JP2001084944A - Charged particle beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sample image focused over the whole or a certain two-dimensional region for providing the two-dimensional image, without blurring all over the image by composing the two-dimensional image of the sample as viewed from the direction of a discharge particle beam source, based on a signal of a part where the charged particle beam is focused among signals outputted from a charged particle beam detector. SOLUTION: Each signal outputted from a charged particle detector is stored for different focus to calculate an arbitrary characteristic amount indicating degree of coincidence of focus from the stored signals, and the characteristic amount is compared between the same coordinates of signal of different focus to form a two-dimensional image. In a semiconductor sample comprising a contact hole, a copy of two-dimensional image which is focused over the entire sample can be made, by picking up both the image focused on a surface of the semiconductor sample and the image focused on a bottom surface of the contact hole, and extracting a coincident part of focus from each image to make a single composite image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charged particle beam apparatus, and more particularly to a charged particle beam apparatus having a function of appropriately adjusting the focus of an image obtained as a result of irradiation with a charged particle beam.

[0002]

2. Description of the Related Art A charged particle beam apparatus such as a scanning electron microscope is
The apparatus is suitable for measuring and observing a pattern formed on a semiconductor wafer that has been miniaturized. By the way, with the increase in the number of layers of a semiconductor wafer or the like, a sample has a more three-dimensional spread. For example, a contact hole formed on the sample has a deeper hole.

[0003]

A charged particle beam apparatus such as a scanning electron microscope is an apparatus for irradiating a sample with a narrowed beam, and it is necessary to appropriately focus (focus) on the sample. . However, with the recent increase in the number of layers of semiconductor wafers, for example, the dimensional difference between the sample surface and the contact hole bottom surface has become larger, and the problem has arisen that the appropriate focal length of the charged particle beam differs between the sample surface and the contact hole bottom surface. Was. That is, if the focal point is adjusted in accordance with the surface of the sample, the bottom of the contact hole becomes out of focus, and as a result, the image of the bottom of the contact hole is blurred.

Japanese Patent Application Laid-Open No. Hei 5-128889 discloses a technique for irradiating a three-dimensional object with an electron beam while changing the focus and extracting a contour of a focused part to construct a three-dimensional image. Have been. For example, when trying to observe a two-dimensional image of a sample including the bottom of a contact hole with such a device, only the contour of the contact hole is displayed, and therefore, it is not possible to observe the condition of the sample surface and the bottom of the contact hole.

Another example is disclosed in Japanese Patent Application Laid-Open No. 5-29904.
No. 8 discloses a technique disclosed in Japanese Patent Application Laid-Open No. H8-209, which basically extracts the contour of a concavo-convex image and obtains a pseudo three-dimensional image such as contour display. That is, differentiation processing is performed on an image obtained by changing the focus, a constant extraction level is set for the value, and a portion larger than that level is extracted.

[0006] This process is performed on a plurality of images obtained by changing the focus, and finally, the images are connected to thereby extract the contour portions of the unevenness of the images. At this time,
No consideration is given to parts below the extraction level. Further, the extraction level serving as an evaluation criterion for determining whether an image is a contour depends on the S / N of an image and the shape of a target, and cannot be set to a constant value. For example, as shown in FIG. 16, when there are two types of irregularities on one image, the shape of 1601 has a steep slope, so that the differential value of the in-focus portion increases, In the shape of 1602, the slope is gentle and the differential value is small. Therefore, if a certain extraction level is applied to this, the contour of 102 will not be extracted depending on how the level is selected. As described above, if an appropriate extraction level cannot be set, a contour portion that is not extracted appears. The example of FIG. 16 is a case where there are two types of irregularities. However, there are innumerable irregularities in an actual image, and it is impossible to set a level for extracting all the contours.

[0007] Further, extraction is performed for each image, and the relationship between the images in the extracted portion is not considered. Therefore, if an appropriate extraction level cannot be set, the synthesized image is formed by joining the extracted portions. In this case, an indefinite area is formed in the image as shown in FIG. 17, or a part that is extracted and overlapped between images appears. That is,
In the invention disclosed in Japanese Patent Application Laid-Open No. 5-299048, it is very difficult to set an extraction level, and no consideration is given to a processing method for a portion extracted between images.

An object of the present invention is to obtain an in-focus image over the entire sample image or over a certain two-dimensional area, and a charged particle beam capable of obtaining a two-dimensional image without blur over the whole. In providing the equipment.

[0009]

In order to solve the above-mentioned problems, the present invention provides a charged particle source, a scanning deflector for scanning a charged particle beam emitted from the charged particle source on a sample, and the charged deflector. Means for changing the focal point of the charged particle beam emitted from the particle source, a charged particle detector for detecting a charged particle obtained at the irradiation position of the charged particle beam on the sample, and a signal output from the charged particle detector And a means for synthesizing a two-dimensional image of the sample viewed from the charged particle beam source direction based on a signal of a focused portion of the charged particle beam. .

[0010] According to this configuration, of the charged particles obtained from the sample, it is possible to select a focused two-dimensional region of the charged particles and form a sample image using the selected region. In other words, a sample image based on the charged particles that are locally focused can be constructed in the beam scanning area, so that a two-dimensional image that is locally focused can be synthesized.

To give a more specific example, the present invention focuses on the change of the differential value or Sobel value of the same coordinate position of a plurality of images obtained by changing the focus, and the original image having the maximum value of these values. Is used as the pixel value of the focus matching. For this reason, an unstable parameter is not set in the synthesis, and an unfocused portion or an overlapped image is not extracted between the images, so that an image having an overall focus can be synthesized.

Hereinafter, other examples will be described in the section of the embodiment of the invention.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description of an embodiment of the present invention, a scanning electron microscope which is one of charged particle beam apparatuses will be described as an example. However, the present invention is not limited to this. To obtain a sample image by scanning
Other charged particle beam devices such as a sed ion beam device may be used.

FIG. 1 is a diagram showing a scanning electron microscope to which the present invention is applied. This scanning electron microscope has a built-in automatic focus control function. In FIG. 1, 101 is a sample stage, 102 is a sample to be photographed on the sample stage, 104 is a cathode, 105 is a scanning coil, 106 is an electron lens, 108 is a scanning coil control circuit, and 109 is a lens control circuit.
The electron beam 114 is emitted from the sample 1 by the scanning coil 105.
The electron emitted from the sample 102 is scanned by the detector 102 and detected by the detector 103. Signal S1 from detector 103
Is input to the AD converter 107 and converted into a digital signal S2.

The digital signal of S2 is input to the image processor 110, where image processing such as differential processing of the image and the extraction of feature values are performed, and the result is sent to the control computer 111.

The processed image is displayed on the display device 112.
Sent to and displayed. The focus control signal S3 from the control computer 111 is input to the lens control circuit 109,
Focus control can be performed by adjusting the excitation current of 106.

An input unit 113 is connected to the control computer 111. The automatic focus control in the scanning electron microscope configured as described above is a control for automatically setting the focus condition of the electron lens to an optimal value. The focus evaluation value is calculated and evaluated from the detection signals of the secondary electrons and the reflected electrons obtained by scanning the frame, and the optimum value is set as the condition of the electron lens. FIG. 2 is a diagram showing a change in the focus evaluation value when the condition of the electronic lens is changed.

Here, as the focus evaluation value, a differential value between pixels or the like is used. The total differential value is calculated for each frame photographed while changing the conditions of the electron lens, and the value is the largest. The condition of the electronic lens at the time of the change becomes the condition for focusing. In FIG. 2, the exciting current value of the electron lens is f
At this time, the focus evaluation value takes the maximum value (Fmax), so that f is a condition with focus.

The scanning electron microscope having such an automatic focus control function has the following problems. First, since the focus evaluation value is calculated by performing a certain process on the frame image or the detection signal, the value is an overall value and local focus matching is not considered. Is a point. In other words, despite the fact that the focus condition is different between the top part and the bottom part, such as when there is unevenness on the sample, the automatic focus control requires that either one of the conditions be met, or an intermediate condition. It is calculated as an optimal value.

Second, there is a problem that it takes time for the automatic focus control. As can be seen from FIG. 2, before searching for the optimum value of the focus evaluation value (in FIG. 2, until searching for the maximum value),
A plurality of frame images had to be captured, and it took several seconds to several tens of seconds to finish.

The apparatus of the embodiment of the present invention is intended to provide a scanning electron microscope capable of suitably solving the above two problems, and the configuration of the apparatus of the embodiment of the present invention will be described in detail below. [Embodiment 1] FIG. 3 is a diagram for explaining focus fluctuation which is a problem to be solved by the present invention. When there is a contact hole on a semiconductor sample, in a scanning electron microscope, when the electron beam is focused on the surface of the semiconductor sample, the focus is shifted on the bottom surface of the contact hole having a high aspect ratio. Conversely, if the focus is focused on the bottom surface of the contact hole, the focus will be shifted on the sample surface. At present, the automatic focus function performed by the scanning electron microscope apparatus is:
Such a local focus variation cannot be dealt with, and the focus position calculated by the automatic focus function is the sample surface or an average position.

FIG. 4 is a schematic diagram for explaining the composition creation according to the present invention. In the semiconductor sample having the contact hole described with reference to FIG. 3, an image in which the focus position is adjusted on the surface of the semiconductor sample and an image in which the focus position is adjusted on the bottom surface of the contact hole are photographed. If one composite image is created, one two-dimensional image focused on the entire surface of the sample can be created. This 2
The images are registered in, for example, two frame memories.

FIG. 5 is a processing flow in the case of extracting a focused part and producing a composite image according to the present invention. Two images AI, j and BI, j with shifted focal positions are taken. As described with reference to FIG. 1, a method of shifting the focus is to send a focus control signal S3 from the control computer 111 to the lens control circuit 1.
09 to adjust the exciting current of the electron lens 106. 501 for the two images taken
And the differential absolute value images ΔxyAi, j, ΔxyB
Create i and j. The differential absolute value image is created using a value obtained by adding the absolute value of the difference between a pixel shifted by n pixels in the X direction and the absolute value of the difference between pixels shifted by n pixels in the Y direction as in Expression 1.

ΔxyAi, j = ΔxAi, j + ΔyAi, j (Equation 1) ΔxyBi, j = ΔxBi, j + ΔyBi, j ΔxAi, j = | Ai, j−Ai + n, j |, ΔxBi, j = | Bi, j−Bi + n, j | ΔyAi, j = | Ai, j−Ai, j + n |, ΔxBi, j = | Bi, j−Bi, j + n | Is performed at 502 to suppress this. At 503, which of the two images is in focus is evaluated to create a composite image. Here, the focus matching evaluation method is performed based on Expression 2. Compare the pixel values of the same coordinates of the two differential absolute value images smoothed in 502,
It is determined that the pixel of the original image having the large pixel value is in focus.

[ΔA] i, j ≧ [ΔB] i, j → Ci, j = Ai, j (Equation 2) [ΔA] i, j <[ΔB] i, j → Ci, j = Bi, j Synthesis The image Ci, j is an image in which the focused portions of Ai, j and Bi, j are combined. FIG. 5 shows a case where two images are combined.
Similar processing can be performed by sequentially processing the sheets.

FIG. 11 is a schematic diagram of the synthesizing process of the present invention. An example in which a focus matching evaluation criterion is a pixel value by a Sobel filter will be described. Like the image differentiation, the Sobel filter is a filter for extracting edge information of an image. If the pixel value after applying the Sobel filter is large, a change in pixels around the pixel value is large. That is,
That means the focus is consistent and there is less blur. 11
Reference numeral 01 denotes a plurality of images taken with different focuses, and reference numeral 1102 denotes an image obtained by applying a Sobel filter to each of the images 1101. Each image shown in 1101 is registered in a plurality of prepared frame memories.

Pixels Sg1 to Sg5 on the same coordinates of a plurality of 1102 images registered in the frame memory are compared, and the largest pixel is detected. That is Sg2
Sg2 to the pixel on the same coordinate of the composite image
G2, which is the pixel value of the original image of. Perform this process for all coordinates on the image, select the largest pixel,
By arranging them as a two-dimensional image, a combined image of 1103 is obtained.

FIG. 6 shows another processing flow for extracting a focused part and producing a composite image according to the present invention. 601,
In step 602, a differential absolute value image is created and the image is smoothed in the same manner as 501 and 502 in FIG. Next, at 603, which of the two images is in focus is evaluated to create a composite image. Here, the focus matching evaluation method is performed based on (Equation 3). The pixel values at the same coordinates of the two differential absolute value images smoothed at 602 are compared, and the pixel values of the original image are synthesized at the ratio of the compared pixel values. Compared to the method of FIG.
Despite the effect of blurring caused by defocus, it has a feature that the portion where the focused portion is switched from the A image to the B image is smooth.

Ci, j = (Ai, j × [ΔA] i, j + Bi, j × [ΔB] i, j) / ([ΔA] i, j + [ΔB] i, j) (Equation 3) Fig. 13 is another processing flow for extracting a focused part and creating a composite image according to the present invention. FIG. 5 at 701 and 702
In the same manner as 501 and 502, a differential absolute value image is created and the image is smoothed. Next, in 703, which of the two images is in focus is evaluated to create a composite image. Here, the focus matching evaluation method is performed based on Expression 4.
The pixel values of the same coordinates of the two differential absolute value images smoothed in 702 are compared, and the ratio of the compared pixel values is weighted to synthesize the pixel values of the original image. This is an intermediate method between FIG. 5 and FIG. If the weighting coefficient k is 1, the method shown in FIG. 6 is used. As the weighting coefficient k becomes larger than 1, the method approaches the method shown in FIG.

[ΔA] i, j ≧ [ΔB] i, j Ci, j = (k × Ai, j × [ΔA] i, j + Bi, j × [ΔB] i, j) / (k × [ΔA] i, j + [ΔB] i, j) (Equation 4) [ΔA] i, j <[ΔB] i, j Ci, j = (Ai, j × [ΔA] i, j + k × Bi, j × [ΔB] i, j) / ([ΔA] i, j + k × [ΔB] i, j) FIGS. 6 and 7 show a case where two images are combined. In the case of n images, Differential absolute values of the same coordinates or pixel values subjected to the Sobel filter may be compared, and the same processing may be performed on the largest one and the second one.

Although FIGS. 6 and 7 use the differential absolute value as the evaluation value of the focus matching, the same processing flow can be obtained by using the pixel value subjected to the Sobel filter.

According to the above configuration, a two-dimensional image that is in focus in all regions in the image plane in consideration of local focusing can be synthesized by simple calculation means. In addition, since it is possible to perform processing for arranging pixels without omission in the entire image plane or in a specific two-dimensional area, a high-resolution sample image can be constructed. [Embodiment 2] FIG. 8 is a processing flow in one embodiment of the present invention in which image acquisition, extraction of a focused part, and creation of a composite image are performed in parallel. Reference numeral 813 denotes a process of changing the focal position, that is, the exciting current of the electron lens over time.

The processing to be performed with time is changed from 801 to 8
This will be described with reference to FIG. An image is taken at a1, and an A1 image 801 is obtained. A differential absolute value image ΔA1 of 803 is created for the image until the next image capturing a2, and an A2 image of 802 is acquired at a2. A differential absolute value image ΔA2 of 804 is created between the next image photographing a3,
A1 is compared with ΔA2 of 804, and an image ΔG1 is created in 805 in which the larger differential absolute value is used as a pixel. Based on ΔG1 of 805, an image S1 having pixels of the original image having the larger differential absolute value at 806 is created for the next synthesis. Here, based on ΔG1 of 805, a combined image F1 of 807 is created using the method described with reference to FIGS. 5 to 7 of the present invention.

F1 is displayed on the display device 112 of FIG. Next, at a3, an A3 image 808 is acquired. 809 differential absolute value image ΔA3 between next image capturing a4
Is generated and compared with ΔG1 of 805 to generate an image ΔG2 in 810 in which the larger differential absolute value is used as a pixel. Based on ΔG2 of 810, an image S2 having pixels of the original image with the larger differential absolute value at 811 is created for the next synthesis. Here, based on ΔG2 of 810, 8
Twelve composite images F2 are created and displayed continuously to F1. That is, at the time of acquiring the next image, a composite image of the image acquired up to the immediately preceding image is completed and displayed. By performing photographing, synthesizing processing, and display in parallel with the same repetition, a synthetic image can be displayed in real time. Further, by performing such parallel processing, the control time required for focus correction can be shortened, and the speed of automatic focus correction control can be increased. [Embodiment 3] FIG. 14 shows a display device 1 of an apparatus according to an embodiment of the present invention.
12 is a diagram showing a display example of No. 12. FIG. In this display example, a combined image of a contact hole formed in a semiconductor wafer is displayed. The device employed in this embodiment is substantially the same as the configuration described in FIG. 1, and the description thereof is omitted.

The apparatus of this embodiment has a cursor 1401
Is provided on the display screen of the display device 112 with a pointing device (not shown). This pointing device is for selecting a specific area on the display screen. The apparatus of this embodiment has a function of replacing a portion selected by the pointing device with another image. The function will be described along with an actual example.

An image of a contact hole formed on a semiconductor wafer is displayed on a display device 112 shown in FIG. This sample image has been subjected to the synthesizing process described above.
When the cursor 1401 is positioned on the center 1402 of the contact hole displayed on the display device 112 and the corresponding portion is selected, a portion where an image is constructed based on an electron beam having substantially the same focal length as the selected portion, that is, A selected area of a specific original image in an original image registered for each of a plurality of different focal points is replaced with another image and displayed. This replacement step is executed based on the address data of a pixel registered on the specific image and having a focus evaluation value equal to or higher than a certain value or a pixel having a focus evaluation value substantially the same as the selected portion.

With this configuration, the edge of the contact hole can be clarified. For example, the selection area (in the case of the present embodiment, the center 1402 of the hole)
Is displayed in black, so that there is a clear contrast difference from the portion other than the selected portion.

This is effective when there is little change in luminance at the edge of the contact hole. In the case of a scanning electron microscope that forms a line profile based on image data and measures the pattern length based on the line profile, if the contrast of the edge portion is low, an erroneous determination of the edge based on the line profile is caused. However, the technical problem can be solved by adopting the apparatus according to the embodiment of the present invention.

In the above description, the replacement of the designated area with another image has been described. However, the focus of the designated area may be adjusted. Specifically, the display device 1
The cursor 1401 is positioned on the center 1402 of the contact hole of the composite image displayed on the screen 12 to select that part.

A pixel which is a specific original image forming an image of the selected area and has a focus evaluation value equal to or higher than a certain value, or a pixel having a focus evaluation value which is substantially the same as the position selected by the cursor 1401, Replace with the same area of another original image. According to such a configuration, it is possible to perform processing as if selective focus adjustment is performed on a specific portion of the sample image.

The area where the image is to be replaced is indicated by the cursor 140
A part where the focus almost coincides with the place designated by 1,
That is, a specific image among images registered for each of a plurality of different focal points is replaced with another registered image and displayed.

In the above description, the image of the portion where the focus almost coincides with the designated area is replaced.
However, the present invention is not limited to this. For example, means for selecting an arbitrary area of the sample image may be provided, and the image of the selected area may be replaced based on the address data of the selected arbitrary area.

In the above description, the operator manually operates the display screen 112 while observing it. However, the present invention is not limited to this. For example, the step of replacing a specific focal image with another image is omitted. It may be performed automatically. [Embodiment 4] FIG. 9 is a display example in the case of displaying a combined image of the present invention in real time. Reference numeral 901 denotes a display example in which an image that is sequentially synthesized is divided and displayed on a display monitor such as a workstation, so that the progress can be relatively understood. Reference numeral 902 denotes an example in which only one latest image to be synthesized on the monitor is displayed. Further, while observing these images, when an image with a necessary portion focused is obtained, a series of steps from image acquisition to display is performed by input from the input unit 113 connected to the control computer 111 in FIG. It has a function to stop the operation.

With this configuration, unnecessary electron beam irradiation irrelevant to image acquisition is not required, and automatic focus control of a target portion can be efficiently performed in the shortest time. [Embodiment 5] Fig. 10 shows an embodiment in which length measurement is performed using a composite image of the present invention. A scanning electron microscope having a function of measuring the shape of a semiconductor is provided with the function of creating a composite image according to the present invention, and the function can be used to measure the shape on the composite image.

It is also possible to select an image having a specific focus, selectively read out a pixel having a focus evaluation value equal to or more than a certain value from the image, and perform length measurement based on the pixel. With this configuration, for example, an image of only the bottom of the contact hole is selectively read out, and the length is measured based on the image. Length can be realized. [Embodiment 6] Fig. 12 shows an arbitrary 2D image on the composite image of the present invention.
FIG. 11 is a schematic diagram in a case where a difference in a height direction between points is calculated from a difference in excitation current when an original image of the pixel is captured. 12
When obtaining the distance in the height direction between two points g1 and g2 on the composite image 01, it is checked where the pixel exists in the original image 1202. g1 exists in 2 of the original image, and g2
Is present in 5 of the original image, the distance Δd between the focal length d2 corresponding to the exciting current of the original image 2 and the focal length d5 corresponding to the exciting current of the original image 5 is obtained from the relationship between the exciting current and the focal length in FIG. The distance in the height direction between the two points g1 and g2 can be calculated.

FIG. 15 shows an example of a GUI (Guide User Interface) screen for designating g1 and g2 on the display device. On this GUI screen, there are provided a cursor 1401 that can be moved by a pointing device, and a display column 1501 of the length measurement result. Cursor 14
If g1 and g2 can be designated by 01, the operator can observe the image of the contact hole, for example,
You can specify the sample surface and the bottom of the contact hole,
This makes it possible to measure the depth of the contact hole.

According to the configuration of the embodiment of the present invention, the locations where g1 and g2 are to be set (reference positions for the measurement in the depth direction) can be accurately grasped by using a two-dimensional image. It is possible to accurately measure the size of the sample in the depth direction that is difficult to adhere to. In the example shown in FIG. 15, since g1 is set at the sample surface and g2 is set at the contact hole bottom, the formation depth of the contact hole with reference to the sample surface can be accurately measured.

In the above description, an example has been described in which two points g1 and g2, which are reference points for dimension measurement, are specified.
It is not limited to this. g3 in addition to g1 and g2
May be set. Then, by incorporating a sequence for measuring the dimensional difference between g1 and g2 and between g1 and g3, for example, the depth of two contact holes can be compared. In the case of this example, since the depth measurement is performed on the basis of the same g1 for both of the two contact holes, the depth of formation of the contact holes can be accurately compared.

The apparatus of this embodiment applies a negative voltage to the sample 102 or the sample stage 101 for placing the sample,
By forming an electric field between the electron lens 106 and the ground potential, a deceleration electric field forming technique of decelerating the energy of the irradiation electron beam reaching the sample can be employed (not shown).

This technique (hereinafter referred to as a retarding technique) reduces the chromatic aberration by passing the electron beam through the electron lens 106 at high acceleration, and charges the electron beam reaching the sample at low acceleration. It is a technology that balances the prevention of up.

In the scanning electron microscope employing the retarding technique, a negative voltage is applied to the sample as described above. However, by adjusting the applied negative voltage,
The focus of the electron beam can be adjusted. In practicing the present invention, the negative voltage applied to the sample is changed stepwise,
Images obtained each time may be stored. In this case, the focal length can be determined according to the magnitude of the applied negative voltage.

Further, a member (such as a cylindrical electrode) to which a positive voltage can be applied is provided so as to surround the optical axis of the electron beam, and the same applies by adjusting the voltage applied to the member. Can be realized. This member is a so-called electrostatic lens. [Embodiment 7] Fig. 18 is a schematic diagram of a synthesizing process according to an embodiment of the present invention, in which different kinds of signals detected simultaneously are used to determine the degree of focus matching. In the case of a scanning electron microscope apparatus, there are secondary electrons and reflected electrons as heterogeneous signals that can be detected simultaneously. Normal SEM images use secondary electrons,
Backscattered electrons may be used to obtain additional information about the sample.

If a backscattered electron signal is weak and the S / N of each of the backscattered electron images having different focuses is poor when creating an all-in-focus image of the backscattered electrons, the determination of the focus coincidence is differentiated to the backscattered electron image. In some cases, the image cannot be satisfactorily performed from an image to which the Sobel filter has been applied. In this case, a method of using the reflected electron image is used for the determination of the focus coincidence with the secondary electronic image and for the combination. Reference numerals 1801 and 1802 denote a plurality of reflected electronic images and secondary electronic images that are simultaneously captured while changing the focus. Therefore, g1 ′ on 1801 and 1802
The upper g1 is at the same position on the sample although the signal intensity is different. Reference numeral 1803 denotes an image obtained by applying a Sobel filter to each of the secondary electronic images 1802.

Pixels Sg1 to Sg5 on the same coordinates of a plurality of images 1803 are compared, and the largest pixel is detected. If it is Sg2, g2 ', which is the pixel value of the backscattered electron image acquired at the same time as the pixel value g2 of the original image of Sg2, is projected onto the pixel at the same coordinates of the composite image. By performing this process for all coordinates on the image, 1
A composite image of reflected electrons 803 can be created.

FIG. 19 shows an example of an image in a case where a comparison cannot be made satisfactorily with one signal in the feature amount comparison, and another heterogeneous signal detected simultaneously is compared and synthesized. FIG. 18 shows an example in which a secondary electron image is used to synthesize a reflected electron image. However, in FIG. 18, a reflected electron image is usually used for determination of focus matching, and the determination of focus matching is good from the reflected electron image. If this is not possible, the secondary electronic image is used as an auxiliary.

In other words, the region 1901 in FIG. 19 is a region where the degree of focus matching can be determined from the backscattered electron image of the first stage, and the region 1902 can be determined from the backscattered electron image of the first stage. In other words, it is an area that can be determined from the second-stage secondary electronic image.

FIG. 20 is a diagram showing a scanning electron microscope having a plurality of detectors to which the present invention is applied. 2001 to 2014 correspond to 101 to 114 in FIG. The electron beam 2014 is applied to the sample 2 by the scanning coil 2005.
002, a plurality of different kinds of electrons emitted from the sample 2002, for example, secondary electrons and reflected electrons are detected by the detector 2003 and reflected electrons are detected by 2015. The signal S1 from the detectors 2003 and 2015 is AD
The signal is input to the converter 2007 and converted into a digital signal S2.

[0058]

As described above in detail, according to the present invention, it is possible to obtain a sample image that is in focus, regardless of the entire sample image or a specific two-dimensional area, regardless of the unevenness of the sample surface.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a scanning electron microscope.

FIG. 2 is a diagram showing a change in a focus evaluation value when conditions of an electronic lens are changed.

FIG. 3 is a diagram for explaining focus fluctuation which is a problem to be solved by the present invention.

FIG. 4 is a schematic diagram for explaining the composition creation of the present invention.

FIG. 5 is a processing flow of extraction of a focused part and creation of a composite image according to the present invention.

FIG. 6 is another processing flow of extracting a focused part and creating a composite image according to the present invention.

FIG. 7 is another processing flow of extracting a focused portion and creating a composite image according to the present invention.

FIG. 8 is a processing flow in which image acquisition, extraction of a focused part, and creation of a composite image are performed in parallel according to an embodiment of the present invention.

FIG. 9 is a view showing a display example when a combined image of the present invention is displayed in real time.

FIG. 10 shows an embodiment in which length measurement is performed using a composite image according to the present invention.

FIG. 11 is a schematic diagram of a synthesis process of the present invention.

FIG. 12 is a schematic diagram of calculating a difference in a height direction between any two points on a composite image according to the present invention.

FIG. 13 is a diagram showing a relationship between an exciting current and a focal length.

FIG. 14 is a diagram showing a display example of the display device of the device according to the embodiment of the present invention.

FIG. 15 is a view exemplifying a GUI screen of the apparatus according to the embodiment of the present invention.

FIG. 16 is a diagram showing a method for detecting an uneven contour.

FIG. 17 is a diagram showing a synthesis result based on unevenness detection.

FIG. 18 is a schematic diagram of a combining process in which the degree of focus matching is determined using heterogeneous signals detected simultaneously.

FIG. 19 is an example of an image obtained by performing feature amount comparison with a plurality of different types of signals and synthesizing the same.

FIG. 20 is a schematic configuration diagram of a scanning electron microscope having a plurality of detectors.

[Explanation of symbols]

101: sample stage, 102: sample, 103: detector, 10
4 cathode, 105 scanning coil, 106 electron lens,
107: AD converter, 108: Scan coil control circuit, 1
09: lens control circuit, 110: image processing processor,
111: control computer, 112: display device, 113: input means, 114: electron beam.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01J 37/28 H01J 37/28 B H01L 21/66 H01L 21/66 J H04N 1/387 H04N 1/387 ( 72) Inventor Hideo Todoko, 882-mo, Ichita-shi, Hitachinaka-shi, Ibaraki Prefecture Within the Hitachi Measuring Instruments Group, Ltd.

Claims (19)

[Claims] 1. A charged particle source, a scanning deflector for scanning a charged particle beam emitted from the charged particle source on a sample, and means for changing a focal point of the charged particle beam emitted from the charged particle source. A charged particle detector that detects charged particles obtained at a charged particle beam irradiation point of the sample, and a signal output from the charged particle detector, based on a signal of a portion where the charged particle beam is focused. A means for synthesizing a two-dimensional image of the sample viewed from the charged particle beam source direction. 2. The method according to claim 1, wherein a signal output from the charged particle detector is stored for each different focus, and an arbitrary feature amount indicating a degree of focus matching is calculated from the stored signals. A charged particle beam apparatus, wherein a feature amount is compared between the same coordinates of signals at different focal points, and the two-dimensional image is formed based on the comparison. 3. The method according to claim 2, wherein the characteristic amount is a differential value between pixels of an image based on the signal for each of the different focuses or an absolute differential value, and the feature amount is between the same coordinates of the image for each of the different focuses. A charged particle beam apparatus, wherein a differential value or an absolute differential value is compared, and a pixel value of an image having a large value is used as a pixel value of the two-dimensional image. 4. The image processing apparatus according to claim 2, wherein the characteristic amount is a differential value between pixels of an image based on the signal for each different focus or an absolute differential value, and the feature amount is the same between the same coordinates of the image for each different focus. A charged particle beam apparatus comprising: comparing a differential value or an absolute differential value; synthesizing a pixel value at a ratio of the value; and forming the two-dimensional image. 5. The image processing apparatus according to claim 2, wherein the characteristic amount is a differential value between pixels of an image based on the signal for each different focus or an absolute differential value, and the feature amount is the same between the same coordinates of the image for each different focus. A charged particle beam apparatus, wherein a differential value or an absolute differential value is compared, a ratio of the value is given a predetermined weight, a pixel value is synthesized, and the two-dimensional image is formed. 6. The charged particle beam apparatus according to claim 2, wherein the characteristic amount is based on a pixel value obtained by applying an Sobel filter to an image based on the signal for each different focus. 7. A charged particle source, a scanning deflector for scanning an electron beam emitted from the charged particle source on a sample, and changing a focus of the charged particle beam emitted from the charged particle source in a stepwise manner. Means, a charged particle detector that detects charged particles obtained at the irradiation position of the charged particle beam of the sample, a storage medium that stores a signal output from the charged particle detector for each focal point, and from the storage medium Means for selectively reading out a signal of a focused portion and constructing a two-dimensional image extending in a direction perpendicular to the optical axis of the charged particle beam based on the read out signal. Line equipment. 8. A charged particle source, a scanning deflector for scanning a charged particle beam emitted from the charged particle source on a sample, and changing a focus of the charged particle beam emitted from the charged particle source in a stepwise manner. A charged particle detector for detecting electrons obtained at a charged particle beam irradiation position of the sample; and a plurality of memories for storing a signal output from the charged particle detector for each of the focal points changed in a stepwise manner. Means for comparing a signal value of the same address of the frame memory with the same address of the plurality of frame memories, selecting a signal indicating a high focus evaluation value among them, and arranging the signal for each address to form a sample image. A charged particle beam device, comprising: 9. A means for adjusting a focal point of a charged particle beam, a storage medium for storing a sample image obtained for each adjusted focal point in a scanning charged particle microscope for constructing a sample image by irradiating the electron beam, Combining means for selectively reading out a specific area of the sample image stored in the storage medium and areas of different focal points read out by the reading means, and extending in a direction perpendicular to the optical axis of the charged particle beam 2 Means for constructing a two-dimensional image. 10. A charged particle source, a scanning deflector for scanning a charged particle beam emitted from the charged particle source on a sample, and a focal point of the charged particle beam emitted from the charged particle source is changed stepwise. Means, a charged particle detector for detecting charged particles obtained at a charged particle beam irradiation position of the sample, a storage medium for storing a signal output from the charged particle detector for each focus, and the storage medium From the in-focus portion, selectively synthesizes a two-dimensional image extending in a direction perpendicular to the optical axis of the charged particle beam based on the read signal, and combines the two-dimensional image with the focus of the charged particle beam. A charged particle beam apparatus, comprising: means for performing the process in parallel with the process of changing the particle size. 11. The charged particle beam apparatus according to claim 10, further comprising display means for displaying the synthesis process. 12. A charged particle beam apparatus according to claim 11, further comprising means for externally stopping irradiation of said sample with said charged particle beam. 13. A charged particle beam apparatus for adjusting a focal point of a charged particle beam, and a charged particle beam apparatus for constructing a sample image based on scanning of the charged particle beam onto a sample. , A means for selecting a specific area of the sample image stored in the storage medium, and replacing the sample image in the area selected by the selecting means with a sample image having a different focus or another image A charged particle beam device comprising means. 14. A charged particle source, and a lens that converges and irradiates a charged particle beam emitted from the charged particle source onto a sample.
A detector for detecting secondary charged particles obtained at the irradiation position of the charged particle beam, a display device for displaying a sample image based on the charged particles obtained by the detector, and a sample displayed on the display device Means for storing position information of the charged particle beam irradiation direction for each specific position of the image; designating means for designating an arbitrary place on the display screen of the display device; and positions of at least two places designated by the designating means Means for calculating a distance between the two in the charged particle beam irradiation direction based on the information. 15. A means for adjusting a focal point of a charged particle beam, a means for constructing a sample image based on scanning of the charged particle beam on a sample, and an object to be observed on the sample based on the sample image. In a charged particle beam apparatus comprising means for performing dimension measurement, a storage medium for storing a plurality of sample images obtained for each adjusted focal point, and a specific sample image selected from the plurality of sample images, Means for forming, as a sample image, a pixel indicating a certain or more focus evaluation value in the selected sample image, and performing the dimension measurement based on the sample image formed by the means. Charged particle beam equipment. 16. A charged particle source, a scanning deflector for scanning a charged particle beam emitted from the charged particle source on a sample, and means for changing a focal point of the charged particle beam emitted from the charged particle source. A plurality of charged particle detectors for detecting a plurality of different kinds of charged particles obtained at the irradiation position of the charged particle beam of the sample, and among the signals output from the charged particle detector, the charged particle beam was focused. A charged particle beam apparatus comprising means for synthesizing a two-dimensional image of a sample viewed from the charged particle beam source direction based on a partial signal. 17. The method according to claim 16, wherein a signal output from the charged particle detector is stored for each different focus, and an arbitrary feature amount indicating a degree of focus matching is calculated from the stored signals. A charged particle beam apparatus, wherein a feature amount is compared between the same coordinates of signals at different focal points, and the two-dimensional image is formed based on the comparison. 18. A method according to claim 16, wherein a plurality of different signals detected simultaneously by said plurality of charged particle detectors are stored for each different focus, and focus matching is performed from one of said stored plurality of different signals. Calculate any feature value indicating the degree,
Comparing the feature amount between the same coordinates of signals of different focal points,
A charged particle beam apparatus, which forms the two-dimensional image including other types of detected signals based on the comparison. 19. The method according to claim 16, wherein in the feature amount comparison, when the comparison cannot be performed satisfactorily, another detected heterogeneous signal is compared, and the two-dimensional image is formed based on the comparison. Charged particle beam equipment.