JPS62249419A - Evaluation of alignment accuracy - Google Patents

Abstract

PURPOSE:To realize highly accurate inspection and evaluation by a method wherein areas surrounded by a foundation pattern and an upper layer pattern are measured and the alignment error is automatically measured and the alignment accruacy is evaluated. CONSTITUTION:An upper layer pattern 2 is formed on a foundation pattern 1 corresponding to the foundation pattern 1. If the upper layer pattern 2 is composed of patterns along the directions X and Y and along the directions of 45 degrees, areas of the respective regions A-H surrounded by the foundation pattern 1 and the upper layer pattern 2 can be measured by counting the number of the smallest units of images by utilizing an image processor. If the areas of the regions A, B...H are expressed by A, B... H, the alignment error Rx of the direction X is expressed by the attached formula. In the formula, a letter Y denotes the distance of the foundation pattern 1 along the direction Y and the area squareXY of the foundation pattern is squareXYapprox.= A+ B+...+ H. The alignment error of the direction Y can be also obtained in the same way. Moreover, if the summation of B- E and the summation of F- H and A are compared, the alignment error of the direction of 45 degrees can be also evaluated. With this constitution, plenty of information can be measured automatically and with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for forming fine patterns using photolithography technology in the manufacturing process of semiconductor integrated circuit devices, etc.
The present invention relates to a method for inspecting and evaluating overlay accuracy.

[Conventional technology]

As a conventional overlay accuracy evaluation method, an evaluation method called the Vernier method as shown in FIG. 2 is used, and overlay errors are read by visual inspection by transferring patterns with different pitches.

Next, the Vernier method, which is a conventional technique, will be explained. As shown in FIG. 2, a first pattern 1 is formed in the previous step, and a second pattern 2 is formed thereon. The first pattern 1 and the second pattern 2 are drawn in advance so that their pitches differ from each other (similar to the minute reading scale of a caliper of a measuring instrument). Therefore, both patterns 1 and 2
For each of the unit patterns (1) to (2), the mutual positions of both patterns 1 and 2 are sequentially shifted as shown. Visually find one spot in the pattern that is even on both sides (Fig. 2-1).
~ Pattern (■ in ■)) was judged as the amount of overlay deviation.

Next, the dimension measurement method, which is another conventional method, will be explained. As shown in FIGS. 3(a) and 3(b), the upper layer pattern 2 formed in the next step is inserted into the base pattern 1 formed on the substrate 3 in the previous step, and both patterns 1
, 2 in four directions (indicated by ← in Figure 3 (Q)) 6!
By measuring, the amount of misalignment in overlay was determined.

[Problem that the invention seeks to solve]

In the conventional Vernier method, the accuracy is low and there is variation because the judgment is made by the human eye, and the data processing method is also very time-consuming, and the size of the vernier needs to be easily readable by humans. There was a drawback.

Furthermore, in the case of the dimension measurement method, there are drawbacks such as a lack of information because data can only be obtained from a limited area, and it is difficult to measure overlay accuracy in any direction.

This invention was developed to solve the above-mentioned problems, and it is possible to measure a rich amount of information accurately and automatically, and also to superimpose not only the X and Y directions but also any direction. The purpose of this invention is to obtain an overlay accuracy evaluation method that can easily measure errors by considering the direction of the pattern when creating a mask.

[Means for solving problems]

The overlay accuracy evaluation method according to the present invention measures the area of a region surrounded by a base pattern to be overlaid and an upper layer pattern, and automatically determines an overlay error amount.

[Effect]

The overlay accuracy evaluation method in this invention measures the area of the area surrounded by the base pattern and the upper layer pattern using image processing, and calculates the amount of overlay error in the direction drawn on the mask pattern in advance. It is calculated and evaluated by finding the sum of the areas of the regions.

〔Example〕

FIGS. 1(a) and 1(b) are a plan view and a sectional view for explaining an embodiment of the overlay accuracy evaluation method of the present invention. In FIGS. 1(a) and 1(b), 1 is a base pattern formed on a substrate 3, and 2 is an upper layer pattern superimposed on the base pattern.

In FIG. 1(a), an upper layer pattern 2 is formed on a base pattern 1 formed in advance.

Now, assuming that the upper layer pattern 2 has a pattern of 45 degrees in each direction in the X and Y directions as shown in FIG. 1(a), the areas surrounded by the base pattern and the upper layer pattern 2 are A and B.
, C, D, E, F, G, and H. The area measurement of each region A-H can be obtained by counting the number of minimum units (pixels) of the image using an image processing device (not shown). For example, using 0.1 μm pixels in area A (in this case, the minimum unit of the image is 0.1 μm x 0, 1 μm = 0,
01 p m 2) If there are 1000 pixels, 0.01 μm2X1000=10.00
The area is μm2. Similarly, measure the area of region B-H. Now, the area of region A is Δ^, the area of the region is ΔB,
...If the area of region H is ΔH, then the overlay error amount R in the X direction.

However, Y is the distance in the Y direction of the base pattern 1, and the area opening xY of the base pattern is 2^+78+...
The amount of overlay error in the Y direction can also be determined in the same manner as between + and -.

Also, the sum of Δl) J C) Δo, As, ΔF, ΔG
.

By comparing the sum of ΔH2Δ8, it is also possible to evaluate the amount of overlay error in the 45-degree direction from the upper right to the lower left.

In this case, the upper layer pattern 2 is limited to X, Y directions and 45 degree patterns, but by actually drawing the upper layer pattern in the same direction as the device structure, it is possible to overlay and evaluate patterns at any angle.

In addition, in the above embodiment, an example was shown in which the rectangular upper pattern 2 is superimposed on the rectangular base pattern 1 in four directions, but even if the base pattern 1 is circular, the upper layer pattern 2 may be a pattern other than a rectangle. It doesn't matter.

Further, although an example has been shown in which the upper layer pattern 2 is a pattern in four directions, it is also possible to include patterns in any number of directions in one pattern.

〔Effect of the invention〕

As explained above, the present invention provides a method for evaluating the overlay accuracy of a base pattern formed on a substrate using photolithography and an upper layer pattern formed on the base pattern. By measuring the area of the enclosed area, the amount of overlay error is automatically determined and the overlay accuracy is evaluated, so the rich amount of information can be automatically used with high precision and regardless of direction (angle). This has the advantage that it is also possible to measure overlay errors.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are a plan view and a sectional view of a pattern to explain an overlay accuracy evaluation method according to an embodiment of the present invention, and FIG. 2 is an illustration of an overlay evaluation method using the conventional Vernier method. Figure 3(a). (b) is a plan view and a cross-sectional view of a pattern explaining another conventional overlay accuracy evaluation method. In the figure, 1 is the base pattern, 2 is the upper layer pattern, and A
−H1, is the region. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Masuo Oiwa (2 others) Figure 1 Figure 2 Figure 3 Procedure amendment (voluntary)

Claims (1)

[Claims] In a method for evaluating the overlay accuracy of a base pattern formed on a substrate using photolithography and an upper layer pattern formed on the base pattern, the area of the area surrounded by the base pattern and the upper layer pattern is An overlay accuracy evaluation method characterized in that the overlay accuracy is evaluated by automatically determining the amount of overlay error through measurement.