JP2000022125A - Solid-state image-pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable stabilization of potential and to provide stable performance, even when a gate is formed of a single-layer film for a solid-state image-pickup device having a transmission part in two-phase drive mode by an embedded channel. SOLUTION: A solid-state image-pickup device has a transmission part in two-phase drive mode by an embedded channel 104, whose transmission gates 101 and 102 are formed of gates of a single-layer film. A part of the underside for each of the gates is doped with impurities (106). A transmission channel having a transmission part and a charge holding part in the same gate is provided. A gap G between the gates which is formed because the gates are formed of a single-layer film is filled with a metal and is set as an embedded metal part 103A. The potential of a part corresponding to the embedded metal part is made controllable by applying biase or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a solid-state imaging device. In particular, the present invention relates to a solid-state imaging device having a transfer unit of a two-phase driving method using a buried channel, wherein the transfer gate is formed by a gate formed from a single-layer film, and a stable potential can be obtained. Is provided.

[0002]

2. Description of the Related Art Conventionally, in a CCD solid-state image pickup device, in a transfer register, particularly in a device utilizing a two-phase driving method, a transfer gate for driving a buried channel may be formed of two layers of polysilicon. Many.

FIG. 4 shows such a conventional example. FIG.
FIG. 4A shows a cross-sectional structure of the solid-state imaging device, and FIG.
(B) shows the potential of each corresponding part (described later). In FIG. 4A, reference numeral 401 denotes a charge holding unit of the first polysilicon transfer gate, and reference numeral 403 denotes a charge holding unit of the second polysilicon transfer gate. Reference numeral 402 is
The transfer portion of the first polysilicon transfer gate,
Reference numeral 04 denotes a transfer section of the second polysilicon transfer gate. Charge holding portion 401 of first polysilicon transfer gate
And the charge holding portion 403 of the second polysilicon transfer gate
Is formed by patterning a single polysilicon layer. A transfer section 402 of a first polysilicon transfer gate;
The transfer portion 404 of the second polysilicon transfer gate is formed by patterning another polysilicon layer.
Thus, the transfer gate is formed of two layers of polysilicon.

However, from the viewpoint of manufacturing cost, it is more cost-effective to form the gate electrode from a single layer. Heretofore, a single-layer gate has not been mainly used because of a gap portion generated when a single-layer polysilicon gate is separated by etching into each transfer electrode. This gap portion is inevitably generated in semiconductor manufacturing. Further, the interval between the gaps is determined by the manufacturing process.

On the other hand, as the voltage of the CCD solid-state imaging device decreases, the gap between the transfer gates is required to be narrower. For example, in a two-phase transfer, when transferring at 5 V amplitude, the gap is 200 nm (= 0.2 μm)
Although it is possible to use a voltage of about 3
(= 0.1 μm) is required. For this reason, it is still technically difficult to form a transfer gate using a single layer of polysilicon so that the transfer gate can be driven at a sufficiently low voltage.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and solves the above-mentioned problems. The present invention relates to a solid-state imaging device having a transfer unit of a two-phase drive method using an embedded channel. It is an object of the present invention to provide a solid-state imaging device capable of stabilizing the potential even when a gate is formed from the solid-state imaging device and achieving stable performance.

[0007]

A solid-state image pickup device according to the present invention has a transfer section of a two-phase drive system using a buried channel, and a transfer gate formed by a gate formed of a single layer film. In the device, a portion below each gate is doped with impurities, and a transfer channel having a transfer portion and a charge holding portion is provided in the same gate,
A metal is buried in a gap between gates formed by forming a gate from a single layer film to form a buried metal portion, and a potential of a portion corresponding to the metal buried metal portion is made controllable. is there.

According to the solid-state imaging device of the present invention, the potential of the buried metal portion buried in the gap between the gates is controlled by, for example, applying a bias (this bias is controlled by a ground, a power supply, or the like). It is also possible to set an external voltage for convenience). By stabilizing the potential, stable performance can be obtained even when the gate is formed from a single-layer film.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be described in more detail below, and specific examples of preferred embodiments of the present invention will be further described with reference to the drawings. I do. However, needless to say, the present invention is not limited to the illustrated embodiment.

The present invention basically provides a solid-state image pickup device having a transfer unit of a two-phase drive system using a buried channel and a transfer gate formed by a single-phase gate. A doping is performed, a transfer channel having a transfer portion and a charge holding portion is provided in the same gate, and a metal is buried in a gap between the gates generated when the transfer gate is formed of one layer of polysilicon. As a metal portion, an electrode for a buried metal is provided as appropriate, and a bias voltage is applied to the electrode so that the potential can be controlled and the potential of the gap is stabilized.

In this case, in the solid-state imaging device,
In order to adjust the bias voltage applied to the metal electrode in the gap to the ground (GND) or an external voltage such as a power supply, a part of the gap may be doped with impurities for potential adjustment.

Further, in the solid-state imaging device, it is possible to have a structure in which a transfer portion and a charge holding portion are provided in the gap by performing impurity doping at different concentrations on a part of the gap portion. Further, the buried metal portion may be formed by forming a metal film, and the metal film may also serve as a light shielding film.

Further, a solid-state image pickup device having any two or more of the above-mentioned constitutions can be provided. Less than,
A specific embodiment will be described with reference to the drawings.

Embodiment 1 FIG. 1A shows an example in which a solid-state imaging device to which the present invention is applied is mounted. In the solid-state imaging device in FIG. 1A, the first transfer gate 101 and the second transfer gate 102
Formed from the same polysilicon and etched,
Separated into different electrodes. Metal film 1 on top of gate
The metal film 103 fills the separation gap between the first transfer gate 101 and the second transfer gate 102 (indicated by G in FIG. 1A). Is formed. The portion of the metal buried in the gap G (buried metal) is indicated by reference numeral 103A.

The minimum size of the gap G is determined by the limit of the performance of the semiconductor manufacturing apparatus.
Can be formed thin with good adhesion, so that it can also cover the minimum dimensional gap. FIG. 1
3A, the gap G is completely filled, but the first and second transfer gates 101 and 102 are shown.
It suffices that the upper side of the channel between the side wall and the gap portion is covered with the metal film 103.

The material of the metal film 103 is not particularly limited as long as it is a metal having good adhesion and burying properties and can be formed thinly. For example, any metal material that can be used as a general semiconductor electrode material is used. Can be used. In addition, if a material having a sufficient light-shielding property and low resistance is used, it is possible to also serve as a light-shielding film for the CCD section. With this configuration, the light-shielding film and the film for filling the gap can be used together, so that an increase in the number of steps can be suppressed. become. As the material of the metal film 103, for example, specifically, Al, Al alloy (A
l-Si, etc.), W, W alloy (W-Si, etc.), Cu, Au
And the like.

The first and second transfer gates 101, 10
2 (substrate side) in the drawing of FIG.
04 is formed. In the illustrated example, the channel is shown as an N ⁺ -type channel in the P well 105, but it goes without saying that P and N may be reversed. Immediately below each of the transfer gates 101 and 102, an impurity for providing a charge holding portion and a transfer portion under the gate is doped. In this example, an impurity doped portion 106 is formed by a P-type impurity for forming a potential barrier in the buried channel 104.

In FIG. 1A, reference numeral 107 denotes a first gate electrode φ1, 108 denotes a second gate electrode φ2, and 109 denotes an embedded metal electrode φg.

FIG. 1B shows a first example of the transfer unit shown in FIG.
FIG. 4 is a diagram showing a potential state when a high level of a transfer clock is applied to a gate electrode 107 (φ1) and a low level is applied to a second gate electrode 108 (φ2). At this time, as shown in the state shown in FIG. 1B, the potential Pg of the gap portion is different from the potential P12 of the transfer portion of the first gate electrode φ1 and the potential P21 of the charge holding portion of the second gate electrode φ2. The bias may be set to the embedded metal electrode φg so as to be in the middle. Note that P1
1 is the potential of the charge holding portion of the first gate electrode φ1, and P22 is the potential of the transfer portion of the second gate electrode φ2.

Since the potential under the first gate electrode 107 and the potential under the second gate electrode 108 have the same potential, the transfer clock level is inverted with the bias of the embedded metal electrode φg set as described above. No problem. This setting stabilizes the potential between the gaps.
Therefore, even if the gate is formed of a single layer, for example, a single layer of polysilicon, the problem associated with the generation of the gap can be solved.

FIG. 4 (b) is a diagram showing the potential in the conventional example corresponding to the above, and FIG. 1 (b)
In this case, the electric field in the gap is weaker than that in the conventional example shown in FIG. However, in practice, the gap portion becomes narrower than the transfer gate, and a portion having the minimum electric field exists below the transfer gate, so that there is no problem with transfer.

As described above, according to the present embodiment, in the transfer register in the case where the gate is formed by one layer of gate material (for example, one layer of semiconductor such as polysilicon), the potential in the transfer gap portion generated in manufacturing is generated. Can be stabilized, so that a transfer gate using a single-layer gate can be created and used in a conventional process.

Further, by forming a metal film for fixing the gap potential (forming a buried metal portion) with a light-shielding film and also serving as a light-shielding film, a one-pit layer can be achieved without increasing the number of steps.

Embodiment 2 Referring to FIG. FIG. 2A shows a cross-sectional structure of the solid-state imaging device of the present example, and FIG. 2B shows a potential state of each corresponding part.

In the example of FIG. 1 described above, a bias is particularly set for the embedded metal electrode φg in order to determine a potential. However, in this case, an external voltage such as a ground (GND) or a power supply is directly used for the embedded metal. The above-mentioned bias voltage can be adjusted to a convenient external voltage so that it can be used across the electrode φg.

That is, here, as shown in FIG. 2A, an impurity is introduced into the gap portion (here, by ion implantation), and an impurity region 201 (here, a high-concentration region P ⁺ ) is formed below the gap. Was formed. Thereby, φg
= L ₀ , the potential Pg of the gap portion was set to be intermediate between the potential P12 of the transfer portion of the first gate electrode φ1 and the potential P21 of the charge holding portion of the second gate electrode φ2. Since the ion implantation for obtaining this configuration can be formed by ion implantation using the polysilicon gap as a mask, it can be formed in an advantageous manner in terms of cost.

Embodiment 3 Referring to FIG. FIG. 3A illustrates a cross-sectional structure of the solid-state imaging device of the present example, and FIG. 3B illustrates a potential state of each corresponding part.

In this embodiment, with respect to the introduction of impurities in the gap portion of the second embodiment described above, the impurity introduction portions are replaced with the first and second two impurity doped portions 301a and 30a.
1b: By setting 302a and 302b, a transfer portion and a charge holding portion were provided in the gap portion. As a result, as can be understood from the state of the potential of each part shown in FIG.
As can be understood from g1, Pg2, Pg1 'and Pg2', the transfer electric field in the gap can be further increased. As a result, the problem of the transfer electric field due to the existence of the gap portion is further improved and advantageous.

[0029]

As described above, according to the present invention, in a solid-state imaging device having a transfer unit of a two-phase driving method using a buried channel, the potential can be stably maintained even when a gate is formed from a single layer film. Numerous advantages such as providing a solid-state imaging device capable of achieving stable performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a conventional technique.

[Explanation of symbols]

101 ... first transfer gate, 102 ... second transfer gate, 103 ... metal film, 103A ... buried metal part, 104 ... buried channel, 106 ...
-Impurity doped part, 201 ... Impurity doped part below the gap, 301 ... First and second impurity introduction parts below the gap.

Claims (5)

[Claims] 1. A solid-state imaging device having a transfer section of a two-phase drive system using a buried channel and a transfer gate formed by a gate formed of a single-layer film. In addition, a transfer channel having a transfer portion and a charge holding portion is provided in the same gate, and a metal is buried in a gap between the gates generated by forming the gate from a single-layer film to form a buried metal portion. A solid-state imaging device, wherein a potential of a portion corresponding to a metal-buried metal portion is controllable. 2. The solid-state imaging device according to claim 1, wherein a potential is stabilized by applying a bias voltage to said buried metal portion. 3. The solid-state imaging device according to claim 2, wherein the gap portion is doped with an impurity, and a bias voltage applied to the buried metal portion is adjusted to an external voltage. 4. The solid according to claim 1, wherein a part of the gap is doped with first and second different impurities, and a transfer part and a charge holding part are provided in the gap. Imaging device. 5. The solid-state imaging device according to claim 1, wherein the buried metal portion is formed by forming a metal film, and the metal film also serves as a light shielding film.