JP3158284B2 - Charge transfer device and 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 charge transfer device and a solid-state imaging device, and more particularly to a structure of a transfer electrode portion in a charge transfer device and a solid-state imaging device using the charge transfer device as a horizontal transfer portion.

[0002]

2. Description of the Related Art As an example of a solid-state imaging device, for example, the configuration of an interline transfer type CCD solid-state imaging device is shown in FIG.
Shown in In FIG. 1, a plurality of photosensitive units 1 are arranged two-dimensionally in pixel units in the vertical and horizontal directions and accumulate signal charges according to the amount of incident light, and signal charges read from these photosensitive units 1 for each vertical column. And a vertical shift register (vertical transfer unit) 2 for transferring the image data in the vertical direction. The signal charges of all pixels photoelectrically converted by the photosensitive unit 1 are instantaneously read out to the vertical shift register 2 for each vertical column during a part of the vertical blanking period.

The signal charge transferred to the vertical shift register 2 is transferred to a horizontal shift register (horizontal transfer section) 4 in order corresponding to one scanning line in a part of a horizontal blanking period. The signal charges for one scanning line are sequentially transferred in the horizontal direction by the horizontal shift register 4. The final end of the horizontal shift register 4 has an FDA (Floating Diffusion Amp
lifier) and the like. The output circuit unit 5 converts signal charges obtained by photoelectric conversion in the photosensitive unit 1 into a voltage and outputs the voltage.

FIG. 4 shows a sectional structure of a transfer electrode portion of the horizontal shift register 4 in the CCD solid-state imaging device. As is apparent from FIG. 3, each of the plurality of transfer electrodes 6 in the horizontal shift register 4 has a first layer of polysilicon (1Po).
ly) and a transfer (TR) gate electrode 8 made of a second-layer polysilicon (2Poly). To these electrode pairs, two-phase transfer clocks Hφ1 and Hφ2 are applied in the same phase, respectively, so that two-phase driving is performed.

[0005]

In the transfer electrode portion of the horizontal shift register 4, between the storage gate electrode 7 and the transfer gate electrode 8 forming a pair, both electrodes 7, 8 are driven by the same phase transfer clock. May be in a short-circuited state, but in practice, the entire storage gate electrode 7 of 1Poly has a thickness of several thousand Å due to insulation between adjacent electrode pairs. The film is covered with an insulating film 9 made of SiO ₂ .

As a result, the insulating film 9 is interposed between the pair of the storage gate electrode 7 and the transfer gate electrode 8, and as shown in the potential diagram of FIG.
A potential dip occurs in the a portion between 8 and
The residual signal charge in the portion causes the transfer efficiency to deteriorate.

Accordingly, the present invention provides a charge transfer device capable of improving transfer efficiency by reducing a potential dip generated between a pair of a storage gate electrode and a transfer gate electrode in a two-phase drive transfer section. And a solid-state imaging device using the same as a horizontal transfer register.

[0008]

In order to achieve the above-mentioned object, a charge transfer device according to the present invention has a plurality of transfer electrodes consisting of an electrode pair of a storage gate electrode and a transfer gate electrode, and has the same phase as the electrode pair. A transfer unit that transfers signal charges by driving the plurality of transfer electrodes in two phases while applying a transfer clock; and forming a pair of storage gate electrodes and an insulating film between the transfer gate electrodes so as to reduce the thickness of the adjacent electrodes. The configuration is such that the thickness of the insulating film between the storage gate electrode and the transfer gate electrode between the pair is made thinner.

Further, the solid-state imaging device according to the present invention comprises a plurality of photosensitive portions arranged two-dimensionally in a pixel unit in the vertical and horizontal directions, and a signal charge read from each of these photosensitive portions for each vertical column. And a plurality of transfer electrodes composed of an electrode pair of a storage gate electrode and a transfer gate electrode, and driving the plurality of transfer electrodes in two phases while applying the same phase transfer clock to the electrode pair. A horizontal transfer unit for transferring the signal charge from the vertical transfer unit in the horizontal direction, the thickness of the insulating film between the pair of storage gate electrodes and the transfer gate electrode, the thickness of the storage gate electrode between adjacent electrode pairs and The configuration is such that the thickness of the insulating film between the transfer gate electrodes is thinner than the thickness of the insulating film.

[0010]

In the charge transfer device having the above-mentioned structure, the thickness of the storage gate electrode forming a pair of the transfer portion and the thickness of the insulating film between the transfer gate electrodes is changed between the storage gate electrode and the transfer film between the adjacent electrode pair. , The potential dip generated between a pair of the storage gate electrode and the transfer gate electrode is reduced. This allows
The amount of signal charge remaining in the potential dip is greatly reduced, and the transfer efficiency of the transfer unit is improved.

In the solid-state imaging device having the above structure, the thickness of the storage gate electrode forming a pair of the horizontal transfer portions and the insulating film between the transfer gate electrodes is such that the insulation between the storage gate electrode and the transfer gate electrode between the pair of adjacent electrodes is formed. When the film thickness is smaller than the film thickness, a potential dip generated between a pair of the storage gate electrode and the transfer gate electrode is reduced. As a result, the amount of signal charges remaining in the potential dip is greatly reduced, and the transfer efficiency of the horizontal transfer unit is improved.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of a transfer electrode portion of a horizontal shift register according to an embodiment of the present invention.

In FIG. 1, a pressure-resistant film 13 made of silicon nitride Si ₃ N ₄ is provided on the surface of a silicon substrate 11 via an insulating film 12 made of a silicon oxide film SiO ₂ to improve the voltage resistance. An insulating film 14 made of a silicon oxide film SiO ₂ is further laminated thereon.
On this insulating film 14, a first layer of polysilicon (1Pol
y), and a transfer (TR) gate electrode 8 made of a _second polysilicon (2Poly) via insulating films 15 and 16 made of a silicon oxide film SiO _2. The pair of electrodes constitute a transfer electrode 6 having a two-layer structure.

Two-phase transfer clocks Hφ1 and Hφ2 are applied in the same phase to the pair of electrodes of the storage gate electrode 7 and the transfer gate electrode 8, respectively, so that two-phase driving is performed. An insulating film 15 between the storage gate electrode 7 and the transfer gate electrode 8,
16, the thickness of the insulating film 15 between the paired electrodes 7 and 8 is smaller than the thickness of the insulating film 16 between the storage gate electrode 7 and the transfer gate electrode 8 between adjacent electrode pairs. ,
The thickness is reduced to about several tens to several hundreds of square meters.

Since an in-phase transfer clock is applied to both electrodes 7 and 8 forming a pair, the electrodes 7 and 8 may be in a short-circuited state. Since the transfer clock is applied, the insulating film 16 between the storage gate electrode 7 and the transfer gate electrode 8 between the adjacent electrode pairs needs to have a high withstand voltage, and thus has a thickness of about several thousand Å. Is set.

As described above, the thickness of the insulating film 15 between the paired storage gate electrode 7 and the transfer gate electrode 8 is sufficiently smaller than the thickness of the insulating film 16 between the adjacent electrode pairs.
As shown in the potential diagram of FIG. 2, a potential dip does not occur between the electrodes 7 and 8 when the film is thinned to about several tens to several hundreds of degrees. The amount of remaining signal charges is greatly reduced, and the transfer efficiency of the horizontal shift register can be improved.

Next, the insulating film 15 which is a feature of the present invention is described.
The method for forming the film will be described.

The steps up to disposing the 1-poly storage gate electrode 7 on the outermost insulating film 14 of the silicon substrate 11 and forming the insulating film 16 made of the silicon oxide film SiO ₂ on the entire surface thereof are the same as those in the prior art. It is. After forming the insulating film 16, the transfer gate electrode 8 paired with the storage gate electrode 7 is formed.
Only the insulating film 16 on the side is removed by etching. At this time, the insulating film 14 located under the transfer gate electrode 8
Will also be removed at the same time. Thereafter, the removed portion by etching is formed by thinning the insulating film 15 of a silicon oxide film SiO ₂ to several tens to several hundreds Å. Then, finally, the transfer gate electrode 8 is provided.

As described above, since the same phase transfer clock is applied to both electrodes 7 and 8 forming a pair, the electrodes 7 and 8 may be short-circuited. After the insulating film 16 on the transfer gate electrode 8 side paired with the storage gate electrode 7 is removed by etching,
It is also possible to provide a direct transfer gate electrode 8. In this case, since the insulating film 14 is also removed by the etching at the same time, the transfer gate electrode 8 comes into direct contact with the breakdown voltage film 13 made of silicon nitride Si ₃ N _4, thereby causing a potential shift. Will occur.

However, in the present invention, since the thin insulating film 15 is interposed between the transfer gate electrode 8 and the breakdown voltage film 13, the transfer gate electrode 8 does not come into direct contact with the breakdown voltage film 13. The transfer efficiency of the horizontal shift register can be improved without causing a shift.

[0021]

As described above, according to the present invention, in the transfer section driven by two phases, the thickness of the storage gate electrode forming a pair and the thickness of the insulating film between the transfer gate electrodes are reduced by the accumulation between the pair of adjacent electrodes. Because the thickness is smaller than the thickness of the insulating film between the gate electrode and the transfer gate electrode,
The potential dip generated between the storage gate electrode and the transfer gate electrode forming a pair is reduced, and the transfer efficiency of the transfer unit can be improved accordingly.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a structure of a transfer electrode section of a horizontal shift register in a solid-state imaging device according to the present invention.

FIG. 2 is a potential diagram of a transfer electrode unit in FIG.

FIG. 3 is a schematic configuration diagram showing an interline transfer type CCD solid-state imaging device.

FIG. 4 is a cross-sectional view showing a conventional structure of a transfer electrode section of a horizontal shift register.

FIG. 5 is a potential diagram of the transfer electrode unit in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive part, 2 ... Vertical shift register, 3 ... Imaging part, 4
... horizontal shift register, 7 ... storage gate electrode, 8 ... transfer gate electrode, 11 ... silicon substrate, 12, 14-16 ...
Insulating film, 13 ... withstand voltage film

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01L 21/339 H01L 27/148 H01L 29/762 H04N 5/335

Claims (2)

(57) [Claims] A plurality of transfer electrodes each comprising an electrode pair of a storage gate electrode and a transfer gate electrode; and applying a transfer clock having the same phase to said pair of electrodes to connect said plurality of transfer electrodes to each other.
A transfer unit that transfers signal charges by phase driving, and sets a film thickness of a pair of the storage gate electrode and the insulating film between the transfer gate electrodes to a value between the storage gate electrode and the transfer gate electrode between the adjacent electrode pair. A charge transfer device characterized in that the thickness is smaller than the thickness of the insulating film. 2. A plurality of photosensitive units arranged two-dimensionally in pixel units in the vertical and horizontal directions, and a vertical transfer for vertically transferring signal charges read from the plurality of photosensitive units for each vertical column. And a plurality of transfer electrodes composed of an electrode pair of a storage gate electrode and a transfer gate electrode. The vertical transfer is performed by driving the plurality of transfer electrodes in two phases while applying an in-phase transfer clock to the pair of electrodes. A horizontal transfer unit for transferring the signal charges from the unit in the horizontal direction, the thickness of the insulating film between the storage gate electrode and the transfer gate electrode forming a pair, the storage gate electrode and the transfer gate between adjacent electrode pairs A solid-state imaging device characterized in that the thickness of the insulating film between the electrodes is made thinner.