JP2812003B2 - Solid-state imaging device and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device for converting two-dimensional information into a time-series electric signal, and a method of manufacturing and driving the same.

[0002]

2. Description of the Related Art In a conventional solid-state imaging device, the impurity concentration of a well below a channel of a vertical charge-coupled device is equal to the impurity concentration of a well below a channel serving as at least a storage region of a horizontal charge-coupled device. .

[0003]

The maximum charge storage capacity per unit area of the charge-coupled device is determined by the charge storage capacity of the charge-coupled device and the shallowest channel when the channel of the charge-coupled device acts as a barrier region. It is obtained by the product of the maximum channel potential difference, which is the channel potential difference between the potential depth and the deepest channel potential depth when acting as a storage region. Charge storage capacitor is dependent on the non-net concentration of the channel, for example, in the case of the embedded type charge-coupled device having a N-type channel region, the larger N-type impurity concentration constituting the channel is in a high concentration. When there is no restriction from external driving conditions, the maximum channel potential difference is, for example, in the case of a buried charge-coupled device having an N-type channel region, that the charge-coupled device keeps an electrically separated state from a peripheral region. It is given by the difference between the deepest channel potential given by the maximum possible gate voltage and the shallowest channel potential determined by the pinning potential of the charge coupled device.

On the other hand, at a temperature at which the ionization of the added impurity cannot be regarded as 100%, the transfer efficiency deteriorates. This deterioration occurs as the impurity concentration of the channel becomes higher and the driving frequency of the charge-coupled device becomes higher. The higher the value, the more noticeable.

[0005] A two-dimensional solid-state imaging device is required to have a large dynamic range. Therefore, it is desirable that a large amount of signal charges can be handled by a charge-coupled device. Since the vertical charge-coupled device in the two-dimensional solid-state imaging device has an area limitation, the maximum charge storage amount per unit area must be increased in order to increase the dynamic range.
In the vertical charge-coupled device, the driving frequency is not high enough to detect the above-described deterioration of the transfer efficiency.
In the case of a buried charge-coupled device having an N-type channel region, the charge storage capacity may be increased by increasing the N-type impurity concentration of the channel.

On the other hand, the horizontal charge-coupled device has no area limitation unlike the vertical charge-coupled device, and has a drive frequency such that the transfer period of all stages of the horizontal charge-coupled device corresponds to the transfer period of one stage of the vertical charge-coupled device. Since it is high and the transfer efficiency is likely to deteriorate, it is advantageous to reduce the impurity concentration of the channel and to handle the channel wide.

As described above, in the above-described conventional solid-state image pickup device, the vertical charge-coupled device and the horizontal charge-coupled device are different in the appropriate amount of the impurity concentration of the channel between the vertical charge-coupled device and the horizontal charge-coupled device. Since the channel impurity concentration is the same, when the channel impurity concentration is increased, the dynamic range can be increased. However, when the channel impurity concentration is cooled, a problem that signal transfer failure occurs in the horizontal charge-coupled device occurs, and conversely, the channel impurity concentration is decreased. In this case, the signal charge transfer failure in the horizontal charge-coupled device does not occur even if the cooling is performed, but the dynamic range cannot be increased.

Further, a conventional solid-state image pickup device in which the channel impurity concentration of the vertical charge coupled device and that of the horizontal charge coupled device are different from each other has been devised to solve the above-mentioned problem (refer to Japanese Patent Application No. 2-294184). In (2), when transferring signal charges from the vertical charge-coupled device to the horizontal charge-coupled device, the gate applied voltage of the charge-coupled device is restricted in order to prevent a barrier generated in the transfer path and to match the channel potential .
As a result, the optimum conditions for both the vertical charge-coupled device and the horizontal charge-coupled device, in particular, a sufficient maximum channel potential difference could not be obtained.

[0009]

There are two inventions for solving the above-mentioned problems .

First, vertical charge-coupled devices and horizontal charge-coupled devices
By combining the elements, the optical signal of the two-dimensional information
The solid-state imaging device that outputs the vertical charge
Coupling device and at least the storage region of the horizontal charge coupled device
Is the channel that transfers signal charges and the wafer immediately below the channel.
Channel type with different conductivity type
The impurity concentration in the channel embedded in the vertical charge-coupled device.
Degree of the channel that becomes the storage region of the horizontal charge-coupled device.
Higher than the impurity concentration, and of the vertical charge-coupled device.
The impurity concentration of the well is lower than that of the horizontal charge-coupled device accumulation region.
Higher than the impurity concentration of the well , a voltage can be applied independently to the junction between the vertical charge-coupled device and the horizontal charge-coupled device separately from the gate electrode between the vertical charge-coupled device and the horizontal charge-coupled device And the impurity concentration of the channel and the well under the independent transfer electrode is the same as the impurity concentration of the channel and the well of the horizontal charge-coupled device, respectively.

[0011] The solid-state image pickup device having the above-described features is provided at the channel portions of the vertical charge coupled device and the horizontal charge coupled device.
Adding a suitable amount and depth distribution of impurities to the wells of the horizontal charge-coupled device, and then adding an amount of impurities suitable for the horizontal charge-coupled device channel to the horizontal charge-coupled device channel; Is added to the vertical charge-coupled device, the impurity amount and the depth distribution in addition to the impurity addition to the well described above are subjected to impurity addition suitable for the well of the vertical charge-coupled device, and then to the above-described channel. The vertical charge-coupled device can be manufactured by adding an impurity suitable for the channel of the vertical charge-coupled device to the vertical charge-coupled device so that the impurity amount and the distribution in the depth direction together with the addition of the impurity are suitable .

[0012]

[0013]

The second is a driving method of the solid-state image pickup device having the first feature. When the channel under the independent transfer electrode of the vertical charge coupled device acts as a barrier region, the channel under the independent transfer electrode is used. The potential depth is a voltage at a level that does not become at least shallower than the channel potential depth when the channel of the other transfer electrode of the vertical charge-coupled device acts as a barrier region , and the magnitude of the fringe electric field and
By expanding the range, obstacles caused by changes in impurity concentration
A voltage of a level sufficient to reduce the wall is applied to the independent transfer electrode.

[0015]

In the solid-state imaging device according to the present invention, the impurity concentration of the channel and the well of the vertical charge-coupled device and the horizontal charge-coupled device are different, and the impurity concentration of the channel and the well of the vertical charge-coupled device is at least the accumulation region of the horizontal charge-coupled device , The maximum charge accumulation per unit area can be increased in the vertical charge-coupled device, and the problem of the transfer efficiency deterioration during cooling in the horizontal charge-coupled device can be eliminated. The maximum charge storage amount is given by the product of the charge storage capacity per unit area and the maximum channel potential difference. The charge storage amount per unit area can be increased by increasing the impurity concentration of the channel. The deterioration of the transfer efficiency during cooling of the horizontal charge-coupled device is caused by the fact that impurities constituting the channel, for example, in the case of a buried charge-coupled device having an N-type channel region, an N-type impurity such as phosphorus is trapped as a charge transfer. Due to behavior. The transfer efficiency can be improved by lowering the concentration of impurities constituting the channel of the horizontal charge transfer element. By independently optimizing the impurity concentration in the wells of the vertical charge-coupled device and the horizontal charge-coupled device, the channel potential of the vertical charge-coupled device and the horizontal charge-coupled device having different channel impurity concentrations can be matched. it can. As a result, the maximum channel potential difference can be increased, and the maximum charge accumulation amount of the vertical charge-coupled device can be increased, the transfer efficiency of the horizontal charge-coupled device can be improved, and the voltage applied to the gate can be reduced.

[0016]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of one embodiment of a solid-state imaging device according to claim 1 of the present invention. This embodiment is a charge coupled device type solid-state imaging device of an interline transfer system.

A photoelectric conversion element 1 is two-dimensionally arranged on a semiconductor chip, and a vertical charge-coupled element 2 having a high channel impurity concentration and a high well impurity concentration is provided in each column.
It is provided for each book. An image area is composed of the two-dimensionally arranged photoelectric conversion elements 1 and the vertical charge-coupled elements 2 arranged in a row, under which a horizontal charge-coupled element 3 having a low channel impurity concentration and a low well impurity concentration.
Is provided. Vertical and horizontal charge coupled devices
Configuration, channel impurity concentration and wells at the junction
The relationship between the impurity concentrations is as shown in FIG. Vertical charge
ΦV4 ′ electrode which is the independent transfer electrode 11e of the
Transfer electrode 11d independent of pole and vertical charge-coupled device
Channel and well at the boundary with the φV3 electrode
Are different. On the side where the φV3 electrode exists
Vertical electrodes with high channel impurity concentration and well impurity concentration
A load coupling element, a φV4 ′ electrode, a gate electrode 12 and
The channel on the side of the horizontal charge-coupled device where the transfer electrode is
Charge-coupled device with low concentration of pure substance and well impurity
You. Following the output terminal of the horizontal charge-coupled device 3, the output unit 4
Is provided.

Although the embodiment described above is of the interline transfer system, the present invention can also be applied to a charge transfer device type solid-state image pickup device of a frame transfer system.

[0019] FIG. 2 is a schematic cross-sectional view of an embodiment relates to a solid-state imaging device according to the first aspect of the present invention. The vertical charge-coupled device is depicted in a four-phase drive scheme.

A P-type well 6 having a high impurity concentration, an N-type channel 7 having a high impurity concentration, a P-type well 8 having a low impurity concentration, and an N-type channel 9 having a low impurity concentration are provided on the surface side of the Si substrate 5. Facing those channels,
Transfer electrode 1 of vertical charge coupled device via SiO ₂ film 10
1a to 11e, a gate electrode φVL12 and a transfer electrode 13 of a horizontal charge-coupled device are provided. The independent transfer electrode φV4′11e is connected to the non-independent transfer electrode φV31
1d and the gate electrode φVL12.
The boundary between the P-type well 6 having a high impurity concentration and the P-type well 8 having a low impurity concentration and the boundary between the N-type channel 7 having a high impurity concentration and the N-type channel 9 having a low impurity concentration are not independent transfer electrodes φV311d. And the independent transfer electrode φV4 '
11e.

[0021] FIG. 3 is a manufacturing process diagram for showing an embodiment of manufacturing method of a solid-state imaging device according to the first aspect of the present invention. This manufacturing method is similar to the solid-state imaging device according to the second embodiment.
Is manufactured with higher precision.

After a base forming step of forming a P ⁺ type channel blocking region (not visible in FIG. 3) and a thick SiO ₂ film 14 on the Si substrate 5, the photoelectric conversion element (not visible in FIG. 3) is completed. .) Is applied (not visible in FIG. 3). By implanting boron ions 15 through a thin SiO ₂ film, a P-type well 8 having a low impurity concentration is formed (FIG. 3A). N-type channel 7 having a low impurity concentration by implantation of phosphorus ions 16 through a thin SiO ₂ film
Is formed (FIG. 3B). Independent transfer electrode 11e in the vertical charge coupled device and one in the horizontal charge coupled device
A transfer electrode 13 of the layer is formed, and a new photoresist mask 17 is applied to cover the photoelectric conversion element (not visible in FIG. 3) and the middle of the independent transfer electrode 11e. Here, additional boron ions 18 are implanted to form a P-type well 6 having a high impurity concentration (FIG. 3C). Additional phosphorus ion 1
9 is implanted to form an N-type channel 7 having a high impurity concentration [FIG. 3 (c)]. An additional phosphorus ion 19 is implanted to form an N-type channel 7 having a high impurity concentration [FIG.
(D)]. Thereafter, of the transfer electrodes that are not independent of the vertical charge-coupled device, the transfer electrode 11a in the same layer as the independent transfer electrode 11e in the vertical charge-coupled device and the first transfer electrode 13 in the horizontal charge-coupled device. , 11c [FIG. 3 (e)]. The transfer electrodes 11b and 11d of the second layer in the vertical charge-coupled device, the gate electrode 12, and the transfer electrode of the second layer in the horizontal charge-coupled device (not shown in FIG. 3) are formed to form both vertical and horizontal electrodes. All the electrodes of the charge-coupled device are completed [FIG. 3 (f)].

[0023] FIG. 4 is a manufacturing process diagram for illustrating a second embodiment relates to a method for manufacturing a solid-state imaging device according to the first aspect of the present invention. This manufacturing method is for manufacturing the first embodiment of the solid-state imaging device with higher accuracy.

After a base forming step of forming a P ⁺ type channel blocking region (not visible in FIG. 4) and a thick SiO ₂ film 14 on the Si substrate 5, the photoelectric conversion element (not visible in FIG. 4). Is applied (not visible in FIG. 4). By implanting boron ions 15 through a thin SiO ₂ film, a P-type well 8 having a low impurity concentration is formed (FIG. 4A). After stripping the photoresist,
A photoresist mask 20 covering the photoelectric conversion element (not visible in FIG. 4) and the horizontal charge-coupled element region at the boundary between the vertical charge-coupled element and the horizontal charge-coupled element is applied, and the thin SiO ₂ film is interposed. The P-type well 6 having a high impurity concentration is formed by implanting additional boron ions 18 [FIG.
(B)]. A new photoresist mask (not visible in FIG. 4) covering the photoelectric conversion element (not visible in FIG. 4) is applied. Phosphorus ions 16 are implanted to form an N-type channel 9 having a low impurity concentration (FIG. 4C). The photoresist is stripped. Photoelectric conversion element (not visible in FIG. 4)
Then, a new photoresist mask 21 is applied to cover the horizontal charge-coupled device region at the boundary between the vertical charge-coupled device and the horizontal charge-coupled device. An additional phosphorus ion 19 is implanted to form an N-type channel 7 having a high impurity concentration [FIG.
(D)]. Transfer electrodes 11a, 1 in a vertical charge-coupled device
1c, 11e, and the first-layer transfer electrode 13 in the horizontal charge-coupled device, and the second-layer transfer electrodes 11b, 11d in the vertical charge-coupled device, the gate electrode 12, and the horizontal charge-coupled device. Then, the transfer electrodes (not visible in FIG. 4) of the second layer are formed, and all the electrodes of both the vertical and horizontal charge-coupled devices are completed [FIG. 4 (e)].

FIG. 5 is a manufacturing process diagram for illustrating a third embodiment relates to a method for manufacturing a solid-state imaging device according to the first aspect of the present invention. This manufacturing method is for manufacturing the first embodiment of the solid-state imaging device with higher accuracy.

After the base forming step of forming a P ⁺ type channel blocking region (not visible in FIG. 5) and a thick SiO ₂ film 14 on the Si substrate 5, the photoelectric conversion element (not visible in FIG. 5). Then, a photoresist mask 22 covering the vertical charge-coupled device region at the position A at the boundary between the vertical charge-coupled device and the horizontal charge-coupled device is applied. By implanting boron ions 15 through a thin SiO ₂ film, a P-type well 8 having a low impurity concentration is formed (FIG. 5A). After removing the photoresist, a photoelectric conversion element (not visible in FIG. 5) and
A new photoresist mask 2 covering the horizontal charge coupled device region at the boundary between the vertical charge coupled device and the horizontal charge coupled device
Then, a P-type well 6 having a high impurity concentration is formed by implanting high-concentration boron ions 24 through the thin SiO ₂ film (FIG. 5B). A new photoresist mask 25 covering the photoelectric conversion element (not visible in FIG. 5) and the vertical charge coupled element region at the boundary between the vertical charge coupled element and the horizontal charge coupled element is applied. Implant phosphorus ions 16,
An N-type channel 9 having a low impurity concentration is formed [FIG.
(C)]. The photoresist is stripped. A new photoresist mask 26 covering the photoelectric conversion element (not shown in FIG. 5) and the horizontal charge coupled element region at the boundary between the vertical charge coupled element and the horizontal charge coupled element is applied. High-concentration phosphorus ions 27 are implanted to form an N-type channel 7 having a high impurity concentration (FIG. 5D). The transfer electrodes 11a, 11c, and 11e in the vertical charge-coupled device and the first-layer transfer electrode 13 in the horizontal charge-coupled device are formed, and the second-layer transfer electrodes 11b, 11d, and A gate electrode 12 and a second-layer transfer electrode (not visible in FIG. 5) in the horizontal charge-coupled device are formed, and all the electrodes of the vertical and horizontal charge-coupled devices are completed (FIG. 5E).

[0027] FIG 6 (a) ~ (d) is a second aspect of the present invention
FIG. 4 is a potential well diagram for explaining an example of a driving method of the solid-state imaging device described above. FIG. 2 also shows a schematic cross-sectional view (FIG. 6A) of a corresponding solid-state imaging device.

The accumulation of charges in the vertical charge coupled device is always performed for two transfer electrodes. As for the transfer, the channel potential under the transfer electrode, which was acting as a barrier on the horizontal charge-coupled device side (right side) of the accumulated transfer electrode, is increased, and the accumulation on the far side (left side) from the horizontal charge-coupled device is performed. This is sequentially performed by lowering the channel potential under the transfer electrode. The impurity concentration of the channel and the well changes at the boundary between the transfer electrode 11d and the independent transfer electrode 11e. This change in the impurity concentration is caused by the misalignment of the photomask and the lateral diffusion of the impurity, and the transfer electrode 11
There is a danger that it will be shifted from the position of the boundary between d and the independent transfer electrode 11e. If the position of the boundary between the impurity and the boundary between the electrodes is displaced, a deep portion and a shallow portion of the potential well may be generated around the boundary even at the same gate applied voltage, which may become a barrier in charge transfer. The barrier can be reduced by the effect of the fringe field. In the present embodiment, the barrier is reduced by increasing the amplitude of the driving pulse applied to the independent transfer electrode 11e which is not subject to the driving restrictions in the image area, thereby increasing the magnitude and range of the fringe electric field.

[0029]

As described in the foregoing, according to the solid-state imaging <br/> element and driving the dynamic process of the present invention, when it increases the maximum charge storage capacity per unit area at the vertical charge coupled devices simultaneously In addition, the problem of transfer efficiency degradation during cooling in the horizontal charge-coupled device can be eliminated. In addition, the potential barrier caused by setting the channel impurity concentration of the vertical charge-coupled device higher than that of the horizontal charge-coupled device can be eliminated. By suppressing the voltage and making the channel potential characteristics of the vertical charge-coupled device and the horizontal charge-coupled device uniform, it is effective in reducing the gate applied voltage and the device applied bias voltage.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of one embodiment of the present invention.

FIG. 2 is a schematic sectional view of one embodiment of the present invention .

FIG. 3 is a manufacturing process diagram for describing one embodiment of a method for manufacturing a solid-state imaging device according to the present invention.

FIG. 4 is a manufacturing process diagram for explaining one embodiment of the method for manufacturing a solid-state imaging device of the present invention.

FIG. 5 is a manufacturing process diagram for explaining one embodiment of the method for manufacturing a solid-state imaging device of the present invention.

FIG. 6 is a potential well diagram for explaining one embodiment of a method for driving a solid-state imaging device according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photoelectric conversion element 2 vertical charge-coupled element with high channel impurity concentration and well impurity concentration 3 horizontal charge-coupled element with low channel impurity concentration and well impurity concentration 4 output unit 5 Si substrate 6 N-type channel with high impurity concentration 7 impurity concentration High P-type well 8 N-type channel with low impurity concentration 9 P-type well with high impurity concentration 10 SiO ₂ films 11 a, 11 b, 11 c, 11 d Transfer electrode 11 e independent of vertical charge-coupled device 11 e Independent of vertical charge-coupled device - transfer electrodes 12 φVL 13 transfer electrodes 14 thick SiO ₂ film 15, boron ions (forming a low P-type well impurity concentration) 16 phosphorus ions (forming the lower N-type channel impurity concentration) of the horizontal charge-coupled device 17 photoresist mask 18 Additional boron ions (P with high impurity concentration in total)
19) Additional phosphorus ions (forming N-type channel with high impurity concentration) 20 Photoresist mask 21 Photoresist mask 22 Photoresist mask 23 Photoresist mask 24 High concentration boron ions 25 Photoresist mask 26 Photoresist mask 27 High Concentration phosphorus ion

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/339 H01L 27/14-27/148 H01L 29/762-29/768 H04N 5/335

Claims (2)

(57) [Claims] 1. A solid-state imaging device that outputs a two-dimensional information optical signal as a time-series signal by a combination of a vertical charge-coupled device and a horizontal charge-coupled device. The region is a buried channel type in which the conductivity type of impurities in the channel for transferring signal charges and the well immediately below the channel are different, and the impurity concentration of the buried channel in the vertical charge-coupled device becomes a storage region of the horizontal charge-coupled device. higher than the impurity concentration of the channel, and wherein the impurity concentration of the well of the vertical charge coupled devices rather higher than the impurity concentration of the well of the horizontal charge-coupled device storage area, said water and said vertical charge coupled device
The vertical charge transfer element and the horizontal charge transfer element
In addition to the gate electrode between the charge transfer element and the
A single transfer electrode capable of applying the voltage;
The impurity concentration of the channel and well under the transmission electrode is
Impurity concentration of channel and well of charge coupled device
Solid-state imaging devices, each being identical . 2. A method for driving a solid-state image sensor according to claim 1.
In the case where the channel under the independent transfer electrode of the vertical charge-coupled device acts as a barrier region, the channel potential depth under the independent transfer electrode sets the channel of the other transfer electrode of the vertical charge-coupled device as the barrier region. Independent transfer of a voltage at a level not at least shallower than the channel potential depth in the case of acting as a channel, and at a level sufficient to reduce the barrier caused by a change in impurity concentration by expanding the magnitude and range of the fringe electric field. A method for driving a solid-state imaging device, wherein the method is applied to an electrode.