Defect inspection method and defect inspection apparatus for a substrate

Abstract

Provided are a method and an apparatus for inspecting defects of a substrate, which can appropriately set a threshold value for determining detection sensitivity and achieve highly reliable inspection of phase defects in dark-field inspection using scattered light from the substrate to be inspected. A method for inspecting defects of a substrate includes: a step of irradiating EUV light from an EUV light source onto the substrate to be inspected in a first condenser optical system; a step of guiding, in a second condenser optical system, scattered light obtained by removing specularly reflected light from the reflected light reflected from the substrate to be inspected to a light-receiving surface of a sensor; and a step of determining that a defect exists at the irradiation position of the EUV light on the substrate to be inspected when the intensity of the received scattered light exceeds a specified threshold value. The method includes: a reflectance acquisition step of obtaining in advance the reflectance of the EUV light of the substrate to be inspected before irradiating the EUV light onto the substrate to be inspected; and a threshold calculation step of determining the specified threshold value based on the reflectance obtained in the reflectance acquisition step.

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for inspecting defects of a substrate such as a mask blank for manufacturing a reflective mask, which is used for manufacturing semiconductor devices, etc. In particular, the present invention relates to a method and an apparatus for inspecting defects of a substrate using extreme ultraviolet (hereinafter referred to as "EUV") light having a wavelength of about 10 to 20 nm as inspection light. Background Art

[0002] In the manufacturing process of semiconductor devices (semiconductor devices), a lithography technique is repeatedly used, in which an exposure beam is irradiated onto a transfer mask, and a circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) via a reduction projection optical system. Conventionally, the wavelength of the exposure beam has been mainly 193 nm using argon fluoride (ArF) excimer laser. By adopting a process such as multiple exposure processes and multi-patterning of processing processes, a pattern smaller than the exposure wavelength is finally formed.

[0003] However, since it is necessary to form finer patterns than the continuous miniaturization of device patterns, an EUV lithography technique using EUV light having a wavelength shorter than that of ArF excimer laser as an exposure beam is being developed. More specifically, the so-called EUV light is light having a wavelength near 13.5 nm. Since the transmittance of this EUV light with respect to substances is extremely low, existing transmissive projection optical systems and masks cannot be used, so reflective optical elements are used. Therefore, masks for pattern transfer and reflective masks have been proposed.

[0004] A reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light is formed in a pattern on the multilayer reflective film. On the other hand, the structure in the state before patterning on the absorber film (including the state where a resist layer is formed) is called a reflective mask blank, which is used as a raw material for the reflective mask.

[0005] Hereinafter, a reflective mask blank that reflects EUV light is also referred to as an EUV mask blank.

[0006] The basic structure of an EUV mask blank includes: a multilayer reflective film that reflects EUV light formed on a low thermal expansion substrate; and an absorber film that absorbs EUV light formed thereon. As the multilayer reflective film, a Mo / Si multilayer reflective film that ensures the reflectivity of EUV light by alternately laminating a molybdenum (Mo) film and a silicon (Si) film is usually used. Moreover, a protective film for protecting the multilayer reflective film is formed. On the other hand, as the absorber film, a material mainly composed of tantalum (Ta) or chromium (Cr) having a relatively large extinction coefficient value with respect to EUV light is used.

[0007] When EUV lithography is used, even a height deviation of approximately 1 nm on the surface of the multilayer reflective film of a reflective mask imparts a phase shift to the EUV reflected light, causing dimensional variations or resolution issues in the transferred absorber film pattern when it is transferred to the wafer. Height deviations in the mask blank that impart such a phase shift are called phase defects. Because phase defects are extremely difficult to correct after patterning the absorber film, they must be inspected for during the mask blank stage, before the absorber film is formed.

[0008] Phase defects are determined not only by surface irregularities of the multilayer reflective film, but also by irregularities within the film or on the surface of the low-thermal expansion substrate. Therefore, conventional inspection methods using laser light cannot adequately detect these defects. Therefore, a so-called same-wavelength inspection method, which uses inspection light with the same wavelength as the EUV light used to expose the reflective mask, is generally considered suitable. Examples of this method include methods using dark-field inspection images, as disclosed in Patent Documents 1 and 2 and Non-Patent Document 1.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-154902

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2014-153326

[0013] Non-patent literature

[0014] Non-Patent Literature 1: Takeshi Yamane, Yongdae Kim, Noriaki Takagi, Tsuneo Terasawa, Tomohisa Ino, Tomohiro Suzuki, Hiroki Miyai, Kiwamu Takehisa, Haruhiko Kusunose, “Performance in practical use of actinic EUVL mask blank inspection,” Proc. of SPIE Vol. 9256, 92560P. Summary of the Invention

[0015] (1) Technical issues to be resolved

[0016] Including the inspection techniques described in the above-mentioned Patent Document 1 and Non-Patent Document 1, generally speaking, the dark-field inspection method has the following advantages compared with the ordinary bright-field inspection method: it can improve the inspection speed while ensuring a relatively high defect detection sensitivity. In addition, the dark-field inspection image is a luminance signal with a higher background level in the defect part than in the surrounding part. Therefore, by setting a specified threshold value, the position where a signal exceeding the threshold value is obtained can be recognized as a defect, and the detection method is also simple. In addition, if the threshold level is lowered, a higher-sensitivity phase defect inspection can be performed.

[0017] However, the setting of this threshold value needs to be determined by empirical or experimental methods.

[0018] In the dark-field inspection method using EUV light as the inspection light, it is assumed that an inspection signal with a constant background level is obtained even in the case of no defect. This is caused by the surface roughness of the multilayer reflective film. The smaller the roughness, the lower the background level. In that case, lowering the threshold value enables high-sensitivity detection.

[0019] However, this background level is represented by the product of the factor due to the surface roughness and the reflectivity depending on the structure (such as the period length) of the multilayer reflective film. Therefore, for example, in the case of obtaining a signal with a lower background level, it is impossible to distinguish whether the surface roughness is small or the reflectivity of the multilayer reflective film is low.

[0020] The luminance signal level obtained when detecting phase defects does not change even if the surface roughness of the multilayer reflective film is reduced, but when the reflectivity of the multilayer reflective film is reduced, the luminance signal level also decreases. In the case of a relatively small surface roughness, defect detection can be performed without problems using a preset threshold value, and it is expected to improve the detection sensitivity by further lowering the threshold value. However, in the case of a reduced reflectivity, it is also possible that defect detection cannot be performed using the preset threshold value, and the same-sized defects cannot be detected if the threshold value is not lowered.

[0021] As described above, setting the threshold value for determining the detection sensitivity requires information on the reflectivity of the multilayer reflective film. However, in the prior art, it is not clearly described that the reflectivity is considered in the process of setting the threshold value helpful for dark-field inspection.

[0022] The present invention is completed in view of the above technical problems, and its object is to provide a method and apparatus for inspecting defects on a substrate, which can appropriately set a threshold value for determining the detection sensitivity in dark-field inspection using scattered light from the substrate to be inspected, and can achieve a highly reliable phase defect inspection.

[0023] (II) Technical Solution

[0024] In order to achieve the above object, a method for inspecting defects on a substrate is provided, comprising:

[0025] A step of irradiating a substrate to be inspected with EUV light emitted from an EUV light source using a first condenser optical system;

[0026] A step of guiding, to a light-receiving surface of a sensor, scattered light obtained by removing specularly reflected light from reflected light reflected from the substrate to be inspected irradiated with the EUV light using a second condenser optical system; and

[0027] A step of determining that a defect exists at an irradiation position of the EUV light on the substrate to be inspected when the intensity of the scattered light received at the light-receiving surface of the sensor exceeds a specified threshold value,

[0028] characterized in that

[0029] before irradiating the substrate to be inspected with the EUV light, it is previously provided with:

[0030] a reflectance acquisition step of obtaining the reflectance of the EUV light of the substrate to be inspected; and

[0031] a threshold calculation step of determining the specified threshold value based on the reflectance obtained in the reflectance acquisition step.

[0032] According to the method for inspecting a defect of a substrate of the present invention as described above, in dark-field inspection, the threshold value (hereinafter also referred to as THR) is determined based on the reflectance of the substrate to be inspected that affects not only the background level (hereinafter also referred to as BGL) but also the luminance signal level of the defect (hereinafter also referred to as SIG). Therefore, the threshold value can be appropriately set. Accordingly, highly reliable phase defect inspection can be performed.

[0033] At this time, in the reflectance acquisition step,

[0034] the structure of the first condenser optical system or the second condenser optical system can be changed, the first condenser optical system is used to irradiate the substrate to be inspected with the EUV light emitted from the EUV light source, the second condenser optical system is used to guide specularly reflected light from the substrate to be inspected irradiated with the EUV light to the light-receiving surface of the sensor, and the reflectance is obtained based on the light-receiving intensity on the light-receiving surface.

[0035] In this way, the reflectance of the substrate to be inspected can be simply obtained.

[0036] Moreover, when the structure of the first condenser optical system is changed,

[0037] the first condenser optical system can be provided with a mirror, and the position and orientation of the mirror can be changed.

[0038] Thus, by simply changing the structure of the first condenser optical system, the specularly reflected light from the substrate to be inspected can be guided to the light-receiving surface of the sensor.

[0039] Alternatively, in the reflectance acquisition step, the reflectance can be obtained using a reflectometer.

[0040] Thus, the reflectance of the substrate to be inspected can be easily obtained using, for example, a commercially available reflectometer.

[0041] In addition, the substrate to be inspected can be a substrate with a multilayer reflective film formed on its surface that reflects EUV light.

[0042] The defect inspection method of the present invention can be preferably used for inspecting substrates with multilayer reflective films such as reflective mask blanks, for example.

[0043] In addition, the reflectance can be set as the average value over the entire inspection area of the substrate to be inspected.

[0044] Alternatively, the inspection area of the substrate to be inspected can be divided into small regions, the reflectance can be set as the average value of each small region, and the specified threshold can be determined for each small region.

[0045] Thus, the reflectance and the threshold can be appropriately determined according to, for example, the size of the inspection area of the substrate to be inspected.

[0046] In addition, the first condenser optical system and the second condenser optical system can be respectively configured to have a structure with a plurality of mirrors formed with a multilayer reflective film.

[0047] Thus, EUV light can be more appropriately irradiated onto the substrate to be inspected, and scattered light from the substrate to be inspected can be introduced to the light-receiving surface of the sensor.

[0048] In addition, the present invention provides a substrate defect inspection apparatus, which includes: an EUV light source that emits EUV light;

[0049] a first condenser optical system that irradiates EUV light from the EUV light source onto the substrate to be inspected;

[0050] a second condenser optical system that guides scattered light, which is the reflected light from the substrate to be inspected irradiated with the EUV light excluding specularly reflected light, to the light-receiving surface of the sensor; and

[0051] an arithmetic processing unit that, when the intensity of the scattered light received on the light-receiving surface of the sensor exceeds a specified threshold, determines that a defect exists at the irradiation site of the EUV light on the substrate to be inspected, and is characterized in that

[0052] It has a threshold operation unit that determines the specified threshold based on the reflectivity of the EUV light of the substrate to be inspected.

[0053] In the dark field inspection of the substrate defect inspection device according to the present invention, the threshold is determined based on the reflectivity of the substrate to be inspected that affects not only the background level but also the luminance signal level of the defect. Therefore, the threshold is appropriately set. As a result, it becomes a device capable of performing highly reliable phase defect inspection.

[0054] At this time, the structure of the first condenser optical system or the second condenser optical system can be changed.

[0055] The first condenser optical system can be used to irradiate the substrate to be inspected with the EUV light emitted from the EUV light source, and the second condenser optical system can be used to guide the specularly reflected light from the substrate irradiated with the EUV light to the light receiving surface of the sensor.

[0056] And it can have a data acquisition unit that obtains the reflectivity based on the light receiving intensity of the specularly reflected light on the light receiving surface.

[0057] According to such a structure, the reflectivity of the substrate to be inspected can be simply obtained.

[0058] Moreover, the first condenser optical system whose structure can be changed has a mirror.

[0059] The position and posture of this mirror can be changed.

[0060] According to such a structure, the structure of the first condenser optical system can be simply changed to guide the specularly reflected light from the substrate to be inspected to the light receiving surface of the sensor.

[0061] In addition, the substrate to be inspected can be a substrate with a multilayer reflective film formed on its surface that reflects the EUV light.

[0062] The defect inspection device of the present invention can be preferably used, for example, for the structure of a substrate with a multilayer reflective film such as a reflective mask blank.

[0063] The first condenser optical system and the second condenser optical system can each have a structure having a plurality of mirrors formed with multilayer reflective films.

[0064] According to such a structure, the irradiation of EUV light to the substrate to be inspected and the introduction of scattered light from the substrate to be inspected to the light receiving surface of the sensor can be more appropriately performed.

[0065] (III) Advantageous Effects

[0066] According to the present invention, it is possible to provide a method and an apparatus for inspecting defects of a substrate, which can achieve highly reliable inspection of phase defects because the threshold value for determining the detection sensitivity of dark-field inspection can be appropriately set. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 It is a schematic diagram showing an example of the defect inspection apparatus of the present invention.

[0068] Figure 2 (A) thereof is a schematic diagram showing an example of an illumination optical system having two mirrors. Figure 2 (B) thereof is a schematic diagram showing an example of an illumination optical system having one mirror.

[0069] Figure 3 It is a schematic diagram showing an example of an optical system when measuring the reflectivity of a substrate to be inspected.

[0070] Figure 4 It is an explanatory diagram showing an example of the inspection signal intensity distribution obtained by a dark-field inspection apparatus.

[0071] Figure 5 (A) and (B) thereof are explanatory diagrams showing examples of the inspection signal intensity distribution obtained by a dark-field inspection apparatus in two cases where the surface roughness and reflectivity of the substrate are different.

[0072] Figure 6 It is a flowchart showing an example of the process of the method for inspecting defects of the substrate of the present invention.

[0073] Figure 7 It is a flowchart showing another example of the process of the method for inspecting defects of the substrate of the present invention.

[0074] Figure 8 It is a schematic diagram showing another example of the first condenser optical system of the defect inspection apparatus of the present invention.

[0075] Figure 9 (A) thereof is a sectional view of a main part of a substrate with a multilayer reflection film for manufacturing a reflective mask blank. Figure 9 (B) thereof is a sectional view of a main part of a reflective mask having an absorber pattern.

[0076] REFERENCE MARK DESCRIPTION

[0077] 1-Defect inspection device of the present invention; 2-Light receiving surface of the sensor; 3-Operation processing unit; 4-Threshold operation unit; 5-Data acquisition unit; 6-First condenser optical system; 7-Second condenser optical system; 8-Zone plate; 101-Substrate made of low thermal expansion material; 102-Multilayer reflection film; 103-Protective film; 104-Conductive film; 105-Absorber pattern; 106-Reflective mask; 200, 201, 202-Dark field inspection image intensity distribution; BGL, BGL1, BGL2-Background level; BM1-EUV light; BM2-Scattered light; BM21-Normal reflected light; DIM-Dark field inspection image; ILO-Illumination optical system; ILS-EUV light source; M0, M01, M1, M2, M3-Mirror; PDT-Phase defect; PRO-Imaging optical system; RMB-Substrate with multilayer reflection film; SE-Two-dimensional array sensor; SIG, SIG1, SIG2-Brightness signal level of defect; STG-Substrate stage; THR, THR1, THR2-Threshold. Detailed implementation mode

[0078] The embodiments of the present invention will be described in more detail below with reference to the accompanying drawings, but the present invention is not limited thereto.

[0079] Before describing the embodiments of the substrate defect inspection device and defect inspection method of the present invention, first, the substrate to be inspected will be exemplified. In addition, in the present invention, the substrate to be inspected is not particularly limited as long as it can reflect EUV light, and here, a substrate with a multilayer reflection film that reflects EUV light, represented by a reflective mask blank, will be described.

[0080] Figure 9 (A) is a cross-sectional view showing the main part of a substrate RMB with a multilayer reflection film for manufacturing a reflective mask blank.

[0081] The substrate RMB with a multilayer reflection film is sequentially formed with a multilayer reflection film 102 and a protective film 103 for the multilayer reflection film 102, and the multilayer reflection film 102 reflects EUV light on the main surface of a substrate 101 made of a low thermal expansion material with a sufficiently flattened surface. On the other hand, a conductive film 104 for electrostatically fixing a reflective mask described below to a mask stage of an exposure device is formed on the main surface on the opposite side (inside) of the surface of the substrate 101 where the multilayer reflection film 102 is formed. The phase defect PDT described below is also shown in this figure.

[0082] Hereinafter, the substrate 101 and the like of the substrate RMB with a multilayer reflection film will be exemplified and described in more detail, but the substrate to be inspected in the present invention is not limited to the following structure.

[0083] Preferably, the substrate 101 has a structure made of a low thermal expansion material with a sufficiently planarized surface. For example, the coefficient of thermal expansion is preferably within ±1.0×10 -8 / °C, and preferably within the range of ±5.0×10 -9 / °C. In addition, the RMS value of the surface roughness of the main surface of the substrate is preferably 0.1 nm or less, and particularly preferably 0.05 nm or less. Such surface roughness can be obtained by grinding the substrate or the like.

[0084] The multilayer reflective film 102 is a multilayer film in which layers made of a low refractive index material and layers made of a high refractive index material are alternately stacked. For EUV light with an exposure wavelength of 13 to 14 nm (usually around 13.5 nm), a Mo / Si stacked film or the like is used. The Mo / Si stacked film is formed, for example, by alternately stacking a molybdenum (Mo) layer as a low refractive index material and a silicon (Si) layer as a high refractive index material for about 40 cycles (40 layers each). The film thickness of the multilayer reflective film is usually about 280 to 300 nm.

[0085] The protective film 103 is also called a capping layer, and is provided to protect the multilayer reflective film when forming the absorber pattern and the modified absorber pattern formed thereon. As the material of the protective film, silicon (Si), ruthenium (Ru), a compound in which niobium (Nb) and zirconium (Zr) are added to ruthenium (Ru), etc. are used. The film thickness of the protective film is usually about 2 to 5 nm.

[0086] The film thickness of the conductive film 104 that fixes the reflective mask to the mask stage of the exposure apparatus is usually about 10 to 50 nm, but there are also thicker cases.

[0087] The so-called phase defect PDT is the result of forming the multilayer reflective film 102 when there are fine recesses or protrusions on the main surface of the substrate 101, and is a defect in which there are recesses or protrusions from the multilayer reflective film 102 formed thereon to the protective film 103. Even when there are fine protrusions or recesses on the main surface of the substrate 101, in the process of forming each layer of the multilayer reflective film 102, sometimes the concave or convex shape is difficult to be gently planarized by the smoothing effect and finally an uneven shape appears on the surface of the multilayer reflective film 102 and the protective film 103. Even in such a case, as long as there are minute uneven shapes in the multilayer reflective film 102, a certain degree of phase difference is applied to the reflected light and it becomes a phase defect that reduces the reflectivity. In addition, even if the main surface of the substrate 101 has no defects, fine particles or the like may be involved in the middle stage of forming the multilayer reflective film 102. If a film with an uneven shape is formed in the subsequent film formation, it also becomes a phase defect.

[0088] Figure 9The (B) of [Figure] shows a cross-section of the main part of the reflective mask 106 in the presence of the phase defect PDT. The reflective mask 106 forms an absorber film that absorbs EUV light on a substrate RMB with a multilayer reflective film, and has an absorber pattern 105 obtained by patterning the absorber film.

[0089] There is no problem if the absorber pattern 105 is formed so as to cover the phase defect PDT. However, if, as shown in (B) of [Figure], the phase defect PDT exists in a state of being exposed between adjacent absorber patterns 105, even if the depth is, for example, about 1 nm, the phase of the reflected light is scattered and the reflectivity decreases, resulting in defects in the pattern projection image. Therefore, it is extremely important to detect this phase defect at the stage before manufacturing the reflective mask. Figure 9 The (B) of [Figure] shows a cross-section of the main part of the reflective mask 106 in the presence of the phase defect PDT. The reflective mask 106 forms an absorber film that absorbs EUV light on a substrate RMB with a multilayer reflective film, and has an absorber pattern 105 obtained by patterning the absorber film.

[0090] Next, Figure 1 A defect inspection apparatus for a substrate of the present invention for detecting a phase defect existing in a multilayer reflective film will be described.

[0091] The main constituent elements of the inspection apparatus 1 are: an EUV light source (plasma light source) ILS that generates EUV light BM1; a substrate stage STG for placing the substrate to be inspected, i.e., a substrate RMB with a multilayer reflective film (hereinafter also referred to as a substrate); an illumination optical system ILO; a mirror M0; an imaging optical system PRO (mirrors M1, M2); and a two-dimensional array sensor (an image detector, also simply referred to as a sensor) SE that has a light-receiving surface 2. In addition, although not shown, generally as constituent elements included in the inspection apparatus 1, there also include: a memory, a signal processing circuit, a system control computer that controls the overall operation of the apparatus, a data input / output unit, a defect inspection image output unit, etc. In the present invention, for example, an arithmetic processing unit 3, a threshold arithmetic unit 4, a data acquisition unit 5, etc. described below are included in the above system control computer. Only these parts in the computer are shown.

[0092] The light source ILS is provided with a wavelength selection filter, a pressure partition unit, a scattered particle suppression unit, etc. as needed. For example, it is a light source that generates EUV light BM1 by a plasma method.

[0093] The illumination optical system ILO guides the EUV light BM1 from the light source ILS to the mirror M0. An example of the illumination optical system ILO is shown in [Figure]. There are cases where it is composed of two mirrors (concave mirrors) M3 as shown in (A) of [Figure], and cases where it is composed of one mirror (concave mirror) M3 as shown in (B) of [Figure]. Figure 2 In [Figure] Figure 2 There are cases where it is composed of two mirrors (concave mirrors) M3 as shown in (A) of [Figure], and cases where it is composed of one mirror (concave mirror) M3 as shown in (B) of [Figure]. Figure 2 There are cases where it is composed of two mirrors (concave mirrors) M3 as shown in (A) of [Figure], and cases where it is composed of one mirror (concave mirror) M3 as shown in (B) of [Figure].

[0094] The mirror M0 irradiates the substrate RMB with the EUV light BM1 from the illumination optical system ILO.

[0095] In addition, the first condenser optical system 6 in the present invention is composed of an illumination optical system ILO and a mirror M0.

[0096] The imaging optical system PRO is composed of a mirror (concave mirror) M1 and a mirror (convex mirror) M2, and is, for example, a Schwarzschild optical system that constitutes a dark-field imaging optical system with a condenser NA of 0.25, a central obstruction NA of 0.1, and a magnification of approximately 30 times. This imaging optical system PRO corresponds to the second condenser optical system 7 in the present invention. At least the scattered light (BM2) excluding the specular reflection light from the reflected light from the substrate RMB can be guided to the sensor SE. The scattered light BM2 is captured by the mirror M1 and reflected toward the mirror M2, and is reflected by this mirror M2 and converged and guided to the sensor SE.

[0097] In addition, the mirrors M0 to M3 described above are not particularly limited as long as they can reflect EUV light, and can be, for example, mirrors formed with a multilayer reflection film. They can efficiently reflect EUV light. Since EUV light can be more appropriately irradiated onto the substrate RMB and the scattered light from the substrate RMB can be introduced to the light-receiving surface 2 of the sensor SE, they are preferred.

[0098] In addition, the above-described first and second condenser optical systems 6 and 7 can change these structures. The change in the structure here means, for example, changing the position and posture (tilt angle) of any one of the mirrors in the first and second condenser optical systems 6 and 7 (especially the mirror M0). The mirror can be supported via an arm, an actuator, etc., and the position of the mirror can be controlled as desired by controlling them. For example, it can be a control mechanism as described in Patent Document 2.

[0099] Here, Figure 1 the above-described structural change is made to a structure (the structure of an optical system for performing dark-field inspection) that can receive the scattered light BM2, and an example of the structure (the optical system for performing bright-field inspection) when measuring the reflectivity of the substrate RMB described below is shown in Figure 3 By using the arrangement of the mirror M01 that changes the position of the mirror M0, etc., the specular reflection light (BM21) in the reflected light from the substrate RMB is captured and converged and can be guided to the sensor SE.

[0100] The stage STG and the two-dimensional sensor SE are not particularly limited, and for example, the same structures as those in the past can be used. As long as the mounted substrate RMB can be appropriately moved and the reflected light from the substrate RMB can be appropriately received for image processing.

[0101] In addition, in the system control computer, the arithmetic processing unit 3 functions as follows: when the intensity of the scattered light BM2 received by the sensor SE exceeds a specified threshold value, it is determined that there is a defect at the irradiation position of the EUV light BM1 on the substrate RMB.

[0102] In addition, the threshold value arithmetic unit 4 determines the above-mentioned threshold value based on the reflectivity of the substrate RMB. The content of the calculation program of the threshold value based on this reflectivity will be described below.

[0103] In addition, the data acquisition unit 5 functions as follows: it obtains the reflectivity based on the light receiving intensity of the specularly reflected light on the light receiving surface 2 of the sensor SE. It is a device that uses the light receiving intensity of the specularly reflected light received by the first and second condenser optical systems 6 and 7 whose structures are changed as described above. Thus, it becomes a device capable of simply obtaining the reflectivity of the substrate RMB. It is a structure required when obtaining the reflectivity of the substrate RMB by using the defect inspection device 1 of the present invention itself. If it is a structure that measures the reflectivity using other reflectometers, for example, the data acquisition unit 5 can be omitted.

[0104] Here, the flow of EUV light in the structure of dark field inspection will be described.

[0105] The substrate RMB with a multilayer reflection film for checking for phase defects is placed on a stage STG that can move in three axial directions, namely the XY direction in the substrate plane and the Z direction perpendicular to it. The EUV light BM1 with a central wavelength of about 13.5 nm emitted from the light source is converted into a convergent beam by the illumination optical system ILO, and then passes through an aperture for adjusting the beam size and is bent by the mirror M0 to irradiate a specified area of the substrate RMB. The position information of the substrate RMB is obtained as the position of the stage STG on which the substrate RMB is placed and moved.

[0106] The light scattered due to phase defects (scattered light BM2) in the reflected light from the substrate RMB is captured by the imaging optical system PRO and forms a convergent beam that is focused on the two-dimensional array sensor SE. That is, a dark field inspection image DIM of the substrate RMB is formed in the two-dimensional array sensor SE. As a result, the phase defect PDT remaining on the substrate RMB is detected as a bright spot SIG in the background level BGL on the defect-free part in the inspection image. Information such as the position of the detected phase defect, that is, the magnitude of the defect signal, is stored in a specified storage device, and various information can be observed via a pattern monitor or an image output unit.

[0107] For the inspection within the specified area of the substrate RMB, for example, a known general method such as operating the two-dimensional array sensor SE in the TDI (time delay and integration) mode in synchronization with the movement of the stage STG on which the substrate RMB is placed can be adopted, and the description thereof is omitted here.

[0108] Next, the significance of considering the reflectivity and setting the threshold based on the reflectivity will be described.

[0109] Figure 4 It is an explanatory diagram showing the intensity distribution 200 of the dark-field inspection image extracted along the X-axis direction line including the phase defect part in the dark-field inspection image DIM obtained by the two-dimensional array sensor. When obtaining an inspection image intensity higher than that of the inspection image intensity (i.e., BGL) in the defect peripheral part and with the intensity level represented by SIG on the phase defect part, as long as the intensity is higher than the preset threshold THR, it is considered that there is a defect. The condition for detecting a defect is SIG > THR, and the lower the THR level, the higher the performance of detecting minute phase defects (the detection sensitivity is improved). In order to prevent the detection noise level, the condition of THR > BGL is necessary.

[0110] Here, the existing threshold level THR can be set to, for example, the level that obtains a specified detection sensitivity by previously inspecting a specified substrate with phase defects of different sizes. In addition, collecting the dark-field inspection signals of various substrates with multi-layer reflective films can also set the level after adding a specified value to its background level as the threshold.

[0111] The inspection device manufacturer prepares this threshold in the inspection device. For example, when inspecting a substrate with a multi-layer reflective film as a standard (specifically, a substrate with a multi-layer reflective film for EUV mask blanks), an experimentally determined value is considered in such a way that defects of a specified size can be detected with a specified detection probability. At this time, the actual reflectivity is about 65% - 67%, and this value has not been considered as a variable in the past. That is, in the calculation of the past threshold, based on the specified reflectivity of the above standard specimen, reflectivities other than this have not been considered, especially the reflectivity of each substrate to be inspected actually involved in the inspection.

[0112] However, the background level BGL obtained in the dark-field inspection varies according to the reflectivity and surface roughness of the multi-layer reflective film of the substrate RMB. The higher the reflectivity, the greater the increase, and the smaller the surface roughness, the lower the decrease. In the case of small surface roughness, the difference from the inspection image intensity level SIG obtained in the phase defect part becomes larger, so the phase defect can be clearly detected. That is, an inspection with lower BGL and higher sensitivity can be performed. In Figure 5 (A) shows this state. Here, the inspection image intensity level SIG1 obtained in the phase defect part in the dark-field inspection image intensity distribution 201 is the same as Figure 4 the SIG shown, and the threshold level THR1 is also the same as Figure 4 the THR shown. Only the background level BGL1 is lower than Figure 4 the BGL shown.

[0113] However, in a case where, for example, the thickness of the mixed layer is increased by (excessive) heat treatment and the reflectance of the multilayer reflective film itself is reduced, as Figure 5 shown in (B) of Figure 4 , the background level in the dark-field inspection image intensity distribution 202 decreases from Figure 4 's BGL to BGL2, and the inspection image intensity level obtained in the phase defect portion also decreases from SIG to SIG2. This SIG2 is lower than THR. Therefore, there are cases where defects cannot be detected by the preset threshold level THR. In such a case, within the range not affected by the noise level, if the threshold level is not reduced to THR2, inspection equivalent to the normal case cannot be performed.

[0114] That is, when the background level BGL of the dark-field inspection image changes, it is necessary to distinguish whether the reason is due to the change in surface roughness or the change in the reflectance of the multilayer reflective film itself. Therefore, by separately inputting the reflectance information for such distinction, an appropriate threshold can be finally set. As a result, highly reliable phase defect inspection can be achieved.

[0115] As described above, the reflectance can be a value separately obtained using a normal reflectometer (reflectance measuring device), or, if the structure of the multilayer reflective film is known, a simulated predicted value can be used. Additionally, it can also be in a state where in the Figure 1 shown inspection optical system, the position and tilt angle of the mirror M0 are made variable to enable bright-field inspection (i.e., the Figure 3 state), and it becomes a value obtained by converting the inspection image intensity obtained in the two-dimensional array sensor SE into reflectance.

[0116] The reflectance and threshold are further described in detail below.

[0117] The reflectance of the multilayer reflective film of the substrate RMB processed here is determined by the combination of the film thickness when two types of materials with different refractive indices (for example, Mo and Si) are alternately laminated. If the mixed layer is also included, there is no deviation in the layer structure, and the surface is completely flat, the theoretical reflectance R0 is obtained.

[0118] However, since there are minute irregularities (surface roughness) on the surface of the substrate on which the multilayer reflective film is actually formed, even if irregularities remain on the surface of the multilayer reflective film, the reflected light is slightly scattered. As a result, the amount of light reflected in the specular reflection direction decreases. Actually, if the reflectance obtained when capturing the reflected light with a sensor is expressed by a formula, it is the following formula (1).

[0119]

Equation 1

[0120]

[0121] Here, R0 represents the theoretically determined reflectance using the above-described stacked structure, and σ rms represents the surface roughness (roughness) (standard deviation), and λ represents the wavelength of the irradiated light (EUV light).

[0122] In a typical substrate for EUV masks, σ rms is 0.08 nm or less than 0.08 nm, and the value within the square brackets {} on the right side of formula (1) is approximately 0.994.

[0123] The reflectance considered when determining the threshold value in the present invention is not the above-described theoretically determined reflectance R0, but the reflectance represented by formula (1), which can be expressed as the actual reflectance.

[0124] Furthermore, when the amount of illumination light collected at the position of the substrate where the sensor is disposed for measuring the reflectance is set to I0, and the amount of reflected light (specularly reflected light) collected at the position (direction) of specular reflection from the substrate by the sensor is set to I1, the method for obtaining this actual reflectance (measured reflectance) is defined as in the following formula (2).

[0125] (I1 / I0)×100 (%) ······ formula (2)

[0126] Furthermore, when measuring using the structure of the optical system as shown in Figure 3 , simply, as I1, it can also be the amount of specularly reflected light (received light intensity) received by the sensor.

[0127] In addition, here, the definition of the threshold value is described as a premise.

[0128] If a phase defect is detected using a dark-field inspection apparatus, then in a portion without defects as described above, the background level BGL is obtained as the defect signal level SIG in a portion with defects. Regarding SIG, the larger the defect size, the higher the level.

[0129] Here, using the above-described theoretically determined reflectance R0, BGL is expressed as in the following formula (3).

[0130]

Equation 2

[0131]

[0132] Here, the integration range is the range of the spatial frequency f that the inspection apparatus can capture, and PSD(f) is the power spectral density representing the surface roughness of the mask blank.

[0133] Here, the "roughness component" and its concept are simply expressed as described above. The above roughness component is generally in the range of 0.2% (=0.002) or less.

[0134] On the other hand, the defect signal SIG varies in various ways depending on the defect shape (size, etc.). Therefore, if its concept is expressed, it is as shown in the following formula (4).

[0135] SIG = BGL + (scattering component caused by phase defect) ∝ R o × (roughness component) + R o × (phase defect size component) …… Formula (4)

[0136] In this way, the second term on the right side of Formula (4) is the product of the theoretical reflectivity R0 and the component depending on the defect size.

[0137] However, the so-called threshold value is the signal level used to distinguish between allowable phase defects (generally small defects) and non-allowable phase defects. Therefore, in Figure 4 it, the threshold value is expressed as THR, which is higher than BGL and lower than the signal component SIG of the phase defect of a non-allowable size. When SIG exceeds THR, it is detected as a phase defect.

[0138] The above threshold value THR is defined by a value based on the zero level, and there is also a case where it is defined based on the background level BGL and its difference. In that case, for SIG in the above Formula (4), as long as "SIG ≤ BGL + threshold value", it is an allowable defect and can not be detected. If "SIG > BGL + threshold value", it indicates a defect that should be detected.

[0139] If the above is compared with Formula (4), it is expressed as follows.

[0140] Threshold value = R0 × (component of the defect with the maximum allowable size) ······ Formula (5)

[0141] According to Formula (5), the threshold value is the product of the theoretical reflectivity R0 and the component depending on the allowable defect size. For example, in a normal EUV mask blank, R0 is about 67% - 69%. If it is constant, the threshold value is a value depending only on the defect size. However, in the case where R0 varies, it is necessary to obtain this value.

[0142] Here, as described above, in the present invention, instead of dealing with the theoretical reflectivity R0, the value of the reflectivity in Formula (1) (actual reflectivity) is dealt with. Therefore, if this actual reflectivity is set as R0', the set value of the threshold value considering the reflectivity in the present invention is the value obtained by multiplying the pre-set threshold value (that is, the threshold value based on the specified reflectivity prepared by the inspection device manufacturer (recommended by the inspection device manufacturer) as described above) by R0' / R0.

[0143] In addition, in a case where the threshold value is not defined as the difference from the background level BGL as described above, but is defined as a value based on the zero level, it is a value obtained by adding BGL to the set value of the threshold value defined by the difference from the background level BGL.

[0144] In addition, in the above calculation of the threshold value multiplied by R0’ / R0, the theoretical reflectivity R0 itself can be calculated from the structure of the substrate to be inspected using a known calculation method. Specifically, by specifying the optical constants (complex refractive indices) of the respective materials constituting the multilayer reflective film, their film thicknesses, the optical constants of the substrate on which the multilayer reflective film is formed, and the incident angle of the EUV light (the angle of the surface of the multilayer reflective film with respect to the plane normal), the reflectivity can be calculated. It can be successively obtained for each substrate to be inspected by such calculation, but not limited thereto, and the threshold value can also be simply calculated by setting the value of the theoretical reflectivity R0 to, for example, 66% and multiplying by the above R0’ / R0 (in this case, R0’ / (66%)).

[0145] In addition, in a case where BGL is added so that the threshold value defined by the difference from the background level BGL as described above is a value based on the zero level, BGL itself can be obtained by formula (3) (it should be noted that in the formula, R0’ is substituted instead of R0). In addition to this, before setting the final value (threshold value + BGL), a preliminary inspection is performed to obtain BGL itself in the inspection apparatus, and the inspection signal of the portion other than the defect of the substrate to be inspected can also be obtained and set as BGL.

[0146] In the threshold value preset in advance by the inspection apparatus manufacturer described above, first, the actually measured reflectivity based on formula (1) is 0.994×R0 or more, and substantially (actually measured reflectivity)≒R0. Therefore, for example, assuming (actually measured reflectivity)≒R0 = 66%, the threshold value (defined by the difference from BGL) is experimentally obtained in consideration of the detection sensitivity and is used as the threshold value recommended by the inspection apparatus manufacturer. However, in the present invention, as repeatedly described, the threshold value is set based on the actually measured reflectivity. As an example, it can be a value obtained by multiplying the threshold value recommended by the inspection apparatus manufacturer by R0’ / R0 (R0’ / (66%)).

[0147] In addition, it is only necessary to set the threshold value corresponding to the actually measured reflectivity value obtained by measurement. Of course, according to the actually measured reflectivity value, the preset threshold value can also be directly used. For example, in a case where the numerical range of the actually measured reflectivity is within 66±0.5%, the threshold value can be set using the preset value.

[0148] The definitions and calculation methods of the reflectance and the threshold have been described in detail above. In the data acquisition unit 5 and the threshold calculation unit 4 in the system control computer, the measurement of the reflectance, the calculation and setting of the threshold can be performed under a program using the above formulas and the like.

[0149] If it is such a defect inspection device, it is a device that determines the threshold based on the reflectance of the substrate to be inspected in dark field inspection. Therefore, an appropriate threshold can be set, and highly reliable phase defect inspection can be performed.

[0150] In addition, an example in which a plurality of mirrors are used in the first and second condenser optical systems 6 and 7 is shown. In addition to this, a structure using a zone plate instead of a part of the mirrors can also be adopted. Figure 8 An example of this structure is shown. A zone plate 8 is arranged in place of the illumination optical system ILO using one or more mirrors in the first condenser optical system. Regarding this zone plate 8, a substrate having a relatively high transmittance (close to transparent) with respect to EUV light can be cited. For example, a substrate having concentric absorption material patterns with pitches different depending on the radius formed on a Si-based thin film can be cited. It can have the function of a convex lens with a transmittance of about 10%.

[0151] Next, the substrate defect inspection method in the present invention using the Figure 1 defect inspection device 1 of the present invention will be described.

[0152] (Embodiment 1)

[0153] In Figure 6 an example of the inspection process of the phase defect is shown. First, in step S101 (reflectance acquisition process), the reflectance of the substrate RMB to be inspected is measured. In addition, a substrate manufactured by the same process as the substrate to be inspected in the dark field inspection described in S105 below can be used for the measurement. Regarding the measurement, for example, the measured value measured by a commercially available reflectometer can also be applied. In addition, when the accuracy is clearly ensured, the predicted value from the film forming process and the simulation predicted value can also be applied.

[0154] Next, in step S102, the substrate to be inspected is placed on the phase defect inspection device, and the information of the measured reflectance is input (step S103). Moreover, in the dark field inspection, a threshold value for identifying the presence of phase defects is set (using the threshold operation unit 4, the threshold value can be obtained and set based on the reflectance) (step S104: threshold operation process). After that, in step S105, the phase defect inspection of the specified area of the substrate to be inspected is performed using the inspection device 1. That is, EUV light BM1 is emitted from the EUV light source ILS, and is irradiated onto the substrate RMB via the first condenser optical system (illumination optical system ILO, mirror M0), and the scattered light BM2 is received by the light receiving surface of the sensor SE via the second condenser optical system (mirrors M1, M2). Moreover, using the arithmetic processing unit 3, when the intensity of the received scattered light BM2 exceeds the threshold value set in step S104, it is determined that a phase defect exists. When a phase defect is detected, since information such as its position and the magnitude of the defect signal is stored in a specified storage device, it is investigated whether new defect information in the substrate to be inspected is stored (step S106). If new information is stored, it is determined that there is a phase defect, and the defect detection information is sorted and stored in a specified storage unit (step S107). On the other hand, when no new information is stored in step S106, it is determined that there is no phase defect, and information indicating no defect is stored in a specified storage unit (step S108).

[0155] Through the above steps, the phase defect inspection is ended.

[0156] (Embodiment 2)

[0157] In the above-described Embodiment 1, an example of measuring the reflectance of the substrate to be inspected, that is, a substrate with a multilayer reflection film, using a reflectometer is described. Here, an example of the method implemented using the inspection optical system of the defect inspection device 1 is described.

[0158] That is, an example of the structure of the optical system using Figure 3 is used. Figure 3 It is a diagram showing the extraction of a part of the first condenser optical system including the mirror M0 and a part near the imaging optical system PRO (second condenser optical system) composed of the mirrors M1 and M2 in the inspection optical system for inspecting the phase defects as described above. The reference numerals shown in this diagram are the same as the corresponding reference numerals in Figure 1 . It shows such a state that the position and posture of the planar mirror M0 in the optical system are changed so as to take in the specular reflection light of the EUV light specularly reflected from the substrate to be inspected RMB into the imaging optical system PRO. Figure 1

[0159] ​In this case, the specular reflection light BM21 reflected from the substrate to be inspected becomes convergent light that uses half of the area of the imaging optical system PRO and is directed toward the two-dimensional array sensor. Figure 3 Compared with Figure 1 , the multilayer mirror M0 becomes M01, the scattered light BM2 directed toward the two-dimensional array sensor becomes the specular reflection light BM21, and there are no other changes. The intensity of the inspection image obtained in the two-dimensional array sensor using this bright-field inspection optical system represents a value that is substantially proportional to the reflectivity of the substrate to be inspected. The proportionality coefficient can be calibrated by inspecting a substrate with a known reflectivity.

[0160] In the collection of the bright-field inspection signal, the stage on which the substrate to be inspected is placed is moved, and the bright-field inspection signal in the desired area of the substrate to be inspected is collected continuously or intermittently, and the average value of the inspection signals in a specified area can be obtained to calculate the reflectivity.

[0161] In addition, the average incident angles in the mirrors M0 and M01 are different, but within the scope of this embodiment, even if the same mirror is used, the reflectivity will not be significantly reduced.

[0162] In Figure 7 , the inspection process for phase defects using the above optical system is shown. First, in step S111, the substrate to be inspected is placed on the phase defect inspection device 1. Next, in step S112, the mirror M0 is moved to the position of M01, and the incident angle of the EUV light irradiating the substrate to be inspected is adjusted, and the bright-field optical system shown in Figure 3 is achieved. After that, the bright-field inspection signal of the substrate to be inspected is collected (step S113), and then, the reflectivity of the EUV light of the substrate to be inspected is calculated and stored in a specified storage unit (data acquisition unit 5) of the inspection device (step S114: reflectivity acquisition process). After the collection of the reflectivity information is completed, in step S115, the mirror M01 is returned to M0, and the incident angle of the EUV light irradiating the substrate to be inspected is restored to achieve the dark-field inspection optical system.

[0163] After that, a threshold value used in the dark-field inspection is set based on the obtained reflectivity (step S104: threshold calculation process), and the process of inspecting for phase defects in a specified area of the substrate to be inspected is the same as the process described in Figure 6 in Embodiment 1 (steps S105 and later). Therefore, in Figure 7 , the setting of the threshold value is shown as step S104, and since the subsequent process is the same as Figure 6 , it is omitted.

[0164] In addition, regarding the reflectivity of the substrate to be inspected, it can be, for example, the average value over the entire inspection area. Generally, the reflectivity of the substrate to be inspected has a distribution within the plane. Of course, it is within the range that satisfies the required specifications of the reflectivity. However, in order to more strictly set the threshold for dark-field inspection, the inspection area can be divided into regions of appropriate size to collect reflectivity information, and a threshold can be set for each such region. For example, the inspection area of the substrate to be inspected can be pre-divided into specified small regions, and the averaged reflectivity can be obtained for each small region, and a threshold corresponding to each small region can be set. In this case, the threshold varies according to the small regions, and phase defect inspection with more appropriate detection sensitivity can be performed.

[0165] As described above, when detecting phase defects of a substrate to be inspected (especially a substrate with a multilayer reflective film) that reflects EUV light by dark-field inspection using EUV light as the inspection light, according to this embodiment, the threshold for determining the detection sensitivity can be appropriately set, and thus highly reliable phase defect inspection can be achieved.

[0166] In addition, by setting the threshold to make the detection sensitivity appropriate, phase defects larger than a specified size can be detected, and substrates with multilayer reflective films containing such defects can be excluded, and defect-free substrates with multilayer reflective films can be effectively selected to provide EUV mask blanks and EUV masks.

[0167]

Example

[0168] Hereinafter, examples will be shown to more specifically illustrate the present invention, but the present invention is not limited thereto.

[0169] (Example)

[0170] Use Figure 1 the inspection apparatus 1 shown in Figure 6 to perform phase defect inspection according to the flow of the inspection method shown in

[0171] That is, after considering the reflectivity of the substrate to be processed and setting the threshold, the inspection is performed. Figure 9 Here, as the substrate to be inspected, a substrate with a multilayer reflective film as shown in (A) of

[0172] is used, in which 40 cycles of molybdenum (Mo) layers and silicon (Si) layers are alternately laminated on a low thermal expansion substrate, and then a Ru film is further formed. Figure 1When the inspection apparatus 1 of the present invention shown performs phase defect inspection (dark field inspection), the reflectivity of EUV light of the substrate with a multilayer reflective film is measured in advance immediately before the start. In this measurement, a reflectometer manufactured by EUV-Tech is used to obtain the average value of the reflectivity within the inspection area of the substrate to be inspected, and a value of 66.5% is obtained at an incident angle of 6 degrees.

[0173] Next, in order to perform phase defect inspection (dark field inspection) in the inspection apparatus 1 shown in Figure 1 the substrate to be inspected whose reflectivity has been measured is placed on the stage of the inspection apparatus. After inputting the information of the reflectivity, a threshold value is set, and then, according to the inspection process of the inspection apparatus, phase defect inspection is performed in the specified area of the substrate to be inspected.

[0174] Here, the incident angle of the EUV light when the reflectivity is measured is 6 degrees, while the incident angle of the principal ray of the irradiation light in the dark field defect inspection apparatus shown in Figure 1 is 0 degree. It should be noted that the actual irradiation light is convergent light, and the actual incident angle is approximately in the range of 0 ± 5 degrees. In addition, in this embodiment, the change in the reflectivity depending on the incident angle of the multilayer reflective film as the object is generally known according to its period length. If the reflectivity at an incident angle of 6 degrees is known, the reflectivity at the irradiation angle of the phase defect inspection apparatus is known. Therefore, based on the information of this reflectivity, it can be judged whether it is good to make the threshold value the previously set value (the conventional threshold value recommended by the inspection apparatus manufacturer), or whether it should be changed. In the above case, since the reflectivity within the specified range is obtained, the value of the threshold is not changed and the previously set value is used.

[0175] Next, the same phase defect inspection was also performed on some substrates with a multilayer reflective film that had been subjected to different heat treatments. Through the heat treatment process, there was no significant change in the uneven shape and roughness of the defect part on the substrate surface, but the mixing within the multilayer reflective film was promoted, and the reflectivity decreased to 64.5%. Therefore, when the reflectivity measurement result was input in the same manner as described above, the threshold was adjusted (that is, relative to the conventional threshold value recommended by the inspection apparatus manufacturer, it was reset to the value obtained by multiplying R0’ / R0 described above), and phase defect inspection was performed in the specified area of the substrate to be inspected. If the actual background level and the like are evaluated, this decrease corresponds to the result shown in (B) of Figure 5 . That is to say, defects should not be detected when the set value of the conventional threshold is maintained, but by adjusting the threshold in advance based on the reflectivity as described above, defects can be detected. The present invention effectively functions and can perform inspection with more appropriate detection sensitivity.

[0176] In addition, the present invention is not limited to the above-described embodiments. The above-described embodiments are merely illustrative, and technical solutions having a structure substantially the same as the technical idea described in the claims of the present invention and achieving the same effects are all included within the technical scope of the present invention.

Claims

1. A method for inspecting defects of a substrate, comprising: a step of irradiating the substrate to be inspected with EUV light emitted from an EUV light source using a first condenser optical system; a step of guiding, using a second condenser optical system, scattered light excluding specularly reflected light among the reflected light reflected from the substrate to be inspected irradiated with the EUV light to a light-receiving surface of a sensor; and a step of determining that there is a defect at the irradiation position of the EUV light on the substrate to be inspected when the intensity of the scattered light received on the light-receiving surface of the sensor exceeds a specified threshold value, characterized in that before irradiating the substrate to be inspected with the EUV light, it preliminarily has: a reflectance acquisition step of obtaining the reflectance of the EUV light of the substrate to be inspected; and a threshold calculation step of determining the specified threshold value based on the reflectance obtained in the reflectance acquisition step.

2. The method for inspecting defects of a substrate according to claim 1, characterized in that in the reflectance acquisition step, changing the structure of the first condenser optical system or the second condenser optical system, irradiating the substrate to be inspected with the EUV light emitted from the EUV light source using the first condenser optical system, guiding specularly reflected light from the substrate to be inspected irradiated with the EUV light to the light-receiving surface of the sensor using the second condenser optical system, and obtaining the reflectance based on the light-receiving intensity on the light-receiving surface.

3. The method for inspecting defects of a substrate according to claim 2, characterized in that when changing the structure of the first condenser optical system, making the first condenser optical system have a structure with a mirror and changing the position and posture of the mirror.

4. The method for inspecting defects of a substrate according to claim 1, characterized in that in the reflectance acquisition step, using a reflectometer to obtain the reflectance.

5. The method for inspecting defects of a substrate according to claim 1, characterized in that setting the substrate to be inspected as a substrate with a multilayer reflective film formed on its surface for reflecting the EUV light.

6. The method for inspecting defects of a substrate according to claim 2, characterized in that setting the substrate to be inspected as a substrate with a multilayer reflective film formed on its surface for reflecting the EUV light.

7. The method for inspecting defects of a substrate according to claim 3, characterized in that setting the substrate to be inspected as a substrate with a multilayer reflective film formed on its surface for reflecting the EUV light.

8. The method for inspecting defects of a substrate according to claim 4, characterized in that setting the substrate to be inspected as a substrate with a multilayer reflective film formed on its surface for reflecting the EUV light.

9. The method for inspecting defects of a substrate according to any one of claims 1 to 8, characterized in that setting the reflectance as the average value over the entire inspection area of the substrate to be inspected.

10. The method for inspecting defects of a substrate according to any one of claims 1 to 8, characterized in that dividing the inspection area of the substrate to be inspected into small areas Set the reflectivity to the average value of each of the small regions. Determine the specified threshold value for each of the small regions.

11. The method for inspecting defects of a substrate according to any one of claims 1 to 8, characterized in that The first condenser optical system and the second condenser optical system are respectively configured to have a structure of a plurality of mirrors formed with a multilayer reflection film.

12. The method for inspecting defects of a substrate according to claim 9, characterized in that The first condenser optical system and the second condenser optical system are respectively configured to have a structure of a plurality of mirrors formed with a multilayer reflection film.

13. The method for inspecting defects of a substrate according to claim 10, characterized in that The first condenser optical system and the second condenser optical system are respectively configured to have a structure of a plurality of mirrors formed with a multilayer reflection film.

14. A substrate defect inspection apparatus having: An EUV light source that emits EUV light; A first condenser optical system that irradiates EUV light from the EUV light source onto a substrate to be inspected; A second condenser optical system that guides scattered light obtained by removing specularly reflected light from the reflected light reflected from the substrate to be inspected irradiated with the EUV light to a light receiving surface of a sensor; and An arithmetic processing unit that, when the intensity of the scattered light received on the light receiving surface of the sensor exceeds a specified threshold value, determines that a defect exists at the irradiation position of the EUV light on the substrate to be inspected, characterized in that It has a threshold value arithmetic unit that determines the specified threshold value based on the reflectivity of the EUV light of the substrate to be inspected.

15. The substrate defect inspection apparatus according to claim 14, characterized in that The structure of the first condenser optical system or the second condenser optical system can be changed, The first condenser optical system can be used to irradiate the substrate to be inspected with the EUV light emitted from the EUV light source, and the second condenser optical system can be used to guide specularly reflected light from the substrate to be inspected irradiated with the EUV light to the light receiving surface of the sensor, It has a data acquisition unit that obtains the reflectivity based on the light receiving intensity of the specularly reflected light on the light receiving surface.

16. The substrate defect inspection apparatus according to claim 15, characterized in that The first condenser optical system whose structure can be changed has a mirror, The position and orientation of the mirror can be changed.

17. The substrate defect inspection apparatus according to any one of claims 14 to 16, characterized in that The substrate to be inspected is a substrate with a multilayer reflection film formed on its surface to reflect the EUV light.

18. The substrate defect inspection apparatus according to any one of claims 14 to 16, characterized in that The first condenser optical system and the second condenser optical system each have a plurality of mirrors formed with a multilayer reflection film.

19. The substrate defect inspection apparatus according to claim 17, characterized in that The first condenser optical system and the second condenser optical system each have a plurality of mirrors formed with a multilayer reflection film.

Images