JPH088082B2 - Minute dimension measuring method and device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for measuring a fine dimension using a scanning electron microscope (SEM), and more particularly, to accurately measuring the dimension of a resist hole pattern. The present invention relates to a possible method and apparatus for measuring minute dimensions.

(Prior Art) With the recent high integration of ICs, LSIs, etc., μm order or sub μm in wafer processing and inspection processes
For measuring the shape and size of resist developed patterns, etching patterns, or hole patterns such as contact holes, a minute size measuring apparatus using a scanning electron microscope has begun to be used.

Of these, the diameter of the hole pattern affects the capacity formed in the IC and the amount of current that can flow in the wiring, so it is very important to accurately control the diameter, especially the maximum value and ellipticity. .

The conventional methods for measuring the maximum value of the hole pattern diameter include the following.

(1) After taking a picture of the hole pattern by SEM,
A method in which the diameter of the photographed hole pattern is measured using a ruler and the maximum value is calculated from the measured values.

(2) As described in JP-A-63-21845, a hole pattern is line-scanned in the X direction and the Y direction to obtain a center point, and the center point is used as a reference to determine a predetermined point in the X direction and the Y direction. A method in which line scanning is performed while sequentially shifting the position within the range to calculate the edge distance on each line, and the maximum value is obtained from the edge distances in the X and Y directions.

The edge detection method is to scan an electron beam on the sample,
This is a method of detecting an edge by changing the amount of a signal generated from a sample such as secondary electrons and reflected electrons. That is, secondary electrons and the like utilize the fact that the amount thereof changes when the sample to be scanned has irregularities.

(Problems to be Solved by the Invention) The above-described conventional technology has the following problems.

(1) In the method of measuring the photographed hole pattern using a ruler or the like, it takes time and effort because the photograph must be taken when measuring the diameter. Further, since the position indicating the maximum diameter is selected by the operator's visual judgment, the measured position is not always the position of the actual maximum diameter, and the actual maximum diameter is not always obtained. was there.

Further, there is a problem in that the operator is troubled because the maximum diameter cannot be automatically obtained by this measuring method.

(2) In the method of obtaining the maximum diameter from the edge distances in the X direction and the Y direction, the edge distance corresponding to the maximum diameter may be in the line scanning direction, that is, the direction parallel to the X direction or the Y direction. However, there is a problem that the measured maximum diameter is not necessarily the actual maximum diameter otherwise.

(Means for Solving the Problems) In order to solve the above problems, the present invention takes the following means.

(1) In the minute dimension measuring method for calculating the distance between edges on each scanning line to be raster-scanned, while rotating the raster scanning direction on the sample, the edge on each scanning line at each rotation angle in the raster scanning direction The distance between the edges is detected, and at least one of the maximum distance between the edges and the minimum distance between the edges is selected from all the distances between the edges as necessary.

(2) A means for raster scanning the electron beam, a means for rotating the raster scanning direction on the sample, a means for detecting a signal generated from the sample by the raster scanning, and a raster scanning direction based on the detection signal. And a means for calculating the distance between edges on each scanning line at each rotation angle, and if necessary, select at least one of the maximum value and the minimum value from all the distances between edges, and select this. Equipped with a means for displaying.

(Operation) According to the configuration described above, even when the portion showing the maximum value or the minimum value of the hole pattern diameter cannot be determined, the maximum diameter or the minimum diameter of the hole pattern is automatically determined from the measurement result. You will be able to measure.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a scanning electron microscope having a minute dimension measuring function according to an embodiment of the present invention. In this embodiment, the case of detecting the maximum diameter of the hole pattern will be described, but the same applies to the case of detecting the minimum diameter.

The electron beam 2 emitted from the electron gun 1 is deflected by the deflection circuits 8 and 9.
Direction deflection coil 5 and Y direction deflection coil 6 controlled by
And is raster-scanned on the sample 4. The rotation angle in the scanning direction of the electron beam by the deflection circuits 8 and 9, that is, the rotation angle in the raster scanning direction is controlled by the raster scanning direction rotation control circuit 12.

The signal indicating the rotation angle in the raster scanning direction designated by the raster scanning direction rotation control circuit 12 is also output to the maximum value selection circuit 13 described later. The control method by the raster scanning direction rotation control circuit 12 will be described later in detail.

Secondary electrons 3 are generated from the sample 4 irradiated with the electron beam 1, the secondary electrons 3 are detected by the secondary electron detector 7, and the detection signal is output to the length measuring circuit 10 and the image display unit 11. To be done. The maximum value selection circuit is the measurement result of the length measurement circuit 10.
It is output to 13.

A method for measuring the maximum diameter of a hole pattern in a scanning electron microscope having a minute dimension measuring function of such a configuration,
This will be described with reference to FIGS. 2 and 3.

FIG. 2 is a flow chart for explaining the minute dimension measuring method according to the present invention, and FIG. 3 is a diagram for explaining the basic concept of the measuring method.

When performing minute dimension measurement, in step S1, the operator displays the hole pattern to be measured on the image display unit 11 in the same manner as when observing with a normal scanning electron microscope. When the operator gives an instruction to measure a small dimension, the rotation angle θ of the electron beam in the raster scanning direction is set to 0 ° in step S2.

Note that the raster scanning direction referred to here is shown in FIG.
In FIG. 3, it is the sub-scanning direction of the raster scanning, and the rotation angle θ is the raster scanning in the normal image observation in which the minute dimension measurement is not instructed, as described later with reference to FIG. The sub-scanning direction of the raster scanning at a minute dimension measurement angle with respect to the sub-scanning direction.

In step S3, the electron beam 1 is raster-scanned on the sample,
As shown in FIG. 3 (a), the distance between edges on each scanning line
A _0-1 , A _0-2 , ..., A _0-n are sequentially measured in the length measuring circuit 10, and the measured value is output to the maximum value selecting circuit 13.

The edge-to-edge distance does not have to be set for all the scanning lines of the raster scanning, and the interval can be freely set by the operator according to the measurement object.

In the maximum value selection circuit 13, the input edge distance A _0-1 ~
A _0-n is stored and the distance between the edges is displayed if necessary. At this time, the maximum value selection circuit 13 also receives a signal indicating the rotation angle in the raster scanning direction from the raster scanning direction rotation control circuit 12, so that the rotation angle can be stored and displayed together with the distance between the edges. Is.

In this way, when the distance measurement between edges at the rotation angle of 0 ° in the raster scanning direction is completed, the maximum value A _0max of the measured values A _{0-1 to} A _0-n is selected by the maximum value selection circuit 13 in step S4. To be done.

When the selection of the maximum distance between edges at the rotation angle of 0 ° in the raster scanning direction is completed, in step S5, the raster scanning direction rotation control circuit 12 determines whether or not the raster rotation angle becomes 90 ° or more.

If it is less than 90 °, the planned angle in step S6,
For example, the deflection circuits 8 and 9 are controlled by the raster scanning direction rotation control circuit 12 so that the rotation angle in the raster scanning direction is changed by 5 °.
Move to.

FIG. 3B shows the distances A _5-1 to A _5-2 between edges, which are executed in step S3 after the raster scanning direction is rotated by 5 °.
FIG. 3 is a diagram showing a method for measuring the length of A _5-n . In the actual measurement of the edge-to-edge distance, the observation image displayed on the display unit 11 rotates by 5 ° due to the rotation of the raster scanning direction, but here, in order to simplify the description, the scanning line The direction is shown to rotate by 5 °.

After that, when the maximum value A _5max at an angle of 5 ° is obtained in the same _manner as described above, the above-described processing is further repeated, and the angle 10
Maximum value A _10Max in °, ... maximum value A _85Max at an angle 85 °, a total of 19 pieces of maximum value of the maximum value A _90Max at an angle 90 ° is calculated.

FIG. 3 (c) shows the edge distances A _90-1 , A which are executed in step S3 after the raster scanning direction is rotated by 90 °.
_90-2 ..., A _90-n is a diagram showing a length measuring method.

After that, when it is determined in step S5 that the raster scanning direction has rotated by 90 ° or more, in step S7, the maximum value A _max among the maximum values A _0max to A _90max at each rotation angle is _increased.
Is selected by the maximum value selection circuit 13, and the maximum value A _max and the raster rotation angle θ at that time are displayed.

In the above description, the maximum value at each rotation angle in the raster scanning direction is obtained, and the maximum value A _max is obtained from the maximum value, but all edges are calculated without obtaining the maximum value at each rotation angle. The maximum value A _max may be obtained directly from the measured value of the distance.

According to this embodiment, even if the portion showing the maximum value of the hole pattern diameter cannot be determined, the maximum diameter can be automatically obtained from the measurement result. Further, according to the present embodiment, the maximum diameter and the rotation angle when the maximum diameter is exhibited are obtained, so that the following effects are achieved.

Normally, a large number of identical ICs and LSIs can be obtained from one wafer, but in this case, wiring patterns and the like are printed at once using a mask on which many identical wiring patterns are printed. There is a method and a method of baking a single wafer a plurality of times using a mask on which a pattern for one IC is printed.

In either method, the size of the mask is larger than the actual wiring pattern. Therefore, when the wafer is exposed, the light transmitted through the mask is reduced by the lens. Then, by changing the mask and performing multiple exposure, an IC having a multilayer wiring structure is completed.

In such a case, if the installation position of each mask for multiple exposure is deviated or if the reducing lens has astigmatism, the hole pattern at the same location of each IC exhibits a uniform elliptical shape. The positions showing the maximum diameter of the ellipse are the same.

Therefore, if the rotation angle of the scanning line when the maximum value is shown together with the maximum diameter of the hole pattern is obtained as in the present invention, the presence or absence of the mask deviation and astigmatism can be confirmed by observing the angle at that time. It is possible to easily determine, and further, it is possible to recognize the shift direction of the mask and the state of astigmatism from the rotation angle, so that it is possible to easily understand the problem and how to deal with it.

The signal used for edge detection is not limited to secondary electrons, but may be backscattered electrons, Auger electrons, X-rays, etc., in which case a detector corresponding to each signal should be installed. .

Further, in the above-described embodiments, the control of the rotation angle of the electron beam on the sample in the raster scanning direction is explained by deflecting the electron beam, but the present invention is not limited to this. Instead, the sample is rotated by rotating the sample mounting table so that the raster scanning direction of the electron beam is substantially rotated on the sample, or the sample is rotated and the electron beam is deflected. The rotation in the raster scanning direction may be performed at the same time.

That is, according to the present invention, raster scanning is performed while changing the relative rotation angle between the sample and the raster scanning direction, and the maximum or minimum value of the edge distance obtained as a result is obtained.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) Since it is not necessary to take a photograph at the time of measuring the diameter, it is possible to obtain the actual maximum diameter or the minimum diameter almost certainly without judging the position showing the maximum value or the minimum value. It enables accurate diameter measurement.

(2) Since the rotation angle at that time is obtained together with the maximum diameter or the minimum diameter, it is possible to easily judge the presence or absence of a mask shift or astigmatism when manufacturing the IC or LSI as the measurement object. Since it is possible to recognize the shift direction of the mask and the state of astigmatism from the rotation angle, it is possible to easily understand the defect and how to deal with it.

[Brief description of drawings]

FIG. 1 is a block diagram of a scanning electron microscope having a minute dimension measuring function according to an embodiment of the present invention, FIG. 2 is a flow chart for explaining the minute dimension measuring method of the present invention, and FIG.
The figure is a diagram for explaining the basic concept of the measuring method. 1 ... Electron gun, 2 ... Electron beam, 3 ... Secondary electron, 4 ...
Sample, 5 ... X-direction deflection coil, 6 ... Y-direction deflection coil, 7 ... Secondary electron detector, 8, 9 ... Deflection circuit, 10 ...
… Length measuring circuit, 11 …… Image display, 12 …… Raster scanning direction rotation control circuit, 13 …… Maximum value selection circuit

Claims (9)

[Claims] 1. A micro-dimension measuring method in which an electron beam is raster-scanned on a sample to calculate an edge-to-edge distance on each scanning line, the raster scanning direction on the sample is relatively rotated, and at each rotation angle. The distance between edges on each scanning line is detected by performing a plurality of scans at predetermined intervals, and at least one of the maximum distance between edges and the minimum distance between edges is selected from all the detected distances between edges. A minute dimension measuring method characterized by the above. 2. The relative rotation in the raster scanning direction on the sample is performed by at least one of the rotation of the sample and the rotation by the deflection in the raster scanning direction. Minute dimension measurement method. 3. The method for measuring minute dimensions according to claim 1 or 2, wherein the rotation angle in the raster scanning direction is changed within a range of 90 °. 4. The scanning performed a plurality of times at the predetermined intervals is
The minute dimension measuring method according to any one of claims 1 to 3, wherein the method is performed at equal intervals in a direction perpendicular to the scanning direction. 5. A mounting table on which a sample is mounted, a means for raster-scanning an electron beam, a means for relatively rotating the raster scanning direction on the sample, and a signal generated from the sample by raster scanning is detected. Means, means for calculating an inter-edge distance on each scanning line by performing a plurality of scans at a predetermined interval at each rotation angle based on the detection signal, among all the calculated inter-edge distances And a means for selecting at least one of the maximum value and the minimum value, and a means for displaying at least one of the selected maximum value and the minimum value. 6. The means for relatively rotating the raster scanning direction on the sample is at least one of a means for rotating a mounting table and a deflection rotating means for deflecting an electron beam to rotate the raster scanning direction. A fine dimension measuring device according to claim 5. 7. The minute dimension measuring apparatus according to claim 5 or 6, wherein the angle in the raster scanning direction is changed within a range of 90 °. 8. The means for calculating / displaying the inter-edge distance and the means for detecting / displaying at least one of the maximum value and the minimum value, together with the inter-edge distance and at least one of the maximum value and the minimum value, the inter-edge distance. And a rotation angle in the raster scanning direction when at least one of the maximum value and the minimum value is detected, and the minute dimension measuring apparatus according to any one of claims 5 to 7. . 9. The scanning performed a plurality of times at the scheduled intervals,
The minute dimension measuring device according to any one of claims 5 to 8, which is performed at equal intervals in a direction perpendicular to the scanning direction.