Process for making a dual implanted drain extension for bucket brigade device tetrode structure

The invention is the structure and process for making a bucket brigade device which comprises the merger of an MOS capacitor with an MOSFET device to form the charge transfer cell. A first thin N-type region is implanted at a first concentration in a portion of the P-type channel region of an FET device adjacent to the drain diffusion. A second region is implanted with N-type dopant at a second concentration less than the first concentration, adjacent to and continuous with the first implanted region. The N-type concentration in the second region is just sufficient to compensate for the P-type background doping in the channel region. This structure increases the charge transfer efficiency for the cell and reduces its sensitivity of the threshold voltage to the source-drain voltage. The gate for the device has a substantial overlap over the drain and a minimal overlap over the source and the gate to drain capacitance per unit area is maximized by maintaining a uniformly thin oxide layer across the gate region.