Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – Insulated gate formation
Reexamination Certificate
2001-02-14
2003-10-07
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Insulated gate formation
C438S287000
Reexamination Certificate
active
06630393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and a semiconductor device manufactured by the same method, and particularly relates to a method for manufacturing a semiconductor device having a high dielectric gate insulating film made of metal oxide and a semiconductor device manufactured by the same method.
2. Background Art
An MIS (Metal Insulator Semiconductor)-type transistor, which is operated by use of either electrons or holes as carriers, is known as one type of semiconductor devices.
With reference to
FIG. 9
, in a MIS-type transistor, a gate electrode
55
is formed through a gate insulating layer
54
on both an N-type source region
52
and a drain region
53
formed on a P-type semiconductor substrate
51
, and a source electrode
56
and a drain electrode
57
are formed respectively on the source region
52
and drain region
53
. This type of transistor is operated by the operating principle that a drain current Id flowing through both regions
52
and
53
is controlled by controlling the concentration of a carrier induced in a channel directly beneath the gate insulating film
54
by a control voltage (gate voltage) VG applied to the gate electrode
55
.
Here, the MOS (Metal Oxide Silicon) type transistor using silicon as a semiconductor substrate and silicon oxide as a gate insulating film
54
is widely adopted as a constituent element for LSI (Large Scale Integrated) circuits because of its simple structure and ease of producing large-scale integrated circuits.
In semiconductor devices having the above-described gate insulating film or the gate oxide film, a fundamental condition for improvement in the performance of the semiconductor devices with respect to operating speed and operating capacity is an increase in the drain current. The drain current Id is shown by the following equation.
Id∝ACox (1)
where, A represents a proportional constant, and Cox represents the capacitance of the gate insulating film.
The capacitance of the gate oxide film Cox is expressed by the following equation (2).
Cox∝&egr;ox/tox (2)
where, &egr; ox represents the dielectric constant of the gate oxide film and tox represents the thickness of the gate oxide film.
As is clearly shown in Equation (1), the drain current Id can be increased by increasing the capacitance Cox of the gate insulating film and the capacitance Cox can be increased by forming a thin gate oxide film, as shown in the equation (2).
Thus, conventionally, in a semiconductor device having the gate oxide film, the oxide film is formed thinner with the aim of improving the performance of the semiconductor device.
However, when the thickness tox of the gate oxide film is too thin, a gate leak current flows through this very thin gate oxide film; therefore the thickness of the gate oxide film is limited so that the gate leak current can be prevented. In general, it is known that, when the thickness of the gate insulating film is less than 3 nm, the gate leak current begins to flow, and when the thickness of the gate insulating film becomes less than 1.5 nm, a limit is reached for normal operating performance of the semiconductor device.
As shown by Eqaution (2), it is anticipated that the performance of this type of semiconductor device can be improved by forming an insulating film with a higher dielectric constant than that of the oxide film (dielectric constant is 3.8 to 4.1), in addition to forming the thin gate oxide film. Metal oxides such as zirconium oxide (the dielectric constant &egr; is 10 to 20) are known to have higher dielectric constants, and thus it is possible to produce insulating films with a higher dielectric constant by use of metal oxides having a dielectric constant higher than that of silicon oxide.
The performance of the semiconductor device can be improved by forming the gate insulating film by use of a material having a high dielectric constant while depositing the film within a thickness range, which allows the prevention or reduction of the generation of a gate leak current.
Two representative methods are conventionally known for forming an insulating film having a high dielectric constant for manufacturing a semiconductor device using an insulating film having a high dielectric constant. One method is a sputtering method.
FIG. 11
illustrates a schematic representation of the high dielectric constant insulating film by a sputtering method. The sputtering method is explained for the case of forming a ZrO
2
film. In a reaction chamber
61
, a silicon substrate
62
, which is to be deposited, is placed on a susceptor
63
and a Zr target is arranged above the susceptor
63
facing the silicon substrate
62
.
In the above arrangement, when plasma
65
is generated in the reaction chamber
61
retained in an atmosphere including oxygen (oxidizing gas) at a desired pressure, plasma ions advance toward the direction of an arrow
66
and impinge the Zr target
64
. The impinging ions recoil zirconium ions from the target toward the direction of an arrow
67
, the zirconium ions react with surrounding oxygen to form zirconium oxide (ZrO
2
), and the zirconium oxide is deposited on the silicon substrate
62
forming a film.
Another method for forming the zirconium oxide film is to apply a CVD method.
FIG. 12
illustrates a schematic representation of forming a high dielectric constant insulating film by the CVD method. A method for forming a ZrO
2
film is described below as an example of forming the high dielectric constant insulating film. In a reaction chamber
71
, a silicon substrate
72
for depositing the film is placed on a susceptor
73
and a showerhead
74
is arranged above the susceptor
73
facing the silicon substrate
72
. The CVD system is constituted such that a metal organic (MO) material
75
containing zirconium such as Zr(DPM)
4
, and a flow-meter (mass flow meter) are provided at the outside of the reaction chamber
71
, and the thus formed vaporized organic metallic materials and oxygen (oxidizing gas) as the oxidizing agent
78
are introduced into the reaction chamber
71
with an Ar carrier gas
77
through a gas introduction passage
79
from the showerhead.
Using the above-described constitution, the vaporized organic metal material
75
and oxygen gas
78
is carried by the Ar carrier gas
77
and introduced into the reaction chamber
71
, while the reaction chamber is maintained at a desired temperature and a desired pressure. In the reaction chamber, the organic metal material
75
is decomposed into metal zirconium and zirconium oxide is formed by the reaction between the metal zirconium and oxygen and deposited on the silicon substrate. A semiconductor device is manufactured using of this zirconium oxide film as the gate insulating film having a high dielectric constant.
However, a problem arises in the above-described semiconductor devices formed by conventional manufacturing methods, such as the sputtering method or the CVD method, in that the performance of these semiconductor devices are degraded. The degradation of the performances of the semiconductor devices is caused by the oxidizing gas used in the conventional manufacturing methods, since the oxidizing gas forms a silicon oxide film having a low dielectric constant in between the gate insulating film having a high dielectric constant and the silicon substrate.
That is, when the oxidizing gas is used for forming the high dielectric constant insulating film by the sputtering method or the CVD method, the oxygen gas used as the oxidizing gas oxidizes the surface of the silicon substrate. As a result, as shown in
FIG. 10
, in the semiconductor device manufactured by the above method, a silicon oxide film is formed between the high dielectric constant gate insulating film
70
and the silicon substrate
51
.
As shown in the semiconductor device in
FIG. 10
, since the gate insulating film
70
having a high dielectric constant (for example, ZrO
2
film: the dielectric constant is 10 to 25
Foong Suk-San
Fourson George
NEC Electronics Corporation
Young & Thompson
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