WO2022070498A1 - 荷電粒子線装置及びそれを用いる試料観察方法 - Google Patents
荷電粒子線装置及びそれを用いる試料観察方法 Download PDFInfo
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- 239000002245 particle Substances 0.000 title claims abstract description 46
- 238000000034 method Methods 0.000 title claims abstract description 25
- 238000004364 calculation method Methods 0.000 claims abstract description 29
- 230000001678 irradiating effect Effects 0.000 claims abstract description 9
- 238000001514 detection method Methods 0.000 claims description 41
- 230000008034 disappearance Effects 0.000 claims description 21
- 238000003776 cleavage reaction Methods 0.000 abstract 2
- 230000007017 scission Effects 0.000 abstract 2
- 239000013598 vector Substances 0.000 description 28
- 238000010894 electron beam technology Methods 0.000 description 25
- 239000004065 semiconductor Substances 0.000 description 8
- 238000003860 storage Methods 0.000 description 8
- 239000011159 matrix material Substances 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000001133 acceleration Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
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- 230000005684 electric field Effects 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/2204—Specimen supports therefor; Sample conveying means therefore
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/20—Means for supporting or positioning the objects or the material; Means for adjusting diaphragms or lenses associated with the support
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/22—Optical or photographic arrangements associated with the tube
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
Definitions
- the present invention relates to a charged particle beam device that forms an observation image of a sample by irradiating the sample with a charged particle beam and a sample observation method for observing a sample using a charged particle beam device.
- the charged particle beam device is a device that forms an observation image for observing the fine structure of a sample by irradiating the sample with a charged particle beam such as an electron beam, and is used in a semiconductor manufacturing process or the like.
- a charged particle beam such as an electron beam
- the tilt angle of the sample table on which the sample is placed is adjusted.
- Patent Document 1 in order to efficiently and accurately arrange the observation surface perpendicular to the irradiation direction of the charged particle beam, an image of the observation surface is acquired and observed while changing the inclination angle of the sample table on which the sample is placed. It is disclosed that the sample table is tilted to the tilt angle at which an image with a larger surface area is obtained.
- Patent Document 1 does not give consideration to the case where the observation surface is larger than the field of view of the charged particle beam device. That is, if the observation surface is larger than the field of view, the area of the observation surface cannot be compared in the images acquired while changing the inclination angle of the sample table, and the inclination angle of the sample table cannot be determined.
- an object of the present invention is to provide a charged particle beam device capable of appropriately setting the tilt angle of the sample table even when the observation surface is larger than the field of view, and a sample observation method using the charged particle beam device.
- the present invention is a charged particle beam device that acquires an observation image of the sample by irradiating the sample with the charged particle beam, and tilts around each of two intersecting tilt axes.
- the boundary between the upper surface of the sample and the fractured surface is detected from each of the sample table holding the sample and the observation image obtained while changing the tilt angle of the sample table, and the charged particle beam at the boundary is detected.
- Top surface detection that detects the top surface from the boundary detection unit that obtains the tilt with respect to the scanning direction and the observation image for each tilt angle, and calculates the top surface disappearance angle that is the tilt angle of the sample table when the top surface disappears from the observation image.
- It is characterized by including a unit and a calculation processing unit that calculates the initial sample orientation, which is the orientation of the fractured surface when the inclination angle is zero, based on the inclination of the boundary and the disappearance angle of the upper surface for each inclination angle. do.
- the present invention is a sample observation method using a charged particle beam device that acquires an observation image of the sample by irradiating the sample with a charged particle beam, and is inclined around each of two intersecting inclination axes.
- the boundary between the upper surface of the sample and the fractured surface is detected from each of the observation images obtained while changing the inclination angle of the sample table holding the sample, and the inclination of the boundary with respect to the scanning direction is obtained.
- the boundary detection step, the top surface detection step that detects the top surface from the observation image for each tilt angle, and calculates the top surface disappearance angle that is the tilt angle of the sample table when the top surface disappears from the observation image, and each tilt angle. It is characterized by comprising a calculation processing step for calculating the initial sample orientation which is the orientation of the fractured surface when the inclination angle is zero, based on the inclination of the boundary and the disappearance angle of the upper surface.
- the present invention it is possible to provide a charged particle beam device capable of appropriately setting the tilt angle of the sample table even when the observation surface is larger than the field of view, and a sample observation method using the charged particle beam device.
- the charged particle beam device is a device that forms an observation image for observing a sample by irradiating the sample with a charged particle beam.
- a scanning electron microscope SEM that forms an observation image of a sample by scanning the sample with an electron beam will be described.
- the configuration of the scanning electron microscope will be described with reference to FIG.
- the scanning electron microscope includes an electron gun 101, a focusing lens 102, an aperture 103, a deflection coil 104, an objective lens 105, a sample table 107, a secondary electron detector 108, an image forming unit 111, a detection unit 112, a calculation processing unit 115, and a control.
- a unit 116 and an input display unit 117 are provided. Hereinafter, each part will be described.
- the electron gun 101 is a radiation source that irradiates the sample 106 with an electron beam 109 accelerated by a predetermined acceleration voltage.
- the focusing lens 102 and the objective lens 105 are lenses that focus the electron beam 109.
- the diaphragm 103 is a plate having an opening through which a part of the electron beam 109 passes, and adjusts the opening angle of the electron beam 109.
- the deflection coil 104 is a coil or electrode that generates a magnetic field or an electric field that deflects the electron beam 109, and the surface of the sample 106 is scanned by the deflected electron beam 109.
- the sample table 107 holds the sample 106, moves the sample 106 in the horizontal direction, and tilts the sample 106 with respect to the horizontal plane.
- FIG. 2A shows a perspective view of the sample 106 used in the semiconductor manufacturing process.
- the sample 106 has an upper surface 118 on which the semiconductor pattern 150 is formed, a fractured surface 119, and a side surface 121.
- an ideal cross section 120 which is a cross section orthogonal to the longitudinal direction of the semiconductor pattern 150 in order to improve the length measurement accuracy.
- the split cross section 119 manually cut is often not orthogonal to the upper surface 118 or the side surface 121.
- the side surface 121 is orthogonal to the upper surface 118.
- the sample table 107 for holding the sample 106 will be described with reference to FIG. 2B.
- the sample table 107 has a first tilt axis 123 and a second tilt axis 124 orthogonal to each other, and is tilted about each of the first tilt axis 123 and the second tilt axis 124. It is desirable that the first tilt axis 123 and the second tilt axis 124 are substantially orthogonal to the irradiation direction of the electron beam 109.
- the tilted state of the sample table 107 is reproduced by designating the tilting order and tilting angle of the first tilting shaft 123 and the second tilting shaft 124. Further, the first tilting shaft 123 and the second tilting shaft 124 do not need to be exposed.
- the sample table 107 is tilted by adjusting the height of each support point of the sample table 107 supported by three points. May be.
- the sample 106 is held on the sample table 107 so that the fractured surface 119 and the ideal cross section 120 face the electron gun 101, and the vicinity of the boundary 122 between the upper surface 118 and the fractured surface 119 is observed.
- the secondary electron detector 108 is an ET detector, a semiconductor detector, or the like composed of a scintillator, a light guide, and a photomultiplier tube, and secondary electrons emitted from the sample 106 irradiated with the electron beam 109. 110 is detected.
- the detection signal output from the secondary electron detector 108 is transmitted to the image forming unit 111.
- a backscattered electron detector for detecting backscattered electrons and a transmitted electron detector for detecting transmitted electrons may be provided.
- the image forming unit 111 is an arithmetic unit that forms an observation image of the sample 106 based on the detection signal transmitted from the secondary electron detector 108, and is, for example, an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), or the like. be.
- the observation image formed by the image forming unit 111 is transmitted to the input display unit 117 for display, or is transmitted to the detection unit 112 and the calculation processing unit 115 for various processing.
- the detection unit 112 is an arithmetic unit that detects the characteristic unit of the sample 106 from the observation image, and is, for example, an MPU or a GPU.
- the detection unit 112 includes a boundary detection unit 113 that detects the boundary 122 from the observation image and a top surface detection unit 114 that detects the upper surface 118 from the observation image.
- the boundary detection unit 113 detects the boundary 122 from the observation image and calculates the inclination of the boundary 122 with respect to the scanning direction of the electron beam 109.
- the inclination of the boundary 122 is calculated for each of the observation images acquired while changing the inclination angle of the sample table 107.
- the top surface detection unit 114 detects the top surface 118 from the observation image, and calculates the top surface disappearance angle, which is the tilt angle of the sample table 107 when the top surface 118 disappears from the observation image.
- the calculation processing unit 115 is the orientation of the fractured surface 119 of the sample 106 when the sample table 107 is in the horizontal state, that is, when the inclination angle of the sample table 107 is zero, based on the inclination of the boundary 122 and the top surface disappearance angle. It is an arithmetic unit that calculates the orientation of the initial sample. Further, the calculation processing unit 115 may calculate the inclination angle of the sample table 107 which is the observation direction specified by the operator by using the initial sample orientation.
- the control unit 116 is an arithmetic unit that controls each unit and processes and transmits data formed by each unit, such as a CPU (Central Processing Unit) and an MPU.
- the control unit 116 may be connected to a storage unit that stores data generated by each unit.
- the storage unit is a device that stores various data and programs, such as an HDD (Hard Disk Drive) and an SSD (Solid State Drive).
- the input display unit 117 is a device for inputting observation conditions, which are conditions for observing the sample 106, and displaying an observation image formed by the image forming unit 111, for example, a keyboard, a mouse, a touch panel, and a liquid crystal display. Display etc.
- the operation screen which is a screen operated by the operator, is displayed on the input display unit 117.
- the operation screen exemplified in FIG. 3 includes an initial sample orientation calculation button 125, a first observation orientation designation unit 126, a second observation orientation designation unit 127, a scanning direction designation unit 128, an inclination angle adjustment button 129, and an observation orientation display unit 130.
- an initial sample orientation calculation button 125 a first observation orientation designation unit 126, a second observation orientation designation unit 127, a scanning direction designation unit 128, an inclination angle adjustment button 129, and an observation orientation display unit 130.
- the initial sample orientation calculation button 125 is a button that causes the calculation processing unit 115 to calculate the initial sample orientation.
- the first observation direction designation unit 126, the second observation direction designation unit 127, and the scanning direction designation unit 128 are boxes for inputting the direction in which the operator wants to observe.
- An angle related to the irradiation direction of the electron beam 109 is input to the first observation direction designation unit 126 and the second observation direction designation unit 127, and an angle related to the scanning direction of the electron beam 109 is input to the scanning direction designation unit 128.
- the tilt angle adjustment button 129 is a button that causes the control unit 116 to adjust the tilt angle of the sample table 107 so as to have a designated observation direction.
- the observation direction display unit 130 is the polar coordinates representing the observation direction, the horizontal axis is the component related to the first observation direction designation unit 126, the vertical axis is the component related to the second observation direction designation unit 127, and the coordinate center is the electron beam. Corresponds to the irradiation direction of 109 orthogonal to the observation plane.
- An observation window 131 indicating the observation direction and the scanning direction is superimposed on the observation direction display unit 130.
- the observation window 131 is rectangular, and the coordinates of the center of the observation window 131 indicate an angle related to the irradiation direction of the electron beam 109, and the direction parallel to the long side of the observation window 131 indicates the scanning direction of the electron beam 109.
- the calculation processing unit 115 calculates the initial sample orientation.
- the calculation processing unit 115 repeats the processing from S501 to S506 a specified number of times.
- the specified number of times may be read out the number of times stored in the storage unit in advance, or may be input by the operator via the input display unit 117. As will be described later, it is desirable that the specified number of times is five or more.
- the control unit 116 sets the tilt angle of the sample table 107.
- the tilt angle to be set may be read out from the storage unit at each iteration process, or may be calculated at each iteration process based on the parameters stored in the storage unit. For example, the first tilt angle may be set to zero, and the second and subsequent tilt angles may be set by sequentially adding the step amount of the tilt angle stored in the storage unit to the previous tilt angle. Since the sample table 107 has a first tilt axis 123 and a second tilt axis 124, an tilt angle for each is set. That is, when the tilt angle with respect to the first tilt axis 123 is T and the tilt angle with respect to the second tilt axis 124 is A, the combination of (T, A) is set.
- the detection unit 112 acquires an observation image at the tilt angle set in S502.
- the observed image acquired is an image formed by the image forming unit 111 based on the detection signal transmitted from the secondary electron detector 108.
- the boundary detection unit 113 detects the boundary 122 from the observation image acquired in S503, and calculates the inclination of the boundary 122 with respect to the scanning direction of the electron beam 109.
- the boundary detection unit 113 performs edge enhancement processing on the observation image acquired in S503 to generate an edge enhancement image.
- a Sobel filter, a Prewitt filter, or the like is used for the edge enhancement process.
- the type of filter and the filter size are preferably selected according to the observation magnification and the number of pixels of the observation image. For example, a 3 ⁇ 3 vertical Prewitt filter is selected.
- the boundary detection unit 113 performs binarization processing on the edge-enhanced image generated in S601 to generate a binarized image.
- the threshold value used in the binarization process may be set by a mode method or the like, or a value stored in advance in the storage unit may be read out.
- the boundary detection unit 113 detects the boundary 122 from the binarized image generated in S602. For example, the Hough transform is performed on the binarized image, and the straight line having the largest number of votes is detected as the boundary 122.
- the boundary detection unit 113 determines whether or not the boundary 122 detected in S603 is appropriate. If it is appropriate, the processing flow ends, and if it is not appropriate, the processing is returned to S601 via S605 and S606. For example, the number of votes of the Hough transform is used for the determination of the boundary 122, and if the number of votes is half or more of the number of pixels of the observation image, it is determined that the detected boundary 122 is appropriate.
- the control unit 116 adjusts the observation conditions.
- the adjustment of the observation conditions may be performed based on the parameters input by the operator via the input display unit 117, or may be automatically performed by the control unit 116.
- the boundary detection unit 113 reacquires the observation image formed based on the observation conditions adjusted in S605.
- the boundary 122 is detected from the observation image acquired at the inclination angle set in S502, and the inclination of the boundary 122 with respect to the scanning direction of the electron beam 109 is calculated.
- the upper surface detection unit 114 sets two regions divided by the boundary 122 with respect to the observation image acquired in S503, and calculates the brightness average value of each set region.
- FIG. 7A shows an observation image including the top surface 118 and the fractured surface 119.
- the observation image of FIG. 7A also includes a sample table region 158, which is a region of the sample table 107, and a boundary 122 detected by the boundary detection unit 113.
- the split cross section 119 is substantially perpendicular to the irradiation direction of the electron beam 109, whereas the upper surface 118 is substantially parallel to the edge. Due to the effect, the upper surface 118 has a higher brightness value than the fractured surface 119.
- the top surface detection unit 114 sets a non-split cross-section region 159 and a split cross-section region 160, which are two regions divided by the boundary 122, with respect to the observation image exemplified in FIG. 7A.
- the non-split section region 159 is a region sandwiched between a dotted line set at a predetermined distance above the boundary 122, for example, 10 pixels away, and the boundary 122, and does not include the split section 119.
- the fractured surface region 160 is a region sandwiched between a dotted line set at a predetermined distance below the boundary 122, for example, 10 pixels away, and the boundary 122, and is a region including the fractured surface 119.
- the upper surface detection unit 114 calculates the brightness average value of each of the set two regions, that is, the non-split section region 159 and the split section region 160.
- the boundary detection unit 113 detects the boundary 122 from each of the tilt angles of the sample table 107, that is, the observation images acquired for each combination of (T, A). , Calculate the slope of the boundary 122 with respect to the scanning direction.
- the upper surface detection unit 114 calculates the brightness average value of the non-split cross-section region 159 and the split cross-section region 160, which are two regions divided by the boundary 122, with respect to the observation image for each inclination angle of the sample table 107. That is, the brightness average values of the non-split cross-section region 159 and the split cross-section region 160 are calculated for each inclination angle of the sample table 107.
- the top surface detection unit 114 calculates the top surface disappearance angle, which is the tilt angle of the sample table 107 when the top surface 118 disappears from the observation image.
- the brightness average values of the non-split cross-section region 159 and the split cross-section region 160 for each inclination angle of the sample table 107 calculated in S505 are used while the processes from S501 to S506 are repeated. Be done.
- FIG. 7A shows an observation image including the upper surface 118, a fractured surface 119, and a sample table area 158
- FIG. 7B shows an observation image not including the upper surface 118
- FIG. 8 shows a graph 162 of the brightness average values of the non-split cross-section region 159 and the split cross-section region 160 with respect to the inclination angle of the sample table 107.
- the luminance value of the fractured surface region 160 is substantially constant regardless of the tilt angle, whereas the luminance value of the non-split cross-section region 159 becomes smaller as the area of the upper surface 118 included in the observation image becomes smaller as the tilt angle changes. It decreases and becomes the minimum value in the observation image that does not include the upper surface 118. Therefore, the top surface disappearance angle is calculated by fitting the average luminance value of the non-split cross-section region 159 of the graph 162 illustrated in FIG. 8 with the sigmoid curve shown in the following equation.
- E a / (1 + exp (-b (T-c))) + d ... (1)
- E is an average luminance value
- T is an inclination angle.
- a, b, c, and d are fitting parameters, and can be obtained by using a non-linear least squares method or the like.
- the top surface disappearance angle ⁇ c is calculated by, for example, the following equation.
- ⁇ c c-ln ( ⁇ -1 -1) / b ... (2)
- ⁇ is a threshold value for obtaining the top surface disappearance angle, and when the ratio of the difference between d and E to a is ⁇ or less, that is, when (d—E) / a ⁇ ⁇ , the top surface 118 is observed. It is considered to have disappeared from the image.
- ⁇ is set to, for example, 0.01.
- the following equation may be used instead of the equation (2).
- the calculation processing unit 115 is based on the tilt angle of the sample table 107, the tilt of the boundary 122 with respect to the scanning direction calculated for each tilt angle, and the top surface disappearance angle, and the fracture surface when the tilt angle of the sample table 107 is zero.
- the initial sample orientation which is the orientation of 119, is calculated. The calculation of the initial sample orientation will be described below together with the principle related to the initial sample orientation.
- the sample orientation can be uniquely determined by specifying the normal direction vector of each face.
- the fractured surface 119 is not perpendicular to the top surface 118, so here we focus on the normal vector of the top surface 118 and the side surface 121.
- the observation image may basically be a parallel projection of the sample. That is, parallel straight lines are projected in parallel in the observation image.
- the reference world coordinate system and the view coordinate system in the observation image are set by the right-handed Cartesian coordinate system.
- the x-axis and y-axis of the world coordinate system are set to be parallel to the first tilt axis 123 and the second tilt axis 124 of the sample table 107, and the z-axis is the first tilt axis 123 and the second tilt axis. It is set to be orthogonal to 124.
- the tilt axes of the sample table 107 are not orthogonal to each other, one tilt axis is set to be parallel to the x-axis and the other tilt axis is set to be parallel to the xy plane.
- the horizontal orientation of the observation image is set as the X-axis
- the vertical orientation is set as the Y-axis. That is, the scanning direction is the X axis, and the irradiation direction of the electron beam 109 is the Z axis. Therefore, the observation direction is expressed as a rotation matrix that converts xyz to XYZ.
- This rotation matrix R xyz is expressed by multiplying R x ( ⁇ x), Ry ( ⁇ y), and Rz ( ⁇ z). However, the order of multiplication is unified.
- N 1 is a normal vector of the side surface 121, that is, a unit vector parallel to the boundary 122 between the fracture surface 119 and the top surface 118. Since it is necessary to obtain the observation direction at the same time in order to obtain N 1 , the two variables representing N 1 and the three variables representing the observation direction are obtained. Since N 1'is parallel to the boundary 122 included in the observation image, (Y component of N 1') / (X component of N 1 ' ) is the slope of the boundary 122. The slope of the boundary 122 contains information relating to the two variables of N1 and the three variables for observation.
- the processes S501 to S506 are repeated five or more times and the slope of the boundary 122 is calculated for each of the five or more different points (T, A), the two variables representing N1 and the observation direction are obtained.
- Five variables with three variables to represent are obtained. That is, it is desirable that the number of times S501 is specified is five or more. If it is difficult to obtain the five variables as an analytical solution, the five variables may be obtained by fitting using a non-linear least squares method or the like.
- N 2 is a normal direction vector of the upper surface 118
- the Z component of N 2 ′ becomes 0 in the observation image when the sample table 107 is set to the upper surface disappearance angle.
- N 2' is obtained by using the binding condition in which N 1'and N 2'are orthogonal to each other and the three variables related to the observation direction obtained together with N 1 .
- the remaining one variable is calculated, so it may be calculated using Newton's method or the like. From the above, the initial sample orientation is calculated. Returning to the description of FIG.
- the boundary detection unit 113 acquires an observation image at the inclination angle set in S509, detects the boundary 122 from the acquired observation image, and calculates the inclination of the boundary 122 with respect to the scanning direction.
- the control unit 116 determines whether or not the slope of the boundary 122 calculated in S510 matches the calculated value. If they match, the processing flow of FIG. 5 ends, and if they do not match, the processing is returned to S501, and the calculation for the initial sample is repeated. Whether or not they match is determined by whether or not the absolute value of the difference between the slope calculated in S510 and the calculated value is equal to or less than a predetermined threshold value. By such a determination, the calculation accuracy for the initial sample can be improved.
- the initial sample orientation is calculated according to the processing flow described with reference to FIG.
- the processing of S509 to S511 is not essential, and may be terminated by calculating the initial sample orientation in S508. Returning to the description of FIG.
- the control unit 116 updates the operation screen based on the initial sample orientation calculated in S401. Specifically, the display range of the polar coordinates of the observation orientation display unit 130 is updated based on the angle range in which the sample table 107 can be tilted and the initial sample orientation.
- the control unit 116 acquires the observation direction via the operation screen updated in S402. That is, the values input by the operator to each of the first observation direction designation unit 126, the second observation direction designation unit 127, and the scanning direction designation unit 128 on the operation screen are acquired.
- the control unit 116 updates the position and inclination of the observation window 131 in polar coordinates based on the acquired observation direction. If the input value is outside the display range of polar coordinates, an error is displayed in the first observation direction designation unit 126 or the like.
- the control unit 116 sets the tilt angle and the scanning direction of the sample table 107 based on the observation direction acquired in S403, triggered by the pressing of the tilt angle adjustment button 129.
- the control unit 116 acquires an observation image by irradiating the sample 106 held on the sample table 107 with the electron beam 109 based on the inclination angle and the scanning direction set in S404.
- the conditions relating to the irradiation of the electron beam 109 may be set by the operator using the input display unit 117, or the conditions stored in advance in the storage unit may be read out.
- the initial sample orientation which is the orientation of the fractured surface 119 when the inclination angle of the sample table 107 is zero. Since the initial sample orientation is calculated without using the area of the observation surface, the observation surface may be larger than the field of view. Further, an observation image is acquired at an inclination angle of the sample table 107 set based on the calculated initial sample orientation and the observation orientation set by the operator. That is, it is possible to provide a charged particle beam device capable of appropriately setting the tilt angle of the sample table even when the observation surface is larger than the field of view, and a sample observation method using the same.
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Abstract
Description
計算処理部115は、初期試料向きを算出する。
計算処理部115は、S501からS506までの処理を指定回数繰り返す。指定回数は、予め記憶部に記憶された回数が読み出されても良いし、入力表示部117を介して操作者によって入力されても良い。なお、後述されるように指定回数は五回以上であることが望ましい。
制御部116は、試料台107の傾斜角度を設定する。設定される傾斜角度は繰り返し処理の度に記憶部から読み出されても良いし、記憶部に記憶されるパラメータに基づいて繰り返し処理の度に算出されても良い。例えば、初回の傾斜角度はゼロに設定され、二回目以降の傾斜角度は記憶部に記憶される傾斜角度のステップ量が前回の傾斜角度に順次加算されて設定されても良い。なお、試料台107は第一傾斜軸123と第二傾斜軸124を有するので、それぞれに関する傾斜角度が設定される。すなわち、第一傾斜軸123に関する傾斜角度をT、第二傾斜軸124に関する傾斜角度をAとするとき、(T、A)の組み合わせが設定される。
検出部112は、S502で設定された傾斜角度のときの観察像を取得する。取得される観察像は、二次電子検出器108から送信される検出信号に基づいて、画像形成部111によって形成された画像である。
境界検出部113は、S503で取得された観察像から境界122を検出するとともに、電子線109の走査方向に対する境界122の傾きを算出する。
境界検出部113は、S503で取得された観察像に対してエッジ強調処理を施し、エッジ強調画像を生成する。エッジ強調処理には、SobelフィルタやPrewittフィルタ等が用いられる。なおフィルタの種類やフィルタサイズは観察倍率や観察像のピクセル数に応じて選択されることが好ましく、例えば3×3の縦方向のPrewittフィルタが選択される。
境界検出部113は、S601で生成されたエッジ強調画像に対して二値化処理を施し、二値化画像を生成する。二値化処理に用いられる閾値は、モード法等によって設定されても良いし、記憶部に予め記憶された値が読み出されても良い。
境界検出部113は、S602で生成された二値化画像から境界122を検出する。例えば、二値化画像に対してHough変換が行われ、投票数が最多の直線が境界122として検出される。
境界検出部113は、S603で検出された境界122が適切か否かを判定する。適切であれば処理の流れは終了となり、適切でなければS605とS606を介してS601に処理が戻される。境界122の判定には、例えばHough変換の投票数が用いられ、投票数が観察像のピクセル数の半分以上であれば、検出された境界122が適切であると判定される。
制御部116は、観察条件を調整する。観察条件の調整は、入力表示部117を介して操作者が入力するパラメータに基づいて行われても良いし、制御部116が自動的に行っても良い。
境界検出部113は、S605で調整された観察条件に基づいて形成された観察像を再取得する。
上面検出部114は、S503で取得された観察像に対して、境界122で分けられる二領域を設定するとともに、設定された各領域の輝度平均値を算出する。
S501からS506までの処理が指定回数繰り返されることにより、境界検出部113は、試料台107の傾斜角度、すなわち(T、A)の組み合わせ毎に取得される観察像のそれぞれから境界122を検出し、走査方向に対する境界122の傾きを算出する。
上面検出部114は、観察像から上面118が消失するときの試料台107の傾斜角度である上面消失角度を算出する。上面消失角度の算出には、S501からS506までの処理が繰り返される間に、S505にて算出された試料台107の傾斜角度毎の非割断面領域159と割断面領域160の輝度平均値が用いられる。
ここで、Eは平均輝度値、Tは傾斜角度である。またa、b、c、dはフィッティングパラメータであり、非線形の最小二乗法等を用いることにより求められる。
ここでαは上面消失角度を求めるための閾値であり、dとEとの差分のaに対する割合がα以下になるとき、すなわち(d-E)/a≦αとなるとき、上面118が観察像から消失したとみなされる。αは例えば0.01に設定される。
(S508)
計算処理部115は、試料台107の傾斜角度と、傾斜角度毎に算出された境界122の走査方向に対する傾きと、上面消失角度に基づいて、試料台107の傾斜角度がゼロのときの割断面119の向きである初期試料向きを算出する。初期試料向きの算出について、初期試料向きに係る原理等とともに、以下で説明する。
試料106を直方体と仮定し、直方体の面の中から互いに直交する二面を選ぶと、各面の法線方向ベクトルを指定することにより、試料向きを一意に決定できる。しかし、多くの場合、割断面119は上面118に対して垂直でないので、ここでは上面118と側面121の法線方向ベクトルに注目する。
SEMなどの荷電粒子線顕微鏡では高倍率にて試料を観察することが多く、ワーキングディスタンスに対して試料の走査範囲が小さいため、基本的に観察像は試料を平行投影したものとして良い。すなわち、平行な直線群は観察像において平行に投影される。
三次元の直交座標系において、座標内の任意の位置に配置されるベクトルVを、任意の回転軸、例えば原点を通過し方向ベクトルがnである回転軸を中心にθ回転させる操作は、ロドリゲスの回転公式によれば回転行列Rn(θ)として表される。ベクトルVの始点を表す位置ベクトルをV1、終点を表す位置ベクトルをV2とするとき、回転後の始点はRn(θ)V1、終点はRn(θ)V2になるので、ベクトルVの回転後の方向ベクトルは、Rn(θ)V2-Rn(θ)V1=Rn(θ)(V2-V1)となる。なお、V2-V1は回転前のベクトルVの方向ベクトルであり、回転後の方向ベクトルはベクトルVの位置に依らない。
試料向きが同じ状態であったとしても、電子線109の照射方向、走査方向によって観察向きが異なるため、試料の見え方も変化する。特に、境界122の傾きの値は観察向きの影響が大きい。そこで、基準となるワールド座標系と観察像におけるビュー座標系を、右手直交座標系により設定する。なお、ワールド座標系のx軸とy軸は、試料台107の第一傾斜軸123と第二傾斜軸124と平行になるように設定され、z軸は第一傾斜軸123及び第二傾斜軸124に直交するように設定される。試料台107の傾斜軸が直交していない場合、一方の傾斜軸はx軸に、他方の傾斜軸はxy平面と平行になるように設定される。また、ビュー座標系は、観察像の横向きがX軸 、縦向きがY軸として設定される。すなわち、走査方向がX軸、電子線109の照射方向がZ軸となる。よって、観察方向はxyzからXYZに変換する回転行列として表現される。この回転行列RxyzはRx(θx)、Ry(θy)、Rz(θz)を掛け合わせることで表現される。ただし、掛け合わせる順序は統一される。
ワールド座標系において、試料台107の傾斜により方向ベクトルを回転させる回転行列RTA(T、A)はロドリゲスの公式によって求められる。なおTは試料台107の第一傾斜軸123の傾斜角度であり、Aは第二傾斜軸124の傾斜角度である。回転行列の要素は試料台107の傾斜機構によって異なる。また傾斜順序によって試料台107の傾斜状態が異なる場合は、観察中の傾斜順序を統一させる。
上面118と側面121の法線方向ベクトルを試料台107の傾斜角度として表現するにあたり、(T、A)=(0、0)のときのワールド座標系での側面121の法線方向ベクトルをN1、上面118の法線方向ベクトルをN2とする。また二つの法線方向ベクトルN1、N2を初期試料向きとして定義する。
初期試料向きの算出はN1、N2を求めることである。まず、N1の算出方法を説明する。N1を側面121の法線ベクトル、すなわち、割断面119と上面118との境界122に平行な単位ベクトルと仮定する。N1を求めるには、観察向きを同時に求める必要があるので、N1を表す二変数とともに観察向きを表す三変数を求めることになる。N1’は観察像に含まれる境界122と平行であるので、(N1’のY成分)/(N1’のX成分)が境界122の傾きになる。境界122の傾きには、N1の二変数と観察向きの三変数に係る情報が含まれる。そこで、S501からS506の処理が五回以上繰り返され、異なる五点以上の(T、A)のそれぞれに対して、境界122の傾きが算出されれば、N1を表す二変数と観察向きを表す三変数との五変数が求められる。つまり、S501の指定回数は五回以上であることが望ましい。なお、五変数を解析解として求めることが困難な場合は、非線形の最小二乗法等を用いたフィッティングにより五変数が求められても良い。
計算処理部115は、S508で算出された初期試料向きに基づいて、理想断面120が電子線109の照射方向と直交するとき、すなわち試料106の法線ベクトルがN1=(0、0、1)、N2=(0、1、0)となるときの試料台107の傾斜角度を算出する。傾斜角度の算出には、N1’=RxyzRTAN1とN2’=RxyzRTAN2が用いられる。またニュートン法等が用いられても良い。試料台107は、算出された傾斜角度に設定される。
境界検出部113は、S509で設定された傾斜角度における観察像を取得し、取得された観察像から境界122を検出するとともに、走査方向に対する境界122の傾きを算出する。
制御部116は、S510で算出された境界122の傾きが計算値と一致するか否かを判定する。一致すれば図5の処理の流れは終了となり、一致しなければS501へ処理が戻され、初期試料向きの算出をやり直す。一致するか否かは、S510で算出された傾きと計算値との差異の絶対値が予め定められた閾値以下であるか否かによって判定される。このような判定により、初期試料向きの算出精度を向上できる。
制御部116は、S401で算出された初期試料向きに基づいて、操作画面を更新する。具体的には、試料台107が傾斜可能な角度範囲と初期試料向きとに基づいて、観察向き表示部130の極座標の表示範囲が更新される。
制御部116は、S402で更新された操作画面を介して、観察向きを取得する。すなわち、操作者が操作画面の第一観察向き指定部126、第二観察向き指定部127、走査方向指定部128のそれぞれに入力する値が取得される。制御部116は、取得した観察向きに基づいて、観察窓131の極座標での位置と傾きを更新する。なお入力された値が極座標の表示範囲外である場合は、第一観察向き指定部126等にエラーが表示される。
制御部116は、傾斜角調整ボタン129の押下をトリガとして、S403で取得された観察向きに基づいて、試料台107の傾斜角度と走査方向を設定する。
制御部116は、S404で設定された傾斜角度と走査方向に基づいて、試料台107に保持される試料106に向かって電子線109を照射させることにより観察像を取得する。電子線109の照射に係る条件は、操作者が入力表示部117を用いて設定しても良いし、記憶部に予め記憶された条件が読み出されても良い。
Claims (6)
- 荷電粒子線を試料に照射することによって前記試料の観察像を取得する荷電粒子線装置であって、
交差する二つの傾斜軸のそれぞれを中心として傾斜するとともに前記試料を保持する試料台と、
前記試料台の傾斜角度を変えながら取得される観察像のそれぞれから、前記試料の上面と割断面との境界を検出し、前記荷電粒子線の走査方向に対する前記境界の傾きを求める境界検出部と、
傾斜角度毎の観察像から前記上面を検出し、観察像から前記上面が消失するときの前記試料台の傾斜角度である上面消失角度を算出する上面検出部と、
傾斜角度毎の前記境界の傾きと前記上面消失角度に基づいて、前記傾斜角度がゼロのときの前記割断面の向きである初期試料向きを算出する計算処理部を備えることを特徴とする荷電粒子線装置。 - 請求項1に記載の荷電粒子線装置であって、
前記上面検出部は、傾斜角度毎の観察像に対して前記境界で分けられる二つの領域を設定し、一方の領域の輝度平均値を用いて前記上面消失角度を算出することを特徴とする荷電粒子線装置。 - 請求項2に記載の荷電粒子線装置であって、
前記上面検出部は、前記傾斜角度に対する前記輝度平均値の変化をシグモイド曲線でフィッティングすることによって前記上面消失角度を算出することを特徴とする荷電粒子線装置。 - 請求項1に記載の荷電粒子線装置であって、
前記境界検出部は、少なくとも五つの異なる傾斜角度に対して、前記境界の傾きを算出することを特徴とする荷電粒子線装置。 - 請求項1に記載の荷電粒子線装置であって、
前記荷電粒子線の照射方向と走査方向とに係る角度を示す観察窓を、前記荷電粒子線の照射方向に係る角度である座標軸を有する極座標に表示する入力表示部をさらに備えることを特徴とする荷電粒子線装置。 - 荷電粒子線を試料に照射することによって前記試料の観察像を取得する荷電粒子線装置を用いる試料観察方法であって、
交差する二つの傾斜軸のそれぞれを中心として傾斜するとともに前記試料を保持する試料台の傾斜角度を変えながら取得される観察像のそれぞれから、前記試料の上面と割断面との境界を検出し、前記境界の前記荷電粒子線の走査方向に対する傾きを求める境界検出ステップと、
傾斜角度毎の観察像から前記上面を検出し、観察像から前記上面が消失するときの前記試料台の傾斜角度である上面消失角度を算出する上面検出ステップと、
傾斜角度毎の前記境界の傾きと前記上面消失角度に基づいて、前記傾斜角度がゼロのときの前記割断面の向きである初期試料向きを算出する計算処理ステップを備えることを特徴とする試料観察方法。
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