Silicon nitride film formation method

Details Silicon nitride film formation method Silicon nitride film formation method

2000-09-14

2002-03-12

Elms, Richard (Department: 2824)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

Reexamination Certificate

active

06355582

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of forming a silicon nitride film used for, e.g., the capacitor of a semiconductor integrated circuit.
As a dielectric film forming the capacitor of a DRAM (Dynamic Random Access Memory) constituted by one transistor and one capacitor, a silicon nitride film is used in terms of high availability and easy handling of a film formation material.
Formation of the silicon nitride film adopts CVD (Chemical Vapor Deposition) using, as source gases, dichlorosilane (SiCl
2
H
2
) as silicon chloride gas, and ammonia gas. If the dichlorosilane supply amount increases in forming a silicon nitride film by CVD, particles as a by-product mainly containing ammonium chloride are undesirably produced in the film formation atmosphere. To prevent this, the dichlorosilane supply amount is set about ⅕ the ammonia supply amount.
In general, a dielectric film forming a capacitor must have a critical voltage at 10 nA/cm
2
of 1 V or more due to the following reason. That is, the operation voltage of a semiconductor integrated circuit using a DRAM is about 1.8 V at present. The critical voltage of the capacitor must be about half this voltage, and must be substantially 1 V or more with a margin. If the operation voltage of the DRAM decreases in the near future, the critical voltage of the capacitor may suffice to be 0.7 V or more.
The dielectric film of the capacitor requires a dielectric characteristic of 4 nm or less in film thickness in conversion into silicon oxide. Hence, the film thickness of silicon nitride is decreased to about 5 nm.
In summary, the silicon nitride film used as a dielectric film forming the capacitor of a DRAM must attain a critical voltage of 0.7 V to 1 V or more with a small film thickness of 5 nm.
However, according to the conventional silicon nitride film formation method, hydrogen readily enters a formed silicon nitride film. When a thin film is formed as described above, a leakage current is readily generated, failing to obtain a critical voltage of 0.7 V or more.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the conventional drawbacks, and has as its object to form a silicon nitride film with a film thickness of about 5 nm and a critical voltage of 0.7 V or more while suppressing generation of any leakage current.
To achieve the above object, according to the present invention, there is provided a silicon nitride film formation method comprising the steps of heating a substrate to be subjected to film formation, and supplying silicon tetrachloride gas and ammonia gas to the substrate heated to a predetermined temperature, wherein the ratio of a partial pressure of the silicon tetrachloride gas to a partial pressure of the ammonia gas is set to not less than 0.5.


REFERENCES:
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