As solid-state imaging devices, a CMOS solid-state imaging device represented by a CMOS image sensor, and a CCD solid-state imaging device represented by a CCD image sensor are known. In solid-state imaging devices, a front-illuminated type solid-state imaging device in which light enters from the front surface side of a semiconductor substrate is widely accepted. On the other hand, a back-illuminated type solid-state imaging device in which sensitivity can be improved by making the region of a photoelectric conversion element larger than that in the front-illuminated type solid-state imaging device is disclosed.
FIG. 6 is an example of a back-illuminated type CMOS solid-state imaging device. A CMOS solid-state imaging device 1 includes: pixel-isolation regions 4 made of p type, that is a second conductive type, semiconductor regions formed in a first conductive type, for example n-type, silicon semiconductor substrate 2 such that unit pixel regions 3 are separated from each other; and a photodiode PD which serves as a photoelectric conversion element and a required number of MOS transistors Tr for reading out signal charges obtained through photoelectric conversion and accumulated in the photodiode PD, which are formed within each of the pixel regions 3 surrounded by the p-type pixel-isolation regions 4.
The p-type pixel-isolation regions 4 are formed in the direction of the depth of the substrate such that the region extends from the front surface to the back surface of the substrate 2. The MOS transistors Tr are formed in p-type semiconductor regions 5 which are connected to the p-type pixel-isolation regions 4 and extend, on the front surface side of the substrate 2. The photodiodes PD are formed extending to the back surface side of the substrate 2 such that the photodiode extends to the lower part of the p-type semiconductor regions where the MOS transistors Tr have been formed. Each photodiode PD includes an n-type semiconductor region 7, which is formed of the n-type substrate 2 surrounded by the p-type pixel-isolation regions 4, and a high concentration p+ semiconductor region 6 that is a lower layer of the p-type semiconductor region 5; and a pn junction j1 is mainly formed between the n-type semiconductor region 7 and the p+ semiconductor region 6.
A p+ accumulation layer 8 for restraining the occurrence of dark current, which is made of a high impurity concentration p-type semiconductor region is formed at the interface on the back surface of the n-type semiconductor region 7 which constitutes a photodiode PD, in common with each pixel. Further, a p+ accumulation layer 11 is formed at the interface on the front surface of the n-type semiconductor region 7 as well. On the other hand, a MOS transistor Tr has an n-type source drain region 9 formed in the p-type semiconductor region 5, and a gate electrode 10 formed above and between a pair of n-type source drain regions 9 with a gate insulating film in between. The MOS transistor Tr shown in the figure includes the photodiode PD, the n-type source drain region 9 and the gate electrode 10 to form a readout transistor.
On the front surface of the semiconductor substrate 2 is formed a multilayer wiring layer 14 in which multilayer wirings 13 are laminated with an interlayer insulating film 12 made, for example, of a silicon dioxide film or the like in between, and on this multilayer wiring layer 14 is formed a supporting substrate 15 for reinforcement that is made of a silicon substrate, for example. On the back surface of the semiconductor substrate 2, which is a light incidence surface, is formed a color filter 17 with an insulating layer 16 in between, and an on-chip microlens 18 is formed thereon.
In this back-illuminated type CMOS solid-state imaging device 1, light enters from the back surface side of the substrate through the on-chip microlens. The light is separated into light beams of red, green and blue by the color filter 17, which enter the photodiodes PD of corresponding pixels, respectively. Subsequently, signal charge of each pixel is read out through the MOS transistor Tr on the front surface side of the substrate, and so a color image is output. Since the back-illuminated type CMOS solid-state imaging device 1 has a large area so that the photodiode PD extending to the lower layer of the MOS transistor Tr, high sensitivity can be obtained.
In the above-described back-illuminated type solid-state imaging device, a pn junction j2 is formed by the p+ accumulation layer 8 and the n-type semiconductor regions 7 of the photodiodes PD which are formed on the light incidence surface side, with the same depth in each pixel; and a pn junction j1 of the photodiode PD is similarly formed with the same depth in each pixel. In order to obtain a color image, such back-illuminated type solid-state imaging device uses the color filter 17 and photoelectrically converts light of a specific wavelength to obtain a signal from each pixel. Accordingly, there has been a problem in which the formation process of a color filter causes the number of production processes to increase, the cost increase, and the yield rate deterioration.
In light of the above, the present invention provides a back-illuminated type solid-state imaging device in which color separation of a pixel is made possible without using a color filter, and a camera module and an electronic equipment module which incorporate this solid-state imaging device.
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