Method of producing semiconductor device

Details Method of producing semiconductor device Method of producing semiconductor device

1996-02-26

2001-12-18

Quach, T. N. (Department: 2814)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S654000, C438S656000, C438S680000

Reexamination Certificate

active

06331485

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of metallization of a semiconductor device. More particularly, this invention relates to a method for producing a highly reliable contact part, which is adapted for improving conformality of a thin film of a group IVB element, preferably a Ti film employed as a barrier metal, by the electron cyclotron resonance (ECR) plasma CVD method.
2. Description of the Related Art
For filling a metallization material into a contact hole of recent VLSI or ULSI, particularly a contact hole for having substrate-contact with an impurity diffused region in a Si substrate, aluminum (Al) and tungsten (W) are broadly used as an electrically conductive material for filling.
In order to enhance reliability of contact by these filling metals, the inner wall of the contact hole is covered with a barrier metal composed of the group IVB element before filling. A barrier metal which has a two-layer structure consisting of a titanium (Ti) film and a titanium nitride (TiN) film is employed as the above-mentioned barrier metal. The barrier metal having a; two-layer structure is employed for providing a Ti film having a capability for reducing a natural oxidation film on the substrate of the Si substrate to assure ohmic property, and for stacking a TiN film thereon to assure barrier property.
The Ti film and TiN film are formed generally by sputtering. The process for forming the latter TiN film is particularly called “reactive sputtering”, in which a Ti target is sputtered in a nitrogen-containing atmosphere.
However, with the sputtering method, the step coverage in a recent contact hole having a high aspect ratio is insufficient. Grains of a film forming material sputtered out from the target are incident on the substrate with a certain directionality. Therefore, the travelling grains are prevented from reaching deep inside of the hole by a shadowing effect from the sidewalls of the contact hole itself.
Thus, the CVD method is expected to be promising as it is capable of forming the barrier metal with a satisfactory coverage on the basis of chemical reactions of the surface in the contact hole.
The TiN film can be formed relatively easily by a known process using various material gases and the CVD method. For instance, an example of forming the TiN film based on methylhydrazine reduction of TiCl
4
using a low pressure CVD device with parallel flat plate single-wafer processing is reported in Monthly Semiconductor World, January 1993, pages 145-151. The formation Gibbs energy in this reaction system of TiN at normal temperatures is approximately −209 kJ/mol (&Dgr;G<0). The system is thermodynamically stable.
On the contrary, the reaction system of film formation of the Ti film by the CVD method is limited to H
2
reduction of TiCl
4
as far as it is known. In addition, the forming Gibbs energy in the reaction system as shown by the following formula is 209 kJ/mol (&Dgr;G>0), which is very high, at temperatures within a range of 100 to 1000° C. for currently practical semiconductor processes.
TiCl
4
+2H
2
→Ti+4HCl
Therefore, film formation of the Ti film by the conventional CVD method has rarely been realized.
Recently, a technique of forming the Ti film by the ECR plasma CVD method utilizing ECR discharge of high dissociation efficiency of material gases has been proposed instead of the conventional heat CVD method.
However, the Ti film formation by this method is not satisfactory in religibility and reproducibility. For instance, if the Ti film grows into grains, not conformal, under certain conditions, the TiN film growing thereon inherits the surface profile of the Ti film, thus further increasing surface irregularities of the barrier metal. Consequently, problems arise, such as generation of a crack in a corner part on the bottom of the contact hole, and difficulty in filling the contact hole with an upper-layer metallization material in the latter process. The Ti film is a critical component for assuring the ohmic property of the contact. The conformality of the Ti film is a requirement for assuring reliability of the contact part.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for producing a semiconductor device which is adapted for improving conformality of the Ti film formed by the ECR plasma CVD method and for improving reliability of the contact part.
According to the present invention, there is provided a method for producing a semiconductor device including the steps of: forming an insulating layer on a substrate; forming a contact hole in the insulating layer to expose a selected portion of the substrate, the contact hole being defined by walls of the insulating layer; forming an adhesion layer of a group IVB element in the contact hole, including the walls, to be in contact with the exposed substrate, the adhesion layer being formed by reducing with H
2
a gas of a halogenated product of the group IVB element in an ECR plasma CVD process, the group IVB element and H
2
being used at a flow ratio of 0.4 and greater; forming a barrier layer in contact with the adhesion layer; and filling the contact hole with an electrically conductive material.
If the flow ratio of the group IVB element to H
2
is smaller than 0.4, grain growth of Ti is observed in a fine contact hole. Although the upper limit of the flow ratio is not particularly defined, an excessively large flow ratio may lower the reduction capability of H
2
, disturbing achievement of practical film forming speed. Therefore, the flow ratio is selected in a range approximately up to 2.
After a thin film of the group IBV element is formed, a nitride film of the group IVB element may be continuously formed on the thin film.
The nitride film may be formed by the CVD method or in a self-aligned manner by annealing the thin-film of the group IVB element in a nitrogen-containing atmosphere.
The group IVB element includes three types, of elements that is, Ti, zirconium (Zr) and hafnium (Hf). Forming the Ti film using a TiCl
4
gas is particularly effective.
In an experiment, when the flow ratio of a TiCl/H
2
mixed gas was set to 0.4 or greater, conformal formation of the Ti film was possible. On the contrary, at a flow ratio of the TiCl/H
2
mixed gas of 0.4 or smaller, grain growth of Ti was observed. The reason for the above results is conceivably as follows. Because an excessive amount of by-products, such as HCl, are generated near the bottom of the fine contact hole in the atmosphere containing an excessive amount of H
2
, vapor pressures in a micro ambient are lowered and release thereof is restricted. Consequently, individual Ti crystalline nuclei grow extraordinarily. From the above phenomenon, it is conceivable that the quantity balance of the by-products from the viewpoint of the vapor pressure can be improved at the flow ratio of 0.4 and greater, and that other Ti crystalline nuclei are sequentially formed on the substrate before the individual crystalline nuclei grow extraordinarily, thus realizing conformality.
As the Ti film is thus formed conformally, even when a TiN film is stacked on the Ti film by the CVD method, a film inheriting the property of the underlying film can be grown. Thus, a risk of generating a crack in the corner part of the contact hole is eliminated.
If the Ti film is annealed in a nitrogen-containing atmosphere, the TiN film is formed conformally and in a self-aligned manner.


REFERENCES:
patent: 4782380 (1988-11-01), Shankar et al.
patent: 4897709 (1990-01-01), Yokoyama et al.
patent: 4960732 (1990-10-01), Dixit et al.
patent: 5173327 (1992-12-01), Sandhu et al.
patent: 5296404 (1994-03-01), Akahozi et al.
patent: 5508066 (1996-04-01), Akahori
Monthly Semiconductor World, Jan. 1993, pp. 145-151, “Cleaning with hydrazine and the development of TiN-CVD Film” by T. Oba.
Nicollet, M., “Diffusion Barriers in Thin Films”,Thin Solid Films, 52(1978), pp. 415-443.

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