JPH1031968A - Scanning charged particle beam microscope and its aligning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a SEM and establish its aligning method, with which the observing point is located in the center of the electron beam scanning range, the observing accuracy is enhanced, and easy operation is secured. SOLUTION: This microscope concerned is composed of a memory means 141 to store a template obtained by scanning a specimen 6 to serve as the reference, a pattern matching means 151 which senses the correlation value of the information signal acquired through scanning of a specimen 16 to be observed relative to the template and determines the position with the highest correlation value to produce a pattern for matching, a driving means 17 to drive a stage for specimen, a deflecting means 3 to deflect an electron beam, and aligning function to make location on the basis of the result from pattern matching. The pattern for pattern matching is located in a position dislocated from the center point so that the observing point on the specimen to be observed lies identical to the center point of the electron beam scanning range, and thus the pattern matching is performed, and movement to the observing point is made with image shift.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning charged particle beam microscope and an alignment method thereof.

[0002]

2. Description of the Related Art When observing / measuring a sample such as a wiring pattern of a chip formed on a semiconductor wafer using a scanning electron beam microscope, an observation point of the sample is set within a visual field of the microscope (scanning of an electron beam). As an alignment method to automatically move and position the image within a range, the electron beam is scanned on a reference sample, and the position data and image of characteristic points suitable for setting the reference position of the chip position on the semiconductor wafer The data is captured as a template, and the sample to be observed later is scanned with an electron beam to obtain image data (hereinafter, referred to as “sample”).
A matching pattern is obtained by comparing the correlation values between the template image and the image of the matching pattern, and matching the pattern so as to position the matching pattern of the sample at the center of the scanning range of the electron beam. After moving and determining the reference point, the electron beam is deflected from the reference point to the observation point of the sample, the electron beam is scanned at this position, and the image of the observation point is displayed at the center of the monitor screen, and the final positioning of the sample is performed. There is an alignment method using pattern matching that performs observation and length measurement.

In order to move a matching pattern for performing pattern matching of a sample to the center of the scanning range of the electron beam, the sample stage on which the sample is placed is driven to move the region where the matching pattern exists to the scanning range of the electron beam. After moving to the center position and obtaining the position of the matching pattern by pattern matching here, the movement from this matching pattern position to the observation point is performed using the previously obtained reference point, that is, the distance data from the matching pattern position. Positioning accuracy is ensured by using a moving method based on an image shift in which an electron beam is deflected by a magnetic coil and moved to an observation point without driving the sample stage.

[0004] That is, the conventional alignment method is shown in FIG.
As shown in (1), when the alignment to the observation point K is performed, the pattern which is the template data represented by the coordinate position on the XY table on which the sample table is placed and stored in the creation of the template, that is, the teaching work. The sample stage is driven to the matching position (T_STG_X, T_STG_Y) to move the observation object (sample) so that the matching pattern P is located at the center (hereinafter referred to as the origin) 0 of the scanning range of the electron beam (FIG. 4A). ). At that position, a pattern matching process is performed using the template stored in the teaching, and the amount of deviation (ALG_X, ALG_Y) of the matching pattern P from the origin 0 caused by an error between samples or an error in transporting the sample. Then, the position Pr of the accurate matching pattern represented by is detected (FIG. 4B). Next, using the following equations (1) and (2), the amount of image shift actually calculated by deflecting the electron beam is calculated, and the image of the observation point K is displayed on the monitor screen by deflecting the electron beam ( (FIG. 4 (C)).

IMG_X = T_IMG_X−ALG_X (1) IMG_Y = T_IMG_Y−ALG_Y (2) where, IMG = actually image shift from origin 0, T_IMG = observed from matching pattern P (template) The final alignment image shift amount, which is the distance to the point K, ALG_ = exact position P of the matching pattern P from the origin 0
The distance to r. That is, using the above equation, the distance from the matching pattern P to the observation point K, that is, the final alignment image shift amount (T_IMG_X, T_IMG_Y), matches the matching pattern P at the position where the sample table is moved based on the template data. The actual image shift amount (IMG_X, IMG_Y) corrected at the correct position Pr (ALG_X, ALG_Y) is obtained, and the electron beam is image-shifted (deflected) from the origin 0 by this image shift amount to the observation point K. Move.

In the above prior art, the observation point K finally positioned by the image shift after the pattern matching is shifted from the center point (origin 0) of the scanning range of the electron beam. Such a shift in the observation position
Since the image shift is deflected by applying a voltage to the magnetic coil, if the amount of movement is large, the final positioning position due to the image shift is set outside the field of view, which is outside the scanning range of the electron beam, and observation is possible. There is a problem in that the resolution may be lost, and the resolution may be degraded because the final positioning position is off the center of the scanning range of the electron beam.

Since the final positioning position moved by this method is out of the center of the scanning range of the electron beam, if it is desired to move to the next observation point, the visual field (deflective area of image shift). There is a region where the possibility of departure from the image is large, and there is also a problem that the moving region to the observation point due to the image shift becomes narrow. Further, in moving from the pattern matching position to the final positioning position by the image shift, it is said that the entirety of one side of the deflectable area of the image shift cannot be used due to an error in the positioning accuracy of the sample stage and the accuracy of the sample transfer system. There were also problems.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention provides a method for adjusting the position of a final position moved by image shift after pattern matching to the center or substantially the center of a charged particle beam scanning range of a microscope. It is an object of the present invention to provide a scanning electron beam microscope in which the observation accuracy can be increased by minimizing the size of the laser beam and the operability thereafter can be easily provided, and an alignment method thereof.

[0009]

In order to solve the above-mentioned problems, the present invention provides a method for moving to a pattern matching position.
The sample stage is driven to a position obtained by subtracting the image shift amount used in the final positioning so that the final positioning position by the image shift is the center of the scanning range of the electron beam,
After the reference point is determined by the pattern matching process, the alignment is performed by the image shift set by inverting the image shift amount.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a scanning electron microscope according to the present invention will be described with reference to FIG. The scanning electron microscope includes an electron gun 1, a condenser lens 2, a deflector 3, and an objective lens 4, and includes an electron optical system for scanning a wafer, which will be described later, and a sample stage on which a pilot wafer 6 or an observation wafer 16 is placed. 5 and 2 for detecting secondary electrons from the wafer
A secondary electron detector 7, an amplifier 8 for amplifying the output of the secondary electron detector, and an analog / digital (A / D) converter 9
A frame memory 10 for temporarily storing image data;
A central processing unit (CPU) 11, a display means 12 such as a CRT, an electron optical system driving circuit 13, software for driving an electron microscope and pattern matching processing, and data and calculation results required for processing. A memory 14 for storing, an arithmetic processing unit 15 for processing image signals by processing signals from the secondary electron detector, and a drive such as a drive motor for moving the sample stage 5 based on the processing result of the central processing unit 11 And an apparatus 17.

The memory 14 stores an alignment method for performing pattern matching and positioning, and stores a part of an information signal obtained by scanning the pilot wafer 6 as a reference sample as a template. 141 are provided. Arithmetic processing unit 15
In the pattern, a correlation value between the information signal obtained by scanning the sample 16 to be observed and the stored template and the image is detected, and the position of the highest correlation value is detected to be a pattern for matching. A matching means 151 is provided. Further, this scanning electron microscope is operated by an alignment method described later so that the observation point is located at the center of the scanning range of the electron beam during observation.

Hereinafter, an alignment method using the above-mentioned electron microscope according to the present invention will be described. Here, a case where alignment is performed at a target position by one-step pattern matching will be described.

In the present specification, the pattern T and the matching pattern P serving as templates are among the wiring patterns in the chip on the semiconductor wafer and have a characteristic that the value can be easily detected. These positions can be represented, for example, as coordinates on the X-axis and the Y-axis when the corner of each chip is the origin. The observation point K refers to, for example, an observation position in the chip where processing such as measuring the line width in the wiring pattern using this microscope is performed. It can be represented as coordinates on the Y axis. In this specification,
The amounts along which the characters X and Y are given are the X-axis component and Y, respectively.
It means the value of the axis component.

[Creation of Template] The creation of a template will be described with reference to FIG. In order to perform alignment using pattern matching, first, a teaching operation for storing a reference image or the like and obtaining a template is required. As shown in FIG. 1, in teaching, first, a final positioning position (for example, an observation point K) which is an observation target position on a standard sample (for example, a pilot wafer) 6 placed on a sample stage 5 is displayed on the screen. The sample stage 5 is moved to a predetermined position (STG_X, STG_Y) on the XY table so as to be substantially at the center, and the amount of image software to the final positioning position at this position (S_IMG_X, S_IMG_Y)
(FIG. 2A). Here, since the pattern T and the observation point K serving as the template have a predetermined size, these positions are treated as the center points of the cursor surrounding the template and the observation point.

Then, the image is shifted to move the deflection position of the electron beam to a position where the pattern T is located, and the pattern T is displayed on the monitor screen 12 (FIG. 2B). The image shift amount (P_IMG) at this time and the XY of the sample stage 15
The position of the sample stage 15 indicated by the coordinate position on the table
(STG_X, STG_Y), template image information, and template image position (CUR) are obtained (FIG. 2B).

Using the following equation, the coordinates (T_STG) on the XY axis of the sample table 15 at the position where the pattern matching is to be performed, and the final alignment image shift amount (T_I
MG) and a template image. That is, the pattern T
The distance from the position to the observation point K, that is, the final alignment image shift amount (T_IMG) is calculated from the image shift amount (P_IMG) at the position where the pattern T is located based on the image shift amount (S_IMG) and the template image position (CUR). It is represented by the value obtained by subtracting the value obtained by subtracting. That is, the distance between the template pattern T and the observation point K, that is, the final alignment image shift amount (T_IMG) is expressed by the following equations (3) and (4) for the X axis and the Y axis, respectively. T_IMG_X = S_IMG_X- (P_IMG_X-CUR_X) ... (3) T_IMG_Y = S_IMG_Y- (P_IMG_Y-CUR_Y) ... (4)

The pattern matching position (T_STG) indicated by the coordinates on the XY axis of the sample table 15 at the position where the pattern matching is executed is the sample indicated by the coordinate position on the XY table of the sample table 15. The position of the table 15 (STG_
(X, STG_Y) can be obtained by adding a value obtained by subtracting a value obtained by subtracting the template image position (CUR) from the image shift amount (P_IMG) of the pattern T to a certain position. That is, the pattern matching position (T_STG) indicated by the coordinates on the XY axis of the sample table 15 at the position where the pattern matching is executed is indicated by the following equations (5) and (6) for the X axis and the Y axis, respectively. It is. T_STG_X = STG_X + (P_IMG_X-CUR_X) (5) T_STG_Y = STG_Y + (P_IMG_Y-CUR_Y) ... (6) where, S_IMG = image shift amount to final positioning position at position STG, P_IMG = pattern T The image shift amount at a certain position, T_IMG = final alignment image shift amount CUR = template image position, T_STG = pattern matching position, STG = position of sample table 15, and all units are the same.

The obtained pattern matching position (T_STG_
X, T_STG_Y) and the final alignment image shift amount (T_I
MG_X, T_IMG_Y) and the template image are stored and used as template data (FIG. 2C).

[Alignment] The alignment method will be described below with reference to FIG. When the alignment stage is performed, when the sample table 15 is driven to move the sample to be observed (for example, a wafer) to the pattern matching position, first, the pattern matching position stored in the standard sample using the following equations (7) and (8). The position (SSTG_X, SSTG_Y) obtained by subtracting the final alignment image shift amount (T_IMG) from (T_STG) is obtained. SSTG_X = T_STG_X + T_IMG_X (7) SSTG_Y = T_STG_Y + T_IMG_Y (8)

Further, the image shift amount (IMG) obtained by inverting the final alignment image shift amount (T_IMG) obtained in the standard sample using the following equations (9) and (10).
Ask for. IMG_X = −1 × (T_IMG_X) (9) IMG_Y = −1 × (T_IMG_Y) (10) Then, the sample stage is moved to the position (SSTG_X, SSTG_Y) and further inverted. The image is shifted to the position where the matching pattern P to be observed is located by the shift amount (IMG) (FIG. 3A). Then, by performing pattern matching at the position using the acquired template, an accurate pattern matching position (ALG_X, ALG_Y) up to a point Pr where the matching pattern P actually exists is detected (FIG. 3).
(B)).

From the following equation, IIMG_X = T_IMG_X−ALG_X (11) IIMG_Y = T_IMG_Y−ALG_Y (12) The image shift amount to the final positioning position is corrected, and the image on the observation target sample is corrected. Shift amount (IIMG_X, IIMG_Y)
Ask for.

By deflecting the electron beam using the image shift amount, positioning is performed at the final positioning position on the sample to be observed, and the observation point K is set at the center of the scanning range of the electron beam (the deflection range of the image shift). (Origin) 0
(FIG. 3C).

Here, if there is no error between the samples or an error in the accuracy of transporting the samples, the alignment error (ALG) is 0, and the image shift ends the final alignment at the origin.
However, in practice, the image shift does not end at the origin, and the alignment often ends near the origin due to errors between samples and the accuracy of the transport system.

In the above embodiment, one-step pattern matching was used.
The same applies to position control.

[0025]

As described above, according to the alignment method of the present invention, the image shift amount is cleared, and the observation point is located at the center or substantially the center of the deflection range of the image shift. Further, since the image shift amount is set in the opposite direction from the set polarity, it is possible to use the entire area on one side of the deflectable area of the image shift.

In the present invention, after performing the alignment,
Since the final positioning position after the image shift is the center or almost the center of the deflection range of the image shift, the observation area in the image shift after the execution of the alignment is the same or almost the same in all directions and is the entire deflectable area of the image shift. Operability is improved. Further, the distance between the pattern matching position and the final positioning position can be extended.

In the above description, the scanning microscope is a scanning electron microscope that scans an electron beam. However, the scanning microscope is not limited to the electron beam, but any problem occurs in a scanning charged particle beam microscope that scans another charged particle beam. It goes without saying that the present invention can be applied without any change.

[0028]

As described above, according to the present invention, the image shift after the alignment is at the center or substantially the center of the deflection range of the image shift, so that the observable area of the image shift after the alignment is deflectable by the image shift. It becomes equivalent to the area, and the operability in observation is improved.

Further, in the movement from the pattern matching position to the final positioning position by the image shift, it is possible to use the entire deflectable area of the image shift on one side.

When measuring the length of an object or taking a picture after alignment, if the image shift is at the center or substantially the center, the electron beam passes off the axis of the objective lens due to deflection due to the image shift. The length measurement and the photographing can be performed on an image in which the influence of various aberrations is smaller, and there is an advantage that a more accurate result can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration of a scanning electron microscope according to the present invention.

FIG. 2 is a diagram for explaining a template creation procedure according to the present invention.

FIG. 3 is a diagram for explaining an alignment procedure according to the present invention.

FIG. 4 is a view for explaining a conventional alignment procedure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron gun 2 Condenser lens 3 Electromagnetic deflector 4 Objective lens 5 Sample stand 6 Standard sample (pilot wafer) 7 Secondary electron detector 8 Amplifier 9 Analog / Digital (A / D) converter 10 Frame memory 11 Central processing unit (CPU) 12 display means such as CRT 13 electron optical system drive circuit 14 memory 15 arithmetic processing unit 16 observation sample 17 drive unit 141 template memory 151 pattern matching means 0 center (origin) of electron beam scanning range T template P matching pattern

Claims (4)

[Claims] 1. A scanning charged particle beam microscope that scans a sample with a charged particle beam and displays an image of the sample based on an information signal obtained from the sample. A storage unit for storing a part of the information signal as a template, detecting a correlation value between the information signal obtained by scanning the sample to be observed and the stored template, and detecting a position of the highest correlation value A pattern matching processing unit that forms a pattern for matching, a driving unit that drives a sample stage on which a sample is placed, a charged particle beam deflecting unit that deflects a charged particle beam with a magnetic field of a scanning coil, and based on a result of the pattern matching. With an alignment function to position the sample at the center or near the center of the scanning range of the charged particle beam. A pattern for pattern matching is arranged at a position deviated from the point so as to be located at a position, and the pattern matching is performed, and the pattern is moved to the observation position by an image shift. 2. The scanning charged particle beam microscope according to claim 1, wherein the charged particles are electrons, and an information signal obtained from the sample by scanning the sample is a secondary electron signal. 3. An alignment method of a scanning type charged particle beam microscope for scanning a sample on a sample table with a charged particle beam and displaying an image of the sample based on an information signal obtained from the sample. A part of the information signal obtained by scanning the sample is stored as a template, a correlation value between the image obtained by scanning the sample to be observed and the stored template is detected, and the highest correlation value is detected. Setting the position as the position of the matching pattern, driving the sample stage to move the matching pattern to a position shifted by the image shift amount from the center of the scanning range of the charged particle beam, and deflecting the charged particle beam by the magnetic field of the scanning coil. The image is shifted to the observation position of the sample so that the position becomes the center or substantially the center of the scanning range, and then becomes the observation target. Alignment method of scanning charged particle beam microscope and displaying an image of the sample on a fee by scanning. 4. The method according to claim 3, wherein the charged particles are electrons, and an information signal obtained from the sample by scanning the sample is a secondary electron signal.