Reflection photolithography mask, and process for fabricating this mask

1. An extreme ultraviolet photolithography mask, operating in reflection, comprising a substrate, a reflecting structure deposited uniformly on the substrate, and an absorbent layer which is absorbent at the operating wavelength of the mask and is deposited on top of the reflecting structure and etched in a desired masking pattern, wherein the absorbent layer contains indium as principal absorbent constituent and wherein the absorbent layer is an indium-based material chosen from the following materials: In, InP, InGaAsP and InSb.

2. The photolithography mask as claimed in claim 1 , wherein the absorbent layer is produced by a stack of indium-based layers and of at least one metallic layer, the metal being chosen from titanium, tantalum and chromium.

3. The photolithography mask as claimed in claim 1 , wherein a buffer layer, facilitating the selective etching of the absorbent layer relative to the reflecting structure, is interposed between the reflecting structure and the absorbent layer.

4. The photolithography mask as claimed in claim 3 , wherein the buffer layer is a layer of aluminum oxide (Al 2 0 3 or silica.

5. The photolithography mask as claimed in claim 3 , wherein the buffer layer is a stack of several layers, chosen from chromium and aluminum oxide layers.

6. The photolithography mask as claimed in claim 4 , wherein, in an InP absorbent layer/Al 2 0 3 buffer layer stack, the InP absorbent layer has a thickness of about 20 nanometers and the Al 2 0 3 buffer layer has a thickness of about 20 nanometers.

7. A process for fabricating an extreme ultraviolet reflection photolithography mask, in which there are deposited, on a substrate coated with a reflecting structure which is reflective at the operating wavelength of the mask, an absorbent layer which is absorbent at the operating wavelength followed by a photolithography resist, the resist is irradiated in a desired exposure pattern, the resist is developed and the absorbent layer is etched through the resist pattern remaining, so as to define a pattern of zones that are absorbent at the operating wavelength of the mask, wherein the absorbent layer is a layer based on indium as principal absorbent constituent of the layer and wherein the absorbent layer is an indium-based material chosen from the following materials: In, InP, InGaAsP and InSb.

8. The process as claimed in claim 7 , comprising the following steps:

deposition of a reflecting structure, consisting of a stack of an alternation of layers that are transparent at the operating wavelength of the mask and have different indices, on a substrate I

deposition of a buffer layer;

deposition of the indium-based absorbent layer on the buffer layer;

spreading of a lithography resist on the indium-based layer;

production of a desired resist pattern by ultraviolet or electron-beam lithography;

plasma etching of the indium-based layer just where the indium-based layer is not protected by the resist; and

removal of the remaining resist and etching of the buffer layer just where it is not protected by the absorbent layer.

9. The process as claimed in claim 8 , wherein the resist photolithography step is carried out with ultraviolet radiation at a wavelength much longer than the operating wavelength of the mask.

10. The process as claimed in claim 7 , wherein the reflecting structure is produced by ion beam sputtering of several tens of pairs of layers, the overall thickness of each pair being about 6.9 nanometers.

11. The process as claimed in claim 7 , wherein the absorbent layer is made of InP with a thickness of about 20 nanometers and a buffer layer is made of aluminum oxide (Al 2 0 3 ) with a thickness of about 20 nanometers.

12. The process as claimed in claim 7 , wherein the absorbent layer is produced by low-temperature deposition (below about 100° C.) of a layer based on indium phosphide.

13. The photolithography mask as claimed in claim 2 , wherein a buffer layer, facilitating the selective etching of the absorbent layer relative to the reflecting structure, is interposed between the reflecting structure and the absorbent layer.

14. The photolithography mask as claimed in claim 13 , wherein the buffer layer is a layer of aluminum oxide (Al 2 0 3 ) or silica.

15. The photolithography mask as claimed in claim 13 , wherein the buffer layer is a stack of several layers, chosen from chromium and aluminum oxide layers.

16. The photolithography mask as claimed in claim 1 , wherein the absorbent layer is produced by a stack of indium-based layers and of at least one metallic layer, the metal being chosen from titanium, tantalum and chromium.

17. The photolithography mask as claimed in claim 1 , wherein a buffer layer, facilitating the selective etching of the absorbent layer relative to the reflecting structure, is interposed between the reflecting structure and the absorbent layer.

18. The process as claimed in claim 8 , wherein the reflecting structure is produced by the ion beam sputtering of several tens of pairs of layers, the overall thickness of each pair being about 6.9 nanometers.

19. The process as claimed in claim 9 , wherein the reflecting structure is produced by the ion beam sputtering of several tens of pairs of layers, the overall thickness of each pair being about 6.9 nanometers.