Patent Number: 
Section: claims

1. An installation for etching at least one wafer coated with a blank photosensitive layer (32), ready to be etched, this wafer having thickness irregularities, wherein:the wafer (30) is arranged to be able to be submitted to a scanning of an irradiation beam,a sheet (33) transparent to the radiation to which the photosensitive layer is sensitive covers the wafer, anda probe beam intended to reflect on the upper portion of said sheet perpendicularly to the irradiation beam spot on the photosensitive layer is provided. 2. The installation for etching a plurality of wafers of claim 1, wherein:each wafer (60) is arranged in a receptacle of a support plate (62) submitted to the scanning of an irradiation beam,said sheet (68) covers all the wafers and the support plate. 3. The etch installation of claim 1, wherein the sheet is glued. 4. The etch installation of claim 1, wherein the sheet has a 100-μm thickness. 5. The etch installation of claim 1, wherein the sheet is an added element having a substantially planar upper portion. 6. A wafer used in the etch installation of claim 1, wherein the photosensitive layer is a layer of a thermosensitive material (2) having its bonding to the wafer (1) modified after a heating. 7. The wafer of claim 6, wherein the thermosensitive is a platinum oxide layer. 8. An installation for etching a plurality of wafers coated with a blank photosensitive layer (32), ready to be etched, thickness irregularities being formed between the wafers, wherein:the wafer (30) is arranged to be able to be submitted to the scanning of an irradiation beam,a sheet (33) transparent to the radiation to which the photosensitive layer is sensitive covers the wafers, anda probe beam intended to reflect on the upper portion of said sheet perpendicularly to the irradiation beam spot on the photosensitive layer is provided. 9. The etch installation of claim 8, wherein the sheet is glued. 10. The etch installation of claim 8, characterized in that the sheet has a 100-μm thickness. 11. The etch installation of claim 8, wherein the sheet is an added element having a substantially planar upper portion.