Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2000-10-05
2003-01-14
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S435000, C257S436000
Reexamination Certificate
active
06507083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor devices, and, in particular, to integrated image/light sensors, such as MOS image sensors, having a light-shielding layer.
2. Description of the Related Art
Image sensors typically employ an array of light-sensing elements (e.g., photodiodes) to generate electrical signals representing light incident on the device. In addition to the array of light-sensing elements, an image sensor typically includes associated circuitry for selectively reading out the electrical signal generated by the individual elements. The light-sensing elements operate by the well-known photoelectric effect by which the incidence of photons of light on each element generates electrons that constitute the electrical signal from that element. Image sensors may be implemented using color filter arrays (e.g., comprising distributions of different color elements, each of which is responsive to one of red, green, and blue light) to generate color output.
As CMOS technology scales down to deep submicron regimes, the aspect ratio becomes smaller. Here, the aspect ratio is the ratio of the width of an opening in a light-shielding layer and the vertical distance from the light-shielding layer to the corresponding light-sensing element. As the aspect ratio decreases, more and more “off axis” light (i.e., light incident at a non-normal angle) cannot reach the light-sensing element, resulting in the so-called pixel vignetting phenomenon. This often leads to a significant reduction in sensor sensitivity. It can also result in significant non-uniformity in pixel response over the sensor array.
FIG. 1A
shows a cross-sectional view of a portion of an image sensor
100
of the prior art. Image sensor
100
has a transparent dielectric layer
102
formed over a substrate
104
. Disposed within dielectric layer
102
is an opaque light-shielding layer
106
having a pattern of transparent openings
108
that selectively allows incident light to pass through dielectric layer
102
towards an array of light-sensing elements
110
formed on substrate
104
at the interface between dielectric layer
102
and substrate
104
. Each light-sensing element
110
corresponds with one of the transparent openings
108
in light-shielding layer
106
.
In an ideal situation, light always impinges upon image sensor
100
at a normal angle (i.e., perpendicular to both light-shielding layer
106
and the array of light-sensing elements
110
). In that case, all of the light that passes through each transparent opening
108
in light-shielding layer
106
reaches the corresponding light-sensing element
110
below. In reality, however, depending on the situation, at least some if not all of the light is incident at non-normal angles and, in those cases, at least some of the light passing through a transparent opening
108
does not reach the corresponding light-sensing element
110
.
FIG. 1A
shows an exemplary situation of a light source (not shown) positioned at a relatively close distance directly over image sensor
100
. In this case, essentially all of the light that passes through transparent opening
108
c
reaches corresponding light-sensing element
110
c
. However, due to the relatively small aspect ratio of image sensor
100
, some of the light passing through transparent openings
108
b
and
108
d
will not reach corresponding light-sensing elements
110
b
and
110
d,
respectively, and even less of the light passing through transparent openings
108
a
and
108
e
will reach corresponding light-sensing elements
110
a
and
110
e.
The light falling outside of the light-sensing elements
110
will impinge on other regions
112
of the substrate
104
between those light-sensing elements
110
, which regions
112
might not be light sensitive and will, in any case, not contribute appropriately to the electrical signal generated by light-sensing elements
110
.
FIG. 1B
illustrates the pixel vignetting that results from the geometry shown in
FIG. 1A
for off-axis elements, such as elements
110
a
and
110
e.
In particular,
FIG. 1B
shows a top view of the active area of a light-sensing element
110
and the actual light pattern
114
that impinges on substrate
104
after passing through the corresponding transparent opening
108
. As shown in
FIG. 1B
, light pattern
114
is offset from element
110
. This offset reduces the sensitivity of this element in the image sensor to such light.
SUMMARY OF THE INVENTION
The present invention addresses the problem of pixel vignetting by providing an image sensor having a reflective optical path between the light-shielding layer disposed within the transparent dielectric layer and each of one or more light-sensing elements formed on the substrate below. Each reflective optical path is preferably implemented using a reflective liner formed in a via between the light-shielding layer and a corresponding light-sensing element. The reflective paths help to direct non-normal incident light towards the appropriate light-sensing elements, thereby enhancing sensor sensitivity as well as uniformity of response across the sensor array.
In one embodiment, the present invention is an integrated sensor comprising (a) one or more light-sensing elements formed on a substrate; and (b) a light-reflecting structure for each light-sensing element, configured within intervening structure above the substrate to reflect incident light towards the light-sensing element.
REFERENCES:
patent: 5352920 (1994-10-01), Morishita et al.
patent: 5461425 (1995-10-01), Fowler et al.
patent: 5552630 (1996-09-01), Miyake
patent: 6057586 (2000-05-01), Bawolek et al.
patent: 6100556 (2000-08-01), Drowley et al.
patent: 6259083 (2001-07-01), Kimura
patent: 6278169 (2001-08-01), Sayuk et al.
patent: 6362513 (2002-03-01), Wester
Gruzdkov Yuri
Meier Stephen D.
Mendelson Steve
Pixim Inc.
Zheng Joe
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