JPH0666247B2 - Mask and wafer alignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a Fresnel Zone plate (Fresnel Zone P).
(hereinafter, abbreviated as FZP) method, which is a method for aligning a wafer and a mask, and most of coherent parallel light rays (usually using a laser beam) incident on the mask reach the wafer surface, and then reach the mask side. reflect.

Of this reflected light, the reflected light from the FZP mark forms a focal spot at a predetermined position, but there is also reflected light from the area other than the FZP mark (hereinafter referred to as interference light), which interfere with each other. To obscure the image of the focal spot of the reflected light from the FZP mark, an interference light prevention film is formed on the mask surface facing the wafer side so that the interference light reflected from the wafer surface does not pass through the mask surface. FZP with strong brightness
The image of the focal spot of is used to accurately align the mask and the wafer.

[Industrial field of application] The present invention accurately detects the image of the focal spot reflected from the FZP mark formed on the surface of the mask and the wafer in the X-ray exposure with high sensitivity. The present invention relates to a method for performing accurate alignment.

Recently, in semiconductor devices, display devices, optical application devices, etc., extremely precise and minute patterning is required. Therefore, various high precision exposure methods such as optical exposure, X-ray exposure, and electron beam exposure are used as exposure methods. Is being considered.

In these exposure methods, it is extremely important to accurately set the mutual positional relationship between the mask and the wafer and the interval in order to eliminate the pattern shift and the defocus. Especially, the submicron patterning is performed by the X-ray exposure. When performing the alignment, alignment using the FZP mark is considered as one of alignment methods.

In this FZP method, on each of the surface of the wafer and the mask, when a parallel light beam is projected on the FZP mark composed of a plurality of line groups arranged according to a certain law, the reflected light is diffracted,
By utilizing the image formation of a focal point at an accurate distance and detecting the image formation position of the focal point, the distance and interval between the mask and the wafer are detected, and the position is adjusted by automatic control.

For example, when the distance between the mask and the wafer is D, different FZP marks are formed on both surfaces of the mask and the wafer, and the focus of the FZP mark of the mask is F and the focus of the wafer is (F + D), respectively. Since the reflected light of is imaged at the position of the point (F + D) at the same distance, the gap between the mask and the wafer and the positional shift can be confirmed at the same time by comparing the spot luminances and the positional shifts. Will be.

However, the projection light transmitted through the mask is also reflected on the wafer surface unrelated to FZP to become interference light, and this interference light is
Since it interferes with the reflected light from the P mark and deteriorates the focus brightness, and there is a disadvantage that the sensitivity decreases, there is a demand for improvement thereof.

[Prior Art] FIG. 2 is a sectional view of an essential part showing a conventional method for aligning a wafer and a mask by the FZP method.

The right and left sides of the mask 1 and the wafer 2 are shown, they are arranged at a distance D, and the mask 1 has a focal length F
An FZP mark 4 having a focal length (F + D) is formed on the FZP mark 3 and the wafer 2.

When the parallel light rays 5 are projected on the surface of the mask 1 as shown by the arrows, the focal spot of the reflected light from the FZP mark on the mask becomes a point P ₁ at a distance F from the mask surface, and similarly, the wafer 3 The focal spot of the reflected light from is the point P ₂ at a distance of (F + D) from the wafer surface.

Therefore, if the FZP marks on the wafer and mask are set to a predetermined focal length in advance, the horizontal and vertical position shifts of points P ₁ and P ₂ are compared by comparing the brightness differences of the imaged spots. However, by comparing the positional relationship of the spots, it is possible to accurately detect the distance and the positional relationship between the mask and the wafer.

However, the mutual position of such a wafer and mask
When detecting by the FZP method, the parallel rays 5 passing through the mask 1 have not only reflected light from the FZP mark 4 on the wafer 2 but also interference light reflected from the area 6 other than the FZP mark 4 on the wafer. In addition, the interference light passes through the mask 1 and interferes with the reflected light that forms an image at the point P _{2, and} there is an inconvenience such as a decrease in the brightness of the spot and defocusing. Therefore, comparison of the brightness is dazzling. Therefore, there is a drawback that the alignment becomes inaccurate.

[Problems to be Solved by the Invention] In conventional alignment of the mask and the wafer by the FZP method, interference light from a region other than the FZP mark on the wafer interferes with the reflected light from the FZP mark, The problem is that the focal spot due to the reflected light from the FZP mark is obscured.

[Means for Solving the Problems] FIG. 1 is a cross-sectional view for explaining the alignment method according to the present invention for solving the above problems. The means for solving the problems are a mask and a wafer surface. , FPZ marks with different focal lengths are formed, and parallel rays are incident on the wafer to align the mask and the wafer.
An interference prevention film is formed on the surface of the mask facing the wafer side so that the reflected light from the area where the FZP mark is not formed does not pass through the mask surface and interfere with the image spot from the FZP mark. It has been solved by doing.

[Operation] According to the present invention, when the FZP mark is formed on the mask and the wafer surface and the mask and the wafer are aligned, the focal spot due to the reflection from the FZP mark on the wafer surface and the F
In order to prevent interference of reflected light from areas other than the ZP mark, a film that blocks transmission of interference light is formed on the mask surface facing the wafer surface. For example, a resist film or magnesium fluoride. Interfering light can be prevented by forming the film.

This anti-interference film naturally has an attenuating action also on the reflected light from the FZP surface of the wafer, but since the reflected light from the FZP surface is usually extremely strong, it is affected by the interference light prevention film of the present invention. The amount of light received is slight, and since there is no interference light, the brightness of the focal spot becomes clear and accurate alignment becomes possible.

[Embodiment] FIG. 1 is a schematic cross-sectional view of a principal part for explaining the alignment of a mask and a wafer by the FZP method of the present invention.

The mask 11 and the wafer 12 are arranged at an interval D, and the mask 11 has an FZP mark 13 having a focal length F and an FZP mark 14 having a focal length (F + D) formed on the wafer 12.

In the figure, when the parallel rays 15 are projected as shown by the arrows,
The focal spots of the reflected light from the FZP marks on the mask and wafer are imaged at points P ₁ and P _2, and the brightness of these imaged spots is compared to determine the positional relationship between the mask and the wafer and the distance between them. Is the same as the conventional one.

According to the present invention, the parallel rays 15 that have passed through the mask 11 are
In order to improve that the reflected light from the area 16 other than the FZP mark retransmits the mask 11 and interferes with the spot imaged at the point P ₂ , the reflected interference light does not pass through the mask. The interference light prevention film 17 is applied to the mask surface facing the wafer.

The interference light prevention film may be a normal photoresist film,
Alternatively, magnesium fluoride (MgF) or the like may be applied and deposited.

With such an interference light prevention film, the interference light is absorbed and reflected by the interference light prevention film without passing through the mask surface, and is gradually attenuated within the gap between the mask and the wafer.

As a result, the brightness of the focal spot due to the reflected light from the FZP mark becomes clear, and accurate wafer-mask alignment becomes possible.

[Effects of the Invention] As described in detail above, by forming the interference prevention film on the mask surface of the present invention, interference light from the wafer does not pass through the mask, and therefore a clear focal spot can be obtained. This makes it possible to perform extremely precise alignment, which makes it possible to perform submicron exposure.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part for explaining the alignment of a mask and a wafer by the FZP method of the present invention, and FIG. 2 is a schematic cross-sectional view of an essential part for explaining the alignment of a conventional mask and a wafer. In the figures and figures, 11 is a mask, 12 is a wafer, 13 and 14 are FZP planes, 15 are parallel rays, 16 is a region other than the FZP plane, and 17 is an interference light prevention film.

Claims (1)

[Claims] 1. Fresnel zone plate marks (13) and (14) are formed on the surfaces of a mask (11) and a wafer (12), respectively, and a parallel light beam (15) is incident on the mask surface to reflect reflected light. In the method of detecting the focal spot and aligning the mask and the wafer, an interference prevention film is formed on the surface of the mask (11) facing the wafer (12) side.
A method for aligning a mask and a wafer, wherein (17) is formed.