Enhanced, protected silver coatings on aluminum for optical mirror and method of making same
AssigneeCorning Incorporated
InventorsJason Ballou, Frederick Gagliardi
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Abstract
The disclosure is directed to enhanced silver coated aluminum substrates for use as optical mirrors in which galvanic corrosion between the silver and aluminum is prevented and a method of making such silver coating and mirrors. The optical mirror according to the disclosure has an in-situ formed “barrier” layer inserted between the aluminum substrate and the silver layer. In addition, selected layers are densified by carrying out their deposition using a high power RF ion source during their deposition.
Claims10
A silver mirror having enhanced galvanic corrosion resistance, said mirror consisting essentially of an aluminum substrate having an in-situ formed chromium nitride layer having a thickness in the range of 50-150 nm on the aluminum substrate, a silver layer having a thickness in the range of 75-150 nm on the chromium nitride layer, a formed chromium oxide layer having a thickness in the range of 0.1 - 0.6 nm on the top of the silver layer, and one or a plurality of enhancing layers formed on the chromium oxide layer;
- wherein when a plurality of enhancing layers is used, different materials are used in alternating adjacent enhancing layers and each individual enhancing layer has a thickness in the range of 10-100 nm.
A silver coated mirror consisting of an aluminum substrate, a 100 nm thick CrN deposited on the substrate, a 120 nm Ag layer deposited on the CrN layer, 0.45 nm chrome oxide layer formed on the silver layer, a 55.3 nm first layer silicon dioxide deposited on the chrome oxide layer, 20.9 nm niobium pentoxide layer deposited on the first silicon dioxide layer and 53.8 nm second layer silicon dioxide layer deposited on the niobium pentoxide layer;
- wherein thickness variation for each layer except the chrome oxide layer is ±5%, and the chrome oxide has a thickness variation of ±10%.
A method of forming a silver mirror using an aluminum substrate and avoiding a galvanic reaction between the aluminum and silver, said method comprising the steps of:
- loading the aluminum substrate to be coated into a coating chamber;
- evacuating the coating chamber to a pressure of <3×10−6 Torr;
- performing an RF pre-clean @300-500 W with approximately 10 sccm argon flow through the chamber for a time in the range of 7-15 minutes;
- depositing the chromium nitride barrier layer to a thickness in the range of 50-150 nm by deposition of chromium in a flow of approximately 30 sccm N2 and 5 sccm Ar at a RF power of 250-400 W that thereby converts the chromium to chromium nitride;
- turning off the RF power and depositing a silver layer to a thickness in the range of 75-150 nm;
- with the RF source off and no gas flowing, depositing a chromium layer having a thickness in the range of 0.1-0.6 nm;
- turning on the RF power to a setting of 250 W and providing an oxygen flow of approximately 50 sccm, and maintaining these conditions to fully oxidize the chrome layer into a chromium oxide layer;
- depositing one or a plurality of enhancing layers;
- and
- venting and clearing the chamber and removing the silver mirror using an aluminum substrate from the chamber.
Dependencies are inferred from the claim text.