A reflective photolithography mask and a method of manufacturing the same

Abstract

The present application relates to extreme ultraviolet lithography mask technical field, disclose a kind of reflective photomask and its preparation method.Reflector mask includes substrate, reflective stack, continuous ruthenium cover layer, ruthenium absorption layer and tantalum absorption layer;Ruthenium absorption layer and tantalum absorption layer have the same planar pattern, and ruthenium absorption layer and ruthenium cover layer are formed by the same continuous ruthenium material layer.The thickness of tantalum absorption layer makes the optical path of light beam in the layer round trip is the odd multiple of half wavelength of exposure light source.The reflective stack, ruthenium layer, tantalum layer and photoresist layer are sequentially formed during preparation, after patterning photoresist layer and tantalum layer, the upper part of ruthenium layer is etched to form ruthenium absorption layer and retain lower continuous ruthenium cover layer;With etching rate, the etching end point of tantalum layer is first obviously changed, and continue etching ruthenium layer in the target time interval of prelabeling.The present application uses tantalum as top layer absorption material, uses destructive interference of light reflection on the upper and lower interface of tantalum layer to improve imaging contrast, while reducing additional film layer interface and film stress.

Description

Technical Field

[0001] This invention relates to the field of extreme ultraviolet lithography mask manufacturing technology, and in particular to a reflective lithography mask and its preparation method. Background Technology

[0002] Extreme ultraviolet (EUV) lithography uses an exposure light source with a wavelength of about 13.5 nm. Almost all materials exhibit strong absorption characteristics in this band, making it difficult to directly apply transmissive masks. Therefore, reflective lithography masks have become one of the core components of EUV lithography systems.

[0003] The contrast of a reflective lithography mask directly affects the quality of the lithography image. The higher the contrast, the better the imaging effect. The absorption capacity of the absorption layer in the reflective lithography mask to absorb the exposure light is the key factor that determines the contrast.

[0004] To improve imaging contrast, existing technologies have proposed various absorption layer design methods, such as using multiple light-absorbing materials to form a stacked absorption structure. By selecting appropriate material combinations and structural parameters, the mask's ability to absorb exposure light can be improved, and the adverse effects of reflection at the film interface on imaging can be suppressed.

[0005] However, in the aforementioned composite absorption layer schemes, improved light absorption performance is usually accompanied by an increase in the number or thickness of film layers, leading to problems such as increased film stress and increased fabrication difficulty. Excessive stress can cause film deformation, warping, or even defects, affecting the quality and stability of the mask. Existing solutions struggle to achieve both high imaging contrast and low film stress. Therefore, there is an urgent need to improve the structure of reflective lithography masks. Summary of the Invention

[0006] The purpose of this invention is to provide a reflective photomask and its preparation method. The tantalum absorption layer is used as the top absorption material. The residual reflection in the absorption area is reduced by utilizing the destructive interference of the reflected light at the upper and lower interfaces of the tantalum absorption layer. The tantalum absorption layer and the tantalum capping layer are formed from the same continuous tantalum material layer, thereby ensuring high imaging contrast while taking into account low film stress.

[0007] To achieve the above objectives, please refer to the appendix. Figure 1-3 The present invention provides a reflective photomask, comprising a substrate, a reflective stack disposed on the substrate, a ruthenium capping layer continuously disposed on the reflective stack, a ruthenium absorption layer disposed on the ruthenium capping layer, and a tantalum absorption layer disposed on the ruthenium absorption layer; The ruthenium absorption layer and the tantalum absorption layer have the same planar pattern. The ruthenium absorption layer and the ruthenium capping layer are formed from the same continuous ruthenium material layer. The ruthenium capping layer continuously covers the reflective stack. The thickness of the tantalum absorption layer is configured such that the round-trip optical path of the light beam of the exposure light source in the tantalum absorption layer is an odd multiple of half the wavelength of the exposure light source.

[0008] Furthermore, the tantalum absorber layer has a thickness of 35 to 40 nm, the ruthenium absorber layer has a height of 10 to 15 nm relative to the ruthenium capping layer, and the ruthenium capping layer has a thickness of 4 to 7 nm.

[0009] Furthermore, the thickness of the tantalum absorber layer satisfies the following formula: , Where D is the thickness of the tantalum absorption layer, and n is the wavelength of the tantalum absorption layer at the exposure light source. The refractive index below, The angle of refraction of the light beam from the exposure light source in the tantalum absorption layer. It is a positive integer.

[0010] Furthermore, the reflective stack is composed of multiple periodically stacked low-refractive-index layers and high-refractive-index layers.

[0011] Furthermore, the low-refractive-index layer is made of silicon, and the high-refractive-index layer is made of molybdenum.

[0012] Furthermore, the substrate is made of ceramic or glass.

[0013] A method for fabricating a reflective photomask, comprising: S1 provides a substrate; S2, a reflective stack is formed on the substrate; S3, a ruthenium layer is formed on the reflective stack; S4, a tantalum layer is formed on the ruthenium layer; S5, deposit a photoresist layer on the tantalum layer; S6, pattern the photoresist layer; S7, using the photoresist layer as a mask, pattern the tantalum layer to form a patterned tantalum absorption layer; S8, using the tantalum absorption layer as a mask, pattern the upper portion of the ruthenium layer to form a ruthenium absorption layer with the same planar pattern as the tantalum absorption layer, and leave the lower portion of the ruthenium layer as a continuous ruthenium cover layer; The thickness of the tantalum absorption layer is configured such that the round-trip optical path of the light beam from the exposure light source in the tantalum absorption layer is an odd multiple of half the wavelength of the exposure light source.

[0014] Furthermore, the method also includes: During the etching process, the etching rate is monitored. When the etching rate changes significantly for the first time, it is determined that the tantalum absorption layer has been patterned. From the moment when the etching rate first changes significantly, the ruthenium layer continues to be etched according to a predetermined target time interval, which is determined in advance based on the required height of the ruthenium absorption layer and the etching process parameters.

[0015] Furthermore, the target time interval is predetermined in the following manner: A ruthenium reference layer with the same material as the ruthenium absorption layer and the same height as the required ruthenium absorption layer is formed on a reference substrate with a different surface material than ruthenium. The ruthenium reference layer is then etched using the same etching process parameters as the ruthenium layer. Record the time interval from the start of etching the ruthenium reference layer to the moment when the etching rate changes significantly, and use this time interval as a reference target time interval; The ruthenium reference layer was etched repeatedly using the same etching process parameters to obtain multiple reference target time intervals. After removing outliers, the average value was taken as the target time interval.

[0016] Furthermore, the thickness of the patterned tantalum absorber layer satisfies the following formula: , in, Where n is the thickness of the tantalum absorption layer, and n is the wavelength of the tantalum absorption layer at the exposure light source. The refractive index below, The angle of refraction of the light beam from the exposure light source in the tantalum absorption layer. It is a positive integer.

[0017] The beneficial effects of this invention are as follows: 1. In this invention, the tantalum absorption layer is set as the top absorption material, which can make full use of the absorption capacity of tantalum material for extreme ultraviolet light. By limiting the thickness of the tantalum absorption layer, the reflected light at the upper and lower interfaces satisfies the destructive interference condition, thereby reducing residual reflection in the absorption area and improving imaging contrast.

[0018] 2. The present invention enables the tantalum absorption layer and the ruthenium absorption layer to have the same planar pattern, and the ruthenium absorption layer is formed by the upper part of the same continuous ruthenium material layer and the ruthenium capping layer is formed by the lower part. This reduces the film interface caused by independently depositing additional ruthenium absorption layers, which is beneficial to reducing film stress and fabrication complexity.

[0019] 3. In this invention, a continuous ruthenium capping layer is retained to cover the reflective stack, so that the ruthenium capping layer has the functions of protecting the reflective stack and stopping the etching; the ruthenium absorption layer supplements the effective thickness of the composite absorption structure, so as to maintain the target absorption performance while protecting the reflective stack.

[0020] 4. The present invention determines the etching endpoint of the tantalum absorber layer by the first significant change in the etching rate, and controls the continued etching depth of the ruthenium layer according to the pre-calibrated target time interval. This enables the formation of a ruthenium absorber layer of target height and the retention of a ruthenium capping layer of target thickness in different batch processes. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments are briefly described below. The drawings are used to illustrate the structure and preparation process of the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0022] Figure 1 This is a schematic diagram of a reflective photolithography mask stack-up structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the relationship between the tantalum absorber layer etching endpoint, the target time interval, and the ruthenium layer etching depth, as provided in an embodiment of the present invention. Figure 3 This is a flowchart of a method for fabricating a reflective photomask provided in an embodiment of the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The following embodiments are used to illustrate the structural relationships, film thickness determination methods, and preparation processes of the present invention, wherein the materials, film thicknesses, and process parameters given are feasible examples. Those skilled in the art can make adjustments according to the exposure wavelength, material optical parameters, and etching equipment characteristics.

[0024] Example 1: This embodiment provides a reflective photomask, including a substrate 5, a reflective stack 4 disposed on the substrate 5, a ruthenium capping layer 3 continuously disposed on the reflective stack 4, a ruthenium absorption layer 2 disposed on the ruthenium capping layer 3, and a tantalum absorption layer 1 disposed on the ruthenium absorption layer 2.

[0025] As shown in the appendix Figure 1 As shown, the ruthenium absorption layer 2 and the tantalum absorption layer 1 have the same planar pattern. The ruthenium absorption layer 2 and the ruthenium capping layer 3 are formed from the same continuous ruthenium material layer. In the patterned region, the upper part of the continuous ruthenium material layer forms the ruthenium absorption layer 2, and the lower part retains the ruthenium capping layer 3. In the position where the ruthenium absorption layer 2 pattern is not formed, the ruthenium capping layer 3 continuously covers the surface of the reflective stack 4, thereby maintaining the continuous coverage of the reflective stack 4 by the ruthenium capping layer 3.

[0026] The tantalum absorption layer 1 is located above the ruthenium absorption layer 2 and serves as the top absorption layer of this reflective photomask. The tantalum absorption layer 1 is a patterned film layer, and its planar pattern is the same as that of the ruthenium absorption layer 2 located below it.

[0027] In this embodiment, the tantalum absorption layer 1 has a thickness of 35–40 nm, the ruthenium absorption layer 2 has a height of 10–15 nm relative to the ruthenium capping layer 3, and the ruthenium capping layer 3 has a thickness of 4–7 nm. The ruthenium absorption layer 2 supplements the overall thickness of the absorption layer, while the ruthenium capping layer 3 protects the reflective stack 4 and ensures the transmission of exposed light. Simultaneously, the portion of the ruthenium capping layer 3 connected to the ruthenium absorption layer 2 continues to contribute to the overall thickness of the absorption layer. The ruthenium capping layer 3 also serves as an etching stop layer for the reflective stack 4 to protect it.

[0028] The thickness of the tantalum absorption layer 1 is determined according to the wavelength of the exposure light source and the refractive index of the tantalum absorption layer 1, so that the round-trip optical path of the light beam from the exposure light source in the tantalum absorption layer 1 satisfies the destructive interference condition. The thickness of the tantalum absorption layer 1 satisfies: , in, The thickness of tantalum absorber layer 1 is given. For tantalum absorber layer 1 at the wavelength of the exposure light source The refractive index below, The angle of refraction of the light beam from the exposure source in the tantalum absorption layer 1. It is a positive integer.

[0029] When the light beam is reflected at the two interfaces of the tantalum absorption layer 1, no abrupt change in the reflection phase occurs. Therefore, the destructive interference condition is determined by the thickness of the tantalum absorption layer 1, ensuring that the round-trip optical path within the tantalum material satisfies an odd multiple of half the wavelength of the exposure light source, i.e.: , The thickness relationship of the aforementioned tantalum absorber layer 1 is obtained through transformation: , Therefore, by configuring the thickness of the tantalum absorption layer 1 located at the top layer, destructive interference is generated between the reflected light formed on the upper and lower surfaces of the tantalum absorption layer 1, thereby reducing the influence of reflected light on the surface of the tantalum absorption layer 1 while utilizing the tantalum absorption layer 1 for light absorption.

[0030] A reflective stack 4 is disposed between the substrate 5 and the ruthenium capping layer 3 to reflect extreme ultraviolet light beams. The reflective stack 4 consists of multiple periodically stacked low-refractive-index layers and high-refractive-index layers, wherein the low-refractive-index layer is made of silicon and the high-refractive-index layer is made of molybdenum. The substrate 5 is made of a material with low thermal expansion properties, such as ceramic or glass.

[0031] With the above structure, the tantalum absorption layer 1 is placed above the ruthenium absorption layer 2, so that tantalum is used as the top layer absorbing material. At the same time, by configuring the thickness of the tantalum absorption layer 1, the reflected light from the upper and lower surfaces of the tantalum absorption layer 1 satisfies the destructive interference condition, thereby reducing the influence of the reflected light from the surface of the tantalum absorption layer 1 while ensuring the light absorption effect, so as to improve the grayscale ratio of the mask image.

[0032] Example 2: This embodiment provides a method for preparing the aforementioned reflective photomask, comprising the following steps.

[0033] S1 provides substrate 5.

[0034] The substrate 5 provided is made of ceramic or glass material.

[0035] S2, a reflective stack 4 is formed on the substrate 5.

[0036] The reflective stack 4 is composed of multiple periodically stacked low-refractive-index layers and high-refractive-index layers, wherein the low-refractive-index layer is made of silicon and the high-refractive-index layer is made of molybdenum.

[0037] S3, a ruthenium layer is formed on the reflective stack 4.

[0038] The ruthenium layer is used to form a ruthenium absorption layer 2 and a continuous ruthenium capping layer 3 in the subsequent patterning process, wherein the upper part that is subsequently patterned forms the ruthenium absorption layer 2, and the lower part that is not removed forms the continuous ruthenium capping layer 3.

[0039] S4, a tantalum layer is formed on the ruthenium layer.

[0040] The formed tantalum layer is located above the ruthenium layer, and a tantalum absorption layer 1 is formed after subsequent patterning.

[0041] S5, depositing a photoresist layer on the tantalum layer.

[0042] S6, patterning the photoresist layer to form a pattern for subsequent tantalum layer patterning.

[0043] S7. Using the patterned photoresist layer as a mask, the tantalum layer is patterned to form a patterned tantalum absorber layer 1.

[0044] S8, using the formed tantalum absorption layer 1 as a mask, the upper part of the ruthenium layer is patterned to form a ruthenium absorption layer 2 with the same planar pattern as the tantalum absorption layer 1, while the lower part of the ruthenium layer is retained, thereby forming a continuous ruthenium capping layer 3.

[0045] In the above preparation process, when patterning the tantalum and ruthenium layers, the corresponding etching process is determined by the change in etching rate.

[0046] Specifically, as shown in the attached document Figure 2As shown, the upper dashed line indicates the etching position at the moment the etching rate first changes, and the double-headed arrows indicate the thickness of the ruthenium layer etched over the target time interval. The etching rate is monitored during the etching process. When the etching rate changes significantly for the first time, the tantalum absorber layer 1 is determined to be patterned. From the moment the etching rate changes significantly for the first time, the ruthenium layer continues to be etched according to the predetermined target time interval. The etching degree of the upper part of the ruthenium layer is controlled by the target time interval, thereby forming a ruthenium absorber layer 2 of predetermined height, while the lower part of the ruthenium layer is retained to form an unpatterned continuous ruthenium capping layer 3.

[0047] The target time interval is predetermined based on the required height of the ruthenium absorption layer 2 and the etching process parameters.

[0048] When determining the target time interval, a ruthenium reference layer is formed on a reference substrate 5 with a surface material different from that of ruthenium. This ruthenium reference layer uses the same material as the ruthenium absorption layer 2 and has the same thickness as the desired ruthenium absorption layer 2. A film layer of a material other than ruthenium, such as a tantalum layer, can be pre-formed on the surface of the reference substrate 5, and then a ruthenium reference layer of corresponding thickness is formed on this film layer.

[0049] The ruthenium reference layer was etched using the same etching process parameters as the ruthenium layer in the reflective lithography mask, and the time interval from the start of etching the ruthenium reference layer to the point where the etching rate changed significantly was recorded. This time interval was used as the reference target time interval.

[0050] Under the same etching process parameters, the above process was measured multiple times to obtain multiple reference target time intervals. For the obtained multiple reference target time intervals, outliers that were significantly higher or lower than other data were removed, and the average value of the remaining data was taken to obtain the target time interval for the actual etching process of the reflective photomask.

[0051] In the actual etching of the reflective photomask, the tantalum layer is first patterned according to the aforementioned steps. When a significant change in the etching rate is detected for the first time, it indicates that the patterning of the tantalum absorber layer 1 is complete. From this moment on, the etching continues for the target time interval while maintaining the same etching process parameters to etch the upper portion of the ruthenium layer, forming a ruthenium absorber layer 2 with a height of 10–15 nm, and retaining a continuous ruthenium capping layer 3 with a thickness of 4–7 nm located below it.

[0052] Thus, in the same continuous film layer of ruthenium, a ruthenium absorption layer 2 is formed by controlling the patterned etching of the upper part, while the lower part is retained as a continuous ruthenium capping layer 3, so that the formed ruthenium absorption layer 2 and tantalum absorption layer 1 have the same planar pattern.

[0053] The formed tantalum absorber layer 1 has a thickness of 35–40 nm and is configured according to the following formula: , in, The thickness of tantalum absorber layer 1 is given. For tantalum absorber layer 1 at the wavelength of the exposure light source The refractive index below, The angle of refraction of the light beam from the exposure source in the tantalum absorption layer 1. It is a positive integer.

[0054] Through the above preparation method, a reflective photomask is finally obtained, which includes a substrate 5, a reflective stack 4, a continuous ruthenium capping layer 3, a ruthenium absorption layer 2 and a tantalum absorption layer 1 in sequence. The tantalum absorption layer 1 and the ruthenium absorption layer 2 have the same planar pattern, and the ruthenium absorption layer 2 and the ruthenium capping layer 3 are formed from the same continuous ruthenium material layer.

[0055] The above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any equivalent substitutions or conventional adjustments made by those skilled in the art regarding material selection, number of film layers, pattern size, and etching monitoring methods without departing from the inventive concept should fall within the protection scope of the invention.

Claims

1. A reflective photolithography mask, characterized in that, The invention includes a substrate, a reflective stack disposed on the substrate, a ruthenium capping layer continuously disposed on the reflective stack, a ruthenium absorbing layer disposed on the ruthenium capping layer, and a tantalum absorbing layer disposed on the ruthenium absorbing layer; The ruthenium absorption layer and the tantalum absorption layer have the same planar pattern. The ruthenium absorption layer and the ruthenium capping layer are formed from the same continuous ruthenium material layer. The ruthenium capping layer continuously covers the reflective stack. The thickness of the tantalum absorption layer is configured such that the round-trip optical path of the light beam of the exposure light source in the tantalum absorption layer is an odd multiple of half the wavelength of the exposure light source.

2. The reflective photomask according to claim 1, characterized in that, The tantalum absorber layer has a thickness of 35 to 40 nm, the ruthenium absorber layer has a height of 10 to 15 nm relative to the ruthenium capping layer, and the ruthenium capping layer has a thickness of 4 to 7 nm.

3. The reflective photomask according to claim 2, characterized in that, The thickness of the tantalum absorption layer satisfies the following formula: ， Where D is the thickness of the tantalum absorption layer, and n is the wavelength of the tantalum absorption layer at the exposure light source. The refractive index below, Let k be the angle of refraction of the light beam from the exposure light source in the tantalum absorption layer, where k is a positive integer.

4. The reflective photomask according to claim 1, characterized in that, The reflective stack consists of multiple periodically stacked low-refractive-index layers and high-refractive-index layers.

5. The reflective photomask according to claim 4, characterized in that, The low-refractive-index layer is made of silicon, and the high-refractive-index layer is made of molybdenum.

6. The reflective photomask according to claim 1, characterized in that, The substrate is made of ceramic or glass.

7. A method for fabricating a reflective photomask, characterized in that, include: S1 provides a substrate; S2, a reflective stack is formed on the substrate; S3, a ruthenium layer is formed on the reflective stack; S4, a tantalum layer is formed on the ruthenium layer; S5, deposit a photoresist layer on the tantalum layer; S6, pattern the photoresist layer; S7, using the photoresist layer as a mask, pattern the tantalum layer to form a patterned tantalum absorption layer; S8, using the tantalum absorption layer as a mask, pattern the upper portion of the ruthenium layer to form a ruthenium absorption layer with the same planar pattern as the tantalum absorption layer, and leave the lower portion of the ruthenium layer as a continuous ruthenium cover layer; The thickness of the tantalum absorption layer is configured such that the round-trip optical path of the light beam from the exposure light source in the tantalum absorption layer is an odd multiple of half the wavelength of the exposure light source.

8. The method for fabricating a reflective photomask according to claim 7, characterized in that, The method further includes: During the etching process, the etching rate is monitored. When the etching rate changes significantly for the first time, it is determined that the tantalum absorption layer has been patterned. From the moment when the etching rate first changes significantly, the ruthenium layer continues to be etched according to a predetermined target time interval, which is determined in advance based on the required height of the ruthenium absorption layer and the etching process parameters.

9. The method for fabricating a reflective photomask according to claim 8, characterized in that, The target time interval is predetermined in the following manner: A ruthenium reference layer with the same material as the ruthenium absorption layer and the same height as the required ruthenium absorption layer is formed on a reference substrate with a different surface material than ruthenium. The ruthenium reference layer is then etched using the same etching process parameters as the ruthenium layer. Record the time interval from the start of etching the ruthenium reference layer to the moment when the etching rate changes significantly, and use this time interval as a reference target time interval; The ruthenium reference layer was etched repeatedly using the same etching process parameters to obtain multiple reference target time intervals. After removing outliers, the average value was taken as the target time interval.

10. The method for fabricating a reflective photomask according to claim 7, characterized in that, The thickness of the patterned tantalum absorber layer satisfies the following formula: ， in, Where n is the thickness of the tantalum absorption layer, and n is the wavelength of the tantalum absorption layer at the exposure light source. The refractive index below, The angle of refraction of the light beam from the exposure light source in the tantalum absorption layer. It is a positive integer.

Images