Oxygen diffusion blocking semiconductor capacitor

Details Oxygen diffusion blocking semiconductor capacitor Oxygen diffusion blocking semiconductor capacitor

2000-04-24

2002-06-18

Flynn, Nathan (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S296000, C257S310000, C438S244000, C438S253000, C438S387000, C438S396000

Reexamination Certificate

active

06407422

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor memory device and particularly, to a semiconductor memory device with a dielectric film made of a high dielectric-constant film material or ferroelectric film material.
2. Description of the Related Art
In recent years, developments have been made of semiconductor memory devices with a dielectric film having a high dielectric constant compared to a silicon oxide film or with a ferroelectric film having a spontaneous polarization characteristic. As high dielectric-constant materials, there can be exemplified STO (SrTiO
3
, strontium titanate), BSTO ((Ba, Sr)TiO
3
, barium strontium titanate) and so forth. As ferroelectric materials, there can be exemplified PZT (Pb(Zr, Ti)O
3
, lead titanate zirconate), PLZT ((Pb, La) (Zr, Ti)O
3
, lead lanthanum zirconate titanate), SBT (SrBi
2
Ta
2
O
9
, strontium bismuth tantalate) and so forth. As fabrication methods for thin films of the above-mentioned materials, there can be exemplified a sol-gel processing method, an MOD (Metal Organic Decomposition) method, a rotary coating method, a sputtering method and an MOCVD (Metal Organic Chemical Vapor Decomposition) method and so forth.
High dielectric-constant materials such as STO and BSTO can be produced at a comparatively low temperature of the order from 300° C. to 600° C. Further, PZT, which is a perovskite structure oxide of a ferroelectric material, can also be produced at a comparatively low temperature of about 600° C. However, a material containing lead as a constituent element, such as PZT, has had a problem: Defects generate in a film of the material during deposition because of evaporation of lead due to high vapor pressures of lead element and an oxide thereof and pin holes are also simultaneously formed in a worse case. As a result, leakage currents from a memory cell increases and when inversion of polarization is repeated million to hundred million times, there arises problematically a kind of fatigue phenomenon of reduction in magnitude of spontaneous polarization. Particularly, in the field of FeRAM constituted of ferroelectric nonvolatile memory, therefore, a ferroelectric film with less of the fatigue phenomenon during the use over time is sought.
On the other hand, development of bismuth layered structure compounds has been in progress. The bismuth layered structure compounds were discovered by Smolenskii et al. in 1959, which is disclosed in G. A. Smolenskii, V. A. Isupov and A. I. Agranovskaya, Soviet Phys. Solid State (USSR), 1 (1959), p. 149 and thereafter, a detailed investigation has been further conducted by Subbarao, which is disclosed in E. C. Subbarao, J. Phys. Chem. Solids (USA), 23 (1962), p. 665. Brsides, Carlos A. Paz de Araujo et al. have uncovered that an SBT film of the bismuth layered structure compounds is suited for FeRAM and has reported an excellent anti-fatigue characteristic that no change occurs in characteristics especially after repetitions of polarization inversion in more than trillion times. In addition, an electric field of an SBT film required for inversion of polarization is low compared with a PTZ film, the SBT film is especially suitable for a highly integrated FeRAM with a decreased drive voltage. In formation of the SBT film, however, a problem has remained since a high temperature process of the order from 700° C. to 800° C. is required.
Then, description will be given of an example of a conventional semiconductor memory device with reference to a simplified, sectional view of a construction thereof of FIG.
5
.
As shown in
FIG. 5
, an inter-element isolation oxide film
112
is formed on a semiconductor substrate (for example, a first conductivity type silicon substrate)
111
to isolate element formation regions. In an element formation region, a transistor
121
is formed. The transistor
121
is constructed of a gate oxide film
122
formed on the semiconductor substrate
111
, a polysilicon word line (including a gate electrode)
123
formed on the gate oxide film
122
, and impurity diffusion regions
124
and
125
of the first conductivity type and a second conductivity type of an opposite polarity therefrom formed on respective both sides of the gate electrode portion on the semiconductor substrate
111
. A side wall insulation film
126
is formed on a side wall of the polysilicon word line
123
.
An interlayer insulation film
113
covering the transistor
121
is formed on the semiconductor substrate
111
. In the interlayer insulation film
113
, a contact hole
114
reaching the impurity diffusion region
124
is formed and in the inside of the contact hole
114
, there is formed a conductive plug
115
of a memory cell section, connected to the impurity diffusion region
124
.
On the interlayer insulation film
113
, a lower electrode
132
of a dielectric capacitor
131
connected to the conductive plug
115
, a dielectric film
133
and an upper electrode
134
are stacked. The dielectric capacitor
131
is covered with an interlayer insulation film
116
and an opening
117
is formed on the upper electrode
134
of the dielectric capacitor
131
. Further, there is provided a plate line
141
connected to the upper electrode
134
through the opening
117
.
Still further, there is provided an interlayer insulation film
118
covering the plate line
141
. In the interlayer insulation films
118
,
116
and
113
, a bit contact hole
119
reaching the other impurity diffusion region
125
is formed and through the bit contact hole
119
, there is formed a bit line
142
connected to the second conductivity type impurity diffusion region
125
.
A semiconductor device
110
with a dielectric capacitor
131
using the dielectric film
133
made of a conventional high dielectric-constant material or a ferroelectric material, as mentioned above, adopts a stacked structure in which the ferroelectric capacitor
131
constructed of the lower electrode
132
, the ferroelectric film
133
and the upper electrode
134
is formed on the transistor
121
. With this stacked structure adopted, a memory cell region is reduced in area, thereby making a high degree of integration possible. In order to realize such a stacked structure, a requirement is a plug structure using a conductive plug to connect between the transistor (selection transistor)
121
and the dielectric capacitor
131
.
As materials of the lower electrode of a dielectric capacitor, there have been used noble metals such as platinum, iridium and ruthenium from the standpoint of resistances to oxidation, reaction and so forth.
In a process of formation of a high dielectric-constant film or a ferroelectric film used in a dielectric capacitor, a treatment in a high temperature oxidative atmosphere at a temperature in the range of from 500° C. to 800° C. is indispensable in order to attain a high dielectric constant or ferroelectricity through crystallization. There have been arisen various problems in the course of commercialization of highly integrated semiconductor memory device with such a dielectric capacitor since, at a high temperature in a process of formation of a dielectric film, a lower noble metal electrode of the dielectric capacitor and polysilicon plug or tungsten plug are reacted with each other; a plug is oxidized to cause defective contact; a noble metal, constituent elements in the dielectric film or the like diffuse into a substrate to deteriorate transistor characteristics; or to cause other inconveniences. Therefore, there has been a necessity to provide a conductive, diffusion barrier layer being thermally stable and serving as a strong barrier against oxygen atoms and constituent elements of the plug and the lower electrode, between the plug and the lower noble metal electrode.
In general, while titanium nitride has thus far used as a material for the diffusion barrier layer, problems have occurred since the titanium nitride is oxidized in a heat treatment in a high temperature oxidative atmosphere to deteriorate conductance, causes peeling or have th

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