JPH0750672B2 - Exposure method - Google Patents

Description

The present invention relates to an exposure method, and is useful for a lithography technique which is necessary when manufacturing a semiconductor device, for example.

(B) Conventional Technique This type of exposure method irradiates an energy beam for exposure onto a pattern mask and transfers the pattern of this mask onto an object to be exposed. From the viewpoint of throughput, X-ray lithography that uses X-rays as energy rays for exposure is regarded as promising.

X-ray lithography has difficulties in forming a pattern mask used for the X-ray lithography and reduction exposure, but it has been proposed to use a Bragg reflection type mask as a technique for improving them (Japanese Patent Laid-Open No. 61-168917). reference). That is, in this method, as shown in FIG. 4, the exposure X-rays (1) are Bragg-reflected by the mask (2) and then directed toward the object (3) to be exposed. The mask (2) is composed of a substrate (4) capable of Bragg reflection with respect to exposure X-rays and a large absorber (5) capable of absorbing exposure X-rays, which form a mask pattern. Substrate (4) and absorber (5)
Are formed of, for example, Si single crystal and Au, respectively. The object to be exposed (3) is, for example, a semiconductor substrate (6) such as Si having a resist film (7) deposited on the surface thereof.

Therefore, when the monochromatic X-ray (1) is incident on the surface of the mask (2) at the Bragg angle θ, Bragg reflection occurs only in the portion where the absorber (5) is absent, and the exposed object (3) is reflected by the reflected X-ray (3). 1B), the exposure pattern reduced by Sinθ of the pattern dimension of the mask (2) in the horizontal direction in the figure is transferred to the exposed body (3).

(C) Problems to be Solved by the Invention In the above mask structure, as shown in FIG. 5, the incident X-rays (1A) and the reflected X-rays (1B) have a black angle θ with respect to the mask substrate (4). Therefore, X-rays pass through the corners of the absorber as shown by the dotted lines in the figure at the pattern edge of the absorber (5). As a result, partial X-ray absorption occurs, resulting in a gentle intensity distribution as shown in the X-ray intensity distribution shown by the curve (10) in the figure, and the reflected X-rays (1B) are reflected by the mask (2). Pattern is not faithfully reflected, resulting in poor pattern transfer accuracy.

(D) Means for Solving the Problems In order to solve the above-mentioned drawbacks, the present invention comprises a base (4) and an absorber (5) in the structure of the mask (2) as shown in FIG. The feature is that they are arranged on the same plane.

(E) Action According to the present invention, as shown in FIG. 2, the incident X-ray (1A) is reflected without being blocked by the absorber (5). Since the Bragg reflection occurs only on the outermost surface of the mask substrate (4), the reflected X-ray intensity becomes sharp according to the mask pattern without being attenuated even at the pattern edge as shown by the line (11) in the figure. .

(F) Embodiment FIGS. 1 and 2 show an embodiment of the present invention, in which a mask (2) is used.
A Si single crystal having a (111) plane is used for the substrate (4) constituting the above, and Au is used for the absorber (5). X for exposure
When the wavelength of the line is 4Å, the Bragg angle is 40 degrees.

In order to obtain a mask contrast of 10 or more, the X-ray intensity reflected by the substrate below the absorber (5) becomes 1/10 or less of the X-ray intensity reflected by the portion not covered by the absorber. Thus the thickness t of the absorber (5) must be chosen. Since Au has a linear absorption coefficient of 3 μm ⁻¹ for a wavelength of 4 Å, the absorption path of X-rays required to obtain contrast 10 is 7700 Å, but since X-rays are incident at the Bragg angle, The thickness t of 5) is set to about 4900Å.

FIG. 3 shows a manufacturing procedure of the mask (2) used in this embodiment. First, a resist (12) is applied to the entire surface of the substrate (4) (Fig. A), and then patterned by photolinography or electron beam drawing (Fig. B). Then, the substrate (4) is dry-etched with CF ₄ + O ₂ gas using the patterned resist (12) as an etching mask (FIG. C), and Au (5A) is deposited (FIG. D). Finally, dissolve the resist (12) with a solvent and lift off Au on it,
The mask (2) is completed by leaving Au as the absorber (5) on the same surface as the surface of the substrate (4).

Although the mask substrate surface and the crystal plane are parallel to each other in the above-mentioned embodiment, the mask substrate surface and the crystal plane may have an offset angle α. In that case, the reduction ratio changes to Sin (θ−α) due to asymmetric Bragg reflection. In addition, if the Bragg reflection is possible as the energy beam for exposure,
Other than X-ray, for example, particle beam may be used. Further, the mask substrate (4) may be other than Si as long as it is a single crystal. The absorber (5) may be a material having a large atomic number such as W or Ta, other than Au. As a method for forming the absorber (5), a sputtering method may be used instead of vapor deposition, and wet etching may be used for etching the mask substrate (4). Other modifications that do not impair the essence of the present invention are allowed.

(G) Effect of the Invention According to the present invention, the exposure energy ray is Bragg-reflected by the mask and then directed toward the exposure target, and the exposure pattern corresponding to the pattern formed on the mask is transferred to the exposure target. In this method, the energy ray incident on the mask is almost completely absorbed by the absorber or is reflected without being blocked by the absorber at all, so that the reflected energy ray intensity is sharp corresponding to the mask pattern. Therefore, highly accurate pattern transfer exposure becomes possible.

[Brief description of drawings]

1 to 3 are for explaining an embodiment of the present invention. FIG. 1 is a sectional view of a mask, FIG. 2 is an enlarged sectional view showing reflection of X-rays on the mask surface, and FIG. 5A to 5E are cross-sectional views for each step showing a mask manufacturing procedure, FIG. 4 is a cross-sectional view showing a conventional example, and FIG. 5 is an enlarged cross-sectional view of the relevant part. (1) ... X-ray, (2) ... Mask, (3) ... Exposed object, (4) ... Substrate, (5) ... Absorber.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G03F 7/20 521 9122-2H

Claims (1)

[Claims] 1. An exposure method in which an energy beam for exposure is Bragg-reflected by a mask, then directed toward an object to be exposed, and an exposure pattern corresponding to a pattern formed on the mask is transferred to the object. The reflective surface of the mask is
An exposure method comprising a substrate capable of Bragg reflection and an absorber that absorbs the energy rays, and the surfaces of the substrate and the absorber are in the same plane.