JPS6364355A - semiconductor equipment - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor device including a multilayer insulating film as a component, and particularly to a method for improving the reliability of an insulating film for a storage capacitor element in a semiconductor circuit. The present invention relates to a semiconductor device suitable for.

[Conventional technology]

Conventionally, MOS dynamic random access memory (dynamic operation/anytime read/write type storage device, hereinafter referred to as DR)
(abbreviated as AM) is the square capacity part.

A silicon oxide (SiO2) film obtained by directly oxidizing a silicon substrate has been mainly used as an insulating film for the capacitive element, which is formed flat on a silicon substrate. As semiconductor devices become more highly integrated, the area occupied by the elements continues to decrease.
In order to obtain the amount of charge necessary to ensure normal operation of the device, it is necessary to make the insulating film of the storage capacitor part thinner.

For example, a DRA with an integration degree of 4p,% pit or more
In order to realize M, the thickness of the silicon oxide film should be 10n.
m or less, deterioration of the confining pressure occurs, and the storage capacitance section is likely to be destroyed during operation of the semiconductor device.

In order to solve this problem, a stacked structure type storage capacitor element was devised (for example, I'l Publication No. 1986-
2377]). This invention actively utilizes the vertical direction of the triplet element, and the storage container element is formed so as to extend over other elements such as MoS transistors.

With this configuration, even if the planar area is small, it can have a large 800 nm, and even if an insulating film of 10 nm or more is formed, the necessary capacitance can be secured. In this device, an insulator is formed on polycrystalline silicon+ah, but the silicon oxide film formed by thermally oxidizing the polycrystalline silicon film has a poor film quality, so its breakdown voltage is 2~ 5M
V/■ and! It is lower than the withstand voltage of the silicon oxide film formed by heat-resistant oxidation of crystalline silicon, which has been a problem when forming accumulated impurities.

One of the ways to solve this breakdown voltage problem is to use the NOJ method, in which silicon nitride is deposited on polycrystalline silicon varnish by CVD, or to slightly oxidize the upper part of this silicon nitride. [A method of forming a two-layer film of silicon nitride film has been devised. By using these films as the dielectric material ++q for a capacitive element, the problem of initial breakdown voltage failure can be solved.

However, no consideration was given to the reliability of the membrane, especially its fracture characteristics over time.

[Problem that the invention seeks to solve]

As an insulating film for a storage device, when a voltage during actual operation is applied, the dielectric breakdown life is 10 with a sufficient margin.
However, the above-mentioned conventional technology did not take this point into consideration. That is, no consideration was given to the breakdown characteristics of the insulating film over time, resulting in problems in terms of reliability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new semiconductor device that can solve the above-mentioned reliability problem of the storage capacitor section and have a longer dielectric breakdown life.

[Means for solving problems]

The above object is achieved by optimizing the thickness of a silicon nitride film in a semiconductor device having a multilayer insulating film that also includes a silicon oxide film and a silicon nitride film as constituent elements.

That is, the present invention reduces the P-1 depth of the silicon nitride film to about 8
The gist is to set it below nm.

Furthermore, the thickness of this silicon nitride film is preferably about 3 nm or more.

[Effect]

Generally, there is a strong correlation between the dielectric breakdown life of an insulation 1tXJ and the applied electric field strength, and the greater the electric field dependence of the breakdown life (field acceleration coefficient), the longer the breakdown life in a low electric field.

As a result of examining the dielectric breakdown life of a two-layer film consisting of silicon oxide and silicon nitride, the authors found that the life of the entire two-layer film changes significantly when the silicon nitride film thickness changes. Ta.

Figure 2 shows a silicon oxide film/silicon nitride film (a two-layer film with a thickness of silicon oxide formed on a silicon nitride film-12).
Show the pattern. Same below. ) during the life test, fil
The relationship between field acceleration coefficient and nitriding 3λ No. 11 is shown. The horizontal axis of the figure shows the silicon nitride film J'; (r+m), and the vertical axis shows the electric field acceleration coefficient (valence/~+V). In the figure, J indicates that the initial film thickness of the silicon nitride film is 5 nm, and ○ indicates l On.
m and Δ are 17 nm, and the opening is 20 nm, and the two-layer film is formed by partially oxidizing the silicon nitride film.

As is clear from the figure, the thickness of the silicon nitride film before oxidation varies from 5 to 20 nm, but in the two-layer film after oxidation, the thinner the silicon nitride film, the larger the electric field acceleration coefficient, and the lower the electric field. It was also confirmed that the fracture life of the In other words, the thinner the silicon nitride film is, the longer the life is, and this effect is particularly noticeable when the silicon nitride film is about 8 nm or less thick.

Figure 4 shows the electric field of 2,5M,
It is a figure which shows the predicted M fracture life when V/am is continued to be applied. 4 (4Φ11) in the figure is the silicon nitride film thickness (,, m
), and the vertical axis shows the time (seconds) k at which 50% failure occurred when 2,5 M, V/Qll was continued to be applied.

When using an insulating film in a device, there are two types of fireflies whose breakdown life exceeds the value of 10 years + 7-gin. The margin is 1.5 digits considering the product warranty: 150°C, and 2 digits considering defects in this insulating film (difference between 0.01% failure and 50% failure), total. 3.5 digit rows are required. In other words, the breakdown life is 1012 seconds or more, 1 core/3:1, and as shown in FIG. 1, the region where the silicon nitride film J7X is about 8 nm or less satisfies this condition.

However, when using such a two-layer film, it is practically difficult to reduce the thickness of the silicon nitride film to less than about 3 nm. This is because when the nitride film becomes thinner, the silicon nitride II value resistance is partially lost.

This is because the oxidation of the polycrystalline silicon film underlying the silicon nitride film progresses and the film thickness becomes significantly non-uniform.

FIG. 5 shows the results of investigating how much of the remaining nitride film should be used to obtain a film with good uniformity when the initial silicon nitride was oxidized with varying amounts of 11molH. The horizontal axis shows the initial silicon nitride film thickness (nm), and the vertical axis shows the silicon nitride film thickness after oxidation (nm). As is clear from the figure,
A silicon nitride film of approximately 3 nm or more is required.

Therefore, by setting the silicon nitride film thickness to about 3 nm or more and 8 nm or less, a multilayer insulating film having a long dielectric breakdown life and having a uniform thickness of the silicon nitride film can be obtained.

〔Example〕

Example 1 Next, a first example of the present invention will be described in which an insulated gate field effect diode is manufactured. Figure 3 (a), (
b) is a cross-sectional view of the manufacturing process of this insulated gate field effect diode.

First, as shown in FIG. 3(a), an N-type silicon substrate 1
A thick element isolation insulating film 2 is formed thereon.

Next, as the lower electrode of the diode, a polycrystalline silicon film 3 (1) is deposited by the VD method, and then pocn.

Phosphorus is diffused into the polycrystalline silicon film 3 using as a diffusion source.

Next, as shown in FIG. 3(b), a silicon nitride film was deposited to a thickness of approximately 10 nm using 5iH2CEI2 and NH as an atmospheric gas by low-pressure CVD, and then this silicon nitride film was oxidized by wet oxidation. A two-layer film of silicon oxide film (8 nm thick)/silicon nitride film (5 nm thick) is then formed. Furthermore, after depositing polycrystalline silicon IFa and diffusing phosphorus into the polycrystalline silicon film, the pattern is cut to form the upper electrode 6 of the diode.
Obtain the structure shown in b).

FIG. 1 shows the dielectric breakdown life-applied electric field characteristics of the field effect diode thus produced. The horizontal axis shows the effective electric field strength (Mv/an), and the vertical axis shows the dielectric breakdown life (seconds).
Silicon oxide film (thickness: 3 nm) / Silicon nitride film (
The characteristics of a film with a film thickness of 15 nm) are shown for comparison.

As is clear from the figure, by reducing the thickness of the silicon nitride film, the linear 1'ζ1 (i.e., the electric field acceleration coefficient) increases, and as a result, the actual electric field (2 to 3 M
It can be assumed that the dielectric breakdown life at V/n) may also have a sufficient margin of 10 years. Furthermore, the dependence of the electric field acceleration coefficient on the thickness of the silicon nitride film described above was similar to the results shown in FIG. 2.

That is, it was confirmed that the two-layer film having a silicon nitride film having a thickness of 5 nm (1) of Example 1 has a large electric field acceleration coefficient and a long breakdown life in a low electric field.

Example 2 Next, another example using the above insulating film.

The structure of a highly reliable capacitor that can be formed on an isolation insulating film or an element region will be described.

FIG. 6 is a sectional view of a DRAM memory cell having a 1M capacitor and a transfer transistor.

In the figure, 61 is a P-type silicon substrate, 62 is an insulating film for element isolation, 63 is a gate insulating film, and 64.65 is a high concentration N
66 is a first electrode of a capacitor made of a polycrystalline silicon film; 67 and 68 are silicon nitride and silicon oxide films serving as dielectric films; 69 is a second electrode made of a polycrystalline silicon film; 70 is an interlayer insulating film, 71 is a bit line made of aluminum wiring, 72.
73 is a first word line made of a polycrystalline silicon film;
This is the word line.

In the memory cell having such a configuration, the first electrode 66 of the storage capacitor is a polycrystalline silicon film, and secondly, the silicon oxide film 68/silicon nitride film 67 according to the structure of the present invention is made of a polycrystalline silicon film. A double layer insulation is formed. The film thickness is the same as the previous example, silicon oxide film (8 nm
)/silicon nitride film (5r+n+). The performance of such a capacitor was the same as that of the capacitor shown in the previous example, and in particular, a value of 20% for practical use was obtained in terms of breakdown life.

As described above, since a capacitor can be formed on an element region or an element isolation insulating film region, the present invention will be extremely effective in manufacturing highly integrated memories in the future.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a highly reliable silicon oxide film/silicon nitride film with excellent temporal breakdown characteristics. Further, by using the present invention as a J m body material for a storage capacitor, the dielectric breakdown life in an actual electric field can be provided with a sufficient margin of 10 years. Therefore.

When the present invention is applied to a semiconductor integrated circuit, the reliability of neck mounting increases, and it is extremely effective in practice.

[Brief explanation of the drawing]

Figures 1, 2, 4, and 5 are diagrams for explaining the present invention in detail, and Figures 3i:51(a), (b), and 6 are examples of the present embodiment. FIG. 1.61...Silicon substrate 2.62...Insulating film for element isolation 3.6.66.69...Polycrystalline silicon electrode 4.67
...Silicon nitride film S, 68...Silicon oxide film 63...Gate insulating film 64,65...Source, drain 70...Interlayer insulating film 71...Bit line 72...First Word line 73...Second word line Representative Patent Attorney Junnosuke Nakamura Director Kyoto Tomo (cq chicken spear 3 figure (a) (b) Diagram Siricore S4 Kosake Shiso (?1 笥) 1'5 Diagram

Claims (1)

Claims: 1. A semiconductor device having a multilayer insulating film including a silicon oxide film and a silicon nitride film as constituent elements, wherein the silicon nitride film has a thickness of about 8 nm or less. 2. The semiconductor device according to claim 1, wherein the silicon nitride film has a thickness of about 3 nm or more. 3. The semiconductor device according to claim 1, wherein the silicon nitride film is a lower layer and the silicon oxide film is an upper layer. 4. Claim 1, wherein the silicon oxide film is a film obtained by partially oxidizing the silicon nitride film.
The semiconductor device according to item 1 or 3. 5. Claim 1, characterized in that the multilayer structure insulating film constitutes a dielectric film of a capacitive element.
1. Semiconductor device described in Section 1.