JP2506635B2 - Semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, to an improved charge transfer device with improved noise and frequency characteristics.

2. Description of the Related Art In recent years, the development of charge transfer devices has progressed, and in particular, their application to solid-state imaging devices has been vigorously made. Particularly, in order to improve the S / N ratio, a structure in which the capacitance of the floating diffusion layer is reduced and noise is suppressed as low as possible is generally used.

Hereinafter, the conventional charge transfer device as described above will be described with reference to the drawings. FIG. 4 is a schematic view of a main part of a conventional semiconductor device. The signal charge is sent to the floating diffusion layer 4 formed by the impurity layer through the transfer electrodes 21 and 22 and the output electrode 3 in the direction of arrow 1 in the figure, and the potential change there is detected and output via the source follower 5. . The detected signal charge is sucked into the reset drain 7 by applying a pulse voltage to the reset electrode 6 to bring the reset drain 7 and the floating diffusion layer 4 into conduction.

Problems to be Solved by the Invention At this time, if the capacitance of the floating diffusion layer 4 is large, noise increases, so the width 8 of the floating diffusion layer 4 is made small so that the area thereof is as small as possible. However, if the channels under the reset electrode 6 are formed in parallel, the width 8
If is too small, the width of the reset electrode 6 becomes small as it is. Therefore, the ratio W / L between the channel width W below the reset electrode 6 and its length L becomes small, and gm decreases, so that it takes a long time to suck the detected signal charge to the reset drain. It has a drawback that the frequency characteristic is deteriorated.

The present invention reduces the effective noise of the reset electrode even if noise is reduced.
A semiconductor device that does not reduce gm.

Means for Solving the Problems In order to solve the above problems, the semiconductor device of the present invention is
An output electrode for controlling the output of the transfer charge, a transfer channel disposed below the output electrode and having a narrow width along the direction of charge transfer, a floating diffusion layer adjacent to the transfer channel and receiving the transfer charge, It has a channel region adjacent to the floating diffusion layer and a reset drain region adjacent to the channel region, and the channel region has a width gradually increasing from the floating diffusion layer side toward the reset drain region side. The reset drain region has a slope, the reset drain region is continuous with the sloped channel region, and the second reset drain region having a slope is rectangular and the second reset drain region is continuous with the first reset drain region. Reset drain region for discharging the transfer charges to the reset drain region side. The set electrode, without covering the second reset drain region, a channel region having the inclined portion, which is a semiconductor device which is disposed at the boundary between the first reset drain region and the channel region.

The present invention also includes an output electrode for controlling output of transfer charge,
A transfer channel disposed below the output electrode and having a narrow width along the direction of charge transfer; a floating diffusion layer adjacent to the transfer channel for receiving the transfer charges; and a reset electrode adjacent to the floating diffusion layer. A channel region disposed under the reset electrode, and a reset drain adjacent to the channel region and having a width larger than that of the floating diffusion layer, wherein the channel region is the floating diffusion layer. And a second portion adjacent to the reset drain and having the same width as the floating diffusion layer, and a second portion adjacent to the reset drain and having the same width as the reset drain. The boundary between the floating diffusion layer and the first portion of the channel region, the second portion of the channel region and the reset region. It is also formed with a semiconductor device so as to cover between the boundary with the ins.

Action With the above configuration, the channel width on the floating diffusion side of the reset electrode is narrowed, and even if the noise characteristic is improved, it is possible to effectively obtain a high transfer conductance gm.
It is possible to prevent deterioration of frequency characteristics. Also, since the area on the reset drain side can be made large, the capacitance can be increased,
As a result, the voltage fluctuation on the reset drain side can be suppressed and the noise can be reduced.

First Embodiment A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic diagram of a semiconductor device according to a first embodiment of the present invention. In the drawing, the signal charge is transferred in the direction of arrow 1 in the drawing, sent to the floating diffusion layer 4 via the transfer electrodes 21 and 22 and the output electrode 3, and detected. Below the output electrode 3, as shown by the dotted line, the charge transfer direction, that is, the floating diffusion layer 4 is formed.
A charge transfer channel 14 is provided whose width 13 is gradually reduced toward the side. The detected signal charge is sucked out to the reset drain 7. At this time, the floating diffusion layer 4 in the channel region 15 below the reset electrode 10
By making the width 12 of the portion in contact with the reset drain 7 longer than the width 11 of the portion in contact with, the average W / L can be increased as compared with the conventional case where the channel regions 15 are parallel. Therefore, even if the width of the floating diffusion layer 4 is narrowed to reduce noise, it is possible to prevent the deterioration of the frequency characteristic.

Further, in the first embodiment, as will be apparent from FIG. 1, the reset drain 7 is formed of two regions, that is, the inclined portion 71 connected to the channel region 15 and the rectangular shape 72 connected to it. Then, the reset electrode 10 does not cover the area of the rectangular shape 72, but is stopped by covering only a part of the inclined portion 71.

By adopting such a configuration, the reset drain region can be made large. That is, as compared with the reset electrode 10 that extends to the end of the rectangular shape 72 of the reset drain, it can be used as a reset drain more than the area of the inclined portion 71. As a result,
The capacitance on the reset drain side increases. Although a DC voltage is applied to the reset drain 7 side, fluctuations in the voltage lead to deterioration of noise characteristics. However, by increasing the capacitance on the reset drain 7 side, the fluctuation can be absorbed, and the noise characteristic is improved. Further, since the reset electrode 10 is formed on the channel sloped portion 71 having the sloped portion, even if the reset electrode 10 is shifted to the reset drain 7 side due to mask misalignment, for example, it is placed on the sloped portion of the channel region. Since the width W of the channel region is increased, it is possible to shift gm in the larger direction.

The potential distribution along the line AA 'in the same figure is shown in FIG. In the figure, reference numerals 4-1 to 10-1 denote the potentials of the floating diffusion layer 4, the channel region below the reset electrode 10, the channel region below the reset electrode 10, and the reset drain, respectively. Regarding the potential 10-1 in the channel region under the reset electrode 10, the potential when the clock pulse applied to the reset electrode 10 is "high" is shown by 10-2, and the potential when it is "low" is 10-. 3 shows. With the configuration as in the present invention, the potential under the reset electrode 10 forms an electric field in the channel toward the reset drain as in 10-1 due to the narrow channel effect. Therefore, even when the applied clock pulse shifts from “high” to “low”, the floating diffusion layer side of the channel region is first blocked as shown in FIG. 10-4, and most of the charges existing in the channel are removed. Since it is pushed out to the reset drain side, there is little variation in the amount of charge left in the floating diffusion layer 4 after reset. As a result, the effect of reducing noise is achieved.

Next, a second embodiment using the present invention will be described with reference to FIG. Below the reset electrode 10, a channel region 15 as shown by a dotted line is formed. The channel region 15 is composed of a first portion 15A having the same width as the width 11 of the floating diffusion layer 4 and a second portion 15B having the same width as the reset drain 7. First part 15A and second part 15B
Are formed in the same impurity layer at the same time in a continuous manner, except that they have different sizes. And the reset electrode 10 is
The boundary P between the floating diffusion layer 4 and the first portion 15A and the second portion 1
It is formed so as to cover between 5B and the boundary Q of the reset drain 7. By adopting such a configuration, the average width of the width W of the channel region 15 is reduced in the first portion 15A having a relatively small area, but the reduction width is small and is almost close to the width 12 of the reset drain 7. Becomes

Further, by forming the reset electrode 10 so as to cover a part of the floating diffusion layer 4 side by the distance m, the variation of the area of the floating diffusion layer 4 caused by the displacement due to mask alignment and the manufacturing variation is reduced. Has been. That is,
The reset electrode 10 bites into the reset drain 7 side due to mask misalignment and the like, and the bited area is not added to the floating diffusion layer 4. That is, the distance is shifted to the floating diffusion side by a distance m with a slight margin from the deviation that may occur due to mask alignment and manufacturing variations.

The potential shown in FIG. 2 is different from the gentle gradient shown in FIG. 2 in that it has a step at the boundary between the first portion 15A and the second portion 15B, but noise is reduced. Has the same effect as that shown in FIG.

As described above, according to the present invention, by making the width of the portion in contact with the reset drain of the channel under the reset electrode of the charge detection portion of the semiconductor device larger than the width of the portion in contact with the floating diffusion layer, Even if noise is reduced by reducing the width of the floating diffusion layer, a large gm can be effectively obtained, so that deterioration of frequency characteristics can be prevented and noise can be reduced. Further, even if the positional relationship between the floating diffusion layer, the reset electrode, and the reset drain region is relatively shifted due to mask misalignment and manufacturing variations, gm and noise characteristics can be prevented from deteriorating. There is a great one.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a semiconductor device according to a first embodiment of the present invention, FIG. 2 is a potential distribution diagram of the same, and FIG. 3 is a schematic configuration diagram of a semiconductor device according to a second embodiment of the present invention. FIG. 4 is a schematic configuration diagram of a conventional semiconductor device. 3 ... Output electrode, 4 ... Floating diffusion layer, 5 ... Source follower, 6 ... Reset electrode, 7 ... Reset drain,
10 ... Reset electrode, 4-1 ... Floating diffusion layer potential, 7-
1 ... Reset drain potential, 10-2,10-3,10-4 ...
Channel potential under reset electrode, 11 ... Floating diffusion layer 4
Width, 12 ... reset drain width, 14 ... transfer channel, 15,15A, 15B ... channel area, 21, 22 ... transfer electrode.

Claims (2)

(57) [Claims] 1. An output electrode for controlling the output of transfer charge, a transfer channel disposed below the output electrode and having a narrow width along the direction of charge transfer, and adjacent to the transfer channel for receiving the transfer charge. It has a floating diffusion layer, a channel region adjacent to the floating diffusion layer, and a reset drain region adjacent to the channel region, and the channel region has a width gradually increasing from the floating diffusion layer side toward the reset drain region side. Has a slanted shape, the reset drain region is continuous with the slanted channel region, and is connected with a first reset drain region having a slanted portion and the first reset drain region. And a rectangular second reset drain region, and discharges the transfer charges to the reset drain region side. A reset electrode for causing the second reset drain region is provided at a boundary between the channel region having the inclined portion and the first reset drain region and the channel region without covering the second reset drain region. Semiconductor device. 2. An output electrode for controlling transfer charge output, a transfer channel disposed below the output electrode and having a narrow width along a charge transfer direction, and adjacent to the transfer channel for receiving the transfer charge. A floating diffusion layer, a reset electrode adjacent to the floating diffusion layer, a channel region disposed under the reset electrode, a reset drain adjacent to the channel region and having a width larger than the width of the floating diffusion layer. A first portion in which the channel region is adjacent to the floating diffusion layer and has the same width as the width of the floating diffusion layer;
A second portion adjacent to the reset drain and having a width equal to the width of the reset drain, wherein the reset electrode is a boundary between the floating diffusion layer and the first portion of the channel region; A semiconductor device formed so as to cover a portion between the second portion of the channel region and the boundary of the reset drain.