Anti-reflective film and optical element having anti-reflective film

FIG. 1 is a schematic view showing an anti-reflective film consisting of eight layers for an F 2 laser (157 nm) in accordance with Example 1 of the present invention. The anti-reflective film of the present example was prepared using an LaF 3 film with a refractive index of 1.765 at a wavelength of 157 nm for a high refractive-index layer, and an MgF 2 film with a refractive index of 1.466 at a wavelength of 157 nm for a low refractive-index layer. Table 1 shows the optical film thickness of each layer of the anti-reflective film for ultraviolet light with a designed central wavelength of λ 0 =157 nm. The refractive-index layers were sequentially formed by use of a vacuum evaporation method so as to have the thicknesses shown in Table 1, respectively. In the present example, calcium fluoride was used as a substrate.

The reflection characteristics of the anti-reflective film shown in Table 1 were measured. In addition, for the purpose of comparison, an anti-reflective film of two layers consisting of an LaF 3 layer and an MgF 2 layer each having a thickness of 0.25λ 0 was also prepared following the same procedure, and the reflection characteristics were measured.

FIG. 2 shows the results of the reflectance measurement of the anti-reflective film of the present example. In addition, FIG. 3 shows the results of the reflectance measurement of the anti-reflective film consisting of two layers as the comparative example. It can be seen from FIG. 2 that the anti-reflective film of the present example has good characteristics with a reflectance of 1.0% or lower within a wide wavelength range of 143 nm to 189 nm, and particularly that in a wide wavelength range of 146 nm to 184 nm, the anti-reflective film has good characteristics with a reflectance of 0.3% or lower.

In contrast to this, it can be seen from FIG. 3 that the comparative example shows good characteristics with a reflectance of 0.3% or lower within a wavelength range of 151 nm to 164 nm. However, at wavelengths of less than 151 nm or more than 164 nm, the reflectance characteristics are degraded.

In addition, FIG. 4 shows the results of measurement for reflectance to an F 2 laser of a wavelength of 157 nm at various incidence angles of the anti-reflective film of the present example. It can be seen from FIG. 4 that the anti-reflective film shows a reflectance of about 1% at an incidence angle of 50°, and therefore that the film shows good anti-reflection characteristics to a light with a large incidence angle.

Similarly, it has also been found that when a designed central wavelength λ 0 is within a wavelength range of 141 nm to 189 nm, and when the first to eighth layers as counted from the substrate have optical film thicknesses d 1 to d 8 respectively and satisfy the equations of:

0.45λ 0 ≦d 1 ≦0.65λ 0 ;

0.05λ 0 ≦d 2 ≦0.20λ 0 ;

0.29λ 0 ≦d 3 ≦0.49λ 0 ;

0.01λ 0 ≦d 4 ≦0.15λ 0 ;

0.05λ 0 ≦d 5 ≦0.20λ 0 ;

0.23λ 0 ≦d 6 ≦0.28λ 0 ;

0.23λ 0 ≦d 7 ≦0.28λ 0 ; and

0.23λ 0 ≦d 8 ≦0.28λ 0

the same effect can be exhibited.

An anti-reflective film in accordance with the present example has a six-layer structure having high refractive-index layers and low refractive-index layers alternately stacked. The anti-reflective film was prepared using an LaF 3 film with a refractive index of 1.765 at a wavelength of 157 nm for a high refractive-index layer, and an MgF 2 film with a refractive index of 1.466 at a wavelength of 157 nm for a low refractive-index layer. Table 2 shows the optical film thickness of each layer of the anti-reflective film for ultraviolet light with a designed central wavelength of λ 0 =157 nm. The refractive-index layers were sequentially formed by use of a vacuum evaporation method so as to have the thicknesses shown in Table 2, respectively. In the present example, calcium fluoride was used as a substrate.

The reflection characteristics of the anti-reflective film shown in Table 2 were measured. FIG. 5 shows the results of the reflectance measurement of the anti-reflective film. It can be seen from FIG. 5 that the anti-reflective film of the present example has good characteristics with a reflectance of 1.0% or lower within a wide wavelength range of 143 nm to 181 nm, and particularly that in a wide wavelength range of 146 nm to 173 nm, the anti-reflective film has good characteristics with a reflectance of 0.2% or lower.

Similarly, it has also been found that when a designed central wavelength λ 0 is within a wavelength range of 143 nm to 181 nm, and when the first to sixth layers as counted from the substrate have optical film thicknesses d 1 to d 6 respectively and satisfy the equations of:

0.05λ 0 ≦d 1 ≦0.27λ 0 ;

0.01λ 0 ≦d 2 ≦0.15λ 0 ;

0.10λ 0 ≦d 3 ≦0.32λ 0 ;

0.23λ 0 ≦d 4 ≦0.29λ 0 ;

0.23λ 0 ≦d 5 ≦0.29λ 0 ; and

0.23λ 0 ≦d 6 ≦0.28λ 0

the same effect can be exhibited.

An anti-reflective film in accordance with the present example has a six-layer structure having high refractive-index layers and low refractive-index layers alternately stacked. The anti-reflective film was prepared using an LaF 3 film with a refractive index of 1.765 at a wavelength of 157 nm for a high refractive-index layer, and an MgF 2 film with a refractive index of 1.466 at a wavelength of 157 nm for a low refractive-index layer. Table 3 shows the optical film thickness of each layer of the anti-reflective film for ultraviolet light with a designed central wavelength of λ 0 =157 nm. The refractive-index layers were sequentially formed by use of a vacuum evaporation method so as to have the thicknesses shown in Table 3, respectively. In the present example, calcium fluoride was used as a substrate.

The reflection characteristics of the anti-reflective film shown in Table 3 were measured. FIG. 6 shows the results of the reflectance measurement of the anti-reflective film. It can be seen from FIG. 6 that the anti-reflective film of the present example has good characteristics with a reflectance of 1.0% or lower within a wide wavelength range of 142 nm to 210 nm, and particularly that in a wide wavelength range of 144 nm to 207 nm, the anti-reflective film has good characteristics with a reflectance of 0.7% or lower.

Similarly, it has also been found that when a designed central wavelength λ 0 is within a wavelength range of 140 nm to 210 nm, and when the first to sixth layers as counted from the substrate have optical film thicknesses d 1 to d 6 respectively and satisfy the equations of:

0.05λ 0 ≦d 1 ≦0.27λ 0 ;

0.01λ 0 ≦d 2 ≦0.15λ 0 ;

0.10λ 0 ≦d 3 ≦0.32λ 0 ;

0.47λ 0 ≦d 4 ≦0.67λ 0 ;

0.23λ 0 ≦d 5 ≦0.29λ 0 ; and

0.23λ 0 ≦d 6 ≦0.28λ 0

the same effect can be exhibited.

In Examples 1 to 3 described above, an LaF 3 film was used for a high refractive-index layer, and an MgF 2 film was used for a low refractive-index layer. However, the present invention is not limited thereto, and an NdF 3 film, a GdF 3 film, a DyF 3 film, a YF 3 film, and a PbF 2 film, other than an LaF 3 film, can also be used for a high refractive-index layer. In addition, an AlF 3 film, an NaF film, an LiF film, a CaF 2 film, a BaF 2 film, an SrF 2 film, and an Na 3 AlF 6 film, other than an MgF 2 film, can also be used for a low refractive-index layer.

In addition, in the above described examples 1 to 3, calcium fluoride was used as a substrate, but quartz is also available.

<Example of Exposure System>

FIG. 7 is a schematic view showing a main part of an exposure system (aligner) for producing a semiconductor device using an optical system. The optical system has an optical element having the anti-reflective film in accordance with Example 1, 2 or 3 described above. In the figure, reference numeral 1 denotes a light source for emitting ultraviolet light of a wavelength of 157 nm. Reference numeral 2 denotes an illumination system for illuminating a reticle 4 with a light beam from the light source 1 . Reference numeral 3 denotes a mirror. Reference numeral 5 denotes a projection optical system for projecting a pattern on the reticle 4 to a wafer 6 . Each of optical elements such as a lens used in the mirror 3 , the illumination system 2 and the projection optical system 5 has an anti-reflective film in accordance with the present invention applied on a surface thereof. Thereby, reflection of the light beam at each surface is prevented to suppress the occurrence of a flare or ghost, thus providing an excellent projected pattern image.

<Example of Production Method of Device>

Described next is a method of producing a semiconductor device using the exposure system shown in FIG. 7 . FIG. 8 shows a production flow of a semiconductor device (a semiconductor chip such as an IC or LSI, a liquid crystal panel or a CCD). In Step 1 (circuit design), a circuit of a semiconductor device is designed. In Step 2 (mask production), a mask (a reticle 4 ) having the designed circuit pattern formed thereon is prepared. On the other hand, in Step 3 (wafer manufacture), a wafer (wafer 6 ) is manufactured using a material such as silicon or the like. In Step 4 (wafer processing) which is called a pre-process, an actual circuit is formed on the wafer using the above prepared mask and the wafer by means of lithography. Next, Step 5 (assembly), which is called a post-process, is a step of making a chip by the use of the wafer prepared in Step 4 and includes an assembling step (dicing and bonding), a packaging step (chip encapsulation) and the like. In Step 6 (inspection), the semiconductor device produced in Step 5 is subjected to tests such as an operation check test and a durability test. A semiconductor device is thus completed through the above steps and is shipped (Step 7 ).

FIG. 9 shows a detailed flow of the above described wafer process. In Step 11 (oxidation), the surface of the wafer (wafer W) is oxidized. In Step 12 (CVD), an insulation film is formed on the surface of the wafer. In Step 13 (electrode formation), an electrode is formed on the wafer through vapor deposition. In Step 14 (ion implantation), ions are implanted into the wafer. In Step 15 (resist treatment), a resist (sensitized material) is applied to the wafer. In Step 16 (exposure), the wafer is exposed through an image of a circuit pattern of the mask (reticle 4 ) with the exposure system. In Step 17 (development), the exposed wafer is developed. In Step 18 (etching), a portion except for a developed resist portion is removed. In Step 19 (resist stripping), the resist is removed which has become unnecessary after completion of the etching step. A circuit pattern is formed on the wafer by repeating these steps.

As described above, according to the present invention, there can be provided an anti-reflective film of a 6-layer or 8-layer structure using fluoride thin films that is effective for a light of a wavelength of about 140 to 210 nm. Further, it is possible to realize an anti-reflective film that has a low reflectance for a light incident at such a large angle as 30 degrees or more, without increasing the whole thickness of the film.

This application claims priority from Japanese Patent Application No. 2004-178534 filed on Jun. 16, 2004, which is hereby incorporated by reference herein.