Multilayer mirror for EUV lithography and process for its production
Provided are a multilayer mirror for EUVL in which deterioration in reflectivity due to oxidation of a Ru protective layer is prevented, and a process for its production. A multilayer mirror for EUV lithography comprising a substrate, and a reflective layer for reflecting EUV light and a protective layer for protecting the reflective layer, formed in this order on the substrate, wherein the reflective layer is a Mo/Si multilayer reflective film, the protective layer is a Ru layer or a Ru compound layer, and an intermediate layer containing from 0.5 to 25 at % of nitrogen and from 75 to 99.5 at % of Si is formed between the reflective layer and the protective layer.
1. A multilayer mirror for EUV lithography comprising a substrate, and a reflective layer for reflecting EUV light and a protective layer for protecting the reflective layer, formed in this order on the substrate, wherein
the reflective layer is a Mo/Si multilayer reflective film,
the protective layer is a Ru layer or a Ru compound layer, and
an intermediate layer containing from 0.5 to 25 at % of nitrogen and from 75 to 99.5 at % of Si is formed between the reflective layer and the protective layer.
2. The multilayer mirror for EUV lithography according to claim 1 , wherein the uppermost layer of the reflective layer made of a Mo/Si multilayer reflective film is a Si film, and the intermediate layer is formed in contact with the Si film.
3. The multilayer mirror for EUV lithography according to claim 1 , wherein the thickness of the intermediate layer is from 0.2 to 2.5 nm.
4. The multilayer mirror for EUV lithography according to claim 1 , wherein the surface roughness rms of the surface of the protective layer is at most 0.5 nm.
5. The multilayer mirror for EUV lithography according to claim 1 , wherein the thickness of the protective layer is from 1 to 10 nm.
6. A process for producing a multilayer mirror for EUV lithography (EUVL), which comprises forming a multilayer reflective film for reflecting EUV light on a film-forming surface of a substrate and then, forming a protective layer for protecting the multilayer reflective film, on the multilayer reflective film, to produce a multilayer mirror for EUVL, wherein
the multilayer reflective film is a Mo/Si multilayer reflective film,
the protective layer is a Ru layer or a Ru compound layer, and
after forming the Mo/Si multilayer reflective film, the surface of a Si layer as the uppermost layer of the Mo/Si multilayer reflective film is exposed to a nitrogen-containing atmosphere without exposing it to the atmospheric air, and then, the protective layer is formed.
7. The process for producing a multilayer mirror for EUVL according to claim 6 , wherein the product of the nitrogen partial pressure (Torr) of the nitrogen-containing atmosphere and the exposure time (s) is at least 1×10 −6 Torr·s, and the temperature of the nitrogen-containing atmosphere is from 0 to 170° C.
8. The process for producing a multilayer mirror for EUVL according to claim 6 , wherein the product of the nitrogen partial pressure (Torr) of the nitrogen-containing atmosphere and the exposure time (s) is at least 1×10 −6 Torr·s, and the temperature of the nitrogen-containing atmosphere is from 0 to 160° C.
9. The process for producing a multilayer mirror for EUVL according to claim 6 , wherein the product of the nitrogen partial pressure (Torr) of the nitrogen-containing atmosphere and the exposure time (s) is at least 1×10 −6 Torr·s, and the temperature of the nitrogen-containing atmosphere is from 0 to 150° C.
10. The process for producing a multilayer mirror for EUVL according to claim 6 , wherein when the surface of the Si layer is exposed to the nitrogen-containing atmosphere, the nitrogen-containing atmosphere is maintained to be in a plasma state, or the surface of the Si layer is subjected to thermal treatment, or the surface of the Si layer is irradiated with ultraviolet rays.
11. A process for producing a semiconductor integrated circuit, which comprises subjecting an object to be exposed to exposure by means of the multilayer mirror for EUV lithography as defined in any one of claims 1 to 5 , to produce a semiconductor integrated circuit.