JP2001110345A - Astigmatism correction method for electron microscope and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide astigmatism correction device of electron microscope that can exactly correct astigmatism in electron microscope within a short time without demand for operator's experience and dexterity. SOLUTION: Radial signal R and a plurality of angular signals θare entered at the reference value (X0, Y0) in a polar coordinate selection/correction circuit 15, display images 11b1 to 11b8 for each angular signal at corrected coordinates are displayed with an astigmatism correction device 20 according to instructions of a control circuit 17, astigmatism correction is exactly conducted by selecting a displayed image of astigmatism satisfiable with visual decision and finely adjusting at least either radius or angle as occasion calls, or high-quality astigmatism correction is conducted with readjustment using selected and specified value (R, θ) as the reference, and high-quality astigmatism correction at a middle position of adjacent display images of astigmatism correction to a similar extent is conducted in intuitive correspondence to the displayed image by a simple operation directed with the angular coordinate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting astigmatism in an electron microscope, which corrects astigmatism in the X-axis and Y-axis directions orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope. The present invention relates to an astigmatism correction device for an electron microscope that corrects astigmatism on an X axis and a Y axis orthogonal to each other on a plane perpendicular to the optical axis.

[0002]

2. Description of the Related Art When astigmatism (axial asymmetric aberration) is present in an objective lens of an electron microscope, the sharpness of an observed image is lost and the performance of the apparatus is reduced. Therefore, the spatial resolution of the apparatus is increased to improve the performance. For this purpose, astigmatism is corrected on an X axis and a Y axis orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope. Although it has been proposed to automatically correct the astigmatism of the electron microscope, at present, satisfactory results cannot be obtained by the automatic correction. The correction of astigmatism of the electron microscope is performed manually by an operator so that an observation image can be obtained.

[0003]

As described above, the correction of astigmatism of the electron microscope is manually performed by the operator, but the X-axis and the X-axis orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope. To correct astigmatism on the Y axis, use X
It is necessary to repeat the correction adjustments in the axial direction and the Y-axis direction independently of each other, and to repeat the correction adjustments in the X-axis direction and the Y-axis direction until the operator finally obtains a visually satisfactory observation image. is there. This correction adjustment requires the experience and skill of the operator, and the correction of astigmatism of the electron microscope requires a great deal of adjustment time for an operator with little experience.

The present invention has been made in view of the above-described current situation of correction of astigmatism of an electron microscope, and a first object of the present invention is to provide an electronic microscope without requiring an operator to have experience and skill. An object of the present invention is to provide a method for correcting astigmatism of an electron microscope, which can accurately correct microscope astigmatism in a short time. Further, a second object of the present invention is to provide an astigmatism of an electron microscope capable of accurately correcting an astigmatism of an electron microscope in a short time without requiring experience and skill. A correction device is provided.

[0005]

In order to attain the first object, the invention according to claim 1 is directed to an X-axis and a Y-axis orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope. This is an astigmatism correction method for an electron microscope that corrects astigmatism, and calculates an aberration correction value (X, Y) with respect to a value (R, θ) centered on a reference value (Xo, Yo) by X = Xo + Rcos θ, Y = Y
It is characterized in that astigmatism is corrected by setting so as to be o + Rsin θ and adjusting the value in combination with the reference value (Xo, Yo) while changing the value (R, θ). .

In order to achieve the second object, an invention according to claim 2 is an electronic microscope for correcting astigmatism in X-axis and Y-axis directions orthogonal to each other on a plane perpendicular to the optical axis of an electron microscope. This is a microscope astigmatism correction device and has reference values (Xo, Yo)
And by changing the value (R, θ), X =
It is characterized by having an aberration correction value setting means for correcting and setting a plurality of aberration correction values (X, Y) so that Xo + Rcos θ and Y = Yo + Rsin θ.

[0007] Similarly, in order to achieve the second object,
The invention according to claim 3 is the invention according to claim 2,
When the value (R, θ) is changed, a function of automatically changing the value θ at a constant cycle is provided.

[0008] Similarly, in order to achieve the second object,
The invention according to claim 4 is an astigmatism correction device for an electron microscope for correcting astigmatism in the X-axis and Y-axis directions orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope, wherein the reference value (Xo ,
An aberration correction value setting unit that corrects and sets a plurality of aberration correction values (X, Y) by changing correction values in the X-axis and Y-axis directions with respect to Yo), and sets the aberration correction value setting unit. Image display means for simultaneously displaying on the monitor a plurality of observation images at the plurality of corrected aberration correction value (X, Y) positions.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment relating to an astigmatism correction device for an electron microscope. Here, the electron microscope includes a transmission electron microscope (TE
M), various electron microscopes such as a scanning electron microscope (SEM), and the present invention further provides an electron beam probe microscopic analyzer (EPMA), an Auger electron spectrometer (AES), focused ion beam processing. The present invention can also be applied to a device (FIB) and the like.

[First Embodiment] A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a configuration of a main part of the present embodiment, and FIG.
FIG. 3 is a schematic diagram illustrating the astigmatism correction device shown in FIG.

In this embodiment, as shown in FIG. 1, an X-axis perpendicular to the optical axis of the electron microscope,
Xo, Yo as reference values for astigmatism correction in the Y-axis direction
And an astigmatism correction value setting circuit 15 having a mechanism for setting and inputting values of R and θ centering on the reference value, and a mechanism for shifting the astigmatism correction value by a fixed value. Is provided. The astigmatism correction value setting circuit 15 is connected to the drive circuit 17. An output terminal of the drive circuit 17 is connected to an astigmatism correction device 20 that corrects astigmatism based on the astigmatism correction value. The astigmatism correction device 20 is configured as shown in FIG.
The configuration is as shown in FIG.

The astigmatism correction value setting circuit 15 is provided with a cosine calculator 1 and a sine calculator 2 to which the angle signal θ is input. The output terminal of cosine calculator 1 for calculating cos θ is connected to one input terminal of multiplier 3, and the output terminal of sine calculator 2 for calculating sin θ is connected to one input terminal of multiplier 4. The other input terminal of the multiplier 3 and the other input terminal of the multiplier 4 have a radius signal R
Is configured to be input. Also, Rcosθ
Is connected to one input terminal of an adder 5, and the output terminal of the multiplier 4 for calculating R sin θ is connected to one input terminal of an adder 6, respectively. Is connected to a reference coordinate signal Xo
However, the other input terminal of the adder 6 has a reference coordinate signal Yo.
Are input, and the corrected astigmatism correction value X is output from the output terminal of the adder 5, and the corrected astigmatism correction value Y is output from the output terminal of the adder 6. ing. Further, a multiplier 3 for calculating Rcos θ and R
an output terminal of a multiplier 4 for calculating sin θ;
6 between the astigmatism correction value and Rcos
A changeover switch (not shown) for selecting whether or not to add θ and Rsinθ is connected to each other. The calculation of these astigmatism correction values can be substituted by a computer.

As an actual adjustment procedure, appropriate values of Xo and Yo are set. (Normally, the first values of X and Y are Xo and Yo). Set an appropriate value of R. θ is changed by 360 ° or more to select the optimal θ. (At this time, if the value of R is inappropriate and the optimum θ is difficult to understand, the value of R is reset and the process is repeated.) The optimum condition is searched by changing R. <Further fine adjustment> Xo and Yo values are set as X and Y values at this time.
~I do. The above operation is repeated while increasing the magnification of the microscope. I do.

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of a main part of the second embodiment of the present invention.

In the present embodiment, as shown in FIG. 3, an angle signal setting is provided before the cosine calculator 1 and the sine calculator 2 as compared with the first embodiment already described with reference to FIG. A frequency value f is input to the angle signal setting device 7, and the cosine operation device 1 is output from the angle signal setting device 7.
The sine calculator 2 is configured to automatically input the angle signal θ periodically. The configuration of the other parts of the configuration of the present embodiment is the same as that of the first embodiment already described with reference to FIG.

In the present embodiment, the angle signal θ is automatically input from the angle signal setting unit 7 to the cosine calculator 1 and the sine calculator 2 at a predetermined angle interval. Is performed as described above.

As an actual adjustment procedure, appropriate values of R and θ are set. Xo, so that the astigmatism shifts to the target while looking at the image
Adjust the value of Yo. (At this time, if the value of R is inappropriate and the astigmatism is difficult to understand, reset the value of R and repeat.) <Furthermore, when making fine adjustments> Increase the magnification of the microscope and increase the value of R. Repeat the above operation while reducing the size. I do.

Next, the astigmatism correction operation of the electron microscope according to the first and second embodiments will be described with reference to FIGS. Here, FIG. 4 is an explanatory diagram showing the operation in the polar coordinate selection mode of the first and second embodiments, and FIG.
FIG. 6 is an explanatory diagram showing a first image display operation of the second embodiment. FIG. 6 is an explanatory diagram showing a second image display operation of the first and second embodiments.

For a plurality of astigmatism correction values (X, Y), observation images with respective settings are simultaneously displayed,
Make adjustments. <Usage Example 1> An optimum image is selected from a plurality of images, and the value is determined as an astigmatism correction value. <Usage example 2> For a plurality of astigmatism correction values (X, Y), the observation image with the respective settings is simultaneously displayed on the coordinates on the display screen, and the coordinates on the display screen are changed by the pointer device. By the selection, the value of (X, Y) corresponding to the coordinates is set as the astigmatism correction value. For example, if it is considered that an intermediate point between the setting of A and the setting of B is optimal, the position at which the observation image at the setting of A is displayed and the position at which the observation image at the setting of B are displayed are indicated by a pointer. By selecting with the device, a setting value intermediate between the setting of A and the setting of B is selected.

<Right-Angle Coordinate Selection Mode> In the right-angle coordinate selection mode, adjustment is performed by varying the normal orthogonal astigmatism correction value (X, Y). A reference astigmatism correction value (Xo, Yo) which is considered to be appropriate is set, and an observation visual field in which astigmatism can be easily determined is selected. Next, a plurality of astigmatism correction values (X1, Y
1), (X1, Y2), (X1, Y3), (X2, Y
1), (X2, Y2), (X2, Y3), (X3, Y
1) Input (X3, Y2) and (X3, Y3). In this case, for example, X1 = Xo- △ X, X2 = Xo, X3
= Xo + △ X, Y1 = Yo + △ Y, Y2 = Yo, Y3 =
Yo− △ Y is set.

By this input operation, the astigmatism correction device 20 is operated under the control of the drive circuit 17 under the control of the drive circuit 17, and based on the astigmatism at the coordinate position corresponding to each corrected coordinate signal, a diagram is obtained. As shown in FIG. 5, display images 11a11 to 11a observed at the corrected coordinate positions are displayed.
a33 is displayed on the display.

Therefore, the operator visually determines the display images 11a11 to 11a33 displayed on the display, and if a display image having a sufficiently small and satisfactory astigmatism can be selected, the selected display image is selected. The image is designated using a keyboard or a pointing device, and the sample is observed with an electron microscope using the corresponding corrected coordinate position as the final astigmatism setting position.

Further, display images 11a11 to 11a-1 shown in FIG.
When it is desired to perform readjustment based on the selected and designated correction coordinates (X, Y) based on the comparison determination of 1a33, the correction coordinates (X, Y) are set to the reference coordinates (Xo, Yo), and the above-described operation is performed. By performing the adjustment again in this manner, higher-quality astigmatism correction is performed. Further, when the adjacent display images are corrected to the same degree of astigmatism, for example, in FIG. 5, the display image 11 of the coordinates (X1, Y1) is displayed.
When a11 and the display image 11a21 of the coordinates (X2, Y1) have been corrected to the same degree of astigmatism, the pointing device specifies an intermediate position between the display image 11a11 and the display image 11a21. With this designation, the correction coordinates (X, Y) for astigmatism correction are expressed as X = (X
1 + X2) / 2, Y = Y1, and higher quality astigmatism correction is performed. In this case, the corrected coordinate value X = (X
1 + X2) / 2 and Y = Y1 can be further readjusted.

As described above, in the astigmatism correction in the rectangular coordinate selection mode, the drive circuit 17 corresponds to a plurality of sets of correction coordinates set at regular intervals with respect to the reference astigmatism correction values Xo and Yo. By inputting the astigmatism correction values X and Y, the astigmatism correction device 20 operates according to a command from the drive circuit 17, and the display images 11a11 to 11a33 at the coordinate positions corrected corresponding to the respective coordinate signals. Appears on the display.

For this reason, the operator can easily select a display image having satisfactory astigmatism by using a keyboard or a pointing device by visual judgment of the display images 11a11 to 11a33 displayed on the display. By performing astigmatism correction accurately or by performing readjustment based on the selected and specified correction coordinates (X, Y), higher-quality astigmatism correction is performed. If the astigmatism has been corrected to the same extent, it is possible to specify an intermediate position between the two corresponding display images and perform higher quality astigmatism correction at the intermediate position between the two. Further, since the irradiation of the sample with the electron beam or the ion beam can be performed only during the operation of taking in a plurality of display images, it is particularly applied to a focused ion beam processing apparatus (FIB) to grind the sample. In the case of performing observation, it becomes possible to reduce the deterioration of the sample.

<Polar coordinate selection mode> The polar coordinate selection mode is a combination of the second and fourth aspects, and corrects astigmatism based on the correction value corrected by the astigmatism correction value setting circuit 15. Is the case. In this state, the reference astigmatism correction values (Xo, Yo) shown in FIG. 4 are input to the astigmatism correction value setting circuit 15 to select an observation field in which the astigmatism can be easily determined, and the value R is set. And a predetermined value θ, cosine calculator 1 calculates cos θ, sine calculator 2 calculates sin θ, multiplier 3 calculates Rcos θ, and multiplier 4 calculates Rsin θ. The adder 5 calculates Xo + Rcos θ, the adder 6 calculates Yo + sin θ, and the adder 5 calculates X = Xo + Rco on the X axis.
The astigmatism correction value X corresponding to the sθ position is output from the adder 6 as the astigmatism correction value Y corresponding to the Y = Yo + Rsinθ position on the Y axis.

As shown in FIG. 4, when the angle signal θ is changed, the astigmatism correction values X and Y become the reference coordinates (Xo, Y
It is set on a circle with a set radius R around o). In this case, for example, θ1 = 0 °, θ2 = 45
゜, θ3 = 90 °, θ4 = 135 °, θ5 = 180 °,
Angle coordinates are set as θ6 = 225 °, θ7 = 270 °, and θ8 = 315 °.

The astigmatism correction values X and Y corresponding to a plurality of sets of values (R, θ) are input from the astigmatism correction value setting circuit 15 to the drive circuit 17, The astigmatism correction device 20 performs astigmatism correction based on each correction value, and display images 11b1 to 11b8 corresponding to each astigmatism correction are displayed on the display as shown in FIG.

Therefore, the operator visually determines the display images 11b1 to 11b8 displayed on the display, and if a display image having a sufficiently small and satisfactory astigmatism can be selected, the selected display image is displayed. the image,
Specify by keyboard or pointing device,
The sample is observed with an electron microscope using the corresponding correction coordinate value as the final astigmatism setting position.

The display images 11b1 to 11b1 shown in FIG.
When it is desired to perform readjustment based on the position of the selected and designated astigmatism correction value (X, Y) by the comparison determination of b8, the astigmatism correction value (X, Y) is set to a new reference astigmatism. By setting the correction value (Xo, Yo) and re-adjusting the astigmatism as described above, higher-quality astigmatism correction is performed.

Further, when fine adjustment is performed on the astigmatism correction value (X, Y) selected and designated to correct astigmatism of higher quality, the value R and the value θ are corrected. Higher quality astigmatism correction is performed by slightly changing at least one of them.

When adjacent display images are corrected to the same degree of astigmatism, for example, in FIG. 6, a display image 11b1 of coordinates (R, θ1) and a display image 11b1 of coordinates (R, θ2)
When the astigmatism of the display image 11b2 is corrected to the same degree, an intermediate position between the display image 11b1 and the display image 11b2 is designated by the pointing device. With this designation, the correction coordinates (R, θ) for astigmatism correction are set to R = R, θ = (θ2−θ1) / 2, and higher-quality astigmatism correction is performed. In this case, readjustment can be further performed around the corrected coordinates {R, (θ2−θ1) / 2}.

As described above, in the astigmatism correction in the polar coordinate selection mode, the astigmatism correction value setting circuit 15 sets a plurality of reference astigmatism correction values Xo and Yo at a predetermined value R and a predetermined interval. By inputting the value θ, the astigmatism correction device 20 operates in accordance with a command from the drive circuit 17, and each value θ
Display image 11b at the coordinate position corrected according to
1 to 11b8 are displayed on the display.

For this purpose, the operator selects a display image having satisfactory astigmatism with a keyboard or a pointing device by visual judgment of the display images 11b1 to 11b8 displayed on the display, and if necessary, Fine adjustment of at least one of the value R and the value θ to easily and appropriately correct astigmatism, or to perform readjustment based on a selected and specified astigmatism correction value (X, Y) By performing higher quality astigmatism correction,
Furthermore, when adjacent display images are corrected to the same degree of astigmatism, an intermediate position between the corresponding two display images is designated, and a higher quality is obtained for the intermediate astigmatism correction value between the two. Astigmatism correction can be performed.

In the astigmatism correction in the polar coordinate selection mode, when a predetermined value R is set, the coordinates (X, Y) at which the astigmatism correction is performed are uniquely set. And the operator can intuitively grasp the displayed image in response to the operation.
Further, similarly to the case of the rectangular coordinate selection mode, the irradiation of the sample with the electron beam or the ion beam can be performed only at the time of a plurality of display image capturing operations. In the case where the observation is performed while grinding the sample, the quality of the sample can be reduced.

In addition to the common effects obtained in the first and second embodiments as described above, in the second embodiment, the angle signal setter 7 automatically outputs a predetermined angle interval. Since the angle signal θ is input to the cosine calculator 1 and the sine calculator 2, the operational burden on the operator can be further reduced as compared with the case of the first embodiment.

In the first and second embodiments described above, a case where the present invention is applied to a scanning electron microscope, a focused ion beam processing device, an electron beam probe microscopic analyzer, and an Auger electron spectroscopic analyzer. Although the built-in image scanning and photographing mechanism and the image memory mechanism can be used as they are, when applied to a transmission electron microscope, it is necessary to use a CCD camera for photographing an image or a personal computer for image memory. is there.

[0038]

According to the first aspect of the present invention, the values (R, θ) are centered on the reference astigmatism correction values (Xo, Yo).
, The astigmatism correction value (X, Y) becomes X = Xo + R
cos θ, Y = Yo + Rsin θ
By adjusting in combination with the reference value (Xo, Yo) while changing the value (R, θ), astigmatism on the X axis and the Y axis orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope Is corrected, the determination of the optimum astigmatism correction value is easily and uniquely and intuitively performed, and the operator can quickly and accurately perform the astigmatism of the electron microscope without any skill in operation. Will be possible.

According to the second aspect of the present invention, the astigmatism correction value (X, Y) is set by the reference value (Xo, Yo) and the value (R, θ) is changed by the aberration correction value setting means.
Are set so that X = Xo + Rcos θ and Y = Yo + Rsin θ. Observation images at a plurality of coordinate positions set by the astigmatism correction value setting means are displayed on the monitor by the image display means. Since the optimal astigmatism correction value is selected based on the visual judgment of the observation image of, the astigmatism is corrected on the X axis and the Y axis orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope. From the astigmatism correction values X and Y to be corrected and the observation images at a plurality of coordinate positions displayed on the monitor, the operator can intuitively and easily set the astigmatism correction value and optimize the astigmatism correction value. By the accurate determination of the astigmatism correction value by visual comparison, the astigmatism of the electron microscope can be quickly and accurately performed without skill in operation.

According to the third aspect of the present invention, in addition to the effect obtained by the second aspect of the present invention, a function for automatically changing the value θ at a constant cycle is provided, so that the operator's operational burden is increased. Can be further reduced.

According to the invention, the astigmatism correction value is corrected in the X-axis and Y-axis directions by the astigmatism correction value setting means with respect to the reference astigmatism correction value (Xo, Yo). Then, a plurality of astigmatism correction values (X, Y) are corrected and set, and a plurality of observations of a plurality of coordinate value (X, Y) positions corrected and set by the astigmatism correction value setting unit are performed by the image display unit. An image is displayed on a monitor, and an optimal astigmatism correction value is selected based on visual judgment of a plurality of observed images by an operator, and an X-axis and a Y-axis orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope. Since astigmatism is corrected on the axis,
From the observation images at a plurality of coordinate positions displayed on the monitor, the operator can quickly adjust the astigmatism of the electron microscope without any skill in operation by making an appropriate determination by visual comparison of the optimal astigmatism correction value. It is possible to do it surely.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating the astigmatism correction device shown in FIG.

FIG. 3 is a block diagram showing a configuration of a main part of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating an operation in a polar coordinate selection mode according to the first and second embodiments.

FIG. 5 is an explanatory diagram showing a first image display operation according to the first and second embodiments.

FIG. 6 is an explanatory diagram illustrating a second image display operation according to the first and second embodiments.

[Explanation of symbols]

Reference Signs List 1 Cosine calculator 2 Sine calculator 3, 4 Multiplier 5, 6 Adder 7 Angle signal setting device 11a11 to 11a33, 11b1 to 11b8 Display image 15 Astigmatism correction value setting circuit 16 Cartesian coordinate value selection correction circuit 17 Drive circuit 20 Astigmatism correction device

Claims (4)

[Claims] An astigmatism correction method for an electron microscope for correcting astigmatism in X-axis and Y-axis directions orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope, wherein reference values (Xo, Yo) With respect to the value (R, θ), the aberration correction value (X, Y) is set so that X = Xo + Rcos θ Y = Yo + Rsin θ, and while changing the value (R, θ),
An astigmatism correction method for an electron microscope, wherein correction of astigmatism is performed by adjusting in combination with a reference value (Xo, Yo). 2. An astigmatism correcting device for an electron microscope for correcting astigmatism in X-axis and Y-axis directions orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope, wherein reference values (Xo, Yo) , And by changing the values (R, θ), there is provided an aberration correction value setting means for correcting and setting a plurality of aberration correction values (X, Y) such that X = Xo + Rcosθ Y = Yo + Rsinθ. Characteristic device for correcting astigmatism in electron microscopes. 3. The astigmatism correction device according to claim 2, further comprising a function of automatically changing the value θ at a constant period when the value (R, θ) is changed. Astigmatism correction device for electron microscope. 4. An astigmatism correcting device for an electron microscope for correcting astigmatism in directions of X axis and Y axis orthogonal to each other on a plane perpendicular to the optical axis of the electron microscope, wherein reference values (Xo, Yo) By changing the correction values in the X-axis and Y-axis directions, a plurality of aberration correction values (X,
An aberration correction value setting means for correcting and setting Y), and an image display means for simultaneously displaying a plurality of observation images at a plurality of aberration correction value (X, Y) positions set by the aberration correction value setting means on a monitor. An astigmatism correction device for an electron microscope, comprising: