JP6394422B2 - Defect inspection method and inspection light irradiation method - Google Patents

Description

  The present invention relates to a defect inspection method suitable for defect inspection of a mask blank or the like used for manufacturing a mask (transfer mask) used in manufacturing a semiconductor device (semiconductor device) or the like, and an inspection suitable for this inspection method. The present invention relates to a light irradiation method.

  A semiconductor device (semiconductor device) irradiates a photomask on which a circuit pattern is drawn with exposure light, and transfers the circuit pattern formed on the photomask onto a semiconductor substrate (semiconductor wafer) via a reduction optical system. It is formed by repeatedly using a photolithography technique. A photomask is manufactured by forming a circuit pattern on a substrate (photomask blank) on which an optical film is formed. Such an optical film is generally a thin film mainly composed of a transition metal compound or a thin film mainly composed of a silicon compound containing a transition metal, and as a film functioning as a light shielding film or a phase shift film, depending on the purpose. A functional membrane or the like is selected.

  Since a transfer mask such as a photomask is used as an original drawing for manufacturing a semiconductor element having a fine pattern, it is required to be defect-free, and this is naturally also defect-free for a mask blank. Will be required. When forming a circuit pattern, for example, a resist film for processing an optical film is formed on a photomask blank on which an optical film is formed, and finally a lithography process such as electron beam drawing is performed. Form a pattern. Therefore, the resist film is required to have no defects such as pinholes. Under these circumstances, many studies have been made on defect detection techniques for transfer masks and mask blanks.

  Japanese Patent Application Laid-Open No. 2001-174415 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-333313 (Patent Document 2) describe a method of irradiating a substrate with a laser beam and detecting defects and foreign matters from irregularly reflected light. In particular, a technique is described in which an asymmetry is given to a detection signal to determine whether it is a convex defect or a concave defect. Japanese Patent Laying-Open No. 2005-265736 (Patent Document 3) describes a technique of using DUV (Deep Ultra Violet) light, which is used for performing pattern inspection of a general optical mask, as inspection light. . Furthermore, Japanese Patent Laid-Open No. 2013-19766 (Patent Document 4) describes a technique in which inspection light is divided into a plurality of spots and scanned, and each reflected beam is received by a light detection element.

JP 2001-174415 A JP 2002-333313 A JP 2005-265736 A JP 2013-19766 Gazette

  With continuous miniaturization of semiconductor devices, technology for improving the resolution of photolithography technology has been actively developed. Until now, ArF lithography technology using an argon fluoride (ArF) excimer laser beam having a wavelength of 193 nm has been developed and applied to mass production of semiconductor devices. Also, development of lithography technology (EUVL: Extreme Ultra Violet Lithography) using EUV (Extreme Ultra Violet) light having a shorter wavelength of 13.5 nm has been made. However, since it is still difficult to handle as a mass-production technology, the ArF lithography technology is continuously used, and by adopting a process called multi-patterning that combines the exposure process and processing process multiple times, the final comparison with the exposure wavelength Therefore, a technique for forming a pattern having a sufficiently small dimension has been energetically studied. In the case of this process, the minimum pattern pitch formed by one exposure with one photomask is about 400 to 600 nm on a photomask (quadruple mask) whose size is 1/4 by reduction projection. Since multi-patterning is premised, it is necessary to improve the fidelity of the shape of the transfer pattern and the accuracy of the pattern edge position, and many fine auxiliary patterns that cannot be transferred alone must be formed on the photomask. The dimension of this auxiliary pattern reaches 100 nm or less on the photomask. Therefore, in such highly accurate pattern formation, it is necessary to make the resist film used for processing thinner than the conventional thickness. In the resist film and the processed optical film, it is necessary to detect all defects such as pinhole defects that are fatal to pattern formation.

  All of the inspection apparatuses described in Patent Documents 1 to 4 are apparatuses that employ an optical defect detection method. The optical defect detection method has an advantage that a wide-area defect inspection can be performed in a relatively short time, and a fine defect can be accurately detected by shortening the wavelength of the light source. However, when illumination light having a narrow wavelength distribution such as laser light is used as inspection light, the intensity of reflected light used for inspection varies depending on the structure of the film. In particular, the resist film is often almost transparent to the inspection light, and the reflectance of the inspection light is as extremely low as less than 1% depending on the film thickness. In such a case, sufficient reflected light intensity cannot be obtained, and it is difficult to detect a minute defect that becomes a fatal defect in pattern formation with high accuracy.

  The present invention has been made to solve the above-described problem, and in the defect inspection of the surface portion of the inspection object, a thin film formed on the surface portion of the inspection object, for example, a mask blank such as a photomask blank. Even if sufficient reflectivity cannot be obtained due to the structure and optical characteristics, etc., a defect inspection method capable of detecting a defect by ensuring the amount of reflected light of the inspection light, and suitable for this inspection method An object is to provide an inspection light irradiation method.

  Since the reflectivity when irradiating the surface of the inspection object with the inspection light varies depending on the incident angle of the inspection light, the reflectance is reduced when the inspection light is irradiated from one incident angle. Even if it is too low and the amount of light is insufficient to detect a minute defect, if the inspection light is irradiated from another incident angle, sufficient reflectivity and light amount can be obtained. Has also been found to be detectable.

As a result of intensive studies to solve the above-described problems, the present inventors irradiate the surface of the inspection object with the inspection light and measure the intensity of the reflected light of the inspection light. Are scanned while irradiating the surface of the inspection object having a substrate and at least one layer of thin film formed on the substrate, and defects on the surface portion of the inspection object are detected from a change in intensity of reflected light of the inspection light. When detecting
(1) The inspection object is irradiated with the inspection light from the first incident angle range, the first reflectance of the inspection light is acquired, and the first reflectance is lower than the predetermined reflectance. When the inspection light is irradiated to the inspection object from a second incident angle range different from the incident angle range of the first to obtain the second reflectance of the inspection light, and the second reflectance is higher than the first reflectance (2) irradiating the inspection object with the inspection light to obtain the reflectance distribution with respect to the incident angle of the inspection light. Based on the rate distribution, select the incident angle range with high reflectance in the reflectance distribution, set the illumination method of the inspection light irradiated from the selected incident angle range,
If the inspection light is irradiated to the inspection object, sufficient reflectance and light quantity can be obtained, and the structure and optical characteristics of the surface portion of the inspection object, for example, the structure of the thin film formed on the surface portion of the inspection object Even when sufficient reflectivity cannot be obtained due to optical characteristics, the amount of reflected light of the inspection light can be secured, and defects on the surface portion of the inspection object can be detected with high sensitivity. It came to.

Accordingly, the present invention provides the following defect inspection method and inspection light irradiation method.
Claim 1:
The surface of the inspection object is scanned from the change in intensity of the reflected light of the inspection light by scanning the inspection light while irradiating the surface of the inspection object having the substrate and at least one thin film formed on the substrate. A defect inspection method for detecting defects in a part,
Irradiating an inspection object with inspection light from a first incident angle range to obtain a first reflectance of the inspection light;
When the first reflectance is lower than a predetermined reflectance, the inspection light is irradiated from the second incident angle range different from the first incident angle range, and the second reflection of the inspection light is performed. Obtaining a rate;
A step of setting an illumination method that provides inspection light in the second incident angle range when the second reflectance is higher than the first reflectance, and the incident angle range is the illumination method. An annular illumination system with a circular ring shape in which the inspection light converges on the inspection area through the objective lens of the inspection optical system, with the incident angle exceeding 0 ° and less than 90 °, with the incident angle being 0 ° as the central axis A defect inspection method comprising: setting a modified illumination system having a cross-sectional arc band shape in which a part of the circular ring shape is missing along the circumferential direction.
Claim 2 :
Placing the inspection object on a stage capable of moving the inspection object along the direction of the inspection surface of the inspection object;
A step of irradiating the inspection light while scanning the surface of the inspection object with the set illumination method,
Collecting the amount of reflected light of the inspection area irradiated with the inspection light as an inspection signal of the inspection area via the objective lens of the inspection optical system;
Detecting the defect when the inspection signal crosses a preset threshold, and detecting the defect;
The defect inspection method according to claim 1, further comprising a step of recording information on the detected defect.
Claim 3 :
The object to be inspected, the defect inspection method according to claim 1 or 2, characterized in that a mask blank used for manufacturing a semiconductor circuit pattern transfer mask.
Claim 4 :
The defect inspection method according to claim 3 , wherein the mask blank is a mask blank having a photoresist film as an outermost layer, and the defect of the photoresist film is inspected.
Claim 5 :
Defect inspection method according to any one of claims 1 to 4, characterized in that the wavelength of the inspection light is 210～550Nm.
Claim 6 :
An inspection light irradiation method for irradiating the surface of an inspection object with inspection light and measuring the intensity of reflected light of the inspection light,
Irradiating an inspection object with inspection light from a first incident angle range to obtain a first reflectance of the inspection light;
When the first reflectance is lower than a predetermined reflectance, the inspection light is irradiated from the second incident angle range different from the first incident angle range, and the second reflection of the inspection light is performed. Obtaining a rate;
A step of setting an illumination method that provides inspection light in the second incident angle range when the second reflectance is higher than the first reflectance, and the incident angle range is the illumination method. An annular illumination system with a circular ring shape in which the inspection light converges on the inspection area through the objective lens of the inspection optical system, with the incident angle exceeding 0 ° and less than 90 °, with the incident angle being 0 ° as the central axis The method of irradiating inspection light according to claim 1, wherein a modified illumination system having a cross-sectional arc band shape in which a part of the circular ring shape is missing along the circumferential direction is set.

  According to the present invention, sufficient reflectivity cannot be obtained due to the structure and optical characteristics of the surface portion of the inspection object, for example, the structure and optical characteristics of the thin film formed on the surface portion of the inspection object. However, the amount of reflected light of the inspection light can be secured, and defects on the surface portion of the inspection object can be detected with high sensitivity.

It is explanatory drawing of an example of the process of manufacturing a photomask from a photomask blank, and is sectional drawing in each step of a manufacturing process. (A), (B) is an example of a photomask blank having a defect, (C) is a cross-sectional view showing an example of a photomask blank having a resist film having a defect, and (D) is a defect. It is a figure which shows the photomask manufactured from the photomask blank which has a resist film in which a photomask blank and a defect exist. It is a figure which shows an example of a structure of the defect inspection apparatus of a mask blank. It is a figure which shows an example of the inspection signal which caught the reflected light of inspection light. It is a figure which shows the relationship between a resist film thickness and the reflectance of test | inspection light. It is a flowchart which shows an example of the process of the irradiation method of test | inspection light. It is a figure which shows the relationship between the incident angle of the inspection light with respect to a resist film, and a reflectance. It is a figure which shows an example of the illumination system of inspection light, and is a figure which shows the vicinity of the objective lens and mask blank of the defect inspection apparatus of FIG. It is a figure which shows the result of having calculated | required the defect inspection image and inspection signal intensity | strength when test | inspecting a pinhole defect with the illumination system of FIG. 8 by optical simulation. It is a figure which shows the other example of the illumination system of inspection light, and is a figure which shows the vicinity of the objective lens and mask blank of the defect inspection apparatus of FIG. It is a figure which shows the result of having calculated | required the test | inspection signal intensity | strength when test | inspecting a pinhole defect with the illumination system of FIG.8 (C) and FIG.8 (D), and the illumination system of FIG. 10 by optical simulation. It is a flowchart which shows an example of the process of a defect inspection method.

Hereinafter, the present invention will be described in more detail.
First, a process for manufacturing a photomask from a photomask blank will be described, and the influence of defects in the photomask blank will be described. FIG. 1 is an explanatory diagram of an example of a process for manufacturing a photomask from a photomask blank, and is a cross-sectional view of the photomask blank, intermediate, or photomask at each stage of the manufacturing process. In the photomask blank, at least one thin film is formed on a transparent substrate.

  In a photomask blank 500 shown in FIG. 1A, an optical thin film 502 that functions as a phase shift film such as a light shielding film or a halftone phase shift film is formed on a transparent substrate 501. A hard mask film (processing auxiliary thin film) 503 of the optical thin film 502 is formed. When manufacturing a photomask from such a photomask blank, first, a resist film 504 for the processing is formed on the hard mask film 503 (FIG. 1B). Next, a resist pattern 504a is formed from the resist film 504 through a lithography process such as an electron beam drawing method (FIG. 1C), and the underlying hard mask film 503 is processed using the resist pattern 504a as an etching mask. A hard mask film pattern 503a is formed (FIG. 1D), and the resist pattern 504a is removed (FIG. 1E). Further, when the lower optical thin film 502 is processed using the hard mask film pattern 503a as an etching mask, the optical thin film pattern 502a is formed, and then the hard mask film pattern 503a is removed to obtain a photomask 500a (FIG. 1 ( F)).

  If defects such as pinholes exist in the thin film of the photomask blank, it finally causes a mask pattern defect on the photomask. An example of typical photomask blank defects is shown in FIG. FIG. 2A shows an example of a photomask blank 500 in which a pinhole defect d exists in a hard mask film 503 formed thereon in order to perform high-precision processing of the optical thin film 502, and FIG. B) is a diagram showing an example of a photomask blank 500 in which a pinhole defect d exists in the optical thin film 502 itself. Further, FIG. 2C is a diagram showing an example in which a pinhole defect d exists in the resist film 504 formed on the photomask blank 500 shown in FIG.

  In any photomask blank, when a photomask is manufactured from such a photomask blank by the manufacturing process shown in FIG. 1, it is derived from the photomask blank as in the photomask 500a shown in FIG. Or the defect d derived from a resist film will become a photomask which exists in the optical thin film pattern 502a. This defect d causes a pattern transfer error in exposure using a photomask. Therefore, defects in the photomask blank and the resist film may occur at the photomask blank stage or photomask before processing the photomask blank. It is necessary to detect at the stage where the resist film is formed on the mask blank, and to eliminate those having defects, or to correct the defects. For these reasons, defects such as pinholes that exist in thin films such as optical thin films, processing auxiliary thin films, resist films, etc. used in photomask blanks, especially the finer details that have become necessary with the miniaturization of semiconductor devices. It is desirable to have a method that can effectively detect defects of a large size by an optical method.

  FIG. 3 is a diagram illustrating an example of a basic configuration of a defect inspection apparatus for a mask blank such as a photomask blank. As shown in FIG. 3, the inspection optical system includes a light source ILS, a beam splitter BSP, an objective lens OBL, a mask blank MB on which an optical film is formed, and a detector SE. In the present invention, it is preferable to use light having a wavelength of about 210 to 550 nm, for example, DUV light (light having a wavelength of about 210 to 300 nm) as the inspection light, and the light source ILS emits such light. The inspection light BM1 emitted from the light source ILS is incident on the beam splitter BSP via the illumination area control aperture AP1 and the lens groups L1 and L2. Then, the light is reflected by the beam splitter BSP, bent, and irradiated to a predetermined area of the mask blank MB through the objective lens OBL.

  The inspection light BM1 irradiated on the mask blank MB is reflected, and the reflected light BM2 is collected by the objective lens OBL, and passes through the beam splitter BSP, the aperture stop AP2, and the lens L3 and reaches the light receiving surface of the detector SE. At this time, the position of the detector SE is adjusted so that an enlarged inspection image of the surface of the mask blank MB is formed on the light receiving surface of the detector SE. By analyzing the enlarged inspection image received by the detector SE, it is possible to detect a defect present on the mask blank MB. Data collected by the detector SE is stored in the inspection image data storage unit 2 and subjected to arithmetic processing described later. The calculated defect information is stored in the memory 3.

  The mask blank MB is placed on the mask stage STG, and is positioned at a position where the defect can be inspected by the objective lens OBL by moving and positioning the mask stage STG. This positioning, collection of inspection images, and various arithmetic processes are centrally controlled by a system control unit 1 including a CPU. The system control unit 1 controls the position of the mask stage STG via the stage driving unit 5 and simultaneously controls the illumination area control aperture AP1 via the illumination aperture driving unit 6 to realize various illumination conditions. Also, various pupil filters can be selected by controlling the aperture stop AP2 via the aperture stop driving means 7. Further, this defect inspection apparatus includes a monitor 4 and displays an observation image of the defect.

  FIG. 4 is a diagram illustrating an example of an inspection signal in which reflected light is captured by a detector. The intensity of the reflected light varies depending on the configuration of the surface portion of the object to be inspected, for example, the configuration of the optical film on the mask blank surface. A curve SIG-11 shown in FIG. 4A shows a change in the inspection signal intensity when the signal intensity level of the defective portion is lower than the intensity level BGL of the defect peripheral portion, and the curve SIG- shown in FIG. Reference numeral 12 denotes changes when the signal intensity level of the defective portion is higher than the signal intensity level BGL of the peripheral portion of the defect.

  FIG. 5 is a diagram showing the relationship between the resist film thickness and the inspection light reflectance. For example, when performing a defect inspection of a resist film provided for mask pattern processing of a mask blank, the resist film often acts as an antireflection film optically. A mask blank in which a two-layer thin film of a MoSi-based material halftone phase shift film and a Cr-based light shielding film is formed, and a resist film (photoresist film) is further formed as an outermost layer thereon On the other hand, for example, the incident angle range includes an incident angle of 0 °, the central axis is the incident angle of 0 °, and the simple illumination method has a circular cross section in which the inspection light converges on the inspection region via the objective lens of the inspection optical system When the relationship between the reflectance of the inspection light and the resist film thickness is examined by irradiating the inspection light having a wavelength of 532 nm with the above, the film is caused by the thin film interference of the resist film as shown by a curve REFC1 shown in FIG. When the thickness is around 80 nm, the reflectance decreases to 1% or less. Since this reflectance correlates with the inspection signal level of the inspection light shown in FIG. 4, if the reflectance becomes extremely low, it becomes difficult to collect inspection signals and the inspection cannot be continued. The film thickness of the resist film is set from the viewpoint of mask blank processing, and 80 to 90 nm may be preferable depending on the object to be processed using the resist pattern. In this example, in this case, accurate defect inspection is performed. Becomes difficult.

  In the defect inspection method of the present invention, the inspection light is scanned while irradiating the surface of the inspection object, for example, the inspection object having a substrate and at least one layer of thin film formed on the substrate. A defect in the surface portion of the inspection object is detected from the intensity change of the reflected light.

  In the present invention, when measuring the intensity of the reflected light of the inspection light by irradiating the surface of the inspection object with the inspection light, the inspection light is applied to the inspection object from the first incident angle range. When the obtained first reflectance is lower than the predetermined reflectance, the inspection light is applied to the inspection object from the second incident angle range different from the first incident angle range. Irradiation is performed to obtain a second reflectance of the inspection light, and when the second reflectance is higher than the first reflectance, an illumination method that provides inspection light in the second incident angle range may be set. Is preferred. In the defect inspection method of the present invention, the inspection light irradiation method is applied, that is, the inspection object is irradiated with the inspection light from the first incident angle range, and the first reflectance of the inspection light is applied. When the obtained first reflectivity is lower than the predetermined reflectivity, the inspection light is irradiated from the second incident angle range different from the first incident angle range, and the inspection light is irradiated. It is preferable to set an illumination system that provides inspection light in the second incident angle range when the second reflectance is obtained and the second reflectance is higher than the first reflectance.

  The process of the inspection light irradiation method of the present invention and the inspection light irradiation method in the defect inspection method of the present invention will be described more specifically with reference to FIG. FIG. 6 is a flowchart of an example of the process of the inspection light irradiation method. First, in the defect inspection or the like, the inspection object is irradiated with the inspection light from the first incident angle range, and the first reflectance of the inspection light is acquired (S101). For example, a method of irradiating inspection light under standard illumination conditions of the inspection apparatus and confirming the reflectance can be employed. Next, it is determined whether or not the first reflectivity is lower than a predetermined reflectivity, compared to a predetermined reflectivity, specifically, a reflectivity at which a defect can be detected by the inspection apparatus (S102). ). Next, when the first reflectance is lower than the predetermined reflectance, the inspection light is irradiated from the second incident angle range different from the first incident angle range, and the second inspection light The reflectance is acquired (S103). Next, the second reflectance is compared with the first reflectance to determine whether the second reflectance is higher than the first reflectance (S104). When the second reflectance is higher than the first reflectance, the illumination condition (incident angle range) is changed to an illumination condition that gives the second incident angle range, and the inspection light illumination method is set (S105). When the first reflectance is equal to or higher than the predetermined reflectance, it is possible to apply the illumination condition that gives the first incident angle range as it is, and apply the inspection light irradiation method of the present invention. However, it may not be applied. On the other hand, in any of the set second incident angle ranges, when the second reflectance is the same as the first reflectance or lower than the first reflectance, the inspection light irradiation method of the present invention is Not applicable.

  In the present invention, when measuring the intensity of the reflected light of the inspection light by irradiating the surface of the inspection object with the inspection light, the inspection light is irradiated to reflect the inspection light with respect to the incident angle. It is also preferable to acquire a rate distribution, select an incident angle range having a high reflectivity in the reflectivity distribution based on the reflectivity distribution, and set an illumination method that gives inspection light in the selected incident angle range. . In the defect inspection method of the present invention, the inspection light irradiation method is applied, that is, the inspection object is irradiated with the inspection light, the reflectance distribution with respect to the incident angle of the inspection light is obtained, and this reflection is obtained. It is also preferable to select an illumination angle range having a high reflectance in the reflectance distribution based on the rate distribution and to set an illumination system that provides inspection light in the selected incident angle range.

  FIG. 7 is a diagram showing the relationship between the incident angle of inspection light and the reflectance with respect to the above-described resist film having a thickness of 80 nm. The reflectance of the inspection light with respect to the resist film changes as shown by a curve REFC2 according to the change in the incident angle of the inspection light. Therefore, in this case, the reflectance is improved by using the range with the incident angle as the high angle side as the inspection light without using the range with the low incident angle as the inspection light, and thus sufficient for defect detection. The strength of the inspection signal can be obtained. In addition, when only the range where the incident angle is high is used as the inspection light, the high output inspection light that is likely to damage the mask blank, that is, the component with the incident angle of 0 ° is not irradiated. This is also advantageous.

  Even if the first reflectance, the second reflectance, and the reflectance distribution are acquired in advance by irradiating inspection light on another inspection object in the same mode as the inspection object to be used for defect inspection or measurement, defect inspection Alternatively, an object to be inspected for measurement, for example, a substrate and a thin film may be optically modeled and acquired in advance by optical simulation.

  Next, the illumination method will be described with a specific example. FIG. 8 is a view showing the vicinity of the objective lens OBL and the mask blank MB in the inspection apparatus shown in FIG. 3, and FIGS. 8B and 8D are respectively the views shown in FIGS. It is a cross-sectional view of the inspection light near the objective lens OBL in FIG. In FIG. 8, ILM1 and ILM2 indicate inspection light, and NA indicates the aperture range of the objective lens. In the illumination method shown in FIGS. 8A and 8B, the incident angle range includes an incident angle of 0 °, the incident angle is 0 ° as a central axis, and the region to be inspected through the objective lens of the inspection optical system. This is a simple illumination method having a circular cross section in which the inspection light converges on the (illumination region). In this case, the upper limit of the incident angle is set narrower than the aperture range of the objective lens. In the case of the above-described resist film having a thickness of 80 nm, this simple illumination method is adopted, and the incident angle of the inspection light to the mask blank MB is set to 0 ° for the minimum value and 55 ° for the maximum value, for example. When the incident angle range is 1, as shown in FIG. 7, since the first reflectance of the inspection light in the first incident angle range is 1 to several percent, an effective reflectance for defect inspection is obtained. I can't.

  On the other hand, in the illumination method shown in FIGS. 8C and 8D, the incident angle range is greater than 0 ° and less than 90 °, and the incident angle is 0 ° as the central axis. This is an annular illumination system having a circular ring shape in which inspection light converges on an inspection area (illumination area) via an objective lens of an optical system. The upper limit of the incident angle in this case can be made to coincide with the aperture range of the objective lens, in other words, an angle corresponding to the numerical aperture of the objective lens. In the case of the above-described resist film having a thickness of 80 nm, this annular illumination method is adopted, and the incident angle of the inspection light to the mask blank MB is set to, for example, a minimum value of 55 ° and a maximum value of 68 °. As shown in FIG. 7, since the second reflectance of the inspection light in the second incident angle range is several to several tens%, the reflectance effective for defect inspection is obtained. It is done.

  FIG. 9 shows a defect inspection image obtained when a pinhole defect having a width of 60 nm existing in the resist film is inspected with respect to the above-described mask blank having a resist film (photoresist film) having a thickness of 80 nm as the outermost layer. It is a figure which shows the result calculated | required by simulation. In the defect inspection apparatus shown in FIG. 3, the inspection wavelength is set to 532 nm, the illumination area control diaphragm AP1 is controlled to adopt normal bright field illumination, the aperture diaphragm AP2 is fully opened, and the aperture of the objective lens is opened. This is a simulation result when an imaging optical condition of number = 0.95 is designated. 9A shows the intensity distribution of the inspection signal when the simple illumination method is applied, and FIG. 9B shows the intensity distribution of the inspection signal when the annular illumination method is applied. 9C shows the inspection signal intensity SIG-21 along the line AA ′ in FIG. 9A and the inspection signal intensity SIG− along the line BB ′ in FIG. 9B. 22 is shown. When the inspection signal strengths SIG-21 and SIG-22 are compared, the intensity level of the reflected light for inspection is improved although there is almost no difference in the amount of change in the inspection signal strength at the defect portion between the two. As a result, it can be seen that an inspection signal capable of sufficient defect detection can be secured by photoelectric conversion of the defect inspection image.

  In the present invention, it is also possible to apply an illumination system obtained by modifying the above-described annular illumination system. FIG. 10 is a view showing the vicinity of the objective lens OBL and the mask blank MB in the inspection apparatus shown in FIG. 3, and FIG. 10B shows the inspection light in the vicinity of the objective lens OBL in FIG. It is a cross-sectional view. In FIG. 9, ILM3 indicates inspection light, and NA indicates the aperture range of the objective lens. The illumination method shown in FIGS. 10A and 10B has an incident angle range of more than 0 ° and less than 90 °, with the incident angle of 0 ° as the central axis, and an objective lens of the inspection optical system. In a ring illumination method with a circular ring shape in cross section in which inspection light converges on the inspection area (illumination area) via a ring, a modified illumination with a circular arc band shape in which a part of the circular ring shape is missing along the circumferential direction It is a method. In particular, the illumination method divided into two regions symmetrically shown in FIG. 10 is also called a dipole illumination method. The upper limit of the incident angle in this case can be made to coincide with the aperture range of the objective lens, in other words, an angle corresponding to the numerical aperture of the objective lens. In the case of the above-described resist film having a thickness of 80 nm, when this modified illumination method is adopted and the incident angle of the inspection light to the mask blank MB is, for example, 55 degrees and the maximum value is 68 degrees, As shown in FIG. 7, since the reflectance of the inspection light in this incident angle range is several to several tens of percent, a reflectance effective for defect inspection can be obtained.

  FIG. 11 shows an optical image of a defect inspection when a pinhole defect having a width of 60 nm existing in the resist film is inspected with respect to the above-described mask blank in which a resist film (photoresist film) having a thickness of 80 nm is formed as the outermost layer. It is a figure which shows the result calculated | required by simulation, and shows the inspection signal strength along one direction which passes along the center of the defect of the surface where an inspection light is irradiated. The inspection wavelength, the illumination area control diaphragm AP1, the aperture diaphragm AP2, and the numerical aperture of the objective lens are the same as those in the simple illumination system and the annular illumination system described above. 11, SIG-23 is the inspection signal intensity when the annular illumination method shown in FIGS. 8C and 8D is applied, and SIG-24 is the dipole illumination method shown in FIG. Indicates the inspection signal strength when applied. In FIG. 11, the vertical axis is enlarged to make it easy to understand the change in signal intensity. When the inspection signal intensity SIG-23 and SIG-24 are compared, the change amount of the inspection signal intensity in the defect portion by the dipole illumination method is substantially equal to the change in the inspection signal intensity in the defect portion by the annular illumination method. Since the change in the signal at the defect portion is steeper, it can be seen that, for example, when the differential signal is generated, the defect inspection with higher reliability can be performed.

  In the above-described example, the inspection light reflectance of the resist film to be inspected is low on the low angle side and high on the high angle side, but depending on the inspection target, it is high on the low angle side, It may be low on the high angle side. In such a case, the first incident angle range and the incident angle range where the reflectance is low in the reflectance distribution are the high angle side, the second incident angle range and the incident angle where the reflectance is high in the reflectance distribution. What is necessary is just to set the illumination system of the inspection light so that the range becomes the low angle side, and the inspection light is irradiated to the inspection area from the low angle side. In that case, the simple illumination system described above may be set. Is possible. For example, in the inspection apparatus shown in FIG. 3, the adjustment and setting of the incident angle of the inspection light can be realized by changing the aperture shape of the illumination area control aperture AP1, and the output of the light source LIS is adjusted as necessary. May be.

  The defect inspection method of the present invention is preferably implemented by applying the illumination method described above. Specifically, as the defect inspection method to which the illumination method described above is applied, in the step of placing the inspection object on a stage that can move the inspection object along the direction of the inspection surface of the inspection object, and the above-described illumination method The process of irradiating the inspection light while scanning the surface of the inspection object with the set illumination method, and the amount of reflected light of the inspection area irradiated with the inspection light through the objective lens of the inspection optical system. By a method having a step of collecting as an inspection signal of an inspection area, a step of detecting a defect when the inspection signal crosses a preset threshold, and a step of recording information of the detected defect Can be implemented.

  The process of such a defect inspection method will be described more specifically with reference to FIG. FIG. 12 is a flowchart of an example of the process of the defect inspection method. First, the inspection light illumination method described above is performed to set the inspection light illumination method (S111). Next, the inspection optical system is set to a predetermined condition (S112). Next, the inspection object is placed on the stage (S113). The inspection object can be stored in a storage container that can store a plurality of inspection objects and set in the inspection apparatus. In this case, the inspection objects may be placed on the stage one by one in order. Next, a defect inspection of the inspection object is performed by operating a normal inspection apparatus. Specifically, first, the inspection light is irradiated while scanning the surface of the inspection object with the set illumination method (S114), and the amount of reflected light of the inspection area irradiated with the inspection light is determined by the inspection optical. It collects as an inspection signal of the inspection area through the objective lens of the system (S115), and detects a defect when the inspection signal crosses a preset threshold value (S116). Then, information on the detected defect is recorded (S117). When the inspection object is stored in a storage container that can store a plurality of inspection objects and set in the inspection apparatus, the inspection object may be replaced and the steps S113 to S117 may be repeated. In this case, the steps S111 to S117 are repeated, and the inspection light illumination method in the step S111 and the conditions of the inspection optical system in the step S112 may be set according to the object to be inspected.

  The present invention can be applied to a mask blank such as a photomask blank used for manufacturing a semiconductor circuit pattern transfer mask. As the mask blank, a mask blank having a resist film such as a photoresist film as the outermost layer is suitable. According to the present invention, a defect of the resist film, particularly a pinhole defect of the resist film can be inspected. By applying the defect inspection method of the present invention to the defect inspection of the mask blank, the mask blank can be selected based on the information on the presence or absence of defects obtained by the inspection by the defect inspection method. Further, according to the present invention, information on the presence / absence of a defect, in particular, information that there is no defect larger than a predetermined size can be obtained, so the defect information obtained by the defect inspection method is accompanied by an inspection form, etc. By this method, it can be applied to the mask blank. Furthermore, based on the information given to the mask blank, a mask blank that does not include a defect can be selected.

  In the above-described example, the case of inspecting the defect of the resist film formed on the substrate as the object to be inspected has been described. However, the inspection object is not limited to the resist film, and various kinds of optical thin films, processing auxiliary films, etc. The present invention can be applied as a defect inspection of a film formed as the uppermost layer in a laminated structure of films. The present invention is particularly suitable when the film to be inspected acts as an antireflection film for the inspection light. According to the present invention, even a thin film that has conventionally been difficult to inspect due to insufficient reflected light intensity can ensure a sufficient amount of reflected light for defect inspection and can be subjected to defect inspection. Spread.

  As described above, the method for inspecting a defect existing on the surface of the mask blank has been described. However, in consideration of the optical principle, the present invention can be used as an object to be inspected in place of a mask blank, for example, various types of A semiconductor wafer having a metal film or the like, a recording medium having various metal films or optical thin films formed on the substrate, etc. can be applied, and a surface having a concave portion such as a pinhole defect as a concave defect. It is easily understood that the defect inspection method of the present invention can be suitably applied to an inspection object, an inspection object having a convex defect on the surface, and the like.

DESCRIPTION OF SYMBOLS 1 System control part 2 Inspection image data storage part 3 Memory 4 Monitor 5 Stage drive means 6 Illumination aperture drive means 7 Aperture aperture drive means 500 Photomask blank 500a Photomask 501 Transparent substrate 502 Optical thin film 502a Optical thin film pattern 503 Hard mask film 503a Hard mask film pattern 504 Resist film 504a Resist pattern AP1 Illumination area control stop AP2 Aperture stop BM1 Inspection light BM2 Reflected light BSP Beam splitter ILS Light source L1 Lens L2 Lens L3 Lens MB Mask blank OBL Objective lens SE Detector STG Stage d Defect

Claims (6)

The surface of the inspection object is scanned from the change in intensity of the reflected light of the inspection light by scanning the inspection light while irradiating the surface of the inspection object having the substrate and at least one thin film formed on the substrate. A defect inspection method for detecting defects in a part,
Irradiating an inspection object with inspection light from a first incident angle range to obtain a first reflectance of the inspection light;
When the first reflectance is lower than a predetermined reflectance, the inspection light is irradiated from the second incident angle range different from the first incident angle range, and the second reflection of the inspection light is performed. Obtaining a rate;
A step of setting an illumination method that provides inspection light in the second incident angle range when the second reflectance is higher than the first reflectance, and the incident angle range is the illumination method. An annular illumination system with a circular ring shape in which the inspection light converges on the inspection area through the objective lens of the inspection optical system, with the incident angle exceeding 0 ° and less than 90 °, with the incident angle being 0 ° as the central axis A defect inspection method comprising: setting a modified illumination system having a cross-sectional arc band shape in which a part of the circular ring shape is missing along the circumferential direction. Placing the inspection object on a stage capable of moving the inspection object along the direction of the inspection surface of the inspection object;
A step of irradiating the inspection light while scanning the surface of the inspection object with the set illumination method,
Collecting the amount of reflected light of the inspection area irradiated with the inspection light as an inspection signal of the inspection area via the objective lens of the inspection optical system;
Detecting the defect when the inspection signal crosses a preset threshold, and detecting the defect;
The defect inspection method according to claim 1, further comprising a step of recording information on the detected defect. The object to be inspected, the defect inspection method according to claim 1 or 2, characterized in that a mask blank used for manufacturing a semiconductor circuit pattern transfer mask. The defect inspection method according to claim 3 , wherein the mask blank is a mask blank having a photoresist film as an outermost layer, and the defect of the photoresist film is inspected. Defect inspection method according to any one of claims 1 to 4, characterized in that the wavelength of the inspection light is 210～550Nm. An inspection light irradiation method for irradiating the surface of an inspection object with inspection light and measuring the intensity of reflected light of the inspection light,
Irradiating an inspection object with inspection light from a first incident angle range to obtain a first reflectance of the inspection light;
When the first reflectance is lower than a predetermined reflectance, the inspection light is irradiated from the second incident angle range different from the first incident angle range, and the second reflection of the inspection light is performed. Obtaining a rate;
A step of setting an illumination method that provides inspection light in the second incident angle range when the second reflectance is higher than the first reflectance, and the incident angle range is the illumination method. An annular illumination system with a circular ring shape in which the inspection light converges on the inspection area through the objective lens of the inspection optical system, with the incident angle exceeding 0 ° and less than 90 °, with the incident angle being 0 ° as the central axis The method of irradiating inspection light according to claim 1, wherein a modified illumination system having a cross-sectional arc band shape in which a part of the circular ring shape is missing along the circumferential direction is set.

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