JPH09252106A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the excess infection of impurities in a horizontal transfer section, and to avoid the deterioration of transfer efficiency effectively by infecting impurities so that concentration partially differs and forming the final stage of the horizontal transfer section by one electrode in place of an electrode pair. SOLUTION: The final stage of a horizontal transfer section 6 is formed of one electrode 13 in place of an electrode pair, and impurities are injected into a region under the electrode 13 so that concentration partially differs. That is, a final horizontal transfer electrode LH is formed of one electrode 13 while impurity concentration under the final transfer electrode LH is set so as to partially differ in the horizontal transfer section 6. Consequently, stored charges can be transferred by the driving pulses of two phases in a CCD solid- state image pickup element. Since the electrode 13 is prepared at the same time as the second layer electrodes 2PS of the horizontal transfer section 6, the deterioration of transfer efficiency in the transfer of stored charges can be avoided effectively in the CCD image pickup element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device, and is applied to, for example, a CCD solid-state image pickup device to form a final horizontal transfer electrode of a horizontal transfer section which operates by two-phase drive pulses with only one electrode. At the same time, by implanting impurities so that the concentration is partially different in the region under the final horizontal transfer electrode, it is possible to effectively avoid a decrease in transfer efficiency due to a mask shift or the like.

[0002]

2. Description of the Related Art Conventionally, in a CCD solid-state imaging device,
The accumulated charge generated by the photoelectric conversion unit is transferred in the order of raster scan, converted into an electric signal, and output, so that 2
The three-dimensional imaging result is output.

That is, FIG. 3 is a plan view showing a CCD solid-state image sensor of this type. In the CCD solid-state imaging device 1, the photosensor units 2 formed of photoelectric conversion units are arranged in a matrix, and the vertical transfer units 3 are arranged between the photosensor units 2 continuous in the horizontal direction. At the lower end of 3, the horizontal transfer unit 4 is arranged. Here, the photo sensor unit 2 photoelectrically converts incident light to generate accumulated charges. Each vertical transfer unit 3 is driven by, for example, four-phase drive pulses, and as shown by an arrow A, each photosensor unit 2 is driven.
After reading out the accumulated charge of 1 in a fixed cycle, subsequently, as indicated by an arrow B, the read accumulated charge is sequentially transferred to the horizontal transfer unit 4.

The horizontal transfer section 4 is driven by, for example, two-phase drive pulses, and as shown by an arrow C, the vertical transfer section 3 is driven.
When the accumulated charges transferred from the vertical transfer unit 3 are sequentially transferred to the charge detection unit 5 and the accumulated charges are transferred for one line, the accumulated charges of one line subsequent to the vertical transfer unit 3 are input. The charge detection unit 5 converts the accumulated charges thus sequentially transferred into an electric signal and outputs the electric signal to the outside, whereby the CCD solid-state image pickup device 1 outputs the image pickup result by the raster scan.

In the CCD solid-state image pickup device 1 having such a structure, electrodes made of polysilicon are arranged on a channel formed on a semiconductor substrate to form a vertical transfer section 3, a horizontal transfer section 4, and a charge detection section 5. As a result, a drive pulse having a predetermined phase is applied to each electrode to transfer the accumulated charge and output the imaging result.

That is, in the vertical transfer section 3, first electrodes are formed on a channel formed in advance on a semiconductor substrate with an insulating layer interposed therebetween at a pitch corresponding to that of the photosensor section 2, and then a second electrode is formed. Electrodes are formed between the first electrodes. Further, the first electrode and the second electrode are connected every four. As a result, the vertical transfer section 3 applies a four-phase drive pulse to the corresponding electrodes and sequentially switches the potentials under each electrode to transfer the accumulated charges.

On the other hand, as shown in FIG. 4, in the horizontal transfer section 4, the first layer electrodes 1 are arranged on the channels which are set to a predetermined potential in advance at a pitch corresponding to the vertical transfer section 3.
PS is formed (FIG. 4 (A)), and subsequently, by ion implantation using the first layer electrode 1PS as a mask, a first
Impurities are injected into the channel between the layer electrodes 1PS (FIG. 4 (B)). As a result, the horizontal transfer portion 4 is connected to the first layer electrode 1
The potential between PS is set shallower than that under the first layer electrode 1PS.

Subsequently, the horizontal transfer portion 4 is formed by partially laminating the second layer electrode 2PS between the first layer electrodes 1PS with the insulating layer interposed therebetween (FIG. 4C). Further, the adjacent first layer electrode 1PS and second layer electrode 2PS are connected to each other, thereby forming a continuous electrode pair (FIG. 4D). The first layer electrode 1PS and the second layer electrode 2PS of the horizontal transfer section 4 are formed simultaneously with the first electrode and the second electrode of the vertical transfer section 3, respectively.

As a result, the horizontal transfer section 4, as shown in FIG. 5, applies driving pulses H1 and H2 (that is, two-phase driving pulses) whose signal levels change complementarily to adjacent electrode pairs. (FIG. 5A), the potential can be set so as to change stepwise toward the output gate HOG side, and this stepwise change can be switched in units of electrode pairs. The accumulated charge can be transferred by setting the potential (FIG. 5 (B)).

Similarly, the charge detector 5 is formed by forming electrodes on a channel set to a predetermined potential, so that as shown in FIG. 6, the potential is changed according to the drive signal of the charge detector 5. , And the accumulated charges are sequentially input from the horizontal transfer section 4.
That is, the charge detection unit 5 sequentially inputs the accumulated charges transferred from the horizontal transfer unit 4 via the output gate HOG into the floating diffusion FD, and outputs the imaging result from the floating diffusion FD. Further, in the charge detection unit 5, a reset gate RG is formed adjacent to the floating diffusion FD, and the charge accumulated in the floating diffusion FD is discharged from the reset drain RD as needed through the reset gate RG.

This output gate HOG is adjacent to the final horizontal transfer electrode LH, which is a final stage electrode pair of the horizontal transfer unit 4, and has a second layer electrode 2PS formed on a continuous channel from the horizontal transfer unit 4. The formed charges are transferred from the horizontal transfer unit 4 to the charge detection unit 5.

In this way, in the CCD solid-state image pickup device 1 which switches the potential of the channel to transfer the accumulated charge, converts it into an electric signal and outputs the electric signal, a drive pulse or the like applied to each electrode is simply generated, It is desirable to be able to transfer the accumulated charges reliably. In addition, it is necessary to suppress the generation of dark current.

For this reason, in this type of CCD solid-state image pickup device 1, impurity implantation is repeated by a plurality of ion implantation steps to form the channels of the horizontal transfer section 4, the vertical transfer section 3, and the output gate HOG. 4, the vertical transfer section 3 and the output gate HOG can be surely transferred between the accumulated charges.

That is, in the horizontal transfer section 4, the output gate HOG is normally held at 0 [V], and the CCD is correspondingly held.
In the solid-state image sensor 1, the drive signal can be easily supplied. In this state, output gate HOG
Needs to store sufficient charges, smoothly transfer the accumulated charges from the final horizontal transfer electrode LH to the charge detection unit 5, and hold the transferred charges so as not to flow backward. Further, the horizontal transfer section 4 reliably transfers the accumulated charges to the output gate HOG by a drive pulse having a low level of 0 [V] and a high level of 5 [V] or less, which is equal to the output level of the CMOS. Is desired.

However, in this way, the output gate H
Both the OG and the low level of the final horizontal transfer electrode LH are held at 0 [V]. Therefore, the output gate HOG needs to set the channel potential deep in the horizontal transfer unit 4. Therefore, in the channel under the output gate HOG, impurities are separately injected to deeply set the channel potential so that the accumulated charges can be reliably transferred even with the same voltage.

Specifically, the charge detecting section 5 is controlled under various conditions.
Since the voltage of the reset drain RD in (1) is limited (normally about 10 to 15 [V]), the channel potential of the output gate HOG is determined by the voltage limitation of the reset drain RD and the amount of charge that can be accumulated in the floating diffusion FD. , This output gate HOG
The channel potential of the horizontal transfer unit 4 is determined by the channel potential of the.

As a result, in the CCD solid-state imaging device 1, in the step of implanting ions between the first layer electrodes 1PS described above with reference to FIG. 4, the formation region of the output gate HOG is shielded by a mask, and in this step, the output gate HOG is formed. Do not inject impurities into the channel. Further, the CCD solid-state image pickup device 1 separately ion-implants only the formation region of the output gate HOG in a separate step (not shown), whereby the channel potential of the output gate HOG and the channel potential of the horizontal transfer unit 4 are set to predetermined values. Set.

On the other hand, since the vertical transfer unit 3 takes a long time to transfer the accumulated charges for one line to the horizontal transfer unit 4 and then to transfer the accumulated charges for one subsequent line,
Dark current is likely to occur. The generation of this dark current, especially the dark current from the surface level, can be suppressed by applying a large negative voltage to the electrode and pinning the surface to embed the surface level. Therefore, in the vertical transfer unit 3, the low level of the drive pulse is set to a sufficiently low negative voltage. On the other hand, the high level of the drive pulse is set to 0 [V], which facilitates the configuration of the drive pulse generation circuit.

The vertical transfer section 3 must reliably transfer the accumulated charges to the horizontal transfer section 4 by this drive pulse. That is, also in this case, in the vertical transfer unit 3, it is necessary to set the channel potential of the horizontal transfer unit 4 to a required value.

Therefore, in the manufacturing process of the CCD solid-state image pickup device 1, as shown in FIG. 7, first, impurities are selectively implanted into the entire area of the CCD solid-state image pickup device 1 using a mask. The channel regions of the vertical transfer unit 3 and the horizontal transfer unit 4 are formed, and the channel potential of the vertical transfer unit 3 is set in this process. Then, as shown in FIG.
In the manufacturing process, impurities are further injected only into the channel region of the horizontal transfer unit 4 by ion implantation using a mask, thereby making the channel potential of the horizontal transfer unit 4 shallower than the channel region of the horizontal transfer unit 4. .

In the manufacturing process of the CCD solid-state image pickup device 1, the channel formation is completed in the vertical transfer section 3 by setting each channel region to a predetermined potential in this way. On the other hand, in the horizontal transfer section 4, impurities are further injected to form a channel through the steps described above with reference to FIG.

[0022]

By the way, when impurities are implanted only in the channel region of the horizontal transfer portion 4 in this manner and subsequently the first layer electrode 1PS is formed,
As shown in FIG. 9, it is difficult to completely prevent the mask shift when masking the horizontal transfer section 4, and thus the first layer electrode 1PS of the horizontal transfer section 4 and the first and second electrodes of the vertical transfer section 3 are formed. There is a possibility that the second electrodes 1PS and 2PS may be formed deviated from the channel (FIG. 9A).

In this case, a barrier E is formed at the connection between the horizontal transfer section 4 and the vertical transfer section 3, and the barrier E cannot reliably transfer the accumulated charge. That is, there is a problem that the efficiency of the transfer of the accumulated charges is lowered due to the mask shift.

Below the second layer electrode of the horizontal transfer section, as shown in FIG.
In the ion implantation step of only the horizontal transfer section 4 described above with respect to the above, impurities are implanted, so that the impurities serving as a barrier to the transfer of accumulated charges are implanted in addition to the impurities introduced into the entire horizontal transfer section. It will be. In this case,
If impurities are excessively injected, the arrow F in FIG.
As shown by, the potential increases at the barrier in the depth direction of the substrate. When this potential collides with 0 [V], this potential does not change, and in this case, the electric field used for the transfer of the accumulated charges decreases, and the transfer efficiency of the accumulated charges decreases accordingly.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a solid-state image pickup device capable of effectively avoiding a decrease in transfer efficiency of accumulated charges due to mask shift or the like.

[0026]

In order to solve such a problem, in the present invention, the final stage of the horizontal transfer section is formed by one electrode instead of the electrode pair, and the region below the one electrode is formed. , Impurity is injected so that the concentration is locally different.

That is, if the final stage of the horizontal transfer portion is formed by using one electrode instead of the electrode pair after implanting the impurities so that the concentrations are locally different, the charge is transferred by the two-phase drive pulse. The necessary internal potential can be formed. At this time, this locally different impurity concentration can be set to a predetermined value, and the channel potential at the final stage can be set to a value suitable for the subsequent output gate. On the other hand, between the vertical transfer unit and the vertical transfer unit, a channel is previously formed as a whole and then ion implantation is performed using the first layer electrode of the horizontal transfer unit as a mask, so that the channel potential between the first layer electrodes is increased. Even if the vertical transfer section is driven so as to suppress the dark current by setting to a predetermined value, the accumulated charges can be transferred reliably.

Therefore, it is possible to omit the conventional ion implantation step only for the horizontal transfer portion before the formation of the first layer electrode, and the transfer efficiency is lowered due to the mask shift which may occur in the ion implantation step only for the horizontal transfer portion. Can be effectively avoided. Further, under the second layer electrode of the horizontal transfer portion, the conventional ion implantation step only for the horizontal transfer portion before the formation of the first layer electrode can be omitted, and excessive impurity implantation can be prevented accordingly.

[0029]

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

FIG. 1 shows a CCD according to an embodiment of the present invention.
FIG. 6 is a plan view showing a horizontal transfer unit of the solid-state image pickup device in comparison with FIG. 5. In addition, in FIG. 1, members common to those in FIG. 5 are denoted by corresponding reference numerals, and redundant description will be omitted.

The horizontal transfer section 6 includes a final horizontal transfer electrode L.
H is formed by one electrode 13, and the impurity concentration under the final horizontal transfer electrode LH is set to be locally different. Therefore, in the CCD solid-state image sensor,
The accumulated charge can be transferred by a phase drive pulse. Furthermore, the electrode 13 of this 1 is formed at the same time as the second layer electrode 2PS of the horizontal transfer portion 6, whereby the CCD
The solid-state image sensor is designed to effectively avoid a decrease in transfer efficiency in transferring accumulated charges.

That is, as shown in FIG. 2, the horizontal transfer section 6
After the channel area is formed with the vertical transfer section,
The first layer electrode 1PS is formed by omitting the conventional ion implantation step only in the horizontal transfer portion before forming the first layer electrode (FIG. 2).
(B)). Note that the vertical transfer portion is set to a predetermined channel potential by ion implantation as a unit, as in the conventional case, whereby the formation of the channel is completed. Further, the vertical transfer unit is the first layer electrode 1 of the horizontal transfer unit 6.
In each of the PS and 2PS forming steps, at the same time, the first electrode and the second electrode are formed on the channel, and then these electrodes are formed by wiring.

On the other hand, in the horizontal transfer section 6, the formation region 1 of the final horizontal transfer electrode LH is formed when the first layer electrode 1PS is formed.
2 is held without forming any electrodes. Further, in the formation region of the output gate HOG following the formation region 12, instead of the conventional formation process of the second layer electrode, the gate electrode 1 is simultaneously formed in the formation process of the first layer electrode 1PS.
0 is formed.

Subsequently, the horizontal transfer section 6 is masked together with the vertical transfer section and the area corresponding to the conventional first layer electrode in the formation area 12 of the final horizontal transfer electrode LH. A region below the layer electrode 2PS is set to a predetermined channel potential (FIG. 2 (B)). At this time, in the channel potential under the second-layer electrode 2PS, the vertical transfer unit and the horizontal transfer unit are driven under the same conditions as in the conventional case in which the generation of dark current can be suppressed, and the vertical transfer unit is surely transferred to the horizontal transfer unit. The channel potential is set so that the accumulated charges can be transferred, and in this embodiment, therefore, the conventional ion implantation step for only the horizontal transfer portion before forming the first layer electrode is omitted. Therefore, between the horizontal transfer unit and the vertical transfer unit, it is possible to prevent the generation of the barrier due to the mask shift described above with reference to FIG. 9, and it is possible to effectively avoid the reduction in the charge transfer efficiency due to the mask shift. .

Subsequently, in the horizontal transfer section 6, regions other than the formation region 12 of the final horizontal transfer electrode LH are masked, and this formation region 12 is selectively ion-implanted (FIG. 2).
(C)). As a result, in the horizontal transfer section 6, the region corresponding to the lower portion of the conventional first layer electrode is set to the channel potential corresponding to the output gate 10. As a result, in the CCD solid-state imaging device according to this embodiment, the accumulated electric charge is surely adjusted only by adjusting the potential at the final horizontal transfer electrode LH, instead of the conventional potential adjustment of the entire horizontal transfer unit by ion implantation of only the horizontal transfer unit. Has been made available for transfer.

Therefore, in the channel of the horizontal transfer section 6, the channel potential is kept deep as a whole (especially under the first layer electrode), and excessive impurity injection is prevented, so that the transfer efficiency is increased accordingly. The drop can be effectively avoided.

As a result, in the horizontal transfer section 6, the second layer electrode 2PS is subsequently formed, and at the same time, the final horizontal transfer electrode LH (13) is formed (FIG. 2 (D)), and subsequently the electrode pair is formed by wiring. Are formed (FIG. 2 (E)).

In the above structure, each photo sensor unit 2
The incident light incident on is converted into accumulated charges by photoelectric conversion, and after the accumulated charges are read out to the vertical transfer unit, the vertical transfer units are sequentially transferred to the horizontal transfer unit 6. At this time, the channels of the vertical transfer unit and the horizontal transfer unit are integrally formed, and subsequently, the conventional ion implantation process of only the horizontal transfer unit is omitted, and the first layer electrode 1PS of the horizontal transfer unit 6 is selectively used as a mask. Since the horizontal transfer part is formed by the stable ion implantation (FIG. 2), the formation of a barrier between the horizontal transfer part and the vertical transfer part due to the mask shift is prevented in advance, which effectively reduces the transfer efficiency due to this barrier. To be avoided.

The accumulated charges transferred to the horizontal transfer section 6 in this way are formed with a shallow potential below the second layer electrode 2PS by selective ion implantation between the first layer electrodes (see FIGS. 1 and 2 ( C)), further adjacent first layer electrode 1PS
And the second layer electrodes 2PS are paired, and driving pulses H1 and H2 whose signal levels change complementarily are applied to the adjacent electrode pairs, and are transferred to the horizontal transfer unit 6 in response to the driving pulses. , To the charge detector. More specifically, these accumulated charges are sent from the final horizontal transfer electrode LH of the horizontal transfer unit 6 to the floating diffusion FD via the output gate HOG of the charge detection unit.

At this time, in this embodiment, the final horizontal transfer electrode LH is selectively implanted with impurities in a part of the formation region 12 in the ion implantation step between the first layer electrodes (FIG. 2B). After that, an impurity is selectively injected into the entire formation region 12 to form a channel (FIG. 2C), and a single-layer electrode 13 is formed on the channel. Therefore, instead of adjusting the potential of the entire horizontal transfer portion by ion implantation of only the horizontal transfer portion (FIG. 2D), the potential adjustment of only the final horizontal transfer electrode LH by the impurity implantation in these two steps results in a predetermined potential. It is set, and thereby the accumulated charges are transferred from the horizontal transfer unit to the charge detection unit. At this time, by adjusting the potential of only the final horizontal transfer electrode LH,
By preventing the excessive implantation of impurities, it is possible to effectively avoid the decrease in transfer efficiency. Further, as described above, the conventional ion implantation process for only the horizontal transfer portion can be omitted.

According to the above structure, after the impurities are implanted so that the concentrations are locally different, the final stage of the horizontal transfer section is formed by one electrode instead of the electrode pair, so that Excessive injection of impurities can be prevented, and the decrease in transfer efficiency can be effectively avoided. Further, the conventional ion implantation step only for the horizontal transfer section can be omitted, and the mask shift can be prevented in advance, whereby the deterioration of the transfer efficiency can be effectively avoided.

[0042]

As described above, according to the present invention, after the impurities are implanted so that the concentrations are locally different, the final stage of the horizontal transfer portion is formed by one electrode instead of the electrode pair. It is possible to prevent excessive implantation of impurities in the horizontal transfer unit, and it is possible to omit the conventional ion implantation process only for the horizontal transfer unit. This makes it possible to effectively avoid the deterioration of the transfer efficiency due to these influences.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a horizontal transfer unit of a CCD solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of the horizontal transfer unit of FIG.

FIG. 3 is a plan view showing a conventional CCD solid-state imaging device.

FIG. 4 is a cross-sectional view showing the manufacturing process of the horizontal transfer unit in the CCD solid-state imaging device of FIG.

5 is a cross-sectional view showing a horizontal transfer unit of the CCD solid-state image sensor of FIG.

6 is a characteristic curve diagram showing the potential of a charge detection unit of the CCD solid-state imaging device of FIG.

FIG. 7 is a first example of impurity implantation of the CCD solid-state image sensor of FIG.
It is a top view showing a process.

FIG. 8 is a plan view showing a step of implanting impurities, which is subsequent to FIG.

9 is a cross-sectional view showing a connection portion of a vertical transfer unit and a horizontal transfer unit of the CCD solid-state image sensor of FIG.

10 is a characteristic curve diagram showing the potential of the charge detection unit of the CCD solid-state imaging device of FIG.

[Explanation of reference numerals] 1 ... CCD solid-state image sensor, 2 ... Photo sensor unit, 3
... Vertical transfer section, 4, 6 ... Horizontal transfer section, 5 ... Charge detection section, 1PS ... 1st layer electrode, 2PS ... 2nd layer electrode,
HOG: output gate, LH: final horizontal transfer electrode

Claims (1)

[Claims] 1. A photoelectric conversion unit that is arranged in a matrix and photoelectrically converts incident light to generate accumulated charges, and is arranged between the photoelectric conversion units to sequentially transfer the accumulated charges in a vertical direction. A vertical transfer unit, a horizontal transfer unit that horizontally transfers the accumulated charges transferred from the vertical transfer unit, and a charge detection unit that converts the accumulated charges transferred from the horizontal transfer unit into an electric signal and outputs the electric signal. The horizontal transfer portion includes a channel formed on a semiconductor substrate, a first layer electrode formed on the channel at a predetermined pitch, and a second layer electrode formed between the first layer electrodes. In a solid-state imaging device formed by a pair of electrodes connected to each other, a gate electrode is formed on a channel adjacent to the final stage of the horizontal transfer unit and extending from the horizontal transfer unit to form an output gate. , The charge stored in the horizontal transfer unit is transferred to the charge detection unit via the output gate, and in the horizontal transfer unit, the final stage is arranged between the first layer electrode and the gate electrode instead of the electrode pair. The solid-state imaging device, wherein the solid-state imaging device is formed by the one electrode formed in 1., and the region below the one electrode is doped with impurities such that the concentration is locally different.