JPH0463415A - Positioning mark and formation thereof - Google Patents

Abstract

PURPOSE:To obtain an alignment signal with a high S/N ratio and enable relative positioning of a mask and a wafer to be performed highly accurately by forming a mark with a high reflectivity metal film. CONSTITUTION:A diffraction grid (mark) 13 is formed by a high reflectivity metal film, thus obtaining a sufficiently high reflection light intensity without depending on the film thickness, a sufficiently large alignment signal, a sufficient difference between reflection intensity of the mark 13 and that of a thin film 11, and highly accurate relative positioning of the mask and the wafer. Also, it is not necessary to consider refractive index of the mark and a resist film 14 which is coated on it, thus obtaining a sufficiently large alignment signal. Thus, it is possible to perform relative positioning of the mask and wafer highly accurately.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to alignment marks (hereinafter referred to as
mark) and its formation method.

As the density of LSI increases, the IC patterns formed on wafers have reached the submicron range, and the exposure light source used to transfer the patterns onto the wafers has also changed from the conventional g
Deep UV or X-rays in a shorter wavelength region than the i-rays and i-rays are being considered. With the miniaturization of IC patterns, the relative positioning accuracy between the X-ray mask pattern and the wafer pattern is also required to be increasingly precise, and the marks formed on the wafer are also required to have high-precision relative positioning. Special efforts are needed to make this a reality.

[Conventional technology]

When performing relative positioning between the X-ray mask and the wafer,
Linear Fresnel zone play on x-ray mask
(LFZP), while forming a linear diffraction grating (LFZP) on the wafer.
The laser beam is applied to the LFZP of the X-ray mask, focused on the diffraction grating (mark) on Ueno 1, and the reflected diffraction light from the diffraction grating (mark) is detected. mark) and relative positional deviation (
In other words, the relative positional deviation between the X-ray mask and the wafer is detected. Such a positioning method using LFZP is shown in, for example, Nikkei Microdevice, April 11986 issue, pages 123 to 127, and Japanese Patent Application Laid-open No. 1-106427.

FIG. 3 is a diagram showing how an alignment signal (positioning signal) is obtained using LFZP.

The X-ray mask L has an opaque part such as an absorber and a transparent part.
On the other hand, a linear diffraction grating (mark) 4 is formed on the wafer 3 using, for example, silicon oxide or silicon nitride, and a parallel laser beam 5 is formed on the LFZP2.
irradiate. Here, the laser beam 5 incident on LFZP2
connects the fish on the surface of the sea urchin L-3, creating a slit-shaped image. When the formed slit image and the diffraction grating (mark) 4 overlap in a straight line, the laser beam 5 is diffracted and returns to the LFZP.
2, the light becomes parallel light, and an alignment signal can be extracted by a detector (not shown).

The LFZP 2 and the diffraction grating (mark) 4 are provided at 3 locations on the mask 1 and the wafer 3, respectively, and by analyzing the alignment signals obtained from these 4 locations, the relative positional deviation between the mask 1 and the wafer 3 can be determined. , and thereby perform their relative positioning.

[Problem to be solved by the invention]

The conventional diffraction grating (mark) 4 is made of silicon oxide or silicon nitride, and the relationship between its film thickness and reflected light intensity is as shown in FIG.
It can be seen that there is considerable variation in the intensity of light reflected by the standing liquid depending on the film thickness of 4 and the wavelength of laser light 5. Therefore, unless the film is formed accurately to a thickness that maximizes the intensity of reflected light, a sufficient alignment signal cannot be obtained.

Further, when the refractive index of the material of the diffraction grating (mark) 4 and the refractive index of the material of the resist film (not shown) covering it are approximately equal, the intensity of the reflected light decreases, and in this case as well, the alignment signal I can't get enough of it.

In this way, if the film thickness of the diffraction grating (mark) 4 cannot be formed accurately or if the refractive index of the diffraction grating (mark) 4 is the same as that of the resist film, it is difficult to obtain a sufficient alignment signal. This results in an error in the alignment between the LFZP 2 and the diffraction grating (mark) 4, and as a result, there is a problem in that the relative alignment between the mask 1 and the wafer 3 cannot be performed accurately.

SUMMARY OF THE INVENTION An object of the present invention is to provide an alignment mark that can obtain a sufficient reflected light intensity and an alignment signal with a high signal-to-noise ratio.

[Means to solve the problem]

FIG. 1 shows a diagram explaining the principle of the present invention. In the figure, 13 is a diffraction grating (mark), which is made of a metal film with high reflectance. The manufacturing process includes a step of forming a resist pattern (not shown) for forming a mark on the substrate 10, and a step of coating this resist pattern (not shown) with a metal film having a high reflectance. The method includes a step of lifting off the pattern to obtain marks 13 of a high reflectance metal film.

[Effect]

In the present invention, since the diffraction grating (mark) 13 is formed of a high reflectance metal film, it is possible to obtain a sufficiently high reflected light intensity without depending on the film thickness, and to obtain a sufficiently large alignment signal. This allows a sufficient difference between the intensity of the reflected light at the mark 13 portion and the intensity of the reflected light at the thin film 11 portion to be maintained, allowing for highly accurate relative alignment between the mask and the wafer. Further, there is no need to take into account the refractive index of the mark and the resist film 14 covering it.
An alignment signal of sufficient size can be obtained.

〔Example〕

FIG. 2 shows a manufacturing process diagram for manufacturing an embodiment of the present invention. In FIG. 1A, a thin film 11 of silicon oxide, PSG, or the like is deposited on a silicon substrate 10. As shown in FIG. Next, in the same figure (B), a resist film 12 is formed on the surface,
Holes 12a are formed at predetermined locations in the resist film 12 in order to form marks later. This is formed by transfer using g-rays, i-rays, electron beams, X-rays, or the like.

Next, as shown in FIG. 2C, the thin film 11 is etched using the resist film (resist pattern) 12 as a mask.

The above steps (A) to (C) in the same figure are performed at the same time as forming an IC pattern (not shown) on this wafer.

Subsequently, in FIG. 1D, a highly reflective metal film 13a made of, for example, tungsten is deposited around the hole 12a. This highly reflective metal film 13 is formed using W(CO)6 gas and G
This is done by FIB (focused ion beam) growth using a-ions. At this time, a highly reflective metal film 13a is formed not only inside the hole 12a but also on the surface of the resist film 12.

Next, the resist film (resist pattern) 12 is removed using a resist stripping solution to obtain a highly reflective metal film 13 (diffraction grating (mark)) as shown in FIG. Next, the same figure (F
), a resist film 14 for forming a new IC pattern is formed on the surface.

Here, as shown in FIG.
The reflected light intensity of the beam light 5 in the part can be obtained sufficiently high without depending on the film thickness if the high-reflection metal film 13 has a film thickness above a certain level, and a sufficiently large SN
It is possible to obtain an alignment signal with a high ratio. As a result, a sufficient difference can be made between the intensity of reflected light at the highly reflective metal film 13 and the intensity of reflected light at the thin film 11, and the relative alignment between the mask and the wafer can be performed with high precision. . In addition, since the diffraction grating (mark) 13 is formed of a highly reflective metal film, there is no need to take into account the respective refractive indices of the diffraction grating (mark) and the resist film 14 as in the conventional example. A magnitude alignment signal can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, since the mark is formed with a high reflectance metal film, it is possible to obtain an alignment signal with a high S/N ratio without depending on the film thickness or the resist film covering it. Relative positioning with the wafer can be performed with high precision.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention. FIG. 2 is a manufacturing process diagram for manufacturing an embodiment of the present invention. FIG. 3 is a diagram showing how to obtain an alignment signal using LFZ, P. FIG. 4 is a diagram showing the relationship between the thickness of a diffraction grating and the intensity of reflected light in a conventional example. In the figure, 5 is a laser beam, 10 is a silicon substrate, 11 is a thin film, 12 is a resist film (resist pattern), 12a is a hole, 13 is a high reflectance metal film (diffraction grating (mark) 13a is a high reflectance metal film) , 14 indicates a resist film. Patent applicant: Fujitsu Ltd. l\-11 (A) FIGS. 2 and 10 A diagram explaining the principle of the present invention. FIG. Figure 3 Thickness of the diffraction grating Figure 4 shows the relationship between the thickness of the diffraction grating and the reflected light intensity in the conventional example

Claims (2)

[Claims] (1) In the grid-like positioning mark used for relative positioning with the mask on which the Fresnel zone plate is formed, positioning is characterized by being formed of a metal film (13) having high reflectance. mark. (2) In the method for forming a grid-like alignment mark used for relative alignment with a mask on which a Fresnel zone plate is formed, a resist pattern (12) for forming a mark is formed on a substrate (10). and a step of depositing a metal film (13a) having a high reflectance on the resist pattern (12) and lifting off the resist pattern (12) to obtain a mark (13). How to form alignment marks.