Method of forming gate oxide layer in semiconductor device

Details Method of forming gate oxide layer in semiconductor device Method of forming gate oxide layer in semiconductor device

1999-11-08

2002-04-02

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

Having insulated gate

C438S216000, C438S591000

Reexamination Certificate

active

06365467

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a gate oxide layer in a semiconductor device.
2. Description of the Related Art
As high integration, high speed, low voltage and low power consumption of a semiconductor device, a gate oxide thickness grows thinner. The gate oxide is generally formed of a silicon oxide(SiO
2
) having dielectric constant of about 3.85 using thermal oxidation process. However, in this case, as the gate oxide thickness becomes thin, direct tunneling effect is occurred, thereby increasing leakage current.
For solving this problem, one method of forming a gate oxide layer using a stacked layer of a silicon oxide layer and a silicon nitride layer(Si
3
N
4
) is suggested. However, since the dielectric constant of the silicon nitride layer is about 7.0, it is difficult to obtain effective gate oxide thickness of 40 Å or less having high reliability and low leakage current.
Therefore, another method of forming a gate oxide layer using a stacked layer of a bottom oxide layer, a tantalum oxide (Ta
2
O
5
) layer having dielectric constant of about 25 higher than the silicon nitride layer and a top oxide layer, is suggested. In detail, a silicon oxide layer as the bottom oxide layer is formed to the thickness of 5 to 20 Å by thermal oxidation, the tantalum oxide layer is formed to the thickness of 30 to 100 Å thereon, a TEOS layer as the top oxide layer is formed to the thickness of 10 to 20 Å, and thermal-treating is performed under O
2
atmosphere. In this case, physical gate oxide thickness is 45 to 140 Å, while effective gate oxide thickness is 40 Å or less due to high dielectric constant of the tantalum oxide layer.
However, in case the bottom oxide layer is formed to thin film as described above, its uniformity and reliability are deteriorated. As a result, the barrier property against leakage current and resistance against oxidation of the tantalum oxide layer formed thereon, are deteriorated.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of forming a gate oxide layer in a semiconductor device which can obtain low leakage current and high reliability with obtaining effective gate oxide thickness of 40 Å or less, for solving the problems in the conventional art.
To accomplish this above object, according to the present invention, a NO-oxynitride layer as a bottom oxide layer is formed on a semiconductor substrate and a tantalum oxide layer as a medium oxide layer is then formed thereon. Next, the oxide layer is formed on the tantalum oxide layer. Thereafter, the substrate is thermal-treated under N
2
O gas atmosphere.
In this embodiment, the NO-oxynitride layer is formed to the thickness of 5 to 20 Å under NO gas atmosphere by a rapid thermal process or a furnace process. Preferably, the rapid thermal process or furnace process is performed at the temperature of 800 to 850° C. with raising or lowering pressure and the flow rate of the NO gas is 5 to 20 l/min.
Furthermore, the tantalum oxide layer is formed to the thickness of 30 to 150 Å by LPCVD or MOCVD. The top oxide layer is formed to the thickness of 10 to 20 Å using a TEOS layer or a HTO layer.
Moreover, the thermal-treating is performed at the temperature of 800 to 850° C. with raising and lowering pressure by a rapid thermal process or furnace process and the flow rate of the N
2
O gas is 5 to 20 l/min.
Additional object, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.


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