JP2814848B2 - Phase shift mask and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask for reduction projection exposure used in a photolithography process for manufacturing a semiconductor device, and more particularly to a phase shift mask for realizing fine lithography and a method for manufacturing the same.

[0002]

2. Description of the Related Art In the conventional photolithography technology, the NA of an exposure apparatus has been increased and the wavelength has been shortened, so that a finer pattern can be formed. At present, it is possible to manufacture a semiconductor element having a minimum dimension of about 0.5 μm.
However, although the resolution is improved by increasing the NA and shortening the wavelength of the exposure apparatus, on the other hand, the depth of focus is reduced, so that securing the depth of focus has become a more important problem. Simple high NA like before in terms of depth of focus
It is difficult to improve the resolution by shortening the wavelength and shortening the wavelength.

[0003] In recent years, a phase shift method has attracted attention as a method of extending the limit of photolithography by improving resolution and depth of focus. This phase shift method is disclosed in, for example, Japanese Patent Application No. 55-136483 and IEEE Trans.
As described in ctron Devices, Vol.ED-29, P1828-P1836, 1982, a transparent film is formed on an adjacent opening on a photomask, and the intensity of light transmitted using the transparent film is used. Are offset to form a light-shielding region to enhance the resolving power. That is, when the phase shift method is not used, when the distance between adjacent openings is reduced, light leaks to a region which is originally a light shielding portion between the openings due to diffraction, and the openings are not separated, but in the phase shift method, the transparent film is not formed. The thickness t is t = λ /
By setting 2 (n−1) (where λ is the wavelength of the exposure light and n is the refractive index of the transparent film), the phase of the light passing through the adjacent openings is shifted by 180 degrees, and the leakage between the adjacent openings is caused. The light beams cancel each other out, and it is possible to form a light-shielding region and separate the light to a fine size.

To manufacture such a phase shift mask, a transparent conductive film such as ITO is formed on a transparent substrate, and a light-shielding film such as chromium or chromium oxide is formed thereon. Then, after this light-shielding film is formed by etching into a required pattern, a transparent film called a phase shifter is formed thereon to a required thickness. As this transparent film, SOG, sputtered SiO ₂ , CVD SiO ₂ , SiN or the like is used.
However, in this configuration, since the transparent film is formed on the patterned light-shielding film, the thickness of the transparent film is difficult to be uniform, and there is a problem that the transparent film cannot be controlled to a required thickness. For example, in a film formed by spin coating such as SOG or the like, the film thickness varies depending on the density of the lower value pattern. In a film formed by sputtering, CVD, or the like, the thickness of the transparent film at the end of the light-shielding film is increased by the thickness of the light-shielding film.

Therefore, for example, Japanese Patent Application No. 60-13413
As shown in No. 8, a phase shift mask in which a transparent film as a phase shifter is formed between the transparent film and a light shielding film on a transparent substrate is being studied. In this phase shift mask, since a transparent film is formed on a flat transparent substrate, there is an advantage that the thickness can be easily controlled. 4 and 5 show a method of manufacturing this phase shift mask.

First, as shown in FIG. 4A, a transparent conductive film 2 such as ITO is formed on a transparent substrate 1 such as quartz, and a transparent film 3 such as SOG having a predetermined thickness is formed thereon. Then, a light-shielding film 4 of chromium, chromium oxide, or the like is formed thereon. The transparent conductive film 2 plays a role of preventing charge-up at the time of drawing an electron beam and serving as an etching stopper. Then, FIG.
As shown in FIG. 4B, the photosensitive resin 5 is applied to the entire surface, and is developed by performing electronic drawing or laser drawing to form a pattern of the photosensitive resin 5 as shown in FIG. 4C. And FIG.
As shown in FIG. 4D, the light shielding film 4 is patterned by dry or wet etching, and then the photosensitive resin 5 is removed as shown in FIG.

Next, as shown in FIG. 5A, a photosensitive resin 6 is applied again and patterned as shown in FIG. 5B. Then, as shown in FIG. 5C, the transparent film 3 where the photosensitive resin 6 is removed is used as a mask with the light shielding film 4 as a mask.
Dry etching is performed with a gas such as F ₄ and CHF ₃ . Finally, as shown in FIG. 5D, the photosensitive resin 6 is removed. In the phase shift mask manufactured by this manufacturing method, since the transparent film 3 is dry-etched, the lower side of the end portion of the light-shielding film is not largely scooped as in the case of wet etching, and the strength of the portion is reduced. It will not be reduced. Therefore, it is possible to prevent the photomask from being damaged when it is cleaned.

[0008]

In such a conventional phase shift mask, since the transparent film is dry-etched using the light-shielding film as a mask, the end of the transmission film coincides with the end of the light-shielding film. In the case where SiO ₂ is used for the transparent film, the ends are slightly tapered. For this reason, light incident on the photomask from an oblique direction is incident on the edge of the transparent film below the edge of the light-shielding film, where the phase is unintentionally changed and reaches the wafer surface. Will be.

For this reason, there arises a problem that the original resolution and depth of focus cannot be obtained due to the undesired light.
In addition, the edge of the transparent film has an adverse effect on the control of the resist size. For example, when exposure is performed on a wafer coated with a negative resist using this phase shift mask, even if the mask pattern has an opening pattern of the same size, the size of the resist pattern due to the opening obtained by etching the transparent film is transparent. It becomes smaller than the size of the resist pattern due to the opening where the film is not etched. That is, there is a problem that the exposure state becomes under the influence of the edge of the transparent film.

If the transparent film is etched by wet etching, the edge of the transparent film is recessed inward from the edge of the light-shielding film. However, since the angle of the edge of the transparent film is about 45 degrees, the light passing through the edge of the transparent film is not necessarily blocked by the light shielding film. Further, as described above, the transparent film below the edge of the light-shielding film is etched, so that the light-shielding film is easily damaged. SUMMARY OF THE INVENTION It is an object of the present invention to provide a phase shift mask that prevents undesired light transmission at an end of a light-shielding film while preventing damage to the light-shielding film, and a method of manufacturing the same.

[0011]

According to the phase shift mask of the present invention, the thickness t between the transparent substrate and the light shielding film is t = λ /.
2 (n-1) (where λ is the wavelength of the exposure light and n is the refractive index of the transparent film) In a phase shift mask having a patterned transparent film, the edge of the transparent film is It is located on the inner side by t / 3 from t / 4. The method for manufacturing a phase shift mask of the present invention includes a step of forming a transparent film on a transparent substrate, a step of forming a light-shielding film on the transparent film, and a step of forming the light-shielding film in a predetermined pattern; A step of applying a photosensitive resin on the light-shielding film and the transparent film, and selectively removing the photosensitive resin in a region including the region where the light-shielding film is removed; and anisotropically forming the transparent film using the photosensitive resin as a mask. And a step of isotropically etching the transparent film. Alternatively, a step of forming a transparent film on a transparent substrate, a step of forming a light shielding film on the transparent film, a step of forming the light shielding film in a predetermined pattern, and a step of forming a photosensitive film on the light shielding film and the transparent film Applying a resin, selectively removing the photosensitive resin in an area smaller than the area from which the light-shielding film is removed, and anisotropically etching the transparent film using the photosensitive resin as a mask; Isotropically etching the transparent film.

[0012]

Next, the present invention will be described with reference to the drawings. 1 and 2 are cross-sectional views showing a phase shift mask of the present invention together with a method for manufacturing the same. First, as shown in FIG. 1A, a transparent conductive film 2 such as ITO is formed on a transparent substrate 1 made of quartz, SOG is applied thereon, and heat treatment is performed to form a transparent film 3. Here, the refractive index n of the SOG is defined as n
= 1.4 and i-line (λ = 365 nm) is used as the exposure light, the thickness t of the transparent film is t = 415 nm. Then, a light-shielding film 4 made of chromium or chromium oxide is formed on the transparent film 3. Next, as shown in FIG. 1B, a photosensitive resin 5 for an electron beam is applied, and an electron beam exposure is performed. Next, as shown in FIG. 1C, the photosensitive resin 5 is developed,
The light shielding film 4 is selectively etched by wet etching to form the light shielding film 4 in a predetermined pattern as shown in FIG. Thereafter, as shown in FIG.
Is peeled off.

Next, as shown in FIG. 2A, a photosensitive resin 6 for an electron beam is applied again, and an electron beam is drawn. Next, as shown in FIG. 2B, the photosensitive resin 6 is developed and the transparent film 3 is developed.
The portions of the photosensitive resin 6 to be etched are removed. Next, as shown in FIG. 2C, dry etching is performed using CF ₄ , and the transparent film 3 is anisotropically etched using the light shielding film 4 as a mask. At this time, since the chromium oxide on the surface of the light shielding film 4 is also slightly etched, it is necessary to increase the film thickness in advance or to protect the light shielding film 4 with polysilicon or the like. Next, as shown in FIG. 2D, the transparent film 3 is etched substantially vertically by dry etching, followed by wet etching to etch the transparent film 3 by about 150 nm. By this wet etching, the transparent film 3 becomes the light shielding film 4.
Is set to about t / 4 to t / 3. Finally, the photosensitive resin 6 is peeled off to complete a phase shift mask as shown in FIG.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a sectional view showing a phase shift mask according to a second embodiment of the present invention in the order of manufacturing steps. First, as shown in FIG. 3A, an ITO film is formed on a transparent substrate 1 made of quartz.
Etc. are formed, SOG is applied thereon,
Heat treatment is performed to form the transparent film 3. And the transparent film 3
A light-shielding film 4 made of chromium or chromium oxide is formed thereon. Next, as shown in FIG. 3B, a photosensitive resin 5 for i-line is applied, drawing is performed using a laser drawing device such as ATEQ CORE-2500, development is performed, and the transparent film 3 is etched. A portion of the photosensitive resin 5 is removed. here,
The range in which the photosensitive resin 5 is removed is reduced, and is set to be about 0.1 μm from the end of the light shielding film 4. This dimension is a dimension in consideration of the alignment accuracy of the laser drawing apparatus so that the portion from which the photosensitive resin 5 is removed does not fall on the light-shielding film 4 even if a positional shift occurs.

Next, as shown in FIG. 3C, dry etching is performed using CF ₄ , and the transparent film 3 is anisotropically etched using the photosensitive resin 5 as a mask. The drawing using the laser drawing apparatus is because the photosensitive resin 5 can be made thicker than in the case of the electron beam, so that the etching of the transparent film 3 is facilitated. Next, as shown in FIG. 3D, the transparent film 3 is etched substantially vertically by dry etching, followed by wet etching to etch the transparent film 3 by about 250 nm. Next, the photosensitive resin 5 is peeled off as shown in FIG. In this method, the light shielding film 4 is protected by the photosensitive resin 5 when the transparent film 3 is anisotropically etched, so that the light shielding film is not damaged.

[0016]

As described above, in the phase shift mask according to the present invention, the edge of the transparent film is located at about t / 4 to t / 3 inside the edge of the light-shielding film. The effect of preventing the influence of the edge of the transparent film below the edge and preventing the light-shielding film from being damaged is obtained. Further, according to the method of manufacturing the phase shift mask of the present invention, a structure in which the edge of the transparent film below the edge of the light-shielding film is located inside can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a phase shift mask of the present invention in the order of manufacturing steps.

FIG. 2 is a process sectional view continued from FIG. 1;

FIG. 3 is a sectional view showing a second embodiment of the present invention in the order of manufacturing steps.

FIG. 4 is a cross-sectional view showing a conventional phase shift mask in the order of manufacturing steps.

FIG. 5 is a process sectional view continued from FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Transparent conductive layer 3 Transparent film 4 Light shielding film 5, 6 Photosensitive resin

Claims (3)

(57) [Claims] 1. A film thickness t between a transparent substrate and a light-shielding film.
t = λ / 2 (n−1) (where λ is the wavelength of the exposure light, n is the refractive index of the transparent film) In a phase shift mask having a patterned transparent film, the edge of the transparent film is A phase shift mask, which is located at an inner side of t / 4 to t / 3 from an end of a light shielding film. 2. A step of forming a transparent film on a transparent substrate;
A step of forming a light-shielding film on the transparent film, a step of forming the light-shielding film in a predetermined pattern, and a region in which a photosensitive resin is applied on the light-shielding film and the transparent film, and the light-shielding film is removed. Selectively removing the photosensitive resin in the region, anisotropically etching the transparent film using the photosensitive resin as a mask, and then isotropically etching the transparent film. Manufacturing method of a phase shift mask. Forming a transparent film on a transparent substrate;
Forming a light-shielding film on the transparent film; forming the light-shielding film in a predetermined pattern; applying a photosensitive resin on the light-shielding film and the transparent film; A step of selectively removing the photosensitive resin in a small area, a step of anisotropically etching the transparent film using the photosensitive resin as a mask, and a step of isotropically etching the transparent film. A method for manufacturing a phase shift mask.