Method of manufacturing reflective mask blank, and reflective mask blank
A reflective mask blank including a substrate, a multilayer reflection film consisting of at least two first layers and at least two second layers that are laminated alternatively and having different optical properties each other, and an absorber film are manufactured by a sputtering method. Each layer is formed by two stages consisting of a first stage applied from when the forming of each layer is started and until a prescribed thickness is formed, and a second stage applied from when the prescribed thickness is formed and until the forming of each layer is completed, and a sputtering pressure of the first stage is set to higher than both a sputtering pressure at which the forming of the layer formed just before is completed, and a sputtering pressure of the second stage.
1. A method of manufacturing a reflective mask blank comprising a substrate, a multilayer reflection film formed on one main surface of the substrate, and an absorber film formed on the multilayer reflection film, the multilayer reflection film consisting of at least two first layers and at least two second layers that are laminated alternatively, the first and second layers having different optical properties each other,
the method comprising the step of forming the first and second layers constituting the multilayer reflection film alternatively by a sputtering method, wherein
in the forming step of the first and second layers constituting the multilayer reflection film, each layer is formed by two stages consisting of a first stage applied from when the forming of said each layer is started and until a prescribed thickness is formed, and a second stage applied from when the prescribed thickness is formed and until the forming of said each layer is completed, and
in forming the second layer subsequent to forming the first layer, or in forming the first layer subsequent to forming second layer, a sputtering pressure of the first stage is set to higher than both a sputtering pressure at which the forming of the layer formed just before is completed, and a sputtering pressure of the second stage.
2. The method of claim 1 wherein the prescribed thickness formed in the first stage is at least 1/20 and less than ½ of the total thickness formed in the whole of the first and second stages.
3. The method of claim 1 wherein the sputtering pressure of the first stage is at least 0.08 Pa, and a sputtering pressure of the second stage is less than 0.08 Pa.
4. The method of claim 1 wherein the sputtering method is a magnetron sputtering method.
5. The method of claim 1 wherein the sputtering pressures of the first and second stages are adjusted by argon gas.
6. The method of claim 1 wherein the first and second layers are a Si layer and a Mo layer, respectively, and the first and second layers are laminated alternatively at least 40 layers, respectively.
7. A reflective mask blank manufactured by the method of claim 1 , comprising the substrate, the multilayer reflection film formed on one main surface of the substrate, and the absorber film formed on the multilayer reflection film.
8. The reflective mask blank of claim 7 wherein the multilayer reflection film has a reflectance of at least 66.5% with respect to extreme ultraviolet (EUV) light having a wavelength of 13 to 14 nm at an incident angle of 6°.
9. The reflective mask blank of claim 7 wherein the first and second layers are a Si layer and a Mo layer, respectively, and the first and second layers are laminated alternatively at least 40 layers, respectively.
10. The reflective mask blank of claim 7 wherein the main surface of the substrate on which the multilayer reflection film is formed has a surface roughness RMS of not more than 0.15 nm.