Titre du document / Document title
Color filter array for CCD and CMOS image sensors using a chemically amplified, thermally cured, pre-dyed, positive-tone photoresist for 365 nm lithography
Auteur(s) / Author(s)MILLER Harris R.
Résumé / Abstract
"On-chip" color filters are commonly used to convert monochromatic, solid-state image sensors into color sensors because they offer a good compromise between cost and resolution for digital cameras. The color filters are fabricated directly onto the surface of the CMOS or CCD image sensor, which generates a mosaic array of pixel-size filter elements. Diazonaphthoquinone (DNQ)-novolac photoresist is used to produce these filters by successively depositing and patterning each color layer. The choice of colors can vary from additive (R,G,B) to subtractive (C,M,Y) or combinations of both. Many of the imaging dyes incorporated in the photoresist interfere by absorbing the same wavelengths of UV radiation required for exposing and patterning the photoresist itself. This unwanted absorption reduces photosensitivity and makes exposure times long and impractical. Pre-dyed photoresists have now been chemically amplified and the exposure times for 365 nm lithography have been reduced, which allows for the fabrication of color pixels as small as 1 micron or less. Photoacid generators incorporated into the pre-dyed photoresist are used to accelerate development in aqueous tetamethyl-ammoniumhydroxide (TMAH) while maintaining a stable photoresist composition with good shelf-life at room temperature. Because the DNQ-novolac photoresist is positive-tone, the patterned photoresist and dye combination must be stabilized by baking or some other means before coating the next colored photoresist. However, the color filter pattern itself is sensitive to the high temperature Stabilization as well as other heat treatments found in the packaging process. Often the photoresist will reflow and discolor, thus reducing the resolution, sensitivity and production yield of the device. Other methods exist for stabilizing the patterned photoresist, such as hexamethylcyclotrisilazane (HMCTS) silylation, which greatly reduces the bake times, eliminates reflow and reduces yellowing, but also requires a vacuum oven to implement the process. A thermosetting, pre-dyed, DNQ-novolac photoresist for 365 nm lithography has now been formulated, which stabilizes the color filter elements after only a few minutes on a hot plate. This greatly reduces the amount of time and equipment required for stabilizing the color filter pattern. Both the silylation process and many hours of bake time have been eliminated so that the time required for completing the entire three-color process has been reduced from several days to only several hours. The thermosetting compound is not activated by the post apply bake, so there is no impact on exposure times or development conditions. Stabilization takes place rapidly at hot plate temperatures slightly higher than the post apply bake temperature. As little as 1% of hydroxymethylmelamine is a sufficient quantity of hardening agent to stabilize the patterned photoresist without interfering with exposure or development. By thermosetting the photoresist on a hot plate, the entire color filter process can be confined to the coating track, developer track and exposure tool.
Revue / Journal TitleProceedings of SPIE, the International Society for Optical Engineering
Source / Source
1999, vol. 3678 (2), pp. 1083-1090 [8 page(s) (article)]
Langue / Language
Editeur / Publisher
Society of Photo-Optical Instrumentation Engineers, Bellingham, WA, ETATS-UNIS
Localisation / Location
INIST-CNRS, Cote INIST : 21760, 35400013482295.0360
Nº notice refdoc (ud4) : 17387091