Method of forming gate electrode in semiconductor device

Details Method of forming gate electrode in semiconductor device Method of forming gate electrode in semiconductor device

1999-12-14

2001-10-16

Bowers, Charles (Department: 2813)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S584000, C438S585000, C438S660000, C438S689000, C438S722000

Reexamination Certificate

active

06303494

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 electrode in a semiconductor device.
2. Description of the Related Art
In general, a gate electrode of a MOS transistor has been formed of a polysilicon layer. The polysilicon layer has the advantage of being stable in forming process. However, as high integration of semiconductor device, the line widths of a gate electrode and other patterns become fine. Recently, the line width is reduced below 0.15 &mgr;m. Therefore, there is problem that it is difficult to apply the doped polysilicon layer to a gate electrode material in a high speed device, since the doped polysilicon layer has a high resistivity.
This problem is also growing more and more serious as the high integration of the semiconductor. Accordingly, to overcome the problem, a gate electrode with a polycide structure in which a silicide layer using refractory metal such as tungsten(W) and titanium(Ti) is formed on the doped polysilicon layer, is proposed. However, since the gate electrode with the polycide structure is limited to speed up an ultra high integration semiconductor device, recently a technique of using refractory metal such as tungsten(W) as a gate electrode material has been researched and developed.
FIG. 1
is a cross sectional view showing a W-gate electrode according to a conventional art.
Referring to
FIG. 1
, a gate oxide layer is grown on a silicon substrate
10
and a doped polysilicon layer
12
is deposited thereon. A WN layer
13
as a diffusion barrier and a W layer
14
are then deposited on the polysilicon layer
12
, in sequence and a mask oxide layer
15
is formed thereon.
Next, the mask oxide layer
15
, the W layer
14
, the WN layer
13
and the polysilicon layer
12
are sequentially etched to form a gate electrode. Thereafter, for removing damage and recovering the reliability of the gate insulating layer
11
due to the etching process, a gate re-oxidation process is performed to form a thermal oxide layer
17
on the side wall of the gate electrode.
Here, the gate re-oxidation process is performed at high temperature under oxygen atmosphere. However, the W layer
14
is abnormally oxidized by the gate re-oxidation process, to form a tungsten oxide(WO
3
) layer
16
on the side wall of the W layer
14
, thereby deteriorating the morphology of the gate electrode, as shown in FIG.
1
. Therefore, it is difficult to perform a side wall spacer process and ion-implantation for forming source/drain subsequently, thereby deteriorating device properties. Furthermore, in case the W layer
14
is extremely oxidized, its W content decreases, thereby increasing the resistivity of the gate electrode.
To overcome the problems, N. Yamamoto proposes Wet Hydrogen Oxidation process (refer to Journal of Electrochemical Society, Vol. 133, pp. 401. (1986)) as a new gate re-oxidation process. However, in this process, since oxidation process is performed at high temperature (for example, about 1,000° C.) for long time in order to form a thermal oxide layer of a selected thickness, very large thermal budget occurs in semiconductor devices in which a metal layer may be used as a gate electrode material.
Furthermore, to overcome the problems, in case the gate re-oxidation process is performed under nitrogen atmosphere, the properties of gate oxide layer is not good comparing with using oxygen atmosphere.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to a method of forming a gate electrode in a semiconductor device which can effectively prevent abnormal oxidation of a metal layer without occurring thermal budget and the deterioration of a gate insulating layer during gate re-oxidation process, for solving the problems in the conventional art.
In the present invention, one selected from a group consisting of an iridium(Ir), a ruthenium(Ru) and an osmium(Os) layer capable of forming a nonvolatile conductive metal oxide layer, is used as a metal layer of a gate electrode instead of a W layer in conventional art. Therefore, although a gate re-oxidation process is performed by a well-known method, abnormal oxidation of the metal layer is effectively prevented, thereby forming a uniform oxide layer on the side wall of the gate electrode. Furthermore, since the oxide layer is conductive, the resistivity of the gate electrode is reduce.
To accomplish this above object, a method of forming a gate electrode in a semiconductor device, comprising the steps of: forming a gate insulating layer and a polysilicon layer on a semiconductor substrate, in sequence; forming a diffusion barrier layer on the polysilicon layer; forming a metal layer on the diffusion barrier layer, the metal layer forming conductive metal oxide layer during oxidation; etching the metal layer, the diffusion barrier layer and the polysilicon layer to form a gate electrode; and oxidizing the resultant substrate by a gate re-oxidation process.
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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