JPS6320013B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to the shape of alignment marks on a photomask used in a photolithography process when manufacturing semiconductor devices such as semiconductor integrated circuits.

[Prior art and its problems]

In the photolithography process for manufacturing semiconductor devices, alignment marks are provided on the photomask to align the photomask and the semiconductor substrate so that a desired pattern is correctly formed at the desired position on the semiconductor substrate. , based on this mark,
It is common practice to overlap a photomask and a semiconductor substrate. The shape of the mark on this photomask is usually a cross or a square, as shown in 1 or 2 in FIG. 1, for example, and is black or transparent depending on the purpose of use. When aligning a photomask with a semiconductor substrate using these marks, since these marks have minute shapes, it is usually done visually under a microscope magnified 100 to 200 times, and the marks themselves are It is not possible to make the size extremely small.
For example, when using a negative photoresist and using a black optical mark, the pattern of the mark will be transferred to the resist and this After removing a portion of the resist, the surface of the semiconductor substrate, such as Si, will be exposed. In the photolithography process in the actual manufacture of semiconductor devices, the photomask and the Si substrate are often aligned using marks with the Si substrate exposed in this manner.

However, when etching is performed using a corrosive solution that etches the Si substrate in the subsequent process, the exposed Si is etched by the transfer of the mark pattern.
Since the ground is simultaneously etched for this Si substrate etching, the mark pattern becomes larger than necessary. As a result, the accuracy of alignment between the photomask and the semiconductor substrate after the next process deteriorates, and sometimes the etching extends to the area of functional elements formed on the semiconductor substrate, significantly impairing the characteristics of the semiconductor element. There is a drawback. Figure 2 shows the state in which the shape of the transferred mark has been enlarged by etching.For example, this means that the cross-shaped mark shown in Figure 1 has expanded to the area indicated by 3. ing.

In order to avoid such problems, if it is possible to use a method such as mask alignment at the edge of the semiconductor chip in the next process, it is possible to eliminate the alignment marks, or to apply a patent application based on the invention of the present inventors. It is also conceivable to consider a method of making the mark described in the specification of 1984-49756 (see Japanese Patent Application Laid-open No. 56-146891) fine so that the mark itself is not transferred onto the substrate. For example, in the photo-etching process for elements such as tire flam type semiconductor pressure sensors, which have a deep groove digging process in the Si semiconductor substrate, it is necessary to align masks on both sides of the semiconductor substrate. For Si surface etching, a transfer pattern of alignment marks must be left.

On the other hand, in order to minimize the enlargement of the shape of the alignment mark due to etching of the Si substrate as mentioned above, it is possible to reduce the shape of the mark in advance.
This has the disadvantage that alignment of the double-sided photomask with the Si substrate becomes difficult, and is not an appropriate solution.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a photomask having an alignment mark shape that can minimize enlargement of the transferred pattern shape due to etching of a semiconductor substrate.

[Key points of the invention]

The present invention is achieved by forming an alignment mark by combining and arranging a size smaller than the resolvable size of the photoresist and a size larger than the resolvable size of the photoresist.

[Embodiments of the invention]

The present invention will be explained below based on examples.

FIG. 3 is an embodiment of the present invention, and shows the contour shape of a positioning mark provided on a photomask. In FIG. 3, a cross-shaped pattern 1a having dimensions slightly larger than that which can be resolved by the photoresist is surrounded by a rectangular pattern 4 having dimensions slightly smaller than dimensions which can be resolved by the photoresist, forming a cross-shaped pattern as the overall pattern shape. This figure shows a state in which a large number of them are arranged so that they are larger than 1a and have contours similar to this.

For example, when a 1 μm negative resist is coated on a Si substrate, the patterns that this negative resist can resolve are approximately 4 μm apart, and patterns finer than this will be affected by light wraparound and swelling during development. The image is not resolved and is not transferred to the resist film. Figure 4 shows a situation in which light enters from above a fine pattern provided on a photomask and exposes the resist.
It is shown that when a negative resist 6 coated on a Si substrate 5 is exposed with a photomask 8 having a black mark 7, light 9 reaches the resist below the mark 7. As can be seen from this, when the fine rectangular pattern 4 on the photomask in Figure 3 is exposed on the Si substrate with this photomask, it is not resolved on the photoresist on the Si substrate, Only the cross-shaped pattern 1a having a size larger than that which can be resolved will be transferred. In this way, for example, when aligning photomasks in double-sided mask alignment, the minute square pattern 4
surrounds the large cross-shaped pattern 1a, and the mark as a whole has a large cross-shaped outline, so positioning can be easily performed using the maximum outer diameter dimension of the mark provided on the photomask. The pattern actually transferred to the photoresist can have the required small shape. Of course, the pattern shapes of these marks may take any shape depending on the situation.

In Figure 5, a square pattern is used instead of the cross pattern in Figure 3, and a large square pattern 2a is surrounded by small square patterns 4, and the mark as a whole is larger than the large square pattern 2a. They are similar shapes with outlines. In addition, as another different embodiment, as shown in FIG. 6, by arranging a small rectangular pattern 4 within the strip pattern 2b, the area of the Si ground to which this mark is transferred and exposed can be minimized. It can be suppressed.

〔Effect of the invention〕

As explained above, according to the present invention, the alignment mark with the semiconductor substrate provided on the photomask used in the photolithography process includes a pattern with a size slightly larger than that which can be resolved by the photoresist, and a pattern of the photoresist. Patterns with dimensions slightly smaller than those that can be resolved are arranged in combination so that the overall mark has a large outline, and the alignment of the semiconductor substrate and photomask is
Not only is it extremely easy to perform this process using a mark with a large outline, but the pattern is not transferred to the resist even when exposed to light in areas with a small mark shape; The underlying surface of the semiconductor substrate exposed by the larger mark on the second side can be kept to a minimum without being enlarged unnecessarily for etching in the next process, which improves the accuracy of photomask alignment in subsequent processes. This completely eliminates any damage to the functional elements formed on the semiconductor substrate, and significantly contributes to improving the working efficiency and product yield of the photolithography process.

[Brief explanation of the drawing]

Figure 1 is an outline diagram of a mark provided on a photomask, Figure 2 is a conceptual diagram of a pattern enlarged and etched, Figures 3, 5, and 6 are outline diagrams of a mark according to the present invention, and Figure 4 is a microscopic diagram. FIG. 2 is a conceptual diagram showing the transmission of light through a photomask with marks. 1, 1a... Cross mark, 2, 2a... Square mark, 3... Enlarged area, 4... Minute square mark, 5... Si substrate, 6... Photoresist, 7...
...Black mark, 8...Photomask, 9...Direction of light.

Claims (1)

[Claims] 1. A large number of patterns having dimensions smaller than the dimensions that can be resolved by the photoresist are arranged around a pattern having dimensions larger than those that can be resolved by the photoresist, and each pattern has an outline similar to the pattern having the larger dimensions. A photo mask characterized by having alignment marks.