JPH07193138A - Semiconductor device - Google Patents

Abstract

PURPOSE:To prevent leak current from increasing by suppressing the reaction between the tantalum oxide film and an upper electrode film. CONSTITUTION:A capacitor is formed by a lower electrode film 5 provided on silicon substrate 1, a dielectric film which is formed by successively laminating silicon nitride film 14 and tantalum oxide film 15 on the lower electrode film 5, and an upper electrode film 19 which is provided on the tantalum oxide film 15 and where tantalum nitride film 17 is formed at the side of the tantalum oxide film 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a dynamic random access memory (hereinafter referred to as DRAM), and more particularly to the structure of a DRAM capacitor.

[0002]

2. Description of the Related Art FIG. 4 is an example of a cross-sectional view of a memory cell of a conventional 4-megabit DRAM. In the figure, 1 is a silicon substrate, 2 is a first silicon oxide film for element isolation, 3 is a word line for forming a gate electrode and the like, 4 is a second silicon oxide film for insulating the word line 3, Reference numeral 5 is a lower electrode film of a capacitor made of polycrystalline silicon.

Reference numeral 6 is an upper electrode film of the capacitor formed of polycrystalline silicon, 7 is a dielectric film of the capacitor formed of a silicon nitride film, and 8 is a third silicon oxide film for insulating the upper electrode film 6 of the capacitor. , 9 is a bit line, 10 is a fourth silicon oxide film for insulating the bit line 9, 11
Is an aluminum wiring, 12 is an impurity diffusion layer, and 13 is a gate insulating film of a transistor.

The conventional 4-megabit DRAM is constructed as described above, and the memory cell structure has been three-dimensionalized in order to increase the capacity of the capacitor. In order to increase the capacity of the capacitor per unit, it is not enough, and it is necessary to apply a thin film material having a high relative dielectric constant to the dielectric film. As an example, as shown in FIG. 27
Therefore, there is one using a tantalum oxide film which is about 3.6 times as thick as a silicon nitride film.

FIG. 5 is a diagram showing a process of forming a capacitor using a tantalum oxide film. In the figure, the same parts as those in FIG. 14 is a silicon nitride film formed by a thermal nitriding method, and 15 is a CVD
It is a tantalum oxide film formed by the method.

The manufacturing process of the capacitor will be described below with reference to FIG. First, as shown in FIG. 5A, the lower electrode film 5 of the capacitor is formed of polycrystalline silicon. Next, as shown in FIG.
A silicon nitride film 14 is formed by a thermal nitriding method in an atmosphere of ammonia (NH ₃ ) at 00 ° C.

Then, pentaethoxy tantalum (Ta) is deposited on the silicon nitride film 14 at, for example, 350 to 400.degree.
A tantalum oxide film 15 is formed by a thermal CVD method using (OC ₂ H ₅ ) ₅ ) and oxygen (O ₂ ). Then, in order to reduce the leakage current of the capacitor, for example, 800 to 950
Heat treatment is performed in an oxygen (O ₂ ) atmosphere at ℃. And FIG.
As shown in (c), the upper electrode film 6 of the capacitor is formed of polycrystalline silicon to form a DRAM capacitor.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The polycrystalline silicon is used for the upper electrode film 6 of the capacitor of the RAM, and therefore, as shown in FIG.
By the heat treatment for forming the silicon oxide film 8 of Ta, Ta of the tantalum oxide film 15 reacts with Si of the upper electrode film 6,
A compound layer 16 made of a conductive compound called aSi ₂ is formed, and Ta of the compound layer 16 is further formed by heat treatment when forming, for example, a bit line, an insulating film, and an aluminum wiring, which are sequentially formed on the capacitor.
Since Si ₂ increases, there is a problem that the compound layer 16 increases the leak current of the capacitor.

The present invention has been made to solve the above-mentioned problems, and a semiconductor device capable of preventing an increase in leak current by preventing a reaction between a tantalum oxide film and an upper electrode film is obtained. Is intended.

[0010]

[Means for Solving the Problems] Claim 1 according to the present invention
The semiconductor device described in (1) includes a lower electrode film provided on a semiconductor substrate, a dielectric film formed by sequentially laminating a silicon nitride film and a tantalum oxide film on the lower electrode film, and a dielectric film provided on the dielectric film. The capacitor is provided with an upper electrode film on which a metal tantalum film is formed.

According to a second aspect of the semiconductor device of the present invention, the metal tantalum film on the dielectric film side made of the tantalum oxide film of the upper electrode film is formed of a tantalum nitride film.

[0012]

The metal tantalum film on the tantalum oxide film side of the upper electrode film of the capacitor of the semiconductor device according to claim 1 of the present invention prevents the reaction between the upper electrode film and the tantalum oxide film in the heat treatment step after the capacitor forming process. To do.

The tantalum nitride film on the tantalum oxide film side of the upper electrode film of the capacitor of the semiconductor device according to claim 2 of the present invention is the reaction between the upper electrode film and the tantalum oxide film in the heat treatment step after the capacitor forming process. Prevent.

[0014]

【Example】

Example 1. Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is a sectional view of a memory cell of a DRAM according to a first embodiment of the present invention. In the figure, the same parts as those in the conventional case are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 17 is a tantalum nitride film formed on the upper surface of the tantalum oxide film 15,
Is polycrystalline silicon formed on the upper surface of the tantalum nitride film 17, and forms the upper electrode film 19 with the tantalum nitride film 17.

Next, the manufacturing process of the capacitor shown in FIG. 1 will be described with reference to FIGS. First, FIG. 1 (a)
As shown in FIG. 5, the lower electrode film 5 of the capacitor is formed of polycrystalline silicon as in the conventional case. Next, FIG.
As shown in (b), the silicon nitride film 14 is formed by a thermal nitriding method in an ammonia (NH ₃ ) atmosphere at 800 to 900 ° C., for example.

Then, pentaethoxytantalum (Ta) is formed on the silicon nitride film 14 at, for example, 350 to 400.degree.
A tantalum oxide film 15 is formed by a thermal CVD method using (OC ₂ H ₅ ) ₅ ) and oxygen (O ₂ ). Then, in order to reduce the leakage current of the capacitor, for example, 800 to 950
Heat treatment is performed in an oxygen (O ₂ ) atmosphere at ℃. And Figure 2
On the tantalum oxide film 15, as shown in FIG.
A tantalum nitride film 17 is formed by a thermal nitriding method in an atmosphere of ammonia (NH ₃ ) at 00 to 950 ° C.

Then, as shown in FIG. 3A, a polycrystalline silicon 18 is formed, and a tantalum nitride film 17 and a two-layer upper electrode film 19 are formed to form a DRAM capacitor. Then, as shown in FIG. 3B, a third silicon oxide film 8 that insulates the polycrystalline silicon 18 is formed as a post-process as in the conventional case.

Since the semiconductor device of Example 1 configured as described above has the chemically stable tantalum nitride film 17 on the side of the upper electrode film 19 opposite to the tantalum oxide film 15,
Tantalum oxide film 15 by heat treatment after the capacitor process
Since the reaction between Ta and Si of the polycrystalline silicon 18 is blocked, it is possible to prevent an increase in the leak current of the capacitor.

Example 2. In the first embodiment, the upper electrode 19
The case where the tantalum nitride film 17 of No. 1 is formed by the thermal nitriding method has been described.
Pentadimethylamino tantalum (Ta [N (C
Even if the tantalum nitride film is formed by the CVD method using H ₃ ) ₂ ] ₅ ) and ammonia (NH ₃ ), the same effect as that of the above-described first embodiment can be obtained.

Example 3. In the first embodiment, the upper electrode film 1
Although the case where 9 has a two-layer structure of the tantalum nitride film 17 and the polycrystalline silicon 18 has been described, the invention is not limited to this. For example, the upper electrode film is formed by a tantalum nitride film, a sputtering method or a CVD method. Even if it is formed with a three-layer structure of a titanium nitride film and polycrystalline silicon, a chemically stable tantalum nitride film is formed on the opposite side of the tantalum oxide film of the upper electrode film. The reaction with the nitride film is prevented, and the same effect as that of the first embodiment is obtained.

[0021]

As described above, according to the first aspect of the present invention, the lower electrode film provided on the semiconductor substrate, and the dielectric formed by sequentially laminating the silicon nitride film and the tantalum oxide film on the lower electrode film. Since the capacitor including the body film and the upper electrode film provided on the dielectric film and having the metal tantalum film formed on the side of the dielectric film is provided, the reaction between the tantalum oxide film and the upper electrode film is prevented. By blocking, it becomes possible to obtain a semiconductor device capable of preventing an increase in leak current.

According to the second aspect of the present invention, since the metal tantalum film on the tantalum oxide film side of the upper electrode film is made of a tantalum nitride film, the reaction between the tantalum oxide film and the upper electrode film. By preventing the above, it becomes possible to obtain a semiconductor device capable of preventing an increase in leak current.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a DRAM according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a part of a manufacturing process of the capacitor in FIG.

FIG. 3 is a cross-sectional view showing the rest of the manufacturing process of the capacitor in FIG.

FIG. 4 is a cross-sectional view showing a configuration of a conventional DRAM.

FIG. 5 is a cross-sectional view showing a manufacturing process of a conventional semiconductor device.

FIG. 6 is a diagram for explaining a defect of the semiconductor device in FIG.

[Explanation of symbols]

 1 Silicon Substrate 5 Lower Electrode Film 6, 19 Upper Electrode Film 15 Tantalum Oxide Film 16 Compound Layer 17 Tantalum Nitride Film 18 Polycrystalline Silicon

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[Procedure amendment]

[Submission date] April 7, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Since the capacitor of the RAM uses polycrystalline silicon for its upper electrode film 6, it is formed between the tantalum oxide film 15 and the upper electrode film 6 as a post-process such as a third process as shown in FIG.
The heat treatment at the time of forming the silicon oxide film 8, react with the tantalum oxide film 1 5 and the upper electrode film 6, a tantalum oxide film
15 is a tantalum oxide film 20 containing high leak current Si,
And, the compound layer 16 upper portion made of a conductive compound of TaSi ₂ is formed, further, for example, the bit lines are formed sequentially top of the capacitor, insulating film, by heat treatment during the formation of aluminum wiring, which
Since the tantalum oxide film 20 containing Si and the compound layer 16 are increased, the tantalum oxide film 20 containing Si increases the leak current of the capacitor.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

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Claims (2)

[Claims] 1. A lower electrode film formed on a semiconductor substrate, a dielectric film formed by sequentially laminating a silicon nitride film and a tantalum oxide film on the lower electrode film, and a dielectric film formed on the dielectric film. A semiconductor device comprising a capacitor including an upper electrode film having a metal tantalum film formed on a dielectric film side. 2. The semiconductor device according to claim 1, wherein the metal tantalum film is a tantalum nitride film.