JPS61283124A - Alignment for mask and wafer - Google Patents

Abstract

PURPOSE:To enable accurately the alignment of a mask on a wafer by forming an interfering light preventive film on the surface of the mask opposed to the wafer side, thereby focusing a focus spot of FZP of high intensity. CONSTITUTION:A mask 11 and a wafer 12 are disposed at a distance D, an FZP mark 13 of focal distance F is formed on the mask 11, and an a FZP mark 14 of focal distance F+D) is formed on the wafer 12. An interfering light preventive film 17 is formed on the side of the mask 11 at the side opposed to the wafer 12. Thus, parallel light beam 15 passing the mask 11 again passes the mask 11 at the reflected light from a region 15 except the FZP mark of the wafer 12 to eliminate the interference with the spot focused on a point P2. The absorption and the reflection are executed by the film 17 without passing the surface of the mask 11 at the interfering light by the film 17, and the light is gradually attenuated in the gap between the mask 11 and the wafer 12. As a result, the focus spot intensity due to the reflection of the FZP mark becomes fresh to accurately align the mask 11 on the wafer 12.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a Fresnel zone plate (FresnelZ
One Plate (hereinafter abbreviated as FZP) is a method for aligning a wafer and a mask, in which most of the coherent parallel light beams (usually laser beams are used) incident on the mask reach the wafer surface, where they are Reflects on the mask side.

Of the reflected light, the reflected light from the FZP mark forms a focal spot at a predetermined position, but there is also reflected light from areas other than the FZP mark (hereinafter referred to as interference light), and they interfere with each other. In order to blur 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 so that the interference light reflected from the wafer surface does not pass through the mask surface. However, accurate mask and wafer alignment is achieved by imaging a focal spot of FZP with strong brightness.

[Industrial Application Field] In X-ray exposure, the present invention accurately detects the imaging of a focal spot reflected from FZP marks formed on the surfaces of a mask and a wafer with high sensitivity. This relates to a method for precise alignment.

Recently, extremely precise and minute patterning is required for semiconductor devices, display devices, optical application equipment, etc., and for this purpose, various high-precision exposure methods have been changed from optical exposure to X-ray exposure and electron beam exposure. It is being considered.

In these exposure methods, it is extremely important to accurately set the mutual positional relationship and spacing between the mask and wafer in order to eliminate pattern shift and defocus. When performing this, alignment using FZP marks is considered as one of the alignment methods.

In this FZP method, on each of the wafer and mask surfaces,
When a parallel beam of light is projected onto an FZP mark consisting of a group of lines arranged according to a certain rule, the reflected light forms an image at a focal point at an accurate distance due to a diffraction phenomenon.Using this fact, the image formation position is detected. By doing this, the distance and spacing between the mask and the wafer are detected, and alignment is performed through automatic control.

For example, if the distance between the mask and the wafer is D, different FZP marks are formed on both sides of the mask and the wafer, and the focus of the FZP mark on the mask is F and the focus of the wafer is (F+D), each Since the reflected light is focused on the (F+D) point at the same distance, the distance and positional deviation between the mask and wafer can be confirmed at the same time by comparing their spot brightness and comparing the positional deviation. It turns out.

However, the projected light that has passed through the mask is also reflected on the wafer surface unrelated to the FZP and becomes interference light, and this interference light interferes with the light reflected from the FZP mark, degrading the focal brightness and reducing sensitivity. Since this is an inconvenience, improvements to this are desired.

[Prior Art] FIG. 2 is a sectional view of a main part showing a method of aligning a wafer and a mask using the conventional FZP method.

The right and left sides of mask I and wafer 2 are shown, spaced apart, with FZP marks 3 of focal length F on mask 1 and focal length (F + D) of wafer 2.
) FZP mark 4 is formed.

When the parallel light ray 5 is projected onto the surface of the mask 1 as shown by the arrow, the focal spot of the FZP mark or Rano reflected light on the mask becomes a point P1 located at a distance of F from the mask surface, and similarly from the wafer 3. The focal spot of the reflected light is a point P2 located 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, P! The horizontal and vertical positional deviations of the 22 points are compared by comparing the brightness differences between the imaged spots, and the positional relationships of the spots are compared to accurately determine the spacing and positional relationship between the mask and the wafer. can be detected.

However, when detecting the mutual position between the wafer and the mask using the FZP method, the parallel light ray 5 passing through the mask 1 is reflected not only from the FZP mark 4 on the wafer 2 but also from the FZP mark 4 on the wafer. Since there is interference light reflected from other areas 6, this interference light passes through the mask I and interferes with the reflected light that forms an image at 22 points, resulting in spot l.
- There are disadvantages such as a decrease in brightness and defocus, which makes comparison of brightness ambiguous and inaccurate positioning.

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

[Means for Solving the Problems] FIG. 1 is a cross-sectional view for explaining an alignment method according to the present invention to solve the above problems. FPZ marks with different focal lengths are formed on the wafer, and when parallel light is incident and the mask and tool are aligned, the reflected light from the area of the wafer where the FZP mark is not formed is detected. This problem was solved by forming an interference prevention film on the surface of the mask facing the wafer side so as not to transmit through the mask surface and interfere with the imaged spot from the FZP mark.

[Function] In the present invention, when an FZP mark is formed on a mask and a wafer surface and the mask and wafer are aligned, a focal spot due to reflection from the FZP mark on the wafer surface;
In order to prevent interference of reflected light from areas other than the FZP mark, a film is formed on the mask surface facing the wafer surface to prevent transmission of the interference light, such as a resist film or magnesium fluoride. By forming a film such as
Interfering light can be prevented.

This anti-interference film naturally has the effect of attenuating the light reflected from the FZP surface of the wafer, but since the light reflected from the F22 surface is normally extremely strong, the anti-interference film of the present invention can reduce its influence. Since the amount of interference is small and there is no interference light, the brightness of the focal spot becomes clear and accurate positioning becomes possible.

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

A mask 11 and a wafer 12 are arranged at intervals, and the mask 1
An FZP mark 13 with a focal length F is formed on the wafer 1, and an FZP mark 14 with a focal length (F+D) is formed on the wafer 12.

In the figure, when a parallel light beam 15 is projected as shown by the arrow, the focal spots of the reflected light from the FZP marks on the mask and the wafer are focused on points P l and P 2,
The brightness of these imaged spots is compared to detect the positional relationship and spacing between the mask and the wafer, as in the conventional method.

The present invention improves the problem of parallel light rays 15 passing through the mask 11 and reflected light from areas 16 other than the FZP mark on the wafer 12 passing through the mask 11 again and interfering with the spots imaged at 22 points. Therefore, in order to prevent this reflected interference light from passing through the mask, an 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, or
Alternatively, magnesium fluoride (MgF) or the like may be coated.

With such an interference light prevention film, the interference light does not pass through the mask surface, but is absorbed and reflected by the interference light prevention film, and is gradually attenuated within the gap between the mask and the wafer.

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

[Effects of the Invention] As explained above in detail, by forming the interference prevention film on the mask surface of the present invention, the interference light from the wafer does not pass through the mask, and therefore a clear focal spot can be obtained. This has the great effect of allowing extremely accurate positioning and submicron exposure.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of main parts for explaining the alignment of a mask and a wafer by the FZP method of the present invention. FIG. 2 is a schematic cross-section of the main parts for explaining the conventional alignment of a mask and a wafer. In the figures, 11 is a mask, 12 is a wafer, and 13.14 is an F.
15 is a parallel ray, 16 is a region other than the FZP plane, and 17 is an interference light prevention film.

Claims (1)

[Claims] Fournel 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 detect reflected light. The method of aligning the mask and the wafer by detecting the focal spot of the mask is characterized in that an interference prevention film (17) is formed on the surface of the mask (11) facing the wafer (12). How to align the mask and wafer.