Self-aligned antiblooming structure for charge-coupled devices and method of fabrication thereof

DETAILED DESCRIPTION The self-aligned element antiblooming structure of this invention provides several important advantages over prior art structures.
There need not be any increase in the combined photoelement well/antiblooming structure size over charge-coupled devices not employing element antiblooming designs.
In addition, the element antiblooming structure of this invention involves minimal processing complication in the manufacture of the charge-coupled device.
The self-aligned element antiblooming structure of this invention is created by modifying the fabrication process for a CCD area imaging device at the step at which the channel stop is fabricated.
In the unmodified prior art process the channel stop is made by introducing typically by ion implantation, a P conductivity type impurity through a columnar pattern of openings in a layer of photoresist.
According to the invention the same arrangement of openings in the photoresist is used, but a unique series of two implantations of impurities and a diffusion are utilized.
In the preferred embodiment, a first dose of N conductivity type impurity is implanted to function as a sink diode for excess charge.
Next, a P type impurity is implanted into the N type region using the same mask.
The mask is then removed and the P and N type impurities are diffused into the substrate.
By choosing an N type impurity which has a substantially smaller diffusivity in silicon than does the P type impurity, the distribution of the N type impurity will remain relatively confined while the P type impurity will diffuse further into the structure.
The result is that a narrow region of P type impurity is formed along the edges of the N type central region.
hence, a heavily doped N type region is defined at the channel stop location and isolated from adjacent channels by a diffused pair of lateral P type barriers.
In a preferred embodiment a charge coupled device fabricated in a semiconductor substrate includes photosensitive means for accumulating charge in response to ambient light; transfer means for transferring charge from the photosensitive means to such other location as desired; and antiblooming means for removing undesired charge from at least one of the photosensitive means and from the transfer means, the antiblooming means including regions in the substrate into each of which both a P and an N conductivity type impurity of significantly different diffusivity have been introduced