KR102295295B1 - Defect inspection method, defect inspection system, selection method, and manufacturing method of photomask blank - Google Patents

Abstract

Inspection light is irradiated on the surface of a photomask blank in which at least one thin film is formed on a transparent substrate, and reflected light from the region irradiated with inspection light is collected through an inspection optical system to form an enlarged image of the region, and enlarged Based on the feature amount of the light intensity distribution extracted from the image and the criterion for determining the defect corresponding to the structure of the optical film of the photomask blank, the concavo-convex shape of the defect existing in the surface portion of the photomask blank is determined.
By using the optical defect inspection method, the concavo-convex shape of the defect can be distinguished with high reliability, and the defect of the photomask blank can be inspected. Moreover, by applying the defect inspection method of this invention, the photomask blank which does not contain a pinhole defect can be provided with lower cost and high yield rate.

Description

DEFECT INSPECTION METHOD, DEFECT INSPECTION SYSTEM, SELECTION METHOD, AND MANUFACTURING METHOD OF PHOTOMASK BLANK

The present invention relates to a defect inspection method of a photomask blank used for manufacturing a photomask (transfer mask) used in the manufacture of semiconductor devices (semiconductor devices), etc., in particular, the thickness formed on the photomask blank is 10 nm or less It relates to a defect inspection method of a photomask blank effective for determination of concave shapes such as pinholes present in a thin film. In addition, the present invention relates to a method for screening and manufacturing a photomask blank to which the method for inspecting concave defects of defects of the photomask blank is applied.

A semiconductor device (semiconductor device) irradiates exposure light to a pattern transfer mask such as a photomask on which a circuit pattern is drawn, and a circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) through a reduction optical system. Photo manufactured by repeated use of lithographic techniques. With the continuous refinement of circuit patterns of semiconductor devices, the wavelength of exposure light is 193 nm using argon fluoride (ArF) excimer laser light is becoming mainstream. By employing it, it is finally possible to form a pattern having a size sufficiently small compared to the exposure wavelength.

The pattern transfer mask is manufactured by forming a circuit pattern on a substrate (mask blank) on which an optical film is formed. Such an optical film (thin film) is generally a film having a transition metal compound as a main component or a film containing a silicon compound containing a transition metal as a main component, and depending on the purpose, a film functioning as a light-shielding film or a film functioning as a phase shift film etc. are selected. Moreover, the hard mask film|membrane which is a process auxiliary film|membrane for the purpose of high-precision processing of an optical film is also included.

Since a transfer mask, such as a photomask, is used as an original plate for manufacturing a semiconductor element having a fine pattern, it is required to be defect-free, which naturally requires that it be defect-free also for the photomask blank. In addition, when forming a circuit pattern, a resist film for processing is formed on the photomask blank on which the film|membrane was formed, and a pattern is finally formed through normal lithography processes, such as an electron beam drawing method. Therefore, it is calculated|required that the resist film also does not have defects, such as a pinhole. For this reason, many studies have been made on a technique for detecting defects in a photomask or a photomask blank.

In Japanese Patent Application Laid-Open No. 2001-174415 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-333313 (Patent Document 2), a laser beam is irradiated to a substrate, and defects and foreign matter are detected from diffusely reflected light. A method is described, and in particular, a technique for imparting asymmetry to a detection signal to determine whether it is a convex part defect or a recessed part defect is described. In addition, Japanese Unexamined Patent Publication No. 2005-265736 (Patent Document 3) describes a technique of using DUV (Deep Ultra Violet) light used for pattern inspection of a general optical mask as inspection light. Further, Japanese Patent Laid-Open No. 2013-19766 (Patent Document 4) describes a technique in which inspection light is divided into a plurality of spots, the plurality of spots are scanned on a substrate, and a reflected beam is received by a photodetector element, respectively. has been On the other hand, Japanese Patent Laid-Open No. 2007-219130 (Patent Document 5) discloses a technique for determining the concavo-convex shape of a defect in an EUV mask blank using EUV (Extreme Ultra Violet) light having a wavelength of around 13.5 nm as inspection light. has been

Patent Document 1: Japanese Patent Laid-Open No. 2001-174415 Patent Document 2: Japanese Patent Laid-Open No. 2002-333313 Patent Document 3: Japanese Patent Laid-Open No. 2005-265736 Patent Document 4: Japanese Patent Laid-Open No. 2013-19766 Patent Document 5: Japanese Patent Laid-Open No. 2007-219130

All of the inspection apparatuses described in said patent documents 1 - 4 employ|adopt the optical defect method, and enable wide area defect inspection and the unevenness|corrugation determination of a defect in a comparatively short time. Moreover, if limited to EUV mask blank, the method by which the unevenness|corrugation of a phase defect can be judged in patent document 5 is described.

However, according to the inspection experiment using an atomic force microscope or an electron microscope in combination as studied by the present inventors, the conventional method of examining the arrangement of the bright and dark parts of the inspection signal of the photomask blank found that there are cases in which unevenness determination cannot be made. That is, the arrangement positional relationship of the bright part and the dark part for distinguishing an unevenness|corrugation in the inspection signal of a pinhole defect may be unclear. In particular, it was found that, in the defect inspection of the processing auxiliary layer formed for the processing of the tip mask, that is, the hard mask thin film having a thickness of 10 nm or less, the problem of difficulty in determining the unevenness as described above tends to occur.

From such a situation, according to the actual inspection experiment based on the inspection apparatus described in said patent document 1-4, it cannot necessarily be said that the unevenness|corrugation shape of the surface of a defect part can be judged with high precision. Moreover, the method described in patent document 5 is applied to the phase defect inherent in EUV mask blank, and it is a method difficult to apply to the photomask blank used for ArF lithography currently mainstream. Therefore, establishment of the method which judges the uneven|corrugated shape of the defect which exists in a hard mask thin film with high precision which is difficult with the conventional method was calculated|required.

The present invention has been made in order to solve the above problems, and a defect inspection method of a photomask blank that can determine with high reliability the unevenness of the surface shape of a defect portion using an optical defect inspection method, particularly during mask pattern processing A method for judging the irregularities of a defective portion present in a hard mask thin film used as a processing auxiliary layer, and a method for selecting a photomask blank for excluding a substrate including a pinhole defect by applying a method for determining irregularities of a defective portion of the photomask blank; and An object of the present invention is to provide a manufacturing method.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, the present inventors repeated examination of the light intensity distribution of the inspection signal in the defect which exists in various optical films from both an inspection experiment and a simulation. As a result, it was found that, depending on the value of the complex refractive index with respect to the inspection light, the optical film and the optical film below it, the change in the contrast of the observed image of the defect and the arrangement positional relationship of the bright and dark parts were different. As a result of further repeating various examinations, it came to achieve this invention.

Accordingly, the present invention provides the following method for inspecting defects of a photomask blank, and a method for selecting and manufacturing a photomask blank to which the method is applied.

[One]

Inspection light is irradiated to the thin film surface of the photomask blank in which at least one thin film is formed on the surface on an optically transparent substrate, and the reflected light from the area irradiated with the inspection light is taken on the surface of the photomask blank. A method for inspecting defects comprising:

(A1) preparing a photomask blank having at least one thin film;

(A2) The photomask blank is moved to move the defect existing on the surface of the photomask blank to the observation position of the inspection optical system, and the inspection light is irradiated to the area including the defect, and the inspection light is irradiated. collecting the reflected light from the inspection optical system as an enlarged image of the region;

(A3) extracting the feature amount of the enlarged image;

(A4) A step of judging the shape of a defect based on the combination of the feature amount and the shape of the thin film of the photomask blank

Defect inspection method of a photomask blank comprising a.

[2]

(A2) The magnified image in the step is generated from the diffraction component that passes through the inspection optical system among the reflected light, and the magnified image is formed from a higher-order diffraction component that is positive and negative with respect to the 0-order diffraction component (specular reflection component) of the reflected light. The defect inspection method of the photomask blank as described in [1] characterized by the above-mentioned.

[3]

The step (A3) includes a processing step of comparing the change in the light intensity level of the defect portion in the magnification with the light intensity level of the defect periphery, the difference in intensity between the bright portion with high light intensity and the dark portion with low light intensity, and The defect inspection method of the photomask blank as described in [1] or [2] characterized by extracting the characteristic quantity of the defect inspection image which is the arrangement positional relationship of a dark part.

[4]

In the step (A4), refer to a table in which pinhole defects or convex defects can be selected, created in advance based on optical simulation or experimental data, based on the above-mentioned enlarged feature amount and information on the shape of the thin film of the photomask blank. Thus, the defect inspection method of the photomask blank according to [1], [2] or [3], characterized in that it is a step of determining the shape of the defect.

[5]

(A3) In the step (A3), when a feature amount is extracted that the enlarged image of the defect is an image in which the bright part is dominant, if the outermost surface of the photomask blank to be inspected is a thin film transparent to the inspection light, it is judged that the detected defect is a pinhole defect. The defect inspection method of the photomask blank as described in [4] characterized by the above-mentioned.

[6]

In the step (A3), when the characteristic quantity that the dark portion is dominant image is extracted from the enlarged image of the defect, if the inspection light reflectance of the thin film of the outermost surface of the inspected photomask blank is higher than the inspection light reflectance of the lower layer, , The defect inspection method of the photomask blank according to [4], wherein the detected defect is judged to be a pinhole defect.

[7]

The defect inspection method for a photomask blank according to any one of [1] to [6], wherein the thin film has a thickness of 10 nm or less.

[8]

The defect inspection method for a photomask blank according to any one of [1] to [7], wherein the inspection light is light having a wavelength of 210 to 550 nm.

[9]

Inspection light is irradiated to the surface of the thin film of the photomask blank in which at least one thin film is formed on an optically transparent substrate, and the reflected light from the area irradiated with the inspection light is taken to remove defects existing on the surface of the photomask blank. an inspection device that inspects

A computer having a program for executing the steps of the photomask blank defect inspection method according to any one of [1] to [8].

Defect inspection system of the photomask blank comprising a.

[10]

A photomask characterized in that a photomask blank containing no pinhole defects is selected based on the concavo-convex shape of the defect determined by the photomask blank defect inspection method according to any one of [1] to [8]. Method of screening blanks.

[11]

forming at least one thin film on an optically transparent substrate;

A step of sorting a photomask blank that does not contain pinhole defects in the thin film by the photomask blank sorting method described in [10].

A method of manufacturing a photomask blank comprising a.

According to the present invention, the concave-convex shape defects in the photomask blank can be distinguished with high reliability using the optical defect inspection method, and concave defects or pinhole defects, which are particularly fatal defects, can be specified. In addition, by applying the defect inspection method of the present invention, a photomask blank having a concave defect, which is a fatal defect, can be reliably excluded, and a photomask blank containing no fatal defect is provided at a lower cost and with a high yield rate can do.

1 is a cross-sectional view showing an example in which defects exist in a photomask blank, (a) and (b) are photomask blanks having pinhole defects that are concave defects, and (c) are photomasks having convex defects. It is a figure which shows a blank.
It is a figure which shows an example of the structure of the inspection apparatus used for the defect inspection of a portmask blank.
3 is a view showing a convex defect existing on the surface of a photomask blank and an example of an inspection image thereof, (a) is a photomask blank plan view of the defective part, (b) is a photomask blank cross-sectional view of the defective part, (c) is The inspection image of the convex defect, (d) is a figure which shows the sectional drawing of the light intensity distribution of an inspection image.
4 is a view showing a concave defect existing on the surface of a photomask blank and an example of an observation image thereof, wherein (a) is a cross-sectional view of a photomask blank of a defect portion, (b) is a cross-sectional view of a light intensity distribution of an inspection image; am.
5 is a view showing the structure and cross-sectional profile of the inspection image in the form of the first film, (a) is a cross-sectional view of a photomask blank in which a pinhole defect of a concave defect exists in the uppermost layer film, (b) is an inspection image of the defect It is a drawing showing
6 is a view showing the structure in the first film form and the cross-sectional profile of the inspection image, (a) is a cross-sectional view of a photomask blank in which a concave defect exists in the second layer from the uppermost layer, (b) is a foreign material defect attached A cross-sectional view of the existing photomask blank, (c) is a cross-sectional view of a photomask blank with convex defects of the same material as the uppermost layer, (d), (e), and (f) are (a), (b), (c), respectively It is a figure which shows the inspection image of the defect shown in.
7 is a view showing the structure and cross-sectional profile of an inspection image in the form of a second film, (a) is a cross-sectional view of a photomask blank in which a pinhole defect exists in the uppermost layer film, (b) is a light of the inspection image of the defect A diagram showing the strength cross-sectional profile.
It is a flowchart which shows an example of the process of the defect inspection method of a photomask blank.
Fig. 9 is a table in which a characteristic amount and a film shape of a defect inspection image are matched with a defect shape.
Fig. 10 is a flowchart showing an example of a process for judging the quality of the photomask blank.
It is a figure which shows the situation which scans the illumination spot for inspection.
Fig. 12(a) is a cross-sectional view of a photomask blank having a concave defect of Example 1, and (b) is a view showing a cross-sectional profile of light intensity distribution of an inspection image.
Fig. 13 (a) is a cross-sectional view of a photomask blank having convex defects of Example 1, (b) is a view showing a cross-sectional profile of the light intensity distribution of an inspection image, (c) is a defect inspection image of different size It is a figure which shows the cross-sectional profile of light intensity distribution.
Fig. 14(a) is a cross-sectional view of a photomask blank having a concave defect of Example 2, and (b) is a view showing a cross-sectional profile of light intensity distribution of an inspection image.
Fig. 15 (a) is a cross-sectional view of a photomask blank having convex defects of Example 2, and (b) is a view showing a cross-sectional profile of light intensity distribution of an inspection image.

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

If defects, such as pinholes, exist in the thin film of a photomask blank, it will become a cause of the defect of the mask pattern on the photomask manufactured using this. An example of a defect of a typical photomask blank is shown in FIG. 1 . Fig. 1 (a) shows a photomask blank 100 in which an optical thin film 102 functioning as a light shielding film or a phase shift film for halftone phase shift masks, etc. is formed on a transparent substrate 101 . It is a drawing. Here, the pinhole defect DEF1 exists in the optical thin film 102 . 1(b) shows an optical thin film 102 functioning as a light-shielding film or a phase shift film for halftone phase shift masks, etc. on a transparent substrate 101, and high-precision processing of the optical thin film 102 It is a view showing the photomask blank 100 in which the processing auxiliary thin film 103 is formed. Here, the pinhole defect DEF2 exists in the processing auxiliary thin film 103 . When a photomask is manufactured from such a photomask blank by a normal manufacturing process, it will become a photomask in which the defect derived from a photomask blank exists. And this defect causes a pattern transfer error in exposure using a photomask. Therefore, it is necessary to detect the defect of a photomask blank at the stage before processing a photomask blank, to exclude the photomask blank which has a defect, or to correct a defect.

On the other hand, FIG. 1( c ) is a view showing an example of a convex defect of a photomask blank, and is a view showing an example of the photomask blank 100 in which the convex defect DEF3 exists on the optical thin film 102 . The defect DEF3 may be a convex defect integrated with the optical thin film 102 or a convex defect attached to a foreign material such as a particle. Even if a photomask is manufactured from such a photomask blank by a normal manufacturing process, a fatal pinhole defect is not necessarily formed. Moreover, if the foreign material defect adhering to the surface can be removed by washing|cleaning, it will not become a fatal defect.

As described above, the determination of whether the defect present in the photomask blank is a concave defect such as a pinhole, which is a fatal defect, or a convex defect, which is not necessarily a fatal defect, is determined by the quality assurance of the photomask blank and the yield rate in the photomask blank manufacturing. hold the key of Then, the method which can distinguish the uneven|corrugated shape of a defect in a short processing time and high reliability by the optical inspection method is calculated|required. In addition, considering that the wavelength of exposure light, which is currently mainstream, is 193 nm using argon fluoride (ArF) excimer laser light, the concavo-convex shape of defects with a size of 200 nm or less, preferably 100 nm or less on the mask blank is distinguished. There needs to be a way to do it.

First, the inspection apparatus suitably used for the defect inspection of a photomask blank, specifically, the inspection apparatus used suitably in order to determine the uneven|corrugated shape of the defect in the surface part of a photomask blank is demonstrated. 2 is a conceptual diagram showing an example of a basic configuration of the defect inspection apparatus 150, and the inspection optical system 151, the control apparatus 152, the recording apparatus 153, and the display apparatus 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 stage STG that can move with a photomask blank MB, and an image detector SE. The light source ILS is configured to emit light with a wavelength of about 210 nm to 550 nm, and the inspection light BM1 emitted from the light source ILS is bent at the beam splitter BSP and passes through the objective lens OBL to a predetermined area of the photomask blank MB. investigate The light BM2 reflected from the surface of the photomask blank MB is condensed by the objective lens OBL, passes through the beam splitter BSP and the lens L1, and reaches the light receiving surface of the image detector SE. At this time, the position of the image detector SE is adjusted so that an enlarged inspection image of the surface of the mask blank MB is formed on the light receiving surface of the image detector SE. Then, the data of the enlarged inspection image collected by the image detector SE is subjected to image processing operation to determine the size of the defect and the concavo-convex shape, and the results are recorded as defect information. The inspection device 150 is controlled and operated by the control device 152 . The control device 152 has a control program and various image operation programs. In addition, the operation of the recording device 153 for storing inspection data and the display device 154 for performing various types of display is also controlled.

The enlarged inspection image is an enlarged inspection image formed by, for example, the image detector SE as a detector in which a plurality of photodetecting elements such as a CCD camera are arranged as pixels, and the light BM2 reflected from the surface of the photomask blank MB passes through the objective lens OBL. The images can be collected by a direct method of collectively collecting the images as two-dimensional images. In addition, the inspection light BM1 is converged on the surface of the photomask blank MB to generate an illumination spot, and the light source ILS emitting inspection light has a scanning function to scan the illumination spot, and the light intensity of the reflected light BM2 is sequentially measured by an image detector. A method of collecting by SE, performing photoelectric conversion and recording, and generating an overall two-dimensional image may be employed.

In addition, when collecting the reflected light BM2 in order to determine the unevenness of the defect, positive and negative higher-order diffraction components (centered on the specular component) may be collected asymmetrically with respect to the 0th-order diffraction component (specular reflection component). Specifically, a method in which the main ray of the inspection light BM1 illuminating the surface of the photomask blank MB is made obliquely incident, or the main ray is vertical illumination, but a spatial filter SPF that blocks a part of the optical path of the reflected light BM2 is provided; A method of grasping the enlarged inspection image with the image detector SE is employable. By employing these methods, it is generally possible to determine the concavo-convex shape of the defect from the difference in light intensity or positional relationship between light and dark in the inspection image light intensity distribution.

Next, the inspection light BM1 is scanned while converging on the surface of the photomask blank MB with the principal ray as vertical illumination, and in the inspection image obtained by sequentially collecting the light intensity of the reflected light BM2, convex and concave defects are inspected. The difference in images will be described. When collecting the light intensity of the reflected light BM2, it is assumed that the right half of the reflected light BM2 directed to the image detector SE is blocked by the action of the spatial filter SPF.

3A and 3B are a plan view and a cross-sectional view, respectively, of a photomask blank 100 having a convex defect DEF4. In these cases, an optical thin film 102 made of a MoSi-based material is formed on a transparent substrate 101 such as a quartz substrate that is transparent to inspection light, and a convex defect DEF4 made of a MoSi-based material or other material is present on the surface MBS of the MBS. indicates the state of being.

When the surface MBS of the photomask blank having the convex defect DEF4 converges, illuminates and scans the inspection light BM1, and the reflected light is collected through the spatial filter SPF, the inspection image of the light intensity distribution shown in Fig. 3(c) this is obtained The light intensity distribution in the cross section taken along the line A-A' in Fig. 3(c) becomes the cross-sectional profile PR1 shown in Fig. 3(d). The cross-sectional profile PR1 has the characteristic shape of the convex defect used as a bright part and the right part on the left side of convex defect DEF4 as a dark part.

Similarly, Fig. 4 (a) is a cross-sectional view of the photomask blank 100 having the concave defect DEF5, and Fig. 4 (b) is a view showing the cross-sectional profile PR2 of the light intensity distribution of the inspection image obtained in this case. The cross-sectional profile PR2 has a characteristic shape of the concave defect in which the left side of the concave defect DEF5 becomes a dark part and the right side becomes a bright part.

However, depending on the form of the film of the photomask blank, it may not be possible to accurately determine whether the defect is a concave defect or a convex defect only by the positional relationship between the light and dark of the inspection image described above. Examples of such a case will be described below.

[Form 1 act]

5 (a) is a cross-sectional view of the photomask blank 100 having a concave defect. This is on a transparent substrate 101 such as a quartz substrate transparent to inspection light, an optical thin film 112 made of a MoSi-based material, an optical thin film 113 made of a Cr-based material, and inspection light having a thickness of about 5 to 10 nm A hard mask thin film 114 made of a substantially transparent material, for example, silicon oxide, is formed, indicating a state in which concave defects DEF6 such as pinhole defects exist in the hard mask thin film 114 . For this concave defect DEF6, using the inspection optical system shown in Fig. 2, when the inspection light is converged and scanned from above on the surface of the photomask blank, and the reflected light is collected through the spatial filter SPF, the light intensity of the inspection image The cross-sectional profile of the distribution becomes the profile PR3 shown in Fig. 5(b). In this case, the light intensity distribution of the inspection image is substantially only bright in the portion of the concave defect DEF6, so that a clear positional relationship of light and dark like the light intensity distribution of the inspection image of the typical concave defect shown in Fig. 4 does not appear. .

Moreover, even if the film|membrane structure is the same as the structure shown to Fig.5 (a), according to the kind of defect, the example from which various inspection images are obtained is shown in FIG. 6(a) shows that concave defects already exist in the optical thin film 113 made of a Cr-based material, and a hard mask thin film 114 having a uniform film thickness without defects is formed thereon, resulting in a concave shape on the surface. indicates the state in which the defect DEF7 is present. 6(b) shows a state in which, although there are no defects until the formation of the hard mask thin film 114, a foreign material mainly composed of silicon has adhered to the surface thereof as a convex defect DEF8. 6(c) shows a state in which a part of the surface of the hard mask thin film 114 exists as a convex defect DEF9. The cross-sectional profiles of the inspection images of these defects DEF7, DEF8, and DEF9 are profile PR4 shown in Fig. 6(d), profile PR5 shown in Fig. 6(e), and profile PR6 shown in Fig. 6(f), respectively. Profile PR4 is an inspection image of a typical concave defect, but an inspection image when no defects exist in the hard mask thin film 114 on the outermost surface, profile PR5 is an inspection image of a typical convex defect, and profile PR6 is inspection image of a concave defect at a glance Although it appears as an image, the case where this profile PR6 is obtained in the case of the first film form is a convex defect of the hard mask thin film 114 transparent to the inspection light.

From the above, it can be determined that the pinhole defect which is a fatal defect exists in the inspection image of the defect in a 1st film|membrane form, when the inspection image in which the bright part dominates is obtained. The criterion for determining the unevenness of the defect in the first film form is a criterion different from the typical case of the convex defect and the concave defect shown in Figs. 3 and 4, and is a criterion unique to the case of the first film form. Moreover, when the film thickness of the film which consists of a material substantially transparent with respect to inspection light is thin, for example, when the film thickness is 10 nm or less, especially 5-10 nm, it is suitable.

[Second Act Form]

7A is a cross-sectional view of a photomask blank 100 having a concave defect. In this case, an optical thin film 122 made of a MoSi-based material and a hard mask thin film 123 made of a Cr-based material having a thickness of about 10 nm are formed on a transparent substrate 101 such as a quartz substrate transparent to inspection light. , shows a state in which concave defects DEF10 such as pinhole defects exist in the hard mask thin film 123 . The second film type is characterized in that the inspection light reflectance of the hard mask thin film 123 is higher than the inspection light reflectance of the optical thin film 122 . For this concave defect DEF10, the cross-sectional profile of the light intensity distribution of the inspection image when the inspection light is converged and scanned from above on the surface of the photomask blank and the reflected light is collected through the spatial filter SPF is shown in Fig. 7(b). The profile PR7 shown in . In this case, the light intensity distribution of the inspection image is substantially only a dark part in the portion of the concave defect DEF10, so that a clear positional relationship of light and dark like the light intensity distribution of the inspection image of the typical concave defect shown in Fig. 4 does not appear. . It is thought that the reason that the concave defect in this case is observed only in the dark part is because the depth of the concave defect DEF10 is shallow, the amount of light reflected from the side surface of the defect is small, and the influence of the reflectance of the inspection light on the light intensity change is greater. .

Moreover, when a convex defect exists in the hard mask thin film 123, the inspection image turns into the inspection image in which the bright part and dark part equal to profile PR1 shown to Fig.3(d) are arranged.

From the above, in the inspection image of the defect in a 2nd film|membrane form, when the inspection image in which a dark part is dominant is obtained, it can be determined that the pinhole defect which is a fatal defect exists. The criterion for determining the unevenness of the defect in the second film form is a criterion different from the typical case of the convex defect and the concave defect shown in Figs. 3 and 4, and is a criterion unique to the case of the second film form.

Next, according to the flowchart shown in FIG. 8, the defect inspection method of this invention is demonstrated more concretely. First, as a step (A1), a photomask blank (to-be-inspected photomask blank) to be inspected having a defect is prepared (step S201). Next, the positional coordinate information of the defect existing on the photomask blank is taken in (step S202). Separately, the position coordinates of the defect may use the position coordinates of the defect specified by a known defect inspection method.

Next, as the step (A2), the position of the defect is aligned with the inspection position of the inspection optical system, the inspection light is irradiated from above the photomask blank through the objective lens (step S203), and the reflected light of the area irradiated with the inspection light is collected as an enlarged image of the area including the defect through the objective lens of the inspection optical system (step S204). In the alignment, the photomask blank of the inspection object is mounted on a stage capable of moving in the in-plane direction, and the stage is moved in the in-plane direction based on the position coordinates of the defect of the photomask blank of the inspection object, so that the defect is detected in the inspection optical system. It may be carried out in a method of keeping the in-focus plane of the objective lens of

Next, from the collected light intensity distribution (image data (inspection image), cross-sectional profile, etc.) of the enlarged image, the characteristic of the part of the change in light intensity of the inspection image in the defect portion, that is, the characteristic amount of the enlarged image is extracted (Step S205) ).

Thereafter, as a step (A4), the concavo-convex shape of the defect is determined based on the feature amount of the enlarged image extracted in the step S205 and the film structure (film shape) of the photomask blank (step S206). The specific example of the determination process of an uneven|corrugated shape is mentioned later. Moreover, a defect size can also be estimated by performing well-known image processing to an inspection image. The predicted values of the concavo-convex shape and defect size of these defects are recorded together with the defect position coordinates as defect information (step S207).

Next, it is judged whether or not the inspection has been completed for all the defects based on the defect position coordinate information taken in in advance (judgment D201). , the collection of inspection image data and the determination of irregularities of defects are repeated. Then, when it is determined that the inspection has been completed for all the defects taken in in advance (decision D201), the defect inspection is finished.

Next, a specific example of the step of determining the concavo-convex shape will be described. In the recording device 152 connected to the control device of the defect inspection apparatus shown in Fig. 2, along with defect information, the characteristics of the inspection signal when a defect is detected shown in Fig. 9 and the optical films (thin films) of the various photomask blanks are provided. ), a table representing the structure of the relationship is stored. The characteristic of the inspection signal is an image in which a bright portion is dominant in a defect portion, an image in which a dark portion is dominant, an image in which the left is a bright portion and a dark portion is the right portion, an image in which the left is a dark portion and the right portion is a bright portion, and the like. In addition, as the structure of the optical film (thin film), for example, the film structure A is the above-mentioned film form 1, and is a structure in which a hard mask thin film transparent to inspection light and having a film thickness of 10 nm or less is formed on the outermost surface. In addition, the film structure B is the above-mentioned film form 2, and it is a case where the inspection light reflectance of the hard mask thin film with a film thickness of 10 nm or less formed on the outermost layer is higher than the inspection light reflectance of the optical thin film of the lower layer. The film structure C is a structure in which an optical thin film made of a MoSi-based material is formed on the outermost surface, and the film structure D is a structure in which an optical thin film made of a Cr-based material having a thickness of 20 nm or more is formed on the outermost surface. .

Referring to the table shown in FIG. 9 , in various film structures, by extracting the characteristics of the inspection image obtained from the defect inspection, it is possible to identify whether the defect is a fatal pinhole defect or a convex defect. That is, since the characteristic amount of the enlarged image is extracted in the above step S205, in the step S206 of determining the concavo-convex shape of the defect, for specifying the type of the defect from the film structure of the substrate to be inspected and the characteristic of the enlarged image, as shown in FIG. With reference to the table, the concavo-convex shape of the defect can be identified. In particular, it is also possible to determine whether or not it is a fatal pinhole defect.

In addition, the judgment criterion of the concave defect in the table shown in FIG. 9 may change depending on the state of light shielding of 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 left and right, the determination of the concave defects and the convex defects corresponding to the arrangement positions of the bright and dark portions, which are characteristics of an enlarged image, is also reversed.

In addition, the table is not limited to the cross-sectional profile of an inspection image, The image of a two-dimensional light intensity distribution may be sufficient. In addition, it is possible to add sequentially according to past defect inspection results or introduction of a new film type.

Next, the selection method of the photomask which employ|adopted the defect inspection method of this invention is demonstrated according to the flowchart shown in FIG. First, a photomask blank to be inspected is prepared (step S211), and defect inspection of the photomask blank shown above is subsequently performed, and defect information including the concavo-convex shapes and sizes of all detected defects is recorded (step S212). ). Thereafter, it is checked whether or not concave defects such as pinhole defects are included in the recorded defect information (judgment D211). If concave defects are included, the photomask blank is selected as a defective product (step S213). If the concave defect is not included, and if it is determined that the size predicted value of the defect is equal to or less than a predetermined allowable value (judgment D212), the photomask blank is selected as a non-defective product (step S214). Conversely, if it is determined that the size predicted value of the defect is equal to or greater than the predetermined allowable value (judgment D212), the photomask blank is selected as a defective product (step S213).

According to the defect inspection method of this invention, when a thin film with a film thickness of 10 nm or less, such as a hard mask thin film, is formed in the outermost surface part of a photomask blank, the characteristic amount of a defect inspection image (enlarged image) By extracting , and referring to a table that determines the defect concavo-convex shape unique to the film shape, the concavo-convex shape of the defect can be distinguished with high reliability.

By applying the defect inspection method of the present invention capable of distinguishing the concave-convex shape of defects with high reliability to the manufacturing process of the photomask blank, photomask blanks having concave defects, particularly pinhole defects, are extracted with high reliability. , a photomask blank that does not contain concave defects such as pinhole defects can be selected. In addition, the information of the uneven|corrugated shape of the defect obtained by the defect inspection method of this invention can be provided to a photomask blank by methods, such as affixing an inspection table.

Conventionally, since it was insufficient to understand that the observed images of pinhole defects differ depending on the film structure, there is no possibility of missing a fatal pinhole defect or excluding a photomask blank having a defect that is not necessarily a fatal defect as a defective product. there was. Although this has been a factor in lowering the yield, the defect inspection method of the present invention can selectively exclude a photomask blank having a concave defect that is a fatal defect existing in the photomask blank. A photomask blank can be provided with a good yield.

(Example)

Hereinafter, although an Example is shown and this invention is demonstrated concretely, this invention is not limited to the following Example.

[Example 1]

Defect inspection of the photomask blank including concave defects and convex defects in the form of the first film was performed. As the inspection apparatus, an apparatus including the inspection optical system 151 shown in FIG. 2 was used. The wavelength of the inspection light emitted from the light source ILS is 532 nm, and the numerical aperture NA of the objective lens OBL is 0.95. The inspection light BM1 converges and illuminates the photomask blank MB from above through the objective lens OBL. As shown in Fig. 11, the converged illumination spot scans the surface MBS of the photomask blank 100 containing the defect DEF6 in one direction by scanning means (not shown). On the other hand, the stage STG on which the photomask blank MB is mounted intermittently or continuously moves in a direction orthogonal to the above-mentioned scanning direction. By combining the scanning of these illumination spots and movement of the stage, the illumination spot was scanned two-dimensionally in a predetermined area including the defect portion. Then, the reflected light from the photomask blank obtained at each illumination spot was converged by passing through the objective lens OBL and the spatial filter SPF and lens L1 that shield the right half of the reflected light, and the light intensity was collected by the photodetector SE. The inspection image (magnified image) of a defect was produced|generated by arranging the collected light intensity two-dimensionally according to the position of an illumination spot. Here, the size of the illumination spot on the surface of the mask blank was about 400 nm, and the two-dimensional irradiation area including the defect portion was a rectangular area of about 30 µm x 30 µm.

Fig. 12(a) is a cross-sectional view of a photomask blank 100 including a pinhole defect in the form of a first film, on a quartz substrate 101 transparent to inspection light, a 75 nm-thick optical A thin film 112, an optical thin film 113 with a thickness of 44 nm made of a Cr-based material, and a hard mask thin film 114 with a thickness of 10 nm made of silicon oxide are formed on the hard mask thin film 114 having a diameter W1. The state in which the pinhole defect DEF6 exists is shown. Assuming the defect size (=diameter) W1 = 80 nm and 300 nm, the area containing these defects is scanned from the above illumination spot, and the inspection magnification defect is obtained as an arrangement of reflected light intensities corresponding to the scanning positions. The cross-sectional profile of the region to be used is shown in Fig. 12(b). The characteristic of this enlarged image is that at any defect size W1, on the basis of the reflected light intensity of the region free of defects, the dark portion hardly appears and the bright portion becomes a dominant profile. Since the hard mask thin film 114 is substantially transparent to the inspection light, it acts as an antireflection film. Therefore, the reflectance of the surface of the hard mask thin film 114 is lowered, and the reflectance of the pinhole defect portion where the lower surface thereof is exposed becomes higher than that of the peripheral portion. As a result, the pinhole part of the inspection image became a bright part. In the step of inspecting the photomask blank, the true concavo-convex shape of the defect is not clear, but the photomask blank to be inspected has an optical thin film structure of the first film type, and the characteristic of the defect observation image (enlarged image) is dominant. Based on the reference to the table shown in FIG. 9, it was determined that a defect was a pinhole defect.

On the other hand, Fig. 13(a) is a cross-sectional view of the photomask blank 100 including the convex defect DEF8 in the same first film form as the film structure shown in Fig. 12(a). As the composition of the convex defect portion, two types were designated: the same composition as that of the hard mask thin film 114 made of silicon oxide and amorphous silicon (Si). The cross-sectional profile of the area|region containing the defect on the inspection enlargement when the width W1 of the convex defect DEF8 is 80 nm and the height H1 is 10 nm and 30 nm is shown in FIG.13(b). In the inspection enlarged image of the convex defect with W1 = 80 nm, the intensity level changes depending on the height and composition, but the defect part becomes an inspection image where the dark part is dominant, and the profile differs from the inspection image of the pinhole defect shown in Fig. 12(b). this is different Thus, it was possible to distinguish from pinhole defects.

Moreover, FIG.13(c) is a figure which shows the cross-sectional profile of the area|region containing the defect in the inspection enlargement when the convex defect size is W1 = 400 nmm. Here, when the composition is silicon oxide, the defect height is H1 = 30 nm, and when the composition is amorphous silicon, H1 = 10 nm. In this case, when the composition was silicon oxide, an inspection image in which the defective portion was a dark portion was obtained, and when the composition was amorphous silicon, an inspection image in which the defective portion was arranged with a bright portion and a dark portion was obtained. Since they are all different from the inspection image of a pinhole defect, they can be distinguished.

Here, a defect size can be estimated from an inspection image by calculation processing using the profile of an inspection image, or the contrast of an image. In the defect inspection process in mask blank manufacture, when the inspection image of FIG.13(c) is obtained, it can be estimated that the defect size is a value exceeding 300 nm. Here, for example, if the allowable defect size is 100 nm, it is judged that there is a convex defect larger than the allowable value although not a fatal pinhole defect, and the photomask blank can be selected as a defective product.

From the above, in the photomask blank in which the thin hard mask thin film acting as an antireflection film is formed on the optical thin film, if the light intensity distribution of the inspection image of the defect is dominated by the bright part, the fatal pinhole defect, or the dark part is dominant, or the left part is the bright part and the right part If it is this dark part, it is a convex defect. These information were previously stored in the table shown in Fig. 9 as features of the inspection enlargement in the film structure A. And in the defect inspection in a 1st film|membrane form, with reference to the film|membrane structure A in a table, an accurate unevenness|corrugation determination could be performed, and fatal pinhole defect was able to be identified.

[Example 2]

Defect inspection of the photomask blank including concave defects and convex defects in the form of the second film was performed. As an inspection apparatus, the apparatus including the inspection apparatus 150 shown in FIG. 2 was used. However, the inspection wavelength was 355 nm, the numerical aperture NA of the objective lens OBL was 0.85, and since the resolution was higher than that of the inspection optical system used in Example 1, the illumination spot size was about 380 nm. The two-dimensional scanning area is the same as in Example 1 above. A photomask blank 100 shown in Fig. 14A is an optical thin film 122 with a thickness of 75 nm made of a MoSi-based material on a quartz substrate 101 transparent to inspection light, and Cr with a thickness of 10 nm The mask thin film 123 which consists of a system material is formed, and the state in which concave defect DEF10, such as a pinhole defect, exists in the hard mask thin film 123 is shown.

The concave defect DEF10 has a width of 80 nm and a depth D2 of 5 nm (concave defects that do not penetrate the hard mask thin film 123) and 10 nm (concave defects that pass through the hard mask thin film 123). Fig. 14(b) shows a cross-sectional profile in a region containing a defect of light intensity of the inspection image when it is set as . At any depth, on the defect inspection, the profile was dominated by dark areas and no highlights.

On the other hand, Fig. 15 (a) is a cross-sectional view of the photomask blank 100 including the convex defect DEF11 in the same second film form as the film structure shown in Fig. 14 (a). Defects in inspection enlargement when the composition of the convex defect DEF11 is made into two types: the hard mask thin film 123 itself made of a Cr-based material and a silicon foreign material (particle), and the width W2 is 80 nm and the height H2 is 10 nm. The cross-sectional profile of the region including the is shown in Fig. 15(b). In the inspection enlarged image of the convex defect, in any composition, the left side of the defect part became a bright part, and the right part became a dark part. Although the intensity level changes depending on a composition, it becomes the positional relationship of the same light intensity distribution (cross-sectional profile PR1) of the typical convex defect shown in FIG.3(d).

From the above, in the photomask blank in which a thin film such as a hard mask thin film made of a high reflectivity material is formed on the optical thin film, the light intensity distribution of the inspection image of the defect is a fatal pinhole defect if the dark part is dominant, the left is the bright part and the right is the right part If it is a dark part, it is a convex defect.

These information when the inspection wavelength was set to 355 nm were previously stored in the table shown in Fig. 9 as the characteristics of the inspection magnification in the film structure B. And in the defect inspection in the 2nd film|membrane form, with reference to the film|membrane structure B in a table, an accurate unevenness|corrugation determination could be performed, and fatal pinhole defect was able to be identified.

100: photomask blank
101: transparent substrate
102, 103, 112, 113, 122: optical thin film
103, 114, 12:3 processing auxiliary thin film or hard mask thin film
150: defect inspection device
151: inspection optical system
152: control device
153: recording device
154: display device
BM1: inspection light
BM2: reflected light
BSP: Beam Splitter
DEF1, DEF2, DEF5, DEF6, DEF7, DEF10: Concave defects or pinhole defects
DEF3, DEF4, DEF8, DEF9, DEF11: Convex defects
ILS: light source
L1: Lens
MB: photomask blank
OBL: objective lens
SE: photodetector
STG: Stage
SPF: Spatial Filter

Claims (18)

A method for inspecting defects on a photomask blank, comprising:
(A1) a step of preparing a photomask blank having at least one thin film on an optically transparent substrate, wherein the photomask blank bears defects on its surface;
(A2) moving the photomask blank to move the defect existing on the surface of the photomask blank to an observation position of the inspection optical system, and irradiating inspection light to the surface area where the defect exists, and the inspection light is irradiated a step of collecting reflected light from the obtained area as an enlarged image of the area through the inspection optical system;
(A3) extracting a feature amount representing distribution of light intensity from the enlarged image;
(A4) determining the shape of the defect based on the feature amount combined with the structure of the thin film of the photomask blank;
The magnified image in the step (A2) is generated as a diffraction component of the reflected light passing through the inspection optical system, and the higher-order diffraction component as the diffraction component is positive or negative with respect to the 0-order diffraction component (specular reflection component) of the reflected light. asymmetric
Defect inspection method of the photomask blank, characterized in that.
The method of claim 1,
(A3) process includes a processing step of comparing a change in the light intensity level of a defect area on the magnification with a light intensity level of a defect-surrounding area, whereby the light intensity level of the defect periphery Extracting the feature amount from a defect inspection image including an intensity difference between a bright part having a higher light intensity level and a dark part having a lower light intensity level, and an arrangement positional relationship between the bright part and the dark part
Defect inspection method of the photomask blank, characterized in that.
3. The method according to claim 1 or 2,
In the step (A4), a pinhole defect or a convex defect can be selected based on the data including the feature amount of the enlarged image and the structure of the thin film of the photomask blank, and based on optical simulation or experimental data in advance. With reference to the table, the shape of the defect is judged
Defect inspection method of the photomask blank, characterized in that.
4. The method of claim 3,
(A3) In the process (A3), the detected defect is a thin film whose outermost surface of the photomask blank to be inspected is a thin film transparent to the inspection light, when a feature amount of an image in which dark portions do not appear substantially and bright portions are dominant is extracted in the enlarged image of the defect. is judged to be a pinhole defect
Defect inspection method of the photomask blank, characterized in that.
4. The method of claim 3,
(A3) In the process (A3), when the feature amount of the image in which the bright part does not appear substantially and the dark part is dominant in the enlarged image of the defect is extracted, the photomask blank to be inspected shows that the inspection light reflectance of the thin film of the outermost layer is higher than the inspection light reflectance of the lower layer. If it has a high film structure, it is determined that the detected defect is a pin hole defect.
Defect inspection method of the photomask blank, characterized in that.
3. The method according to claim 1 or 2,
The film thickness of the said thin film is 10 nm or less
Defect inspection method of the photomask blank, characterized in that.
3. The method according to claim 1 or 2,
that the inspection light is light with a wavelength of 210 to 550 nm
Defect inspection method of the photomask blank, characterized in that.
A system for inspecting defects on a photomask blank having at least one thin film on an optically transparent substrate, the system comprising:
an inspection device for irradiating inspection light to the surface area of the thin film, taking reflected light from the area irradiated with the inspection light, and inspecting defects present on the surface of the photomask blank;
A computer having a program for executing the process of the method for inspecting a photomask blank according to claim 1 or 2;
Defect inspection system for photomask blanks.
Selecting a photomask blank that does not contain a pinhole defect based on a determination as to whether a defect is a bump or a pit shape by the defect inspection method of a photomask blank according to claim 1 or 2 to include
A method of screening a photomask blank, characterized in that
A method for manufacturing a photomask blank, comprising:
forming a thin film of at least one layer on an optically transparent substrate to form a photomask blank;
Step of sorting a photomask blank containing no pinhole defects by the photomask blank screening method according to claim 9
A method of manufacturing a photomask blank comprising a.
A method for inspecting defects on a photomask blank, comprising:
(A1) a step of preparing a photomask blank having at least one thin film on an optically transparent substrate, wherein the photomask blank bears defects on its surface;
(A2) moving the photomask blank to move the defect existing on the surface of the photomask blank to an observation position of the inspection optical system, and irradiating inspection light to the surface area where the defect exists, and the inspection light is irradiated a step of collecting reflected light from the obtained area as an enlarged image of the area through the inspection optical system;
(A3) a step of extracting a feature amount from the enlarged image;
(A4) determining the shape of the defect based on the feature amount combined with the structure of the thin film of the photomask blank;
In the step (A4), a pinhole defect or a convex defect can be selected based on the data including the feature amount of the enlarged image and the structure of the thin film of the photomask blank, and based on optical simulation or experimental data in advance. With reference to the table in which the shape of the defect is determined,
i) In the process (A3), in the case where the feature amount that the dark portion does not appear substantially and the bright portion is dominant image is extracted in the enlarged image of the defect, if the outermost surface of the photomask blank to be inspected is a thin film transparent to the inspection light, the detected The defect is determined to be a pin hole defect, or,
ii) In the process (A3), in the case where the bright part does not appear substantially in the enlarged image of the defect and the feature amount that the dark part is dominant image is extracted, the photomask blank to be inspected has the inspection light reflectance of the outermost thin film and the inspection light of the lower layer If it has a film structure higher than the reflectance, it is determined that the detected defect is a pinhole defect.
Defect inspection method of the photomask blank, characterized in that.
12. The method of claim 11,
The magnified image in the step (A2) is generated as a diffraction component of the reflected light passing through the inspection optical system, and the higher-order diffraction component as the diffraction component is positive or negative with respect to the 0-order diffraction component (specular reflection component) of the reflected light. asymmetric
Defect inspection method of the photomask blank, characterized in that.
13. The method according to claim 11 or 12,
(A3) process includes a processing step of comparing a change in the light intensity level of a defect area on the magnification with a light intensity level of a defect-surrounding area, whereby the light intensity level of the defect periphery Extracting the feature amount from a defect inspection image including an intensity difference between a bright part having a higher light intensity level and a dark part having a lower light intensity level, and an arrangement positional relationship between the bright part and the dark part
Defect inspection method of the photomask blank, characterized in that.
13. The method according to claim 11 or 12,
The film thickness of the said thin film is 10 nm or less
Defect inspection method of the photomask blank, characterized in that.
13. The method according to claim 11 or 12,
that the inspection light is light with a wavelength of 210 to 550 nm
Defect inspection method of the photomask blank, characterized in that.
A system for inspecting defects on a photomask blank having at least one thin film on an optically transparent substrate, the system comprising:
an inspection device for irradiating inspection light to the surface area of the thin film, taking reflected light from the area irradiated with the inspection light, and inspecting defects present on the surface of the photomask blank;
A computer having a program for executing the process of the method for inspecting a photomask blank according to claim 11 or 12;
Defect inspection system for photomask blanks.
Based on the determination as to whether the defect is a bump or a pit shape by the defect inspection method of the photomask blank according to claim 11 or 12, a photomask blank containing no pinhole defect is selected to include
A method of screening a photomask blank, characterized in that
A method for manufacturing a photomask blank, comprising:
forming a thin film of at least one layer on an optically transparent substrate to form a photomask blank;
A step of sorting a photomask blank containing no pinhole defects by the photomask blank screening method according to claim 17 .
A method of manufacturing a photomask blank comprising a.

Images