Backside thinning of image array devices

• US 20040180462A1
• Filed: 03/05/2004
• Published: 09/16/2004
• Est. Priority Date: 01/31/2003
• Status: Active Grant

• Current Assignee: Eotech, LLC
• Original Assignee: Intevac
• Inventors: Fairbairn, Kevin P., Yin, Edward, Gober, Patricia, Chung, Yun, Costello, Kenneth A., Brown, David W.
• Granted Patent: US 7,005,637 B2
• Time in Patent Office: Days
• US Class Current: 438/48
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• CPC Class Codes: H01L 27/14623 Optical shielding
• CPC Class Codes: H01L 27/14625 Optical elements or arrangements associated with the device
• CPC Class Codes: H01L 27/14629 Reflectors
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers

Abstract

Backthinning in an area selective manner is applied to imaging sensors 12 for use in electron bombarded devices. A further arrangement results in an array of collimators 51 aligned with pixels 42 or groups of pixels providing improved image contrast of such image sensor. Provision of a thin P-doped layer 52 on the illuminated rear surface provides both a diffusion barrier resulting in improved resolution and a functional shield for reference pixels. A gradient in concentration of P-doped layer 52 optimizes electron collection at the pixel array.

Claims

1. The method of reducing image artifact in an electron bombarded active pixel array device comprising the steps of

converting an optical image to a photoelectron flux distribution,

accelerating said flux distribution toward an active pixel sensor array to interact therewith,

interposing an array of collimators to constrain said photoelectron flux through a single collimator to parallel trajectories for normal incidence on at least one corresponding pixel.

2. The method in accordance with claim 1 in which said at least one corresponding pixel comprises a sub-array of pixels.

3. The method in accordance with claim 1 in which said array of collimators comprises a selected shape and each said collimator of said collimator array comprises a cross section transverse to said directed electron flux, said cross section comprising a shape geometrically similar to said selected shape and passing a photoelectron flux through said collimators and to said array of pixels.

4. The method of sensing an image projected on the rear surface of a back illuminated semiconductor pixel array, comprising

forming a P-doped layer of selected thickness on said rear surface to achieve a desired conductivity therein, whereby a conduction band potential barrier is created,

preparing a flux distribution of electrons corresponding to said image,

accelerating said electrons to a selected energy,

intercepting said electrons on said P-doped layer of semiconductor,

generating entirely within said P-doped layer a plurality of electron-hole pairs for each said selected energy electron,

collecting said generated electrons at pixels correspondingly proximate each said generated electron-hole pair, whereby said pixel array contains information comprising said image.

5. The method of claim 4 wherein said step of forming comprises varying the conductivity of said P-doped layer within the thickness of said P-doped layer.