Reflection type mask plate and preparation method thereof

Abstract

The invention relates to the technical field of semiconductor devices, in particular to a reflective mask and a preparation method thereof. The reflective mask provided by the invention comprises a substrate, a reflective laminated layer and a patterned absorption layer, wherein the absorption layer comprises a ruthenium absorption layer and a tantalum absorption layer positioned below the ruthenium absorption layer; the thickness D of the ruthenium absorption layer meets the formula: D = m lambda / 2ncos theta; wherein m is a positive integer, lambda represents the wavelength of the light source, n represents the refractive index of the ruthenium material, and theta represents the incident angle of the light beam from the ruthenium absorption layer to the tantalum absorption layer. According to the reflective mask plate provided by the invention, the gray scale ratio between the light beam reflected by the photomask and the absorbed light beam can be increased, and the photoetching quality of the mask plate is improved. The invention also provides a preparation method of the reflective mask plate.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a reflective mask and a preparation method thereof. Background Art

[0002] The mask is an indispensable component in the photolithography process. Light passes through the pre-prepared pattern on the mask, and then passes through the projection lens to focus the light on the photoresist. It can be said that the photolithography accuracy is closely related to the mask performance.

[0003] According to the characteristics of the mask itself, photolithography masks can be classified into: transmissive masks and reflective masks.

[0004] Before the mass production of EUV lithography, the masks used were generally transmissive masks such as bipolar masks, phase-shift masks, etc. In order to meet the transmittance requirements, the mask will use a thin film material with high transmittance as a support, but this structure is relatively fragile and will undergo severe thermal deformation after being heated.

[0005] However, the EUV lithography machine will no longer use a transmissive mask. The EUV lithography system uses a reflective mask, which uses a low-expansion material as the substrate, a solid back support structure, and cooling technology to reduce the operating temperature and deformation caused by heat. The performance of the mask is closely related to the quality of the lithography process. As an indispensable component in the lithography process, its low image contrast has a great impact on the quality of lithography imaging. Summary of the invention

[0006] The object of the present invention is to provide a mask and a method for preparing the same, so as to improve the image grayscale ratio of a reflective mask. In order to solve the problems and deficiencies in the prior art, the present invention provides a reflective mask and a method for preparing the same. The mask provided by the present invention comprises a substrate, a reflective stack and a patterned absorption layer, wherein the reflective stack is located above the substrate; the absorption layer is located above the reflective stack,

[0007] The absorption layer includes a ruthenium absorption layer and a tantalum absorption layer located below the ruthenium absorption layer; and the thickness D of the ruthenium layer satisfies:

[0008] D = mλ / 2n cosθ;

[0009] Wherein, m is a positive integer, λ represents the wavelength of the light source, n represents the refractive index of the ruthenium material, and θ represents the incident angle of the light beam from the ruthenium absorption layer to the tantalum absorption layer.

[0010] Optionally, the mask further includes:

[0011] A cover layer is located between the absorption layer and the reflective stack.

[0012] Optionally, the reflective stack is formed by periodically stacking a molybdenum layer as a high-refractive material layer and a silicon layer as a low-refractive material layer multiple times.

[0013] Optionally, the covering layer is a ruthenium material layer.

[0014] Optionally, the thickness of the ruthenium absorption layer is between 15 nm and 15.5 nm.

[0015] Furthermore, the present invention also provides a method for preparing a reflective mask, the method comprising:

[0016] providing a substrate;

[0017] forming a reflective stack on the substrate;

[0018] forming a covering layer on the reflective stack, wherein the covering layer is a ruthenium material layer;

[0019] forming an absorption layer having a double-layer structure consisting of a tantalum absorption layer and a ruthenium absorption layer on the cover layer;

[0020] The absorbent layer is patterned.

[0021] Optionally, patterning the absorption layer comprises:

[0022] forming a hard mask layer on the absorption layer;

[0023] forming a photoresist layer on the hard mask layer;

[0024] patterning the photoresist layer;

[0025] etching the hard mask layer based on the patterned photoresist layer;

[0026] removing the photoresist layer, and etching the absorption layer based on the patterned hard mask layer;

[0027] The hard mask layer is removed.

[0028] Optionally, when etching the absorption layer, the covering layer serves as an etching stop layer.

[0029] Optionally, the covering layer has a thickness of 8-11 nm.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) A ruthenium absorption layer and a tantalum absorption layer are selected to form a double-layer structure, and based on the refractive index characteristics of the ruthenium material and the tantalum material, the thickness of the ruthenium absorption layer is set to meet special thickness requirements, thereby increasing the grayscale ratio between the light beam reflected by the mask and the light beam absorbed, and improving the mask lithography accuracy.

[0032] (2) A metal ruthenium layer is selected as a covering layer in the mask. Since ruthenium has a low etching rate, selecting ruthenium as an etching stop layer can prevent excessive etching from damaging the reflective stack, thereby protecting the reflective stack.

[0033] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0035] Figure 1 is a schematic structural diagram of a reflective mask according to an embodiment of the present invention;

[0036] Figure 2 is a flow chart of preparing a reflective mask according to an embodiment of the present invention;

[0037] Figure 3 is a process flow chart of a patterned absorption layer according to an embodiment of the present invention;

[0038] Figure 4 It is a flow chart of preparing an absorption layer according to an embodiment of the present invention.

[0039] In the figure: 1-reflective mask, 2-substrate, 3-reflective stack, 4-covering layer, 5-tantalum absorption layer, 6-ruthenium absorption layer. DETAILED DESCRIPTION

[0040] Refer to the following Figures 1 to 4 To describe a reflective mask and a preparation method of an embodiment of the present invention. In the description of this embodiment, it should be understood that the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features, that is, include one or more of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. When a feature "includes or contains" one or some of the features it covers, unless otherwise specifically described, this indicates that other features are not excluded and may further include other features.

[0041] In the description of the present embodiment, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0042] Figure 1 Schematic diagram of the structure of a reflective mask according to an embodiment of the present invention. Figure 1 As shown, the present invention provides a reflective mask, wherein the reflective mask 1 comprises a substrate 2, a reflective stack 3, a cover layer 4 and a patterned absorption layer composed of a ruthenium absorption layer and a tantalum absorption layer.

[0043] The substrate 2 is a material with a relatively low thermal expansion coefficient, such as glass or ceramic.

[0044] The reflective stack 3 is covered on the substrate 2 and is used to reflect the extreme ultraviolet light beam. To meet the extremely high light reflectivity requirement, the reflective stack 3 is a multi-optical period material layer formed by stacking a high refractive index material layer and a low refractive index material layer. In this embodiment, the high refractive index material layer is made of molybdenum material, and the low refractive index material layer is made of silicon material. As an example, the molybdenum material layer and the silicon material layer are alternately arranged to finally form a reflective stack with 30 to 36 optical periods.

[0045] The cover layer 4 covers the reflective stack 3 and serves as an etching stop layer to prevent the etching process from damaging the reflective stack 3. In this embodiment, the cover layer 4 is made of ruthenium material.

[0046] The patterned absorption layer covers the cover layer 4. In the light beam reflected by the reflective stack 3, the part covered by the absorption layer is absorbed, and the part not covered by the absorption layer forms a photolithography mask pattern. In addition, the absorption layer is a double-layer structure formed by a tantalum absorption layer 5 and a ruthenium absorption layer 6; the ruthenium absorption layer 6 is located above the tantalum absorption layer 5, and the ruthenium absorption layer 6 and the tantalum absorption layer 5 have the same photolithography pattern, and together define the mask pattern of the reflective mask 1. In addition, the thickness D of the ruthenium absorption layer satisfies:

[0047] D = mλ / 2n cosθ.

[0048] Wherein, m is a positive integer, such as 2, 5, 8, etc.; λ represents the wavelength of the light source, n represents the refractive index of the ruthenium material, and θ represents the incident angle of the light beam from the ruthenium absorption layer to the tantalum absorption layer.

[0049] In this embodiment, for extreme ultraviolet light, the refractive index of ruthenium is lower than that of tantalum. When the light beam is incident from vacuum to ruthenium absorption layer 6, it is incident from light dense to light sparse, and the phase of the reflected light beam does not change; when the light beam is incident from ruthenium absorption layer 6 to tantalum absorption layer 5, it is incident from light sparse to light dense, and the phase of the reflected light beam differs by 180°. At this time, when the thickness of the ruthenium absorption layer 6 satisfies the above formula, the light beams reflected from the two dielectric surfaces (vacuum and ruthenium material dielectric surface, ruthenium material and tantalum material dielectric surface) can be interfered and destructively reflected, which helps to improve the grayscale ratio of the photolithography mask pattern.

[0050] In some embodiments, the thickness of the ruthenium absorption layer 6 should be controlled within the range of 15nm to 15.5nm. The ruthenium material has a lower refractive index and a lower extinction coefficient than the tantalum material. In the design indicators of the mask, the thickness of the absorption layer will affect the projection effect. It is generally believed that the lower the thickness of the absorption layer, the better when achieving the same light beam absorption effect. This makes it easier to use materials with a higher extinction coefficient to prepare the absorption layer during design. When the ruthenium absorption layer 6 is used to achieve the purpose of improving the grayscale ratio of the mask pattern, the application of ruthenium material will increase the total thickness of the absorption layer accordingly. Limiting the thickness of the ruthenium absorption layer 6 to 15nm to 15.5nm can not only satisfy the formula D=mλ / 2n cosθ to improve the grayscale ratio, but also avoid the thickness of the material layer being too low (when it is lower than 10nm, waveguide optics should be used for analysis when the light beam enters the film layer), which cannot meet the phase adjustment conditions.

[0051] This embodiment also provides a method for preparing a reflective mask 1, the method comprising:

[0052] Step S10, providing a substrate 2;

[0053] Step S20, forming a reflective stack 3 on the substrate 2;

[0054] Step S30, forming a cover layer 4 on the reflective stack 3, wherein the cover layer 4 is a ruthenium material layer;

[0055] Step S40, forming an absorption layer having a double-layer structure consisting of a tantalum absorption layer 5 and a ruthenium absorption layer 6 on the cover layer 4;

[0056] Step S50, patterning the absorption layer.

[0057] In this embodiment, a reflective stack 3 is first formed on the substrate 2, and then a cover layer 4 is formed on the reflective stack 3. Then, a double-layer structure absorption layer consisting of a tantalum absorption layer 5 and a ruthenium absorption layer 6 is formed on the cover layer 4. Then, Cl-O2 reactive ion etching is used to pattern the top ruthenium absorption layer 6, and Cl2-N2 reactive ion etching is used to pattern the bottom tantalum absorption layer 5, and finally a mask pattern is formed on the absorption layer.

[0058] In this embodiment, the mask prepared by the above preparation method can alleviate the three-dimensional effect of the mask and improve the photolithography quality of the mask.

[0059] In a further embodiment of the present invention, the deposition method of the formation method of the covering layer 4, the reflective stack 3 and the absorption layer can be magnetron sputtering, an ion sputtering system, ion beam deposition, electron beam evaporation, radio frequency sputtering, atomic layer deposition, pulsed laser deposition, physical vapor deposition, or a combination thereof.

[0060] like Figure 3 As shown, in some embodiments of the method for preparing the reflective mask 1 of the present invention, the patterned absorption layer includes:

[0061] Step S51, forming a hard mask layer on the absorption layer;

[0062] Step S52, forming a photoresist layer on the hard mask layer;

[0063] Step S53, patterning the photoresist layer;

[0064] Step S54, etching the hard mask layer based on the patterned photoresist layer;

[0065] Step S55, removing the photoresist layer, and etching the absorption layer based on the patterned hard mask layer;

[0066] Step S56, removing the hard mask layer.

[0067] In this embodiment, plasma etching is used to etch the absorption layer. Since the etching resistance of the photoresist is relatively weak, a hard mask layer needs to be set as a mask for etching the absorption layer. The hard mask layer is made of silicon nitride and / or silicon oxide layers with higher resistance than the photoresist. During the plasma etching process, the ruthenium absorption layer 6 is etched based on Cl2-O2 gas. Ru and O2 generate volatile RuO4. Cl2 can catalyze the formation of RuO4 to obtain a higher etching rate. The tantalum absorption layer 5 is etched based on Cl2-N2 gas. Ta reacts with Cl2 and is catalyzed by N2 to obtain a higher etching rate. At the same time, its etching rate for ruthenium is very low. The ruthenium material is selected as the covering layer 4, which can be used as an etching calibration, so that the covering layer 4 plays the role of an etching stop layer to prevent excessive etching from damaging the reflective stack 3.

[0068] In some embodiments of the method for preparing the reflective mask 1 of the present invention, the deposition thickness of the cover layer 4 is 8-11 nm, preferably 10 nm.

[0069] In this embodiment, the thickness of the cover layer 4 is 8-11 nm, which can ensure its protective effect on the reflective stack 3 on the one hand, and its transmittance to the exposure light on the other hand.

[0070] In some embodiments of the method for preparing the reflective mask 1 of the present invention, the above-mentioned forming of the absorption layer having a double-layer structure consisting of the tantalum absorption layer 5 and the ruthenium absorption layer 6 on the cover layer 4 includes:

[0071] Step S41, depositing a tantalum absorption layer 5 on the cover layer 4, wherein the thickness of the tantalum absorption layer 5 is 36-40 nm;

[0072] Step S42, depositing a ruthenium absorption layer 6 on the tantalum absorption layer 5, wherein the thickness of the ruthenium absorption layer 6 is 13-16 nm.

[0073] Preferably, the tantalum layer is deposited to a thickness of 38 nm, and the ruthenium layer is deposited to a thickness of 15 nm.

[0074] In this embodiment, when the extreme ultraviolet light beam enters the ruthenium absorption layer 6 from the incident medium, the phase of the reflected light does not change; when entering the tantalum absorption layer 5 from the ruthenium absorption layer 6, the phase of the reflected light changes by 180°. As a result, the reflected light beams on the ruthenium surface and the tantalum surface in the absorption layer cancel each other out, thereby increasing the grayscale ratio between the light beam reflected by the mask and the absorbed light beam.

[0075] In some embodiments of the present invention, the temperature when the absorbent layer is deposited on the cover layer 4 is 20-30°C and the pressure is 4.0-5.0×10 -4 Pa. The preferred temperature is 25°C and the pressure is 4.5×10 -4 Pa.

[0076] In some embodiments of the method for preparing the reflective mask 1 of the present invention, the thickness of the reflective stack 3 is 45-60 nm, preferably 50 nm.

[0077] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all these other variations or modifications.

Claims

1. A reflective mask, characterized in that: The mask plate includes: substrate; a reflective stack, the reflective stack being located above the substrate; A patterned absorption layer, the absorption layer is located above the reflective stack, the absorption layer includes a ruthenium absorption layer and a tantalum absorption layer located below the ruthenium absorption layer; and the thickness D of the ruthenium absorption layer satisfies the following formula [1]: D=λ / 2n cosθ----------Formula [1]; Wherein, m is a positive integer, λ represents the wavelength of the light source, n represents the refractive index of the ruthenium material, and θ represents the incident angle of the light beam from the ruthenium absorption layer to the tantalum absorption layer.

2. The reflective mask according to claim 1, characterized in that: The mask also includes: A cover layer is located between the absorption layer and the reflective stack.

3. The reflective mask according to claim 2, characterized in that: The reflective stack is formed by periodically stacking a molybdenum layer as a high-refractive material layer and a silicon layer as a low-refractive material layer multiple times.

4. The reflective mask according to claim 2, characterized in that: The cover layer is a ruthenium material layer.

5. The reflective mask according to claim 2, characterized in that: The thickness of the ruthenium absorption layer is between 15nm and 15.5nm.

6. A method for preparing a reflective mask as claimed in any one of claims 2 to 5, characterized in that: The preparation method comprises: providing a substrate; forming a reflective stack on the substrate; forming a covering layer on the reflective stack, wherein the covering layer is a ruthenium material layer; forming an absorption layer having a double-layer structure consisting of a tantalum absorption layer and a ruthenium absorption layer on the cover layer; The absorbent layer is patterned.

7. The method for preparing a reflective mask according to claim 6, characterized in that: The patterning of the absorption layer comprises: forming a hard mask layer on the absorption layer; forming a photoresist layer on the hard mask layer; patterning the photoresist layer; etching the hard mask layer based on the patterned photoresist layer; removing the photoresist layer, and etching the absorption layer based on the patterned hard mask layer; The hard mask layer is removed.

8. The method for preparing a reflective mask according to claim 7, characterized in that: When etching the absorption layer, the cover layer serves as an etching stop layer.

9. The method for preparing a reflective mask according to claim 8, characterized in that: The thickness of the covering layer is 8-11 nm.

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