Euv mask defect detection apparatus and method

Abstract

The application relates to an EUV mask defect detection device and method, the device comprising an EUV light source, an EUV polarizer, an EUV mask, an off-axis wave band piece and a detector arranged in sequence along the light transmission direction, the EUV light source being used for emitting linearly polarized EUV light, the EUV polarizer being used for adjusting the polarization state of the linearly polarized EUV light, so that the reflected light of the EUV polarizer is s-polarized EUV light; the EUV mask has a preset positional relationship with the EUV polarizer, so that the s-polarized light is converted into p-polarized light relative to the EUV mask when the s-polarized light is incident on the EUV mask, and the incident angle of the p-polarized light incident on the EUV mask is the quasi-Brewster angle of the EUV mask; the p-polarized light is reflected by the EUV mask after being incident on the EUV mask, the off-axis wave band piece is used for focusing the reflected light of the EUV mask, and the detector is used for receiving the reflected light focused by the off-axis wave band piece and imaging, so as to obtain the image of the EUV mask.

Description

Technical Field

[0001] This invention relates to the field of mask technology, and more specifically to an EUV mask defect detection device and method. Background Technology

[0002] As semiconductor chips rapidly advance towards higher precision and density, extreme ultraviolet (EUV) lithography has become a core supporting technology for the manufacturing of advanced process chips at 7nm and below. It uses a projection system to precisely print circuit patterns from an EUV mask onto the wafer surface, achieving efficient transfer of chip circuit patterns and is a key step in driving the continued advancement of Moore's Law. The EUV mask, as a core component of the EUV lithography process, is a complex patterned precision component, mainly composed of a mask substrate made of a material with a low coefficient of thermal expansion, Mo / Si multilayer films, and a TaN absorption layer. The integrity and precision of each structure directly determine the quality of the lithographic pattern transfer, thus affecting the chip's performance and yield.

[0003] However, Mo / Si multilayer films on EUV masks are highly susceptible to defects, primarily originating from two sources: first, phase defects inherited from residual defects in the mask substrate and propagated to the multilayer film; and second, defects introduced during the multilayer film deposition process. Specifically, defects caused by contamination in the early stages of deposition are phase defects, while those arising near or after the deposition process are amplitude defects. Both types of defects affect EUV lithography imaging: amplitude defects directly influence the intensity distribution of the mask's spatial image and may be replicated onto the silicon wafer; phase defects alter the phase of the mask's diffraction spectrum, making their impact on imaging more complex and difficult to accurately identify.

[0004] Any defects on the EUV mask will directly interfere with the propagation path of 13.5nm extreme ultraviolet light, causing distortion of the circuit patterns transferred on the wafer. This distortion can lead to reduced chip circuit performance and even short-circuit failures, ultimately resulting in decreased chip functionality, reduced production yield, and shortened lifespan, causing huge economic losses to semiconductor manufacturers. As semiconductor fabrication processes advance to 7nm and below, extremely high requirements are placed on defect control of EUV masks. Current industry standards for commercial 6-inch EUV masks clearly stipulate that there must be no defects larger than 50nm on the mask, and the number of defects between 15nm and 50nm must not exceed three. To meet this stringent requirement, EUV mask defect detection technology must possess both rapid detection capabilities and high sensitivity to achieve accurate detection of large-area, low-density nanoscale defects.

[0005] In existing technologies, amplitude defects in EUV masks can be detected and analyzed using traditional non-actinic defect analysis methods, including 193nm mask defect detection equipment, atomic force microscopy (AFM), scanning electron microscopy (SEM), and Auger electron microscopy (AES). These methods can effectively identify and analyze amplitude defects. However, for phase defects, because the Mo / Si multilayer film of the EUV mask is opaque in the ultraviolet to visible light range, traditional non-13.5nm detection techniques cannot reproduce the real scene of EUV lithography exposure, making it difficult to accurately detect and analyze phase defects. If a phase defect is not effectively detected, it will be replicated on all chips with that part of the mask pattern during the lithography process, potentially damaging tens of thousands of chip devices and causing extremely heavy economic losses. Summary of the Invention

[0006] The purpose of this invention is to provide an EUV mask defect detection device and method to achieve accurate and rapid detection of EUV mask defects, especially phase defects, thereby ensuring the production yield and product quality of advanced process chips.

[0007] To achieve the above objectives, the present invention provides an EUV mask defect detection device, comprising an EUV light source, an EUV polarizer, an EUV mask, an off-axis zone plate, and a detector arranged sequentially along the light transmission direction. The EUV light source emits linearly polarized EUV light, which is incident on the EUV polarizer. The EUV polarizer modulates the polarization state of the linearly polarized EUV light so that the reflected light from the EUV polarizer is s-polarized EUV light. The EUV mask and the EUV polarizer are in a predetermined positional relationship. The method is as follows: s-polarized light emitted from the EUV polarizer is converted into p-polarized light relative to the EUV mask when it is incident on the EUV mask. The incident angle of the p-polarized light on the EUV mask is the quasi-Brewster angle of the EUV mask. After the p-polarized light is incident on the EUV mask, it is reflected by the EUV mask. The off-axis zone plate is used to focus the reflected light from the EUV mask. The detector is used to receive the reflected light after it has been focused by the off-axis zone plate and to perform imaging to obtain an image of the EUV mask.

[0008] Optionally, the linearly polarized EUV light propagates along the u direction and has the v direction as the main polarization direction. The normal of the EUV polarizer is located in the uw plane, and the incident angle of the linearly polarized EUV light onto the EUV polarizer is the quasi-Brewster angle of the EUV polarizer. Here, uvw is a predefined three-dimensional rectangular coordinate system, and the u, v, and w directions are orthogonal to each other.

[0009] Optionally, the EUV polarizer includes a substrate and a multilayer film structure formed on the substrate. The multilayer film structure is composed of alternating Mo layers and Si layers, with one Mo layer and one Si layer forming a periodic unit. The multilayer film structure includes multiple periodic units.

[0010] Optionally, the EUV polarizer has 30 periodic units, each with a thickness of 9.29 nm, wherein the Mo layer accounts for 34% of the thickness and the Si layer accounts for 66%.

[0011] Optionally, both the EUV polarizer and the EUV mask have square surfaces. A first local coordinate system is established with any point on the surface of the EUV polarizer as the origin, the longer side as the X direction, the shorter side as the Y direction, and the direction perpendicular to the surface of the EUV polarizer as the Z direction. A second local coordinate system is established with any point on the surface of the EUV mask as the origin, the longer side as the X' direction, the shorter side as the Y' direction, and the direction perpendicular to the surface of the EUV polarizer as the Z' direction. The first local coordinate system and the second local coordinate system satisfy the following relationship:

[0012] ,

[0013] Wherein, α is the quasi-Brewster angle of the EUV polarizer, and β is the quasi-Brewster angle of the EUV mask.

[0014] Optionally, the EUV light source is an undulator light source.

[0015] Optionally, the detector is a CCD camera.

[0016] Another aspect of the present invention provides a method for detecting defects in EUV masks, comprising:

[0017] An EUV mask defect detection device as described above is provided;

[0018] The EUV light source emits linearly polarized EUV light, which passes sequentially through an EUV polarizer, an EUV mask, and an off-axis zone plate before being received and imaged by a detector to obtain an image of the EUV mask.

[0019] Defect detection is performed based on the image from the EUV mask.

[0020] Optionally, defect detection of the EUV mask is performed based on the image of the EUV mask, specifically including:

[0021] Identify the brightness of different regions in the image of the EUV mask;

[0022] Defect detection is performed based on the brightness of different regions of the image from the EUV mask.

[0023] Optionally, defect detection is performed based on the brightness of different regions of the EUV mask image, specifically including:

[0024] For each region of the EUV mask image, if the brightness of that region exceeds a preset threshold, then that region is considered a defective region; or,

[0025] The brightness of different regions in the EUV mask image is compared, and regions with significantly higher brightness than the rest are identified as defective regions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of an EUV mask defect detection device according to an embodiment of the present invention;

[0027] Figure 2 This is a one-dimensional photon number distribution map of the imaging surface of a CCD camera according to an exemplary embodiment of the present invention;

[0028] Figure 3 This is a one-dimensional photon number distribution map of the imaging surface of a CCD camera obtained using a traditional mask defect detection method.

[0029] Figure 4 This is a flowchart of an EUV mask defect detection method according to an embodiment of the present invention. Detailed Implementation

[0030] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0031] like Figure 1As shown, this embodiment of the invention provides an EUV mask defect detection device, which includes an EUV light source 100, an EUV polarizer 200, an EUV mask 300, an off-axis zone plate 400, and a detector 500 arranged sequentially along the light transmission direction. The EUV light source 100 is used to emit linearly polarized EUV light, and the EUV polarizer 200 is used to modulate the polarization state of the linearly polarized EUV light to output s-polarized EUV light. The EUV mask 300 and the EUV polarizer 200 are in a preset positional relationship so that when the s-polarized EUV light output by the EUV polarizer 200 is incident on the surface of the EUV mask, its polarization direction is relative to the EUV mask. The incident surface of EUV mask 300 is converted from s-polarization to p-polarization. That is, the s-polarized EUV light emitted from EUV polarizer 200 is converted into p-polarized EUV light incident on EUV mask 300. The incident angle between the p-polarized EUV light and EUV mask 300 is the quasi-Brewster angle of EUV mask 300. After the p-polarized EUV light is incident on EUV mask 300, it will be reflected to form reflected light. Off-axis zone plate 400 is used to focus the EUV light reflected by EUV mask 300. Detector 500 is used to receive the EUV light focused by off-axis zone plate 400 and perform imaging to obtain an image of EUV mask 300. When p-polarized EUV light is incident on the EUV mask 300 at a quasi-Brewster angle, if it illuminates a defect-free area, the p-polarized EUV light will be suppressed, and the reflectivity will be significantly reduced. However, in a defective area, the EUV mask structure is distorted, and the reflectivity of the p-polarized EUV light will be significantly increased. Thus, in the image of the EUV mask 300 detected by the detector 500, the brightness of the defective area will be significantly higher than that of the defect-free area. Therefore, the presence and location of defects in the EUV mask 300 can be determined from the image of the EUV mask 300, thereby achieving defect detection of the EUV mask 300. Alternatively, the brightness of different areas of the image can be detected, and areas with brightness exceeding a preset threshold can be identified as defective areas, thereby determining whether the EUV mask 300 has defects and their specific locations.

[0032] In some embodiments, the EUV light source 100 can be an undulator light source, which can produce highly polarized linearly polarized EUV light. Taking the BL07U beamline of the Shanghai Synchrotron Radiation Facility as an example, it uses an undulator light source. When the gap (GAP) of the undulator magnet assembly is 29.2 mm, the polarization degree of the EUV light it produces at 92.5 eV energy is 83%.

[0033] In some embodiments, a three-dimensional Cartesian coordinate system uvw can be defined, where the u direction is the first direction, the v direction is the second direction (perpendicular to the first direction), and the w direction is the third direction (perpendicular to both the first and second directions). Linearly polarized EUV light propagates along the u direction, with the v direction as its dominant polarization direction, meaning the electric field direction primarily vibrates along the v direction. By adjusting the position of the EUV polarizer 200, the normal to the EUV polarizer 200 is located in the uw plane, and the incident angle of the linearly polarized EUV light onto the EUV polarizer 200 is the quasi-Brewster angle of the EUV polarizer 200. Thus, the EUV polarizer 200 has the highest reflectivity for EUV light polarized in the v direction, while its reflectivity for EUV light polarized in the w direction is lower. Since the reflectivity of the line polarizer is the lowest, the polarization degree in the v direction of linearly polarized EUV light will be greatly increased after passing through the EUV polarizer 200. That is, the reflected light after passing through the EUV polarizer 200 is highly polarized in the v direction (the polarization degree in the v direction can be increased to more than 99.99%). Since the normal of the EUV polarizer 200 is located in the uw plane, the incident surface of the EUV polarizer 200 is the uw plane. Since the v direction is perpendicular to the uw plane, the linearly polarized EUV light in the v direction is s-polarized light relative to the EUV polarizer 200. After being reflected by the EUV polarizer 200, the linearly polarized EUV light will become highly polarized in the v direction, that is, highly polarized s-polarized EUV light. By adjusting the position of the downstream EUV mask 300, the incident surface formed by the reflected light from the EUV polarizer 200 incident on the EUV mask 300 can be made perpendicular to the incident surface of the linearly polarized EUV light incident on the EUV polarizer 200. In this way, the vibration direction of the s-polarized light in the reflected light from the EUV polarizer 200 will be parallel to the incident surface of the EUV mask 300. That is, the emitted s-polarized light from the EUV polarizer 200 is p-polarized light relative to the EUV mask 300, thereby realizing the conversion of the reflected light from the EUV polarizer 200 from s-polarized light to p-polarized light.

[0034] The EUV polarizer 200 can be a multilayer film polarizer, comprising a substrate and a multilayer film structure formed on the substrate. The multilayer film structure is composed of alternating layers of molybdenum (Mo) and silicon (Si), with one Mo layer and one Si layer forming a periodic unit. For example, the number of periodic units in the multilayer film structure is 30, and the thickness of each periodic unit can be 9.29 nm, where the thickness of the Mo layer accounts for 34% and the thickness of the Si layer accounts for 66%. In this case, the quasi-Brewster angle of the EUV polarizer 200 is 42.8°. When incident light is incident on the EUV polarizer 200 at a quasi-Brewster angle, the reflectivity of the s-polarized light of the EUV polarizer 200 is 71%, and the reflectivity of the p-polarized light is 0.0018%. The polarization efficiency of the EUV polarizer 200 can reach 99.995%. Ideally, the EUV polarizer 200 can increase the polarization degree of linearly polarized EUV light in the v direction to 99.9995%.

[0035] The off-axis zone plate 400 can separate the direct-transmitted zero-order light and the first-order diffracted light, avoiding interference signals from the zero-order diffraction. The off-axis zone plate 400 can achieve 1000x magnification imaging.

[0036] Both the EUV polarizer 200 and the EUV mask 300 have square surfaces. A first local coordinate system, XYZ, is established with any point on the surface of the EUV polarizer 200 as the origin, the longer side as the X direction, the shorter side as the Y direction, and the direction perpendicular to the surface of the EUV polarizer 200 as the Z direction. A second local coordinate system, X'-Y'-Z', is established with any point on the surface of the EUV mask 300 as the origin, the longer side as the X' direction, the shorter side as the Y' direction, and the direction perpendicular to the surface of the EUV mask 300 as the Z' direction. The positional relationship between the EUV polarizer 200 and the EUV mask 300 can be defined by the relationship between the two local coordinate systems. Assuming the quasi-Brewster angle of the EUV polarizer 200 is α and the quasi-Brewster angle of the EUV mask 300 is β, the relationship between the two local coordinate systems is:

[0037] .

[0038] In one exemplary embodiment, the EUV light source 100 is a BL07U beamline station of the Shanghai Synchrotron Radiation Facility, with a GAP value of 29.2 nm for the undulator light source and a monochromator energy of 92.5 eV. The EUV polarizer 200 has 30 periods, a period thickness of 9.29 nm, and Mo and Si layers accounting for 34% and 66% of the total thickness, respectively. The quasi-Brewster angle α = 42.8°, and considering parameter errors, the actual polarization degree is approximately 99.99%. The EUV mask 300 is located at a beamline of 42.5 meters. Its substrate is silicon dioxide, and the multilayer film material is also Mo and Si. It has 40 periods, a period thickness of 6.95 nm, and Mo and Si layers accounting for 40% and 60% of the total thickness, respectively. The quasi-Brewster angle is 42.8°. The EUV mask has a 0.8° angle, and the mask defect is located on the substrate. The defect is a spherical nanoparticle with a diameter of 40 nm. After multilayer film deposition, the surface deformation range of the EUV mask is 200 nm (L) × 200 nm (W) × 3 nm (H). The parameters of the off-axis zone plate are: the substrate material is Si3N4, the surface is gold-plated, the focal length is 750 μm, the diameter is 245 μm, the outermost ring width is 20.8 nm, the minimum off-axis angle is 1.2°, the EUV light diffraction efficiency is 10%, and the distance between the off-axis zone plate 400 and the EUV mask is 750.75 μm. The detector 500 is a CCD (charge-coupled element) camera, which is located 750.75 mm behind the off-axis zone plate 400. The CCD camera pixel array is 2048 × 2048, and the pixel size is 13.5 μm. The apparatus described in the exemplary embodiment above performs defect detection on the EUV mask 300. When the incident angle of the EUV mask 300 is its quasi-Brewster angle of 42.8° and the exposure time of the CCD camera is 1 second, the one-dimensional p-polarized photon number distribution on the CCD imaging surface is as follows: Figure 2 As shown, from Figure 2 It can be seen that the central region of the photon number distribution, 200 μm (approximately 11 pixels), is the imaging range of the mask defect, with an average photon number per pixel of approximately 14.5 phs; the remaining pixel area represents the mask background photon number distribution, with an average photon number per pixel of approximately 0.08 phs. Due to the high sensitivity of the CCD camera, it is possible to image defects even with low photon counts. In summary, the single-pixel photon number contrast between defective and defect-free areas in this invention is approximately (14.5 - 0.08) / 0.08 = 180.25. In contrast, in the prior art, a 6° incident angle is used for mask detection, and the CCD imaging surface has a photon number distribution as shown in the figure. Figure 3 As shown; according to Figure 3 The average photon count per pixel in the central region (200 μm) is approximately 1.36 × 10⁻⁶. 5 phs; the remaining pixel area represents the photon number distribution of the mask background, with an average photon number per pixel of approximately 1.82 × 10⁻⁶. 5 Phs. The single-pixel photon count contrast at a 6° incident angle between defective and defect-free locations is approximately (1.82 × 10⁻⁶). 5 -1.36×105 ) / 1.82×10 5 =0.25. That is to say, compared with the traditional mask defect detection method, the present invention can improve the mask defect detection sensitivity by about 180.25 / 0.25=721 times.

[0039] The EUV mask defect detection device of this invention improves the polarization degree of s-polarized light by using EUV polarizer 200. By utilizing the positional relationship between EUV polarizer 200 and EUV mask 300, the high polarization degree s-polarized light relative to EUV polarizer 200 is converted into high polarization degree p-polarized light relative to EUV mask 300. By utilizing the significant difference between the reflectivity of p-polarized light in EUV mask defect and non-defect regions, high-precision detection of EUV mask defects is achieved.

[0040] like Figure 4 As shown, this embodiment of the invention also provides a method for detecting defects in EUV masks, which includes the following steps:

[0041] S10: Provide an EUV mask defect detection device as described in the above embodiments;

[0042] S20: The EUV light source 100 emits linearly polarized EUV light. The linearly polarized EUV light passes through the EUV polarizer 200, EUV mask 300 and off-axis zone plate 400 in sequence and is received and imaged by the detector 500 to obtain the image of EUV mask 300.

[0043] S30: Defect detection based on the image from EUV mask 300.

[0044] In some embodiments, step S30 specifically includes:

[0045] S31: Identify the brightness of different regions in the image of the EUV mask 300;

[0046] S32: Defect detection based on the brightness of different regions of an image using an EUV mask 300.

[0047] In some embodiments, step S32 specifically includes:

[0048] For each region of the image from the EUV mask 300, if the brightness of that region exceeds a preset threshold, then that region is considered a defective region; or,

[0049] The brightness of different regions in the EUV mask 300 image is compared, and regions with significantly higher brightness than the rest are identified as defective regions.

[0050] The EUV mask defect detection method of this invention improves the polarization degree of s-polarized light by using EUV polarizer 200. By utilizing the positional relationship between EUV polarizer 200 and EUV mask 300, the high polarization degree s-polarized light relative to EUV polarizer 200 is converted into high polarization degree p-polarized light relative to EUV mask 300. By utilizing the significant difference between the reflectivity of p-polarized light in EUV mask defect and non-defect regions, high-precision detection of EUV mask defects is achieved.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. An EUV mask defect detection device, characterized in that, The device includes an EUV light source, an EUV polarizer, an EUV mask, an off-axis zone plate, and a detector arranged sequentially along the light transmission direction. The EUV light source is used to emit linearly polarized EUV light. The linearly polarized EUV light is incident on the EUV polarizer. The EUV polarizer is used to modulate the polarization state of the linearly polarized EUV light so that the reflected light from the EUV polarizer is s-polarized EUV light. The EUV mask and the EUV polarizer are in a predetermined positional relationship, so that the s-polarized light emitted from the EUV polarizer is converted into p-polarized light relative to the EUV mask when it is incident on the EUV mask. The incident angle of the p-polarized light on the EUV mask is the quasi-Brewster angle of the EUV mask. After the p-polarized light is incident on the EUV mask, it is reflected by the EUV mask. The off-axis zone plate is used to focus the reflected light from the EUV mask. The detector is used to receive the reflected light after it has been focused by the off-axis zone plate and to perform imaging to obtain an image of the EUV mask.

2. The EUV mask defect detection device according to claim 1, characterized in that, The linearly polarized EUV light propagates along the u direction and has the v direction as its main polarization direction. The normal of the EUV polarizer is located in the uw plane and the incident angle of the linearly polarized EUV light onto the EUV polarizer is the quasi-Brewster angle of the EUV polarizer. Here, uvw is a predefined three-dimensional rectangular coordinate system, and the u, v, and w directions are orthogonal to each other.

3. The EUV mask defect detection device according to claim 1, characterized in that, The EUV polarizer includes a substrate and a multilayer film structure formed on the substrate. The multilayer film structure is composed of alternating Mo layers and Si layers, with one Mo layer and one Si layer forming a periodic unit. The multilayer film structure includes multiple periodic units.

4. The EUV mask defect detection device according to claim 3, characterized in that, The EUV polarizer has 30 periodic units, each with a thickness of 9.29 nm, of which the Mo layer accounts for 34% of the thickness and the Si layer accounts for 66%.

5. The EUV mask defect detection device according to claim 1, characterized in that, Both the EUV polarizer and the EUV mask have square surfaces. A first local coordinate system is established with any point on the surface of the EUV polarizer as the origin, the longer side as the X direction, the shorter side as the Y direction, and the direction perpendicular to the surface of the EUV polarizer as the Z direction. A second local coordinate system is established with any point on the surface of the EUV mask as the origin, the longer side as the X' direction, the shorter side as the Y' direction, and the direction perpendicular to the surface of the EUV polarizer as the Z' direction. The first local coordinate system and the second local coordinate system satisfy the following relationship: ， Wherein, α is the quasi-Brewster angle of the EUV polarizer, and β is the quasi-Brewster angle of the EUV mask.

6. The EUV mask defect detection device according to claim 1, characterized in that, The EUV light source is an oscillator light source.

7. The EUV mask defect detection device according to claim 1, characterized in that, The detector is a CCD camera.

8. A method for detecting defects in an EUV mask, characterized in that, include: An EUV mask defect detection device as described in any one of claims 1-7 is provided; The EUV light source emits linearly polarized EUV light, which passes sequentially through an EUV polarizer, an EUV mask, and an off-axis zone plate before being received and imaged by a detector to obtain an image of the EUV mask. Defect detection is performed based on the image from the EUV mask.

9. The mask defect detection method according to claim 8, characterized in that, Defect detection of the EUV mask based on its image specifically includes: Identify the brightness of different regions in the image of the EUV mask; Defect detection is performed based on the brightness of different regions of the image from the EUV mask.

10. The mask defect detection method according to claim 9, characterized in that, Defect detection is performed based on the brightness of different regions of the image from the EUV mask, specifically including: For each region of the EUV mask image, if the brightness of that region exceeds a preset threshold, then that region is considered a defective region; or, The brightness of different regions in the EUV mask image is compared, and regions with significantly higher brightness than the rest are identified as defective regions.

Images