JPS5928045B2 - How to position the mask for pattern formation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for positioning a pattern forming mask in a semiconductor device, an integrated circuit, a thin film circuit, etc.
The present invention relates to a method for positioning a mask for a pattern.

Conventionally, in this type of pattern forming mask positioning method, a third photomask is moved to a predetermined position on a substrate in order to further form a third pattern on the substrate with respect to the pattern already formed on the substrate using two photomasks. Typical methods used for positional superimposition are shown in FIGS. 1 and 2.

In the conventional method shown in FIG. 1, 5. Two alignment marks designated by numbers M, l, and Ml2 are provided, and these alignment marks are exposed and transferred to the photoresist on the wafer 1, that is, the substrate, by a predetermined method, and the substrate surface is oxidized after development. It is formed by etching the film and filtering out the recesses.

The alignment marks formed as recesses in the oxide film on the surface of the substrate are indicated by numbers Wll and Wl2. The second layer photomaster has an alignment mark M2l that is aligned with either the alignment mark W, or W,2 (Wl in the case of FIG. 1) and is slightly smaller than the alignment mark.
and the other alignment mark Wl already formed on the board.
2 has another alignment mark M23 that does not match.

This second layer photomask has alignment marks M2,
The pattern of the second layer photomask is exposed and transferred to the photoresist coated on the substrate again, and Together with the pattern, these alignment marks M2l and M23 are also etched by a predetermined method and stamped on the substrate. At this time, the alignment mark M2l is formed as a deeper recess by etching the oxide film formed on the substrate surface of the recess in the recess formed as the alignment mark Wl, and this is formed as a deeper recess.
is shown as Further, another alignment mark M23 is formed as a recess by etching the oxide film at a predetermined position on the substrate, and is indicated by W23. Next, the third layer pattern is superimposed, and the third layer photomask has alignment marks W already formed on the substrate 5.
, 2, and W23, respectively, and alignment marks M32 and M33 that are slightly smaller than the alignment marks are provided.

This third layer photomask has alignment mark M32.
, M33 are aligned with alignment marks Wl2, W2 formed on the substrate.
3. The pattern was then exposed and transferred onto a photoresist coated on the substrate. According to this conventional registration method, two registration marks must always be observed at the same time.
No.

Moreover, if there is an error in the overlay of the second layer photomask on the first layer pattern, the alignment mark M3 is used when overlapping the third layer pattern photomask.
It was very difficult to accurately align the marks Wl2 and W23 already formed on the substrate. Therefore, there was a risk that a relatively large error would occur in overlaying the photomask having the third layer pattern onto the substrate. Further, as other conventional methods shown in FIG. 2, there are the following methods.

First, an alignment mark indicated by the number M is provided on the first layer photomask, and the pattern is exposed and transferred to the photoresist on the substrate, and after development, it is etched by a predetermined method to form an oxide film on the surface of the substrate. Form a recess. The recess formed in this manner is shown as an alignment mark W1 on the substrate. The next second layer of the photomask has an alignment mark M2 aligned with and slightly smaller than the alignment mark W, and by aligning this alignment mark M2 with the alignment mark W, a second layer is formed. A photomask for each layer is positioned on the substrate. Thereafter, the alignment mark M2 of this second layer photomask, together with its pattern, is exposed and transferred onto a photoresist coated on the substrate again, and after development processing, it is etched to form a recessed portion. That is, a deeper recess is formed at the bottom of the first recess formed with the alignment mark W1, and the alignment mark W? Become. The third layer photomask is provided with an alignment mark M3 that is slightly smaller than the alignment mark M2 of the second layer photomask so as to further align with the alignment marks Wl and W2.

Then, move this alignment mark M3 to the alignment mark W on the board.
A third layer photomask is positioned on the substrate so as to align with 2. According to this method, only one alignment mark is required to observe the marks during alignment, but the third
There was a drawback that alignment margins of the alignment marks W, , W2 with respect to alignment marks M3 provided in the layers were different.

Furthermore, if there is an error in the overlay of the pattern formed by the first layer photomask and the pattern formed by the second layer photomask, the third layer photomask is based on the alignment mark of the second layer photomask. Since the positioning is performed using the same method, the error with the first layer pattern becomes very large. In this way, it is extremely difficult to superimpose the third layer photomask on the substrate in a manner that minimizes errors with respect to the patterns of the previous two layers.Therefore, the object of the present invention is to This method solves the drawbacks of the conventional pattern forming mask positioning method, and allows one alignment mark to have equal margins with respect to alignment marks made with two photomasks, and eliminates overlap caused by the first and second layers. It is an object of the present invention to provide a method for positioning a substrate so that the third layer photomask can be easily overlapped even in the case of an alignment error.

Hereinafter, the method for positioning a pattern forming mask according to the present invention will be further explained with reference to FIGS. 3 and 4 showing preferred embodiments of the present invention.

In each embodiment of the present invention, the method of forming the alignment mark itself on the substrate is the same as the conventional method, and this point will also be explained in more detail. Further, in the present invention, the resist applied to the substrate can be either a negative resist or a positive resist, but in the embodiments described below, a case will be explained in which a negative resist is used. FIG. 3 shows one embodiment of the invention.

Alignment marks Mll, M, 2 are provided on the first layer photomask, and the alignment marks are exposed and transferred to the photoresist on the substrate along with the pattern of the photomask by a predetermined method, and after development processing, the oxide film on the substrate surface is etched. The substrate surface is exposed and the alignment mark is formed as a recess. The alignment marks thus formed as recesses in the base are indicated by the numbers W, , W, 2. By the way, in the recesses on the substrate surface where these alignment marks Wll and Wl2 are formed, an oxide film grows again on the exposed surface of the substrate at the bottom by chemical action with oxygen (of course, an oxide film is grown instead of this). may be coated on the substrate). However, the growth of this oxide film is not enough to fill the recessed portion, and together with the fact that some oxide film grows on the oxide film that was not etched, the alignment marks W, l, Wl2 as a whole are It is configured as a recess with a step on the surface. The concave portions of the alignment marks Wll and Wl2, in other words, the step portions, can be recognized as interference colors when viewed from the substrate. The second layer photomask has an alignment mark M2l that is aligned with either alignment mark Wl or Wl2 (W, , in FIG. 3) already formed on the substrate and is slightly smaller than the alignment mark. , an annular portion defined by an alignment mark W22 that is smaller than the alignment mark Wl2 and formed by the alignment mark Wl2 and the alignment mark M22, the alignment mark M22 being aligned with the other alignment mark Wl2. An alignment mark M22 having a size that allows alignment of an alignment mark M3 of a third-layer photomask, which will be described later, is provided at .

When superimposing the second layer photomask having such alignment marks M2, M22 on the substrate, this second layer photomask is
The photomask for the second layer is positioned so that the alignment marks M2l, M22 of the photomask for the second layer are aligned with the alignment marks W, , W, 2 on the substrate, which are recognized as the interference colors described above.

Next, the alignment mark M2,,M? ! 2 and its pattern are exposed and transferred onto a photoresist coated on the substrate again, and after development processing, etching is performed. As a result, these alignment marks M2l and M22 form alignment marks W2l as deeper recesses as shown in FIG. 3b.
, W22. Since the oxide film is again formed on the bottom of the recesses as the alignment marks W2l and W22, the entire recess including the previous alignment marks W, l, and Wl2 becomes a stepped recess with a step formed on the inner periphery. . In particular, the stepped portions of the step-like recesses formed as alignment marks W, 2 and W22 have relatively large widths, so even if photoresist is applied again on this substrate, the interference color will not be visible from above the substrate. It is clearly recognized as an annular part by That is, for example, the alignment mark W22 is purple, the alignment mark Wl2 remaining as an annular portion around it is red, and the area around it is yellow. The third layer photomask has a corresponding shape that can be aligned with the annular portion which is a stepped portion divided by the alignment marks Wl2 and W22 already formed on the substrate, for example, a hollow alignment mark M3.
l is provided.

This third layer photomask has alignment mark M3l.
is superimposed on the substrate such that it aligns with the annular portion formed by alignment marks Wl2 and W22 already formed on the substrate. After that, the third layer pattern is exposed and transferred to the photoresist coated on the substrate again, developed,
It is engraved on the substrate through an etching process. When positioning the third layer photomask on the substrate, such annular alignment mark M3l can be aligned with both alignment marks M12 and W22 so that the margin thereof is equal. As described above, according to the present invention, the alignment mark of the photomask having the third layer pattern is the alignment mark Wl2 formed by the first layer photomask already formed on the substrate and the alignment mark Wl2 formed by the second layer photomask. Since an equal margin can be given to W22, matching can be performed quickly.

Also, when superimposing the third layer photomask on the substrate,
One alignment mark is enough to observe. Moreover, since the alignment mark M3l is aligned with the annular portion defined by the alignment marks Wl2 and W22, when the first layer photomask and the second layer photomask are superimposed on the substrate, Even if there is an error in positioning, if the alignment mark M3l is aligned with alignment marks W, 2, and W22 as references when overlapping the third layer photomask, the error added to the above error can be eliminated. This eliminates the occurrence of this problem, allowing extremely accurate positioning on the substrate. FIG. 4 shows another embodiment of the invention.

An example in which the sizes of the alignment mark Ml2 provided on the first layer photomask and the alignment mark M22 provided on the second layer photomask are reversed compared to the embodiment shown in FIG. It is. In this case, the process of marking the second layer alignment mark M22 on the substrate will be briefly explained. A small alignment mark W, 2 has already been formed as a recess on the substrate, and the alignment mark M22 is exposed and transferred to a photoresist coated on the substrate, and after development processing, it is etched. At that time, when aligning the large alignment mark M22 on the second layer photomask with the small alignment mark Wl2 on the substrate, if a see-through mask is used for the photomask, the large alignment mark M22 can be aligned with the small alignment mark W, 2 on the substrate. There is no problem with matching. By etching the part of the substrate corresponding to this alignment mark M22, the substrate surface at the bottom of the small alignment mark Wl2 and the oxide film formed under the surface are removed, resulting in a deeper recess. Since the oxide film around the concave portion is also removed in a shape corresponding to the alignment mark M22 and is shallower than the concave portion, as a result, the step-like shape formed by the alignment marks W, 2 and W22 is removed as in the case of the embodiment shown in FIG. A concave portion is formed, and the stepped portion can be recognized as an annular portion by interference color. Therefore, even in such an embodiment, the alignment mark M3l of the third layer photomask is aligned with the alignment marks W, 2 and W22 already formed on the substrate by leaving equal margin between them. If the photomask is positioned as shown and superimposed on the substrate, an effect similar to that of the embodiment shown in FIG. 3 will be produced.

In both of the above-mentioned embodiments, alignment marks were formed on the substrate using a negative resist, but even when a positive resist was used, the above-mentioned concave portions only became convex portions, and the alignment marks were formed in a stepped shape. can do.

Further, in both of the above two embodiments, the alignment mark was formed on the substrate by etching, but in the present invention, as in the past, the shape corresponding to the alignment mark of the photomask can be etched on the substrate as unevenness. It is not necessary to limit the marking means to etching. Furthermore, its shape is not limited to the square shape shown in the figure, but can be applied to any shape of commonly used overlay marks. In either case, for the two matching alignment marks engraved by the first and second layer photomasks, there is a mark on the third layer photomask that can be aligned between the two marks. The effects of the present invention are produced by providing alignment marks. As described above, according to the pattern forming mask positioning method of the present invention, when the patterns formed on the first layer, the second layer, and the third layer are exposed and transferred onto the substrate and are stamped, Because positioning of the photomask for each layer can be done extremely easily and accurately,
The pattern finally formed on the substrate has very high precision.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams for explaining a conventional pattern-forming mask positioning method, and FIGS. 3 and 4 are diagrams for explaining respective embodiments of a pattern-forming mask positioning method according to the present invention. It is. Ml,,M,2... Alignment marks formed on the first layer photomask, Wll, Wl2... Alignment marks engraved on the substrate for the first layer, M2l, M22
... Alignment marks provided on the second layer photomask, W2l, W22... Alignment marks of the second layer engraved on the substrate, M3l... Third Alignment marks made on the photomask of each layer.

Claims (1)

[Claims] 1. A first mask having first and second alignment marks is superimposed on a substrate, and the first and second alignment marks are imprinted on the substrate together with the pattern of the first mask. applying a second mask having a third alignment mark smaller than the first alignment mark and a fourth alignment mark smaller than the second alignment mark to the substrate; imprinting the third and fourth alignment marks on the substrate together with the pattern of the second mask in superimposition such that each of the alignment marks aligns with the first and second alignment marks on the substrate; and a third mask having a fifth alignment mark having a shape in which a portion smaller than the second alignment mark and slightly larger than the fourth alignment mark is removed, is attached to the substrate to form the fifth alignment mark. and imprinting the fifth alignment mark on the substrate together with the pattern of the third mask so as to further align with the second and fourth alignment marks on the substrate. How to position the mask. 2. superimposing a first mask having first and second alignment marks on the substrate and imprinting the first and second alignment marks on the substrate together with the pattern of the first mask; A second mask having a third alignment mark smaller than the alignment mark and a fourth alignment mark larger than the second alignment mark is applied to the substrate so that each of the third and fourth alignment marks imprinting the third and fourth alignment marks on the substrate together with the pattern of the second mask in alignment with the first and second alignment marks on the substrate; A fifth alignment mark having a shape in which a portion smaller than the alignment mark and slightly larger than the second alignment mark is removed.
superimposing a third mask having alignment marks on the substrate such that the fifth alignment mark further aligns with the second and fourth alignment marks on the substrate; A method for positioning a pattern forming mask, comprising the step of stamping the fifth alignment mark on the substrate together with the pattern.