Optimized low leakage diodes, including photodiodes

Details Optimized low leakage diodes, including photodiodes Optimized low leakage diodes, including photodiodes

1999-07-22

2003-03-18

Pham, Long (Department: 2823)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

C438S075000, C438S144000, C438S197000, C438S199000

Reexamination Certificate

active

06534335

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to an improved diode for use in semiconductor devices The invention also relates generally to an improved photodiode having lower charge leakage to the substrate for use in imaging devices.
BACKGROUND OF THE INVENTION
Diodes find use in many solid-state devices. Diodes which respond to light, known as photodiodes, are widely used in many solid-state image sensors, also known as imagers, which were developed in the late 1960s and early 1970s primarily for video image acquisition, transmission, and display. An imager employing a photosensitive diode absorbs incident radiation of a particular wavelength (such as optical photons, x-rays, or the like) and generates an electrical signal corresponding to the absorbed radiation. Typical devices which use photosensitive diodes include charge coupled devices (CCDs), photodiode arrays, charge injection devices, hybrid focal plan arrays, memory and logic circuits and CMOS imagers.
In the case of photosensitive devices such as CCD's or CMOS imagers, the photosensitive region is typically a p-n junction. This junction is reverse biased by applying an electrical potential Vo which reverse biases the p-n junction. The p-n junction is then isolated typically by turning off a “reset transistor” that is used to reverse bias the junction. Under illumination, incident light photons create electron-hole pairs that are separated by the electric field in a depletion region of the p-n junction. This separation by the electric field results in one charge type being stored in the depletion region, thus collapsing the depletion region, and reducing the voltage Vo across the p-n junction. It is this reduction in voltage across the diode p-n junction due to light exposure that is measured.
To provide context for the invention, an exemplary prior art photodiode is described below with reference to FIG.
1
. However, it is to be understood that the invention also has utility in any semiconductor diode device which includes a p-n junction where there is leakage to the substrate. Accordingly, the present invention may also find utility in semiconductor devices where p-n junctions are shielded from light, where p-n junctions are formed in a p-well, where p-n junctions are formed in an n-well, or more complicated junctions such, for example, a p-n-p junction. Also, while
FIG. 1
shows a simplified photodiode
15
for use as a pixel of an imager, it should be understood that the single photodiode pixel
15
in practical use will be a part of either a row of pixels or an M×N array of pixels arranged in rows and columns.
The photodiode
15
of
FIG. 1
is shown in part as a cross-sectional view of a semiconductor substrate
10
doped with a p-type material to form p-well
12
. A field oxide region
20
, which serves to surround and isolate the photodiode
15
may be formed by thermal oxidation of the doped substrate
10
, or by chemical vapor deposition of an oxide material as in the STI (shallow trench isolation) process. More highly doped p-type regions
40
are formed under the field oxide region
20
and an n-type implant
30
is formed between the field oxide regions
20
. The field oxide regions
20
may be formed before or after doped regions
30
,
40
. As shown in
FIG. 1
, p-type regions
40
and n-type implant
30
are typically doped so as to form a junction of regions
30
and
40
that is aligned or self-aligned to the edge of the field oxide
20
. However, the overlapping of the p-type region
40
and the n-type region
30
results in current leakage from the photodiode to the substrate
10
through the depletion region.
The resolution of the imaging device is a function of the size and performance of each photodetector. To improve resolution, such as by presenting more image lines per inch of visual display, a greater number of photoconductors are required per unit area of the photodetector array. Imager performance is degraded if individual photodiodes have high charge leakage. It is important that the photodetector array be fabricated to allow the photodiode charge to be accurately read within the allowed data sampling time of the system.
There is needed, therefore, an improved photodiode for use in an imager apparatus that exhibits decreased charge leakage to the substrate through the depletion region. There is also need for an improved p-n junction diode for other integrated circuit applications, such as DRAM applications, which likewise exhibits reduced charge leakage to the substrate through a depletion region. A method of fabricating diodes, including photodiodes exhibiting these improvements is also needed.
SUMMARY OF THE INVENTION
The present invention provides a photodiode having improved leakage characteristics to the substrate and improved dark current characteristics. A photodiode comprises a first conductive region of the photodiode that is spaced away from the edge of a field oxide. The present invention also provides methods for forming the photodiode of the present invention.
The present invention also relates to a p-n junction diode used in other integrated circuit applications where charge leakage to the substrate through the depletion region may occur, such as where a p-n junction is formed adjacent to field oxide isolation at the memory storage node of a DRAM. In this case too the invention also provides a p-n junction with reduced leakage to substrate and method for fabricating the same by spacing the p-n junction from high leakage areas.
Additional advantages and features of the present invention will be apparent from the following detailed description and drawings which illustrate preferred embodiments of the invention.


REFERENCES:
patent: 4280271 (1981-07-01), Lou et al.
patent: 4663645 (1987-05-01), Komori et al.
patent: 5032535 (1991-07-01), Kamijo et al.
patent: 5352620 (1994-10-01), Komori et al.
patent: 5495116 (1996-02-01), Funakoshi et al.
patent: 5496750 (1996-03-01), Moslehi
patent: 5861655 (1999-01-01), Kozuka et al.
patent: 5942775 (1999-08-01), Yiannoulos
patent: 5956588 (1999-09-01), Choi et al.
patent: 6143612 (2000-11-01), Derhacobain et al.
patent: 6150676 (2000-11-01), Sasaki
patent: 6201270 (2001-03-01), Chen
patent: 6128691 (2001-04-01), Chung et al.
patent: 6448104 (2002-09-01), Watanabe
patent: 4-315442 (1992-04-01), None
patent: 5-102403 (1993-04-01), None

Affiliated with

Also associated with

Rating

Optimized low leakage diodes, including photodiodes does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optimized low leakage diodes, including photodiodes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optimized low leakage diodes, including photodiodes will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3069893