Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Utility Patent
1999-02-11
2001-01-02
Ng{circumflex over (o)}, Ng{circumflex over (a)}n V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S292000
Utility Patent
active
06169317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image sensor used for an image scanner, facsimile device, video camera, digital camera, and the like, and a photoelectric conversion device (element) constituted by the image sensor.
2. Related Background Art
Amplifier and non-amplifier type solid-state image sensors using a charge coupled device (CCD), phototransistor, and photodiode are widely used as line and area sensors serving as electronic eyes of information devices such as the image scanner.
In a photoelectric conversion element in which a photoelectric conversion portion (light-receiving element) and a peripheral circuit such as a signal transfer portion are fabricated on a single substrate, the light-receiving element has a multilayered structure formed from an interlevel insulating film, protective film, and the like. If these layers are made of different materials, they exhibit different diffractive indices to cause multiple interference of light. The spectral sensitivity of the multilayered structure is examined to find a ripple. As a result, even a slight wavelength difference may greatly change the sensitivity of the photoelectric conversion element.
Variations in thickness of the multilayered film on the light-receiving element change the spectral sensitivity in accordance with the film thickness, thereby varying the sensitivity with respect to a given wavelength. This means that the sensitivity with respect to a certain wavelength varies within one chip in a photoelectric conversion element constituted by aligning a plurality of light-receiving elements.
A technique for making the film thickness on the light-receiving element uniform is disclosed in Japanese Patent Application Laid-Open No. 9-55488.
FIG. 15
shows a section of a conventional photoelectric conversion element. A light-receiving element
2
, a first polysilicon gate layer
3
, a second polysilicon gate layer
4
, a light-shielding layer
5
, and a protective film
6
are formed on a substrate
1
. A planarization layer
7
is formed on the resultant structure. In this element, an on-chip lens
9
and a color filter
8
are formed on the planarization layer.
This planarization layer
7
is formed by forming a precursor planarization layer of an insulating material and removing unevenness by chemical mechanical polishing (CMP). In the CMP process, the running costs of an abrasive and polishing pad are high. Further, cleaning must be precisely performed after polishing in order to remove an alkaline abrasive used for polishing and polishing dust produced by polishing. The CMP process therefore requires very high cost.
To form a flat insulating film on a light-shielding layer without any CMP process, a coating insulating film was employed.
The light-shielding layer, however, functioned as a coating barrier, which made the thickness of the coating insulating film different between light-receiving elements on the same chip.
For example, as shown in
FIG. 16
, when the position of the light-receiving element is determined by openings OP defined by the light-shielding layer
5
, the light-shielding layer
5
is interposed between adjacent openings, so the precursor material of the coating insulating film is difficult to flow over the light-shielding layer. Accordingly, a coating insulating film on a light-receiving element near the center in the photoelectric conversion element and a film on a light-receiving element near the end of the element may be different in thickness. This difference becomes larger on a single wafer for forming a plurality of photoelectric conversion elements. In the following case, this film thickness difference appears conspicuously as characteristics of the photoelectric conversion element.
In an image sensor in which a photoelectric conversion element having many aligned light-receiving elements is arranged on a substrate, an original is illuminated to read a color image by sequentially switching three, red, green, and blue LEDs as a light source in time-series. In this case, even if the total thickness of a multilayered film on the light-receiving element is uniform, different thicknesses of respective films vary the spectral sensitivity to change the sensitivity distribution curve at each wavelength, failing to obtain a correct image.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photoelectric conversion element and image sensor in which a light-shielding layer does not become a coating barrier, and the thickness of a coating insulating film hardly varies between light-receiving elements on a single chip.
According to the present invention, there is provided a photoelectric conversion element comprising a plurality of photoelectric conversion portions, and light-shielding means having openings formed above the photoelectric conversion portions, the light-shielding means having first light-shielding layers, and second light-shielding layers formed on the first light-shielding layers via an interlevel insulating film, the first light-shielding layers having gaps for allowing two adjacent openings to communicate with each other, and the second light-shielding layers having light-shielding portions above the gaps of the first light-shielding layers.
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patent: 5159186 (1992-10-01), Ohzu
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patent: 5514888 (1996-05-01), Sano et al.
patent: 5929470 (1999-07-01), Harada et al.
patent: 0 557 098 A1 (1993-02-01), None
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Chye Huat Aw, et al., “A 128x128-Pixel Standard-CMOS Image Sensor with Electronic Shutter ”, Paper FA 11.2, Session 11, IEEE International Solid State Circuits Conference (XP002914009), pp. 180-181.*
Kozuka Hiraku
Nishimura Shigeru
Sawada Koji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ng{circumflex over (o)} Ng{circumflex over (a)}n V.
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