Retrograde well structure for a CMOS imager
AssigneeMicron Technology, Inc.
InventorsHoward E. Rhodes, Mark Durcan
Life of this patent
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Abstract
A retrograde well structure for a CMOS imager that improves the quantum efficiency and signal-to-noise ratio of the imager. The retrograde well comprises a doped region with a vertically graded dopant concentration that is lowest at the substrate surface, and highest at the bottom of the well. A single retrograde well may have a single pixel sensor cell, multiple pixel sensor cells, or even an entire array of pixel sensor cells formed therein. The highly concentrated region at the bottom of the retrograde well repels signal carriers from the photosensor so that they are not lost to the substrate, and prevents noise carriers from the substrate from diffusing up into the photosensor. Also disclosed are methods for forming the retrograde well.
Claims45
A CMOS imager comprising:
- a substrate having at least one retrograde well of a first conductivity type, wherein said at least one retrograde well has a vertically graded dopant of said first conductivity type between a bottom of said at least one retrograde well having a highest concentration of said dopant of said first conductivity type and a top of said at least one retrograde well;
- an array of pixel sensor cells formed in said at least one retrograde well, wherein each pixel sensor cell has a photosensor;
- and
- a circuit electrically connected to receive and process output signals from said array.
An imager comprising:
- an array of pixel sensor cells formed in a substrate having at least one retrograde well of a first conductivity type, wherein each pixel sensor cell has a photosensor and said at least one retrograde well comprises a dopant of said first conductivity type which is at a highest concentration at a bottom of said at least one retrograde well;
- a circuit formed in the substrate and electrically connected to the array for receiving and processing signals representing an image output by the array and for providing output data representing the image;
- and
- a processor for receiving and processing data representing the image.
An imager comprising:
- a CMOS imager comprising
- an array of pixel sensor cells formed in a retrograde well defined by a dopant of a first conductivity type on a substrate having a second conductivity type, wherein each pixel sensor cell has a photosensitive region, a photosensor formed on the photosensitive region, and a floating diffusion region for receiving and outputting image charge received from the photosensitive region, and wherein said retrograde well has a vertical profile having a greatest concentration of said dopant of said first conductivity type at a bottom of said retrograde well and said concentration diminishes toward a top of said retrograde well;
- a circuit formed in the substrate and electrically connected to the array for receiving and processing signals representing an image output by the array and for providing output data representing the image;
- and
- a processor for receiving and processing data representing the image.
Dependencies are inferred from the claim text.