Process for making a CMOS image sensor

Abstract

An image sensor includes a semi-conducting substrate having a photo-sensitive region and doping for forming a path to a charge-to-voltage mechanism; a dielectric spanning the substrate; and a semi-conducting layer, which is less than approximately 1 micrometer, spanning the dielectric which contains electrodes and circuit elements that control flow of charge.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This is a divisional of application Ser. No. 10 / 753,246, filed Jan. 8, 2004.FIELD OF THE INVENTION [0002] The invention relates to the field of image sensors and, more particularly, to making an image sensor in a wafer that has the structure of a semi-conductor layer over a dielectric layer that is over a semi-conducting substrate. More specifically, the invention relates to making an image sensor with the photosensitive region in the semi-conducting substrate and most of the signal transport and processing circuits in the semi-conducting layer. BACKGROUND OF THE INVENTION [0003] CMOS technology continues to have a trend of finer dimensions with shallower active device volumes. When CMOS technology is used to fabricate an image sensor, then a tradeoff conflict arises as a shrinking active device volume means the quantum efficiency is severely reduced, i.e., the optical sensitivity of an image sensor drops. This trend is most clearly see...

AI Technical Summary

Benefits of technology

[0008] The present invention has the following advantages. Sufficient semi-conducting volume is retained for the image sensor built in SOI to have a quantum efficiency comparable to that of image sensors built in standard semi-conductor wafers. The semi-conducting layer over the photosensitive region may be replaced by a dielectric layer or dielectric layers that permit increased quantum efficiency by the reduction of absorptive or reflective losses in the layers over the photosensitive region.

Problems solved by technology

When CMOS technology is used to fabricate an image sensor, then a tradeoff conflict arises as a shrinking active device volume means the quantum efficiency is severely reduced, i.e., the optical sensitivity of an image sensor drops.

However, thinning is a difficult operation that has the possibility of a low success rate.

Amorphous silicon is a challenging material from which to extract photo-generated carriers, since amorphous silicon generally has a high density of trapping sites for the carriers.

However, the fabrication requires many instances of non-standard process steps.

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