JP2001148016A - Sample inspection device, sample display device, and sample display method - Google Patents

Abstract

(57) Abstract: A sample target device and a sample target method capable of easily finding and positioning a target pattern existing in a repetitive pattern group of a semiconductor element. In order to facilitate positioning and positioning of a target pattern present in a repeating pattern group of a semiconductor element, a function of learning a basic pattern constituting the repeating pattern, a function of automatically counting the number of the basic patterns, and And a function of positioning and positioning the target pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning electron microscope (Scanni) for observing and inspecting a semiconductor device having a repeating pattern group.
The present invention relates to a sample inspection device, a sample display device, and a sample display method such as a nanometer electron microscope, a laser scanning microscope, an atomic force microscope, and a length measurement SEM.

[0002]

2. Description of the Related Art The prior art will be described below with reference to an example of a length measuring SEM used for manufacturing a semiconductor device using the above-mentioned scanning electron microscope. The length measurement SEM is an apparatus for measuring the size of a circuit pattern of a semiconductor element formed on a wafer.

FIG. 3 shows the basic principle and configuration of a length measuring SEM.
This will be described with reference to FIG. FIG. 3 is a longitudinal sectional view showing the configuration of the length measuring SEM. It should be noted that the device related to signal processing is shown in a block diagram on the right side of the figure. In FIG. 3, an electron beam 2 emitted from an electron gun 1 is accelerated and then narrowed down by a converging lens 3 and an objective lens 4 to focus on a surface of a wafer 5 taken out of a wafer cassette 10. At the same time, the trajectory of the electron beam 2 is bent by the deflector 6 and scans the wafer surface two-dimensionally or one-dimensionally. On the other hand, secondary electrons 7 are emitted from the wafer portion irradiated with the electron beam 2. After the secondary electrons 7 are detected and converted into electric signals by the secondary electron detector 8, they undergo signal processing such as analog-to-digital conversion in the signal processing unit 14. The processed image signal is stored in the memory unit 15, and the display 9 is subjected to luminance modulation or Y modulation.
Used to modulate. The display 9 is scanned in synchronization with the scanning of the electron beam 2 on the wafer surface, and a sample image is formed on the display 9. If two-dimensional scanning is performed and luminance modulation is performed, a sample image is displayed. If one-dimensional scanning is performed and Y modulation is performed, a line profile is drawn. Using the sample image and the line profile, the pattern size is measured in the following procedure.

(1) A sample image is formed, and a measurement pattern is positioned.

(2) The electron beam is one-dimensionally scanned to form a line profile. The scanning is performed so as to cross the measurement pattern in the direction in which the dimensions are to be obtained.

(3) The obtained line profile is sent to the dimension measuring unit 16.

(4) The dimension measuring section 16 determines a pattern edge position from the line profile according to a predetermined pattern edge determination algorithm.

(5) The dimension measuring section 16 calculates the dimension of the measured pattern from the obtained interval between pattern edges. The calculated value of the edge interval is converted from the corresponding electron beam deflection amount.

(6) The obtained calculated value is stored in the dimension measuring unit 16
Is output as a dimension measurement result. Device control unit 17
Are the display 9, the memory unit 15, the signal processing unit 1
4. Control of the dimension measuring unit 16 and control of the deflection coil 6 and the XY-stage 12 are also performed.

FIG. 2 shows an example of an image displayed on the display 9 in FIG. FIG. 2A is an example of an image of a repeating pattern group on a wafer. The procedure for measuring the size of a certain portion in such a repeating pattern group using a length measurement SEM is, for example, as follows.

In FIG. 3, the wafer 5 is pre-aligned after being taken out of the wafer cassette 10.
The pre-alignment is an operation for adjusting the direction of the wafer based on an orientation flat, a notch, or the like formed on the wafer 5. After the pre-alignment, the wafer 5 is transferred and mounted on the XY-stage 12 in the sample chamber 11 kept in a vacuum.

The wafer 5 loaded on the XY-stage 12 is aligned using the optical microscope 13 mounted on the upper surface of the sample chamber 11. The alignment is for correcting between the position coordinates of the XY-stage 12 and the position coordinates of the pattern in the wafer 5, and is called a pattern matching method, using an alignment pattern formed on the wafer 5, It is performed as follows.

An optical microscope image enlarged to about several hundred times of the alignment pattern is compared with a reference image of the alignment pattern registered in the memory unit 15 in advance, and its visual field is exactly overlapped with the visual field of the reference image. Next, the stage position coordinates are corrected. After alignment, the operator
The following operations after alignment must be performed by themselves.

(1) Attention is paid to a corner pattern in a repetitive pattern group in which a pattern of a portion to be measured is present, and after moving the stage so that the corner pattern comes to the center of the visual field,
Set the appropriate magnification.

(2) After repeating the visual field movement while counting the number of repeated patterns with the corner pattern as a base point, the target pattern is positioned at a predetermined number of repeated patterns.

(3) After focusing the target pattern,
Measure the dimensions of the location to be measured.

When such a target pattern exists in a group of repeated patterns, finding the target pattern from the group of repeated patterns requires a great deal of labor for the operator and also has poor workability. For example, in a semiconductor memory device, there are nearly one million memory cells in one memory cell array. If one tries to find a specific memory cell out of one million for the purpose of grasping the correlation between the memory cell characteristics and the pattern processing quality, the difficulty will be serious.

On the other hand, the progress of miniaturization of patterns, three-dimensional device structures, and multi-layer wiring in the manufacture of semiconductor devices further reduces the process margin and device characteristic margin. Such a decrease in the margin increases a demand not only for a single pattern but also for a pattern in a repetitive pattern group. On the other hand, such an increase in demand brings an expectation that the target pattern existing in the repetitive pattern group can be easily found and positioned. However, at the moment,
There is no known technique for easily finding and positioning a target pattern existing in a repeated pattern group.

[0019]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sample inspection apparatus, a sample display apparatus, and a sample display method capable of easily finding and positioning a target pattern existing in the above-described repetitive pattern group of a semiconductor element. It is to be.

[0020]

In order to achieve the above object, the present invention provides a function for learning a basic pattern constituting a repetitive pattern of a semiconductor device, a method for automatically counting the number of basic patterns, and a method for learning a target pattern. Is provided with a function of positioning and positioning.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where a new function according to the present invention is added to the above-described length measuring SEM will be described below as an example.

The device control unit 17 of the length measuring SEM shown in FIG.
Has the following functions with respect to the prior art.

(1) Learning basic patterns constituting a repetitive pattern (2) Automatically counting the number of basic patterns, locating a target pattern, and positioning The above functions are executed in the following procedure. The procedure for positioning the target pattern existing in the repeating pattern group as shown in FIG. 2 will be described below. This procedure is roughly divided into an operation for learning the positioning condition (learning operation) and an operation for positioning the target pattern (target pattern positioning operation).

The learning operation will be described with reference to FIGS. 1, 2 and 4. FIG. 1 is a flowchart showing the procedure of the learning operation, and FIG. 4 is an example of a screen display.

First, in steps 31 and 32 of FIG.
Perform alignment pattern learning. A sample image is formed at a low magnification at a position which is located at the end of the group of repeated patterns as shown in FIG. The location where the position can be easily confirmed is, for example, a region where the corners of the pattern group are viewed. FIG. 2A shows an example of a region including the pattern 24 at the lower left end of the repeated pattern group. The observation magnification at this time is, for example, approximately several thousand times.

If the image shown in FIG. 2A is sufficient, this sample image is determined. Determining means to load the sample image into the memory unit 15. For example, as shown in FIG.
A window 42 for a confirmation message "Yes, No" is displayed, and the confirmation is executed by clicking Yes or No.

When determined, the position coordinate data of the center of the visual field of the image, the observation conditions such as the acceleration voltage, the electron beam current, and the observation magnification, and the sample image are stored in the memory unit 15 shown in FIG. The position coordinate data of the center of the visual field is position coordinates in the wafer coordinate system obtained as a result of the alignment operation described in the related art. The position coordinate data of the center of the field of view and the sample image are used as field-of-view data and a positioning reference image, respectively, which will be described later. In addition, all the operations of confirmation or designation, including the subsequent operations, are performed using input means provided in the device control unit 17.

Next, in step 33 of FIG. 1, the starting point is repeatedly learned. As shown in FIG. 2B, on the sample image determined above, a point is clicked by clicking a mouse button or the like on the screen near the end of the repetitive pattern group, in the example in the figure, the pattern at the lower left corner. When specified, the coordinates of this point are stored and become the repeat start point. This point 22 is indicated by X in the example of FIG.

Further, by this designation, the distance from the center of the visual field to the repetition start point is calculated, and is stored in the memory unit 15 as positioning data described later. This distance is a numerical value converted from the amount of deflection of the electron beam.

Next, in step 34 of FIG. 1, the pattern image of the repetition start point is learned. As shown in FIG. 2 (c), the magnification is adjusted to be as large as possible such that at least a plurality of patterns of the repetitive pattern group enter the visual field with the repetition start point as the center of the visual field. The observation magnification in the length measurement SEM is, for example,
More than tens of thousands of times is appropriate. Then, the pattern image shown in FIG. 2C is determined. The determination is performed, for example, by the method shown in FIG. Once determined, the data is stored in the memory unit 15 together with the observation conditions such as the acceleration voltage, the electron beam current, and the observation magnification.

Next, in step 35 of FIG. 1, a basic pattern as a unit of repetition is learned. On the determined pattern image shown in FIG. 2C, the image area of the basic pattern which is a unit of repetition is specified. Fig. 2
As shown in (d), the basic pattern is specified by surrounding the basic pattern with a mouse button drag or a display light pen, for example. In this example, two sets of trapezoidal patterns 24 and 25 are designated as basic patterns, as indicated by a trajectory indicated by a broken line 23 in the figure. The image of the area designated in this manner is stored in the memory unit 15 as a basic pattern, and is used as a reference image when positioning a target pattern described later.

Next, in step 36 of FIG. 1, FIG.
As shown in, the pitch as the unit of repetition is specified.
At this time, as shown in FIG. 2E, the enclosed patterns 24 and 25 are displayed in different colors to distinguish them from each other, or as shown in FIG. In other words, it is easy to specify this pitch.

When the pattern groups as shown in FIG. 2E are two-dimensionally arranged, this designation operation is performed in each of the X direction and the Y direction. The designation is performed, for example, by clicking two adjacent repeating patterns. In the figure, the pattern adjacent in the X direction is a point 26.
, A pattern adjacent in the Y direction is designated by a point 27. Thus, a pattern having the same shape as the basic pattern in the X method of the basic pattern including the patterns 24 and 25 is specified. The same applies to the Y direction.

With the above designation, the pitch interval is calculated,
It is stored in the memory unit 15 as a movement unit at the time of a target pattern positioning operation described later. This pitch data is a value converted from the amount of electron beam deflection between designated patterns.

Next, the target pattern positioning operation will be described. FIG. 5 is a flowchart showing the procedure of the target pattern positioning operation, and FIGS. 6 and 7 are examples of screen display.

A region to be observed having an object pattern similar to the learned pattern shown in FIG. 2 is aligned in step 51 of FIG. The sample image of the target pattern is formed with the same magnification and target conditions as the reference image learned in step 33 of FIG.

First, using the image learned in step 32 of FIG. 1 as a reference image, the corners of the repetitive pattern group of the target pattern are aligned using the pattern matching method as shown in FIG.

Next, in step 52 of FIG. 5, the image is displayed using the distance data between the visual field center and the repetition start point of the image learned in steps 32 and 33 of FIG.
A sample image is formed with the same magnification and target conditions as the reference image learned in step 2, and the starting point of the repetitive pattern is positioned.

Next, in step 53 of FIG. 5, the direction to move and the number of basic patterns are designated. For example, as shown in FIG. 6, a window 62 for designating each is displayed, and designation is performed by using a mouse or the like, or by entering a number from a keyboard.

With this designation, in step 54 of FIG.
The basic pattern learned in step 35 of FIG. 1 is used as a reference image, and the pitch data of the basic pattern set in step 36 of FIG. Thereafter, as shown in FIG. 7, the target pattern is positioned.

If the maximum allowable movement distance is determined in advance, and the number of basic patterns to be moved, that is, the movement distance is large and the movement error exceeds the allowable error range of the pattern matching, the movement distance of each step is reduced. The movement may be divided into a plurality of steps so as to fall within the range of the maximum movement distance, and the position may be corrected for each step while moving to the target pattern area at the end point.

At this time, a pattern matching method is used for position confirmation at the time of the step movement. However, at this time, areas other than the basic pattern area specified in step 35 of FIG. 1 are masked and excluded from the target of the matching operation.

By the above procedure, the target pattern is displayed, and the dimensions of the desired pattern are measured by the operator. In the case of repeatedly measuring the same portion of the same kind of sample, the following function may be provided, and the above-described learning result and the positioning condition may be incorporated in the recipe. The recipe defines operation procedures and operation conditions so that subsequent operations are performed automatically or semi-automatically.

Next, an example of a procedure for measuring the dimension of a wafer pattern using a length measuring SEM will be described with reference to FIG.

After the wafer 5 is taken out of the wafer cassette 10, it is pre-aligned. The wafer 5 is assigned a unique wafer number, and after pre-alignment, the wafer number formed on the wafer 5 is read. Based on the read wafer number, a recipe corresponding to the wafer 5 registered in advance is read.
The recipe defines the measurement procedure and measurement conditions for the wafer 5. Subsequent operations are performed automatically or semi-automatically according to this recipe. After reading the recipe, the wafer 5 is transported and mounted on the XY-stage 12 in the sample chamber 11 held in a vacuum.

The wafer 5 loaded on the XY-stage 12 is aligned with the optical microscope 13 mounted on the upper surface of the sample chamber 11 and the alignment pattern formed on the wafer 5. The alignment pattern is compared with an alignment pattern reference image registered in the memory unit 15 in advance, and the stage position coordinates are corrected so that the field of view just overlaps the field of view of the reference image. After the alignment, the stage is moved to a predetermined pattern located at the corner of the group of repetitive patterns in which the measurement pattern exists, and is positioned. Positioning is performed by moving the corner pattern to the stage immediately below the electron beam, irradiating the electron beam, focusing, and forming an image, and comparing the image with the positioning pattern reference image registered in the memory unit 15 in advance, similarly to the alignment operation. Then, the scanning area of the electron beam is finely adjusted so that the two images just overlap.

After positioning at the corner pattern, the field of view is moved by a predetermined number in a predetermined direction using the pattern of the corner as a base point and a repetition basic pattern previously registered in the memory unit 15 as a unit of movement. . After moving the field of view, precise positioning and focusing of the measurement pattern are performed based on a reference image registered in the memory unit 15 in advance. After positioning the measurement pattern, the dimensions of the measurement pattern are measured.

The dimensions of all the predetermined measurement locations in the wafer 5 are measured by repeatedly performing the operations after the alignment. Thus, the measurement of one wafer is completed. When a plurality of wafers to be measured remain in the wafer cassette 10, the next wafer is taken out of the wafer cassette 10, and then the measurement is repeated according to the above procedure. The dimension measurement result is output together with the position coordinate data of the measurement point, the image of the measurement point, and the like, registered in a database (not shown), and used for subsequent analysis.

For an insulator sample which takes a long time to saturate the charge-up, it is preferable to irradiate an electron beam for a predetermined time and then to take in the sample image. It is also possible to determine the irradiation time after obtaining the saturation characteristics in advance and incorporate the irradiation time into the recipe.

In the above-described example, the case where the target pattern existing in the repeated pattern group is found and positioned has been described. However, by applying the basic function of the present invention, the target pattern existing in the repeated pattern group can be determined. , A position up to a predetermined origin pattern can also be calculated. The calculation data obtained in this way is, for example,
From the target location (defect or defect occurrence location), point out the corresponding location in the logic circuit or electric circuit,
In order to perform a more detailed analysis, it is used when, for example, the position of a corresponding portion is determined by another analysis device. The learning for performing such an operation is performed, for example, as follows.

First, a pattern image is formed with a magnification as large as possible so that at least a plurality of repetitive patterns enter the field of view and including the target pattern.
Determine. By determining, the position coordinate data of the center of the field of view of the pattern image is calculated. The calculated value is the acceleration voltage,
It is stored in the memory unit together with the electron beam current, observation conditions such as observation magnification, and the pattern image. The pattern image is used for target pattern positioning described later.

Next, the target pattern is designated by clicking with a mouse or the like. By specifying, the target pattern position with respect to the center of the pattern image field is calculated and stored together with the target pattern image.

Next, a basic pattern which is a repetition unit of the repetition pattern group is designated by dragging a mouse, a display light pen, or the like. When there is a pattern defect in the target pattern, the basic pattern may be determined so as to exclude the target pattern. By the designation, the positional relationship of the basic pattern with respect to the center of the visual field is calculated and stored in the memory unit together with the basic pattern image.

Next, the repetition pitch of the basic pattern is designated by clicking. By specifying, the repetition pitch is calculated and stored in the memory unit.

Next, the observation magnification is switched to a low magnification at which the position of the repetitive pattern group in which the observation pattern exists can be easily confirmed, for example, a corner at which a corner can be seen, and a low magnification image is formed.

Next, a temporary starting point is designated at the corner in the low magnification image. By specifying, the number and distance of the basic patterns from the observation pattern to the temporary start point are calculated. The distance and the number of basic patterns are simply calculated from the target pattern and the amount of electron beam deflection at the temporary start point.

If the calculated distance is smaller than a predetermined allowable maximum moving distance, the corner is moved by the number of calculated basic patterns (the fractional part is cut off) so that the corner is located immediately below the electron beam. An image is formed under the observed conditions. If the calculated distance is larger than a predetermined allowable maximum movement distance, the distance is divided into a plurality of steps so that the movement distance of each step falls within the range of the maximum movement distance, and pattern matching by the basic pattern is performed. While repeatedly correcting the position coordinate data and the movement amount,
The image is moved by the number of calculated basic patterns (rounded down to the decimal point) and an image is formed under the above-described observation conditions. The final basic pattern portion in the image is displayed by, for example, color coding so that it can be identified. As described above, the visual field movement in the case where the number of calculated basic patterns is a non-integer is performed by an integer equal to the number of basic patterns whose decimals are rounded down.

Next, the field of view is adjusted so that the corner pattern and the final basic pattern portion are included, and the image is determined. By determining, the positional relationship between the center of the visual field and the final basic pattern portion is calculated. The calculated value and the pattern image are stored in a memory unit for alignment described below. The center of the visual field is a starting point when positioning the target pattern.

Next, an image with a low observation magnification for easy position confirmation is formed and determined. When the pattern image is determined, the pattern image is stored in the memory unit for alignment described below.

Then, a positioning recipe is created based on the learning result. The target pattern positioning is performed as follows according to the recipe.

First, the repetitive pattern group is aligned using the determined image as a reference image. Next, the starting point is aligned using the determined image as a reference image. Move the field of view in the reverse order. The target pattern is positioned using the determined image as a reference image. The target pattern is displayed, for example, by color so as to be easily identified.

In the above embodiment, an electron beam is used for image formation. However, the same effect can be obtained by using an ion beam, a light beam, a mechanical probe, or the like instead. In addition, the same effect of the invention can be obtained even in the case of one probe / one pixel or in a method of forming an image with multiple probes or multiple pixels.

In the above embodiment, a wafer having semiconductor elements is shown as a sample, but a sample such as an image sensor or a display element may be used as long as it has a repetitive pattern group.

With the configuration of the present invention described above, the target pattern existing in the repetitive pattern group of the semiconductor element can be easily located and positioned, thereby reducing the operator's labor and improving the workability. Is done. As a result, a large amount of accurate process quality information,
Detailed device characteristic information can be obtained, and defect / defect analysis work becomes easy. This makes it possible to improve the performance and reliability of the semiconductor element and to improve the yield in a short period.

[0065]

As described above, according to the present invention, a sample inspection apparatus, a sample target apparatus, and a sample target method capable of easily finding and positioning a target pattern existing in a repetitive pattern group of a semiconductor element are obtained. be able to.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of a learning operation.

FIG. 2 is a diagram showing an example of an image displayed on a display.

FIG. 3 is a longitudinal sectional view showing a configuration of a length measuring SEM.

FIG. 4 is an example of a screen display.

FIG. 5 is a flowchart showing a procedure of a target pattern positioning operation.

FIG. 6 is an example of a screen display.

FIG. 7 is an example of a screen display.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron beam, 5 ... Wafer, 7 ... Secondary electron, 9 ... Display, 10 ... Wafer cassette, 14 ...
Signal processing unit, 15: memory unit, 17: device control unit.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H01L 21/66 G06F 15/62 405C F-term (Reference) 2F067 AA54 BB01 BB04 CC17 FF16 GG01 HH06 JJ05 KK04 LL00 NN02 PP12 QQ02 QQ03 SS13 2G001 AA03 AA05 BA07 FA06 GA03 GA04 GA05 GA06 GA09 GA11 GA19 HA09 JA03 JA07 JA11 JA20 KA03 LA11 MA05 PA02 4M106 AA01 BA02 BA03 BA04 CA39 DB05 DB08 DB18 DB30 DH24 DH32 DH33 DJ18 DJ23 DJ27 5B057 AA03 BA01 DC21 DA03 DA01

Claims (3)

[Claims] 1. A charged particle source for irradiating a charged particle beam to a sample having a repetitive pattern group, a detector for detecting secondary electrons generated from the sample by irradiation of the charged particle beam, and detection by the detector In the sample inspection apparatus that displays an image from the obtained signal and inspects the sample based on the information of the image, a start point is specified and learned in a part of the repeating pattern group, and at least one of the repeating pattern group is learned. A basic pattern learning means for designating and learning a pattern as a basic pattern, a positioning means for repeatedly positioning a target pattern to be displayed on the basis of a learning result of the basic pattern learning means, and a starting point positioned by the positioning means. Movement control means for moving a predetermined number in a predetermined direction in units of the basic pattern; and Specimen inspection apparatus characterized by comprising a display means for displaying the elephant pattern. 2. A sample display apparatus for displaying a pattern of a sample having a repeating pattern group, wherein a learning point is designated by designating a starting point in a part of the repeating pattern group, and at least one pattern in the repeating pattern group is used as a basic pattern. Basic pattern learning means for designating and learning as a target pattern, positioning means for repeatedly positioning a target pattern to be displayed at a starting point based on the learning result of the basic pattern learning means, and the basic pattern from the starting point positioned by the positioning means. A sample display device comprising: movement control means for moving a predetermined number of units in a predetermined direction; and display means for displaying the target pattern moved by the movement control means. 3. A sample display method for displaying a pattern of a sample having a repeating pattern group, wherein a learning is performed by designating a starting point in a part of the repeating pattern group, and at least one pattern in the repeating pattern group is used as a basic pattern. And the target pattern to be displayed is repeatedly positioned based on the learning result at the start point, and is moved from the start point by a predetermined number in a predetermined direction in units of the basic pattern and displayed. Sample display method.