Creating Patterned Multispectral Filters

Tuesday, July 01 2008 Optical coatings as thick as 20 μm with features as small as 5 μm have been successfully and repeatedly produced using the resist lift-off process. As many as four patterns have been successfully applied to an individual substrate or CCD using resist lift-off.

An example of a 100-mm wafer containing hundreds of patterned filters that are 10 μm thick and produced using the lift-off method is shown in Figure 6. The wafer contains 232 four-color chips and 52 large color pads on the wafer. The large color pads are used to verify the performance of each of the four coatings over the entire surface of the wafer. The actual spectral performance of each of the color filters is shown in Figure 7.

Durability & Stability

The patterned multispectral filters discussed and shown in Figure 6 are coated at DSI using their patented MicroDyn® activated sputtering process. In MicroDyn, reactive sputtering of oxides is augmented by a microwave plasma that forms a wider range of oxygen species (ozone, etc.) to enhance the reaction process.

In all sputtering techniques, the sputtered target atoms come out with a large amount of energy, leading to inherently hard coatings. By hard coatings, we mean coatings that have greater mechanical and thermal stability than similar coatings produced by evaporation or PICVD. Due to the low stresses associated with sputtered coatings, multilayer coatings as thick as 100 micrometers have successfully been produced by this deposition technology.

MicroDyn sputtering can deposit a wide variety of materials including alloys and graded index of refraction materials. The process is very stable and allows the thickness of the vast majority of coatings deposited by this method to be controlled by time.

This article was written by Michael Tommervik, Process Engineer, Deposition Sciences, Inc. (Santa Rosa, CA). For more information, contact Mr. Tommervik at This e-mail address is being protected from spambots. You need JavaScript enabled to view it , or click here.