preferably, the working gas for ion source bombardment and thinning is argon, the working gas pressure is 0.08~0.15Pa, the volumetric flow rate of the working gas is 50~70sccm, and the sputtering voltage is 1000~2000V.

[0014] Preferably, the multilayer film comprises, in sequence, a stacked MoSi multilayer reflective layer, a Ru protective layer, and a TaN absorber layer, wherein the MoSi multilayer reflective layer is disposed on the surface of the roughness control layer.

[0015] This invention provides an EUV mask prepared by the method described above, comprising a substrate, a roughness control layer, and a multilayer film stacked sequentially, wherein the roughness control layer is [Cr / Ion]. x In the layer, x is not less than 1, and [Cr / Ion] x In the middle, Cr represents the chromium layer, and Ion represents the atomic layer thinning treatment.

[0016] This invention provides a method for fabricating an EUV mask with adjustable roughness, comprising the following steps: Chromium layer deposition and ion source bombardment thinning are performed alternately on the substrate, repeated x times to form a periodic structure, resulting in a roughness control layer; multilayer films are deposited on the roughness control layer to obtain the EUV mask.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first deposits a chromium layer, then thins it using an ion source bombardment. This "deposition-bombardment" cyclic structure enables precise control of roughness, significantly improving the process repeatability and roughness controllability in EUV mask manufacturing. The results of the embodiments show that the roughness uniformity (9.5%) of the method provided by this invention is significantly better than that of the pure Cr process (27.5%), achieving precise and stable roughness control.

[0018] Furthermore, by controlling the number of cycles x of the roughness control layer, the present invention can adjust the substrate surface to an ideal roughness, which is 0~6nm and not 0, and then continue to deposit a MoSi multilayer reflective layer, a Ru protective layer and a TaN absorber layer to complete the fabrication of the entire product.

[0019] The present invention also provides an EUV mask prepared by the preparation method described above. Attached Figure Description

[0020] Figure 1 This is a diagram showing the structural changes of each layer during the fabrication of the EUV mask in Example 1; Figure 2 This is a flowchart illustrating the fabrication process of the EUV mask in Example 1; Figure 3 The graph shows the repeatability test results for the examples and comparative examples; Figure 4 This is a graph showing the relationship between roughness and the number of cycles x. Detailed Implementation

[0021] This invention provides a method for fabricating an EUV mask with adjustable roughness, comprising the following steps: Chromium layer deposition and ion source bombardment thinning are performed alternately on the substrate, with the alternation occurring x times to form a periodic structure, resulting in a roughness control layer; where x is not less than 1. A multilayer film is deposited on the roughness control layer to obtain the EUV mask.

[0022] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0023] In this invention, the film thickness was measured by X-ray diffraction and the roughness was measured by atomic force microscopy.

[0024] The present invention involves alternating chromium layer deposition and ion source bombardment thinning on a substrate, with the alternation occurring x times to form a periodic structure, thereby obtaining a roughness control layer, wherein x is not less than 1.

[0025] In this invention, the substrate is preferably quartz, the substrate is preferably 25.4 mm in diameter and 6.35 mm in thickness, the surface accuracy of the substrate is preferably PV < λ / 10, the surface accuracy of the substrate is preferably tested by an interferometer, and the roughness of the substrate is preferably < 0.3 nm.

[0026] In this invention, the substrate is preferably ultrasonically cleaned before the roughness control layer is prepared. The ultrasonic cleaning preferably uses a weak alkaline reagent with a pH value between 7 and 9. This invention does not have any particular limitation on the specific type of weak alkaline reagent. Conventional weak alkaline reagents in the art can be used, with a pH value between 7 and 9. The ultrasonic frequency is preferably 40 to 80 Hz, and the ultrasonic time is preferably 3 to 5 minutes.

[0027] In this invention, the chromium layer deposition is preferably performed using DC magnetron sputtering, and the background vacuum level before DC magnetron sputtering is preferably <9×10⁻⁶.-5 Pa, the DC magnetron sputtering method is preferably a grazing target, the target material is preferably a chromium target, and the purity of the chromium target is preferably >99.5%.

[0028] In this invention, the sputtering power of the DC magnetron sputtering is preferably 1000~2500W, specifically 1500, 1800, 2000 or 2300W, the working gas is preferably argon, the working pressure is preferably 0.1~0.2Pa, and the volumetric flow rate is preferably 50~70sccm, specifically 55, 60 or 65sccm.

[0029] In this invention, the thickness of the chromium layer deposition is preferably 10-14 nm, specifically 11, 12, or 13 nm.

[0030] In this invention, the working gas for ion source bombardment and thinning is preferably argon, the working gas pressure is preferably 0.08~0.15 Pa, specifically 0.1, 0.12 or 0.14 Pa, the volumetric flow rate of the working gas is preferably 50~70 sccm, specifically 55, 60 or 65 sccm, and the sputtering voltage is preferably 1000~2000 V, specifically 1300, 1500 or 1800 V.

[0031] In this invention, the thickness of a single thinning step by the ion source bombardment is preferably 2-3 nm.

[0032] This invention transforms the crystallization and roughness of chromium from a one-time abrupt change to a layer-by-layer controllable growth combined with interface blocking. Chromium begins to weakly crystallize and form fine grains within a thickness range of 8-12 nm. When deposited to 12 nm, the chromium layer just enters the microcrystalline region and has not yet grown into coarse columnar crystals. Subsequently, the ion source thins the layer by 2-3 nm, breaking up the newly crystallized grains on the surface and introducing a disordered interface. This disordered interface effectively blocks the vertical interconnection of grain growth, avoiding the surge in roughness caused by the appearance of large grains. The "deposition-bombardment" process constitutes a complete cycle. Within each cycle, the grain size of the chromium layer remains consistent and uniformly distributed. The roughness exhibits a linear relationship with the number of cycles. By controlling the number of cycles x, precise and repeatable control of the roughness can be achieved.

[0033] In this invention, x is preferably a positive integer from 1 to 50, specifically 10, 20, 30 or 40.

[0034] After obtaining the roughness control layer, the present invention deposits a multilayer film on the roughness control layer to obtain the EUV mask.

[0035] In this invention, the multilayer film preferably comprises, in sequence, a MoSi multilayer reflective layer, a Ru protective layer, and a TaN absorber layer. The MoSi multilayer reflective layer is preferably disposed on the surface of the roughness control layer. The multilayer film is manufactured by a fixed process, namely, DC magnetron sputtering, which keeps the change in overall roughness constant.

[0036] In this invention, the multilayer film deposition is preferably performed using DC magnetron sputtering, and the background vacuum level before DC magnetron sputtering is preferably <9×10⁻⁶. -5 Pa, the preferred method of DC magnetron sputtering is target grazing.

[0037] In this invention, the DC magnetron sputtering parameters for depositing the MoSi multilayer reflective layer preferably include: the target material is preferably a molybdenum target and a polycrystalline silicon target, the purity of the target material is preferably >99.99%, the working gas is preferably argon, the volumetric flow rate is preferably 40~60 sccm, specifically 45, 50 or 55 sccm, the working pressure is preferably 0.07~0.09 Pa, the sputtering voltage of the molybdenum target is preferably 1000~2000V, specifically 1200, 1500 or 1800V, the sputtering voltage of the polycrystalline silicon target is preferably 2000~3000V, specifically 2200, 2500 or 2700V; the thickness ratio of Mo to Si in each cycle of the MoSi multilayer reflective layer is preferably 0.35~0.45:0.55~0.65, the thickness of each cycle is preferably 6.92~7.00 nm, and the MoSi multilayer reflective layer preferably includes 40 cycles.

[0038] In this invention, the DC magnetron sputtering parameters of the Ru protective layer preferably include: a ruthenium target with a purity >99.9%; argon as the working gas with a volumetric flow rate of 50~100 sccm (specifically 55, 60, 70, 80, or 90 sccm); a working pressure of 0.08~0.20 Pa (specifically 0.10, 0.12, 0.15, or 0.18 Pa); and a sputtering voltage of 800~1500 V (specifically 1000, 1200, or 1400 V). The thickness of the Ru protective layer is preferably 1.5~4 nm.

[0039] In this invention, the DC magnetron sputtering parameters of the TaN absorber layer preferably include: a tantalum target with a purity >99.99%; a working gas mixture of argon and nitrogen; a preferred argon flow rate of 50-100 sccm, specifically 60, 70, 80, or 90 sccm; a preferred nitrogen flow rate of 20-50 sccm, specifically 25, 30, 35, or 40 sccm; a preferred working pressure of 0.10-0.25 Pa, specifically 0.12, 0.15, 0.18, or 0.20 Pa; and a preferred sputtering voltage of 2000-3000 V; the preferred thickness of the TaN absorber layer is 60-80 nm.

[0040] The present invention provides an EUV mask prepared by the preparation method described above, comprising a substrate, a roughness control layer and a multilayer film stacked sequentially, wherein the roughness control layer is a [Cr / Ion]x layer, and x is not less than 1.

[0041] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0042] Example 1 Substrate preparation: The quartz substrate was ultrasonically cleaned using ammonia water at a frequency of 80 Hz for 3 minutes, resulting in an initial roughness of 0.3 nm. The vacuum chamber was evacuated to a vacuum level of 9×10⁻⁶. -5 Pa, The DC magnetron sputtering parameters for chromium layer deposition include: a Cr target with a purity of 99.5%, argon as the working gas with a volumetric flow rate of 70 sccm, a working pressure of 0.1 Pa, a sputtering power of 2000 W, and a chromium layer thickness of 12 nm. The ion source bombardment parameters include: working gas is argon, volumetric flow rate is 50 sccm, working gas pressure is 0.08 Pa, sputtering voltage is 2000 V, and the chromium layer thickness is reduced to 10 nm. The process of chromium layer deposition and ion source bombardment was repeated 30 times (i.e., the number of cycles x=30) to form a roughness control layer; The MoSi multilayer reflective layer was deposited with the following parameters: the target materials were Mo and polycrystalline Si, the target purity was 99.99%, the working gas was argon, the volumetric flow rate was 50 sccm, the working pressure was 0.08 Pa, the sputtering voltage of the Mo target was 1500 V, the sputtering voltage of the polycrystalline Si target was 2500 V, the thickness of the MoSi film in a single cycle was 6.96 nm, the cycle was repeated for 40 cycles, and the thickness ratio of Mo to Si was 4:6. The parameters for depositing a Ru protective layer include: the target material is a Ru target with a purity of 99.9%, the working gas is argon with a flow rate of 70 sccm, the working pressure is 0.10 Pa, the sputtering voltage is 1200 V, and the thickness is 2 nm. The parameters for depositing a TaN absorber layer include: the target material is a Ta target with a purity of 99.99%; the working gas is a mixture of argon and nitrogen with a volumetric flow rate of 70 sccm and a volumetric flow rate of 30 sccm; the working pressure is 0.12 Pa; the sputtering voltage is 3000 V; and the thickness is 70 nm. The roughness of the EUV mask is 3.93 nm.

[0043] Figure 1 This is a diagram showing the structural changes of each layer during the fabrication of the EUV mask in Example 1, including a quartz substrate, a roughness control layer, a MoSi multilayer reflective layer, a Ru protective layer, and a TaN absorber layer stacked sequentially.

[0044] Figure 2 The flowchart for the preparation of the EUV mask in Example 1 shows that chromium layer deposition and ion source bombardment are performed alternately on a quartz substrate to thin the chromium layer, and the roughness control layer is formed alternately and repeatedly. Then, a MoSi multilayer reflective layer, a Ru protective layer and a TaN absorber layer are deposited.

[0045] Comparative Example Similar to Example 1, the only difference is that ion source bombardment is not used for thinning. To achieve the roughness of Example 1, the total thickness of the pure chromium layer needs to be adjusted to 258 nm.

[0046] The complete process flow of Example 1 and the comparative example was repeated 10 times each, denoted as Cr and Cr / Ion respectively. The roughness of the EUV mask obtained each time was measured, and the results are shown in [Figure 1]. Figure 3 ,from Figure 3 It can be seen that the roughness of both Example 1 and the comparative example was adjusted to 4 nm and repeated 10 times. The roughness of Example 1 was between 3.9 and 4.3 nm, and the roughness of the comparative example was between 3.7 and 4.8 nm. The roughness fluctuation range of Example 1 was narrower. The roughness non-uniformity of Example 1 and the comparative example was tested, and the results are shown in Table 1.

[0047] Table 1. Roughness uniformity of Example 1 and Comparative Example

[0048] As shown in Table 1, the roughness uniformity of Example 1 is 9.5%, while that of the comparative example is 27.5%. The roughness uniformity of Example 1 is significantly better than that of the comparative example. Although both processes can achieve the desired roughness, the roughness of the comparative example becomes more dispersed after repeated use, resulting in much poorer uniformity. In practical applications, the application effect of Example 1 will be far stronger than that of the comparative example.

[0049] Example 2 Similar to Example 1, the only difference is that the number of periods x is 5, 10, 15, 20, 25, 35, 40, 45, and 50, and the roughness obtained is 0.58nm, 0.83nm, 1.49nm, 2.12nm, 2.77nm, 4.93nm, 5.47nm, 5.81nm, and 6.22nm, respectively.

[0050] Figure 4 This is a graph showing the relationship between roughness and the number of cycles x in Example 2. Figure 4 It can be seen that as the number of cycles x increases, the roughness increases, and the roughness is roughly linearly related to the number of cycles x.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating an EUV mask with adjustable roughness, characterized in that, Includes the following steps: Chromium layer deposition and ion source bombardment thinning are performed alternately on the substrate, with the alternation occurring x times to form a periodic structure, resulting in a roughness control layer; where x is not less than 1. A multilayer film is deposited on the roughness control layer to obtain the EUV mask.

2. The preparation method according to claim 1, characterized in that, x is a positive integer from 1 to 50.

3. The preparation method according to claim 1, characterized in that, The thickness of the chromium layer deposition is 10~14 nm.

4. The preparation method according to claim 1, characterized in that, The single-pass thinning thickness of the ion source bombardment is 2~3 nm.

5. The preparation method according to claim 1, characterized in that, The chromium layer deposition was performed using DC magnetron sputtering, and the background vacuum level before DC magnetron sputtering was <9×10⁻⁶. -5 Pa.

6. The preparation method according to claim 5, characterized in that, The DC magnetron sputtering method is target grazing, and the sputtering power of the DC magnetron sputtering is 1000~2500W.

7. The preparation method according to claim 6, characterized in that, The working gas for the DC magnetron sputtering is argon, with a working pressure of 0.1~0.2 Pa and a volumetric flow rate of 50~70 sccm.

8. The preparation method according to claim 1, characterized in that, The working gas for the ion source bombardment and thinning is argon, with a working pressure of 0.08~0.15Pa, a volumetric flow rate of 50~70sccm, and a sputtering voltage of 1000~2000V.

9. The preparation method according to claim 1, characterized in that, The multilayer film comprises, in sequence, a stacked MoSi multilayer reflective layer, a Ru protective layer, and a TaN absorber layer, wherein the MoSi multilayer reflective layer is disposed on the surface of the roughness control layer.

10. The EUV mask prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The material comprises a substrate, a roughness control layer, and a multilayer film stacked sequentially, wherein the roughness control layer is [Cr / Ion]. x In the layer, x is not less than 1, and [Cr / Ion] x In the middle, Cr represents the chromium layer, and Ion represents the atomic layer thinning treatment.

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