JP2663697B2 - Charge transfer device and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge transfer device and a method of manufacturing the same, and more particularly, to a structure and a method of forming a transfer electrode made of a multi-layer polycrystalline silicon film.

[Conventional technology]

3 (a) to 3 (c) are cross-sectional views in the order of steps for explaining the conventional charge transfer device along the manufacturing steps.

First, as shown in FIG. 3 (a), an insulating film 2 such as silicon oxide is formed on a silicon substrate 1, and then a polycrystalline silicon film is deposited on the entire surface by a CVD method. Are selectively removed to form first polycrystalline silicon electrodes 3i, 3j,
... is formed.

Then, as shown in FIG. 3 (b) first polysilicon electrodes 3i, 3j, ..., the silicon substrate 1 formed of, for example, O ₂
By heating in an atmosphere, the surface of the first polycrystalline silicon electrode is oxidized to form an insulating film 4 made of a silicon oxide film.
To form

Thereafter, as shown in FIG. 3 (c), the first polycrystalline silicon electrode is close to the side surface and partially overlaps the first polycrystalline silicon electrode 3 by the CVD method and the photolithography method. By forming the second polycrystalline silicon electrodes 5h, 5i,..., A charge transfer element provided with a required number of polycrystalline silicon electrodes can be obtained.

[Problems to be solved by the invention]

In the conventional charge transfer device described above, the internal wiring of the first and second polycrystalline silicon electrodes shown in FIG.
Because of the RC time constant, the pulse potential applied to each electrode from outside is distorted, and as shown in FIG. 4, the longer the internal wiring length, the more the frequency of the applied pulse potential There is a disadvantage that the charge transfer capability decreases as the height increases.

As a countermeasure, there is a method using a well-known high melting point metal electrode or silicide electrode instead of the polycrystalline silicon electrode. However, there are problems in work function, interface trap level, chemical resistance, and formation of a good interelectrode insulating film. There is a drawback that it is difficult.

[Means for solving the problem]

The charge transfer device according to the present invention includes a plurality of first polycrystalline silicon electrodes arranged at predetermined intervals on a semiconductor substrate with an insulating film interposed therebetween, and each region interposed between the first polycrystalline silicon electrodes. A plurality of second polycrystalline silicon electrodes each partially provided on an edge of the adjacent first polycrystalline silicon electrode provided on the insulating film, and having a spacer insulating film on a side surface; A refractory metal film is provided on a portion of the surface of the first polycrystalline silicon electrode except for a portion under the second polycrystalline silicon electrode and the spacer insulating film, and on a surface of the second polycrystalline silicon electrode. That is.

The method of manufacturing a charge transfer device according to the present invention further comprises the steps of: forming a plurality of first polycrystalline silicon electrodes on a semiconductor substrate via an insulating film at predetermined intervals; After forming a silicon oxide film on the side and surface of the crystalline silicon electrode and depositing and patterning a polycrystalline silicon film, a second polycrystalline silicon film is formed on the insulating film in each region sandwiched between the first polycrystalline silicon electrodes. A step of forming a crystalline silicon electrode; a step of forming a silicon oxide film on side surfaces and a surface of the second polycrystalline silicon electrode; and a part of a surface of the first polycrystalline silicon electrode by performing anisotropic etching. And a step of exposing the surface of the second polycrystalline silicon electrode, and forming a refractory metal film on the first polycrystalline silicon electrode and the second polycrystalline silicon electrode by a selective CVD method. Is that and a degree.

〔Example〕

FIG. 1 is a sectional view showing an embodiment of the charge transfer device of the present invention.

In this embodiment, a plurality of first polysilicon electrodes 3i, 3j,... Arranged at predetermined intervals on a semiconductor substrate (silicon substrate 1) with an insulating film 2 interposed therebetween, A spacer insulating film (insulating film 6) is provided on the insulating film 2 in each region sandwiched between the crystalline silicon electrodes and partially overlaps the edge of the adjacent first polycrystalline silicon electrode.
A plurality of second polycrystalline silicon electrodes 5h, 5i, 5j,
, And a portion of the surface of the first polycrystalline silicon electrode other than the second polycrystalline silicon electrode and the portion under the spacer insulating film (6), and the second polycrystalline silicon The refractory metal film 7 is provided on the surface of each electrode.

The difference from the conventional charge transfer device shown in FIG. 3 (c) is that the insulation of the portion of the surface of the first polysilicon electrodes 3i, 3j,... Which does not overlap with the second polysilicon film. A high-melting point metal film 7 such as W is provided on the trace where the film 4 is removed,
Similarly, the refractory metal film is provided also on the surface of the second polycrystalline silicon electrodes 5h, 5i, 5i,. Accordingly, the resistance of the transfer electrode is reduced, and the charge transfer capability is prevented from lowering. In addition, since it is based on a polycrystalline silicon film, the work function and the interface trap level do not need to be considered again.

2 (a) to 2 (d) are cross-sectional views in the order of steps for explaining one embodiment of the method of manufacturing the charge transfer device of the present invention.

First, as shown in FIG. 2 (a), after an insulating film 2 is formed on a silicon substrate 1, a CV
The first polycrystalline silicon electrodes 3i, 3j,... Are formed by depositing by the method D and selectively removing unnecessary portions by a photolithography method.

Next, as shown in FIG. 2 (b), the silicon substrate 1 on which the first polycrystalline silicon electrodes 3i, 3j,.
By heating in an O ₂ atmosphere, the surface of the first polycrystalline silicon electrode is oxidized to form an insulating film 4 made of a silicon oxide film.

Next, as shown in FIG. 2 (c), the second polysilicon film is formed by a CVD method and a photolithography method so that a part thereof is close to the side surface of the first polysilicon electrode and partially overlaps the first polysilicon charge. Are formed as the polycrystalline silicon electrodes 5h, 5i, 5j,. Up to this point, it is exactly the same as the conventional example.

Further, as shown in FIG.
A silicon oxide film-based insulating film having good step coverage represented by a high-temperature oxide film or the like is formed on the entire surface, and an insulating film 6 is formed on side walls of the first and second polycrystalline silicon electrodes by anisotropic etching. To form

Finally, as shown in FIG.
(Tungsten) 100-300nm, preferably
By selectively forming a high melting point metal film 7 of about 200 nm on the first and second polycrystalline silicon electrodes, the charge transfer device of the present invention can be obtained.

Since the selective CVD method is used, it is possible to form the refractory metal film in a self-aligned manner.

〔The invention's effect〕

As described above, the present invention achieves low resistance by providing a high melting point metal film in a self-aligned manner on each polycrystalline silicon electrode of a charge transfer device having a relatively long polycrystalline silicon electrode having a multilayer structure. There is an effect that it is possible to suppress a decrease in the charge transfer capability due to the RC time constant without causing a new problem regarding the function and the interface trap level.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the charge transfer device of the present invention, and FIGS. 2 (a) to 2 (d) are sectional views in the order of steps for explaining a method of manufacturing the charge transfer device of the present invention. 3 (a) ~
FIG. 4C is a step-by-step cross-sectional view for explaining the charge transfer device of the conventional example along the manufacturing process, and FIG. 4 is a characteristic diagram showing the influence of the length of the polycrystalline silicon electrode on the charge transfer capability. 1 silicon substrate, 2 insulating film, 3i, 3j,... First polycrystalline silicon electrode, 4 insulating film, 5h, 5i, 5j,
..., Second polycrystalline silicon electrode, 6, insulating film, 7
…… High melting point metal film.

Claims (2)

(57) [Claims] A plurality of first polycrystalline silicon electrodes arranged at predetermined intervals on a semiconductor substrate via an insulating film;
A plurality of insulating films provided on the insulating film in the respective regions sandwiched between the first polycrystalline silicon electrodes, each partially overlapping an edge of the adjacent first polycrystalline silicon electrode, and having a spacer insulating film on a side surface; A second polycrystalline silicon electrode, a portion of the surface of the first polycrystalline silicon electrode excluding a portion under the second polycrystalline silicon electrode and a spacer insulating film, and the second polycrystalline silicon electrode. A charge-transfer device, wherein a high-melting-point metal film is provided on each of the surfaces. 2. The method according to claim 1, further comprising the steps of:
Forming a polycrystalline silicon electrode at predetermined intervals, forming a silicon oxide film on the side and surface of the first polycrystalline silicon electrode, and then depositing and patterning the polycrystalline silicon film. Forming a second polycrystalline silicon electrode on the insulating film in each region sandwiched by the first polycrystalline silicon electrode; and forming a silicon oxide film on the side and surface of the second polycrystalline silicon electrode. Forming, exposing a part of the surface of the first polycrystalline silicon electrode and the surface of the second polycrystalline silicon electrode by performing anisotropic etching, and forming the first polycrystalline silicon electrode by selective CVD. Forming a refractory metal film on the crystalline silicon electrode and the second polycrystalline silicon electrode.