JPH07333824A - Photomask - Google Patents

Abstract

PURPOSE:To provide a photomask being a halftone phase shift mask on which plural fine openings or formed with fine openings having two-dimensional periods are formed and which is capable of suppressing the sub-peaks generated in non-exposed parts without lowering the transmittance of translucent phase shift films. CONSTITUTION:The photomask in which the fine openings 3 having the two-dimensional periods are formed on the translucent phase shift film 2 formed on a transparent substrate 1, is so constituted that the pitch in one direction of the fine openings 3 is made to be 2.5lambda/NA on an imaging plane and the pitch in a direction orthogonal therewith is made to be 2.5lambda/NA or 1.48lambda/NA (wherein lambda is a wavelength [mum[ of exposing light and NA is the numerical aperture of an exposure device).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask,
More specifically, the present invention relates to a halftone phase shift mask in which a plurality of fine openings (hereinafter referred to as hole patterns) are formed or a hole pattern having a two-dimensional period is formed.

[0002]

2. Description of the Related Art As shown in FIG. 1, a so-called halftone phase in which a phase-reversing semitransparent phase shift film 2 is formed on a transparent substrate 1 and a hole pattern 3 is formed on the phase shift film 2. When the hole pattern is exposed and developed using the shift mask, the resolution is improved due to the interference between the light transmitted through the hole 3 and the light transmitted through the semitransparent phase shift film 2 having a phase difference of 180 °, and the focus is improved. It is known that the depth also increases.

Since the phase shift film 2 is semi-transparent, some light intensity is generated even in the non-exposed portion on the wafer. Therefore, the light transmittance of the semi-transparent phase shift film 2 is changed by the resist in the non-exposed portion. It is necessary to set and use it so that it will not dissolve by development.

[0004]

When the hole patterns of the halftone phase shift mask are formed close to each other, as shown in FIG. 7, in addition to the hole transmitted light 5, the transmitted light of the semitransparent phase shift film 2 is transmitted. A phenomenon occurs in which the sub-peak 6 having a light intensity that is 40 to 90% higher than the intensity is generated in the non-exposed portion, and the non-exposed portion is exposed. This sub-peak is generated when the first-order maximum of the diffraction image by the transmitted light of the hole pattern 3 is added to the transmitted light intensity of the semitransparent phase shift film 2. Therefore, in order to prevent the non-exposed portion from being exposed, the transmissivity of the semitransparent phase shift film 2 needs to be lowered, but if the transmissivity is lowered, the resolution and the depth of focus deteriorate.

An object of the present invention is to eliminate this drawback, and to provide a photomask capable of suppressing the sub-peak generated in the non-exposed portion without lowering the transmittance of the semitransparent phase shift film. is there.

[0006]

The above object can be achieved by any of the following means.

The first means is to use one fine opening in a photomask in which a plurality of fine openings (3) are formed in a semitransparent phase shift film (2) formed on a transparent substrate (1). The distance between the center and the center of the minute aperture adjacent to this one minute aperture is the first maximum of the diffraction image by this one minute aperture and the second maximum of the diffraction image by the minute aperture adjacent to this one minute aperture. Are photomasks selected so as to cancel each other out. The distance between the center of the one fine aperture and the center of the fine aperture adjacent to the one fine aperture is (2.50 ± 10%) · λ / NA on the image plane.
[Μm] where λ is the wavelength of each exposure [μm], and NA is the numerical aperture of the exposure apparatus. Is preferred.

As a second means, in a photomask in which a plurality of fine openings (3) are formed in a semitransparent phase shift film (2) formed on a transparent substrate (1), one fine opening is formed. The distance between the center and the center of the minute aperture adjacent to this one minute aperture is such that the first-order maximum of the diffraction image by this one minute aperture and the bottom of the zero-order light by the minute aperture adjacent to this one minute aperture. It is a photomask that is selected so as to cancel each other out. The distance between the center of the one fine aperture and the center of the fine aperture adjacent to the one fine aperture is (1.48 ± 10%) · λ / NA [μ
m] is preferable.

A third means is a photomask in which a semi-transparent phase shift film (2) formed on a transparent substrate (1) is provided with fine openings (3) having a two-dimensional period.
The period in one direction of the fine aperture (3) is (2.50 ± 10%) · λ / NA [μm] on the image plane, and the period in the direction orthogonal thereto is (2 .50 ± 10
%) ・ Λ / NA [μm] or (1.48 ± 10%) ・
The photomask has a λ / NA [μm].

[0010]

The first maximum of the amplitude of the diffracted light is a negative value (the phase is 18
By using the fact that the 2nd-order maximum is a positive value, as shown in FIG. 2, the 1st-order maximum of the diffraction image and the 2nd-order maximum of the diffraction image of the adjacent hole cancel each other. Or the pitch of the hole pattern so that the first-order maximum of the diffraction image and the skirts of the 0th-order light of the adjacent holes cancel each other, as shown in FIG. As a result, the sub-peak intensity of the non-exposed portion can be reduced.

When the pitch of the hole pattern is changed,
Shown in Figures 8-10 the results of assimilation calculates how changes Gado ratio I _R of the sub-peak intensity 6 and the Hall transmitted light intensity 5 shown in FIG. 7 and a numerical aperture NA of the hole width HW an exposure device as a variable . FIG. 8 shows the case where the NA is 0.54, and when the pitch is 1.0 μm, the ratio I _R between the sub-peak intensity 6 and the hole transmitted light intensity 5 becomes the minimum, and this pitch 1.0 μm is 1.48λ / Equivalent to NA. Figure 9 is NA
There shows the case of 0.57, the pitch becomes minimum ratio I _R at 0.95 .mu.m, the pitch 0.95 .mu.m likewise corresponds to 1.48λ / NA. In Fig. 10, NA is 0.6
3 is shown, and the ratio I _R is obtained when the pitch is 0.86 μm.
Is minimized, and the pitch of 0.86 μm is 1.4
This corresponds to 8λ / NA. That is, if the pitch of the hole pattern is selected to be 1.48λ / NA, as shown in FIG. 3, the first-order maximum of the diffraction image of a certain hole and the skirt of the 0th-order light of the adjacent hole cancel each other. The sub-peak intensity is reduced.

As a result of simulation calculation, it was confirmed that the above ratio I _R becomes minimum even when the hole pattern pitch is 2.50λ / NA. In this case,
As shown in FIG. 2, the first-order maximum of the diffraction image of a certain hole and the second-order maximum of the diffraction image of an adjacent hole cancel each other, and the sub-peak intensity is reduced.

Since the diffraction pattern of the hole pattern is circularly formed with the center of the hole as the center, the pitch of the hole pattern in one direction and the direction orthogonal thereto is 1.48.
If λ / NA μm is set, as shown in FIG. 4, the first-order maximums 4 of the diffraction images of four adjacent holes overlap each other at point P and the sub-peak intensity increases, which is not preferable. The pitch in the direction and the pitch in the direction orthogonal to it are 2.5λ / NAμm and 1.4, respectively.
It is preferably 8λ / NAμm or 2.5λ / NAμm in either direction as shown in FIG.

However, when the pitches of the hole patterns in two directions orthogonal to each other are set to 1.48λ / NAμm and 2.5λ / NAμm as shown in FIG. 5, the first-order maximum 4 of the diffraction images of adjacent holes is It is unavoidable that the peaks overlap in some areas and the sub-peaks increase only in that area.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Photomasks according to two embodiments of the present invention will be described below with reference to the drawings.

First Example See FIGS. 1 and 11 A semitransparent phase shift film 2 for inverting the phase on a transparent substrate 1.
And a hole pattern 3 is formed in the phase shift film 2, and an image is formed using an exposure device having a numerical aperture NA of 0.63 and a light source wavelength λ of 0.365 μm. The hole width is 0.4, for example.
FIG. 11 shows an arrangement example of hole patterns for exposing a 0 μm hole. Hole pattern unidirectional pitch A
2.5λ / NA = 2.5 ・ 0.365 / 0.63 =
The pitch B is 1.45 μm, and the pitch B in the direction orthogonal thereto is also 1.45 μm.

In this case, 1 of the diffraction image of one hole
It is avoided that the second maximum and the second maximum of the diffraction image of the hole adjacent to this hole cancel each other, and as shown in FIG. 6, the first maximums of the diffraction images of the adjacent holes overlap each other. Sub-peak intensity is reduced.

Second Example As in the first example, the pitch A in one direction of the hole pattern is 1.45 μm, and the pitch B in the direction orthogonal thereto is 1.48λ / NA = 1.48 · 0.365 / 0. 63 =
0.86 μm.

In this case, in the pitch of 1.45 μm, the sub-peak is reduced by the same action as in the first example, and in the pitch of 0.86 μm, the first-order maximum of the diffraction image of one hole is obtained. 0 of the adjacent hole
The sub-peak intensity is reduced because the tails of the next lights cancel each other out. However, in this case, there is a drawback that the first-order maximums of the diffraction images of adjacent holes overlap in a partial area as shown in FIG. 5 and the sub-peak increases in that area.

[0020]

As described above, when exposure is performed using a halftone phase shift mask, the 1st and 2nd maxima of the diffraction images of adjacent holes, or the 1st and 0th order light components of the diffraction patterns of adjacent holes. Since the pitch of the hole pattern having a two-dimensional period is selected so that the hem and the hem cancel each other out,
The resolution can be improved by reducing the sub-peak intensity generated in the non-exposed portion without lowering the transmittance of the semitransparent phase shift film.

[Brief description of drawings]

FIG. 1 is a sectional view of a halftone phase shift mask (a).
It is a top view (b).

FIG. 2 is an explanatory diagram of the principle.

FIG. 3 is an explanatory diagram of the principle.

FIG. 4 is a diagram showing a relationship between a pitch of a hole pattern and a region where a first-order maximum of a diffraction image is generated.

FIG. 5 is a diagram showing a relationship between a pitch of a hole pattern and a region where a first-order maximum of a diffraction image is generated.

FIG. 6 is a diagram showing a relationship between a pitch of a hole pattern and a region where a first-order maximum of a diffraction image is generated.

FIG. 7 is a graph showing hole transmitted light and sub peak light intensities.

FIG. 8 is a graph showing the relationship between hole pitch and sub-peak intensity / hole transmitted light intensity when NA is 0.54.

FIG. 9 is a graph showing the relationship between hole pitch and sub-peak intensity / hole transmitted light intensity when NA is 0.57.

FIG. 10 is a graph showing the relationship between hole pitch and sub-peak intensity / hole transmitted light intensity when NA is 0.63.

FIG. 11 is a diagram showing an arrangement of hole patterns on a photomask.

[Explanation of symbols]

 1 transparent substrate 2 semitransparent phase shift film 3 aperture 4 first-order maximum of diffraction image 5 hole transmitted light 6 sub-peak

Claims (5)

[Claims] 1. A photomask in which a plurality of fine openings (3) are formed in a semitransparent phase shift film (2) formed on a transparent substrate (1). The distance from the center of the minute aperture adjacent to the one minute aperture is 1 of the diffraction image by the one minute aperture.
A photomask, characterized in that the second maximum and the second maximum of a diffraction image by a fine aperture adjacent to the one fine aperture cancel each other. 2. The distance between the center of the one fine aperture and the center of the fine aperture adjacent to the one fine aperture is (2.50 ± 10%) · λ / NA [μm] on the image plane. Here, λ is the wavelength [μm] of each exposure, and NA is the numerical aperture of the exposure apparatus. The photomask according to claim 1, wherein 3. A photomask in which a plurality of fine openings (3) are formed in a semitransparent phase shift film (2) formed on a transparent substrate (1), the center of one fine opening and the The distance from the center of the minute aperture adjacent to the one minute aperture is 1 of the diffraction image by the one minute aperture.
A photomask, characterized in that it is selected such that the next maximum and the skirt of the 0th order light due to the fine aperture adjacent to the one fine aperture cancel each other out. 4. The distance between the center of the one fine aperture and the center of the fine aperture adjacent to the one fine aperture is (1.48 ± 10%) · λ / NA [μm] on the image plane. The photomask according to claim 3, wherein 5. A fine aperture (3) having a two-dimensional period in a semitransparent phase shift film (2) formed on a transparent substrate (1).
In the photomask in which the fine openings (3) are formed, the unidirectional cycle of the fine openings (3) is (2.
50 ± 10%) · λ / NA [μm], and the period in the direction orthogonal thereto is (2.50 ± 10%) · λ on the image plane.
/ NA [μm] or (1.48 ± 10%) ・ λ / NA
A photomask characterized by having a thickness of [μm].