JPH116725A - Method for measuring accuracy of superposition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for measuring the superposition accuracy of mask patterns in the photolithography step of semiconductor device production process in which measurement error is prevented from increasing through apparent deformation at the pattern edge of a reference layer due to irregularities of a layer for forming the mask pattern. SOLUTION: An outer box mark pattern 1a is formed on a reference layer 5. Subsequently, a mask pattern forming layer 6 is formed and an inner box mark pattern 3 is formed thereon. The inner and outer box mark patterns 3, 1a are superposed while matching the apparent centers of coordinate. Superposition accuracy of a comparison pattern, i.e., the inner box mark pattern 3, is then measured with respect to a reference pattern, i.e., the outer box mark pattern 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring the overlay accuracy between mask patterns in a photolithography process in the manufacture of semiconductor devices.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring the overlay accuracy between mask patterns, as shown in FIGS. 1 and 2, a pattern for overlay accuracy measurement having a box-in-box structure composed of a reference layer and a comparative layer is measured. There is known a method of arranging one point for each point, detecting a pattern edge, and measuring overlay accuracy from a positional relationship of the pattern edge.

[0003]

However, in the prior art, as shown in FIG. 3, the pattern edge of the reference layer is apparently deformed due to the unevenness of the layer to be masked, resulting in a large measurement error. There was a problem that.

Accordingly, the present invention provides an overlay accuracy measuring method for improving the accuracy of measurement when the pattern edge of the reference layer is apparently deformed due to the unevenness of the mask pattern forming layer and the measurement error increases. The purpose is to provide.

[0005]

The overlay accuracy measuring method according to the present invention has the following features.

[0006] A plurality of overlay accuracy measurement patterns are arranged at one measurement point, and a plurality of measurement results obtained by measuring a plurality of patterns are averaged to obtain an overlay accuracy at one measurement point. It is characterized by improving accuracy.

According to the above-described structure, the pattern edge of the reference layer is apparently deformed due to the unevenness of the layer to be masked, and the measurement accuracy is improved when the measurement error increases. Have.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a plan view showing an embodiment of a pattern for measuring overlay accuracy of a box-in-box structure according to the first aspect of the present invention. Also, FIG.
-I sectional drawing. In the drawing, 5 is a reference layer, 6 is a mask pattern formation layer, 1a is an outer box mark pattern formed on the reference layer, 1b is an apparent outer box mark pattern formed on the mask pattern formation layer, 2a is An outer box mark pattern edge formed on the reference layer, 2b is an apparent outer box mark pattern edge formed on the masked pattern forming layer, 3 is an inner box mark pattern formed of photoresist, and 4 is an inner box mark. The pattern edge 7 is the coordinate center of the measurement point.

The pattern for measuring overlay accuracy of the box-in-box structure shown in FIG. 4 is formed in a scribe line space of a wafer or inside a chip.

In FIG. 5, an outer box mark pattern 1a is formed on the reference layer 5 through a photolithography step and an etching step. Next, the mask pattern forming layer 6 is formed, and the inner box mark pattern 3 is formed thereon using a photoresist. At this time, the inner box mark pattern 3 is formed by overlapping the apparent outer box mark pattern 1b so that the coordinate center of the inner box mark pattern 3 is the same as the coordinate center of the inner box mark pattern 3. At the time of overlay accuracy measurement, the apparent outer box mark pattern 1b is a reference pattern and the inner box mark pattern 3 is a comparison pattern. Measure alignment accuracy.

Concerning the relationship between the reference pattern and the comparison pattern, on the contrary, the apparent box mark pattern 1b serving as the reference pattern may be formed inside and the box mark pattern 3 serving as the comparison pattern may be formed outside. .

If the apparent box mark pattern edge formed on the mask pattern forming layer is deformed due to the unevenness of the mask pattern forming layer 6, it is better to dispose the reference pattern outside the apparent BOX mark pattern edge. Since the length can be increased, the measurement accuracy is improved.

Next, a method of measuring overlay accuracy will be described.

For each of the four overlay measurement patterns formed as shown in FIG. 3, the apparent outer box mark pattern edge 2b and inner box mark pattern edge 4 are detected, and the x component is determined from the positional relationship of the patterns. And a measurement result of the overlay accuracy of the y component. With respect to the four measurement results obtained by this, x
An average value is calculated for each of the component and the y component, and the average value is obtained as an overlay component x component and a y component of the coordinate center 7 of the measurement point.

In the case where four 1/4 size patterns are measured, the total pattern edge length is twice that of the case where one overlay accuracy measurement pattern is used for one measurement point. Therefore, even if the pattern edge of the reference layer is apparently deformed due to the unevenness of the mask pattern formation layer 6 and the measurement error increases, the overlay accuracy is measured based on twice the information. Therefore, the measurement accuracy can be significantly improved.

In the method of arranging a plurality of overlay accuracy measurement patterns, the same measurement accuracy can be obtained in both the x and y directions by arranging the same number of patterns in the x and y directions. If only one of them requires high measurement accuracy, the number of overlay accuracy measurement patterns may be increased only in the direction in which the accuracy is required.

As the number of overlay accuracy measurement patterns per measurement point increases, the measurement accuracy improves.
The number of overlay accuracy measurement patterns to be arranged is determined according to the required measurement accuracy.

[0019]

As described above, according to the present invention, even when the pattern edge of the reference layer is apparently deformed due to the unevenness of the layer to be masked and the measurement error increases, the measurement accuracy is high. By performing overlay accuracy measurement, productivity, yield can be improved, and production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a conventional pattern for measuring overlay accuracy.

FIG. 2 is a cross-sectional view of a conventional pattern for measuring overlay accuracy.

FIG. 3 is a plan view showing a problem of a conventional overlay accuracy measuring method.

FIG. 4 is a plan view showing an embodiment of the overlay accuracy measuring method of the present invention.

FIG. 5 is a sectional view showing an embodiment of the overlay accuracy measuring method of the present invention.

[Explanation of symbols]

1a Outer box mark pattern formed on reference layer 1b Apparent outer box mark pattern formed on masked pattern formation layer 2a Outer box mark pattern edge 2b Apparent outer box mark formed on masked pattern formation layer Pattern edge 3 Inner box mark pattern 4 Inner box mark pattern edge 5 Reference layer 6 Masked pattern formation layer 7 Coordinate center of measurement point

Claims (1)

[Claims] When measuring the overlay accuracy between mask patterns, a plurality of overlay accuracy measurement patterns are arranged at one measurement point, and a plurality of measurement results obtained by measuring the plurality of patterns are obtained. A superposition accuracy measuring method characterized by improving the measurement accuracy by averaging and obtaining the superposition accuracy at one measurement point.