JPH01128468A - CCD solid-state image sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a CCD solid-state image pickup device, and relates to a technique that is effectively used in a vertical CCD in an interline transfer CCD area sensor, for example.

[Conventional technology]

A CCD solid-state image sensor uses a polysilicon gate.
A light shielding film such as an aluminum layer is formed on the CD transfer path to prevent smearing and blooming. That is, since the polysilicon gate itself does not have a light-shielding property, the PN junction in the CCD transfer path acts as a parasitic photodiode, generating false signals such as smear and pluming as described above.

Regarding such a CCD solid-state image pickup device, there is, for example, rCCD Camera Technology J, written by Hiroo Takemura, published by Radio Gijutsusha on November 3, 1986, pages 46 to 49.

[Problem that the invention seeks to solve]

The reason why the aluminum film is used only for light shielding as described above is that if the transfer gate of the CCD is made of an aluminum layer, there will be reliability problems such as disconnection. For this reason, not only does the number of manufacturing steps increase, but when forming a large number of gates including the above-mentioned light-shielding film, the area occupied by the CCD transfer path becomes large in order to secure a margin for mask alignment to form each gate. Become.

In particular, with interline transfer CCD area sensors,
Since the vertical CCD is arranged so as to obstruct the aperture of the photodiode, if the area occupied by the CCD transfer path is large, the aperture ratio decreases accordingly, causing a decrease in sensitivity. This becomes a big problem when increasing the number of pixels to achieve high resolution.

Therefore, the inventor of the present application considered using a polysilicon metal composite conductive film having both reliability and light shielding properties as a gate constituting a CCD.

An object of the present invention is to provide a CCD solid-state image sensor with a simplified structure.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A summary of typical inventions disclosed in this application is as follows.

In other words, as a CCD transfer path that receives signal charges formed by photodiodes in parallel and transfers them serially, a CCD first layer gate and a second gate, and an insulating film extending above them in the transfer direction, are used as CCD transfer paths. and a CCD third N gate made of a polysilicon-gold-N composite conductive film.

[For production]

According to the above-described means, the third layer gate can have a light shielding property, so that its structure can be simplified.

〔Example〕

FIG. 1 shows a schematic cross-sectional view of one embodiment of a CCD transfer path used in a CCD solid-state imaging device according to the present invention.

Although not particularly limited, a P-type well region 2 is formed on an N-type semiconductor substrate 1 . A P′ type second well region 3 is formed in this P type well region.

An N-type buried channel N4 constituting a CCD transfer channel is formed on the surface of the P0 type second well region 3.

A first N4 gate 5 and a second layer gate 6 made of a conductive polysilicon layer are formed on the surface of the N-type buried channel layer 4, respectively, with a gate insulating film interposed therebetween. The first round gate 5 and the second layer gate are separated from each other in the signal charge transfer direction. In contrast, the third
The N gate 7 is configured to extend in the transfer direction through a gate insulating film on the surfaces of the first and second layer gates and the surface of the N-type buried channel layer 4.

This third RF5 gate 7 has a lower layer made of a conductive polysilicon layer and an upper layer made of a metal silicide film made of a metal layer such as molybdenum or tungsten in order to have light blocking properties in addition to conductivity as a gate electrode. is used. That is, the third layer gate 7 is composed of a polysilicon metal composite conductive film.

The first gate 5 and the second gate are supplied with transfer pulses φ2 and φ3, respectively, and the third layer gate 7 is supplied with a transfer pulse φ1. Since the first gate 5 and the second gate 6 are formed separately in the transfer direction,
As will be described later, transfer pulses φ2 and φ3 are supplied, respectively, through wiring made of a polysilicon layer formed integrally with the gates 5 and 6, respectively. On the other hand, since the third layer gate 7 is formed integrally in the transfer direction, special wiring for supplying the transfer pulse φ1 is unnecessary. The metal film acts as a wiring, and as a result,
The portion facing the surface of the N-type buried channel N4 via the gate insulating film, in other words, the rounding of the waveform of the transfer pulse φl supplied to the substantial third N gate that forms a potential distribution for transferring signal charges. Furthermore, since the upper metal film of the third layer gate 7 is formed to extend in the CCD transfer direction and cover the CCD transfer path, it also has a light shielding effect. .

FIG. 2 shows a schematic layout diagram of an embodiment in which the above CCD transfer path is applied to a CCD area sensor for frame interline transfer.

In an interline transfer CCD, a CCD transfer path is provided in a vertical direction adjacent to a photodiode. The space between the photodiodes arranged in the vertical direction is used as wiring for supplying transfer pulses φ2 and φ3 to the first layer gate and the second layer gate, as described later. One photodiode is provided with a unit CCD transfer path driven by three phases, which includes the first layer gate, second layer gate, and third layer gate as described above.

The figure shows an example of a color CCD area sensor. In a color CCD area sensor, one pixel is composed of four color filters: W (transparent), cy (cyan), Ye (yellow), and G (green). In this embodiment, in order to output the four color signal charges independently, a switching gate 1 is provided at the output section of the three-phase vertical CCD (BCD), and the signal charges are once transferred to the storage section. . By its switching control, the switching gate 1 is configured to control c according to the arrangement of the color filters.
When y is transferred, it is transferred to the storage section on the right side, and when W is transferred, it is transferred to the storage section on the left side. As a result, the above 2
The two color signal charges are separated. This also applies to the color signals G and Ya in other columns constituting one pixel.

The color signal transferred to the storage section is transferred to the horizontal CGDI by the switching gate 2. This horizontal CGDI is also coupled to the horizontal CCD 2 via a transfer gate, and the color signal cy from the storage section is first transferred to the horizontal CCD 1 and then transferred to the horizontal CCD 2 under the control of the transfer gate.
Transferred to D2. In parallel with this transfer operation, switching control of the changeover switch 2 is performed, and the horizontal CCD
1, the color signal W is transferred. This also applies to the other color signals G and Ye constituting one pixel. In this way, when a signal corresponding to one horizontal line is transferred to horizontal CCD1 and CCD2, horizontal CCD1
and CCD2 start horizontal transfer operations, and from the output of horizontal C0DI, W and Ye are transferred to horizontal CCD2 in the order of
Color signals corresponding to the color filters forming one pixel are outputted independently in the order of cy and c from the outputs of .

When a three-phase vertical CCD transfer path is provided as described above,
Transfer operations in both directions are possible depending on the order in which the transfer pulses φ to φ3 are supplied. Taking advantage of this, the maximum sensitivity is achieved when the signal charge formed by the photodiode is transferred to the vertical CCD between one frame (field), and the signal charge of the photodiode is swept out in the middle of the frame. , and may have variable sensitivity. That is, the maximum storage time of the photodiode is one frame (field), and the storage time can be made variable by sweeping out the signal charge. During such a signal charge sweeping operation, the three-phase vertical CC
D has its transfer direction reversed.

FIG. 3 shows a pattern diagram of an embodiment of one photodiode and a corresponding unit of CCD transfer path.

In the figure, solid lines indicate the first WJ gate 5 and the second layer gate 6 made of polysilicon layers, and wirings for supplying transfer pulses φ2 and φ3, respectively. That is, the polysilicon layer has a two-layer structure, with the first polysilicon layer serving as the first layer gate 5 and the wiring for supplying the transfer pulse φ2 thereto, and the second layer polysilicon serving as the second layer gate 6 and the wiring for supplying the transfer pulse φ2 thereto. The wiring is used to supply the transfer pulse φ3 thereto. The above wiring is extended horizontally in the same figure, and 2
Two wiring lines are formed by overlapping each other with an insulating film in between. The 1Mth wiring 5 arranged horizontally above the photodiode section is used to supply the transfer pulse φ2 to the first layer gate 5 corresponding to the photodiode one above, and the second The third layer wiring 6 is used to supply a transfer pulse φ3 to the second layer gate 6 corresponding to the photodiode section. Therefore, the transfer pulse φ2 is supplied to the first layer gate 5 corresponding to the photodiode section by the first layer wiring 5 arranged laterally on the lower side.

In the figure, the photogate and the channel top gate are indicated by broken lines. The photogate extends along the transfer direction at the boundary between the photodiode and the CCD transfer path. By supplying a transfer pulse to the photogate, signal charges formed by the photodiode section are transferred in parallel to the potential well under the third layer gate of CCD transfer. Channel stop gate is CCD
This creates a potential barrier between the transfer path and the adjacent photodiode.

Along the above-mentioned CCD transfer path, there is a third
A layer gate 7 is integrally formed. As described above, this third layer gate is composed of a polysilicon layer as a lower layer and a metal layer as an upper layer. This third layer gate also serves as a light shielding function as described above, so in addition to the above CCD transfer path,
It is also formed to cover the photogate and channel stop gate.

As in this embodiment, the third layer gate 7 is used as a CCD transfer gate and also has a light shielding function using a metal silicide gate, so that an aluminum layer for light shielding is unnecessary. Therefore, the manufacturing process is simplified, and in order to ensure a mask alignment margin between the third N gate and the light-shielding aluminum film, the aluminum layer acts to reduce the aperture ratio of the photodiode part. As a result, the aperture ratio of the photodiode part is high (which makes it possible to improve the sensitivity. Also, if the photodiode structure shown in Figure 3 is used, the signal 4 of each pixel can be read out independently. Is possible.

The effects obtained from the above examples are as follows. That is, (1) As a CCD transfer path that receives signal charges formed by photodiodes in parallel and transfers them serially, a CCD first N gate and a second gate are connected along the transfer direction via an insulating film on top of them. The CCD third layer gate is made of a polysilicon metal composite conductive film, and the third layer gate has a light shielding property. As a result, the light-shielding aluminum film and the like can be omitted, resulting in the effect that the number of manufacturing steps can be simplified.

(2) Because (1) above eliminates the need for a special light-shielding film, it is possible to prevent the aperture ratio of the photodiode from decreasing due to the mask alignment margin used to form the light-shielding film, making it possible to achieve higher sensitivity. This effect can be obtained.

(3) By using a polysilicon-metal composite conductive film as the third layer gate, mechanical strength is increased and reliability is achieved, and the waveform of the transfer pulse supplied to the third layer gate is less rounded. Therefore, it is possible to obtain the effect that the transfer characteristics can be improved.

(4) By employing a photodiode having the structure shown in FIG. 3, it becomes possible to read out signals from each pixel independently. As a result, it is possible to obtain the effect that the resolution can be higher than that of the pixel mixed readout method.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the Examples and can be modified in various ways without departing from the gist thereof. For example, Fu2! - The diode section may have a VOD (vertical overflow drain) structure. When the VOr) structure is adopted in this manner, excess charge generated in the photodiode does not flow into the vertical CCD, but instead flows in the thickness direction of the substrate.

In addition, the substrate method (generated charges also flow toward the substrate and disappear. This can reduce blooming and smearing. In this way, various embodiments of semiconductor structures such as photodiodes can be adopted.

Further, the structure of the CCD transfer path can also take various embodiments provided that it has a three-layered transfer gate as described above.

Furthermore, when applied to a color solid-state image sensor, the types of color filters and their arrangement can take various embodiments.

The present invention can be similarly applied to CCD line sensors and the like in addition to CCD area sensors.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows. In other words, as a CCD transfer path that receives signal charges formed by photodiodes in parallel and transfers them serially, a CCD first layer gate and a second gate, and an insulating film extending above them in the transfer direction, are used as CCD transfer paths. CCD made of polysilicon metal composite conductive film
By providing the third layer gate with a light-shielding property by forming the third N gate, it is possible to omit a light-shielding aluminum film, etc., thereby simplifying the number of manufacturing steps.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of one embodiment of a CCD transfer path used in a CCD solid-state image sensor according to the present invention, and FIG. 2 is a case in which the above CCD transfer path is applied to a frame interline transfer CCD area sensor. Schematic layout diagram of one embodiment. FIG. 3 is a pattern diagram of one embodiment of one photodiode and a corresponding unit of CCD transfer path. 1...N-type silicon substrate, 2...P-type well layer, 3...
P0 type second well layer, 4...N-rational channel layer,
5..First layer polysilicon gate, 6..Second N polysilicon gate, 7..Third layer metal silicide gate 7 :\Figure 1Figure 2Figure 3

Claims (1)

[Claims] 1. A CCD third layer formed on the CCD first layer gate and the CCD second layer gate so as to extend along the transfer direction via an insulating film, and made of a polysilicon metal composite conductive film. A CCD solid-state image sensor comprising a layer gate and comprising a CCD transfer path that receives signal charges formed by a photodiode in parallel and transfers them serially. 2. The CCD solid-state imaging device according to claim 1, wherein the CCD first layer gate and the CCD second layer gate are made of a conductive polysilicon layer. 3. The above CCD transfer path is an interline transfer type C
3. A CCD solid-state image sensor according to claim 1, which constitutes a vertical CCD in a CD area sensor.