JP3469105B2 - Amplification type solid-state imaging device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a unit pixel structure of an amplification type solid-state image pickup device, and provides an amplification type solid-state image pickup device having low noise and high sensitivity.

[0002]

2. Description of the Related Art A solid-state image pickup device having an amplification function inside a pixel is amplified by modulating the potential of a signal charge storage portion with signal charges generated by photoelectric conversion and modulating the amplification transistor inside the pixel with the potential. This type of solid-state imaging device is capable of low-voltage single-power-supply operation and can be equipped with a logic circuit such as a drive circuit on a chip, so it is expected as a mainstream element for future solid-state imaging devices. ing.

The basic structure of a pixel in an amplification type solid-state imaging device is a photodiode for photoelectric conversion and a reset transistor for initializing the voltage of this photodiode, a transistor for amplification, a transistor for line selection, or The wiring is for capacitive coupling, and connects the photodiode and the amplification transistor gate.

[0004] Further, in the case of temporarily storing the photoelectrically converted signal charges, provided the storage diode in a region different from the photodiode, is provided between the photodiode and the storage diode Ru provided transfer gate. That is, as shown in FIG.
To form a photodiode on the p-type semiconductor substrate 1
N-type impurity layer 4 and p + -type impurity layer 5 for forming
Be done. Adjacent to this photodiode is the gate of the transfer gate.
The gate electrode 3 is arranged, and the storage electrode is further adjacent to the transfer gate.
Product diodes are arranged. This storage diode
Through the contact hole, the n-type impurity layer 6 to be formed is
The wiring 7 is connected. These photodiodes and
The surface of the transfer gate and storage diode is covered by the insulating film 2.
Is covered. With this configuration, the photo
The signal charge photoelectrically converted in the diode is
After being accumulated in the diode, it is transferred via the transfer gate.
Stored in the storage diode.

[0005]

When the embedded photodiode structure, which is a low noise photodiode structure, is applied to the amplification type solid-state image pickup device having such a structure, the embedded photodiode is originally However, there is a problem that the low noise characteristic of cannot be obtained.

That is, CC which is a conventional mainstream imaging device
In D, when the signal charge of the photodiode is read out, a relatively high voltage of 10 V or more is applied to the transfer gate, so that the transfer channel completely reads out the charge inside the photodiode. Although it was possible to completely deplete the inside, in the amplification type solid-state imaging device characterized by low voltage and single power source drive, the voltage applied to the transfer gate is as low as 3.3 V. Therefore, if the embedded photodiode structure is simply introduced, it becomes impossible to completely read out the charges inside the photodiode, and due to this incomplete reading, the photodiode is completely depleted. Noise resulting from fluctuations in the potential when resetting the signal charge of the photodiode. A problem that can not be removed occurs.

Further, when considering low power consumption and low power supply voltage operation, it was considered to reduce the operating voltage from the 3.3 volt single power supply to, for example, 1.5 volt single power supply. In this case, neither complete depletion nor complete transfer operation is possible.

[0008]

According to the present invention, even when an embedded photodiode structure, which is a low noise photodiode structure, is applied to an amplification type solid-state image pickup device driven at a low voltage, the embedded photodiode is completely depleted. Since the bottom of the potential inside the photodiode is formed to the same depth as the channel region of the transfer transistor, the photodiode is fully depleted / completely transferred even in low voltage driving, which is a feature of the amplification type solid-state imaging device. Therefore, it is possible to remove the reset noise that is the thermal noise at the time of resetting the photodiode, and as a result, it is possible to obtain an amplification type solid-state imaging device with low noise and high sensitivity.

Further, according to the present invention, not only is the potential bottom inside the fully depleted buried photodiode formed to a depth approximately the same as the channel region of the transfer transistor, but it is also approximately the same as the channel region of the transfer transistor. Since the storage diode potential at the depth of is equal to the surface potential of the storage diode, even when the low drive voltage, which is a feature of the amplification type solid-state imaging device, is further lowered, the photodiode is completely depleted and at the same time completely Therefore, reset noise, which is thermal noise at the time of resetting the photodiode, can be removed, and as a result, an amplification type solid-state imaging device with low noise and high sensitivity can be obtained.

Further, according to the present invention, the impurity of the same conductivity type as that of the semiconductor substrate is present in the vicinity of the surface of the channel region of the transfer transistor arranged adjacent to the buried photodiode, and the impurity concentration is higher than that of the semiconductor substrate. since the impurity regions are formed, the noise current is also generated in Si- SiO ₂ interface in the channel region of the transfer transistor recombine the high concentration impurity layer of the photodiode near the surface without being accumulated in the photodiode or,
Alternatively, since it is discharged to the side of the storage diode, it is possible to obtain an amplification type solid-state imaging device with lower noise and higher sensitivity.

Further, according to the present invention, the potential at the same depth as the channel region of the transfer transistor is formed at the same depth as the surface potential also in the storage diode region, so that when driving at a lower voltage. also it is possible to completely depleted, the complete transfer operation the photodiode, thus it is possible to remove the reset noise is the thermal noise at the time of resetting of the photodiode, as a result, can be ultra-low voltage drive kinematic A low noise and high sensitivity amplification type solid-state imaging device can be obtained.

[0012]

[0013]

[0014]

[0015]

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to examples.

FIG. 1 is a sectional structural view for explaining a unit pixel structure of an amplification type solid-state image pickup device according to a first embodiment of the present invention. The essential features of the present invention are a photodiode, a transfer transistor, and a storage. The cross-sectional structure of the area | region containing a diode is shown. Since the structure other than the structure shown in FIG. 1 is the same as that of the conventional amplification type solid-state imaging device, the description thereof will be omitted.

[0018] In actual施例of the present invention, as shown in FIG. 1, p-type projections on the surface of the semiconductor substrate 1 is formed, n-type impurity for forming the photodiode embedded in the convex area The object layer 4 and the p + type impurity layer 5 are formed.

The convex portions on the surface of the p-type semiconductor substrate 1 are formed on the p-type semiconductor substrate 1 by RIE (Reactive Ion Etc) prior to the formation of an oxide film for element isolation, for example.
It can be formed by performing anisotropic etching such as (hing).

Alternatively, even after the oxide film forming step for element isolation, the RIE (Reactive Ion Etching) is performed on the p-type semiconductor substrate 1 in an appropriate step before the transfer transistor gate structure forming step.
It can also be formed by performing anisotropic etching such as.

The step of the concavo-convex structure formed at this time is represented by S.

The p-type semiconductor substrate 1 may be an n-type semiconductor substrate as long as the region for diode / transistor operation on the surface side is a p-type region such as a p-well structure.

[0023] Embedding two impurity layer for the photodiode, for example n-type impurity material layer 4 by ion implantation of phosphorus, a p-type impurity material layer 5 is ion implantation of boron, can be respectively formed.

The photoelectrically-converted signal charges in the photo diode, via <br/> transfer gate formed adjacent to the photodiode after being accumulated in the photodiode are transferred to and stored in the storage diode It

The transfer gate is a p-type semiconductor substrate 1 and the gate electrodes 3 by CVD or the like after the thermal oxidation, for example, polysilicon is deposited or the like, combined with the etching such photolithography and RIE As a result, it is possible to process / form the shape shown in FIG.

N-type impurity for forming storage diode
The material layer 6 can be formed by ion implantation of phosphorus, for example.

N-type impurity layer 6 forming a storage diode
A metal wiring 7 made of aluminum or the like is connected to the via a contact hole. The metal wiring 7 is connected to the gate electrode (not shown) of the amplification transistor inside the unit pixel, so that the gate voltage applied to the gate electrode of the amplification transistor is modulated by the amount of signal charges accumulated in the accumulation diode. It The photodiode and
The surface of the transfer gate and storage diode is covered by the insulating film 2.
Covered.

The signal charge accumulated in the storage diode is discharged to a reset drain (not shown) via a reset gate (not shown) provided adjacent to the storage diode. The amplification transistor structure and the reset transistor structure are the same as those of the conventional amplification type solid-state imaging device, and are general structures that can be formed by a normal MOS process. Omit it.

FIG. 3 shows an impurity concentration profile inside the buried photodiode shown in FIG.

In the vicinity of the surface of the photodiode, a p + layer containing boron at a high concentration is formed, an n layer containing phosphorus is formed in a region slightly deeper than the p + layer, and a p-type semiconductor is formed in a deeper region. It becomes the substrate. At this time, two types of pn junctions are formed in the photodiode at depths J1 and J2. Further, the depth of the portion where the phosphorus concentration is maximum in the n-type impurity layer is P.

FIG. 4 shows the potential profile inside the photodiode when the n-type impurity layer of the embedded photodiode having the impurity profile shown in FIG. 3 is completely depleted. At this time, since the p + -type impurity layer formed near the surface has a high concentration, the depletion layer on the surface side does not reach the semiconductor surface, and the influence of the interface state of the semiconductor / oxide film interface can be eliminated. It will be possible.

Further, by operating the embedded photodiode in the fully depleted state, the maximum potential φPD of the photodiode is kept constant in the transfer of the signal charge from the photodiode to the storage diode.
By setting the potential under the transfer gate higher than φPD, it is possible to eliminate the thermal noise caused by the fluctuation of the potential generated during charge transfer.

[0033] However, the conventional amplifying solid-state imaging device may be operated with the buried photodiode in fully depleted state is difficult. It is about the amplification type solid-state imaging device that features a low voltage driving, which is why it can not be sufficiently high potential under the transfer gate.

In the amplification type solid-state image pickup device having the conventional structure,
The potential profile (A) under the transfer gate and the potential profile (B) of the embedded photodiode are as shown in FIG. In order to facilitate understanding of the figure, FIG. 6 shows the impurity layer structure below the transfer gate and the impurity layer structure of the photodiode, with reference to the photodiode surface.

The potential (A) under the transfer gate shows the maximum value φS on the surface of the semiconductor substrate and monotonically decreases toward the inside of the semiconductor substrate. Here, although it is easy to obtain φS> φPD, since φPD is formed at the depth b as shown in FIG. 4, two types of potential profiles (A) as shown in FIG. 6 are obtained. The signal charge is transferred at the intersection of (B), and as a result, the residual charge Q remains in the embedded photodiode. Due to the presence of this residual charge, the operation of complete depletion, which is a feature of the embedded photodiode, is not performed, and therefore thermal noise during transfer remains.

On the other hand, according to the structure shown in FIG. 1, since the embedded photodiode is formed on the convex portion of the semiconductor substrate, the fully depleted operation of the embedded photodiode is achieved even in the low voltage operation amplification type solid-state imaging device. Is possible.

The potential profile (A) under the transfer gate and the potential profile (B) of the buried photodiode in the structure of FIG. 1 are as shown in FIG. In order to facilitate understanding of the drawing, the impurity layer structure under the transfer gate and the impurity layer structure of the photodiode are also shown in FIG. 5 with reference to the photodiode surface.

As shown in FIG. 5, the depth b of the maximum potential φPD of the buried photodiode which is completely depleted by forming the photodiode in the convex portion is
Due to the presence of the unevenness step S on the surface of the semiconductor substrate, the potential under the transfer gate is moved close to the maximum depth. In FIG. 5, as in the conventional structure of FIG. 6, although the gate voltage is applied so that the maximum potential becomes φS, the charge transfer is completely performed from φPD existing inside the semiconductor substrate. , It can be seen that the embedded photodiode is completely depleted.

Therefore, according to the present invention, even in a low voltage drive amplification type solid-state image pickup device, the embedded photodiode can be operated in a completely depleted state, and generation of thermal noise due to incomplete charge transfer is eliminated. It As a result, an amplification type solid-state imaging device with high sensitivity and low noise can be obtained.

[0040] to the next, it will be described with reference to FIG.

[0041] Figure 2 is another arrangement for explaining a unit pixel structure of an amplification type solid state imaging device according to a real施例of the present invention
A cross-sectional structure diagram showing, and a photodiode which is a gist of the present invention, the cross-sectional structure of a region including a transfer transistor, and the storage diode shown. Since the structure other than the structure shown in FIG. 2 is the same as that of the conventional amplification type solid-state imaging device, it is omitted.

[0042] In actual施例of the present invention, as shown in FIG. 2 are recesses formed on the p-type semiconductor substrate 1 of the surface, the gate electrode 3 to form a transfer gate to the concave region formed Has been done.

The concave portion on the surface of the p-type semiconductor substrate 1 is formed on the p-type semiconductor substrate 1 by RIE (Reactive Ion Etc) prior to formation of an oxide film for element isolation, for example.
It can be formed by performing anisotropic etching such as (hing).

The step of the concavo-convex structure formed at this time is S.

The p-type semiconductor substrate 1 may be an n-type semiconductor substrate as long as the region for diode / transistor operation on the surface side is a p-type region such as a p-well structure.

The embedding two impurity layer for the photodiode, for example n-type impurity material layer 4 by ion implantation of phosphorus, a p-type impurity material layer 5 is ion implantation of boron, can be respectively formed.

The photoelectrically-converted signal charges in the photodiode, after being accumulated in the photodiode, a transfer gate which is formed adjacent to the photodiode
Through, it is transferred to and accumulated in the accumulation diode.

The transfer gate is a p-type semiconductor substrate 1 and the gate electrodes 3 by CVD or the like after the thermal oxidation, for example, polysilicon is deposited or the like, combined with etching such as photo lithography and RIE By doing
It can be processed and formed into the shape shown in FIG.

N-type impurity for forming storage diode
The material layer 6 can be formed by ion implantation of phosphorus, for example.

N-type impurity layer 6 forming a storage diode
A metal wiring 7 made of aluminum or the like is connected to the via a contact hole. The metal wiring 7 is connected to the gate electrode (not shown) of the amplification transistor inside the unit pixel, so that the gate voltage applied to the gate electrode of the amplification transistor is modulated by the amount of signal charges accumulated in the accumulation diode. It

The signal charge accumulated in the storage diode is discharged to a reset drain (not shown) via a reset gate (not shown) provided adjacent to the storage diode. The amplification transistor structure and the reset transistor structure are the same as those of the conventional amplification type solid-state imaging device, and are general structures that can be formed by a normal MOS process. Omit it.

According to the structure shown in FIG. 2, the impurity profile of the buried photodiode, the potential profile, and the potential profile under the transfer gate are:
Similar to the structure of FIG. 1, provided as FIGS. 3, 4 and 5, respectively. Therefore, if the same way in FIG. 1, is operable to be buried photodiode The amplifying solid-state imaging device of low driving voltage in a fully depleted state, generation of thermal noise caused by incomplete charge transfer eliminates To be done. As a result, an amplification type solid-state imaging device with high sensitivity and low noise can be obtained.

The step S of the uneven portion in the structure shown in FIGS. 1 and 2 is preferably formed as follows.

As shown in FIG. 4, the depth b at which the maximum potential φPD of the fully depleted buried photodiode is formed is the depth P at which the phosphorus concentration becomes maximum in the impurity profile formed by phosphorus ion implantation. Generally agrees. This is because the p + layer near the surface of the embedded photodiode and the p-type semiconductor substrate are both set to the same substrate potential (0 in FIGS. 4 to 6), and the phosphorus concentration formed by ion implantation is almost the same. Considering that it can be approximated by a symmetric Gaussian distribution, and that the depth J1 of the p + layer near the surface is sufficiently shallow as compared with the depth b of the maximum potential and the depth J2 of the n layer, a generally reasonable approximation is obtained. Can be said.

On the other hand, as shown in FIG. 5, the maximum potential φ of the embedded photodiode formed at the depth b.
In order to transfer PDs most efficiently and completely, the unevenness step S should be matched with the maximum potential depth b.

Therefore, after obtaining the structure of FIG. 1 or FIG. 2, as a guideline for efficiently realizing a fully depleted buried photodiode, the uneven step S in FIG. 1 and FIG. It can be said that it is preferable that the depth P at which the phosphorus concentration of the layer is maximum is approximately equal.

As for the structures of the buried photodiode and the transfer gate in the concavo-convex structure shown in FIG. 1 or 2, variations as shown in FIG. 7 can be considered.

FIG. 7A is the same as FIG. 1 and FIG. 2, and offsets are provided at the step portion and the transfer gate end portion due to the concavo-convex structure.

FIG. 7B shows a structure in which the step portion due to the concavo-convex structure and the end of the transfer gate are aligned with each other, and FIG.
Provides an offset between the step portion and the transfer gate end portion due to the concavo-convex structure in the opposite direction to (a).

It is needless to say that the fully-depleted buried photodiode can be driven at a low voltage as described above in any of FIGS. 7B and 7C.
Compared to (a), it is possible to make the light incident area on the photodiode relatively large, and therefore there is the effect of higher sensitivity, which is also preferable. Since the distance in the charge transfer direction between the potential portion and the maximum potential portion under the transfer gate is shorter than that in FIG. 7A, the effect is more remarkable and preferable.

Further, the present invention is configured as shown in FIG.
is doing.

[0062] Figure 8 is a sectional view illustrating a unit pixel structure of the amplification type solid-state imaging device according to the present onset Akira,
1 shows a cross-sectional structure of a region including a photodiode, a transfer transistor, and a storage diode, which are the gist of the present invention. Since the structure other than the structure shown in FIG. 8 is the same as that of the conventional amplification type solid-state imaging device, the description thereof will be omitted.

That is, as shown in FIGS. 8A and 8B , the channel region formed on the side wall of the step adjacent to the photodiode is further provided near the surface of the semiconductor substrate.
An impurity region 101 made of p- type impurities is formed. The presence of the p-type impurity region 101, the depletion layer toward the transfer gate side wall portion of the n-type impurity material layer 4 inside the photodiode, the transfer gate sidewall portion Si- SiO
₂ is prevented from reaching the interface.

[0064] Si- SiO ₂ interface of the transfer gate sidewall portions, unlike Si- SiO ₂ interface photodiode region surface, the upper surface to be protected by the gate oxide film and the transfer gate electrode 3, the relative The interface state density is low. However, it is not always appropriate to ignore the existence when low noise characteristics are important.

[0065], therefore, according to the structure shown in FIG. 8, the noise current caused by the interface state of Si- SiO ₂ interface of the transfer gate sidewall portion without being accumulated in the photodiode, a further low noise characteristics It becomes possible to obtain.

At this time, in order to obtain a sufficient interface state shielding effect by the p-type impurity region 101 on the transfer gate side wall and to obtain a sufficient low noise characteristic, the impurity concentration (N1 the), impurity concentration of the p-type impurity material layer 5 formed on the photodiode surface (N2)
Set higher or equal. That is, N1
It can be said that it is more preferable that ≧ N2.

[0067] To obtain this structure, for example before forming machining irregularities of the semiconductor substrate surface, a wide span a p-type impurity region 101 in FIG. 8, a recess adjacent to the p-type impurity regions 101 This can be achieved by ion-implanting p-type impurities into the region and then processing the uneven shape of the surface of the semiconductor substrate.

Alternatively, it can be realized by forming an uneven shape on the surface of the semiconductor substrate and then implanting a p-type impurity ion with a proper incident angle with respect to the sidewall of the p-type impurity region 101.

Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 9 is a sectional structural view for explaining the unit pixel structure of the amplification type solid-state image pickup device according to the second embodiment of the present invention.
The cross-sectional structure of the area | region containing a transfer transistor and a storage diode is shown. Since the structure other than the structure shown in FIG. 9 is the same as that of the conventional amplification type solid-state imaging device, it is omitted.

In this embodiment, FIGS. 9A and 9B are used.
As shown in FIG. 3, an impurity region 101 made of a p-type impurity is formed in the vicinity of the surface of the semiconductor substrate in the channel region formed on the side wall of the step portion adjacent to the photodiode, and is parallel to the surface of the semiconductor substrate. p-type impurity region 102 is formed in the vicinity of the semiconductor substrate surface of the channel region formed in the third lower transfer gate electrode in a plane.

[0072] Effect of the presence of p-type impurity region 101 in the transfer gate electrode 3 side wall portion is the same as the first embodiment above.

[0073] In this embodiment, further transfer gate conductive
Also in the channel region formed at the bottom of the pole 3 , the p-type impurity region 102 is formed near the surface of the semiconductor substrate. The presence of the p-type impurity regions 102, transferred from the n-type impurity material layer 4 of the internal photodiode gate electrode 3
Depletion layer towards the bottom, the transfer gate electrode 3 bottom of Si-
Reaching the SiO ₂ interface is prevented.

The Si- SiO ₂ interface at the bottom of the transfer gate is different from the Si- SiO ₂ interface at the surface of the photodiode region in the same manner as the Si- SiO ₂ interface at the sidewall of the transfer gate described above. Since it is protected by the film and the transfer gate electrode 3, the interface state density is relatively low. However, similarly, when importance is attached to the low noise characteristic, it cannot always be said that it is appropriate to ignore its existence. Therefore, according to the structure shown in this embodiment, the transfer gate electrode 3 bottom of Si- S
The noise current due to the interface state of the iO ₂ interface does not accumulate in the photodiode, and it is possible to obtain further low noise characteristics.

In order to obtain the structure of this embodiment, for example, after forming the uneven shape of the semiconductor substrate surface, this p
This can be achieved by implanting p-type impurities into the region of the type impurity region 102.

[0076] Further, as in the third embodiment shown in FIG. 10, the channel region more formed on the transfer gate, in all the channel region of the bottom and side wall,
A p-type impurity region (102, 10) is formed near the surface of the semiconductor substrate.
3, for the surface of the surface and Zuoku side of the other figures near side by forming a not shown), to cut off the noise current from Si- SiO ₂ interface state in the entire channel region of the transfer gate This structure can be said to be more preferable because it is possible.

The structure shown in FIG. 10 can be realized by so-called solid phase diffusion, for example, after forming and processing the uneven shape of the surface of the semiconductor substrate, depositing a p-type impurity layer and thermally diffusing it.

[0078] Also, n-type impurities of the photodiode region
From the condition that a depletion layer from the layer 4 does not reach the Si- SiO ₂ interface, to transfer gate electrode 3 bottom p-type impurity region 102 of the most distance is short, the impurity concentration (N
C1) is relatively it high concentration of is required, p-type impurity region of the transfer in the opposite gate electrode 3 side wall portion (FIG front-
(Not shown because it is on the far side of the drawing), the object can be achieved even if the impurity concentration (NC2) is relatively low. That is, NC1> NC2
It is possible to reduce noise even in.

In this case, as a method for realizing the structure, a method other than the solid phase diffusion described above can be applied. For example, after forming the uneven shape on the surface of the semiconductor substrate, the uneven shape is formed and processed. It can be said that it is more preferable because the impurity region can be formed by the rotating ion implantation method of the tilted ion incidence in a self-aligned manner by using the resist mask of (1) and the manufacturing method can be configured by more general steps. Next, with reference to FIG. 11, a description will be given of a fourth embodiment of the present invention. FIG. 11 is a cross-sectional structural view for explaining a unit pixel structure of an amplification type solid-state imaging device according to the fourth embodiment of the present invention, which shows a photodiode, a transfer transistor, and a storage diode, which are the main features of the present invention. The cross-sectional structure of the area | region containing is shown. The structure other than the structure shown in FIG. 11 is the same as that of the conventional amplification type solid-state imaging device, and therefore its description is omitted.

In this embodiment, as shown in FIG. 11, an impurity region 101 made of p-type impurities is formed in the vicinity of the surface of the semiconductor substrate in the channel region formed on the side wall of the step adjacent to the photodiode. in terms of being, transferred gate conductive in a plane parallel to the semiconductor substrate surface
Electrode 3 in the vicinity of the semiconductor substrate surface of the channel region formed in the lower and p-type impurity region 102 is formed, even in the channel region is further formed on the side wall portion of the transfer gate electrode 3, near the surface of the semiconductor substrate P-type impurity region 1
03 (the front side and the back side in the figure are not shown) are formed.

[0081] p-type impurity region in the channel region surface formed by the transfer gate electrode 3) 101,
The effect due to the existence of the front side surface and the back side surface in the drawing is the same as in the second embodiment.

[0082] In this embodiment, the more the same plane as the first n-type impurity material layer 6 of the storage diode, the first n
The type impurity material layer 6 second n that the impurity concentration distribution is different
The type impurity region 104 is formed.

[0083] That is, the first n-type impurity material layer 6, the impurity concentration in the vicinity the surface of the semiconductor substrate has an impurity concentration distribution such that the maximum, while the second n-type impurity regions 104, impurity concentration has an impurity concentration distribution such that a maximum in the transfer gate electrode 3 bottom depth comparable to the semiconductor substrate surface in the channel region of the.

[0084] According to the structure of FIG. 11, the transfer gate electrode 3
It is possible to make the potential at the end of the bottom channel region on the side of the storage diode substantially equal to the potential at the surface of the storage diode. Therefore, the potential of the wiring 7 connected to the first n-type impurity layer 6 of the storage diode is directly transferred without the influence of the potential drop due to the depletion from the first n-type impurity layer 6 of the storage diode region. It is possible to apply it to the channel region at the bottom of the gate electrode 3 . Therefore, according to the present embodiment, further low voltage operation becomes possible.

[0085] To obtain the structure of this embodiment, for example, a first n-type impurity material layer 6, immediately after formed by n-type impurity ion implantation photo registry such as a mask, a mask of the same photoresist Can be easily realized by increasing the ion implantation acceleration and re-implanting the n-type impurities.

[0086] Also, as in the fifth embodiment shown in FIG. 12, the first n-type impurity material layer 6 and the second n-type impurity regions 10
The second n-type impurity region 1 does not have the same formation range.
05 also by the forming only in a region adjacent to the transfer gate electrode 3, it is possible to obtain the same effects.

In the present embodiment, this is caused by adding the second n-type impurity region 105 to the storage diode.
It can be said that it is more preferable in that the increase in the storage diode capacitance can be suppressed.

That is, in the amplification type solid-state image pickup device, a so-called floating diffusion amplifier structure for converting incident optical signal charges photoelectrically converted in the photodiode into a signal voltage is constituted by the storage diode. Since the conversion gain used as an index of performance as (signal voltage / signal charge) in the amplifier structure is approximately inversely proportional to the storage diode capacitance, the structure of this embodiment can prevent the storage diode capacitance from increasing.

[0089] Furthermore, for the impurity concentration distribution of the second n-type impurity regions 105 in those storage diode, it would be preferably the same as the impurity concentration of the n-type impurity material layer 4 in the photodiode. This is because the maximum potential position in the photodiode, the maximum potential position in the transfer gate channel, and the maximum potential position in the storage diode are all formed on the same plane at the same depth, which allows the device to operate most efficiently. The reason is as described above. As for such structures, for example, a transfer gate electrode 3 after processing form, it is capable of self-aligned impurity ion implantation to the transfer gate electrode 3 can be easily realized.

In addition, various modifications can be made without departing from the scope of the present invention.

[0091]

According to the present invention, it is possible to realize an amplification type solid-state image pickup device which can be driven at a low voltage and has low noise and high sensitivity.

[Brief description of drawings]

Real施例photo in the unit pixel structure of an amplification type solid state imaging device according to a diode, the transfer transistors, and a cross-sectional structure diagram illustrating a cross sectional structure of a storage diode of the present invention; FIG.

Real施例photo in the unit pixel structure of an amplification type solid state imaging device according to a diode, the transfer transistors, and a cross-sectional structure diagram illustrating a cross sectional structure of another configuration of the storage diode of the present invention; FIG.

FIG. 3 is an impurity concentration profile for explaining the depthwise distribution of the impurity concentration in the embedded photodiode.

FIG. 4 is a potential profile for explaining a depth-direction distribution of a potential in a fully depleted embedded photodiode.

FIG. 5 shows a potential profile under a transfer gate and a potential profile inside a fully depleted embedded photodiode in an amplification type solid-state imaging device according to an embodiment of the present invention.

FIG. 6 shows a potential profile below a transfer gate and a potential profile inside a fully depleted embedded photodiode in a conventional amplification type solid-state imaging device.

FIG. 7 is a cross-sectional structure diagram illustrating structures of an embedded photodiode and a transfer gate in a unit pixel structure of an amplification type solid-state imaging device according to an example of the present invention.

[8] Real施例photo in the unit pixel structure of an amplification type solid state imaging device according to a diode, the transfer transistors, and a cross-sectional structure diagram illustrating a cross sectional structure of a storage diode of the present invention.

FIG. 9 is a sectional structural view for explaining a sectional structure of a photodiode, a transfer transistor, and a storage diode in a unit pixel structure of an amplification type solid-state imaging device according to a second example of the present invention.

FIG. 10 is a sectional structural view for explaining a sectional structure of a photodiode, a transfer transistor, and a storage diode in a unit pixel structure of an amplification type solid-state imaging device according to a third example of the present invention.

FIG. 11 is a sectional structural view for explaining sectional structures of a photodiode, a transfer transistor, and a storage diode in a unit pixel structure of an amplification type solid-state imaging device according to a fourth example of the present invention.

FIG. 12 is a sectional structural view for explaining a sectional structure of a photodiode, a transfer transistor, and a storage diode in a unit pixel structure of an amplification type solid-state imaging device according to a fifth example of the present invention.

FIG. 13 is a sectional structural view for explaining a sectional structure of a photodiode, a transfer transistor, and a storage diode in a unit pixel structure of a conventional amplification type solid-state imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... P-type semiconductor substrate 2 ... Insulating film 3 ... Gate electrode 4 ... N-type impurity layer 5 ... P + -type impurity layer 6 ... N-type impurity layer 7 ... Metal wiring 101, 102, 103 ... P-type impurity region 104, 105 ... Second n-type impurity region of storage diode

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 27/14-27/148 H04N 5/335

Claims (8)

(57) [Claims] 1. A plurality of unit pixels are two-dimensionally arranged on a semiconductor substrate, and a photodiode for photoelectric conversion and a storage diode for accumulating signal charges obtained by the photodiode are provided in each unit pixel. a photodiode for transferring the signal charge obtained by the photodiode to the storage diode
A transfer transistor having a transfer gate disposed between the storage diode, a reset transistor for resetting the signal charge stored in the storage diode, an amplifying transistor modulated by the signal charges stored in the storage diode, the amplifier transistor An amplification type solid-state imaging device provided with a signal readout unit for reading out a signal voltage of, wherein the photodiode is a semiconductor substrate of a first conductivity type or an impurity well structure of a first conductivity type, and the vicinity of the surface of the semiconductor substrate. Of the first conductivity type formed in the vicinity of the surface of the semiconductor substrate and a first PN junction formed by an impurity region of the second conductivity type opposite to the first conductivity type formed inside the semiconductor substrate. An impurity region and a second conductivity type impurity region formed inside the semiconductor substrate near the surface of the semiconductor substrate. In the region where the unit pixels are two-dimensionally arranged, a concavo-convex shape having the same arrangement as the pixel arrangement is formed on the surface of the semiconductor substrate, and a structure forming the unit pixel is formed. at least the photodiode of is formed within the semiconductor substrate where the convex shape is formed on the semiconductor surface, at least the transfer of the structure constituting the unit pixel
The gate structure of the transistor has a concave shape on the semiconductor surface.
Concavo- convex shape formed in the formed semiconductor substrate region and in the region in which the unit pixels are two-dimensionally arranged.
Inside the semiconductor substrate near the surface of the semiconductor substrate
Second conductivity in the impurity region of the second conductivity type formed in
Photo that maximizes the concentration distribution of the impurity concentration in the depth direction
If it is formed to be almost equal to the depth from the diode surface,
Mostly, the concavo-convex shape formed in the area where the unit pixels are two-dimensionally arranged.
Of the transfer transistor formed on the stepped portion
At least adjacent to the photodiode in the
Of the channel region formed on the side wall of the step
Impurities containing impurities of the first conductivity type near the surface of the body substrate
Amplification type solid-state imaging characterized by the formation of a physical layer
apparatus. 2. The stage adjacent to the photodiode.
Semiconductor substrate surface of channel region formed on side wall of difference portion
Impurity formed near the surface and containing the impurity of the first conductivity type
The impurity concentration in the material layer is N1,
The impurities of the first conductivity type formed near the surface of the
When the impurity concentration of the containing impurity layer is N2, N1 ≧ N
2. The amplification type solid-state imaging device according to claim 1, wherein
Image device. 3. A channel region of the transfer transistor
At a surface formed parallel to the surface of the semiconductor substrate.
The first conductivity type is provided near the surface of the semiconductor substrate in the channel region.
Characterized by the formation of an impurity region containing the impurities of
The amplification type solid-state imaging device according to claim 1 or 2. 4. A channel region of the transfer transistor
Is formed on a surface orthogonal to the surface of the semiconductor substrate.
In the vicinity of the surface of the semiconductor substrate in the channel region, the first conductive material
Is characterized in that an impurity region containing a type impurity is formed.
Amplification type according to any one of claims 1 to 3
Solid-state imaging device. 5. A channel region of the transfer transistor
At a surface formed parallel to the surface of the semiconductor substrate.
The first portion formed near the surface of the semiconductor substrate in the channel region
Impurity of first channel impurity region containing conductivity type impurity
The material concentration is NC1, and the channel of the transfer transistor is
In a region, formed on a surface orthogonal to the semiconductor substrate surface
A second channel region containing impurities of the first conductivity type.
When the impurity concentration in the pure region is NC2, NC1> N
The amplification type solid according to claim 4, wherein the amplification type solid is C2.
Imaging device. 6. The storage diode comprises at least the storage diode.
Maximum impurity concentration near the surface of the semiconductor substrate
Containing the second conductivity type impurity having such an impurity concentration distribution.
A first impurity layer and a pixel array on the surface of the semiconductor substrate.
At the same depth as uneven steps formed in the same array
The impurity concentration distribution that maximizes the impurity concentration
And a second impurity layer containing the second conductivity type impurity.
6. The method according to claim 1, further comprising:
The amplification type solid-state imaging device according to. 7. The second element forming the storage diode
The impurity layer of the storage diode and the transfer transistor
Is formed only near the boundary area with the
The amplification type solid-state imaging device according to claim 6. 8. The second diode forming the storage diode
The impurity layer of is the first layer that constitutes the photodiode.
The same impurity concentration distribution as the impurity layer containing 2 conductivity type impurities
8. The amplification according to claim 6 or 7, characterized in that
Type solid-state imaging device.