JPS60158621A - Superposing mark - Google Patents

Abstract

PURPOSE:To omit the forming process of a mark by a method wherein projection of an electron beam is performed for the prescribed hours to the referential mark part. CONSTITUTION:Thick oxide films 2 for oxide isolation formed on an Si semiconductor substrate 1 are formed normally according to the LOCOS method, etc. Even when marks 4 for electron beam directly drawing are formed by thick oxide films, because the step difference is not steep, the marks are not formed as the step difference marks. However, when an electron beam is projected for the prescribed hours to this construction, electrons are caught to the thick oxide films, surface electric potential is reduced, and a strong mark signal can be obtained. Accordingly, a mark forming process can be omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electron beam direct writing method, and particularly to a structure of an overlay mark that can obtain high overlay accuracy.

[Background of the invention]

Conventional marks for electron beam direct writing are often specially formed with a structure different from that obtained in the normal LSI manufacturing process, such as by forming a special step or using heavy metal as a mark. There were drawbacks such as increased complexity and increased number of restrictions on process conditions.

[Purpose of the invention]

An object of the present invention is to eliminate such drawbacks of the conventional method and to provide a mark for direct writing with an electron beam using a structure that can be easily obtained in a normal LSI manufacturing process.

[Summary of the invention]

In the electron beam direct writing method, marks are the reference for detecting the relative positional relationship between the electron beam and the semiconductor wafer. Marks usually have steep steps or a material with a different atomic weight than the surrounding area, which changes the size of the reflected electrons and uses them as a signal. It is known from backscattered electron images taken with a scanning electron microscope that these backscattered electrons vary greatly depending on the surface potential of the semiconductor.

For example, insulating films of different thicknesses formed on a semiconductor substrate or insulators placed in a conductor are charged up by electron beam irradiation and generate strong reflected electrons. By using such a change in the film thickness of the insulating film as a mark, an overlay mark, which was conventionally formed by a special process, can be formed without adding a completely new process.

[Embodiments of the invention]

The present invention will be explained in detail below.

Example 1 In this example, an oxide isolation layer of MO5LSI was used as a mark.

As shown in FIG. 1, the thick oxide film 2 for oxide isolation formed on the Si semiconductor substrate 1 is usually formed by the LOCO5 method, etc., and the boundary with the surrounding thin oxide film region 3 has a gradual thickness change. Even if the mark 4 for electron beam direct drawing is formed of a thick oxide film, it will not become a step mark because the step is not steep. Here, part a in the figure is a mark forming part, and part b is an element part.

However, when applying a 30kV electron beam to this structure at 10A/cI1,
When irradiation was performed for 10 mS at No. 12, electrons were captured in the thick oxide film, the surface potential decreased, and a strong mark signal was obtained.

Example 2 Another example of the present invention is shown in FIG. This embodiment is an example in which the present invention is applied to a MO5LSI whose surface is flattened. In this case, no mark signal was obtained using the conventional method, but as in Example 1, the voltage was 30 kV.

After irradiating the electron beam of 10 A/a part 2 for 1.0 mS, a good mark signal was obtained.

Example 3 Another example of the present invention is shown in FIG. This uses a through-hole hole 8 formed in a first interlayer film 6 of a multilayer wiring of an LSI as a mark.

The through hole formed here is etched into a tapered shape, so it cannot be used as a step mark. However, the first wiring 7
The thick interlayer film 9 isolated on the top can be used as a mark by short-time electron beam irradiation before mark detection, as in Example 1.2.

〔Effect of the invention〕

According to the present invention, thick oxide films and interlayer insulating films, which are used for insulation isolation between elements, can be actively used among semiconductor element structures that have been difficult to utilize in the past. This has the effect of omitting the step of forming marks, which was considered indispensable in drawing.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view when the mark structure according to the present invention is applied to a MO5LSI with a normal LOCO5 structure, Figure 2 is an example when the surface is flattened, and Figure 3 is an example when an interlayer film of multilayer wiring is used. This is an example of a case. ■...Si substrate, 2...Thick element isolation insulating film, 3
... Thin insulating film, 4... Mark formed by LOCO5 method, 5... J-resistant oxide film, 6... Interlayer insulating film, 7
...first wiring layer, 8...first through hole, 9...
・Shaped I opening and 3rd opening due to interlayer insulating film

Claims (1)

[Claims] In the electron beam direct writing method, a mark that serves as a reference for overlay is formed by a combination of a thick insulating film and a thin insulating film, or a combination of an insulating film and a conductive film, and electrons are applied to the reference mark portion for a certain period of time. An overlay mark characterized by line irradiation.