JPH07161618A - Alignment mark and photo-mask having alignment mark - Google Patents

Abstract

PURPOSE:To prevent the dissipation and deformation of an alignment mark by forming the alignment mark of a plurality of rectangular parts, and by not forming the surface, whose etching rate is quick, without forming a protruding part. CONSTITUTION:The mask having the pattern of an alignment mark is used, and exposure and development are performed. The shape of the alignment mark is constituted of a plurality of rectangular parts. Then, the reacting gas of CF4 is used, and silicon is exposed by dry etching. The silicon is etched by using powerful aqueous alkali solution such as KOH. At this time, the etching does not reach the thickness of a wafer because a place 1 of the alignment mark is surround by a surface, whose etching rate is slow, even if an intrinsic part to be etched 4 is etched only by the thickness of the wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment mark used for a wafer or a photomask.

[0002]

2. Description of the Related Art In recent years, semiconductor devices have been completed through a plurality of steps. This is, for example, a step of forming an oxide film on a silicon substrate (wafer), a step of diffusing diffused impurities into a part of the silicon substrate, or the like, and a photolithography technique is generally used for such a step. . For example, if there are first, second, and third layers and these layers are formed in different patterns, a resist is applied to the substrate in advance, and a photomask suitable for each pattern is prepared. The resist on the substrate is exposed using the photomask. Then, development is performed to form a resist in the pattern of the photomask. This resist pattern is used to form a pattern of the first layer. Then, this process is repeated to form the second and third layers. However, in such a case, there are cases where the first, second and third layers must be formed while maintaining their respective predetermined positional relationships. An alignment mark is used for that purpose.

The pattern of the alignment mark formed on the conventional general silicon wafer has a cross shape as shown in FIG. This is for aligning the alignment mark already formed on the silicon wafer with the alignment mark formed on the photomask. The two alignment marks are aligned with each other in two directions on a plane, and therefore, two orthogonal sides of the alignment marks are used. In the cross portion, a cross pattern and a pattern for etching silicon are formed in advance on a mask such as an oxide film or a nitride film,
A cross pattern is formed by using this pattern.

As described above, the pattern of the alignment mark can be easily identified by the silicon or the mask material.

[0005]

However, the conventional method has a problem that the shape of the alignment mark is deformed when etching is performed and the alignment cannot be performed. The present invention has been made in view of the above problems, and an object of the present invention is to provide an alignment mark that is not deformed even when etching is performed.

[0006]

As a result of earnest research, the present inventor has found that anisotropic etching of silicon has a high etching rate at the convex portions of the mask pattern. This is because the etching rate varies depending on the plane orientation of the silicon crystal, but a surface having a high etching rate appears on the convex portion. Although it depends on the etching time, as shown in FIG. 5, as the etching progresses, the convex portion recedes rapidly as shown by the dotted line, and finally the alignment mark pattern becomes only 4 as shown in FIG. It becomes a rectangular shape and cannot be used as an alignment mark in the subsequent steps. Even if the oxide film and the nitride film of the mask material remain, they cannot be used as alignment marks because they are turned over due to the residual stress of the film.

The present inventor, while carrying out earnest research,
It has been found that the disappearance of the alignment mark after etching is caused by the appearance of a surface having a high etching rate. Therefore, it was found that the alignment mark can be prevented from disappearing and being deformed by forming a pattern in which a surface having a high etching rate does not appear, and has completed the present invention.

Therefore, the alignment mark of the present invention is
"In the alignment mark for alignment formed on the wafer or on the photomask, the alignment mark is composed of a plurality of rectangular portions (claim 1)". Further, the photomask of the present invention is constituted by "providing alignment marks composed of a plurality of rectangular portions (claim 2)".

[0009]

According to the present invention, when the alignment mark is formed, no convex portion is formed (a surface having a high etching rate is not exposed), so that the alignment mark is deformed even when etching is performed and alignment (positioning) is performed. Therefore, the alignment work can be performed easily and accurately.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0011]

1 is a schematic diagram showing an alignment mark according to a first embodiment of the present invention. A part of the etching mask material 2 is removed, and the silicon 1 is exposed. This silicon 1 portion serves as an alignment mark. The vertical alignment mark is divided into two and does not intersect with the horizontal alignment mark.

FIG. 3 is an explanatory view showing the process sequence of silicon etching using the photomask on which the alignment mark of FIG. 1 is formed. A silicon wafer having a crystal plane orientation (100) is used. The orientation of the orientation flat is equivalent to (011). A silicon nitride film that serves as a mask during etching is formed on a silicon wafer by a method such as LP-CVD (a). Next, a photoresist is applied by spin coating (b). Exposure and development are performed using a mask having the pattern to be etched and the alignment mark pattern of FIG. 1 (c).

The alignment mark has a width of 10 μm,
The length is 30 μm. The size of the alignment mark can be arbitrarily selected. Further, there is no problem even if the left and right lengths and widths are different. Then, dry etching is performed using a reactive gas such as CF4 to expose the silicon (d). Etch silicon using a strong alkaline aqueous solution such as KOH (e). At this time, even if the location 4 to be originally etched is etched by the thickness of the wafer, since the location 1 of the alignment mark is surrounded only by the surface having a slow etching rate, the etching does not proceed to the thickness of the wafer. Also, each side of the alignment mark should be parallel or perpendicular to the orientation flat. Even after the etching is completed, the alignment mark is increased only by the amount of etching on the surface having a slow etching rate. Therefore, it is easy to design the alignment mark on the mask in the next process after predicting this size in advance.

In the present embodiment, as shown in FIG. 1, the shape of the alignment mark has a long pattern in the horizontal direction, but this pattern in the horizontal direction can also be divided into two in the same manner as in the vertical direction. Further, this pattern may be divided into a plurality of patterns instead of being divided into two. Further, even when the shape of the alignment mark as shown in FIG. 3 was similarly etched, the shape of the alignment mark did not change and good alignment could be performed.

Although a silicon substrate is used in this embodiment, any single crystal substrate may be used.

[0016]

According to the alignment mark of the present invention, a surface having a high etching rate does not appear during etching,
Even if the etching is performed, the alignment mark is not deformed and cannot be used for the alignment work. Therefore, the alignment work can be performed with high accuracy even in the process after the etching.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an alignment mark according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an alignment mark according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a process sequence of silicon etching using an alignment mark according to an example of the present invention.

FIG. 4 shows the shape of a typical conventional alignment mark.

FIG. 5 is a view for explaining how the convex portion retracts due to a conventional alignment mark.

FIG. 6 is an explanatory diagram showing a state after etching is completed when a conventional alignment mark is used.

[Explanation of symbols]

 1 ... Silicon 2 ... Etching mask material 3 ... Resist

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Claims (2)

[Claims] 1. An alignment mark for alignment formed on a wafer or a photomask, wherein the alignment mark comprises a plurality of rectangular portions. 2. A photomask having an alignment mark composed of a plurality of rectangular portions.