JPS59148331A - Positioning mark - Google Patents

Abstract

PURPOSE:To improve the accuracy in overlapping of patterns by obtaining the signal having high S/N by forming the positioning mark in a manner its cross- sectional shape shows an equilateral triangle which swells over the substrate. CONSTITUTION:When a fundamental substrate 1 is etched, the side etching makes a cross-sectional shape of a positioning mark 21 an equilateral triangle swelling over the substrate 1. By utilizing that, the positioning mark 21 is formed as an equilateral triangle without no flat part. After forming the positioning mark 21, the resist 3 for electron beam is coated. When the positioning mark 21 having such shape is scanned with electron beam, mark signal 41 is obtained. This signal 41 has high signal intensity and is keen without decreasing the strength in the central part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an alignment mark used when exposing a pattern overlapping an underlying pattern when manufacturing semiconductor devices by direct electron beam exposure. It is related to.

[Prior art]

When manufacturing semiconductor devices by direct electron beam exposure, it is necessary to expose the pattern overlapping the underlying pattern. In this case, in order to accurately overlap the two patterns, alignment marks are formed in the base pattern, and a reflected electron signal is detected when the alignment marks are scanned with an electron beam. Find its position. Then, based on the obtained values, the onset of the base pattern coordinates with respect to the coordinate system of the electron beam exposure apparatus is set.

A method is used in which the underlying pattern and the exposed pattern are accurately superimposed by calculating the amounts of rotation and expansion/contraction and correcting these amounts during exposure. At this time, since the S/N ratio of the reflected electron signal (hereinafter abbreviated as mark signal) obtained when the alignment mark is scanned with an electron beam directly affects the overlay accuracy, the
~ It is desirable that the ratio is as large as possible.

FIG. 1(,) shows an example of alignment marks that are commonly used at present. This mark is made by etching a base substrate (1) made of single crystal silicon (Si) to a depth of 2 μm using reactive ion beam etching to form a mark (2) with a width of 1011 m. 1. Electron beam resist (3) for exposure.
It was coated with a film thickness of 0 μm.

Then, apply an acceleration voltage of 10 KV over this mark (2).

FIG. 1(b) shows a mark signal obtained by scanning with an electron beam having a probe diameter of 0.5 μm and a globe current of 40 nA at a scanning frequency of 200 Hz.

Under the above electron beam conditions, the mark signal (4) shown in FIG. 1(b) is aligned with the resist (3).
) is determined by the relationship between In other words, since the film thickness of the resist (3) is thin at the mark step part (2 m) shown in Fig. 1(, ), the reflected electrons from this mark step part are larger than those other than the mark. The signal corresponding to the difference becomes the mark signal (4). Since the resist (3) is thick in the central part of the mark flat part (2b), the mark signal intensity decreases as shown in FIG. 1(b). In this case, as shown in Figure 3, if the signal strength obtained from the alignment mark equivalent to Figure 1 (,) is S, and the signal strength similarly obtained from the resist is N, then the ratio of these signal strengths is If (-) is defined as the S/N ratio of the mark signal, the 8/N ratio of this signal will greatly improve mark detection accuracy and pattern overlay accuracy.

However, in the above-mentioned conventional alignment map, since flat portions exist, as the resist film thickness increases, the mark signal ratio deteriorates and the mark detection accuracy also deteriorates. Also, since the signal level drops at the center of the mark signal (
(see FIG. 1(b)), this acts as noise during detection and causes a decrease in detection accuracy, and has the disadvantage that sufficient overlay accuracy cannot be obtained. This became particularly noticeable as the resist film thickness increased.

[Summary of the invention]

In view of the above points, the present invention has been made in order to eliminate the drawbacks of the conventional method. The present invention provides an alignment mark that can improve pattern overlay accuracy by obtaining a signal with a large /N ratio.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail using FIG. 2.

FIGS. 2(a) and 2(b) are a sectional view of an alignment mark and a waveform diagram of the mark signal according to an embodiment of the present invention. In this example, when alignment marks with a width of 2 μm are used, when the base substrate (1 layer) is etched using the same conventional reactive ion beam etching method, the side etching is performed as shown in FIG. 2(a). As shown in FIG.
An alignment mark (21) is formed in the form of an isosceles triangle without a flat part. In FIG. 2, the same or corresponding parts as in FIG. 1 are denoted by the same reference numerals, and after the alignment mark (21) is formed, an electron beam resist (3) is applied as in the conventional case.

Therefore, when the alignment mark (21) having such a shape is scanned by an electron beam under the same conditions as above,
The mark signal is a mark signal (4) as shown in Fig. 2(b).
1) is obtained, and this mark signal (41) is shown in FIG.
) The signal strength is higher than that of mark signal (4) in case 1, and the phenomenon of the mark signal strength decreasing in the center of the signal as shown in Fig. 1(b) does not occur, and the signal strength is not sharp. Become. This is because the resist (3
This is because the coating will cause the K to become thicker.

According to the inventor's experimental results, the conventional alignment mark 0) had a sZN ratio of about 3.5 as shown in FIG. 1(b), whereas the present F! AK alignment mark (
21) According to K, as is clear from Figure 2(b), 8/
It was said that the N ratio could be raised to about 7.5. In addition, with the conventional alignment mark (2), as shown in Figure 1(b), the mark signal strength decreases at the center of the signal, which acts as noise during signal processing and causes the mark to be detected. However, according to the alignment mark (21) of the present invention, there is no influence of such noise, and the mark detection accuracy can be dramatically improved. Furthermore, in the present invention, if the depth of the alignment mark (21) is further increased, the tip of the mark (21) will not protrude above the resist (3), and the 8/N ratio will be higher. It is also possible to obtain.

〔Effect of the invention〕

As explained above, according to the present invention, the cross-sectional shape of the alignment mark is formed into an isosceles triangular shape that is raised from the substrate. ), since a mark signal with a large S/N ratio is obtained, the mark detection accuracy is high, and therefore the pattern overlay accuracy can be improved.

[Brief explanation of the drawing]

Figures 1 (,) and (b) are a sectional view of a conventional alignment mark and a waveform diagram of its Zouk signal;
Figures (,) and (b) are a cross-sectional view of an alignment mark and a waveform diagram of the mark signal showing an embodiment of the present invention, and Figure 3 is a diagram showing each position of the mark defining the 8/N ratio of the mark signal. FIG. 4 is a waveform diagram showing relative signal intensities obtained on alignment marks and resist. (1)...Base substrate, (21)...Positioning mark, (3)...Resist. Agent Shin Kuzuno - Figure 1 Figure 2 (CI) Figure 3

Claims (1)

[Claims] An alignment mark characterized in that its cross-sectional shape has an isosceles triangular shape that is raised above a substrate.