JP2591469B2 - Method for manufacturing phase shift mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a phase shift mask.

[0002]

2. Description of the Related Art Optical lithography, which is generally used as a lithography technique for manufacturing a semiconductor device, comprises:
Until now, high NA (numerical aperture: numerical aperture) of exposure optical systems has been mainly used for high density and high integration of semiconductor devices.
As a result, a finer pattern can be formed. At present, mass production of semiconductor elements having a minimum dimension of 0.5 μm or less is possible by optical lithography.

[0003] However, although the resolution is improved by increasing the NA and shortening the wavelength of the exposure optical system, on the other hand, the depth of focus is reduced, and the resolution of the resist film on a device having a step is reduced. Therefore, securing the depth of focus has become a more important issue. Therefore, in terms of the depth of focus, it has become difficult to improve the resolving power by simply increasing the NA and shortening the wavelength as in the past.

Therefore, in recent years, a phase shift method has attracted attention as a method for improving resolution and depth of focus and extending the limit of optical lithography. The phase shift method has been proposed for about ten years, but its practical use has been delayed due to the difficulty in manufacturing a phase shift mask. In this method, a transparent film is formed on one of the adjacent openings on a photomask, and the thickness t of the transparent film is set to t = λ / 2 (n−1) (where λ is the wavelength of the exposure light). , N are the refractive indices of the transparent film), so that the phases of the transmitted light are shifted from each other by 180 degrees. In the case where the phase shift method is not used, when the distance between the adjacent openings becomes narrow, light leaks to an area which should be a light shielding portion between the openings due to diffraction, and the adjacent openings are not separated. On the other hand, in the phase shift mask, the phases of the light transmitted through the adjacent openings are shifted by 180 degrees from each other, so that the light leaked between the adjacent openings cancels each other to form a light shielding region. Therefore, it is possible to separate and resolve even finer dimensions (see Japanese Patent Publication No. 62-50811).

Next, a method for manufacturing a conventional phase shift mask will be described with reference to the drawings. Although there are mainly two types of phase shift mask structures, a so-called shifter mounting type structure method in which a phase shifter film is formed on a light-shielding film will be described.

FIGS. 3A to 3D are cross-sectional views illustrating a conventional method of manufacturing a phase shift mask in the order of steps.

First, as shown in FIG. 3A, an etching stopper film 2 is formed on a transparent substrate 1 made of synthetic quartz or the like, and a chromium film and a chromium oxide film are laminated on the etching stopper film 2. The light shielding film 3 is formed to form a mask blank. Next, a photosensitive resin film 4 is applied and patterned on the light shielding film 3 of the mask blank.

Next, as shown in FIG. 3B, the light-shielding film 3 is etched by dry etching using a chlorine-based gas using the photosensitive resin film 4 as a mask to form a predetermined light-shielding mask pattern.

Next, as shown in FIG. 3C, after the photosensitive resin film 4 is peeled off, the pattern of the light shielding film 3 is inspected and corrected, and the entire surface is spin-coated with an SOG film to form a transparent film 7. Is formed, and a photosensitive resin film 8 for forming a phase shifter film is selectively formed on the transparent film 7.

Next, as shown in FIG. 3D, the transparent film 7 is etched by dry etching using a gas containing carbon and fluorine using the photosensitive resin film 8 as a mask to form a phase shifter film 7a. Here, it is necessary to use a material satisfying the following conditions as the etching stopper film 2 for preventing the transparent substrate 1 of substantially the same material from being eroded by the etching of the transparent film 7.

(A) SiO used as a phase shifter film
₍₂₎ the etching selectivity with the film is 10 or more;
(B) The optical constants (n, k) are close to those of the transparent substrate 1 and the phase shifter film 3 (if the optical constants are different, reflection occurs at the interface and the transmittance is reduced). (High light resistance); (D) not deteriorated by acid and alkali solutions used during mask manufacturing process and production line use (high chemical resistance)
In addition, a metal oxide such as tin oxide is used as an etching stopper film satisfying such conditions.

As another method of manufacturing a phase shift mask, a method of selectively forming a phase shifter film instead of once forming a phase shifter film over the entire mask, that is, a photosensitive resin film A method of selectively forming a phase shifter film by lift-off using a mask as a mask has been proposed. In this method, since an etching stopper film is not necessary,
Although there is an advantage that there is no variation in transmittance in the mask plane, the method of manufacturing a phase shift mask using this lift-off can only perform mask cleaning with the photosensitive resin film attached before forming the phase shifter film. And foreign substances (mainly organic substances attached during application and development of the photosensitive resin film)
May not be completely removed and may remain as it is between the quartz substrate and the shifter film.

Further, it is difficult to control the thickness of the phase shifter film, and it is not practical because the thickness of the shifter film changes due to the step of the light shielding film. In addition to the lift-off method, as described in JP-A-4-284452, there is a method of selectively oxidizing a light-shielding film to form a phase shifter film. A method of forming a film and then selectively oxidizing the film to form a SiO ₂ film to form a shifter film. In this phase shift mask, a boundary between a light-shielding portion and a light-transmitting portion (an oxidation boundary) is used. ) Is not clear, there is a problem that the dimensional accuracy of the mask cannot be obtained, and the degree of oxidation becomes non-uniform, resulting in abnormal phases and transmittances, and cannot be put to practical use.

[0014]

In this conventional phase shift mask, both the transparent substrate and the phase shifter film are made of SiO.sub.2.
_It is composed of _two materials and their refractive indices are almost the same.
It is about 46. On the other hand, since the etching stopper film is a metal oxide film, the refractive index is generally 2 or more regardless of which metal is used, and has a value different from that of the transparent substrate and the phase shifter film. Therefore, in the portion where the phase shifter film is provided (phase shifter film / etching stopper film / transparent substrate) and the portion where the phase shifter film is not provided (etching stopper film / transparent substrate), the transmittance is inevitable due to the difference in the refractive index of the material. Will be different.

In addition to this principle factor, there is also a problem of a change in transmittance due to damage during etching of the light shielding film or the phase shifter film. Although the etching selectivity between the phase shifter film and the etching stopper film is 10 or more, the etching stopper film is also slightly etched. When the etching stopper film is etched, its thickness changes and its surface is roughened, so that the transmittance changes, and in-plane uniformity of dry etching of the mask substrate may not be good. Causes a variation in transmittance. Further, an ion beam is usually used to correct the light-shielding film. At this time, ions are particularly easily injected into the etching stopper film as compared with the transparent substrate, so that the optical constant of the etching stopper film in the ion-implanted portion changes. However, there is a problem that the transmittance is locally reduced.

An object of the present invention is to provide a method of manufacturing a phase shift mask in which the in-plane uniformity of a mask is improved by eliminating the problem of non-uniformity of transmittance due to an etching stopper film.

[0017]

According to a first method of manufacturing a phase shift mask of the present invention, a step of forming an etching stopper film and a light shielding film sequentially on a transparent substrate, and selectively forming the light shielding film. Forming a light-shielding mask pattern by etching the light-shielding mask pattern, and selectively etching the etching stopper film exposed in the light-transmitting region of the light-shielding mask pattern to form a phase shift film that exposes the surface of the transparent substrate. Forming a first opening, and forming and patterning a transparent film on a surface including the first opening to form a phase shifter film to be directly laminated on the transparent substrate in the first opening. And forming a second opening exposing the surface of the transparent substrate by etching the etching stopper film exposed in the light transmitting region other than the first opening. Nde constructed.

According to a second method of manufacturing a phase shift mask of the present invention, a light shielding film is formed on a transparent substrate and selectively etched to form a light shielding mask pattern, and then an etching stopper film is formed on a surface including the light shielding film. And a step of selectively etching the etching stopper film to form a first opening for forming a phase shift film exposing a surface of the transparent substrate in a light transmitting region of the light shielding mask pattern. Forming a transparent film on the surface including the first opening and patterning to form a phase shifter film directly laminated on the transparent substrate in the first opening; and the remaining etching stopper Forming a second opening that exposes the surface of the transparent substrate in a light transmitting region other than the first opening by removing the film by etching.

[0019]

Next, the present invention will be described with reference to the drawings.

FIGS. 1A to 1E are cross-sectional views showing a first embodiment of the present invention in the order of steps for explaining the first embodiment.

First, as shown in FIG. 1A, an etching stopper film 2 made of tin oxide is formed on a transparent substrate 1 made of synthetic quartz or the like to a thickness of 20 nm by sputtering. The light-shielding film 3 is formed by laminating a chromium film having a thickness of 70 nm and a chromium oxide film having a thickness of 30 nm in this order. Next, a photosensitive resin film 4 is applied on the light shielding film 3 and patterned.

Next, as shown in FIG. 1B, the light shielding film 3 is etched by dry etching using a chlorine-based gas using the photosensitive resin film 4 as a mask to form a light shielding mask pattern.

Next, as shown in FIG. 1C, after the photosensitive resin film 4 is peeled off, a photosensitive resin film 5 is applied to the surface including the light-shielding film 3 and is patterned. Using the mask 5 as a mask, the etching stopper film 2 exposed in the light transmission region of the light-shielding mask is selectively removed by wet etching, an opening 6 is formed in the phase shifter film formation region, and the surface of the transparent substrate 1 is exposed.

Next, as shown in FIG. 1D, after the photosensitive resin film 5 is peeled off, a SOG film is spin-coated on the entire surface to a thickness of 380 nm to form a transparent film 7. Next, the transparent film 7
A photosensitive resin film 8 is applied on the substrate 6 and patterned to form a pattern for forming a phase shifter film on the opening 6.

Next, as shown in FIG. 1E, the transparent film 7 is removed by dry etching using fluorine gas with the photosensitive resin film 8 as a mask and using the etching stopper film 2 as an etching stopper. A phase shift film 7a directly laminated on the surface of the transparent substrate 1 in the opening 6 is formed. Next, the etching stopper film 2 exposed in the remaining light transmitting region is removed by wet etching to form an opening 9, and the photosensitive resin film 8 is peeled to form a phase shift mask.

Here, the transmittance of the opening 9 of only the transparent substrate 1 and the opening 6 having the transparent substrate and the phase shifter film 7a by exposure light i-line (λ = 0.365 μm) is 92.5%.
Thus, the difference between the two transmittances can be eliminated.

FIGS. 2A to 2E are cross-sectional views showing a second embodiment of the present invention in the order of steps for explaining the same.

First, as shown in FIG.
A light-shielding film 3 composed of a laminated film of a chromium film and a chromium oxide film is formed thereon, and a photosensitive resin film 4 is applied on the light-shielding film 3 and patterned. Next, the light shielding film 3 is dry-etched using the photosensitive resin film 4 as a mask to form a light shielding mask pattern.

Next, as shown in FIG. 2B, after the photosensitive resin film 4 is peeled off, an ITO film is formed to a thickness of 20 nm on the entire surface to form an etching stopper film 2. next,
A photosensitive resin film 5 is applied on the etching stopper film 2 and patterned.

Next, as shown in FIG. 2C, the etching stopper film 2 is removed by wet etching using an acid with the photosensitive resin film 5 as a mask, and an opening 6 is formed in the phase shifter film forming region. Then, the surface of the transparent substrate 1 is exposed. Next, after the photosensitive resin film 5 is peeled off, an SOG film is spin-coated to a thickness of 380 nm on the surface including the opening 6 to form a transparent film 7. Next, a photosensitive resin film 8 is applied on the transparent film 7 and patterned to form a pattern for forming a phase shifter film on the opening 6.

Next, as shown in FIG. 2D, the transparent film 7 is dry-etched using the photosensitive resin film 8 as a mask.
A phase shifter film 7a directly laminated on the transparent substrate 1 is formed.

Next, as shown in FIG. 2E, the remaining etching stopper film 2 is completely removed by wet etching using an acid, an opening 9 is formed, and the photosensitive resin film 8 is peeled off. A phase shift mask is formed.

In this embodiment, since the etching stopper film is completely removed, the mask can be easily cleaned, and a material having no chemical resistance, such as ITO or alumina, can be used as the etching stopper film. There is. Further, since there was no material for the etching stopper film having light resistance to the excimer laser, it was difficult to manufacture a phase shift mask for the excimer laser. Therefore, there is an advantage that the phase shift mask for the excimer laser can be easily manufactured.

Although the shifter upper type has been described in the embodiment, the same configuration and effect can be obtained with the shift lower type.

[0035]

As described above, according to the present invention, the phase shifter film and the etching stopper film in the light transmitting region are completely removed by completely removing the etching stopper film from the light transmitting region of the light shielding mask pattern formed on the transparent substrate. This has the effect of eliminating a decrease in transmittance, eliminating non-uniformity in transmittance due to the presence or absence of the etching stopper film, and improving in-plane uniformity of the mask.

In the case where the etching stopper film is completely removed from the entire surface of the mask, a material having low chemical resistance or light resistance can be used as the etching stopper film.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a first embodiment of the present invention in the order of steps for explaining the same.

FIG. 2 is a cross-sectional view shown in the order of steps for explaining a second embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a conventional method for manufacturing a phase shift mask in the order of steps for explaining the method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Etching stopper film 2 Light shielding film 4,5,8 Photosensitive resin film 6,9 Opening 7 Transparent film 7a Phase shifter film

Claims (5)

(57) [Claims] A step of sequentially forming and forming an etching stopper film and a light shielding film on a transparent substrate; a step of selectively etching the light shielding film to form a light shielding mask pattern; Selectively etching the etching stopper film exposed to the light transmitting region to form a first opening for forming a phase shift film exposing the surface of the transparent substrate; and forming the first opening. Forming a transparent film on the surface including, and patterning to form a phase shifter film directly laminated on the transparent substrate in the first opening, and exposing the phase shifter film to a light transmitting region other than the first opening Forming a second opening exposing the surface of the transparent substrate by etching the etching stopper film. 2. The method according to claim 1, wherein the etching stopper film is made of tin oxide. 3. A step of forming a light-shielding film on a transparent substrate and selectively etching to form a light-shielding mask pattern, and then forming an etching stopper film on a surface including the light-shielding film, and selecting the etching stopper film. Forming a first opening for forming a phase shift film exposing a surface of the transparent substrate in a light transmitting region of the light shielding mask pattern by etching, and forming a first opening on the surface including the first opening. Forming and patterning a transparent film to form a phase shifter film directly laminated on the transparent substrate in the first opening; and etching and removing the remaining etching stopper film to form the first opening. Forming a second opening that exposes the surface of the transparent substrate in a light transmission region other than the other. 4. The method of manufacturing a phase shift mask according to claim 3, wherein the etching stopper film is made of any one of ITO, alumina, and tin oxide. 5. The method according to claim 1, wherein the etching of the transparent film is anisotropic dry etching and the etching of the etching stopper film is wet etching.