JPH05267355A - Manufacture of charge transfer device - Google Patents

Abstract

PURPOSE:To improve a dielectric strength between electrodes of a charge transfer device and to manufacture even a device having many number of elements in high yield. CONSTITUTION:Three films of a silicon oxide film 2, a silicon nitride film 3 and a silicon oxide film 4 are used as a gate insulating film, a first gate electrode 5 of polycrystalline silicon is formed, its surface is oxidized, a gate insulating film except a part directly under the electrode 5 is removed, a silicon oxide film 6 is grown by a CVD method as a gate insulating film of a second gate electrode 8, and a dielectric strength between the electrodes is reinforced.

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, and more particularly to a method for forming a charge transfer electrode.

[0002]

2. Description of the Related Art At present, a charge-coupled device (hereinafter referred to as a CCD), which is a charge transfer device widely used in a solid-state image pickup device, has a large number of Ms electrically separated at extremely narrow intervals.
It has a structure in which OS capacitors are arranged, and voltage pulses are applied to each MOS capacitor one after another.
It has a mechanism for transferring charges along the columns of the OS capacitors. The most important point in forming such a row of MOS capacitors is that each electrode must be formed with an extremely narrow interval of about several hundred nm. Since it is difficult to separate the electrodes at such a narrow interval by the current photolithography technology, the following method is generally used to form the electrode array having such a structure. That is, as shown in FIG. 3, the first gate electrode 1 made of polycrystalline silicon is formed on the semiconductor substrate 12 via the gate insulating film 13.
4 is formed by the CVD method and the photolithography method, a thin silicon oxide film 15 is formed on the surface of the first gate electrode 14 by thermal oxidation, and then a thin film of polycrystalline silicon is formed thereon by the CVD method and the photolithography method. Two
The gate electrode 16 is formed. By thus forming a structure in which the electrodes of a plurality of layers are superposed with a thin insulating film interposed therebetween, it is possible to form gate electrode rows at intervals of about several hundreds of nm with a margin by the current photolithography technology.

[0003]

However, in the above-described conventional method for manufacturing a CCD, polycrystalline silicon is thermally oxidized as an interlayer insulating film of the polycrystalline silicon layer formed with the first gate electrode and the second gate electrode. The formed silicon oxide film is used. This silicon oxide film contains a large amount of unoxidized silicon and phosphorus added as a conductive impurity at a high concentration as compared with a silicon oxide film formed by thermally oxidizing single crystal silicon, and thus the film quality is significantly inferior. Further, since the thermal oxidation progresses along the grain boundaries of the polycrystal, the surface of the electrode after the oxidation has extremely large irregularities, and there are a large number of portions having low insulating properties between layers. Therefore, CCD with a large number of elements
In the case of, the probability of insulation failure between electrodes is high, and CC
There is a problem that the manufacturing yield of D is significantly reduced.

The present invention solves the above problems, makes it possible to sufficiently increase the withstand voltage between electrodes, and has a large number of elements.
However, it is intended to provide a method that can be manufactured with a high yield.

[0005]

A method of manufacturing a charge transfer device according to the present invention comprises a step of forming a film having a protective property against oxidation of the semiconductor substrate on the surface of the semiconductor substrate, and a step of forming polycrystalline silicon on the gate insulating film. Forming a first gate electrode, forming a silicon oxide film on the surface of the first gate electrode by thermal oxidation, and superimposing C on the silicon oxide film.
The method includes a step of forming an interlayer insulating film by the VD method and a step of forming a second gate electrode made of polycrystalline silicon via the interlayer insulating film.

[0006]

The present invention will be described below with reference to the drawings. 1 (a) to 1 (e) are sectional views showing the procedure of one embodiment of the present invention. First, as shown in FIG. 1 (a), a silicon oxide film 2 having a thickness of 40 nm is formed on a semiconductor substrate 1 by thermal oxidation, and then a silicon nitride film 3 having a thickness of 40 nm 3 and a thickness of 20 nm are formed by a CVD method. The CVD silicon oxide film 4 is continuously grown. Then, as shown in FIG.
A polycrystalline silicon film having a thickness of 50 nm is grown by the CVD method, the first gate electrode 5 is formed by the photolithography method, and then a silicon oxide film 6 having a thickness of 200 nm is formed on the surface of the first gate electrode 5 by thermal oxidation. .. At this time, since the surface of the semiconductor substrate 1 is covered with the silicon nitride film 3, the oxidation does not proceed. Then, as shown in FIG.
The VD silicon oxide film 4, silicon nitride film 3, and silicon oxide film 2 are removed. At this time, it is desirable to use a phosphoric acid solution when removing the silicon nitride film 3 and a hydrofluoric acid solution when removing the CVD silicon oxide film 4 and the silicon oxide film 2. Excessive etching must be avoided so that the depletion amount of the silicon oxide film 6 is 100 nm or less. Continuing with Figure 1
As shown in (d), a 50-nm-thick CVD silicon oxide film 7 is grown on the semiconductor substrate 1 by the CVD method. C
Since the VD silicon oxide film has a much higher dielectric strength than the silicon oxide film obtained by thermally oxidizing polycrystalline silicon, this forms an interlayer insulating film having sufficient characteristics. Then, as shown in FIG. 1 (e), a second polysilicon film is formed by CVD and photolithography.
The gate electrode 8 is formed.

By forming the polycrystalline silicon electrode array in this way, the probability of occurrence of insulation failure between electrodes is extremely low even in a CCD having a large number of elements, and the manufacturing yield of the CCD can be greatly improved. it can.

FIGS. 2A to 2C are sectional views showing the procedure of the second embodiment of the present invention. That is, as in FIGS. 1A and 1B, a silicon thermal oxide film 2, a silicon nitride film 3, and a CVD silicon oxide film 4 are formed on the semiconductor substrate 1 to have a thickness of 40 nm, 40 nm, and 20 nm, respectively. After that, the first gate electrode 5 of polycrystalline silicon is formed by the CVD method and the photolithography method, and the silicon oxide film 6 having a thickness of 200 nm is formed on the surface of the first gate electrode 5 by thermal oxidation. Subsequently, as shown in FIG. 2A, the CVD silicon oxide film 4 and the silicon nitride film 5 are removed by a hydrofluoric acid solution and a phosphoric acid solution, respectively. Here, the silicon thermal oxide film 2 is not removed but left as it is. Further, when the CVD oxide film 4 is removed, the reduction amount of the silicon oxide film 6 is set to 40 nm or less. Subsequently, as shown in FIG. 2B, a silicon nitride film 9 and a CVD silicon oxide film 10 are grown on the semiconductor substrate 1 by the CVD method to have a thickness of 40 nm and 20 nm, respectively. Since the withstand voltage of the silicon oxide film 6 is reinforced by the silicon nitride film 9 and the CVD silicon oxide film 10, an interlayer insulating film having sufficient characteristics can be formed. Subsequently, as shown in FIG. 2C, a second gate electrode 11 of polycrystalline silicon is formed by the CVD method and the lithography method.

In this embodiment, the first gate electrode and the gate insulating film immediately below the second gate electrode have the same structure, and therefore, there is an advantage that there is no difference in characteristics.

[0010]

As described above, according to the present invention, the step of forming a film as a gate insulating film on the surface of a semiconductor substrate and having a protection property against oxidation of the semiconductor substrate, and the step of forming polycrystalline silicon on the gate insulating film are performed. No. 1 gate electrode, a step of forming a silicon oxide film on the surface of the first gate electrode by thermal oxidation, and a step of overlaying C on the silicon oxide film.
The method includes a step of forming an interlayer insulating film by the VD method and a step of forming a second gate electrode made of polycrystalline silicon via the interlayer insulating film, thereby sufficiently increasing the dielectric strength voltage between the electrodes. Therefore, there is an effect that a CCD having a large number of elements can be manufactured with a high yield.

[Brief description of drawings]

FIG. 1 is a sectional view showing a procedure of an embodiment of the present invention.

FIG. 2 is a sectional view showing the procedure of the second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional charge transfer device.

[Explanation of symbols]

 1 semiconductor substrate 2 silicon oxide film 3 silicon nitride film 4 CVD silicon oxide film 5 first gate electrode 6 silicon oxide film 7 CVD silicon oxide film 8 second gate electrode 9 silicon nitride film 10 CVD silicon oxide film 11 second gate electrode 12 Semiconductor substrate 13 Gate insulating film 14 First gate electrode 15 Silicon oxide film 16 Second gate electrode

Claims (1)

[Claims] 1. A step of forming a film having a protection property against oxidation of the semiconductor substrate as a gate insulating film on a surface of the semiconductor substrate, and a step of forming a first gate electrode of polycrystalline silicon on the gate insulating film. A step of forming a silicon oxide film on the surface of the first gate electrode by thermal oxidation, a step of forming an interlayer insulating film on the silicon oxide film by a CVD method, and a polycrystal via the interlayer insulating film. And a step of forming a second gate electrode made of silicon.