JPH05129178A - Misalignment measurement method - Google Patents

Abstract

(57) [Abstract] [Purpose] Automatic measurement of deviation is possible, and error is unlikely to occur,
It is to provide a highly reliable method of measuring misalignment. [Structure] Reference patterns 11, 12 ... Formed in the previous step
And the measured patterns 13 to 18 formed in the subsequent process are imaged by the image pickup device, and the measured patterns 13 to 18 are compared with the reference patterns 11, 12 ... ~
18 In the misalignment measuring method for measuring the misalignment at the time of forming, each line width of each pattern is set to 2 μm or more in absolute amount and 8 pixels or more on the image sensor, and the distance between each line in each pattern is set. The absolute amount is 2 μm or more and 8 pixels or more on the image sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misalignment measuring method for automatically measuring misalignment of a mask or a reticle when manufacturing a semiconductor device or a liquid crystal device.

[0002]

2. Description of the Related Art For example, in the manufacture of semiconductor devices, liquid crystal devices, etc., circuit patterns are sequentially formed using a plurality of masks and reticles. If the mask (or reticle) is not aligned with a predetermined accuracy in each step of forming the circuit pattern, the formed circuit will not function sufficiently,
Defective product occurs. Therefore, generally, the misalignment is visually measured and inspected by using the cross marks 1 and 2 and the vernier pattern shown in FIGS.

In FIG. 5, two cross marks 1 and 2 are formed, and one cross mark 1 is the other cross mark.
It is larger than the second cross mark 2 and is located outside the other cross mark 2. The outer cross mark 1 is the first PEP (Photo Engra
ving process) and becomes the reference for mask alignment in the subsequent PEP. Further, the inner cross mark 2 shown by hatching in FIG. 5 is formed after the second PEP.

If the centers of the above-mentioned two cross marks 1 and 2 are coincident with each other, it is judged that the mask alignment is accurately performed, and the inner cross mark 2 is located on the outer cross mark. If it is outside the mark 1, it is determined that the amount of deviation of the inner cross mark 2 exceeds the allowable value.

In the examples shown in FIGS. 5 and 6, the allowable value of the deviation amount is ± 1 μm, and the distance between the two cross marks 1 and 2, that is, the two cross marks 1 and 2. The size difference is 1 μm.

Further, in the example shown in FIG. 6, the centers of both cross marks 1 and 2 coincide with each other. In FIG. 6, A indicates the distance between the side edge portions of both cross marks 1 and 2, and B indicates the distance between the end edge portions of both cross marks 1 and 2. Further, C is the line width of the outer cross mark 1, D is the line width of the inner cross mark 2, and E is the outer cross mark 2.
Shows the length of the side edge of the. The value of each part is A =
1 μm, B = 2 μm, C = 20 μm, D = 18 μm, E
= 20 μm.

[0007]

By the way, the above-described misalignment measuring method in which the cross marks 1 and 2 are superposed is a method for examining the limit of misalignment, and a quantitative value of the misalignment amount is to be obtained. I can't.

The above-described misalignment measuring method is effective if a person visually judges OK / NG, but for example, a plurality of marks (patterns) to be compared with each other.
It is not suitable for automatic measurement in which the image of (1) is input to the image sensor and the misalignment measurement is automatically performed. That is, the boundary position of the mark tends to be unclear, and it is difficult to judge OK / NG when the deviation amount is near the limit value.

Further, when the misalignment is automatically measured on the basis of the vernier pattern, a quantitative value of the misalignment amount can be obtained, but the pattern shape is too complicated, so that sufficient reliability can be obtained. Is difficult. An object of the present invention is to provide a misalignment measuring method which is capable of automatically measuring a deviation, is less likely to cause an error, and has high reliability.

[0010]

In order to achieve the above object, the present invention provides a reference pattern formed in the previous step.
And the measured pattern formed in the subsequent process are imaged by the image sensor, and the measured pattern is compared with the reference pattern,
In a misalignment measuring method for measuring a deviation when forming a pattern to be measured, each line width of each pattern is set to 2 μm or more in absolute amount and 8 pixels or more on an image sensor, and each pattern is
The absolute distance between the lines in each pixel is 2 μm or more, and 8 pixels or more on the image sensor. In this way, the present invention is capable of automatically measuring the deviation, preventing the occurrence of an error, and improving the reliability of the misalignment measurement.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

1 to 4 show an embodiment of the present invention. Figure 1 shows the first PEP (Photo Engraving Proce
., formed in ss), and FIG. 2 shows patterns 13 to 18 after completion of all steps.

In the first PEP, pattern 1 in FIG.
.. are formed, and the pattern is formed in the second PEP.
Pattern 11, 12, ... as the reference pattern.
12 ... is combined with the next pattern which is the pattern to be measured. And the final pattern is pattern 1 in FIG.
It becomes like 3-18.

At each step, an image of the pattern formed in the previous step (reference pattern) and the pattern combined with this pattern (measured pattern) is obtained by an optical microscope. After that, the image is enlarged and taken into an image pickup device such as a CCD camera. Then, the output signal of the image pickup device is sampled and held, for example, and after A / D conversion, the deviation amount of the measured pattern from the reference pattern is calculated.

A pattern 11 shown in FIG. 1 comprises two large and small L-shaped patterns 19 and 20 arranged so as to draw a substantially square shape. These L-shaped patterns 19 and 20 are set so that the lengths of the two pieces are substantially equal to each other. Further, in the pattern 11, two L-shaped patterns 19 and 20 are provided.
Three straight line patterns 2 of approximately equal length inside each other
1, 21, 21 are drawn. The straight line patterns 21, 21 and 21 are arranged parallel to each other and parallel to the respective pieces of the L-shaped patterns 19 and 20.

In FIG. 1, five patterns 12 ... Are formed in addition to the pattern 11 described above. These five patterns 12 ... Are L-shaped like the L-shaped pattern 20 on the smaller side of the pattern 11,
Together with the L-shaped pattern 20, they are arranged at substantially equal intervals in the row direction and the column direction. The line width and direction of each pattern 12 are set to be substantially the same as the L-shaped pattern 20. In FIG. 1, the dimensions and distances of the respective parts of the patterns 11, 12, ... Are denoted by the symbols F to P.

F indicates the length of each piece of the L-shaped pattern 19 on the large side, and G indicates the length of each piece of the L-shaped pattern 20 on the small side. Further, H indicates the line width of the L-shaped pattern 19 on the large side, and I indicates the line width of the L-shaped pattern 20 on the small side.

Further, J indicates the line width of the straight line patterns 21, ... And K indicates the distance between the straight line patterns 21. Furthermore, L, M, and N are two L-shaped patterns, respectively.
The shortest distance between the buttons 19 and 20, the straight line pattern 21 in the direction in which the straight line patterns 21 are arranged, and the L-shaped pattern on the smaller side.
And the shortest distance between the straight line patterns 21 in the longitudinal direction of the straight line patterns 21 and the L-shaped pattern 20 on the smaller side. 1 indicates the distance between the pattern 11 and the adjacent pattern 12 ... And the distance between the patterns 12 ... The above-mentioned dimensions and distance values are set as follows, for example. F = 80 μm, G = 60 μm, H = I = J = K = 8 μ
m, L = M = N = 12 μm, O = 44 μm.

Patterns 13-18 after the completion of all steps
Is a pattern having two L-shaped patterns 19 and 20.
It has a shape substantially similar to the connector 11. And each pattern
13 to 18, the L-shaped pattern 22 on the large side
27 to 27 and L-shaped patterns 28 to 33 on the smaller side are arranged so as to draw a substantially square, and both L-shaped patterns 13 to 1 are arranged.
Three parallel linear patterns 34 are formed on the inner sides of 8, 22 to 27.

Among the L-shaped patterns 22 to 27 on the large side, there are those having small patterns 35 whose end portions are divided into a plurality of parts and which are arranged in a substantially equal shape and arranged at equal intervals. The number of small patterns 35 ... Is L-shaped patterns 22 to 27.
It is different for each, and the number is set to, for example, 1 to 5. The line width and interval of each small pattern 35 are set to 2 μm or more.

Each of the above patterns 11, 12, ..., 13 to 1
The image of 8 is captured by an image pickup device such as a CCD. The magnification of the optical microscope that guides the images of the patterns 11, 12, ...
The line width of each of the patterns that make up ~ 18, and
The distance between these patterns is adjusted to correspond to 8 pixels or more. And each pattern 11, 12 ... 1
Each pattern constituting 3 to 18 and a portion between these patterns are input to the image pickup device by using at least 8 pixels or more of the image pickup device. Here, the magnification of the optical microscope for guiding the pattern image to the image pickup device is set so that one pixel of the image pickup device corresponds to 1 μm.

In the misalignment measuring method as described above, the line width and distance of each pattern are set to 2 μm or more in absolute amount, and to 8 pixels or more on the image pickup device. Therefore, it is possible to automatically measure the misalignment using the image pickup device. Then, the measurement error can be reduced, and the reliability of the misalignment measurement can be improved.

That is, as shown in FIG. 3 (a), for example, when imaging two closely spaced patterns 36, 37, the line widths P, Q of these patterns 36, 37 have a dimension of several μm.
It is known that the intensity of an image obtained through the magnifying optical system and the image sensor is represented by the signal shown in FIG. 38 in FIG. 3 (b)
Is a signal representing the left pattern 36 in FIG. 3 (a), and 39 is a signal representing the right pattern 37.

Since the two patterns 36 and 37 are separated by the distance R, theoretically, the signal between the two patterns 36 and 37 does not appear, but in reality, the signals 38 and 39 overlap each other. The portion between the two signals 38 and 39 does not become zero level.

In FIG. 4, the signal 38 in FIG. 3 (b) is enlarged. In the figure, the solid line 38a represents the actual signal, and the chain double-dashed line 38b represents the theoretical signal. As shown in FIG. 4, the widths S and T of both signals 38a and 38b are different, and both signals 3 at the peak position U are different.
The sizes of 8a and 38b are also slightly different.

Therefore, even if the misalignment is automatically measured based on the signals 38 and 39 as described above, the patterns 36 and 3
It is not possible to determine the exact position of 7, and as a result, an error of, for example, a submicron unit occurs in the measurement. Therefore, in order to measure the misalignment with high accuracy, it is necessary to set the line widths and distances of both patterns 36 and 37 sufficiently large.

On the other hand, even if the line widths and distances of both patterns 36 and 37 satisfy the conditions for highly accurate measurement, both patterns 36 and 37 are too thin and close to each other on the side of the image pickup device. If so, an error occurs as in the case described above. In particular, if the sample hold or A / D conversion of the signal is performed in the image processing, the error becomes larger. Therefore, it is necessary to use a sufficient number of pixels on the image pickup device to capture the line widths and distances of both patterns 36 and 37.

The signal 38 in FIG. 3A is obtained as shown in FIG. In other words, regarding the image of pattern 36,
The intensity is measured at a predetermined pitch in the width direction, and a histogram is obtained. The intensity of the image of the pattern 36 shows a substantially normal distribution shape, which is the strongest at the center of the pattern 36 in the width direction, and becomes weaker toward the outside. Then, the least squares method is used for this histogram, and the solid line 38 in FIG. 5 is created.

However, the shape of the histogram obtained by measuring the image of the pattern 36 is different from the perfect normal distribution, and the axial position of the central column 40 and the peak position U _{1 of the} signal 38 do not match. .. When the measurement pitch ΔP is 1, the deviation δ is generally about 0.2. That is, when the magnification of the optical microscope is 1 μm / pixel, an error of about 0.2 μm occurs when the solid line 38 is created.

Further, comparing the accuracy of the optical microscope for guiding the image of the pattern 36 to the image pickup device with the measurement accuracy of the SEM, FIG.
As shown in, the accuracy of the optical microscopes are substantially the same as each other if the measurement target is sufficiently large. However, the accuracy of the optical microscope decreases as the size of the object decreases, and sharply decreases for minute objects of 1 μm or less.

In this embodiment, each pattern 11, 1
Line widths and distances of 2 ..., 13 to 18 are set to an absolute amount of 2 μm or more, and further set to 8 pixels or more on the image pickup device. That is, an area having a size of 0.25 μm or more per pixel is imaged.

If the misalignment is measured under these conditions,
The positions of the patterns 36 and 37 are accurately recognized without being affected by the error generated when the signal 38 is generated and the accuracy of the optical microscope. Further, the patterns do not affect each other, and it is possible to prevent an error from occurring in the image capturing and the image processing. Therefore, it is possible to largely eliminate an error factor in the property of light, image processing, and the like, and more accurate misalignment measurement becomes possible.

Here, in this embodiment, the pattern 1
The absolute amount of the line width of 1, 12, ..., 13 to 18 means the distance between the edges of each line. Also, patterns 11 and 12
The absolute amount of the intervals of 13 to 18 means the distance between the contours of the lines. The present invention can be variously modified without departing from the scope of the invention.

[0034]

As described above, according to the present invention, the reference pattern formed in the preceding process and the measured pattern formed in the succeeding process are imaged by the image pickup device, and the measured pattern is measured. In a misalignment measuring method for measuring a deviation when forming a pattern to be measured as compared with a reference pattern, each line width of each pattern is 2 μm or more in absolute amount and 8 pixels or more on an image sensor. At the same time, the distance between each line in each pattern is set to 2 μm or more in absolute amount and 8 pixels or more on the image sensor. Therefore, the present invention has the effects of enabling automatic measurement of misalignment, preventing the occurrence of errors, and improving the reliability of misalignment measurement.

[Brief description of drawings]

FIG. 1 is a diagram showing a pattern formed in a first PEP according to an embodiment of the present invention.

FIG. 2 is a diagram showing a pattern after all steps are completed.

FIG. 3 is an explanatory diagram showing an example of a cause of occurrence of a measurement error.

FIG. 4 is an explanatory diagram showing an example of a cause of occurrence of a measurement error.

FIG. 5 is a graph showing the intensity distribution of a pattern image.

FIG. 6 is a graph comparing the accuracy of an optical microscope with the accuracy of SEM.

FIG. 7 is a view showing a conventional alignment mark.

FIG. 8 is an enlarged view of a portion surrounded by a circle V in FIG.

[Explanation of symbols]

 11, 12 ..., 13-18 ... Pattern.

Claims (1)

[Claims] 1. A reference pattern formed in a previous step and a measured pattern formed in a subsequent step are imaged by an image pickup device, and the measured pattern is compared with the reference pattern. ,
In a misalignment measuring method for measuring a deviation when forming a pattern to be measured, each line width of each of the above patterns is 2 μm in absolute amount.
m or more, 8 pixels or more on the image sensor, and
The absolute distance between the lines in each pattern is 2 μm.
As described above, the misalignment measuring method is characterized in that the number of pixels is 8 or more on the image pickup device.