Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2000-04-10
2001-09-18
Lee, Eddie (Department: 2815)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S250000, C438S253000, C438S393000, C438S396000
Reexamination Certificate
active
06291291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, a semiconductor device having a capacitor employing ferroelectrics as a capacitor insulating film and a method of manufacturing the same.
2. Description of the Prior Art
In recent years, in the semiconductor integrated circuit device, miniaturization of a capacitor has been requested according to the high integration density.
Then, in the prior art, an application of material (ferroelectrics, etc.) such as (Sr,Ba)TiO
3
, Pb(Zr,Ti)O
3
, or the like having a high dielectric constant to a capacitor insulating film of a semiconductor memory device has been expected. Meanwhile, in order to increase an integration degree of DRAM, etc., it is effective to reduce an area of the capacitor. In this case, if a ferroelectrics film which has the high dielectric constant rather than a silicon oxide film, a silicon nitride film, etc. in the prior art is employed as the capacitor insulating film, the area of the capacitor can be reduced. As shown in
FIG. 13
, normally the ferroelectrics have a perovskite crystal structure and are distinguished into an A site and a B site according to their orientation locations. In (Sr, Ba)TiO
3
and Pb(Zr,Ti)O
3
, Sr and Ba, or Pb are oriented at the A site respectively and Ti, or Zr and Ti are oriented at the B site respectively.
FIGS. 1A and 1B
are sectional views showing a method of forming a capacitor using the ferroelectrics as the capacitor insulating film in the prior art.
As shown in
FIG. 1A
, an insulating film
2
is formed on a semiconductor substrate
1
and then a two-layered metal film
3
consisting of a Ti film
301
and a Pt film
302
formed on the Ti film
301
is formed.
Then, a ferroelectrics film
4
made of (Pb,La)(Zr,Ti )O
3
(referred to as “PLZT” hereinafter) is formed and then a Pt film
5
is formed.
Then, as shown in
FIG. 1B
, an upper electrode
5
a
made of the Pt film, a capacitor insulating film
4
a
made of the PLZT film, and a lower electrode
3
a
made of the two-layered metal film
3
consisting of the Ti film
301
and the Pt film
302
are formed by patterning these films in order of the Pt film
5
, the PLZT film
4
, and the Ti/Pt film
3
separately. With the above, the capacitor has been completed.
Since the capacitor formed as above has employed the ferroelectrics film as the capacitor insulating film
4
a
, the area of the capacitor can be reduced and thus such ferroelectrics film would be desired for miniaturization of the device.
However, in the capacitor employing the above material having a high dielectric constant as the capacitor insulating film
4
a
, the characteristics of the capacitor are changed considerably if the composition is changed.
In other words, there have been the problems that, if the particular composition is employed, the leakage current can be reduced smaller but the hysteresis loop is also reduced smaller. In contrast, there has been the problem that, if the hysteresis loop is enhanced by changing the composition, the leakage current would be increased inevitably.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device which is capable of suppressing a leakage current of a capacitor using ferroelectrics material as a capacitor insulating film and also enhancing the hysteresis characteristic and a method of manufacturing the same.
In the present invention, a capacitor insulating film which is formed by laminating a ferroelectrics film including lead (Pb) having a face orientation (
111
) and a ferroelectrics film including Pb having a face orientation (
100
) is employed.
In the meanwhile, the inventors of the present invention have found that a Pb content can be controlled by adjusting film forming conditions such as a flow rate of a sputter gas, a power for plasmanizing the sputter gas, etc. and that a face orientation can be changed in terms of the change in the Pb content. In the case of PLZT, La as well as Pb may be employed as elements oriented at A sites, but especially Pb of such elements has a larger effect on the control of face orientation.
In addition, according to the experiment, in the ferroelectrics film including Pb having the face orientation (
111
), the leakage current is large but the polarization width also becomes large whereas, in the ferroelectrics film including Pb having the face orientation (
100
), the polarization width is small but the leakage current also becomes small.
It is preferable that a ratio of elements including Pb oriented at A sites of a perovskite crystal structure, which are constituent elements of the ferroelectrics film in practical use, to other constituent elements should be set in a range of 0.9 to 1.4 from viewpoints of a leakage current and a polarization width. In this case, the reason of that a lower limit is set to 0.9 is due to that deficits of the elements including Pb of the ferroelectrics film oriented at A sites become remarkable if the lower limit is set less than 0.9.
The A site denotes an A site in a perovskite crystal structure shown in FIG.
13
. In Pb(Zr,Ti)O
3
or (Pb,La) (Zr,Ti)O
3
, Pb or Pb and La are orientated at the A sites respectively.
Accordingly, in the capacitor formed by laminating these ferroelectrics films, since the capacitor includes the ferroelectrics film having the face orientation (
111
), it has the large polarization width.
In the meanwhile, if the ferroelectrics film having the face orientation (
111
) is employed solely in the capacitor, it has the large leakage current. In the present invention, the defect of the ferroelectrics film having the face orientation (
111
), i.e., the ferroelectrics film has the large leakage current, can be compensated by laminating the ferroelectrics film having the face orientation (
111
) and the ferroelectrics film having the face orientation (
100
). As a result, the leakage current can be reduced smaller in the overall capacitor.
With the above, the capacitor having the large polarization width can be formed while reducing the leakage current smaller.
In the semiconductor memory device having such capacitor, an outflow of charges can be suppressed because the capacitor has the small leakage current. In addition, since the polarization width is large, the dielectric constant of the capacitor insulating film can be enhanced and also miniaturization of the device can be achieved by reducing the capacitor area.
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Roeder et al., Liquid delivery MOCVD of ferroelectric PZT, 1996, Mater. Res. Soc, 415, 123-128.*
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Armstrong Westerman Hattori McLeland & Naughton LLP
Brock II Paul E
Fujitsu Limited
Lee Eddie
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