JPS60121449A - Mask for exposure - Google Patents

Abstract

PURPOSE:To prevent sticking foreign matters onto the surface of a pattern and to prevent images of foreign matters on the surface of a mask from being resolved on a base material by forming a film coating the pattern provided on the main face of a substrate so that the face in the side opposite to the substrate of this film is at a prescribed distance from the substrate and is parallel with the main face of the substrate approximately. CONSTITUTION:In a mask 1 for exposure consisting of a substrate 1a, a pattern 1c provided on its main face, and a film 1b coating the pattern 1c, the face in the side opposite to the substrate 1a of the film 1b is at a prescribed distance from the substrate and is parallel with the main face of the substrate approximately. Since this transparent shielding plate 1b is formed on the pattern 1c in the mask for exposure, foreign matters from the external are not stuck onto the pattern 1c but are stuck onto the shielding plate 1b. When this mask is used for exposure, images of foreign matters 4 are not focused on the surface of a base material (wafer) 3 and are blurred as images 6 and are not resolved because stuck foreign matters 4 are distant from the pattern 1c. Thus, foreign matters 4 are not defects in the exposure process to prevent degradation of yield.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure method and the structure of an exposure mask used in a patented projection aligner. Generally IC and LSI
Yield is an issue in the manufacture of products in which fine patterns such as the following are formed by photolithography. One of the causes of yield reduction is defects that occur during exposure in the photolithography process, which is a particularly serious problem in LSI manufacturing. Therefore, the density of defects that occur during exposure is one of the major factors that determines the exposure method. Exposure methods can be roughly divided into two types: a contact exposure method in which an exposure mask and a substrate (wafer) are brought into close contact with each other for exposure, and a projection method in which a pattern from an exposure mask is projected onto a substrate (wafer) for exposure. Projection type exposure has the advantage that the exposure mask does not wear out compared to contact type exposure, but on the other hand, compared to contact type exposure, foreign matter attached to the pattern surface of the exposure mask is more likely to be deposited on the substrate (wafer). It has the disadvantage that it is easily resolved. Therefore, in the projection type exposure method, foreign matter adhering to the surface of the exposure mask is the main cause of a decrease in yield. For this reason, in the conventional projection exposure method, the exposure mask must be cleaned frequently, reducing the practicality of the projection aligner.

For example, a photomask in which the mask surface is coated with a transparent coating for antireflection is disclosed in Japanese Patent Laid-Open No. 114306/1983.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure method that solves the above-mentioned problems of the conventional projection exposure method and improves the practicality of the projection exposure method. In order to achieve such objects, the present invention prevents IC foreign matter from adhering to the pattern surface of the exposure mask, and prevents foreign matter adhering to the surface of the exposure mask from being resolved onto the substrate (wafer). This realizes a projection-type exposure method.

Hereinafter, the present invention will be specifically explained using examples. 1st
The figure is a sectional view of an exposure mask that is an embodiment of the present invention. As schematically shown in FIG. 1, there is a pattern 1c on a substrate la of an exposure mask to be transferred to a substrate (wafer). The exposure mask of the present invention is characterized by having a transparent shielding plate or a transparent coating film 1b on the pattern lc.

In this case, the foreign matter from the outside is not on the pattern lc,
It is deposited on a transparent shielding plate or a transparent coating film lb. In the embodiment shown in FIG. 1, a 200 μm thick quartz glass plate was used as the transparent shielding plate or transparent coating film 1b, and was bonded to the substrate 1a using an epoxy adhesive at the peripheral portion 1d of the exposure mask. In addition to quartz glass, various oxides and various organic resins can be used as the transparent shielding plate or transparent coating film 1b, and adhesion and coating with the substrate 1a or pattern 1c can be easily realized using existing techniques. The thickness of the transparent shielding plate or the transparent coating film 1b is an important parameter that affects the effectiveness of the present invention against foreign substances, and is usually expressed as
Although it is in the range of 0 μm to several 100 μm, it is desirable to determine it so as to satisfy the relationship of the following equation (1). For example, 3 μm
For foreign particles of a certain size, the thickness of 1b should be approximately 30 μm.
Based on the above, when foreign matter of about 2 μm in size becomes a problem, it is desirable to set the thickness to 20 μm or more.

D>Dankoyu ・・・・・・・・・ （1）Here, D
; Thickness d of the transparent shielding plate or tracing film; Size L(d) of the foreign object in question; Depth of focus n of the aligner with respect to d; Refractive index of the transparent shielding plate or shielding film Next, use the mask of the present invention. The projection exposure method used will be explained in comparison with a conventional projection exposure method. FIG. 2 shows a conventional projection type exposure method, and FIG. 3 schematically shows a projection type exposure method using the mask of the present invention. In Figures 2 to 3, 2
represents the entire optical system of a projection aligner, and is generally composed of a lens group or a reflecting mirror group. 1 in FIG. 2 is a conventional exposure mask, and 1 in FIG. 3 is an exposure mask having the structure shown in FIG. 1 according to the present invention having a transparent shielding plate or a transparent coating film. In FIGS. 2 and 3, the light that has passed through the pattern 1c of the exposure mask is reflected or refracted by the optical system 2, forming a real image 5 of the pattern 1c on the surface of a substrate (wafer) 3 coated with photoresist. In FIGS. 2 and 3, the optical system 2 of the aligner is adjusted so that the pattern 1c of the exposure mask forms a real image 5 on the substrate (wafer). In the conventional exposure method shown in Figure 2, foreign particles 4
is attached at the same position as the pattern 1c of the exposure mask.

Therefore, when the image 5 of the pattern 1c is formed on the surface of the substrate (wafer) 3, the image 6 of the foreign object 4 is also formed on the surface of the substrate (wafer) 3.
Since the image is formed on the surface of the film, it becomes a defect during exposure and leads to a decrease in yield. On the other hand, in FIG. 3, which shows the exposure method using the mask of the present invention, since the pattern 1c and the attached foreign matter 4 are separated from each other, the image of the foreign matter 4 is not formed on the surface of the substrate (wafer) 3. In this case, foreign matter 4 on the surface of the substrate (wafer) 3
A blur occurs in the image 6, and the blurred image 6 is not resolved by development. Therefore, the foreign matter 4 shown in FIG. 3 does not become a defect in the exposure process, and a decrease in yield due to the foreign matter 4 can be prevented.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an exposure mask structure according to an embodiment of the present invention. FIG. 2 is a sectional view of the main parts of an exposure apparatus for explaining a conventional projection-type exposure method, and FIG. 3 is a main part of an exposure apparatus for explaining a projection-type exposure method using a mask of the present invention. FIG. 1a... Exposure mask substrate, 1b... Transparent shielding plate (quartz glass plate 200μ), 1c... Exposure mask pattern, 1d... Adhesion part between transparent shielding plate and substrate, 2. ... Optical system representing the entire optical system of the projection aligner, 3... Photoresist coated substrate (
wafer), 4... Foreign matter attached to the exposure mask, 5
. . . Image of the pattern of the exposure mask on the photoresist coating film, 6 . . . Image of foreign matter on the photoresist coating film. Figure 1 - Figure 2

Claims (1)

[Claims] 1. a substrate; a pattern provided on the main surface of the substrate;
an exposure mask comprising a film covering the pattern, wherein a surface of the film opposite to the substrate is located at a predetermined distance from the substrate and substantially parallel to the main surface of the substrate. .