Sample Milling Apparatus and Method of Adjustment Therefor

A sample milling apparatus includes an ion source, a swinging mechanism for swinging a sample, a positioning camera for bringing a target milling position on the sample into coincidence with the impact point of an ion beam, and a display section for displaying an image captured by the positioning camera. The adjustment method starts with observing the trace of the impinging ion beam left on the sample with the positioning camera while the position of the positioning camera is held relative to the swing axis of the swinging mechanism and capturing an observation image. Then, a display image to be displayed on the display section is extracted from the observation image based on the position of the trace, thus bringing the beam impact point and the position of the field of view of the display image into coincidence.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2021-036229 filed Mar. 8, 2021, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sample milling apparatus and a method of adjusting it.

2. Description of the Related Art

Cross Section Polisher (a trademark registered) for milling sample cross sections and Ion Slicer (a trademark registered) for preparing thin film samples are known as apparatus for milling samples using an ion beam. Such a sample milling apparatus is disclosed, for example, in JP-A-2005-91094.

With such a sample milling apparatus, prior to milling, the position of a positioning camera is adjusted such that the field of view of the positioning camera is brought into coincidence with the impact point of the ion beam.

An adjustment of the positioning camera is carried out, for example, as follows. First, a test sample is set on a sample stage of a sample milling apparatus and an impact point of the ion beam is determined. As an example, a silicon wafer having an oxide film thereon can be used as the test sample.

Then, the sample chamber is evacuated to a vacuum and the test sample is illuminated with an ion beam. This results in a trace of the impinging ion beam on the test sample.

The positioning camera is then set in position and the trace of the impinging beam is observed. The position of the positioning camera is mechanically adjusted so that the trace of the impinging beam coincides with the center of the field of view of the positioning camera, thus bringing the center of the field of view of the positioning camera and the beam impact point into coincidence with each other. Finally, the test sample is taken out of the sample stage. Because of the processing steps, an adjustment of the positioning camera can be accomplished.

After the adjustment of the positioning camera, a sample is set on the sample stage. The position of the sample is adjusted such that a target milling position on the sample agrees with the center of the field of view of the positioning camera. As a result, the ion beam can be directed at the target milling position on the sample.

In the sample milling apparatus, in order to reduce topography generated on the milled cross section through the sample, the sample is illuminated with an ion beam while swinging the sample to and fro. In this sample milling apparatus, if the distance between the swing axis and the beam impact point exceeds a tolerable range, the milling position may deviate from the field of view of the observation camera used to observe the sample being milled, in which case it is impossible to precisely judge the timing at which the milling is ended.

If the aforementioned adjustment of the positioning camera is performed, its position moves and so it is impossible to trace the position of the swing axis. Consequently, it is impossible to make a decision as to whether the distance between the swing axis and the beam impact point is excess of the tolerable range.

SUMMARY OF THE INVENTION

One aspect of the method of adjustment associated with the present invention is for use in a sample milling apparatus which includes: an ion source for emitting an ion beam at a sample such that a trace of the impinging ion beam is left on the sample; a swinging mechanism having a swing axis and operative to swing the sample; a positioning camera for bringing a target milling position on the sample into coincidence with a beam impact point on the sample; and a display section for displaying an image captured by the positioning camera. The method of adjustment comprises the steps of: observing the trace of the impinging beam left on the sample with the positioning camera while the positioning camera is positionally held relative to the swing axis of the swinging mechanism and obtaining an observation image; and extracting a display image to be displayed on the display section from the observation image based on the position of the trace of the impinging beam to thereby bring the impact point of the ion beam and the position of a field of view of the display image into coincidence with each other.

In this method of adjustment for a sample milling apparatus, if the impact point of the ion beam and the position of the field of view of the display image are brought into coincidence, the positional relationship between the field of view of the observation image from the positioning camera and the swing axis does not vary. Therefore, the position of the swing axis can be easily identified. Consequently, it is easy to make a decision as to whether the distance between the swing axis and the impact point of the ion beam is in excess of the tolerable range.

One aspect of the sample milling apparatus associated with the present invention includes: an ion source for emitting an ion beam at a sample; a swinging mechanism having an swing axis and operative to swing the sample; a positioning camera for bringing a target milling position on the sample into coincidence with an impact point of the ion beam; a display section for displaying an observation image captured by the positioning camera; and a display controller for extracting a display image from the observation image captured by the positioning camera and displaying the display image on the display section. The display controller modifies the field of view of the display image by modifying the position at which the display image is extracted from the observation image.

In this sample milling apparatus, the field of view of the display image can be varied by varying the position at which the display image is extracted from the observation image and, therefore, if the impact point of the ion beam and the position of the field of view of the display image are brought into coincidence, the positional relationship between the field of view of the observation image from the positioning camera and the swing axis does not vary. This facilitates identifying the position of the swing axis. Accordingly, it is easy to make a decision as to whether the distance between the swing axis and the impact point of the ion beam exceeds a tolerable range.

DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention are hereinafter described in detail with reference to the drawings. Note that the embodiments provided below are not intended to unduly restrict the contents of the present invention delineated by the claims and that not all the configurations set forth below are essential constituents of the present invention.

1. Sample Milling Apparatus

A method associated with one embodiment of the present invention for adjusting a sample milling apparatus is described. This sample milling apparatus is first described by referring toFIGS. 1 and 2in the following.FIGS. 1 and 2show the configuration of the sample milling apparatus,100, to be adjusted by the method associated with the present embodiment.

InFIGS. 1 and 2, X-, Y-, and Z-axes are shown as three axes perpendicular to each other.

The sample milling apparatus100is an ion milling apparatus which emits an ion beam at a sample S, mills it, and prepares a specimen used for observation or analysis. The sample milling apparatus100is the Cross Section Polisher (a trademark registered) for milling a cross section through a sample, for example.

The sample milling apparatus100is used for preparation of specimens for electron microscopes such as scanning electron microscopes (SEMs), transmission electron microscopes (TEMs), and scanning transmission electron microscopes (STEMs). Furthermore, the sample milling apparatus100is used for preparation of specimens for electron probe microanalyzers (EPMAs) and Auger microprobes.

As also shown inFIGS. 1 and 2, the sample milling apparatus100includes an ion source10, a sample stage pull-out mechanism20, a sample stage30, a swinging mechanism40, a positioning camera50, a milling observation camera60, a chamber housing70defining a sample chamber72, and an image processor80.FIG. 2shows an operational state in which the sample stage pull-out mechanism20has been opened or stretched to extract the sample stage30from the sample chamber72.FIG. 1shows an operational state in which the sample stage pull-out mechanism20has been closed or compressed to push the sample stage30into the sample chamber72.

The ion source10produces and emits an ion beam at the sample S. The ion source10is mounted at the top of the chamber housing70. The ion source10is an ion gun, for example. The ion source10emits the ion beam by accelerating it with a given acceleration voltage. For example, an Ar ion beam can be used as the ion beam. The diameter of the ion beam is on the order of hundreds of micrometers, for example.

The sample stage pull-out mechanism20is mounted to the chamber housing70so as to be opened and closed. The pull-out mechanism20constitutes a cover over the chamber housing70. The sample stage30is mounted to the sample stage pull-out mechanism20. The sample stage30can be pulled out from the sample chamber72as shown inFIG. 2by opening or stretching the stage pull-out mechanism20. Consequently, the interior of the chamber housing70, i.e., the sample chamber72, can be opened to the atmosphere. Also, by opening the sample stage pull-out mechanism20, the positioning camera50is placed over the sample S and so the sample S can be observed with the positioning camera50.

The sample stage30can be pushed into the sample chamber72by closing the sample stage pull-out mechanism20as shown inFIG. 1. In consequence, the chamber housing70can be made airtight. Under this condition, the sample chamber72can be evacuated or depressurized by operating vacuum pumping equipment (not shown). By closing the sample stage pull-out mechanism20, the ion source10is placed over the sample S and the sample S can be milled with the ion beam emitted from the ion source10.

The sample stage30is mounted to the swinging mechanism40. The sample stage30mechanically supports the sample S to be milled. The sample stage30has an X drive mechanism32and a Y drive mechanism34which are capable of moving the sample S along the X-axis and Y-axis, respectively. The X drive mechanism32and Y drive mechanism34permit the sample S to be moved horizontally in two dimensions. Hence, the sample S can be placed in position. The sample milling apparatus100is equipped with a beam shielding plate (not shown) for shielding the ion beam. The sample S is supported on the sample stage30and has portions protruding from the shielding plate. These protruding portions are sputtered.

The swinging mechanism40is mounted to the sample stage pull-out mechanism20. By opening the pull-out mechanism20, the swinging mechanism40is pulled out, and the sample stage30is also pulled out.

The swinging mechanism40tilts the sample stage30around a swing axis A (tilt axis). The swinging mechanism40swings the sample S by tilting the sample stage30around the swing axis A at regular cycles. In the illustrated example, the swing axis A is parallel to the Y-axis.

The positioning camera50is mounted at the upper end of the sample stage pull-out mechanism20. For example, the positioning camera50is a camera attached to an optical microscope. That is, the image captured by the positioning camera50is an image observed with the optical microscope. The positioning camera50is used to bring a target milling position for the sample S into coincidence with the impact point of the ion beam. The observation image captured by the positioning camera50is sent to the image processor80.

When the sample stage pull-out mechanism20is in its open state, the positioning camera50is placed at a position where it can observe the sample S. In this open state, the optical axis of the positioning camera50is parallel to the Z-axis. When the sample stage pull-out mechanism20is in its closed state, the positioning camera50is placed outside the sample chamber72by a camera tilting mechanism52.

The milling observation camera60is disposed outside the sample chamber72and can observe the inside of the sample chamber72through an observation window74formed in the chamber housing70. The optical axis of the milling observation camera60is parallel to the Y-axis. The image captured by the observation camera60is sent to the image processor80.

The sample stage30is disposed within the chamber housing70. As mentioned previously, the sample chamber72is an interior space of the chamber housing70. In the sample chamber72, the sample S is irradiated with an ion beam.

The image processor80performs processing such that the image captured by the positioning camera50is displayed on the display section. The image processor80extracts a part of the image captured by the positioning camera50, creates a display image, and displays the created display image on the display section. Furthermore, the image processor80performs processing such that the image captured by the milling observation camera60is displayed on the display section.

FIG. 3illustrates the configuration of the image processor80. The processor80includes a processing section82, a manual control section84, the above-described display section86, and a storage section88. The manual control section84permits a user to enter information about manipulations and to output the entered information to the processing section82. The functions of the manual control section84can be realized by hardware devices such as a keyboard, a mouse, buttons, a touch panel, and a touch pad.

The display section86displays the image created by the processing section82. The functions of the display section86can be accomplished by an LCD, a CRT, or a touch panel that functions also as the manual control section84.

Computer programs and various kinds of data which permit a computer to function as various portions of the processing section82are stored in the storage section88. The storage section88also functions as a working area for the processing section82. The function of the storage section88can be realized by a hard disk, a RAM (random access memory), or the like.

The functions of the processing section82can be realized by executing computer programs using a hardware device such as any one of various processors (e.g., a CPU and a DSP). The processing section82includes a positioning image acquisition portion820, a milling image acquisition portion822, and a display controller824.

The image acquisition portion820for positional coincidence acquires the image captured by the positioning camera50by receiving image data sent from the positioning camera50.

The image acquisition portion822for acquiring an image used for milling obtains the image captured by the milling observation camera60by receiving image data sent from the milling observation camera60.

The display controller824receives image data of the positioning camera50derived by the image acquisition portion820for positional coincidence, extracts a part of the observation image captured by the positioning camera50, generates a display image, and displays the generated display image on the display section86.

The positioning camera50is a higher pixel count camera and incorporates a low-magnification lens. Therefore, the positioning camera50can capture a wide field-of-view camera image at high resolution. Accordingly, the camera can extract a display image from the wide field-of-view observation image and hence obtain a high-resolution display image.

The display controller824receives the image data from the milling observation camera60, the image data being derived by the milling image acquisition section822, and displays the image captured by the milling observation camera60on the display section86.

2. Method of Adjustment for Sample Milling Apparatus

In the sample milling apparatus100, the position of the swing axis A is fixed. Also, in the state ofFIG. 2where the sample stage pull-out mechanism20is open, the position of the positioning camera50is fixed. The positioning camera50is held at a position where the swing axis A passes through the center of the field of view of the observation image from the positioning camera50. Therefore, when the sample stage pull-out mechanism20is open, the field of view of the observation image from the positioning camera50is fixed. The swing axis A invariably passes through the center of the field of view of the observation image from the positioning camera50.

In this way, the sample milling apparatus100is not equipped with any adjusting mechanism for adjusting the position of the positioning camera50relative to the impact point of the ion beam.

Accordingly, in the sample milling apparatus100, when the sample stage pull-out mechanism20is open as shown inFIG. 2, the center of the field of view of the display image is so adjusted as to agree with the optical axis of the ion source10when the sample stage pull-out mechanism20is closed as shown inFIG. 1. Consequently, the target milling position can be brought into coincidence with the impact point of the ion beam by bringing the target milling position on the sample S into coincidence with the center of the field of view of the display image. The display image is created by extracting a part of the observation image from the positioning camera50using the display controller824.

A method of adjustment for bringing the field of view of a display image into coincidence with the impact point of the ion beam is described in the following.FIG. 4is a flowchart illustrating one example of the method of adjustment associated with the present embodiment for a sample milling apparatus. First, as shown inFIG. 2, the sample stage pull-out mechanism20is opened or stretched, a test sample is set on the sample stage30, and an impact point of an ion beam on the sample is determined (S100). As an example, a silicon wafer having an oxide film thereon can be used as the test sample.

Then, the sample stage pull-out mechanism20is closed or compressed as shown inFIG. 1, the sample chamber72is hermetically sealed, and the sample chamber72is evacuated to a vacuum (S102).

Then, the test sample is irradiated with the ion beam to produce a trace of the impinging ion beam on the test sample (S104). Since the silicon wafer having the oxide film thereon is irradiated with the ion beam, the oxide film is removed, and the silicon is exposed. As a result, the trace of the impinging beam is left on the test sample.

Then, the sample chamber72is opened to the atmosphere. As shown inFIG. 2, the sample stage pull-out mechanism20is opened to pull out the sample stage30, and the positioning camera50is set (S106). Consequently, the test sample can be observed with the positioning camera50.

FIG. 5illustrates the manner in which the test sample is being observed with the positioning camera50.FIG. 6illustrates an observation image I2from the positioning camera50and a display image I4. The observed field of view2shown inFIG. 5is the field of view of the observation image I2from the positioning camera50. The displayed field of view4shown inFIG. 5is the field of view of the display image I4displayed on the display section86.

The trace T of the impinging ion beam can be observed with the positioning camera50as shown inFIGS. 5 and 6by opening the sample stage pull-out mechanism20and pulling out the sample stage30. The positioning camera50captures the observation image I2of the field of view2being observed. The display controller824extracts a part of the observation image I2, generates the display image I4, and displays it on the display section86.

When the sample stage pull-out mechanism20has been opened, the positioning camera50is held in a position where the swing axis A of the positioning camera50passes through the center of the observed field of view2of the positioning camera50. Therefore, the display controller824draws, on the observation image I2, a virtual swing axis VA passing through the center of the observed field of view2such that the virtual axis VA coincides with the swing axis A. On the display section86, the virtual swing axis VA is superimposed on the display image I4. That is, the virtual swing axis VA is displayed over the display image I4. In this way, in the sample milling apparatus100, the swing axis A is visualized.

Then, a decision is made as to whether the distance between the swing axis A and the impact point of the ion beam exceeds a tolerable range (S108). This distance between the swing axis A and the beam impact point is taken in a direction perpendicular to the swing axis A, i.e., in the X direction. In the sample milling apparatus100, as shown inFIG. 6, the display image I4and the virtual swing axis VA are displayed on the display section86and so the distance between the swing axis A and the beam impact point can be found by measuring the distance between the virtual swing axis VA and the trace T of the impinging beam T on the display image I4.

If the decision of step S110is Yes, indicating that the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range, the position of the ion source10is so adjusted that the distance between the swing axis A and the impact point of the beam is within the tolerable range (S112). This adjustment is carried out by reassembling the ion source10or adjusting the position using a position-adjusting mechanism for the ion source10.

After the adjustment of the position of the ion source10, control returns to step S100, and steps S102, S104, S106, S108, S110, and S112are performed. In this way, the steps S100, S102, S104, S106, S108, S110, and S112are repeatedly performed until it is determined in step S110that the distance between the swing axis A and the beam impact point does not exceed the tolerable range.

If the decision of step S110is negative (No), indicating that the distance between the swing axis A and the impact point of the ion beam does not exceed the tolerable range, the impact point of the beam and the position of the displayed field of view4are brought into coincidence (S114).

FIGS. 7 and 8illustrate a step of bringing the impact point of the ion beam and the position of the displayed field of view4into coincidence.FIGS. 7 and 8correspond toFIGS. 5 and 6, respectively.

In the present step, the displayed field of view4is modified such that the impact point of the ion beam and the center of the displayed field of view4coincide. In the sample milling apparatus100, when the sample stage pull-out mechanism20has been stretched, the field of view2under observation of the positioning camera50is held fixed. Accordingly, the impact point of the ion beam and the position of the displayed field of view4are brought into coincidence by modifying the position at which the display image I4is extracted from the observation image I2captured by the positioning camera50. In this example, the position at which the display image I4is extracted from the observation image I2is modified such that the beam impact point lies at the center of the displayed field of view4. As a result, the center of the displayed field of view4and the impact point of the ion beam come into coincidence.

For example, if an instruction for modifying the displayed field of view4is entered via the manual control section84, the display controller824extracts the display image I4from the observation image I2at a position complying with the instruction, and displays the display image14on the display section86. Where the manual control section84is a touch panel, the instruction for modifying the displayed field of view4can be entered by performing a drag operation on the display image I4such that the trace T of the impinging beam overlaps a marker indicative of the center of the displayed field of view4.

In this way, the manual control section84accepts the manipulative action for modifying the displayed field of view4by altering the position at which the display image I4is extracted from the observation image I2. The display controller824accepts manual control information from the manual control section84, modifies the position at which the display image I4is extracted from the observation image I2based on the manual control information, generates the display image I4, and displays it on the display section86.

Then, information about the position of the displayed field of view4is stored (S116). That is, information about the coordinates of the position at which the display image I4is extracted on the observation image I2is stored. The test sample is taken out of the sample stage30. Because of the processing steps described so far, the sample milling apparatus100can be adjusted.

After the sample milling apparatus100is adjusted in this way, the target milling position for the sample is brought into coincidence with the impact point of the ion beam. In particular, the sample stage pull-out mechanism20is opened or stretched to pull out the sample stage30as shown inFIG. 2. A sample to be milled is then set on the sample stage30. The sample stage30is adjusted in position such that the target milling position is located at the center of the displayed field of view4. Then, the sample stage pull-out mechanism20is closed or compressed as shown inFIG. 1, and the sample chamber72is evacuated to a vacuum. An ion beam is emitted from the ion source10. Consequently, the ion beam impinges at the target milling position.

In the foregoing description, the impact point of the ion beam and the center of the displayed field of view4are brought into coincidence. Alternatively, the beam impact point and an arbitrary position on the displayed field of view4may be brought into coincidence, in which case a method of adjustment can be implemented similarly to the above-described method of adjustment.

The method of adjustment associated with the present embodiment is for use in the sample milling apparatus which includes: the ion source10; the swing mechanism40for swinging the sample S; the positioning camera50for bringing the target milling position on the sample S into coincidence with the impact point of the ion beam; and the display section86for displaying the image captured by the positioning camera50. This method of adjustment involves the steps: observing the trace T of the impinging beam on the sample S with the positioning camera50while the positioning camera50is held in position relative to the swing axis A of the swinging mechanism40and obtaining the observation image I2; and bringing the impact point of the ion beam and the position of the field of view of the display image I4into coincidence by extracting the display image I4from the observation image I2based on the position of the trace T of the impinging beam.

In this method of adjustment for the sample milling apparatus100, if the impact point of the ion beam and the position of the field of view of the display image I4are brought into coincidence, the positional relationship between the observed field of view2of the positioning camera50and the swing axis A does not vary. Therefore, within the field of view2under observation, the position of the swing axis A can be identified easily. Consequently, it is easy to make a decision as to whether the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range.

FIG. 9illustrates images taken by the milling observation camera60when the swing axis A and the impact point of the ion beam are coincident.FIGS. 10-12illustrate images taken by the milling observation camera60when the swing axis A and the impact point of the ion beam are out of coincidence with one another. InFIG. 12, the amount of deviation between the swing axis A and impact point of the ion beam is greatest. InFIG. 10, the amount of deviation between the swing axis A and the impact point of the ion beam is smallest.FIGS. 9-12illustrate cases where the tilt angle θ of the sample S is 0° (θ=0°), −30° (θ=−30°), and +30° (θ=+30°, respectively.

If the swing axis A and the impact point of the ion beam are coincident as shown inFIG. 9, the milling position is within the field of view of the milling observation camera60, and the milling position can be checked with the milling observation camera60. If the swing axis A and the impact point of the ion beam slightly deviate from each other and the distance between the swing axis A and the impact point of the ion beam does not exceed the tolerable range as shown inFIG. 10, the milling position is within the field of view of the milling observation camera60and can be checked with the observation camera60.

However, if the positional deviation between the swing axis A and the impact point of the beam is so great that the distance between the swing axis A and the impact point of the beam exceeds the tolerable range as shown inFIGS. 11 and 12, the milling position will be out of the field of view of the milling observation camera60and so the milling position cannot be checked. Especially, where the timing of the end of a milling operation is judged automatically from the image from the observation camera60by image processing technology, if the milling position is out of the field of view, then it is impossible to correctly judge the timing of the end of the milling operation.

In the method associated with the present embodiment for adjusting the sample milling apparatus, the positional relationship between the observed field of view2of the positioning camera50and the swing axis A remains unchanged as described previously and, therefore, it is easy to make a decision as to whether the distance between the swing axis A and the impact point of the ion beam is within the tolerable range. Consequently, in the present embodiment, during milling, the milling position can be prevented from deviating from the field of view of the milling observation camera60.

In the method associated with the present embodiment for adjusting the sample milling apparatus, during the step of bringing the impact point of the ion beam and the position of the displayed field of view4into coincidence, the display image I4is extracted from the observation image I2so as to bring the impact point of the beam into the center of the displayed field of view4. Because the impact point of the beam is placed at the center of the displayed field of view4, the ion beam can be made to impinge at the target milling position.

In the method associated with the present embodiment for adjusting the sample milling apparatus, the positioning camera50is so held that the swing axis A passes through the center of the field of view2under observation. Therefore, the positional relationship between the swing axis A and the positioning camera50remains unchanged. Consequently, the swing axis A passes through the center of the field of view2under observation at all times, and the swing axis A can be identified easily.

In the method associated with the present embodiment for adjusting the sample milling machine, the virtual swing axis VA that is an image indicative of the swing axis A is displayed superimposed on the display image I4. Therefore, the swing axis A can be visualized.

The sample milling apparatus100includes the ion source10, the swinging mechanism40for swinging the sample S, the positioning camera50for bringing the target milling position on the sample into coincidence with the impact point of the ion beam, the display section86for displaying the image captured by the positioning camera50, and the display controller824for extracting the display image I4from the observation image I2captured by the positioning camera50and displaying the extracted image on the display section86. The display controller824modifies the displayed field of view4by modifying the position at which the display image I4is extracted from the observation image I2. Therefore, in the sample milling apparatus100, the impact point of the beam and the position of the displayed field of view4can be brought into coincidence by varying the position at which the display image I4is extracted from the observation image I2.

The sample milling apparatus100includes the manual control section84for accepting a manipulation for modifying the displayed field of view4. The display controller824modifies the displayed field of view4by modifying the position at which the display image I4is extracted from the observation image I2based on the manual control information from the manual control section84. Therefore, in the sample milling apparatus100, the impact point of the ion beam and the position of the displayed field of view4can be brought into coincidence by varying the position at which the display image I4is extracted from the observation image I2.

In the sample milling apparatus100, the display controller824operates such that the virtual swing axis VA being an image representing the swing axis A is superimposed on the display image I4on the display section86. Therefore, in the sample milling apparatus100, the virtual swing axis VA can be visualized.

In the sample milling apparatus100, the positioning camera50can be placed such that the sample can be observed. Under this condition, the positioning camera50is held so that the swing axis A passes through the center of the field of view2under observation. For this reason, in the sample milling apparatus100, the positional relationship between the swing axis A and the positioning camera50remains unchanged. Accordingly, the swing axis A always passes through the center of the observed field of view2and thus the swing axis A can be identified easily.

Modifications of the present embodiment for adjusting a sample milling apparatus are described next. In the following, only the differences with the above-described adjustment method associated with the present embodiment for a sample milling apparatus are described; a description of similarities is omitted.

4.1. First Modified Embodiment

In the foregoing embodiment, in the step S108for making a decision as to whether the distance between the swing axis A and the impact point of the ion beam as shown inFIG. 4exceeds the tolerable range, the distance between the virtual swing axis VA and the trace of impinging beam T is measured on the display image I4. In contrast, in a first modified embodiment, an image representing a range in which the distance between the swing axis A and the impact point of the beam exceeds the tolerable range is shown superimposed on the display image I4.

FIGS. 13-16illustrate an image I8representing a range in which the distance between the swing axis A and the impact point of the ion beam exceeds a tolerable range.FIGS. 13 and 15illustrate the manner in which the trace T of the impinging ion beam is being observed with the positioning camera50.FIG. 13illustrates a case where the swing axis A and the impact point of the ion beam are coincident.FIG. 15illustrates a case where the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range.FIG. 14shows the observation image I2from the positioning camera50shown inFIG. 13.FIG. 16illustrates the observation image I2from the positioning camera50shown inFIG. 15.

As shown inFIGS. 13 and 15, a range8in which the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range gives a range where the distance from the swing axis A is greater than a tolerable range in the X direction.

As shown inFIGS. 14 and 16, it is easy to make a decision as to whether the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range by drawing the image I8in a region equivalent to the range8where the tolerable range on the observation image I2is exceeded. The image I8is hatched or shaded, for example. The image18may be so created that the range8in which the tolerable range is exceeded is identified by a distinct color or gray level.

If at least a part of the trace T of the impinging ion beam overlaps the image I8as shown inFIG. 16, it can be determined that the distance between the swing axis A and the impact point of the ion beam is in excess of the tolerable range.

In the first modified embodiment, the display controller824causes the image I8indicating the range8in which the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range to be displayed superimposed on the displayed field of view4shown on the display section86. Therefore, it is easy to make a decision as to whether the distance between the swing axis A and the impact point of the beam exceeds the tolerable range.

In the example shown inFIGS. 14 and 16, the image I8gives the wider range8in which the tolerable range is exceeded, the wider range8being hatched or otherwise marked. Representation of the image I8is not restricted to this example. For example, the image I8may give the wider range8in which the tolerable range is exceeded by hatching or shading the inside of the tolerable range.

4.2. Second Modified Embodiment

In a second modified embodiment, a decision step S108of making a decision as to whether the distance between the impact point of the ion beam and the swing axis A exceeds a tolerable range, a positioning step S114of bringing the impact point of the ion beam and the position of the displayed field of view4into coincidence, and a storing step S116of storing positional information about the displayed field of view4are performed by the image processor80. That is, in the sample milling apparatus100, the decision step S108, positioning step S114, and storing step S116are automatically performed.FIGS. 17-19illustrate the processing steps of the display controller824.

The display controller824recognizes the trace T of the impinging ion beam from the observation image I2by image recognition technology and obtains information about the position and the size (contour) of the trace T. For example, the display controller824obtains the observation image I2preceding the generation of the trace T of the impinging beam shown inFIG. 17and compares the observation image I2preceding the generation of the trace T and the observation image I2succeeding the generation of the trace T shown inFIG. 6, thus deriving information about the position and size of the trace T of the beam. These kinds of information are stored in the storage section88.

The display controller824displays an image I9so as to be superimposed on the display image I4based on the information about the position and size of the trace T of the impinging beam as shown inFIG. 18, the image I9representing the impact point of the ion beam and the irradiated area. In the illustrated example, the image I9is a circle of the size of the trace T of the impinging beam and drawn at the position of the trace T.

The display controller824makes a decision as to whether the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range, based on the information about the position of the trace T of the impinging beam.

If the decision is affirmative, indicating that the distance between the swing axis A and the impact point of the ion beam exceeds the tolerable range, the display controller824provides a notice that the position of the ion source10is to be adjusted. The notice is effected by displaying a message on the display section86, for example.

If it is determined that the distance between the swing axis A and the impact point of the ion beam does not exceed the tolerable range, the display controller824automatically provides notice that the positioning step S114will be performed. The notice is effected by displaying a message on the display section86, for example.

The display controller824may effect automatic positioning only if permission of the automatic positioning is confirmed after a message is displayed on the display section86to prompt the user to confirm whether to effect automatic positioning.

As described above, in the second modified embodiment, the display controller824performs the steps of: obtaining the observation image I2of the trace T of the impinging ion beam left on the test sample, the image being captured by the positioning camera50; obtaining information about the position and size of the ion beam from the observation image I2; and displaying, on the display section86, the image I9representing the position and range of that portion of the sample which is impacted by the ion beam based on the information about the position and size. Therefore, when the target milling position on the sample is brought into coincidence with the impact point of the ion beam, the positioning can be effected while using the image I9as an indicia. Consequently, the target milling position can be readily brought into coincidence with the impact point of the ion beam.

When the target milling position is brought into coincidence with the impact point of the ion beam, a part of the display image I4displayed on the display section86can be enlarged. This permits the user to check the target milling position precisely. Even if a part of the display image I4is shown in enlarged form, the image I9is superimposed on the enlarged display image14and, therefore, the impact point of the ion beam can be easily checked. This permits the user to check the impact point of the ion beam with greater ease.

As illustrated inFIG. 19, the display controller824extracts the display image I4from the observation image I2based on the information about the position and size of the trace T of the impinging beam and displays the display image I4on the display section86such that the trace T is located, for example, in the center of the field of view of the display image I4.

In this way, the display controller824performs the steps of: obtaining information about the position of the trace T of the impinging ion beam, determining the position at which the display image I4is extracted from the observation image I2based on the information about the position of the trace T of the impinging beam, and bringing the impact point of the ion beam and the position of the displayed field of view4into coincidence. Consequently, in the sample milling apparatus100, the impact point of the ion beam and the position of the displayed field of view4can be automatically brought into coincidence.

The information about the position on the observation image I2at which the display image I4is extracted is stored in the storage section88by the display controller824. Also, the information about the position and size of the trace T of the impinging beam is stored in the storage section88by the display controller824.

In the second modified embodiment, the display controller824performs the steps of:

obtaining information about the position of the trace T of the impinging ion beam left on the sample; and extracting the display image I4from the observation image I2based on the information about the position of the trace T of the impinging beam and bringing the impact point of the ion beam and the position of the field of view of the display image I4into coincidence. Therefore, in the second modified embodiment, the impact point of the ion beam and the position of the field of view of the display image I4can be automatically brought into coincidence.

In the second modified embodiment, the display controller824performs the steps of obtaining information about the size of the trace T of the impinging beam and displaying, on the display section86, the image I9representing the position and range of that portion of the sample which is impacted by the ion beam based on the information about the position and size of the trace T of the impinging beam. Therefore, in the second modified embodiment, when the target milling position on the sample is brought into coincidence with the impact point of the ion beam, the positioning can be performed while using the image I9as an indicia. Consequently, the target milling position can be easily brought into coincidence with the impact point of the ion beam.

4.3. Third Modified Embodiment

In the sample milling apparatus100, the position and range (diameter) of that portion of the sample which is impacted by the ion beam vary according to the operative conditions of the ion source10under which the ion beam is emitted. The operative conditions include the accelerating voltage of the ion beam. As the accelerating voltage is increased, the ion beam has a smaller diameter. The operative conditions also include voltages applied to electrodes for focusing the ion beam. The diameter of the ion beam can be varied by changing the voltages applied to the electrodes.

In this way, the position and range of the portion of the sample impacted by the ion beam vary according to the operating conditions relating to emission of the ion beam. Therefore, in the above-described “4.2.1 storing step S116”, information about the position and size of the trace T of the impinging beam is stored in the storage section88for each different set of operating conditions relating to emission of the ion beam. Consequently, the display controller824can display the image I9according to the operating conditions relating to ion beam irradiation.

For example, where the target milling position on the sample is brought into coincidence with the impact point of the ion beam, if operating conditions for ion beam irradiation are set for the ion source10, the display controller824reads information about the position and size of the trace T of the impinging beam which meet the set operating conditions from the storage section88and displays the image I9on the display section86based on the read information.

As a result, if the target milling position is brought into coincidence with the position of the image I9, the target milling position can be brought into coincidence with the impact point of the ion beam. Consequently, this positional coincidence can be achieved easily.

4.4. Fourth Modified Embodiment

In the foregoing embodiment, the sample milling apparatus is the Cross Section Polisher (a trademark registered) for preparing a cross-sectional sample. Alternatively, the sample milling apparatus may also be the Ion Slicer (a trademark registered) for preparing a thin-film sample. The Ion Slicer is equipped with a shield belt for blocking an ion beam and thus the sample can be sliced into thin sections.

Note that the foregoing embodiments and modified embodiments are only exemplary and that the present invention is not restricted to them. For example, such embodiments and modified embodiments may be appropriately combined.

It is to be understood that the present invention is not restricted to the embodiments described above and that the invention can be practiced in variously modified forms. For example, the present invention embraces configurations substantially identical to the configurations described in the embodiments. What are meant by substantially identical configurations are configurations identical in functions, method, and results or in purposes and effects, for example. Furthermore, the present invention embraces configurations which are similar to those described in the foregoing embodiments except that nonessential portions have been replaced. In addition, the present invention embraces configurations which are identical in yielded advantageous effects or achieved purposes to the configurations described in the foregoing embodiments. Further, the present invention embraces configurations similar to those described in the foregoing embodiments except that a well-known technique is added.