JPH0749927B2 - Overlay inspection method - Google Patents

Description

The present invention relates to an overlay inspection method for an exposure apparatus used in an optical lithography process in an LSI manufacturing process.

[Prior Art] Conventionally, this type of overlay inspection method for an exposure apparatus is performed through the steps shown in FIGS. 4 (a) and 4 (b). That is, incident light (42) is irradiated onto the resist film previously applied to the wafer (10) to draw the first mark (40). Then, after the wafer (10) is arbitrarily moved, the second mark (41) is drawn at the same position again.

Next, the difference (43) between the positions of the right end of the first mark (40) and the second mark (41) and the difference (44) between the positions of the left end of the second mark (41) are measured,
Evaluate the overlay accuracy of the exposure device.

At this time, if the difference (43) on the right side is a and the difference (44) on the left side is b, the lateral position shift x between the first mark 40 and the second mark 41 can be expressed by the following equation. it can.

x = (ab) / 2 The above description is for the horizontal direction (x direction) in FIG. 4 (b), but it can be similarly determined for the y direction, which is the vertical direction.

[Problems to be Solved by the Invention] According to the conventional overlay inspection method for an exposure apparatus as described above, since the positional deviation between the first mark and the second mark depends on the actual measurement, the measurement accuracy is high. Is limited.
Therefore, it is becoming difficult to meet the overlay accuracy of the exposure apparatus, which is required more and more in the future.

The present invention has been made in view of such circumstances,
An object of the present invention is to provide an overlay inspection method for an exposure apparatus that enables highly accurate evaluation of the overlay accuracy of the exposure apparatus.

[Means for Solving the Problems] In the overlay inspection direction of the present invention, the following steps are provided.

First, a first grating pattern in which diffraction gratings are arranged at a predetermined distance d is formed on a semiconductor substrate. Then, coherent light is made incident on the first grating pattern to generate first diffracted light.

Next, the first diffracted light is observed to obtain a first diffraction pattern. Then, the diffraction grating is arranged on the semiconductor substrate having the first grating pattern formed thereon so that the diffraction gratings are arranged in a line with a pitch of d / 2, and a second grating pattern is formed.

Next, coherent light is incident on the second grating pattern to generate second diffracted light. Then, the second diffracted light is observed to obtain a second diffraction pattern.

Next, the second diffraction pattern is standardized based on the first diffraction pattern. After that, the overlay accuracy of the exposure apparatus is evaluated by obtaining the ratio of the light intensity of the odd-order diffracted light and the light intensity of the even-order diffracted light in the normalized second diffraction pattern.

[Operation] According to the present invention, when the pitch of the diffraction grating of the second diffraction pattern is accurately arranged at d / 2, the light intensity of the odd-order diffracted light of the normalized second diffraction pattern is obtained. Approaches 0 without bound. Therefore, by obtaining the ratio of the light intensity of the odd-order diffracted light of the second diffraction pattern and the light intensity of the even-order diffracted light, the second value is obtained as the value of this ratio approaches 0.
This means that the pitch of the diffraction grating of the grating pattern is accurately arranged at d / 2. As a result, when the second grating pattern is formed, the diffraction gratings are accurately arranged between the diffraction gratings of the first grating pattern, which makes it possible to evaluate the overlay accuracy of the exposure apparatus.

[Example] The overlay inspection method of the exposure apparatus according to the present invention will be described below with reference to the drawings.

In FIG. 1 (a), 10 is a semiconductor substrate, 11 is a diffraction grating arranged at an interval d, 13 is incident light, and 14 is diffracted light. Further, in FIG. 1 (b), 12 is a diffraction grating 11
The diffraction grating is newly formed between the two, and the distance between the diffraction gratings is d / 2.

First, as shown in FIG. 1A, a diffraction grating (11) having a grating interval d is formed on a semiconductor substrate (10). Next, the coherent light (13) is incident on the diffraction grating (11). Then, diffracted light (14) is generated from the diffraction grating (11). By observing the diffracted light (14) with a one-dimensional counter (not shown), the first diffraction pattern shown in FIG. 2 (a) can be obtained. In FIG. 2 (a), (20) is the 0th order light,
(21) shows odd-order diffracted light, and (22) shows even-order diffracted light.

Next, the semiconductor substrate (10) is moved from the position shown in FIG. 1 (a) by d / 2 in the direction in which the diffraction grating 11 is arranged. After that, by again forming the diffraction grating having the diffraction grating interval d, the diffraction grating 12 having the grating interval d / 2 is formed as shown in FIG. 1 (b).

After that, again, the diffraction grating 12 is irradiated with coherent light,
This produces diffracted light (14). By observing the diffracted light 14 with a one-dimensional counter (not shown), as shown in FIG.
Three types of second diffraction patterns can be obtained depending on the degree of positional deviation of the semiconductor substrate 10 shown in (c) and (d).

Hereinafter, these three types of second diffraction patterns will be described.

1) When the displacement of the semiconductor substrate is large (when the distance between the diffraction gratings is not d / 2), a diffraction pattern as shown in FIG. 2B is obtained. This is the first in FIG. 2 (a).
The pattern is similar to the diffraction pattern, and there is no difference other than the scale factor.

2) When the positional deviation of the semiconductor substrate is close to 0 (when the diffraction grating interval is approximately d / 2), the diffraction pattern shown in FIG. 2 (c) is obtained. When compared with the diffraction pattern shown in FIG. 2 (b), the light intensity of the odd-order diffracted light decreases and the light intensity of the even-order diffracted light increases. The displacement of the semiconductor substrate can be evaluated from the degree of increase and decrease of the light intensity.

3) When the displacement of the semiconductor substrate is 0 (when the distance between the diffraction gratings is exactly d / 2), the diffraction pattern shown in FIG. 2D is obtained. At this time, the light intensity of the odd-order diffracted light disappears and becomes 0, and only the light intensity of the even-order diffracted light is observed.

Next, FIGS. 2 (b) to (d) obtained as described above.
The second diffraction pattern shown in is standardized by using the first diffraction pattern shown in FIG. The normalization in this case is performed, for example, by obtaining the ratio of the light intensities of the corresponding orders. Then, the ratio between the even-ordered light intensity and the odd-ordered light intensity of the normalized second diffraction pattern is measured. The closer the ratio (odd light intensity / even light intensity) to 0, the better the overlay accuracy of the exposure apparatus.

Here, FIG. 3 shows a diagram of changes in the light intensity of the diffracted light with respect to the magnitude of the positional deviation of the diffraction grating. In the figure, (30) indicates the light intensity of the even-order diffracted light, and (31) indicates the light intensity of the odd-order diffracted light. From this figure, if the displacement is 0,
The light intensity of the odd-order diffracted light has a minimum value of 0, and the light intensity of the even-order diffracted light has a maximum value. As described above, when the positional deviation is 0, the odd-order light intensity / even-order light intensity ratio becomes 0, so that the exposure apparatus is much more accurate than the overlay inspection method in the conventional measurement. The overlay accuracy of can be evaluated.

It should be noted that in the above embodiment, the positional deviation only in the direction in which the diffraction gratings shown in FIG. 1 are arranged is described.
By performing the same operation in the direction orthogonal to this direction, the overlay accuracy of the exposure apparatus in the orthogonal direction can be evaluated. Further, although the number of spots on the diffraction grating is not described in the above embodiment, the larger the number of spots, the higher the overlay accuracy of the exposure apparatus.

[Effects of the Invention] As described above, according to the present invention, the second diffraction pattern is standardized based on the first diffraction pattern, and the odd-order diffracted light of the standardized second diffraction pattern The overlay accuracy of the exposure apparatus is evaluated by obtaining the ratio between the light intensity and the light intensity of the even-order diffracted light. As a result, the closer the light intensity ratio is to 0, the higher the evaluation of overlay accuracy, and the overlay inspection method can be performed with higher accuracy than the conventional overlay inspection direction by actual measurement.

[Brief description of drawings]

FIG. 1 is a diagram showing an evaluation method in an example of the present invention. FIG. 2 is a diagram showing a diffraction pattern obtained in the example of the present invention. FIG. 3 is a diagram showing the diffracted light intensity obtained in the example of the present invention. FIG. 4 is a diagram showing a conventional overlay accuracy evaluation method. (11) is the first diffraction grating, (13) is the incident light, (14) is the diffracted light, and (12) is the second diffraction grating. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A step of forming a first grating pattern in which diffraction gratings are arranged at a predetermined distance d on a semiconductor substrate in a process of evaluating overlay accuracy of an exposure apparatus, and coherently interfering with the first grating pattern. Injecting light to generate first diffracted light, observing the first diffracted light to obtain a first diffraction pattern, and the diffraction grating forming a pitch of d / 2 in a line. Arranging the diffraction grating on the semiconductor substrate on which the first grating pattern is formed so as to be aligned, and forming a second grating pattern; and injecting coherent light into the second grating pattern, Generating a second diffracted light, observing the second diffracted light to obtain a second diffraction pattern, and normalizing the second diffraction pattern based on the first diffraction pattern. , The standardized above The second diffraction pattern, by determining the ratio between the light intensity of the light intensity of the odd order diffracted light and the even-order diffracted light, superposition inspection method comprising the steps, a to evaluate the overlay accuracy of the exposure apparatus.