1. Field of the Invention
The present invention relates to a solid-state imaging device, a manufacturing method thereof, and a camera, and particularly to a solid-state imaging device in which pixels having photodiodes on the light sensing surfaces thereof are arranged in a matrix shape, a manufacturing method thereof, and a camera which includes the solid-state imaging device.
2. Description of the Related Art
There has been a problem that in a solid-state imaging device, it becomes more difficult to efficiently transmit the incident light to a photoelectric converting unit as the pixel size is reduced, which results in lowering the sensitivity.
In order to solve this problem, Japanese Unexamined Patent Application Publication No. 2004-221532 proposed a technique in which an optical waveguide was provided above a light sensing unit and below an on-chip lens (OCL) in one pixel in order to reduce a light propagation loss.
The Bayer arrangement has been known widely as a color filter arrangement for pixels of the solid-state imaging device.
For example, the OCL is formed for each pixel, and the optical waveguide is formed between the photodiode and the OCL for each pixel. In addition, each pixel has the photodiode with a same area.
In the solid-state imaging device with the above-described configuration, the shape of the OCL is the same as that of the optical waveguide for the pixels with respective colors of the color filters.
In addition, a configuration in which the shape of the OCL is changed for each color of the color filter has been also known as disclosed in Japanese Unexamined Patent Application Publication No. 2008-172091.
Since the CMOS process which has high affinity with a logic circuit is employed in the CMOS image sensor, there is an advantage in that a peripheral circuit such as a digital signal processor can be mounted on a same semiconductor chip.
The peripheral circuit has been devised in order to reduce its occupying area as much as possible by using a multi-layer wiring, such as a four-layer wiring.
If the number of the wiring layers is increased for the pixels along with the numbers of those for the peripheral circuit, the distance between the semiconductor substrate on which the photodiodes (PD) are formed and the OCL becomes longer, which may lower the light collection efficiency.
In addition, with regard to a camera module for a mobile phone, it is necessary to lower the height of the module in order to downsize the entire size and the thickness of the mobile phone.
For this expectation, the angle of a light beam, which is incident to the periphery of the angle of view of the mounted image sensor, tends to be wider.
If the obliquely incident light in the periphery of the angle of view is not efficiently guided to the photodiodes, there may occur a great difference in the sensitivities between the periphery of the angle of view and the center of the angle of view, which results in a so-called shading which is the deterioration in the pixel characteristic.
Generally, in the formation of the color filters, the color filters of adjacent pixels may possibly overlap with each other if the color arrangements are different in the adjacent pixels. The overlapped portion blocks the light transmission, and becomes a non-effective region.
Specifically, when the adjacent pixels of the green pixel (G) are the red pixel (R) and the blue pixel (B) in the Bayer arrangement, the color filters for G and B and the color filters for G and R are respectively overlapped in the adjacent parts, and the overlapped portions become non-effective regions.
In addition, if the opening of the optical waveguide becomes smaller, the light collection effect may possibly be lowered.
In Japanese Unexamined Patent Application Publication Nos. 58-175372, 2000-69491, and 5-243543, for example, there are descriptions of solid-state imaging devices in each of which pixels with photodiodes provided on their light sensing surfaces are arranged in a matrix shape.