JP5754694B2 - Foreign matter removing apparatus and foreign matter removing method - Google Patents

Description

  The present invention relates to a foreign matter removing apparatus and a foreign matter removing method that can perform a foreign matter height measuring operation and a removing operation in conjunction with a foreign matter existing on a sample surface.

  The development of EUV lithography (Extreme Ultra Violet Lithography) is drawing attention as a next-generation semiconductor manufacturing equipment. In this exposure system, EUV light having a wavelength of 13.5 nm is used as exposure light, and the optical system is constituted by a reflection optical system. Further, the reflectance of the mask is about 60%, and the illumination power for transferring the pattern is set to be considerably high. For this reason, since a lot of illumination energy becomes thermal energy in the mask, it is necessary to dissipate the mask. Therefore, the mask is supported on the stage by electrostatic adsorption. In addition, since EUV lithography is composed of a reflective optical system, the optical axis of the illumination optical system that projects the illumination light onto the mask is set to be inclined by about 4 ° from the vertical direction with respect to the mask surface. The optical axis of the projection optical system for projecting the reflected light toward the wafer is also set to be inclined by about 4 ° from the vertical direction with respect to the mask surface.

  Since EUV lithography has the above-described specific configuration, when foreign matter is adhered to the back surface of the mask, when the mask is fixed on the stage by an electrostatic chuck, minute distortion or deflection occurs in the mask. When the mask is bent, a problem arises in that the mask pattern transferred onto the wafer is displaced (for example, see Non-Patent Document 1). Therefore, in EUV lithography, backside inspection for detecting foreign matter defects present on the backside of the mask is extremely important.

  As an EUVL mask defect detection apparatus, an inspection apparatus based on a scattered light method is known. However, the scattered light type inspection apparatus can detect the presence of a defect with high sensitivity, but cannot measure the height of the defect. Further, in EUV lithography, when the height of the foreign matter adhering to the back surface is smaller than a predetermined height, the amount of bending that occurs in the mask itself is small, so that it is allowed. Therefore, in EUV lithography, there is a strong demand for the development of a height measuring device that can detect the height of foreign matter adhering to the back surface of an EUVL mask or mask blank with high accuracy.

A method using a confocal microscope is known as a technique for measuring the height of foreign matter existing on various masks and substrates. If the height is measured using a confocal microscope, there is an advantage that the height can be measured with a resolution of several tens of nm. As another height measurement method, it is known to measure using a scanning probe microscope (see, for example, Patent Document 1). In this scanning probe microscope, the probe provided at the tip of the cantilever is scanned along the sample surface, and the height distribution on the sample surface is measured.
J. Vac. Sci. Technol. B 20 (6), Nov / Dec 2002 2840-2843 JP2009-300322A

  The height measurement technique using the above-described confocal microscope has an advantage that the height of the sample surface can be measured with a resolution of several tens of nm. However, in the case of a confocal microscope, the height is measured using specularly reflected light from the sample surface. Therefore, if the foreign matter adhering to the back surface of the mask is an acute-angled protrusion, the specularly reflected light is the aperture angle of the objective lens. In some cases, the height could not be measured accurately. In addition, when height measurement is performed using a scanning probe microscope, there is an advantage that the height of the sample surface can be detected with high accuracy, but when the probe provided at the tip of the cantilever comes into contact with foreign matter, the probe is contaminated. There is a drawback that the cleaning and replacement of the probe becomes complicated.

  Furthermore, the height measurement by the confocal microscope can measure the height of the foreign matter on the sample surface, but since there is no function to remove the foreign matter whose height has been measured, if a foreign matter exceeding a predetermined height is detected, The foreign matter must be removed using a separate foreign matter removing device, which is complicated in terms of removing the foreign matter. On the other hand, if the height measurement operation of the detected foreign matter and the foreign matter removal operation can be performed in the same apparatus, the above-described complexity is eliminated. In particular, if the foreign object height measurement and the foreign object removal can be performed in conjunction with each other, the foreign object height measurement and the foreign object removal can be performed in a short time, and the throughput is greatly improved. Such a problem is a problem that occurs not only in the EUVL mask but also in various samples such as a color filter substrate.

An object of the present invention is to provide a foreign matter removing apparatus and a foreign matter removing method capable of performing both the height measurement and foreign matter removal operation of foreign matter attached to the front or back surface of various samples such as EUVL mask and EUVL mask blank. It is to be realized.
Moreover, this invention is providing the foreign material removal apparatus and foreign material removal method which can remove the foreign material of the magnitude | size exceeding a predetermined threshold value with high throughput.

A foreign matter removing device according to the present invention is a foreign matter removing device that removes foreign matter existing on a sample surface with a cantilever,
A stage for supporting the sample;
A measurement optical system for detecting the height of a foreign substance existing on the sample surface;
A cantilever having an elastically deformable lever portion and arranged so that the free end of the lever portion contacts the sample surface at an oblique angle;
First moving means for relatively moving a sample or a cantilever on a stage in a first direction perpendicular to the sample surface;
Second moving means for relatively moving a sample or a cantilever on the stage in a second direction orthogonal to the first direction;
Third moving means for relatively moving a sample or a cantilever on the stage in a third direction opposite to the second direction;
The measurement optical system includes a measurement light source that generates a measurement beam, an optical system that projects the measurement beam toward the cantilever, and a light detection unit that receives the reflected beam emitted from the cantilever.
The foreign matter removing apparatus further includes means for detecting a displacement amount of the cantilever in the first direction during relative movement in the second direction by the cantilever or the sample based on the output signal from the light detecting means. Have
The relative movement of the cantilever or sample in the second direction is performed such that the free end of the cantilever scans on a foreign object located on the sample surface;
When the detected displacement amount of the cantilever in the first direction exceeds a predetermined displacement amount, the cantilever or the sample is relatively moved in a third direction opposite to the second direction to remove foreign matters. It is characterized by.

  In the present invention, the cantilever functioning as the foreign matter removing means is also used as a sensor means for measuring the height of the foreign matter. That is, the free end of the cantilever is set to be in contact with the sample surface at an angle of several degrees to several tens of degrees, and the sample surface is scanned by the free end of the cantilever. During scanning, the free end of the cantilever is displaced in a direction perpendicular to the sample surface according to the uneven state of the sample surface. Therefore, when the free end of the cantilever scans over the foreign matter, the free end of the cantilever is displaced according to the height of the foreign matter. Therefore, the height of the foreign matter can be detected by detecting the amount of displacement in the direction orthogonal to the sample surface at the free end during scanning. When the height of the detected foreign matter exceeds a predetermined threshold, if the cantilever or the sample is relatively moved in the direction opposite to the scanning direction, it acts on the foreign matter from the free end of the cantilever in a direction parallel to the sample surface. A pressing force acts. The foreign matter is scraped off by the free end edge of the cantilever by the applied pressing force and can be removed from the sample surface. As described above, in the present invention, the cantilever is used as the foreign matter removing means and the height measuring sensor means. Therefore, the cantilever is merely reciprocated relative to the sample surface, and the predetermined height is not increased. Foreign matter exceeding the size can be removed.

The foreign matter removal method according to the present invention is a foreign matter removal method for removing foreign matter present on the surface of a sample placed on a stage using a cantilever,
The extension line of the free end of the cantilever is set to obliquely intersect the sample surface, and the cantilever or sample is moved relative to the first direction perpendicular to the sample surface, so that the free end of the cantilever is in contact with the sample surface diagonally. A process of
A first scanning step in which a cantilever or a sample is relatively moved along a first scanning direction orthogonal to the first direction, and a foreign object existing on the sample surface is scanned by a free end of the cantilever ;
During the first scanning step, the measurement beam is projected toward the cantilever, the spatial displacement amount of the reflected beam from the cantilever in the first scanning step is detected, and the cantilever of the cantilever is detected based on the detected displacement amount. A displacement measuring step for measuring a displacement in a direction perpendicular to the sample surface;
Determining whether the measured displacement of the cantilever in a direction perpendicular to the sample surface exceeds a predetermined displacement;
When the measured displacement of the cantilever exceeds a predetermined displacement, a second scanning step of relatively moving the cantilever or the sample in a second scanning direction opposite to the first scanning direction,
In the second scanning step, foreign matter present on the sample surface is removed by a cantilever.

  In the present invention, the cantilever is used as a foreign matter removing means and a sensor means for detecting the height distribution of the sample surface, the sample surface is scanned by the free end of the cantilever, and the free end during scanning is orthogonal to the sample surface. Since the amount of displacement in the direction to be measured is measured, the height of the foreign matter can be measured by scanning the sample surface once. Therefore, it is determined whether or not the height of the detected foreign matter exceeds a predetermined threshold value. If the height exceeds the threshold value, the foreign matter can be removed from the sample surface simply by relatively moving the cantilever or the stage in the opposite direction. As a result, the height measurement and removal of foreign matter can be performed in conjunction with each other, and foreign matter can be removed with high throughput.

It is a figure which shows the structure of an example of the optical system of the foreign material removal apparatus by this invention. It is a figure which shows an example of the cantilever by this invention. It is a figure which shows the spatial displacement of a measurement beam when a cantilever is displaced in the direction orthogonal to a sample surface when the sample surface is scanned with a cantilever. It is a figure for demonstrating the foreign material removal method by this invention. It is a figure for demonstrating a series of operation | movement at the time of scraping off a foreign material with a cantilever. It is a figure which shows the time change of the displacement amount of the free end of a cantilever during the scanning by a cantilever. It is a figure which shows the modification of a cantilever.

  FIG. 1 is a diagram showing a configuration of an example of a foreign matter removing apparatus according to the present invention. The foreign matter removing apparatus according to the present invention functions as a measurement optical system 1 for measuring the height of foreign matter existing on the sample surface, an observation optical system 2 for observing the foreign matter, and foreign matter removing means and in the height direction of the sample surface. A cantilever 3 that functions as a sensor means for detecting the displacement (height of the foreign matter), and a signal processing device 4 that outputs two-dimensional image information of the sample surface and height information of the foreign matter.

  The measurement optical system 1 has a measurement light source 10 that generates a measurement beam. A laser diode that acts as a point light source can be used as the measurement light source. The laser diode generates a laser beam having a wavelength of, for example, 405 nm or 680 nm. The measurement beam emitted from the measurement light source 10 is converted into a parallel light beam by the collimator lens 11 and enters the first relay lens 12. The measurement beam passes through one half region (in FIG. 1, half region below the optical axis) across the optical axis of the first relay lens and enters the second relay lens 13. . The incident measurement beam passes through the half area on the opposite side across the optical axis of the second relay lens (in FIG. 1, the upper half area across the optical axis).

The measurement beam emitted from the second relay lens 13 enters the dichroic mirror 14. The dichroic mirror 14 has a characteristic of reflecting the wavelength light of the measurement beam and transmitting the other wavelength light. In this example, the measurement beam is not completely reflected, but a part of the light, for example, about 0.1% of light is transmitted. The measurement beam reflected by the dichroic mirror 14 is incident on a half region of the objective lens 15. Then, the light is refracted by the objective lens 15 and is incident on the surface on the free end side of the lever portion of the cantilever 3. In this example, the cantilever 3 is connected to the lens barrel of the objective lens 15. The cantilever 3 is positioned so that its free end is located in a position displaced from the optical axis of the objective lens in the objective lens field of view.

  A sample stage 16 is disposed below the cantilever 3, and a sample 17 from which foreign matter is removed is placed on the sample stage 16. In this example, an EUVL mask blank is used as a sample, and foreign matters existing on the back surface of the EUVL mask blank are removed. Note that the foreign matter present on the back surface of the EUVL mask is detected by another defect inspection apparatus, and the foreign matter address information is known. Note that the foreign matter removing apparatus of the present invention can be mounted on a defect inspection apparatus that detects foreign matter.

  In this example, the sample stage 16 uses an XYZ stage that is movable in a direction (optical axis direction: Z-axis direction) orthogonal to the sample surface and in three axial directions of X and Y directions in the sample surface. Therefore, by moving the stage 16 in the X and Y directions using the address information of the foreign matter that has already been detected, the foreign matter can be positioned within the field of view of the objective lens. In addition, the objective lens can be focused on the sample surface by moving the stage in the optical axis direction. Further, by moving the stage upward along the Z-axis direction, the free end of the cantilever 3 can be brought into contact with the surface of the sample 17, and by moving downward the sample surface and the free end of the cantilever A desired distance can be provided between the two.

  The cantilever 3 is composed of silicon nitride, single crystal silicon, or a composite of single crystal silicon and silicon nitride, and has a characteristic capable of elastic deformation. The cantilever 3 is set so as to form an angle of about 2 ° to 15 ° with respect to the sample surface. Therefore, even if the stage 16 is displaced upward and the surface of the sample 17 and the free end of the cantilever come into contact with each other, the cantilever can be elastically displaced according to the height change of the sample surface. In addition, by moving the stage in the X or Y direction with the tip of the cantilever in contact with the sample surface, the sample surface is scanned by the cantilever, and the free end of the cantilever is changed according to the height change of the sample surface. It is displaced in a direction (optical axis direction) perpendicular to the surface. In the present invention, the displacement in the direction orthogonal to the sample surface during scanning of the sample surface by the cantilever is detected using the spatial displacement amount of the measurement beam. Therefore, the cantilever functions as sensor means for detecting the amount of displacement of the sample surface in the height direction.

  The measurement beam reflected near the free end of the lever portion of the cantilever passes through the opposite region across the optical axis of the objective lens 15 and enters the dichroic mirror 14. The measurement beam reflected by the dichroic mirror passes through the region on the opposite side of the optical axis of the second relay lens 13, passes through the region on the opposite side of the first relay lens, and enters the half mirror 18. . The measurement beam reflected by the half mirror 18 enters the first light detection means 20 through the imaging lens 19. The light detection means 20 functions as a means for detecting the spatial position of the incident measurement beam, and can be constituted by, for example, a two-division photodiode, a two-dimensional CCD sensor, a line sensor, or a PSD (Position Sensitive Device). The output signal from the first light detection means is supplied to the signal processing device 4. The signal processing device 4 calculates the position of the free end of the cantilever 3 in the optical axis direction using the output signal from the first light detection means, and outputs the height information of the foreign matter. That is, when the free end of the cantilever 3 is displaced in the optical axis direction, the incident position of the measurement beam with respect to the light detection means is displaced according to the displacement amount of the free end of the cantilever in the optical axis direction. Therefore, the displacement amount in the optical axis direction of the free end of the cantilever can be detected using the output signal from the light detection means 20.

  The second light detection means 21 is arranged at the rear stage of the half mirror 18 to receive the measurement beam transmitted through the half mirror. In this example, the second light detection means 21 is constituted by a PSD that functions as a means for performing the function of detecting the spatial position of the incident measurement beam. The PSD 21 detects the spatial displacement of the incident measurement beam and detects the inclination of the cantilever 3 with respect to the sample surface. That is, when the surface of the lever portion of the cantilever 3 is tilted from a state parallel to the sample surface, the tilt amount is detected. And it can adjust so that the front-end | tip of a cantilever may become parallel with respect to the sample surface using the detected inclination amount.

  Next, the imaging optical system 2 will be described. The imaging optical system 2 includes an illumination light source 30 that generates illumination light. For example, a xenon lamp can be used as the illumination light source. The illumination beam emitted from the illumination light source 30 is collected by the condenser lens 31 and enters the half mirror 33 through the relay lens 32. The illumination beam reflected by the half mirror 33 passes through the dichroic mirror 14 and is focused by the objective lens 15 to illuminate the sample 17 and the cantilever 3. The illumination light reflected by the sample is collected by the objective lens 15 and passes through the dichroic mirror 14. The illumination light emitted from the dichroic mirror passes through the half mirror 33 and forms an image on the imaging device 35 through the imaging lens 34. In this example, a two-dimensional CCD can be used as the imaging device. The image signal output from the imaging device 35 is supplied to the signal processing device 4 through an amplifier (not shown). The signal processing device 4 forms a two-dimensional image of the sample surface and the free end of the cantilever and its vicinity. The formed two-dimensional image can be displayed on the monitor, and the operator can confirm the position of the foreign matter and the free end of the cantilever from the image displayed on the monitor. Furthermore, the operator can determine whether or not the foreign material needs to be removed based on the shape and size of the foreign material displayed on the monitor.

  In this example, since the dichroic mirror 14 has a transmittance of about several percent with respect to the wavelength light of the measurement beam, a part of the measurement beam reflected by the region on the tip side of the cantilever 3 is transmitted through the dichroic mirror 14. An image is formed on the imaging device 35 via the half mirror 33 and the imaging lens 34. Therefore, the position of the measurement beam in the field of view is displayed as a bright point in the two-dimensional image captured by the imaging device.

  2A and 2B are diagrams showing an example of a cantilever, FIG. 2A is a plan view (a plan view seen from the optical axis direction), and FIG. 2B is a cross-sectional view taken along the line II-II in FIG. 2 (C) is a diagram showing the field of view of the objective lens, and FIG. 2 (D) is a diagram showing the positional relationship of the free end of the cantilever with respect to the sample surface. The cantilever 3 includes a support portion 3a, a plate-like lever portion 3b formed integrally with the support portion, and a linear free end edge 3c extending in a direction orthogonal to the lever portion. The cantilever of this example is formed by etching using a composite of a silicon single crystal and a silicon nitride layer 3d. The support portion 3a can be fixed to the support frame of the objective lens 15, or can be movably mounted in the X and Z directions on the support frame of the objective lens or other support members. The lever portion 3b is composed of a composite of single crystal silicon and a silicon nitride layer, and is elastically deformable. Further, the spring constant of the lever portion can be set to about 0.005 to 50 N / m, for example. The length of the lever portion 3b is about 50 to 500 μm, and the thickness is set to 1 to 10 μm. Moreover, the width | variety of a lever part is set to 10-100 micrometers. The thickness of the silicon nitride film is, for example, 0.1 to 10 μm. Furthermore, it is also possible to form a DLC (Diamond like Carbon) film so as to include a free end edge on the surface of the silicon nitride film 3d. DLC has a small coefficient of friction and is excellent in wear resistance, so it is useful for removing foreign substances. The numerical example described above is merely an example, and can be set to an optimum value in consideration of the size of the foreign matter to be removed, the characteristics of the sample, and the like.

  FIG. 2C shows the positional relationship between the field of view of the objective lens and the cantilever. The field of view of the objective lens is indicated by reference numeral 36, and the foreign matter 37 exists on the sample surface 17a. The free end of the cantilever 3 is set and positioned so as to be located within the field of view of the imaging apparatus and to be displaced from the center of the field of view. Further, an incident point (bright point) formed by the height measuring beam is denoted by reference numeral 38. The measurement beam is not incident on the sample surface, but is incident near the free end of the lever portion 3b of the cantilever. As described above, in this example, since the dichroic mirror 14 is configured to have a transmittance of about 0.1% with respect to the wavelength light of the measurement beam, the measurement beam reflected near the free end of the lever portion. Is transmitted through the dichroic mirror 14 and received by the imaging device via the half mirror 33 and the imaging lens 34. Therefore, the incident point of the measurement beam is displayed in the two-dimensional image captured by the imaging device.

  FIG. 2D shows the relative positional relationship of the cantilever with respect to the surface 17a of the sample 17 and the operation for removing foreign matter. The cantilever lever portion 3b is disposed so as to be inclined by θ = 2 to 15 ° with respect to the sample surface 17a, and is set so that the linear free end edge 3c is parallel to the sample surface. While the cantilever is stationary, the stage 16 is moved in the Z-axis direction to bring the sample surface 17a into contact with the free end edge 3c of the cantilever. Upon contact, the lever portion of the cantilever is bent, an elastic deformation force acts on the sample surface from the cantilever, and a pressing force acts on the sample surface from the free end edge 3c of the cantilever. When the sample 17 and the cantilever 3 are relatively moved along the sample surface (XY plane) with the free end edge 3c of the cantilever pressed against the sample surface 17a, the pressing force on the sample surface from the free end edge of the cantilever A pressing force along the sample surface against the foreign matter 37 acts. As a result, a force to peel off the foreign matter from the sample surface acts on the foreign matter, the bond between the foreign matter and the sample surface is released, and the binding force on the foreign matter disappears. In this state, an electrostatic attractive force acts between the foreign matter and the free end edge of the cantilever, and the fine foreign matter scraped off is attached to the free end of the cantilever. Therefore, after the foreign matter removal operation is finished, the stage is appropriately moved, and the free end of the cantilever is brought into contact with the adhesive sheet provided at the end of the stage, so that the foreign matter moves from the cantilever to the adhesive sheet side, and from the sample surface. Foreign matter will be removed.

  Next, the height measurement of the foreign material existing on the sample surface will be described. In the present invention, the cantilever is used as a movable sensor for height measurement. The cantilever or the sample is relatively moved along the sample surface, and the sample surface is scanned by the free end of the cantilever. During the scanning, if there are irregularities or foreign matter on the sample surface, the lever portion 3b of the cantilever 3 is elastically deformed, and the free end is displaced in a direction perpendicular to the sample surface according to the height of the foreign matter. In the present invention, the amount of displacement of the cantilever in the direction perpendicular to the sample surface during scanning of the sample surface is detected by the measurement beam.

  FIG. 3 shows the spatial displacement of the measurement beam when the cantilever is displaced in a direction perpendicular to the sample surface when the sample surface is scanned by the cantilever. In FIG. 3, the code | symbol 40 shows the surface of the free end side of the lever part 3b of a cantilever. The measurement beam emitted from the objective lens 15 is reflected by the surface 40 of the lever portion, enters the objective lens again, and enters the first light detection means 20 through the dichroic mirror 14 (see FIG. 1). In FIG. 3, the solid line shows the state where the cantilever is located at the reference position. If the sample surface has irregularities or foreign objects during scanning of the sample surface by the cantilever, the free end of the cantilever is displaced in a direction perpendicular to the sample surface, and the surface 40 of the lever portion is also perpendicular to the sample surface. It is displaced to. The displaced lever surface is indicated by a broken line. The reflected measurement beam is also displaced according to the displacement of the lever portion surface, and the position of the measurement beam incident on the first light detection means 20 is also displaced. Therefore, by detecting the incident position of the measurement beam in the first light detection means 20, the displacement amount of the sample surface and the height of the foreign matter existing on the sample surface can be measured. In this case, when the first light detection means is constituted by a two-divided photodiode, the amount of displacement of the sample surface, that is, the height of the foreign matter is measured by forming a difference between output signals from the two photodiodes. be able to.

  FIG. 4 is a view for explaining a foreign matter removing method according to the present invention. In FIG. 4, foreign matter 37 exists on the surface 17 a of the sample 17, and this foreign matter is removed by the cantilever 3. FIG. 4A shows a state where the free end edge 3c of the cantilever is pressed against the sample surface 17a, the sample 17 is stationary, and the cantilever is relatively moved in the direction a. In this case, the free end edge 3c is in pressure contact with the sample surface, but the foreign matter is in a state of being bonded to the sample surface and the friction coefficient of the silicon nitride layer of the cantilever is small, so that the cantilever 3 moves relative to the a direction. However, the foreign matter is kept stationary and slips out of the free end edge 3c of the cantilever.

  FIG. 4B shows a state in which the sample 3 is stationary and the cantilever 3 is relatively moved in the b direction, which is the opposite direction to the a direction. In this case, the free end edge 3c of the cantilever moves relative to the foreign material in the direction b in a state where a pressing force is applied to the sample surface. Therefore, the free end edge 3c does not pass through the foreign material 37 and moves the foreign material in the direction b. Acts like pressing. The foreign matter is scraped off from the sample surface by the pressing force acting on the foreign matter, and the foreign matter is removed. In the present invention, the height of the foreign matter is measured and the foreign matter is removed by effectively utilizing the action of the cantilever described above.

  FIG. 5 is a diagram for explaining a series of operations when the cantilever 3 scrapes off the foreign matter 37 existing on the sample surface 17a. In this example, the cantilever is stationary, and the stage 16 that supports the sample 17 is in the Z-axis direction perpendicular to the sample surface with respect to the cantilever, and the + X direction (right direction on the drawing) and −X direction (on the drawing) perpendicular to the Z-axis. Move to the left). During relative movement in the + X direction, the surface of the sample containing foreign matter is scanned by a cantilever, and the height of the foreign matter is measured by detecting the Z-axis displacement of the free end of the cantilever using a measurement optical system. When the value exceeds the predetermined value, the foreign matter removal operation is performed by moving in the −X direction.

  First, as shown in FIG. 5 (A), the sample surface 17a is set to be separated from the cantilever 3 by a predetermined distance. Further, the operator uses the two-dimensional image of the sample surface displayed on the monitor to move the stage in the −X direction so that the foreign matter is positioned on the cantilever support side.

  From the state described above, the stage is moved in the Z-axis direction and raised until the sample surface 17a comes into pressure contact with the free end edge 3c of the cantilever. This state is shown in FIG. Since the cantilever can be elastically deformed in the pressure contact state, its free end is displaced so as to be elastically deformable in a direction perpendicular to the sample surface. This pressure contact is detected by detecting the start of displacement of the free end of the cantilever in the Z-axis direction by the measurement optical system.

  After the pressure contact is detected, the sample starts to move in the + X direction. In this state, the cantilever lever portion 3b is set so as to obliquely intersect the sample surface, so that the cantilever lever portion first comes into contact with the foreign matter. This state is shown in FIG. Further, when the sample moves in the + X direction, the free end of the cantilever moves while being gradually displaced in the Z-axis direction, and the free end of the cantilever is positioned on the foreign matter. This state is shown in FIG.

  Since a silicon nitride film having a small friction coefficient is formed on the back surface of the lever portion of the cantilever, the foreign matter passes through the free end of the cantilever, and the free end of the cantilever shifts to a state in pressure contact with the sample surface. This state is shown in FIG. When the foreign object passes through the cantilever, the free end of the cantilever is suddenly displaced in the −Z-axis direction. Therefore, by detecting the sudden displacement by the measurement optical system, it is detected that the foreign object passes through the cantilever. At this point, the relative movement in the + X direction is stopped. This state is shown in FIG.

  A maximum displacement amount of the Z-axis of the free end of the cantilever during the scanning in the + X direction is detected, and the detected maximum displacement amount corresponds to the height of the foreign matter. When the measured height of the foreign material exceeds a predetermined height, the sample is relatively moved in the −X direction, and the foreign material is scraped off from the sample surface by the relative movement. When foreign matter is scraped from the sample surface, electrostatic attraction or intermolecular force acts between the free end edge of the cantilever and the foreign matter, and the scraped foreign matter is attached to the free end edge. . Thereafter, the foreign substance can be removed from the free end edge by moving the stage and bringing the free end edge into contact with the adhesive sheet provided at the end of the stage.

  FIG. 6 is a diagram showing a change over time in the amount of displacement of the free end of the cantilever output from the signal processing device 4 during scanning by the cantilever. In FIG. 6, the horizontal axis indicates time, and the vertical axis indicates the amount of displacement in the direction perpendicular to the sample surface at the free end of the cantilever. When removing the foreign matter, the stage starts relative movement in the Z-axis direction. During the period until the sample surface comes into contact with the free end of the cantilever, the detected displacement of the cantilever does not change. On the other hand, when the free end comes into contact with the sample surface, the free end is displaced as the sample surface moves in the Z-axis direction. Therefore, by detecting the displacement of the free end, it is detected that the sample surface is in pressure contact with the free end of the cantilever.

  When the pressure contact is detected, the stage stops moving in the Z-axis direction and starts relative movement in the + X-axis direction. The free end of the cantilever is not displaced until a foreign matter that is moving in the + X-axis direction comes into contact with the lever portion of the cantilever, and a certain amount of displacement is output. When the foreign object moves further and comes into contact with the back surface of the lever portion, the free end gradually starts to be displaced in the Z-axis direction. When the free end is positioned on the foreign object, the amount of displacement becomes maximum, and when the foreign object passes through the free end, it immediately comes into contact with the sample surface, and a displacement amount equal to the displacement amount while scanning the sample surface is detected. At this point, the height measurement ends.

  The signal processing device determines the detected maximum displacement amount as the height of the foreign object, and determines whether the maximum displacement amount exceeds a predetermined threshold value. If the threshold is not exceeded, it is determined that the foreign matter is a foreign matter that does not need to be removed. On the other hand, when the threshold value is exceeded, it is determined that the foreign matter is a foreign matter to be removed, and the stage starts moving in the opposite direction, -X direction. And the foreign material is scraped off and removed from the sample surface by the movement in the −X direction.

  FIG. 7 is a view showing a modified example of the cantilever. 7A is a plan view of the cantilever, and FIG. 7B is a cross-sectional view taken along the line II-II in FIG. 7A. The cantilever 50 of this example has a support portion 50a, two elastically deformable lever portions 50b and 50c, and a free end 50d where the two lever portions are coupled, and has a triangular ring shape. Thus, by using two lever portions that cross each other at an angle, torsion resistance is improved and rolling rigidity is improved. That is, even if the position of the foreign matter is deviated from the center line of the cantilever, an effect of being hardly twisted is exhibited. When measuring the height of a foreign object, the height of the foreign object is measured by projecting a measurement beam toward the free end 50d of the cantilever 50 and detecting the amount of displacement of the reflected beam from the free end 50d. Can do.

  7C and 7D show a state in which the protrusion defect 37 existing on the sample is removed. When removing foreign matter, the stage is moved in the X and Y directions so that the foreign matter is positioned inside the inner periphery of the triangle. Subsequently, the stage is moved in the Z-axis direction and adjusted so that the free end 50d of the cantilever comes into contact with the sample surface. In this state, the cantilever is relatively moved in the direction of the arrow, and the foreign matter can be peeled off from the sample surface by the edge of the inner periphery of the triangle. In this example, since the foreign matter is removed by the pulling force against the foreign matter, the problem that the cantilever is buckled is solved.

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiment, the height of the foreign matter is measured and the foreign matter removal operation is performed by moving the stage supporting the sample relative to the cantilever. However, the foreign matter is obtained by moving the cantilever relative to the sample. It is also possible to perform height measurement (scanning of the sample surface) and foreign matter removal operation. Moreover, you may combine the relative movement of a cantilever and a stage.

  In the above-described embodiment, the cantilever is connected to the support frame of the objective lens. However, the cantilever may be connected to a support member other than the objective lens and moved independently from the objective lens.

  In the above-described embodiments, the method for removing the foreign matter adhering to the front or back surface of the EUVL mask blank as the object to be inspected has been described, but not only the EUVL mask blank but also the surfaces of various samples such as EUVL masks and color filter substrates. It is also applied to the case of removing foreign matter adhering to the back surface.

DESCRIPTION OF SYMBOLS 1 Measurement optical system 2 Imaging optical system 3 Cantilever 4 Signal processing apparatus 10 Measurement light source 11 Collimator lens 12, 13, 32 Relay lens
14 Dichroic mirror 15 Objective lens 16 Stage 17 Sample 18, 33 Half mirror 19 Imaging lens 20 First light detection means 21 Second light detection means 30 Illumination light source 31 Condensing lens 32 Relay lens 33 Half mirror 34 Imaging lens 35 Imaging device

Claims (11)

A foreign matter removing device that removes foreign matter existing on the sample surface with a cantilever,
A stage for supporting the sample;
A measurement optical system for detecting the height of a foreign substance existing on the sample surface;
A cantilever having an elastically deformable lever portion and arranged so that the free end of the lever portion contacts the sample surface at an oblique angle;
First moving means for relatively moving a sample or a cantilever on a stage in a first direction perpendicular to the sample surface;
Second moving means for relatively moving a sample or a cantilever on the stage in a second direction orthogonal to the first direction;
Third moving means for relatively moving a sample or a cantilever on the stage in a third direction opposite to the second direction;
The measurement optical system includes a measurement light source that generates a measurement beam, an optical system that projects the measurement beam toward the cantilever, and a light detection unit that receives the reflected beam emitted from the cantilever.
The foreign matter removing apparatus further includes means for detecting a displacement amount of the cantilever in the first direction during relative movement in the second direction by the cantilever or the sample based on the output signal from the light detecting means. Have
The relative movement of the cantilever or sample in the second direction is performed such that the free end of the cantilever scans on a foreign object located on the sample surface;
When the detected displacement amount of the cantilever in the first direction exceeds a predetermined displacement amount, the cantilever or the sample is relatively moved in a third direction opposite to the second direction to remove foreign matters. Foreign matter removing device characterized by   2. The foreign matter removing apparatus according to claim 1, wherein the signal processing device includes height detecting means for obtaining the height of the foreign matter from the detected displacement amount of the cantilever in the first direction, and the detected height of the foreign matter. When the height exceeds a predetermined height, the foreign matter is removed by moving the cantilever or the sample in a third direction opposite to the second direction to remove the foreign matter. 3. The foreign matter removing apparatus according to claim 1, wherein the cantilever includes a support portion, a lever portion that is formed integrally with the support portion and is elastically deformable, and a free end edge located at a tip of the lever portion. The cantilever is composed of silicon nitride, single crystal silicon, or a composite material of single crystal silicon and silicon nitride. The foreign matter removing apparatus according to claim 1, 2, or 3, wherein the foreign matter removing device further includes an imaging optical system that images the sample surface, and the imaging optical system includes an illumination light source that generates an illumination beam; An objective lens that projects an illumination beam toward the sample surface; and an imaging device that receives reflected light from the sample surface and outputs two-dimensional image information of the sample surface;
The measurement beam of the measurement optical system is projected toward the cantilever via the objective lens, and the measurement beam reflected by the cantilever is incident on the light detection means via the objective lens. .   5. The foreign matter removing apparatus according to claim 4, wherein the free end of the cantilever is positioned in the field of view of the objective lens, and the image signal output from the imaging device includes an image of the sample surface and the free end of the cantilever. A foreign matter removing device. 6. The foreign matter removing apparatus according to claim 5, wherein a dichroic mirror that selectively reflects part of a measurement beam is disposed in an optical path between an objective lens of the imaging optical system and the imaging apparatus, and measurement is performed by the dichroic mirror. The measurement beam of the optical system and the illumination beam of the imaging optical system are separated,
A part of the measurement beam passes through the dichroic mirror and enters the imaging device, and in the two-dimensional image output from the imaging device, a bright point indicating the incident point of the measurement beam formed on the cantilever A foreign matter removing device characterized in that is formed. 7. The foreign matter removing apparatus according to claim 1, wherein the cantilever is fixed to the objective lens or is movable in a second direction and a third direction. A foreign matter removing device, which is attached to the device. The foreign matter removing apparatus according to any one of claims 1 to 7, wherein the stage that supports the sample is configured by an XYZ stage that is movable in three axial directions of X, Y, and Z axes orthogonal to each other.
The foreign substance removing apparatus, wherein the first to third moving means are constituted by the XYZ stage.   The foreign matter removing apparatus according to any one of claims 1 to 8, wherein EUVL mask blanks are used as the sample. A foreign matter removal method for removing foreign matter present on the surface of a sample placed on a stage using a cantilever,
The extension line of the free end of the cantilever is set to obliquely intersect the sample surface, and the cantilever or sample is moved relative to the first direction perpendicular to the sample surface, so that the free end of the cantilever is in contact with the sample surface diagonally. A process of
A first scanning step in which a cantilever or a sample is relatively moved along a first scanning direction orthogonal to the first direction, and a foreign object existing on the sample surface is scanned by a free end of the cantilever ;
During the first scanning step, the measurement beam is projected toward the cantilever, the spatial displacement amount of the reflected beam from the cantilever in the first scanning step is detected, and the cantilever of the cantilever is detected based on the detected displacement amount. A displacement measuring step for measuring a displacement in a direction perpendicular to the sample surface;
Determining whether the measured displacement of the cantilever in a direction perpendicular to the sample surface exceeds a predetermined displacement;
When the measured displacement of the cantilever exceeds a predetermined displacement, a second scanning step of relatively moving the cantilever or the sample in a second scanning direction opposite to the first scanning direction,
In the second scanning step, the foreign matter removing method is characterized by removing foreign matter existing on the sample surface with a cantilever. 11. The foreign matter removing method according to claim 10, wherein EUVL mask blanks are used as the sample, and foreign matters existing on the back surface of the EUVL mask blanks are removed.

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