JP2817404B2 - Method for manufacturing charge transfer 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 method for manufacturing a charge transfer device using a refractory metal or a silicide thereof as a gate electrode.

[0002]

2. Description of the Related Art As a conventional charge transfer device, FIG.
As shown in (b), the first gate electrode 8 and the second gate electrode 9 have a structure in which the first gate electrode 8 and the second gate electrode 9 overlap to increase the charge transfer efficiency, and polysilicon is used for the gate electrode in consideration of compatibility with the Si process. Some have a single-layer gate structure as shown in FIG. 3, and gate electrodes 10a and 10b are made of a high melting point metal. As a manufacturing process,
In the former, first, as shown in FIG. 2A, the surface of the Si substrate 1 is oxidized to form a first gate oxide film 2, on which a first gate electrode 8 is formed and then refreshed to perform a second gate oxidation.
The second gate electrode 9 is formed so as to overlap with the first gate electrode 8 to obtain a structure shown in FIG. In the latter, the first gate electrode 10a and the second gate electrode 10b are simultaneously formed by etching.

[0003]

In the case of the structure shown in FIG. 2, problems such as the waveform of a driving pulse becoming round at the time of high-speed transfer occur due to the large wiring resistance of polysilicon. This is a particularly significant problem when a charge transfer device is used in a solid-state imaging device in which the number of pixels has been increased and the polysilicon wiring is long.

In the case of the structure shown in FIG. 3, a gap is formed between adjacent gate electrodes, so that a potential dip occurs in a portion at the time of charge transfer, resulting in deterioration of charge transfer efficiency.

However, when a charge transfer device having a gate electrode made of a refractory metal having an overlapping structure or a silicide thereof is formed by using the conventional process described with reference to FIGS. When forming a two-gate oxide film,
Since the high melting point metal or its silicide is easily oxidized, the first gate electrode is oxidized and becomes powdery, and does not function as a gate.

The present invention suppresses the oxidation of the first gate electrode at the time of forming the second gate oxide film without deteriorating the film quality of the second gate oxide film. An object is to create a charge transfer element serving as a gate electrode.

[0007]

After the upper portion and the side wall of the first gate electrode are covered with an insulating film formed at a low temperature, a second gate oxide film is formed, and then the second gate electrode is partially covered with the first gate electrode.
The above problem is solved by overlapping the gate electrode.

[0008]

According to the present invention, the first gate electrode is covered with an insulating film formed at a low temperature before the high-temperature treatment, thereby preventing the first gate electrode from being oxidized.

[0009]

FIG. 1D is a sectional view for explaining an embodiment of the structure of the charge transfer device according to the present invention. The gate electrodes 3 and 7 are made of tungsten for resistance reduction, and the first gate electrode 3 is covered with CVD oxide films 4 and 5b formed at 450 ° C. so as not to be oxidized when the second gate oxide film 6 is formed. A part of the second gate electrode 7 overlaps the first gate electrode 3 via an oxide film in order to increase transfer efficiency.

Here, the case of manufacturing a charge transfer device having such a configuration will be specifically described. First, a first gate oxide film 2 having a thickness of 700A is formed on the surface of a Si substrate 1 by thermal oxidation, and then the first gate film (tungsten) is formed to a thickness of 200A.
0A, then a CVD oxide film (forming temperature 450 ° C.) is formed to a thickness of 2000 A and etched into gate shapes 3 and 4 (FIG. 1A). Further, the CVD oxide film 5a (forming temperature 4
50 ° C.) was formed over the entire surface of a 2000A thickness (FIG. 1).
(B)) After the etching back, the side wall 5b is formed (FIG. 1 (c)). Thereafter, the second gate oxide film 6 (HT
O, a forming temperature of 850 ° C.), a thickness of 700 A, a part of the second gate electrode 7 (tungsten), and a first gate electrode 3
(Tungsten) overlapped to a thickness of 2000
A is formed. Instead of the above tungsten, another high melting point metal (Mo, Ti, etc.) or its silicide (WS
i) or another insulating film (plasma nitride film, forming temperature 3) which can be formed at a low temperature instead of the CVD oxide film.
00 ° C.).

[0011]

According to the present invention, it is possible to form a charge transfer element having low wiring resistance and high transfer efficiency.

Further, when the second gate oxide film is formed, the oxidation of the first gate electrode made of a refractory metal or a silicide thereof can be suppressed without deteriorating the film quality of the second gate oxide film.

In addition, by using the method of the present invention, ion implantation is performed when the upper portion and the side wall of the first gate electrode are covered with an insulating film formed at a low temperature, so that the implanted ions are stopped by the CVD oxide film. Alternatively, the disadvantage that the silicide causes channeling at the time of ion implantation can be suppressed, and ions can be implanted below the second gate electrode by self-alignment.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a process in one embodiment of the present invention.

FIG. 2 is a sectional view showing a conventional example.

FIG. 3 is a sectional view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 1st gate oxide film (thermal oxide film) 3 1st gate electrode (tungsten) 4 5a, 5b, CVD oxide film 6 2nd gate oxide film (HTO) 7 2nd gate electrode (tungsten) 8 1st gate Electrode (polysilicon) 9 Second gate electrode (polysilicon) 10 Gate electrode (high melting point metal or silicide)

Claims (1)

(57) [Claims] A step of forming a film made of a refractory metal or a silicide thereof on a substrate having an oxide film formed on a surface thereof, and forming an insulating film thereon at a low temperature of 450 ° C. or less ; Or a step of patterning a film made of the silicide and an insulating film thereover into a gate shape, and a step of forming an insulating film over the entire surface at a low temperature of 450 ° C. or less and etching back to form a sidewall on a gate electrode side wall. Forming a second gate oxide film;
Forming a second gate electrode made of a refractory metal or a silicide thereof on the gate oxide film so as to overlap the first gate electrode.