JP3512994B2 - Adjusting the charged particle optical column - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for correcting astigmatism and focusing in a charged particle optical lens barrel such as a charged particle beam drawing apparatus used for forming a fine pattern on a semiconductor wafer. The present invention relates to a method for adjusting a charged particle optical lens barrel.

[0002]

2. Description of the Related Art In recent years, in the electron beam writing technique used in semiconductor manufacturing processes, in addition to the conventional round beam technique, a beam having a rectangular, triangular or arbitrary cross section is used to increase throughput. A variable shaping or character projection type electron beam drawing apparatus for generating and drawing is used. Further, as the pattern formation becomes finer and more precise, the electron beam drawing apparatus of this kind is also required to have a higher beam dimension.

As one of the conditions for realizing the high precision of the beam dimension, the focus of the beam is accurately adjusted,
Furthermore, it is required to remove astigmatism. In order to accurately obtain the focal position of the beam, for example, as shown in FIG. 1A, the beam 1 is scanned over the fine mark 2 and the reflected electron signal obtained at this time as shown in FIG. The degree of focus is obtained from the steepness of the rising and falling edges of the signal at the edge. It is considered that the narrower the length of the line shown by the arrow in FIG. 1B, the closer to the in-focus position. Further, the degree of astigmatism is obtained from the directivity of the steepness, for example, the difference in steepness between when the mark is scanned in the x direction and when it is scanned in the y direction.

When the mark is formed by, for example, making a fine hole in a heavy metal thin film, the polarities of the signals are reversed.
The inflow current can also be measured by using a mark having a minute Faraday cup structure.

By the way, the following problems occur when highly accurate measurement is performed in this type of beam adjustment. That is, the shape of the mark is not necessarily a perfect circle but has directionality. Particularly in the case of fine marks, it is difficult to make the shape a perfect circle. Further, in the case of an apparatus using a shaped beam or a character beam, the anisotropy of the mark shape becomes a problem.

On the other hand, the present inventors have already proposed a method for determining the astigmatic direction and the in-focus position based on the difference in the Fourier transform of the two-dimensional image obtained from the mark (Japanese Patent Application No. 7- 237456). However, with this method, when there are a plurality of candidates for the in-focus position, it is difficult to accurately obtain the in-focus position.

In order to obtain the in-focus position with higher accuracy, it is better that the mark is as small as possible. However, since the signal from the mark is approximately proportional to the area of the mark, the signal becomes smaller in proportion to the square of the size of the mark. In other words, if the mark is made smaller in order to improve the accuracy, the SN ratio of the signal will decrease. This situation will be described with reference to FIGS. In FIG. 2A, the mark is large and thus the signal to noise ratio is high, but the obtained resolution is low. In FIG. 2B, the mark is smaller than that in FIG. 2A, so the resolution is high, but the SN ratio is low. Further, in FIG. 2C, since the mark is small, the SN ratio of the signal is small, and therefore the beam resolution cannot be measured.

As described above, the size of the mark is determined by the allowable SN ratio. That is, the measurement resolution is limited by the SN ratio of the signal. This is a serious problem from the viewpoint of high precision beam adjustment.

[0009]

As described above, in the conventional method of adjusting the charged particle optical lens barrel, when the astigmatism is present and the focal length is further finely adjusted, a plurality of focusing position candidates are obtained. There was a problem that it could not be adjusted accurately. Further, in the beam adjusting method using the single mark up to now, there is a problem that the resolution is limited by the SN ratio of the signal, and the accurate adjustment cannot be performed.

The present invention has been made in consideration of the above circumstances, and an object thereof is to be able to accurately correct astigmatism even when there are a plurality of candidates for the in-focus position. It is an object of the present invention to provide a method for adjusting a charged particle optical lens barrel that enables a high degree of astigmatism correction and focusing.

Another object of the present invention is that the resolution is not limited by the signal-to-noise ratio of the signal and both high resolution and high signal-to-noise ratio can be satisfied, and higher astigmatism correction and focus can be achieved. It is an object of the present invention to provide a method of adjusting a charged particle optical lens barrel that enables adjustment.

[0012]

(Structure) In order to solve the above problems, the present invention adopts the following structure. (1) In the method for adjusting a charged particle optical lens barrel, a two-dimensional signal distribution obtained by two-dimensionally scanning a mark on a sample surface with a charged particle beam is used to focus the beam on the sample surface. Determining the direction of the astigmatism using a step of obtaining in a plurality of settings having different focal lengths and a first evaluation function determined by the difference of the Fourier transform of the two-dimensional signal distribution obtained by the step, And the step of obtaining the in-focus position from the change in the focus setting of the second evaluation function obtained by processing the first evaluation function.

(2) A two-dimensional signal distribution obtained by two-dimensionally scanning a mark on a sample surface with a charged particle beam is set to a plurality of settings with different focal lengths of a lens for converging the beam on the sample surface. And a second obtained by processing the first evaluation function determined by the difference in the Fourier transform of the two-dimensional signal distribution obtained in the step
Seek from focus position change to the focus setting of the evaluation function
A method of adjusting a charged particle optical lens barrel, the method including: a step of adjusting a position of the second evaluation function, wherein a candidate for the focus position is provided at two or more positions near the focus position when the value of the second evaluation function has no astigmatism. The first evaluation function is obtained by using the Fourier transform signals at two of them, and the direction of astigmatism is obtained from this first evaluation function.

(3) In (1) or (2), when the Fourier transform of the two-dimensional signal distribution obtained at different focal lengths of the lens is given by I (kx, ky), I '(kx, ky) , The first evaluation function is I (kx, ky), I ′
The sign is positive or negative depending on the magnitude of the absolute value of (kx, ky), and the second evaluation function is the average or weighted average of the first evaluation function in the target wave number region. .

(4) A two-dimensional signal distribution obtained by two-dimensionally scanning a mark on the sample surface with a charged particle beam, a plurality of settings with different focal lengths of the lens for converging the beam on the sample surface. Or the first evaluation function determined by the difference between the Fourier transforms of the two-dimensional signal distributions obtained in the above step, or the direction of the astigmatism is determined, or the first evaluation function is determined. Second obtained by processing
The method of adjusting a charged particle optical lens barrel according to claim 1, wherein at least one of obtaining a focused position from a change in the focus setting of the evaluation function of It is characterized in that a dependent third evaluation function is obtained, and the astigmatism is corrected so that the third evaluation functions corresponding to the respective directions give candidates for the in-focus position to the same focus setting position.

(5) In (4), the Fourier transform of the two-dimensional signal distribution obtained at different focal lengths of the lens is I
When given by (kx, ky), I '(kx, ky), the first evaluation function is I (kx, ky), I' (kx,
ky) is a function whose sign is determined to be positive or negative according to the magnitude of the absolute value of ky), and the third evaluation function is the first in the wave number region of interest.
It should be the weighted average of the evaluation function of the weight that changes in the angular direction.

(6) A two-dimensional signal distribution obtained by two-dimensionally scanning a mark on a sample surface with a charged particle beam is set to a plurality of settings with different focal lengths of lenses for converging the beam on the sample surface. And the step of performing at least one of determining the direction of astigmatism and obtaining the in-focus position using the difference in the Fourier transform of the two-dimensional signal distribution obtained in the step. A method for adjusting a charged particle optical lens barrel including: a signal obtained when one-dimensionally scanning a beam area corresponding to a beam used for the measurement with a beam smaller than the beam, having two or more maxima or minima. The mark is arranged so as to enable

(7) In (6), the maximum value of the two-dimensional signal distribution is within the range where the linearity of the signal measuring system is established. (8) In (6), two or more of the marks are arranged in an area where the beam used for the measurement can be irradiated at one time.

(9) In (6), the maximum value of the two-dimensional signal distribution is in a region where the SN ratio of the signal measuring system is sufficiently larger than 1. (Operation) In the present invention (claims 1 to 5), when the astigmatism in the charged particle optical lens barrel is corrected and the focusing is performed, the second evaluation function has an extreme value at two or more positions near the in-focus position. In the case of, the astigmatism direction is obtained by using a two-dimensional image near two points on both sides of the center. Alternatively, the third evaluation function is used to find candidates for the in-focus position in different directions, and adjustment is made so that they match. As a result, even if there are a plurality of in-focus position candidates, astigmatism can be accurately corrected, and higher-level astigmatism correction and focusing can be performed.

Further, in the present invention (claims 6 to 8), the mark is arranged so that the high-frequency component of the two-dimensional image obtained from the mark becomes large, and the mark is provided so as to obtain a sufficient SN ratio, and further measurement is performed. The signal is obtained in the range where the linearity of the system holds. Under this condition, the in-focus position and the astigmatism are detected from the change of the Fourier transform of the two-dimensional image obtained from the reflection signal from the mark. As a result, a large SN ratio is obtained, and from the change of the Fourier transform of the two-dimensional image obtained from the reflected signal,
Since the in-focus position and the astigmatism are detected, the adjustment can be performed with a required resolution.

[0021]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described below with reference to the illustrated embodiments. (First Embodiment) First, a beam adjustment method (frequency space image change method: FSI) already proposed by the present inventors.
Method D, Japanese Patent Application No. 7-237456).

The signal distribution obtained by scanning the mark with the electron beam is I (x, y), and the current distribution of the beam is b (xx).
0, y−y0), and the mark distribution is m (x, y).
Here, x0 and y0 are the positions of the center of the beam. I
(X, y), b (x-x0, y-y0), m (x, y)
If the constant of proportionality is ignored, the following relational expression may hold.

I (x, y) = ∫∫b (x-x ', y-y') m (x ', y') dx'dy '(1) Here, the integration range marks the beam. If the signal is obtained by scanning to a position not included, ± infinity may be taken with sufficient approximation. Now, the functions I (x, y), b (x,
y) and m (x, y) Fourier transforms are respectively I (kx, k)
y), B (kx, ky), M (kx, ky),
The following relational expression holds.

I (kx, ky) = B (kx, ky) M (kx, ky) (2) By the way, b (x, y) is an ideal beam distribution b0 (x, y) without blurring. , B (x, y) = ∫∫t (x-x ', y-y') b0 (x ', y') dx'dy 'using the function t (x, y) representing blurring. It is expressed as (3). However, the integration range is ± infinity. Therefore, the Fourier transform of t (x, y), b0 (x, y) is T
When expressed as (kx, ky) and B0 (kx, ky), the following relationship holds: B (kx, ky) = T (kx, ky) B0 (kx, ky) (4). Therefore, the relational expression I (kx, ky) = T (kx, ky) B0 (kx, ky) M (kx, ky) (5) holds.

Now, the reflected electron signal distributions at different focal length settings of the objective lens are i1 (x, y) and i2 (x, y).
And the Fourier transform of each of them is I1 (kx, ky),
Let I2 (kx, ky). Where I1 (kx, k
y), I2 (kx, ky), the evaluation function R (kx, ky) whose sign is determined depending on the magnitude of the absolute value is, for example, R (kx, ky) = log (| I1 (kx, ky) | / | I2 ( kx, ky) |) ... It is defined as (6). In equation (5), only T (kx, ky) changes with a good approximation when the focal length of the lens is changed, so T corresponding to I1 (kx, ky), I2 (kx, ky) Let (kx, ky) be T1 (kx, ky), T
When 2 (kx, ky) is set, R (kx, ky) = log (| T1 (kx, ky) | / | T2 (kx, ky) |) ... (7) That is, R (kx, ky) is determined regardless of the beam shape, the mark shape, or the like.

First, consider the case where there is no astigmatism. In that case, T (kx, ky) obtained by Fourier transforming t (x, y) is expressed as T (kx, ky) = α exp (−ka ² k ² ) ... (8). However, k ² = kx ² + ky ² , α is a proportional constant, and ka is a parameter indicating the spread of the beam. Here, it may be considered that α does not depend on the focal length of the lens as long as the current is constant.

Now, assuming that T1 (kx, ky) = α exp {-(k / k1) ² } T2 (kx, ky) = α exp {-(k / k2) ² } ... (9), R ( kx, ky) =-(k / k1) ² + (k / k2) ² (10). In principle, the code of R (kx, ky) is k1, except for the origin, that is, the point of k = 0, as shown in FIG. 3 (a).
Determined by the size of k2. That is, if k1> k2, R (kx, ky)> 0 If k1 <k2, R (kx, ky) <0 (11)

Practically, for example, the sign of the average value of R (kx, ky) in the spatial frequency domain of interest may be used. Thereby, even if there is astigmatism, the in-focus position can be approximately calculated.

In order to obtain the in-focus position, the secondary particle image is measured while changing the focal length, and based on the secondary particle images under two continuous focal length setting conditions, the above R (kx, k)
y) is calculated. Focal length, z1, z2, ..., Zn, R
(Kx, ky) is obtained and is set as R1, ..., Rn,
When R0 = 0, the second evaluation function Fi (kx, ky) is introduced in zi (i = 1,2, ..., n), and Fi
= R0 + R1 + ... + Ri. T (k
If the spread of (x, ky) is the maximum, F (kx, ky) is the minimum at that position. Here again, it is practical to use the sign of the average value of R (kx, ky) in the spatial frequency domain of interest, instead of using Fi (kx, ky) at a certain point.

When an astigmatism exists, R (kx, k
The code distribution of y) is a two-fold symmetrical distribution as shown in FIG. The determination of the direction of astigmatism is R (kx, ky)
In the frequency domain of
The term proportional to (i2θ) is obtained, and the astigmatic direction can be obtained from the phase angle. Practically, it is advantageous to use the focal length setting condition sandwiching the in-focus position obtained above.

In order to correct astigmatism, the stigmata intensity corresponding to the target lens is adjusted and the above ex
The absolute value of the ratio of the term proportional to p (i2θ) to the term proportional to exp (i0θ) is minimized. Alternatively,
It is also possible to adjust the stigmata under the condition that the direction of the astigmatism is not changed, and use the stigmata intensity at which the code distribution in the angular direction is inverted as the intensity that gives the condition for correct correction.

By the way, the subsequent detailed studies by the present inventors have revealed that the second evaluation function can have a plurality of extreme values near the in-focus position. That is, when the astigmatism is present, the focal length that converges in one direction and the focal length that converges in the other direction are different, so that as shown in FIG. It is possible that a minimum value is taken. Further, when the astigmatism is almost corrected, it is possible that local minimum values occur on both sides of the in-focus position as shown in FIG. 4B, for example.

Therefore, in this embodiment, the following processing is performed in FIG. That is, when there are two candidates (A, B) for the in-focus position, it is considered that there is astigmatism, and the direction of astigmatism is determined from the Fourier transform image at A and B. Next, the astigmatism is corrected by using the stigmator based on the obtained direction of the astigmatism. When the astigmatic difference becomes small and three candidates (A, B, C) of in-focus positions appear, the direction of astigmatism is determined from the Fourier transform images in A and C. Next, the astigmatism is corrected by using the stigmator based on the obtained direction of the astigmatism. The adjustment is performed until the candidates for the in-focus position approach within a predetermined distance. Alternatively, for example, FIG.
It is also possible to make adjustments until the ratios Ez / Fz ', Fz / Rz "of the values of the second evaluation function in the focusing point candidates indicated by Fz, Fz', Fz" in (b) become equal to or greater than a predetermined value.

Further, the direction of astigmatism can be determined as follows. Instead of directly obtaining the astigmatism from R (kx, ky), as shown in FIG.
A new coordinate system (kx ', rotated in the angle θ direction with respect to the x-axis
ky ′), in the new coordinate system, for example, R (kx, ky) in the frequency range of interest within the region surrounded by the line drawn by ± 45 degrees with respect to the kx ′ axis as shown by the diagonal lines. )
The difference from the value obtained by the reference focal length of the integrated amount is defined as the third evaluation function.

In this case, the value of the third evaluation function at the reference focal length is set to 0 for convenience. Alternatively, R (kx,
When integrating ky), for example, when the angle formed with respect to the kx ′ axis is α, cos (α) can be integrated as a weighting function to emphasize the directivity. The third evaluation function is considered to give the sharpness of the image in the α direction.

As θ, 0 °, 90 °, 45 °, 135
The degree is determined, and the focus position dependency of the third evaluation function is obtained for each. This is, for example, as shown in FIG. 6, the minimum is z0 in the 0 ° direction and the minimum in z90 in the 90 ° direction.
It has two extreme values in the directions of 135 degrees and 135 degrees. Here, the third evaluation function is displayed with its absolute value shifted for ease of viewing. First, the stigmata corresponding to 0 ° -90 ° is adjusted so that z0 and z90 match. Further, the stigmata corresponding to 45 ° -135 ° is adjusted so that the focal positions that give the extreme values also in the 45 ° and 135 ° directions coincide with each other within a predetermined range.

As described above, according to this embodiment, when there are a plurality of in-focus position candidates, the astigmatic direction is obtained from the first evaluation function obtained from the Fourier transform images obtained at the two points at both ends. Adjustment is performed, or adjustment is performed so that the candidates of the in-focus position of the third evaluation function that gives the sharpness of the image in the angular direction match. As a result, even when there are a plurality of in-focus position candidates, astigmatism can be accurately corrected, and more advanced astigmatism correction and focusing can be performed.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 7A shows an example of a cross-sectional shape of the beam 1 to be measured on the sample and an arrangement example of the marks 2 in this embodiment. Here, it is desirable that the size of the mark 2 be sufficiently smaller than the resolution of the beam 1 to be measured. In this example, a rectangular beam is considered.
The two-dimensional distribution of the signal obtained in this case is roughly as shown in FIG.
It becomes like (b). The signal distribution along the broken line in FIG. 7B is as shown in FIG. 7C, for example. Although it has a higher SN ratio than the conventional example of FIG. 2 (b), the conventional method for checking the blur of the beam from the rising and falling of the signal waveform accurately obtains the in-focus position and produces astigmatism. It cannot be corrected.

By the way, as described above, the inventors of the present invention can accurately determine the in-focus position even in the case of a shaped beam or a character beam from the change of the Fourier transform of the two-dimensional distribution of the signal of secondary particles such as backscattered electrons. Has been proposed or a method of correcting astigmatism (FSID method) has been proposed. However, at this time, no specific mark arrangement method was mentioned.

In this embodiment, the marks are arranged as follows. That is, it is arranged so that the signal obtained when one-dimensionally scanning with a beam smaller than the beam within the beam area corresponding to the beam to be measured has two or more maximums or minimums. More specifically, the marks are arranged so that a plurality of marks are included in the region irradiated with the beam at one time.

As a result, detection of the in-focus position using the FSID method under the condition that a sufficient SN ratio and resolution are obtained,
By correcting the astigmatism, it becomes possible to perform adjustment with extremely high precision as compared with the case of using the conventional single fine mark. In particular, the high spatial frequency component to be measured is made larger. Furthermore, the sensitivity of the measurement system cannot always maintain linearity at all signal intensities. Therefore, by using this method, it is possible to perform the measurement so that the main measurement signal falls within the region where the linearity of the measurement type is maintained. Further, although not shown in the drawing, the two-dimensional signal distribution has a large spatial frequency component higher than that in the example of FIG.

Here, the case where the FSID method is applied to a rectangular beam in the mark arrangement as in this embodiment will be described. The signal distribution obtained in FIG. 7B is I (x, y), and the beam current distribution is b (x-x0, y-).
y0), and the mark distribution is m (x, y). here,
Let x0 and y0 be the positions of the center of the beam. I (x,
It may be considered that the relational expression of the above formula (1) is established if the proportional constant is neglected between y), b (x-x0, y-y0) and m (x, y).

Now, the functions I (x, y), b (x, y),
The Fourier transform of m (x, y) is I (kx, ky),
B (kx, ky) and M (kx, ky) represent the above formula
The relational expression (2) holds.

By the way, b (x, y) is an ideal beam distribution b0 (x, y) with no blur, and a function t representing the blur.
It is expressed by the above equation (3) using (x, y).
Therefore, if the Fourier transform of t (x, y) and b0 (x, y) is expressed as T (kx, ky), B0 (kx, ky), the relation of the above equation (4) is established, and the above equation (4) is established. The relational expression of 5) is established.

Now, the reflected electron signal distributions at different focal length settings of the objective lens are i1 (x, y) and i2 (x, y).
And the Fourier transform of each of them is I1 (kx, ky),
Let I2 (kx, ky). Where I1 (kx, k
y), I2 (kx, ky), the evaluation function R (kx, ky) whose sign is determined by the magnitude of the absolute value of
Define as in (6). In Eq. (5), it is a good approximation that T (kx, k changes when the focal length of the lens is changed.
y) only, so I1 (kx, ky), I2 (k
T (kx, ky) corresponding to x, ky) is T1 (k)
x, ky) and T2 (kx, ky), the above equation (7)
It is represented by. That is, R (kx, ky) is the beam shape,
Determined regardless of the mark shape.

First, consider the case where there is no astigmatism. In that case, T (kx, ky) obtained by Fourier transforming t (x, y) is expressed by the above equation (8). Further, R (kx, ky) from the above equation (9) is represented by the above equation (10). Also, for example, R (kx, ky) = {I1 (kx, ky) -I2 (kx, ky)} / {I1 (kx, k
y) + I2 (kx, ky)} may be defined. in this case, Becomes

The equation (10) is considered below. In principle also in the case of the equations (10) and (12), the code of R (kx, ky) is k1, except for the origin, that is, the point of k = 0, as shown in FIG.
Determined by the size of k2. That is, if k1> k2, R (kx, ky)> 0. If k1 <k2, R (kx, ky) <0. Practically, for example, the sign of the average value of R (kx, ky) in the target spatial frequency domain may be used. Thereby, even if there is astigmatism, the in-focus position can be approximately calculated.

In order to obtain the in-focus position, the secondary particle image is measured while changing the focal length, and based on the secondary particle images under two continuous focal length setting conditions, the above R (kx, k)
y) is obtained, and the position at which the sign is reversed may be set as the focus position. The step of changing the focal length can be made as fine as necessary to improve the measurement accuracy of the in-focus position.

When an astigmatism exists, R (kx, k
The code distribution of y) is, for example, a two-fold symmetrical distribution as shown in FIG. The determination of the direction of astigmatism is R (kx,
In the frequency domain of ky), the term proportional to exp (i2θ) with respect to the angular direction θ is obtained, and the astigmatic direction can be obtained from the phase angle. Practically, it is advantageous to use the focal length setting condition sandwiching the in-focus position obtained above. Specifically, it is convenient to use the first embodiment.

As described above, according to this embodiment, by disposing a plurality of marks in the area irradiated with the measurement beam at one time, the resolution is not limited by the SN ratio of the signal and is high. Both the resolution and the high SN ratio can be satisfied, and more advanced astigmatism correction and focusing can be achieved. Further, since the high frequency component of the two-dimensional signal distribution obtained from the mark is emphasized, it is possible to measure with higher accuracy.

To correct the astigmatism, it is convenient to use the first embodiment. Also, by adjusting the stigmata intensity corresponding to the target lens, the above exp (i
The absolute value of the ratio of the term proportional to 2θ) to the term proportional to exp (i0θ) is minimized. Alternatively, the stigmata may be adjusted under the condition that the direction of astigmatism is not changed, and the stigmata intensity at which the code distribution in the angular direction is inverted may be set as the intensity that gives the condition for correct correction.

In the present embodiment, in principle, adjustment is possible without depending on the beam shape or the mark shape. But,
The linearity of the signal intensity with respect to the irradiation current is assumed. Therefore, the condition is that most of the signals to be processed are in the linear region, as shown in FIG. Therefore, it is desirable that the size and arrangement of the marks be within a range in which a sufficient SN ratio is obtained and the linearity of the signal is established.

As for the mark structure, the backscattered electrons are measured by using a heavy metal dot formed on a substrate having a low atomic number such as silicon or a heavy metal thin film having fine holes, or For example, the electron current passing through the hole may be measured. The point is that it has only to have a necessary spatial frequency. Further, as the shape of the mark, it is not always necessary to use the dot-shaped mark as shown in FIG. For example, it is obvious that similar effects can be obtained even with the ones shown in FIGS. If the required signal strength is obtained and a signal containing the necessary spatial frequency information is obtained, the shape of the mark,
There is no limitation on the signal acquisition method.

The present invention is not limited to the above embodiments. The shape of the beam to be measured is not limited to a rectangle and may be a circular beam. Further, the present invention can be applied not only to electron beams but also to ion beams. In addition, various modifications can be made without departing from the scope of the present invention.

[0055]

As described above, according to the present invention, astigmatism can be accurately corrected even when there are a plurality of in-focus position candidates, and more advanced astigmatism correction and focusing can be performed. Is possible. Further, the resolution is not limited by the SN ratio of the signal, both high resolution and high SN ratio can be satisfied, and higher-level astigmatism correction and focusing can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for measuring a beam resolution using a conventional single mark.

FIG. 2 is a diagram showing an example of a backscattered electron signal obtained when linearly scanning a beam on a single mark.

FIG. 3 shows R (kx, k with and without astigmatism.
The figure which shows the example of y).

FIG. 4 is a diagram showing a distribution of a third evaluation function when there is astigmatism.

FIG. 5 is a diagram for giving a range for obtaining a third evaluation function in the θ direction.

FIG. 6 is a diagram showing an example of distribution of a third evaluation function.

FIG. 7 is a view showing an arrangement example of marks used in the second embodiment and signals obtained.

FIG. 8 is a diagram showing a state of code distribution of an evaluation function.

FIG. 9 is a diagram showing that the maximum value of a two-dimensional signal distribution is in a range where the linearity of a signal measuring system is established.

FIG. 10 is a diagram showing another example of a mark.

[Explanation of symbols]

1 ... Electron beam 2 ... mark

Claims (8)

(57) [Claims] 1. A charged particle beam is directed onto a mark on a sample surface.
A step of obtaining a two-dimensional signal distribution obtained by dimensional scanning at a plurality of settings with different focal lengths of the lens for converging the beam on the sample surface;
The focus of the second evaluation function obtained by processing the first evaluation function by determining the direction of astigmatism using the first evaluation function determined by the difference between the Fourier transforms of the dimensional signal distributions. And a step of obtaining a focused position from a change with respect to a setting. 2. A charged particle beam is directed onto a mark on a sample surface.
A step of obtaining a two-dimensional signal distribution obtained by dimensional scanning at a plurality of settings with different focal lengths of the lens for converging the beam on the sample surface;
Request focus position from the changes to the focus setting of the second evaluation function obtained by processing the first evaluation function determined by the respective differences of the Fourier transform of dimensional signal distribution
A method for adjusting a charged particle optical lens barrel including the steps of: providing a candidate for a focus position at two or more positions near the focus position when the value of the second evaluation function has no astigmatism. A method for adjusting a charged particle optical lens barrel, characterized in that the first evaluation function is obtained by using the Fourier transform signals at the two positions, and the direction of astigmatism is obtained from the first evaluation function. 3. The Fourier transform of the two-dimensional signal distribution obtained at different focal lengths of the lens is I (kx, ky), I
When given by ′ (kx, ky), the first evaluation function is a function whose sign is determined to be positive or negative corresponding to the magnitude of the absolute value of I (kx, ky), I ′ (kx, ky). 3. The charged particle optical lens barrel adjusting method according to claim 1, wherein the evaluation function of 2 is an average or weighted average of the first evaluation function in a target wave number region. 4. A charged particle beam is directed onto a mark on the surface of a sample.
A step of obtaining a two-dimensional signal distribution obtained by dimensional scanning at a plurality of settings with different focal lengths of the lens for converging the beam on the sample surface;
The astigmatism direction is determined using the first evaluation function determined by the difference in the Fourier transform of the dimensional signal distribution, or the focus of the second evaluation function obtained by processing the first evaluation function. A method of adjusting a charged particle optical lens barrel, comprising the step of determining at least one of a focused position from a change with respect to a setting, the third evaluation method being dependent on a directionality of a wave number spatial distribution from a first evaluation function. The evaluation function is obtained and the third corresponding to each direction is obtained.
The method for adjusting a charged particle optical lens barrel is characterized in that astigmatism is corrected so that the evaluation functions of (1) to (3) provide candidates for in-focus positions at the same focus setting position. 5. The Fourier transform of a two-dimensional signal distribution obtained at different focal lengths of the lens is I (kx, ky), I
When given by ′ (kx, ky), the first evaluation function is a function whose sign is determined to be positive or negative corresponding to the magnitude of the absolute value of I (kx, ky), I ′ (kx, ky). 5. The method of adjusting an electron particle optical lens barrel according to claim 4, wherein the evaluation function of 3 is a weighted average of the first evaluation function in the wave number region of interest in which the weight changes in the angular direction. 6. A charged particle beam is directed onto a mark on a sample surface.
Measuring the two-dimensional signal distribution obtained by dimensional scanning at a plurality of settings with different focal lengths of the lens for converging the beam on the sample surface, and the two-dimensional signal distribution obtained by the step. A method for adjusting a charged particle optical lens barrel, which comprises the step of determining at least one of a direction of astigmatism and a focus position by using a difference between respective Fourier transforms, which is used for the measurement. Charged particle optics characterized in that the marks are arranged so that two or more maximums or minimums can be obtained in a signal obtained by one-dimensional scanning with a beam smaller than the beam within a beam area corresponding to the beam. How to adjust the lens barrel. 7. The maximum value of the two-dimensional signal distribution is in a range where the linearity of the signal measuring system is established.
A method for adjusting a charged particle optical lens barrel as described above. 8. The method of adjusting a charged particle optical lens barrel according to claim 6, wherein two or more marks are arranged in a region where the beam used for the measurement can be irradiated at one time.