Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2002-10-25
2004-05-18
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S053000, C257S225000, C257S290000, C438S070000, C438S710000
Reexamination Certificate
active
06737719
ABSTRACT:
TECHNICAL FIELD
The present invention relates to image sensors, and more particularly, towards an image sensor that has a short focal length.
BACKGROUND
Image sensors are electronic integrated circuits that can be used to produce still or video images. Solid state image sensors can be either of the charge coupled device (CCD) type or the complimentary metal oxide semiconductor (CMOS) type. In either type of image sensor, a light gathering pixel is formed in a substrate and arranged in a two-dimensional array. Modern image sensors typically contain millions of pixels to provide a high resolution image. An important part of the image sensor are the color filters and micro-lens structures formed atop of the pixels. The color filters, as the name implies, are operative, in conjunction with signal processing, to provide a color image. The micro-lenses serve to focus the incident light onto the pixels, and thus to improve the fill factor of each pixel.
Conventionally, micro-lenses are formed by spin coating a layer of micro-lens material onto a planarized layer. The micro-lens material is then etched to form cylindrical or other shaped regions that are centered above each pixel. Then, the micro-lens material is heated and reflowed to form a convex hemispherical micro-lens.
FIG. 1
shows a prior art cross-sectional simplified diagram of an image sensor
101
having micro-lenses formed thereon. As seen in
FIG. 1
, the image sensor includes a plurality of pixels that have light detecting elements
103
formed in the substrate. The light detecting elements
103
may be one of several types, such as a photodiode, a photogate, or other solid state light sensitive element. Formed atop of each pixel is a micro-lens
105
. The micro-lens
105
focuses incident light onto the light detecting elements
103
. Moreover, in the region between the light detecting elements
103
and the micro-lens
105
, denoted by reference numeral
107
, there are various intervening layers that would typically include the color filter layers and various metal conducting lines. These components are excluded from the diagram in order to simplify the explanation herein and not to obscure the invention.
It has been found that the convex shape of the micro-lenses will sometimes result in a greater likelihood of particle contamination, due to later processing steps. Furthermore, because of the particular processes used to form the micro-lenses, it is difficult to eliminate gaps between the micro-lenses
105
. Generally, it is desirable to minimize the gaps between the micro-lenses, since a larger micro-lens will result in a higher degree of light concentration.
Further, the combination of the convex micro-lens and the color filter layer provides a combined thickness that would normally require a micro-lens with a relatively long focal length, which can be difficult to manufacture at higher, integration densities.
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Flynn Nathan J.
Forde Remmon R
OmniVision International Holding Ltd
Perkins Coie LLP
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