JPH02230718A - Aligning mark and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a secondary electron signal having the sufficient strength for mark detection by using a silicon groove comprising a silicon step part wherein the end part of a selected oxide film that is formed on a silicon substrate as a profile as an aligning mark. CONSTITUTION:A mask comprising a silicon nitride film 4 is used, and a silicon oxide film 5 and a silicon substrate 1 undergo dry etching, and a silicon groove is formed. Then, an element isolating silicon oxide film (selected oxide film) 6 is formed by thermal oxidation. The silicon nitride film 4 and the silicon oxide film 5 as a buffer are removed by wet type etching. Then, an element region 7 is covered with photoresist. With the selected oxide film 6 as an etching mask, the silicon substrate 1 is directly etched by reactive ion etching, and an aligning mark 8 is formed. When said aligning mark 8 is used, the strength of the secondary electron signal that is five times or more the strength when the step of an ordinary selected oxide film is used as a mask can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to alignment marks necessary for manufacturing semiconductor devices by electron beam direct writing and a method for manufacturing the same.

[Prior art 1] Conventionally, in the case of silicon semiconductor devices, alignment marks for electron beam direct writing have been made by directly providing a step on a silicon substrate 1 to form a groove 2, as shown in FIG. , 4th
As shown in the figure, a method was used in which the step difference between the selective oxidation layers 11g3 formed by selective oxidation of silicon was utilized as is.

[Problems to be Solved by the Invention] However, since silicon steps are not formed at the beginning of the semiconductor device manufacturing process, as the process progresses and selective oxide film formation and film deposition are repeated, the steps decrease and alignment becomes difficult. Therefore, it becomes difficult to obtain a secondary electron signal from the step end. In addition, when using the step difference in the selective oxide film, as the integration and miniaturization of semiconductor devices progress, in order to narrow the selective oxidation region for element isolation, measures are being taken to suppress the step difference in the selective oxide film, and Since the selective oxide film thickness also tends to decrease, it is becoming difficult to obtain secondary electron signals from the step part, similar to the silicon step.

The present invention has been made in response to the above-mentioned conventional circumstances, and it is an object of the present invention to provide an alignment mark for electron beam direct writing, which is suitable for high integration and miniaturization of semiconductor devices, and a method for manufacturing the same. With the goal.

[Means for Solving the Problems] The present invention provides an alignment method characterized in that it is constituted by a silicon groove consisting of a silicon stepped portion whose contour is the edge of a selective oxide film formed on a silicon substrate. mark,
The manufacturing method includes the steps of forming a selective oxide film at a predetermined position on a silicon substrate, exposing silicon in areas other than the selective oxide film area, and exposing silicon in areas other than alignment marks. The method is characterized by comprising a step of covering with a protective film, and a step of etching silicon using the protective film and the selective oxide film as a mask to form a silicon groove.

Further, the first step in the method of the present invention includes a step of forming a mask with a silicon nitride film as a step before forming a selective oxide film, and a step of forming a silicon groove in the selective oxidation part using the formed mask. It may also include a step of.

[Function] The difference in etching speed during anisotropic etching of the silicon substrate and silicon oxide film can be made sufficiently large.
If the oxide film after selective oxidation is used as an etching mask, it is possible to form a silicon step whose outline is the edge of the oxide film. Further, since the depth can be freely adjusted by etching, it is possible to obtain a secondary electron signal with sufficient intensity for mark detection.

[Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of an alignment mark portion showing an embodiment of the present invention in the order of steps.

The method is to first form a mask made of silicon nitride film 4 before selective oxidation, as shown in FIG. Form. At that time, the thickness of the buffering silicon oxide film 5 under the silicon nitride film 4 is 0.
．． 05l! The thickness of the In, silicon nitride film 4 is 0.17μ
s, the etching depth of the silicon groove was 0.22 mm.

Next, as shown in FIG. 1(b), a silicon oxide film (selective oxide film) 6 for element isolation is formed for 0.5s1 by thermal oxidation, and the silicon nitride film 4 and the silicon oxide film 5 for buffering are wet etched. Remove by.

Next, the element region 7 is covered with photoresist by photolithography, and the alignment mark portion is exposed.
Silicon substrate 1 is directly etched by reactive ion etching using chlorine gas using selective oxide film 6 as an etching mask. After etching, the foot resist is removed using oxygen plasma to form alignment marks 8 as shown in FIG. 1(C). The silicon groove etching depth at that time was set to 0.5 depth.

When using the alignment mark with the structure shown in Figure 1(C), it is possible to obtain a secondary electron signal intensity that is 5 times or more than when using the step of the normal selective oxide film as shown in Figure 1(b) as a mark. was completed.

FIG. 2 is a cross-sectional view of an alignment mark portion showing an embodiment of the present invention in the order of steps.

The method is to first form a first silicon nitride film mask 4a before selective oxidation, then roughly deposit a second silicon nitride film 4b over the entire surface by CVD, and then form a selective oxide film by a photolithography process. After opening a hole in the resist portion and removing the silicon nitride film 4b by dry etching, a groove is formed in the silicon substrate 1 by rough and continuous dry etching (2nd (a)). At this time, the thickness of the silicon oxide film 5 for buffering under the silicon nitride film is 0.05 μm, and the thickness of the first silicon nitride film 4a is Oi
7ptn, the thickness of the second silicon nitride film 4b is 0.03
41a, the etching depth of the silicon groove is 0.22/J
Met.

Thereafter, as shown in FIG. 2(b), a silicon oxide film (selective oxide film) 6 for element isolation is formed with a thickness of 0.5 cm by thermal oxidation, and silicon nitride films 4a and 4b and a silicon oxide film for buffering are formed. 5 is removed by wet etching.

Next, the element region 7 is covered with photoresist by photolithography, and the alignment mark portion is exposed.
Silicon substrate 1 is directly etched by reactive ion etching using chlorine gas using selective oxide film 6 as an etching mask. After etching, the photoresist is removed using oxygen plasma to form alignment marks 8 as shown in FIG. 2(C). The silicon groove etching depth at this time was set to 0.5 mm.

When using the alignment mark with the structure shown in FIG. 2(C), it is possible to obtain a secondary electron signal intensity that is 10 times higher than when using the normal selective oxide film step shown in FIG. 2(b) as a mark. I was able to do it.

[Effects of the Invention] As explained above, according to the present invention, there is provided an alignment mark and a method for producing the same that can obtain a secondary electron signal with sufficient intensity necessary for mark detection by electron beam direct writing. .

[Brief explanation of the drawing]

FIGS. 1 and 2 are sectional views of an alignment mark portion showing an embodiment of the present invention in the order of steps, and FIGS. 3 and 4 are sectional views of an alignment mark portion according to the prior art. ]...Silicon base temporary 2...Groove 3, 6...
Selective oxide film 4. 4a, 4b...Silicon nitride film 5...Silicon oxide 111J 7...Element region 8...Alignment mark

Claims (2)

[Claims] (1) An alignment mark comprising a silicon groove formed by a silicon step portion whose outline is the edge of a selective oxide film formed on a silicon substrate. (2) Forming a selective oxide film at a predetermined position on the silicon substrate, exposing silicon in areas other than the selective oxide film area, and covering the exposed silicon surface with a protective film in areas other than the alignment marks. 1. A method for producing an alignment mark, comprising the steps of: covering with a silicone film and etching silicon using the protective film and the selective oxide film as a mask to form a silicon groove.