Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-12-11
2003-09-30
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S296000, C257S306000, C257S310000
Reexamination Certificate
active
06627939
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a semiconductor device and a method for manufacturing same and, more particularly to, the semiconductor device provided with a capacitor in such a configuration that its capacity insulator film consists of a high-permittivity insulator film and a method for manufacturing the same.
The present application claims priority of Japanese Patent Application No. Hei 11-350894 filed on Dec. 9, 1999, which is hereby incorporated by reference.
2. Description of the Related Art
Large-Scale Integrations (LSIs) known as a representative of semiconductor devices are roughly divided into memory devices and logic devices, the former of which in particular has been developed remarkably by recent improvements in semiconductor manufacturing technologies. The memory devices are further divided into Dynamic Random Access Memories (DRAMs) and Static Random Access Memories (SRAMs), mostly all of which are comprised of Metal Oxide Semiconductor (MOS) transistors excellent in integration density. DRAMs, moreover, can enjoy the above-mentioned advantage of high integration density more than SRAMs, to reduce cost, thus finding a wide range of applications in a variety of memory units used in information equipment or a like.
Since DRAMs utilize each capacitor as an information storing capacitive element to store information based on existence
on-existence of charge held therein, with increasing storage capacity an area occupied by each capacitor becomes restricted which is formed on a semiconductor substrate. Therefore, the capacitors each need to have a larger capacitance. If the capacitance does not have a capacitance enough to hold information, an external noise or a like may cause malfunction readily, thus tending to yield an error represented by a software error.
To increase the above-mentioned capacitance of each capacitor, an insulating material employed as a capacity insulator film needs to have a large permittivity, such as tantalum oxide (Ta
2
O
5
), one of metal oxides widely used as a high-permittivity insulating material. The tantalum oxide film has approximately ten times the permittivity of a silicon oxide (SiO
2
) film conventionally used as the capacity insulator film and also approximately four times the permittivity (25 to 30) of a silicon nitride (Si
3
N
4
) film conventionally used as well. Therefore, the storage capacity can be increased by making the capacitors using tantalum films as the capacity insulator film.
Also, the capacitor having such a Metal Insulator Metal (MIM)-structure is widely adopted that, along with a tantalum oxide film used as the capacity insulator film, a titanium nitride (TiN) film excellent in step coverage is used to form upper and lower electrodes on opposite vertical surfaces of this capacity insulator film.
FIG. 11
is a cross-sectional view showing a configuration of a prior art semiconductor device having such a MIM-structure capacitor (hereinafter referred simply to as capacitor). As shown in
FIG. 11
, in an active region surrounded by an element isolating insulator film
52
formed for example on a P-type silicon substrate
51
, a gate oxide film
53
and a gate electrode (word line)
54
are formed to thereby locally form an N-type diffused region
55
serving as a source or drain region, a surface of which is covered by an inter-layer insulator film
56
consisting of a silicon oxide film or a like. For simplicity in explanation, the N-type diffused regions
55
, which are formed in pair, are illustrated as only one.
The inter-layer insulator film
56
on the N-type diffused region
55
has a contact hole
57
formed therein, which in turn has a capacitor
61
formed therein, which is connected to the N-type diffused region
55
. The capacitor
61
comprises a lower electrode
58
A consisting of a titanium nitride film, a capacity insulator film
59
A consisting of a tantalum oxide film formed thereon, and an upper electrode
60
A consisting of a titanium nitride formed thereon.
The following will describe a method for manufacturing the above semiconductor device along the following steps with reference to
FIGS. 13A
to
13
D.
First, as shown in
FIG. 13A
, on the P-type silicon substrate
51
, for example, the element isolating insulator film
52
made of silicon oxide is formed using a known method of LOCal Oxidation of Silicon (LOCOS) or a like and then, in an active region surrounded by this element isolating insulator film
52
are formed a silicon oxide film and a poly-silicon film in this order, which films are subsequently patterned into desired shapes to form the gate oxide film
53
and the gate electrode
54
respectively. Next, using the gate oxide film
53
and the gate electrode
54
as masks in self-alignment, an N-type impurity is introduced to the P-type silicon substrate
51
using a known impurity introducing method such as ion implantation, to locally form the N-type diffused region
55
constituting a source or drain region, following which the inter-layer insulator film
56
made of silicon oxide film or the like is formed throughout thereon using Chemical Vapor Deposition (CVD) or the like.
Next, as shown in
FIG. 13B
, the contact hole
57
is formed in the inter-layer insulator film
56
on the surface of the N-type diffused region
55
using photolithography and then, by use of CVD or the like, a titanium nitride film
58
which provides a lower electrode film is formed everywhere thereon. Next, as shown in
FIG. 13D
, using CVD or the like, a tantalum oxide film
59
which provides the capacity insulator film
59
A is formed on the titanium nitride
58
in an atmosphere containing oxygen.
Next, In an oxidizing atmosphere consisting of a UV (Ultraviolet)-O
3
(ozone atmosphere given by irradiation of ultraviolet light), the silicon substrate
51
is subject to heat treatment at about 500° C. (annealing) to oxidize the tantalum oxide film
59
, thereby improving film quality of the tantalum film
59
so that it can serve as the capacity insulator film
59
A correctly. That is, the tantalum oxide film
59
has a problem in terms of a leakage characteristic if it is used as the capacity insulator film
59
A, so that it must be oxidized to enhance its insulation performance, thus suppressing a leakage current.
Specifically, if, for example, this tantalum oxide film
59
is not sufficiently oxidized (that is, x≦4 for Ta
2
O
x
), it is to be further oxidized to a sufficient level to improve its quality, thus providing a stable film (that is, Ta
2
O
5
).
Next, as shown in
FIG. 13D
, on the tantalum film
59
, a titanium nitride film
60
is formed which provides an upper electrode film
60
A, using CVD or the like. Next, the titanium nitride film
58
, the tantalum oxide film
59
, and the titanium nitride film
60
are patterned using photolithography to form the upper electrode
60
A, thus completing a semiconductor device having the capacitor
61
as shown in FIG.
11
.
By the prior-art semiconductor device manufacturing method, however, the titanium nitride film
58
which provides the lower electrode
58
A is readily oxidized and, in fact, is oxidized during the above-mentioned heat treatment of the silicon substrate in an oxidizing atmosphere, so that as shown in
FIG. 12
, a titanium oxide (TiO
2
) film
58
B is formed on the surface of the lower electrode
58
A consisting of the titanium nitride film
58
. With this, this titanium oxide film
58
B problematically acts as a low-permittivity film. If the titanium oxide film
58
B having a low permittivity is thus formed on an interface of the lower electrode
58
A and the capacity insulator film
59
A, this titanium oxide film
58
B is connected in series with the capacity insulator film
59
A to act as part of that capacity insulator film
59
A, so that total capacitance of the capacitor
61
decreases because it is affected by the low-permittivity film. Therefore, even if a tantalum oxide film which provides a high-permittivity film is employed, it is difficult to increase the capacitan
Dickey Thomas L
NEC Corporation
Sughrue & Mion, PLLC
Tran Minh Loan
LandOfFree
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