TWI646324B - Defect inspecting method, sorting method, and producing method for photomask blank - Google Patents

Abstract

The solution is to set the distance between the defect and the objective lens of the inspection optical system as the defocus distance by using the inspection optical system for the defect of the surface portion of the mask substrate which is formed on the substrate with at least one film. The light is irradiated to the defect through the objective lens, and the reflected light that is irradiated to the region of the inspection light is collected as an enlarged image through the objective lens, and the changed portion of the light intensity of the enlarged image is defined, and the light intensity of the changed portion of the light intensity of the enlarged image is changed. To determine the concave and convex shape of the defect.

The effect is that the defect of the mask substrate can be inspected by using an optical defect inspection method to distinguish the uneven shape of the defect with high reliability. Further, by applying the defect inspection method of the present invention, the convex defect is not mistakenly judged as a concave defect, and the mask substrate having the concave defect which is a fatal defect can be surely excluded, and the defect can be provided at a lower cost and higher yield. A mask substrate with a fatal defect.

Description

Mask inspection method, selection method and manufacturing method of mask substrate

The present invention relates to a defect inspection method for a mask substrate for manufacturing a photomask used in the manufacture of a semiconductor device (semiconductor device) or the like, and more particularly to a defect inspection method for determining the uneven shape of a surface of a fine defect. . Further, the present invention relates to a method and a method for selecting a mask substrate to which defect inspection of a photomask substrate is applied.

In a semiconductor device (semiconductor device), a mask (transfer mask) for a mask having a circuit pattern or the like is repeatedly irradiated with light for exposure, and a loop pattern formed in the mask is passed through the reduction optics. The system is manufactured by photolithography technology transferred onto a semiconductor substrate (semiconductor wafer). The transfer mask is manufactured by forming a circuit pattern on a substrate (mask substrate) on which an optical film is formed. Such an optical film is generally a film mainly composed of a transition metal compound or a film containing a ruthenium compound containing a transition metal as a main component, and depending on the purpose, a film which functions as a light shielding film is selected or used as a phase. A membrane that functions as a function of the offset film.

Since the mask for transfer such as a photomask is used as a master for manufacturing a semiconductor element having a fine pattern, it is required to be free from defects. Therefore, it is a matter of course that the mask substrate is required to be free from defects. Further, when forming a circuit pattern, a resist film for processing is formed on a mask substrate on which an optical film is formed, and a general lithography step such as electron beam lithography is performed to finally form a pattern. Therefore, the resist film also requires defects such as no pinholes. From this point of view, many studies have been conducted on defect detection techniques for transfer masks or mask substrates.

Japanese Patent Publication No. 2001-174415 (Patent Document 1) discloses a method of detecting a defect or an impurity by diffused light by irradiating laser light onto a substrate. In particular, it describes a technique for imparting asymmetry to a detection signal to discriminate it as a convex defect or a concave defect. Japanese Patent Publication No. 2005-265736 (Patent Document 3) discloses a technique of using DUV (Deep Ultra Violet) light for performing pattern inspection of a general optical mask for inspection light. Japanese Laid-Open Patent Publication No. 2013-19766 (Patent Document 4) discloses a technique of dividing an inspection light into a plurality of points for scanning and receiving a reflected beam by a photodetecting element. On the other hand, Japanese Laid-Open Patent Publication No. 2007-219130 (Patent Document 5) discloses a technique of using EUV (Extreme Ultra Violet) light having a wavelength of 13.5 nm as a difference between the inspection light and the unevenness of the EUV mask substrate.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2001-174415

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-333313

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-265736

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2013-19766

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2007-219130

With the continued miniaturization of semiconductor devices, we have adopted the ArF lithography technology using argon fluoride (ArF) excimer laser light with a wavelength of 193 nm, and the multi-pattern process of combining multiple exposure processes or processing processes. The technique of finally forming a pattern of a size that is extremely small compared to the exposure wavelength is devoted to research. For example, since the transfer mask is used as a master of a fine pattern, it is necessary to eliminate all defects on the transfer mask which would impair the faithfulness of the pattern transfer. Therefore, in the manufacturing stage of the mask substrate, it is also necessary to detect all defects that may become barriers when the mask pattern is formed.

In the transfer mask, concave defects, especially pinhole defects, become fatal when the mask pattern is formed. On the other hand, in terms of convex defects, depending on the height of the defect, it is sometimes not fatal when the mask pattern is formed. Further, the convex defects caused by the impurities adhering to the surface do not become fatal defects as long as they can be removed by washing. Therefore, if these convex defects are all regarded as fatal defects, the mask substrate is excluded as defective products. This will result in a decrease in yield. Therefore, in the defect inspection, it is extremely important to distinguish the uneven shape of the defect with high precision from the fact that the mask substrate having a fatal defect is surely excluded and the yield is ensured.

Each of the inspection apparatuses described in Patent Documents 1 to 4 is an apparatus using an optical defect detection method. The optical defect detection method can perform a wide range of defect inspection in a short period of time, and can accurately detect the fine defect by the short wavelength of the light source. Moreover, it is a method of determining the unevenness of a defect by the relationship between the arrangement position of the bright portion and the dark portion of the inspection signal obtained by the inspection optical system using the oblique illumination method and the spatial filter. Further, Patent Document 5 describes a method in which the object to be inspected is limited to the EUV mask substrate, but the unevenness of the phase defect can be distinguished.

However, according to the actual inspection test of the inspection apparatus described in the above Patent Documents 1 to 4, among the defects determined as the concave defects by the arrangement of the light and dark of the inspection signal of the photomask substrate, if the defect is caused by an atomic force microscope or It was confirmed by real image observation or the like of an electron microscope, and it was found that convex defects were sometimes included. In other words, the inspection apparatuses described in Patent Documents 1 to 4 do not necessarily distinguish the uneven shape of the defects with high precision. Moreover, the method described in the above Patent Document 5 is applied to a phase defect inherent to an EUV mask substrate, and is not easily applied to a current mainstream mask using a KrF excimer laser, an ArF excimer laser, or an F ₂ laser. The method of the substrate. Therefore, it is hoped to establish a method in which convex defects that are not easily achieved by current methods are not misjudged as concave defects.

The present invention has been completed in order to solve the above problems. Provided is a defect inspection method using an optical defect detection method that does not erroneously determine a convex defect as a concave defect, and which can distinguish a defect of a defect of a mask substrate with high reliability, and a selection of a mask substrate to which the defect inspection is applied Method and method of manufacture.

As described above, when the defect inspection is performed by a conventional method of distinguishing the unevenness by the arrangement of the bright portion and the dark portion in the inspection image, the concave defect such as the pinhole formed in the film of the photomask substrate can be correctly determined as the concave defect. However, a convex defect such as a state in which an impurity such as a particle having a different material from the film adheres to the surface of the film of the photomask substrate or a state partially embedded in the film may be mistakenly determined as a concave defect.

Therefore, the inventors of the present invention have made efforts to repeat the above-mentioned research in order to solve the above problems, and have found that, in the case of a defect determined to be a concave defect by a conventional method, the focus state determined by the concave defect deviates from the focus position of the inspection optical system. In the so-called defocused state, the inspection image of the defect is collected and the light intensity distribution of the inspection image is evaluated, especially the difference between the light and dark arrangement or the light intensity of the light and dark, and the defect determined to be a concave defect in the focused state can be further distinguished into true. The concave defect and the convex defect are completed until the present invention is completed.

Therefore, the present invention provides the following defect inspection method, selection method and manufacturing method of the reticle substrate:

Claim 1 : A defect inspection method of a photomask substrate, which is an inspection optical system for inspecting a photomask base existing on a film on which at least one layer is formed on a substrate A method of forming a defect in a surface portion of a plate, comprising: (A1) causing the defect to be close to an objective lens of the inspection optical system, setting a distance thereof to a focus distance, and setting the focus distance; a step of irradiating the inspection light to the defect via the objective lens; (A2) a step of collecting the reflected light irradiated to the region of the inspection light through the objective lens as the first enlarged image of the region; (A3) defining the first enlarged image a first determination step of determining a concavo-convex shape of the defect by a change in the intensity of the light intensity of the first enlarged image, and determining the defect and the objective lens of the inspection optical system The distance is set to a defocus distance that deviates from the above-described focus distance, and in the state where the defocus distance is set, the inspection light is irradiated to the defect via the objective lens; (B2) the reflected light that is irradiated to the region of the inspection light, a step of collecting through the objective lens as the second enlarged image of the region; and (B3) defining a portion of the change in the light intensity of the second enlarged image, and the second amplification The second determination step of determining the uneven shape of the defect by changing the light intensity of the portion of the change in the light intensity of the image.

Item 2: The defect inspection method of claim 1, wherein in the step (B3), the light intensity change of the change portion of the light intensity of the true concave defect is obtained in advance by simulation, and then the light intensity is obtained according to the obtained light intensity The change is compared with the change in the light intensity of the portion of the change in the light intensity of the second enlarged image, and the uneven shape of the defect to be inspected is again determined.

Item 3: The defect inspection method of claim 1 or 2, wherein the inspection light is light having a wavelength of 210 to 550 nm.

The defect inspection method according to any one of claims 1 to 3, wherein in the two steps (A1) and (B1), the optical axis thereof is inclined obliquely to the surface of the photomask substrate The above inspection light is irradiated to the illumination.

The defect inspection method according to any one of claims 1 to 3, wherein in the two steps (A2) and (B2) above, spatial filtering for shielding a part of the reflected light is provided on the optical path of the reflected light. And collect the reflected light through the spatial filter.

The defect inspection method according to any one of claims 1 to 5, wherein in the step (A1), the photomask substrate is placed on a stage movable in an in-plane direction thereof, and the above The stage is moved in the in-plane direction so that the above-mentioned defects are close to the objective lens of the inspection optical system.

The defect inspection method according to any one of claims 1 to 6, wherein in the first determining step, when the defect shape is determined to be a concave shape, the steps (B1) to (B3) are performed, and The uneven shape of the defect is again determined.

Item 8: A method for selecting a reticle substrate, characterized by being based on a request item In the uneven shape of the defect which is determined again in the second determination step of the defect inspection method of 7, the mask substrate containing no concave defect is selected from the mask substrate on which the above steps (B1) to (B3) have been performed.

Clause 9: A method of manufacturing a reticle substrate, comprising: forming a film of at least one layer on a substrate; and determining a presence by a defect inspection method according to any one of claims 1 to 7. The step of the uneven shape of the defect of the above film.

According to the present invention, it is possible to inspect the defect of the photomask substrate by using an optical defect inspection method to distinguish the uneven shape of the defect with high reliability. Further, by applying the defect inspection method of the present invention, the convex defect is not mistakenly judged as a concave defect, and the mask substrate having the concave defect which is a fatal defect can be surely excluded, and the defect can be provided at a lower cost and higher yield. A mask substrate with a fatal defect.

100‧‧‧Photomask substrate

100a‧‧‧Photomask

101‧‧‧Transparent substrate

102‧‧‧Optical film

102a‧‧‧Optical film pattern

103‧‧‧hard mask film

103a‧‧‧Hard mask film pattern

104‧‧‧Resist film

104a‧‧‧Resistor pattern

BM1‧‧‧Check light

BM2‧‧‧ reflected light

BSP‧‧ ‧ Beamsplitter

DEF1, DEF2, DEF3, DEF5, DEF8‧‧‧ concave defects

DEF4, DEF6, DEF7, DEF9‧‧‧ convex defects

ILS‧‧‧ light source

L1‧‧ lens

Side of the left side of the LSF‧‧‧ defect

MB‧‧‧Photomask substrate

The surface of the MBS‧‧‧mask substrate

OBL‧‧‧ objective lens

Side of the right side of the RSF‧‧‧ defect

SE‧‧‧ Image Detector

STG‧‧‧ stage

Fig. 1 is an explanatory view showing an outline of an example of a procedure for producing a photomask from a photomask substrate, which is a cross-sectional view of each stage of the manufacturing process.

Fig. 2 is a cross-sectional view showing an example in which a concave defect exists on a photomask substrate; (A) and (B) are photomask substrates showing the presence of concave defects, and (C) is a photomask showing the presence of concave defects. The reticle of the substrate Figure.

Fig. 3 is a cross-sectional view showing an example in which a convex defect is present on a photomask substrate; (A) is a photomask substrate showing a convex defect, and (B) is a photomask substrate having a convex defect; A picture of a reticle.

Fig. 4 is a view showing an example of a configuration of an inspection optical system for defect inspection of a photomask substrate.

Fig. 5(A) is a view showing a form of reflected light corresponding to the inspection light irradiated to the concave defect on the mask substrate by oblique illumination; (B) is a view showing a profile curve of the light intensity distribution of the inspection image.

Fig. 6(A) is a view showing a form of reflected light corresponding to the inspection light irradiated to the convex defect on the mask substrate by oblique illumination; (B) is a view showing a profile curve of the light intensity distribution of the inspection image.

Fig. 7(A) is a plan view of a photomask substrate having a convex defect in a state in which a part of an impurity composed of a low refractive index material is protruded from an optical film; (B) is a sectional view; (C) is a convex defect The inspection image, (D) is a diagram showing a profile curve of the light intensity distribution of the inspection image.

Fig. 8(A) is a cross-sectional view of a photomask substrate having a convex defect in a state in which a part of impurities are protruded by an optical film; (B) is a cross-sectional view of a photomask substrate having a true concave defect; (C) and ( D) is a graph showing a profile of the light intensity distribution of the inspection image in which each defect is in a positive defocus state; (E) and (F) are profiles showing the light intensity distribution of the inspection image in which each defect is in a focused state. The graph of the curve; (G) and (H) are the light intensity distributions of the inspection images indicating the respective defects in the negative defocus state. Diagram of the profile curve.

Figure 9(A) is a plan view of a photomask substrate having a convex defect formed by an adherend made of a material substantially transparent to the inspection light; (B) is a cross-sectional view; (C) is a cross-sectional view; (D) is a diagram showing a profile curve of the light intensity distribution of the inspection image.

Fig. 10(A) is a cross-sectional view of a photomask substrate having convex defects formed by adhering substances made of a material substantially transparent to inspection light; (B) to (D) are respectively shown in positive dispersion A graph of a profile curve of a light intensity distribution of an inspection image in a focus state, a focus state, and a negative defocus state.

Fig. 11 is a flow chart showing an example of the procedure of the defect inspection method.

Fig. 12 is a flow chart showing another example of the procedure of the defect inspection method.

Fig. 13(A) is a cross-sectional view showing a photomask substrate having a convex defect of the first embodiment; (B) to (D) are diagrams showing a positive defocus state, a focus state, and a negative defocus state, respectively. A diagram of the profile curve of the light intensity distribution of the image.

Fig. 14(A) is a cross-sectional view of the photomask substrate having a true concave defect of the comparison object; (B) to (D) are respectively shown in a positive defocus state, a focus state, and a negative defocus state. A diagram of the profile curve of the light intensity distribution of the image.

Fig. 15(A) is a cross-sectional view showing a photomask substrate having a convex defect of Example 2; (B) to (D) are diagrams showing a positive defocusing state, respectively. A graph of a profile curve of a light intensity distribution of an inspection image in a focal state and a negative defocus state.

[Formation of the Invention]

Hereinafter, the present invention will be described in more detail.

First, the step of manufacturing a photomask from a photomask substrate will be described. Fig. 1 is an explanatory view showing an example of a procedure for producing a photomask from a photomask substrate, and is a cross-sectional view of a mask substrate, an intermediate body, or a photomask in each stage of the manufacturing process. In the photomask substrate, at least one optical film, a processing auxiliary film, or the like is formed on the transparent substrate.

In the mask substrate 100 shown in FIG. 1(A), an optical film 102 that functions as a phase shift film such as a light shielding film or a halftone phase shift film is formed on the transparent substrate 101, and an optical film is formed on the optical film. A hard mask film (processing auxiliary film) 103 is formed on 102. When the reticle is manufactured from such a reticle substrate, the resist film 104 for processing thereof is first formed on the hard mask film 103 (Fig. 1(B)). Next, after the lithography step by electron beam lithography or the like, the resist pattern 104a is formed from the resist film 104 (Fig. 1(C)), and the resist pattern 104a is used as an etch mask to harden the lower layer. The mask film 103 is processed to form a hard mask pattern 103a (Fig. 1(D)), and the resist pattern 104a (Fig. 1(E)) is removed. Further, by using the hard mask pattern 103a as an etching mask and processing the lower optical film 102, the optical film pattern 102a is formed, and thereafter, the hard mask pattern 103a is removed, that is, the mask 100a is obtained. (Fig. 1 (F)).

If a film of the reticle substrate has a concave defect such as a pinhole defect, it eventually becomes a cause of the defect of the mask pattern on the reticle. An example of a concave defect of a typical photomask substrate is shown in Fig. 2. Fig. 2(A) is a view showing an example of the mask substrate 100 in which the hard mask film 103 formed thereon has the concave defect DEF1 due to high-precision processing of the optical film 102 formed on the transparent substrate 101. FIG. 2(B) is a cross-sectional view showing an example of the mask substrate 100 in which the optical film 102 formed on the transparent substrate 101 itself has the concave defect DEF2.

In any of the photomask substrates, when the photomask substrate is manufactured by the manufacturing process as shown in Fig. 1, the photomask 100a is formed as in the photomask 100a shown in Fig. 2(C). The concave defect DEF3 exists in the photomask of the optical film pattern 102a. Moreover, this concave defect DEF3 may cause a pattern transfer error in exposure using a photomask. Therefore, the concave defect of the reticle substrate needs to be detected at the stage before the reticle substrate is processed, and the defective reticle substrate or the repair of the defect is eliminated.

On the other hand, Fig. 3 shows a case where a convex defect such as a particle defect exists on the photomask substrate, and Fig. 3(A) shows a convex defect formed on the optical film 102 formed on the transparent substrate 101. A cross-sectional view of an example of a reticle substrate 100 of DEF4. When the reticle is manufactured by the manufacturing process as shown in FIG. 1 of the reticle substrate, the convex defect DEF4 remains in the light like the reticle 100a shown in FIG. 3(B). The mask on the film pattern 102a is learned. However, in the case of a convex defect, depending on the size of the defect, it is sometimes not fatal; in addition, the convex defect caused by the impurities attached to the surface does not become a fatal defect as long as it can be removed by washing.

In this way, the defect that the defect of the photomask substrate is a concave defect such as a pinhole which is a fatal defect, or the convex defect which is not a fatal defect in many cases, grasps the quality assurance of the photomask substrate, and the mask substrate. The key to yield in manufacturing. Therefore, a method of distinguishing the uneven shape of a defect with high reliability by an optical method is desired.

Next, an inspection optical system that is applied to the defect inspection of the mask substrate is specifically described as an inspection optical system that is applied to the uneven shape for determining defects in the surface portion of the mask substrate. 4 is a schematic view showing an example of a basic configuration of an inspection optical system, and includes a light source ILS, a beam splitter BSP, an objective lens OBL, and a movable stage STG and a video detector SE on which the mask substrate MB is placed. The light source ILS is configured to emit light having a wavelength of about 210 nm to 550 nm, and the inspection light BM1 emitted from the light source ILS is bent by the beam splitter BSP, and is irradiated to a predetermined region of the mask substrate MB by the objective lens OBL. The light BM2 reflected on the surface of the mask substrate MB is collected by the objective lens OBL, and passes through the beam splitter BSP and the lens L1 to reach the light receiving surface of the image detector SE. At this time, the position of the image detector SE is adjusted so that the enlarged inspection image of the surface of the mask substrate MB is formed on the light receiving surface of the image detector SE. Thereafter, the image processing calculation is performed on the data of the enlarged inspection image collected by the image detector SE, and the size calculation of the defect or the determination of the unevenness is performed, and the results are recorded by the defect information. record.

For example, the image detector SE may be used as a detector for arranging a plurality of photodetecting elements as pixels in a CCD camera to form an enlarged image of the light BM2 reflected on the surface of the mask substrate MB via the objective lens OBL. A direct method of collecting two-dimensional images in one piece is collected. Further, the inspection light BM1 may be scanned on the surface of the mask substrate MB by scanning means, and the light intensity of the reflected light BM2 may be sequentially collected by the image detector SE, photoelectrically converted and recorded, and the entire two-dimensional image may be generated. The method of imagery. Furthermore, the spatial filter SPF for shielding a part of the reflected light BM2 may be disposed at the pupil position of the inspection optical system, for example, on the optical path of the reflected light BM2, especially between the beam splitter BSP and the lens L1. At the time, a part of the optical path of the reflected light BM2 is blocked as needed, and the image is detected by the image detector SE. The incident angle of the inspection light BM1 can be set to a predetermined angle with the mask substrate MB. In addition, the positioning of the defect to be inspected may be positioned at a position where the defect of the object can be observed by the objective lens OBL; at this time, the mask substrate MB is placed on the mask stage STG and transmitted through the mask stage STG. By moving, it can be positioned at a position that can be observed with the objective lens OBL.

Next, with respect to the inspection optical system shown in FIG. 4, the distance between the defect and the objective lens of the inspection optical system is set as the focus distance (focus point) to collect the difference between the concave defect and the convex defect detection image when the reflected light is collected. 5 and 6 are illustrated. Fig. 5(A) is a view showing the surface of the inspection optical system shown in Fig. 4 from the left side of the inspection light BM1 with respect to the mask substrate including the typical concave defect DEF5. A schematic of an example of oblique illumination. Such oblique illumination can be controlled, for example, by the position of the optical aperture (located between the light source ILS and the beam splitter BSP) from the position of the inspection light BM1 emitted from the light source ILS shown in FIG. 4 toward the mask substrate MB. to realise. At this time, the reflected light BM2 reflected by the left side LSF in the figure of the concave defect DEF5 is concentrated toward the right side of the objective lens OBL by the regular reflection, and therefore the objective lens OBL is not sufficiently ingested. On the other hand, the reflected light reflected by the side surface RSF in the figure of the concave defect DEF5 is sufficiently intruded into the objective lens OBL by the regular reflection. As a result, the light intensity distribution of the inspection image obtained by the image detector SE is such that the left side of the concave defect DEF5 becomes a dark portion and the right side becomes a bright portion, and a profile curve PR1 as shown in Fig. 5(B) is formed.

On the other hand, Fig. 6(A) is a view showing an example in which the inspection light BM1 is obliquely illuminated from the left side with respect to the surface MBS of the photomask substrate including the typical convex defect DEF6 from the inspection optical system shown in Fig. 4. . At this time, the reflected light BM2 reflected by the side LSF on the left side in the figure of the convex defect DEF6 is sufficiently intruded into the objective lens OBL by the regular reflection. On the other hand, the reflected light reflected by the right side RSF in the figure of the convex defect DEF6 is concentrated toward the right side of the objective lens OBL by the regular reflection, and therefore the objective lens OBL is not sufficiently ingested. As a result, the light intensity distribution of the inspection image obtained by the image detector SE is such that the left side of the convex defect DEF6 becomes a bright portion and the right side becomes a dark portion, and a profile curve PR2 as shown in Fig. 6(B) is formed.

In this way, by applying the oblique illumination, the uneven shape of the defect can be determined from the positional relationship of the brightness of the obtained inspection image. In Figure 5 And Fig. 6 shows an example of oblique illumination from the left side in the figure, but the illumination direction can be arbitrarily set, and the position of the light and dark of the image can be checked based on the incident side of the inspection light in the obtained inspection image. Or the difference in light intensity is similarly determined as the uneven shape of the defect.

Further, as shown in Fig. 4, in the inspection optical system, a spatial filter SPF for shielding a part of the reflected light is provided on the optical path of the reflected light, and when the reflected light is collected by the spatial filter SPF, the mask is formed. The surface of the substrate is irradiated with the inspection light from the vertical direction, and the inspection image may be made bright or dark as in the case of the oblique illumination described above. At this time, for example, if half of the optical path of the reflected light is shielded, the uneven shape of the defect can be determined from the difference in the positional relationship between the brightness and the light intensity of the inspection image based on the incident side of the inspection light.

However, when impurities such as particles are embedded in the optical film on the surface of the mask substrate, and a part of the film is protruded from the optical film to form a convex defect, the brightness and darkness of the image may not be checked. It is correctly determined that the defect is a concave defect or a convex defect. Fig. 7 (A) and (B) are a plan view and a cross-sectional view (first form) of the mask substrate 100 having such a convex defect, respectively. These are the surface portions of the optical film 102 made of a MoSi-based material formed on the quartz substrate 101 which is transparent to the inspection light, and the optical film 102 has a convexity formed of impurities composed of a low refractive index material. The state of the defect DEF7.

For the convex defect DEF7, the distance between the defect and the objective lens of the inspection optical system is set as the focus distance (focus point), like the concave defect shown in Fig. 5 or the convex defect shown in Fig. 6, using Fig. 4 Inspection In the optical system, when the inspection surface light is irradiated from the left side of the image by oblique illumination on the surface of the mask substrate, and the reflected light is collected, the inspection image of the light intensity distribution shown in FIG. 7(C) is obtained. In the cross section of the line A-A' of Fig. 7(C), the light intensity distribution forms a curve PR3 as shown in Fig. 7(D). At this time, when compared with the case shown in FIG. 5 and FIG. 6, it is judged as a concave defect, but it is actually a convex defect.

However, for the convex defect determined to be a concave defect as shown in FIGS. 7(A) and (B) and the true concave defect, the distance between the defect and the objective lens of the inspection optical system is set as a defocus distance deviating from the focus distance. When the reflected light is collected, in a state in which the defocus distance is set (defocus state), it is known that there is a difference in the inspection image and the light intensity distribution.

Fig. 8(A) is a cross-sectional view similar to Fig. 7(B). On the other hand, Fig. 8(B) is a cross-sectional view of the mask substrate 100 having the actual concave defect DEF8 of the optical film 102 made of the MoSi-based material formed on the quartz substrate 101 transparent to the inspection light.

If the convex defect DEF7 and the concave defect DEF8 are used as the concave defect shown in FIG. 5 or the convex defect shown in FIG. 6, the inspection optical system shown in FIG. 4 is used, and the surface of the photomask substrate is used. The oblique illumination illuminates the inspection light from the left side of the figure and collects the reflected light, and the distance between the defect and the objective lens of the inspection optical system is set to the focus state of the focus distance (Δz=0; in addition, Δz indicates the difference from the focus distance In the case of (the same below), the profile curve PR6 (Fig. 8(E)) of the light intensity distribution of the convex defect DEF7 and the profile curve PR7 of the light intensity distribution of the concave defect DEF8 (Fig. 8(F)) There is no difference in positional relationship between light and dark. again The distance between the defect and the objective lens of the inspection optical system is a positive defocus distance, and even if the mask stage STG on which the mask substrate MB is placed rises, the defocus state close to the focus distance is set (Δz>0). In the case of the light-dark position between the profile curve PR4 (Fig. 8(C)) of the light intensity distribution of the convex defect DEF7 and the profile curve PR5 (Fig. 8(D)) of the light intensity distribution of the concave defect DEF8 There is no difference in relationship. On the other hand, even if the distance between the defect and the objective lens of the inspection optical system is negative, even if the mask stage STG on which the mask substrate MB is placed is lowered, the defocus state is set to be away from the negative focus distance ( In the case of Δz<0), the profile curve PR8 of the light intensity distribution of the convex defect DEF7 (Fig. 8(G)) and the profile curve PR9 of the light intensity distribution of the concave defect DEF8 (Fig. 8(H)) The positional relationship between the light and the dark is reversed.

That is, both the inspection image and the light intensity distribution obtained in the in-focus state or in the positive defocus state are determined to have the same shape. However, if the inspection image and the light intensity distribution obtained in the negative defocus state are the concave defects DEF8 of the true concave defect, the left side of the figure becomes a bright part, the right side becomes a dark part, and the light and dark are arranged to be reversed; In the convex defect DEF7 in which a part of the impurity is formed by the state in which the optical film is protruded, the bright portion and the dark portion are not reversed. Checking the light intensity distribution of the bright and dark parts of the image varies with the width, height, depth, defocus amount, etc. of the defect, and in any case, the positional relationship between the bright part and the dark part of the image is negative defocusing There will be differences in the status. By using this difference, it is possible to accurately determine a defect which is actually a convex defect but is mistakenly judged as a concave defect in a focused state as a convex defect.

Next, a case where the deposit made of a material substantially transparent to the inspection light is present in the form of a defect as shown in Fig. 9 will be described. Fig. 9 (A) and (B) are a plan view and a cross-sectional view (second form) of the mask substrate 100 having such convex defects, respectively. These are the surfaces of the optical film 102 made of a MoSi-based material formed on the quartz substrate 101 which is transparent to the inspection light, and are formed of deposits made of a material substantially transparent to the inspection light. The state of the convex defect DEF9. At this time, the optical film 102 itself is flat.

For the convex defect DEF9, the distance between the defect and the objective lens of the inspection optical system is set as the focus distance (focus point), as shown in the concave defect shown in Fig. 5 or the convex defect shown in Fig. 6, using Fig. 4 In the inspection optical system, when the inspection surface light is irradiated from the left side of the image by the oblique illumination on the surface MBS of the mask substrate, and the reflected light is collected, the inspection image of the light intensity distribution shown in FIG. 9(C) can be obtained. The section of the A-A' line of Fig. 9(C) shows a light intensity distribution forming a curve PR10 as shown in Fig. 9(D). At this time, when compared with the case shown in FIG. 5 and FIG. 6, it is judged as a concave defect, but it is actually a convex defect.

However, for the convex defect determined to be a concave defect as shown in FIGS. 9(A) and (B) and the true concave defect, the distance between the defect and the objective lens of the inspection optical system is set as a defocus distance deviating from the focus distance. When the reflected light is collected, at this time, in a state in which the defocus distance is set (defocus state), it is also known that there is a difference in the inspection image and the light intensity distribution.

Fig. 10(A) is a cross-sectional view similar to Fig. 9(B). On the other hand, the reticle substrate 100 having the true concave defect DEF8 The cross-sectional view is shown in Figure 8 (B).

If the convex defect DEF9 and the concave defect DEF8 are used as the concave defect shown in FIG. 5 or the convex defect shown in FIG. 6, the inspection optical system shown in FIG. 4 is used, and the surface of the photomask substrate is used. The oblique illumination illuminates the inspection light from the left side of the figure and collects the reflected light, in the case of the focus state (Δz=0), the positive defocus state (Δz>0), and the negative defocus state (△) In either case of z<0), the profile curve PR12 of the light intensity distribution of the light intensity distribution of the convex defect DEF9 (Fig. 10(C)) and the light intensity distribution of the concave defect DEF8 (Fig. 8 (Fig. 8 ( F)) between the profile curve PR11 (Fig. 10 (B)) of the light intensity distribution of the convex defect DEF9 and the profile curve PR5 (Fig. 8 (D)) of the light intensity distribution of the concave defect DEF8, convex defect There is no difference in the positional relationship between the light and dark between the profile curve PR13 of the light intensity distribution of DEF9 (Fig. 10(D)) and the profile curve PR9 of the light intensity distribution of the concave defect DEF8 (Fig. 8(H)). Therefore, according to the same method as the first aspect described above, it is impossible to distinguish a defect which is determined to be a concave defect in a focused state, although it is actually a convex defect.

However, in the positive defocusing state, if the light intensity distribution of the convex defect DEF9 formed by the adherend composed of the material substantially transparent to the inspection light and the light intensity distribution of the true concave defect DEF8 are compared, The difference between the light intensity of the defect-free area and the light intensity of the bright part (absolute value) is the ratio of the difference between the light intensity of the defect-free area and the light intensity of the dark part (absolute value) (the lower case ratio), and the convex defect DEF9 high. Thus, in the form of an attachment composed of a material that is substantially transparent to the inspection light. When a convex defect is formed, there is a tendency that the bright portion is strengthened. The difference between the light intensity of the defect-free region and the light intensity of the bright portion, and the difference between the light intensity of the defect-free region and the light intensity of the dark portion vary with the size of the convex defect, and is obtained in a defect-free region sufficiently far away from the convex defect. The reference intensity is defined by the configuration of the optical film of the reticle substrate and is constant in the defect free area. Moreover, in terms of true concave defects, for various sizes or depths, the light intensity of the bright portion and the dark portion can be grasped in advance by actual measurement or simulation. Therefore, the light intensity in the defect-free region sufficiently far away from the defect is used as the reference intensity, and the light intensity of the bright portion and the dark portion relative to the reference intensity is compared, for example, a predetermined threshold value is predetermined for the light-dark ratio, and the threshold value is set. The following (for example, 0.9 or less) is regarded as a true concave defect, and if a threshold value is exceeded as a convex defect, a defect which is actually a convex defect but is determined to be a concave defect in a focused state can be correctly determined as a convexity. defect.

Further, in the above-described first and second aspects, an example of a defect of an optical film made of a MoSi-based material existing on a quartz substrate is shown, but the other optical film used in the photomask substrate is processed. A film such as an auxiliary film, for example, a defect of a film made of a chromium-based material, can be similarly used as a defect inspection method of the present invention.

In the present invention, when the defect of the surface portion of the photomask substrate in which at least one film is formed on the substrate is inspected by the inspection optical system, first, the following steps (A1) to (A3) are employed. , which is (A1) a step of bringing the defect to the objective lens of the inspection optical system, setting the distance to the focus distance, and irradiating the inspection light to the defect via the objective lens in a state where the focus distance is set; (A2) a step of collecting the reflected light that has been irradiated to the region of the inspection light through the objective lens as the first enlarged image of the region; and (A3) A first determination step of determining a change portion of the light intensity of the first magnified image and determining a concavo-convex shape of the defect by a change in the light intensity of the change portion of the light intensity of the first magnified image, and determining the defect in the in-focus state The concave and convex shape, followed by the following steps (B1) to (B3), that is, (B1) a step of setting a distance between the defect and the objective lens of the inspection optical system to a defocus distance deviating from the focus distance, and irradiating the inspection light to the defect via the objective lens in a state where the defocus distance is set; (B2) a step of collecting the reflected light that has been irradiated to the region of the inspection light through the objective lens as the second enlarged image of the region; and (B3) a second determination step of determining the change in the light intensity of the second enlarged image and changing the light intensity of the portion of the change in the light intensity of the second enlarged image to determine the uneven shape of the defect again, in the defocused state again Determine the uneven shape of the defect. By inspecting the defect in this way, for example, the defect which is a convex defect is not mistakenly judged as a concave defect, and the uneven shape of the defect can be more accurately determined.

In one or both of the steps (A3) and (B3), the light intensity variation obtained by the above steps (B1) to (B3) can be compared with the concave defect or the convex defect of the object, especially the true concave defect. And determining the uneven shape of the defect of the object to be inspected with the change in the intensity of the light of the first magnified image or the second magnified image. However, it is also possible to refer to the concave defect or the convex defect of the object, especially the true concave defect, and compare the simulation result. The change in light intensity and the intensity of light in the first magnified image or the second magnified image To determine the uneven shape of the defect of the inspection object. At this time, in particular, the light intensity change of the true concave defect is obtained by simulation, and it is determined that the change in the light intensity is determined as a concave defect, and it is determined that the light defect is not a convex defect, and an effective determination can be obtained.

Moreover, the method of determining the step of forming the uneven shape of the defect of the film by the step of forming a film of at least one optical film, processing auxiliary film, or the like on the substrate and the defect inspection method according to the present invention By manufacturing a reticle substrate, a reticle substrate having a fatal defect can be eliminated, and a reticle substrate having a non-lethal defect such as a detachable defect or a repairable defect can be selected, directly or after being regenerated .

In the present invention, in the case of performing the above steps (A1) to (A3), in the case where the defect shape is determined to be concave in the first determination step, the above steps (B1) to (B3) are performed again. When the uneven shape of the defect is determined, the defect which is a convex defect is not mistakenly determined as a concave defect, and the original convex shape can be determined, which is particularly effective. Further, by applying such a defect inspection method, it is possible to select no concave defects from the mask substrate subjected to the above steps (B1) to (B3) based on the uneven shape of the defect which is determined again in the second determination step. Photomask substrate.

In the defect inspection method of the present invention, the inspection light is preferably light having a wavelength of 210 to 550 nm. Further, in one or both of (A1) and (B1), the inspection light may be illuminated by oblique illumination with an optical axis and a surface of the mask substrate; one of (A2) and (B2) Or in two steps, a part of the reflected light may be disposed on the optical path of the reflected light. A spatial filter collects reflected light through a spatial filter. The defocus distance depends on the size and depth of the defect, and is preferably in the range of -300 nm to +300 nm, more preferably in the range of -250 nm to +250 nm. In any case, 0 nm is excluded; in particular, it is preferable to set the defocus distance in a range excluding more than -100 nm to less than +100 nm.

Further, in the above step (A1), if the mask substrate is placed on a stage movable in the in-plane direction, and the stage is moved in the in-plane direction, the defect and the inspection optical system are caused. When the objective lenses are close to each other, the easy alignment of the defects can be achieved, and since the continuous defect inspection of the plurality of defects existing on the photomask substrate can be performed, it contributes to high efficiency.

Next, the defect inspection method of the present invention will be described more specifically in accordance with the flowchart shown in Fig. 11.

First, a photomask substrate (inspected photomask substrate) having a defective inspection target is prepared (step S201). Next, the position coordinate information of the defect existing on the photomask substrate is read (step S202). The position coordinates of the defect may use position coordinates of the defect defined by the well-known defect inspection.

Next, as the step (A1), the position of the defect is aligned with the inspection position of the inspection optical system, specifically, the defect is made close to the objective lens of the inspection optical system, and the distance between the defect and the objective lens of the inspection optical system is set to The focus distance (focus distance) is maintained, and the focus distance is maintained, and the inspection light is irradiated from the oblique direction via the objective lens (step S203). The position alignment can be performed by placing the mask substrate of the inspection object on a stage movable in the in-plane direction thereof, based on the position of the defect of the mask substrate of the inspection object. The method of moving the stage in the in-plane direction and bringing the defect close to the objective lens of the inspection optical system is carried out. Next, in the step (A2), the reflected light that has been irradiated to the region of the inspection light is collected through the objective lens of the inspection optical system as the first enlarged image of the region including the defect (step S204). Next, in the step (A3), the image data (inspection image) of the first enlarged image is collected, and the changed portion of the light intensity of the inspection image of the defective portion is defined (step S205), and the incident side of the inspection light is detected. Based on the reference, the first determination step of determining the uneven shape of the defective portion is performed by checking the positional relationship between the bright portion and the dark portion of the image (step S206).

Here, in step S206, if the concave defect is not determined, the defect information is recorded as a convex defect (decision D201, step S212).

On the other hand, when it is determined as a concave defect in step S206, as the step (B1), the distance between the defect and the objective lens of the inspection optical system is set to a distance (positive or negative defocus distance) different from the focus distance, and The defocus distance is maintained, and the inspection light is irradiated from the oblique direction via the objective lens (step S207). Next, in the step (B2), the reflected light that has been irradiated to the region of the inspection light is collected through the objective lens of the inspection optical system as the second enlarged image of the region including the defect (step S208). Next, in the step (B3), the image data (inspection image) of the second enlarged image that is collected is used to define a portion of the light intensity of the inspection image of the defective portion (step S209), and in the first mode, Based on the incident side of the inspection light, and by checking the positional relationship between the bright portion and the dark portion of the image, When the second form is used, the light intensity of the defect-free area that is sufficiently far away from the defect is used as the reference intensity, and the light intensity of the bright portion and the dark portion relative to the reference intensity is compared to determine the defect. The second determination step of the partial uneven shape (step S210).

On the other hand, if it is determined as a concave defect in step S210, the defect information is recorded as a concave defect (decision D202, step S211). On the other hand, if it is not determined to be a concave defect, the defect information is recorded as a convex defect (decision D202, step S212). Next, it is judged whether or not the inspection is completed for all the defects specified in advance (decision D203), and if not, the new defect position is designated (step S213), the process returns to step S203, and the steps (A1) to (A3) are repeated, and the process is repeated (B1). )~(B3) step. Then, when it is determined that all the defects specified in advance are the end of the inspection (decision D203), the defect check ends.

Next, a convex defect (first form) formed by inspecting impurities composed of a low refractive index substance in a series of steps and a material which is substantially transparent to the inspection light will be described in accordance with a flow chart shown in FIG. An example of a convex defect (second form) formed by the deposit. At this time, in the flowchart shown in FIG. 11, steps S207 to S210 and subsequent judgments D202 and S211 and 212 corresponding to the steps (B1) to (B3) are replaced as follows.

When it is determined as a concave defect in step S206, as the step (B1), first, the distance between the defect and the objective lens of the inspection optical system is set to a negative defocus distance different from the focus distance, and the negative defocus distance is maintained. The inspection light is irradiated obliquely from the objective lens (step S221). its In the step (B2), the reflected light that has been irradiated to the region of the inspection light is collected through the objective lens of the inspection optical system as the second enlarged image of the region including the defect (step S222). Next, as a step (B3), the image data (inspection image) of the second enlarged image collected is used to define a portion of the light intensity of the inspection image of the defective portion (step S223), and the incident side of the inspection light is used. Based on the reference, the second determination step of determining the uneven shape of the defective portion is performed by checking the positional relationship between the bright portion and the dark portion of the image (step S224).

Next, the distance between the defect and the objective lens of the inspection optical system is set to a positive defocus distance different from the focus distance, and a positive defocus distance is maintained, and the inspection light is irradiated from the oblique direction via the objective lens (step S225). Next, in the step (B2), the reflected light that has been irradiated to the region of the inspection light is collected through the objective lens of the inspection optical system as the second enlarged image of the region including the defect (step S226). Next, as a step (B3), the image data (inspection image) of the second enlarged image collected is used to define a portion of the light intensity of the inspection image of the defective portion (step S227), and the defect is sufficiently far from the defect. The light intensity of the region is used as the reference intensity, and the second determination step of determining the uneven shape of the defective portion is determined by comparing the light intensities of the bright portion and the dark portion with respect to the reference intensity (step S228).

On the other hand, if it is not determined as a concave defect in step S224, the defect information is recorded as the convex defect of the first aspect (decision D221, step S230). On the other hand, if it is determined to be a concave defect, the process proceeds to the determination result in step S228. Then, in step S228, if When the concave defect is determined, the defect information is recorded as a true concave defect (decision D222, step S229); if the concave defect is not determined, the defect information is recorded as the convex defect of the second form (decision D222, step S230) ). In addition, a series of steps may be performed separately in the scope of the integration process. For example, after performing steps S225 to S228 performed with a positive defocus distance, steps S221 to S224 performed with a negative defocus distance, or The steps performed with a negative defocus distance and the steps performed with a positive defocus distance are interactively implemented.

The defect inspection method of the present invention which can be distinguished by high reliability without erroneously determining the uneven shape of the defect is applied to the manufacturing process of the photomask substrate, and the concave defect can be extracted with high reliability, in particular, the needle The mask substrate with the hole defect can be selected from the mask substrate without the pinhole defect. Further, the information on the uneven shape of the defect obtained by the defect evaluation method of the present invention can be supplied to the mask substrate by a method such as attaching a test mark. Further, based on the information supplied to the photomask substrate, a photomask substrate containing no concave defects such as pinholes may be selected. Conventionally, in the case where the convex defect caused by the deposit is determined to be a concave defect in the optical inspection, the mask substrate having the defect which is not necessarily a fatal defect is likely to be excluded as a defective product, and the yield is high. The main cause of the reduction, but according to the inspection method of the present invention, since the photomask substrate having the concave defect which is a fatal defect of the photomask substrate can be selectively excluded, the photomask substrate conforming to the product specification can be provided at a high yield. .

[Examples]

Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to the following examples.

[Example 1]

The defect inspection of the photomask substrate including the convex defect of the first aspect was carried out. As the inspection optical system, the inspection optical system shown in Fig. 4 was used, and the number of openings NA was set to 0.75, the inspection wavelength was set to 248 nm, and the inspection light system was subjected to defects on the mask substrate, and the average was from the upper left in the figure. Inclined illumination with an incident angle of 38 degrees. The surface portion of the optical film 102 made of a MoSi-based material formed on the quartz substrate 101 transparent to the inspection light as shown in Fig. 13(A) is composed of a substance having a refractive index lower than that of the optical film 102. The convex defect DEF7 formed by the impurity is used as an inspection object, and an inspection image showing the light intensity distribution and a light intensity curve of the cross section thereof are obtained. Further, the true concave defect DEF8 of the surface portion of the optical film 102 composed of the MoSi-based material formed on the quartz substrate 101 transparent to the inspection light as shown in Fig. 14(A) is used as a comparison. The object to be inspected is obtained, and an inspection image showing the light intensity distribution and a profile curve of the light intensity are obtained.

The height F1 of the protrusion of the defect DEF7 is 10 nm, the width W1 of the defect is 100 nm, and the buried depth D1 of the defect is 10 nm or 20 nm. Fig. 13(B) is a cross-sectional curve showing the light intensity at a distance of +200 nm where the defocus distance is positive; and Fig. 13(C) is a cross-sectional curve showing the focus distance, that is, the light intensity at the focus; Figure (D) shows the light intensity at a defocusing distance of -200 nm. Profile curve.

On the other hand, the true concave defect DEF8 takes the width W0 of the defect to be 100 nm. Since the amount of change in the light intensity of the inspection image varies depending on the depth D0 of the defect, the depth D0 is 20 nm, 40 nm, and 75 nm. By. Fig. 14(B) is a cross-sectional curve showing the light intensity at a distance of +200 nm where the defocus distance is positive; and Fig. 14(C) is a cross-sectional curve showing the focus distance, that is, the light intensity at the time of the focus; Fig. 14(D) is a cross-sectional curve showing the light intensity at a defocusing distance of -200 nm.

Take the focus distance (△z=0nm), that is, when the focus is on, the true concave defect DEF8, the distribution of the inspection image (the section curve of the light intensity) is the dark part on the left side and the bright part on the right side, in the case of the convex defect DEF7 Similarly, the left side is a dark part and the right side is a bright part, so that it is impossible to distinguish between the two. Further, when a positive defocus distance (Δz = +200 nm) is taken, both of them are dark portions on the left side and bright portions on the right side. On the other hand, when a negative defocus distance (Δz=-200 nm) is taken, the left side is a dark portion and the right side is a bright portion with respect to the convex defect DEF7, and the true concave defect DEF8 has a bright portion on the left side and a dark portion on the right side. The positional relationship between light and dark is reversed.

From this result, it can be seen that the buried convex defect which is determined to be a concave defect in the conventional method, that is, the focus check is transmitted, can be transmitted through the positional relationship between the inspection image and the contrast in the negative defocus state. The ground is judged to be a convex defect.

[Example 2]

The defect inspection of the photomask substrate including the convex defect of the second aspect was performed. As the inspection optical system, the inspection optical system shown in Fig. 4 was used, and the number of openings NA was set to 0.75, the inspection wavelength was set to 248 nm, and the inspection light system was subjected to defects on the mask substrate, and the average was from the upper left in the figure. Inclined illumination with an incident angle of 38 degrees. The surface portion of the optical film 102 made of a MoSi-based material formed on the quartz substrate 101 transparent to the inspection light as shown in Fig. 15(A) is made of a material substantially transparent to the inspection light. The convex defect DEF9 formed by the deposit is used as an inspection object, and an inspection image showing the light intensity distribution and a light intensity curve of the cross section thereof are obtained.

The height F2 of the defect DEF9 is 60 nm or 80 nm, and the width W2 of the defect is 100 nm. Fig. 15(B) is a cross-sectional curve showing the light intensity at a distance of +200 nm where the defocus distance is positive; and Fig. 15(C) is a cross-sectional curve showing the focus distance, that is, the light intensity at the focus point; Figure (D) shows a profile of the light intensity at a wavelength of -200 nm where the defocus distance is negative. On the other hand, the cross-sectional curve of the light intensity when the true concave defect DEF8 shown in Fig. 14(A) is the object to be inspected for comparison is as shown in Figs. 14(B) to (D).

At this time, when the focus distance (Δz = 0 nm), that is, the focus point and the positive defocus distance (Δz = +200 nm), the left side is the dark part and the right side is the bright part, and the negative side is taken. When the defocus distance (Δz=-200nm) is the bright part on the left side and the dark part on the right side, the difference between the two can be distinguished by the positional relationship between the light and the dark; in the positive defocus state, the image of the convex defect DEF9 is examined. The light intensity level of the bright part is significantly higher than the real concave defect DEF8 By.

These light intensity levels were evaluated in detail, and the light intensity at the position where the defect strength was sufficiently far from the defect was 0.166. On the other hand, when the height H2 of the convex defect DEF9 is 80 nm, the amount of change from the reference intensity of the bright portion is 0.076 in the focus point and 0.095 in the positive defocus state. On the other hand, the amount of change from the reference intensity of the dark portion is 0.089 in the focus point and slightly decreased to 0.084 in the positive defocus state. That is, the light-dark ratio at the focus point is 0.85, and the light-dark ratio at the positive defocus state is 1.13. In the case of the positive defocusing state, the average light intensity level of the inspection image is increased, and the amount of change with respect to the bright portion of the reference intensity is higher than the amount of change of the dark portion. Further, when the height H2 of the convex defect DEF9 is 60 nm, the amount of change in the bright portion and the dark portion with respect to the reference intensity is also slightly the same (that is, the light-dark ratio is slightly 1).

On the other hand, in the case of the true concave defect DEF8, when the depth D0 at which the average light intensity level of the inspection image is the highest is 20 nm, the amount of change from the reference intensity of the bright portion is 0.024 in the positive defocus state. The amount of change from the reference intensity of the dark portion is 0.031, and the light-dark ratio is 0.77, which is lower than the case of the convex defect DEF9. Further, with respect to the true concave defect DEF8 of 40 nm or 75 nm deeper than the depth D0, the average light intensity level of the inspection image is lower than this, and the light-dark ratio is further lowered.

From this result, it is understood that the ratio of the difference between the light intensity of the defect-free region and the light intensity of the bright portion (absolute value) to the difference between the light intensity of the defect-free region and the light intensity of the dark portion (absolute value), that is, the light-dark ratio In the positive In contrast to the light-dark ratio of the true concave defect DEF8 in the focal state, the convex defect which is determined to be a concave defect in the conventional method, that is, the inspection of the focus point, can be correctly determined as a convex defect.

Claims (17)

A method for inspecting a defect existing in a surface portion of a photomask substrate using an inspection optical system, the photomask substrate comprising at least one film formed on the substrate, the method comprising: (A1) making the defect and the inspection optical system The objective lenses are close to each other, the distance between the above-mentioned defect and the objective lens is set as a focus distance, and in the state where the focus distance is set, the inspection light is applied to the defect via the objective lens; (A2) is supplied via the objective lens The reflected light in the region irradiated with the inspection light collects the first enlarged image as the region; (A3) the light intensity change portion of the first enlarged image is found, and the light intensity change portion of the first enlarged image is obtained. a first determining step of determining the uneven shape of the defect by the change in the light intensity; (B1) setting a distance between the defect and the objective lens of the inspection optical system to a defocus distance deviating from the focus distance, and setting the defocus In the state of the distance, the step of applying the light to the above-mentioned defect via the above objective lens; (B2) from the inspection light via the objective lens The reflected light in the irradiation region collects the second enlarged image as the region; and (B3) finds the light intensity change portion of the second enlarged image and changes the light intensity according to the light intensity change portion of the second enlarged image. The second determination step of determining the uneven shape of the defect again; and in the first determination step, when the defect shape is determined to be concave, the steps (B1) to (B3) are performed, and the defect is again determined. Concave shape. The defect inspection method of claim 1, wherein in the step (B3), the uneven shape of the defect to be inspected is determined again by comparing the following: a portion of the light intensity change portion of the true concave defect obtained by simulation in advance a change in light intensity; and a change in light intensity of a portion of the light intensity change of the second enlarged image. The defect inspection method of claim 1, wherein the inspection light is light having a wavelength of 210 to 550 nm. The defect inspection method of claim 2, wherein the inspection light is light having a wavelength of 210 to 550 nm. The defect inspection method of claim 1, wherein in the two steps (A1) and (B1), the inspection light is applied by oblique illumination, wherein an optical axis of the inspection light and a surface of the photomask substrate Tilted. The defect inspection method of claim 1, wherein in the two steps (A2) and (B2), a spatial filter for shielding a part of the reflected light is disposed on the optical path of the reflected light, and the reflection is collected by the spatial filter. Light. The defect inspection method of claim 1, wherein in the step (A1), the photomask substrate is placed on a stage movable in an in-plane direction thereof, and the stage is moved in the in-plane direction, thereby The above defects are close to the objective lens of the inspection optical system described above. A method of inspecting a defect existing on a surface portion of a reticle substrate using an inspection optical system, the reticle substrate containing at least one film formed on the substrate, the method comprising: (A1) setting the defect to the objective lens of the inspection optical system, setting a distance between the defect and the objective lens as a focus distance, and applying the inspection light to the above-mentioned objective lens through the objective lens while setting the focus distance a step of forming a defect; (A2) collecting, by the objective lens, the reflected light from the region irradiated with the inspection light as a first enlarged image of the region; (A3) finding a portion of the light intensity change of the first enlarged image, and a first determining step of determining the uneven shape of the defect based on a change in light intensity of the light intensity change portion of the first enlarged image; (B1) setting a distance between the defect and the objective lens of the inspection optical system to be offset from the focus a defocusing distance of the distance, and a step of applying the inspection light to the defect via the objective lens in a state where the defocus distance is set; (B2) collecting, as the region, the reflected light from the region irradiated with the inspection light via the objective lens a second enlarged image step; and (B3) finding a light intensity change portion of the second enlarged image and based on the second enlarged image The second determination step of determining the unevenness of the defect is determined based on whether or not the change in the light intensity of the light intensity change portion is reversed depending on whether the positional relationship between the light and the dark is reversed. The defect inspection method of claim 8, wherein in the step (B3), the uneven shape of the defect to be inspected is again determined by comparing the following: a portion of the light intensity change portion of the true concave defect obtained by the simulation in advance a change in light intensity; and a change in light intensity of a portion of the light intensity change of the second enlarged image. The defect inspection method of claim 8, wherein the inspection light is light having a wavelength of 210 to 550 nm. The defect inspection method of claim 9, wherein the inspection light is light having a wavelength of 210 to 550 nm. The defect inspection method of claim 8, wherein in the two steps (A1) and (B1), the inspection light is applied by oblique illumination, wherein an optical axis of the inspection light and a surface of the photomask substrate Tilted. The defect inspection method of claim 8, wherein in the two steps (A2) and (B2), a spatial filter for shielding a part of the reflected light is disposed on the optical path of the reflected light, and the reflection is collected by the spatial filter Light. The defect inspection method of claim 8, wherein in the step (A1), the photomask substrate is placed on a stage movable in an in-plane direction thereof, and the stage is moved in the in-plane direction, thereby The above defects are close to the objective lens of the inspection optical system described above. The defect inspection method according to any one of claims 8 to 11, wherein, in the first determination step, when the defect shape is determined to be a concave shape, the steps (B1) to (B3) are performed, and the unevenness of the defect is determined again. shape. A method of selecting a reticle substrate, comprising: a concave-convex shape based on a defect determined again in a second determining step of the defect inspection method of claim 1 or 15, by performing the above steps (B1) to (B3) In the reticle substrate, a reticle substrate having no concave defects is selected. A method of manufacturing a photomask substrate, comprising: The step of forming a film of at least one layer on the substrate; and the step of determining the uneven shape of the defect of the film by the defect inspection method according to any one of claims 1 to 15.