JPS61276330A - Film-forming method - Google Patents

Abstract

PURPOSE:To suppress a leakage current by adhering a metal film of a body centered cubic crystal on a substrate, heating to oxidize the film to convert it to a metal film, thereby reducing crystallization based on heat treatment in the later steps and preventing pinholes from increasing. CONSTITUTION:A body centered crystal Ta film 2 is adhered through an Si3N4 film on an Si substrate 1 as a semiconductor substrate, and heated to convert the film 2 to an oxide metal film of Ta2O5 film 2A. Thus, the crystallization based on the heat treatment of the later steps can be reduced to prevent pinholes from increasing and to suppress a leakage current.

Description

[Detailed Description of the Invention] [Summary] A film of a high melting point transition metal such as tantalum (Ta) deposited on a semiconductor substrate is thermally oxidized to form tantalum pentoxide (Tag').
s) When forming the film, if the body-centered cubic Ta film is thermally oxidized after being deposited, the crystallization of the Ta and OS films will not proceed despite the heat treatment at 700°C or higher in the subsequent process. As a result, the generation of pinholes that cause leakage current is suppressed.

[Industrial application field]

The present invention relates to a metal oxide film used as a dielectric of a capacitor for storing information in a semiconductor device, particularly a dynamic random access memory (DRAM), and relates to a method for forming the film that suppresses leakage current caused by heat treatment.

The degree of integration of DRAMs is increasing year by year, and devices with capacities of IMbit or higher are beginning to be put into practical use.

Under these circumstances, the following measures have been taken for dielectric films of DRAM capacitors in response to higher integration and higher density.

(1) Thinning of the film Conventionally, a silicon dioxide (Sing) film is mainly used as the dielectric material of the capacitor of a DRAM, and in response to higher integration and density, the film thickness has been reduced to about 150 mm.

When the Si0g film is thinned in this way, slight damage or pinholes can cause leakage, which poses problems in terms of manufacturing yield and device reliability.
A double film made of SiJ4) film or the like may be used.

(2) Physical property constants On the other hand, a dielectric material with a high dielectric constant, such as Ta205, is selected to reduce the area occupied by the capacitor on the semiconductor chip.

In this case, since the Ta205 film is usually formed in a relatively earlier process, the crystallization of the 0° Ta film progresses due to heat treatment in the later process, so a method for suppressing this is desired.

[Conventional technology]

FIGS. 2(1) and 2(2) are cross-sectional views of a substrate showing the formation of a Ta2O film according to a conventional example in the order of steps.

In FIG. 2 (1), the semiconductor substrate 1 has a thickness of 10
A silicon (Si) substrate having a SiJ film 11 of 00 Å or less deposited on its surface is used.

Here, the Si, N, and film 11 are used to prevent the influence of high temperature on the substrate when the Ta film 2 is deposited.

A Ta film 2 having a thickness of about 300 layers is deposited on the StJ film 11 by vapor deposition using an electron gun.

In Figure 2 (2), 500
Thermal oxidation is performed at .degree. C. to form a Ta,05 film 2A.

Formed Ta, 0. The film 2A is amorphous and has a thickness approximately twice that of the Ta film 2, and has a thickness of about 600.

Thereafter, a device is formed by depositing an electrode film of doped polycrystalline silicon (polySt) or the like on the TazOs film 2A to form a capacitor between it and the St substrate 1.

[Problems that the invention attempts to solve]

A Ta film deposited under conventional vapor deposition conditions is called β-Ta and has a tetragonal crystal structure. When the Tag's film formed by thermally oxidizing β-Ta is heat-treated at about 700° C. or higher, crystallization progresses as the temperature rises, increasing leakage current and significantly deteriorating capacitor characteristics.

[Means for solving problems]

The above problem can be solved by depositing a body-centered cubic metal film (2) on a semiconductor substrate (1) and heating the metal film (2).
) to a metal oxide film (2A) according to the present invention.

For example, the effect is remarkable when the metal coating (2) is tantalum and the semiconductor substrate (1) has an insulating film (11) deposited on its surface.

[Effect]

The present inventor has proposed that a body-centered cubic (bcc) crystal system Ta film called α-Ta has a bulk crystal structure of single crystal Ta, and a face-centered cubic (fcc) crystal system or the aforementioned β-T
Focusing on the fact that it is the densest Ta film, which has a tetragonal crystal structure called a,
It was confirmed from the experimental results shown in FIG. 1 that the Ta205 film formed by thermally oxidizing the -Ta film does not undergo crystallization due to post-process heat treatment.

FIG. 1 is a diagram showing the relationship between the crystal structure of a Ta film and the crystallinity of a Ta, 0° film formed by thermally oxidizing the Ta film, using the heat treatment temperature as a parameter.

In the figure, the scale of the crystallinity of the Ta2O film is expressed in arbitrary units as a value proportional to the peak value corresponding to the plug reflection condition of the X-ray diffraction spectrum.

The heat treatment of the TazOs film was carried out for 30 minutes in 02 at heat treatment temperatures of 800° C. and 1100° C. shown as parameters.

It is clear from the figure that in the case of bcc-Ta, it is 800 as expected.
It was found that even when heat treatment was performed at ~1100°C, crystallization was suppressed.

〔Example〕

The Ta2O film 2A is formed in exactly the same process as the conventional example shown in FIG. 2, but by vapor deposition using an electron gun in FIG. In the step of depositing the Ta film 2, the surface condition of the substrate, T
A bcc structure can be obtained by selecting the growth temperature, growth rate, etc. of the a film.

The conditions for obtaining a bcc structure depend particularly on the growth rate, and in the case of vapor deposition using an electron gun, 4λ5ec-'
It is necessary to do the following.

Whether a bcc structure has been obtained can be confirmed by electron beam diffraction.

The Ta,05 film 2A obtained in this way is clearly less likely to crystallize as shown in the experimental results shown in FIG. 1, and the number of pinholes in the film is reduced, thereby suppressing the generation of leakage current.

Although it is not clear whether pinholes are caused by crystallization, at least as crystallization progresses, the number of pinholes increases and leakage current becomes more likely to occur.

〔Effect of the invention〕

As explained in detail above, according to the present invention, a TazOs film formed by thermally oxidizing a body-centered cubic α-Ta film reduces crystallization caused by post-process heat treatment and increases the number of pinholes. This prevents leakage current and suppresses the occurrence of leakage current.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the crystal structure of a Ta film and the crystallinity of a Ta, O1 film formed by thermally oxidizing the Ta film, using heat treatment temperature as a parameter. ) is a cross-sectional view of a substrate showing the formation of a Ta2es film in the order of steps according to a conventional example. In the figure, 1 is a semiconductor substrate, which is an St substrate, 11 is a 5iJ4 film, 2 is a Ta film, and 2A is a Ta205 film.

Claims (3)

[Claims] (1) Body-centered cubic metal coating (
2) and heating to convert the metal film (2) into a metal oxide film (2A). (2) The film forming method according to claim 1, wherein the metal film (2) is tantalum. (3) The semiconductor substrate (1) has an insulating film (11
) is coated with the first claim.
The film forming method described in Section 1.