Flash memory device and a fabrication process thereof,...

Details Flash memory device and a fabrication process thereof,... Flash memory device and a fabrication process thereof,...

2001-05-31

2003-04-22

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

C438S770000

Reexamination Certificate

active

06551948

ABSTRACT:

TECHNICAL FIELD
The present invention generally relates to semiconductor devices and a fabrication process thereof. More particularly, the present invention relates to a method of forming a dielectric film and fabrication process of a non-volatile semiconductor memory device capable of rewriting information electrically, including a flash memory device.
There are various volatile memory devices such as DRAMs and SRAMs. Further, there are nonvolatile memory devices such as a mask ROM, PROM, EPROM, EEPROM, and the like. Particularly, a flash memory device is an EEPROM having a single transistor for one memory cell and has an advantageous feature of small cell size, large storage capacity and low power consumption. Thus, intensive efforts are being made on the improvement of flash memory devices. In order that a flash memory device can be used stably over a long interval of time with low voltage, it is essential to use a uniform insulation film having high film quality.
BACKGROUND ART
First, the construction of a conventional flash memory device will be explained with reference to
FIG. 1
showing the concept of a generally used flash memory device having a so-called stacked gate structure.
Referring to
FIG. 1
, the flash memory device is constructed on a silicon substrate
1700
and includes a source region
1701
and a drain region
1702
formed in the silicon substrate
1700
, a tunneling gate oxide film
1703
formed on the silicon substrate
1700
between the source region
1701
and the drain region
1702
, and a floating gate
1704
formed on the tunneling gate oxide film
1703
, wherein there is formed a consecutive stacking of a silicon oxide film
1705
, a silicon nitride film
1706
and a silicon oxide film
1707
on the floating gate
1704
, and a control gate
1708
is formed further on the silicon oxide film
1707
. Thus, the flash memory of such a stacked structure includes a stacked structure in which the floating gate
1704
and the control gate
1708
sandwich an insulating structure formed of the insulation films
1705
,
1706
and
1707
therebetween.
The insulating structure provided between the floating gate
1704
and the control gate
1705
is generally formed to have a so-called ONO structure in which the nitride film
1706
is sandwiched by the oxide films
1705
and
1707
for suppressing the leakage current between the floating gate
1704
and the control gate
1705
. In an ordinary flash memory device, the tunneling gate oxide film
1703
and the silicon oxide film
1705
are formed by a thermal oxidation process, while the silicon nitride film
1706
and the silicon oxide film
1707
are formed by a CVD process. The silicon oxide film
1705
may be formed by a CVD process. The tunneling gate oxide film
1703
has a thickness of about 8 nm, while the insulation films
1705
,
1706
and
1707
are formed to have a total thickness of about 15 nm in terms of oxide equivalent thickness. Further, a low-voltage transistor having a gate oxide film of 3-7 nm in thickness and a high-voltage transistor having a gate oxide film of 15-30 nm in thickness are formed on the same silicon in addition to the foregoing memory cell.
In the flash memory cell having such a stacked structure, a voltage of about 5-7V is applied for example to the drain
1702
when writing information together with a high voltage larger than 12V applied to the control gate
1708
. By doing so, the channel hot electrons formed in the vicinity of the drain region
1702
are accumulated in the floating gate via the tunneling insulation film
1703
. When erasing the electrons thus accumulated, the drain region
1702
is made floating and the control gate
1708
is grounded. Further, a high voltage larger than 12V is applied to the source region
1701
for pulling out the electrons accumulated in the floating gate
1704
to the source region
1701
.
Such a conventional flash memory device, on the other hand, requires a high voltage at the time of writing or erasing of information, while the use of such a high voltage tends to cause a large substrate current. The large substrate current, in turn, causes the problem of deterioration of the tunneling insulation film and hence the degradation of device performance. Further, the use of such a high voltage limits the number of times rewriting of information can be made in a flash memory device and also causes the problem of erroneous erasing.
The reason a high voltage has been needed in conventional flash memory devices is that the ONO film, formed of the insulation films
1705
,
1706
and
1707
, has a large thickness.
In the conventional art of film formation, there has been a problem, when a high-temperature process such as thermal oxidation process is used in the process of forming an oxide film such as the insulation film
1705
on the floating gate
1704
, in that the quality of the interface between the polysilicon gate
1704
and the oxide film tends to become poor due to the thermal budget effect, etc. In order to avoid this problem, one may use a low temperature process such as CVD process for forming the oxide film. However, it has been difficult to form a high-quality oxide film according to such a low-temperature process. Because of this reason, conventional flash memory devices had to use a large thickness for the insulation films
1705
,
1706
and
1707
so as to suppress the leakage current.
However, the use of large thickness for the insulation films
1705
,
1706
and
1707
in these conventional flash memory devices has caused the problem in that it is necessary to use a large writing voltage and also a large erasing voltage. As a result of using large writing voltage and large erasing voltage, it has been necessary to form the tunneling gate insulation film
1703
with large thickness so as to endure the large voltage used.
DISCLOSURE OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful flash memory device and fabrication process thereof and further a method of forming an insulation film, wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a high-performance flash memory device having a high-quality insulation film that is formed at a low temperature process, the thickness of the tunneling gate insulation film or the thickness of the insulation film between the floating gate and the control gate can be reduced successfully without causing the problem of leakage current, and enabling writing and erasing at low voltage.
Another object of the present invention is to provide a method of forming an insulation film wherein a high-quality insulation film can be formed on polysilicon.
Another object of the present invention is to provide a flash memory device, comprising:
a silicon substrate,
a first electrode formed on the silicon substrate with a tunneling insulation film interposed therebetween, and
a second electrode formed on the first electrode with an insulation film interposed therebetween,
said insulation film having a stacked structure including at least one silicon oxide film and one silicon nitride film, at least a part of said silicon oxide film containing Kr with a surface density of 10
10
cm
−2
or more.
According to the present invention, the quality of the insulation film used in a flash memory device between a floating gate electrode and a control gate electrode is improved by forming the insulation film by an oxidation reaction or nitriding reaction conducted in Ar or Kr plasma in which atomic state oxygen O* or hydrogen nitride radicals NH* are formed efficiently. Further, it becomes possible to reduce the thickness of the insulation film without causing unwanted increase of leakage current. As a result, the flash memory device of the present invention can operate at high speed with low voltage and has a long lifetime.
Another object of the present invention is to provide a method of fabricating a flash memory device comprising a silicon substrate, a first electrode of polysilicon formed on

Affiliated with

Also associated with

Rating

Flash memory device and a fabrication process thereof,... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Flash memory device and a fabrication process thereof,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flash memory device and a fabrication process thereof,... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3012002