JP2005347655A - Solid state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state imaging device which can apply high voltage to a gate of a transistor of a pixel, and reduce an area of a capacitor of a memory. <P>SOLUTION: The device is characterized in that it has the pixel performing photoelectric conversion and the memory which temporarily accumulates a signal outputted from the pixel, and in that a capacitance per unit area of the capacitor constituting the memory is different from that of a gate insulating film of the transistor constituting the above-mentioned pixel. And the device is characterized in that it has the pixel performing photoelectric conversion, the memory which temporarily accumulates a signal outputted from the pixel, and a peripheral circuit which performs controls of the pixel and the memory, or treatments of output signals from the pixel and the memory, and in that a capacitance per unit area of the capacitor constituting the memory is different from that of a gate insulating film of the transistor constituting the peripheral circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging device, and more specifically to an imaging device having a CMOS area sensor and a memory.

  As an area sensor, there are generally a CCD type and a MOS type. The CCD type is a system in which the charge obtained by the photoelectric conversion unit is moved to the transfer unit at the same time for all the pixels, and then the transfer unit sequentially transfers the charge by the bucket relay method to obtain an image signal. On the other hand, the MOS type is a system in which charges obtained by the photoelectric conversion unit are sequentially taken out for each pixel selected by the scanning signal and used as an image signal.

  As described in Patent Document 1, in the MOS type, the photoelectric conversion time of the odd field and the photoelectric conversion time of the even field are shifted by 1/60 seconds. Therefore, in the case of a moving subject, the image is blurred for each field. As a result, a good frame image cannot be obtained. In order to solve this problem, Patent Document 2 employs a system in which a memory corresponding to a pixel is provided, all outputs from the pixel are once transferred to the memory, and then signals are sequentially extracted. FIG. 2 shows a block configuration diagram thereof.

  A memory including the same number of capacitors 15M and transistors 15N as the number of pixels 10C is provided, and all signals obtained from the pixels are temporarily stored in the memory, and then sequentially read out from the memory. The shift can be reduced. A cross-sectional view of the solid-state imaging device at this time is shown in FIG.

  In FIG. 3, 1 is a gate electrode, 2 is a source / drain diffusion layer, 3 is an insulating film, 4 is a capacitance forming electrode, 5 is a capacitance forming diffusion layer, 6 is a charge transfer gate, 7 is a photodiode diffusion layer, and 8 is A photodiode surface shield layer 9 is a semiconductor substrate. In such a structure, the gate insulating film of the transistor of the pixel and the peripheral circuit is formed, and at the same time, the insulating film of the capacitor is formed.

  As a problem when the memory is mounted on the solid-state imaging device in this way, the chip area is increased by the area of the memory, which hinders cost reduction of the chip. Therefore, the area of the memory is preferably as small as possible. As a method for reducing the area of the memory, a method of thinning the insulating film of the capacitor constituting the memory can be easily considered. As a result, the capacity per unit area of the capacitor increases, and as a result, the area of the memory can be reduced.

Japanese Patent No. 2737947 JP-A-2-065380

  However, in the conventional manufacturing method, as described above, the capacitor insulating film is formed, and at the same time, the gate insulating film of the transistor of the pixel and the peripheral circuit is formed. The gate insulating film of the transistor is also thinned.

  Here, assuming that the power supply voltage is 5 V, the voltage applied to the insulating film of the capacitor and the voltage applied to the gate insulating film are considered. The voltage applied to the insulating film of the capacitor is the output signal voltage of the pixel, and its maximum amplitude is about 1 to 2V. On the other hand, the voltage applied to the gate insulating film is a power supply voltage, and the maximum amplitude is 5V.

  Therefore, when the insulating film is thinned, a large electric field is applied to the gate insulating film, and the insulating film is destroyed. Such a problem is common to semiconductor devices on which transistors and capacitors are mounted. For example, in a dynamic random access memory, the power supply voltage is lowered from 5 V to 3.3 V and further to 2.5 V. Thus, the gate insulating film of the transistor is prevented from being broken. Thus, when the power supply voltage decreases, the amount of charge that can be stored in the capacitor decreases. However, in the case of a dynamic random access memory, the final output is a digital signal of “0” or “1”. Even if the charge amount decreases, there is no problem as long as the charge amount is sufficient to determine whether the charge is “0” or the charge is “1”.

  On the other hand, in the solid-state imaging device, when the charge accumulated in the photodiode is transferred to the readout circuit, the amount of signal charge that can be transferred is reduced if the voltage applied to the transfer gate is lowered. In addition, with the recent increase in the number of pixels, output amplifiers are required to be capable of high-speed operation, but in general, amplifiers are capable of high-speed operation, and noise characteristics may deteriorate if gain is set high. Are known. For this reason, it is difficult to increase the gain of the output amplifier. Therefore, a decrease in signal charge that can be transferred leads to a decrease in output signal. As a result, the S / N of the solid-state imaging device is lowered and the dynamic range is reduced.

  As described above, there is a particular problem in the solid-state imaging device in which the output signal is an analog signal, and it is impossible to use a means for reducing the power supply voltage as a means for preventing the gate insulating film from being broken.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a solid-state imaging device that can apply a high voltage to the gate of a pixel transistor and can reduce the area of a capacitor of a memory. There is to do.

  In order to achieve the above object, the present invention includes a pixel that performs photoelectric conversion and a memory that temporarily stores a signal output from the pixel, and a capacitance per unit area of a capacitor that constitutes the memory is The capacitance per unit area of the gate insulating film of the transistor constituting the pixel is different.

  A pixel that performs photoelectric conversion; a memory that temporarily stores a signal output from the pixel; and a peripheral circuit that performs control of the pixel and the memory, or processing of an output signal from the pixel and the memory. And the capacitance per unit area of the capacitor constituting the memory is different from the capacitance per unit area of the gate insulating film of the transistor constituting the peripheral circuit.

  According to the solid-state imaging device according to the present invention, the capacity per unit area of the memory capacitor can be increased, the area of the memory can be reduced, and a high voltage can be applied to the transfer gate of the photodiode unit, and more Since the signal charge can be read out, it is possible to obtain the effects of improving the S / N of the output signal and expanding the dynamic range.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
FIG. 1 is a cross-sectional view of the solid-state imaging device according to the first embodiment.

  In FIG. 1, 1 is a gate electrode, 2 is a source / drain diffusion layer, 3 is an insulating film, 4 is a capacitance forming electrode, 5 is a capacitance forming diffusion layer, 6 is a charge transfer gate, 7 is a photodiode diffusion layer, and 8 is A photodiode surface shield layer 9 is a semiconductor substrate. The capacitor region refers to the capacitor 15M in FIG. 2, the transistor region refers to, for example, transistors in peripheral circuits such as the transistors 15N, 15T, and 22 in FIG. 2, and the photodiode region exists in the pixel 10C in FIG. Refers to a photodiode.

  In FIG. 1, the insulating film thickness in the capacitor region is thinner than the insulating film thickness in the transistor region and the photodiode region. Thereby, the capacity per unit area of the capacitor is increased, and as a result, the area of the capacitor can be reduced. In addition, since the gate insulating film in the transistor and photodiode regions is thick, a high voltage can be applied.

<Embodiment 2>
FIG. 4 is a cross-sectional view of the solid-state imaging device according to the second embodiment.

  In FIG. 4, 1 is a gate electrode, 2 is a source / drain diffusion layer, 3 is an insulating film, 4 is a capacitance forming electrode, 5 is a capacitance forming diffusion layer, 6 is a charge transfer gate, 7 is a photodiode diffusion layer, and 8 is A photodiode surface shield layer 9 is a semiconductor substrate. The capacitor region refers to the capacitor 15M in FIG. 2, the transistor region refers to, for example, transistors in peripheral circuits such as the transistors 15N, 15T, and 22 in FIG. 2, and the photodiode region exists in the pixel 10C in FIG. Refers to a photodiode.

  In the first embodiment, the gate insulating film thickness of the transistor region and the photodiode region is the same. However, if a high voltage is not applied to the gate in some or all of the transistors in the peripheral circuit, FIG. Thus, even if the gate insulating film of the transistor is thinned, there is no problem, and the effect of increasing the capacitance per unit area of the capacitor can be obtained as in the first embodiment.

<Embodiment 3>
FIG. 5 is a cross-sectional view of the solid-state imaging device according to the third embodiment.

  In FIG. 5, 1 is a gate electrode, 2 is a source / drain diffusion layer, 3 is an insulating film, 4 is a capacitance forming electrode, 5 is a capacitance forming diffusion layer, 6 is a charge transfer gate, 7 is a photodiode diffusion layer, and 8 is A photodiode surface shield layer 9 is a semiconductor substrate. The capacitor region refers to the capacitor 15M in FIG. 2, the transistor region refers to, for example, transistors in peripheral circuits such as the transistors 15N, 15T, and 22 in FIG. 2, and the photodiode region exists in the pixel 10C in FIG. Refers to a photodiode.

  In FIG. 3, the insulating film 3 'in the capacitor region is made of, for example, silicon nitride, and has a higher dielectric constant than the insulating film 3 (for example, made of silicon oxide) in the transistor region and the photodiode region. Thus, if the capacitor insulating film is made of a material having a high dielectric constant, the effect of increasing the capacitance per unit area of the capacitor can be obtained as in the first embodiment.

<Embodiment 4>
FIG. 6 is a cross-sectional view of the solid-state imaging device according to the fourth embodiment.

  In FIG. 6, 1 is a gate electrode, 2 is a source / drain diffusion layer, 3 is an insulating film, 4 is a capacitance forming electrode, 5 is a capacitance forming diffusion layer, 6 is a charge transfer gate, 7 is a photodiode diffusion layer, and 8 is A photodiode surface shield layer 9 is a semiconductor substrate. The capacitor region refers to the capacitor 15M in FIG. 2, the transistor region refers to, for example, transistors in peripheral circuits such as the transistors 15N, 15T, and 22 in FIG. 2, and the photodiode region exists in the pixel 10C in FIG. Refers to a photodiode. The insulating film 3 ′ in the capacitor region and the transistor region is made of, for example, silicon nitride, and has a dielectric constant higher than that of the insulating film 3 in the photodiode region (for example, made of silicon oxide).

  In the third embodiment, the constituent materials of the gate insulating film in the transistor region and the photodiode region are the same. However, in some or all of the transistors in the peripheral circuit, the gate insulating film of the transistor as shown in FIG. As long as there is no problem in characteristics even if it is made of a material having a high dielectric constant, the effect of increasing the capacitance per unit area of the capacitor can be obtained even in such a configuration as in the first embodiment.

It is sectional drawing of the solid-state imaging device in Embodiment 1 of this invention. It is a block block diagram of the solid-state imaging device in a prior art example. It is sectional drawing of the solid-state imaging device in a prior art example. It is sectional drawing of the solid-state imaging device in Embodiment 2 of this invention. It is sectional drawing of the solid-state imaging device in Embodiment 3 of this invention. It is sectional drawing of the solid-state imaging device in Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gate electrode 2 Source / drain diffusion layer 3 Insulating film 4 Capacitance formation electrode 5 Capacitance formation diffusion layer 6 Charge transfer gate 7 Photodiode diffusion layer 8 Photodiode surface shield layer 9 Semiconductor substrate

Claims (6)

  A pixel that performs photoelectric conversion; and a memory that temporarily stores a signal output from the pixel; and a capacitance per unit area of a capacitor that constitutes the memory is a unit of a gate insulating film of a transistor that constitutes the pixel A solid-state imaging device characterized by being different from a capacity per area.   A pixel that performs photoelectric conversion; a memory that temporarily stores a signal output from the pixel; and a peripheral circuit that performs control of the pixel and the memory, or processing of an output signal from the pixel and the memory A solid-state imaging device, wherein a capacitance per unit area of a capacitor constituting the memory is different from a capacitance per unit area of a gate insulating film of a transistor constituting the peripheral circuit.   A pixel that performs photoelectric conversion and a memory that temporarily stores a signal output from the pixel, and an insulating film thickness of a capacitor that forms the memory is a gate insulating film thickness of a transistor that forms the pixel A solid-state imaging device characterized by being different.   A pixel that performs photoelectric conversion; a memory that temporarily stores a signal output from the pixel; and a peripheral circuit that performs control of the pixel and the memory, or processing of an output signal from the pixel and the memory A solid-state imaging device characterized in that an insulating film thickness of a capacitor constituting the memory is different from a gate insulating film thickness of a transistor constituting the peripheral circuit.   A pixel that performs photoelectric conversion; and a memory that temporarily stores a signal output from the pixel; and a dielectric constant of an insulating film of a capacitor that forms the memory is equal to a gate insulating film of a transistor that forms the pixel. A solid-state imaging device characterized by being different from a dielectric constant.   A pixel that performs photoelectric conversion; a memory that temporarily stores a signal output from the pixel; and a peripheral circuit that performs control of the pixel and the memory, or processing of an output signal from the pixel and the memory A solid-state imaging device, wherein a dielectric constant of an insulating film of a capacitor constituting the memory is different from a dielectric constant of a gate insulating film of a transistor constituting the peripheral circuit.

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