JP7544658B2 - Composite Beam Device - Google Patents

Description

The present invention relates to a composite beam device, and in particular to controlling the attitude of a sample relative to a processing beam.

A composite beam device is a device that processes and observes samples, and is also called a composite beam processing and observation device. A composite beam device includes, for example, a focused ion beam (FIB) processing device and a scanning electron microscope (SEM).

Specifically, the composite beam device includes a stage, a processing beam irradiation unit, an observation beam irradiation unit, a detection unit, a control unit, etc. The stage holds the sample while changing the position and orientation of the sample. The processing beam irradiation unit irradiates the sample with a focused ion beam as a processing beam. The observation beam irradiation unit irradiates the sample with an electron beam as an observation beam. Secondary electrons and the like emitted from the sample when the sample is irradiated with the electron beam are detected by the detection unit.

The processing beam irradiation unit has a first optical axis and irradiates a processing beam along the first optical axis. The observation beam irradiation unit has a second optical axis and irradiates an observation beam along the second optical axis. The first optical axis and the second optical axis pass through a fixed point (reference point) within the sample storage space. The stage has a stage surface on which the sample holder is placed.

In a composite beam device, the sample to be processed and observed is a metal, a semiconductor, etc., and is usually flat. The sample is placed on the sample holding surface of the sample holder, and a cross section (usually a vertical cross section) is formed on the sample to observe the internal structure. A number of streaky irregularities may appear on the cross section that is formed. This phenomenon is called the curtain phenomenon, curtain effect, or curtaining.

In order to remove the multiple irregularities caused by the curtain effect, the azimuth angle of the processing beam is changed and the cross section is subsequently processed, i.e., flattened. For example, in the primary processing, the cross section is formed by a processing beam with an azimuth angle of zero degrees, and then in the secondary processing, the cross section is subsequently processed by a processing beam with an azimuth angle ranging from a few degrees to a few tens of degrees. Sometimes processing is performed three or more times with different azimuth angles of the processing beam.

As will be described in detail later, when the stage has only one tilt axis, it is possible to rotate the stage 90 degrees and tilt it to change the azimuth angle of the processing beam. However, if this method is adopted, it is necessary to return the stage to its original state in order to observe the processed area after processing, and the processed area cannot be observed immediately. In a composite beam device, the ability to immediately observe the processed area is a great advantage, but the above configuration loses this advantage. Incidentally, if two tilt axes are provided that are orthogonal to the stage, it is possible to achieve both changing the azimuth angle and observation immediately after processing, but in that case the stage configuration becomes complicated.

Patent Document 1 discloses a composite beam device capable of removing multiple irregularities caused by the curtain effect. Figure 7 of the document discloses an inclined sample holder. A thin sample is placed on the inclined surface of the inclined sample holder, and a processing beam is irradiated onto the surface of the thin sample (referred to as a cross section in Patent Document 1). The processing beam is presumed to be a broad beam for finishing processing. Patent Document 1 does not disclose the formation of a cross section perpendicular to the surface of the sample, or the removal of multiple irregularities that occur on the cross section.

Patent Document 2 also discloses a composite beam device capable of removing multiple irregularities caused by the curtain effect. The configuration disclosed therein solves the problems caused by the configuration disclosed in Patent Document 1 (see paragraph 0004 of Patent Document 2), that is, it is an alternative to the configuration disclosed in Patent Document 1. The tilt movement of the stage creates a tilted state of the sample, and in that state, a tilted cross section is formed on the sample. The tilted cross section is then processed afterwards. In the after-processing, a combination of the tilt angle and the rotation angle is calculated. However, according to the configuration disclosed in Patent Document 2, in principle, it is not possible to form a cross section perpendicular to the surface of the sample. For example, in semiconductor parts, patterns are stacked horizontally and vertically on a crystal substrate such as a silicon substrate. When observing the cross section of a semiconductor part with a transmission electron microscope or the like to evaluate the part, it is a basic premise that the observed cross section is formed perpendicular to the sample surface. This is because if the cross section is tilted to the sample surface, the vertical relationship between each pattern cannot be grasped.

JP 2014-63726 A JP 2017-174748 A

The objective of the present invention is to enable a composite beam device to form a cross section of a sample and then remove multiple irregularities that occur on the cross section, assuming that the processed area can be immediately observed.

The composite beam device according to the present invention includes a processing beam irradiation unit having a first optical axis passing through a reference point and irradiating a processing beam, an observation beam irradiation unit having a second optical axis intersecting the first optical axis at the reference point and irradiating an observation beam, a stage having a tilt axis that is perpendicular to a reference plane including the first optical axis and the second optical axis and passes through the reference point, a rotation axis that passes through the reference point and moves within the reference plane, and a stage surface perpendicular to the rotation axis, a tilt holder attached to the stage and having a sample holding surface tilted at a fixed tilt angle with respect to the stage surface, a determination unit that determines the tilt angle of the stage surface, the rotation angle of the stage surface, and the rotation angle of the scanning direction of the processing beam based on the azimuth angle of the processing beam when a cross section is created for a sample held on the sample holding surface, and a control unit that controls the operation of the stage based on the tilt angle of the stage surface and the rotation angle of the stage surface, and controls the operation of the processing beam irradiation unit based on the rotation angle of the scanning direction.

According to the present invention, in a composite beam device, a cross section can be formed in a sample under conditions that allow immediate observation of the processed area, and multiple irregularities that occur on the cross section can then be removed.

FIG. 2 is a diagram showing a general coordinate system of a stage. FIG. 2 is a diagram illustrating an example of a stage configuration. FIG. FIG. FIG. 13 is a diagram showing a state in which the sample is rotated by 90 degrees. FIG. 13 is a diagram showing a state in which the sample is further tilted. FIG. 1 is a diagram illustrating an example of the configuration of a composite beam device according to an embodiment. FIG. 2 is a diagram showing a coordinate system of a stage on which a tilt holder is mounted. FIG. 13 is a diagram showing the realization of an azimuth angle by combining a rotation angle and a tilt angle. 13 is a diagram showing the rotation angle of the scanning direction in the processing beam irradiation unit. FIG. FIG. 2 illustrates a first exemplary configuration of a parameter determination unit; FIG. 13 is a diagram illustrating a second configuration example of the parameter determination unit. 10 is a flowchart illustrating an operation example according to the embodiment. FIG. 1 is a diagram showing the processing of a thin film sample. FIG. 13 is a diagram showing a tilt holder according to a first modified example. FIG. 13 is a diagram showing a tilt holder according to a second modified example.

The following describes the embodiment with reference to the drawings.

(1) Overview of the embodiment The composite beam device according to the embodiment includes a processing beam irradiating unit, an observation beam irradiating unit, a stage, a tilt holder, a determination unit, and a control unit. The processing beam irradiating unit has a first optical axis passing through a reference point, and irradiates a processing beam. The observation beam irradiating unit has a second optical axis intersecting the first optical axis at the reference point, and irradiates an observation beam. The stage has a tilt axis that is orthogonal to a reference plane including the first optical axis and the second optical axis and passes through the reference point, a rotation axis that passes through the reference point and moves within the reference plane, and a stage surface that is orthogonal to the rotation axis. The tilt holder is attached to the stage and has a sample holding surface that is inclined at a fixed tilt angle (pre-tilt angle) with respect to the stage surface. The determination unit determines the tilt angle of the stage surface, the rotation angle of the stage surface, and the rotation angle of the scan direction of the processing beam based on the azimuth angle of the processing beam when a cross section is prepared for a sample held on the sample holding surface. The control unit controls the operation of the stage based on the tilt angle of the stage surface and the rotation angle of the stage surface, and controls the operation of the processing beam irradiation unit based on the rotation angle of the scan direction.

With the above configuration, even if the stage has one tilt axis, the desired azimuth angle of the processing beam can be achieved by changing the combination of the tilt angle and rotation angle of the stage surface, assuming the use of an inclined holder. During the cross-section production process, the processing area can be quickly observed at the required timing. With the above configuration, even if the combination of the tilt angle and rotation angle of the stage surface changes, the orthogonality of the tilt axis to the reference plane and the movement of the rotation axis within the reference plane are always maintained.

The processing beam is a charged particle beam, such as a focused ion beam. The observation beam is a charged particle beam, such as an electron beam. In an embodiment, the stage surface is a physical surface on which the sample holder is placed, although the concept can include virtual surfaces.

In an embodiment, the cross section is a cross section perpendicular to the surface of the sample. For example, if one wishes to observe the internal structure of a semiconductor, a vertical cross section showing the internal structure is formed on the semiconductor. The surface of the sample is the surface on the beam irradiated side (front surface). The front and back surfaces of the sample are generally parallel to each other.

The composite beam device according to the embodiment includes a setting unit that sets the azimuth angle of the processing beam and the incidence angle of the processing beam when creating a cross section. The determination unit determines the tilt angle of the stage surface, the rotation angle of the stage surface, and the rotation angle of the scanning direction of the processing beam based on the azimuth angle and the incidence angle. With this configuration, the user can freely specify the azimuth angle and incidence angle. The azimuth angle and incidence angle may be automatically set according to the processing conditions.

If a sample normal axis is defined for the sample, a plane including the sample normal axis and tilt axis (a plane including a cross section formed on the sample) is defined as a first plane, and a plane including the sample normal axis and perpendicular to the first plane is defined as a second plane, the inclination angle of the processing beam relative to the sample normal axis in the first plane is the azimuth angle, and the inclination angle of the processing beam relative to the sample normal axis in the second plane is the incidence angle.

In an embodiment, the tilt holder has a marker that serves as a guide when adjusting the orientation of the sample when fixing the sample to the sample holding surface. With this configuration, the sample can be placed in the correct orientation when placed on the tilt holder. The marker includes a line parallel to the tilt axis. Since the cross section is formed parallel to the tilt axis, it is easy to recognize in which direction the cross section is formed by referring to the line.

(2) Details of the embodiment First, a general coordinate system defined for a stage and problems that arise under this coordinate system will be described with reference to FIGS.

Figure 1 shows a sample 10 on a sample holder. The sample holder is fixed on the stage surface of the stage. However, the stage and the sample holder are not shown. The reference point O is a fixed point in the space that contains the sample. The first optical axis 24 and the second optical axis 26 intersect at the reference point O at a predetermined angle. A processing beam is irradiated along the first optical axis 24, and an observation beam is irradiated along the second optical axis 26. In the illustrated example, the reference point O is located on the surface 10A of the sample 10. A plane including the first optical axis 24 and the second optical axis 26 constitutes the reference plane. In addition, in Figure 1, the first optical axis 24 and the second optical axis 26 are each represented diagrammatically as an arrow pointing toward the reference point O.

The stage has a tilt axis (T axis) 14, a rotation axis (R axis) 16, an x axis, and a y axis 18. The T axis 14 passes through a reference point O and is perpendicular to the reference plane. The R axis 16 passes through the reference point O and moves within the reference plane. In the illustrated state, the x axis coincides with the T axis 14, and the z axis coincides with the R axis 16. The x axis and the y axis 18 are perpendicular to each other and parallel to the surface 10A of the sample 10. The z axis is the sample normal axis, which is perpendicular to the x axis and the y axis 18. The rotational movement around the R axis 16 as the rotational center axis is indicated by the reference symbol 20. The rotational movement (tilt movement) around the T axis 14 as the rotational center axis is indicated by the reference symbol 22.

The tilting of the stage causes the R-axis 16 and y-axis 18 to tilt around the T-axis 14. The rotation of the stage causes the x-axis and y-axis 18 to rotate around the R-axis 16. In FIG. 1, an absolute coordinate system in the space that contains the sample is shown, specifically the X-axis, Y-axis, and Z-axis. A relative coordinate system based on the stage surface is made up of the T-axis 14, R-axis 16, x-axis, y-axis 18, and z-axis. However, the T-axis 14 is stationary.

By processing the sample 10 with the processing beam, a cross section 28 is created in the sample 10. As a result, a wedge-shaped recess 30 is created in the sample 10. The cross section 28 is a vertical cross section perpendicular to the surface 10A.

Figure 2 shows the schematic configuration of the stage 32. The stage 32 has a lifting mechanism 38, a tilt mechanism 40, an xy slide mechanism 42, and a rotation mechanism 44. These mechanisms are stacked in that order from bottom to top. The stage 32 (specifically, the rotation mechanism 44) has a stage surface 34, on which a sample holder 36 holding a sample is placed. A typical sample holder has a cylindrical shape, and its bottom and top surfaces are parallel. The top surface functions as the sample holding surface.

The incidence angle and azimuth angle of the processing beam will be explained using Figures 3 and 4. In Figure 3, a reference point O exists on the surface of the sample 10. The first reference plane 45A is a plane that includes the reference point O, the first optical axis, and the second optical axis. The second reference plane 45B is a plane that includes the reference point O and is perpendicular to the first reference plane 45A. The cross section 28 created in the sample 10 belongs to the second reference plane 45B. The incidence angle 46 of the processing beam 24A is the inclination angle of the processing beam 24A within the first reference plane 45A, that is, the inclination angle of the processing beam 24A with respect to the second reference plane 45B or the sample normal axis.

In FIG. 4, the cross section 28 and the T-axis created in the sample 10 are shown. The azimuth angle 48 is the inclination angle of the processing beam 24A in the second reference plane 45B, i.e., the inclination angle of the processing beam 24A relative to the first reference plane 45A or the sample normal axis.

Returning to FIG. 1, when observing the surface 10A of the sample 10, the tilt angle is adjusted so that the surface 10A is perpendicular to the second optical axis 26. When forming a cross section 28 on the sample 10, the tilt angle is adjusted so that the surface 10A of the sample 10 is perpendicular to the first optical axis 24. As already explained, the T-axis 14 is perpendicular to the reference plane that includes the first optical axis 24 and the second optical axis 26.

In the configuration shown in FIG. 2, a rotation mechanism 44 is mounted on the tilt mechanism 40 via an xy slide mechanism 42. Assuming this configuration, in FIG. 1, the R axis 16 and the y axis 18 tilt during tilt operation. When an arbitrary tilt angle is set, the stage surface can be rotated around the R axis 16, and when an arbitrary tilt angle and an arbitrary rotation angle are set, the stage surface can be slid in the x-axis direction and the y-axis 18 direction.

As described above, the first optical axis 24 and the second optical axis 26 intersect at the reference point O, and the T-axis 14 is perpendicular to the reference plane. When a cross section 28 is created using a processing beam, the cross section 28 can be immediately observed as an electron microscope image (SEM image). In this case, no stage movement is required. This is a major advantage of the composite beam device. In order to observe the processed cross section 28 as it is without stage movement, the cross section 28 is created so that it belongs to the second reference plane that includes the tilt axis.

By the way, it is also possible to observe the sample by detecting the signal emitted from the sample while scanning the processing beam, but in this case, it is necessary to tilt the stage after processing the sample. This extends the time for the entire sample processing process.

However, when a cross section 28 is made on the sample 10, a curtain effect occurs due to the fact that the degree of ease of processing varies locally in the sample, resulting in multiple irregularities on the cross section 28. To solve this problem, it is necessary to perform multiple processing beam scans while maintaining the angle of incidence on the cross section 28 and setting multiple azimuth angles. However, in the case of the configuration shown in Figure 1, the azimuth angle cannot be changed even if the tilt angle or rotation angle is changed.

In this regard, it is possible to rotate the stage surface 90 degrees around the R axis, as indicated by reference numeral 50 in FIG. 5, and tilt the stage surface around the T axis by an angle corresponding to the desired azimuth angle, as indicated by reference numeral 52 in FIG. 6. Note that the first optical axis 24 and the second optical axis 26 are shown in FIG. 5 and FIG. 6. The R axis after tilting is indicated by reference numeral 53 in FIG. 6.

In FIG. 6, the cross section 28 created in the sample 10 has an inclined attitude. In this state, if the processing beam is scanned along the x-axis, it is possible to suppress multiple irregularities caused by the curtain effect.

However, when the above method is adopted, the processed area cannot be observed in the state shown in Figure 6. To observe the processed area, for example, the stage surface needs to be rotated 90 degrees. This increases the time required to create the cross section. To create a high-quality cross section, processing and observation need to be repeated, but when the method shown in Figures 5 and 6 is used, the time for the entire sample processing process is significantly increased. In particular, when the object to be observed is very small, processing needs to be stopped immediately when the object to be observed is exposed, so processing and observation need to be repeated alternately at short intervals. In that case, sample processing will take even longer.

In addition, several methods for removing the multiple irregularities caused by the curtain effect are described in the Background Art section above. However, these methods do not allow for the creation of a vertical cross section on the sample. More specifically, these methods are based on the premise that the processed area can be immediately observed as necessary, and do not allow for the creation of a vertical cross section on the sample and the removal of the multiple irregularities that occur on that cross section.

Next, the composite beam device according to the embodiment will be described in detail with reference to Figures 7 to 16. Figure 7 shows a schematic configuration of the composite beam device according to the embodiment.

The composite beam device is composed of a processing and observation unit 60 and an arithmetic and control unit 62. The processing and observation unit 60 has a processing beam irradiation unit 66, an observation beam irradiation unit 68, a stage 70, a detector 72, etc.

The processing beam irradiation unit 66 constitutes the first lens barrel, which has a first optical axis 24. The processing beam irradiation unit 66 irradiates a processing beam along the first optical axis 24. Specifically, the processing beam is a focused ion beam (FIB). The processing beam irradiation unit 66 has an electrically controlled beam scanning function. This function allows the processing beam to be scanned in any direction with the first optical axis 24 as the center.

The observation beam irradiating unit 68 constitutes a second lens barrel, which has a second optical axis 26. The observation beam irradiating unit 68 irradiates an observation beam along the second optical axis 26. Specifically, the observation beam is an electron beam. The observation beam irradiating unit 68 and the detector 72 correspond to a scanning electron microscope.

The stage 70 has the configuration shown in FIG. 2, for example. That is, the stage 70 has a lifting mechanism, a tilt function, an xy slide mechanism, a rotation mechanism, and the like. Reference numeral 74 denotes the stage surface. A plurality of sample holders are prepared, from which a specific sample holder is selected and used. The plurality of sample holders includes an inclined sample holder (hereinafter referred to as an inclined holder) 76, which will be described in detail later. When forming a cross section of the sample, the inclined holder 76 is selected and attached to the stage surface 74. The inclined holder 76 has an inclined sample holding surface, on which the sample 64 is placed. In FIG. 7, the tilt angle of the stage surface 74 is adjusted so that the surface of the sample 64 is perpendicular (directly facing) to the first optical axis 24.

The detector 72 detects signals (two-dimensional electrons, backscattered electrons, etc.) emitted from the sample 64 when the sample is irradiated with an electron beam. A detector that detects signals other than electrons may also be provided.

The calculation control unit 62 has an information processing unit 78, an input unit 84, a display unit 86, etc. The information processing unit 78 has a processor, a memory, etc. The processor is, for example, a CPU that executes a program. The processor performs multiple functions. In FIG. 7, two representative functions are shown, namely, a parameter determination unit 80 and a processing control unit 82.

The information processing unit 78 controls the operation of the processing and observation unit 60. The information processing unit 78 also forms an SEM image based on the output signal from the detector 72. The input unit 84 is composed of, for example, a keyboard.

Using the input device 84, the user can specify the incidence angle and azimuth angle of the processing beam. In the cross-section preparation process, the azimuth angle during primary processing may be 0 degrees, and the azimuth angle during secondary processing for removing irregularities may be set to an angle within a range of several degrees to several tens of degrees. The difference between two azimuth angles may be specified, or individual azimuth angles may be specified. Two or more azimuth angles may be defined. The incidence angle may also be specified at any angle. The display 86 displays an SEM image, and also displays multiple parameters that have been set or calculated.

The parameter determination unit 80 determines the tilt angle of the stage surface, the rotation angle of the stage surface, and the rotation angle of the scanning direction of the processing beam based on the tilt angle (fixed tilt angle) of the tilt holder 76 and the azimuth angle of the processing beam. When the incidence angle of the first optical axis 24 is specified, the parameter determination unit 80 determines each parameter while taking the incidence angle into consideration. The calculation formulas for determining each parameter will be described in detail later.

The processing control unit 82 controls the operation of the stage 70 according to the determined tilt angle and rotation angle of the stage surface. The processing control unit 82 also controls the operation of the processing beam irradiation unit 66 according to the determined rotation angle of the scan direction.

Figure 8 shows a sample 64 held by a tilt holder 76. The sample 64 has a plate-like shape, and its surface (front surface) 64A is flat. In the sample 64, the front surface 64A and the rear surface are in a parallel relationship. The sample 64 is, for example, a semiconductor. In order to investigate and confirm the internal structure, a cross section 110 perpendicular to the surface 64A is formed.

The tilt holder 76 has a wedge shape as a whole. Its upper surface constitutes the sample holding surface 76A. Its bottom surface is removably fixed onto the stage surface 74. The tilt angle of the sample holding surface 76A relative to the stage surface 74 is the fixed tilt angle (pretilt angle) 94.

The stage surface 74 is the upper surface of the top plate 90 of the stage. A first engagement structure is formed on the top plate 90 or the stage surface 74, while a second engagement structure is formed on the bottom or bottom surface of the tilt holder 76. The second engagement structure removably engages with the first engagement structure. This naturally optimizes the position and orientation of the tilt holder 76 relative to the stage surface 74.

In FIG. 8, an absolute coordinate system defined with respect to the first optical axis 98 is shown. The absolute coordinate system includes an X-axis, a Y-axis, and a Z-axis. The Z-axis and the first optical axis 98 are parallel. However, the illustrated absolute coordinate system is merely an example.

At the reference point O, the first optical axis 98 and the second optical axis 100 intersect. A first reference plane is defined as a plane to which the first optical axis 98 and the second optical axis 100 belong. The tilt axis (T axis) 102 passes through the reference point O and is perpendicular to the first reference plane. The rotation axis (R axis) 104 passes through the reference point O and moves within the first reference plane. In the state shown in FIG. 8, the x axis coincides with the T axis 102. The y axis 106 is inclined with respect to the sample horizontal axis 108 shown for reference. The sample horizontal axis 108 passes through the reference point O, is perpendicular to the T axis 102, and is an axis parallel to the surface of the sample 64. The x axis and the y axis 106 are each an axis parallel to the stage surface 74.

In the state shown in FIG. 8, the stage surface 74 is tilted at a tilt angle 96 with respect to the XY plane. The tilt angle is the same as the fixed tilt angle 94 (but the orientation is different). The surface 64A of the sample 64 is perpendicular to the first optical axis 98. When the stage surface 74 tilts, the R-axis 104 and the y-axis 106 also tilt. When the stage surface 74 rotates around the R-axis 104, the x-axis and the y-axis 106 also rotate.

In the state shown in Fig. 8, the processing beam is moved relative to the sample 64 in a direction along the T-axis 102 to form a cross section 110. The cross section 100 has a width direction and a depth direction. As is clear from the above description and as shown in Fig. 8, the width direction of the cross section 100 and the T-axis 102 are parallel, and in this state, the fixed tilt angle 94 corresponds to an angle around the T-axis 102.

In the illustrated state, the azimuth angle of the processing beam is 0 degrees. It is also possible to set the azimuth angle to an angle other than 0 degrees using the technique described below. If necessary, during the cross-section production process, it is possible to observe the cross-section 110 from the direction of the second optical axis 100. At that time, the tilt angle may be changed to make the cross-section 110 perpendicular to the second optical axis 100.

After the cross section 110 is formed, multiple irregularities are generated on the cross section 110 due to the curtain effect. In order to remove these irregularities, the cross section 110 is processed afterwards. In this after-processing, the tilt angle and rotation angle are adjusted to achieve the desired azimuth angle. In other words, the combination of tilt angle and rotation angle that achieves the azimuth angle is determined.

Figure 9 shows a cross section 110 produced by performing the primary processing step. When the cross section 110 is produced, the azimuth angle of the processing beam 98A is 0 degrees. The first optical axis, the second optical axis, the T axis 114, the R axis 118, and the sample vertical axis (z axis) 115 pass through the reference point O. When the cross section 110 is produced, the z axis (sample vertical axis) 115 coincides with the first optical axis. The processing beam 98A is irradiated along the first optical axis.

Prior to the execution of the secondary processing step, the tilt angle of the stage surface, the rotation angle of the stage surface, and the rotation angle of the scan direction are determined according to the set azimuth angle. The stage operation is controlled according to the determined tilt angle and rotation angle of the stage. In the process, the attitude of the cross section 110 changes. Reference numeral 112 indicates the cross section after the attitude change. As the stage moves, the R-axis 118 moves within the first reference plane as indicated by reference numeral 122. The R'-axis 120 is the R-axis after the movement. As the stage moves, the z-axis 115 moves as indicated by reference numeral 124. The z'-axis 116 is the sample vertical axis after the movement.

The cross section 112 belongs to a plane including the first optical axis and the z' axis 116. The processing beam 98A is inclined by an azimuth angle of 125 with respect to the z' axis 116. The processing beam 98A is scanned at the determined angle of the scanning direction, thereby removing irregularities on the cross section 112 and flattening the cross section 112. The scanning direction is a direction along the cross section 112 as viewed from the processing beam irradiation unit. Three or more processing steps may be performed with different azimuth angles.

During the process of processing the cross section 112, the cross section 112 can be observed from the second optical axis direction, if necessary. In this case, it is not necessary to operate the stage to observe the cross section 112. For example, processing and observation may be repeated in short cycles. It is also possible to observe the cross section 112 after orthogonally orthogonalizing the cross section 112 to the second optical axis by controlling the operation of the stage.

In practice, each parameter is determined so that the set incidence angle is realized in the primary processing step and the secondary processing step. Specifically, prior to the primary processing step, the tilt angle is adjusted according to the set incidence angle. Prior to the secondary processing step, the tilt angle of the stage surface, the rotation angle of the stage surface, and the rotation angle of the scan direction are determined according to the incidence angle and azimuth angle.

Figure 10 shows the scanning direction 134 of the processing beam. As described above, the rotation angle of the scanning direction is determined according to the set azimuth angle, etc. The rotation angle corresponds to the inclination angle of the cross section 130 in the absolute coordinate system.

11 shows a first example of the parameter determination unit shown in FIG. 7. The parameter determination unit 80A is composed of a parameter calculation unit 136. The parameter calculation unit 136 calculates the tilt angle θt of the stage surface, the rotation angle φr of the stage surface, and the rotation angle φs of the scanning direction of the processing beam as a parameter set based on the fixed tilt angle θp and azimuth angle θIB of the tilt holder. For example, the azimuth angle of the processing beam in the primary processing step is set to 0 degrees. In that case, the azimuth angle θIB is the azimuth angle of the processing beam in the secondary processing step. The parameter calculation unit 136 may further be given the incident angle of the processing beam.

12 shows a second example of the parameter determination unit shown in FIG. 7. The parameter determination unit 80B is composed of a parameter table 138. The parameter table 138 calculates the tilt angle θt of the stage surface, the rotation angle φr of the stage surface, and the rotation angle φs of the scanning direction of the processing beam as a parameter set based on the azimuth angle θIB. The fixed tilt angle θp is known, and the calculation result taking it into consideration is registered in advance in the parameter table 138. The incident angle of the processing beam may be further provided to the parameter table 138. The azimuth angle θi of the processing beam set in the first processing step and the azimuth angle θi of the processing beam set in the second processing step may be provided to the parameter table 138 individually.

Next, we will explain how to calculate the parameter set. For ease of explanation, we will define an absolute coordinate system based on the first optical axis. That is, we will define a Z axis that coincides with the first optical axis, an X axis that coincides with the tilt axis, and a Y axis that is perpendicular to the Z axis and X axis.

If the first optical axis is denoted by u _fib , it is defined by the following equation (1).

In order to make the surface of the sample perpendicular to the first optical axis, the stage surface is rotated around the T axis. The angle (tilt angle) is _θp . The R axis of the stage rotates around the T axis, and its direction changes as shown in the following formula (2).

In a state where the surface of the sample is perpendicular to the first optical axis, a cross section perpendicular to the surface of the sample can be created in the sample by performing primary processing on the sample using a processing beam. If the irradiation direction of the processing beam in the primary processing step is _u1 , _u1 coincides with the above u _fib , and therefore _u1 can be expressed as the following formula (3).

If the normal vector of the cross section created in the sample is _n1 , _n1 can be expressed by the following equation (4).

A secondary process is applied to the cross section created in the primary process step to suppress multiple irregularities caused by the curtain effect. In order to suppress these irregularities, the processing beam azimuth angle with respect to the cross section may be changed by an arbitrary angle θ _IB while maintaining the incident angle of the processing beam with respect to the cross section. If the azimuth angle during the primary process is 0 degrees, θ _IB is set as the azimuth angle during the secondary process.

To achieve this azimuth angle, tilting the stage surface and rotating the stage surface are used in combination. In what follows, the tilting motion of the stage surface is represented as q, and the rotational motion of the stage surface is represented as p.

When the direction of the processing beam in the secondary processing step is _u2 and the normal vector of the cross section is _n2 , they are expressed by the following equations (5) and (6).

The tilt angle and rotation angle of the stage surface are determined so that the two conditions shown in the following expressions (7) and (8) are satisfied.

Here, θ _IB is the difference between the azimuth angle of the processing beam in the primary processing step and the azimuth angle of the processing beam in the secondary processing step. Specifically, if the azimuth angle of the processing beam in the primary processing step is 0 degrees, θ _IB is the azimuth angle of the processing beam in the secondary processing step. θ _IB is a value that can be arbitrarily input by the user.

The tilt movement p of the stage surface is expressed by the following equation (9): where θt is the tilt angle of the stage surface.

Due to the tilt movement of the stage surface, the rotation axis of the stage changes as shown in the following equation (10): where θ _p is the fixed tilt angle of the tilt holder.

Since the rotational motion of the stage surface is a rotation about the above rotation axis, if the rotation angle is _φr , then the rotational motion q can be expressed by the following equation (11).

By applying the above equations (9) and (11) to the equations (5) and (6) and then solving the equations (7) and (8), the following equations (12) and (13) are derived.

In the above formulas (12) and (13), _θp and _θIB are known parameters, and there are two unknown parameters, _θt and _φr . From the above formulas (12) and (13), the tilt angle _θt and rotation angle _φr of the scan plane for realizing the azimuth angle can be obtained.

The processing beam irradiation unit is equipped with an X-direction deflection electrode and a Y-direction deflection electrode. Using these, the scanning direction of the processing beam can be determined in any direction. The tilt angle _θt and the rotation angle _φr of the stage surface obtained by the above parameter calculation make the normal vector _n2 of the cross section perpendicular to the first optical axis. Under this condition, it is possible to match the scanning direction with the cross section line in the XY plane by adjusting the rotation angle _φs of the scanning direction.

The rotation s of the scanning direction of the processing beam is expressed by the following equation (14).

The condition for determining _φs is given by the following formula (15): Formula (15) determines whether the normal vector _n1 of the cross section in the primary processing coincides with the normal vector _n2 of the cross section in the secondary processing.

As described above, the tilt angle θ _t and rotation angle φ _r of the scan plane and the rotation angle φ _s of the scan direction of the processing beam for achieving a desired azimuth angle θ _IB can be obtained.

Figure 13 shows the operation according to the embodiment as a flowchart. In S10, the user specifies the azimuth angle, incident angle, cross-sectional width, cross-sectional depth, etc. Processing conditions are set based on these. In S12, a tilt holder is placed on the stage surface. In S14, the stage operation is controlled and the primary processing step is carried out, thereby creating a cross-section in the sample. The cross-section is observed during or after the primary processing step.

In S16, a parameter set is calculated based on the azimuth angle of the processing beam, etc., i.e., the tilt angle and rotation angle of the stage surface, and the rotation angle of the scanning direction of the processing beam are calculated. In S18, the operation of the stage is controlled based on these parameter sets, and the operation of the processing beam irradiation unit is also controlled. The cross section is observed during or after the secondary processing step. Note that, as shown in S20, finishing processing may be performed repeatedly. In this case, the azimuth angle is changed for each finishing processing.

Figure 14 shows the process of preparing a thin sample 140 for observation in a transmission electron microscope. A processing beam generally has a certain degree of divergence. Each cross section produced by such a processing beam is a surface inclined at a small angle relative to the angle of incidence of the processing beam (see, for example, reference numerals 146A and 146B).

In order to make each cross section a vertical cross section, it is necessary to tilt the incident direction of the processing beams 144A, 144B by θ _d with respect to the axis lines 142A, 142B perpendicular to the end face of the sample. In such a case, the value obtained by adding or subtracting the value θ _d for adjusting the angle to the fixed tilt angle θ _p of the tilt holder may be substituted into each of the above calculation formulas. Alternatively, a signed value θ _d may be added to the fixed tilt angle θ _p . The above-mentioned method may also be applied when a single cross section is prepared on a flat sample instead of a thin sample. In other words, the above-mentioned method corresponds to the adjustment of the incident angle of the processing beam.

An appropriate θ _d varies depending on the configuration and irradiation conditions of the processing beam irradiation unit. In general, the larger the probe current, the larger the angle θ _d . Therefore, in rough processing with a large probe current, a relatively large angle (e.g., 0 degrees to 3 degrees) may be adopted as the angle θ _d , and in finish processing with a small probe current, a relatively small angle (0 degrees to 1 degree) may be adopted as the angle θ _d . Since θ _d is a different value for each processing stage, it is desirable to treat it as one independent parameter.

Figure 15 shows a first modified example of the tilt holder. The tilt holder 150 is installed relative to the stage surface 152. The tilt holder 150 has a tilted sample holding surface 150A, on which a sample 154 is attached. A first axis 157 and a second axis 158 can be defined for the sample holding surface 150A, which pass through the center point of the sample holding surface 150A and are orthogonal to each other. The sample holding surface 150A has an elliptical shape, with the first axis 157 corresponding to the major axis of the ellipse and the second axis 158 corresponding to the minor axis of the ellipse.

A step surface 156 is formed at the upper end of the sample holding surface of the tilt holder 150. The step surface 156 has a side (line) 156A that is parallel to the tilt axis and axis 158. When placing the sample 154 on the sample holding surface 150A, the side 156A functions as a marker. In other words, the orientation of the sample 154 is determined so that a reference line (e.g., a side surface) of the sample 154 is parallel to the side 156A. This makes it possible to accurately form a cross section at the desired position.

Figure 16 shows a second modified example of the tilt holder. In the tilt holder 160, the tilted sample holding surface 160A is formed with markers 162 that serve as a guide when placing a sample thereon. In the illustrated example, the markers 162 include a plurality of lines parallel to the tilt central axis (long axis, vertical axis) on the sample holding surface 160A and a plurality of lines parallel to the orthogonal axes (short axis, horizontal axis) on the sample holding surface 160A. Line 166 is a line representing the tilt central axis, which passes through the center point 168. Line 164 is a line representing an orthogonal axis perpendicular to the tilt central axis, which also passes through the center point 168. When placing a sample on the sample holding surface 160A, the position and orientation of the sample can be adjusted while looking at the markers 162.

24 First optical axis, 26 Second optical axis, 60 Processing and observation section, 62 Calculation control section, 64 Sample, 66 Processing beam irradiation section, 68 Observation beam irradiation section, 70 Stage, 74 Stage surface, 76 Tilt holder, 80 Parameter determination section, 82 Processing control section.

Claims (5)

a processing beam irradiation unit having a first optical axis passing through a reference point and irradiating a processing beam;
an observation beam irradiating unit that has a second optical axis that intersects with the first optical axis at the reference point and irradiates an observation beam;
a stage having a tilt axis that is perpendicular to a reference plane including the first optical axis and the second optical axis and passes through the reference point, a rotation axis that passes through the reference point and moves within the reference plane, and a stage surface that is perpendicular to the rotation axis;
a tilt holder attached to the stage and having a sample holding surface tilted at a fixed tilt angle with respect to the stage surface;
a determination unit that determines a tilt angle of the stage surface, a rotation angle of the stage surface, and a rotation angle of a scan direction of the processing beam based on an azimuth angle of the processing beam when a cross section is created on the sample held on the sample support surface;
a control unit that controls an operation of the stage based on a tilt angle of the stage surface and a rotation angle of the stage surface, and controls an operation of the processing beam irradiation unit based on a rotation angle of the scan direction;
Including,
The cross-section has a width direction and a depth direction,
When the width direction of the cross section is parallel to the tilt axis, the fixed tilt angle corresponds to an angle around the tilt axis.
A composite beam device comprising: a processing beam irradiation unit having a first optical axis passing through a reference point and irradiating a processing beam;
an observation beam irradiating unit that has a second optical axis that intersects with the first optical axis at the reference point and irradiates an observation beam;
a stage having a tilt axis that is perpendicular to a reference plane including the first optical axis and the second optical axis and passes through the reference point, a rotation axis that passes through the reference point and moves within the reference plane, and a stage surface that is perpendicular to the rotation axis;
a tilt holder attached to the stage and having a sample holding surface tilted at a fixed tilt angle with respect to the stage surface;
a determination unit that determines a tilt angle of the stage surface, a rotation angle of the stage surface, and a rotation angle of a scan direction of the processing beam based on an azimuth angle of the processing beam when a cross section is created for the sample held on the sample support surface;
a control unit that controls an operation of the stage based on a tilt angle of the stage surface and a rotation angle of the stage surface, and controls an operation of the processing beam irradiation unit based on a rotation angle of the scan direction;
Including,
the cross section is perpendicular to the surface of the sample;
A composite beam device comprising: a processing beam irradiation unit having a first optical axis passing through a reference point and irradiating a processing beam;
an observation beam irradiating unit that has a second optical axis that intersects with the first optical axis at the reference point and irradiates an observation beam;
a stage having a tilt axis that is perpendicular to a reference plane including the first optical axis and the second optical axis and passes through the reference point, a rotation axis that passes through the reference point and moves within the reference plane, and a stage surface that is perpendicular to the rotation axis;
a tilt holder attached to the stage and having a sample holding surface tilted at a fixed tilt angle with respect to the stage surface;
a determination unit that determines a tilt angle of the stage surface, a rotation angle of the stage surface, and a rotation angle of a scan direction of the processing beam based on an azimuth angle of the processing beam when a cross section is created on the sample held on the sample support surface;
a control unit that controls an operation of the stage based on a tilt angle of the stage surface and a rotation angle of the stage surface, and controls an operation of the processing beam irradiation unit based on a rotation angle of the scan direction;
Including,
a setting unit that sets an azimuth angle of the processing beam and an incident angle of the processing beam when the cross section is created,
the determination unit determines a tilt angle of the stage surface, a rotation angle of the stage surface, and a rotation angle of the scan direction based on the azimuth angle and the incident angle.
A composite beam device comprising: a processing beam irradiation unit having a first optical axis passing through a reference point and irradiating a processing beam;
an observation beam irradiating unit that has a second optical axis that intersects with the first optical axis at the reference point and irradiates an observation beam;
a stage having a tilt axis that is perpendicular to a reference plane including the first optical axis and the second optical axis and passes through the reference point, a rotation axis that passes through the reference point and moves within the reference plane, and a stage surface that is perpendicular to the rotation axis;
a tilt holder attached to the stage and having a sample holding surface tilted at a fixed tilt angle with respect to the stage surface;
a determination unit that determines a tilt angle of the stage surface, a rotation angle of the stage surface, and a rotation angle of a scan direction of the processing beam based on an azimuth angle of the processing beam when a cross section is created for the sample held on the sample support surface;
a control unit that controls an operation of the stage based on a tilt angle of the stage surface and a rotation angle of the stage surface, and controls an operation of the processing beam irradiation unit based on a rotation angle of the scan direction;
Including,
the tilt holder has a marker that serves as a guide for adjusting the orientation of the sample when fixing the sample to the sample support surface;
A composite beam device comprising: 5. The composite beam device of claim 4,
The marker includes a line parallel to the tilt axis.
A composite beam device comprising:

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