Photomask blank, photomask, and photomask manufacturing method
A photomask blank has a light-shielding film composed of at least two layers on a transparent substrate. The light-shielding film includes a light-shielding layer made of a material mainly containing tantalum nitride and containing less than 62 at % nitrogen. The material is capable of being dry-etched with a chlorine-based gas containing no oxygen. The light-shielding film further includes a front-surface antireflection layer formed on the light-shielding layer and made of a material not capable of being dry-etched with a chlorine-based gas, but capable of being dry-etched with a fluorine-based gas.
1. A method of manufacturing a photomask comprising the steps of:
preparing a photomask blank having a light-shielding film, the light-shielding film comprising a light-shielding layer and a front-surface antireflection layer on a transparent substrate;
dry-etching the front-surface antireflection layer with a fluorine-based gas containing no oxygen using, as a first etching mask, a resist film having a transfer pattern; and
dry-etching the light-shielding layer with a chlorine-based gas containing no oxygen using, as a second etching mask, the front-surface antireflection layer being dry-etched using the first etching mask and having the transfer pattern,
wherein the light-shielding layer is formed in contact with the transparent substrate, the light shielding layer being made of a material consisting of tantalum and nitrogen, and containing 7 at % or more and 51 at % or less nitrogen, the material being capable of being dry-etched with the chlorine-based gas containing no oxygen,
wherein the front-surface antireflection layer is formed in contact with the light-shielding layer, the front-surface antireflection layer being made of a material consisting of tantalum and oxygen and containing 50 at % or more oxygen, the material not being capable of being dry-etched with the chlorine-based gas and capable of being dry-etched with the fluorine-based gas.
2. The method of manufacturing a photomask according to claim 1 , wherein the light-shielding film has a surface roughness of 0.26 nmRms or more and 0.49 nmRms or less.
3. The method of manufacturing a photomask according to claim 1 , wherein the light-shielding film has a transmittance of 0.2% or less and a back-surface reflectance of less than 40% with respect to a ArF excimer laser exposure light.
4. The method of manufacturing a photomask according to claim 1 , wherein the light-shielding film has a stacked structure comprising the light-shielding layer and the front-surface antireflection layer,
wherein the light-shielding layer is made of a material having a first refractive index n 1 of more than 1.65 and less than 2.44 and a first extinction coefficient k 1 of more than 1.70 and less than 2.50,
wherein the front-surface antireflection layer is made of a material having a second refractive index n 2 of 2.23 or more and 2.42 or less and a second extinction coefficient k 2 of 0.63 or more and 1.09 or less.
5. The method of manufacturing a photomask according to claim 1 , wherein the light-shielding film has a thickness of less than 65 nm.
6. The method of manufacturing a photomask according to claim 1 , wherein the front-surface antireflection layer has a thickness of 5 nm or more and 20 nm or less.