JP7494672B2 - Photomask blanks, photomask blanks manufacturing method, learning method, and photomask blanks inspection method - Google Patents

Description

The present invention relates to photomask blanks, a manufacturing method for photomask blanks, a learning method, and a method for inspecting photomask blanks.

Conventionally, defects have been inspected using reflected light from photomask blanks (for example, see Patent Document 1). However, it has been difficult to inspect tiny defects called half pinholes by only measuring reflected light.

JP 2018-120211 A

According to a first aspect, there is provided a photomask blank having a laminated film including a first layer and a second layer on a glass substrate, wherein the laminated film has 0.003 or less half pinholes/cm2 or less having a size of 1 μm or more and ³ μm or less.
According to a second aspect, a method for manufacturing a photomask blank includes a step of forming a photomask blank by forming a laminated film including a first layer and a second layer on a glass substrate, a first inspection step of acquiring first information including information regarding a position of a foreign matter in the laminated film, a cleaning step of cleaning the photomask blank after the first inspection step, a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step, and a half pinhole detection step of detecting a half pinhole based on the second information.
According to a third aspect, a learning method includes a step of forming a photomask blank by forming a laminated film including a first layer and a second layer on a glass substrate, a first inspection step of acquiring first information including information regarding a position of a foreign matter in the laminated film, a step of acquiring information regarding a size of the foreign matter, a cleaning step of cleaning the photomask blank after the first inspection step, a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step, and a learning step of learning the relationship between the first information, the information regarding the size of the foreign matter, and the second information.
According to a fourth aspect, a method for inspecting a photomask blank having a laminated film including a first layer and a second layer on a glass substrate includes a first inspection step of acquiring first information including information regarding a position of a foreign matter in the laminated film, a cleaning step of cleaning the photomask blank after the first inspection step, a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step, and a half pinhole detection step of detecting a half pinhole based on the second information.

FIG. 2 is a diagram illustrating a cross-sectional structure of a photomask blank according to an embodiment. 1 is a flowchart illustrating a method for manufacturing a photomask blank in an embodiment. 1 is a block diagram illustrating an example of a configuration of a main part of an inspection device according to an embodiment. FIG. 10 is a diagram illustrating an example of a movement path of an inspection position during an inspection process. FIG. 13 is a diagram showing the relationship between a foreign substance detected at an inspection position in a first inspection process and a defect detected at the same position in a second inspection process in an embodiment. FIG. 11 is a block diagram illustrating an example of a main process of an inspection device in Modification 1. 13 is a flowchart illustrating a learning method in the first modified example. 11 is a flowchart illustrating a method for manufacturing a photomask blank in Modification 1.

Hereinafter, the embodiments will be described in detail with reference to the drawings.
In the photomask blank of the present embodiment, the number of half pinholes having a size of 1 μm or more and 3 μm or less in the laminate film formed on the glass substrate is 0.003 pieces/cm ² or less.
Fig. 1 shows a schematic cross-sectional structure of a photomask blank 1 according to the present embodiment. For convenience of explanation, an orthogonal coordinate system consisting of an X-axis, a Y-axis, and a Z-axis is set as shown in Fig. 1. That is, the X-axis is set in the horizontal direction of the paper surface of Fig. 1, the Z-axis is set in the vertical direction of the paper surface, and the Y-axis is set in a direction perpendicular to the X-axis and Z-axis (into the depth direction of the paper surface). In Fig. 1, the top surface of the photomask blank 1 is shown parallel to the XY plane.

Figure 1 (a) shows a schematic cross-sectional structure of a photomask blank. The laminated film 11 includes a light-shielding layer 12, which is a first layer, and an anti-reflection layer 13, which is a second layer, on a glass substrate 10. The glass substrate 10 is, for example, synthetic quartz glass. The light-shielding layer 12 is, for example, a metal thin film such as chromium, and the anti-reflection layer 13 is, for example, a metal oxide thin film such as chromium oxide. In this embodiment, as shown in the figure, the film thickness of the light-shielding layer 12 is greater than the film thickness of the anti-reflection layer 13. The film thickness of the light-shielding layer 12 is, for example, 80 nm, and the film thickness of the anti-reflection layer 13 is, for example, 20 nm.

Next, a method for manufacturing and inspecting the above-mentioned photomask blanks 1 will be described with reference to the flow chart shown in FIG.
In step S1, a photomask blank 1 is formed by depositing a light-shielding layer 12 and an anti-reflection layer 13, which are a laminated film 11, on a glass substrate 10 (a formation step). In step S2, an inspection device described below is used to identify the position of a foreign object in the laminated film 11 of the photomask blank 1, and first information including information on the position of the foreign object is obtained (a first inspection step). Examples of foreign objects include fragments of material from a target when the laminated film 11 is deposited by a sputtering method, and material peeled off from a shield in a deposition device.

In step S3, the photomask blank 1 after the first inspection step is cleaned (cleaning step). In step S4, second information including image information at the position of the foreign object identified in the first inspection step is obtained for the photomask blank 1 after the cleaning step (second inspection step). In step S5, it is determined whether or not a predetermined determination criterion is satisfied based on the second information (determination step).
The process performed in each of the above steps will be described in detail below. Note that the inspection method may be performed by performing the above steps S2 (first inspection step) to S5 (determination step).

<Forming process>
When forming the laminated film 11 on the glass substrate 10, for example, a known sputtering method or the like can be applied. As the sputtering method, either a bipolar sputtering method or a magnetron sputtering method can be applied. As the power source for sputtering, either a direct current power source or a high frequency power source can be applied. By the sputtering method or the like, the light-shielding layer 12 is formed on the glass substrate 10, and further, the anti-reflection layer 13 is formed on the light-shielding layer 12.

<Inspection equipment>
Here, the inspection device 20 used in the first inspection process and the second inspection process will be described. Fig. 3 is a block diagram for explaining the main configuration of the inspection device 20. The inspection device 20 has a light source 21, a first detection unit 22, a second detection unit 23, a third detection unit 24, an imaging unit 25, a driving unit 26, a control unit 27, a mounting table 28, a light source 29, and a light source 31. The light source 21, the first detection unit 22, the second detection unit 23, the third detection unit 24, the imaging unit 25, the light source 29, and the light source 31 are accommodated in the same inspection unit 30. Note that in Fig. 3 as well, an orthogonal coordinate system consisting of an X-axis, a Y-axis, and a Z-axis is set as in Fig. 1.
The light source 21 emits, for example, a laser beam toward the photomask blank 1 placed on the placement table 28, that is, toward the negative Z direction in Fig. 3. The light source 21 emits, for example, a laser beam having a wavelength of 532 nm.

The first detector 22 is disposed on the same side of the photomask blanks 1 as the light source 21 (i.e., the + side in the Z direction). The first detector 22 is, for example, a photomultiplier tube, and is disposed at a position offset from the optical axis of the laser light from the light source 21. As a result, it receives scattered light (backscattered light) of the laser light from the light source 21 that is scattered by the photomask blanks 1 and travels toward the + side in the Z direction. The first detector 22 outputs a detection signal (first detection signal) corresponding to the intensity of the received backscattered light to the control unit 27.

The second detector 23 is disposed on the opposite side of the photomask blanks 1 to the light source 21 (i.e., the - side in the Z direction). The second detector 23 is, for example, a photomultiplier tube, and is disposed at a position offset from the optical axis of the laser light from the light source 21. As a result, it receives scattered light (forward scattered light) of the laser light from the light source 21 that passes through the photomask blanks 1 and travels toward the - side in the Z direction. The second detector 23 outputs a detection signal (second detection signal) corresponding to the intensity of the received forward scattered light to the control unit 27.

The third detector 24 is disposed on the same side (+ side in the Z direction) as the light source 21 with respect to the photomask blanks 1. The third detector 24 is, for example, an image sensor (photodiode), and receives reflected light from the laser light from the light source 21 that is reflected by the photomask blanks 1 and travels toward the + side in the Z direction. The third detector 24 also receives scattered light (backscattered light) scattered by the photomask blanks 1, but since the intensity of the scattered light is so low that it is difficult to detect with the sensitivity of the third detector 24, the third detector 24 essentially detects only the reflected light. The third detector 24 outputs a detection signal (third detection signal) corresponding to the intensity of the received reflected light to the control unit 27.
The imaging unit 25 captures an image obtained by, for example, differential interference observation. Differential interference observation is performed using an objective lens with a relatively high magnification, and for example, the magnification of the objective lens is preferably 50 times or more. The imaging unit 25 captures reflected light from the light source 29 that is reflected by the surface of the photomask blanks 1 (i.e., the anti-reflection layer 13) and travels toward the + side in the Z direction. In addition, the imaging unit 25 captures transmitted light from the light source 31 provided on the - side of the photomask blanks 1 in the Z direction that passes through the photomask blanks 1 toward the + side in the Z direction. The light source 29 and the light source 31 are, for example, white LEDs. An image signal obtained by imaging is output to the control unit 27.

The driving unit 26 has, for example, a motor and a guide rail, and is controlled by the control unit 27 to change the relative positional relationship between the inspection unit 30 and the mounting table 28 (i.e., the photomask blank 1). The driving unit 26 changes the relative positional relationship between the inspection unit 30 and the mounting table 28, for example, by moving the inspection unit 30 in at least one of the X direction and the Y direction. The driving unit 26 may also change the relative positional relationship by moving the mounting table 28 in at least one of the X direction and the Y direction. The driving unit 26 causes the inspection unit 30 (i.e., the light source 21, the first detector 22, the second detector 23, the third detector 24, and the imaging unit 25) to move two-dimensionally on the XY plane relative to the photomask blank 1, so that the inspection unit 30 can perform two-dimensional scanning on the surface of the photomask blank 1 on the XY plane.

The control unit 27 is a processor that includes a microprocessor and its peripheral circuits, and controls each part of the inspection device 20 by reading and executing a control program prestored in a storage medium (e.g., a flash memory, etc.) not shown. The control unit 27 may be configured with a CPU, an ASIC, a programmable MPU, etc. The control unit 27 includes a light source control unit 271, a drive control unit 272, a light receiving control unit 273, an inspection unit 274, an image generation unit 275, and a judgment unit 276. The light source control unit 271 controls the operation of the light source 21 (e.g., the emission intensity and emission timing of the laser light, etc.). The drive control unit 272 outputs a signal to the drive unit 26 instructing the amount and direction of movement of the inspection unit 30 relative to the mounting table 28 in order to perform the above-mentioned two-dimensional scanning. The light receiving control unit 273 controls the first detector 22, the second detector 23, the third detector 24, and the imaging unit 25 to output a first detection signal, a second detection signal, a third detection signal, and an imaging signal, respectively. The inspection unit 274 inspects the position of defects and the state of defects in the laminated film 11 of the photomask blanks 1 based on the first detection signal, the second detection signal, and the third detection signal. The image generation unit 275 generates image data of the laminated film 11 of the photomask blanks 1 based on the imaging signal output from the imaging unit 25, and displays an image of the laminated film 11 on a display monitor (not shown).

<First inspection process>
The inspection device 20 having the above configuration is used to inspect the laminated film 11 of the photomask blank 1 formed in the formation process. In the first inspection process, first information including the position of a foreign object in the laminated film 11 and its detection intensity is obtained. Details of the first inspection process are described below. In the following example, an example in which all of the first detection signal, second detection signal, and third detection signal are detected in the first inspection process will be described, but only the first detection signal may be detected.
The drive control unit 272 controls the drive unit 26 to move the inspection unit 30 to a predetermined position (inspection position) in the XY plane relative to the photomask blanks 1. When the inspection unit 30 reaches the inspection position, the light source control unit 271 causes the light source 21 to emit laser light at a predetermined intensity. The light receiving control unit 273 controls the first detector 22, the second detector 23, and the third detector 24 to output a first detection signal from the first detector 22, a second detection signal from the second detector 23, and a third detection signal from the third detector 24. The first detection signal is a signal corresponding to the intensity of the backscattered light described above among the scattered light from the laser light from the light source 21 scattered by the laminated film 11 of the photomask blanks 1. The second detection signal is a signal corresponding to the intensity of the forward scattered light described above among the scattered light from the laser light from the light source 21 scattered by the laminated film 11. The third detection signal is a photoelectric conversion signal corresponding to the intensity of the reflected light from the laser light from the light source 21 reflected by the laminated film 11.
The inspection unit 274 stores the output first detection signal, second detection signal, and third detection signal in a memory (not shown) in association with position information indicating the coordinates of the inspection position, etc. Note that it is not necessary to associate all of the first detection signal, second detection signal, and third detection signal with position information, and any one or more of the detection signals may be associated with the position information.

Next, the drive control unit 272 controls the drive unit 26 to move the inspection unit 30 to an inspection position different from the above inspection position. The amount of movement at this time may be a predetermined amount of movement, or may be an amount of movement set by the user via, for example, an input device (not shown). At the new inspection position, an operation similar to the above-mentioned operation is performed, and the first detection signal, second detection signal, and third detection signal at the different inspection position are associated with position information and stored in memory.

The drive control unit 272 moves the inspection unit 30 to the inspection position so as to inspect the entire surface of the laminated film 11 of the photomask blank 1 .
Fig. 4 shows a schematic example of a movement path of the inspection position. Fig. 4 shows a case where the shape of the photomask blank 1 in the XY plane is rectangular. In this embodiment, the drive control unit 272 controls the drive unit 26 so that the inspection unit 30 moves in the XY plane along a path shown by the arrow Ar in Fig. 4, for example. The first detection signal, the second detection signal, and the third detection signal at a plurality of inspection positions on this path are associated with position information and stored in memory.

The inspection unit 274 detects foreign matter in the laminated film 11 based on the signal intensity of the acquired first detection signal.
Here, examples of foreign matter in the laminated film 11 detected by the inspection unit 274 are shown in Figs. 1(b) and (c). Figs. 1(b) and (c) are schematic cross-sectional views of the photomask blanks 1, showing a state in which foreign matter is present in the laminated film 11. Fig. 1(b) shows a case in which a foreign matter F1 is included across the light-shielding layer 12 and the anti-reflection layer 13 of the laminated film 11. Fig. 1(c) shows a case in which a foreign matter F2 is included only in the anti-reflection layer 13 of the laminated film 11, and is not included in the light-shielding layer 12. Note that these foreign matters shown in Figs. 1(b) and (c) will fall off in a later cleaning process, but at this time, partial peeling of the laminated film 11 may occur as shown in Figs. 1(d) and (e). Fig. 1(d) shows an opening (hereinafter referred to as a pinhole) F3 penetrating the light-shielding layer 12 and the anti-reflection layer 13 of the laminated film 11. FIG. 1E shows an opening F4 (hereinafter referred to as a half pinhole) that penetrates only the antireflection layer 13 of the laminated film 11 and exposes a part of the upper surface of the light-shielding layer 12.

When a foreign object present in the laminated film 11 is irradiated with laser light from the light source 21, the foreign object generates scattered light. The inspection unit 274 receives the scattered light (backscattered light) with the first detector 22 and detects a first detection signal. If the signal strength of the first detection signal is equal to or greater than a predetermined first threshold, it is determined that a foreign object exists. In this embodiment, the first threshold is set to, for example, 500, but is an arbitrary unit and can be set appropriately depending on the device used, etc. In this embodiment, a first detection signal with a signal strength of less than 500 is considered to be at the noise level.
When a pinhole in the laminated film 11 is irradiated with laser light from the light source 21, scattered light occurs at the edge of the pinhole. The inspection unit 274 receives the scattered light (forward scattered light) passing through the photomask blank 1 with the second detector 23 and detects a second detection signal. If the signal strength of the second detection signal is equal to or greater than a predetermined second threshold, it is determined to be a pinhole (see FIG. 1(d)). In this embodiment, the second threshold is set to, for example, 300, but is an arbitrary unit and can be set appropriately depending on the device used, etc. In this embodiment, a second detection signal with a signal strength of less than 300 is considered to be at the noise level.
When the laser light from the light source 21 is irradiated onto the half pinhole 1 present in the laminated film 11, light is reflected from the exposed light-shielding layer 12. Reflected light may also occur in an area where the anti-reflection layer 13 is normally formed, but the half pinhole has a stronger reflected light because the anti-reflection layer 13 is not formed therein. The inspection unit 274 receives the reflected light with the third detector 24 and detects a third detection signal. When the signal strength of the third detection signal is equal to or greater than a third threshold value, it is determined to be a half pinhole. In this embodiment, the third threshold value is set to, for example, 370, but is an arbitrary unit and can be set appropriately according to the device used. In this embodiment, a third detection signal having a signal strength of less than 370 is considered to be at the noise level.
When the inspection unit 274 detects a defect as described above, it acquires the signal intensity of each detection signal for the defect and the associated position information of the defect as first information and records it in a memory (not shown). Note that the inspection unit 274 may record only the position information associated with the detection signal when the defect is detected as the first information in the memory. Note that the defect in this embodiment refers to the above-mentioned foreign matter, pinhole, and half pinhole.
As described above, the drive control unit 272 causes the inspection unit 30 to two-dimensionally scan the photomask blank 1 in the XY plane. This allows the inspection unit 274 to detect a position where a defect has occurred in the laminated film 11 of the photomask blank 1, and obtain first information including information on the detected position.

<Cleaning process>
The cleaning is carried out by a known method such as cleaning with an acid such as sulfuric acid or ozone cleaning with ozone water or UV ozone, and foreign matter and the like adhering to the laminated film 11 is removed.
The cleaning process peels off the foreign matter attached to the laminated film 11. As described above, when the foreign matter F1 shown in Fig. 1(b) peels off, a pinhole F3 shown in Fig. 1(d) may occur in the laminated film 11. When the foreign matter F2 shown in Fig. 1(c) peels off, a half pinhole F4 shown in Fig. 1(e) may occur in the laminated film 11.

<Second inspection process>
The laminate film 11 of the photomask blank 1, which has been cleaned in the cleaning process, is inspected. In the second inspection process, at the position where the foreign matter was detected in the first inspection process (i.e., the position where the signal strength of the first detection signal in the first inspection process was equal to or greater than a predetermined first threshold), light is irradiated from the light source 29 and the light source 31, and a reflected image and a transmitted image of the surface of the laminate film 11 are captured by the imaging unit 25, and second information including imaging information at the position where the inspection was performed is obtained.

The drive control unit 272 controls the drive unit 26 to move the imaging unit 25 to the position (specific inspection position) specified by the first information. The imaging unit 25 images the surface of the laminated film 11 of the photomask blank 1 at the position moved by the drive unit 26 and outputs a signal obtained by the imaging to the control unit 27, and the image generation unit 275 generates image data of the laminated film 11 at the above-mentioned specified position based on the input signal. By performing the above process at all specific inspection positions, image data regarding the state of the laminated film 11 of the photomask blank 1 at the specific inspection position is generated.

After the cleaning process, an inspection similar to the first inspection process may be performed as necessary. The inspection similar to the first inspection process may be performed before the second inspection process, after the second inspection process, or simultaneously with the second inspection process.

<Determination step>
The determination unit 276 determines whether the half pinhole in the laminated film 11 satisfies a predetermined determination criterion based on the second information acquired in the second inspection process. More specifically, first, when a defect is detected only in the reflected image out of the reflected image and the transmitted image at the position where the foreign matter is detected (i.e., the position where the signal strength of the first detection signal in the first inspection process is equal to or greater than the predetermined first threshold), it is determined that the foreign matter is a half pinhole. Note that, when a defect is detected in both the reflected image and the transmitted image, it is determined that the foreign matter is a pinhole. Then, the size of the half pinhole is obtained based on the above-mentioned image data, and it is determined whether the half pinhole satisfies the predetermined determination criterion. As an example of the predetermined determination criterion, the number of half pinholes in the laminated film 11 that is 1 μm or more and 3 μm or less is 0.003 pieces/cm2 ^or less (i.e., 22 pieces or less in the case of a photomask blank 1 having a size of 800 mm x 920 mm, and 51 pieces or less in the case of a photomask blank 1 having a size of 1220 mm x 1400 mm).

The half pinholes (hereinafter referred to as micro half pinholes) of 1 μm or more and 3 μm or less, which are the above-mentioned predetermined judgment criteria, correspond to, for example, half pinholes F4 as shown in FIG. 1(e) that are generated when foreign matter F2 as shown in FIG. 1(c) is peeled off during the cleaning process. Such micro half pinholes have an extremely small intensity of backscattered light when irradiated with laser light, making them difficult to detect in the inspection performed in the first inspection process. For this reason, it is difficult to detect micro half pinholes unless the second inspection process is performed.

In this embodiment, first information on the position of a foreign matter F2 (see FIG. 1(c)) that will cause a tiny half pinhole to occur after the cleaning process is identified as a specific inspection position based on a first detection signal from the first inspection process. Furthermore, in a second inspection process after the cleaning process, second information on the specific inspection position identified by the first information is obtained. The judgment unit 276 judges whether the number of the tiny half pinholes is equal to or less than a predetermined value (0.003 pieces/ ^cm2 ) based on the second information.

According to the above-described embodiment, the following advantageous effects can be obtained.
The manufacturing method of the photomask blank 1 includes a formation step of forming the photomask blank 1 by forming a laminate film 11 including a light-shielding layer 12 and an anti-reflection layer 13 on a glass substrate 10, a first inspection step of acquiring first information including information regarding the position of a foreign substance in the laminate film 11, a cleaning step of cleaning the photomask blank 1 after the first inspection step, a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step, and a judgment step of judging whether or not a predetermined judgment criterion is satisfied based on the second information.
The inspection method for a photomask blank 1 having a laminate film 11 including a light-shielding layer 12 and an anti-reflection layer 13 on a glass substrate 10 includes a first inspection step of acquiring first information including information regarding the position of a foreign substance in the laminate film 11, a cleaning step of cleaning the photomask blank 1 after the first inspection step, a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step after the cleaning step, and a judgment step of judging whether or not a predetermined judgment criterion is satisfied based on the second information.
As a result, minute half pinholes occurring in the laminated film 11 are detected, so that the inspection accuracy can be improved, contributing to the improvement of the quality of the photomask blanks 1. In addition, since the position of the foreign matter is specified before cleaning, the minute half pinhole can be detected by simply inspecting the position in the second inspection process after cleaning. Although it is possible to inspect the entire laminated film 11 with the imaging unit 25 and detect the minute half pinhole, it takes a huge amount of time because it is necessary to image the area that can be imaged by the imaging unit 25 one by one. In this embodiment, the minute half pinhole can be detected by inspecting the position of the foreign matter specified in advance with the imaging unit 25 after cleaning, so that the inspection time can be significantly reduced compared to the case where the entire surface of the laminated film 11 is inspected with the imaging unit 25.

[Example]
In FIG. 5, each of the measurement data 1 to 5 indicates each data measured at a position where it was determined that a foreign object exists in the first inspection process before the cleaning process. Each measurement data includes an inspection position and detection values of the first detection signal, the second detection signal, and the third detection signal before and after the cleaning process. The inspection position indicates the X coordinate and Y coordinate values of the position where the measurement data 1 to 5 were measured in the photomask blank 1. In FIG. 5, category 1 indicates the result of the determination that a foreign object exists in the first inspection process and the size of the foreign object measured using the image signal of the foreign object captured by the imaging unit 25 using an objective lens with a magnification of 50 times, and category 2 indicates the result of the determination that a foreign object exists as a pinhole or a half pinhole based on the second inspection process and the size of the foreign object measured using the image data captured by the imaging unit 25 using an objective lens with a magnification of 50 times.

As shown in FIG. 5, before the cleaning process, the first detection signal is equal to or greater than the first threshold (500 in this embodiment), the second detection signal is less than the second threshold (300 in this embodiment), and the third detection signal is less than the third threshold (370 in this embodiment). That is, as shown in category 1, it is determined to be a foreign body by the first inspection process before the cleaning process. When the photomask blank 1 for which such a measurement result was obtained before the cleaning process is measured in the same manner after the cleaning process, the values of the first detection signal, the second detection signal, and the third detection signal in the measurement data 1 and the measurement data 2 are all below the detection limit, and no signal is detected. On the other hand, the signal strength of the second detection signal in the measurement data 3 is equal to or greater than the second threshold, the signal strength of the third detection signal in the measurement data 4 is equal to or greater than the third threshold, and the signal strength of the third detection signal in the measurement data 5 is equal to or greater than the third threshold.

From the above, the following can be seen. When only the same inspection as the first inspection process is performed on the photomask blanks 1 after the cleaning process, in the measurement data 3 to 5, defects can be detected based on the first detection signal, the second detection signal, and the third detection signal, but in the measurement data 1 and 2, the first detection signal, the second detection signal, and the third detection signal are below the detection limit, so it is determined that there is no defect at the position where the foreign matter was detected. However, it can be seen that by inspecting the laminated film with the imaging unit 25 after the cleaning process, half pinholes of sizes 1 μm and 1.2 μm can be detected, as shown in classification 2. In other words, when inspecting a minute half pinhole of size 3.0 μm or less after the cleaning process, it cannot be detected with the third detector, and it is effective to inspect the laminated film with the imaging unit 25 having a high magnification objective lens as in this embodiment. And in this embodiment, the first inspection process is performed before the cleaning process of the photomask blanks 1 to identify the position of the foreign matter, and the identified position of the foreign matter is inspected by the imaging unit 25 after the cleaning process (second inspection process) to detect the minute half pinhole. By inspecting in this manner, the inspection time can be significantly reduced compared to inspecting the entire surface of the laminated film using the imaging unit 25 after the cleaning process.

The following modifications are also within the scope of the present invention, and one or more of the modifications may be combined with the above-described embodiment.
(Variation 1)
The relationship between the first information acquired in the first inspection step by the inspection device 20 in the above-mentioned embodiment, the information on the size of the foreign matter, and the second information acquired in the second inspection step may be learned. The information on the size of the foreign matter is, for example, an image of the foreign matter captured by the imaging unit 25 or the size of the foreign matter measured using the image. In this case, as shown in the block diagram of FIG. 6, the control unit 27 of the inspection device 201 has a learning unit 279. The other configuration is the same as the configuration of the inspection device 20 in the embodiment shown in FIG. 3. The learning unit 279 performs learning, for example, by a neural network using the acquired first information, information on the size of the foreign matter, and the second information. It is to be noted that a known method is used for learning by the neural network. For example, the neural network uses the first information and information on the size of the foreign matter as input data, and uses information on the minute half pinhole at the position included in the first information as output data. For example, when the control unit 27 acquires the first information, information relating to the size of the foreign object, and second information, and registers the relationship between the first information, the information relating to the size of the foreign object, and the second information, the control unit 27 performs learning using a neural network using the second information as teacher data (correct answer data).

FIG. 7 is a flowchart for explaining a learning method when the inspection device 201 performs learning.
Each process from step S11 (forming process) to step S14 (second inspection process) is shown similarly to each process from step S1 (forming process) to step S4 (second inspection process) shown in FIG. 2, but here, it is assumed that the process of acquiring information on the size of the foreign matter is carried out simultaneously with step 12 (first inspection process). The information on the size of the foreign matter may be acquired by the imaging unit 25 simultaneously with step 12 (first inspection process), or may be acquired after step 12 (first inspection process). In step S15, the learning unit 279 learns the relationship between the first information acquired in the first inspection process, the information on the size of the foreign matter, and the second information acquired in the second inspection process (learning process), and ends the process.

In the case where the inspection device 201 learns as described above and uses the learning result, when manufacturing the photomask blanks 1, the judgment unit 276 of the control unit 27 inputs the first information acquired in the first inspection process and information on the size of the foreign matter to the learning unit 279 that has learned by the above learning method, and judges whether the photomask blanks 1 after the cleaning process meets a predetermined judgment criterion. That is, unlike the case of the embodiment, the inspection device 201 does not perform the second inspection process. By inputting the first information acquired in the first inspection process and information on the size of the foreign matter, the learning unit 279 outputs information indicating whether the defect at the specific position is a minute half pinhole based on the learning result. The judgment unit 276 counts the number of pieces of information indicating a minute half pinhole among the pieces of information output by the learning unit 279, and judges the photomask blanks 1 to be a non-defective product when the counted number is equal to or less than a predetermined value (0.003 pieces/cm ² ).

FIG. 8 is a flowchart illustrating the manufacturing method of the photomask blanks 1 performed by the inspection device 201.
Each process from step S21 (forming process) to step S23 (cleaning process) is the same as each process from step S1 (forming process) to step S3 (cleaning process) shown in Fig. 2. In step S24, the determination unit 276 inputs the first information acquired in the first inspection process and information on the size of the foreign matter to the learning unit 279, counts the number of minute half pinholes based on the information output from the learning unit 279, and determines that the photomask blank 1 is good or bad if the counted number is equal to or less than a predetermined value (determination process), and ends the process.

By the above process, it is possible to detect minute half pinholes occurring in the laminated film 11 and judge the quality of the photomask blanks 1 without performing the second inspection process. As a result, it is possible to shorten the time required for manufacturing the photomask blanks 1. Note that, in the process shown in FIG. 8, an embodiment in which the judgment process is performed after the cleaning process has been described, but this is not limited to this. For example, the judgment process may be performed after the first inspection process and before the cleaning process. Also, the judgment process may be performed after the first inspection process, and the product may be shipped without performing the cleaning process. Note that in this case, the cleaning process may be performed in a different factory, etc.

(Variation 2)
The judgment unit 276 may detect minute half pinholes based only on the transmission image acquired by the imaging unit 25 during the second inspection step, and judge the quality of the photomask blanks 1 based on the number of detected minute half pinholes. In this case, the image generation unit 275 gradates the defect and a predetermined number of pixels around it based on image data generated based on a signal from the imaging unit 25. The image generation unit 275 extracts the maximum gradation value (i.e., the brightest point in the image corresponding to the defect).

Generally, pinholes have brighter areas in the captured image than half pinholes. That is, the maximum value of gradation on the captured image is larger. If the maximum value of gradation is smaller than a predetermined value, the determination unit 276 determines that the defect is a minute half pinhole. In this case, the predetermined value may be set to a preferable value by simulation, testing, or the like. The determination unit 276 counts the number of defects determined to be minute half pinholes as described above, and determines the photomask blank 1 as a non-defective product if the counted number is equal to or less than a predetermined value (0.003 pieces/ ^cm2 ).

Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments that are conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention.

Reference Signs List 1... photomask blank 10... glass substrate 11... laminated film 12... light-shielding layer 13... anti-reflection layer 20, 201... inspection device 22... first detector 23... second detector 24... third detector 27... control unit 274... inspection unit 276... judgment unit 279... learning unit

Claims (26)

forming a photomask blank by forming a laminated film including a first layer and a second layer on a glass substrate;
a first inspection step of acquiring first information including information regarding a position of a foreign substance in the laminated film;
a cleaning step of cleaning the photomask blanks after the first inspection step;
a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step after the cleaning step;
and detecting a half pinhole based on the second information. 2. The method for producing a photomask blank according to claim 1 ,
The method for producing a photomask blank, wherein the first layer is a light-shielding layer and the second layer is an anti-reflection layer. 3. The method for producing a photomask blank according to claim 1 ,
The method for producing a photomask blank, wherein the first layer contains chromium and the second layer contains chromium and oxygen. 4. The method for producing a photomask blank according to claim 1 ,
In the first inspection step, light scattered from the laminated film is detected. 5. The method for producing a photomask blank according to claim 1 ,
In the second inspection step, an image of reflected light from the laminated film is captured. 6. The method for producing a photomask blank according to claim 5 ,
a determination step of determining whether or not the half pinhole detected in the half pinhole detection step satisfies a predetermined determination criterion,
In the determination step, it is determined whether or not the determination criterion is satisfied based on the intensity of the reflected light.
A method for manufacturing photomask blanks. 7. The method for producing a photomask blank according to claim 6 ,
A method for manufacturing photomask blanks, wherein the judgment criteria include a number of half pinholes having a diameter of 1 μm or more and 3 μm or less in the laminated film being 0.003 pcs/ ^cm2 or less. The method for producing a photomask blank according to any one of claims 1 to 7 ,
The method for manufacturing photomask blanks, wherein in the second inspection step, the imaging information is generated at a magnification of 50 times or more. 9. The method for producing a photomask blank according to claim 1, wherein in the cleaning step, the foreign matter at least a part of which is contained inside the laminated film is removed from the laminated film. The method for producing a photomask blank according to any one of claims 1 to 9,
A method for manufacturing a photomask blank, wherein the half pinhole is an opening that penetrates the first layer in the laminated film but does not penetrate the second layer. forming a photomask blank by forming a laminated film including a first layer and a second layer on a glass substrate;
a first inspection step of acquiring first information including information regarding a position of a foreign substance in the laminated film;
acquiring information regarding the size of the foreign object;
a cleaning step of cleaning the photomask blanks after the first inspection step;
a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step after the cleaning step;
a learning step of learning a relationship between the first information, the information relating to the size of the foreign matter, and the second information. The learning method according to claim 11 ,
A learning method, wherein in the first inspection step, scattered light from the laminated film is detected and an image of reflected light from the laminated film is captured. The learning method according to claim 11 or 12 ,
A learning method, wherein in the second inspection step, an image of reflected light from the laminated film is captured. A learning method according to any one of claims 11 to 13 ,
A learning method, wherein in the second inspection step, the imaging information is generated using an objective lens having a magnification of 50 times or more. forming a photomask blank by forming a laminated film including a first layer and a second layer on a glass substrate;
a first inspection step of acquiring first information including information regarding a position of a foreign substance in the laminated film;
acquiring information regarding the size of the foreign object;
and a judgment step of inputting the first information and information regarding the size of the foreign matter into a learning unit that has been trained by the learning method according to any one of claims 11 to 14 , and judging whether the photomask blank after cleaning satisfies a predetermined judgment criterion. 16. The method for producing a photomask blank according to claim 15 ,
A method for manufacturing photomask blanks, wherein the judgment criteria include a number of half pinholes having a diameter of 1 μm or more and 3 μm or less in the laminated film being 0.003 pcs/ ^cm2 or less. 1. A method for inspecting a photomask blank having a laminated film including a first layer and a second layer on a glass substrate, comprising:
a first inspection step of acquiring first information including information regarding a position of a foreign substance in the laminated film;
acquiring information regarding the size of the foreign object;
15. A photomask blank inspection method comprising: a judgment step of inputting the first information and information regarding the size of the foreign matter to a learning unit trained by the learning method according to any one of claims 11 to 14 , and judging whether the photomask blank after cleaning satisfies a predetermined judgment criterion. 18. The photomask blank inspection method according to claim 17 ,
The method for inspecting photomask blanks, wherein the judgment criteria include a number of half pinholes having a diameter of 1 μm or more and 3 μm or less in the laminated film being 0.003 pcs/ ^cm2 or less. 1. A method for inspecting a photomask blank having a laminated film including a first layer and a second layer on a glass substrate, comprising:
a first inspection step of acquiring first information including information regarding a position of a foreign substance in the laminated film;
a cleaning step of cleaning the photomask blanks after the first inspection step;
a second inspection step of acquiring second information including imaging information of the position identified in the first inspection step after the cleaning step;
and a half pinhole detection step of detecting a half pinhole based on the second information. 20. The photomask blank inspection method according to claim 19 ,
A method for inspecting a photomask blank, wherein the first layer is a light-shielding layer and the second layer is an anti-reflection layer. 21. The photomask blank inspection method according to claim 19 , further comprising:
The method for inspecting a photomask blank, wherein the first layer contains chromium and the second layer contains chromium and oxygen. 22. The method for inspecting a photomask blank according to claim 19 ,
A photomask blank inspection method, comprising: detecting light scattered from the laminated film in the first inspection step. 23. The method for inspecting a photomask blank according to any one of claims 19 to 22 ,
The photomask blank inspection method further comprises: capturing an image of light reflected from the laminated film in the second inspection step. 24. The photomask blank inspection method according to claim 23 ,
a determination step of determining whether or not the half pinhole detected in the half pinhole detection step satisfies a predetermined determination criterion,
A photomask blank inspection method, comprising: determining, in the determining step, whether or not the determination criterion is satisfied based on the intensity of the reflected light. 25. The photomask blank inspection method according to claim 24 ,
The photomask blank inspection method includes determining whether or not the judgment criterion is satisfied based on the intensity of the reflected light in the judgment step, the judgment criterion including that the number of the half pinholes having a diameter of 1 μm or more and 3 μm or less in the laminate film is ^0.003 pcs/cm2 or less. 26. The method for inspecting a photomask blank according to claim 19 ,
A photomask blank inspection method, wherein in the second inspection step, the imaging information is generated using an objective lens having a magnification of 50 or more.

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