TW201841220A - Methods for defect inspection, sorting and manufacturing photomask blanks - Google Patents

Abstract

A photomask blank having a thin film on a transparent substrate is inspected for defects by irradiating inspection light to a surface region of the blank, collecting the reflected light from the irradiated region via an optical inspection system to form a magnified image of the region, extracting a feature parameter of light intensity distribution from the magnified image, and identifying the bump/pit shape of the defect based on the feature parameter combined with the structure of the thin film. The defect inspection method is effective for discriminating defects of bump or pit shape in a highly reliable manner. On application of the defect inspection method, photomask blanks having no pinhole defects are available at lower costs and higher yields.

Description

Blank mask defect inspection method, sorting method and manufacturing method

The present invention relates to a defect inspection method for a blank mask for manufacturing a photomask (transfer mask) used in the manufacture of a semiconductor device or the like, and more particularly to a defect inspection method for a blank mask. It is effective for the determination of a concave shape such as a pinhole existing in a film having a thickness of 10 nm or less formed on a blank mask. Further, the present invention relates to a sorting method and a manufacturing method of a blank mask, which employs a concave defect inspection method for a defect of a blank mask.

In the semiconductor device, the exposure light is irradiated by repeatedly using the pattern transfer mask for the mask or the like in which the circuit pattern is drawn, and the circuit pattern formed on the mask is transferred to the semiconductor substrate through the reduction optical system. Manufactured by photolithography on (semiconductor wafer). As the circuit pattern of the semiconductor device continues to be finer, the wavelength of the exposure light is 193 nm using argon fluoride (ArF) excimer laser light, and the pattern is multiplied by a plurality of combined exposure programs or processing programs. The procedure ultimately results in a pattern of sufficiently small dimensions compared to the exposure wavelength.

The pattern transfer mask is manufactured by forming a circuit pattern on a substrate (blank mask) on which an optical film is formed. Such an optical film (thin film) is generally a film containing a transition metal compound as a main component or a film containing a transition metal-containing cerium compound as a main component, and a film which functions as a light-shielding film or a phase-shift film is selected according to the purpose. Functional membranes, etc. Further, a hard mask film for processing an auxiliary film for the purpose of high-precision processing of an optical film is also included.

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, and thus it is naturally required that the blank mask is free from defects. Further, when forming a circuit pattern, a photoresist film for processing is formed on a blank mask on which a film is formed, and a normal lithography step such as an electron beam drawing method is performed to form a pattern. Therefore, defects such as pinholes are also required for the photoresist film. Based on such a situation, there have been many discussions on techniques for detecting defects in a photomask or a blank mask.

In Japanese Patent Laid-Open Publication No. 2001-174415 (Patent Document 1), JP-A-2002-333313 (Patent Document 2) discloses that laser light is irradiated onto a substrate, and defects or foreign matter are detected from diffusely reflected light. In particular, a method of imparting asymmetry to a detection signal and discriminating a defect of a convex portion or a defect of a concave portion is described. In the Japanese Patent Publication No. 2005-265736 (Patent Document 3), a technique of using DUV (Deep Ultra Violet) light for performing pattern inspection of a general optical mask is used as the inspection light. Japanese Patent Publication No. 2013-19766 (Patent Document 4) discloses that the inspection light is divided into a plurality of light spots, a plurality of light spots are scanned on the substrate, and each of the reflection beams is received by the light detecting element. Light technology. On the other hand, Japanese Laid-Open Patent Publication No. 2007-219130 (Patent Document 5) discloses a concave-convex shape in which EUV (Extreme Ultra Violet) light having a wavelength of 13.5 nm is used as an inspection light to determine a defect of an EUV blank mask. Technology. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Laid-Open Patent Publication No. JP-A-2005-265313 (Patent Document 3) JP-A-2005-265736 (Patent Document 4) JP-A-2013-19766 Japanese Patent Publication No. 2007-219130

[Problems to be solved by the invention]

Each of the inspection apparatuses described in Patent Documents 1 to 4 employs an optical defect method, and enables wide-area defect inspection and unevenness determination of defects in a relatively short period of time. Further, in the case of the EUV blank mask, Patent Document 5 describes a method for determining the unevenness of the phase defect.

However, the inventors of the present invention have found that it is impossible to determine the unevenness by a conventional method of investigating the arrangement of the bright portion and the dark portion of the inspection signal of the blank mask by using an atomic force microscope or an electron microscope inspection test. Happening. In other words, in the inspection signal of the pinhole defect, the positional relationship between the bright portion and the dark portion for distinguishing the unevenness is unclear. In particular, it has been found that in the defect inspection of the hard mask film having a thickness of 10 nm or less, which is a processing auxiliary layer formed for the processing of the tip mask, the problem of the above-described unevenness determination is likely to be difficult.

In the actual inspection experiment based on the inspection apparatus described in the above Patent Documents 1 to 4, it is not always possible to accurately determine the uneven shape of the surface of the defective portion. Further, the method described in Patent Document 5 is applied to a phase defect inherent to an EUV blank mask, and is a method that is difficult to apply to a blank mask used in current mainstream ArF lithography. Therefore, it has been desired to establish a method of judging the uneven shape of a defect existing in a hard mask film with high precision in a conventional technique.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a defect inspection method for a blank mask capable of determining the unevenness of the surface shape of a defective portion with high reliability by using an optical defect inspection method, and particularly The method for determining the unevenness of the defect portion of the hard mask film used for the processing auxiliary layer during the mask processing, and the method for determining the unevenness of the defect portion using the blank mask, and eliminating the blank mask of the substrate including the pinhole defect Sorting method and manufacturing method. [Means for solving the problem]

In order to solve the above problems, the inventors of the present invention repeatedly examined the light intensity distribution of the inspection signals existing in the defects of various optical films from both the inspection experiment and the simulation. As a result, it has been found that depending on the value of the complex refractive index of the optical film and the optical film of the lower layer described above for the inspection light, the change in the brightness of the observed image of the defect or the positional relationship between the bright portion and the dark portion is further repeated, and various discussions are further repeated. As a result, the present invention was achieved.

Accordingly, the present invention provides the following method for inspecting a defect of a blank mask, and a method and a method for sorting a blank mask to which the method is applied. [1] A method for inspecting a defect of a blank mask, wherein at least one layer of a film is formed on an optically transparent substrate, and the surface of the film of the blank mask on the surface is irradiated with inspection light to capture light from the inspection light. A method of detecting a defect existing in a surface portion of a blank mask, comprising: (A1) a step of preparing a blank mask having at least one film, and (A2) moving the blank mask, The defect existing in the surface portion of the blank mask is moved to the observation position of the inspection optical system, the inspection light is irradiated to the region including the defect, and the reflected light from the region irradiated with the inspection light is collected by the inspection optical system as The step of magnifying the image in the above region, (A3) the step of extracting the feature amount of the enlarged image, and (A4) the step of determining the shape of the defect based on the combination of the feature amount and the film pattern of the blank mask. [2] The defect inspection method of the blank mask according to [1], wherein the magnified image in the step (A2) is generated by the diffraction component of the inspection optical system in the reflected light while being at a position relative to the reflected light. An enlarged image formed by asymmetrical high-order diffraction components that are positive and negative for the secondary diffraction component (positive reflection component). [3] The method for inspecting a defect of a blank mask according to [1] or [2], wherein the step (A3) comprises comparing a change in a light intensity level of the defective portion in the enlarged image with a light intensity level at a peripheral portion of the defect In the processing step, the intensity difference between the bright portion having a high light intensity and the dark portion having a low light intensity, and the feature amount of the defect inspection image in the positional relationship between the bright portion and the dark portion are extracted. [4] The method for inspecting a defect of a blank mask as described in [1], [2] or [3], wherein the step (A4) is based on a characteristic amount of the enlarged image and a state of a film of the blank mask. Basically, a step of determining a shape of a defect by referring to a table in which a pinhole defect or a convex defect is selected based on optical simulation or experimental data in advance is used. [5] The defect inspection method of the blank mask according to [4], wherein in the step (A3), when the enlarged image of the defect extracts the feature amount of the image in which the bright portion is dominant, as long as the blank light is inspected When the outermost surface of the cover is transparent to the inspection light, it is judged that the detected defect is a pinhole defect. [6] The method for inspecting a defect of a blank mask as described in [4], wherein in the step (A3), when the enlarged image of the defect extracts a characteristic amount of the image in which the dark portion is dominant, as long as the blank mask is inspected When the inspection light reflectance of the film on the outermost surface is higher than the inspection light reflectance of the lower layer, it is judged that the detected defect is a pinhole defect. [7] The method for inspecting a defect of a blank mask according to any one of [1] to [6] wherein the film thickness of the film is 10 nm or less. [8] The method of inspecting a defect of a blank mask according to any one of [1] to [7] wherein the inspection light is light having a wavelength of 210 to 550 nm. [9] A defect inspection system for a blank mask, comprising: irradiating an inspection light to a surface of a film of a blank mask having at least one film formed on an optically transparent substrate, capturing an area from which the inspection light is irradiated; A computer that reflects the light, checks the defect existing in the surface portion of the blank mask, and a program having a program for performing the defect inspection method of the blank mask shown in any one of [1] to [8]. [10] A method of sorting a blank mask, which is characterized in that the uneven shape of the defect determined by the defect inspection method of the blank mask according to any one of [1] to [8] is used. Select a blank mask that does not contain pinhole defects. [11] A method of manufacturing a blank mask, comprising: a step of forming at least one film on an optically transparent substrate, and sorting by a sorting method of a blank mask as described in [10] The step of blanking the mask without pinhole defects in the above film. [Effects of the Invention]

According to the present invention, it is possible to distinguish the uneven shape defects in the blank mask with high reliability by using an optical defect inspection method, and in particular, to define a concave defect or a pinhole defect as a fatal defect. Further, by applying the defect inspection method of the present invention, it is possible to surely exclude a blank mask having a concave defect as a fatal defect, and it is possible to provide a blank mask free from fatal defects at a lower cost and at a higher yield.

[Formation of the Invention]

Hereinafter, the present invention will be described in more detail. If a defect such as a pinhole exists in the film of the blank mask, it is a cause of the defect of the mask pattern on the photomask produced by this. An example of a defect of a typical blank mask is shown in FIG. Fig. 1(A) shows a blank mask 100 in which an optical film 102 that functions as a light-shielding film or a phase shift film for a halftone phase shift mask is formed on a transparent substrate 101. Here, the pinhole defect DEF1 is present in the optical film 102. Fig. 1(B) shows an optical film 102 that functions as a light-shielding film or a phase shift film for a halftone phase shift mask, and a high-precision process for performing the optical film 102 on the transparent substrate 101. A diagram of the blank mask 100 of the auxiliary film 103 is processed. Here, the pinhole defect DEF2 is present in the processing auxiliary film 103. If such a blank mask is used to manufacture a photomask by a usual manufacturing process, it will become a mask from the defect of a blank mask. Moreover, this defect is caused by the exposure of the reticle, which causes the transfer failure of the pattern. Therefore, the defect of the blank mask must be detected in the stage before processing the blank mask, the blank mask with defects is excluded, or the correction of the defect is applied.

On the other hand, Fig. 1(C) is a view showing an example of a convex defect of a blank mask, which is an example of a blank mask 100 in which a convex defect DEF3 is present on the optical film 102. The defect DEF3 has a convex defect integrated with the optical film 102, or a case where a foreign matter adheres to a foreign matter. Even from such a blank mask, the mask is manufactured by a usual manufacturing process, and a fatal pinhole defect is not necessarily formed. Moreover, if the foreign matter defect adhering to the surface can be removed by washing, it does not become a fatal defect.

In this way, the determination of the concave defect of the pinhole or the like, which is a defect of the blank mask, or the convex defect which is not necessarily a fatal defect, is the quality assurance of the blank mask and the yield in the manufacture of the blank mask. The key. Therefore, a method in which the uneven shape of the defect can be distinguished by high-reliability processing by a short inspection process by optical inspection is desired. In addition, considering that the wavelength of the exposure light which is now mainstream is 193 nm using argon fluoride (ArF) excimer laser light, it is desirable to distinguish the unevenness of the defect having a size of 200 nm or less and preferably 100 nm or less on the blank mask. The method of shape.

First, an inspection apparatus for defect inspection applied to a blank mask will be described. Specifically, an inspection apparatus suitable for determining the uneven shape of a defect in the surface portion of the blank mask will be described. 2 is a conceptual diagram showing an example of a basic configuration of the defect inspection device 150. The inspection optical system 151, the control device 152, the recording device 153, and the display device 154 are main components. The inspection optical system 151 includes a light source ILS that emits inspection light, a beam splitter BSP, an objective lens OBL, a movable stage STG on which the blank mask MB is placed, and an image detector SE. The light source ILS is configured to emit light having a wavelength of about 210 nm to 550 nm, whereby the inspection light BM1 emitted from the light source ILS is bent by the beam splitter BSP, and the designated area of the blank mask MB is irradiated through the objective lens OBL. . The light BM2 reflected by the surface of the blank mask MB is collected by the objective lens OBL while penetrating 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 blank mask MB is formed on the light receiving surface of the image detector SE. Then, the data of the enlarged inspection image collected by the image detector SE is subjected to an image processing operation to perform size calculation of the defect or determination of the uneven shape, and the results are recorded as the defect information. The inspection device 150 is operated by the control device 152. The control device 152 has a control program or various image calculation programs. Further, the operation of the recording device 153 storing the inspection data or the display device 154 performing various displays is also controlled.

For example, the image detector SE can be used as a detector of a pixel such as a CCD camera, and the light BM2 reflected by the surface of the blank mask MB can be formed by the objective lens OBL. The magnified image is collected as a direct method of batch collection of 2 dimensional images. Moreover, the inspection light BM1 may be concentrated on the surface of the blank mask MB to generate an illumination spot, and the light source ILS that emits the inspection light may have a scanning function to scan the illumination spot, and the reflected light BM2 is sequentially collected by the image detector SE. The method of generating the entire 2-dimensional image by recording the light intensity and photoelectric conversion.

Further, in order to determine the unevenness of the defect, when the reflected light BM2 is collected, it is also possible to asymmetrically collect high-order diffraction with respect to the zero-order diffraction component (positive reflection component) (centered on the positive reflection component). ingredient. Specifically, a method of causing the chief ray of the inspection light BM1 on the surface of the illumination blank reticle MB to be obliquely incident, or a spatial filter SPF in which the principal ray is a vertical illumination but shielding a part of the optical path of the reflected light BM2 may be employed. The method like the detector SE captures an enlarged inspection image. By adopting such a method, it is generally possible to determine the uneven shape of the defect from the positional relationship between the light and dark of the image light intensity distribution or the difference in light intensity.

Then, the inspection light BM1 is vertically illuminated by the chief ray, and is concentrated by the surface of the blank reticle MB, and simultaneously scanned, and the light intensity of the reflected light BM2 is sequentially collected. In the obtained inspection image, the convex defect and the concave defect are described. Check the image for differences. When the light intensity of the reflected light BM2 is collected, the right half of the reflected light BM2 toward the image detector SE is shielded by the action of the spatial filter SPF.

3(A) and (B) are a plan view and a cross-sectional view, respectively, of a blank mask 100 having a convex defect DEF4. This indicates that the optical film 102 made of a MoSi-based material is formed on the transparent substrate 101 such as a quartz substrate transparent to the inspection light, and a convex defect formed of a MoSi-based material or other material on the surface MBS is formed. The state of existence of DEF4.

For the surface MBS of the blank mask having the convex defect DEF4, the inspection light BM1 is concentrated and illuminated while being scanned, and the reflected light is collected by the spatial filter SPF, and the light intensity distribution shown in FIG. 3(C) is obtained. Check the image. The light intensity distribution in the cross section along the line A-A' of Fig. 3(C) is the cross-sectional profile PR1 as shown in Fig. 3(D). The cross-sectional profile PR1 has a shape unique to a convex defect, and the left side of the convex defect DEF4 is a bright part, and the right side is a dark part.

Similarly, Fig. 4(A) is a cross-sectional view of the blank mask 100 having the concave defect DEF5, and Fig. 4(B) is a view showing the cross-sectional contour PR2 of the light intensity distribution of the inspection image obtained at this time. The cross-sectional profile PR2 has a shape peculiar to a concave defect, and the left side of the concave defect DEF5 is a dark portion, and the right side is a bright portion. However, depending on the aspect of the film of the blank mask, not only the positional relationship between the brightness and the darkness of the above-mentioned inspection image but also the defect is a concave defect or a convex defect, and it is impossible to determine it correctly. An example of such a case will be described below.

[First film state] Fig. 5(A) is a cross-sectional view of a blank mask 100 having concave defects. In the transparent substrate 101 such as a quartz substrate which is transparent to the inspection light, an optical film 112 made of a MoSi-based material, an optical film 113 made of a Cr-based material, and a thickness of about 5 to 10 nm are formed. A material which is substantially transparent to the inspection light, for example, a hard mask film 114 made of yttrium oxide, and a concave defect DEF6 such as a pinhole defect are present in the hard mask film 114. For the concave defect DEF6, the inspection optical system shown in FIG. 2 is used, and the inspection light is concentrated and irradiated onto the surface of the blank mask from above to scan, and when the reflected light is collected by the spatial filter SPF, the light intensity distribution of the image is checked. The profile of the profile is the profile PR3 shown in Fig. 5(B). At this time, the light intensity distribution of the inspection image is in the portion of the concave defect DEF6, and substantially only the bright portion, and the clear light and dark positional relationship of the light intensity distribution of the inspection image of the typical concave defect as shown in FIG. 4 does not occur. .

In addition, in FIG. 6, even if the film structure is the same as the structure shown in FIG. 5(A), an example of various types of inspection images is obtained depending on the type of the defect. Fig. 6(A) shows that the concave defect is existing in the optical film 113 made of the Cr-based material, and the hard mask film 114 having a uniform film thickness without defects is formed thereon, and as a result, the defect DEF7 of the concave shape exists on the surface. status. Further, Fig. 6(B) shows a state in which the foreign matter having ruthenium as a main component is adhered to the surface as a convex defect DEF8, although there is no defect before the formation of the hard mask film 114. Further, Fig. 6(C) shows a state in which a part of the surface of the hard mask film 114 exists as a convex defect DEF9. The cross-sectional contours of the inspection images of the defects DEF7, DEF8, and DEF9 become the contour PR4 shown in Fig. 6(D), the contour PR5 shown in Fig. 6(E), and the contour PR6 shown in Fig. 6(F). . Although the outline PR4 is an inspection image of a typical concave defect, the inspection image is a defect when the defect is not present on the outermost hard mask film 114, and the contour PR5 is a typical convex defect inspection image, and the contour PR6 is further In the case of the first film state, when the outline PR6 is obtained, it is a convex defect of the hard mask film 114 which is transparent to the inspection light.

According to the above, in the inspection image of the defect in the first film state, when an inspection image in which the bright portion is dominant is obtained, it is possible to determine that a pinhole defect system which is a fatal defect exists. The criterion for determining the unevenness of the defect in the first film state is different from the case of the typical convex defect and the concave defect shown in FIGS. 3 and 4, and is a criterion specific to the case of the first film state. Further, it is suitable for a case where the film thickness of the film formed of the material substantially transparent to the inspection light is thin, for example, the film thickness is 10 nm or less, particularly 5 to 10 nm.

[Second Film Aspect] Fig. 7(A) is a cross-sectional view of a blank mask 100 having concave defects. In the transparent substrate 101 such as a quartz substrate which is transparent to the inspection light, an optical film 122 made of a MoSi-based material and a hard mask film 123 made of a Cr-based material having a thickness of about 10 nm are formed. A concave defect DEF10 such as a pinhole defect exists in the state of the hard mask film 123. The inspection light reflectance of the hard mask film 123 is higher than the inspection light reflectance of the optical film 122 as a feature of the second film state. For the concave defect DEF10, the inspection light is concentrated and irradiated onto the surface of the blank mask for scanning, and when the reflected light is collected by the spatial filter SPF, the cross-sectional profile of the light intensity distribution of the inspection image is as shown in Fig. 7(B). The contour PR7 is shown. At this time, the light intensity distribution of the inspection image is in the portion of the concave defect DEF10, and substantially only the dark portion, and the clear light-dark positional relationship of the light intensity distribution of the inspection image of the typical concave defect as shown in FIG. 4 does not occur. The reason why the concave defect at this time is observed only in the dark portion is that the depth of the concave defect DEF10 is shallow, and the amount of reflected light from the side surface of the defect is small, and the influence of the reflectance of the inspection light is large for the change in the light intensity.

Further, when the convex defect exists in the hard mask film 123, the inspection image is an inspection image in which the bright portion and the dark portion are equal to the contour PR1 shown in FIG. 3(D).

According to the above, in the inspection image of the defect in the second film state, when an inspection image in which the dark portion is dominant is obtained, it is possible to determine that the pinhole defect is a fatal defect. The criterion for determining the unevenness of the defect in the second film state is different from the case of the typical convex defect and the concave defect shown in FIGS. 3 and 4, and is a specific criterion for the second film state.

Next, the defect inspection method of the present invention will be described more specifically along the flowchart shown in FIG. First, as a step (A1), a blank mask (a blank mask to be inspected) having a defective inspection object is prepared (step S201). Next, the position coordinate information of the defect existing on the blank mask is input (step S202). The position coordinates of the defect may additionally use the position coordinates of the defect defined by the well-known defect inspection method.

Next, in the step (A2), the position of the defect is aligned with the inspection position of the inspection optical system, and the inspection light is passed through the objective lens to be irradiated from above the blank mask (step S203), and the reflected light of the region irradiated with the inspection light is passed. The objective lens of the optical system is inspected as an enlarged image collection of the region containing the defect (step S204). The position alignment system can mount the blank reticle of the inspection object on the stage which can be moved in the in-plane direction thereof, and check the position coordinates of the defect of the blank reticle of the object, so that the stage is on the above surface The method of moving in the inner direction to maintain the defect on the focus surface of the objective lens of the inspection optical system is implemented.

Then, from the light intensity distribution (image data (inspection image) or cross-sectional contour, etc.) of the collected enlarged image, the feature of the change portion of the light intensity of the inspection image in the defective portion is extracted, that is, the feature amount of the enlarged image (Step S205).

Then, as the step (A4), the uneven shape of the defect is determined based on the feature amount of the enlarged image extracted in step S205 and the film structure (film state) of the blank mask (step S206). Specific examples of the determination step of the uneven shape are as follows. Furthermore, the defect size can also be predicted by applying well-known image processing to the inspection image. The predicted value of the uneven shape or the defect size of the defects is recorded as the defect information together with the defect position coordinates (step S207).

Next, based on the defect position coordinate information input in advance, it is determined whether or not the inspection is completed for all the defects (decision D201), and if not, the position of the new defect is specified (step S208), and the process returns to step S203 to repeat the inspection. Collection of image data and bump determination of defects. Then, when it is determined that all the defects input in advance are the end of the inspection (decision D201), the defect inspection system ends.

Next, a specific example of the determination step of the uneven shape will be described. In the recording device 153 to which the control device of the defect inspection device shown in FIG. 2 is connected, the defect information is stored, together with the characteristics of the inspection signal when detecting the defect as shown in FIG. 9, and various blank masks. A table of the relationship between the construction of the optical film (film). The feature of the inspection signal is an image in which the bright portion is dominant in the defect portion, an image in which the dark portion is dominant, an image in which the left side is the bright portion and the right side is the dark portion, and the left side is the dark portion and the right side is the bright portion image. In addition, as the structure of the optical film (thin film), for example, the film structure A is the film state 1 described above, and the hard mask film which is transparent to the inspection light and has a film thickness of 10 nm or less is formed on the outermost surface. Further, the film structure B is the film state 2 described above, and the inspection light reflectance of the hard mask film having a film thickness of 10 nm or less on the outermost surface is higher than the inspection light reflectance of the optical film of the lower layer. In addition, the film structure C is a structure in which an optical film made of a MoSi-based material is formed on the outermost surface, and the so-called film structure D is formed by forming a Cr-based material having a thickness of 20 nm or more on the outermost surface. The construction of an optical film.

Referring to the table shown in Fig. 9, in various film structures, if the characteristics of the inspection image obtained by the defect inspection are extracted, it is possible to identify a pinhole defect or a convex defect whose defect is fatal. In other words, in the step S206 of determining the uneven shape of the defect in the step S205, the step S206 of determining the uneven shape of the defect can be referred to in order to define the type of the defect from the film structure of the substrate to be inspected and the feature of the enlarged image. The table shown in Fig. 9 identifies the uneven shape of the defect. In particular, it is also possible to determine whether it is a fatal pinhole defect.

In addition, the criterion for determining the concave defect in the table shown in FIG. 9 is changed depending on the shielding state of light by the spatial filter SPF. For example, in the film structure C or the film structure D, if the light shielding portion of the spatial filter is set to the opposite side, the concave defect and the convex defect corresponding to the arrangement position of the bright portion and the dark portion of the enlarged image feature are also determined. in contrast. Further, the form is not limited by the cross-sectional profile of the inspection image, and may be an image of a 2-dimensional light intensity distribution. Furthermore, the introduction of past defects or the introduction of novel film patterns can be added one by one.

Next, a sorting method of the photomask using the defect inspection method of the present invention will be described along the flow chart shown in FIG. First, a blank mask to be inspected is prepared (step S211), and then the defect inspection of the blank mask described above is performed, and defect information including the uneven shape and size of all the detected defects is recorded (step S212). Then, among the recorded defect information, it is investigated whether or not a concave defect such as a pinhole defect is included (judgment D211). If a concave defect is included, the blank mask is sorted as a defective product (step S213). When the concave defect is not included, if it is further determined that the size prediction value of the defect is equal to or less than the specified allowable value (decision D212), the blank mask is sorted as a good product (step S214). On the other hand, if it is determined that the size prediction value of the defect is equal to or greater than the specified allowable value (decision D212), the blank mask is sorted as a defective product (step S213).

According to the defect inspection method of the present invention, when a film having a thickness of 10 nm or less, such as a hard mask film, is formed on the outermost surface portion of the blank mask, the feature amount of the defect inspection image (enlarged image) is extracted, and the film is referred to The aspect stipulates a table of inherent defect relief shapes, whereby the uneven shape of the defect can be distinguished with high reliability.

By applying the defect inspection method of the present invention which can distinguish the uneven shape of the defect with high reliability to the manufacturing process of the blank mask, the blank mask having the concave defect, especially the pinhole defect can be extracted with high reliability, and the sorting is not included. A blank mask for concave defects such as pinhole defects. Further, the information on the uneven shape of the defect obtained by the defect inspection method of the present invention can be imparted to the blank mask by a method such as an inspection mark.

In the past, since the observation image of the pinhole defect depending on the film structure is not sufficiently understood, there is a leaky pinhole defect or a blank mask having a defect which is not necessarily a fatal defect is excluded as a defective product. The possibility. This is a major cause of the decrease in yield, but by the defect inspection method of the present invention, since the blank mask having the concave defect which is a fatal defect existing in the blank mask can be selectively excluded, the product specification can be provided at a high yield. Blank reticle. [Examples]

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

[Example 1] A defect inspection of a blank mask including a concave defect and a convex defect in the first film state was carried out. As the inspection device, the device including the inspection optical system 151 shown in Fig. 2 is used. The wavelength of the inspection light emitted from the light source ILS was 532 nm, and the numerical aperture NA of the objective lens OBL was 0.95. The inspection light BM1 passes through the objective lens OBL to converge the blank mask MB from above. As shown in FIG. 11, the concentrated illumination spot is scanned by a scanning means (not shown) to unidirectionally scan the surface MBS of the blank mask 100 including the defect DEF6. On the other hand, the stage STG carrying the blank mask MB is intermittently or continuously moved in a direction orthogonal to the scanning direction. By combining the scanning of the illumination spot with the movement of the stage, the illumination spot is scanned in a second dimension in a designated area including the defective portion. Then, the reflected light from the blank mask obtained by the respective illumination spots is concentrated by the objective lens OBL and the spatial filter SPF of the right half of the shielded reflected light and the lens L1, and the light intensity is collected by the photodetector SE. The collected light intensity is aligned to the position of the illumination spot and arranged in 2 dimensions, thereby generating a defective inspection image (enlarged image). Here, the size of the illumination spot in the surface of the blank mask is about 400 nm, and the 2-dimensional search area including the defect portion is a rectangular area of about 30 μm ́ 30 μm.

Fig. 12(A) is a cross-sectional view of a blank mask 100 including a pinhole defect in a first film state, showing that a thickness of 75 nm formed of a MoSi-based material is formed on a quartz substrate 101 which is transparent to inspection light. The optical film 112, the optical film 113 having a thickness of 44 nm made of a Cr-based material, and the hard mask film 114 having a thickness of 10 nm formed of yttrium oxide, and the pinhole defect DEF6 having a diameter W1 are present on the hard mask film 114. status. When the defect size (=diameter) W1=80 nm and 300 nm is assumed, the region containing the defects is scanned with the illumination spot described above, and the arrangement of the reflected light intensity corresponding to the scanning position is shown in FIG. 12(B), and the resulting inspection is performed. Magnifies the profile of the area of the image containing the defect. The enlarged image is characterized in any of the defect sizes W1, and the intensity of the reflected light in the defect-free region is used as a reference, and the dark portion is hardly present, and becomes a contour in which the bright portion is dominant. The hard mask film 114 has an antireflection film because it is substantially transparent to the inspection light. Therefore, the surface reflectance of the hard mask film 114 is lowered, and the reflectance of the pinhole defect portion exposed on the lower layer is higher than that of the peripheral portion. As a result, the pinhole portion of the inspection image becomes a bright portion. In the stage of inspecting the blank mask, the true concave and convex shape of the defect is unclear, but the optical film structure in which the blank mask is inspected as the first film state, and the characteristic image of the defect observation image (enlarged image) Based on the advantage, when referring to the table shown in FIG. 9, the defect is determined to be a pinhole defect.

On the other hand, Fig. 13(A) is a cross-sectional view of the blank mask 100 including the convex defect DEF8, which is the same first film state as the film structure shown in Fig. 12(A). As the composition of the convex defect portion, two kinds of the same composition and amorphous bismuth (Si) as those of the hard mask film 114 made of yttrium oxide were specified. FIG. 13(B) shows a cross-sectional profile of a region including a defect in which the width W1 of the convex defect DEF8 is 80 nm and the height H1 is 10 nm and 30 nm. In the inspection magnified image of the convex defect of W1=80 nm, although the intensity level changes depending on the height or the composition, it becomes an inspection image in which the dark portion of the defect portion is dominant, and the contour is the needle shown in Fig. 12(B). The inspection image of the hole defect is different. Therefore, it can be distinguished from pinhole defects.

Further, Fig. 13(C) is a view showing a cross-sectional profile of a region including a defect in the magnified image when the convex defect size is W1 = 400 nm. Here, when the composition is yttrium oxide, the defect height is H1 = 30 nm, and when the composition is amorphous yttrium, H1 = 10 nm. At this time, when the composition is yttrium oxide, an inspection image in which the defective portion becomes a dark portion is obtained, and when the composition is amorphous, an inspection image in which the defective portion is aligned with the dark portion is obtained. Since it is different from the inspection image of the pinhole defect, it can be distinguished.

Here, the defect size can be predicted from the inspection image by using the arithmetic processing of checking the outline of the image or the contrast of the image. In the defect inspection step in the manufacture of the blank mask, when the inspection image of FIG. 13(C) is obtained, it is estimated that the defect size is a value exceeding 300 nm. Here, for example, when the allowable defect size is set to 100 nm, it is determined that it is not a fatal pinhole defect, but a convex defect having a tolerance value or more exists, and the blank mask can be sorted as a defective product.

According to the above, in the blank mask in which the hard mask film of the film which acts as an anti-reflection film is formed on the optical film, if the light intensity distribution of the inspection image of the defect is a bright advantage, it is a fatal pinhole defect. If the dark part is dominant or the left side is the bright part and the right side is the dark part, it is a convex defect. These pieces of information are previously used as features of the inspection enlarged image in the film structure A, and are stored in the table shown in FIG. Then, in the defect inspection in the first film state, the film structure A in the table can be referred to, and correct bump determination can be performed to define a fatal pinhole defect.

[Example 2] A defect inspection of a blank mask including a concave defect and a convex defect in the second film state was carried out. As the inspection device, a device including the inspection optical system 151 shown in Fig. 2 was used. However, the inspection wavelength was 355 nm, and the numerical aperture NA of the objective lens OBL was 0.85. Since the resolution of the inspection optical system used in the first embodiment was higher, the illumination spot size was about 380 nm. The 2-dimensional scanning area is the same as that of the first embodiment described above. The blank mask 100 shown in FIG. 14(A) shows that an optical film 122 having a film thickness of 75 nm and a Cr layer having a thickness of 10 nm formed of a MoSi-based material is formed on the quartz substrate 101 which is transparent to the inspection light. A hard mask film 123 made of a material, a concave defect DEF10 such as a pinhole defect, exists in the state of the hard mask film 123.

14(B) shows that the width of the concave defect DEF10 is set to 80 nm, the depth D2 is set to 5 nm (the concave defect which does not penetrate the hard mask film 123), and 10 nm (the concave defect of the hard mask film 123). In the case of the type, the cross-sectional profile of the region containing the defect of the light intensity of the image is examined. At any depth, the defect inspection image is the outline of the dark portion, and the bright portion does not appear.

On the other hand, Fig. 15(A) is a cross-sectional view of the blank mask 100 including the convex defect DEF11 in the second film state similar to the film structure shown in Fig. 14(A). 15(B) shows that the composition of the convex defect DEF11 is also two kinds of the hard mask film 123 itself and the foreign matter (particles) formed of the Cr-based material, and the width W2 is set to 80 nm, and the height H2 is set to At 10 nm, the cross-sectional profile of the region containing the defect of the magnified image is examined. The inspection image of the convex defect is in any composition, and the left side of the defect portion is the bright portion, and the right side is the dark portion. Although the intensity level changes depending on the composition, it has the same light-dark positional relationship as the light intensity distribution (cross-sectional profile PR1) of a typical convex defect shown in Fig. 3(D).

According to the above, in the blank mask in which the film of the hard mask film or the like formed of the high reflectance material is formed on the optical film, if the light intensity distribution of the defect inspection image is dominant, it is fatal. Pinhole defects are convex defects if the left side is the bright part and the right side is the dark part.

The information of the inspection wavelength when the wavelength is 355 nm is previously used as a feature of the inspection enlarged image in the film structure B, and is stored in the table shown in FIG. Then, in the defect inspection of the second film state, the film structure B in the table can be referred to, and correct bump determination can be performed to define a fatal pinhole defect.

100‧‧‧ Blank mask

101‧‧‧Transparent substrate

102, 103, 112, 113, 122‧‧‧ optical film

103, 114, 123‧‧‧Processing auxiliary film or hard mask film

150‧‧‧ Defect inspection device

151‧‧‧Check optical system

152‧‧‧Control device

153‧‧‧recording device

154‧‧‧ display device

BM1‧‧‧Check light

BM2‧‧‧ reflected light

BSP‧‧ ‧ Beamsplitter

DEF1, DEF2, DEF5, DEF6, DEF7, DEF10‧‧‧ concave or pinhole defects

DEF3, DEF4, DEF8, DEF9, DEF11‧‧‧ convex defects

ILS‧‧‧ light source

L1‧‧ lens

MB‧‧‧ Blank mask

OBL‧‧‧ objective lens

SE‧‧‧Photodetector

STG‧‧‧ stage

SPF‧‧‧ spatial filter

1 is a cross-sectional view showing an example in which a defect exists in a blank mask, (A), (B) a blank mask showing the presence of a pinhole defect of a concave defect, and (C) a blank mask showing the presence of a convex defect. Figure. Fig. 2 is a view showing an example of the configuration of an inspection apparatus used for defect inspection of a blank mask. 3 is a view showing an example of a convex defect existing on the surface of a blank mask and an inspection image thereof, (A) a plan view of the blank mask of the defective portion, and (B) a sectional view of the blank mask of the defective portion, ( C) is an inspection image of the convex defect, and (D) is a cross-sectional view showing the light intensity distribution of the inspection image. 4 is a view showing an example of a concave defect existing on the surface of a blank mask and an observation image thereof, (A) a sectional view of the blank mask of the defective portion, and (B) showing the light intensity distribution of the inspection image. A diagram of the section view. Fig. 5 is a view showing the structure of the first film state and the profile of the inspection image, (A) the pinhole defect of the concave defect exists in the blank mask section of the uppermost film, and (B) shows the defect. Check the image of the image. Fig. 6 is a view showing the structure of the first film state and the cross-sectional profile of the inspection image, (A) the concave defect is present in the second mask from the uppermost layer, and the (B) is attached. A blank mask cross-section of the foreign matter defect, (C) is a blank mask cross-section of the same material as the uppermost layer, and (D), (E), and (F) are respectively displayed (A), (B) And (C) a diagram of the inspection image of the defect shown in (C). Figure 7 is a view showing the structure of the second film state and the cross-sectional profile of the inspection image, (A) a cross-sectional view of the blank mask in which the pinhole defect exists in the uppermost film, and (B) showing the defect thereof. Check the image of the light intensity profile of the image. Fig. 8 is a flow chart showing an example of the steps of the defect inspection method of the blank mask. Fig. 9 is a table in which the feature amount and the film state of the defect inspection image correspond to the defect shape. Fig. 10 is a flow chart showing an example of a procedure for determining a good result of a blank mask. Fig. 11 is a view showing the state of an illumination spot for scanning inspection. Fig. 12(A) is a cross-sectional view showing a blank mask having a concave defect in the first embodiment, and Fig. 12(B) is a view showing a cross-sectional contour of a light intensity distribution of an inspection image. Figure 13 (A) is a cross-sectional view of a blank mask having a convex defect of Embodiment 1, (B) is a diagram showing a profile of a light intensity distribution of an inspection image, and (C) is a defect inspection diagram showing different sizes. A diagram of the profile of the light intensity distribution of the image. Fig. 14(A) is a cross-sectional view showing a blank mask having concave defects in the second embodiment, and Fig. 14(B) is a view showing a cross-sectional contour of a light intensity distribution of an inspection image. Fig. 15(A) is a cross-sectional view showing a blank mask having a convex defect in the second embodiment, and (B) is a view showing a cross-sectional profile of a light intensity distribution of an inspection image.

Claims (11)

A method for inspecting a defect of a blank mask for forming a film having at least one layer on an optically transparent substrate, irradiating the inspection light on the surface of the film of the blank mask on the surface, and capturing the reflection from the region irradiated with the inspection light Light, a method of inspecting defects existing in a surface portion of a blank mask, comprising: (A1) a step of preparing a blank mask having at least one film, (A2) moving the blank mask to The defect existing in the surface portion of the blank mask is moved to the observation position of the inspection optical system, the inspection light is irradiated to the region including the defect, and the reflected light from the region irradiated with the inspection light is collected by the inspection optical system as the above region. The step of magnifying the image, (A3) the step of extracting the feature amount of the enlarged image, and (A4) the step of determining the shape of the defect based on the combination of the feature amount and the pattern of the film of the blank mask. The defect inspection method of the blank mask of claim 1, wherein the enlarged image in the step (A2) is generated by the diffraction component of the inspection optical system in the reflected light while the diffraction component is 0 times with respect to the reflected light. (Positive reflection component) An enlarged image formed by a positive and negative asymmetric high-order diffraction component. The defect inspection method of the blank mask of claim 1 or 2, wherein the step (A3) includes a processing step of comparing a change in the light intensity level of the defective portion in the enlarged image with a light intensity level of the peripheral portion of the defect, and The feature amount of the defect inspection image in which the difference between the bright portion having a high light intensity and the dark portion having a low light intensity and the positional relationship between the bright portion and the dark portion are extracted is extracted. The defect inspection method of the blank mask of claim 1 or 2, wherein the step (A4) is based on the information of the feature quantity of the enlarged image and the state of the film of the blank mask, and refers to optical simulation or experimental data in advance. A step of determining a shape of a defect by selecting a table of pinhole defects or convex defects. The defect inspection method of the blank mask of claim 4, wherein in the step (A3), when the enlarged image of the defect extracts the feature quantity of the image in which the bright portion is dominant, as long as it is the outermost surface of the blank mask to be inspected For a film that is transparent to the inspection light, it is judged that the detected defect is a pinhole defect. The defect inspection method of the blank mask of claim 4, wherein in the step (A3), when the enlarged image of the defect extracts the feature quantity of the image in which the dark portion is dominant, as long as it is the outermost surface of the blank mask to be inspected When the inspection light reflectance of the film is higher than the inspection light reflectance of the lower layer, it is judged that the detected defect is a pinhole defect. The defect inspection method of the blank mask of claim 1 or 2, wherein the film thickness of the film is 10 nm or less. The defect inspection method of the blank mask of claim 1 or 2, wherein the inspection light is light having a wavelength of 210 to 550 nm. A blank mask defect inspection system comprising: the surface of the film of a blank mask having at least one film formed on an optically transparent substrate, irradiating the inspection light, and capturing the reflected light from the region irradiated with the inspection light, An inspection apparatus for inspecting defects existing in the surface portion of the blank mask, and a computer having a program for performing the steps of the defect inspection method of the blank mask of any one of claims 1 to 8. A method for sorting a blank mask, characterized in that the defect is not included in the defect based on the uneven shape of the defect determined by the defect inspection method of the blank mask of any one of claims 1 to 8. Blank reticle. A method of manufacturing a blank mask, comprising: forming a film of at least one layer on an optically transparent substrate, and sorting in the film by a sorting method of a blank mask as claimed in claim 10 The step of a blank mask without pinhole defects.