The combination shown in FIG. 4 is then obtained, which has a support layer 1 on one surface of which rests a layer 2 of a substrate to be etched. On the layer 2 rest stacks 8 made up of residual islets 7 of the layer 3 resistant to plasma etching and residual islets 5 of the layer 4. 

The combination obtained in this way is then etched to eliminate the exposed parts of the layer 2 not protected by the stacks 8. 

The combination shown in FIG. 5 is then obtained, which includes residual islets 9 of the layer 2 that correspond to the areas not protected by the stacks 8 and represent the pattern of the mask 5 from FIG. 1. The presence of the residual islets 5 is dependent on the resistance of the material used to make the first polymer resin layer 3. 

In the negative second development mode the combina› tion shown in FIG. 3 is subjected to dry development, for example using an oxygen-based plasma. 

The combination shown in FIG. 6 is then obtained, which includes areas 6 that have been subjected to the deep ultraviolet light and are resistant to plasma etching resting on a layer 2 of a substrate to be etched in turn resting on a surface of a support layer 1. The areas 6 are present because they are resistant to the oxygen-based plasma when the layer 3 has been exposed. In this embodiment, a material is preferably chosen for the layers 3 and 4 that has no intrinsic resistance to an oxygen-based plasma. 

The combination produced in this way is then etched to eliminate the exposed parts of the layer 2 not protected by the areas 6 of the layer 3, in the same way as for positive development. 

The combination shown in FIG. 7 is then obtained, which has stacks 10 consisting of the areas 6 of the layer 3 and the residual islets 11 of the layer 2 protected by the areas 6 of the layer 3. The negative of the pattern of the mask 5 from FIG. 1 is then obtained. 

I claimed: 

1. A semiconductor substrate etching masking layer com› prising an upper layer and a lower layer, wherein the upper layer comprises a material sensitive to wavelengths of light less than 100 nm and at least 10 nm, and wherein the upper layer material is resistant to wavelengths of light from 300 to 100 nm and/or wavelengths of light from 700 nm to 300 nm, and wherein the lower layer comprises a material resistant to wavelengths of light less than 100 nm and greater than 10 nm, and wherein the lower layer material is sensitive to wavelengths of light from 300 to 100 nm and/or wave› lengths of light from 700 nm to 300 nm, and wherein the lower layer material is resistant to plasma etching when the lower layer has developed. 

2. The masking layer claimed in claim 1 wherein said upper layer comprises a material selected from the group 

consisting of resins based on nitrocellulose, resins based on polyphthalaldehyde and mixtures thereof. 

3. The masking layer claimed in claim 1 wherein said lower layer comprises a material that can be converted into pseudo-silica. 

4. The masking layer claimed in claim 3 wherein said lower layer is convertible by treatment with an oxygen› based plasma. 

5. The masking layer claimed in claim 1 wherein said lower layer comprises an organosilicon material. 

6. The masking layer claimed in claim 5 wherein said organosilicon material is selected from the group consisting of polysiloxanes, polysilazanes and mixtures thereof. 

7. The masking layer claimed in claim 6 wherein said organosilicon material is selected from the group consisting of polyphenylmethylsilsesquioxane and perhydrosilazane. 

8. The masking layer claimed in claim 1 wherein said lower layer is deposited from a polymethylsilane plasma. 

9. A process for fabricating a double masking layer for semiconductor substrate etching comprising coupling a photo-ablation layer sensitive to extreme ultraviolet light wavelengths less than 100 nm and at least 10 nm and resistant to deep ultraviolet light wavelengths from 300 to 100 nm and/or to ultraviolet light wavelengths from 700 to 300 nm to a second polymer resin layer resistant to extreme ultraviolet light wavelengths less than 100 nm and at least 10 nm, resistant to plasma etching when said second polymer resin layer has been developed and sensitive to deep ultra› violet light wavelengths from 300 to 100 nm and/or to ultraviolet light wavelengths from 700 to 300 nm. 

10. The process claimed in claim 9 wherein said photo› ablation layer comprises a material selected from the group consisting of resins based on nitrocellulose, resins based on polyphthalaldehyde and mixtures thereof. 

11. The process claimed in claim 9 wherein said second polymer resin layer comprises a material that can be con› verted into pseudo-silica. 

12. The process claimed in claim 11 wherein said second polymer resin layer is convertible by treatment with an oxygen-based plasma. 

13. The process claimed in claim 9 wherein said second polymer resin layer comprises an organosilicon material. 

14. The process claimed in claim 13 wherein said orga› nosilicon material is selected from the group consisting of polysiloxanes, polysilazanes and mixtures thereof. 

15. The process claimed in claim 14 wherein said orga› nosilicon material is selected from the group consisting of polyphenylmethylsilsesquoxane and perhydrosilazane. 

16. The process claimed in claim 9 wherein said second polymer resin layer is deposited from a polymethylsilane plasma. 

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