JPS63276272A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve dielectric strength of an insulating film between first and second gate electrodes and to improve charge holding characteristics of the first gate electrode, by forming the insulating film thick on the edges or the first gate electrode. CONSTITUTION:A field oxide film 2 and a first gate oxide film 3 are formed on a silicon substrate 1 and then a first gate polycrystalline silicon film 4 is deposited thereon. A thin oxide film 5 is formed on the first polycrystalline silicon film 4 and, further, a silicon nitride film 6 is deposited thereon. An oxide film 7 is formed only on the side walls of the first gate polycrystalline silicon film by the thermal oxidation process. The silicon nitride film 6 and the thermal oxide film 5 are etched and a second gate insulating film 8 is deposited thereon. Subsequently, polycrystalline silicon, tungsten side or the like is deposited thereon for providing a second gate electrode 9.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor device, particularly a nonvolatile semiconductor memory device having a double gate structure, between a first conductive layer and a second conductive layer. The present invention relates to a structure of an insulating oxide film of a second gate and a method of forming the same.

(Prior Art) Figures 3 (a), (b), (CJ, and d) are sectional views of essential parts of an example of a nonvolatile semiconductor memory device having a double gate structure according to a conventional manufacturing process. In the figure, ! is a silicon substrate, 2 is this substrate!'' 2 is an element isolation insulating film formed on it, 3 is a first gate oxide film, and 4 is a polycrystalline silicon which is a first conductive layer. 8 is a second gate oxide 11Q, and 9 is a polycrystalline silicon film (hereinafter referred to as a second gate electrode) which is a second conductive layer.

Hereinafter, the conventional manufacturing method will be explained using FIG.

First, as shown in FIG. 3(a), a field oxide film 2 is formed on the field region of the silicon substrate 1 by selective oxidation.
is formed, and a first gate oxide [3 is formed by thermal oxidation in the element formation region. Then, polycrystalline silicon 1 and 4 are grown over the entire surface, and a first gate electrode is formed by photolithography.

Next, as shown in FIG. 3(b), a second gate insulating film 8 (for example, a silicon oxide film) is formed on the polycrystalline silicon film 4, which is the first gate electrode, by thermal oxidation or chemical vapor deposition. Form using.

Next, as shown in FIG. 3(c), a polycrystalline silicon film 9 serving as a second gate electrode is deposited on the second gate oxide film 8.
Formed by chemical vapor deposition or the like.

(Problems to be Solved by the Invention) The conventional manufacturing method for this type of semiconductor device is shown in FIG. 3(d).
As shown in the enlarged view of the main part of FIG. If the voltage leading to breakdown (hereinafter such a voltage is referred to as withstand voltage) is low and a certain voltage or higher is applied to the second gate electrode 9, the insulation between the first gate electrode 4 and the second gate electrode 9 will be reduced. There was a problem that it became impossible. Further, there is a problem in that the charge retention characteristics are poor when charges are stored in the second gate voltage Vi44.

This invention was made to solve the problems of the conventional manufacturing method as described above, and it improves the withstand voltage of the insulating film between the first gate electrode and the second gate electrode, and reduces the charge in the first gate electrode. It is an object of the present invention to provide a semiconductor device that can improve retention characteristics and a method for manufacturing the same.

(Means for Solving the Problems) Therefore, in the method for manufacturing a semiconductor device according to the present invention, the upper part of the polycrystalline silicon that is the first gate electrode is covered with silicon nitride, the sidewall portion is oxidized, and the polycrystalline silicon is covered with silicon nitride. Adopt a step of removing the nitrided portion and etching the polycrystalline silicon serving as the first gate electrode to a thickness equal to or greater than the thickness of the next second gate insulating film, and then forming a second gate insulating film on the polycrystalline silicon. This aims to achieve the above objective.

(Function) In the semiconductor device according to the present invention formed by the manufacturing method described above, the oxide film thickness at the edge portion of the first gate polycrystalline silicon is increased due to the sidewall oxide film of the first gate polycrystalline silicon. , the dielectric strength is improved, and the charge retention characteristics in the first gate electrode are also improved.

(Examples) The present invention will be described below based on Examples. Figure 1 (a), (b), (e) and Figure 2 (a), (b),
(c) shows a sectional view of each essential part according to the process order of an embodiment of the method for manufacturing a non-volatile semiconductor memory device according to the present invention. Regarding the manufacturing method of this embodiment, after forming a field oxide film 2 and a first gate oxide film 3 on a silicon substrate i, a first gate polycrystalline silicon film 4 is grown by chemical vapor deposition. Then, a thin oxide film 5 is formed on the first gate polycrystalline silicon 4 by thermal oxidation. After that, 1 g of silicon nitride was added on top of it by chemical vapor deposition.
16 (Fig. 1(a)). Through self-alignment,
Only the upper part of the first polycrystalline silicon 4 is covered with the oxidized WA 5 and the silicon nitride film 6 (FIG. 1(b)).
, oxidation +1Q7 is formed only on the sidewalls of the first gate polycrystalline silicon by a thermal oxidation method (FIG. 1(C)).

FIGS. 2(a), 2(b), and 2(c) are sectional views of main parts showing subsequent steps. First, as shown in FIG. 2(a), the silicon nitride film 6 and thermal oxide film 5 in the previous step of FIG. 1(C) are removed, and the first gate polycrystalline silicon 4 is formed in the next step. The second gate Zetsu MII! Etch a little thicker than 8. Then, on top of this, thermal oxidation method,
Alternatively, the second gate insulating film 8 is grown by chemical vapor deposition (FIG. 2(b)), and then polycrystalline silicon, tungsten side, etc., which are the second gate electrode 9, are formed thereon (see FIG. 2(b)). Figure 2 (C)).

As is clear from the structure of this semiconductor device (FIG. 2(C)) formed by the manufacturing method of the above embodiment, in this embodiment, the second gate on the edge portion of the first gate polycrystalline silicon 4 is The insulating film 8 is thicker due to the sidewall oxidation M7, and the withstand voltage capability of the insulating film at the edge portion is improved.
The above objective can be achieved.

(Effects of the Invention) As explained above, according to the method of the present invention, since the thickness of the insulating film of the edge E of the first gate electrode is increased, the withstand voltage capacity of the insulating film between the first gate electrode and the second gate electrode is It is possible to obtain the effect that the charge retention characteristics of the first gate electrode are improved.

[Brief explanation of drawings]

Figure 1 (a), (b), (c), Figure 2 (a), (b)
, (c) is a sectional view of each main part according to the manufacturing process of the nonvolatile semiconductor memory device according to the present invention, and FIGS. 3(a), (b),
(c) and (d) are sectional views of the main parts of the conventional semiconductor device according to the manufacturing process. In the figure, 1 is a silicon substrate, 2 is a field oxide film, 3 is a gate oxide film, 4 is a first conductive layer, a first gate electrode, and 5
6 is a thin thermal oxide film, 6 is a silicon nitride film, 7 is a thermal sidewall thermal oxide film, 8 is a second gate insulating film, and 9 is a second gate electrode. Note that in each figure, the same reference numerals indicate the same or equivalent components.

Claims (2)

[Claims] (1) In a method for manufacturing a nonvolatile semiconductor memory device with a double gate structure, after forming a first conductive layer, a thin oxide film is formed by thermal oxidation, and then nitrided by chemical vapor deposition. a step of growing a silicon film; and a step of growing a silicon film;
After selectively etching the conductive layer and forming a thin oxide film on its sidewall by thermal oxidation, and removing the silicon nitride film and the thin oxide film, the first conductive layer is removed.
etching and forming a second gate insulating film thereon;
A semiconductor manufacturing method comprising the step of: then forming a second conductive layer. (2) In a nonvolatile semiconductor memory device with a double gate structure, the thickness of the second gate insulating film on the edge of the first conductive layer is configured to be thicker than the thickness of the surface of the first conductive layer. A semiconductor device characterized by: