Patent ID: 8350209

Claim:
A method for adapting an index of refraction of an optically active window of a photo electronic device, wherein the method comprises: producing a nanostructure in a surface area of the window by means of a self-organized plasma etch process for etching a silicon base layer; and adjusting an aspect ratio of structural elements of the nanostructure formed in the silicon base layer to a value of 4 or higher depending on an operating wavelength range of the photo electronic device; the structural elements are formed as pin-type structural elements during the plasma etch process by using the working gases oxygen (O 2 ) and sulphur hexafluorine (SF 6 ) without application of additional means for a certain mask formation in a single process step, wherein the silicon base layer is maintained at a constant temperature in the range of 27° C.±5° C. during the process and wherein a plasma power in the range of approximately 100 to 300 Watt is used, wherein a higher plasma power is required at higher process pressures and the ratio of the working gas flow rates is adjusted in correlation to the geometrical tool parameters such that the oxygen exhibits a self-masking effect on the silicon base layer at the point of reaction, which is accomplished in a range of the gas flow rates for SF 6 of 50 to 150 sccm and for O 2 of 20 to 200 sccm and wherein the process time is only a few minutes.