Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1998-09-08
2001-06-26
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S216000, C257S432000, C438S069000
Reexamination Certificate
active
06252216
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention includes to a solid state image pick-up device in which sensitivity characteristics are graded up in improving condensing efficiency of light to be led to a light receiving sensor.
In recent years, in the case of solid state image pick-up devices, the tendency of miniaturizing or high density arrangement of pixels has been promoted. Along with the promotion or such a tendency the light receiving area of an device is made smaller. This causes the degradation of characteristics such as the deterioration in sensitivity or the increase in smear.
As a measure to counter the deterioration in sensitivity, for example, on-chip-lenses (OCL) are provided on respective units of pixels. This may effectively utilize the incident light on pixels for the purpose of grading up the condensing efficiency of light to be led to light receiving sensors.
An ordinary manufacturing method of on-chip-lenses is discussed next. As shown in
FIG. 4A
, on a substrate
1
, on which respective constitutional devices of solid state image pick-up devices
400
are formed, a smoothing layer
2
and a color filter layer
3
are formed. Over the color filter layer
3
a lens material made of resin, etc. is applied. The applied lens material is patterned to form dots to cover respective pixels formed on the substrate
1
, thus a lens pattern
4
is formed.
After that, the lens pattern
4
is heated at a temperature of 150 to 200° C. for a thermal reflow process, and on-chip-lenses
5
of convex shapes are obtained as shown in FIG.
4
B.
In the case of solid state image pick-up device
400
, the aspect ratio of a unit pixel is changed by the type of image pick-up device. With the change in the aspect ratio of a unit pixel, the aspect ratio of the lens pattern
4
is also changed; therefore, the shape of an on-chips-lens
5
which is obtained as the result is also changed with the change of the type of image pick-up device.
On-chip-lenses
5
are originally formed to improve the condensing efficiency of light to be led to light receiving sensors. In order to optimize the condensing efficiency of light in any type of an image pick-up device, the shape of the on-chip-lens
5
has to be changed independent from the aspect ratio of a unit pixel. It is possible to adjust the radius of curvature of an on-chip-lens
5
to have a desirable form by properly selecting the thickness of an applied film of a lens material, the volume and the shape of a lens pattern
4
formed like scattered dots, and further the reflow temperature at a reflow process.
SUMMARY OF THE INVENTION
Generally, in the case of a solid state image pick-up device, the unit pixel U has a square shape as shown with a two-dot chain line in
FIG. 5A
, and since a transfer electrode
6
or the like is disposed in the unit pixel U, the shape of an opening portion (light receiving portion)
7
of the light receiving sensor becomes a rectangle. Therefore, if the shape of the bottom surface of an on-chip-lens
5
is a circular form as shown in
FIG. 5B
, a square with its corners rounded as shown in
FIG. 5C
, or an elliptical form (not shown in a figure), the areas on which an on-chip-lens
5
is not formed can be produced, and in the result, these areas become useless and enough high condensing efficiency of light cannot be obtained.
On the other hand, when it is intended to decrease the useless areas to the utmost to improve the condensing efficiency of light with an on-chip-lens, it is needed that the shape of the bottom surface of the on-chip-lens
5
is a square to meet the shape of a unit pixel U. However, it is difficult to make a convex lens having the square shaped bottom surface with the present techniques in which a lens pattern
4
is reflow-processed to form a convex lens as described in the above, and an on-chip-lens may be shaped to be a square with its corners rounded as shown in
FIG. 5C
, or a shape which is deviated from the optimum shape to lead an incident light securely to the opening portion
7
of the light receiving sensor.
When the corners of an on-chip-lens are rounded as shown in
FIG. 5C
, as described in the above, four corners of a unit pixel U become useless areas, and when the shape is deviated from the optimum shape, a light incident on the corners of the on-chip-lens is apt to be led into an edge part of the opening portion
7
of the light receiving sensor, and in some cases it can be reflected toward the on-chip-lens again, or in some case it can be a smear component which degrades characteristics.
The present invention was invented in consideration of the above mentioned circumstances, and the purpose of it is to offer a solid state image pick-up device in which useless areas are not produced in the corners of a unit pixel and almost the whole area of the unit pixel becomes an effective area for collecting light. Therefore, the condensing efficiency of light will be enhanced and a solid state image pick-up device having improved sensitivity characteristics will be obtained.
A solid state image pick-up device according to the present invention comprises a plurality of light receiving sensors which perform photoelectric conversion being disposed in vertical and horizontal directions on the surface of a substrate, electric charge transfer portions which transfer signal charges read out from the light receiving sensors, transfer electrodes disposed approximately right upper positions of the electric charge transfer portions on the substrate with an insulating film therebetween, and a smoothing layer covering the transfer electrodes, and over the smoothing layer, first stripe-on-chip-lenses having approximate semicylindrical shapes are formed along the vertical or horizontal lines of the light receiving sensors covering the light receiving portions of the light receiving sensors, and upon the first stripe-on-chip-lenses, second stripe-on-chip-lenses having approximate semicylindrical shapes are formed along the other vertical or horizontal lines of the light receiving sensors covering the light receiving portions of the light receiving sensors.
In the case of the solid state image pick-up device according to the present invention, the first stripe-on-chip-lenses and the second stripe-on-chip-lenses, both having approximate semicylindrical shapes, are formed along the vertical or horizontal lines of the light receiving sensors in different directions from each other; thereby, the first stripe-on-chip-lenses and the second stripe-on-chip-lenses are disposed making a right angle with each other when they are viewed in a plan view, so that the condensing of light in X direction can be done by the lenses in a direction and that in Y direction can be done by the lenses in another direction. Therefore, the condensing of light in both X and Y directions is made possible by forming the second stripe-on-chip-lenses overlapped upon the first stripe-on-chip-lenses.
The overlapping areas of the first stripe-on-chip-lenses and the second stripe-on-chip-lenses viewed in a plan view are square or rectangular shaped, and since the condensing of light in both X and Y directions is made possible in the overlapping areas, an incident light can be securely led to the light receiving sensor even at the corners of a light receiving sensor and further of a unit pixel including the light receiving sensor portion.
As explained in the above, in the case of a solid state image pick-up device according to the present invention, the first stripe-on-chip-lenses and the second stripe-on-chip-lenses having approximate semicylindrical shapes are formed along the vertical or horizontal lines of light receiving sensors in different directions from each other; thereby since the first stripe-on-chip-lenses and the second stripe-on-chip-lenses are disposed in making a right angle with each other when they are viewed in a plan view, the condensing of light in X direction can be performed with a group of lenses and the condensing of light in Y direction can be performed with another group of lenses.
Therefore, it is made
Lee John R.
Sonnenschein Nath & Rosenthal
Sony Corporation
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