Planarization of optical substrates
Planarization of defects in laser mirror and other optical component manufacture is disclosed. The planarization is performed by first depositing a relatively thick planarization layer, then carrying out a sequential deposition and etch process. The technique takes advantage of the non-uniform material removal rate as a function of etchant incident angle, and effectively buries the inclusion in a thick film with a near planar top surface. The process enables faster, more reliable manufacture of a non-defective high fluence multilayer mirror particularly suitable for high energy laser applications.
1. A method of making an optical component in which a substrate surface has at least a one micron size nodular defect, the method comprising:
depositing a planarization layer over the nodular defect;
depositing an ion beam etchable layer over the planarization layer;
etching away a portion of the ion beam etchable layer;
depositing a layer of a metal oxide over the ion beam etchable layer; and
repeating the steps of depositing an ion beam etchable layer, etching away a portion of the ion beam etchable layer, and depositing a layer of the metal oxide, until the nodular defect is reduced in size a predetermined amount.
2. The method of claim 1 wherein:
the optical component comprises a mirror;
the ion beam etchable layer comprises silicon dioxide (SiO 2 ); and
the layer of the metal oxide comprises hafnium dioxide.
3. The method of claim 2 wherein the planarization layer comprises silicon dioxide (SiO 2 ).
4. The method of claim 1 wherein the step of depositing an ion beam etchable layer comprises depositing at least a one micron thick layer of silicon dioxide.
5. The method of claim 4 wherein the step of etching away a portion of the ion beam etchable layer comprises removing 25% to 75% of the layer of silicon dioxide.
6. The method of claim 5 wherein the step of etching away a portion of the ion beam etchable layer comprises removing about half of the layer of silicon dioxide.
7. The method of claim 4 wherein the layer of silicon dioxide is at least two microns thick.
8. The method of claim 1 wherein the step of depositing at least one of the planarization layer or the ion beam etchable layer comprises sputtering silicon dioxide.
9. The method of claim 8 wherein sputtering silicon dioxide comprises ion beam sputtering silicon dioxide.
10. The method of claim 1 wherein the step of etching away a portion of the ion beam etchable layer comprises ion beam etching.
11. The method of claim 1 wherein the step of depositing a layer of a metal oxide comprises sputtering hafnium dioxide.
12. The method of claim 11 wherein sputtering hafnium dioxide comprises ion beam sputtering hafnium dioxide.