Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-09-07
2004-11-23
Nguyen, Cuong (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S303000, C257S306000
Reexamination Certificate
active
06822276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device of an element using a ferroelectric thin film, particularly to a polarization inversion type non-volatile memory or a dynamic random access memory preferable to a large scale integrated circuit (LSI) and its fabrication method.
2. Description of the Prior Art
There are ferroelectric substances having an extremely large relative dielectric constant ranging from several hundreds to several thousands. Therefore, when a thin film made of these ferroelectric substances is used in a capacitor insulating film, there is provided a capacitor having a small area and a large capacitance preferable to a large scale integrated circuit (LSI). Further, a ferroelectric substance is provided with capacitor dielectric and its direction can be inverted by an outside electric field and accordingly, there is provided a non-volatile memory by using the characteristic.
There is disclosed a memory using a conventional ferroelectric substance in, for example, JP-A-5-90606. As shown by
FIG. 22
, a ferroelectric capacitor is formed by forming successively a lower Pt electrode
225
, a ferroelectric thin film
226
, an upper Pt electrode
227
and a Ti electrode
228
above an interlayer insulating film
224
. Further, in the drawing, numeral
221
designates an isolation insulating film, numeral
222
designates a word line, numeral
223
designates an impurity diffused layer and numeral
229
designates an aluminum wiring layer. However, according to the technology, the respective layers are fabricated by independent masks and accordingly, there poses a problem of dimensional accuracy and matching accuracy. Hence, there has been proposed a structure disclosed in JP-A-2-288368. That is, as shown by
FIG. 23
, this is a method of subjecting an upper electrode layer
238
, a ferroelectric film
237
and a lower electrode layer
236
summarizingly to dry etching. However, by the summarizing fabrication, leakage current is increased. Hence, there is a method disclosed in JP-A-3-256358 in which as shown by
FIG. 24
, only a lower electrode is fabricated and a ferroelectric film and an upper electrode are not fabricated for each cell but fabricated as a large pattern at an outer side of a memory mat or the like to thereby realize a highly integrated memory having a structure dispensing with matching allowance.
In the meantime,
FIG. 25
shows a structure of another conventional memory cell disclosed in JP-A-7-14993. Although according to the structure, only a lower electrode is finely fabricated and a ferroelectric film and an upper electrode are not fabricated for each cell, there is a feature in that an adhesion layer
251
is interposed between an interlayer insulating film and a capacitor insulating film. It is described that as the adhesion layer, a layer of TiO
2
, ZrO
2
, Ta
2
O
5
, Si
3
N
4
or the like is effective.
Further, as another conventional memory cell structure, there has been proposed a structure disclosed in JP-A-7-169854 in which as shown by
FIG. 26
, a lower electrode and a diffusion barrier layer are embedded in a reaction barrier film. This structure is obtained by the following process. First, an interlayer insulating film
248
and a polycrystal silicon film
246
are formed, thereafter, a titanium film
261
is formed, successively, a diffusion barrier layer
249
and a lower electrode
251
are formed. Thereafter, a ferroelectric film
252
is formed. In piling up the ferroelectric film
252
, the titanium film is oxidized and the TiO
2
film
261
of a reaction barrier layer is formed.
SUMMARY OF THE INVENTION
When lead zirconate titanate (PZT) is used in a capacitor insulating film in the above-described method disclosed in JP-A-3-256358, according to an investigation of the inventors, at a portion where PZT and a silicon oxide film which is an interlayer insulating film are brought into direct contact with each other, a reaction is caused therebetween. The reaction is caused even at low temperature of about 500° C. and particularly when PZT is formed at temperatures equal to or higher than 700° C., the silicon oxide layer completely reacts with PZT and a melted state is brought about. It becomes apparent that this phenomenon is caused by lead which is a major constituent element of PZT.
Further, in respect of the above-described method disclosed in JP-A-7-14993, according to an investigation of the inventors, it has been found that although Si
3
N
4
, in the adhesion layer reacts with PZT similar to the silicon oxide film, when TiO
2
, ZrO
2
, Ta
2
O
5
is used for the adhesion layer, the adhesion layer serves as a reaction barrier layer between PZT and the silicon oxide film and therefore, the above-described problem of reaction between PZT and the silicon oxide film can be resolved. However, according to the structure, it has been clearly found that since side faces of a diffusion barrier layer
249
disposed below a lower electrode is exposed, when the PZT film is formed by CVD process or the like necessitating a heated oxidizing Ad atmosphere in the film forming operation, there poses a problem in which the diffusion barrier layer
249
is oxidized and the film is exfoliated. It has been found that even in the case of using sol-gel process, sputtering process, vapor deposition process or the like, there poses a similar problem in which in carrying out heat treatment of crystallization, the diffusion barrier layer
249
is oxidized. It seems that although a metal nitride of TiN, (Ti, Al)N, WN or the like is widely used in the diffusion barrier layer
249
and when the metal nitride is oxidized, nitrogen is discharged and therefore, exfoliation of the film formed thereon becomes significant.
In the meantime, according to the method disclosed in JP-A-7-169854, when Ti is oxidized, the volume is expanded and exfoliation of the ferroelectric film is brought about.
It is an object of the present invention to achieve a semiconductor device preventing reaction between a ferroelectric film and an insulating film and preventing film exfoliation and its fabrication method.
The above-described object is achieved by constituting a semiconductor device in which a reaction barrier film is provided between a ferroelectric film and an interlayer insulating film, side faces of the diffusion
2
II barrier film and the ferroelectric film are not brought into contact with each other and side walls of a lower electrode and the ferroelectric film are brought into contact with each other.
By constructing the above-described constitution, in the case in which, for example, TiO
2
is used for the reaction barrier film, when the film thickness is equal to or larger than 2 nm, it is effective in preventing a reaction between a silicon-species interlayer insulating film and lead included in a capacitor insulating film even in rapid heat treatment at about 700° C. which is needed in crystallizing a PZT film. Further, only the diffusion barrier film is embedded into the reaction barrier film and therefore, the side walls of the lower electrode can be utilized as a capacitor, which is particularly effective in the case of applying to DRAM.
Further, the above-described object is achieved by embedding the diffusion barrier film in the interlayer insulating film as plugs and interposing the reaction barrier film between the capacitor insulating film and the interlayer insulating film. Also in this structure, a lower electrode is formed on the plug and accordingly, a ferroelectric film is installed from a side face to an upper face of the lower electrode, the side walls of the lower electrode can also be utilized as capacitor, which is particularly effective in the case of applying to DRAM.
Further, the above-described object is achieved by forming the reaction barrier film functioning to prevent reaction on the interlayer insulating film and thereafter forming the diffusion barrier film and the ferroelectric film. Before forming the diffusion barrier film and the ferroelectric film, the reaction ba
Fujisaki Yoshihisa
Miki Hiroshi
Torii Kazuyoshi
Antonelli Terry Stout & Kraus LLP
Nguyen Cuong
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