Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-09-06
2002-10-01
Ngô, Ng{circumflex over (n)}n V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S440000, C257S640000, C438S070000
Reexamination Certificate
active
06459131
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the present invention relates to a CMOS image sensor capable of preventing scum formation and overlapping of neighboring color filters. A method for fabricating the same is also disclosed.
2. Description of the Prior Art
As is well known, an image sensor is an apparatus for sensing a light beam reflected from an object to generate an image data. Especially, an image sensor fabricated by using a complementary metal oxide semiconductor (CMOS) technology is called a CMOS image sensor.
Generally, the CMOS image sensor includes a plurality of unit pixels. Each of the unit pixels also includes a light sensing element and a plurality of transistors. The light sensing element such as a photodiode senses incident light beam to generate photoelectric charges corresponding to an amount of the incident light beam. The transistors perform switching operations to control a transfer of the photoelectric charges.
FIG. 1
is a circuit diagram showing a unit pixel contained in a CMOS image sensor. Here, a reference symbol ML denotes a load transistor for controlling a current that flows via an output node NO of the unit pixel
10
.
Referring to
FIG. 1
, the unit pixel
10
includes a photodiode
12
and four transistors. Four transistors also include a transfer transistor MT, a reset transistor MR, a drive transistor MD and a select transistor MS.
The photodiode
12
senses an incident light to generate photoelectric charges. The transfer transistor MT, coupled between the photodiode
12
and a sensing node NS, transfers the photoelectric charges to the sensing node NS. The reset transistor MR, coupled between a power terminal VDD and the sensing node NS, transfers a reset voltage level from a voltage source to the photodiode
12
and the drive transistor MD.
The drive transistor MD, whose drain is coupled to the power terminal VDD, amplifies a voltage level of the sensing node NS to output an amplified signal. The select transistor MS, coupled between the drive transistor MD and an output node NO, performs a switching operation to output the amplified signal as an image data via the output node NO.
FIG. 2
is a cross-sectional view showing a conventional CMOS image sensor.
As shown, a passivation layer
20
is formed on a semiconductor structure (not shown) including a photodiode and a peripheral circuit. Dyed photoresists are coated on the passivation layer
20
and then patterned to sequentially form color filters. However, due to an influence of the previously formed color filter, a scum is formed in the color filter and an overlap of neighboring color filters is occurred so that a sensitivity of the color filters is degraded.
SUMMARY OF THE DISCLOSURE
A CMOS image sensor is disclosed for preventing a formation of scum and overlapping of neighboring color filters.
An image sensor is disclosed which comprises: a semiconductor structure; a first color filter formed on the semiconductor structure, wherein the first color filter includes a first stacked layer, the first stacked layer having a first nitride layer and a first oxide layer; a second color filter, wherein the second color filter is formed with a dyed photoresist and in contact with the first color filter; and a third color filter formed on a portion where is not overlapped with the first and the second color filter, wherein the third color filter includes a second stacked layer, the second stacked layer having a second nitride layer and a second oxide layer.
A method for fabricating an image sensor is also disclosed which comprises: a) providing a semiconductor structure; b) forming a first color filter on the semiconductor structure, wherein the first color filter includes a first stacked layer having a first nitride layer and a first oxide layer; c) forming a second color filter in contact with the first color filter; and d) forming a third color filter on a portion where is not overlapped with the first and the second color filter, wherein the third color filter includes a second stacked layer having a second nitride layer and a second oxide layer.
REFERENCES:
patent: 5739548 (1998-04-01), Shigeta et al.
patent: 6008511 (1999-12-01), Tokumitsu et al.
Hyundai Electronics Industries Co,. Ltd.
Marshall Gerstein & Borun
Ngô Ng{circumflex over (n)}n V.
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