A novel tungsten light-shield structure for high-density CCD image sensors

A novel tungsten light-shield structure has been developed. Tungsten film properties, the device configuration with the tungsten light-shield structure, and experimentally achieved results regarding device characteristics are described. Optical measurement clarified that tungsten film has a sufficiently low transmittance value for practical use for more than 200-nm-thick film and is stable up to 1000 degrees C. The good step coverage and low reflectance, such as 20-40% for aluminum, required for light-shield film were also obtained. A tungsten light-shield structure was applied to a 1/2-in format 668(H)-pixel*575(V)-pixel charge coupled-device (CCD) image sensor. An extremely low smear value, less than 0.001%, was obtained for a 300-nm film thickness.<
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