Semiconductor memory apparatus

A high dielectric film instead of an oxidizing film conventionally used is used in the non-volatile memory of an MoNoS construction. Using a mixed film composed of a high dielectric constant film and an amorphous insulating film for the trap film, the ratio of the voltage applied to the tunnel oxidizing film is increased so that writing and erasing operations can be effected with a low voltage. Penetration of the electrons into the electrode and the flow of positive holes from the electrode are prevented so as to increase the flow efficiency.

BACKGROUND OF THE INVENTION 
The present invention relates to a semiconductor memory apparatus, and more 
particularly, to a non-volatile memory of MoNoS construction. 
The semiconductor memory apparatus of this type has a tunnel oxidizing film 
on a silicon substrate, an electric charge trap film on the tunnel 
oxidizing film, and a gate electrode on the trap film. The charge is 
trapped on the trap film from the channel portion by the application of a 
voltage to the gate electrode so as to remove the voltage from the gate. 
Thereafter, the channel is retained with the channel being retained in an 
ON or OFF condition by an electric field from the trapped electric charge. 
A nitride film or a mixed film is conventionally used as a trap film, with 
a defect in that the writing and erasing voltages must be high, because a 
high voltage is applied to the trap film. 
An oxidizing film is provided on the trap film so that the size of the film 
may made thinner and so that the erasing and writing operations can be 
effected with low voltage. The oxidizing film prevents the flow of 
positive holes from the electrode and the penetration of electrons into 
the electrode, with a defect in that the writing and erasing voltages 
become higher as a high voltage is applied to the oxidizing film. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention has been developed with a view to 
substantially eliminating the above discussed drawbacks inherent in the 
prior art, and its essential object is to provide an improved non-volatile 
memory cell. 
Another important object of the present invention is to provide an improved 
non-volatile memory cell which is capable of effecting writing and erasing 
operations with a low voltage. 
In accomplishing these and other objects according to one preferred 
embodiment of the present invention, the semiconductor memory apparatus 
has a tunnel oxidizing film formed on a Si substrate, a mixed film 
composed of a high dielectric constant insulating film and an amorphous 
insulating film formed on the tunnel oxidizing film, a high dielectric 
film formed on the mixed film, and a gate electrode formed on the high 
dielectric film. 
The present invention uses a mixed film composed of a high dielectric 
constant insulating film and the amorphous insulating film for the trap 
film, becomes larger than the MoNoS construction with a high dielectric 
film (that is-a specific dielectric constant of 10 or more) being provided 
on it. Using the band gap of the high dielectric film, the penetration of 
electrons into the electrode and the flow of positive holes from the 
electrode are prevented so as to achieve an effect of increasing the flow 
efficiency of the electrons. The wiring and erasing operations can be 
effected with a low voltage.

DETAILED DESCRIPTION OF THE INVENTION 
Before the description of the present invention proceeds, it is to be noted 
that like parts are designated by like reference numerals throughout the 
accompanying drawings. 
The semiconductor memory apparatus of the present invention will be 
described hereinafter with reference to the embodiments of the drawings. 
The semiconductor memory apparatus shown in FIG. 1 is provided with a 
tunnel oxidizing film 5 formed on a Si substrate 6, a mixed film 4 
composed of a high dielectric constant insulating film and an amorphous 
insulating film formed on the tunnel oxidizing film 5, a high dielectric 
film 2 formed on the mixed film 4, and a gate electrode 1 formed on the 
high dielectric film 2. 
The semiconductor memory apparatus of such construction as shown in FIG. 1 
has a tunnel oxidizing film formed on the silicon substrate, a mixed film 
4 formed between a high dielectric constant insulating film and the 
amorphous insulating film (including Al.sub.2 O.sub.3 film) as the trap 
film on it. In the example of FIG. 1, the high dielectric film 2 (having a 
specific dielectric constant of at least 10) is sputtered on the trap film 
4 or is formed by a MoCVD process and the gate electrode is attached 
thereby a subsequent manufacturing operation. 
In the semiconductor memory apparatus constructed as described hereinabove, 
the trap film 4 and the high dielectric film 2 have a high specific 
dielectric constant. More of the voltage applied to the gate is applied to 
the tunnel oxidizing film so that the erasing and writing voltages can be 
lowered. 
The semiconductor memory apparatus shown in FIG. 2 is provided with a 
tunnel oxidizing film 5 formed on a Si substrate 6, a mixed film 4 
composed of a high dielectric constant insulating film and an amorphous 
insulting film formed on the tunnel oxidizing film 5, a metallic film 3 
formed on the mixed film 4, a high dielectric film 2 formed on the 
metallic film 3, and a gate electrode formed on the high dielectric film 
2. 
The semiconductor memory apparatus of the construction shown in FIG. 2 has 
a tunnel oxidizing film formed on the silicon substrate, a mixed film 4 
formed between the high dielectric constant insulating film and the 
amorphous insulting film (including for example, an Al.sub.2 O.sub.3 film) 
as the trap film on it. In the example of FIG. 2, a metallic film 
(platinum, tungsten or the like) is sputtered on the trap film 4 so as to 
improve the orientation of the high dielectric film (including strong 
dielectric film) 2; thereafter, the high dielectric film (including strong 
dielectric film) 2 is sputtered or is formed by a MoCVD process and the 
gate electrode is attached thereto by a subsequent manufacturing 
operation. 
In the semiconductor memory apparatus constructed as descried hereinabove, 
the trap film 4 and the high dielectric film 2 have a high specific 
dielectric constant. Most of the voltage applied to the gate is applied to 
the tunnel oxidizing film so that the erasing and writing voltages can be 
lowered. 
As is clear from the foregoing description, according to the arrangement of 
the present invention, a high dielectric film (having the higher 
dielectric constant of Al.sub.2 O.sub.3 or the like) instead of an 
oxidizing film conventionally used is used in the non-voltage memory of 
the MoNoS construction. The ratio of the voltage to be applied to the 
tunnel oxidizing film is increased so that the writing and erasing 
operations can be effected by a low voltage. Using the band gap of the 
high dielectric film, the penetration of electrons into the electrode and 
the flow of positive holes from the electrode are prevented so as to 
achieve an effect of increasing the flow efficiency.